Holding device and control method

Abstract

The present invention prevents a held object from falling out.　A holding device (1) is provided with: a holding part (7) that is for holding an object (200); a drive mechanism (6) that drives the holding part (7) in accordance with a rotational force of a motor (5) and that has a self-locking function which limits the movement of the holding part (7) while the energization of the motor 5 is stopped; and a motor drive control device (2) that drives the motor (5). When a drive command signal (Sc) including information indicating driving the holding part (7) is input, the motor drive control device (2) drives the motor (5) so that the holding part (7) holds the object (200). If stepping-out of the motor (5) is detected, the motor drive control device (2) supplies the motor (5) with a smaller current than that supplied to the motor (5) before the stepping-out detection, thereby fixing a rotor (50) of the motor (5).

Description

Grip device and control method

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

[0002] Gripping devices such as electric grippers are used in manufacturing sites to grip objects (workpieces) such as mechanical parts, electronic parts, etc. Generally, an electric gripper includes a gripping unit that grips the object, a motor, and a drive mechanism that drives the gripping unit in response to the rotational force of the motor.

[0003] In recent years, an increasing number of electric grippers have been equipped with drive mechanisms that have a self-locking function, which limits the movement of the gripping part when the motor is de-energized (see Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2020-104188

[0005] However, in conventional electric grippers, the force with which the object is gripped decreases over time due to the self-locking function, which may cause the object to fall off the gripping portion.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to prevent a grasped object from falling off.

[0007] A gripping device according to a representative embodiment of the present invention comprises a motor, a gripping unit for gripping an object, a drive mechanism that drives the gripping unit in accordance with the rotational force of the motor and has a self-locking function that limits movement of the gripping unit when power to the motor is stopped, and a motor drive control device that drives the motor. The motor drive control device has a drive circuit that drives the motor by supplying current to the motor based on a drive control signal, and a control circuit that generates the drive control signal based on a drive command signal. The control circuit includes a drive control signal generation unit that generates the drive control signal, and a synchronism loss detection unit that detects synchronism loss of the motor. The drive control signal generation unit generates the drive control signal that drives the gripping unit so that the gripping unit grips the object when the drive command signal including information instructing driving of the gripping unit is input, and when synchronism loss of the motor is detected by the synchronism loss detection unit, generates the drive control signal that supplies a current to the motor that is smaller than the current supplied to the motor before the synchronism loss was detected, so as to fix the rotor of the motor.

[0008] According to the gripping device of the present invention, it is possible to prevent the gripped object from falling off.

[0009] Fig. 1 is a diagram schematically showing the configuration of a gripping device according to an embodiment; Fig. 2 is a diagram schematically showing the configuration of a motor and a motor drive control device in the gripping device according to an embodiment; Fig. 3 is a block diagram showing the configuration of a control circuit in the gripping device according to an embodiment; Fig. 4 is a diagram showing an equivalent circuit of the periphery of a motor when the rotor of the motor is fixed; Fig. 5 is a flowchart showing the flow of processing by the motor drive control device when an object is gripped by the gripping device according to an embodiment; Fig. 6 is a flowchart showing the flow of processing by the motor drive control device after an object has been gripped by the gripping device according to an embodiment.

[0010] Specific examples of embodiments of the present invention will be described below with reference to the drawings. In the following description, components common to each embodiment will be given the same reference numerals, and repeated description will be omitted. It should be noted that the drawings are schematic, and the dimensional relationships and ratios of each element may differ from the actual situation. The drawings may also include portions with different dimensional relationships and ratios.

[0011] FIG. 1 is a diagram schematically illustrating the configuration of a gripping device 1 according to an embodiment.

[0012] 1 shows an example in which a three-dimensional coordinate system (XYZ Cartesian coordinate system) is set, consisting of mutually orthogonal X-, Y-, and Z-axes, and the gripping device 1 is placed in this three-dimensional coordinate system. Regarding the Y-axis, which is a coordinate axis perpendicular to the plane of the drawing, a black circle inside a circle on the coordinate axis indicates that the positive direction is toward the front of the plane of the drawing. In FIG. 1, the X-axis direction is the direction in which the gripping unit 7, which will be described later, moves to grip or release the object 200.

[0013] The gripping device 1 is a so-called electric gripper that is used to grip a workpiece such as a mechanical part or an electronic part as an object, transport the workpiece to a desired position, and attach the workpiece to the desired position. Specifically, the gripping device 1 grips the object 200 between fingers 9_1 and 9_2, which will be described later.

[0014] As shown in FIG. 1 , the gripping device 1 includes a gripping unit 7 , a drive mechanism 6 , a motor 5 , and a motor drive control device 2 .

[0015] The gripping unit 7 is a mechanism for gripping the object 200. The gripping unit 7 is configured to be operable using the rotational force of the motor 5 as power. The gripping unit 7 has, for example, moving units 8_1 and 8_2 and finger units 9_1 and 9_2. The moving units 8_1 and 8_2 are connected to a drive mechanism 6, which will be described later, and are configured to be relatively movable in the X-axis direction by the drive mechanism 6. In other words, the moving units 8_1 and 8_2 move in opposite directions to each other in the X-axis direction.

[0016] The fingers 9_1 and 9_2 grip or release the object 200 in response to the movement of the moving units 8_1 and 8_2. The fingers 9_1 and 9_2 are arranged to protrude from the moving units 8_1 and 8_2 to the positive side in the Z-axis direction. The fingers 9_1 and 9_2 are formed, for example, in a plate shape. One end of the finger 9_1 is fixed to the moving unit 8_1 by a holding mechanism (e.g., a screw, etc.) not shown, and one end of the finger 9_2 is fixed to the moving unit 8_2 by a holding mechanism (e.g., a screw, etc.) not shown. As will be described in detail later, the fingers 9_1 and 9_2 grip or release the object 200 at the other end of each of the fingers 9_1 and 9_2 by moving in the X direction in conjunction with the movement of the moving units 8_1 and 8_2 in the X direction.

