Printronix, Inc.

Bell + Howell Company

Pertec Corporation

Jerry Matula

Gordon B Barrus

Robert A Kleist

Glen R Radke

William J Gervais

An arrangement for bidirectionally driving a hammer bank shuttle assembly along a linear path in a line printer includes an opposite pair of circular, rotatable elements having an elongated shuttle assembly mounting element and an elongated counterbalancing element extending between the pair of rotatable elements on the opposite sides thereof. Pole pieces and a magnet disposed between and adjacent the shuttle assembly mounting element and the counterbalancing element provide magnetic flux which flows through portions of the opposite elements to attract and maintain the elements in contact with the opposite rotatable elements. A pair of serially coupled coils mounted on the counterbalancing element and disposed within the air gaps formed by the pole pieces and the magnet are energized by a cyclically varying signal to bidirectionally drive the shuttle assembly mounting element and its included hammer bank shuttle assembly along the linear path as the counterbalancing element is caused to reciprocate between opposite limits of movement defined by an opposite pair of resilient elements in the path of movement of the counterbalancing element. In an alternative embodiment the coils are disposed between the counterbalancing element and the shuttle assembly mounting element so as to form air gaps with and magnetically interact with a first pair of magnets mounted in spaced-apart relation along the length of the counterbalancing element and a second pair of magnets mounted in spaced-apart relation along the length of the shuttle assembly mounting element.

Counterbalanced bidirectional shuttle drive having linear motor

In a dot matrix line printer in which selected ones of a plurality of hammers mounted on a reciprocating hammer bank are released in response to successive sets of serial data to print dots on a paper, the changing hammer release characteristics which are caused by different numbers of hammers being released with each new set of serial data are compensated for by an arrangement providing a varying hammer release signal in accordance with the number of hammers being released. The variable release signal is provided in the form of a variation in the time interval during which the drive amplifiers associated with hammer release coils are turned on, thereby effectively varying the length of a current pulse provided to each coil in direct proportion to the number of hammers to be released. A counter is preset, then counted down from the preset value in accordance with the number of hammers to be released as represented by a set of serial data being provided to a shift register. When the shift register is loaded, latches associated with the various stages of the shift register containing hammer release signals are set so as to turn on associated ones of the drive amplifiers. The counter counts up in response to clock pulses until it overflows and clears the latches so as to turn off the drive amplifiers.

Printer having variable hammer release drive

In a print hammer mechanism in which an elongated, resilient hammer element mounted at a fixed end thereof has an opposite free end thereof selectively released from a retract position for impact of a dot imprinting element carried by the free end of the element, an improved magnetic circuit is provided for use in release and retraction of the hammer element. The improved magnetic circuit includes a pair of elongated pole pieces of like configuration having back ends thereof mounted on opposite sides of a rare earth magnet and tips at the opposite front ends thereof disposed adjacent the free end of the hammer element to form a pair of gaps therewith. Improved magnetic properties are provided by the presence of two gaps, the close proximity of the tips so as to minimize the high reluctance magnetic path through the hammer element and the maintenance of a small air gap between one of the tips and the hammer element when the element is in the retract position in contact with the other tip to facilitate quick release of the hammer element. The magnetic characteristics are even further improved by the physical design of the magnetic circuit which minimizes fringing magnetic fluxes and which utilizes a pair of magnetic coils, each of which is mounted on a different one of the pole pieces adjacent the tip thereof. The use of two coils provides for substantially complete cancellation of the magnetic fields in both gaps upon energization to provide for quicker release of the hammer element from the retract position.

Print hammer mechanism having dual electromagnetic coils and pole pieces

A counterbalanced bidirectional drive for a hammer bank shuttle assembly within a line printer utilizes a band formed into an endless loop extending around and between an opposite pair of rotatable pulleys on opposite sides of the pulleys. A hammer bank-carrying shuttle assembly is coupled to a portion of the band between the pulleys on one side of the pulleys and is counterbalanced by an elongated bar of similar mass coupled to a portion of the band between the pulleys on the opposite side of the pulleys from the shuttle assembly. A DC motor coupled to one of the pulleys is alternately energized in opposite senses so as to bidirectionally drive the shuttle assembly along a linear path between opposite limits defined by resilient members impacted by an element mounted on the counterbalancing bar.

