Variable force generator and equipment including the same

Abstract

To provide a variable force generator capable of easily varying the generated force.SOLUTION: The variable force generator includes a case formed of a cylindrical ferromagnetic material extending in the axial direction, a stator disposed within the case, and a rod-shaped shaft disposed within the stator with a gap. The shaft is axially movable relative to the stator. The stator includes N (where N is an even number of 2 or greater) electromagnets arranged at equal angular intervals of (360 / N) degrees, generating magnetic flux radially toward the shaft. The shaft has at least a shaft portion made of magnetic material.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a variable force generator, and more particularly to a variable force generator that can be used as a thrust assist mechanism for assisting a linear motor used to drive a driven body in a vertical direction with thrust against gravity. [Background technology]

[0002] Linear motors are sometimes used to drive a driven object in a vertical direction. For example, in a dispensing device that draws in and dispenses small amounts of liquid, a linear motor is used to move the dispensing head, which is the driven object, up and down (moving it vertically).

[0003] Such a linear motor is composed, for example, of a motor shaft with a central axis extending in the vertical direction and a field coil arranged around the motor shaft. The motor shaft is made up of multiple permanent magnets magnetized in the axial direction, connected in series with the same magnetic poles facing each other, and fixed in place. The field coil is made up of multiple cylindrical coils connected in series so as to concentrically surround the motor shaft with a gap between them. Such a linear motor is configured, for example, with the motor shaft as the moving part and the field coil as the fixed part. A linear motor with such a configuration is called a fixed-coil linear motor or a moving-magnet linear motor.

[0004] On the other hand, unlike the fixed coil (moving magnet) linear motor described above, there is also known a linear motor configured so that the motor shaft is the fixed part and the field coil is the moving part. A linear motor with this configuration is called a fixed magnet linear motor or a moving coil linear motor.

[0005] In the fixed-coil (moving-magnet) linear motor described above, the field coil consists of at least three coils, U-phase, V-phase, and W-phase, to form a three-phase linear motor. In a three-phase linear motor, AC current with an electrical phase difference of 120 degrees flows through each coil, controlling the current flow to each coil. By controlling the current flow in this way, the three-phase linear motor is configured to generate thrust that drives the motor shaft in the central axis direction (vertical direction) due to the interaction between the magnetic field generated by the permanent magnet and the current flowing through the field coil (the so-called Fleming's left-hand rule).

[0006] In a fixed-coil (moving-magnet) linear motor with this configuration, when no current flows through the field coil, no electromagnetic force acts between the field coil and the permanent magnet. As a result, the motor shaft of the linear motor falls downward along with the driven object due to their gravity. For example, if the power supply that supplies current to the field coil suddenly fails, the driven object, including the motor shaft, will fall. This driven object may collide with equipment placed below the linear motor and cause damage to that equipment.

[0007] As mentioned above, linear motors are broadly divided into two types. Whether they are fixed coil (moving magnet) linear motors or fixed magnet (moving coil) linear motors, permanent magnets are arranged in series, alternating N and S positions, and operate by attraction and repulsion with the magnetic field of the field coil. Therefore, even in fixed magnet (moving coil) linear motors, if the field coil is not energized, the driven object will fall.

[0008] To prevent the driven body from falling, devices using linear motors are provided with a thrust assist mechanism to assist the thrust against the gravity of the driven body. Conventional thrust assist mechanisms for preventing such falls include compression / tension springs, air compressors, and counterweights.

[0009] Such thrust assist mechanisms are used not only to prevent the driven object from falling, but also to provide a constant thrust force against gravity while the linear motor is in operation. In particular, in the above-mentioned dispensing devices, which require precise position control, servo-controlled linear motors, i.e., linear servo motors, are often used as linear motors. Servo-controlling a linear servo motor requires a process called gain adjustment. Gain adjustment is easy when the load is constant. However, gain adjustment is difficult when the load fluctuates. Furthermore, it is known that linear servo motors rarely operate optimally, even after gain adjustment. Therefore, a thrust assist mechanism that provides constant thrust force is advantageous when using such a linear servo motor.

[0010] However, each of these conventional thrust assist mechanisms has the following drawbacks.

[0011] More specifically, the restoring force of a compression / tension spring increases in proportion to the amount of deflection, and the force is not constant. Also, because compression / tension springs undergo inertial deformation, the spring constant changes due to high loads or long-term loads. Furthermore, the longer the compression / tension spring, the smaller the spring constant, so the change in force relative to the amount of deflection becomes smaller. Therefore, in order to reduce the change in force relative to the amount of deflection, it is necessary to use a spring that is sufficiently long in the longitudinal direction. If a linear motor that drives a long stroke is to be assisted by a spring, a spring that is quite long in the longitudinal direction must be used to reduce the change in force relative to the amount of deflection.

[0012] Like compression / extension springs, the force of an air compressor increases in proportion to the compression rate of the piston. Air compressors also experience air leaks and changes in force over time.

[0013] Counterbalances require a lot of space due to their structure, and wires and other components can deteriorate.

[0014] Therefore, what is desired is a constant force generator that does not suffer from the above-mentioned drawbacks and that can maintain a constant force at any position in the stroke of the linear motor.

[0015] Patent Document 1 discloses a "constant force generator" including a fixedly disposed portion and a portion disposed axially movable relative to the fixedly disposed portion. At least one of the two portions comprises a magnetically conductive region or a permanent magnet region. The other portion comprises a permanent magnet region. The magnetization of the permanent magnet is such that at least a portion of the generated magnetic flux exits the permanent magnet region perpendicular to the axial direction of the movement of the movably disposed portion, enters the magnetically conductive region, is guided therein, exits the magnetically conductive region again, and returns to the permanent magnet region. Patent Document 1 discloses, as an embodiment, a case made of a hollow cylindrical ferromagnetic material. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] US Patent Application Publication No. 2004 / 0004405 Summary of the Invention [Problem to be solved by the invention]

[0017] The above-mentioned Patent Document 1 has the following problems.

