An automatic feeding system with a linear piezoelectric actuator, driving circuit and position sensors

To smoothly drive an electron microscope sampling container, we designed a novel stage that includes a piezoelectric actuator to achieve an automatic feeding system for microfluidic sampling processes, utilizing capillary action. The capacitive sensor measures the capacitance value that is used to identify the distance between the sample container and microfluidic samples; according to this value, the microcontroller adjusts the velocity of the piezoelectric actuator through pulse-width modulation and the microstepping motion is realized. We developed the automatic feeding system from this concept by using a linear piezoelectric actuator, a driving circuit, and a position-sensing integrated circuit. When the driving signal was at 100% duty ratio, the velocity of the sampling container achieved to 72 mm/s. To slowly approach liquid sample, driving the actuator at 5% duty cycle, the microstepping resolution was 1 µm. Moreover, a driving circuit for the piezoelectric actuator involving a phase-locked loop was developed to automatically track the resonance frequency of the piezoelectric actuator.