ABSTRACT
Objective To design and implement a control algorithm in a 6 degree of freedom (DOF) robotic manipulator, so as to simulate the spinal motion and provide stable and efficient testing plan for biomechanical tests on spinal implants. Methods The recognition method of stiffness matrix for L2-5 spinal system was firstly studied for decoupling purpose. Secondly, the direct force control system under each axial motion was established by combining the 6-axis manipulator control system with the incremental proportion integration differentiation (PID) control algorithm. By using the 6-axis direct force control system, pure moment of 7.5 N·m was applied in the direction of main motion axis to simulate flexion-extension (FE), lateral bending (LB) and axial rotation (AR) motion of L2-5 spinal segment. Results The range of motion (ROM) of L2-5 segment in FE, LB and AR direction was 23.01°,27.92°,9.81°, respectively. A 7.5 N·m pure moment could be achieved in the main motion axis, while maintaining zero force/moment in the unconstrained axis with root mean square (RMS) errors being less than 3 N and 0.1 N·m, respectively. Conclusions The proposed algorithm of direct force control using PID controller with predetermined stiffness decoupling matrix was capable of applying pure moment to the spine under FE, LB, AR motion. The research findings have a relatively high value of engineering application for various biomechanical testing of lumbar vertebrae.
ABSTRACT
Objective To design and implement a control algorithm in a 6 degree of freedom (DOF) robotic manipulator, so as to simulate the spinal motion and provide stable and efficient testing plan for biomechanical tests on spinal implants. Methods The recognition method of stiffness matrix for L2-5 spinal system was firstly studied for decoupling purpose. Secondly, the direct force control system under each axial motion was established by combining the 6-axis manipulator control system with the incremental proportion integration differentiation (PID) control algorithm. By using the 6-axis direct force control system, pure moment of 7.5 N·m was applied in the direction of main motion axis to simulate flexion-extension (FE), lateral bending (LB) and axial rotation (AR) motion of L2-5 spinal segment. Results The range of motion (ROM) of L2-5 segment in FE, LB and AR direction was 23.01°,27.92°,9.81°, respectively. A 7.5 N·m pure moment could be achieved in the main motion axis, while maintaining zero force/moment in the unconstrained axis with root mean square (RMS) errors being less than 3 N and 0.1 N·m, respectively. Conclusions The proposed algorithm of direct force control using PID controller with predetermined stiffness decoupling matrix was capable of applying pure moment to the spine under FE, LB, AR motion. The research findings have a relatively high value of engineering application for various biomechanical testing of lumbar vertebrae.
ABSTRACT
Although attention plays an important role in cognitive and perception, there is no simple way to measure one's attention abilities. We identified that the strength of brain functional network in sustained attention task can be used as the physiological indicator to predict behavioral performance. Behavioral and electroencephalogram (EEG) data from 14 subjects during three force control tasks were collected in this paper. The reciprocal of the product of force tolerance and variance were used to calculate the score of behavioral performance. EEG data were used to construct brain network connectivity by wavelet coherence method and then correlation analysis between each edge in connectivity matrices and behavioral score was performed. The linear regression model combined those with significantly correlated network connections into physiological indicator to predict participant's performance on three force control tasks, all of which had correlation coefficients greater than 0.7. These results indicate that brain functional network strength can provide a widely applicable biomarker for sustained attention tasks.
ABSTRACT
Objective To evaluate the ability of force control of elbow and shoulder during isometric contraction in patients with chronic stroke. Methods From January to December, 2015, 22 chronic stroke patients and 12 healthy people were measured the maximum force dur-ing shoulder abduction/adduction and elbow flexion/extension with instrument for measuring force of upper extremity. The coefficient of variation was calculated. Results The maximum force was less in the patients than in the healthy controls (t>2.349, P1.974, P<0.05), except those of elbow extension. Conclusion The force measure and the coefficient of varia-tion can reflect the force control in shoulder and elbow motion in stroke patients.