[0018] The constant force generator disclosed in Patent Document 1, as the term suggests, only generates a constant force, meaning that the force generated cannot be easily varied.

[0019] Therefore, there is a demand for a variable force generator that can easily vary the force that it generates.

[0020] Therefore, an object of the present invention is to provide a variable constant force generator that can easily vary the force that is generated, and an apparatus equipped with the same.

[0021] Other objects of the present invention will become apparent as the description proceeds.

[0022] The terms "upper", "top", "top section" and "top surface" used in the description of the present invention refer to the vertical direction (up-down direction) of the equipment (linear motor) in which the variable force generator of the present invention is mounted, and the terms "lower", "bottom", "lower section" and "bottom surface" refer to the vertical direction (up-down direction) of the equipment (linear motor) in which the variable force generator of the present invention is mounted. [Means for solving the problem]

[0023] According to an exemplary aspect of the present invention, there is provided a variable force generator including: a case extending in an axial direction and made of a cylindrical ferromagnetic material; a stator extending in the axial direction and disposed within the case; and a rod-shaped shaft extending in the axial direction and disposed within the stator with a gap therebetween, the shaft being movable in the axial direction relative to the stator; wherein the stator includes N electromagnets (N is an even number equal to or greater than 2) disposed at equal angular intervals of (360 / N) degrees and generating magnetic flux radially toward the shaft, and the shaft has at least a shaft portion made of a magnetic material.

[0024] In the variable force generator, the stator may include a core and a coil wound around the core, and the core may include a cylindrical base body fixed to the inner wall surface of the case. Also, it is preferable that the core is made of a laminated core.

[0025] In the above variable force generator, the N electromagnets may include, as the core, N salient poles protruding radially inward from the base and N tip portions formed at the tips of the N salient poles and facing the shaft, and the N electromagnets may include, as the coils, N coil portions wound around the N salient poles, respectively. In this case, the N electromagnets have magnetic poles such that the tip portions adjacent in the circumferential direction have opposite polarities when a direct current is passed through the N coil portions.

[0026] In the above variable force generator, N may be 2. In this case, the stator may be made up of two electromagnets, and the shaft portion may include one permanent magnet magnetized to a polarity opposite to that of the tip portions of the two electromagnets.

[0027] In the variable force generator, the shaft may include a magnetic shaft as the shaft portion; and a non-magnetic shaft extending continuously from the magnetic shaft in the axial direction.

[0028] In the above variable force generator, N may be 4. In this case, the stator may be made up of four electromagnets, and the shaft portion may be made up of a rod-shaped ferromagnetic body and four permanent magnets arranged on the outer circumferential side of the ferromagnetic body so as to be magnetized with polarities opposite to those of the tip portions of the four electromagnets and to face each other. The rod-shaped ferromagnetic body configured in this manner may have a square cross section and four side faces. In this case, it is preferable that the four permanent magnets are arranged on the four side faces of the ferromagnetic body so as to be magnetized with polarities opposite to those of the tip portions of the four electromagnets and to face each other.

[0029] In the above variable force generator, it is preferable that the case is cylindrical, the base body of the core is cylindrical, and the shaft is columnar.

[0030] According to another exemplary aspect of the present invention, there is provided an apparatus comprising: a driven body extending in a longitudinal direction; a linear motor that drives the driven body in the longitudinal direction; and the variable force generator described above that is attached to the driven body, the longitudinal direction being the axial direction.

[0031] According to yet another exemplary embodiment of the present invention, there is provided an apparatus including: a driven body extending in a vertical direction and having first and second side surfaces facing each other; a linear motor attached to the first side surface of the driven body and driving the driven body in the vertical direction; and the variable force generator described above attached to the second side surface of the driven body, the vertical direction being the axial direction. [Effects of the Invention]

[0032] According to the present invention, it is possible to provide a variable force generator that can easily vary the force that is generated, and a device equipped with the variable force generator. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a perspective view of the exterior of a device in which a variable force generator according to the present invention is mounted, viewed obliquely from the front upper right. [Figure 2] FIG. 2 is a front view of the device shown in FIG. [Figure 3] 1 is a perspective view of the appearance of a variable force generator according to a first embodiment of the present invention; [Figure 4] FIG. 4 is a front view of the variable force generator shown in FIG. 3. [Figure 5] FIG. 4 is a plan view of the variable force generator shown in FIG. 3. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 4. [Figure 7] FIG. 7 is a vertical cross-sectional view taken along line VII-VII in FIG. 5. [Figure 8] FIG. 4 is an exploded perspective view of the variable force generator shown in FIG. 3. [Figure 9] 4 is a circuit diagram showing a method of connecting coils that constitute a stator used in the variable force generator shown in FIG. 3. FIG. [Figure 10] FIG. 10 is a perspective view of the appearance of a variable force generator according to a second embodiment of the present invention. [Figure 11] FIG. 11 is a front view of the variable force generator shown in FIG. 10. [Figure 12] FIG. 11 is a plan view of the variable force generator shown in FIG. 10. [Figure 13] FIG. 13 is a cross-sectional view taken along line XIII-XIII in FIG. 11. [Figure 14] FIG. 14 is a longitudinal cross-sectional view taken along line XIV-XIV in FIG. [Figure 15] FIG. 11 is an exploded perspective view of the variable force generator shown in FIG. 10. [Figure 16] FIG. 11 is a circuit diagram showing a method of connecting coils that constitute a stator used in the variable force generator shown in FIG. [Figure 17] FIG. 10 is a cross-sectional view of a variable force generator according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0034] To facilitate understanding of the present invention, an apparatus equipped with a variable force generator according to the present invention will be described with reference to Figures 1 and 2. Figure 1 is an external perspective view of the apparatus 100 as seen obliquely from the front upper right. Figure 2 is a front view of the apparatus 100.

