 Galvo Motors are limited-rotation DC motors that drive mirrors for laser-beam steering or scanning applications. Controlled motion is achieved with an internal position detector, or PD. The PD enables closed loop servo control of the motor by providing a position signal proportional to the rotation of the motor shaft.
First generation of position detectors were “Capacitance PDs”. Motor rotation changed the capacitor’s value, which in turn, changed the output current of the PD. These devices were large and prone to thermal drift over time. Today’s scanner motor uses a light source, a modulator and a detector to produce a feedback signal. Called an “Optical PD”, it is far smaller and much less sensitive to thermal effects. The optical PD yields superior scanner motor performance and reliability.
Limited motor rotation results in other challenges, specifically ball bearing life. Conventional full rotation motors use bearings designed to circulate lubricant and are less prone to localized ware. Galvo Motors, on the other hand, suffered early bearing failure when conventional bearing assemblies were used. General Scanning’s motors utilize a hybrid bearing design with ceramic balls in metal races to provide the longest life possible.
Another scanner motor design offered by General Scanning is based on a metallic flexure bearing. In this design, flexures replace the ball bearings for virtually unlimited life as long as the motor is operated within its specified rotation range.
Lastly, for very high scanning frequencies, General Scanning offers a unique family of motors called resonant scanners. These scanners employ a torsion bar instead of bearings or flexures. The torsion bar, which includes the mirror and a counter-weight, is tuned to resonate at a specific frequency. Used primarily in scanning frequencies up to 20kHz these motors consume very little energy and provide infinite life. They also operate without transmitting vibrations to the rest of the system.
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General Scanning Galvo Motors |
