JP2006272529A - Industrial robot controlling device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an industrial robot controlling device capable of curtailing residual vibration of a welding torch during its stoppage as much as possible without being affected by the mass of an arm and/or posture of the welding robot. <P>SOLUTION: A welding robot controlling device 20 is equipped with a deceleration control means, designed to control the deceleration for individual joints in a way to attain the following formula: Deci≤(Wvamp/Li)×(Ki/Ii). In this formula, [Deci] represents the deceleration [rad/s<SP>2</SP>]; [Wvamp] indicates the maximum permissible amplitude [mm] of the welding torch; [Li] shows distance from the tip of the welding torch to the rotation axis of each joint; [Ki] represents the spring constant of the reduction gear [N/rad]; and [Ii] indicates inertia moment at each joint [kg m<SP>2</SP>]. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control device for an industrial robot that performs, for example, arc welding on a workpiece (workpiece).

  2. Description of the Related Art Conventionally, in an articulated welding robot that performs arc welding on a workpiece, for example, a plurality of arms and a motor (servo motor) for shifting each of the arms are provided. A reduction gear for increasing the torque of the motor is provided between each arm and each motor. The reduction gear normally includes a spring element. For example, when the welding torch attached to the tip of the arm is moved and stopped at a desired welding start point on the workpiece, the spring element is There is a case where the reaction force is generated and the tip of the welding torch vibrates (hereinafter, this vibration is referred to as “residual vibration”).

  If this residual vibration occurs, it may cause a problem in arc welding. That is, normally, when arc welding is performed after stopping the welding torch at the welding start point, if arc welding is started before the residual vibration is completely converged, that is, while the residual vibration is occurring, spattering is performed. May increase, and the appearance of the workpiece after arc welding may be impaired. Therefore, when residual vibration occurs, it is necessary to wait until the residual vibration has completely converged before starting arc welding.

  Therefore, conventionally, when the residual vibration occurs, arc welding is started after the residual vibration is settled, and therefore there is a problem that the total time of the welding work increases. In particular, when the moving welding torch is decelerated rapidly and the welding torch is stopped, the residual vibration of the welding torch appears prominently. Therefore, the waiting time until the residual vibration converges increases, and the welding work time Increases further.

  Patent Document 1 below describes a method for determining the acceleration / deceleration time of a welding robot for reducing the overall time of welding work. In other words, the technique described in Patent Document 1 is based on teaching data including the position and orientation of teaching points of the welding robot, the operating direction of each axis, and the operating speed, as the load (welding torch) moves in accordance with the change in the attitude of the welding robot. And calculating the acceleration / deceleration time of each joint of the welding robot by calculating from the mass and the center of gravity position of each arm of the welding robot.

JP-A-7-261822

  According to the technique described in Patent Document 1, the allowable peak torque of the motor that drives each joint of the welding robot can be utilized to the maximum, so that the welding operation of the welding robot can be completed in a shorter time. it can. However, the technique described in Patent Document 1 cannot be said to take into account the spring element of the reduction gear provided in each joint, and therefore has the disadvantage that it cannot suppress residual vibration caused by this spring element. Have.

  By the way, the vibration width of the residual vibration when the welding torch is stopped increases depending on the configuration and posture of the articulated welding robot. That is, for example, when the weight of one arm constituting the multi-joint welding robot becomes heavier than the conventional one, the vibration frequency of the residual vibration in each joint becomes small. That is, generally, when the welding torch moves linearly, the natural frequency in the welding torch is expressed by the following equation.

  Here, f is a natural frequency, K is a spring constant, and m is mass.

  That is, since the spring constant K is constant, the natural frequency f decreases as the mass m increases. When the natural frequency f is decreased, the amplitude width of the residual vibration when the welding torch is stopped is increased.

  Further, for example, when considering a state where the multi-joint welding robot is extended, in this state, the moment of inertia at each joint becomes very large. That is, generally, when the welding torch rotates, the natural frequency in the welding torch is expressed by the following equation.

  Here, f is a natural frequency, K is a spring constant, and J is a moment of inertia.

  That is, since the spring constant K is constant, when the moment of inertia J increases, the natural frequency f decreases. When the natural frequency f is decreased, the amplitude width of the residual vibration when the welding torch is stopped is increased.

