Manuel Cestari

Identifying Ground-Robot Impedance to Improve Terrain Adaptability in Running Robots

To date, running robots are still outperformed by animals, but their dynamic behaviour can be described by the same model. This coincidence means that biomechanical studies can reveal much about the adaptability and energy efficiency of walking mechanisms. In particular, animals adjust their leg stiffness to negotiate terrains with different stiffnesses to keep the total leg-ground stiffness constant. In this work, we aim to provide one method to identify ground-robot impedance so that control can be applied to emulate the aforementioned animal behaviour. Experimental results of the method are presented, showing well-differentiated estimations on four different types of terrain. Additionally, an analysis of the convergence time is presented and compared with the contact time of humans while running, indicating that the method is suitable for use at high speeds.

A lower-limb exoskeleton for gait assistance in quadriplegia

The potential of lower-limb exoskeletons and powered orthoses in gait assistance applications for patients with locomotive disorders would have a terrific impact in the society of the near future. This paper presents the development and main features of a lower limb exoskeleton being developed as an active orthosis to allow a quadriplegic child to walk. As the patient is not able to move any of her limbs, the device will produce her basic motions in everyday-life activities: stand up, sit down, and walk stably. Synergic biarticular actuation in the ankle, compliance controller based on the force measured by insoles at the feet and the definition of parameterized hip and foot trajectories that allow to choose the characteristics of gait are some of the new features included in this prototype. Experiments validate the improved performance of gait based on the proposed approach.

Control Motion Approach of a Lower Limb Orthosis to Reduce Energy Consumption

By analysing the dynamic principles of the human gait, an economic gait-control analysis is performed, and passive elements are included to increase the energy efficiency in the motion control of active orthoses. Traditional orthoses use position patterns from the clinical gait analyses (CGAs) of healthy people, which are then de-normalized and adjusted to each user. These orthoses maintain a very rigid gait, and their energy cost is very high, reducing the autonomy of the user. First, to take advantage of the inherent dynamics of the legs, a state machine pattern with different gains in each state is applied to reduce the actuator energy consumption. Next, different passive elements, such as springs and brakes in the joints, are analysed to further reduce energy consumption. After an off-line parameter optimization and a heuristic improvement with genetic algorithms, a reduction in energy consumption of 16.8% is obtained by applying a state machine control pattern, and a reduction of 18.9% is obtained by...

Generation and control of adaptive gaits in lower-limb exoskeletons for motion assistance

Lower-limb exoskeletons and powered orthoses in gait assistance applications for patients with locomotive disorders possess the potential to significantly affect society in the near future. This paper presents the primary features of a lower-limb exoskeleton under development as an active orthosis to enable paralysed children to walk. Because these patients are unable to move their limbs, the device generates their basic motions in everyday life, e.g. standing up, sitting down and stable ambulation. Novel features of this prototype include synergic biarticular actuation in the ankle, a compliance controller based on the force measured using insoles and the definition of parameterised hip and foot trajectories that facilitate the adaptation of gait characteristics. The improved gait performance that results from the proposed approach was experimentally validated. Graphical Abstract

ARES, a variable stiffness actuator with embedded force sensor for the ATLAS exoskeleton

Purpose – The purpose of this study is to present a variable stiffness actuator, one of whose main features is that the compliant elements simultaneously allow measuring of the torque exerted by the joint. Conceived as a force-controlled actuator, this actuator with Adjustable Rigidity and Embedded Sensor (ARES) is intended to be implemented in the knee of the ATLAS exoskeleton for children to allow the exploitation of the intrinsic dynamic during the locomotion cycle. Design/methodology/approach – A set of simulations were performed to evaluate the behavior of the actuator mechanism and a prototype of the variable impedance actuator was incorporated into the exoskeleton’s knee and evaluations of the torque measurements capabilities along with the rigidity adjustments were made. Findings – Mass and inertia of the actuator are minimized by the compact design and the utilization of the different component for more than one utility. By a proper match of the compliance of the joint and the performed task, goo...

Exploiting joint synergy for actuation in a lower‐limb active orthosis

– Lower‐limb exoskeletons and powered orthoses are external devices that assist patients with locomotive disorders to achieve correct limb movements. Current batteries cannot meet the long‐term power requirements for these devices, which operate for long periods of time. This issue has become a major challenge in the development of these portable robots. Conversely, legged locomotion in animals and humans is efficient; to emulate this behaviour, biomimetic actuation has been designed attempting to incorporate elements that resemble biological elements, such as tendons and muscles, in the mechanical systems. The purpose of this paper is to present a mechanism that resembles a human tendon to achieve and utilise the synergic actuation of the leg joints., – In this paper, we present a mechanism that resembles a human tendon to move the ankle joint and utilise the synergic actuation of hip and knee joints. Implementation of the proposed transmission system in the ATLAS active orthosis prototype allowed for a better ankle gait fit, which resulted in a more natural stride and, as expected, optimised energy consumption in the locomotion cycle and actuation energy requirements., – The fitted passive ankle motion provides toe‐off impulse, increases support force, and helps provide ground clearance., – A synergetic underactuated movement in the ankle joint, implemented by two cables in each leg, improves the functionality of the device without increasing the leg weight and while maintaining a reduced size. To achieve a correct and efficient motion in the ankle of an active orthosis, two steel cables were attached in the ATLAS orthosis. These cables act as a synergic biarticular linkage and transfer motion from the hip and knee joints. Synergic ankle motion provides impulse in the toe‐off, increases support force, and provides ground clearance. These goals are achieved with low energy expenditure because of synergical actuation, and high inertia is prevented in the more distal limb.

