Linear motor with built-in LVDT

Abstract

In the linear motor which drives a driving part of a hydraulic device in a reciprocating manner, a permanent magnet is provided with a first magnet on the near side of the hydraulic device and a second magnet on the far side of the hydraulic device which are divided into two parts in the length direction, and is provided with a first coil and a second coil which are arranged at intervals and are wound on a coil framework in opposite directions. An LVDT housing member in which a solenoid coil constituting an LVDT is embedded in a region further forward than the end of the first magnet closer to the hydraulic device is provided so as to protrude from the end of the inner yoke on the hydraulic device side. An iron core of an LVDT, which moves linearly inside the solenoid coil along with the bobbin, is connected to a protruding part extending in a substantially tapered shape from the end edge of the cylindrical body of the bobbin, and the linear motor is further provided with a magnetic ring made of a soft magnetic material, which is disposed so as to abut against the end of the first magnet, which is close to the hydraulic device.

Description

Technical Field

[0001] The present invention relates to a linear motor for driving a valve body of a direct-acting servo valve in the axial direction thereof, and more particularly to a linear motor having a built-in LVDT as a valve body position detector so as to suppress the influence of magnetic flux of a permanent magnet. Background Art

[0002] In direct-acting servo valves that are required to be compact and highly responsive, a linear motor consisting of a cylindrical voice coil, the so-called voice coil motor (VCM), has been used as the valve core drive source. Figure 8 As shown in FIG. 1 , such a linear motor is generally configured by coaxially arranging a cylindrical permanent magnet 34 fixed to the inner side of the outer yoke 31 in an annular space 33 between a cylindrical outer cylindrical member (outer yoke) 31 and an inner yoke 32 coaxially arranged at the center thereof, a coil bobbin 35 made of a non-magnetic material arranged inside the outer yoke 32 and a cylindrical coil 36 wound around the outer circumference of the coil bobbin 35. The coil 36 is linearly moved in the direction of the central axis X along the coil bobbin 35 as a mover (movable coil) by the thrust generated by passing a current through the coil 36 in the magnetic field generated by the permanent magnet 34. Therefore, the valve core 40 connected to the front end of the tapered protrusion 35P extending from the cylindrical main body of the coil bobbin 35 moves linearly in the sleeve of the valve body 50, and the opening and closing of each port provided in the valve body 50 and the switching of the communication between the ports are performed.

[0003] According to such a linear motor, compared with the case of using an iron core as a mover, the coil as the movable part does not require an inductance component for magnetizing the iron core, and accordingly, the current response is high, and the valve core connected to the coil frame moves linearly. Therefore, compared with other actuators, the action responsiveness is excellent, and high-speed drive and high-precision positioning can be achieved.

[0004] In addition, in the direct-acting servo valve, a position detector for controlling the position of the valve core is provided. This position detector is mostly a position detector that uses a linear voltage differential transformer (LVDT) as a displacement sensor to detect the displacement of the mechanical linear motion. A general LVDT is composed of three solenoid coils, namely a primary coil wound around the center of the iron core and secondary coils on both sides of the primary coil. When the iron core linked to the valve core moves in these coils while the primary coil is excited and an electromotive force is generated in each secondary coil, the mutual inductance of the two secondary coils corresponding to the primary coil changes according to the amount of movement, and a voltage corresponding to the difference in the induced voltage of the two coils is output. Therefore, by detecting the change in the output signal level, the displacement of the iron core, that is, the movement of the valve core, can be measured. Therefore, the valve core position detected based on the movement is feedback controlled.

[0005] However, such a magnetic displacement sensor has a problem in detection accuracy when it is affected by the magnetic flux of the permanent magnet, and therefore, an LVDT is provided on the opposite side of the valve core to the linear motor (for example, refer to Patent Documents 1, 2, and 3).

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 62-278303

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 63-259203

[0010] Patent Document 3: Japanese Patent Application Publication No. 2007-187296

[0011] Patent Document 4: Japanese Patent Application Laid-Open No. 06-300007 Summary of the invention

[0012] Problems to be solved by the invention

[0013] In addition, in a structure in which a linear motor is arranged on one of the two ends of the valve core of the valve body and an LVDT is arranged on the other end, the device structure including wiring is complicated and handling becomes troublesome, so a structure in which the LVDT and a cylindrical voice coil are integrated and arranged on one end side of the valve core can be considered (for example, refer to Patent Document 4). In this case, the degree of freedom of the structure of the valve body itself is also improved compared to a case in which both end sides of the valve core are constrained.

