Gripping apparatus and control method

Abstract

The present invention detects a drop-off of a gripped object.　A gripping apparatus (1) comprises: a gripping part (7) that is for gripping an object (200); a drive mechanism (6) that drives the gripping part (7) in accordance with the rotational force of a motor (5); and a motor drive control device (2) that drives the motor (5). The motor drive control device (2) performs a drop-off determination process for determining whether or not the object (200) has dropped off from the gripping part (7) after the gripping part (7) has gripped the object (200). In the drop-off determination process, the motor drive control device (2): measures a current rise time (dT), which is a time from the start of excitation of coils (51a, 51b) of the motor (5) until currents (Ia, Ib) reach a current reference value (Ith), a plurality of times; and, on the basis of the presence or absence of a change in the current rise times (dT), determines whether or not the object (200) has dropped off from the gripping part (7).

Description

Gripping device and control method

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

[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 according to the rotational force of the motor.

[0003] In recent years, as an electric gripper employing a stepping motor, a sensorless electric gripper without a sensor such as an encoder that detects the rotational speed of the stepping motor has been increasing (see Patent Document 1).

[0004] Japanese Unexamined Patent Application Publication No. 2020-104188

[0005] However, in a sensorless electric gripper, since the position of the rotor or the like cannot be detected, it is not easy to detect the dropping of the gripped object.

[0006] The present invention has been made in view of the above-described problems, and an object thereof is to detect the dropping of a gripped object.

[0007] A gripping device according to a typical embodiment of the present invention comprises a motor having a coil, a gripping unit for gripping an object, a drive mechanism for driving the gripping unit in accordance with the rotational force of the motor, and a motor drive control device for driving the motor. The motor drive control device includes 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 drive control signal generation unit that generates the drive control signal so as to excite the coil until the current of the coil reaches a current reference value, and to stop the excitation of the coil when the current reaches the current reference value, and a detachment determination unit that performs a detachment determination process to determine whether or not the object has detached from the gripping unit after the object has been gripped by the gripping unit. The detachment determination unit measures the current rise time multiple times, which is the time from when the excitation of the coil is started until the current reaches the current reference value, and determines whether or not the object has detached from the gripping unit based on whether or not there is a change in the current rise time.

[0008] The gripping device according to the present invention makes it possible to detect when a gripped object falls off.

[0009] This is a schematic diagram showing the configuration of the gripping device according to the embodiment. This is a schematic diagram showing the configuration of the motor and motor drive control device in the gripping device according to the embodiment. This is a block diagram showing the configuration of the control circuit in the gripping device according to the embodiment. This is a diagram showing the relationship between the rotor position and the current rise time in a stepping motor. This is a diagram for explaining the processing content included in the detachment determination process. This is a diagram for explaining the method of measuring the current rise time. This is a flowchart showing an example of the processing flow by the motor drive control device when gripping an object with the gripping device according to the embodiment. This is a flowchart showing the flow of the detachment determination process (step S5). This is a flowchart showing the flow of the detachment determination process (step S5). This is a timing chart showing an example of the operating state of the gripping device according to the embodiment.

[0010] 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.

[0011] Figure 1 is a schematic diagram showing the configuration of the gripping device 1 according to an embodiment.

[0012] In Figure 1, a three-dimensional coordinate system (XYZ Cartesian coordinate system) consisting of mutually orthogonal X, Y, and Z axes is set up, and an example is shown in which the gripping device 1 is positioned within this three-dimensional coordinate system. Note that for the Y axis, which is a coordinate axis perpendicular to the plane of the drawing, a black circle inside the coordinate axis indicates that the direction towards the viewer is the positive direction relative to the plane of the drawing. In Figure 1, the X-axis direction is the direction in which the gripping part 7, which will be described later, moves to grip or release the object 200.

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

[0014] As shown in Figure 1, the gripping device 1 comprises a gripping section 7, a drive mechanism 6, a motor 5, and a motor drive control device 2.

[0015] The gripping section 7 is a mechanism for gripping the object 200. The gripping section 7 is configured to operate using the rotational force of the motor 5 as its power source. The gripping section 7 has, for example, movable sections 8_1, 8_2 and finger sections 9_1, 9_2. The movable sections 8_1, 8_2 are connected to a drive mechanism 6, which will be described later, and are configured to move relative to each other in the X-axis direction by the drive mechanism 6. That is, movable section 8_1 and movable section 8_2 move in opposite directions to each other in the X-axis direction.

[0016] The finger portions 9_1 and 9_2 grip or release the object 200 as the movable parts 8_1 and 8_2 move. The finger portions 9_1 and 9_2 are positioned to protrude from the movable parts 8_1 and 8_2 on 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 of finger portion 9_1 is fixed to the movable part 8_1 by a retaining mechanism (e.g., a screw, etc.) not shown, and one end of finger portion 9_2 is fixed to the movable part 8_2 by a retaining mechanism (e.g., a screw, etc.) not shown. As will be described in detail later, the finger portions 9_1 and 9_2 move in the X direction in conjunction with the movement of the movable parts 8_1 and 8_2 in the X direction, thereby gripping or releasing the object 200 at the other end of each finger portion 9_1 and 9_2.

[0017] In Figure 1, the center position P is defined as the reference position when the gripping device 1 grips the object 200.

[0018] Motor 5 is a power source for driving the gripping section 7. Motor 5 is, for example, a stepping motor. Motor 5 operates by receiving power from the motor drive control device 2, as will be described later. In this embodiment, as an example, motor 5 is assumed to be a two-phase stepping motor having A-phase and B-phase coils. The details of the configuration of motor 5 will be described later.

[0019] The drive mechanism 6 is a mechanism that drives the gripping part 7 by transmitting the rotational force of the motor 5 to the gripping part 7. The drive mechanism 6 is composed of a combination of mechanical parts (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 movable parts 8_1 and 8_2 of the gripping part 7. The drive mechanism 6 converts the rotational motion of the motor 5 into linear motion. That is, the drive mechanism 6 moves the movable parts 8_1 and 8_2 relative to each other in the X-axis direction according to the rotational force of the motor 5.

[0020] 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., in a direction that would separate the moving parts 8_1 and 8_2 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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).

[0027] 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.

[0028] Coils 51a and 51b are driven by inverter circuits 40a and 40b. As a result, currents Ia and Ib, which are in different phases from each other, flow through coils 51a and 51b. For example, currents Ia and Ib, which are 90 degrees out of phase from each other, flow through coils 51a and 51b.

