Conceptual Design of Lower-Mobility Parallel Manipulators Based on Wrench Graphs

2014 ◽  
Author(s):  
Gamal El-Ghazaly ◽  
Stéphane Caro
Keyword(s):  
Degrees Of Freedom ◽  
A Priori ◽  
Three Dimensional ◽  
Main Idea ◽  
Parallel Manipulators ◽  
Geometric Constraints ◽  
Design Stage ◽  
Case Scenario ◽  
Worst Case ◽  
Lower Mobility

This paper presents a design methodology for lower-mobility parallel manipulators based on classification of wrench systems into four main classes. Wrench systems are represented in a three-dimensional projective space ℙ3 using wrench graphs where it is easy to incorporate geometric constraints to have simple singularity conditions using Grassmann-Cayley algebra (GCA). The main idea of the approach is to design a PM with an overall (constraint and actuation) wrench system that complies with a given wrench graph for which singularity conditions have been predetermined. The main advantage of this methodology is that the singularity conditions are already known a priori and consequently, it gives an opportunity to avoid such conditions at the design stage and make them unreachable. In the worst case scenario, where none of singularity conditions cannot be avoided, one can have a PM with known singular configurations which are always difficult to determine for already designed manipulators. As illustrative examples, two different five degrees-of-freedom (dof) mechanisms have been designed based on some of the defined wrench graphs giving 3T2R motion pattern. The first mechanism has some avoided singularities and the second one is free of singularity.

Determination of the Workspace of a Three-Degrees-of-Freedom Parallel Manipulator Using a Three-Dimensional Computer-Aided-Design Software Package and the Concept of Virtual Chains1

2015 ◽  
Vol 8 (2) ◽  
Author(s):  
Andrew Johnson ◽  
Xianwen Kong ◽  
James Ritchie
Keyword(s):  
Computer Aided Design ◽  
Parallel Manipulator ◽  
Degrees Of Freedom ◽  
Graphical Representation ◽  
Three Dimensional ◽  
Parallel Manipulators ◽  
Workspace Analysis ◽  
Computer Aided ◽  
Aided Design

The determination of workspace is an essential step in the development of parallel manipulators. By extending the virtual-chain (VC) approach to the type synthesis of parallel manipulators, this technical brief proposes a VC approach to the workspace analysis of parallel manipulators. This method is first outlined before being illustrated by the production of a three-dimensional (3D) computer-aided-design (CAD) model of a 3-RPS parallel manipulator and evaluating it for the workspace of the manipulator. Here, R, P and S denote revolute, prismatic and spherical joints respectively. The VC represents the motion capability of moving platform of a manipulator and is shown to be very useful in the production of a graphical representation of the workspace. Using this approach, the link interferences and certain transmission indices can be easily taken into consideration in determining the workspace of a parallel manipulator.

An Enhanced Multi-GNSS Navigation Algorithm by Utilising a Priori Inter-System Biases

2017 ◽  
Vol 71 (2) ◽  
pp. 339-351 ◽  
Author(s):  
Zhounan Dong ◽  
Changsheng Cai ◽  
Rock Santerre ◽  
Cuilin Kuang
Keyword(s):  
Moving Average ◽  
A Priori ◽  
Three Dimensional ◽  
Main Idea ◽  
Experimental Tests ◽  
Satellite Observation ◽  
Satellite System ◽  
Estimation Algorithms ◽  
Navigation Algorithm ◽  
Sky Conditions

The integration of multi-constellation Global Navigation Satellite System (GNSS) measurements can effectively improve the accuracy and reliability of navigation and positioning solutions, while the Inter-System Bias (ISB) is a key issue for compatibility. The ISB is traditionally estimated as an unknown parameter along with three-dimensional position coordinates and a receiver clock offset with respect to Global Positioning System (GPS) time. ISB estimation of this sort will sacrifice a satellite observation for each integrated GNSS system. These sacrificed observations could be vital in situations of limited satellite visibility. In this study, an enhanced multi-GNSS navigation algorithm is developed to avoid sacrificing observations under poor visibility conditions. The main idea of this algorithm is to employ a moving average filter to smooth the ISBs estimated at previous epochs. The filtered value is utilised as a priori information at the current epoch. Experimental tests were conducted to evaluate the enhanced algorithm under open and blocked sky conditions. The results show that the enhanced algorithm effectively improves the accuracy and availability of navigation solutions under the blocked sky condition, with performance being comparable to traditional ISB estimation algorithms in open sky conditions. The improvement rates of the three-dimensional position accuracy and availability reach up to 63% and 21% in the blocked sky environment. Even in the case of only four different GNSS satellites, a position solution can still be obtained using the enhanced algorithm.

