Jeremy Olivier

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

Technological advancements have led to the development of numerous wearable robotic devices for the physical assistance and restoration of human locomotion. While many challenges remain with respect to the mechanical design of such devices, it is at least equally challenging and important to develop strategies to control them in concert with the intentions of the user.This work reviews the state-of-the-art techniques for controlling portable active lower limb prosthetic and orthotic (P/O) devices in the context of locomotive activities of daily living (ADL), and considers how these can be interfaced with the user’s sensory-motor control system. This review underscores the practical challenges and opportunities associated with P/O control, which can be used to accelerate future developments in this field. Furthermore, this work provides a classification scheme for the comparison of the various control strategies.As a novel contribution, a general framework for the control of portable gait-assistance devices is proposed. This framework accounts for the physical and informatic interactions between the controller, the user, the environment, and the mechanical device itself. Such a treatment of P/Os – not as independent devices, but as actors within an ecosystem – is suggested to be necessary to structure the next generation of intelligent and multifunctional controllers.Each element of the proposed framework is discussed with respect to the role that it plays in the assistance of locomotion, along with how its states can be sensed as inputs to the controller. The reviewed controllers are shown to fit within different levels of a hierarchical scheme, which loosely resembles the structure and functionality of the nominal human central nervous system (CNS). Active and passive safety mechanisms are considered to be central aspects underlying all of P/O design and control, and are shown to be critical for regulatory approval of such devices for real-world use.The works discussed herein provide evidence that, while we are getting ever closer, significant challenges still exist for the development of controllers for portable powered P/O devices that can seamlessly integrate with the user’s neuromusculoskeletal system and are practical for use in locomotive ADL.

Mechanisms for actuated assistive hip orthoses

Mobility is often a central problem for people having muscle weaknesses. The need for new devices to assist walking and walk related activities is therefore growing. Lower limb actuated orthoses have already proven their positive impact with paraplegic patients and are potentially promising for assisting people with weak muscles. However, the transfer from the existing systems of mobilization towards assistance implies several technical challenges as the seamless integration and the reduction of power consumption. In this paper two assistive orthoses which use different types of actuation mechanisms are presented and discussed. The first one is based on a ball screw and an excavator-like mechanism while the second one is based on a double differential actuation. Their technical capabilities are compared and contextualized for diverse activities. Objective characteristics such as the range of motion of the devices, the transparency, the maximal torque that they can provide or the RMS torque during cyclic trajectories are compared to point out which device is better adapted for specific situations. We presented two different hip orthoses with novel types of actuation.The two orthoses are optimized for assistance in various situations.Different characteristics are assessed in order to objectively compare our orthoses.

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

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 sufficent 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.

The LegoPress: A Rehabilitation, Performance Assessment and Training Device Mechanical Design and Control

In this paper we present the LegoPress, a simple and cost-effective robotic device intended to be used for leg-press movements in rehabilitation and training. Basic adjustments can be done on the sitting position so as to maximize comfort and adapt the posture of the user depending on the desired training. The LegoPress has two motorized axes independently acting on the two legs. By means of force sensors positioned at the pedal level, a precise monitoring is possible. The force sensor is as well used to improve the impedance control, which enables to reproduce various behaviors. The device is not only able to mobilize the user’s legs but also to interact with her/him.

From gait measurements to design of assistive orthoses for people with neuromuscular diseases

Neuromuscular diseases (NMD) such as myopathies are characterized by symptomatic patterns of degenerative muscle weakness leading to severe walking disability. Due to low prevalence and great variability of symptoms, very little effort has been spent on assistive devices as compared e.g. to spinal cord injury (SCI) or stroke rehabilitation. The needs for assistance for persons with NMD are specific and existing solutions for SCI or stroke patients are not adapted to them. This study investigates design specifications of assistive orthoses with the goal of adding months or years of near normal mobility for patients with muscle weakness. Data on strength affection and gait kinematics of 14 subjects (5 Facioscapulohumeral muscular dystrophy, 3 Charcot-Marie-Tooth neuropathy, 2 Becker muscular dystrophy, 2 Myotonic dystrophy and 2 Inclusion body myositis) has been collected. The results highlight the effect of muscle weakness on gait pattern and walking velocity. Design specifications of walk assist exoskeletons for such patients are then proposed and discussed. A novel architecture of a lower limb orthosis is proposed based on these observations.

