Method for controlling a robot system and robot system

Abstract

To provide a control method for a robot system having excellent followability to sudden changes in a transport speed of an object, and a robot system.SOLUTION: According to a control method for a robot system having a transport device for transporting an object and a robot for performing work while following the object transported by the transport device, the robot is made to follow the object by a control signal that is calculated on the basis of a transport speed of the object detected from an output signal of an encoder located on the transport device, and when the transport speed exceeds a threshold, a calculation method for the control signal is changed.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method for controlling a robot system and a robot system.

Background Art

[0002] Conventionally, a robot system that performs a follow-up operation on an object conveyed by a conveying device such as a belt conveyor has been known. In such a robot system, the conveyance speed of the object is detected based on the encoder value of the belt conveyor, and the driving of the robot is controlled based on the detection result. In such a configuration, Patent Document 1 describes obtaining a virtual encoder value based on the encoder value of the belt conveyor in order to reduce the influence of noise and vibration, and detecting the conveyance speed of the object based on this virtual encoder value. Further, in Patent Document 1, a virtual encoder value is calculated using the past encoder values and a filter function, and the parameters of the filter function are set according to the magnitude of the vibration.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the invention described in Patent Document 1, there is a possibility that the robot may not be able to follow the change in the conveyance speed of the belt conveyor during operation.

Means for Solving the Problems

[0005] The method for controlling a robot system according to the present invention is a method for controlling a robot system including a conveying device that conveys an object and a robot that performs an operation while following the object conveyed by the conveying device, The robot is made to follow the object by a control signal calculated based on the transport speed of the object detected from the output signal of an encoder located in the transport device. The method for calculating the control signal is changed when the transport speed exceeds a threshold.

[0006] The robot system of the present invention comprises a conveying device for transporting an object, A robot that performs work while following the object being transported by the transport device, The robot has a control device that controls the drive of the robot, The control device causes the robot to follow the object by a control signal calculated based on the transport speed of the object detected from the output signal of the encoder located in the transport device. The method for calculating the control signal is changed when the transport speed exceeds a threshold. [Brief explanation of the drawing]

[0007] [Figure 1] This is an overall configuration diagram of the robot system according to the first embodiment. [Figure 2] This graph shows the difference Δ between the output signal P1 and the smoothed signal P2. [Figure 3] This is a block diagram of the filter circuit included in the control unit. [Figure 4] This graph illustrates how to set thresholds. [Figure 5] This graph illustrates the control method for a robotic system. [Figure 6] This is a flowchart illustrating the control method for a robotic system. [Figure 7] This figure shows an example of a graphic interface. [Figure 8] This is a graph showing the threshold values ​​set in the robot system according to the second embodiment. [Figure 9] This is a block diagram of the filter circuit included in the control unit. [Figure 10]This is a graph showing the threshold values ​​set in the robot system according to the second embodiment. [Modes for carrying out the invention]

[0008] The control method and robot system of the present invention will be described in detail below based on embodiments shown in the accompanying drawings.

[0009] <First Embodiment> Figure 1 is an overall configuration diagram of the robot system according to the first embodiment. Figure 2 is a graph showing the difference Δ between the output signal P1 and the smoothed signal P2. Figure 3 is a block diagram of the filter circuit provided by the control device. Figure 4 is a graph illustrating the threshold setting method. Figure 5 is a graph illustrating the control method of the robot system. Figure 6 is a flowchart illustrating the control method of the robot system. Figure 7 is a diagram showing an example of a graphic interface.

[0010] The robot system 1 shown in Figure 1 comprises a robot 2, an imaging unit 3, a control device 4, a transport device 6, and a display device 8. In the robot system 1, the transport device 6 transports the object W along the transport direction A, the control device 4 detects the transport status of the object W based on the image G acquired by the imaging unit 3 and the transport speed of the object W, and the robot 2 performs work while following the transported object W. The work performed on the object W is not particularly limited and can include, for example, drilling holes, connecting with other components (insertion, screwing, threading, etc.), cleaning, inspection, etc. The object W is also not particularly limited and can include any object that can be worked on by the robot 2, such as industrial products such as printers and automobiles or their parts.

