JPH082187B2 - Servo amplifier for linear motor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo amplifier for a linear motor having a built-in protection circuit.

2. Description of the Related Art FIG. 4A is an example of an external view of a linear motor, in which 1 is a linear motor and 2 is a movable part of the linear motor, which moves vertically. Reference numeral 3 denotes an indicator plate fixed to the movable portion 2, 4 is a tool attached to the movable portion 2, 5 is a spring for preventing the jig 4 from descending when the linear motor is powered off, and 6 is a vertical position. Is a position detector, and 7 is a speed detector.
FIG. 4b is a schematic configuration diagram of the linear motor, in which a coil is wound around the movable portion 2 and a magnet 10 is generated by passing a current through the coil.
The coil moves up and down due to the electromagnetic force generated between
The greatest feature of such a linear motor is that it has a faster moving speed and shorter positioning time than other motors, but the structure with the spring 5 as shown in Fig. 4a receives the repulsive force of the spring. , Positioning time is longer than that without spring.

On the other hand, there may be a case where the moving part of the linear motor does not complete the movement to the target position due to some failure (for example, mechanical twisting or failure of the position detector). At this time, if the power of the servo amplifier is left without being turned off, an excessive current continues to flow in the coil of the linear motor, and the coil is burned.

FIG. 5 shows an example of a conventional servo amplifier with an overcurrent protection circuit for a motor. In FIG. 5, a target position command 12 from a numerical controller or the like is converted into an analog voltage by a digital-analog converter 13, and a position deviation which is a difference from the output (current position) of the position detector 7 at an addition point 14. The amount is ΔP. Δ
P is amplified by the deviation amplifier 15 and the drive amplifier 17, and a current proportional to ΔP flows through the linear motor 1 to move the movable portion of the linear motor so that the servo system is balanced. However, as described above, when the movable part does not completely reach the target position, the position deviation amount ΔP does not become zero and overcurrent continues to flow to the linear motor, so that the on-delay type thermal relay is used. 18 operates and shuts off the linear motor current. A coil burnout protection circuit in which the thermal relay 18 is replaced with an electronic circuit has also been devised.

Problems to be Solved by the Invention However, when the servo amplifier having the above-described configuration is used to drive a linear motor whose up-down direction is a movable direction, the movable portion moves down when the overcurrent protection circuit operates. Since the lowered tip tool 4 of the linear motor hits a moving mechanism section (not shown) such as an XY table below it, an accident occurs in which the tool 4 is damaged if the moving mechanism section is accidentally moved. Therefore, as shown in FIG. 4a, the spring 5 must be supported so as not to descend. Then, as described above, there is a drawback that the positioning time of the linear motor becomes longer than that without the spring. Therefore, the present invention proposes a servo amplifier having a coil burnout protection circuit for a linear motor without a spring.

Means for Solving the Problems The present invention is directed to a linear motor having a structure in which a movable part moves in a vertical direction, a deviation amplifier for amplifying a deviation between a target command position and a current position, and power amplification for driving the linear motor. And a window comparator for turning off the output of the deviation amplifier within a preset voltage centered around zero volt, and a case where the output of the window comparator continues to be on for more than a preset time T. When set and the window comparator turns off,
A timer circuit that is reset in a shorter time than the time T, and a relay that is turned on / off by the output of the timer,
Current command value that can move the moving part of the linear motor upward
It is composed of a bias power source for supplying a i _m, the relay b
Contacts to the deviation amplifier, a contact of the relay to the bias power supply, the common contact of the relay is connected to the input of the drive amplifier, current command value i _m of the bias supply, the weight of the linear motor movable portion The lower limit is a value at which the linear motor is not supported and falls, and the upper limit and a value at which the heat generation and the heat radiation are in a balanced state when the current continues to flow through the linear motor.

