JPH0122641B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device that improves the operational characteristics of an industrial robot.

Generally, in a control device for an industrial robot, the current value is negatively fed back to the command value of the work axis so that the work axis moves so that the amount of positional deviation between the two becomes zero.

Conventionally, a hydraulic cylinder driven by a servo valve is used as a working end, a means for detecting the operating force of the cylinder is provided, and a signal obtained from this detecting means is subtracted from a signal for driving the servo valve to control the control system. For example, the technology to stabilize
44-18409 and the like. In other words, the pressure receiving area of one chamber of the double-acting hydraulic cylinder is B1,
When the oil pressure is Q1, the pressure-receiving area of the other chamber is B2, and the oil pressure is Q2, the operating force F of the cylinder is, assuming there is no effect of gravity, F = B1・Q1−B2・Q2 …(1). Immediately after this operating force F is detected, feedback is provided.

According to such prior art, on a work axis where gravity acts, the operating force F does not become zero in steady state;
A steady value corresponding to at least gravity is output from the detection means. If there is such a steady value output, the driving speed of the cylinder in one direction and the opposite direction will be unbalanced, and the positioning accuracy and trajectory accuracy of the work axis will decrease. That is, in such prior art, since the signal obtained from the detection means is simply fed back directly as described above, it is desired to improve the static characteristics.

SUMMARY OF THE INVENTION An object of the present invention is to provide a control device for an industrial robot that can achieve vibration-free and highly accurate operation by preventing deterioration of static characteristics caused by gravity fluctuations of the work axis. .

The present invention drives a double-acting cylinder by an electro-hydraulic servo mechanism according to a position deviation drive signal between an axis condition command value and a current value of the work axis, and the work axis operated by the double-acting cylinder A control device for an industrial robot that performs work using a storage device 2 that stores in advance axis condition command values for a work axis of the industrial robot, and a storage device 2 that detects the current position of the work axis when the industrial robot repeats work. an encoder 8 that outputs a current value at the time of repeating the work; and an encoder 8 that responds to the output from the storage device 2 and the encoder 8 during the work repeat, and detects that the deviation between the current position and the command position of the store command value is less than a certain small value. When , the deviation drive signal is not output,
a converting means 10 having such an input/output characteristic that outputs a deviation drive signal corresponding to the deviation when the value exceeds the deviation; and a teaching time in which the axis condition is stored in advance in the storage device 2 during the work repeat. means 1 for generating a low-speed drive signal for driving the work shaft at a low speed; detecting the driving force on both sides of the piston of the double-acting cylinder 6, and transmitting the gravitational force on the work shaft 7 where gravity is applied to the cylinder; 6 is converted into the driving force, and from this, a feedback compensation signal is derived for suppressing the occurrence of vibration of the work shaft 6 and achieving high operating speed and positioning accuracy of the work shaft 6. Feedback compensation circuit 20
subtracting means 3 for calculating the difference between the low speed drive signal and the feedback compensation signal; adding means 4 for adding the deviation drive signal and the output of the subtracting means; The feedback compensation circuit 20 includes a control means 5 that does not generate a drive signal when the work axis reaches the command position, and adjusts each driving force on both sides of the piston of the double-acting cylinder by a servo mechanism. The driving force P1 on both sides of the piston is
Means for detecting A1, P2 and A2 21, 22, 23,
24, a clamp level setting circuit 28 for deriving a signal representing a value W obtained by converting the gravity on the work shaft 7 to the driving force of the cylinder 6, and one of the driving force detecting means 21, 22, 23, 24. one driving force detection means 21 on which gravity acts;
A clamp circuit 25 that subtracts the value W determined by the clamp level setting circuit 28 from the driving force P1・A1 detected by the clamp circuit 23, and the output from the clamp circuit 25 (=P1・A1−W)
The output of the other driving force detection means 22, 24 from
It includes a subtracter 26 that subtracts P2 and A2, and a high frequency converter 27 that converts the output from the subtracter 26 into a high frequency band to derive a feedback compensation signal, and the transfer function H of the high frequency converter 27 is , is expressed by the following formula, H=sT/1+sT where s is a Laplace variable, T is a time constant, and 1/T is approximately lower than the natural frequency of the working axis.
This is an industrial robot control device characterized in that the value is selected to be about 1.5 to 3 octaves low.

FIG. 1 is a system diagram of one embodiment of the present invention.
A circuit 1 generates a low-speed drive signal s1 for causing the work axis of an industrial robot to move at a low speed (creep speed) to accurately reach a predetermined position.

