Robot control method and control device

Abstract

To perform stable control by suppressing the occurrence of vibrations regardless of changes in the mass of work held by a robot, when controlling an articulated robot.SOLUTION: A control device 10 that controls an articulated robot whose joint shafts are driven by a motor 50, is equipped with a state feedback control portion 11 that executes state feedback control on the basis of a motor position command, a single inertia system control portion 12 that executes control based on a signal inertia system model on the basis of the motor position command, and a selecting portion 13 that selects the state feedback control portion 11 when the mass of work held by the robot is a threshold value or less, and otherwise, selects the single inertia system control portion 12. The motor 50 is controlled by the output of either one of the control portions 11 or 12 selected by the selecting portion 13 according to the mass of the work.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and a device for controlling a robot, and more particularly to a method and a device for controlling the position and speed of a multi-joint robot in which each axis is driven by a motor. [Background technology]

[0002] A multi-joint robot (hereinafter, simply referred to as a robot) such as a horizontal multi-joint robot in which multiple links or arms are connected via joints is driven by a motor provided at the joint, and for example, a workpiece is grasped at the tip of the robot or a workpiece is placed on the tip of the robot. The term "a robot holds a workpiece" is used to refer to a robot grasping a workpiece or placing a workpiece on the tip of the robot. In a large robot, the moment of inertia of the link around the joint axis changes depending on the mass of the workpiece held at the tip (i.e., the hand), and the characteristics of the robot, which is the object of control, change. If the nominal model for control is fixed regardless of the mass of the workpiece, a model mismatch occurs due to the change in the mass of the workpiece, and the feedback-based control may become unstable or vibration may occur. In particular, in a robot, a motor is generally connected to the joint axis via a reducer, and the reducer also has properties as a spring element, so that if the control is inappropriate, vibration is likely to be induced in the robot due to the spring element including the reducer. There is a need for a control method and a control device that can stably control the position and speed of a robot regardless of changes in the mass of a workpiece held by the robot.

[0003] Patent Document 1 discloses that a positioning control device used for controlling robots and the like is provided with a classical control means for performing positioning control by P-PI (proportional-proportional integral) control and a modern control means for performing positioning control by state feedback control by a two-inertia system state observer, and when the moment of inertia around a joint axis is smaller than a threshold, P-PI control (or PID (proportional integral differential) control) is performed, and when it is equal to or greater than the threshold, state feedback control is performed, thereby suppressing vibration and performing high-speed and high-precision positioning control. Non-Patent Document 1 also discloses that in an RPP type robot, PID control is performed under normal conditions, and state feedback control is performed when the arm is extended to suppress vibration at the hand. Patent Document 2 discloses that when a robot is controlled by state feedback control by a two-inertia system state observer, the physical model of the state observer, i.e., the control parameters, are switched depending on the mass of the load at the tip of the robot. Patent Document 3 discloses one specific example of state feedback control by a two-inertia system state observer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-319546 [Patent Document 2] Patent No. 6097174 [Patent Document 3] International Publication No. 2018 / 061097 [Non-patent literature]

[0005] [Non-Patent Document 1] Yoshiaki Ito, "Vibration Control of Large Robots", Toyota Central R&D Labs. R&D Review, March 1995, Vol. 30, No. 1, p. 57 Summary of the Invention [Problem to be solved by the invention]

[0006] The method described in Patent Document 1 switches between P-PI control and state feedback control depending on the magnitude of the moment of inertia around the joint axis, and when this method is applied to the control of a robot, state feedback control is selected as the control method for the robot when the mass of the workpiece held on the tip side as viewed from the joint axis of the control target in the robot is large. According to the study by the present inventors, when the method of Patent Document 1 is applied to a multi-joint robot, particularly a horizontal multi-joint robot, a sufficient vibration suppression effect cannot be obtained when the mass of the workpiece held by the robot is large.

[0007] An object of the present invention is to provide a control method and a control device for controlling an articulated robot, which is capable of performing stable control by suppressing the occurrence of vibrations regardless of changes in the mass of the workpiece held by the robot. [Means for solving the problem]

[0008] As a result of the inventors' investigation, it was found that in an articulated robot, when the mass of the workpiece held by the robot's hand is large, vibrations generated in the robot can be suppressed and the robot can be controlled more stably by controlling the motors of the robot's joint axes using a single-inertia system model rather than by controlling the motors using state feedback control. On the other hand, when the mass of the workpiece is small, greater vibration suppression performance can be obtained by implementing state feedback control. The state feedback control usable in the control device of the present invention is, for example, state feedback control by a two-inertia system state observer, and an example is the state feedback control described in Patent Document 3. The control based on a single-inertia system model usable in the control method of the present invention is, for example, P-PI control or PID control. The command is, for example, a motor position command.

