Gripping device, gripping system, and method for detecting slippage of a gripping device

Abstract

To provide a gripping device which can detect slip of a gripping object when the gripping object has slipped therein.SOLUTION: A gripping device comprises: a motor rotating according to an operation value; a gripping part with a first finger part and a second finger part that changes a space between the first finger part and the second finger part by the motor and grips an object with the first finger part and the second finger part; a force detection part which detects a gripping force of the first finger part and the second finger part for gripping the object when gripping the object with the first finger part and the second finger part; and a control part which outputs the operation value so that a force detection value of the gripping force detected by the force detection part becomes a force command value. The control part detects changes in the gripping force detected by the force detection part, and detects slip of the object.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a gripping device, a gripping system, and a method for detecting slippage of a gripping device.

Background Art

[0002] When automating a product manufacturing line using a robot or the like, a gripping device called a robot hand or a gripper is used to grip a gripping object such as a mechanical part or an electrical part.

[0003] In a production apparatus using a robot arm, the application range of the gripping device is expanding to cope with various production problems. Conventionally, fragile gripping objects or soft gripping objects that were not targets have come to be treated as targets of the gripping device.

[0004] On the other hand, in order to grip a fragile gripping object or a soft gripping object with a gripping device, it is required to grip the gripping object delicately with a weak force. However, when gripping a gripping object with a weak force, the gripping object may slip within the gripping device.

[0005] Patent Document 1 discloses a slip sensation detection device that detects a slip sensation using a force sensor. Patent Document 2 discloses a method for detecting a tangential component of the fingertip force of a robot hand that can more preferably detect the tangential component of the fingertip force of a robot hand.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] When a gripping device attached to a robot arm grips an object, transports it to a predetermined position, and performs assembly or other operations, the positional relationship between the gripped object and the destination workpiece or jig becomes crucial. If the gripped object slips within the gripping device during transport, the positional relationship of the gripped object relative to the destination workpiece or jig shifts. Therefore, it is necessary to detect when the gripped object has slipped within the gripping device and correct the amount of this positional shift.

[0008] This disclosure provides a gripping device capable of detecting when an object being gripped slips within the gripping device. [Means for solving the problem]

[0009] In one aspect of the present disclosure, a gripping device is provided comprising: a motor that rotates according to an operating value; a first finger portion; a second finger portion; a gripping portion that grips an object with the first finger portion and the second finger portion by changing the distance between the first finger portion and the second finger portion using the motor; a force detection unit that detects the gripping force exerted by the first finger portion and the second finger portion when the object is gripped by the first finger portion and the second finger portion; and a control unit that outputs the operating value such that the force detection value of the gripping force detected by the force detection unit becomes a force command value, wherein the control unit detects fluctuations in the gripping force detected by the force detection unit and detects slippage of the object. [Effects of the Invention]

[0010] According to the gripping device of this disclosure, if the object being gripped slips within the gripping device, it is possible to detect that the object has slipped. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 shows an example of the configuration of the gripping device according to this embodiment. [Figure 2] Figure 2 is a diagram illustrating the functional configuration of the gripping device according to this embodiment. [Figure 3]Figure 3 is a diagram illustrating the functional configuration of the processing calculation unit in the control unit of the gripping device according to this embodiment. [Figure 4] Figure 4 is a diagram illustrating the functional configuration of the operation value calculation unit of the processing calculation unit in the control unit of the gripping device according to this embodiment. [Figure 5] Figure 5 is a diagram illustrating the functional configuration of the admittance control calculation unit of the processing calculation unit in the control unit of the gripping device according to this embodiment. [Figure 6] Figure 6 is a diagram illustrating the functional configuration of the position velocity calculation unit of the processing calculation unit in the control unit of the gripping device according to this embodiment. [Figure 7] Figure 7 is a diagram illustrating the functional configuration of the current calculation unit of the processing calculation unit in the control unit of the gripping device according to this embodiment. [Figure 8] Figure 8 is a diagram illustrating the stick-slip phenomenon. [Figure 9] Figure 9 shows an example of the configuration of a gripping system using the gripping device according to this embodiment. [Figure 10] Figure 10 is a diagram illustrating the functional configuration of a gripping system using the gripping device according to this embodiment. [Figure 11] Figure 11 is a flowchart illustrating the processing of a gripping system using the gripping device according to this embodiment. [Modes for carrying out the invention]

[0012] ≪Gripping device≫ <Gripping device 1> The gripping device according to this embodiment will be described in detail below with reference to the drawings. Figure 1 is a diagram showing an example of the configuration of the gripping device 1 according to this embodiment. Figure 2 is a diagram illustrating the functional configuration of the gripping device 1 according to this embodiment.

[0013] In FIG. 1, for the convenience of explanation, a virtual three-dimensional coordinate system (XYZ orthogonal coordinate system) composed of an X-axis, a Y-axis, and a Z-axis (XYZ axes) orthogonal to each other is set. For example, for the coordinate axis perpendicular to the plane of the drawing, when a black dot is shown inside the circle of the coordinate axis, it indicates that the front side with respect to the plane of the drawing is the positive region of the coordinate axis. However, this coordinate system is defined for the purpose of explanation and does not limit the posture of the gripping device 1.

[0014] In FIG. 1, the X-axis direction is the direction in which each of the first finger portion 21a and the second finger portion 21b extends. Also, the Y-axis direction is the direction in which each of the first finger portion 21a and the second finger portion 21b moves. The Z-axis is the direction perpendicular to the X-axis and the Y-axis.

