Application of Shape Memory Alloys in Locking Devices

Abstract

Networked and automated locking systems are an easy to use and to administer solution for governmental and commercial use, especially in combination with advanced authentication technologies like RFID-based keys. Regardless of the advances of authentication technologies locking systems still use electric motor transmission units, which are controlled by an authentication and control unit. From an economic and an engineering point of view this approach has significant weaknesses. The main issue is the transformation of the rotational movement generated by the motor into a translational movement, which is necessary for locking applications. This leads to the implementation of a complex transmission and an inappropriate and inefficient mode of operation for the used electric motors, inflicting the reliability and increasing the overall cost as well as the required building space of the system. Consequently, there is a need to reduce the complexity and the cost of locking systems by optimizing the actuator and the mechanical components. An alternative approach for actuators is usable with Shape Memory Alloys (SMA) and the Shape Memory Effect. Components made from SMA can return after a deformation into a pre-trained shape under certain thermal and mechanical conditions. SMA-based components can provide mechanical work as well as high forces while returning to their previous shape. Common SMA-based actuators have the form wire and provide significant pull forces when activated thermally. So it becomes possible to replace conventional electric motors and the necessary transmission with SMA-based wire actuator. The article provides an overview of the requirements and restrictions for the application of SMA in locking systems, illustrating the issues of existing locking system designs and an approach to overcome their limitations with a system based on SMA. After a short introduction chapter two introduces SMA as an alternative approach for actuators. Chapter three focuses on the main issues of locking systems and explains the requirements for the development of new actuators for locking devices. Chapter 4 describes the conceptual development of an approach for a SMA-based locking system illustrating security issues. The article concludes with a summery and an outlook.