Polaroid Corporation

Magnetar Technologies, Inc.

Marc T Thompson

Edward M Pribonic

William T Plummer

Douglas S Goodman

Peter P Clark

Bryan A Santarelli

Eddy current braking apparatus includes an array of spaced apart permanent magnets and a plurality of flux steering magnets may be disposed in gaps between the spaced apart permanent magnets. The flux steering magnets are orientated in a manner to provide a steering flux polarity that is rotated about 90 with respect to a polarity magnet flux of the spaced apart permanent magnets in order to increase the flux density in the air gap which results in better performance of the brake. Alternatively, cubic magnets may be used with each magnet being arranged to provide a change in flux polarity between adjoining magnets. An electrically conductive member is provided for engaging the magnetic flux provided by the array of permanent magnets and the magnets and conductive member are mounted for enabling relative motion between the magnet and the conductive member to produce eddy currents in the conductive member and resulting in a braking force between the magnets and the conductive member.

Curvilinear eddy current braking apparatus

Eddy current braking Apparatus is provided which includes a single array of permanent magnet for providing a magnet flux. A electrically conducted member for exclusively engaging the magnetic flux provided by the single array of permanent magnet. The magnets and conductive member are mounted for enabling relative motion between the magnet array and the conductive member to produce any currents in the conductive member resulting in the braking force between magnets and the conductive member. The configuration of the magnets and the conductive member enable the braking system to be installed over curvilinear paths.

Eddy current braking apparatus

Permanent magnet eddy brake with flux-steering poles

Disclosed is a two-level current driver suitable for driving a semiconductor laser for printing applications, the laser driver including a primary power source for producing a first current pulse of amplitude I.sub.1 and of duration T.sub.2, a secondary power source for producing a second current pulse of amplitude I.sub.2 and of duration T.sub.1, means for combining the outputs of the power sources, and sensing means for detecting the current pulse output from the primary power source.

Two-level semiconductor laser driver

A driver circuit applies electric current to a semiconductor laser for emission of light suitable for use in a laser printer wherein a photosensitive medium is exposed by the light for imprinting an image of marks or pixels upon the medium. The current is the sum of bias current plus signal current, the latter being a sequence of pulses providing image data. The circuit includes a bypass around the laser, and the signal current is pulsed by using a switching circuit which applies a steady input current alternately to the laser and the bypass under control of a digital data signal. The switching circuit is an array of emitter-coupled logic elements operating in parallel for reduced inductance and higher switching speed. The steady input current is provided by a switching current regulator wherein a power transistor, driven by a pulse width modulator, alternately connects and disconnects current from a DC power supply in conjunction with a smoothing filter comprising an inductor and a capacitor. A current sensing resistor connects in series with the parallel circuit of laser and bypass to output a sense signal representing the amplitude of the steady input current. The sensor signal drives the pulse width modulator via a loop compensation element to establish an average value of laser current. An additional ripple current source, responsive to a high frequency component of the sensor signal, is added to the input current to counteract any ripple from the regulator.

Laser driver circuit

A laser driver circuit pulses of current to a laser diode to activate the diode to emit pulses of radiation suitable for operation of a laser printer. A field-effect transistor (FET) is serially connected with the laser diode and with a feedback resistor for applying the current pulses, the feedback resistor serving as a source of a feedback signal indicative of the magnitude of current flow. A photodetector senses radiation outputted by the laser diode and emits an optical feedback signal representative of radiated power of the laser diode. A combiner circuit, responsive to an input digital command signal, combines the current feedback signal and the optical feedback signal with the command signal to signal generate a drive signal for activating the FET. The combiner circuit includes an input section in which a current source powers a differential amplifier operating in a switching mode in response to the command signal, a drive section wherein a current source powers a differential amplifier operating in a linear mode and connecting between the input section and the FET, and a threshold section connected to the input section for establishing a threshold current level in the drive signal which activates the FET.

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Watertown, MA, United States of America

Marc T Thompson