Kinematic Design Research Articles

The Effects on Muscle Activity and Discomfort of Varying Load Carriage With and Without an Augmentation Exoskeleton

Load carriage is a key risk factor for Muscular Skeletal Disorders (MSDs). As one way to decrease such injuries, some exoskeletons have been developed for regular load carriage. We examined the ergonomic potential of an augmentation exoskeleton. Nine subjects completed eight trials of carrying tasks, using four loading levels (0, 15, 30, and 45 kg) and two carrying conditions (with and without the exoskeleton). Electromyography (EMG) and the extended NASA-TLX rating scales were investigated and analyzed by linear mixed modeling and two-way ANOVA methods. Noraxon MR3.8, SPSS19.0, and MATLAB R2014b software were adapted. The results show that most of the muscle mean activities increased significantly (p < 0.05) with exoskeleton assistance. However, the interactive effects illustrate a decreasing trend with increase of load level. The mean discomfort rating scale values were generally higher, but subjects generally preferred using the exoskeleton in heavier loading tasks. The exoskeleton can effectively augment the performance of humans in heavy load carriage. The main reasons for higher muscle activity are from inflexible structures and inharmonious human–robot interactions. In order to decrease the MSD risks and increase comfort, optimal human–robot control strategies and adaptable kinematic design should be improved.

Complete Path Planning for a Tetris-Inspired Self-Reconfigurable Robot by the Genetic Algorithm of the Traveling Salesman Problem

The efficiency of autonomous systems that tackle tasks such as home cleaning, agriculture harvesting, and mineral mining depends heavily on the adopted area coverage strategy. Extensive navigation strategies have been studied and developed, but few focus on scenarios with reconfigurable robot agents. This paper proposes a navigation strategy that accomplishes complete path planning for a Tetris-inspired hinge-based self-reconfigurable robot (hTetro), which consists of two main phases. In the first phase, polyomino form-based tilesets are generated to cover the predefined area based on the tiling theory, which generates a series of unsequenced waypoints that guarantee complete coverage of the entire workspace. Each waypoint specifies the position of the robot and the robot morphology on the map. In the second phase, an energy consumption evaluation model is constructed in order to determine a valid strategy to generate the sequence of the waypoints. The cost value between waypoints is formulated under the consideration of the hTetro robot platform’s kinematic design, where we calculate the minimum sum of displacement of the four blocks in the hTetro robot. With the cost function determined, the waypoint sequencing problem is then formulated as a travelling salesman problem (TSP). In this paper, a genetic algorithm (GA) is proposed as a strong candidate to solve the TSP. The GA produces a viable navigation sequence for the hTetro robot to follow and to accomplish complete coverage tasks. We performed an analysis across several complete coverage algorithms including zigzag, spiral, and greedy search to demonstrate that TSP with GA is a valid and considerably consistent waypoint sequencing strategy that can be implemented in real-world hTetro robot navigations. The scalability of the proposed framework allows the algorithm to produce reliable results while navigating within larger workspaces in the real world, and the flexibility of the framework ensures easy implementation of the algorithm on other polynomial-based shape shifting robots.

Exploitation of a Multifunctional Twistable Wing Trailing-Edge for Performance Improvement of a Turboprop 90-Seats Regional Aircraft

Modern transport aircraft wings have reached near-peak levels of energy-efficiency and there is still margin for further relevant improvements. A promising strategy for improving aircraft efficiency is to change the shape of the aircraft wing in flight in order to maximize its aerodynamic performance under all operative conditions. In the present work, this has been developed in the framework of the Clean Sky 2 (REG-IADP) European research project, where the authors focused on the design of a multifunctional twistable trailing-edge for a Natural Laminar Flow (NLF) wing. A multifunctional wing trailing-edge is used to improve aircraft performance during climb and off-design cruise conditions in response to variations in speed, altitude and other flight parameters. The investigation domain of the novel full-scale device covers 5.15 m along the wing span and the 10% of the local wing chord. Concerning the wing trailing-edge, the preliminary structural and kinematic design process of the actuation system is completely addressed: three rotary brushless motors (placed in root, central and tip sections) are required to activate the inner mechanisms enabling different trailing-edge morphing modes. The structural layout of the thin-walled closed-section composite trailing-edge represents a promising concept, meeting both the conflicting requirements of load-carrying capability and shape adaptivity. Actuation system performances and aeroelastic deformations, considering both operative aerodynamic and limit load conditions, prove the potential of the proposed structural concept to be energy efficient and lightweight for real aircraft implementation. Finally, the performance assessment of the outer natural laminar flow (NLF) wing retrofitted with the multifunctional trailing-edge is performed by high-fidelity aerodynamic analyses. For such an NLF wing, this device can improve airplane aerodynamic efficiency during high speed climb conditions.

