Drive system and method for ink jet printer

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.

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.

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.