Calcomp Inc.

Sanders Associates Limited

James S Watson

Dana Doubrava

Waldo L Landmeier

Andrew Mitchell Harris

Lynn H Rockwell

Jason J Hoendervoogt

Kenneth B Jacobson

Steven M Palay

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.

Digitizer cursor velocity offset error correction system

A device for indicating the phase of the a full-frequency alternating current (AC) magnetic field signal transmitting from the pointing device of a cordless digitizer and for determining if the phase of a half-frequency alternating current (AC) magnetic field signal transmitting from the pointing device is approximately the same or approximately inverted from an immediately preceding half-frequency signal from the pointing device. The indication of the phase of the full-frequency pointing device signal is used by the digitizer logic circuits to determine the location of the pointing device on the tablet's sensing surface. The information concerning the change in phase of the half-frequency signal is used by the digitizer logic circuits to decode the status of various pointing device buttons. If the phase in the induced half-frequency signal is unchanged from the last, this no-change condition represents one binary state. If the phase has changed, the condition represents the other binary state. Accordingly, a binary encoded message may be transferred from the pointing device to the digitizer tablet for decoding via this phase change method.

Cordless transducer phase reference and data communication apparatus and

A device for imparting a signal phase status of an alternating current (AC) magnetic field signal transmitting from a cursor in a cordless digitizer. The device includes an apparatus for causing the cursor to temporarily emit a signal having a frequency which is lower than the frequency of a basic cursor signal, and an apparatus for determining and imparting the signal phase status of the AC magnetic field signal transmitting from the cursor as derived from the temporarily emitted lower frequency signal.

Half normal frequency regime phase encoding in cordless digitizers

In a pen cursor for use in performing writing motions on the surface of a tablet, this is a sensor for mounting in a tip portion of the pen cursor to develop a signal output indicating longitudinal force on a writing tip of the pen cursor. A tip member extends from the tip portion of the pen cursor and is mounted for longitudinal movement. It has a plunger portion extending therefrom within the pen cursor. A resistive member and a conductive member are disposed within the pen cursor behind the plunger portion. The plunger portion forces the resistive member and the conductive member together in electrical contact over a contacting area which is directly proportional to the amount of longitudinal pressure on the plunger portion. A voltage is connected across the contacting area whereby resistance as a function of longitudinal pressure on the plunger portion can be measured.

Pressure sensing apparatus for digitizer pen tip

In a cordless, electro-magnetic digitizing system having a drive circuit outputting a square wave drive signal of known initial polarity to a transducer coil in a cursor to oscillate the transducer coil and cause a magnetic field output therefrom which is detected in an associated tablet, a method of operation and associated apparatus for determining the phase of a response signal induced by the magnetic field from the response signal itself. The method comprises the steps of, outputting bursts of a square wave drive signal of known initial polarity to the transducer coil; outputting a signal indicating the start of each burst to the transducer coil; additively outputting a single large current square wave signal pulse to the transducer coil of the same polarity and in phase with a first square wave pulse of the square wave drive signal when initially outputting a burst of the square wave drive signal to the transducer coil whereby additive initial drive currents cause the transducer coil to oscillate immediately and produce a detectable first half-wave in a response signal in the tablet; and, employing the first half-wave of the response signal of known polarity to determine the phase.

Phase reference system for cordless looping digitizer

A hand-operated optical scanning system which can be used to scan a large document in multiple passes. There is a digitizing tablet containing position-sensing circuitry for outputting a signal indicating the position of a sensing coil in an x-y coordinate system associated with a working surface of the digitizing tablet as well as a buffer memory for receiving pixelized data associated with optical scanning of a document. A hand scanner for scanning the document comprises, a case having a longitudinal axis, guide rollers for allowing movement of the case only substantially along the longitudinal axis, a read bar centered on the longitudinal axis and perpendicular thereto for optically scanning a one-dimensional line of pixels and for outputting a signal reflecting an instantaneous scanned image, and a sensing coil carried by the case centered on the longitudinal axis at a pre-established distance from the read bar for being positionally sensed by the position-sensing circuitry of the digitizing tablet. There is also logic for continuously determining the position and orientation of the read bar, inputting the signal from the read bar, and storing pixelized information into locations of the buffer memory associated with respective locations of the document in the x-y coordinate system.

Single coil digitizer-coupled image scanner

In an electro-magnetic, cordless digitizer system wherein a transducer emits an AC magnetic field which is detected by a first grid of scanned parallel first wires in a tablet to provide positional data for the transducer in a first axis of a coordinate system and which are detected by a second grid of scanned second wires in the tablet to provide positional data for the transducer in a second perpendicular axis of the coordinate system, a method and associated apparatus for obtaining a phase reference signal; to be used in a demodulator demodulating data signals from the first and second grids of scanned first and second wires. The method comprises the steps of, scanning the first wires to determine ones of the first wires close to a present location of the transducer; connecting to a one of the first wires displaced from the ones of the first wires close to a present location of the transducer a sufficient distance to provide a valid and usable voltage for use in generating a phase reference signal; and, using a voltage from the one of the first wires to generate a phase reference signal to the demodulator when processing data signals from both the first grid of scanned parallel wires and the second grid of scanned wires.

