The motion subsystem provides motion to the interferometer's moving mirror, which then creates the interferogram. In this context, the components involved are (1) the actuator, (2) the coupling mechanism (bearing assembly), (3) the position sensor and associated electronics, and (4) the motion controller.
In today's FT spectrometers, the motion systems use feedback control (sometimes called servo control or close-loop feedback control) to regulate the position of the moving mirror. A feedback-controlled interferometric system contains one or more sensors that measure the actual position of the moving mirror at all times, and then performs corrections in real time so that the actual mirror trajectory matches the intended trajectory. A well-designed feedback-control system is insensitive to external disturbances. Figure 5.1 shows a generic architecture of a feedback-control motion system using a digital motion controller.
In this chapter, the types and the design aspects of some of the actuators, bearings, sensors, and motion controllers that are appropriate for use in FT spectrometers are discussed.
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