Michele Xiloyannis

Modelling and design of a synergy-based actuator for a tendon-driven soft robotic glove

The need for a means of assistance in human grasping, to compensate for weakness or to augment performance, is well documented. An appealing new way of doing so is through soft, wearable robots that work in parallel with the human muscles. In this paper we present the design and modelling of a tendon-driving unit that empowers a wearable, soft glove. Being portability one of our main objectives, we use only 1 motor to move 8 degrees of freedom of the hand. To achieve this we use an underactuation strategy based on the human hands first postural synergy, which explains alone ≈60% of activities of daily living. The constrains imposed by the underactuation strategy are softened, to allow adaptability during grasping, by placing elastic elements in series with the tendons. A simulation of the dynamic behaviour of the glove on a human hand allows us to quantify the magnitude and distribution of the forces involved during usage. These results are used to guide design choices such as the power of the motor and the stiffness of the springs. The designed tendon-driving unit comprises a DC motor which drives an array of spools dimensioned according to the first postural synergy, an electromechanical clutch to hold the hand in position during static posture and a feeder mechanism to avoid slacking of the tendons around the spool. Finally, the tendon-driving unit is tested to verify that it satisfies motion and force characteristics required to assist its wearer in activities of daily living.

Adaptive backlash compensation in upper limb soft wearable exoskeletons

A new frontier of assistive devices aims at designing exoskeletons based on fabric and flexible materials for applications where kinematic transparency is the primary requirement. Bowden-cable transmission is the widely employed solution in most of the aforementioned applications due to advantages in durability, lightweight, safety, and flexibility. The major advantages of soft assistive devices driven by bowden-cable transmissions can be identified in the superior ergonomics and wearability, allowing users to freely move and allocating the actuation stages far from the end-effector. However, control accuracy in bowden-cable transmission presents some intrinsic limitation due to nonlinearities such as static and dynamic friction, occurring between the cables and the bowden sheaths, and backlash hysteresis. Friction and backlash effects are known to be related to the curvature of the flexible sheath, which is not directly measurable and can vary during human motion. In this paper we describe our new wearable exosuit for upper limb assistance and in particular we introduce a mathematical model for backlash hysteresis compensation. The implementation of a nonlinear adaptive controller is described in detail and experimentally tested on the proposed design as a backlash compensation strategy: results report that the adaptive controller improves the accuracy in position tracking (i.e.RMSE in trajectory tracking 1) by compensating for time-varying backlash and continuously updating the model parameters. The backlash hysteresis model and the proposed control scheme are validated first on a custom-designed test bench and then applied to control the soft exoskeleton worn by a subject affected by bilateral brachial plexus injury. Soft exosuit driven by Bowden cables for human arm assistance.Backlash hysteresis in Bowden-cable transmission.Nonlinear adaptive controller for backlash compensation.

Hierarchical Cascade Controller for Assistance Modulation in a Soft Wearable Arm Exoskeleton

In recent years soft wearable exoskeletons, commonly referred to as exosuits, have been widely exploited in human assistance. Hence, a shared approach for a systematic and exhaustive control architecture is extremely important. Most of the exosuits developed so far employ a bowden cable transmission to conveniently place the actuator away from the end-effector. While having many advantages this actuation strategy presents some intrinsic limitations caused by the presence of nonlinearities, such as friction and backlash of the cables, which make it difficult to predict and control the dynamics between the device and the user. In this letter, we propose a novel hierarchical control paradigm for a cable-driven upper limb exosuits that aims at evaluating and consequently deliver the appropriate assistive torque to the users elbow joint. The proposed control method comprises three main layers: an active impedance control which estimates the users arm motion intention and guarantees an intuitive response of the suit to the wearers motion; a mid-level controller which compensates for the backlash in the transmission and converts the reference arm motion to the desired position of the actuator; a low-level controller which is responsible for driving the actuation stage by compensating for the nonlinear dynamics occurring in the bowden cable to provide the desired assistive torque at the joint. Tests on healthy subjects show that wearing the exosuit reduces by

Preliminary design and control of a soft exosuit for assisting elbow movements and hand grasping in activities of daily living

48.3\%

Design and Preliminary Testing of a Soft Exosuit for Assisting Elbow Movements and Hand Grasping

the muscular effort required to lift 1 kg and that the controller is able to modulate its level of assistance to the wearers motor ability.

