Control device, magnet gripper, sensor, and control method

Abstract

A control device (12) controls an electro-permanent magnet (10) which is provided with a first permanent magnet (10a), a second permanent magnet (10b), and a coil (10c), and in which the magnetization direction of the second permanent magnet (10b) is reversed when a drive voltage (Vd) is applied to the coil (10c). The control device (12) is provided with: a switching control unit (42) which switches between a detection voltage application control in which a detection voltage (Vt) is applied to the coil (10c), and a detection voltage application stop control in which the application of the detection voltage (Vt) is stopped; and a detection unit (46) which, when the detection voltage (Vt) is applied to the coil (10c), detects whether or not a magnetic body (W) is present on the basis of a measured value (Mv) of a coil current (Ic).

Description

Control Device, Magnet Gripper, Sensor, and Control Method

[0001] The present disclosure relates to a control device, a magnet gripper, a sensor, and a control method.

[0002] International Publication No. 99 / 08293 discloses a lift device that lifts a load, which is a ferromagnetic material, using magnetic force. The lift device has an electropermanent magnet and a magnetic sensor for measuring the magnetic force of the electropermanent magnet.

[0003] According to the technique disclosed in International Publication No. 99 / 08293, it is not known whether a magnetic material is in the vicinity of the electropermanent magnet until the electropermanent magnet with an adsorption force contacts the magnetic material. Therefore, the electropermanent magnet can have an adsorption force even though there is no magnetic material in the vicinity of the electropermanent magnet. When the electropermanent magnet moves toward the magnetic material in a state with an adsorption force from a position away from the magnetic material, iron powder or the like may cover the electropermanent magnet during the movement. If the magnetic material is held by the electropermanent magnet in that state, the magnetic material may be damaged.

[0004] An object of the present disclosure is to solve the above-described problems.

[0005] A first aspect of the present disclosure includes a first permanent magnet and a second permanent magnet, and a coil wound around at least an outer periphery of the second permanent magnet. When a driving voltage is applied to the coil, the magnetization direction of the second permanent magnet is reversed, and the magnetization direction of the second permanent magnet is maintained until the driving voltage is applied to the coil again after the application of the driving voltage to the coil is stopped. A control device for controlling an electropermanent magnet, the control device including a detection voltage application control for applying a detection voltage lower than the driving voltage to the coil, a switching control unit for switching between the detection voltage application control and a detection voltage application stop control for stopping the application of the detection voltage to the coil, and a detection unit for detecting whether there is a magnetic material that can be held when the electropermanent magnet has an adsorption force based on a measured value of a coil current flowing through the coil when the detection voltage is applied to the coil by the detection voltage application control.

[0006] A second aspect of this disclosure is a magnet gripper comprising a control device according to the first aspect and the permanent electromagnet.

[0007] A third aspect of this disclosure is a sensor comprising a control device according to the first aspect and an output unit that outputs the detection result from the detection unit to the outside.

[0008] A fourth aspect of the present disclosure is a control method for controlling a permanent electromagnet comprising a first permanent magnet, a second permanent magnet, and a coil wound at least around the outer circumference of the second permanent magnet, wherein when a driving voltage is applied to the coil, the magnetization direction of the second permanent magnet is reversed, and the magnetization direction of the second permanent magnet is maintained from the time the application of the driving voltage to the coil is stopped until the application of the driving voltage to the coil is applied again, the control method comprising: a detection voltage application control step of applying a detection voltage lower than the driving voltage to the coil; a detection voltage application stop control step of stopping the application of the detection voltage to the coil; and, when the detection voltage is applied to the coil in the detection voltage application control step, a detection step of detecting whether or not there is a magnetic material that can be held when the permanent electromagnet has an attractive force, based on a measured value of the coil current flowing through the coil.

[0009] According to this disclosure, it is possible to prevent a permanent electromagnet from possessing an attractive force even when there is no magnetic material in its vicinity.

[0010] The above-mentioned objectives, features, and advantages will be readily apparent from the following description of the embodiments, which will be illustrated with reference to the attached drawings.

[0011] Figure 1A shows a permanent electromagnet and a control device that controls the permanent electromagnet. Figures 1B and 1C schematically show the magnetic flux corresponding to the magnetic force generated by the permanent electromagnet. Figure 2 shows an example of the configuration of a voltage application circuit. Figure 3 shows an example of the configuration of a control device. Figures 4A and 4B illustrate the change in coil current flowing through the coil of the permanent electromagnet over time. Figure 5 shows an example of determining a threshold used in the detection process by the detection unit of the control device. Figures 6A and 6B show examples of detection processing by the detection unit of the control device. Figure 7 is an example of a time chart for explaining voltage application control and voltage application stop control to the coil of the permanent electromagnet. Figure 8 is a flowchart illustrating the control processing procedure of the permanent electromagnet. Figures 9A and 9B illustrate the change in coil current flowing through the coil of the permanent electromagnet over time. Figure 10 shows an example of determining a predetermined current. Figure 11 shows an example of the configuration of a control device. Figure 12 is a diagram for explaining the phase difference between the detection voltage and the coil current. Figures 13A and 13B show examples of detection processing by the detection unit of the control device. Figure 14 shows an example of the configuration of a voltage application circuit. Figure 15 is an example of a time chart for explaining the control of voltage application to the coil of a permanent electromagnet and the control of stopping voltage application. Figure 16 shows an example of the configuration of a sensor. Figure 17A shows a permanent electromagnet. Figures 17B and 17C schematically show the magnetic flux corresponding to the magnetic force generated by the permanent electromagnet.

[0012] Robots are sometimes used to supply workpieces to industrial equipment. For example, a robot may supply a steel plate to be pressed to a press machine. If the supplied workpiece is a magnetic material such as a steel plate, a magnetic gripper with a permanent electromagnet may be used as the robot's end effector. If there is a magnetic material within the range of the permanent electromagnet's magnetic force, the magnetic material can be held by the permanent electromagnet, which has an attractive force based on that magnetic force.

[0013] If there is no magnetic material within the range of the magnetic force of the permanent electromagnet, iron filings or similar materials attracted to the electromagnet with its magnetic force may cover the electromagnet. If the electromagnet is then moved to a position where there is a magnetic material and the magnetic material is held by the electromagnet, the magnetic material may be damaged by the iron filings or similar materials covering the electromagnet. Therefore, it is preferable to be able to detect whether the permanent electromagnet is in a state where it can hold a magnetic material by its magnetic force, and whether there is a magnetic material within the range of the magnetic force of the permanent electromagnet.

[0014] In the press processing of steel plates using the press machine described above, the steel plates are pressed one at a time. In such cases, the steel plates must be supplied one at a time. If two overlapping steel plates are supplied to the press machine's die at the same time, the press processing will be attempted on both steel plates. This can lead to problems such as defective press processing or die failure.

[0015] If no steel plates are supplied, the press working process cannot proceed, which presents a problem. Furthermore, if, for example, there are no steel plates at the location where they are to be placed before supply, the robot may attempt to hold a steel plate in place using a permanent electromagnet, potentially causing iron filings or other debris present at that location to cover the electromagnet.

[0016] In other words, the robot needs to supply one magnetic material to the industrial equipment at a time. The robot cannot supply two or more superimposed magnetic materials to the industrial equipment at once. It is also undesirable for the robot to supply zero magnetic materials to the industrial equipment. Therefore, it is preferable that the number of superimposed magnetic materials held by the permanent electromagnet can be detected.

[0017] Figure 1A shows a permanent electromagnet 10 and a control device 12 that controls the permanent electromagnet 10. The permanent electromagnet 10 has a first permanent magnet 10a, a second permanent magnet 10b, and a coil 10c. The permanent electromagnet 10 also has a yoke (not shown). In this embodiment, as shown in Figure 1A, the first permanent magnet 10a and the second permanent magnet 10b are arranged adjacent to each other.

[0018] Specifically, the cylindrical first permanent magnet 10a covers the outer surface of the cylindrical second permanent magnet 10b. That is, the second permanent magnet 10b is housed in the hollow part of the first permanent magnet 10a. The first permanent magnet 10a is a neodymium magnet containing, for example, neodymium in addition to iron. The second permanent magnet 10b is an alnico magnet containing, for example, aluminum, nickel, and cobalt in addition to iron.

[0019] The coil 10c is wound around at least the outer circumference of the second permanent magnet 10b. In this embodiment, as shown in Figure 1A, the coil 10c is wound around the outer circumference of the first permanent magnet 10a, which is located outside the second permanent magnet 10b. The coil 10c is electrically connected to the drive power supply 14 and the detection power supply 16, respectively, via a voltage application circuit 18. The drive power supply 14 is a DC power supply that supplies a drive voltage Vd to the coil 10c. The detection power supply 16 is a DC power supply that supplies a detection voltage Vt lower than the drive voltage Vd to the coil 10c. The control device 12 controls the permanent electromagnet 10 by operating the voltage application circuit 18.

[0020] When the control device 12 operates the voltage application circuit 18, the drive voltage Vd supplied from the drive power supply 14 is applied to the coil 10c, causing a current to flow. This can reverse the magnetization direction of the second permanent magnet 10b. When the magnetization direction of the second permanent magnet 10b is reversed, the permanent electromagnet 10 acquires an attractive force based on its magnetic force. In this case, the magnetic material W can be held by the permanent electromagnet 10.

[0021] The control device 12 operates the voltage application circuit 18, thereby applying the detection voltage Vt supplied from the detection power supply 16 to the coil 10c, causing current to flow. This allows the control device 12 to perform the detection process described later. An example of the configuration of the voltage application circuit 18 used to apply the driving voltage Vd and the detection voltage Vt to the coil 10c will be described later with reference to Figure 2. An example of the configuration of the control device 12 will be described later with reference to Figure 3.

[0022] In this embodiment, the control device 12 is provided in the magnet gripper having the permanent electromagnet 10. This eliminates the need to provide a signal line connecting the control device 12 and the magnet gripper, thus realizing a user-friendly magnet gripper. However, the control device 12 may also be provided outside the magnet gripper.

[0023] Figures 1B and 1C schematically show the magnetic flux B corresponding to the magnetic force generated by the permanent electromagnet 10. In Figure 1B, the magnetization direction of the second permanent magnet 10b is the first direction. The magnetization direction of the second permanent magnet 10b is opposite to that of the first permanent magnet 10a. The magnetic flux B emanating from the first permanent magnet 10a enters the second permanent magnet 10b through a yoke (not shown). The magnetic flux B emanating from the second permanent magnet 10b enters the first permanent magnet 10a through a yoke (not shown). In other words, the magnetic flux B is confined within the permanent electromagnet 10.

[0024] In that case, the magnetic flux B does not pass through the magnetic material W. Thus, when the magnetic circuit formed by the magnetic flux B is closed and formed between the first permanent magnet 10a and the second permanent magnet 10b, the permanent electromagnet 10 does not possess any attractive force. Therefore, the permanent electromagnet 10 does not hold the magnetic material W. The permanent electromagnet 10 is in a state where it cannot hold the magnetic material W.

[0025] When a driving voltage Vd is applied to the coil 10c, a current flows through the coil 10c in a predetermined direction, which can reverse the magnetization direction of the second permanent magnet 10b shown in Figure 1B. That is, as shown in Figure 1C, the magnetization direction of the second permanent magnet 10b can be made to match the magnetization direction of the first permanent magnet 10a.

[0026] In Figure 1C, the magnetization direction of the second permanent magnet 10b is a second direction opposite to the first direction. The magnetization direction of the second permanent magnet 10b is the same as the magnetization direction of the first permanent magnet 10a. The magnetic flux B emitted from the first permanent magnet 10a returns to the first permanent magnet 10a without entering the second permanent magnet 10b. The magnetic flux B emitted from the second permanent magnet 10b returns to the second permanent magnet 10b without entering the first permanent magnet 10a. Neither of the magnetic fluxes B are confined within the permanent electromagnet 10, but pass outside the permanent electromagnet 10.

