Linear measuring device

Abstract

Linear measuring instrument (100) comprising: a spindle (110); a guide cylinder part (220) configured to guide the spindle (110) so that it moves back and forth in an axis line direction; a guide slot section (240) formed parallel to the axis line of the guide cylinder part (220), providing a gap between the guide slot section (240) and the guide cylinder part (220); and a position adjustment pin (400) attached to a side face of the spindle (110) passing through the guide slot section (240), the position adjustment pin (400) being an eccentric pin.

Description

TECHNICAL AREA The present invention relates to a linear measuring instrument. More precisely, the present invention relates to the alignment adjustment in a linear measuring instrument. GENERAL STATE OF THE ART A linear measuring instrument is known as a small precision measuring instrument (for example, patent specifications 1 to 5). (It should be noted that terms such as digital dial gauge, electronic micrometer, Digimatic dial gauge ("Digimatic" is a trademark), linear measuring instrument, and the like are also used.) A linear measuring instrument measures a workpiece with extremely high precision by using a digital encoder to accurately detect the axial displacement of a spindle. Fig. 1 schematically depicts the internal mechanism of a linear measuring instrument. In Fig. 1, a spindle 110 is a cylindrical rod guided through a sleeve 10 to move back and forth. A pin 112 is inserted into a side face of the spindle 110 to prevent it from rotating, and a guide slot 11 is formed in the sleeve 10. The guide slot 11 is shaped to allow the pin 112 to pass through it, and it is longer in the axial direction. The guide slot 11 guides the pin 112, allowing the spindle 110 to move back and forth in the axial direction, but restricting its rotation about the axis. An encoder 300 is provided on one side of the rear end of the spindle 110. The encoder 300 consists of a scale 310 and a detection head 320. The scale 310 is attached to the rear end of the spindle 110, and the detection head 320 is positioned opposite the scale 310, with a predetermined gap provided between them. The measuring accuracy of a linear measuring device depends on the processing accuracy of the components and the detection accuracy of the encoder 300. With regard to the machining accuracy of the components, it is extremely important, for example, that the spindle moves straight. Therefore, every effort is made to maximize the straightness of the spindle 110 itself, as well as the machining accuracy of the inner surface of the sleeve 10. Conversely, to increase the detection accuracy of the encoder 300, the scale 310 and the detection head 320 must be kept parallel over the entire measuring range. If the spindle 110 rotates even slightly around its axis, the relative positions of the scale 310 and the detection head 320 shift, destabilizing the detection accuracy by that amount. Thus, every effort is made to smooth the outer diameter of the pin 112 and the width of the guide slot 11 with a high degree of precision, so that there is no play (gap, clearance) between the pin 112 and the guide slot 11.Furthermore, DE 101 36 360 A1 describes a measuring instrument comprising a body, an axially movable spindle therein, and a sleeve movable in the same direction. The spindle and sleeve are connected by a connector that allows relative movement over a specific stroke. A preload, typically a compression spring, is located in the sleeve, which preloads the spindle via the connector in the direction of a workpiece. A preload force indicator is essential, displaying the force currently exerted by the preload. DE 32 16 259 A1 discloses a micrometer. Its spindle drive device has a helical groove with a comparatively large pitch for the rapid axial movement of a spindle, as well as a cooperating engagement section. A separate device prevents rotation of the spindle during axial displacement. A display device driven by the axial spindle movement serves to show the measured value. LITERATURE PORTRAITS patent specifications Patent Specification 1: Japanese Patent JP H08-27161B2; Patent Specification 2: Japanese Patent JP 2557171B2; Patent Specification 3: Japanese Patent Interpretation JP 2007-322248A; Patent Specification 4: Japanese Patent Interpretation JP 2015-75397A; Patent Specification 5: Japanese Patent Interpretation JP 2016-14534A; Patent Specification 6: DE 10136360A1; Patent Specification 7: DE 3216259A1 BRIEF SUMMARY OF THE INVENTION Technical problem Aligning the scale surface of the scale 310 and the detection surface of the detection head 320 with a high level of precision is extremely important to ensure a high level of detection accuracy in the encoder 300. However, there are of course limitations to the actual processing accuracy of components, and thus a situation in which the scale surface of the scale 310 and the detection surface of the detection head 320 shift from a parallel state is sometimes unavoidable when the device is assembled as a product. One line of reasoning is to simply assume that the measurement accuracy