skip to main content


Title: Approximating Hinges With Multimaterial Compliant Joints
Abstract

This paper investigates the use of multimaterial compliant joints produced through additive manufacturing in order to approximate a revolute joint. Compliant joints benefit from low friction and reduced wear, but at the cost of increased joint stiffness, reduced range of motion, and a reduced ability to resist loading. In addition, they might also provide a poor approximation of the revolute joints they intend to replace. In this paper, we experiment with three multimaterial compliant joint configurations. The first joint emphasizes accurate kinematics, the second joint aims to reduce axis-aligned stiffness, and the third joint compromises between the two. Samples were fabricated on a desktop 3D printer using PLA (polylactic acid) as the rigid material and TPU (thermoplastic polyurethane) for its flexibility. Samples were measured for tensile stiffness, torsional stiffness, range of motion, and approximation of a hinge motion. Our results indicate design trade offs where joints that measure most ideal for one property will be least ideal for another. The most novel design in this paper straddles this trade off. In the end, the suitability of each joint design is determined by the loading, accuracy, and range of motion requirements posed by a given application.

 
more » « less
Award ID(s):
2041789
PAR ID:
10311447
Author(s) / Creator(s):
; ;
Date Published:
Journal Name:
2021 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Movement in compliant mechanisms is achieved, at least in part, via deformable flexible members, rather than using articulating joints. These flexible members are traditionally modeled using Finite Element Models (FEMs). In this article, an alternative strategy for modeling compliant cantilever beams is developed with the objectives of reducing computational expense, and providing accuracy with respect to design optimization solutions. The method involves approximating the response of a flexible beam with an n-link/m-joint Pseudo-Rigid Body Dynamic Model (PRBDM). Traditionally, PRBDM models have shown an approximation of compliant elements using 2 or 3 revolute joints (2R/3R-PRBDM). In this study, a more general nR-PRBDM model is developed. The first n resonant frequencies of the PRBDM are matched to exact or FEM solutions to approximate the response of the compliant system. These models can be used for co-design studies of flexible structural members, and are capable of modeling higher deflection of compliant elements. 
    more » « less
  2. Movement in compliant mechanisms is achieved, at least in part, via deformable flexible members, rather than using articulating joints. These flexible members are traditionally modeled using finite element analysis (FEA)-based models. In this article, an alternative strategy for modeling compliant cantilever beams is developed with the objectives of reducing computational expense and providing accuracy with respect to design optimization solutions. The method involves approximating the response of a flexible beam with an n-link/m-joint pseudo-rigid-body dynamic model (PRBDM). Traditionally, static pseudo-rigid-body models (PRBMs) have shown an approximation of compliant elements using two or three revolute joints (2R/3R-PRBM). In this study, a more general nR-PRBDM model is developed. The first n resonant frequencies of the PRBDM are matched to exact or FEA solutions to approximate the response of the compliant system and compared with existing PRBMs. PRBDMs can be used for co-design studies of flexible structural members and are capable of modeling large deflections of compliant elements. We demonstrate PRBDMs that show dynamically accurate response for a random geometry cantilever beam by matching the steady-state and frequency response, with dynamical response accuracies up to 10% using a 5R-PRBDM. 
    more » « less
  3. Abstract In this paper, the realization of any specified planar Cartesian compliance for an object grasped by a compliant hand is addressed. The hands considered have 2 or more fingers for which each has 3 modulated elastic joints and predetermined link lengths. Geometric construction-based compliance synthesis procedures are developed. Using these procedures, a large set of compliant behaviors can be realized by a single hand simply by adjusting the configuration of each finger and by adjusting the joint stiffness (using variable stiffness actuation) of each finger joint. 
    more » « less
  4. Abstract Sensing for wearable robots is an ongoing challenge, especially given the recent trend of soft and compliant robots. Recently, a wearable origami exoshell has been designed to sense the user’s torso motion and provide mobility assistance. The materials of the exoshell contribute to a lightweight design with compliant joints, which are ideal characteristics for a wearable device. Common sensors are not ideal for the exoshell as they compromise these design characteristics. Rotary encoders are often rigid metal devices that add considerable weight and compromise the flexibility of the joints. Inertial measurement unit sensors are affected by environments with variable electromagnetic fields and therefore not ideal for wearable applications. Hall effect sensors and gyroscopes are utilized as alternative compatible sensors, which introduce their own set of challenges: noisy measurements and drift due to sensor bias. To mitigate this, we designed the Kinematically Constrained Kalman filter for sensor fusion of gyroscopes and Hall effect sensors, with the goal of estimating the human’s torso and robot joint angles. We augmented the states to consider bias related to the torso angle in order to compensate for drift. The forward kinematics of the robot is incorporated into the Kalman filter as state constraints to address the unobservability of the torso angle and its related bias. The proposed algorithm improved the estimation performance of the torso angle and its bias, compared to the individual sensors and the standard Kalman filter, as demonstrated through bench tests and experiments with a human user. 
    more » « less
  5. Abstract

    While soft robots enjoy the benefits of high adaptability and safety, their inherent flexibility makes them suffer from low load-carrying capacity and motion precision, which limits their applications to a broader range of fields. To address this problem, we propose a novel compliant hinge joint with a stiff backbone for load-carrying coupled with soft pneumatic networks (PneuNets) bending actuators. We derive a pseudo-rigid-body model of the joint design and validate it through experiments and simulations. The results show that the joint can achieve a large range of bending angles. The off-axis stiffness is from 16.74 to 627.63 times the in-axis stiffness. This design can carry a heavy load off-axis while maintaining the in-axis flexibility. This work lays out the foundation for designing high-performance soft robots by combining various flexure mechanisms and pneumatic bending actuators.

     
    more » « less