The low speed drive signal s1 is a small constant value, as shown in FIG.

This low-speed drive signal s1 is used during so-called teaching, in which an axis condition command value for the work axis to follow a predetermined work trajectory is stored in the storage device 2 in advance, and is transmitted via a comparator 3 and an adder 4, which will be described later. , given to the servo valve 5. The servo valve 5 drives a double-acting hydraulic cylinder 6 and thus a working shaft 7.

The low-speed drive signal s1 is also used during so-called work repeats, and is always added to the drive signal corresponding to the deviation between the store command value from the storage device 2 and the current value of the work axis 7 from the encoder 8. . This will be explained in more detail below. The store command value from the storage device 2 is subtracted by the current value from the encoder 8 by the comparator 9, and its deviation signal e is given to the conversion circuit 10.

FIG. 2 shows the input/output characteristics of the conversion circuit 10.
When the input deviation signal e is less than the small value e1, that is, when the work axis is close to the command position of the store command value, the output of the conversion circuit 10 is zero. When the deviation signal e exceeds the value e1, a deviation drive signal i corresponding to the deviation is output.

The rising waveform of the deviation drive signal i is shaped by the circuit 11 so that it starts slowly, and the waveform-shaped signal is input to the adder 4. Servo valve 5
, a low speed drive signal s1 is applied by the adder 4 until the work axis 7 reaches the target value during the work repeat.

The output from the adder 4 during work repeat is the sum of the output from the waveform shaping circuit 11 and the low speed drive signal s1, as shown in FIG. 5, when there is no feedback signal s2, which will be described next. Therefore, the work shaft 7 approaches the designated position and the conversion circuit 10
When the deviation drive signal i becomes zero, the work shaft 7 can accurately reach the designated position at a low speed, that is, at a creep speed, only by the low speed drive signal s1. Immediately before the work axis is positioned at the commanded position, the output of the comparator 9 is close to zero, and the input to the servo valve 5, that is, the driving force is at a minimum. At this time, the load side (servo valve, hydraulic cylinder,
If there is a reaction force due to a slight disturbance on the work shaft 7 and the work shaft, the work shaft 7 may be overcome by the force and stop just before positioning, and may not reach the commanded position. To compensate for this, a low-speed drive signal s1 is added to provide a force to overcome the disturbance and cause the work shaft 7 to reach the commanded position.

The feedback compensation circuit 20 detects the driving force on both sides of the piston of the double-acting cylinder, and
In order to obtain the value of the gravity on the work axis where gravity is applied and convert it into the driving force of the cylinder, and thereby to suppress the occurrence of vibration of the work axis and still achieve high operating speed and positioning accuracy of the work axis. Since the feedback compensation signal of 1 is derived, it is possible to improve the positional accuracy at the time of stopping and improve the work efficiency.

The low speed drive signal s1 is not generated when the work axis reaches the commanded position. This allows the working axis to reach the commanded position accurately. The servomechanism adjusts the respective driving forces on both sides of the piston of the double-acting cylinder so that the working shaft reaches the commanded position, so that the working shaft smoothly reaches the commanded position.

The feedback compensation circuit 20 is provided to detect the operating force of the working shaft 7 by the hydraulic cylinder 6 and to compensate the operation of the working shaft 7 so that the working shaft 7 does not generate undesirable vibrations. What should be noted is that the feedback signal s2 of the feedback compensation circuit 20 is given to the comparator 3 inserted between the low-speed drive signal generation circuit 1 and the adder 4, but this low-speed drive signal s1 is As mentioned above, it is always used during both teaching and repeating. Therefore, the operation of the work axis 7 is always compensated during teaching and repeating. Comparator 3 serves to subtract feedback signal s2 from low speed drive signal s1. Servo valve 5 drives hydraulic cylinder 6 at a speed corresponding to the level of the signal from adder 4. In order to determine the direction of movement of the work shaft 7 by this hydraulic cylinder 6, a chamber 6a,
The pressure oil supplied to the servo valve 6b is controlled by a processing circuit (not shown) provided in association with the servo valve 5 and implemented by a microprocessor or the like.

