JPH06320463A - Method for discriminating load direction of robot arm - Google Patents

Abstract

PURPOSE:To perform detection of the load direction of a robot arm by a method wherein the load direction of a robot control coordinate system is discriminated from the direction of the direction of a torque command to a servo motor for driving an arm during the stop of a robot arm and the rotation direction of a shaft on the output side to the rotation direction of a shaft on the input side coupled to the servo motor coupled to a reduction gear. CONSTITUTION:During the stop of a robot, the code of a torque command outputted to a servo amplifier 10 is fetched and it is decided whether the code is positive or negative to decide the direction of a torque command to a servo motor 11. A relation of the rotation direction of a shaft on the input side coupled to the servo motor 11 of a reduction gear with the rotation direction of a shaft on the output side to be decelerated is fetched from a shared RAM 4 to check positive and negative. From the check result and the positive negative check result of the code of a torque command outputted to the servo amplifier 10, a mechanical drive direction is decided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a robot control method, and more particularly to a method for determining a load direction of a robot arm.

[0002]

2. Description of the Related Art A control process for a robot to move to a target position is a movement command for each axis of a robot arm based on a position taught by a calculation unit and interpolation information until the position is reached. It is general that the movement command is passed to the servo unit and the position is controlled to move to the target position. Most of the position loop control in the servo section has been softwareized in recent years, and further softwareization is progressing to speed loop control and current loop control. On the other hand, in the robot stop state (stop during operation when the power is turned on), the above-described various loop controls are performed by the servo unit in order to maintain its posture. That is, with respect to the load such as the speed reducer installed in the robot arm and the drive unit of the arm,
A torque command is issued to the servomotor to overcome this and maintain balance. In that case, the latter is the case of the servo motor when the operation is stopped in the opposite direction of the load (the direction in which the robot arm is lifted) and when the operation is stopped in the direction of the load (the direction in which the robot arm is lifted). Low power consumption. Therefore, when the robot arm is stopped in the lifting direction, it is necessary to once perform a minute movement (lifting) in the direction opposite to the load direction, and then return to the original position (hold down) and stop it (Japanese Patent Application No. Hei 3). -3
07651).

[0003]

However, conventionally, the method of Japanese Patent Application No. 3-307651 could not be implemented because the load direction of the robot arm could not be detected. Therefore, an object of the present invention is to provide a method capable of determining the load direction.

[0004]

In order to solve the above-mentioned problems, the present invention provides a method for determining a load direction of a robot arm in which at least one axis is driven by a servomotor through a speed reducer, wherein the robot arm is stopped. The robot control coordinate system is based on the torque command direction given to the servo motor when the shaft is rotating and the rotation direction of the output side shaft that is decelerated with respect to the rotation direction of the input side shaft connected to the servo motor of the speed reducer. It is characterized in that the load direction in is determined.

[0005]

The present invention focuses on the fact that the current loop works even when the robot arm is stopped by the positioning control. When the robot arm is stopped, the torque command (current command) is sent to the servo motor. Is given, the direction in which the load is applied can be known from the relationship between the rotation direction of the output side shaft that is decelerated and the rotation direction of the input side shaft that is connected to the servomotor of the speed reducer. .

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a robot controller according to the present invention. Motor control parameters are calculation CPU
5 is stored in the ROM 6 which is connected to 5. When the system is initialized, the motor control parameters are stored in ROM6.
→ bus 24 → arithmetic CPU 5 → bus 23 → shared RAM 4 →
The data is transferred to the shared RAM 3 via the path of the bus 22 → shared RAM 3.

The control parameters transferred to the shared RAM 3 can be changed by an operator by operating the input / output device 13 coupled to the peripheral CPU 12 via the bus 21. The control parameters stored in the shared RAM 3 are transferred to the shared RAM 4 via the route of the shared RAM 3 → the main CPU 1 → the bus 22 → the shared RAM 4, and the servo CPU 7 can access the control parameters.

During normal robot control,
A program execution command from the main CPU 1 is sent to the bus 22,
The signal is transmitted to the servo CPU 7 via the shared RAM 4 and the bus 23, and the servo CPU 7 sends a control signal D via the bus 25.
Send to the / A converter 9. The D / A converter 9 converts the digital signal into an analog signal and outputs a torque command to the servo amplifier 10. The servo amplifier 10 includes an inverter, for example, and outputs a current command to the servo motor 11 to drive the robot arm.