Wearable exoskeletons for the physical treatment of children with quadriparesis

Quadriparesis, caused by a number of congenital and acquired neuropathologies, affects children with the symptoms of weakness and motor impairment in all four limbs. The physical treatment of this disease could be hypothetically improved by the use of wearable exoskeletons which would contribute to avoiding the side effects of the permanent sitting position: scoliosis, osteoporosis, spasticity, respiratory disorders, blood circulation problems, among others. Overall, the use of a wearable exoskeleton would contribute substantially to the improvement of these childrens quality of life. This paper presents the first pédiatrie wearable exoskeleton for the physical treatment of this disease. The paper shows the main components of the device and the laboratory proof of concept in two voluntary subjects.

On the Necessity of Including Joint Passive Dynamics in the Impedance Control of Robotic Legs

Bioinspired quadruped robots are among the best robot designs for field missions over the complex terrain encountered in extraterrestrial landscapes and disaster scenarios caused by natural and human-made catastrophes, such as those caused by nuclear power plant accidents and radiological emergencies. For such applications, the performance characteristics of the robots should include high mobility, adaptability to the terrain, the ability to handle a large payload and good endurance. Nature can provide inspiration for quadruped designs that are well suited for traversing complex terrain. Horse legs are an example of a structure that has evolved to exhibit good performance characteristics. In this paper, a leg design exhibiting the key features of horse legs is briefly described. This leg is an underactuated mechanism because it has two actively driven degrees of freedom (DOFs) and one passively driven DOF. In this work, two control laws intended to be use in the stan ce phase are described: a control law that considers passive mechanism dynamics and a second law that neglects these dynamics. The performance of the two control laws is experimentally evaluated and compared. The results indicate that the first control law better achieves the control goal; however, the use of the second is not completely unjustified.

Development of a Lower-Limb Active Orthosis and a Walker for Gait Assistance

Lower-limb exoskeletons and powered orthoses in gait assistance applications for patients with locomotive disorders possess the potential to significantly affect society in the near future. This paper presents the primary features of a lower-limb exoskeleton to enable paralysed children to walk. Because these patients are unable to move their limbs, the device generates their basic motions in everyday life, e.g., standing up, sitting down, and stable ambulation. A walker provides stability in the lateral plane, while the active orthosis provides stability in the sagittal plane while walking. The walker has been devised with a two degree of freedom mechanism to allow the user to sit down and stand up in a stable and comfortable way without the movement of the walker itself. The gait of the orthosis parameters such as step height, body height or step length are modified online, based on an impedance control approach, providing a safe and smooth gait pattern. Two shoe insole pressure measurement systems provide ground reaction force and center of pressure to adapt these gait parameters online. An adjustable compliance actuator has been designed and incorporated to the knee joint of the active orthosis. This Actuator with Adjustable Rigidity and Embedded Sensor (ARES) fulfills the demanding characteristics required in an active orthosis’s joint, namely, intrinsic compliance to allow human-machine interaction, high power-to-weight ratio, high peak torque, small size and low weight. Exploiting the characteristics of ARES actuator a control scheme has been designed and implemented to achieved a reduction in the energy expenditure while keeping compliant to accommodate unexpected disturbances. The final ATLAS exoskeleton has been successfully tested in a healthy user, in a quadriplegic child, and in a patient with neuromuscular disease.

Parameterized inverted and double pendulum model for controlling lower-limb active orthosis

Lower-limb active orthosis have been traditionally controlled by tracking clinical gait analysis (CGA) angle patterns. This approach however is very rigid and difficult to modify. This paper proposes a method based on the parameterization of simple dynamic models that explain human walking, which is more flexible and more intuitively modified than directly applied CGA patterns. In addition, a comparison between the angle trajectories obtained by this method and CGA is presented. In order to further test the method, it is applied to a simulated biped featuring the same mass and limb length distribution as a quadriplegic girl showing good results with the simplest possible controller, even in step-to-step transitions which are not explicitly considered by the parameterization. Finally, the joint coordinates used in the simulation were also implemented in the ATLAS prototype showing a natural looking gait.