[0009] Therefore, the control method of the present invention performs control by switching according to the mass of at least one motor based on a motor position command, such that when the mass of a workpiece held by the articulated robot is equal to or less than a threshold, a first control is performed, and when the mass exceeds the threshold, a second control is performed. Here, the first control is state feedback control by a two-inertia system state observer that uses the motor position command and a fed-back motor position, and the second control is P-PI control or PID control that uses the motor position command and a fed-back motor position.

[0010] In the control method of the present invention, the operation of the articulated robot is controlled based on an operation program that defines at least a load operation for causing the articulated robot to hold a workpiece and an unload operation for removing the held workpiece from the articulated robot, and the operation program 1. Control and SecondThe control can be switched. The operation of a robot used for transporting a workpiece is usually controlled based on an operation program, and such an operation program defines at least a loading operation and an unloading operation. If the operation program defines how to transport the workpiece, the mass of the workpiece can be considered to be known when the operation program is executed. 1. Control and Second By switching the control, it is possible to perform the control switching with a smaller amount of processing.

[0011] In the control method of the present invention, when a robot is controlled by an operation program, when an articulated robot not holding a workpiece is moved to a workpiece receiving position based on the operation program, 1. Control is then performed, and if the mass exceeds the threshold, the workpiece and the articulated robot come into contact with each other. Second It is preferable to switch to the control in this way. 1. It is possible to prevent the occurrence of vibrations caused by holding a heavy workpiece while performing control.

[0012] In the control method of the present invention, when a robot is controlled by an operation program, the articulated robot is moved to a workpiece unloading position while holding a workpiece based on the operation program, and an unloading operation is performed. 1. By controlling in this way, when the workpiece is not being held, 1. The control is implemented, allowing the robot to move quickly and stably.

[0013] In the control method of the present invention, the mass of the workpiece is measured or estimated. 1. Control and SecondFor example, if a vertical axis motor is provided on an articulated robot, the mass of the workpiece may be determined based on a torque command value for the vertical axis motor. Since the mass of each part of the robot's mechanism is known, the mass of the workpiece can be determined by determining the mass corresponding to the torque command value for the vertical axis motor and subtracting the mass of each part on the robot side from that mass. Alternatively, if the articulated robot is provided with a load sensor that detects whether it is holding a workpiece that satisfies predetermined conditions, when the load sensor detects a workpiece that satisfies predetermined conditions, Second The load sensor may be one that detects mass. Also, since a workpiece with a large thickness or planar dimensions can be estimated to have a large mass, the load sensor may be a sensor that detects thickness or planar dimensions. By measuring or estimating the mass of the workpiece using the torque command value of the vertical axis motor or the load sensor, even if there is a program error when switching control by the operation program, it is possible to estimate the mass of the workpiece when a heavy workpiece is being held. 1. It is possible to prevent the robot from being controlled by the control.

[0014] In the control method of the present invention, the articulated robot is, for example, a horizontal articulated robot. Horizontal articulated robots are often used to hold a workpiece in their hands and transport the workpiece. By applying the control method of the present invention to such a horizontal articulated robot, the effect of the present invention of suppressing the generation of vibrations in the robot and executing stable control can be more effectively achieved.

[0015] The control device of the present invention is a control device for controlling a multi-joint robot in which joint shafts are driven by motors, Motor Position Based on the directive , using the motor position command and the feedback motor position, using a two-inertia system state observer A first control unit that executes state feedback control; Motor Position Based on the directive , P-PI control or PID control using the motor position command and the feedback motor positionThe robot is equipped with a second control unit that executes control, and a selection unit that selects the first control unit when the mass of the workpiece held by the articulated robot is equal to or less than a threshold value, and selects the second control unit when the mass exceeds the threshold value, and controls the motor by the output of the control unit selected by the selection unit according to the mass.

