Publications

In Press
L. U. Odhner, et al., “A compliant, underactuated hand for robust manipulation,” International Journal of Robotics Research, In Press. Publisher's VersionAbstract
This paper introduces the {iRobot-Harvard-Yale} ({iHY)} Hand, an underactuated hand driven by 5 actuators that is capable of performing a wide range of grasping and in-hand repositioning tasks. This hand was designed to address the need for a durable, inexpensive, moderately dexterous hand suitable for use on mobile robots. The primary focus of this paper will be on the novel simplified design of the {iHY} Hand, which was developed by choosing a set of target tasks around which the hand was optimized. Particular emphasis is placed on the development of underactuated fingers that are capable of both firm power grasps and low-stiffness fingertip grasps using only the compliant mechanics of the fingers. Experimental results demonstrate successful grasping of a wide range of target objects, the stability of fingertip grasping, as well as the ability to adjust the force exerted on grasped objects using highimpedance actuators and underactuated fingers.
Submitted
N. Pestell, B. Ward-Cherrier, L. Cramphorn, and N. Lepora, “Tactile exploration by autonomous contour following using a biomimetic fingertip,” Submitted.Abstract

 

Touch is used by humans to estimate object shape using the contour following exploratory procedure. Here we demonstrate autonomous robotic contour following with a biomimetic tactile fingertip, the TacTip, using an active touch method previously developed for different types of touch sensors. We use Bayesian sequential analysis for perception and implement an active control strategy to follow an object contour. The technique is tested on a 110mm diameter circle and yields results comparable with those previously achieved on different sensors. We intend to extend the work onto a different robot platform with improved trajectory control to improve robustness, speed and match with human performance.

 

 

Forthcoming
Y. Menguc, et al., “Wearable Soft Sensing Suit for Human Gait Measurement,” International Journal of Robotics Research, Forthcoming.
2018
L. Cappello, et al., “Assisting hand function after spinal cord injury with a fabric-based soft robotic glove,” Journal of NeuroEngineering and Rehabilitation, 2018. PDFAbstract

Background

Spinal cord injury is a devastating condition that can dramatically impact hand motor function. Passive and active assistive devices are becoming more commonly used to enhance lost hand strength and dexterity. Soft robotics is an emerging discipline that combines the classical principles of robotics with soft materials and could provide a new class of active assistive devices. Soft robotic assistive devices enable a human-robot interaction facilitated by compliant and light-weight structures. The scope of this work was to demonstrate that a fabric-based soft robotic glove can effectively assist participants affected by spinal cord injury in manipulating objects encountered in daily living.

Methods

The Toronto Rehabilitation Institute Hand Function Test was administered to 9 participants with C4-C7 spinal cord injuries to assess the functionality of the soft robotic glove. The test included object manipulation tasks commonly encountered during activities of daily living (ADL) and lift force measurements. The test was administered to each participant twice; once without the assistive glove to provide baseline data and once while wearing the assistive glove. The object manipulation subtests were evaluated using a linear mixed model, including interaction effects of variables such as time since injury. The lift force measures were separately evaluated using the Wilcoxon signed-rank test.

Results

The soft robotic glove improved object manipulation in ADL tasks. The difference in mean scores between baseline and assisted conditions was significant across all participants and for all manipulated objects. An improvement of 33.42 ± 15.43% relative to the maximal test score indicates that the glove sufficiently enhances hand function during ADL tasks. Moreover, lift force also increased when using the assistive soft robotic glove, further demonstrating the effectiveness of the device in assisting hand function.

Conclusions

The results gathered in this study validate our fabric-based soft robotic glove as an effective device to assist hand function in individuals who have suffered upper limb paralysis following a spinal cord injury.