[0029] In the following explanation, when coil 51a and coil 51b are not distinguished, they will simply be referred to as "coil 51".

[0030] 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.

[0031] 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.

[0032] 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.

[0033] As shown in Figure 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 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.

[0035] 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.

[0036] 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.

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

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

[0039] For example, as shown in Figure 2, when the A-phase coil 51a is excited in the positive (+) direction, the inverter circuit 40a causes a current Ia(+) to flow from terminal AP to terminal AN of the A-phase coil 51a by, for example, applying a voltage of "+Va" to terminal AP relative to terminal AN of the coil 51a. On the other hand, when the A-phase coil 51a is excited in the negative (-) direction, the inverter circuit 40a causes a current Ia(-) to flow from terminal AN to terminal AP of the A-phase coil 51a by, for example, applying a voltage of "-Va" to terminal AP relative to terminal AN of the coil 51a. When the B-phase coil 51b is excited in the positive (+) direction, the inverter circuit 40b causes a current Ib(+) to flow from terminal BP to terminal BN of the B-phase coil 51b by, for example, applying a voltage of "+Vb" to terminal BP relative to terminal BN of the 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.

[0040] 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 example, 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 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 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 current Ib.

[0041] 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 Vbef.

[0042] 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.

[0043] 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).

[0044] The control circuit 3 is a program processing device having components (hardware elements) such as a processor like 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, etc., and each component is connected to each other via a bus or a dedicated line. The control circuit 3 is, for example, a microcontroller (MCU: Micro Control Unit). The control circuit 3 has, as a memory, a rewritable non-volatile storage device such as a flash memory or an EEPROM (Electrically Erasable Programmable Read-Only Memory), etc. For example, with respect to the above non-volatile storage device, a first value I0 that can be set as a current reference value Ith and a threshold value dTth, etc., which will be described later, can be rewritten.

[0045] In addition, in the present embodiment, the control circuit 3 is packaged as an IC (integrated circuit), for example, but is not limited thereto. Note that the control circuit 3 and the drive circuit 4 may be packaged together.

[0046] The control circuit 3 has a function of controlling the operation of gripping the object 200 by the gripping portion 7 and the operation of releasing the object 200 by switching the energization of the coils 51a and 51b of the motor 5. Further, the control circuit 3 has a function of determining whether or not the object 200 has fallen off from the gripping portion 7 after gripping the object 200. Hereinafter, a specific configuration example of the control circuit 3 for realizing these functions will be described using 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 has a drive control signal generation unit 12, a demagnetization detection unit 17, a dropout determination unit 18, and a storage unit 23 as functional blocks for realizing the above-described respective functions. These functional blocks are realized, for example, when a processor in the above-described MCU executes various operations according to a program stored in a memory and controls peripheral circuits such as a timer and a counter, an A / D conversion circuit, and an input / output I / F circuit. Note that some or all of these functional blocks may be realized by a dedicated hardware circuit (such as a logic circuit). Further, the control circuit 3 may have functional blocks for realizing other functions in addition to the above functions.

[0049] The storage unit 23 is a functional unit for storing data and the like necessary for overall control of the gripping device 1 by the control circuit 3. For example, the storage unit 23 stores a first value I0 which is information regarding a current reference value Ith which is a reference for energization switching of the coil 51 of the motor 5, a demagnetization determination threshold value Vth which is a reference for detecting occurrence of demagnetization of the motor 5, a threshold value dTth which is a reference for determining whether or not an object 200 has dropped from the gripping unit 7, and current rise times dT1, dT2, etc. which will be described later. Details of this information will be described later.

[0050] The demagnetization detection unit 17 is a functional unit for detecting demagnetization of the motor 5. The demagnetization detection unit 17 determines whether or not demagnetization of the motor 5 has occurred based on the demagnetization determination threshold value Vth stored in the storage unit 23 and the counter electromotive voltage generated in the coils 51a, 51b of the motor 5. When the demagnetization detection unit 17 detects demagnetization of the motor 5, the demagnetization detection unit 17 outputs a demagnetization detection signal Sz.

[0051] Here, a method for measuring the counter electromotive voltage of the coils 51a, 51b of the motor 5 used for demagnetization determination by the demagnetization detection unit 17 will be described.

[0052] 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.

[0053] Therefore, during the period when the A-phase coil 51a is de-energized, the out-of-step detection unit 17 monitors the voltage between terminal AP and terminal AN as the back electromotive force Vapn of coil 51a, based on the voltages Vap and Van detected by the voltage detection circuit 42. Similarly, during the period when the B-phase coil 51b is de-energized, the out-of-step detection unit 17 monitors the voltage between terminal BP and terminal BN as the back electromotive force Vbpn of 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 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 detection unit 17 compares the back electromotive force Vapn and Vbpn with the stepping loss determination threshold Vth stored in the memory unit 23. The stepping loss detection unit 17 determines that a stepping loss has occurred in the motor 5 and outputs a stepping loss detection signal Sz when the back electromotive force Vapn and Vbpn are smaller than the stepping loss determination threshold Vth, and determines that a stepping loss has not occurred in the motor 5 when the back electromotive force Vapn and Vbpn are greater than or equal to the stepping loss determination threshold Vth. The control circuit 3 drives the motor 5 to grip the object 200 with the gripping unit 7, and then, if it detects a stepping loss in the motor 5 using the method described above, it determines that the object 200 has been gripped by the gripping unit 7.

[0055] The method for determining a step loss by the step loss detection unit 17 is not limited to the example described above, and other known methods can also be employed. For example, the rotational speed of the motor 5 may be monitored while the motor 5 is running, and it may be determined that a step loss has occurred when the rotational speed falls below a predetermined threshold.

[0056] The drive control signal generation unit 12 is a functional unit that generates drive control signals Sd (Sda, Sdb). Based on the drive command signal Sc, the drive control signal generation unit 12 generates drive control signals Sda, Sdb so as to switch between energizing and de-energizing the A-phase coil 51a and the B-phase coil 51b at predetermined timings based on a predetermined excitation method in order to move the rotor 50 of the motor 5 to a target rotation position (target amount of movement). Here, the predetermined excitation method is, for example, one of the following: a one-phase excitation method, a one-to-two-phase excitation method, a two-phase excitation method, and a microstep method. Specifically, the drive control signal generation unit 12 generates a drive control signal Sd so as to energize the coil 51 until the current of the coil 51 reaches a current reference value Ith, and then stop energizing the coil 51 when the current of the coil 51 reaches the current reference value Ith.

