Marko B. Popovic

Wearable soft robotic device for post-stroke shoulder rehabilitation: Identifying misalignments

Stroke is the leading cause of long-term disability in the United States, affecting over 795,000 people annually. In order to regain motor function of the upper body, patients are usually treated by regular sessions with a dedicated physical therapist. A cost-effective wearable upper body orthotics system that can be used at home to empower both the patients and physical therapists is described. The system is composed of a thin, compliant, lightweight, cost-effective soft orthotic device with an integrated cable actuation system that is worn over the upper body, an embedded limb position sensing system, an electric actuator package and controller. The proposed device is robust to misalignments that may occur during actuation of the compliant brace or when putting on the system. Through simulations and experimental evaluation, it was demonstrated i) that the soft orthotic cable-driven shoulder brace can be successfully actuated without the production of off-axis torques in the presence of misalignments and ii) that the proposed model can identify linear and angular misalignments online.

Design considerations for an active soft orthotic system for shoulder rehabilitation

Strokes affect over 750,000 people annually in the United States. This significant and disabling condition can result in paralysis that must be treated by regular sessions with a dedicated physical therapist in order to regain motor function. However, the use of therapists is expensive, in high demand, and requires patient travel to a rehabilitation clinic. We propose an inexpensive and wearable upper body orthotics system that can be used at home to provide the same level of rehabilitation as the current physical therapy standard of care. The system is composed of a soft orthotic device with an integrated cable actuation system that is worn over the upper body, a limb position sensing system, and an actuator package. This paper presents initial design considerations and the evaluation of a proof of concept system for shoulder joint rehabilitation. Through simulations and experimental evaluation, the system is shown to be adjustable, easily wearable, and adaptable to misalignment and anatomical variations. Insights provided by these initial studies will inform the development of a complete upper body orthotic system.

Linear One-to-Many (OTM) system

We report on progress on the One-To-Many (OTM) concept that allows a single electric motor to store energy in the form of elastic potential energy to drive multiple (e.g. hundred) motor units or independently controlled mechanical degrees of freedom. Critical to this concept is the OTM architecture which utilizes light weight, high-speed, energy efficient, robust, and cost-effective clutches that provide positional feedback. Here, we address linear springs as elastic mediums for energy storage and bi-stable solenoid based clutches that require minimal energy to transition between states. We analyze the power transfer of the system, discuss current and future designs and suggest avenues for potential applications of this practical technology.

Hydro Muscle -a novel soft fluidic actuator

Hydro Muscles are linear actuators resembling ordinary biological muscles in terms of active dynamic output, passive material properties and appearance. The passive and dynamic characteristics of the latex based Hydro Muscle are addressed. The control tests of modular muscles are presented together with a muscle model relating sensed quantities with net force. Hydro Muscles are discussed in the context of conventional actuators. The hypothesis that Hydro Muscles have greater efficiency than McKibben Muscles is experimentally verified. Hydro Muscle peak efficiency with (without) back flow consideration was 88% (27%). Possible uses of Hydro Muscles are illustrated by relevant robotics projects at WPI. It is proposed that Hydro Muscles can also be an excellent educational tool for moderate-budget robotics classrooms and labs; the muscles are inexpensive (in the order of standard latex tubes of comparable size), made of off-the-shelf elements in less than 10 minutes, easily customizable, lightweight, biologically inspired, efficient, compliant soft linear actuators that are adept for power-augmentation. Moreover, a single source can actuate many muscles by utilizing control of flow and/or pressure. Still further, these muscles can utilize ordinary tap water and successfully operate within a safe range of pressures not overly exceeding standard water household pressure of about 0.59 MPa (85 psi).

Design and test of biologically inspired multi-fiber Hydro Muscle actuated ankle

Advancements in robotics are expected to have a profound impact on the economy, industry, jobs, education, health, warfare, space and planetary exploration etc. Progress in fields like Biomechatronics has the potential to further redefine the notion of human identity. An experimental platform for study of a biologically inspired muscular aproach to joint actuation by synthetic Gastrocnemius, Soleus, and Tibialis Anterior muscles has been designed and the prototype tested. Three major lower leg muscle groups, that actuate a one degree of freedom ankle, have a multi-fiber composition allowing for active control of stiffness and force similar to recruitment in biological muscles. Muscle fibers actuating the lower leg utilize Hydro Muscle technology; fibers efficiently elongate when internal fluid, either water or air, is pressurized and contract when pressure is relieved. In contrast to the Pneumatic Artificial Muscle (PAM), McKibben artificial muscle, the Hydro Muscle can achieve strains identical to and even beyond a biological muscle. The viscoelastic properties of muscle fibers are also characterized. Results of preliminary position, stiffness, and force tests suggest that a substantial range of biological muscle performance can be achieved by the proposed muscle fiber recruitment approach. This platform could also provide a basis to create more realistic prosthetic legs that are able to mimic properly the form and movements of a human leg, allowing for not only better prosthetic integration but also more biologically accurate humanoid robotics. Furthermore this soft robotics platform allows for safer interaction and interface with the human body. The Hydro Muscle is an inexpensive actuator that could help reduce the high cost of current robotic options, allowing for a more wide spread adoption by society.