Gripping device and control method for the gripping device

Abstract

To provide a holding device capable of stably holding objects to be held (holding objects) having different hardness levels.SOLUTION: A holding device includes: a motor which rotates in response to an operation value; a holding part which holds an object with a first finger part and a second finger part; a force detection part which detects a holding force of the first finger part and the second finger part holding the object when the object is held by the first finger part and the second finger part; and a control unit which outputs the operation value so that the force detection value of the holding force detected by the force detection part becomes a force command value. The control unit may perform first control processing in which a position command value for determining a clearance between the first finger part and the second finger part based on the force detection value to calculate the operation value based on the position command value and second control processing in which the operation value is calculated based on a difference between the force detection value and the force command value. The control unit selects one of the first control processing and the second control processing according to hardness of the object to execute the selected processing.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a gripping device and a method for controlling the gripping device.

Background Art

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

[0003] Patent Document 1 discloses a robot hand mechanism that realizes movement control with an optimal gripping force and speed according to the hardness of an object having an unspecified hardness. Patent Document 2 discloses a robot hand that performs object gripping controlled by either a position control system or a force control system according to the hardness of the gripping object.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] When gripping a gripping object with a gripping device, there are cases where a plurality of gripping objects with different hardnesses are individually and continuously gripped. Each time the gripping device grips a gripping object, it is required to accurately and stably hold the gripping object even if the hardness of the gripping object is different.

[0006] The present disclosure provides a gripping device capable of stably holding gripping objects with different hardnesses.

Means for Solving the Problems

[0007] 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 is capable of performing a first control process that calculates a position command value that determines the distance based on the force detection value and calculates the operating value based on the position command value, and a second control process that calculates the operating value based on the difference between the force detection value and the force command value, wherein the control unit selects and performs either the first control process or the second control process according to the hardness of the object. [Effects of the Invention]

[0008] The gripping device of this disclosure can stably hold objects of different hardness. [Brief explanation of the drawing]

[0009] [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 flowchart illustrating the functional configuration of the force control unit of the processing calculation unit in the control unit of the gripping device according to this embodiment. [Figure 9] Figure 9 is a diagram illustrating the operation of the gripping device according to this embodiment. [Figure 10] Figure 10 is a Bode plot of the gripping device according to this embodiment. [Figure 11] Figure 11 is a flowchart illustrating the processing of the processing calculation unit in the control unit of the gripping device according to this embodiment. [Figure 12] Figure 12 is a diagram illustrating the operation of the gripping device according to this embodiment. [Modes for carrying out the invention]

[0010] <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.

[0011] For the sake of explanation, Figure 1 sets up a virtual three-dimensional coordinate system (XYZ Cartesian coordinate system) consisting of mutually orthogonal X, Y, and Z axes (XYZ axes). For example, when a black circle is shown inside a circle representing a coordinate axis perpendicular to the plane of the drawing, it indicates that the positive region of the coordinate axis is on the near side of the drawing plane. However, this coordinate system is defined for explanatory purposes only and does not limit the orientation of the gripping device 1.

[0012] In Figure 1, the X-axis direction is the direction in which the first finger portion 21a and the second finger portion 21b extend, respectively. The Y-axis direction is the direction in which the first finger portion 21a and the second finger portion 21b move, respectively. The Z-axis direction is perpendicular to the X-axis and the Y-axis.

[0013] The gripping device 1 is attached to the tip of, for example, the arm of a robot and grips the object to be gripped TGT. Specifically, the gripping device 1 grips the object to be gripped 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. Details of each element of the gripping device 1 will be described.

[0014] Note that the control unit 50 and the motor drive unit 40 are connected by a wiring Lm1. Further, 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. Furthermore, 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.

[0015] [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.

[0016] The drive unit 10 includes a power unit 11 and a motion conversion unit 12. Details of each of the power unit 11 and the motion conversion unit 12 will be described.

[0017] (Power Unit 11) The power unit 11 rotates a rotating shaft based on the power supplied from the motor drive unit 40 via the wiring Lm2. The power unit 11 converts the power into rotational motion and transmits it to the motion conversion unit 12.

[0018] 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.

[0019] 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.

[0020] (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.

[0021] 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.

[0022] 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.

