Computer graphics processing and selective visual display system – Display peripheral interface input device – Cursor mark position control device
Patent
1995-07-05
1998-08-11
Lao, Lun-Yi
Computer graphics processing and selective visual display system
Display peripheral interface input device
Cursor mark position control device
345167, 345179, 250221, G09G 508
Patent
active
057933570
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a device for and method of determining movement of a surface. The device and method can be applied to a wide range of practical devices such as high resolution pointing devices for computers ("pens", and mouse or tracker ball input devices), seismic detectors, digital microphones, precision instruments or machine tools, and computer output devices such as electrostatic plotters.
BACKGROUND TO THE INVENTION
There is a need for an accurate pointing device for use with smaller personal computers, especially the notebook sized computers which are now becoming increasingly popular, and even smaller "tablet" computers, for which conventional keyboards cannot readily be used. Conventional pointing devices are not readily usable with such computers, because of their size, and "pen" pointing devices have been developed to meet this need. However, these typically have resolutions of the order of 100 dpi (dots per inch) equivalent to 250 .mu.m, which is far too low for precise applications such as online, hand-written character recognition. Such applications become ever more desirable as size and other considerations lead away from the use of conventional keyboards as the means of inputting data.
The conventional pointing devices used with desk-top computers, for example the mouse and the tracker ball, typically rely on sensing mechanically the movement of the ball. Resolutions are still relatively low, being of the order of 400 dpi, and the devices are subject to problems of reliability.
When light impinges on a rough surface (in this context almost all surface are "rough"), for example paper, local interference of the reflected light via multiple path lengths gives rise to a pattern. This pattern depends upon the relative positions of the light source, the detector and the surface. The effect can be greatly enhanced by the use of an intense beam such as is available from a laser and is commonly known as laser speckle. As the surface moves with respect to the source, the speckle pattern moves in a way that is directly related to the relative motion. It has been found that by detecting the movement of this pattern, the movement relative to the surface can be detected with greatly enhanced resolution.
It has previously been proposed to use laser speckle in velocity measurement. For example, EP-A-0 295 720 discloses a device for measuring the speed of a manufacturing line which has a spaced pair of detectors detecting the passage of intensity peaks in laser light scattered back from the moving surface of the line. Length of an object on the line can also be measured by the device. Dobrido et al (Opt. Spectrosc. (USSR) 65(1), July 1988, 125-6) disclose a speckle correlator for studying rough surface displacements using photographically recorded speckle images. Neither of these proposals permits real-time movement detection in two dimensions.
Attempts have been made to use speckle patterns in the construction of a pad-less optical mouse, for example in U.S. Pat. No. 4,794,384 (Xerox Corporation).
This technology uses "bit wise auto correlation" to compare a given bit value for each of the 256 cells in a 16.times.16 sensor array with the bit value of neighbouring cells surrounding the given cell to determine how many such comparisons are the same and then a count is made of the number of such comparisons for different groups of identical cell pair comparisons.
The Xerox system is, therefore, based upon a preponderance of "votes" determining a direction movement. The system utilizes the concept of comparing values of samples neighbouring a previous sample with each array cell value in a new sample to determine if they are the same. If any of the 8 comparisons provide an indication of being the same, whether a dark feature or a light feature, then there is a possibility that the pattern feature being detected has "moved" to a new cell position. An identical cell pair value counts as one point and the appropriate counter representing that pair comparison is incremented. It
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patent: 4794384 (1988-12-01), Jackson
patent: 4847484 (1989-07-01), Kikuchi
patent: 4920260 (1990-04-01), Victor et al.
Houghton Andrew David
Ivey Peter Anthony
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