During teaching, the operations of the conversion circuit 10 and the rising waveform shaping circuit 11 are stopped, and the level of the signal applied from the rising waveform shaping circuit 11 to the adder 4 is zero. At this time, the difference obtained by the comparator 3 between the signal s1 from the low speed drive signal generating circuit 1 and the signal s2 from the feedback compensation circuit 20 is given to the servo valve 5 from the adder 4.
The operator can bring the work shaft 7 to a desired position at a speed corresponding to the level of the signal from the adder 4 by controlling the servo valve 5 through the aforementioned processing device. When the working axis 7 reaches a desired position, the operator operates the processing device to store the current position of the working axis in the storage device 2. Such a control operation during teaching was disclosed in Japanese Patent Publication No. 51-34180, which was known before the filing of this application, and is well known to those skilled in the art. In this way, even during teaching, the operational performance is improved by the signal s2 from the feedback compensation circuit 20.

In the feedback compensation circuit 20, the hydraulic pressure in the chamber 6a on the head side of the piston of the hydraulic cylinder 6 is
P1 and the oil pressure P2 in the rod-side chamber 6b are detected by pressure detectors 21 and 22, respectively. The coefficient unit 23 calculates the product P1·A1 of the oil pressure P1 on the head side of the piston of the hydraulic cylinder 6 and its pressure receiving area A1. This product P1·A1 represents the driving force on the head side. If the pressure receiving area on the rod side of the hydraulic cylinder 6 is A2, the coefficient unit 24 calculates the rod side driving force.
Calculate P2 and A2. These coefficient units 23, 24
It also serves to equalize the output sensitivity characteristics of the pressure detectors 21 and 22. The output of the coefficient multiplier 23 is applied to a subtracter 26 via a clamp circuit 25, and the output of the coefficient multiplier 24 is applied as is.

It is assumed that a gravitational force acting toward the left in FIG. 1 is acting on the work shaft 7. Therefore, an extra force corresponding to the gravity is applied to one chamber 6a of the double-acting cylinder 6, and the clamp circuit 2
5 acts to subtract this gravity. That is, the clamp circuit 25 is the clamp level setting circuit 2.
The output from the coefficient multiplier 23 is clamped or subtracted by a clamp level defined by 8. The clamp level setting circuit 28 detects the weight of the object being held, the length of the work shaft 7 in a polar coordinate system industrial robot, and the vertical position in the vertical plane, etc., and adjusts the gravity on the work shaft 7 where gravity is applied to the cylinder 6
The clamp level corresponding to the value W converted to the operating force is determined.

Therefore, the output of the clamp circuit 25 is (P1・
A1-W).

The subtracter 26 calculates the operating force F of the work shaft 7 as shown in the following equation, and provides an electric signal corresponding to the operating force F to the high frequency unit 27.

F=P1・A1−P2・A2−W (3) The transfer function H of the high frequency converter 27 is expressed by the following equation.

H=sT/1+sT...(4) Here, s is a Laplace variable and T is a time constant. Generally speaking, the working axis of a multi-degree-of-freedom industrial robot has different natural frequencies depending on its length, its own weight, and the weight of the object held at the working end. in the frequency range. By the way, in order to sufficiently reduce or eliminate the vibration of the work shaft 7, the time constant T of the high frequency generator 27 should be set such that 1/T is approximately 1.5 less than 0.
It must be selected so that the value is ~3 octaves lower. For the purpose of absorbing vibrations, the time constant T should be selected to be infinite, that is,
The most effective method is to directly feed back the operating force without going through the high frequency device 27, but this high frequency device 27 improves steady-state characteristics that would be lost when direct feedback is used, and ensures practical reliability. inserted for.

The work axis 7 is affected by fluctuations in frictional force due to changes over time, drifts caused by temperature changes in electric circuits such as pressure detectors and amplifiers, and fluctuations in the gravity acting on the work axis 7. axis 7
It is desirable to select the time constant T of the high-frequency wave generator 27 as small as possible in order to prevent imbalance in operating speed in the left-right, front-back, and up-down directions, and to prevent positioning accuracy from decreasing.

However, when the time constant T is chosen to be small, another problem arises. In industrial robots, the natural frequency of the work shaft 7 is a small value as described above, so if the time constant T is made small, the work shaft 7
It becomes impossible to remove the natural vibration of Therefore, the time constant T cannot be reduced unnecessarily.

