Robot control device and robot system

Abstract

A robot control device according to one embodiment of the present disclosure is capable of appropriately starting welding and controls a robot that performs welding of a welded object by using a welding torch that feeds a welding wire. The robot control device comprises: a welding command unit that commands the welding; an external force acquisition unit that acquires a value of external force acting on the robot; a robot stopping unit that stops operation of the robot if a value acquired by the external force acquisition unit is a first threshold value or greater; and a wire stopping unit that stops feeding of the welding wire if a value acquired by the external force acquisition unit is a second threshold value or greater at the beginning of the welding.

Description

Robot control device and robot system

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

[0002] Robot welding, in which a welding torch is held at the tip of a robot and moved by the robot to perform welding work, is widely used. In arc welding, which uses a welding wire as a welding material, the welding wire must be fed at an appropriate speed. Particularly at the start of welding, an appropriate arc discharge may not be established, causing the fed welding wire to come into contact with the workpiece. The reaction force of the welding wire contacting the workpiece may affect other control operations based on external forces acting on the robot. For example, if an emergency stop control is performed in response to the detection of an abnormal external force acting on the robot for safety reasons, the reaction force of the welding wire contacting the workpiece may be mistakenly interpreted as an abnormal external force, resulting in an emergency stop of the robot. To prevent such adverse effects on control operations based on other external forces, a technology has been proposed that sets a higher external force detection threshold than normal at the start of welding (see, for example, Patent Document 1).

[0003] International Publication No. WO2021 / 182243

[0004] When the external force detection threshold is increased for safety reasons, external forces below the increased threshold are tolerated even if they are above the normal threshold. While such external forces do not cause problems if they are applied for a short period of time, they can have adverse effects on the robot and welding torch if they continue to act during the start of welding. Therefore, a technology that can start welding appropriately is desired.

[0005] A robot control device according to one aspect of the present disclosure is a robot control device that controls a robot that welds workpieces using a welding torch that feeds out welding wire, and includes a welding instruction unit that instructs the welding, an external force acquisition unit that acquires a value of an external force acting on the robot, a robot stopping unit that stops operation of the robot if the acquired value from the external force acquisition unit is equal to or greater than a first threshold value, and a wire stopping unit that stops feeding out the welding wire if the acquired value from the external force acquisition unit is equal to or greater than a second threshold value at the start of the welding.

[0006] According to the present disclosure, welding can be started without affecting other controls that are performed in response to external forces acting on the robot.

[0007] FIG. 1 is a schematic diagram illustrating a configuration of a robot system according to a first embodiment of the present disclosure.

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The following describes embodiments of the present disclosure with reference to the drawings. Fig. 1 is a schematic diagram showing the configuration of a robot system 1 according to a first embodiment of the present disclosure.

[0009] Robot system 1 includes robot 10, welding torch 20, welding power source 30, wire supply device 40, gas supply device 50, and robot control device 60. Robot system 1 is an apparatus that uses robot 10 to move welding torch 20 to weld workpieces M. Generally, workpieces M consist of two parts, and welding is performed to integrate these two parts.

[0010] Robot 10 holds welding torch 20 at its tip and is controlled by robot control device 60 to position welding torch 20, i.e., to bring welding torch 20 facing the portion to be welded of workpiece M. Robot 10 can typically be a vertical articulated robot having arm 11 with a plurality of links that can rotate relative to one another, as shown in the figure, but is not limited to this and may be, for example, a Cartesian coordinate robot, a SCARA robot, a parallel link robot, or the like.

[0011] The robot 10 also has an external force detection unit 12 that detects an external force acting on the arm 11 directly or via the welding torch 20. The external force detection unit 12 may be configured to include, for example, a force sensor that detects an external force acting on the arm 11. The external force detection unit 12 may also be configured to calculate the external force acting on the arm 11 from the torque of the motor of the robot 10. Therefore, the external force detection unit 12 may be configured as a component of the robot control device 60 to calculate the value of the external force acting on the arm 11 based on a feedback value from the robot 10.

