JP7654490B2 - Position Control Mechanism - Google Patents

Description

The present invention relates to a position control mechanism.

Conventionally, there is known a position control mechanism that maintains a constant distance between two control objects connected by a spring. For example, the optical length measuring machine (position control mechanism) described in Patent Document 1 includes at least a main body base, a slider (first control object) having a slider drive mechanism (first moving means), a bellows-driven carriage (second control object) having a bellows drive mechanism (second moving means), a laser light source, a reflecting mirror, a bellows (spring) that connects the two control objects, and an interferometer unit.

The main body base has a fixed portion disposed at a predetermined position. The slider is provided on the main body base and moves on the main body base by a slider drive mechanism. The bellows drive carriage is provided on the main body base and moves on the main body base in synchronization with the slider by a bellows drive mechanism. The laser light source is fixed on the main body base and emits laser light toward the reflecting mirror. The reflecting mirror is fixed to the end of the slider and reflects the light emitted from the laser light source back to the interferometer section.

The bellows has a main bellows with one end connected to the fixed part and the other end connected to the bellows-driven carriage, a first sub-bellows with one end connected to the bellows-driven carriage and the other end connected to the reflecting mirror on the slider, and a second sub-bellows with one end connected to the interferometer part and the other end connected to the fixed part. Each of these bellows functions as a spring that can expand and contract in the direction of movement of the slider. The main bellows expands and contracts with the movement of the bellows-driven carriage, which is driven synchronously with the slider while maintaining a constant distance therebetween. The first sub-bellows expands and contracts according to the distance between the slider and the bellows-driven carriage as the slider and/or the bellows-driven carriage move. The interferometer part and the fixed part connected by the second sub-bellows are both fixedly provided on the main body base, so the second sub-bellows basically always maintains a constant length. The laser light source emits laser light into the bellows, and the bellows is used as a light guide path.

The interferometer section is equipped with a half mirror, etc., and measures the distance to the reflecting mirror fixed to the end of the slider as the slider position by detecting the phase difference between the direct light emitted from the laser light source and the reflected light that passes through the bellows and returns from the reflecting mirror. When measuring an object with such an optical length measuring machine, the object is placed on the slider, and the measurement is made using the output signal of the sensor that detects the measurement point of the object and the position of the slider.

The bellows maintains the laser optical path in a substantially vacuum state by evacuating the air inside the bellows to a substantially vacuum state using a vacuum pump. Therefore, the optical length measuring machine can eliminate the variation in the laser wavelength caused by the change in the refractive index due to the variation in the temperature, pressure, humidity, and _CO2 concentration of the air in the atmosphere, and can perform highly accurate length measurement. In addition, the optical length measuring machine uses a bellows-driven carriage that is driven synchronously with the slider while maintaining a constant distance from the slider, thereby preventing the geometrical attitude change of the slider and the speed fluctuation during driving caused by the force generated by the expansion and contraction of the bellows accompanying the movement of the slider.

JP 2000-055617 A

Here, as in the above optical length measuring machine (position control mechanism), two control objects (slider, bellows-driven carriage) connected by a spring (first sub-bellows) may be moved and positioned synchronously while maintaining a constant separation distance between the control objects. In this case, in order to minimize the force generated by the expansion and contraction of the spring, it is preferable that the separation distance between the two control objects is set to the free length of the spring. However, the free length of the spring differs for each spring due to variations in the manufacturing process. In addition, the free length of the spring varies with the environmental temperature based on the linear expansion coefficient of the spring. If the separation distance is not set to the free length, it is necessary to apply an external force to expand or contract the spring in order to maintain a constant separation distance between the two control objects connected by the spring.

For example, when controlling the positions of two controlled objects using a motor or the like, if you try to maintain the distance between the two controlled objects by expanding and contracting a spring, you will have to constantly generate an external force that expands and contracts the spring in addition to the forces associated with normal movement to control the position of the controlled object. This creates problems such as the motor generating heat and increasing its power consumption.

One approach to this problem is to use a sensor to detect the external force and set the distance between the two controlled objects to the optimum distance (free length of the spring). However, installing the sensor requires separate wiring and electrical circuits. This makes the position control mechanism complicated and expensive. Furthermore, if a force sensor that directly measures external force is used in a position control mechanism that has a friction element such as a linear guide, the measurement results may be affected by the static friction force acting on the controlled object, resulting in errors.

The object of the present invention is to provide a low-cost position control mechanism that maintains the distance between two control objects connected by a spring at the free length of the spring.

The position control mechanism of the present invention connects a first control object movable along a predetermined direction to a second control object movable along a predetermined direction with an expandable spring, and controls the positions of the first control object and the second control object while maintaining a separation distance between the first control object and the second control object. The position control mechanism includes a first moving means for driving the first control object using a current to move it along the predetermined direction, a second moving means for driving the second control object using a current to move it along the predetermined direction, a position measurement means for measuring the positions of the first control object and the second control object, and a control means for controlling the first moving means and the second moving means. The control means includes a position control unit that controls the first moving means so as to move and stop the position of the first control object measured by the position measurement means at an arbitrary position, and controls the second moving means so as to move and stop the position of the second control object measured by the position measurement means at an arbitrary position, a current value detection unit that detects a current value flowing through at least one of the first moving means and the second moving means, and a calculation unit that calculates an appropriate separation distance between the first control object and the second control object based on the current value detected by the current value detection unit, at which the inter-object force acting between the first control object and the second control object is equal to or less than a predetermined allowable value. The position control unit controls the first moving means and the second moving means so as to maintain the appropriate separation distance calculated by the calculation unit.

In the present invention, the control means uses the appropriate separation distance calculated by the calculation unit to control the separation distance between the two control objects so that the force between the objects is equal to or less than a predetermined allowable value, so there is no need to apply an external force to expand or contract the spring. Therefore, the position control mechanism can suppress heat generation and power consumption of the first moving means and second moving means (e.g., motors, etc.) that generate external forces to expand and contract the spring. In addition, since control can be performed without using a sensor, it is possible to suppress the device of the position control mechanism from becoming complicated and expensive, and the occurrence of errors due to the influence of static friction force. Therefore, the position control mechanism can maintain the separation distance between the two control objects connected by the spring at low cost by the free length of the spring.

At this time, it is preferable that the calculation unit calculates the appropriate separation distance that minimizes the inter-object force using a current value that flows through at least one of the first moving means or the second moving means when the first control object and the second control object are positioned at a predetermined initial position, a constant (thrust constant) for calculating the inter-object force from the current value, and a spring constant of the spring.

With this configuration, the calculation unit can easily calculate the appropriate separation distance that minimizes the inter-object force by using the current value flowing through at least one of the first moving means or the second moving means when the first control object and the second control object are positioned at a predetermined initial position, a constant (thrust constant) for calculating the inter-object force from the current value, and the spring constant of the spring.

Alternatively, it is preferable that the calculation unit calculates the appropriate separation distance using a first current value flowing through at least one of the first moving means or the second moving means when the separation distance is a first distance, and a second current value of the moving means corresponding to the first current value when the separation distance is a second distance different from the first distance.

With this configuration, the calculation unit can easily calculate the appropriate separation distance that minimizes the inter-object force even if certain constants, such as the spring constant of the spring or the thrust constant of the first moving means or the second moving means, are not known.

