Passive Degrees Of Freedom Research Articles

The LIBRA NeuroLimb: Hybrid Real-Time Control and Mechatronic Design for Affordable Prosthetics in Developing Regions.

Globally, 2.5% of upper limb amputations are transhumeral, and both mechanical and electronic prosthetics are being developed for individuals with this condition. Mechanics often require compensatory movements that can lead to awkward gestures. Electronic types are mainly controlled by superficial electromyography (sEMG). However, in proximal amputations, the residual limb is utilized less frequently in daily activities. Muscle shortening increases with time and results in weakened sEMG readings. Therefore, sEMG-controlled models exhibit a low success rate in executing gestures. The LIBRA NeuroLimb prosthesis is introduced to address this problem. It features three active and four passive degrees of freedom (DOF), offers up to 8 h of operation, and employs a hybrid control system that combines sEMG and electroencephalography (EEG) signal classification. The sEMG and EEG classification models achieve up to 99% and 76% accuracy, respectively, enabling precise real-time control. The prosthesis can perform a grip within as little as 0.3 s, exerting up to 21.26 N of pinch force. Training and validation sessions were conducted with two volunteers. Assessed with the "AM-ULA" test, scores of 222 and 144 demonstrated the prosthesis's potential to improve the user's ability to perform daily activities. Future work will prioritize enhancing the mechanical strength, increasing active DOF, and refining real-world usability.

Design of a Novel Exoskeleton with Passive Magnetic Spring Self-locking and Spine Lateral Balancing

This paper proposes a new upper-limb exoskeleton to reduce worker physical strain. The proposed design is based on a novel PRRRP (P-Prismatic; R-Revolute) kinematic chain with 5 passive Degrees of Freedom (DoF). Utilizing a magnetic spring, the proposed mechanism includes a specially designed locking mechanism that maintains any desired task posture. The proposed exoskeleton incorporates a balancing mechanism to alleviate discomfort and spinal torsional effects also helping in limb weight relief. This paper reports specific models and simulations to demonstrate the feasibility and effectiveness of the proposed design. An experimental characterization is performed to validate the performance of the mechanism in terms of forces and physical strain during a specific application consisting of ceiling-surface drilling tasks. The obtained results preliminarily validate the engineering feasibility and effectiveness of the proposed exoskeleton in the intended operation task thereby requiring the user to exert significantly less force than when not wearing it.

CURER: A Lightweight Cable-Driven Compliant Upper Limb Rehabilitation Exoskeleton Robot

Upper limb exoskeletons show promise for improving functionalities required for stroke patients. Despite recent progress, most of current upper limb rehabilitation devices are still bulky, heavy, and less compliant to be applied. This article presents a cable-driven compliant upper limb rehabilitation exoskeleton robot (CURER) with a lightweight frame and comfortable human–robot interaction. A modular series elastic actuator (SEA) was designed to provide controlled torque for each active robotic joint, and Bowden cables were applied to transfer controlled torque to distal joints. A six-bar double parallelogram mechanism was designed to implement 3 active degrees of freedom (DOFs) of a shoulder. An actuated elbow with 1 DOF and a wrist with a passive DOF were also developed for CURER. The anthropomorphic shoulder, elbow, and wrist joints can minimize misalignment between human upper limbs and the robot. The length of anthropomorphic arm was adjustable for a wide range of users. It can apply up to a 33 N·m torque in shoulder flexion/extension, abduction/adduction, intra/extra rotation, and elbow flexion/extension, with a range of 7.6–8.0 Hz position bandwidth in each actuation. CURER has a large range of motion and can provide accurate torque control for stroke patients’ requirements. Besides, a comprehensive rehabilitation strategy including robot-in-charge mode and human-in-charge mode was developed for different recovery stages. Experiments carried out on CURER actuation units demonstrated good position and impedance control performance. Finally, a virtual reality training system was developed to assist the subjects to accomplish upper limb rehabilitation efficiently.