[0023] As described above, the drive unit 10 can change the distance between the moving parts 12a and 12b by rotating the motor 11m.

[0024] [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.

[0025] 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 central axis 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 provided with a fixing portion 15a for fixing the first force sensor 31a to the moving portion 12a.

[0026] 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 central axis 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.

[0027] 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.

[0028] 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.

[0029] [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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] [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.

[0037] 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.

[0038] [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.

[0039] 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.

[0040] 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 the position detection value PVθ of the rotation axis of the motor 11m and the 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. Details of each element are described below.

[0041] (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 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.

[0042] (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.

[0043] The motor control unit 52 may output an analog signal such as a voltage signal or a current signal, or a digital signal, as the 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.

[0044] (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.

[0045] 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.

[0046] 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.

[0047] (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 the first gripping force value Fma from the first force sensor 31a. The force measurement data acquisition unit 54 also acquires the second gripping force value Fmb from the second force sensor 31b.

[0048] 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.

[0049] 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.

[0050] <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 each step performed in the control method of the gripping device 1, will now be explained. 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 control target OBJ of the arithmetic processing unit 51. The control target 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.

[0051] 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.

[0052] The arithmetic processing unit 51 comprises an operation value calculation unit 51a, a force command generation unit 51b, and a determination unit 51c.

[0053] [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, "1 / s" means integral.

[0054] 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, a switching unit 51a4, a current calculation unit 51a5, and a force control calculation unit 51a6. Each calculation unit will be described below.

[0055] (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.

[0056] 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.

[0057]

number

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] The admittance control performed by the admittance control calculation unit 51a1 described above is just one example of processing. 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.

[0065] 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.

[0066] (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.

[0067] (Position speed calculation unit 51a3) The position-velocity calculation unit 51a3 calculates and outputs a current command value SVi1 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 SVi1 so 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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 SVi1 as the output of the position / velocity calculation unit 51a3. The gains such as gain K21 are determined appropriately considering the system response, etc.

[0072] (Switching section 51a4) Based on the switching signal SW, the switching unit 51a4 outputs either the current command value SVi1 output by the position and velocity calculation unit 51a3 or the current command value SVi2 output by the force control calculation unit 51a6 (described later) as the current command value SVi to the current calculation unit 51a5.

[0073] The switching unit 51a4 has two signal inputs to which current command values ​​are input. One of the signal inputs of the switching unit 51a4 is connected to the position and velocity calculation unit 51a3. The other signal input of the switching unit 51a4 is connected to the force control calculation unit 51a6. The switching unit 51a4 also has one signal output. The signal output of the switching unit 51a4 is connected to the current calculation unit 51a5. Furthermore, the switching unit 51a4 has a control input to which a control signal, specifically a switching signal SW, is input. The control input of the switching unit 51a4 is connected to the determination unit 51c.

[0074] In this embodiment, the gripping device 1 switches control based on the hardness of the object to be gripped TGT, using a switching unit 51a4 and a determination unit 51c. Specifically, when the determination unit 51c determines that the object to be gripped TGT is hard, a current command value SVi2 is input to the current calculation unit 51a5 as the current command value SVi. That is, the gripping device 1 in this embodiment can execute a first control process using the current command value SVi1 and a second control process using the current command value SVi2, using the switching unit 51a4 and the determination unit 51c. Furthermore, the gripping device 1 in this embodiment can select and execute either the first control process or the second control process using the switching unit 51a4 and the determination unit 51c.

[0075] (Current calculation section 51a5) The current calculation unit 51a5 is, Switching section 51a4 The current command value SVi output from is converted into a current operation value MVi. The current calculation unit 51a5 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 51a5 performs PI control on the current. Figure 7 is a diagram illustrating the functional configuration of the current calculation unit 51a5 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 51a5 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 detected current value PVi. The addition / subtraction block A31 outputs the calculation result to the gain block B31 and the integration block B32.

[0078] Gain block B31 multiplies the output of addition / subtraction block A31 by gain K31 and outputs it to addition / subtraction block A32. Integrate block B32 integrates the output from addition / subtraction block A31 and multiplies the integrated result by gain K32. Integrate block B32 outputs the calculation result to 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 51a5. The gains such as gain K31 are determined appropriately considering the system response, etc.

