Abstract:
An electronic feeler gauge and a method of using the same which provides an objective means of determining the width of a gap between two surfaces. The gauge comprises a measuring element which is insertable into the gap and an indicator coupled to the measuring element for automatically indicating when the gap has been set to a predetermined distance. The measuring element comprises two plates which act as an electrical switch in an electrical circuit. When the gap gauge is inserted into a gap of predetermined width, the plates press against each other and current from a power source lights up a light emitting diode. Conversely, when the plates are inserted into a gap that is too wide, the plates do not press against each. The circuit, therefore, is not complete, and the light emitting diode does not light up. Thus, this invention provides an objective, reliable means for confirming the width of a gap. The invention can be used for gaps of different widths by varying the thicknesses of the plates.

Description:
TECHNICAL FIELD 
     The present invention relates in general to measuring instruments, and in particular, to a method and apparatus for ascertaining the gap between opposing parts. 
     BACKGROUND INFORMATION 
     In manufacturing quality control, it is often necessary to verify the width of a gap between two adjacent, opposing surfaces. For example, when servicing a computer printer, it is required to optimally set the distance between an end part of a printing head and a surface of a printing medium in order to obtain high quality printing on the printing medium. This distance is called a print gap. It is, therefore desirable to preset the print gap in accordance with the thickness of the recording medium, such as paper. 
     Currently, print gaps and similar gaps are measured with a plurality of shim or wire gauges (“feeler” gauges). Feeler gauges are thin steel plates of a predetermined thickness. The width of a gap is measured by a feeler gauge by inserting the gauge into the gap and moving the gauge back and forth within the gap. The amount of frictional resistance between the gauge and the opposing surfaces increases as thicker gauges are inserted into the gap. A gauge that is too thin will result in little or no frictional resistance when inserted into the gap. On the other hand, if the gauge is too thick, insertion will be impossible or will be achieved with great difficulty. Thus, it is possible to determine width of the gap by judging the degree of frictional resistance. 
     Judging the correct amount of frictional resistance is subjective and is dependent on the experience of the operator. Often an inexperienced operator may not be able to repeat the same result because he is relying on his judgment regarding the correct degree of frictional resistance. Furthermore, other operators may not be able to reproduce the results even with the same gauge. 
     What is needed, therefore, is an inexpensive device to objectively determine whether a gap has been set to the proper tolerances. 
     SUMMARY OF THE INVENTION 
     The previously mentioned needs are fulfilled with the present invention. Accordingly, there is provided, in a first form, a feeler gauge which provides an objective means of determining the width of a gap. The feeler gauge comprises a gap measuring element which is insertable into the gap and an indicator coupled to the gap measuring element for automatically indicating when said gap has been set to a predetermined distance. The measuring element comprises two plates which act as a switch in an electrical circuit. When the gap gauge is inserted into a gap of predetermined width, the plates press against each other and current from a power source lights up a light emitting diode. Conversely, when the plates are inserted into a gap that is too wide, the plates do not press against each. The circuit, therefore, is not complete, and the light emitting diode does not light up. Thus, this invention provides an objective, reliable means for confirming the width of a gap. The invention can be used for gaps of different widths by varying the thicknesses of the plates. 
     These and other features, and advantages, will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. It is important to note the drawings are not intended to represent the only form of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is an isometric view incorporating one embodiment of the present invention; 
     FIG. 2 is an exploded isometric view of the shim plate unit of one embodiment of the present invention; 
     FIG. 3 is an electrical schematic diagram of the control unit of one embodiment of the present invention; 
     FIG. 4 is an isometric view incorporating another embodiment of the present invention; 
     FIGS. 5A and 5B are cross-section views of the embodiment illustrated in FIG. 2; and 
     FIGS. 6A and 6B are cross-section views of the embodiment illustrated in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The principles of the present invention and their advantages are best understood by referring to the illustrated embodiments depicted in FIGS. 1-4 of the drawings, in which like numbers designate like parts. In the following description, well-known elements are presented without detailed description in order not to obscure the present invention in unnecessary detail. For the most part, details unnecessary to obtain a complete understanding of the present invention have been omitted inasmuch as such details are within the skills of persons of ordinary skill in the relevant art. 
     Turning now to FIG. 1, there is illustrated an isometric view of gap gauge  100 . In this embodiment, gap gauge  100  is a hand held device adaptable for measuring the print gap between a printer head (not shown) and a platen (not shown). Note, however, the present invention is not limited to measuring gaps in printers, but can be used for any other application where a gap needs to be measured. When panel unit  104  is inserted into a print gap, an electrical contact is made sending an electrical current to a suitable indicator, such as a light emitting diode, LED  102 , which provides a visual indication to the user of the magnitude of the gap to be measured. Another, such indicator could be a “beeper” or sound generator chip coupled to a small speaker to provide an audible indication. Such sound generator chips and speakers are commercially available and well known by those who practice the relevant art. 
