A. Ortlieb

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.

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.

AUTONOMYO: Design Challenges of Lower Limb Assistive Device for Elderly People, Multiple Sclerosis and Neuromuscular Diseases

Lower limb wearable robotics also known as exoskeleton or power suit is a booming field of research. Potential medical applications cover a large range of gait disorders from rehabilitation to assistance in daily mobility. Surprisingly, or not, paraplegia seems to be the first target of all commercialized exoskeleton. In this paper we will try to understand this choice and look at other disorders leading to the inability to walk. Neuromuscular, autoimmune or neurological diseases such as muscular dystrophy, multiple sclerosis or stroke, can lead to similar gait disorders and are mostly incurable today. SCI (Spinal Cord Injury) symptoms are quite dissimilar from theirs and reveal specific design challenges. Existing devices’ architecture and human-robot interaction are presented and discussed in terms of adaptation toward non-SCI disorders.

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.

Influence of an Assistive Hip Orthosis on Gait

Powered orthoses are leading to an imminent change in the field of assistance. The major challenges faced by the technology concern the management of the interaction between the user and the wearable device and the coordination between the user intention and the actuated motion. In the present study, we used the HiBSO (Hip Ball-Screw Orthosis) to investigate the contribution of an assistance to the hip flexion/extension motion during walking. Four healthy subjects wearing the HiBSO performed a controlled walking at 3.6 km/h on a treadmill. Three conditions were evaluated: free walking (without orthosis), a transparent mode (orthosis providing no assistance) and an assistive mode (orthosis assisting 10% of walking torque). Kinematics tracking and heart rate recording have been used for the assessment of the assistance. The observations exhibited a clear influence of the assistance on the hip flexion velocity during the swing phase. The ranges of motion of the hip and the knee tend to increase in the assistive mode whereas the ankle range of motion is reduced. Thus the assistance of the hip has a global influence on all the joints. The heart rate acquisitions demonstrated a higher energy expenditure while wearing the orthosis in both transparent and assistive mode.

Impact of ankle locking on gait implications for the design of hip and knee exoskeletons

Patients affected by spinal cord injury cannot usually regain unassisted walking. This is why several research groups and companies have developed exoskeletons which enable these people to regain mobility in a standing position. The simplest joint configuration for exoskeletons is to actuate the knees and the hips in the sagittal plane. The ankles and feet are then unactuated and their range of motion is limited. In this paper we investigate the impact of locking the ankle joint on gait. We therefore recorded gait trajectories on seven subjects whose ankles and feet were restrained. This pilot study demonstrates that hip and knee trajectories change when the subjects cannot move their ankles. The implications for the design and control of exoskeletons with active degrees of freedom at the hips and knees are discussed.