Kinematic modeling and design optimization of flexure-jointed planar mechanisms using polynomial bases for flexure curvature

Kinematic design optimization of compliant mechanisms requires accurate yet efficient mathematical models of elastic behavior. A method to predict large-deflection behavior of flexure joint elements using polynomial curvature functions is described in this paper. The method is generalized and extended for kinematic prediction and design optimization of planar multi-flexure mechanisms. It is shown that the kinostatic configuration problem may be solved efficiently and accurately via an energy-based constrained relaxation approach. A class of design optimization problems is further considered where prescribed link positions must be achieved within an overall motion path. Case studies are introduced and theoretical solutions presented. The first of these involves a double Hoeken’s linkage, designed to achieve rectilinear translation of an end link. The second involves an X-Y motion stage mechanism, designed to achieve translational motion of a platform over a targeted workspace while minimizing its rotation. Experimental results involving a realization of the optimized X-Y motion stage design are reported and compared with numerical predictions. To complete the paper, a sensitivity analysis for assembly errors is undertaken via a Monte Carlo simulation. This gives further insight on expected mechanism performance and confirms the efficiency and practical utility of the proposed methods.

Kinematic and Power Characteristics of the Active Frameless Aircraft Control Sidestick

The article is devoted to the actual topic of a small-sized active aircraft control sidestick design and identification of parameters that influence its energy consumption characteristics. The analysis of structural regularities of active control sidestick kinematics design is carried out. The analysis demonstrates that the disadvantage of the known frame constructions, apart from the large dimensions, is the difference in the dynamic characteristics of the channels when using the same actuators, because the mass of a frame mounted actuator is the load for a fixed base mounted actuator. According to results of the analysis, a synthesis of the active control sidestick building based on using of kinematic pairs having one degree of motion was carried out. Hinged mechanisms were used that convert rotational motion of the input link (the actuator output shaft) to the swinging motion of the output link (the control sidestick handgrip) in a single plane. When using two such actuators, so that their links are located perpendicularly and connected to each other by a lever through one-degree-offreedom rotating pairs, a kinematic scheme with two degrees of motion is obtained. As a result the kinematic scheme of an active control sidestick which don’t use a frame is offered. The frameless scheme contains two identical actuators mounted on the fixed base, at that the interference of channels is excluded. The derivation of the actuator gear ratio between the rotation angle of the actuator output shaft and the handgrip deflection angle is given. It is shown that this dependence is of a sinusoidal type and that it is close to linear in the range of the handgrip operating angles. The given results of the parametric synthesis of the control sidestick electromechanical actuator allow to determine the electric motor minimum power and the gear ratio providing the required values of torque and speed at the actuator output link. In consequence of the research of the active control sidestick specific operation modes it is shown that the electric motor power depends on the required values of the maximum speed of the handgrip movement by a pilot and on the force applied to the handgrip, as well as on the handgrip inertia moment.

A Novel Elastic Structure for Three-Axis Force/Torque Sensor: Kinematic Design and Feasibility Study

In this paper, we present a new elastic structure for a three-axis force/torque (F/T) sensor to enhance the compliant characteristics of an F/T sensor. Compliant sensor structure is desirable for safe human-robot interaction when the F/T sensor is used to measure the interaction force. The proposed structure is composed of a serial connection of three flexure hinges. While elastic structures of most F/T sensors are determined by experience and experiments, the proposed sensor structure is determined by analyzing the geometric structure of the desired compliance matrix. Observing the geometric characteristics of the desired compliance matrix reveals a unique form of the spring model, which consists of three serially connected torsional springs whose axes lie on the same plane. From this spring model, a new concept of a serial-based sensor structure is designed to sense the magnitude and point of action of an applied force. Feasibility of the proposed concept as an F/T sensor structure is confirmed by a finite-element analysis and experiments with a sensor test bed.

