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Sounding Out Moving Magnets

02 November 2012

The ElectroForce Systems Group of Bose Corporation provides materials testing equipment to research institutions, universities, medical device companies and engineering companies worldwide. It builds upon and transcends the company's 40-year history of audio innovation

Well before the formation of the ElectroForce Systems Group, Bose engineers had developed a specialised moving-magnet linear motor for an experimental loudspeaker. Bose patented that linear motor, recognising its potential in non-audio settings.

In 1999, Bose began supplying the linear motor and related components to EnduraTEC Systems Corporation, who saw how these elements could enhance their materials testing business.

Five years later, Bose acquired company assets related to the development, manufacture and sales of materials testing equipment. EnduraTEC became the ElectroForce Systems Group.

Applications in materials testing include the characterisation of engineering materials, soft tissue and biomaterials and durability simulation of medical devices. Moving-magnet motors have high frequency capabilities, which is especially useful for fatigue testing of components used in industrial and consumer applications.

Now that linear motors are becoming increasingly practical for general motion, with many being used for long strokes of a few metres or more, the core ElectroForce technology, where magnets move relative to a stationary coil set, is finding a niche, primarily because of its fast response, but also where efficient, clean, compact, and programmable linear motor technology is needed. Examples range from programmable fluid pumping to pressure control applications to active vibration isolation.

 

AREAS WHERE ELECTROFORCE IS COMPETITIVE

  • Controlled force is essential (high dynamic force up to 15,000 N)
  • Broad frequency (0.0001 to 300Hz), bandwidth (up to 300Hz) and velocity performance (High acceleration up to 150G) is critical
  • Precise position and force control with accurate waveform control
  • Power density is important
  • System durability and reliability is paramount
  • Quiet operation or a low noise level is desirable
  • Simple installation and setup is valued
  • Minimal infrastructure requirements are important
  • High efficiency (approximately 80% to 90%)
  • Clean and environmentally friendly design

The magnetic portion of a moving magnet motor is comprised of three basic elements: magnet, coils, and core. The magnet moves back and forth, while the coils and core remain stationary. The magnet is charged (magnetized) with two polarities. The coil-core stator assembly carries and modulates flux across the gap where the magnet resides. The two sections of core are connected to complete a magnetic path.


LM1 motor dimensions reference

MAGNETIC FLUX

The coils are wound and connected so that magnetic flux generated by the current in each coil adds constructively in the motor gap. This flux interacts with the flux generated by the magnet, causing the magnet to react with a force in one of two directions, depending on coil flux polarity.


The linear motors are available in several sizes and capacities, allowing scalability for a wide variety of applications. Bose can customise solutions for novel linear motion applications. With no wear surfaces or friction, ElectroForce motors have proven to be very reliable. They have been tested over billions of cycles, and can provide nearly infinite life for a variety of applications. To meet heavier requirements, some motors include high density neodymium-iron-boron (NdFeB) magnets, which also make the motor's moving portion very light, for high acceleration capabilities.

Key Points

  • Recognising its potential in non-audio settings, Bose patented a specialised moving-magnet linear motor originally developed for an experimental loudspeaker
  • Applications in materials testing include the characterisation of engineering materials, soft tissue and biomaterials and durability simulation of medical devices
  • The linear motors are available in several sizes and capacities, allowing scalability for a wide variety of applications

 
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