Ketao Zhang

Topology and Constraint Analysis of Phase Change in the Metamorphic Chain and Its Evolved Mechanism

This paper presents a metamorphic kinematic pair extracted from origami folds in the context of mechanisms, its evolved metamorphic chain, and the novel metamorphic parallel mechanism. This paper starts from the generic issues of topological representation for metamorphic mechanism, leading to unified elementary matrix operation for presentation of topological variation. Phase matrix and augmented adjacency matrix are developed to present the topological state and geometry of metamorphic mechanism in an evolutionary process. The metamorphic kinematic pair has the ability of changing mobility to generate different motion patterns based on mobility change correlated with the link annex induced topological phase change. This paper then investigates topological variation of the metamorphic chain and the topological subphases are enumerated in accordance with structure evolution. Using the metamorphic chain as chain-legs, a multiloop metamorphic mechanism with ability of performing phase change and orientation switch is constructed. The disposition of constraints and geometric constraints induced bifurcated motion are analyzed based on screw theory. The topological variation of the metamorphic parallel mechanism is addressed and the foldability is verified by physical device.

Geometric Constraint and Mobility Variation of Two 3SvPSv Metamorphic Parallel Mechanisms

This paper presents a unique feature of geometric constraint of adjacent axes of the variable-axis (vA) joint and analyses the effectiveness in the constructed limb, resulting in variation of mobility configuration of two 3SvPSv metamorphic parallel mechanisms. The underlying principle of the metamorphosis of this vA joint is unravelled by investigating the dependence of the corresponding screw system comprising of line vectors, leading to evolution of the vA joint from the source phase Sv to the variable Hooke’s joint phase Uv and the variable revolute-joint phase Rv. The kinematic chain installed with the vA joint forms a reconfigurable limb and is then used to construct two 3SvPSv metamorphic parallel mechanisms proposed in this paper. The phase change of the vA joints incurs the constraint change of the SvPSv limb and subsequently results in the change of mobility configuration of the metamorphic parallel mechanisms. The paper further addresses the geometrical condition for constructing 3SvPSv metamorphic parallel mechanisms following the constraints delivered by the reconfigurable limbs, leading to the analysis of mobility change of the mechanisms induced by the phase change of the limbs.

A novel 4-DOFs origami enabled, SMA actuated, robotic end-effector for minimally invasive surgery

Minimally invasive Surgery (MIS) is one of the most challenging fields for robot designers due to the limited size of the access points, to the high miniaturization level and to the dexterity needed for performing surgical tasks. For this reason, the integration of actuators should proceed in parallel with the identification of the most effective transmission mechanisms and kinematics. Conversely, only a few microfabrication technologies are adequate for developing small size mechanisms with safe operation in the human body. In this paper a SMA actuated, miniaturized, origami-enabled, parallel structure is presented as a versatile module for novel robotic tool in MIS, the parallel structure has been combined with a twisting module and a gripper obtaining a 4-DOFs on board actuated end-effector.

An Extensible Continuum Robot with Integrated Origami Parallel Modules

This paper presents a novel design for extensible continuum robots in light of origami inspired folding techniques. The design starts from a modularized crease pattern, which consists of two triangular bases and three waterbomb bases, and the folding process for creating an origami parallel structure from the crease pattern. The process further progresses to generate a compliant module with the origami parallel structure and a helical compression spring. A novel extensible continuum robot with integrated compliant parallel modules is then proposed to imitate not only the bending motion but also the contraction of continuum apparatus in nature. Mapping the origami parallel structure to an equivalent kinematic model, the motion characteristics of the origami structure are unraveled in terms of kinematic principles. The analysis reveals the mixed rotational and translational motion of the origami parallel module and the virtual axis for yaw and pitch motion in particular. According to the kinematics of the proposed continuum robot and features of the integrated helical spring in each module, three actuation schemes and resultant typical working phases with a tendon driven system are presented. A prototype of the extensible continuum robot with six modules connected in serial is produced as a proof of concept. The functionality of the proposed continuum robot with integrated origami parallel structure as its skeleton and helical springs as the compliant backbone is validated by the preliminary experimental results.

Reciprocal screw theory based singularity analysis of a novel 3-DOF parallel manipulator

Singularity analysis is an essential issue for the development and application of parallel manipulators. Most of the existing researches focus on the singularity of parallel manipulators are carried out based on the study of Jacobian matrices. A 3-DOF parallel manipulator with symmetrical structure is presented. The novel parallel manipulator employs only revolute joints and consists of four closed-loop subchains connecting to both base and platform via revolute joints. The closed-loop subchain in each chain-leg is a spherical 6R linkage. The motion characteristics of the output link in the spherical 6R linkage with symmetrical structure are analyzed based on the interrelationships between screw systems. The constraints that are exerted on the platform by each chain-leg are investigated applying the concept of generalized kinematic pair in terms of equivalent screw system. Considering the geometric characteristics of the parallel manipulator, the singularity criteria of the parallel manipulator corresponding to different configurations are revealed based on the dependency of screw system and line geometry. The existing conditions of certain configuration that a singularity must occur are determined. This paper presents a new way of singularity analysis based on disposition of constraint forces on the geometrically identified constraint plane and the proposed approach is capable of avoiding the complexity in solving the Jacobian matrices.

