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Magnetic-slider linear drive targets general automation
Integral-magnetic encoder cuts costs, no moving cables improve reliability
By John Lewis -- Design News, May 3, 1998
Hauppauge, NY--Direct-drive motion control typically uses ball screws or belt drives. Although linear motors are expanding into this scene, higher installed costs, reliability issues, and the complexity of installation, have limited their use in general-automation applications.
Challenging conventional thinking, Anorad engineers inverted the traditional moving-coil design. The result: Lightning MM-NS (moving magnet no steel) puts the magnets in the slider, and moves them over a stationary coil. This approach has many advantages over conventional moving-coil motors, including:
- Integral encoder simplifies assembly.
- No exposed magnets for safer operation.
- Fewer magnets lower cost.
- No moving cables improve reliability.
- Larger coil surface for cool operation.
- Better heat dissipation for greater force output/area.
Lightning delivers greater accuracy, speed, and acceleration for about the cost of a ball screw or belt drive, and is as easy to install. Typically, when designers install an off-the-shelf motor, they add an encoder and bearing structure to guide the coil over the magnets. "This motor is 'plug and play.' When we ship one of these, we don't have to ship an engineer along with it. It's as easy to use as a ball screw or belt drive, but it delivers much better performance," says Director of Linear Motors Business Development Boaz Eidelberg.
For safer operation and lower costs, Lightning's design uses fewer magnets than moving-coil motors. Traditional moving-coil motors drive the coil over a long magnet track. Lightning has no exposed magnets, so ferrous material won't collect on the long track.
"Magnets are a sizable chunk of total motor cost," says Eidelberg. "Most of the time, magnets sit there unused, waiting for the coil to glide over. At any given instant, only a small portion is actually being used. It just makes sense to put them in the slider. Fewer magnets reduce cost, eliminate ferrous material attraction, and more fully utilize the magnets." The tradeoff with this design is that the coil must be as long as the axis stroke. Eidelberg says Lightning's coils are relatively inexpensive to produce in volume on automated-winding machines.
Lightning's integral-magnetic encoder, not only simplifies assembly, but it cuts costs even more. "Some linear scales can cost up to $1,000/m," says Eidelberg. The magnetic encoder eliminates the need for expensive scales, and reduces setup time because engineers don't have to mount reader head and scale units. "While moving cables fatigue and fail after a certain number of cycles, Lightning's stationary cables are not subject to fatigue," says Eidelberg.
Engineers typically must increase overall cycle time to provide adequate dwell time for the coil to cool down in conventional linear motors. In contrast, Lightning's stationary coil is larger and cools faster. A switching circuit, built into the stage, only energizes the coils directly below the magnets. "That means you get more force from the same size motor," says Eidelberg. Although the peak force output would be the same, continuous output is greater. In addition, a stationary coil is much simpler to force cool--extending continuous output even higher. That means even higher continuous currents won't burn out the coil.
Applications include material handling, pick and place, winding machines, flying shear, metrology, and dispensing. Stainless-steel construction is available for pharmaceutical and food and beverage applications.
Additional details...Contact Tom Schmidt, Anorad, 110 Oser Ave., Hauppauge, NY 11788; (516) 231-1995.
Other Applications
- Material handling
- Pick and place
- Winding and flying-shear machines
