JP4228965B2 - Robot control method - Google Patents

Description

    The present invention relates to a control method for a robot driven by a motor via a reduction gear.

    In recent years, robots are required to have high accuracy in collision detection in order to improve safety at the time of collision and to prevent loss due to destruction. However, the use of a high-precision collision sensor increases the cost, and the weight of the sensor provided on the robot arm acts as a load, which is against the speeding up and energy saving of the robot. Therefore, it is required to detect the collision force with high accuracy without using a sensor.

    As a method for obtaining such a collision force without a sensor, the robot power obtained by the inverse dynamics calculation of the robot is obtained from the motor generated torque obtained by subtracting the torque lost by the motor and the reducer from the torque generated by the motor drive current. A common method is to determine the collision force by subtracting the academic torque.

    However, the frictional force (= viscous friction + dynamic friction) in motors and speed reducers has a large measurement error due to individual differences and environment (temperature, aging, etc.), and whether the margin of error is taken by increasing the collision detection threshold (detection) Sensitivity dulled) or frictional force estimation was performed. In friction force estimation, there are a method of estimating in advance with a specific action (for example, see Patent Document 1) and a method of estimating by adding a state estimation observer in real time (for example, see Patent Document 2).

    As described above, when subtracting the robot driving force obtained by the robot dynamics calculation from the motor generated torque to obtain the collision force without a sensor, or feeding the dynamic torque to maximize the motor driving force. In the case of improving the servo tracking characteristic by the forward control, it is required to accurately calculate the motor generated torque and the robot dynamic torque. In this case, the motor generated torque τm during the robot operation is expressed by (Equation 1) when viewed from the motor driving side and by (Equation 2) when viewed from the load side.

    Since the motor and the robot arm are connected via a speed reducer, the terms other than the motor inertia J in (Equation 2) need to be converted to the motor shaft end using the speed reduction ratio.

    The collision force τdis can be obtained by transforming into the following (Equation 3) by assuming that τmm = τml in (Equation 1) and (Equation 2).

    If an error occurs in the dynamic friction torque τμ in (Equation 3), the collision torque τdis includes an error.

    Therefore, when dealing with the error of the dynamic friction force τμ, increasing the collision torque detection threshold for judging whether or not a collision has occurred and taking a margin for the dynamic friction torque error reduces the collision detection sensitivity and reduces the collision force. Becomes smaller.

    Further, in the method of estimating the friction torque by a specific operation in advance (see, for example, Patent Document 3), the dynamic friction force τμ can be correctly estimated when it is constant regardless of the dynamic torque τdyn. Since the torque τμ varies in proportion to the dynamic torque τdyn, it cannot be estimated correctly.

    FIGS. 6 and 7 show the dynamic friction torque τμ of a typical reduction gear used in the robot measured with respect to the fluctuation of the dynamic torque τdyn under the condition of disturbance torque τdis = 0.

    FIG. 6 shows the characteristics of the harmonic reduction gear, and FIG. 7 shows the characteristics of the RV reduction gear.

    6 and 7 show that the dynamic friction torque τμ increases in proportion to the increase in the dynamic torque τdyn, and can be approximated by (Equation 4).

    In (Equation 4), A, B, C, D, E, and F are approximate constants, and τth is a set threshold value.

    The above parameters in FIG. 6 and FIG.

    That is, in the friction torque estimation method using the specific operation pattern, the motor generated torque is also the specific pattern, and it can be understood that the actual motor generated torque that changes from moment to moment cannot be estimated with sufficient accuracy.

In addition, there is a method for estimating the friction torque τμ by adding a state estimation observer in real time (see, for example, Patent Document 4), but since the friction torque τμ fluctuates greatly in a short period of acceleration / deceleration, When the estimation algorithm is used, a phase delay occurs in the friction torque estimation, and there is a possibility that the detection accuracy of the collision torque τdis is deteriorated.
JP-A-8-252787 JP-A-6-83403 JP-A-8-252787 JP-A-6-83403

    As described above, each of the conventional collision detection methods has a problem.

    The present invention has been made to solve these problems, and an object of the present invention is to provide a control method capable of accurately detecting a dynamic friction error in collision torque detection and improving collision detection accuracy.

In order to solve the above-mentioned problem, in a robot driven by a motor via a speed reducer , a robot control method for detecting a collision , which is obtained by calculating a dynamic torque based on a position command. The motor receives a current command obtained by adding the current command and the feedback current command obtained by feedback control for eliminating the deviation between the position feedback obtained by the rotation detector of the motor and the position command. The feedback current command is added to the set value of the collision detection threshold value to obtain a new collision detection threshold value, and the new collision detection threshold value is compared with the feedback current command obtained by the feedback control during the next cycle operation. This is a control method for a robot that performs detection.

    As described above, in the robot control method of the present invention, in the robot driven by the motor via the speed reducer, by subtracting the dynamic torque obtained by the reverse dynamics calculation of the robot from the motor generated torque, This is a robot control method that detects the external force due to a collision without using a sensor.By controlling the robot by feedforward adding the dynamic torque to the current command obtained by feedback control, the feedback current command is converted into the error parameter error. As a result, the accuracy of collision detection can be improved by increasing the accuracy of the calculation of friction loss in the torque generated by the motor during the next cycle operation.

(Embodiment)
Hereinafter, embodiments of the robot control method of the present invention will be described with reference to the drawings.
In addition, the same code | symbol is attached | subjected about the same structure in each figure, and the description is abbreviate | omitted.
FIG. 1 is a block diagram showing a control method in the present embodiment.

    In FIG. 1, dynamic torque feedforward (hereinafter abbreviated as FF) compensation (2) calculates the dynamic torque based on the position command θcom (1), thereby obtaining the torque required for robot operation by the motor (8). FF current command IFF (3) to be generated is calculated.

