Joint Actuators Research Articles

Design and control of a passive compliant actuation with positioning measurement by LED and photodiode detector for medical application

Control of assistive exoskeleton robot recently has to be crucial of development and innovation of medical application. To support daily motions for humans, control application of assistive exoskeleton robot allows for limb movement with increased strength and endurance during patient’s wearable exoskeleton robot application. The interaction between such exoskeleton device and the human body at the connecting joint, especially the knees, is the main interest of this design formation. The assistive device requires to design and to develop into innovation design aspect. This research presents the novel design of an active compliant actuation joint in order to increasing the higher torque of actuation than conventional actuation joint. Control design of the higher torque actuation usually difficult priori to conventional torque control. This will contributed to applying the supervisory control for compliant actuation that verified by experiment method. Then the hybrid Radial Basis Function neural network (RBFNN) and PID were proposed for actuating torque control methods. Experimental results show that the design of supervisory control is get better response, and higher producing torque output than the conventional design. Error of torque control of compliant actuation is not instead of [Formula: see text] N·m for applying supervisory control, RBFNN with PID controller. Indeed, the low electromagnetic interference (EMI) positioning system using LED and photodiode detector is proposed to be usable in medical application.

Analysis of the PU-2UPS antenna parallel mechanism

In order to meet the requirements of the antenna pedestal for supporting and driving antenna to complete specific trajectory movement, the PU-2UPS parallel mechanism is proposed for antenna pedestal, where P, U and S represent the prismatic joint, universal joint and spherical joint, respectively. The screw theory is applied to analyze the mobility of the PU-2UPS antenna parallel mechanism (APM). Meanwhile, kinematic analysis of the mechanism is carried out based on the theory of twist and spatial acceleration. Based on the wrench and force balance relationship, the dynamic model of the PU-2UPS APM is established. Therefore, the actuation forces of each actuation joint are obtained. Afterward, the work-space of the PU-2UPS APM is constructed based on the boundary search method. Finally, the mathematical model of the PU-2UPS APM is established by MATLAB software, and the theoretical analysis of the PU-2UPS APM is verified by ADAMS software. The studies have been performed that the PU-2UPS APM is suitable for antenna pedestal in respect of mobility, kinematics and dynamics properties. This research results serve as a fundamental theoretical basis for design and analysis of the APM.

Dynamic Modeling and Mobility Analysis of the 3-R(RRR)R+R Antenna Mechanism

SUMMARY A novel 3-R(RRR)R+R (R as revolute joint) hybrid antenna mechanism (HAM) is proposed for noncircular polarized antenna. First, its mobility characteristic is analyzed. Besides, its kinematics is deduced, and the velocity and acceleration are obtained. Afterward, its dynamic model is established. The actuation torques of each actuation joint are obtained. Its actuation torques are verified by mathematical model analysis and dynamic simulation. Furthermore, its workspace is also presented. Finally, the motion characteristics experimental results show that the 3-R(RRR)R+R HAM can carry out the azimuth and pitch motion. This research work serves as a fundamental theoretical basis for its further application.

Development of lower body exoskeleton, mathematical modeling and video analysis of its prototype for obtaining customized joint actuation

Exoskeleton technology have shown its importance in various fields of application such as military, medical, industrial and commercial. But wide use of this technology is limited due high cost and Customized application according to user. If the exoskeleton has different gait cycle than unique natural gait cycle of user, it will lead to the injuries. Customization of exoskeleton gait cycle can overcome this challenge. Customized gait cycle according to user means control unit should provide output in form of position and torque in accordance to natural gait cycle of unique user. In this paper, A methodology is proposed and validated to obtain customized gait cycle for exoskeleton using video analysis and MATLAB simulation. Validation of Methodology is performed on normal human walking gait cycle. Video analysis performed in HALEX (Human Assistive Lower Limb Exoskeleton)is considered as basic method to conduct video analysis of gait cycle for unique user and data obtained from their experiment considered as base data for position vs time analysis. Later data obtained from video analysis is used as input data to obtain results fromMATLABSimscape-Simulink simulations using genetic algorithm. Above method is applied on biped robot to obtain results for normal human gait analysis. Simulations gives results in both position and torque wrt time. Torque values are compared with values obtained from mathematical model and position values are compared with values obtain from Video gait analysis. Validation of methodology gave satisfactory results and later suggested method can be used to obtain resulted torque and gait cycle for exoskeleton.

