Abstract:
A scale fixating device includes a fixing block unmovably fixating a first end of a scale to an object, and a pulling block fixating a second end of the scale to the object while pulling the second end of the scale to the second end side. The pulling block includes a fixated base fixated to an object, a slide holding the second end of the scale and installed slidably with respect to the fixated base, and a pulling mechanism having a first end engaged to the slide and a second end engaged to the fixated base, the pulling mechanism pulling the slide toward the second end relatively with respect to the fixated base. The scale fixating device either prevents a friction force from changing between the slide and the fixated base or generates an extremely large friction force between the slide and the fixated base.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. §119 of Japanese Application No. 2014-266856, filed on Dec. 27, 2014, and Japanese Application No. 2015-140317, filed on Jul. 14, 2015, the disclosures of which are expressly incorporated by reference herein in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a scale fixating device. Specifically, the present invention relates to a device for fixating a scale enabling accuracy of a scale to be maintained when mounting and fixating an elongated scale to an object. 
     2. Description of Related Art 
     As a scale in an instrument measuring length (linear encoder), a tape scale formed in a thin tape shape made of glass or a metal is known. (Japanese Patent Laid-open Publication No. 2011-237310, Japanese Patent No. 4,477,442, Japanese Patent Laid-open Publication No. 2013-7718, and Japanese Patent Laid-open Publication No. S63-252213.) The tape scale provides advantages such as easy lengthening, easy transportation, and simple mounting. 
     When a tape scale is mounted and fixated to an object, tension is applied in a measurement axis direction. For example, a first end of the tape scale is unmovably fixated to the object and a second end of the tape scale is fixated to a sliding member allowing the second end of the tape scale to move relative to the object. In addition, the tension is applied to the sliding member so as to pull the second end of the tape scale. As a result, even in a case where the tape scale is expanded/contracted by a change in temperature, the tape scale maintains straightness. Generally, a guarantee temperature is set from 0° C. to 50° C. and the tension is applied such that the straightness is maintained within this range. For example, when the tape scale is made of a SUS material, there is about 10.5 μm expansion/contraction per 1 meter with a change in temperature of 1° C. In order to absorb the expansion/contraction, when the encoder is installed at a temperature of 20° C., a pull of 250 μm per 1 meter is required. 
     As described above, the predetermined tension is applied to the tape scale via the sliding member, however, when inspected after some time following the encoder installation, the tension is often changed. In other words, the sliding member is pulled by the predetermined amount (250 μm per 1 meter), however, a position of the sliding member is displaced from an initial installed position when inspected after some time. A user of the encoder does not check if the tension of the tape scale is appropriate or not once the encoder is installed, which may lead to a measurement error. 
     Displacement does not occur in all cases and although a cause was unknown, was thought to be a difference in ability during encoder installation. The present inventors have carried out extensive studies and succeeded in shedding light on a fundamental cause, as well as devising a countermeasure to achieve the present disclosure. 
     SUMMARY OF THE INVENTION 
     An advantage of the present disclosure is to provide a scale fixating device capable of maintaining accuracy of a scale while preventing tension of the scale from changing. 
     The scale fixating device according to the present disclosure installs and fixates the scale to an object and includes a fixing block part unmovably fixating a first end of the scale to the object and a pulling block part fixating a second end of the scale to an object while pulling the second end of the scale. The pulling block part includes a fixated base fixated to the object, a slide part holding the second end of the scale and installed slidably with respect to the fixated base, and a pulling mechanism (also referred to as a “puller”) having a first end engaged to the slide part and a second end engaged to the fixated base, the pulling mechanism pulling the slide part toward the second end relatively with respect to the fixated base. A surface of the slide part contacting the fixated base is beveled. 
     The scale fixating device according to the present disclosure installs and fixates the scale to the object and includes the fixing block part unmovably fixating the first end of the scale to the object and the pulling block part fixating the second end of the scale to the object while pulling the second end of the scale. The pulling block part includes the fixated base fixated to the object, the slide part holding the second end of the scale and installed slidably with respect to the fixated base, and the pulling mechanism having the first end engaged to the slide part and the second end engaged to the fixated base, the pulling mechanism pulling the slide part toward the second end relatively with respect to the fixated base. At least one of a mutual contact surface of the slide part and a mutual contact surface of the fixated base is mirror finished. 
     The scale fixating device according to the present disclosure installs and fixates the scale to the object and includes the fixing block part unmovably fixating the first end of the scale to the object and the pulling block part fixating the second end of the scale to the object while pulling the second end of the scale. The pulling block part includes the fixated base fixated to the object, the slide part holding the second end of the scale and installed slidably with respect to the fixated base, and the pulling mechanism having the first end engaged to the slide part and the second end engaged to the fixated base, the pulling mechanism pulling the slide part toward the second end relatively with respect to the fixated base. One of the mutual contact surface of the slide part and the mutual contact surface of the fixated base has a rough surface while the other is covered in a resin film. 
