JPS63153610A - Robot controller - Google Patents

Abstract

PURPOSE:To eliminate non-uniformity in rotation and to perform path control and positioning control inexpensively, stably, and exactly, by correcting its own position command signal. CONSTITUTION:A correction signal generating means 11 outputs a correction signal thetaR with a phase opposite to and the same cycle T as that of error oscillation in a harmonic driving speed reducer 2. When the path control and the positioning control of a robot arm 3 are performed, the position command signal thetain can be obtained in the adder 17 of the position command signal generating means 18 by adding the correction signal thetaR on a position command base signal thetain0 from a robot arithmetic unit 10, and the feedback control of the robot can be performed by the position command signal thetain. In such a way, it is possible to eliminate the error oscillation in a transmission mechanism without necessitating a corrector, etc., in a feedback system, and to perform the path control and the positioning control inexpensively, stably, and exactly.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a robot equipped with a transmission mechanism such as a reduction gear that has error vibrations (uneven rotation) between a movable object such as a robot arm and a motor. Especially regarding devices for performing path control and positioning control.

The present invention relates to a robot control device that cancels error vibrations according to the error vibration characteristics of the transmission mechanism.

[Prior Art] Conventionally, as shown in FIG. 3, a speed detector 4 and a position detector (pulse encoder) 5 are attached to a motor 1, and a harmonic drive reducer 2 is attached to the output shaft of the motor 1.
An industrial robot has been proposed in which a robot arm 3 as a movable body is connected via a robot arm 3 as a movable body. Although not shown, the harmonic drive reducer 2 is a wave generator.

Consists of circular splines and flex splines.

According to this robot, when the motor 1 is driven to rotate, the robot arm 3 is decelerated by the required reduction ratio.
is now operational.

[Problems to be Solved by the Invention] Generally, in industrial robots, NG machines, etc., rotational unevenness may cause error vibrations (chattering). In particular, welding robots and their peripheral equipment (work positioners), such as welding robots that synthesize multiple axes to obtain tool trajectories, such as multi-jointed robots.

It is known that vibration appears as distortion of the tool trajectory in robot sliders.

Accurate path control and positioning control are important points for industrial robots such as welding robots, but due to the above-mentioned rotational unevenness, they often contain error vibrations of about ±0.5+++m. There are various causes for the occurrence of error vibrations due to rotational unevenness.

For example, this may be caused by poor servo control performance, the resolution or angle error of the position detector, or calculation errors during control, but there are many factors that can cause problems between the motor and the movable object, such as a robot arm. Rotation irregularities caused by angular transmission errors in transmission mechanisms such as speed reducers also have a large effect.

As an example of the above transmission mechanism, transmission unevenness in a harmonic drive reduction gear will be explained with reference to FIGS. 3-4.

The harmonic drive reducer 2 shown in FIG. There is a relationship as shown in the graph shown in FIG. In the graph of Fig. 4, the horizontal axis represents the rotation angle of the input shaft 2a, that is, the motor 1, and the vertical axis represents the rotation angle of the output shaft 2b. Input shaft 2a and output shaft 2 in an ideal case with no transmission unevenness
The relationship with b is shown.

However, in reality, as shown by curve j (deceleration curve at a typical harmonic reduction ratio) in FIG. It is known that a rotation of 2b can be obtained. Therefore, as shown in FIG. 1, the width δ of the song 11Xj indicates the rotation transmission error of the harmonic drive reducer 2. In FIG. 4, T is the period of the rotational unevenness, and a is the phase difference indicating the zero point position of strain.

This transmission error is about 1 to 2 minutes, but there are many other reduction gears that are even larger than this value. The magnitude that this transmission error affects the trajectory of the tip of the robot arm is small, about ±0.1 to 0.211 IIm, but it becomes a source of vibration that affects the natural frequencies of other component machines and the natural frequencies of the servo circuit. When the frequency of transmission error and transmission error match, a resonance phenomenon occurs.

If the result is large, ±2~2~ at the tip of the robot arm.
There is also a risk of vibrations of up to 3 mm.

Note that, although the case where a harmonic drive reducer is used as the transmission mechanism in 1 or more is described, a similar transmission error occurs also with a cycloreduction gear or a planetary reduction gear. In addition, robot drive mechanisms with a ball screw structure have a transmission error called "stagger," and robot transmission mechanisms such as chain sprockets have "wobble."
A transmission error called "polygonal motion" occurs.

Therefore, a robot control device as shown in FIG. 5 has also been proposed.

This device basically uses a rotational position detection signal of the motor 1 detected via a converter (pulse counter) 6 from a position detector (pulse encoder) 5 directly connected to the motor 1, and a 1-position command signal generator. Compare the position command signal from 8 and set the motor 1 by the servo amplifier based on the deviation.
is feedback-controlled to perform path control and positioning control of the robot arm 3.

Then, in order to cancel the rotational unevenness on the output shaft side of the harmonic drive reducer 2, correction is made based on the position detection signal from the converter 6 and the deceleration characteristics (error vibration characteristics) of the harmonic drive reducer 2 that have been investigated in advance. The correction signal output from the converter (function generator) 7 is added to the position detection signal from the converter 6, and harmonic drive deceleration@
After correcting the transmission error No. 2, feedback control is performed using this position detection signal to cancel rotational unevenness.