Alternatively, it is preferable to calculate the appropriate separation distance by repeating a series of steps in which the second current value is a current value with a positive and negative opposite to the first current value, the calculation unit calculates a new target separation distance using a dichotomy method, the position control unit controls the separation distance to the new target separation distance, and the current value detection unit detects the current value while the separation distance is controlled to the new target separation distance.

With this configuration, the calculation unit can easily use the bisection method to calculate the appropriate separation distance to control the inter-object force to be equal to or less than a predetermined allowable value.

Alternatively, the position control unit positions one of the first control object or the second control object at a predetermined position, and moves the other of the first control object or the second control object at a constant speed using the other moving means within the allowable stroke of the spring. It is preferable that the calculation unit continuously obtains the separation distance and the current value flowing through at least one of the first moving means or the second moving means, and calculates the appropriate separation distance using the continuously obtained separation distance and current value.

According to this configuration, the calculation unit continuously acquires the separation distance and the current value flowing through at least one of the first moving means or the second moving means, and can easily calculate the appropriate separation distance that minimizes the force between the objects using the continuously acquired separation distance and current value. In addition, by moving the other of the first control object or the second control object at a constant speed, the effect of static friction force can be suppressed.

The position control mechanism of the present invention connects a first control object movable along a predetermined direction and a second control object movable along a predetermined direction with an expandable spring, and controls the positions of the first control object and the second control object while maintaining a separation distance between the first control object and the second control object. The spring is an air spring. The position control mechanism includes a first moving means for driving the first control object using an electric current to move it along the predetermined direction, a second moving means for driving the second control object using an electric current to move it along the predetermined direction, a position measuring means for measuring the positions of the first control object and the second control object, and a control means for controlling the first moving means, the second moving means, and the internal pressure for adjusting the free length of the air spring. The control means includes a position control unit that controls the first moving means so as to move and stop the position of the first control object measured by the position measurement means at an arbitrary position, and controls the second moving means so as to move and stop the position of the second control object measured by the position measurement means at an arbitrary position, an internal pressure control unit that controls the internal pressure of the air spring, a current value detection unit that detects a current value flowing through at least one of the first moving means and the second moving means, and a calculation unit that calculates an appropriate internal pressure of the air spring based on a current value detected by the current value detection unit when the first moving means and the second moving means are controlled by the position control unit so that the separation distance becomes a predetermined set separation distance, at which the inter-object force acting between the first control object and the second control object is equal to or less than a predetermined allowable value. The internal pressure control unit is characterized by controlling the internal pressure of the air spring so as to maintain the appropriate internal pressure calculated by the calculation unit.

In the present invention, the control means controls the free length of the air spring using the appropriate internal pressure calculated by the calculation unit at a predetermined set separation distance so that the target force is equal to or less than a predetermined allowable value, eliminating the need to apply an external force to expand or contract the spring. Therefore, the position control mechanism can suppress heat generation and power consumption of the first moving means and second moving means (e.g., motors, etc.) that generate external forces to expand or contract the spring. In addition, because the free length of the air spring can be controlled, the separation distance can be set to a predetermined set separation distance.

Alternatively, it is preferable that the calculation unit calculates the appropriate internal pressure using a first current value flowing through at least one of the first moving means or the second moving means when the internal pressure is a first internal pressure, and a second current value of the moving means corresponding to the first current value when the internal pressure is a second internal pressure different from the first internal pressure.

With this configuration, the calculation unit can easily calculate the appropriate internal pressure that minimizes the inter-target force even if the characteristics of the air spring, such as the relationship between the internal pressure of the air spring and the free length of the air spring, are not known.

Alternatively, it is preferable to calculate the appropriate internal pressure by repeating a series of steps in which the second current value is a current value with a positive and negative inverse to the first current value, the calculation unit calculates a new target internal pressure using a dichotomy method, the internal pressure control unit controls the internal pressure to become the new target internal pressure, and the current value detection unit detects the current value while the internal pressure is controlled to the new target internal pressure.

With this configuration, the calculation unit can easily use the bisection method to calculate the appropriate internal pressure for controlling the inter-subject force to be equal to or less than a predetermined allowable value.

Alternatively, the internal pressure control unit changes the internal pressure at a constant rate of change over time. It is preferable that the calculation unit continuously acquires the internal pressure controlled by the internal pressure control unit and the value of the current flowing through at least one of the first moving means or the second moving means, and calculates the appropriate internal pressure using the continuously acquired internal pressure and current value.

With this configuration, the calculation unit continuously acquires the internal pressure controlled by the internal pressure control unit and the current value flowing through at least one of the first moving means or the second moving means, and can easily calculate the appropriate internal pressure that minimizes the inter-subject force using the continuously acquired internal pressure and current value.

Alternatively, when the current value detection unit detects the current value, it is preferable that the position control unit controls the first moving means and the second moving means so as to move the first control object and the second control object at the same and constant speed while keeping the separation distance constant.

With this configuration, the position control unit controls the first moving means and the second moving means to move the first control object and the second control object at the same and constant speed while keeping the separation distance constant, so that the calculation unit can easily calculate at least one of the appropriate separation distance or the appropriate internal pressure that minimizes the force between the objects.

In this case, it is preferable that the spring is an air spring arranged between one end connected to the first control object and the other end connected to the second control object.

With this configuration, the spring is an air spring, which provides high vibration isolation between the two controlled objects and hardly ever causes the surging phenomenon seen with normal springs.

Alternatively, it is preferable that the air spring is a parallel double air spring separated into two spaces, a first space and a second space.

According to this configuration, the air spring is a parallel double air spring having two spaces, the first space and the second space, so that when the position control mechanism is applied to the optical length measuring device described above, the second space can be made into a substantially vacuum state and the laser optical path for length measurement can be arranged. By using the above-mentioned laser optical path for length measurement, it is possible to eliminate the variation in the laser wavelength caused by the change in the refractive index due to the variation in the temperature, pressure, humidity, and _CO2 concentration of the air in the atmosphere, and to enable highly accurate length measurement.

FIG. 2 is a schematic diagram showing a configuration of a position control mechanism according to the first embodiment. FIG. 2 is a block diagram showing a configuration of the position control mechanism. 6 is a flowchart showing a method for setting an appropriate separation distance in the position control mechanism. 6 is a graph showing the relationship between the position of a second controlled object and a spring force in the position control mechanism. FIG. 11 is a schematic diagram showing a configuration of a position control mechanism according to a second embodiment. FIG. 2 is a block diagram showing a configuration of the position control mechanism. 6 is a flowchart showing a method for setting an appropriate internal pressure in the position control mechanism. 5 is a graph showing the relationship between the internal pressure of the spring and the air spring force in the position control mechanism. FIG. 13 is a schematic diagram showing a configuration of a position control mechanism according to a third embodiment.

First Embodiment
A first embodiment of the present invention will now be described with reference to FIGS.
Fig. 1 is a schematic diagram showing the configuration of a position control mechanism 1 according to the first embodiment. As shown in Fig. 1, the position control mechanism 1 controls the positions of the first control object W1 and the second control object W2 while maintaining the separation distance between the first control object W1 and the second control object W2. Specifically, the position control mechanism 1 synchronously controls the first control object W1 and the second control object W2.

As shown in FIG. 1, the first control object W1 is movable along the X direction. The second control object W2 is also movable along the X direction. The first control object W1 and the second control object W2 are connected by a spring 2 that can expand and contract. The spring 2 is a coil spring that can expand and contract in the X direction. One end of the spring 2 is connected to the first control object W1, and the other end of the spring 2 is connected to the second control object W2. The X direction corresponds to the predetermined direction in this invention.