[0080] (Force control calculation unit 51a6) The force control calculation unit 51a6 converts the force command value SVf into a current command value SVi2. The force control calculation unit 51a6 calculates (generates) the current command value SVi2 so that the gripping force detection value PVf matches the force command value SVf. Figure 8 is a diagram illustrating the functional configuration of the force control calculation unit 51a6 of the calculation processing unit 51 of the control unit 50 of the gripping device according to this embodiment.

[0081] The force control calculation unit 51a6 calculates the current command value SVi2 such that the difference between the force command value SVf and the gripping force detection value PVf is minimized. Specifically, the force control calculation unit 51a6 performs PI control with respect to force.

[0082] The force control calculation unit 51a6 includes an addition / subtraction block A41, an addition / subtraction block A42, a gain block B41, and an integration block B42.

[0083] The addition / subtraction block A41 calculates the difference between the force command value SVf and the gripping force detection value PVf. The addition / subtraction block A41 outputs the calculation result to the gain block B41 and the integration block B42.

[0084] Gain block B41 multiplies the output of addition / subtraction block A41 by gain K41 and outputs it to addition / subtraction block A42. Integrate block B42 integrates the output from addition / subtraction block A41 and multiplies the integrated result by gain K42. Integrate block B42 outputs the calculation result to addition / subtraction block A42.

[0085] The addition / subtraction block A42 calculates the sum of the output of the gain block B41 and the output of the integration block B42. Then, the addition / subtraction block A42 outputs the current command value SVi2 as the output of the force control calculation unit 51a6. The gains such as gain K41 are determined appropriately considering the system response, etc.

[0086] [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 first set value as the force command value SVf that is suitable for gripping the hardest object TGT within the expected range. When the object TGT is hard, even if the gripping device 1 grips the object TGT with a strong gripping force, the deformation of the object TGT is small. Therefore, in order for the gripping device 1 to stably grip the object TGT, the gripping device 1 grips the object TGT with the strongest possible gripping force.

[0087] On the other hand, if the object to be gripped TGT is soft, there is a possibility that the object to be gripped TGT may be crushed if the gripping device 1 grips the object to be gripped TGT with a strong gripping force. Therefore, when the gripping device 1 grips a soft object to be gripped TGT, the gripping device 1 grips the object to be gripped TGT with the weakest possible gripping force. Accordingly, if the determination unit 51c determines that the object to be gripped TGT is soft, the force command generation unit 51b outputs a second set value lower than the first set value as the force command value SVf based on the switching signal SW.

[0088] [Determination unit 51c] The determination unit 51c determines the hardness of the object to be gripped, TGT. If the determination unit 51c determines that the object to be gripped, TGT, is hard, it outputs a switching signal SW to the switching unit 51a4 of the operation value calculation unit 51a and the force command generation unit 51b.

[0089] Figure 9 shows the results of gripping force detection when the gripping device 1 according to this embodiment grips a hard object TGT and when gripping a soft object TGT. The horizontal axis indicates the elapsed time since the gripping device 1 came into contact with the object TGT. The vertical axis indicates the gripping force detected by the force sensor.

[0090] In the graph of Figure 9, line Lh represents the detection result from the force sensor when gripping a hard object TGT. In the graph of Figure 9, line Ls represents the detection result from the force sensor when gripping a soft object TGT. Note that F1 indicates the first setting value suitable for gripping the hardest object TGT within the expected range.

[0091] Comparing the gripping of a hard object TGT with that of a soft object TGT, the gripping force increases more quickly when gripping a hard object TGT compared to when gripping a soft object TGT. Furthermore, the gripping force stabilizes more quickly when gripping a hard object TGT compared to when gripping a soft object TGT.

[0092] For example, if we compare the results of detecting the gripping force when time t1 has elapsed since the gripping device 1 made contact with the object to be gripped TGT, when a hard object to be gripped TGT is gripped, the force is Fah, whereas when a soft object to be gripped TGT is gripped, the force Fas is lower than Fah.

[0093] Therefore, the determination unit 51c uses the detected force value after a certain period of time to determine the hardness of the object TGT gripped by the gripping device 1. For example, if the detected force value after a certain period of time is above a threshold, the determination unit 51c determines that the object TGT is hard. If the detected force value after a certain period of time is below the threshold, the determination unit 51c determines that the object TGT is soft. If the determination unit 51c determines that the object is hard, it outputs a switching signal SW.

