An LVDT-based self-actuating displacement transducer

A novel linear actuator with inherent sensing capabilities is developed from a linear variable differential transformer (LVDT). By superposition of dc currents upon high-frequency excitation signals, the coils of the LVDT are capable of exerting a push/pull force on the armature while retaining the original displacement-sensing function. LC resonant circuits and active bandpass filters are designed to effectively isolate the sensing signals from the dc energizing sources. Linearity and sensitivity of the device are largely preserved compared to the original LVDT. For actuation, it is found that the magnetic force on the armature can be maximized by energizing a specific combination of the three coils according to armature positions. A simple control algorithm is developed for closed-loop control. It is implemented with an 8-bit microcomputer. Real-time testing shows that rest-to-rest control can be achieved with positioning errors of 0.02–0.04 mm and settling time below 0.2 s.