Constant force generator

Abstract

To provide a constant force generator capable of lengthening strokes.SOLUTION: A constant force generator includes a longitudinally extending fixed portion and a movable portion disposed longitudinally extending and longitudinally movable relative to the fixed portion. The fixed portion has a slit having a substantially U-shaped cross section opening along the longitudinal direction and having a fixing length in the longitudinal direction, in which the slit has a first end surface and a second end surface which are orthogonal to a central axis extending in the longitudinal direction and are opposed to each other while being spaced apart from each other, and a first side surface parallel to the central axis. The movable portion is arranged to extend in the longitudinal direction in a state of being partially inserted into the slit, and has a movable length equal to the fixed length in the longitudinal direction within a predetermined tolerance.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a constant force generator, and more particularly to a constant force generator for use with a linear actuator. [Background technology]

[0002] A linear actuator is used to drive a driven body in the longitudinal direction (axial direction).

[0003] Such a linear actuator may, for example, be comprised of an actuator shaft having a central axis extending in the longitudinal direction and a field coil arranged around the actuator shaft. The actuator 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 enclose the actuator shaft with a gap between them. The field coil is covered by an actuator case. That is, the field coil is attached and fixed to the inner wall surface of the actuator case. Such a linear actuator may, for example, be configured so that the actuator shaft is the fixed part and the combination of the field coil and the actuator case is the moving part. A linear actuator with such a configuration is called a moving-coil linear actuator or a fixed-magnet linear actuator.

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

[0005] In the above-mentioned moving-coil (fixed-magnet) linear actuator, the field coil consists of at least three coils, U-phase, V-phase, and W-phase, to form a three-phase linear actuator. In a three-phase linear actuator, AC current with an electrical phase difference of 120 degrees flows through each coil, controlling the current to each coil. By controlling the current in this way, the three-phase linear actuator is configured to generate thrust to drive the moving part, which is the combination of the field coil and the actuator case, in the central axis direction (longitudinal 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 moving coil type (fixed magnet type) linear actuator, the driven body is fixed to the actuator case. Therefore, as the moving part, which is made up of the combination of the field coil and the actuator case, moves in the central axis direction (longitudinal direction), the driven body is driven in the central axis direction (longitudinal direction). There are cases where it is desired to drive the driven body in the vertical direction (vertical direction). An example of such a driven body is a dispensing head of a dispensing device that draws in and dispenses small amounts of liquid. In such cases, the central axis direction (longitudinal direction) of the moving coil type (fixed magnet type) linear actuator extends in the vertical direction (perpendicular direction). Driving the driven body in the vertical direction (perpendicular direction) in this way will be referred to as "vertical drive" hereinafter.

[0007] In a moving-coil (fixed-magnet) linear actuator with this configuration, when no current flows through the field coil, no electromagnetic force acts between the field coil and the permanent magnet. Therefore, in the case of vertical drive, the moving part of the linear actuator will fall downward due to gravity along with the driven object. For example, if the power supply that supplies current to the field coil suddenly fails, the driven object, including the moving part, will fall. This driven object may collide with equipment placed below the linear actuator, potentially damaging that equipment.

[0008] As mentioned above, linear actuators are broadly divided into two types. Whether they are moving coil (fixed magnet) linear actuators or moving magnet (fixed coil) linear actuators, permanent magnets are arranged in series, alternating N and S directions, and operate by attraction and repulsion with the magnetic field of a field coil. Therefore, in the case of vertical drive, even in a moving magnet (fixed coil) linear actuator, if no current is applied to the field coil, the driven object will drop along with the moving part, which is the actuator shaft.

[0009] Therefore, in order to prevent the driven body from falling in the case of such vertical drive, equipment using a linear actuator is provided with a thrust assist mechanism that assists the thrust against the gravity of the driven body including the moving part. Conventionally, such thrust assist mechanisms for preventing falling have used compression / tension springs, air compressors, counterweights, etc.

[0010] 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 actuator is in operation. In particular, in dispensing devices that require precise position control, servo-controlled linear actuators, i.e., linear servo actuators, are often used as linear actuators. Servo-controlling a linear servo actuator 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, even with gain adjustment, it is known that linear servo actuators rarely perform optimal operation. Therefore, a thrust assist mechanism that provides constant thrust force offers advantages when using such linear servo actuators.

[0011] However, each of these conventional thrust assist mechanisms has the following drawbacks.

[0012] 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 you are trying to use a spring to assist a linear actuator that drives a long stroke, you will have to use a spring that is quite long in the longitudinal direction to reduce the change in force relative to the amount of deflection.

[0013] 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.

[0014] Counterbalances require a lot of space due to their structure, and wires and other components can deteriorate.

[0015] Therefore, what is desired is a constant force generator that can maintain a constant force at any position in the stroke of a linear actuator without the drawbacks mentioned above.

[0016] Patent Document 1 discloses a "constant force generator" including a fixedly disposed portion and a portion 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 generates at least a portion of the magnetic flux that exits the permanent magnet region perpendicular to the axial direction 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 constant force generator that uses a cylindrical fixed portion as the fixedly disposed portion and a cylindrical movable portion as the movable portion that is movably disposed along the longitudinal direction within the fixed portion. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] US Patent Application Publication No. 2004 / 0004405 Summary of the Invention [Problem to be solved by the invention]

[0018] The above-mentioned Patent Document 1 has the following problems.

[0019] The constant force generator disclosed in Patent Document 1 has a problem in that it is difficult to increase the stroke. More specifically, in the embodiment of the constant force generator disclosed in Patent Document 1, the movable part moves in the longitudinal direction relative to the fixed part. In order to maximize the stroke of a constant force generator with such a structure, the longitudinal length of the movable part (hereinafter referred to as the "movable length") needs to be longer than the length of the fixed part (hereinafter referred to as the "fixed length"). Specifically, for example, the movable length may be set to approximately twice the fixed length. In this case, when the movable part moves, the tip of the movable part protrudes significantly from the tip of the fixed part by a protrusion amount. In order to incorporate a constant force generator with such a structure into a device that employs a linear actuator, the protrusion amount needs to be minimized. As a result, the fixed length of the fixed part must be shortened, resulting in a short stroke. Therefore, a constant force generator that can increase the stroke is desired.

[0020] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a constant force generator that is capable of providing a long stroke.

