Tension balancer

Abstract

This tension balancer is provided with first through n-th cylindrical members, first through (n − 1)th coil springs, a first hook that is attached to the first cylindrical member, a second hook that is attached to the n-th cylindrical member, and a scale that is attached to the n-th cylindrical member. The scale extends in a first direction that is parallel to a central axis of the first through n-th cylindrical members, is located outside the n-th cylindrical member, overlaps with the n-th cylindrical member in a second direction that is perpendicular to the first direction, and can expand and contract in the first direction. The first through n-th cylindrical members are disposed so that each (j + 1)th cylindrical member selected from among the first through n-th cylindrical members is surrounded by the j-th cylindrical member. The cylindrical members and the coil springs mutually alternate. n is a natural number of 3 or greater, and j is a variable selected from natural numbers and at least 1 and no more than (n − 1).

Description

Tension balancer

[0001] SUMMARY OF THE INVENTION An embodiment of the present invention relates to a tension balancer that can be used on overhead lines.

[0002] Tension balancers are attached to overhead wires, such as those used in railways, as devices for tensioning the wires with an appropriate tension even when they expand or contract due to temperature changes. For example, Patent Documents 1 and 2 disclose tension balancers whose basic configuration includes multiple cylindrical members arranged coaxially and coil springs arranged between the cylindrical members. Furthermore, a graduated scale is attached to the tension balancer as an index for measuring its displacement, which makes it possible to grasp the condition of the coil springs inside the tension balancer.

[0003] JP 2014-108766 A JP 2009-303301 A

[0004] One of the objects of the embodiments of the present invention is to provide a tension balancer with a novel structure, or to provide a tension balancer that can be used with an appropriate stroke length for a long period of time.

[0005] One embodiment of the present invention is a tension balancer. The tension balancer includes first to n-th cylindrical members, first to (n-1)-th coil springs, a first hook attached to the first cylindrical member, a second hook attached to the n-th cylindrical member, and a scale attached to the n-th cylindrical member. The scale extends in a first direction parallel to the central axis of the first to n-th cylindrical members, is located outside the n-th cylindrical member, overlaps with the n-th cylindrical member in a second direction perpendicular to the first direction, and is configured to be expandable and contractible in the first direction. The first to n-th cylindrical members are arranged such that a j-th cylindrical member selected from the first to n-th cylindrical members is surrounded by a (j+1)-th cylindrical member selected from the first to n-th cylindrical members. The cylindrical members and the coil springs alternate with each other. n is a natural number equal to or greater than 3, and j is a variable selected from natural numbers equal to or greater than 1 and equal to (n-1).

[0006] 1 is a schematic perspective view of a tension balancer according to an embodiment of the present invention; a schematic end view of a tension balancer according to an embodiment of the present invention; a schematic side view of a portion of a tension balancer according to an embodiment of the present invention; a schematic side view of a portion of a tension balancer according to an embodiment of the present invention; a schematic end view of a portion of a tension balancer according to an embodiment of the present invention; a schematic side view of a portion of a tension balancer according to an embodiment of the present invention; a schematic side view of a portion of a tension balancer according to an embodiment of the present invention; a schematic side view of a portion of a tension balancer according to an embodiment of the present invention; a schematic side view of a portion of a tension balancer according to an embodiment of the present invention; a schematic side view of a portion of a tension balancer according to an embodiment of the present invention; a schematic end ....

[0007] Hereinafter, each embodiment of the invention disclosed in this application will be described with reference to the drawings. However, the present invention can be embodied in various forms without departing from the spirit of the invention, and should not be construed as being limited to the description of the embodiments exemplified below.

[0008] In order to clarify the description, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual embodiment, but these are merely examples and do not limit the interpretation of the present invention. Furthermore, in this specification and each drawing, elements having the same functions as those explained in the previous drawings may be assigned the same reference numerals, and duplicate explanations may be omitted.

[0009] In this specification and drawings, the same reference numeral is used to collectively represent multiple identical or similar components, and a hyphen and a number are added after the reference numeral to represent each of the components individually. When multiple parts of a single component are to be distinguished from one another, the same reference numeral and alphabetic characters are used.

[0010] In this specification and claims, the expression "a structure exposed from another structure" means a state in which a part of a structure is not covered by another structure, and includes a state in which the part not covered by another structure is covered by yet another structure. The state expressed by this expression also includes a state in which a structure is not in contact with another structure.

