control device

Abstract

The purpose of the present invention to set a detection parameter, in which contact to a workpiece or holding of the workpiece is used for detection or the like, to an appropriate value without troubling a user. Control devices 40, 50 according to one aspect of the present disclosure are control devices that control a servomotor 35 for driving a tool 30 that grips a workpiece W1 or applies treatment to the workpiece W1. The control devices include: a control unit 41 that controls the servomotor selectively in a pre-adjustment mode in which the tool is operated without existence of the workpiece or an activation mode in which the tool is operated with existence of the tool; and a parameter adjusting unit 42 that adjusts the detection parameter in the pre-adjustment mode. The control unit uses the detection parameter adjusted by the parameter adjusting unit to control the servomotor.

Description

Technical Field

[0001] The present invention relates to a control device.

Background Art

[0002] There is a technique for detecting contact of a device with a workpiece or clamping of a workpiece by a device by monitoring / limiting the current value of a servo motor provided in a device such as a robot, a robot hand, and a spot welding gun (for example, Patent Document 1). Since this method does not require an external sensor or a floating mechanism, it has a great advantage in terms of cost. On the other hand, in this method, it is necessary to determine in advance a threshold value for detecting contact with the workpiece or clamping of the workpiece.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventionally, the threshold value has been set manually by the user. However, the optimal threshold value varies depending on the type of servo motor and device. If the threshold value is set to a value larger than the optimal value, the load on the workpiece and the device increases, which may cause factors such as failure. If the threshold value is set to a value smaller than the optimal value, false detections increase. Therefore, the threshold setting operation needs to be performed carefully and accurately, which is a very time-consuming operation. Therefore, it is desired that the user can set the threshold value to an appropriate value without taking much trouble.

Means for Solving the Problems

[0005] A control device according to one aspect of the present disclosure is a control device for controlling a servo motor that drives a tool for gripping or processing a workpiece. The control device comprises a control unit that selectively controls the servo motor in a pre-adjustment mode in which the tool is operated without a workpiece and an operation mode in which the tool is operated with a workpiece, and a parameter adjustment unit that adjusts detection parameters in the pre-adjustment mode. In the operation mode, the control unit controls the servo motor using the detection parameters adjusted by the parameter adjustment unit. [Effects of the Invention]

[0006] According to this embodiment, detection parameters used for detecting contact with or gripping of a workpiece can be set to appropriate values ​​without requiring any effort from the user. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a diagram showing the configuration of a welding system including a control device according to the first embodiment. [Figure 2] Figure 2 is a functional block diagram of the control device according to the first embodiment. [Figure 3] Figure 3 is a supplementary diagram illustrating the threshold calculation process performed by the threshold calculation unit in Figure 2. [Figure 4] Figure 4 is a flowchart showing an example of pre-adjustment by the control device according to the first embodiment. [Figure 5] Figure 5 is a flowchart showing an example of the procedure for the search operation portion of the welding operation by the control device according to the first embodiment. [Figure 6] Figure 6 is a supplementary diagram that further explains the search operation shown in Figure 5. [Figure 7] Figure 7 is a functional block diagram of the control device according to the second embodiment. [Figure 8] Figure 8 is a supplementary diagram illustrating the clamping operation by the control device according to the second embodiment. [Figure 9] Figure 9 is a supplementary diagram illustrating the clamping operation by the control device according to the second embodiment. [Figure 10] Figure 10 is a functional block diagram of the control device according to the third embodiment. [Figure 11] Figure 11 is a supplementary diagram illustrating the search operation by the control device according to the third embodiment. [Figure 12] Figure 12 is a functional block diagram of the control device according to the fourth embodiment. [Figure 13] Figure 13 is a flowchart showing an example of gain calculation processing by the control device according to the fourth embodiment. [Modes for carrying out the invention]

[0008] The control devices according to the first, second, third, and fourth embodiments will be described below with reference to the drawings. In the following description, components having substantially the same function and configuration will be denoted by the same reference numerals, and redundant explanations will be given only when necessary.

[0009] The control device according to the first embodiment will be described below with reference to Figures 1 to 6. In the first embodiment, a spot welding gun for welding a workpiece is used as an example of a tool for treating a workpiece, and a robot arm mechanism is used as an example of a movement mechanism for moving the tool for treating the workpiece. The description will focus on detecting contact between the spot welding gun and the workpiece. The detection parameter is a parameter for detecting when a tool such as a spot welding gun or robot hand has come into contact with the workpiece, and specifically corresponds to the threshold value of the servo motor described later.

[0010] As shown in Figure 1, the welding system including the control device according to the first embodiment includes a robot arm mechanism 20 having a plurality of joints, a spot welding gun 30 mounted on the wrist of the robot arm mechanism 20, a robot control device 40 that controls the robot arm mechanism 20, a welding gun control device 50 that controls the spot welding gun 30, and a teaching control panel 60 connected to the robot control device 40. The robot arm mechanism 20 and the spot welding gun 30 constitute a welding robot 10.

[0011] The teaching operation panel 60 functions as an input device for inputting user instructions to the robot control device 40 and a display device for displaying the output results of the robot control device 40. The welding gun control device 50 and the robot control device 40 are communicably connected to each other. The robot arm mechanism 20 has a plurality of servo motors that drive a plurality of joint portions. The plurality of servo motors are driven by control signals from the robot control device 40, and by rotating each joint portion, the position and orientation of the spot welding gun 30 can be changed.

[0012] The control device according to the first embodiment is a concept including the robot control device 40 and the welding gun control device 50. In the first embodiment, the welding gun control device 50 and the robot control device 40 are provided separately as separate devices, but a configuration in which a single control device has both functions of the welding gun control device 50 and the robot control device 40 may also be adopted.

[0013] As shown in FIG. 2, the spot welding gun 30 includes a fixed electrode tip 31, a movable electrode tip 32 provided at a position facing the fixed electrode tip 31, a C-shaped fixed arm 33 that supports the fixed electrode tip 31, a movable arm 34 that supports the movable electrode tip 32 so as to be movable along the gun axis, a servo motor 35 that generates power for driving the movement of the movable arm 34, and an encoder 36 that detects the rotational position of the drive shaft of the servo motor 35. The fixed arm 33 and the movable arm 34 constitute an opening / closing mechanism. Data regarding the rotational position of the drive shaft of the servo motor 35 detected by the encoder 36 is sent to the welding gun control device 50.