[0014] Therefore, in the case of constructing a linear motor with a built-in LVDT in which the LVDT and the cylindrical voice coil are integrated, the following considerations are firstly made: Figure 8As shown in the schematic longitudinal sectional view, the LVDT is arranged in a hollow area at the center of the inner yoke, which is an area with little magnetic flux leakage.

[0015] However, in the case of seeking further miniaturization and higher thrust of the linear motor, if the magnetic flux density is increased while suppressing the radial dimension in the cylindrical voice coil, the magnetic flux leakage to the inside of the inner yoke becomes significant, and it is no longer possible to arrange the LVDT inside the center. Therefore, for example, it is conceivable to set a large intermediate block with a built-in LVDT between the yoke and the valve body, but this will go against the miniaturization of the linear motor.

[0016] In view of the above problems, an object of the present invention is to provide a small-sized high-thrust linear motor capable of incorporating an LVDT without being affected by magnetic flux leakage.

[0017] Solutions to Solve Problems

[0018] In order to achieve the above-mentioned purpose, the linear motor with built-in LVDT of the invention described in Technical Solution 1 comprises an outer member and an inner magnetic yoke arranged at the center of the internal space of the outer member and connected to the outer member at the end. In the space formed between the outer member and the inner magnetic yoke, there are arranged a permanent magnet fixed to the inner side of the outer member, a coil frame made of non-magnetic material arranged to be linearly movable on the inner side of the permanent magnet and the outer side of the inner magnetic yoke, and a coil wound on the outer periphery of the coil frame. By controlling the power supply of the coil, the driving part of the hydraulic device is reciprocated through the coil frame that moves linearly together with the coil.

[0019] It is characterized in that

[0020] The internal space of the outer casing, the inner yoke, the coil bobbin, and the coil each have a substantially cylindrical shape and are coaxially arranged with each other.

[0021] The permanent magnet is divided into two in the longitudinal direction, including a first magnet arranged on the proximal side of the hydraulic device and a second magnet arranged on the distal side of the hydraulic device.

[0022] The coil includes a first coil and a second coil arranged at a distance from each other.

[0023] The first coil and the second coil are formed by winding coil wires in opposite directions to each other, and the first magnet and the second magnet have magnetic pole directions in opposite directions in the radial direction.

[0024] The coil frame includes a cylindrical body and a protrusion, the cylindrical body is wound around the first coil and the second coil, the protrusion extends from the end edge of the cylindrical body in a substantially conical shape, and transmits the linear motion to the driving part of the hydraulic device at its front end.

[0025] An LVDT housing member is protrudingly provided at the end of the inner yoke on the hydraulic device side, and the LVDT housing member has a solenoid coil constituting a linear voltage differential transformer (LVDT) built in a region forward of an end of the first magnet close to the hydraulic device.

[0026] The iron core of the linear voltage differential transformer is connected to the protruding portion of the coil bobbin, and the iron core moves linearly inside the solenoid coil built into the LVDT housing member as the coil bobbin moves linearly.

[0027] The linear motor further includes a magnetic ring made of a soft magnetic material, and the magnetic ring is arranged to abut against an end portion of the first magnet that is close to the hydraulic device.

[0028] The linear motor with built-in LVDT of the invention described in claim 2 is the linear motor with built-in LVDT described in claim 1, wherein the length of the first magnet in the longitudinal direction of the cylindrical permanent magnet is smaller than the length of the second magnet.

[0029] The linear motor with built-in LVDT of the invention described in claim 3 is the linear motor with built-in LVDT described in claim 2, characterized in that a division ratio of the first magnet to the second magnet in the length direction of the cylindrical permanent magnet is 35:65.

[0030] The linear motor with built-in LVDT of the invention described in Technical Solution 4 is a linear motor with built-in LVDT described in any one of Technical Solutions 1 to 3, characterized in that the first magnet and the second magnet are formed by combining multiple partial magnets magnetized in a predetermined direction into a circular ring shape in the circumferential direction.