HiBSO Hip Exoskeleton: Toward a Wearable and Autonomous Design

HiBSO is an active orthosis designed to assist the hip flexion-extension of the elderly. A fully autonomous system with untethered power electronics and energy supply is now available. Going beyond the restricted walking conditions of a treadmill unveils many opportunities for the understanding of human-robot interaction. Previous works have presented the mechanical design optimized for high transparency and light weight, while dedicated kinematics allow high torque for sit-to-stand transition and high speed for level walking. The control strategies are currently in the evaluation process. In this document, the recent improvements to the device will be described, from the mechanical design to the control electronics. Some specific aspects such as the remote communication for the controller are emphasized. The assessment of the power autonomy is addressed with two sessions of walking in different conditions, and revealed a maximum operating time of more than 80 min. In this context, the controller is based on adaptive oscillators for the gait detection and is combined with a 40% torque assistance based on biomechanics from the literature.

Series Elastic Actuation for Assistive Orthotic Devices: Case Study of Pneumatic Actuator

Wearable assistive robotics is a modern field where intelligent actuated systems work in collaboration with the body to replace a lost limb, to enhance performances (e.g. carrying load, walking, running, jumping) or to train or rehabilitate specific activities. Wearability (e.g. weight, bulkiness) and power are the two main competing characteristics of most assistive wearable devices. Energy efficient actuation systems with high power density per mass and volume are thus preferred. The biological muscle-tendon solution is very interesting for energy storage and generation of efficient cyclic patterns. The present study investigates on the capacity to replicate these biological properties using series elastic actuator (SEA) based on pneumatic cylinder technology. While classic SEA designs are composed of electric actuator in series with steel springs, pneumatic actuators are intrinsically compliant due to the compressibility of the fluid. The study starts by presenting an experimental approach for characterizing the elastic behavior of a pneumatic cylinder actuation targeting the assistance of the hip flexion. Results are then confronted to measurements of lower limb joints’ stiffness observed during walking to identify the suitability of the solution with the targeted application..

A Robotic Platform for Lower Limb Optical Motion Tracking in Open Space

Conventional human motion tracking techniques based on optical systems reports important limitations for mobile applications (e.g. small spatial covering, poor environment flexibility). The present paper addresses a novel approach for optical motion tracking in open space. The measurement unit is transferred from its stationary basis onto a robotic moving platform. The platform design and limitations are described in the first place. It follows a comparative analysis of the measurement data accuracy for the stationary and mobile system. Post-processing techniques to convert acquired motion from the platform coordinate system into the ground’s absolute one are evaluated for the specific application of gait analysis.

Exoskeletons as Mechatronic Design Example

Exoskeletons are a perfect example of a mechatronics product. They illustrate the close integration and interdependence of mechanical design, drive train, sensors, control strategy and user interface. Recent developments of our lab will be discussed in detail. Application examples include paraplegics, amputees, muscular dystrophy patients. The motivations of the users exoskeletons are as diverse as sporting challenge, life quality improvement for daily living, rehabilitation and social integration. Links to Cognitive Neurosciences will also be briefly discussed.

Dionis Surgical Positioner

A few years ago, we presented a new parallel robot kinematics (called “Dionis”) suitable for positioning an endoscopic tool above a patient, with a virtual center of rotation at the insertion point. A first prototype has been realized. This enables us to address a few specific mechanical design issues with the purpose of significantly increasing the stiffness of this design. FEM simulations presented here show promising results.