[0016] According to the control device of the present invention, when the mass of the workpiece is small, Using a two-inertia frame state observer The robot operates using state feedback control, and when the mass of the workpiece is large, P-PI control or PID Since the robot operates through control, it is possible to suppress vibration and control the robot stably regardless of the mass of the workpiece. 。

[0017] An articulated robot having a function of holding a workpiece is usually controlled based on an operation program that controls the operation of the articulated robot by defining at least a loading operation for causing the articulated robot to hold a workpiece and an unloading operation for removing the held workpiece from the articulated robot. Therefore, in the control device of the present invention, it is preferable to provide a calculation unit that executes such an operation program, and to have the selection unit select either the first control unit or the second control unit in response to a switching command from the calculation unit. By configuring in this way, state feedback control and P-PI control or PID control and This allows the control to be switched with a smaller amount of processing.

[0018] In the control device of the present invention, when a calculation unit is provided, it is preferable that the calculation unit selects the first control unit by the selection unit when moving the articulated robot not holding a workpiece to a workpiece receiving position, and then selects the second control unit by the selection unit before the workpiece and the articulated robot come into contact when the mass exceeds a threshold value. By selecting the control unit in this manner, it is possible to prevent the occurrence of vibrations caused by holding a heavy workpiece while state feedback control is being performed.

[0019] In the control device of the present invention, when a calculation unit is provided, the calculation unit may move the articulated robot to a workpiece unloading position while holding a workpiece, execute an unloading operation, and then select the first control unit by the selection unit. By selecting the first control unit in this manner, state feedback control is performed when the robot is not holding a workpiece, and the robot can be moved quickly and stably.

[0020] In the control device of the present invention, the mass of the workpiece can be measured or estimated to switch between the first control unit and the second control unit. For example, when the articulated robot is equipped with a vertical axis motor, the calculation unit calculates the mass of the workpiece based on a torque command value for the vertical axis motor. The switching command is output to the selection unit according to the calculated mass. Alternatively, if the articulated robot is equipped with a presence sensor that detects whether a workpiece that satisfies a predetermined condition is being held, the second control unit may be selected when the presence sensor detects a workpiece that satisfies the predetermined condition. By measuring or estimating the mass of the workpiece using the torque command value of the vertical axis motor or the presence sensor, it is possible to prevent the robot from being controlled by state feedback control when holding a heavy workpiece, even if there is a program error when switching control using the operation program.

[0021] The articulated robot to be controlled by the control device of the present invention is, for example, a horizontal articulated robot. Horizontal articulated robots are often used to hold a workpiece in their hands and transport the workpiece. By using the control device of the present invention to control the horizontal articulated robot, the effect of the present invention of suppressing the generation of vibrations in the robot and executing stable control can be more effectively achieved. Effect of the Invention

[0022] According to the present invention, when controlling an articulated robot, it is possible to suppress the occurrence of vibrations regardless of changes in the mass of a workpiece held by the robot, thereby enabling stable control. [Brief description of the drawings]

[0023] [Figure 1] 1 is a block diagram showing a configuration of a control device according to an embodiment of the present invention; [Diagram 2] 1A and 1B are diagrams showing an example of the configuration of a horizontal articulated robot, in which FIG. [Diagram 3] FIG. 11 is a waveform diagram illustrating vibrations of the tip of the robot when state feedback control is performed and when P-PI control is performed. [Figure 4] 4(a) and 4(b) are pole-zero arrangement diagrams when state feedback control is performed. [Diagram 5] (a) and (b) are pole-zero point arrangement diagrams when P-PI control is performed. [Figure 6] FIG. 11 is a block diagram showing a configuration of a control device according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Next, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 shows a control device according to an embodiment of the present invention.

[0025] The control device 10 shown in FIG. 1 is used for driving control of a multi-joint robot in which a motor 50 is provided for each joint axis to drive the joint axis. A link 60 is mechanically connected to the motor 50, which is driven by the motor 50 and applies a reaction force or disturbance to the motor 50. The link 60 shown in FIG. 1 does not only show a link or arm directly connected to the motor 50 of interest, but abstractly shows all parts of the robot that have a mechanical effect on the motor 50 of interest. Therefore, the link 60 shown in FIG. 1 includes, in addition to the arm of the robot, a reducer connected to the motor 50 and a workpiece 70 (see FIG. 2) held by the robot. The motor 50 is a motor with an encoder, and the motor position is fed back to the control device 10. Although FIG. 1 shows only a part used for controlling one joint axis in the multi-joint robot, in reality, a mechanism for controlling the motor 50 is provided for the motor 50 of each joint axis.

