Xilun Ding

Compliance analysis of a three-legged rigidly-connected platform device

The platform based vibratory bowl feeders are essential elements in automatic assembly. Taking the bowl feeder as a typical three-legged rigidly connected compliant platform device, this paper applies von Mises compliance matrix to each of the leaf-spring legs, establishes screw systems of the legs and develops the Jacobian of the platform using the adjoint transformation. Based on the force equilibrium between the supporting and external wrenches and the twist deflection, a platform compliance matrix is proposed as a congruence transformation of the legs compliance matrices. The matrix is then decomposed into a central compliance matrix and an adjoint transformation, leading to the decomposition of the legs parameter effect from the platform assembly influence. The analysis presents the necessary and sufficient condition for the existence of the twist deflection that is equivalent to the characteristics equation of the compliant platform. Further based on the eigencompliances and eigentwist decomposition, the legs parameter effect and the platform assembly parameter influence are identified. This reveals the compliance characteristics of this type of devices and the parameters effect on the compliance and presents a suitable parameter range for design of the compliant platform device.

Compliance Analysis of Mechanisms with Spatial Continuous Compliance in the Context of Screw Theory and Lie Groups

This paper investigates the compliance effect on both serial and parallel mechanisms based on study of deflections of a finite segment of elastic beam with spatial compliance and applies eigenvectors and eigenvalues to identify principal screws in the mechanisms and parallel devices with spatial continuous compliance. With the analysis, compliance characteristics of both serial mechanisms and parallel devices can be identified with effect of compliance. Case studies are presented with numerical examples.

Morphological synthesis of metamorphic mechanisms based on constraint variation

A metamorphic mechanism can be considered as a mechanism set composed by multiple kinematic chains which have the ability to be transformed sequentially from one to another following specific rules in order to meet different requirements of tasks. The process of its configuration transformation results from the variation of constraints. A special classification approach of constraints is proposed based on its characteristic of multi-configuration. The basic modes to achieve configuration transformation of metamorphic mechanisms and the design principle of metamorphic kinematic pairs are further presented. Finally, a configuration synthesis methodology of the metamorphic mechanism is proposed based on a morphological matrix. The essence of this methodology is to realize variation and coupling of mechanisms in adjacent configurations by applying metamorphic kinematic joints according to the functions, constraints, and configuration sequence. The approach is verified by developing a vehicle that can convey materials with a metamorphic driving mechanism. This study provides a fundamental theory for the design of new metamorphic mechanisms.

Design and Testing of a Highly Reconfigurable Fixture With Lockable Robotic Arms

The paper describes an innovative fixture created within the AUTORECON project of the European Commissions 7th Framework Program. The fixture is designed to respond to the automotive industrys needs of high modularity and full flexibility, by allowing the secure multishape grasping of a very wide range of (often large and heavy) metal workpieces typical for car-assembly operations. The fixture is used as an end-effector of an industrial robot, which in turn acts in cooperation with other machines, such as other robots performing machining or other processes on the part. The fixturing device is both a highly reconfigurable structure and a robotic mechanism: moving as a programmable robot to reconfigure and acting as a supporting structure once a hold on the part has been established. This dual functioning has been made possible by the development of a key component, a stepless lockable revolute joint, described herein. In order to get a readily modifiable system, all parts of the fixture are designed as modules. Prototypes of the main parts and the whole fixture have been fabricated and experiments validating the design are reported.

Geometric and Kinematic Analysis of the Hoberman Switch-Pitch Ball and Its Variant

This paper investigates geometry and kinematics of the Hoberman switch-pitch ball and its variant as an extended case of the ball. The paper starts from examining the geometry of the ball variant and its composition and decomposes it into loops each of which is an eight-bar radial linkage. Based on this, the paper investigates the geometry of the eight-bar radial linkage and the variant and subsequently extends the study to their kinematics. The Hoberman switch-pitch ball as a special case of the ball variant with bevel gears is investigated and a numerical example is employed to illustrate the kinematic characteristics of the eight-bar radial linkage and the Hoberman switch-pitch ball.Copyright

Design of a biologically inspired lower limb exoskeleton for human gait rehabilitation