[0027] When the permanent electromagnet 10 approaches or is in contact with the magnetic material W, the magnetic flux B passes through the magnetic material W. In this way, when the magnetic circuit formed by the magnetic flux B is formed independently by the first permanent magnet 10a and the second permanent magnet 10b, the permanent electromagnet 10 possesses an attractive force. When the magnetic material W is within the range of the magnetic force of the permanent electromagnet 10, which possesses an attractive force, the permanent electromagnet 10 holds the magnetic material W. The permanent electromagnet 10 is in a holding state in which it can hold the magnetic material W due to this attractive force.

[0028] When the driving voltage Vd is applied to the coil 10c, a current flows through the coil 10c in the opposite direction to the predetermined direction described above, which can reverse the magnetization direction of the second permanent magnet 10b shown in Figure 1C. That is, as shown in Figure 1B, the magnetization direction of the second permanent magnet 10b can be made opposite to the magnetization direction of the first permanent magnet 10a. In that case, as described above, the magnetic flux B does not pass through the magnetic material W. Therefore, the permanent electromagnet 10 does not possess an attractive force, and the magnetic material W detaches from the permanent electromagnet 10. That is, the permanent electromagnet 10 does not hold the magnetic material W. The state of the permanent electromagnet 10 returns to the state of non-retention described above.

[0029] As described above, when the driving voltage Vd is applied to the coil 10c and current flows through the coil 10c, the magnetization direction of the second permanent magnet 10b is reversed. Even after the application of the driving voltage Vd to the coil 10c is stopped and the current flowing through the coil 10c stops, the magnetization direction of the second permanent magnet 10b remains unchanged until the driving voltage Vd is applied to the coil 10c again.

[0030] In other words, if the permanent electromagnet 10 enters the above-described holding state by applying the driving voltage Vd to the coil 10c, the attractive force of the permanent electromagnet 10 is maintained even after the application of the driving voltage Vd to the coil 10c is stopped, and therefore the holding state is maintained. If the permanent electromagnet 10 holds the magnetic material W, that state continues. If the permanent electromagnet 10 enters the above-described non-holding state by applying the driving voltage Vd to the coil 10c, the attractive force of the permanent electromagnet 10 remains released even after the application of the driving voltage Vd to the coil 10c is stopped, and therefore the non-holding state is maintained. The state in which the permanent electromagnet 10 cannot hold the magnetic material W continues.

[0031] Figure 2 shows an example of the configuration of the voltage application circuit 18. The voltage application circuit 18 is used to apply the drive voltage Vd supplied from the drive power supply 14 and the detection voltage Vt supplied from the detection power supply 16 to the coil 10c of the permanent electromagnet 10. In this embodiment, the drive power supply 14 and the detection power supply 16 are different power sources. This makes it possible to realize a power source that supplies the voltage applied to the coil 10c at low cost.

[0032] Switch SW1 and Switch SW2 are connected in series from the positive terminal to the negative terminal of the drive power supply 14. Switch SW3 and Switch SW4 are connected in series from the positive terminal to the negative terminal of the drive power supply 14. One end Pa of coil 10c is electrically connected between switch SW1 and switch SW2. The other end Pb of coil 10c is electrically connected between switch SW3 and switch SW4.

[0033] In other words, switch SW1 is interposed between the positive terminal of the drive power supply 14 and one end Pa of the coil 10c. Switch SW2 is interposed between the negative terminal of the drive power supply 14 and one end Pa of the coil 10c. Switch SW3 is interposed between the positive terminal of the drive power supply 14 and the other end Pb of the coil 10c. Switch SW4 is interposed between the negative terminal of the drive power supply 14 and the other end Pb of the coil 10c.

[0034] Switch SWa, coil 10c, and switch SWb are connected in series from the positive terminal to the negative terminal of the detection power supply 16. In other words, switch SWa is interposed between the positive terminal of the detection power supply 16 and one end Pa of coil 10c. Switch SWb is interposed between the negative terminal of the detection power supply 16 and the other end Pb of coil 10c.

[0035] Assume that the control device 12 turns on switches SW1 and SW4, and turns off switches SW2 and SW3. In this case, a driving voltage Vd is applied to coil 10c, and current flows from one end Pa to the other end Pb of coil 10c. The driving voltage Vd applied to coil 10c is a positive voltage. The magnetization direction of the second permanent magnet 10b is reversed. In this embodiment, the magnetization direction of the second permanent magnet 10b is the same as the magnetization direction of the first permanent magnet 10a. The permanent electromagnet 10 is in the holdable state described above.

[0036] Subsequently, the control device 12 turns off switches SW1, SW2, SW3, and SW4. In this way, the magnetization direction of the second permanent magnet 10b is maintained from the time the application of the driving voltage Vd to the coil 10c is stopped until the driving voltage Vd is applied to the coil 10c again. Since the magnetization direction of the second permanent magnet 10b is maintained, the holding state of the permanent electromagnet 10 is maintained. Therefore, the use of the permanent electromagnet 10 can be performed with lower power consumption than the use of an electromagnet.

[0037] Assume that the control device 12 turns on switches SW2 and SW3, and turns off switches SW1 and SW4. In this case, a driving voltage Vd is applied to coil 10c, and current flows from the other end Pb to the first end Pa of coil 10c. The driving voltage Vd applied to coil 10c is a negative voltage. The magnetization direction of the second permanent magnet 10b is reversed. In this embodiment, the magnetization direction of the second permanent magnet 10b is opposite to that of the first permanent magnet 10a. The permanent electromagnet 10 is in the non-holding state described above.

[0038] Subsequently, the control device 12 turns off switches SW1, SW2, SW3, and SW4. In this way, the magnetization direction of the second permanent magnet 10b is maintained from the time the application of the driving voltage Vd to the coil 10c is stopped until the driving voltage Vd is applied to the coil 10c again. Since the magnetization direction of the second permanent magnet 10b is maintained, the non-holding state of the permanent electromagnet 10 is maintained. Therefore, the use of the permanent electromagnet 10 can be performed with lower power consumption than the use of an electromagnet.

[0039] Assume that the control device 12 turns on switches SWa and SWb. In this case, a detection voltage Vt is applied to coil 10c, and current flows from one end Pa to the other end Pb of coil 10c. The detection voltage Vt applied to coil 10c is a positive voltage. Since the detection voltage Vt is sufficiently lower than the driving voltage Vd, the magnetization direction of the second permanent magnet 10b is maintained without reversing.

[0040] As will be described later using Figures 4A and 4B, the coil current Ic flowing through coil 10c is measured. For example, the measured value of the coil current Ic can be obtained using an ammeter. Based on the obtained measured value of the coil current Ic, the control device 12 performs the detection process described later. Note that multiple measured values ​​of the coil current Ic can be obtained by repeatedly turning switches SWa and SWb on and off multiple times.

[0041] Subsequently, the control device 12 turns off both switches SWa and SWb. This state is maintained until the next detection process is performed.

[0042] Figure 3 shows an example of the configuration of the control device 12. The control device 12 has an arithmetic unit 30 and a storage unit 32. The arithmetic unit 30 includes a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit). In other words, the arithmetic unit 30 includes processing circuitry.

[0043] The memory unit 32 includes a volatile memory such as a RAM (Random Access Memory) and a non-volatile memory such as a ROM (Read Only Memory) or a flash memory. The volatile memory is used as the working memory of the processor. The non-volatile memory stores programs executed by the processor, predetermined threshold values, etc. The predetermined threshold values will be described later using FIG. 6.

[0044] The arithmetic unit 30 includes a drive control unit 40, a switching control unit 42, a measurement value acquisition unit 44, and a detection unit 46. By executing the program stored in the memory unit 32 by the arithmetic unit 30, the drive control unit 40, the switching control unit 42, the measurement value acquisition unit 44, and the detection unit 46 are realized. At least a part of the drive control unit 40, the switching control unit 42, the measurement value acquisition unit 44, and the detection unit 46 may be realized by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array), or an electronic circuit including discrete devices.

[0045] The drive control unit 40 performs drive control of the coil 10c of the permanent magnet 10. The drive control is control in which a drive voltage Vd is applied to the coil 10c. The drive voltage Vd is supplied from the drive power source 14.

[0046] When it is detected by the detection unit 46 described later that the magnetic body W is present in a state where the permanent magnet 10 does not have an attracting force, the drive control unit 40 performs drive control for reversing the magnetization direction of the second permanent magnet 10b. As the drive control, the drive control unit 40 turns on the switch SW1 and the switch SW4 in the voltage application circuit 18 shown in FIG. 2 and turns off the switch SW2 and the switch SW3. A positive drive voltage Vd is applied to the coil 10c. Thus, the drive control unit 40 can provide the permanent magnet 10 with an attracting force. Thereby, the drive control unit 40 can hold the magnetic body W by the permanent magnet 10.

[0047] After that, the drive control unit 40 turns off all of the switches SW1, SW2, SW3, and SW4. Since the magnetization direction of the second permanent magnet 10b is maintained, the holdable state in the permanent magnet 10 is maintained. The state in which the permanent magnet 10 having an adsorption force holds the magnetic body W continues.

[0048] When detaching the magnetic body W from the permanent magnet 10 in the state where the permanent magnet 10 having an adsorption force holds the magnetic body W, the drive control unit 40 performs drive control for reversing the magnetization direction of the second permanent magnet 10b again. As the drive control, the drive control unit 40 turns on the switch SW2 and the switch SW3 in the voltage application circuit 18 shown in FIG. 2, and turns off the switch SW1 and the switch SW4. A drive voltage Vd with a negative voltage is applied to the coil 10c. Thus, the drive control unit 40 can make the permanent magnet 10 in a state without an adsorption force. Thereby, the magnetic body W can be detached from the permanent magnet 10.

[0049] After that, the drive control unit 40 turns off all of the switches SW1, SW2, SW3, and SW4. Since the magnetization direction of the second permanent magnet 10b is maintained, the non-holdable state in the permanent magnet 10 is maintained. The state in which the permanent magnet 10 has no adsorption force continues. Thus, by the drive control unit 40 performing drive control, the state of the permanent magnet 10, which is a holdable state or a non-holdable state, can be easily switched.

[0050] The switching control unit 42 performs detection voltage application control and detection voltage application stop control for the coil 10c of the permanent magnet 10, and switches between the detection voltage application control and the detection voltage application stop control. The detection voltage application control is control in which a detection voltage Vt is applied to the coil 10c. The detection voltage Vt is supplied from the detection power supply 16. The detection voltage application stop control is control in which the application of the detection voltage Vt to the coil 10c is stopped.

[0051] With switches SW1, SW2, SW3, and SW4 all in the OFF position, the switching control unit 42 performs detection voltage application control. As part of this detection voltage application control, the switching control unit 42 turns on switches SWa and SWb. A positive detection voltage Vt is applied to coil 10c. In this state, the coil current Ic flowing through coil 10c is measured. The coil current Ic thus measured is used by the measurement value acquisition unit 44 and the detection unit 46, which will be described later.

[0052] The switching control unit 42 can stop the detection voltage application control by switching the detection voltage application control to the detection voltage application stop control. As part of this detection voltage application stop control, the switching control unit 42 turns off switches SWa and SWb. The application of the positive voltage detection voltage Vt to the coil 10c is stopped.

[0053] The measurement value acquisition unit 44 acquires the measured value of the coil current Ic, which is measured while the detection voltage Vt is applied to the coil 10c by the detection voltage application control described above.

[0054] When the detection voltage Vt is applied to the coil 10c of the permanent electromagnet 10 by the detection voltage application control performed by the switching control unit 42, the detection unit 46 performs a magnetic material W detection process and a permanent electromagnet 10 state detection process based on the measured value acquired by the measured value acquisition unit 44 and the threshold value stored by the storage unit 32. As the magnetic material W detection process, the detection unit 46 performs a process to detect whether or not there is a magnetic material W that can be held when the permanent electromagnet 10 has the above-described attraction force. As the permanent electromagnet 10 state detection process, the detection unit 46 performs a process to detect whether the state of the permanent electromagnet 10 is the above-described non-holding state or the holding state.

