Abstract:
A measuring device which reduces reading errors caused by parallax. The measuring device has a gauge head abutting against an object to be measured, and includes a pointer-type display part which displays displacement of the gauge head obtained by being enlarged by an enlarging mechanism and being converted into a rotation amount of a pointer. The measuring device further includes a transparent cover plate provided so as to cover the pointer-type display part, and the cover plate has an antireflection film on the surface. The cover plate further has an antifouling film on the antireflection film. The cover plate has a flat surface.

Description:
INCORPORATION BY REFERENCE 
       [0001]    This application is based upon and claims the benefit of priority from Japanese patent application No. 2015-244669, filed on Dec. 15, 2015, the disclosure of which are incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a measuring device. More specifically, the present invention relates to a measuring device having a pointer-type display part such as a lever-type dial gauge and a dial gauge. 
         [0004]    2. Description of Related Art 
         [0005]    There is known a lever-type dial gauge (JP 3675587 B and JP 4399186 B). The lever-type dial gauge is used to inspect whether there is a machining error or whether the error is within a tolerance by performing comparative measurement mainly between a master or a block gauge and an object to be measured. The comparative measurement by the lever-type dial gauge has an extremely important role in inspection of dimensional accuracy of products. 
       SUMMARY OF THE INVENTION 
       [0006]    If the exactly same lever-type dial gauge is used, the inspection result is frequently different from measurer to measure. As a result of the earnest investigation of the cause, the inventors of the present invention noticed that measurers&#39; unintentional posture change is one of the reasons. 
         [0007]    To perform comparative measurement, measurers should not change the posture when reading a scale. If the measurer changes the posture when measuring a master from that when measuring an object to be measured, the visual line to read the scale is changed, and the difference in the visual line directly causes a measurement error. 
         [0008]    The reason why the measurer unintentionally changes the posture is that the pointer and the scale (graduation line) can be difficult to see sometimes. 
         [0009]      FIG. 1  is a diagram illustrating a using state of a lever-type dial gauge  80 . Typically, the lever-type dial gauge  80  is mainly used with a display part  82  facing upward. Then, light of the illumination on the ceiling reflects on a cover plate  83 . 
         [0010]    If the cover plate  83  has a slightly curved convex surface, the reflection is dispersed into a plurality of weak reflection spots  91 . However, light in various directions is reflected on the cover plate  83 . 
         [0011]    If the cover plate  83  has a flat surface, light in only one direction is reflected, but a large strong reflection spot  91  appears. 
         [0012]    Although a measurer determines the posture so as to easily see the pointer position (reference point) when a master or a gauge is measured, if the pointer position when a workpiece (object to be measured) is measured is covered with the reflection spot  91 , the measurer changes the posture to read the scale (graduation line) indicated by a pointer  84 . 
         [0013]    In another case, when the difference in height between the left and the right of an object to be measured is measured, a dial gauge is moved to a measurement point to perform the measurement. For example, a dial gauge is attached to a jig or the like, and the reference point is adjusted at the measurement point of the left end of the object to be measured. Then, the dial gauge is moved together with the jig, and the difference from the reference point is read at the measurement point of the right end. In this measurement, although illumination is not reflected at the time when the reference point is adjusted, the illumination can be reflected at the position to which the dial gauge is moved. In this case, the measurer unintentionally changes the posture at the position to read the scale, which leads to a measurement error. 
         [0014]    It is supposed to start the measurement of the master or the gauge again, but the remeasuement is troublesome. Furthermore, not all users correctly recognize the importance of not changing the posture, that is, fixing the angle of the visual line. 
         [0015]    Thus, a purpose of the present invention is to provide a measuring device which reduces reading errors caused by parallax. 
         [0016]    A measuring device according to an embodiment of the present invention has a gauge head to be contacted to an object to be measured, and includes: 
         [0017]    a pointer-type display part configured to display displacement of the gauge head obtained by being enlarged by an enlarging mechanism and converted into a rotation amount of a pointer; and 
         [0018]    a transparent cover plate provided so as to cover the pointer-type display part, in which the cover plate has an antireflection film on a surface. 
         [0019]    In an embodiment of the present invention, it is preferable that the cover plate further has an antifouling film on the antireflection film. 
         [0020]    In an embodiment of the present invention, it is preferable that the cover plate has a flat surface. 
         [0021]    In an embodiment of the present invention, it is preferable that the pointer-type display part has a graduated dial plate, and the dial plate is rotatable about an axis of the pointer. 
