11. Lifetime and Reliability – of Piezo Actuators
When considering the lifetime of piezo elements two factors must be considered:
1. Working under dynamic conditions
2. Lifetime of stages with solid state hinges
11.1 Working Under Dynamic Conditions
Working under static conditions, an electric break can occur because of the migration of the electrode material into the ceramic layers. The reason may be high humidity and a constant electric field under high voltage. Working dynamically the reliability is much higher. A changing electric field converts the direction of the electrodes, migration is much less than under static conditions. There is no formula describing reliability under dynamic conditions because of the large number of technical parameters.
Piezoelements of piezosystem jena have been used for over 24 years in many different applications in research and development as well as in many industrial applications. Year after year many thousands of new actuators are delivered to many customers. Proper handling during the construction of piezoelectric stages and working together with our costumers ensures a long term reliability of our products without any significant failure rates.
11.2. Lifetime of Stages with Solid State Hinges
Piezo elements consisting of a piezo stack integrated into a metal stage with solid state hinges are stable over a long period of time, if designed properly. The solid state hinges result in a lever transmission of the motion of the stack, which is amplified several times. If care is taken that the bending always keeps in its elastic range, a long lifetime exceeding billions of (109) of cycles can be guaranteed.
Because of our many years of experience, we know how to develop stages with a long and reliable lifetime. When operating piezoelements avoid excitation in the range of the resonant frequency of the stage. When this resonant frequency is excited, ringing and overshooting can lead to oscillations much higher than the resonant frequency, finally leading to a break of the solid state hinges.
Most failures of piezo elements occur because of improper mechanical handling and use of the elements. For proper handling and use please see also section 2.