JPH07136953A - Controlling method for industrial robot - Google Patents

Abstract

PURPOSE:To suppress vibration in a robot arm due to elastic force of a decelerating mechanism when the decelerating mechanism having an unignorable elastic factor is provided between a driving source and the robot arm. CONSTITUTION:After values found by subtracting a motor rotation angle thetam from a position command thetaord are passed through a position controller 11, an integral element 12, and a position controller 13, which are connected together in parallel, so as to be added up, arm rotation angle acceleration is found on the basis of estimated external force, which is found on the basis of the motor rotation angle thetam and a speed input (u) in an observer 23, and the value found by subtracting the arm rotation angle acceleration from the added value is determined as a speed input to a speed controller 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an industrial robot provided with a reduction mechanism having a non-negligible elastic element between a drive source and a robot arm.

[0002]

2. Description of the Related Art FIG. 1 is a schematic view of a general industrial robot, in which 1 is a base. A control device 2 is provided on the base 1.
A drive motor and deceleration mechanism (not shown) are installed, and an arm 3 connected by a joint 4 is supported on the base 1 so as to bend, extend, and rotate. A manipulator 5 is provided on the tip arm of the arm 3 and executes a predetermined work based on a command from the control device 2.

For industrial robots, the basic goals are to improve the accuracy of the current position and speed up the operation. Improvements in position accuracy include aspects related to trajectory accuracy and positioning accuracy. The former is the difference between the given locus and the actual locus, so that collisions and interference with peripheral equipment can be eliminated and efficient painting work etc. can be performed, and the latter performs loading of conveyed goods, spot welding work etc. Each is emphasized above.

On the other hand, speeding up the operation is an important factor that is directly linked to productivity. For this speeding up, in addition to speeding up the speed itself determined by the robot actuator and deceleration mechanism, residual vibration suppression technology is also used. However, the latter is a very important factor because it has a close relationship with the positioning completion time and controls the cycle time of the entire operation.

[0005]

By the way, in order to realize high precision, simply designing a high-gain control system that reduces the difference between the command value and the actual value is necessary. At present, industrial robots have a wide operating range, and the weight reduction of the arm reducer and the like has been attempted in order to increase the speed. However, these weight reductions lower the rigidity and cause undesirable vibrations in the robot.

The robot arm can be approximated to a spring vibration system,
In a situation where mechanical dynamics cannot be ignored, particularly when high gain control is performed, the control system becomes sensitive, and the spring vibration system of the robot arm resonates with the control system to generate residual vibration. To suppress such vibration, it is better to increase the mechanical rigidity, but this results in increasing the weight of the arm.

On the other hand, the control system includes acceleration feedback control or state feedback control using an observer, but the former requires an expensive sensor, and the latter is ineffective in non-linear elements such as posture changes. There is. For this reason, the conventional method is to reduce the position loop gain and suppress the vibration, and it is not possible to achieve sufficiently high accuracy and speed.

As mentioned above, the present inventor has paid attention to the fact that the cause of the vibration of the robot arm is due to the resonance between the mechanical vibration system and the high gain control system, and as a result of an experimental study, it acts on the motor. It was found that the external force and the acceleration of the robot arm have a predetermined relationship. As a result, the external force is estimated using the disturbance observer of the motor, the acceleration is estimated based on the above relational expression, and this is negatively fed back to the position command for the motor, whereby effective anti-vibration control becomes possible.

The present invention has been made in view of such circumstances, and an object thereof is to control an industrial robot capable of effectively suppressing residual vibration of a robot arm and shortening a work cycle. There is a way to provide.

[0010]

A method for controlling an industrial robot according to the present invention comprises the steps of moving and positioning an arm of a robot having a speed-reducing mechanism whose elasticity cannot be ignored between a drive source and a drive source. In an industrial robot control method that gives an operation command to a drive source, the operation position of the drive source is detected during operation, and the external force acting on the drive source is estimated based on the detected position and the operation command, The vibration of the robot arm is calculated based on the estimated external force, and the calculated value is negatively fed back to the operation command.

[0011]

According to the present invention, the observer is used to estimate the acceleration of the robot arm and the vibration of the robot arm is calculated, so that non-linear elements such as posture changes can be compensated for and vibration control can be performed by changing software. Become.

