44 results found
Baron N, Philippides A, Rojas N, 2019, A novel kinematically redundant planar parallel robot manipulator with full rotatability, Journal of Mechanisms and Robotics, Vol: 11, Pages: 011008-011008, ISSN: 1942-4302
This paper presents a novel kinematically redundant planar parallel robot manipulator, which has full rotatability. The proposed robot manipulator has an architecture that corresponds to a fundamental truss, meaning that it does not contain internal rigid structures when the actuators are locked. This also implies that its rigidity is not inherited from more general architectures or resulting from the combination of other fundamental structures. The introduced topology is a departure from the standard 3-RPR (or 3-RRR) mechanism on which most kinematically redundant planar parallel robot manipulators are based. The robot manipulator consists of a moving platform that is connected to the base via two RRR legs and connected to a ternary link, which is joined to the base by a passive revolute joint, via two other RRR legs. The resulting robot mechanism is kinematically redundant, being able to avoid the production of singularities and having unlimited rotational capability. The inverse and forward kinematics analyses of this novel robot manipulator are derived using distance-based techniques, and the singularity analysis is performed using a geometric method based on the properties of instantaneous centers of rotation. An example robot mechanism is analyzed numerically and physically tested; and a test trajectory where the end effector completes a full cycle rotation is reported. A link to an online video recording of such a capability, along with the avoidance of singularities and a potential application, is also provided.
Clark AB, Rojas N, Stiffness-Tuneable Limb Segment with Flexible Spine for Malleable Robots, 2019 International Conference on Robotics and Automation (ICRA)
Bai G, Rojas N, 2018, Self-adaptive monolithic anthropomorphic finger with teeth-guided compliant cross-four-bar joints for underactuated hands, 2018 IEEE-RAS International Conference on Humanoid Robots (Humanoids), Publisher: IEEE
This paper presents a novel approach for modelingone-degree-of-freedom human metacarpophalangeal/ interpha-langeal joints based on a teeth-guided compliant cross-four-barlinkage. The proposed model allows developing self-adaptiveanthropomorphic fingers able to be 3D printed in a singlestep without any accessories, except for simple tendon wiringafter the printing process, using basic single-material additivemanufacturing. Teeth-guided compliant cross-four-bar linkagesas finger joints not only provide monolithic fabrication withoutassembly but also increase precision of anthropomorphic robotfingers by removing nonlinear characteristics, thus reducing thecomplexity of control for delicate grasping. Kinematic analysisof the proposed compliant finger joints is detailed and nonlinearfinite element analysis results demonstrating their advantagesare reported. A two-fingered underactuated hand with teeth-guided compliant cross-four-bar joints is also developed andqualitative discussion on grasping is conducted.
Baron N, Philippides A, Rojas N, 2018, A geometric method of singularity avoidance for kinematically redundant planar parallel robots, Advances in Robot Kinematics 2018, Publisher: Springer, Pages: 187-194
Methods for avoiding singularities of closed-loop robot mechanisms havebeen traditionally based on the value of the determinant or the condition number ofthe Jacobian. A major drawback of these standard techniquesis that the closeness ofa robot configuration to a singularity lacks geometric, physical interpretation, thusimplying that it is uncertain how changes in the robot pose actually move furtheraway the mechanism from such a problematic configuration. This paper presentsa geometric approach of singularity avoidance for kinematically redundant planarparallel robots that eliminates the disadvantages of Jacobian-based techniques. Theproposed method, which is based on the properties of instantaneous centres of rota-tion, defines a mathematical distance to a singularity and provides a reliable way ofmoving the robot further from a singular configuration without changing the poseof the end-effector. The approach is demonstrated on an example robot mechanismand the reciprocal of the condition number of the Jacobian isused to show its ad-vantages.
