JP4570343B2 - Electromagnetic pump - Google Patents

Description

The present invention relates to an electromagnetic pump, and more particularly to a compact electromagnetic pump used for transporting a fluid such as gas or liquid.

The applicant of the present invention first accommodates a mover made of a magnetic material in a cylinder chamber on the stator side so as to be able to reciprocate, and energizes electromagnetic coils fitted around the cylinder so that both sides of the mover move in the moving direction. Among the pump chambers formed between both end faces of the cylinder, in one pump chamber, the fluid is sucked from the outside through the first valve and sent out to the outside through the second valve, and the other pump chamber is the same. We proposed a miniaturized and thin electromagnetic pump that can function as a pump. (See Patent Document 1). In FIG. 11, the magnetic flux generated from the N pole side of the magnet 103 of the mover 101 is divided into an inner yoke 104a, an outer yoke 105 on the stator 102 side,
A magnetic circuit is formed that returns to the S pole side of the magnet 103 via the inner yoke 104b.
By energizing the electromagnetic coils 106a and 106b, the electromagnetic coils 106a and 106 are connected.
Although b receives electromagnetic force from the magnetic field described above, the electromagnetic coils 106a and 106b are fixed to the stator 102.
Since it is fixed to the side, the mover 101 moves in the axial direction of the cylinder (vertical direction in FIG. 11) as a reaction.
Japanese Patent Application No. 2002-286188

In the electromagnetic pump, whether or not the mover 101 housed in the cylinder part 109 closed at both ends by the upper frame body 107 and the lower frame body 108 is operating normally, or the mover 101 is in an appropriate movable range. Various methods can be considered as a method of detecting the movement of the mover such as whether or not it is operating at. As an example of the operation detection method of the mover 101, FIG.
As shown in FIG. 1, a magnetic sensor (such as a Hall element) 110 is provided outside the lower frame body 108. The magnetic sensor 110 can detect the movable position of the movable element 101 by detecting the leakage magnetic flux generated from the magnet 103 of the movable element 101.

In the configuration of the mover electromagnetic pump using the magnetic sensor shown in FIG. 11, the mover 101 is housed in the cylinder portion 109 closed by the upper and lower frame bodies 107 and 108, so that the magnet is located near the mover 101. The sensor 110 cannot be arranged. Further, when the magnetic flux leakage of the mover 101 is small and the magnetic sensor 110 is provided at a position away from the mover 101, the apparatus becomes larger and the magnetic flux density detected by the magnetic sensor 110 becomes further smaller and the magnetic flux density. It becomes difficult to detect changes in Specifically, when provided on one side of the upper and lower frame bodies 107 and 108, the change in the magnetic flux density of the magnetic sensor 110 is always in the same direction. There is a limit.

Further, the magnetic sensor 110 is easily affected by a magnetic field generated by energizing the electromagnetic coils 106a and 106b. That is, the cycle of the reciprocating motion of the mover 101 is the same as the cycle of the magnetic flux density change of the leakage flux of the mover 101. Also, the excitation cycle by energization of the electromagnetic coil is the same.
Therefore, it is difficult to determine whether the change in magnetic flux density detected by the magnetic sensor is caused by the reciprocating motion of the mover 101 or the excitation of the electromagnetic coils 106a and 106b.

The present invention has been made to solve these problems. The object of the present invention is to accurately detect the operating position of the mover without enlarging the apparatus and to generate a magnetic field generated by energizing the electromagnetic coil. The object is to provide an electromagnetic pump which is not easily affected.

In order to achieve the above object, the present invention comprises the following arrangement.
A mover in which a flange portion serving as a magnetic flux acting surface is formed on the outer peripheral surface portion of a magnetic body provided on both axial end surfaces of a disk-shaped permanent magnet is accommodated in a cylinder, and a plurality of movers are fitted around the cylinder. An electromagnetic that transports fluid from a pump chamber formed in the cylinder by reciprocating the mover in the axial direction in the cylinder by energizing air core electromagnetic coils that are set so that currents in opposite directions flow. a formula pump, the detection coil of the air core for detecting the reciprocating motion of the mover around the cylinder is fitted adjacent to the axial end faces each other the electromagnetic coil is opposite to the electromagnetic coil coaxially and the detection A yoke is provided adjacent to both end surfaces in the axial direction of the coil, and an outer yoke is provided on the outer peripheral surface of the detection coil, which is generated from the mover as the mover reciprocates. A magnetic circuit through which the magnetic flux passes through one yoke, the outer yoke, and the other yoke increases the amount of magnetic flux interlinking with the detection coil. The position of the movable element is detected by providing a threshold value in a detection range in which the fluctuation of the induced voltage caused by the excitation is small .

