Motion System Design

Lights, switches, action

Electromagnetic motors have one thing in common: They're all driven by magnetic fields. How the fields are produced and how they couple the rotor and stator is limited only by the imagination of the designer, which is where the story begins for a novel motor developed by engineers at DynaMotors Inc., Cleveland, Ohio.

The new motor consists of a wound stator and a slotted armature (rotor) wrapped with multiple coils. Energizing the stator induces voltage in the armature coils that's subsequently employed to create a reactive magnetic field. How the induced voltage is converted to magnetic flux is what sets the motor apart.

Embedded in the armature coils are current-control switches. When actuated, the switches short the coils, creating a low-resistance path that allows the flux-producing current to flow. The resulting field repels that of the stator, thus generating torque.

According to the motor's developers, the switches are photoelectric devices that turn on and off in response to light. Light-emitting diodes (LEDs) incorporated in the motor's end-bell provide the actuation signals. By manipulating magnetic interactions, the optical switching technique controls torque right where it's produced.

One advantage of the new design is that it's inherently noise-free. Even at high speeds, the armature fields switch at a relatively low frequency. This reduces line, EMI, and RFI noise by up to 99% compared to high-frequency PWM, the control method typically used in most adjustable-speed drives. It also eliminates the need for filters, isolation transformers, special cables, and grounding brushes, and extends the life of bearings and electrical insulation.

Another advantage is the amount of torque the motors produce at low speeds. Their speed-torque curves are, in fact, similar to those of dc or universal motors, characterized by high torque that increases with diminishing speed. In many cases, the motors can simplify, if not eliminate, mechanical drives. They can also run in torque mode, producing a set torque regardless of speed.

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