Abstract: 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.

Abstract: This is a dual-mode digitizing tablet system for providing inputs to a user program. There is a tablet with an active surface and an output connected to the computer. A cursor is moveable over the surface for generating a first signal reflecting the position thereof. Two switch-activating buttons on the cursor generate a second signal when pushed. A position history table holds a last position of the cursor and a menu definition table holds entries defining menu selections associated with the user program as a function of pre-established positions on the tablet. Dual-mode logic is disposed between the tablet and the user program for determining and storing a present location of the cursor, for outputting the present location of the cursor when one of the buttons is pressed, for otherwise outputting both the present location and relative movement of the cursor, and for outputting an indication when the other button is pressed.

Abstract: This is a method and associated implementation logic for plotting circles with a pen plotter to obtain a substantial and unexpected increase in throughput of the plotter when plotting circles having a radius equal to or smaller than a small radius lower limit. The method comprises the steps of, employing an independently calculated chord length and number of chords at the independently calculated chord length for plotting circles having a radius greater than the small radius lower limit; and, employing a maximum chord length which is not separately discernable to the naked eye in a circle of a desired radius and an associated number of maximum length chords when plotting a circle having a radius equal to or smaller than the small radius lower limit. In tested embodiments, the method has provided a twelve-fold increase in plotter throughput when plotting small radius circles.

Abstract: A media stripper mechanism for a plotter in which the media is supported by a support having a recess therein adapted to be covered by the media. A stripper is positioned external of the support and is adapted to be extended a preselected distance into the recess. A mover is provided for moving the stripper into the recess prior to the covering thereof by the media, whereby the media is stripped from the support by the stripper.

Abstract: In order to determine without ambiguity the grid sections on which the pointer is located in a cordless electromagnetic digitizer having x and y locating grids, a third, "phase" grid has conductors that form elongated, narrow open loops, spaced so that each location on the work surface is enclosed by loops formed by a minority of the phase grid conductors. Any phase grid conductor with sufficient induced voltage can serve as a phase reference to determine the relative phases of the signals induced in all of the phase grid conductors. A phase grid conductor determined to have the relative phase of the minority can then serve as phase reference to identify the locating grid section unambiguously, and digitize the pointer location.

Abstract: 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.

Abstract: A digitizer includes a tablet having an array of conductors, and a pen-shaped, coil-containing stylus. The digitizer applies an energizing signal to either the conductors or the stylus, which signal induces voltages in the other. Then, the digitizer detects the induced voltages corresponding to the conductors, which define a voltage waveform having a positive peak, a negative peak, and a zero-crossing therebetween. The digitizer corrects for pen tilt in determining stylus position on the tablet by determining a position value for the zero-crossing using voltages in a region between the positive and negative peaks of the waveform and generating a pen tilt correction value using the position value and voltages in a region outside the positive and negative peaks. Then, the pen-tilt correction value and a preferably cyclic-error-corrected value for the position of the zero-crossing are combined to yield a relatively accurate pen-tilt-compensated determination of stylus position.

Abstract: A loopback conductor arrangement for a digitizer grid employs rotation sequencing of the conductors. The conductors in each of the X- and Y-directions are looped back and forth in a parallel, spaced relationship across the active grid area so as to provide a plurality of crossing conductor segments, with the positions of selected conductors (e.g., alternate conductors) in each successive loop shifting in sequential positions by a constant offset with respect to the other conductors in those loops.

Abstract: This invention is directed to simplified menu display and inputting apparatus for use in a pen plotter having a set of up, down, left, and right control buttons used for pen control. There is an alpha-numeric display for displaying menu choices, an ON LINE button for placing the plotter in an on line mode of operation wherein the pen control buttons are employed in their normal manner, and a MENU button for placing the plotter in a menu input mode wherein the pen control buttons are employed to move from top to bottom through top level menu definitions and from left to right through subfunction menu definitions. Displayed menu choices are selected for insertion into a current parameter value list while in the menu input mode. Provision is made to identify a number of users and store their operating parameters separately and individually so that users can return and use the plotter with their values without having to re-enter them each time.

Abstract: 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.

Abstract: 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.

Abstract: In a digitizer system, a primary set of conductors is formed by looping spaced conductors in pairs through four quarter sections of a grid active area in such a way that the unexcited or directional polarities of each pair are different in each quarter section. A secondary set of conductors is formed by looping at least one additional conductor back and forth through the active area in the spaces between the conductor pairs of the primary set. A coil in a pen tip is movable relative to the grid, and used to inductively couple signals in the conductors of the grid. This intertwined conductor loopback arrangement permits coverage of relatively large grid active areas with a minimal number of multiplexers for switching the conductors to signal processing circuitry.

Abstract: In a multi-position graphics plotter pen carousel system employing a pen capping mechanism therein at each pen position for capping and uncapping pens held by the carousel, an improvement for allowing the sensing of pen presence at the pen positions and the indexing of the carousel with a single sensor. Each pen capping mechanism is adapted to assume a first position with a pen in the pen position and assume a second position with no pen in the pen position. A plurality of first sensible attributes are associated with respective ones of the pen capping mechanisms for exhibiting a first characteristic when a pen is contained at the associated pen position and for exhibiting a second characteristic when no pen is contained at the pen position. A plurality of second sensible attributes are associated with respective ones of the pen positions for constantly exhibiting the first characteristic.

Abstract: In a digitizer system, adjacent conductors in pairs are looped through four quarter sections of a grid active area in such a way that the unexcited polarities of the pair are different in each quarter section. A coil in a pen tip is moveable relative to the grid, and used to inductively couple signals in the conductors of the grid. The number of conductors required to span a given grid active area, and the number of multiplexers required to handle such conductors, are reduced by a factor of four. The polarities of signals induced in the conductors by the coil are selectively changed depending upon the quarter section in which the coil is located and sampled to coarsely locate the coil as being between two particular adjacent conductors. In the disclosed embodiment, a ratio of the magnitudes of the signals induced in the two particular conductors is then used to precisely locate the coil between these two adjacent conductors.