Abstract:
A measuring device of the caliper type especially adapted to making inside diameter measurements. The caliper features the ability to change its set position and provide accurate measurements over an adjustable measurement range. The caliper is of compact configuration and is preferably formed from a single block of metallic material including machined features to provide a number of cooperating elements which are elastically coupled to one another. These features allow the separation distance between the probe tips to be adjusted without changing the output of the measuring device.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a gaging device, and particularly to one of the caliper type, adapted for measuring dimensions of work pieces by the difference in position between two probe tips. 
     Gaging devices are in widespread use in industrial applications. It is frequently necessary during machining or other fabricating processes to make precise dimensional measurements of features of a work piece. For example, during an internal grinding operation, it is often necessary to measure the inside diameter of a workpiece to stop the grind cycle when correct size has been achieved. Numerous types of gaging devices are presently in use. Typically, these devices include two or more probe tips, which are capable of relative movement upon contacting the features to be measured. The probe tips are coupled to a measuring device to provide an output related to the difference in position of the probe tips. For example, so-called air gage devices can be used in which a moveable, variable obstruction device causes a change in pressure drop across an orifice to occur with changes in relative probe tip positioning. An external air source and pressure measuring system is used to provide an output related to the dimension being gaged. Other devices, such as linear variable differential transformers (LVDTs) are also in use in such gaging devices. 
     In many gaging applications, compactness is an essential feature. For example, when measuring a workpiece diameter on an internal grinder, it is desirable to fit the gaging device within the confines of the workhead spindle of the grinder. For example, in some instances related to internal grinding, the measuring device must reach the workpiece diameter through the clearance in the center of the workhead spindle while the grinding wheel enters the workpiece from the opposite side. In such instances, the gage must be sufficiently compact so it makes no contact with the internal diameter of the workhead spindle. 
     In many gaging operations it is desirable for a gaging device to be readily adaptable for making various ranges of measurement. Typically, a gage device has a pre-determined and fixed measurement range. Only variations within the measurement range provide an output for the gage. In machine operations where various workpieces are machined and various features having varying dimensions must be measured, it is desirable to provide a gaging device useable for such varying situations. At the same time, expanding the measurement range should not occur at the cost of a lack of measurement accuracy. 
     Designers of gaging devices further strive to achieve temperature stability, accuracy, repeatability, low cost, and low maintenance requirements for the devices. 
     SUMMARY OF THE INVENTION 
     The caliper gage device in accordance with the present invention, achieves the above-referenced desirable features. The gage device includes a pair of probe tips mounted to a gage body. The gage body is formed from one piece of metal material and is machined, preferably using electrical discharge machining (EDM) processes for forming a number of relatively moving segments. The body features a split along its diametric plane which interacts with an adjustment device to cause these two halves to separate by a desired amount. This separation in turn enables probe tips mounted to the gage body to have varying set positions, without changing the output of the gage device. Thus, the device can be used for making distance measurements over a range of set positions. The design of the gage of the present invention is compact, such that it can be mounted to an internal grinding machine and reach the workpiece through the workhead spindle for diameter measurements. Furthermore, the gage device has few parts which reduce variability and fabrication cost, and improves reliability. 
    
    
     Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of the adjustable caliper gage device in accordance with this invention. 
     FIG. 2 is an isometric view, similar to FIG. 1, but showing the gage device from a different perspective. 
     FIG. 3 is an isometric view of the gage device in accordance with this invention, showing a side-plate element exploded away from the remainder of the gage. 
     FIG. 4 is a longitudinal sectional view of the gage device, showing the gage adjusted to an initial set position. 
     FIG. 5 is a longitudinal cross-sectional view of the gage device, similar to FIG. 4, but showing the gage tips adjusted to a second displaced position. 
     FIG. 6 is an enlarged, partial cross-sectional view taken from FIG. 4, showing the relatively moving elements of the gage body. 
     FIG. 7 is an enlarged, partial cross-sectional view, taken from FIG. 5 showing the relatively moving components of the body in a displaced position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The gage device, in accordance with this invention, is shown in its fully assembled configuration in FIGS. 1 and 2, and is generally designated there by reference number  10 . Gage  10  is principally comprised of gage body  12 , probe tips  14  and  16 , gage support block  18 , and gage adjustment mechanism  20 . 