L. Cappello, et al., “Exploiting Textile Mechanical Anisotropy for Fabric-Based Pneumatic Actuators,” Soft Robotics, 2018. PDFAbstract
Knit, woven, and nonwoven fabrics offer a diverse range of stretch and strain limiting mechanical properties that can be leveraged to produce tailored, whole-body deformation mechanics of soft robotic systems. This work presents new insights and methods for combining heterogeneous fabric material layers to create soft fabric-based actuators. This work demonstrates that a range of multi-degree-of-freedom motions can be generated by varying fabrics and their layered arrangements when a thin airtight bladder is inserted between them and inflated. Specifically, we present bending and straightening fabric-based actuators that are simple to manufacture, lightweight, require low operating pressures, display a high torque-to-weight ratio, and occupy a low volume in their unpressurized state. Their utility is demonstrated through their integration into a glove that actively assists hand opening and closing.
O. D. Yirmibesoglu, et al., “Direct 3D Printing of Silicone Elastomer Soft Robots and Their Performance Comparison with Molded Counterparts,” in IEEE-RAS International Conference on Soft Robotics (ROBOSOFT), 2018.Abstract
Additive manufacturing has a wide range of applications and addresses many challenges inherited from conventional molding techniques such as human error, multistep fabrication, and manual handling. However, 3D printing soft functional robots with two-part platinum cure silicones requires development to match the material performance of the molded counterparts. In this paper, we present a custom 3D printer and an extrusion mechanism capable of 3D printing soft functional robots. Moreover, we compare the performance differences between our 3D printed soft robots and molded counterparts via lamination casting and lost wax casting. We validate our results by conducting multiple experiments such as blocked force, bend angle, failure pressure, and dimensional quality analyses. We demonstrate that our method enables 3D printing of soft robots that can perform better, or match the performance of molded counterparts while being more reliable and robust with the usage of the same materials.
Y. S. Narang, A. Degirmenci, J. J. Vlassak, and R. D. Howe, “Transforming the Dynamic Response of Robotic Structures and Systems Through Laminar Jamming,” IEEE Robotics and Automation Letters, vol. 3, no. 2, 2018. WebsiteAbstract

Researchers have developed variable-impedance mechanisms to control the dynamic response of robotic systems and improve their adaptivity, robustness, and efficiency. However, these mechanisms have limitations in size, cost, and convenience, particularly for variable damping. We demonstrate that laminar jamming structures can transform the dynamic response of robotic structures and systems while overcoming these limitations. In laminar jamming, an external pressure gradient is applied to a laminate of compliant material, changing its stiffness and damping. In this latter, we combine analysis, simulation, and characterization to formulate a lumped-parameter model that captures the nonlinear mechanical behavior of jamming structures and can be used to rapidly simulate their dynamic response. We illustrate that by adjusting the vacuum pressure, the fundamental features of the dynamic response (i.e., frequency, amplitude, decay rate, and steady-state value) can be tuned on command. Finally, we demonstrate that jamming structures can be integrated into soft structures and traditional rigid robots to considerably alter their response to impacts. With the models and demonstrations provided here, researchers may move further toward building versatile and transformative robots.

Y. S. Narang, J. J. Vlassak, and R. D. Howe, “Mechanically Versatile Soft Machines Through Laminar Jamming,” Advanced Functional Materials, vol. 28, no. 17, 2018. WebsiteAbstract

There are two major structural paradigms in robotics: soft machines, which are conformable, durable, and safe for human interaction; and traditional rigid robots, which are fast, precise, and capable of applying high forces. Here, we bridge the paradigms by enabling soft machines to behave like traditional rigid robots on command. To do so, we exploit laminar jamming, a structural phenomenon in which a laminate of compliant strips becomes strongly coupled through friction when a pressure gradient is applied, causing dramatic changes in mechanical properties. We develop rigorous analytical and finite element models of laminar jamming, and we experimentally characterize jamming structures to show that the models are highly accurate. We then integrate jamming structures into soft machines to enable them to selectively exhibit the stiffness, damping, and kinematics of traditional rigid robots. The models allow jamming structures to be rapidly designed to meet arbitrary performance specifications, and the physical demonstrations illustrate how to construct systems that can behave like either soft machines or traditional rigid robots at will, such as continuum manipulators that can have joints appear and disappear. Our study aims to foster a new generation of mechanically versatile machines and structures that cannot simply be classified as “soft” or “rigid.”