New Indices for Optimal Design of Redundantly Actuated Parallel Manipulators

2016 ◽  
Vol 9 (1) ◽  
Author(s):  
Qinchuan Li ◽  
Ningbin Zhang ◽  
Feibo Wang
Keyword(s):  
Optimal Design ◽  
Degrees Of Freedom ◽  
Parallel Manipulators ◽  
Mean Value ◽  
Transmission Performance ◽  
Transmission Index ◽  
Redundantly Actuated ◽  
Lower Mobility ◽  
Six Dof ◽  
Force Transmissibility

Redundantly actuated parallel manipulators (PMs) receive growing interest due to their reduced singularity and enlarged workspace. This paper proposes new indices for optimal design and analysis of redundantly actuated PMs by evaluating their motion/force transmissibility. First, we proposed a method to extract a multi-DOF (degrees-of-freedom) redundantly actuated PM into several subsidiary one-DOF PMs with two or more actuators by locking some actuators in an ergodic manner. Then, a new index of output transmission performance is proposed by investigating the mean value of the instantaneous power produced by the multiple actuation wrenches and one twist of the moving platform of one-DOF PMs. A local transmission index (LTI) is defined as the minimum value of the index of output and input transmission performance. A global transmission index (GTI) is then established based on the LTI. The proposed LTI and GTI are coordinate-free and have clear physical interpretation. Finally, the validity and universality of the new indices are demonstrated by optimization and analysis of redundantly actuated lower-mobility PMs with extra articulated six-DOF or limited-DOF limbs.

Kinematic Modeling and Analysis of a Novel Bio-Inspired and Cable-Driven Hybrid Shoulder Mechanism

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
A. S. Niyetkaliyev ◽  
E. Sariyildiz ◽  
G. Alici
Keyword(s):  
Degrees Of Freedom ◽  
Kinematic Model ◽  
Three Dimensional ◽  
Parallel Manipulators ◽  
Kinematic Modeling ◽  
Interaction Forces ◽  
Modeling And Analysis ◽  
Shoulder Joints ◽  
Hybrid Mechanism ◽  
Simulation Results

Abstract The robotic shoulder rehabilitation exoskeletons that do not take into consideration all shoulder degrees-of-freedom (DOFs) lead to undesirable interaction forces and cause discomfort to the patient due to the joint axes misalignments between the exoskeleton and shoulder joints. In order to contribute to the solution of this human–robot compatibility issue, we present the kinematic modeling and analysis of a novel bio-inspired 5-DOFs hybrid human–robot mechanism (HRM). The human limbs are regarded as the inner passive restrained links in the proposed hybrid constrained anthropomorphic mechanism. The proposed hybrid mechanism combines serial and parallel manipulators with rigid and cable links enabling a match between human and exoskeleton joint axes. It is designed to cover the whole range of motion of the human shoulder with the workspace free of singularities. The numerical and simulation results from the computer-aided drawing model of the mechanism are presented to demonstrate the validity of the kinematic model, and the kinematic and singularity merits of the proposed mechanism. A three-dimensional printed prototype of the hybrid mechanism was fabricated to further validate the kinematic model and its overall advantages.

An assembling algorithm for fixture in an assembly process planning system

2020 ◽  
Vol 234 (8) ◽  
pp. 1133-1155
Author(s):  
Xiaojun Liu ◽  
Xiaokang Xu ◽  
Yang Yi ◽  
Zhonghua Ni ◽  
Yang Zhang
Keyword(s):  
Process Planning ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Information Model ◽  
Geometric Constraints ◽  
Planning System ◽  
Assembly Process ◽  
Assembly Process Planning ◽  
Process Planning System ◽  
Assembly Constraints

Three-dimensional assembly process planning is a precondition for achieving full product lifecycle management based on three-dimensional modelling. Information expression and management operations of fixture models are key to three-dimensional assembly process planning systems. To reasonably and efficiently achieve the goal of planning assembly processes with a fixture model, the application of a fixture information model to a three-dimensional assembly process planning system is investigated. First, to manage tooling information, a fixture information model is defined that consists of management information, display information, geometric information, assembly constraints and degrees of freedom. Then, based on the analysis of the degrees of freedom of components and the assembly constraint relationship, a method of solving assembly constraints based on degrees of freedom reasoning is proposed. Finally, by using the method of solving assembly positioning based on geometric constraints, the pose transformation and assembly positioning of parts are achieved. Through the development of a tooling function module, the three-dimensional assembly process planning system is improved. The feasibility of the above method is verified using part of a spacecraft as an example.