This paper proposes a novel bionic model of the human leg according to the theory of physiology. Based on this model, we present a biologically inspired 3-degree of freedom (DOF) lower limb exoskeleton for human gait rehabilitation, showing that the lower limb exoskeleton is fully compatible with the human knee joint. The exoskeleton has a hybrid serial-parallel kinematic structure consisting of a 1-DOF hip joint module and a 2-DOF knee joint module in the sagittal plane. A planar 2-DOF parallel mechanism is introduced in the design to fully accommodate the motion of the human knee joint, which features not only rotation but also relative sliding. Therefore, the design is consistent with the requirements of bionics. The forward and inverse kinematic analysis is studied and the workspace of the exoskeleton is analyzed. The structural parameters are optimized to obtain a larger workspace. The results using MATLAB-ADAMS co-simulation are shown in this paper to demonstrate the feasibility of our design. A prototype of the exoskeleton is also developed and an experiment performed to verify the kinematic analysis. Compared with existing lower limb exoskeletons, the designed mechanism has a large workspace, while allowing knee joint rotation and small amount of sliding.

Novel Deployable Mechanisms With Decoupled Degrees-of-Freedom

A novel family of deployable mechanisms (DMs) is presented. Unlike most such devices, which have one degree-of-freedom (DOF), the proposed DM can be deployed and compacted independently in two or three directions. This widens the range of its potential applications, including flexible industrial fixtures and deployable tents. The mechanisms basic deployable unit (DU) is assembled by combining a scissor linkage and a Sarrus linkage. The kinematic properties of these two components and of the combined unit are analyzed. The conditions under which the unit can be maximally compacted and deployed are determined through singularity analysis. New 2DOF DMs are obtained by linking the DUs: each mechanisms shape can be modified in two directions. The relationship between the degree of overconstraint and the number of DUs is derived. The magnification ratio is calculated as a function of link thickness and the number of DUs. The idea of deployment in independent directions is then extended to three dimensions with a family of 3DOF mechanisms. Finally, kinematic simulations are performed to validate the proposed designs and analyses.

A Network of Type III Bricard Linkages

Among Bricard’s overconstrained 6R linkages, the third type has two collapsed configurations, where all joint axes are coplanar. The paper presents a one-degree-of-freedom network of such linkages. Using the two coplanar states of the constituent Bricard units, the network is able to cover a large surface with a specific outline when deployed, and can be folded compactly into a stack of much smaller planar shapes. Five geometric parameters describing each type III Bricard mechanism are introduced. Their influence on the outline of one collapsed configuration is discussed and inverse calculation to obtain the parameter values yielding a desired planar shape is performed. The network is built by linking the units, either using scissor linkage elements, if the thickness of the panels can be ignored, or with hinged parallelograms, for a thicker material. Two case studies, in which the Bricard network deploys as a rectangle and a regular hexagon, respectively, are presented, validating the analysis and design methods.Copyright

A Novel Deployable Mechanism With Two Decoupled Degrees of Freedom

This paper presents a novel deployable mechanism. Unlike most deployable structures, which have one degree of freedom, the proposed device can be deployed and compacted independently in two directions. This widens the range of its potential applications, including flexible industrial fixtures and deployable tents. The mechanism’s basic deployable unit is assembled by combining a scissor linkage and a Sarrus linkage. The kinematic properties of the two component linkages and the combined unit are analyzed. The new deployable mechanism is obtained by linking the deployable units. The Mobility and kinematics are analyzed. The relationship between the degree of overconstraint and the number of deployable units is derived. The magnification ratio is calculated as a function of the geometry of the link and the number of deployable units. Finally, kinematic simulations are performed to validate the proposed design and analysis.Copyright

Reconfigurable Chains of Bifurcating Type III Bricard Linkages

This paper presents the construction of a family of reconfigurable mechanisms composed of an unlimited number of doubly collapsible (type III) Bricard linkages. First, the geometries of these overconstrained six-hinge spatial loops are parameterized and their kinematics is investigated. The configuration-space curve is computed; its bifurcation behavior is analyzed and illustrated by projections. It is then shown that type III Bricard linkages can be connected in series in a one-degree-of-freedom chain. Such a multi-loop mechanism has the ability to reconfigure in multiple ways due to the bifurcations of the individual Bricard units. Consequently, the chain has multiple states where all joint axes are coplanar. In each such configuration, the physical links, every one realized as a planar figure, spread out to cover a curving stripe in the plane. Several simulations and case studies are performed.