Development of an assistive motorized hip orthosis: Kinematics analysis and mechanical design

Abstract

With the increase of life expectancy, a higher number of elderly need assistance to maintain their mobility and their independance. The hip joint is crucial for walking and is problematic for a large number of aged people. In this paper we present a novel design of a motorized hip orthosis to assist elderly people while walking, stair climbing and during the sit-to-stand transistions. The kinematics was developed based on biomechanics considerations. To be able to achieve a large assistance rate, velocity and torques of the hip joint were studied from the literature. In order to fit with these requirements, an amplification mechanism inspired by excavators was developed and implemented. Comfort considerations were also taken into account and a custom interface was designed with the collaboration of a professional orthopaedic technician. First tests with the prototype showed that the workspace is sufficient for walking, for stair climbing as well as for sit-to-stand transitions. The assistance rate can go up to 30% for a 70 kg subject during walking at a cadence of 100 steps/min. The comfort is guaranteed despite the important weight (4.3 kg) of this first prototype.

Control strategies for active lower extremity prosthetics and orthotics: a review

“…The fraction of the load borne by the device is termed the support ratio [ 60 ] or the assistance ratio [ 216 ], and is normalized to either the net torque required of the joint for a particular movement or to the maximum torque of the device. The load carried by the physiological joint can be estimated from muscle activity [ 60 , 70 , 154 , 216 ] or through direct force measurement [ 217 ].…”

“…Additional considerations are the performance limitations and saturation effects of the actuator and power source [ 14 , 60 , 170 ]. Even state-of-the-art portable devices must be driven beyond their continuous operating range to achieve the power outputs required during energetically demanding activities, such as sit-to-stand, stair ascent, running, or jumping [ 61 , 217 ]. While this is generally acceptable for short bursts, it may be necessary for the controller to derate the actuator if these conditions are sustained for long periods.…”

Mechanisms for actuated assistive hip orthoses

“…In order to avoid a b the above-mentioned parasitic rotation, a cam mechanism is implemented so as to progressively lock the rotation of the first pivot joint. If this pivot angle goes out of the allowed range, a force is transferred from the flexion/extension axis to the first axis by means of the cam [25].…”

Kinematics and performance analysis of a serial hip assistive mechanism

“…In D'Elia et al, 18 an APO was developed, by D'Elia, et al, for 1-degree-of-freedom (DOF) hip FL/EX assistance, in which eight passive joints were introduced to improve the PHRI performance (each branch contains four passive DOFs). In another study, Olivier et al 19 designed the assistive motorized hip orthosis (AMPO) for assisting sagittal plane motion in the human hip joint. Five passive DOFs were added to minimize the effect of undesired human-robot interactional loads and thereby enhance the PHRI performance of the device.…”