[0015] The gripping device 1 is attached, for example, to the tip of a robot arm and grips a gripping object TGT. Specifically, the gripping device 1 grips the gripping object TGT between the first finger portion 21a and the second finger portion 21b. The gripping device 1 includes a drive unit 10, a gripping unit 20, a force detection unit 30, a motor drive unit 40, and a control unit 50. In some cases, the drive unit 10, the gripping unit 20, and the force detection unit 30 are collectively referred to as a mechanism unit 60. Details of each element of the gripping device 1 will be described.

[0016] The control unit 50 and the motor drive unit 40 are connected by a wiring Lm1. Also, the motor drive unit 40 and the drive unit 10 are more specifically connected by a wiring Lm2 between the motor drive unit 40 and the power unit 11 (motor 11m) of the drive unit 10. Further, the control unit 50 and the drive unit 10 are more specifically connected by a wiring Lm3 between the control unit 50 and the power unit 11 (encoder 11e) of the drive unit 10.

[0017] [Drive Unit 10] The drive unit 10 changes the distance between the first finger portion 21a and the second finger portion 21b. Specifically, the drive unit 10 moves each of the first finger portion 21a and the second finger portion 21b in the Y direction in opposite directions to each other.

[0018] The drive unit 10 comprises a power unit 11 and a motion conversion unit 12. Details of the power unit 11 and the motion conversion unit 12 will be described below.

[0019] (Power part 11) The power unit 11 rotates the rotating shaft based on the power supplied from the motor drive unit 40 via wiring Lm2. The power unit 11 converts the power into rotational motion and transmits it to the motion conversion unit 12.

[0020] The power unit 11 comprises a motor 11m and an encoder 11e. The motor 11m is, for example, an AC (Alternating Current) motor or a stepping motor. The motor 11m rotates the rotating shaft based on the power supplied from the motor drive unit 40 (supplied power Pd). As will be described later, the supplied power Pd is determined based on the current control value MVi. Therefore, the motor 11m rotates based on the current control value MVi. The motor 11m has a configuration that is well known as a motor, such as a rotating shaft, stator, and rotor.

[0021] The encoder 11e detects the position and rotational speed of the motor 11m's rotation axis. The encoder 11e outputs the detected results to the control unit 50 via the wiring Lm3.

[0022] (Motion conversion unit 12) The motion conversion unit 12 converts the rotational motion transmitted from the motor 11m into linear motion in the Y-axis direction. The motion conversion unit 12 is composed of mechanical components such as gears, worm gears, and cams. The motion conversion unit 12 includes movable parts 12a and 12b that protrude from the housing 12c. Each of the movable parts 12a and 12b is movable relative to the housing 12c. The motion conversion unit 12 converts the rotational motion transmitted from the motor 11m into linear motion that moves the movable parts 12a and 12b in the Y-axis direction relative to the housing 12c.

[0023] When motor 11m rotates in one direction, for example, the moving part 12a moves in the +Y direction in the Y-axis direction. When motor 11m rotates in the opposite direction, for example, the moving part 12a moves in the -Y direction in the Y-axis direction. Also, when motor 11m rotates in one direction, for example, the moving part 12b moves in the -Y direction in the Y-axis direction. When motor 11m rotates in the opposite direction, for example, the moving part 12b moves in the +Y direction in the Y-axis direction.

[0024] In other words, when the motor 11m rotates in one direction, the movable parts 12a and 12b move in opposite directions in the Y-axis direction, specifically, away from each other in the Y-axis direction. Therefore, when the motor 11m rotates in one direction, the distance between the movable parts 12a and 12b increases. Conversely, when the motor 11m rotates in the opposite direction, the movable parts 12a and 12b move in opposite directions in the Y-axis direction, specifically, towards each other in the Y-axis direction. Therefore, when the motor 11m rotates in the opposite direction, the distance between the movable parts 12a and 12b decreases.

[0025] As described above, the drive unit 10 can change the distance between the moving parts 12a and 12b by rotating the motor 11m.

[0026] [Gripping part 20] The gripping portion 20 grips the object to be gripped TGT between the first finger portion 21a and the second finger portion 21b by the drive portion 10 changing the distance between the movable portion 12a and the movable portion 12b.

[0027] The gripping portion 20 includes a first finger portion 21a and a first holding portion 22a that holds the first finger portion 21a, located on the +Y side in the Y-axis direction with respect to the center position Ac. The first finger portion 21a is fixed to the first holding portion 22a. The first holding portion 22a is fixed to the moving portion 12a via a first force sensor 31a, which will be described later. The gripping device 1 is also provided with a fixing portion 15a for fixing the first force sensor 31a to the moving portion 12a. The center position Ac is the center position of the gripping position that the gripping device 1 grips.

[0028] The gripping portion 20 includes a second finger portion 21b and a second holding portion 22b that holds the second finger portion 21b, located on the -Y side in the Y-axis direction with respect to the center position Ac. The second finger portion 21b is fixed to the second holding portion 22b. The second holding portion 22b is fixed to the moving portion 12b via a second force sensor 31b, which will be described later. The gripping device 1 is provided with a fixing portion 15b for fixing the second force sensor 31b to the moving portion 12b.

[0029] The first finger portion 21a moves in the Y-axis direction along with the movable portion 12a when it moves in the Y-axis direction. Similarly, the second finger portion 21b moves in the Y-axis direction along with the movable portion 12b when it moves in the Y-axis direction. Therefore, when the distance between the movable portions 12a and 12b changes, the distance D between the first finger portion 21a and the second finger portion 21b changes. By narrowing the distance D between the first finger portion 21a and the second finger portion 21b, the gripping portion 20 grips the object to be gripped TGT with the first finger portion 21a and the second finger portion 21b.

