Structural analysis of traditional Chinese blocked-keyhole padlocks

The use of locks has a history of thousands of years. Barbed-spring padlocks are the typical locks used in ancient China and can be divided into three main types, namely open-keyhole, hidden-keyhole, and blocked-keyhole padlocks. Since the mechanical structures of padlocks differ in terms of the opening process, they are reconfigurable mechanisms. With the combinations and changes of springs, keys, and keyholes, the padlocks have a variety of different unlocking methods which provide higher security. This work uses variable chains to analyze the structures of the blocked-keyhole padlocks. The representations of joints and chains are presented first. The structures and characteristics of representative barbed-spring padlocks are introduced. Six examples are provided to demonstrate the opening processes of blocked-keyhole padlocks. The result shows that it is a useful tool to realize the structural difference in the padlocks during operation.