Computation apparatus for robot system

Abstract

A computation apparatus (1) is for simulating a robot system that comprises a robot having one or more joints and that has a stop function for stopping the robot such that a load acting on at least one of the joints and the end of a hand of the robot does not exceed an allowable value. The computation apparatus (1) for the robot system comprises at least one processor (4) and at least one memory (3). The memory (3) stores a mathematical model that represents the robot system and a prescribed threshold value corresponding to the allowable value. The processor (4) acquires input information on an external force received by the robot, estimates the load by simulation based on the input information and the mathematical model, and determines that the robot stops when the value based on the estimated load has exceeded the threshold value.　

Description

Robot system computing unit

[0001] The present disclosure relates to a computing device for a robot system.

[0002] A control unit is known that brings a robot working on a production line to an emergency stop in order to protect the robot and surrounding equipment when the robot collides with the surrounding equipment (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2015-217468

[0004] When a robot experiences an emergency stop, not only does it interrupt the ongoing work, but it also takes time to recover from the situation, resulting in a decline in productivity. Therefore, when introducing a robot with an emergency stop function, it is necessary to have the robot perform test operations in advance to check whether an emergency stop will occur, which requires a lot of man-hours and costs.

[0005] Therefore, when considering the introduction of a robot system equipped with a robot having an emergency stop function, it is desirable to be able to easily check the possibility of the robot making an emergency stop while working.

[0006] One aspect of the present disclosure is a computing device that performs a simulation of a robot system including a robot having one or more joints and a stopping function that stops the robot so that a load acting on a hand of the robot and at least one of the joints does not exceed an allowable value, the computing device including at least one processor and at least one memory, the memory storing a mathematical model representing the robot system and a predetermined threshold value corresponding to the allowable value, the processor acquiring input information regarding an external force received by the robot, estimating the load through a simulation based on the input information and the mathematical model, and determining that the robot will stop when a value based on the estimated load exceeds the threshold value.

[0007] FIG. 1 is a side view showing a robot system to which a computing device according to an embodiment of the present disclosure is applied. FIG. 2 is a perspective view showing a nut runner of the robot system of FIG. 1. FIG. 3 is a block diagram showing a computing device according to an embodiment of the present disclosure. FIG. 4 is a schematic diagram showing a dynamic model corresponding to the robot system of FIG. 1. FIG. 5 is a front view showing a display device of a computing device according to an embodiment of the present disclosure. FIG. 6 is a flowchart illustrating the operation of a computing device according to an embodiment of the present disclosure. FIG. 7 is a schematic diagram showing a dynamic model corresponding to another robot system to which a computing device according to an embodiment of the present disclosure is applied.

[0008] A computing device 1 that performs a simulation of a robot system according to an embodiment of the present disclosure will be described below with reference to the drawings. First, a robot system 10 that is the target of the simulation performed by the computing device 1 of this embodiment will be described.

[0009] The robot system 10 is, for example, a screw tightening system as shown in Fig. 1. The robot system 10 includes a robot 20 fixed to a horizontal floor surface F, a control device 30 that controls the operation of the robot 20, and a nut runner (tool, screw tightening device) 40 attached to the robot 20. The robot system 10 also includes a work object 50 that is fixed to the floor surface F and to which a screw 55 is fastened by the nut runner 40. That is, the robot system 10 is configured such that the robot 20, the nut runner 40, and the work object 50 form a closed loop with the screw 55 and the floor surface F interposed therebetween.

[0010] The robot 20 is, for example, a six-axis articulated robot, and is a collaborative robot that performs a predetermined task in collaboration with a worker. The robot 20 includes a base 21 installed on a floor F and a rotating body 22 supported relative to the base 21 so as to be rotatable about a vertical first axis J1. The robot 20 also includes a first arm 23 supported relative to the rotating body 22 so as to be rotatable about a horizontal second axis J2, and a second arm 24 supported relative to the tip of the first arm 23 so as to be rotatable about a horizontal third axis J3. The robot 20 also includes a three-axis wrist unit 25 supported at the tip of the second arm 24.

