Publications

In Press
D. P. Holland, et al., “Strategies for overcoming obstacles to the wide dissemination of soft robotic hardware,” IEEE Robotics and Automation Magazine, Special Issue on Open Source and Widely Disseminated Robot Hardware, In Press.
2017
Assistance magnitude versus metabolic cost reductions for a tethered multiarticular soft exosuit
B. T. Quinlivan, et al., “Assistance magnitude versus metabolic cost reductions for a tethered multiarticular soft exosuit,” Science Robotics, vol. 2, no. 2, 2017. Publisher's VersionAbstract

When defining requirements for any wearable robot for walking assistance, it is important to maximize the user’s metabolic benefit resulting from the exosuit assistance while limiting the metabolic penalty of carrying the system’s mass. Thus, the aim of this study was to isolate and characterize the relationship between assistance magnitude and the metabolic cost of walking while also examining changes to the wearer’s underlying gait mechanics. The study was performed with a tethered multiarticular soft exosuit during normal walking, where assistance was directly applied at the ankle joint and indirectly at the hip due to a textile architecture. The exosuit controller was designed such that the delivered torque profile at the ankle joint approximated that of the biological torque during normal walking. Seven participants walked on a treadmill at 1.5 meters per second under one unpowered and four powered conditions, where the peak moment applied at the ankle joint was varied from about 10 to 38% of biological ankle moment (equivalent to an applied force of 18.7 to 75.0% of body weight). Results showed that, with increasing exosuit assistance, net metabolic rate continually decreased within the tested range. When maximum assistance was applied, the metabolic rate of walking was reduced by 22.83 ± 3.17% relative to the powered-off condition (mean ± SEM).

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F. Connolly, C. J. Walsh, and K. Bertoldi, “Automatic design of fiber-reinforced soft actuators for trajectory matching,” Proceedings of the National Academy of Sciences (PNAS), vol. 114, no. 1, pp. 51-56, 2017. Publisher's VersionAbstract

Soft actuators are the components responsible for producing motion in soft robots. Although soft actuators have allowed for a variety of innovative applications, there is a need for design tools that can help to efficiently and systematically design actuators for particular functions. Mathematical modeling of soft actuators is an area that is still in its infancy but has the potential to provide quantitative insights into the response of the actuators. These insights can be used to guide actuator design, thus accelerating the design process. Here, we study fluid-powered fiber-reinforced actuators, because these have previously been shown to be capable of producing a wide range of motions. We present a design strategy that takes a kinematic trajectory as its input and uses analytical modeling based on nonlinear elasticity and optimization to identify the optimal design parameters for an actuator that will follow this trajectory upon pressurization. We experimentally verify our modeling approach, and finally we demonstrate how the strategy works, by designing actuators that replicate the motion of the index finger and thumb.

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T. Ranzani, S. Russo, F. Schwab, C. J. Walsh, and R. J. Wood, “Deployable stabilization mechanisms for endoscopic procedures,” in IEEE International Conference on Robotics and Automation (ICRA), Singapore, 2017.
J. B. Gafford, R. J. Wood, and C. J. Walsh, “A high-force, high-stroke distal robotic add-on for endoscopy,” in IEEE International Conference on Robotics and Automation (ICRA), Singapore, 2017.
Soft robotic sleeve supports heart function
E. T. Roche, et al., “Soft robotic sleeve supports heart function,” Science Translational Medicine, vol. 9, no. 373, 2017. Publisher's VersionAbstract

There is much interest in form-fitting, low-modulus, implantable devices or soft robots that can mimic or assist in complex biological functions such as the contraction of heart muscle. We present a soft robotic sleeve that is implanted around the heart and actively compresses and twists to act as a cardiac ventricular assist device. The sleeve does not contact blood, obviating the need for anticoagulation therapy or blood thinners, and reduces complications with current ventricular assist devices, such as clotting and infection. Our approach used a biologically inspired design to orient individual contracting elements or actuators in a layered helical and circumferential fashion, mimicking the orientation of the outer two muscle layers of the mammalian heart. The resulting implantable soft robot mimicked the form and function of the native heart, with a stiffness value of the same order of magnitude as that of the heart tissue. We demonstrated feasibility of this soft sleeve device for supporting heart function in a porcine model of acute heart failure. The soft robotic sleeve can be customized to patient-specific needs and may have the potential to act as a bridge to transplant for patients with heart failure.

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2016
Y. Ding, et al., “Effect of timing of hip extension assistance during loaded walking with a soft exosuit,” Journal of NeuroEngineering and Rehabilitation, vol. 2016, no. 13, pp. 87, 2016. Publisher's VersionAbstract

 

Background
Recent advances in wearable robotic devices have demonstrated the ability to reduce the metabolic cost of walking by assisting the ankle joint. To achieve greater gains in the future it will be important to determine optimal actuation parameters and explore the effect of assisting other joints. The aim of the present work is to investigate how the timing of hip extension assistance affects the positive mechanical power delivered by an exosuit and its effect on biological joint power and metabolic cost during loaded walking. In this study, we evaluated 4 different hip assistive profiles with different actuation timings: early-start-early-peak (ESEP), early-start-late-peak (ESLP), late-start-early-peak (LSEP), late-start-late-peak (LSLP).

