Abstract: A capacitive position encoder which provides a digital output indication of the relative position between two plates. One of the plates includes first and second conductive input areas which are separated by a gap having the shape corresponding to a square wave. The second plate includes a number of rectangular output pads whose length is equal to one-half of the wavelength of the square wave. The pads are separated from one another by an integral fraction of the wavelength. Periodic input signals which are the inverse of one another are applied to the input areas and are capacitively coupled to the output pads. When the degree of overlap between an output pad and the input areas is equal, a null signal will be generated. Each pad will provide a null signal corresponding to a different position of the plates.

Abstract: A capacitive position encoder which provides a digital output indication of the relative position between two plates. One of the plates includes first and second conductive input areas which are separated by a gap having the shape corresponding to a square wave. The second plate includes a number of rectangular output pads whose length is equal to one-half of the wavelength of the square wave. The pads are separated from one another by an integral fraction of the wavelength. Periodic input signals which are the inverse of one another are applied to the input areas and are capacitively coupled to the output pads. When the degree of overlap between an output pad and the input areas is equal, a null signal will be generated. Each pad will provide a null signal corresponding to a different position of the plates.

Abstract: A head positioning system for a magnetic disk memory to position the head over a reference track so that track seeking operations can proceed from a known reference location. A plurality of control tracks are recorded adjacent the reference track with the first control track having a first type of control signal recorded thereon and the remainder having a second type of control signal. Means are provided to move the head a sub-multiple of the track spacing is to establish the head as close as possible to the centerline of the track, and to thereafter move the head integral multiples of the track spacing toward the reference track. The head is moved sequentially over the control tracks until the first type of control signal is detected. One more step then positions the head over the reference track. The sub-multiple movement capability is achieved through the use of a position encoder having a polyphase output, movement between zero crossings of the polyphase outputs being said submultiple.

Abstract: Disclosed is a rotational speed control system for comparing the rotational speed of a rotating disk as indicated by index pulses occurring one or more times per revolution of the disk, with a reference time representing the desired time between successive index pulses. The system employs logic circuitry external to any microprocessor control system employed by the rotating disk system. The reference time may be supplied by counters counting externally supplied clock pulses to a fixed value. The speed control system provides a speed up command or slow down command in a manner proportional to the speed error to the disk drive motor where the time between successive index pulses is greater or less, respectively, than the reference time.