  As described above, when the mass of the arm of the welding robot is increased or the posture of the welding robot is extended, the amplitude width of the residual vibration is increased, and the residual vibration becomes more obvious.

  The present invention has been conceived under the circumstances described above, and can suppress residual vibration when the welding torch is stopped as much as possible without being affected by the mass of the arm or the posture of the welding robot. An object of the present invention is to provide an industrial robot controller.

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

  The industrial robot control apparatus provided by the first aspect of the present invention transmits the driving force of a plurality of servo motors provided at each joint of an industrial robot having a plurality of joints to an arm via a reduction gear. By moving the machining tool provided at the tip of the arm on the teaching trajectory and decelerating the machining tool, the machining tool reaches a specific position in the machining process on the workpiece. A control device for an industrial robot that performs processing, characterized by comprising a deceleration control means for controlling the deceleration of each joint of the industrial robot so that the following equation is satisfied when the processing tool is decelerated: (Claim 1).

In the above formula,
“Deci” is the deceleration [rad / sec ² ] of each joint (i is the joint number, i = 1, 2,...), “Wvamp” is the allowable maximum vibration width [mm] of the machining tool, and “Li” is The distance [mm] between the tip of the processing tool and the rotation center axis of each joint (i is the joint number, i = 1, 2,...), “Ki” is the spring constant [N / rad] (i Is a joint number, i = 1, 2,..., And “Ii” is a moment of inertia [kg · m ² ] (i is a joint number, i = 1, 2,...) At each joint.

  According to this configuration, when the machining tool is decelerated, the deceleration of each joint of the industrial robot is controlled so that the above equation is satisfied, so that the residual vibration when the machining tool reaches a specific position is appropriately adjusted. Can be suppressed. Further, according to the above equation, since the moment of inertia is taken into account, the residual vibration can be suppressed as much as possible without being affected by the mass of the arm or the attitude of the industrial robot. Here, the “processing tool” refers to, for example, a welding torch for performing a welding process such as arc welding, spot welding, or laser welding, or a cutting device for performing a cutting process such as plasma cutting or laser cutting. In particular, in spot welding, the above-described method for suppressing residual vibration is particularly effective when moving to the spot welding spot position. This is because when the spot vibration for spot welding is performed when the residual vibration is not sufficiently suppressed, the pressurizing control, which is important for the nugget quality, will not function correctly, which will increase dust and fume. . The “specific position” refers to a machining start position, a position in the middle of machining, a machining end position, or the like.

  In the industrial robot control apparatus, the specific position may be a machining start position.

  The industrial robot control apparatus provided by the second aspect of the present invention executes a plurality of teaching steps for moving the processing tool from the operation start position to the processing start position, and moves to the processing start position. A control device for an industrial robot that performs machining processing later, wherein the teaching step includes a content of moving the machining tool to the machining start position among the plurality of teaching steps, and is provided by the first aspect of the present invention. According to the present invention, the machining tool is controlled to be decelerated by the decelerating control means of the industrial robot controller.

  According to this configuration, the deceleration control is performed in the teaching step including the content of moving the machining tool to the machining start position among the plurality of teaching steps, and the deceleration control is not performed in the other teaching steps. Deceleration control can be performed at a necessary appropriate timing, and the entire welding time can be easily shortened.

  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. This robot control system performs arc welding on a workpiece (workpiece to be welded) W by a welding torch (described later) provided in a welding robot. In particular, the robot control system according to the present embodiment includes a welding torch. There is provided a control (hereinafter referred to as “residual vibration suppression control”) for suppressing as much as possible the residual vibration generated at the welding start position on the workpiece W.

  This robot control system is roughly constituted by a welding robot 10, a robot control device 20, and a welding power supply 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 reduction gear (not shown) and a plurality of drive motors (servo motors) 13 (partially omitted) are 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 18 for guiding the welding wire 15 is connected to the wire feeder 16, and the tip of the coil liner 18 is connected to the welding torch 14. As a result, the welding wire 15 delivered by the wire feeding device 16 is guided to the welding torch 14 via the coil liner 18. 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.

  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.