[0017] In FIG. 1, a reference position when the gripping device 1 grips the object 200 is referred to as a center position P.

[0018] The motor 5 is a power source for driving the gripper 7. The motor 5 is, for example, a stepping motor. As will be described later, the motor 5 is operated by receiving power from the motor drive control device 2. In this embodiment, as an example, the motor 5 is a two-phase stepping motor having A-phase and B-phase coils. The configuration of the motor 5 will be described in detail later.

[0019] The drive mechanism 6 is a mechanism that drives the gripping unit 7 by transmitting the rotational force of the motor 5 to the gripping unit 7. The drive mechanism 6 is configured by combining mechanical components (not shown), such as gears, worm gears, and cams. The drive mechanism 6 is connected between the output shaft of the motor 5 and the moving units 8_1 and 8_2 of the gripping unit 7. The drive mechanism 6 converts the rotational motion of the motor 5 into linear motion. In other words, the drive mechanism 6 moves the moving units 8_1 and 8_2 relatively in the X-axis direction in accordance with the rotational force of the motor 5.

[0020] The drive mechanism 6 has a self-locking function that restricts movement of the gripping unit 7 when the supply of current to the motor 5 is stopped. Specifically, when the supply of current to the motor 5 is stopped, the drive mechanism 6 restricts movement of the moving units 8_1 and 8_2 in a direction that releases the object 200 that they are gripping, i.e., in a direction that moves the moving units 8_1 and 8_2 away from each other. For example, the drive mechanism 6 achieves the self-locking function by a known anti-reversal mechanism that uses a worm gear.

[0021] As described above, the drive mechanism 6 converts the rotational motion transmitted from the motor 5 into linear motion that moves the moving units 8_1 and 8_2 (finger units 9_1 and 9_2) of the gripper 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 moving unit 8_1 to the positive side of the X-axis direction and moves the moving unit 8_2 to the negative side of the X-axis direction. In other words, the moving units 8_1 and 8_2 move in directions approaching each other toward the center position P. This narrows the gap between the moving units 8_1 and 8_2, making it possible to pinch and grip the object 200 between the finger unit 9_1 fixed to the moving unit 8_1 and the finger unit 9_2 fixed to the moving unit 8_2.

[0022] Furthermore, for example, when the motor 5 rotates in the direction opposite to the predetermined direction, the drive mechanism 6 moves the moving unit 8_1 to the negative side in the X-axis direction and the moving unit 8_2 to the positive side in the X-axis direction. That is, the moving units 8_1 and 8_2 move in directions away from each other from the center position P. This increases the distance between the moving units 8_1 and 8_2, making it possible to release the object 200 that has been gripped between the finger unit 9_1 fixed to the moving unit 8_1 and the finger unit 9_2 fixed to the moving unit 8_2.

[0023] Note that the gripping of the object 200 by the gripping unit 7 is not limited to the method of pinching the object 200 between the finger units 9_1 and 9_2. For example, if the object 200 is annular, the finger units 9_1 and 9_2 may be inserted into the inner periphery of the annular object 200, and the finger units 9_1 and 9_2 may be moved away from each other from the inner periphery toward the outer periphery of the object 200, thereby gripping the object 200.

[0024] The motor drive control device 2 is a device that drives the motor 5. The configurations of the motor 5 and the motor drive control device 2 will be described below with reference to the drawings.

[0025] FIG. 2 is a diagram schematically illustrating the configuration of the motor 5 and the motor drive control device 2 in the gripping device 1 according to the embodiment.

[0026] As described above, the motor 5 is a two-phase stepping motor. As shown in Fig. 2, the motor 5 includes, for example, a rotor 50, an A-phase coil 51a, a B-phase coil 51b, and a two-phase stator (not shown).

[0027] The coils 51a and 51b are elements that excite a stator (not shown). The coil 51a has a positive terminal AP and a negative terminal AN. The coil 51b has a positive terminal BP and a negative terminal BN. The terminals AP and AN of the coil 51a and the terminals BP and BN of the coil 51b are connected to the inverter circuits 40a and 40b that constitute the drive circuit 4, respectively.

[0028] The coils 51 a and 51 b are driven by the inverter circuits 40 a and 40 b. As a result, currents Ia and Ib that are out of phase with each other flow through the coils 51 a and 51 b. For example, currents Ia and Ib that are out of phase with each other by 90 degrees flow through the coils 51 a and 51 b.

[0029] In the following description, when there is no need to distinguish between the coils 51a and 51b, they will simply be referred to as "coils 51."

[0030] The rotor 50 is provided with a single-pole or multi-pole magnetized permanent magnet such that south poles 50s and north poles 50n alternate along the circumferential direction. Note that Fig. 2 shows an example in which the rotor 50 has two poles.

[0031] A stator (not shown) is disposed around the rotor 50 and close to the outer periphery of the rotor 50. The rotor 50 rotates by periodically switching the phases of currents Ia and Ib flowing through coils 51a and 51b, respectively. An output shaft (not shown) is connected to the rotor 50, and is driven by the rotational force of the rotor 50. A drive mechanism 6 is coupled to the output shaft.

[0032] 2, the motor drive control device 2 communicates with, for example, a host device 100. Based on a drive command signal Sc received from the host device 100, the motor drive control device 2 controls the energization state of the coils 51a, 51b of each phase of the motor 5, thereby controlling the rotation and stopping of the motor 5 and the operation of the entire gripping device 1. When the motor drive control device 2 drives the motor 5, 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, as described above. This controls the gripping and release of the object 200 by the gripping unit 7.

[0033] As shown in FIG. 2, the motor drive control device 2 includes, for example, a control circuit 3 and a drive circuit 4.

[0034] Based on the drive command signal Sc transmitted from the higher-level 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, and supplies these signals to the drive circuit 4, thereby rotating the motor 5 to a target rotation position. In the following description, when there is no need to distinguish between the drive control signal Sda and the drive control signal Sdb, the drive control signal Sda and the drive control signal Sdb will be referred to as the "drive control signal Sd." Details of the control circuit 3 will be described later.