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

[0058] Furthermore, in the detachment determination process performed after the gripping unit 7 has gripped the object 200, the drive control signal generation unit 12 generates a drive control signal Sd to excite the coils 51a and 51b of each phase for a short time in response to instructions from the detachment determination unit 18. 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 period in which one PWM signal is generated, is also referred to as the "PWM period".

[0059] The drive control signal generation unit 12 includes, for example, a drive command acquisition unit 13, a current reference value setting unit 14, a current measurement unit 15, and a signal output unit 16.

[0060] The drive command acquisition unit 13 is a functional unit that analyzes the information contained in the drive command signal Sc transmitted from the higher-level device 100 and the instructions from the detachment determination unit 18, and gives instructions to the signal output unit 16. For example, when a drive command signal Sc containing information instructing the gripping of the object 200 is input to the control circuit 3, 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 so that the motor 5 rotates in a predetermined direction.

[0061] Furthermore, for example, 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 13 instructs the current reference value setting unit 14 and the signal output unit 16 to generate a drive control signal Sd so as to rotate the motor 5 in the opposite direction to the predetermined direction.

[0062] Furthermore, when an instruction is received from the detachment determination unit 18, the drive command acquisition unit 13 instructs the signal output unit 16 to excite the coil 51 of a predetermined phase for a short time (for example, 1 PWM period), and instructs the current reference value setting unit 14 to set the current reference value Ith to a first value I0.

[0063] 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.

[0064] 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 may output the digital values ​​of the current detection signals Sia and Sib as the measured values ​​of the currents Ia and Ib.

[0065] The current reference value setting unit 14 is a functional unit that sets the current reference value Ith, which serves as the reference for the current (currents Ia and Ib of each phase) supplied to the motor 5. For example, when the motor 5 is driven by a microstepping method, the current reference value Ith is changed in a stepwise manner at each PWM period so that the currents Ia and Ib of the coils 51a and 51b of the motor 5 become sinusoidal.

[0066] Furthermore, the current reference value setting unit 14 sets the current reference value Ith to the first value I0 when it receives an instruction from the drive command acquisition unit 13 to set the current reference value Ith to the first value I0 during the detachment determination process. The information of the first value I0 is stored, for example, in the storage unit 23.

[0067] The signal output unit 16 generates a PWM signal of a predetermined period in response to an instruction from the drive command acquisition unit 13 and outputs it as a 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 drive control signals Sda and Sdb so that the excitation phase switches periodically (coils 51a and 51b commutate) based on a predetermined excitation method. Also, when the drive command acquisition unit 13 instructs the detachment determination process to excite coil 51, the signal output unit 16 generates drive control signals Sda and Sdb so that each phase coil 51a and 51b is individually excited for 1 PWM period. Specifically, the signal output unit 16 generates the drive control signal Sd by the method shown below.

[0068] The signal output unit 16 compares the measured values ​​of 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 each PWM cycle. For example, during the A-phase excitation period, the signal output unit 16 starts comparing the measured value of current Ia with the current reference value Ith at the start of one PWM cycle. If the measured value of 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 if the measured value of 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 (e.g., low level), which is the opposite of the first logic level. After that, the signal output unit 16 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 reference 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 16 starts comparing the measured value of current Ia with the current reference value Ith again to generate the drive control signal Sda (PWM signal) for the next cycle.

[0069] Similarly, during the B-phase excitation period, the signal output unit 16 generates a PWM signal as a drive control signal Sdb by comparing the measured value of current Ib with the current reference value Ith at each PWM cycle.

[0070] In this way, the signal output unit 16 generates PWM signals as drive control signals Sda and Sdb by repeatedly comparing the currents Ia and Ib of each phase with the current reference value Ith for each phase PWM period. 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 makes it possible to drive the motor 5 while limiting the currents Ia and Ib of the motor 5 so that they do not exceed the current reference value Ith.

[0071] The detachment determination unit 18 is a functional unit that performs a detachment determination process to determine whether or not the object 200 has detached from the gripping unit 7. The detachment determination process uses the current rise time dT as a parameter for determining whether or not the object 200 has detached. The outline of the detachment determination process is described below.

[0072] Figure 4 shows the relationship between the rotor position and the current rise time dT in a stepping motor.

[0073] In Figure 4, the horizontal axis represents the electrical angle [deg] corresponding to the rotor position, and the vertical axis represents the current rise time dT.

[0074] Here, the current rise time dT refers to the time from when the excitation of the coil 51 is started until the currents Ia and Ib reach the current reference value Ith. For example, the period during which the drive control signals Sda and Sdb (PWM signals) generated by the comparison process between the measured values ​​of currents Ia and Ib and the current reference value Ith are at the first logic level (e.g., high level) corresponds to the current rise time dT.

[0075] Note that the current rise time dT shown on the vertical axis in Figure 4 is expressed as a relative value with the maximum value set to "1".

[0076] As shown in Figure 4, in a stepping motor, the current rise time dT changes depending on the rotor position (electrical angle). Therefore, if the rotor position does not change, the current rise time dT does not change. In other words, if the rotor position changes when the stepping motor is driven, the current rise time dT will also change.

[0077] Therefore, the motor drive control device 2 (control circuit 3) according to this embodiment performs a step-out determination process after gripping the object 200 with the gripping part 7, and measures the current rise time dT multiple times when the motor 5 is driven so that the rotor rotates a small amount, and determines whether or not the object 200 has fallen from the gripping part 7 based on whether or not there is a change in the current rise time dT.

[0078] In this embodiment, the detachment determination unit 18 performs the detachment determination process at least once after the gripping unit 7 has gripped the object 200. Preferably, the detachment determination unit 18 repeatedly performs the detachment determination process after the gripping unit 7 has gripped the object 200. For example, the detachment determination unit 18 periodically performs the detachment determination process after the gripping unit 7 has gripped the object 200. For example, the detachment determination unit 18 starts executing the detachment determination process when the motor 5 is driven to grip the object 200 by the gripping unit 7 and the motor 5 has lost step.

[0079] In the detachment determination process, the detachment determination unit 18 measures the current rise time dT multiple times, which is the time from when the excitation of the coil 51 is started until the currents Ia and Ib reach the current reference value Ith. Based on whether or not there is a change in the measured current rise time, it determines whether or not the object 200 has detached from the gripping unit 7.