  A welding robot 10 according to the present embodiment is a multi-joint welding robot having a plurality of joints as shown in FIG. 1, and a welding torch 14 as shown in FIG. Is moved from a predetermined operation start point S0 to a welding start point AS where arc welding is performed via a plurality of teaching points Pn (n = 1, 2,..., N in FIG. 2). Yes. That is, the welding torch 14 passes the teaching locus W1 from the operation start point S0 to the teaching point P1, the teaching locus W2 from the teaching point P1 to the teaching point P2, and the teaching locus W3 from the teaching point P2 to the welding start point AS. It is like that.

  When the welding torch 14 passes the teaching locus shown in FIG. 2 and reaches the welding start point AS, a reaction force is usually generated due to the spring element of the reduction gear (not shown) and remains at the tip of the welding torch 14. Vibration occurs. Therefore, in the present embodiment, residual vibration suppression control is performed in the robot control device 20 to suppress residual vibration that occurs at the welding start point AS of the welding torch 14. Details of this residual vibration suppression control will be described later.

  Returning to FIG. 1, 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 pre-stored teaching work program, current position information from an encoder (not shown), etc. Move to the welding position.

  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. A reduction gear 19 is connected to each drive motor 13.

  The CPU 21 serves as a control center of the robot control apparatus 20, and is based on a predetermined teaching work program, an operation signal from the teaching pendant 33 or the operation box 34, or current position information from an encoder (not shown). Then, predetermined data processing is performed according to control software stored in the ROM 23 described later, 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 software for controlling the operation of the welding robot. The ROM 23 also stores control logic for residual vibration suppression control of this embodiment.

  The hard disk 25 stores a teaching work program in which the operation of the welding robot 10 (including collision detection, stop processing, etc.), data indicating execution conditions of the teaching work program, data indicating control constants, and the like are stored. . In particular, in the present embodiment, the hard disk 25 stores mechanism parameters (described later) of the welding robot 10. The hard disk 25 stores a spring constant Ki (i is a joint number, i = 1, 2,...) Of each joint of the welding robot 10 for each joint. The hard disk 25 stores an allowable residual vibration width Wvamp at the welding start position of the welding torch 14. Here, the allowable residual vibration width Wvamp refers to the vibration width of the residual vibration that is allowable when arc welding by the welding torch 14 is started, and is, for example, within about 0.5 mm. These mechanism parameter, spring constant Ki, and allowable residual vibration width Wvamp are used for residual vibration suppression control described later.

  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.

  Functions realized by the CPU 21 in accordance with the control software stored in the ROM 23 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 are represented by an operation command buffer 41, 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. Note that the residual vibration suppression control, which is a feature of the present embodiment, is mainly realized in the trajectory generation unit 37.

  The interpolation point generation unit 38 reads the trajectory data from the trajectory buffer 42, divides the trajectory data at predetermined times called “interpolation periods”, and the welding torch 14 represented by orthogonal coordinates for each interpolation period. Interpolation point data indicating the position to be reached and the attitude of the welding torch 14 is calculated. As shown in FIG. 2, the trajectory data represents the movement trajectory of the welding torch 14 from the operation start point S0 to the welding start point AS by a plurality of teaching points Pn, and a method for moving the welding torch 14 between the teaching points Pn. Is defined by linear movement or arc movement. 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 of the welding torch 14 and the attitude of the welding torch 14 into data indicating the joint angle at each joint of the welding robot 10, The joint interpolation point buffer 44 is temporarily stored.

  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 the speed reducer 19.

  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 12) is acquired by the encoder 56. 52.

  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, residual vibration suppression control, which is a feature of the present embodiment, will be described. As described above, this residual vibration suppression control is realized in the trajectory generation unit 37 (see FIG. 4), and the trajectory generation unit 37 calculates the deceleration at each joint of the welding robot 10 in the procedure shown in FIG. . Then, the residual vibration is suppressed by moving each joint of the welding robot 10 with the calculated deceleration speed pattern.

  First, in step S1, inertia moment Ii (i is a joint number, i = 1, 2,...) Of each joint of welding robot 10 at welding start point AS (see FIG. 2) is calculated. More specifically, the inertia moment Ii of each joint of the welding robot 10 at the welding start point AS is determined using the rotation angle of each joint of the welding robot 10 at the welding start point AS and a preset mechanism parameter. Calculated by performing inverse dynamics calculation.