that can be ensured in the product is limited by machining errors in the components. This means, for example, that one assumes that, given the cumulative machining error in the components, a measurement resolution of 0.1 µm can be guaranteed. Another approach involves using an encoder where positional misalignment has no impact on measurement accuracy. For example, patent specification 2 (Japanese patent no. 2557171) uses a laser holoscale (LHS) as such a high-precision and stable encoder. This ensures high precision and high resolution, such as a measurement accuracy of 0.01 µm, even with cumulative machining errors in the components. However, small encoders that are very robust with respect to positional misalignment, which of course includes laser holoscales (LHS), are extremely expensive and thus inevitably increase product costs. Such products can offer ten times the measurement accuracy, but are also ten times more expensive (or more). Therefore, one object of the present invention is to provide a linear measuring device that has high measuring accuracy without increasing the cost. Problem solving A linear measuring instrument according to the present invention comprises: a spindle; a guide cylinder section configured to guide the spindle so that it moves back and forth in the direction of an axis; a guide slot section formed parallel to the axis of the guide cylinder section, with a gap provided between the guide slot section and the guide cylinder section; and a position adjustment pin passing through the guide slot section and attached to a side face of the spindle. The position adjustment pin is an eccentric pin. Preferably, in the present invention, the position adjustment pin comprises: a screw with two ends, having screws on both a side of the tip end and a side of the base end, wherein the screw on the side of the base end is screwed into the side surface of the spindle; and a pin head into which the screw on the side of the tip end of the screw with two ends is screwed, and wherein at least one of the screw with two ends and the pin head is eccentric. Preferably in the present invention, a rubber sleeve is inserted between the screw with two ends and the pin head. Preferably in the present invention, a scale or a detection head of a reflective photoelectric encoder is attached to the spindle. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a diagram schematically illustrating the internal mechanism of a conventional linear measuring instrument, serving as an example from the prior art. Figure 2 shows a cross-sectional view seen from line II-II in Figure 1. Figure 3 shows a cross-sectional view seen from line II-II in Figure 1. Figure 4 shows a cross-sectional view seen from line II-II in Figure 1. Figure 5 shows an external perspective view of a linear measuring instrument. Figure 6 shows a cross-sectional view of the linear measuring instrument. Figure 7 shows an external perspective view of a holding cylinder. Figure 8 shows an enlarged partial view of the holding cylinder. Figure 9 shows a diagram illustrating an eccentric nut. Figure 10 shows a diagram illustrating a cross-section obtained by cutting in a direction perpendicular to the axis of a spindle, from the direction following the axis of the spindle.Fig. 11 is a diagram showing a cross-section obtained by cutting in a direction perpendicular to the axis of the spindle, from the direction following the axis of the spindle. Fig. 12 is a diagram showing a cross-section (of an end face) of the holding cylinder. Fig. 13 is a diagram showing a cross-section obtained by cutting in a direction perpendicular to the axis of the spindle, from the direction following the axis of the spindle, halfway through the assembly of the linear measuring instrument. Fig. 14 is a diagram showing a cross-section obtained by cutting in a direction perpendicular to the axis of the spindle, from the direction following the axis of the spindle, halfway through the assembly of the linear measuring instrument. DESCRIPTION OF THE EXECUTION FORMS A feature of the present invention is that a locking pin is provided with a position adjustment mechanism. However, before the specific configuration of the present invention is described, a problem of earlier techniques will be described in some detail to clarify the significance of the present invention. These descriptions refer to Figures 2, 3 to 4. Fig. 2 is a cross-sectional view seen from line II-II in Fig. 1, showing the spindle 110 and the pin 112 alone. As shown in Fig. 2, an internal thread 111 is provided in the spindle 110 perpendicular to an axis line (XS) of the spindle 110. The extent of an axis line of the internal thread 111 is represented by ZS. The spindle 110 has a perfectly circular cross-section, and the internal thread 111 is provided at right angles such that the ZS axis passes through the center of the spindle 110. It should be noted that the axis line of the spindle 110 corresponds to the XS axis, and an axis that is perpendicular to both the ZS axis and the XS axis is a YS axis. A scale mounting surface 113 is provided in the spindle 110 to mount and secure the