[0080] Specifically, the detachment determination unit 18 determines that the object 200 has detached from the gripping unit if the measured current rise time dTn has changed compared to the previously measured current rise time dT(n-1) (n is an integer of 2 or more). For example, the detachment determination unit 18 determines that the object 200 has detached from the gripping unit 7 if the difference between the measured current rise time dTn and the previously measured current rise time dT(n-1) exceeds the threshold dTth. The step-out determination process will be described in detail below.

[0081] Figure 5 is a diagram illustrating the processing steps included in the elimination determination process.

[0082] As shown in Figure 5, the detachment determination process includes a reference data acquisition process that measures and acquires a reference current rise time dT1 (also referred to as "reference data dT1"), a comparison data acquisition process that measures and acquires a comparison current rise time dT2 (also referred to as "comparison data dT2") for comparison with the reference, and a determination process that determines whether or not the object 200 has detached based on the comparison result between the reference data dT1 and the comparison data dT2. In other words, the detachment determination process includes the reference data acquisition process, the comparison data acquisition process, and the determination process as a set of processes.

[0083] As shown in Figure 5, the detachment determination process may include a threshold calculation process that calculates a threshold value that serves as the criterion for determining whether or not the object 200 has detached in the determination process. The threshold calculation process only needs to be performed before the determination process. For example, as shown in Figure 5, the threshold calculation process may be performed between the reference data acquisition process and the comparison data acquisition process, or between the comparison data acquisition process and the determination process. In this embodiment, as an example, the threshold calculation process is performed between the reference data acquisition process and the comparison data acquisition process. Furthermore, the detachment determination process is considered to be a set of processes consisting of the reference data acquisition process, the comparison data acquisition process, the threshold calculation process, and the determination process.

[0084] As shown in Figure 3, the elimination determination unit 18 has a reference data acquisition unit 19, a comparison data acquisition unit 20, a threshold calculation unit 21, and a determination unit 22, which are functional units that perform reference data acquisition processing, comparison data acquisition processing, threshold calculation processing, and determination processing, respectively.

[0085] The reference data acquisition unit 19 is a functional unit that performs reference data acquisition processing and acquires reference data dT1. The comparison data acquisition unit 20 is a functional unit that performs comparison data acquisition processing and acquires comparison data dT2.

[0086] The reference data acquisition unit 19 measures the current rise time dT for the currents Ia and Ib flowing through the coils 51a and 51b of each phase by exciting the coils 51a and 51b one phase at a time, and stores this as reference data dT1 in the storage unit 23. Similarly, the comparison data acquisition unit 20 measures the current rise time dT for the currents Ia and Ib flowing through the coils 51a and 51b of each phase by exciting the coils 51a and 51b one phase at a time, and stores this as comparison data dT2 in the storage unit 23.

[0087] The method for measuring the current rise time dT by the reference data acquisition unit 19 (reference data acquisition process) and the method for measuring the current rise time dT by the comparison data acquisition unit 20 (comparison data acquisition process) are the same. Therefore, the method for measuring the current rise time dT by the reference data acquisition unit 19 will be explained using Figure 6 as a representative example.

[0088] Figure 6 is a diagram illustrating the method for measuring the current rise time dT. In Figure 6, the horizontal axis represents time, and the vertical axis represents current.

[0089] In the reference data acquisition process, the reference data acquisition unit 19 first instructs the drive command acquisition unit 13 to energize a coil 51 of a predetermined phase in a predetermined direction for a predetermined period of time. At this time, it is preferable to energize the coil 51 to the extent that the rotor 50 does not move too much. For example, as shown in Figure 6, the reference data acquisition unit 19 sets the current reference value Ith to a first value I0 (+I0 or -I0) and instructs the drive command acquisition unit 13 to energize either coil 51a or 51b in a first direction (positive direction) or a second direction (negative direction) opposite to the first direction for 1 PWM period.

[0090] The drive command acquisition unit 13 reads a first value I0 from the storage unit 23 in response to an instruction from the reference data acquisition unit 19, sets it as the current reference value Ith, and energizes the specified coil 51. Here, it is preferable to set the first value I0 to a size that does not cause the rotor 50 to move too much and that allows for accurate measurement of the current rise time dT.

[0091] The reference data acquisition unit 19 measures the time from when the coil 51 is excited until the current flowing through the coil 51 reaches the current reference value Ith (= I0) in one PWM cycle. For example, as shown in Figure 6, the reference data acquisition unit 19 measures the time dTap from the time t1 when the excitation of the A-phase coil 51a is started until the time t2 when the current Ia(+) flowing through the A-phase coil 51a reaches the current reference value Ith (= + I0), and uses this as the measured value of the current rise time. For example, the reference data acquisition unit 19 may measure the period during which the PWM signals as drive control signals Sda and Sdb are at a high level and acquire this as the measured value of the current rise time.

[0092] As shown in Figure 6, the reference data acquisition unit 19 may measure the current rise times dTap, dTan, dTbp, and dTbn when the coils 51a and 51b are excited in the first direction (positive direction) and the second direction (negative direction), respectively, and store them in the storage unit 23 as reference data dT1.

[0093] For example, current rise time dTap is the current rise time for the current Ia(+) that flows when the A-phase coil 51a is excited in the first direction (positive direction). Current rise time dTan is the current rise time for the current Ia(-) that flows when the A-phase coil 51a is excited in the second direction (negative direction). Current rise time dTbp is the current rise time for the current Ib(+) that flows when the B-phase coil 51b is excited in the first direction (positive direction). Current rise time dTbn is the current rise time for the current Ib(-) that flows when the B-phase coil 51b is excited in the second direction (negative direction).

[0094] In the following explanation, the measured current rise time dTap may be referred to as "first measured value dTap," the measured current rise time dTan as "second measured value dTan," the measured current rise time dTbp as "third measured value dTbp," and the measured current rise time dTbn as "fourth measured value dTbn."

[0095] As shown in Figure 6, the reference data acquisition unit 19 measures the current rise time while switching between the coils 51a and 51b to be excited and the excitation direction. For example, the reference data acquisition unit 19 first excites the A-phase coil 51a in the positive direction to acquire a first measurement value dTap, then excites the B-phase coil 51b in the positive direction to acquire a third measurement value dTbp, then excites the A-phase coil 51a in the negative direction to acquire a second measurement value dTan, and finally excites the B-phase coil 51b in the negative direction to acquire a fourth measurement value dTbn. The reference data acquisition unit 19 then stores the acquired first measurement value dTap, second measurement value dTan, third measurement value dTbp, and fourth measurement value dTbn as reference data (current rise time) dT1 in the storage unit 23.