(Principle) The equation of motion of a drive motor and the equation of motion of a robot arm in a robot are generally given as follows. The elastic term of the robot arm is assumed to be a one-point concentrated type of reduction gear, and only the primary mode is considered.

[0013]

[Equation 1]

The bracket in the right side of the equation (4) is the difference between the theoretical rotation angle of the output shaft of the reduction gear and the rotation angle of the robot arm, and means the twist angle in the turning direction due to elasticity.
(1) is of T _i is the torque T ₂ of the torque T ₁ or the robot arm of the drive motor, the torque constant K _t, the torque T ₁ of the drive motor the motor current is I _m in equation (5), Further, since there is no torque generation source in the arm portion, the arm torque T ₂ can be expressed by equation (6).

T ₁ = K _t I _m (5) T ₂ = 0 (6)

From equations (1) to (6), equation (7), which is the equation of motion of the motor, and equation (8), which is the equation of motion of the robot arm, are obtained. FIG. 2 shows the equations (7) and (8) as a block diagram.

[0017]

[Equation 2]

FIG. 2 is a block diagram showing the conventional control relationship between the drive motor and the robot arm. The motor current I _m for the drive motor enters a summing point via a proportional element (K _t : torque constant) 17, and here, I _m
From K _t , the value obtained by passing the motor rotation angular velocity, which is the feedback data from the motor unit, through the viscous friction element (D _m : motor viscous friction 20) and the value through the deceleration element 33, which is the feedback data from the reduction gear unit, That is, external force ( _Tm )
And are subtracted and the motor is entered. In the motor section, the inertial element (J _m : motor inertial moment) 18 is converted into a motor rotation angular acceleration, then an integration element 19 is converted into a motor rotation angular velocity, and further the integration section 22 is entered to enter the speed reducer section. In the reduction gear unit, a deceleration element (N: axis reduction ratio) 31 is entered as a set angle to enter an addition point, where the arm rotation angle θ _a from the robot arm unit, which is feedback data, is subtracted, and the deviation θ _err is The addition point is entered via the proportional element 32. Here, the value obtained by passing the arm rotation angular velocity, which is the feedback data, through the viscous friction element (D _a : arm viscous friction) 36 is subtracted, and the result enters the robot arm unit. In the robot arm, inertia element 34 and integral element 3
After 5 and 37, the arm rotation angle θ _a is extracted.

As shown in FIG. 2, the robot arm rotates the drive motor.
The vibration force (T _p) Forced vibration
It is a system. Expression (9) is modified from expression (8) into a forced vibration system.
It is an expression. Excitation force T here_pIs regarded as zero, and the equation (10) is
If the robot arm is
It becomes a vibration system, and its general solution is given by equation (11).

[0020]

[Equation 3]

From the equation (11), it can be considered that the robot arm is a simple vibration whose amplitude decreases exponentially with respect to time. When the initial values of the velocity and the acceleration are set to zero and the equation (12) is present at a certain time, the output of the integrating element 22 in FIG. 2 is that the deviation θ _err in the equation (12) can be approximated to a trigonometric function, and the loop The value fed back at A is integrated twice and the sign changes, so that the value instantaneously makes a negative rotation by the angle Δθ _m shown in equation (13). This is the motor rotation angle θ _m in order to suppress the deviation θ _err by the loop A.
Is controlled, and as a result, vibration is suppressed.

[0022]

[Equation 4]

By the way, when the motor rotation angle θ _m changes by Δθ _m1 as shown in the equation (13), a position deviation occurs, and the position controller in the control device as shown in FIG. 3 performs control for suppressing the deviation. Be done.