scale 310 to the spindle 110. The scale mounting surface 113 is machined so that it is perpendicular to the ZS axis. (Thus, the scale mounting surface 113 is normally parallel to the XS and YS axes.) This results in a scale surface 311 of the scale 310 and the axis of the pin 112 (the ZS axis) being perpendicular. (Note that the axis of the pin 112 normally corresponds to the axis ZS of the internal thread 111.) Next, Fig. 3 is a cross-sectional view seen from line II-II in Fig. 1, showing the socket 10 alone. The guide slot 11 is formed in the sleeve 10. The guide slot 11 is provided such that it is parallel to an axis XB of the sleeve 10. An axis passing through the center of the guide slot 11 on its wider side and perpendicular to the axis XB of the sleeve 10 is represented by ZB. The sleeve 10 is cylindrical and therefore has an outer circle 13 and an inner circle 14 when viewed in cross-section. The machining accuracy of the inner circle 14 (e.g., straightness and roughness) determines the precision of the spindle movement, and thus the inner circle 14 is smoothed to an extremely high degree of precision. The outer circle 13 and the inner circle 14 of the socket 10 are designed to be concentric circles. However, it is extremely difficult to machine the socket 10 in such a way that the outer circle 13 and the inner circle 14 are perfectly concentric. In particular, small variations in thickness will inevitably occur, even when attempting to smooth the inner circle 14 with an extremely high level of precision. Furthermore, the curing of the sleeve 10 to increase its service life makes it difficult to avoid deviations from the ideal theoretical values. The previously mentioned axis line XB of the sleeve 10 can also be regarded as a mean axis line XB in relation to the outer circle 13 of the sleeve 10. In Fig. 3, it is assumed that the center CI of the inner circle 14 has shifted slightly to the left relative to the center of the outer circle 13 (XB). For clarity, this shift is exaggerated in Fig. 3. The central axis of the inner circle 14 is represented by XI. An axis passing through the center of the guide slot 11 on the wider side and perpendicular to the central axis XI of the inner circle 14 is represented by ZI. This naturally results in a slight offset between the axis ZB and the axis ZI. Fig. 4 is a cross-sectional view seen from line II-II in Fig. 1. The spindle 110 is inserted into the sleeve 10. The pin 112 is then passed through the guide slot 11 and attached to the spindle 110 to prevent the spindle 110 from rotating. As previously described, if the outer circle 13 and the inner circle 14 of the sleeve 10 have been displaced from their concentric position, there is a slight offset between the axis ZBund and the axis ZI. (It should be noted that the illustration in Fig. 4 is exaggerated and the actual offset is on the order of 1 / 100°.) Once the pin 112 has been passed through the guide slot 11 and attached to the spindle 110, the axis of the pin 112 (ZS) coincides with the axis line ZI, but is slightly inclined with respect to the axis line ZBein. Thus, the scale mounting surface 113 and, consequently, the scale surface 311 of the scale 310 are slightly inclined with respect to the axis line ZBein, instead of being perpendicular to it. The outer shape of the sleeve 10 (the outer circle 13) serves as a reference when determining the mounting position, orientation, and the like between the sleeve 10 and the detection head 320. As exemplified in Fig. 4, even if a detection surface 321 of the detection head 320 is perpendicular to the axis ZB, which is based on the outer shape of the sleeve 10 (the outer circle 13), the detection surface 321 is still inclined relative to the axis ZS of the pin 112 (i.e., the axis ZI). Therefore, there is also an offset between the scale surface 311 of the scale 310 and the detection surface 321 of the detection head 320, which directly affects the detection accuracy of the encoder 300. This is not a problem, however, if an expensive laser holoscale is used. If a relatively inexpensive encoder is used, however, the alignment of the positions of the scale surface 311 and the detection surface 321 of the detection head 320 is extremely important. A reflective photoelectric encoder can be taken as an example of an encoder that is relatively inexpensive and has the advantage of a small size. Even compared to a transparent type, the detection accuracy of a reflective photoelectric encoder is greatly affected by the misalignment of the positions of the scale 310 and the detection head 320. The above is, of course, only one example. It is also possible that the axis of the internal thread 111 is slightly inclined or that the detection head 320 is mounted at a slightly angled position. As long as the spindle 110 is a cylindrical rod, the error resulting from even a slight rotation of the scale 310 (or the detection head 320) around the axis remains, in both cases, a problem that is difficult to solve. An embodiment of the present invention will now be described with reference to the drawings and the reference numerals assigned to the elements depicted