Design and fabrication of a modularized humanoid arm with pneumatic artificial muscles

Capstone Project submitted to the Department of Engineering, Ashesi University in partial fulfillment of the requirements for the award of Bachelor of Science degree in Mechanical Engineering, May 2021With increase investment in the development of humanoids, there offers a window of opportunity to leverage the rapidly growing market of soft robotics in our strides towards more accurate biomimetic motion and study of humanoids and their applicatory areas. This project encompasses the systematic design, implementation and testing of a lightweight low-cost humanoid arm that utilizes Pneumatic Artificial Muscles (PAM). These muscles do not only exhibit twistable and bendable human-like muscle contractions but modularized in design to stand as a complete controllable unit which may be dissociated and mountable on a support frame on its own. This project achieves the design of a mobile arm unit with total weight of less than 2kg of which is distributed with one-third the weight being borne on the arm. The realized powerto- weight ratio of near 5W per kilogram, under an approximate 13.5 litre per minute rate of pressurization is of desired muscle force, and flex speeds. The McKibben tubing choice of PAM is experimentally validated under a linear fit for its force-contraction performance. This design makes considerable strides in cutting down weight, leveraging power, and being much cheaper than existing solutions. Comparable lightweight arm designs of which some are commercially available have weights of 38kg (Mitsubishi PA10arm), 14kg (KUKA lightweight arm), etc., with power-to-weight ratios of near 1W/kg. However, this project designs cuts down these weights drastically to about 2kg (without any sensory unit yet) and more than doubles the power to weight ratios mentioned.Ashesi Universit

Waveform analysis of forearm muscle activity during dynamic wrist flexion and extension: Effects of forearm posture and torque direction

Background and Aim: For both isometric and dynamic movements at the wrist, a popular analysis technique for forearm muscle activation includes averaged time-series data that may not represent changes in muscle activity throughout the task. Changes in muscle fiber length and environmental stimuli can alter forearm/upper arm muscle activity during dynamic tasks (D. A. Forman et al., 2020a). The purpose of this study was to determine the effects of forearm posture and torque on forearm muscle activity using waveform analysis. Methods: 12 participants performed a controlled wrist flexion/extension (±40°) tracking task using a wrist manipulandum. Participants were positioned in a neutral, 30° pronated, or 30° supinated forearm posture and the manipulandum applied a constant torque that resisted either wrist extension or flexion. Posture-torque combinations were performed once each, with six flexion/extension repetitions completed per condition. Wrist kinematics were tracked using the manipulandum and the movement cycle was time normalized. Surface electromyography from eight forearm/upper arm muscles were normalized to maximum voluntary contractions. Statistical non-parametric mapping analyzed waveforms for each muscle using a two-way repeated measures ANOVA for main/interaction effects (p=0.05), with post-hoc t-tests. Results: All muscles showed main effects for both posture and torque direction. Decreases in activity were observed in non-neutral forearm postures (flexors: 53-70%, extensors: 5-23% of the cycle). Flexion torque increased muscle activity for FCR, FDS, and FCU during 0-56% and 75-100%, 9-81%, and 22-51% of the movement cycle, respectively. ED and ECU had significantly increased activity during 0-26% and 70-100% of the movement cycle during the extension torque direction. During the neutral-flexion condition, FCR activity increased compared to all other conditions during 58-70% of the movement. Conclusion: When evaluating the entire waveform, non-neutral forearm postures decreased activity for all muscles during specific ranges. The extension torque increased ED and ECU activity at the start and end of the movement, while the flexion torque increased FCR and FDS activity for the majority of the movement. Also, FCR was important in supporting wrist extension during the neutral-flexion condition. Waveform analysis demonstrated complex forearm muscle activity patterns that could provide insight into neuromuscular control, performance, and fatigue progression

