Position detector

Abstract

To provide a position director that can simplify computation processing for detecting the position of a plunger of a solenoid.SOLUTION: A position detector includes: a solenoid 100 that attracts a plunger 12 as a movable magnetic pole onto a fixed magnetic pole 13 by passing a current 16 through a magnetizing coil and releases the plunger 12 from the fixed magnetic pole 13 by stopping the current 16 flowing through the coil 11; a drive circuit 51 which is electrically connected to one terminal 11a and another terminal 11b of the coil 11, and which feeds currents 16, 17 through the coil 11; a drive control unit 52 for controlling the drive circuit; a back-electromotive-force detecting unit 53 for detecting a back electromotive force occurring in the coil 11; and a position detecting unit 54 for determining a position of the plunger 12 based on the back back-electromotive-force detecting unit 53.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a position detection device that detects the position of a plunger in a solenoid. [Background technology]

[0002] A solenoid is configured so that a plunger is attracted to a fixed magnetic pole by passing a current through an excitation coil, and the plunger is released from the fixed magnetic pole by stopping the current through the coil. Such solenoids have a variety of uses. For example, they are often used as locking functions for coin mechanisms in vending machines, safety devices, and security. They are also used as parts of paper feeders in multifunction machines and printers.

[0003] On the other hand, it is required to be able to detect whether the plunger is in an accurate position when the solenoid is in use. Patent Document 1 discloses a plunger position detection device.

[0004] However, the above-mentioned plunger position detection device has problems such as complicated analog signal processing, large circuit size, and high costs. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5107843 Summary of the Invention [Problem to be solved by the invention]

[0006] SUMMARY OF THE PRESENT DISCLOSURE An object of various aspects of the present invention is to provide a position detection device capable of simplifying the calculation process for detecting the position of a plunger of a solenoid. [Means for solving the problem]

[0007] Various aspects of the present invention are described below.

[0008] [1] A solenoid that attracts a plunger as a movable magnetic pole to a fixed magnetic pole by passing a current through an excitation coil, and detaches the plunger from the fixed magnetic pole by stopping the current flowing through the coil; a drive circuit electrically connecting one terminal and the other terminal of the coil and causing a current to flow through the coil; A drive control unit that controls the drive circuit; A back electromotive force detection unit that detects a back electromotive force generated in the coil; a position detector that detects a position of the plunger based on the back electromotive force detector; having the drive control unit has a function (x) of controlling the drive circuit to stop application of the first voltage for a first period while maintaining a state in which the plunger is attracted to the fixed magnetic pole by applying a first voltage to the coil to pass a current therethrough, the position detection unit has a function of detecting a back electromotive force generated in the coil at the start of the first period using the back electromotive force detection unit, causing a positive voltage to be generated at the other terminal of the coil, measuring a first pulse waveform which is compared with a first reference voltage and binarized when the positive voltage at the other terminal decreases toward the end of the first period, detecting that the plunger is in an attracted position when a pulse width in the first pulse waveform is longer than a first threshold width, and detecting that the plunger is in a released position when the pulse width is shorter than the first threshold; the drive control unit has a function (y) of controlling to apply a second voltage for a second period to flow a current in a direction opposite to the current flowing through the coil when the plunger is maintained in the attracted state, while maintaining the state in which the plunger is separated from the fixed magnetic pole by not flowing a current through the coil; The position detection unit has a function of detecting a back electromotive force generated in the coil at the end of the second period using the back electromotive force detection unit, causing a voltage of 0 V to be generated at the other terminal of the coil, measuring a second pulse waveform which is compared with a second reference voltage and digitized when the voltage of 0 V at the other terminal gradually rises to a positive voltage from the end of the second period, detecting that the plunger is in a release position if the pulse width in the second pulse waveform is shorter than a second threshold width, and detecting that the plunger is in an adsorption position if the pulse width is longer than the second threshold width.

