Abstract:
An apparatus for measuring a dimension of a workpiece includes a pair of rods positioned within a channel of a baseplate. At least one wedge member is mounted between the rods and forces the rods in a direction away from each other. A guide plate is adjustably mounted with respect to the baseplate, the guide plate having a cutout positioned at least partially over the rods for accepting the workpiece. A measuring tool is adjustably mounted with respect to the baseplate for moving in at least a linear direction.

Description:
This application claims benefit of Provisional Appln. Ser. No. 60/125,091 filed Mar. 11, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an apparatus and a method for precision measuring a dimension, preferably but not necessarily a length, of a workpiece or a portion of the workpiece. 
     2. Description of Related Art 
     Precision measurements require a predictable, consistent surface across which to take such measurements. Traditionally, granite or other similar surfaces have been used as a base or platform upon which to measure dimensions of a workpiece. 
     It is desirable to provide an apparatus and method for precision measuring a dimension of a workpiece wherein a predictable, consistent surface is maintained upon which to position the workpiece. 
     SUMMARY OF THE INVENTION 
     It is one object of this invention to provide a predictable, consistent surface upon which to position a workpiece. 
     It is another object of this invention to provide an apparatus wherein a pair of rods maintain a precise surface when engaged within a channel. 
     It is still another object of this invention to provide guide plate having a cutout for positioning a workpiece upon a precise surface created by a pair of rods. 
     An apparatus according to one preferred embodiment of this invention includes a base, a baseplate, a guide plate and mounting brackets. The baseplate is preferably fixed with respect to the base. The baseplate comprises a channel. Preferably, but not necessarily, a micrometer or other measuring device is mounted so that a point of contact of the measuring device intersects a centerline of the channel. 
     Preferably, a rod is fixedly mounted within each corner area of the channel. A wedge member, such as a screw having a tapered head is tightened to effectively force each rod downward and outward, so that each rod establishes linear contact with the baseplate. Two or more wedge members, such as screws, are preferably used to mount the two rods within the channel. 
     Preferably, a guide plate is slidably mounted with respect to the baseplate. The guide plate has two generally parallel channels through which an adjustment screw can be positioned to facilitate adjustment between the guide plate is and the baseplate. 
     The guide plate preferably includes a cutout for accommodating a workpiece. The workpiece is positioned within the cutout and rests upon the rods. As the workpiece and/or the guide plate is moved with respect to the baseplate, dimensions may be taken with the measuring device. Such an arrangement results in a predictable, consistent surface upon which to position the workpiece. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and objects of this invention will be better understood from the following detailed description taken in conjunction with the drawings wherein: 
     FIG. 1 is a front perspective view of an apparatus, including a base and a baseplate, according to one preferred embodiment of this invention; 
     FIG. 2 is a side perspective view of the apparatus shown in FIG. 1; 
     FIG. 3 is a side view of an apparatus, including a base, according to one preferred embodiment of this invention; 
     FIG. 4 is a front view of the apparatus shown in FIG. 3 without the base; 
     FIG. 5 is a side view of the apparatus shown in FIG. 3 without the base; 
     FIG. 6 is a top view of several operative components of an apparatus according to one preferred embodiment of this invention; 
     FIG. 7 is a top view of a baseplate according to one preferred embodiment of this invention; 
     FIG. 8 is a side view of the baseplate shown in FIG. 7; 
     FIG. 9 is a top view of a guide plate according to one preferred embodiment of this invention; 
     FIG. 10 is a side view of a master blank plug according to one preferred embodiment of this invention; 
     FIG. 11 is a diagrammatical side view of a workpiece positioned on two rods according to one preferred embodiment of this invention; 
     FIG. 12 is a bottom perspective view of the apparatus shown in FIG. 1 without the base or the baseplate; 
     FIG. 13 is a front, close-up perspective view of a baseplate, rods and screw of an apparatus according to one preferred embodiment of this invention; and 
     FIG. 14 is a top perspective view of the apparatus shown in FIG.  13 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 each show a perspective view from a different upper corner of measuring apparatus  10 , according to one preferred embodiment of this invention. FIGS. 1 and 2 show measuring apparatus  10  comprising base  15 , baseplate  20 , guide plate  25  and mounting brackets  30  and  35 . 
     Preferably, although not necessarily, components of apparatus  10 , including base  15 , baseplate  20 , guide plate  25  and mounting brackets  30  and  35  are constructed from steel, such as A 2  steel, having an appropriate hardness, such as approximately 62 Rc. Other appropriate materials known to those having ordinary skill in the art such as carbide steel may also be used provided such materials exhibit high hardness, resist deformation and are workable to precise tolerances. 
     In one preferred embodiment of this invention, micrometer 12 is detachably mounted in a fixed position with respect to mounting brackets  30  and  35  and guide plate  25 . Micrometer 12 is shown in FIG. 1 as a digital micrometer. However, it is apparent that micrometer 12 can be any other suitable micrometer or measuring device that records a change in a linear direction or a distance traveled in a linear direction. As shown in FIG. 1, measuring shaft  13  of micrometer 12 moves in a linear direction parallel to a longitudinal axis of measuring shaft  13 . Micrometer 12 is preferably fixedly mounted within bore  36  of mounting plate  35 , as best shown in FIG. 3, in any suitable manner known to those skilled in the art. 
