Piezoelectric Inertia-Friction Actuator With Thermal Effect:Design, Modeling And Control

Piezoelectric inertia-friction actuator (PIFA) is a hybrid actuator which combines the piezoelectric driving principle and inertia-friction driving principle. It has many good characteristics, such as the long motion range (theoretically unlimited), the high resolution(several nanometers), and the simple structure. Thus, it has many advantages in the field of the macro-range and nano-resolution actuator (MRNS) technology.PIFA is in fact a step movementsystem, which consists of the forward motion and backward motion and one is longer than the other in one period of motion, resulting in a net step motion (i.e., either the forward motion minus the backwad motion or the backward motion minus the forward motion).In PIFA, one direction of movement is called "stick" movement, and the the opposite direction of movement is called "slip" movement. A step motion is in fact with the slip movement minus the stick movement. Such a kind of the step movement behavior is achievedby a carefully configured system to make use of the friction and inertia properties of the components in the PIFA.Particularly, in the stick movement, the friction is desired to be as large as possible (on the other hand, the inertia is expected to be as small as possible), while in the slip movement, the friction is desired to be as small as possible (on the other hand, the inertia is expected to be as large as possible). In fact, the PIFA is very volunerable to disturbances (with the robustness concept) and to changes in the system structure (with the resilience concept) due to the conflicting roles with the friction. At this point, it is worth to mention that the friction existed in any two contact objects is highlysensitive and uncertain, whichis a fundamental reason to be responsisble for the behavior of PIFA. Therefore, to a PIFA system, its behaviorincludes not only the conventional one such as positioning or trajectory tracking, stability and robustness but also the output integrity and resiliene.The MRNS technology has some unique applications, e.g., micro-chips assembly, high energy beam positioning control, less intrusive medical technology, industrial pipe inspection. PIFA is an important principle for the MRNS tehnology. However, knowledge about the PIFA, especiallycontrolof PIFA system, is still not enough. The overall objective of this thesis was to advance our understanding of PIFA and to develop a more effective control technology for PIFA. Specific works are performed.First, a comprehensive analysis of the existingpiezoelectric inertial-friction actuatorswas made.The two kinds of piezoelectric inertial-friction actuatorsare generalized into one general driving principle (namely inertia-friction).The general principles can cover allthe existing piezoelectric inertial-friction actuator principles. It provides a theoretical guidance to design and optimization of piezoelectric inertial-friction actuators.Second, all theconventional piezoelectric inertial-friction actuatorswere compared from the aspects of mechanical design, system modeling, controller design under the framework of the above-mentioned general principle. The main issues of the developmentof piezoelectric inertial-friction actuators were identified. The first issue is regarding the design of PIFA. The current piezoelectric inertial-friction actuatorsare without consideration of the measurement and adjustment of temperature and pressure onthe friction surfaceas well as the material of the interface.The second issue is regarding modeling of PIFA. There is no model that considers all the factors that affect the performance ofpiezoelectric inertial-friction actuators, particularly in the modeling of friction.Due to the level of development of the theory of friction, the modeling of friction in piezoelectric inertial-friction actuatorsis stilla difficulty. The third issue is regarding control of PIFA. Knowledge regarding the control of piezoelectric inertial-friction actuatorsis very limited, and the current state of arts is at the level of open-loop control or a simple PID feedback control.Third, apiezoelectric inertial-friction actuator system with the optimum physical properties was designed and constructed, particularly including the system that allows for adjusting the pressure on the frictional interface and the measurement system for temperaturerise on the interface. The positioning accuracy, the driving speed and driving range of thedevelopedsystem are much better than the existing piezoelectric inertial-friction actuator systems. The significane of the developed system is that it provides evidence that the temperature rise on the interface of thematerial is an important problem to the system, and a careful deisgn and control of the system can however overcome the problem.Fourth, a comparehensive model was built, which integrate various models that account for the factors such as the piezoelectric actuator hysteresis nonlinearity, the dynamics of the driving object and piezoelectric actuator, friction-induced temperature rise and thus change in friction force. The experiment was carried out to show the improved accuracy of the model.Fifth, a control scheme was designed for piezoelectric inertial-friction actuators. Based on the characteristics of piezoelectric inertia-friction drive principle, the driving process was divided into step mode and fine mode. Different controllers were designed for different modes. The experiment was conducted to show:(1) the step mode controller significantly improves the driving speed; and (2) the fine mode controllerimproves theoverall positioning accuracy and positioning speed by thecombination of the feedforward control and the feedback control.Sixth, the concept of the resilience of the PIFA system was studied. The friction-induced temperature rise changes the friction force and then causes failures of the system. To overcome this failure during the operation and after operation, the conventional control strateggy cannot achieve. Two control strategies was proposed to overcome this system failure and to improve the resilience of the PIFA system. The experimentwas conducted to show the effectiveness of these two control strategies.