JP2006059037A - Welding robot controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a welding robot controller capable of surely and accurately carrying out weaving action with a previously taught amplitude. <P>SOLUTION: By means of this welding robot controller 20, a plurality of drive motors 13 arranged in respective joints of a welding robot 10 are driven by feedback control, and the welding robot 10 carries out welding by generating an arc while performing weaving action of a welding torch 14 in each interpolation point. The welding robot controller 20 is provided with a CPU 21. By means of the CPU 21, in each interpolation point, a difference between a joint angle of each joint not in a weaving operation and that in a weaving operation is computed as a weaving shift for each joint, a gain in a feedback control system of the driving motor 13 is computed based on a servo control constant of the driving motor 13 and a predetermined weaving frequency, the weaving shift is multiplied by an inverse number of the computer gain and the obtained value is added to the joint angle of each joint not in the weaving operation, and a joint angle for each joint as an operation instruction to the driving motor 13 is computed for each interpolation point. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control device for a welding robot that performs welding on a workpiece.

  Conventionally, some articulated welding robots that perform welding on a workpiece perform an operation called a weaving operation (see, for example, Patent Document 1). The weaving operation refers to an operation of swinging the welding torch in a direction orthogonal to the welding progress direction by rotating each axis of the welding robot by a drive motor according to a work program stored in advance.

In this weaving operation, the welding torch performs a linear interpolation operation or a circular interpolation operation along the shape of the welded portion based on the teaching playback method, and the tool center point (TCP) of the welding torch is set to the amplitude taught in advance. Move based on frequency and waveform. By performing this weaving operation, good and reliable welding can be realized.
JP-A-7-24574.

  By the way, in the control of the articulated welding robot, in order to improve the dynamic characteristics of the welding robot, the control constant of the motor that drives each arm of the welding robot is changed in real time.

  The position of each joint of the welding robot is controlled by feedback control of the motor. For example, the position of the welding robot is contracted (that is, the plurality of arms are not extended), and the moment of inertia that is the load of the motor Is small, the gain in the feedback control system of the motor for controlling the position (hereinafter referred to as feedback gain) is increased to improve the position followability at each joint. Conversely, when multiple arms are extended and the moment of inertia is large, control is performed such that the feedback gain for position control is reduced, the position followability at each joint is intentionally deteriorated, and the amplitude of residual vibration is reduced. It has been broken.

  However, as described above, when the control for changing the feedback gain for position control in the feedback control system of the motor in real time is performed, the position follow-up performance at each joint changes. There is a problem in that it affects the dependent weaving operation, and the amplitude taught by the weaving operation changes in advance.

  In the control of the multi-joint welding robot, the weaving operation is realized by combining a plurality of joints of the welding robot. For example, in a weaving operation in a welding robot with a serial link mechanism, an interference torque is generated between the joints of the welding robot, and the reduction gear connecting the motor and the arm may bend by this interference torque. For this reason, the amount (angle) to be originally rotated in each axis may not be obtained accurately, and there is a problem that the amplitude taught by the weaving operation cannot be observed.

  The present invention has been conceived under the circumstances described above, and it is an object of the present invention to provide a welding robot control device capable of reliably and accurately performing a weaving operation with an amplitude taught in advance. To do.

  In order to solve the above problems, the present invention takes the following technical means.

  The welding robot control apparatus provided by the first aspect of the present invention is an interpolation that divides a welding track on a predetermined time basis by driving a plurality of servo motors provided at each joint of the welding robot by feedback control. A welding robot controller for causing the welding robot to perform welding while performing a weaving operation of a welding torch for each point, and for each interpolation point, a joint angle of each joint when the weaving operation is not performed The weaving displacement calculating means for calculating the difference between the joint angles of the joints when the weaving operation is performed as the weaving displacement for each joint, the servo control constant of the servo motor, and a predetermined weaving frequency based on the servo. Gain calculating means for calculating gain in motor feedback control system By multiplying the reciprocal of the gain calculated by the gain calculating means by the weaving displacement calculated by the weaving displacement calculating means and adding the value to the joint angle of each joint when the weaving operation is not performed, And an operation command calculating means for calculating a joint angle of each joint as an operation command for the servo motor for each interpolation point.

  According to this configuration, the reciprocal of the gain in the feedback control system of the motor is multiplied by the value of the weaving displacement, and this is added to the joint angle at each joint when the weaving operation is not performed, and this is the motor that drives each joint Is given to each motor as an operation command. Accordingly, it is possible to acquire an appropriate amplitude in the weaving operation in consideration of the gain in the motor feedback control system. Therefore, the weaving operation can be performed with a more accurate amplitude.

  According to a preferred embodiment, the servo control constant may be a time constant representing a delay system of position control of the servo motor.