[0035] The drive circuit 4 is a circuit that drives the motor 5 by supplying current to 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.

[0036] The inverter circuits 40a, 40b supply drive power to the motor 5 based on the drive control signals Sda, Sdb. The inverter circuits 40a, 40b are provided, for example, corresponding to the coils 51a, 51b to be driven. For example, as shown in FIG. 2, an inverter circuit 40a for driving the A-phase coil 51a and an inverter circuit 40b for driving the B-phase coil 51b are provided. The inverter circuits 40a, 40b are configured, for example, by an H-bridge circuit.

[0037] 2, the inverter circuit 40a is connected to the positive terminal AP of the A-phase coil 51a and the negative terminal AN of the coil 51a, and the inverter circuit 40b is connected to the positive terminal BP of the B-phase coil 51b and the negative terminal BN of the coil 51b.

[0038] The inverter circuit 40a applies a voltage Va between terminals AP and AN based on a drive control signal Sda output from the control circuit 3, thereby causing a current Ia to flow through the coil 51a. The inverter circuit 40b applies a voltage Vb between terminals BP and BN based on a drive control signal Sdb output from the control circuit 3, thereby causing a current Ib to flow through the coil 51b.

[0039] For example, as shown in FIG. 2, during an "A-phase (+) excitation period" in which a current +Ia flows from terminal AP to terminal AN of the A-phase coil 51a, the inverter circuit 40a applies a voltage of "+Va" to terminal AP of the coil 51a, for example, with respect to terminal AN. On the other hand, during an "A-phase (-) excitation period" in which a current -Ia flows from terminal AN to terminal AP of the A-phase coil 51a, the inverter circuit 40a applies a voltage of "-Va" to terminal AP of the coil 51a, for example, with respect to terminal AN. During a "B-phase (+) excitation period" in which a current +Ib flows from terminal BP to terminal BN of the B-phase coil 51b, the inverter circuit 40b applies a voltage of "+Vb" to terminal BP of the coil 51b, for example, with respect to terminal BN. During the "B-phase (-) excitation period" in which current -Ib flows from terminal BN to terminal BP of B-phase coil 51b, inverter circuit 40b applies a voltage of "-Vb" to terminal BP relative to terminal BN of coil 51b.

[0040] The current detection circuits 41a, 41b are circuits that detect the currents Ia, Ib flowing through the coils 51a, 51b. The current detection circuits 41a, 41b include, for example, shunt resistors. The shunt resistors are provided, for example, for each of the coils 51a, 51b, and are connected in series with the inverter circuits 40a, 40b on the ground potential side or power supply voltage side of the inverter circuits 40a, 40b. The A-phase current detection circuit 41a outputs the voltage across the shunt resistor as a current detection signal Sia representing the measured value of the A-phase coil current Ia. The B-phase current detection circuit 41b outputs the voltage across the shunt resistor as a current detection signal Sib representing the measured value of the B-phase coil current Ib.

[0041] The voltage detection circuit 42 is a circuit that detects the voltages of the coils 51a, 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, 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, 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 configured to include known circuits, such as a resistive voltage divider circuit. The voltages Vap, Van, Vbp, and Vbn output from the voltage detection circuit 42 may be collectively referred to as voltage Vbef.

[0042] The voltage detection circuit 42 may include 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.

[0043] The control circuit 3 is a circuit that generates a drive control signal Sd for controlling the drive of the motor 5 based on a drive command signal Sc from the higher-level device 100. Here, the drive command signal Sc includes information that indicates a target state of the motor 5. For example, the drive command signal Sc includes information that specifies the rotation speed of the motor 5 and information that specifies a target rotation angle (target rotation position) of the motor 5. The information that specifies the target rotation position may be, for example, information that specifies the number of drive steps (number of pulses) of the motor 5 that corresponds to the amount of movement to the target rotation position (target movement amount).

[0044] The control circuit 3 is a program processing device (e.g., a microcontroller: MCU (Micro Control Unit)) that has components (hardware elements) such as a processor such as a CPU (Central Processing Unit), various memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory), a timer, a counter, an A / D conversion circuit, an input / output I / F circuit, and a clock generation circuit, and each component is connected to each other via a bus or a dedicated line. The control circuit 3 also has a rewritable non-volatile storage device such as a flash memory or an EEPROM (Electrically Erasable Programmable Read-Only Memory). For example, the nonvolatile memory device can be rewritten with a first value I1 and a second value I2 that can be set as the current reference value Ith, a step-out determination threshold Vth, a grip determination threshold dDth, and the like, which will be described later.

[0045] In this embodiment, the control circuit 3 is packaged as, for example, an IC (integrated circuit), but this is not limiting. The control circuit 3 and the drive circuit 4 may also be packaged together.

[0046] The control circuit 3 has a function of controlling the operation of the gripping unit 7 to grip the object 200 and the operation of releasing the object 200 by switching the energization of the coils 51 a, 51 b of the motor 5. The control circuit 3 also has a function of assisting the self-locking function of the drive mechanism 6 by controlling the motor 5 to lock the rotor 50 of the motor 5 when the object 200 is gripped. Furthermore, the control circuit 3 has a function of determining whether the gripping unit 7 is gripping the object 200 by monitoring changes in the duty ratio of the PWM signal serving as the drive control signal Sd. Below, a specific example configuration of the control circuit 3 for realizing these functions will be described with reference to FIG. 3.

[0047] FIG. 3 is a block diagram showing the configuration of the control circuit 3 in the gripping device 1 according to the embodiment.

[0048] The control circuit 3 includes functional blocks for implementing the above-described functions, such as a drive control signal generator 12, a step-out detector 17, a grip determination unit 18, and a memory unit 23. These functional blocks are implemented, for example, by a processor in the MCU executing various calculations according to programs stored in memory and controlling peripheral circuits such as timers and counters, A / D converters, and input / output I / F circuits. Note that some or all of these functional blocks may be implemented by dedicated hardware circuits. Furthermore, the control circuit 3 may include functional blocks for implementing other functions in addition to the above-described functions.

