robot

Abstract

To provide a robot that is capable of detecting, with a simple configuration and in short time, failure of a force sensor for detecting a load of a tool.SOLUTION: A robot 100 comprises: an arm 102; a force sensor 104 provided on the arm; a tool 106 attached to the arm via the force sensor; and a robot controller 108 for controlling operation of the arm. The robot controller acquires an output value of the force sensor, and also obtains a calculated value of inertial force applied to the force sensor from a total mass of the tool and the force sensor, and acceleration speed according to operation of the arm, in order to compare the output value to the calculated value. If a difference thereof exceeds a predetermined threshold, the robot controller detects failure of the force sensor.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a robot that detects a failure of a force sensor provided on an arm.

Background Art

[0002] As an example, in a production site such as a factory, a robot having an arm is used. The arm has an electric motor which is an actuator provided at each joint thereof. The electric motor is driven by a drive signal to realize a target operation of the arm. Further, a tool is attached to the tip of the arm. The tool is an end effector for performing operations such as polishing and chamfering of a workpiece, for example.

[0003] Conventionally, a force sensor for measuring the force applied to a tool (end effector) may be provided, and a configuration for detecting a failure (abnormality) of the force sensor is known. Patent Document 1 describes a robot. The robot includes a robot arm, an end effector having a gripping force sensor attached to the tip of the robot arm, a first member and a second member disposed between the base of the robot arm and the installation portion, and a first force sensor and a second force sensor that contact both the first member and the second member. In this robot, an abnormality of the first force sensor or the second force sensor is detected based on the difference between the output of the first force sensor and the output of the second force sensor.

[0004] Patent Document 2 describes a legged mobile robot. The legged mobile robot includes a base body, a plurality of legs connected to the base body, feet connected to the tips of the plurality of legs, and a force sensor. This force sensor is disposed between the foot and the leg and generates an output indicating the floor reaction force acting from the floor surface on which the foot is grounded.

[0005] In the legged mobile robot described in Patent Document 2, when the robot is started, the operation of the robot is controlled to perform a foot-tapping operation, it is determined whether or not the output of the force sensor during the foot-tapping operation is within a predetermined range, and an abnormality of the force sensor is detected based on the determination result. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-019067 [Patent Document 2] Japanese Patent Publication No. 2006-082201 [Overview of the project] [Problems that the invention aims to solve]

[0007] The robot described in Patent Document 1 detects abnormalities in a first force sensor or a second force sensor that contacts a first member and a second member positioned between the base of the robot arm and the part being installed. Therefore, this robot requires two sensors that detect exactly the same force.

[0008] The legged mobile robot described in Patent Document 2 detects failures in force sensors placed between the feet and legs. In this legged mobile robot, in order to detect the failure of the force sensors, it is necessary to perform work using the force sensors. If the force sensors are faulty, the reaction force from the floor cannot be detected properly, and there is a risk that the robot will tip over. Furthermore, it is necessary to perform a stepping motion, which is otherwise unnecessary, so extra time is required.

[0009] Furthermore, Patent Documents 1 and 2 do not consider the detection of failures in force sensors that detect the load on a tool. A force sensor that detects the load on a tool is a sensor used to control machining processes such as grinding and chamfering by applying load.

[0010] In view of these problems, the present invention aims to provide a robot that can detect a failure in a force sensor that detects the load on a tool with a simple configuration and in a short amount of time. [Means for solving the problem]

[0011] To solve the above problems, a typical configuration of the robot according to the present invention comprises an arm, a force sensor provided on the arm, a tool attached to the arm via the force sensor, and a control device for controlling the movement of the arm. The control device acquires the output value of the force sensor, calculates the inertial force acting on the force sensor from the total mass of the tool and the force sensor and the acceleration due to the movement of the arm, compares the output value with the calculated value, and detects a failure of the force sensor if the difference exceeds a predetermined threshold.

[0012] The control device described above should ideally perform a comparison between the output value and the calculated value before using the force sensor.

[0013] The control device described above should operate the arm with an acceleration that allows for the detection of the difference between the output value and the calculated value, and then compare the output value and the calculated value.

[0014] The control device described above should move the arm in all directions detectable by the force sensor and compare the output value with the calculated value. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a robot that can detect a failure in a force sensor that detects the load of a tool with a simple configuration and in a short amount of time. [Brief explanation of the drawing]

[0016] [Figure 1] This figure illustrates a robot in an embodiment of the present invention. [Figure 2] Figure 1 is a flowchart showing the operation of the robot. [Figure 3] This graph plots the acceleration of the arm shown in the flowchart in Figure 2 against the output value of the force sensor. [Modes for carrying out the invention]

[0017] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Dimensions, materials, and other specific numerical values shown in such embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In this specification and the drawings, elements having substantially the same functions and configurations are denoted by the same reference numerals to omit redundant descriptions, and elements not directly related to the present invention are not shown.

[0018] FIG. 1 is a diagram for explaining a robot 100 according to an embodiment of the present invention. The robot 100 is used, for example, at a production site such as a factory, and includes a robot arm (arm 102), a force sensor 104, a tool 106, and a robot controller 108.

