Robotics

Dual-Axis Robotic Platform for Posture and Locomotion Studies

Development of a Two-Axis Robotic Platform for the Characterization of Two-Dimensional Ankle Mechanics

Accurate characterization of ankle mechanics in lower extremity function is essential to advance the design and control of robots physically interacting with the human lower extremities, such as lower limb exoskeletons, active orthoses, and prostheses. This paper presents a two-axis robotic platform developed for the characterization of important neuromechanical properties of the human ankle, namely mechanical impedance and energetic passivity. This robotic platform is capable of simulating a wide range of mechanical (haptic) environments as well as applying precisely controlled perturbations to the ankle in 2 degrees-of-freedom (DOF) spanning both the sagittal and frontal planes. These features provide us with a unique way to characterize two-dimensional ankle mechanics while humans perform various lower extremity tasks in realistic physical environments. A series of validation experiments demonstrated that the platform can provide rapid perturbations up to an angular velocity of 100°/s with an error less than 0.1° even under excessive loading and simulate a wide range of haptic environments, from compliant to highly stiff environments, with an error less than 2.1% of the commanded values. A pilot human study demonstrated that the robotic platform could accurately quantify intrinsic ankle impedance in 2 DOFs with reliability higher than 97.5%. This study also confirmed that the platform could be utilized to quantify energetic passivity of the ankle in 2 DOFs. Implications for the design and control of lower extremity robots are discussed.

Parallel-Actuated Shoulder Exoskeleton

Development of a Low Inertia Parallel Actuated Shoulder Exoskeleton Robot for the Characterization of Neuromuscular Property during Static Posture and Dynamic Movement

The purpose of this work is to introduce a newly developed exoskeleton robot designed to characterize the neuromuscular properties of the shoulder, including intrinsic and reflexive mechanisms, during static posture and dynamic movement in a 3-dimensional space. Quantitative characterization of these properties requires fast perturbation (>100°/s) to separate their contribution from that of voluntary mechanism. Understanding these properties of the shoulder control could assist in the rehabilitation or enhancement of upper limb performance during physical human-robot interaction. The device can be described as a new type of spherical parallel manipulator (SPM) that utilizes three 4-bar (4B) substructures to decouple and control roll, pitch and yaw of the shoulder. By utilizing a parallel architecture, the 4BSPM exoskeleton has the advantage of high acceleration, fast enough to satisfy the speed requirement for the characterization of distinct neuromuscular properties of the shoulder. In this work, the prototype is presented, along with an evaluation of its position accuracy and step response. The development and preliminary testing of the 4B-SPM exoskeleton presented in this work demonstrates its potential to be a useful tool for studying the neuromuscular mechanisms of the shoulder joint.


A New Parallel Actuated Architecture for Exoskeleton Applications Involving Multiple Degree-of-Freedom Biological Joints

The purpose of this work is to introduce a new parallel actuated exoskeleton architecture that can be used for multiple degree-of-freedom (DoF) biological joints. This is done in an effort to provide a better alternative for the augmentation of these joints than serial actuation. The new design can be described as a type of spherical parallel manipulator (SPM) that utilizes three 4 bar substructures to decouple and control three rotational DoFs. Four variations of the 4 bar spherical parallel manipulator (4B-SPM) are presented in this work. These include a shoulder, hip, wrist, and ankle exoskeleton. Also discussed are three different methods of actuation for the 4B-SPM, which can be implemented depending on dynamic performance requirements. This work could assist in the advancement of a future generation of parallel actuated exoskeletons that are more effective than their contemporary serial actuated counterparts.