Methods
Eight healthy participants walked on a treadmill at a constant speed of 1.5 m · s-1 while carrying a 23 kg backpack load. We tested five different conditions: four with the assistive profiles described above and one unpowered condition where no assistance was provided. We evaluated participants’ lower limb kinetics, kinematics, metabolic cost and muscle activation.

Results
The variation of timing in the hip extension assistance resulted in a different amount of mechanical power delivered to the wearer across conditions; with the ESLP condition providing a significantly higher amount of positive mechanical power (0.219 ± 0.006 W · kg-1) with respect to the other powered conditions. Biological joint power was significantly reduced at the hip (ESEP and ESLP) and at the knee (ESEP, ESLP and LSEP) with respect to the unpowered condition. Further, all assistive profiles significantly reduced the metabolic cost of walking compared to the unpowered condition by 5.7 ± 1.5 %, 8.5 ± 0.9 %, 6.3 ± 1.4 % and 7.1 ± 1.9 % (mean ± SE for ESEP, ESLP, LSEP, LSLP, respectively).

Conclusions
The highest positive mechanical power delivered by the soft exosuit was reported in the ESLP condition, which showed also a significant reduction in both biological hip and knee joint power. Further, the ESLP condition had the highest average metabolic reduction among the powered conditions. Future work on autonomous hip exoskeletons may incorporate these considerations when designing effective control strategies.

 

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D. P. Holland, G. J. Bennett, G. M. Whitesides, R. J. Wood, and C. J. Walsh, “The 2015 Soft Robotics Competition,” IEEE Robotics & Automation Magazine, vol. 23, no. 3, pp. 25-27, 2016. Publisher's Version PDF
N. Karavas, et al., “Autonomous Soft Exosuit for Hip Extension Assistance,” in International Symposium on Wearable Robotics (WeRob) 2016, La Granja, Spain, 2016.
T. Miyatake, et al., “Biomechanical analysis and inertial sensing of ankle joint while stepping on an unanticipated bump,” in International Symposium on Wearable Robotics (WeRob) 2016, La Granja, Spain, 2016.
M. Grimmer, et al., “Comparison of Ankle Moment Inspired And Ankle Positive Power Inspired Controllers for a Multi-articular Soft Exosuit for Walking Assistance,” in International Symposium on Wearable Robotics (WeRob) 2016, La Granja, Spain, 2016.
H. Su, et al., “Evaluation of Force Tracking Controller with Soft Exosuit for Hip Extension Assistance,” in International Symposium on Wearable Robotics (WeRob) 2016, La Granja, Spain, 2016.
O. Araromi, C. J. Walsh, and R. J. Wood, “Fabrication of Stretchable Composites with Anisotropic Electrical Conductivity for Compliant Pressure Transducers,” in IEEE Sensors Conference 2016, Orlando, Florida, 2016. Publisher's VersionAbstract

We present a simple fabrication approach for anisotropically conductive stretchable composites, towards novel flexible pressure transducers. Flexible electronic systems have gained great interest in recent years, and within this space, anisotropic conducting materials have been explored for enhanced sensing performance. However, current methods for producing these materials are complex or are limited to small fabrication areas. Our method uses film applicator coating to render commercially available conductive RTVs anisotropically conductive. A ratio of in-plane surface resistance to through-thickness resistance of 1010 was achieved using our method. Furthermore, we show that when a normal pressure is applied to such films, the in-plane resistance can be reduced by seven orders of magnitude for an applied pressure of 10 kPa. Hence these materials show great promise for the development of novel, robust pressure transducers.

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Z. Wang, P. Polygerinos, J. T. B. Overvelde, K. C. Galloway, K. Bertoldi, and C. J. Walsh, “Interaction Forces of Soft Fiber Reinforced Bending Actuators,” IEEE/ASME Transactions on Mechatronics, vol. PP, no. 99, 2016. Publisher's VersionAbstract

Soft bending actuators are inherently compliant, compact, and lightweight. They are preferable candidates over rigid actuators for robotic applications ranging from physical human interaction to delicate object manipulation. However, characterizing and predicting their behaviors are challenging due to the material nonlinearities and the complex motions they can produce. This paper investigates a soft bending actuator design that uses a single air chamber and fiber reinforcements. Additionally, the actuator design incorporates a sensing layer to enable real-time bending angle measurement for analysis and control. In order to study the bending and force exertion characteristics when interacting with the environment, a quasistatic analytical model is developed based on the bending moments generated from the applied internal pressure and stretches of the soft materials. Comparatively, a finite-element method model is created for the same actuator design. Both the analytical model and the finite-element model are used in the fiber reinforcement analysis and the validation experiments with fabricated actuators. The experimental results demonstrate that the analytical model captures the relationships of supplied air pressure, actuator bending angle, and interaction force at the actuator tip. Moreover, it is shown that an off-the-shelf bend angle sensor integrated to the actuator in this study could provide real-time force estimation, thus eliminating the need for a force sensor.