[0030] Furthermore, when gripping the object TGT with the gripping portion 20, it is not limited to the case where the object TGT is sandwiched between the first finger portion 21a and the second finger portion 21b. For example, in the case of a ring-shaped object to be gripped, the finger portion may be inserted into the inside of the ring and the finger portion may be opened from the inside to the outside to grip it.

[0031] [Force detection unit 30] The force detection unit 30 detects the force (gripping force) applied between the first finger portion 21a and the second finger portion 21b when the gripping portion 20 grips the object TGT to be gripped. The force detection unit 30 includes a first force sensor 31a and a second force sensor 31b. Each of the first force sensor 31a and the second force sensor 31b is, for example, a 6-axis force sensor.

[0032] The first force sensor 31a is connected to the control unit 50 via wiring La. The second force sensor 31b is also connected to the control unit 50 via wiring Lb. The force detection unit 30 uses the detection results for the force in the Y-axis direction from the output of the 6-axis force sensors.

[0033] The first force sensor 31a is fixed to the first holding part 22a which holds the first finger part 21a. The first force sensor 31a is also fixed to the moving part 12a via the fixing part 15a. The first force sensor 31a detects the force exerted by the object TGT pushing against the first finger part 21a when the gripping part 20 grips the object TGT.

[0034] The second force sensor 31b is fixed to the second holding part 22b, which holds the second finger part 21b. The second force sensor 31b is also fixed to the moving part 12b via the fixing part 15b. The second force sensor 31b detects the force exerted by the object TGT pushing against the second finger part 21b when the gripping part 20 grips the object TGT.

[0035] In this embodiment, the gripping device 1 includes a force detection unit 30 between the drive unit 10 and the gripping unit 20, but the location of the force detection unit 30 is not limited to between the drive unit 10 and the gripping unit 20. For example, the gripping device 1 may have a first force sensor 31a and a second force sensor 31b at the tips of the first finger portion 21a and the second finger portion 21b, respectively.

[0036] Furthermore, the type of force sensor is not limited as long as it can detect the gripping force applied between the first finger portion 21a and the second finger portion 21b. As the force sensor, for example, a MEMS (Micro Electro Mechanical Systems) sensor capable of detecting force may be used, or a piezoelectric element or strain gauge may be used. In the case of using a MEMS sensor or strain gauge, for example, a strain generating body that generates strain due to an external force may be used to detect force, or a part of the gripping portion 20 may be used as a strain generating body.

[0037] In this embodiment, the force detection unit 30 includes a first force sensor 31a and a second force sensor 31b, but it may also include only one of the first force sensor 31a and the second force sensor 31b. That is, it may be possible to provide a force sensor in only one of the first finger portion 21a and the second finger portion 21b.

[0038] [Motor drive unit 40] The motor drive unit 40 supplies power (supplied power Pd) to the drive unit 10, more specifically to the motor 11m, based on an operation command (current control signal Ip) from the control unit 50. The drive unit 10 is driven by the power supplied from the motor drive unit 40. As the drive unit 10 is driven by the power supplied from the motor drive unit 40, the drive unit 10 performs operations in accordance with the operation command from the control unit 50.

[0039] The motor drive unit 40 outputs the current value (drive current value Im) of the power supplied to the drive unit 10 to the control unit 50. The control unit 50 uses the current value of the current supplied by the motor drive unit 40 to the drive unit 10 to control the drive unit 10.

[0040] [Control Unit 50] The control unit 50 controls the drive unit 10 so that the gripping force (first gripping force value Fma and second gripping force value Fmb) detected by the force detection unit 30 becomes the desired gripping force. The control unit 50 also controls the rotation using the position (position information θm) and rotational speed (speed information vm) of the rotation axis detected by the encoder 11e, and the current signal (drive current value Im) from the motor drive unit 40.

[0041] The control unit 50 is composed of, for example, a microprocessing unit that includes a CPU (Central Processing Unit), RAM (Random Access Memory), and ROM (Read Only Memory). The control unit 50 performs processing by having the CPU load the program stored in ROM into RAM and execute it.

[0042] The control unit 50 comprises an arithmetic processing unit 51, a motor control unit 52, a motor operation data acquisition unit 53, and a force measurement data acquisition unit 54. The arithmetic processing unit 51 outputs a current operation value MVi to the motor control unit 52. The motor operation data acquisition unit 53 outputs a current detection value PVi, which is the current value of the drive current supplied from the motor drive unit 40 to the power unit 11 (motor 11m), as well as a position detection value PVθ of the rotation axis of the motor 11m and a rotation axis speed detection value PVv to the arithmetic processing unit 51. The force measurement data acquisition unit 54 outputs a gripping force detection value PVf, which is the gripping force F received from the gripping object TGT detected by the force detection unit 30, to the arithmetic processing unit 51. The force measurement data acquisition unit 54 also outputs a first gripping force detection value PVfa, which indicates the force applied to the first finger portion 21a, and a second gripping force detection value PVfb, which indicates the force applied to the second finger portion 21b, to the arithmetic processing unit 51. Details of each element are explained below.