[0009] According to the position detection device of the above [1] according to one aspect of the present invention, the drive control unit has a function (x) of controlling the drive circuit to stop the application of the first voltage for a first period while maintaining the state in which the plunger is attracted to the fixed magnetic pole by applying a first voltage to the coil and passing a current through it. That is, after applying the first voltage to the coil so that a current flows from one terminal of the coil to the other terminal, the application of the first voltage is stopped, and a back electromotive force is generated in the coil at the start of the first period. The back electromotive force is detected by the back electromotive force detection unit, and a positive voltage is generated in the other terminal of the coil. When the positive voltage of the other terminal decreases toward the end of the first period, a first pulse waveform is measured, which is compared with a first reference voltage and binarized, and when the pulse width of the first pulse waveform is longer than a first threshold width, the position detection unit detects that the plunger is in the attracted position, and when the pulse width is shorter than the first threshold width, the position detection unit detects that the plunger is in the released position. In addition, the drive control unit has a function (y) of controlling the application of a second voltage for a second period to flow a current in the opposite direction to the current flowing through the coil when maintaining the above-mentioned attracted state, while maintaining the state in which the plunger is released from the fixed magnetic pole by not passing a current through the coil. That is, a back electromotive force is generated in the coil at the end of the second period. The back electromotive force detection unit detects this back electromotive force, generating a voltage of 0V at the other terminal of the coil, and the position detection unit has a function of measuring a second pulse waveform that is compared with a second reference voltage and binarized when the voltage of 0V at the other terminal gradually rises to a positive value from the end of the second period, and detecting that the plunger is in the released position if the pulse width of this second pulse waveform is shorter than a second threshold width, and detecting that the plunger is in the attracted position if the pulse width is longer than the second threshold width. As described above, by changing the direction of the drive current, the plunger position is detected using the voltage at the same terminal (the other terminal) of the coil whether the plunger is in the attracted or released state. Therefore, the plunger position can be detected by simplified signal processing.

[0010] [2] In paragraph [1] above: The position detection device, wherein the drive circuit includes an H-bridge circuit.

[0011] [3] In paragraph [1] above: The position detection device according to claim 1, wherein the back electromotive force detection unit includes a comparator.

[0012] [4] In any one of paragraphs [1] to [3] above, The function (x) is (a) applying a first voltage to the coil so that a current flows from one terminal of the coil to the other terminal of the coil; A function (b) of stopping application of the first voltage of the function (a); and a function (c) of applying the first voltage to the coil by the function (a) when the first period has elapsed after the application of the first voltage is stopped by the function (b) while attracting the plunger to the fixed magnetic pole by applying the first voltage to the coil by the function (a) to cause the current to flow through the coil, The function (y) is (d) a function of applying the second voltage to the coil so that a current flows in the reverse direction through the coil; A function (e) of stopping the application of the second voltage of the function (d); and a function (f) of applying the second voltage to the coil by the function (d) while separating the plunger from the fixed magnetic pole by not passing the current through the coil, and then stopping the application of the second voltage by the function (e) when the second period has elapsed.

[0013] [5] In paragraph [2] above: The H-bridge circuit includes: Power supply, one end of a first switching element electrically connected to a positive terminal of the power supply; the other end of the first switching element and one end of the second switching element electrically connected to one terminal of the coil; one end of the first switching element and one end of a third switching element electrically connected to one end of the first switching element and a positive terminal of the power supply; the other end of the third switching element and one end of the fourth switching element electrically connected to the other terminal of the coil; the other end of the second switching element and the other end of the fourth switching element are electrically connected to a negative terminal of the power supply, the first current flows when the drive control unit controls the first switching element and the fourth switching element to be on and the second switching element and the third switching element to be off, A position detection device characterized in that the second current flows when the drive control unit controls to turn off each of the first switching element and the fourth switching element and to turn on each of the second switching element and the third switching element. Effect of the Invention

[0014] According to various aspects of the present invention, it is possible to provide a position detection device that can simplify the calculation process for detecting the position of a plunger of a solenoid. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a block diagram for explaining a position detection device according to an embodiment of the present invention, and is a schematic diagram showing a state in which the position detection device is electrically connected to a coil of a solenoid. [Diagram 2] 1 is a schematic diagram showing a solenoid in a state where a plunger is separated from a fixed magnetic pole; [Diagram 3] 4 is a timing chart of a drive signal transmitted from a drive control unit shown in FIG. 1 to a drive circuit. [Figure 4] 4 is a timing chart of a driving current flowing through a coil. [Diagram 5] 5 is a diagram including a timing chart of a first voltage V1 applied to the coil in order to pass the attraction and holding drive current shown in FIG. 4 from one terminal 11a to the other terminal 11b of the coil shown in FIG. [Figure 6] 5 includes a timing chart of a second voltage V3 applied to the coil in order to intermittently pass a current in a direction opposite to the attraction drive while stopping the drive current passed through the coil shown in FIG. 4 in order to separate the plunger shown in FIG. 2 from the fixed magnetic pole. [Figure 7] 2 is a diagram illustrating a comparator included in the back electromotive force detection unit illustrated in FIG. 1. [Figure 8] 2A and 2B are diagrams illustrating an H-bridge circuit as an example of the drive circuit shown in FIG. [Figure 9] 2 is an H-bridge circuit as an example of the drive circuit shown in FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it is easily understood by those skilled in the art that the form and details of the present invention can be modified in various ways without departing from the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited to the description of the embodiments shown below.