[0011] The following describes a tension balancer 100 according to an embodiment of the present invention. The tension balancer 100 can be used to tension an overhead wire with an appropriate tension.

[0012] 1. Overall Structure Figure 1 shows a schematic perspective view of a tension balancer 100. The tension balancer 100 comprises multiple cylindrical members arranged coaxially and with different outer diameters. The tension balancer 100 shown in Figure 1 is a two-stage tension balancer with three cylindrical members: a first cylindrical member 110, a second cylindrical member 120, and a third cylindrical member 130. There are no restrictions on the number of cylindrical members, and it is typically between two and four, and may be five or more. In the tension balancer 100, a cylindrical member with a smaller outer diameter is partially inserted into a cylindrical member with a larger outer diameter. More specifically, if tension balancer 100 has first to nth cylindrical members (n is a natural number greater than or equal to 2) and the outer diameters decrease in the order from the first cylindrical member to the nth cylindrical member, the (j+1)th cylindrical member (j is a variable selected from natural numbers greater than or equal to 1 and greater than (n-1)) is arranged so that it is surrounded by the jth cylindrical member, and the (j+1)th cylindrical member can reversibly slide inside the jth cylindrical member in the direction of the central axis of each cylindrical member. Below, we will continue the explanation using a two-stage tension balancer 100 (i.e., a tension balancer where n is 3).

[0013] A pole-side mounting member (hereinafter referred to as the first hook) 102 is attached directly or indirectly to one end of the first cylindrical member 110, which has the largest outer diameter. This first hook 102 can be used to connect the tension balancer 100 to a fixed structure such as a pole. As an optional configuration, a hanger hook 106 and / or an opening (not shown) for hanging the tension balancer 100 during assembly or installation may be provided on the upper part of the first cylindrical member 110. Meanwhile, an overhead-line-side mounting member (hereinafter referred to as the second hook) 104, which is connected to an overhead line, is attached directly or indirectly to one end of the cylindrical member having the smallest outer diameter (here, the third cylindrical member 130). As will be described later, a coil spring is disposed in a compressed state between adjacent cylindrical members, and multiple cylindrical members and multiple coil springs alternate with each other. The elastic force of the coil spring as it tries to expand generates a force that pulls the adjacent inner cylindrical member inward, allowing the overhead wire to be pulled with the appropriate tension.

[0014] Hereinafter, the lengthwise direction of the tension balancer 100 is referred to as the x-direction, and the vertical direction when the tension balancer 100 is installed so that the x-direction is horizontal is referred to as the z-direction. The direction perpendicular to the x-direction and z-directions is referred to as the y-direction. The x-direction is parallel to the central axes of the tension balancer 100 and each cylindrical member, and is the direction in which the second through n-th cylindrical members slide.

[0015] 2. First Cylindrical Member FIG. 2 shows a schematic diagram of the end surface along the chain line A-A' extending in the x direction in FIG. 1 . As shown in FIG. 2 , a first back plate 140 forming the bottom surface can be provided at one end of the first cylindrical member 110 where the first hook 102 is located. The first hook 102 may be attached to the first back plate 140 by welding or bolting, or may be fixed to the first cylindrical member 110 without the first back plate 140. Although not shown, the first cylindrical member 110 may also be provided with an opening for draining water that has infiltrated inside. A detachment prevention mechanism for preventing the second cylindrical member 120 and the third cylindrical member 130 from detaching is further provided at the one end where the first hook 102 is located. There are no restrictions on the structure of the detachment prevention mechanism, and in the example shown in FIGS. 1 and 2 , a U-shaped bar 142 is provided as the detachment prevention mechanism. The U-shaped bar 142 extends in a direction perpendicular to the z direction and penetrates the first cylindrical member 110, and a collar 144 provided at the end of the U-shaped bar 142 prevents the U-shaped bar 142 from falling off. The first back plate 140 moves toward the first hook 102 due to the elastic forces of the first coil spring 112 provided between the first cylindrical member 110 and the second cylindrical member 120, and the second coil spring 122 provided between the second cylindrical member 120 and the third cylindrical member 130, but this movement is restricted by the U-shaped bar 142 and the first back plate 140.