The position control mechanism 1 includes a first moving means 11 and a second moving means 12. The first moving means 11 includes a drive mechanism for moving the first control object W1 and a guide mechanism for moving it along the X direction. Similarly, the second moving means 12 includes a drive mechanism for moving the second control object W2 and a guide mechanism for moving it along the X direction. The drive mechanism includes a linear motor, a combination of a motor and a ball screw, etc. Note that the actuator used in the drive mechanism is not limited to a motor, and any actuator that can move the drive object (i.e., the first control object W1 or the second control object W2) using an electric current may be used. The guide mechanism includes a linear guide, a hydrostatic guide, or the like, and the drive object moves on the same axis. The first moving means 11 and the second moving means 12 may share one guide mechanism.

Figure 2 is a block diagram showing the configuration of the position control mechanism 1. As shown in Figure 2, the position control mechanism 1 further includes a position measurement means 3 and a control means 4. The position measurement means 3 measures the positions of the first control object W1 and the second control object W2. For example, a scale can be used as the position measurement means 3. Specifically, the position measurement means 3 may be an absolute type scale (ABS scale) that can obtain the absolute positions of the first control object W1 and the second control object W2. The ABS scale can directly obtain the separation distance between the two control objects W1 and W2 from the absolute positions of the first control object W1 and the second control object W2. Note that the position measurement means 3 is not limited to the ABS scale, and any means may be used as long as it can measure the positions of the first control object W1 and the second control object W2. For example, the position measurement means 3 may be an incremental type scale (INC scale). If the position measurement means 3 is an INC scale, the position at the time of initialization, such as when the system is started, should be set as the origin, and the distance between the first control object W1 and the second control object W2 at the origin should be set as the initial setting value of the appropriate distance described below.

The control means 4 includes a position control unit 5, a current value detection unit 6, a calculation unit 7, and a resetting unit 8, and controls the first moving means 11 and the second moving means 12.

The position control unit 5 controls the first moving means 11 to move and stop the position of the first control object W1 measured by the position measurement means 3 to an arbitrary position. Similarly, the position control unit 5 controls the second moving means 12 to move and stop the position of the second control object W2 measured by the position measurement means 3 to an arbitrary position.

The current value detection unit 6 detects the value of a current flowing through at least one of the first moving means 11 and the second moving means 12. Specifically, the current value detection unit 6 detects the value of a current flowing through the second moving means 12.

The calculation unit 7 calculates the appropriate separation distance between the first control object W1 and the second control object W2 based on the current value detected by the current value detection unit 6. The "appropriate separation distance" is a separation distance at which the inter-object force acting between the first control object W1 and the second control object W2 is equal to or less than a predetermined allowable value. The "inter-object force" is a force acting between the first control object W1 and the second control object W2 via the spring 2. In order to maintain the separation distance in a state in which the separation distance and the free length of the spring 2 do not match, a force is required to maintain the separation distance against the inter-object force. In order to generate the force to maintain the separation distance, current is consumed by the first moving means 11 and the second moving means 12. In the state in which the "inter-object force is equal to or less than a predetermined allowable value," it is preferable that the value of the current consumed to generate the force against the inter-object force is sufficiently small and close to zero. If the distance between the first control target W1 and the second control target W2 is an appropriate distance that is sufficiently close to the free length of the spring 2, the inter-target force will be sufficiently small, and if the distance matches the free length of the spring 2, the inter-target force will be zero. A specific method for calculating the appropriate distance by the calculation unit 7 will be described later.

The resetting unit 8 resets the appropriate separation distance calculated by the calculation unit 7 as the separation distance between the two control objects W1 and W2. The position control unit 5 controls the first moving means 11 and the second moving means 12 so as to maintain the appropriate separation distance calculated by the calculation unit 7.

Next, we will explain how to set the appropriate distance for the position control unit 5 in the position control mechanism 1. Figure 3 is a flowchart showing how to set the appropriate distance for the position control mechanism 1.

First, the current value detection unit 6 executes a current value detection process to detect the current value of the second moving means 12 (first moving means 11) (step ST01). Next, the current value detection unit 6 executes a current value determination process to determine whether the detected current value is equal to or less than a predetermined allowable value (step ST02).

If it is determined that the detected current value is equal to or less than the predetermined allowable value (YES in step ST02), the position control mechanism 1 terminates the procedure for setting the appropriate distance, assuming that the currently set separation distance is the appropriate separation distance. If it is determined that the detected current value is not equal to or less than the predetermined allowable value (NO in step ST02), the calculation unit 7 executes a calculation process for calculating the appropriate separation distance for controlling the target separation force to be equal to or less than the predetermined allowable value based on the current value detected by the current value detection unit 6 (step ST03).

Next, the resetting unit 8 executes a resetting process to reset the appropriate separation distance calculated by the calculating unit 7 (step ST04). The position control unit 5 executes a position control process to control the second moving means 12 based on the reset appropriate separation distance (step ST05). After executing the position control process (step ST05), the current value detection unit 6 again executes a current value detection process to detect the current value of the second moving means 12 (first moving means 11) (step ST01). Then, if it is determined that the detected current value is equal to or less than the predetermined allowable value (YES in step ST02), the position control mechanism 1 determines that the set separation distance is the appropriate separation distance and ends the procedure for setting the appropriate separation distance.

A method for calculating the appropriate separation distance by the calculation unit 7 will be specifically described below.
First, the variables, constants, formulas, etc. used in calculating the appropriate separation distance will be described. As shown in Fig. 1, the length of the spring 2 is D1, the position of the first control object W1 is X1, the length from the position X1 to the connection position of one end of the spring 2 is L1, the position of the second control object W2 is X2, and the length from the position X2 to the connection position of the other end of the spring 2 is L2. The lengths L1, L2, and the free length D0 of the spring 2 are constants.

Next, the length D1 of spring 2 can be expressed by equation (1). If the spring constant of spring 2 is K and the free length of spring 2 is D0, the spring force F acting on the spring can be expressed by equation (2) from Hooke's law.

Here, the spring force F is the inter-object force. If the force acting on the first control object W1 is F1 and the force acting on the second control object W2 is F2, then as expressed in equation (3), the spring force F is equal to the force F1 acting on the first control object W1 and the force F2 acting on the second control object W2. Note that it is assumed that the static friction force acting on the first control object W1 and the second control object W2 is small enough to be negligible.

D1=X2-X1-(L1+L2)...(1)
F=K・(D1-D0)...(2)
F=F1=F2...(3)

When the first control object W1 is driven by a first moving means 11 using a linear motor, the thrust constant of the first moving means 11 is KT1, and the current flowing through the first moving means 11 is I1, the force F1 acting on the first control object W1 is expressed by equation (4).

If the second control object W2 is driven by the second moving means 12 using a linear motor, the thrust constant of the second moving means 12 is KT2, and the current flowing through the second moving means 12 is I2, then the force F2 acting on the second control object W2 is expressed by equation (5). The thrust constants KT1 and KT2 are examples of constants used in the present invention to calculate the inter-object force from the current value. Note that, if a rotary motor is used for the first moving means 11 or the second moving means 12, it is advisable to use constants equivalent to each thrust constant as KT1 and KT2, calculated from the torque constant and the torque-thrust conversion coefficient of the drive mechanism.

