Collaborative robot system

Abstract

To provide a collaborative robot system that has a collision detection function and an escape mode function, and that ensures safety even in a state where external force cannot be accurately estimated.SOLUTION: A collaborative robot system 1 comprises a collaborative robot 2 and a control device 3. The collaborative robot 2 has a torque sensor 25 that measures the torque of a joint 24. The control device 3 determines, as external force torque, the difference between the measured torque measured by the torque sensor 25 and the estimated torque, which is calculated based on a mass point model including parameters of the mass and center of gravity of an arm 21 and a tool 23 of the collaborative robot 2 and a workpiece W, and performs control to stop the collaborative robot 2 in the case where the external force torque is equal to or greater than a first threshold value. After stopping the collaborative robot 2, in the case where the external force torque becomes equal to or greater than a second threshold value, the control device 3 performs control not to enable the escape mode that assists escape of a worker, if the external force torque is equal to or greater than a third threshold value, and to enable the escape mode if the external force torque is less than the third threshold value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a collaborative robot system with collision detection and escape mode capabilities. [Background technology]

[0002] Generally, a collaborative robot system is equipped with a collision detection function that safely stops the collaborative robot when it detects a collision between the collaborative robot and a worker, etc. One example of a collision detection function is a method that estimates the difference between the torque measured by a torque sensor and the torque calculated based on a mass point model that includes parameters for the mass and center of gravity of the arm and tool of the collaborative robot and the workpiece as an external force torque, and stops the collaborative robot if the external force torque is equal to or greater than a threshold value.

[0003] Furthermore, when a collaborative robot stops after detecting a collision, a worker may become trapped between the collaborative robot and a structure, becoming unable to move. To deal with such situations, an escape mode function that assists workers in escaping is known. Patent Document 1 discloses, as an example of the escape mode function, an escape mode function that allows a person to push the arms of a collaborative robot to retract the arms on each axis.

[0004] The aforementioned collision detection function and escape mode function are premised on accurate estimation of external forces. To accurately estimate external forces, sensor calibration and accurate input of settings for the robot's tool and workpiece are required after the robot is installed. Patent Document 2 discloses that a load check is performed each time the power is turned on to check whether the selected load setting matches the actual robot load. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7260727 [Patent Document 2] Patent No. 7288158 Summary of the Invention [Problem to be solved by the invention]

[0006] However, checking the load each time the power is turned on is time-consuming, and even if the load is checked, the external force cannot be accurately estimated if an input error in the setting value is overlooked or if there is an abnormality in the torque sensor measurement.

[0007] If the external force cannot be accurately estimated, the robot controller may mistakenly determine that the robot is being pushed by a person in the escape mode function and may erroneously control the robot's operation. In such cases, for example, the tool may drop the workpiece it is holding, or the arm may collide with a structure.

[0008] The present invention has been made in consideration of the above-mentioned circumstances, and its purpose is to ensure safety in a collaborative robot system equipped with a collision detection function and an escape mode function even in a state in which external forces cannot be accurately estimated. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, the present invention provides a collaborative robot system comprising a collaborative robot and a control device that controls the operation of the collaborative robot, wherein the collaborative robot is equipped with a torque sensor that measures the torque of a joint, and the control device defines an external force torque as the difference between the measured torque measured by the torque sensor and an estimated torque calculated based on a mass point model including parameters of the mass and center of gravity of the arm, tool, and workpiece of the collaborative robot, and controls the control device to stop the collaborative robot if the external force torque is equal to or greater than a first threshold, and after stopping the collaborative robot, if the external force torque becomes equal to or greater than a second threshold, and further if the external force torque is equal to or greater than a third threshold, does not enable an escape mode that assists a worker in escaping, and if the external force torque is less than the third threshold, controls to enable the escape mode.

[0010] The third threshold value may be a value based on the difference between the estimated torque calculated using the mass of the workpiece in the mass point model as the transportable weight of the collaborative robot and the estimated torque calculated using the mass of the workpiece in the mass point model as 0. [Effects of the Invention]

[0011] According to the present invention, in a collaborative robot system having a collision detection function and an escape mode function, safety can be ensured even in a state in which external forces cannot be accurately estimated. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating an outline of a collaborative robot system according to an embodiment of the present invention. [Figure 2] 1. A flowchart showing an example of a processing flow by the control device of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram illustrating an outline of a collaborative robot system according to an embodiment of the present invention. As shown in FIG. 1, the collaborative robot system 1 includes a collaborative robot 2 and a control device 3 that controls the operation of the collaborative robot 2. The collaborative robot 2 is a robot that can work in collaboration with a worker M in a defined collaborative workspace. The collaborative robot 2 and the worker M work together on a workpiece W placed on a table T, for example.

[0014] The collaborative robot 2 has an installation base 22 that supports an arm 21, and a tool 23 is attached to the tip of the arm 21. The arm 21 is configured with a link mechanism having multiple links, and has joints 24 that connect the links. Each joint 24 is provided with a drive motor (not shown) and a torque sensor 25 that measures the torque of the joint 24 of the collaborative robot 2. Although only one torque sensor 25 is shown in FIG. 1, multiple torque sensors 25 may be provided, and one may be provided for each of some or all of the joints 24. The torque sensors 25 are periodically inspected and calibrated after the collaborative robot 2 is installed.