Design and Evaluation of a Pediatric Lower-Limb Exoskeleton Joint Actuator

Lower-limb exoskeletons have undergone significant developments for aiding in the ambulation of adults with gait impairment. However, advancements in exoskeletons for the pediatric population have comparatively been lacking. This paper presents a newly developed joint actuator designed to drive the hip and knee joints of a pediatric lower-limb exoskeleton. The performance requirements associated with the actuators were determined based on a target audience of children ages 6–11 years old. The developed actuators incorporate a hybrid belt-chain transmission driven by a frameless brushless DC motor. One actuator underwent benchtop testing to evaluate its performance with respect to their torque production, bandwidth properties, backdrivability in terms of inertia and friction characteristics, speed capabilities, and operational noise levels. As a preliminary validation, a set of actuators were placed in a prototype orthosis to move a pediatric test dummy in gait tracking via state-feedback control. The results showed that the newly developed actuators meet the design specifications and are suitable for use in the pediatric exoskeleton being developed.

Learning-Based Real-Time Detection of Robot Collisions Without Joint Torque Sensors

Robots operating in close proximity to humans require fast and reliable detection of collisions, which can range from sharp impacts (hard collisions) to pulling-pushing-catching motions (soft collisions). Because joint torque sensors can be costly, the external joint torques caused by collisions are typically estimated from motor current measurements at the joint actuators. For reliable detection, however, these methods require accurate models of dissipative friction at the joints. In this letter we design two learning-based detection methods – a support vector machine (SVM), and a convolutional neural network (CNN) – that require only motor current measurements together with a robot dynamics model and a momentum observer; no friction model is needed, and manual tuning of collision detection thresholds for each of the joints can be avoided. Extensive experiments with a six-dof industrial collaborative robot trained with stacks of four- and six-dimensional time series data validate our algorithms for a wide range of hard and soft collisions. The CNN-based method shows better performance if more training data is available, whereas the SVM-based method performs better with less data.

Влияние роботизированных тренировок на биомеханику голеностопного сустава у пациентов с постинсультным парезом

The key factor promoting post-stroke gait disturbances is motor impairment of the ankle joint (AJ) which results in pathological synergies. Robotic devices used for gait training are equipped with hip and knee joint actuators. However, there is no consensus in the literature on their effect on AJ movements. The aim of this study was to investigate the effect of robot-assisted gait training on AJ movements in patients with post-stroke paresis. The study recruited 22 hemispheric stroke survivors. They motor function was assessed using clinical scales and motion capture analysis. All patients received 11 robot-assisted gait training session. After rehabilitation, the total score on the Fugl-Meyer Assessment scale increased from 146.5 to 152 points (p < 0.05); for the lower limb, the score increased from 18 to 20.5 points (p < 0.05). The muscle tone of ankle extensors decreased from 2.5 to 2.0 points on the modified Ashworth scale (p < 0.05). The duration of the stance phase increased from 28.0 to 33.5% relative to the total gait cycle (GC). The main difference in the GC structure before and after rehabilitation is the presence of 3 GC parts instead of 5, suggesting consolidation of patients’ goniograms at 1-61% of GC. Comparison of joint angles before and after rehabilitation revealed that only the interquartile ranges (IR) were different (р < 0.05). The authors conclude that robot-assisted training with knee and hip joint actuators indirectly affects the kinematic parameters of AJ by promoting a shift towards the average gait kinematics.

Geometric and constrained control for a string of tethered drones

In this study, we present a novel concept of a multi tethered drone system. The system includes an arbitrary number of drones connected serially to an active ground station. The considered drones are of quadrotor type. Utilizing a unique pulley–gimbal mechanism, each drone can freely move along the tether, and its state is measured with respect to the ground station without the use of standard onboard inertial sensors or GPS. The proposed system can be thought of as a robotic arm where each tether section acts as a variable-length link and each drone is a joint actuator. We model the coupled behavior of the ground station and the string, taking into account an arbitrary number of drones. Then, a controller that combines tools from geometric-control and Model Predictive Control is suggested. The developed model and control approach are also applicable for other swarm applications where the position of agents is to be controlled to a string-like form. Finally, the concept is demonstrated using numerical simulations and an initial experiment, which illustrate its potential effectiveness.