[0012] The welding torch 20 may be configured to perform arc welding by feeding a welding wire (linear filler metal) W supplied from a wire supply device 40 at the same speed, generating an arc discharge between the welding wire W and a workpiece M using a welding current supplied from a welding power source 30, and melting the material of the welding wire W into the workpiece M using heat generated by the arc discharge. The welding torch 20 may also be configured to prevent oxidation of the weld by injecting a shielding gas supplied from a gas supply device 50. Examples of arc welding performed by the welding torch 20 include MIG welding, MAG welding, and TIG welding. Therefore, the welding torch 20 is designed appropriately depending on the welding method to be adopted, and may use a consumable electrode for the welding wire W, or may supply the welding wire W to a region where a non-consumable electrode discharges.

[0013] Welding power source 30 supplies welding current to welding torch 20 for performing arc welding, i.e., applies voltage between workpiece M and welding torch 20. A known welding power supply device can be used as welding power source 30. Furthermore, welding power source 30 is preferably configured to be able to adjust the value of the welding current or welding voltage in real time in response to a setting signal input from robot control device 60. Furthermore, welding power source 30 may output signals to control wire supply device 40 and gas supply device 50. While wire supply device 40 and gas supply device 50 are typically controlled in conjunction with the welding current, it is preferable that at least wire supply device 40 be configured to be able to be controlled by an instruction independent of an instruction specifying the welding current from robot control device 60.

[0014] Wire supply device 40 supplies welding wire W to welding torch 20 based on instructions from welding power source 30 or robot control device 60. Wire supply device 40 draws welding wire W from a wire supply source (not shown), such as a wire drum, and supplies the wire to welding torch 20 at a specified speed. Wire supply device 40 may be a well-known device that can change the supply amount (linear speed) of welding wire W in response to an external signal.

[0015] Gas supply device 50 supplies shielding gas to welding torch 20 based on instructions from welding power source 30 or robot control device 60. As the shielding gas, a gas containing an inert gas such as carbon dioxide gas or argon gas as a main component is used.

[0016] The robot controller 60 is itself one embodiment of a robot controller according to the present disclosure. The robot controller 60 controls the robot 10, the welding power source 30, the wire supply device 40, and, if necessary, the welding torch 20 and the gas supply device 50. The robot controller 60 may also control the wire supply device 40 via the welding power source 30. The robot controller 60 may be realized by one or more computers having, for example, a memory, a processor, an input / output interface, etc., and executing an appropriate control program.

[0017] The robot control device 60 includes a robot control unit 61, a welding instruction unit 62, an external force acquisition unit 63, a robot stopping unit 64, a wire stopping unit 65, a threshold adjustment unit 66, a restart control unit 67, and a notification unit 68. Note that these components categorize the functions of the robot control device 60, and do not necessarily have to be clearly distinguishable in terms of physical configuration and program configuration.

[0018] The robot control unit 61 operates the robot 10 according to a welding program that specifies the operations required of the welding torch 20, such as the welding position and welding speed, and the operating conditions of the welding power source 30, the wire supply device 40, and the gas supply device 50.

[0019] Welding instructing unit 62 instructs welding power source 30 and wire supply device 40 to perform welding in accordance with a welding program. That is, welding instructing unit 62 instructs welding power source 30 to supply welding current, etc., so as to synchronize with the operation of robot 10, and instructs wire supply device 40, either directly or via welding power source 30, to start and stop feeding of welding wire W and the speed at which to feed the welding wire W. Even if welding power source 30 has a speed for welding wire W depending on other parameters, welding power source 30 or wire supply device 40 is configured to prioritize the command value from welding instructing unit 62.

[0020] The external force acquisition unit 63 acquires the value of the external force acting on the robot 10 from the external force detection unit 12. The external force acquisition unit 63 may have a function of converting the value of the external force acting on the robot 10 into information that can be processed by the robot control device 60, for example, by A / D conversion.

[0021] When the value acquired by the external force acquisition unit 63 is equal to or greater than the first threshold, the robot stopping unit 64 stops the operation of the robot 10. In other words, when the external force acting on the robot 10 is equal to or greater than the first threshold, the robot stopping unit 64 determines that the robot 10 may have come into contact with an unexpected person or object, and brings the robot 10 to an emergency stop for safety.

