Wen-Tzong Lee

On cam system design to replicate spatial four-bar mechanism coupler motion

The coupler motion of a planar four-bar mechanism can be reproduced by rotating the mechanisms moving centrode over its fixed centrode. For spatial four-bar mechanisms, coupler motion can be replicated by moving the mechanisms moving axode over its fixed axode in a screw motion – a combination of simultaneous rotations and translations. This study presents a model to calculate the fixed and moving axodes of the revolute–revolute–spherical–spherical (RRSS) mechanism – one of the most basic spatial four-bar mechanisms. The axodes are useful in producing the contact surfaces for a cam system to replicate RRSS coupler motion.

On the application of CAD technology for the synthesis of spatial revolute-revolute dyads

This work presents a method based on Computer Aided Design or CAD for facilitating the synthesis of Revolute-Revolute (R-R) dyads with adjustable moving pivots. The CAD-based method presented in this work ensures that all prescribed rigid-body parameters used to synthesize the R-R dyad satisfy particular kinematic requirements of an R-R dyad. Through the application of this CAD method, five of the six general R-R dyad constraint equations are satisfied and therefore not essential for the synthesis of the R-R dyad. By reducing the number of dyad design constraints from six to one, the user can synthesize R-R links with adjustable moving pivots for multi-phase motion and path generation applications. The example included demonstrates the use of the CAD method in the synthesis of an RRSS path generator with adjustable moving pivots.

Developments in quantitative dimensional synthesis (1970-present): four-bar motion generation

Abstract Dimensional synthesis is a type of inverse problem in linkage kinematics where the objective is to calculate the linkage dimensions required to achieve prescribed linkage output motion. Motion generation is a particular category of dimensional synthesis where the objective is to calculate the linkage dimensions required to achieve a group of prescribed link positions. In motion generation for a four-bar linkage, positions are prescribed for the coupler link. While early motion generation methods were primarily qualitative, ongoing advancements in computing hardware and software continue to make quantitative motion generation more practical. By providing overviews of works representative of developments in quantitative four-bar motion generation since 1970, this work is essentially an overview that spans over 40 years of developments in quantitative four-bar motion generation.

On the application of RRSS motion generation and RRSS Axode generation for the design of a concept prosthetic knee

ABSTRACT In this work, equation systems for RRSS motion generation and RRSS axode generation are applied to produce a concept above the transfemoral amputation prosthetic knee. First, an RRSS linkage is synthesized to approximate a series of tibial positions during knee flexion. Next, the fixed and moving axodes of the synthesized RRSS linkage are generated. Because the coupler motion of an RRSS linkage can be replicated by rolling its moving axode over its fixed axode, the axodes for the synthesized RRSS linkage are incorporated as gears to produce a concept prosthetic knee. The resulting prosthetic knee approximates the natural spatial motion of the tibia during knee flexion and extension (unlike prosthetic knee designs that include simple pin joints).

On Two-Phase Spherical Motion Generation

This work presents a method to design four revolute spherical mechanisms to approximate two phases of prescribed rigid-body positions. Using this method, four revolute spherical motion generators can be designed to approximate two phases of prescribed rigid-body positions using the same mechanism hardware. This work considers moving-pivot adjustable four revolute spherical motion generators with constant crank and follower lengths for two-phase motion generation.

Revolute-Cylindrical-Cylindrical-Cylindrical linkage optimum dimensional synthesis with static structural loading

General optimization models for the dimensional synthesis of defect-free Revolute-Cylindrical-Cylindrical-Cylindrical linkages with static loading are formulated and evaluated in this work. With these optimization models, Revolute-Cylindrical-Cylindrical-Cylindrical linkage dimensions required to approximate coupler positions or coupler path points while achieving static equilibrium (given coupler loads) within a maximum driver static torque are calculated. These models also include constraints that eliminate order, branch and circuit defects-defects that are common in traditional dyad-based dimensional synthesis. Therefore, the novelty of this work is the development of optimization models that permit the synthesis of order, branch and circuit defect-free Revolute-Cylindrical-Cylindrical-Cylindrical motion and path generators that also achieve static equilibrium within a maximum specified driver torque magnitude for specified coupler loads. This work conveys both the benefits and drawbacks realized when implementing these optimization models on a personal computer using the commercial mathematical analysis software package Matlab.

Developments in quantitative dimensional synthesis (1970–present): four-bar path and function generation

Abstract Dimensional synthesis is a type of inverse problem in linkage kinematics where the objective is to calculate the linkage dimensions required to achieve prescribed linkage output motion. It includes three distinct subcategories: motion generation, path generation and function generation. The authors’ first work surveyed developments in quantitative four-bar motion generation. This work concludes the presentation of developments in four-bar dimensional synthesis by surveying the developments made in quantitative four-bar path and function generation since 1970. While early path and function generation methods (like motion generation methods) were primarily qualitative, ongoing advancements in computing hardware and software continue to make quantitative motion generation more practical.

An Evaluation of Primer Preseating in Small Caliber Cartridge Production

This work presents the findings of a study to quantify the relative effectiveness of the primer preseating operation in small caliber cartridge production. In theory, primer preseating would enable cartridge stamping tools to achieve deeper stamping penetration depths and subsequently, greater primer retention forces. This is because, with preseating incorporated in the existing small caliber cartridge production process, a cartridge stamping tool would be fully dedicated to performing the case stamping operation (rather than the simultaneous primer seating and case stamping operations it currently performs). The findings presented in this work include measured percentages of total stamping tool force dedicated to primer seating, stamping tool penetration depths with and without primer preseating and primer retention forces with and without primer preseating. These findings and their underlying principles were produced through a static force equilibrium analysis and finite element modeling and simulation studies.