ABSTRACT
Los exoesqueletos son sistemas electro-mecánicos acoplados a las extremidades del cuerpo humano enfocados al incremento de su fuerza, velocidad y rendimiento principalmente. Las principales aplicaciones son en la milicia, en la industria y en la medicina, en particular se pueden utilizar para la rehabilitación de las extremidades. En este artículo se presenta un exoesqueleto de dos grados de libertad para realizar ejercicios de rehabilitación en tobillo y rodilla. El diseño y construcción del exoesqueleto está basado en la instrumentación y control de una ortesis del miembro inferior derecho. El Exoesqueleto utiliza sensores que estiman la fuerza producida por el humano y se encuentran acoplados a los actuadores SEA (Series Elastic Actuator) que se utilizan para amplificar la fuerza humana. La amplificación de la fuerza puede aumentarse o disminuirse según se necesite, permitiendo al usuario una mejora evolutiva hasta llegar a la rehabilitación. Además mediante sensores se estima la posición y velocidad angular de las articulaciones, que se utilizan para controlar el movimiento de la pierna. En resumen, el objetivo perseguido es de contar con un diseño propio de bajo costo de un exoesqueleto que ofrezca una disminución en el esfuerzo requerido por el usuario para mantenerse en pie y hacer algunos ejercicios de rehabilitación estáticos independientes como flexionar y extender la pierna derecha o izquierda.
Exoskeletons are electro-mechanical systems coupled to the body limbs focused mainly in increasing strength, speed and performance. The main applications are in the military, industry and medicine, particularly used for the rehabilitation in the extremities. In this paper we presented a exoskeleton with two degrees of freedom for rehabilitation of ankle and knee. The design and construction are based on the instrumentation and control of a right lower limb orthoses. The Exoskeleton uses sensors that estimate the force produced by the human, these sensors are coupled in the SEA (Series Elastic Actuator) used for amplify human strength. The amplification strength can be increased or decreased as needed, allowing the user an evolutionary improvement to reach rehabilitation. The exoskeleton has sensors for estimated angular position and angular velocity of joints, which are used to control the leg movement. The goal is to design a low-cost exoskeleton that provides a reduction in the effort required by the user to remain in in a standing position and to do some static rehabilitation exercises such as flexion and extension of the legs.
ABSTRACT
Objective To study the control problem in dynamic foot biomechanical simulator and propose a complete multi-axis control algorithm which could be more competitive than that of current gait simulators in aspects as simulations in degree-of-freedom (DOF), velocity, precision, weight-bearing and trial efficiency. Methods A novel custom-made foot and ankle biomechanical simulator was developed to simulate both motion and force characteristics in a stance phase with 5 DOF. A model of the simulator was built in Matlab based on gait analysis and reasonable simplification. Iteration learning control (ILC) was proposed to control multi-axis forces and was verified in Simulink. Finally, the control strategy was validated in the simulation platform with a prosthetic foot. Results The novel simulator could complete the motion and force loading process within 5 seconds in one stance after 4-5 iterations. All 3D ground reaction forces (Fz, Fy and Fx) had high verified repeatability. The tracking curves of Fz and Fy with 50% of real body weight could converge to the target ones with root mean square (RMS) error of 20 N and 8 N using ILC, respectively, which was smaller than 10% of simulated loads. Conclusions The proposed control strategy greatly improved intelligence of the simulator and provided a good foundation to further improve the simulation speed and accuracy. The development of the simulator is of great significance to the cadaveric experiments on foot and ankle biomechanics.
ABSTRACT
Recently the unique functional characteristics of bi-articular muscles have been revealed by means of EMG kinesiological analysis and control engineering analysis. A two-joint limb link mechanism provided with one antagonistic pair of bi-articular muscles passing over two adjacent joints as well as two antagonistic pairs of mono-articular muscles at both end joints could control output forces exerted at the end point of the link mechanism in an arbitral direction with only a single input command signal informing the desired direction. The output force distribution of the limb link mechanism with three pairs of six muscles showed a hexagonal shape, whereas the link mechanism without the paired bi-articular muscles and only with the two pairs of mono-articular muscles showed a tetragonal shape. Configurational characteristics of the hexagonal output force distribution indicated that an individual functionally different effective muscular strength can be evaluated from the output force values of four designated points on the output force distribution line. Such a limb link mechanism could also dissolve contact tasks in order to maintain postural stability. Clinical applications utilizing the unique control properties of bi- articular muscles may shed light on future rehabilitation medicine therapies.