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

[0022] In addition, 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 actuator) in which the constant 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 actuator) in which the constant force generator of the present invention is mounted. [Means for solving the problem]

[0023] According to an exemplary embodiment of the present invention, there is provided a constant force generator including a fixed portion extending in a longitudinal direction; and a movable portion disposed in the longitudinal direction and movable relative to the fixed portion, the fixed portion having a first end face and a second end face perpendicular to a central axis extending in the longitudinal direction and spaced apart from each other, a first side face parallel to the central axis, a substantially U-shaped cross-section slit opening along the longitudinal direction, and a fixed length in the longitudinal direction. The movable portion is disposed in a state partially inserted into the slit and extends in the longitudinal direction, and has a movable length in the longitudinal direction equal to the fixed length within a predetermined tolerance. Here, the fixed length is L1 and the movable length is L2, and the relationship 0.80L1≦L2≦1.20L1 is satisfied. In this case, the predetermined tolerance is ±20%.

[0024] In the above-mentioned constant force generator, it is desirable that the fixed portion comprises: a single rod-shaped body extending in the longitudinal direction on a second side surface that is parallel to the central axis and faces the first side surface, the rod-shaped body being made of a ferromagnetic material; a pair of magnetic plates extending in the longitudinal direction on third and fourth side surfaces that are parallel to the central axis, perpendicular to the first and second side surfaces, and facing each other at a distance, the pair of magnetic plates having a pair of opposing surfaces spaced a predetermined distance apart in a direction perpendicular to the central axis so as to sandwich the rod-shaped body therebetween, the pair of magnetic plates being made of a ferromagnetic material; and a pair of permanent magnetic plates extending in the longitudinal direction on the first side surface, the pair of permanent magnetic plates being arranged in contact with the pair of opposing surfaces of the pair of magnetic plates, respectively, to form the slit.

[0025] In the above constant force generator, the rod-shaped body may have a substantially rectangular parallelepiped shape that is long in the longitudinal direction and has a pair of contact surfaces that contact the pair of opposing surfaces of the pair of magnetic plates. In this case, the fixing portion may further include fastening members that fasten the pair of magnetic plates to the rod-shaped body so that the pair of opposing surfaces of the pair of magnetic plates contact the pair of contact surfaces of the rod-shaped body.

[0026] In the constant force generator, the pair of magnetic plates may have a pair of recesses extending in the longitudinal direction on the first side surface side and provided on the pair of opposing surfaces. In this case, it is preferable that the pair of permanent magnet plates are respectively disposed in the pair of recesses.

[0027] In the above constant force generator, each of the pair of permanent magnet plates may be composed of N (N is an integer of 2 or more) permanent magnet pieces divided in the longitudinal direction.

[0028] In the above constant force generator, it is preferable that each of the pair of permanent magnet plates includes a main magnet plate magnetized in a thickness direction perpendicular to the longitudinal direction and facing the opposing permanent magnet plate, and two sub-magnet plates magnetized in a width direction and arranged to sandwich the main magnet plate from both sides in a direction perpendicular to the longitudinal direction, so that the magnetic poles of the sub-magnet plates facing both sides of the sandwiched main magnet plate have the same polarity as the magnetic pole on the inside of the sandwiched main magnet plate. Alternatively, each of the pair of permanent magnet plates may be composed of a single magnet plate magnetized in a thickness direction perpendicular to the longitudinal direction and facing the opposing permanent magnet plate.

[0029] In the above-described constant force generator, the movable part may include a movable plate made of a ferromagnetic material inserted into the slit and extending in the longitudinal direction with a gap between it and the pair of permanent magnet plates; a guide made of a non-magnetic material spaced apart from the movable plate at a position away from the slit and extending in the longitudinal direction parallel to the movable plate; and a connecting member connecting the movable plate to the guide. The connecting member may be a pair of connecting members connecting the movable plate to the guide near the first end face and the second end face in a magnetically stable state in which the fixed part and the movable part are magnetically stable. It is also desirable that the pair of connecting members be made of a non-magnetic material. [Effects of the Invention]

[0030] According to the present invention, a constant force generator capable of increasing the stroke can be provided. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a perspective view of the exterior of a device in which a constant force generator according to the present invention is mounted, viewed obliquely from the upper front left. FIG. [Figure 2] 1 is an external perspective view of a constant force generator according to a first embodiment of the present invention, as viewed diagonally from the upper front left. FIG. [Figure 3] FIG. 3 is an external perspective view of the constant force generator shown in FIG. 2, seen obliquely from the rear upper right. [Figure 4] FIG. 3 is a front view of the constant force generator shown in FIG. 2. [Figure 5] FIG. 3 is a plan view of the constant force generator shown in FIG. 2. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 4. [Figure 7] FIG. 3 is an external perspective view of a fixing portion used in the constant force generator shown in FIG. 2, seen obliquely from the upper front left. [Figure 8] FIG. 8 is an exploded perspective view of the fixing portion shown in FIG. 7. [Figure 9]FIG. 3 is an external perspective view of a movable part used in the constant force generator shown in FIG. 2, seen obliquely from the upper front left. [Figure 10] FIG. 10 is an exploded perspective view of the movable portion shown in FIG. 9. [Figure 11] FIG. 10 is a plan view of a constant force generator according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] To facilitate understanding of the present invention, an apparatus equipped with a constant force generator according to the present invention will be described with reference to Fig. 1. Fig. 1 is an external perspective view of an apparatus 100 as seen obliquely from the upper front left.

[0033] Here, a Cartesian coordinate system (X, Y, Z) is used as shown in Fig. 1. In the state shown in Fig. 1, 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-to-down direction (height direction; vertical direction).

[0034] The device 100 includes a mounting plate 114 that extends vertically (parallel to the YZ plane). The mounting plate 114 has a front surface 114f that extends vertically and parallel to the YZ plane. The constant force generator 10, linear actuator 20, and guide mechanism 30 according to the present invention, which will be described later, are attached to the front surface 114f of the mounting plate 114.

[0035] The device 100 includes a driven body 150 that faces the front surface 114f of the mounting plate 114 across a gap. That is, the back surface (not shown) of the driven body 150 faces the front surface 114f of the mounting plate 114 at a predetermined distance. The driven body 150 has a substantially plate shape that extends vertically parallel to the YZ plane. The mounting plate 114 has a right side surface 114rs and a left side surface 114ls that face each other in the left-right direction Y. The right side surface 114rs and the left side surface 114ls each extend in the up-down direction Z (vertical direction). The left side surface 114ls is also referred to as the first side surface, and the right side surface 114rs is also referred to as the second side surface.

