Gripping device and control method

Abstract

Reduces variations in gripping force. [Solution] The gripping device 1 comprises a gripping section 7 for gripping an object 200, a drive mechanism 6 that drives the gripping section 7 in accordance with the rotational force of the motor 5, and a motor drive control device 2 that drives the motor 5. The motor drive control device 2 performs a first process to generate a drive control signal Sd to drive the motor 5 in the direction of gripping the object 200, and if it is determined during the first process that the motor 5 has lost step, it performs a second process to generate a drive control signal Sd to continue gripping the object 200. In the second process, the motor drive control device 2 generates a drive control signal Sd based on the measured value Vbef of the back electromotive force when the motor 5 loses step so that the torque of the motor 5 stays within a certain range.

Description

Technical Field

[0001] The present invention relates to a gripping device and a control method.

Background Art

[0002] In a manufacturing site or the like, a gripping device such as an electric gripper that grips an object (work) such as a mechanical part or an electronic part is used. Generally, an electric gripper includes a gripping part that grips an object, a motor, and a drive mechanism that drives the gripping part in accordance with the rotational force of the motor.

[0003] In recent years, as an electric gripper employing a stepping motor, a sensorless type electric gripper having no sensor such as an encoder for detecting the rotational speed of the stepping motor has been increasing (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Generally, in an electric gripper that grips a work such as a mechanical part or an electronic part as an object, it is desirable to adjust the gripping force according to the shape and size of the work. For example, if the gripping force is too large, the work may be damaged, and if the gripping force is too small, the work may fall off.

[0006] However, in a sensorless type electric gripper, it is difficult to accurately detect the position of the rotor or the like, so it is not easy to make the gripping force constant depending on the size of the work, and there is a problem that the gripping force is likely to vary.

[0007] This invention has been made in view of the above-mentioned problems, and aims to suppress variations in gripping force. [Means for solving the problem]

[0008] A gripping device according to a typical embodiment of the present invention comprises a motor having a coil, a gripping part for gripping an object, a drive mechanism for driving the gripping part in accordance with the rotational force of the motor, and a motor drive control device for driving the motor. The motor drive control device has a drive circuit for driving the motor by switching the excitation state of the coil based on a drive control signal, and a control circuit for generating the drive control signal. The control circuit includes a back electromotive force measuring unit for measuring the back electromotive force generated in the coil, and compares the measured value of the back electromotive force measured by the back electromotive force measuring unit with a predetermined threshold value which is a step-out determination threshold, and measures the back electromotive force. The system includes: a step-out determination unit that determines that the motor has lost step when a constant value falls below the step-out determination threshold; a drive control signal generation unit that performs a first process to generate a drive control signal to drive the motor in the direction of gripping the object, and if the step-out determination unit determines that the motor has lost step during the first process, it performs a second process to generate a drive control signal to continue gripping the object, wherein the drive control signal generation unit generates the drive control signal in the second process based on the measured value of the back electromotive force at the time the motor loses step so that the torque of the motor stays within a certain range. [Effects of the Invention]

[0009] The gripping device according to the present invention makes it possible to suppress variations in gripping force. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram schematically shows the configuration of the gripping device according to Embodiment 1. [Figure 2] This diagram schematically shows the configuration of the motor and motor drive control device in the gripping device according to Embodiment 1. [Figure 3] This is a block diagram showing the configuration of the control circuit in the gripping device according to Embodiment 1. [Figure 4] This diagram illustrates how to set the current command value during the holding operation process by the control circuit according to Embodiment 1. [Figure 5] This flowchart shows an example of the processing flow by the motor-driven control device according to Embodiment 1 when gripping an object. [Figure 6] This is a block diagram showing the configuration of the control circuit in the gripping device according to Embodiment 2. [Figure 7] This diagram illustrates how to set the current command value during the holding operation process by the control circuit according to Embodiment 2. [Figure 8] This flowchart shows an example of the processing flow by the motor drive control device when gripping an object with the gripping device according to Embodiment 2. [Figure 9A] This figure shows the simulation results of the variation in gripping force with respect to the size of the object being gripped by a conventional gripping device. [Figure 9B] This figure shows the simulation results of the variation in gripping force with respect to the size of the object being gripped, using the gripping device according to Embodiment 2. [Modes for carrying out the invention]

[0011] Specific examples of embodiments of the present invention will be described below with reference to the drawings. In the following description, common components in each embodiment will be denoted by the same reference numerals, and repeated explanations will be omitted. It should also be noted that the drawings are schematic, and the dimensional relationships and ratios of each element may differ from reality. There may also be parts where the dimensional relationships and ratios differ between drawings.

[0012] <Embodiment 1> Figure 1 is a schematic diagram showing the configuration of the gripping device 1 according to Embodiment 1.

[0013] In FIG. 1, a three-dimensional coordinate system (XYZ orthogonal coordinate system) composed of an X-axis, a Y-axis, and a Z-axis orthogonal to each other is set, and an example is shown where the gripping device 1 is arranged in the three-dimensional coordinate system. Regarding the Y-axis, which is a 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 direction. In FIG. 1, the X-axis direction is the direction in which the gripping portion 7 described later moves to grip or release the object 200.

[0014] The gripping device 1 is, for example, a device used to grip a workpiece such as a mechanical part or an electronic part as an object and transport it to a desired position for attachment. The gripping device 1 is a so-called electric gripper. Specifically, the gripping device 1 grips the object 200 between the finger portions 9_1 and 9_2 described later.

[0015] As shown in FIG. 1, the gripping device 1 includes a gripping portion 7, a drive mechanism 6, a motor 5, and a motor drive control device 2.

[0016] The gripping portion 7 is a mechanism for gripping the object 200. The gripping portion 7 is configured to be operable using the rotational force of the motor 5 as power. The gripping portion 7 has, for example, moving portions 8_1, 8_2 and finger portions 9_1, 9_2. The moving portions 8_1, 8_2 are connected to the drive mechanism 6 described later and are configured to be relatively movable in the X-axis direction by the drive mechanism 6. That is, the moving portion 8_1 and the moving portion 8_2 move in opposite directions to each other in the X-axis direction.

[0017] The finger portions 9_1 and 9_2 grip or release the object 200 by the movement of the moving portions 8_1 and 8_2. The finger portions 9_1 and 9_2 are arranged to protrude from the moving portions 8_1 and 8_2 toward the positive side in the Z-axis direction. The finger portions 9_1 and 9_2 are formed, for example, in a plate shape. One end side of the finger portion 9_1 is fixed to the moving portion 8_1 by a holding mechanism (such as a screw etc.) not shown in the figure, and one end side of the finger portion 9_2 is fixed to the moving portion 8_2 by a holding mechanism (such as a screw etc.) not shown in the figure. Although details will be described later, the finger portions 9_1 and 9_2 grip or release the object 200 at the respective other end sides of the finger portions 9_1 and 9_2 by moving in the X direction as the moving portions 8_1 and 8_2 move in the X direction.

[0018] In addition, in FIG. 1, the central position P is set as the reference position when the gripping device 1 grips the object 200.

[0019] The motor 5 is a power source for driving the gripping portion 7. The motor 5 is, for example, a stepping motor. As will be described later, the motor 5 operates by being supplied with electric power from the motor drive control device 2. In the present embodiment, as an example, it is assumed that the motor 5 is a two-phase stepping motor having coils of phase A and phase B. The details of the configuration of the motor 5 will be described later.

[0020] The drive mechanism 6 is a mechanism that drives the gripping portion 7 by transmitting the rotational force of the motor 5 to the gripping portion 7. The drive mechanism 6 is configured by combining mechanical components (not shown) such as gears, worm gears, and cams, for example. The drive mechanism 6 is connected between the output shaft of the motor 5 and the moving portions 8_1 and 8_2 of the gripping portion 7. The drive mechanism 6 converts the rotational motion of the motor 5 into a linear motion. That is, the drive mechanism 6 relatively moves the moving portion 8_1 and the moving portion 8_2 in the X-axis direction according to the rotational force of the motor 5.

[0021] The drive mechanism 6 has a self-locking function that restricts the movement of the gripping part 7 when the motor 5 is de-energized. Specifically, when the motor 5 is de-energized, the drive mechanism 6 restricts the movement of the moving parts 8_1 and 8_2 from moving in a direction that would release the object 200 being gripped, i.e., from moving away from each other. For example, the drive mechanism 6 achieves its self-locking function by using a known anti-reversal mechanism with a worm gear.