Cordless digitizer local conductor phase reference system

A battery powered oscillator in a freely movable pointer drives a coil and a divider. A grid of spaced conductors in a base unit is inductively coupled to the coil. A conductive plate that lies parallel to the conductor grid capacitively couples the signal from the divider to a phase locked loop to provide a reference signal that has a constant phase in relation to the oscillator. Detection circuitry uses the signals induced in selected grid conductors and the phase reference signal to determine the location of the pointer relative to the conductors. As an alternative to the phase locked loop, the signal induced in an idle reference conductor can be combined with the capacitively coupled reference signal to aid in demodulating the induced signals. As an alternative to an oscillator in the pointer, the coil may be driven by a signal capacitively coupled from the base unit.

Digitizer with capacitive and inductive coupling

In a digitizer tablet system employing a tablet having equally spaced parallel grid wires disposed in a plane along an axis parallel to the tablet's upper surface and a pen cursor having a sensing coil disposed concentric with and perpendicular to a longitudinal axis of the pen cursor to develop a characteristic output waveform from electromagnetic inductance between the grid wires and the sensing coil, this invention is the method of compensating a calculation of the position of the pen's tip on the tablet's upper surface and along the axis determined from an interpolation of the characteristic output waveform to find its zero voltage crossing point for tilt of the pen cursor longitudinal axis from perpendicular to the tablet's upper surface comprising using voltage values from grid wires next on opposite sides of the zero crossing point to calculate a pen tilt compensation factor.

Digitizer pen tilt correction employing wires near the data point

A method and associated circuitry for use in an electromagnetic digitizer having a plurality of first grid conductors connected from a first multiplexer controlled by a first enable input to ground and a plurality of second grid conductors connected from a second multiplexer controlled by a second enable input to ground and crossing over the first grid conductors at multiple points for eliminating errors caused by capacitively coupled signals between the grid conductors at the cross over points. The method comprises, connecting a first switch having a control input for switching the first switch to a closed position in series with the connection of the first grid conductors to ground; connecting a second switch having a control input for switching the second switch to a closed position in series with the connection of the second grid conductors to ground; applying the first enable input simultaneously to the control input of the second switch and the first multiplexer whereby the connection to ground of the second grid conductors is broken when the first multiplexer is enabled; and, applying the second enable input simultaneously to the control input of the first switch and the second multiplexer whereby the connection to ground of the first grid conductors is broken when the second multiplexer is enabled.

Ground switching technique for silkscreened digitizer grids

In a digitizer system, a grid comprises a group of X conductors and a group of Y conductors, each such group comprising a first and second set of conductors. The first set in each group is formed by looping a predetermined number of conductors back and forth across the grid active area so as to provide a plurality of crossing conductors segments. The second group is formed by looping a different number of conductors back and forth across the active area in the spaces between the conductors of the first set so as to provide a plurality of second set crossing conductor segments alternating with said first set crossing conductor segments. Due to the differing number of conductors in the sets and their alternate looping across the grid active area, the positional and directional polarity relationships between the crossing conductor segments shift across the active area, enabling segments to be distinguished from one another and treated as if they were separate and distinct wires. This shifting wire sequence conductor arrangement permits coverage of relatively large grid active areas with a minimal number of multiplexers for switching the conductors to signal processing circuitry.

Shifting wire sequence digitizer system

An improvement to position digitizing devices wherein sensed response voltages caused by the interaction of a movable instrument relative to conductors beneath a planar surface are converted to digital form and digitally processed to determine instrument position. An integrating voltage to frequency converter is used to produce a frequency with a correspondence to the voltage applied to it. By counting the frequency for a defined length of time, a resultant count is obtained which also corresponds to the applied voltage. By varying the counting period under microprocessor control, acquisition rate and resolution can be varied over several orders of magnitude without changing circuit components. The digitizer includes conductive elements disposed across the digitizing surface and incorporated into an instrument for producing an analog voltage signal having a DC component related to the position of the instrument on the digitizing surface. There is a voltage to frequency converter for receiving the analog voltage signal and for converting it to a pulsed signal at a frequency which is a monotonically increasing or decreasing function of the voltage level of the analog voltage signal. There is a counter for receiving the pulsed signal from the voltage to frequency converter, for counting the pulses of the pulsed signal, and for producing a digital value output proportional to the counted pulses whereby the digital value is similarly related to the voltage level of the analog voltage signal.

Low-cost, high-accuracy digitizer signal acquisition apparatus and method

A digitizer wherein the transduction frequency is controlled (automatically or manually) to minimize the interference effect of sources of external AC fields, such as CRT monitors. The digitizer implements the method of operation comprising the steps of, connecting a source of a frequency higher than the frequency to be employed as the transduction frequency of the digitizer to the first input of a counter; receiving input pulses from the source at the first input of the counter; outputting output pulses which are employed to generate the transduction frequency in the digitizer at an output of the counter; selectively setting an initial count value at a second input of the counter; and, repeatedly counting from the initial count value at the second input to a terminal value, outputting an output pulse upon reaching the terminal value, and resetting to the initial count value after outputting each output pulse. The preferred automated method includes reading and saving the induced position voltages being employed by the digitizer, testing the saved voltages for any flutter, and setting the initial count value to an optimum level.

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Phoenix, AZ, United States of America

James S Watson