[0011] As shown in Figure 1, robot 2 is a 6-axis vertical articulated robot with six drive axes, and includes a base 21, a robot arm 22 rotatably connected to the base 21, and an end effector 23 attached to the tip of the robot arm 22. The robot arm 22 is a robotic arm in which multiple arms 221, 222, 223, 224, 225, and 226 are rotatably connected, and has six joints J1 to J6. Of these, joints J2, J3, and J5 are bending joints, and joints J1, J4, and J6 are torsion joints. The end effector 23 is selected as appropriate according to the intended work.

[0012] Furthermore, each of the joints J1, J2, J3, J4, J5, and J6 is equipped with a motor M and an encoder E that detects the amount of rotation of the motor M. During the operation of the robot system 1, the control device 4 performs servo control (feedback control) for each joint J1 to J6 to match the rotation angle of the joints J1 to J6 indicated by the output of the encoder E with the target position, which is the control target.

[0013] The conveying device 6 is a belt conveyor and includes a belt 62, conveying rollers 63 that move the belt 62, a motor 61 that drives the conveying rollers 63, and an encoder 64 that outputs a signal to the control device 4 corresponding to the amount of rotation of the belt 62. While the robot system 1 is in operation, the control device 4 performs servo control (feedback control) to match the conveying speed of the object W indicated by the output of the encoder 64 with the target conveying speed, which is the control target.

[0014] The imaging unit 3 is a camera that images the object W from above the conveying device 6 and outputs the captured image to the control device 4. The imaging area of the imaging unit 3 is located upstream of the working area of the robot 2 in the conveying direction A. The imaging unit 3 has an angle of view that includes the object W conveyed on the belt 62. The position in the image output from the imaging unit 3 is associated with the position in the conveying path by the control device 4. Therefore, when the object W exists within the angle of view of the imaging unit 3, the coordinates of the object W at the time when the image was captured can be specified based on the position of the object W in the image of the imaging unit 3.

[0015] The control device 4 controls the driving of the robot 2, the imaging unit 3, and the conveying device 6 respectively. The control device 4 is composed of, for example, a computer, and has a processor (CPU) that processes information, a memory communicably connected to the processor, and an external interface for connecting to an external device. Various programs executable by the processor are stored in the memory, and the processor can read and execute various programs and the like stored in the memory. Note that some or all of the components of the control device 4 may be arranged inside the housing of the robot 2. Also, the control device 4 may be composed of a plurality of processors.

[0016] The configuration of the robot system 1 has been briefly described above. Such a robot system 1 operates as follows. First, the control device 4 operates the transfer device 6 and controls the drive of the control device 4 so that the transfer speed of the object W detected based on the output of the encoder 64 becomes the target transfer speed. In this state, the object W is supplied to the transfer device 6, and the transfer of the object W by the transfer device 6 is started. Next, the control device 4 images the object W passing through the imaging area with the imaging unit 3 and acquires an image G in which the object W is shown. Next, the control device 4 detects the coordinates of the object W at the time when the image G is acquired from the image G. Next, the control device 4 calculates the position of the object W at each future time from the coordinates of the object W at the time when the image G is acquired and the transfer speed of the object W, and calculates a control signal for the robot 2 based on the calculated position. Then, the control device 4 drives the robot 2 with the calculated control signal and causes the robot 2 to perform a predetermined operation while following the object W being transferred.

[0017] Here, the transfer roller 63 mounted on the transfer device 6 is designed to be a perfect cylindrical shape in order to smoothly transfer the belt 62, but depending on the forming accuracy, the overall shape may deviate from the perfect cylinder. Also, even if the transfer roller 63 is formed into a perfect cylindrical shape, the rotation axis may deviate from the central axis and be eccentric. When the shape of the transfer roller 63 deviates from the perfect cylinder or is eccentric, high-frequency noise caused thereby rides on the output signal of the encoder 64. Also, when the shape of the transfer roller 63 deviates from the perfect cylinder, periodic unevenness occurs in the transfer speed of the object W.