[0022] If the acquired value of the external force acquisition unit 63 is equal to or greater than the second threshold value at the start of welding, the wire stop unit 65 stops the feeding of the welding wire. In other words, if the external force acting on the robot 10 increases at the start of welding, the start of welding (establishment of an appropriate arc discharge) is likely to fail, and the wire stop unit 65 detects a reaction force caused by the welding wire W contacting the workpiece M without melting. Therefore, the wire stop unit 65 temporarily stops the feeding of the welding wire W to prevent a further increase in the reaction force. The "start of welding" at which the wire stop unit 65 performs the above control refers to the period from when the welding instructing unit 62 issues a command to start welding until it is determined that stable welding has started. For example, the start of welding can be, for example, the period from the start of welding or a command to retry (described later) until a predetermined waiting time has elapsed, or the period from when a command to start welding is issued until the establishment of a stable arc discharge is detected by some method. The movement of the welding torch 20 is usually started after that.

[0023] Because the wire stopping unit 65 uses a second threshold that is set independently of the first threshold used by the robot stopping unit 64, it can appropriately determine whether to start welding regardless of the operating state of the robot stopping unit 64. The second threshold used by the wire stopping unit 65 is preferably smaller than the first threshold used by the robot stopping unit 64. This allows for a new attempt to start welding without stopping the robot 10, even if an external force acts on the robot 10 due to a failed attempt to start welding.

[0024] The threshold adjustment unit 66 adjusts the value of the second threshold used by the wire stopping unit 65 according to one or more of the welding conditions and the state of the robot 10. The magnitude of the reaction force detected when the welding wire W contacts the workpiece M changes depending on the welding conditions and the state of the robot 10. Therefore, by having the threshold adjustment unit 66 adjust the value of the second threshold according to these conditions, the wire stopping unit 65 can more appropriately detect a failure to start welding.

[0025] More specifically, it is preferable that the threshold adjustment unit 66 adjusts the value of the second threshold in accordance with one or more of the feed rate, material, and diameter of the welding wire W, and the posture of the robot 10. The deformation of the welding wire W can dissipate or delay the force transmission between the workpiece M and the welding torch 20. Therefore, by having the threshold adjustment unit 66 adjust the value of the second threshold in accordance with the conditions of the welding wire W, the wire stop unit 65 can appropriately detect a failure to start welding. Furthermore, the posture of the robot 10 changes the distance from the position where the external force detection unit 12 detects force to the tip of the welding torch 20, thereby changing the detection sensitivity of the external force detection unit 12. Therefore, by having the threshold adjustment unit 66 increase or decrease the second threshold to compensate for this change in detection sensitivity, the wire stop unit 65 can appropriately detect a failure to start welding.

[0026] The restart control unit 67 executes a welding restart procedure to restart welding. The welding restart procedure executed by the restart control unit 67 may include a step of stopping the supply of welding current to the welding torch 20, a step of retracting the welding wire W, and a step of resuming the supply of welding current and the feeding of the welding wire W. In other words, the restart control unit 67 may be configured to instruct the welding power source 30 or the wire supply device 40 to retract and resume the feeding of the welding wire W when the wire stop unit 65 stops the feeding of the welding wire W. That is, the restart control unit 67 may execute an arc retry sequence in which the welding wire W is retracted to separate it from the workpiece M, thereby returning the positional relationship to an initial state, and the welding start procedure, which attempts to establish an arc discharge, is retried from the beginning. In this way, by reattempting welding start after a failed attempt, welding can be started properly without the user having to perform any additional operations.

[0027] The restart control unit 67 may operate the robot 10 to move the welding torch 20 along the workpiece M when the wire stopping unit 65 stops the feeding of the welding wire W. Specifically, the welding restart procedure may include a step of stopping the supply of welding current to the welding torch 20, a step of retracting the welding wire W, and a step of operating the robot 10 to resume the supply of welding current, the feeding of the welding wire W, and the reciprocating movement of the welding torch 20 along the workpiece M. That is, the restart control unit 67 may be configured to execute a scratch start sequence in which the welding wire W scrapes the surface of the workpiece M to remove an insulating coating or the like on the surface of the welding wire W or the workpiece M, or to induce an arc discharge by forming a minute gap due to, for example, minute irregularities on the surfaces of the welding wire W and the workpiece M, the elasticity of the welding wire W, or the like. In this way, even if an attempt to start welding fails, by attempting to start welding while moving the welding torch 20 along the workpiece M, welding can be started properly without the user having to perform another operation.

