3D Workspace Research Articles

Velocity anisotropy of an industrial robot

Industrial robots are part of production systems and it is important to place them into the system according to their properties and behaviour. The information, obtained from the technical sheets of robots, about workspace (its dimensions and shape) is insufficient for designing the production system. The information about mobility is missing. To represent the behaviour of the robot in the workspace, velocity anisotropy of the robot is introduced and defined as the length of the shortest velocity ellipsoid axes, which can be constructed for any position of robot in its tool centre point. The position of a tool centre point is equivalent to the point in the workspace. A graphical representation of the 3D workspace with included velocity anisotropy is then performed and an example for a design of a robotised welding production system is given. In this example the benefits of the graphical representation of the workspace with included velocity anisotropy are presented and discussed.

Mapping Proprioception across a 2D Horizontal Workspace

Relatively few studies have been reported that document how proprioception varies across the workspace of the human arm. Here we examined proprioceptive function across a horizontal planar workspace, using a new method that avoids active movement and interactions with other sensory modalities. We systematically mapped both proprioceptive acuity (sensitivity to hand position change) and bias (perceived location of the hand), across a horizontal-plane 2D workspace. Proprioception of both the left and right arms was tested at nine workspace locations and in 2 orthogonal directions (left-right and forwards-backwards). Subjects made repeated judgments about the position of their hand with respect to a remembered proprioceptive reference position, while grasping the handle of a robotic linkage that passively moved their hand to each judgement location. To rule out the possibility that the memory component of the proprioceptive testing procedure may have influenced our results, we repeated the procedure in a second experiment using a persistent visual reference position. Both methods resulted in qualitatively similar findings. Proprioception is not uniform across the workspace. Acuity was greater for limb configurations in which the hand was closer to the body, and was greater in a forward-backward direction than in a left-right direction. A robust difference in proprioceptive bias was observed across both experiments. At all workspace locations, the left hand was perceived to be to the left of its actual position, and the right hand was perceived to be to the right of its actual position. Finally, bias was smaller for hand positions closer to the body. The results of this study provide a systematic map of proprioceptive acuity and bias across the workspace of the limb that may be used to augment computational models of sensory-motor control, and to inform clinical assessment of sensory function in patients with sensory-motor deficits.

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A study of improvement of D* algorithms for mobile robot path planning in partial unknown environments

PurposeThe purpose of this paper is to improve the D* algorithm which has been used usually in robotics for mobile robot navigation in unknown or dynamic environments.Design/methodology/approachFirst, the model of 2D workspace with some obstacles is expressed in regularity grids. The optimal path is planned by using the improved D* algorithm by searching in the neighbor grid cells in 16 directions. It makes the robot that the smallest turning angle drops to π/8. The robot moving angle discrete precision is raised and the unnecessary cost of path planning is reduced so the robot motion path is smoother. Then, the improved D* algorithm is simulated in MOBOTSIM software environment and is tested by the WiRobotX80 mobile robot.FindingsTo search in the neighbor grid cells in 16 directions instead of eight directions by using D* algorithms for path planning.Research limitations/implicationsThe map should be expressed in regularity grids.Originality/valueThe improved D* algorithm is effective and it can result in a higher quality path than the conventional D* algorithm at the same map environment.

Algorithmic path planning of static robots in three dimensions using configuration space metrics

SUMMARYCollision-free path planning for static robots is a demanding manifold of contemporary robotics research, vastly due to the growing industrial applications. In this paper, a novel ‘visibility map’-based heuristic algorithm is used to generate near-optimal safe path for a three-dimensional congested robot workspace. The final path is obtainable in terms of joint configurations, by considering the Configuration Space of the task space. The developed algorithm has been verified initially by considering representative 2D workspaces, cluttered with different obstacles with regular geometries and then after with the spatial endeavour. A case study reveals the effectiveness of the developed modules of the configuration space mapping, pertaining to a five degrees-of-freedom low payload articulated robot.

