Joint Angle Control Research Articles

Encrypted Simultaneous Control of Joint Angle and Stiffness of Antagonistic Pneumatic Artificial Muscle Actuator by Polynomial Approximation

Encrypted Simultaneous Control of Joint Angle and Stiffness of Antagonistic Pneumatic Artificial Muscle Actuator by Polynomial Approximation

Backstepping model‐free adaptive control for a class of second‐order nonlinear systems

SummaryThis paper proposes a backstepping model‐free adaptive control (BS‐MFAC) algorithm for the trajectory tracking control problem of a class of second‐order nonlinear systems. Firstly, the model‐free adaptive control (MFAC) is employed to track the virtual desired velocity. Then, based on the measured state data at the current moment, a virtual desired velocity is designed, combining MFAC with backstepping control in a clever manner. By designing a discrete form of Lyapunov function, it is proven that the system velocity error under this algorithm converges asymptotically and stably. Furthermore, a nonhomogeneous difference equation solution related to the system position is obtained through calculations. The analysis of the solution indicates that the system position output error will slide into a neighborhood around zero. This algorithm possesses advantages such as simple structure, model independence, and strong robustness. Additionally, a planar two‐link space robot arm model is constructed using the Mbdyn platform, a multibody dynamics simulation software. Trajectory tracking control of joint angles is achieved under the proposed control algorithm in this paper. The simulation outcomes unequivocally establish the efficacy of the algorithm, which adeptly exploits the pseudo partial derivatives (PPD) estimation for second‐order nonlinear systems in MFAC. The algorithm yields expedited and superior trajectory tracking control of said systems.

A Torque Control Strategy for a Robotic Dolphin Platform Based on Angle of Attack Feedback.

Biological fish can always sense the state of water flow and regulate the angle of attack in time, so as to maintain the highest movement efficiency during periodic flapping. The biological adjustment of the caudal fin's angle of attack (AoA) depends on the contraction/relaxation of the tail muscles, accompanying the variation in tail stiffness. During an interaction with external fluid, it helps to maintain the optimal angle of attack during movement, to improve the propulsion performance. Inspired by this, this paper proposes a tail joint motion control scheme based on AoA feedback for the high-speed swimming of bionic dolphins. Firstly, the kinematic characteristics of the designed robot dolphin are analyzed, and the hardware basis is clarified. Second, aiming at the deficiency of the tail motor, which cannot effectively cooperate with the waist joint motor during high-frequency movement, a compensation model for the friction force and latex skin-restoring force is designed, and a joint angle control algorithm based on fuzzy inference is proposed to realize the tracking of the desired joint angle for the tail joint in torque mode. In addition, a tail joint closed-loop control scheme based on angle of attack feedback is proposed to improve the motion performance. Finally, experiments verify the effectiveness of the proposed motion control scheme.

A Prediction of Fingertip Force and Joint Kinematics of Individual Fingers using Motoneuron Firing Activities

<h3>Research Objectives</h3> Advanced assistive robotic hands can help individuals with hand impairment to perform daily activities. The detection of intended motor output of individual fingers, however, remains a challenge. The objective of this study was to develop a decoding method to continuously and simultaneously predict fingertip forces and joint kinematics of individual fingers using motoneuron firing frequency. <h3>Design</h3> Blind source separation method was applied to EMG signals to obtain motor unit (MU) firing activities. MU refinement procedure was used to determine finger- and task-specific MU pools. Obtained MU pools were tested on different datasets involving both isometric and dynamic tasks (combined). Populational MU firing frequencies were calculated to estimate the fingertip forces and joint angles concurrently using regression models. Model performance was compared with conventional EMG amplitude-based approach. <h3>Setting</h3> The study was carried out at the NC State/UNC Joint Department of Biomedical Engineering. <h3>Participants</h3> Seven healthy volunteers (Age: 28±7) participated in this study. No participant had any prior neuro-muscular ailments. All participants provided an informed consent. <h3>Interventions</h3> Not applicable. <h3>Main Outcome Measure(s)</h3> Concurrent and continuous prediction of finger kinetics and kinematics via motoneuron activities. <h3>Results</h3> MU approach led to better performance (higher correlation between the predicted and measured output and lower prediction error) in predicting both joint angles and fingertip forces than the EMG amplitude approach. <h3>Conclusion(s)</h3> MU pools can be identified for specific finger-task combinations, which allows concurrent control of fingertip forces and joint angles with assistive robot hands. Separation matrix derived from single finger trials was used applied to combined trials to avoid the computationally intensive nature of HD-EMG decomposition and to determine its usability in real-time. Further development of this method could provide concurrent and continuous control of individual finger movements of highly dexterous robotic hands.