[0031] Effects of the Invention

[0032] According to the linear motor with built-in LVDT of the present invention, by arranging the magnetic ring made of soft magnetic material at the terminal of the permanent magnet, the influence of leakage flux on LVDT can be well suppressed. Therefore, it is not necessary to set a large intermediate block for LVDT arrangement between the voice coil and the valve body, which will cause the device to be large-scale, and the LVDT can be built in the area adjacent to the permanent magnet, so that the linear motor can be miniaturized and have a high thrust. In addition, by appropriately making the proportion of the first magnet close to the LVDT in the entire length of the permanent magnet in the longitudinal direction smaller than that of the second magnet, the leakage flux suppression effect with respect to the LVDT brought by the magnetic ring can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 1 is a schematic structural diagram of a linear motor according to an embodiment of the present invention, wherein (a) is a side sectional view showing the main body portion excluding peripheral structures such as wiring in a stroke neutral state of the voice coil, (b) is a G-G arrow view of (a) and a sectional view showing the end face of the second magnet, and (c) is a F-F arrow view of (a) and a sectional view showing only the magnetic ring.

[0034] Figure 2 The (a) is in Figure 1 The effective stroke length K of the main body of the linear motor shown is a side sectional view showing a state of retreating a stroke distance K / 2 at the upper part and a state of advancing a stroke distance K / 2 at the lower part, (b) is a schematic enlarged view illustrating the coil thrust at the interval g within the circle T in (a), and (c) is a schematic enlarged view illustrating the coil thrust when there is no interval g as a comparison with (b).

[0035] Figure 3 As Figure 1 A schematic configuration diagram of a linear motor is shown in which the division ratio of the permanent magnet in the longitudinal direction is set to 2 equal parts as a comparative example of the embodiment.

[0036] Figure 4 (a) is Figure 1 The magnetic field distribution diagram of the linear motor, (b) is as Figure 1 Magnetic field distribution diagram of a control example of a linear motor without a magnetic ring.

[0037] Figure 5 (a) is Figure 3 The magnetic field distribution diagram of the linear motor, (b) is as Figure 3 Magnetic field distribution diagram of a control example of a linear motor without a magnetic ring.

[0038] Figure 6 As Figure 1The LVDT characteristics of a linear motor are plotted in a graph showing the output (V) on the vertical axis and the core stroke distance (mm) on the horizontal axis when the coil of the linear motor is energized (solid line) and de-energized (dashed line).

[0039] Figure 7 The output (V) is plotted on the vertical axis against the core stroke distance (mm) on the horizontal axis when the coil of the linear motor is energized (solid line) and de-energized (dashed line). Figure 1 A graph showing LVDT characteristics of a control example of a linear motor without a magnetic ring.

[0040] Figure 8 This is a schematic longitudinal sectional view showing the structure of an example of a conventional linear motor with built-in LVDT. DETAILED DESCRIPTION

[0041] The present invention is a linear motor, which includes an outer casing and an inner yoke arranged at the center of its internal space. In the space formed between the outer casing and the inner yoke, there are arranged a permanent magnet fixed to the inner side of the outer casing, a coil frame made of non-magnetic material arranged to be linearly movable on the inner side of the permanent magnet and the outer side of the inner yoke, and a coil wound on the outer periphery of the coil frame. By controlling the energization of the coil, the drive part of the hydraulic device is reciprocated through the coil frame that moves linearly together with the coil. In the present invention, the internal space of the outer casing, the inner yoke, the coil frame and the coil each have a substantially cylindrical shape and are arranged coaxially with each other. The permanent magnet is divided into two in the length direction thereof, and includes a first magnet arranged on the proximal side of the hydraulic device and a second magnet arranged on the distal side of the hydraulic device. The coil includes a first coil and a second coil arranged with a spacing therebetween, and the first coil and the second coil are wound in opposite directions. The linear motor is formed by a line, and the first magnet and the second magnet have magnetic pole directions in opposite directions in the radial direction. The coil skeleton has a cylindrical body and a protrusion, and the first coil and the second coil are wound around the outer circumference of the cylindrical body. The protrusion extends from the end edge of the cylindrical body in a roughly conical shape and transmits the linear motion to the driving part of the hydraulic device at its front end. An LVDT housing component is protrudingly provided at the end of the inner magnetic yoke on the hydraulic device side. The LVDT housing component has a solenoid coil constituting a linear voltage differential transformer (LVDT) built in an area forward of the end of the first magnet close to the hydraulic device. The core of the linear voltage differential transformer is connected to the protrusion of the coil skeleton. The core moves linearly inside the solenoid coil built in the LVDT housing component as the coil skeleton moves linearly. The linear motor also has a magnetic ring made of soft magnetic material, and the magnetic ring is arranged in contact with the end of the first magnet close to the hydraulic device.