[0011] The wrist unit 25 includes a first wrist element 25a supported rotatably relative to the second arm 24 about a fourth axis J4 extending along a plane perpendicular to the third axis J3. The wrist unit 25 also includes a second wrist element 25b supported rotatably relative to the first wrist element 25a about a fifth axis J5 perpendicular to the fourth axis J4. The wrist unit 25 also includes a third wrist element 25c supported rotatably relative to the second wrist element 25b about a sixth axis J6 perpendicular to the fifth axis J5 and intersecting the fourth axis J4. In other words, the robot 20 includes six joints A1 to A6.

[0012] Each of the joints A1 to A6 is equipped with a motor (not shown) and a reducer that slows down the rotation of the motor. The rotation of each motor is slowed down by the corresponding reducer, amplifying the torque of each motor and driving the joints A1 to A6 to rotate with high torque. In addition, each of the joints A1 to A6 is equipped with a six-axis force sensor (not shown) that detects the force (load) acting on the joint axis.

[0013] The control device 30 includes one or more processors (not shown) including hardware. The control device 30 executes a pre-taught operation program to drive the motors attached to the joints A1 to A6 of the robot 20, thereby changing the posture of the robot 20 to a posture that allows it to perform a predetermined task.

[0014] The control device 30 also acquires the forces acting on each joint axis detected by the force sensors attached to the joints A1 to A6. The control device 30 then stops the motors of the joints A1 to A6 when there is a possibility that the forces detected by the force sensors will exceed the tolerances of the respective joints. That is, the control device 30 has a stopping function that stops the operation of the robot 20 to protect the robot 20 when an excessive load acts on any of the joints A1 to A6 as the robot 20 performs a predetermined task. The tolerances in this case are determined by the load-bearing capacity of the components that make up the respective joints A1 to A6, such as the motors, reducers, and bearings.

[0015] 1, the nut runner 40 includes a main body 41 fixed to the tip of the third wrist element 25c, and a socket 45 connected to the tip of the main body 41. As shown in Fig. 2, the main body 41 includes a motor 42, a drive shaft 43 rotated about an axis B by the motor 42, and a frame 44 surrounding the drive shaft 43. The frame 44 is fixed to the tip of the third wrist element 25c in an orientation in which the axis B is perpendicular to the sixth axis J6.

[0016] The socket 45 includes a housing 46 coaxially connected to the tip of the drive shaft 43. A tool S corresponding to a screw 55 to be fastened to the workpiece 50 is detachably fitted into a hole (not shown) provided at the tip of the housing 46 and having the axis B as its central axis. That is, when the motor 42 of the main body 41 is operated, the housing 46 and the tool S rotate integrally with the drive shaft 43 about the axis B.

[0017] The robot system 10 configured in this manner can rotate the joints A1 to A6 of the robot 20 by a predetermined angle to place the screw 55 attached to the tool S at a predetermined fastening position on the workpiece 50. Then, in this state, the motor 42 of the nut runner 40 is operated to rotate the tool S about the axis B, thereby fastening the screw 55 into the workpiece 50 with a predetermined fastening torque, i.e., performing a screw tightening operation.

[0018] Next, a description will be given of the arithmetic device 1 according to this embodiment. The arithmetic device 1 is, for example, an offline computer that simulates the operation of the robot system 10. As shown in Fig. 3 , the arithmetic device 1 includes an input device 2, at least one memory 3 such as a ROM or a RAM, at least one processor 4 such as a CPU, and a display device 5.

[0019] The input device 2 is configured, for example, by a keyboard, a touch panel, an operation panel, a serial interface such as USB, or a combination of these, and accepts input information from an operator. The input information includes information such as the posture of the robot 20 and the positions of the nut runner 40 and the workpiece 50. The input information also includes the magnitude and direction of the tightening torque generated by the nut runner 40.

[0020] The memory 3 stores a mathematical model corresponding to the robot system 10. The memory 3 also stores tolerances set for the joints A1 to A6 as thresholds for the loads acting on the joints A1 to A6.