Towards stabilization and navigational analysis of humanoids in complex arena using a hybridized fuzzy embedded PID controller approach

In this study, path planning and stabilization of humanoids are carried out in an uneven path and dynamic environment. The importance of the work focuses on avoiding local minima and trapping in dead-ends during navigation. The sole purposes of this research are to i) Stabilize the humanoid on an uneven surface. ii) Develop proper path planning for the humanoid so that it can adequately navigate through obstacle-rich terrain. For achieving the above said objectives, the robot's controller is designed by tuning the Proportional-integral-derivative (PID) controller with a fuzzy logic controller (FLC) for better performance. The PID controller does joint angle control and torque control respectively. In contrast, a complicated task like generating optimized turning angle (OTA) and adjusting feet angle during stepping upon an uneven path is done by FLC. Gait generation during stepping on and off an uneven surface for the humanoid robot is discussed and implementation of the inverted pendulum plus flywheel method (LIPPFM) is used for the analysis of the dynamics of motion and removing the height constraint (center of mass) where the upper body is considered as the mass of the pendulum. Petri net controller is used to navigate humanoids in an environment with multiple humanoids. To examine the proposed controller’s performance, the controller undergoes testing in simulation and experimental set up, and the obtained results are compared with recently developed techniques. V-REP software is used for conducting the simulation with an arena-size of 240*160 dimensions to test the effectiveness of the developed controller. A less than 5 % deviation is found because of friction and signal delay is noticed between simulation and the experimental result obtained for navigation while comparing to the previously developed technique such as PEM. There is a significant improvement in path length by 10.49 % is noticed and a decrease of 2.98 % in computational time is noticed. When the navigation parameter of the FUZZY-PID controller is compared with Genetic Potential Field (GPF), Pseudo Bacterial Potential Field (PBPF), and Bacterial Potential Field (BPF), there is an improvement of 15.41 %, 12.51 %, and 8.56 % respectively are noticed. It has been seen that the FUZZY-PID controller minimizes the settling time and lower the peak overshoot. When the humanoid robot crosses the uneven path using the proposed FUZZY-PID controller, the graph obtained is smoother than the previously developed technique. It displays the body attitude angle falling between less than ±1.5 degrees compared to ±2 degrees by the previously developed method which justify the selection of the FUZZY-PID controller.

Liquid Metal-Based Flexible and Wearable Sensor for Functional Human-Machine Interface.

Rigid sensors are a mature type of sensor, but their poor deformation and flexibility limit their application range. The appearance and development of flexible sensors provide an opportunity to solve this problem. In this paper, a resistive flexible sensor utilizes gallium−based liquid metal (eutectic gallium indium alloy, EGaIn) and poly(dimethylsiloxane) (PDMS) and is fabricated using an injecting thin−line patterning technique based on soft lithography. Combining the scalable fabrication process and unique wire−shaped liquid metal design enables sensitive multifunctional measurement under stretching and bending loads. Furthermore, the flexible sensor is combined with the glove to demonstrate the application of the wearable sensor glove in the detection of finger joint angle and gesture control, which offers the ability of integration and multifunctional sensing of all−soft wearable physical microsystems for human–machine interfaces. It shows its application potential in medical rehabilitation, intelligent control, and so on.

Electro-prosthetic E-skin Successfully Delivers Elbow Joint Angle Information by Electro-prosthetic Proprioception (EPP).

