Voice-coil actuators are electromagnetic devices which produce accurately controllable forces over a limited stroke with a single coil or phase. They are also often called linear actuators, a name also used for other types of motors. A related form is the swing-arm actuator, which is used to rotate a load through a limited angle (usually 30 degrees or less). These devices are capable of extremely high accelerations (more than 20 times gravitational acceleration, or "g"), and great positioning accuracy when suitably controlled (one-millionth of an inch or better). A properly designed device may have a settling time (the time required for structural vibration to settle down to below the measurement threshold after a high acceleration move) of two milliseconds or less. The major use of this type of actuator is in computer peripheral disk drives. They are also used in shaker tables, lens focusing, medical equipment, laser cutting tools and elsewhere.
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