Rather than a commutator, the patented DynaMotorô electronic brushless repulsion (EBR) motor uses controlling electronic switches on a circuit board on the rotor shaft that turns with the armature. Photo detectors, located on the rotating board that move past infrared LEDs mounted on the stationary portion of the motor short circuit the switches to form a closed armature winding. The torque, speed, and direction of rotation depends on the duration of the light pulse triggering the switches and the angle of the armature winding to the stator magnetic field (established by direct ac excitation) at the time of the pulse.
The motor does not use rotation of a magnetic field to produce torque. Rather, the magnetic field induced in the armature has its poles offset from the field of the stator. This proximity of like poles in each field produces a repulsive torque.
According to General Manager Doug Toman, optical triggering, as opposed to magnetic radio frequency methods, is "cheap, simple, and reliable." Like a brushed dc motor, the Dynamotor produces high torque at low speeds but without the limited-life and contamination concerns of using brushes. While optical control coupling may raise concerns about "dirt deposits" affecting the optics, Toman notes that the infrared optics "can take a lot of typical industrial contamination."
Reliability is enhanced by attention to dynamically balancing the rotating circuitry, including component orientation, and use of adhesives to counter upwards of 10,000 Gs at the edge of the circuit board. Engineers incorporated speed feedback into the motor electronics so speed regulation is possible without an external encoder.
Spinning Electronics: This version of the DynaMotor mounts the rotating circuit board (with photo detectors to trigger the torque-controlling solid-state switches)outside the motor bearing for easy access in larger, more expensive versions. Low-cost consumer applications have the electronics within the motor
EBR noise generated is rather low compared to motors controlled by, for example, pulse width modulation. For instance with a switching frequency typically at 480 Hz for an EBR, the equivalent for pulse width modulation would be more than 10 kHz, inducing noise in proportionally shorter wire runs, says Toman.
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