  The welding robot control device provided by the second aspect of the present invention is an interpolation in which a plurality of servo motors provided at each joint of the welding robot are driven by feedback control to divide the welding track at predetermined time intervals. A welding robot controller for causing the welding robot to perform welding while performing a weaving operation of a welding torch for each point, and for each interpolation point, a joint angle of each joint when the weaving operation is not performed A weaving displacement calculating means for calculating a difference between the joint angles of the joints during the weaving operation as a weaving displacement for each joint, and a first torque calculation for calculating the torque generated around the joint axis for each joint. Means for calculating torque generated when the weaving operation is not performed for each interpolation point; Torque calculated by the torque calculating means and the first torque calculating means, and torque generated when the weaving operation is not performed, calculated by the second torque calculating means. And subtracting the subtracted value by a predetermined spring constant in each joint, and adding the divided value to the joint angle of each joint when the weaving operation is performed. And an operation command calculating means for calculating a joint angle of each joint as an operation command for the servo motor for each point.

  According to this configuration, the torque generated when the weaving operation is not performed is subtracted from the torque generated around the axis of the joint, divided by the spring constant of each joint, and the divided value when each weaving operation is performed. In addition to the joint angle of the joint, this is given to each motor as an operation command for the motor that drives each joint. Thereby, the joint angle of each joint given to each motor can be corrected using the deflection amount of the speed reducer due to the interference torque generated between the arms. Therefore, a weaving operation having an appropriate amplitude can be performed.

  According to a preferred embodiment, the second torque calculating means, for each interpolation point, the torque generated at the right end of the weaving operation and the torque generated at the left end of the weaving operation for each cycle of the weaving operation. It is preferable to calculate a torque generated when the weaving operation is not performed by calculating an average value.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

  Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the accompanying drawings.

  FIG. 1 is a configuration diagram showing a robot control system to which a robot control apparatus according to the present invention is applied. In this robot control system, welding is performed on a workpiece (workpiece) by a welding torch provided in the welding robot.

  The robot control system is roughly constituted by a welding robot 10, a robot control device 20, and a welding power source device 30.

  The welding robot 10 automatically performs, for example, arc welding on the workpiece W. The welding robot 10 includes a base member 11 fixed to an appropriate place such as a floor, a plurality of arms 12 connected to the base member 11 via a plurality of axes, and a plurality of arms 12 provided at both ends or one end of the arms 12. A drive motor (servo motor) 13 (partially omitted) is configured.

  The welding robot 10 is provided with a welding torch 14 at the distal end portion of the arm 12 provided on the most distal end side. The welding torch 14 guides a welding wire 15 having a diameter of, for example, about 1 mm as a filler material to a predetermined welding position of the workpiece W.

  A wire feeding device 16 is provided on the upper portion of the welding robot 10. The wire feeding device 16 is for feeding the welding wire 15 to the welding torch 14. The wire feeding device 16 includes a reel (not shown) around which the welding wire 15 is wound, and a feeding motor 17 that rotates the reel. The feeding motor 17 is rotationally driven by a welding power source device 30.

  A coil liner 19 for guiding the welding wire 15 is connected to the wire feeder 16, and the tip of the coil liner 19 is connected to the welding torch 14. As a result, the welding wire 15 delivered by the wire feeder 16 is guided to the welding torch 14 via the coil liner 19. The welding wire 15 projects outward from the welding torch 14 and functions as a consumable electrode. That is, welding is performed on the workpiece W by generating an arc between the tip of the welding wire 15 and the workpiece W by the welding power source device 30 and melting the welding wire 15 with the heat.

  The drive motor 13 is rotationally driven by a drive signal from the robot control device 20, and the respective drive motors 13 are rotationally driven, whereby each arm 12 is displaced, and as a result, the welding torch 14 moves up, down, front, back, left, and right. It is possible.

  Further, in the present embodiment, the weaving operation of the welding torch 14 is performed by driving the drive motors 13 to rotate. As described above, the weaving operation refers to an operation of swinging the welding torch 14 in a direction orthogonal to the welding progress direction. As shown in FIGS. 1 and 2, the welding robot 10 according to the present embodiment is a multi-joint welding robot having a plurality of joints, and the welding torch 14 is welded by performing a combined operation of the plurality of joints. It is controlled to swing in a direction orthogonal to the direction (see the sinusoidal locus in FIG. 2). FIG. 2 shows a case where the welding robot 10 has three degrees of freedom.

  The drive motor 13 is provided with an encoder (not shown). The output of the encoder is given to the robot controller 20, and the robot controller 20 recognizes the current position of the welding torch 14 by the output of the encoder.

  The robot control device 20 is for controlling the operation of the welding robot 10. The robot control device 20 drives and controls each drive motor 13 of the welding robot 10 based on a work program stored in advance, current position information from an encoder (not shown), etc. Move to welding point. Further, the robot control device 20 performs the weaving operation by driving and controlling the drive motors 13 to swing the welding torch 14.

  The welding power source device 30 includes a welding power source (not shown), and the welding power source supplies a high welding voltage between the welding torch 14 and the workpiece W. Moreover, the welding power supply device 30 also has a function of driving the feeding motor 17 of the wire feeding device 16 at a predetermined timing.

  FIG. 3 is a block diagram showing the internal configuration of the robot control device 20 and its peripheral devices. The robot control device 20 includes a CPU 21, a RAM 22, a ROM 23, a timer (TIMER) 24, a hard disk 25, a teaching pendant I / F 26, an operation box I / F 27, and a servo driver I / F 28. Each unit is a bus (BUS). 31 are connected to each other.