D. Holland, S. Berndt, M. Herman, and C. Walsh, “Growing the Soft Robotics Community Through Knowledge-Sharing Initiatives,” Soft Robotics, vol. 5, no. 2, 2018. PDF
2017
P. Preechayasomboon, C. Richburg, and E. Rombokas, “MULTI-MODAL SENSING AND ACTUATION IN BIOMECHANICAL HYDRAULIC AND PNEUMATIC SYSTEMS,” Northwest Biomechanics Symposium. 2017. PDF
E. H. Skorina, M. Luo, W. Tao, F. Chen, J. Fu, and C. D. Onal, “Adapting to Flexibility: Model Reference Adaptive Control of Soft Bending Actuators,” IEEE Robotics and Automation Letters , vol. 2, no. 2, pp. 964 - 970, 2017.Abstract
Soft pneumatic actuators enable robots to interact safely with complex environments, but often suffer from imprecise control and unpredictable dynamics. This letter addresses these challenges through the use of model reference adaptive control, which modulates the input to the plant to ensure that it behaves similarly to a reference dynamic model. We use adaptive control to standardize the performance of soft actuators and eliminate their nonlinear behavior. We implement an adaptive controller chosen for its simplicity and efficiency, and study the ability of this controller to force different soft pneumatic actuators to behave uniformly under a variety of conditions. Next, we formulate an inverse dynamic feedforward controller, allowing soft actuators to quickly follow reference trajectories. We test the performance of the proposed feedforward controller with and without the adaptive controller, to study its open-loop effectiveness and highlight the improvements the adaptive controller offers. Our experimental results indicate that soft actuators can follow unstructured continuous signals through the use of the proposed adaptive control approach.
M. Luo, et al., “Toward Modular Soft Robotics: Proprioceptive Curvature Sensing and Sliding-Mode Control of Soft Bidirectional Bending Modules,” Soft Robotics, vol. 4, no. 2, 2017.Abstract
Real-world environments are complex, unstructured, and often fragile. Soft robotics offers a solution for robots to safely interact with the environment and human coworkers, but suffers from a host of challenges in sensing and control of continuously deformable bodies. To overcome these challenges, this article considers a modular soft robotic architecture that offers proprioceptive sensing of pressure-operated bending actuation modules. We present integrated custom magnetic curvature sensors embedded in the neutral axis of bidirectional bending actuators. We describe our recent advances in the design and fabrication of these modules to improve the reliability of proprioceptive curvature feedback over our prior work. In particular, we study the effect of dimensional parameters on improving the linearity of curvature measurements. In addition, we present a sliding-mode controller formulation that drives the binary solenoid valve states directly, giving the control system the ability to hold the actuator steady without continuous pressurization and depressurization. In comparison to other methods, this control approach does not rely on pulse width modulation and hence offers superior dynamic performance (i.e., faster response rates). Our experimental results indicate that the proposed soft robotic modules offer a large range of bending angles with monotonic and more linear embedded curvature measurements, and that the direct sliding-mode control system exhibits improved bandwidth and a notable reduction in binary valve actuation operations compared to our earlier iterative sliding-mode controller.
C. Laschi, J. Rossiter, F. Iida, M. Cianchetti, and L. Margheri, Soft Robotics: Trends, Applications and Challenges: Proceedings of the Soft Robotics Week, April 25-30, 2016, Livorno, Italy. Springer International Publishing, 2017.
M. Calisti, G. Picardi, and C. Laschi, “Fundamentals of soft robot locomotion,” Journal of The Royal Society Interface, vol. 14, no. 130, 2017.Abstract
Soft robotics and its related technologies enable robot abilities in several robotics domains including, but not exclusively related to, manipulation, manufacturing, human–robot interaction and locomotion. Although field applications have emerged for soft manipulation and human–robot interaction, mobile soft robots appear to remain in the research stage, involving the somehow conflictual goals of having a deformable body and exerting forces on the environment to achieve locomotion. This paper aims to provide a reference guide for researchers approaching mobile soft robotics, to describe the underlying principles of soft robot locomotion with its pros and cons, and to envisage applications and further developments for mobile soft robotics.
J. Shintake, H. Sonar, E. Piskarev, J. Paik, and D. Floreano, “Soft pneumatic gelatin actuator for edible robotics,” IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS). 2017.Abstract
We present a fully edible pneumatic actuator based on gelatin-glycerol composite. The actuator is monolithic, fabricated via a molding process, and measures 90 mm in length, 20 mm in width, and 17 mm in thickness. Thanks to the composite mechanical characteristics similar to those of silicone elastomers, the actuator exhibits a bending angle of 170.3 {\deg} and a blocked force of 0.34 N at the applied pressure of 25 kPa. These values are comparable to elastomer based pneumatic actuators. As a validation example, two actuators are integrated to form a gripper capable of handling various objects, highlighting the high performance and applicability of the edible actuator. These edible actuators, combined with other recent edible materials and electronics, could lay the foundation for a new type of edible robots.
D. Holland, et al., “The Soft Robotics Toolkit: Strategies for Overcoming Obstacles to the Wide Dissemination of Soft-Robotic Hardware,” IEEE Robotics and Automation Magazine, vol. 24, no. 1, pp. 57-64, 2017.Abstract
