JPH0727410B2 - Direct teaching type industrial robot controller - Google Patents

Description

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

Generally, the teaching methods for industrial robots are roughly divided into a remote control type teaching method in which an operator operates a switch of a remote control box to move and teach the robot by inching operation, and an operator teaches the tip of a robot arm or a wrist or tool. There is a direct teaching (also referred to as manual teaching) method of directly operating and teaching by input. The latter has the advantage that the teaching time can be shortened and a complicated trajectory can be taught efficiently compared to the former, but in order to enable easy teaching operation manually, the drive source and robot elements such as arms are It is necessary to provide a mechanism for lightening by inserting a clutch mechanism or the like between them, and as a result of providing such a lightening mechanism, it is necessary to attach the position detector of the robot element to the rear side of the clutch, that is, the robot element side. There is (if the position detector is attached to the drive source side such as the motor as in the remote teaching method, the position data cannot be fetched when the clutch is OFF, that is, when teaching). Usually, the robot element is provided with a transmission means such as a speed reducer between the drive source and the robot element, and the transmission means has a control delay due to backlash, twisting, bending, etc. of the gear. When the output from the position detector attached to the robot element side is used as the main feedback amount, vibration etc. by the transmission means enters the control loop and the control becomes unstable. Therefore, when the loop gain is increased to speed up the control, there is a drawback that an oscillation state is brought about.

In order to solve the above-mentioned drawbacks, the present inventor uses a drive source to drive a robot element such as an arm through a transmission unit such as a speed reducer in a direct teaching type industrial robot control device. First position detecting means for detecting the position of the source, second position detecting means for detecting the position of the robot element and feeding back the position information to the input side of the control system, first and second position detecting From the position information obtained by the means, position difference information corresponding to the displacement between the drive source and the robot element is calculated, and the conversion means feeds this back to the input side of the control system, and the second position detection at the time of teaching. Position storing means for sequentially storing the teaching position data of the robot element sent from the means, and reset means for clearing the difference between the positions of the first and second position detecting means generated at the time of teaching at the time of reproduction. And a control unit for multiplying the signal of the difference between the teaching position data and the position difference information taken out from the position storage unit at the time of birth and the signal of the difference between the teaching position data by a constant gain and outputting to the drive system. A patent application has already been filed for inventing a direct teaching type industrial robot characterized by the above (Japanese Patent Application No. 57-190093).

This is to correct the position as it is detecting the position on the drive source side while detecting the position from the robot element side such as the robot arm. For this reason, a position detector is attached to the drive source side as well. The position on the drive source side is obtained 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),
Delay due to flexure and twist of the reducer is offset, and the control is stable as if the position signal on the drive element side is used while detecting the position on the robot element side, and oscillation occurs even if the loop gain is increased. Inconvenience such as being in a state does not occur.

However, in order for such control to be performed accurately, it is a condition that there is no slippage of the clutch when the clutch is engaged (at the time of playback). When a friction clutch is used, it is difficult to eliminate such slippage, and the slippage of this clutch reduces the positioning accuracy. Positioning accuracy is similarly reduced due to backlash such as gears and reduction gears interposed in the power transmission system from the drive source to the robot element, and other mechanical deviations.

Further, in the above invention (Japanese Patent Application No. 57-190093), the position detection error due to the shift of the meshing position of the clutch before and after the teaching work is made zero by clearing the position difference information when the clutch is engaged to zero. This is based on the premise that there is no deformation of the flexible element such as a speed reducer existing between the robot element and the drive source at the time of zero clear. For this reason, the robot is equipped with a spring balance device, but even with such a spring balance mechanism, it is difficult to completely reduce the deformation of the speed reducer and the like, and a small amount of error occurs each time it is reset. was there.

