Leonardo Cappello

Robot-Aided Assessment of Wrist Proprioception

Introduction Impaired proprioception severely affects the control of gross and fine motor function. However, clinical assessment of proprioceptive deficits and its impact on motor function has been difficult to elucidate. Recent advances in haptic robotic interfaces designed for sensorimotor rehabilitation enabled the use of such devices for the assessment of proprioceptive function. Purpose This study evaluated the feasibility of a wrist robot system to determine proprioceptive discrimination thresholds for two different DoFs of the wrist. Specifically, we sought to accomplish three aims: first, to establish data validity; second, to show that the system is sensitive to detect small differences in acuity; third, to establish test–retest reliability over repeated testing. Methodology Eleven healthy adult subjects experienced two passive wrist movements and had to verbally indicate which movement had the larger amplitude. Based on a subject’s response data, a psychometric function was fitted and the wrist acuity threshold was established at the 75% correct response level. A subset of five subjects repeated the experimentation three times (T1, T2, and T3) to determine the test–retest reliability. Results Mean threshold for wrist flexion was 2.15°± 0.43° and 1.52°± 0.36° for abduction. Encoder resolutions were 0.0075°(flexion–extension) and 0.0032°(abduction–adduction). Motor resolutions were 0.2°(flexion–extension) and 0.3°(abduction–adduction). Reliability coefficients were rT2-T1 = 0.986 and rT3-T2 = 0.971. Conclusion We currently lack established norm data on the proprioceptive acuity of the wrist to establish direct validity. However, the magnitude of our reported thresholds is physiological, plausible, and well in line with available threshold data obtained at the elbow joint. Moreover, system has high resolution and is sensitive enough to detect small differences in acuity. Finally, the system produces reliable data over repeated testing.

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.

Design and preliminary characterization of a soft wearable exoskeleton for upper limb

Exoskeletons targeting the upper limb have been broadly developed both for rehabilitation and to augment users physical performance. Generally, they are rigid robotic interfaces characterized by a non negligible mechanical impedance at the end effector and consequently perceived by the upper limbs as an external body. The rigid frame, moreover, adds kinematic constrains to the natural joint kinematics which may result in discomfort and ultimately in pain. The concept of soft wearable exoskeleton (or exosuit) has been developed and tested for the lower limb and the hand to address such issues thanks to their minimal inertial contribution and influence on the natural kinematics. In the current paper the design of an soft robotic interface for the elbow joint is presented, whose aim is to provide assistance torque to the targeted joint to facilitate the execution of the activities of daily living. Differently from the state-of-the-art design solutions, our system is able to drive both flexion and extension of the same joint with a single motor in an agonist-antagonist fashion, making the actuation stage compact and energy efficient. A clutching mechanism is also included in the design in order to save power during static configuration, preventing the motor to hold the joint position for a large amount of time. An exosuit has been designed to transfer the torque of the actuator to the biomechanical joint by means of Bowden cables. Two series elastic elements are employed to overcome the drawbacks of the agonist-antagonist mechanism and to provide additional compliance at the end effector. A preliminary test has been finally performed in order to characterize the actuation.

CARAPACE: A novel composite advanced robotic actuator powering assistive compliant exoskeleton preliminary design

A novel actuator is introduced that combines an elastically compliant composite structure with conventional electromechanical elements. The proposed design is analogous to that used in Series Elastic Actuators, its distinctive feature being that the compliant composite part offers different stable configurations. In other words, its elastic potential presents points of local minima that correspond to robust stable positions (multistability). This potential is known a priori as a function of the structural geometry, thus providing tremendous benefits in terms of control implementation. Such knowledge enables the complexities arising from the additional degrees of freedom associated with link deformations to be overcome and uncover challenges that extends beyond those posed by standard rigidlink robot dynamics. It is thought that integrating a multistable elastic element in a robotic transmission can provide new scenarios in the field of assistive robotics, as the system may help a subject to stand or carry a load without the need for an active control effort by the actuators.