Here, the mechanism parameters of the welding robot 10 are composed of the four items shown in Table 1, that is, the mass of the arm 12 connected to the joint, the position of the center of gravity, the inertia tensor, and the length of the link. In addition, the number in Table 1 is a value per one arm connected to the joint. The link in “the mass of the link connected to the joint” shown in Table 1 indicates the first link L ₁ or the second link L ₂ shown in FIG.

  Here, as shown in FIG. 7, a reference coordinate system and a tool coordinate system are set in the welding robot 10 as coordinate systems for controlling each joint. 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 of the welding torch 14 (tool center point TCP), and moves with the movement of the welding torch 14. 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.

FIG. 7 illustrates a welding robot 10 having three degrees of freedom, for example. A first link L ₁ is formed between the first joint and the second joint, and the second joint and the third joint are arranged. A second link L ₂ is configured. A welding torch 14 is connected from the third joint to the distal end side. In the following description, as shown in FIG. 7, it is assumed that the welding robot 10 has a configuration with three degrees of freedom.

FIG. 8 is a diagram in which the second link L ₂ is taken as an example in order to explain “the position of the center of gravity of the link connected to the joint” shown in Table 1. According to FIG. 8, the reference coordinate system of the inertial tensor I at the center of gravity of the second link L ₂ is set.

  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 1, 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.

  The moments of inertia Ix, Iy, and Iz represent the difficulty of 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 mass in a minute volume. Note that x, y, and z in the formula are expressed with reference to a predetermined link coordinate system. Here, as a basic link coordinate system, as shown in FIG. 8, for example, in the second link L ₂ (corresponding to the arm) extending between the second joint and the third joint, the second joint the center of rotation as the origin, the link coordinates assigned to the second joint is defined, the x-direction is the direction of the length of the second link L _2, z-direction is the rotation direction of the second joint, y-direction Is the direction of the right-handed coordinate system.

Reference coordinates of the second link L ₂ of the inertia tensor I2 shown in FIG. 7 and FIG. 8 is a coordinate system when the user moves the link coordinate system assigned to the second joint in the second position of the center of gravity of the links L ₂ The The same applies to other joints.

  Next, considering the inertia matrix H used in the inverse dynamic model, generally, when the number of joints of the welding robot 10 is n, the inertia matrix H is represented by an nxn symmetric matrix, and each joint of the welding robot 10 This shows the torque generated in the joint itself due to the angular acceleration and the interference torque generated due to the angular acceleration of other joints.

  The inertia matrix H in the current posture of the welding robot 10 can be obtained by using the inertia tensor I of each joint of the welding robot 10 expressed by the above equations (4) to (6), but the contents thereof are publicly known. Therefore, detailed description here is omitted. For example, when the welding robot 10 includes three joints, the inertia matrix H is expressed by the following equation.

  Here, the inertia matrix H11, H22, H33 is the inertia moment of each joint. That is, the inertia moments I1, I2, and I3 of each joint are expressed by the following equations.

  Next, in step S2 of FIG. 6, based on the mechanism parameters of the welding robot 10 and the joint position of the welding robot 10 at the welding start point AS, as shown in FIG. A distance Li to the center point (TCP) (i is a joint number, i = 1, 2,...) Is calculated.

  Here, an A matrix generally known as defining a link coordinate system assigned to each joint is used. For example, the A matrix of the n-th joint of the welding robot 10 is An, and it is known that the relative position and posture between the joints can be calculated by accumulating the A matrix at each joint.

  For example, when the dimension of the welding torch 14 attached to the tip of the welding robot 10 is included in the third joint as the final link, the relative position and orientation from the first joint (see FIG. 9) to the TCP are homogeneous. The conversion matrix R is calculated by the following formula. Note that n, o, and a in Equation 14 indicate numerical values representing a rotation matrix.

  Further, the relative position and orientation from the second joint to the TCP can be obtained by the following equation. Note that n, o, and a in Equation 15 indicate numerical values representing a rotation matrix.

  Furthermore, the relative position and orientation from the third joint to the TCP is obtained by the following equation. Note that n, o, and a in Equation 16 indicate numerical values representing a rotation matrix.

  The homogeneous transformation matrix R is a matrix representing the position and orientation of the coordinate system. In the link coordinate system, the rotation direction of the joint coincides with the Z direction, so the distance Li from the desired rotation center axis of the joint to the TCP can be calculated as follows. That is, the distance L1 from the first joint to the TCP is expressed by the following equation.