[0042] The permanent magnet of the linear motor is set to a length that can fully fill the moving area of ​​the movable part so that the coil can obtain a uniform magnetic field, so as to avoid the change of thrust caused by the change of the magnetic field. According to the above structure of the present invention, the permanent magnet is divided into two magnets, the first magnet and the second magnet, in the length direction. The polarities of the divided magnets are different. Therefore, the magnetic flux between the magnets of different polarities increases compared with the magnetic flux of the same polarity passing through the yoke, and the magnetic flux density in the inner direction is increased compared with the case of no division. As a result, the thrust can be increased without increasing the size of the cylindrical voice coil in the radial direction.

[0043] In addition, at this time, the first coil and the second coil are formed of coil wires wound around the outer circumference of the coil frame in opposite directions on the inner side of the two permanent magnets in the areas facing each other. The two first magnets and the second magnets corresponding to the first coil and the second coil respectively form a magnetic circuit with each coil with the magnetic pole directions in the radial direction opposite to each other, and the thrust becomes larger than the case of magnets and coils composed of the same polarity.

[0044] Furthermore, in the present invention, a linear voltage differential transformer (hereinafter referred to as LVDT) consisting of a solenoid coil built into an LVDT housing member protruding from the end of the inner magnetic yoke on the hydraulic device side and an iron core connected to the protruding portion of the coil frame is arranged at a position least susceptible to the leakage flux of the permanent magnet, such as an area in front of the end of the first magnet close to the hydraulic device, and a magnetic ring made of a soft magnetic material is arranged in contact with the end of the first magnet close to the hydraulic device, that is, the terminal end of the permanent magnet. Therefore, the magnetic ring can function as a magnetic shielding member to further suppress the influence of the leakage flux on the LVDT, and there is no need to provide a large intermediate block for configuring the LVDT between the voice coil and the valve body, so that a small high-thrust linear motor that can ensure good LVDT characteristics can be realized.

[0045] In addition, as the material of the magnetic ring of the present invention, any soft magnetic material is sufficient, but as a magnetic ring that exerts the effect of suppressing leakage magnetic flux, the higher the magnetic permeability and the smaller the coercive force, the more preferred. For example, permalloy can be cited, and other materials that are free-cutting pure iron, carbon steel, etc. with lower cost are also preferred. In addition, the outer casing is a magnetic shell, which functions as an outer yoke by being composed of the same type of soft magnetic material as the inner yoke.

[0046] As described above, in the present invention, the influence of magnetic flux leakage on the LVDT is avoided mainly by configuring the magnetic ring at the terminal of the permanent magnet, and this effect can be further improved by further reducing the influence from the first magnet. That is, the length of the first magnet in the longitudinal direction of the permanent magnet can be made smaller than the length of the second magnet.

[0047] The shorter the first magnet is, the better the effect is. However, if it is too short, it is difficult to ensure sufficient thrust. Therefore, it is preferable to maintain the lower limit condition that most effectively ensures sufficient thrust and suppresses the influence of leakage flux. This condition is to set the total length of the permanent magnet in the longitudinal direction to 100 and the division ratio of the first magnet to the second magnet to 35:65.

[0048] In addition, the first magnet and the second magnet are respectively annular magnets having magnetic pole directions in the radial direction, but it is difficult to manufacture an integral annular magnet that is well magnetized in the radial direction to have a high magnetic flux density, so it can be manufactured in a simpler splitting method. That is, the unmagnetized hard magnetic body formed into an annular shape is equally divided into a plurality of parts in the circumferential direction, and after magnetizing the divided parts in the radial direction of a predetermined direction, the magnetized divided parts are combined into an annular shape, thereby forming an annular magnet.