[0017] Fig. 1 is a block diagram for explaining a position detection device according to one embodiment of the present invention, and is a schematic diagram showing a state in which the position detection device is electrically connected to a coil 11 of a solenoid. Fig. 1 shows the solenoid in a state in which a plunger 12 as a movable magnetic pole is attracted to a fixed magnetic pole 13. Fig. 2 is a schematic diagram showing the solenoid in a state in which the plunger 12 is detached from the fixed magnetic pole 13.

[0018] The solenoid 100 is configured to attract a plunger 12 as a movable magnetic pole to a fixed magnetic pole 13 by passing a drive current 16 through an exciting coil 11 as shown in FIG. 1, and to detach the plunger 12 from the fixed magnetic pole 13 by stopping the drive current 16 flowing through the coil 11 as shown in FIG. 2. In detail, the rod-shaped plunger 12 and the coil 11 wound around the outside of the plunger 12 are disposed in a case 10, and the fixed magnetic pole 13 is disposed on the tip side of the plunger 12 in the case 10. A return spring mounting plate 22 for mounting a return spring 21 is formed on the base end side of the plunger 12. The return spring 21 is disposed between the end of the case 10 on the base end side of the plunger 12 and the return spring mounting plate 22. As shown in FIG. 1, when the plunger 12 magnetized by passing a drive current through the coil 11 is attracted to the fixed magnetic pole 13, the return spring 21 is in a contracted state. As shown in Figure 2, when the driving current flowing through coil 11 is stopped and the unmagnetized plunger 12 loses its force of attraction to fixed magnetic pole 13, the force of the return spring 21 expanding causes the plunger 12 to detach from fixed magnetic pole 13, and the return spring 21 enters an expanded state, causing the plunger 12 to detach from fixed magnetic pole 13.

[0019] The position detector shown in FIG. 1 has a drive circuit 51, to which one terminal 11a and the other terminal 11b of the coil 11 are electrically connected. Drive currents 16, 17 can be passed from the drive circuit 51 to the coil 11. The drive circuit 51 is electrically connected to a drive control unit 52, which controls the operation of the drive circuit 51. The position detector also has a back electromotive force detection unit 53, which can detect the back electromotive force generated in the coil 11. The back electromotive force detection unit 53 is electrically connected to a position detection unit 54, which can detect the position of the plunger 12 based on the back electromotive force detected by the back electromotive force detection unit 53.

[0020] The drive control unit 52 has a function (x) of controlling the drive circuit 51 to stop application of the first voltage V1 for a first period T1 shown in Fig. 5 while maintaining a state in which the plunger 12 is attracted to the fixed magnetic pole 13 by applying a first voltage V1 shown in Fig. 5 to the coil 11 and flowing a drive current 16 shown in Fig. 1 and Fig. 4. In other words, the function (x) is a function of performing an attraction drive for attracting the plunger 12 to the fixed magnetic pole 13, and pausing the attraction drive for a short period of time after attraction so that the plunger 12 can be held in an attracted state.

[0021] The first period T1 here is a period during which the plunger 12 can maintain the state of being attracted to the fixed magnetic pole 13 even if the application of the first voltage V1 is stopped for that period T1. FIG. 4 is a timing chart of the drive current applied to the coil 11. During the attraction drive for attracting the plunger 12 to the fixed magnetic pole 13, the drive current 16 is applied in the direction of the arrow shown in FIG. 1, and during the attraction and holding, a first period T1 is intermittently provided during which the drive current 16 is stopped. FIG. 5 is a diagram including a timing chart of the first voltage V1 applied to the coil 11 in order to pass the attraction and holding drive current shown in FIG. 4 from one terminal 11a to the other terminal 11b of the coil 11 shown in FIG. 1.