[0015] An example of the collaborative robot 2 is a vertical articulated robot with six joints 24. However, the present invention is also applicable to robots with five or fewer or seven or more joints 24, horizontal articulated robots, etc. Furthermore, the collaborative robot 2 is not limited to a single-arm robot, and may also be a dual-arm robot.

[0016] The control device 3 may be built into the installation base 22 of the collaborative robot 2, or may be installed outside the collaborative robot 2. In the latter case, the collaborative robot 2 and the control device 3 are connected to each other so that they can communicate with each other via a communication cable or wirelessly.

[0017] The CPU (Central Processing Unit) 31, memory 32, auxiliary storage device 33, and input / output interface 34 of the control device 3 are connected via a bus 35. The CPU 31 reads a control program stored in advance in the auxiliary storage device 33 or the like into the memory 32 and sequentially executes a plurality of instructions. The auxiliary storage device 33 is a hard disk drive, a solid state drive, or the like, and stores data used in processing described below. The input / output interface 34 inputs and outputs signals from and to the collaborative robot 2, a teaching pendant (not shown), other devices, and the like.

[0018] The collaborative robot system 1 in this embodiment has a collision detection function that safely stops the collaborative robot 2 when it detects a collision between the collaborative robot 2 and a worker M or the like. The collaborative robot system 1 also has an escape mode function that assists the worker M in escaping when the collision detection function stops the collaborative robot 2 and the worker M becomes trapped between the collaborative robot 2 and a structure (such as a table T in FIG. 1 ). In the escape mode function in this embodiment, when the arm 21 of the collaborative robot 2 is pushed by an external force, the control device 3 controls the operation of the collaborative robot 2 so as to move the arm 21 in the pushed direction. The collision detection function and the escape mode function ensure safety by controlling the operation of the collaborative robot 2 based on processing by the control device 3, which will be described later.

[0019] Fig. 2 is a flowchart showing an example of the flow of processing by the control device of Fig. 1. As shown in Fig. 2, the control device 3 acquires a measured torque measured by the torque sensor 25 for each joint 24 at which the torque sensor 25 is provided (step S1). Next, the control device 3 calculates an estimated torque for each joint 24 at which the torque sensor 25 is provided based on a mass point model (step S2).

[0020] The estimated torque can be calculated using a model such as Equation 1 based on the Newton-Euler method. Estimated torque = f(d, m, x) (Equation 1) f: Drive torque calculation function using the Newton-Euler method, etc. d: Link parameters (DH parameters) m: Mass point model (mass and center of gravity of arm 21, tool 23, workpiece W, etc.) x: Position on each axis

[0021] The Newton-Euler method is a technique that treats the constraint forces and relative motion between links as vector quantities and derives equations of motion from the balance of forces and moments. Link parameters are parameters that determine the geometric positional relationship between the links of the arm 21 and the joints 24, and DH parameters using the Denavit-Hartenberg notation (DH method) are known. A mass point model is a simplified simulation of the robot's mechanism, in which mass points are set at each joint of the robot. The mass point model in this embodiment includes parameters for the mass and center of gravity of the arm 21, tool 23, and workpiece W of the collaborative robot 2. Of the parameters included in equation (1), the mass of the tool 23, workpiece W, etc. are input by the worker M and stored in the control device 3.

[0022] The control device 3 determines, for each joint 24 provided with a torque sensor 25, the difference between the measured torque measured by the torque sensor 25 and the estimated torque calculated based on the mass point model as the external force torque, and checks whether the external force torque is equal to or greater than a first threshold (step S3). The first threshold is a threshold for determining whether a collision has occurred between the collaborative robot 2 and an external object (such as the worker M or the table T). If the external force torque for at least one joint 24 is equal to or greater than the first threshold (Yes in step S3), the control device 3 performs control to stop the collaborative robot 2 (step S4). Alternatively, if the external force torque for all joints 24 is less than the first threshold (No in step S3), the control device 3 repeats the process from step S1.

[0023] After confirming that the collaborative robot 2 has stopped, the control device 3 acquires the measured torque measured by the torque sensor 25 for each joint 24 (step S5), similar to steps S1 and S2, and calculates an estimated torque based on the mass point model (step S6). Then, the control device 3 checks whether the external force torque is equal to or greater than a second threshold (step S7). The second threshold is a threshold for determining whether the arm 21 has been pushed aside by an external force, and is a value different from the first threshold. If the external force torque is equal to or greater than the second threshold (Yes in step S7), the control device 3 proceeds to threshold determination in step S7. Alternatively, if the external force torque is less than the second threshold (No in step S7), the control device 3 repeats from step S5.

