A digitizer tablet providing hysteresis compensation in which the X and Y coordinates of a pointing device are measured at different times. In order to enable the tablet to report X and Y coordinates that when displayed will more accurately reflect the pointing device movements, a correction algorithm, built, for example, into the controlling software, estimates and reports what the first measured coordinate would have been, measured when the second coordinate is measured, based upon the calculated velocity and acceleration of the pointing device. A similar technique can be used to correct the reported value of the second coordinate. In a preferred embodiment, constant coefficients of a linear equation having as variables three consecutive coordinate values or three consecutive preprocessed coordinate values are predetermined and used in the correction algorithm. The preferred embodiment integrates the velocity and acceleration hysteresis compensation into a three point recursive noise filter.
Methods and apparatus for setting the signal-sampling period of each grid wire in a digitizing tablet having grid wires that are sequentially and repetitively scanned to develop a positional signal related to a cursor so as to reduce jitter associated with non-movement of the cursor and signal error associated with rapid movement of the cursor. The method comprises setting the signal-sampling period of each grid wire to a longest signal-sampling period the digitizer tablet is designed to employ if the cursor is not moving and setting the signal-sampling period of each grid wire to a value inversely related to the present speed of movement of the cursor such that the faster the present speed of movement of the cursor the shorter the signal-sampling period of each grid wire as compared to the longest signal-sampling period the digitizer tablet is designed to employ. The present position of the cursor is then saved as the prior position of the cursor for the next time the steps of the method are performed. The method can also be applied to other positional determination devices in which a cursor is moved over a scanned sensing surface. The apparatus performs the method.
A method for driving a touch panel that detects and compensates a double touch includes sequentially inputting coordinate values of touched points on the touch panel at predetermined time intervals, measuring a variation of the inputted coordinate values, determining the inputted coordinate values as a double touch when the measured variation is greater than a predetermined value, and compensating the inputted coordinate values if determined as a double touch.
Methods and apparatus are shown for correcting velocity-induced offset errors in a digitizing system when the cursor is moved diagonally across a sensing grid. Primarily, this is a system for reducing the offset error in the actual and depicted cursor position when a pen cursor is moved rapidly over a digitizing screen of a pen-driven computer. It also provides double the number of positional outputs for added accuracy. A triplet of data is formed by taking two samples from one axis and one from the second axis. The two samples are averaged to form one component of the cursor position and then the average along with the single sample from the other axis are output as the positional coordinates. A second sample is then taken from the second axis to form a new data triplet. The averaging process is repeated with the two data points from the second axis and the average along with the second sample from the first axis are output as a next position of the cursor. The process of inputting a next data point from the axis other than the last sampled to form sequential data triplets is repeated to track the movement of the cursor and output its position.
A method for reducing errors in electrographic digitizer systems where the horizontal and vertical coordinates are quantized at various time intervals. The method minimizes the time skew generated during quantizations and doubles the quantized coordinate pair output rate by utilizing a time-weighted linear interpolation.
The invention relates to the determination of the velocity of a conductive pen 102 along a graphic tablet 100. Generation of successive pulses in successive conductors, arranged in a regular pattern in the tablet, produces an electromagnetic signal in a conductive pen situated in the vicinity of the tablet. When the pen is near the writing surface of the tablet, the pen signal exhibits a local maximum which is indicative of the location of the pen. The distance between the edges to both sides of this local maximum constitutes an indication of the velocity of the pen.