     In the present disclosure, the slide part includes a elongated aperture and is pressed against the fixated base with a first screw inserted through the elongated aperture and screwed to the fixated base, and a first flanged sleeve is preferably mounted between the first screw and the elongated aperture. 
     In the present disclosure, the second end of the scale is screwed to the slide part with a second screw and a second flanged sleeve is preferably installed between the second screw and the second end of the scale. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present disclosure, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein: 
         FIG. 1  is an exploded perspective view of a tape scale fixating device; 
         FIG. 2  is an external view of the tape scale fixating device; 
         FIG. 3  is a cross-sectional view of a pulling block part; 
         FIG. 4  is an expanded view of a fixated base and a slide part; 
         FIG. 5  illustrates a beveled slide part; 
         FIG. 6  illustrates a flanged sleeve; 
         FIG. 7  illustrates assessment results; and 
         FIG. 8  illustrates a case where a base portion has a rough surface and a thin film is formed on a holding piece. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the forms of the present invention may be embodied in practice. 
     An embodiment of the present disclosure is shown and described with reference to numerals given to each element in the drawings. 
     First Embodiment 
     A primary configuration of a tape scale fixating device  100  is described with reference to  FIGS. 1 to 4 . Points of the present disclosure are described thereafter.  FIG. 1  is an exploded perspective view of the fixating device  100  of a tape scale  10 .  FIG. 2  is an external view of an assembled state. The fixating device  100  of the tape scale  10  includes an elongated scale holder  110 , a fixing block part  120  arranged on a first end side of the scale holder  110  in a length direction, and a pulling block part  200  arranged on a second end side of the scale holder  110  in the length direction. The scale holder  110 , the fixing block part  120 , and the pulling block part  200  are formed mainly of metals such as aluminum, an aluminum alloy, or a SUS material. 
     The scale holder  110  includes a groove into which the tape scale  10  fits. The fixing block part  120  is fixated to an object (not shown) by fixing screws  121 . Furthermore, the fixing block part  120  is screwed to a first end of the tape scale  10  by screws  122 . 
       FIG. 3  is a cross-sectional view of the pulling block part  200  and  FIG. 4  is an expanded view of a fixated base  210  and a slide part  240 . The pulling block part  200  includes the fixated base  210 , the slide part  240 , and a pulling screw (pulling mechanism or puller)  290 . 
     The fixated base  210  is fixated to an object. The fixated base  210  includes a base portion  220  and a pulling wall  230 . The base portion  220  is long in a measurement axis direction and includes a groove  221  where the slide part  240  can slide along the length direction (measurement axis direction). The base portion  220  includes a slit  222  in the groove  221 , with a length from a first end partway toward a second end of the base portion  220  in the length direction. In addition, the base portion  220  includes four screw holes  223  and  224  along the length direction between substantially a center of the groove  221  and the second end. Of the four screw holes, the two on each end ( 223 ) are holes to screw the fixated base  210  to the object. The two in the middle ( 224 ) are holes for screwing in screws  253 , which press the slide part  240  provided inside the groove  221  of the fixated base  210  against the fixated base  210 . 
     The pulling wall  230  is upright in an L-shape on the second end of the base portion  220  in the length direction (so as to be substantially perpendicular to the object when the base portion  220  is fixated to the object) and is a wall on the fixating side pulling the slide part  240 . Furthermore, the pulling wall  230  includes a hole  231  through which the pulling screw  290  passes. 
     The slide part  240  includes a holding piece  250  and an end plate  260 . The holding piece  250  is arranged in the groove  221  of the base portion  220  and is slidable along the measurement axis direction. The second end of the tape scale  10  is screwed with screws ( 251 ) onto a top surface of a first end side of the holding piece  250  (an opposite surface to a surface facing the base portion  220 ), and the holding piece  250  holds the second end of the tape scale as a result. Moreover, a tip of each of the screws  251  enters the slit  222  of the base portion  220  such that the tape scale  10  is not fixated to the base portion  220 . When the slide part  240  slides with respect to the fixated base  210 , the tape scale  10  and the slide part  240  are integrally slidable with respect to the fixated base  210 . In addition, the holding piece  250  includes a elongated aperture  252  along the length direction between substantially the center and the second end. The elongated aperture  252  has a width through which threaded portions of the screws  253  can pass but head portions of the screws  253  cannot. Also, the threaded portions of the screws  253  are screwed into the screw holes  224  of the base portion  220  and the slide part  240  is pressed against the fixated base  210  by the head portions of the screws  253  while slide movement of the slide part  240  is allowed by the elongated aperture  252 . 
