Hong-Sen Yan

Topological Representations and Characteristics of Variable Kinematic Joints

There exist some mechanisms with variable topologies that have interesting applications, for examples, legged walking machines, mechanical push-button stopper locks, and various toys. A variable kinematic joint is a kinematic joint that is capable of topological variation in a mechanism with variable topology. This work aims at the topological representations and characteristic analysis of variable kinematic joints. During the operation process of a mechanism, the topology states of a variable kinematic joint can be expressed symbolically as the joint sequences, graphically the digraphs, and mathematically the matrices. With the applications of graph theory, it proves that the topological characteristics of variable kinematic joints appeared with the abilities of reversibility, continuity, variability of degrees of freedom, joint homonorphism, contractibility, and expansibility. Two examples are provided for illustrating how the proposed concepts can be used to analyze and synthesize the variable joints. The results of this work provide a logical foundation for the systematic structural synthesis regarding the kinematic joints and mechanisms with variable topologies.

A methodology for creative mechanism design

This paper summarizes the authors research efforts in the creative design of mechanisms in the past years. A design methodology is presented for the generation of all possible design concepts of mechanisms with required topological characteristics. This methodology provides a powerful tool to avoid existing designs which have patent protection. The rear suspension of off-road motorcycles is used as an example to illustrate this methodology.

On the Mobility and Configuration Singularity of Mechanisms With Variable Topologies

The mechanisms with variable topologies (MVTs) are usually changing their topological structures in accordance with the varying mobility and quasi-singular configurations. The mobility analysis and configuration singularity of MVTs are studied via screw theory in this paper. The configurations of MVTs are formulated by a set of variable combinations of screw coordinates. For the mobility analysis, two examples provided show that the proposed approach is adoptable for dealing with common MVTs. For the configuration singularity, the concepts of stationary configuration and uncertainty configuration are utilized to demonstrate the topology varying strategy of MVTs. The result in this work provides the theoretical basis and inspiration for the configuration synthesis and analysis of mechanisms with variable topologies.

Optimal Synthesis of Cam-Linkage Mechanisms for Precise Path Generation

The paper proposes a method for the optimal synthesis of planar mechanisms, where a combination of cams and linkages is used in order to obtain a precise path generation. As a first step, based on Gruebler s mobilize criterion, a linkage mechanism is considered, with as many degrees of freedom as required by the generation task. One or more disk cams are then synthesized in order to reduce the systems mobility and to obtain a single-input combined mechanical system. The final combined mechanism is able to guide a coupler point through any number of precision positions. A strategy for the global optimization of the synthesis process, based on evolutionary theory, is also proposed. A goal function is defined on the basis of dimensional and kinematic constraints and performance criteria, while a genetic algorithm is employed as an optimum searching procedure. An industrial application of the proposed methodology is described, where a path generation problem with time prescription is dealt with. The objective of the generation task is to guide a coupler point along a figure-eight trajectory, with a constant tangential velocity. Such a task is required by polishing machines for fiber optic connectors and similar components. A kinematic simulation of the optimal mechanism is used to validate the proposed synthesis methodology.

Kinematic and dynamic design of four-bar linkages by links counterweighing with variable input speed

A novel method for four-bar linkages, that satisfies kinematic design requirements and also attains trade-off of dynamic balance, is presented. By properly designing the speed trajectory of the input link, the disk counterweight of moving links, and link dimensions of the given or desired mechanisms, the expected output motion characteristics and dynamic balancing performance are obtained. The input motion characteristics are designed with Bezier curves. Optimization is applied to find out optimal design parameters for reaching the trade-off of dynamic balance. The input speed trajectory of the input link could be generated by a servomotor. Examples are given to demonstrate the design procedure of this approach.

On the output motion characteristics of variable input speed servo-controlled slider-crank mechanisms

Abstract The input speed of the crank of a slider-crank mechanism is traditionally assumed to be constant. However, this paper proposes a novel concept by varying the speed of the crank to obtain the desired output motions. This approach uses a servomotor as the power input of the mechanism. By properly designing the input speed of the mechanism, the output motion can pass through a desired trajectory. The input motion characteristics are planned with Bezier curves. Optimization is used to improve the output characteristics of the system. Guidelines for defining the optimization problems are discussed and control algorithm regarding how this servo system works is presented. Three design examples are given to demonstrate the procedure of this work. Results of experiments are also given to verify the feasibility of this work.

The specialization of mechanisms

Abstract A methodology is presented, based on combinatorial theory, for complete enumerating non-isomorphic specialized mechanisms precisely from a specified kinematic chain. An algorithm for finding the defined permutation groups of kinematic chain from its labelled link adjacency matrix is developed. According to these permutation groups, another algorithm for generating all non-isomorphic specialized mechanisms by assigning various types to the links and joints of the kinematic chain is proposed. Finally, based on Polyas theory, we derived mathematical expressions for counting the number of the specialized mechanisms. The results of this work are beneficial to the automation of the creative design of mechanisms.

Geometry design and machining of roller gear cams with cylindrical rollers

Abstract This paper derives equations for the surface geometry of roller gear cams with cylindrical rollers based on coordinate transformation, differential geometry, and theory of conjugate surfaces. Mathematical expressions for the principal curvatures and directions and the pressure angles are also presented. A five-axis machining center is adopted for obtaining the coordinates and directions of the cutter for the final cutting. The conditions of undercutting is discussed for avoiding singular points occurs on the globoidal cam surface during machining process. A roller gear cam in an automatic tool changer for exchanging two parallel cutters is used as an example for illustration.

Creative design of a wheel damping mechanism

Abstract The objective of this work is to provide a systematic method for the creation of all possible wheel damping mechanisms based on a parent mechanism. The original mechanism is generalized into a linkage type kinematic chain according to the rules defined. The self-assortment and the related assortments of this kinematic chain are derived by using the technqiue of number synthesis. These derived kinematic chains are respecialized, by applying the generalized rules backward based on some design constraints, to create a total of 98 new wheel damping mechanisms.

Motion control of cam mechanisms

Abstract In this paper, optimal control theory is applied to create a theoretical frame of ‘Active Control of Cam Mechanisms.’ The investigation presented here deals with the problem of ‘Motion Control’ which is the foundation of ‘Active Control.’ It is shown that, from a kinematics point of view, the motion characteristics of the follower can be improved by applying an optimal control to the cam speed. Some examples are given to demonstrate the procedure.