Design and analysis of a multi-DOF compliant gait rehabilitation robot

Robot-assisted rehabilitation is a rapidly advancing field whereby robotic devices are used for the treatment of disabilities. Mechanism design and actuation of these devices play important roles in the treatment and the non-ergonomic designs may even increase the cardiorespiratory load and cause discomfort leading to further gait disorders. This article identifies crucial design and actuation aspects of gait rehabilitation robots and presents the first intrinsically compliant gait robot design with three actuated and five passive degrees of freedom, alleviating the prevalent issues. The gait robot joints remain aligned with the human anatomical joints during the swing and the stance phases due to the use of special bushes and dampers. The intrinsically compliant actuators on the new gait robot make it safe to work with human subjects. Increased degrees of freedom allow for natural walking dynamics instead of canceling or constraining them. The robot firmware, including the kinematic modeling, is designed using multiple adaptive neuro-fuzzy inference system to save on the computational time of the robot controller. The new robot design is finally validated for its intended use in gait rehabilitation, by employing a fuzzy logic controller and evaluating the position, velocity, and acceleration profiles of its joints.

A Self-Aligning Upper-Limb Exoskeleton Preserving Natural Shoulder Movements: Kinematic Compatibility Analysis.

NESM- γ is an upper-limb exoskeleton to train motor functions of post-stroke patients. Based on the kinesiology of the upper limb, the NESM- γ includes a four degrees-of-freedom (DOF) active kinematic chain for the shoulder and elbow, along with a passive chain for self-aligning robotic joint axes with the glenohumeral (GH) joint's center of rotation. The passive chain accounts for scapulohumeral rhythm and trunk rotations. To assess self-aligning performance, we analyzed the kinematic and electromyographic data of the shoulder in eight healthy subjects performing reaching tasks under three experimental conditions: moving without the exoskeleton (baseline), moving while wearing the exoskeleton with the passive DOFs properly functioning, i.e., unlocked (human-in-the-loop(HIL)-unlocked), and with the passive DOFs locked (HIL-locked). Comparison of baseline and HIL-unlocked conditions showed nearly unchanged anatomical movement patterns, with a root-mean-square error of shoulder angle lower than 5 deg and median deviations of the GH center of rotation below 20 mm. Peak muscle activations showed no significant differences. In contrast, the HIL-locked condition deviated significantly from the baseline, as observed by the trunk and GH trajectory deviations up to 50 mm, accompanied by increased peak muscle activations in the Deltoid and Upper Trapezius muscles. These findings highlight the need for kinematic solutions in shoulder exoskeletons that can accommodate the movements of the entire shoulder complex and trunk to achieve kinematic compatibility.

Design of a Novel Tendon-Sheath-Driven Upper Limb Exoskeleton for Assisting Surgeon Performing Microlaryngoscopic Surgery

Abstract Microlaryngoscopic surgery is a type of laryngeal surgery performed by surgeons using microsurgical instruments under the observation of a specially designed laryngoscope. While performing a microlaryngoscopic operation, the surgeons must maintain their arms' position for a long time, which can cause arms' soreness and affect the accuracy of the operation. In this study, a tendon-sheath-driven upper limb auxiliary exoskeleton (TULAE) is proposed and developed. The flexible cables are compressed by a wave-shaped pressing mechanism to fix the TULAE's rotating joints. The TULAE can assist surgeons in laryngoscopy operations by providing suitable support for their arms to reduce the surgical risks caused by muscle fatigue. The TULAE has four degrees-of-freedom (DOFs) on each arm. The shoulder flexion/extension, shoulder abduction/adduction, and elbow internal rotation/external rotation can be fixed by the control box. The shoulder internal rotation/external rotation is a passive DOF obtained using hinges. The TULAE's shoulder, upper arm and forearm links are designed with lengths adjustable to accommodate wearers of different heights and weights. A large-scale but risk-free workspace is analyzed through rigid body kinematics using the spinor method. The control hardware of the TULAE is developed based on the open-source Arduino board. Finally, the experimental results show that this TULAE can significantly reduce the range of wrists shaking and assist surgeons in laryngoscopy surgery.

