Robot control device

Abstract

A robot control device (1) controls a robot on which a sensor capable of measuring a force is mounted, and the robot control device (1) includes: a measurement value acquisition section (2) that acquires a first measurement value measured by the sensor when a first tool having a known mass and a center-of-gravity position is arranged at a front end of a wrist of the robot and the wrist is caused to perform a specific motion, and a second measurement value measured by the sensor when a second tool having a known mass and a center-of-gravity position is arranged and the wrist is caused to perform a specific motion; a measurement value storage section (3) that stores the first measurement value and the second measurement value acquired by the measurement value acquisition section (2); and a correction section (4) that, when a tool having an unknown mass is arranged, corrects a measurement value measured by the sensor on the basis of the first measurement value and the second measurement value stored in the measurement value storage section (3).

Description

Technical Field

[0001] This invention relates to robot control devices. Background Technology

[0002] It is known that in robots equipped with force sensors, the robot is controlled based on the force and torque detected by the force sensors (for example, see Patent Document 1).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2014-14902 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] The force and torque detected by the force sensor are affected by factors such as the rigidity of the tool (e.g., the hand attached to the robot's wrist) and the weight of the workpiece being manipulated, as well as the tool's orientation. Therefore, the sensor output cannot be calibrated at the factory considering the rigidity of the user-attached tool. It is desirable that users be able to easily calibrate the sensor output in the field.

[0008] Solution for solving the problem

[0009] One aspect of the present invention is a robot control device for controlling a robot equipped with a force-measuring sensor. The robot control device includes: a measurement value acquisition unit that acquires a first measurement value measured by the sensor when a first tool with a known mass and center of gravity is positioned at the front end of the robot's wrist and the wrist performs a specific action; and a second measurement value measured by the sensor when a second tool with a known mass and center of gravity is positioned and the wrist performs the specific action; a measurement value storage unit that stores the first measurement value and the second measurement value acquired by the measurement value acquisition unit; and a correction unit that, when a tool of unknown mass is positioned, corrects the measurement value measured by the sensor based on the first measurement value and the second measurement value stored in the measurement value storage unit. Attached Figure Description

[0010] Figure 1 This is an overall structural diagram of a robot system equipped with a robot control device according to one embodiment of the present invention.

[0011] Figure 2 This is an explanation of the reason. Figure 1 A diagram showing the robot's wrist movements, performed by the robot's control unit to correct the force sensor readings.

[0012] Figure 3 It means Figure 1 A block diagram of the robot control device. Detailed Implementation

[0013] Hereinafter, a robot control device 1 according to one embodiment of the present invention will be described with reference to the accompanying drawings.

[0014] like Figure 1 As shown, the robot system 100 includes: a robot 50, which is equipped with a force sensor (sensor) 51; and a robot control device 1 according to this embodiment.

[0015] Force sensor 51 is, for example, a six-axis sensor capable of detecting the magnitude of forces acting along three mutually orthogonal axes and the magnitude of torques acting around the three axes.

[0016] For example, such as Figure 1 As shown, the force sensor 51 is fixed between the flange 53 at the front end of the wrist 52 of the robot 50 and the tool 200 installed at the front end of the wrist 52.

[0017] Tool 200 is, for example, a hand with two or more fingers that can open and close and is able to hold the workpiece W between the fingers.

[0018] The hand 200 has a known mass and center of gravity position, and the mass and center of gravity position do not change significantly due to the opening and closing of the fingers 210, but the mass and center of gravity position of the workpiece W change by holding the workpiece W between the fingers 210.

[0019] like Figure 1 as well as Figure 2 As shown, the wrist 52 of the robot 50 is a three-axis wrist unit comprising a first wrist element 52a, a second wrist element 52b, and a third wrist element 52c. The first wrist element 52a is supported at the front end of the arm 54 in a manner that allows it to rotate about a first axis A, which is the major axis of the arm 54. The second wrist element 52b is supported on the first wrist element 52a in a manner that allows it to rotate about a second axis B, which is orthogonal to the first axis A. The third wrist element 52c has a flange 53 that is supported on the second wrist element 52b in a manner that allows it to rotate about a third axis C, which is orthogonal to the second axis B and intersects the first axis A.

[0020] The robot control device 1 of this embodiment includes at least one processor and a memory. The memory stores an action program that is executed when acquiring data for correcting the force sensor 51. For example... Figure 3As shown, the robot control device 1 includes: a measurement value acquisition unit 2, which acquires the force measurement value measured by the force sensor 51 during a specific action performed by the robot 50 according to an action program stored in a memory; and a storage unit (measurement value storage unit) 3, which stores the acquired force.