[0026] The control device 10 controls the position and speed of the motor 50 based on a command, for example, a motor position command. To control the position and speed of the motor 50, the control device 10 includes a state feedback control unit 11 that executes state feedback control of the motor 50 based on the motor position command, a single-inertia system control unit 12 that executes control based on a single-inertia system model of the motor 50 based on the motor position command, and a selection unit 13 that selects either the output of the state feedback control unit 11 or the output of the single-inertia system control unit 12. The state feedback control unit 11 receives feedback of the motor position, and executes state feedback control by a two-inertia system state observer, for example, state feedback control described in Patent Document 3. The motor position is also fed back to the single-inertia system control unit 12, and executes, for example, P-PI control or PID control. The selection unit 13 selects the state feedback control unit 11 when the mass of the workpiece 70 held by the articulated robot is equal to or less than a threshold value, and selects the single-inertia system control unit 12 when the mass of the workpiece 70 exceeds the threshold value. The motor 50 is driven by a motor current based on the output selected by the selection unit 13.

[0027] FIG. 2 shows an example of a multi-joint robot controlled by the control device 10 shown in FIG. 1. The multi-joint robot shown here is a horizontal multi-joint robot used to transport a workpiece 70. In FIG. 2, (a) is a plan view of the horizontal multi-joint robot, and (b) is a front view of the horizontal multi-joint robot. FIG. 2(b) also shows the control device 10 connected to the robot. The illustrated robot includes a first link 60A that is attached at one end to a base 55 and extends horizontally, a second link 60B that is attached at one end to the other end of the first link 60A and extends horizontally, and a hand 61 that is attached at the other end of the second link 60B and serves as an end effector of the robot. A workpiece 70 that is an object to be transported is placed on the hand 61. The tip of the hand 61 on the opposite side to the connection position with the second link 60B becomes the hand position of the robot.

[0028] The connection position between the base 55 and the first link 60A is a joint A, and a motor 50A and a reducer 51A are provided in the base 55 to drive the joint A. The first link 60A is driven by the motor 50A via the reducer 51A so as to rotate in a horizontal plane around the joint A as a rotation center. Similarly, the connection position between the first link 60A and the second link 60B is a joint B, and a motor 50B and a reducer 51B are provided in the first link 60A to drive the joint B. The second link 60B is driven by the motor 50B via the reducer 51B so as to rotate in a horizontal plane around the joint B as a rotation center. The connection position between the second link 60B and the hand 61 is a joint C, and a motor 50C and a reducer 51C are provided in the second link 60B to drive the joint C. The hand 61 is driven by the motor 50C via the reducer 51C so as to rotate in a horizontal plane around the joint C as a rotation center. As a result, in this robot, by driving the motors 50A, 50B, and 50C, the hand 61 can be moved in a horizontal plane toward or away from the base 55 while maintaining the orientation of the hand 61, as indicated by the arrow in the travel direction in the figure. The direction in the horizontal plane that is perpendicular to the travel direction is defined as the lateral direction. In the robot, the portion from joint A to the hand 61 is a horizontal multi-joint mechanism. Furthermore, the robot is provided with a lifting mechanism 56 inside the base 55 to raise and lower the hand 61 in the vertical direction. The lifting mechanism 56 includes a ball screw and is driven by a vertical-axis motor 50Z via a reducer 51Z to raise and lower the horizontal multi-joint mechanism of the robot.

[0029] Next, the switching between state feedback control and control by a single-inertia system model in this embodiment will be described with reference to FIG. 3. Consider that the motors 50A, 50B, and 50C in the robot shown in FIG. 2 are driven to move the hand 61 back and forth along the travel direction shown in FIG. 2 between a state in which the first link 60A and the second link 60B are completely folded and a state in which the first link 60A and the second link 60B are fully extended in a straight line. The waveform shown in FIG. 3(a) shows the time change of the position command related to the hand end position of the robot. Then, the velocity of vibration in the lateral direction at the hand end position when the hand 61 is moved back and forth in this manner was examined. As the workpiece 70 held by the hand 61, one with a mass of 2 kg (corresponding to "workpiece mass: small") and one with a mass of 80 kg (corresponding to "workpiece mass: large") were used. In addition, the velocity of vibration in the lateral direction was examined in both cases where state feedback control and P-PI control are used for controlling the motors 50A, 50B, and 50C based on the position command. The results are shown in Figure 3(b) to (e).