[0022] The drive circuit 51 has an H-bridge circuit as shown in, for example, Figures 8(A) and (B). This H-bridge circuit has a power source 60 and a coil 11, and one end of a first switching element 61 is electrically connected to the positive terminal of the power source 60. The other end of the first switching element 61 and one end of a second switching element 62 are electrically connected to one terminal 11a of the coil 11. One end of a third switching element 63 is electrically connected to one end of the first switching element 61 and the positive terminal of the power source 60. The other end of the third switching element 63 and one end of a fourth switching element 64 are electrically connected to the other terminal 11b of the coil 11. The other end of the second switching element 62 and the other end of the fourth switching element 64 are electrically connected to the negative terminal of the power source 60.

[0023] When the drive control unit 52 shown in FIG. 1 controls the first switching element 61 and the fourth switching element 64 to be turned on and the second switching element 62 and the third switching element 63 to be turned off, a drive current 16 flows (see FIG. 8(A)).

[0024] 1 controls the first switching element 61 and the fourth switching element 64 to be turned off and the second switching element 62 and the third switching element 63 to be turned on, a current 17 flows in a direction opposite to the direction of the driving current 16 (see FIG. 8(B)). In this way, the H-bridge circuit as the driving circuit 51 can switch the direction of the current flowing through the coil 11 in response to a command from the driving control unit 52 (see FIGS. 8(A) and 8(B)).

[0025] The above function (x) has the following functions (a) to (c). Function (a): A function of applying a first voltage V1 to the coil 11 so that a current 16 flows from one terminal 11a to the other terminal 11b of the coil 11. Function (b): A function of stopping the application of the first voltage V1 of function (a) above. Function (c): A function of applying a first voltage V1 to the coil 11 by the above function (a) and flowing a current 16 to the coil 11, thereby attracting the plunger 11 to the fixed magnetic pole 13, and then stopping the application of the first voltage V1 by the above function (b) and then applying the first voltage V1 to the coil 11 by the above function (a) after the first period T1 has elapsed.

[0026] The above functions (a) to (c) will be explained in detail below. First, the function (a) is a function in which, for example, a drive signal during drive On shown in Fig. 3 is sent from the drive control unit 52 shown in Fig. 1 to the drive circuit 51, whereby a first voltage V1 is applied to the coil 11 from the drive circuit 51 and an attraction drive current 16 flows from one terminal 11a to the other terminal 11b of the coil 11. For example, as shown in Fig. 8(A), the drive control unit 52 controls the first switching element 61 and the fourth switching element 64 to be on and the second switching element 62 and the third switching element 63 to be off, whereby the attraction drive current 16 flows to the coil 11.

[0027] The above function (b) is a function of, for example, sending a drive signal during drive off shown in Fig. 3 from the drive control unit 52 shown in Fig. 1 to the drive circuit 51 to stop application of the first voltage V1 to the coil 11 from the drive circuit 51 and prevent the above-mentioned attraction drive current 16 from flowing. For example, as shown in Fig. 8(A), the drive control unit 52 controls each of the first switching element 61, the second switching element 64, the third switching element 62, and the fourth switching element 63 to be turned off, so that the attraction drive current 16 does not flow.

[0028] The above function (c) is a function in which, for example, after stopping the application of the first voltage V1 by the above function (b) while the plunger 11 shown in FIG. 1 is attracted to the fixed magnetic pole 13, a drive signal for drive On is sent from the drive control unit 52 shown in FIG. 1 to the drive circuit 51 after the first period T1 shown in FIG. 3 has elapsed, so that the first voltage V1 is again applied to the coil 11 from the drive circuit 51, and an attraction drive current 16 is caused to flow from one terminal 11a to the other terminal 11b of the coil 11. FIG. 3 is a timing chart of the drive signal transmitted from the drive control unit 52 to the drive circuit 51 shown in FIG.

[0029] The position detection unit 54 has a function of detecting the back electromotive force (voltage change at both ends of the coil 11) generated in the coil 11 at the start of the first period T1 shown in Fig. 5 (from the time of attraction driving to the time of driving pause) by the back electromotive force detection unit 53, so that a positive voltage V2 shown in Fig. 5 is generated at the other terminal 11b of the coil 11, and measuring the first pulse waveforms 31, 32 which are compared with the first reference voltage 33 and binarized when the positive voltage V2 at the other terminal 11b of the coil 11 decreases toward the end of the first period T1, detecting that the plunger 12 is in the attraction position when the pulse width 31a in the first pulse waveforms 31, 32 is longer than the first threshold width 35, and detecting that the plunger 12 is in the release position when the pulse width 32a is shorter than the first threshold width 35 (see Fig. 5). The first threshold width 35 is preferably set to be approximately the middle between the detection pulse width at the release position and the detection pulse width at the attraction position.

