Measuring instrument

Abstract: An electrical base 32 having a stationary detection element 31 is fixed to a body case 11 movably supporting a spindle 13, and a synthetic-resin-made scale holder 34 is provided to move synchronously with the spindle 13 through a guide 33. In addition, a scale 36 having a movable detection element 35 is adherently fixed to the scale holder 34 at a plurality of points. More specifically, a projection 51 is fixed through an adhesive layer 52 to the back of the scale 36, and then adhered through an adhesive layer 53 in the circumferential direction, with the projection 51 held in a accommodating hole 46 formed in the scale holder 34. As a result, the reduction in weight can be achieved and an accompanying disadvantage (fluctuation of a gap between a stationary detection element and a movable detection element) can be resolved.

Description: BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION This invention relates to a measuring instrument for measuring a length or a thickness of an object by the moving displacement amount of a spindle. More specifically, this invention relates to an attachment structure of a movable detection element in an instrument for detecting the moving displacement amount of the spindle by a detecting means having a stationary detecting means and a movable detecting means. 2. DESCRIPTION OF THE RELATED ART There is a known measuring instrument having a body; a spindle movably disposed in the body; and a detecting means including a stationary detection element secured to the body and a movable detection element placed opposite to the stationary detection element at a predetermined gap and moving synchronously with the spindle in the moving direction thereof, and being for detecting the relative moving displacement amount between both detecting elements as an electric signal. For example, it is conventionally known a digital readout dial gauge to detect the moving displacement amount of a spindle movably disposed in a body as an electric signal by a detecting means such as an optical type, a capacitance type or the like provided with a scale having a stationary detection element (e.g., a light emitting and receiving portion, an electrode) disposed in the body and a movable detection element (e.g., a light emitting and receiving portion, an electrode) placed opposite to the stationary detection element at a predetermined gap and moving synchronously with the spindle in the moving direction thereof, and display the detected value in a digital form. Conventionally, in the measuring instrument as described above, because miscount occurs when a gap between the stationary detection element and the movable detection element is fluctuated, and the stable and precise measurement is not achieved, a structure capable of assembling while a processing dimension error of each component is being absorbed is employed. More specifically, the stationary detection element is fixed in the body, and a metal scale holder is integrally fixed to the spindle or a metal scale holder is movably disposed in the body. The scale holder is forcibly pressed to abut to the end portion constantly by a spring or the like in order to be moved synchronously with the spindle in the moving direction thereof. And then a scale having the movable detection element is adhered onto the substantially whole surface of the scale holder through an adhesive layer. Thereby, the measuring instrument is assembled to retain the constant gap between the stationary detection element and the movable detection element while the processing dimension error of each component is absorbed by the adhesive layer. Because the scale holder is made of metal, though the conventional structure has advantages in that the contour precision is easily achieved and the rigidity is high, it also has disadvantages that weight is heavy and portability and operability is not so good for a measuring instrument used for measurement by hand. In order to resolve above disadvantages, it is preferable to reduce the weight of the scale holder, for example, by making the scale holder from synthetic resin. When the scale holder is made by synthetic resin, however, shrinkage in cure of the adhesive layer causes warpage on the scale holder in adhering the scale having the movable detection element through the adhesive layer onto the overall surface of the scale holder, and consequently. warpage also occurs on the scale, whereby the gap between the stationary detection element and the movable detection element is fluctuated, resulting in the difficulty of obtaining a precise measurement. Even when the stationary detection element and the movable detection element is assembled with the constant gap therebetween, an adhesive on the adhesive layer is repeatedly expanded and shrunk every time it experiences temperature cycles and humidity change. As a result, the surface state of the movable detection element adhered is changed by the residual internal stress, thus deteriorating the preciseness of the products. US-Patent 5 289 729 describes a displacement detector having a spindle, a spring for pushing one of a main scale and grid toward the other, protrusions for maintaining a predetermined clearance between the urged one of the main scale and grid and the other, and a clearance limiting device for limiting a displacement of the urged one of the main scale and grid of the other to a limited clearance distance to prevent a loss of measuring continuity. It is an object of the present invention to provide a measuring instrument in which the conventional disadvantages as described above are resolved, reduction in weight is achieved, and the disadvantages with the reduction in weight are also resolved; in other words, to provide a measuring instrument in which a constant gap between a stationary detection element and a movable detection element is ensured while absorbing a processing dimension error of each component, and which is seldom effected by the shrinkage of adhesive layer. SUMMARY OF THE INVENTION A measuring instrument according to the present invention, which includes a body; a spindle movably provided in the body; and a detecting means having a stationary detection element fixed in the body and a movable detection element placed oppositely to the stationary detection element at a predetermined gap therebetween, and synchronously moves with the spindle in the moving direction thereof, the detecting means detecting the relative moving