A soft wearable robot for the shoulder: Design, characterization, and preliminary testing

In this paper, we present a soft wearable robot for the shoulder which has the potential to assist individuals suffering from a range of neuromuscular conditions affecting the shoulder to perform activities of daily living. This wearable robot combines two types of soft textile pneumatic actuators which were custom developed for this particular application to support the upper arm through shoulder abduction and horizontal flexion/extension. The advantage of a textile-based approach is that the robot can be lightweight, low-profile, comfortable and non-restrictive to the wearer, and easy to don like an item of clothing. The actuators ability to fold flat when not in use allows the robot to be almost invisible under clothing, potentially allowing the user to avoid any stigma associated with using assistive devices in public. To abduct the arm, a textilebased pneumatic actuator was developed to fit within the axilla to push the arm upwards, while a pair of smaller actuators pivot the abduction actuator to allow for horizontal extension and flexion. The individual textile actuators were experimentally evaluated before being integrated into a wearable garment. Human subject testing was performed to evaluate the ability of the robot to assist the arm by monitoring changes in biological muscle activity when comparing the robot powered on and off. Preliminary results show large reductions in muscular effort in targeted muscles, demonstrating the feasibility and promise of such a soft wearable robot for the shoulder.

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.

A series elastic composite actuator for soft arm exosuits

The paper introduces a novel type of actuator for soft wearable exoskeletons providing assistance to the elbow joint motion. The mechanism consists of two DC motors, a multistable composite transmission which introduces series elastic properties, a high-efficiency non-backdrivable mechanism and a pair of Bowden cables to transmit the motion from the actuator to the joint. A test bench has been designed to experimentally characterize the performance of the proposed device. The control architecture is then introduced and described. The results of preliminary tests are shown and discussed. In conclusion, future developments and a embodiment of the envisioned application are introduced.

Evaluation of wrist joint proprioception by means of a robotic device

Stroke, Parkinsons disease and other neurological conditions often cause proprioceptive deficits which impact the neural control of movement. Proprioception, which is the sense of body awareness, is central to assess accurate interaction with external environment and when compromised it results in several limitations in the activities of daily living. On the other hand, clinical assessment of the impact of proprioceptive deficits on motor functions has been difficult to elucidate mostly for the lack of accurate measurement devices especially for multi-DoF. Haptic robotic interfaces can be exploited to quantitatively evaluate proprioceptive acuity. We introduce a new method based on the use of a three-DoF robotic device to deliver accurate wrist kinematics and perform fine measurements in order to assess wrist joint proprioceptive acuity. Research protocol consists of passive movement in single-DoF configuration providing variable amplitude position stimuli. Data were collected from a group of healthy subjects who were instructed to discriminate the difference between stimuli intensities. Results highlight the efficacy and intrinsic simplicity of the proposed method marking the milestone for further investigations and characterization of proprioceptive acuity in pathologies and age related degradation of sensory motor functions. Moreover the robotic system can be used to design patient-customized therapies based on the particular impairment level and evaluate after every session the effectiveness of the therapeutic exercise.

3D‐Structured Stretchable Strain Sensors for Out‐of‐Plane Force Detection

Stretchable strain sensors, as the soft mechanical interface, provide the key mechanical information of the systems for healthcare monitoring, rehabilitation assistance, soft exoskeletal devices, and soft robotics. Stretchable strain sensors based on 2D flat film have been widely developed to monitor the in-plane force applied within the plane where the sensor is placed. However, to comprehensively obtain the mechanical feedback, the capability to detect the out-of-plane force, caused by the interaction outside of the plane where the senor is located, is needed. Herein, a 3D-structured stretchable strain sensor is reported to monitor the out-of-plane force by employing 3D printing in conjunction with out-of-plane capillary force-assisted self-pinning of carbon nanotubes. The 3D-structured sensor possesses large stretchability, multistrain detection, and strain-direction recognition by one single sensor. It is demonstrated that out-of-plane forces induced by the air/fluid flow are reliably monitored and intricate flow details are clearly recorded. The development opens up for the exploration of next-generation 3D stretchable sensors for electronic skin and soft robotics.

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