JPH05313752A - Robot controller - Google Patents

Abstract

PURPOSE:To compensate the change of the settling action for control system switching to reduce the overshoot and the residual oscillation by setting the initial value of an integral element in a servo control means in accordance with the initial speed at the time when the servo control means is validated and setting the value of the integral element to 0 at the time of arrival of the position response at the peak. CONSTITUTION:n servo systems from a servo control system 101 to a servo control system 102 perform the servo control of respective joints independently of one another. An interference eliminating means 103 calculates a set of coefficients determined by the attitude of a robot; and when the controlled variable of each joint is outputted, this means 103 multiplies the controlled variable outputted from the servo system of this joint and that outputted from the servo system of another joint by calculated coefficients and adds the multiplication results. An integral value setting means 104 sets the initial value of the integral element in each servo system based on the initial speed for servo system switching at the time of position settling and sets the value of the integral element to 0 by the peak of the first position response during settling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for controlling the position of robot joints.

[0002]

2. Description of the Related Art Conventionally, a method of changing the structure of a control system is known as a means for improving the characteristics of robot joints and magnetic disks. For example, in the MR 90-66 report of the Magnetic Recording Research Society of the Institute of Electronics, Information and Communication Engineers, the optimum initial value setting of the integrator when the control system is switched at the time of position setting in the magnetic disk device head positioning system is examined.

[0003]

The above-mentioned prior art solves the Lyapunov equation by using the square integral of the deviation between the position and the speed at the time of settling as an evaluation function to determine the optimum initial value from the position deviation and the speed at the time of switching the control system. The coefficient of the formula for obtaining is calculated.

However, the control system design method in the above-mentioned prior art is very complicated and the amount of calculation is enormous. Also,
The above-mentioned prior art does not consider the position settling problem of a multi-axis mechanism such as an articulated robot in which inter-axis interference occurs.

An object of the present invention is to provide a robot control device which prevents deterioration of settling behavior due to an initial speed at the time of switching control systems, with a small amount of calculation and a simple algorithm.

[0006]

In order to achieve the above object, the present invention provides a servo control means for independently controlling each joint of a robot and a servo control means for controlling servo state of other joints. Interference component removal means input to the control means,
Integral value setting means for changing the value of the integral element in the servo control means is provided, and the interference component removing means includes a current control unit of each servo control means for the control amount for the own joint and the control amount for the other joint, respectively. The product obtained by adding the products obtained by multiplying the coefficient obtained according to the state of each joint angle is output, and the integral value setting means, in accordance with the initial speed at the time when the servo control means becomes effective, The initial value of the integral element in the servo control means is set, and the value of the integral element is set to zero when the position response reaches a peak.

[0007]

According to the present invention, the change in the settling behavior due to the initial velocity when the control system of the robot is switched can be compensated, and the overshoot and the residual vibration can be greatly reduced.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows a configuration of a control system for two main axes of a controller for a horizontal articulated (SCARA) type robot according to an embodiment of the present invention. This control system is a servo control system 201 and 20 that independently servo-controls the command value of each joint angle.
2, the interference removal means 203 for multiplying each of the control amount output by the servo system of the own joint and the control amount output by the servo system of the other joint by a coefficient determined by the posture of the robot and adding them, and position setting Integral value that sets the initial value of the integral element in the servo system based on the initial speed when the servo system is switched and sets the value of the integral element to zero at the peak of the first position response during settling. It comprises a setting means 204, a robot actuator, and a mechanical system 205.

Next, the interference removing means according to the present invention will be described.

When the joint angle is defined as shown in FIG. 4, SC
The equation of motion for the two main axes of the ARA robot is expressed as follows.

[0012]

[Equation 1]

Here, m _i , I _i , L _i , and a _i are links i (i
= 1, 2), the moment of inertia around the center of gravity, the distance from the axis to the center of gravity, and the link length. J _{11 to} J ₂₂ are defined by the following equations.

[0014]

[Equation 2]

R _i is the reduction ratio of the reducer of the i-axis motor, I _im
Is the equivalent moment of inertia of the motor rotor. Since the velocity of each axis is small at the time of position settling, the velocity term in Equation 1 is considered to be negligible as compared with the inertial term. Therefore, equation 1 can be expressed as follows.

[0016]

[Equation 3]

The relationship between the torque τ _i and the control amount i _ci of each axis servo system can be expressed as follows.

[0018]

[Equation 4]

Here, K _Ti is the torque constant of the i-axis actuator. The following equation is derived from the equations 3 and 4.

[0020]

[Equation 5]

[0021] When inertia term by modifying the time i _c a i _{c *} is decoupled, the relationship such as the following holds between the i _c and i _{c *.}

[0022]

[Equation 6]

When this is solved for i _{c *} , it becomes as follows.

[0024]

[Equation 7]

That is, in FIG. 2, a _{11 to} a ₂₂ may be arranged as follows.

[0026]

[Equation 8]

The interference removing means as described above makes the dynamic characteristics of each axis non-interference constant inertia at the time of position settling, and it becomes possible to independently design the servo control system as shown in FIG.

Next, the integral value setting means for setting the output value of the integral element at the time of position settling will be described. Since this means is common to all axes, subscripts are omitted in the following description.