[0019] The force sensor 104 is provided on the arm 102. As shown in the figure, the tool 106 is attached to the arm 102 via the force sensor 104 and is supported only by the force sensor 104. The tool 106 is, for example, an end effector that performs operations such as polishing or chamfering a predetermined workpiece.

[0020] The arm 102 is operationally controlled by the robot controller 108, and the tool 106 can be moved to a predetermined position by driving an electric motor (servo motor 110), which is an actuator provided at each joint of the arm 102.

[0021] In the robot 100, the tool 106 is supported only by the force sensor 104. Therefore, the force sensor 104 receives the load applied to the tool 106 generated as the arm 102 operates and detects this load. If it is not noticed that the force sensor 104 has failed and work is performed using the failed force sensor 104, the processing accuracy may decrease or the processing may fail, resulting in waste of the workpiece. Therefore, the information from the force sensor 104 is important for performing operations such as polishing or chamfering of the workpiece.

[0022] Therefore, the robot 100 focuses on the fact that the force sensor 104 outputs a value corresponding to the inertial force applied to the tool 106 and the force sensor 104 generated as the arm 102 operates, and adopts a configuration for detecting a failure of the force sensor 104. This will be specifically described below.

[0023] As shown in FIG. 1, the robot control device 108 includes a robot position / acceleration monitoring device 112, a force sensor monitoring device 114, and a force sensor failure determination device 116. The robot position / acceleration monitoring device 112 is connected to an encoder attached to the servo motor 110 and acquires information from the encoder. The force sensor monitoring device 114 is connected to the force sensor 104 and acquires information from the force sensor 104. The force sensor failure determination device 116 detects a failure of the force sensor 104 based on information from the robot position / acceleration monitoring device 112 and the force sensor monitoring device 114.

[0024] FIG. 2 is a flowchart showing the operation of the robot 100 in FIG. 1. The operation of the robot 100 shown in FIG. 2 is an operation for detecting a failure of the force sensor 104 and is executed at every fixed control cycle. This failure detection operation is performed, for example, before an operation using the force sensor 104, when the tool 106 is approaching the workpiece but has not yet contacted it, during a so-called air cut operation. In the air cut operation, the approaching operation to the workpiece is performed at high speed in order to shorten the tact time.

[0025] Also, as a condition for starting the failure detection operation, the operator may specify it in the teaching program, or the robot control device 108 may automatically execute it based on the acceleration of the robot 100, that is, the acceleration of the arm 102.

[0026] In robot 100, first, the robot position and acceleration monitoring device 112 of the robot control device 108 obtains the axis angle θ of the arm 102 from an encoder attached to the servo motor 110 (step S100). Next, the robot position and acceleration monitoring device 112 calculates the end-effector position of robot 100, i.e., the position r of the arm 102, based on the axis angle θ (step S102).

[0027] Furthermore, the robot position and acceleration monitoring device 112 reads the previous position r' of arm 102 stored in a suitable memory and calculates the velocity v of arm 102 based on the difference between this position and the current position r of arm 102 (step S104).

[0028] Next, the robot position and acceleration monitoring device 112 reads the previous velocity v' of arm 102 from an appropriate memory and calculates the acceleration a of arm 102 based on the difference between this and the current velocity v of arm 102 (step S106).

[0029] Next, the robot position and acceleration monitoring device 112 calculates the inertial force F based on the acceleration a of the arm 102, shown by the following equation (1), and the total mass M of the tool 106 and the force sensor 104 (step S108). The mass of the tool 106 and the mass of the force sensor 104 are measured in advance and stored in appropriate memory. In this way, step S108 mechanically calculates the inertial force F acting on the force sensor 104. F = Ma …Equation (1)

[0030] Here, the force sensor 104 outputs a value corresponding to the inertial force F acting on the tool 106 and the force sensor 104 as a result of the movement of the arm 102. The output value of the force sensor 104 is also input in real time to the force sensor monitoring device 114 of the robot control device 108. The force sensor monitoring device 114 then obtains the force sensor output value Fs at the moment the inertial force F is calculated in step S108 from the force sensor 104 (step S110).

[0031] Figure 3 is a graph plotting the acceleration a of arm 102 and the force sensor output value Fs, as shown in the flowchart of Figure 2. Figure 3(a) illustrates the X component of the acceleration a of arm 102 with respect to time. In this way, the robot 100 operates arm 102 with a constant control period, and the X component of acceleration a changes periodically.

[0032] Figure 3(b) illustrates the force sensor output value Fs as a function of time, output from the force sensor 104 in response to the movement of the arm 102 in Figure 3(a). As shown, the force sensor output value Fs changes in accordance with the X component of the acceleration a of the arm 102. However, since the force sensor output value Fs is a value based on the force sensor 104's own coordinate system, it cannot be directly compared with the inertial force F acting on the force sensor 104.

