Abstract: The receiver of a facsimile system includes a modulator for generating a signal for transmission to a remote transmitting location during predetermined intervals in the absence of received signals during those intervals. The signal from the receiver provides a periodic handshake function. The duration of the signal is short as compared with the duration of the predetermined intervals in which the received signals are absent.

Abstract: A variable reluctance motor of the stepper type is operated as a brushless constant speed DC motor by sensing the position of the rotor during rotation and generating a tachometric signal representing the speed of the rotor in response to the sensed position of the rotor. The tachometric signal is compared with a reference signal to generate a supply voltage to the windings of the stepper motor which will maintain the speed of the rotor substantially constant. The windings of the stepper motor are sequentially energized by the supply voltage in response to sensed position of the rotor. During start-up and prior to the time the motor reaches the predetermined speed, a start-up signal is utilized in addition to the sensed rotary position to sequentially energize the windings with the supplied voltage. The motor is utilized to drive a floppy magnetic data storage disc.

Abstract: A facsimile transmitter comprises a rotatable drum and a sensor for detecting dark-light variations in a document mounted on the drum. A facsimile receiver comprises a rotatable drum and a writing stylus for reproducing dark-light variations on a copy medium mounted on the drum. Prior to transmission of modulated signals representing the dark-light variations in the document, synchronizing signals are transmitted from the transmitter to the receiver. The synchronizing signals comprise pulses of selected and controlled frequency duration and time lapse therebetween to signal the transmission mode. The various modes signaled include different and variable scanning rates, different frequency bandwidths and different forms of modulation.

Abstract: In a facsimile transmission system, a transmitter comprises a read photodetector which scans a document for video content and a lead photodetector which scans the document in advance of the read photodetector. The output of the read photodetector is coupled to a modulator which generates signals for transmission to a facsimile receiver at a remote location. The output of the read photodetector and the lead photodetector are also coupled to timing circuitry which automatically initiates a fast scanning mode for the read and lead photodetectors after a predetermined time lapse without detection of a dark, information-bearing area on the document. The facsimile receiver which comprises a stylus for scanning a copy medium and a demodulator for controlling marking on the copy medium by the stylus also includes timing circuitry for automatically initiating a fast scanning mode after a predetermined lapse in time between received signals representing dark, information-bearing areas.

Abstract: A facsimile transmitter detects dark-light variations in an illuminated document by means of a photodetector. After amplification, the output from the photodetector is applied to a threshold detector generating a multilevel digital signal. When the magnitude of the amplified photodetector signal is greater than one fixed threshold level, one level of the digital signal is generated. When the magnitude of the amplified photodetector signal is less than another fixed threshold level, another level of the digital signal is generated. When the magnitude of the amplified photodetector output lies between the two threshold levels, one level of the digital signal is generated when the peaked, amplified photodetector signal is greater than the unpeaked amplified photodetector signal and the other level of the digital signal is generated when the peaked amplified photodetector signal is less than the unpeaked, amplified photodetector signal.

Abstract: A serial impact printing element is mounted on the slider of a high performance linear stepper motor. The slider moves through the stator-to-stator air gap of the linear motor stator comprising an active stator portion having windings associated therewith and a passive stator portion without windings. In order to achieve high performance of the motor, the slider is relatively short as compared with the stator, and longitudinal flux leakage through and the weight of the slider are minimized by the use of nonmagnetic discontinuities therein. The impact printing element includes a wheel having a plurality of circumferentially spaced character elements which are rotated to the printing position by means of a rotary stepper motor.

Abstract: In a facsimile transceiver, the scanning drum is driven by a DC motor which is coupled to a source of drive pulses having a duty cycle which controls the speed of the DC motor. Dynamic braking pulses are applied to the motor between the drive pulses. The braking current pulses are generated as a result of armature counter EMF and flow through a low impedance path around the DC motor.

Abstract: In a facsimile system, rotation of a transmitter drum carrying a document is synchronized with the rotation of a receiver drum carrying a copy medium. Synchronization of the rotating transmitter drum and the rotating receiver drum is assured by driving the transmitter drum from an AC power line and locking the receiver drum to the AC power line frequency once synchronization of the transmitter drum and the receiver drum have been achieved. In order to achieve initial synchronization, the drive for the receiver drum is initially locked to a source of controlled frequency until a predetermined angular position of the receiver drum relative to a predetermined angular position of the transmitter drum is attained. The receiver motor which is of the DC type is controlled in angular frequency after initial synchronization by generating a signal having a frequency phase locked to the AC power line frequency.

Abstract: Frequency modulated pulses representing dark/light variations on a document are applied to a frequency limiting circuit prior to synthesizing a low distortion sinewave voice band signal from the pulses. The frequency limiting circuit detects the frequency of the pulses and divides the frequency when the frequency exceeds a predetermined level. Detection of frequencies in excess of the predetermined level is achieved by a counter which counts clock pulses applied to the counter during each cycle of the frequency modulated pulses to determine the time between pulses and thus the frequency of the pulses. A gate only passes the pulses after a predetermined count has been reached.

Abstract: A frequency modulated facsimile signal is synthesized from a high frequency signal having a frequency which varies in response to dark/light variations on a document. The higher frequency signal which comprises pulses is coupled to a synthesizing network which includes a digital-to-analog converter for producing synthesized frequency modulated facsimile signals. Enabling circuitry is associated with the digital-to-analog converter which assures that the frequency modulated facsimile signal will not terminate or begin except at axis crossing times.

Abstract: FM signals within a predetermined bandwidth representing dark-light variations in a document are transmitted over a communications network to a facsimile receiver. Signals are demodulated by a single-shot multivibrator which is triggered at a frequency in response to the FM signals. An average DC voltage detector is connected to the output of the multivibrator to generate an average DC voltage representing the ratio of the astable state duration to the multivibrator cycle. A bandpass filter in the receiver input substantially attenuates signals outside the range of the FM signals thereby enhancing facsimile quality and precluding an erroneous receiver shutdown by a control circuit responsive to the frequency and presence of signals being transmitted. Contrast and brightness controls are included in the stylus drive circuit of the receiver.

Abstract: A facsimile transceiver comprising a document/copy receiving drum, a motor for rotation of the drum about the drum axis and a read/write head mounted for linear movement in a direction parallel with the drum axis. When the transceiver is operating in the receive mode, the copy medium having adhesive along at least one edge circumscribes the drum in a closed loop so as to eliminate the necessity for transmitter-receiver angular synchronizing signals which would otherwise be required for locating the copy margin adjacent the edge of the copy paper. After completion of a transmission, the copy medium is severed along a line so as to provide an appropriate margin for the copied information content. In one embodiment of the invention, the closed loop is formed from a single sheet having adhesive along one edge for purposes of forming a bond between opposite edges of the sheet when the sheet is applied to the drum.