in the drawings. First embodiment A first embodiment of the present invention will now be described. Fig. 5 is an external perspective view of a linear measuring device 100. The linear measuring device 100 comprises a spindle 110 and a holding cylinder 120, which holds the spindle 110 in a movable position. The spindle 110 itself is the same as the typical spindle 110 presented in Figs. 1, 2, 3 to 4. For example, as shown in Figs. 6 and 7, an internal thread 111 for holding a pin 400 and a scale mounting surface 113 for attaching and securing a scale 310 of an encoder 300 are formed in the spindle 110. The main body 120 holds the spindle 110 so that it moves back and forth in an axial direction and detects any displacement of the spindle 110. Fig. 6 is a cross-sectional view of the linear measuring device 100. The main body 120 comprises a holding cylinder 200, the encoder 300, the position adjustment pin 400, and a cover part 500. Fig. 7 is an external perspective view of the holding cylinder 200, and Fig. 8 is an enlarged partial view of the holding cylinder 200. The holding cylinder 200 is a cylindrical element that holds the spindle 110 so that it can move back and forth in the axial direction, but is designed in such a way that other functions are also integrated within it. That is, the holding cylinder 200 is formed in an integrated state with an end plate 210, a guide cylinder part 220, a guide slot section 240, and a bracket 250. To facilitate understanding of the descriptions, the left side of the drawing in Fig. 6 is referred to as the “front” of the linear measuring instrument 100 and the right side is referred to as the “back” of the linear measuring instrument 100. (In other words, a tip side of the spindle 110 corresponds to the front side of the linear measuring instrument 100 and a base side of the spindle 110 corresponds to the rear side of the linear measuring instrument 100.) References to “above” and “below” are also based on the directions in the drawing in Fig. 6. The retaining cylinder 200 comprises the end plate 210, which is rectangular and closes off a front end of the cover part 500. The guide cylinder part 220, the guide slot section 240, and the bracket 250 are integrated onto the end plate 210. As shown, for example, in Fig. 6, the guide cylinder part 220 is a cylinder into which the spindle 110 is inserted in a front-to-back direction, and an inner surface of the guide cylinder part 220 is smoothed to a high precision to support the spindle 110. Although the drawings depict the spindle 110 being directly supported by the inner surface of the guide cylinder part 220, a separate bearing may be inserted between the guide cylinder part 220 and the spindle 110. For example, a roller bearing may be used as the bearing. The guide cylinder part 220 is provided to extend to both the front (221) and rear (230) of the end plate 210. The portion of the guide cylinder part 220 that extends from the front of the end plate 210 like a nozzle is referred to as the front guide cylinder 221. A rear guide cylinder 230 is provided on the rear of the end plate 210 to have a cylinder hole that communicates with a cylinder hole of the front guide cylinder 221. The guide cylinder part 220 consists of the front guide cylinder 221, which extends to the front of the end plate 210, and the rear guide cylinder 230, which extends to the rear of the end plate 210, with the end plate 210 situated between them. The rear guide cylinder 230 extends along the rear side of the end plate 210, and the guide slot section 240 is also formed on the rear side of the end plate 210 on the upper side of the rear guide cylinder 230, whereas the bracket 250 is formed on the lower side of the rear guide cylinder 230. Since the retaining cylinder 200 is formed as an integral part, the rear guide cylinder 230 and the bracket 250 are completely connected. Thus, no boundary can be clearly defined between the rear guide cylinder 230 and the bracket 250. However, even if one goes so far as to define the rear guide cylinder 230 and the bracket 250 as the same unit, this does not present any serious problems with regard to the following descriptions. The guide slot section 240 is a slot formed parallel to the axis of the guide cylinder part 220 (the rear guide cylinder 230) with a gap L provided between the guide slot section 240 and the rear guide cylinder 230 in the perpendicular direction. The length of the guide slot section 240 must not be shorter than the measuring travel of the spindle 110. The position adjustment pin 400 passes through the guide slot section 240 and is attached to a side face of the spindle 110, such that the guide slot section 240 restricts the rotation of the position adjustment pin 400, which in turn prevents rotation of the spindle 110. Various methods for forming a slot to serve as a guide slot section 240 above the rear guide cylinder 230 are conceivable. In this embodiment, two guide rails 241 are provided parallel to each other on the broad side of the guide slot section 240 above the rear guide cylinder 230 at a distance corresponding to the gap L. A wall 242, oriented