Development of Soft Artificial Muscles towards a Smart Assistive Suit

Abstract

Impaired mobility is one of the major issues in human life, affecting and limiting independent living, especially for older adults. Although many conventional rigid exoskeletons and soft orthoses have been developed to strengthen the human body for workers, and improve the mobility of people with disabilities, there remain many challenges to overcome before we can create an assistive suit for healthy elderly individuals. Advanced wearable assistive devices should have light weight, low cost, high exibility, and high adaptability. This will enable them to fit the user's body while remaining inconspicuous (possibly being embedded with standard clothing), and also provide suffcient mechanical power to maintain effective and safe assistance to the body. To achieve these required features, this thesis describes the study and development of novel artificial muscles based on two potentially disruptive technologies: pneumatically-driven and electrically-driven soft actuators.

First, a lightweight, flexible, inexpensive pneumatic actuator, namely Bubble Artificial Muscle (BAM), was developed. BAMs are capable of generating either high contraction or high tensile force, by adjusting their material properties. This provides BAMs with high flexibility, allowing them to be designed to suit the various capabilities of human muscles. An actuation model was developed to predict the real-world performance of BAMs, and a design methodology to maximise BAM performance metrics is presented. A mobility assistance demonstrator was built to investigate how an effective orthosis can theoretically reduce muscle work of a user while walking. BAMs were used to create soft
orthoses to assist two human locomotion movements: walking and sit-to-stand transition, providing support forces and assisting the lower limb's motions. However, since the BAM is pneumatically driven, it has a major drawback due to its associated air power source, e.g. a large, heavy, noisy pump or compressor for actuation. This limits the portability and fast actuation response of a BAM-driven orthotic. To address this limitation, electrically-driven actuators were investigated.

The electro-ribbon actuator (ERA) is an electrostatic zipping actuator, which exhibits high stress and contraction, along with fast actuation speed and low power consumption. This actuator was studied to overcome the disadvantages associated with pneumatic actuators. In this research, an effective control algorithm was developed to improve the controllable actuation range of the ERA. Alternative materials and fabrication methods were also explored, resulting in a new version of the ERA with wider designs and applications, including three-dimensional motion. The ERA was developed further by fully encapsulating the zipping mechanism, leading to a novel lightweight, soft pneumatic pump, the Electro-pneumatic Pump (EPP). The EPP is capable of exerting air pressure and pumping its internal air volume to a connecting device. EPPs allow for high-flow-rate continuous pumping while being portable and controllable, and showing low power consumption. Combining the EPP and the BAM together results in an entirely soft pneumatic actuation system, which can deliver high contraction and mechanical work as a wearable device for assisting human body movement. This new electropneumatic system fulls the ultimate research outcome and has high potential as a future robotic device and articial muscle, paving the way for the creation of a smart assistive suit that will restore the independence of older adults and people living with disabilities.

Date of Award	29 Sept 2020
Original language	English
Awarding Institution	University of Bristol
Supervisor	Jonathan M Rossiter (Supervisor), Tim N Helps (Supervisor) & Majid Taghavi (Supervisor)