displacement amount between both detecting elements as an electric signal, said measuring instrument further comprising a synthetic-resin-made holder synchronously moving with the movement of the spindle, the holder being adhered with the movable detection element at a plurality of points. According to the aforementioned structure, because the holder is made of synthetic resin, the weight can be decreased as compared with a holder made of metal. Therefore, the portability and operability may be improved. And, because the movable detection element is adherently fixed to the holder at a plurality of points, the movable detection element is less likely to be effected by the expansion and shrinkage of the adhesive layer as compared to a movable detection element of which whole face is adhered to a holder through an adhesive layer. Therefore, the gap between the stationary detection element and the movable detection element is retained to be constant while absorbing a processing dimension error of each component, and stably retaining the constant gap for a long time. In this point, the number of adhering points of the movable detection element and the holder can be determined in any manner. However, because the larger number of adhering points causes an inefficient assembly, it is beneficial for assembling to fix the movable detection element and the holder adherently at two points along the moving direction of the spindle separated from each other at a predetermined distance, for example. More specifically, where the movable detection element is adherently fixed to the holder at a plurality of points, for example, it is preferable to provide a plurality of projections on a face of the movable detection element opposite to the other face confronting the stationary detection element, and a plurality of accommodating holes for holding the projections at the positions of the holder corresponding to the respective projections, so that the movable detection element is adherently fixed to the holder through an adhesive layer laid between the outer circumferential face of the projection and the inner circumferential face of the accommodating hole with the projections respectively inserted into the accommodating holes. The movable detection element is adherently fixed to the holder through the adhesive layer laid between the outer circumferential face of the projection on the movable detection element and the inner circumferential face of the accommodating hole on the holder, so that the gap between the stationary detection element and the movable detection element is adjusted through the displacement the movable detection element in the extending direction of the projection. Therefore, the adjustable range can be set large without increasing the thickness of the adhesive layer. That is to say the processing dimension error of each component can be absorbed even when it is relatively large. In addition, the expansion and shrinkage ot the adhesive layer has little effect because of the adhesion through the adhesive layer in the circumferential direction of the projection. In the above structure, each projection may be integrally and projectingly formed on the face of the movable detection element oppositely to the other face facing the stationary detection element. Alternatively, the projection may be formed as an independent component and adhered to the face through an adhesive layer. According to the above formation, the movable detection element is easily structured, and the adhesive layer between the movable detection element and the projection also absorbs the processing dimension error of each component. In the above structure, the holder may be formed integrally with the spindle. Alternatively, the holder may be formed as an independent component, and is movably held with a guide made of synthetic resin and disposed in the body. In this case, the holder and the guide can be formed of synthetic resin of the same material or synthetic resin of a different material from each other. For example, where the holder and the guide are made of synthetic resin of the same material, a glass nylon type polyamide resin is preferable. A glass nylon type polyamide resin enables to maintaining the sliding performance of the holder with respect to the guide for a long time because of its hardness and strength. Where the holder and the guide are made of synthetic resin of a different material from each other, it is advisable that the holder is made of a nylon type polyamide resin, and the guide is made of an acetal resin. In this case, as compared with the scale holder and the guide of a glass nylon type polyamide resin, easier production, the reduction in warpage and so on can be obtained, and the production costs can be reduced while obtaining similar hardness and strength. In a further preferred embodiment, an electrical base is secured to the guide and carries said stationary detection element, wherein the holder is placed in a space between the electrical base and the guide, and wherein the movable detection element has a scale which faces the stationary detection element at a predetermined gap. According to the above structure, in addition to the aforementioned effects, i.e. the reduction in weight and the solution of the disadvantage therewith, the holder is stably moved in the same direction as the moving direction of the spindle while maintaining a specific posture with respect to the electrical base because the holder is movably placed in the space between the electrical base and the guide. Therefore, the gap between the movable detection element disposed in the holder and the stationary detection element fixed in the body is retained to be constant, so that the high precise measurement is ensured. In the aforementioned description, as means for retaining the gap between the stationary detection element and the movable detection element constant, the holder (and further, the scale and the movable detection element) may be held at the predetermined position by the guide, Alternatively, a projection slidably abutted to both sides of the electrical base can be formed on the face of the holder on which the movable detection element is attached with the stationary detection element therebetween. As a result, the gap between the stationary detection element and the movable detection element is set according to the height from the face of the holder having the movable detection element to the projection, so that the gap between the