JP6091272B2 - Spring constant correction device for articulated robot - Google Patents

Description

  The present invention relates to an articulated robot used for, for example, arc welding, and more particularly to a technique for correcting a spring constant in an articulated robot in which a speed reducer acts as a spring element and elastically deforms.

  When welding a plurality of base materials by arc welding, weaving welding is employed in which welding is performed while a sine wave weaving operation is performed in the left-right direction of the welding line while the welding electrode is advanced in the welding direction. Conventionally, this weaving welding is performed by swinging the welding torch itself to the left or right, or tilting the welding torch left and right about the welding torch itself. When letting an articulated robot perform such weaving welding, high trajectory accuracy is required.

  In an articulated robot that performs such weaving welding, high trajectory accuracy is realized in consideration of elastic deformation of the speed reducer in the power transmission system of the robot. For this purpose, it is important to identify the spring constant of the elastic deformation element of the robot. For example, a method for identifying the rigidity of the robot disclosed in Japanese Patent Laid-Open No. 9-123077 (Patent Document 1) is applied. .

  The stiffness identification method disclosed in Patent Document 1 is a method of identifying the stiffness of a robot based on at least output data from a sensor attached to the robot, and each parameter representing the characteristics of the robot is represented by a stiffness parameter or In the method of identifying the rigidity of a robot that is individually identified after separating the parameter including the rigidity and the other non-rigid parameters, frequency analysis is performed on the output data from the external sensor and / or the internal sensor. And the rigidity parameter is identified based on the separately prepared non-rigidity parameter and the frequency analysis result.

Japanese Patent Laid-Open No. 9-123077

However, in the stiffness identification method disclosed in Patent Document 1, it is necessary to measure the tip position measurement value and the measurement value obtained by an internal sensor such as a motor angle at the same time. That is, it is necessary to measure tip position measurement (outside world) data and robot (inside world) data in synchronization, and the spring constant cannot be easily identified or corrected.
The present invention has been made in view of the above-described problems. In an articulated robot having a plurality of axes, a spring constant is easily corrected in an articulated robot in which a speed reducer acts as a spring element and elastically deforms. It is an object of the present invention to provide a spring constant correction device for an articulated robot that can be used.

In order to solve the above problems, the articulated robot spring constant correcting apparatus according to the present invention employs the following technical means.
In other words, the spring constant correcting device for an articulated robot according to the present invention is applied to an articulated robot that is elastically deformed by a speed reducer acting as a spring element. The articulated robot is operated in a state where elastic deformation is compensated based on a spring constant of the spring element by an elastic deformation compensator included in a robot controller. The spring constant correction device includes: a position value and a posture measurement value of the articulated robot measured by a sensor when the articulated robot is operated in a state where the elastic deformation is compensated; and the articulated robot. And a correction unit that corrects the spring constant using a result of comparison by the comparison unit.

Preferably, the correction unit converts an error of the tip position and posture, which is a result of comparison by the comparison unit, into a robot joint angle error, and calculates an estimated torque at the weaving tip position using a model of an articulated robot. Then, the spring constant error can be calculated based on the relationship between the robot joint angle error and the estimated torque, and the spring constant can be corrected using the calculated spring constant error.

More preferably, the correction unit may be configured to calculate a spring constant error using a least square method based on a relationship between the robot joint angle error and the estimated torque.
More preferably, only the position of the tip of the articulated robot is measured by the sensor, and the spring constant error is calculated on the assumption that the tip posture of the articulated robot is the same as the target posture. can do.
The most preferred form of the spring constant correction device according to the present invention is a spring constant correction device applied to an articulated robot that is elastically deformed by a speed reducer acting as a spring element, the articulated robot being a robot controller. The elastic deformation compensator included is operated in a state where elastic deformation is compensated based on the spring constant of the spring element, and the spring constant correction device is operated in a state where the articulated robot is compensated for the elastic deformation. The comparison unit that compares the measured value of the position and orientation of the tip of the articulated robot with the target value of the position and orientation of the tip of the articulated robot is compared by the comparison unit. A correction unit that corrects the spring constant using the result of the measurement, and the correction unit includes the position of the tip and the result of comparison by the comparison unit. Converts posture error to robot joint angle error, calculates estimated torque at the weaving tip position using a multi-joint robot model, and calculates spring constant error based on the relationship between the robot joint angle error and estimated torque The spring constant is corrected using the calculated spring constant error.