Action In the above configuration, when the movable portion of the linear motor does not reach the target position, the burnout alarm is turned on, and the input signal of the drive amplifier of the servo amplifier becomes a constant low voltage,
A constant current that moves the movable portion upward flows in the linear motor coil. If this current value is set to a small value that supports the weight of the moving part and does not burn the coil, the moving part of the linear motor is kept pressed against the upper limit of the linear motor with a weak force. .

EXAMPLES Examples of the present invention will be described below with reference to the drawings. The portion surrounded by the alternate long and short dash line in FIG. 1 is a block diagram of the servo amplifier of the present invention. Reference numeral 1 is a linear motor, 6 is a position detector mechanically coupled to the linear motor, and 7 is a speed detector. The target position command value 12 from the numerical controller or the like is converted into an analog voltage by the digital / analog converter 13, and at the addition point 20, the difference between the target position command and the output P _S of the position detector, that is, the position deviation amount ΔP Becomes Position deviation amount Δ
P is amplified by the deviation amplifier 21 and becomes a difference Δv with the output v _S of the speed detector 7 at the second addition point 22. Δv is the deviation amplifier 23
It is amplified by and is connected to the third addition point 24 via the contact of the relay 29. 26 is a current detector whose output i _S is also connected to the adding point 24. Now the gain of the drive amplifier 25 is much larger than 1 (20
More than twice), the negative feedback from the current detector 26
The positive input i _{a at} summing point 24 and the output i _{S of the} current detector are approximately equal. Therefore, a current flows through the linear motor 1 in proportion to the voltage i _a on the positive input side of the addition point 24.

27 is a window comparator, which is the output of the deviation amplifier 2323
Turns off only when i _C is between + V _x and -V _x (V). V _x is the maximum error voltage between the target position and the current position caused by the dead zone of the power amplifier 25, mechanical friction, hysteresis, etc. when the linear motor is normally positioned. Therefore, the output of the deviation amplifier 23 is + V _x ~ when the positioning is completed.
It will be in the range of -V _X (V), but will be out of the range if positioning is not completed. 28 is a timer circuit, and if a predetermined time T (several seconds) elapses while the output of the window comparator 27 remains on, this timer circuit 28 is turned off even if the output of the window comparator is short (several milliseconds). Reset. Therefore, once the timer circuit
When the movable portion of the linear motor 1 is moved by hand to pass the target position after the operation of 28, the timer circuit is reset and the servo amplifier returns to the original state. Now, 30 Setsu換Ru the bias power source, the positive input voltage i _m is the summing point 24 of the bias power supply 30 when the relay 29 is turned on. Then, a current flows through the coil of the linear motor so as to move the movable portion of the linear motor in the upward direction. The voltage i of the bias power supply is not burned out in a state where the amount of heat generated by the linear motor (I _m ² R _m : I _m is the power supply of the linear motor, R _m is the resistance value) and the amount of heat radiated from the surface of the linear motor are in balance. The value is the upper limit. In the examples, the temperature rise was set to 30 ° C. or less. Further, the lower limit of the voltage i is a value that generates a thrust that allows the movable portion to move upward due to gravity. Therefore, even if current is constantly flowing, the coil is not burned and the movable part can be kept in a state where it does not descend.