[0021] The mathematical model is, for example, a plurality of state equations that represent a dynamic model corresponding to the robot system 10 as shown in Fig. 4. In this case, the dynamic model is such that six joints A1 to A6 of the robot 20 are each connected to a single rotational elastic element k J１ ~k J６ The nut runner 40 and the workpiece 50 are defined as follows: an input element M that generates a tightening torque, and three rotational elastic elements k １ ~k ３ and three linear elastic elements k ４ ~k ６ That is, this dynamic model is divided into a robot domain T1 corresponding to the robot 20 and a nut runner domain T2 corresponding to the nut runner 40 and the workpiece 50.

[0022] By solving the mathematical model derived based on the dynamic model configured in this way, the reaction force of the tightening torque of the nut runner 40, i.e., the force (external force) and moment (external force) acting on the hand of the robot 20, are calculated. J１ ~k J６ By calculating the force balance equations of each link connecting the joints A1 to A6 in order from the hand end, the loads acting on the joints A1 to A6 can be determined.

[0023] The processor 4 retrieves the mathematical model from the memory 3 and performs calculations on the retrieved mathematical model based on input information input by operating the input device 2. In other words, the processor 4 executes a simulation of the operation of the robot system 10 using the mathematical model derived from the dynamic model corresponding to the robot system 10. In this way, the processor 4 calculates the loads acting on the joints A1 to A6 when the robot system 10 is made to perform a predetermined task.

[0024] The processor 4 also retrieves the thresholds corresponding to the joints A1 to A6 stored in the memory 3 and compares them with the loads acting on the joints A1 to A6 calculated by the simulation. If at least one of the calculated loads acting on the joints A1 to A6 exceeds the corresponding threshold, the processor 4 determines that the robot 20 should be stopped by the stop function of the control device 30. The result of this determination is then sent to the display device 5, along with the calculated ratios of the loads acting on the joints A1 to A6 to the thresholds.

[0025] The display device 5 is an output device such as a monitor. As shown in Fig. 5, the display device 5 displays the ratios of the loads acting on the joints A1 to A6 to the threshold values ​​sent from the processor 4, corresponding to the joints A1 to A6. The display device 5 also displays the results of the judgment sent from the processor 4, i.e., whether or not a load exceeding the threshold value is acting on the joints A1 to A6 of the robot 20 during work, causing the operation of the robot 20 to stop.

[0026] For example, when the display device 5 receives from the processor 4 a determination result that there is one or more joints on which a load exceeding a threshold acts, the display device 5 displays the ratio of that joint in a different color from the display colors of the other ratios, as shown in Fig. 5. In addition, the display device 5 displays a text message indicating that the operation of the robot 20 will be stopped by the stop function of the control device 30.

[0027] The operation of the computing device 1 according to this embodiment configured as described above will be described below with reference to the flowchart shown in Fig. 6. This will be described by taking as an example a method for checking whether a stop function for stopping the robot 20 is activated by the reaction force of the tightening torque when a screw is tightened in a robot system 10 that performs screw tightening work as shown in Fig. 1.

[0028] First, the operator operates the input device 2 to input input information for the robot system 10 (step S1). As a result, the processor 4 acquires the posture of the robot 20 during the screw tightening operation, i.e., the angles of the joints A1 to A6, the positions of the nut runner 40 and the workpiece 50, and the magnitude and direction of the tightening torque of the nut runner 40.

[0029] Next, the processor 4 retrieves the mathematical model from the memory 3 and calculates the rotational elastic element k based on the input information. J１ ~k J６ and the rotational elastic element k １ ~k ３ , linear elastic element k ４ ~k ６ and input element M. Then, processor 4 solves the mathematical model in which these elements are set to determine the load acting on the hand of robot 20, i.e., the external force input from nut runner area T2 to robot area T1 (step S2). Furthermore, processor 4 calculates the magnitude of each load acting on joints A1 to A6 by solving a force balance equation using the calculated load acting on the hand of robot 20 in order from the joint on the tip side (step S3).

