An Extension-Based Compliant Constant-Force Mechanism For the Rigid-Body Replacement Approach Using a Novel Pseudo-Rigid Body Model

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Author:
Thomason, Bradon
Graduate Program:
Engineering Design
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 01, 2026
Committee Members:
Jared Butler, Thesis Advisor/Co-Advisor
Matt Parkinson, Committee Member
Nicholas Meisel, Professor in Charge/Director of Graduate Studies
Matt Parkinson, Thesis Advisor/Co-Advisor
Jessica Dolores Menold, Thesis Advisor/Co-Advisor
Keywords:
Compliant Mechanisms
Pseudo-Rigid Body Models
Constant Force
Rigid-Body Replacement
Abstract:
This work presents a generalized pseudo‑rigid body model (PRBM) for non‑collinear fixed‑guided beams, enabling planar compliant geometries with large ranges of motion and straightforward stress validation not captured in existing PRBMs. The rigid‑body replacement approach (RBRA) employs PRBMs in the design of compliant constant‑force mechanisms (CCFMs), providing a straightforward method for synthesizing such mechanisms; however, existing RBRA‑based CCFM configurations are primarily limited to compression‑based designs. To expand these capabilities, this study introduces a CCFM architecture that operates in extension while retaining the simplicity of the RBRA. A slider‑crank configuration is proposed to generate the constant‑force behavior, leveraging an offset‑initialized fixed‑guided segment modeled using the new PRBM. The derivation and governing equations for this new PRBM, denoted a double-precurved beam, are set forth. The governing equations for this new PRBM are set forth, and rigid-body replacement is performed to formulate the compliant geometry. The proposed CCFM and PRBM are validated through tensile testing of three waterjet-cut polypropylene specimens over a total of nine tensile tests, which deviate from the predicted force-deflection curve by only 5.12%. Furthermore, corresponding finite-element analysis of the configuration deviates from the predicted results by only 1.40%. The experimental results confirm that the model achieves the desired constant‑force behavior, thus extending the RBRA framework to applications requiring constant force in extension and introducing a fundamentally new PRBM for fixed-guided configurations originating from an offset position.