[0030] At the start of the first period T1, that is, when the drive is switched from On to Off as shown in FIG. 3, the voltage across the coil 11 swings largely in the opposite direction and then gradually converges. Specifically, as shown in FIG. 5, the coil terminal 11b swings largely in the opposite direction and then gradually converges. The manner in which this voltage swings and converges varies depending on the energy and inductance stored in the coil 11. When the plunger 12 is at the adsorption position, the swing is large because the energy is high, and the convergence is gradual because the inductance is high. In addition, the back electromotive force detection unit 53 has a comparator as shown in FIG. 7. The signal from the other terminal 11b of the coil 11 due to the back electromotive force is binarized by comparing the voltage change with the first reference voltage 33 by the comparator. In other words, the position of the plunger 12 can be detected by measuring the pulse width of the binarized signal. The pulse width means the width of a HIGH level pulse from when the drive is switched from On to Off until the voltage of the coil terminal 11b shown in FIG. 5 crosses the first reference voltage 33, and this pulse width is used to determine whether the plunger 12 is at the release position or the adsorption position.

[0031] As described above, even if the application of the first voltage V1 is stopped for only the first period T1, the state in which the plunger 12 is attracted to the fixed magnetic pole 13 should be maintained, but it is also possible that the plunger 12 may be detached from the fixed magnetic pole 13 for some reason. In such a case, the above-mentioned function of the position detection unit 54 makes it possible to detect whether or not the attracted state of the plunger 12 is being maintained.

[0032] The drive control unit 52 has a function (y) of controlling the current 17 in the opposite direction to the drive current 16 flowing through the coil 11 when maintaining the state in which the plunger 12 is attracted to the fixed magnetic pole 13, as shown in FIG. 2, by applying a second voltage V3 for a second period T2 as shown in FIG. 6, while maintaining the state in which the plunger 12 is separated from the fixed magnetic pole 13 by not flowing the drive current 16 through the coil 11 as shown in FIG. 4. That is, the function (y) is a function of performing attraction drive for a short period (second period T2) to the extent that the plunger 12 is maintained in the state in which it is separated from the fixed magnetic pole 13 (i.e., to the extent that it does not move in the attracting direction). The reverse current 17 is a current flowing from the other terminal 11b to one terminal 11a of the coil 11 as shown in FIG. 1.

[0033] The second period T2 here is a period during which the plunger 12 can maintain a state in which it is separated from the fixed magnetic pole 13 even if the second voltage V3 is applied to the coil 11 for only the period T2. Note that Fig. 6 is a diagram including a timing chart of the second voltage V3 applied to the coil 11 in order to intermittently pass a current 17 in the opposite direction to the attraction drive while stopping the drive current flowing through the coil 11 shown in Fig. 4 in order to separate the plunger 12 shown in Fig. 2 from the fixed magnetic pole 13.

[0034] The above function (y) has the following functions (d) to (f). Function (d): A function of applying a second voltage V3 to the coil 11 so that a current 17 flows through the coil 11 in the opposite direction to the drive current 16. Function (e): A function of stopping the application of the second voltage V3 of function (d) above. Function (f): A function of separating the plunger 12 from the fixed magnetic pole 13 by not passing the drive current 16 through the coil 11, and then applying the second voltage V3 to the coil 11 using the above function (d), and then stopping the application of the second voltage V3 using the above function (e) when the second period T2 has elapsed.

[0035] The above functions (d) to (f) are explained in detail below. First, the function (d) is a function of applying the second voltage V3 to the coil 11 so that the current 17 for the detachment drive, i.e., the current 17 in the opposite direction to the drive current 16, flows from the other terminal 11b to the one terminal 11a of the coil 11 after the second voltage V3 applied to the coil 11 from the drive circuit 51 is stopped by transmitting a drive signal during drive off shown in Fig. 3 from the drive control unit 52 shown in Fig. 1 to the drive circuit 51. For example, as shown in Fig. 8(b), the drive control unit 52 controls the first switching element 61 and the fourth switching element 64 to be turned off and the second switching element 62 and the third switching element 63 to be turned on, so that the current 17 in the opposite direction to the drive current 16 flows.

