JPS6072004A - Control device of direct teaching type industrial robot - Google Patents

Abstract

PURPOSE:To prevent a drop of a control accuracy by eliminating a low frequency component from a compared output of the first and the second position detectors. CONSTITUTION:A control device of a robot inputs a value of a target position data theta1 from an operating device 204, and a value of a counter 105 for showing a position of an arm 107, etc., to a position control device 102, and a position command omegan is obtained from a difference of both of them. By this position command omegan, a motor M is rotated through a D/A converter 103, a comparator 111 and an amplifier 201, and the arm 107, etc. are rotated. In this case, the first position detector E1 is provided on the motor side, too, and a difference counter 106 for counting a value of a difference of pulse signals from the first and the second position detectors E1, E2 is provided. It is fed back to the comparator 111 through a D/A converter 109 and a low cut filter 152. This filter 152 eliminates a variation component of a low frequency at the time of a slide, etc. of a clutch 51.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a control device that is not affected by clutch slippage in a direct teaching type industrial robot and has excellent stability.

In general, teaching methods for industrial robots can be broadly divided into two methods: remote control teaching methods, in which an operator operates a switch on a remote control box to move the robot in an inching operation; There is a direct teaching method (also called manual teaching) in which teaching is performed by direct operation and input. The latter has the advantage of shortening the teaching time and being able to teach complex trajectories more efficiently than the former, but in order to make teaching operations easier with human power, it is necessary to connect the drive source and robot elements such as arms. A mechanism for lightening movement by inserting a clutch mechanism or the like in between is required, and as a result of providing such a lightening mechanism, the position detector of the robot element needs to be installed on the rear side of the clutch, that is, on the robot element side. Yes (°If a position detector is attached to the drive source side such as a motor as in the remote teaching method, position data cannot be captured when the clutch is OFF, that is, during teaching)
. Furthermore, the lightning and robot elements are equipped with a transmission means such as a reducer between the drive source and the robot element, and such transmission means have control delays due to gear backlash, twisting, deflection, etc. If the output from the position detector attached to the robot element side is used as the main feedback amount, vibrations from the transmission means will enter the control loop, making the control unstable, so increase the loop gain to speed up the control. This had the disadvantage of causing an oscillation state.

In order to eliminate the above-mentioned drawbacks, the present inventor has developed a control system for a direct teaching type industrial robot in which a drive source drives robot elements such as an arm through a transmission means such as a reducer. a first position detecting means for detecting the position of the robot element; a second position detecting means for detecting the position of the robot element and feeding the position information to the input side of the control system; A conversion means calculates position difference information corresponding to the positional deviation between the drive source and the robot element from the position information obtained by the detection means, and feeds this information to the input side of the control system. position storage means for sequentially storing teaching position data of the robot/nodo element sent from the position detection means;
and a reset means for clearing the difference in position of the second position detecting means at the time of reproduction, and a composite value of the taught position data retrieved from the position storage means and the position difference information at the time of reproduction, and a combination value of the taught position data. A direct teaching type industrial robot has been invented and has already been filed (Japanese Patent Application No. 57-190093), which is characterized by having a control means for multiplying the difference signal by a constant gain and outputting the result to the drive system.

This is to correct the position detection from the side of the robot element such as the robot arm as if it were detecting the position on the drive source side.For this purpose, a position detector is also attached to the drive source side, and two position detectors are installed on the drive source side. The position of the drive source side was determined by adding the difference between the detectors to the output value of the position detector on the robot element side.

Therefore, in the case of the above invention (Japanese Patent Application No. 57-190093), delays caused by deflection and twisting of the reducer etc. are canceled out, and while the position of the robot element side is detected, control is performed as if using the position signal of the drive source side. Control is stable as you do,
Even when the loop gain is increased, problems such as oscillation no longer occur.

However, in order for this kind of control to be performed accurately, it is necessary that there is no slippage of the clutch when it is engaged (during regeneration), but in order to save installation space and reduce weight, it is necessary to use a simple friction method. When a clutch is used, it is difficult to completely eliminate such slippage, and positioning accuracy decreases due to clutch slippage.

