A 1-Degree-of-Freedom Double-Crank Spring Gravity Balancer and Its Extension to Multi-Degree-of-Freedom Serial Manipulator
Journal
Journal of Mechanisms and Robotics
Journal Volume
17
Journal Issue
10
Start Page
101011
ISSN
1942-4302
1942-4310
Date Issued
2025-06-27
Author(s)
Abstract
This article introduces a pioneering double-crank spring gravity balancer (DSGB) with a specialized spring arrangement that overcomes the spring free-length constraint observed in previous rotating-type balancers and achieves perfect static balancing. The gravitational energy associated with a ground-connected rotary link to be balanced is represented in quadratic sine form. The DSGB employs a double-crank mechanism comprising two ground-connected cranks and a cable passing through their ends, encircling one crank's pivot, and connected to a ground-connected spring. The elongation of the spring, reflecting the distance between the ends of the cranks, is formulated as a sine function, ensuring compatibility with gravitational energy through angular and geometric constraints. Two variants of the DSGB, namely constrained and unconstrained central distance DSGB, are introduced. By maintaining a constant total of gravitational and elastic energy, constraints including spring stiffness and motion compatibility with the rotary link are established. Aligning the central distance axis of the DSGB with the rotary link and ensuring motion compatibility result in a compact ground-connected in-line DSGB module. The article illustrates the viability of DSGB modules in balancing a multi-degree-of-freedom (multi-DOF) serial manipulator by proposing modifications to spring stiffness constraints and maintaining motion-compatible constraints using pseudo bases. Prototypes and experimental studies of both 1-DOF rotary link and 2-DOF manipulator with DSGBs are developed, showing torque reduction rates up to 94.8% and 97.5%, respectively, validating the DSGB's effectiveness.
Subjects
gravity balancer
mechanism synthesis and analysis
mechanisms and robots
multi-degree-of-freedom
planar mechanism
static balance
Publisher
ASME International
Type
journal article