[0035] Here, a Cartesian coordinate system (X, Y, Z) is used as shown in Figures 1 and 2. In the state shown in Figures 1 and 2, in the Cartesian coordinate system (X, Y, Z), the X-axis direction is the front-to-back direction (depth direction), the Y-axis direction is the left-to-right direction (width direction), and the Z-axis direction is the up-down direction (height direction; vertical direction).

[0036] The apparatus 100 includes a stage 110. The stage 110 includes a base 112 extending horizontally (parallel to the XY plane) and a mounting plate 114 extending vertically (parallel to the YZ plane) from the front end of the base 112. The mounting plate 114 has a front surface 114f extending vertically, parallel to the YZ plane. A variable force generator 10 and a linear motor 20 according to the present invention, which will be described later, are attached to the front surface 114f of the mounting plate 114.

[0037] The device 100 includes a driven body 120 that faces the front surface 114f of the mounting plate 114 with a gap therebetween. That is, the back surface (not shown) of the driven body 120 faces the front surface 114f of the mounting plate 114 at a predetermined distance. The driven body 120 has a substantially plate shape that extends vertically parallel to the YZ plane. The driven body 120 has a right side surface 120rs and a left side surface 120ls that face each other in the left-right direction Y. The right side surface 120rs and the left side surface 120ls each extend in the up-down direction Z (vertical direction). The left side surface 120ls is also referred to as the first side surface, and the right side surface 120rs is also referred to as the second side surface.

[0038] The linear motor 20 is attached to a left side surface 120ls of the driven body 120. On the other hand, the variable force generator 10 is attached to a right side surface 120rs of the driven body 120. The linear motor 20 and the variable force generator 10 each extend in the up-down direction (vertical direction) Z.

[0039] As described above, linear motor 20 is composed of motor shaft 22 having a central axis CA extending in vertical direction Z, and a field coil (not shown) arranged around motor shaft 22. Motor shaft 22 is made up of multiple permanent magnets magnetized in the direction of central axis CA, connected in series with like magnetic poles facing each other, and fixed in place. The field coil is made up of multiple cylindrical coils connected in series so as to concentrically surround motor shaft 22 with a gap between them. Therefore, linear motor 20 shown in the figure is a fixed-coil (moving-magnet) linear motor, in which motor shaft 22 is the moving part and field coils are the fixed part.

[0040] The linear motor 20 includes a cylindrical hollow square tubular case 24 that covers the field coil. That is, the field coil is attached to the inner wall surface of the case 24. The case 24 is fixed to the front surface 114f of the mounting plate 114 via a fixing member (not shown).

[0041] The lower end of the motor shaft 22 is attached and fixed to the lower end of the left side surface 120ls of the driven body 120 by a lower connecting member 27. On the other hand, the upper end of the motor shaft 22 is attached and fixed to the upper end of the left side surface 120ls of the driven body 120 by an upper connecting member 28. Therefore, the driven body 120 can be moved up and down as the motor shaft 22 is moved up and down along the central axis CA.

[0042] The variable force generator 10 has an axial direction A that is parallel to the up-down direction (vertical direction) Z. The variable force generator 10 includes a rod-shaped shaft 12 extending in the axial direction A, a stator (described later) extending in the axial direction A, and a cylindrical case 14 extending in the axial direction A. The case 14 is made of a cylindrical ferromagnetic material. The stator is disposed within the case 14. In the illustrated example, the stator is fixed to the inner wall surface of the case 14 as described later. As will be described in detail later, in the variable force generator 10 according to the present invention, the stator is composed of a plurality of electromagnets, each including a core and a coil wound around the core. The shaft 12 is disposed within the stator with a gap therebetween and is movable in the axial direction A relative to the stator.

[0043] The case 14 is fixed to the front surface 114 f of the mounting plate 114 by a fixing member 16 .

[0044] The lower end of the shaft 12 is attached and fixed to the lower end of the right side surface 120rs of the driven body 120 by a lower connecting member 17. On the other hand, the upper end of the shaft 12 is attached and fixed to the upper end of the right side surface 120rs of the driven body 120 by an upper connecting member 18.

[0045] As mentioned above, the variable force generator 10 configured as described above is intended to prevent the driven body 120 including the motor shaft 22 from falling. In more detail, suppose that the power supply for supplying current to the field coil of the linear motor 20 suddenly fails. In this case, the driven body 120 including the motor shaft 22 and the shaft 12 is pulled downward by gravity F due to their own weight. G The variable force generator 10 controls this gravity F G Thrust F againstT By keeping the magnitude of the DC current flowing through the stator coil constant, the variable force generator 10 generates a constant thrust F at any position in the stroke of the linear motor 20. T In other words, by changing the magnitude of the DC current flowing through the stator coil, the thrust F generated by the variable force generator 10 can be maintained. T In the following description, the driven body 120 including the motor shaft 22 and the shaft 12 will be simply referred to as the driven body 120.

[0046] Furthermore, by making the magnitude of the DC current flowing through the stator coil constant, the variable force generator 10 not only prevents the driven body 120 from falling, but also reduces the force of gravity F while the linear motor 20 is being driven. G A constant thrust force F opposes T The variable force generator 10 can also function as a thrust assist mechanism to assist the thrust of the rotor. In the following, we will explain the case where the magnitude of the DC current flowing through the stator coil is constant and the variable force generator 10 is used as a constant force generator. Therefore, the variable force generator 10 will also be referred to as a constant force generator 10.

[0047] Next, a method of using the constant force generator 10 that operates as a thrust assist mechanism will be described in detail. First, assume that the constant force generator 10 is used alone and not attached to the device 100. However, assume that the constant force generator 10 is disposed so that its axial direction A is aligned with the up-down direction (vertical direction) Z. In this situation, the constant force generator 10 is stopped at a position where the stator and shaft 12 are magnetically stable (hereinafter simply referred to as the "stable position"). Here, the stable position is a point (position) where the center of the shaft 12 and the center of the stator coincide. In this stable position, assume that a force is applied to the constant force generator 10 to push the shaft 12 in the up-down direction (vertical direction) Z. In this case, a thrust force is generated in the constant force generator 10 that attempts to return to the stable position. Specifically, assume that a force is applied to the constant force generator 10 to push the shaft 12 downward. In this case, an upward thrust F is generated in the constant force generator 10 that attempts to return to the stable position.T occurs.