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If the electromagnetic pump described above is used, an air-core detection coil that detects the reciprocating motion of the mover is fitted around the cylinder where the leakage flux of the mover is large. Thus, the induced voltage generated in the detection coil can be increased, the detection accuracy can be improved, and the operation of the mover can be detected without increasing the size of the pump.
Further, since the yoke made of a magnetic material axially opposite end faces and an outer peripheral surface of the detection coil is provided, the detection coil and the magnetic flux interlinking the number of magnetic flux generated from the armature increases, generated in the detection coil Detection sensitivity can be improved by increasing the induced voltage value.
In addition, the magnetic flux generated from the mover as the reciprocating movement of the mover passes through one yoke, the outer yoke, and the other yoke, and the amount of magnetic flux linked to the detection coil is increased. The position of the mover is detected by providing a threshold value in a detection range in which the amount of change in the current flowing to the electromagnetic coil is small and the fluctuation of the induced voltage caused by excitation of the electromagnetic coil is small. The change in magnetic flux density and the change in magnetic flux density caused by excitation of the electromagnetic coil can be easily separated, and the detection accuracy can be improved.
Furthermore, the reciprocating motion of the mover and the flow rate of the pump can be detected based on the induced voltage of the detection coil, and the drive control of the mover can also be performed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best embodiment of an electromagnetic pump according to the present invention will be described in detail with reference to the accompanying drawings. The electromagnetic pump of the present embodiment accommodates a mover having a permanent magnet in a cylinder, and reciprocates the mover in the axial direction in the cylinder by energizing an air-core electromagnetic coil fitted around the cylinder. The present invention can be widely applied to an electromagnetic pump that moves a fluid from a pump chamber formed in a cylinder by being moved.

In FIG. 1, a typical configuration of an electromagnetic pump will be described. The mover 10 is housed in a sealed cylinder and is provided so as to be able to reciprocate in the axial direction of the cylinder. Mover 1
0 is composed of a magnet 12 formed in a disk shape and a pair of inner yokes 14a and 14b that sandwich the magnet 12 in the thickness direction. Magnet 12 has N pole on one side and S on the other side.
The pole is a permanent magnet that is magnetized in the thickness direction (vertical direction in FIG. 1). The inner yokes 14a and 14b are made of a magnetic material, and each inner yoke 14a and 14b
A flat plate portion 15a having a slightly larger diameter than the magnet 12 and a flange portion 15b standing in a short cylindrical shape at the peripheral portion of the flat plate portion 15a are provided. The outer peripheral surface of the flange portion 15b is a magnet 1
2 is a magnetic flux acting surface on the movable element 10 side of the magnetic flux generated from 2.

The sealing material 16 is a non-magnetic material such as plastic that covers the outer peripheral side surface of the magnet 12.
The sealing material 16 has a function of covering the magnet 12 so that the magnet 12 is not exposed to the outside so as not to rust, and a function of integrally forming the magnet 12 and the inner yokes 14a and 14b. The sealing material 16 is a magnet 12 sandwiched between inner yokes 14a and 14b.
However, the outer peripheral diameter of the sealing material 16 is the inner yoke 1.
It is formed slightly smaller than the outer diameter of 4a and 14b. When the sealing material 16 is formed in this way, when the outer peripheral surfaces of the inner yokes 14a and 14b are finish-ground, the sealing material 16 does not come into contact with the grinding blade and can be operated without damaging the grinding blade. When the pump is used at a high temperature when the thermal expansion coefficient of the sealing material 16 is larger than that of the inner yokes 14a and 14b, the gap between the mover 10 and the cylinder is the heat of the sealing material 16. There is an advantage that it is possible to prevent the pump from being reduced or eliminated by the expansion and to operate the pump stably.

