JPS59107881A - Industrial robot - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an industrial robot, and more particularly to an industrial robot having a control device for preventing transient vibrations.

In order to reduce weight and increase the range of motion, the structure of the industrial robot is "open", that is, the ends of the 'T' moving parts of A-I and Q are free ends. Therefore, the mechanism of an industrial robot has a low natural frequency and a small damping coefficient.

Therefore, when trying to control a trajectory at higher speeds than in industrial robot robots, large changes in acceleration occur in the rotary motor in areas where the curvature of the trajectory is narrow, resulting in undesirable transient vibrations in the mechanism. , causing orbital errors.

The basic measure to prevent this transient vibration of the mechanical part is to increase the rigidity and damping rate of the mechanical part, but such improvement of the mechanical part depends on the size of the mechanical part.

This is not easy as it would lead to a small increase in quantity and therefore cost.

The above orbit error can be reduced by reducing the curvature of the orbit, but since the magnitude of the acceleration generated by a rotating motor on the same orbit is proportional to the tangential velocity of the orbit, it is necessary to perform high-speed orbit control. It is necessary to prevent excessive IJ1 vibration of the mechanical part.

The present applicant has proposed a method for increasing the rigidity of a mechanical system having vibrational characteristics or controlling it in a non-vibratory manner, as described in Japanese Patent Application Laid-Open No. 54-31877R, ``Mechanical Stiffness Compensation Servo Control Device.'' 92155r electric machine control system”
I proposed it. The former has the effect of mainly reducing transient vibrations, and the latter has the effect of mainly reducing sustained vibrations (forced vibrations). All of these methods are basically for ~-axis servo systems.

In general, the motion of an industrial robot is a combination of (1) regular motion based on data instructed in advance through teaching, etc., and (2) the above-mentioned undesirable transient vibrations. These two motions can be distinguished by the difference in frequency components of the motion.The motion of ■ usually has a period of several seconds to several tens of seconds, and the motion of ■ has a resonant frequency of 5 to 50H of the mechanical system.
The frequency is higher than z. Therefore, from the perspective of the normal servo system, the motion of ■ can be considered to be a DC component, and the false motion can be considered to be an AC component. In order to dampen this transient vibration, the AC component of the motion of the robot's tip, v
(t) (a three-dimensional vector as a function of time) should be converged to zero. - Regarding the servo system of the axis, if the signal of the acceleration of the transient vibration is fed back to the control device of the rotary motor of the servo axis along with the rotational position and rotational speed according to the method described in the above patent publication, a damping effect will be exerted on fluctuations in acceleration. occurs, and the acceleration converges to zero in steady state. When acceleration is zero, velocity is constant and the alternating current component of velocity is zero.

However, industrial robots generally have a multi-axis configuration, and each axis often mechanically interferes strongly with each other. Therefore, in industrial robots, vibrations that occur in one axis also cause vibrations in other axes, resulting in beats or complex vibrations that are a combination of vibrations from multiple axes. For this reason, even if the method of the patent publication is applied only to a specific axis of an industrial robot, for example, a shaft with particularly large vibrations, a large effect of damping transient vibrations and sustained vibrations (forced vibrations) cannot be obtained. Figure 1 (a) shows the attenuation of one axis when there is no I-crossing between the axes, but between two axes that strongly intersect with each other, as shown in Figure 1 (b), the beat may occur. In such a case, if the method of the patent publication is applied only to one axis, the vibration damping effect will be effective only during the period when the amplitude of vibration of the applied axis increases, and the amplitude of vibration of the other axis will increase. After all, there is no damping effect during this period.

The vibration of the shaft to which the method of the above-mentioned patent publication is applied also cannot be rapidly damped. FIG. 11(C) shows an example of a vibration experiment when the method of the above-mentioned patent publication is applied to an axle load. The broken line P corresponds to the beat (FIG. 1(b)) when there is no vibration suppression control.

Therefore, the present applicant proposed in Japanese Patent Application No. 178153/1983 (Industrial Robot) J a method for preventing transient vibrations during high-speed trajectory control for an industrial robot composed of a multi-axis servo system.

However, in this proposed method, the motion of each axis of the robot with respect to the stationary coordinate system (earth) is different from that of other axes, such as a Cartesian coordinate type, a cylindrical coordinate type, and a joint type composed of parallelograms. This is limited to non-interfering cases, and when the motion of each axis with respect to the stationary coordinate system depends not only on the position of the corresponding rotary motor but also on the position of the rotary motor of the other axis, The acceleration of a point on the corresponding sliding mechanism element includes not only the acceleration information of the corresponding axis relative to the stationary coordinate system, but also the motion acceleration of the axis on which the motion depends. Therefore, in order to detect the acceleration signal and extract only the acceleration of the corresponding axis relative to the stationary coordinate system, it is necessary to remove other signal components. Removal of this signal generally requires a multidimensional matrix operation (essentially equivalent to a coordinate transformation operation from the robot's coordinate system 2 to the stationary dust d system) in a mechanism with a complex configuration such as an industrial robot. Therefore, the configuration was complicated and could not be put to practical use for signals that require high-speed processing, such as acceleration.

