Design and Construction of A-3 Degree of Freedom Compliant Mechanism For Precision Motions

Abstract

In the new competitive environment, the necessity to produce devices that have more precision is emerging. Their construction must be economical and provide high quality. In this way, applications which need high precision in a range of micrometers or nanometers demand more research on different topics related to micro mechanism and micro electromechanical systems (MEMS). Compliant Mechanism is a topic which helps to meet requirements for high precision. In the case of devices for microhandling such as micropositioners, compliant mechanisms play an important role because these elements are able to provide movement in the range of 10-6 m. Also, the compliant mechanisms have some advantages that are appropriate for micropositioners. This thesis has such an objective: design and construct a 3 degree of Freedom micropositioner that uses flexure hinges to provide motion with a precision on the order of micrometers. For this objective, the first step was a literature review where the state of the art with respect to flexure elements, compliant mechanism and stages of movement was founded. With this state of the art set up, the proposed design of the micropositioner was defined with some features. Also, the flexure element was designed with respect to some requirements and considering simplex geometries that were not used by other designs. The flexure element was evaluated through an analytic model and a comparison was made with FEM simulations (CATIA). This comparison was made to check if results from FEM simulations are sound. On the other hand, the compliant mechanism was made with the main requirement to provide a relation of 10 to 1 in displacement of input with displacement of output. This design was evaluated with FEM simulations. These simulations were evaluated with respect to the number of elements and appropriate element type. Also, the results from FEM simulations work as a parameter of comparison against the results from experiments that were developed with the prototype of design and test bench developed in this research thesis. The prototype was made in Aluminium with wire EDM. The test bench incorporates a measure system and actuators. The measure system is made for load cells (strain gages) and actuators use Nitinol. The Nitinol actuator provides a continuous force and is an economical option. These actuators have advantage over other actuators that are used in compliant mechanism. For this reason, the Nitinol actuator is characterized in this research. Finally, the research concluded with the proposed design is innovative because it uses a new design of flexure elements. Also the flexural element geometry advantages are that is simple, more economical and robust. ITESM-Campus Monterrey vi The prototype of this design, has a resolution in the movement is 0.005 mm. the resolution can be decrease but the control of force is necessary. The Nitinol actuators provided the required displacement. Also, the main contribution with this actuators is that they provide a continuous force, which is an advantage over other actuators used with compliant mechanism. With the comparison between simulations and test results, a difference was found with has different sources as measurement system, control of force, tolerances in manufacturing process and tolerance in material properties. Some points as to develop to control for Nitinol actuators that consider the continuous force and temperature and to develop a measurement system that is be able to measure this movements are tasks for future research.