  A teaching pendant 33 is connected to the teaching pendant I / F 26, and an operation box 34 is connected to the operation box I / F 27. The servo driver I / F 28 is connected to a plurality of servo drivers 35 provided in the robot control device 20, and the six drive motors 13 provided in the welding robot 10 are connected to the servo driver 35. Has been.

  The CPU 21 is a control center of the robot control device 20, and is based on a predetermined work program, an operation signal from the teaching pendant 33 or the operation box 34, current position information from an encoder (not shown), or the like. Predetermined data processing is performed, and an operation command is given to the servo driver 35 via the bus 31 and the servo driver I / F 28. Thereby, the drive motor 13 is rotationally driven, and the welding torch 14 is moved.

  The RAM 22 provides a work area for the CPU 21 and temporarily stores calculation data and the like. The RAM 22 functions as, for example, an operation command buffer 41, a trajectory buffer 42, an interpolation point buffer 43, or a joint interpolation point buffer 44 described later.

  The ROM 23 stores a work program in which the operation of the welding robot 10 (including collision detection, stop processing, and the like) is defined, data indicating the execution conditions of the work program, data indicating a control constant, and the like.

  The hard disk 25 stores teaching data representing a welding operation of the welding robot 10.

  The timer 24 generates a synchronization signal to the CPU 21 at predetermined time intervals. The synchronization signal is used as an update timing when the CPU 21 outputs an operation command signal to the servo driver 35.

  The teaching pendant I / F 26 serves as an interface with the teaching pendant 33. The teaching pendant 33 has a display device 33a and a keyboard 33b, for example, and is operated by a user when the welding robot 10 is manually operated. The CPU 21 performs predetermined data processing by receiving an operation signal from the teaching pendant 33 and sends display data to the teaching pendant 33 to display operation information.

  The operation box I / F 27 serves as an interface with the operation box 34. The operation box 34 enables various operations such as selection, activation, start, and stop of the automatic operation mode or the manual mode by the user. The CPU 21 performs predetermined data processing by receiving an operation signal from the operation box 34.

  The servo driver I / F 28 manages the interface with the servo driver 35. The servo driver 35 drives and controls each of the six drive motors 13 based on an operation command signal from the CPU 21.

  FIG. 4 is a configuration diagram when the actual functions of the CPU 21 and the RAM 22 are represented as blocks.

  The functions of the CPU 21 are represented by an operation command reading unit 36, a trajectory generation unit 37, an interpolation point generation unit 38, a joint interpolation point generation unit 39, and a servo output unit 40. The functions of the RAM 22 include an operation command buffer 41, It is represented by a trajectory buffer 42, an interpolation point buffer 43, and a joint interpolation point buffer 44. Each of the buffers 41 to 44 is configured as a FIFO (first-in first-out) buffer, and data is processed in first-in and first-out.

  The operation command reading unit 36 reads information related to the operation command of the welding robot 10 from the teaching data stored in the hard disk 25 (for example, a trajectory command including data such as coordinates and speed information) and stores it in the operation command buffer 41.

  The trajectory generation unit 37 reads out information (motion command command) related to the motion command from the motion command buffer 41, and plans the work trajectory of the welding torch 14 of the welding robot 10 on the orthogonal coordinates in the three-dimensional space based on the information. The trajectory generator 37 stores the planned trajectory data in the trajectory buffer 42.

  The interpolation point generation unit 38 reads the trajectory data from the trajectory buffer 42 and divides the trajectory data at predetermined time intervals called “interpolation periods”. Then, interpolation point data indicating the position and orientation to be reached by the welding torch 14, which is represented by orthogonal coordinates for each interpolation cycle, is calculated. In other words, the trajectory data represents the movement trajectory of the welding torch 14 from the welding start point to the welding end point by a plurality of teaching points, and the moving method of the welding torch 14 between the teaching points is defined by linear movement or arc movement. It is. The interpolation point generator 38 interpolates data such as a point to which the welding torch 14 should pass between adjacent teaching points and the attitude of the welding torch 14 at each point for each interpolation period. The interpolation point generation unit 38 stores the calculated interpolation point data in the interpolation point buffer 43.

  The joint interpolation point generation unit 39 performs an operation of inversely converting the interpolation point data indicating the arrival position and posture of the welding torch 14 into data indicating the joint angle at each joint of the welding robot 10, and converts it into a joint interpolation point buffer 44. Memorize temporarily. Note that the weaving operation that is a feature of the present embodiment is realized mainly in the joint interpolation point generation unit 39.

  Data indicating the joint angle at each joint of the welding robot 10 stored in the joint interpolation point buffer 44 is notified to the servo output unit 40 in synchronization with the synchronization signal SYNC generated by the timer 24. The data indicating the joint angle is output from the servo output unit 40 to the servo driver 35 via the servo driver I / F 28 as a position command for each joint (operation command for the drive motor 13) at a predetermined timing.

  FIG. 5 is a block diagram showing the concept of servo control by the servo driver 35. According to this figure, the position command at each joint of the welding robot 10 is input to the position control block 51, and the output of the position control block 51 is input to the speed control block 52. The output of the speed control block 52 is input to the current control block 53, and the output of the current control block 53 is input to the drive motor 13. The output of the drive motor 13 is given to the arm 12 as a load via a spring element block 54 of a speed reduction mechanism including a speed reducer, for example.