[0049] Example

[0050] As an embodiment of the present invention, Figure 1 The schematic structure diagram shows a linear motor with built-in LVDT, in which a permanent magnet is divided into a first magnet and a second magnet in the length direction, and an LVDT is integrally combined with a voice coil having two first coils and a second coil corresponding to each magnet. Figure 1 (a) is a side sectional view of the main body excluding peripheral structures such as wiring. Figure 1 (b) is a cross-sectional view of (a) taken along the arrow GG and showing the end face of the second magnet, and (c) is a cross-sectional view of (a) taken along the arrow FF and showing only the magnetic ring. Figure 3 As a comparative example of this embodiment, the Figure 1 A schematic cross-sectional view of a linear motor in which a division ratio between the first magnet and the second magnet in the longitudinal direction of the permanent magnet is different.

[0051] The linear motor 10 of the present embodiment includes an outer casing 11 and a cylindrical inner yoke 12, wherein an annular space 13 is formed between the outer casing 11 and the inner yoke 12. The outer casing 11 is formed by hollowing out the inside of a prismatic member into a cylindrical shape to form an inner space, and the inner yoke 12 is coaxially arranged at the center of the cylindrical inner space and connected to the outer casing 11 at the rear end. A cylindrical permanent magnet 14 and a coil bobbin 15 made of a non-magnetic material are coaxially arranged in the annular space 13. The permanent magnet 14 is fixed to the inner side of the outer casing 11, and the coil bobbin 15 is arranged inside the permanent magnet 14 and outside the inner yoke 12 so as to be linearly movable in the direction of the central axis X. A coil 16 forming a magnetic circuit with the permanent magnet 14 is cylindrically wound around the outer periphery of the coil bobbin 15 to form a voice coil.

[0052] Therefore, the linear motor 10 can reciprocate a driving part, such as a valve core, of a hydraulic device (not shown) such as a direct-acting servo valve located on the left side of the drawing by controlling the power supply of the coil 16, via the coil frame 15 that moves linearly along the central axis X direction together with the coil 16. Here, the hydraulic device side, that is, the left side when facing the drawing, is set as the front, and the right side is set as the rear.

[0053] Furthermore, in the present embodiment, the permanent magnet 14 is composed of two annular first magnet 14A and second magnet 14B divided in the length direction, the rear end of the first magnet 14A and the front end of the second magnet 14B are arranged in abutment, and the corresponding coil 16 is also composed of two first coil 16A and second coil 16B. Moreover, in the first magnet 14A and the second magnet 14B, the magnetic pole directions in the radial direction are opposite to each other, and the first coil 16A and the second coil 16B are respectively formed into cylindrical shapes by winding the same coil wire (not necessarily the same coil wire) in opposite directions at a prescribed interval on the outer periphery of the coil skeleton 15. In addition, the annular first magnet 14A and the second magnet 14B are formed by dividing the annular member into eight equal parts in the circumferential direction ( Figure 1 The divided parts 14p in (b) (divided at equal angular intervals α at about 44°) are respectively magnetized in the radial direction of a predetermined direction and then combined in the circumferential direction into a circular ring shape.

[0054] In addition, the coil frame 15 is provided with a protrusion 15P, which extends in a roughly conical shape from the front side edge of the cylindrical body on which the first coil 16A and the second coil 16B are wound around the outer circumference. By connecting the front end of the protrusion 15P to the end of the driving part of the hydraulic device, the linear motion of the coil frame 15 is transmitted to the driving part of the hydraulic device.

[0055] Furthermore, an LVDT housing member 17 extending toward the inner side of the protrusion 15P of the coil frame 15 is protruded from the end portion on the hydraulic device side, i.e., the front side, of the inner yoke 12. A hollow hole 18 is formed in the LVDT housing member 17 along the central axis X, and three solenoid coils constituting the LVDT, i.e., the primary coil S1 and two secondary coils S2 on both sides thereof, are built in coaxially with the central axis X in the area around the hollow hole 18 that is closer to the front side than the front side end portion of the first magnet 14A. On the other hand, the core C of the LVDT is coaxially connected with the central axis X to the protrusion 15P of the coil frame 15 in a manner extending toward the rear side, and the core C is a structure that moves linearly inside the hollow hole 18 of the LVDT housing member 17, i.e., inside the solenoid coils (S1, S2), as the coil frame 15 moves linearly.