[0055] Details of the detection process for the magnetic material W and the state detection process for the permanent electromagnet 10, which are performed by the detection unit 46 based on the measured value and threshold, will be described later. Through the detection process for the magnetic material W and the state detection process for the permanent electromagnet 10, the detection unit 46 can also detect whether or not the magnetic material W is actually held by the permanent electromagnet 10.

[0056] The operation of the drive control unit 40 and the detection unit 46 will be explained using an example in which a robot equipped with a magnetic gripper having a permanent electromagnet 10 as an end effector supplies a magnetic material W to industrial equipment. In order for the magnetic material W to be held by the permanent electromagnet 10 of the magnetic gripper, the permanent electromagnet 10 does not possess any attractive force at the time before the robot brings the magnetic gripper close to the pre-prepared magnetic material W. This is because if the permanent electromagnet 10 possessed an attractive force, the permanent electromagnet 10 may be covered with iron powder or the like before it can hold the magnetic material W.

[0057] Assume that when the permanent electromagnet 10 does not possess an attractive force, a detection voltage Vt is applied to the coil 10c of the permanent electromagnet 10 by detection voltage application control. In this case, the detection unit 46 detects whether or not there is a magnetic material W that can be held when the permanent electromagnet 10 possesses the attractive force described above. The detection process for such a magnetic material W is performed while the magnet gripper, which has a permanent electromagnet 10 that does not possess an attractive force, is brought closer to the magnetic material W by a robot.

[0058] As a result of the magnetic gripper approaching the magnetic material W, the magnetic material W may be included in the range affected by the magnetic force of the permanent electromagnet 10 when the permanent electromagnet 10 is equipped with an attractive force. In that case, the detection unit 46 detects the presence of the magnetic material W. When the detection unit 46 detects the presence of the magnetic material W, the drive control unit 40 performs drive control to equip the permanent electromagnet 10 with an attractive force. This prevents the permanent electromagnet 10 from being equipped with an attractive force even when there is no magnetic material W in its vicinity. Once the permanent electromagnet 10 is equipped with an attractive force after the presence of the magnetic material W is detected, it can hold the magnetic material W with that attractive force.

[0059] The robot moves the magnetic gripper to the industrial equipment while the magnetic material W is held in place by the permanent electromagnet 10 of the magnetic gripper. The drive control unit 40 performs drive control to supply the magnetic material W to the industrial equipment. As a result, the permanent electromagnet 10 no longer has any attractive force, and the magnetic material W detaches from the permanent electromagnet 10. In this way, the magnetic material W is supplied to the industrial equipment.

[0060] The detection unit 46 detects whether or not the magnetic material W is present. When the detection unit 46 detects that the magnetic material W is absent, it can be confirmed that the magnetic material W detaches from the permanent electromagnet 10 and is no longer held by the permanent electromagnet 10. The robot can then supply the magnetic material W to the industrial equipment again.

[0061] Figures 4A and 4B illustrate the change in the coil current Ic flowing through the coil 10c of the permanent electromagnet 10 with respect to time T. Graph Im shows the change in the coil current Ic with respect to time T when there is a magnetic material W that can be held when the permanent electromagnet 10 has an attractive force. Graph In shows the change in the coil current Ic with respect to time T when there is no magnetic material W that can be held when the permanent electromagnet 10 has an attractive force.

[0062] Figure 4A shows graph Im when the magnetic material W is present and graph In when the magnetic material W is absent, in a state where the permanent electromagnet 10 does not possess attractive force and is unable to hold the magnetic material W. At time Tsr, the switching control unit 42 starts the detection voltage application control, and the detection voltage Vt is applied to the coil 10c of the permanent electromagnet 10. As the detection voltage Vt is applied to the coil 10c, the coil current Ic starts to rise, as shown in both graph Im and graph In. The coil current Ic goes through a transient state of gradually rising and then reaches a constant current Ip corresponding to the detection voltage Vt.

[0063] The rate of increase of the coil current Ic in the transient state is greater in graph In (when there is no magnetic material W) than in graph Im (when there is a magnetic material W). In the example shown in Figure 4A, the difference in coil current Ic between graph In and graph Im is large at time Twr, after a predetermined time Tp has elapsed since the switching control unit 42 started the detection voltage application control at time Tsr. The predetermined time Tp is determined in advance according to a time constant τ obtained based on, for example, the inductance value and resistance value of the coil 10c.

[0064] As shown in graph In, at time Twr, the value of the coil current Ic when the magnetic material W is absent is value Inr. As shown in graph Im, at time Twr, the value of the coil current Ic when the magnetic material W is present is value Imr. The values ​​Inr and Imr of the coil current Ic are obtained by measurement.

[0065] Figure 4B shows graph Im when the magnetic material W is present and graph In when the magnetic material W is absent, in a state where the permanent electromagnet 10 has an attractive force and can hold the magnetic material W by that attractive force. At time Tsh, the switching control unit 42 starts the detection voltage application control, and the detection voltage Vt is applied to the coil 10c of the permanent electromagnet 10. As the detection voltage Vt is applied to the coil 10c, the coil current Ic starts to rise, as shown in both graph Im and graph In. The coil current Ic goes through a transient state of gradually rising and then reaches a constant current Ip corresponding to the detection voltage Vt.

[0066] The rate of increase of the coil current Ic in the transient state is greater in graph In (when there is no magnetic material W) than in graph Im (when there is a magnetic material W). In the example shown in Figure 4B, the difference in coil current Ic between graph In and graph Im is large at time Twh, after a predetermined time Tp has elapsed since the switching control unit 42 started the detection voltage application control at time Tsh. The predetermined time Tp is determined in advance according to the time constant τ as described above.

[0067] As shown in graph In, at time Twh, the value of the coil current Ic when the magnetic material W is absent is value Inh. As shown in graph Im, at time Twh, the value of the coil current Ic when the magnetic material W is present is value Imh. The values ​​Inh and Imh of the coil current Ic are obtained by measurement.

[0068] In this way, the coil current Ic value Inr is obtained when the permanent electromagnet 10 is unable to hold and there is no magnetic material W; the coil current Ic value Imr is obtained when the permanent electromagnet 10 is unable to hold and there is a magnetic material W; the coil current Ic value Inh is obtained when the permanent electromagnet 10 can hold and there is no magnetic material W; and the coil current Ic value Imh is obtained when the permanent electromagnet 10 can hold and there is a magnetic material W. By performing multiple measurements, the average values ​​of the coil current Ic values ​​Inr, Imr, Inh, and Imh may be obtained. Using these four coil current Ic values, a threshold value used in the detection process by the detection unit 46 is determined.

[0069] Figure 5 shows an example of determining threshold values ​​H1, H2, and H3 used in the detection process by the detection unit 46 of the control device 12. The threshold values ​​H1, H2, and H3 used in the detection process by the detection unit 46 are determined using the following values: Inr, the value of the coil current Ic when the permanent electromagnet 10 is unable to hold and there is no magnetic material W, Imr, the value of the coil current Ic when the permanent electromagnet 10 is unable to hold and there is a magnetic material W, Inh, the value of the coil current Ic when the permanent electromagnet 10 can hold and there is no magnetic material W, and Imh, the value of the coil current Ic when the permanent electromagnet 10 is unable to hold and there is a magnetic material W, as shown in Figure 4.

[0070] As shown in Figure 5, the coil current Ic value Inr is highest when the permanent electromagnet 10 is in a non-holding state and there is no magnetic material W. The coil current Ic value Inh is second highest when the permanent electromagnet 10 is able to hold but there is no magnetic material W. The coil current Ic value Imh is second lowest when the permanent electromagnet 10 is able to hold but there is a magnetic material W. The coil current Ic value Imr is lowest when the permanent electromagnet 10 is in a non-holding state but there is a magnetic material W.

[0071] The threshold H1 is used in the detection process of the magnetic material W by the detection unit 46. The value between the value Inr and the value Imr is determined as the threshold H1. More preferably, the value between the value Inh and the value Imh is determined as the threshold H1. The storage unit 32 stores the threshold H1 thus determined as a threshold for distinguishing between a state in which there is a magnetic material W that can be held when the permanent electromagnet 10 has an attractive force and a state in which there is no such magnetic material W.

[0072] The detection unit 46 performs the above-described magnetic material W detection process based on the measured value of the coil current Ic after a predetermined time Tp has elapsed since the switching control unit 42 started the detection voltage application control, and the threshold H1. In other words, the detection unit 46 performs a process to detect whether or not there is a magnetic material W that can be held when the permanent electromagnet 10 has the above-described attraction force. This makes the magnetic material W detection process easy to perform.

[0073] The thresholds H2 and H3 are used by the detection unit 46 for detecting the state of the permanent electromagnet 10. The value between the value Inr and the value Inh is determined as threshold H2. The value between the value Imh and the value Imr is determined as threshold H3. The storage unit 32 stores the thresholds H2 and H3 thus determined as thresholds for distinguishing between an unretainable state and a retainable state.

[0074] The detection unit 46 performs detection processing for the magnetic material W and the state detection processing for the permanent electromagnet 10 based on the measured value of the coil current Ic after a predetermined time Tp has elapsed since the switching control unit 42 started the detection voltage application control, and the thresholds H1, H2, and H3. In other words, the detection unit 46 performs detection processing for the magnetic material W and also performs processing to detect whether the state of the permanent electromagnet 10 is the non-holding state or the holding state described above. This makes it possible to easily perform detection processing for the magnetic material W and state detection processing for the permanent electromagnet 10.

[0075] Normally, the state of the permanent electromagnet 10 can be determined from the control history of the permanent electromagnet 10 by the control device 12. However, as described above, since the detection unit 46 can detect the state of the permanent electromagnet 10, even if the control history of the permanent electromagnet 10 by the control device 12 is lost, the state of the permanent electromagnet 10 can be accurately determined.

[0076] Figures 6A and 6B show examples of detection processing by the detection unit 46 of the control device 12. As shown in Figure 6A, if the measured value Mv of the coil current Ic acquired by the measurement value acquisition unit 44 is higher than or equal to the threshold H1, the detection unit 46 determines that there is no magnetic material W that can be held when the permanent electromagnet 10 has an attractive force. If the measured value Mv of the coil current Ic acquired by the measurement value acquisition unit 44 is lower than the threshold H1, the detection unit 46 determines that there is a magnetic material W that can be held when the permanent electromagnet 10 has an attractive force.

[0077] As shown in Figure 6B, if the measured value Mv of the coil current Ic acquired by the measurement value acquisition unit 44 is higher than or equal to the threshold H2, the detection unit 46 determines that the state of the permanent electromagnet 10 is in a state where it cannot be maintained and that there is no magnetic material W. If the measured value Mv of the coil current Ic acquired by the measurement value acquisition unit 44 is lower than the threshold H2 and higher than or equal to the threshold H1, the detection unit 46 determines that the state of the permanent electromagnet 10 is in a state where it can be maintained and that there is no magnetic material W.

[0078] If the measured value Mv of the coil current Ic acquired by the measurement value acquisition unit 44 is higher than or equal to the threshold H3 and lower than the threshold H1, the detection unit 46 determines that the state of the permanent electromagnet 10 is in a state where it can be maintained and that there is a magnetic material W. If the measured value Mv of the coil current Ic acquired by the measurement value acquisition unit 44 is lower than the threshold H3, the detection unit 46 determines that the state of the permanent electromagnet 10 is in a state where it cannot be maintained and that there is a magnetic material W.

[0079] If the detection unit 46 determines that the state of the permanent electromagnet 10 is in a state where it can hold the magnetic material W, then it is considered that the permanent electromagnet 10 is actually holding the magnetic material W due to the attractive force generated on the permanent electromagnet 10. If the detection unit 46 determines that the state of the permanent electromagnet 10 is in a state where it cannot hold the magnetic material W, or that there is no magnetic material W, then it is considered that the permanent electromagnet 10 is not actually holding the magnetic material W.