[0096] The comparison data acquisition unit 20 measures the current rise time dT using the same method as the reference data acquisition process. Specifically, the comparison data acquisition unit 20 first energizes the A-phase coil 51a in the positive direction to acquire a first measurement value dTap, then energizes the B-phase coil 51b in the positive direction to acquire a third measurement value dTbp, then energizes the A-phase coil 51a in the negative direction to acquire a second measurement value dTan, and finally energizes the B-phase coil 51b in the negative direction to acquire a fourth measurement value dTbn. The comparison data acquisition unit 20 then stores the acquired first measurement value dTap, second measurement value dTan, third measurement value dTbp, and fourth measurement value dTbn as comparison data (current rise time) dT2 in the storage unit 23.

[0097] Furthermore, in the reference data acquisition process and the comparison data acquisition process, the order in which the first measurement value dTap, the second measurement value dTan, the third measurement value dTbp, and the fourth measurement value dTbn are acquired is not limited to the example above and is arbitrary.

[0098] Furthermore, in the reference data acquisition process and the comparison data acquisition process, the number of times the first measurement value dTap, second measurement value dTan, third measurement value dTbp, and fourth measurement value dTbn are acquired (measured) is not limited to once, but may be two or more times. For example, the reference data acquisition unit 19 may measure the first measurement value dTap, second measurement value dTan, third measurement value dTbp, and fourth measurement value dTbn twice, and store the first measurement value dTap, second measurement value dTan, third measurement value dTbp, and fourth measurement value dTbn acquired in the second measurement as reference data dT1 in the storage unit 23, rather than the first measurement value dTap, second measurement value dTan, third measurement value dTbp, and fourth measurement value dTbn acquired in the first measurement. This makes it possible to acquire appropriate reference data dT1 even if an appropriate current rise time dT cannot be obtained by the first measurement in the unstable state immediately after gripping the object 200.

[0099] The threshold calculation unit 21 is a functional unit that executes the threshold calculation process. The threshold calculation unit 21 calculates the threshold dTth based on the reference data dT1. Specifically, as shown in Figure 4, the threshold calculation unit 21 selects the maximum value dTmax and the minimum value dTmin from the first measurement value dTap, the second measurement value dTan, the third measurement value dTbp, and the fourth measurement value dTbn included in the reference data dT1. Then, the threshold calculation unit 21 determines the threshold dTth based on half the difference between the maximum value dTmax and the minimum value dTmin (= (dTmax - dTmin) / 2) and stores it in the storage unit 23. For example, the threshold dTth may be half the difference between the maximum value dTmax and the minimum value dTmin (= (dTmax - dTmin) / 2).

[0100] The determination unit 22 is a functional unit that performs a determination process. Based on the reference data dT1, comparison data dT2, and threshold dTth, the determination unit 22 determines whether or not the object 200 has fallen from the gripping unit 7. For example, the determination unit 22 calculates the difference ΔdT (for example, |dT2 - dT1|) between the reference data dT1 and the comparison data dT2, and determines whether or not the object 200 has fallen from the gripping unit 7 based on the comparison result of the difference ΔdT and the threshold dTth.

[0101] For example, the determination unit 22 calculates the difference between the reference data dT1 and the comparison data dT2 for each of the first measured value dTap, second measured value dTan, third measured value dTbp, and fourth measured value dTbn. That is, the determination unit 22 calculates the difference ΔdTap between the first measured value dTap included in the reference data dT1 and the first measured value dTap included in the comparison data dT2. The determination unit 22 calculates the difference ΔdTan between the second measured value dTan included in the reference data dT1 and the second measured value dTan included in the comparison data dT2. The determination unit 22 calculates the difference ΔdTbp between the third measured value dTbp included in the reference data dT1 and the third measured value Tbp included in the comparison data dT2. The determination unit 22 calculates the difference ΔdTbn between the fourth measured value dTbn included in the reference data dT1 and the fourth measured value dTbn included in the comparison data dT2.

[0102] Next, the determination unit 22 compares the calculated difference with the threshold dTth and determines whether the difference is greater than or equal to the threshold. For example, the determination unit 22 compares the differences ΔdTap, ΔdTan, ΔdTbp, and ΔdTbn with the threshold dTth and determines whether the differences ΔdTap, ΔdTan, ΔdTbp, and ΔdTbn are greater than or equal to the threshold dTth.

[0103] The determination unit 22 determines that the object 200 has fallen from the gripping unit 7 if, in the determination process, at least two of the differences ΔdTap, ΔdTan, ΔdTbp, and ΔdTbn exceed the threshold dTth.

[0104] More preferably, the determination unit 22 determines that the object 200 has detached from the gripping unit 7 if it continuously detects that at least two of the differences ΔdTap, ΔdTan, ΔdTbp, and ΔdTbn exceed the threshold dTth during the determination process.

[0105] For example, the determination unit 22 counts the number of differences ΔdTap, ΔdTan, ΔdTbp, and ΔdTbn that are greater than or equal to the threshold dTth, and stores the count value CNTa in the storage unit 23.

[0106] Next, the determination unit 22 determines whether the count value CNTa is m (where m is an integer greater than or equal to 1). The value of "m" is not particularly limited, but in this embodiment, m = 2. If the count value CNTa is m (= 2) or greater, the determination unit 22 increments the count value CNTb (+1) and stores it in the storage unit 23. If the count value CNTa is less than m (= 2), the determination unit 22 clears the count value CNTb stored in the storage unit 23.

[0107] Next, the determination unit 22 determines whether the count value CNTb is greater than or equal to k (where k is an integer greater than or equal to 1). The value of "k" is not particularly limited, but in this embodiment, k = 2. The determination unit 22 determines that the object 200 has fallen from the gripping unit 7 if the count value CNTb is greater than or equal to k (= 2). On the other hand, if the count value CNTb is less than k (= 2), the determination unit 22 may determine that the gripping unit 7 is gripping the object 200.

[0108] Thus, the determination unit 22 determines that the object 200 has detached from the gripping unit 7 when it detects that m of the differences ΔdTap, ΔdTan, ΔdTbp, and ΔdTbn exceed the threshold dTth for k consecutive times.