Counterbalanced bidirectional shuttle drive

A print hammer mechanism which forms a magnetic path between the opposite fixed and free ends of an elongated resilient hammer element using a permanent magnet, a first pole piece terminating in a pole tip adjacent the free end of the hammer element and electromagnetic means for cancelling the effects of the permanent magnet employs a second pole piece having a pole tip disposed adjacent the free end of the hammer element between the first pole piece and the fixed end of the hammer element. The relatively short magnetic path of low reluctance along the hammer element between the pole pieces combines with the effect of flux flowing in two gaps perpendicular to the flat surface of the hammer element to significantly improve the magnetic properties of the print hammer mechanism including the ability to quickly release and then retract the hammer element and the ability to increase the resonant frequency and/or the amount of energy stored in the hammer element for a given amount of magnetic flux available. The second pole piece forms a gap with the hammer element when the hammer element is in a spring-loaded retract position against the first pole piece, providing better retraction of the hammer after release and reducing the amount of magnetic energy required to overcome the effects of the permanent magnet and release the hammer element. The electromagnetic means for cancelling the effects of the permanent magnet consists of a coil wound about the first pole piece in direct contact therewith, enabling the first pole piece and adjacent parts of the magnetic circuit to provide adequate heat dissipating without the need for fins or other heat dissipating elements on the coil.

Print hammer mechanism having dual pole pieces

A printer hammer bank for a dot matrix or other type printer is reciprocated at high speed along a printing position by a low mass, low inertia servo-controlled drive. Precise control is maintained even though a positive drive structure is not used. A reciprocable drive mechanism supporting the hammer bank is mounted to undergo free flight with low friction along a selected axis parallel to a printing line. At each limit of movement, the drive mechanism encounters resilient stop members which reverse the direction of motion of the drive mechanism and included hammer bank following a natural cosine function of the spring mass of the stop members and with low kinetic energy loss. Losses occurring during reversal are compensated by an energy impulse from a coupled linear electromagnetic drive and an associated velocity servo system which eliminates the need for close servo control during reversal, allowing the drive mechanism to rebound naturally. During reversal the servo system which is driven into saturation senses the occurrence of zero motion of the drive mechanism and reverses the direction of energization of the electromagnetic drive. Hammer bank velocity during movement through a print span is sensed, and further kinetic energy is supplied by the servo system as required to compensate for friction losses, braking effects during printing, and other causes of variation in hammer bank speed.

Reciprocating linear drive mechanism

An impact printer ribbon drive of the reel-to-reel type, in which a length of ink ribbon extending between and wound around opposite reels is disposed between a reciprocating hammer bank and print paper on a platen, drives the ribbon at substantially constant speed and tension independent of varying ribbon pack diameter on the two reels. Each one of the reels is driven by a different one of a pair of DC permanent magnet motors. The motors are energized by a circuit which maintains the sum of the currents through the two motors substantially constant and which also maintains the voltage at the leading or take-up motor substantially constant. The sum of the currents and the voltage are maintained substantially constant by a pair of servo circuits associated with different ones of the motors and coupled to be alternately actuated in response to external direction commands. Also included is circuitry responsive to voltages in different parts of the circuit for signalling unwanted conditions such as a run-away ribbon, a jammed ribbon or a loose hub at one of the reels.

Printer system ribbon drive having constant ribbon speed and tension

An improved print hammer actuator for dot matrix printers employs a substantially closed loop magnetic path including a resilient magnetic hammer, a number of such hammers being aligned in a hammer bank assembly which is shuttled back and forth along a printing line at a high rate of speed, while the hammers are individually actuated by energizing coils which overcome a permanent magnetic field normally maintaining the hammers in retracted position. Heat conducting elements are mounted in heat transfer relationship with each of the different ones of the coils in the hammer bank, and high surface area fins on the elements extend into an air flow directed across one side of the hammer bank. For this purpose the hammer bank assembly is configured to define an interior air channel along its length and includes a fixed top cover and spaced apart circuit board forming part of a plenum and directing air frontwardly from a rear mounted fan. Heat generated in the coils during high duty cycle energization is effectively dissipated into the environment with substantial improvements in the uniformity of printer operation.

Print hammer actuator for dot matrix printers

A tape transport system having a capstan servomechanism for velocity control of tape across a read/write head and separate reel servomechanisms for tape supply and take-up control, and also having tape loops in vacuum columns, is provided with tape position feedback to each reel servomechanism to stabilize reel positions in a standby (zero capstan speed) condition from AC tachometers of the induction-generator type normally used during steady state (steady capstan speed) for velocity feedback.

Tape transport reel servomechanism

A rotational position sensor is disclosed in which the beam from a light emitting diode mounted on a rotatable element is directed onto a pair of adjacent photocells. The portion of the beam falling upon each of the photocells determines the photocell output signal. The output signals are combined to form a signal which varies generally linearly with the rotational position of the element upon which the light emitting diode is mounted. The photocells are disposed in relatively close relation to one another, and the light emitting diode is disposed relatively close to each of the photocells and a short distance from the axis of rotation of the element. By use of appropriate masks the size of the beam from the light emitting diode can be varied so as to provide linear response over varying angular ranges of movement of the rotatable element.

Growing community of inventors

Culver City, CA, United States of America

Jerry Matula