[0094] <Behavior of admittance control> Figure 10 shows the Bode plot of the gripping device 1 according to this embodiment when admittance control is being performed. Specifically, it is a Bode plot when a hard gripping object TGT is gripped using parameters corresponding to a soft gripping object TGT during admittance control.

[0095] As shown in Figure 10, the phase difference at a gain of 0 dB is approximately 40°. Generally, a phase margin of 45° or more is desirable. Therefore, when gripping a hard object TGT with parameters designed for a soft object TGT, the phase margin is insufficient. Due to the insufficient phase margin, the control system may become unstable.

[0096] In this embodiment, the gripping device 1 changes the control from admittance control to force control when the determination unit 51c determines that the object to be gripped TGT is hard.

[0097] <Processing of gripping device 1> The operation of the gripping device 1 according to this embodiment will now be described. Figure 11 is a flowchart illustrating the processing of the arithmetic processing unit 51 of the control unit 50 of the gripping device 1 according to this embodiment.

[0098] (Step S10) When processing begins, the arithmetic processing unit 51 determines whether it has detected that the gripping device 1 has come into contact with the object to be gripped TGT. If contact is detected (Yes in step S10), the arithmetic processing unit 51 proceeds to step S20. If contact is not detected (No in step S10), the processing in step S10 is repeated.

[0099] (Step S20) The arithmetic processing unit 51 first performs a first control process. The first control process is admittance control. The gripping device 1 calculates the current operation value MVi by performing admittance control on the gripping force detection value PVf.

[0100] Specifically, the switching unit 51a4 of the operation value calculation unit 51a outputs the current command value SVi1 as the current command value SVi to the current calculation unit 51a5. By outputting the current command value SVi1 as the current command value SVi to the current calculation unit 51a5, the operation value calculation unit 51a performs admittance control with respect to the gripping force detection value PVf.

[0101] (Step S30) The arithmetic processing unit 51 starts measuring time. Specifically, the arithmetic processing unit 51 starts a timer and begins measuring time.

[0102] (Step S40) The arithmetic processing unit 51 determines whether a predetermined time has elapsed. If the predetermined time has elapsed (Yes in step S40), the arithmetic processing unit 51 terminates the time measurement and proceeds to step S50. If the predetermined time has not elapsed (No in step S40), the arithmetic processing unit 51 repeats the process in step S40.

[0103] (Step S50) The calculation processing unit 51 determines the hardness of the object to be gripped TGT. Specifically, the determination unit 51c determines the hardness of the object to be gripped TGT based on the gripping force detection value PVf after a predetermined time has elapsed since contact. For example, if the gripping force detection value PVf after a predetermined time has elapsed since contact is greater than or equal to a threshold, the determination unit 51c determines that the object to be gripped TGT is hard. If the gripping force detection value PVf after a predetermined time has elapsed since contact is less than a threshold, the determination unit 51c determines that the object to be gripped TGT is soft.

[0104] (Step S60) If the determination unit 51c determines that the object to be grasped TGT is soft (Yes in step S60), the calculation processing unit 51 proceeds to step S70. If the determination unit 51c does not determine that the object to be grasped TGT is soft, that is, if it determines that the object to be grasped TGT is hard (No in step S60), the calculation processing unit 51 proceeds to step S80.

[0105] (Step S70) The arithmetic processing unit 51 changes the parameters of the first control process. Specifically, it changes the force command value SVf output by the force command generation unit 51b of the arithmetic processing unit 51 to a second set value that is lower than the first set value.

[0106] (Step S80) The arithmetic processing unit 51 switches the control process from the first control process to the second control process. The second control process is direct force control. The gripping device 1 calculates the current operation value MVi by directly comparing the gripping force detection value PVf with the force command value SVf.

[0107] Specifically, the switching unit 51a4 of the operation value calculation unit 51a outputs the current command value SVi2 as the current command value SVi to the current calculation unit 51a5. By the switching unit 51a4 of the operation value calculation unit 51a outputting the current command value SVi2 as the current command value SVi to the current calculation unit 51a5, the operation value calculation unit 51a performs direct force control with respect to the gripping force detection value PVf.