[0036] The linear actuator 20 is attached to the front surface 114f of the mounting plate 114, on the left side surface 114ls of the mounting plate 114. Meanwhile, the constant force generator 10 is attached to the right side surface 114rs of the mounting plate 114. In the illustrated example, the guide mechanism 30 is attached to the front surface 114f of the mounting plate 114 between the linear actuator 20 and the constant force generator 10. Each of the linear actuator 20 and the constant force generator 10 extends in the up-down direction (vertical direction) Z. Therefore, in this example, the up-down direction (vertical direction) Z is the longitudinal direction.

[0037] As described above, the linear actuator 20 is composed of an actuator shaft 22 having a central axis CA extending in the vertical direction Z, and a field coil (not shown) arranged around the actuator shaft 22. The actuator shaft 22 is formed by fixing a plurality of permanent magnets magnetized along the central axis CA in series with the same magnetic poles facing each other. The field coil is formed by connecting a plurality of cylindrical coils in series so as to concentrically enclose the actuator shaft 22 with a gap between them. The field coil is enclosed by a cylindrical, hollow, rectangular actuator case 24. That is, the field coil is attached to the inner wall surface of the actuator case 24. Therefore, the illustrated linear actuator 20 is a moving-coil (fixed-magnet) linear actuator, in which the motor shaft 22 is the fixed part and the combination of the field coil and the actuator case 24 is the moving part.

[0038] The lower end of the actuator shaft 22 is attached and fixed to the lower end of the left side surface 114ls on the front surface 114f of the mounting plate 114 by a lower connecting member 27. On the other hand, the upper end of the actuator shaft 22 is attached and fixed to the upper end of the left side surface 114ls on the front surface 114f of the mounting plate 114 by an upper connecting member 28. On the other hand, a driven body 150 is attached and fixed to the actuator case 24 by a connecting member 29. Therefore, the driven body 150 can be moved up and down as the actuator case 24 is moved up and down along the actuator shaft 22.

[0039] The constant force generator 10 has a central axis A that is parallel to the longitudinal direction, ie, the up-down direction (vertical direction) Z. The constant force generator 10 includes a fixed part 12 that extends in the longitudinal direction, and a movable part 14 that is arranged to extend in the longitudinal direction. The movable part 14 is movable in the longitudinal direction relative to the fixed part 12.

[0040] The fixed portion 12 is fixed to the right side surface 114rs of the mounting plate 114 via a fixing member 16.

[0041] As will be described in detail later, the movable part 14 includes a guide 144 arranged to extend in the longitudinal direction. The driven body 150 is attached to this guide 144 so that the driven body 150 can slide on the front surface 114f of the mounting plate 114. The guide mechanism 30 guides the driven body 150 together with the movable part 14 in the longitudinal direction Z along the guide 144, causing it to slide on the front surface 114f of the mounting plate 114. In the illustrated example, the guide 144 is rod-shaped, but as will be described later, the shape of the guide 144 is not limited to being rod-shaped.

[0042] As mentioned above, the constant force generator 10 configured as described above is intended to prevent the driven body 150, including the movable part of the linear actuator 20, from falling. In more detail, suppose that the power supply for supplying current to the field coil of the linear actuator 20 suddenly fails. In this case, the driven body 150, including the movable part of the linear actuator 20 and the movable part 14 of the constant force generator 10, is pulled downward by gravity F due to their own weight.G The constant force generator 10 generates this gravity F G The opposing upward thrust F TU As described above, the constant force generator 10 can maintain a constant thrust at any position in the stroke of the linear actuator 20. In the following description, the driven body 150 including the movable part of the linear actuator 20 and the movable part 14 of the constant force generator 10 will be simply referred to as the driven body 150.

[0043] Furthermore, the constant force generator 10 can not only prevent the driven body 150 from falling, but also function as a thrust assist mechanism for assisting the linear actuator 20 in providing a constant thrust while the linear actuator 20 is being driven.

[0044] Next, a method of using the constant force generator 10 operating as a thrust assist mechanism will be described in detail. First, assume that the constant force generator 10 is installed independently and not attached to the device 100. However, assume that the constant force generator 10 is disposed so that the direction of its central axis A is the up-down direction (vertical direction) Z. In this situation, the constant force generator 10 is stopped in a position where the fixed part 12 and the movable part 14 are magnetically stable (hereinafter simply referred to as the "stable position"). This state will be referred to as the "magnetically stable state." Here, the stable position is the point (position) where the center of the movable part 14 and the center of the fixed part 12 coincide. In this stable position (magnetically stable state), assume that a force is applied to the constant force generator 10 to push the movable part 14 in the up-down direction (vertical direction) Z. In this case, a thrust force is generated in the constant force generator 10 to return to the stable position (magnetically stable state). Specifically, suppose that a force that pushes the movable part 14 upward is applied to the constant force generator 10. In this case, the constant force generator 10 is subjected to a downward thrust F that tries to return to the above-mentioned stable position (magnetically stable state). TL occurs.

[0045] As described above, it is assumed that the constant force generator 10 is attached to the device 100 as shown in Fig. 1 while the movable part 14 is being pushed upward. In this case, the constant force generator 10 generates a downward thrust F that tries to push the driven body 150 downward. TL Therefore, in a state where no current flows through the field coil of the linear actuator 20, the constant force generator 10 generates a downward thrust F that attempts to return the driven body 150 to the above-mentioned stable position (magnetically stable state). TL Then, when the movable part 14 of the constant force generator 10 moves further downward from the stable position (magnetically stable state), the constant force generator 10 generates an upward thrust F that tries to return the driven body 150 to the above-mentioned stable position (magnetically stable state). TU As a result, the constant force generator 10 generates a downward force F acting on the driven body 150. G and the above upward thrust F TU The constant force generator 10 stops at an equilibrium position where the force is equal to the force of the movable part 14. It is clear that the equilibrium position at this time is a position where the movable part 14 of the constant force generator 10 is shifted downward from the stable position.

[0046] In the above-mentioned equilibrium position, suppose that a current is passed through the field coil of the linear actuator 20 to drive the movable part of the linear actuator 20 to move upward, thereby pushing the driven body 150 upward. In this case, if the movable part 14 of the constant force generator 10 moves upward from the above-mentioned stable position (magnetically stable state), the constant force generator 10 will generate a downward thrust F TL occurs.

[0047] 1 uses a moving coil type (fixed magnet type) linear actuator as the linear actuator 20, in which the actuator shaft 22 is the fixed part and the combination of the magnetic field coil and the actuator case 24 is the moving part. However, it goes without saying that a moving magnet type (fixed coil type) linear actuator may also be used as the linear actuator, in which the actuator shaft 22 is the moving part and the combination of the magnetic field coil and the actuator case 24 is the fixed part.