Design of 2-DOF Compliant Mechanisms to Form Grip-and-Move Manipulators for 2D Workspace

This paper demonstrates the design of compliant grip-and-move manipulators by structural optimization using genetic algorithms. The manipulator is composed of two compliant mechanisms (each with two degrees of freedom) that work like two fingers so that the manipulator can grip an object and convey it from one point to another anywhere within a two-dimensional workspace. The synthesis of such compliant mechanisms is accomplished by formulating the problem as a structural topology and shape optimization problem with multiple objectives and constraints to achieve the desired behavior of the manipulator. A multiobjective genetic algorithm is then applied coupled with an enhanced morphological representation for defining and encoding the structural geometry variables. The solution framework is integrated with a nonlinear finite element code for large-displacement analyses of the compliant structures to compute the paths generated by these mechanisms, with the resulting optimal designs used to realize various manipulator configurations.

Orientation workspace analysis of a special class of the Stewart–Gough parallel manipulators

SUMMARYThe workspace of a robotic manipulator is a very important issue and design criteria in the context of optimum design of robots, especially for parallel manipulators. Though, considerable research has been paid to the investigations of the three-dimensional (3D) constant orientation workspace or position workspace of parallel manipulators, very few works exist on the topic of the 3D orientation workspace, especially the nonsingular orientation workspace and practical orientation workspace. This paper addresses the orientation workspace analysis of a special class of the Stewart–Gough parallel manipulators in which the moving and base platforms are two similar semisymmetrical hexagons. Based on the half-angle transformation, a polynomial expression of 13 degree that represents the orientation singularity locus of this special class of the Stewart–Gough parallel manipulators at a fixed position is derived and graphical representations of the orientation singularity locus of this special class of the Stewart–Gough manipulators are illustrated with examples to demonstrate the result. Exploiting this half-angle transformation and the inverse kinematics solution of this special class of the Stewart–Gough parallel manipulators, a discretization method is proposed for computing the orientation workspace of this special class of the Stewart–Gough parallel manipulators taking limitations of active and passive joints and the link interference all into consideration. Based on this algorithm, this paper also presents a new discretization method for computing the nonsingular orientation workspace of this class of the manipulators, which not only can satisfy all the kinematics demand of this class of the manipulators but also can guarantee the manipulator is nonsingular in the whole orientation workspace, and the practical orientation workspace of this class of the manipulators, which not only can guarantee the manipulator is nonsingular and will never encounter any kinematic interference but also can satisfy the demand of the orientation workspace with a regular shape in practical application, respectively. Examples of a 6/6-SPS Stewart–Gough parallel manipulator of this special class are given to demonstrate these theoretical results.

Analysis of tetraplegic reaching in their 3D workspace following posterior deltoid-triceps tendon transfer

Cross-sectional study. To quantify three-dimensional (3D) reachable workspace in different groups of tetraplegic participants and to assess their reaching performance within this workspace. Northwest Regional Spinal Injuries Centre, UK. The 3D reachable workspace of three groups of tetraplegics (NON-OP, operated group (OP) and tetraplegic control group (CON(Tetraplegic)) with varying levels of triceps function together with a healthy control group (CON(Healthy))) was defined by reaching to five target positions (anterior, medial, lateral, superior and inferior) located on the periphery of their workspace. Joint angles and inter-joint co-ordination were analysed after a 3D reconstruction of the thorax, humerus and forearm. The performance related variables of movement time, peak velocity, time-to-peak velocity and curvature index were also examined. The reachable volumes covered were consistent with the level of triceps function as CON(Healthy) covered a significantly greater volume than the tetraplegic groups and in turn the OP covered a larger workspace volume than NON-OP. The reduced workspace of tetraplegics was identified as being due to restrictions in workspace above shoulder height and across the body. Co-ordination data identified some differences in movement patterns but when reaching to targets on the workspace there were no significant differences between the OP and NON-OP groups. This study provided a detailed assessment of reachable workspace and target reaching. Tetraplegic participants found the superior and medial parts of the workspace were the most challenging directions. Standardised biomechanical analysis of tetraplegic upper-limb function is required for objective assessment.

