The experimental investigation of foot slip-turning motion of the musculoskeletal robot on toe joints

Owing to their complex structural design and control system, musculoskeletal robots struggle to execute complicated tasks such as turning with their limited range of motion. This study investigates the utilization of passive toe joints in the foot slip-turning motion of a musculoskeletal robot to turn on its toes with minimum movements to reach the desired angle while increasing the turning angle and its range of mobility. The different conditions of plantar intrinsic muscles (PIM) were also studied in the experiment to investigate the effect of actively controlling the stiffness of toe joints. The results show that the usage of toe joints reduced frictional torque and improved rotational angle. Meanwhile, the results of the toe-lifting angle show that the usage of PIM could contribute to preventing over-dorsiflexion of toes and possibly improving postural stability. Lastly, the results of ground reaction force show that the foot with different stiffness can affect the curve pattern. These findings contribute to the implementations of biological features and utilize them in bipedal robots to simplify their motions, and improve adaptability, regardless of their complex structure

Bipedal humanoid robot control by fuzzy adjustment of the reference walking plane

The two-legged humanoid structure has advantages for an assistive robot in the human living and working environment. A bipedal humanoid robot can avoid typical obstacles at homes and offices, reach consoles and appliances designed for human use and can be carried in human transport vehicles. Also, it is speculated that the absorption of robots in the human shape into the human society can be easier than that of other artificial forms. However, the control of bipedal walk is a challenge. Walking performance on solely even floor is not satisfactory. The complications of obtaining a balanced walk are dramatically more pronounced on uneven surfaces like inclined planes, which are quite commonly encountered in human surroundings. The difficulties lie in a variety of tasks ranging from sensor and data fusion to the design of adaptation systems which respond to changing surface conditions. This thesis presents a study on bipedal walk on inclined planes with changing slopes. A Zero Moment Point (ZMP) based gait synthesis technique is employed. The pitch angle reference for the foot sole plane −as expressed in a coordinate frame attached at the robot body − is adjusted online by a fuzzy logic system to adapt to different walking surface slopes. Average ankle pitch torques and the average value of the body pitch angle, computed over a history of a predetermined number of sampling instants, are used as the inputs to this system. The proposed control method is tested via walking experiments with the 29 degreesof- freedom (DOF) human-sized full-body humanoid robot SURALP (Sabanci University Robotics Research Laboratory Platform). Experiments are performed on even floor and inclined planes with different slopes. The results indicate that the approach presented is successful in enabling the robot to stably enter, ascend and leave inclined planes with 15 percent (8.5 degrees) grade. The thesis starts with a terminology section on bipedal walking and introduces a number of successful humanoid robot projects. A survey of control techniques for the walk on uneven surfaces is presented. The design and construction of the experimental robotic platform SURALP is discussed with the mechanical, electronic, walking reference generation and control aspects. The fuzzy reference adjustment system proposed for the walk on inclined planes is detailed and experimental results are presented