Furthermore, in the above invention (Japanese Patent Application No. 57-190093), by clearing the position difference information when the clutch is engaged to zero, the position detection error due to the shift in the clutch engagement position before and after the teaching operation is made zero. This is based on the premise that there is no deformation of flexible elements such as reducers that exist between the robot element and the drive source during cell clearing. The robot is equipped with a spring balance device for this purpose, but even with such a spring balance mechanism, it is difficult to completely eliminate deformation of the reducer, etc., and the disadvantage is that a small amount of error occurs each time it is reset. was there.

The present invention aims to prevent the decrease in control accuracy caused by latch slippage as described above, and its gist is a motor.

In a control device for a direct teaching type industrial robot that drives robot elements such as a robot arm through a reducer, clutch mechanism, etc. using a drive source such as a hydraulic cylinder,
a first position detector that detects the movement of the drive source; a second position detector that detects the position of the robot element and feeds back the position information to the input side of the control system; and a low-cut filter that removes low frequency components from the output signal of the comparison means and transmits it to the control system. This invention provides a control device for a certain direct teaching type industrial robot.

FIG. 1 shows an example of a direct teaching type welding robot to which the present invention can be applied.

The swivel table 301 has driving parts such as a motor, a speed reducer, and a clutch inside, and rotates in the direction of the arrow θ1.

The arm and wrist drive sections 302 are surrounded by a cover and provided one each on the left and right sides of the robot, and each arm and wrist drive section is built in one each.

That is, the first arm motor 314 attached to the side surface of the drive section 302 is connected to the first arm link 313 through a reducer and a clutch, as will be described later in detail with reference to FIG. Swirl. An arm 304a integrally attached to the first arm 304 that is swingable about the shaft 10 directly above the first arm moke 314, and the first arm link 313. and,
Furthermore, these arms 313a and 304. The links 313 and 313 that connect the two constitute parallel links. link 31
3. As the arm 304a and the first arm 30 rotate,
4 rotates in the same direction and by the same angle as the arm 313a in the direction of arrow θ2.

The second arm 305 is swingably attached to the shaft 11 attached to the tip of the first arm 304.
a link 14 rotatably driven by a second arm motor (314') attached to the back side of the second arm (the back side of the motor 314 in the figure); and a link 13 rotatably supported around the shaft 10; A first parallel link is formed by a wave link 316 connecting the links 13 and 14, and the link 13, the tip of the link 13, and the second
A connecting link 303 connecting the rear end portion 12 of the arm;
The rear end portions 1 of the first arm 304 and the second arm 305
2 constitute a second parallel link, and the second arm 305 is rotated in the direction of arrow θ3 by the rotation of the second arm motor 314' by these two sets of parallel links.

Furthermore, regarding the wrist, a swinging motor 315 is attached to the left and right side of the base of the first arm 304, and a rotating motor 3'5' is attached to the back side of the first arm 304. The chains built into the first arm and the second arm rotate, and the end of the chain reaches the wrist mechanism section 306, giving the wrist 3063 a rocking motion in the θ, force direction, and a turning motion in the 05 direction. and guide the welding torch 308 attached to the wrist 306a to an arbitrary position and to take an arbitrary posture necessary for the welding operation.

Next, a gravity balance mechanism for offsetting the gravitational moments of the first arm and the second arm will be explained. First, regarding the first arm, as described above, the first arm 30
4, a link 13 rotatably supported around an axis IO, a link 4 parallel to the link 13, and the link 13.
A vertical wade link 316 connecting the links 13 and 14 forms a parallel link, and the upper end B of the wade link 316 is always on the vertical line of the connection point between the link 13 and the wade link 316, and the upper end B and the second A spring balance mechanism 310 consisting of a tension spring or the like is provided between the rear end A of the arm and the rear end A of the arm.
is stretched, and due to the shape of the triangle ABD and the tension of the spring balance mechanism 310, a rotational moment in two directions of θ° acts on the first arm 304, and the gravitational moment of the first arm 304 is canceled out. Additionally, the spring balance mechanism 310
The tensile force can be balanced regardless of the value of the inclination angle θ2 of the first arm if it is configured to be proportional to the distance between A and B, which is the installation length. Regarding the second arm, the gravitational moment around the axis 11 of the second arm 305 is calculated by the weight of the spring balance mechanism 310 and the wave link 31.
This is offset by the weight of 6th grade. By using such a gravity balance, no force is required for the operation during teaching, and as will be described later, the accuracy of position control is improved.