[0036] The above function (e) is a function for, for example, transmitting a drive signal for drive off shown in Fig. 3 from the drive control unit 52 shown in Fig. 1 to the drive circuit 51 to stop application of the second voltage V3 to the coil 11 from the drive circuit 51 and prevent the above-mentioned attraction drive current 17 from flowing. For example, as shown in Fig. 8(B), the drive control unit 52 controls each of the first switching element 61, the second switching element 64, the third switching element 62, and the fourth switching element 63 to be turned off, so that the attraction drive current 16 does not flow.

[0037] The above function (f) is a function in which, for example, while the plunger 11 shown in FIG. 1 is removed from the fixed magnetic pole 13, the second voltage V3 is applied to the coil 11 by the above function (d), and then, when the second period T2 shown in FIG. 3 has elapsed, a drive signal for drive off is sent from the drive control unit 52 shown in FIG. 1 to the drive circuit 51 by the above function (e), thereby stopping the application of the second voltage V3 from the drive circuit 51 to the coil 11 and stopping the adhesion drive current 17 flowing from the other terminal 11b to the one terminal 11a of the coil 11.

[0038] The position detection unit 54 shown in Fig. 1 has a function of detecting the back electromotive force (voltage change at both ends of the coil 11) generated in the coil 11 at the end of the second period T2 by the back electromotive force detection unit 53, generating a voltage of 0V shown in Fig. 6 at the other terminal 11b of the coil 11, measuring the second pulse waveforms 41, 42 which are compared with the second reference voltage 43 and binarized when the voltage of 0V at the other terminal 11b of the coil 11 gradually rises to a positive value from the end of the second period T2 shown in Fig. 6, detecting that the plunger 12 is in the release position when the pulse width 41a in the second pulse waveforms 41, 42 is shorter than the second threshold width 45, and detecting that the plunger 12 is in the attracted position when the pulse width 42a is longer than the second threshold width 45 (see Fig. 6). The second threshold width 45 is preferably set to be approximately the middle between the detection pulse width at the release position and the detection pulse width at the attracted position. In addition, the second threshold width 45 is different from the first threshold width 35 .

[0039] At the end of the second period T2, that is, when the drive is switched from On to Off as shown in FIG. 3, the voltage across the coil 11 swings largely in the opposite direction and then gradually converges. Specifically, as shown in FIG. 6, the coil terminal 11a swings largely in the opposite direction and then gradually converges. The way in which this voltage swings and converges varies depending on the energy and inductance stored in the coil 11. When the plunger 12 is in the release position, the voltage swings largely because the energy is low, and convergence is fast because the inductance is low. That is, the signal from the other terminal 11b of the coil 11 due to the back electromotive force is binarized by comparing the voltage change with the second reference voltage 43 by the comparator shown in FIG. 7, and the position of the plunger 12 can be detected by measuring the pulse width of the binarized signal. The pulse width means the width of a HIGH level pulse from when the drive is switched from On to Off until the voltage of the coil terminal 11b shown in FIG. 6 crosses the second reference voltage 43, and this pulse width is used to determine whether the plunger 12 is in the release position or the attraction position. Furthermore, the second reference voltage 43 may be different from the first reference voltage 33 or may be the same as it.

[0040] As described above, the reason why the current 17 in the opposite direction to the drive current 16 flowing through the coil 11 when the plunger 12 is attracted to the fixed magnetic pole 13 while maintaining the detached state of the plunger 12 shown in Fig. 2 is to flow is that the potential difference between both ends of the coil is the difference between the coil terminal voltages, and calculations are required unless the direction of the drive current is switched. In detail, calculations are performed using the voltages of both ends of the coil (both one terminal 11a of the coil 11 and the other terminal 11b of the coil), two comparators are used, etc., and analog signal processing becomes complicated, the circuit configuration becomes complicated, the circuit size becomes large, and the product cost becomes high. In other words, by switching to the current 17 in the opposite direction to the attraction drive current 16, the back electromotive force can be detected using only the voltage of the coil terminal 11b, so the analog circuit only needs a comparator, and the processing such as calculations for detecting the position of the plunger can be simplified.

