LAUSR

Abstract Some locks namely “open-keyhole puzzle locks” with exposed keyholes can be very tricky to open. This work analyzes the structures of open-keyhole puzzle locks, which were widely used with plentiful types in ancient China. Open-keyhole puzzle locks are reconfigurable mechanisms that have different topological structures in the operation. Based on the study of mechanisms, the structural characteristics and the representation of joints of open-keyhole puzzle locks are proposed. Then, using the concepts of variable chains and the proposed representation of joints, the topological variabilities of open-keyhole puzzle locks during operation are analyzed and presented. There are three main types, including locks with extra obstacle, locks with indirect insertion, and multi-stage locks. Six examples are provided to illustrate the changes in their variable chains during operation. This process provides a logical foundation to analyze and realize the topological structures of open-keyhole puzzle locks.