F1=KT1・I1...(4)
F2=KT2・I2...(5)

The position control unit 5 (see FIG. 2) executes position control to position the first control object W1 at position X1. At that time, the value of the current I1 flowing through the first moving means 11 is detected by the current value detection unit 6 (see FIG. 2), and the force F1 acting on the first control object W1 can be obtained by substituting the detected value of the current I1 into equation (4).

The position control unit 5 also executes position control to position the second control object W2 at position X2. At that time, the value of the current I2 flowing through the second moving means 12 is detected by the current value detection unit 6, and the force F2 acting on the second control object W2 can be calculated by substituting the detected value of the current I2 into equation (5).

Now, by substituting equation (1) into equation (2) and rearranging, the spring force F is expressed as a linear equation of the position X2 of the second control object W2, as shown in equation (6).

F=K・X2−K・(X1+(L1+L2)+D0)…(6)

Next, to clarify the relationship between the spring force F, which is the inter-object force, and the position X2 of the second control object W2, the position control unit 5 issues a command to the first moving means 11 to position the first control object W1 at position X1, thereby keeping the position of the first control object W1 constant, and changes the position X2 of the second control object W2 by the second moving means 12.

Here, the spring force F when the second control object W2 is at position X2 can be calculated by detecting the current I1 flowing through the first moving means 11 with the current value detection unit 6 (see FIG. 2) and substituting the value of the detected current I1 into equation (4). Note that the spring force F can also be calculated by detecting the current I2 flowing through the second moving means 12 with the current value detection unit 6 and substituting the value of the detected current I2 into equation (5).

Figure 4 is a graph showing the relationship between the position X2 of the second control object W2 in the position control mechanism 1 and the spring force F. In the graph of Figure 4, the vertical axis is the spring force F, and the horizontal axis is the position X2 of the second control object W2. The position X2 of the second control object W2 at the initial setting value of the appropriate separation distance is set as the origin (P0) of the horizontal axis, and the result of calculating the spring force F at the initial setting value of the appropriate separation distance is set as F(P0). The position X2 of the second control object W2 at which the inter-object force is minimum (i.e. F(P2) = 0) is shown as P2.

The calculation method of the calculation unit 7 for the appropriate separation distance that minimizes the inter-object force will be described below with reference to FIG. 4. The calculation unit 7 calculates the appropriate separation distance based on the position P2 of the second control object W2 using any one of the first to fifth calculation methods.

<First Method>
Hereinafter, a first method for calculating the appropriate separation distance by the calculation unit 7 will be described. The first method is a method that can easily calculate the appropriate separation distance if the position and current value of the second measurement target W2, a constant (thrust constant, etc.) for calculating the inter-target force from the current value, and the spring constant of the spring 2 are known. Specifically, in the first method, the appropriate separation distance based on the position P2 is found using the initial setting value P0 of the second control target W2, the current I1 flowing through the first moving means 11 when positioned at the initial setting value P0, and the spring constant of the spring 2.

Let F(P0) be the spring force of the second control object W2 at the origin position P0=0. Let P2 be the position of the second control object W2 where the inter-object force is set to 0. Substituting these into the above-mentioned equation (6), equations (7) and (8) are obtained. Then, substituting equation (7) into equation (8) and solving for the position P2 of the second control object W2, equation (9) is obtained.

F(P0)=K・0−K・(X1+(L1+L2)+D0)…(7)
0=K・P2−K(X1+(L1+L2)+D0)…(8)
P2=-F(P0)/K...(9)

If the current flowing through the first moving means 11 when positioned at the initial setting value P0 is I1(P0), then the spring force F(P0) at the initial setting value P0 of the appropriate separation distance can be expressed from equation (4) by equation (10). Then, by substituting equation (10) into equation (9), equation (11) is obtained. In this way, the position P2 of the second control object W2 that minimizes the inter-object force can be calculated from equation (11) using the current I1(P0) flowing through the first moving means 11.

F(P0)=KT1・I1(P0)...(10)
P2=-KT1・I1(P0)/K...(11)

In other words, in the first method, the calculation unit 7 calculates the appropriate separation distance that minimizes the inter-object force using the current value flowing through at least one of the first moving means 11 or the second moving means 12 when the first control object W1 and the second control object W2 are positioned at a predetermined initial position, a constant (such as a thrust constant) for calculating the inter-object force from the current value, and the spring constant of the spring 2.

<Second Method>
Hereinafter, a second method for calculating the appropriate separation distance by the calculation unit 7 will be described. In the second method, when the spring constant K of the spring 2 or the constant (such as a thrust constant) KT1 for calculating the inter-object force of the first moving means 11 from the current value is not known, it is possible to find the appropriate separation distance based on the position P2 of the second control object W2 that minimizes the inter-object force.

The spring force of the second control object W2 at the origin position P0=0 is defined as F(P0). The origin position P0 is the position of the second control object W2 that corresponds to the first distance in the present invention. In addition, the position of the second control object W2 that minimizes the inter-object force is defined as P2.

Here, the position of the newly set second control object W2 is set as P1. This P1 is the position of the second control object W2 that corresponds to the second distance in the present invention. If the spring force when the second control object W2 is located at P1 is set as F(P1), then equation (12) can be obtained from equation (6) above. By substituting equation (7) into equation (12) and rearranging for the spring constant K, equation (13) can be obtained. By substituting the spring constant K of equation (13) into equation (9), equation (14) can be obtained.

F(P1)=K・P1−K・(X1+(L1+L2)+D0)…(12)
F(P1)=K・P1+F(P0)
K=(F(P1)-F(P0))/P1...(13)
P2=-F(P0)・P1/(F(P1)-F(P0))...(14)

Here, if the current of the first moving means 11 at the position P0 of the second control object W2 is I1 (P0), and the current of the first moving means 11 at the position P1 of the second control object W2 is I1 (P1), then equations (15) and (16) are obtained from equation (4). Furthermore, equation (17) is obtained by substituting equations (15) and (16) into equation (14).

F(P0)=KT1・I1(P0)...(15)
F(P1)=KT1・I1(P1)...(16)
P2=-KT1・I1(P0)・P1/(KT1・I1(P1)-KT1・I1(P0))
P2=-I1(P0)・P1/(I1(P1)-I1(P0))...(17)

In this way, the position P2 of the second control object W2 that makes the inter-object force zero can be calculated using equation (17) from the current I1 (P0) at the position P0 of the second control object W2, the newly set position P1 of the second control object W2, and the current I1 (P1) flowing through the first moving means 11 at the position P1 of the second control object W2. Note that the new position P1 of the second control object W2 may be the design value of the spring constant K or an estimated position of the second control object W2 that minimizes the inter-object force calculated by the first method from the approximate value. Also, any value within the allowable stroke of the spring 2 may be set based on the allowable stroke of the spring 2.

In addition, in the method of setting the predetermined separation distance shown in FIG. 3, the second method may be repeated multiple times to obtain the position P2 of the second control target W2 that minimizes the inter-target force. If the current I1 of the first moving means 11 does not converge to 0 due to the influence of measurement noise, static friction force, etc., it is advisable to end the above-mentioned repetition when the current I1 of the first moving means 11 becomes equal to or less than the set current value.

That is, in the second method, the calculation unit 7 calculates the appropriate separation distance using a first current value flowing through at least one of the first moving means 11 or the second moving means 12 when the separation distance is a first distance, and a second current value of the moving means corresponding to the first current value when the separation distance is a second distance different from the first distance.