Optimizing Stiffness of a Novel Parallel-Actuated Robotic Shoulder Exoskeleton for a Desired Task or Workspace

The purpose of this work is to optimize the stiffness of a novel parallel-actuated robotic exoskeleton designed to offer a large workspace. This is done in an effort to help provide a solution to the issue wearable parallel actuated robots face regarding a tradeoff between stiffness and workspace. Presented in the form of a shoulder exoskeleton, the device demonstrates a new parallel architecture that can be used for wearable hip, ankle and wrist robots as well. The stiffness of the architecture is dependent on the placement of its actuated substructures. Therefore, it is desirable to place these substructures effectively so as to maximize dynamic performance for any application. In this work, an analytical stiffness model of the device is created and validated experimentally. The model is then used, along with a method of bounded nonlinear multi-objective optimization to configure the parallel actuators so as to maximize stiffness for the entire workspace. Furthermore, it is shown how to use the same technique to optimize the device for a particular task, such as lifting in the sagittal plane.


A Novel Shoulder Exoskeleton Robot Using Parallel Actuation and a Passive Slip Interface

This paper presents a five degrees-of-freedom (DoF) low inertia shoulder exoskeleton. This device is comprised of two novel technologies. The first is 3DoF spherical parallel manipulator (SPM), which was developed using a new method of parallel manipulator design. This method involves mechanically coupling certain DoF of each independently actuated linkage of the parallel manipulator in order to constrain the kinematics of the entire system. The second is a 2DoF passive slip interface used to couple the user upper arm to the SPM. This slip interface increases system mobility and prevents joint misalignment caused by the translational motion of the user's glenohumeral joint from introducing mechanical interference. An experiment to validate the kinematics of the SPM was performed using motion capture. The results of this experiment validated the SPM's forward and inverse kinematic solutions through an Euler angle comparison of the actual and command orientations. A computational slip model was created to quantify the passive slip interface response for different conditions of joint misalignment. In addition to offering a low inertia solution for the rehabilitation or augmentation of the human shoulder, this device demonstrates a new method of motion coupling, which can be used to impose kinematic constraints on a wide variety of parallel architectures. Furthermore, the presented device demonstrates a passive slip interface that can be used with either parallel or serial robotic systems.

Soft Ankle Foot Orthosis (SR-AFO)

Design and Validation of a Soft Robotic Ankle-Foot Orthosis (SR-AFO) Exosuit for Inversion and Eversion Ankle Support

This study presents a soft robotic ankle-foot orthosis (SR-AFO) exosuit designed to provide support to the human ankle in the frontal plane without restricting natural motion in the sagittal plane. The SR-AFO exosuit incorporates inflatable fabric-based actuators with a hollow cylinder design which requires less volume than the commonly used solid cylinder design for the same deflection. The actuators were modeled and characterized using finite element analysis techniques and experimentally validated. The SR-AFO exosuit was evaluated on healthy participants in both a sitting position using a wearable ankle robot and a standing position using a dual-axis robotic platform to characterize the effect of the exosuit on the change of 2D ankle stiffness in the sagittal and frontal planes. For both sitting and standing test protocols, a trend of increasing ankle stiffness in the frontal plane was observed up to 50 kPa while stiffness in the sagittal plane remained relatively constant over pressure levels. However, stiffness increase was significantly more noticeable during standing, the condition for which the exosuit is primarily designed, than under no loading on the ankle in seated. During quiet standing, the exosuit could effectively change eversion stiffness at the ankle joint from about 20 to 70 Nm/rad at relatively low-pressure levels (< 30 kPa). Eversion stiffness was 84.9 Nm/rad at 50 kPa, an increase by 387.5% from the original free foot stiffness.

  • C. Thalman and H. Lee, IEEE International Conference on Robotics and Automation (ICRA 2020)


Toward A Soft Robotic Ankle-Foot Orthosis (SR-AFO) Exosuit for Human Locomotion: Preliminary Results in Late Stance Plantarflexion Assistance