[0022] As described above, the drive mechanism 6 converts the rotational motion transmitted from the motor 5 into linear motion that moves the movable parts 8_1 and 8_2 (finger parts 9_1 and 9_2) of the gripping part 7 connected to the drive mechanism 6 in the X-axis direction. For example, when the motor 5 rotates in a predetermined direction, the drive mechanism 6 moves the movable part 8_1 to the positive side of the X-axis direction and the movable part 8_2 to the negative side of the X-axis direction. That is, the movable parts 8_1 and 8_2 move toward each other towards the center position P. As a result, the distance between the movable parts 8_1 and 8_2 is narrowed, making it possible to grip the object 200 by sandwiching it between the finger part 9_1 fixed to the movable part 8_1 and the finger part 9_2 fixed to the movable part 8_2.

[0023] Furthermore, for example, when the motor 5 rotates in the opposite direction to a predetermined direction, the drive mechanism 6 moves the movable part 8_1 to the negative side in the X-axis direction and the movable part 8_2 to the positive side in the X-axis direction. That is, the movable parts 8_1 and 8_2 move away from each other from the center position P. As a result, the distance between the movable parts 8_1 and 8_2 increases, making it possible to release the object 200 that was being held between the finger part 9_1 fixed to the movable part 8_1 and the finger part 9_2 fixed to the movable part 8_2.

[0024] Furthermore, the gripping of the object 200 by the gripping portion 7 is not limited to the method of sandwiching the object 200 between the finger portions 9_1 and 9_2. For example, if the object 200 is annular, the object 200 may be gripped by inserting the finger portions 9_1 and 9_2 into the inner circumference of the annular object 200, respectively, and moving the finger portions 9_1 and 9_2 away from each other from the inner circumference to the outer circumference of the object 200.

[0025] The motor drive control device 2 is a device that drives the motor 5. The configuration of the motor 5 and the motor drive control device 2 will be explained below with reference to the diagrams.

[0026] Figure 2 is a schematic diagram showing the configuration of the motor 5 and motor drive control device 2 in the gripping device 1 according to the embodiment.

[0027] As described above, motor 5 is a two-phase stepping motor. As shown in Figure 2, motor 5 has, for example, a rotor 50, a coil 51a for phase A, a coil 51b for phase B, and a two-phase stator (not shown).

[0028] Coils 51a and 51b are elements that excite the stator (not shown), respectively. Coil 51a has a positive terminal AP and a negative terminal AN. Coil 51b has a positive terminal BP and a negative terminal BN. Terminals AP and AN of coil 51a and terminals BP and BN of coil 51b are connected to inverter circuits 40a and 40b, respectively, which constitute the drive circuit 4.

[0029] Coils 51a and 51b are driven by inverter circuits 40a and 40b. As a result, currents Ia and Ib with different phases flow through coils 51a and 51b. For example, currents Ia and Ib with a 90-degree phase difference flow through coils 51a and 51b.

[0030] In the following explanation, when coil 51a and coil 51b are not distinguished, they will simply be referred to as "coil 51".

[0031] The rotor 50 is equipped with a unipolar or multipolar magnetized permanent magnet such that the south pole 50s and north pole 50n alternately reverse direction along the circumferential direction. Figure 2 shows an example where the rotor 50 has two poles.

[0032] The stator (not shown) is positioned around the rotor 50, close to its outer circumference. The rotor 50 rotates due to the periodic switching of the phases of the currents Ia and Ib flowing through coils 51a and 51b, respectively. An output shaft (not shown) is connected to the rotor 50, and the output shaft is driven by the rotational force of the rotor 50. A drive mechanism 6 is connected to the output shaft.

[0033] As shown in Figure 2, the motor drive control device 2 communicates with, for example, a higher-level device 100. Based on the drive command signal Sc received from the higher-level device 100, the motor drive control device 2 controls the rotation and stopping of the motor 5 by controlling the energization state of the coils 51a and 51b of each phase of the motor 5, thereby controlling the operation of the entire gripping device 1. When the motor drive control device 2 drives the motor 5, as described above, the rotational force of the motor 5 is transmitted to the gripping unit 7 via the drive mechanism 6 connected to the output shaft of the motor 5. This controls the gripping and release of the object 200 by the gripping unit 7.

[0034] As shown in Figure 2, the motor drive control device 2 includes, for example, a control circuit 3 and a drive circuit 4.

[0035] Based on the drive command signal Sc transmitted from the host device 100, the control circuit 3 generates a drive control signal Sda for exciting the A-phase coil 51a of the motor 5 and a drive control signal Sdb for exciting the B-phase coil 51b of the motor 5, respectively, and supplies them to the drive circuit 4, thereby rotating the motor 5 to the target rotation position. In the following description, when the drive control signal Sda and the drive control signal Sdb are not distinguished, both the drive control signal Sda and the drive control signal Sdb will be referred to as "drive control signal Sd". Details of the control circuit 3 will be described later.

[0036] The drive circuit 4 is a circuit that drives the motor 5 by switching the excitation state of the coils 51a and 51b of the motor 5 based on the drive control signal Sd. The drive circuit 4 includes, for example, inverter circuits 40a and 40b, current detection circuits 41a and 41b, and a voltage detection circuit 42.

[0037] The inverter circuits 40a and 40b supply drive power to the motor 5 based on the drive control signals Sda and Sdb. The inverter circuits 40a and 40b are provided, for example, corresponding to each coil 51a and 51b to be driven. For example, as shown in Figure 2, an inverter circuit 40a is provided for driving the A-phase coil 51a and an inverter circuit 40b is provided for driving the B-phase coil 51b. The inverter circuits 40a and 40b are configured, for example, by H-bridge circuits.

[0038] As shown in Figure 2, inverter circuit 40a is connected to the positive terminal AP and the negative terminal AN of the A-phase coil 51a. Inverter circuit 40b is connected to the positive terminal BP and the negative terminal BN of the B-phase coil 51b.

[0039] Inverter circuit 40a causes current Ia to flow through coil 51a by applying a voltage Va between terminals AP and AN based on the drive control signal Sda output from control circuit 3. Inverter circuit 40b causes current Ib to flow through coil 51b by applying a voltage Vb between terminals BP and BN based on the drive control signal Sdb output from control circuit 3.

[0040] For example, as shown in Figure 2, when the A-phase coil 51a is excited in the positive (+) direction, the inverter circuit 40a applies a voltage of "+Va" to terminal AP relative to terminal AN of the coil 51a, thereby causing a current Ia(+) to flow from terminal AP to terminal AN of the A-phase coil 51a. On the other hand, when the A-phase coil 51a is excited in the negative (-) direction, the inverter circuit 40a applies a voltage of "-Va" to terminal AP relative to terminal AN of the coil 51a, thereby causing a current Ia(-) to flow from terminal AN to terminal AP of the A-phase coil 51a. When the B-phase coil 51b is excited in the positive (+) direction, the inverter circuit 40b applies a voltage of "+Vb" to terminal BP relative to terminal BN of the coil 51b, thereby causing a current Ib(+) to flow from terminal BP to terminal BN of the B-phase coil 51b. When the B-phase coil 51b is excited in the negative direction (-), the inverter circuit 40b applies a voltage of "-Vb" to terminal BP relative to terminal BN of the coil 51b, thereby causing a current Ib(-) to flow from terminal BN to terminal BP of the B-phase coil 51b.

[0041] The current detection circuits 41a and 41b are circuits that detect the currents Ia and Ib flowing through the coils 51a and 51b. The current detection circuits 41a and 41b include, for example, shunt resistors. The shunt resistors are provided for each coil 51a and 51b and are connected in series with the inverter circuits 40a and 40b on the ground potential side or the power supply voltage side of the inverter circuits 40a and 40b. The current detection circuit 41a on the A-phase side outputs a current detection signal Sia representing the measured value of the A-phase current Ia from the voltage across the shunt resistor. The current detection circuit 41b on the B-phase side outputs a current detection signal Sib representing the measured value of the B-phase current Ib from the voltage across the shunt resistor.