     The present invention is designed to measure a particular width with a small amount of tolerance. Thus, gaps of different widths will require separate gauges. However, in several industries, such as computer printers, the width of the gap must be preset to a particular distance. The width of the gap is set by a trial and error method. It is set, then measured. If it is not within a particular tolerance, another attempt is made to set the gap. The steps of setting the gap and then checking the gap by measuring its width is repeated until the gap is within a particular tolerance to a predetermined distance. 
     The primary components of gap gauge  100  are panel unit  104  and housing unit  106 . Housing unit  106  acts as a handle for gap gauge  100 . Housing unit  106  comprises of enclosure  108  which is made of plastic or another suitable material. Housing unit  106  may be set at an angle relative to panel unit  104  to clear any structure such as a printer cover. Enclosure  108  encloses most of the electronics of the present invention. As will be discussed in reference to FIG. 3, the basic electrical components housed in enclosure  108  is a battery (FIG.  3 ), LED  102 , on/off switch  110 , and the circuitry connecting the components. 
     In the embodiment illustrated in FIG. 1, panel unit  104  is made from two closely spaced, generally rectangular metal shims (FIG.  2 ). Panel unit  104  is designed to be inserted into the print gap to be checked. If the print gap is the correct width, the shims make contact and complete an electrical circuit (see FIG. 3) which in turn, causes LED  102  to light up. Depending on the embodiment, there may also be a guide installed to help align gap gauge  100  to the print gap to be measured. In this embodiment, which is designed to be used for printers, guide  112  is attached to panel unit  104  to assist in aligning gap gauge  100  into a print gap. Guide  112  is made from plastic or another suitable material. Its dimensions are governed by the dimensions and configuration of the printer head. 
     FIG. 2 is an exploded view of gap gauge  100 . Shim  202  is a substantially flat metal plate with a small rectangular protrusion  204  at one corner. Shim  202  is used as a base for panel unit  104  (FIG.  1 ). When gap gauge  100  is assembled, protrusion  204  is inserted into slot  212  of housing unit  106  (where it makes electrical contact with the electrical circuitry (not shown) housed in housing unit  106 . 
     Shim  216  is a flat metal plate that is substantially the mirror image of shim  202 . Shim  216  can be of variable thickness to correspond to the thickness of the gap the particular gap gauge is designed to be measured. Shim  216  also has a small rectangular protrusion  218 , which when assembled, is inserted into slot  214  of housing unit  106  where it makes electrical contact with the electrical circuitry (not shown). 
     Tape strips  208   a  and  208   b  are strips of double-sided adhesive tape which adhere shim  202  to shim  216 . Tape strips  206   a  and  206   b  are strips of electrical insulating tape which act as spacers and keep shim  202  and shim  216  from making electrical contact when panel unit  104  is not in a print gap. 
     FIG. 3 schematically illustrates a typical electronic arrangement of the present invention. A suitable power supply, such as a replaceable or rechargeable battery  302  supplies power to the electronics of the invention. Battery  302  powers LED  102  when the circuit is closed. On/off switch  110  prevents battery drain by keeping the circuit open when gap gauge  100  is not in use. On/off switch  110  is a typical on/off switch designed to be mounted on a standard electric circuit board. Such on/off switches are common in the marketplace and are well known by those who practice the art. Panel unit  104  is shown in FIG. 3 as another switch because, panel unit  104  operates as a switch. Resistor  301  is provided to limit the current flow and, thus conserve power from battery  302 . 
     When operating this embodiment, the user first turns gap gauge on by means of on/off switch  110 . The user then uses housing unit  106  (FIG. 1) as a handle to insert panel unit  104  (FIG. 1) into the gap to be measured, for instance, the gap between a printhead and a platen. If the gap is the correct thickness, shim  216  (FIG. 2) will be pressed against shim  202  (FIG. 2) and the electric circuit will be complete. 
     Referring back to FIGS. 2 and 3, once shim  216  is pressed against shim  202 , the current from battery  302  flows through LED  102  which illuminates indicating to the user that the gap is set at a predetermined distance. Current then flows through on/off switch  110  (which is switched on) and around to a common electrical connection (not shown) in housing unit  106  which is connected to protrusion  218 . The current flows through shim  216  to shim  202 , then to protrusion  204 . Protrusion  204  connects to another common electrical connection (not shown) which is connected, to resistor  301 , then to the negative terminal of battery  302 , thus completing the circuit. 
     Panel unit  104  acts similar to a spring-loaded electrical switch. Shim  216  is relatively thin compared to shim  202  which is the base. Not only do tape strips  206   a ,  206   b ,  208   a , and  208   b  separate shim  216  from shim  202 , but these strips hold the edges of shim  216  in place. FIG. 5A represents a section view of the embodiment illustrated in FIG. 1 when panel unit  104  is not inserted into a gap. The section was cut at approximately the midpoint of shim  202  and through tape strips  208   a  and  208   b . The thicknesses of the shims and strips of tape have been greatly exaggerated for illustration purposes. When the panel unit is not inserted, shim  216  spans between the strips of tape. It does not, therefore, make contact with shim  202  and the electrical circuit (see FIG. 3) is not complete. 
     FIG. 5B, on the other hand, illustrates how shim  216  deflects when inserted into an appropriate gap between surface  502  and surface  504 . If the gap is at the correct distance, shim  216  will deflect enough so that it makes contact with shim  202 . This contact completes the electrical circuit, thereby causing LED  102  to illuminate. Thereafter, when LED  102  is removed from the gap, shim  216  flexes back to its original shape (illustrated in FIG. 5A) similar to the way a trampoline deflects when there is a load on it and springs back into shape when the load is removed. Once shim  216  has returned to its original shape, the electrical circuit (see FIG. 3) is broken and LED  102  is no longer illuminated. 
     A second embodiment is illustrated in FIG. 4 which is an exploded isometric view of gap gauge  400 . The second embodiment is similar to the first embodiment except that it uses a t-shaped upper shim, rather than a rectangular shaped plate. 
     For brevity and clarity, a description of those parts which are identical or similar to those described in connection with the first embodiment illustrated in FIGS. 1-3 will not be repeated here. Reference should be made to the foregoing paragraphs with the following description to arrive at a complete understanding of this second embodiment. 
     The embodiment shown in FIG. 4 uses an identical housing unit to the first embodiment. The panel unit is different and a mylar film is also used as a cover. In the second embodiment, shim  402  is a substantially flat metal plate with a small rectangular protrusion  404  at one corner. Shim  402  is used as a base for this embodiment. Upper shim  416  is a flat metal plate that is shaped similar to a “t.” Upper arm  419  of shim  416  extends to a length that is substantially the same as the width of base shim  402 . Bottom leg  417  of shim  416  extends from the midpoint of arm  419  to a distance that is substantially the width of base shim  402 . The ends of upper arm  419  and leg  417  thus, are substantially flush with the edges of shim  402  when shim  416  is placed over shim  402 . Additionally, one end of arm  419  has protrusion  418  which when the invention is assembled, is inserted into slot  214  of housing unit  106  where it makes electrical contact with the electrical circuitry (not shown). Shim  416  can be of variable thickness to correspond to the thickness of the gap the particular gap gauge is designed to be measured. 
     Tape strips  408   a  and  408   b  are strips of double-sided adhesive tape which adhere shim  402  to shim  416 . Depending whether guide  112  (FIG. 1) is used, tape strip  406  is a strip of electrical insulating tape or a strip of adhesive tape. In any case tape strip  406  acts as a spacer and keeps shim  402  and top arm  419  from making electrical contact when the panel unit is not in a print gap. Tape strip  410  is also a double-sided adhesive tape designed to adhere the lower end of leg  417  to shim  402 . Mylar film  420  is provided to keep dust out of the space between shim  416  and shim  402 . Such mylar film is commercially available in extremely thin thicknesses. 
     In operation, the panel unit of the second embodiment acts in a similar manner to the panel unit of the first embodiment. Shim  416  is relatively thin compared to shim  402  which is the base. Tape strips  406 ,  408   a ,  408   b , and  410  separate upper shim  416  from base shim  402 . They secure the edges of shim  416  in place. FIG. 6A represents a section view of the second embodiment illustrated in FIG. 4 when the panel unit is not inserted into a gap. The section view was cut approximately at the midpoint of shim  402  and through tape strips  410  and  406 . The thicknesses of the shims and strips of tape have been exaggerated for illustration purposes. When the panel unit is not inserted into a gap, shim  416  spans between the strips of tape. It does not, therefore, make contact with shim  402  and the electrical circuit is not complete. 
     FIG. 6B illustrates how shim  416  deflects when inserted into an appropriate gap between surface  602  and surface  604 . If the gap is at the correct distance, shim  416  will deflect enough to make contact with shim  402 . This contact completes the electrical circuit (FIG.  3 ), thereby causing LED  102  (FIG. 1) to illuminate. Thereafter, when the panel unit is removed from the gap, shim  416  flexes back to its original shape (illustrated in FIG. 6A) breaking the electrical circuit. 
     In sum, the electronic feeler gauge has several substantial advantages over the prior art. Judging the correct amount of frictional resistance is often subjective and is dependent on the experience of the operator. The present invention provides an objective indication when the gap has been adjusted correctly. Thus, the learning curve is greatly reduced and the present invention may be used by more inexperienced technicians. Additionally, more consistent results will be obtained by different operators because of the objectivity introduced by the present invention. 
     Although the invention has been described with reference to specific embodiments, these descriptions are not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore, contemplated that the claims will cover any such modifications or embodiments that fall within the true scope of the invention.