[0030] When state feedback control was used to control the motors 50A, 50B, and 50C, a good vibration suppression effect was obtained if the mass of the workpiece 70 was small, as shown in FIG. 3(b). However, when the mass of the workpiece 70 was large, the vibration did not converge, but diverged, as shown in FIG. 3(c). In other words, it was found that when the mass of the workpiece 70 was large, the state feedback control made the control unstable. On the other hand, when P-PI control was used to control the motors 50A, 50B, and 50C, a vibration suppression effect was obtained both when the mass of the workpiece 70 was small (FIG. 3(d)) and when the mass of the workpiece 70 was large (FIG. 3(e)). However, when the mass of the workpiece 70 was small, the state feedback control showed a better vibration suppression effect than the P-PI control.

[0031] The change in control behavior according to the mass of the workpiece will be described with reference to Figs. 4 and 5. Figs. 4 and 5 show the arrangement of poles and zeros from the position command of the motor 50A of the joint A to the angle of the joint A in each of the cases shown in Fig. 3(b) to (e), and the poles surrounded by dashed lines in the figures are representative poles. Fig. 4 shows a case where state feedback control is used for motor control, with (a) being a pole-zero arrangement diagram when the workpiece mass is small, and (b) being a pole-zero arrangement diagram when the workpiece mass is large. Fig. 5 shows a case where P-PI control is used for motor control, with (a) being a pole-zero arrangement diagram when the workpiece mass is small, and (b) being a pole-zero arrangement diagram when the workpiece mass is large.

[0032] In the case of a multi-joint robot, an inter-axis interference force occurs in the torque between the joints. When the mass of the workpiece is large, the inter-axis interference force becomes large, and each axis cannot be approximated by a two-inertia system, so single-inertia system control is more robust than state feedback control. When holding a light workpiece, the representative pole from each axis motor position command value to each axis joint angle is farther away from the imaginary axis in the negative direction in state feedback control than in control based on a single-inertia system model (P-PI control), as can be seen by comparing Figures 4(a) and 5(a). Therefore, state feedback control has higher vibration suppression performance. Conversely, when holding a heavy workpiece, the real part of the representative pole is negative in control based on a single-inertia system model, but positive in state feedback control, which is in the so-called unstable region, as can be seen by comparing Figures 4(b) and 5(b). Therefore, control based on a single-inertia system model is more stable.

[0033] Therefore, in this embodiment, the control mode of the motor is switched to state feedback control when the mass of the workpiece 70 is small, and to control based on a single inertia system model when the mass is large, thereby ensuring stability when a heavy workpiece is placed on the motor while ensuring vibration suppression performance when transporting a light workpiece. In state feedback control, the control becomes unstable when holding a heavy workpiece when the spring element component due to a reducer or the like in the system becomes large, or when the distance from the joint of interest to the workpiece becomes long. Therefore, in the robot shown in FIG. 2, the state feedback control according to the mass of the workpiece 70 and the control based on a single inertia system model may be switched only for the motor far from the holding position of the workpiece 70, for example, only for the motor 50A of the joint A, or only for the motors 50A and 50B of the joints A and B.

[0034] In the embodiment described above, by controlling the motor by switching between state feedback control and control based on a single-inertia system model depending on the mass of the workpiece held by the robot, it is possible to suppress the occurrence of vibrations and perform stable control regardless of changes in the mass of the workpiece held by the robot.

[0035] FIG. 6 shows a control device 10 according to another embodiment of the present invention. In general, the operation of an articulated robot is controlled by executing an operation program. The operation program of a robot that transports or holds a workpiece 70 defines at least a loading operation in which the workpiece 70 is held by, for example, the hand 61 of the articulated robot, and an unloading operation in which the held workpiece is removed from the articulated robot, and further defines the movement path of the robot. Assuming that the workpiece 70 is transported between user devices, in the loading operation, the robot 10 in a state where it does not hold the workpiece 70 moves to a receiving position of the workpiece 70 in the user device from which the workpiece 70 is transported. When the workpiece 70 is actually held on the hand 61 of the robot 10 in the loading operation, for example, the workpiece 70 may be placed on the hand 61 by the movement of the robot 10 in the vertical axis direction, or the workpiece 70 may be placed on the hand 61 by the movement of the user device. When a gripping hand is used, the workpiece may be grasped by the hand. Similarly, in the unloading operation, the robot 10 holding the workpiece 70 moves to a loading / unloading position of the workpiece 70 in the user device to which the workpiece 70 is transported. When the workpiece 70 is actually unloaded from the hand 61 of the robot 10 in the unloading operation, the workpiece 70 may be unloaded onto the user device by the movement of the robot 10 in the vertical axis direction, or the workpiece 70 may be unloaded by the movement of the user device. When a gripping hand is used, the hand may release the workpiece that it is holding.