[0033] Therefore, as shown in Figure 2, the force sensor fault detection device 116 of the robot control device 108 calculates a force sensor output value Fr based on the robot coordinate system, using the force sensor output value Fs shown in equation (2) below, the axis angle θ of the arm 102, and the rotation matrix rRs that converts from the sensor coordinate system to the robot coordinate system, in order to unify the coordinate systems of both (step S112). Fr = rRs(θ)·Fs …Equation (2)

[0034] In this way, step S112 converts the force sensor output value Fs into a force sensor output value Fr based on the robot coordinate system. Note that the acceleration a of arm 102, the inertial force F acting on force sensor 104, and the force sensor output values ​​Fs and Fr are all three-dimensional vectors with (x, y, z) components in three-dimensional space.

[0035] Next, the force sensor failure determination device 116 compares the inertial force F applied to the force sensor 104, which was mechanically calculated in step S108, with the force sensor output value Fr based on the robot coordinate system, which was calculated in step S112, using the following equation (3), and determines whether the difference exceeds a predetermined threshold s (step S114). The threshold s is the threshold at which the force sensor 104 is judged to be faulty. |F-Fr|>s …Equation (3)

[0036] The force sensor failure detection device 116 then indicates that the force sensor 104 is faulty if the difference between the inertial force F and the force sensor output value Fr is greater than the threshold s (step S114, Yes), and terminates the failure detection operation if the difference between the two is less than or equal to the threshold s (step S114, No).

[0037] Therefore, according to the robot 100, the robot control device 108 can detect a failure of the force sensor 104, which detects the load on the tool 106, in a simple configuration and in a short time by comparing the force sensor output value Fr relative to the robot coordinate system with the inertial force F, which is a mechanically calculated value, applied to the force sensor 104.

[0038] Furthermore, the robot control device 108 compares the force sensor output value Fr, relative to the robot coordinate system, with the inertial force F applied to the force sensor 104, before the operation using the force sensor 104, i.e., during the air cut operation.

[0039] This allows the robot 100 to detect a malfunction in the force sensor 104 before performing any work using the force sensor 104. Therefore, it is possible to avoid situations where work is performed using a faulty force sensor 104, preventing workpiece waste. Furthermore, since there is no need to perform any actions different from normal operations to detect a malfunction in the force sensor 104, no extra time is required.

[0040] Furthermore, as shown in equation (1) above, the greater the acceleration a, the greater the inertial force F. Therefore, during the air-cut operation, which involves high-speed approach to the workpiece, the difference between the inertial force F acting on the force sensor 104 and the force sensor output value Fr relative to the robot coordinate system can be easily detected. As a result, the robot 100 can more accurately detect malfunctions of the force sensor 104.

[0041] If the difference between the inertial force F and the force sensor output value Fr is not sufficiently detectable (i.e., no significant difference is observed), the robot control device 108 may intentionally operate the arm 102 with an acceleration greater than the acceleration originally required in order to compare the inertial force F and the force sensor output value Fr. In this way, the inertial force F will increase, allowing for reliable detection of the difference between the two and enabling more accurate detection of a malfunction in the force sensor 104.

[0042] Furthermore, the robot control device 108 may move the arm 102 in all directions detectable by the force sensor 104 in order to compare the inertial force F with the force sensor output value Fr. In this way, even if there is an axis direction in which the arm 102 does not move according to the original motion program, a failure of the force sensor 104 along this axis direction can be detected.

[0043] Preferred embodiments of the present invention have been described above with reference to the attached drawings, but it goes without saying that the present invention is not limited to these examples. It will be obvious to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these will naturally also fall within the technical scope of the present invention. [Industrial applicability]

[0044] This invention can be used as a robot to detect failures in force sensors mounted on an arm. [Explanation of Symbols]

[0045] 100...Robot, 102...Arm, 104...Force sensor, 106...Tool, 108...Robot control device, 110...Servo motor, 112...Robot position / acceleration monitoring device, 114...Force sensor monitoring device, 116...Force sensor fault detection device

Claims

1. Arm and The arm is equipped with a force sensor, A tool is attached to the arm via the force sensor, The system includes a control device for controlling the movement of the arm, The control device acquires the output value of the force sensor, calculates the inertial force acting on the force sensor from the total mass of the tool and the force sensor and the acceleration due to the movement of the arm, compares the output value with the calculated value, and detects a malfunction of the force sensor if the difference exceeds a predetermined threshold. The control device is characterized by operating the arm with an acceleration capable of detecting the difference between the output value and the calculated value, and comparing the output value and the calculated value.

2. An arm and, The arm is equipped with a force sensor, A tool is attached to the arm via the force sensor, The system includes a control device for controlling the movement of the arm, The control device acquires the output value of the force sensor, calculates the inertial force acting on the force sensor from the total mass of the tool and the force sensor and the acceleration due to the movement of the arm, compares the output value with the calculated value, and detects a malfunction of the force sensor if the difference exceeds a predetermined threshold. The control device is a robot characterized by moving the arm in all directions detectable by the force sensor and comparing the output value with the calculated value.

3. The robot according to claim 1 or 2, characterized in that the control device compares the output value with the calculated value before performing work using the force sensor.

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