[0030] The processor 4 then compares the calculated loads acting on the joints A1 to A6 with the thresholds corresponding to the joints A1 to A6 stored in the memory 3 (step S4). The processor 4 then determines whether the calculated loads acting on the joints A1 to A6 exceed the allowable values ​​of the respective joints. Based on the determination result, the processor 4 then transmits to the display device 5 a signal indicating whether any joint is subjected to a load exceeding the threshold, and the ratio of each load acting on the joints A1 to A6 to its threshold.

[0031] Next, the display device 5 displays each ratio received from the processor 4 in the form of a percentage, and also displays a text sentence indicating whether or not the movement of the robot 20 will be stopped based on the signal received from the processor 4. In other words, if the processor 4 determines, as a result of the simulation, that there is one or more joints on which a load exceeding the threshold acts, the display device 5 displays the ratios exceeding 100% in a different color from the display colors of the other ratios. The display device 5 also displays a text sentence indicating that the movement of the robot 20 will be stopped (step S5).

[0032] This allows the operator to understand that when the robot system 10 performs screw tightening work, a load exceeding the allowable value will be applied to at least one of the joints A1 to A6, which may cause the operation of the robot 20 to stop.

[0033] On the other hand, if the processor 4 determines, as a result of the simulation, that there is no joint on which a load exceeding the threshold acts, all of the ratios displayed on the display device 5 are displayed in the same color. Also, a text message indicating that the operation of the robot 20 will not stop is displayed. This allows the operator to confirm that there is no risk of the operation of the robot 20 stopping even if the robot system 10 performs the planned screw tightening task.

[0034] As a result, an operator considering introducing a robot system 10 equipped with a stopping function for protecting the robot 20 can check whether the robot 20 will stop during work without actually operating the robot 20. This reduces the man-hours and costs required to consider introducing a robot system 10 equipped with a stopping function.

[0035] In this embodiment, the processor 4 determines whether or not the stopping function of the robot system 10 is activated based on the six loads acting on the joints A1 to A6. Alternatively, the processor 4 may determine whether or not the stopping function is activated based on the load acting on the hand of the robot 20 and at least one of the joints A1 to A6. For example, when the robot 20 is to perform a task that places a load only on a specific joint, the processor 4 may calculate only the load acting on that joint and determine whether or not the stopping function is activated based on the calculated load. This reduces the amount of calculation required for the simulation and the calculation load on the processor 4.

[0036] In addition, in this embodiment, the processor 4 simulates a case where a load acts on the joints A1 to A6 due to a reaction force of the fastening torque of the nut runner 40. Alternatively, the processor 4 may simulate a case where a load acts on the joints A1 to A6 due to the robot 20 or the nut runner 40 coming into contact with an external object or a person.

[0037] In this case, the processor 4 omits the input element M of the dynamic model shown in Fig. 4 and solves a mathematical model derived from the dynamic model in which external force elements corresponding to the magnitude and direction of the expected contact force are added to the expected contact position. This allows the operator to confirm whether the robot 20 will stop appropriately if the robot 20 or the nut runner 40 comes into contact with a cooperating worker or a peripheral device. This allows the operator to easily perform a preliminary risk assessment before introducing the robot system 10.

[0038] Furthermore, in the present embodiment, the arithmetic device 1 is applied to a robot system 10 including a robot 20, a control device 30, a nut runner 40, and a workpiece 50. Alternatively, the arithmetic device 1 may be applied to a robot system 10 that does not include the nut runner 40 and the workpiece 50. In this case, the processor 4 may calculate a mathematical model derived based on a dynamic model in which only the robot region T1 is defined, as shown in FIG.

[0039] In the present embodiment, the processor 4 determines whether or not the stopping function is activated based on the loads acting on the joints A1 to A6 calculated by simulation. Alternatively, the processor 4 may determine whether or not the stopping function is activated based on values ​​obtained by multiplying the loads acting on the joints A1 to A6 calculated by simulation by a predetermined coefficient.

