Ambulatory Estimation of Relative Foot Positions using Ultrasound

The recording of human movement is used for biomedical applications like physical therapy and sports training. Over the last few years inertial sensors have been proven to be a useful ambulatory alternative to traditional optical systems. An example of a successful application is the instrumented shoe, which contains two 6D force/moment sensors beneath the heel and the forefoot and two inertial sensors rigidly attached to the force/moment sensors [1]. These shoes can be used for ambulatory assessment of walking kinetics and kinematics. The relative position of the feet is currently not measured directly but estimated from double integration of feet accelerations. However, this method immediately leads to large position errors (drift) when the estimated inertial accelerations are inaccurate. In this study we investigated the ambulatory estimation of the relative positions of the feet using ultrasound transducers. On one shoe we mounted a 400PT120 Air Ultrasonic Ceramic Transducer (13 mm diameter, 10 mm height, 85º beam angle) sending a 40 kHz pulse to a similar transducer on the other shoe. Using the time of flight, the distance is estimated. Under static conditions a mean error of 5.7 ±0.8 mm was obtained over a range of 5 till 75 cm [2]. From this pilot study we concluded that the distance between the feet can be estimated ambulatory using small and low-cost ultrasound transducers. Future research includes the use of multiple transducers on each foot for a distance measure during different daily-life activities. Also the relative positions of the feet will be investigated by fusing the distance estimates with inertial sensor data

Control and omni-directional locomotion of a crawling quadruped

Traversing unstructured environments, (statically stable) legged robots could be applied effectively but, they face two main problems: the high complexity of the system and the low speed of locomotion. To address the complexity of the controller, we apply a control layer that abstracts the legged robot to an omni-directional moving mass. In this control scheme, we apply the gait generator as proposed by Estremera and de Santos. We present theory to determine the theoretically maximum achievable velocity of a quadruped and compare the (omni-directional) maximum velocity of the selected gait generator with this optimum to validate its performance. For our use case the theoretically maximum achievable velocity is 1 ms − 1; in simulations we achieve a velocity for straight movement of maximum 0.75 ms − 1. Normal turns with a radius larger than 0.45 m are possible at a velocity of at least 0.1 ms − 1; the performance of crab turns is too unpredictable to be useful. The gait generator as proposed by Estremera and de Santos is partially capable of supporting omni-directional movement at satisfactory velocities