Optimization-Based Investigation of Bioinspired Variable Gearing of the Distributed Actuation Mechanism to Maximize Velocity and Force

Transmission between high speed and high force motions is a classic, but challenging problem for most engineering disciplines as well as robotics. This study optimizes the performances (i.e., both velocity and force) of the distributed actuation mechanism (DAM) based on the novel concept of continuously variable gearing, which is inspired by muscle movement. To quantify continuously variable gearing in the DAM, the structural gear ratio (defined as joint speed/motor speed) is mathematically derived in terms of the slider position and the joint angle. Then, for a DAM-based three-revolute joint manipulator, a multi-objective optimization problem is formulated to determine the maximum end-effector velocity according to varying payloads. An optimization framework consisting of the analysis and optimization modules is constructed to verify the proposed concept with a comparison of an equivalent joint actuation mechanism (JAM)-based three-revolute joint manipulator. The numerical results demonstrate that the bioinspired variable gearing of the DAM allows for a significant enhancement of end-effector velocity and force, depending on a given task.

Design of a portable anthropomimetic upper limb rehabilitation device for patients suffering from neuromuscular disability.

An upper limb anthropomimetic rehabilitation device has been designed for patients suffering from a neuromuscular disability. The developed device has been designed as a wearable device and attempts to supplement all known functions of the human hand and fingers. The actuation of individual joints of the hand and wrist has been implemented by using DC motors interfaced to a control system. A pulley system was adopted to ensure a low device profile with the aim of maximising functionality in the affected hand. Both actuators and the electronic assembly are sited in the forearm assembly for this purpose. The device is designed to fulfill multiple roles. At its simplest instance, it is designed as a device for providing resistance training in patients suffering from reversible neuromuscular weakness. The device also aims to provide support as an exoskeleton device in patients suffering from partial but permanent neuromuscular weakness. The measurement of finger and wrist bending in axial and radial directions were investigated by an array of potentiometers mounted around the wearable device covering different joints of the fingers and wrist, and were further analyzed to characterize the range of the device. The system is a composite device with diverse functions fulfilling all the requirements of an upperlimb orthotic device. The device is planned to be part of a comprehensive exoskeleton device for quadriparetic patients in the future.

On stability and performance of disturbance observer-based-dynamic load torque compensator for assistive exoskeleton: A hybrid approach

A disturbance observer-based-dynamic load-torque compensator for current-controlled DC-drives, as joint actuator of assistive exoskeletons, has been recently proposed. It has been shown that this compensator can effectively linearize and decouple the coupled nonlinear dynamics of the human-exoskeleton system, by more effectively compensating the associated nonlinear load-torques of the exoskeleton at the joint level. In this paper, a detailed analysis of the current controlled DC drive-servo system using the said compensator, with respect to performance and stability is presented, highlighting the key factors and considerations affecting both the stability and performance of the compensated servo system. It is shown both theoretically and through simulation results that the stability of the compensated servo system is compromised as performance is increased and vice-versa. Based on the saturation state of the servo system, a new hybrid switching control strategy is then proposed to select stability or performance-based compensator and controller optimally. The strategy is then experimentally verified both at the joint and task space level by using the developed four active-degree of freedom exoskeleton test rig.

Electromagnetic and Thermal Analysis of a Permanent Magnet Motor Considering the Effect of Articulated Robot Link

This paper presents the electromagnetic and thermal characteristics of a permanent magnet synchronous motor (PMSM) in a joint actuator which is used for articulated robot application. In an attempt to design a compact PMSM for the articulated robot, robot link should be taken into consideration during the motor design process as it can reduce the temperature distribution on motor, thus reducing the volume of the motor. A lumped-parameter thermal model of PMSM with and without a link is proposed considering the core loss, copper loss, and mechanical loss as heat sources. The electromagnetic and thermal analysis results are well confirmed by the experiment in a 400 W 20-pole/24-slot PMSM. The experiment results show that the robot link helps to reduce the motor end-winding temperature by about 40%, and this leads to an increase in power density of the motor.

