Vibration control system on the test unit Shaker for testing and calibration of High-G MEMS.

The great technological evolution on the MEMS field, with the growth of their complexity into a smaller dimensions, comes alongside the development of more sophisticated and precise testing and calibration techniques to ensure the functionalities of these devices. Reliability of the MEMS devices is now-days essential in all the engineering fields, from automotive to aeronautical, space and medical one. SPEA is an Italian industry world leader in testing and calibration of MEMS devices. SPEA has developed an automatic machine, called Shaker, able to test and calibrate high-g MEMS accelerometers through three-axes simultaneous excitation tests characterized by the generation of sinusoidal acceleration stimuli at high amplitudes and high frequencies. An important feature of the Shaker is its ability to produce a precise and clean sinusoidal stimulus using four linear three-phase induction motors . The cleaner the stimulus is, the better is the test and the calibration carried on the MEMS accelerometers. Parameter used to quantify the quality of the generated stimulus is the total harmonic distortion, better known as THD. Originally, the Shaker had to be able to produce an acceleration sinusoidal stimulus at 40g of amplitude and frequency of 120 Hz while maintaining the THD values lower than 1.5% in all the three axes-directions of the machine. With the current set-up, the machine is not able to achieve these requirements, therefore, performance limitations have been accepted and the acceleration amplitude has been lowered to 28g and the frequency to 90 Hz. The purpose of the thesis is to bring the system to the original performance requirements. The thesis has been entirely developed in SPEA. The work starts with the assembly of the system, and then with the characterization in amplitude and frequency of the current Shaker set-up in order to analyse its maximum performance and its limitations. Then, it goes on with the modification of the motor set-up changing the motor drives from 400 VDC to 600 VDC type. Parameterization of the PID controllers is the core of the thesis. Relations on the PID parameters tuning with its effect on the THD values are searched for, hypothesized and demonstrated. Once an optimal control has been found, numerous experimental tests have been conducted on the new system set-up in order to obtain a proper system stability, great system strength and THD values always lower than 1.5% when an acceleration stimulus of 40g of amplitude and frequency of 120 Hz is applied for long machine working time. Great effort has been reserved to find causes and give answers on particular phenomena that occur on the THD and affect its values during the performed tests. On the basis of the hypothesis done, further modifications and improvements have been adopted to the system. Characterization in amplitude and frequency has been done also for the new system set-up in order to compere it with the old one. Finally, a simulation of an entire test cycle has been conducted showing the real possibility to obtain a Shaker able to produce a sinusoidal acceleration stimulus with 40g of amplitude and frequency of 120 Hz with THD values always lower than 1.5% in all the three axes directions of the machine.