    However, the position feedback (9) obtained by the rotation detector (9) of the motor (8) can be obtained only by the FF current command IFF (3) due to the influence of disturbance such as the collision torque (17) and parameter error in the dynamics calculation. It is impossible to make θFB (4) follow the position command θcom (1).

    Therefore, in order to eliminate the deviation between the position command θcom (1) and the position FBθFB (4), the FB controller (5) generates the FB current command IFB (6) by performing, for example, PID calculation of the deviation. By adding this to the FF current command IFF (3), a current command Icom (7) is generated, and the error of the FF current command IFF (3) is corrected.

    FIG. 2 illustrates this state.

    FIG. 2 shows the operation of acceleration → constant speed → deceleration as indicated by the rotational speed ωcom (21) obtained by subtracting the position command θcom (1) of the motor (8).

    The dynamic torque FF compensation block (2) generates the FF current command IFF (3) according to the operation pattern of the position command θcom (1) (ωcom (21) in speed unit).

    In FIG. 1, when the robot operates in the first cycle, the collision detection threshold value Ihr (12) uses the collision detection threshold initial value Ih0 (10) with a large margin for the dynamic friction torque error. In the initial operation, the collision detection threshold Ihr (12) is selected as the collision detection threshold initial value Ih0 (10) by the collision detection threshold switching SW (11). As the collision detection threshold initial value Ih0 (10), a value with a large error margin is selected in consideration of friction loss as usual.

    FIG. 3 is a block diagram showing a collision detection method in the next operation after the one-cycle operation.

    In the operation after the one cycle operation, the FB current command IFB (6) created by the FB controller (5) is used during the first cycle operation in order to eliminate the deviation between the position command θcom (1) and the position FBθFB (4). Then, the FF current command IFF (3) appears as an error value of the friction force parameter that could not be compensated.

    In other words, the FB current command IFB (6) is stored in the storage device, and in addition to the collision detection threshold setting value Ihd (14) preliminarily determined, this added result is used as the collision detection threshold Ihr (12). Thus, it is possible to set a value including a friction loss in the collision detection threshold value in which the margin of error is large.

    FIG. 4 shows this state.

    In FIG. 4, the operation of acceleration → constant speed → deceleration is shown as indicated by the rotational speed ωcom (21) as in FIG.

    Therefore, in the next operation from the one-cycle operation, the value obtained by adding the FB current command IFBA (16) obtained by averaging the FB current command IFB (6) to the preset collision detection threshold value Ihd (14) By using it as the detection threshold value Ihr (12), it is possible to improve the collision detection accuracy in consideration of friction loss.

    The FB current command IFBA (16) is always a value obtained by adding and averaging (15) the FB current command IFB (6) of the current cycle and updating it every cycle.

When the collision torque (17) is applied, the force is converted into a current value by using the motor torque constant Kt (18), and the FB controller (5) sends an FB current command to compensate for this. IFB (6) will be increased.
Therefore, the FB current command IFB (6) takes a value larger than the collision detection threshold set value Ihd (14), and a collision can be detected.

    FIG. 5 shows this state.

    In the conventional technique, the collision detection threshold setting value Ihd (14) is selected as a value with a large margin of error in consideration of the loss of friction like the collision detection threshold initial value Ih0. The collision detection time τ1 (23) is caused by a margin of error with respect to the collision occurrence time τ0 (22), which causes a delay.

    In this embodiment, a value obtained by adding the FB current command IFBA (16) obtained by averaging the FB current command IFB (6) to the collision detection threshold setting value Ihd (14) is used as the collision detection threshold Ihr (12). The timing of collision detection is the collision detection time τ2 (24), and the collision detection accuracy can be improved with respect to the collision occurrence time τ0 (22).

  According to the robot control method of the present invention, it is possible to improve the collision detection accuracy, which is useful for a robot used for production, for example.

The block diagram which shows the collision torque detection method of this invention The figure which shows an example of the electric current command with respect to the fluctuation | variation of rotational speed, FF electric current command, and FB electric current command characteristic in the driving | operation of acceleration of robot → constant speed → deceleration Block diagram of collision torque detection method in the next operation after one cycle operation The figure which shows an example of the characteristic of a collision detection threshold value The figure which shows an example of FB electric current command value when a collision torque is added The figure which shows an example of the dynamic friction torque characteristic in a harmonic reduction gear The figure which shows an example of the dynamic friction torque characteristic in RV reduction gears

Explanation of symbols

7 Current command 8 Motor 11 Collision detection threshold switching SW
12 Collision detection threshold 13 Collision detection judgment

Claims (3)

In a robot driven by a motor via a speed reducer, this is a robot control method for detecting a collision , and a feedforward current command obtained by calculating a dynamic torque based on a position command and a motor rotation detection. The motor receives a current command obtained by adding a feedback current command obtained by feedback control for eliminating a deviation between the position feedback obtained by the detector and the position command, and detects the collision of the feedback current command. A robot control method for performing collision detection by adding a new collision detection threshold value to a set value of the threshold value, and comparing the new collision detection threshold value with a feedback current command obtained by feedback control during the next cycle operation. The resulting feedback current command was by feedback control you added to the set value of the collision detection threshold, the control method according to claim 1, wherein the robot is a value updated in each cycle by adding and averaging at each cycle. In the first cycle operation of the robot, the initial value of the collision detection threshold set in advance is used as the collision detection threshold. In the next operation after the first cycle operation , the feedback current command obtained by the feedback control is stored and this is detected as a collision. The robot control method according to claim 1, wherein the robot control method is used as a collision detection threshold by adding to a set value of the threshold.