[0018] Therefore, if the control signal is calculated using the transport speed of the object W detected from the output signal of the encoder 64, the operation of the robot 2 may be disrupted due to the aforementioned high-frequency noise and speed fluctuations. For this reason, the control device 4 can, for example, smooth the output signal of the encoder 64 with a filter circuit and detect the transport speed of the object W from the smoothed signal output from the filter circuit. By smoothing the output signal of the encoder 64 with a filter circuit in this way, the effects of the aforementioned high-frequency noise and speed fluctuations can be suppressed, and the operation of the robot 2 can be stabilized.

[0019] While there are these advantages, depending on the filter time constant τ set in the filter circuit, when the transport speed of the object W changes abruptly, such as when the transport device 6 is temporarily stopped and restarted, the waveform of the smoothing signal P2 becomes blunted relative to the waveform of the output signal P1 of the encoder 64, as shown in Figure 2, and a shift Δ occurs between the output signal P1 and the smoothing signal P2. Therefore, if the control signal is calculated using the transport speed of the object W detected from the smoothing signal, when the transport speed of the object W changes abruptly, the shift Δ causes a positional shift of the robot 2 relative to the transported object W, making it impossible to perform work on the object W properly. In other words, even with a filter circuit, if there is only one method for calculating the control signal, it is not possible to respond to abrupt changes in the transport speed of the object W.

[0020] Therefore, the robot system 1 is equipped with multiple methods for calculating control signals, and by changing the control signal calculation method when the transport speed of the object W exceeds the threshold SH, the positional deviation of the robot 2 relative to the object W is reduced compared to the calculation method before the change. With this method, even if the transport speed of the object W changes abruptly, the positional deviation of the robot 2 relative to the object W during transport is suppressed, and appropriate work can be performed on the object W. In this specification, "the transport speed of the object W exceeds the threshold SH" means that the transport speed of the object W is above or below the threshold SH. This will be explained in detail below.

[0021] As shown in Figure 3, the control device 4 has a filter circuit 41 consisting of a first filter circuit 411 and a second filter circuit 412. The first filter circuit 411 and the second filter circuit 412 are each band-blocking filter circuits that cut out predetermined frequency components, and in this embodiment, high-frequency components above a predetermined frequency. However, the first filter circuit 411 and the second filter circuit 412 may be band-pass filters. In this case, they should be set to pass frequency components below the predetermined frequency.

[0022] The first filter circuit 411 smooths the output signal P1 of the encoder 64 and outputs a smoothed signal P21. Similarly, the second filter circuit 412 smooths the output signal P1 of the encoder 64 and outputs a smoothed signal P22. Furthermore, the first filter time constant τ1 set in the first filter circuit 411 and the second filter time constant τ2 set in the second filter circuit 412 are different from each other, and in this embodiment, the first filter time constant τ1 is larger than the second filter time constant τ2. In other words, the cutoff frequency fc of the first filter circuit 411 is lower than that of the second filter circuit 412.

[0023] Therefore, while the smoothing signal P21 is superior to the smoothing signal P22 in removing high-frequency noise, it exhibits a larger deviation Δ when the transport speed of the object W changes abruptly. Conversely, while the smoothing signal P22 is inferior to the smoothing signal P21 in removing high-frequency noise, it has a higher responsiveness and exhibits a smaller deviation Δ when the transport speed of the object W changes abruptly.

[0024] Furthermore, the control device 4 has a first calculation mode in which it calculates the control signal for the robot 2 using a smoothing signal P21, and a second calculation mode in which it calculates the control signal for the robot 2 using a smoothing signal P22. The control device 4 then compares the transport speed of the object W detected from the output signal P1 of the encoder 64 with a threshold SH related to the transport speed stored in memory, and selects one of the first calculation mode or the second calculation mode based on the comparison result.

[0025] The threshold SH is set lower than the target transport speed V0 of the object W, taking into account the amplitude of high-frequency noise. For example, in a teaching operation, the transport device 6 is driven at the target transport speed V0, and the output signal P1 of the encoder 64 is measured as shown in Figure 4. This output signal P1 contains high-frequency noise caused by misalignment or eccentricity of the transport roller 63, and the transport speed of the object W fluctuates periodically. Next, the minimum speed Vmin is detected from the output signal P1. Then, the threshold SH is set to a value lower than the minimum speed Vmin. Note that the threshold SH is not particularly limited as long as it is lower than the minimum speed Vmin, but it is preferable that it be as high as possible within the range lower than the minimum speed Vmin.