[0048] As described above, it is assumed that the constant force generator 10 is attached to the device 100 as shown in Figures 1 and 2, with the shaft 12 being pushed downward. In this case, the constant force generator 10 generates a thrust F that tends to push the driven body 120 upward. T Therefore, in a state where no current flows through the field coil of the linear motor 20, the constant force generator 10 generates the downward gravity F acting on the driven body 120. G and the above thrust F T It is clear that the equilibrium position at this time is a position where the shaft 12 of the constant force generator 10 is shifted downward from the stable position.

[0049] In the above-mentioned equilibrium position, suppose that a current is passed through the field coil of the linear motor 20 to drive the motor shaft 22 of the linear motor 20 to move upward along the central axis CA, thereby pushing the driven body 120 upward. In this case, if the shaft 12 of the constant force generator 10 moves upward beyond the above-mentioned stable position, a downward thrust will be generated in the constant force generator 10. Therefore, the upper limit position of the stroke range of the linear motor 20 is regulated (limited) to the above-mentioned stable position.

[0050] Whether the constant force generator 10 should be pushed downward or upward depends on how the constant force generator 10 is attached to the device 100. Specifically, in the example shown in Figures 1 and 2, the constant force generator 10 is a movable-shaft constant force generator in which the stator (case 14) is fixed to a mounting plate 114 and the shaft 12 is movable. In such a movable-shaft constant force generator, the movable-shaft constant force generator is attached to the device 100 with the shaft 12 pressed downward, as described above.

[0051] On the other hand, unlike (or conversely to) the movable-shaft constant force generator as shown in Figures 1 and 2, a fixed-shaft constant force generator may be used as the constant force generator, in which the shaft 12 is fixed to the mounting plate 114 and the stator (case 14) is movable. In such a fixed-shaft constant force generator, the fixed-shaft constant force generator is attached to the device 100 with the shaft 12 pressed upward. In this case as well, the fixed-shaft constant force generator generates a thrust F that tends to push the driven body 120 upward. T Therefore, when no current flows through the field coil of the linear motor 20, the shaft-fixed constant force generator generates a force F acting on the driven body 120 in the downward direction. G and the above thrust F T It is clear that the equilibrium position at this time is a position where the shaft 12 of the fixed-shaft constant force generator is shifted upward from the stable position.

[0052] 1 and 2, a fixed-coil (moving-magnet) linear motor configured so that the motor shaft 22 is the moving part and the magnetic field coil is the fixed part is used as the linear motor 20. However, it goes without saying that a fixed-magnet (moving-coil) linear motor configured so that the motor shaft 22 is the fixed part and the magnetic field coil is the moving part may also be used as the linear motor.

[0053] The above description can be summarized as follows: For example, as shown in FIGS. 1 and 2, when a gravitational force F of 1 N (Newton) is applied to the driven body 120 of the device 100, G When gravity F acts on the object, G To counter this, a thrust force F equal to 1 N is generated by the constant force generator 10. T In this case, when the field coil of the linear motor 20 is not energized, the constant force generator 10 (driven body 120) can be stopped at any position. However, as mentioned above, the upper limit position of the stroke range of the linear motor 20 is limited to the above stable position.

[0054] In contrast, the constant force generator 10 generates a thrust force F greater than 1 N. T In this case, the constant force generator 10 (driven body 120) will stop at the stable position or at an upper end point set up to the stable position.

[0055] On the other hand, the constant force generator 10 generates a thrust force F smaller than 1 N. T In this case, the constant force generator 10 (driven body 120) will stop at the lower end point.

[0056] The upward thrust F by the constant force generator 10 T At first glance, this may be an unnecessary load when the linear motor 20 is driven by passing a current through the field coil to move the driven body 120 downward. However, when the driven body 120 is moved downward, the driven body 120 is always (originally) subjected to the force of gravity F due to its own weight. G Therefore, the linear motor 20 is driven by the difference (F G -F T This is also true when moving the driven body 120 in the upward direction. Therefore, the upward thrust F by the constant force generator 10 is T Thanks to this, the linear motor 20 only needs to be driven with a smaller thrust than in the case where there is no constant force generator 10. In other words, it can be seen that the constant force generator 10 is intended to supplement the thrust of the linear motor 20 required when driving the driven body 120 upward. The above is an explanation of the operation when the variable force generator 10 is used as a constant force generator.

[0057] As is clear from the above explanation, by using the variable force generator 10 as a thrust assist mechanism, the linear motor 20 can be made smaller. This is because, if the thrust of a linear motor were to be increased using only the linear motor without using the variable force generator 10 as a thrust assist mechanism, it would be necessary to increase the volume of the permanent magnets that make up the linear motor or increase the number of turns of the field coil that makes up the linear motor. This would result in a larger linear motor. Furthermore, neodymium magnets, which have strong magnetic force, are generally used as permanent magnets that make up linear motors. However, neodymium magnets are expensive. Therefore, by using the variable force generator 10 as a thrust assist mechanism, it is possible to employ a low-thrust linear motor 20 that uses inexpensive permanent magnets other than neodymium magnets as the permanent magnets that make up the linear motor, thereby reducing costs.

[0058] 1 and 2, the driven body 120 extends in the vertical direction Z and has a first side surface (left side surface 120ls) and a second side surface (right side surface 120rs) that face each other. The linear motor 20 is attached to the first side surface (left side surface 120ls) of the driven body 120 and drives the driven body 120 in the vertical direction Z. The variable force generator 10 is attached to the second side surface (right side surface 120rs) of the driven body 120, and the vertical direction Z is the axial direction A.

