Computer graphics processing and selective visual display system – Display peripheral interface input device – Touch panel
Reexamination Certificate
1999-08-12
2001-09-11
Jankus, Almis R. (Department: 2675)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Touch panel
C345S174000, C345S177000, C345S179000, C178S018010, C178S018030, C178S018070
Reexamination Certificate
active
06288710
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a digitizing tablet, more particularly to a method and apparatus for detecting the position of a coordinate probe relative to a digitizing tablet.
2. Description of the Related Art
Generally, a digitizing tablet is used with a coordinate probe that radiates an electromagnetic coordinate signal. The coordinate signal is received by a sensing coil grid that is provided on a working region of the digitizing tablet. When the coordinate probe is located between two sensing coils of the grid, the electric currents induced in these sensing coils have a 180° phase difference therebetween, as shown in
FIG. 1. A
series of processing circuits, such as signal amplifiers, filters, signal conditioners, counters and processors, are employed to process the electric currents induced in the sensing coils of the grid so as to generate a corresponding coordinate data output.
It is noted that the circuitry needed to process the current signals captured in the conventional digitizing tablet is relatively complicated, thereby resulting in relatively high operating power consumption and relatively high manufacturing costs. Particularly, the conventional digitizing tablet incorporates a multiplexer array associated with the sensing coil grid for connecting the latter to the processing circuitry. The multiplexer array includes a plurality of switches, and each switch is connected to one of the sensing coils. Since the number of switches is equal to the number of sensing coils in the grid, the conventional digitizing tablet is relatively costly to implement.
Further, there are two types of coordinate probes, wired and wireless, available for use with a digitizing tablet. Wired coordinate probes require a cable connection with the digitizing tablet for receiving an excitation signal therefrom. Once excited, the wired coordinate probes radiate the coordinate signal that is received by the sensing coil grid on the working region of the digitizing tablet. On the other hand, wireless coordinate probes do not require a cable connection with the digitizing tablet, and are capable of being activated to radiate the coordinate signal that is received by the sensing coil grid on the working region of the digitizing tablet. The sensing coils of the grid are scanned sequentially with the use of the multiplexer array to determine the position of the coordinate probe relative to the digitizing tablet.
However, regardless of the type of coordinate probe that is in use, erroneous operation of the digitizing tablet, which can inconvenience the user, easily occurs due to phantom images arising from noise or detection of electric current induced in the sensing coils albeit the coordinate probe is not disposed on the working region of the digitizing tablet.
SUMMARY OF THE INVENTION
Therefore, the main object of the present invention is to provide a method and apparatus for detecting the position of a coordinate probe relative to a digitizing tablet, where a phase selection circuit is employed to permit a reduction in the number of the sensing coils, as well as the switches of the multiplexer array, in order to simplify the circuitry of the digitizing tablet and reduce the manufacturing costs.
Another object of the present invention is to provide a method and apparatus for detecting the position of a coordinate probe relative to a digitizing tablet, where electric current induced in the sensing coils are verified to minimize erroneous operation of the digitizing tablet.
According to one aspect of the invention, there is provided a method for detecting the position of a coordinate probe, which radiates an electromagnetic coordinate signal, relative to a digitizing tablet. The method comprises:
(a) providing a sensing coil grid on a working region of the digitizing tablet, the sensing coil grid including a plurality of sensing coils, each of which is U-shaped and has a front section and a grounded rear section, the sensing coils being arranged in parallel along an axis of the working region in an overlapping manner with the front sections of consecutive ones of the sensing coils being arranged in succession, and with the ear sections of the consecutive ones of the sensing coils also being arranged in succession, wherein electric currents are induced in the sensing coils by virtue of the coordinate signal when the coordinate probe is disposed on the working region;
(b) performing a front scanning operation, including
scanning in sequence the sensing coils in order to detect the electric currents induced therein and to generate a grid signal,
generating an inverted signal by inverting a predetermined one of front and rear half-cycles of the grid signal, and
detecting a predetermined transition of the inverted signal from a first logic state to a second logic state;
(c) performing a rear scanning operation when the predetermined transition of the inverted signal is not detected after the front scanning operation has been completed, including
repeating sequential scanning of the sensing coils in order to continue generation of the grid signal,
generating the inverted signal by inverting the other one of the front and rear half-cycles of the grid signal, and
detecting the predetermined transition of the inverted signal from the first logic state to the second logic state;
(d) generating a count output corresponding to time elapsed before the predetermined transition of the inverted signal is detected; and
(e) converting the count output into a coordinate of the coordinate probe along the axis of the working region of the digitizing tablet.
According to another aspect of the invention, there is provided an apparatus for detecting the position of a coordinate probe, which radiates an electromagnetic coordinate signal, relative to a digitizing tablet. The apparatus comprises:
a sensing coil grid adapted to be provided on a working region of the digitizing tablet, the sensing coil grid including a plurality of sensing coils, each of which is U-shaped and has a front section and a grounded rear section, the sensing coils being arranged in parallel along an axis of the working region in an overlapping manner with the front sections of consecutive ones of the sensing coils being arranged in succession, and with the rear sections of the consecutive ones of the sensing coils also being arranged in succession, wherein electric currents are induced in the sensing coils by virtue of the coordinate signal when the coordinate probe is disposed on the working region;
a multiplexer array circuit connected to the front sections of the sensing coils;
a phase selection circuit connected to the multiplexer array circuit;
a signal processing circuit connected to the phase selection circuit; and
processor means connected to the multiplexer array circuit, the phase selection circuit and the signal processing circuit.
The processor means is operable to perform a front scanning operation, where the processor means controls the multiplexer array circuit to connect the sensing coils in sequence to the phase selection circuit such that the sensing coils are scanned sequentially in order to detect the electric currents induced therein and in order to generate a grid signal that is received by the phase selection circuit, where the processor means controls the phase selection circuit to generate an inverted signal by inverting a predetermined one of front and rear half-cycles of the grid signal, and where the signal processing circuit detects a predetermined transition of the inverted signal from a first logic state to a second logic state.
The processor means is further operable so as to perform a rear scanning operation when the predetermined transition of the inverted signal is not detected by the signal processing circuit after the front scanning operation has been completed, where the processor means controls the multiplexer array circuit to repeat sequential scanning of the sensing coils in order to continue generation of the grid signal, where the processor means controls t
Lee Wen-Chin
Lin Shun-Pin
Awad Amr
Christensen O'Connor Johnson & Kindness PLLC
Jankus Almis R.
UC-Logic Technology Corp.
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