[0080] Therefore, the detection unit 46 can detect whether or not the magnetic material W is held by the permanent electromagnet 10 based on the measured value Mv of the coil current Ic and the threshold values ​​H1, H2, and H3. This allows for remote detection of whether or not the magnetic material W is held by the permanent electromagnet 10 without relying on visual inspection by workers at the site where the permanent electromagnet 10 and the magnetic material W are located.

[0081] Figure 7 is an example of a time chart illustrating the control of voltage application and voltage application stoppage to the coil 10c of the permanent electromagnet 10. Figure 7 shows an example in which the switches SW1, SW2, SW3, SW4, SWa, and SWb that constitute the voltage application circuit 18 shown in Figure 2 are switched on or off according to time T.

[0082] As each switch is turned on or off, the applied voltage applied to the coil 10c of the permanent electromagnet 10 changes according to time T. The drive control unit 40 of the control device 12 switches switches SW1, SW2, SW3, and SW4 on or off, so that the state of the permanent electromagnet 10 changes according to time T to a state where it can be held or a state where it cannot be held.

[0083] In the example shown in Figure 7, at time T=T0, the permanent electromagnet 10 is in a state where it can be held. That is, the permanent electromagnet 10 is in a state where it possesses attractive force. The magnetization direction of the second permanent magnet 10b is in a second direction, which is the same direction as the magnetization direction of the first permanent magnet 10a. Also, at time T=T0, switches SW1, SW2, SW3, SW4, SWa, and SWb are all turned off. Therefore, the applied voltage applied to the coil 10c of the permanent electromagnet 10 is zero.

[0084] At the time T=T1, the switching control unit 42 of the control device 12 turns on switches SWa and SWb as detection voltage application control. A positive detection voltage Vt (also called detection positive voltage + Vt) is applied to the coil 10c. After a predetermined time Tp has elapsed since the switching control unit 42 started the detection voltage application control at time T=T1, the coil current Ic is measured. After that, the switching control unit 42 switches the detection voltage application control to detection voltage application stop control. As detection voltage application stop control, the switching control unit 42 turns off switches SWa and SWb. The applied voltage applied to the coil 10c of the permanent electromagnet 10 returns to zero.

[0085] At the time T=T2, the drive control unit 40 of the control device 12 turns on switches SW2 and SW3 as drive control, while keeping switches SW1 and SW4 off. As shown in Figure 7, the drive control unit 40 may turn on switch SW2 before time T=T2 and then turn on switch SW3 at time T=T2. At time T=T2, a negative drive voltage Vd (also called negative drive voltage -Vd) is applied to coil 10c.

[0086] The magnetization direction of the second permanent magnet 10b reverses, and it now faces a first direction that is opposite to the magnetization direction of the first permanent magnet 10a. The permanent electromagnet 10 becomes in a state where it does not possess any attractive force. That is, at time T=T2, the state of the permanent electromagnet 10 changes from a state where it can hold to a state where it cannot hold. After that, the drive control unit 40 turns off both switch SW2 and switch SW3.

[0087] Therefore, switches SW1, SW2, SW3, and SW4 are all turned off. The applied voltage applied to the coil 10c of the permanent electromagnet 10 is zero. Since the magnetization direction of the second permanent magnet 10b is maintained in the first direction, the non-holding state in the permanent electromagnet 10 is maintained.

[0088] At the time T=T3, the switching control unit 42 turns on switches SWa and SWb as detection voltage application control. A positive detection voltage Vt (detection positive voltage + Vt) is applied to the coil 10c. After a predetermined time Tp has elapsed since the switching control unit 42 started the detection voltage application control at time T=T3, the coil current Ic is measured. After that, the switching control unit 42 switches the detection voltage application control to detection voltage application stop control. As detection voltage application stop control, the switching control unit 42 turns off switches SWa and SWb. The applied voltage applied to the coil 10c of the permanent electromagnet 10 returns to zero.

[0089] At the time T=T4, the drive control unit 40 turns on switches SW1 and SW4 while keeping switches SW2 and SW3 off as part of the drive control. As shown in Figure 7, the drive control unit 40 may also turn on switch SW4 before time T=T4 and then turn on switch SW1 at time T=T4. At time T=T4, a positive drive voltage Vd (also called positive drive voltage + Vd) is applied to coil 10c.

[0090] The magnetization direction of the second permanent magnet 10b reverses and faces a second direction, which is the same direction as the magnetization direction of the first permanent magnet 10a. The permanent electromagnet 10 becomes capable of attracting. That is, at time T=T4, the state of the permanent electromagnet 10 changes from a non-holding state to a holding state. After that, the drive control unit 40 turns off both switch SW1 and switch SW4.

[0091] Therefore, switches SW1, SW2, SW3, and SW4 are all turned off. The applied voltage applied to the coil 10c of the permanent electromagnet 10 is zero. Since the magnetization direction of the second permanent magnet 10b is maintained in the second direction, the holding state of the permanent electromagnet 10 is maintained.

[0092] At the time T=T5, the switching control unit 42 turns on switches SWa and SWb as detection voltage application control. A positive detection voltage Vt (detection positive voltage + Vt) is applied to the coil 10c. After a predetermined time Tp has elapsed since the switching control unit 42 started the detection voltage application control at time T=T5, the coil current Ic is measured. After that, the switching control unit 42 switches the detection voltage application control to detection voltage application stop control. As detection voltage application stop control, the switching control unit 42 turns off switches SWa and SWb. The applied voltage applied to the coil 10c of the permanent electromagnet 10 returns to zero.

[0093] At the time T=T6, the drive control unit 40 turns on switches SW2 and SW3 as drive control, while keeping switches SW1 and SW4 off. As shown in Figure 7, the drive control unit 40 may turn on switch SW2 before time T=T6 and then turn on switch SW3 at time T=T2. At time T=T6, a negative drive voltage Vd (negative drive voltage -Vd) is applied to coil 10c.

[0094] The magnetization direction of the second permanent magnet 10b reverses, and it now faces a first direction that is opposite to the magnetization direction of the first permanent magnet 10a. The permanent electromagnet 10 becomes in a state where it does not possess any attractive force. That is, at time T=T6, the state of the permanent electromagnet 10 changes from a state where it can hold to a state where it cannot hold. After that, the drive control unit 40 turns off both switch SW2 and switch SW3.

[0095] Therefore, switches SW1, SW2, SW3, and SW4 are all turned off. The applied voltage applied to the coil 10c of the permanent electromagnet 10 is zero. Since the magnetization direction of the second permanent magnet 10b is maintained in the first direction, the non-holding state in the permanent electromagnet 10 is maintained.

[0096] At the time T=T7, the switching control unit 42 of the control device 12 turns on switches SWa and SWb as detection voltage application control. A positive detection voltage Vt (detection positive voltage + Vt) is applied to the coil 10c. After a predetermined time Tp has elapsed since the switching control unit 42 started the detection voltage application control at time T=T7, the coil current Ic is measured. After that, the switching control unit 42 switches the detection voltage application control to detection voltage application stop control. As detection voltage application stop control, the switching control unit 42 turns off switches SWa and SWb. The applied voltage applied to the coil 10c of the permanent electromagnet 10 returns to zero.

[0097] In the example shown in Figure 7, as described above, the coil current Ic is measured after a predetermined time Tp has elapsed since the switching control unit 42 started the detection voltage application control at each of the times T=T1, T=T3, T=T5, and T=T7. The measured coil current Ic is acquired by the measurement value acquisition unit 44 of the control device 12, as described above, and is used for the detection process of the magnetic material W by the detection unit 46 and for the state detection process of the permanent electromagnet 10.

[0098] In the example shown in Figure 7, the detection voltage Vt applied to the coil 10c is always the detection positive voltage + Vt. However, a negative voltage may be applied to the coil 10c each time instead of the detection positive voltage + Vt. Alternatively, a positive voltage and a negative voltage may be applied to the coil 10c alternately. The detection voltage Vt may be either a positive voltage or a negative voltage, as long as the magnetization direction of the second permanent magnet 10b is maintained without reversal.

[0099] Figure 8 is a flowchart illustrating the control procedure for the permanent electromagnet 10. This procedure is performed when an instruction is given to the control device 12 regarding at least one of the following: the detection process for the magnetic material W and the state detection process for the permanent electromagnet 10. This procedure is performed by executing a program stored in the memory unit 32 of the control device 12.

[0100] When this processing procedure is started, in step S1, the switching control unit 42 controls the application of a detection voltage to the coil 10c of the permanent electromagnet 10. A detection voltage Vt is applied to the coil 10c. In step S2, the measurement value acquisition unit 44 acquires a measurement value Mv of the coil current Ic, measured for example using a voltmeter while the detection voltage Vt is applied to the coil 10c.

[0101] In step S3, the detection unit 46 performs a magnetic material W detection process and a permanent electromagnet 10 state detection process based on the measured value Mv obtained in step S2 and the thresholds H1, H2, and H3 stored in the storage unit 32. As part of the magnetic material W detection process, the detection unit 46 performs a process to detect whether or not there is a magnetic material W that can be held when the permanent electromagnet 10 has an attractive force. As part of the permanent electromagnet 10 state detection process, the detection unit 46 performs a process to detect whether the state of the permanent electromagnet 10 is an unholdable state or a holdable state.

[0102] In step S4, the switching control unit 42 controls the stopping of the application of the detection voltage to the coil 10c. Once the process in step S4 is completed, this processing procedure is terminated.

[0103] The embodiments described above may be modified as follows. In the following modifications, explanations that overlap with those in the embodiments will be omitted. Also, in the figures used in the following modifications, components identical to those described in the embodiments will be denoted by the same reference numerals.

[0104] (Modification 1) In the above-described embodiment, the detection unit 46 performs detection processing of the magnetic material W and the state detection processing of the permanent electromagnet 10 based on the measured value Mv of the coil current Ic after a predetermined time Tp has elapsed since the switching control unit 42 started the detection voltage application control, and threshold values ​​H1, H2, and H3. However, other measured values ​​may be used. The measured value of the time required from when the switching control unit 42 starts the detection voltage application control until the coil current Ic reaches a predetermined value may be used.

[0105] In this modified example 1, the measured time Tq, which is the time required from when the switching control unit 42 starts the detection voltage application control until the coil current Ic reaches a predetermined current Ie, is used for the detection process by the detection unit 46.

[0106] Figures 9A and 9B illustrate the change in the coil current Ic flowing through the coil 10c of the permanent electromagnet 10 with respect to time T. Graph Im shows the change in the coil current Ic with respect to time T when there is a magnetic material W that can be held when the permanent electromagnet 10 has an attractive force. Graph In shows the change in the coil current Ic with respect to time T when there is no magnetic material W that can be held when the permanent electromagnet 10 has an attractive force.

[0107] Figure 9A, like Figure 4A, shows graph Im for the case where the magnetic material W is present and graph In for the case where the magnetic material W is absent, in a state where the permanent electromagnet 10 does not possess attractive force and is unable to hold the magnetic material W. At time Tsr, the switching control unit 42 starts the detection voltage application control, and the detection voltage Vt is applied to the coil 10c of the permanent electromagnet 10. As the detection voltage Vt is applied to the coil 10c, the coil current Ic starts to rise, as shown in both graph Im and graph In. The coil current Ic goes through a transient state of gradually rising and then reaches a constant current Ip corresponding to the detection voltage Vt.

[0108] The rate of increase of the coil current Ic in the transient state is greater in graph In (when there is no magnetic material W) than in graph Im (when there is a magnetic material W). In the example shown in Figure 9A, the time required from when the switching control unit 42 starts the detection voltage application control at time Tsr until the coil current Ic reaches a predetermined current Ie is different in graph In and graph Im.

[0109] When there is no magnetic material W, as shown in graph In, the coil current Ic reaches a predetermined current Ie at time Twrn. At time Twrn, after the required time Tnr has elapsed from time Tsr, when the detection voltage application control is started, the coil current Ic reaches a predetermined current Ie. When there is a magnetic material W, as shown in graph Im, the coil current Ic reaches a predetermined current Ie at time Twrm. At time Twrm, after the required time Tmr has elapsed from time Tsr, when the detection voltage application control is started, the coil current Ic reaches a predetermined current Ie. The required time Tnr when there is no magnetic material W is shorter than the required time Tmr when there is a magnetic material W.