[0049] The memory unit 23 is a functional unit for storing data and the like necessary for the overall control of the gripping device 1 by the control circuit 3. For example, the memory unit 23 stores a first value I1 and a second value I2, which are information about the current reference value Ith that serves as a reference for switching the energization of the coil 51 of the motor 5, information about a step-out determination threshold Vth that serves as a reference for detecting the occurrence of step-out of the motor 5, and information about a grip determination threshold dDth that serves as a reference for determining whether the gripper 7 is gripping the object 200. Details of this information will be described later.

[0050] The out-of-step detection unit 17 is a functional unit that detects out-of-step of the motor 5. Specifically, the out-of-step detection unit 17 determines whether or not out-of-step of the motor 5 has occurred based on an out-of-step determination threshold Vth stored in the storage unit 23 and the back electromotive force generated in the coils 51 a, 51 b of the motor 5. When the out-of-step detection unit 17 detects out-of-step of the motor 5, it outputs an out-of-step detection signal Sz.

[0051] Here, a method for measuring the back electromotive force of the coils 51a and 51b of the motor 5, which is used by the out-of-step detector 17 to determine out-of-step, will be described.

[0052] Generally, when a stepping motor rotates, a back electromotive force is generated in the coil of a non-excited phase. For example, when a stepping motor is driven by a one-phase excitation method, a back electromotive force is generated in the coil 51b of the non-excited phase of the B phase during an A-phase excitation period when the coil 51a of the A phase is excited. On the other hand, a back electromotive force is generated in the coil 51a of the non-excited phase of the A phase during a B-phase excitation period when the coil 51b of the B phase is excited.

[0053] Therefore, during a period in which the A-phase coil 51a is not excited, the out-of-sync detector 17 monitors the voltage between the terminals AP and AN as the back electromotive force Vapn of the coil 51a based on the voltages Vap and Van detected by the voltage detection circuit 42. Similarly, during a period in which the B-phase coil 51b is not excited, the out-of-sync detector 17 monitors the voltage between the terminals BP and BN as the back electromotive force Vbpn of the coil 51b based on the voltages Vbp and Vbn detected by the voltage detection circuit 42.

[0054] Generally, in a stepping motor, the back electromotive force generated in a non-excited coil when out of synchronism occurs is smaller than the back electromotive force generated in a non-excited coil when the stepping motor is operating normally. Therefore, the out-of-synchronization detection unit 17 compares the back electromotive force Vapn, Vbpn with the out-of-synchronization determination threshold Vth stored in the memory unit 23. If the back electromotive force Vapn, Vbpn is smaller than the out-of-synchronization determination threshold Vth, the out-of-synchronization detection unit 17 determines that the motor 5 has lost synchronism and outputs an out-of-synchronization detection signal Sz. If the back electromotive force Vapn, Vbpn is equal to or greater than the out-of-synchronization determination threshold Vth, the out-of-synchronization detection unit 17 determines that the motor 5 has not lost synchronism.

[0055] The method of determining whether or not a step-out has occurred by the step-out detection unit 17 is not limited to the above example, and other known methods may also be employed. For example, the rotation speed of the motor 5 may be monitored while the motor 5 is being driven, and if the rotation speed falls below a predetermined threshold, it may be determined that a step-out has occurred.

[0056] The drive control signal generation unit 12 is a functional unit that generates the drive control signals Sd (Sda, Sdb). Based on the drive command signal Sc, the drive control signal generation unit 12 generates the drive control signals Sda, Sdb so as to switch between excitation and non-excitation of the A-phase coil 51a and the B-phase coil 51b at predetermined timing based on a predetermined excitation method, in order to move the rotor 50 of the motor 5 to a target rotation position (target movement amount). Here, the predetermined excitation method is, for example, any one of a one-phase excitation method, a one-two-phase excitation method, a two-phase excitation method, and a microstep method.

[0057] When a drive command signal Sc instructing the gripping portion 7 to be driven is input, the drive control signal generating portion 12 generates drive control signals Sda and Sdb that drive the gripping portion 7 so that the gripping portion 7 grips the object 200.

[0058] Furthermore, when out-of-sync detection unit 17 detects out-of-sync of motor 5, drive control signal generation unit 12 generates drive control signals Sda and Sdb that supply a current to motor 5 that is smaller than the current supplied to motor 5 before out-of-sync detection so as to fix rotor 50 of motor 5. Specifically, when out-of-sync detection unit 17 detects out-of-sync, drive control signal generation unit 12 generates drive control signals Sda and Sdb using, for example, a two-phase excitation method that excites both two-phase coils 51 a and 51 b, thereby fixing rotor 50 of motor 5. For example, when out-of-sync detection unit 17 detects out-of-sync, drive control signal generation unit 12 rotates rotor 50 by one step using the two-phase excitation method and then fixes rotor 50. Here, one step is a control unit for driving motor 5.

[0059] Here, the drive control signals Sda and Sdb are, for example, PWM signals. In this embodiment, one cycle of the PWM signal, that is, the cycle in which one PWM signal is generated, is also referred to as a "PWM cycle."

[0060] The drive control signal generating unit 12 includes, for example, a drive command acquiring unit 13 , a current reference value setting unit 14 , a current measuring unit 15 , and a signal output unit 16 .

[0061] The drive command acquisition unit 13 is a functional unit that acquires and analyzes information included in the drive command signal Sc transmitted from the higher-level device 100 and issues an instruction to the signal output unit 16. For example, when a drive command signal Sc including information instructing the control circuit 3 to grip the target object 200 is input, the drive command acquisition unit 13 instructs the current reference value setting unit 14 and the signal output unit 16 to generate a drive control signal Sd to rotate the motor 5 in a predetermined direction. Furthermore, for example, when a drive command signal Sc including information instructing the control circuit 3 to release the target object 200 is input, the drive command acquisition unit 13 instructs the current reference value setting unit 14 and the signal output unit 16 to generate a drive control signal Sd to rotate the motor 5 in a direction opposite to the predetermined direction.