[0042] The voltage detection circuit 42 is a circuit that detects the voltages of the coils 51a and 51b of the motor 5. For example, the voltage detection circuit 42 detects the voltages at the positive terminal AP and the negative terminal AN of the A-phase coil 51a, respectively, and converts them into voltages Vap and Van, respectively, that can be input to the control circuit 3, and outputs them. Similarly, the voltage detection circuit 42 detects the voltages at the positive terminal BP and the negative terminal BN of the B-phase coil 51b, respectively, and converts them into voltages Vbp and Vbn, respectively, that can be input to the control circuit 3, and outputs them. The voltage detection circuit 42 is composed of known circuits, such as a resistive voltage divider circuit. Note that the voltages Vap, Van, Vbp, and Vbn output from the voltage detection circuit 42 are sometimes collectively referred to as voltage Vs.

[0043] The voltage detection circuit 42 may also have an analog-to-digital conversion circuit. For example, the voltage detection circuit 42 may convert the detected voltages Vap, Van, Vbp, and Vbn into digital signals and output them.

[0044] The control circuit 3 is a circuit that generates a drive control signal Sd to control the drive of the motor 5 based on a drive command signal Sc from the host device 100. Here, the drive command signal Sc includes information that indicates the target state of the motor 5. For example, the drive command signal Sc includes information that specifies the rotational speed of the motor 5, and information that specifies the target rotation angle (target rotation position) of the motor 5. The information that specifies the target rotation position may, for example, be information that specifies the number of drive steps (number of pulses) of the motor 5 corresponding to the amount of movement to the target rotation position (target amount of movement).

[0045] Control circuit 3 is a program processing unit that has components (hardware elements) such as a processor (CPU, Central Processing Unit), various memories such as ROM (Read Only Memory) and RAM (Random Access Memory), timers, counters, A / D conversion circuits, input / output I / F circuits, and clock generation circuits, with each component connected to the others via buses or dedicated lines. Control circuit 3 is, for example, a microcontroller (MCU, Micro Control Unit). Control circuit 3 has a rewritable non-volatile memory, such as flash memory or EEPROM (Electrically Erasable Programmable Read-Only Memory), as its memory. For example, the reference value Iref for setting the current command value Ith, adjustment values ​​R1, R2, the step-out detection threshold Vth, the gripping force detection thresholds Vth1, Vth2, etc., which will be described later, are rewritable to the above non-volatile memory.

[0046] In this embodiment, the control circuit 3 is packaged as an IC (integrated circuit), for example, but is not limited to this. The control circuit 3 and the drive circuit 4 may also be packaged together.

[0047] The control circuit 3 has a gripping and releasing function that controls the operation of gripping the object 200 with the gripping unit 7 and the operation of releasing the object 200 by switching the energization of the coils 51a and 51b of the motor 5. Furthermore, the control circuit 3 has a gripping force adjustment function that determines whether or not the object 200 has been gripped and adjusts the gripping force after the object 200 has been gripped. The outline of the gripping force adjustment function will be described below.

[0048] The inventors of this application have found that the smaller the back electromotive force generated when the motor loses step, the greater the gripping force at the moment the gripping device grips the object. This is based on the phenomenon that the back electromotive force generated in the motor coil decreases as the load applied to the motor increases. Therefore, in order to suppress variations in gripping force after gripping the object 200, the control circuit 3 adjusts the gripping force by the gripping unit 7 according to the magnitude of the back electromotive force generated when the motor loses step, as a gripping force adjustment function. The following describes a specific configuration example of the control circuit 3 for realizing the gripping / releasing function and the gripping force adjustment function.

[0049] Figure 3 is a block diagram showing the configuration of the control circuit 3 in the gripping device 1 according to Embodiment 1.

[0050] The control circuit 3 includes a back electromotive force measurement unit 11, a step-out determination unit 12, a storage unit 13, and a drive control signal generation unit 14 as functional blocks for realizing the gripping / releasing function and gripping force adjustment function described above.

[0051] These functional blocks are realized, for example, by the processor within the MCU described above, which performs various calculations according to a program stored in memory, and controls peripheral circuits such as timers and counters, A / D conversion circuits, and input / output I / F circuits. Some or all of these functional blocks may be realized by dedicated hardware circuits (logic circuits, etc.). In addition, the control circuit 3 may have functional blocks for realizing other functions in addition to the above functions.

[0052] The memory unit 13 is a functional unit for storing parameters and calculation results necessary for the overall control of the gripping device 1 by the control circuit 3. For example, the memory unit 13 stores the reference value Iref, adjustment values ​​R1, R2, step-out determination threshold Vth, gripping force determination thresholds Vth1, Vth2, and measured values ​​of back electromotive force Vbef_1 to Vbef_n (where n is an integer of 2 or more).

[0053] The reference value Iref and adjustment values ​​R1 and R2 are parameters used to determine the current command value Ith, which serves as the reference for switching the energization of the coil 51 of the motor 5. The reference value Iref is the reference value for determining the current command value Ith. The adjustment values ​​R1 and R2 are values ​​used to adjust the magnitude of the reference value Iref. Details of the adjustment values ​​R1 and R2 will be described later.

[0054] The step-out detection threshold Vth is a reference value for detecting the occurrence of step-out in the motor 5. The gripping force detection thresholds Vth1 and Vth2 are reference values ​​for determining the strength of the gripping force on the object 200 by the gripping part 7. The gripping force detection thresholds Vth1 and Vth2 and the measured values ​​of back electromotive force Vbef_1 to Vbef_n will be described later.

[0055] The back electromotive force measurement unit 11 is a functional unit that measures the back electromotive force of the coils 51a and 51b of the motor 5.

[0056] Here, we will explain the method for measuring the back electromotive force of the coils 51a and 51b of the motor 5, which is used for determining step loss by the back electromotive force measurement unit 11.

[0057] Generally, when a stepping motor is rotating, a back electromotive force is generated in the coils of the unexcited phase. For example, when a stepping motor is driven by a single-phase excitation system, during the A-phase excitation period when the A-phase coil 51a is excited, a back electromotive force is generated in the B-phase coil 51b, which is the unexcited phase. On the other hand, during the B-phase excitation period when the B-phase coil 51b is excited, a back electromotive force is generated in the A-phase coil 51a, which is the unexcited phase.

[0058] Therefore, during the period when the A-phase coil 51a is de-energized, the back electromotive force measurement unit 11 measures the voltage between terminals AP and AN as the back electromotive force Vbef of coil 51a based on the voltages Vap and Van detected by the voltage detection circuit 42, and stores it in the storage unit 13. Similarly, during the period when the B-phase coil 51b is de-energized, the back electromotive force measurement unit 11 measures the voltage between terminals BP and BN as the back electromotive force Vbef of coil 51b based on the voltages Vbp and Vbn detected by the voltage detection circuit 42, and stores it in the storage unit 13.

[0059] The back electromotive force measurement unit 11 measures the back electromotive force Vbref for each step, which is the drive unit of the stepping motor, and stores it in the storage unit 13. For example, if the drive amount for one step corresponds to an electrical angle of 90 degrees, the back electromotive force measurement unit 11 measures the back electromotive force Vbref for every 90 degrees of electrical angle and stores it in the storage unit 13.

[0060] The back electromotive force measurement unit 11 stores the measured value Vbref_1 of the back electromotive force measured in the first step in the storage unit 13, and stores the measured value Vbref_n of the back electromotive force measured in the nth step (where n is an integer of 2 or more) in the storage unit 13.

[0061] The memory unit 13 may store multiple step-by-step back electromotive force measurement values ​​Vbef_1 to Vbef_n as described above, or it may store only the latest back electromotive force measurement value Vbef. If the back electromotive force measurement values ​​Vbef_1 to Vbef_n are not distinguished, they may be referred to as "back electromotive force measurement value Vbef".

[0062] The step-out determination unit 12 is a functional unit that determines whether or not step-out has occurred in the motor 5. Generally, in a stepping motor, the back electromotive force generated in the unexcited coil when a stepping motor loses step is smaller than the back electromotive force generated in the unexcited coil when the stepping motor is operating normally. Therefore, the stepping loss determination unit 12 determines whether or not a stepping loss has occurred by comparing the back electromotive force Vbef with the stepping loss determination threshold Vth stored in the memory unit 13.

[0063] Specifically, the step-out detection unit 12 determines that a step-out has occurred in the motor 5 and outputs a step-out detection signal Sz when the back electromotive force Vbef is less than the step-out detection threshold Vth, and determines that a step-out has not occurred in the motor 5 when the back electromotive force Vbef is equal to or greater than the step-out detection threshold Vth. The control circuit 3 drives the motor 5 to grip the object 200 with the gripping unit 7, and then determines that the object 200 has been gripped by the gripping unit 7 when the step-out detection unit 12 determines that a step-out has occurred in the motor 5 using the method described above.