[0056] Therefore, in this embodiment, the LVDT is built in a position where the influence of the leakage magnetic flux in the area forward of the front terminal of the voice coil is minimized. In addition, a magnetic ring 19 made of a soft magnetic material is arranged in contact with the front terminal of the permanent magnet 14 to suppress the influence of the magnetic flux leakage on the LVDT. In addition, in this embodiment, the total length L of the permanent magnet 14 in the longitudinal direction is set to 100, and the division ratio of the first magnet 14A and the second magnet 14B is set to 35:65, so that the length 14A1 of the first magnet 14A in the longitudinal direction is smaller than the length 14B1 of the second magnet 14B in the longitudinal direction, thereby suppressing the magnetic flux density flowing to the LVDT. In addition, as for the length of the first coil 16A and the second coil 16B in the direction of the central axis X, since each coil is meaningless if it is outside the range of the magnetic flux formed by the corresponding first magnet 14A and the second magnet 14B, it is set to the minimum length considering the effective stroke length of the voice coil (coil frame 15 and coil 16).

[0057] In addition, a gap g is provided between the first coil 16A and the second coil 16B in the direction of the central axis X where no coil is formed. This gap g is equivalent to the effective stroke length K of the voice coil. Figure 2 As shown in (a), each coil (16A, 16B) will not enter the reverse polarity interval during the travel of the coil frame 15 in the front-to-back direction. Figure 2 As shown in (c), for example, when the coil frame 15 retreats a stroke distance K / 2, the rear end of the first coil 16A passes over the rear end position of the first magnet 14A without the gap g, a reverse thrust rt is generated relative to the thrust at of the first coil 16A, and the total thrust together with the thrust bt of the second coil 16B is reduced. Figure 2 (b) shows that the rear end of the first coil 16A does not exceed the rear end position of the first magnet 14A. Figure 1 In the stroke neutral state of (a), the first coil 16A has a length such that its rear end is located at a distance g / 2 in front of the rear end position of the first magnet 14A. Similarly, as a setting that the front end of the second coil 16B does not exceed the front end position of the second magnet 14B when the coil frame 15 advances a stroke distance K / 2, the second coil 16B has a length such that its front end is located at a distance g / 2 behind the front end position of the second magnet 14B in the stroke neutral state. As a result, a structure is formed in which a gap g is provided between the rear end of the first coil 16A and the front end of the second coil 16B.

[0058] Therefore, the magnetic field distribution in the linear motor 10 of this embodiment is analyzed. Figure 4 The analysis results are shown in (a) of the present invention, and, as a control, in Figure 4(b) shows the analysis result of the magnetic field distribution in the case of the same structure but without the magnetic ring 19. In these magnetic field distribution diagrams, the ellipse located downward toward the paper plane corresponds to the LVDT built-in area.

[0059] In addition, the analysis of the magnetic field distribution is performed by simulation using the analysis software: ANSYS Electronics Desktop 2019R2 Maxwell3D / Maxwell2D. The analysis conditions are set as follows: the axial force acting on the coil is calculated as thrust, the boundary conditions are set as insulating boundary (Insulating) for 3D and balloon (Ballon) for 2D, and the calculation area is set to be twice the size of the analysis model from the coordinate center to the XYZ directions. In addition, the main parameters of the parameters of each component set are as follows.

[0060] First, the materials of each component are set as follows: the outer component 11 and the inner yoke 12 are made of free-cutting pure iron (ME1F), the LVDT housing component 17 is made of SUS, the permanent magnet 14 is made of a neodymium magnet (N48H or N48HT equivalent), the coil 16 is made of a polyester coated wire (PEW) with a diameter of 0.5 mm, and the magnetic ring 19 is made of free-cutting pure iron (ME1F). In addition, in this embodiment, the coil skeleton 15 is made of aluminum. In addition, it can also be made of a synthetic resin, such as a polyphenylene sulfide resin (PPS) containing 30% glass. In addition, a copper tube (C1100) is arranged on the inner periphery of the permanent magnet 14.

