Kinematic Performance Research Articles

Many Faces of Singularities in Robotics

In this survey paper some issues concerning a singularity concept in robotics are addressed. Singularities are analyzed in the scope of inverse kinematics for serial manipulator, a motion planning task of nonholonomic systems and the optimal control covering a large area of practical robotic systems. An attempt has been made to define the term singularity, which is independent on a specific task. A few classifications of singularities with respect to different criteria are proposed and illustrated on simple examples. Singularities are analyzed from a numerical and physical point of view. Generally, singularities pose some problems in motion planning and/or control of robots. However, as illustrated on the example on force/momenta transformation in serial manipulators, they can also be desirable is some cases. Singularity detection techniques and some methods to cope with them are also provided. The paper is intended to be didactic and to help robotic researchers to get a general view on the singularity issue.

Design and Performance Verification of a Novel RCM Mechanism for a Minimally Invasive Surgical Robot.

Minimally invasive surgical robots have the advantages of high positioning accuracy, good stability, and flexible operation, which can effectively improve the quality of surgery and reduce the difficulty for doctors to operate. However, in order to realize the translation of the existing RCM mechanism, it is often necessary to add a mobile unit, which is often bulky and occupies most space above the patient's body, thus causing interference to the operation. In this paper, a new type of planar RCM mechanism is proposed. Based on this mechanism, a 3-DOF robotic arm is designed, which can complete the required motion for surgery without adding a mobile unit. In this paper, the geometric model of the mechanism is first introduced, and the RCM point of the mechanism is proven during the motion process. Then, based on the establishment of the geometric model of the mechanism, a kinematics analysis of the mechanism is carried out. The singularity, the Jacobian matrix, and the kinematic performance of the mechanism are analyzed, and the working space of the mechanism is verified according to the kinematic equations. Finally, a prototype of the RCM mechanism was built, and its functionality was tested using a master-slave control strategy.

A Dynamic Approach to Low-Cost Design, Development, and Computational Simulation of a 12DoF Quadruped Robot

Robots equipped with legs have significant potential for real-world applications. Many industries, including those concerned with instruction, aid, security, and surveillance, have shown interest in legged robots. However, these robots are typically incredibly complicated and expensive to purchase. Iron Dog Mini is a low-cost, easily replicated, and modular quadruped robot built for training, security, and surveillance. To keep the price low and its upkeep simple, we designed our quadruped robot in a modular manner. We provide a comparative study of robotic manufacturing cost between our proposed robot and previously established robots. We were able to create a compact femur and tibia structure with sufficient load-bearing capacity. To improve stability and motion efficiency, we considered the novel Watt six-bar linkage mechanism. Using the SolidWorks modeling software, we analyzed the structural integrity of the robot’s components, considering their respective material properties. Furthermore, our research involved developing URDF data for our quadruped robot based on its CAD model. Its gait trajectory is planned using a 14-point Bezier curve. We demonstrate the operation of the simulation model and briefly discuss the robot’s kinematics. Computational methods are emphasized in this research, coupled with the simulation of kinematic and dynamic performances and analytical/numerical modeling.

Comprehensive Performance Evaluation of Landing Gear Retraction Mechanism in a Certain Model of Aircraft Based on RPCA Method

The performance of landing gear retraction mechanism in aircraft directly affects its safe operation. Therefore, it is important to analyze and evaluate its comprehensive performance during the design process. Multiple single kinematic and dynamic performance indexes of landing gear retraction mechanism could be solved by CAD/CAE software. The weighting factors of every single performance index are used to distinguish the different effects of comprehensive evaluation, and also achieved by the expert investigation method. Combining the a priori information of the mechanism, the comprehensive performance of landing gear retraction mechanism could be analyzed by Relative Principal Component Analysis (RPCA) method, and the scale of the landing gear retraction mechanism with the best comprehensive performance could be effectively selected. Further, RPCA could also provide a scientific reference basis for the optimization design of landing gear retraction mechanism.

An inverse kinematics framework of mobile manipulator based on unique domain constraint

This paper presents the collision-free solution to the inverse kinematics of a mobile manipulator. The main contribution is to propose a novel inverse kinematics solution framework combining unique domains. The inverse kinematics problem is formulated as an optimization problem in this work. Firstly, the objective function is simplified by the kinematics decoupling method based on improved disconnection and re-connection. Then, the joint variables are decoupled and constrained, and an approach to initialize the variables is proposed. An inverse kinematic solution framework for the manipulator body to avoid obstacles is further presented, and CMA-ES is applied to the framework. Finally, the simulation results demonstrate the effectiveness of the proposed method.