FIG. 2 is a flow chart showing an embodiment of the present invention executed by the servo CPU 7 when the robot is stopped. In step 100, the code of the torque command output to the servo amplifier 10 after being created by the servo loop processing which is software-servoed is taken out. In step 110, it is determined whether the sign is positive or negative, and the process branches below for each sign. In steps 120 and 130, data on the rotation direction of the servo motor 11 with respect to the rotation direction of the speed reducer incorporated in the robot arm (for the output side to be decelerated with respect to the rotation direction of the input side shaft connected to the servo motor of the speed reducer). The relationship of the rotation direction of the shaft) is taken out from the shared RAM 4 in which the contents of the data are set in advance. At steps 140 and 150, the positive / negative check is performed. From the above, it can be understood in which direction the mechanical drive is being performed. However, in reality, the position loop of the robot arm is prioritized, so that the torque is applied to hold the position, not to change the position by driving. Therefore, it can be seen that a load is applied if the actual robot arm is stopped (that is, the servo motor is stopped) regardless of which direction the mechanical drive is attempted. As a result of the above,
In steps 170 and 180, positive load direction data in the robot control coordinate system is created, and in steps 160 and 1,
At 90, negative load direction data is created. It should be noted that the data referred to here may be 1 bit since it is only necessary to know whether the sign is positive or negative.

The above is the part relating to the basic processing of the present invention, but an example of application to stop processing during robot operation will be described below. FIG. 3 is a schematic diagram of load lifting and lowering operations in a three-axis robot showing the above-described application example.
FIG. 4 is a flowchart of processing in the servo CPU. In FIG. 4, in step 200, it is determined whether or not the robot is stopped depending on whether or not there is a position command from the arithmetic CPU 5 in FIG. 1, and if it is stopped, wait until the time designated in advance in step 210 has elapsed. . At the time when the time is up (judged to be stopped), the size of the motor load on each axis is determined (determined from the current value flowing to the motor (not shown)) in step 220, and only the axis with a large load is selected as the target axis. To do. Further, in step 230, the direction of the load on the target axis is obtained from the sign of the torque command at the time of stop, and in step 240 preset rotation direction data of the servo motor is taken out. In step 250, this code is determined and created as a position command in a minute movement command specified in advance based on the load direction of the target axis obtained in step 230 and the rotation direction data extracted in step 240. By inputting this into the servo position loop in step 260, the robot arm makes a minute movement opposite to the direction of the load and stops. After stopping, by step 270,
The robot arm returns to its original position and stops by reversing the sign of the previously calculated position command and creating it as a new position command and inputting this into the servo position loop in step 280. The servo CPU executes step 220.
During execution of step 280 to step 280, the standby instruction is output from the servo CPU 7 to the main CPU 1 so that the execution instruction of the work program from the main CPU 1 is not output to the servo CPU, and the processing of step 280 is completed. By outputting the release signal of the standby command, the operation of the present invention is prevented from being interfered by another program. Further, after the operation of the present invention is once completed, the servo CPU is independently provided with an execution end flag so as to prevent the operation from satisfying the condition again.

[0012]

As described above, according to the present invention, since the load direction of the robot arm can be detected, it is possible to control the robot consuming less power.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a robot controller according to the present invention.

FIG. 2 is a flowchart showing an embodiment of the present invention when the robot is stopped.

FIG. 3 is a schematic diagram of load lifting and lowering operations in a three-axis robot showing an application example of the present invention.

FIG. 4 is a flowchart of processing performed by a servo CPU according to an application example of the present invention.

[Explanation of symbols]

 7 Servo CPU 10 Servo amplifier 11 Servo motor W Load

Claims (2)

[Claims] 1. A method for determining a load direction of a robot arm in which at least one axis is driven by a servomotor via a speed reducer, and a torque command direction given to the servomotor when the robot arm is stopped, and A load of a robot arm characterized by determining a load direction in a robot control coordinate system based on a rotation direction of an output-side shaft that is decelerated with respect to a rotation direction of an input-side shaft connected to the servomotor of the speed reducer. Direction determination method. 2. The method for determining a load direction of a robot arm according to claim 1, wherein the load direction determination is performed only for a previously designated axis.