Abstract: An apparatus and method are disclosed for positioning magnetic heads relative to the recording tracks of a recording medium such as a floppy disk having circular, concentric recording tracks formed thereon. The magnetic heads are mounted on a head carriage, and the head carriage is moved, in response to received command pulses, so that the heads are moved linearly, by step increments, along a radius of the floppy disk. The heads are thereby moved across the spaced tracks on the disk, with each incremental movement of the heads being a distance less than the distance between the tracks, and being, for example, one-half or one-fourth of the total distance between tracks. Acoustic noise due to head movement is minimized by moving the heads by increments less than the distance between the tracks, with such movement avoiding exciting the resonances of the head moving apparatus.

Abstract: The speed of a DC motor (10) is controlled by a servo which includes a digital phase lock loop. The motor drives a tachometer whose pulse (22) frequency is low relative to the frequency of a clock (21). The clock continuously drives a counter (200) whose ever increasing number content is gated to a data latch (26) upon the occurrence of each successive tachometer pulse, thus this data latch contains a first time-number of ever increasing magnitude. A second data latch (24) contains a second number. The difference in magnitude of two consecutive time-numbers is indicative of motor speed. Initially, this second number is set to contain a reference number (REF) which is equal in magnitude to the number of clock pulses which will occur between adjacent tachometer pulses when the motor is running at desired speed. A pair of limit numbers (RANGEL and RANGEH) are provided to define the upper and lower limits of servo saturation.

Abstract: A servo-controlled recirculating automatic document feeder (RADF) includes a plurality of independently driven document transport devices. A picker mechanism separates documents in seriatim from a stack. An entry turnaround transport device buffers and delivers picked documents to a platen transport device for exposure. After exposure, the document is transported along a simplex or duplex path for duplex or simplex copying. The document is then buffered in an exit turnaround transport device and is subsequently returned to the stack. Each transport device is independently driven by a motor and a closed-loop servo. A common reference oscillator generates source signals for the servo-loops. A microcomputer operates on the source signals and generates reference signals for driving the transport devices.