Ortho-planar Spring Research Articles

Study of an eletrostatically actuated torsional micromirror with compliant planar springs

This paper presents modelling, fabrication and testing of a torsional micromirror suspended by two compliant ortho-planar springs attached at the sides. The proposed cantilevered serpentine spring is a single-chain frame, composed of nine beam segments to form a serpentine together with an initial segment and a final segment. Castigliano theory is used to formulate the spring constants under certain loads. Two equivalent spring constants for the micromirror are obtained according to structure analysis. The 2-DOF model for torsion and bending of the micromirror is presented. Finite element analysis (FEA) of the coupled domain of the structure is performed to verify the analytical results. Further validation of the prediction is carried out through static testing of a fabricated micromirror using a PSD (position sensing detector) sensor based experimental set-up. Due to relative compliancy of the dominant torsion mode, the fabricated micromirror is actuated to some angle at a lower voltage. The comparison between FEA and analytical results shows good agreement, demonstrating the accuracy prediction by the derived model. Small deviation from experiments is expected due to the nonlinear nature of electrostatic field.

Mechanical Design of Compliant Microsystems—A Perspective and Prospects

The field of microsystems, or microelectromechanical systems (MEMS) as it is popularly known, is a truly multidisciplinary area of research. It combines a wide variety of physical, chemical, and biological phenomena into an integrated system on a chip. This unprecedented integration naturally calls for new systems design approaches as well as efficient ways to analyze a single system or a component that is governed by many types of partial and ordinary differential equations from different physical and chemical domains. The key component of almost all MEMS devices, with the exception of microfluidic systems, is a movable mechanical structure of micron dimensions. Since the early works in this area dating back to the late sixties of the 20th Century, simple mechanical structures such as beams and diaphragms have dominated MEMS. Thus, the mechanical design in MEMS is mainly concerned with the design of such elastically deforming structures subjected to a variety of forces ranging from electrostatic, thermal, magnetic, piezoelectric, radiation pressure, etc. In addition to these unconventional forces and the accompanying complex equations that govern them, micromachining brings additional difficulties in microsystem design.

A polymeric piezoelectric micropump based on lamination technology

This paper presents the first micropumps assembled using polymeric lamination technology. Each pump consists of two 100 µm thick, 10 mm diameter SU-8 discs; two 1.5 mm thick, 15 mm diameter polymethylmethacrylate (PMMA) discs; and one piezo disc. The SU-8 parts were fabricated by a two-mask polymeric surface micromachining process with silicon as the sacrificial material. Each SU-8 disc has one micro check valve. The valve is a 1 mm plate suspended on a compliant orthoplanar spring. The cross section of the spring beam has a dimension of 100 µm × 100 µm. The PMMA parts were machined from an extrusion PMMA sheet by CO2 laser. An off-the-shelf piezo bimorph disc worked as both actuator and pump membrane. The pump was assembled using adhesive bonding. The adhesive tapes were cut by the same laser system. Alignment pins were used in the assembly process. With a drive voltage of ±150 V the fabricated micropumps have been able to provide flow rates up to 2.9 ml min−1 and back pressures up to 1.6 m of water. The pump design and the polymeric technologies prove the feasibility of making more complex microfluidic systems based on the presented lamination approach.

A fully polymeric micropump with piezoelectric actuator

This paper presents a new concept of designing and fabricating polymeric micropumps. The micro pump is made of SU-8 photoresist and polymethylmethacrylate (PMMA). The key elements of the micropump are the micro check valves, which are fabricated in a 100-μm-thick SU-8 film. The SU-8 part is designed as a disc with 10-mm diameter. The check valves are 1-mm discs suspended on a compliant orthoplanar spring with four arms. The cross section of the spring beam has a dimension of 100 μm×100 μm. The pump is designed as a stack of different layers, which are made of PMMA and SU-8. In contrast to their silicon counterparts, the low spring constant of the SU-8 check valves allows the use of relatively low drive voltages on the order of several 10 V for the piezodisc, which works as the pump’s actuator. Pump rates up to 1 ml/min and back pressures up to 200 mm water have been achieved. The pump design shows the feasibility of our current effort to make microfluidic systems based on the lamination of different polymeric materials.

POLYMERIC STACK-ASSEMBLED MICROPUMP WITH SU-8 CHECK VALVES

This paper presents a new concept of designing and fabricating polymeric micropumps. The micropump is made of SU-8 photoresist and polymethylmethacrylate (PMMA). The key elements of the micropump are the micro check valves, which are fabricated in a 100-μm-thick SU-8 film. The SU-8 part is designed as a disc with 10-mm diameter. The check valves are 1-mm discs suspended on a compliant orthoplanar spring with 4 arms. The cross section of the spring beam has a dimension of 100 μm × 100 μm. The pump is designed as a stack of different layers, which are made of PMMA and SU-8. The low spring constant of the SU-8 check valves allows the use of relatively low drive voltages on the order of several 10 volts for the piezodisc, which works as the pump's actuator. Pump rates up to 1 ml/min and back pressures up to 200 mm water have been achieved. The pump design shows the feasibility of our current effort to make microfluidic systems based on the lamination of different polymeric materials.

Ortho-planar linear-motion springs

This paper presents an ortho-planar spring design that operates by raising or lowering its platform relative to the base with no rotation. The compact nature of the design, and its non-rotating motion, eliminates the problem of rotation against adjoining surfaces and is less sensitive to variation in assemblies than many current compact springs. Nomenclature is presented to identify different configurations, mathematical equations are provided that accurately model the force–deflection relationships, and a pneumatic valve positioner application is demonstrated.