[0014] The welding gun control device 50 has a motor control unit 51, a welding current control unit 52, a current detection unit 53, a storage unit 54, and a communication control unit 55. The motor control unit 51 controls the driving of the servo motor 35. Specifically, the motor control unit 51 supplies current to the servo motor 35 based on the operation position command and the pressing force command defined in the welding program and the pre-adjustment program. Thereby, the servo motor 35 is driven to realize the commanded position and pressing force, and the movable electrode tip 32 is moved along the gun axis in a direction approaching or separating from the fixed electrode tip 31.

[0015] The welding current control unit 52 controls the welding current supplied to the fixed electrode tip 31 and the movable electrode tip 32. Specifically, the welding current control unit 52 supplies a welding current having a value corresponding to the welding current command defined in the welding program to the electrode tips 31 and 32 at the timing defined in the welding program. The current detection unit 53 detects the current value flowing through the servo motor 35. Existing methods such as a current sensor can be used for detecting the current value. The storage unit 54 stores various information related to the welding operation and pre-adjustment. The various information includes information regarding the time change of the current value of the servo motor 35 detected by the current detection unit 53.

[0016] The communication control unit 55 controls the transmission and reception of various information with the robot control device 40. Through the processing of the communication control unit 55, the welding gun control device 50 sequentially transmits information regarding the current value of the servo motor 35, and receives control signals of the spot welding gun 30 such as a pressing force command and a welding current command based on the welding program and the pre-adjustment program from the robot control device 40.

[0017] The robot control device 40 includes a processor constituted by a CPU, a GPU, etc., a RAM functioning as a main memory and a work area of the processor, and a storage device storing various programs, various setting information, etc.

[0018] The memory device stores a welding program and a pre-adjustment program. The welding program is executed according to the operating mode selected by the user and is a program that causes the welding robot 10 to perform a predetermined welding operation. The pre-adjustment program is executed according to the pre-adjustment mode selected by the user and is a program that calculates in advance the threshold used for the welding operation. By executing the pre-adjustment program, the time change of the current value flowing through the servo motor 35 of the spot welding gun 30 during the search operation without a workpiece can be obtained and the threshold can be calculated. The search operation is an operation that moves the movable electrode tip 32 in the direction that brings it closer to the fixed electrode tip 31. This operation is achieved by controlling the servo motor 35 that drives the movable arm 34. Typically, the search operation in pre-adjustment is performed in a predetermined specific posture. The threshold obtained from the search operation performed in a specific posture can be used for the search operation during welding in various postures. This is because the fluctuation range of the current value is almost independent of the posture of the spot welding gun 30, so it is sufficient to adjust the workpiece detection threshold only in a specific posture. Being able to handle various postures with only pre-adjustments for a specific posture reduces pre-adjustment time and contributes to shorter cycle times. Of course, pre-adjustments can be performed for each posture in the operating mode, or thresholds can be determined for various postures.

[0019] The welding program describes the operating position commands for the robot arm mechanism 20, the operating position commands for the spot welding gun 30, the pressure commands, and the welding current commands. The pre-adjustment program describes the operating position commands for the robot arm mechanism 20 and the operating position commands for the spot welding gun 30.

[0020] The robot control device 40 functions as a welding robot control unit 41, a threshold calculation unit 42, a distance calculation unit 43, a contact detection unit 44, an input unit 45, an output unit 46, a storage unit 47, and a communication control unit 48. The welding robot control unit 41 controls the welding robot 10. Specifically, the welding robot control unit 41 controls the welding gun control device 50 (spot welding gun 30) according to a pre-adjustment program in order to have the spot welding gun 30 perform a search operation. The welding robot control device 41 also controls the robot arm mechanism 20 and the welding gun control device 50 (spot welding gun 30) according to a welding program in order to have the welding robot 10 perform a welding operation.

[0021] The threshold calculation unit (corresponding to the parameter adjustment unit) 42 calculates a threshold value based on the time change of the current value of the servo motor 35 during the search operation in the pre-adjustment. The method of calculating the threshold value by the threshold calculation unit 42 will be described later. The current value of the servo motor 35 while the spot welding gun 30 is performing a search operation is detected by the current detection unit 53 of the welding gun control device 50.

[0022] The distance calculation unit 43 calculates the distance from the start of the search operation until the servo motor's current value stabilizes, based on the time change of the servo motor's current value during the search operation in the pre-adjustment. The method of distance calculation by the distance calculation unit 43 will be described later.

[0023] The contact detection unit 44 detects contact between the spot welding gun 30 (movable electrode tip 32) and the workpiece by comparing the current value of the servo motor 35 detected by the current detection unit 53 of the welding gun control device 50 during welding operation with a threshold value calculated in the pre-adjustment.

[0024] The input unit 45 inputs user operations to the robot control device 40 via an input device such as the teaching control panel 60. Through processing by the input unit 45, for example, the robot control device 40 receives input for a pre-adjustment mode or an operating mode according to the user's instructions. The output unit 46 creates and outputs screen data for displaying information related to welding operations and pre-adjustments, such as thresholds calculated by the threshold calculation unit 42 and distances calculated by the distance calculation unit 43, to a display device such as the teaching control panel 60. The memory unit 47 stores various information related to welding operations and pre-adjustments. For example, the memory unit 47 stores information regarding the threshold calculated by the threshold calculation unit 42 during pre-adjustments and information regarding the distance calculated by the distance calculation unit 43 during pre-adjustments. The memory unit 47 also stores a predetermined value for determining whether the threshold calculated by the threshold calculation unit 42 is too high.

[0025] The communication control unit 48 controls the transmission and reception of various information with the welding gun control device 50. Through processing by the communication control unit 48, the robot control device 40 transmits control signals such as pressure commands and welding current commands based on the welding program and pre-adjustment program to the welding gun control device 50, and sequentially receives information regarding the current value of the servo motor 35 from the welding gun control device 50.

