INSTITUTO TECNOL ´ OGICO Y DE ESTUDIOS SUPERIORES DE MONTERREY

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INSTITUTO TECNOL ´ OGICO Y DE ESTUDIOS SUPERIORES DE MONTERREY

CAMPUS MONTERREY

SCHOOL OF ENGINEERING AND SCIENCES

MECHANICAL DESIGN AND ASSESSMENT OF A BIOMIMETIC UPPER-LIMB EXOSKELETON WITH SHOULDER MOBILITY

ENHANCEMENT

DISSERTATION

PRESENTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE ACADEMIC DEGREE OF:

DOCTOR OF PHILOSOPHY IN ENGINEERING SCIENCE

by

EDUARDO PI ˜NA MART´INEZ

MONTERREY, N.L. MAY, 2019

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Eduardo Pi˜c na Mart´ınez, 2019

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Instituto Tecnol´ ogico y de Estudios Superiores de Monterrey

Campus Monterrey

School of Engineering and Sciences

Dissertation

Presented in Partial Fulfilment of the Requirements for the Academic Degree of:

Doctor of Philosophy in Engineering Science

Mechanical Design and Assessment of a Biomimetic Upper-Limb Exoskeleton with Shoulder Mobility

Enhancement

by

Eduardo Pi˜na Mart´ınez 1127895

Monterrey, N.L., May of 2019

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Dedication

This thesis work, which I hope will help me fulfill one of the most important goals in my professional live, is completely dedicated to the little society that I like to call my family. I have to state that at this point in my life, my family is not only conformed by my parents, sisters, and my sisters consequences, which have awarded me with their love, confidence and everlasting support; but also it is importantly conformed since a couple years by my beloved wife Luc´ıa, and her awesome family. It is to this magnificent social circle, to whom my gratitude, this thesis, and the goal it may help me reach, is dedicated. Thanks for the amazing journey that you help me take, for the always needed patience, and for the constant support and love that fueled my way through this work.

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Acknowledgements

I would like to express my deepest gratitude to those who, within the battle ground, made this research work possible. Thanks to the WeaRobot family, for building an unbeatable platform over which this project was constructed, and for giving this project a powerful name and goal. Thanks especially to Renato Gonzalez and Mauricio Hernandez, for creating an incredible team in the electronics design and development tasks, for bringing a unique atmosphere to the working areas, and for always giving their best in a project that they made their own. I also acknowledge the collaboration of Jos´e Julio Le´on, for making possible the correct use of the Biomechanics Laboratory and the VICON system. Moreover, I thank my main advisor Dr. Ernesto Rodriguez-Leal, for conceiving this project, and letting me be part of it and ultimately lead it.

My whole gratitude is also directed to my colleages and co-authors, Ricardo Roberts and Salvador Leal-Merlo. I especially thank their contribution in this work, which made the whole project possible either way by bringing their unique experience and expertise to it, or by secondarily supporting and encouraging its development.

A years long project such as the one presented in this thesis would have never been possible without the constant feedback of a top tier research group. I cheerfully thank the Robotics Research group, led by Dr. José Luis Gordillo Moscoso, for bringing this enriching feedback, and its members for creating a terrific and heartwarming team. I particularly thank César Cantú, for acting as well as the main photographer of this project, its results and its processes.

I would also like to acknowledge the support of the institutions that made possible my passing trough this doctorate program, supporting national science, young entrepreneurs and talent prospects. I deeply thank Tecnol´ogico de Monterrey, for supporting on tuition and on bringing the needed infrastructure to develop this research, such as the National Robotics Lab and the Biomechanics Laboratory at its School of Medicine. I also thank Consejo Nacional de Ciencia y Tecnolog´ıa (CONACyT), for supporting me on the living expenses during the time this project lasted.

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Abstract

Exoskeletons raise as the common ground between Robotics and Biomechanics, where rehabilitation is the main field in which these two disciplines find cohesion. Fur- thermore, the everlasting debate between the use of human labour or robotic machines could find a solution in these outstanding devices, which are intended to actuate in harmony with their wearers, maintaining the strength, precision, and accuracy commonly attributed to robots; and the dexterity, versatility, adaptability, and problem solving skills of human workers. To reach this point however, it becomes necessary to overcome the barriers that this robotic technology still has, such as the mechanical complexity that this devices demand.

One of the most relevant challenges in upper-limb exoskeleton design relies in the high complexity of the human shoulder, where current devices implement elaborate systems only to emulate the drifting center of rotation of the shoulder joint. The main goal of this thesis project is to develop an upper limb exoskeleton mechanism, with the ability to allow complete movement of its wearer. This work proposes the use of 3D scanning vision technologies to ease the design process and its implementation on a variety of subjects, while a motion tracking system based on vision technologies is applied to assess the exoskeleton reachable workspace compared with an asymptomatic subject. Furthermore, the anatomic fitting index is proposed, which compares the anatomic workspace of the user with the exoskeleton workspace and provides insight into its features. This work proposes an exoskeleton architecture that considers the clavicle motion over the coronal plane whose workspace is determined by substituting the direct kinematics model with the dimensional parameters of the user. Simulations and numerical examples are used to validate the analytical results and to conciliate the experimental results provided by the vision tracking system.