Path planning algorithm of dual arm space intelligent robot

In order to solve the cooperation problem between the two arms of the dual arm robot, improve the effect and accuracy of the path planning of the intelligent robot, in this study, a new path planning algorithm for dual arm space (DAS) intelligent robot is designed. By analyzing the kinematics performance of DAS intelligent robot, the operation law of DAS intelligent robot is determined. By analyzing the collision that needs to be considered during the operation of DAS intelligent manipulator, a collision detection method based on capsule envelope is proposed to detect the collision of obstacles in the running path. Finally, the path planning model of DAS intelligent robot is designed by using immune genetic algorithm. The experimental results show that the path planned by this method can avoid obstacles and dangerous areas, and the accuracy of path planning for the existing environment is always higher than 90%. With the increase of iteration times, the planning time is relatively stable, about 5.5 seconds. The proposed method can enhance the effect and accuracy of path planning, effectively shorten the time of path planning, and improve the work efficiency of DAS intelligent robot.

An iterative path-following method for hyper-redundant snake-like manipulator with joint limits

PurposeThis paper aims to present an iterative path-following method with joint limits to solve the problem of large computation cost, movement exceeding joint limits and poor path-following accuracy for the path planning of hyper-redundant snake-like manipulator.Design/methodology/approachWhen a desired path is given, new configuration of the snake-like manipulator is obtained through a geometrical approach, then the joints are repositioned through iterations until all the rotation angles satisfy the imposed joint limits. Finally, a new arrangement is obtained through the analytic solution of the inverse kinematics of hyper-redundant manipulator. Finally, simulations and experiments are carried out to analyze the performance of the proposed path-following method.FindingsSimulation results show that the average computation time is 0.1 ms per step for a hyper-redundant manipulator with 12 degrees of freedom, and the deviation in tip position can be kept below 0.02 mm. Experiments show that all the rotation angles are within joint limits.Research limitations/implicationsCurrently , the manipulator is working in open-loop, the elasticity of the driving cable will cause positioning error. In future, close-loop control based on real-time attitude detection will be used in in combination with the path-following method to achieve high-precision trajectory tracking.Originality/valueThrough a series of iterative processes, the proposed method can make the manipulator approach the desired path as much as possible within the joint constraints with high precision and less computation time.

Piezoelectric vibration suppression of a flexible mounting link for precise space robot operating

In large-range manipulator operating mission, it is essential to connect an additional link with end-effectors to enlarge the operation space, which unavoidably introduces the vibration disturbance. An active piezoelectric vibration suppression method is proposed in this paper. The multiple piezoelectric patches shunted with time-variant resonant circuit are mounted on the link and an adaptive controller acting on circuit is utilized for suppressing the vibration due to excitation on various mass on the tip of the link during the robot operating. The electro-mechanical system of a kinematic manipulator model and an analytical flexible link model is established. The vibration controller is designed using the neural network which maps the relationship between the output voltage of piezoelectric sensors and the proper impedance of the circuit. The simulation study shows that the proposed method in this paper could be well applied in space robot operating.

Mechanical design and position-tracking control of a novel robotic joint with a circular rotary electro-hydraulic actuator

Robotic exoskeletons with different actuators have been extensively investigated for decades, but designing a robot joint with compact structure, sufficient output torque, and satisfactory kinematic performance still remains a challenge. The paper introduces the mechanical design and control scheme of a novel joint with a circular rotary electro-hydraulic actuator in order to provide walking assistance for the hip joint. First, measurement and analysis techniques are applied in the gait recognition to determine an accurate swing range of the target joint and provide essential information for the structure design of the hydraulic rotary drive joint. Secondly, the functional structure and working principle of the hydraulic rotary joint are described in detail and the corresponding mathematical model is established for the valve-controlled hydraulic servo system. In addition, an adaptive sliding mode control (ASMC) method is proposed for position-tracking and improving the anti-disturbance ability of the controlled system. The global asymptotic stability and finite-time convergence of the closed-loop system are proved by Lyapunov stability theory. Finally, the feasibility and position-tracking performance of the designed ASMC controller were experimentally verified. Compared to the PID controller and the conventional sliding mode control scheme, the proposed controller improved the position-tracking control accuracy by 20%.