[0043] (Arithmetic processing unit 51) The arithmetic processing unit 51 calculates the manipulated amount for operating the drive unit 10 so that the control value becomes the target value. Specifically, the arithmetic processing unit 51 calculates the current manipulated value MVi so that the gripping force detection value PVf, which is the control value, becomes the force command value SVf, which is the target gripping force value. Details of the arithmetic processing unit 51 will be described later. In this embodiment, the arithmetic processing unit 51 outputs the current manipulated value MVi as the manipulated value, but depending on the controlled object, power, voltage, etc., may be used as the manipulated value, not limited to current.

[0044] (Motor control unit 52) The motor control unit 52 outputs an operating value to the motor drive unit 40 for operating the power unit 11, specifically the motor 11m. Specifically, the motor control unit 52 converts the current operating value MVi output by the calculation processing unit 51 into a current control signal Ip that can be input to the motor drive unit 40. Then, the motor control unit 52 outputs the converted current control signal Ip to the motor drive unit 40.

[0045] The motor control unit 52 may output an analog signal such as a voltage signal or a current signal, or a digital signal, as a current control signal Ip, if it is available for input to the motor drive unit 40. Based on the current control signal Ip, the motor drive unit 40 supplies power Pd to the motor 11m of the power unit 11.

[0046] (Motor operation data acquisition unit 53) The motor operation data acquisition unit 53 acquires motor operation data relating to the operating status of the power unit 11 from the power unit 11 and the motor drive unit 40. Specifically, the motor operation data acquisition unit 53 acquires the drive current value Im of the supplied power Pd supplied by the motor drive unit 40 to the power unit 11 from the motor drive unit 40. In addition, the motor operation data acquisition unit 53 acquires the position information θm and speed information vm of the rotation axis of the motor 11m from the encoder 11e.

[0047] The motor operation data acquisition unit 53 may acquire the drive current value Im from the motor drive unit 40, for example, as an analog signal or as a digital signal. Similarly, the motor operation data acquisition unit 53 may acquire the position information θm and the speed information vm from the encoder 11e, for example, as an analog signal or as a digital signal.

[0048] The motor operation data acquisition unit 53 outputs a current detection value PVi to the arithmetic processing unit 51 based on the acquired drive current value Im. The motor operation data acquisition unit 53 also outputs a position detection value PVθ to the arithmetic processing unit 51 based on the acquired position information θm. Furthermore, the motor operation data acquisition unit 53 outputs a speed detection value PVv to the arithmetic processing unit 51 based on the acquired speed information vm.

[0049] (Force measurement data acquisition unit 54) The force measurement data acquisition unit 54 acquires measurement data of the gripping force F from the force detection unit 30. Specifically, the force measurement data acquisition unit 54 acquires a first gripping force value Fma, which indicates the magnitude of the force applied to the first finger portion 21a, from the first force sensor 31a. The force measurement data acquisition unit 54 also acquires a second gripping force value Fmb, which indicates the magnitude of the force applied to the second finger portion 21b, from the second force sensor 31b.

[0050] The force measurement data acquisition unit 54 may acquire the first gripping force value Fma from the first force sensor 31a, for example, as an analog signal or as a digital signal. Similarly, the force measurement data acquisition unit 54 may acquire the second gripping force value Fmb from the second force sensor 31b, for example, as an analog signal or as a digital signal.

[0051] The force measurement data acquisition unit 54 outputs a gripping force detection value PVf to the calculation processing unit 51 based on the acquired first gripping force value Fma and second gripping force value Fmb. For example, the force measurement data acquisition unit 54 may output the average gripping force value of the first gripping force value Fma and the second gripping force value Fmb as the gripping force detection value PVf.

[0052] Furthermore, the force measurement data acquisition unit 54 outputs a first gripping force detection value PVfa to the calculation processing unit 51 based on the first gripping force value Fma. Similarly, the force measurement data acquisition unit 54 outputs a second gripping force detection value PVfb to the calculation processing unit 51 based on the second gripping force value Fmb.

[0053] <Details of the processing in the arithmetic processing unit 51> The processing of the arithmetic processing unit 51, or in other words, the details of the slip detection method performed in the gripping device 1, will now be described. Figure 3 is a diagram illustrating the functional configuration of the arithmetic processing unit 51 in the control unit 50 of the gripping device 1 according to this embodiment. In Figure 3, the external components of the arithmetic processing unit 51 are collectively shown as the OBJ controlled by the arithmetic processing unit 51. The OBJ controlled by the OBJ includes, for example, the drive unit 10, the force detection unit 30 and the motor drive unit 40, and the motor control unit 52, the motor operation data acquisition unit 53 and the force measurement data acquisition unit 54.

[0054] The arithmetic processing unit 51 determines the force command value SVf of the gripping force F. The arithmetic processing unit 51 also calculates the current operation value MVi so that the gripping force detection value PVf becomes the force command value SVf. The arithmetic processing unit 51 uses the current detection value PVi, the position detection value PVθ, and the velocity detection value PVv to calculate the current operation value MVi.

[0055] The arithmetic processing unit 51 comprises an operation value calculation unit 51a, a force command generation unit 51b, and a slip detection unit 51c.

[0056] [Operation Value Calculation Unit 51a] The operation value calculation unit 51a calculates the current operation value MVi so that the gripping force detection value PVf becomes the force command value SVf set by the force command generation unit 51b. Figure 4 is a diagram illustrating the functional configuration of the operation value calculation unit 51a of the calculation processing unit 51 of the control unit 50 of the gripping device 1 according to this embodiment. In the block diagram of this disclosure, "1 / s" means integral.