Characterization of Soft 3D Printed Actuators for Parallel Networks

Soft pneumatic actuators allow compliant force application and movement for a variety of tasks. While most soft actuators have compliance in directions perpendicular to their direction of force application, they are most often analyzed only in their direction of actuation. In this work, we show a characterization of a soft 3D printed bellows actuator that considers shear and axial deformations, modeling both active and passive degrees of freedom. We build a model based on actuator geometry and a parallel linear and torsional spring system which we fit to experimental data in order to obtain the model constants. We demonstrate this model on a soft delta mechanism and show how this single actuator model can be used to predict parallel structures of actuators with average positional errors of 4.0%. These results verify that the presented model and modeling approach can be used to speed up the design and simulation of more complex soft robot models by characterizing both active and passive forces of their one degree-of-freedom soft actuators.

Modeling and dynamic analysis of multi-loop RSSR-SS parallel manipulator

A spatial mechanism is frequently utilized in industrial applications such as parallel robot manipulators, machine positioning platforms, etc. The RSSR-SS Platform, with its 2-dof capacity, is a trailblazer in terms of parallel manipulator use. The present study focuses on developing control algorithms to increase performance by utilizing more structural system data. The Newton-Euler technique is used to construct the exact compact closed form of dynamic equations in the dimensionless form for the RSSR-SS manipulator. Rotary Spherical Spherical Rotary - Spherical Spherical (RSSR-SS) is a spatial mechanism with rigid body guidance and a passive degree of freedom. To analyze the dynamics of the RSSR-SS, an appropriate control system was developed using the Simulink and Sim Mechanics 2018b Simulink block technique. A Simulink model was created with the aid of the MATLAB 2018b translator. The simulation results illustrate the efficiency of the suggested approach, the dynamic equations of the RSSR-SS manipulator, and the influence of Leg/ Actuator inertia and its components on the dynamics of the entire system. Solidworks2021 was used to model the RSSR-SS. Finally, the article used to investigate dynamic issues with a certain RSSR-SS manipulator.

On-Line Learning for Planning and Control of Underactuated Robots With Uncertain Dynamics

We present an iterative approach for planning and controlling motions of underactuated robots with uncertain dynamics. At its core, there is a learning process which estimates the perturbations induced by the model uncertainty on the active and passive degrees of freedom. The generic iteration of the algorithm makes use of the learned data in both the planning phase, which is based on optimization, and the control phase, where partial feedback linearization of the active dofs is performed on the model updated on-line. The performance of the proposed approach is shown by comparative simulations and experiments on a Pendubot executing various types of swing-up maneuvers. Very few iterations are typically needed to generate dynamically feasible trajectories and the tracking control that guarantees their accurate execution, even in the presence of large model uncertainties.

A Novel Exoskeleton with Fractional Sliding Mode Control for Upper Limb Rehabilitation

SUMMARYThe robotic intervention has great potential in the rehabilitation of post-stroke patients to regain their lost mobility. In this paper, firstly, we present a design of a novel, 7 degree-of-freedom (DOF) upper limb robotic exoskeleton (u-Rob) that features shoulder scapulohumeral rhythm with a wide range of motions (ROM) compared to other existing exoskeletons. An ergonomic shoulder mechanism with two passive DOF was included in the proposed exoskeleton to provide scapulohumeral motion with corresponding full ROM. Also, the joints of u-Rob have more range of motions compared to its existing counterparts. Secondly, we propose a fractional sliding mode control (FSMC) to control u-Rob. Applying the Lyapunov theory to the proposed control algorithm, we showed the stability of it. To control u-Rob, FSMC has shown effectiveness to handle unmodeled dynamics (e.g. friction, disturbance, etc.) in terms of better tracking and chatter compared to traditional SMC.

Underactuated mechanical systems: Whether orbital stabilization is an adequate assignment for a controller design?

Abstract The paper contributes to developing algorithms for motion planning and motion control for mechanical systems with two and more passive degrees of freedom by exploring a challenging example in details. As shown, some of arguments of motion planning methods developed for systems of underactuation degree one can be generalized for novel demanding settings, while corresponding arguments and concepts for controller design should be substantially reconsidered and updated. Rigorous theoretical results are well supported by numerical studies.