[0061] In addition, assuming that the total length L of the permanent magnet 14 in the longitudinal direction is 100, the size ratio of each component is as follows: the outer diameter y1 of the outer casing member 11 is 67.7, the outer diameter y2 of the inner yoke 12 is 38, the outer diameter M of the permanent magnet 14 is 60, the outer diameter B of the coil frame 15 and the coil 16 is 50, the outer diameter R1 of the magnetic ring 19 is 60, the inner diameter R2 is 48, and the length z in the direction of the central axis X is 4.3. In addition, the distance y3 of the LVDT built-in area in the direction of the central axis X of the LVDT housing member 17 is 41.3.

[0062] according to Figure 4 The results of (a) and (b) show that, in the linear motor 10 of the present embodiment, the magnetic flux leakage to the LVDT built-in position is reliably suppressed due to the presence of the magnetic ring 19 .

[0063] Here, in Figure 5 In the figure, the case with the magnetic ring 19 (a) and the case without the magnetic ring 19 (b) are shown for the comparative example. Figure 3 The analysis results of the magnetic field distribution of the linear motor 20 are shown. Figure 3The linear motor 20 has the same structure as the permanent magnet 24 except that the first magnet 24A and the second magnet 24B are divided into two equal parts at a ratio of 50:50 in the length direction of the permanent magnet 24. Figure 1 Therefore, in Figure 3 In, with Figure 1 The same reference numerals are used to denote common parts.

[0064] according to Figure 5 The analysis results show that the leakage flux suppression effect at some LVDT built-in positions can be observed through the magnetic ring 19. Figure 4 By comparison, it can be seen that the leakage flux suppression effect of the magnetic ring 19 is greatly improved by setting the division ratio of the permanent magnets in the longitudinal direction such that the first magnet is shorter than the second magnet.

[0065] In addition, Figure 6 The LVDT characteristics of the linear motor 10 of this embodiment are shown in the line diagram of Figure 7 The graphs of show the LVDT characteristics without a magnetic ring. Each graph plots the output value (V) on the vertical axis relative to the stroke distance (mm) of the core C on the horizontal axis. The output values ​​when the core C is mechanically moved when the coil 16 is energized (current 3A) and when it is not energized are represented by solid and dotted lines, respectively.

[0066] exist Figure 7 In the case of the non-magnetic ring 19, even if the mechanical movement of the core C is the same, the output value of the LVDT will deviate due to the influence of the leakage flux when the coil is energized. Figure 6 As shown in FIG. 1 , there is no such deviation when the magnetic ring 19 is provided. That is, if the mechanical movement of the core C is the same when the coil 16 is energized (current 3A) and when it is not energized, the output of the LVDT is consistent, and it can be seen that the magnetic ring 19 suppresses the influence of the leakage flux on the LVDT in this embodiment.

[0067] As described above, according to the linear motor 10 of this embodiment, even if an LVDT is built into the area adjacent to the permanent magnet 14, by arranging the magnetic ring 19 made of soft magnetic material at the terminal end of the permanent magnet 14 and appropriately making the proportion of the first magnet 14A close to the LVDT in the entire length of the permanent magnet 14 in the longitudinal direction smaller than that of the second magnet 14B, the influence of the leakage magnetic flux on the LVDT can be well suppressed. Therefore, there is no need to set a large intermediate block for LVDT configuration between the voice coil and the valve body, which will cause the device to be enlarged, and the linear motor with a built-in LVDT can be miniaturized and have a higher thrust.

[0068] Furthermore, the materials of the components of the linear motor of the present invention are not limited to those used in the above-mentioned embodiments, and it is needless to say that any components having properties of the same degree may be substituted.

[0069] Industrial Applicability

[0070] The linear motor with built-in LVDT of the present invention can be used not only as a driving unit of a direct-acting servo valve requiring high responsiveness, but can also be incorporated into various precision micro-motion mechanisms requiring high-speed driving and high-precision positioning.