Design, Fabrication, and Control of an Upper Arm Exoskeleton Assistive Robot

Stroke is the primary cause of permanent impairment and neurological damage in the United States and Europe. Annually, about fifteen million individuals worldwide suffer from stroke, which kills about one third of them. For many years, it was believed that major recovery can be achieved only in the first six months after a stroke. More recent research has demonstrated that even many years after a stroke, significant improvement is not out of reach. However, economic pressures, the aging population, and lack of specialists and available human resources can interrupt therapy, which impedes full recovery of patients after being discharged from hospital following initial rehabilitation. Robotic devices, and in particular portable robots that provide rehabilitation therapy at home and in clinics, are a novel way not only to optimize the cost of therapy but also to let more patients benefit from rehabilitation for a longer time. Robots used for such purposes should be smaller, lighter and more affordable than the robots currently used in clinics and hospitals. The common human-machine interaction design criteria such as work envelopes, safety, comfort, adaptability, space limitations, and weight-to-force ratio must still be taken into consideration.;In this work a light, wearable, affordable assistive robot was designed and a controller to assist with an activity of daily life (ADL) was developed. The mechanical design targeted the most vulnerable group of the society to stroke, based on the average size and age of the patients, with adjustability to accommodate a variety of individuals. The novel mechanical design avoids motion singularities and provides a large workspace for various ADLs. Unlike similar exoskeleton robots, the actuators are placed on the patient\u27s torso and the force is transmitted through a Bowden cable mechanism. Since the actuators\u27 mass does not affect the motion of the upper extremities, the robot can be more agile and more powerful. A compact novel actuation method with high power-to-weight ratio called the twisted string actuation method was used. Part of the research involved selection and testing of several string compositions and configurations to compare their suitability and to characterize their performance. Feedback sensor count and type have been carefully considered to keep the cost of the system as low as possible. A master-slave controller was designed and its performance in tracking the targeted ADL trajectory was evaluated for one degree of freedom (DOF). An outline for proposed future research will be presented

Soft Robotics: Design for Simplicity, Performance, and Robustness of Robots for Interaction with Humans.

This thesis deals with the design possibilities concerning the next generation of advanced Robots. Aim of the work is to study, analyse and realise artificial systems that are essentially simple, performing and robust and can live and coexist with humans. The main design guideline followed in doing so is the Soft Robotics Approach, that implies the design of systems with intrinsic mechanical compliance in their architecture. The first part of the thesis addresses design of new soft robotics actuators, or robotic muscles. At the beginning are provided information about what a robotic muscle is and what is needed to realise it. A possible classification of these systems is analysed and some criteria useful for their comparison are explained. After, a set of functional specifications and parameters is identified and defined, to characterise a specific subset of this kind of actuators, called Variable Stiffness Actuators. The selected parameters converge in a data-sheet that easily defines performance and abilities of the robotic system. A complete strategy for the design and realisation of this kind of system is provided, which takes into account their me- chanical morphology and architecture. As consequence of this, some new actuators are developed, validated and employed in the execution of complex experimental tasks. In particular the actuator VSA-Cube and its add-on, a Variable Damper, are developed as the main com- ponents of a robotics low-cost platform, called VSA-CubeBot, that v can be used as an exploratory platform for multi degrees of freedom experiments. Experimental validations and mathematical models of the system employed in multi degrees of freedom tasks (bimanual as- sembly and drawing on an uneven surface), are reported. The second part of the thesis is about the design of multi fingered hands for robots. In this part of the work the Pisa-IIT SoftHand is introduced. It is a novel robot hand prototype designed with the purpose of being as easily usable, robust and simple as an industrial gripper, while exhibiting a level of grasping versatility and an aspect comparable to that of the human hand. In the thesis the main theo- retical tool used to enable such simplification, i.e. the neuroscience– based notion of soft synergies, are briefly reviewed. The approach proposed rests on ideas coming from underactuated hand design. A synthesis method to realize a desired set of soft synergies through the principled design of adaptive underactuated mechanisms, which is called the method of adaptive synergies, is discussed. This ap- proach leads to the design of hands accommodating in principle an arbitrary number of soft synergies, as demonstrated in grasping and manipulation simulations and experiments with a prototype. As a particular instance of application of the method of adaptive syner- gies, the Pisa–IIT SoftHand is then described in detail. The design and implementation of the prototype hand are shown and its effec- tiveness demonstrated through grasping experiments. Finally, control of the Pisa/IIT Hand is considered. Few different control strategies are adopted, including an experimental setup with the use of surface Electromyographic signals