[0064] The drive control signal generation unit 14 is a functional unit that generates drive control signals Sd(Sda,Sdb). When a drive command signal Sc instructing the gripping unit 7 to grip the object 200 is input, the drive control signal generation unit 14 performs a gripping operation process (first process) that generates drive control signals Sda,Sdb so that the gripping unit 7 drives the motor 5 in the direction of gripping the object 200.

[0065] Furthermore, if the drive control signal generation unit 14 determines that the motor 5 has lost step during the gripping operation, it performs a holding operation process (second process) which generates a drive control signal Sd to continue gripping the object 200.

[0066] Furthermore, when a drive command signal Sc instructing the gripping unit 7 to release the object 200 is input, the drive control signal generation unit 14 performs a release operation process (third process) that generates drive control signals Sda and Sdb so that the gripping unit 7 drives the motor 5 in the direction of releasing the object 200.

[0067] For example, in the gripping operation process, the holding operation process, and the releasing operation process, the drive control signal generation unit 14 generates drive control signals Sda and Sdb so as to switch between excitation and non-excitation of the A-phase coil 51a and the B-phase coil 51b at a predetermined timing based on a predetermined excitation method so that the motor 5 reaches a desired state. Here, the predetermined excitation method is any one of a one-phase excitation method, a 1-2 phase excitation method, a two-phase excitation method, and a microstep method. Details of the method for generating the drive control signal Sd will be described later.

[0068] In order to suppress variations in the gripping force when continuously gripping the object 200, the drive control signal generation unit 14 generates the drive control signal Sd so that the torque of the motor 5 is within a certain range based on the measured value Vbef of the back electromotive voltage when the motor 5 loses synchronization in the holding operation process. Specifically, in the holding operation process, the drive control signal generation unit 14 generates the drive control signal Sd so that the current in the coil 51 decreases as the measured value Vbef of the back electromotive voltage when the motor 5 loses synchronization decreases.

[0069] More specifically, in the holding operation process, the drive control signal generation unit 14 controls the magnitude of the current in the coil 51 based on the comparison results between the gripping force determination threshold values (first threshold value) Vth1 and the gripping force determination threshold values (second threshold value) Vth2 and the measured value Vbef of the back electromotive voltage. For example, the gripping force determination threshold values (first threshold value) Vth1 and the gripping force determination threshold values (second threshold value) Vth2 for determining the gripping force are set in the control circuit 3. The gripping force determination threshold value Vth1 is set to a value lower than the out-of-synchronization determination threshold value Vth, and the gripping force determination threshold value Vth2 is set to a value lower than the gripping force determination threshold value Vth1 (Vth2 < Vth1 < Vth). For example, Vth1 = 0.7 × Vth and Vth2 = 0.3 × Vth. The gripping force determination threshold values Vth1 and Vth2 are stored in the storage unit 13 in advance, for example.

[0070] When the measured value Vbef_k of the back electromotive force at the time of out-of-step occurrence of the motor 5 is between the gripping force determination threshold value Vth1 and the gripping force determination threshold value Vth2 (Vth2 ≤ Vbef_k < Vth1), the drive control signal generation unit 14 generates the drive control signal Sd so that the current in the coil 51 becomes the reference value Iref in the holding operation process.

[0071] When the measured value Vbef_k of the back electromotive force at the time of out-of-step occurrence of the motor 5 is greater than the gripping force determination threshold value Vth1 (Vth1 ≤ Vbef_k), the drive control signal generation unit 14 generates the drive control signal Sd so that the current in the coil 51 becomes a value (I1) greater than the reference value Iref in the holding operation process.

[0072] When the measured value Vbef_k of the back electromotive force at the time of out-of-step occurrence of the motor 5 is less than the gripping force determination threshold value Vth2 (Vbef_k < Vth2), the drive control signal generation unit 14 generates the drive control signal Sd so that the current in the coil 51 becomes a value (I2) less than the reference value Iref in the holding operation process.

[0073] As shown in FIG. 3, the drive control signal generation unit 14 has a drive command acquisition unit 16, a current measurement unit 15, a current command value setting unit 17, and a signal output unit 18 as functional blocks for realizing the above-described functions.

[0074] The drive command acquisition unit 16 is a functional unit that analyzes the information included in the drive command signal Sc transmitted from the host device 100 and gives an instruction to the signal output unit 18 based on the analyzed information and the out-of-step detection signal Sz output from the out-of-step determination unit 12.

[0075] For example, when a drive command signal Sc including information instructing gripping of the object 200 is input to the control circuit 3, the drive command acquisition unit 16 executes the gripping operation process. That is, the drive command acquisition unit 16 instructs the signal output unit 18 to generate the drive control signal Sd so as to rotate the motor 5 in a predetermined direction. For example, the drive command acquisition unit 16 causes the signal output unit 18 to generate the drive control signals Sda and Sdb of the 1-2 phase excitation system so that the motor 5 rotates in a predetermined direction.

[0076] Furthermore, if a step-out detection signal Sz is output from the step-out detection unit 12 during the gripping operation, the drive command acquisition unit 16 stops the gripping operation and executes the holding operation. That is, the drive command acquisition unit 16 instructs the signal output unit 18 to generate a drive control signal Sd so that the gripping unit 7 continues to hold the object 200. For example, the drive command acquisition unit 16 instructs the signal output unit 18 to generate two-phase excitation drive control signals Sda and Sdb so that the rotor 50 of the motor 5 is fixed.

[0077] Furthermore, when a drive command signal Sc containing information instructing the release of the object 200 is input to the control circuit 3, the drive command acquisition unit 16 instructs the signal output unit 18 to generate a drive control signal Sd so as to rotate the motor 5 in the opposite direction to the predetermined direction. For example, the drive command acquisition unit 16 instructs the signal output unit 18 to generate 1-2 phase excitation drive control signals Sda and Sdb so that the motor 5 rotates in the opposite direction to the predetermined direction.

[0078] The current measurement unit 15 is a functional unit that calculates and outputs measured values ​​of the currents Ia and Ib of each phase based on the current detection signals Sia and Sib output from the current detection circuits 41a and 41b. For example, if the current detection signals Sia and Sib are analog signals, the current measurement unit 15 converts the voltage of the current detection signal Sia into a digital value and outputs it as the measured value of the current Ia of phase A. The current measurement unit 15 also converts the voltage of the current detection signal Sib into a digital value and outputs it as the measured value of the current Ib of phase B. For example, the current measurement unit 15 outputs the measured value of the current Ia of phase A and the measured value of the current Ib of phase B, respectively, for each PWM period.

[0079] Furthermore, if the current detection signals Sia and Sib output from the current detection circuits 41a and 41b are digital values, the current measurement unit 15 should output the digital values ​​of the current detection signals Sia and Sib as the measured values ​​of the currents Ia and Ib.

[0080] The current command value setting unit 17 is a functional unit that sets the current command value Ith, which serves as the reference for the current (currents Ia and Ib for each phase) supplied to the motor 5. Based on instructions from the drive command acquisition unit 16, the current command value setting unit 17 sets the current command value Ith according to the gripping operation process, release operation process, and holding operation process. In the gripping operation process and release operation process, for example, the current command value setting unit 17 sets the current command value Ith to the reference value Iref. The method for setting the current command value Ith during the holding operation process will be described later.

[0081] The signal output unit 18 is a functional unit that generates a PWM signal of a predetermined period in response to an instruction from the drive command acquisition unit 16 and outputs it as a drive control signal Sd. In this embodiment, one period of the PWM signal, that is, the period in which one PWM signal is generated, is also referred to as the "PWM period".

[0082] In the gripping and release operations, when the drive command acquisition unit 16 instructs the motor 5 to rotate in a predetermined direction or the opposite direction, the signal output unit 18 generates drive control signals Sda and Sdb so that the excitation phase switches periodically (coils 51a and 51b commutate) based on a predetermined excitation method (for example, a 1-2 phase excitation method).