Altered Bimanual Kinetic and Kinematic Motor Control Capabilities in Older Women.

Older women may experience critical neuromuscular impairments interfering with controlling successful bimanual motor actions. Our study aimed to investigate altered bimanual motor performances in older women compared with younger women by focusing on kinetic and kinematic motor properties. Twenty-two older women and 22 younger women performed bimanual kinetic and kinematic motor tasks. To estimate bimanual kinetic functions, we calculated bimanual maximal voluntary contractions (i.e., MVC) and force control capabilities (i.e., mean force, accuracy, variability, and regularity of the total force produced by two hands) during bimanual hand-grip submaximal force control tasks. For bimanual kinematic performances, we assessed the scores of the Purdue Pegboard Test (i.e., PPT) in both hands and assembly tasks, respectively. For the bimanual MVC and PPT, we conducted an independent t-test between two groups. The bimanual force control capabilities were analyzed using two-way mixed ANOVAs (Group × Force Level; 2 × 2). Our findings revealed that the older women showed less bimanual MVC (p = 0.046) and submaximal force outputs (p = 0.036) and greater changes in bimanual force control capabilities as indicated by a greater force variability (p = 0.017) and regularity (p = 0.014). Further, the older women revealed lower scores of PPT in both the hands condition (p < 0.001) and assembly task condition (p < 0.001). The additional correlation analyses for the older women showed that lower levels of skeletal muscle mass were related to less bimanual MVC (r = 0.591; p = 0.004). Furthermore, a higher age was related to lower scores in the bimanual PPT assembly task (r = -0.427; p = 0.048). These findings suggested that older women experience greater changes in bimanual motor functions compared with younger women.

Magnetic-field-induced propulsion of jellyfish-inspired soft robotic swimmers.

The multifaceted appearance of soft robots in the form of swimmers, catheters, surgical devices, and drug-carrier vehicles in biomedical and microfluidic applications is ubiquitous today. Jellyfish-inspired soft robotic swimmers (jellyfishbots) have been fabricated and experimentally characterized by several researchers that reported their swimming kinematics and multimodal locomotion. However, the underlying physical mechanisms that govern magnetic-field-induced propulsion are not yet fully understood. Here, we use a robust and efficient computational framework to study the jellyfishbot swimming kinematics and the induced flow field dynamics through numerical simulation. We consider a two-dimensional model jellyfishbot that has flexible lappets, which are symmetric about the jellyfishbot center. These lappets exhibit flexural deformation when subjected to external magnetic fields to displace the surrounding fluid, thereby generating the thrust required for propulsion. We perform a parametric sweep to explore the jellyfishbot kinematic performance for different system parameters-structural, fluidic, and magnetic. In jellyfishbots, the soft magnetic composite elastomeric lappets exhibit temporal and spatial asymmetries when subjected to unsteady external magnetic fields. The average speed is observed to be dependent on both these asymmetries, quantified by the glide magnitude and the net area swept by the lappet tips per swimming cycle, respectively. We observe that a judicious choice of the applied magnetic field and remnant magnetization profile in the jellyfishbot lappets enhances both these asymmetries. Furthermore, the dependence of the jellyfishbot swimming speed upon the net area swept (spatial asymmetry) is twice as high as the dependence of speed on the glide ratio (temporal asymmetry). Finally, functional relationships between the swimming speed and different kinematic parameters and nondimensional numbers are developed. Our results provide guidelines for the design of improved jellyfish-inspired magnetic soft robotic swimmers.

Design of a Dynamic Secondary Mirror Truss Adjustment Mechanism for Large Aperture Telescopes

This study focuses on the dynamic secondary mirror truss adjustment mechanism for large aperture telescopes. The relative positions between the primary and secondary mirrors have stringent requirements for large aperture optical telescopes, with an aperture of more than 2 m. Due to the large mass of the primary mirror, the secondary mirror system is designed as an adjustable mechanism with multiple degrees of freedom, dramatically impacting telescope imaging. The kinematic modeling is followed by a detailed description of the designed adjustment mechanism, and then a static and modal analysis of the designed mechanism is performed. Subsequently, a kinematic performance test of the experimental prototype is conducted. The developed mechanism can travel up to ±5 mm in the z-direction with an accuracy of 16 µm and deflection of ±0.574° in the xy-direction. It provides accuracy better than 6.4 arcseconds.

