A voice coil is an electromechanical actuator or motor of the same type as that used in a loudspeaker, where it has the task of vibrating the loudspeaker diaphragm. The voice coils we work with are, however, used in completely different applications. A voice coil consists of a copper coil wound onto a bobbin that is moved axially in a housing of soft magnetic material, often an iron core, with permanent magnets. This results in a simple and robust design providing high linearity (the force is proportional to the current through the coil) and backlash-free motion. A voltage across the motor terminals results in a movement in one direction and when the polarity is reversed, the motor moves in the opposite direction. Our voice coils are supplied in sizes ranging from a few millimetres in diameter up to around 10 cm and several hundred Newtons in force.
The linear design of the motor means that it is not possible to gear it as it is with a traditional rotary motor, and it is therefore not possible to increase its power by mechanical means. This type of motor is used in a variety of different applications, often in medical technology, and also of course in loudspeakers, which is where the name voice coil came from. In some applications where precise positioning is required, a voice coil is combined with some type of position feedback. These often consist of Hall-effect sensors or tape scale optical encoders. With the right feedback a precision manufactured voice coil can achieve a positioning precision of less than 1 µm.
Combined with a powerful motion controller, a voice coil can achieve an impressive performance in terms of acceleration, speed and precision in servo applications requiring short cycle times or highly precise movements.