JPH0149962B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an industrial robot, and more particularly to an industrial robot equipped with a control device for preventing transient vibrations thereof.

In order to reduce weight and increase the range of motion, industrial robots have an "open" structure, that is, the ends of movable parts such as arms are free ends. For this reason,
The mechanism of industrial robots has a low natural frequency and a small damping coefficient.

Therefore, when attempting to perform high-speed trajectory control with an industrial robot, large changes in acceleration occur in the rotary motor at parts of the trajectory with large curvature, resulting in undesirable transient vibrations in the mechanism. , causing orbital errors.

The basic measure to prevent this transient vibration of the mechanical part is to increase the rigidity and damping rate of the mechanical part, but improvements to the mechanical part can be made by changing the size of the mechanical part,
This is not easy because it increases weight and therefore costs.

The above orbit error can be reduced by reducing the curvature of the orbit, but since the magnitude of the acceleration generated by a rotating motor on the same orbit is proportional to the tangential velocity of the orbit, it is necessary to perform high-speed orbit control. It is essentially necessary to prevent transient vibrations of the mechanism.

The present applicant filed a patent application in 1983 for a method for equivalently increasing the rigidity of a mechanical system having vibrational characteristics or controlling it in a non-vibratory manner. -Proposed in 92155 "Control method for electric machines". The former has the effect of mainly reducing transient vibrations, and the latter has the effect of mainly reducing sustained vibrations (forced vibrations). All of these methods basically apply to a uniaxial servo system.

In general, the motion of an industrial robot is a combination of the above-mentioned undesirable transient vibrations on a normal motion based on data instructed in advance by teaching or the like. These two motions can be distinguished by the difference in the frequency components of the motion. The motion of is usually at a period of several seconds to several tens of seconds, and the motion of is at a frequency of 5 to 50 Hz or more, which is the resonant frequency of the mechanical system. It is. Therefore, in terms of the responsiveness of a normal servo system, the motion of can be considered to be a DC component, and the motion of can be considered to be an AC component. In order to dampen this transient vibration, v(t) (a three-dimensional vector as a function of time), which is an alternating current component of the motion of the robot's tip, should be converged to zero. For a single-axis servo system, when the signal of the acceleration of transient vibration is fed back to the control device of the rotary motor of the servo axis along with the rotational position and rotational speed according to the method disclosed in the above-mentioned patent publication, a damping effect is produced against fluctuations in acceleration. In steady state, acceleration converges to zero. When acceleration is zero, velocity is constant and the alternating current component of velocity is zero.

However, industrial robots generally have a multi-axis configuration, and each axis often mechanically interferes strongly with each other. Therefore, in industrial robots, vibrations that occur in one axis also cause vibrations in other axes, resulting in beats or complex vibrations that are a combination of vibrations from multiple axes. For this reason, even if the method of the patent publication is applied only to a specific axis of an industrial robot, for example, a shaft with particularly large vibrations, a large effect of damping transient vibrations and sustained vibrations (forced vibrations) cannot be obtained. Although FIG. 1a shows the attenuation of one axis when there is no interference between axes, a beat may occur between two axes that strongly interfere with each other, as shown in FIG. 1b. In such a case, if the method described in the patent publication is applied only to one axis, the vibration damping effect will be effective only during the period when the amplitude of vibration of the applied shaft increases, and the amplitude of vibration of the other axis will increase. Since there is no damping effect during this period, the vibration of the shaft to which the method of the above-mentioned patent publication is applied cannot be rapidly damped. FIG. 1c shows an example of a vibration experiment when the method of the above-mentioned patent publication is applied to a shaft. The broken line P corresponds to the beat (FIG. 1b) when there is no vibration suppression control.

Therefore, the present applicant proposed a method for preventing transient vibrations during high-speed trajectory control for industrial robots composed of multi-axis servo systems in a patent application filed in 1983-
Proposed in 178153 "Industrial Robots".

However, in the method proposed by this proposal, the motion of each axis of the robot with respect to the stationary coordinate system (earth) does not interfere with other axes, such as a Cartesian coordinate type, a cylindrical coordinate type, and a joint type composed of parallelogram links. Limited to certain cases, when the motion of each axis with respect to the stationary coordinate system depends not only on the position of the corresponding rotary motor but also on the position of the rotary motors of the other axes, the corresponding movable The acceleration of a point on a mechanical element includes not only the acceleration information of the corresponding axis relative to the stationary coordinate system, but also the motion acceleration of the axis on which the motion depends. Therefore, in order to detect the acceleration signal and extract only the acceleration of the corresponding axis relative to the stationary coordinate system, it is necessary to remove other signal components. Removal of this signal generally requires multidimensional matrix calculations (essentially equivalent to coordinate transformation calculations from the robot's coordinate system to the stationary coordinate system) in complexly configured mechanisms such as industrial robots. The structure was complicated and was not practical for signals that required high-speed processing, such as acceleration.

