In this paper, we present the design and evaluation of a novel soft cable-driven exosuit that can apply forces to the body to assist walking. Unlike traditional exoskeletons which contain rigid framing elements, the soft exosuit is worn like clothing, yet can generate moments at the ankle and hip with magnitudes of 18% and 30% of those naturally generated by the body during walking, respectively. Our design uses geared motors to pull on Bowden cables connected to the suit near the ankle. The suit has the advantages over a traditional exoskeleton in that the wearer's joints are unconstrained by external rigid structures, and the worn part of the suit is extremely light, which minimizes the suit's unintentional interference with the body's natural biomechanics. However, a soft suit presents challenges related to actuation force transfer and control, since the body is compliant and cannot support large pressures comfortably. We discuss the design of the suit and actuation system, including principles by which soft suits can transfer force to the body effectively and the biological inspiration for the design. For a soft exosuit, an important design parameter is the combined effective stiffness of the suit and its interface to the wearer. We characterize the exosuit's effective stiffness, and present preliminary results from it generating assistive torques to a subject during walking. We envision such an exosuit having broad applicability for assisting healthy individuals as well as those with muscle weakness.
The small scale of minimally-invasive surgery (MIS) presents significant challenges to developing robust, smart, and dexterous tools for manipulating millimeter and sub-millimeter anatomical structures (vessels, nerves) and surgical equipment (sutures, staples). Robotic MIS systems offer the potential to transform this medical field by enabling precise repair of these miniature tissue structures through the use of teleoperation and haptic feedback. However, this effort is currently limited by the inability to make robust and accurate MIS end effectors with integrated force and contact sensing. In this paper, we demonstrate the use of the novel Pop-Up Book MEMS manufacturing method to fabricate the mechanical and sensing elements of an instrumented MIS grasper. A custom thin-foil strain gage was manufactured in parallel with the mechanical components of the grasper to realize a fully-integrated electromechanical system in a single manufacturing step, removing the need for manual assembly, bonding and alignment. In preliminary experiments, the integrated grasper is capable of resolving forces as low as 30 mN, with a sensitivity of approximately 408 mV/N. This level of performance will enable robotic surgical systems that can handle delicate tissue structures and perform dexterous procedures through the use of haptic feedback guidance.
Established design and fabrication guidelines exist for achieving a variety of motions with soft actuators such as bending, contraction, extension, and twisting. These guidelines typically involve multi-step molding of composite materials (elastomers, paper, fiber, etc.) along with specially designed geometry. In this paper we present the design and fabrication of a robust, fiber-reinforced soft bending actuator where its bend radius and bending axis can be mechanically-programed with a flexible, selectively-placed conformal covering that acts to mechanically constrain motion. Several soft actuators were fabricated and their displacement and force capabilities were measured experimentally and compared to demonstrate the utility of this approach. Finally, a prototype two-digit end-effector was designed and programmed with the conformal covering to shape match a rectangular object. We demonstrated improved gripping force compared to a pure bending actuator. We envision this approach enabling rapid customization of soft actuator function for grasping applications where the geometry of the task is known a priori.
Motion sensing has played an important role in the study of human biomechanics as well as the entertainment industry. Although existing technologies, such as optical or inertial based motion capture systems, have relatively high accuracy in detecting body motions, they still have inherent limitations with regards to mobility and wearability. In this paper, we present a soft motion sensing suit for measuring lower extremity joint motion. The sensing suit prototype includes a pair of elastic tights and three hyperelastic strain sensors. The strain sensors are made of silicone elastomer with embedded microchannels filled with conductive liquid. To form a sensing suit, these sensors are attached at the hip, knee, and ankle areas to measure the joint angles in the sagittal plane. The prototype motion sensing suit has significant potential as an autonomous system that can be worn by individuals during many activities outside the laboratory, from running to rock climbing. In this study we characterize the hyperelastic sensors in isolation to determine their mechanical and electrical responses to strain, and then demonstrate the sensing capability of the integrated suit in comparison with a ground truth optical motion capture system. Using simple calibration techniques, we can accurately track joint angles and gait phase. Our efforts result in a calculated trade off: with a maximum error less than 8%, the sensing suit does not track joints as accurately as optical motion capture, but its wearability means that it is not constrained to use only in a lab.
This paper presents preliminary results for the design, development and evaluation of a hand rehabilitation glove fabricated using soft robotic technology. Soft actuators comprised of elastomeric materials with integrated channels that function as pneumatic networks (PneuNets), are designed and geometrically analyzed to produce bending motions that can safely conform with the human finger motion. Bending curvature and force response of these actuators are investigated using geometrical analysis and a finite element model (FEM) prior to fabrication. The fabrication procedure of the chosen actuator is described followed by a series of experiments that mechanically characterize the actuators. The experimental data is compared to results obtained from FEM simulations showing good agreement. Finally, an open-palm glove design and the integration of the actuators to it are described, followed by a qualitative evaluation study.