[0026] The threshold calculation process by the threshold calculation unit 42 and the distance calculation process by the distance calculation unit 43 will be explained below with reference to Figure 3. Figure 3 shows an example of the time change of the current value of the servo motor 35 during the search operation in the pre-adjustment.

[0027] As shown in Figure 3, immediately after the start of the search operation, the movable arm 34 is accelerating, so the current value of the servo motor 35 that drives the movable arm 34 gradually increases. The current value of the servo motor 35 is unstable in the section where the movable arm 34 is accelerating. Since the detection accuracy of contact with the workpiece decreases in the section where the current value is unstable, the start position of the search operation is adjusted so that the movable electrode tip 32 does not come into contact with the workpiece in the section where the current value of the servo motor 35 is unstable.

[0028] When the search operation is started and a predetermined time has elapsed, the movable arm 34 moves at a constant speed, so the current value of the servo motor 35 oscillates within a predetermined fluctuation range and stabilizes. The fluctuation in the current value of the servo motor 35 is caused by factors such as friction in the speed reducer that reduces the rotational speed of the servo motor 35. When the movable arm 34 driven by the servo motor 35 and the movable electrode tip 32 attached to the movable arm 34 come into contact with the workpiece, this becomes a load, and the current flowing to the servo motor 35 increases. Therefore, the threshold is calculated using a formula such that the threshold value is greater than the maximum value of the current value of the servo motor 35 during the constant-speed period in which the fluctuation in the current value of the servo motor 35 stays within a predetermined fluctuation range (referred to as the maximum value of the fluctuation range). Typically, the threshold calculation unit 42 calculates the threshold value as a value obtained by adding a predetermined margin to the maximum value of the fluctuation range. Typically, the threshold is an absolute value. However, the threshold is not limited to an absolute value. For example, since the current value of the servo motor 35 can be monitored even while in operation, the threshold value may be a value obtained by multiplying the value relative to the maximum value of the fluctuation range by a predetermined coefficient greater than 1.0 as a ratio.

[0029] The distance calculation unit 43 calculates the distance from the start of the search operation until the current value of the servo motor 35 stabilizes. For example, the time from the start of the search operation until the current value stabilizes can be determined by the time change of the current value of the servo motor 35. Based on the encoder position at the start of the search operation and the encoder position after the time has elapsed from the start of the search operation until the current value stabilizes, the distance calculation unit 43 calculates the distance from the start of the search operation until the current value of the servo motor 35 stabilizes. For example, the point in time when the current value of the servo motor 35 stabilizes can be set to a predetermined time after the current value begins to settle within a predetermined fluctuation range.

[0030] The control of the search operation in pre-adjustment by the control device according to the first embodiment will be described below with reference to Figure 4. Upon receiving the user's selection of the pre-adjustment mode, the control device starts control of the spot welding gun 30 according to the pre-adjustment program and starts the search operation by the spot welding gun 30 (S11). The current detection unit 53 detects the time change in the current value of the servo motor 35 during the search operation (S12). Based on the time change in the current value of the servo motor 35 during the search operation, the threshold and distance are calculated (S13, S14). If the threshold is smaller than a predetermined value (S15; NO), the threshold is confirmed (S16). Then, the threshold and distance calculated in steps S13 and S14 are displayed on the teaching operation panel 60 (S17). On the other hand, when the threshold is greater than a predetermined value (S15; YES), an alarm is displayed on the instruction control panel 60 to notify the user that the threshold is too large, along with the threshold and distance calculated in steps S13 and S14 (S18).

[0031] Pre-adjustment is preferably performed immediately before the actual welding operation begins. This allows for the determination of thresholds in conditions close to those of the welding operation, thereby improving the accuracy of detecting contact with the workpiece during the welding operation. Here, pre-adjustment is performed according to user instructions, but pre-adjustment may also be included as the first step in a series of welding operations, and the pre-adjustment may be performed automatically before the welding operation begins.

[0032] The control of the welding operation by the control device according to the first embodiment will be described below with reference to Figures 5 and 6. Figure 5 shows the procedure of the search operation by the spot welding gun 30 in a series of welding operations by the welding robot 10.

[0033] Upon receiving the user's selection of the operating mode, the control device starts controlling the welding robot 10 according to the welding program and initiates the welding operation by the welding robot 10. The robot arm mechanism 20 moves the spot welding gun 30 from the standby position to the welding point position and controls the servo motor 35 to start the search operation by the spot welding gun 30 (S21), and also starts the process of detecting contact with the workpiece (S22). As a result of the process in step S21, the movable electrode tip 32 is moved toward the workpiece W1 as shown in Figure 6(a).

[0034] The control device waits until the current value of the servo motor 35 exceeds a threshold (S23; NO). When the current value of the servo motor 35 exceeds the threshold (S23; YES), the control device considers that the movable electrode tip 32 has come into contact with the workpiece W1, as shown in Figure 6(b), and terminates the workpiece contact detection process (S24), and also terminates the search operation by the spot welding gun 30 (S25).

[0035] The control device initiates a contact operation on the welding robot 10. As shown in Figure 6(c), during the contact operation, the spot welding gun 30 is moved upward by the robot arm mechanism 20, and the movable arm 34 is moved at the same speed as the robot arm mechanism 20 to move the movable electrode tip 32 closer to the fixed electrode tip 31. This allows the workpiece W1 to be clamped between the movable electrode tip 32 and the fixed electrode tip 31 without the workpiece W1 moving. After the contact operation is completed, welding current is supplied to the movable electrode tip 32 and the fixed electrode tip 31, and the workpiece W1 clamped between the electrode tips 31 and 32 is welded. Once welding is complete, the spot welding gun 30 is returned to the standby position, and the series of welding operations is completed.

[0036] One feature of the control device according to the first embodiment is that, in addition to the operating mode for causing the welding robot 10 to perform actual welding operations, it also has a pre-adjustment mode. The pre-adjustment mode is a mode in which the welding robot 10 performs a search operation, which is also included in the welding operation, without a workpiece. Based on the time change of the current value of the servo motor 35 in the pre-adjustment mode, the detection threshold for contact between the spot welding gun 30 and the workpiece, which is used during the search operation included in the welding operation, can be calculated. In this way, since the user is not involved in the calculation of the threshold, it is not affected by the user's experience or skill level, and the user's workload can be reduced.