[0026] As shown in Figure 5, when the transport speed of the object W detected from the output signal P1 is greater than or equal to the threshold SH, the transport speed of the object W is stable near the target transport speed V0, and deviation Δ is unlikely to occur. Therefore, the control device 4 selects a first calculation mode in which it calculates the control signal for the robot 2 using a smoothing signal P21 with a high noise reduction effect. On the other hand, when the transport speed of the object W detected from the output signal P1 is less than the threshold SH, the transport speed of the object W may be changing abruptly, and deviation Δ is likely to occur. Therefore, the control device 4 selects a second calculation mode in which it calculates the control signal for the robot 2 using a smoothing signal P22 with a small deviation Δ.

[0027] This method allows for a smaller deviation Δ when the transport speed of the object W changes abruptly, compared to always calculating the control signal in the first calculation mode. Therefore, the discrepancy between the transport speed of the object W and the tracking speed of the robot 2 can be suppressed. As a result, the positional deviation of the robot 2 relative to the object W during transport is suppressed, enabling appropriate work to be performed on the object W. In particular, this method allows for easy modification of the control signal calculation method, as it only requires switching the filter time constant.

[0028] Furthermore, by setting the threshold SH lower than the minimum speed Vmin, it is possible to avoid frequent switching between the first and second calculation modes due to high-frequency noise in unnecessary situations (such as when the object W is being transported at the target transport speed V0), thereby enabling stable calculation of the control signal for robot 2.

[0029] Here, an example of how to switch between the first and second calculation modes will be explained based on the flowchart in Figure 6. First, in step S1, the control device 4 sets the control signal calculation mode to the first calculation mode. Next, in step S2, the control device 4 detects the transport speed of the object W from the output signal P1. Next, in step S3, the control device 4 determines whether the transport speed of the object W detected in step S2 is less than the threshold SH. If the transport speed of the object W is less than the threshold SH, in step S4, the control device 4 increments the count by 1. On the other hand, if the transport speed of the object W is greater than or equal to the threshold SH, in step S5, the control device 4 does not count. Next, in step S6, the control device 4 determines whether the count has reached a predetermined number of times N. If the count has not reached the specified number of times N, it returns to step S2. If the count has reached the specified number of times N, in step S7, the control device 4 switches the control signal calculation mode from the first calculation mode to the second calculation mode.

[0030] Next, in step S8, the control device 4 detects the transport speed of the object W from the output signal P1. Next, in step S9, the control device 4 determines whether the transport speed of the object W detected in step S8 is equal to or greater than the threshold SH. If the transport speed of the object W is equal to or greater than the threshold SH, in step S10, the control device 4 increments the count by 1. On the other hand, if the transport speed of the object W is less than the threshold SH, in step S11, the control device 4 does not count. Next, in step S12, the control device 4 determines whether the count has reached a predetermined number of times N. If the count has not reached the specified number of times N, it returns to step S8; if the count has reached the specified number of times N, it returns to step S1 and switches the control signal calculation mode from the second calculation mode to the first calculation mode.

[0031] Depending on the characteristics of the transport device 6 and the operating environment, sudden large noises may occur in the output signal P1. The aforementioned specified number N is set to prevent the calculation mode from switching due to such sudden changes in transport speed.

[0032] Furthermore, as mentioned above, the control device 4 servo-controls each joint J1 to J6 of the robot 2. Specifically, for each joint J1 to J6, the control device 4 performs position loop control based on the position command and the position feedback signal from the encoder E to output a velocity command, performs velocity loop control based on the velocity command and the velocity feedback signal from the encoder E to output an acceleration command, generates a control signal which is a current command based on the acceleration command, and drives each motor M with the generated control signal.