[0057] The operation value calculation unit 51a comprises an admittance control calculation unit 51a1, an integral calculation unit 51a2, a position and velocity calculation unit 51a3, and a current calculation unit 51a4. Each calculation unit will be described below.

[0058] (Admittance control calculation unit 51a1) The admittance control calculation unit 51a1 converts the force command value SVf into a displacement command value SVd. The admittance control calculation unit 51a1 calculates (generates) the displacement command value SVd so that the gripping force detection value PVf matches the force command value SVf. Figure 5 is a diagram illustrating the functional configuration of the admittance control calculation unit 51a1 of the calculation processing unit 51 of the control unit 50 of the gripping device 1 according to this embodiment.

[0059] The admittance control calculation unit 51a1 adjusts the parameters of the virtual spring-mass-damper system model by solving the differential equation shown in Equation 1. Hereinafter, ΔF is the difference between the force command value SVf and the gripping force detection value PVf, M is the mass, C is the damping coefficient of the damper, K is the spring constant of the spring, and x is the displacement.

[0060]

number

[0061] The admittance control calculation unit 51a1 includes addition / subtraction blocks A11, A12, A13, integration block B11, integration block B12, gain block B13, and gain block B14. The addition / subtraction blocks output the result of addition or subtraction of multiple inputs. The integration blocks output the result of integration of an input. The gain blocks output the result of multiplying an input by a gain. The same applies hereafter.

[0062] Addition / subtraction block A11 calculates the difference between the force command value SVf and the gripping force detection value PVf. Addition / subtraction block A11 outputs the calculation result to addition / subtraction block A12. Addition / subtraction block A12 adds the output of addition / subtraction block A11 and the output of gain block B14. Addition / subtraction block A12 outputs the calculation result to addition / subtraction block A13. Addition / subtraction block A13 adds the output of addition / subtraction block A12 and the output of gain block B13. Addition / subtraction block A13 outputs the calculation result to integration block B11.

[0063] The integration block B11 integrates the output from the addition / subtraction block A13 and multiplies the integrated result by the gain K11. The integration block B11 outputs the calculation result to the integration block B12 and the gain block B13.

[0064] The integration block B12 integrates the output from integration block B11 and outputs the result. The integration block B12 outputs the displacement command value SVd, which is the calculation result, as the output of the admittance control calculation unit 51a1. The integration block B12 also outputs the calculation result to the gain block B14.

[0065] Gain block B13 multiplies the output of integration block B11 by gain K12 and outputs it to addition / subtraction block A13. Gain block B14 multiplies the output of integration block B12 by gain K13 and outputs it to addition / subtraction block A12.

[0066] Gain K11 corresponds to the mass M in Equation 1. Gain K12 corresponds to the damping coefficient C in Equation 1. Gain K13 corresponds to the spring constant K in Equation 1.

[0067] The admittance control performed by the admittance control calculation unit 51a1 described above is just one example of the process. In addition to the control described above, force control may also be performed, for example, by calculating the displacement command value SVd from the gripping force detection value PVf using only the spring constant K.

[0068] The admittance control calculation unit 51a1 is an example of a force control calculation unit that converts a force command value SVf to a displacement command value SVd. The method for converting the force command value SVf to the displacement command value SVd in the force control calculation unit is not limited to the admittance control calculation unit 51a1; various methods can be applied.

[0069] (Integral calculation unit 51a2) The integral calculation unit 51a2 integrates the displacement command value SVd output from the admittance control calculation unit 51a1 and converts it into a position command value SVθ. The admittance control calculation unit 51a1 and the integral calculation unit 51a2 adjust the positions of the first finger portion 21a and the second finger portion 21b so that the gripping force detection value PVf balances with the force command value SVf.

[0070] (Position speed calculation unit 51a3) The position-velocity calculation unit 51a3 calculates and outputs a current command value SVi such that the first finger portion 21a and the second finger portion 21b are positioned at the position command value SVθ output from the integral calculation unit 51a2. The position-velocity calculation unit 51a3 calculates (generates) the current command value SVi such that the position detection value PVθ matches the position command value SVθ. Specifically, the position-velocity calculation unit 51a3 performs P (Proportional) control for position and PI (Proportional-Integral) control for velocity. Figure 6 is a diagram illustrating the functional configuration of the position-velocity calculation unit 51a3 of the calculation processing unit 51 of the control unit 50 of the gripping device 1 according to this embodiment.

[0071] The position-velocity calculation unit 51a3 includes an addition / subtraction block A21, an addition / subtraction block A22, an addition / subtraction block A23, a gain block B21, a gain block B22, and an integration block B23.

[0072] Addition / subtraction block A21 calculates the difference between the position command value SVθ and the position detection value PVθ. Addition / subtraction block A21 outputs the calculation result to gain block B21. Gain block B21 multiplies the output of addition / subtraction block A21 by gain K21 and outputs it to addition / subtraction block A22. Addition / subtraction block A22 calculates the difference between the output of gain block B21 and the velocity detection value PVv. Addition / subtraction block A22 outputs the calculation result to gain block B22 and integration block B23.

[0073] Gain block B22 multiplies the output of addition / subtraction block A22 by gain K22 and outputs it to addition / subtraction block A23. Integrate block B23 integrates the output from addition / subtraction block A22 and multiplies the integrated result by gain K23. Integrate block B23 outputs the calculation result to addition / subtraction block A23.

[0074] The addition / subtraction block A23 calculates the sum of the output of the gain block B22 and the output of the integration block B23. Then, the addition / subtraction block A23 outputs the current command value SVi as the output of the position / velocity calculation unit 51a3. The gains, such as gain K21, are determined appropriately considering the system response, etc.