Kinematic arrangement optimization of a quadruped robot with genetic algorithms

Background: As research on quadruped robots grows, so does the variety of designs available. These designs are often inspired by nature and finalized around various technical, instrumentation-based constraints. However, no systematic methodology of kinematic parameter selection to reach performance specifications is reported so far. Kinematic design optimization with objective functions derived from performance metrics in dynamic tasks is an underexplored, yet promising area. Methods: This article proposes to use genetic algorithms to handle the designing process. Given the dynamic tasks of jumping and trotting, body and leg link dimensions are optimized. The performance of a design in genetic algorithm search iterations is evaluated via full-dynamics simulations of the task. Results: The article presents comparisons of design results optimized for jumping and trotting separately. Significant dimensional dissimilarities and associated performance differences are observed in this comparison. A combined performance measure for jumping and trotting tasks is studied too. It is discussed how significantly various structural lengths affect dynamic performances in these tasks. Results are compared to a relatively more conventional quadruped design too. Conclusions: The task-specific nature of this optimization process improves the performances dramatically. This is a significant advantage of the systematic kinematic parameter optimization over straight mimicking of nature in quadruped designs. The performance improvements obtained by the genetic algorithm optimization with dynamic performance indices indicate that the proposed approach can find application area in the design process of a variety of robots with dynamic tasks.

Kinematic optimization for bipedal robots: a framework for real-time collision avoidance

Bipedal locomotion is more than dynamically stable walking. The redundant kinematic design of humanoid robots allows for complex motions in complex scenarios. One challenge of current robotic research is the exploitation of the capacities of redundant robots in real-time applications. In this paper, we present and evaluate methods for real-time motion generation of redundant robots. The proposed methods are based on a model-predictive approach. We propose and compare methods for optimization of robot motions defined by parameterized task-space trajectories and for redundancy resolution. The approaches are successfully combined in a novel algorithm. The methods are introduced with the help of a minimal model. It shows their applicability for a wide range of complex robotic systems. We apply and validate their effectiveness and their real-time character in several experiments with different environments with the humanoid robot Lola.

Kinematics analysis, design, and simulation of a dual-arm robot for upper limb physiotherapy

Robot-assisted therapy offers a promising approach to rehabilitation, particularly for severely to moderately impaired stroke patients. This paper presents the Dual-Arm End-Effector-Based Rehabilitation Robot (DEREROB), which is a robotic system for upper limb physiotherapy including two co-operating robot arms. With this configuration, the robot arms of DEREROB are connected to the patient’s upper arm and forearm respectively, which mimics the therapist’s arms to provide the rehabilitation treatment. The kinematics model has been framed by D-H method and kinematics simulation has been carried out to verify that the DEREROB can assist the affected arm move in 3D space.

Kinematic performance evaluation of 2-degree-of-freedom parallel mechanism applied in multilayer garage

In this article, our recent work on a kind of 2-degree-of-freedom lower-mobility parallel mechanism, which has one rotation degree of freedom and one translational degree of freedom, used in multilayer garage is presented. It has the following characteristics: lower-mobility, non-symmetric structure but can realize symmetric movement and a good compatibility for different kinds of lifting work. Kinematic performance should be considered in the first of designing a new kind of mechanism, the optimal kinematic design and analysis of this lower-mobility parallel mechanism are primarily investigated. In process of study, the global conditioning index over workspace is adopted, we establish a new evaluation method for the lower-mobility parallel mechanism, called global symmetry index and simulation results are shown. In addition, the flexible workspace of this lower-mobility parallel mechanism is also proposed. The evaluation index can be also applied on other lower-mobility parallel mechanism, which needs steady and symmetric movement.

A folding analysis method for origami based on the frame with kinematic indeterminacy

The kinematic analysis of the folding process is important in practical engineering applications of the mechanism of origami. This paper proposes an efficient methodology for tracing the folding process of origami in a three-dimensional space. This method directly controls the nodal coordinates in the origami model activated by external force on the vertices. The deforming path is obtained using an algorithm based on the generalized inverse theory. An improved type of origami unit is presented for the computational calculation. The results demonstrate that the computational efficiency is strongly related not only to the number of the unknowns, but also the singular value of the compatibility matrix of the origami model. Furthermore, the validity and versatility of the proposed method are confirmed through numerical examples, including general origami models, origami with gravity, origami with special boundary conditions, and curved-crease origami. The proposed method is validated to be feasible and efficient in analyzing the folding mechanism of origami structures for kinematic design in structural and mechanical applications.