[0062] Furthermore, when out-of-sync detection unit 17 determines that out-of-sync has occurred, drive command acquisition unit 13 instructs current reference value setting unit 14 and signal output unit 16 to fix rotor 50 of motor 5. For example, when a drive command signal Sc including information instructing gripping of object 200 is input to control circuit 3 and an out-of-sync detection signal Sz is output after instructing to generate a drive control signal Sd to rotate motor 5 in a predetermined direction, drive command acquisition unit 13 instructs current reference value setting unit 14 to change current reference value Ith (described later) to a second value I2 and instructs signal output unit 16 to fix rotor 50.

[0063] The current measurement unit 15 is a functional unit that calculates and outputs measured values ​​of the coil 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 A-phase coil current Ia. 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 B-phase coil current Ib. The current measurement unit 15 outputs the measured value of the A-phase coil current Ia and the B-phase coil current Ib, for example, for each PWM period.

[0064] In addition, 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 simply outputs the digital values ​​of the current detection signals Sia and Sib as the measurement values ​​of the coil currents Ia and Ib.

[0065] The current reference value setting unit 14 is a functional unit that sets a current reference value Ith that serves as a reference for the currents (coil currents Ia and Ib of each phase) supplied to the motor 5. For example, when instructed by the drive command acquisition unit 13 to generate a drive control signal Sd to rotate the motor 5 in a predetermined direction or the opposite direction, the current reference value setting unit 14 sets the current reference value Ith to a first value I1 (Ith = I1). Information about the first value I1 is stored in, for example, the storage unit 23.

[0066] The current reference value setting unit 14 may set the first value I1 as the initial value of the current reference value Ith when the gripping device 1 (control circuit 3) is started up.

[0067] Furthermore, when the out-of-step detection unit 17 detects out-of-step of the motor 5, the current reference value setting unit 14 sets the current reference value Ith to a second value I2 smaller than the first value I1 (Ith = I2). The second value I2 is stored in the storage unit 23, for example, in the same manner as the first value I1. Here, the second value I2 is preferably set to, for example, one-tenth or less of the first value I1. For example, if the first value I1 is 500 mA, the second value I2 may be set to 30 mA.

[0068] The signal output unit 16 generates a PWM signal with a predetermined period in response to an instruction from the drive command acquisition unit 13 and outputs it as the drive control signal Sd. Specifically, when the drive command acquisition unit 13 instructs the motor 5 to rotate in a predetermined direction or the opposite direction, the signal output unit 16 generates the drive control signals Sda and Sdb so that the excitation phase is periodically switched (the coils 51 a and 51 b are commutated) based on a predetermined excitation method. Furthermore, when the drive command acquisition unit 13 instructs the rotor 50 of the motor 5 to be fixed, the signal output unit 16 generates the drive control signals Sda and Sdb so that the two-phase coils 51 a and 51 b are both excited using a two-phase excitation method so that the rotor 50 does not rotate.

[0069] Specifically, the signal output unit 16 generates the drive control signal Sd in the following manner. For each PWM period, the signal output unit 16 compares the measured values ​​of the coil currents Ia and Ib acquired by the current measurement unit 15 with the current reference value Ith set by the current reference value setting unit 14. For example, during an A-phase excitation period, the signal output unit 16 starts comparing the measured value of the coil current Ia with the current reference value Ith at the start of one PWM period. When the measured value of the coil current Ia is lower than the current reference value Ith, the signal output unit 16 sets the drive control signal Sda to a first logic level (e.g., high level), and when the measured value of the coil current Ia is equal to or greater than the current reference value Ith, the signal output unit 16 sets the drive control signal Sda to a second logic level opposite to the first logic level (e.g., low level). Thereafter, the signal output unit 16 maintains the drive control signal Sda at the second logic level until the end of that PWM period, regardless of the magnitude relationship between the measured value of the coil current Ia and the current reference value Ith. Then, when one PWM period ends and the next PWM period begins, the signal output unit 16 again starts the process of comparing the measured value of the coil current Ia with the current reference value Ith to generate the drive control signal Sda (PWM signal) for the next period.

[0070] Similarly, during the B-phase excitation period, the signal output unit 16 compares the measured value of the coil current Ib with the current reference value Ith for each PWM period, thereby generating a PWM signal as the drive control signal Sdb.

[0071] In this way, the signal output unit 16 repeatedly compares the coil currents Ia and Ib of each phase with the current reference value Ith for each PWM period of each phase to generate PWM signals as the drive control signals Sda and Sdb. For example, the inverter circuit 40a excites 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 exciting it when the drive control signal Sda is at a second logic level (e.g., low level). Similarly, the inverter circuit 40b excites 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 exciting 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 coil currents Ia and Ib of the motor 5 so that they do not exceed the current reference value Ith.

[0072] The grip determination unit 18 is a functional unit that determines whether the grip unit 7 is gripping the object 200. The grip determination unit 18 determines whether the grip unit 7 is gripping the object 200 based on the amount of change in the duty ratio of the PWM signal as the drive control signals Sda and Sdb.

[0073] Hereinafter, a method for determining whether the object 200 is being grasped by the grasp determination unit 18 will be described.

[0074] FIG. 4 is a diagram showing an equivalent circuit around the motor 5 when the rotor 50 of the motor 5 is fixed.

[0075] As an example, Fig. 4 shows an equivalent circuit around the A-phase coil La. In Fig. 4, La represents the inductance of the A-phase coil 51a, Ra represents the resistance component of the coil 51a, Va represents the voltage across the coil La, and E represents the back electromotive force generated in the coil La.