The Qualitative Synthesis of Parallel Manipulators

2004 ◽  
Vol 126 (4) ◽  
pp. 617-624 ◽  
Author(s):  
Jorge Angeles
Keyword(s):  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Parallel Manipulators ◽  
Qualitative Reasoning ◽  
Rigid Bodies ◽  
Three Dimensions ◽  
Qualitative Synthesis ◽  
Motion Representation ◽  
Six Degrees Of Freedom ◽  
Three Degrees Of Freedom

As shown in this paper, when designing parallel manipulators for tasks involving less than six degrees of freedom, the topology can be laid out by resorting to qualitative reasoning. More specifically, the paper focuses on cases whereby the manipulation tasks pertain to displacements with the algebraic structure of a group. Besides the well-known planar and spherical displacements, this is the case of displacements involving: rotation about a given axis and translation in the direction of the same axis (cylindrical subgroup); translation in two and three dimensions (two- and three-dimensional translation subgroups); three independent translations and rotation about an axis of fixed direction, what is known as the Scho¨nflies subgroup; and similar to the Scho¨nflies subgroup, but with the rotation and the translation in the direction of the axis of rotation replaced by a screw displacement. For completeness, the fundamental concepts of motion representation and groups of displacements, as pertaining to rigid bodies, are first recalled. Finally, the concept of Π-joint, introduced elsewhere, is generalized to two and three degrees of freedom, thereby ending up with the Π2-and the Π3-joints, respectively.

Prediction of the Mass Sensitivity of Phage-Coated Magnetoelastic Biosensors for the Detection of Single Pathogenic Bacteria

2011 ◽  
Vol 1301 ◽  
Author(s):  
Shin Horikawa ◽  
Suiqiong Li ◽  
Yating Chai ◽  
Valerly A. Petrenko ◽  
Bryan A. Chin
Keyword(s):  
Pathogenic Bacteria ◽  
Longitudinal Vibration ◽  
Three Dimensional ◽  
Case Scenario ◽  
Worst Case ◽  
Mass Sensitivity ◽  
Boltzmann Function ◽  
Frequency Changes ◽  
Three Dimensional Finite Element ◽  
Mass Position

ABSTRACTFreestanding, strip-shaped magnetoelastic (ME) biosensors are a class of wireless, mass-based biosensors that are being developed for the real-time detection of pathogenic bacteria for food safety and bio-security. The mass sensitivity of these biosensors operating in longitudinal-vibration modes is known to be largely dependent on the position of masses attached to the sensor surfaces. Hence, considering this dependence is crucial to the detection of low-concentration target pathogens, including single pathogenic bacteria, because their local attachment may cause varying sensor responses. In a worst case scenario, the resultant sensor responses (i.e., mass-induced resonance frequency changes of the sensor) may be too small to be detected despite the attachment of the target pathogenic masses. To address the issue, phage-coated ME biosensors (magnetostrictive strips (4 mm × 0.8 mm × 30 μm) coated with a phage probe specifically binding streptavidin protein) with localized masses (streptavidin-coated polystyrene beads) were fabricated, and mass-position-dependence of the sensor’s sensitivity under the fundamental-mode vibration was experimentally measured. In addition, three-dimensional finite element (FE) modal analysis was performed using the CalculiX software to simulate the phenomena. The experimental and theoretical results show close agreement: (1) the mass sensitivity was low when the mass was positioned in the middle of the sensor’s longest dimension and (2) a much higher mass sensitivity was, by contrast, obtained for the equivalent masses placed at both ends of the strip-shaped sensor. Furthermore, FE models were constructed for differently sized, phage-coated ME biosensors (100 – 500 μm in length with different widths and thicknesses) loaded with a single bacterial mass (2 μm × 0.4 μm × 0.4 μm, 1.05 g/cm3) at varying longitudinal positions. The mass sensitivity was found to be approximated by a mass-position-dependent Boltzmann function whose amplitude is inversely proportional to the length squared, width, and thickness of the sensor.

scholarly journals The cospecification of the shape and material properties of light permeable materials

2021 ◽  
Vol 118 (14) ◽  
pp. e2024798118
Author(s):  
Phillip J. Marlow ◽  
Barton L. Anderson
Keyword(s):  
Material Properties ◽  
A Priori ◽  
Three Dimensional ◽  
Surface Curvature ◽  
Geometric Constraints ◽  
Subsurface Scattering ◽  
3D Shape ◽  
Occluding Contours ◽  
3D Surface ◽  
Ill Posed

