An X-Y coordinate position locating or measuring digitizing device in which a cursor (inductor), moveable within an electromagnetic field generated by successively activated grid wires, develops a voltage from the field, and, in conjunction with conditioning circuits, yields the electrical intelligence required to indicate its position with a high degree of precision. Currents are successively passed through parallel grid lines for a given axis at discretely separate distances, the resultant successively generated field inducing a time variant voltage at the cursor coil output with amplitude and phase dependent upon the position of the cursor in relation to the actuated grid line. Conditioning circuitry to which the cursor coil output is coupled uniquely detects the phase reversal in the cursor coil output signal, interprets this reversal point in a manner which very accurately and linearly relates cursor position to time, and generates a "STOP" pulse indicating that the above phase reversal has been sensed. An enable signal initiated at an arbitrary reference point and terminated by the "STOP" pulse is then used to permit a precision clock to relate the distance of the cursor from this arbitrary point to the time needed to reach the cursor center from that reference point. Cursor position then becomes a function of precisely generated pulses accumulated in a counter.
A backlit digitizer tablet providing uniform illumination of the working surface, comprising biaxial fluorescent lamps supplying wide-area light emission under a sandwich top construction including an apertured shield electrode, a first clear spacer, an electrode array, a second clear spacer, and a translucent top, with optically transparent support means for the top.
Digitizer tablet and digitizer tablet structure having an illuminable working surface are disclosed. A space between a top translucent layer having the working surface and a source of light is provided so as to eliminate or minimize undesirable lighting effects at the working surface. In the preferred embodiments, the space is an air gap (e.g. 0.060-0.250 inch) immediately adjacent the top translucent layer. The air gap is formed by transparent optical fibers or solid glass or acrylic rods. Back-lighted, translucent, back-lightable (without light source) and surface lighted digitizer tablet embodiments are described.
A digitizer cursor is provided with a multifunctional control panel. The panel is comprised of a multiplicity of switches for defining various modes of cursor operation in use with a digitizer coordinate axes grid assembly or pad. Novel circuitry provides for a cursor of convenient size with a complex control panel in combination with a point locating device used in conjunction with the coordinate grid assembly. The circuitry provides for electrical communication through a coaxial cable permitting easy maneuverability of the cursor assembly relative to the pad and a simple electrical path for processing of the cursor coil induced point location signal, to determine coordinate location, and the cursor control signals originating as a function of switch operation initiated on the cursor panel by the operator. One digitizer grid pattern is used for each of two coordinate axes, i.e. X and Y. Each grid pattern is used for coarse and fine digitizing to determine cursor positioning on each respective axis. The digitizer has two basic modes of operation which relate to digitally representing the position of a cursor on a grid pattern. The first mode is for coarse digitizing designed to identify the position of the cursor within 11/2 grid lines of its actual position on the grid. The second mode is the fine digitizing mode which is operative to positively locate the cursor at its actual position within a triad of grid lines which have been identified through the coarse digitizing operation. Both modes are operative for each of the two axes. For coarse digitizing, a sequential line-to-ling pulsing technique is applied. For fine digitizing, a pulsed three phase system is utilized and any odd multiple of three grid lines.
A digitizer having a pointer or cursor driven by an alternating carrier signal and a grid of sequentially enabled parallel spaced conductors inductively coupled to the cursor includes an AM demodulator for detecting the instantaneous time of change of phase of the signal induced in the grid. In a preferred embodiment of the invention, a multiplier is used as the demodulator.
A coordinate position digitizing system to be used with a cathode ray tube, comprises a position determining plate having a plurality of conductors extending parallel with one another at regularly spaced intervals, and driving means for supplying a constant current selectively to the conductors, one after another, within a horizontal scanning period of the cathode ray tube. Magnetic flux detecting means detects magnetic flux on the position determining plate, and a band pass filter eliminates a noise component resulting from the deflection magnetic field of the cathode ray tube. Positional data defining a position of the magnetic flux detecting means on the position determining plate is produced in response to the output of the band pass filter.