[0016] A ring-shaped first front washer 114 is provided on the end of the first cylindrical member 110 opposite the first hook 102 (i.e., the end on the second hook 104 side). The first front washer 114 can be provided so as to be surrounded by the first cylindrical member 110, blocking a portion of the first cylindrical member 110. An opening in the first front washer 114 serves as an opening through which the second cylindrical member 120 slides within the first cylindrical member 110, with a portion of the second cylindrical member 120 exposed from the first cylindrical member 110. Although not shown, the first front washer 114 may not be surrounded by the first cylindrical member 110, but may instead have an outer diameter identical or substantially identical to the outer diameter of the first cylindrical member 110, blocking a portion of the first cylindrical member 110. Alternatively, the first front washer 114 may be integral with the first cylindrical member 110.

[0017] 3. Second Cylindrical Member The second cylindrical member 120 is disposed within the first cylindrical member 110. A ring-shaped first rear washer 124 is provided on the end of the second cylindrical member 120 on the first hook 102 side. In the example shown in FIG. 2 , the first rear washer 124 is disposed so as to surround the second cylindrical member 120. However, the first rear washer 124 may not surround the second cylindrical member 120, and the first rear washer 124 may be disposed on the end of the second cylindrical member 120, having an inner diameter that is the same as or substantially the same as the inner diameter of the second cylindrical member 120. The first rear washer 124 may be integral with the second cylindrical member 120. The first coil spring 112 is disposed between the first front washer 114 and the first rear washer 124 in the space between the first cylindrical member 110 and the second cylindrical member 120. Therefore, the compressed first coil spring 112 pushes the first front washer 114 and the first rear washer 124 in opposite directions due to the elastic force of the spring as it tries to expand, resulting in a force that pulls the second cylindrical member 120 into the first cylindrical member 110.

[0018] Similar to the first cylindrical member 110, a ring-shaped second front washer 126 is provided on the end of the second cylindrical member 120 on the second hook 104 side. The second front washer 126 can be provided so as to be surrounded by the second cylindrical member 120, blocking a portion of the second cylindrical member 120. The opening in the second front washer 126 serves as an opening through which the third cylindrical member 130 slides within the second cylindrical member 120, with a portion of the third cylindrical member 130 exposed from the second cylindrical member 120. Although not shown, the second front washer 126 may not be surrounded by the second cylindrical member 120, but may instead have an outer diameter identical or substantially identical to the outer diameter of the second cylindrical member 120, blocking the second cylindrical member 120. Alternatively, the second front washer 126 may be integral with the second cylindrical member 120.

[0019] 4. Third Cylindrical Member Similar to the second cylindrical member 120, the third cylindrical member 130 is disposed within the second cylindrical member 120, and a ring-shaped second rear washer 132 is provided at the end of the third cylindrical member 130 on the side of the first hook 102. In the example shown in FIG. 2 , the second rear washer 132 is provided so as to surround the third cylindrical member 130, but the second rear washer 132 may not surround the third cylindrical member 130, and the second rear washer 132 may have an inner diameter that is the same as or substantially the same as the inner diameter of the third cylindrical member 130 and be provided at the end of the third cylindrical member 130. The second rear washer 132 may be integral with the third cylindrical member 130. The second coil spring 122 is disposed between the second front washer 126 and the second rear washer 132 in the space between the second cylindrical member 120 and the third cylindrical member 130. Therefore, the compressed second coil spring 122 pushes the second front washer 126 and the second rear washer 132 in opposite directions due to the elastic force of the second coil spring 122 as it tries to expand. As a result, a force is generated that pulls the third cylindrical member 130 into the second cylindrical member 120.

[0020] When the second cylindrical member 120 and the third cylindrical member 130 slide relative to the first cylindrical member 110, the first coil spring 112 and the second coil spring 122 expand and contract. At this time, the first coil spring 112 and the second coil spring 122 rotate about the x-direction, which may result in the second cylindrical member 120 and the third cylindrical member 130 also rotating. Therefore, as an optional configuration, a second back plate 134 having a slit may be provided on the first hook 102 side so as to cover a portion of the third cylindrical member 130, and a plate-shaped guide plate 146 may be further disposed so as to penetrate the slit in the second back plate 134. The guide plate 146 may be disposed so as to penetrate the first back plate 140. In this case, the guide plate 146 may function as the first hook 102, or the first hook 102 may be fixed to the end of the guide plate 146. By providing a second back plate 134 having a slit and a plate-shaped guide plate 146 that passes through this slit, rotation of the third cylindrical member 130, which is located innermost, is prevented, and therefore rotation of the cylindrical member (here, the second cylindrical member 120) located between the first cylindrical member 110 and the cylindrical member with the smallest diameter (here, the third cylindrical member 130) can also be restricted.

