A two-dimensional probability model for evaluating reliability of piezoelectric micro-actuators

In this paper, a probabilistic approach is presented for the evaluation of the reliability of piezoelectric micro-actuators that takes into account the effects of both driving voltage and temperature. Based on the relationships between the lifetime and degradation mechanism of piezoelectric actuators and the electric field strength, as well as the actuator working temperature, a two-dimensional probability model for evaluating reliability of piezoelectric micro-actuators is described. The concept of two-dimensional strength is proposed to incorporate the electric driving voltage and the working temperature of the piezoelectric actuators at a specified lifetime. The lifetime (number of cycles to failure) of piezoelectric actuator, electric load and temperature are considered as the random variables and their probability distributions are discussed. A two-dimensional strength probability distribution function is derived. A two-dimensional interference model between the two-dimensional strength and load is also used to derive the reliability expression. Using this approach, the relationship among the reliability, lifetime, driving voltage and temperature can be described analytically. The relationship between reliability and the lifetime of piezoelectric actuator can be obtained. A case study of a piezoelectric micro-actuator used for head positioning in a disk drive head positioning system demonstrates the application of the approach. It is shown that the two-dimensional probability model can be used for reliability evaluation and lifetime estimation of piezoelectric micro-actuators according to design requirements.