Next, an arm drive mechanism will be described with reference to FIG. 2 as an example of a drive mechanism equipped with a lightening mechanism and a position detector that are essential for direct teaching. Such a drive mechanism can be used not only for operating the arm but also for rotating the swivel base 301 and operating the wrist portion.

In FIG. 2, M is a DC servo motor for driving, and on the side opposite to the output shaft of this motor M is a pulse encoder E that generates pulses according to changes in the rotation angle of the motor M.
A tacho generator rake 81 as a speed detector is attached. Also, a harmonic drive reducer 41 (product name: manufactured by Harmonisoku Drive System Co., Ltd.) is installed on the output side, and a clutch 51 is attached to the output shaft of the reducer. installed. This clutch is connected to the output shaft 42 of the reducer 41 when the friction plates 56 and 57 come into contact with or separate from each other.
The rotation of is transmitted (ON) to the robot element drive shaft 59,
Or it is shut off (OFF).

The structure of the clutch 51 includes a rotor 5 surrounding a coil 53.
2 is fixed to the output shaft 42, the coil 53 and the rotor 52 are not in contact with each other, and the coil 53 is attached to the case 54 of the drive mechanism.
is fixed to.

The armature 55 is spline-fitted to a spline shaft 58 integrally attached to the robot element drive shaft 59 and is slidable in the axial direction. When the coil 53 is excited, the rotor 5
The friction plates 56 and 57 are brought into close contact with each other. Conversely, when the coil 53 is not excited, a spring (not shown) causes the armature 55 to move toward the coil 53.
The friction plates 56, 57 are moved in the opposite direction, and the friction plates 56, 57 are separated.

Furthermore, a large gear 6 is coaxially connected to the robot element drive shaft 59.
The large gear 60 meshes with a small gear 63 coaxially integrated with a shaft 61 rotatably attached to the casing, and a large gear 64 coaxially integrated with the shaft 61 drives the pulse encoder E2. It meshes with a small float 66 attached to a shaft 68. A portion of the parallel link shown in FIG. 1 is attached to the robot element drive shaft 59, and rotation of the robot element drive shaft 59 drives the first arm 304 or the second arm 305.

The pulse encoder E is a component of a first position detection means for detecting the position of the drive source motor M, which will be described later, and the pulse encoder E2 is a component of a second position detecting means for detecting the position of the robot element. It is a component of the detection means.

Therefore, when the motor M rotates, the output shaft 42 of the reducer 41 rotates at a low speed, and when the clutch 51 is in the ON state, the rotation of the output shaft 420 is directly transmitted to the robot element drive shaft 59. And the robot element drive shaft 590 rotation is gear 60,
63, 64, and 66 to the pulse encoder E2. Pulse encoder E1 on the motor (drive source) M side
In order to equalize the number of output pulses of pulse encoder E2 on the robot element drive shaft 59 side, gear trains 60.63 and 64.6 are used.
6 has been inserted. That is, if the reduction ratio of the reducer 41 is, for example, 300, the speed increase ratio of the gear train is 30, and the number of pulses generated per one revolution of the drive shaft 68 of the pulse encoder E2 is 100 pulses, then the pulse encoder E
2 should be one that outputs 1000 pulses per rotation. By making the numbers of output pulses of both pulse encoders the same, subsequent calculations become easier.

However, a frequency divider or the like may be used to equalize the number of pulses.

Position detectors E1 and E2 installed at two locations like this
The output shaft 42 of the motor M is calculated by adding up the respective number of pulses.
The count number θ and θd corresponding to the rotation angle of the robot element such as the arm and the rotation angle of the robot element such as the arm can be obtained. Under constant speed operation, there is no twisting such as deceleration 1M41, so these θ□ and θ! corresponds to one to one.