  By using the spring constant correction device for an articulated robot according to the present invention, the spring element of the speed reducer of the power transmission system of the articulated robot is simply corrected in the articulated robot suitable for arc welding that requires a weaving operation. be able to.

It is the schematic which shows the whole structure of the articulated robot with which the spring constant correction apparatus which concerns on embodiment of this invention is applied. It is a schematic diagram which shows the model of one joint axis of the articulated robot shown in FIG. It is a control block diagram containing the spring constant correction apparatus which concerns on embodiment of this invention. It is a flowchart which shows a spring constant correction process. It is a figure for demonstrating the process of S5 of the flowchart shown in FIG. It is a figure for demonstrating the process of S8 of the flowchart shown in FIG.

Hereinafter, a spring constant correcting apparatus for an articulated robot according to an embodiment of the present invention will be described in detail with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.
[overall structure]
First, an outline of a vertical articulated robot (hereinafter, simply referred to as an articulated robot) to which the spring constant correction device according to the present embodiment is applied will be described. In the following description, an articulated robot to which the spring constant correction device according to the present embodiment is applied will be described as a robot for welding applications, but the present invention is applied only to such a welding robot. It is not a thing.

  FIG. 1 is an example of a robot that tilts a welding torch (weaving operation), and is a diagram showing an outline of an articulated robot 1 to which a spring constant correction device according to the present embodiment is applied. This articulated robot 1 is a vertical articulated type and includes six joints J1 to J6. A welding torch is provided at the tip of the J6 axis, and arc welding is performed with a welding wire fed from the welding torch. The articulated robot 1 is a welding work section between a predetermined welding start point and a welding end point, and moves the welding wire in the direction of the welding line connecting the welding start point and the welding end point. It is set so as to perform an operation (weaving operation) tilting at a predetermined amplitude and frequency.

FIG. 2 shows a model of one joint axis of the multi-joint robot 1. As shown in FIG. 2, one joint shaft includes a motor 2 including an encoder 3 that measures a motor rotation angle, an arm 4 that is rotated by the motor 2, and a deceleration that connects the motor 2 and the arm 4. And a model including the container 5.
Since the speed reducer 5 can be modeled as an elastic element, assuming that the elastic coefficient (spring constant) is K, the rotation angle on the motor 2 side is θm, and the rotation angle on the arm 4 side is θl, the arm 4 side The torque τl can be expressed by τl = K · (θl−θm).

The operation of the multi-joint robot 1 in which one joint axis is modeled in this way is controlled by a control device shown below.
[Control device]
The operation of each axis of the articulated robot 1 shown in FIG. 1 is performed by the robot controller 10 shown in FIG.
Servo-controlled by The robot controller 10 includes a teaching pendant, and the spring constant correction device according to the present embodiment is realized by the robot controller 10 (more specifically, by the elastic deformation compensator 11). The robot controller 10 and the elastic deformation compensator 11 do not realize the spring constant correction device according to this embodiment, but the spring constant correction device according to this embodiment is connected to the robot controller 10. Alternatively, it may be realized by an upper computer (upper CPU) or may be realized in another manner.

  The robot controller 10 controls the multi-joint robot 1 so that the welding torch provided in the multi-joint robot 1 moves by performing a weaving operation following the weld line according to a program taught in advance. The teaching program may be created using a teaching pendant connected to the robot controller 10 or may be created using an offline teaching system using a host computer. In any case, the teaching program is created in advance before the actual operation.

  The articulated robot 1 whose operation is controlled by such a robot controller 10 is subjected to a shipping inspection, for example, before product shipment after manufacture. One such shipping inspection is a left and right weaving inspection. In this right and left weaving inspection, the spring constant of the speed reducer 5 is corrected from the initial value. In Patent Document 1, identification is performed using tip position data (outer world data) measured in synchronization with motor angle data (inner world data). However, in this embodiment, only the tip position data is used in this left and right weaving inspection. The spring constant is corrected as one of the shipping inspections.