stationary detection element and the movable detection element can be precisely set with a simple structure. The guide is required to movably hold the holder between the guide and the electrical base. For example, when the guide includes a pair of guiding blocks which are fixed on both sides of the face of the electrical base with the stationary detection element therebetween, and a guiding plate which extends across a pair of the guiding sections, all the periphery of the holder is encircled, so that the holder is stably held movably in the moving direction of the spindle. Here, when a pair of protrudent portions for guiding both sides of the holder are formed on each inner side of the guiding block and a pair of protrudent portions abutting onto the face of the holder oppositely to the face having the movable detection element are formed on the inner face of the guiding plate, the sliding resistance in moving the holder can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view showing a preferred embodiment of a measuring instrument according to the present invention; Fig. 2 is a sectional view of the preferred embodiment; Fig. 3 is a perspectively exploded view showing a detecting means of the preferred embodiment; and Fig. 4 is a sectional view showing an adhered state of a scale to a scale holder in the preferred embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) A preferred embodiment according to the present invention will he described below with reference to the attached drawings. Fig. 1 shows a perspective view of a dial gauge according to the preferred embodiment, and Fig. 2 shows a sectional view thereof. As shown in the drawings, the dial gauge of the embodiment includes a rectangular box-shaped body case 11 as a body; a spindle 13 disposed to the bottom face of the body case 11 via a stem 12 to move in the axis direction; a detecting means 14 for detecting the moving displacement amount of the spindle 13; and a digital display 15 displaying the moving displacement amount (i.e. a measured value) of the spindle 13, detected by the detecting means 14, in a digital form. The spindle 13 has a probe 21 abutting to an object to be measured at the bottom end thereof, and is provided with a rotation stop pin 22 at the upper end thereof. The rotation stop pin 22 is slidably inserted into a guide groove 23 which is formed along the axis direction of the spindle 13 in the body case 11. Thereby, the spindle 13 can be moved only in the axis direction without rotating. As shown in Fig. 2 and Fig. 3, the detecting means 14 is composed of an electrical base 32 having a stationary detection element 31 and fixed along the axis direction of the spindle 13 in the body case 11; a guide 33 secured onto the electrical base 32 through a plurality of screws; a scale holder 34 placed in a space between the electrical base 32 and the guide 33 and moving in the same direction of the spindle 13; and a scale 36 having a movable detection element 35 opposite to the stationary detection element 31 at a predetermined gap G in the scale holder 34. In this case, a light emitting and receiving portion IC for the stationary detection element 31 and an optical lattice for the movable detection element 35 constitute the optical detecting means 14 for optically detecting the relative moving displacement amount between the detection elements 31 and 35. The guide 33 is composed of a pair of guiding blocks 37 fixed to both sides of the face of the electrical base 32 with the stationary detection element 31 in between, and a plate shaped guiding plate 38 extended across a pair of the guiding blocks 37. The guide is formed of synthetic resin, in this case, a glass nylon type polyamide resin contains 30% of glass. A vertical pair of protrudent portions 39 guiding, both sides of the scale holder 34 are formed on the inner side face of the guiding block 37. A vertical pair of protrudent portions 40 abutting to the back face of the scale holder 34 are formed on the inner face of the guiding plate. The scale holder 34 is formed of synthetic resin which is the same material as that of the guide 33, and is provided on the lower end face thereof with an abutting portion 41 abutting the top end of the spindle 13, and an engaging pin 42 on the back face thereof. The engaging pin 42 engages a spring 43 (see Fig. 2) forcibly pressing the scale holder 34 in a direction in which the abutting portion 41 is constantly abutted to the top end of the spindle 13. On the front face of the scale holder 34, namely, the face confronting the stationary detection element 31, a recess portion 44 for holding the scale 36 is formed. On each side of the face with the recess portion 44 therebetween, a vertical pair of projections 45 abutting to each side of the face of the electrical base 32 are formed. In an upper area and a lower area of the recess portion 44, an accommodating hole 46 is formed to pass through. As shown in Fig. 4, the scale 36 is provided with a pair of projections 51 at positions on the back face (which is opposite to the face confronting the stationary detection element 31) corresponding to the accommodating holes 46. Each projection 51 is adhered onto the back face of the scale 36 through an adhesive layer 52, and adhered to the scale holder 34 in the circumferential direction, namely, through an adhesive layer 53 laid between the outer circumferential face of the projection 51 1 and the inner circumferential face of the accommodating hole 46 in the state that the projection 51 is inserted into the accommodating hole 46 of the scale holder 34. In other words, the scale 36 is adherently fixed to the scale holder 34 at two points (the two points of projections 51). Here, as shown in Fig. 4, by using a jig 61, the distance from the distal end of the projection 45 to the surface of the scale 36, namely, the distance between the stationary detection element 31 and the movable detection element 35 is adjusted to be a predetermined gap G. In the aforementioned structure, the spindle 13 is displaced in the axial direction, whereupon the scale holder 34 is synchronized with the displacement of the spindle 13 and moved in the moving direction of the spindle 13. At this time, the movable detection element 35 fixed to the scale holder 34 through the scale 36 is moved while maintaining the predetermined gap G with respect to the stationary detection element 31, so that the moving displacement amount of the movable detection element 35 with respect to the