[0059] However, the device to which the present invention is applied is not limited to the device 100 shown in Figures 1 and 2. In general, the device to which the present invention is applied may include a driven body 120 extending in the longitudinal direction, a linear motor 20 that drives the driven body 120 in the longitudinal direction, and a variable force generator 10 that is attached to the driven body 120 and whose longitudinal direction is the axial direction A. The longitudinal direction here is not limited to the vertical direction (up-down direction) Z, and may be any direction.

[0060] [First embodiment] A variable force generator 10 according to a first embodiment of the present invention will be described with reference to Figs. 3 to 9. Fig. 3 is an external perspective view of the variable force generator 10. Fig. 4 is a front view of the variable force generator 10. Fig. 5 is a plan view of the variable force generator 10. Fig. 6 is a horizontal cross-sectional view taken along line VI-VI in Fig. 4. Fig. 7 is a vertical cross-sectional view taken along line VII-VII in Fig. 5. Fig. 8 is an exploded perspective view of the variable force generator 10. The above-mentioned Cartesian coordinate system (X, Y, Z) is also used in Figs. 3 to 8. Fig. 9 is a circuit diagram showing a method of connecting the coils that make up the stator.

[0061] The illustrated variable force generator 10 is a two-pole variable force generator. The illustrated variable force generator 10 includes a cylindrical case 14, a stator 13, and a cylindrical shaft 12. In this specification, "two poles" refers to the number of magnetic poles facing the shaft 12. More specifically, "two poles" refers to the case where the number of electromagnets (described later) that make up the stator 13 is two.

[0062] 6, the stator 13 includes two electromagnets 13-2. More specifically, the two electromagnets 13-2 generate magnetic flux in the radial direction toward the shaft 12, at equal angular intervals of 180 degrees.

[0063] The stator 13 includes a core 132 and a coil 134 wound around the core 132 as described below. The core 132 includes a cylindrical base 132-2 fixed to the inner wall surface of the case 14. The illustrated core 132 is configured as a laminated core. The laminated core 132 is formed by stacking multiple silicon steel plates in the axial direction A. The thickness of each silicon steel plate is preferably in the range of 0.5 mm to 0.15 mm. For example, if 100 silicon steel plates each 0.35 mm thick are stacked in the axial direction A, the length (thickness) of the laminated core 132 in the axial direction A will be 35 mm. By using a laminated core as the core 132, iron loss due to eddy currents can be reduced.

[0064] The material of the laminated core 132 is not limited to silicon steel plate, and other magnetic steel plates such as other electromagnetic steel plates or amorphous steel plates may be used. Furthermore, the core 132 is not limited to a laminated core, and other cores may be used. For example, the core 132 may be a dust core manufactured by compacting soft magnetic powder.

[0065] Each of the two electromagnets 13-2 includes a core 132 that includes two salient poles 132-4 and two tip portions 132-6. The two salient poles 132-4 protrude radially inward from the base 132-2. The two tip portions 132-6 are formed at the tips of the two salient poles 132-4, respectively, and face the shaft 12. Each tip portion 132-6 has an arc shape with a constant width (thickness) in the radial direction in a plan view. Each of the two electromagnets 13-2 includes, as the coil 134, two coil portions 134-2 that are wound around the two salient poles 132-4, respectively. When a direct current is applied to the two coil portions 134-2, the two electromagnets 13-2 have magnetic poles such that the circumferentially adjacent tip portions 132-6 have opposite polarities. For example, if the magnetic pole of the tip portion 132-6 of one electromagnet 13-2 is an N pole, then the magnetic pole of the tip portion 132-6 of the other electromagnet 13-2 will be an S pole of the opposite polarity. In this way, the stator 13 is made up of two electromagnets 13-2.

[0066] As shown in Fig. 8, the stator 13 configured as described above is inserted into a cylindrical case 14 made of a ferromagnetic material, and its base 132-2 is adhered with an adhesive to the inner wall surface of the case 14. As a result, the stator 13 is fixed to the inner wall surface of the case 14, as shown in Fig. 7. Thereafter, both ends of the case 14 are closed with a pair of annular end caps 15-1 and 15-2. As is clear from Fig. 7, the length L1 of the case 14 in the axial direction A is longer than the length L2 of the stator 13 in the axial direction A (L1 > L2).

[0067] The shaft 12 has a shaft portion 12-2 made of at least a magnetic material. Specifically, the illustrated shaft 12 is composed of a shaft body 12-4 and a shaft portion 12-2. The shaft body 12-4 has an opening 12-4a into which the shaft portion 12-2 is inserted. Thus, the shaft portion 12-2 is adhered to the shaft body 12-4 with an adhesive in a state of being inserted into this opening 12-4a.

[0068] As shown in FIG. 6, the illustrated shaft portion 12-2 is composed of one permanent magnet magnetized with a magnetic pole of opposite polarity to the magnetic poles of the tip portions 132-6 of the two electromagnets 13-2 of the stator 13. For example, assume that the magnetic pole of the tip portion 132-6 of a certain electromagnet 13-2 is the N pole. In this case, the magnetic pole of the permanent magnet 12-2 facing the tip portion 132-6 is the S pole. As is clear from FIG. 7, the length L3 of the shaft body 12-4 in the axial direction A is longer than the length L1 of the case 14 in the axial direction A (L3>L1). On the other hand, the length L4 of one permanent magnet 12-2 in the axial direction A is shorter than the length L1 of the case 14 in the axial direction A and longer than the length L2 of the stator 13 in the axial direction A (L1>L4>L2). Also, the diameter D1 of the shaft 12 is smaller than the inner diameter D2 of the stator 13 (D1<D2). Thereby, the shaft 12 is arranged in the stator 13 with a gap. Incidentally, as is clear from FIGS. 4 and 7, in the vertical direction (up and down direction) Z, the upper portion of the shaft 12 protruding above the case 14 is longer than the lower portion protruding below the case 14. This is because when the variable force generator 10 is attached to the device 100 (see FIGS. 1 and 2), it is assumed that this upper portion is pushed into the case 14.