[0033] Therefore, the control device 4 changes the servo gain set in the servo control according to the transport speed of the object W. The servo gain is a parameter that determines responsiveness and operational stability; the higher the servo gain, the better the responsiveness, but if it is too high, it may cause vibration. The servo gain consists of a position loop gain in position loop control and a velocity loop gain in velocity loop control, and the values ​​of one or both of these can be changed.

[0034] The control device 4 has a first servo gain and a second servo gain used to calculate the control signal for the robot 2. The second servo gain is higher than the first servo gain. When the transport speed of the object W detected from the output signal P1 is above the threshold SH, i.e., in the first calculation mode, the transport speed of the object W is stable around the target transport speed V0, and positional deviation of the robot 2 relative to the object W during transport due to servo delay is unlikely. Therefore, the control device 4 calculates the control signal for the robot 2 using the first servo gain, which has high vibration damping properties. On the other hand, when the transport speed of the object W detected from the output signal P1 is below the threshold SH, i.e., in the second calculation mode, the transport speed of the object W may be changing rapidly, and positional deviation of the robot 2 relative to the object W during transport due to servo delay is likely to occur. Therefore, the control device 4 calculates the control signal for the robot 2 using the second servo gain, which has high responsiveness properties.

[0035] This method suppresses servo lag when the transport speed of the object W changes abruptly, compared to always calculating the control signal in the first calculation mode. Therefore, it can suppress the discrepancy between the transport speed of the object W and the tracking speed of the robot 2. As a result, the positional deviation of the robot 2 relative to the object W during transport is suppressed, and appropriate work can be performed on the object W. In particular, this method allows for easy modification of the control signal calculation method, as it only requires switching the servo gain.

[0036] Here, when changing the filter time constant or servo gain, sudden acceleration or deceleration may occur in the control signal of robot 2. If this acceleration or deceleration exceeds the maximum allowable value set for robot 2, robot 2 may automatically stop due to an error. Therefore, it is preferable to set the first and second filter time constants τ1 and τ2 and the first and second servo gains so that the acceleration or deceleration that occurs during the change does not exceed the maximum allowable value. It is also preferable to limit or correct the control signal to prevent acceleration or deceleration that exceeds the maximum allowable value.

[0037] The control device 4 can display a graphic interface 40 on the display device 8 as shown in Figure 7, and can accept input from the user via the graphic interface 40. The graphic interface 40 displays the output signal P1 of the encoder 64 obtained during the teaching process, as well as fields for setting the second filter time constant τ2, threshold SH, specified number of repetitions N, and second servo gain. The user can then freely determine the second filter time constant τ2, threshold SH, specified number of repetitions N, and second servo gain based on the displayed output signal P1. However, the control device 4 may also automatically set these parameters based on information obtained during the teaching process (characteristics of the transport device 6), etc.

[0038] The robot system 1 has been described above. As mentioned above, the control method for such a robot system 1 is a control method for a robot system 1 having a transport device 6 that transports an object W and a robot 2 that performs work while following the object W being transported by the transport device 6. The robot 2 is made to follow the object W by a control signal calculated based on the transport speed of the object W detected from the output signal of an encoder 64 located on the transport device 6, and the method of calculating the control signal is changed when the transport speed exceeds a threshold SH. With this method, the deviation Δ when the transport speed of the object W changes abruptly can be kept small. As a result, the positional deviation of the robot 2 relative to the object W during transport is suppressed, and appropriate work can be performed on the object W.

[0039] Furthermore, as mentioned above, in the control method of the robot system 1, a filter circuit 41 that processes the output signal of the encoder 64 is used to calculate the control signal, and the calculation method is changed by changing the filter time constant of the filter circuit 41 when the transport speed of the object W exceeds the threshold SH. With this method, the method of calculating the control signal can be changed in a simple manner.

[0040] Furthermore, as mentioned above, in the control method of robot system 1, the first filter time constant τ1, which is the filter time constant when the transport speed of the object W is above the threshold SH, is greater than the second filter time constant τ2, which is the filter time constant when the transport speed of the object W is below the threshold SH. This makes it possible to more reliably suppress the deviation Δ when the transport speed of the object W changes abruptly.

