We describe a new series pneumatic artificial muscle (sPAM) and its application as an actuator for a soft continuum robot. The robot consists of three sPAMs arranged radially around a tubular pneumatic backbone. Analogous to tendons, the sPAMs exert a tension force on the robot’s pneu- matic backbone, causing bending that is approximately constant curvature. Unlike a traditional tendon driven continuum robot, the robot is entirely soft and contains no hard components, making it safer for human interaction. Models of both the sPAM and soft continuum robot kinematics are presented and experimentally verified. We found a mean position accuracy of 5.5 cm for predicting the end-effector position of a 42 cm long robot with the kinematic model. Finally, closed-loop control is demonstrated using an eye-in-hand visual servo control law which provides a simple interface for operation by a human. The soft continuum robot with closed-loop control was found to have a step-response rise time and settling time of less than two seconds.
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Pneumatic Reel Actuator: Design, modeling, and implementation
We present the design, modeling, and implemen- tation of a novel pneumatic actuator, the Pneumatic Reel Actuator (PRA). The PRA is highly extensible, lightweight, capable of operating in compression and tension, compliant, and inexpensive. An initial prototype of the PRA can reach extension ratios greater than 16:1, has a force-to-weight ratio over 28:1, reach speeds of 0.87 meters per second, and can be constructed with parts totaling less than $4 USD. We have developed a model describing the actuator and have conducted experiments characterizing the actuator’s performance in regards to force, extension, pressure, and speed. We have implemented two parallel robotic applications in the form of a three degree of freedom robot arm and a tetrahedral robot.
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- Award ID(s):
- 1637446
- PAR ID:
- 10032228
- Date Published:
- Journal Name:
- IEEE International Conference on Robotics and Automation
- Page Range / eLocation ID:
- 626-633
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The inspection, maintenance, and repair of pipeline and tunnel infrastructure have motivated the increasing research in the development of suitable robots with high flexibility, good adaptability, and large load capacity. Herein, a worm‐inspired soft robot that is capable of operating and performing a variety of tasks in a complicated pipeline/tunnel environment is reported. The soft tubular robot consists of elongation pneumatic actuators (EPAs), radial expansion pneumatic actuators (REPAs), and a spatial bending pneumatic actuator (SBPA). A series of experiments are performed to demonstrate the capability of the soft robot to crawl robustly under different pipeline conditions, including varying diameter, different cross‐sectional shapes, and wet or oil‐covered internal surfaces, and underwater environment. The soft robot can carry a load of more than 11 times of its own weight in a vertical pipeline. Equipped with a visualization unit, the soft robot can detect the internal conditions of the pipeline and cross the multibranched pipeline as needed. The tubular soft robot provides a useful tool for the inspection, cleaning, and maintenance of pipelines and tunnels.
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A pneumatic soft robot can be made autonomous by carrying a liquid chemical fuel. In the existing design, to transmit the fuel, the pressure of the fuel tank must exceed that of the actuator. Consequently, the fuel tank must be sufficiently stiff, which hardens the robot. Herein, inspired by pit membranes in trees, a chemical pump is developed, which is consisting of a nanoporous membrane between the fuel tank and the actuator, and coated with a catalyst on the side of the actuator. The fuel in the fuel tank migrates across the membrane and, on meeting the catalyst, decomposes into a pressurized gas and inflates the actuator. The chemical pump is driven by the free energy of reaction, against the difference in pressure. The pores in the membrane are large enough for the fuel molecules to migrate through, but small enough to block the pressurized gas to tunnel back. In a demonstration, the fuel tank has ambient pressure, and the actuator has a pressure of 350 kPa, comparable to the pressure in a car tire. The chemical pump enables pneumatic robots to be autonomous, powerful, and soft.
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Soft pneumatic actuators have become indispensable for many robotic applications due to their reliability, safety, and design flexibility. However, the currently available actuator designs can be challenging to fabricate, requiring labor-intensive and time-consuming processes like reinforcing fiber wrapping and elastomer curing. To address this issue, we propose to use simple-to-fabricate kirigami skins—plastic sleeves with carefully arranged slit cuts—to construct pneumatic actuators with pre-programmable motion capabilities. Such kirigami skin, wrapped outside a cylindrical balloon, can transform the volumetric expansion from pneumatic pressure into anisotropic stretching and shearing, creating a combination of axial extension and twisting in the actuator. Moreover, the kirigami skin exhibits out-of-plane buckling near the slit cut, which enables high stretchability. To capture such complex deformations, we formulate and experimentally validates a new kinematics model to uncover the linkage between the kirigami cutting pattern design and the actuator’s motion characteristics. This model uses a virtual fold and rigid-facet assumption to simplify the motion analysis without sacrificing accuracy. Moreover, we tested the pressure-stroke performance and elastoplastic behaviors of the kirigami-skinned actuator to establish an operation protocol for repeatable performance. Analytical and experimental parametric analysis shows that one can effectively pre-program the actuator’s motion performance, with considerable freedom, simply by adjusting the angle and length of the slit cuts. The results of this study can establish the design and analysis framework for a new family of kirigami-skinned pneumatic actuators for many robotic applications.more » « less
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Soft robots have shown great potential to enable safe interactions with unknown environments due to their inherent compliance and variable stiffness. However, without knowledge of potential contacts, a soft robot could exhibit rigid behaviors in a goal-reaching task and collide into obstacles. In this paper, we introduce a Sliding Mode Augmented by Reactive Transitioning (SMART) controller to detect the contact events, adjust the robot’s desired trajectory, and reject estimated disturbances in a goal reaching task. We employ a sliding mode controller to track the desired trajectory with a nonlinear disturbance observer (NDOB) to estimate the lumped disturbance, and a switching algorithm to adjust the desired robot trajectories. The proposed controller is validated on a pneumatic-driven fabric soft robot whose dynamics is described by a new extended rigid-arm model to fit the actuator design. A stability analysis of the proposed controller is also presented. Experimental results show that, despite modeling uncertainties, the robot can detect obstacles, adjust the reference trajectories to maintain compliance, and recover to track the original desired path once the obstacle is removed. Without force sensors, the proposed model-based controller can adjust the robot’s stiffness based on the estimated disturbance to achieve goal reaching and compliant interaction with unknown obstacles.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1109/ICRA.2017.7989078
