ANALYSIS OF AN AUTO-WINDING SYSTEM WITH THE PAWL-LEVER MECHANISM

ABSTRACT

Human body contains rich chemical energy, part of which up to 200W can be converted to mechanical energy when walking; thus it is an ideal sustainable energy resource for portable electronic devices. The auto-winding system of mechanical watch movement is one of the most successful devices to harvest energy from human body motion. For effective utilization of this available energy, the auto-winding system with a pawl-lever mechanism is studied. First, kinematic model is considered, which consists of a double pendulum, a four bar mechanism and a reduction gear train. Next, simulation results are studied to evaluate its performance. Finally, based on this, a new device for energy harvesting is proposed which can be adapted for charging electronic devices, such as mobile phone, GPS receiver etc.
 With increasing concerns about environment, energy harvesting has become a hot R&D topic. For mobile electronic devices, such as mobile phones, MP3 players and GPS receivers, because it uses only small amount of power and does not require continuous operation, it is ideal to use renewable energy. Based on the literatures, there have been a number of ways to extract energy from the environment, such as heat, vibration, light, pressure, movement, etc. Among these methods, the auto-winding system built for mechanical watch movement is one of the most effective devices.

Tracing back to 1770, the auto-winding watches made their first debut in the world. The invention was attributed to a Swiss watchmaker, Abraham-Louis Perrelet, whose core idea of invention was to collect energy through the wearer’s arm movements. When the wearer swings his arm, the oscillating weight of the auto-winding system worn on his wrist will rotate and drive a gear train to wind the mainspring, which is energy resource of the mechanical watch movement. Throughout the years various designs have been developed to address different aspects of improvement, such as using different types of oscillating weight, winding the main spring in both directions, etc. For the mechanisms winding the mainspring in both directions, what distinguishes them from each other is the design of the mechanical device named ‘‘reverser’’. It is embedded between the oscillating weight and the reduction gear train so as to enable the auto-winding mechanism winding the mainspring no matter which direction the oscillating weight rotates. The most common type of the reversers includes the cam mechanism with toothed wheels, which gear alternately and the pawl-lever mechanism, with a wheel and pinion coupling. This study focuses on the second type. It shall be mentioned although the mechanism has been used for some years, few have studied its dynamics and efficiency, which is the objective in this study.

Keywords: Pawl Lever Mechanism, Four bar Mechanism, Kinematic Analysis