Next, a block diagram of the entire control device according to the first embodiment of the present invention is shown in Part 3-1. As shown in the figure, this control device includes target position data θ, which is output from an arithmetic unit 204 generally constituted by a CPU of a microcomputer;
and the value of the counter 105 indicating the position of the robot element 107 such as an arm, that is, θβ, are taken into the position control device 102, and the difference between the two (θ□−θ is multiplied by an appropriate gain Kl) to determine the position. Command ω.Then output the position command ω.
□ is converted into an analog quantity by the D/A converter 103, the motor M is rotated through the comparator 111 and the amplifier 201, and the robot element 1 is
A normal proportional control system that rotates 07 is adopted. The position detector E2 (see Figure 2) that drives the counter 105 uses an incremental type pulse encoder, and in this case, an integrator is used to calculate the absolute value of the rotation angle of the arm. It is necessary to provide a counter 105, and when such an incremental pulse encoder is used, the position detector E2 corresponds to the second position detector.

In the present invention, in addition to the conventional control means as described above, a first position detector E as described above is provided on the motor side, and furthermore, first and second position detectors E and E2 are provided on the motor side. A difference counter 106, which is a kind of comparison means, is provided which integrates the pulse signals from and simultaneously counts the difference value. In this case, the first position detector El also uses an incremental pulse encoder, the output of which is input to the counter 104 and then input to the difference counter 106 as an integrated value. However, it is also possible to use absolute type pulse encoders as the first and second position detectors, in which case the counters 105 and 104 are omitted, and the difference counter 106 calculates the difference between the output values from both position detectors. It suffices if it simply performs calculations. In the case of the embodiment shown in the third figure,
The difference counter 106 is θ□ and θ! Position difference information (θ, −
θ.

) to the D/A converter 109. Amplifier 108. The signal is then passed through the low-cut filter 152 and then fed back to the comparator 111.

Further, the signal from the counter 105 is configured to be transmitted to the arithmetic unit 204, and when teaching, the arithmetic unit 204
4 is the robot element 107 input from the counter 105
location information is stored in the storage device 112 in the order of work operations.

The low-cut filter 152 is for removing low-frequency fluctuation components that rarely occur, such as slippage of the clutch 51. The cutoff frequency of this low-cut filter 152 is strongly related to the natural frequency of the machine, and mechanical vibrations must be sufficiently transmitted, so it is desirable to set the cutoff frequency to a value less than half the natural frequency of the machine. . Generally, the natural frequency of a robot is about 10 Hz, so a low cut filter with a cutoff frequency of 5H2 or less may be used.

In the case of the present invention, the slippage of the clutch 51 and the error at the time of reset are included in the output value (θ□−θ) of the difference counter 106, but by passing this output value through the low-cut filter 152, the slippage of the clutch 51 is For a moment when it slips, it passes through the low-power filter 152 and causes an error, but once the slipping stops, the amount of slipping does not pass through the filter, so it does not become an error thereafter.

Further, since the error at the time of reset does not appear as a change, it does not pass through the filter and does not lead to a detection position error of the robot element.

For playback control, the teaching values sequentially retrieved from the storage device 112 are given as the command value θ1 from the arithmetic unit 204 to the position control device 102, where the output value θ! of the counter 105 is given. ω, which is the difference between θ1−θI and a constant gain multiplied by 1. is calculated, and after this ω□ is converted into an analog quantity through the D/A converter 103, the comparator 1
given to 11. In the comparator 111, ω□−(θ, −
θ is calculated (when the gain Kf of amplifier 108 is 1), and the result is θ1-θa(θ□-θl)-θ1-θ
, is given to the motor M, so that θ! Although it is used as position information, θ□ is apparently controlled as the main feed puncture amount, and vibrations, torsions, etc. of the mechanical system due to transmission means such as reducers are controlled from within the control loop. Can be excluded. In other words, the control characteristics of a direct teaching type robot have been improved to those of a remote teaching type robot. Also, difference information θ, +l
-θl is multiplied by an appropriate value Kf (Kf > 1) to obtain ω. Compared to this, it is possible to produce an acceleration feedback effect and further improve control performance.

Furthermore, the relationship between θ□ and θl does not match when the clutch 51 is OFF, that is, when the teaching operation is being performed, because they are unrelated, and even at the starting point when the clutch 51 is reconnected during playback, the values are different from the beginning. Become something. With this, θ is displayed during playback.
□ - θl cannot be measured correctly, so clutch 5
1, it is necessary to reset the value of the difference counter 106 (clear to zero) at the time of 0NLk, that is, at the start of reproduction. When this difference counter 106 is reset, the difference between θ□ and θ becomes O, and the value of the difference information θ1−θ generated thereafter represents the amount of torsion, vibration, etc. of the reduction gear 41 and the like.