Innovation in patient care requires both clinical and technical skills, and this paper presents the methods and outcomes of a nine-year, clinical-academic collaboration to develop and evaluate new medical device technologies, while teaching mechanical engineering. Together, over the course of a single semester, seniors, graduate students, and clinicians conceive, design, build, and test proof-of-concept prototypes. Projects initiated in the course have generated intellectual property and peer-reviewed publications, stimulated further research, furthered student and clinician careers, and resulted in technology licenses and start-up ventures.
Up to eight percent of patients develop steal syndrome after prosthetic dialysis access graft placement, which is characterized by low blood flow to the hand. Steal syndrome results in a cold hand, pain, and in extreme cases, loss of function and tissue damage. A practical and easy way of adjusting the fluidic resistance in a graft to attenuate the risk of steal physiology would greatly benefit both surgeons and patients. This paper describes the design and development of a device that can be attached to a dialysis access graft at the time of surgical implantation to enable providers to externally adjust the resistance of the graft postoperatively. Bench level flow experiments and magnetic setups were used to establish design requirements and test prototypes. The Graft Resistance Adjustment Mechanism (GRAM) can be applied to a standard graft before or after it is implanted and a non-contact magnetic coupling enables actuation through the skin for graft compression. The device features a winch-driven system to provide translational movement for a graft compression unit. We expect such a device to enable noninvasive management of steal syndrome in a manner that does not change the existing graft and support technologies, thus reducing patient complications and reducing costs to hospitals.
Wearable assistive robotic devices are characterized by an interface, a meeting place of living tissue and mechanical forces, at which potential and kinetic energy are converted to one or the other form. Ecological scientists may make important contributions to the design of device interfaces because of a functional perspective on energy and information exchange. For ecological scientists, (a) behavioral forms are an assembly of whole functional systems from available parts, emerging in energy flows, and (b) nature explores for informationally based adaptive solutions to assemble behavioral forms by generating spontaneous patterns containing fluctuations. We present data from ongoing studies with infants that demonstrate how infants may explore for adaptive kicking solutions. Inspired by the ecological perspective and data from developing humans, ecological scientists may design interfaces to assist individuals with medical conditions that result in physical and/or mental impairment. We present one such device, what is called the “second skin,” to illustrate how a soft, prestressed material, worn on the skin surface, may be used synergistically with synthetic and biological muscles for assisting action. Our work on the second skin, thus far, suggests a set of ecologically inspired principles for design of wearable assistive robotic devices.
In this paper, we describe our prototype of an ultrasound guidance system to address the need for an easy-touse, cost-effective, and portable technology to improve ultrasound-guided procedures. The system consists of a lockable, articulating needle guide that attaches to an ultrasound probe and a user-interface that provides real-time visualization of the predicted needle trajectory overlaid on the ultrasound image. Our needle guide ensures proper needle alignment with the ultrasound imaging plane. Moreover, the calculated needle trajectory is superimposed on the real-time ultrasound image, eliminating the need for the practitioner to estimate the target trajectory, and thereby reducing injuries from needle readjustment. Finally, the guide is lockable to prevent needle deviation from the desired trajectory during insertion. This feature will also allow the practitioner to free one hand to complete simple tasks that usually require a second practitioner to perform. Overall, our system eliminates the experience required to develop the fine hand movement and dexterity needed for traditional ultrasound-guided procedures. The system has the potential to increase efficiency, safety, quality, and reduce costs for a wide range of ultrasound-guided procedures. Furthermore, in combination with portable ultrasound machines, this system will enable these procedures to be more easily performed by unskilled practitioners in non-ideal situations such as the battlefield and other disaster relief areas.
This paper proposes an analytical approach to the robust design of mechanisms, to achieve motion and accuracy requirements given a desired transmission ratio and allowable geometrical variations. The focus is on four-bar and slider-crank mechanisms, which are common elements for the transmission of rotary motion, especially over distances, which are too big for the use of conventional elements such as gears, and motion along a predefined guide-curve, which often is a straight line. For many power transmission applications, a constant relation between the motions of an input and corresponding output element is required. For a four-bar linkage, a value of 1 is the only possible constant transmission ratio—achieved when the mechanism has a parallelogram configuration. In the case of a slider-crank linkage a constant transmission ratio can be achieved with a properly designed circular guide-curve, which makes the slider-crank essentially equivalent to a four-bar. In practice, however, as a result of variations in link lengths due to manufacturing tolerances and load-induced or thermal deformations, the transmission ratio for a parallelogram four-bar linkage will deviate substantially from its ideal theoretical value of 1. Even small changes in link lengths due to deformations or joint backlash can cause unacceptable instantaneous transmission ratio variations. The concepts presented are not limited to the design of four-bars and slider-cranks but can also be applied universally in the design of other mechanisms.