[0109] The detachment determination unit 18 may also transmit the result of the determination process to the higher-level device 100. For example, the detachment determination unit 18 may output a determination signal So of a first logic level (e.g., high level) when the object 200 is being held by the gripping unit 7, and output a determination signal So of a second logic level (e.g., low level) when the object 200 has detached from the gripping unit 7 (is not being held).

[0110] Next, we will explain the process flow when the gripping device 1 grips the object 200.

[0111] Figure 7 is a flowchart showing an example of the processing flow by the motor drive control device 2 when gripping an object 200 with the gripping device 1 according to the embodiment.

[0112] 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 driving the motor 5 for gripping the object 200.

[0113] 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 12 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, thereby moving the finger portions 9_1 and 9_2 of the gripping portion 7 toward the center position P.

[0114] The motor drive control device 2 starts the process of determining whether the motor 5 has lost step when the motor 5 starts to drive (step S2). Specifically, the step-out detection unit 17 starts the process of determining whether or not the motor has lost step.

[0115] The step-out detection unit 17 determines whether or not step-out has occurred in the motor 5 using the method described above (step S3). If step-out has not been detected (step S3: NO), the motor drive control device 2 continues to rotate the motor 5 in a predetermined direction (step S1).

[0116] On the other hand, if a step loss is detected (step S3: YES), the motor drive control device 2 determines that the object 200 has been gripped by the gripping part 7 (step S4). As a result, the motor drive control device 2 stops the rotation of the motor 5. At this time, the self-locking function of the drive mechanism 6 allows the gripping state of the object 200 to be maintained. Alternatively, after a step loss is detected, the motor drive control device 2 may generate drive control signals Sda and Sdb to rotate the motor 5 by one step. This allows the rotor 50 of the motor 5 to be fixed (rotor lock function) in addition to the self-locking function of the drive mechanism 6, making it possible to further stabilize the gripping state of the object 200 by the gripping part 7.

[0117] Next, the motor drive control device 2 starts the detachment determination process (step S5).

[0118] Figures 8A and 8B are flowcharts showing the flow of the elimination determination process (step S5).

[0119] First, in the elimination determination process, the reference data acquisition unit 19 instructs the drive control signal generation unit 12 to set the current reference value Ith to a first value I0, and the current reference value setting unit 14 sets the current reference value Ith to a first value I0 in response to the instruction from the drive control signal generation unit 12 (step S51).

[0120] Next, the reference data acquisition unit 19 acquires reference data dT1 (step S52). Specifically, the reference data acquisition unit 19 instructs the drive control signal generation unit 12 to energize the coils 51a and 51b one phase at a time using the method described above, measures the current rise time dT for the currents Ia and Ib flowing through the coils 51a and 51b of each phase, and stores the reference data dT1 in the storage unit 23.

[0121] Next, the threshold calculation unit 21 calculates the threshold dTth using the method described above and stores it in the storage unit 23 (step S53).

[0122] Next, the comparison data acquisition unit 20 acquires comparison data dT2 (step S54). Specifically, the comparison data acquisition unit 20 instructs the drive control signal generation unit 12 to energize the coils 51a and 51b one phase at a time using the method described above, measures the current rise time dT for the currents Ia and Ib flowing through the coils 51a and 51b of each phase, and stores the comparison data dT2 in the storage unit 23.

[0123] Next, the determination unit 22 calculates the difference ΔdT between the reference data dT1 and the comparison data dT2 (step S55). Specifically, the determination unit 22 calculates the differences ΔdTap, ΔdTan, ΔdTbp, and ΔdTbn for each of the first measurement value dTap, second measurement value dTan, third measurement value dTbp, and fourth measurement value dTbn using the method described above.

[0124] Next, the determination unit 22 compares the difference ΔdT calculated in step S55 with the threshold dTth calculated in step S53 (step S56). Specifically, the determination unit 22 determines whether the differences ΔdTap, ΔdTan, ΔdTbp, and ΔdTbn are greater than or equal to the threshold dTth.

[0125] Next, the determination unit 22 counts the number of differences ΔdTap, ΔdTan, ΔdTbp, and ΔdTbn that are greater than or equal to the threshold dTth, based on the comparison result from step S56, and stores the count value CNTa in the storage unit 23 (step S57).

[0126] Next, the determination unit 22 determines whether the count value CNTa is m (=2) or greater (step S58). If the count value CNTa is m or greater (step S58: YES), the determination unit 22 increments the count value CNTb (step S59). On the other hand, if the count value CNTa is less than m (step S58: NO), the determination unit 22 clears the count value CNTb (step S60).

[0127] Next, the determination unit 22 determines whether the count value CNTb is k (=2) or greater (step S61). If the count value CNTb is k or greater (step S61: YES), the determination unit 22 determines that the object 200 has fallen from the gripping unit 7 (released state) (step S59). On the other hand, if the count value CNTb is less than k (step S61: NO), the determination unit 22 may determine that the object 200 has not fallen from the gripping unit 7 (gripped state). With this, the detachment determination process (step S5) is completed.

[0128] After step S5, the motor drive control device 2 determines whether the object 200 has been detached by the detachment determination process (step S6). If the detachment of the object 200 is not detected (step S6: NO), the motor drive control device 2 performs the detachment determination process again (step S5). On the other hand, if the detachment of the object 200 is detected (step S6: YES), the motor drive control device 2 (determination unit 22) outputs a determination signal So to notify the higher-level device 100 that the object 200 has been detached from the gripping unit 7 (step S7).

[0129] Figure 9 is a timing chart showing an example of the operating state of the gripping device according to the embodiment.

[0130] In Figure 9, the horizontal axis represents time. From the top to the bottom of Figure 9, the current Ia of the A-phase coil 51a, the current Ib of the B-phase coil 51b, the voltage Va of the A-phase coil 51a, the voltage Vb of the B-phase coil 51b, and the gripping state of the object 200 by the gripping part 7 are shown, respectively. Note that the waveform shown in the bottom row of Figure 9 represents the gripping state of the object 200 and is not the judgment signal So.

[0131] As shown in Figure 9, when the gripping unit 7 is not gripping the object 200 (released state), the motor 5 is driven, causing the gripping unit 7 to grip the object 200 at time t1 (gripping state). Subsequently, the motor drive control device 2 periodically performs the detachment determination process using the method described above. Figure 9 shows that the detachment determination process was performed at times t2, t3, t4, and t6.