Next, the configuration on the stator side of the electromagnetic pump in FIG. 1 will be described. A cylindrical cylinder is formed by combining the upper frame body 20a and the lower frame body 20b made of a pair of nonmagnetic materials, and the above-described movable element 10 is accommodated in the cylinder so as to be able to reciprocate. In the present embodiment, a cylinder portion 24 formed in a cylindrical shape is integrally formed with the frame body 22b of the lower frame body 20b. By fitting the end portion of the cylinder portion 24 into the fitting groove 28 provided in the frame body 22a of the upper frame body 20a, a pair of frame bodies 20a,
A cylinder having both axial end faces closed by 20b is formed. A sealing material 29 is provided at a portion of the fitting groove 28 where the end surface of the cylinder portion 24 abuts, and the inside of the cylinder is sealed from the outside by abutting the end surface of the cylinder portion 24 against the sealing material 29. The cylinder portion 24 can be extended from the upper frame body 20a and can be fitted to the lower frame body 20b. Further, the cylinder portion 24 may be formed separately from the upper frame body 20a and the lower frame body 20b.

In this way, both end surfaces of the cylinder are closed by the upper frame body 20a and the lower frame body 20b, and the pump chambers 30a, 30b are respectively provided between both side surfaces in the moving direction of the mover 10 and the inner wall surfaces of the upper and lower frame bodies 20a, 20b. Is formed. The pump chambers 30a and 30b correspond to gap portions formed between both end faces of the mover 10 and the frame main body 22a of the upper frame 20a and the frame main body 22b of the lower frame 20b. The movable element 10 slides in a state of being in airtight or liquid tight seal with the cylinder part 24 while being in contact with the inner surface of the cylinder part 24. Mover 1
In order to improve the slidability of 0, the outer yoke of the inner yokes 14a and 14b is provided with a coating having both lubricity and rust prevention such as fluororesin coating and DLC (diamond-like carbon) coating. Further, it is possible to provide a detent that prevents the mover 10 from rotating in the circumferential direction.

A damper 32 is attached to end surfaces (inner wall surfaces) of the frame main bodies 22a and 22b. The damper 32 is provided to absorb an impact when the inner yokes 14a and 14b come into contact with the end surfaces of the frame main bodies 22a and 22b at the end position of the moving range of the mover 10.
The damper 32 may be provided on the end surfaces of the inner yokes 14a and 14b and in contact with the frame main bodies 22a and 22b, instead of being provided on the end surfaces of the frame main bodies 22a and 22b.

A suction valve 34a and a delivery valve 36a are provided in the frame body 22a of the upper frame 20a so as to communicate with the pump chamber 30a. Frame body 2 of lower frame 20b
In 2b, a suction valve 34b and a delivery valve 36b are provided in communication with the pump chamber 30b.

The upper frame 20a and the lower frame 20b are provided with suction flow paths 38a and 38b communicating with the suction valves 34a and 34b. The upper frame 20a and the lower frame 20b
Are provided with delivery passages 40a, 40b communicating with the delivery valves 36a, 36b. The suction flow path 38a of the upper frame 20a and the suction flow path 38b of the lower frame 20b are communicated with each other by a communication pipe 42, and the delivery flow path 40a of the upper frame 20a and the lower frame 20b are communicated.
The communication channel 44b communicates with the delivery channel 40b. As a result, the upper frame 20
a and the lower frame 20b have a suction channel and a delivery channel, respectively, one suction port 38 and one delivery port 4;
Communicate to 0.

In FIG. 1, air-core electromagnetic coils 50a and 50b are fitted around the cylinder. The electromagnetic coils 50a and 50b are slightly spaced apart from each other in the axial direction of the cylinder, and are arranged at equal positions with respect to the center position in the axial direction of the cylinder. Electromagnetic coils 50a, 50b
The axial length is set longer than the movable range of the flange portion 15b of the inner yokes 14a and 14b. Note that the winding directions of the electromagnetic coil 50a and the electromagnetic coil 50b are opposite to each other, and currents in opposite directions flow when energized by the same power source. The winding direction of the electromagnetic coils 50a and 50b is reversed because the force acting on the current flowing through the electromagnetic coils 50a and 50b interlinked with the magnetic flux of the magnet 12 is superimposed on the mover 10 as a reaction force. This is because this force acts and this force becomes a thrust.

