JPH0825260A - Deflection correcting method for industrial robot - Google Patents

Abstract

PURPOSE:To correct the deflection of the arm of an industrial robot used for the deburring work in which a large load is applied to the tip of the arm in particular. CONSTITUTION:Each of multiple joints of an industrial robot controlled by a control device is provided with a means 28 calculating the torque applied to the reduction gears connected to a motor in each action state of the robot based on the current value 21 flowing in the motor driving the joint and the correction coefficient set in advance according to the action state of an arm and a means calculating the deflection quantity of each joint of the arm based on the calculated torque of the reduction gears and the spring constant of the reduction gears. The command angle of each joint commanded by a control device is corrected 30 based on the calculated deflection quantity of each joint of the arm. When the command angle of each joint is set by a teaching playback system, and the joint angle corrected with the calculated deflection quantity of each joint is recorded in the memory of the control device as the command angle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting deflection of a robot arm when a work such as deburring is performed using an industrial robot (hereinafter referred to as "robot").

[0002]

2. Description of the Related Art Generally, in a production line composed of a plurality of machine tools, a dedicated deburring machine is arranged behind a cutting machine, and a transfer machine is provided with a deburring unit after a cutting unit. . Since most of these production facilities are for small-scale mass production, the deburring machine and deburring unit used for this can also be handled by a device with a relatively simple mechanism. However, in recent years, in order to cope with the production of a wide variety of products by promoting the flexibility of the production line, a method of deburring with a robot having a deburring tool has begun to be introduced.

The advantage of allowing the robot to carry out deburring work is that it is easy to cope with the production of a wide variety of products by means of programming means, and the movable area relative to the size of the robot main body is large compared to machine tools, so that the installation area of the main body It is small and generally cheaper than a deburring machine. However, in general, the speed reducer (hereinafter referred to as "speed reducer") used for the drive unit of the joint of a robot has low rigidity. Therefore, when the deburring tool is pressed against the work piece with a strong force, the reaction force causes the robot to react. The arm joint of the robot bends (hereinafter, the deflection of the robot arm joint is referred to as "arm deflection"), and also depending on the weight of the deburring tool attached to the arm tip and the chuck holding this. Similarly, the arm bends. For this reason, the positioning accuracy of the deburring tool deteriorates, and the deburring tool cannot be used in machining requiring high accuracy, and the application is limited to use with relatively rough accuracy.

In order to increase the rigidity of the arm, it is conceivable that the mechanism of the arm is of the orthogonal coordinate type instead of the joint type, but this makes the movable range small, and there is not much difference from a machine for deburring machine tools. Further, the use of a high-rigidity reducer leads to an increase in size of the robot body and an increase in cost.

Therefore, as a method of correcting the deflection of the arm, Japanese Patent Laid-Open No. 4-233602 discloses a joint torque applied to each axis of the robot from the posture of the robot corresponding to the command value of the arm tip position (tool tip position). Then, a bending angle is obtained as a bending amount of each axis from the joint torque, and a correction amount of a command value for each axis is calculated from the bending angle of each axis.

[0006]

However, this method is
Since the joint torque is obtained from the posture of the robot, only the flexure of the arm due to the influence of gravity when the arm is stationary, that is, in the static state is taken into consideration. It does not take into consideration the bending of the arm in the state of pressing the arm, that is, in the dynamic state. Therefore, this method reduces the weight of the arm,
Moreover, the movement speed of the arm is slow and the load applied to the arm tip is small, which is effective in applications such as spot welding, but the tip of the arm is loaded for a long time such as deburring work, and the There is a problem that it cannot be applied to work that requires accuracy.

An object of the present invention is to precisely position an industrial robot used for deburring work or the like in which a large load is applied to the tip of an arm.

[0008]

Therefore, in order to solve the above-mentioned problems of the prior art, the present invention is an articulated type for performing a predetermined process on a workpiece by a tool attached to the tip of an arm. In the method of correcting the deflection of the arm of the industrial robot, the joints of the plurality of joints of the industrial robot controlled by the controller are set in advance according to the current value flowing in the motor that drives the joints and the operating state of the arm. Means for calculating the torque applied to the speed reducer connected to the motor in each operating state of the robot from the correction coefficient, and the amount of flexure of each joint of the arm from the calculated torque of the speed reducer and the spring constant of the speed reducer. Means to calculate,
From the amount of deflection of each joint of the calculated arm,
It is intended to provide a bending correction method for an industrial robot, which is characterized by correcting a command angle of each joint commanded by a control device.

The correction coefficient for each motor according to each operating state of the arm is 1.
00, the ratio of the current values when the arm is raised from the bottom to the top when the motor current value during operation of the arm is set to 1.00 when the arm is raised from the bottom to the top and held, When the motor current value was 1.00 when the motor current value during operation of the arm was set to 1.00 and was stopped and held, the ratio of the current value when the arm was lowered from top to bottom and stopped and held.