Exoskeleton kinematic design robustness: An assessment method to account for human variability.

Exoskeletons are wearable devices intended to physically assist one or multiple human joints in executing certain activities. From a mechanical point of view, they are kinematic structures arranged in parallel to the biological joints. In order to allow the users to move while assisted, it is crucial to avoid mobility restrictions introduced by the exoskeleton's kinematics. Passive degrees of freedom and other self-alignment mechanisms are a common option to avoid any restrictions. However, the literature lacks a systematic method to account for large inter- and intra-subject variability in designing and assessing kinematic chains. To this end, we introduce a model-based method to assess the kinematics of exoskeletons by representing restrictions in mobility as disturbances and undesired forces at the anchor points. The method makes use of robotic kinematic tools and generates useful insights to support the design process. Though an application on a back-support exoskeleton designed for lifting tasks is illustrated, the method can describe any type of rigid exoskeleton. A qualitative pilot trial is conducted to assess the kinematic model that proved to predict kinematic configurations associated to rising undesired forces recorded at the anchor points, that give rise to mobility restrictions and discomfort on the users.

A novel hand exoskeleton with series elastic actuation for modulated torque transfer

Among wearable robotic devices, hand exoskeletons present an important and persistent challenge due to the compact dimensions and kinematic complexity of the human hand. To address these challenges, this paper introduces HandeXos-Beta (HX-β), a novel index finger-thumb exoskeleton for hand rehabilitation. The HX-β system features an innovative kinematic architecture that allows independent actuation of thumb flexion/extension and circumduction (opposition), thus enabling a variety of naturalistic and functional grip configurations. Furthermore, HX-β features a novel series-elastic actuators (SEA) architecture that directly measures externally transferred torque in real-time, and thus enables both position- and torque-controlled modes of operation, allowing implementation of both robot-in-charge and user-in-charge exercise paradigms. Finally, HX-β’s adjustable orthosis, passive degrees of freedom, and under-actuated control scheme allow for optimal comfort, robot-user joint alignment, and flexible actuation for users of various hand sizes. In addition to the mechatronic design and resulting functional capabilities of HX-β, this work presents a series of physical performance characterizations, including the position- and torque-control system performance, frequency response, end effector force, and output impedance. By each measure, the HX-β exhibited performance comparable or superior to previously reported hand exoskeletons, including position and torque step response times on the order of 0.3 s, −3 dB cut-off frequencies ranging from approximately 2.5 to 4 Hz, and fingertip output forces on the order of 4 N. During use by a healthy subject in torque-controlled transparent mode, the HX-β orthosis joints exhibited appropriately low output impedance, ranging from 0.42 to −0.042 Nm/rad at 1 Hz, over a range of functional grasps performed at real-life speeds. This combination of lab bench characterizations and functional evaluation provides a comprehensive verification of the design and performance of the HandeXos Beta exoskeleton, and its suitability for clinical application in hand rehabilitation.

DMP-Based Motion Generation for a Walking Exoskeleton Robot Using Reinforcement Learning

For the purpose of the assistance for human walking, this paper describes a novel coupled movement sequences planning and motion adaption based on dynamic movement primitives (DMPs) for a walking exoskeleton robot. The developed exoskeleton robot has eight degrees of freedom (DOFs). The hip and knee of each artificial leg can provide two electric-powered DOFs to flexion or extension, two passive-installed DOFs of the ankle are to achieve the motion of inversion/eversion and plantarflexion/dorsiflexion, and two passive DOFs of the hip are to achieve the motion of roll or yaw. A novel trajectory-learning scheme based on reinforcement learning (RL) combined with DMPs is presented for a lower limb exoskeleton robot, aiming to give assistance to human walking. In the proposed strategy, a two-level planning is designed. In the first level, the inverted pendulum approximation under the consideration of the locomotion parameters is utilized to guarantee the zero-moment point within the ankle joint of the support leg in the phase of single support. In the second level, the joint trajectories are modeled and learned by DMPs. Meanwhile, the RL is adopted to learn the trajectories for eliminating the effects of uncertainties in joint space. The experiment involving four subjects based on a lower limb exoskeleton robot demonstrates that the proposed scheme can effectively suppress the disturbances and uncertainties.