  A current detection block 55 is connected to the drive motor 13, a current flowing through the drive motor 13 is detected in the current detection block 55, and the value is fed back to the current control block 53. In addition, an encoder 56 is connected to the drive motor 13, and data on the current rotational speed (corresponding to the moving speed of the arm) is acquired by the encoder 56. Feedback.

  In the position control block 51, the feedback rotational speed data is integrated by the integration block 57 to be converted into position data and input to the subtractor 61. The subtractor 61 uses the current position with respect to the position command (joint angle). Error data of (joint angle) is calculated. The error data is level-corrected by the amplifier 58 with a predetermined gain Kpp (hereinafter referred to as position feedback gain) and then input to the adder 62.

  In the position control block 51, position command data at each joint of the welding robot 10 is converted into speed data by being differentiated by the differentiation block 59, and further, a predetermined gain Kff (hereinafter referred to as speed feed forward) is converted by the amplifier 60. After level correction is performed with the gain), the signal is input to the adder 62. The adder 62 adds the speed data output from the speed feedforward gain Kff and the error data output from the position feedback gain Kpp, and outputs the result to the speed control block 52 described above.

  In this way, by performing feedback control of the operation of the drive motor 13 with respect to the position command at each joint of the welding robot 10, the reproduction operation of the teaching data taught in advance can be performed more accurately.

  Next, the action relating to the weaving operation according to the present embodiment will be described with reference to the flowchart shown in FIG. 6 and the diagram showing the relationship between the reference coordinate system and the tool coordinate system shown in FIG.

  Control regarding the characteristic weaving operation in the present embodiment is mainly executed in the joint interpolation point generation unit 39 (see FIG. 4). That is, in step S <b> 1, the joint interpolation point generation unit 39 reads the interpolation point data IPi from the interpolation point buffer 43. Here, the interpolation point data IPi refers to a position (including a position to be welded) where the tip of the welding torch 14 moves from the welding start position to the target position (welding end position), and It is the data showing the attitude | position of the welding torch 14 in the position.

  In the welding robot 10, a reference coordinate system and a tool coordinate system are set as coordinate systems for controlling each joint, as shown in FIG. The reference coordinate system is fixedly set at the installation position of the welding robot 10. On the other hand, the tool coordinate system is set at the tip (tool center point) of the welding torch 14 and moves as the welding torch 14 moves. That is, the position of the origin position of the tool coordinate system in the reference coordinate system is changed by the movement of the welding torch 14.

  The interpolation point data IPi is obtained by converting the position and orientation of the welding torch 14 as viewed from the reference coordinate system (see FIG. 7) of the welding robot 10, that is, the position and orientation of the tool coordinate system into coordinate values of the reference coordinate system. It is a representation. The interpolation point data IPi is expressed by the following determinant.

  Here, xi represents the X coordinate position (mm) of the tool coordinate system origin viewed from the reference coordinate system, yi represents the Y coordinate position (mm) of the tool coordinate system origin viewed from the reference coordinate system, and zi represents the reference. The Z coordinate position (mm) of the origin of the tool coordinate system viewed from the coordinate system is indicated, ai indicates the rotation posture (rad) of the X axis of the tool coordinate system viewed from the reference coordinate system, and bi is viewed from the reference coordinate system. The Y-axis rotation posture (rad) of the tool coordinate system is indicated, and ci indicates the Z-axis rotation posture (rad) of the tool coordinate system as viewed from the reference coordinate system.

  Next, in step S2, the joint interpolation point generation unit 39 calculates a joint angle ANGorg at each joint of the welding robot 10 when the weaving operation is not performed. Specifically, the interpolation point data IPi represented by orthogonal coordinates and indicating the arrival position and orientation of the welding torch 14 is inversely converted into data indicating the joint angle at each joint of the welding robot 10. Then, data indicating the joint angle at each joint of the welding robot 10 is stored in the RAM 22 (joint interpolation point buffer 44). In addition, since the inverse calculation algorithm of the articulated welding robot is a technique generally used in the playback teaching system, detailed description thereof is omitted here. The joint angle ANGorg at each joint of the welding robot 10 when the weaving operation is not performed is expressed by the following determinant.

  Here, n represents the number of joints of the welding robot 10, ANGorg1 represents the joint angle (rad) of the first joint of the welding robot 10, ANGorg2 represents the joint angle (rad) of the second joint of the welding robot 10, ANGorgn indicates the joint angle (rad) of the n-th joint of the welding robot 10.

  Next, in step S3, the joint interpolation point generation unit 39 calculates a joint angle ANGwv at each joint of the welding robot 10 when performing the weaving operation. Specifically, the weaving displacement is added to the interpolation point data IPi represented by orthogonal coordinates and representing the arrival position and orientation of the welding torch 14, and is converted back to data indicating the joint angle at each joint of the welding robot 10. . Then, it is stored in the RAM 22 (joint interpolation point buffer 44). The joint angle ANGwv at each joint of the welding robot 10 when performing the weaving operation is expressed by the following determinant.