     Baseplate  20  is preferably fixedly mounted with respect to base  15 , such as with fasteners, adhesives, or in any suitable manner known to those skilled in the art. As shown in FIGS. 6-8, according to one preferred embodiment of this invention, baseplate  20  comprises channel  21 . Preferably, but not necessarily, micrometer 12 is mounted so that the longitudinal axis of measuring shaft  13  intersects a centerline of channel  21 . 
     In one preferred embodiment of this invention, one rod  40  is fixedly mounted within each corner area  22  of channel  21 . A wedge member, such as a screw  42  which preferably has a tapered head, such as about 45°, is tightened to effectively force each rod  40  downward and outward, relative to the orientation of FIG. 7, so that each rod  40  establishes linear contact with baseplate  20  at points  43  and  44 , as shown in FIG.  8 . According to one preferred embodiment of this invention, channel  21  forms a horizontal surface and a vertical surface such that single linear contacts are formed in the horizontal plane and the vertical plane. Two or more wedge members, such as screws  42 , are preferably used to mount two rods  40  within channel  21 , as shown in FIG.  8 . Each rod  40  preferably but not necessarily has a precisely circular cross section, as shown in FIGS. 8,  11 ,  13  and  14  and is constructed of a relatively hard material, such as a suitable carbide metal. 
     According to one preferred embodiment of this invention, shown in FIGS. 8 and 13, each rod  40  extends above a planar surface of baseplate  20 . Correspondingly, each screw  42  is preferably sunk below an exposed surface of each rod  40 . 
     In one preferred embodiment of this invention, guide plate  25  is slidably mounted with respect to baseplate  20 . As shown in FIGS. 1 and 9, for example, guide plate  25  has two generally parallel channels  26  through which adjustment screw  27  or another suitable bolt or fastener can be positioned so that adjustment screw  27  can be engaged within a threaded bore within baseplate  20 . As shown in FIGS. 1-5, guide plate  25  is positioned against and slidably contacts baseplate  20 . Adjustment screws  27  can be loosened to allow guide plate  25  to slide with respect to baseplate  20  for adjustment, so that all contact areas of rods  40  can be used until spent. Each rod  40  can also be rotated to expose a new contact area and thus further conserve replacement of each rod  40 . 
     Preferably, guide plate  25  slides with respect to baseplate  20  without contacting or interfering with rods  40  or screws  42 . Therefore, workpiece  50  and not guide plate  25  makes the only contact with rods  40  above a planar surface of baseplate  20 . 
     A method for measuring workpiece  50 , according to one preferred embodiment of this invention, begins with positioning master blank plug  45  within cutout  28  of guide plate  25 , as shown in FIG. 13, so that an external surface of master blank plug  45  forms two line contacts with a sidewall of guide plate  25  that forms cutout  28 . The line contacts ensure that with the appropriate geometry of cutout  28 , such as having a perpendicular cutout and sidewall, the longitudinal axis of master blank plug  45  is parallel to the longitudinal axis of measuring shaft  13 . Master blank plug  45  has a known length. With master blank plug  45  positioned within cutout  28 , measuring shaft  13  of micrometer 12 is adjusted to contact master blank plug  45 , and upon such contact, the readout of micrometer 12 is set to zero. 
     In one preferred embodiment of this invention, measuring apparatus  10  and the method for measuring are used to determine distance  51  of workpiece  50 , as diagrammatically shown in FIG.  11 . Distance  51  includes the length of cylindrical portion  53  plus a certain length along the longitudinal axis of workpiece  50  which is perpendicular to contact point  54  on conical portion  52  of workpiece  50 . In one preferred embodiment according to this invention, distance  51  is used to determine at which point machining of conical portion  52  is complete. For example, workpiece  50  can be used as a valve plug that operates in a high-pressure fluid system, which requires extremely accurate dimensions on the valve plug seat, conical portion  52 . 
     Workpiece  50  is then positioned within cutout  28  in the same manner as master blank plug  45 , but with conical portion  52  contacting the external contact surface of each rod  40 , as schematically shown in FIG.  11 . Dimension  51  of workpiece  50  can be reduced by further machining of the surface of conical portion  52 , until abutting measuring shaft  13  against workpiece  50  results in a zero reading on the readout of micrometer 12. 
     The diameter of rod  40 , the width of channel  21  and/or the depth of channel  21  can be can be varied to achieve different values for dimension  51  of workpiece  50 . Geometry and trigonometric functions, known to those having ordinary skill in the art, can be used to calculate the precise position, diameter and/or dimension of any one or more components to accomplish a desired measurement result. 
     While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration, it will be apparent to those skilled in the art that apparatus  10  and method is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.