An object of the present invention is to prevent a decrease in control accuracy caused by slipping of the clutch as described above, and the gist of the invention is a drive source such as a motor or a hydraulic cylinder and a robot element such as a robot arm. And the reduction mechanism,
The clutch mechanism is provided with a second position detector which is connected through a mechanical transmission system having a crack mechanism and which detects the position of the robot element and feeds back the position information to the input side of the control system. Is released and the robot element is operated to teach, and the clutch mechanism is connected at the time of reproduction to connect the drive source to the robot element, and the teaching is obtained by the second position detector at the time of teaching. In a controller for a direct teaching industrial robot that replays the robot element based on the position information, a first position detector that detects the drive position of the drive source, a first position detector, and a first position detector. The comparison means for obtaining the difference between the output values of the second position detector and the output signal of the comparison means removes the DC component generated by the deviation of the mechanical transmission system. And a correction means for correcting the position information obtained by the second position detector based on the signal input through the low cut filter. The present invention provides a control device for a direct teaching type industrial robot, which is described below.

FIG. 1 shows an example of a direct teaching type welding robot to which the present invention can be applied. The swivel base 301 has driving parts such as a motor, a speed reducer, and a clutch therein, and swivels in the direction of the arrow θ ₁ . Drives 30 for arms and wrists
2 is surrounded by a cover, and one is provided for each of the left and right sides of the robot, and each has one arm drive unit and one wrist drive unit incorporated therein.

That first arm motor 314 attached to the side of the drive unit 302, as speed reducer will be described in detail with reference to FIG. 2 after to pivot the first arm link 313 _a through the clutch.
An arm 304 _a mounted integrally with the first arm 304 swingable about a shaft 10 immediately above the first arm motor 314,
The first arm link 313 _a, further arms 313
and links 313 _b connecting the _a and 304 _a constitute a parallel link. With the rotation of the link 313 _a , the arm 304 _a and the first arm 304 rotate in the same direction and the same angle as the arm 313 _a in the direction of the arrow θ ₂ .

The second arm 305 is a shaft 11 attached to the tip of the first arm 304.
A link 14 that is swingably attached to the second arm motor (314 ') attached to the back side of the drive unit 302 (back side of the motor 314 in the figure).
And a link rotatably supported about the shaft 10
13 and a weight link 316 connecting the links 13 and 14
Forming a first parallel link by means of a link 13, a connecting link 303 connecting the tip of the link 13 and the rear end 12 of the second arm, the first arm 304, and the second arm.
305 and the rear end 12 form a second parallel link,
With the two sets of parallel links, the second arm motor 31
The rotation of 4 ′ causes the second arm 305 to rotate in the direction of the arrow θ ₃ .

As for the wrist, a swinging motor 315 and a swinging motor 315 'provided on the back side of the first arm 304 are attached to the left and right sides of the root of the first arm 304. The wrist driving motors are used to drive the first arm. And the chain built in the second arm rotates, and the end of the chain reaches the wrist mechanism section 306, and gives the wrist 306a _a swinging motion in the θ ₄ direction and a swinging motion in the θ ₅ direction. , guides the welding torch 308 which is attached to the wrist 306 _a at an arbitrary position,
Take any posture necessary for welding operation.

Next, a gravity balance mechanism for canceling the gravity moments of the first arm and the second arm will be described. First, regarding the first arm, as described above, the first arm 304
Link 13 rotatably supported around the axis 10 at the lower end of
And the parallel link 14 and the vertical weight link 316 connecting the links 13 and 14 form a parallel link,
The upper end B of the weight link 316 is always on the vertical line of the connection point D between the link 13 and the weight link 316, and between the upper end B and the rear end A of the second arm, a spring such as a tension spring is provided. The balance mechanism 310 is stretched, and due to the shape of the triangle ABD and the tension of the spring balance mechanism 310, a rotational moment in the θ ′ ₂ direction acts on the first arm 304,
The gravity moment of the first arm 304 is canceled. The tension force of the spring balance mechanism 310 can be balanced regardless of the value of the tilt angle θ ₂ of the first arm if it is configured to be proportional to the distance between AB, which is the mounting length. The second
Regarding the arm, the gravitational moment about the axis 11 of the second arm 305 is canceled by the weight of the spring balance mechanism 310 and the weight of the weight link 316. By using such gravity balance, a force is not required for the operation at the time of teaching, and the accuracy of position control is improved as described later.

Next, a drive mechanism for an arm as an example of a drive mechanism having a lightening mechanism essential for direct teaching and a position detector for positioning will be described with reference to FIG. Such a drive mechanism can be used not only for arm operation, but also for swivel drive of the swivel base 301 and actuation of the wrist.