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J. B. Gafford, F. Doshi-Velez, R. J. Wood, and C. J. Walsh, “Machine learning approaches to environmental disturbance rejection in multi-axis optoelectronic force sensors,” Sensors and Actuators A: Physical, vol. 248, pp. 78 - 87, 2016. Publisher's VersionAbstract

Light-Intensity Modulated (LIM) force sensors are seeing increasing interest in the field of surgical robotics and flexible systems in particular. However, such sensing modalities are notoriously susceptible to ambient effects such as temperature and environmental irradiance which can register as false force readings. We explore machine learning techniques to dynamically compensate for environmental biases that plague multi-axis optoelectronic force sensors. In this work, we fabricate a multisensor: three-axis LIM force sensor with integrated temperature and ambient irradiance sensing manufactured via a monolithic, origami-inspired fabrication process called printed-circuit MEMS. We explore machine learning regression techniques to compensate for temperature and ambient light sensitivity using on-board environmental sensor data. We compare batch-based ridge regression, kernelized regression and support vector techniques to baseline ordinary least-squares estimates to show that on-board environmental monitoring can substantially improve sensor force tracking performance and output stability under variable lighting and large (>100C) thermal gradients. By augmenting the least-squares estimate with nonlinear functions describing both environmental disturbances and cross-axis coupling effects, we can reduce the error in Fx, Fy and Fz by 10%, 33%, and 73%, respectively. We assess viability of each algorithm tested in terms of both prediction accuracy and computational overhead, and analyze kernel-based regression for prediction in the context of online force feedback and haptics applications in surgical robotics. Finally, we suggest future work for fast approximation and prediction using stochastic, sparse kernel techniques.

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T. Ranzani, S. Russo, C. J. Walsh, and R. J. Wood, “A soft pop-up proprioceptive actuator for minimally invasive surgery,” in The 9th Hamlyn Symposium on Medical Robotics, London, England, 2016.
T. Ranzani, S. Russo, C. J. Walsh, and R. J. Wood, “A soft suction-based end effector for endoluminal tissue manipulation,” in The 9th Hamlyn Symposium on Medical Robotics, London, England, 2016.
J. B. Gafford, T. Ranzani, S. Russo, S. B. Kesner, R. J. Wood, and C. J. Walsh, “Toward Medical Devices with integrated Mechanisms, Sensors and Actuators via Printed-Circuit MEMS,” ASME Journal of Medical Devices, vol. 11, no. 1, pp. 011007-011018, 2016. Publisher's VersionAbstract

Recent advances in medical robotics have initiated a transition from rigid serial manipulators to flexible or continuum robots capable of navigating to confined anatomy within the body. A desire for further procedure minimization is a key accelerator for the development of these flexible systems where the end goal is to provide access to the previously inaccessible anatomical workspaces and enable new minimally invasive surgical (MIS) procedures. While sophisticated navigation and control capabilities have been demonstrated for such systems, existing manufacturing approaches have limited the capabilities of millimeter-scale end-effectors for these flexible systems to date and, to achieve next generation highly functional end-effectors for surgical robots, advanced manufacturing approaches are required. We address this challenge by utilizing a disruptive 2D layer-by-layer precision fabrication process (inspired by printed circuit board manufacturing) that can create functional 3D mechanisms by folding 2D layers of materials which may be structural, flexible, adhesive, or conductive. Such an approach enables actuation, sensing, and circuitry to be directly integrated with the articulating features by selecting the appropriate materials during the layer-by-layer manufacturing process. To demonstrate the efficacy of this technology, we use it to fabricate three modular robotic components at the millimeter-scale: (1) sensors, (2) mechanisms, and (3) actuators. These modules could potentially be implemented into transendoscopic systems, enabling bilateral grasping, retraction and cutting, and could potentially mitigate challenging MIS interventions performed via endoscopy or flexible means. This research lays the ground work for new mechanism, sensor and actuation technologies that can be readily integrated via new millimeter-scale layer-by-layer manufacturing approaches.

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S. Lee, F. Panizzolo, T. Miyatake, D. M. Rossi, C. Siviy, and C. J. Walsh, “Lower limb biomechanical analysis of unanticipated step on a bump,” in Dynamic Walking, Holly, Michigan, USA, 2016.
J. Bae, et al., “Assisting paretic ankle motion with a soft exosuit can reduce whole-body compensatory gait patterns and improve walking efficiency for patients after stroke,” in Dynamic Walking, Holly, Michigan, USA, 2016.

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