3D turning analysis of a Bipedal Robot

Thesis (MEng)--Stellenbosch University, 2022.ENGLISH ABSTRACT: There is stark contrast between the abilities of legged locomotion found in nature, and locomotion found in lab environments. This performance gap is indicative of a large knowledge gap. Roboticists are required to bridge these gaps to truly invite robots to detach from their support rigs, and actuate within the real world. In this thesis, non-planar contact and discontinuous locomotive dynamics were modeled as a trajectory optimization problem. Consequently, this made understanding the complexities of legged locomotion more tractable. Understanding, and being able to leverage, contact is crucial to successful legged locomotion. Therefore, a comprehensive investigation was conducted into non-planar contact dynamics using a monopod robot. Here, methods of modeling the Coulomb friction cone in contact implicit trajectory optimization were implemented. Literature suggests replacing the friction cone with a polyhedral approximation thereof. However, this method is known to underestimate the resultant friction in non-planar environments. This thesis presents a novel method of modeling the 3D friction cone and compares it to an implementation of the polyhedral approximation. Results from this comparison show that the novel method was significantly more computationally efficient than the polyhedral approximation, without underestimating the friction cone. Dynamic bipedal locomotion remains a struggle for most robotic platforms. Robotics literature provides few examples of robots achieving agile, dynamic locomotion. Therefore, trajectories realizing non-planar dynamic bipedal motion were generated. Experiments were conducted into acceleration, steady-state, deceleration, and rapid turning off the sagittal plane. Optimal trajectories displayed the robot walking at speeds resulting in a Froude number less than 0.5, and running at speeds resulting in a higher Froude number. This is consistent with dynamic gaits found in nature. A sliding-mass velocity profile emerged when conducting long-time-horizon trajectories where the robot accelerated from a rest position and decelerated back to rest after completing multiple steps in a periodic steady-state gait. Additionally, when turning off the sagittal plane, slip occurred at least 93.32% of the duration of contact, and turn overshoot is present in all turn trajectories.AFRIKAANSE OPSOMMING: Daar is skerp kontras tussen die vermoëns van voortbeweging wat in die natuur voorkom, en di`e wat in laboratoriumomgewings voorkom. Hierdie prestasiegaping is aanduidend van ’n groot kennisgaping. Robotiste is verwag om hierdie gapings te oorbrug om robotte uit van hul ondersteuningplatforms uit te kom en in die werklike wˆereld te aandryf. In hierdie tesis word 3D kontak en diskontinue lokomotiefdinamika gemodelleer as ’n trajekoptime ringsprobleem. Gevolglik maak dit die verstandhouding van robotik gebeendebeweging makliker. Die verstaan van kontak, en hoe om dit te gebruik, is noodsaaklik vir suksesvolle voortbeweging. Daarom is ’n omvattende ondersoek uitgevoer, met behulp van ’n monopod robot, om kontakdinamika beter te verstaan. Hier word metodes van modellering van die Coulomb wrywings-keel in kontak-implisiete-trajek-optimering ge¨ımplementeer. Literatuur stel voor dat die wrywingskegel vervang word met ’n veelvlakkige benadering daarvan. Dit is bekend dat hierdie metode die gevolglike wrywing in 3D omgewings onderskat. Hierdie tesis bied ’n nuwe metode om die 3D-wrywingskegel te modelleer, en vergelyk dit met ’n implementering van die veelvlakkige benadering daarvan. Uitslae van hierdie vergelyking toon dat die nuwe metode meer berekeningsdoeltreffend was as die veelvlakkige benadering, sonder om die wrywingskegel te onderskat. Dinamiese tweevoetige voortbeweging bly ’n stryd vir die meeste robotplatforms. Robotikaliteratuur verskaf min voorbeelde van robotte wat dinamiese voortbeweging bereik. Daarom is trajekte gegenereer wat 3D dinamika van tweevoetbeweging realiseer. Eksperimente word uitgevoer na accelerasie, bestendige toestand, verlangsaming en draaie van die sagittale vlak af. Optimale trajekte het die robot laat stap teen ’n spoed wat ’n Froude-getal minder as 0.5 laat kom, en hardloop teen spoed wat ’n ho¨er Froude-getal gehad het. Dit stem ooreens met dinamiese voetvalpatrone wat in die natuur voorkom. ’n Glymassa-spoedprofiel het voor gekom toe die lang-tyd-horison trajekte uitgevoer word: waar die robot van ’n rusposisie versnel het en terug versnel is na rus nadat hy verskeie stappe in periodieke bestendige-toestand voltooi het. Wanneer die robot van die sagittale vlak afdraai, gly hy ten minste 93.32% van die tyd wat kontak plaasgevind, en beurtoorskiet is teenwoordig in alle draaie.Master

Bio-Inspired Robotics

Modern robotic technologies have enabled robots to operate in a variety of unstructured and dynamically-changing environments, in addition to traditional structured environments. Robots have, thus, become an important element in our everyday lives. One key approach to develop such intelligent and autonomous robots is to draw inspiration from biological systems. Biological structure, mechanisms, and underlying principles have the potential to provide new ideas to support the improvement of conventional robotic designs and control. Such biological principles usually originate from animal or even plant models, for robots, which can sense, think, walk, swim, crawl, jump or even fly. Thus, it is believed that these bio-inspired methods are becoming increasingly important in the face of complex applications. Bio-inspired robotics is leading to the study of innovative structures and computing with sensory–motor coordination and learning to achieve intelligence, flexibility, stability, and adaptation for emergent robotic applications, such as manipulation, learning, and control. This Special Issue invites original papers of innovative ideas and concepts, new discoveries and improvements, and novel applications and business models relevant to the selected topics of ``Bio-Inspired Robotics''. Bio-Inspired Robotics is a broad topic and an ongoing expanding field. This Special Issue collates 30 papers that address some of the important challenges and opportunities in this broad and expanding field

The role of inter-enlargement propriospinal neurons in locomotion following spinal cord injury.