[0037] Since the pre-adjustment is performed using the spot welding gun 30 that will actually be used, the threshold can be set to a more appropriate value, and it can also flexibly accommodate changes in tools, such as changes in the spot welding gun 30. Since the optimal threshold may change due to aging and temperature changes, pre-adjustment may be performed periodically. Setting the threshold to an appropriate value improves the accuracy of workpiece detection.

[0038] Furthermore, if the threshold is higher than expected, the system can notify the user with an alarm. If the threshold is higher than expected, it may indicate that the spot welding gun 30's reducer or servo motor 35 is malfunctioning, or even if there is no malfunction, that there is excessive friction in the spot welding gun 30's reducer, etc., or that the search operation is malfunctioning due to inappropriate search speed, acceleration time, gain, etc. By being able to identify problems with the spot welding gun 30 or the search operation, the user can address these issues before actually performing the welding operation, thereby improving work efficiency. In addition, by checking the distance the movable electrode tip 32 moves from the start of the search operation until the current value of the servo motor 35 stabilizes, as displayed on the teaching control panel 60, the user can adjust the starting position of the search operation in the welding program as needed. This contributes to shortening the search operation time or to stable detection of contact with the workpiece.

[0039] The method for calculating the threshold by the threshold calculation unit 42 is not limited to this embodiment. For example, the threshold calculation unit 42 may calculate the threshold as a value obtained by adding a predetermined margin to the center value of the fluctuation range. Also, in cases such as the third embodiment described later, where contact with a workpiece by a pair of fingers of a robot hand is detected, the pair of fingers may be pushed or pulled in the direction of movement by the workpiece. In such cases, the threshold calculation unit 42 may calculate the threshold as a value obtained by subtracting a predetermined margin from the minimum value of the fluctuation range.

[0040] In pre-adjustment mode, the search operation by the spot welding gun 30 is repeatedly performed to acquire multiple data files relating to the time change of the servo motor 35 during the search operation, and the threshold calculation unit 42 may calculate a threshold based on the acquired multiple data files. For example, the threshold calculation unit 42 may use a value obtained by adding a predetermined margin to the average value of the maximum value of the fluctuation range for each search operation, based on the multiple data files, as the threshold.

[0041] The control device according to the first embodiment only displayed the distance calculated in the pre-adjustment on the teaching operation panel 60. However, the control device may also have a program modification unit that modifies the welding program based on the distance calculated in the pre-adjustment. The program modification unit modifies the starting position of the search operation in the welding operation defined in the welding program based on the distance traveled by the movable electrode tip 32 from the start of the search operation until the current value of the servo motor 35 stabilizes. For example, if in the welding program before modification the position of the movable electrode tip 32 at the start of the search is close to the fixed electrode tip 31, and the movable electrode tip 32 reaches a position where it contacts or is about to contact the workpiece to be welded before the current value of the servo motor 35 stabilizes, the program modification unit modifies the position of the movable electrode tip 32 at the start of the search to a position farther away from the fixed electrode tip 31. This allows for stable detection of the workpiece. On the other hand, if, in the welding program before modification, the position of the movable electrode tip 32 at the start of the search is far from the fixed electrode tip 31, and even after the current value of the servo motor 35 stabilizes, the movable electrode tip 32 needs to move a long distance before it can contact or be on the verge of contacting the workpiece to be welded, the program modification unit modifies the position of the movable electrode tip 32 at the start of the search to a position closer to the fixed electrode tip 31. This makes it possible to set the travel distance of the movable electrode tip 32 to an appropriate distance that is not too long, thereby avoiding a situation where the welding time is unnecessarily prolonged.

[0042] (Second Embodiment) In the first embodiment, the threshold was used to detect contact with the workpiece, but it may also be used to detect gripping (holding) of the workpiece. The control device according to the second embodiment will be described below with reference to Figures 7, 8, and 9. In the second embodiment, a robot hand is used as an example of a tool for gripping a workpiece, and a robot arm mechanism is used as an example of a movement mechanism for moving the tool for gripping the workpiece. An example of gripping a workpiece with the robot hand will be described. The detection parameter is, for example, a parameter for detecting that a workpiece has been gripped, and specifically corresponds to the limit value of the servo motor's current value.

[0043] As shown in Figure 7, the picking robot 70 has a robot arm mechanism 71 and a robot hand 73 equipped on the wrist portion of the robot arm mechanism 71. The robot hand 73 has a pair of fingers 731, 732 that are provided to open and close, and a servo motor 733 that drives the opening and closing of the pair of fingers 731, 732. The control device 80 according to the second embodiment controls the picking robot 70.

[0044] The control device 80 includes a processor composed of a CPU and a GPU, RAM which functions as the processor's main memory and work area, and a storage device which stores various programs and setting information. The storage device includes a picking program which causes the picking robot 70 to perform a predetermined picking operation when an operating mode is selected, and a pre-adjustment program which causes the picking robot 70 to perform a gripping operation when a pre-adjustment mode is selected.

[0045] The control device 80 functions as a picking robot control unit 81, a limit value calculation unit 82, a pinching detection unit 84, an input unit 85, an output unit 86, a storage unit 87, and a current detection unit 89.

[0046] The picking robot control unit 81 controls the picking robot 70. Specifically, the picking robot control unit 81 controls the robot hand 73 according to a pre-adjustment program in order to have the robot hand 73 perform a gripping operation. The picking robot control unit 81 also controls the picking robot 70 according to a picking program in order to have the picking robot 70 perform a picking operation.

[0047] The limit value calculation unit (corresponding to the parameter adjustment unit) 82 corresponds to the threshold value calculation unit 42 in the first embodiment. The limit value calculation unit 82 calculates the limit value based on the time change of the current value of the servo motor 733 while the robot hand 73 is performing a gripping operation without a workpiece in the pre-adjustment mode. The limit value here is used to limit the torque (force) used to grip the workpiece with the pair of fingers 731 and 732. Since no current greater than the limit value flows through the servo motor 733 that drives the pair of fingers 731 and 732, the pair of fingers 731 and 732 will not grip the workpiece with a force stronger than expected, thereby suppressing deformation of the workpiece such as crushing. Therefore, the limit value is also a threshold value for detecting when the pair of fingers 731 and 732 have gripped the workpiece with a constant force. The calculation process of the limit value by the limit value calculation unit 82 is performed in the same way as the calculation process of the threshold value by the threshold value calculation unit 42 in the first embodiment, so it is omitted here.