Moreover, this development is extended to the evaluation of the resulting prototype in tasks that depend on the users mobility freedom, where gross motion tracking was selected. The evaluation of this task is made by a real time comparison of the instrumented exoskeleton data and data obtained by a gross motion tracking commercial system, widely used in the state of the art developments and research works.

Results from these design, development and assessment tasks show the proficiency of the proposed mechanism, reaching portability, mobility and lightness.

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List of Figures

2.1 End effector mechanism (left) and exoskeleton mechanism (right). . . . 8 2.2 Timeline representation of the exoskeletons field development from the

work in [3] to the development of the Hardiman Exoskeleton [4]. . . 8 2.3 Exoskeleton robots developed at U.C., Berkeley by [7] for both lower

limb (a) and upper limb (b). . . 9 2.4 ReWalk lower limb exoskeleton, first device to obtain FDA commercial

clearance, admit three DoF per leg (hip, knee and ankle). . . 11 2.5 Exoskeleton presented in [33]. This device is cable driven and fixed to a

wheelchair. . . 13 2.6 ARMin II upper limb exoskeleton. Device with a vertical DoF to allow

shoulder CR mobility. . . 14 2.7 Shoulder exoskeleton patented. Allows shoulder pose and translation by

the use of parallel mechanisms. . . 15 2.8 Common mechanical architecture for lower limb exoskeletons with 7 DoF

for each leg. . . 16 2.9 Upper limb exoskeleton architecture that allows shoulder CR translation

over the X-Y plane [44]. . . 17 2.10 Upper limb exoskeleton with scapula and clavicle mobility at the Shoul-

der CR. Work presented in [45]. . . 18 2.11 Exoskeletons tested by their metabolic cost reduction ability: ankle (a)

and hips (b) powered exoskeletons presented in [50] and [52] respectively. 19 2.12 Harmony exoskeleton (NASA). This device was evaluated by means of

its range of motion (ROM) when under use [56]. . . 19 3.1 Human shoulder skeletal system. . . 23 3.2 Coronal plane back view representing the CR displacement of the shoul-

der driven by the clavicle and scapula in: (a) resting position, (b) abduction, (c) elevation and (d) depression. Dotted line represents the sternoclavicular joints position as reference and dashed lines represent the displacement limits of the acromioclavicular joint (∆Z). . . 24 3.3 Human shoulder skeletal system kinematic model. . . 26

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xx xx 3.4 Fitting scenarios between human and exoskeleton workspaces: (a) par-

tial intersection, (b) user workspace engulfs mechanism, (c) mechanism engulfs user workspace, and (d) no intersection. . . 28 3.5 Three dimensional scanning technologies, used in this thesis to obtain

the design anatomic canvas. . . 29 3.6 (a) Front view, and (b) top view of the subject’s scanning posture, where

red shaded areas are exposed. . . 30 3.7 (a) Identification of the main rotational axes for the exoskeletal sys-

tem, and (b) first shoulder axis allocation from the subject coronal view.

Plane B is positioned as a parallel reference to the coronal plane. . . . 32 3.8 Exoskeleton mechanism design obtained from the axes allocation and

surface offsets of the anatomic canvas (Isometric view). . . 33 3.9 Exoskeleton mechanism design with aligned axes. . . 35 3.10 Ball bearing model 625ZZ. . . 39 3.11 Joints design for the first prototype iteration: joints assembly (a) and

joint schematic (b). . . 40 3.12 Circular sliding joint for shoulder rotation in section (a), top (b) and

front (c) view. This joint allows shoulder rotation and is placed over the arm. . . 41 3.13 Thrust ball bearings models 61103 (a) and 51106 (b), used in the second

and third prototype iteration. . . 42 3.14 Exoskeleton joints designed with thrust ball bearings (a) for models

