CONTROL OF A ROBOT, CONTROL METHOD AND SYSTEM

Abstract

A control apparatus, a control method and a system are provided which include a function for preventing deterioration of machining precision due to foreign matter trapped between a workpiece and a fixing mechanism.This controller controls a robot configured to feed a held workpiece to a fixing mechanism and having a force detection unit for detecting force and moment acting on the workpiece, the controller comprising: a function of performing force control to correct the position of the workpiece relative to the fixing mechanism while the robot is feeding the workpiece to the fixing mechanism and then correcting the orientation of the workpiece relative to the fixing mechanism; and a function of determining that foreign objects are wedged between the workpiece and the fixing mechanism when, during the correction of the position of the workpiece, the force detection unit detects that the moment acting in the direction in which the orientation of the workpiece is corrected exceeds a first limit value.

Description

TECHNICAL AREA

[0001] The present invention relates to a controller and a control method for a robot, and to a system. STATE OF THE ART

[0002] A robot can be used as a means for feeding a workpiece to a machine, such as a machine tool. For example, a technique is known in which a robot feeds a workpiece to be machined into a chuck of a machine tool (see, for example, Patent Literature 1).

[0003] A technique for detecting foreign objects located between an object and a fixture when the object is seated on the fixture has also been proposed (see, for example, Patent Literature 2).

[0004] Furthermore, a technique was proposed in which two robots grip the respective workpieces and force control is used when one workpiece is placed on the other (see, for example, Patent Literature 3). [CITATION LIST][PATENT LITERATURE] [PTL 1] WO 2022 / 0172873 A1 [PTL 2] JP 2015-104759 A [PTL 3] JP 2018-024049 A SUMMARY OF THE INVENTION [TECHNICAL PROBLEM]

[0005] When a workpiece held by a robot is fed to a clamping mechanism such as a chuck of a machine tool and foreign matter such as cutting chips or debris adheres to or is trapped in the clamping mechanism or the workpiece, the workpiece may be clamped with the foreign matter trapped between the workpiece and the clamping mechanism, which may result in deterioration of the machining accuracy of the workpiece. [SOLVING THE PROBLEM]

[0006] One aspect of the present disclosure provides a controller of a robot configured to feed a workpiece held by the robot to a fixing mechanism, and having a force detection unit for detecting a force and a moment acting on the workpiece, the controller comprising: a function of performing position control in which a position of the workpiece relative to the fixing mechanism is corrected while the robot is feeding the workpiece to the fixing mechanism, and then a posture of the workpiece relative to the fixing mechanism is corrected;and a function for determining that, when the force detection unit detects that the moment acting in a direction that corrects the attitude of the workpiece exceeds a first limit value while the position of the workpiece is being corrected, a foreign object is caught between the workpiece and the fixing mechanism;

[0007] Another aspect of the present disclosure provides a controller of a robot configured to feed a workpiece held by the robot to a fixing mechanism, and having a force detection unit for detecting a force and a moment acting on the workpiece, the controller comprising: a function of executing force control in which a position of the workpiece relative to the fixing mechanism is corrected while the robot is feeding the workpiece to the fixing mechanism, and then a posture of the workpiece relative to the fixing mechanism is corrected; a function of storing the position and posture of a first workpiece when the force control is normally executed;and a function for determining that, when the force detection unit detects that a difference between a position and a posture of a second workpiece when the force control is executed and the stored position and posture of the first workpiece exceeds a second threshold value, a foreign matter is caught between the second workpiece and the fixing mechanism.;