[0069] As described with reference to FIGS. 1 and 2, when the variable force generator 10 is attached to the device 100, it is accurately positioned and attached so that the above-mentioned gap is formed. For example, as disclosed in Patent Document 1, a highly slidable cylindrical member may be inserted between the stator 13 and the shaft 12 to form the above-mentioned gap.

[0070] With the variable force generator 10 configured as described above, even if the thickness of the case 14 is thin, it is possible to prevent the magnetic flux generated from the two electromagnets 13-2 of the stator 13 from leaking to the outside from the case 14. This is because most of the magnetic flux generated from the two electromagnets 13-2 passes through the base 132-2. Therefore, it is possible to provide a small-sized variable force generator 10 that can minimize leakage magnetic flux.

[0071] FIG. 9 is a circuit diagram showing a connection method of the coil 134 constituting the stator 13. FIG. 9(A) shows an example in which two coil portions 134-2 are connected in series to the DC power supply 30. FIG. 9(B) shows an example in which two coil portions 134-2 are connected in parallel to the DC power supply 30. The voltage of the DC power supply 30 is V [V], and the resistance of each coil portion 134-2 is R [Ω]. However, the internal resistance of the DC power supply 30 is ignored. In this case, a DC current of I1 = V / 2R [A] flows through the coil 134 in which two coil portions 134-2 are connected in series as shown in FIG. 9(A). On the other hand, a DC current of I2 = 2V / R [A] flows through the coil 134 in which two coil portions 134-2 are connected in parallel as shown in FIG. 9(B).

[0072] According to the variable force generator 10 configured as described above, the force generated can be easily varied by changing the magnitude of the direct current flowing through the coil 134.

[0073] In the first embodiment, the shaft 12 has the shaft portion 12-2 made of a single permanent magnet, but the present invention is not limited to this. For example, the shaft may be a cylindrical magnetic shaft whose shaft portion is made of a ferromagnetic material.

[0074] [Second embodiment] A variable force generator 10A according to a second embodiment of the present invention will be described with reference to Figs. 10 to 16. Fig. 10 is an external perspective view of the variable force generator 10A. Fig. 11 is a front view of the variable force generator 10A. Fig. 12 is a plan view of the variable force generator 10A. Fig. 13 is a horizontal cross-sectional view taken along line XIII-XIII in Fig. 11. Fig. 14 is a vertical cross-sectional view taken along line XIV-XIV in Fig. 12. Fig. 15 is an exploded perspective view of the variable force generator 10A. The above-mentioned Cartesian coordinate system (X, Y, Z) is also used in Figs. 10 to 15. Fig. 16 is a circuit diagram showing a method of connecting the coils that make up the stator.

[0075] The illustrated variable force generator 10A is a four-pole variable force generator. The illustrated variable force generator 10A has substantially the same configuration and operates as the variable force generator 10 according to the first embodiment described above, except for the configuration of the shaft and stator. Therefore, the shaft and stator are given reference numerals 12A and 13A, respectively. In the variable force generator 10A, components similar to those of the variable force generator 10 according to the first embodiment described above are given the same reference numerals, and for simplicity of explanation, only the differences will be described below. Note that "four poles" refers to a case where the stator is made up of four electromagnets.

[0076] As shown in FIG. 14, the shaft 12A is composed of a magnetic shaft 12A-2 and a non-magnetic shaft 12A-4 as shaft portions. The non-magnetic shaft 12A-4 extends continuously from the magnetic shaft 12A-2 in the axial direction A. Specifically, the magnetic shaft 12A-2 has a male thread 12A-2a at one end (upper end) thereof. On the other hand, the non-magnetic shaft 12A-4 has a female thread 12A-4a at one end (lower end) opposite the one end (upper end) of the magnetic shaft 12A-2. Therefore, the shaft 12A is formed (configured) by threading the male thread 12A-2a of the magnetic shaft 12A-2 into the female thread 12A-4a of the non-magnetic shaft 12A-4. Note that in the second embodiment, a screw member is used as the fastening means, but the present invention is not limited to this. For example, the magnetic shaft 12A-2 and the non-magnetic shaft 12A-4 may be fastened together by other fastening means, such as adhesive bonding or crimping. The magnetic shaft 12A-2 is made of, for example, a ferromagnetic material such as stainless steel. Examples of such ferromagnetic stainless steel include stainless steel (SUS420J2). On the other hand, the non-magnetic shaft 12A-4 is made of, for example, a non-magnetic material such as stainless steel. Examples of such stainless steel include stainless steel (SUS303).

[0077] Therefore, the first main difference from the variable force generator 10 according to the first embodiment described above is that the variable force generator 10A uses a magnetic shaft 12A-2 as the shaft portion instead of one permanent magnet 12-2. Since the magnetic shaft 12A-2 is used as the shaft portion, the thrust F generated from the variable force generator 10A is T However, even with the variable force generator 10A having such a configuration, a constant thrust F can be generated by passing a constant amount of direct current through the coils that make up the stator 13A. T can be maintained.

[0078] 13, the stator 13A includes four electromagnets 13A-2. More specifically, the four electromagnets 13A-2 are spaced at equal angular intervals of 90 degrees and generate magnetic flux in the radial direction toward the shaft 12A.

[0079] The stator 13A includes a core 132A and a coil 134A wound around the core 132A as described below. The core 132A includes a cylindrical base 132A-2 fixed to the inner wall surface of the case 14. As in the first embodiment described above, the core 132A shown in the figure is also made of a laminated core.

[0080] The core 132A is not limited to a laminated core, and other cores may be used. For example, the core 132A may be a dust core manufactured by compacting soft magnetic powder.