Visual evaluation and fuzzy voice commands for controlling a robot manipulator

This paper proposes a method for learning and controlling an industrial robot manipulator through Fuzzy Voice Commands (FVCs) guided by visual motor coordination. Supervised Self-Organising Map (SSOM) is proposed to implement the visual motor coordination. The FVCs are used to control the robot manipulator toward a goal. Visual evaluation process is adapted by the supervision of the human coach. The learned system is capable of navigating the robot manipulator to a point in 3D working space as instructed by the voice commands. The proposed idea is demonstrated with a PA-10 industrial manipulator.

Visibility-based modelling and control for network-based robotics

We present an algorithm to model 3D workspace and to understand test scene for navigation or human computer interaction in network-based mobile robot. This was done by line-based modelling and recognition algorithm. Line-based recognition using 3D lines has been tried by many researchers however its reliability still needs improvement due to ambiguity of 3D line feature information from original images. To improve the outcome, we approach firstly to find real planes using the given 3D lines and then to implement recognition process. The methods we use are principle component analysis (PCA), plane sweep, visibility test, and iterative closest point (ICP). During the implementation, we also use 3D map information for localization. We apply this algorithm to real test scene images and to find out our result can be useful to identify doors or walls in indoor environment with better efficiency.

Motion planning for multiple non-holonomic robots: a geometric approach

SUMMARYIn this paper, a geometrical approach is developed to generate simultaneously optimal (or near-optimal) smooth paths for a set of non-holonomic robots, moving only forward in a 2D environment cluttered with static and moving obstacles. The robots environment is represented by a 3D geometric entity called Bump-Surface, which is embedded in a 4D Euclidean space. The multi-motion planning problem (MMPP) is resolved by simultaneously finding the paths for the set of robots represented by monoparametric smoothC2curves onto the Bump-Surface, such that their inverse images onto the initial 2D workspace satisfy the optimization motion-planning criteria and constraints. The MMPP is expressed as an optimization problem, which is solved on the Bump-Surface using a genetic algorithm. The performance of the proposed approach is tested through a considerable number of simulated 2D dynamic environments with car-like robots.

Motion Planning for Haptic Guidance

Haptic devices allow a user to feel either reaction forces from virtual interactions or reaction forces reflected from a remote site during a bilateral teleoperation task. Also, guiding forces can be exerted to train the user in the performance of a virtual task or to assist him/her to safely teleoperate a robot. The generation of guiding forces relies on the existence of a motion plan that provides the direction to be followed to reach the goal from any free configuration of the configuration space ( ${\mathcal C}$ -space). This paper proposes a method to obtain such a plan that interleaves a sampling-based exploration of ${\mathcal C}$ -space with an efficient computation of harmonic functions. A deterministic sampling sequence (with a bias based on harmonic function values) is used to obtain a hierarchical cell decomposition model of ${\mathcal C}$ -space. A harmonic function is iteratively computed over the partially known model using a novel approach. The harmonic function is the navigation function used as motion plan. The approach has been implemented in a planner (called the Kautham planner) that, given an initial and a goal configuration, provides: (a) a channel of cells connecting the cell that contains the initial configuration with the cell that contains the goal configuration; (b) two harmonic functions over the whole ${\mathcal C}$ -space, one that guides motions towards the channel and another that guides motions within the channel towards the goal; and (c) a path computed over a roadmap built with the free samples of the channel. The harmonic functions and the solution path are then used to generate the guiding forces for the haptic device. The planning approach is illustrated with examples on 2D and 3D workspaces.

Synthesis of an 8S5R mechanism in four-point rigid body guidance problem using Maple

In this paper, an accurate and graphical based method for synthesis of a nine-bar 8S5R mechanisms as a possible solution for four-point spatial rigid body guidance is presented. In the problem we are looking for a mechanism locating a rigid body in four specified postures in a 3D workspace. The posture includes position and orientation of a body. The degree of freedom of the mechanism is one, so by just one rotational or translational driving member, the desired motion can be generated. The method is based on the synthesis and design of two linkages; a six-bar 8S linkage and a spherical four-link 4R linkage. Coupler of the former is the desired body which should be navigated on the four desired postures and a coupler point of the latter, provides suitable movement for the input link of the former. The two linkages are connected using a revolute joint. Therefore, they form a nine-bar 8S5R mechanism. Since the graphical construction cannot be implemented in 3D design procedures by the conventional drawings, the symbolic mathematical software Maple-V is used to visualize the 3D concepts of the problem as well as accomplishing the accurate geometrical computations in the modeling. For completeness and simplicity, through the whole of the paper the associated commands of Maple are described. The mechanism can be used in the wide variety of motion generation problem in three-dimensional workspaces.