The focus of this dissertation is to explore the functional role of two anatomically-defined pathways in the adult rat spinal cord before and after spinal cord injury (SCI). To do this, a TetOn dual virus system was used to selectively and reversibly silence neurons with cell bodies at spinal segment L2 and projections to spinal segment C6 (long ascending propriospinal neurons, LAPNs) and neurons that originate in the C6 spinal segment and terminate at L2 spinal segment (long descending propriospinal neurons, LDPNs). This dissertation is divided into five chapters. Chapter One provides background information regarding spinal cord injury, locomotion, and a brief introduction to propriospinal neurons. Chapter Two details the functional consequences of silencing LAPNs and LDPNs in uninjured animals, with specific regard to sensory context during overground locomotion. Chapter Three describes the consequences of silencing LAPNs following a mild/moderate spinal cord contusion injury. Spinal cord injury (SCI) fundamentally affects the ability to maintain patterned weight-supported stepping. Chapter Four focuses on the functional outcomes of silencing the reciprocal descending inter-enlargement pathway, LDPNs, after mild/moderate spinal cord contusion injury. Finally, Chapter Five compares the differential roles of LAPNs and LDPNs in left-right coordination prior to injury, especially in a sensory context-dependent manner. A section of this chapter is devoted to a recap of injured data for both LAPN and LDPN silencing post-injury and attempts to place this work in context with other studies whose focus is on propriospinal pathways after SCI

Using Model-based Optimal Control for Conceptional Motion Generation for the Humannoid Robot HRP-2 14 and Design Investigations for Exo-Skeletons

The research field of bipedal locomotion has been active since a few decades now. At one hand, the legged locomotion principle comprises highly flexible and robust mobility for technical applications. At the other hand, a thorough technical understanding of bipedalism supports efforts of clinicians and engineers to help people, suffering from reduced locomotion capabilities caused by fatal incidents. Since the technology enabled the construction of numerous robotic devices, among them: various humanoids, researchers started to investigate bipedalism by abstraction and adoption for technical applications. Findings from humanoid robotics are further exploited for the construction of devices for human performance augmentation and mobility support or gait rehabilitation, among them: orthosis and exo-skeletons. Although this research continuously progresses, the motion capacities of humanoid robots still lack far behind those of humans in terms of forward velocity, robustness and appearance of the overall motion. Generally, it is claimed that the difference of performance between humans and robotics is not only due to the limiting characteristics of the employed technology, e.g. constructive lack of specific determinants of gait for bipedalism or dynamic limits of the actuation system, but as well to the adopted methods for motion generation and control. For humanoid robotics, methods for motion generation are classified into optimization-based methods and those that employ heuristics, that are mostly distinguished based on the problem complexity (computation time) and the resulting dynamic error between the generated motion and the dynamics of the real robot. The implementation of the dynamic motion on the robotic platform is usually comprised with an on-line stabilizing control system. This control system must then identify and resolve instantaneously the dynamic error to maintain a continuously stable operation of the device. A large dynamic error and breach of the dynamic limits of the actuation system can quickly lead to a fatal destabilization of the device. This work proposes a contribution to the model computation and the strategy of the problem formulation of direct multiple-shooting based optimal control (Bock et. al.) for dynamically stable optimization-based motion generation. The computation of the whole-body dynamic model inside the optimization relies either on forward or inverse dynamics approach. As the inverse dynamics approach has frequently been perceived as less resource intensive than the forward dynamics approach, a new generic algorithm for insufficiently constrained, under-actuated dynamic systems has been developed and thoroughly tested to comply with all numerical restrictions of the enveloping optimization algorithm. Based on this contribution, various optimal control problems for the humanoid platform HRP-2 14 have been formulated to assess the influence of different biologically inspired optimization criteria on the final motion characteristics of walking motions. From thorough bibliographic researches a dynamically more accurate model was comprised, by taking into account the impact absorbing element in the ankle joint complex. Based on the experiences of the previous study, a problem formulation for the limiting case of, dynamically overstepping an obstacle of 20cm x 11cm (height x width) with only two steps, while maintaining its stable operation was accomplished. This is a new record for this platform. In a further part, this work proposes an iterative comprehensive model-based optimal control approach for the conception of a lower limb exo-skeleton that respects the integrated nature of such a mechatronic device. In this contribution, a human effectively wearing such a lower limb exo-skeleton is modeled. The approach then substantiates all system components in an iterative procedure, based on the complete system model, effectively resolving all complex inter-dependencies between the different components of the system. The study in this work is conducted on an important benchmark motion, walking, of a healthy human being. From this study the limiting characteristics of the system are determined and substantial propositions to the realization of various system components are formulated

The control of Schwann cell myelination during development and after nerve injury