[0008] Another aspect of the present disclosure provides a controller of a robot configured to feed a workpiece held by the robot to a fixing mechanism, and having a force detection unit for detecting a force and a moment acting on the workpiece, the controller comprising: a function of executing force control in which a position of the workpiece relative to the fixing mechanism is corrected while the robot is feeding the workpiece to the fixing mechanism, and then a posture of the workpiece relative to the fixing mechanism is corrected; a function of storing the position and posture of a first workpiece when the force control is normally executed;a function for performing position control in which a position and a posture of a second workpiece are corrected so that the position and posture of the second workpiece coincide with the stored position and posture of the first workpiece; and a function for determining that, when the force detection unit detects that a force applied to the second workpiece or a moment applied to the second workpiece exceeds a third limit value when the second workpiece is fastened by the fastening mechanism after the position control, a foreign object is caught between the second workpiece and the fastening mechanism. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view of a main part of a robot system according to an embodiment. Fig. 2 shows a view in which the position of a workpiece is corrected. Fig. 3 is a view showing a state in which the workpiece is fixed by a chuck. Fig. 4 is a view showing a flowchart of a method in a first example. Fig. 5 is a view showing a flowchart of a process in a second example. Fig. 6 is a view showing a flowchart of a process in a third example. DESCRIPTION OF THE EMBODIMENTS

[0009] Fig. Figure 1 is a schematic view of a main part of a robot system 10 according to a preferred embodiment. The robot system 10 includes a robot 12 and a controller 14 configured to control the robot 12. Fig. 1 shows only a movable part, namely, a robot arm 16 and a robot hand 18 provided at a front end of the robot arm 16, among the components of the robot 12, and does not show the other components. The robot 12 is, for example, an industrial vertical articulated robot with six drive axes. However, the present disclosure is not limited to this, and any robot that can change position and attitude through any mechanism may be used.

[0010] The robot 12 is configured to feed a workpiece 22, which is an object to be machined, to a machine tool 20, wherein Fig. 1 only one fastening mechanism (e.g., a chuck) 24 of the machine tool 20 is shown. The robot hand 18 has a gripping mechanism 26 for gripping the workpiece 22 and, in the example shown, has a plurality of gripper fingers that can grip the substantially cylindrical workpiece 22. The hand 18 also has a force detection unit 28 configured to detect the force, bending moment, deformation, etc. acting on the gripping mechanism 26 or the workpiece 22 gripped by the gripping mechanism 26. As the force detection unit 28, for example, a three- or six-axis force sensor can be used that is configured to detect at least one external force or moment acting on the workpiece 22.However, the force detection unit is not limited to this, and, for example, a torque sensor (not shown) provided on each axis of the robot 12 or a means (not shown) for estimating torque based on a current value of a motor provided on each axis of the robot 12 may be used as the force detection unit.

[0011] The machine tool 20 is configured to perform predetermined machining operations, such as cutting, on the workpiece 22 mounted on the chuck 24. The machine tool 20 may include a cleaning device such as a nozzle 30 configured to spray a fluid such as compressed air or a coolant toward the chuck 24 to remove foreign matter such as cutting chips adhering to the chuck 24 or the workpiece 22 mounted on the chuck 24. However, a cleaning device such as a nozzle having a function corresponding to that of the nozzle 30 may also be provided on the robot 12 or on another robot or peripheral device (not shown). In any case, the cleaning device may spray fluid to clean the chuck 24 based on a command issued from the controller 14 of the robot in a method described below.

[0012] In the robot system 10 that feeds the workpiece 22 to the machine tool 20, foreign matter 32, such as chips, may adhere to the chuck 24, as shown in Fig. 1. If the workpiece 22 is mounted on the chuck 24 in such a state, the foreign matter 32 may be caught between the workpiece 22 and the chuck 24, causing the center of the workpiece 22 to shift relative to the chuck 24, which may result in a reduction in machining accuracy. Even if no foreign matter adheres to the chuck 24, foreign matter such as workpiece fragments left over from previous machining may adhere to the workpiece 22 held by the robot 12, and in such a case, the same problem may occur. Therefore, means and methods for detecting the presence of such foreign matter are described in the following examples.