However, in such a robot control device, it is necessary to provide a corrector 7 that performs arithmetic processing in the servo driver, which leads to increased costs, and if the correction signal is added in the feedback system. , there was a problem that the control system might become unstable.

The present invention aims to solve these problems, and by correcting the position command signal itself, rotational unevenness can be canceled out, and path control and positioning control can be performed stably and accurately at low cost. The object of the present invention is to provide a robot control device that achieves the following.

[Means for Solving the Problems] Therefore, the robot control device of the present invention has a position command signal generating means that outputs a reference position command base signal, and a position command base signal generating means that outputs a position command base signal as a reference. a correction signal generating means for outputting a correction signal having the same period and in opposite phase to the error vibration of a transmission mechanism interposed between the body and the motor;
and an addition means for adding the above-mentioned position command base signal and correction signal and outputting the result as a position command signal.

[Function] In the above-described robot control device of the present invention, when performing path control and positioning control of a movable object (robot arm, etc.) in the robot, the addition means uses the position command base from the one position command pace signal generation means. A 1-position command signal is obtained by adding to the signal a correction signal of the same period and in opposite phase to the error vibration (rotation unevenness) of the transmission mechanism from the correction signal generation means, and this position command signal is used as the position command ( is output from the M number generating means.Then, the position command signal and the position detection signal from the position detector are compared,
By performing path control and positioning control of the robot, error vibrations of the transmission mechanism are canceled out.

[Embodiments of the Invention] A robot control device as an embodiment of the present invention will be explained below with reference to the drawings. Fig. 1 is a block diagram showing its overall configuration, and Fig. 2 is a graph for explaining its operation. It is.

In FIG. 1, 1 is a motor, 2 is a harmonic drive reducer as a transmission mechanism having error vibration, 3 is a robot arm as a movable body connected to the motor 1 via the harmonic drive reducer 2, and 5 is a robot arm as a movable body. a position detector (pulse encoder) attached to the output shaft of the motor 1 to detect the rotational position of the motor 1; 6 a converter (pulse counter) that obtains the absolute position from the position detector 5;
Reference numeral 9 denotes a servo amplifier that performs feedback control of the motor 1 based on a deviation between a position command signal θin from a position command generation means 18 and a position detection signal from the converter 6, which will be described later.

Further, in this embodiment, 1o is a robot arithmetic unit as a position command base signal generating means that outputs a position command base signal θina as a reference, and 11 is an opposite phase and the same period as the error vibration of the harmonic drive reducer 2. This correction signal generation means 11 outputs a correction signal θR of T (see FIGS. 2 and 4).
9 Phase setter 13. Adder 14. It is composed of a distortion amplitude setter 15 and a function generator 16.

Here, the divider 12 divides the position command base signal θ1no from the robot arithmetic unit 10 by an amount corresponding to the known period T of error vibration of the harmonic drive reducer 2 (see FIGS. 2 and 4). The adder 14 calculates the remainder information Rθ obtained as a result of division by the divider 12 and the phase difference a set by the phase setter 13 (see FIGS. 2 and 4; the zero point position of distortion and the position command). This is to perform addition (including subtraction) with the deviation from the starting point of the base signal θinn.

Further, the function generator 16 receives information (Rθ
+a) and the amplitude X of the error vibration set by the distortion amplitude setter 15 (see FIG. 2), a correction signal OR is output according to the following equation (1).

θR: -(x/2)・5in((R6+a)・27C
/T)...(1) Furthermore, 17 is an addition means for adding the position command base signal θino from the robot arithmetic unit 1o and the correction signal θR from the correction signal generating means 11 and outputting the result as a position command signal θ1n. It is an adder as an adder.

The position command signal generating means 18 is connected to the above-mentioned robot arithmetic device 10. Correction signal generation means 11 and adder 1
Consists of 7.

Since the robot control device as an embodiment of the present invention is configured as described above, when performing path control and positioning control of the robot arm 3 in an industrial robot, the adder 17 of the position command signal generating means 18 , the position command base signal θ from the robot arithmetic unit 10
ino, the correction signal θR(
The calculation procedure for the correction signal θR will be described later) to obtain the position command signal θin, and this position command signal θ1n is output from the position command signal generating means 18.

By the way, the period T of error vibration is almost determined by the type of reducer (for example, in a harmonic drive reducer, one rotation of the input shaft has two cycles.

In the case of a robot drive mechanism with a cyclo reducer or a ball screw structure, the phase difference a is one cycle, and in the case of a chain sprocket, it is one cycle per pitch, etc.), but the phase difference a differs depending on how the reducer is assembled. Although it is possible to adjust this phase difference a mechanically, in this embodiment, the phase difference a is set electrically from the phase setter 13 by using a dip switch or key-in.

In addition, in this embodiment, a distortion amplitude setting device 1 is provided so that the amplitude X of the error vibration can be set and inputted as needed.
The amplitude X is set from 5 onwards.