[0021] 5. Scale and Pointer Member As shown in FIGS. 1 and 2 , a scale 150 extending in a direction parallel to the central axis of each cylindrical member (i.e., the x-direction) is attached to the innermost third cylindrical member 130. The scale 150 is located outside the third cylindrical member 130 and is arranged so as to overlap the first cylindrical member 110 to the third cylindrical member 130 in the z-direction. The scale 150 and the third cylindrical member 130 are fixed to each other by any method, and even if the cylindrical members move, the relative distance and positional relationship between the third cylindrical member 130 and the scale 150 remain constant. There are no limitations on the method for fixing the scale 150 and the third cylindrical member 130. For example, as shown in FIGS. 1 and 2 , a plate-shaped front plate 152 may be fixed to the end of the third cylindrical member 130, and the scale 150 may be fixed to the front plate 152 by welding or bolting. Although not shown, instead of the front plate 152, the scale 150 and the third cylindrical member 130 may be fixed using a single rod or a plurality of posts.

[0022] Graduations are provided on the outer surface of the scale 150. The graduations may be formed, for example, by ink printed in stripes extending in a direction perpendicular to the x-direction, by tape wound around the scale 150, or by engraving.

[0023] Here, scale 150 is configured so as to be reversibly expandable and contractible in the x direction (see the dotted arrow in FIG. 1). There are no restrictions on the mechanism for expanding and contracting in the x direction, and for example, as shown in FIG. 3A, scale 150 may be configured to include a beam 156 fixed to third cylindrical member 130 and a cylindrical slide member 154 that houses beam 156. Graduations are marked on the outer surface of slide member 154.

[0024] The beam 156 is connected to the third cylindrical member 130 directly or via, for example, the front plate 152, and its relative position with respect to the third cylindrical member 130 does not change. The shape of the end face of the beam 156 (the end face perpendicular to the x-direction) can also be set arbitrarily, and may be a circle, an ellipse, or a polygon such as a square. On the other hand, the slide member 154 is configured as a cylinder so that it can move in the x-direction along the beam 156 while housing the beam 156. The slide member 154 may be formed with a through hole penetrating in the x-direction, or may be formed with a blind hole extending in the x-direction. The shape of the through hole or blind hole (the shape of the end face perpendicular to the x-direction) of the slide member 154 may be formed to match the shape of the end face of the beam 156. The slide member 154 may be configured to be detachable from the beam 156, or a stopper (not shown) may be provided to prevent it from falling off the beam 156.

[0025] Furthermore, in order to fix the scale 150 at a desired length, the beam 156 is provided with a plurality of through holes 156a arranged in the x direction. Similarly, the slide member 154 is provided with at least one through hole 154a arranged to overlap with the through hole 156a. The at least one through hole 154a may include a plurality of through holes 154a. As shown in FIG. 3B and the schematic end view (FIG. 3C) taken along the dashed line B-B' in FIG. 3B, for example, by inserting a bolt 158 ​​into the through holes 154a and 156a and fixing the bolt 158 ​​with a nut 160, the length of the scale 150 can be adjusted and fixed in increments of the pitch of the through holes 156a. Note that, when fixing the scale 150, a washer 162 may be used in addition to the bolt 158 ​​and nut 160 as an optional configuration. Although not shown, if the end surface of the slide member 154 has a curved shape, the washer 162 may also be configured to fit the curved surface.

[0026] The pointer member 170 is fixed to the outermost cylindrical member, i.e., the first cylindrical member 110. Therefore, its position remains constant and is not dependent on the expansion and contraction of the tension balancer 100. The pointer member 170 overlaps with the scale 150 in the z direction, and is positioned so that the scale 150 is sandwiched between the first cylindrical member 110 and the pointer member 170. The pointer member 170 functions as a reference for reading the graduations on the scale 150. As long as this function can be realized, the configuration of the pointer member 170 can be determined arbitrarily; for example, the pointer member 170 can be configured to include a rod or flat plate extending in the y direction. Furthermore, the method of fixing the pointer member 170 to the first cylindrical member 110 can also be determined arbitrarily, and bolting, welding, or the like can be used.