Kinematic Design of a New Four Degree-of-Freedom Parallel Robot for Knee Rehabilitation

Rehabilitation robots are increasingly being developed in order to be used by injured people to perform exercise and training. As these exercises do not need wide range movements, some parallel robots with lower mobility architecture can be an ideal solution for this purpose. This paper presents the design of a new four degree-of-freedom (DOF) parallel robot for knee rehabilitation. The required four DOFs are two translations in a vertical plane and two rotations, one of them around an axis perpendicular to the vertical plane and the other one with respect to a vector normal to the instantaneous orientation of the mobile platform. These four DOFs are reached by means of two RPRR limbs and two UPS limbs linked to an articulated mobile platform with an internal DOF. Kinematics of the new mechanism are solved and the direct Jacobian is calculated. A singularity analysis is carried out and the gained DOFs of the direct singularities are calculated. Some of the singularities can be avoided by selecting suitable values of the geometric parameters of the robot. Moreover, among the found singularities, one of them can be used in order to fold up the mechanism for its transportation. It is concluded that the proposed mechanism reaches the desired output movements in order to carry out rehabilitation maneuvers in a singularity-free portion of its workspace.

Optimization design using a global and comprehensive performance index and angular constraints in a type of parallel manipulator

The kinematic optimization of a type of parallel manipulator is addressed. Based on the kinematic analysis, the pressure angles within a limb and among the limbs are introduced, which have definite physical and geometrical meanings. In particular, a type of new pressure angle among the limbs (referred to as the second type of pressure angle among the limbs) is defined and considered to be one of the pressure angle constraints to ensure the kinematic performance. In the kinematic optimization phase, a global and comprehensive performance index, which combines the conditioning number of Jacobian matrix and pressure angles with the volume of workspace, is formulated as an objective function for minimization. One optimal kinematic design example that determines the dimensional parameters is provided to clarify the availability of the proposed approach. The analytical results indicate that good kinematic and dynamic performance can be guaranteed with the suggested design approach. Furthermore, the mutual effect between the dexterity and new pressure angle is analyzed. The effects of the pressure angle constraints on the minimum and maximum conditioning numbers and global dynamic performance indices through the entire workspace are discussed. The proposed research provides a method for the kinematic optimization design of parallel manipulators.

Asymptotically Optimal Kinematic Design of Robots using Motion Planning.

In highly constrained settings, e.g., a tentaclelike medical robot maneuvering through narrow cavities in the body for minimally invasive surgery, it may be difficult or impossible for a robot with a generic kinematic design to reach all desirable targets while avoiding obstacles. We introduce a design optimization method to compute kinematic design parameters that enable a single robot to reach as many desirable goal regions as possible while avoiding obstacles in an environment. Our method appropriately integrates sampling based motion planning in configuration space into stochastic optimization in design space so that, over time, our evaluation of a design's ability to reach goals increases in accuracy and our selected designs approach global optimality. We prove the asymptotic optimality of our method and demonstrate performance in simulation for (i) a serial manipulator and (ii) a concentric tube robot, a tentacle-like medical robot that can bend around anatomical obstacles to safely reach clinically- relevant goal regions.

Inverse kinematic tension analysis and optimal design of a cable-driven parallelseries hybrid joint towards wheelchairmounted robotic manipulator

Inverse kinematic tension analysis and optimal design of a cable-driven parallelseries hybrid joint towards wheelchairmounted robotic manipulator

Optimal Kinematic Design of a 6-UCU Kind Gough-Stewart Platform with a Guaranteed Given Accuracy

The 6-UCU (U-universal joint; C-cylinder joint) kind Gough-Stewart platform is extensively employed in motion simulators due to its high accuracy, large payload, and high-speed capability. However, because of the manufacturing and assembling errors, the real geometry may be different from the nominal one. In the design process of the high-accuracy Gough-Stewart platform, one needs to consider these errors. The purpose of this paper is to propose an optimal design method for the 6-UCU kind Gough-Stewart platform with a guaranteed given accuracy. Accuracy analysis of the 6-UCU kind Gough-Stewart platform is presented by considering the limb length errors and joint position errors. An optimal design method is proposed by using a multi-objective evolutionary algorithm, the non-dominated sorting genetic algorithm II (NSGA-II). A set of Pareto-optimal parameters was found by applying the proposed optimal design method. An engineering design case was studied to verify the effectiveness of the proposed method.