[0071] Description of Reference Numerals

[0072] 10, 20, 30: Linear motor

[0073] 11, 31: Exterior components

[0074] 12, 32: Inner yoke

[0075] 13, 33: Ring Space

[0076] 14, 24, 34: Permanent magnets

[0077] 14A, 24A: First magnet

[0078] 14B, 24B: Second magnet

[0079] 14p: Split part

[0080] 15, 35: Coil skeleton

[0081] 15P, 35P: protrusion

[0082] 16, 36: Coil

[0083] 16A: First coil

[0084] 16B: Second coil

[0085] g: The distance between the first coil and the second coil

[0086] K: Effective stroke length

[0087] at: thrust of the first coil

[0088] rt: thrust in the opposite direction to at

[0089] bt: thrust of the second coil

[0090] 17: LVDT housing components

[0091] 18: Hollow hole

[0092] 19: Magnetic ring

[0093] S1: Primary coil

[0094] S2: Secondary coil

[0095] C: Iron core

[0096] X: Center axis

[0097] L: Total length of permanent magnet

[0098] 14Al: Length of the first magnet in the longitudinal direction

[0099] 14Bl: Length of the second magnet

[0100] y1: Outer diameter of the outer component

[0101] y2: outer diameter of inner yoke

[0102] y3: Distance of LVDT built-in area

[0103] M: outer diameter of permanent magnet

[0104] B: outer diameter of the coil frame

[0105] R1: outer diameter of magnetic ring

[0106] R2: Inner diameter of magnetic ring

[0107] z: The length of the central axis of the magnetic ring

[0108] 40: Valve core

[0109] 50: Valve body.

Claims

1. A linear motor with a built-in LVDT, the linear motor comprising an outer casing and an inner yoke disposed at a central portion of an inner space of the outer casing, wherein a permanent magnet fixed to the inner side of the outer casing, a coil frame made of a non-magnetic material disposed linearly movably on the inner side of the permanent magnet and the outer side of the inner yoke, and a coil wound around the outer periphery of the coil frame are disposed in a space formed between the outer casing and the inner yoke, wherein the driving portion of a hydraulic device is reciprocally driven via the coil frame that linearly moves together with the coil by controlling the power supply to the coil, It is characterized in that The internal space of the outer casing, the inner yoke, the coil bobbin, and the coil each have a substantially cylindrical shape and are coaxially arranged with each other. The permanent magnet is divided into two in the longitudinal direction, including a first magnet arranged on the proximal side of the hydraulic device and a second magnet arranged on the distal side of the hydraulic device. The coil includes a first coil and a second coil arranged at a distance from each other. The first coil and the second coil are formed by winding coil wires in opposite directions to each other, and the first magnet and the second magnet have magnetic pole directions in opposite directions in the radial direction. The coil frame includes a cylindrical body and a protrusion, the cylindrical body is wound around the first coil and the second coil, the protrusion extends from the end edge of the cylindrical body in a substantially conical shape, and transmits linear motion to the driving part of the hydraulic device at its front end. An LVDT housing component is protrudingly provided at the end of the inner yoke on the hydraulic device side, and the LVDT housing component has a solenoid coil constituting a linear voltage differential transformer, i.e., an LVDT, built in a region forward of the end of the first magnet close to the hydraulic device. The iron core of the linear voltage differential transformer is connected to the protruding portion of the coil bobbin, and the iron core moves linearly inside the solenoid coil built into the LVDT housing member as the coil bobbin moves linearly. The linear motor further includes a magnetic ring made of a soft magnetic material, and the magnetic ring is arranged to abut against an end portion of the first magnet that is close to the hydraulic device.

2. The linear motor with built-in LVDT according to claim 1, characterized in that: The length of the first magnet in the longitudinal direction of the cylindrical permanent magnet is smaller than the length of the second magnet.

3. The linear motor with built-in LVDT according to claim 2, characterized in that: Assuming that the total length of the cylindrical permanent magnet in the longitudinal direction is 100, the division ratio of the first magnet to the second magnet is 35:

65.

4. The linear motor with built-in LVDT according to any one of claims 1 to 3, characterized in that: The first magnet and the second magnet are each formed by combining a plurality of partial magnets magnetized in a predetermined direction into a circular ring shape in the circumferential direction.

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