vertically, is connected to the rear ends of the two guide rails 241, and the front ends of the two guide rails 241 are connected to a rear surface of the end plate 210. A slot 231, parallel to the guide slot section 240, is formed in the rear guide cylinder 230 with a slightly greater width than the guide slot section 240. The slot 231 is simply intended to allow the position adjustment pin 400 to be loosely inserted and is nothing more than a gap for the position adjustment pin 400 to pass through to the spindle 110 from the guide slot section 240. Thus, the slot 231 is referred to as the loose insertion slot 231. Although the loose insertion slot 231 is described here as being wider than the guide slot section 240, part of the lower section of the position adjustment pin 400 may instead have a reduced diameter. In either case, the loose insertion slot 231 is necessary to avoid completely restricting the position adjustment pin 400. The width of the guide slot section 240 and the diameter of the (upper part of the) position adjustment pin 400 are finely smoothed so that there is no play between them. Furthermore, machining is performed so that a line connecting the center of the guide slot section 240 on the wider side with the center of the cylinder bore of the guide cylinder part 220 (of the rear guide cylinder 230) coincides with a center line of the outer shape of the retaining cylinder 200. (This point will be described later (Fig. 12).) The bracket 250 is formed as a cuboid element to extend a lower part of the rear guide cylinder 230 and serves as a mounting bracket for the detection head 320. Since the bracket 250 serves as a mounting bracket for the detection head 320, the position of the detection head 320 is, in a sense, determined by the surface precision of the bracket 250. If the rear side of the mounting cylinder 200 is considered a cuboid element, it is assumed that the parallelism, right angles, and similar features of its planes are formed with a high degree of precision. Next, the position adjustment pin 400 is described. The position adjustment pin 400 is an adjustment mechanism for finely adjusting the spindle 110 around its axis at very small angles (roll angles) during product assembly and prevents the spindle 110 from rotating after assembly. These fine adjustments to the spindle 110 around its axis at very small angles (roll angles) are, of course, made to adjust the angle of the scale face 311 of the scale 310. The position adjustment pin 400 is essentially an eccentric pin. A base end of the position adjustment pin 400 is attached to a side face of the spindle 110, and a tip end of the position adjustment pin 400 is inserted into the guide slot section 240. In view of the adjustment process that is carried out when the product is assembled, the position adjustment pin 400 in the embodiment consists of three elements, namely a screw with two ends 410, a rubber sleeve 420 and an eccentric nut (a pin head) 430, as shown, for example, in Fig. 7. The two-ended screw 410 has two external threads, the external thread on the lower side being a first external thread 411 and the external thread on the upper side being a second external thread 412. A middle section 413, the diameter of which is larger than the threaded sections, is provided between the first external thread 411 and the second external thread 412, and an upper surface of the middle section 413 is a flat surface 414. This flat surface is referred to below as the “bearing surface 414”. The rubber sleeve 420 is a thin, elastic ring made of resin. The second external thread 412 is inserted into the hole of the rubber sleeve 420, and the rubber sleeve 420 is then inserted between the bearing surface 414 and the eccentric nut 430 (see, for example, Fig. 8). The rubber sleeve 420 serves to exert slight pressure on the eccentric nut 430 to prevent the eccentric nut 430 from rotating freely during the position adjustment process when assembling the product. As shown in Fig. 9, the eccentric nut 430 has an off-center internal thread 431. The internal thread 431 is designed to be slightly offset relative to the center CN of the outer circle. The center of the internal thread 431 is represented by CE. A direction from the center CN to the center CE is referred to as the eccentricity direction DE of the eccentric nut 430. Furthermore, the eccentric nut 430 is designed such that its diameter matches the width of the guide slot section 240, so that when the eccentric nut 430 is inserted into the guide slot section 240, there is no play between them. Adjusting the position of the spindle 110 using the position adjustment pin 400 will be described later. The cover part 500 consists of a cube-shaped outer housing 510 and a cap 520 that closes off a rear end of the outer housing 510. The end plate 210 of the retaining cylinder 200 is fitted into a front end of the outer housing 510. Adjustment process using the position adjustment pin The alignment adjustment using the position adjustment pin 400 is described next with reference to Figures 10, 11, 12, 13 to 14. Figures 10, 11, 12, 13 to 14 are diagrams showing a