When speed, accuracy, acceleration, and reliability in motion-control applications simply cannot be compromised, direct-drive linear motors promise a solid solution regardless of cost or installation complexity. Linear motors provide fractional micron repeatability in semiconductor production, and enable machine tools to maintain minimum curve radii with positional accuracy that is within three to five microns. No alternative positioning mechanism can equal high-performance linear motors in applications requiring a high degree of precision. Table 1 provides

Given the high levels of performance from linear motors, it may come as a surprise that they are not applied more universally in motion-control and positioning applications. But there are several barriers to be overcome before linear motors are more widely adopted. For one thing, cost is a limiting factor for some applications. For mainstream positioning applications, the cost of linear motors has been a principal barrier to widespread use. Although linear motors dispense with the rotary-to-linear conversion hardware of ballscrews and belt drives—which accounts for their superior bandwidth—the expense of their permanent magnets offsets this cost advantage. Worse, the linear motor requires an external linear encoder to provide position feedback.

A high-resolution encoder can cost almost as much as the motor itself.

Linear motors also involve a certain degree of installation complexity. Most positioning applications have required Industrial equipment to be built from the ground up to accommodate the linear motor. A further integration barrier to widespread linear motor adoption is cooling. The magnetic coils of U-channel linear motors travel inside the U-shaped permanent magnet assembly, with the potential for building up heat within the assembly that must be effectively removed. In addition, linear motors are not naturally suited to vertical applications, and few effective electromechanical brakes have been available to aid positional control of the motor. In some linear motor designs magnetic attraction between coil assembly and magnets creates forces that oppose motor travel.
Source: read the complete article at http://www.roboticsworld.com/feature.asp

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	Creative Projects with LEGO Mindstorms by Benjamin Erwin Buy new: $20.64 / Used from: $13.00 A good place to start, especially for kids, with Lego Mindstorms
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