In FIG. 2, M is a driving DC servo motor, and a pulse encoder E ₁ for generating a pulse according to a change in the rotation angle of the motor M and a speed detector on the side opposite to the output shaft of the motor M. And a tacho generator 81 as. Also, on the output side, a harmonic drive reducer 41 (product name: manufactured by Harmonic Drive System Co., Ltd.) that is concentric and can obtain a large reduction ratio is installed.
A clutch 51 is attached to the output shaft of the speed reducer. In this clutch, the friction plates 56 and 57 contact (connect)
Alternatively, by releasing (releasing), the rotation of the output shaft 42 of the speed reducer 41 is transmitted (ON) or interrupted (OFF) to the robot element drive shaft 59. The structure of the clutch 51 is such that the rotor 52 surrounding the coil 53 is fixed to the output shaft 42.
And the rotor 52 are not in contact with each other, and the coil 53 is the case of the drive mechanism.
It is stuck to 54.

The armature 55, which is spline-fitted to the spline shaft 58 integrally attached to the robot element drive shaft 59 and is slidable in the axial direction, is attracted to the rotor 52 side when the coil 53 is excited, and the friction plate 56 and 57 sticks. On the contrary, when the coil 53 is not excited, the armature 55 is moved in the direction opposite to the coil 53 by a spring (not shown), and the friction plates 56 and 57 are separated from each other.

Further, on the robot element drive shaft 59, a large gear 60 is coaxially engraved, and the large gear 60 meshes with a small gear 63 coaxially integrated with a shaft 61 rotatably attached to a casing,
Further, the large gear 64 coaxially integrated with the shaft 61 is a pulse encoder E ₂
Meshes with a small gear 66 attached to a drive shaft 68 of the. A part of the parallel link shown in FIG. 1 is attached to the robot element drive shaft 59, and the first arm 304 or the second arm 305 is rotated by the rotation of the robot element drive shaft 59.
Is driven.

The pulse encoder E ₁ is a constituent element of the first position detector for detecting the position on the side of the drive source motor M, which will be described later, and the pulse encoder E ₂ is the _second constituent element for detecting the position of the robot element. It is a component of the position detector.

Therefore, when the motor M rotates, the output shaft 42 of the speed reducer 41 rotates at a low speed, and when the clutch 51 is in the ON state, the rotation of the output shaft 42 is directly transmitted to the robot element drive shaft 59. The rotation of the robot element drive shaft 59 is transmitted to the pulse encoder E ₂ via gears 60, 63, 64, 66. Motor (drive source) M
Side gear encoder E ₁ and robot element drive shaft 59 side pulse encoder E ₂
0,63,64,66 are inserted. That is, when the reduction ratio of the reduction gear 41 is, for example, 300, the speed increasing ratio of the gear train is 30,
If the number of pulses generated per revolution of the drive shaft 40 of the pulse encoder E ₁ is 100 pulses, the pulse encoder E ₂ will be 1
Anything that outputs 1000 pulses per rotation may be used. By making the number of output pulses of both pulse encoders uniform, the subsequent calculation becomes easy. However, a frequency divider or the like may be used to make the number of pulses uniform. The pulse numbers of the pulse encoders E ₁ and E ₂ attached at these two places are integrated to obtain the count numbers θ _m and θ _m corresponding to the rotation angle of the output shaft 42 of the motor M and the rotation angle of the robot element such as an arm. It is possible to obtain θ _l . Since there is no twist of the speed reducer 41 etc. in the constant speed operation state, this θ _m and θ _l are 1
Corresponds to one-to-one.