cross-section obtained by cutting from the axis of the spindle 110 in a direction perpendicular to the axis of the spindle 110, slightly in front of the position adjustment pin 400. The spindle 110 is not hatched here to improve the readability of the diagrams. The upper surface of the eccentric nut 430 is also shown at the top of each drawing. Bevor der Justierprozess beschrieben wird, wird zuerst ein Beispiel des zu justierenden Fehlers mit Bezug auf Fig. 10 , Fig. 11 bis Fig. 12 beschrieben. Fig. 10 und Fig. 11 sind Diagramme, welche die Spindel 110 und den Lagejustierzapfen 400 alleine abbilden. In Fig. 10 ist der Lagejustierzapfen 400 in einem auseinandergezogenen Zustand, wohingegen der Lagejustierzapfen 400 in Fig. 11 in eine seitliche Oberfläche der Spindel 110 eingeschraubt ist. Es wird hier vorausgesetzt, dass die Spindel 110 gemäß der Bauform bearbeitet wurde, wie in Fig. 10 und Fig. 11 abgebildet. In other words, assuming that the axis of the internal thread 111 is represented by ZS, the scale mounting surface 113 is perpendicular to the axis ZS, and thus the scale surface 311 of the scale 310 is also perpendicular to the axis ZS. In contrast, Fig. 12 is a diagram showing a cross-section of the retaining cylinder 200. For the sake of clarity, this drawing depicts an end face. It is assumed that the inner surface of the guide cylinder part 220 has been smoothed with an extremely high level of precision, but that the position of its cylinder bore is slightly offset from the intended design. An axis passing through the center of the guide slot section 240 on the wide side and perpendicular to a cylinder axis line XI of the guide cylinder part 220 is represented by ZI. Since this is the case, the axis ZI is slightly inclined relative to the ideal central axis ZB of the retaining cylinder 200. (This inclination is extremely small, for example, by about 1 / 100°.) The alignment is adjusted during the assembly of the linear measuring device 100, assuming a machining error such as the one described above. As shown in Fig. 13, an assembler passes the spindle 110 through the guide cylinder part 220 and then passes the position adjustment pin 400 through the guide slot section 240 and screws the pin into the side surface of the spindle 110. (Note that the size of the gap in Figs. 13 and 14 is exaggerated for clarity.) The first external thread 411 of the two-ended screw 410 and the internal thread 111 of the spindle 110 are then tightly joined using an adhesive or similar material so that the two-ended screw 410 does not rotate. In contrast, the eccentric nut 430 is screwed onto the second external thread 412 to press the rubber sleeve 240 firmly against the support surface 414, but is not yet connected to it.The eccentric nut 430 can be turned back and forth using a tool, such as a wrench. Even if the eccentricity direction DE of the eccentric nut 430 is parallel to the axis line of the guide slot section 240 (i.e., even if the position adjustment pin 400 is not off-center due to the eccentric nut 430), a machining defect in the retaining cylinder 200 (the guide cylinder part 220) causes the position adjustment pin 400 to be slightly inclined (arrow A in Fig. 13), and thus the spindle 110 also rotates slightly about its axis (arrow B in Fig. 13). The rotation of the spindle 110 (arrow B in Fig. 13) also causes the scale mounting surface 113 to rotate, which means that the scale surface 311 of the scale 310 is inclined. Since this is the case, the scale surface 311 of the scale 310 is no longer parallel to the detection surface 321 of the detection head 320, which leads to a reduction in detection accuracy. Furthermore, it is not really possible to visually confirm whether the scale surface 311 is skewed due to a machining error. Therefore, the encoder 300 is activated to obtain a detection signal from the detection head 320 and to confirm the signal's status. For example, it is confirmed whether the detection signal is strong enough or not. Changes in the detection signal, such as when the spindle 110 is moved back and forth, are also checked. For example, a photoelectric encoder extracts two or more phase signals to generate a Lissajous figure representing circular motion. The circularity of the Lissajous figure is directly related to the interpolation precision, and therefore the Lissajous figure becomes distorted and the interpolation precision decreases if the positions of the scale 310 and the detection head 320 are misaligned. Particularly with reflective photoelectric encoders, even extremely small misalignments of the scale 310 and the detection head 320 have a significant impact on the distortion of the detection signal. Therefore, adjusting the positions of the scale 310 and the detection head 320 is extremely important. The technician observes the detection signal while moving the spindle 110 and performs the adjustment process upon determining that the positions of the scale 310 and the detection head 320 are misaligned. In other words, the technician uses a tool (for example, a wrench) to move the eccentric nut 430 very slightly, checks the effect of this adjustment by