[0040] For example, the processor 4 calculates values ​​by multiplying each load acting on the joints A1 to A6 calculated by simulation by a coefficient greater than 1, and compares these values ​​with the corresponding threshold values. This makes it possible to determine whether the stopping function operates with a margin for each tolerance of the joints A1 to A6. Furthermore, by multiplying only the load acting on a specific joint by a coefficient greater than 1, it is possible to increase the sensitivity of the determination of the stopping function for only that joint.

[0041] In addition, in this embodiment, the processor 4 may compare each load acting on the joints A1 to A6 calculated by simulation with a value obtained by multiplying each threshold value of the joints A1 to A6 by a coefficient smaller than 1.

[0042] In this embodiment, the thresholds for the joints A1 to A6 may be divided into multiple levels. For example, the threshold set for the joint A6 may be divided into three levels within a range that does not exceed the allowable value for the load on the joint A6. In this case, the processor 4 compares the load acting on the joint A6 calculated by simulation with all of the thresholds at the three levels and determines whether the stopping function is activated for each threshold.

[0043] This allows the operator to easily understand how much margin there is in the magnitude of the load acting on joint A6 compared to the allowable value. The same applies to the other joints. Therefore, during setup work when introducing the robot system 10, the threshold values ​​for the loads of the joints A1 to A6 used in the stopping function can be adjusted to optimal values ​​depending on the application or environment of the robot system 10.

[0044] In addition, in this embodiment, if the processor 4 determines that there is one or more joints on which a load exceeding a threshold acts, it may search for a posture or movement speed of the robot 20 that reduces the load acting on those joints.

[0045] For example, the processor 4 modifies each parameter of the mathematical model and performs a simulation corresponding to the posture of the robot 20 in which the angles of the joints A1 to A6 are slightly rotated while maintaining the position of the nut runner 40. The processor 4 then compares each of the calculated loads acting on the joints A1 to A6 with the corresponding threshold values. By repeating this operation, it is possible to search for the posture of the robot 20 in which the ratio of each of the loads acting on the joints A1 to A6 to the threshold value is minimized.

[0046] This allows the operator to easily review the posture of the robot 20 during screw tightening work based on the search results of the computing device 1. Similarly, when the processor 4 searches for the operating speed of the robot 20 that minimizes the ratio of each load acting on the joints A1 to A6 to the threshold value, it can do so by repeating simulations with slight modifications to each parameter of the mathematical model.

[0047] Furthermore, in this embodiment, when the processor 4 determines that there is one or more joints on which a load exceeding a threshold acts, it may search for an attachment position or attachment orientation of the nut runner 40 that reduces the load acting on those joints. In this case, as in the case of searching for the orientation or operating speed of the robot 20 described above, the processor 4 may simply repeat the calculation of the mathematical model that corresponds to a slight change in the attachment position or attachment orientation of the nut runner 40.

[0048] Furthermore, in this embodiment, the display device 5 displays the determination result of whether the stopping function of the robot 20 is activated in the form of a text sentence, but the display of the determination result is not limited to this.

[0049] Furthermore, in this embodiment, the arithmetic device 1 is an offline computer, but instead, the arithmetic device 1 may be configured integrally with the control device 30 that controls the robot system 10 .

[0050] Furthermore, in this embodiment, the robot 20 included in the robot system 10 to which the arithmetic device 1 is applied is a collaborative robot, but the robot 20 may be any other industrial robot.

[0051] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible to these embodiments without departing from the gist of the invention or the concept and spirit of the present invention derived from the content of the claims and their equivalents. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as examples and are not limited to these.

