An official website of the United States government
Abstract Soft robotic grippers can gently grasp and maneuver objects. However, they are difficult to model and control due to their highly deformable fingers and complex integration with robotic systems. This paper investigates the design requirements as well as the grasping capabilities and performance of a soft gripper system based on fluidic prestressed composite (FPC) fingers. An analytical model is constructed as follows: each finger is modeled using the chained composite model (CCM); strain energy and work done by pressure and loads are computed using polynomials with unknown coefficients; net energy is minimized using the Rayleigh–Ritz method to calculate the deflected equilibrium shapes of the finger as a function of pressure and loads; and coordinate transformation and gripper geometries are combined to analyze the grasping performance. The effects of prestrain, integration angle, and finger overlap on the grasping performance are examined through a parametric study. We also analyze gripping performance for cuboidal and spherical objects and show how the grasping force can be controlled by varying fluidic pressure. The quasi-static responses of fabricated actuators are measured under pressures and loads. It is shown that the actuators’ modeled responses agree with the experimental results. This work provides a framework for the theoretical analysis of soft robotic grippers and the methods presented can be extended to model grippers with different types of actuation.
more »
« less
Modeling of Fluidic Prestressed Composite Actuators With Application to Soft Robotic Grippers
Soft and continuously controllable grippers can be assembled from fluidic prestressed composite (FPC) actuators. Due to their highly deformable features, it is difficult to model such actuators for large deflections. This article proposes a new method for modeling large deflections of FPC actuators called the chained composite model (CCM) to characterize the quasi-static response to an applied fluid pressure and load. The CCM divides an FPC actuator into discrete elements and models each element by a small rotation model. The strain energy of each element and the work done by pressure and loads are computed using third-order displacement polynomials with unknown coefficients; then, the total energy is minimized to calculate stable shapes using the Rayleigh–Ritz method. This study provides a set of systematic design rules to help the robotics community create FPC actuators by understanding how their responses vary as a function of input forces and pressures for a number of modeling and design parameters. Composite actuators are fabricated and a soft gripper is developed to demonstrate the grasping ability of the FPCactuators. Pneumatic pressure and end loads are applied to the composite actuators, and their responses are measured. The modeled responses of the actuators are shown to be in agreement with the measured responses.
more »
« less
- Award ID(s):
- 1637656
- PAR ID:
- 10331194
- Date Published:
- Journal Name:
- IEEE Transactions on Robotics
- ISSN:
- 1552-3098
- Page Range / eLocation ID:
- 1 to 13
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Soft robotic devices containing multiple actuating elements have successfully recapitulated complex biological motion, leading to their utility in biomedical applications. However, there are inherent nonlinear mechanics associated with soft composite materials where soft actuators are embedded in elastomeric matrices. Predicting their overall behavior prior to fabrication and subsequent experimental characterization can therefore present a hurdle in the design process and in efficiently satisfying functional requirements and specifications. In this work, a computational design framework for optimizing the motion and function of biomimetic soft robotic composites is demonstrated by conducting a design case study of soft robotic cardiac muscle (myocardium) with a particular focus on applications including replicating and assisting cardiac motion and function. A finite element model of a soft robotic myocardium is built, in which actuators are prescribed with anisotropic strain to simulate local deformation, and various design parameters are investigated by evaluating the performance of each configuration in terms of ventricular twist, volumetric output, and pressure generation. Then, an optimized design is proposed that recapitulates the physiological motion and hemodynamics of the heart, and its thrombogenicity is further explored using a fluid‐structure interaction model. This framework has broader utility in predicting the performance of other soft robotic embedded composites.more » « less
-
Experimentally Identified Models of McKibben Soft Actuators as Primary Movers and Passive Structuresnull (Ed.)Abstract Soft robots join body and actuation, forming their structure from the same elements that induce motion. Soft actuators are commonly modeled or characterized as primary movers, but their second role as support structure introduces strain–pressure combinations outside of normal actuation. This article examines a more complete set of possible strain–pressure combinations for McKibben actuators, including passive or unpressurized, deformation, pressurized extension and compression of a pressurized actuator beyond the maximum actuation strain. Each region is investigated experimentally, and empirical force–displacement–pressure relationships are identified. Particular focus is placed on ensuring that empirical relationships are consistent at boundaries between an actuator’s strain–pressure regions. The presented methodology is applied to seven McKibben actuator designs, which span variations in wall thickness, enclosure material, and actuator diameter. Empirical results demonstrate a trade-off between maximum contraction strain and force required to passively extend. The results also show that stiffer elastomers require an extreme increase in pressure to contract without a compensatory increase in maximum achieved force. Empirical force–displacement–pressure models were developed for each variant across all the studied strain–pressure regions, enabling future design variation studies for soft robots that use actuators as structures.more » « less
-
This paper focuses on recent advances made in design, development, manufacturing, evaluation and modeling of load bearing fiber reinforced polymer (FRP) composite sandwich panel systems including tongue and groove joints. Several processes have been researched in collaboration with industry partners for production of composite panels, including: 1) pultrusion, 2) high temperature resin spread and infusion, 3) vacuum assisted resin transfer molding (VARTM), and 4) compression molding. The advantages and disadvantages of each process are discussed with emphasis on the high temperature resin infusion process. Composite laminates are characterized in terms of strength and stiffness under tension, bending, and shear in relation to longitudinal and transverse fiber orientations. Thermo-mechanical property variations of the FRP composite sandwich panels including joint responses are presented in terms of: 1) production processes, 2) carbon versus E-glass fiber, 3) vinyl ester versus epoxy, and 4) panel and joint design and efficiency including classical lamination theory. The sandwich panels are evaluated at component and full scales under static four point bending loads and further analyzed using classical finite element models for their mechanical responses.more » « less
-
This article presents a sensor for detecting the distribution of forces on a surface. The device with nine buttons consisted of an elastomer-based layer as a touch interface resting on a substrate of patterned metallized paper. The elastomer-based layer included a three-by-three array of deformable, hemispherical elements/reliefs, facing down toward an array of interdigitated capacitive sensing units on patterned metallized paper. Each hemispherical element is 20 mm in diameter and 8 mm in height. When a user applied pressure to the elastomer-based layer, the contact area between the hemispherical elements and the interdigitated capacitive sensing units increased with the deformation of the hemispherical elements. To enhance the sensitivity of the sensors, embedded particles of hydrogel in the elastomer-based layer increased the measured electrical responses. The measured capacitance increased because the effective dielectric permittivity of the hydrogel was greater than that of air. Electromechanical characterization verified that the hydrogel-filled elastomer was more sensitive to force at a low range of loads (23.4 pF/N) than elastomer alone without embedded hydrogel (3.4 pF/N), as the hydrogel reduced the effective elastic modulus of the composite material by a factor of seven. A simple demonstration suggests that the force-sensing array has the potential to contribute to wearable and soft robotic devices.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1109/TRO.2021.3139770
