Abstract: A digitizing tablet system having a stylus which is inductively coupled to a grid is disclosed. The grid includes a first plurality of narrow uniformly sized and spaced U shaped loops of conductive material disposed to define a first coordinate axis of the grid and a second plurality of narrow uniformly sized and spaced U shaped loops of conductive material disposed to define a second coordinate axis of the grid. One end point of each loop in each plurality of loops is connected to a common conductor which serves as one output terminal for that plurality of loops. The other end point of each loop in the same plurality of loops is connected to a multiplexor whose output is connected to a conductor which serves as the other output terminal for that plurality of loops. Voltage signals induced in the loops when the stylus is positioned above the grid and a coil in the stylus is energized are processed to generate data signals corresponding to the position of the stylus relative to the grid structure.

Abstract: A digitizing tablet is disclosed in which two multiplexors are connected to alternate conductive loop elements in each plane of elements. The two multiplexors are connected to a differential amplifier. The signals from the differential amplifier are demodulated. The demodulated signal is provided to an integrator. A microprocessor controlled reset switch is connected across the integrator to reset the integrator after the completion of each measurement. Grounded copper strips are used in the space formed within and between the conductive loop elements of the digitizing tablet to shield the loop elements from capacitive interference.

Abstract: A position indicating implement is disclosed having a first coil connected to a current source and a second coil inductively coupled with the first coil. A capacitor is connected in series with the second coil so that the current in the first coil induces a phase shifted current in the second coil. A tip extends from the barrel of the position indicating implement of the present invention. The tip is designed for placement on and movement over a digitizing tablet. A switch has been located near the tip so that it is easily accessible to a user's finger while holding the implement.The power source providing an alternating current to the first coil includes a digital switching circuit for producing a step function which approximates a sine wave and lacks any components at the second, third, fourth, fifth and sixth harmonics. The step function is filtered to produce a sine wave for delivery to the first coil.

Abstract: A method and apparatus are described for processing a series of digital signals representing a stroke of a stylus on a tablet to remove signals at the ends of the stroke caused by retracing, the series of signals corresponding to the X and Y coordinates of a series of points along the direction of travel of the stroke. The signals for each point in the series are compared to the signals of the points adjacent to it to form a second series of signals which contain only those signals corresponding to points having an ordinate value more extreme than the corresponding ordinate value of its adjacent points. The first three points in the second series of signals are then processed to determine the ratio of the distance from the first point to the second point to the distance from the second point to the third point and to determine the size of the angle formed by the three points. The distance ratio is fed into a table-look-up which outputs a reference angle signal which is compared to the processed angle signal.

Abstract: A digitizing tablet interactive with a stylus which is inductively coupled to a grid is disclosed. The grid includes a first plurality of narrow uniformly sized and spaced U shaped loops of conductive material disposed to define a first coordinate axis of the grid and a second plurality of narrow uniformly sized and spaced U shaped loops of conductive material disposed to define a second coordinate axis of the grid. One end point of each loop in each plurality of loops is connected to a common conductor which serves as one output terminal for that plurality of loops. The other end point of each loop in the same plurality of loops is connected to a multiplexor whose output is connected to a conductor which serves as the other output terminal for that plurality of loops. Voltage signals induced in the loops when the stylus is positioned above the grid and a coil in the stylus is energized are processed to generate data signals corresponding to the position of the stylus relative to the grid structure.

Abstract: A digitizing tablet system of the type including a tablet, a stylus and associated electronics which is constructed to correct for tilt errors when the stylus axis is tilted relative to the tablet is disclosed. The tablet includes a housing having a rectangular coordinate grid of electrical conductors. The stylus includes an elongated tubular member having a tip at one end, a first coil which is located at a first axial distance from the tip and a second coil which is located at a second axial distance from the tip, the second distance being different from the first distance. A voltage signal is applied to each coil sequentially. The signal applied to each coil induces a voltage in each conductor in the grid.

Abstract: An apparatus and method are disclosed for emulating computer keyboard input from a handprint terminal, the output of the handprint terminal comprising character data along with row and column position data for each character. A line buffer memory temporarily holds characters from the same row. While the characters belonging to any given row are stored in the line buffer memory, local editing may be performed to delete and/or add and/or change characters, with function signals being outputted from the apparatus by the control unit equivalent to function signals that would be outputted from a keyboard. When a character received is in a different row from the character preceeding it, the line buffer memory is cleared of all previous characters that had been loaded into it and carriage return or carriage-up signals are outputted from the control unit corresponding to the row change. The character is then loaded into the line buffer memory to start a new row.

Abstract: A method and apparatus are described for processing a series of digital signals representing a stroke of a stylus on a tablet to minimize noise at the ends of the stroke, the series of signals corresponding to the X and Y coordinates of a series of points along the direction of travel of the stroke. First the signals for the X and Y coordinates of each point in the series are compared to the signals for the X and Y coordinates of the points adjacent to it to form a second series of signals comprising only those signals having an ordinate value more extreme than the corresponding ordinate value of its adjacent points. The first point in the second series of signals is then compared with points succeeding the first point to identify the point in the second series that is furthest from the first point but within a predetermined distance from the first point. The point so located is identified as the end point at that end of the stroke.

Abstract: Apparatus for filtering a sequence of digital values representing a stroke of a stylus on a tablet averages sets of digital values, resamples the averaged digital values to accept only those having greater than a minimum amplitude separation and then averages sets of the resampled digital values.