[0024] The control device 3 checks whether the external force torque is equal to or greater than a third threshold (step S8). The third threshold is a threshold for determining whether the external force torque is an abnormal value, and is a value different from the first threshold and the second threshold. If the external force torque is equal to or greater than the third threshold (Yes in step S8), the control device 3 waits until a certain time has elapsed without enabling an escape mode that assists the worker M in escaping (step S9), and after the certain time has elapsed, the process repeats from step S5. During the standby period, the collaborative robot 2 is in a stopped state. Alternatively, if the external force torque is less than the third threshold (No in step S8), the control device 3 performs control to enable the escape mode and proceeds to escape mode processing (step S10).

[0025] Since the external force torque is the difference between the measured torque and the estimated torque, if there is an abnormality in the measurement by the torque sensor 25 or if there is an input error in the set values ​​for the mass of the tool 23 or the workpiece W, the control device 3 cannot accurately estimate the external force torque. Therefore, as in steps S8 to S10, if the external force torque has an abnormal value, the control device 3 does not activate the escape mode. This makes it possible to prevent the tool 23 from dropping the workpiece W or the arm 21 from colliding with a structure such as the table T.

[0026] For example, when the control device 3 determines that the external force torque is an abnormal value through the determination process in step S8, it may output an alarm sound or an alarm message to notify the worker M that the external force torque has been determined to be an abnormal value. This allows the worker M to take appropriate action during the fixed waiting time in step S9.

[0027] In the escape mode process of step S10, the control device 3 controls the operation of the collaborative robot 2 to move the arm 21 in the pushed direction. For example, the control device 3 may move the arm 21 a fixed distance in the pushed direction, or may move the arm 21 in the pushed direction only while it is being pushed.

[0028] While the escape mode is enabled, the control device 3 checks whether or not to disable the escape mode (step S11). If the escape mode is to be disabled (Yes in step S11), the control device 3 repeats the process from step S5, and if the escape mode is not to be disabled (No in step S11), the control device 3 continues the escape mode processing in step S10. The determination conditions for disabling the escape mode include, for example, whether a certain amount of time has elapsed since the start of the escape mode, or whether an interrupt notification to disable the escape mode has been received. For example, an interrupt notification is sent to the control device 3 when the worker M presses the escape mode end button on the teaching pendant.

[0029] Here, the thresholds of steps S3, S7, and S8 will be explained. The first threshold is a relatively small value for detecting an external force when a collision occurs. The second threshold is a value larger than the first threshold for detecting an external force when pushed by a person. The third threshold is a value larger than the second threshold for detecting an abnormal value of the external force. Therefore, the three thresholds can have a magnitude relationship of first threshold < second threshold < third threshold. However, in the embodiment of the present invention, the magnitude relationship of the three thresholds is not particularly limited.

[0030] The third threshold may be a value based on the transportable weight of the collaborative robot 2. For example, if the tool 23 is erroneously set to not grip the workpiece W when in fact the tool 23 grips the workpiece W, the control device 3 will erroneously estimate the external force torque by the mass of the workpiece W. Therefore, the third threshold may be a value based on the difference between the estimated torque calculated using the mass of the workpiece W in the mass point model as the transportable weight of the collaborative robot 2, and the estimated torque calculated using the mass of the workpiece W in the mass point model as 0. Here, the value based on the difference between the two estimated torques is not limited to the actual value of the difference between the two estimated torques, but also includes a value obtained by multiplying the value of the difference between the two estimated torques by a coefficient, a value obtained by adding or subtracting a constant from the value of the difference between the two estimated torques, etc.

[0031] Furthermore, since the third threshold is a threshold for detecting an abnormal value of the pushing force by a human, it may be a value based on the strength of a standard human force. Furthermore, the third threshold may be changeable by the worker M when installing the collaborative robot 2.

[0032] As described above, in the collaborative robot system 1 according to the embodiment of the present invention, when the external force torque has an abnormal value, the control device 3 does not activate the escape mode. This ensures safety even in a state where the external force cannot be accurately estimated.

[0033] While preferred embodiments of the collaborative robot system according to the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that those skilled in the art can conceive of various modifications and alterations within the scope of the technical ideas disclosed herein, and it is understood that such modifications and alterations also fall within the technical scope of the present invention. [Explanation of symbols]

[0034] 1. Collaborative robot system 2. Collaborative robot 3...Control device 21...Arm 23...Tools 24...Joint 25...Torque sensor W...Work

Claims

1. A collaborative robot system comprising a collaborative robot and a control device that controls an operation of the collaborative robot, the collaborative robot includes a torque sensor that measures torque at a joint; The control device a difference between a measured torque measured by the torque sensor and an estimated torque calculated based on a mass point model including parameters of mass and center of gravity of the arm, tool, and workpiece of the collaborative robot as an external force torque, and when the external force torque is equal to or greater than a first threshold value, control is performed to stop the collaborative robot; After the collaborative robot is stopped, if the external torque becomes equal to or greater than a second threshold, and if the external torque becomes equal to or greater than a third threshold, an escape mode for assisting the worker in escaping is not enabled, and if the external torque is less than the third threshold, the escape mode is enabled. A collaborative robot system characterized by:

2. The third threshold value is a value based on the difference between the estimated torque calculated using the mass of the workpiece in the mass point model as the transportable weight of the collaborative robot and the estimated torque calculated using the mass of the workpiece in the mass point model as 0. The collaborative robot system according to claim 1 .

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