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Micro/Nano Lithography

Using micro electromechanical systems for coded locks

A safety device contains metal counter-meshing gears that are directly driven by permanent-magnet micromotors.
6 July 2009, SPIE Newsroom. DOI: 10.1117/2.1200906.1689

Locks have been applied widely and for many years in high-consequence systems that are subject to catastrophic loss due to accidental or malevolent causes. Traditionally, they are fabricated using conventional machining practices.1 Our current research focuses on development of novel locking devices based on micro-electromechanical-system (MEMS) technology to achieve cost reduction and broaden application opportunities. For example, Sandia National Laboratories (USA) designed a surface-micromachining lock containing a polysilicon counter-meshing gears discriminator that is driven by a polysilicon electrostatic micro-engine. The discriminator is based on linear comb-drive actuators connected to the output gear through linkages. The lock is made of multilayered polysilicon films (layer thickness: 1–2.5μm), which results in low strength. A complex configuration, sliding friction, and dynamic problems also affect the device's performance.

Figure 1. Configuration of the micro-electromechanical-system (MEMS)-coded lock. (a) Cut-away view, (b) the two main assembly parts, and (c) explosion diagram.

Figure 2. A novel safety device based on MEMS technology.

We developed a novel lock based on a LiGA (x-ray lithography, electroplating, and molding)-like microtechnology where the metal counter-meshing gears discriminator is directly driven by axial-flux permanent-magnet micromotors.2 We also explored code-mechanical solidification and verification to transfer the lock's encoding to its mechanical structure.3 In our design, the number of parts is reduced, leading to increased reliability and cost reduction. The associated dynamic problems are also reduced.

Our MEMS-coded lock (see Figures 1 and (2)) consists of three parts, including drivers, the discriminator, and an energy-coupling element. It has a size of 24×18×13mm3 (length, width, height). Drivers are rotary actuators. They are used to drive the discriminator's mechanical mechanism, which functions as a coded locking device. The energy-coupling element allows energy or an information signal to pass the safety lock upon receiving the correct code. It can interpret a 24bit unlock code in 15ms. Resisting both high and low temperatures and strong vibrations, the lock has a simple configuration, high strength and reliability, a small number of dynamic problems, and low cost. These features make it suitable for use in traditional high-consequence systems and also broaden its applicability to other settings, such as radiation-therapy machines and special information and computerized security-authentication systems (see Figure 3).

The main differences between our system and conventional locks are twofold. First, the key is a physical code stored in the counter-meshing gears. Second, user passwords can be distinguished by the MEMS-coded lock. The overall system is composed of the MEMS-coded lock, a peripheral-component-interconnect (PCI) card with a printed circuit board (PCB), and software on a basic input/output system (BIOS) chip. In contrast to older versions of MEMS-coded locks, two reset micromotors and an optoelectronic coupler are included in the new lock. We are working on development of the PCI card's PCB, which drives the lock's four micromotors. Tests carried out on the prototype show that our MEMS-coded lock can effectively distinguish user passwords. We are developing applications of our MEMS-coded lock in hard-disk encryption/decryption systems, which we hope to achieve as our next milestone.

Figure 3. Computerized security-authentication system based on a MEMS-coded lock. PCI: Peripheral component interconnect. PCB: Printed circuit board. BIOS: Basic input/output system.

Weiping Zhang, Wenyuan Chen
National Key Laboratory of Nano/Micro Fabrication Technology
Key Laboratory for Thin Film and Microfabrication of the Ministry of Education
Institute of Micro and Nano Science and Technology
Shanghai Jiaotong University
Shanghai, China

Weiping Zhang is an associate professor. His research interests focus on MEMS.