[0048] The above description can be summarized as follows: For example, as shown in FIG. 1, when a gravitational force F of 1 N (Newton) is applied to the driven body 150 of the device 100, G When gravity F acts on the object, G To counter this, a constant force generator 10 generates an upward thrust F equal to 1 N. TU In this case, within the range where the movable part 14 of the constant force generator 10 is lower than the stable position (magnetically stable state), the constant force generator 10 (driven body 150) can be stopped at any position when the field coil of the linear actuator 20 is not energized.

[0049] In response to this, the constant force generator 10 generates an upward thrust F TU In this case, when the field coil of the linear actuator 20 is not energized, the constant force generator 10 (driven body 150) stops at the upper end point.

[0050] On the other hand, the constant force generator 10 generates an upward thrust F TU In this case, when the field coil of the linear actuator 20 is not energized, the constant force generator 10 (driven body 150) stops at the lower end point.

[0051] The upward thrust F by the constant force generator 10 TUAt first glance, this may be an unnecessary load when the linear actuator 20 is driven by passing a current through the field coil to move the driven body 150 downward. However, when the driven body 150 is moved downward, the driven body 150 is always (originally) subjected to gravity F due to its own weight. G Therefore, the linear actuator 20 is operated by the difference (F G -F T This is also true when moving the driven body 150 in the upward direction. Therefore, the upward thrust F by the constant force generator 10 is TU As a result, the linear actuator 20 only needs to be driven with a smaller thrust than in the absence of the 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 actuator 20 required to drive the driven body 150 upward.

[0052] As is clear from the above description, by using the constant force generator 10 as a thrust assist mechanism, the linear actuator 20 can be made smaller. This is because, if the thrust of the linear actuator were to be increased without using the constant force generator 10 as a thrust assist mechanism, it would be necessary to increase the volume of the permanent magnets constituting the linear actuator or increase the number of turns of the field coil constituting the linear actuator. This would result in a larger size of the linear actuator. Furthermore, neodymium magnets, which have strong magnetic force, are generally used as permanent magnets constituting linear actuators. However, neodymium magnets are expensive. Therefore, by using the constant force generator 10 as a thrust assist mechanism, it is possible to employ a low-thrust linear actuator 20 equipped with inexpensive permanent magnets other than neodymium magnets as the permanent magnets constituting the linear actuator, thereby reducing costs.

[0053] In the device 100 shown in FIG. 1 , the mounting plate 114 extends in the vertical direction Z and has a first side surface (left side surface 114ls) and a second side surface (right side surface 114rs) that face each other. The driven body 120 can be driven in the vertical direction Z on the mounting plate 114. The linear actuator 20 is attached to the first side surface (left side surface 114ls) of the mounting plate 114 and drives the driven body 150 in the vertical direction Z. The constant force generator 10 is attached to the second side surface (right side surface 114rs) of the mounting plate 114, and the vertical direction Z is its longitudinal direction. The constant force generator 10 is configured such that the driven body 150 is attached to a guide 144 so that the driven body 150 can slide on the mounting plate 114. The guide mechanism 30 guides the driven body 150 together with the movable part 14 while sliding it on the mounting plate 114 along the guide 144 in the vertical direction Z.

[0054] However, the device to which the present invention is applicable is not limited to the device 100 shown in Fig. 1. In general, the device to which the present invention is applicable may include a mounting plate 114 extending in the longitudinal direction, a driven body 150 that can be driven in the longitudinal direction on the mounting plate 114, a linear actuator 20 attached to the mounting plate 114 and driving the driven body 150 in the longitudinal direction, a constant force generator 10 attached to the mounting plate 114 and having the driven body 150 attached to a guide 144 so that the driven body 150 can slide on the mounting plate 114, and a guide mechanism 30 that guides the driven body 150 together with the movable part 14 along the guide 144 in the longitudinal direction on the mounting plate 114 while sliding it. The longitudinal direction here is not limited to the vertical direction (up and down direction) Z, and may be any direction.

[0055] The illustrated guide mechanism 30 is composed of a ball spline bearing 32, one rail 34, and a linear guide 36. The ball spline bearing 32 is fixed to the front surface 114f of the mounting plate 114. The ball spline bearing 32 supports the guide 144 as a spline shaft. The rail 34 is laid on the front surface 114f of the mounting plate 114, parallel to and spaced apart from the guide 144. The rail 34 is firmly fixed to the front surface 114f of the mounting plate 114 using a number of bolts. The linear guide 36 is attached to the driven body 120 with the guide 144 sandwiched therebetween and slides on the rail 34. In this way, the illustrated guide mechanism 30 uses two types of guide members to guide the guide 144. Using two types of guide members prevents the fixed part 12 and the movable part 14 that constitute the constant force generator 10 from magnetically attracting and sticking to each other.

[0056] Therefore, if the magnetic attraction force acting between the fixed part 12 and the movable part 14 is weak, the guide mechanism 30 may be composed of only one type of guide member. That is, the guide mechanism 30 may be composed of only the ball spline bearing 32. Alternatively, the guide mechanism 30 may be composed of only the combination of the rail 34 and the linear guide 36. In this case, as described above, the shape of the guide 144 does not need to be rod-like, and any shape may be adopted.

[0057] Furthermore, the method of mounting the guide mechanism 30 to the mounting plate 114 is not limited to the above example, and any other method may be used. For example, instead of the rail 34 described above, a linear guide rail 34A may be mounted on the movable part 14 of the constant force generator 10, as shown in FIG. 1.

[0058] In the above-described assembly example, the movable part 14 of the constant force generator 10 is attached to the guide mechanism 30, and the guide mechanism 30 is attached to the movable part of the linear actuator 20. However, the assembly example is not limited to this. For example, the movable part 14 of the constant force generator 10 may be attached directly to the linear actuator 20. In this case, the movable part of the linear actuator 20 is attached to the guide mechanism 30.

[0059] [First embodiment] A constant force generator 10 according to a first embodiment of the present invention will be described with reference to Figures 2 to 10. Figure 2 is an external perspective view of the constant force generator 10 as seen obliquely from the front upper left. Figure 3 is an external perspective view of the constant force generator 10 as seen obliquely from the rear upper right. Figure 4 is a front view of the constant force generator 10. Figure 5 is a plan view of the constant force generator 10. Figure 6 is a cross-sectional view taken along line VI-VI in Figure 4. Figure 7 is an external perspective view of the fixed part 12 used in the constant force generator 10 as seen obliquely from the front upper left. Figure 8 is an exploded perspective view of the fixed part 12. Figure 9 is an external perspective view of the movable part 14 used in the constant force generator 10 as seen obliquely from the front upper left. Figure 10 is an exploded perspective view of the movable part 14. The above-described Cartesian coordinate system (X, Y, Z) is also used in Figures 2 to 10.