[0075] (Current calculation unit 51a4) The current calculation unit 51a4 converts the current command value SVi output from the position velocity calculation unit 51a3 into a current operation value MVi. The current calculation unit 51a4 calculates (generates) the current operation value MVi so that the detected current value PVi matches the current command value SVi. Specifically, the current calculation unit 51a4 performs PI control on the current. Figure 7 is a diagram illustrating the functional configuration of the current calculation unit 51a4 of the calculation processing unit 51 of the control unit 50 of the gripping device 1 according to this embodiment.

[0076] The current calculation unit 51a4 includes an addition / subtraction block A31, an addition / subtraction block A32, a gain block B31, and an integration block B32.

[0077] The addition / subtraction block A31 calculates the difference between the current command value SVi and the current detection value PVi. The addition / subtraction block A31 outputs the calculation result to the gain block B31 and the integration block B32.

[0078] The integration block B32 multiplies the output of the addition / subtraction block A31 by the gain K31 and outputs it back to the addition / subtraction block A32. The integration block B32 integrates the output from the addition / subtraction block A31 and multiplies the integrated result by the gain K32. The integration block B32 outputs the calculation result back to the addition / subtraction block A32.

[0079] The addition / subtraction block A32 calculates the sum of the output of the gain block B31 and the output of the integration block B32. Then, the addition / subtraction block A32 outputs the current operation value MVi as the output of the current calculation unit 51a4. The gains such as gain K31 are determined appropriately considering the system response, etc.

[0080] [Force command generation unit 51b] The force command generation unit 51b generates a force command value SVf. The force command generation unit 51b outputs a force command value SVf corresponding to the hardness of the expected object to be gripped.

[0081] [Slip detection unit 51c] The slip detection unit 51c detects that the object to be gripped TGT has slipped within the gripping device 1, that is, between the first finger portion 21a and the second finger portion 21b. The slip detection unit 51c receives a first gripping force detection value PVfa, which indicates the first gripping force value Fma, and a second gripping force detection value PVfb, which indicates the second gripping force value Fmb, from the force measurement data acquisition unit 54. Based on the first gripping force detection value PVfa and the second gripping force detection value PVfb, the slip detection unit 51c detects that the object to be gripped TGT has slipped.

[0082] When the gripping device 1 is gripping the object TGT between the first finger portion 21a and the second finger portion 21b, if the object TGT slips against the first finger portion 21a, for example, the force applied to the first finger portion 21a will fluctuate periodically due to the stick-slip phenomenon. Therefore, the first gripping force value Fma detected by the first force sensor 31a, which detects the force applied to the first finger portion 21a, will fluctuate periodically.

[0083] Similarly, when the gripping device 1 is gripping the object TGT between the first finger portion 21a and the second finger portion 21b, if the object TGT slips against the second finger portion 21b, for example, the force applied to the second finger portion 21b will fluctuate periodically due to the stick-slip phenomenon. Therefore, the second gripping force value Fmb detected by the second force sensor 31b, which detects the force applied to the second finger portion 21b, will fluctuate periodically.

[0084] Figure 8 illustrates the stick-slip phenomenon. In Figure 8, the vertical axis represents the frictional force between two contacting objects, and the horizontal axis represents time. The line Lss represents the frictional force between the two objects. The stick-slip phenomenon is an intermittent vibration that occurs when two contacting objects slide, in which sliding and adhesion repeatedly occur alternately at the contact surface.

[0085] When two contacting objects slide against each other at the contact surface, the frictional force decreases rapidly, as shown by the line Lslip. On the other hand, when two contacting objects stick together at the contact surface, the frictional force increases gradually, as shown by the line Lstick. As shown in Figure 8, when the stick-slip phenomenon occurs, sliding and sticking alternate repeatedly.

[0086] In the gripping device 1 according to this embodiment, the slip detection unit 51c detects periodic and minute force changes when a stick-slip phenomenon occurs using the first force sensor 31a or the second force sensor 31b. When the slip detection unit 51c detects periodic and minute force changes from the first force sensor 31a or the second force sensor 31b, it determines that the object to be gripped TGT is slipping at the first finger portion 21a or the second finger portion 21b. In other words, the slip detection unit 51c can detect slippage of the object to be gripped TGT at the first finger portion 21a or the second finger portion 21b by detecting periodic and minute force changes from the first force sensor 31a or the second force sensor 31b.

[0087] Furthermore, the slip detection unit 51c includes a slip amount calculation unit 51c1. When the slip amount calculation unit 51c1 detects that the object to be gripped TGT has slipped within the gripping device 1, that is, between the first finger portion 21a and the second finger portion 21b, it calculates the amount of slippage of the object to be gripped TGT.

[0088] The slip amount calculation unit 51c1 may, for example, calculate the amount of slip of the gripped object TGT from the change (amplitude) of the gripping force and the duration when the stick-slip phenomenon occurs. The amount of slip differs depending on the change in gripping force due to the stick-slip phenomenon. For example, it is estimated that the amount of slip is large when the change in gripping force is large, and small when the change in gripping force is small. Therefore, the amount of slip can be calculated from the change in gripping force and the time it occurs. Note that data on the relationship between the change in gripping force and the amount of slip may be acquired in advance.

