US 5,442,147 AGranted

Position-sensing apparatus

AssigneeHewlett-Packard Company

InventorsJohn Burns, Sheelagh A. Lloyd

Life of this patent

Estimating the term…

Loading patent…

Abstract

Position-sensing apparatus is provided which includes a passive coded surface formed by a pattern element with an arrangement of indicia that together form a two-dimensional windowing pattern; by "windowing pattern" is meant a pattern having the property that any local portion of the pattern of given size in terms of pattern features (a "sub-pattern"), when considered in isolation, is so characterized by its 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. The apparatus further includes an indicator element movable across the pattern, and a sub-pattern detector with a sensor for sensing the pattern indicia in the locality of the indicator element. The detector is operative to process the output of the sensor to derive sub-pattern data representative of a sub-pattern local to the indicator element in an orientation enabling its position to be uniquely determined. The sub-pattern data is passed to a position-determining unit which uses this data, together with data on the overall pattern, to determine the position of the indicator element relative to the pattern element.

Claims57

Dependent claims

Position sensing apparatus comprising:

a pattern element with an arrangement of indicia that together present a two-dimensional windowing pattern, said two-dimensional windowing pattern having windowing property characteristics such any portion of said two-dimensional windowing pattern of predetermined minimum extent forms a corresponding unique sub-pattern is that is locatable within said two-dimensional windowing pattern for at least one orientation of said unique sub-pattern relative to said two-dimensional windowing pattern;
an indicator element moveable relative to said pattern element across said arrangement of indicia;
sub-pattern detector means including sensor means for sensing said indicia, such that for any one position of the indicator element the sensing means is operative to sense a portion of said two-dimensional windowing pattern which lies in the locality of said indicator element and is smaller in extent than said unique 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 two-dimensional windowing pattern, the sub-pattern detector means derives sub-pattern data representative of a said unique sub-pattern in proximity to said indicator element in a said at least one orientation of the unique sub-pattern relative to said two-dimensional windowing pattern;
and
position-determining means including a memory for holding pattern data representative of said two-dimensional windowing pattern, the position-determining means being responsive to the sub-pattern data derived by said sub-pattern detector means to determine, by reference to said pattern data, a position of said indicator element relative to said pattern element.

2 more elements

A method of determining the location of an indicator along a predetermined sequence of pattern features relative to which the indicator is movable, said method involving determining an initial location for said indicator along said sequence and thereafter incrementally updating the determined location by:

A. sensing a portion of said sequence of pattern features in the locality of said indicator and monitoring the sensed sequence portion to detect an incremental change therein,
B. upon detecting an incremental change in said sensed portion, comparing the sensed sequence portion with that predicted as present in said locality, this prediction using a stored representation of said predetermined sequence and being effected on the basis of an incremental change having occurred in the currently determined location in an assumed direction of movement, and
C. acting on the result of said comparison as follows:
(i) where said comparison produces a match between the sensed and predicted sequence portions, updating the determined location of the indicator by an incremental change in said assumed direction of movement,
(ii) where said comparison produces a mismatch between the sensed and predicted sequence portions, carrying out a recovery process to recover the location of the indicator along said sequence, said recovery process involving deriving at least one candidate location for the indicator on the basis that the direction of movement of the indicator has been reversed, and directly or indirectly comparing the sequence portions sensed along the track of the indicator with those predicted to lie along the indicator's track in reaching the or each said candidate location whereby to test the validity of the or each such location.

2 more elements

Dependencies are inferred from the claim text.