Below, the above-mentioned problems will be explained in detail with respect to one form of industrial robot. Figure 2 shows the symbols representing the basic mechanism of an industrial robot. Figure a shows that the arm C is fixed to a stationary coordinate system, and Figure b shows that the arm C is moved in the θ direction by the drive unit B. Fig. 1c shows a rotating mechanism in which the arm C rotates in the θ direction about the joint J by a drive unit attached to the joint J. Figure 3 shows one form of an industrial robot, in which arm A rotates in the θ direction, arm B rotates in the φ direction around joint J ₁ , and arm C rotates in φ direction around joint J ₂ . Rotate in the direction. The above arms are expressed as θ
axis, φ axis, and ψ axis. Now, for the θ-axis and the φ-axis, the motion relative to the stationary coordinate system is θ
Since it is defined only by the position of the axis and the φ axis, the previous application (Japanese Patent Application Laid-Open No. 178153/1983) can be applied. However, ψ
Regarding the axes, motion with respect to the stationary coordinate system is not only related to the position of the ψ axis, but also to the position of the φ axis. Fourth
The figure is a diagram showing the acceleration relationship of the ψ axis. The acceleration of joint J ₂ with respect to the stationary coordinate system is αJ ₂ , and this ψ at point Q at distance l from joint J ₂ on the ψ axis
If the linear acceleration in the direction perpendicular to the axis is lαψ, then the point Q
The linear acceleration with respect to the stationary coordinate system is the acceleration αJ ₂ and
It becomes the composite vector α of lαψ. If a linear acceleration detector for the stationary coordinate system is mounted at point Q perpendicular to this axis, the output of this detector is αQ = f(αJ ₂ ,
lαψ), which is a function of both the acceleration αJ ₂ and lαψ. Therefore, even if this output αQ is fed back to the ψ-axis control device, it is not useful for preventing ψ-axis vibration since it includes information αJ ₂ unrelated to the ψ-axis. In other words, regarding the ψ axis, the previous application (patent application 1983)
-178153) cannot be applied, and furthermore, it is very complicated to calculate the rotational acceleration of the ψ axis relative to the stationary coordinate system from the output of the linear acceleration detector attached to the ψ axis and the positions of the φ and ψ axes. It is difficult to realize.

The present invention also provides for the rotary motor to be placed at different positions on the movable mechanism element even for a servo axis where the position of the movable mechanism element with respect to the stationary coordinate system is not defined only by the rotational position of the servo axis. Two linear acceleration detectors are arranged in a direction parallel to the tangential direction of the motion caused by rotation, and the rotational acceleration signal with respect to the stationary coordinate system of the servo axis is detected by subtracting the outputs of both linear acceleration detectors. By feeding back the rotational position signal and rotational speed signal of the rotary motor to the control device of the rotary motor of the servo axis, transient vibrations during high-speed trajectory control of the industrial robot can be prevented, and the high-speed control of the industrial robot can be prevented. The purpose is to realize highly accurate orbit control.

The principle of the present invention will be explained in detail below with reference to FIG.

Two points at distances l ₁ and l ₂ (l ₁ ≠ l ₂ ) from joint J ₂ on arm C of the industrial robot shown in Figure 3.
If Q ₁ and Q ₂ are taken, the accelerations regarding these two points Q ₁ and Q ₂ will be as shown in the figure. In other words, the acceleration αJ ₂ of the joint J ₂ is the same value at the two points Q ₁ and Q ₂ ;
The rotational acceleration of the ψ axis at Q ₁ and Q ₂ is, respectively,
l ₁ αψ, l ₂ αψ (αψ; rotational acceleration of the ψ axis). Therefore, if linear acceleration detectors are installed perpendicular to the α axis at points Q ₁ and Q ₂ , their outputs will be the direction components perpendicular to the ψ axis of the vector composite value α ₁ of the rotational accelerations l ₁ αψ and αJ ₂ , respectively. αQ ₁ becomes the direction component αQ ₂ perpendicular to the ψ axis of the vector composite value α ₂ of the rotational acceleration l ₂ αψ and αJ ₁ . In both outputs αQ ₁ and αQ ₂ , the component related to αJ ₂ of the acceleration of joint J ₂ is common, so if we take the difference, αQ ₂ −αQ ₁ = (l ₂ − l ₁ )αψ, and αψ, that is, ψ A signal proportional only to the rotational acceleration of the shaft can be obtained. Therefore,
By multiplying (αQ ₂ −αQ ₁ ) by an appropriate gain and feeding it back to the ψ-axis control device, it is possible to damp the ψ-axis vibration.