[0013] In the present embodiment, the term "foreign matter" refers to an object that may become trapped between the workpiece 22 and the chuck 24, reducing the positioning accuracy of the workpiece relative to the fixture mechanism and thus reducing machining accuracy. Foreign matter may include, for example, chips and debris generated during machining of the workpiece, as well as operator hair and dust in certain work environments. Chips may include, for example, chips generated during machining of a previous workpiece that adhere to the chuck, and foreign matter may include chips that adhered to the workpiece during previous machining. (First example)

[0014] Fig. 4 is a flowchart showing an example of a process according to a first example in the robot system 10. First, force control is performed to correct the position and attitude of the workpiece 22 held by the robot 12 with respect to the chuck 24 of the machine tool 20. In this case, as shown in Fig. 2, first, the position of the workpiece 22 is corrected by pressing the workpiece 22 against a spindle or the chuck 24 of the machine tool 20, and then the position of the workpiece 22 is corrected by following the chuck 24 when the chuck 24 closes (steps S11 and S12).

[0015] Next, in step S12, that is, when the position of the workpiece 22 is corrected, it is determined whether the force detection unit 28 detects a moment (hereinafter referred to as position correction moment) acting in a direction that corrects the position of the workpiece 22 or not. If there is no foreign object between the workpiece 22 and the chuck 24, no position correction moment is generated when the position is corrected. However, if the foreign object 32, as shown in Fig. 1, a significant posture correction moment is generated during position correction. Therefore, when the force detection unit 28 detects a posture correction moment equal to or greater than a predetermined threshold, it can be determined that a foreign object is present, and therefore, it is desirable to interrupt the feeding operation of the workpiece 22 by the robot 12 and proceed to step S14 to remove the foreign object.

[0016] When the position correction torque detected by the force detection unit 28 during the position correction (execution of step S12) exceeds a predetermined first threshold value, a processor, etc., of the robot controller 14 determines that the foreign object is located between the workpiece 22 and the chuck 24, which is a specific process of step S13. At this time, the first threshold value may be determined, for example, as a maximum value within a range that does not affect the machining accuracy of the workpiece 22, and may be determined empirically based on past performance, for example.In other words, even if the moment of position correction is detected equal to or smaller than the first threshold value, the trapped foreign matter is extremely small and is considered not to affect the machining accuracy, so that the process proceeds to step S15 and the machining of the workpiece 22 can be continued.

[0017] In step S14, coolant or air is sprayed from the nozzle 30 onto the mounting mechanism (here, the chuck 24) to clean the chuck 24 (or remove the foreign matter 32). This operation may be performed automatically based on a command from the robot controller 14. Alternatively or additionally, the robot controller 14, etc., may have the function of issuing an alarm. By issuing the alarm, the operator, etc., who recognizes the alarm, can manually clean the chuck 24.

[0018] When the cleaning of the chuck 24 (removal of the foreign matter 32) in S14 is completed and the moment of position correction is no longer detected, the workpiece 22 is fixed by the chuck 24, as in Fig. 3. In this way, the machine tool 20 can machine the workpiece 22 with high precision. (Second example)

[0019] Fig. 5 is a flowchart showing an example of a process according to a second example in the robot system 10. First, in a state where it is confirmed that no foreign matter exists between a first workpiece and the chuck 24 (hereinafter also referred to as a normal state), force control substantially similar to steps S11 and S12 described in the first example is performed for the first workpiece (step S21). When the force control is completed (that is, when the first workpiece is accurately positioned with the correct posture relative to the chuck 24), information regarding the position and posture of the first workpiece (position data and posture data, etc.) is stored in a suitable storage device (e.g., a memory included in the robot controller 14) (step S22).

[0020] Next, in step S23, in a state different from the normal state (namely, when a workpiece different from the normal state is fed to the chuck 24 in which the presence of foreign matter is unknown), a force control substantially corresponding to steps S11 and S12 described in the first example is carried out on a second workpiece different from the first workpiece.