[0132] At time t5, the object 200 detaches from the gripping part 7, resulting in the gripping part 7 no longer gripping the object 200 (releasing state). The motor drive control device 2 detects that the object 200 has detached from the gripping part 7 through a detachment detection process performed at time t6, after time t5. As can be seen from Figure 9, the motor drive control device 2 stops executing the periodic detachment detection process.

[0133] As described above, the gripping device 1 according to the embodiment drives the gripping unit 7 by generating a drive control signal Sd to excite the coils 51a and 51b of the motor 5 until the currents Ia and Ib of the coils 51a and 51b reach a current reference value Ith, and then stopping the excitation of the coils 51a and 51b when the currents Ia and Ib reach the current reference value Ith, thereby gripping the object 200. After the object 200 is gripped by the gripping unit 7, the motor drive control device 2 performs a detachment determination process. In the detachment determination process, the motor drive control device 2 measures the current rise time dT multiple times and determines whether or not the object 200 has detached from the gripping unit 7 based on whether or not there is a change in the current rise times dT1 and dT2.

[0134] As described above, a change in the position of the rotor 50 manifests as a change in the current rise time dT (see Figure 4). Therefore, when the object 200 is gripped by the gripping part 7, the position of the rotor 50 does not change even when the motor is driven, and the current rise time dT also does not change. On the other hand, if the object 200 falls out of the gripping part 7, driving the motor 5 changes the position of the rotor 50, and the current rise time dT also changes. Therefore, with the gripping device 1, since the change in the current rise time dT is detected after the object 200 is gripped by the gripping part 7, it is possible to appropriately detect when the object 200 falls out of the gripping part 7.

[0135] Furthermore, in the gripping device 1, the motor drive control device 2 determines that the object 200 has fallen from the gripping part 7 if the measured current rise time dT2 has changed compared to the current rise time dT1 measured previously. This makes it easy to detect changes in the current rise time dT.

[0136] Furthermore, in the gripping device 1, the motor drive control device 2 repeatedly performs a detachment determination process, and in the detachment determination process, if the difference between the measured current rise time dT1 and the previously measured current rise time dT2 exceeds a threshold, it is determined that the object 200 has detached from the gripping part 7. This makes it possible to reliably detect changes in the current rise time dT with a simple process.

[0137] Furthermore, in the gripping device 1, the detachment determination process includes a reference data acquisition process to acquire reference data dT1, which is a reference current rise time; a comparison data acquisition process to acquire comparison data dT2, which is a current rise time to be compared with the reference; and a determination process to determine whether or not the object 200 has detached based on the comparison result between the reference data dT1 and the comparison data dT2. The motor drive control device 2 repeatedly executes the detachment determination process after the gripping unit 7 has gripped the object 200. This makes it possible to constantly monitor the gripping state after the gripping unit 7 has gripped the object 200.

[0138] Furthermore, in the gripping device 1, the motor drive control device 2 starts executing a detachment determination process when it detects a step loss in the motor 5 while the motor 5 is being driven to grip the object 200 by the gripping unit 7. This makes it possible to detect that the gripping unit 7 has gripped the object 200, and to start the step loss determination process as a trigger for gripping the object 200.

[0139] Furthermore, in the gripping device 1, the measured value of the current rise time dT includes the first measured value dTap, the second measured value dTan, the third measured value dTbp, and the fourth measured value dTbn, which are measured values ​​of the current rise time when the coils 51a and 51b are excited in the first direction (positive direction) and the second direction (negative direction). In the motor drive control device 2, in the reference data acquisition process, the first measured value dTap, the second measured value dTan, the third measured value dTbp, and the fourth measured value dTbn are acquired as reference data dT1, and in the comparison data acquisition process, the first measured value dTap, the second measured value dTan, the third measured value dTbp, and the fourth measured value dTbn are acquired as comparison data dT2. In the determination process, the motor drive control device 2 calculates the following: a first difference ΔdTap, which is the difference between the first measurement value dTap of the reference data dT1 and the first measurement value dTap of the comparison data dT2; a second difference ΔdTan, which is the difference between the second measurement value dTan of the reference data dT1 and the second measurement value dTan of the comparison data dT2; a third difference ΔdTbp, which is the difference between the third measurement value dTbp of the reference data dT1 and the third measurement value dTbp of the comparison data dT2; and a fourth difference ΔdTbn, which is the difference between the fourth measurement value dTbn of the reference data dT1 and the fourth measurement value dTbn of the comparison data dT2. The motor drive control device 2 determines that the object 200 has fallen from the gripping part 7 if at least two of the first difference ΔdTap, second difference ΔdTan, third difference ΔdTbp, and fourth difference ΔdTbn exceed the threshold dTth.

[0140] According to this method, by using multiple current rise time measurements, it becomes possible to prevent false detections compared to using only one measurement, thereby improving the accuracy of detachment detection.

[0141] Furthermore, the motor drive control device 2 may determine that the object 200 has detached from the gripping part 7 if it continuously detects that at least two of the differences ΔdTap, ΔdTan, ΔdTbp, and ΔdTbn exceed the threshold dTth during the determination process. This allows for adjustment of the detection sensitivity of the detachment determination, thereby reducing the probability of false determinations.

[0142] Furthermore, the detachment determination process further includes a threshold calculation process for calculating a threshold. In the threshold calculation process, the motor drive control device 2 selects the maximum value dTmax and the minimum value dTmin from the first measured value dTap, second measured value dTan, third measured value dTbp, and fourth measured value dTbn of the reference data dT1, and calculates the threshold value dTth based on half the difference between the maximum value dMax and the minimum value dMin. This makes it possible to determine an appropriate threshold value dTth according to the position of the rotor 50 when the object 200 is gripped, thereby improving the accuracy of detachment determination.

[0143] Furthermore, in the gripping device 1, the motor drive control device 2 acquires the first measurement value dTap, the second measurement value dTan, the third measurement value dTbp, and the fourth measurement value dTbn by exciting the coils 51a and 51b one phase at a time during the reference data acquisition process and the comparison data acquisition process. This makes it possible to measure the first measurement value dTap, the second measurement value dTan, the third measurement value dTbp, and the fourth measurement value dTbn with greater accuracy, thereby improving the accuracy of the detachment judgment.

[0144] <<Expansion of Embodiments>> The present invention has been described in detail above based on embodiments, but it goes without saying that the present invention is not limited thereto and can be modified in various ways without departing from its essence.