Now, based on the phase difference a and the amplitude is calculated. That is, the position command base signal θin+ from the robot arithmetic device 10 is divided by a known period T in the divider 12, and the remainder information Rθ is output from the divider 12 to the adder 14.

In this adder 14, the phase difference a from the phase setter 13 is added to the remainder information Rθ, and the added information (Rθ+
a) is output to the function generator 16.

Then, in this function generator 16, the amplitude X from the distortion amplitude setter 15, the known period T, and the addition information (R6+a)
From there, an operation is performed based on the above equation (1), and the result of the operation is output to the adder 17 as a correction signal θR.

In this way, a correction signal OR having the opposite phase and the same period T as the error vibration of the harmonic drive reducer 2 is calculated, and by adding this correction signal OR to the position command base signal θinn in the adder 17, the As shown in Figure 2,
Error vibration of harmonic drive reducer 2 (uneven rotation;
It becomes possible to obtain a position command signal θ1n that cancels out the signal (see FIG. 4).

Therefore, the position command signal θ1n is compared with the position detection signal from the position detector 5 (obtained via the converter 6), and the servo amplifier 9 drives and controls the motor 1 based on the deviation. By controlling the path and positioning of the arm 3, error vibrations (uneven rotation) of the harmonic drive reduction gear 2 are canceled out.

In addition, in reality, the phase difference a set by the phase setter 13
Since this differs depending on the case, this phase difference a is changed little by little during adjustment before the start of control, and the phase difference a that minimizes the error vibration is actually determined. Further, the amplitude X set by the distortion amplitude setter 15 is also determined to be an appropriate value by actually measuring (or calculating) the amplitude value of the error vibration in advance or by gradually changing the set value.

As a result, rotational irregularities of the harmonic drive reducer 2 can be canceled out without providing a corrector or the like in the far pack system, and path control and positioning control can be performed stably and accurately at low cost.

It is also possible to incorporate the correction signal generating means 11 and the adder 17 into software and into the robot arithmetic device 10. In this case, the device of the present invention can be realized only by adding software, and the device of the present invention can be realized by simply adding software. Another advantage is that control accuracy can be improved at an extremely low cost without the need for additional mechanical parts or high-precision parts.

In the above embodiment, the phase difference a is added to the remainder information Rθ, but after adding an appropriate phase difference to the position command base signal θ1no from the robot arithmetic unit 10, the remainder is calculated by dividing by one cycle T. You may also try to obtain information.

Further, in the above embodiment, the correction signal θR output from the function generator 16 is set to have a sine curve shape according to the error vibration characteristics of the harmonic drive reducer 2 as a transmission mechanism. The mechanism is something else, such as a cyclo reducer.

In the case of a ball screw structure or a chain sprocket, function generator 1 is used depending on the error vibration characteristics.
The correction signal θR from 6 may be set to have an arbitrary periodic curve, and in this case as well, the same effect as in the above embodiment can be obtained.

[Effects of the Invention] As detailed above, according to the robot control device of the present invention, error vibrations (rotation unevenness, chatter phenomenon) caused by passing through a transmission mechanism such as a reducer are synchronized in opposite phase. The correction signal added to the position command base signal is
It is output as a position command signal, and the position command signal is used to perform feedback control of the robot, so error vibrations in the transmission mechanism can be canceled out without the need for a corrector or the like in the feedback system, making it inexpensive and stable. This has the effect of allowing efficient and accurate path control and positioning control.

In addition, it is easy to convert into software, and the device of the present invention can be realized simply by adding software, and control accuracy can be improved at an extremely low cost without the need for additional mechanical parts or high-precision parts. There are some effects that can be achieved.

[Brief explanation of the drawing]

1 and 2 show a robot control device as an embodiment of the present invention, FIG. 1 is a block diagram showing its overall configuration, and FIG. 2 is a graph for explaining its operation. 3 and 4 show a conventional robot control device, FIG. 3 is a schematic diagram of the robot drive section, FIG. 4 is a graph for explaining the angular transmission error, and FIG.
The figure is a block diagram showing the overall configuration of an example of another robot control device. In the figure, 1 - motor, 2 - harmonic drive reducer as a transmission mechanism, 3 - robot arm as a movable object, 5 - position detector (pulse encoder), 6 - converter (pulse counter), 9. Servo amplifier, 1o-
robot arithmetic device as position command base signal generation means, 11-correction signal generation means, 12-divider, 13-phase setter, 14-adder, 15-distortion amplitude setter, 16
-Function generator, 17--Adder as addition means, 1
8-Position command signal generation means.

Claims (1)

[Claims] A position detector for detecting the rotational position of the motor on a robot whose movable body is connected to the motor via a transmission mechanism;
a position command signal generation means for outputting a position command signal, and compares the position detection signal from the position detector with the position command signal from the position command signal generation means to perform path control and positioning of the robot. In the control device, the position command signal generating means outputs a reference position command base signal and the error vibration of the transmission mechanism generates a correction signal having the same period and in opposite phase. 1. A robot control device comprising: a correction signal generating means for outputting; and an addition means for adding the above position command base signal and the correction signal and outputting the resultant as the position command signal.