[0076] As described above, after gripping the target object 200, the drive control signal generator 12 uses two-phase excitation to excite the A-phase coil 51a and the B-phase coil 51b to fix (lock) the rotor 50, and generates drive control signals Sda and Sdb so that the coil currents Ia and Ib do not exceed (are constant with) the current reference value Ith (=I2). While the rotor 50 is fixed, the coil current Ia does not change in the A-phase coil 51a, and therefore no back electromotive force is generated (E=0). Therefore, the following equation (1) holds:

[0077]

[0078] As described above, the motor 5 is in two-phase excitation mode during the period in which the rotor 50 is fixed. Therefore, if the grasped object 200 falls off, the position of the rotor 50 changes, and a back electromotive force is generated in the coils 51a and 51b. Meanwhile, during this period, the coil current Ia is controlled so as not to exceed (be constant with) the current reference value Ith (=I2). Therefore, even if the grasped object 200 falls off, the coil current Ia is kept constant, and the following equation (2) is established.

[0079]

[0080] Here, when the duty ratio of the drive control signal Sda is Dx and the power supply voltage supplied to the inverter circuits 40a and 40b is Vsource, the voltage Va across the coil 51a is expressed by the following equation (3).

[0081]

[0082] From the above equations (2) and (3), the duty ratio Dx of the drive control signal Sda is expressed by the following equation (4).

[0083]

[0084] As described above, when the object 200 is gripped, the back electromotive force E = 0, and when the gripped object 200 falls off, the back electromotive force E ≠ 0. Therefore, from equation (4), it can be seen that the duty ratio Dx of the drive control signal Sda changes as the back electromotive force E changes before and after the object 200 falls off.

[0085] Therefore, when PWM signals are generated as drive control signals Sda and Sdb to fix the rotor 50, the grip determination unit 18 determines that the grip of the object 200 by the gripping unit 7 has been released if the change in the duty ratio of the PWM signal for one period relative to the duty ratio of the PWM signal for the period prior to that period is greater than a threshold value.

[0086] More specifically, the grip determination unit 18 includes a duty ratio measurement unit 19 , an average duty ratio calculation unit 20 , a difference calculation unit 21 , and a determination unit 22 .

[0087] The duty ratio measurement unit 19 measures the duty ratio Dx of the PWM signal serving as the drive control signal Sd. For example, the duty ratio measurement unit 19 measures the duty ratio Dx of the drive control signal Sd for each PWM period (one period) and stores the measured value in the storage unit 23. When the motor 5 is driven by two-phase excitation, it is sufficient to measure the duty ratio of at least one of the A-phase drive control signal Sda and the B-phase drive control signal Sdb. The storage unit 23 also stores measured values ​​of the duty ratios for multiple periods required for calculating the average duty ratio, which will be described later.

[0088] The average duty ratio calculation unit 20 calculates an average value Dav of the duty ratios over a plurality of PWM periods based on the measurement results of the duty ratios by the duty ratio measurement unit 19. For example, when one PWM period starts, the average duty ratio calculation unit 20 calculates an average value (average duty ratio) Dav of the duty ratios of the drive control signals Sd over a plurality of PWM periods (e.g., 10 periods) prior to that PWM period, and stores this in the storage unit 23. Note that the calculation method for the average duty ratio Dav can be a known calculation method for calculating an average value.

[0089] The difference calculation unit 21 calculates the difference dD between the average duty ratio Dav of the duty ratios of the drive control signal Sd and the duty ratio Dx of the drive control signal Sd. For example, the difference calculation unit 21 stores the absolute value (=|Dav−Dx|) of the value obtained by dividing the duty ratio Dx from the average duty ratio Dav in the storage unit 23 as the difference dD.

[0090] The determination unit 22 compares the difference dD with a grip determination threshold dDth when the drive control signal Sd is generated to fix the rotor 50. The grip determination threshold dDth is a threshold for determining whether or not the grip unit 7 is gripping the object 200, and is stored in the storage unit 23.

[0091] For example, when the difference dD is greater than the grip determination threshold dDth, the determination unit 22 determines that the gripping unit 7 has released the object 200. When the difference dD is equal to or less than the grip determination threshold dDth, the determination unit 22 determines that the object 200 is being gripped by the gripping unit 7. Note that the determination unit 22 may transmit a determination signal So indicating whether or not the object 200 is being gripped to the higher-level device 100.

[0092] Next, the flow of processing when the gripping device 1 grips the target object 200 will be described.

[0093] FIG. 5 is a flowchart showing the flow of processing by the motor drive control device 2 when the gripping device 1 grips the object 200 in this embodiment.

[0094] After starting up the gripping device 1, the current reference value setting unit 14 of the drive control signal generation unit 12 in the motor drive control device 2 sets the current reference value Ith to a first value I1 (Ith=I1). After that, for example, when a drive command signal Sc including information instructing to grip the object 200 is input to the motor drive control device 2, the motor drive control device 2 starts driving the motor 5 to grip the object 200.

[0095] 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 generator 12 generates a drive control signal Sd to switch between excitation and de-excitation of the A-phase coil 51 a and the B-phase coil 51 b at a timing based on a predetermined excitation method, thereby moving the fingers 9_1 and 9_2 of the gripper 7 toward the center position P.

[0096] The motor drive control device 2 starts the process of determining whether the motor 5 has lost synchronism (step S2) when the drive of the motor 5 starts. Specifically, the step-out detection unit 17 starts the process of determining whether or not a step-out has occurred.

[0097] The out-of-step detector 17 determines whether or not out-of-step has occurred in the motor 5 using the method described above (step S3). If out-of-step has not been detected (step S3: NO), the motor drive control device 2 continues to rotate the motor 5 in the predetermined direction (step S1).

[0098] On the other hand, if a loss of synchronism is detected (step S3: YES), the motor drive control device 2 determines that the object 200 is gripped by the gripper 7 (step S4). Next, the motor drive control device 2 starts motor drive control to assist the self-locking function of the drive mechanism 6 in order to maintain the state in which the object 200 is gripped by the gripper 7.