[0083] Specifically, during the gripping and release operations, the signal output unit 18 generates a PWM signal as a drive control signal Sd to energize the coil 51 until the current of the coil 51 reaches the current command value Ith, and to stop energizing the coil 51 when the current of the coil 51 reaches the current command value Ith. More specifically, the signal output unit 18 compares the measured values ​​of currents Ia and Ib obtained by the current measurement unit 15 with the current command value Ith set by the current command value setting unit 17 for each PWM cycle. For example, during the A-phase excitation period, the signal output unit 18 starts comparing the measured value of current Ia with the current command value Ith at the start of one PWM cycle. If the measured value of current Ia is lower than the current command value Ith, the signal output unit 18 sets the drive control signal Sda to the first logic level (e.g., high level), and if the measured value of current Ia is equal to or greater than the current command value Ith, the signal output unit 18 sets the drive control signal Sda to the second logic level (e.g., low level), which is the opposite of the first logic level. After that, the signal output unit 18 maintains the drive control signal Sda at the second logic level, regardless of the relative magnitudes of the measured value of current Ia and the current command value Ith, until the end of that PWM cycle. Then, when one PWM cycle ends and the next PWM cycle begins, the signal output unit 18 starts comparing the measured value of current Ia with the current command value Ith again to generate the drive control signal Sda (PWM signal) for the next cycle.

[0084] Similarly, during the B-phase excitation period, the signal output unit 18 generates a PWM signal as a drive control signal Sdb by comparing the measured value of current Ib with the current command value Ith for each PWM period.

[0085] In this way, the signal output unit 18 generates PWM signals as drive control signals Sda and Sdb, respectively, by repeatedly comparing the currents Ia and Ib of each phase with the current command value Ith for each phase PWM period during the gripping and release operation processes. The inverter circuit 40a, for example, energizes the coil 51a to be driven when the input drive control signal Sda is at a first logic level (e.g., high level), and regenerates the coil 51a without energizing it when the drive control signal Sda is at a second logic level (e.g., low level). Similarly, the inverter circuit 40b, for example, energizes the coil 51b to be driven when the input drive control signal Sdb is at a first logic level (e.g., high level), and regenerates the coil 51b without energizing it when the drive control signal Sdb is at a second logic level (e.g., low level). This allows the motor 5 to be driven while limiting the currents Ia and Ib of the motor 5 so that they do not exceed the current command value Ith.

[0086] Furthermore, during the holding operation process, when the drive command acquisition unit 16 instructs the signal output unit 18 to fix the rotor 50 of the motor 5, it generates drive control signals Sda and Sdb to excite the coil 51 specified by a predetermined excitation method. In this embodiment, as an example, the motor 5 is driven by a two-phase excitation method during the holding operation process.

[0087] Specifically, during the holding operation process, the signal output unit 18 generates a PWM signal as a drive control signal Sd such that the current of the coil 51 to be excited becomes the current command value Ith. More specifically, the signal output unit 18 generates a drive control signal Sd such that the A-phase coil 51a and the B-phase coil 51b are both excited in the same direction (positive or negative), and the measured values ​​of currents Ia and Ib obtained by the current measurement unit 15 do not exceed the current command value Ith set by the current command value setting unit 17.

[0088] The current command value setting unit 17 sets the current command value Ith according to the instructions from the drive command acquisition unit 16 and the instructions from the out-of-step detection signal Sz. Specifically, when the execution of the gripping operation process is instructed from the drive command acquisition unit 16, the current command value setting unit 17 sets the current command value Ith to the reference value Iref, for example (Ith = Iref). As described above, the information of the reference value Iref is stored in the storage unit 13, for example. Similarly, when the execution of the release operation process is instructed from the drive command acquisition unit 16, the current command value setting unit 17 sets the current command value Ith to the reference value Iref, for example (Ith = Iref). Note that the current command value Ith during the gripping operation process and the current command value Ith during the release operation may be different from each other, or may be different from the reference value Iref.

[0089] Also, when the execution of the holding operation process is instructed from the drive command acquisition unit 16, the current command value setting unit 17 determines the current command value Ith based on the measured value Vbef_k of the back electromotive voltage at the time of out-of-step detection.

[0090] FIG. 4 is a diagram for explaining a method of setting the current command value Ith during the holding operation process by the control circuit 3 according to Embodiment 1.

[0091] In FIG. 4, the horizontal axis represents the number of steps (electrical angle) of the motor 5, and the vertical axis represents the back electromotive voltage Vbef. As shown by the reference numeral 402 in FIG. 4, when the measured value Vbef_k of the back electromotive voltage at the time of out-of-step occurrence of the motor 5 is between the gripping force determination threshold value Vth1 and the gripping force determination threshold value Vth2 (Vth2 ≤ Vbef_k < Vth1), the current command value setting unit 17 sets the current command value Ith during the holding operation process to the reference value Iref (Ith = Iref).

[0092] As shown by reference numeral 401 in FIG. 4, when the measured value Vbef_k of the back electromotive force at the time of out-of-step occurrence of the motor 5 is greater than the gripping force determination threshold value Vth1 (Vth1≦Vbef_k), the current command value setting unit 17 sets the current command value Ith during the holding operation process to a value greater than the reference value Iref. Specifically, the drive control signal generation unit 14 sets a value (Iref×(1 + R1)) adjusted so that the reference value Iref becomes larger based on the adjustment value R1 as the current command value Ith. For example, when the adjustment value R1 = 20%, the drive control signal generation unit 14 sets the current command value Ith during the holding operation process to “Iref×(1 + 0.2)”. Thereby, the current command value Ith becomes 1.2 times the size of the reference value Iref.

[0093] As shown by reference numeral 403 in FIG. 4, when the measured value Vbef_k of the back electromotive force at the time of out-of-step occurrence of the motor 5 is smaller than the gripping force determination threshold value Vth2 (Vbef_k<Vth2), the current command value setting unit 17 sets the current command value Ith during the holding operation process to a value smaller than the reference value Iref. Specifically, the drive control signal generation unit 14 sets a value (Iref×(1 - R2)) adjusted so that the reference value Iref becomes smaller based on the adjustment value R2 as the current command value Ith. For example, when the adjustment value R2 = 20%, the drive control signal generation unit 14 sets the current command value Ith during the holding operation process to “Iref×(1 - 0.2)”. Thereby, the current command value Ith becomes 0.8 times the size of the reference value Iref.

[0094] Note that the adjustment value R1 and the adjustment value R2 may be the same value or different from each other. Also, the adjustment values R1 and R2 may be values indicating the ratio (%) with respect to the reference value Iref as described above, or may be values indicating the current value itself. For example, the adjustment value R1 may be a value indicating a current I1 greater than the reference value Iref, or the adjustment value R2 may be a value indicating a current I2 smaller than the reference value Iref.

[0095] Next, the flow of the process when the gripping device 1 according to Embodiment 1 grips the object 200 will be described.

[0096] Figure 5 is a flowchart showing an example of the processing flow by the motor drive control device 2 according to Embodiment 1 when gripping the object 200.

[0097] After the gripping device 1 is activated, if a drive command signal Sc containing information instructing the device to grip the object 200 is input to the motor drive control device 2, the motor drive control device 2 starts the gripping operation process.

[0098] First, the motor drive control device 2 drives the motor 5 (rotor 50) to rotate in a predetermined direction (step S1). Specifically, the drive control signal generation unit 14 generates a drive control signal Sd to switch between energizing and de-energizing the A-phase coil 51a and the B-phase coil 51b at timings based on a predetermined excitation method, using the method described above. As a result, the finger portions 9_1 and 9_2 of the gripping portion 7 move toward the center position P.

[0099] The motor drive control device 2 measures the back electromotive force after the motor 5 starts to drive (step S2). Specifically, the back electromotive force measurement unit 11 measures the back electromotive force at each step using the method described above, and stores the measured values ​​of the back electromotive force Vbef_1 to Vbef_n in the storage unit 13.

[0100] The motor drive control device 2 determines whether or not a step loss has occurred in the motor 5 (step S3). Specifically, the step loss determination unit 12 determines whether or not a step loss has occurred by comparing the measured value of the back electromotive force Vbef with the step loss determination threshold Vth using the method described above. If the motor drive control device 2 determines that a step loss has not occurred (step S3: NO), it performs the processing of steps S1 to S3 again.

[0101] If the motor drive control device 2 determines that a step loss has occurred (step S3: YES), it transitions from the gripping operation process to the holding operation process. Specifically, first, the motor drive control device 2 obtains the measured value Vbef_k of the back electromotive force at the time of step loss from the memory unit 13 (step S4). Next, the current command value setting unit 17 of the motor drive control device 2 determines, for example, whether the measured value Vbef_k of the back electromotive force at the time of step loss is greater than or equal to the gripping force determination threshold Vth1 (step S5). If the measured value Vbef_k of the back electromotive force at the time of step loss is greater than or equal to the gripping force determination threshold Vth1 (step S5: YES), the current command value setting unit 17 sets the current command value Ith to a value greater than the reference value Iref (Ith = I1 = Iref × (1 + R)) using the method described above (step S7).