[0081] Each of the four electromagnets 13A-2 includes a core 132A that includes four salient poles 132A-4 and four tip portions 132A-6. The four salient poles 132A-4 protrude radially inward from the base 132A-2. The four tip portions 132A-6 are formed at the tips of the four salient poles 132A-4, respectively, and face the shaft 12A. Each tip portion 132A-6 has an arc shape with a constant width (thickness) in the radial direction in a plan view. Each of the four electromagnets 13A-2 includes a coil 134A that includes four coil portions 134A-2 wound around the four salient poles 132A-4, respectively. When a direct current is applied to the four coil portions 134A-2, the four electromagnets 13A-2 have magnetic poles such that adjacent tip portions 132A-6 in the circumferential direction have opposite polarities. For example, if the magnetic pole of the tip portion 132A-6 of one electromagnet 13A-2 is a north pole, the magnetic pole of the tip portion 132A-6 of the electromagnet 13A-2 adjacent to it in the circumferential direction will be a south pole of the opposite polarity. In this way, the stator 13A is made up of four electromagnets 13A-2.

[0082] As described above, in the second embodiment, the shaft 12A uses the magnetic shaft 12A-2 made of a ferromagnetic material as a shaft portion. Therefore, as shown in FIG. 13, the portion of the magnetic shaft 12A-2 facing the magnetic pole of the tip portion 132A-6 of each of the four electromagnets 13A-2 of the stator 13A is magnetically induced to have a magnetic pole of the opposite polarity. For example, suppose the magnetic pole of the tip portion 132A-6 of one electromagnet 13A-2 is a north pole. In this case, the portion of the magnetic shaft 12A-2 facing the tip portion 132A-6 is magnetically induced to have a south pole.

[0083] As shown in Fig. 15, the stator 13A configured as described above is inserted into a cylindrical case 14 made of a ferromagnetic material, and its base 132A-2 is adhered with an adhesive to the inner wall surface of the case 14. As a result, the stator 13A is fixed to the inner wall surface of the case 14, as shown in Fig. 14. Thereafter, both ends of the case 14 are closed with a pair of annular end caps 15-1 and 15-2. As is clear from Fig. 14, the length of the case 14 in the axial direction A is longer than the length of the stator 13A in the axial direction A.

[0084] With variable force generator 10A configured as described above, even if case 14 is thin, it is possible to prevent magnetic flux generated from four electromagnets 13A-2 of stator 13A from leaking to the outside from case 14. This is because most of the magnetic flux generated from the four electromagnets 13A-2 passes through base 132A-2. Therefore, it is possible to provide a small-sized variable force generator 10A that can minimize leakage magnetic flux.

[0085] FIG. 16 is a circuit diagram showing a connection method for the coils 134A constituting the stator 13A. FIG. 16(A) shows an example in which four coil portions 134A-2 are connected in series to the DC power supply 30. FIG. 16(B) shows an example in which two coil portions 134A-2 connected in parallel and another two coil portions 134A-2 connected in parallel are connected in series to the DC power supply 30. FIG. 16(C) shows an example in which four coil portions 134A-2 are connected in parallel to the DC power supply 30. The voltage of the DC power supply 30 is V [V], and the resistance of each coil portion 134A-2 is R [Ω]. However, the internal resistance of the DC power supply 30 is ignored. In this case, a DC current of I3 = V / 4R [A] flows through the coil 134A in which four coil portions 134A-2 are connected in series as shown in FIG. 16(A). On the other hand, as shown in Fig. 16(B), a direct current of I4 = V / R (A) flows through a coil 134A in which two coil portions 134A-2 connected in parallel are further connected in series. And as shown in Fig. 16(C), a direct current of I5 = 4V / R (A) flows through a coil 134A in which four coil portions 134A-2 are connected in parallel.

[0086] In variable force generator 10A having such a configuration, the force generated can also be easily varied by changing the magnitude of the direct current flowing through coil 134A.

[0087] Although the illustrated variable force generator 10A is a variable force generator equipped with a 4-pole (i.e., equipped with four electromagnets) stator 13A, it may also be applied to a variable force generator equipped with an 8-pole stator. That is, a shaft 12A may be provided for such an 8-pole stator. Note that "8 poles" refers to the case where the number of electromagnets constituting the stator is eight.

[0088] [Third embodiment] A variable force generator 10B according to a third embodiment of the present invention will be described with reference to Fig. 17. Fig. 17 is a cross-sectional view of the variable force generator 10B. The above-mentioned Cartesian coordinate system (X, Y, Z) is also used in Fig. 17.

[0089] The illustrated variable force generator 10B is a four-pole variable force generator. The illustrated variable force generator 10B has substantially the same configuration and operates as the variable force generator 10A according to the second embodiment described above, except for the configuration of the shaft. Therefore, the shaft will be indicated by the reference numeral 12B. In the variable force generator 10B, components similar to those of the variable force generator 10A according to the second embodiment described above will be designated by the same reference numerals, and in the following, for simplicity of explanation, only the differences will be described.

[0090] The illustrated shaft 12B has the same configuration as the shaft 12A according to the second embodiment, except for the difference in the configuration of the shaft portion, which is therefore denoted by the reference symbol 12B-2.

[0091] The illustrated shaft portion 12B-2 is composed of a rod-shaped ferromagnetic material 12B-22 and four permanent magnets 12B-24. As shown in FIG. 17, the rod-shaped ferromagnetic material 12B-22 has a square cross section in a plan view and four side surfaces. The four permanent magnets 12B-24 are arranged on the four side surfaces of the ferromagnetic material 12B-22. Each permanent magnet 12B-24 has a semi-cylindrical shape in a plan view. Specifically, the four permanent magnets 12B-24 are adhered and fixed to the four side surfaces of the ferromagnetic material 12B-22 with an adhesive. The four permanent magnets 12B-24 are arranged so that they are magnetized with polarities opposite to and face the polarities of the tip portions 132A-6 of the four electromagnets 13A-2 of the stator 13A.