Design of a robot-assisted exoskeleton for passive wrist and forearm rehabilitation

Abstract. This paper presents a new exoskeleton design for wrist and forearm rehabilitation. The contribution of this study is to offer a methodology which shows how to adapt a serial manipulator that reduces the number of actuators used on exoskeleton design for the rehabilitation. The system offered is a combination of end-effector- and exoskeleton-based devices. The passive exoskeleton is attached to the end effector of the manipulator, which provides motion for the purpose of rehabilitation process. The Denso VP 6-Axis Articulated Robot is used to control motion of the exoskeleton during the rehabilitation process. The exoskeleton is designed to be used for both wrist and forearm motions. The desired moving capabilities of the exoskeleton are flexion–extension (FE) and adduction–abduction (AA) motions for the wrist and pronation–supination (PS) motion for the forearm. The anatomical structure of a human limb is taken as a constraint during the design. The joints on the exoskeleton can be locked or unlocked manually in order to restrict or enable the movements. The parts of the exoskeleton include mechanical stoppers to prevent the excessive motion. One passive degree of freedom (DOF) is added in order to prevent misalignment problems between the axes of FE and AA motions. Kinematic feedback of the experiments is performed by using a wireless motion tracker assembled on the exoskeleton. The results proved that motion transmission from robot to exoskeleton is satisfactorily achieved. Instead of different exoskeletons in which each axis is driven and controlled separately, one serial robot with adaptable passive exoskeletons is adequate to facilitate rehabilitation exercises.

An Adaptive Robust Approach to Modeling and Control of Flexible Arm Robots

In this paper, a novel adaptive robust approach to modeling and control of a class of flexible-arm robots subject to actuators unmodeled dynamics is proposed. It is shown how real-time signals measured from a dynamical system can be utilized to improve the accuracy of the mathematical model of flexible robots. Given the elasticity of the robot’s arms, flexible manipulators have both passive and active degrees of freedom. A nonlinear robust controller is designed for the active degrees of freedom to enable the robot to follow desired trajectories in the presence of actuators unmodeled dynamics. Furthermore, it is shown that under some feasible conditions, another nonlinear robust controller is designed for the passive degrees of freedom. Moreover, to use the system response for model extraction, two auxiliary signals are proposed to provide sufficient information for improving the accuracy of the dynamics of the system numerically. Additionally, two adaptive laws are proposed in each case to update the two introduced auxiliary signals. As a result, the controller controls the passive degrees of freedom after the active degrees of freedom converge to their desired trajectories. Simultaneously, the information collected from the system to update the auxiliary signals enhances the model accuracy. In the end, simulation results are presented to verify the performance of the proposed controller.

Physical human-robot interaction of an active pelvis orthosis: toward ergonomic assessment of wearable robots