moving the spindle 110 back and forth, and finds the optimal angle of the eccentric nut 430. It is assumed here that a slight counterclockwise rotation of the eccentric nut 430 from the state shown in Fig. 13 leads to the state shown in Fig. 14. The eccentricity (DE) of the eccentric nut 430 causes the second external thread 412 of the two-ended screw 410 to shift slightly to the left (arrow C in Fig. 14). It should be noted that the eccentric nut 430 has a circular outer shape and is inserted into the guide slot section 240 with minimal play, thus ensuring that the position of the eccentric nut 430 itself does not change. The eccentric nut 430 only rotates. When the second external thread 412 shifts (arrow C in Fig. 14), the two-ended screw 410 also shifts (arrow D in Fig. 14). This also shifts the internal thread 111 of the spindle 110 to the left. The shift of the internal thread 111 causes the spindle 110 to rotate about its axis (arrow E in Fig. 14). The rotation of the spindle 110 also causes the angle of the scale mounting surface 113 to rotate, thus changing the position of the scale 310. The technician turns the eccentric nut 430 slightly, moves the spindle 110 back and forth, and checks the detection signal. When the spindle 110 moves, the eccentric nut 430 slides along the guide slot section 240, but the eccentric nut 430 does not rotate freely. This means that the rubber sleeve 420 is inserted between the eccentric nut 430 and the contact surface 414, and thus the eccentric nut 430 does not rotate freely. If the eccentric nut 430 is rotated to be slightly off-center relative to the guide slot section 240, it is possible that the eccentric nut 430 will establish a pre-tensioned contact with the guide slot section 240. It is possible that the edge of the guide slot section 240, where the preloaded contact is made, may attempt to rotate the eccentric nut 430 in one direction when the spindle 110 is moved in that direction.Given this situation, the position adjustment pin 400 consists of a multitude of elements, with the rubber sleeve 420 inserted between the eccentric nut 430 and the bearing surface 414. The technician can therefore repeatedly move the spindle 110 back and forth and find the angle of the eccentric nut 430 that provides the best detection signal, without having to worry about unintentional rotation of the eccentric nut 430. Although a similar effect can be achieved by using a spring washer instead of the rubber sleeve 420, the nature of the deformation of the spring washer means that the eccentric nut 430 is not pushed straight upwards but rather at a slight angle. This creates the risk that the spring washer will exert an unexpected force on the position adjustment pin 400 and the spindle 110. The rubber sleeve 420, which has a highly symmetrical shape, is therefore preferred. Once an optimal detection signal has been obtained from the detection head 320, a small amount of adhesive is injected into the internal thread 431 of the eccentric nut 430 to fully secure the eccentric nut 430. The remaining components are then attached, and the linear measuring device 100 is complete. In this way, a machining error in components (for example in the holding cylinder 200) can be compensated for by the position adjustment pin 400, and thus the linear measuring device 100 can provide high measuring accuracy according to the embodiment, even when a relatively inexpensive encoder 300 is used. Further descriptions regarding the effect of providing the gap L between the guide slot section 240 and the guide cylinder part 220 (the rear guide cylinder 230) are now given. Compared to providing the guide slot 11 in the sleeve 10 as before (for example, Fig. 4), providing the gap L between the guide slot section 240 and the guide cylinder part 220 (the rear guide cylinder 230), as in the embodiment, reduces the play when the spindle 110 rotates about its axis. It is assumed here that the same degree of machining error exists in the conventional example (for example, Fig. 4) and in the embodiment. In other words, it is assumed that the play between the guide slot 11 and the journal 112 in the conventional example (for example, Fig. 4) is the same as in the embodiment.4) ΔG is the amount, and the clearance between the eccentric nut 430 and the guide slot section 240 in the embodiment (Fig. 14) is also ΔG. Furthermore, it is assumed that the rotational play about the axis of the spindle 110 is ΔθP in the conventional example (for example, Fig. 4), and that the rotational play of the spindle 110 in the embodiment is ΔθE (Fig. 14). ΔθP and ΔθE are as specified below, and ΔθE is significantly smaller than the amount of the gap L. Thus, the embodiment provides a smaller offset amount between the positions of the scale 310 and the detection head 320, which further stabilizes the measuring accuracy of the encoder 300, where r is the radius of the spindle. A user of the linear measuring instrument 100 will sometimes hold the spindle 110 directly in their hand during use (measurement). Situations have arisen where the user unintentionally exerts a rotational force on the spindle 110, resulting