[0048] The grip detection unit 84 monitors the current value flowing to the servo motor 733 in operating mode, and detects that the workpiece has been gripped by the robot hand 73 when the current value flowing to the servo motor 733 in operating mode reaches a limit value (threshold) calculated in the pre-adjustment. The picking robot control unit 81 limits the current value output to the servo motor 733 so that a current value larger than the limit value does not flow to the servo motor 733.

[0049] The input unit 85 inputs user operations to the control device 80 via an input device such as the teaching control panel 60. The output unit 86 creates screen data for displaying information related to the picking program and pre-adjustment program, such as limit values ​​calculated by the limit value calculation unit 82, on the teaching control panel 60, and outputs it to the teaching control panel 60. The storage unit 87 stores various information related to the picking operation and pre-adjustment. For example, the storage unit 87 stores information related to limit values ​​calculated by the limit value calculation unit 82. The current detection unit 89 detects the current value flowing through the servo motor 733.

[0050] The control of the picking operation by the control device 80 according to the second embodiment will be explained below with reference to Figures 8 and 9. Here, only the gripping operation of workpieces W2 and W3 by the robot hand 73, which is part of a series of picking operations by the picking robot 70, will be explained. Figure 8 shows the gripping operation for the small workpiece W2, and Figure 9 shows the gripping operation for the large workpiece W3.

[0051] Upon receiving input for the operating mode selected according to user instructions, control of the picking robot 70 is initiated according to the picking program, causing the picking robot 70 to start picking. When the robot arm mechanism 71 moves the robot hand 73 from the standby position to the picking position, the robot hand 73 is controlled to perform a gripping operation on the workpieces W2 and W3.

[0052] When the gripping operation of workpieces W2 and W3 begins, the pair of fingers 731 and 732 move toward each other, as shown in Figures 8(a) and 9(a). As shown in Figures 8(b) and 9(b), even when the pair of fingers 731 and 732 make contact with workpieces W2 and W3, the pair of fingers 731 and 732 continue to move toward each other as long as the current flowing to the servo motor 733 has not reached the limit value. When the current flowing to the servo motor 733 reaches the limit value, the current output to the servo motor 733 is clamped at the limit value. The workpieces W2 and W3 are gripped by the pair of fingers 731 and 732 with a predetermined torque, and the movement of the pair of fingers 731 and 732 stops, as shown in Figures 8(c) and 9(c). After the gripping operation is completed, the robot arm mechanism 71 moves the robot hand 73 to the release position, and the robot hand 73 performs a release operation at the release position, releasing the workpieces W2 and W3. Subsequently, the robot hand 73 is returned to the standby position by the robot arm mechanism 71, and the series of picking operations is completed. The picking system, including the control device 80 and the picking robot 70 according to the second embodiment, only detects that the workpiece has been gripped with a certain torque by the pair of fingers 731 and 732. Therefore, as long as the workpiece can be gripped with that torque, it can handle the picking operations of multiple types of workpieces W2 and W3 of different sizes, as shown in Figures 8 and 9. The control device according to the second embodiment exhibits the same effects as the control device according to the first embodiment. That is, the user's effort in setting the limit value for gripping the workpiece can be reduced by pre-adjustment.

[0053] (Third embodiment) The control device according to the third embodiment will be described below with reference to Figures 10 and 11. The third embodiment will be described using the detection of a workpiece by a picking robot equipped with a robot hand as an example. The difference between the third embodiment and the second embodiment is that the servo motor to be monitored is different, and the detection operation is different. Specifically, in the second embodiment, the servo motors that drive a pair of fingers of the robot hand are monitored, and it is detected that the workpiece is gripped by the pair of fingers with a predetermined torque. On the other hand, in the third embodiment, the servo motors that drive each joint of the robot arm mechanism equipped with the robot hand are monitored, and it is detected that the workpiece is in contact with the pair of fingers. Since only the servo motor to be monitored is different, and the functions of the control device according to the third embodiment have almost the same configuration as the control device according to the second embodiment, details regarding the common configuration will be omitted. The detection parameter is a parameter for detecting that the workpiece has come into contact with the fingers, and specifically corresponds to the threshold value of the servo motor current value described later.

[0054] As shown in Figure 10, the picking robot 70 has a robot arm mechanism 71 and a robot hand 73 equipped on the wrist portion of the robot arm mechanism 71. The robot hand 73 has a pair of fingers 731 and 732 that are provided to open and close. The robot arm mechanism 71 has a plurality of servo motors 711, 712, 713, and 714 corresponding to a plurality of joints.

[0055] The control device 90 includes a processor composed of a CPU and a GPU, RAM which functions as the processor's main memory and work area, and a storage device which stores various programs and setting information. The storage device includes a picking program which causes the picking robot 70 to perform a predetermined picking operation when an operating mode is selected, and a pre-adjustment program which causes the picking robot 70 to perform a search operation when a pre-adjustment mode is selected.

[0056] The control device 90 functions as a picking robot control unit 91, a threshold calculation unit 92, a contact detection unit 94, an input unit 95, an output unit 96, a storage unit 97, and a current detection unit 99.

[0057] The picking robot control unit 91 controls the picking robot 70. Specifically, the picking robot control unit 91 controls the robot hand 73 according to a pre-adjustment program in order to have the robot hand 73 perform a search operation. The picking robot control unit 91 also controls the picking robot 70 according to a picking program in order to have the picking robot 70 perform a picking operation.

[0058] The threshold calculation unit (corresponding to the parameter adjustment unit) 92 corresponds to the threshold calculation unit 42 in the first embodiment. The threshold calculation unit 92 calculates a threshold based on the time change of the current values ​​of the servo motors 711, 712, 713, and 714 while the robot hand 73 is performing a search operation in the pre-adjustment mode without a workpiece. The threshold calculation process by the threshold calculation unit 92 is performed in the same way as the threshold calculation process by the threshold calculation unit 42 in the first embodiment, so it is omitted here.