As mentioned above, the causes of deterioration in the operating speed and positioning accuracy of the work shaft 7 include fluctuations in the frictional force acting on the work shaft 7, drifts in the pressure detector and amplifier, and fluctuations in gravity. Among the two causes, fluctuations and drifts in the frictional force are relatively small in value and have a small rate of change over time, and therefore do not have a large adverse effect on operating speed and positioning accuracy. In contrast, the fluctuation of gravity has a large value and a large rate of change over time. Therefore, even if the time constant T of the high-frequency wave generator 27 cannot be selected to be small, it is necessary to control the adverse effects on the operating speed and positioning accuracy caused by fluctuations in the gravity of the work shaft 7. The present invention solves this problem.

Referring to FIG. 6, the work shaft 7 is a double-acting cylinder 6.
Assume that the workpiece 31 is removably attached to the work shaft 7 and is driven up and down by the work shaft 7. At this time, the driving force of the chamber 6a is A1.P1 as described above, the driving force of the chamber 6b is A2.P2, and the operating force F3 is expressed by the following equation as described above.

F3=A1・P1−A2・P2−W
...(5) Assume that the work 31 is removed at time t1 shown in FIG. 7, while the work 31 is attached to the work shaft 7. At this time, the operating force F3 changes in steps due to the gravity W of the workpiece 31. Input signal i to high frequency amplifier 27
becomes a step signal as shown in FIG. 72. When the value of this step signal is set to a, the output signal of the high frequency converter 27 follows the time course as shown in FIG. 7. At time t1, the high frequency converter 27 has an output level a, and when the time constant T is small, it follows the course of line l2, and as the time constant T increases, it follows lines l3 and l4. From this, it can be seen that it is necessary to reduce the time constant T of the high frequency converter 27 to quickly reduce its output, or to reduce the level of a of the input signal i. Since reducing the time constant T causes natural vibration as described above, the time constant T cannot be reduced unnecessarily. Therefore, in the present invention, the gravity W determined in the clamp level setting circuit 28 is The circuit 25 subtracts the signal, thereby calculating the third equation, thereby reducing the level a of the input signal i. Therefore, even if the time constant T of the high frequency amplifier 27 is large, the output level of the step response can be reduced.

As shown in FIG. 8, a working shaft 7 is driven by a double-acting cylinder 6, the end of which is connected by a pin 32 to another double-acting cylinder 33; Piston rod 3 of cylinder 33
A workpiece 35 is attached to cylinder 4, and cylinder 6
It is assumed that the end of the cylinder 33 is pivoted at a fixed position by a pin 36, and the cylinder 33 is angularly displaceable by the pin 37. room 6
The operating force due to the driving forces A1, P1, A2, and P2 of a and 6b is caused by the gravity of the workpiece 35, etc. when the piston rod 34 of the double-acting cylinder 33 expands over time as shown in FIG. 91. changes to become larger due to Therefore, as shown in FIG. 9, the input signal i of the high frequency converter 27 changes linearly over time, forming a so-called ramp input waveform. When the input signal shown in FIG. 92 is inputted to the high frequency converter 27, its output waveform becomes as shown in FIG. 93. If the slope of the input signal i is b, the steady value of the output signal is bT, and the steady value increases as the time constant T increases. From this point of view, it is desirable to select a small time constant T of the high frequency amplifier 27, but if the time constant T is selected small as described above, natural vibration will occur. Therefore, even if it is not possible to select a small time constant T, it is necessary to reduce the level of the input signal i to the high frequency amplifier 27 in order to reduce the level bT of the output signal.
In the present invention, a clamp level setting circuit 28 and a clamp circuit 25 are provided in order to reduce this input signal i.

In this way, according to the present invention, by suppressing the occurrence of vibration, it is possible to achieve high operating speed and high positioning accuracy of the work shaft 7.

Figure 3 shows the left and right operating forces F1 and F2 at creep speed when the work shaft 7 is driven in the left and right direction.
shows. As shown in FIG. 3, the friction of each component of the work shaft 7 generally differs in the left and right directions, so
The magnitudes of the operating forces F1 and F2 required to drive the work shaft 7 at a constant speed in the left-right direction are not equal. Therefore, if the time constant T of the high frequency converter 27 is large, the operating speeds in the left and right directions will be unbalanced. It is desirable to avoid such velocity imbalances, especially at creep rates. For this purpose, the clamp circuit 25 increases or decreases the DC level of the output corresponding to the operating force from the coefficient unit 23, that is, the clamp circuit 25 increases or decreases the DC level of the output corresponding to the operating force from the coefficient unit 23. Alternatively, the DC level is superimposed so as to relatively lower the output from 24, and the clamp level l of the operating forces F1 and F2 is thereby made so that the apparent operating forces F1 and F2 are approximately equal (see Figure 3). can be set.