Further, when the command angle of each joint is set by the teaching playback system, the joint angle in which the calculated bending amount of each joint of the arm is corrected is recorded in the memory of the control device.

[0011]

According to the deflection correction method for an industrial robot of the present invention, even when a general industrial robot is used to perform highly accurate machining, the current values flowing in the motors that drive the joints of the robot are detected. , When calculating the torque applied to each speed reducer from the current value, the calculated value of the torque is corrected according to the operation state of the robot, and the amount of arm deflection is calculated from the corrected calculated value of the torque and the spring constant of the speed reducer. Since it is required, it is possible to instruct the robot of the tool tip position in which the bending amount of the arm is corrected.

Further, since the detected current value of each motor is multiplied by the correction coefficient calculated by the actual arm operation for each motor in advance, the torque applied to each speed reducer, which varies depending on the operation state of the arm, is accurately measured. It becomes possible to calculate.

Further, when the command angle of each joint is set by the teaching playback system, the joint angle in which the calculated bending amount of each joint of the arm is corrected is recorded in the memory of the control device. It is also possible to improve the positioning accuracy when reproducing the created program.

[0014]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an outline of a system in which a deburring tool (hereinafter referred to as “tool”) 2 is attached to a tip of an arm 1 of a robot controlled by a control device 4 and deburring a work piece 3. ing.

FIG. 2 is a block diagram showing the configuration of the present invention. The robot controller 4 is controlled by the CPU 5,
The CPU 5 reads the program data and various data required for the deflection correction from the memory 6 and instructs the position control unit 7. The position control unit 7 performs position feedback as the current joint angle of the robot detected by the encoder 11 connected to the motor 10, and current feedback as the current value flowing through the motor 10 detected by the current detector 9, The deflection amount of the arm 1 is calculated from the position command from the CPU 5, and the velocity / current control unit 8 is instructed with the velocity command after the deflection is corrected. The speed / current control unit 8 calculates the drive current to be passed to the motor 10 from the speed command transmitted from the position control unit 7, the position feedback from the encoder 11 and the current feedback from the current detector 9, and the motor 1
Command to 0. The motor 10 is driven based on the drive current transmitted from the speed / current control unit 8 and drives the arm 1 via the speed reducer 12.

Although FIG. 2 shows the case where the number of joints controlled by the robot controller 4 is one, when there are a plurality of joints controlled, the number of motors, encoders, and speed reducers is the same as the number of joints. Will increase.

In the prior art in which the deflection is not corrected, as shown in FIGS. 8 and 9, in the position control section 7, the position feedback detected by the encoder 11 and the CPU 5 are performed.
The speed command calculated from the position command from (5) is commanded to the speed / current control unit 8. However, in the present invention, as shown in FIG.
The deflection angle of the arm is calculated as a correction amount from the current feedback from the CPU, and this correction amount is added to the position command from the CPU 5, and the difference between this value and the position feedback from the encoder 11 is used as a speed command to the speed / current control unit. It is designed to output to 8. Therefore, the deflection angle of the arm calculated from the current feedback from the current detector 9 is added to the speed command commanded to the speed / current control unit 8 as a correction amount. It becomes possible to instruct the motor 10 to supply a drive current in consideration of the bending of the.

Next, a method of calculating the deflection correction amount of the present invention performed in the correction amount calculation unit 13 will be described. When the coordinate position for deburring the workpiece 3 is set by directly inputting the coordinate value, the joint angle for realizing the position of the robot at the coordinate value is set to Hn, and the joint is moved to the joint angle Hn. Command, the gravity and the processing reaction force from the workpiece 3 are applied to the speed reducer 12, and the arm 1 is bent by an angle of ΔHn. The torque applied to the speed reducer 12 can be approximately calculated by detecting the current value flowing through the motor 10 at this time. However, due to the friction of the mechanical system, the current value flowing through the motor 10 is as shown in FIG. The holding current is significantly different between the case where 1 is lowered from the top and held down, and the case where the arm 1 is raised from the bottom to the top and held as shown in FIG. The holding current is higher when the signal is raised to stop and held.

Therefore, the motor current Ia is calculated by multiplying the current value I detected by the current detector 9 by the correction coefficient Ka as shown in the equation (1). The value of the correction coefficient Ka is the arm 1
It is set to 1.00 during the operation of, but is set to Kb when the arm 1 is raised from the bottom to the stop and held, and is set to Kc when the arm 1 is lowered from the top to the bottom and held. This Kb,
Kc is a motor current value of 1.
00, the ratio of the current value when the arm 1 is raised from the bottom to the stop and held, and the ratio of the current value when the arm 1 is lowered from the top to the bottom and stopped and held. Since it is a unique value, it must be obtained in advance by actual arm operation.

[0020]

[Equation 1]

At this time, the torque T applied to the speed reducer 12 is the motor current Ia obtained from the equation (1), the torque constant Kt of the motor 10, the speed reduction ratio R of the speed reducer 12, and the speed reducer 1.
From the efficiency η of 2, the equation (2) is obtained.