FIG. 3 is a block diagram showing a control system of a conventional controller. In FIG. 3, at the addition point, the motor rotation angle θ _m , which is feedback data, is subtracted from the position command θ _ord , and the subtraction value is connected in parallel to the position controller (K _pp : proportional gain) 11 and the integral element 12, It is passed through the position controller (K _pi : integral gain) 13 and added at the addition point. Further, the motor rotation angular velocity, which is feedback data, is subtracted from the added value at the addition point, and the subtracted value is passed to a speed controller (K _vp : speed proportional gain) 14, and the armature current i, which is feedback data, at the addition point. And subtract the current controller (K
_i : proportional gain) 15, a value obtained by passing the motor rotation angular velocity as feedback data to a proportional element (K _e : back electromotive force constant) 21 at the addition point is subtracted, and this is used as the input of the armature. An armature (R: armature resistance, L: armature reactance) 16 and a proportional element (K _t : ratio of generated torque to torque component current) 17 are passed through an external force T at an addition point.
_In addition to adding _m , a value obtained by passing the motor rotation angular velocity through the viscous friction element (D _m : motor viscous friction) 20 is subtracted, and this is set as the motor rotation angle θ _m via the inertia element 18 and the integration elements 19 and 22. Will be obtained. Assuming that the equivalent gain of the signal from K _pp to K _t in FIG. 3 is K _all , Δθ _m2 is given by the equation (14) to suppress the position deviation, and instantaneously rotates forward by the angle θ _m2 .

[0025]

[Equation 5]

The motor rotation angle θ _m is moved to the target position by position feedback, but at the moment when the target value and θ _m match, elastic energy due to θ _err exists and the motor rotation angle θ _m remains stationary. Instead, vibration with slow damping is generated due to the influence of the position feedback loop and the elastic force of the robot arm. When K _all in the equation (14) is increased, the vibration becomes remarkable. From this, it is considered that the resonance is caused by the loop A between the high-gain control system having the feedback mechanism and the mechanical vibration system of the robot arm.

Therefore, paying attention to the attenuation term of the equation (11),
The vibration damping effect can be obtained by increasing the motor viscous friction D _a or decreasing the arm inertia moment J _a . Therefore, if an exciting force (proportional constant K _a × arm acceleration) in the same phase as the arm rotation angular acceleration is given to the equation (9), the equation (15) is obtained. (15) so that the arm inertia J _a is J _a -K _a and becomes the arm inertia moment J _a is apparently smaller becomes vibration damping effect is obtained by the equation.

[0028]

[Equation 6]

That is, in FIG. 2, a double integrator exists between the motor drive current I _m and T _p (θ _m / N), and the arm rotation angular acceleration can be regarded as a trigonometric function from the equation (11). Consider the case where this is negatively fed back to the torque source, that is, the drive current I _m . Since the trigonometric function is integrated twice and the sign is changed, it means that the excitation force in the same phase as the arm rotation angular acceleration is applied, and the vibration isolation effect is obtained as shown in the equation (15). The arm rotational acceleration is given by the equation (16) because the arm viscous friction D _a is very small in the case of the robot arm.

[0030]

[Equation 7]

Since θ _err << θ _a , by considering θ _err to be zero, the arm inertia moment J in the equation (16) is calculated.
_a can be calculated easily. Accordingly, if the external force T _m can be measured, the arm rotation angular acceleration is obtained from the equation (16), and the acceleration feedback can be realized by feeding back the result. This is the concept of the industrial robot control method according to the present invention.

【Example】

Next, a method for controlling the industrial robot according to the present invention
The method will be specifically described. FIG. 4 shows a control device according to the present invention.
It is a block diagram showing a control system. K in Figure 4 _gIs anti-vibration
It is a gain. Paired with the block diagram of the conventional method shown in FIG.
As is clear from comparison, this anti-vibration gain K_gIs zero
For example, it becomes the same as the conventional control device shown in FIG.

At the addition point, the motor rotation angle θ _m , which is the feedback data, is subtracted from the position command θ _ord , and this subtracted value is connected in parallel to the position controller (K _pp :
The proportional gain) 11, the integral element 12, and the position controller (K _pi : integral gain) 13 are used to add at the addition point. The observer 22 is calculated from the added value at the next addition point.
The estimated external force obtained in step S2 is an element (N: shaft reduction ratio, J _a arm inertia moment) 24, element (K _g : anti-vibration gain) 25
The pseudo acceleration passed through is subtracted, and this is used as the speed input u to the speed controller. This speed input u is (17)
Given by the formula.