[0059] The contact detection unit 94 detects when the robot hand 73 has made contact with a workpiece by comparing the current value detected by the current detection unit 99 in the operating mode with a threshold value calculated in the pre-adjustment. The input unit 95 inputs user operations to the control device 90 via an input device such as the teaching control panel 60. The output unit 96 creates screen data for displaying information related to the picking program and pre-adjustment program, such as the threshold value calculated by the threshold calculation unit 92, on the teaching control panel 60, and outputs it to the teaching control panel 60. The storage unit 97 stores various information related to the picking operation and pre-adjustment. For example, the storage unit 97 stores information related to the threshold value calculated by the threshold calculation unit 92. The current detection unit 99 detects the current values ​​flowing through the servo motors 711, 712, 713, and 714.

[0060] The control of the picking operation by the control device 90 according to the third embodiment will be described below with reference to Figure 11. Here, the workpiece search operation portion by the robot hand 73 in a series of picking operations by the picking robot 70 will be described.

[0061] Upon receiving input for the operating mode selected according to user instructions, control of the picking robot 70 is initiated according to the picking program, causing the picking robot 70 to begin picking. When the robot arm mechanism 71 moves the robot hand 73 from the standby position to the picking position, the robot hand 73 starts a search operation to have the robot hand 73 perform a search operation for the workpiece W4.

[0062] When the search operation for workpiece W4 is started, the picking robot 70 is moved by the robot arm mechanism 71 with the robot hand 73 released, as shown in Figure 11(a). The robot arm mechanism 71 monitors the current values ​​of the servo motors 711, 712, 713, and 714 while they are operating. When the current values ​​of the servo motors 711, 712, 713, and 714 exceed a threshold, as shown in Figure 11(b), it detects that the workpiece W4 has come into contact with the finger 732 and stops the movement of the robot hand 73. Then, as shown in Figure 11(c), the robot hand 73 is made to start a gripping operation of the workpiece W4. After the gripping operation is completed, the robot arm mechanism 71 moves the robot hand 73 to the release position, and the robot hand 73 performs a release operation at the release position, releasing the workpiece W4. Then, the robot hand 73 is returned to the standby position by the robot arm mechanism 71, and the series of picking operations is completed. The control device according to the third embodiment exhibits the same effects as the control device according to the first embodiment. In other words, pre-adjustment reduces the effort required of the user to set the threshold for detecting contact with the workpiece to an appropriate value.

[0063] (Fourth Embodiment) In the first, second, and third embodiments, the threshold and limit values ​​of the current value were determined as detection parameters through pre-adjustment, but the loop gain of the feedback control may also be adjusted as a detection parameter. When performing position / velocity feedback control, flexible control can be performed to follow external forces by reducing the gain of the feedback loop. By reducing the gain, the tool can be stopped without placing an excessive load on the workpiece when it comes into contact with the workpiece. However, if the gain is reduced too much, problems may occur such as the tool or the robot equipped with the tool stopping before contacting the workpiece due to friction of the reduction gear during the search operation, or the speed fluctuating. Therefore, the gain needs to be adjusted to an appropriate value. Detection parameters are, for example, parameters for detecting that a workpiece has been gripped, and specifically, the position / velocity loop gain corresponds to this.

[0064] The control device according to the fourth embodiment will now be described with reference to Figures 12 and 13. The fourth embodiment will be described using the detection of a workpiece W2 by a robot hand 73 as an example. The control device 100 according to the fourth embodiment is configured by replacing the limit value calculation unit 82 in the control device 80 according to the second embodiment with a gain calculation unit 101, the current detection unit 89 with a position detection unit 102, and the current limiting unit 84 with a speed difference calculation unit 103. In the fourth embodiment, the contents described in the second embodiment will be omitted.

[0065] The memory unit 87 stores the initial value of the gain, as well as the updated gain calculated by the gain calculation unit 101 through pre-adjustment. It also stores a threshold value for comparing the speed difference between the command speed and the feedback speed. The memory unit 87 stores the pre-adjustment program. This pre-adjustment program contains commands for the picking robot 70, such as the operating position commands.

[0066] The gain calculation unit (corresponding to the parameter adjustment unit) 101 calculates the gain to be used in the operating mode through pre-adjustment. Specifically, when the speed difference calculated by the speed difference calculation unit 103 during pre-adjustment is below a threshold, the gain calculation unit 101 calculates the updated gain by subtracting a predetermined amount from the current gain. Details of the gain calculation process will be described later.

[0067] The position detection unit 102 detects the positions of the pair of fingers 731 and 732 (the rotational position of the servo motor 733) based on the output of the encoder of the servo motor 733.

[0068] The speed difference calculation unit 103 calculates the speed difference between the command speed and the feedback speed. Specifically, the speed difference calculation unit 103 calculates the command speed based on the operating position command described in the pre-adjustment program, and calculates the feedback speed based on the time change in the position of the pair of fingers 731, 732 detected by the position detection unit 102. The command speed is the ideal speed of the pair of fingers 731, 732 when no load is applied, and the feedback speed is the actual speed of the pair of fingers 731, 732. In other words, the speed difference calculation unit 103 calculates the speed difference between the ideal speed and the actual speed.

[0069] The gain calculation process by the control device 100 according to the fourth embodiment will now be described with reference to Figure 13. As shown in Figure 13, upon receiving the user's selection of the pre-adjustment mode, the control device sets an initial value for the gain to be adjusted (S31), and starts control of the picking robot 70 according to the pre-adjustment program, causing the picking robot 70 to start a search operation (S32). The search operation is performed by position / velocity feedback control using the initial value of the gain. Based on the output of the encoder of the servo motor 733 during the search operation, the position detection unit 102 calculates the positions of the pair of fingers 731 and 732. Then, the velocity difference calculation unit 103 calculates the command velocity and the feedback velocity, and calculates the velocity difference between them (S33). When the velocity difference is less than or equal to a threshold (S34; Yes), the gain calculation unit 101 calculates the updated gain (S35), and the search operation continues with position / velocity feedback control using the updated gain (S36). The processes S33 through S36 are repeatedly executed until the speed difference exceeds a threshold. When the speed difference exceeds the threshold (S34; No), the gain calculation unit 101 calculates the gain to be used in the operating mode (S37), stores it in the storage unit 87, and the search operation is terminated (S38).

