JPH03130808A - Method and device for control of robot - Google Patents

Abstract

PURPOSE:To set the proper servo gain and the maximum acceleration by detecting the weight of a work held by a hand, calculating the moment of inertia after conversion of the work weight into the mass, and setting the proper servo gain and the maximum acceleration. CONSTITUTION:A vertical axis 2 of a robot is provided with a sensor 10 to detect the weight of a work 6 held by the robot and a hand 4 of the robot. Then the signals outputted from the sensor 10 are inputted to the robot controllers 18 and 20. An arithmetic means calculates the load moment of inertia related to the joint motors 3 and 7 based on the signals inputted to both controllers 18 and 20 and the attitude information on the robot itself. Then the proper servo gain and the maximum acceleration are automatically set to the calculated moment of inertia. Thus it is possible to automatically set the proper servo gain and the maximum acceleration in accordance with the mass of the work 6 held by the robot and the robot attitude. Then the load of a user is reduced.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a control device.

[Conventional technology]

The most common work performed by industrial robots is to grasp a part at a certain point and transport it along a fixed path to a certain point. Therefore, the criteria for evaluating the performance of industrial robots are the maximum acceleration, which governs the agility of the robot's movements, and the payload, which is the weight of the workpiece that can be transported with the maximum acceleration.

On the other hand, the servo controller that drives the robot's joint motors is designed assuming a certain load weight.
A constant dynamic response cannot be guaranteed in an environment where the moment of inertia of the load constantly changes depending on the posture of the robot and the mass of the workpiece gripped by the robot. In some cases, an unstable state may occur due to the load moment of inertia being too large or too small. For example, if a part of a certain weight is held and an excessive acceleration command is given, the servo controller will not be able to follow it and an overcurrent condition will occur, causing the robot to come to an emergency stop.

On the other hand, if the acceleration command is too small, the robot's speed will not reach a sufficient level, resulting in an unnecessary drop in work efficiency. Also, for the preset servo gain,
If the weight of the workpiece is excessive, the characteristics during positioning will deteriorate and a long settling time will be required.

In order to avoid such inconveniences, conventional industrial robots either unnecessarily limit the specified payload, or set the acceleration programmably at the expense of the user.

[Problem to be solved by the invention]

However, this method not only does not bring out the full performance of the robot, but also requires trial-and-error efforts to set the optimal acceleration, which places an excessive burden on the user.

In order to solve such problems, an object of the present invention is to automatically set an appropriate servo gain and maximum acceleration according to the mass of the workpiece held by the robot and the posture of the robot. It is.

[Means to solve the problem]

In order to achieve the above object, the present invention equips the vertical axis of the robot with a sensor that detects the weight of the workpiece and hand held by the robot, and inputs the output signal from the sensor to the robot controller. The calculation means calculates the load inertia moment for each joint motor from the posture information, and automatically sets the appropriate servo gain and maximum acceleration for this.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is an explanation of the case where the present invention is applied to a so-called SCARA type robot. The first arm 1 is disposed internally and drives the 27th arm 8. A vertical shaft 2 is attached to the tip of the second arm 8. Further, a force sensor 10 is equipped at the tip of the vertical shaft 2, and this force sensor 1
A robot hand 4 is attached to the robot hand 4 through the wire 0, and this robot hand 4 grips a workpiece 6. Therefore, the force sensor 10 detects the total weight of the hand and the gripped workpiece.

FIG. 2 is a configuration diagram of the control system. The movement target value is sent to the trajectory generator 16 according to the operation program 12 stored in the memory within the robot controller. Trajectory generation part 1
6 sends position commands to the servo controllers 18 and 20 from time to time according to a prespecified acceleration/deceleration curve.

Acceleration/deceleration curves are generally created as shown in Figure 3. The slope of acceleration song #30 corresponds to acceleration. Although this acceleration is programmable, it should not exceed the maximum acceleration. Returning to Figure 2, furthermore, in this example, the case/slot 1
A signal 11 from 0 is input to the gain acceleration determining section 14. On the other hand, from the trajectory generating section 16 to the gain acceleration determining section 14
The rotation device signal 15 of each joint motor is input to the . Using these two signals 11.15, the gain acceleration determination unit 14 determines an appropriate gain based on an algorithm described later, and the servo controller 18.20.22.24
Send to. Further, the gain acceleration determining section 14 determines an appropriate maximum acceleration using an algorithm described later, and sends it to the trajectory generating section 16. Next, the above algorithm will be explained.

Algorithm for Determining Appropriate Servo Gain and Appropriate Maximum Acceleration> FIG. 4 is a block diagram of the servo algorithm for driving each joint motor.

The position command 52 input to the servo controller is subtracted by the robot's actual joint orientation θ, and the position loop gain Kp4 is
The speed command is multiplied by 2.