The outer yoke 52 is provided in a cylindrical shape so as to surround the outer periphery of the electromagnetic coils 50a and 50b. The outer yoke 52 is made of a magnetic material, and is provided to increase the number of magnetic fluxes linked to the electromagnetic coils 50a and 50b so that the electromagnetic force is effectively applied to the mover 10. Further, since the flange portion 15b is erected in the axial direction around the inner yokes 14a and 14b constituting the mover 10, the magnetic flux generated from the magnet 12 is transferred to the inner yoke 1.
The magnetic resistance of the magnetic circuit from 4a, 14b to the outer yoke 52 can be lowered.
Thereby, while increasing the total magnetic flux amount which acts from the needle | mover 10 (a magnetic path is ensured),
By causing the magnetic flux generated by the magnet 12 to interlink with the current flowing through the electromagnetic coils 50a and 50b at right angles to the axial direction, the movable element 10 can effectively generate axial thrust. Further, since the mover 10 according to this configuration has a lighter mass than the generated thrust, a high-speed response is possible and the output flow rate can be increased.

When the upper frame 20a and the lower frame 20b are combined, the electromagnetic coils 50a and 50b and the outer yoke 52 are fitted into the fitting grooves 2 provided in the upper frame 20a and the lower frame 20b.
8 can be assembled concentrically with the cylinder portion 24 by fitting the outer yoke 52 to the cylinder 8.

The mover 10 is reciprocally driven (moved up and down) by the action of electromagnetic force generated by the electromagnetic coils 50a and 50b by applying an alternating current to the electromagnetic coils 50a and 50b. The electromagnetic force generated by the electromagnetic coils 50a and 50b pushes the mover 10 in one direction and the other depending on the energization direction of the electromagnetic coils 50a and 50b.
By controlling the energization time and the energization direction to a and 50b, the movable element 10 can be reciprocated with an appropriate stroke. When the movable element 10 contacts the inner surfaces of the frame main bodies 22a and 22b, the shock can be absorbed by the action of the damper 32.

The pumping action of the electromagnetic pump of the present embodiment is achieved by the action of the fluid being alternately sucked into the pump chambers 30a and 30b and sent out by reciprocating the mover 10 by the electromagnetic coils 50a and 50b. That is, when the mover 10 moves downward in the state of FIG. 1, the fluid is introduced into one pump chamber 30a, and at the same time, the fluid is delivered from the other pump chamber 30b. Conversely, when the mover 10 moves upward, the fluid is sent out from one pump chamber 30a, and the fluid is introduced into the other pump chamber 30b. Thus, the fluid is sucked and discharged when the mover 10 moves to either side, and the fluid pulsation can be suppressed and the fluid can be transported efficiently.

In the electromagnetic pump of this embodiment, inner yokes 14a and 14b having flange portions 15b are attached to the mover 10, and suction valves 34a and 34b are provided close to both end faces of the mover 10.
By providing the delivery valves 36a and 36b, it becomes possible to provide an extremely thin and small pump. In the case of the electromagnetic pump of the embodiment, the height is 15 mm and the width is 2
It can be formed into a small pump of about 0 mm.

Moreover, the electromagnetic pump of this embodiment can be used for transport of gas or liquid, and the kind of fluid is not limited. When using as a liquid pump, if a single mover 10 has insufficient transport pressure, it is a multi-stage movable unit in which a plurality of identical unit movers comprising a magnet 12 and inner yokes 14a and 14b are connected. The child 10 may be used.
By connecting the unit movers in multiple stages, a mover having a large thrust can be obtained, and an electromagnetic pump having a required transport pressure can be obtained.

Reference example

Next, a configuration of the reciprocating motion detection unit of the above-described electromagnetic pump mover and a preferred reference example of the detection operation will be described with reference to FIGS. In FIG. 2, an air-core detection coil 53 for detecting the reciprocating motion of the mover 10 is fitted around the cylinder coaxially with the electromagnetic coils 50a and 50b. Specifically, the detection coil 53 is fitted around the cylinder adjacent to both end surfaces in the axial direction of the electromagnetic coil 50a and the electromagnetic coil 50b.

  The state of magnetic flux acting on the detection coil 53 according to the operating position of the mover 10 when the mover 10 reciprocates is shown in FIGS. 3 shows a state in which the mover 10 is displaced upward in the movable range, FIG. 4 shows a state in which the mover 10 is displaced to the center, and FIG. 5 shows a state in which the mover 10 is displaced downward. The amount of magnetic flux interlinked with the detection coil 53 becomes maximum when the mover 10 is displaced to the center of the movable range (state of FIG. 4), and when the mover 10 is displaced upward or downward (FIGS. 3 and 5). In the state). The mover 10 repeats reciprocation in the order of FIG. 3 → FIG. 4 → FIG. 5 → FIG. 4 → FIG. While the mover 10 reciprocates once, increase / decrease in the amount of magnetic flux passing through the detection coil 53 occurs two cycles. Therefore, the induced voltage generated in the detection coil 53 is also generated in two cycles. Note that the detection operation by the detection coil 53 may be performed only while the mover 10 moves between FIGS. 3 and 4 or only while the mover 10 moves between FIGS. 4 and 5. good. In this case, the induced voltage generated in the detection coil 53 during one reciprocation of the mover 10 is one cycle. Further, the inner yokes 14 a and 14 b may be omitted from the mover 10.