[0021] In the next step S24, information about the position and attitude of the second workpiece when the force control in step S23 is completed is compared with the stored information in the normal state. More specifically, if the respective differences between the values ​​representing the position and attitude of the second workpiece in step S23 and the stored values ​​representing the position and attitude of the first workpiece in the normal state are within a predetermined second limit value, the position and attitude of the second workpiece at the time of executing step S23 are substantially equivalent to those in the normal state, and then the processor, etc., of the robot controller 14 can determine that no foreign matter exists between the second workpiece and the chuck 24. Therefore, the process proceeds to step S26, in which the second workpiece is fixed by the chuck 24, as shown in Fig. 3, and a predetermined machining process is performed. The second limit value may be set as the difference in position and the difference in attitude of the workpiece, as described above, and may be determined as the maximum value in a range that does not affect the machining accuracy of the workpiece, as in the first example, and may be determined empirically, for example, based on past performance. In other words, if the difference in position or attitude between the execution of S23 and the normal state is equal to or smaller than the second limit value, even if the foreign matter is caught, it is considered that the machining accuracy is not affected, so the process can proceed to step S26 to continue machining the workpiece.The second limit value can be set as a ratio of the position or attitude between the time of executing S23 and the normal state. For example, the ratio between the position or attitude when executing S23 and the position or attitude in the normal state can be set to a value within ±5% or ±3%.

[0022] If at least one of the positions and attitudes of the workpiece in step S23 deviates significantly from that in the normal state, it may be determined that a foreign matter is located between the second workpiece and the chuck 24, so it is desirable to interrupt the feeding operation of the second workpiece by the robot 12 and proceed to step S25 to remove the foreign matter. The content of step S25 may be substantially the same as step S14 in the first example.

[0023] When the cleaning of the chuck 24 (or the removal of the foreign matter 32) is completed in S25 and the position and attitude of the second workpiece during the execution of the force control are substantially the same as in the normal state, the second workpiece is fixed by the chuck 24 as shown in Fig. 3. For this reason, the machine tool 20 can machine the workpiece 22 with high precision. (Third example)

[0024] Fig. 6 is a flowchart showing an example of a process according to a third example in the robot system 10. First, in a state where it is confirmed that no foreign matter exists between the first workpiece and the chuck 24 (hereinafter also referred to as a normal state), force control substantially similar to steps S11 and S12 described in the first example is performed for a first workpiece (step S31). When the force control is completed (that is, when the first workpiece is accurately positioned with the correct posture relative to the chuck 24), information regarding the position and posture of the first workpiece (position data and posture data, etc.) is stored in a suitable storage device (e.g., a memory included in the robot controller 14) (step S32).

[0025] In the next step S33, the position and attitude of a second workpiece are controlled in a non-normal state (specifically, when a second non-normal workpiece in which the presence of foreign matter is unknown is fed to the chuck 24) based on the information stored in step S32. This control is different from the force control in the first or second example and is a position control for changing the position and attitude of the second workpiece so that they coincide with the final position and attitude of the first workpiece in step S31.

[0026] In the next step S34, the chuck 24 is closed, and at this time, it is detected whether or not a force or moment has been applied to the second workpiece or the hand 18. In other words, if there is no foreign object between the second workpiece and the chuck 24, no force or moment is applied to the second workpiece when the chuck is closed. However, if a foreign object is present, a force or moment of a certain value or more is applied. Therefore, if no force or moment is detected, the process proceeds to step S36, and the process of fixing the second workpiece with the chuck 24 is completed, as shown in Fig. 3 shown.

[0027] After executing S33, if the force detection unit 28 detects a force or moment equal to or greater than a predetermined third threshold value while the chuck 24 is gripping the second workpiece, the processor of the robot controller 14 determines that the foreign object is present between the second workpiece and the chuck 24. Here, the third threshold value may be determined as a maximum value within a range that does not affect the machining accuracy of the workpiece, as in the first or second example, and may be determined empirically, for example, based on past performance.In other words, when the maximum value of the force or moment detected during the clamping of the workpiece by the chuck 24 after execution of S33 is equal to or less than the third threshold value, it is considered that even if the foreign matter is caught, the machining accuracy is not affected, so that the process proceeds to step S36 and the machining of the workpiece can be continued.