[0021] Furthermore, the robot control device 1 includes a correction unit 4, which corrects the force sensor 51's measurement value when a workpiece W of unknown mass is held by the hand 200 based on the force measurement value stored in the storage unit 3, and calculates the mass of the workpiece W. The robot control device 1 also includes a control unit 5, which controls the robot 50 based on the mass of the workpiece W calculated by the correction unit 4.

[0022] The specific action is as follows: for example, taking a state where the third axis C is oriented vertically downward as a reference, the second wrist element 52b is rotated about the second axis (axis) B, which is arranged approximately horizontally. With the flange 53 of the third wrist element 52c set at a predetermined angle β about the third axis C, the measurement value acquisition unit 2 acquires the force measured by the force sensor 51 at predetermined angular intervals, such as 5° intervals, of the tilt angle θ about the second axis B, during the specific action of the second wrist element 52b. Furthermore, the specific action is repeated each time the angle β of the third wrist element 52c about the third axis C changes at predetermined angular intervals, such as 5° intervals.

[0023] In this embodiment, the user, with a known workpiece W prepared and holding the workpiece W in hand 200, repeats the same specific actions as when the workpiece W is not being held. Preferably, the workpiece W prepared has a mass greater than the mass of the workpiece W manipulated in actual operation.

[0024] When the workpiece W is being held and when the workpiece W is not being held, the center of gravity position of the hand 200 containing the workpiece W changes. That is, the measurement value acquisition unit 2 acquires: the measurement value of the force sensor 51 when the workpiece W is not being held and the hand (first tool) 200 is positioned at the first center of gravity position (first measurement value), and the measurement value of the force sensor 51 when the workpiece W of known mass is being held and the hand (second tool) 200 is positioned at the second center of gravity position (second measurement value). Moreover, the acquired first measurement value and second measurement value are stored in the storage unit 3 corresponding to the same posture of the wrist 52.

[0025] The details are as follows.

[0026] With a workpiece W of known weight Ga being held (Ga = 0 when workpiece W is not held), the measured value Fa, measured by force sensor 51, is obtained at an inclination angle θ = θ1 around the second axis B and rotation angles β = β1 and β2 around the third axis C. 11 Fa 12 Furthermore, while holding a workpiece W with a known weight Ga, the measured value Fa obtained by the force sensor 51 is acquired under the conditions of an inclination angle θ = θ2 about the second axis B and rotation angles β = β1 and β2 about the third axis C. 21 Fa 22 . β2=β1+5°, θ2=θ1+5°.

[0027] Then, while holding a workpiece W with a known mass Gb, the measured value Fb, measured by the force sensor 51, is obtained under the conditions of an inclination angle θ = θ1 around the second axis B and rotation angles β = β1 and β2 around the third axis C. 11 、Fb 12 Furthermore, while holding a workpiece W with a known mass Gb, the measured value Fb, obtained by the force sensor 51, is acquired under the conditions of an inclination angle θ = θ2 around the second axis B and rotation angles β = β1 and β2 around the third axis C. 21 、Fb 22 .

[0028] The obtained measurement value F corresponds to the weight G of the workpiece W, the angle θ around the second axis B, and the rotation angle β around the third axis C.

[0029] (Ga, θ1, β1, Fa) 11 ),

[0030] (Ga, θ1, β2, Fa) 12 ),

[0031] (Ga, θ2, β1, Fa) 21 ),

[0032] (Ga, θ2, B2, Fa) 22 ),

[0033] (Gb, θ1, β1, Fb) 11 ),

[0034] (Gb, θ1, β2, Fb) 12 ),

[0035] (Gb, θ2, β1, Fb) 21 ),

[0036] (Gb, θ2, β2, Fb) 22 ),

[0037] …stored in storage section 3.

[0038] In this state, when the user manipulates a workpiece W with an unknown mass Gc using the same hand 200, the correction unit 4 corrects the measured value of the force sensor 51 in the following manner, and the mass Gc is calculated.

[0039] That is, when the tilt angle θ = θ3 (θ1 ≤ θ3 < θ2) around the second axis B and the rotation angle β = β3 (β1 ≤ β3 < β2) around the third axis C, and the measured value measured by the force sensor 51 is Fc, the correction unit 4 outputs the mass Gc that corrects the output value Fc of the force sensor 51 according to the following formula (1).