The Soft Robotics Toolkit (SRT) is an open-access website containing detailed information about the design, fabrication, and characterization of soft-robotic components and systems (Figure 1). Soft robotics is a growing field of research concerned with the development of electromechanical technology composed of compliant materials or structures. The SRT website hosts design files, multimedia fabrication instructions, and software tutorials submitted by an international community of soft-robotics researchers and designers. In this article, we describe the development of the SRT and some challenges in developing widely disseminated robotic-hardware resources. Our attempts to overcome these challenges in the development of the toolkit are discussed by focusing on strategies that have been used to engage participants ranging from K-12 grade students to robotics research groups. A series of design competitions encouraged people to use and contribute to the toolkit. New fabrication methods requiring only low-cost and accessible materials were developed to lower the entry barriers to soft robotics and instructional materials and outreach activities were used to engage new audiences. We hope that our experiences in developing and scaling the toolkit may serve as guidance for other open robotic-hardware projects.
PDF
C. K. Harnett and B. P. Wagner, “Expanding the Robotics Materials Set with Machine Embroidery,” Material Robotics (MaRo) workshop. 2017.
H. Jiang, et al., “A two-level approach for solving the inverse kinematics of an extensible soft arm considering viscoelastic behavior,” in 2017 IEEE International Conference on Robotics and Automation (ICRA), IEEE International Conference, 2017.Abstract
Soft compliant materials and novel actuation mechanisms ensure flexible motions and high adaptability for soft robots, but also increase the difficulty and complexity of constructing control systems. In this work, we provide an efficient control algorithm for a multi-segment extensible soft arm in 2D plane. The algorithm separate the inverse kinematics into two levels. The first level employs gradient descent to select optimized arm's pose (from task space to configuration space) according to designed cost functions. With consideration of viscoelasticity, the second level utilizes neural networks to figure out the pressures from each segment's pose (from configuration space to actuation space). In experiments with a physical prototype, the control accuracy and effectiveness are validated, where the control algorithm is further improved by an optional feedback strategy.
G. - Y. Gu, J. Zhu, L. - M. Zhu, and X. Zhu, “A survey on dielectric elastomer actuators for soft robots,” Bioinspiration & Biomimetics, vol. 12, no. 1, 2017.Abstract
Conventional industrial robots with the rigid actuation technology have made great progress for humans in the fields of automation assembly and manufacturing. With an increasing number of robots needing to interact with humans and unstructured environments, there is a need for soft robots capable of sustaining large deformation while inducing little pressure or damage when maneuvering through confined spaces. The emergence of soft robotics offers the prospect of applying soft actuators as artificial muscles in robots, replacing traditional rigid actuators. Dielectric elastomer actuators (DEAs) are recognized as one of the most promising soft actuation technologies due to the facts that: i) dielectric elastomers are kind of soft, motion-generating materials that resemble natural muscle of humans in terms of force, strain (displacement per unit length or area) and actuation pressure/density; ii) dielectric elastomers can produce large voltage-induced deformation. In this survey, we first introduce the so-called DEAs emphasizing the key points of working principle, key components and electromechanical modeling approaches. Then, different DEA-driven soft robots, including wearable/humanoid robots, walking/serpentine robots, flying robots and swimming robots, are reviewed. Lastly, we summarize the challenges and opportunities for the further studies in terms of mechanism design, dynamics modeling and autonomous control.
Y. Li, Y. Chen, Y. Yang, and Y. Wei, “Passive Particle Jamming and Its Stiffening of Soft Robotic Grippers,” IEEE Transactions on Robotics, vol. 33, no. 2, 2017.Abstract
The compliance of soft grippers contributes to their great superiority over rigid grippers in grasping irregularly shaped objects and forming soft contact with environments. Due to a relatively small pressure, soft grippers lack the stiffness required for wider applications. Particle jamming has been frequently reported as a means of stiffness control. Unlike previous research using vacuum for particle jamming, this paper proposes a novel passive particle jamming principle that does not need any vacuum power or other control means. The proposed method is by simply patching a silicone rubber soft actuator and a pack (made of strain-limiting membrane) of particles to form an integral gripping finger. The inflation of the soft actuator applies a pressure to the particle pack causing particles inside it to jam. A larger squeezing pressure will result in tighter particle jamming, thus increasing the stiffness of the finger. The stiffness of the finger is controllable as it is proportional to the actuator's air pressure, which has been verified by experiments in this research. The stiffness can increase more than six fold when air pressure changes from 20 to 80 kPa in the experimental studies. The reported discovery may enhance the capabilities of soft robotic grippers so that more robotic picking operations could be performed by soft grippers.

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