Development of Active Lower Limb Robotic-Based Orthosis and Exoskeleton Devices: A Systematic Review

The basic routine movements for elderly people are not easily accessible due to the weak muscles and impaired nerves in their lower extremity. In the last few years, many robotic-based rehabilitation devices, like orthosis and exoskeletons, have been designed and developed by researchers to provide locomotion assistance to support gait behavior and to perform daily activities for elderly people. However, there is still a need for improvement in the design, actuation and control of these devices for making them cost-effective in the worldwide market. In this work, a systematic review is presented on available lower limb orthosis and exoskeleton devices, to date. The devices are broadly reviewed according to joint types, actuation modes and control strategies. Furthermore, tabular comparisons have also been presented with the types and applications of these devices. Finally, the needful improvements for realizing the efficacy of lower limb rehabilitation devices are discussed along with the development stage. This review will help the designers and researchers to develop an efficient robotic device for the rehabilitation of the lower limb.

A survey: dynamics of humanoid robots

The mathematical foundation to describe the dynamics of a humanoid mechanism is reviewed. The discussion begins with the kinematics of an anthropomorphic mechanism, followed by the equation of motion of the system and the contact mechanics that accompanies with the motions. Some compact representations of both the robot dynamics and the contact mechanics are summarized. The former is referred to as the centroidal dynamics derived from the total momenta of the system, while the latter includes the contact wrench sum and the zero-moment point. They are naturally joined as a reduced-order dynamics model derived from an approximate relationship between the center of mass and the zero-moment point. Finally, some techniques to synthesize the intended motion into the joint actuation torques under limitations of contact forces are shown. This is basically a translation of a Japanese version with some modifications and reorganizations.

A Fault-Tolerant Method for Motion Planning of Industrial Redundant Manipulator

Nowadays, industrial redundant manipulators have been playing important roles in manufacturing fields, such as welding and assembling, by performing repetitive and dull work. Such long-term industrial operations usually require redundant manipulators to keep good working conditions and maintain steadiness of joint actuation. However, some joints of redundant manipulators may fall into fault status after enduring long-period heavy manipulations, causing that the desired industrial tasks cannot be accomplished accurately. In this article, we propose a novel fault-tolerant method with simultaneous fault-diagnose function for motion planning and control of industrial redundant manipulators. The proposed approach is able to adaptively localize which joints run away from the normal state to be fault, and it can guarantee to finish the desired path tracking control even when these fault joints lose their velocity to actuate. Simulation and experiment results on a Kuka LBR iiwa manipulator demonstrate the efficiency of the proposed fault-tolerant method for motion control of the redundant manipulator.

A separation theorem for joint sensor and actuator scheduling with guaranteed performance bounds

We study the problem of jointly designing a sparse sensor and actuator schedule for linear dynamical systems while guaranteeing a control/estimation performance that approximates the fully sensed/actuated setting. We further prove a separation principle, showing that the problem can be decomposed into finding sensor and actuator schedules separately. However, it is shown that this problem cannot be efficiently solved or approximated in polynomial, or even quasi-polynomial time for time-invariant sensor/actuator schedules; instead, we develop deterministic polynomial-time algorithms for a time-varying sensor/actuator schedule with guaranteed approximation bounds. Our main result is to provide a polynomial-time joint actuator and sensor schedule that on average selects only a constant number of sensors and actuators at each time step, irrespective of the dimension of the system. The key idea is to sparsify the controllability and observability Gramians while providing approximation guarantees for Hankel singular values. This idea is inspired by recent results in theoretical computer science literature on sparsification.

Classification of standing and sitting phases based on in-socket piezoelectric sensors in a transfemoral amputee.

A transfemoral prosthesis is required to assist amputees to perform the activity of daily living (ADL). The passive prosthesis has some drawbacks such as utilization of high metabolic energy. In contrast, the active prosthesis consumes less metabolic energy and offers better performance. However, the recent active prosthesis uses surface electromyography as its sensory system which has weak signals with microvolt-level intensity and requires a lot of computation to extract features. This paper focuses on recognizing different phases of sitting and standing of a transfemoral amputee using in-socket piezoelectric-based sensors. 15 piezoelectric film sensors were embedded in the inner socket wall adjacent to the most active regions of the agonist and antagonist knee extensor and flexor muscles, i.e. region with the highest level of muscle contractions of the quadriceps and hamstring. A male transfemoral amputee wore the instrumented socket and was instructed to perform several sitting and standing phases using an armless chair. Data was collected from the 15 embedded sensors and went through signal conditioning circuits. The overlapping analysis window technique was used to segment the data using different window lengths. Fifteen time-domain and frequency-domain features were extracted and new feature sets were obtained based on the feature performance. Eight of the common pattern recognition multiclass classifiers were evaluated and compared. Regression analysis was used to investigate the impact of the number of features and the window lengths on the classifiers' accuracies, and Analysis of Variance (ANOVA) was used to test significant differences in the classifiers' performances. The classification accuracy was calculated using k-fold cross-validation method, and 20% of the data set was held out for testing the optimal classifier. The results showed that the feature set (FS-5) consisting of the root mean square (RMS) and the number of peaks (NP) achieved the highest classification accuracy in five classifiers. Support vector machine (SVM) with cubic kernel proved to be the optimal classifier, and it achieved a classification accuracy of 98.33 % using the test data set. Obtaining high classification accuracy using only two time-domain features would significantly reduce the processing time of controlling a prosthesis and eliminate substantial delay. The proposed in-socket sensors used to detect sit-to-stand and stand-to-sit movements could be further integrated with an active knee joint actuation system to produce powered assistance during energy-demanding activities such as sit-to-stand and stair climbing. In future, the system could also be used to accurately predict the intended movement based on their residual limb's muscle and mechanical behaviour as detected by the in-socket sensory system.