[0040] Number 1

[0041] Gc=Ga+(Gb-Ga)(Fc-Fa) / (Fb-Fa) (1)

[0042] in,

[0043] Number 2

[0044] Fa={Fa1(θ2-θ3)+Fa2(θ3-θ1)} / (θ2-θ1) (2)

[0045] Number 3

[0046] Fb={Fb1(θ2-θ3)+Fb2(θ3-θ1)} / (θ2-θ1) (3)

[0047] Number 4

[0048] Fa1={Fa 11 (β2-β3)+Fa 12 (β3-β1)} / (β2-β1) (4)

[0049] Number 5

[0050] Fa2={Fa 21 (β2-β3)+Fa 22 (β3-β1)} / (β2-β1) (5)

[0051] Number 6

[0052] Fb1={Fb 11 (β2-β3)+Fb 12 (β3-β1)} / (β2-β1) (6)

[0053] Number 7

[0054] Fb2={Fb 21(β2-β3)+Fb 22 (β3-β1)} / (β2-β1) (7).

[0055] If the mass Gc of the unknown workpiece W is determined, then based on the information of the mass Gc and center of gravity of workpiece W, as well as the known mass and center of gravity of hand 200, the mass and center of gravity of hand 200 containing workpiece W can be calculated.

[0056] Thus, according to the robot control device 1 of this embodiment, in two states—where the user mounts the tool 200 to the robot 50 and changes the center of gravity of the tool 200—the user can cause the robot 50 to perform specific actions to acquire and store the measured values ​​measured by the force sensor 51. Therefore, when the user uses the tool 200 at an unknown center of gravity position, even if the measured value of the force sensor 51 is affected by the rigidity of the tool 200, the user can correct the measured value of the force sensor 51 based on the stored measured values ​​and calculate a more realistic center of gravity position for the tool 200.

[0057] For example, the tool is a hand 200, and even if the mass of the workpiece W held by the hand 200 is unknown during actual operation, the unknown mass can be determined with high precision by obtaining the measured value measured by the force sensor 51 using a workpiece W with a known weight before the operation. This provides advantages such as: for example, in the positioning action of the hand 200, the deflection of the robot 50 based on the determined weight of the workpiece W can be corrected with high precision, and the hand 200 can be positioned with high precision.

[0058] In particular, by utilizing the state of holding a workpiece W with a known mass and the state of not holding the workpiece W, two states that change the center of gravity of the hand 200 can be achieved, thus requiring only a single workpiece w with a known mass to be prepared. Furthermore, the mass difference between the two states of the workpiece W can be easily and significantly ensured.

[0059] Furthermore, in this embodiment, the magnitude of the tilt angle θ around the second axis B and the magnitude of the rotation angle β around the third axis C are set to 5°. However, they can also be set to any angle magnitude. By setting them to smaller magnitudes, the accuracy of the correction is improved. However, since the amount of data acquired by the user beforehand is increased, it is not necessary to set them smaller than necessary.

[0060] In addition, in this embodiment, if the ambient temperature changes during the user's actual operation, the output change of the force sensor 51 caused by the change in ambient temperature can also be corrected.

[0061] In this case, for example, the same measurement as described above is performed at an ambient temperature T = T1. Alternatively, for example, at an ambient temperature T = T2, a workpiece W having a known weight Ga is held, and the measured value Fc, measured by the force sensor 51, is obtained at an inclination angle θ = θ1 about the second axis B and a rotation angle β = β1 about the third axis C. 11 .

[0062] In this case, the robot control device 1 needs to have a temperature sensor that measures the ambient temperature T, and the information stored is as described below. The output of the temperature sensor is input to the measurement acquisition unit 2.

[0063] (Ga, T1, θ1, β1, Fa) 11 ),

[0064] (Ga, T1, θ1, β2, Fa) 12 ),

[0065] (Ga, T1, θ2, β1, Fa) 21 ),

[0066] (Ga, T1, θ2, β2, Fa) 22 ),

[0067] (Gb, T1, θ1, β1, Fb) 11 ),

[0068] (Gb, T1, θ1, β2, Fb) 12 ),

[0069] (Gb, T1, θ2, β1, Fb) 21 ),

[0070] (Gb, T1, θ2, β2, Fb) 22 ),

[0071] (Ga, T2, θ1, β1, Fc) 11 ),

[0072] …

[0073] The ambient temperature during actual operation is T = T3 (T1 ≤ T3 < T2).

[0074] In this state, when the user manipulates a workpiece W with an unknown mass Gc at an ambient temperature T3 using the same hand 200, the correction unit 4 corrects the sensor output in the following manner.

[0075] That is, when the tilt angle θ = θ3 (θ1 ≤ θ3 < θ2) around the second axis B and the rotation angle β = β3 (β1 ≤ β3 < β2) around the first axis A, and the output value of the force sensor 51 is Fc, the correction unit 4 outputs the mass Gc that corrects the output value Fc of the force sensor 51 according to the above formula (1).

[0076] Here, instead of formulas (4) to (7), the following formulas (8) to (19) are applied.