  Here, n represents the number of joints of the welding robot 10, ANGwv1 represents the joint angle (rad) of the first joint of the welding robot 10, ANGwv2 represents the joint angle (rad) of the second joint of the welding robot 10, ANGwvn represents the joint angle (rad) of the n-th joint of the welding robot 10.

  Next, in step S4, a difference between the joint angle ANGorg at each joint of the welding robot 10 when the weaving operation is not performed and the joint angle ANGwv at each joint of the welding robot 10 when the weaving operation is performed is obtained. Then, the difference is stored in the RAM 22 (joint interpolation point buffer 44) as a weaving displacement ANGamp for each joint.

  FIG. 8 is a diagram showing a difference between an interpolation point when the weaving operation is not performed (see white circle) and an interpolation point when the weaving operation is performed (see black circle). In the example of this figure, a sine waveform weaving pattern is superimposed on the progress of welding. Since the weaving pattern generation method is a known technique, the description thereof is omitted here. The weaving displacement ANGamp for each joint of the welding robot 10 is expressed by the following determinant.

  Here, n represents the number of joints of the welding robot 10, ANGamp1 represents the joint angle (rad) of the first joint of the welding robot 10, and ANGamp2 represents the joint angle (rad) of the second joint of the welding robot 10. ANGampn indicates the joint angle (rad) of the n-th joint of the welding robot 10. ANGamp1, ANGamp2, and ANGampn are each expressed by the following equations.

  Next, in step S5, the gain GAIN of each drive motor 13 in the feedback control system is calculated based on the servo control constant of the drive motor 13 that drives each joint of the welding robot 10 and the weaving frequency specified in advance. . The gain GAIN is expressed by the following determinant.

  Here, n indicates the number of joints of the welding robot 10, GAIN1 indicates the gain (non-dimensional) of the first joint of the welding robot 10, GAIN2 indicates the gain (non-dimensional) of the second joint of the welding robot 10, GAINn represents the gain (dimensionalless) of the nth joint of the welding robot 10.

  Hereinafter, for example, a procedure for obtaining the gain GAIN for the j-th joint of the welding robot 10 will be described.

  The method of obtaining the gain of the drive motor 13 differs depending on the servo control method and the servo calculation method, but here, a general position feedback and speed feedforward two-degree-of-freedom control system as shown in FIG. 5 is taken as an example. I will explain to you. In addition, in the example shown in FIG. 5, the feedback control system of the speed loop and the current loop is included, but the delay system by the servo shows the dominant role of the position loop, and here the speed loop and the current loop are Think of it as unnecessary.

  The position feedback gain Kppj and the speed feedforward gain Kffj of the drive motor 13 that drives the j-th joint are values generally used in servo control and are known values. These gains Kppj and gain Kffj are often changed depending on the posture and operation mode of the welding robot 10, but since the change command is issued from the CPU 21 of the robot controller 20, joint interpolation is performed. The value can also be read by the point generator 39.

  First, using the position feedback gain Kppj and the velocity feedforward gain Kffj, a time constant TSj (sec) representing a delay system of position control of the drive motor 13 that drives the j-th joint is calculated by the following equation. In this case, the time constant TSj is positioned as a servo control constant for the drive motor 13.

  Next, based on a predetermined weaving frequency FRQ and a time constant TSj, a gain GAINj of the j-th joint is calculated by the following equation.

  Here, GAINj represents the gain [no dimension] of the motor driving the j-th joint, and the weaving frequency FRQ represents the taught weaving frequency (Hz). In the welding robot 10 that employs the teaching playback system, the weaving frequency FRQ is data taught in advance, and is stored in the hard disk 25 (see FIG. 3) and played back in the same manner as the teaching position of the welding robot 10. Sometimes it is read out.

  Using the above equation, for example, by changing j from 1 to n (n is the number of joints of the welding robot 10), the gain GAIN for all joints of the welding robot 10 is calculated.

  Next, in step S <b> 6, a corrected joint angle ANGcomp at each joint of the welding robot 10 is calculated as a position command (operation command for the drive motor 13) at each joint of the welding robot 10. Specifically, the inverse of the gain GAINj is multiplied by the weaving displacement ANGamp for each joint. The value after the multiplication is added to the joint angle ANGorg at each joint of the welding robot 10 when the weaving operation is not performed. The corrected joint angle ANGcomp at each joint of the welding robot 10 is represented by the following determinant.

  Here, n represents the number of joints of the welding robot 10, ANGcomp1 represents the joint angle (rad) after correction of the first joint of the welding robot 10, and ANGcomp2 represents the joint angle after correction of the second joint of the welding robot 10. (Rad), and ANGcompn represents the joint angle (rad) after the correction of the n-th joint of the welding robot 10. ANGcomp1, ANGcomp2, and ANGcompn are each expressed by the following equations.

  Here, GAIN1 indicates the gain of the drive motor 13 that drives the first joint, GAIN2 indicates the gain of the drive motor 13 that drives the first joint, and GAINn indicates the gain of the drive motor 13 that drives the nth joint. Indicates the gain.

