This paper presents a method to change the excitation frequency such that a piezoelectric actuator keeps the levitation height of a floating object suspended on a layer of air at its maximal possible height, despite changes to the system. An ultrasonic actuator capable of injecting ultrasonic vibrations to an air layer is being using as a demonstrator in this work. The high frequency oscillations and the compressibility of air generate an average pressure higher than the ambient one thus causing a flat object to float. Environmental changes and temperature effects render this system inefficient, unless the excitation frequency is constantly varied to maintain the best possible efficiency of energy transfer. An adaptive method with which an optimal excitation frequency is generated is shown to yields the best mechanical efficiency and it thus essential when the available input power is restricted. The proposed method uses a minimal amount of frequency dither to revive an identification process that is otherwise singular. With this identified model, the algorithm seeks the best momentary excitation frequency. The algorithm is validated in a simulation and on a dedicated experimental apparatus.
Traditionally, miniature scanning mirrors with which raster-scan displays are designed, oscillate sinusoidally while being operated in resonance. The operation in resonance gives rise to large vibration amplitudes under a small driving force/torque and can thus be realized in MEMS scale to oscillate at 15,000 per second and beyond. Unfortunately, sinusoidal scanning creates images with highly non-uniform intensity levels. It was therefore suggested to create a resonating mirror that performs a near triangular-wave periodic motion. Presented in this paper is a closed-form synthesis procedure with which a suitable multi degrees of freedom scanning mirror can be realized. It is shown that a special topology can be used to generate many periodic oscillatory motions under low operating forces. Specifically, a large scale electromagnetically driven system and a MEMS mirror have been designed and built to demonstrate the applicability of this approach. It is shown that the necessary excitation voltage, in the electrostatically driven MEMS mirror, can be reduced from over 1000 Volt into a more realistic 40 Volt range.
Laser interferometers are being used to measure a single linear degree of freedom reflecting the motion in a direction of a pointing laser beam. In a recent study, the need to measure both linear and angular transient behavior of a slowly sliding rigid mass has risen. For this purpose a special signal processing method, which is backed by a special hardware, was developed. An experimental system set- up to measure the motion of a mass connected to a cantilever beam sliding upon a rough surface will be described in this work. During sliding, the mass is subject to friction forces that give rise to stick-slip type of motion in the horizontal direction of motion and to vibration of the dragged mass in the vertical and angular directions. The basis of the proposed method is described and the relevant physical assumptions alongside with the mathematical procedure are provided.
This paper presents a method, which allows one to use a single point laser vibrometer as a continuous sensor measuring along a line or a 2D surface. The mathematical background of the curve-fitting procedure and the necessary signal processing allowing one to extract the amplitude of sinusoidal vibration are discussed. In the current work, use has been made with an ordinary laser interferometer equipped with galvanometer-based x,y mirrors. This system is not designed for continuous scanning therefore some effort needs to be spent in order to overcome the dynamical characteristics of this system. The potential of such an instrument, as demonstrated in this work, may encourage the development of mechanically better scanning devices.
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