Next, FIG. 3 shows a block diagram of the entire control device according to the first embodiment of the present invention. As shown in the figure, this control device is a counter 1 which indicates the value of target position data θ _i output from a computing device 204 which is generally constituted by a CPU of a microcomputer and the position of a robot element 107 such as an arm.
05 value, i.e. captures and theta _l to the position controller 102, where it is multiplied by an appropriate gain K ₁ to both the difference (θ _i -θ _l) is outputted as a position command omega _n, the position command omega _n Is converted into an analog amount by the D / A converter 103, the motor M is rotated via the comparator 111 (correction means) and the amplifier 201, and the rotation of the motor causes the robot element 107 to rotate via the speed reducer 41. The proportional control method of is adopted. Counter 105
An incremental (incremental) pulse encoder is used as the pulse encoder E ₂ (see FIG. 2) that drives the counter. In this case, a counter 105, which is an integrator, is used to calculate the absolute value of the arm rotation angle. Need to be installed. In the present invention, in addition to the conventional control means as described above, the above-mentioned pulse encoder E ₁ is also provided on the motor side, and the pulse signals from the pulse encoders E ₁ and E ₂ are integrated and at the same time the difference is obtained. A difference counter 106, which is a kind of comparison means for counting the value of, is provided. In this case, the pulse encoder E _{1 is} also an incremental pulse encoder, the output of which is input to the counter 104 and is input to the difference counter 106 as an integrated value. The difference counter 106 converts the position difference information (θ _m −θ ₁ ) between θ _m and θ _l into the D / A converter 1
09, amplifier 108, and low-cut filter 152, then comparator
Give feedback to 111.

Further, the signal from the counter 105 is configured to be transmitted also to the arithmetic device 204, and at the time of teaching, the arithmetic device 204 outputs the position information of the robot element 107 input from the counter 105 to the storage device 112 in the order of the work operation. Store.

The low-cut filter 152 is for removing a DC component caused by slippage of the clutch 51, and its cut-off frequency is in consideration of the natural frequency of the mechanical system, that is, the natural frequency of the robot is generally about 10 Hz. Since the frequency before and after that must be sufficiently transmitted, if it is at least half of that frequency, 5 Hz or less, it is sufficiently practical.

In the case of the present invention, the slippage of the clutch 51 and the error at the time of resetting are included in the output value (θ _m −θ _l ) of the difference counter 106, but this output value passes through the low-cut filter 152, so that the clutch 51 Sliding passes through the low-cut filter 152 for a moment when it slips, causing an error, but while sliding, the change in sliding is insignificant and does not pass through the filter.
If the slippage stops, the slipped amount will be cut and not an error. All you need is a momentary slippage error.

In addition, 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 detected position error of the robot element.

In the reproduction control, the teaching value sequentially fetched from the storage device 112 is given as a command value θ _i from the arithmetic device 204 to the position control device 102, where the output value θ _l of the counter 105 is given.
Ω _n is calculated by multiplying the difference θ _i −θ ₁ with a constant gain K _1, and this ω _n is further converted into an analog amount through the D / A converter 103, and then the comparator 111 Given to. In the comparator 111, ω _n − (θ _m −θ _l ) (when the gain K _{f of the} amplifier 108 is K _f = 1) is calculated, and as a result, θ _i −θ
_l - By signal _{(θ m -θ l) = θ} i -θ m is applied to the motor M, despite the position information theta _l, the apparent theta _m by controlling the main feedback amount As a result, vibrations and twists of the mechanical system due to transmission means such as reduction gears can be excluded from the control loop. That is, the control characteristics of the direct teaching robot are improved to the control characteristics of the remote teaching robot. Matasa information theta _m - [theta] _l to appropriate values _K f _{(K f}
If it is multiplied by> 1) and compared with ω _n , the effect of acceleration feedback is produced and the control performance can be further improved.

Also, the relationship between θ _m and θ _l does not match because the clutch 51 is off, that is, when the teaching operation is being performed, and therefore does not match, and the value is different from the beginning even at the starting point when reconnected. It becomes a thing. With this, at birth θ _m −θ
_{Since l} cannot be measured correctly, it is necessary to reset (clear to zero) the value of the difference counter 106 when the clutch 51 is turned on, that is, when reproduction is started. When the difference counter 106 is reset, the difference between θ _m and θ ₁ becomes 0, and the value of the difference information θ _m −θ ₁ generated thereafter indicates the amount of twist or vibration of the speed reducer 41 or the like.

The timing for generating this reset signal is
Strictly speaking, it is desirable to perform it just before starting the reproduction operation. This is because the speed reducer 41 is twisted at the time of acceleration and θ
_{This is because m} and θ _l do not already match. However, such a reset operation is not limited to the above-described reset operation for completely setting the value of the difference counter 106 to 0, and the value of the difference counter 106 generated at the end of teaching or immediately before the start of reproduction is stored as an initial difference. If you play, the difference counter 10
The same resetting effect can be obtained even if the difference obtained by subtracting the initial difference from the position difference information transmitted from 6 is input to the comparator 111 as the true position difference information.