  In this way, the inverse of the gain GAIN in the feedback control system of the drive motor 13 is multiplied by the value of the weaving displacement ANGamp and added to the joint angle ANGorg at each joint of the welding robot 10 when the weaving operation is not performed. Is given to each drive motor 13 as a position command at each joint of the welding robot 10. Thereby, it is possible to acquire an appropriate amplitude in the weaving operation in consideration of the gain GAIN in the feedback control system of the drive motor 13. Therefore, the weaving operation can be performed with a more accurate amplitude.

  By the way, in the above-described weaving operation in the multi-joint welding robot, an interference torque generated between the joints of the welding robot may cause a reduction gear (not shown) that connects the drive motor 13 and the arm 12 to bend. The amount (angle) to be obtained may not be obtained accurately. Therefore, there has been a problem that the amplitude taught in the weaving operation taught in advance cannot be observed.

  However, as will be described below, if the amount of flexure of the speed reducer in the weaving operation is obtained, and the joint angle at each joint of the welding robot 10 when performing the weaving operation is corrected based on this, the accurate amplitude is obtained. A weaving operation can be performed. Details will be described below.

  FIG. 9 is a flowchart for explaining the operation according to this embodiment. The process according to this flowchart is mainly performed by the joint interpolation point generation unit 39 as in the above-described embodiment. 9 is the same as step S1 to step S4 shown in FIG. 6, description thereof will be omitted below, and steps S15 to S17 will be described.

  In step S15, the torque TRQj generated around the joint axis of the welding robot 10 is obtained for each joint. More specifically, the mechanism parameters of the welding robot 10 (the center of gravity position, mass, inertia tensor, and length of the arm 12 connected to the joint), the joint position ANGwvj, the joint angular velocity VELwvj, and the joint angular acceleration ACCwvj of the welding robot 10. The torque TRQj is obtained by performing inverse dynamics calculation using. The subscript j in the torque TRQj, joint position ANGwvj, joint angular velocity VELwvj, and joint angular acceleration ACCwvj represents the joint number of the welding robot 10.

  In general, the torque generated in each joint is based on the mechanism parameters of the welding robot 10 (the position of the center of gravity of the arm 12 connected to the joint, the mass, the inertia tensor, the length), the position of each joint, the angular velocity, and the angular acceleration. Therefore, it is known that it is calculated by the following formula, and this is called “inverse dynamic model”.

  Here, each term of the above formula has the meaning shown in Table 1.

  The inverse dynamic model shown in the above equation (1) is composed of an inertia matrix H, a viscosity matrix C, and a gravity matrix G. When the number of joints of the welding robot 10 is n, the inertia matrix H is n × n symmetrical. It is represented by a matrix, and shows the torque generated in the joint itself due to the angular acceleration of each joint of the welding robot 10 and the interference torque generated due to the angular acceleration of other joints. The viscosity matrix C is represented by an n × 1 matrix, and indicates a torque composed of a centrifugal force and a Coriolis force generated by the angular velocity of each joint of the welding robot 10. The gravity matrix G is represented by an n × 3 matrix and indicates torque generated by the influence of gravity acceleration.

  Here, the mechanism parameters of the welding robot 10 are composed of four items shown in Table 2. In addition, the number in Table 2 is a value per one arm connected to the joint.

  The inertia tensor I is generally used to indicate the difficulty of rotation of an object (for example, the arm 12 of the welding robot 10), and is represented by a 3 × 3 symmetric matrix in Table 2 as is well known. . The diagonal components represent the inertia moments Ix, Iy, Iz of each joint of the welding robot 10, and the other components represent the negative values of the inertial products Ixy, Iyz, Izx.

  Further, the inertia moments Ix, Iy, and Iz represent the difficulty in turning and stopping the object, and are obtained by the following equation, for example.

  Further, the inertial products Ixy, Iyz, and Izx represent moments that disturb the motion of the object when it is rotating, and are obtained by the following equations.

  Here, dm indicates the mass of a minute volume. Note that x, y, and z in the formula are expressed with reference to a predetermined link coordinate system. The basic link coordinate system will be described with reference to FIGS. 10 and 11. For example, in the second link L2 (corresponding to the arm) extending between the second joint and the third joint, the second joint A link coordinate assigned to the second joint is determined with the rotation center of the origin as the origin, the x direction is the direction of the length of the second link L2, the z direction is the rotation direction of the second joint, and the y direction is The direction of the right-handed coordinate system.

  The reference coordinates of the inertia tensor I of the second link L2 shown in FIGS. 10 and 11 are the coordinate system when the link coordinate system assigned to the second joint is moved to the center of gravity of the second link L2. The same applies to other joints.

  The mechanism parameter of the welding robot 10 is a known fixed value that can be obtained in advance from the mechanism of the welding robot 10 and the shape and material of the arm 12. Therefore, the torque TRQj generated in each joint can be obtained by calculation based on the joint position ANGwvj, the joint speed VELwvj, and the joint acceleration ACCwvj of each joint.

  That is, since the calculation method of the inertia matrix H, the viscosity matrix C, and the gravity matrix G is well known, detailed description thereof is omitted here. For example, when the welding robot 10 includes three joints, the inertia matrix H, the viscosity matrix C, and the gravity matrix G are expressed by the following equations.