[0022]

[Equation 2]

Therefore, the bending angle ΔHn as the bending amount of the arm 1 is given by the equation (3), where K is the spring constant of the speed reducer 12.

[0024]

(Equation 3)

Therefore, as shown in FIG. 4 and equation (4),
The joint angle Hn instructed by the CPU 5 is instructed by the position control unit 7 by instructing the joint angle Hn ′ corrected by the bending angle ΔHn obtained from the equation (3), so that the joint angle Hn instructed by the CPU 5 is the actual arm. Can be realized in operation.

[0026]

[Equation 4]

Next, a deflection correction method in the teaching playback system for teaching the position of the robot by actually moving the robot will be described. As shown in FIG.
When the robot is moved to the joint angle Ha as the teaching position, the arm is actually bent, so that the motor 10 is held at the joint angle Ha '. Encoder 1
Since the joint angle Ha 'is output to the position control unit 4 from 1, the joint angle Ha' is recorded in the memory 6 as it is. Therefore, similarly to the above, the bending angle ΔHa is calculated using the equations (1) to (3), and the joint angle Ha ′ detected by the encoder 11 is obtained as shown in the equation (5).
The joint angle Ha obtained from the difference between the calculated deflection angle ΔHa is recorded in the memory 6 as a teaching position.

[0028]

(Equation 5)

As a result, since the joint angle that is not affected by the bending of the arm 1 is recorded in the memory 6, by performing the same correction using the equations (1) to (4) again when the arm operation is reproduced. , It becomes possible to reproduce the taught position.

[0030]

According to the present invention, when the value of the current flowing through the motor that drives each joint of the robot is detected and the torque applied to each speed reducer is calculated from the detected current value, the torque depends on the operating state of the robot. It is possible to correct the calculated value of, calculate the amount of arm deflection from the corrected calculated value of torque and the spring constant of the reducer, and then command the tool tip position with the corrected amount of arm deflection to the robot. Therefore, even when the robot is used for work such as deburring that requires a large load, it is possible to perform highly accurate positioning without particularly increasing the rigidity of the speed reducer.

Further, when the command angle of each joint is set by the teaching playback system, the joint angle in which the calculated bending amount of each joint of the arm is corrected is recorded in the memory of the control device. The positioning accuracy when reproducing the created program was also improved.

Further, in the structure of the present invention, since no new external device is added to achieve the object of the present invention, the bending of the arm can be flexed by a slight improvement of the existing control device without increasing the cost. Correction is possible.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a system for deburring, which is an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a control device of the present invention.

FIG. 3 is a block diagram showing a configuration of a position control unit in the control device of the present invention.

FIG. 4 is a diagram showing a relationship between a joint angle Hn commanded by a CPU 5, a calculated deflection angle ΔHn, and a corrected joint angle Hn ′.

FIG. 5 is a joint angle H detected by an encoder 11.
It is a figure showing the relationship of a ', the calculated bending angle (DELTA) Ha, and the joint angle Ha recorded as a teaching position.

FIG. 6 is a view showing a state in which the arm 1 is lowered from the top and stopped and held.

FIG. 7 is a diagram showing a state in which the arm 1 is raised from bottom to top and stopped and held.

FIG. 8 is a block diagram showing a configuration of a conventional control device.

FIG. 9 is a block diagram showing a configuration of a position control unit in a conventional control device.

FIG. 10 is a flowchart showing a method for calculating the amount of arm deflection according to the present invention.

[Explanation of symbols]

 1 Robot arm 2 Tool 3 Workpiece 4 Control device 6 Memory 11 Motor 12 Reducer

Claims (3)

[Claims] 1. A method for correcting the deflection of an arm of an articulated industrial robot that performs a predetermined process on a workpiece with a tool attached to the tip of the arm, wherein the industry is controlled by a controller. For each of the plurality of joints of the robot for use, the torque applied to the speed reducer connected to the motor in each operating state of the robot based on the correction value preset by the current value flowing in the motor driving the joint and the operating state of the arm And a means for calculating the amount of flexure of each joint of the arm from the calculated torque applied to the reducer and the spring constant of the reducer, and the calculated amount of flexure of each joint of the arm. A deflection correction method for an industrial robot, comprising correcting a command angle of each joint commanded by the control device. 2. The correction coefficient preset according to the operating state of the arm is 1.0 during the operation of the arm.
0, when the arm is raised from the bottom to stop and hold, the ratio of the current values when the arm is raised from the bottom to stop and hold when the motor current value during operation of the arm is 1.00, When the arm is lowered from the upper side and stopped and held, the ratio of the current values when the arm is lowered from the upper side and stopped and held when the motor current value during operation of the arm is set to 1.00. The method for correcting deflection of an industrial robot according to claim 1, characterized in that. 3. When the command angle of each joint is set by a teaching playback system, the joint angle corrected for the calculated bending amount of each joint of the arm is recorded in the memory of the control device. The method for correcting deflection of an industrial robot according to claim 1, characterized in that.