A new Constant Pushing Force Device for human walking analysis

Walking mechanics has been studied for a long time, being essentially simple but nevertheless including quite tricky aspects. During walking, muscular forces are needed to support body weight and accelerate the body, thereby requiring a metabolic demand. In this paper, a new Constant Pushing Force Device (CPFD) is presented. Based on a novel actuation concept, the device is totally passive and is used to apply a constant force to the pelvis of a subject walking on a treadmill. The device is a serial manipulator featuring springs that provide gravity balancing to the device and exert a constant force regardless of the pelvis motion during walking. This is obtained using only two extension springs and no auxiliary links, unlike existing designs. A first experiment was carried out on a healthy subject to experimentally validate the device and assess the effect of the external force on gait kinematics and timing. Results show that the device was capable of exerting an approximately constant pushing force, whose action affected subject´s cadence and the motion of the hip and ankle joints.