         [0022]    In an embodiment of the present invention, it is preferable that the measuring device is a lever-type dial gauge or a dial gauge. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a diagram illustrating a using state of a lever-type dial gauge; 
           [0024]      FIG. 2  is a front view of a dial gauge (measuring device); 
           [0025]      FIG. 3  is an exploded view of the dial gauge (measuring device); 
           [0026]      FIG. 4  is a diagram illustrating an experimental example in the case that a cover plate having a convexly curved surface with no antireflection film is used; 
           [0027]      FIG. 5  is a diagram illustrating an experimental example in the case that a cover plate having a flat surface with no antireflection film is used; and 
           [0028]      FIG. 6  is a diagram illustrating an experimental example using an embodiment of the present embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    An embodiment of the present invention is illustrated and described with reference to the reference signs attached to the elements in the drawings. 
       First Exemplary Embodiment 
       [0030]    In the present embodiment, a dial gauge  10  is exemplified, but the present invention is effective in a lever-type dial gauge  80 , a pointer display type caliper, or micrometer. In other words, the present invention is effective in any of pointer display type small measuring devices. 
         [0031]      FIG. 2  is a front view of the dial gauge  10  (measuring device). 
         [0032]      FIG. 3  is an exploded view of the dial gauge  10  (measuring device). 
         [0033]    The dial gauge  10  is to display displacement of a spindle  50  as a rotation amount of a pointer  71 . 
         [0034]    The dial gauge  10  includes a main body case  40 , a spindle  50 , an enlarging mechanism  30 , and a main body cover  20 . 
         [0035]    The main body case  40  is a short cylindrical case body one end face of which is opening. A stem  60  is provided in a protruding manner on the side face of the main body case  40 , and the stem  60  is a bearing of the spindle  50 . 
         [0036]    The spindle  50  has a gauge head  51  at the tip, and the based end side is housed in the main body case  40 . The spindle  50  is supported by the stem  60  so as to be movable backward and forward in the axis direction. 
         [0037]    The enlarging mechanism  30  enlarges and converts linear displacement of the spindle  50  into a rotation amount of a pointer  71 . The enlarging mechanism  30  is formed by combining a plurality of gears and housed inside the main body case  40 . The enlarging mechanism  30  has a pinion (not illustrated) which engages with a rack (not illustrated) provided to the spindle  50 , and enlarges the rotation of the pinion with a plurality of gear trains. 
         [0038]    The main body cover  20  has an external frame part  21  and a cover plate  22 . 
         [0039]    The external frame part  21  is a short cylinder both ends of which are opening, and attached to the opening side end face of the main body case  40  by sandwiching, for example, an O ring  41  in-between. 
         [0040]    Here, when the external frame part  21  is attached to the end face of the main body case  40 , by sandwiching a dial plate  42  between the end face of the main body case  40  and the external frame part  21 , the dial plate  42  is fixed to the end face of the main body case  40 . 
         [0041]    Furthermore, the pointer  71  is arranged on the dial plate  42 , and a pointer axis  72  is coupled to a center pinion (not illustrated) which is the final stage of the enlarging mechanism  30 . 
         [0042]    Here, the pointer  71  and the dial plate  42  constitute a pointer-type display part. 
         [0043]    The external frame part  21  is rotatable with respect to the main body case  40 , and when the external frame part  21  is rotated, the dial plate  42  is rotated about an axis  72  of the pointer  71  together with the external frame part  21 . 
         [0044]    By rotating the dial plate  42 , it is possible to adjust the position of the origin (“0” on the dial plate) to an arbitrary position, and the measurement value of, for example, a master or a block gauge is adjusted to the origin (“0” on the dial plate). 
         [0045]    The cover plate  22  is a transparent disk-shape thin plate. The cover plate  22  may be glass or may be formed of transparent resin such as acrylic resin. The cover plate  22  is fixed to the end face of the external frame part  21  so as to close the opening face of the external frame part  21 . 
         [0046]    In the present embodiment, the cover plate  22  has a front and a rear faces which are flat. 
         [0047]    There is also known a convexly curved cover plate  22 , and the convexly curved cover plate  22  may be used in the present embodiment. 
         [0048]    However, if the cover plate  22  is convex, the scale and the pointer look slightly distorted due to refraction of light. Thus, it is desirable that the cover plate  22  is plane. For example, in precise measurement, in which a scale (graduation) is 0.001 mm, the clearly recognizable difference appears. 
         [0049]    Conventionally, since reflection largely appears and impairs the visibility if a cover plate is plane, a cover plate has been convex to diminish the influence although affected by refraction of light. In this regard, by performing antireflection processing to the cover plate  22  in the present embodiment as described later, it is possible to use a complete plane cover plate  22  which is not affected by refraction of light, and to achieve both of visibility and high-precision measurement. 
