| Piezoelectric bimorphs are a special type of piezoelectric devices, and nowadays have been widely used as displacement transducers or actuators in precise submicron increments. Piezoelectric ceramics are effective actuation elements in numerous applications that require rapid response and/or ultra-high motion resolution. These applications include optical fiber alignment, mask alignment, scanning by a scanning electron microscope, high precision machining. These days engineering and scientist require high goal on precision of the actuators. Since most of the actuators are mechanical, they have many clearances and drive processes , the movement precision, precision positioning can't be achieved.Piezoelectric ceramics have advantages of high resolution, high stiffness, quick response, and so on. They have become the main modes on precision actuators these years. Piezoelectric materials have many superiority on precision actuate.2. The output characteristics of MPA The MPA (multilayer piezoelectric actuators) is spliced by bimorphs. The bimorphs are parallel connection on the electric and in series on the structure. So the MPA can output large displacement and power while needn't high voltage. And this piezoelectricity effect will be steady. Hysteresis is an input/output non-linearity with effects of non-local memory. That is, the output of the system depends not only on the instantaneous input but also on the history. The hysteresis curves of the Piezoelectric ceramics is asymmetrical namely the ascend and the descend contrail isn't the same. 3. The principle of the multifreedom precision linear stepping actuatorThe principle of the more freedom precision linear stepping actuator bring out from the animals creep on the ground. The moving process of the actuator is:First, MPA A stretches and holds the parallel trajectory when the voltage rises;Second, MPA B stretches when the voltage rises;Third, MPA C stretches and holds the parallel trajectory when the voltage rises;Fourth, MPA A losses from the parallel trajectory when the voltage falls;Fifth, the voltage falls and MPA B shortens. The voltage falls and MPA C shortens and losses from the parallel trajectory. So the actuator walks one step forward. The upper figure shows the actuator can walks back and forth in a line. If two or more such an actuator integrated, the actuator can drive on more freedoms. 4. The design of the power supply of the actuators The more freedom stepping actuators of piezoelectric ceramics is a precision driving mechanism. So the requires on the power supply of the actuators will be strict. The output voltage must be very smooth and the charge and discharge current also must be enough. The actuator need special wave to drive it. We elect the trapezium wave and its ascending edge is similar to the letter "S". The power can work alone or controlled by PC from RS232.The power supply of the actuators which is composed of MSC-51 single chip computer,DA converter,power supply,power amplifier,and communication part.The power supply of the actuator must be reliable, in order to make the actuators move in precision.5. The control of the actuators and the experiments Some papers have proposed the hysteresis model of piezoelectric ceramics, ferromagnetic materials and shape memory alloys. One approach to modeling hysteresis non-linearity, based upon the direct displacement feedback, PID in tradition is widely used. Another is to create a MAP to demarcate the actuators. Similarly, someone employ the Preisach model to compensate for the tracking error of piezoelectric actuators, and a model-based feed-forward compensator. The precision linear stepping actuator in the paper is hard to controlled by feedback because of the large travel, more freedoms. Here we create the MAP to demarcate because of sensor equipments. The precision actuator has a good performance proved by many experiments.Many institutes and graduate schools study piezoelectric actuator. The precisi...
|
PDF Full Text Request