Linear motor control system for brushless DC motor

Claim 1

A motor control system for controlling a brushless direct current motor of the type including a rotor(76)having a' plurality of permanent magnet poles (78) at equal angular locations about the axis thereof, the angular spacing therebetween being 360°/N where N is the number of poles, and a stator 12 having at least three windings(14, 16, & 18) for providing at least three fields per pole,said system characterized by a) a rotor position sensor assembly(20, 160)for sensing the position of the rotor relative to the stator, including a multisector marker(80)secured to said rotor for identifying each pole and at least four sensors(22, 24, 26 and 28; 86, 88, 90 & 92, 162, 164, 166 & 168)positioned proximate to said marker for detecting said sectors of the marker and, being angularly spaced from each other to provide at least three sequential signals indicative of the incremental passage of a pole through an angular segment corresponding to said angular spacing, each sensor providing a square wave output signal, each transition of which denotes the passage of one pole past that sensor, b) a multiplexer(30, 94, 170)for alternately selecting and passing therethrough output signals from a first or second group of said sensors, the first group including a succession of at least three equally angularly spaced sensors, and the second group including a similar succession of at least three equally angularly spaced sensors including the second and third sensor of said first group, whereby switching from the first to the second group enables the processing of square wave output signals indicative of a set of incremental positions of the rotor advanced in time over that provided by said first group to offset subsequent electrical time delays, c) a filter (32; 96)including at least three independent filter sections(34, 36, & 38; 98, 100 & 102), each filter section being coupled to process signals corresponding to a given sensor output passed through said multiplexer, and having a limited upper frequency cutoff to provide, in response thereto, time delayed motor control signals having an essentially sinusoidal waveform, d) a driver amplifier (40, 104)including at least three linear amplifier sections(42, 44, & 46, 106, 108, & 110), each of which is coupled to one of said filter sections for amplifying one of said motor control signals and is further coupled between a direct current power source (48) and a selected winding (14, 16 or 18) for sequentially energizing said windings to provide a succession of fields corresponding to the incremental passage of a pole through said angular segment, and e) a negative feedback path including at least three separate feedback loops (58, 60 & 62)between each of said linear amplifiers and an associated filter section for responding to the current supplied to each of said windings to thereby control the intensity of each of said motor control signals such as to maintain said supplied current at a relatively constant level, whereby improved control over motor speed is effected, the substantially sinusoidal drive through said linear amplifiers markedly reducing motor noise and incremental speed variations.