     The end plate  260  is upright in an L-shape on the second end of the holding piece  250  and includes a screw hole  261  into which the pulling screw  290  is screwed. The pulling screw  290  is passed through the hole  231  of the pulling wall  230  and screwed into the screw hole  261 . As the pulling screw  290  is tightened, the end plate  260  is pulled toward the pulling wall  230 . By tightening the pulling screw  290 , a predetermined tension is applied to the tape scale  10 . 
     In  FIG. 3 , triangle marks show measurement points measured by an electric micrometer. A first electric micrometer ( 401 ) confirms that the fixated base  210  does not move. A second electric micrometer ( 402 ) monitors displacement of the slide part  240 . While watching a detection value from the second electric micrometer ( 402 ), the pulling screw  290  is tightened until an amount of displacement of the slide part  240  reaches the predetermined value. 
     Next, a force applied to the slide part  240  is focused. The slide part  240  is pulled toward the second end side by the pulling screw  290 . This force is called “a second end side pulling force F 2 ” (see  FIG. 3 ). In addition, the slide part  240  is pulled toward the first end side by the tape scale  10 . This force is called “a first end side pulling force F 1 ” (see  FIG. 3 ). 
     Furthermore, the slide part  240  is pressed against the fixated base  210  by the screws  253  inserted into the elongated aperture  252  of the holding piece  250 . Specifically, a friction force F 3  acts between a reverse surface of the holding piece  250  and a front surface of the base portion  220  (a bottom surface of the groove  221 ). When installed with tension applied to the tape scale  10 , the slide part  240  stays at a position with three forces in balance: the second end side pulling force F 2 , the first end side pulling force F 1 , and the friction force F 3 . (Of course, other forces are applied such as a friction force between the screws  253  and the holding piece  250 , but the three main forces are named to facilitate understanding.) 
     The second end side pulling force F 2  and the first end side pulling force F 1  are considered to be unchanged over time. Instead, the present inventors focus on the friction force F 3 , which has been disregarded until now, and realize that the slide part  240  may be displaced by changes to the friction force F 3 . When environmental temperature is changed from 0° C. to 50° C. for example, the base portion  220  and the holding piece  250  are slightly thermally deformed and the friction force F 3  between the base portion  220  and the holding piece  250  changes. For example, the friction force F 3  may become smaller. Then, the balance between the second end side pulling force F 2 , the first end side pulling force F 1 , and the friction force F 3  changes, and therefore the balance position is displaced. 
     Based on such findings, the present inventors have confirmed that there are three measures for effective solutions. A first measure is to prevent the friction force from changing even when there is a change in temperature. A second measure is to have no friction from the beginning. A third measure is to render the slide part  240  unmovable by generating an extremely large friction force. Descriptions are provided in that order. 
     (1) Bevel Reverse Surface of Slide Part  240 . 
     The slide part  240  is processed by cutting and therefore a burr may remain on an edge. When the burr remains, the burr comes in contact with the base portion  220 , and thus a contact area between the slide part  240  and the base portion  220  becomes extremely small. If there is a change in temperature and the like, the friction force F 3  changes and the slide part  240  may experience an unexpected slide. Therefore, the edge of the reverse surface of the slide part  240  is preferably beveled. As shown in  FIG. 5 , the reverse surface of the slide part  240  has two projecting legs  270  on both sides in a width direction. Accordingly, an outer edge and an inner edge of each leg  270  are beveled ( 271 ). As a result, the slide part  240  and the base portion  220  come into surface-to-surface contact, and therefore the change of the friction force within a guaranteed temperature range becomes sufficiently small. Therefore, the slide part  240  is not displaced, or, even if displaced, the amount of displacement can be made sufficiently small. 
     (2) Compensate for Variation in Components. 
     The slide part  240  is pressed against the base portion  220  by pressing the screws  253  through the elongated aperture  252  of the holding piece  250  and screwing the screws  253  into the screw holes  224  of the base portion  220 . However, variations in a pressing force may be caused due to variations in components. For example, a length from a bearing surface to a tip of the screw  253 , roundness of a screw neck, and flatness of the bearing surface are likely to introduce variations. As a result, even if the screws  253  are tightened with the predetermined force, there is a possibility that the pressing force may be too strong or too weak. As shown in  FIG. 6 , flanged sleeves  254  are mounted between the screws  253  and the elongated aperture  252 . As a result, variations in the components (the screws  253  and the slide part  240 ) are covered and the slide part  240  can be pressed against the base portion  220  with the predetermined pressing force every time when the screws  253  are tightened with the predetermined force. 