[0036] The control device 10 shown in FIG. 6 is similar to the control device 10 shown in FIG. 1, but further includes a calculation unit 14 that executes an operation program to generate a motor position command, and a storage unit 15 that stores the operation program. An operation program is generally created assuming that what kind of processing is to be performed on what kind of workpiece, for example, from where to where the workpiece is to be transported, is known, so that the mass of the workpiece can be considered to be known when the operation program is executed. Therefore, if the operation program describes whether the motor is to be controlled by state feedback control or control based on a single-inertia system model, the calculation unit 14 can output a switching command to the selection unit 13 when the operation program is executed, and the selection unit 13 can switch between the output of the state feedback control unit 11 and the output of the single-inertia system control unit 12 based on the switching command.

[0037] When the robot is controlled by the operation program executed by the calculation unit 14, the state feedback control unit 11 is selected when the robot is moved to a receiving position of the workpiece 70 in a state where the workpiece 70 is not held, and then, when a heavy workpiece (a workpiece having a mass exceeding a threshold value) is held, the output of the single inertia system control unit 12 can be selected by the selection unit 13 before the workpiece 70 and the hand 61 come into contact with each other. By performing control in this manner, it is possible to prevent the occurrence of vibration caused by holding a heavy workpiece 60 in a state where state feedback control is being performed. Also, when the robot is controlled by the operation program executed by the calculation unit 14, the robot holding the workpiece 70 is moved to a loading / unloading position of the workpiece 70, and after performing an unloading operation, the output of the state feedback control unit 11 can be selected by the selection unit 13. By performing control in this manner, the state feedback control is performed when the workpiece 70 is not held, and the robot can be moved at high speed and stably.

[0038] When the calculation unit 14 outputs a switching command to the selection unit 13 based on the operation program, there is a risk that state feedback control will be executed when a heavy workpiece 70 is being held due to a programming error in the operation program. In addition, in a manual operation in which the robot is operated without using an operation program, it is preferable to be able to automatically switch between state feedback control and control based on a single-inertia system model. Therefore, the control device 10 of this embodiment can also be configured to measure or estimate the mass of the workpiece and switch between state feedback control and control based on a single-inertia system model.

[0039] As shown in Fig. 2, the control device 10 for controlling a robot equipped with a vertical-axis motor 50Z is provided with a vertical-axis control unit 16 for controlling the vertical-axis motor 50Z. Even when the robot is not ascending or descending, the vertical-axis motor 50Z generates a holding torque for holding the mass of the robot and the workpiece 70, and the vertical-axis control unit 16 generates a torque command value corresponding to the holding torque and drives the motor 50Z with a motor current corresponding to the torque command value. Since the mass of each part of the robot mechanism is known, the calculation unit 14 can obtain the mass corresponding to the torque command value for the vertical-axis motor, and obtain the mass of the workpiece 70 by subtracting the mass of each part on the robot side from the mass, and can output a switching command according to the mass of the workpiece 70.

[0040] The robot may be configured such that a presence sensor 62 is provided in the hand 61 to detect whether or not a workpiece 70 that satisfies a predetermined condition is being held, and the detection result of the presence sensor 62 is transmitted to the calculation unit 14. When such a presence sensor 62 is provided, when the presence sensor 62 detects a workpiece that satisfies a predetermined condition, the selection unit 13 may select the output of the single-inertia system control unit 12 in response to a switching command. The presence sensor may be one that detects mass, but may also be one that detects workpieces 70 whose thickness or planar dimensions are equal to or greater than a predetermined value. Since a workpiece that is large in thickness or planar dimensions is presumed to be a workpiece with a large mass, by switching between state feedback control and control based on the single-inertia system model according to the detection result of the presence sensor 62, it is possible to prevent the robot from being controlled by state feedback control when holding a heavy workpiece.