BackgroundIn human-centered robotics, exoskeletons are becoming relevant for addressing needs in the healthcare and industrial domains. Owing to their close interaction with the user, the safety and ergonomics of these systems are critical design features that require systematic evaluation methodologies. Proper transfer of mechanical power requires optimal tuning of the kinematic coupling between the robotic and anatomical joint rotation axes. We present the methods and results of an experimental evaluation of the physical interaction with an active pelvis orthosis (APO). This device was designed to effectively assist in hip flexion-extension during locomotion with a minimum impact on the physiological human kinematics, owing to a set of passive degrees of freedom for self-alignment of the human and robotic hip flexion-extension axes.MethodsFive healthy volunteers walked on a treadmill at different speeds without and with the APO under different levels of assistance. The user-APO physical interaction was evaluated in terms of: (i) the deviation of human lower-limb joint kinematics when wearing the APO with respect to the physiological behavior (i.e., without the APO); (ii) relative displacements between the APO orthotic shells and the corresponding body segments; and (iii) the discrepancy between the kinematics of the APO and the wearer’s hip joints.ResultsThe results show: (i) negligible interference of the APO in human kinematics under all the experimented conditions; (ii) small (i.e., < 1 cm) relative displacements between the APO cuffs and the corresponding body segments (called stability); and (iii) significant increment in the human-robot kinematics discrepancy at the hip flexion-extension joint associated with speed and assistance level increase.ConclusionsAPO mechanics and actuation have negligible interference in human locomotion. Human kinematics was not affected by the APO under all tested conditions. In addition, under all tested conditions, there was no relevant relative displacement between the orthotic cuffs and the corresponding anatomical segments. Hence, the physical human-robot coupling is reliable. These facts prove that the adopted mechanical design of passive degrees of freedom allows an effective human-robot kinematic coupling. We believe that this analysis may be useful for the definition of evaluation metrics for the ergonomics assessment of wearable robots.

A unified dynamic algorithm for wheeled multibody systems with passive joints and nonholonomic constraints

This paper presents a systematic approach to develop a generalized symbolic/numerical dynamic algorithm for modeling and simulation of multibody systems with branches and wheels. The proposed dynamic algorithm includes the direct kinematic and inverse dynamic models of the wheeled systems with prismatic/revolute as well as actuated/passive degrees of freedom. Using the geometric configuration of the system through modified Denavit–Hartenberg convention, symbolic equations in general algorithmic form are developed for kinematic constraints associated with the wheel–ground contacts. The Newton–Euler equations are used to develop an algorithm for the inverse dynamic model of the multibody system. The complete algorithm is then used to solve the kinematics and dynamics of the system, and computes: (i) the kinematics of the external/internal passive degrees of freedom of the system, (ii) the Lagrange multipliers associated with the wheel–ground contacts, and (iii) the driving forces/torques of the actuated degrees of freedom. Some examples are solved with the help of the proposed algorithm, using MATLAB, to illustrate its implementation on different wheeled systems. These examples include a differential wheeled robot, a snake-like wheeled system, and a bicycle.

TWO-DEGREE ADJUSTABLE EXOSKELETON FOR ASSISTANCE OF THE HUMAN ARM USING A MECHANICAL SYSTEM OF FAST ASSEMBLY AND UPGRADABILITY

Abstract Stroke affects about 975,000 people annually. Currently different robotic systems are used, such as exoskeletons that support motor rehabilitation, where they sometimes increase the patient’s possible recovery rate. But these systems are expensive and often require adequate locations for therapy routines. This article offers the mechanical design of an exoskeleton concept for human upper limbs that allows the attachment to the arm and forearm, offering protection, torque, and movement, plus the possibility to adapt to different arm sizes. The biomechanics of the human arm, the kinematics required by the exoskeleton, different design criteria for this type of system, the CAD model, and the simulation of a robotic exoskeleton with an active and passive degree of freedom are considered. As a main result, the exoskeleton includes the biomechanics of the human arm so that its kinematics allow for adequate human arm movements for providing mechanical assistance, data acquisition and analysis, but also safety.

A Prediction Model for State Observation and Model Predictive Control of Biped Robots

AbstractBiped walking robots present a class of mechanical systems with many different challenges such as nonlinear multi‐body dynamics, a large number of degrees of freedom and unilateral contacts. The latter impose constraints for physically feasible motions and in stabilization methods as the robot can only interact due to pressure forces with the environment. This limitation can cause the system to fall under unknown disturbances such as pushing or uneven terrain. In order to face such problems, an accurate and fast model of the robot to observe the current state and predict the state evolution into the future has to be used. This work presents a nonlinear prediction model with two passive degrees of freedom (dof), point masses and compliant unilateral contacts. We show that the model is applicable for real‐time model predictive optimization of the robot's motion. Experiments on the biped robot LOLA [1] underline the effectiveness of the proposed model to increase the system's long term stability under large unknown disturbances. (© 2016 Wiley‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)