3D active workspace of human hand anatomical model

BackgroundIf the model of the human hand is created with accuracy by respecting the type of motion provided by each articulation and the dimensions of articulated bones, it can function as the real organ providing the same motions. Unfortunately, the human hand is hard to model due to its kinematical chains submitted to motion constraints. On the other hand, if an application does not impose a fine manipulation it is not necessary to create a model as complex as the human hand is. But always the hand model has to perform a certain space of motions in imposed workspace architecture no matter what the practical application does.MethodsBased on Denavit-Hartenberg convention, we conceived the kinematical model of the human hand, having in mind the structure and the behavior of the natural model. We obtained the kinematical equations describing the motion of every fingertip with respect to the general coordinate system, placed on the wrist. For every joint variable, a range of motion was established. Dividing these joint variables to an appropriate number of intervals and connecting them, the complex surface bordering the active hand model workspace was obtained.ResultsUsing MATLAB 7.0, the complex surface described by fingertips, when hand articulations are all simultaneously moving, was obtained. It can be seen that any point on surface has its own coordinates smaller than the maximum length of the middle finger in static position. Therefore, a sphere having the centre in the origin of the general coordinate system and the radius which equals this length covers the represented complex surface.ConclusionWe propose a human hand model that represents a new solution compared to the existing ones. This model is capable to make special movements like power grip and dexterous manipulations. During them, the fingertips do not exceed the active workspace encapsulated by determined surfaces. The proposed kinematical model can help to choose which model joints could be eliminated in order to preserve only the motions important for a certain application. The study shows that all models, simplified or not, exhibit a pronounced similitude with the real hand motion, validated by the fingertips' computed trajectories. The results were used to design an artificial hand capable to make some of the hand's functions with a reduced set of degrees of freedom.

A Visual Tracking Method for a Moving Object Using Stereo Vision Robot

In this paper, we propose a visual tracking method for a moving object without tracking delay. On visual servoing, image-based method with image Jacobian is often taken for target-centering camera motion control because it does not require target's 3D position estimation and is robust to modeling errors and noises. In an ordinary visual servoing approach, it is assumed that the target object would be fixed in the workspace. Therefore, for the purpose of tracking to a moving target, the image errors always exist between the target position and camera optical axis, that is, the visual tracking delay. In our proposed method, the target object's 3D position is estimated with the technique based on triangulation on stereo vision system. Then, the moving velocity is calculated in the camera coordinate frame. The image Jacobian concerns the camera velocity with the target velocity in the image plane. Additionally, the target velocity in 3D workspace is also converted into the velocity in the image plane. The converted velocity compensates the camera velocity to compensate the camera motion delay. This approach enables to achieve non-delayed tracking for moving target.

AN ART GALLERY-BASED APPROACH: ROADMAP CONSTRUCTION AND PATH PLANNING IN GLOBAL ENVIRONMENTS

In this paper, we present a novel near-optimal art gallery-based algorithm for placing a small (but sufficient) number of robot configurations to plan its path in a 2D environment cluttered with obstacles. The solution of the problem is inspired from the well-known art gallery problem (AGP) which asks to position the minimum number of guards required to cover a gallery that is represented as a simple polygon with n vertices and h holes. The proposed algorithm efficiently computes the placement of guards in simple polygons with holes, which runs in O(n log n) time and requires a linear storage complexity. The proposed algorithm can be useful in a variety of applications such as 3D model construction of a workspace, navigation and inspection tasks, medical surgery, and virtual reality exploration systems. It can also be used to solve the robot motion planning problem for an autonomous mobile robot in a global environment. A 2D workspace for an autonomous robot can be modeled as a gallery and the obstacles are presented as holes. The proposed placement guarantees to compute the near-optimal distribution of guards that fully cover the entire free space. Such guards can then be used as milestones along the path of the robot. The proposed algorithm is not only offering a better performance in terms of computational cost but also ease in implementation. Simulation results demonstrate the efficiency, robustness, and potential of the proposed algorithm compared to other visibility-based techniques.