In the present invention, in the transfer function H of the high frequency converter 27 shown in the above-mentioned second equation, 1/T is approximately 1.5 to 3 times lower than the natural frequency of the working axis of the industrial robot.
The value is selected to be about an octave lower. According to experiments by the inventor of the present invention, the total weight of the movable parts including the working shaft 7, the piston and piston rod of the hydraulic cylinder 6 connected thereto, and the welding machine connected to the working shaft 7 is, for example, 120 kg. The total length of the movable part is, for example, 300 cm, and the natural frequency of the working shaft 7 is about 6 Hz. At this time, when the high-pass filter time constant T is set to 0.1 seconds, where 1/T is 2 octaves lower than its natural frequency, it is possible to prevent the natural vibration of the work shaft 7 from occurring, and also to prevent the adverse effects caused by fluctuations in gravity. It was confirmed that it was possible to achieve high accuracy in operation speed and positioning accuracy. In industrial robots that are generally widely used for applications such as spot welding and painting, 1/T is approximately 1.5 to 3 octaves lower than the natural frequency of the work shaft 7, so the present invention It is possible to achieve the effect of

Regarding the low-speed drive signal, the output of the comparator 3 is cut off, for example, so that when the working axis reaches the specified position, the output of the comparator 9 becomes zero, so that no low-speed drive signal is generated. As such, control means (not shown) are achieved. Therefore, the hydraulic cylinder 6 and the work shaft stop at the desired positioning position. Also, by the output of the storage device 2 and the encoder 8, that is, by the output of the comparator 9, the servo valve 5 is sent to the room 6a or 6b.
A signal is given from the control means to determine which of them should be given hydraulic pressure. Therefore, the moving direction of the hydraulic cylinder 6 and the work shaft is determined.

In the above embodiment, the comparator 3 is interposed between the circuit 1 and the adder 4, but in another embodiment of the present invention, the comparator 3 is interposed between the adder 4 and the servo valve 5. It is also possible to intervene.

In this way, the feedback circuit works both during work repeats and during teaching, making it possible to improve the operational performance of the industrial robot.
In particular, according to the present invention, when the deviation between the current position and the command position of the store command value of the storage device is less than a certain small value, the conversion means does not output the deviation drive signal, and therefore does not output the low speed drive signal. Since the low-speed drive signal from the generating means is given to the servo mechanism, the work axis is driven at a low speed, and the low-speed drive signal is corrected by a feedback signal during this low-speed drive, resulting in good operating performance. , accurate positioning becomes possible. Therefore, the operating speed during repeat operation can be increased,
Work efficiency can be improved. Furthermore, the above-mentioned low-speed drive signal is used not only during repeat operation but also during teaching, so
Work efficiency during teaching can also be improved.

As described above, according to the present invention, the feedback circuit works both during repeat work and during teaching, thereby making it possible to improve the operational performance of the industrial robot. In particular, according to the present invention, when the deviation between the current position and the command position of the store command value of the storage device is less than a certain small value, the conversion means does not output the deviation drive signal, and therefore does not output the low speed drive signal. Since the low-speed drive signal from the generating means is given to the servo mechanism, the work axis is driven at a low speed, and the low-speed drive signal is corrected by a feedback signal during this low-speed drive, resulting in good operating performance. , accurate positioning becomes possible. Therefore, the operation speed during repeat operation can be increased, and work efficiency can be improved. Furthermore, since the above-mentioned low-speed drive signal is used not only during the repeat operation but also during teaching, the work efficiency during teaching can also be improved.

Further, according to the present invention, a high frequency generator is used for feedback compensation, and when the time constant is T, 1/T is approximately 1.5 to 3 times higher than the natural frequency of the work shaft.
By selecting a value as low as an octave, it is possible to prevent the natural vibration of the work shaft from occurring.

Moreover, even if the time constant T is selected to be a relatively large value that prevents such natural vibrations, the value W obtained by converting gravity into the driving force of the cylinder 6 is subtracted by the action of the clamp circuit, and the high frequency Since the level of the input signal that is not related to the generation of vibration to the high frequency generator 27 is lowered, it is possible to suppress the level of the output signal that degrades the static characteristics from the high frequency generator 27 due to fluctuations in gravity to a small level. . In this way, it is possible to prevent the adverse effects of gravity fluctuations and achieve high operating speed and positioning accuracy. Fluctuations in the frictional force acting on the work shaft 7 and drifts in the pressure detector and amplifier are relatively small values, and the rate of change over time is much smaller than the fluctuations in gravity, so these two causes are Therefore, the operating speed and positioning accuracy do not decrease significantly, and there is no problem in practice.