<Third Method>
Hereinafter, a third method for calculating the appropriate separation distance by the calculation unit 7 will be described. In the third method, the appropriate separation distance can be easily calculated in a predetermined case by using a bisection method. Specifically, the third method can be applied when the new position X2 of the second control object W2 in the second method (the position corresponding to the second distance in the present invention) is a current value I1 (P3) whose positive and negative are opposite to those of the current I1 (P0) of the first moving means 11, as shown in FIG. 4, and the appropriate separation distance based on the position P2 of the second control object W2 that minimizes the inter-object force is obtained by using a bisection method.

By repeating the position setting of the second control object W2 multiple times using the bisection method, it is possible to calculate the position P2 of the second control object W2 that minimizes the inter-object force even when the spring 2 has nonlinear spring characteristics, when the thrust constant KT1 of the first moving means 11 has nonlinearity that differs depending on the current value, or when the thrust constant KT1 has position dependency that differs depending on the position of the moving means 11.

In other words, in the third method, the new position X2 of the second control object W2 (the position corresponding to the second distance in the present invention) is set to a position where the second current value has an opposite positive and negative current value. Then, the calculation unit 7 calculates a new target separation distance using the bisection method, the position control unit 5 controls the separation distance to the new target separation distance, and the current value detection unit 6 detects the current value in a state where the separation distance is controlled to the new target separation distance. A series of these steps are repeated to calculate the appropriate separation distance.

<Fourth Method>
A fourth method for calculating the appropriate separation distance by the calculation unit 7 will be described below. The fourth method is a method for calculating the appropriate separation distance when one of the two control objects W1 and W2 can be moved at a constant speed. Specifically, as shown in FIG. 4, the fourth method is a method for continuously acquiring the position X2 of the second control object W2 and the current I1 of the first moving means 11 while moving the second control object W2 at a constant speed within the allowable stroke of the spring 2 in a state where the first control object W1 is positioned at the position X1, and determining the position X2 of the second control object W2 at which the current I1 becomes 0 from the data, and setting the appropriate separation distance based on the position P2 of the second control object W2 that minimizes the inter-object force.

The calculation unit 7, for example, applies the least squares method to the continuously acquired data on position X2 and current I2 to approximate the relationship between the position X2 of the second control object W2 and the current I1 of the first moving means 11 with a polynomial of position X2, determines the position where current I1 = 0 from this polynomial, and calculates the appropriate separation distance based on the position P2 of the second control object W2 that minimizes the inter-object force.

That is, in the fourth method, the position control unit 5 positions one of the first control object W1 or the second control object W2 at a predetermined position, and moves the other of the first control object W1 or the second control object W2 at a constant speed using the other moving means within the allowable stroke of the spring 2. The calculation unit 7 continuously obtains the separation distance and the current value flowing through at least one of the first moving means 11 or the second moving means 12, and calculates the appropriate separation distance using the continuously obtained separation distance and current value.

<Fifth Method>
Hereinafter, a fifth method for calculating the appropriate separation distance by the calculation unit 7 will be described. The fifth method is a method for calculating the appropriate separation distance when the two control objects W1 and W2 can be moved at the same and constant speed, and the kinetic friction force of either the first control object W1 or the second control object W2 is sufficiently small. Specifically, the fifth method is a method for calculating the appropriate separation distance when the first control object W1 and the second control object W2 are moved at the same and constant speed while maintaining a predetermined separation distance between them, and the current value detection unit 6 detects the current of the moving means in which the kinetic friction force of either the first control object W1 or the second control object W2 is sufficiently small. Then, this is executed multiple times by changing the predetermined separation distance, and the relationship between the set predetermined separation distance and the detected current is obtained by the same method as the first to third methods, and the appropriate separation distance that minimizes the force between the objects is obtained.

When the kinetic friction force of either the first control object W1 or the second control object W2 is sufficiently small, it is possible to measure the force between the objects excluding the effect of static friction force. If there is no kinetic friction force, the current of the drive means of the control object without kinetic friction force during uniform motion will be 0 at a specified separation distance that minimizes the force between the objects.

In other words, in the fifth method, when the current value detection unit 6 detects the current value, the position control unit 5 controls the first moving means 11 and the second moving means 12 to move the first control object W1 and the second control object W2 at the same and constant speed while keeping the separation distance constant, and the calculation unit 7 uses the current value obtained by this control, etc. to calculate the appropriate separation distance excluding the influence of static friction force.

The calculation unit 7 calculates the appropriate separation distance using any one of these first to fifth methods. The resetting unit 8 resets the appropriate separation distance calculated by the calculation unit 7 as the separation distance between the two control objects W1 and W2. The position control unit 5 controls the first moving means 11 and the second moving means 12 based on the appropriate separation distance reset by the resetting unit 8. As a result, the separation distance between the first control object W1 and the second control object approximately matches the free length of the spring 2, and the current flowing through the moving means 11 and 12 to maintain the separation distance between the control objects W1 and W2 can be suppressed.

According to the first embodiment, the following actions and effects can be achieved.
(1) The control means 4 uses the appropriate separation distance calculated by the calculation unit 7 to control the separation distance between the two control objects W1 and W2 so that the inter-object force is equal to or less than a predetermined allowable value, so there is no need to apply an external force to expand or contract the spring 2. Therefore, the position control mechanism 1 can suppress the heat generation and power consumption of the first moving means 11 and the second moving means 12 that generate the external force for expanding or contracting the spring 2. In addition, since control can be performed without using a sensor, it is possible to suppress the structure of the position control mechanism 1 from becoming complicated and costly, and the occurrence of errors due to the influence of static friction force. Therefore, the position control mechanism 1 can maintain the separation distance between the two control objects W1 and W2 connected by the spring 2 at low cost by the free length of the spring 2.

(2) The calculation unit 7 can easily calculate the appropriate separation distance that minimizes the inter-object force by using the current value flowing through at least one of the first moving means 11 or the second moving means 12 when the first control object W1 and the second control object W2 are positioned at a predetermined initial position, a constant for calculating the inter-object force from the current value, and the spring constant of the spring 2.
(3) The calculation unit 7 can easily calculate the appropriate separation distance that minimizes the force between the objects, even if certain constants such as the spring constant of the spring 2 or the thrust constant of the first moving means 11 or the second moving means 12 are not known.

(4) The calculation unit 7 can easily calculate the appropriate separation distance for controlling the inter-object force to be equal to or less than a predetermined allowable value using the bisection method.
(5) The calculation unit 7 continuously acquires the separation distance and the current value flowing through at least one of the first moving means 11 or the second moving means 12, and can easily calculate the appropriate separation distance that minimizes the force between the objects using the continuously acquired separation distance and current value.
(6) The position control unit 5 controls the first moving means 11 and the second moving means 12 to move the first control object W1 and the second control object W2 at the same and constant speed while keeping the separation distance constant, so that the calculation unit 7 can calculate the appropriate separation distance that minimizes the force between the objects excluding the influence of static friction force.

Second Embodiment
A second embodiment of the present invention will be described below with reference to Figures 5 to 8. In the following description, the same components as those in the first embodiment will be denoted by the same reference numerals and the description thereof will be omitted.