[0041] Furthermore, as mentioned above, in the control method of robot system 1, the robot 2 is servo-controlled, and when the transport speed of the object W exceeds the threshold SH, the servo gain of the servo control is changed, thereby changing the method of calculating the control signal for robot 2. With this method, the method of calculating the control signal can be changed in a simple manner.

[0042] Furthermore, as mentioned above, in the control method of robot system 1, the first servo gain, which is the servo gain when the transport speed of the object W is below the threshold SH, is greater than the second servo gain, which is the servo gain when the transport speed of the object W is above the threshold SH. This makes it possible to more reliably suppress the deviation Δ when the transport speed of the object W changes abruptly.

[0043] As mentioned above, the robot system 1 includes a transport device 6 for transporting an object W, a robot 2 that performs work while following the object W being transported by the transport device 6, and a control device 4 that controls the drive of the robot 2. The control device 4 causes the robot 2 to follow the object W using a control signal calculated based on the transport speed of the object W detected from the output signal of an encoder 64 located on the transport device 6, and changes the method of calculating the control signal when the transport speed of the object W exceeds a threshold SH. With this configuration, the deviation Δ when the transport speed of the object W changes abruptly can be kept small. As a result, the positional deviation of the robot 2 relative to the object W during transport is suppressed, and appropriate work can be performed on the object W.

[0044] <Second Embodiment> Figure 8 is a graph showing the threshold values ​​set in the robot system according to the second embodiment. Figure 9 is a block diagram of the filter circuit provided by the control device.

[0045] The robot system 1 of this embodiment is the same as the robot system 1 of the first embodiment described above, except that the method for setting the threshold value SH is different. Therefore, in the following description, this embodiment will be described mainly in terms of the differences from the first embodiment described above, and similar matters will not be described. In addition, in each figure of this embodiment, the same reference numerals are used for components that are the same as in the previously described embodiment.

[0046] In the robot system 1 of this embodiment, as shown in Figure 8, multiple threshold values ​​SH are set. Specifically, a first threshold value SH1 and a second threshold value SH2 that is lower than the first threshold value SH1 are set as threshold values ​​SH.

[0047] Furthermore, as shown in Figure 9, the control device 4 has a filter circuit 41 comprising a first filter circuit 411, a second filter circuit 412, and a third filter circuit 413. The first, second, and third filter circuits 411, 412, and 413 smooth the output signal P1 of the encoder 64 and output smoothed signals P21, P22, and P23, respectively. In addition, the first filter time constant τ1 set in the first filter circuit 411, the second filter time constant τ2 set in the second filter circuit 412, and the third filter time constant τ3 set in the third filter circuit 413 are different from each other. In this embodiment, the first filter time constant τ1 > second filter time constant τ2 and the first filter time constant τ1 > third filter time constant τ3. The relative magnitudes of the second filter time constant τ2 and the third filter time constant τ3 are not particularly limited.

[0048] When the transport speed of the object W detected from the output signal P1 is greater than or equal to the first threshold SH1, the transport speed of the object W is stable and a deviation Δ is unlikely to occur. Therefore, the control device 4 selects a first calculation mode in which it calculates the control signal for the robot 2 using a smoothing signal P21 with a high noise reduction effect. Also, when the transport speed of the object W detected from the output signal P1 is greater than or equal to the second threshold SH2 and less than the first threshold SH1, the transport speed of the object W may be changing abruptly, and a deviation Δ is likely to occur. Therefore, the control device 4 selects a second calculation mode in which it calculates the control signal for the robot 2 using a smoothing signal P22 with a small deviation Δ. Also, when the transport speed of the object W detected from the output signal P1 is less than the second threshold SH2, the transport speed of the object W may be changing abruptly, and a deviation Δ is likely to occur. Therefore, the control device 4 selects a third calculation mode in which it calculates the control signal for the robot 2 using a smoothing signal P23 with a small deviation Δ.

[0049] In this way, by setting multiple threshold values ​​SH, the acceleration and deceleration regions of the object W can be subdivided, and the optimal filter time constant can be set for each region. Therefore, the displacement Δ when the transport speed of the object W changes abruptly can be kept small. Consequently, the positional displacement of the robot 2 relative to the object W during transport is suppressed, and appropriate work can be performed on the object W.