[Brief explanation of drawings]

FIG. 1 is a system diagram of an embodiment of the present invention, FIG. 2 is an input/output characteristic diagram of the conversion circuit 10 of FIG. 1, and FIG. 3 is a diagram for explaining the operation of the clamp circuit 25 of FIG. 1. , FIG. 4 is a diagram showing the waveform of the low-speed drive signal s1, FIG. 5 is a diagram showing the output waveform of the adder 4, and FIG.
The figure is a simplified diagram showing a state in which the work shaft 7 is provided extending vertically, FIG. 7 is a diagram showing the step response characteristics of the wave device 27 in the configuration of FIG. 6, and FIG. Driving double acting cylinder 3
FIG. 9 is a diagram showing the lamp response characteristics of the high frequency amplifier 27 in the configuration of FIG. 8. 1...Low speed drive signal generation circuit, 2...Storage device, 3, 9...Comparator, 4...Adder, 5...Servo valve, 6...Double acting hydraulic cylinder, 7...Work axis, 8... Encoder, 10... Conversion circuit, 11
... Rising waveform shaping circuit, 20 ... Feedback compensation circuit, 21, 22 ... Pressure detector, 23,
24...Coefficient unit, 25...Clamp circuit, 26...
...Subtractor, 27...High frequency device.

Claims (1)

[Claims] 1. A double-acting cylinder is driven by an electro-hydraulic servomechanism according to a position deviation drive signal between an axis condition command value and a current value of the work axis, and is operated by the double-acting cylinder. A control device for an industrial robot that performs work using a work axis includes a storage device 2 in which axis condition command values for the work axis of the industrial robot are stored in advance, and a current position of the work axis when the work of the industrial robot is repeated. an encoder 8 that detects and outputs a current value; and an encoder 8 that responds to outputs from the storage device 2 and the encoder 8 during the work repeat to detect a deviation between the current position and the command position of the store command value. When the value is less than a small value, the deviation drive signal is not output,
a converting means 10 having such an input/output characteristic that outputs a deviation drive signal corresponding to the deviation when the value exceeds the deviation; and a teaching time in which the axis condition is stored in advance in the storage device 2 during the work repeat. means 1 for generating a low-speed drive signal for driving the work shaft at a low speed; detecting the driving force on both sides of the piston of the double-acting cylinder 6, and transmitting the gravitational force on the work shaft 7 where gravity is applied to the cylinder; 6 is converted into the driving force, and from this, a feedback compensation signal is derived for suppressing the occurrence of vibration of the work shaft 6 and achieving high operating speed and positioning accuracy of the work shaft 6. Feedback compensation circuit 20
subtracting means 3 for calculating the difference between the low speed drive signal and the feedback compensation signal; adding means 4 for adding the deviation drive signal and the output of the subtracting means; The feedback compensation circuit 20 includes a control means 5 that does not generate a drive signal when the work axis reaches the command position, and adjusts each driving force on both sides of the piston of the double-acting cylinder by a servo mechanism. The driving force P1 on both sides of the piston is
Means for detecting A1, P2 and A2 21, 22, 23,
24, a clamp level setting circuit 28 for deriving a signal representing a value W obtained by converting the gravity on the work shaft 7 to the driving force of the cylinder 6, and one of the driving force detecting means 21, 22, 23, 24. one driving force detection means 21 on which gravity acts;
A clamp circuit 25 that subtracts the value W determined by the clamp level setting circuit 28 from the driving force P1・A1 detected by the clamp circuit 23, and the output from the clamp circuit 25 (=P1・A1−W)
The output of the other driving force detection means 22, 24 from
It includes a subtracter 26 that subtracts P2 and A2, and a high frequency converter 27 that converts the output from the subtracter 26 into a high frequency band to derive a feedback compensation signal, and the transfer function H of the high frequency converter 27 is , is expressed by the following formula, H=sT/1+sT where s is a Laplace variable, T is a time constant, and 1/T is approximately lower than the natural frequency of the working axis.
A control device for an industrial robot, characterized in that the value is selected to be about 1.5 to 3 octaves low.