Figure 5 is a schematic diagram showing the configuration of a position control mechanism 1A according to the second embodiment. In the first embodiment, the spring 2 was a coil spring that was expandable and contractable in the X direction. In the second embodiment, as shown in Figure 5, the spring 2A in the position control mechanism 1A is an air spring that is expandable and contractable in the X direction, which is different from the first embodiment. Also, the control means 4A of the position control mechanism 1A is different from the first embodiment in that, in addition to the position control unit 5, current value detection unit 6, calculation unit 7, and reset unit 8, it further includes an internal pressure control unit 13 that controls the internal pressure of the spring 2A.

The spring 2A is an air spring that utilizes the elasticity of compressed gas and has a bellows portion 20A. One end of the spring 2A is connected to the first control object W1, and the other end is connected to the second control object W2. The bellows portion 20A is made of a diaphragm, a bellows-shaped metal, etc., and expands and contracts in the X direction. The inside of the bellows portion 20A is a space that can be filled with compressed gas, and is filled with compressed gas such as air by a pressure pump. The free length of the spring 2A is determined by the spring characteristics of the bellows portion 20A, the atmospheric pressure, and the pressure of the compressed gas (hereinafter referred to as "internal pressure"). The free length of the spring 2A is controlled by the internal pressure control unit 13. The free length of the spring 2A can be changed by controlling the internal pressure using the internal pressure control unit 13.

Figure 6 is a block diagram showing the configuration of the position control mechanism 1A. In the second embodiment, as shown in Figure 6, the control means 4A includes an internal pressure control unit 13, and is different from the control means 4 in the first embodiment in that it controls the internal pressure to adjust the free length of the spring 2A. In addition, while the calculation unit 7 calculates the appropriate separation distance in the first embodiment, the calculation unit 7A in the second embodiment is different from the first embodiment in that it calculates the appropriate internal pressure. Here, the "appropriate internal pressure" is an internal pressure at which the inter-object force acting between the first control object W1 and the second control object W2 is equal to or less than a predetermined allowable value. If the internal pressure of the spring 2A is the appropriate internal pressure, the free length of the spring 2A approximately matches the separation distance between the first control object W1 and the second control object W2, and the inter-object force is sufficiently small.

The calculation unit 7A calculates the appropriate internal pressure based on the current value detected by the current value detection unit 6 in a state in which the first moving means 11 and the second moving means 12 are controlled by the position control unit 5 so that the separation distance becomes a predetermined set separation distance. The internal pressure control unit 13 controls the internal pressure of the spring 2A via a compressor and a pressure regulating valve (not shown) so as to maintain the appropriate internal pressure calculated by the calculation unit 7A. The internal pressure control unit 13 may also control the internal pressure of the spring 2A by configuring a feedback control system using a sensor that measures the internal pressure of the spring 2A.

Next, a method for setting an appropriate internal pressure in the position control mechanism 1A will be described with reference to a flowchart shown in FIG 7.
First, the current value detection unit 6 executes a current value detection step of detecting a current value of the first moving means 11 (second moving means 12) (step ST11). Next, the current value detection unit 6 executes a current value determination step of determining whether the detected current value is equal to or less than a predetermined allowable value (step ST12).

If it is determined that the detected current value is equal to or less than the predetermined allowable value (YES in step ST12), the position control mechanism 1A terminates the procedure for setting the appropriate internal pressure, assuming that the currently set internal pressure of the spring 2A (the pressure applied to the gas sealed in the bellows portion 20A) is the appropriate internal pressure. If it is determined that the detected current value is not equal to or less than the predetermined allowable value (NO in step ST12), the calculation unit 7A executes a calculation process for calculating the appropriate internal pressure based on the current value detected by the current value detection unit 6 (step ST13).

Next, the resetting unit 8A executes a resetting process to reset the appropriate internal pressure calculated by the calculation unit 7A (step ST14). The internal pressure control unit 13 executes an internal pressure control process to control the length of the spring 2A based on the appropriate internal pressure reset by the resetting unit 8A (step ST15). After executing the internal pressure control process (step ST15), the current value detection unit 6 again executes a current value detection process to detect the current value of the first moving means 11 (second moving means 12) (step ST11). Then, if it is determined that the detected current value is equal to or less than the predetermined allowable value (YES in step ST12), the position control mechanism 1A determines that the set internal pressure of the spring 2A is the appropriate internal pressure and ends the procedure for setting the appropriate internal pressure.

A specific method for calculating the appropriate internal pressure in the position control mechanism 1A will be described below.
First, the variables, constants, formulas, etc. used to calculate the appropriate internal pressure will be described. When the length D1 (see FIG. 5) of the spring 2A is kept constant, the force FA applied to the spring 2A can be expressed by formula (18) using the spring constant K of the bellows portion 20A, the internal pressure PP of the spring 2A, the atmospheric pressure PA, and the proportionality constant KA of the spring 2A. Here, D0 is the free length of the spring 2A. The force FA applied to the spring 2A is proportional to the internal pressure PP of the spring 2A, and the force FA applied to the spring 2A can be set to an arbitrary value using the internal pressure PP of the spring 2A.

FA=KA・(PP-PA)-K・(D1-D0)
FA=KA・PP−(KA・PA+K・(D1−D0))…(18)

As in the first embodiment, the current I1 flowing through the first moving means 11 is detected by the current value detection unit 6, and the air spring force FA can be calculated by substituting the detected current I1 into formula (4). The current I2 flowing through the second moving means 12 can also be detected by the current value detection unit 6, and the air spring force FA can be calculated by substituting the detected current I2 into formula (5). That is, as in the first embodiment, the calculation unit 7A calculates the appropriate internal pressure using any one of the first to fifth calculation methods, and the internal pressure control unit 13 controls the length of the spring 2A based on the appropriate internal pressure reset by the reset unit 8A. As described below, as in the first embodiment, the calculation unit 7A calculates the appropriate internal pressure using any one of the first to fifth calculation methods.

Figure 8 is a graph showing the relationship between the internal pressure of spring 2A in position control mechanism 1A and the air spring force. The graph in Figure 8 is a graph when the atmospheric pressure PA is a constant value. The vertical axis is the air spring force FA, and the horizontal axis is the internal pressure of spring 2A. The initial setting value of the internal pressure of spring 2A is set as the origin (PP0), and the result of calculating the air spring force FA at the initial setting value of the internal pressure of spring 2A is set as FA(PP0). Furthermore, the internal pressure of spring 2A at which the inter-objective force is minimum (i.e. FA(PP2) = 0) is shown as PP2.

Comparing equation (6) and equation (18), it can be seen that equation (6) is a linear expression for the position X2 of the second control object W2, and equation (18) is a linear expression for the internal pressure PP of spring 2A. Similarly, comparing the graph in FIG. 3 with the graph in FIG. 8, it can be seen that they are graphs that represent the same linear expression. That is, by using any one of the first to fifth calculation methods similar to those in the first embodiment in the calculation unit 7A to calculate the internal pressure PP that can be set to the free length of spring 2A as the appropriate internal pressure, and then resetting it using the resetting unit 8A, the internal pressure control unit 13 can keep the inter-object force below a predetermined allowable value.

In the first method, the calculation unit 7A calculates the appropriate internal pressure that minimizes the inter-target force using the current value that flows through at least one of the first moving means or the second moving means when the internal pressure of the air spring is set to a predetermined initial internal pressure, a constant for calculating the inter-target force from the current value, and a proportionality constant of the spring 2A. The first method can be used when the constant for calculating the inter-target force from the current value and the proportionality constant of the spring 2A are known.