[0077] Number 8

[0078] Fa1={Fa 11 T(β2-β3)+Fa 12T (β3-β1)} / (β2-β1) (8)

[0079] Number 9

[0080] Fa2={Fa 21T (β2-β3)+Fa 22T (β3-β1)} / (β2-β1) (9)

[0081] Count 10

[0082] Fb1={Fb 11T (β2-β3)+Fb 12T (β3-β1)} / (β2-β1) (10)

[0083] Number 11

[0084] Fb2={Fb 21T (β2-β3)+Fb 22T (β3-β1)} / (β2-β1) (11)

[0085] Number 12

[0086] Fa 11T ={Fa 11 (T2-T3)+Fc 11 (T3-T1)} / (T2-T1) (12)

[0087] Number 13

[0088] Fa 12T ={Fa 12 (T2-T3)+Fc 11 (T3-T1)} / (T2-T1) (13)

[0089] Number 14

[0090] Fa 21T ={Fa 21(T2-T3)+Fc 11 (T3-T1)} / (T2-T1) (14)

[0091] Number 15

[0092] Fa 22T ={Fa 22 (T2-T3)+Fc 11 (T3-T1)} / (T2-T1) (15)

[0093] Number 16

[0094] Fb 11T ={Fb 11 (T2-T3)+Fc 11 (T3-T1)} / (T2-T1) (16)

[0095] Number 17

[0096] Fb 12T ={Fb 12 (T2-T3)+Fc 11 (T3-T1)} / (T2-T1) (17)

[0097] Number 18

[0098] Fb 21T ={Fb 21 (T2-T3)+Fc 11 (T3-T1)} / (T2-T1) (18)

[0099] Number 19

[0100] Fb 22T ={Fb 22 (T2-T3)+Fc 11 (T3-T1)} / (T2-T1) (19)

[0101] Therefore, even when the ambient temperature T changes, the measured value measured by the force sensor 51 can be corrected with high accuracy.

[0102] Furthermore, in this embodiment, regardless of whether a workpiece w of known mass exists or not, the measured values ​​of the force sensor 51 are obtained in advance in a discrete manner for the tilt angle θ around the second axis B, the rotation angle β around the third axis C, and the ambient temperature T, and a database is constructed. Moreover, in actual operation, the mass of the unknown workpiece W obtained from the measured values ​​of the force sensor 51 is corrected by using the measured values ​​in the database constructed by linear interpolation.

[0103] Alternatively, corrections can be made using other interpolation methods. Furthermore, a calculation formula can be constructed to determine the mass of the workpiece W based on the measured values ​​of the force sensor 51. When the calculation formula is obtained, a learning function can also be used. In this case, to obtain a more accurate calculation formula, a corresponding amount of data collection is required. Additionally, to address aging, the calculation formula can be periodically recalibrated.

[0104] Alternatively, the temperature of the force sensor 51 can be measured instead of the ambient temperature T.

[0105] In addition, in this embodiment, a hand 200 capable of holding workpiece W is exemplified as a tool, but it can also be applied to any other robot with a movable part that has a large range of motion and whose center of gravity changes before and after the movement.

[0106] Explanation of reference numerals in the attached figures:

[0107] 1: Robot control device

[0108] 2: Measurement Value Acquisition Department

[0109] 3: Storage Department (Measurement Value Storage Department)

[0110] 4: Correction Department

[0111] 50: Robot

[0112] 51: Force sensor (sensor)

[0113] 52: Wrist

[0114] 200: Hand (first tool, second tool)

[0115] B: Second axis (axis)

[0116] W: Workpiece

Claims

1. A robot control device for controlling a robot equipped with a force-measuring sensor, characterized in that, The robot control device includes: The measurement value acquisition unit acquires multiple first measurement values ​​measured by the sensor when the wrist is made to perform a specific action while the tool with a known mass and center of gravity position is disposed at the front end of the robot's wrist and the workpiece is not held; and multiple second measurement values ​​measured by the sensor when the wrist is made to perform the specific action while holding the workpiece with a known mass. The measurement value storage unit stores the plurality of first measurement values ​​and the plurality of second measurement values ​​acquired by the measurement value acquisition unit in correspondence with the robot's posture at the time of measuring each of the plurality of first measurement values ​​and the plurality of second measurement values, and constructs a database. as well as The correction unit, when the tool for holding a workpiece of unknown mass is configured, corrects the measurement values ​​measured by the sensor based on the database constructed by the measurement value storage unit.

2. The robot control device according to claim 1, characterized in that, The specific action causes the tool to rotate about an axis that is generally horizontally positioned. For each predetermined angle around the axis, the plurality of first measurement values ​​and the plurality of second measurement values ​​are obtained.

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