[0089] Alternatively, the slip amount calculation unit 51c1 may obtain a table in advance showing the relationship between vibration frequency and slip amount, and then calculate the slip amount from the vibration frequency and the number of vibrations. The slip amount differs depending on the frequency (vibration frequency) at which the stick-slip phenomenon occurs. For example, it is estimated that the slip amount is large when the vibration frequency is low, and small when the vibration frequency is high. Therefore, if the relationship between vibration frequency and slip amount is obtained in advance as a table, the slip amount can be calculated from the obtained vibration frequency and the number of vibrations.

[0090] Furthermore, if a strain sensor that detects the amount of strain in the first finger portion 21a or the second finger portion 21b is used as the first force sensor 31a or the second force sensor 31b, the amount of slip can be detected by using the change in the amount of strain generated when the gripping position changes. The amount of strain can be calculated, for example, by the following formula.

[0091] Strain amount = α × Gripping force (set value) × Gripping position (distance to sensor)

[0092] Furthermore, instead of the slip amount calculation unit 51c1, another slip amount detection unit may be used to detect the slip amount. For example, a camera may be provided to detect the slip amount, and the slip amount may be detected from images before and after the slip is detected. For example, the control unit 50 may control the slip detection unit, such as a camera, to detect the slip amount when the slip detection unit 51c detects slip. The control unit 50 acquires the slip amount detected by the slip detection unit and processes it.

[0093] The slip detection unit 51c is connected to the force command generation unit 51b. The slip detection unit 51c outputs a control signal Ctl to the force command generation unit 51b. When the force command generation unit 51b detects slippage in the slip detection unit 51c, it increases the force command value SVf to stop the slippage. The extent to which the force command value SVf is increased is not particularly limited, but the changed force command value SVf should be less than or equal to the maximum allowable gripping force for the object to be gripped TGT.

[0094] ≪Gripping System≫ <Gripping system 100> Next, a gripping system 100 using the gripping device according to this embodiment will be described. Figure 9 is a diagram showing an example configuration of the gripping system 100 using the gripping device according to this embodiment. Figure 10 is a diagram illustrating the functional configuration of the gripping system 100 using the gripping device according to this embodiment.

[0095] The gripping system 100 comprises a gripping device 2 and a robot 5.

[0096] The gripping device 2 includes a control unit 150 in place of the control unit 50 of the gripping device 1. The control unit 150 includes all the functions of the control unit 50. The control unit 150 also transmits control signals to the robot 5.

[0097] Robot 5 comprises a robot arm 70 and a robot control unit 80. The robot arm 70 is, for example, a multi-joint robot arm. The mechanism 60 of the gripping device 2 is attached to the tip of the robot arm 70. The robot arm 70 is a so-called multi-joint robot. The robot arm 70 moves the mechanism 60 in three axial directions and rotates in three axial directions.

[0098] <Processing of the gripping system 100> The operation of the gripping system 100 using the gripping device according to this embodiment will be described. Figure 11 is a flowchart illustrating the processing of the gripping system 100 using the gripping device according to this embodiment. Here, we will describe the case in which an object to be gripped is gripped by the gripping device 2 and the gripped object is moved to another location.

[0099] (Step S10) Robot 5 moves the gripping device 2 to the vicinity of the object to be gripped. Specifically, the robot control unit 80 of robot 5, which is part of the gripping system 100, controls the mechanism 60 to move to the vicinity of the object to be gripped. Robot 5 moves the mechanism 60 to the vicinity of the object to be gripped.

[0100] (Step S20) The gripping device 2 grips the object to be gripped. Specifically, the calculation processing unit 151 of the gripping device 2 controls the gripping device 2 to start its gripping operation. Specifically, the calculation processing unit 151 moves the first finger portion 21a and the second finger portion 21b in a direction that narrows the distance between them. Then, once the gripping device 2 has gripped the object to be gripped, the calculation processing unit 151 controls the gripping force (gripping force detection value PVf) to match the force command value SVf. Furthermore, for example, when gripping a fragile or soft object with the gripping device, the device grips the object delicately with a weak force.

[0101] (Step S30) Next, the robot 5 begins to move the object grasped by the gripping device 2 from the place where it was grasped to another location.

[0102] (Step S40) While the robot 5 is moving the object being gripped by the gripping device 2, the gripped object may slip. In particular, when the gripping device is gripping a fragile or soft object, the gripping force is weak, which can cause the object to slip within the gripping device.

[0103] In the gripping system 100 according to this embodiment, the slip detection unit 51c of the gripping device 2 is used to determine whether the gripping device 2 has detected slippage of the object to be gripped. If the slip detection unit 51c detects slippage of the object to be gripped (Yes in step S40), the process proceeds to step S50. If the slip detection unit 51c does not detect slippage of the object to be gripped (No in step S40), the process proceeds to step S80.

[0104] (Step S50) When the gripping device 2 detects slippage of the object to be gripped, it increases the force command value SVf to grip the object more firmly. Specifically, when the slip detection unit 51c detects slippage of the object to be gripped, the force command generation unit 51b increases the force command value SVf. When the force command value SVf is increased, the calculation processing unit 151 controls the gripping device 2 to grip the object more firmly.

[0105] The gripping device 2 firmly grips the object to be gripped, thereby stopping the object from sliding inside the gripping device 2 and preventing it from sliding further or falling.

[0106] (Step S60) Next, the gripping device 2 calculates the amount of slip. Specifically, the slip amount calculation unit 51c1 calculates the distance the gripped object has slid, i.e., the amount of slip.