In the second method, the calculation unit 7A may calculate the appropriate internal pressure using a first current value flowing through at least one of the first moving means or the second moving means when the internal pressure is a first internal pressure, and a second current value of the moving means corresponding to the first current value when the internal pressure is a second internal pressure different from the first internal pressure. By using the first current value when the first internal pressure is set and the second current value when the second internal pressure is set, the second method can calculate the appropriate internal pressure even when the constant for calculating the target inter-subject force from the current value and the proportionality constant of the spring 2A are unknown.

In the third method, the calculation unit 7A uses the first current value when the first internal pressure is set and the second current value when the second internal pressure is set, as in the second calculation method, but sets the first internal pressure and the second internal pressure so that the second current value has a current value with a positive and negative inverse to the first current value, and calculates a new target internal pressure using a dichotomy method with the first current value and the second current value as initial values. Then, the internal pressure control unit controls the internal pressure to the new target internal pressure, and the current value detection unit detects the current value with the internal pressure controlled to the new target internal pressure. The above series of steps are repeated to calculate the appropriate internal pressure.

In the fourth method, the internal pressure control unit 13 changes the internal pressure at a constant rate of change over time. The calculation unit 7A continuously acquires the internal pressure controlled by the internal pressure control unit 13 and the value of the current flowing through at least one of the first moving means 11 or the second moving means 12, and calculates the appropriate internal pressure using the continuously acquired internal pressure and current value. For example, the calculation unit 7A may apply the least squares method to the continuously acquired internal pressure and current value to obtain a relational equation between the two as a function such as a polynomial, and calculate the appropriate internal pressure at which the current value is zero in the relational equation.

In a fifth method that can be applied when the kinetic friction force of either the first control object W1 or the second control object W2 is sufficiently small, when the current value detection unit 6 detects the current value, the position control unit 5 controls the first moving means 11 and the second moving means 12 to move the first control object W1 and the second control object W2 at the same and constant speed with the internal pressure set to a predetermined internal pressure while keeping the separation distance constant. This is then performed multiple times by changing the predetermined internal pressure, and the relationship between the set predetermined internal pressure and the current of the moving means with a sufficiently small kinetic friction force is found using a method similar to the first to third methods, and an appropriate separation distance that minimizes the force between the objects is found.

According to the second embodiment, the following actions and effects can be achieved.
(7) The control means 4A uses the appropriate internal pressure calculated by the calculation unit 7A to control the free length of the spring 2A so that the inter-object force is equal to or less than a predetermined allowable value, so there is no need to apply an external force to expand or contract the spring 2A. Therefore, the position control mechanism 1A can suppress the heat generation and power consumption of the first moving means 11 and the second moving means 12 that generate the external force to expand or contract the spring 2A. In addition, as an effect of using an air spring, high vibration insulation is obtained between the two control objects, and the surging phenomenon seen in normal springs can be avoided.

(8) The calculation unit 7A can easily calculate the appropriate internal pressure that minimizes the inter-object force by using the current value flowing through at least one of the first moving means 11 or the second moving means 12 when the internal pressure of the spring 2A is set to a predetermined initial internal pressure, a constant for calculating the inter-object force from the current value, and the proportionality constant of the spring 2A.
(9) The calculation unit 7A can easily calculate the appropriate internal pressure that minimizes the inter-object force even if certain constants, such as the proportional constant of the spring 2A or the thrust constant of the first moving means 11 or the second moving means 12, are not known.
(10) The calculation unit 7A can easily calculate the appropriate internal pressure for controlling the inter-object force to be equal to or less than a predetermined allowable value using the bisection method.

(11) The calculation unit 7A continuously acquires the internal pressure controlled by the internal pressure control unit 13 and the current value flowing through at least one of the first moving means 11 or the second moving means 12, and can easily calculate the appropriate internal pressure that minimizes the inter-subject force using the continuously acquired internal pressure and current value.
(12) The position control unit 5 controls the first moving means 11 and the second moving means 12 to move the first control object W1 and the second control object W2 at the same and constant speed while keeping the separation distance constant, so that the calculation unit 7A can calculate the appropriate internal pressure that minimizes the force between the objects excluding the effects of static friction force.
(13) Since the spring 2A is an air spring, high vibration isolation is achieved between the two controlled objects, and the surging phenomenon seen in normal springs hardly occurs.

Third Embodiment
A third embodiment of the present invention will now be described with reference to Fig. 9. In the following description, the same reference numerals will be used to designate parts that have already been described, and description thereof will be omitted.

Figure 9 is a schematic diagram showing the configuration of a position control mechanism 1B according to the third embodiment. In the second embodiment, the spring 2A was an air spring. As shown in Figure 9, the spring 2B of the position control mechanism 1B of the third embodiment differs from that of the second embodiment in that it is a parallel double air spring.

The spring 2B is a parallel double air spring that utilizes the elasticity of compressed gas and has a bellows portion 20B. One end of the spring 2B is connected to the first control object W1, and the other end is connected to the second control object W2. The bellows portion 20B is made of a diaphragm or a bellows-shaped metal, etc., and expands and contracts in the X direction. The inside of the bellows portion 20B is separated into two spaces, a first space 21B and a second space 22B. The first space 21B is filled with compressed gas such as air. The second space 22B is evacuated by a vacuum pump and is in a substantially vacuum state.

The free length of the spring 2B is determined by the spring characteristics of the bellows portion 20B, the atmospheric pressure, the internal pressure of the compressed gas in the first space 21B, and the negative vacuum pressure in the second space 22B.
The free length of the spring 2B is controlled by the internal pressure control unit 13. The length of the spring 2B expands or contracts by controlling the internal pressure using the internal pressure control unit 13.

When the length D1 of spring 2B is kept constant, the air spring force FB acting on spring 2B can be expressed by equation (19) using the spring constant K of bellows portion 20B, the internal pressure PP of first space 21B of spring 2B, atmospheric pressure PA, the proportionality constant KB of spring 2B, and the pressure-receiving area S of second space 22B. Note that the pressure-receiving area S of second space 22B is a constant.

FB=KB・(PP-PA)-K・(D1-D0)-S・PA
FB=KB・PP−((KB+S)・PA+K・(D1−D0))…(19)

The air spring force FB applied to spring 2B is proportional to the internal pressure PP of the first space 21B of spring 2B. Therefore, the air spring force FB applied to spring 2B can be set to any value using the internal pressure PP of spring 2B.

Here, equation (19) is equation (18) plus the negative pressure due to atmospheric pressure PA acting on the pressure-receiving area S of second space 22B. When atmospheric pressure PA is a constant value, the negative pressure is constant, so it can be seen that equation (19) is a linear equation for internal pressure PP, the same as in the second embodiment. Therefore, position control mechanism 1B can calculate the internal pressure PP of spring 2B that minimizes the inter-object force as the appropriate internal pressure, using the same method as position control mechanism 1A in the second embodiment.

In the first to third embodiments, the atmospheric pressure PA is a constant value. However, the atmospheric pressure changes due to weather conditions, etc. For this reason, the position control mechanisms 1, 1A to 1B may use the calculation units 7, 7A to calculate the appropriate separation distance and appropriate internal pressure that minimize the inter-object force at any time during operation, and reset them in the reset units 8, 8A. This minimizes the inter-object force each time it is reset, making it possible to follow changes in the atmospheric pressure.