Immediate effects of forefoot wedges on multi-segment foot kinematics during jogging in recreational runners with a symptomatic pronated foot.

Background: Foot orthoses (FOs) have been used to alter lower limb kinematics and kinetics in pronated feet. A clear relationship between FOs' features, e.g., the amount of wedging and support, and the corresponding biomechanical responses is vital for the design and prescription of FOs. In this study, we sought to determine if changing the level of the forefoot wedge would cause a linear response in the multi-segment foot kinematics during jogging, and if this effect would be enhanced by an arch support. Methods: Ten pairs of 3D printed FOs with five levels of forefoot wedges and two levels of arch supports were tested on 12 recreational runners with a symptomatic pronated foot. Multi-segment foot kinematic data during jogging was measured using the Oxford Foot Model. Two-way ANOVAs were performed to examine the main effect of the forefoot wedge and arch support, as well as their interaction on peak joint angles. Statistical parametric mapping and paired-t tests were used to identify differences in the foot kinematic traces and the joint range of motion (ROM) between each FO and the control, respectively. Results: Linear main effects for the forefoot wedge level were found in the forefoot peak dorsiflexion, eversion and rearfoot peak dorsiflexion of jogging. FOs with a medial forefoot wedge caused an average of 2.5° reduction of the forefoot peak abduction during jogging. Furthermore, forefoot wedges showed an opposite effect on the sagittal ROM of the forefoot and rearfoot. Adding an arch support did not improve the kinematic performance of a forefoot wedge during jogging. Conclusion: This study highlights a linear dose-response effect of a forefoot wedge on forefoot kinematics during jogging, and suggests using a medial forefoot wedge as an anti-pronator component for controlling forefoot motion of a pronated foot.

Design and kinematic performance analysis of a ship shell plate spraying manipulator

In order to solve the problems of low efficiency and pollution of the existing artificial ship outer plate spraying, a parallel spraying manipulator for ship outer plate is presented and analyzed. The structure analysis of the 3-DOF (degree of freedom) spraying manipulator is carried out using screw theory, and the mechanism diagram and virtual prototype are given. The position of the spraying manipulator is studied, and the expressions of the inverse position solution and the forward position solution are obtained. The Jacobian matrix is developed velocity analysis, and three singular configurations of the spraying manipulator are analyzed. The rotation ability of the gun of the spraying manipulator is described and the reachable workspace is drawn. Results show that the proposed manipulator can accomplish more flexible output trajectories than traditional spraying operations, which has higher spraying efficiency and can save more labor.

Tailoring Upper-Limb Robot-Aided Orthopedic Rehabilitation on Patients' Psychophysiological State.

Physical therapy keeps exploiting more and more the capabilities of the robot of adapting the treatments to patients' needs. This paper aims at presenting a psychophysiological-aware control strategy for upper limb robot-aided orthopedic rehabilitation. The main features are the capability of i) generating point-to-point trajectories inside an adaptable workspace, ii) providing assistance in guiding the patients' limbs in accomplishing the assigned task allowing them to freely move with a certain degree of spatial and temporal autonomy and iii) tuning the control parameters according to the patients' kinematics performance and psychophysiological state. The implemented control strategy is validated in a real clinical setting on eight orthopedic patients undergoing twenty daily robot-aided rehabilitation sessions. The psychophysiological-aware control strategy evidenced a positive impact on the enrolled participants since they are effectively conducted in a calmer condition with respect to the patients who did not receive the psychophysiological adaptation. Moreover, clinical performance indicators suggest that the proposed tailored control strategy improves motor functions.

On Forward Kinematics of a 3SPR Parallel Manipulator

This letter presents a new numerical method to solve the forward kinematics (FK) of a parallel manipulator with a three-limb spherical-prismatic-revolute (3SPR) structure. Unlike the existing numerical approaches that require the manipulator’s Jacobian matrix and its inverse at each iteration, the proposed algorithm requires much less complex computations to estimate the FK parameters. A cost function is introduced that measures the difference between actual FK values and its estimates. At each iteration, the problem is handled in two steps. First, the estimates of the platform orientation from the heave estimates are obtained. Then, the heave estimates are updated along the gradient direction of the proposed cost function. To evaluate the performance of the proposed algorithm, we compare results with those of a Jacobian-based (JB) approach for a 3SPR parallel manipulator.