[0028] If a force or moment equal to or greater than the third threshold value is detected in step S34, it may be determined that a foreign object is located between the workpiece 22 and the chuck 24, and therefore, it is desirable to interrupt the feeding operation of the workpiece 22 by the robot 12, proceed to step S35, and perform an operation to remove the foreign object. The content of step S35 may be substantially the same as step S14 in the first example.

[0029] When the cleaning of the chuck 24 (or the removal of the foreign matter 32) is completed in S35 and the position and attitude of the second workpiece during the execution of the position control are substantially the same as in the normal state, the second workpiece is fixed by the chuck 24 as shown in Fig. 3. For this reason, the machine tool 20 can machine the workpiece 22 with high precision.

[0030] The above-mentioned functions of the controller 14 may also be provided by a computer program that can be executed by the processor of the controller 14. The controller 14 may also include a storage device, such as a memory, configured to store the data used in each process and the data generated by each process. The computer program may be recorded on a non-transitory, computer-readable recording medium, such as a semiconductor memory, a magnetic recording medium, or an optical recording medium, e.g., a CD-ROM, or may be provided from a server device in a WAN (Wide Area Network) or LAN (Local Area Network) via a wired or wireless connection.

[0031] According to the examples described above, the presence of foreign matter between the workpiece fed by the robot and the workpiece fixing mechanism can be detected by a simple method, thereby preventing deterioration of the machining accuracy of the workpiece due to the trapped foreign matter.

[0032] Although the present disclosure has been described in detail, it is not limited to the above-mentioned individual embodiments. For these embodiments, various additions, replacements, modifications, partial deletions, etc. are possible within the scope of the present disclosure or within the scope of the present disclosure as understood from the claims and their equivalents. These embodiments may also be implemented in combination. For example, in the above-mentioned embodiments, the order of each operation and the order of each process are exemplified and are not limited to them. The same applies when using numerical values ​​or formulas in the description of the above-mentioned embodiments.

[0033] The following supplementary clauses are further disclosed with respect to the above-described embodiment and modified examples. (Clause 1)

[0034] A controller of a robot configured to feed a workpiece held by the robot to a fixing mechanism, and having a force detection unit for detecting a force and a moment applied to the workpiece, the controller comprising: a function of executing position control in which a position of the workpiece relative to the fixing mechanism is corrected while the robot feeds the workpiece to the fixing mechanism, and then a posture of the workpiece relative to the fixing mechanism is corrected; and a function of determining that, when the force detection unit detects that the moment acting in a direction that corrects the posture of the workpiece exceeds a first limit value while the position of the workpiece is being corrected, a foreign matter is caught between the workpiece and the fixing mechanism. (Clause 2)

[0035] A controller of a robot configured to feed a workpiece held by the robot to a fixing mechanism, and having a force detection unit for detecting a force and a moment applied to the workpiece, the controller comprising: a function for executing force control in which a position of the workpiece relative to the fixing mechanism is corrected while the robot is feeding the workpiece to the fixing mechanism, and then a posture of the workpiece relative to the fixing mechanism is corrected; a function for storing the position and posture of a first workpiece when the force control is normally executed;and a function for determining that, when the force detection unit detects that a difference between a position and a posture of a second workpiece when the force control is executed and the stored position and posture of the first workpiece exceeds a second limit value, a foreign object is caught between the second workpiece and the fixing mechanism.; (Clause 3)

[0036] A controller of a robot configured to feed a workpiece held by the robot to a fixing mechanism, and having a force detection unit for detecting a force and a moment applied to the workpiece, the controller comprising: a function for executing force control in which a position of the workpiece relative to the fixing mechanism is corrected while the robot is feeding the workpiece to the fixing mechanism, and then a posture of the workpiece relative to the fixing mechanism is corrected; a function for storing the position and posture of a first workpiece when the force control is normally executed;a function for performing position control in which a position and a posture of a second workpiece are corrected so that the position and posture of the second workpiece coincide with the stored position and posture of the first workpiece; and a function for determining that, when the force detection unit detects that a force applied to the second workpiece or a moment applied to the second workpiece exceeds a third limit value when the second workpiece is fixed by the fixing mechanism after the position control, a foreign object is caught between the second workpiece and the fixing mechanism. (Clause 4)