Porta JM, Rojas N, Thomas F, 2018, Distance Geometry in Active Structures, Mechatronics for Cultural Heritage and Civil Engineering, Editors: Ottaviano, Pelliccio, Gattulli, Publisher: Springer
Ward-Cherrier B, Rojas N, Lepora NF, 2017, Model-Free Precise in-Hand Manipulation with a 3D-Printed Tactile Gripper, IEEE Robotics and Automation Letters, Vol: 2, Pages: 2056-2063
Rojas N, Dollar AM, 2017, Distance-based kinematics of the five-oblique-axis thumb model with intersecting axes at the metacarpophalangeal joint, 2017 IEEE RAS/EMBS International Conference on Rehabilitation Robotics, Publisher: IEEE
This paper proposes a novel and simple methodto compute all possible solutions of the inverse kinematicsproblem of the five-oblique-axis thumb model with intersectingaxes at the metacarpophalangeal joint. This thumb model isone of the suggested results by a magnetic-resonance-imaging-based study that, in contrast to those based on cadaver fingersor on the tracking of the surface of the fingers, takes intoaccount muscle and ligament behaviors and avoids inaccuraciesresulting from the movement of the skin with respect to thebones. The proposed distance-based inverse kinematics methodeliminates the use of arbitrary reference frames as is usuallyrequired by standard approaches; this is relevant because thenumerical conditioning of the resulting system of equationswith such traditional approaches depends on the selectedreference frames. Moreover, contrary to other parametrizations(e.g., Denavit-Hartenberg parameters), the suggested distance-based parameters for the thumb have a natural, human-understandable geometric meaning that makes them easier tobe determined from any posture. These characteristics makethe proposed approach of interest for those working in, forinstance, measuring and modeling the movement of the humanhand, developing rehabilitation devices such as orthoses andprostheses, or designing anthropomorphic robotic hands.
Kanner O, Rojas N, Dollar AM, 2017, Between-leg coupling schemes for passively-adaptive non-redundant legged robots, 2017 IEEE International Conference on Robotics and Automation (ICRA), Publisher: IEEE
Bircher WG, Dollar AM, Rojas N, 2017, A two-fingered robot gripper with large object reorientation range, 2017 IEEE International Conference on Robotics and Automation (ICRA), Publisher: IEEE
It is very challenging for a robotic gripper to achieve large reorientations with grasped objects without accidental object ejection. This paper presents a simple gripper that can repeatedly achieve large reorientations over 흅/ퟐrad through the kinematics of the hand-object system alone, without the use of high fidelity contact sensors, complex control of active finger surfaces, or highly actuated fingers. This gripper is the result of two kinematic parameter search optimizationsconnected in cascade. Besides the large range of reorientation attained, the obtained gripper also corresponds to a novel topology since ternary joints in the palm are presented. The in-hand planar reorientation capabilities of the proposed gripper are experimentally tested with success.
Rojas N, Thomas F, 2017, Forward kinematics of the general triple-arm robot using a distance-based formulation, 7th IFToMM International Workshop on Computational Kinematics, Publisher: Springer
Distance-based formulations have successfully been used to obtain closure polynomialsfor planar mechanisms without relying, in most cases, on variable eliminations. The methods re-sulting from previous attempts to generalize these techniques to spatial mechanisms exhibit somelimitations such as the impossibility of incorporating orientation constraints. For the first time, thispaper presents a complete satisfactory generalization. As an example, it is applied to obtain a clo-sure polynomial for the the general triple-arm parallel robot (that is, the 3-RPS 3-DOF robot). Thispolynomial, not linked to any particular reference frame, is obtained without variable eliminationsor tangent-half-angle substitutions.
Kanner OY, Rojas N, Odhner LU, et al., 2017, Adaptive Legged Robots Through Exactly Constrained and Non-Redundant Design, IEEE Access, Vol: 5, Pages: 11131-11141
Ma RR, Rojas N, Dollar AM, 2016, Spherical Hands: Toward Underactuated, In-Hand Manipulation Invariant to Object Size and Grasp Location, Journal of Mechanisms and Robotics, Vol: 8, Pages: 061021-061021, ISSN: 1942-4302
Rojas N, Dollar AM, 2016, Gross Motion Analysis of Fingertip-Based Within-Hand Manipulation, IEEE Transactions on Robotics, Vol: 32, Pages: 1009-1016, ISSN: 1552-3098
Rojas N, Ma RR, Dollar AM, 2016, The GR2 Gripper: An Underactuated Hand for Open-Loop In-Hand Planar Manipulation, IEEE Transactions on Robotics, Vol: 32, Pages: 763-770, ISSN: 1552-3098
Rojas N, Dollar AM, 2016, Classification and Kinematic Equivalents of Contact Types for Fingertip-Based Robot Hand Manipulation, Journal of Mechanisms and Robotics, Vol: 8, Pages: 041014-041014, ISSN: 1942-4302
Rojas N, Dollar AM, 2016, The coupler surface of the RSRS mechanism, Journal of Mechanisms and Robotics, Vol: 8, Pages: 014505-014505, ISSN: 1942-4302
Two degree-of-freedom (2-DOF) closed spatial linkages can be useful in the design of robotic devices for spatial rigid-body guidance or manipulation. One of the simplest linkages of this type, without any passive DOF on its links, is the revolute-spherical-revolute-spherical (RSRS) four-bar spatial linkage. Although the RSRS topology has been used in some robotics applications, the kinematics study of this basic linkage has unexpectedly received little attention in the literature over the years. Counteracting this historical tendency, this work presents the derivation of the general implicit equation of the surface generated by a point on the coupler link of the general RSRS spatial mechanism. Since the derived surface equation expresses the Cartesian coordinates of the coupler point as a function only of known geometric parameters of the linkage, the equation can be useful, for instance, in the process of synthesizing new devices. The steps for generating the coupler surface, which is computed from a distance-based parametrization of the mechanism and is algebraic of order twelve, are detailed and a web link where the interested reader can download the full equation for further study is provided. It is also shown how the celebrated sextic curve of the planar four-bar linkage is obtained from this RSRS dodecic.