On the Discrete Implementation of the Filtered Inverse Method for Serial Robots

In this paper, the filtered inverse algorithm for dynamic inversion of matrices is revisited and additional analysis regarding its discrete implementation and related gain limitations are presented. The method is used to provide a solution to the inverse kinematics of a serial redundant robot manipulator with 7-DoF for both position and orientation control. The theoretical results obtained and the performance of the discrete method are validated on a relevant robotics simulation environment that also incorporates visual perception components, such as an eye-in-hand camera and artificial markers.

Unsupervised Learning-based Analytical Inverse Kinematics for High-redundancy Mobile Manipulators

Redundant manipulators are of interest to the robotics community because they can perform additional tasks beyond the primary ones. Coupling them with a mobile platform increases the number of degrees of freedom (DOF) and allows them to perform more complex tasks in a larger workspace. However, the increase in the number of DOFs significantly complicates the establishment of the inverse kinematic model. Indeed, several joint configurations can be associated with a given end-effector (EE) pose. In this paper, we parameterize some joints of the mobile manipulator (MM) to transform it into a non-redundant counterpart by clustering its workspace and configuration space. Thus, conventional methods can be applied to derive the IK of the resulting non-redundant counterpart. A series of simulations validate the proposed approach.

STRUCTURAL SYNTHESIS OF SERIAL SPHERICAL MANIPULATORS

Serial manipulators are a serial of links connected by joints. The manipulator is called serial, because the drives of this manipulator are arranged in series, one after the other. Most often, the drives of the sequential manipulator are located on jointes or are coordinated with the joint. All links, the base, as well as the executive link, make up the kinematic chain of the manipulator. Serial manipulators have a large working area, it is much larger than the working area of parallel manipulators, which allows them to work with large parts, which undoubtedly increases the area in which the manipulator is capable of working. Mass-produced robots typically have six joints because at least six degrees of freedom are required to place a controlled object in an arbitrary position and orientation in the robot's workspace. The inverse kinematics of sequential manipulators with six rotary joints and with three consecutive intersecting joints can be solved in closed form, i.e. analytically This result had a huge impact on the design of industrial robots. This section provides a unified work for the calculation of the mobility and constraints in a general over constraint spherical manipulators based on spherical serial manipulator plus the different spherical structural groups with two, three and four classes. The results of the section can be considered by knowledges of structural groups with general constraint three constructed to the serial spherical manipulator with 3DoF. The 3DoF serial spherical manipulators represent as a series of 1DoF revolute joints with the axises intersecting in the center of sphere. Three illustrative examples showcasing the method are presented.

Functional evaluation of optimal index finger proximal interphalangeal joint fusion angle using a simulated joint arthrodesis

This study aims at qualitatively and quantitatively evaluating the effects of simulated index finger proximal interphalangeal (PIP) joint fusion angles on hand kinematic function and performance. Although arthrodesis of the index finger PIP joint is an effective medical procedure that produces a durable, pain-free, and stable joint, it permanently immobilizes the joint. Twenty healthy subjects performed basic functional hand activities with the index finger PIP joint unconstrained (UC) and constrained to selected angles under surveillance of a motion capture system. Our results indicate differences in perceived difficulty, time performance, and the functional ROM of the hand joints when the index finger PIP joint is UC and constrained to 0, 20, and 40 degrees of flexion. The mean total perceived difficulty scores for all 6 tasks were higher for the PIP at 0 degrees than for the UC condition (p < 0.001) and for the PIP at 40 degrees (p = 0.048). The functional ROM presented a smaller total number of hand joints affected by the PIP at 20 degrees (25 in total) than the PIP at 0 (31 in total) and 40 (27 in total) degrees during execution of all 6 tasks tested. Therefore, the decision on the appropriate index finger PIP angle for arthrodesis may be between 20 and 40 degrees, as globally for all 6 tasks tested, 0 degrees exhibited the worst results regarding perceived difficulty, performance time, and number of joints with affected ROM. Selecting the appropriate angle for arthrodesis should consider a more complete set of functional activities.