[0037] The controller according to any one of clauses 1 to 3 further comprises a function for issuing a command to clean the fastening mechanism when it is judged that the foreign matter is trapped. (Clause 5)

[0038] The controller according to any one of clauses 1 to 4 further comprises a function for issuing an alarm when the controller judges that the foreign object is trapped. (Clause 6)

[0039] Robot system with the controller according to one of clauses 1 to 5 and a robot controlled by the controller. (Clause 7)

[0040] The robot system according to clause 6 further comprises a cleaning device configured to clean the attachment mechanism when it is judged that the foreign object is trapped. (Clause 8)

[0041] A control method of a robot configured to feed a workpiece held by the robot to a fixing mechanism, and having a force detection unit for detecting a force and a moment acting on the workpiece, the control method comprising: performing position control in which a position of the workpiece relative to the fixing mechanism is corrected while the robot is feeding the workpiece to the fixing mechanism, and then a posture of the workpiece relative to the fixing mechanism is corrected; and judging that, when the force detection unit detects that the moment acting in a direction that corrects the posture of the workpiece exceeds a first limit value while the position of the workpiece is being corrected, a foreign matter is caught between the workpiece and the fixing mechanism. (Clause 9)

[0042] A control method of a robot configured to feed a workpiece held by the robot to a fixing mechanism, and having a force detection unit for detecting a force and a moment acting on the workpiece, the control method comprising: executing force control in which a position of the workpiece relative to the fixing mechanism is corrected while the robot is feeding the workpiece to the fixing mechanism, and then a posture of the workpiece relative to the fixing mechanism is corrected; storing the position and posture of a first workpiece when the force control is normally executed;and judging that, when the force detection unit detects that a difference between a position and a posture of a second workpiece when the force control is executed and the stored position and posture of the first workpiece exceeds a second threshold value, a foreign object is caught between the second workpiece and the fixing mechanism; (Clause 10)

[0043] A control method of a robot configured to feed a workpiece held by the robot to a fixing mechanism, and having a force detection unit for detecting a force and a moment acting on the workpiece, the control method comprising: executing force control in which a position of the workpiece relative to the fixing mechanism is corrected while the robot is feeding the workpiece to the fixing mechanism, and then correcting a posture of the workpiece relative to the fixing mechanism; storing the position and posture of a first workpiece when the force control is normally executed; executing position control in which a position and posture of a second workpiece are corrected so that the position and posture of the second workpiece coincide with the stored position and posture of the first workpiece;and judging that, when the force detection unit detects that a force applied to the second workpiece or a moment applied to the second workpiece exceeds a third limit value when the second workpiece is fixed by the fixing mechanism after the position control, a foreign object is caught between the second workpiece and the fixing mechanism; LIST OF REFERENCE SYMBOLS 10 Robot system 12 robots 14 Robot control 16 Robot arm 18 Robot hand 20 machine tools 22 Workpiece 24 clamping nut 26 gripping fingers 28 Force detection unit 30 nozzle 32 foreign bodies QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2022 / 0172873 A1

[0004] JP 2015-104759 A

[0004] JP 2018-024049 A

[0004]

