Penn Engineering & Manufacturing Corp.

Howard F Hendricks

Richard C Green

Frank S Nolt

Charles A Pittman, Iii

A brushless DC motor includes a rotor having an iron core affixed to a motor shaft. Permanent magnets are affixed to the core and separated by aluminum inserts which are keyed to the core. An annular groove in one end of the rotor core is dimensioned so that its outer diameter coincides with the inner tips of the aluminum inserts. The inner diameter of the groove and its depth provide only minimal clearance around commutation transistors which occupy the space within the groove. The commutation transistors are affixed and electrically connected to a circuit board which, in turn, is secured to the motor body by attachment to a removable motor end plate. With this structure, the commutation transistors are surrounded on three sides by the rotor and are triggered by its drive magnets. This structure permits the commutation transistor to be triggered by a strong magnetic flux which is more accurately directed through the transistor at its switch plane.

Inner-rotor commutation device

12-step motor commutation is provided by a three-phase sinusoidal signal generator and related circuitry. Circuitry which compares the voltage outputs of two primary signals provides two additional switching points for every 360 electrical degrees. Three comparator circuits provide six additional switching points. Primary voltage outputs are weighted in the ratio of 2:1 prior to comparison.

Sinusoidal signal decoder for 12-step motor commutation

A 12-step commutation in a brushless DC motor is achieved by six shaft-mounted commutation sensors and circuitry which permits inexpensive shaft-angle decoding for coil excitation. The commutation signal devices are Hall sensors arranged in two sets. A first set is arranged to produce the desired switching signals every 120 electrical degrees; a second set of three Hall sensors is similarly arranged equally spaced between the electrical switch points of the first set, however, the second set of sensors is wired together through the process of EXCLUSIVE-ORing to form a single, fourth output. Thus, the six Hall sensors are configured to produce four output signals which may be inexpensively decoded using a standard 32.times.8 PROM. A further refinement includes current modulation to the field coils in order to equalize the torque output of alternate steps. In one embodiment, this is accomplished by reducing the gain of the motor's servo amplifier so that the desired current shift is achieved by changes in the motor's load impedance.

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Schwenksville, PA, United States of America

Howard F Hendricks