[0027] The tension balancer 100 is used within a stroke range that provides an appropriate tension, taking into consideration its stroke-tension characteristics. The stroke length can be determined using the scale 150 and pointer member 170, and the condition of the coil spring can be determined from the stroke length.

[0028] However, the characteristics of mass-produced tension balancers 100 are not necessarily all the same, and a certain level of variation exists. For this reason, if the length of the scale 150 cannot be adjusted, the initially set position of the scale 150 may be inappropriate. In extreme cases, the pointer member 170 may overlap outside the range of the scale, or the pointer member 170 may not overlap with the scale in the z direction.

[0029] However, in a tension balancer 100 according to one embodiment of the present invention, the scale 150 is extendable in the x direction and can be fixed at any position in the x direction. This makes it possible to precisely adjust the length of the scale 150 in accordance with characteristic variations that occur during the manufacture of the tension balancer, and to accurately determine the stroke length of the tension balancer 100 when in use. This makes it possible to provide a tension balancer that can be used with an appropriate stroke length over a long period of time.

[0030] 6. Modifications The configuration of the scale 150 is not limited to the above-described configuration, and various modifications are possible. Modifications will be described below.

[0031] (1) Modification 1 For example, as shown in FIG. 4A , a slit 156 b extending in the x direction may be provided in the beam 156. The slit 156 b may penetrate the beam 156 in the y direction, or, although not shown, may penetrate the beam 156 in the z direction. Here, the slit 156 b is an opening having its longitudinal direction in the x direction, and the aspect ratio (length in the x direction / length in the z direction or y direction) is, for example, 5 or more and 30 or less. The beam 156 and the slide member 154 may also be fixed by any method, and for example, as shown in FIG. 4B , one or more bolts 158 and nuts 160 that engage with the bolts 158 may be used.

[0032] When the slit 156b is provided, the width of the slit 156b (the length in the z-direction or y-direction perpendicular to the x-direction) may be changed periodically in the x-direction, continuously or intermittently, in order to prevent unintended movement of the slide member 154 in the x-direction. For example, as shown in the enlarged views of the slit 156b (FIGS. 5A and 5B), the width may be changed continuously or intermittently by providing a convex portion 156c and a concave portion 156d on the inner wall that constitutes the slit 156b. The minimum width W of the slit 156b ２ is smaller than the outer diameter of the threaded portion of the bolt 158, and the maximum width W １ The convex portion 156c and the concave portion 156d are formed so that the outer diameter of the convex portion 156c is larger than the outer diameter of the threaded portion of the bolt 158. By giving the slit 156b such a shape, it is possible to prevent unintended movement of the slide member 154 in the x direction.

[0033] (2) Modification 2 The slide member 154 does not necessarily have to surround the entire beam 156 on the end surface perpendicular to the x-direction. For example, as shown in FIGS. 6A, 6B, and the schematic diagram of the end surface along the chain line CC' in FIG. 6B (FIG. 6C), the slide member 154 may have a C-shaped groove. In this case, the slide member 154 is provided so that the C-shaped opening faces the third cylindrical member 130, so that the scale on the slide member 154 can be seen. The beam 156 is formed into a plate shape to fit the shape of the groove in the slide member 154. As in Modification 1, the slide member 154 and the beam 156 can be fixed together using a bolt 158 ​​passing through the slit 156b and the through-hole 154a, a nut 160 engaging with the bolt 158, a washer 162, and the like. In addition to the through-hole 154a used for fixing to the beam 156, the slide member 154 may be formed with one or more through-holes 154b for draining rainwater and the like. The size of the through-hole 154b may be smaller than that of the through-hole 154a. Although not shown, the width of the slit 156b may be changed periodically, continuously, or intermittently along the x-direction, as in the first modification.