[0099] Specifically, first, the drive control signal generator 12 generates drive control signals Sda and Sdb using a two-phase excitation method to rotate the rotor 50 of the motor 5 by one step (step S5). This allows the motor 5 to exert maximum torque, enabling the gripper 7 to securely grip the object 200. Next, the drive control signal generator 12 changes the current reference value Ith to a second value I2 using the current reference value setting unit 14 (step S6). Then, the drive control signal generator 12 generates drive control signals Sda and Sdb that excite both the A-phase coil 51a and the B-phase coil 51b to lock the rotor 50 (step S7). This locks the rotor 50 of the motor 5 in addition to the self-locking function of the drive mechanism 6 (rotor lock function), making it possible to more stably grip the object 200 with the gripper 7.

[0100] Next, the flow of processing by the gripping device 1 after gripping the target object 200 will be described.

[0101] FIG. 6 is a flowchart showing the flow of processing by the motor drive control device 2 after the gripping device 1 grips the object 200 in this embodiment.

[0102] In the gripping device 1, when the object 200 is gripped by the self-locking function of the drive mechanism 6 and the rotor locking function of the motor 5, the motor drive control device 2 executes a gripping determination process to determine whether or not the object 200 is being gripped by the gripping unit 7.

[0103] Specifically, first, the average duty ratio calculation unit 20 of the grip determination unit 18 calculates the average value (average duty ratio) Dav of the duty ratio of the drive control signal Sd in multiple PWM periods prior to the current PWM period using the above-mentioned method (step S11).

[0104] Next, the duty ratio measurement unit 19 of the grip determination unit 18 measures the duty ratio Dx of the drive control signal Sd at that time (step S12). Note that the drive control signal whose duty ratio is to be measured in steps S11 and S12 may be the drive control signal Sd corresponding to the excited coil 51. That is, in this embodiment, since both the A-phase coil 51a and the B-phase coil 51b are excited, the duty ratio of at least one of the A-phase drive control signal Sda and the B-phase drive control signal Sdb may be measured, and the average value thereof may be calculated.

[0105] Next, the difference calculation unit 21 of the grip determination unit 18 calculates the difference ΔdD between the duty ratio Dx measured in step S12 and the average duty ratio Dav calculated in step S11 using the method described above (step S13).

[0106] Next, the determination unit 22 of the grip determination unit 18 compares the difference ΔdD calculated in step S13 with the grip determination threshold dDth (step S14). If the difference ΔdD is equal to or less than the grip determination threshold dDth (step S14: NO), the determination unit 22 determines that the object 200 is being gripped by the grip unit 7 (step S16). Thereafter, the motor drive control device 2 returns to step S1 and executes the above-described grip determination process again.

[0107] On the other hand, if the difference ΔdD is greater than the grip determination threshold dDth (step S14: YES), the determination unit 22 determines that the object 200 has fallen off the gripping unit 7 (released state) (step S15). Thereafter, the motor drive control device 2 transmits, for example, a determination signal So indicating that the gripped object 200 has fallen off to the higher-level device 100.

[0108] As described above, the gripping device 1 according to the embodiment includes the gripping unit 7 for gripping the object 200, the drive mechanism 6 that drives the gripping unit 7 in response to the rotational force of the motor 5 and has a self-locking function that limits movement of the gripping unit 7 when the motor 5 is de-energized, and the motor drive control device 2 that drives the motor 5. As described above, when a drive command signal Sc instructing to drive the gripping unit 7 is input, the motor drive control device 2 drives the motor 5 so that the gripping unit 7 grips the object 200, and when a step-out of the motor 5 is detected, the motor drive control device 2 supplies a current to the motor 5 that is smaller than the current supplied to the motor 5 before the step-out was detected, thereby fixing the rotor 50 of the motor 5.

[0109] As described above, this makes it possible to detect that the gripping unit 7 has gripped the object 200 by detecting loss of synchronism of the motor 5 after the gripping unit 7 has started to operate to grip the object 200. Then, by locking the rotor 50 of the motor 5 after detecting loss of synchronism, the self-locking function of the drive mechanism 6 can be assisted, thereby enabling the object 200 to be gripped more stably. That is, the gripping device 1 according to this embodiment can reliably prevent the gripped object 200 from falling off. Furthermore, by setting the current supplied to the motor 5 when locking the rotor 50 after detecting loss of synchronism to a value smaller than the current when the rotor 50 is rotating, it becomes possible to assisted the self-locking function while suppressing power consumption.

[0110] Furthermore, in the gripping device 1, as described above, when fixing the rotor 50 after detecting loss of synchronism, the motor drive control device 2 excites both of the two-phase coils 51a and 51b of the stepping motor 5 (two-phase excitation). This allows the motor 5 to generate a larger torque to fix the rotor 50, making it possible to more reliably prevent the gripped object 200 from falling off.

[0111] Furthermore, as described above, when the motor drive control device 2 is generating a drive control signal Sd to fix the rotor 50, if the change in the duty ratio of one period of the PWM signal as the drive control signal Sd relative to the duty ratio of the period prior to that period is greater than the grip determination threshold, the motor drive control device 2 determines that the grip of the object 200 by the gripping portion 7 has been released.

[0112] In conventional gripping devices such as electric grippers, when the stepping motor inside the gripping device is controlled in an open loop, it is difficult to detect that an object has fallen off the gripping device, and it has been necessary to provide a separate sensor such as a load cell to detect that the object has fallen off.

[0113] In contrast, as described above, the gripping device 1 according to this embodiment drives the motor 5 by a PWM signal (drive control signal Sd) to fix the rotor 50 when the self-locking function of the drive mechanism 6 is operating, while monitoring the duty ratio of the PWM signal and determining whether the amount of change in the duty ratio has become greater than the grip determination threshold. This makes it possible to detect whether the object 200 has fallen off by detecting a change in the duty ratio of the PWM signal due to the back electromotive force generated when the gripped object 200 falls off, and therefore, for example, there is no need to provide a separate sensor such as a load cell even when the stepping motor is controlled in an open loop.