[0102] If the measured value Vbef_k of the back electromotive force at the time of step loss is smaller than the gripping force determination threshold Vth1 (Step S5: NO), the current command value setting unit 17 determines whether the measured value Vbef_k of the back electromotive force at the time of step loss is smaller than the gripping force determination threshold Vth2 (Step S6). If the measured value Vbef_k of the back electromotive force at the time of step loss is smaller than the gripping force determination threshold Vth2 (Step S6: YES), the current command value setting unit 17 sets the current command value Ith to a value smaller than the reference value Iref (Ith = I2 = Iref × (1 - R)) using the method described above (Step S8).

[0103] On the other hand, if the measured value Vbef_k of the back electromotive force at the time of step loss is greater than or equal to the gripping force determination threshold Vth2 (step S6: NO), the current command value setting unit 17 sets the current command value Ith to the reference value Iref (step S9).

[0104] Next, the motor drive control device 2 fixes the rotor 50 of the motor 5 (step S10). Specifically, the drive control signal generation unit 14 generates two-phase excitation drive control signals Sda and Sdb so that the currents of coil 51a and coil 51b do not exceed the current command value Ith set in step S7, step S8, or step S9, and energizes coil 51a and coil 51b in the same direction. As a result, the rotor 50 is fixed and the gripping unit 7 holds the object 200.

[0105] As described above, in the gripping device 1 according to Embodiment 1, during the holding operation process after the gripping unit 7 grips the object 200, a drive control signal Sd is generated based on the measured value Vbef_k of the back electromotive force when the motor 5 loses step, so that the torque of the motor 5 stays within a certain range. This makes it possible to suppress variations in gripping force when continuously gripping the object 200.

[0106] Furthermore, in the gripping device 1, as described above, the drive control signal generation unit 14 generates a drive control signal Sd in the holding operation process such that the current in the coil 51 decreases as the measured value Vbef_k of the back electromotive force when the motor 5 loses step. This makes it easy to control the magnitude of the torque when the gripping unit 7 grips the object 200 so that it stays within a certain range.

[0107] In particular, as described above, when the measured value Vbef_k of the back electromotive force at the time of out-of-tune occurrence is between the gripping force determination threshold value Vth1 and the gripping force determination threshold value Vth2 (Vth2 ≤ Vbef_k < Vth1), the drive control signal generation unit 14 generates the drive control signal Sd so that the current of the coil 51 during the holding operation process becomes the reference value Iref. Further, when the measured value Vbef_k of the back electromotive force at the time of out-of-tune occurrence is greater than the gripping force determination threshold value Vth1 (Vth1 ≤ Vbef_k), the drive control signal generation unit 14 generates the drive control signal Sd so that the current of the coil 51 during the holding operation process becomes a value greater than the reference value Iref. Furthermore, when the measured value Vbef_k of the back electromotive force at the time of out-of-tune occurrence is less than the gripping force determination threshold value Vth2 (Vbef_k < Vth2), the drive control signal generation unit 14 generates the drive control signal Sd so that the current of the coil 51 during the holding operation process becomes a value less than the reference value Iref. According to this, in the holding operation process, it becomes easy to adjust so that the smaller the measured value Vbef_k of the back electromotive force at the time of out-of-tune occurrence of the motor 5 is, the smaller the current of the coil 51 becomes, and it becomes easy to suppress the variation in the gripping force.

[0108] ≪Embodiment 2≫ FIG. 6 is a block diagram showing the configuration of the control circuit 3A in the gripping device 1A according to Embodiment 2.

[0109] The gripping device 1A according to Embodiment 2 is different from the gripping device 1 according to Embodiment 1 in that the current command value Ith is determined using a plurality of measured values Vbef_1 to Vbef_n of the back electromotive force instead of one measured value of the back electromotive force, and is the same as the gripping device 1 according to Embodiment 1 in other respects.

[0110] In the control circuit 3A of the gripping device 1A according to Embodiment 2, the back electromotive force measurement unit 11 measures the back electromotive force every time the electrical angle of the motor 5 changes by a predetermined amount (for example, 90 degrees) and outputs the measured values Vbef_1 to Vbef_n of the back electromotive force. For example, the back electromotive force measurement unit 11 measures the back electromotive force every one step and stores the measured values Vbef_1 to Vbef_n of the back electromotive force in the storage unit 13.

[0111] The drive control signal generation unit 14A sets the current command value Ith by comparing a plurality of measured values Vbef_1 to Vbef_n of the back electromotive voltage with the set gripping force determination threshold value (second threshold value) Vth3 and the gripping force determination threshold value (first threshold value) Vth4. Specifically, the drive control signal generation unit 14A compares the measured value Vbef_k of the back electromotive voltage at the time of out-of-step occurrence and the measured value Vbef_(k - 1) of the back electromotive voltage before (one step before) the out-of-step occurrence with the gripping force determination threshold values Vth3 and Vth4 to set the current command value Ith.

[0112] Here, the gripping force determination threshold value Vth3 is set to a value higher than the out-of-step determination threshold value Vth, and the gripping force determination threshold value Vth4 is set to a value lower than the out-of-step determination threshold value Vth (Vth4 < Vth < Vth3). For example, Vth3 = 4.0V and Vth4 = 0.7V. The gripping force determination threshold values Vth3 and Vth4 are stored in the storage unit 13 in advance, for example.

[0113] FIG. 7 is a diagram for explaining a method of setting the current command value Ith during the holding operation process by the control circuit 3A according to the second embodiment.

[0114] In FIG. 7, the horizontal axis represents the number of steps (electrical angle) of the motor 5, and the vertical axis represents the back electromotive voltage Vbef.

[0115] As shown by reference numeral 701 in FIG. 7, when the measured value Vbef_k of the back electromotive voltage at the time of out-of-step occurrence of the motor 5 is higher than the gripping force determination threshold value Vth4 and the measured value Vbef_(k - 1) of the back electromotive voltage before (one step before) the out-of-step occurrence of the motor 5 is higher than the gripping force determination threshold value Vth3, the drive control signal generation unit 14A generates the drive control signal Sd so that the torque of the motor 5 in the holding operation process is larger than the torque at the time of out-of-step occurrence.

[0116] For example, the drive control signal generation unit 14A generates the drive control signal Sd by setting the current command value Ith during the holding operation process to a value greater than the reference value Iref. Specifically, the current command value setting unit 17A sets the current command value Ith to a value (Iref × (1 + R1)) adjusted so that the reference value Iref is larger based on the adjustment value R1. For example, if the adjustment value R1 = 50%, the current command value setting unit 17A sets the current command value Ith during the holding operation process to "Iref × (1 + 0.5)". As a result, the current command value Ith becomes 1.5 times the size of the reference value Iref.

[0117] Alternatively, the drive control signal generation unit 14A may generate a drive control signal Sd such that the current command value Ith during the holding operation process is set to a value smaller than the reference value Iref, and the electrical angle advances by a predetermined amount (for example, 90 degrees). For example, the current command value setting unit 17A sets the current command value Ith to a value (Iref × (1 - R2)) adjusted based on the adjustment value R2 so that the reference value Iref becomes smaller. For example, if the adjustment value R2 = 50%, the current command value setting unit 17A sets the current command value Ith during the holding operation process to "Iref × (1 - 0.5)". As a result, the current command value Ith becomes 0.5 times the size of the reference value Iref. The drive command acquisition unit 16 also instructs the signal output unit 18 to excite the A-phase coil 51a and the B-phase coil 51b in opposite directions (positive and negative directions).

[0118] As shown by reference numeral 703 in Figure 7, if the measured value Vbef_k of the back electromotive force at the time of motor 5's step-out is lower than the gripping force determination threshold Vth4, and the measured value Vbef_k of the back electromotive force before the time of motor 5's step-out (one step prior) is lower than the gripping force determination threshold Vth3, then a drive control signal Sd is generated in the holding operation process so that the torque of motor 5 becomes less than the torque at the time of step-out.