         [0050]    The cover plate  22  is subjected to antireflection processing, that is, an antireflection film  24  (AR coating) is formed on the surface of the cover plate  22 . 
         [0051]    The antireflection film  24  may be monolayer or multilayer. Furthermore, the antireflection film  24  may be formed only on the surface of the cover plate  22  or on both of the front and the rear surfaces. The wavelength region or reflectivity of corresponding light is not particularly limited. Actually, these are determined according to a grade or price of a product. 
         [0052]    However, if the antireflection film  24  is not provided, in the case of acrylic resin or the like commonly used as cover plate materials, the reflectivity is about 8%, and a measurer clearly sees a reflection spot  91  by illumination. 
         [0053]    Thus, in order for the measurer not to unconsciously change the posture without caring about a reflection spot at all, the reflectivity of light on the cover plate  22  is to be less than 1%, preferably less than 0.5%, and more preferably less than 0.2%. By providing the antireflection film  24 , the reflection spot is eliminated, and the measurer does not unintentionally change the posture. 
         [0054]    Most of factories use bright illumination for workers&#39; working efficiency or ensuring security. Furthermore, because of high reflectivity of the walls, there are reflection materials, such as a metal member, in many factories. Thus, a factory is an environment in which strong reflection spots easily appear on a plurality of positions of the cover plate  22 , and the positions of reflection spots are greatly changed according to the using place in the factory. 
         [0055]    Note that, when the dial gauge  10  is used, the gauge head does not always face downward, and the dial gauge is mainly used in a lateral posture. 
         [0056]    Furthermore, when products are inspected, the position (graduation) indicated by the pointer  71  is to be a different value in one rotation (360°) according to a workpiece. Although the scale and the pointer  71  are easily seen at the time when the reference point is adjusted firstly, it does not necessarily mean that the scale (graduation) and the pointer  71  are easily seen when a workpiece (object to be measured) is measured. The pointer  71  can be easily seen or difficult to be seen according to the measurement value of a workpiece (object to be measured). 
         [0057]    Thus, variation in measurement values can be caused depending on a measurer, a measurement place, or a workpiece (object to be measured). 
         [0058]    In this regard, since the reflection spots are eliminated by the antireflection film  24  in the present embodiment, the measurer does not unintentionally change the posture. 
         [0059]    Not only when the scale (graduation line) indicated by the pointer  71  is read and but also when the dial plate  42  is rotated to adjust the reference point, the measurer does not unintentionally change the posture. 
         [0060]    Thus, with the dial gauge  10  (measuring device) of the present embodiment, it is possible to stably perform measurement. 
         [0061]    Furthermore, the cover plate  22  has an antifouling film  26  on the antireflection film  24 . 
         [0062]    The antifouling film  26  preferably has water repellency and oil repellency such as fluoro-resin coating. 
         [0063]    In the place where the dial gauge  10  (measuring device) is used, machine oil or cutting oil are used. 
         [0064]    Such oil can be attached to the cover plate  22  by splashing or floating in the air. Furthermore, the cover plate  22  can be unintentionally wiped with dirty hands to clearly see the display part. 
         [0065]    If oil films are attached on some positions of the cover plate  22 , a measurer unintentionally changes the posture to read the pointer  71  or the scale. 
         [0066]    In this regard, by performing the antifouling processing to the cover plate  22  not to get dirty in the present embodiment, the visibility of the pointer  71  cannot be impaired. 
         [0067]    Thus, in a severe environment such as a factory, the visibility of the pointer  71  or the scale is enhanced, and measurement errors caused by parallax are extremely reduced. 
       Experimental Example 
       [0068]    An experimental example is described below. 
         [0069]      FIG. 4  is a cover plate having a convexly curved surface with no antireflection film. 
         [0070]    The illumination is reflected on the cover plate, the four reflection spots  91  appear. 
         [0071]      FIG. 5  illustrates a cover plate having a flat surface with no antireflection film. 
         [0072]    Although the reflection spot  91  is one, the large and strong reflection spot appears on the surface of the cover plate. 
         [0073]    In contrast,  FIG. 6  is an example of the present embodiment. 
         [0074]    There is no reflection spot on the surface of the cover plate, the pointer and the scale are clearly seen although the pointer  71  is positioned anywhere in one rotation. 
         [0075]    Note that, the present invention is not limited to the above embodiment, configurations appropriately changed without deviating from the scope belong to the technical scope of the present invention.