Screw-System-Variation Enabled Reconfiguration of the Bennett Plano-Spherical Hybrid Linkage and Its Evolved Parallel Mechanism

This paper presents the Bennett plano-spherical hybrid linkage and proposes a novel metamorphic parallel mechanism consisting of this plano-spherical linkage as part of limbs. In light of geometrical modeling of the Bennett plano-spherical linkage, and with the investigation of the motion-screw system, the paper reveals for the first time the reconfigurability property of this plano-spherical linkage and identifies the design parameters that lead to change of constraint equations, and subsequently to variation of the order of the motion-screw system. Arranging this linkage as part of limbs, the paper further investigates the reconfiguration property of the plano-spherical linkage evolved parallel mechanism. The analysis reveals that the platform constraint-screw system varies following both bifurcation and trifurcation with motion branch variation in the 6R linkage integrated limb structure. Consequently, this variation of the platform constraintscrew system leads to reconfiguration of the proposed metamorphic parallel mechanism. The paper presents a way of analyzing reconfigurability of kinematic structures based on the screw-system approach. [DOI: 10.1115/1.4030015]

A Novel 4-DOF Origami Grasper With an SMA-Actuation System for Minimally Invasive Surgery

Minimally invasive surgery (MIS) is one of the most challenging techniques for robot designers due to the limited size of access points, the high miniaturization level, and the dexterity needed for performing surgical tasks. Conversely, only a few microfabrication technologies are currently available for developing such small-sized systems, which allow safe operations in human bodies. In order to match these challenges in MIS, both design and integration of actuation systems should proceed in parallel with an identification of most effective transmission mechanisms and kinematics. In this paper, an origami parallel module that generates two rotations and one translation is integrated with a twisting module and a compliant gripper to form a novel four-degree-of-freedom grasper. The rotational motion leads to the pitch and yaw motion of the gripper, while the translational motion is converted to a roll motion of the gripper via the twisting module that is stacked on top of the parallel module. In light of plane-symmetric properties of the origami structure in the parallel module, both inverse and forward kinematics are resolved with a geometric approach, revealing a unique joint space and a kinematic mapping of the parallel module, leading to the design of two sets of on-board actuation systems. During the analysis, bending motion of a central spring and static properties of the compliant gripper are modeled using finite-element methods. The structure of the twisting module for motion transmission of the grasper is designed and fabricated using origami folding techniques. Gripping forces of the compliant gripper are evaluated in experimental tests. Further analyses of the system performance are addressed in accordance with the scaling ratio of miniaturization and the scalability of the system is demonstrated by a millimeter-sized origami parallel module produced by the smart composite microstructure fabrication process.

Analysis of the Motion Mode Change of a Metamorphic 8R Linkage

By definition, metamorphic mechanisms can change their mobility. This change can be achieved by actively locking certain elements, or can be due to the inherent kinematics of the linkage. In the latter case the mobility is altered when passing through configuration space singularities. In a recent development, these two phenomena are combined. As such it was shown that a single-loop 8R linkage, possessing certain symmetry, turns into an overconstrained 6R linkage by only locking one joint while another joint is then implicitly constrained. This phenomenon has been analyzed by means of a first-order analysis in terms of instantaneous joint screw system. Thereupon the metamorphism was concluded and verified experimentally. An analytic proof was not yet provided. In this paper finite kinematics of the metamorphic 8R linkage is established and its ability to change to a 6R linkage by means of locking only one joint is shown analytically. The presented methodology is general and applicable to arbitrary mechanisms. It does provides a basis for the analysis and eventually the synthesis of novel metamorphic mechanisms.

Classification of origami-enabled foldable linkages and emerging applications

In the context of mechanisms, origami folds can be represented as equivalent mechanisms by taking creases as revolute joints and panels as links. This paper systematically presents various foldable closed-loop linkages extracted from origami folds and origami tessellations. The geometrical characteristics of typical origami crease patterns and patterned assemblies as well as the corresponding equivalent closed-loop linkage are investigated. The basic closed-loop linkages and complicated assemblies are classified according to their mobility in general configuration and the motion characteristics of these origami-enabled linkages are analyzed in terms of screw theory. Based on the geometry and motion analysis, possible simplified mechanisms of each complicated assembly are derived. The existing applications of the origami-inspired foldable closed-loop linkages in packaging and deployable structures, and emergence of new practical use in advanced robotics are addressed.Copyright

Topology and Constraint Analysis of Reconfiguration in Metamorphic Mechanisms

This paper investigates the reconfiguration of the metamorphic mechanisms and proposes mechanism topology matrix, phase matrix and augmented adjacency matrix to identify variation of geometric and topological configurations. This is then used to investigate the two generic ways in the study of induced constraint change of the metamorphic mechanisms. The topological phase change of the metamorphic mechanisms correlative to the variable-axis revolute joints and link annex is hence investigated and constraint analysis is then presented in the working phases of the new metamorphic mechanisms.Copyright