[0110] The predetermined current Ie is predetermined such that, for example, the required time Tnr or Tmr is near the time constant τ obtained based on the inductance and resistance values ​​of the coil 10c. This makes it possible to increase the difference between the required time Tnr and Tmr from zero until the coil current Ic reaches the predetermined current Ie, as shown in Figure 9A. Alternatively, the predetermined current Ie may be determined such that the required time Tnh or Tmh, as described later using Figure 9B, is near the time constant τ obtained based on the inductance and resistance values ​​of the coil 10c.

[0111] The measurement value acquisition unit 44 acquires the coil current Ic measured when a detection voltage Vt is applied to the coil 10c by detection voltage application control. When a magnetic material W is present, the measurement value acquisition unit 44 acquires a measured value of the required time Tmr by measuring the time it takes for the coil current Ic to go from zero to a predetermined current Ie. When there is no magnetic material W, the measurement value acquisition unit 44 acquires a measured value of the required time Tnr by measuring the time it takes for the coil current Ic to go from zero to a predetermined current Ie.

[0112] Figure 9B, like Figure 4B, shows graph Im when the magnetic material W is present and graph In when the magnetic material W is absent, in a state where the permanent electromagnet 10 has an attractive force and can hold the magnetic material W by that attractive force. At time Tsh, the switching control unit 42 starts the detection voltage application control, and the detection voltage Vt is applied to the coil 10c of the permanent electromagnet 10. As the detection voltage Vt is applied to the coil 10c, the coil current Ic starts to rise, as shown in both graph Im and graph In. The coil current Ic goes through a transient state of gradually rising and then reaches a constant current Ip corresponding to the detection voltage Vt.

[0113] The rate of increase of the coil current Ic in the transient state is greater in graph In (when there is no magnetic material W) than in graph Im (when there is a magnetic material W). In the example shown in Figure 9B, the time required from when the switching control unit 42 starts the detection voltage application control at time Tsh until the coil current Ic reaches a predetermined current Ie is different in graph In and graph Im.

[0114] When there is no magnetic material W, as shown in graph In, the coil current Ic reaches a predetermined current Ie at time Twhn. At time Twhn, after the required time Tnh has elapsed from time Tsh, when the detection voltage application control is started, the coil current Ic reaches a predetermined current Ie. When there is a magnetic material W, as shown in graph Im, the coil current Ic reaches a predetermined current Ie at time Twhm. At time Twhm, after the required time Tmh has elapsed from time Tsh, when the detection voltage application control is started, the coil current Ic reaches a predetermined current Ie. The required time Tnh when there is no magnetic material W is shorter than the required time Tmh when there is a magnetic material W.

[0115] As described above, the predetermined current Ie is predetermined such that the required times Tnr, Tmr, Tnh, or Tmh are near the time constant τ obtained based on the inductance and resistance values ​​of the coil 10c. This makes it possible to increase the difference between the required times Tnr and Tmr from zero until the coil current Ic reaches the predetermined current Ie, as shown in Figure 9B.

[0116] The measurement value acquisition unit 44 acquires the coil current Ic measured when a detection voltage Vt is applied to the coil 10c by detection voltage application control. When a magnetic material W is present, the measurement value acquisition unit 44 acquires a measured value of the required time Tmh by measuring the time it takes for the coil current Ic to go from zero to a predetermined current Ie. When there is no magnetic material W, the measurement value acquisition unit 44 acquires a measured value of the required time Tnh by measuring the time it takes for the coil current Ic to go from zero to a predetermined current Ie.

[0117] In this way, the measured time Tnr when the permanent electromagnet 10 is unable to hold and there is no magnetic material W, the measured time Tmr when the permanent electromagnet 10 is unable to hold and there is a magnetic material W, the measured time Tnh when the permanent electromagnet 10 can hold and there is no magnetic material W, and the measured time Tmh when the permanent electromagnet 10 can hold and there is a magnetic material W are obtained.

[0118] By performing multiple measurements, the average values ​​of the measured required times Tnr, Tmr, Tnh, and Tmh may be obtained. Using these four previously obtained required time measurements, threshold values ​​H1, H2, and H3 used in the detection process by the detection unit 46 are determined, similar to the embodiment described above.

[0119] The threshold H1 is used in the detection process of the magnetic material W by the detection unit 46. The value between the required time Tnr and the required time Tmr is determined as the threshold H1. More preferably, the value between the required time Tnh and the required time Tmh is determined as the threshold H1. The storage unit 32 stores the threshold H1 thus determined as a threshold for distinguishing between a state in which there is a magnetic material W that can be held when the permanent electromagnet 10 has an attractive force, and a state in which there is no such magnetic material W.

[0120] The measurement value acquisition unit 44 acquires a measurement of the time Tq required from the time the switching control unit 42 starts the detection voltage application control until the coil current Ic reaches a predetermined current Ie. The detection unit 46 performs the above-described magnetic material W detection process based on the measurement value Tq acquired by the measurement value acquisition unit 44 and the threshold H1. That is, the detection unit 46 performs a process to detect whether or not there is a magnetic material W that can be held when the permanent electromagnet 10 has the above-described attraction force. This makes the magnetic material W detection process easy to perform.

[0121] The thresholds H2 and H3 are used by the detection unit 46 for detecting the state of the permanent electromagnet 10. The value between the required time Tnr and the required time Tnh is determined as threshold H2. The value between the required time Tmh and the required time Tmr is determined as threshold H3. The storage unit 32 stores the thresholds H2 and H3 thus determined as thresholds for distinguishing between an unretainable state and a retainable state.

[0122] The measurement value acquisition unit 44 acquires a measurement of the time Tq required from the time the switching control unit 42 starts the detection voltage application control until the coil current Ic reaches a predetermined current Ie. The detection unit 46 performs detection processing of the magnetic material W and the state detection processing of the permanent electromagnet 10 described above, based on the measurement value Tq obtained by the measurement value acquisition unit 44 and the thresholds H1, H2, and H3.

[0123] In other words, the detection unit 46 performs detection processing for the magnetic material W and also performs processing to detect whether the state of the permanent electromagnet 10 is the aforementioned non-holding state or the holding state. This makes it possible to easily perform the detection processing for the magnetic material W and the state detection processing for the permanent electromagnet 10.

[0124] (Modification 2) In Modification 1 described above, the detection process by the detection unit 46 uses the measured time Tq from the time the switching control unit 42 starts applying the detection voltage until the coil current Ic of the coil 10c reaches a predetermined current Ie. The predetermined current Ie is determined based on the time constant τ obtained from the inductance value and resistance value of the coil 10c, as described above. However, the predetermined current Ie may also be determined by multiplying the actual value Ia reached by the coil current Ic in response to the detection voltage application control by a predetermined ratio.

[0125] Figure 10 shows an example of determining a predetermined current Ie. Figure 10 shows graph Im when the permanent electromagnet 10 is in a state where it can be maintained and there is a magnetic material W, and graph In when there is no magnetic material W. As described above, when the permanent electromagnet 10 is in a state where it can be maintained, the permanent electromagnet 10 has an attractive force, and the magnetic material W can be held by this attractive force. Figure 10 shows an example in which the switching control unit 42 of the control device 12 performs detection voltage application control and detection voltage application stop control to the coil 10c of the permanent electromagnet 10 twice.

[0126] First, at time T = Ta, the first detection voltage application control is initiated. As a result, the coil current Ic begins to rise, as shown in both graph Im and graph In. The coil current Ic goes through a transient state of gradually increasing, and then reaches a constant current Ip corresponding to the detection voltage Vt.

[0127] The predetermined current Ie described above is determined by multiplying the actual value Ia reached by the coil current Ic in response to the first detection voltage application control by a predetermined ratio. The actual value Ia of the coil current Ic used to determine the predetermined current Ie corresponds to the values ​​on graphs Im and In based on the first detection voltage application control.

[0128] In this modified example 2, the constant current Ip reached by the coil current Ic in response to the first detection voltage application control is used as the actual value Ia. The constant current Ip of the coil current Ic is acquired by the measurement value acquisition unit 44. A predetermined current Ie is determined by multiplying the constant current Ip, which is the actual value Ia, by a predetermined ratio. Because the actual value Ia is used, the detection process of the magnetic material W and the state detection process of the permanent electromagnet 10 can be performed more accurately. Thereafter, at time T = Tb, the first detection voltage application stop control is started. As a result, the coil current Ic decreases and returns to zero, as shown in both graph Im and graph In.

[0129] Subsequently, at time Tsh, the second detection voltage application control is initiated. As a result, the coil current Ic begins to rise again, as shown in both graph Im and graph In. If there is no magnetic material W, as shown in graph In, the coil current Ic reaches a predetermined current Ie at time Twhn, after the required time Tnh has elapsed from time Tsh. If there is a magnetic material W, as shown in graph Im, the coil current Ic reaches a predetermined current Ie at time Twhm, after the required time Tmh has elapsed from time Tsh.

[0130] The measurement value of the required time Thnh or the required time Tmh is acquired by the measurement value acquisition unit 44. Similarly, even when the state of the permanent electromagnet 10 is in a state where it cannot be maintained, the measurement value of the required time Tnr or the required time Tmr is acquired by the measurement value acquisition unit 44. The detection unit 46 performs detection processing based on the acquired measurement values ​​of the required time Thnh, required time Tmh, required time Tnr or required time Tmr and threshold values ​​H1, H2, and H3. The detection processing by the detection unit 46 is, as described above, a detection process for the magnetic material W and a state detection process for the permanent electromagnet 10.

[0131] As described in the explanation of Modification 1, the thresholds H1, H2, and H3 used in the detection process by the detection unit 46 are determined using the four previously obtained measured values ​​of the required time and are stored in the storage unit 32. In this Modification 2, the predetermined current Ie can take on various values. Therefore, it is preferable that the storage unit 32 stores thresholds H1, H2, and H3 corresponding to the various values ​​that the predetermined current Ie can take.

[0132] Figure 11 shows an example configuration of the control device 12. Compared to Figure 3, Figure 11 differs in that the arithmetic unit 30 of the control device 12 further includes a decision unit 48. The decision unit 48 is realized by the arithmetic unit 30 executing a program stored in the storage unit 32. The decision unit 48 may be realized by an integrated circuit such as an ASIC or FPGA, or by an electronic circuit including discrete devices.

[0133] The measurement value acquisition unit 44 acquires the coil current Ic generated in the coil 10c of the permanent electromagnet 10 in response to the detection voltage application control to the coil 10c. The determination unit 48 then determines a predetermined value to which the coil current Ic will reach in response to the detection voltage application control that is performed again thereafter. The determination unit 48 determines this predetermined value by multiplying the actual value Ia to which the coil current Ic acquired by the measurement value acquisition unit 44 reaches by a predetermined ratio. The measurement value acquisition unit 44 acquires a measurement of the time required from the start of the detection voltage application control by the switching control unit 42 until the coil current Ic reaches the predetermined value.

[0134] In this modified example 2, as explained with reference to Figure 10, the measurement value acquisition unit 44 acquires the measured values ​​of the time Tnh, Tmh, Tnr, or Tmr required from the time the switching control unit 42 starts the detection voltage application control until the coil current Ic reaches a predetermined current Ie. The detection unit 46 performs detection processing of the magnetic material W and the state detection processing of the permanent electromagnet 10 based on the measured values ​​of the time Tnh, Tmh, Tnr, or Tmr acquired by the measurement value acquisition unit 44 and the threshold values ​​H1, H2, and H3 described above.

[0135] The detection unit 46 performs a process to detect whether or not there is a magnetic material W that can be held when the permanent electromagnet 10 has an attractive force, as part of the magnetic material detection process for the magnetic material W. The detection unit 46 also performs a process to detect whether the state of the permanent electromagnet 10 is an unholdable state or a holdable state.