Next, an embodiment of the reciprocating motion detection unit of the mover of the electromagnetic pump will be described with reference to FIG. The same members as those in FIG. In FIG. 6, the detection coil 53 is the same in that it is fitted adjacent to both end surfaces in the axial direction of the electromagnetic coil 50a and the electromagnetic coil 50b around the cylinder. In this embodiment, yokes 26 a and 26 b made of a magnetic material are provided on both end surfaces in the axial direction of the detection coil 53, and an outer yoke 52 is provided on the outer peripheral surface of the detection coil 53. Thus, a magnetic circuit is formed in which the magnetic flux generated from the mover 10 passes through the yoke 26a, the outer yoke 52, and the yoke 26b. As a result, the number of magnetic fluxes linked to the detection coil 53 among the magnetic fluxes generated from the mover 10 increases, so that the induced voltage value generated in the detection coil 52 can be increased to improve the detection sensitivity. The outer yoke 52 can be omitted if the yokes 26a and 26b are provided on both end surfaces in the axial direction of the detection coil 53.

Next, an application example based on detection of the reciprocating motion of the mover of the electromagnetic pump will be described with reference to FIGS. The same members as those in FIG. The present embodiment is characterized in that the flow rate of the pump is detected based on the induced voltage detected by the detection coil 53. That is, the flow rate of the pump depends on the speed V at which the mover 10 reciprocates and the cross-sectional area S of the mover 10.
And product. If the speed V at which the mover 10 reciprocates increases, the flow rate of the pump increases and the induced voltage of the detection coil also increases. Therefore, in FIG. 7, the flow rate of the pump can be estimated by the magnitude of the amplitude of the induced voltage generated in the detection coil 53.

  In FIG. 8, it is also possible to determine whether or not the mover 10 is reciprocating by setting a threshold value based on the induced voltage detected by the detection coil 53. That is, a threshold voltage corresponding to a constant flow rate is set in the induced voltage of the detection coil 53. Then, the detected induced voltage and the threshold voltage are compared by a comparator circuit or the like and converted into a pulse output. A pulse is generated when the flow rate is larger than the constant flow rate, and no pulse is generated when the flow rate is smaller than the constant flow rate. Further, when the electromagnetic coils 50a and 50b are energized from the controller or the like under certain conditions, the upper limit or lower limit of the amplitude range of the induction voltage of the detection coil 53 when the mover 10 operates normally. By using as a threshold voltage, it is also possible to detect whether or not the pump movable element 10 is operating normally.

Next, an application example based on detection of the reciprocating motion of the mover of the electromagnetic pump will be described with reference to FIGS. The same members as those in FIG. The present embodiment is characterized in that drive control of the mover 10 is performed based on the induced voltage detected by the detection coil 53. In other words, feedback control is performed with a control unit (not shown) so that the mover 10 operates normally, thereby controlling the energization amount to the electromagnetic coils 50a and 50b, controlling the pump flow rate, The movable range of the child 10 is the upper and lower frame bodies 22a, 22
It can be controlled not to hit b.

Furthermore, it is desirable to detect the induction voltage of the detection coil in a detection voltage range in which the fluctuation of the induction voltage caused by excitation of the electromagnetic coils 50a and 50b is small. There are electromagnetic coils 50a and 50b above and below the detection coil 53, and an induced voltage is generated in the detection coil 53 due to a change in current of the electromagnetic coils 50a and 50b. FIG. 9 shows a graph of the induced voltage of the detection coil 53 including the influence of the current change amount of the electromagnetic coils 50a and 50b. Immediately after switching the excitation directions of the electromagnetic coils 50a and 50b, the amount of change in the current value with respect to time is large, and the influence on the induced voltage of the detection coil 53 is large. Therefore, when the amount of current change of the electromagnetic coils 50a and 50b is small, that is, the induced voltage generated by the reciprocating motion of the mover 10 is the negative side in FIG. 9, the induced voltage waveform (A portion and B in the graph of FIG. 9). By providing a voltage threshold at (portion), it is possible to reduce the influence of current changes in the electromagnetic coils 50a and 50b. In FIG. 9, when the amount of current change in the electromagnetic coils 50a and 50b in the A part and the B part is large, the average value of the induced voltages in the A part and the B part is calculated, and the pulse widths in the A part and the B part are calculated. The average value may be calculated by detection, or only the frequency component of the induced voltage of the detection coil 53 (the double component of the reciprocating frequency of the mover 10) may be detected.

