Passive Gravity Compensation for Robot Manipulator Joints Using a Compression Spring–Cam Mechanism: Modeling, Design, and Experimental Validation
- 1Department of Robot System Engineering, Keimyung University, 1095 Dalgubeol-daero, Dalseo-gu, Daegu 42601, Republic of Korea
- 2Department of Robot Engineering, Keimyung University, 1095 Dalgubeol-daero, Dalseo-gu, Daegu 42601, Republic of Korea
Abstract
Gravitational torque at manipulator joints persists even at rest and thus determines the continuous torque rating of the actuator. This study developed and validated a passive gravity-compensation joint wherein a cam plate extends a compression-spring link with an offset pin joint. Spring torque was derived by virtual work for an arbitrary cam profile, and the pitch curve was distinguished from the machined surface by a normal-offset correction omitted under the point-contact assumption. Because each harmonic coefficient of the Fourier-parameterized profile contributes to curvature with a weight proportional to the square of its order, raising the order trades curvature for accuracy: over the converged orders, the minimum curvature radius (the largest follower admitted without undercutting) fell by 20–34% while the residual fell 4.5- to 6.9-fold. Attainable accuracy was governed not by stiffness but by whether the springs can store the gravitational energy within their allowable stroke. A 5 kg prototype reduced the peak joint torque by 73.2% on the hysteresis-removed basis but by 20.8% in actuator demand, which includes friction. The measured spring torque matched the model within 5%; half the shortfall from simulation stemmed from a load 11% above design, and the gap between bases from sliding friction.
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BibTeX
@article{lee2026passive,
title = {{Passive Gravity Compensation for Robot Manipulator Joints Using a Compression Spring–Cam Mechanism: Modeling, Design, and Experimental Validation}},
author = {Seung-Min Lee and Seong-yeol Yoo},
journal = {Mathematics},
year = {2026},
month = nov,
doi = {10.3390/math14213998},
url = {https://www.mdpi.com/2227-7390/14/21/3998},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Passive Gravity Compensation for Robot Manipulator Joints Using a Compression Spring–Cam Mechanism: Modeling, Design, and Experimental Validation
AU - Seung-Min Lee
AU - Seong-yeol Yoo
PY - 2026
DA - 2026/11/02
JO - Mathematics
DO - 10.3390/math14213998
UR - https://www.mdpi.com/2227-7390/14/21/3998
AB - Gravitational torque at manipulator joints persists even at rest and thus determines the continuous torque rating of the actuator. This study developed and validated a passive gravity-compensation joint wherein a cam plate extends a compression-spring link with an offset pin joint. Spring torque was derived by virtual work for an arbitrary cam profile, and the pitch curve was distinguished from the machined surface by a normal-offset correction omitted under the point-contact assumption. Because each harmonic coefficient of the Fourier-parameterized profile contributes to curvature with a weight proportional to the square of its order, raising the order trades curvature for accuracy: over the converged orders, the minimum curvature radius (the largest follower admitted without undercutting) fell by 20–34% while the residual fell 4.5- to 6.9-fold. Attainable accuracy was governed not by stiffness but by whether the springs can store the gravitational energy within their allowable stroke. A 5 kg prototype reduced the peak joint torque by 73.2% on the hysteresis-removed basis but by 20.8% in actuator demand, which includes friction. The measured spring torque matched the model within 5%; half the shortfall from simulation stemmed from a load 11% above design, and the gap between bases from sliding friction.
SN - 2227-7390
ER -