Telegraphy – Systems – Position coordinate determination for writing
Patent
1993-09-15
1995-08-15
Chin, Stephen
Telegraphy
Systems
Position coordinate determination for writing
345166, G08C 2100, G09G 100
Patent
active
054421470
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to position-sensing apparatus and in particular, but not exclusively, to apparatus for sensing the position of an indicator element over a two-dimensional patterned surface by detecting pattern features of the surface.
BACKGROUND ART
It is known to detect linear position by providing a linear pattern that encodes a pseudo-random binary sequence (PRBS, also known as an "m-sequence") and then using the window property of such a sequence to effect position detection by detecting a window-length subsequence of the pattern. An example of such a system is described in the article "New Pseudorandom/Natural Code Conversion Method" by E. M. Petriu appearing in Electronic Letters 27th Oct. 1988 Vol.24 No.22.
By "window property" is meant the property that for a PRBS of length (2.sup.k -1), where k is an integer, any subsequence of length k will be unique and therefore uniquely locatable in the sequence; this and other properties of PRBSs are described, for example, in the article "Pseudo-Random Sequences and Arrays" by F. Jessie MacWilliams and Neil J. A. Sloane appearing in the Proceedings of the IEEE, Vol.64, No.12 December 1976.
The prior-art systems utilising the window-property of a PRBS for position sensing are essentially limited to linear position-sensing, although the path followed by the PRBS pattern may, of course, be other than rectilinear (for example, circular or serpentine).
It is an object of the present invention to provide position-sensing apparatus for sensing position over a two-dimensional surface.
DISCLOSURE OF THE INVENTION
According to one aspect of the present invention, there is provided position-sensing apparatus comprising: two-dimensional pattern having features that make said pattern a windowing pattern in that any local portion of the pattern of given extent in terms of its features (herein a "sub-pattern"), when considered in isolation, is so characterised by said features as to permit the location of the sub-pattern to be determined, for at least one orientation of the sub-pattern relative to said pattern; such that for any one position of the indicator element, the sensing means is operative to sense a portion of said pattern which lies in the locality of said indicator element and is smaller in extent than a said sub-pattern, the detector means being operative to process the output of the sensor means such that as the indicator element is moved over the pattern, the detector means is operative to derive sub-pattern data representative of a whole sub-pattern local to said indicator element in a said at least one orientation of the sub-pattern relative to said pattern; and representative of said windowing pattern, the position determining means being responsive to the sub-pattern data derived by said detector means to determine, by reference to said pattern data, the position of said indicator element relative to said pattern element.
Preferably, in said position-sensing apparatus: which when any given sub-pattern of said pattern is considered in isolation from the pattern, that sub-pattern may be in any of M possible orientations relative to the pattern where M is a positive integer greater than zero; correctly located in the pattern for N of said M possible orientations where N is a positive integer in the range 0<N.ltoreq.M; and arrangement of features to identify a said sub-pattern in the locality of said indicator element, and to provide sub-pattern data to said position-determining means which is representative of the said sub-pattern in one of said N of said M possible orientations relative to the pattern in which it can be correctly located.
Advantageously, said features are discernibly arranged in rows and columns extending parallel to respective first and second coordinate axes with each feature being presented in a notional cell that has line contact with a plurality of neighbouring such cells. A rectangular pattern of cells is preferred for which each said cell has line contact with four neighbouring cells, M has a v
REFERENCES:
patent: 4521773 (1985-06-01), Lyon
patent: 4691199 (1987-09-01), Shell
patent: 4751380 (1988-06-01), Victor et al.
patent: 4880967 (1989-11-01), Kwang-chien
patent: 5051736 (1991-09-01), Bennett et al.
patent: 5086197 (1992-02-01), Liou
Proceedings of the IEEE, "Psudo Random Sequences and Arrays", Dec. 1976, MacWilliams et al, pp. 1715-1730.
Burns John
Lloyd Sheelagh A.
Chin Stephen
Hewlett--Packard Company
Kim Kevin
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