Method, sensing device and optical pointing device including...

Details Method, sensing device and optical pointing device including... Method, sensing device and optical pointing device including...

2001-12-05

2004-10-19

Luu, Thanh X. (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

Reexamination Certificate

active

06806458

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to pointing devices, in particular for controlling the position of a cursor on a screen, such as the display of a personal computer, workstation or other computing devices having a graphic user interface. Such pointing devices may for instance include mice, trackballs and other computer peripherals for controlling the position of a cursor on a display screen.
The present invention more particularly relates to the field of optical pointing devices which comprise an optical sensing device including a photodetector array for measuring the varying intensity pattern of a portion of a surface which is illuminated with radiation and for extracting information about the relative motion between the photodetector array and the illuminated portion of the surface.
BACKGROUND OF THE INVENTION
Optical pointing devices are already known in the art. U.S. Pat. No. 5,288,993, which is incorporated herein by reference, for instance discloses a cursor pointing device utilizing a photodetector array and an illuminated target ball having randomly distributed speckles. U.S. Pat. No. 5,703,356 (related to the above-mentioned U.S. Pat. No. 5,288,993), which is also incorporated herein by reference, further discloses (in reference to FIGS. 23A and 23B of this document) an optical cursor pointing device in the form of a mouse which does not require a ball and wherein light is reflected directly from the surface over which the pointing device is moved.
The imaging technique used in above-cited U.S. Pat. Nos. 5,288,993 and 5,703,356 in order to extract motion-related information is based on a so-called “Edge Motion Detection” technique. This “Edge Motion Detection” technique essentially consists in a determination of the movement of edges (i.e. a difference between the intensity of pairs of pixels) in the image detected by the photodetector array. Edges are defined as spatial intensity differences between two pixels of the photodetector array. The relative motion of each of these edges is tracked and measured so as to determine an overall displacement measurement which is representative of the relative movement between the photodetector array and the illuminated portion of the surface.
More particularly, according to U.S. Pat. No. 5,288,993, edges are determined between pairs of pixels aligned along a first axis of the photodetector array (for example in each row of the photodetector array) and between pairs of pixels aligned along a second axis of the photodetector array (for example in each column of the photodetector array).
FIG. 10
depicts three pixels of the photodetector array, a first pixel or current pixel P, a second pixel Pright aligned with the first pixel P along a first axis
101
, and a third pixel Pup aligned with the first pixel P along a second axis
102
. Pixels Pright and Pup are show as being disposed on the right side and top side of pixel P for the purpose of explanation only. It will be appreciated that axes
101
and
102
may be orthogonal (as shown) or alternatively non orthogonal. It will also be appreciated that the pixel are not necessarily disposed so as to form a regular array having rows and columns. Other suitable arrangements may very well be envisaged.
For the purpose of simplification, the pixels of
FIG. 10
are either shown as being white or black, a black pixel denoting an illuminated pixel. In this case, pixel P is illuminated and first and second edge conditions Ex, Ey exist respectively between pixels P and Pright along the first axis
101
and between pixels P and Pup along the second axis
102
.
According to U.S. Pat. No. 5,288,993 and U.S. Pat. No. 5,703,356, the displacement measurement is evaluated, on the one hand, based on a normalized difference between the number of edges Ex which move in a first direction along the first axis
101
and edges Ex which move in the opposite direction along the first axis
101
(for example edges which from left to right and right to left in each row of the photodetector array), and, on the other hand, based on a normalized difference between the number of edges Ey which move in a first direction along the second axis
102
and edges Ey which move in the opposite direction along the second axis
102
(for example edges which move downwards and upwards in each column of the photodetector array).
Relative motion of edges is determined by comparing the position of these edges in the photodetector array at a first point in time with the position of edges in the photodetector array at a subsequent point in time. The optical pointing device thus typically comprises a light source (such as an infrared LED) which intermittently illuminates the portion of the surface in accordance with a determined sequence, and the pixel outputs of the photodetector array are sampled in accordance with the determined sequence to provide two successive sets of edge data that are compared to each other in order to determine a relative motion measurement.
According to one embodiment of U.S. Pat. No. 5,288,993 and U.S. Pat. No. 5,703,356 a differential technique is advantageously used in order to determine an edge condition between two pixels. According to this embodiment, an edge is defined as laying between two pixels if the ratio of intensities of the two photosensitive elements is larger than a determined level. An edge may thus be defined mathematically by the following Boolean expression:
Intensity[PIXEL 1]>K Intensity[PIXEL 2]
OR
K Intensity[PIXEL 1]<Intensity[PIXEL 2]  (1)
where K is the selected scaling factor.
It will be appreciated that the first and second parts of the above expression, taken individually, each define an edge condition between the two pixels.
According to U.S. Pat. No. 5,703,356, the differences of intensities or edges between pixels is sensed as a difference in currents. More particularly, FIG. 17A of this document shows a differential current sensor for detecting an edge condition between two pixels.
FIG. 1
of the present specification illustrates this differential current sensor. In this example, the current iout generated by the photosensitive element
1000
of the pixel is applied (after charge amplification by means of the charge amplifier
1705
) on a input branch
1710
A-B of a current mirror comprising eight output branches
1710
,
1715
,
1720
,
1725
,
1730
,
1735
,
1740
and
1745
, four of which (output branches
1710
,
1715
,
1730
and
1735
) output a non-scaled image of the input current iout. The other four output branches
1720
,
1725
,
1740
,
1745
output a scaled image of the input current iout (K times the input current iout), the scaling factor K being defined by an adequate choice of the dimensions of the corresponding transistors of the current mirror. Two output branches
1715
,
1720
supply the image io1I and the scaled image ioKI of the input current iout to the pixel on the left. Similarly two output branches
1735
,
1740
supply the image io1d and the scaled image ioKd of the input current iout to the pixel below.
The differential current sensor further comprises two pairs of comparator circuits
1750
A-
1750
B and
1750
C-
1750
D, one pair
1750
A-
1750
B for determining the edge condition, denoted Ex, between two pixels in the same row (in this case between the current pixel and the pixel on its right), the other pair
1750
C-
1750
D for determining the edge condition, denoted Ey, between two pixels in the same column (in this case between the current pixel and the pixel on top). Each comparator circuit has one input connected to a non-scaled output
1710
,
1730
or scaled output
1725
,
1745
of the current mirror and a second input connected to a non-scaled output (supplying current ii1r, ii1u) or scaled output (supplying current iiKr, iiKu) of the current mirror of the pixel on the right or of the pixel on top. In this example, the outputs of each pair of comparator circuits are additionally combined by means of a logic NAND gates
1765
,
1775
to provide

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