[0070] The process in step S34 is equivalent to determining whether the search operation is being performed stably. When the speed difference between the command speed and the feedback speed is small, it means that the search operation is being performed stably. In other words, it indicates that there is room to lower the gain. On the other hand, when the speed difference between the command speed and the feedback speed is large, the effects of friction in the reduction gear become large, the feedback speed slows down, and it means that the search operation is not being performed stably. In other words, it indicates that the previous gain was the minimum gain required to perform the search operation. The gain calculation process shown in Figure 13 allows for obtaining a gain that enables stable search operation while following external forces.

[0071] In this embodiment, the servo motor current value and servo motor rotation position were used when adjusting detection parameters during pre-adjustment and when detecting workpieces in operation mode. However, estimated disturbance torque may be used instead. Here, estimated disturbance torque is the difference between the torque actually output to the motor and the theoretically required motor torque, and the theoretically required torque can be calculated based on the physical model of the mechanism.

[0072] In this embodiment, the threshold value, limit value, and position / velocity loop gain of the servo motor current were pre-adjusted as detection parameters for detecting when a tool such as a spot welding gun or robot hand made contact with a workpiece or gripped a workpiece. However, the detection parameters to be pre-adjusted are not limited to these. For example, in pre-adjustment mode, the search operation speed and acceleration time may be adjusted as detection parameters. In this embodiment, fluctuations in the current value were tolerated, but high-frequency components included in the fluctuations in the current value may be removed by a low-pass filter, and the threshold value, limit value, and position / velocity loop gain may be calculated based on the time change of the current value after the removal of high-frequency components.

[0073] This embodiment was described using the contact of a spot welding gun with a workpiece, gripping of a workpiece by a robot hand, and contact of a robot hand with a workpiece as examples. One feature of each embodiment is that a threshold value (limit value) for detecting contact with a workpiece and gripping of a workpiece during actual operation is calculated in advance based on the time change of the current value flowing to the servo motor when an operation similar to the actual operation is performed without a workpiece. Therefore, this embodiment can be applied to various devices that need to detect contact with a workpiece and gripping of a workpiece. For example, it can be applied to a moving mechanism for moving a device having an opening / closing mechanism, such as a robot hand or a spot welding gun, to an arbitrary position and orientation. By comparing the current value of the servo motor driving the moving mechanism with a threshold value, contact of the opening / closing mechanism equipped on the moving mechanism with a workpiece can be detected. Also, by comparing the current value of the servo motor driving a moving mechanism equipped with a member for contacting a workpiece with a threshold value, contact of the member equipped on the moving mechanism with a workpiece can be detected.

[0074] One feature of the control device according to this embodiment is the inclusion of a pre-adjustment mode. This mode allows the parameters used to control the tool during actual operation to be pre-adjusted to appropriate values ​​before actual operation. Therefore, this embodiment can be widely applied to various tasks and devices that have pre-adjustable parameters.

[0075] The tool for gripping the workpiece is not limited to a robot hand, but can be an end effector that grips the workpiece using vacuum suction, an end effector that grips the workpiece using magnetic force, etc. Furthermore, the treatment of the workpiece is not limited to welding or contact with the workpiece. For example, the treatment of the workpiece can be riveting, which involves driving in rivets consisting of a head and a body without threads, FSW (Friction Stir Welding), clinching, which joins sheet metal by sandwiching it, or seam welding, which joins the workpiece by sandwiching it with cylindrical electrodes. Also, the tool for performing the treatment on the workpiece is not limited to a spot welding gun, but can be various tools used for the above treatments. Furthermore, the moving mechanism is not limited to a robot arm mechanism, but can be various moving mechanisms such as a slider mechanism driven by a servo motor. According to this embodiment, the parameters used to control the operation of these tools or moving mechanisms can be adjusted in advance in the pre-adjustment mode.

[0076] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols]

[0077] 30... Spot welding gun, 31... Fixed electrode tip, 32... Movable electrode tip, 33... Fixed arm, 34... Movable arm, 35... Servo motor, 36... Encoder, 40... Robot control device, 41... Welding robot control unit, 42... Threshold calculation unit, 43... Distance calculation unit, 44... Contact detection unit, 45... Input unit, 46... Output unit, 47... Memory unit, 48... Communication control unit, 50... Welding gun control device, 51... Motor control unit, 52... Welding current control unit, 53... Current detection unit, 54... Memory unit, 55... Communication control unit.

Claims

1. A control device for controlling a servo motor that drives a tool for gripping or processing a workpiece, A control unit that selectively controls the servo motor in a pre-adjustment mode in which the tool is operated without the workpiece, and in an operation mode in which the tool is operated with the workpiece present. The aforementioned pre-adjustment mode includes a parameter adjustment unit for adjusting detection parameters, The detection parameter is at least one of the following: a threshold or limit value for the current flowing through the servo motor, a gain related to position or velocity, the speed or acceleration of the search operation, or the estimated disturbance torque of the servo motor. The control unit is a control device that controls the servo motor in the operating mode using the detection parameters adjusted by the parameter adjustment unit.

2. A control device for controlling a servo motor that drives a moving mechanism for moving a tool that grips a workpiece or processes a workpiece, A control unit that selectively controls the servo motor in a pre-adjustment mode in which the moving mechanism is operated when there is no workpiece, and in an operating mode in which the moving mechanism is operated when there is a workpiece. The aforementioned pre-adjustment mode includes a parameter adjustment unit for adjusting detection parameters, The detection parameter is at least one of the following: a threshold or limit value for the current flowing through the servo motor, a gain related to position or velocity, the speed or acceleration of the search operation, or the estimated disturbance torque of the servo motor. The control unit is a control device that controls the servo motor in the operating mode using the detection parameters adjusted by the parameter adjustment unit.

3. A control device for controlling a servo motor that drives a tool for gripping or processing a workpiece, A control unit that selectively controls the servo motor in a pre-adjustment mode in which the tool is operated without the workpiece, and in an operation mode in which the tool is operated with the workpiece present. In the aforementioned pre-adjustment mode, a parameter adjustment unit adjusts the detection parameters, The system comprises a current detection unit for detecting the current value flowing through the servo motor, The parameter adjustment unit adjusts the detection parameter based on the time change of the current value detected by the current detection unit. The control unit is a control device that controls the servo motor in the operating mode using the detection parameters adjusted by the parameter adjustment unit.