[0060] As described above, the illustrated constant force generator 10 includes a fixed portion 12 extending in the longitudinal direction Z and a movable portion 14 disposed to extend in the longitudinal direction Z. The movable portion 14 is movable in the longitudinal direction Z relative to the fixed portion 12. First, the fixed portion 12 will be described in detail, followed by a detailed description of the movable portion 14.

[0061] 7, the fixing portion 12 has a central axis A extending in the longitudinal direction Z, and is substantially in the shape of a rectangular parallelepiped that is long in the longitudinal direction Z. That is, the fixing portion 12 has an upper end surface 12 UE and bottom surface 12 LE and left side 12 LS and right side 12 RS and front 12 FS and rear 12 BSThe upper end surface 12 has a virtual rectangular parallelepiped shape. UE and bottom surface 12 LE and are perpendicular to the central axis A and face each other at a distance in the longitudinal direction Z. UE is also called the first end face, and the lower end face 12 LE is also called the second end face. LS and right side 12 RS are parallel to the central axis A and face each other with a gap in the left-right direction Y. LS is also called the first side, and the right side 12 RS is also called the second side. FS and rear 12 BS are parallel to the central axis A and spaced apart in the front-rear direction X. FS and rear 12 BS Left side (first side) 12 LS and right side (second side) 12 RS It is perpendicular to the front 12 FS is also called the third side, and the rear 12 BS is also called the fourth aspect.

[0062] As can be seen from Fig. 7, the fixed portion 12 has a configuration (structure) that is plane-symmetric (mirror-symmetric) with respect to the YZ plane that passes through the central axis A. Therefore, as is clear from Fig. 2 and Fig. 3, the constant force generator 10 also has a configuration (structure) that is plane-symmetric (mirror-symmetric) with respect to the YZ plane that passes through the central axis A. In other words, the fixed portion 12 (constant force generator 10) has a configuration (structure) in which the YZ plane that passes through the central axis A is the plane of symmetry (mirror plane).

[0063] The fixing portion 12 has a slit 122 having a substantially U-shaped cross section. The slit 122 is formed on the upper end surface (first end surface) 12 UE and the lower end surface (second end surface) 12 LE and left side (first side) 12 LS , and is open along the longitudinal direction Z. The fixing part 12 has a fixed length L1 in the longitudinal direction Z (see FIG. 4).

[0064] Meanwhile, although the detailed configuration will be described later, the movable part 14 is disposed so as to extend in the longitudinal direction Z while being partially inserted into the slit 122. The movable part 14 has a movable length L2 in the longitudinal direction Z (see FIG. 4). In the illustrated example, this movable length L2 is substantially equal to the fixed length L1 (L1 ≈ L2). Specifically, the movable length L2 is slightly longer than the fixed length L1 by an amount obtained by adding a small thickness to the thickness of a pair of connecting members 146 that constitute the movable part 14, which will be described later.

[0065] However, the movable length L2 is not limited to being substantially equal to the fixed length L1, and may be equal to the fixed length L1 within a predetermined tolerance. Specifically, the relationship may be 0.80L1≦L2≦1.20L1. That is, the predetermined tolerance may be ±20%.

[0066] As described above, the constant force generator 10 according to the first embodiment is configured such that the fixed length L1 of the fixed portion 12 and the movable length L2 of the movable portion 14 are substantially equal (within a predetermined tolerance) (L1≈L2). As a result, compared to known constant force generators, it is possible to reduce the amount of protrusion of the tip of the movable portion 14 from the tip of the fixed portion 12. Therefore, even when the constant force generator 10 having such a structure is incorporated into a device 100 employing a linear actuator 20 as shown in FIG. 1, the amount of protrusion can be reduced. As a result, the fixed length L1 of the fixed portion 12 can be increased, thereby enabling a longer stroke. Therefore, it is possible to provide a constant force generator 10 capable of increasing the stroke.

[0067] 5, the fixed portion 12 includes a rod-shaped body 124, a pair of magnetic plates 125, and a pair of permanent magnet plates 126. The rod-shaped body 124 is attached to the right side surface (second side surface) 12. RSThe rod-shaped body 124 extends in the longitudinal direction Z on the side of the rod-shaped body 124. The rod-shaped body 124 is made of a ferromagnetic material. For example, nickel-plated rolled steel for general structure (SS400) can be used as the material of the ferromagnetic body. However, the material of the ferromagnetic body is not limited to this, and it goes without saying that other ferromagnetic bodies can also be used.

[0068] The pair of magnetic plates 125 are disposed on the front surface (third side surface) 12 FS Side and rear (fourth side) BS The pair of magnetic plates 125 extend in the longitudinal direction Z on the side of the central axis A. The pair of magnetic plates 125 have a pair of opposing surfaces 125 spaced a predetermined distance apart in the direction (front-rear direction) X perpendicular to the central axis A, so as to sandwich the rod-shaped body 124 therebetween. OS (See FIG. 5). The pair of magnetic plates 125 are also made of a ferromagnetic material. For example, nickel-plated rolled steel for general structure (SS400) can be used as the ferromagnetic material. However, the ferromagnetic material is not limited to this, and other ferromagnetic materials can of course be used.

[0069] The pair of permanent magnet plates 126 are attached to the left side surface (first side surface) 12 LS 5, the pair of permanent magnet plates 126 are arranged on the pair of opposing surfaces 125 of the pair of magnetic plates 125 so as to form the slits 122. OS The pair of magnetic plates 125 are arranged in contact with each other. As the material for the pair of magnetic plates 125, for example, a permanent magnet such as a sintered neodymium magnet can be used. However, the material for the permanent magnet is not limited to this, and it goes without saying that other permanent magnets may also be used.

[0070] As shown in FIG. 8, the pair of magnetic plates 125 are provided on the left side surface (first side surface) 12. LS A pair of opposing surfaces 125 extending in the longitudinal direction Z on the side OS A pair of recesses 125 provided in C The pair of permanent magnet plates 126 each have a pair of recesses 125. C In this example, each of the pair of permanent magnet plates 126 is divided in the longitudinal direction Z and is arranged in N (N is an integer of 2 or more) permanent magnet pieces 126. PIn the illustrated example, N is equal to 4. Therefore, each of the pair of permanent magnet plates 126 has four permanent magnet pieces 126. P It consists of:

[0071] However, each of the pair of permanent magnet plates 126 may be formed from a single magnet plate without being divided.