  Each component of the above formulas is composed of only the mechanism parameter, joint position θ, and joint speed θd shown in Table 2, and all other values than θ and θd are known values. The joint angle ANGwv of each joint when performing the weaving operation calculated in step S13 (see FIG. 9) can be applied to the joint position θ. Further, the joint angular velocity VELwv calculated by performing first-order differentiation on the joint angle ANGwv of each joint when performing the weaving operation can be applied to the joint velocity θd. Therefore, by substituting the joint position ANGwv and joint angular velocity VELwv at each joint when performing the weaving operation into θ and θd, respectively, the inertia matrix H, the viscosity matrix C, and the gravity matrix G in the above equation (1) are obtained. Calculated. θ, θd, and joint angular velocity VELwv are expressed by the following equations.

  Here, n represents the number of joints of the welding robot 10, VELwv1 represents the joint angular velocity (rad / sec) of the first joint of the welding robot 10, and VELwv2 represents the joint angular velocity (rad / sec) of the second joint of the welding robot 10. VELwvn represents the joint angular velocity (rad / sec) of the n-th joint of the welding robot 10.

  Since the gravitational acceleration vector g in the equation (1) is a vector indicating the direction in which the gravitational acceleration works, it can also be determined in advance from the installation posture of the welding robot 10.

  As the joint acceleration θdd in the equation (1), the joint acceleration ACCwv calculated by second-order differentiation of the joint angle ANGwv of each joint when performing the weaving operation calculated every interpolation cycle can be applied. Therefore, by setting the joint angular acceleration ACCwv as shown in the following equation, each joint should be generated in order to realize the specified weaving motion based on the inverse dynamics model expressed by the above equation (1). Torque TRQ is calculated. θdd and joint angular acceleration ACCwv are expressed by the following equations.

Here, n represents the number of joints of the welding robot 10, ACCwv1 represents the joint angular acceleration (rad / sec ² ) of the first joint of the welding robot 10, and ACCwv2 represents the joint angular acceleration of the second joint of the welding robot 10 (rad / sec ² ). rad / sec ² ) and ACCwvn represents the joint angular acceleration (rad / sec ² ) of the n-th joint of the welding robot 10.

  From the above, equation (1) is expressed by the following equation.

  The torque TRQ is expressed by the following equation.

  Here, n indicates the number of joints of the welding robot 10, TRQ 1 indicates the generated torque (N · m) of the first joint of the welding robot 10, and TRQ 2 indicates the generated torque (N · m) of the second joint of the welding robot 10. , TRQn represents the generated torque (N · m) of the n-th joint of the welding robot 10.

  The torque TRQ at each joint calculated by the above equation includes not only the torque necessary for accelerating the joint but also the interference torque received by the joint speed and joint acceleration at the other joints.

  FIG. 12 is a diagram illustrating a relationship among the joint angle ANGwv, the joint velocity VELwv, and the joint acceleration ACCwv in each joint, which is calculated for each interpolation cycle.

  Next, in step S16, an average value of torque generated for each cycle of the weaving operation is calculated. Specifically, as shown in FIG. 13, the generated torque TRQrj at the right end point in the weaving operation and the generated torque TRQlj at the left end point in the weaving operation are calculated, and the average value thereof is calculated, and the average The value is stored in the RAM 22 as the torque TRQavej generated when the weaving operation is not performed.

  Here, n represents the number of joints of the welding robot 10, TRQr1 represents the torque (N · m) generated during the weaving operation at the right end point of the first joint of the welding robot 10, and TRQr2 represents the second joint of the welding robot 10. The torque generated at the right end point of the welding robot (N · m) during the weaving operation is shown, and TRQrn shows the torque generated at the right end point of the nth joint of the welding robot 10 during the weaving operation (N · m).

  Here, n represents the number of joints of the welding robot 10, TRQl1 represents the torque (N · m) generated during the weaving operation at the left end point of the first joint of the welding robot 10, and TRQl2 represents the second joint of the welding robot 10. Represents the generated torque (N · m) at the left end point of the welding robot 10, and TRQln represents the generated torque (N · m) at the left end point of the nth joint of the welding robot 10 during the weaving operation.

  Here, n represents the number of joints of the welding robot 10, TRQave1 represents the average torque (N · m) of the first joint of the welding robot 10, and TRQave2 represents the average torque (N · m) of the second joint of the welding robot 10. TRQaven represents the average torque (N · m) of the n-th joint of the welding robot 10.

  TRQave1, TRQave2, and TRQaven are each expressed by the following equations.

  In the above description, the average torque TRQave in one cycle of the weaving operation is obtained by calculating the average at the left and right end points of the weaving operation. Instead of this method, the average of all sampling points in one cycle is calculated. You may make it obtain | require by this.

  Next, in step S17, the amount of deflection of a reduction gear (not shown) that connects the drive motor 13 and the arm 12 caused by the torque generated by the weaving operation is calculated as the amount by which the amplitude in the weaving operation changes, and is used. Then, the joint angle at each joint of the welding robot 10 when performing the weaving operation is corrected.

  Specifically, the amount of flexure of the reducer is obtained by subtracting the average torque TRQave in one cycle of the weaving operation from the torque TRQ generated in each joint calculated earlier, and extracting the torque generated by the weaving operation. The value is calculated by dividing by the spring constant Kj at each joint of the welding robot 10.