[0119] For example, the drive control signal generation unit 14A generates the drive control signal Sd by setting the current command value Ith during the holding operation process to a value smaller than the reference value Iref. Specifically, the current command value setting unit 17A sets the current command value Ith to a value (Iref × (1 - R2)) adjusted based on the adjustment value R2 so that the reference value Iref becomes smaller. For example, if the adjustment value R2 = 50%, the current command value setting unit 17A sets the current command value Ith during the holding operation process to "Iref × (1 - 0.5)". As a result, the current command value Ith becomes 0.5 times the size of the reference value Iref.

[0120] If neither the first nor the second condition described above is met, the drive control signal generation unit 14A generates a drive control signal Sd by setting the current command value Ith during the holding operation process to the reference value Iref (Ith = Iref). For example, as shown by reference numeral 702 in Figure 7, if the measured value Vbef_k of the back electromotive force when the motor 5 loses step is higher than the gripping force determination threshold Vth4, and the measured value Vbef_(k-1) of the back electromotive force before the motor 5 loses step (one step prior) is lower than the gripping force determination threshold Vth3, the current command value setting unit 17A sets the current command value Ith to the reference value Iref.

[0121] Next, the processing flow when gripping the object 200 with the gripping device 1A according to Embodiment 2 will be described.

[0122] Figure 8 is a flowchart showing an example of the processing flow by the motor drive control device 2A when gripping an object 200 with the gripping device 1A according to Embodiment 2.

[0123] After the gripping device 1A is activated, if a drive command signal Sc containing information instructing the gripping of the object 200 is input to the motor drive control device 2A, the motor drive control device 2A starts the gripping operation process. First, the motor drive control device 2A performs the processing from step S1 to step S3, similar to the motor drive control device 2 according to Embodiment 1.

[0124] If the motor drive control device 2A determines that a step loss has occurred (step S3: YES), it stops the gripping operation and performs the holding operation. Specifically, first, the motor drive control device 2A obtains the measured value of the back electromotive force Vbef_k at the time of the step loss and the measured value of the back electromotive force Vbef_(k-1) one step prior to the time of the step loss (step S14).

[0125] Next, the current command value setting unit 17A of the motor drive control device 2A determines, for example, whether the measured value Vbef_k of the back electromotive force at the time of step loss is greater than or equal to the gripping force determination threshold Vth4 (step S15). If the measured value Vbef_k of the back electromotive force at the time of step loss is greater than or equal to the gripping force determination threshold Vth4 (step S15: YES), the current command value setting unit 17A determines, for example, whether the measured value Vbef_(k-1) of the back electromotive force one step prior to the time of step loss is greater than or equal to the gripping force determination threshold Vth3 (step S16).

[0126] If the measured value Vbef_(k-1) of the back electromotive force one step prior to the occurrence of a step-out is greater than or equal to the gripping force determination threshold Vth3 (step S16: YES), the current command value setting unit 17 sets the current command value Ith to a value greater than the reference value Iref (Ith=I1=Iref×(1+R1)) using the method described above (step S18). Alternatively, the current command value setting unit 17 may set the current command value Ith to a value less than the reference value Iref (Ith=I2=Iref×(1-R2)), and then instruct the drive command acquisition unit 16 to generate a drive control signal Sd so that the electrical angle advances by 90 degrees (rotates by one step).

[0127] On the other hand, if the measured value Vbef_k of the back electromotive force at the time of step loss is smaller than the gripping force determination threshold Vth4 (step S15: NO), the current command value setting unit 17A determines, for example, whether the measured value Vbef_(k-1) of the back electromotive force one step prior to the time of step loss is smaller than the gripping force determination threshold Vth3 (step S17).

[0128] If the measured value Vbef_(k-1) of the back electromotive force one step prior to the occurrence of a step-out is smaller than the gripping force determination threshold Vth3 (step S17: YES), the current command value setting unit 17 sets the current command value Ith to a value smaller than the reference value Iref (Ith=I2=Iref×(1-R2)) using the method described above (step S20).

[0129] On the other hand, if in step S17 the measured value Vbef_(k-1) of the back electromotive force one step prior to the occurrence of a step-out is greater than or equal to the gripping force determination threshold Vth3, or if in step S16 the measured value Vbef_(k-1) of the back electromotive force one step prior to the occurrence of a step-out is less than the gripping force determination threshold Vth3, the current command value setting unit 17 sets the current command value Ith to the reference value Iref (step S19).

[0130] Next, the motor drive control device 2 fixes the rotor 50 of the motor 5 (step S21). Specifically, if a current command value Ith is set in steps S19 and S20, or if the current command value Ith is set to a value greater than the reference value Iref in step S18, the drive control signal generation unit 14 generates two-phase excitation drive control signals Sda and Sdb so that the currents of coil 51a and coil 51b do not exceed the current command value Ith set in step S18, step S19, or step S20, and energizes coil 51a and coil 51b in the same direction. As a result, the rotor 50 is fixed and the gripping unit 7 holds the object 200 with the desired gripping force.

[0131] Furthermore, if the current command value Ith is set to a value smaller than the reference value Iref in step S18, the drive control signal generation unit 14 generates two-phase excitation drive control signals Sda and Sdb so that the currents of coil 51a and coil 51b do not exceed the current command value Ith set in step S18, and energizes coil 51a and coil 51b in opposite directions. As a result, the rotor 50 rotates for one step and then locks in place, and the gripping unit 7 holds the object 200.

[0132] As described above, the gripping device 1A according to Embodiment 2 generates a drive control signal Sd in the holding operation process after the gripping unit 7 has gripped the object 200, based on the measured value Vbef_k of the back electromotive force when the motor 5 loses step and the measured value Vbef_(k-1) of the back electromotive force before the motor 5 loses step, so that the torque of the motor 5 stays within a certain range. This makes it possible to suppress variations in gripping force when continuously gripping the object 200, similar to the gripping device 1 according to Embodiment 1.

[0133] Furthermore, as described above, the drive control signal generation unit 14A generates a drive control signal Sd such that the torque of the motor 5 becomes greater than the torque of the motor 5 at the time of motor 5 loss of step when the measured value of the back electromotive force Vbef_k when the motor 5 loses step is higher than the gripping force determination threshold Vth4, and the measured value of the back electromotive force Vbef_(k-1) before the motor 5 loses step is higher than the gripping force determination threshold Vth3, which satisfies the first condition (Vth4≦Vbef_k & Vth3≦Vbef_(k-1)). Furthermore, if the second condition (Vth4>Vbef_k & Vth3>Vbef_(k-1)) is met, where the measured value of the back electromotive force Vbef_k at the time of motor 5's step-out is lower than the gripping force determination threshold Vth4, and the measured value of the back electromotive force Vbef_(k-1) before the motor 5's step-out is lower than the gripping force determination threshold Vth3, then a drive control signal Sd is generated in the holding operation process so that the torque of motor 5 becomes smaller than the torque at the time of motor 5's step-out.

[0134] According to this, the torque of motor 5 during the holding operation is adjusted using not only the measured value Vbef_k of the back electromotive force when motor 5 loses step, but also the measured value Vbef_(k-1) of the back electromotive force before motor 5 loses step (for example, one step earlier). This makes it possible to more reliably suppress variations in gripping force when continuously gripping an object. In particular, even when the gripping force varies due to hardware such as the magnetization of the rotor magnet in a stepping motor, it becomes possible to further reduce that variation.

[0135] Figure 9A shows the simulation results of the variation in gripping force with respect to the size of the object being gripped, using a conventional gripping device. Figure 9B shows the simulation results of the variation in gripping force with respect to the size of the object being gripped, using the gripping device according to Embodiment 2.

[0136] In Figures 9A and 9B, the horizontal axis represents the size of the object being gripped, i.e., the distance [mm] from the center position P in the gripping device, and the vertical axis represents the gripping force, i.e., the torque [N].

[0137] For example, consider a case where the specifications for a gripping device require a standard gripping force of 16 [N] and the variation in gripping force must be kept within a predetermined range ΔT (±30%). As shown in Figure 9A, in conventional gripping devices, the variation in gripping force exceeds the predetermined range ΔT as the size of the object being gripped (distance from the center position P) increases.

[0138] In contrast, with the gripping device 1A according to Embodiment 2, as shown in Figure 9B, it is understood that the variation in gripping force can be suppressed to not exceed a predetermined range compared to conventional gripping devices. Thus, according to the gripping device 1A of Embodiment 2, it is possible to more reliably suppress variations in gripping force when continuously gripping an object.