Ma RR, Rojas N, Dollar AM, 2016, Towards Predictable Precision Manipulation of Unknown Objects with Underactuated Fingers, Advances in Reconfigurable Mechanisms and Robots II, Editors: Ding, Kong, Dai, Cham, Publisher: Springer International Publishing, Pages: 927-937, ISBN: 978-3-319-23327-7
Rojas N, Dollar AM, Thomas F, 2015, A unified position analysis of the Dixon and the generalized Peaucellier linkages, Mechanism and Machine Theory, Vol: 94, Pages: 28-40, ISSN: 0094-114X
Kanner OY, Rojas N, Dollar AM, 2015, Design of a Passively-Adaptive Three Degree-of-Freedom Multi-Legged Robot With Underactuated Legs, ASME 2015 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference (IDETC/CIE), Pages: V05AT08A062-V05AT08A062
This paper discusses the design of a three degree-of-freedom (3-DOF) non-redundant walking robot with decoupled stance and propulsion locomotion phases that is exactly constrained in stance and utilizes adaptive underactuation to robustly traverse terrain of varying ground height. Legged robots with a large number of actuated degrees of freedom can actively adapt to rough terrain but often end up being kinematically overconstrained in stance, requiring complex redundant control schemes for effective locomotion. Those with fewer actuators generally use passive compliance to enhance their dynamic behavior at the cost of postural control and reliable ground clearance, and often inextricably link control of the propulsion of the robot with control of its posture. In this paper we show that the use of adaptive underactuation techniques with constraint-based design synthesis tools allows for lighter and simpler lower mobility legged robots that can adapt to the terrain below them during the swing phase yet remain stable during stance and that the decoupling of stance and propulsion can greatly simplify their control. Simulation results of the swing phase behavior of the proposed 3-DOF decoupled adaptive legged robot as well as proof-of-concept experiments with a prototype of its corresponding stance platform are presented and validate the suggested design framework.
Tan N, Rojas N, Elara Mohan R, et al., 2015, Nested Reconfigurable Robots: Theory, Design, and Realization, International Journal of Advanced Robotic Systems, Vol: 12, Pages: 110-110, ISSN: 1729-8814
N Rojas, J Borràs, F Thomas, 2015, On quartically-solvable robots, 2015 IEEE International Conference on Robotics and Automation (ICRA), Publisher: Institute of Electrical and Electronics Engineers (IEEE), Pages: 1410-1415, ISSN: 1050-4729
This paper presents a first attempt at a unified kinematics analysis of all serial and parallel solvable robots, that is, robots whose position analysis can be carried out without relying on numerical methods. The efforts herein are focused on finding a unified formulation for all quartically-solvable robots, as all other solvable robots can be seen as particular cases of them. The first part is centered on the quest for the most general quartically-solvable parallel and serial robots. As a result, representatives of both classes are selected. Then, using Distance Geometry, it is shown how solving the forward kinematics of the parallel representative is equivalent to solve the inverse kinematics of the serial representative, thus providing a unified formulation. Finally, it is shown that the position and singularity analysis of these robots reduces to the analysis of the relative position of two coplanar ellipses.