  Here, P1x is the value in the first row and the fourth column of the homogeneous transformation matrix R1 in the first joint, and represents the X-direction position component, and P1y is the value of the homogeneous transformation matrix R1 in the first joint. This is the value in the second row and the fourth column and represents the Y-direction position component.

  A distance L2 from the second joint to TCP is expressed by the following equation.

  Here, P2x is the value in the first row and the fourth column of the homogeneous transformation matrix R2 in the second joint, and represents the position component in the X direction, and P2y is the value of the homogeneous transformation matrix R2 in the second joint. This is the value in the second row and the fourth column and represents the Y-direction position component.

  Furthermore, the distance L3 from the third joint to the TCP is expressed by the following equation.

  Here, P3x is the value in the first row and the fourth column of the homogeneous transformation matrix R3 in the third joint, and represents the X-direction position component, and P3y is the value of the homogeneous transformation matrix R3 in the third joint. This is the value in the second row and the fourth column and represents the Y-direction position component.

  Next, in step S3 of FIG. 6, the maximum deceleration Deci at each joint of the welding robot 10 is calculated.

  Here, the equation of motion at each joint of the welding robot 10 is generally expressed by the following equation.

Here, Ii represents the moment of inertia [kg · m ² ] at the i-th joint of the welding robot 10, θid represents the acceleration [rad / sec ² ] at the i-th joint of the welding robot 10, and Ki represents the 1st joint of the welding robot 10. i represents the spring constant [N / rad] at the i-joint, θi represents the torsion angle [rad] at the i-th joint of the welding robot 10, and ci represents the viscosity coefficient [N / rad / sec] at the i-th joint of the welding robot 10. Θid represents the speed [rad / sec] at the i-th joint of the welding robot 10.

  Strictly speaking, in the case of a multi-joint welding robot, it is necessary to consider interference torque from other joints in the above equation of motion. Since the analysis requires an enormous amount of time and is not practical, the analysis is performed with the interference torque from other joints ignored.

  Further, when the welding torch 14 is stopped, the speed of the welding torch 14 is in the vicinity of 0, so that the generation of torque due to the speed can be ignored. Strictly speaking, when the welding torch 14 is stopped, the speed due to the residual vibration is generated, but the speed is very small and can be ignored (θid≈0). From these things, said (20) Formula is represented by the following formula | equation.

  Here, the torsion angle θi of the i-th joint is expressed by the following expression when expressed by the allowable maximum vibration width Wvamp in TCP and the distance Li from the TCP to each joint.

  When the equation (22) is substituted into the equation (21), the angular acceleration θidd of each joint for suppressing the residual vibration in the TCP to the allowable maximum vibration width Wvamp is as follows.

  In the equation (23), the moment of inertia Ii has been calculated in step S1, and the distance Li between the TCP and each joint has also been calculated in step S2. The spring constant Ki is a value unique to the speed reducer 19 provided in the welding robot 10 and is stored in the hard disk 25 as described above.

  The allowable maximum vibration width Wvamp is the amplitude [mm] of the residual vibration, and its appropriate value varies depending on the work content performed by the welding robot 10. For example, in the case of arc welding, the diameter of the welding wire 15 is generally used. Is about 1/2 (about 0.5 mm). Therefore, the allowable maximum vibration width Wvamp is a known value capable of setting an appropriate value in advance according to the work content of the welding robot 10 and is stored in the hard disk 25 as described above.

  The angular acceleration θidd at each joint is expressed as a deceleration Deci when the welding torch 14 is decelerated. If the deceleration at the time of deceleration at each joint is equal to or less than the maximum deceleration Deci, the residual vibration at the welding start point AS is allowed to remain. The vibration width can be suppressed to less than Wvamp.

  That is, when the equation (24) is calculated for each joint, the deceleration Dec1 in the first joint is expressed by the following equation.

  Further, the deceleration Dec2 in the second joint is expressed by the following equation.

  Furthermore, the deceleration Dec3 at the third joint is expressed by the following equation.

  According to these equations (25) to (27), the optimum deceleration for the welding torch 14 to decelerate and stop at the welding start point AS is determined according to the spring constant Ki of the i-th joint of the welding robot 10. can do. Therefore, the residual vibration when the welding torch 14 is stopped can be suppressed as much as possible, and the welding operation time can be shortened.