Hereinafter, the above-mentioned problems will be explained in detail regarding one form of industrial robot. Figure 2 is an industrial robot.

This symbol represents the basic mechanism of arm C. Figure (a) shows that arm C is fixed in a stationary coordinate system;
b) shows a rotation mechanism in which the fur LXC is rotated in the θ direction by the drive unit B, and (c) in the same figure shows a rotation mechanism in which the arm C is rotated in the θ direction around the joint J by the drive unit attached to the joint J. respectively. Figure 3 shows two forms of an industrial robot, where arm A is θ
The arm B rotates in the φ direction about the joint J2, and the arm C rotates in the ψ direction about the joint J2. The above arms are shown below as θ
axis, φ axis, and ψ axis. Now.

Regarding the θ-axis and the φ-axis, since the motion with respect to the stationary coordinate system is defined only by the positions of the θ-axis and the φ-axis, respectively, the previous application (Japanese Patent Application No. 178153/1987) can be applied. but,
Regarding the ψ-axis, motion with respect to the stationary coordinate system is related not only to the position of the ψ-axis, but also to the position of the φ-axis. FIG. 4 is a diagram showing the acceleration relationship of the ψ axis. If the acceleration of joint J2 with respect to the stationary coordinate system is αJ2, and the linear acceleration of joint J2 on the ψ axis in the direction perpendicular to this ψ axis at point Q in the distance statement is αψ, then the linear acceleration of point Q with respect to the stationary coordinate system is acceleration This becomes a composite vector α of αJ2 and the sentence αψ.

If a linear acceleration detector for the stationary coordinate system is attached at point Q perpendicular to this axis, the output of this detector is αQ=f(α
J2, sentence αψ) becomes a function of the values of both acceleration αJ2 and αψ. Therefore, even if this output αQ is fed back to the ψ-axis control device, it is not useful for preventing ψ-axis vibration since it includes information αJ2 unrelated to the ψ-axis. In other words, regarding the φ axis, the previous application (Japanese Patent Application No. 57-17815)
3) cannot be applied, and furthermore, it is extremely complicated to calculate the rotational acceleration of the ψ axis relative to the stationary coordinate system from the output of the linear acceleration detector attached to the ψ axis and the positions of the φ and ψ axes. is difficult.

The present invention also provides for the rotary motor to be placed at different positions on the movable mechanism element for a servo axis where the position of the movable mechanism element with respect to the stationary coordinate system is not defined only by the rotational position of the servo axis, as described in L. Two linear acceleration detectors are placed in a direction parallel to the tangential direction of the motion caused by the rotation of the servo axis, and the rotational acceleration signal with respect to the stationary coordinate system of the servo axis is detected by subtracting the outputs of both of the linear acceleration detectors. By feeding back the rotational position signal and rotational speed signal of the rotary motor to the control device of the rotary motor of the servo axis, transient vibrations during high-speed trajectory control of the industrial robot can be prevented and the industrial robot can be controlled. The purpose is to realize high-speed and highly accurate orbit control.

Hereinafter, the principle of the present invention will be explained in detail with reference to FIG.

If two points Q r and Q2 are taken from the joint J2 on the arm C of the industrial robot shown in FIG. Q2
The acceleration related to ・ is as shown in the figure. In other words, the acceleration αJ2 of the joint J2 is at two points Q r and Q 2
But with the same value, 1 point Q1. The rotational accelerations of the ψ axis in Q2 are respectively sentence 1 αψ and sentence 1 αψ (αψ: rotational acceleration of the ψ axis). Therefore, point Q1. If a linear acceleration detector is installed perpendicular to the ψ axis in Q2, its output will be the direction component αQ+ perpendicular to the ψ axis of the vector composite value α1 of the rotational acceleration signal αψ and αJ2, the rotational acceleration type and αJ, respectively.
is the direction component αQ2 perpendicular to the ψ axis of the vector composite value α2. At both outputs αQ+ and αQ2, joint J
Since the components related to αJ2 of the accelerations of 2 are common, taking the difference gives αQ2 - αQ = (9, 2 - father,) αψ, and it is possible to obtain a signal proportional only to αψ, that is, the rotational acceleration of the ψ axis. I can do it. Therefore, (αQ2−αQ+
) by an appropriate gain and fed back to the ψ-axis control device, it becomes possible to damp the ψ-axis vibration.