FIG. 3 is a control block diagram of the robot controller 10 that controls the articulated robot 1 of FIG. In this control block diagram, each axis of the articulated robot 1 is servo-controlled (including other controls), and the spring constant correction process according to the present embodiment is executed.
As a servo control, the robot controller 10 drives a plurality of joint axes so that a tool (here, a welding torch) attached to the multi-joint robot 1 performs a desired operation (here, a weaving operation). In FIG. 3, the control block of the servo control is not described in detail because a known technique or the like may be applied.

  The spring constant correction process according to the present embodiment is realized by, for example, the elastic deformation compensation unit 11 included in the robot controller 10. The elastic deformation compensator 11 includes a target position comparison unit 13 that compares position data of the welding torch tip measured by the tip position measurement sensor 12 in, for example, an XY plane coordinate system, and preset target position data. A spring constant correction unit 14 that corrects the initial value of the spring constant of the speed reducer 5 that is modeled based on the comparison result, and elastic deformation compensation using the spring constant corrected by the elastic deformation compensation unit 11 The robot controller 10 servo-controls each axis motor 15 of the articulated robot 1 while the unit 11 compensates for elastic deformation.

[Spring constant correction method]
The details of the spring constant correction processing method according to the present embodiment will be described with reference to the flowchart shown in FIG. In the following description, one of the six axes will be described.
In step (hereinafter referred to as “S”) 1, the elastic deformation compensator 11 performs a left and right weaving inspection process. At this time, for example, the servo controller is manually operated with the robot controller 10 in the inspection mode, and the arm tip of the articulated robot 1 is weaved left and right. At this time, as shown in FIG. 5, the coordinate data (for example, the vertical direction (Z direction) and the horizontal direction (X direction)) of the weaving tip position is acquired and stored.

  In S2, the elastic deformation compensator 11 performs a pass / fail determination. At this time, if the deviation is smaller than a predetermined threshold value (difference between the target value and the measured value), it is determined as acceptable, otherwise it is not determined as acceptable. If it is determined to be acceptable (YES at S2), the process proceeds to S3. If not (NO in S2), the process proceeds to S4. In S <b> 3, the elastic deformation compensator 11 determines and stores, for example, a spring constant as the pass determination process or shifts the robot controller 10 from the inspection mode to the normal mode.

In S <b> 4, the elastic deformation compensator 11 acquires various robot parameters of the articulated robot 1. At this time, for example, the inertia term (J), nonlinear term (C), gravity term (G), and spring constant before correction (K) in each axis of the articulated robot 1 stored in the robot controller 10 or the host computer. Is acquired. Since the spring constant is overwritten in the course of the repetitive processing, in S4, the spring constant calculated and stored by the previous correction processing or the initial value of the spring constant is acquired.

  In S5, the elastic deformation compensator 11 extracts an error at the weaving end point position. At this time, as shown in FIG. 5, the difference between the ideal waveform (dotted line) and the measurement waveform measured by the tip position measurement sensor 12 is extracted as an error. The measurement waveform is represented by the following equation (1), and the error is represented by the following equation (2).

In this equation (2),
x, y, z: position coordinates of the robot tip α, β, γ: posture angle of the robot tip (Euler angle or roll pitch yaw angle)
It is.
Here, it is preferable that all six degrees of freedom (x, y, z, α, β, and γ) described above can be measured. However, at least two degrees of freedom (for example, in the case of left-and-right weaving) Only two directions (the horizontal direction and the vertical direction) are measured, and dα, dβ, dγ = 0 are assumed (assuming that the tip posture is the same as the target posture), and dx or dy = Assuming 0, even when there are only two sensors for measuring the robot tip position (or posture), the spring constant correction processing method according to the present embodiment can be realized. That is, under such assumption, if there are at least two tip position measurement sensors 12, the spring constant correction processing according to the present embodiment can be realized. Note that the present invention is not limited to the invention under such assumptions.

  In S6, the elastic deformation compensator 11 converts the position error into the robot joint angle error using the Jacobian matrix as shown in the following equation (3).

   In S7, the elastic deformation compensator 11 calculates the estimated torque at the weaving end point position using the model of the multi-joint robot 1 as shown in the following equation (4). At this time, the inertia term (J), nonlinear term (C), and gravity term (G) in the joint axis of the articulated robot 1 acquired in S4 are used.