[0052] The following supplementary notes are further disclosed regarding the above-described embodiments and modified examples. (Supplementary Note 1) A computing device for simulating a robot system including a robot having one or more joints and a stopping function for stopping the robot so that a load acting on a hand of the robot and at least one of the joints does not exceed an allowable value, the computing device for the robot system including at least one processor and at least one memory, the memory storing a mathematical model representing the robot system and a predetermined threshold value corresponding to the allowable value, the processor acquiring input information regarding an external force received by the robot, estimating the load through a simulation based on the input information and the mathematical model, and determining that the robot will stop when a value based on the estimated load exceeds the threshold. (Supplementary Note 2) The computing device for the robot system according to Supplementary Note 1, wherein the robot is a collaborative robot that shares one or more tasks with a worker. (Supplementary Note 3) The computing device for the robot system according to Supplementary Note 2, wherein the external force is a contact force caused by contact between the robot and the worker. (Supplementary Note 4) The arithmetic device for a robot system according to Supplementary Note 1 or Supplementary Note 2, wherein the external force is a contact force due to contact between the robot and an external object. (Supplementary Note 5) The arithmetic device for a robot system according to Supplementary Note 1 or Supplementary Note 2, wherein the robot system includes a tool attached to the hand of the robot and performs a predetermined task on a work object, and the external force is at least one reaction force to a force and torque generated by one of the tool and the work object on the other. (Supplementary Note 6) The arithmetic device for a robot system according to Supplementary Note 5, wherein the tool is a screw fastening device that fastens a screw into a screw hole formed in the work object, and the external force is a reaction force to a torque generated by the screw fastening device. (Supplementary Note 7) The arithmetic device for a robot system according to any of Supplementary Note 1 to Supplementary Note 6, wherein the threshold is set in a plurality of stages. (Supplementary Note 8) The arithmetic device for a robot system according to any of Supplementary Note 1 to Supplementary Note 7 ... processor searches for a posture or operating speed of the robot that reduces the load estimated by the simulation.(Supplementary Note 9) The arithmetic device of the robot system according to Supplementary Note 5 or Supplementary Note 6, wherein the processor searches for an attachment position or attachment posture of the tool that reduces the load estimated by the simulation. (Supplementary Note 10) The arithmetic device of the robot system according to any one of Supplementary Notes 1 to 9, further comprising a display device that displays a ratio of a value based on the load estimated by the processor to the threshold value.

[0053] DESCRIPTION OF SYMBOLS 1 arithmetic unit 3 memory 4 processor 5 display device 10 robot system 20 robot 40 nut runner (tool, screw tightening device) 50 work object 55 screw A1 to A6 joint

Claims

1. An arithmetic unit that performs simulation of a robot system including a robot having one or more joints, the arithmetic unit having a stop function for stopping the robot so that a load acting on at least one of the end effector of the robot and the joints does not exceed an allowable value, the arithmetic unit comprising at least one processor and at least one memory, the memory storing a mathematical model representing the robot system and a predetermined threshold corresponding to the allowable value, the processor obtaining input information regarding an external force received by the robot, estimating the load by simulation based on the input information and the mathematical model, and determining that the robot stops when a value based on the estimated load exceeds the threshold.

2. The arithmetic unit of the robot system according to claim 1, wherein the robot is a collaborative robot that shares one or more operations with an operator.

3. The arithmetic unit of the robot system according to claim 2, wherein the external force is a contact force due to contact between the robot and the operator.

4. The arithmetic unit of the robot system according to claim 1 or claim 2, wherein the external force is a contact force due to contact between the robot and an external object.

5. The robot system includes a tool attached to the end effector of the robot for performing a predetermined operation on a work object, and the external force is at least one reaction force of a force and a torque generated by one of the tool and the work object with respect to the other. The arithmetic unit of the robot system according to claim 1 or claim 2.

6. The tool is a screw tightening device for tightening a screw into a screw hole formed in the work object, and the external force is a reaction force of the torque generated by the screw tightening device. The arithmetic unit of the robot system according to claim 5.

7. The arithmetic unit of the robot system according to any one of claims 1 to 6, wherein the threshold is set in multiple stages.

8. The arithmetic unit of the robot system according to any one of claims 1 to 7, wherein the processor searches for a posture or an operating speed of the robot that reduces the load estimated by the simulation.

9. The arithmetic unit of the robot system according to claim 5 or claim 6, wherein the processor searches for an attachment position or an attachment posture of the tool that reduces the load estimated by the simulation.

10. The arithmetic unit of the robot system according to any one of claims 1 to 9, further comprising a display device that displays a ratio of a value based on the load estimated by the processor to the threshold value.

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