[0114] Furthermore, in the gripping device 1, when the drive control signal Sd is generated to fix the rotor 50, the motor drive control device 2 calculates a difference dD between the average value (average duty ratio Dav) of the duty ratio of the PWM signal (drive control signal Sd) over multiple periods and the duty ratio (Dx) of the PWM signal over one period, compares the difference dD with a grip determination threshold dDth, and determines that the grip of the object 200 by the gripping unit 7 has been released if the difference dD is greater than the grip determination threshold dDth. This makes it possible to reliably detect a change in the duty ratio of the PWM signal due to the back electromotive force generated when the gripped object 200 falls off, which is expected to improve the accuracy of detecting whether the gripped object 200 has fallen off.

[0115] <<Extending the Embodiments>> The invention made by the present inventor has been specifically described above based on the embodiments, but it goes without saying that the present invention is not limited thereto and can be modified in various ways without departing from the spirit of the invention.

[0116] For example, in the above embodiment, when the gripper 7 is driven to grip the object 200, if the coil currents Ia and Ib are changed sinusoidally by the microstep method to rotate the motor 5 in a predetermined direction, the first value I1 also changes sinusoidally. In this case, the second value I2 may be set to be sufficiently smaller than the maximum value that the first value I1 can take (the peak value of the sine wave).

[0117] In the above embodiment, the number of phases of the motor 5 (stepping motor) is not limited to 2. Furthermore, the motor 5 is not limited to a stepping motor, and may be, for example, a brushless DC motor.

[0118] Furthermore, the above-described flowcharts are merely examples for explaining the operation, and are not intended to be limiting. That is, the steps shown in each diagram of the flowchart are specific examples, and the present invention is not limited to these flows. For example, the order of some processes may be changed, other processes may be inserted between processes, or some processes may be performed in parallel.

[0119] 1...gripping device, 2...motor drive control device, 3...control circuit, 4...drive circuit, 5...motor (stepping motor), 6...drive mechanism, 7...gripping unit, 8_1, 8_2...moving unit, 9_1, 9_2...finger unit, 12...drive control signal generating unit, 13...drive command acquiring unit, 14...current reference value setting unit, 15...current measuring unit, 16...signal output unit, 17...out-of-step detecting unit, 18...gripping judgment unit, 19...duty ratio measuring unit, 20...average duty ratio calculating unit, 21...difference calculating unit, 22...judgment unit, 23...storage unit, 40a, 40b...inverter circuit, 41a, 41b, 41c, 41d, 41e 1b...current detection circuit, 42...voltage detection circuit, 50...rotor, 50s...south pole, 50n...north pole, 51a, 51b...coil, 100...host device, 200...object, Dx...duty ratio, Dav...average duty ratio, dD...difference, Ia, Ib...coil current, Ith...current reference value, I1...first value, I2...second value, Sc...drive command signal, Sd, Sda, Sdb...drive control signal, Sia, Sib...current detection signal, So...determination signal, Vap, Van, Vbp, Vbn, Vbef...voltage, Vth...out-of-step determination threshold, 100...host device.

Claims

1. A gripping device comprising: a motor; a gripping part for gripping an object; a drive mechanism having a self-locking function that drives the gripping part in accordance with the rotational force of the motor and restricts the movement of the gripping part when the energization of the motor stops; and a motor drive control device that drives the motor, wherein the motor drive control device includes a drive circuit that drives the motor by supplying current to the motor based on a drive control signal, and a control circuit that generates the drive control signal based on a drive command signal, the control circuit includes a drive control signal generation unit that generates the drive control signal, and a demagnetization detection unit that detects demagnetization of the motor, the drive control signal generation unit generates the drive control signal for driving the gripping part so that the gripping part grips the object when the drive command signal including information for instructing the drive of the gripping part is input, and when demagnetization of the motor is detected by the demagnetization detection unit, generates the drive control signal for supplying a current smaller than the current supplied to the motor before the detection of the demagnetization to the motor so as to fix the rotor of the motor.

2. The gripping device according to claim 1, wherein the motor is a stepping motor having a two-phase coil, and the drive control signal generation unit generates the drive control signal by a two-phase excitation method of exciting both of the two-phase coils to fix the rotor.

3. The gripping device according to claim 2, wherein when the demagnetization is detected by the demagnetization detection unit, the drive control signal generation unit rotates the rotor by one step by the two-phase excitation method and then fixes the rotor.

4. In the gripping device according to claim 1, the control circuit further includes a gripping determination unit that determines whether or not the object is gripped by the gripping unit. The drive control signal generation unit includes a current measurement unit that measures the current supplied to the motor, a current reference value setting unit that sets the current reference value serving as a reference for the current supplied to the motor to a first value and sets the current reference value to a second value smaller than the first value when the out-of-tune is detected by the out-of-tune detection unit, and a signal output unit. The signal output unit generates a PWM signal having a predetermined period so that the current measured by the current measurement unit does not exceed the current reference value and outputs the PWM signal as the drive control signal. The gripping determination unit determines that the gripping of the object by the gripping unit is released when the change amount of the duty ratio of the PWM signal in one period with respect to the duty ratio of the PWM signal in the period before the one period is greater than a threshold value in a state where the drive control signal is generated to fix the rotor. Gripping device.

5. In the gripping device according to claim 4, the gripping determination unit includes a duty ratio measurement unit that measures the duty ratio of the PWM signal, an average duty ratio calculation unit that calculates an average value of the duty ratio in a plurality of the periods, a difference calculation unit that calculates a difference between the average value of the duty ratio and the duty ratio, and a determination unit that compares the difference with the threshold value and determines that the gripping of the object by the gripping unit is released when the difference is greater than the threshold value in a state where the drive control signal is generated to fix the rotor. Gripping device.

6. A control method for a gripping device including a motor, a gripping part for gripping an object, a drive mechanism having a self-locking function that drives the gripping part according to the rotational force of the motor and restricts movement of the gripping part when the energization of the motor stops, and a motor drive control device for driving the motor, the control method including: a first step of driving the motor so that the gripping part grips the object; a second step of determining whether or not the motor is out of synchronization while driving the motor in the first step; and a third step of fixing the rotor of the motor by supplying a current smaller than the current supplied to the motor when driving the motor in the first step when the out-of-synchronization is detected in the second step.

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