Optimal high-bandwidth control of ball-screw drives with acceleration and jerk feedback

This paper presents an optimal non-collocated control strategy for flexible ball-screw feed drives. Within the non-collocated controller framework, all the feedback measurements are taken from table (load) side. The table acceleration and jerk feedback measurements are used to control both rigid body and the structural dynamics, which enables modal damping capability. Linear quadratic regulator (LQR) framework is then utilized to achieve optimal placement of the poles. State based LQR weights are mapped to frequency domain performance targets, i.e. crossover frequency and phase margin, and hence a novel frequency domain optimal tuning strategy is achieved. A kinematic state observer design is also presented to fuse analog accelerometer measurements with linear encoder feedback to realize high-fidelity state feedback and wide bandwidth motion control. Finally, robustness analysis of non-collocated control is carried out, and comparison against conventional full closed-loop collocated controllers is presented. Comprehensive experimental validations and performance benchmarks are conducted on an industrial scale precision ball-screw driven motion stage.

Robust optimization of constrained mechanical system with joint clearance and random parameters using multi-objective particle swarm optimization

Joint clearance and uncertainty are inevitable in mechanical systems due to design tolerance, abrasion, manufacture error, assembly error and imperfections. In this study, kinematic analysis and robust optimization of constrained mechanical systems with joint clearance and random parameters were performed. Joint clearance was modeled by Lankarani-Nikravesh contact force model, and probability space was applied for characterizing uncertain parameters. A kinematic analysis method based on Baumgarte approach and confidence region method was presented to predict kinematic error of the mechanical system. Slider-crank mechanism, an illustrative example was presented to show the influence of clearance and uncertainty on the kinematic accuracy. Then, a novel multi-objective robust optimization methodology was presented for kinematic accuracy robust optimization design of the constrained mechanical system. In this approach, a multi-objective robust optimization model derived from 95% confidence region is constructed to reduce the effects of clearance and parameter uncertainty on 95% confidence region of kinematic error. The robust optimization model is a double-loop process. A multi-objective robust optimization strategy, combing Kriging surrogate model, multi-objective particle swarm optimization, confidence region and Monte Carlo methods, was proposed to search the design variables for minimizing the optimization objectives derived from confidence region while balancing computational accuracy and efficiency of the optimization process. The optimal results of the slider-crank mechanism demonstrated the validity and feasibility of the proposed robust optimization method.

Kinematics, singularity, and optimal design of a novel 3T1R parallel manipulator with full rotational capability

Parallel manipulators (PMs) with 3T1R (three translational and one rotational degrees of freedom) or Schonflies motion are very useful in industry. However, most 3T1R PMs have a limited range of rotation less than 90° while many practical tasks require a large range of rotation over 180°. Furthermore, there are no 3T1R PMs with full rotational capability that has small number of single-DOF joints and fixed actuators. A novel 2-(RRR)2RH PM with full rotational capability is proposed, where R and H denote a revolute joint and a helical joint, respectively. The moving platform is connected to the fixed base by two identical (RRR)2RH chains, where (RRR)2 denotes a 2- RRR closed chain. First, kinematic analysis of the proposed 2-(RRR)2RH PM, including mobility analysis, inverse and direct kinematics, singularity analysis, and workspace is presented. Second, the local conditioning index is used to evaluate the kinematic performance of the PM. Finally, optimal kinematic design of the 2-(RRR)2RH PM is investigated. The 2-(RRR)2RH PM has only 16 single-DOF joints and can be actuated by four fixed revolute joints. These features make it a good candidate in many applications.

Optimal Kinematic and Elastodynamic Design of Planar Parallel Robot with Flexible Joints

This paper proposes a procedure for the optimal design of a flexible-joint planar parallel robot based on the kinematic and elastodynamic performance criteria. The optimal design consists of determining the dimensions of links to maximize the size of the workspace and the elastodynamic performance simultaneously. Consequently, the optimal design is performed using a multi-objective optimization that permits to obtain the set of the optimal solutions. The set of the optimal solutions are analyzed by assessing the properties of four different solutions to establish the appropriate solution the accomplished a specific task.