FIG. 9 shows the case where the frequency of the induced voltage of the detection coil 53 is twice the reciprocating frequency of the mover 10, but the frequency is the same. The induced voltage of the detection coil 53 is peaked at the C part and the D part.
However, it is difficult to detect whether the reciprocating motion of the mover 10 is appropriate because both are similarly affected by the current change of the electromagnetic coils 50a and 50b. Therefore, by making the frequency of the induced voltage of the detection coil 53 twice the reciprocating frequency of the mover 10,
It turns out that it becomes easy to detect the propriety of the reciprocating motion of the needle 10.

The electromagnetic pump shown in FIG. 1 communicates suction flow paths 38a and 38b provided on one side and the other side of the mover 10, and is used for sending on the one side and the other side of the mover 10. Flow path 40a,
In this example, the flow paths 40b are connected in parallel, and the flow paths are connected in parallel. However, a plurality of electromagnetic pumps may be used in series with the flow paths. In this case, the delivery channel 40a may be communicated with the suction channel 38b, or the delivery channel 40b may be communicated with the suction channel 38a.

It is sectional drawing which shows the structure of the electromagnetic pump which concerns on this invention. It is sectional drawing which shows the principal part structure of the electromagnetic pump which concerns on a reference example. It is state explanatory drawing of the magnetic flux which acts on a detection coil by the movement of a needle | mover. It is state explanatory drawing of the magnetic flux which acts on a detection coil by the movement of a needle | mover. It is state explanatory drawing of the magnetic flux which acts on a detection coil by the movement of a needle | mover. It is a cross-sectional view showing the essential structure of the electromagnetic pump according to the actual施例. It is a graph of the flow rate detecting electromagnetic pump according to the actual施例. It is a graph of the flow rate detecting electromagnetic pump according to the actual施例. Is a graph illustrating the operation detection of the electromagnetic pump armature according to actual施例. Is a graph illustrating the operation detection of the electromagnetic pump armature according to actual施例. It is a fragmentary sectional view which shows the operation | movement detection of the conventional needle | mover.

DESCRIPTION OF SYMBOLS 10 Movable element 12 Magnet 14a, 14b Inner yoke 15a Flat plate part 15b Flange part 16 Sealing material 20a Upper frame 20b Lower frame 22a, 22b Frame main body 24 Cylindrical part 28 Fitting groove 29 Sealing material 30a, 30b Pump chamber 32 Damper 34a , 34b Suction valve 36a, 36b Delivery valve 38a, 38b Suction channel 40a, 40b Delivery channel 42, 44 Communication pipe 50a, 50b Electromagnetic coil 52 Outer yoke

Claims (1)

A mover in which a flange portion serving as a magnetic flux acting surface is formed on the outer peripheral surface portion of a magnetic body provided on both surfaces of a disk-shaped permanent magnet is accommodated in a cylinder, and a plurality of fittings are fitted around the cylinder in opposite directions. an electromagnetic pump for transporting fluid from the movable element is reciprocated in the axial direction in the cylinder pumping chamber formed in the cylinder by energizing the air core of the electromagnetic coil is set to flow a current of There ,
An air-core detection coil that detects the reciprocating motion of the mover around the cylinder is fitted adjacent to the axial end face of the detection coil that is coaxial with the electromagnetic coil, and both end faces in the axial direction of the detection coil A yoke is provided adjacent to the outer peripheral surface of the detection coil, and an outer yoke is provided on the outer peripheral surface of the detection coil. Magnetic flux generated from the mover along with the reciprocation of the mover is applied to one yoke, the outer yoke, and the other. Utilizing the fact that the magnetic flux passing through the yoke increases the amount of magnetic flux linked to the detection coil, the amount of change in the current flowing to the electromagnetic coil is small, and the variation in the induced voltage due to the excitation of the electromagnetic coil is small. An electromagnetic pump characterized in that a threshold is provided in a detection range to detect the position of the mover .

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