Neurotraumas and neurological diseases often result in compromised proprioceptive feedback, which plays a critical role in motor control by delivering real-time position information. Electro-prosthetic proprioception (EPP) using frequency-modulated electrotactile feedback is a promising solution, as it can deliver proprioceptive information such as a joint angle via tactile channel. Prior works demonstrated that EPP successfully delivered distance information between the end effector and the target object. In this study, we implemented the electronic skin (E-skin) monitoring the elbow joint angle and delivering it to the nervous system via tactile channel. We also demonstrated that EPP improved both accuracy and precision of the elbow joint angle control. The gyroscope measuring the elbow joint angle and electrodes delivering electrotactile feedback were integrated together as a skin using thin silicon coating and polyurethane film. We call this novel E-skin, monitoring and delivering joint angle information, as an electro-prosthetic E-skin. Elbow joint angle matching test with two healthy human subjects showed that the EPP, via electro-prosthetic E-skin, enhanced 101.7% accuracy and 63.8% precision in elbow joint angle control. Clinical Relevance-Presented electro-prosthetic E-skin will address the compromised proprioceptive feedback by delivering joint angle information by electro-prosthetic proprioception (EPP) via tactile channel. This novel E-skin will open up a new path to assist and rehabilitative motor control problems after neurotraumas and neurological diseases.

Misencoding of ankle joint angle control system via cutaneous afferents reflex pathway in chronic ankle instability.

This study aimed to investigate how the cutaneous reflexes in the peroneus longus (PL) muscle are affected by changing the ankle joint position in patients with chronic ankle instability (CAI). We also investigated the correlation between the degree of reflex modulation and angle position sense of the ankle joint. The participants were 19 patients with CAI and 20 age-matched controls. Cutaneous reflexes were elicited by applying non-noxious electrical stimulation to the sural nerve at the ankle joint in the neutral standing and eversion/inversion standing positions. The suppressive middle latency cutaneous reflex (MLR; ~ 70-120ms) and angle position sense of the ankle joint were assessed. During neutral standing, the gain of the suppressive MLR was more prominent in the CAI patients than in controls, although no significant difference was seen during 30° inversion standing. In addition, the ratios of the suppressive MLR and background electromyography in a neutral position were significantly larger than those at the 15°, 25°, and 30° inversion positions in CAI patients. No such difference was seen in control individuals. Furthermore, the correlations between reflex modulation degree and position sense error were quite different in CAI patients compared to controls. These findings suggest that the sensory-motor system was deteriorated in CAI patients due to changes in the PL cutaneous reflex pathway excitability and position sense of the ankle joint.

Sensorless Grasping Stiffness Control Considering Rolling Constraints by a Multi-fingered Robotic Hand

This paper proposes a grasping stiffness control method using a multi-fingered robot hand. This method does not need any information of a grasped object, such as geometry and attitude. The grasping stiffness is derived from geometrical constraints including rolling contact between a multi-fingered robot hand and a grasped object. To estimate the grasping stiffness without the use of external sensors, a contact point position of each fingertip is estimated by a relative relationship between the initial contact position and a virtual object frame. The proposed method is designed so that the desired grasping stiffness optimally transforms into a joint stiffness, and the desired joint stiffness is realized through each joint angle control. Finally, the usefulness of the proposed method is demonstrated through several numerical simulation results.

A lateral ankle sprain during a lateral backward step in badminton: A case report of a televised injury incident

BackgroundThis study presents a kinematic analysis of an acute lateral ankle sprain incurred during a televised badminton match. The kinematics of this injury were compared to those of 19 previously reported cases in the published literature. MethodsFour camera views of an acute lateral ankle sprain incurred during a televised badminton match were synchronized and rendered in 3-dimensional animation software. A badminton court with known dimensions was built in a virtual environment, and a skeletal model scaled to the injured athlete's height was used for skeletal matching. The ankle joint angle and angular velocity profiles of this acute injury were compared to the summarized findings from 19 previously reported cases in the published literature. ResultsAt foot strike, the ankle joint was 2° everted, 33° plantarflexed, and 18° internally rotated. Maximum inversion of 114° and internal rotation of 69° was achieved at 0.24 s and 0.20 s after foot strike, respectively. After the foot strike, the ankle joint moved from an initial position of plantarflexion to dorsiflexion—from 33° plantarflexion to 53° dorsiflexion (range = 86°). Maximum inversion, dorsiflexion, and internal rotation angular velocity were 1262°/s, 961°/s, and 677°/s, respectively, at 0.12 s after foot strike. ConclusionA forefoot landing posture with a plantarflexed and internally rotated ankle joint configuration could incite an acute lateral ankle sprain injury in badminton. Prevention of lateral ankle sprains in badminton should focus on the control and stability of the ankle joint angle during forefoot landings, especially when the athletes perform a combined lateral and backward step.