From this, the actual joint speed θ dot is subtracted, and this becomes the torque command via the PI compensator 44. The coefficient of the proportional element of the PI compensator is KV, and the coefficient of the integral element is TV. The torque command passes through the current loop transfer characteristic Gl(S) 46 and becomes the actual torque τ. The robot is driven by τ, but to simplify the design, the robot is assumed to have one inertia Jm. Robot load 4 expressing this
8, the actual joint speed and actual joint position of the robot are obtained.

However, Jm changes depending on the posture of the robot and the weight of the robot tip, and is not a constant value, so it must be adjusted as needed. The algorithm will be explained below.

First, the moment of inertia (2) received by the first motor 6 (FIG. 1) is composed of the moment of inertia (I) of the first arm 1 itself around the center of the first motor 6, and the moment of inertia (I) of the second arm 8, as shown in FIG.
, the moment of inertia around the center of the first motor 6 ■,
The part from the second arm, that is, the hand 4 and the workpiece 6
The moment of inertia about the center of the first motor 6 is the sum of 03 and the moment of inertia about the center of the first motor 6. These are the fifth
Based on the figure, it is calculated as follows.

II =i, +MS, 2 1 no I, =i, +M, l 2i, +M, (1,' + 3: + 2 l, 5
2 cos θ2) I, = ml ”m (G + l: + 21. l, cos θ2
)I=I, +I, +I.

Here, I: Total moment of inertia ■,: Moment of inertia of the first arm ■2: Moment of inertia of the second arm ■,: Moment of inertia of the hand and workpiece (all of the above are around the center of the first motor) 11: First arm Moment of inertia i around the center of gravity of the first arm: Moment of inertia e around the center of gravity of the second arm of the second arm: First arm length e2: Second arm length S: From the center of the first motor to the first arm Length S from the center of gravity of the second motor to the center of gravity of the second arm L: Length from the center of the first motor to the center of the hand L: Length from the center of the first motor to the center of gravity of the second arm Ml : 1st arm mass M, : 2nd arm mass m : Mass of hand and workpiece On the other hand, moment of inertia, appropriate servo gains Kp, KV, 'l'v, and appropriate maximum acceleration a□
8 (FIG. 6) is created in advance and stored in the memory within the robot controller. The gain acceleration determination unit 14 applies the appropriate servo gain determined from this table to the servo controller 18.20.22.
．． Output to 24.

Further, the appropriate maximum acceleration obtained in the same manner is sent to the trajectory generating section 16 (FIG. 2).

The description of the second motor is also omitted since it is almost the same.

〔Effect of the invention〕

According to the present invention, the working speed of the robot is improved because an appropriate servo gain and maximum acceleration are set regardless of the posture of the robot and the weight of the workpiece held by the robot.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram when the present invention is applied to a 2-axis SCARA robot, Fig. 2 is a configuration diagram of a control system when the present invention is applied to a 2-axis SCARA robot, and Fig. 3 is a typical acceleration/deceleration diagram. 4 is a block diagram of the control system of the joint motor, FIG. 5 is a schematic diagram of the SCARA robot, and FIG. 6 is a graph showing the relationship between the load inertia moment and various appropriate parameters. 14...Gain acceleration determining section, 16...
・Trajectory generator, 18.20... Servo controller. Figure 2

Claims (2)

[Claims] (1) It has a plurality of arms rotatably connected via a shaft, the distal arm moves in a substantially horizontal plane, and the distal arm has a direction substantially perpendicular to the moving plane of the distal arm. In a robot that is provided with a moving axis and a hand at the tip of this moving axis, a predetermined value regarding the arm is memorized, the weight of the hand and the workpiece held by this hand is detected, and this weight is calculated. After converting into mass, the moment of inertia regarding the motor that drives the arm is calculated based on this mass, the predetermined value, and the rotational position of the arm, and the appropriate servo gain and maximum acceleration are calculated according to this moment of inertia. A robot control method characterized by setting. (2) It has a plurality of arms rotatably connected via a shaft, the tip arm moves in a substantially horizontal plane, and the tip arm has a direction substantially perpendicular to the moving plane of the tip arm. A control device for a robot, which is provided with a moving axis at the arm, and a hand at the tip of the moving axis, and which is provided corresponding to a trajectory generating section, a gain acceleration determining section, and a motor for driving the arm. and a servo controller, the trajectory generating section sends a movement target value of the arm to the servo controller as a position command according to a prespecified acceleration/deceleration curve, and determines the rotational position of the motor according to the gain acceleration. The gain acceleration determining unit inputs weight information of the hand and the workpiece gripped by the hand, determines an appropriate servo gain based on this weight information and the rotational position, and outputs the gain acceleration to the servo controller. A control device for a robot, characterized in that the control device sends the robot to the trajectory generating section, determines an appropriate maximum acceleration, and sends the determined maximum acceleration to the trajectory generating section.