[0136] (Modification 3) In the above-described embodiment, the detection power supply 16 is a DC power supply. However, the detection power supply 16 may be an AC power supply. In this modification 3, the detection voltage Vt supplied to the coil 10c of the permanent electromagnet 10 by the detection power supply 16 changes sinusoidally. In that case, the coil current Ic generated in the coil 10c also changes sinusoidally. A phase difference Pd occurs between the detection voltage Vt and the coil current Ic. When the detection voltage Vt changes sinusoidally, the measured values ​​used in the detection process by the detection unit 46 are the phase difference Pd between the detection voltage Vt and the coil current Ic, and the amplitude Ac of the coil current Ic.

[0137] Figure 12 is a diagram illustrating the phase difference Pd between the detection voltage Vt and the coil current Ic. The phase difference Pd between the detection voltage Vt and the coil current Ic, and the amplitude Ac of the coil current Ic, may change depending on whether or not there is a magnetic material W, and whether the permanent electromagnet 10 is in a non-holding state or a holding state.

[0138] When magnetic material W is present, the phase difference Pd is larger and the amplitude Ac is smaller compared to when magnetic material W is absent. As the number of superimposed magnetic materials W increases, the phase difference Pd becomes larger and the amplitude Ac becomes smaller. When the permanent electromagnet 10 is in a holding state, the phase difference Pd is larger and the amplitude Ac is smaller compared to when the permanent electromagnet 10 is in a non-holding state.

[0139] The measurement value acquisition unit 44 acquires a measured value Mv of the coil current Ic generated in the coil 10c of the permanent electromagnet 10 in response to the control of applying a detection voltage to the coil 10c, and also acquires a measured value Pd of the phase difference between the detection voltage Vt and the coil current Ic. The measured value Mv of the coil current Ic includes a measured value of the amplitude Ac.

[0140] Depending on whether or not there is a magnetic material W that the permanent electromagnet 10 can hold, and whether the state of the permanent electromagnet 10 is either a non-holding state or a holding state, the combination of the measured amplitude Ac of the coil current Ic and the measured phase difference Pd changes. Based on these changes in the combination of measured values, thresholds H1, H2, and H3 used in the detection process by the detection unit 46 are predetermined and stored in the storage unit 32.

[0141] The detection unit 46 performs detection processing for the magnetic material W and state detection processing for the permanent electromagnet 10 based on the measured values ​​measured by the measurement value acquisition unit 44 and the threshold values ​​H1, H2, and H3 stored by the storage unit 32. As part of the detection processing for the magnetic material W, the detection unit 46 performs processing to detect whether or not there is a magnetic material W that can be held when the permanent electromagnet 10 has an attractive force. As part of the state detection processing for the permanent electromagnet 10, the detection unit 46 performs processing to detect whether the state of the permanent electromagnet 10 is an unholdable state or a holdable state. This makes it possible to easily perform the detection processing for the magnetic material W and the state detection processing for the permanent electromagnet 10.

[0142] Furthermore, if the phase difference Pd between the detection voltage Vt and the coil current Ic, and the amplitude Ac of the coil current Ic, change, the inductance value of the coil 10c also changes. Therefore, in addition to the measured values ​​of the phase difference Pd and amplitude Ac, the inductance value of the coil 10c that can be calculated from these measured values ​​can also be used to perform the detection process for the magnetic material W and the state detection process for the permanent electromagnet 10.

[0143] (Modification 4) In the embodiment described above, the detection unit 46 of the control device 12 performs a process to detect whether or not there is a magnetic material W that can be held when the permanent electromagnet 10 has an attractive force. However, the detection unit 46 may also detect the number of superpositions of magnetic material W that can be held when the permanent electromagnet 10 has an attractive force. In this modification 4, if there is no magnetic material W, zero is detected as the number of superpositions. If there is a magnetic material W that can be held when the permanent electromagnet 10 has an attractive force, a value of 1 or more is detected as the number of superpositions of magnetic material W. When the state of the permanent electromagnet 10 is in a holdable state, the number of superpositions detected by the detection unit 46 indicates the number of superpositions of magnetic material W actually held by the permanent electromagnet 10.

[0144] Figures 13A and 13B show examples of detection processing by the detection unit 46 of the control device 12. As shown in Figure 13A, if the measured value Mv of the coil current Ic acquired by the measurement value acquisition unit 44 is higher than or equal to the threshold H1, the detection unit 46 detects zero as the number of superpositions of magnetic material W that can be held when the permanent electromagnet 10 has an attractive force. In other words, it is determined that there is no magnetic material W.

[0145] If the measured value Mv of the coil current Ic acquired by the measurement value acquisition unit 44 is lower than threshold H1 and higher than or equal to threshold H4, the detection unit 46 detects 1 as the number of superpositions of magnetic material W that can be held when the permanent electromagnet 10 has an attractive force. In other words, it is determined that there is one magnetic material W.

[0146] If the measured value Mv of the coil current Ic acquired by the measurement value acquisition unit 44 is lower than the threshold H4 and higher than or equal to the threshold H6, the detection unit 46 detects 2 as the number of superpositions of magnetic material W that the permanent electromagnet 10 can hold when it has an attractive force. In other words, it is determined that there are two magnetic material W. In this way, the number of superpositions of magnetic material W can be easily detected.

[0147] The thresholds H1, H4, and H6 used in the detection process by the detection unit 46 are predetermined according to the number of superpositions of the magnetic material W, similar to threshold H1 in the embodiment described above, and are stored in the storage unit 32. By pre-determining thresholds even smaller than threshold H6, it becomes possible to detect the number of superpositions of the magnetic material W even when the number of superpositions is 3 or more.

[0148] As shown in Figure 13B, if the measured value Mv of the coil current Ic acquired by the measurement value acquisition unit 44 is higher than or equal to the threshold H2, the detection unit 46 detects that the state of the permanent electromagnet 10 is in a state where it cannot be maintained, and also detects zero as the superposition number of the magnetic material W. In other words, it is determined that there is no magnetic material W. If the measured value Mv of the coil current Ic acquired by the measurement value acquisition unit 44 is lower than the threshold H2 and higher than or equal to the threshold H1, the detection unit 46 detects that the state of the permanent electromagnet 10 is in a state where it can be maintained, and also detects zero as the superposition number of the magnetic material W. In other words, it is determined that there is no magnetic material W.

[0149] If the measured value Mv of the coil current Ic acquired by the measurement value acquisition unit 44 is lower than the threshold H1 and higher than or equal to the threshold H3, the detection unit 46 detects that the state of the permanent electromagnet 10 is in a state where it can be maintained, and also detects 1 as the number of superpositions of magnetic material W that can be maintained when the permanent electromagnet 10 has an attractive force. In other words, it is determined that there is one magnetic material W.

[0150] If the measured value Mv of the coil current Ic acquired by the measurement value acquisition unit 44 is lower than threshold H3 and higher than or equal to threshold H4, the detection unit 46 detects that the state of the permanent electromagnet 10 is in a state where it cannot be held, and also detects 1 as the magnetic material W that can be held if the permanent electromagnet 10 has an attractive force. In other words, it is determined that there is one magnetic material W.

[0151] If the measured value Mv of the coil current Ic acquired by the measurement value acquisition unit 44 is lower than the threshold H4 and higher than or equal to the threshold H5, the detection unit 46 detects that the state of the permanent electromagnet 10 is in a state where it can be held, and also detects 2 as the magnetic material W that can be held when the permanent electromagnet 10 has an attractive force. In other words, it is determined that there are two magnetic materials W.

[0152] If the measured value Mv of the coil current Ic acquired by the measurement value acquisition unit 44 is lower than the threshold H5 and higher than or equal to the threshold H6, the detection unit 46 detects that the state of the permanent electromagnet 10 is in a state where it cannot maintain its position, and also detects 2 as the magnetic material W that can be held if the permanent electromagnet 10 has an attractive force. In other words, it is determined that there are two magnetic materials W. In this way, the number of superimposed magnetic materials W can be easily detected, and the state detection process of the permanent electromagnet 10 can be easily performed.

[0153] The threshold values ​​H1, H2, H3, H4, H5, and H6 used in the detection process by the detection unit 46 are predetermined according to the number of superpositions of magnetic material W, similar to the threshold values ​​H1, H2, and H3 in the above-described embodiment, and are stored in the storage unit 32. By pre-determining threshold values ​​even smaller than threshold value H6, it becomes possible to detect the number of superpositions of magnetic material W and the state of the permanent electromagnet 10 even when the number of superpositions of magnetic material W is 3 or more.

[0154] (Modification 5) In the embodiment described above, the drive power supply 14 that supplies the drive voltage Vd to the coil 10c of the permanent electromagnet 10 and the detection power supply 16 that supplies the detection voltage Vt to the coil 10c are different power supplies. However, the drive power supply 14 and the detection power supply 16 may be the same power supply. This makes it possible to minimize the number of power supplies that supply the voltage applied to the coil 10c. In this modification 5, a common power supply 60 capable of changing the voltage applied to the coil 10c is used as the drive power supply 14 and the detection power supply 16.

[0155] Figure 14 shows an example of the configuration of a voltage application circuit 18. The voltage application circuit 18 is used to apply a drive voltage Vd supplied from a drive power supply 14 and a detection voltage Vt supplied from a detection power supply 16 to the coil 10c of the permanent electromagnet 10. In the example shown in Figure 14, a common power supply 60 is used as the drive power supply 14 and the detection power supply 16. The voltage application circuit 18 shown in Figure 14 has switches SW1, SW2, SW3, and SW4, similar to Figure 2, but unlike Figure 2, it does not have switches SWa and SWb.

[0156] The voltage supplied to the coil 10c by the common power supply 60 is variable. For example, when a driving voltage Vd is applied to the coil 10c, the drive control unit 40 switches the switches SW1, SW2, SW3, and SW4 on and off using PWM (Pulse Width Modulation) based on a first duty cycle R1. When a detection voltage Vt is applied to the coil 10c, the switching control unit 42 switches the switches SW1, SW2, SW3, and SW4 on and off using PWM based on a second duty cycle R2 which is smaller than the first duty cycle R1. As a result, the voltage applied to the coil 10c from the common power supply 60 can be set to either the driving voltage Vd or the detection voltage Vt.

[0157] Figure 15 is an example of a time chart illustrating the control of voltage application and voltage application stoppage to the coil 10c of the permanent electromagnet 10. Figure 15 shows an example in which the switches SW1, SW2, SW3, and SW4 that constitute the voltage application circuit 18 shown in Figure 14 are switched on or off according to time T.

[0158] In the example shown in Figure 15, at time T=T50, the permanent electromagnet 10 is in a state where it cannot maintain its position. That is, the permanent electromagnet 10 does not possess any attractive force. The magnetization direction of the second permanent magnet 10b is in the first direction, which is opposite to the magnetization direction of the first permanent magnet 10a. Also, at time T=T50, switches SW1, SW2, SW3, and SW4 are all turned off. Therefore, the applied voltage applied to the coil 10c of the permanent electromagnet 10 is zero.

[0159] At the time T=T51, the switching control unit 42 of the control device 12 turns on switches SW2 and SW3 as detection voltage application control. Switch SW3 is switched on / off with a second duty cycle R2. As a result, a detection voltage Vt (also called detection negative voltage -Vt) of a negative voltage is applied to the coil 10c. The coil current Ic is measured after a predetermined time Tp has elapsed since the switching control unit 42 started the detection voltage application control at time T=T51.

[0160] Subsequently, the switching control unit 42 switches the detection voltage application control to the detection voltage application stop control. As part of the detection voltage application stop control, the switching control unit 42 turns off switches SW2 and SW3. The applied voltage applied to the coil 10c of the permanent electromagnet 10 returns to zero.

[0161] At the time T=T52, the drive control unit 40 of the control device 12 turns on switches SW1 and SW4 as drive control, while keeping switches SW2 and SW3 off. As shown in Figure 15, the drive control unit 40 may turn on switch SW4 before time T=T52 and then turn on switch SW1 at time T=T52. Switch SW1 is switched on / off with a first duty cycle R1. That is, at time T=T52, a positive drive voltage Vd (positive drive voltage + Vd) is applied to coil 10c.