HERCULES: A Three Degree-of-Freedom Pneumatic Upper Limb Exoskeleton for Stroke Rehabilitation.

This paper outlines the construction, current state, and future goals of HERCULES, a three degree-of-freedom (DoF) pneumatically actuated exoskeleton for stroke rehabilitation. The exoskeleton arm is capable of joint-angle control at the elbow in flexion and extension, at the shoulder in flexion and extension, and at the shoulder in abduction and adduction. In the near future we plan to embed kinematic synergies into the control system architecture of this arm to gain dexterous and near-natural movements.Clinical Relevance- This device can be used as an upper limb rehabilitation testbed for individuals with complete or partial upper limb paralysis. In the future, this system can be used to train individuals on synergy-based rehabilitation protocols.

Development of Hiryu-II: A Long-Reach Articulated Modular Manipulator Driven by Thrusters

Robotic manipulators using thrusters for weight compensation are an active research topic due to their potential to exceed the limits of maximum length. However, existing manipulators that use thrusters have limitations of maximum length because the hardware design is not sufficiently refined. This letter focuses on overcoming these limitations and realizing an articulated manipulator more than twice the length of conventional ones. To cancel the moment for each link, we performed static analysis considering the torsional deformation around the link axis to derive the thruster position. Weight compensation and joint angle control of the manipulator can be realized with simple proportional integral derivative control for each link by numerical simulation. Consequently, we demonstrated the feasibility of the proposed manipulator by lifting a 0.6 kg payload at the arm end with a prototype of length 6.6 m. Theoretically, each thrust force control input was almost constant, regardless of link attitude. This suggests modular properties that contribute to the practicality of the proposed manipulator for various tasks.

Generation of Stealth Walking Gait on Low-friction Load Surface for Biped Robot with Semicircular Feet

This paper proposes a method to generate a stable stealth walking gait on frictionless road surface without double-limb support phase for a biped robot, and discusses the effect of semicircular feet on the gait properties. First, we introduce a mathematical model of a biped robot with an upper body and semicircular feet, and develop the control law to keep the horizontal ground reaction force at zero while achieving trajectory tracking control of the hip joint angle. Second, we derive an approximate analytical solution for an appropriate initial state of the robot based on the linearized equation of motion. Third, we perform numerical simulations of the linearized model and investigate the effect of the semicircular feet. Furthermore, we extend the method to the nonlinear model. The initial state of the nonlinear model is obtained by the analysis of the linearized model. We numerically investigate the gait generated by the nonlinear model.

Simultaneous Control of Joint Angle and Joint Stiffness Using Functional Electrical Stimulation

Simultaneous Control of Joint Angle and Joint Stiffness Using Functional Electrical Stimulation

Three-dimensional modeling and input saturation control for a two-link flexible manipulator based on infinite dimensional model

In this paper, the modeling and controlling problem is studied for a two-link rigid-flexible manipulator in three-dimensional (3D) space under input saturation. The dynamics of the 3D manipulator is first derived in infinite dimension model, which is represented by partial differential equations (PDEs). The controller can achieve joint angle control and vibration suppression control in the presence of input constraint. The stability analysis of the closed-loop system is given based on LaSalle’s Invariance Principle. Numerical simulations illustrate the effectiveness of the proposed controller.

Parametric Research on Underactuated Tendon-Driven Grasping Mechanism for Space Capture Operation

Space objects always stay in rotation mode with various nutation according to their different inertia parameters during free flying. It is hard for designing a grasping mechanism to capture a rotating target with unknown velocity and unknown size. An under-actuated tendon-driven grasping mechanism is designed and researched in this paper, and which could handle the uncertainties during the capturing using its structural flexibility and strong adaption to space unknown rotating objects for taking the advantage of under-actuation. The under-actuated grasping mechanism consists of four fingers, and each finger has four joints, but driven by only one tendon and four pre-designed springs, which make it a typical under-actuated mechanism. The partial feedback linearization method is modified for the control with time varying constraints and the parametric design method is proposed to complete the tracking control of multiple joint angle using a single driven tendon, and which is validated by the simulation of the whole capturing procedure.