A window comparator and a timer circuit as an embodiment of the second invention are shown. The part surrounded by the one-dot chain line shows the window comparator. In the figure, R _{1 to} R ₆ are resistors VR ₁ and
VR ₂ is a variable resistor, C ₁ is a capacitor, D ₁ and D ₂ are diodes,
Q ₁ is a transistor and IC _{1 to} IC ₃ are integrated comparator circuits (equivalent to NS LM311). R ₂ and R ₃ are resistors of equal value that adjust VR ₁ and _connect the negative input terminal of I _C1 to the-
Set V _s (V) to + V _s (V) at the positive input terminal of I _C2 . When the input voltage i _c (V) is in the range of + V _s to −V _s , the outputs of I _C1 and I _C2 are + V _cc (V). At this time, the transistor Q ₁ is turned on, the electric charge of the capacitor C ₁ is discharged with the time constant of T ₁ = C ₁ R ₆ , the negative input terminal voltage of I _C3 is lowered, and the relay 29 is turned off. Input voltage i _c (V) exceeds + V _s (V) or −V _s
When it is less than (V), the output of I _C1 or I _C1 becomes O (V), so that the transistor Q ₁ is turned off. Then capacitor C ₁
Is charged with a time constant of T ₂ = C ₁ · (VR ₂ ), and relay 29 turns on when the voltage of the input terminal of IC ₃ is 1/2 V _cc or more.
The resistance of VR ₂ is about 1000 times higher than that of R ₆ . Therefore, this timer circuit takes a few seconds for the relay 29 to turn on, but a few milliseconds for it to turn off. Therefore, during the normal positioning operation of the linear motor, the positioning movement time of the linear motor is less than 1 second, and during that time, the stop time, that is, the time when i _c is in the range of + V _x to −V _x (V) is 1/100. Relay 29 remains off as it is secured for more than a second. The diode D ₁ is used for discharging the electric charge of the capacitor C ₁ when the power of the servo amplifier is off, and the diode D ₂ is used for level shifting. Since the relay 29 should have a short operating time, a reed relay or a semiconductor analog switch is used.

FIG. 3 is a second embodiment of the present invention and shows a block diagram when a speed detector is not used. Burning of the coil of the linear motor can be prevented by the same principle as in the first embodiment.

As described above, the drive amplifier of the servo amplifier and the relay circuit of the deviation amplifier are inserted, the output of the deviation amplifier is monitored by the window comparator, and the timer circuit detects that the output of the window comparator is turned on for a set time or longer, When the linear motor positioning is not completed for the set time or more by turning on the relay as a burnout alarm signal with the output of the timer circuit and switching the output of the bias power supply to the input of the drive amplifier when the relay is on. The burnout of the linear motor coil can be prevented, and the spring for preventing the lowering of the movable portion of the linear motor whose moving direction is the vertical direction can be eliminated to shorten the time required for positioning. In addition, regardless of the reset signal from the outside, when the deviation amount becomes a predetermined value or less, the window comparator detects this and resets for a short time, so in the above case, remove the obstacle,
If you move the moving part of the linear motor to the target position by hand, you can return to normal.

[Brief description of drawings]

FIG. 1 is a block diagram of a servo amplifier for a linear motor in a first embodiment of the present invention, FIG. 2 is a concrete circuit diagram of the window comparator and timer circuit of FIG. 1, and FIG. 3 is a second circuit diagram of the present invention. 4 is a perspective view of the linear motor, FIG. 4b is a sectional view of the linear motor, and FIG. 5 is a block diagram of the servo amplifier of the conventional linear motor in the embodiment. 1 …… Linear motor, 6 …… Position detector, 7 …… Speed detector, 13 …… Digital / analog converter, 20,22,24 ……
Addition point, 21,23 …… Deviation amplifier, 25 …… Drive amplifier, 26
...... Current detector, 27 …… Wind comparator, 28 ……
Timer circuit, 29 …… Relay circuit, 30 …… Bias power supply.

Claims (1)

[Claims] 1. A linear motor having a structure in which a movable portion moves vertically, a deviation amplifier for amplifying a deviation between a target command position and a current position, a drive amplifier for amplifying electric power for driving the linear motor, and Set when the output of the deviation amplifier turns off within a preset voltage centered around zero volt, and when the output state of the find comparator continues beyond a preset time T, and when the window comparator turns off And a timer circuit which is reset in a shorter time than the time T,
A relay that is turned on and off by the output of the timer is configured movable portion of the linear motor in a bias power source for supplying a movable current command value i _m upwards, b contact of the relay to the deviation amplifier, a contact of the relay to the bias power supply, the common contact of the relay is connected to the input of the drive amplifier, current command value i _m of the bias supply, the lower limit values that do not fall bears the weight of the linear motor movable portion A servo amplifier for a linear motor, wherein the upper limit is a value that does not cause burnout in a state where heat generation and heat dissipation are balanced when the current continues to flow through the linear motor.