     Gage body  12  is best described with reference to FIGS. 4 through 7 and is preferably formed of a dimensionally stable metal, such as Type  17 - 4  stainless steel. As is evident from the following description of gage body  12 , a number of precision features are formed in the body. These features are preferably formed using EDM processes. Gage body  12  begins as a solid, cylindrically shaped, elongated blank. Gage body  12  features a cut through the body, along a diametric plane from distal end  22  to near the proximal end  24 . This separation is designated by reference number  26  and forms a pair of body halves  27  and  29 . Gage body  12  further features a pair of cuts  28  and  30 , which extend from holes  32  and  34 , and extend to proximal end  24 . These cuts  28  and  30  define a pair of legs  36  and  38 , which displace in response to a gaging measurement process, as will be described in more detail in the following. During measurement, legs  36  and  38  are permitted to spread away from the remainder of gage body  12 . Holes  32  and  34  are cut to leave a thin web of material in the areas designated by reference numbers  40  and  42 . These webs act as hinge points for legs  36  and  38 . 
     A pair of probe tips  14  and  16  are mounted to gage body  12  using threaded fasteners (not shown) installed within bores  48  and  50 . When making a diameter measurement, probe tips  14  and  16  interact with features of a workpiece and are deflected inwardly upon contact with the workpiece as designated by the arrows A. This deflection causes gage body legs  36  and  38  to spread away from the remainder of gage body  12 , in the direction of arrows B. This deformation occurs through yielding of body  12  principally at webs  40  and  42 , which act as hinges for this motion. Air bleed orifices  52  and  54  are connected with a pneumatic gaging system. As legs  36  and  38  spread away from body  12 , the degree to which the orifices  52  and  56  are blocked changes, thus providing a gage output in accordance with well-known pneumatic gaging techniques. Various other types of gaging mechanisms could be implemented for measuring the separation of legs  36  and  38  from body  12  in accordance with this invention. Examples of such alternative gaging mechanisms include LVDT devices, piezo-electric devices, and devices using optical interference or other electrical, magnetic, or optical phenomenon for providing such an output. 
     Gage body  12  further includes a number of features which enable the set position between probe tips  14  and  16  to be adjusted. Along the diametric center plane separation  26 , gage body  12  forms a pair of wedge or ramp surfaces  56  and  58 . Through interaction with gage adjustment mechanism  20 , which will be described below, adjustment pin  60  can be moved between the positions shown in FIG. 4, to that shown in FIG. 5, and acts on the ramp surfaces  56  and  58 , causing the two diametric halves of gage body  12  to become separated, thus causing probe tips  14  and  16  to also become separated. 
     Gage body  12  includes a number of additional formations related to the adjustability of the device. Slits  62  and  64  extend to proximal end  24 . Slits  74  and  76  cooperate with through-holes  66 ,  68 ,  70 , and  72  to form webs  78 ,  80 ,  82 , and  84  which enable gage body  12  to deform in a manner similar to the articulation of four-bar linkages during the adjustment process. 
     FIG. 4 shows gage  10  in an initial adjusted position. In this condition, adjustment pin  60  is displaced in its left-most position. In that position, adjustment pin  60  rests on leading edge areas of ramps  56  and  58 . In FIG. 5, gage  10  is shown adjusted to a position where probe tips  14  and  16  are separated from the position shown in FIG.  4 . That condition is caused by displacing adjustment pin  60  in the right-hand direction, thus causing it to ride “deeper” into ramp surfaces  56  and  58 , separating the halves of gage body  12 . This causes articulation of webs  78 ,  80 ,  82 , and  84 , as shown in FIG.  5 . This articulation occurs without changing the separation between gage legs  36  and  38  and web  83  and  85 , as shown in FIG.  5 . Since the gage device essentially measures the change in position between legs  36  and  38  and webs  83  and  85 , adjustment occurs without changing the output of the gage device. 
     Gage adjustment mechanism  20  includes components mounted to support block  18 . Support block  18  is cylindrical in shape and is adapted for allowing gage  10  to be mounted within a stainless steel tubular casing with an outside diameter of 24.5 mm. Support block  18  is connected with gage body  12  by central plate  88 . Support block  18  has a hollow interior, with threaded adjuster  90  mounted therein. Adjustment nut  20  can be rotated along threaded shaft  94 , which, in turn, moves bushing  96 . Displacement of bushing  96  causes displacement of side plates  98  and  100 , which are, in turn, connected to opposite ends of adjustment pin  60 . By rotating nut  92 , the position of side plates  98  and  100  changes, thus moving adjustment pin  60  with respect to ramps  56  and  58 , and causing a change in adjusted position between probe tips  14  and  16 , as described previously. 
     Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims taken in conjunction with the drawings.