[0139] Furthermore, in the gripping device 1A, as described above, the drive control signal generation unit 14 generates a drive control signal Sd such that the current of the coil 51 becomes the reference value Iref during the holding operation process if neither the first condition (Vth4≦Vbef_k & Vth3≦Vbef_(k-1)) nor the second condition (Vth4>Vbef_k & Vth3>Vbef_(k-1)) is met; generates a drive control signal Sd such that the current of the coil 51 becomes a value greater than the reference value Iref (I1) during the holding operation process if the first condition is met; and generates a drive control signal Sd such that the current of the coil 51 becomes a value less than the reference value Iref (I2) during the holding operation process if the second condition is met. According to this, it becomes easy to control the gripping force (torque) while holding the object so that it remains within a certain range, depending on the gripping force when the object is gripped by the gripping part 7.

[0140] Furthermore, in the gripping device 1A, as described above, the drive control signal generation unit 14 may generate a drive control signal Sd such that the current of the coil 51 becomes a reference value Iref during the holding operation process if neither of the first condition (Vth4≦Vbef_k & Vth3≦Vbef_(k-1)) nor the second condition (Vth4>Vbef_k & Vth3>Vbef_(k-1)) is met; generate a drive control signal Sd such that the current of the coil 51 becomes a value smaller than the reference value Iref (I2) and the electrical angle advances by a predetermined amount (for example, 90 degrees) during the holding operation process if the first condition is met; and generate a drive control signal Sd such that the current of the coil 51 becomes a value smaller than the reference value Iref (I2) during the holding operation process if the second condition is met.

[0141] According to this, it becomes easy to control the gripping force (torque) while holding the object so that it remains within a certain range, depending on the gripping force when the object is gripped by the gripping part 7. Furthermore, when the first condition is met, not only is the rotor 50 rotated by one step, but the coil current is set to a value smaller than the reference value, thereby preventing the gripping force from becoming too large.

[0142] <<Extension of the Embodiment>> Although the present invention has been specifically described above based on embodiments, it goes without saying that the present invention is not limited thereto and can be modified in various ways without departing from its essence.

[0143] For example, in the above embodiment, the number of phases of the motor 5 (stepping motor) is not limited to two phases. Also, the motor 5 is not limited to a stepping motor, but may be, for example, a brushless DC motor.

[0144] Furthermore, while Embodiment 2 illustrates the case where the current command value Ith is determined using two measured values ​​of back electromotive force Vbef, the current command value Ith may also be determined using three or more measured values ​​of back electromotive force Vbef.

[0145] Furthermore, the flowchart described above is merely an example illustrating the operation and is not limited to it. In other words, the steps shown in each diagram of the flowchart are specific examples and are not limited to this flow. For example, the order of some processes may be changed, other processes may be inserted between each process, or some processes may be performed in parallel. [Explanation of symbols]

[0146] 1,1A...Gripping device, 2,2A...Motor drive control device, 3,3A...Control circuit, 4...Drive circuit, 5...Motor (stepping motor), 6...Drive mechanism, 7...Gripping part, 8_1,8_2...Moving part, 9_1,9_2...Finger part, 11...Back EMF measurement part, 12...Step out of step determination part, 13...Storage part, 14...Drive control signal generation part, 15...Current measurement part, 16...Drive command acquisition part, 17...Current command value setting part, 18...Signal output part, 40a,40b...Inverter circuit, 41a,41b...Current detection circuit, 42...Voltage detection circuit, 50...Low Ta, 50s...South pole, 50n...North pole, 51a, 51b...Coil, 100...Higher device, 200...Object, Ia, Ib...Current, Ith...Current command value, Iref...Reference value, R1, R2...Adjustment value, Sc...Drive command signal, Sd, Sda, Sdb...Drive control signal, Sia, Sib...Current detection signal, So...Decision signal, Vap, Van, Vbp, Vbn, Vs...Voltage, Vbef, Vbef_1~Vbef_n...Measured value of back electromotive force, Vth...Step-out judgment threshold, Vth1~Vth4...Gripping force judgment threshold, 100...Higher device.

Claims

1. A motor having a coil, A gripping part for grasping an object, A drive mechanism that drives the gripping portion in accordance with the rotational force of the motor, The motor includes a motor drive control device that drives the motor, The motor drive control device includes a drive circuit that drives the motor by switching the excitation state of the coil based on a drive control signal, and a control circuit that generates the drive control signal. The aforementioned control circuit is A back electromotive force measuring unit for measuring the back electromotive force generated in the coil, A step-out determination unit compares the measured value of the back electromotive force measured by the back electromotive force measurement unit with a predetermined threshold value, which is a step-out determination threshold, and determines that the motor has lost step if the measured value of the back electromotive force falls below the step-out determination threshold. The drive control signal generation unit performs a first process to generate a drive control signal to drive the motor in the direction of gripping the object, and if the step-out determination unit determines that step-out has occurred in the motor during the first process, it performs a second process to generate a drive control signal to continue gripping the object. In the second process, the drive control signal generation unit generates the drive control signal based on the measured value of the back electromotive force at the time of motor step loss, such that the motor torque falls within a certain range. gripping device.

2. In the gripping device according to claim 1, In the second process, the drive control signal generation unit generates the drive control signal such that the current in the coil decreases as the measured value of the back electromotive force at the time of motor step loss decreases. gripping device.

3. In the gripping device according to claim 2, A first threshold lower than the aforementioned step-out detection threshold and a second threshold lower than the first threshold are set. The drive control signal generation unit generates a drive control signal in the second process so that the coil current becomes a reference value when the measured value of the back electromotive force at the time of motor step loss is between the first threshold and the second threshold; generates a drive control signal in the second process so that the coil current becomes a value greater than the reference value when the measured value of the back electromotive force at the time of motor step loss is greater than the first threshold; and generates a drive control signal in the second process so that the coil current becomes a value less than the reference value when the measured value of the back electromotive force at the time of motor step loss is less than the second threshold. gripping device.

4. In the gripping device according to claim 1, A first threshold lower than the aforementioned loss-of-sync determination threshold and a second threshold higher than the aforementioned loss-of-sync determination threshold are set. The back electromotive force measuring unit measures the back electromotive force each time the electrical angle of the motor changes by a predetermined amount and outputs the measured value of the back electromotive force. The drive control signal generation unit generates a drive control signal in the second process such that the torque of the motor becomes greater than the torque at the time of motor loss if the first condition is met, namely that the measured value of the back electromotive force at the time of motor loss is higher than the first threshold, and the measured value of the back electromotive force before the motor loss occurs is higher than the second threshold. The drive control signal generation unit generates a drive control signal in the second process such that the torque of the motor becomes less than the torque at the time of motor loss if the second condition is met, namely that the measured value of the back electromotive force at the time of motor loss is lower than the first threshold, and the measured value of the back electromotive force before the motor loss occurs is lower than the second threshold. gripping device.

5. In the gripping device according to claim 4, The drive control signal generation unit generates the drive control signal in the second process so that the coil current becomes a reference value if neither the first condition nor the second condition is met; generates the drive control signal in the second process so that the coil current becomes a value greater than the reference value if the first condition is met; and generates the drive control signal in the second process so that the coil current becomes a value less than the reference value if the second condition is met. gripping device.

6. In the gripping device according to claim 4, The drive control signal generation unit generates the drive control signal in the second process so that the coil current reaches a reference value if neither the first nor the second condition is met; generates the drive control signal in the second process so that the coil current becomes less than the reference value and the electrical angle advances by a predetermined amount if the first condition is met; and generates the drive control signal in the second process so that the coil current becomes less than the reference value if the second condition is met. gripping device.

7. A control method for a gripping device comprising a motor having a coil, a gripping part for gripping an object, a drive mechanism for driving the gripping part in accordance with the rotational force of the motor, and a motor drive control device for generating a drive control signal for driving the motor, The motor drive control device starts a first process of generating a drive control signal so that the gripping part grips the object, The motor drive control device performs a second step of measuring the back electromotive force generated in the coil during the first process, The motor drive control device compares the measured value of the back electromotive force measured in the second step with a predetermined threshold value, which is a step-out determination threshold, and determines that the motor has lost step if the measured value of the back electromotive force falls below the step-out determination threshold. The motor drive control device includes a fourth step in which, if it is determined in the third step that the motor has lost step, it performs a second process to generate a drive control signal to continue gripping the object, The fourth step includes the motor drive control device generating a drive control signal in the second process based on the measured value of the back electromotive force at the time of motor step loss so that the motor torque falls within a certain range. Control method.

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