In S8, the elastic deformation compensator 11 calculates the robot joint angle error (calculated in S6) and the estimated torque (when calculated in S6) in a plurality of postures in the multi-joint robot 1 as shown in the following equation (5). (Calculated in S7) is calculated, and an error dE used for correcting the spring constant is calculated from the obtained value.
At this time, the processes in S6 and S7 are repeatedly executed until the result of the left and right weaving inspection is passed (YES in S2). In this case, the posture of the articulated robot 1 is changed, and a plurality of sets of robot joint angle errors and estimated torques during weaving are calculated. For this reason, as shown in FIG. 6, a plurality of points are scattered (with a certain correlation). That is, in the weaving inspection (in S1), the weaving inspection is performed in a plurality of robot postures, and one point in FIG. 6 is calculated for each data measured in each robot posture. In S1, there are as many points as the number of postures of the robot inspected in S1. As shown in FIG. 6, the slope of the linear function (correlation indicated by the straight line shown) by the weighted least square method is calculated as an error dE for correcting the spring constant, and is substituted into equation (5). Thus, the updated spring constant (after correction) is calculated and stored. Thereafter, the process returns to S1.

[Spring constant correction operation and effect]
The left and right weaving inspection of the articulated robot 1 is performed, the arm tip is moved to the left and right, and the coordinate data (for example, X value) of the weaving end point position (tip position) with respect to the time axis is acquired and stored ( S1). If the result of the left and right weaving inspection is not determined to be acceptable (NO in S2), various robot parameters including the spring constant before update (initial value for the first time) are acquired (S4).

  A position error at the weaving end point position is acquired (S5), and the position error is converted into a robot joint angle error (S6). The estimated torque at the weaving end point position is calculated by the model (formula (4)). A spring constant error dE is calculated using the robot joint angle error converted in S6 and the torque calculated in S7 (S8). The updated spring constant is obtained using this error dE (Equation (5)), and the left and right weaving inspection is performed again using the updated spring constant (S1).

Such an operation of obtaining the error dE and correcting the spring constant is repeatedly executed until the result of the left and right weaving inspection is acceptable (YES in S2). It should be noted that other processing may be performed when the left and right weaving inspection results are not determined to be acceptable even if the spring constant is corrected repeatedly a predetermined number of times.
As described above, by using the spring constant correction device for an articulated robot according to the present embodiment, in the articulated robot suitable for arc welding that requires a weaving operation, the speed reducer of the power transmission system of the articulated robot The spring element can be easily corrected. That is, the initial value of the spring constant was calculated on the assumption that the deviation of the tip position in the state controlled by the elastic deformation compensator of the robot controller (compensated based on the initial value of the spring constant) is due to the spring constant. Correct using the error. In calculating this error, the absolute amount of elastic deformation was conventionally calculated using the motor inner world data and the robot tip position data (outer world data) acquired in synchronization, but in this embodiment, By focusing on the relative change (error) from the spring constant, and without using internal data (motor angle), external data (
The spring constant can be easily corrected by calculating the angle error from the tip position data) using a model.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Articulated robot 10 Robot controller 11 Elastic deformation compensation part 12 Tip position measurement sensor 13 Target position comparison part 14 Spring constant correction part 15 Each axis motor

Claims (3)

A spring constant correction device applied to an articulated robot that is elastically deformed by a speed reducer acting as a spring element, wherein the articulated robot adjusts the spring constant of the spring element by an elastic deformation compensator included in a robot controller. Based on the compensated elastic deformation,
The spring constant correction device includes: a position value and a posture measurement value of the articulated robot measured by a sensor when the articulated robot is operated in a state where the elastic deformation is compensated; and the articulated robot. a comparator for comparing of the target value of the position and orientation of the tip, with a result of comparison by the comparison unit, seen including a correction unit, a for correcting the spring constant,
The correction unit converts a tip position and posture error, which is a result of comparison by the comparison unit, into a robot joint angle error, and calculates an estimated torque at a weaving tip position by a model of an articulated robot, A spring constant correction device that calculates a spring constant error based on a relationship between the robot joint angle error and the estimated torque, and corrects the spring constant using the calculated spring constant error . The spring constant correction apparatus according to claim 1 , wherein the correction unit calculates a spring constant error using a least square method based on a relationship between the robot joint angle error and the estimated torque. The spring constant error is calculated on the assumption that only the position of the tip of the articulated robot is measured by the sensor, and the posture of the tip of the articulated robot is the same as a target posture. Item 3. The spring constant correction device according to Item 1 or 2 .

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