[0107] (Step S70) In this embodiment, the gripping system 100 corrects the movement location of the mechanism 60 by the robot 5 based on the amount of slip calculated in step S60. That is, the robot 5 moves the mechanism 60 of the gripping device 2 based on the calculated amount of slip. For example, based on the calculated amount of slip, the robot 5 corrects the movement location to a location higher than the original movement location by the amount of slip.

[0108] (Step S80) Determine whether to end the movement. For example, the operation ends when the movement reaches the destination. If the operation ends (Yes in step S80), the process ends. If the movement does not end (No in step S80), return to step S40 and repeat the process.

[0109] <Effects and Actions> According to the gripping device of this embodiment, it is possible to detect slippage of the object being gripped within the gripping device. According to the gripping device of this embodiment, the object being gripped is gripped by controlling the gripping force detected by a force sensor, and slippage can be detected using the force sensor used for this control. Therefore, slippage can be detected in a gripping device that performs gripping by force control without adding any new sensors. Furthermore, according to the gripping device of this embodiment, when the object being gripped slips within the gripping device, the amount of slippage can be detected.

[0110] Furthermore, according to the gripping device of this embodiment, when slippage of the object to be gripped is detected within the gripping device, the control can be changed, for example, by increasing the gripping force, thereby preventing further slippage or dropping of the object to be gripped. Moreover, according to the gripping device of this embodiment, by controlling based on the amount of slippage of the object to be gripped within the gripping device, the control of a robot using the gripping device can be corrected, for example, to enable more accurate control.

[0111] Although the gripping device has been described above with reference to embodiments, the present invention is not limited to the above embodiments, and may, for example, have three or more finger parts. Various modifications and improvements, such as combinations or substitutions with parts or all of other embodiments, are possible within the scope of the present invention. [Explanation of symbols]

[0112] 1, 2 Gripping device 5 Robots 100 Gripping System 10 Drive unit 11 Power section 20 Gripping part 21a 1st finger 21b 2nd finger 30 Force detection unit 31a First force sensor 31b Second force sensor 40 Motor drive unit 50 Control Unit 51 Arithmetic Processing Unit 51a Operation Value Calculation Unit 51a1 Admittance control calculation unit 51a2 Integral calculation section 51a3 Position speed calculation section 51a4 Current calculation section 51b Force command generation section 51c Slip detection unit 70 Robot Arms PVf gripping force detection value PVi current detection value PVv speed detection value PVθ position detection value SVf force command value SVi Current Command Value SVθ Position command value TGT Grasped object

Claims

1. A motor that rotates according to the input value, A gripping part comprising a first finger portion and a second finger portion, wherein the distance between the first finger portion and the second finger portion is changed by the motor, and the first finger portion and the second finger portion grip an object, A force detection unit that detects the gripping force exerted by the first finger and the second finger when the object is gripped by the first finger and the second finger, A control unit that outputs the operation value so that the force detection value of the gripping force detected by the force detection unit becomes the force command value, Equipped with, The control unit detects the fluctuation in the gripping force detected by the force detection unit and detects the slippage of the object. The control unit detects the amount of slip, which is the distance the object has slid, based on the amplitude and duration of the fluctuation in the gripping force. gripping device.

2. A motor that rotates according to an operating value, A gripping part comprising a first finger portion and a second finger portion, wherein the distance between the first finger portion and the second finger portion is changed by the motor, and the first finger portion and the second finger portion grip an object, A force detection unit that detects the gripping force exerted by the first finger and the second finger when the object is gripped by the first finger and the second finger, A control unit that outputs the operation value so that the force detection value of the gripping force detected by the force detection unit becomes the force command value, Equipped with, The control unit detects the fluctuation in the gripping force detected by the force detection unit and detects the slippage of the object. The control unit detects the amount of slip, which is the distance the object has slid, based on the vibration frequency and number of vibrations of the fluctuation in the gripping force. gripping device.

3. The control unit detects periodic fluctuations in the gripping force and detects slippage of the object. A gripping device according to either claim 1 or claim 2.

4. A gripping device according to any one of claims 1 to 3, The system includes a robot that moves the gripping device, The robot moves the gripping device based on the amount of slip. Gripping system.

5. A motor that rotates according to the input value, A gripping part comprising a first finger portion and a second finger portion, wherein the distance between the first finger portion and the second finger portion is changed by the motor, and the first finger portion and the second finger portion grip an object, A force detection unit that detects the gripping force exerted by the first finger and the second finger when the object is gripped by the first finger and the second finger, Equipped with, A method for detecting slippage in a gripping device, wherein the operation value is output so that the magnitude of the gripping force detected by the force detection unit becomes a force command value, The force detection unit detects the fluctuation in the gripping force and detects the slippage of the object. Based on the amplitude and duration of the fluctuation in the gripping force, the amount of slip, which is the distance the object has slid, is detected. A method for detecting slippage in a gripping device.

6. A motor that rotates according to an operating value, A gripping part comprising a first finger portion and a second finger portion, wherein the distance between the first finger portion and the second finger portion is changed by the motor, and the first finger portion and the second finger portion grip an object, A force detection unit that detects the gripping force exerted by the first finger and the second finger when the object is gripped by the first finger and the second finger, Equipped with, A method for detecting slippage in a gripping device, wherein the operation value is output so that the magnitude of the gripping force detected by the force detection unit becomes a force command value, The force detection unit detects the fluctuation in the gripping force and detects the slippage of the object. Based on the vibration frequency and number of vibrations of the fluctuation in the gripping force, the amount of slip, which is the distance the object has slid, is detected. A method for detecting slippage in a gripping device.

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