[0072] As shown in FIG. 5, four permanent magnet pieces 126 P Each of the magnet pieces 126 PP and two sub-magnet pieces 126 PS Sub magnet piece 126 PS is also called an auxiliary magnet piece. PP Each main magnet piece 126 is arranged to be magnetized in the thickness direction (front-rear direction X) perpendicular to the longitudinal direction Z and facing the opposing permanent magnet piece 126. PP is the distance between the main magnet pieces 126 facing each other in the front-rear direction X with respect to the YZ plane (plane of symmetry; mirror plane) passing through the central axis A. PP On the other hand, the two sub-magnet pieces 126 PS 1 main magnet piece 126 P The two sub-magnet pieces 126 are magnetized in the width direction (left-right direction Y) so as to sandwich the magnet piece 126 from both sides in a direction perpendicular to the longitudinal direction Z. PS The sandwiched main magnet piece 126 PP Sub-magnet pieces 126 facing both sides of PS The magnetic poles of the sandwiched main magnet pieces 126 PP For example, the main magnet pieces 126 are sandwiched so that the magnetic poles of the two main magnet pieces 126 have the same polarity as the magnetic poles of the two main magnet pieces 126. PP In this case, the pair of sub-magnet pieces 126 on both sides of the inner magnetic pole is the N pole. PS The main magnet pieces 126 sandwiched between them are arranged so that they have the same polarity as the north poles. PP In this way, each permanent magnet piece 126 P One main magnet piece 126 PP and a pair of auxiliary magnet pieces 126 sandwiching it. PS This forms a permanent magnet region with a Halbach structure.

[0073] As shown in FIG. 8, the pair of permanent magnet plates 126 having such a configuration are formed by a pair of opposing surfaces 125 of a pair of magnetic plates 125 made of a ferromagnetic material. OS The pair of recesses 125 of the pair of magnetic plates 125 are arranged C 7, the pair of recesses 125 of the pair of magnetic plates 125 are bonded to the magnetic plates 125 with an adhesive. C A pair of permanent magnet plates 126 are fixed to the

[0074] In addition, when each of the pair of permanent magnet plates 126 is composed of one magnet plate, each of the pair of permanent magnet plates 126 is composed of one main magnet plate 126 PP and two sub-magnet plates 126 PS It consists of:

[0075] The rod-shaped body 124 has a substantially rectangular parallelepiped shape that is long in the longitudinal direction Z. As shown in FIG. OS A pair of contact surfaces 124 that contact CS have.

[0076] 8, the fixing portion 12 further includes a fastening member 127. The fastening member 127 is fixed to a pair of opposing surfaces 125 of the pair of magnetic plates 125. OS and a pair of contact surfaces 124 of the rod-shaped body 124 CS The pair of magnetic plates 125 and the rod-shaped body 124 are fastened together so that they come into contact with each other.

[0077] More specifically, as shown in FIG. 8, the pair of magnetic plates 125 have a plurality of through holes 125 TH A plurality of through holes 125 TH are arranged at predetermined intervals in the longitudinal direction Z and are formed in the pair of magnetic plates 125 in the direction (front-rear direction) X perpendicular to the longitudinal direction Z. In the illustrated example, there are eight through holes 125 in each of the magnetic plates 125, so that there are a total of 16 through holes 125 in the pair of magnetic plates 125. TH The illustrated fastening member 127 has 16 screw holes 127. SH and 16 screws 127 SIt consists of 16 screw holes 127 SH The pair of contact surfaces 124 of the rod-shaped body 124 CS 16 through holes 125 TH 16 screws 127 are drilled at positions corresponding to the S 16 through holes 125 TH 16 screw holes through each 127 SH It is screwed onto the

[0078] As shown in FIG. 6, 16 through-holes 125 TH 16 corresponding screws 127 S Screw head 127 H 16 screw head accommodation holes 125 THA Each screw has 127 S Screw head 127 H The thickness (height) of each screw head receiving hole is 125mm. THA Therefore, each screw 127 S The corresponding through hole 125 TH Through the corresponding screw hole 127 SH When screwed into the screw, the screw 127 S Screw head 127 H The outer surfaces (front surfaces 12) of the pair of magnetic plates 125 FS and rear 12 BS ) and does not protrude outward beyond the screw head receiving hole 125 THA be housed within.

[0079] In the first embodiment, the fastening members 127 are a plurality of screws 127. S and multiple screw holes 127 SH The pair of magnetic plates 125 and the rod-shaped body 124 are firmly fastened together using the fastening members 127, but the fastening members 127 are not limited to this. OS and a pair of contact surfaces 124 of the rod-shaped body 124 CS Any fastening member may be used as long as it can firmly fasten the pair of magnetic plates 125 and rod-shaped body 124 together so that they come into contact with each other.

[0080] As shown in FIG. 9, the illustrated movable part 14 includes a movable plate 142, the guide 144, and the pair of connecting members 146. As shown in FIGS. 2 and 6, the movable plate 142 is inserted into the slit 122 of the fixed part 12. The movable plate 142 is disposed extending in the longitudinal direction Z with a gap between it and the pair of permanent magnet plates 126. The movable plate 142 is made of a ferromagnetic material. In the illustrated example, stainless steel (SUS420J2) is used as the ferromagnetic material. However, the ferromagnetic material is not limited to this, and it goes without saying that other ferromagnetic materials may also be used.

[0081] 9, the movable part 14 also has a configuration (structure) that is plane-symmetric (mirror-symmetric) with respect to the YZ plane that passes through the central axis A. In other words, the movable part 14 has a configuration (structure) in which the YZ plane that passes through the central axis A is the plane of symmetry (mirror plane).

[0082] The guide 144 is spaced apart from the fixed part 12 at a position away from the slit 122. The guide 144 is disposed parallel to the movable plate 142 and extends in the longitudinal direction Z. The guide 144 is made of a non-magnetic material. In the illustrated example, stainless steel (SUS303) is used as the non-magnetic material to prevent rust. However, the non-magnetic material is not limited to this, and it goes without saying that other non-magnetic materials may also be used.

[0083] In the magnetically stable state described above, the pair of connecting members 146 have upper end surfaces (first end surfaces) 12 UE and the lower end surface (second end surface) 12 LE The movable plate 142 and the guide 144 are connected at a position near the position.