Next, examples of the present invention will be shown. FIG. 6a shows the form of an industrial robot according to a first embodiment of the present invention, which is applied to the industrial robot of the form shown in FIG. FIG. 6b is a block diagram of the ψ axis. Arms A and B were previously filed (patent application 1982-
178153) is applicable. Regarding arm C, the motion of the movable mechanical element of this axis relative to the stationary coordinate system cannot be defined only by the rotational position of the rotary motor Mψ of this axis. two linear acceleration detectors AC ₁ in the direction parallel to the tangential direction of
Place AC ₂ and these linear acceleration detectors AC ₁ ,
Subtract both outputs of AC ₂ and multiply by an appropriate gain in amplifier K to obtain the rotational acceleration αψ of the ψ axis with respect to the stationary coordinate system.The rotational speed signal vψ is the output of the tacho generator TGψ, and the output of the pulse generator PGψ is the rotational acceleration αψ. The control device Gψ of the ψ axis with the signal ψ of the rotational position
to return to.

In the case of an industrial robot in which arms D and E are further connected by joints J ₃ and J ₄ as shown in FIG. 7, the same method as for arm C described above is applied to arms D and E.

Consisting of a plurality of servo axes, the rotary motor of each servo axis is coupled directly or via a mechanical transmission mechanism to a movable mechanism element of the servo axis, and causes the movable mechanism element to move linearly or rotationally, and In a multi-axis industrial robot including a servo axis in which the position of the movable mechanism element with respect to the stationary coordinate system is not defined only by the rotational position of the rotary motor of the servo axis, the position of the movable mechanism element with respect to the stationary coordinate system is For axes that are not defined only by the rotational position of the rotary motor of the servo axis, the rotational position signal and rotational speed signal of the rotary motor are returned to the control device of each servo axis for each servo axis, and two linear acceleration detectors disposed at different positions on a movable mechanical element connected to the rotary motor and in a direction parallel to the tangential direction of the motion caused by the rotation of the rotary motor; detecting the rotational acceleration signal of the servo axis relative to the stationary coordinate system by subtracting both output signals;
By feeding back the rotational acceleration signal for each servo axis to the control device for each servo axis,
This prevents transient vibrations of industrial robots due to changes in the drive torque of the rotating motor, torque ripples of the rotating motor, or resonance phenomena of the mechanical system that occur when controlling the industrial robot's high-speed trajectory.
This enables high-speed and highly accurate orbit control. In other words, the same effect as that obtained by increasing the synthesis of only the mechanical parts of an industrial robot by several times can be obtained. The present invention can be realized easily and inexpensively by simply arranging an acceleration detector in an existing industrial robot and does not require any changes to the mechanism or control device of the industrial robot.

[Brief explanation of drawings]

Figure 1 is a diagram showing the vibration state of the shaft, Figure 2 is a diagram showing the basic mechanism of an industrial robot, Figure 3 is a diagram showing one form of an industrial robot, and Figure 4 is a diagram showing the Figure 5 is a diagram showing the principle of the present invention applied to the industrial robot of the form shown in Figure 3. Figure 6 is an industrial robot according to an embodiment of the present invention. FIG. 7 is a diagram showing the form of an industrial robot according to another embodiment of the present invention. ψ...Servo axis, Mψ...Rotating motor, AC ₁ , AC ₂
...linear acceleration detector, Gψ...control device, ψ...rotational position signal, vψ...rotational speed signal, αψ...rotational acceleration signal.

Claims (1)

[Scope of Claims] 1. Consisting of a plurality of servo axes, the rotation motor of each servo axle is coupled to a movable mechanism element of the servo axle directly or via a mechanical transmission mechanism,
Multi-axis industrial use, including a servo axis, in which the movable mechanism element is moved linearly or rotationally, and the position of the movable mechanism element with respect to a stationary coordinate system during the movement is not defined only by the rotational position of the rotary motor of the servo axis. In the robot, for servo axes where the position of the movable mechanism element relative to the stationary coordinate system is not defined only by the rotational position of the rotational motor of the servoaxis, the rotational position signal and rotational speed signal of the rotational motor are determined for each servoaxis. 2 at different positions on the movable mechanical element connected to the rotary motor for each servo axis, and in a direction parallel to the tangential direction of the movement caused by the rotation of the rotary motor. A rotational acceleration signal with respect to the stationary coordinate system of the servo axis is detected by arranging two linear acceleration detectors and subtracting both output signals of the linear acceleration detector. An industrial robot characterized in that feedback is returned to a control device for each servo axis.