[0162] The magnetization direction of the second permanent magnet 10b reverses and faces a second direction, which is the same direction as the magnetization direction of the first permanent magnet 10a. The permanent electromagnet 10 becomes capable of attracting. That is, at time T=T52, the state of the permanent electromagnet 10 changes from a non-holding state to a holdable state. After that, the drive control unit 40 turns off the switch SW1. The applied voltage applied to the coil 10c of the permanent electromagnet 10 is zero. Since the magnetization direction of the second permanent magnet 10b is maintained in the second direction, the holdable state of the permanent electromagnet 10 is maintained.

[0163] At the time T=T53, the switching control unit 42 turns on switches SW1 and SW4 as detection voltage application control. Switch SW1 is switched on / off with a second duty cycle R2. As a result, a positive detection voltage Vt (detection positive voltage + Vt) is applied to the coil 10c. The coil current Ic is measured after a predetermined time Tp has elapsed since the switching control unit 42 started the detection voltage application control at time T=T53.

[0164] Subsequently, the switching control unit 42 switches the detection voltage application control to the detection voltage application stop control. As part of the detection voltage application stop control, the switching control unit 42 turns off switches SW1 and SW4. The applied voltage applied to the coil 10c of the permanent electromagnet 10 returns to zero.

[0165] At the time T=T54, the drive control unit 40, as part of the drive control, turns on switches SW2 and SW3 while keeping switches SW1 and SW4 off. As shown in Figure 15, the drive control unit 40 may also turn on switch SW2 before time T=T54 and then turn on switch SW3 at time T=T54. Switch SW3 is switched on / off with a first duty cycle R1. That is, at time T=T54, a negative drive voltage Vd (negative drive voltage -Vd) is applied to coil 10c.

[0166] The magnetization direction of the second permanent magnet 10b reverses and faces a first direction, which is opposite to the magnetization direction of the first permanent magnet 10a. The permanent electromagnet 10 becomes in a state where it does not possess any attractive force. That is, at time T=T54, the state of the permanent electromagnet 10 changes from a state where it can hold to a state where it cannot hold. After that, the drive control unit 40 turns off the switch SW3. The applied voltage applied to the coil 10c of the permanent electromagnet 10 is zero. Since the magnetization direction of the second permanent magnet 10b remains facing the first direction, the non-holding state of the permanent electromagnet 10 is maintained.

[0167] At the time T=T55, the switching control unit 42 turns on switches SW2 and SW3 as detection voltage application control. Switch SW3 is switched on / off with a second duty cycle R2. As a result, a detection voltage Vt (detection negative voltage - Vt) of a negative voltage is applied to the coil 10c. The coil current Ic is measured after a predetermined time Tp has elapsed since the switching control unit 42 started the detection voltage application control at time T=T55.

[0168] The detection voltage application control performed at time T=T55 and the subsequent detection voltage application stop control are the same as the detection voltage application control performed at time T=T51 and the subsequent detection voltage application stop control described above.

[0169] In the example shown in Figure 15, as described above, the coil current Ic is measured after a predetermined time Tp has elapsed since the switching control unit 42 started the detection voltage application control at each of the times T=T51, T=T53, and T=T55. The measured coil current Ic is acquired by the measurement value acquisition unit 44 of the control device 12, as described above, and is used for the detection process of the magnetic material W by the detection unit 46 and for the state detection process of the permanent electromagnet 10.

[0170] (Modification 6) In the embodiment described above, the permanent electromagnet 10 controlled by the control device 12 is capable of holding the magnetic material W. However, the control device 12 may be a sensor 70 that controls a permanent electromagnet 10A that is different from the permanent electromagnet 10 capable of holding the magnetic material W. Figure 16 shows an example of the configuration of the sensor 70.

[0171] In this modified example 6, the permanent electromagnet 10A controlled by the sensor 70 is not used for the purpose of holding the magnetic material W. The permanent electromagnet 10A is used for the detection process of the magnetic material W by the sensor 70. The control device 12 controls the permanent electromagnet 10A by operating the voltage application circuit 18A. The voltage application circuit 18A is used to apply the detection voltage Vt supplied from the detection power supply 16 to the coil 10c of the permanent electromagnet 10.

[0172] The sensor 70 according to this modified example 6 has the same configuration as the control device 12 according to the embodiment described above. However, since the permanent electromagnet 10A for the sensor does not hold the magnetic material W, as shown in Figure 16, the calculation unit 30 of the sensor 70 does not have a drive control unit 40, unlike the control device 12 shown in Figure 3. The calculation unit 30 of the sensor 70 also has an output unit 80. The output unit 80 is realized by the calculation unit 30 executing a program stored in the storage unit 32. The output unit 80 may be realized by an integrated circuit such as an ASIC or FPGA, or by an electronic circuit including discrete devices.

[0173] The output unit 80 outputs the detection result related to the detection process of the magnetic material W by the detection unit 46 to the outside. The output unit 80 outputs the detection result to, for example, the display device 90 via communication. This makes it possible to realize a user-friendly sensor 70.

[0174] As described above, the sensor 70 in this modified example 6 controls a permanent electromagnet 10A that is separate from the permanent electromagnet 10 capable of holding the magnetic material W, and performs detection processing for the magnetic material W. The sensor 70 can be used, for example, to detect a magnetic material W held by a permanent electromagnet 10 of a magnetic gripper. However, the sensor 70 may also control a permanent electromagnet 10A of a device other than the magnetic gripper.

[0175] For example, the sensor 70 may control a permanent electromagnet 10A located inside the cylinder. When the piston, which is a magnetic material W, reaches the end of its stroke, the permanent electromagnet 10A locks the piston with an attractive force based on its magnetic force. The sensor 70 can detect that the piston is locked.

[0176] For example, the sensor 70 may control the permanent electromagnet 10A provided in the jig. When a workpiece, which is a magnetic material W, is fixed to the jig, the permanent electromagnet 10A locks the workpiece in place with an attractive force based on its magnetic field. The sensor 70 can detect that the workpiece is locked.

[0177] For example, the sensor 70 may control the permanent electromagnet 10A provided in the compliance unit. When the misalignment of a component that is a magnetic material W is adjusted, the permanent electromagnet 10A locks the component in place with an attractive force based on its magnetic force. The sensor 70 can detect that the component is locked.

[0178] For example, the sensor 70 may control the permanent electromagnet 10A provided in the coupling mechanism. Since the permanent electromagnet 10A can connect the objects to be coupled, which are magnetic materials W, by the attractive force based on its magnetic force, there is no need to provide a coupling structure on the objects to be coupled. The sensor 70 can detect that the objects to be coupled have been connected.

[0179] (Modification 7) In the embodiment described above, the first permanent magnet 10a and the second permanent magnet 10b are arranged adjacent to each other. However, the first permanent magnet 10a and the second permanent magnet 10b do not have to be arranged adjacent to each other. For example, the first permanent magnet 10a and the second permanent magnet 10b may be arranged in the permanent electromagnet 10 such that the magnetization direction of the first permanent magnet 10a intersects with the magnetization direction of the second permanent magnet 10b.

[0180] Figure 17A shows a permanent electromagnet 10. The permanent electromagnet 10 has a first permanent magnet 10a, a second permanent magnet 10b, and a coil 10c. The permanent electromagnet 10 further has a yoke. Figure 17A shows the top yoke 10y, which covers the second permanent magnet 10b. The permanent electromagnet 10, which has an attractive force, can hold a magnetic material W via the top yoke 10y.

[0181] In this modified example 7, the first permanent magnet 10a is positioned between two top yokes 10y. The magnetization direction of the first permanent magnet 10a is aligned horizontally in Figure 17A, and therefore intersects with the magnetization direction of the second permanent magnet 10b, which is aligned vertically. The coil 10c is wound around the outer circumference of the second permanent magnet 10b, as shown in Figure 17A. When a driving voltage Vd supplied from the driving power supply 14 is applied to the coil 10c and a current flows, the magnetization direction of the second permanent magnet 10b can be reversed.

[0182] Figures 17B and 17C schematically show the magnetic flux B corresponding to the magnetic force generated by the permanent electromagnet 10. In Figure 17B, of the two second permanent magnets 10b, the magnetization direction of one second permanent magnet 10ba is the first direction. The magnetization direction of the other second permanent magnet 10bb is the second direction, opposite to the first direction. The magnetization direction of the first permanent magnet 10a is the third direction, which intersects both the first and second directions.

[0183] The magnetic flux B emanating from one of the second permanent magnets 10ba passes through the top yoke 10y and enters the first permanent magnet 10a. The magnetic flux B emanating from the first permanent magnet 10a enters the other second permanent magnet 10bb. The magnetic flux B emanating from the other second permanent magnet 10bb passes through a bottom yoke (not shown) and enters the first second permanent magnet 10ba. In other words, the magnetic flux B is confined within the permanent electromagnet 10.

[0184] In that case, the magnetic flux B does not pass through the magnetic material W. Thus, when the magnetic circuit formed by the magnetic flux B is closed and formed between the first permanent magnet 10a and the two second permanent magnets 10b, the permanent electromagnet 10 does not possess any attractive force. Therefore, the permanent electromagnet 10 does not hold the magnetic material W. The permanent electromagnet 10 is in a state where it cannot hold the magnetic material W.

[0185] When a driving voltage Vd is applied to the coil 10c and current flows through the coil 10c, the magnetization directions of the two second permanent magnets 10b shown in Figure 17B can be reversed. In Figure 17C, the magnetization direction of one of the second permanent magnets 10ba is a second direction, opposite to the first direction. The magnetization direction of the other second permanent magnet 10bb is a first direction, opposite to the second direction.

[0186] The magnetic flux B emanating from the first permanent magnet 10a passes through the top yoke 10y and returns to the first permanent magnet 10a without entering either of the two second permanent magnets 10b. The magnetic flux B emanating from one of the second permanent magnets 10ba passes through a bottom yoke (not shown) and enters the other second permanent magnet 10bb. The magnetic flux B emanating from the other second permanent magnet 10bb passes through the top yoke 10y and enters the other second permanent magnet 10ba without entering the first permanent magnet 10a. None of the magnetic flux B is confined within the permanent electromagnet 10, and all pass outside of the permanent electromagnet 10.

[0187] When the permanent electromagnet 10 approaches or is in contact with the magnetic material W, the magnetic flux B passes through the magnetic material W. In this way, when the magnetic circuit formed by the magnetic flux B is formed independently of each other by the first permanent magnet 10a and the two second permanent magnets 10b, the permanent electromagnet 10 possesses an attractive force. When the magnetic material W is within the range of the magnetic force of the permanent electromagnet 10, which possesses an attractive force, the permanent electromagnet 10 holds the magnetic material W. The permanent electromagnet 10 is in a holding state in which it can hold the magnetic material W due to this attractive force.

[0188] When the driving voltage Vd is applied to the coil 10c, currents flow in opposite directions through the coil 10c, the magnetization direction of the second permanent magnet 10b shown in Figure 17C can be reversed. That is, it can be returned to the magnetization direction of the second permanent magnet 10b shown in Figure 17B. In that case, as described above, the magnetic flux B does not pass through the magnetic material W. Therefore, the permanent electromagnet 10 does not possess an attractive force, and the magnetic material W detaches from the permanent electromagnet 10. That is, the permanent electromagnet 10 does not hold the magnetic material W. The state of the permanent electromagnet 10 returns to the state of non-retention described above.

[0189] The above-mentioned variations 1 to 7 may be combined as appropriate, within the bounds of consistency.

[0190] With regard to the embodiments described above, the following additional information is disclosed.