Schwann cells are the principal glial cell of the peripheral nervous system and are responsible for axon maintenance, regeneration and increasing saltatory conduction of neurons. Schwann cell differentiation and myelination is mediated by a core network of transcription factors and signalling pathways, which have been divided into two groups; positive and negative regulators. Sox10, NFATc4, Oct6, Krox20 and the ERK 1/2 signalling pathway have been characterised as positive regulators of Schwann cell differentiation and myelination; with Sox10 and Krox20 also playing critical roles in myelin maintenance. On the other hand, transcription factors cJun, Pax3, Id2 and signalling pathways Notch and p38 mitogen activated protein (MAP) kinases (MAPK) have been identified as negative regulators of Schwann cell differentiation and myelin formation. Recently, the HMG transcription factor Sox2 was identified as a negative regulator of Schwann cell myelination in vitro, however its role in Schwann cell myelination in vivo has not yet been studied. This study therefore aimed to examine the role of Sox2 overexpression in Schwann cells and how it effects Schwann cell differentiation and myelination during development and after injury. In addition, we aimed to investigate for the first time the specific role of p38α (the major isoform of p38 MAPK) in Schwann cell myelination in vivo, by generating Schwann cell specific p38α conditional knockout mice. Sox2 is highly expressed in immature Schwann cells, but is downregulated as Schwann cells being to mature and differentiate. This study shows that continued expression of Sox2 during development and after injury, impairs Schwann cell differentiation and myelination by directly downregulating the expression of two core transcription factors; Sox10 and Krox20, as well as myelin proteins, P0 and MBP. In addition, we observe that continued Sox2 expression significantly increases Schwann cell proliferation and maintains Schwann cells in an immature state. Unexpectedly, we also observed that continued Sox2 expression significantly increases the number of macrophages present in the nerves of Sox2 overexpressing mice at both P60 and 21 days post injury. Phenotypically, Sox2 overexpressing mice 6 show signs of a peripheral neuropathy and animals have impaired motor and sensory function. These findings confirm that Sox2 is a negative regulator of Schwann cell myelination and suggests that continued Sox2 expression is sufficient to drive the progressive development of a peripheral nerve disorder which may resemble Charcot-Marie-Tooth type 1 demyelinating neuropathy and congenital hypomyelinating neuropathy. As a negative regulator of Schwann cell myelination, activity of the p38 MAPK pathway has been shown to inhibit myelin formation in vitro and to also induce the Schwann cell injury response; by driving Schwann cell dedifferentiation and demyelination following injury. Here we show that specific removal of the p38α isoform in Schwann cells leads to an increase in myelin thickness at early developmental time-points, along with an elevated expression of myelin proteins, P0 and MBP. Further analysis following nerve injury revealed that removal of p38α results in an initial decrease in Schwann cell demyelination, yet improves axon remyelination at 21 days post injury. These results demonstrate the specific role of p38α in regulating Schwann cell myelination, and how it could be a direct therapeutic target for improving nerve repair after injury

Legged robotic locomotion with variable impedance joints

Humans have a complex musculoskeletal arrangement which gives them great behavioural flexibility. As well as simply moving their legs, they can modulate the impedance of them. Variable impedance has become a large field in robotics, and tailoring the impedance of a robot to a particular task can improve efficiency, stability, and potentially safety. Locomotion of a bipedal robot is a perfect example of a task for which variable impedance may provide such advantages, since it is a dynamic movement which involves periodic ground impacts. This thesis explores the creation of two novel bipedal robots with variable impedance joints. These robots aim to achieve some of the benefits of compliance, while retaining the behavioural flexibility to be truly versatile machines. The field of variable impedance actuators is explored and evaluated, before the design of the robots is presented. Of the two robots, BLUE (Bipedal Locomotion at the University of Edinburgh) has a 700mm hip rotation height, and is a saggital plane biped. miniBLUE has a hip rotation height of 465mm, and includes additional joints to allow hip adduction and abduction. Rapid prototyping techniques were utilised in the creation of both robots, and both robots are based around a custom, high performance electronics and communication architecture. The human walking cycle is analysed and a simple, parameterised representation developed. Walking trajectories gathered from human motion capture data, and generated from high level gait determinants are evaluated in dynamic simulation, and then on BLUE. With the robot being capable of locomotion, we explore the effect of varying stiffness on efficiency, and find that changing the stiffness can have an effect on the energy efficiency of the movement. Finally, we introduce a system for goal-based teleoperation of the robots, in which parameters are extracted from a user in a motion capture suit and replicated by the robot. In this way, the robot produces the same overall locomotion as the human, but with joint trajectories and stiffnesses that are more suited for its dynamics