stationary detection element 31 is detected as an electric signal, and then it is displayed on the digital display 15 in a digital form. In consequence, according to the embodiment, the scale holder 34 is formed of synthetic resin, so that the total weight of the dial gauge can be reduced as compared with a scale holder made of metal, thus improving of portability and operability. The scale 36 is adhered at two points of the scale holder 34, so that the movable detection element 35 is less effected by the expansion and shrinkage of the adhesive layer as compared with a scale of which overall face is adhered to a scale holder through an adhesive layer. Therefore, the constant gap G between the stationary detection element 31 and the movable detection element 35 can be ensured while absorbing a processing dimension error of each component, and the constant gap G can be retained stably for a long time. In processes for adhering the scale 36 having the movable detection element 35 to the scale holder 34, a pair of the projections 51 are disposed on the back face of the scale 36, and each projection 51 is inserted into the accommodating hole 46 formed in the scale holder 34, and in this state, the projection 51 is adhered thereto through the adhesive layer 53 laid between the projection 51 and the accommodating hole 46 in the circumferential direction, so that the gap G between the stationary detection element 31 and the movable detection element 35 can be adjusted while displacing the scale 36 displaced in the extending direction of the projection 51, therefore the adjustable range can be defined to be larger without the increase of the thickness of the adhesive layer 53. That is to say, even relatively large processing-dimension-error of each component can be absorbed. The scale 36 is adhered through the adhesive layer 53 in the circumferential direction of the projection 51, so that the influence of the expansion and shrinkage of the adhesive layer 53 can be decreased. Each projection 51 is adhered through the adhesive layer 53 to the back face of the scale 36, so that the production of the scale 36 is simplified and the processing dimension error of each component is also absorbed by the adhesive layer 52 between the scale 36 and the projection 51. The guide 33 is secured to the electrical base 32 and the scale holder 34 is movably disposed in a space between the electrical base 32 and the guide 33, so that the scale holder 34 is stably moved in the same direction as the moving direction of the spindle 13 while retaining a constant posture with respect to the electrical base 32. Therefore, the gap G between the movable detection element 35 disposed in the scale holder 34 and the stationary detection element 31 fixed on the electrical base 32 is retained to be constant, thus assuring of a high precise measurement. The projection 45 is formed on the face of the scale holder 34 which has the scale 36, and the projection 45 abuts to each side of the face of the electrical base 32 with the stationary detection element 31 between, so that the gap G between the stationary detection element 31 and the movable detection element 35 can be defined in the range from the face of the scale holder 34 with the scale 36 to the projection 45 (the range of the depth of the recess portion 44 and the height of the projection 45). Therefore, the gap G between the stationary detection element 31 1 and the movable detection element 35 is accurately defined with a simple structure. A pair of the protrudent portions 39 guiding both sides of the scale holder 34 are formed on the inner side face of the guiding block 37 constituting the guide 33, and a pair of the protrudent portions 40 abutting to the back face of the scale holder 34 are formed on the inner face of the guiding plate 38, so that the sliding resistance against the movement of the scale holder 34 is decreased. The scale holder 34 and the guide 33 are formed of a glass nylon type polyamide resin, so that the sliding performance of the scale holder 34 with respect to the guide 33 is retained for a long time. That is to say a glass nylon type polyamide resin has the high hardness and the high strength, so that the sliding performance of the scale holder 34 with respect to the guide 33 is retained for a long time. In the aforementioned embodiment, the scale holder 34 is described as an independent component from the spindle 13, but the scale holder 34 can be directly united to the spindle 13. In this case, the guide 33 is unnecessary. In the aforementioned embodiment, the projection 51 is adhered through the adhesive layer 52 onto the back face of the scale 36. However, the projection 51 can be unitedly formed on the back face of the scale 36 in advance. In this way, the adhering process of the projection 51 onto the back face of the scale 36 through the adhesive layer 52 can be omitted. Further, in the aforementioned embodiment, the scale holder 34 and the guide 33 are formed of a glass nylon type polyamide resin, but the scale holder 34 may be formed of other type of synthetic resin, such as polyacetal(s), or polybutylene terephthalate. Alternatively, the scale holder 34 and the guide 33 may be formed of different type of synthetic resin from each other. Preferably, the scale holder 34 is made of a nylon type polyamide resin and the guide 33 is made of an acetal resin. In this case, in addition to the hardness and the strength similar to the scale holder 34 and the guide 33 of glass nylon type polyamide resin. merits such as an easy production, the reduction in warpage and so on can be obtained, and the production costs can be reduced. In the embodiment described herein, the optical detecting means 14 is used, but, for example, a capacitance detecting means can be used. Although the aforementioned embodiment is described using the dial gauge as an example, this invention can be applied for any measuring instrument detecting the moving displacement amount of the spindle with the stationary detection element and the movable detection element. According to the measuring instrument of the present invention, the reduction in weight is achieved simultaneously resolving accompanying disadvantages with the reduction in weight. That is to say, there are effects that the constant gap between the stationary detection element and the movable detection element is ensured while absorbing a processing dimension error of each component, and less influenced by the shrinkage of the adhesive layer.