[0191] (Note 1) The control device (12) of the present disclosure is a control device for a permanent electromagnet (10) comprising a first permanent magnet (10a) and a second permanent magnet (10b), and a coil (10c) wound at least around the outer circumference of the second permanent magnet, wherein when a driving voltage (Vd) is applied to the coil, the magnetization direction of the second permanent magnet is reversed, and the magnetization direction of the second permanent magnet is maintained from the time the application of the driving voltage to the coil is stopped until the driving voltage is applied to the coil again, The system includes a switching control unit (42) that switches between a detection voltage application control, in which a detection voltage (Vt) lower than the driving voltage is applied to the coil, and a detection voltage application stop control, in which the application of the detection voltage to the coil is stopped; and a detection unit (46) that, when the detection voltage is applied to the coil by the detection voltage application control, detects whether or not there is a magnetic material (W) that can be held when the permanent electromagnet has an attractive force, based on a measured value (Mv) of the coil current (Ic) flowing through the coil. With this configuration, it is possible to prevent the permanent electromagnet from having an attractive force even though there is no magnetic material in its vicinity.

[0192] (Note 2) In the control device described in Note 1, the detection unit may further detect whether or not the magnetic material is held by the permanent electromagnet based on the measured value. With such a configuration, it is possible to remotely detect whether or not the magnetic material is held by the permanent electromagnet.

[0193] (Note 3) The control device described in Note 1 further comprises a storage unit (32) that stores predetermined threshold values ​​(H1, H2, H3), and the detection unit may detect whether or not the magnetic material is present based on the measured value after a predetermined time (Tp) has elapsed since the switching control unit started the detection voltage application control, and the threshold values. With such a configuration, the magnetic material detection process can be carried out in a simple manner.

[0194] (Note 4) The control device described in Note 1 further comprises a storage unit that stores a predetermined threshold value, wherein the measured value is the time (Tq) required from the time the switching control unit starts the detection voltage application control until the coil current reaches a predetermined value, and the detection unit may detect whether or not the magnetic material is present based on the measured value and the threshold value. With such a configuration, the magnetic material detection process can be carried out simply.

[0195] (Note 5) The control device described in Note 1 further comprises a storage unit that stores a predetermined threshold value, and when the detection voltage changes sinusoidally, the measured value is the phase difference (Pd) between the detection voltage and the coil current, and the amplitude (Ac) of the coil current, and the detection unit may detect whether or not the magnetic material is present based on the measured value and the threshold value. With such a configuration, the magnetic material detection process can be carried out simply.

[0196] (Note 6) The control device described in Note 4 may further include a determination unit (48) that determines the predetermined value to which the coil current will reach in response to the detection voltage application control performed again after the detection voltage application control by multiplying the actual value (Ia) to which the coil current reaches in response to the detection voltage application control by a predetermined percentage. With such a configuration, the detection process of magnetic materials and the state detection process of permanent electromagnets can be performed more accurately.

[0197] (Note 7) A control device as described in any one of Notes 3 to 5, wherein when the magnetization direction of the second permanent magnet is the first direction, the permanent electromagnet is in a non-holding state in which it does not possess the adsorption force and is unable to hold the magnetic material, and when the magnetization direction of the second permanent magnet is the second direction opposite to the first direction, the permanent electromagnet is in a holding state in which it possesses the adsorption force and is able to hold the magnetic material by the adsorption force, the storage unit stores the threshold value that distinguishes the non-holding state from the holding state, and the detection unit detects whether or not the magnetic material is present and, based on the measured value and the threshold value, detects whether the state of the permanent electromagnet is the non-holding state or the holding state. With such a configuration, even if the control history of the permanent electromagnet by the control device is lost, the state of the permanent electromagnet can be accurately grasped.

[0198] (Note 8) The control device described in Note 1 may further include a drive control unit (40) that performs drive control to apply the drive voltage to the coil. With this configuration, the state of the permanent electromagnet, which is in a holdable state or a non-holdable state, can be easily switched by the drive control unit performing drive control.

[0199] (Note 9) In the control device described in Note 8, when the permanent electromagnet does not possess the attraction force, and the detection voltage is applied to the coil by the detection voltage application control, the detection unit detects whether or not the magnetic material is present, and if the detection unit detects the presence of the magnetic material, the drive control unit may perform the drive control to cause the permanent electromagnet to possess the attraction force, thereby causing the permanent electromagnet to hold the magnetic material. With such a configuration, it is possible to prevent the permanent electromagnet from possessing an attraction force even though there is no magnetic material in its vicinity.

[0200] (Note 10) The control device described in Note 9 may further include a storage unit that stores threshold values ​​(H1, H2, H3, H4, H5, H6) corresponding to the number of superpositions of the magnetic material, and the detection unit may detect the number of superpositions of the magnetic material held by the permanent electromagnet based on the measured value and the threshold values. With such a configuration, the number of superpositions of the magnetic material can be easily detected.

[0201] (Note 11) In the control device described in Note 1, the drive power supply (14) that supplies the drive voltage to the coil and the detection power supply (16) that supplies the detection voltage to the coil may be the same power supply. With such a configuration, the number of power supplies that supply the voltage applied to the coil of the permanent electromagnet can be minimized.

[0202] (Note 12) The control device described in Note 1 may have different power supplies for supplying the drive voltage to the coil and for supplying the detection voltage to the coil. With such a configuration, a power supply that supplies the voltage applied to the coil of the permanent electromagnet can be realized at low cost.

[0203] (Note 13) The magnetic gripper of this disclosure comprises the control device described in Note 1 and the permanent electromagnet. With this configuration, a user-friendly magnetic gripper can be realized.

[0204] (Note 14) The sensor (70) of this disclosure comprises the control device described in Note 1 and an output unit (80) that outputs the detection result from the detection unit to the outside. With such a configuration, a user-friendly sensor can be realized.

[0205] (Note 15) The control method of the present disclosure is a control method for controlling a permanent electromagnet comprising a first permanent magnet and a second permanent magnet and a coil wound at least around the outer circumference of the second permanent magnet, wherein when a driving voltage is applied to the coil, the magnetization direction of the second permanent magnet is reversed, and the magnetization direction of the second permanent magnet is maintained from the time the application of the driving voltage to the coil is stopped until the driving voltage is applied to the coil again, the control method comprising: a detection voltage application control step of applying a detection voltage lower than the driving voltage to the coil; a detection voltage application stop control step of stopping the application of the detection voltage to the coil; and, when the detection voltage is applied to the coil in the detection voltage application control step, a detection step of detecting whether or not there is a magnetic material that can be held when the permanent electromagnet has an attractive force, based on a measured value of the coil current generated in the coil. With such a configuration, it is possible to prevent the permanent electromagnet from having an attractive force even though there is no magnetic material in the vicinity of the permanent electromagnet.

[0206] While this disclosure has been described in detail, it is not limited to the individual embodiments described above. These embodiments can be added, replaced, modified, partially deleted, etc., in any way that does not depart from the gist of this disclosure or from the spirit of this disclosure derived from the claims and their equivalents. These embodiments can also be implemented in combination. For example, the order of operations and processes in the embodiments described above are given as examples only and are not limited thereto. The same applies when numerical values ​​or mathematical formulas are used in the description of the embodiments described above.

Claims

1. A control device (12) for controlling a permanent electromagnet (10) comprising a first permanent magnet (10a) and a second permanent magnet (10b), and a coil (10c) wound at least around the outer circumference of the second permanent magnet, wherein when a driving voltage (Vd) is applied to the coil, the magnetization direction of the second permanent magnet is reversed, and the magnetization direction of the second permanent magnet is maintained from the time the application of the driving voltage to the coil is stopped until the application of the driving voltage to the coil is applied again, the control device (12) comprising: a switching control unit (42) that switches between a detection voltage application control in which a detection voltage (Vt) lower than the driving voltage is applied to the coil and a detection voltage application stop control in which the application of the detection voltage to the coil is stopped; and a detection unit (46) that, when the detection voltage is applied to the coil by the detection voltage application control, detects whether or not there is a magnetic material (W) that can be held when the permanent electromagnet has an attractive force, based on a measured value (Mv) of the coil current (Ic) flowing through the coil, A control device equipped with the following features.

2. A control device according to claim 1, wherein the detection unit further detects whether or not the magnetic material is held by the permanent electromagnet based on the measured value.

3. A control device according to claim 1, further comprising a storage unit (32) that stores predetermined threshold values ​​(H1, H2, H3), wherein the detection unit detects whether or not the magnetic material is present based on the measured value after a predetermined time (Tp) has elapsed since the switching control unit started the detection voltage application control, and the threshold values.

4. A control device according to claim 1, further comprising a storage unit for storing a predetermined threshold value, wherein the measured value is the time (Tq) required from the time the switching control unit starts the detection voltage application control until the coil current reaches a predetermined value, and the detection unit detects whether or not the magnetic material is present based on the measured value and the threshold value.

5. A control device according to claim 1, further comprising a storage unit for storing a predetermined threshold value, wherein when the detection voltage changes sinusoidally, the measured value is the phase difference (Pd) between the detection voltage and the coil current, and the amplitude (Ac) of the coil current, and the detection unit detects whether or not the magnetic material is present based on the measured value and the threshold value.

6. A control device according to claim 4, further comprising a determination unit (48) that determines the predetermined value to which the coil current reaches in response to the detection voltage application control performed again after the detection voltage application control by multiplying the actual value (Ia) to which the coil current reaches in response to the detection voltage application control by a predetermined ratio.

7. A control device according to any one of claims 3 to 5, wherein when the magnetization direction of the second permanent magnet is a first direction, the permanent electromagnet is in a non-holding state in which it does not possess the adsorption force and is unable to hold the magnetic material; when the magnetization direction of the second permanent magnet is a second direction opposite to the first direction, the permanent electromagnet is in a holding state in which it possesses the adsorption force and is able to hold the magnetic material by the adsorption force; the storage unit stores the threshold value for distinguishing between the non-holding state and the holding state; and the detection unit detects whether or not the magnetic material is present and, based on the measured value and the threshold value, detects whether the state of the permanent electromagnet is the non-holding state or the holding state.

8. A control device according to claim 1, further comprising a drive control unit (40) that performs drive control to apply the drive voltage to the coil.

9. A control device according to claim 8, wherein when the permanent electromagnet does not possess the attraction force, the detection unit detects whether or not the magnetic material is present when the detection unit applies the detection voltage to the coil by the detection voltage application control, and when the detection unit detects the presence of the magnetic material, the drive control unit performs the drive control to provide the permanent electromagnet with the attraction force, thereby causing the permanent electromagnet to hold the magnetic material.

10. A control device according to claim 9, further comprising a storage unit for storing threshold values ​​(H1, H2, H3, H4, H5, H6) corresponding to the number of superpositions of the magnetic material, wherein the detection unit detects the number of superpositions of the magnetic material held by the permanent electromagnet based on the measured value and the threshold values.

11. A control device according to claim 1, wherein the drive power supply (14) that supplies the drive voltage to the coil and the detection power supply (16) that supplies the detection voltage to the coil are the same power supply.

12. A control device according to claim 1, wherein the power supply for supplying the drive voltage to the coil and the power supply for supplying the detection voltage to the coil are different power supplies.

13. A magnetic gripper comprising the control device described in claim 1 and the permanent electromagnet.

14. A sensor (70) comprising: a control device according to claim 1; and an output unit (80) that outputs the detection result from the detection unit to the outside.

15. A control method for controlling a permanent electromagnet comprising a first permanent magnet and a second permanent magnet, and a coil wound at least around the outer circumference of the second permanent magnet, wherein when a driving voltage is applied to the coil, the magnetization direction of the second permanent magnet is reversed, and the magnetization direction of the second permanent magnet is maintained from the time the application of the driving voltage to the coil is stopped until the application of the driving voltage to the coil is applied again, the control method comprising: a detection voltage application control step of applying a detection voltage lower than the driving voltage to the coil; a detection voltage application stop control step of stopping the application of the detection voltage to the coil; and, when the detection voltage is applied to the coil in the detection voltage application control step, a detection step of detecting whether or not there is a magnetic material that can be held when the permanent electromagnet has an attractive force, based on a measured value of the coil current flowing through the coil.

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