[0041] As described above, even if the second voltage V3 is applied to the coil 11 for only the second period T2, the state in which the plunger 12 is separated from the fixed magnetic pole 13 should be maintained, but it is possible that the plunger 12 may be attracted to the fixed magnetic pole 13 for some reason. In such a case, the above-described function of the position detection unit 54 makes it possible to detect whether the separated state of the plunger 12 is being maintained.

[0042] FIG. 9 is a diagram illustrating details of the H-bridge circuit shown in FIG. In the H-bridge circuit shown in FIG. 9, a first switching element 61 and a third switching element 63 are P-channel MOSFETs, and a second switching element 62 and a fourth switching element 64 are N-channel MOSFETs.

[0043] Even if the H-bridge circuit shown in FIG. 9 is used for the drive circuit 51 shown in FIG. 1, the same effects as those of the present embodiment described above can be obtained. [Explanation of symbols]

[0044] 11 Excitation coil 11a One end of the coil 11b Other terminal of coil 12 Plunger 13 Fixed magnetic pole 16 Drive Current 17 Reverse Current 31,32 First pulse waveform 31a, 32a Pulse width 33 First Reference Voltage 35 First Threshold Width 41,42 Second Pulse Waveform 41a, 42a Pulse width 43 Second Reference Voltage 45 Second Threshold Width 51 Drive circuit 52 Drive control unit 53 Back electromotive force detector 54 Position detection unit V1 First voltage V2 positive voltage V3 Second voltage T1 First Period T2 Second Period

Claims

1. a solenoid 100 that attracts a plunger as a movable magnetic pole to a fixed magnetic pole by passing a current through an excitation coil, and detaches the plunger from the fixed magnetic pole by stopping the current flow through the coil; a drive circuit electrically connecting one terminal and the other terminal of the coil and causing a current to flow through the coil; A drive control unit that controls the drive circuit; A back electromotive force detection unit that detects a back electromotive force generated in the coil; a position detector that detects a position of the plunger based on the back electromotive force detector; having the drive control unit has a function (x) of controlling the drive circuit to stop application of the first voltage for a first period while maintaining a state in which the plunger is attracted to the fixed magnetic pole by applying a first voltage to the coil to pass a current therethrough, the position detection unit has a function of detecting a back electromotive force generated in the coil at the start of the first period using the back electromotive force detection unit, causing a positive voltage to be generated at the other terminal of the coil, measuring a first pulse waveform which is compared with a first reference voltage and binarized when the positive voltage at the other terminal decreases toward the end of the first period, detecting that the plunger is in an attracted position when a pulse width in the first pulse waveform is longer than a first threshold width, and detecting that the plunger is in a released position when the pulse width is shorter than the first threshold width; the drive control unit has a function (y) of controlling to apply a second voltage for a second period to flow a current in a direction opposite to the current flowing through the coil when the plunger is maintained in the attracted state, while maintaining the state in which the plunger is separated from the fixed magnetic pole by not flowing a current through the coil, The position detection unit detects the back electromotive force generated in the coil at the end of the second period using the back electromotive force detection unit, causing a voltage of 0 V to be generated at the other terminal of the coil, and measures a second pulse waveform which is compared with a second reference voltage and digitized when the voltage of 0 V at the other terminal gradually rises to a positive voltage from the end of the second period, and detects that the plunger is in a release position if the pulse width in the second pulse waveform is shorter than a second threshold width, and detects that the plunger is in an adsorption position if the pulse width is longer than the second threshold width.

2. In claim 1, The position detection device according to claim 1, wherein the drive circuit includes an H-bridge circuit.

3. In claim 1, The position detection device according to claim 1, wherein the back electromotive force detection unit includes a comparator.

4. In any one of claims 1 to 3, The function (x) is (a) applying a first voltage to the coil such that a current flows from one terminal of the coil to the other terminal of the coil; A function (b) of stopping application of the first voltage of the function (a); and and a function (c) of applying the first voltage to the coil by the function (a) when the first period has elapsed after the application of the first voltage is stopped by the function (b) while attracting the plunger to the fixed magnetic pole by applying the first voltage to the coil by the function (a) to cause the current to flow through the coil, The function (y) is (d) a function of applying the second voltage to the coil so that a current flows in the reverse direction through the coil; A function (e) of stopping the application of the second voltage of the function (d); and a function (f) of applying the second voltage to the coil by the function (d) while separating the plunger from the fixed magnetic pole by not passing the current through the coil, and then stopping the application of the second voltage by the function (e) when the second period has elapsed.

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