Calibration for Precision Kinematic Control of an Articulated Serial Robot

Robot calibration to provide an accurate kinematic model is widely adopted in the advanced controller development of articulated serial robot performing complicated tasks. Conventional calibration methods mainly focus on the complete, continuous, and minimal error modeling. The generation and accumulation of errors have not been explicitly explained. In addition, the error identification and compensation sometimes are not practical for controller establishment. This article presents a robot calibration method using finite and instantaneous screw theory. From the differentiation of finite screw, the errors are defined by the deviations of instantaneous screws at initial pose. The error modeling is explicit. We also propose an advanced optimization algorithm based identification method and regard the geometry of redundant errors as constraints. The identified instantaneous screw errors are then converted to the joint actuation errors. Without modifying existing motion controller, errors are compensated by modified inputs. A UR3 robot is taken as an example to illustrate the calibration method. Simulation and experiment are implemented for verification. Comparing with the accuracy before calibration, the position and orientation accuracy of UR3 robot after calibration has improved by 94.75% and 89.29%. The results also show that modified inputs can be conveniently connected to controller development.

Biologically inspired swimming robotic frog based on pneumatic soft actuators

Research on soft robots and swimming robots has been widely reported and demonstrated. However, none of these soft swimming robots can swim flexibly and efficiently using legs, just like a frog. This paper demonstrates a self-contained, untethered swimming robotic frog actuated by 12 pneumatic soft actuators, which can swim in the water for dozens of minutes by mimicking the paddling gait of the natural frog. We designed two kinds of pneumatic soft actuators as the joints on the robotic frog’s legs, which allows the legs to be lighter and more compact. It is found that such soft actuators have great potential in developing amphibious bionic robots, because they are fast-responding, inherently watertight and simple in structural design. The kinematic analysis in swimming locomotion was conducted for the prototype robotic frog, and the locomotion trajectory of each leg was planned based on the analysis of the paddling gait of frogs. Combined with the deformation model of the soft actuators, the robotic frog’s legs are controlled by coordinating the air pressure of each joint actuator. The robotic frog’s body is compact and the total mass is 1.29 kg. Different paddling gaits were tested to investigate swimming performance. The results show that the robotic frog has agile swimming ability and high environmental adaptability. The robotic frog can swim forward more than 0.6 m (3.4 times the body length) in one paddling gait cycle(6 s), whose average swimming velocity is about 0.1 m s−1, and the minimum turning radius is about 0.15 m (less than 1 body length).

Design of quasi-zero stiffness joint actuator and research on vibration isolation performance

This paper proposes a new QZS joint actuator, which uses a torsion electromagnetic spring (TES) that can generate negative stiffness in parallel with a flexible rod with positive stiffness to obtain QZS characteristics with high static and low motion. In this paper, the expression of TES magnetic moment and stiffness is obtained by static analysis, the simulation is carried out by ANSYS Maxwell finite element software and the effect of TES structure parameters and current on its negative stiffness characteristics is analyzed. Then the dynamic model of QZS joint actuator is established, and the amplitude-frequency response function and torque transmissibility analytical expression are obtained by harmonic balance method, the good vibration isolation performance of QZS joint actuator is revealed. Finally, the stiffness and vibration isolation performance experiments are carried out with the QZS joint actuator to verify the correctness of the theoretical analysis, which indicates that it has a wide range of application background and research significance.