[0028] The restart control unit 67 may operate the robot 10 to reciprocate the welding torch 20 along the workpiece M without rewinding the welding wire W when the wire stop unit 65 stops the feeding of the welding wire W. In other words, the welding restart procedure may further include an operation of the robot 10 to reciprocate the welding torch 20 along the workpiece M after stopping the supply of welding current to the welding torch 20 and before retracting the welding wire W. In this way, by reciprocating the robot 10 with the welding wire W in contact with the workpiece M, an insulating coating or the like is removed from the surface of the welding wire W or the workpiece M, and then welding is restarted with the welding torch 20 accurately repositioned at the position where welding should start. This facilitates the start of welding and prevents deviation of the welding start position. The welding restart procedure after reciprocating the welding wire W in contact with the workpiece M may be performed while the welding torch 20 is moving or without moving the welding torch 20.

[0029] If the acquired value of the external force acquisition unit 63 becomes equal to or greater than the third threshold during the welding restart procedure, the restart control unit 67 may stop feeding the welding wire W and then execute the welding restart procedure from the beginning. By detecting contact of the welding wire W with the workpiece M at the start of welding using the third threshold, it is possible to more appropriately determine whether an arc discharge has been established. The third threshold may be equal to or greater than the second threshold. However, since the likelihood of the welding wire W contacting the workpiece M due to factors other than the success or failure of an arc discharge, such as the shape of the workpiece M, is lower at the start of welding than when welding is continuing, setting the third threshold to a value smaller than the second threshold allows for more rapid detection of a welding start failure. The restart control unit 67 may not set the third threshold, and may instead enable detection of contact of the welding wire W with the workpiece M using the second threshold during the welding restart procedure.

[0030] If welding cannot be restarted, that is, if contact of the welding wire W with the workpiece M is detected during the welding restart procedure, the restart control unit 67 may be configured to repeat the welding restart procedure a predetermined number of times or a number of times determined by predetermined conditions. The restart control unit 67 may be configured to perform multiple welding restart procedures in a predetermined order.

[0031] When the wire stopping unit 65 stops feeding of the welding wire, the notification unit 68 issues a notification to that effect. The content of the notification may be changed depending on the result of a retry of the welding start by the restart control unit 67. The provision of the notification unit 68 makes it possible to prompt the user to take action such as starting welding manually or optimizing parameters of the welding start procedure.

[0032] In the robot system 1 equipped with the robot control device 60 as described above, the wire stopping unit 65 detects contact of the welding wire W with the workpiece M, which is detected as an external force acting on the robot 10, by comparing it with a second threshold value, and prevents further increase in the external force by stopping the feed of the welding wire, thereby suppressing the impact of a failure to start welding on other controls based on the external force acting on the robot 10, such as the robot stopping unit 64.

[0033] Although the embodiments of the present disclosure have been described above, the present invention is not limited to the above-described embodiments. Furthermore, the effects described in the above-described embodiments are merely a list of preferred effects resulting from the present invention, and the effects of the present invention are not limited to those described in the above-described embodiments.

[0034] In the robot control device of the present invention, the first threshold value is not limited to being used to determine whether the robot should be stopped in an emergency by the robot stopping unit, but may also be used, for example, to determine whether or not to correct parameters for the robot's posture control.

[0035] In the robot control device according to the present invention, the threshold adjustment unit is optional. Also, in the robot control device according to the present invention, the restart control unit and the notification unit are also optional, and instead of these, components that perform other processes that can be employed as a response to a welding start failure may be provided.

[0036] According to the present disclosure, it is also possible to provide a robot control unit that does not include a robot stopping unit, but includes a wire stopping unit and a restart control unit. A robot control device according to another aspect of the present disclosure is a robot control device that controls a robot that welds workpieces using a welding torch that feeds out welding wire, and includes a welding instruction unit that instructs welding, an external force acquisition unit that acquires a value of an external force acting on the robot, a wire stopping unit that stops the feed of the welding wire when the acquired value from the external force acquisition unit is equal to or greater than a predetermined threshold (the second threshold in the above-described embodiment), and a restart control unit that executes a welding restart procedure for restarting welding when the wire stopping unit stops the feed of the welding wire, wherein the welding restart procedure includes a step of stopping the supply of welding current to the welding torch, a step of moving the welding torch back and forth along the workpieces, a step of pulling back the welding wire, and a step of resuming the supply of welding current and the feed of the welding wire.

