Drive system and method for ink jet printer
First Claim
1. In a device having a rotating drum and scanning means for traversing the surface of said drum, the combination comprisinga stepper motor having a magnetic rotor and a plurality of fixed windings,a plurality of voltage generating means each producing a continuous repetitive waveform varying in amplitude between predetermined maximum and minimum values,a plurality of current generating means each coupled to one of said windings and under the control of one of said voltage generating means, thereby to create a rotating magnetic field of substantially constant intensity throughout the cycle of rotation, andmechanical means connecting said rotor to said drum.
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Accused Products
Abstract
For requirements where constant velocity is important and positional error must be small and non-cumulative, a bipolar or unipolar, two-phase, permanent magnet stepper motor is driven by sawtooth currents in such manner as to produce a rotating magnetic field that exerts a substantially constant torque on the rotor. When using a bipolar stepper motor with windings electrically offset by 90°, two drive currents are generated that increase and decrease in amplitude linearly between predetermined maximum and minimum values. With a unipolar motor, four sawtooth waveforms, of single polarity, are provided. In either case, the currents are displaced by 90° to produce a rotating magnetic field of uniform amplitude.
A microprocessor controls the generation of a number of voltage ramps that control current generators for either the bipolar or unipolar stepper motor.
To control speed and torque, the slope of the current ramp and the repetition rate are varied until the motor has attained a steady operating state. The amplitude of the driving currents is determined indirectly by controlling the rate of the current increase of the ramp and the time before current directions of the phases are indexed.
48 Citations
20 Claims
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1. In a device having a rotating drum and scanning means for traversing the surface of said drum, the combination comprising
a stepper motor having a magnetic rotor and a plurality of fixed windings, a plurality of voltage generating means each producing a continuous repetitive waveform varying in amplitude between predetermined maximum and minimum values, a plurality of current generating means each coupled to one of said windings and under the control of one of said voltage generating means, thereby to create a rotating magnetic field of substantially constant intensity throughout the cycle of rotation, and mechanical means connecting said rotor to said drum.
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8. In a printer having a scanning head and an imaging drum, drive means comprising
a stepper motor having a permanent magnet rotor and a plurality of windings, means coupling said rotor to said imaging drum, current drive means connected to said windings for generating a plurality of current waveforms wherein the current of each waveform continuous increases and decreases periodically to produce a rotating magnetic field of substantially constant intensity throughout the period of rotation, and microprocessor means for controlling the repetition rate of said waveforms.
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10. In an ink jet printer having a cylindrical imaging drum on which images are produced by a print head on a medium carried by the drum, the method of driving said drum comprising the steps of
providing a stepper motor having a permanent magnet rotor and a plurality of discrete circumferentially-positioned windings, generating a plurality of continuous repetitive current waveforms displaced in phase and varying periodically between predetermined maximum and minimum values, and connecting said current waveforms respectively to each of said windings, said current waveforms producing a rotating magnetic field of substantially constant intensity.
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17. The method of driving a stepper motor having a permanent magnet rotor and a plurality of windings to produce substantially uniform rotational torque comprising the steps of
generating a plurality of continuous repetitive voltage waveforms each increasing and decreasing successively between predetermined maximum and minimum values, producing under the control of said voltage waveforms a plurality of current waveforms each being directly related in rate of current increase and decrease to one of said voltage waveforms, and connecting said current waveforms to said windings.
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20. In a stepper motor drive system, the combination comprising
a stepper motor having a permanent magnet rotor and a plurality of windings, voltage generating means producing a continuous repetitive sawtooth voltage waveform in which the voltage in each waveform increases and decreases periodically between predetermined minimum and maximum values, and current generating means connected to said windings under the control of said voltage generating means for producing repetitive current waveforms each directly related in ramp angle and maximum amplitude to one of said voltage waveforms to produce a rotating magnetic field of substantially constant magnitude.
Specification