MEMS Optical Force Sensor Enhancement Via Compliant Mechanism

Abstract

Although there are capacitive surface micromachined force sensors with adequate resolution for cell manipulation and microneedle injections, it comes with the sacrifice of dynamic range and linearity. In contrast, optical based force sensors can provide the desired resolution and maintain relatively large sensing ranges compared to similar capacitive sensors. Plus, optical interferometry provides a sensing method that uncouples the conflicting design parameters, such as sensitivity and linearity. The current drawback to optical interferometry is the large off-chip equipment that is currently used in the operation of optical sensors. However, innovative techniques are being applied to surface micromachined microphones that allow off-chip components to be integrated onto the sensing chip. These same techniques can easily translate to the force sensor presented in this research, due to the similarities in the sensing methods. The thrust of this work is to explore a mechanism approach for enhancing the performance of a surface micromachined optical force sensor. A new design is presented which introduces a special mechanism, known as the Robert’s mechanism, as an alternate means in which the device is structurally supported. The new design’s implementation is achievable using an equivalent compliant mechanism. Initially, an analytical set of pseudo-rigid-body-model equations were developed to model the compliant design. A more accurate model was then constructed using FEA methods. The geometric parameters of the compliant Robert’s mechanism were then optimized to obtain a sensor with improved linearity and sensitivity. Overall, the force sensor provides higher sensitivity, larger dynamic range and higher linearity compared to a similar optical force sensor that uses a simple structural supporting scheme. In summary, this paper demonstrates the effectiveness of using a mechanism approach for enhancing the performance of MEMS sensors. The expected impact is to improve biomedical experiments and help further advance research that can improve quality of life.

Accuracy Assessment of Pseudo-Rigid-Body Model for Dynamic Analysis of Compliant Mechanisms

“…This characteristics offer compliant mechanisms prominent advantages, such as simple/compact structure, high precision, low friction, reduced assembly, and manufacturability [1]. Compliant mechanisms are widely used in high-precision instrumentation, harsh environments, aerospace, and micro-electromechanical systems [2][3][4][5][6][7]. In recent year, many researchers studied the configuration design and optimization, and kinetostatic (kinematic and static) analysis of compliant mechanisms [8][9][10][11][12].…”

Development of a novel uniaxial force sensor with two-stage force resolutions

“…In addition, Zhao et al [5] designed a three-axial micro-force sensor based on piezoresistive effect. Roman et al [9] developed a MEMS optical force sensor using a compliant Roberts mechanism for micromanipulation. Other techniques such as smart materials and flexible circuitry have also been used in the design of force sensors [10,11].…”