The problem of extracting the three-dimensional (3D) shape and material properties of surfaces from images is considered to be inherently ill posed. It is thought that a priori knowledge about either 3D shape is needed to infer material properties, or knowledge about material properties are needed to derive 3D shape. Here, we show that there is information in images that cospecify both the material composition and 3D shape of light permeable (translucent) materials. Specifically, we show that the intensity gradients generated by subsurface scattering, the shape of self-occluding contours, and the distribution of specular reflections covary in systematic ways that are diagnostic of both the surface’s 3D shape and its material properties. These sources of image covariation emerge from being causally linked to a common environmental source: 3D surface curvature. We show that these sources of covariation take the form of “photogeometric constraints,” which link variations in intensity (photometric constraints) to the sign and direction of 3D surface curvature (geometric constraints). We experimentally demonstrate that this covariation generates emergent cues that the visual system exploits to derive the 3D shape and material properties of translucent surfaces and demonstrate the potency of these cues by constructing counterfeit images that evoke vivid percepts of 3D shape and translucency. The concepts of covariation and cospecification articulated herein suggest a principled conceptual path forward for identifying emergent cues that can be used to solve problems in vision that have historically been assumed to be ill posed.

Geometric Error Effects on Manipulators' Positioning Precision: A General Analysis and Evaluation Method

2016 ◽  
Vol 8 (6) ◽  
Author(s):  
Henrique Simas ◽  
Raffaele Di Gregorio
Keyword(s):  
Degrees Of Freedom ◽  
Evaluation Method ◽  
Geometric Error ◽  
Design Stage ◽  
Positioning Precision ◽  
Six Degrees Of Freedom ◽  
Analysis And Evaluation ◽  
Lower Mobility ◽  
General Method

Manufacturing and assembly (geometric) errors affect the positioning precision of manipulators. In six degrees-of-freedom (6DOF) manipulators, geometric error effects can be compensated through suitable calibration procedures. This, in general, is not possible in lower-mobility manipulators. Thus, methods that evaluate such effects must be implemented at the design stage to determine both which workspace region is less affected by these errors and which dimensional tolerances must be assigned to match given positioning-precision requirements. In the literature, such evaluations are mainly tailored on particular architectures, and the proposed techniques are difficult to extend. Here, a general discussion on how to take into account geometric error effects is presented together with a general method to solve this design problem. The proposed method can be applied to any nonoverconstrained architecture. Eventually, as a case study, the method is applied to the analysis of the geometric error effects of the translational parallel manipulator (TPM) Triflex-II.

scholarly journals APIX: Analysis From Pixellated Inputs in Early Design Using a Pen-Based Interface

2011 ◽  
Author(s):  
Sundar Murugappan ◽  
Vinayak ◽  
Karthik Ramani ◽  
Maria C. Yang
Keyword(s):  
Product Development ◽  
Early Stage ◽  
Three Dimensional ◽  
Geometric Constraints ◽  
Design Stage ◽  
Two Dimensional ◽  
Element Analysis ◽  
Early Design ◽  
Early Design Stage ◽  
Simulation Tools

Product development is seeing a paradigm shift in the form of a simulation-driven approach. Recently, companies and designers have started to realize that simulation has the biggest impact when used as a concept verification tool in early stages of design. Early stage simulation tools like ANSYS™ Design Space and SIMULIA™ DesignSight Structure help to overcome the limitations in traditional product development processes where analyses are carried out by a separate group and not the designers. Most of these commercial tools still require well defined solid models as input and do not support freehand sketches, an integral part of the early design stage of product development. To this extent, we present APIX (acronym for Analysis from Pixellated Inputs), a tool for quick analysis of two dimensional mechanical sketches and parts from their static images using a pen-based interface. The input to the system can be offline (paper) sketches and diagrams, which include scanned legacy drawings and freehand sketches. In addition, images of two-dimensional projections of three dimensional mechanical parts can also be input. We have developed an approach to extract a set of boundary contours to represent a pixellated image using known image processing algorithms. The idea is to convert the input images to online sketches and use existing stroke-based recognition techniques for further processing. The converted sketch can now be edited, segmented, recognized, merged, solved for geometric constraints, beautified and used as input for finite element analysis. Finally, we demonstrate the effectiveness of our approach in the early design process with examples.

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