     More preferably, when screwing the second end of the tape scale  10  to the holding piece  250 , flanged sleeves  255  are preferably mounted between the screws  251  and the tape scale  10 . When a diameter of holes  11  drilled in the tape scale  10  is larger than the diameter of the screws  251 , a gap is created between the hole  11  and the screw  251 . The gap can produce a margin in which the tape scale  10  relatively displaces with respect to the holding piece  250 . Therefore, it is better to mount the flanged sleeves  255  between the screws  251  and the tape scale  10  so as to eliminate the gap between the holes  11  and the screws  251  as much as possible and to firmly press the tape scale  10  with the screws  251 . 
     Moreover, the tape scale  10  is thin such that sleeves of the flanged sleeves  255  need to be processed to be fairly short. If a thickness of the tape scale  10  is 0.2 mm, the length of the sleeve portion of the flanged sleeve  255  is processed to about 0.1 mm. When the length of the sleeve portion of the flanged sleeve  255  is to be several mm (about 1 mm, for example), the thickness of the first end side of the tape scale  10  can be slightly thicker or a shallow dent can be provided around a periphery of the screw holes  256  of the holding piece  250 . 
     (3) Mirror Finish One Side Only. 
     By mirror finishing one of the bottom surface of the groove  221  of the base portion  220  and the reverse surface of the holding piece  250 , the friction between the two becomes minimal, and is ideally zero. If there is no friction between the base portion  220  and the holding piece  250  from the beginning, the slide part  240  will not be displaced by a change in the friction force F 3 . A mirror surface may be defined as, for example, an arithmetic average roughness Ra of several tens of nm or less (such as 80 nm or less), and preferably 10 nm or less if possible. 
     (4) Mirror Finish Both Sides. 
     By mirror finishing both the bottom surface of the groove  221  of the base portion  220  and the reverse surface of the holding piece  250 , the friction between the two is extremely increased. The extremely large friction force is generated when both mirror-finished metals (such as aluminum) come in close contact. As a result, the slide part  240  is not displaced by a change in the friction force F 3 . The mirror surface may be defined as, for example, the arithmetic average roughness Ra of several tens of nm or less (such as 80 nm or less), and preferably 10 nm or less if possible. 
     Results of Assessment 
       FIG. 7  shows results of an assessment.  FIG. 7  shows results of measuring the displacement of the slide part  240  with the second electric micrometer ( 402 ) after tightening the pulling screw  290  until an amount of pulling of the slide part  240  reaches the predetermined value. (A positive value indicates displacement to the first end side.) The length of the tape scale is 1 m. A line at a pulling force at  600  N is shown in the drawing.  600  N corresponds to the pulling force which can absorb an amount of expansion/contraction at a temperature change of 40° C. Line (A) in the drawing shows the result when the slide part  240  is not beveled. Line ( 1 ) in the drawing shows the result when the slide part  240  is beveled. Line ( 2 ) in the drawing shows the result when the slide part  240  is beveled and further mounted with the flanged sleeves  254  between the screws  253  and the elongated aperture  252 . Line ( 3 ) in the drawing shows the result when the bottom surface of the groove  221  of the base portion  220  and the reverse surface of the holding piece  250  are mirror finished. 
     Based on the results in  FIG. 7 , the measures mentioned above show positive results. 
     (5) One Rough Surface and Other Surface Covered in Resin Film. 
     When a first member has a rough surface and a second member is covered in a resin film, the first member holds on to the second. As shown in  FIG. 8 , for example, the bottom surface of the groove  221  of the base portion  220  is configured to be rough and the reverse surface of the holding piece  250  is covered with a thin film  272  of resin, for example. Naturally, the reverse surface of the holding piece  250  may instead be configured to be rough and the bottom surface of the groove  221  of the base portion  220  may be covered in the resin film. As a result, the friction force between the two is maintained, preventing the displacement of the slide part  240 . A rough surface may be defined as, for example, the arithmetic average roughness Ra of between several tenths of a μm and several tens of μm, with between 0.1 μm and 50 μm given as an example. 
     Moreover, the present invention is not limited to the embodiments described above, and may be modified as needed without departing from the scope of the present invention. For example, so long as the slide part is pulled relatively to the second end side with respect to the fixated base, the pulling screw can be replaced by an elastic body such as a spring. The shapes of the fixated base and the slide part are merely examples. 
     It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to exemplary embodiments, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular structures, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. 
     The present invention is not limited to the above described embodiments, and various variations and modifications may be possible without departing from the scope of the present invention.