Research on Angle and Stiffness Cooperative Tracking Control of VSJ of Space Manipulator Based on LESO and NSFAR Control

With the increase in on-orbit maintenance and support requirements, the application of space manipulator is becoming more promising. However, how to control the vibration generated by the space manipulator has been a difficult problem to be solved. The advent of variable stiffness joint (VSJ) has brought about a dawn in solving this problem. But how to achieve coordinated control of joint angle and stiffness is still a problem to be solved, especially when considering system model parameter uncertainty, unknown disturbance and control input saturation. In order to realize the controllable attenuation of the vibration of the space flexible manipulator based on the variable stiffness joint, the dynamic model of the variable stiffness joint was constructed. Then the linear transformation and feedback linearization method are used to transform its complex nonlinear dynamic model system into a pseudo-linear system containing aggregate disturbance and input saturation constraints. This paper constructs a linear extended state observer (LESO) for estimating the state of unknown systems in pseudo-linear systems. Based on the idea of state feedback control, a Neural State Feedback Adaptive Robust (NSFAR) control is constructed by using Radial Basis Function Neural Network. The adaptive input saturation compensation control law is also designed by using Radial Basis Function Neural Network to deal with the input saturation compensation problem. The ultimate uniform bounded stability of the constructed system is proved by the stability analysis based on Lyapunov function. Finally, the effectiveness and superiority of the constructed tracking algorithm are verified by compared simulation and semi-physical experiment.

Partial differential equation modeling and vibration control for a nonlinear 3D rigid‐flexible manipulator system with actuator faults

SummaryIn this paper, modeling and controlling problem for a two‐link rigid‐flexible manipulator in three‐dimensional (3D) space is studied under actuator faults. For modeling, the dynamics of the 3D mechanical system is represented by nonlinear partial differential equations, which is first derived in infinite dimension form. Based on the nonlinear model, the controller is proposed, which can achieve joint angle control and vibration suppression control in the presence of actuator faults. The stability analysis of the closed‐loop system is given based on LaSalle invariance principle. Numerical simulations illustrate the effectiveness of the proposed controller. This study will promote the development of nonlinear flexible manipulator systems in 3D space.

An Inverse Dynamics Optimization Formulation With Recursive B-Spline Derivatives and Partition of Unity Contacts: Demonstration Using Two-Dimensional Musculoskeletal Arm and Gait.

In this study, an inverse dynamics optimization formulation and solution procedure is developed for musculoskeletal simulations. The proposed method has three main features: high order recursive B-spline interpolation, partition of unity, and inverse dynamics formulation. First, joint angle and muscle force profiles are represented by recursive B-splines. The formula for high order recursive B-spline derivatives is derived for state variables calculation. Second, partition of unity is used to handle the multicontact indeterminacy between human and environment during the motion. The global forces and moments are distributed to each contacting point through the corresponding partition ratio. Third, joint torques are inversely calculated from equations of motion (EOM) based on state variables and contacts to avoid numerical integration of EOM. Therefore, the design variables for the optimization problem are joint angle control points, muscle force control points, knot vector, and partition ratios for contacting points. The sum of muscle stress/activity squared is minimized as the cost function. The constraints are imposed for human physical constraints and task-based constraints. The proposed formulation is demonstrated by simulating a trajectory planning problem of a planar musculoskeletal arm with six muscles. In addition, the gait motion of a two-dimensional musculoskeletal model with sixteen muscles is also optimized by using the approach developed in this paper. The gait optimal solution is obtained in about 1 min central processing unit (CPU) time. The predicted kinematics, kinetics, and muscle forces have general trends that are similar to those reported in the literature.

Joint Angle Control of an 8-inch Gas Pipeline Inspection Robot to Pass through Bends

Joint Angle Control of an 8-inch Gas Pipeline Inspection Robot to Pass through Bends