[0092] In this way, the shaft portion 12B-2 is made up of a combination of the ferromagnetic material 12B-22 and the four permanent magnets 12B-24, so that the thrust F generated by the variable force generator 10B is T In the variable force generator 10B having such a configuration, a constant thrust F can be generated at any position in the stroke of the linear motor 20 by passing a DC current of a constant magnitude through the coil 134A constituting the stator 13A. Tcan be maintained.

[0093] Even in variable force generator 10B configured as described above, even if case 14 is thin, it is possible to prevent magnetic flux generated from four electromagnets 13A-2 of stator 13A from leaking to the outside from case 14. This is because, as described above, most of the magnetic flux generated from four electromagnets 13A-2 of stator 13A passes through base 132A-2. Therefore, it is possible to provide a small-sized variable force generator 10B that can minimize leakage magnetic flux.

[0094] In variable force generator 10B having such a configuration, the force generated can also be easily varied by changing the magnitude of the direct current flowing through coil 134A.

[0095] The structure (configuration) of the shaft portion 12B-2 is not limited to that shown in Fig. 17. For example, a cylindrical ferromagnetic body may be used as the rod-shaped ferromagnetic body. In this case, each of the four permanent magnets may be a permanent magnet that is tile-shaped in plan view and attached to the outer circumferential side of the cylindrical ferromagnetic body.

[0096] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

[0097] For example, while the constant force generators 10 to 10B according to the first to third embodiments have been described using examples of two and four poles, the present invention is generally applicable to N-pole (N is an even number equal to or greater than two) poles. In this case, the stator includes N electromagnets. The N electromagnets are arranged at equal angular intervals of (360 / N) degrees and generate magnetic flux radially toward the shaft. Furthermore, in the variable force generators 10 to 10B according to the first to third embodiments, the case and the base of the stator are cylindrical, and the shaft is columnar, but the present invention need not limit these shapes. For example, the case and the base of the stator may be cylindrical, and the shaft may be rod-shaped. [Industrial Applicability]

[0098] The variable force generator according to the present invention is not limited to use as the thrust assist mechanism described above, but can also be used in other mechanisms that require variable thrust. Furthermore, the variable force generator according to the present invention can be used either for fall prevention only or for thrust assistance only. [Explanation of symbols]

[0099] 10, 10A, 10B Variable Force Generator 12, 12A, 12B shaft 12-2 Shaft part (permanent magnet) 12A-2 Shaft part (magnetic shaft) 12A-2a male thread 12B-2 shaft part 12B-22 Ferromagnetic material 12B-24 permanent magnet 12-4 Shaft body 12-4a opening 12A-4 Non-magnetic shaft 12A-4a female thread 13, 13A Stator 13-2, 13A-2 Electromagnet 132, 132A core 132-2, 132A-2 base 132-4, 132A-4 salient pole 132-6, 132A-6 tip part 134, 134A coil 134-2, 134A-2 coil part 14 cases 15-1, 15-2 End caps 20 Linear motor 30 DC power supply A axis direction X Anteroposterior direction Y left / right direction Z vertical direction

Claims

1. a cylindrical case extending in the axial direction and made of a ferromagnetic material; a stator extending in the axial direction and disposed within the case; a rod-shaped shaft extending in the axial direction and disposed within the stator with a gap therebetween, the shaft being movable in the axial direction relative to the stator; A variable force generator comprising: The stator includes N electromagnets (N is an even number of 2 or more) that are arranged at equal angular intervals of (360 / N) degrees and generate magnetic flux in a radial direction toward the shaft, the shaft having at least a shaft portion made of a magnetic material; A variable force generator characterized by:

2. The stator includes a core and a coil wound around the core, 2. The variable force generator according to claim 1, wherein the core includes a cylindrical base body fixed to an inner wall surface of the case.

3. 3. The variable force generator of claim 2, wherein the core comprises a laminated core.

4. The N electromagnets each have the following cores: N salient poles protruding radially inward from the base; N tip portions formed at the tips of the N salient poles, respectively, and facing the shaft, the N electromagnets each include, as the coil, N coil portions wound around the N salient poles, 4. The variable force generator according to claim 2 or 3, wherein the N electromagnets have magnetic poles such that circumferentially adjacent tip portions have opposite polarities when a direct current is passed through the N coil portions.

5. wherein N is 2; The stator is composed of two electromagnets, The shaft portion includes one permanent magnet magnetized to a polarity opposite to the polarity of the tip portions of the two electromagnets.

5. The variable force generator of claim 4.

6. The shaft a magnetic shaft as the shaft portion; a non-magnetic shaft extending continuously from the magnetic shaft in the axial direction; 5. The variable force generator of claim 4, comprising:

7. wherein N is 4; The stator is composed of four electromagnets, The shaft portion A rod-shaped ferromagnetic material, four permanent magnets arranged on the outer peripheral side surface of the ferromagnetic body so as to be magnetized with magnetic poles opposite to the magnetic poles of the tip portions of the four electromagnets and to face each other; Consists of 5. The variable force generator of claim 4.

8. The rod-shaped ferromagnetic body has a square cross section and four sides, the four permanent magnets are arranged on the four side surfaces of the ferromagnetic body so as to be magnetized with magnetic poles opposite to the magnetic poles of the tip portions of the four electromagnets and to face each other; 8. The variable force generator of claim 7.

9. The case is cylindrical, The substrate of the core is cylindrical, The shaft is cylindrical. A variable force generator according to claim 2 or 3.

10. a driven body extending in a longitudinal direction; a linear motor that drives the driven body in the longitudinal direction; The variable force generator according to any one of claims 1 to 9, which is attached to the driven body, and the longitudinal direction is the axial direction; Equipment comprising:

11. a driven body extending in a vertical direction and having first and second side surfaces facing each other; a linear motor attached to the first side surface of the driven body and driving the driven body in a vertical direction; The variable force generator according to claim 1 , which is attached to the second side surface of the driven body, and the vertical direction is the axial direction; Equipment comprising:

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