FIG. 3 shows an example of the PID control system. This can be written as the equation of motion as follows.

[0030]

[Equation 9]

Here, K _p , K _i , and K _d are a proportional gain, an integral gain, and a differential gain, respectively, and the closed-loop pole arrangement of this control system is set so as to be a stable real root and a pair of conjugate roots. Be present. IC is the initial value of the integral element. θ _r is the target position, the time when the servo system is switched is t = 0, and the initial position θ (0) is 0.
K _T is the torque constant, and J is the load inertia moment of the motor. Switching from the acceleration / deceleration operation control system to the position settling control system shall occur when the deviation between the final target position and the current position becomes a certain value. Here, if the time integration of θ is Δ, then Equation 9 can be rewritten as the following equation.

[0032]

[Equation 10]

A general solution of Δ can be expressed as follows.

[0034]

[Equation 11]

C _{1 to} C ₃ are arbitrary constants determined by initial conditions. λ ₁ is the real root, and λ _r and λ _i are the values of the real and imaginary parts of the conjugate root. To determine the values of three arbitrary constants, three initial conditions are necessary. Then, the first-order and second-order differentials with respect to time of equation 11 are as follows.

[0036]

[Equation 12]

[0037]

[Equation 13]

Substituting t = 0 into equations 11, 12 and 13 and arranging C _{1 to} C ₃ results in the following.

[0039]

[Equation 14]

Here, ω ₀ is the value of the initial speed when the servo is switched. Therefore, C = [C ₁ C ₂ C ₃ ] can be obtained by calculating the following equation.

[0041]

[Equation 15]

From this, it can be seen that θ (t) can be calculated when IC and ω ₀ are given when θ _r is constant.

By using the above results, the initial value IC of the integral element for moving the first peak in the position settling behavior to the target position for an arbitrary initial velocity ω ₀ .
Can be asked. Since this calculation solves the transcendental equation, it is difficult to find an analytical solution. But solving this numerically is very easy. In addition, a graph showing the relationship between ω ₀ and the IC obtained numerically is not so complicated. Therefore, it suffices to store the solutions in the form of a table and, at the time of position settling, calculate IC by calculating the low-order polynomial whose coefficient is determined by using the least square method or the like, or by performing a table lookup with interpolation. It is considered to be practical. After that, the value of the integral element may be set to zero at the time when the velocity first becomes zero during the position settling operation (here, θ should be equal to θ _r ). FIG. 5 shows the step response of the PID control system set so as to exhibit a relatively oscillatory behavior with a damping ratio ζ≈0.3. Next, FIG. 6 shows a step response when a certain initial velocity is given. It can be seen that the overshoot is larger in FIG. 6 than in FIG. On the other hand, FIG. 7 shows the response when the initial value of the integral element calculated by the above method is given. It can be seen that the response peak has dropped to the target value. Further, FIG. 8 shows the response when the output value of the integration element is set to zero at the peak of the response. It can be seen that there is no overshoot and the convergence is faster than in FIG. FIG. 9 shows an example in which the relationship between ω ₀ and IC in this control system is calculated at several points and interpolated by a quadratic polynomial using the least square method.

As described above, the initial value of the integral element is given to each axis of the robot which has been made non-interference constant inertia by the interference removing means according to the initial speed at the time of switching the servo system, and at the first peak at the time of position settling. By setting the output value of the integral element to zero, it is possible to suppress the occurrence of overshoot and residual vibration in the position settling response and accelerate the convergence to the target value.

[0045]

According to the present invention, it is possible to compensate for a change in the settling behavior caused by the initial velocity when switching the control system of the robot with a small amount of calculation and a simple algorithm, and when the robot has a plurality of axes. , Its dynamic characteristics can be made non-interfering constant inertia, shortening the position settling time,
The behavior during settling can be improved and stabilized, and control parameter tuning can be simplified.

[Brief description of drawings]

FIG. 1 is a block diagram of a control system according to the present invention.

FIG. 2 is a block diagram of an embodiment of a horizontal articulated robot of the present invention.

FIG. 3 is an equivalent block diagram in the case of using the interference removing means of the present invention.

FIG. 4 is an explanatory diagram of a model of a SCARA robot.

FIG. 5 is a step response characteristic diagram of a control system that is adjusted slightly vibrationally.

FIG. 6 is a characteristic diagram of the same system as in FIG. 5 with an initial velocity.

FIG. 7 is a characteristic diagram when an optimum initial value of the integral element is set with respect to FIG.

FIG. 8 is a characteristic diagram when the value of the integration element is set to zero at the first peak of the position response.

FIG. 9 is a characteristic diagram of an example in which ICs are calculated for several kinds of ω ₀ and they are interpolated by the least square method.

[Explanation of symbols]

101 ... Servo control system, 102 ... Servo control system, 103
... interference removing means, 104 ... integral value setting means, 105 ... dynamic characteristics of the articulated robot.

Claims (1)

[Claims] 1. A controller for a robot, comprising servo control means for controlling joints of the robot, and an integral element in the servo control means in accordance with an initial speed at the time when the servo control means becomes effective. The control device for the robot is provided with an integral value setting means for setting an initial value of, and setting the value of the integral element to zero when the position response reaches a peak.