Nansai S, Rojas N, Elara MR, et al., 2015, A novel approach to gait synchronization and transition for reconfigurable walking platforms, Digital Communications and Networks, Vol: 1, Pages: 141-151, ISSN: 2352-8648
Nansai S, Rojas N, Elara MR, et al., 2015, On a Jansen leg with multiple gait patterns for reconfigurable walking platforms, Advances in Mechanical Engineering, Vol: 7, Pages: 168781401557382-168781401557382, ISSN: 1687-8140
Nansai S, Mohan RE, Tan N, et al., 2015, Dynamic Modeling and Nonlinear Position Control of a Quadruped Robot with Theo Jansen Linkage Mechanisms and a Single Actuator, Journal of Robotics, Vol: 2015, Pages: 1-15, ISSN: 1687-9600
N Rojas, A M Dollar, 2014, Characterization of the precision manipulation capabilities of robot hands via the continuous group of displacements, 2014 IEEE/RSJ International Conference on Intelligent Robots and Systems, Publisher: IEEE, Pages: 1601-1608, ISSN: 2153-0858
In robot hands, precision manipulation, defined as repositioning of a grasped object within the hand workspace without breaking or changing contact, is a fundamental operation for the accomplishment of highly dexterous manipulation tasks. This paper presents a method to characterize the precision manipulation capabilities of a given robot hand regardless of the particularities of the grasped object. The technique allows determining the composition of the displacement manifold (finite motion) of the grasped object relative to the palm of the robot hand and defining the displacements that can actually be controlled by the hand actuators without depending on external factors to the hand. The approach is based on a reduction of the graph of kinematic constraints related to the hand-object system through proper manipulations of the continuous subgroups of displacements generated by the hand joints and contacts. The proposed method is demonstrated through three detailed and constructive examples of common architectures of simplified multi-fingered hands.
M R Elara, N Rojas, A Chua, 2014, Design principles for robot inclusive spaces: a case study with Roomba, 2014 IEEE International Conference on Robotics and Automation (ICRA), Publisher: Institute of Electrical and Electronics Engineers (IEEE), Pages: 5592-5599, ISSN: 1050-4729
Research focus on service robots that deals with applications related to healthcare, logistics, residential, search and rescue are gaining significant momentum in the recent years. Their social and economic relevance is more than evident. Yet, while much has been researched about “designing robots” focusing on sensing, actuation, mobility and control of service robots, little work has been done on “design for robots” that looks at designing preferred artefacts or environments for such robots. In this work, we propose a new philosophy of robot inclusive spaces, a cross disciplinary approach that brings together roboticians, architects and designers to solve numerous unsettled research problems in robotics community through design of inclusive interior spaces for robots where the latter live and operate. With a residential floor cleaning robot as a case study, we inductively derived a set of four design principles namely observability, accessibility, activity and safety that guides the realization of an inclusive space for these service robots. Also, the suggested principles are further defined, analysed and validated for their merits in this paper.
V Kee, N Rojas, M R Elara, et al., 2014, Hinged-Tetro: A self-reconfigurable module for nested reconfiguration, 2014 IEEE/ASME International Conference on Advanced Intelligent Mechatronics, Pages: 1539-1546, ISSN: 2159-6247
N Rojas, F Thomas, 2013, The closure condition of the double banana and its application to robot position analysis, 2013 IEEE International Conference on Robotics and Automation, Publisher: Institute of Electrical and Electronics Engineers (IEEE), Pages: 4641-4646, ISSN: 1050-4729
A double banana is defined as the bar-and-joint assembly of two bipyramids joined by their apexes. Clearly, the bar lengths of this kind of assembly are not independent as we cannot assign arbitrary values to them. This dependency can be algebraically expressed as a closure condition fully expressed in terms of bar lengths. This paper is devoted to its derivation and to show how its use simplifies the position analysis of many well-known serial and parallel robots thus providing a unifying treatment to apparently disparate problems. This approach permits deriving the univariate polynomials, needed for the closed-form solution of these position analysis problems, without relying on trigonometric substitutions or difficult variable eliminations.
Rojas N, Mohan R, Sosa R, 2013, Reconfiguration in linkages by variable allocation of joint positions: a modular design approach, 3rd IFToMM International Symposium on Robotics and Mechatronics, Pages: 587-596
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