A 2D–3D integrated tabletop environment for multi‐user collaboration

AbstractThis paper proposes a novel tabletop display system for natural communication and flexible information sharing. The proposed system is specifically designed to integrate two‐dimensional (2D) and three‐dimensional (3D) user interfaces by using a multi‐user stereoscopic display, IllusionHole. The proposed system takes awareness into consideration and provides both 2D and 3D information and user interfaces. On the display, a number of standard Windows desktop environments are provided as personal workspaces, as well as a shared workspace with a dedicated graphical user interface. In the personal workspaces, users can simultaneously access existing applications and data, and exchange information between personal and shared workspaces. In this way, the proposed system can seamlessly integrate personal, shared, 2D, and 3D workspaces with conventional user interfaces and effectively support communication and information sharing. To demonstrate the capabilities of the proposed display system, a modeling application was implemented. A preliminary experiment confirmed the effectiveness of this system. Copyright © 2006 John Wiley & Sons, Ltd.

An Enhanced Ray-Shooting Approach to Force-Closure Problems

Force-closure is a fundamental topic in grasping research. Relevant problems include force-closure test, quality evaluation, and grasp planning. Implementing the well-known force-closure condition that the origin of the wrench space lies in the interior of the convex hull of primitive wrenches, Liu presented a ray-shooting approach to force-closure test. Because of its high efficiency in 3D work space and no limitation on the contact number of a grasp, this approach is advanced. Achieving some new results of convex analysis, this paper enhances the above approach in three aspects. (a) The exactness is completed. In order to avoid trouble or mistakes, the dimension of the convex hull of primitive wrenches is taken into account, which is always ignored until now. (b) The efficiency is increased. A shortcut which skips some steps of the original force-closure test is found. (c) The scope is extended. Our simplified ray-shooting approach yields a grasp stability index suitable for grasp planning. Numerical examples in fixturing and grasping show the enhancement superiority.

Human-Assisted Obstacle Avoidance System Using 3D Workspace Modeling for Construction Equipment Operation

Equipment operation on construction sites is a major source of construction accidents and injuries related to crushing, electrocution, and falls. Primarily, this is because the operator’s field of view, reaction speed, attention, and depth perception are limited, and also because the construction site is a dynamic environment. Accelerating advances in sensing and equipment control sophistication present new opportunities to address these safety problems. The research described here provides the basis for the development of obstacle-avoidance systems that use models of objects generated by rapid three-dimensional (3D) workspace modeling methods and by sophisticated equipment control capabilities. An explanation of the proposed obstacle avoidance system, together with preliminary results, is presented. Implementation of this system in practice is feasible in the near term for critical and particularly hazardous operations.

On the comparison of model-based and modeless robotic calibration based on a fuzzy interpolation method

Traditional robot calibrations implement either model-based or modeless methods. A model-based calibration method normally involves four steps: kinematic model definition of the robot, measurement process of the robot’s positions, identification of the kinematic model of the robot and compensation of the position errors. This type of method can be both time consuming and complicated because of the identification and compensation processes. Most traditional modeless methods are relatively simple and practical, but their calibration accuracy is relatively low and most of them are only suitable for the robot’s calibration in the 2D domain and in relative small workspaces. This paper provides a novel modeless fuzzy interpolation method to improve the compensation accuracy for robot calibration in the 3D workspace. A comparison between the model-based and modeless fuzzy interpolation calibration method is made. The simulated results show that the modeless fuzzy interpolation method is compatible with the model-based calibration method, and even outperforms a model-based counterpart in terms of accuracy and complexity in a relatively compact workspace.