[0041] By using the control device 10 shown in FIG. 6, switching between state feedback control and control based on a single-inertia system model can be performed by an operating program, so that control switching can be performed with a smaller amount of processing. [Explanation of symbols]

[0042] 10...control device; 11...state feedback control unit; 12...single inertia system control unit; 13...selection unit; 14...calculation unit; 15...memory unit; 50, 50A, 50B, 50C, 50Z...motor; 51A, 51B, 51C, 51Z...reduction gear; 55...base; 56...lifting mechanism; 60, 60A, 60B...link; 61...hand; 62...load sensor; 70...work.

Claims

1. A control method for controlling an articulated robot in which joint shafts are driven by motors, comprising the steps of: for at least one of the motors, switching control is performed according to the mass based on a motor position command such that a first control is performed when a mass of a workpiece held by the articulated robot is equal to or smaller than a threshold value, and a second control is performed when the mass exceeds the threshold value; the first control is a state feedback control by a two-inertia system state observer using the motor position command and a fed-back motor position; The second control is P-PI control or PID control using the motor position command and the fed back motor position.

2. controlling the operation of the articulated robot based on an operation program that defines at least a loading operation for causing the articulated robot to hold the workpiece and an unloading operation for removing the held workpiece from the articulated robot; The control method according to claim 1 , wherein the first control and the second control are switched by the operation program.

3. The control method according to claim 2, further comprising the steps of: implementing the first control when the articulated robot not holding the workpiece is moved to a receiving position for the workpiece based on the operating program; and then switching to the second control before the workpiece comes into contact with the articulated robot if the mass exceeds the threshold value.

4. 4. The control method according to claim 2 or 3, further comprising moving the articulated robot to a position for unloading the workpiece while holding the workpiece based on the operation program, executing the unloading operation, and then switching to the first control.

5. A vertical axis motor is provided on the articulated robot, The control method according to claim 1 , further comprising determining a mass of the workpiece based on a torque command value for the vertical axis motor.

6. The articulated robot is provided with a presence sensor that detects whether the workpiece that satisfies a predetermined condition is being held, The control method according to claim 1 , further comprising switching to the second control when the workpiece that satisfies the predetermined condition is detected by the load sensor.

7. The control method according to claim 1 , wherein the articulated robot is a horizontal articulated robot.

8. A control device for controlling an articulated robot in which joint shafts are driven by motors, comprising: a first control unit that executes state feedback control by a two-inertia system state observer using the motor position command and a fed-back motor position based on the motor position command; a second control unit that executes P-PI control or PID control using the motor position command and the fed-back motor position based on the motor position command; a selection unit that selects the first control unit when a mass of a workpiece held by the articulated robot is equal to or smaller than a threshold value, and selects the second control unit when the mass exceeds the threshold value; Equipped with A control device that controls the motor using an output of a control unit selected by the selection unit in accordance with the mass.

9. a calculation unit that executes an operation program to control the operation of the articulated robot by defining at least a loading operation for causing the articulated robot to hold the workpiece and an unloading operation for removing the held workpiece from the articulated robot; The control device according to claim 8 , wherein the selection unit selects either the first control unit or the second control unit in response to a switching command from the calculation unit.

10. The control device according to claim 9, wherein the calculation unit selects the first control unit using the selection unit when the articulated robot not holding the workpiece is moved to a receiving position for the workpiece, and then selects the second control unit using the selection unit before the workpiece and the articulated robot come into contact with each other if the mass exceeds the threshold value.

11. The control device according to claim 9 or 10, wherein the calculation unit moves the articulated robot to a position for unloading the workpiece while holding the workpiece, executes the unloading operation, and then selects the first control unit using the selection unit.

12. The articulated robot is equipped with a vertical axis motor, The control device according to claim 9 , wherein the calculation unit determines the mass of the workpiece based on a torque command value for the vertical axis motor, and outputs the switching command to the selection unit according to the determined mass.

13. The articulated robot is provided with a presence sensor that detects whether the workpiece satisfies a predetermined condition, The control device according to claim 8 , wherein the second control unit is selected when the workpiece that satisfies the predetermined condition is detected by the load sensor.

14. The control device according to claim 8 , wherein the articulated robot is a horizontal articulated robot.

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