[0084] More specifically, as shown in FIG. 10, in the magnetically stable state, the movable plate 142 has an upper end surface (first end surface) 12 UE and the lower end surface (second end surface) 12 LE Two plate screw holes 142 drilled in each of both end surfaces of the movable plate 142 at positions near SH In the magnetically stable state, the guide 144 has an upper end surface (first end surface) 12UE and the lower end surface (second end surface) 12 LE A pair of rod screw holes 144 are drilled at both ends of the guide 144 at positions near the SH have.

[0085] The pair of connecting members 146 is made up of a pair of connecting plates 146 P and six screws 146 S A pair of connecting plates 146 P In the magnetically stable state, the upper end surface (first end surface) 12 UE and the lower end surface (second end surface) 12 LE The pair of connecting plates 146 are provided in the vicinity of the pair of connecting plates 146 and contact both end surfaces of the movable plate 142 and both end portions of the guide 144. P , the plate screw hole 142 SH and a pair of rod screw holes 144 SH Six through holes 146 drilled at positions corresponding to the TH Therefore, each connecting plate 146 P There are three through holes 146 TH There are six screws 146 S There are six through holes 146 TH through the plate screw hole 142 SH and rod screw hole 144 SH The pair of connecting members 146 are made of a non-magnetic material. In the illustrated example, stainless steel (SUS303) is used as the non-magnetic material to prevent rust. However, the non-magnetic material is not limited to this, and it goes without saying that other non-magnetic materials may also be used.

[0086] In the illustrated example, two plate screw holes 142 are provided on each of both end surfaces of the movable plate 142. SH However, it is not limited to this. For example, at least one plate screw hole 142 is provided on each of both end surfaces of the movable plate 142. SH In the illustrated first embodiment, the pair of connecting members 146 are formed by a pair of connecting plates 146. P and several screws 146 SThe movable plate 142 and the guide 144 are firmly connected to each other by using a combination of these, but it is needless to say that the present invention is not limited to this. For example, the pair of connecting members 146 may be a combination of a pair of connecting plates and an adhesive, which firmly connects the movable plate 142 and the guide 144 to each other.

[0087] As described above, in the movable part 14 of this example, a pair of coupling members 146 are used as connecting members that connect the movable plate 142 and the guide 144, but the connecting members are not limited to this. Specifically, the movable plate 142 and the guide 144 may be connected using connecting members whose thickness is equal to or smaller than the width of the slit 122. In this case, it is not necessary to provide such connecting members on both end surfaces of the movable plate 142.

[0088] In the illustrated first embodiment, a single plate made of a ferromagnetic material is used as the movable plate 142 of the movable part 14, but the movable plate is not limited to this. For example, the movable plate may be composed of a movable body having an opening in the front-rear direction X, and four permanent magnet pieces that are inserted into this opening and adhered to the movable body with an adhesive. In this case, each permanent magnet piece of the movable plate is sandwiched between the corresponding pair of permanent magnet pieces 126 of the pair of permanent magnet plates 126 of the fixed part 12. P Main magnet piece 126 PP For example, the main magnet piece 126 is magnetized to have a polarity opposite to that of the inner magnetic pole of the main magnet piece 126. PP In this case, the magnetic pole of the permanent magnet piece on the movable plate facing it is a south pole.

[0089] In the first embodiment, each permanent magnet plate 126 is divided into four permanent magnet pieces 126 in the longitudinal direction Z. P The illustrated constant force generator 10 has a stroke of 160 mm. P The length in the longitudinal direction Z of each permanent magnet plate 126 is 50 mm. Therefore, the fixed length L1 of the fixed portion 12 is equal to 200 mm. PIt can be seen that the number N of the constant force generators 10 and the length in the longitudinal direction Z can be selected arbitrarily depending on the stroke required for the constant force generator 10.

[0090] As shown in FIG. 1 and explained above, when the constant force generator 10 is attached to the device 100, it is positioned and attached with high precision so that the above gap is provided.

[0091] With the constant force generator 10 configured as described above, even if the thickness of the pair of magnetic plates 125 is thin, it is possible to prevent the magnetic flux generated from the permanent magnet region of the fixed part 12 from leaking to the outside from the fixed part 12. This is because, as described above, the permanent magnet region of the fixed part 12 has a Halbach structure. Therefore, it is possible to provide a constant force generator 10 that can minimize leakage magnetic flux.

[0092] [Second embodiment] A constant force generator 10A according to a second embodiment of the present invention will be described with reference to Fig. 11. Fig. 11 is a plan view of the constant force generator 10A. The above-mentioned Cartesian coordinate system (X, Y, Z) is also used in Fig. 11.

[0093] The illustrated constant force generator 10A has substantially the same configuration and operates as the constant force generator 10 according to the first embodiment described above, except for the difference in the configuration of the fixed portion. Therefore, the fixed portion is given the reference symbol 12A. In the constant force generator 10A, components similar to those of the constant force generator 10 according to the first embodiment described above are given the same reference symbols, and for simplicity of explanation, only the differences will be described below.

[0094] The illustrated fixed portion 12A has substantially the same configuration as the fixed portion 12 of the constant force generator 10 according to the first embodiment described above, except for the difference in the configuration of the pair of permanent magnet plates. Therefore, the pair of permanent magnet plates is given the reference symbol 126A. In the fixed portion 12A, components similar to those of the fixed portion 12 of the constant force generator 10 according to the first embodiment described above are given the same reference symbols, and for simplicity of explanation, only the differences will be described below.

[0095] In the fixed portion 12 of the constant force generator 10 according to the first embodiment described above, each of the pair of permanent magnet plates 126 is divided in the longitudinal direction Z into four permanent magnet pieces 126. P And four permanent magnet pieces 126 P Each of the magnet pieces 126 PP and two sub-magnet pieces 126 PS It was composed of:

[0096] In contrast, in the fixed portion 12A of the constant force generator 10A according to the second embodiment, each of the pair of permanent magnet plates 126A is divided in the longitudinal direction Z into four permanent magnet pieces 126A. P However, the four permanent magnet pieces 126A P Each of the permanent magnet pieces 126A is perpendicular to the longitudinal direction Z and faces the P Each permanent magnet piece 126A is composed of only one magnet piece that is magnetized in the thickness direction (front-rear direction X) facing the magnet piece 126A. P is the distance between the permanent magnet pieces 126A facing each other in the front-rear direction X with respect to the YZ plane (plane of symmetry; mirror plane) passing through the central axis A. P are magnetized with opposite polarities.

[0097] In the constant force generator 10A according to the second embodiment, the fixed length L1 of the fixed part 12A and the movable length L2 of the movable part 14 are also configured to be equal within a predetermined tolerance range. Therefore, it is possible to provide a constant force generator 10A that can extend the stroke.