Position control using adaptive backlash compensation for bowden cable transmission in soft wearable exoskeleton

The development of a portable assistive device to aid patients affected by neuromuscular disorders has been the ultimate goal of assistive robots since the late 1960s. Despite significant advances in recent decades, traditional rigid exoskeletons are constrained by limited portability, safety, ergonomics, autonomy and, most of all, cost. In this study, we present the design and control of a soft, textile-based exosuit for assisting elbow flexion/extension and hand open/close. We describe a model-based design, characterisation and testing of two independent actuator modules for the elbow and hand, respectively. Both actuators drive a set of artificial tendons, routed through the exosuit along specific load paths, that apply torques to the human joints by means of anchor points. Key features in our design are under-actuation and the use of electromagnetic clutches to unload the motors during static posture. These two aspects, along with the use of 3D printed components and off-the-shelf fabric materials, contribute to cut down the power requirements, mass and overall cost of the system, making it a more likely candidate for daily use and enlarging its target population. Low-level control is accomplished by a computationally efficient machine learning algorithm that derives the system’s model from sensory data, ensuring high tracking accuracy despite the uncertainties deriving from its soft architecture. The resulting system is a low-profile, low-cost and wearable exosuit designed to intuitively assist the wearer in activities of daily living.

Characterisation of Pressure Distribution at the Interface of a Soft Exosuit: Towards a More Comfortable Wear

Most of the currently available exoskeletons for upper limbs are constrained by limited portability, ergonomics, weight and, energy-wise, autonomy. Moreover, their high cost makes them available only for the most affluent users, ruling out the majority of the population in need. By replacing rigid aluminum links and transmissions with fabrics and bowden cables, we can both cut down the cost of the assistive device and design it to be portable, comfortable and lightweight. We present the design and a preliminary testing of a soft exosuit for assisting elbow flexion/extension and hand open/close. Our system comprises two proximally located tendon-driving actuators, and two textile-based frames that route the tendons and transmit forces to the human joints, namely an elbow sleeve and a glove. A preliminary test on a healthy subject is presented with an adaptive controller that achieves good tracking accuracy despite of the system’s non-linear and time-varying dynamics.

A Soft Tendon-Driven Robotic Glove: Preliminary Evaluation

In recent years, bowden-cable transmissions have been developed and utilized widely in many robotic applications due to advantages in durability, lightweight, safety, and flexibility. Especially, over the last decade, a substantial number of soft wearable exoskeletons using bowden cables for motion transmission have been designed for human assistance, empowerment and rehabilitation. The major advantage of soft assistive devices driven by bowden-cable transmissions is to allow decentralizing the actuation stages proximally such that their mass has the least effect on the end-effector. Besides the advantage, the main drawback of the bowden cable-driven system comes from the presence of nonlinearities such as friction and backlash hysteresis that affects their control accuracy. Hence, in this paper, we introduce a mathematical model for backlash hysteresis and propose a solution based on the nonlinear adaptive control to compensate for the backlash effect. The backlash hysteresis model and control scheme are validated first on a custom-designed test bench and then applied to control a soft exoskeleton in a preliminary human trial.

Comparison of a Soft Exosuit and a Rigid Exoskeleton in an Assistive Task

The rapid growth of wearable robots in the last decade requires tackling practical issues that arise from their daily use, among which comfort is of great importance. In this work we quantify the level of comfort of a soft exosuit for the elbow by measuring the distribution of pressures at its interface with the human body. We do so with five different cushioning materials, commonly used in sport equipment and orthoses, and identify the ones exhibiting lower peaks of pressure. Polyethylene sponge and neoprene result in the best padding.

Actuation for robot-aided rehabilitation: Design and control strategies

Soft wearable robots promise to be the new frontier for assistance and augmentation of human motor abilities. In this work, we present the design, controller and a preliminary assessment of a soft, textile based glove for assisting hand movements. The device is shown to reduce the muscular effort required for grasping an object in healthy subjects, for forces up to 25 N but slows hand movements in free space.