Next, examples of the present invention will be shown. FIG. 6(a) shows the form of an industrial robot according to a first embodiment of the invention, which is applied to the industrial robot of the form shown in FIG. FIG. 6(b) is a block diagram of the ψ axis. Regarding arms A and H, the previous application (Japanese Patent Application No. 57-178153) can be applied. Regarding arm C, since the interlocking of the movable mechanical elements of this axis with respect to the stationary coordinate system cannot be defined only by the rotational position of the rotating motor Mψ of this axis, the movement caused by the rotation of the motor Mψ of one rotation at different positions on arm C Two linear acceleration detectors A C+ in the direction parallel to the tangential direction of
, A C2 are arranged, and these linear acceleration detectors AC,,
By subtracting both outputs of AC2 and multiplying the amplifier by an appropriate gain, the rotational acceleration αψ of the ψ axis relative to the stationary coordinate system is obtained, and the rotational speed signal Vψ, which is the output of the tacho generator TGψ, is obtained.
The rotational position signal ψ which is the output of the pulse generator PGφ
At the same time, it is returned to the ψ-axis control device Gψ.

In the case of an industrial robot with arms D and E further connected by joints J3 and J4 as shown in Fig. coupled to the movable mechanism element of the servo shaft directly or through a mechanical transmission mechanism, causing the movable mechanism element to move linearly or rotationally;
and a multi-axis industrial robot including a servo axis whose position with respect to a stationary coordinate system of the movable mechanism element during the movement is not defined only by the rotational position of a rotating motor of the servo axis, the stationary coordinate system of the movable mechanism element. For an axis whose position relative to the servo axis is not defined only by the rotational position of the rotary motor of the servo axis, the rotational position signal and rotational speed signal of the rotary motor are fed back to the control device of each servo axis for each servo axis, and Two linear acceleration detectors are disposed for each axis at different positions on the sliding mechanism element connected to the rotary motor and in a direction parallel to the tangential direction of the motion caused by the rotation of the rotary motor, A rotational acceleration signal with respect to the stationary coordinate system of the servo axis is detected by subtracting the Ryokawa force signal of the linear acceleration detector, and the rotational acceleration signal is fed back to the control device of each servo axis for each servo axis. Due to this, changes in the driving torque of the rotary motor that occur when controlling the trajectory of an industrial robot at high speed, torque ripple of the rotary motor, or resonance phenomena in the mechanical system.
It prevents transient vibrations in industrial robots and enables high-speed, highly accurate trajectory control. In other words, the same effect as that obtained by increasing the synthesis rate of only the mechanical part of an industrial robot can be obtained. The present invention can be realized easily and inexpensively by simply arranging an acceleration detector in an existing industrial robot and does not require any changes to the mechanism or control device of the industrial robot.

[Brief explanation of drawings]

Figure 881 is a diagram showing the state of shaft vibration, Figure 2 is a diagram showing the basic mechanism of an industrial robot, Figure 3 is a diagram showing one form of an industrial robot, and Figure 4 is a diagram showing the basic mechanism of an industrial robot. FIG. 5 is a diagram showing the principle of the present invention applied to the industrial robot of the form shown in FIG. 3, and FIG. 6 is an industrial robot according to an embodiment of the present invention. FIG. 7 is a diagram showing the form of an industrial robot according to another embodiment of the present invention. ψ... Servo axis, Mψ... Rotating motor, AC,, AC2... Linear acceleration detector, Gψ... Control device, ψ... Rotational position signal. Vψ...rotational speed signal, αψ...rotational acceleration signal.

Claims (1)

[Claims] Consisting of a plurality of servo axes, the rotary motor of each servo axis is coupled directly or via a mechanical transmission mechanism to a movable mechanism element of the servo axis, and the movable mechanism element is moved linearly or A multi-axis industrial robot robot comprising a servo axis that rotates and the position of the movable mechanical element relative to a stationary coordinate system during the movement is not defined only by the rotational position of a rotary motor of the servo axis. 11. For servo axes where the position of the moving mechanism element with respect to the static coordinate system is not defined only by the rotational position of the rotary motor of the servo axis, the rotational position signal and rotational speed signal of the rotary motor are determined for each servo axis. is returned to the control device of each servo axis, and at different positions on the movable mechanism element connected to the rotary motor for each servo axis, and in a direction parallel to the tangential direction of the motion caused by the rotation of the rotary motor. Two linear acceleration detectors are placed in the servo axis, and by calculating both image force signals of the linear acceleration detector, a rotational acceleration signal with respect to the stationary coordinate system of the servo axis is detected, and the rotational acceleration signal is detected for each servo axis. An industrial robot characterized in that an acceleration signal is fed back to a control device for each of the servo axes.