[0098] In the constant force generator 10A according to the second embodiment, unlike the constant force generator 10 according to the first embodiment described above, the permanent magnet region of the fixed portion 12A does not have a Halbach structure. Therefore, although there is more leakage magnetic flux compared to the first embodiment, it is possible to provide a constant force generator 10A with a simpler configuration than the first embodiment.

[0099] In addition, when each of the pair of permanent magnet plates 126A is composed of one magnet plate, each of the pair of permanent magnet plates 126A is composed of one magnet plate 126A. P It consists only of

[0100] 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. [Industrial Applicability]

[0101] The constant 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 a constant thrust. Furthermore, the constant force generator according to the present invention can be used either for fall prevention only or for thrust assistance only. [Explanation of symbols]

[0102] 10, 10A constant force generator 12, 12A fixation site 12 UE Top end surface (first end surface) 12 LE Bottom end face (second end face) 12 LS Left side (first side) 12 RS Right side (second side) 12 FS Front (third side) 12 BS Rear (fourth side) 122 Slit 124 Rod-shaped body 124CS contact surface 125 Magnetic plate 125 OS Opposing surface 125 C recess 125 TH through holes 125 THA Screw head accommodation hole 126, 126A permanent magnet plate 126 P , 126A P Permanent magnet piece (magnet plate) 126 PP Main magnet piece (main magnet plate) 126 PS Sub magnet piece (auxiliary magnet piece; sub magnet plate) 127 Fastening members 127 SH screw holes 127 S Screw 127 H screw head 14 Movable parts 142 Movable plate 142 SH Plate screw holes 144 Guide (spline shaft) 144 SH Rod screw hole 146 Connecting member 146 P connecting plate 146 TH through holes 146 S Screw 20 Linear Actuators 22 Actuator shaft 24 Actuator case 27 Lower connecting member 28 Upper connecting member 29 Connecting members 30 Guide mechanism 32 Ball spline bearing 34, 34A rail 36 Linear guide 100 equipment 114 Mounting plate 114f front 114ls left side (first side) 114rs right side (second side) 150 Driven body A center axis X Anteroposterior direction Y left / right direction Z vertical direction (longitudinal direction) F G gravity F TU Upward thrust F TL Downward thrust L1 fixed length L2 movable length

Claims

1. a longitudinally extending fixation portion; a movable portion disposed to extend in the longitudinal direction and movable in the longitudinal direction relative to the fixed portion; 1. A constant force generator comprising: the fixing portion has a first end face and a second end face that are perpendicular to a central axis extending in the longitudinal direction and spaced apart from each other and opposed to each other, and a first side face that is parallel to the central axis, the fixing portion has a slit that has a generally U-shaped cross section that opens along the longitudinal direction, and has a fixed length in the longitudinal direction; the movable portion is arranged to extend in the longitudinal direction while being partially inserted into the slit, and has a movable length in the longitudinal direction that is equal to the fixed length within a predetermined tolerance range. A constant force generator characterized by:

2. 2. The constant force generator according to claim 1, wherein the fixed length is L1 and the movable length is L2, and the relationship is 0.80L1≦L2≦1.20L1.

3. The fixing portion is a single rod-shaped body extending in the longitudinal direction on a second side surface side parallel to the central axis and facing the first side surface, the rod-shaped body being made of a ferromagnetic material; a pair of magnetic plates extending in the longitudinal direction on third and fourth side surfaces that are parallel to the central axis, perpendicular to the first and second side surfaces, and spaced apart from each other, the pair of magnetic plates having a pair of opposing surfaces spaced a predetermined distance apart in a direction perpendicular to the central axis so as to sandwich the rod-shaped body therebetween, the pair of magnetic plates being made of a ferromagnetic material; a pair of permanent magnet plates extending in the longitudinal direction on the first side surface side, the pair of permanent magnet plates being arranged in contact with the pair of opposing surfaces of the pair of magnetic plates so as to form the slit; 3. The constant force generator of claim 1 or 2, comprising:

4. the rod-shaped body has a substantially rectangular parallelepiped shape that is long in the longitudinal direction, and has a pair of contact surfaces that contact the pair of opposing surfaces of the pair of magnetic plates, The fixing portion further includes fastening members that fasten the pair of magnetic plates and the rod-shaped body so that the pair of opposing surfaces of the pair of magnetic plates contact the pair of contact surfaces of the rod-shaped body.

4. The constant force generator of claim 3.

5. The pair of magnetic plates have a pair of recesses extending in the longitudinal direction and provided on the pair of opposing surfaces on the first side surface side, The pair of permanent magnet plates are respectively disposed in the pair of recesses.

4. The constant force generator of claim 3.

6. Each of the pair of permanent magnet plates is divided in the longitudinal direction and consists of N (N is an integer of 2 or more) permanent magnet pieces.

6. A constant force generator according to claim 3 or 5.

7. Each of the pair of permanent magnet plates is a main magnet plate magnetized in a thickness direction perpendicular to the longitudinal direction and facing the opposing permanent magnet plate; two sub-magnetic plates magnetized in the width direction so as to sandwich the main magnetic plate from both sides in a direction perpendicular to the longitudinal direction, the two sub-magnetic plates sandwiching the main magnetic plate such that the magnetic poles of the sub-magnetic plates facing both sides of the sandwiched main magnetic plate have the same polarity as the magnetic poles on the inner sides of the sandwiched main magnetic plates; 6. The constant force generator of claim 3 or 5, comprising:

8. 6. The constant force generator according to claim 3, wherein each of the pair of permanent magnet plates is composed of one magnet plate that is magnetized in a thickness direction perpendicular to the longitudinal direction and facing the opposing permanent magnet plate.

9. The movable portion is a movable plate made of a ferromagnetic material, inserted into the slit and extending in the longitudinal direction with a gap between the pair of permanent magnet plates; a guide made of a non-magnetic material, the guide being spaced apart from the movable plate at a position away from the slit, and extending in the longitudinal direction in parallel with the movable plate; a connecting member that connects the movable plate and the guide; 5. The constant force generator of claim 3 or 4, comprising:

10. 10. The constant force generator according to claim 9, wherein the connecting member comprises a pair of coupling members that couple the movable plate and the guide at positions near the first end face and the second end face in a magnetically stable state in which the fixed portion and the movable portion are magnetically stable.

11. 11. The constant force generator according to claim 10, wherein the pair of connecting members are made of a non-magnetic material.

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