[0037] In this way, by moving the welding torch back and forth along the workpiece without supplying welding current when it is thought that the welding wire will come into contact with the workpiece, it is possible to remove insulating coatings and the like from the surfaces of the welding wire and the workpiece, and then by retracting the welding wire and then resuming the supply of welding current and the supply of welding wire, it is more likely that an arc discharge will be established. In the welding restart procedure, the steps of stopping the supply of welding current to the welding torch, moving the welding torch back and forth along the workpiece, retracting the welding wire, and resuming the supply of welding current and the feed of welding wire may be performed immediately after the wire stopping unit stops the feed of the welding wire, or may be performed when an attempt is made to restart welding using a procedure that does not include these steps and it is determined that the welding wire has come into contact with the workpiece again, for example, when the acquired value from the external force acquisition unit in the above-described embodiment becomes equal to or greater than the third threshold.

[0038] REFERENCE SIGNS LIST 1 Robot system 10 Robot 11 Arm 12 External force detection unit 20 Welding torch 30 Welding power source 40 Wire supply device 50 Gas supply device 60 Robot control device 61 Robot control unit 62 Welding instruction unit 63 External force acquisition unit 64 Robot stopping unit 65 Wire stopping unit 66 Threshold adjustment unit 67 Restart control unit 68 Notification unit M Workpiece to be welded W Welding wire

Claims

1. A robot control device that controls a robot that welds a workpiece using a welding torch that delivers a welding wire, A welding instruction unit that instructs the welding; an external force acquisition unit that acquires a value of an external force acting on the robot; a robot stopping unit that stops an operation of the robot when the acquired value of the external force acquiring unit is equal to or greater than a first threshold value; a wire stop unit that stops feeding of the welding wire when the acquired value of the external force acquisition unit is equal to or greater than a second threshold value at the start of the welding; A robot control device comprising:

2. The robot control device according to claim 1 , wherein the second threshold value is smaller than the first threshold value.

3. The robot control device according to claim 1 , further comprising a threshold adjustment unit that adjusts a value of the second threshold in accordance with at least one of the welding conditions and a state of the robot.

4. The robot control device according to claim 3 , wherein the threshold adjustment unit adjusts the value of the second threshold depending on at least one of a feed speed, a material and a diameter of the welding wire, and an attitude of the robot.

5. The robot control device according to claim 1 or 2, further comprising a restart control unit that executes a welding restart procedure for restarting the welding when the wire stopping unit stops feeding of the welding wire.

6. The robot controller of claim 5 , wherein the welding restart procedure includes stopping the supply of welding current to the welding torch, retracting the welding wire, and resuming the supply of the welding current and the delivery of the welding wire.

7. 6. The robot control device according to claim 5, wherein the welding restart procedure includes stopping the supply of welding current to the welding torch, pulling back the welding wire, and restarting the supply of the welding current, resuming the feeding of the welding wire, and operating the robot to reciprocate the welding torch along the workpiece.

8. 8. The robot control device according to claim 7, wherein when the acquired value of the external force acquisition unit becomes equal to or greater than a third threshold during the welding restart procedure, the restart control unit stops feeding of the welding wire and then executes the welding restart procedure from the beginning.

9. The robot control device according to claim 6 , wherein the welding restart procedure further includes an operation of the robot that moves the welding torch back and forth along the workpiece after stopping the supply of welding current to the welding torch and before pulling back the welding wire.

10. The robot control device according to claim 1 , further comprising an alarm unit that issues an alarm when the wire stopping unit stops feeding of the welding wire.

11. The robot control device according to claim 1 or 2, a robot controlled by the robot control device to position the welding torch; A robot system comprising:

12. A welding torch held by the robot; a wire feeder for feeding the welding wire to the welding torch; a welding power source for supplying a welding current to the welding torch; The robotic system of claim 11 further comprising: