Contact width sensors

Details Contact width sensors Contact width sensors

1999-04-13

2001-05-01

Metjahic, Safet (Department: 2858)

Electricity: measuring and testing

Impedance, admittance or other quantities representative of...

Lumped type parameters

C073S862680

Reexamination Certificate

active

06225814

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to detecting contact between two surfaces, and more particularly to an apparatus for detecting the contact or nip width between such surfaces.
BACKGROUND OF THE INVENTION
There are many applications, such as with pinch rollers and seals, where it is desired that, at some minimum pressure, physical contact be made between two contacting surfaces over a selected width or distance. While in most instances such contact width could be assured by applying greater pressure, in many such applications it is desirable that the pressure applied not be substantially greater than that required to establish good contact over the desired width. There are also applications where information on contact width is required, sometimes with a resolution down to a fraction of a mil. In all such contact width determination applications, it is desirable that such determination be made quickly, with minimum interference with the mechanism having the contacting surfaces, with maximum flexibility, and at low cost.
Existing mechanisms for performing width determination do not meet all of these objectives. One technique used in the prior art is to mount sensors in one of the contacting surfaces of for example a pair of contacting pinch rollers, which sensors can be oriented to provide an indication of both contact width and contact location. However, because of the size of such sensors, it is difficult to achieve resolution of much less than 30 mils using this technique. The sensors are also difficult to mount and to replace and, once mounted, provide limited flexibility, such limited flexibility being achieved generally through external control circuitry and not through the sensors themselves.
Alternatively, matrix pressure sensor arrays, such as those taught in U.S. Pat. Nos. 4,856,993, 5,033,291, 5,505,072 and 5,756,904 may be utilized for performing this function, such a disposable matrix array being placed between the contacting surfaces for which width is to be measured, and a width determination being made by detecting the boundary rows of high pressure regions. However, since approximately 10 mils spacing between adjacent lines is currently the practical limit for printing conductive patterns and conductive ink patterns involving the technology of these patents, and since this resolution limit applies on both sides of a contact area, and there may be more than one contact area for a given measurement, the actual width resolution provided using this technique is typically at least 25 mils. This technique also involves a relatively expensive sensor array and scanning circuitry for determining contact points which then must be processed in a computer to determine contact width. This results in a relatively expensive array and a relatively time-consuming scanning process which, while advantageous in some applications in that it also provides a full pressure profile for the contacting surfaces, may be more expensive than is required for many applications.
A need therefore exists for improved techniques for performing contact width measurements and determination, which techniques provide higher resolution than is achievable using any existing technique and/or which are faster, more flexible, and/or less expensive than existing techniques.
SUMMARY OF THE INVENTION
In accordance with the above, this invention provides apparatus for measuring contact width between two contacting surfaces. The apparatus includes first and second insulating substrates having spaced facing inner surfaces and outer surfaces, the substrates being adapted to be fitted between contacting surfaces to measure contact width. A pattern of conductive material is formed on each of the facing inner surfaces, the patterns being spaced from each other and selectively overlapping.
For a first embodiment of the invention, the pattern of conductive material on the inner surface of one substrate includes a pair of conductive terminals spaced by a distance L, where L is greater than a contact width W to be measured, and the conductive pattern on the inner surface for the other substrate includes a conductor which extends over at least a distance greater than the maximum width W to be measured. A resistance path is provided between the conductive terminals, which path has a resistance R
0
, R
0
being higher than the resistance of the conductor. Material is also provided in the space between the conductor and the resistance path which material has a high resistance, substantially preventing current flow therethrough between the conductor and the resistance path in areas where the conducting surfaces is not in contact and which has a lower resistance less than R
0
between the conductor and resistance path in areas where the conducting surfaces are in contact. Finally, circuitry is provided for applying current to one of the terminals and for utilizing a difference in current flow between the terminals to determine contact width between the contacting surfaces. For preferred embodiments, the resistance path includes a first layer in contact with the spaced terminals and having the substantially fixed resistance R
0
. The material layer may for example be an air gap or may be a layer of pressure sensitive material having the high resistance in the absence of pressure and the low resistance when at least a selected minimum pressure is applied thereto.
For this embodiment, the circuitry may include circuitry for applying a constant current across the conductive terminals and for measuring the voltage across the terminals when there is contact between the contacting surfaces, such voltage being indicative of contact width. Alternatively, the circuitry may include a bridge circuit having fixed resistors in two legs, resistances proportional to the resistance between the terminals in two other legs, a constant current applied across two terminals of the bridge and a voltage output across two other terminals of the bridge, the voltage output being proportional to the contact width to be measured.
Finally, this embodiment of the invention may also include a mechanism for measuring pressure between the contacting surfaces which mechanism may include at least one additional layer adjacent an outside surface of a substrate or additional circuitry on the substrates, with pressure-sensitive material positioned between such additional circuitry, either of such mechanisms providing a pressure indication.
For an alternative embodiment of the invention, the pattern of conductive material on the inner surface of one substrate includes N substantially parallel and evenly spaced conductive columns, and the pattern on the inner surface of the other substrate is a plurality of substantially parallel and evenly spaced rows. The columns are divided into M groups, where M is an integer which is at least 2, and each of the rows is at an angle &thgr; to a line perpendicular to the columns when extending across alternate ones of the groups and at an angle −&thgr; when extending across the remaining groups. The number of columns in each group is selected to achieve a desired resolution for the apparatus, and &thgr; is selected so that the distance in the direction of the columns between the ends of a row for each group is substantially equal to the spacing between adjacent rows. For a preferred embodiment, M=4 and there are 10 columns in each of the groups, resulting in resolution being improved by a factor of 10 over what resolution would be if the rows were not angled.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawings.


REFERENCES:
patent: 5060527 (1991-10-01), Burgess

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