Claims

A controller of a robot configured to feed a workpiece held by the robot to a fixing mechanism, and having a force detection unit for detecting a force and a moment acting on the workpiece, the controller comprising: a function of executing force control in which a position of the workpiece relative to the fixing mechanism is corrected while the robot is feeding the workpiece to the fixing mechanism, and then a posture of the workpiece relative to the fixing mechanism is corrected; and a function of determining that, when the force detection unit detects that the unidirectional moment correcting the posture of the workpiece exceeds a first limit value during the correction of the position of the workpiece, a foreign object is caught between the workpiece and the fixing mechanism. A controller of a robot configured to feed a workpiece held by the robot to a fixing mechanism, and having a force detection unit for detecting a force and a moment acting on the workpiece, the controller comprising: a function of executing force control in which a position of the workpiece relative to the fixing mechanism is corrected while the robot is feeding the workpiece to the fixing mechanism, and then a posture of the workpiece relative to the fixing mechanism is corrected; a function of storing the position and posture of a first workpiece when the force control is normally executed;anda function for determining that, when the force detection unit detects that a difference between a position and a posture of a second workpiece when the force control is executed and the stored position and posture of the first workpiece exceeds a second threshold, a foreign object is caught between the second workpiece and the fixing mechanism.; A controller of a robot configured to feed a workpiece held by the robot to a fixing mechanism, and having a force detection unit for detecting a force and a moment applied to the workpiece, the controller comprising: a function of executing force control in which a position of the workpiece relative to the fixing mechanism is corrected while the robot is feeding the workpiece to the fixing mechanism, and then a posture of the workpiece relative to the fixing mechanism is corrected; a function of storing the position and posture of a first workpiece when the force control is normally executed; a function of executing position control in which a position and posture of a second workpiece are corrected so that the position and posture of the second workpiece coincide with the stored position and posture of the first workpiece;anda function for determining that, when the force detection unit detects that a force applied to the second workpiece or a torque applied to the second workpiece exceeds a third limit value when the second workpiece is fastened by the fastening mechanism after the position control, a foreign object is caught between the second workpiece and the fastening mechanism.; A controller according to any one of claims 1 to 3, further comprising a function for issuing a command to clean the fastening mechanism when it is judged that the foreign matter is trapped. A controller according to any one of claims 1 to 4, further comprising a function for outputting an alarm when it is judged that the foreign matter is trapped. A robot system comprising the controller according to any one of claims 1 to 5 and a robot controlled by the controller. The robot system according to claim 6, further comprising a cleaning device configured to clean the attachment mechanism when it is judged that the foreign matter is trapped. A control method of a robot configured to feed a workpiece held by the robot to a fixing mechanism, and having a force detection unit for detecting a force and a moment acting on the workpiece, the control method comprising: performing force control in which a position of the workpiece relative to the fixing mechanism is corrected while the robot is feeding the workpiece to the fixing mechanism, and then correcting a posture of the workpiece relative to the fixing mechanism; and judging that, when the force detection unit detects that the unidirectional moment correcting the posture of the workpiece exceeds a first limit value while the position of the workpiece is being corrected, a foreign matter is caught between the workpiece and the fixing mechanism. A control method of a robot configured to feed a workpiece held by the robot to a fixing mechanism, and having a force detection unit for detecting a force and a moment acting on the workpiece, the control method comprising:executing force control in which a position of the workpiece relative to the fixing mechanism is corrected while the robot is feeding the workpiece to the fixing mechanism, and then a posture of the workpiece relative to the fixing mechanism is corrected;storing the position and posture of a first workpiece when the force control is normally executed;and judging that, when the force detection unit detects that a difference between a position and a posture of a second workpiece when the force control is executed and the stored position and posture of the first workpiece exceeds a second threshold value, a foreign matter is caught between the second workpiece and the fixing mechanism.; A control method of a robot configured to feed a workpiece held by the robot to a fixing mechanism, and having a force detection unit for detecting a force and a moment acting on the workpiece, the control method comprising: performing force control in which a position of the workpiece relative to the fixing mechanism is corrected while the robot is feeding the workpiece to the fixing mechanism, and then a posture of the workpiece relative to the fixing mechanism is corrected; storing the position and posture of a first workpiece when the force control is normally performed; performing position control in which a position and posture of a second workpiece are corrected so that the position and posture of the second workpiece coincide with the stored position and posture of the first workpiece;and judging that, when the force detection unit detects that a force applied to the second workpiece or a moment applied to the second workpiece exceeds a third limit value when the second workpiece is fastened by the fastening mechanism after the position control, a foreign object is caught between the second workpiece and the fastening mechanism.;

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