The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Apr. 19, 1988
Filed:
May. 09, 1986
Dennis J Buckley, Nashua, NH (US);
Advanced Color Technology, Inc., Cambridge, MA (US);
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.degree., 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.degree. 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.