  Further, according to the equations (25) to (27), the deceleration Deci is an optimum value in consideration of the inertia moment Ii that changes depending on the attitude of the welding robot 10 and the distance Li (rotation radius) from each joint to the TCP. Can be sought. Since the inertia moment Ii takes into account the mass of the link, the deceleration Deci takes into account the weight of the arm 12, and the deceleration Deci corresponding to the weight of the arm 12 and the inertia moment Ii is calculated. can do.

  Next, an example in which the deceleration calculated in the residual vibration suppression control is applied to the actual teaching pattern (speed pattern) of the welding torch 14 will be described.

  FIG. 10 is a diagram showing a speed pattern of the welding torch 14 from the operation start point S0 to the welding start point AS. FIG. 10 shows the speed pattern of the welding torch 14. The speed pattern of the welding torch 14 is a combination of speed patterns at the respective joints.

  The speed pattern shown in FIG. 10 includes three speed patterns VP1, VP2, and VP3. The welding torch 14 shown in FIG. 2 teaches from the teaching locus W1 from the operation start point S0 to the teaching point P1, and from the teaching point P1. This corresponds to the teaching locus W2 up to the point P2 and the teaching locus W3 from the teaching point P2 to the welding start point AS. Taking the speed pattern VP1 as an example, the welding torch 14 is accelerated at a constant acceleration until the time t1 at the operation start point S0, and then shifted at a constant speed until the time t2, and then at a constant deceleration until the time t3. It is slowing down. Here, the teaching point P1 is reached at time t3, and the vehicle is accelerated again at a constant acceleration until time t4 with time t3 as a boundary.

  In the present embodiment, the residual vibration suppression control described above is performed in the speed pattern VP3 from the teaching point P2 to the welding start point AS, that is, in the speed pattern VP3 before reaching the welding start point AS.

  FIG. 11 is a flowchart when the residual vibration suppression control is applied to the speed pattern. FIG. 12 is a diagram illustrating an example of a teaching work program stored in the hard disk 25.

  The operation command reading unit 36 shown in FIG. 4 reads the teaching work program stored in the hard disk 25, and extracts the operation command for the welding robot 10 from the teaching work program (S1).

  At this time, the operation command reading unit 36 checks the type of operation command in the next step of the operation command read this time (S2). That is, it is determined whether or not the type of operation command in the next step is an operation command to start arc welding (S3), and the type of operation command in the next step is an operation command to start arc welding. In the case (S3: YES), the residual vibration suppression control execution flag VC is changed from "0" to "1" (S4). The operation command reading unit 36 stores the value of the execution flag VC in the operation command buffer 41 (S5). Here, the execution flag VC “0” indicates that the residual vibration suppression control is not executed, and the execution flag VC “1” indicates that the residual vibration suppression control is executed.

  On the other hand, when the type of the operation command in the next step is not an operation command to start arc welding (S3: NO), the execution flag VC of the residual vibration suppression control remains “0” (S6). When the execution flag VC is “1”, it is changed to “0”. Next, the operation instruction reading unit 36 stores the extracted operation instruction and the value of the execution flag VC in the operation instruction buffer 41 (S7).

  Next, the trajectory generation unit 37 reads an operation command from the operation command buffer 41 (S8), and generates trajectory data. At this time, the trajectory generation unit 37 refers to the execution flag VC of the residual vibration suppression control and determines whether or not the execution flag VC is “1” (S9). If the execution flag VC of the residual vibration suppression control is “0” (S9: NO), the trajectory data of the speed pattern that makes the maximum use of the allowable torque of the drive motor 13 is generated for the operation according to the operation command (S10). ). On the other hand, if the execution flag VC of the residual vibration suppression control is “1” (S9: YES), the trajectory data of the speed pattern with the residual vibration suppression control is generated for the operation in the operation command (S11).

  Thereafter, it is determined whether or not there is a next operation command (S12). If there is a next operation command (S12: YES), the process returns to step S1, and if there is no next operation command (S12: NO). This process is terminated.

  According to the teaching work program shown in FIG. 12, the first step is an operation command “P1” (command to move the welding torch 14 to P1), and the next second step is an operation command “P2”. (Command to move welding torch 14 to P2) and not an operation command “AS” (command to move to welding start point AS and start arc welding), execution flag VC remains “0”. Yes, residual vibration suppression control is not performed in the first step.