4. A control device for controlling a servo motor that drives a moving mechanism for moving a tool that grips a workpiece or processes a workpiece, A control unit that selectively controls the servo motor in a pre-adjustment mode in which the moving mechanism is operated when there is no workpiece, and in an operating mode in which the moving mechanism is operated when there is a workpiece. In the aforementioned pre-adjustment mode, a parameter adjustment unit adjusts the detection parameters, The system comprises a current detection unit for detecting the current value flowing through the servo motor, The parameter adjustment unit adjusts the detection parameter based on the time change of the current value detected by the current detection unit. The control unit is a control device that controls the servo motor in the operating mode using the detection parameters adjusted by the parameter adjustment unit.

5. The control device according to claim 3 or 4, further comprising a detection unit that detects contact of the tool with the workpiece or gripping of the workpiece by the tool by comparing or limiting the current value detected by the current detection unit with the detection parameter in the operating mode.

6. A control device for controlling a servo motor that drives a tool for gripping or processing a workpiece, A control unit that selectively controls the servo motor in a pre-adjustment mode in which the tool is operated without the workpiece, and in an operation mode in which the tool is operated with the workpiece present. In the aforementioned pre-adjustment mode, a parameter adjustment unit adjusts the detection parameters, The system comprises a position detection unit for detecting the rotational position of the servo motor, The parameter adjustment unit adjusts the detected parameters based on the time change of the rotational position detected by the position detection unit. The control unit is a control device that controls the servo motor in the operating mode using the detection parameters adjusted by the parameter adjustment unit.

7. A control device for controlling a servo motor that drives a moving mechanism for moving a tool that grips a workpiece or processes a workpiece, A control unit that selectively controls the servo motor in a pre-adjustment mode in which the moving mechanism is operated when there is no workpiece, and in an operating mode in which the moving mechanism is operated when there is a workpiece. In the aforementioned pre-adjustment mode, a parameter adjustment unit adjusts the detection parameters, The system comprises a position detection unit for detecting the rotational position of the servo motor, The parameter adjustment unit adjusts the detected parameters based on the time change of the rotational position detected by the position detection unit. The control unit is a control device that controls the servo motor in the operating mode using the detection parameters adjusted by the parameter adjustment unit.

8. The control device according to any one of claims 1 to 4, 6 to 7, further comprising a notification unit that notifies the user of an alarm when the detection parameter is greater than a predetermined value.

9. A control device for controlling a servo motor that drives a tool for gripping or processing a workpiece, A control unit that selectively controls the servo motor in a pre-adjustment mode in which the tool is operated without the workpiece, and in an operation mode in which the tool is operated with the workpiece present. In the aforementioned pre-adjustment mode, a parameter adjustment unit adjusts the detection parameters, A current detection unit for detecting the current value flowing through the servo motor, In the aforementioned pre-adjustment mode, a distance calculation unit calculates the distance required for the current value to settle within a predetermined fluctuation range based on the time change of the current value detected by the current detection unit, The system comprises a display unit for displaying the aforementioned distance, The control unit is a control device that controls the servo motor in the operating mode using the detection parameters adjusted by the parameter adjustment unit.

10. A control device for controlling a servo motor that drives a moving mechanism for moving a tool that grips a workpiece or processes a workpiece, A control unit that selectively controls the servo motor in a pre-adjustment mode in which the moving mechanism is operated when there is no workpiece, and in an operating mode in which the moving mechanism is operated when there is a workpiece. In the aforementioned pre-adjustment mode, a parameter adjustment unit adjusts the detection parameters, A current detection unit for detecting the current value flowing through the servo motor, In the aforementioned pre-adjustment mode, a distance calculation unit calculates the distance required for the current value to settle within a predetermined fluctuation range based on the time change of the current value detected by the current detection unit, The system comprises a display unit for displaying the aforementioned distance, The control unit is a control device that controls the servo motor in the operating mode using the detection parameters adjusted by the parameter adjustment unit.

11. A control device for controlling a servo motor that drives a tool for gripping or processing a workpiece, A control unit that selectively controls the servo motor in a pre-adjustment mode in which the tool is operated without the workpiece, and in an operation mode in which the tool is operated with the workpiece present. In the aforementioned pre-adjustment mode, a parameter adjustment unit adjusts the detection parameters, A current detection unit for detecting the current value flowing through the servo motor, In the aforementioned pre-adjustment mode, a distance calculation unit calculates the distance required for the current value to settle within a predetermined fluctuation range based on the time change of the current value detected by the current detection unit, The system comprises a program modification unit that modifies the operating program used in the operating mode based on the distance, The control unit is a control device that controls the servo motor in the operating mode using the detection parameters adjusted by the parameter adjustment unit.

12. A control device for controlling a servo motor that drives a moving mechanism for moving a tool that grips a workpiece or processes a workpiece, A control unit that selectively controls the servo motor in a pre-adjustment mode in which the moving mechanism is operated when there is no workpiece, and in an operating mode in which the moving mechanism is operated when there is a workpiece. In the aforementioned pre-adjustment mode, a parameter adjustment unit adjusts the detection parameters, A current detection unit for detecting the current value flowing through the servo motor, In the aforementioned pre-adjustment mode, a distance calculation unit calculates the distance required for the current value to settle within a predetermined fluctuation range based on the time change of the current value detected by the current detection unit, The system comprises a program modification unit that modifies the operating program used in the operating mode based on the distance, The control unit is a control device that controls the servo motor in the operating mode using the detection parameters adjusted by the parameter adjustment unit.

13. The control device according to any one of claims 1 to 4, 6 to 7, or 9 to 12, wherein the tool is a spot welding gun. The control device described above.

14. The control device according to any one of claims 1 to 4, 6 to 7, or 9 to 12, wherein the tool is a robot hand.

15. The control device according to any one of claims 2, 4, 7, 10, or 12, wherein the moving mechanism is a robot arm mechanism, and the servo motor drives the joint portion of the robot arm mechanism.

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