Patent Publication Number: US-2009223074-A1

Title: Gage for measuring disc brake thickness

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a non-provisional of, and makes claim of the benefit of priority to, U.S. provisional patent application Ser. No. 61/034,650, filed 7 Mar. 2008, which is incorporated by reference as if fully recited herein. 
    
    
     TECHNICAL FIELD 
     This application relates to the field of gages, particularly, to the field of gages for measuring the thickness of a disc brake. Even more particularly, it relates to a device and method for measuring the minimum thickness of a disc brake. 
     BACKGROUND OF THE ART 
     In the field of maintaining disc brakes, it is important and known to measure certain aspects of a disc brake to a high degree of accuracy and precision. One measurement that is required is a determination of the minimum thickness of the disc brake. 
     In particular, when referring to the minimum thickness of the disc brake, it is the brake pad, a sacrificial member, to which this application refers. While it is desirable that a disc brake have a consistent value of the minimum thickness as one moves around the circumference, actual observation is that the thickness may vary, in both the circumferential and the radial direction. 
     At least two problems exist in the known prior art gages for measuring disc brake thickness. First, many known gages provide a first, flat tipped spindle and a second spindle with a pointed tip. The purpose is to assure that the respective spindles are each in normal position relative to the respective disc brake surfaces, with the flat tipped spindle providing the required alignment, through its shape. However, the flat tip will generally be unable to fit into any groove in the surface, as the groove will be smaller than the surface dimensions of the flat tip. Second, even if the point of minimum thickness is located, the known gages make the act of obtaining accurate results and simultaneously recording these results in a useful manner a difficult task. 
     Therefore, it is an unmet objective of the prior art as known to provide a gage for both accurately and precisely measuring the minimum thickness of a disc brake. 
     SUMMARY OF THE INVENTION 
     This and other objectives are achieved by a gage for measuring the minimum thickness of a disc brake. 
     In an exemplary embodiment, the device comprises a frame with a pair of spaced-apart clovis arms. First and second anvils are positioned in the respective arms of the clovis, with the first anvil arranged in fixed position, but with the second anvil mounted for sliding motion in a bore in the second clovis arm. The anvils are directed towards the interior of the clovis, in a co-axial facing relationship, the second anvil movable along the axis. A means, such as a vernier, is provided to measure axial translation of the second anvil in the bore. By communicating an output of this axial translation measurement means to a readout device, such as a meter positioned on the second anvil, a user is able to monitor the measurement. A lift device on the second anvil allows fine control of the translation of the anvil in the bore. 
     In most aspects, it will be advantageous to provide the facing tips of the anvils with pointed ends. 
     In most aspects, it will also be advantageous to provide a means for biasing the second anvil in the bore. This biasing means acts to urge the tip on the second anvil toward the tip of the first anvil. Where the biasing means is provided, it will be preferred to also provide a delimiter to the biasing force, such the engagement of the readout device against the clovis arm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the invention will be had by reference to the accompanying FIGURE, wherein identical parts are identified by identical part numbers and wherein: 
         FIG. 1  is a front elevation view of an embodiment of a disc brake gage, in isolation. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring to  FIG. 1 , an embodiment of a digital disc brake gage  10  is seen in front elevation view. The gage comprises a frame  12  with a pair of spaced-apart clovis arms  14 ,  16 . A first anvil  24  is arranged in fixed position in clovis arm  14 , and a second anvil  26  is mounted in the second clovis arm  16 . Anvils  24 ,  26  are positioned relative to each other in a co-axial facing manner, with second anvil  26  movable along the axis. A readout device  30  is positioned on second anvil  26 . A lift device  40  is also positioned on second anvil  26 . 
     In the embodiment shown, the facing tips  44 ,  46  of anvils  24 ,  26  are pointed, so as to be able to reach into any grooves encountered on the surface of a disc brake being measured. In other embodiments, each end may be provided with a rounded surface of small diameter, such as would be encountered on a fine point roller-ball pen. This latter design allows entry into small grooves, while also allowing lateral movement across the surface. 
     Typically, as is known in this art, second anvil  26  is maintained in a bore through second clovis arm  16  by a biasing means that urges the anvil tip inwardly of the clovis, that is, in the direction of tip  44  on the first anvil  24 . 
     The readout device  30  is connected to the second anvil  26 . Readout device  30  may provide a stop means, delimiting the inward movement of the anvil that is urged by the biasing means, although another delimiting means may be provided and used. 
     The readout device  30  will be provided with a display face  32 . Prominent on the display face  32  is a display area  33 , which will be filled by a display means, typically a liquid crystal diode (LCD). Various control buttons are depicted. Among these are an “on/off” function button  34 , a units selection button  35 , a “hold” button  36 , a “set” button  37  and a “min” button  38 . Of particular note is the “min” button  38 . Internal to the readout device  30  is a digital chip for operating the readout device  30 , as well as a power source, typically a small battery. Integral to the digital chip is a logic circuit that allows a minimum measured distance value to be stored in a memory register. Use of the “min” button  38  causes the value stored in the memory register to be displayed. 
     It will be readily known to those of skill in this art to properly connect the digital chip in the readout device  30  to known means in the bore, so that movement of the second anvil in the bore is accurately and precisely measured. 
     By placing the disc brake to be measured within the clovis while lifting the second anvil  26  by use of the lift device  40  and then allowing the respective anvil tips  44 ,  46  to come into contact with the opposing surfaces of the disc brake, an initial reading of the thickness may be obtained. 
     With the device  10  so positioned, the digital chip of the readout member  30  powered up and the minimum value register either “zeroed” or set to a value that is clearly larger than the diameter, device  10  may be moved around the disc brake surface, constantly making thickness measurements. Keeping in mind that the shortest distance between any two points on the opposing faces is a normal line between the surfaces, and that by keeping the tips  44 ,  46  in contact with the surfaces, slight lateral movement of the tips will seek out the true minimum thickness over the portion of the disc which is scanned with the device. This value will be recorded as the minimum value.