[0034] (3) Modification 3 Alternatively, as shown in FIG. 7A , the scale 150 may be configured such that the beam 156 and the slide member 154 are each threaded, and the slide member 154 slides relative to the beam 156 by rotating the beam 156 around the x-direction. Specifically, the outer peripheral surface of the beam 156 is externally threaded in whole or in part, and the inner wall of the cylindrical slide member 154 is internally threaded in whole or in part. The beam 156 and the slide member 154 are threaded so that they mesh with each other. By configuring the scale 150 in this manner, as shown in FIG. 7B and the schematic diagram of the end surface along the dashed line D-D' in FIG. 7C , the slide member 154 can slide along the x-direction by rotating the slide member 154 around the x-direction (see the dotted arrow in FIG. 7B ).

[0035] Alternatively, as shown in Fig. 8, the scale 150 may be formed of a single member whose outer surface is threaded. In this case, the outer surface of the scale 150 may be externally threaded, a through-hole may be formed in a structure for connecting the scale 150 to the third cylindrical member (for example, a front plate 152), and the inner wall of the through-hole may be internally threaded. With this structure, the scale 150 can be adjusted to any position relative to the third cylindrical member 130, and the positional relationship between the third cylindrical member 130 and the scale 150 at this position can be fixed.

[0036] The above-described embodiments of the present invention may be combined as appropriate as long as they are not mutually inconsistent. Furthermore, even if a person skilled in the art adds or deletes components or modifies the design based on each embodiment, the addition, deletion, or modification of components is included in the scope of the present invention as long as the gist of the present invention is maintained.

[0037] Furthermore, even if there are other effects and advantages different from those brought about by the above-mentioned embodiments, those that are clear from the description in this specification or that can be easily predicted by a person skilled in the art are naturally understood to be brought about by the present invention.

[0038] 100: tension balancer, 102: first hook, 104: second hook, 106: hanger hook, 110: first cylindrical member, 112: first coil spring, 114: first front washer, 120: second cylindrical member, 122: second coil spring, 124: first rear washer, 126: second front washer, 130: third cylindrical member, 132: second rear washer, 134: second back plate , 140: first back plate, 142: U-shaped bar, 144: collar, 146: guide plate, 150: scale, 152: front plate, 154: slide member, 154a: through hole, 154b: through hole, 156: beam, 156a: through hole, 156b: slit, 156c: convex portion, 156d: concave portion, 158: bolt, 160: nut, 162: washer, 170: pointer member

Claims

1. A tension balancer comprising: first to nth cylindrical members; the first to (n-1)th coil springs; a first hook attached to the first cylindrical member; a second hook attached to the nth cylindrical member; and a scale attached to the nth cylindrical member, extending in a first direction parallel to a central axis of the first to nth cylindrical members, located outside the nth cylindrical member, overlapping with the nth cylindrical member in a second direction perpendicular to the first direction, and extensible in the first direction; the first to nth cylindrical members are arranged such that a (j+1)th cylindrical member selected from the first to nth cylindrical members is surrounded by a jth cylindrical member selected from the first to nth cylindrical members; the cylindrical members and the coil springs alternate with each other; n is a natural number equal to or greater than 2, and j is a variable selected from natural numbers equal to or greater than 1 and equal to (n-1).

2. A tension balancer as claimed in claim 1, further comprising a pointer member extending in said second direction and disposed between said scale and said nth cylindrical member.

3. The tension balancer according to claim 1, wherein the scale comprises: a beam connected to the nth cylindrical member and extending in the first direction; and a slide member housing the beam, slidable along the beam, and having a scale.

4. A tension balancer as claimed in claim 3, wherein said beam has a plurality of through holes arranged in said first direction, and said sliding member has at least one opening overlapping one of said through holes.

5. A tension balancer as claimed in claim 3, wherein said beam has a slit extending in said first direction and passing through said beam, and said sliding member has at least one opening overlapping said slit.

6. A tension balancer as claimed in claim 5, wherein the width of said slit changes periodically.

7. A tension balancer as described in claim 3, wherein the end face shape of said beam in a plane perpendicular to said first direction is circular.

8. A tension balancer according to claim 3, wherein the beam is plate-shaped, and an end face of the slide member in a plane perpendicular to the first direction is C-shaped.

9. A tension balancer as claimed in claim 3, wherein the outer periphery of said beam has an externally threaded surface, and said sliding member has an internal wall that is internally threaded and has a blind hole or a through hole extending in said first direction.

10. A tension balancer as claimed in claim 3, wherein said scale is connected to said nth cylindrical member by a front plate having an internally threaded through hole, and said slide member has an externally threaded surface.

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