[0108] An example of the operation of the gripping device 1 according to this embodiment will be described. Figure 12 is a diagram illustrating the operation of the gripping device 1 according to this embodiment. Figure 12 is a diagram showing the detection results of the gripping force when the gripping device 1 according to this embodiment grips a hard object TGT and when gripping a soft object TGT. The horizontal axis shows the elapsed time since the gripping device 1 came into contact with the object TGT. The vertical axis shows the gripping force detected by the force sensor.

[0109] In the graph of Figure 12, line Lh represents the detection result from the force sensor when gripping a hard object TGT. In the graph of Figure 12, line Ls2 represents the detection result from the force sensor when gripping a soft object TGT. In the graph of Figure 12, line Ls represents the detection result from the force sensor when gripping a soft object TGT without changing the force command value SVf. Note that F1 indicates the first setting value suitable for gripping the hardest object TGT within the expected range. F2 indicates the second setting value which is smaller than the first setting value.

[0110] The arithmetic processing unit 51 performs admittance control during the period P1 up to time t1. The determination unit 51c determines from the output of the force sensor at time t1 that if the force is Fah, it is hard, and if the force is Fas, it is soft.

[0111] When gripping a hard object TGT, i.e., a wire Lh, the calculation processing unit 51 switches the control from admittance control to direct force control during the period P2 after time t1. The gripping device 1 according to this embodiment can stably grip objects TGT of various hardnesses by switching the force control from admittance control to direct force control.

[0112] On the other hand, when the arithmetic processing unit 51 grips a soft object TGT, i.e., a line Ls, it performs admittance control during the period P2 after time t1. The force command generation unit 51b also reduces the force command value SVf by a difference ΔSVf. That is, it changes the force command value SVf from the first set value F1 to the second set value F2. By changing the force command value SVf from the first set value F1 to the second set value F2, the force can be converged more quickly.

[0113] <Effects and Actions> According to the gripping device 1 of this embodiment, objects TGT of different hardness can be held stably. Specifically, according to the gripping device 1 of this embodiment, when a hard object TGT is to be gripped, the object TGT can be held stably by switching the control method.

[0114] Furthermore, according to the gripping device 1 of this embodiment, by controlling using the gripping force detection value PVf detected by the force detection unit 30, the object to be gripped TGT can be gripped stably with a constant gripping force. Furthermore, according to the gripping device 1 of this embodiment, by controlling using the gripping force detection value PVf detected by the force detection unit 30, stable gripping can be achieved with a low gripping force.

[0115] Furthermore, according to the gripping device 1 of this embodiment, gripping can be performed quickly and stably by changing the force command according to the hardness of the object to be gripped TGT.

[0116] Although the gripping device has been described above with reference to embodiments, the present invention is not limited to the above embodiments. Various modifications and improvements, such as combinations or substitutions with some or all of other embodiments, are possible within the scope of the present invention. For example, the technology of this disclosure can also be applied to robot hands with three or more fingers. [Explanation of Symbols]

[0117] 1 Gripping device 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 Switching section 51a5 Current calculation section 51a6 Force control calculation unit 51b Force command generation section 51c Judgment section 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, A first control process that calculates a position command value that determines the interval based on the force detection value, and calculates the operation value based on the position command value, A second control process is performed to calculate the operation value based on the difference between the force detection value and the force command value. The control unit, If the force detection value of the force detection unit after a predetermined time has elapsed since contact with the object is equal to or greater than the threshold value, the object is determined to be hard, and the second control process is selected and executed. If the detected value is less than the threshold, the system determines that the object is soft, selects and executes the first control process, and changes the force command value. gripping device.

2. 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 control method for a gripping device that outputs an operating value such that the magnitude of the gripping force detected by the force detection unit becomes a force command value, wherein A first control process that calculates a position command value for determining the interval based on the force detection value detected by the force detection unit, and calculates the operation value based on the position command value, A second control process is performed to calculate the operation value based on the difference between the force detection value and the force command value. If the force detection value of the force detection unit after a predetermined time has elapsed since contact with the object is equal to or greater than the threshold value, the object is determined to be hard, and the second control process is selected and executed. If the detected value is less than the threshold, the system determines that the object is soft, selects and executes the first control process, and changes the force command value. A method for controlling a gripping device.

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