in a displacement of the encoder 300. With this in mind, the position adjustment pin 400 is longer in this embodiment. The principle described above works such that the additional length significantly restricts the rotation of the spindle 110. Thus, the precision of the encoder 300 does not decrease, even when the user holds the spindle 110 directly. If the aforementioned value ΔG is considered the eccentricity rate (eccentricity level) of the eccentric nut 430, it is evident that the embodiment ensures a smaller rotation angle in the spindle 110 when the eccentric nut 430 is rotated only slightly. In other words, this means that the position of the spindle 110 can be adjusted to an extremely fine degree (the roll angle offset can be adjusted). Nevertheless, the adjustment of the spindle's rotation about its axis using the position adjustment pin 400 is on the order of 1 / 100°, which is close to the limit of human vision. If, in the conventional configuration (Fig. 4), the pin is simply replaced by an eccentric pin, it is still possible that the adjustment will not function correctly. However, with regard to this point, this embodiment makes it easier to make fine adjustments. Although it is preferable for the gap L to be as long as possible, the upper limit of the gap length L is normally a length at which the retaining cylinder 200 (the guide slot section 240) fits into the cover part 500. There is no specific restriction on the lower limit, and any value greater than 0 may be used. However, if a value is to be specified, the guide slot section 240 is preferably not smaller than r (where r is the radius of the spindle) from the inner surface of the guide cylinder part 220, and more preferably not smaller than 2r. According to the embodiment described so far, a linear measuring device that achieves a high level of balance between cost reduction and high measurement accuracy can be provided. The present invention is not intended to be limited to the embodiment described above, and suitable variations can be made to it without departing from the essential spirit of the present invention. It is sufficient that the position adjustment pin functions as an eccentric pin, and thus the screw with two ends can be eccentric instead of the nut. Although the foregoing describes the screw with two ends as having an external thread and the pin head as an eccentric nut, the internal and external threads can, of course, be reversed. Although the encoder's detection head is described as being attached to the holding cylinder, and the scale as being attached to the spindle, this can, of course, be reversed. In the case of a photoelectric encoder, the scale is a glass scale incorporating a diffraction grating, and the detection head is a unit comprising an LED (which need not be a semiconductor laser (LD)) and an array of light-receiving elements. However, the type of encoder is not particularly restricted. An electrostatic capacitor-type encoder, a magnetic encoder, or a transmissive photoelectric encoder can be used, and, of course, a laser holoscale (LHS) can also be employed. REFERENCE MARK LIST 100 Linear measuring device 110 Spindle 111 Internal thread 113 Scale mounting surface 120 Main body 200 Retaining cylinder 210 End plate 220 Guide cylinder section 221 Front guide cylinder 230 Rear guide cylinder 231 Loose insertion slot 240 Guide slot section 250 Bracket 300 Encoder 310 Scale 311 Scale surface 320 Detection head 321 Detection surface 400 Position adjustment pin 410 Double-ended screw 411 First external thread 412 Second external thread 413 Middle section 414 Flat surface 414 Contact surface 420 Rubber sleeve 430 Eccentric nut 431 Internal thread 500 Cover part 510 Outer housing 520 Cap

Claims

Linear measuring instrument (100) comprising: a spindle (110); a guide cylinder part (220) configured to guide the spindle (110) so that it moves back and forth in an axis line direction; a guide slot section (240) formed parallel to the axis line of the guide cylinder part (220), providing a gap between the guide slot section (240) and the guide cylinder part (220); and a position adjustment pin (400) attached to a side face of the spindle (110) passing through the guide slot section (240), the position adjustment pin (400) being an eccentric pin. Linear measuring device (100) according to claim 1, wherein the position adjustment pin (400) comprises: a two-ended screw (410) having screws on both a tip end and a base end, wherein the screw on the base end side is screwed into the side surface of the spindle (110); and a pin head (430) into which the screw on the tip end side of the two-ended screw (410) is screwed, wherein at least one of the two-ended screw (410) and the pin head (430) is eccentric. Linear measuring device (100) according to claim 2, wherein a rubber sleeve (420) is inserted between the screw with two ends (410) and the pin head (430). Linear measuring device (100) according to one of claims 1 to 3, wherein a scale (310) or a detection head (320) of a reflective photoelectric encoder is attached to the spindle (110).

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