structural analysis of traditional chinese hidden-keyhole padlocks

Hidden-keyhole padlocks use a plate or some other means to cover the keyhole and are a category of traditional Chinese padlocks. The topological structures of traditional hidden-keyhole padlocks have distinct arrangements in the operation. Therefore, they are reconfigurable mechanisms. This paper presents the structures of traditional Chinese hidden-keyhole padlocks, which were popular and had abundant types. The structural characteristics of hidden-keyhole padlocks are described first. Then, the representation for kinematic pairs appeared in operating steps is introduced. The variable chains of hidden-keyhole padlocks are presented by using the representation of kinematic pairs, from which all topology variabilities of hidden-keyhole padlocks in the operation are derived. Four main types of hidden-keyhole padlocks are provided as examples to illustrate the configuration transformations. This work presents a useful procedure to indicate and analyze the topology variabilities of hidden-keyhole padlocks.