Claims: A measuring instrument including a body (11), a spindle (13) movably provided in said body (11), and a detecting means (14) having a stationary detection element (31) fixed in said body (11) and a movable detection element (35) which is placed opposite to the stationary detection element (31) at a predetermined gap (G), the movable detection element (35) synchronously moving with said spindle (13) in the moving direction thereof, and said detecting means (14) detecting the relative moving displacement amount between both detecting elements (31, 35) as an electric signal, said measuring instrument further comprising: a synthetic-resin-made holde (34) moving synchronously with the movement of said spindle (13), said holder (34) being adhered with the movable detection element (35) at a plurality of points. The measuring instrument according to claim 1, wherein the movable detection element (35) is adherently fixed to said holder (34) at two points separated from each other along the moving direction of said spindle (13) at a predetermined distance. The measuring instrument according to claim 1, wherein a plurality of projections (51) are provided on a face of the movable detection element (35) opposite to the other face confronting the stationary detection element (31) , and wherein a plurality of accommodating holes (46) for holding said projections (51) are disposed on said holder (34) at the positions corresponding to said projections (51), so that the movable detection element (35) is adhered to said holder (34) through an adhesive layer (53), laid between the outer circumferential face of said projection (51) and the inner circumferential face of said accommodating hole (46) when said projections (51) are respectively inserted into said accommodating holes (46). The measuring instrument according to claim 3, wherein said projections (51) are adhered through an adhesive layer onto the face of the movable detection element (35) which is opposite to the other face confronting the stationary detection element (31). The measuring instrument according to claims 1 to 4, wherein said holder (34) is movably held by a guide (33) made of synthetic resin and disposed in said body (11). The measuring instrument according to claim 5, wherein an electrical base (32) is secured to said guide (33) and carries said stationary detection element (31), wherein said holder (34) is placed in a space between the electrical base (32) and the guide (33), and wherein said movable detection element (35) has a scale (36) which faces said stationary detection element (31) at a predetermined gap. The measuring instrument according to claim 6, wherein projections (45) are formed on the face of said holder (34), on which the movable detection element (35) is attached, which projections (45) slidably abut the face of said electrical base (32) on both sides of said stationary detection element (31). The measuring instrument according to claim 6 or 7, wherein said guide (33) includes a pair of guiding blocks (37) fixed on both sides of the face of said electrical base (32) with the stationary detection element (31) therebetween, and a guiding plate (38) extending across the pair of the guiding blocks (37). The measuring instrument according to claim 8, wherein a pair of protrudent portions (39) for guiding both sides of said holder (34) are formed on each side of said guiding blocks (37). The measuring instrument according to claim 8 or 9, wherein the inner face of said guiding plate (38) is provided with a pair of protrudent portions (40) abutting onto the face of said holder (34) which is opposite to the face having the movable detection element (35). The measuring instrument according to claims 4 to 10, wherein said holder (34) and said guide (33) are formed of a glass nylon type polyamide resin. The measuring instrument according to claims 4 to 10, wherein said holder (34) is formed of a nylon type polyamide resin, and wherein said guide (33) is formed of an acetal resin.

Inventors: HAYASHIDA SHUUJI, SUZUKI MIKIO, HAYASHIDA, SHUUJI, SUZUKI, MIKIO, Hayashida, Shuuji c/o Mitutoyo Corporation,, Suzuki, Mikio c/o Mitutoyo Corporation,
Applicants: MITUTOYO CORP, MITUTOYO CORPORATION
Application year: 1998
Main classification: G01B3
IPC codes: G01B3, G01B21