JP2710065B2 - Robot servo control device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a servo control device for smoothly operating an articulated industrial robot.

(Prior Art) The position transmission mechanism has some nonlinearity. In order to correct this, conventionally, a value obtained by subtracting the non-linear characteristic has been added to the position command as it is. This is the method used for relatively stiff machines or relatively slow movements. For example, an example in which a precision lathe measures and corrects a feed pitch error of a ball screw in advance is known.

A study on suppression of vibration with a rigid machine is described in "Study on anti-vibration control of robots: Mukai et al .; The 14th Technical Conference of the Japan Society of Mechanical Engineers, No.860-1, P21, 1986"
(Hereinafter abbreviated as Conventional Example (1)). Since the speed or the torque is corrected in consideration of the resonance model, this is ineffective when the speed is relatively slow and a position transmission error appears.

(Problems to be Solved by the Invention) As a typical example of a machine having a relatively soft elastic element after a motor, there is an articulated industrial robot. At this time, in the case of the static reverse application of the position transmission characteristic according to the conventional method, the correction effect is lost because the position transmission characteristic changes when the rotation speed of the motor changes. Further, in the method of the conventional example (1), it is difficult to correct the position transfer characteristic at a low speed deviating from the resonance state.

As described above, there has been no conventional method of suppressing rotational unevenness in a low-speed region that has deviated from the resonance state.

SUMMARY OF THE INVENTION An object of the present invention is to provide a robot that solves the conventional drawbacks and completely suppresses the fluctuation that occurs when a position transmission error of a position transmission mechanism is added to a resonance system having relatively soft elasticity in a low-speed range. It is to provide a servo control device.

(Means for Solving the Problems) A servo control device for a robot according to the present invention includes a servo motor, a control device for controlling the position and speed of the servo motor, and an input and output position coupled to the servo motor. A speed reducer having a non-linear characteristic as a transmission error, a servo system including a robot arm coupled to the speed reducer, and a position correction signal generator for generating a signal having the same cycle as the rotation unevenness generated by the robot arm; A gain setting device that determines the gain of the output signal of the position correction signal generator based on the rotation speed of the servo motor; and a phase setting that determines the phase of the output signal of the position correction signal generator based on the rotation speed of the servo motor. And an adder for adding an output signal of the position correction signal generator to a phase command signal given to the control device. .

(Operation) According to the present invention, since the gain and phase of the position correction signal are changed to appropriate values by changing the rotation speed of the motor, rotation unevenness can be completely suppressed in a low speed range.

(Embodiment) In this embodiment, an example in which position control and speed control are applied to a digital servo that performs digital control by a high-speed CPU will be described. In the gain and phase setting device used in the present invention, digital servo is suitable because it needs to be changed every moment depending on the rotation speed of the motor.

Various types of disturbance can be considered as a disturbance applied to the robot arm. Motor rotation torque unevenness called cogging torque, load fluctuation due to posture change of the arm connected to the end of the robot arm, viscous resistance change if grease is used, influence of gravity and speed for vertical articulated robot In the case of high speed, Coriolis may be considered, but in the following, the rotational unevenness of the reduction gear, which has the greatest influence, will be considered. In particular, a description will be given of a speed reducer called a harmonic drive (hereinafter abbreviated as HDC) often used in a robot arm. H.
DC has a position transmission error with a period twice as long as the motor speed. Therefore, when the rotation unevenness of the HDC is present, the rotation unevenness theta _L of the robot arm _{θ L = K L · sin (} 2nθ M + ψ L) ...... (1) n = 1,2, expressed as ..., Assuming that the harmonic component of n = 2 or more is considerably smaller than the fundamental component of n = 1, it is expressed in the form of θ _L = K _L · sin (2n θ _M + ψ _L ) (2). Therefore, the position correction signal Δθ that cancels out the rotation unevenness has the following form.

Δθ = K · sin (2θ _M + ψ) (3) However, when Expression (3) for canceling the component of Expression (2) is obtained in an actual system, the gain K and the phase に よ っ て are determined by the rotation speed ω _{M of the} motor. Needs to be changed. Therefore, Δθ (ω _M ) is Δθ (ω _M ) = K (ω _M ) · sin [2ω _M t + ψ
(Ω _M )]... (4) However, a case where the motor is rotated at a constant speed is considered (θ _M = ω _M t). The theta _M is the rotational position of the motor, K is the gain, [psi represents the phase.

Next, the configuration of the entire system will be described with reference to the drawings.

FIG. 1 is a block diagram of a servo control device for a robot according to one embodiment of the present invention. In the figure, 1 is a control device for controlling the position and speed, 2 is a servomotor, 3 is a speed reducer (HDC), and 4 is a robot arm. Reference numeral 5 denotes a position correction signal generator which generates a position correction signal (sine wave) having a period twice as long as the rotation speed of the motor. 6 is a gain setting unit for determining the gain K of the correction signal of the position correction signal generator 5 (omega _M) by the rotation speed omega _M of the motor. K
(Ω _M ) is obtained in advance by an experiment while changing ω _M so as to eliminate rotational unevenness at the tip of the robot arm, and realized as a data table on a program. FIG. 2 shows this. 7 position [psi the (omega _M) of the correction signal of the position correction signal generator 5, a phase setting unit which determines the rotation speed omega _M of the motor, [psi
(Ω _M ) is also realized in the same manner as K (ω _M ).

FIG. 3 is a diagram showing ψ (ω _M ). Reference numeral 8 denotes an adder that adds a position correction signal (Δθ (ω _M )) to the position command signal (θref). The above is the overall configuration, and a system capable of changing the gain and the phase of the position correction signal using the data table by the rotation speed of the motor is realized on software.

(Effects of the Invention) According to the present invention, the gain and the phase of the position correction signal can be appropriately changed according to the change in the rotation speed of the servomotor that is the drive source of the robot arm.
In the low-speed range, the rotation unevenness generated in the robot arm can be completely suppressed, and the practical effect is great.

[Brief description of the drawings]

Block diagram of a servo control apparatus for a robot in an embodiment of Figure 1 the present invention, FIG. 2 shows a data table of the gain K (ω _M), Figure 3 is the same phase ψ of (omega _M) It is a figure showing a data table. 1 ... Control device for controlling position and speed, 2 ... Servo motor, 3 ... Reducer (HDC), 4 ... Robot arm, 5 ... Position correction signal generator, 6 ... Gain setting device,
7 ... Phase setting unit, 8 ... Adder.

Claims (1)

(57) [Claims] 1. A servomotor, a control device for controlling the position and speed of the servomotor, a speed reducer coupled to the servomotor and having a non-linear characteristic as an input and output position transmission error, and the speed reducer A position correction signal generator that generates a signal having the same cycle as the rotation unevenness generated by the robot arm, and a gain of an output signal of the position correction signal generator. A gain setting device that determines the rotation speed of the servomotor, a phase setting device that determines the phase of the output signal of the position correction signal generator based on the rotation speed of the servomotor, and a position command signal that is given to the control device. A servo control device for a robot, comprising: an adder for adding an output signal of the position correction signal generator.