[0050] As described above, in the control method of the robot system 1 of this embodiment, multiple threshold values ​​SH are set. By setting multiple threshold values ​​SH in this way, the acceleration and deceleration regions of the object W can be subdivided, and the optimal filter time constant can be set for each region. Therefore, the displacement Δ when the transport speed of the object W changes abruptly can be kept small. Consequently, the positional displacement of the robot 2 relative to the object W during transport is suppressed, and appropriate work can be performed on the object W.

[0051] This second embodiment can also achieve the same effects as the first embodiment described above.

[0052] <Third Embodiment> Figure 10 is a graph showing the thresholds set in the robot system according to the third embodiment.

[0053] The robot system 1 of this embodiment is the same as the robot system 1 of the first embodiment described above, except that the method for setting the threshold value SH is different. Therefore, in the following description, the differences between this embodiment and the first embodiment described above will be the focus, and similar matters will not be explained. Also, in the figures of this embodiment, the same reference numerals are used for components that are the same as those in the previously described embodiment.

[0054] In the robot system 1 of this embodiment, as shown in Figure 10, multiple thresholds SH are set. Specifically, the thresholds SH include a deceleration threshold SH3, which is used when the transport speed of the object W decreases, and an acceleration threshold SH4, which is used when the transport speed of the object W increases. Furthermore, the acceleration threshold SH4 is lower than the deceleration threshold SH3.

[0055] The control device 4 switches the control signal calculation method from the first calculation mode to the second calculation mode when the transport speed of the object W detected from the output signal P1 decreases from above the deceleration threshold SH3 to below the deceleration threshold SH3. Furthermore, the control device 4 switches the control signal calculation method from the second calculation mode to the first calculation mode when the transport speed of the object W detected from the output signal P1 increases from below the acceleration threshold SH4 to above the acceleration threshold SH4. By using different threshold SH values ​​for switching between the first and second calculation modes depending on whether the transport speed of the object W decreases or increases, the displacement Δ can be kept small in both cases. Therefore, the positional displacement of the robot 2 relative to the object W during transport is suppressed, enabling appropriate work to be performed on the object W.

[0056] As described above, in the control method of the robot system 1 of this embodiment, the multiple set thresholds SH include a deceleration threshold SH3 that is used when the transport speed of the object W decreases, and an acceleration threshold SH4 that is used when the transport speed of the object W increases. As a result, the displacement Δ can be kept small whether the transport speed of the object W decreases or increases sharply. Therefore, the positional displacement of the robot 2 relative to the object W during transport is suppressed, and appropriate work can be performed on the object W.

[0057] This third embodiment can also achieve the same effects as the first embodiment described above.

[0058] The control method and robot system of the present invention have been described above based on the illustrated embodiments. However, the present invention is not limited thereto, and the configuration of each part can be replaced with any configuration having a similar function. Furthermore, other arbitrary components may be added to the present invention. Also, each embodiment may be combined as appropriate. [Explanation of symbols]

[0059] 1...Robot system, 2...Robot, 21...Base, 22...Robot arm, 221...Arm, 222...Arm, 223...Arm, 224...Arm, 225...Arm, 226...Arm, 23...End effector, 3...Imaging unit, 4...Control device, 40...Graphic interface, 41...Filter circuit, 411...First filter circuit, 412...Second filter circuit, 413...Third filter circuit, 6...Transport device, 61...Motor, 62...Belt, 63...Transport roller, 64...Encoder, 8...Display device, A...Transport direction, E...Encoder, G...Image, J1...Joint, J2...Joint, J3...Joint, J4...Joint, J5...Joint J6...Joint, M...Motor, N...Specified number of times, P1...Output signal, P2...Smoothing signal, P21...Smoothing signal, P22...Smoothing signal, P23...Smoothing signal, S1...Step, S2...Step, S3...Step, S4...Step, S5...Step, S6...Step, S7...Step, S8...Step, S9...Step, S10...Step, S11...Step, S12...Step, SH...Threshold, SH1...First threshold, SH2...Second threshold, SH3...Deceleration threshold, SH4...Acceleration threshold, V0...Target transport speed, Vmin...Minimum speed, W...Object, Δ...Deviation, τ1...First filter time constant, τ2...Second filter time constant, τ3...Third filter time constant