This study presents the design of a soft robotic ankle-foot orthosis (SR-AFO) exosuit to aid in plantarflexion for gait rehabilitation in individuals who suffer from irregular gaits due to stroke or other injuries. The SR-AFO exosuit is a sock-like garment fabricated from compliant fabrics. The SR-AFO exosuit aids in late stance of the walking gait in plantarflexion by contracting the actuator to pull the posterior end of the foot upward. This helps to reduce the muscle effort of the user during plantarflexion. The addition of a second actuator shows a 45.3% increase to 13.51+/-0.31 kg payload capacity. The actuators are oriented at an optimal angle of 5° to produce the highest pulling force. Three healthy participants are evaluated during walking trials with and without SR-AFO exosuit assistance while ankle angle and muscle activity are monitored. The gastrocnemius (GA) and soleus (SOL) muscle activity during late stance is reduced by 13.4% and 16.6% respectively. Tibialis anterior (TA) increases slightly during swing most likely due to the hysteresis in the system deflating during that window. The ankle range of motion remains within natural walking limitations and plantarflexion angle increases when the SR-AFO exosuit is active.

  • C. Thalman, T. Hertzell and H. Lee, IEEE International Conference on Soft Robotics (RoboSoft 2020)


The Multi-material Actuator for Variable Stiffness (MAVS): Design, Modeling, and Characterization of a Soft Actuator for Lateral Ankle Support

This study presents the design of the Multimaterial Actuator for Variable Stiffness (MAVS), which consists of an inflatable soft fabric actuator fixed between two layers of rigid retainer pieces. The MAVS is designed to be integrated with a soft robotic ankle-foot orthosis (SR-AFO) exosuit to aid in supporting the human ankle in the inversion/eversion directions. This design aims to assist individuals affected with chronic ankle instability (CAI) or other impairments to the ankle joint. The MAVS design is made from compliant fabric materials, layered and constrained by thin rigid retainers to prevent volume increase during actuation. The design was optimized to provide the greatest stiffness and least deflection for a beam positioned as a cantilever with a point load. Geometric programming of materials was used to maximize stiffness when inflated and minimize stiffness when passive. An analytic model of the MAVS was created to evaluate the effects in stiffness observed by varying the ratio in length between the rigid pieces and the soft actuator. A finite element analysis (FEA) was generated to analyze and predict the behavior of the MAVS prior to fabrication. The results from the analytic model and FEA study were compared to experimentally obtained results of the MAVS. The MAVS with the greatest stiffness was observed when the gap between the rigid retainers was smallest and the rigid retainer length was smallest. The MAVS design with the highest stiffness at 100 kPa was determined, which required 26.71+/-0.06 N to deflect the actuator 20 cm, and a resulting stiffness of 1335.5 N/m and 9.1% margin of error from the the model predictions.

  • C. Thalman, T. Hertzell, M. Debeurre, and H. Lee, IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2020)


Soft Robotic Hip Exosuit (SR-HExo)

  • Soft Robotic Hip Exosuit (SR-HExo) to Assist Hip Flexion and Extension during Human Locomotion

  • This study presents the design, fabrication, and preliminary results of a soft hip exosuit to assist hip flexion and extension during walking. The exosuit uses soft and compliant materials to create a wearable robot that has a low profile, low mass, and is highly flexible to freely move with the user’s natural range of motion. The Soft Robotic Hip Exosuit (SRHExo) consists of flat fabric pneumatic artificial muscles (ff-PAM) that contract when pressurized. The ff-PAM actuators are oriented in an ‘X’ shape to allow for natural range of motion across the hip joint and can generate 190 N of force at 200 kPa in a 0.3 sec window. The ‘X’ configuration (X-ff-PAM) actuators were placed on the anterior and posterior sides of the hip joint with height adjustable Velcro straps. Extension assistance and flexion assistance was provided in 10-45% and 50-90% of the gait cycle, respectively. To evaluate the effectiveness of the SR-HExo with healthy participants, hip range of motion and muscle activity during walking were monitored using a motion capture system and surface electromyography sensors. The impact of the SR-HExo on the range of motion was minimal with only a 4.0 deg reduction from the target range of motion of 30 deg. The exosuit contributed to reducing hip muscle activity. Hip extensor muscles showed a reduction of 13.1% for the gluteus maximus and 6.6% for the biceps femoris. Hip flexor muscles showed a reduction of 10.7% for the iliacus and 27.7% for the rectus femoris.

  • C. Thalman, L. Baye-Wallace, and H. Lee, IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2021)