  However, since the operation instruction is P2 in the second step and the operation instruction is AS in the next second step, the execution flag VC is changed from “0” to “1”. In the third step, residual vibration suppression control is performed when the welding torch 14 is moved from P2 to the welding start point AS. According to FIG. 10, the slope at the time of deceleration of the speed pattern VP3 from the teaching point P2 to the welding start point AS is slightly looser than the speed patterns VP1 and VP2 because the residual vibration suppression control is performed.

  As described above, according to the above-described operation control, the residual vibration suppression control is performed in the speed pattern when the welding start point AS is reached (see the speed pattern VP3 in FIG. 10), and an appropriate timing that requires the residual vibration suppression control. Thus, residual vibration suppression control can be performed.

  Further, by using the residual vibration suppression control execution flag VC, it is possible to easily determine whether to execute the residual vibration suppression control and to determine the timing at which the residual vibration suppression control should be executed. Note that a method other than the method using the execution flag VC described above may be employed for determining whether to execute the residual vibration suppression control.

  Of course, the scope of the present invention is not limited to the embodiment described above. For example, in the residual vibration suppression control of the above embodiment, the suppression level may be divided in stages according to the strength, and the suppression level may be arbitrarily selected by the user. For example, the suppression level is divided into three levels of “strong”, “medium”, and “weak”, and the level of suppression increases as it goes from “weak” to “strong”. If it does in this way, the welding operation which considered the quality accuracy of welding according to the workpiece | work W can be performed.

  Moreover, in the said embodiment, although the welding robot which performs arc welding with respect to the workpiece | work W using a consumable electrode and its control apparatus were described, residual vibration suppression control of this invention is applied to the said welding robot. For example, the present invention may be applied to a welding robot that performs non-consumable arc welding, spot welding, laser welding, or the like. Further, the residual vibration suppression control is not limited to the welding robot, but may be applied to a cutting robot that performs a cutting process such as plasma cutting or laser cutting, or other processes that process the workpiece W by applying heat to the workpiece W. You may make it apply to a processing robot.

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 the teaching locus | trajectory of a welding torch. 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 residual vibration suppression control. It is a figure which shows the relationship between the reference coordinate system of a welding robot, and a tool coordinate system. 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 for demonstrating the distance between each joint and TCP. It is a figure which shows the relationship between a speed pattern and time. It is a flowchart for demonstrating residual vibration suppression control. It is a figure which shows an example of a teaching work program.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Welding robot 12 Arm 13 Drive motor 14 Welding torch 15 Welding wire 19 Reducer 20 Robot controller 21 CPU
22 RAM
30 Welding power supply device 37 Trajectory generator 41 Operation command buffer W Workpiece (workpiece to be welded)

Claims (3)

By transmitting the driving force of a plurality of servo motors provided at each joint of an industrial robot having a plurality of joints to the arm via a speed reducer, the processing tool provided at the tip of the arm is moved on the teaching trajectory. An industrial robot control device that moves and decelerates the machining tool to cause the machining tool to reach a specific position in the machining process on the workpiece and perform the machining process at the specific position,
An industrial robot control apparatus comprising: a deceleration control means for controlling the deceleration of each joint of the industrial robot so that the following formula is satisfied when the machining tool is decelerated.

In the above formula,
“Deci” is the deceleration [rad / sec ² ] of each joint (i is the joint number, i = 1, 2,...),
“Wvamp” is an allowable maximum vibration width of the processing tool [mm],
“Li” is a distance [mm] between the tip of the processing tool and the rotation center axis of each joint (i is a joint number, i = 1, 2,...),
“Ki” is the spring constant of the reducer [N / rad] (i is the joint number, i = 1, 2,...),
“Ii” indicates the moment of inertia [kg · m ² ] (i is a joint number, i = 1, 2,...) At each joint.   The industrial robot control device according to claim 1, wherein the specific position is a machining start position. A control device for an industrial robot that executes a plurality of teaching steps for moving the processing tool from an operation start position to a processing start position, and performs processing after moving to the processing start position,
In the teaching step including the content of moving the machining tool to the machining start position among the plurality of teaching steps, the deceleration control of the machining tool is performed by the deceleration control unit according to claim 2, Industrial robot controller.

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