Claims

1. A control method for a robot system having a transport device for transporting an object, and a robot that performs work while following the object being transported by the transport device, The robot is made to follow the object by a control signal calculated based on the transport speed of the object detected from the output signal of an encoder located in the transport device. If the transport speed exceeds the threshold, the method for calculating the control signal is changed. A filter circuit that processes the output signal of the encoder is used to calculate the aforementioned control signal. When the transport speed exceeds the threshold, the calculation method is changed by changing the filter time constant of the filter circuit. A method for controlling a robot system, characterized in that the filter time constant when the transport speed is greater than or equal to the threshold is greater than the filter time constant when the transport speed is less than the threshold.

2. A control method for a robot system having a transport device for transporting an object, and a robot that performs work while following the object being transported by the transport device, The robot is made to follow the object by a control signal calculated based on the transport speed of the object detected from the output signal of an encoder located in the transport device. If the transport speed exceeds the threshold, the method for calculating the control signal is changed. Multiple thresholds are set. A method for controlling a robot system, characterized in that the multiple thresholds set include a deceleration threshold used when the transport speed decreases and an acceleration threshold used when the transport speed increases.

3. A control method for a robot system having a transport device for transporting an object, and a robot that performs work while following the object being transported by the transport device, The robot is made to follow the object by a control signal calculated based on the transport speed of the object detected from the output signal of an encoder located in the transport device. If the transport speed exceeds the threshold, the method for calculating the control signal is changed. The robot is servo controlled, When the transport speed exceeds the threshold, the method for calculating the control signal is changed by changing the servo gain of the servo control. A method for controlling a robot system, characterized in that the servo gain when the transport speed is less than the threshold is greater than the servo gain when the transport speed is equal to or greater than the threshold.

4. A filter circuit that processes the output signal of the encoder is used to calculate the control signal, A control method for a robot system according to claim 2 or 3, wherein the calculation method is changed by changing the filter time constant of the filter circuit when the transport speed exceeds the threshold.

5. The robot is servo controlled, A control method for a robot system according to claim 1 or 2, wherein the method for calculating the control signal is changed by changing the servo gain of the servo control when the transport speed exceeds the threshold.

6. A conveying device for conveying an object, A robot that performs work while following the object being transported by the transport device, The robot has a control device that controls the drive of the robot, The control device causes the robot to follow the object by a control signal calculated based on the transport speed of the object detected from the output signal of the encoder located in the transport device. If the transport speed exceeds the threshold, the method for calculating the control signal is changed. A filter circuit that processes the output signal of the encoder is used to calculate the aforementioned control signal. When the transport speed exceeds the threshold, the calculation method is changed by changing the filter time constant of the filter circuit. A robot system characterized in that the filter time constant when the transport speed is greater than or equal to the threshold is greater than the filter time constant when the transport speed is less than the threshold.

7. A conveying device for transporting an object, A robot that performs work while following the object being transported by the transport device, The robot has a control device that controls the drive of the robot, The control device causes the robot to follow the object by a control signal calculated based on the transport speed of the object detected from the output signal of the encoder located in the transport device. If the transport speed exceeds the threshold, the method for calculating the control signal is changed. Multiple thresholds are set. The robot system is characterized in that the multiple thresholds set include a deceleration threshold used when the transport speed decreases and an acceleration threshold used when the transport speed increases.

8. A conveying device for transporting objects, A robot that performs work while following the object being transported by the transport device, The robot has a control device that controls the drive of the robot, The control device causes the robot to follow the object by a control signal calculated based on the transport speed of the object detected from the output signal of the encoder located in the transport device. If the transport speed exceeds the threshold, the method for calculating the control signal is changed. The robot is servo controlled, When the transport speed exceeds the threshold, the method for calculating the control signal is changed by changing the servo gain of the servo control. A robot system characterized in that the servo gain when the transport speed is less than the threshold is greater than the servo gain when the transport speed is equal to or greater than the threshold.

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