When the gain K _{f of the} amplifier 108 is increased and the twist amount of the speed reducer 41 is fed back excessively, this twist amount is proportional to the acceleration, so that the well-known acceleration feedback effect is added, and as described above. Control is more stable.

FIG. 4 shows a step response in a general direct teaching robot in which the difference information θ _m −θ ₁ as described above is not fed back, but only θ _l is fed back, and vibration due to torsion of the speed reducer is significant.

Difference information theta _m - [theta] _l Fig. 5 as _K f = 1 contrast
It is understood that the control is fairly stable due to the feedback. Further, _if the gain Kf 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 connects a drive source such as a motor and a hydraulic cylinder to a robot element such as a robot arm through a mechanical transmission system including a speed reduction mechanism and a crack mechanism, and detects the position of the robot element. A second position detector that feeds back its position information to the input side of the control system, teaches by releasing the clutch mechanism and operating the robot element at the time of teaching, and connects the clutch mechanism at the time of reproduction. In the controller for the direct teaching type industrial robot, the driving source and the robot element are connected to each other, and the robot element is regenerated based on the position information obtained by the second position detector during teaching. A first detecting the drive position of the drive source
Position detector, comparing means for obtaining the difference between the output values of the first position detector and the second position detector, and the direct current generated by the deviation of the mechanical transmission system from the output signal of the comparing means. A low-cut filter that removes the component and transmits it to the input side of the control system; and a correction unit that corrects the position information obtained by the second position detector based on the signal input through the low-cut filter. Since it is a direct teaching type industrial robot controller characterized by including, the main feedback amount is taken out from the load side (robot element side), and the difference between the load side and the drive source side is changed by a low-cut filter. By forming a feedback loop for compensation by detecting only the minute, accurate positioning can be performed without being affected by slippage of the clutch and deformation of the reducer. It is possible to stabilize the control characteristics without being influenced by the twist of the reducer or the vibrating object, and the difference information between the load side and the drive source side shows the acceleration, and by feeding back this, it becomes more stable. We have succeeded in providing a control device that can obtain control characteristics and has the advantages of both the closed-loop control system and the semi-closed-loop control system.

[Brief description of drawings]

FIG. 1 is a side view of the entire conventional general welding robot, FIG. 2 is a side sectional view showing an example of a drive mechanism of a robot arm to which the present invention can be applied, and FIG. FIG. 4 is a block diagram showing a signal transmission system in a control device according to an embodiment, and FIGS. 4 to 6 are graphs of step responses showing effects of the present invention. (Explanation of reference numerals) 204 ... Arithmetic unit, 102 ... Position control unit, 111 ... Comparator, 41 ... Reducer, 51 ... Clutch, 107 ... Robot element, 104, 105 ... Counter, 152 ... Low cut filter, M ...... motor (driving source), 106 ...... difference counter (comparing means), E _1, E ₂ ...... pulse encoder.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Murata, No. 100 Takegahana Town, Ise City, Mie Prefecture, Ise Plant, Shinko Electric Co., Ltd. (56) References JP-A-58-121407 (JP, A) JP-A-59- 79312 (JP, A)

Claims (1)

[Claims] 1. A drive source such as a motor or a hydraulic cylinder and a robot element such as a robot arm are connected via a mechanical transmission system having a speed reduction mechanism and a crack mechanism, and the position of the robot element is detected to detect the position. A second position detector that feeds back position information to the input side of the control system is provided, teaching is performed by releasing the clutch mechanism and operating the robot element at the time of teaching, and connecting the clutch mechanism at the time of reproduction. In the controller for the direct teaching type industrial robot, the drive source and the robot element are connected by means of, and the robot element is regenerated based on the position information obtained by the second position detector during teaching. The difference between the output values of the first position detector that detects the drive position of the drive source and the first position detector and the second position detector is calculated. And a low-cut filter for removing the DC component generated from the output of the comparison means by the displacement of the mechanical transmission system and transmitting it to the input side of the control system, and the low-cut filter. A controller for a direct teaching type industrial robot, comprising: a correction unit that corrects the position information obtained by the second position detector based on a signal.