[0145] For example, in the above embodiment, a method for detecting whether or not there is a change in the current rise time in the detachment determination process is provided as an example of determining whether or not the difference between the measured current rise time dT2 and the current rise time dT1 measured before it exceeds a threshold, but the method is not limited to this. For example, the presence or absence of a change in the current rise time may be detected by determining whether or not the quotient (ratio) between the measured current rise time dT2 and the current rise time dT1 measured before it exceeds a threshold.

[0146] Furthermore, in the above-mentioned reference data acquisition process and comparison data acquisition process, the first measurement value dTap, the second measurement value dTan, the third measurement value dTbp, and the fourth measurement value dTbn may be measured multiple times, and the average value of multiple measurements for each of the first measurement value dTap, the second measurement value dTan, the third measurement value dTbp, and the fourth measurement value dTbn may be calculated and used as the reference data dT1 and comparison data dT2.

[0147] In the above embodiment, the number of phases of the motor 5 (stepping motor) is not limited to two. Furthermore, the motor 5 is not limited to a stepping motor, but may be, for example, a brushless DC motor.

[0148] 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.

[0149] 1...Gripping device, 2...Motor drive control device, 3...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, 12...Drive control signal generation unit, 13...Drive command acquisition unit, 14...Current reference value setting unit, 15...Current measurement unit, 16...Signal output unit, 17...Step out detection unit, 18...Dropout determination unit, 19...Reference data acquisition unit, 20...Comparison data acquisition unit, 21...Threshold calculation unit, 22...Determination unit, 23...Storage unit, 40a, 40b...Inverter circuit, 41a, 41b...Current detection circuit, 42...Voltage detection circuit, 50...Rotor, 50s...S pole, 50n...N pole, 51a, 51b...Coil, 100...Higher-level device, 200...Target object, CNTa, CNTb...Count value, dTth...Threshold, dT1...Reference data (current rise time), dT2...Comparison data (current rise time), dTap...First measurement value, dTan...Second measurement value, dTbp...Third measurement value, dTbn...Fourth measurement value, ΔdT, ΔdTap, ΔdTan, ΔdTbp, ΔdTbn...Difference, Ia, Ib...Current, Ith...Current reference value, I0...First value, Sc...Drive command signal, Sd, Sda, Sdb...Drive control signal, Sia, Sib...Current detection signal, So...Decision signal, Vap, Van, Vbp, Vbn, Vbef...Voltage, Vth...Step-out determination threshold, 100...Higher-level device.

Claims

1. 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 driving the motor, wherein 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, wherein the control circuit includes: a drive control signal generation unit for generating the drive control signal so as to energize the coil until the current of the coil reaches a current reference value, and to stop the excitation of the coil when the current reaches the current reference value; and a detachment determination unit for performing a detachment determination process to determine whether or not the object has detached from the gripping part after the object has been gripped by the gripping part, wherein the detachment determination unit measures the current rise time, which is the time from when the excitation of the coil is started until the current reaches the current reference value, multiple times in the detachment determination process, and determines whether or not the object has detached from the gripping part based on whether or not there is a change in the current rise time.

2. A gripping device according to claim 1, wherein the detachment determination unit determines that the object has detached from the gripping unit when the measured current rise time has changed compared to the current rise time measured previously in the detachment determination process.

3. A gripping device according to claim 2, wherein the detachment determination unit determines that the object has detached from the gripping unit when the difference between the measured current rise time and the current rise time measured before that exceeds a threshold in the detachment determination process.

4. The gripping device according to claim 3, wherein the detachment determination process includes a reference data acquisition process for acquiring reference data which is a reference current rise time; a comparison data acquisition process for acquiring comparison data which is a comparison target current rise time for comparison with the reference; and a determination process for determining whether or not the object has detached based on the comparison result of the reference data and the comparison data, wherein the detachment determination unit repeatedly executes the detachment determination process after the object has been gripped by the gripping unit.

5. The gripping device according to claim 4, further comprising a step-out detection unit for detecting step-out of the motor, wherein the step-out determination unit starts executing the step-out determination process when the step-out detection unit detects step-out of the motor while the motor is being driven to grip the object by the gripping unit.

6. In the gripping device according to claim 4, the motor is a stepping motor having a first phase coil and a second phase coil as the coils, and the measured value of the current rise time includes a first measured value which is the current rise time when the first phase coil is excited in a first direction, a second measured value which is the current rise time when the first phase coil is excited in a second direction opposite to the first direction, a third measured value which is the current rise time when the second phase coil is excited in the first direction, and a fourth measured value which is the current rise time when the second phase coil is excited in the second direction, and the detachment determination unit acquires the first measured value, the second measured value, the third measured value, and the fourth measured value as the reference data in the reference data acquisition process, and the detachment determination unit acquires the first measured value, the second measured value, the third measured value, and the fourth measured value as the comparison data in the comparison data acquisition process. The detachment determination unit calculates, in the determination process, a first difference which is the difference between the first measurement value of the reference data and the first measurement value of the comparison data, a second difference which is the difference between the second measurement value of the reference data and the second measurement value of the comparison data, a third difference which is the difference between the third measurement value of the reference data and the third measurement value of the comparison data, and a fourth difference which is the difference between the fourth measurement value of the reference data and the fourth measurement value of the comparison data, and determines that the object has detached from the gripping unit if at least two of the first difference, second difference, third difference, and fourth difference exceed the threshold.

7. A gripping device according to claim 6, wherein the detachment determination unit determines that the object has detached from the gripping unit when it continuously detects in the determination process that at least two of the first difference, second difference, third difference, and fourth difference exceed the threshold.

8. A gripping device according to claim 7, wherein the detachment determination process includes a threshold calculation process for calculating the threshold, and the detachment determination unit, in the threshold calculation process, selects the maximum and minimum values ​​from the first measured value, second measured value, third measured value, and fourth measured value of the reference data, and calculates the threshold based on half the difference between the maximum value and the minimum value.

9. A gripping device according to claim 6, wherein the detachment determination unit obtains the first measurement value, the second measurement value, the third measurement value, and the fourth measurement value by exciting the coil one phase at a time in the reference data acquisition process and the comparison data acquisition process.

10. 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 driving the motor, the control method comprising: a first step of driving the motor so that the gripping part grips the object; a second step of measuring the current rise time multiple times, which is the time from when the excitation of the coil is started until the current in the coil reaches a current reference value, after the gripping part has gripped the object; and a third step of determining whether or not the object has fallen from the gripping part based on whether or not there has been a change in the current rise time measured in the second step.

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