[0034]

[Equation 8]

At the next addition point, the motor rotation angular velocity which is the feedback data is subtracted from the velocity input u, and the subtracted value is the velocity controller (K _vp : proportional gain) 14
Then, the armature current of the drive motor, which is the feedback data, is subtracted at the addition point, and the current controller (K
_i : Proportional gain) 15, and at the addition point, a value obtained by passing the motor rotation angular velocity as feedback data through a proportional element (K _e : back electromotive force constant) 21 is subtracted, and this is input to the armature input of the drive motor. And The armature current i of the drive motor goes through a proportional element (K _t : the ratio of the generated torque to the torque component current) 17 and is added to the external force T _m at the addition point.
And a value obtained by passing the motor rotation angular velocity through a viscous friction element (D _m : motor viscous friction) 20 is subtracted, and this is obtained through an inertia element 18 and integration elements 19 and 22 to obtain a motor rotation angle θ _m . . As an external force T _m measuring method described above, an estimation calculation is performed using an observer 22 as shown in FIG. This will be described below.

First, since the inductance L is much smaller than the armature resistance R shown in FIG. 4, the equation (18) is obtained.

[0037]

[Equation 9]

The motor rotational angular acceleration shown in FIG. 4 is given by equation (19) using equation (18), where u is the velocity input to the velocity controller. By setting the equation (19) and the time derivative of the external force T _m to zero, the continuous time system state equation (21) of the motor can be obtained.

[0039]

[Equation 10]

When the equation (21) is discretized with a certain control period, a discrete time system state equation (22) is obtained.

[0041]

[Equation 11]

Since the motor rotation angle θ _m is obtained from the encoder, the output matrix is C = [100]. From the C matrix and the equation (22), the (25) and (2
The disturbance observer 22 as shown in the equation (6) is designed.

[0043]

[Equation 12]

From equations (25) and (26), the external force QT _m can be estimated and calculated using the speed input u and the motor rotation angle θ _m . The estimated external force estimated by the disturbance observer 22 is substituted into the following equation (27) to calculate the pseudo force velocity.

[0045]

[Equation 13]

Next, the comparison test results of the method of the present invention and the conventional method will be described. FIG. 5 is a graph showing the results of the comparative test, and FIG. 5 (a) shows the results by the method of the present invention.
(B) shows the result of the conventional method in which the image stabilization control is not performed. 5A and 5B, the horizontal axis represents time (seconds) and the vertical axis represents acceleration (G).

As is clear from a comparison between the two, FIG.
Compared with the conventional method shown in FIG. 5B, the method of the present invention shown in FIG. 5A has a small vibration of the robot arm and is rapidly damped. In the conventional method, the time required for settling is 700 msec. On the other hand, in the method of the present invention, 3
It was reduced to 40 msec.

[0048]

As described above, according to the method of the present invention, the disturbance of the motor is estimated by using the observer and the acceleration of the arm is obtained, so that the non-linear element such as the posture change can be compensated, and the degree of the vibration isolation is the vibration isolation gain. The present invention has excellent effects such as a simple change and a simple adjustment, a high movement trajectory accuracy of the arm, a short work cycle, and improved productivity.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a general industrial robot.

FIG. 2 is a block diagram showing a relationship between a robot arm and a drive motor in a conventional robot control method.

FIG. 3 is a block diagram showing a control system of a control device in a conventional robot control method.

FIG. 4 is a block diagram showing a control system in a control device for an industrial robot according to the present invention.

FIG. 5 is a graph showing the results of comparative tests between the method of the present invention and the conventional method.

[Explanation of symbols]

 11 Position Controller 12 Integral Element 13 Position Controller 14 Speed Controller 15 Current Controller 23 Observer 24 Inertial Element 25 Proportional Element

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location G05D 3/12 306 G 9179-3H

Claims (1)

[Claims] 1. A method of controlling an industrial robot, wherein an operation command is given to the drive source in order to move and position an arm of a robot having a speed reduction mechanism whose elasticity cannot be ignored between the drive source and the drive source. In, the operating position of the driving source during operation is detected, the external force acting on the driving source is estimated based on the detected position and the operation command, and the vibration of the robot arm is calculated based on this estimated external force.
A method for controlling an industrial robot, characterized by negatively feeding back a calculated value to the operation command.