Design and 3D printing of compliant mechanisms

• Main Author: Pham, Minh Tuan
• Other Authors: Yeo Song Huat
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Mechanical engineering::Mechanics and dynamics; DRNTU::Engineering::Mechanical engineering::Kinematics and dynamics of machinery; DRNTU::Engineering::Mechanical engineering::Machine design and construction; DRNTU::Engineering::Mechanical engineering::Prototyping
• Online Access: https://hdl.handle.net/10356/82990; http://hdl.handle.net/10220/47565
• Institution: Nanyang Technological University

Compliant mechanism has been a popular solution for developing precision motion systems. The working principle of compliant mechanism is based on elastic deformation of flexure elements, capable of providing highly repeatable motions that conventional bearing-based counterparts fail to deliver. In positioning applications, compliant parallel mechanism (CPM) is preferred because its closed-form architecture has high payload allowance and can better reject external mechanical disturbances. However, the performance of CPMs is often constrained by the limitations of synthesis techniques and fabrication methods. At present, it is still a challenge to synthesize multiple degrees-of-freedom (DOF) CPMs with spatial motions, optimized stiffness and dynamic properties. In addition, using conventional machining methods to fabricate the structure of CPMs by sub-parts will incur assembly errors. To address the limitations, this research focuses on the development of a new synthesis method for multi-DOF CPMs and the investigation on the mechanical characteristics of CPMs that are monolithically fabricated by 3D printing technology. A novel beam-based structural optimization method is proposed to synthesize CPMs with multi-DOF, optimized stiffness and desired dynamic properties. A well-defined objective function for the optimization process is also presented where the different units of components within the stiffness matrix of CPMs are normalized. It is shown that the desired motions of CPMs can be obtained by determining specific geometries of the curved-and-twisted beams. The effectiveness of the beam-based method is demonstrated by synthesizing a 3-DOF spatial-motion (θX – θY – Z) CPM with high stiffness ratios of more than 200 for rotations and 4000 for translations, a large workspace of 8° × 8° × 5.5 mm and a targeted dynamic response of 100 Hz. A monolithic prototype of the synthesized CPM is fabricated by electron beam melting (EBM) technology and the characteristics of the 3D-printed CPM are experimentally investigated. By introducing a coefficient factor to compensate the difference between the designed thickness and effective thickness, the mechanical properties of 3D-printed CPMs can be well predicted. Experimental results show that EBM technology can be used to fabricate compliant devices for high-precision positioning systems. CPMs with motion-decoupling capability are desirable to eliminate parasitic motions. Several design criteria are analytically derived for synthesizing 3-legged CPMs with any DOF and fully-decoupled motions. A design of 3-DOF (θX – θY – Z) CPM with decoupled output motions is presented and experimentally evaluated. A new CPM with 6-DOF is also synthesized to demonstrate the versatility of the beam-based method and the decoupled-motion criteria. Experimental investigations show that the EBM-printed prototype of the 6-DOF CPM has motion-decoupling capability and is able to produce a large workspace of more than 6 mm in translations and 12° in rotations. It is envisaged that results of this research can help engineers to develop a variety of high-precision machines with optimal performances.