  Then, by adding this deflection amount to the joint angle ANGwv at each joint of the welding robot 10 when performing the weaving operation, it is used as a position command (operation command for the drive motor 13) at each joint of the welding robot 10. A corrected joint angle ANGcompj at each joint of the welding robot 10 is calculated. The corrected joint angle ANGcompj and the spring constant K are expressed by the following equations.

  Here, n represents the number of joints of the welding robot 10, K1 represents the spring constant (rad / N · m) of the first joint of the welding robot 10, and K2 represents the spring constant (rad of the second joint of the welding robot 10). / N · m), and Kn represents the spring constant (rad / N · m) of the n-th joint of the welding robot 10. The spring constant K is a constant that can be known based on the reduction gear to be used, and is stored in the hard disk 25 in advance.

  As described above, when the torque TRQave generated when the weaving operation is not performed is subtracted from the torque TRQ generated around the joint axis, and divided by the spring constant K of each joint, the divided value is performed when the weaving operation is performed. In addition to the joint angle ANGwv of each joint, this is given to each drive motor 13 as an operation command of the drive motor 13 that drives each joint. As a result, the joint angle ANGwv of each joint given to each drive motor 13 can be corrected using the amount of flexure of the speed reducer (not shown) due to the interference torque generated between the arms 12. Therefore, a weaving operation having an appropriate amplitude can be performed.

  Of course, the scope of the present invention is not limited to the embodiment described above.

It is a block diagram which shows the robot control system with which the robot control apparatus which concerns on this invention is applied. It is a figure for demonstrating a weaving operation | movement. It is a block diagram which shows the internal structure of a robot control apparatus, and its peripheral device. It is a block diagram at the time of expressing the actual function of CPU and RAM as a block. It is a block diagram which shows the concept of the servo control by a servo driver. It is a flowchart for demonstrating the effect | action in a weaving operation | movement. It is a figure which shows the relationship between the reference coordinate system of a welding robot, and a tool coordinate system. It is the figure which showed the difference between the interpolation point when not performing a weaving operation | movement, and the interpolation point when performing a weaving operation | movement. It is a flowchart for demonstrating the other effect | action in a weaving operation | movement. It is a figure which shows the relationship between the link and joint in a welding robot. It is a figure which shows the relationship of the link coordinate system of a 2nd link and a 2nd joint. It is a figure which shows the relationship between the joint angle in the case of performing a weaving operation | movement, the joint speed in each joint, and a joint acceleration. It is a figure which shows the relationship between a weaving pattern and time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Welding robot 12 Arm 13 Drive motor 14 Welding torch 15 Welding wire 20 Robot controller 21 CPU
22 RAM
30 Welding power supply device 35 Servo driver 39 Joint interpolation point generator 44 Joint interpolation point buffer 51 Position control block 58 Position feedback gain W Workpiece (workpiece to be welded)

Claims (4)

By driving a plurality of servo motors provided at each joint of the welding robot by feedback control, an arc is generated while performing a weaving operation of the welding torch at each interpolation point divided on the welding track every predetermined time. A welding robot control device for causing a welding robot to perform welding,
Weaving displacement calculation means for calculating, as the weaving displacement for each joint, a difference between the joint angle of each joint when the weaving operation is not performed and the joint angle of each joint when the weaving operation is performed for each interpolation point;
A gain calculating means for calculating a gain in a feedback control system of the servo motor based on a servo control constant of the servo motor and a predetermined weaving frequency;
The interpolation is performed by multiplying the reciprocal of the gain calculated by the gain calculating means by the weaving displacement calculated by the weaving displacement calculating means and adding the value to the joint angle of each joint when the weaving operation is not performed. An operation command calculating means for calculating a joint angle of each joint as an operation command for the servo motor for each point;
A welding robot control device comprising:   The welding robot control device according to claim 1, wherein the servo control constant is a time constant representing a delay system of position control of the servo motor. By driving a plurality of servo motors provided at each joint of the welding robot by feedback control, an arc is generated while performing a weaving operation of the welding torch at each interpolation point divided on the welding track every predetermined time. A welding robot control device for causing a welding robot to perform welding,
Weaving displacement calculation means for calculating, as the weaving displacement for each joint, a difference between the joint angle of each joint when the weaving operation is not performed and the joint angle of each joint when the weaving operation is performed for each interpolation point;
First torque calculating means for calculating for each joint the torque generated around the joint axis;
Second torque calculating means for calculating torque generated when the weaving operation is not performed for each interpolation point;
The value of the torque generated around the joint axis calculated by the first torque calculating unit and the value of the torque generated by the second torque calculating unit when the weaving operation is not performed are subtracted. The subtracted value is divided by a predetermined spring constant at each joint, and the divided value is added to the joint angle of each joint when the weaving operation is performed. An operation command calculating means for calculating a joint angle of each joint as an operation command for the motor;
A welding robot control device comprising: The second torque calculating means includes
When the weaving operation is not performed by calculating the average value of the torque generated at the right end of the weaving operation and the torque generated at the left end of the weaving operation every cycle of the weaving operation for each interpolation point The welding robot control device according to claim 3, wherein torque generated in the welding robot is calculated.

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