In the third embodiment, in addition to the same actions and effects as those (7) to (13) in the second embodiment, the following actions and effects can be achieved.
(14) The spring 2B is a parallel double air spring including the bellows portion 20B having two spaces, the first space 21B and the second space 22B, so that the second space can be made substantially vacuum and the laser optical path for length measurement can be arranged. By using the laser optical path for length measurement, it is possible to eliminate the fluctuation of the laser wavelength caused by the change of the refractive index due to the fluctuation of the temperature, pressure, humidity, and _CO2 concentration of the air in the atmosphere, and to perform the length measurement with high accuracy.

[Modifications of the embodiment]
It should be noted that the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of the present invention that can achieve the object of the present invention are included in the present invention.

For example, in the first embodiment, the appropriate separation distance calculated by the calculation unit 7 was based on the position P2 of the second control object W2 that minimizes the inter-object force, but the appropriate separation distance calculated by the calculation unit may be based on the position of the first control object, or may be based on both the position of the first control object and the position of the second control object.

In the first embodiment, a coil spring is used as the spring 2, but the spring 2 is not limited to a coil spring. For example, the air spring described in the second embodiment or the parallel double air spring described in the third embodiment may be used as the spring 2.

In each of the above embodiments, the position control mechanism 1, 1A to 1B includes a resetting unit 8, 8A, but the calculated appropriate separation distance or appropriate internal pressure may be set without using a resetting unit. For example, the appropriate separation distance or appropriate internal pressure may be set manually.

As described above, the present invention can be suitably used in position control mechanisms.

REFERENCE SIGNS LIST 1, 1A to 1B Position control mechanism 2, 2A to 2B Spring 3 Position measurement means 4, 4A Control means 5 Position control section 6 Current value detection section 7 Calculation section 8, 8A Reset section 11 First movement means 12 Second movement means 13 Internal pressure control section W1 First control object W2 Second control object

Claims (12)

A position control mechanism that connects a first control object movable along a predetermined direction and a second control object movable along the predetermined direction by a spring that can expand and contract, and controls positions of the first control object and the second control object while maintaining a separation distance between the first control object and the second control object,
a first moving means for driving the first control object by using a current to move the first control object along the predetermined direction;
a second moving means for driving the second control object by using a current to move the second control object along the predetermined direction;
a position measuring means for measuring positions of the first control object and the second control object;
A control means for controlling the first moving means and the second moving means;
Equipped with
The control means
a position control unit that controls the first moving means so as to move and stop the position of the first control object measured by the position measurement means at an arbitrary position, and controls the second moving means so as to move and stop the position of the second control object measured by the position measurement means at an arbitrary position;
a current value detection unit that detects a value of a current flowing through at least one of the first moving means and the second moving means;
a calculation unit that calculates an appropriate separation distance between the first control object and the second control object such that an inter-object force acting between the first control object and the second control object is equal to or smaller than a predetermined allowable value based on the current value detected by the current value detection unit,
The position control mechanism is characterized in that the position control unit controls the first moving means and the second moving means so as to maintain the appropriate separation distance calculated by the calculation unit. The position control mechanism according to claim 1, characterized in that the calculation unit calculates the appropriate separation distance that minimizes the inter-object force using a current value flowing through at least one of the first moving means or the second moving means when the first control object and the second control object are positioned at a predetermined initial position, a constant for calculating the inter-object force from the current value, and a spring constant of the spring. The position control mechanism according to claim 1, characterized in that the calculation unit calculates the appropriate separation distance using a first current value flowing through at least one of the first moving means or the second moving means when the separation distance is a first distance, and a second current value of the moving means corresponding to the first current value when the separation distance is a second distance different from the first distance. The second current value has a positive and negative opposite current value to the first current value,
4. The position control mechanism according to claim 3, wherein the appropriate separation distance is calculated by repeating a series of steps, in which the calculation unit calculates a new target separation distance using a bisection method, the position control unit controls the separation distance to become the new target separation distance, and the current value detection unit detects the current value in a state in which the separation distance is controlled to become the new target separation distance. the position control unit positions one of the first controlled object or the second controlled object at a predetermined position, and moves the other of the first controlled object or the second controlled object at a constant speed within an allowable stroke of the spring using the moving means for the other of the first controlled object or the second controlled object;
The position control mechanism according to claim 1, characterized in that the calculation unit continuously acquires the separation distance and a current value flowing through at least one of the first moving means or the second moving means, and calculates the appropriate separation distance using the continuously acquired separation distance and current value. A position control mechanism that connects a first control object movable along a predetermined direction and a second control object movable along the predetermined direction by a spring that can expand and contract, and controls positions of the first control object and the second control object while maintaining a separation distance between the first control object and the second control object,
The spring is an air spring,
a first moving means for driving the first control object by using a current to move the first control object along the predetermined direction;
a second moving means for driving the second control object by using a current to move the second control object along the predetermined direction;
a position measuring means for measuring a position of the first control object and a position of the second control object;
a control means for controlling the first moving means, the second moving means, and an internal pressure for adjusting a free length of the air spring;
Equipped with
The control means
a position control unit that controls the first moving means so as to move and stop the position of the first control object measured by the position measurement means at an arbitrary position, and controls the second moving means so as to move and stop the position of the second control object measured by the position measurement means at an arbitrary position;
An internal pressure control unit that controls the internal pressure of the air spring;
a current value detection unit that detects a value of a current flowing through at least one of the first moving means and the second moving means;
a calculation unit that calculates, based on the current value detected by the current value detection unit, an appropriate internal pressure of the air spring such that an inter-object force acting between the first control object and the second control object is equal to or smaller than a predetermined allowable value when the first movement means and the second movement means are controlled by the position control unit so that the separation distance becomes a predetermined set separation distance;
The position control mechanism is characterized in that the internal pressure control unit controls the internal pressure of the air spring so as to maintain the appropriate internal pressure calculated by the calculation unit. The position control mechanism according to claim 6, characterized in that the calculation unit calculates the appropriate internal pressure using a first current value flowing through at least one of the first moving means or the second moving means when the internal pressure is a first internal pressure, and a second current value of the moving means corresponding to the first current value when the internal pressure is a second internal pressure different from the first internal pressure. The second current value has a positive and negative opposite current value to the first current value,
The position control mechanism according to claim 7, characterized in that the appropriate internal pressure is calculated by repeating a series of steps in which the calculation unit calculates a new target internal pressure using a dichotomy method, the internal pressure control unit controls the internal pressure to become the new target internal pressure, and the current value detection unit detects the current value while the internal pressure is controlled to become the new target internal pressure. The internal pressure control unit changes the internal pressure at a constant time rate of change,
The position control mechanism described in claim 6, characterized in that the calculation unit continuously acquires the internal pressure controlled by the internal pressure control unit and the current value flowing through at least one of the first moving means or the second moving means, and calculates the appropriate internal pressure using the continuously acquired internal pressure and current value. The position control mechanism according to any one of claims 1 to 4 and claims 6 to 9, characterized in that when the current value detection unit detects the current value, the position control unit controls the first moving means and the second moving means to move the first control object and the second control object at the same and constant speed while keeping the separation distance constant. The position control mechanism according to any one of claims 1 to 10, characterized in that the spring is an air spring disposed between one end connected to the first control target and the other end connected to the second control target. The position control mechanism according to claim 11, characterized in that the air spring is a parallel double air spring separated into two spaces, a first space and a second space.

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