Method of determining the pen velocity along a graphic...

Computer graphics processing and selective visual display system – Display peripheral interface input device – Touch panel

Reexamination Certificate

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Details

C345S179000

Reexamination Certificate

active

06271836

ABSTRACT:

The invention relates to a method of determining a velocity of a pen in a direction along a graphic tablet, provided with a regular pattern of conductors, by measurement of an electromagnetic signal caused in the pen by a series, being a succession of elements, each element consisting of successive electric pulses generated in respective conductors and each element of the series causing in the pen a pen signal which is a combination of responses to the pulses of this element.
The invention further relates to a graphic tablet provided with a pen, a regular pattern of conductors and a first drive unit for generating a first series, being a succession of elements, each element consisting of successive electric pulses in respective conductors, each element of the first series causing in the pen a respective pen signal which is a combination of responses to the pulses of this element
Graphic tablets are widely used as data input devices. By positioning a pointing means (referred to hereinafter as pen) at or near a specific area on the tablet, the user can trigger a given action in a manner which is experienced as being natural. Generally speaking, a graphic tablet is integrated with an LCD display screen. A first possible use of such a combination is to reproduce symbols on the display screen which represent user options which the user can select by means of the graphic tablet by positioning the pen in the vicinity of such a symbol. A second possible use is the input of text, for example for a word processing application where text is input by writing the text on the tablet by means of the pen. Accurate determination of the position of the pen along the tablet is important for both possible uses.
According to U.S. Pat. No. 5,229,551, not only the position but also the velocity of the pen is determined. This is because the velocity information can be used to achieve more accurate determination of the position. Because the pen positions are determined successively in two directions, a kind of hysteresis effect occurs. Compensation for this effect can be achieved by utilizing a correction algorithm having the pen velocity as one of its parameters.
It follows from the cited Patent that the pen position is determined in first instance by generating a succession of pulses in respective conductors, arranged in a matrix pattern, the pen position being derived from a pen signal arising as a consequence of these pulses. The pen velocity in a direction along the tablet is subsequently derived from a number of successive pen positions thus determined. Finally, this velocity information is used to compensate for said hysteresis effect. It is a drawback of this indirect method of determining the velocity that the measurements are not efficiently used.
It is inter alia an object of the invention to provide a method of the kind set forth which utilizes the information contained in the pen signal more efficiently. To this end, a method according to the invention is characterized in that the pen velocity in said direction is derived from the shape of the pen signal to both sides of a local maximum in the pen signal. It has been found experimentally that the shape of the pen signal is velocity-dependent.
A graphic tablet according to the invention is characterized in that the graphic tablet is provided with a detection unit for deriving a pen velocity in a first direction along the tablet from the shape of the pen signal to both sides of a local maximum in the pen signal.
An advantage of the invention, demonstrated in the preferred embodiment of the invention, consists in that the samples generated for the determination of one position in one direction suffice to determine the velocity in the same direction. Therefore, the determination of the velocity in that direction does not require a second position determination. Moreover, the information in the pen signal is utilized better and the trajectory of the pen along the tablet can be accurately determined, while using fewer measured pen positions, by utilizing interpolation on the basis of the velocity information also obtained. The velocity information can also be used to activate adaptive filtering of the pen signal, before extraction of the pen position, in order to suppress noise. This application of the velocity information is disclosed in U.S. Pat. No. 5,053,757. Information concerning the pen velocity may also be useful for aspects other than accurate position determination, for example for the recognition of handwriting.
Further attractive aspects of the invention are disclosed in the dependent claims. Relevant prior art is given in U.S. Pat. No. 5,231,381 (PHN 13.100) and U.S. Pat. No. 5,402,151 (PHN 13.100) and European Patent Applications EP-A 0 756 733 and EP-A 0 756 723, corresponding to U.S. patent applications Ser. No. 08/602,547 (PHN 15.210) and Ser. No. 08/603,958 (PHN 15.209) in the name of Applicant.


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