The timing to generate this reset signal is at the start of playback,
Strictly speaking, it is desirable to perform this immediately before starting the playback operation. This is because the reducer 41 is twisted when accelerating and θ
□ and θ! This is because they no longer match. However, this type of cent operation is performed using the difference counter 106 as described above.
In addition to the reset operation that completely sets the value of 10 to O, the difference counter 10 that occurs at the end of teaching or just before the start of playback
The value of 6 may be stored as an initial difference, and the result obtained by subtracting the above-mentioned initial difference from the device difference information constituted by the difference counter 106 at the time of reproduction is inputted to the comparator 111 as true position difference information. A similar adhesive effect can be obtained.

When absolute type encoders are used as the first and second position detectors, the values of the second position detector are set to the values of the first position detector in order to match the values of these position detectors before playback. Use a reset signal such as transmitting it to the device.

When the gain Kf of the amplifier 108 is increased and the amount of torsion of the reducer 41 is fed back, since this amount of torsion is proportional to the acceleration, the effect of the well-known acceleration feedback is added, and the control is performed as described above. becomes more stable.

Figure 4 shows the difference information θ□−θ! This is a step response in a general direct teaching type robot that does not feed back θI but only θI, and vibrations due to torsion of the reducer etc. are significant.

On the other hand, in FIG. 5, Kt=1 and the difference information θ1−θl
It is understood that the control is quite stable due to the feedback. Furthermore, if the gain of the amplifier 108 is increased to promote the effect of acceleration feedback, the control becomes more stable as shown in FIG.

As described above, the present invention controls the movement of a direct teaching type industrial robot in which a robot element such as a robot arm is driven by a drive source such as a motor or a hydraulic cylinder through a reducer clutch mechanism or the like. a first position detector for detecting the position of the robot element; a second position detecting means for detecting the position of the robot element and feeding the position information to an input end of the control system; and the first position detector and the second position. A direct teaching type industry characterized by comprising a comparison means for determining the difference in output value from a detector, and a low-cut filter for removing low frequency components from the output signal of the comparison means and transmitting the signal to a control system. Since this is a robot control device for robots, the main feedback amount is extracted from the load side (robot element side), and a feedback loop is formed for compensation by detecting only the variation between the load side and the drive source side using a low-cut filter. By doing so, it is possible to perform accurate positioning that is not affected by clutch slippage or deformation of the reducer, and at the same time, it is possible to stabilize control characteristics without being affected by twisting of the reducer or vibrating objects. In addition, the difference information between the load side and the drive source side represents acceleration, and by feeding back this information, more stable control characteristics can be obtained, and the advantages of both closed-loop and semi-closed-loop control methods can be obtained. We have succeeded in providing a control device that has both functions.

[Brief explanation of drawings]

FIG. 1 is a side view of an entire conventional general welding robot, FIG. 2 is a side sectional view showing an example of a robot arm drive mechanism to which the present invention can be applied, and FIG. A block diagram showing a signal transmission system in a control device according to an embodiment, and FIGS. 4 to 6 are step response graphs showing the effects of the present invention. (Explanation of symbols) 204...Arithmetic device 102...Position control device 11
1...Comparator 41...Reducer 51...Clutch 107...Robot element 104.105...Counter 152...Low cut filter M...Motor (drive source) 106...Difference Counter (comparison means) E,, E2...Pulse encoder. Figure 4 Figure 6 Figure 5 Time t(s)

Claims (1)

[Scope of Claims] A control device for a direct teaching industrial robot that drives a robot element such as a robot arm by a drive source such as a motor or a hydraulic cylinder via a speed reducer, a clutch mechanism, etc. a first position detector that detects movement; ■ a second position detection means that detects the position of the robot element and feeds back the position information to the input side of the control system; ■ the first position detector; Comparing means for determining the difference in the output value from the second position detector; and (1) a low-frequency filter for removing low frequency components from the output signal of the comparing means and transmitting the removed signal to the control system. A control device for a direct teaching type industrial robot, characterized by the following.