Smart Lacelock: A Novel Shoelace Tensioning Device for Human Motion Sensing

Shoe-mounted wearable sensors may serve a variety of important purposes (activity recognition, energy expenditure estimation, and so on) by providing rich information about human locomotion. However, reliably attaching such sensors to shoes still remains a challenge. Furthermore, pressure-sensing elements in such shoe sensor systems often suffer from poor durability due to the large dynamic load. This work presents a novel shoe-mounted sensor named Smart Lacelock, which takes the form of a common shoelace tensioning device (shoelace lock). With its unique form factor, the Smart Lacelock can be securely attached to the top of a shoe with minimal effort, enabling its embedded inertia measurement unit (IMU) to provide reliable 3-D motion measurement of the foot. Furthermore, the Smart Lacelock incorporates a load cell to measure the force applied by the shoelace, providing valuable information related to ankle movement, foot/shoe shape change, and ground force. Design details of the device are presented, including the mechanical structure and electronic circuitry. We also conducted a ten-participant human study, in which signals were recorded during free ankle swing, body weight (BW) shifting, sit-to-stand (STS), and overground walking. The results demonstrated the Smart Lacelock’s capability of providing consistent and observable responses to single contributing factors (ankle movement and foot loading) as well as complex movements with clearly defined events of interest (STS and walking). Such unique capability suggests that the Smart Lacelock may serve as an important source of human movement information to support related applications such as activity recognition and gait event detection.