51103 (b) and 51106 (c). . . 43 3.15 Iteration two of the circular sliding joint mechanism. . . 44 3.16 Exoskeleton parametrization process applied to back (a) and arm (b) links. 44 3.17 Miniature ball bearing model M R62ZZ, used for the third iteration of

the circular sliding mechanism. . . 45 3.18 Circular slider joint third iteration. Final design is shown in (a), and the

simplified architecture of the joint upper half is presented in (b). . . 45 3.19 Final 3D scanned surface obtained from an asymptomatic subject and

used as an anatomic canvas for the exoskeleton design process. . . 46 3.20 Final exoskeleton prototype used for the experimental process, this pro-

totype includes the aforementioned sensory system, mounting straps, and VICON markers plates. . . 46 4.1 VICON camera view and characterization of markers to obtain position

of their centroids. . . 49 4.2 (a) Back markers plate, and (b) bracelet markers plate. . . 50 4.3 VICON setup scheme. Six cameras connected to the motion tracking

system placed around a moving object. . . 52 4.4 VICON setup. (a) Set of cameras and markers plates as positioned for

the recording sessions. (b) VICON digital environment NEXUS, where every non marker is deleted from the digital scenario. . . 53

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List of Figures xxi 4.5 Obtained P_v trajectories for two different recorded session at the VICON

vision system. . . 54 4.6 Anatomic dimensional parameters of the test according to Tables 3.1

and 3.2. Light gray circles represent the corresponding VICON markers. 56 4.7 Workspace for different radius R. . . 59 4.8 Resulting graph from the R testing process against the obtained volume

of the resulting surface. The volume stabilization region is circled for clarification. . . 60 4.9 Experimental human workspace for the upper limb. . . 60 4.10 Trajectories obtained from the vision system experimental process: sin-

gle recorded session (above), and merged trajectories of all 11 sessions (below). . . 61 4.11 Resulting workspaces from the proposed mechanism (a), the variant with

no clavicle movement (b), an alternative mechanism with transverse clavicle (c), and the anatomic system (d). . . 63 4.12 Intersections between real and modeled workspaces. . . 64 4.13 Performance index plot for every k. . . 65 5.1 ADC data conversion to be sent for each accelerometer axis. B_i repre-

sents a Byte written on the USB buffer, b_i represents the bit value at position i in the 10 bits ADC, and ID constructs the axis identification from 0 to 32. . . 70 5.2 Analog system general architecture. Data is collected from accelerome-

ters by their analog outputs. . . 70 5.3 Digital system general architecture. Data is collected from accelerome-

ters by means of their SPI digital interface. . . 71 5.4 ADC data conversion to be sent for each accelerometer axis. Data is

constructed from the 12 bits resolution ADC at each digital sensor, and sent by groups of 7 Bytes B_i. . . 72 5.5 Sensor axes initial transformation to comply with the pose determina-

tions requirements. Note that, by design, all sensors are mounted to have frames parallel to the kinematic chain local frames. . . 75 5.6 Simplified diagram of the exoskeleton mechanism with mounting straps.

The device is attached to its user at its back, arms and forearms. . . . 76 5.7 Markers plates mounting and configuration at the clavicle and shoulder

links (right arm). . . 77 5.8 Final scene configuration and experimental setup applied to the VICON

system for the exoskeleton assessment process under gross motion tracking tasks. . . 78 5.9 Control panel of the LabVIEW custom recording program used to re-

trieve the exoskeleton sensory system data from the experimental process. 79

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xxii xxii 5.10 Two dimensional exemplification of the local reference frame obtention

for each markers plate, where axes x and y are aligned to vectors ~B and C, respectively. . . .~ 80 5.11 Raw data series obtained from accelerometers model ADXL335 (a), by

an ADC of 10 bits and a full scale range of ±3 g; and model LIS3DH (b), with a built-in 12 bits ADC and a selected full scale range of ±2 g.

Notice that the useful inertial measurement scale for posture is ±1 g. . 82 5.12 Angle data series of motion directly exerted over the elbow and shoulder

(adduction/abdution) joints as seen in LabVIEW after the data processing seen in Chapter 5 from VICON (a) and exoskeleton sensory system (b). . . 83 5.13 Data series of the average VICON allocation error between markers in

every markers plates. The plot shows the error obtained for a single session (elbow flexion/extension, Session 01) for illustration purposes. . 84 5.14 Comparison of measured angles obtained from the vision process, and

from the exoskeleton sensory system. Plots shown represent the corresponding joint angle for a particular motion task in a single recording session. . . 86 A.1 Raise3D printer model N2 Plus, precision of over 10 µm. . . 94 A.2 Final assembly of the exoskeleton mechanism obtained from the third

manufacturing iteration. . . 95 B.1 VICON camera hardware model Vero, used in the vision assessment

process (v1.3). . . 98 B.2 VICON motion tracking software NEXUS, used in the vision assessment

process. . . 99 C.1 Inertial sensor used for the analog approach of the exoskeleton sensory

system. A product from Analog Devices (www.analog.com). . . 102 C.2 Inertial sensor used for the digital approach of the exoskeleton sensory

system. A product from ST Microelectronics (www.st.com). . . 103

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List of Tables

3.1 Euler parameters (ZXZ) for the kinematic model of the proposed ex-

oskeletal system. . . 36

3.2 Euler parameters identification . . . 36

3.3 Dimensional parameters obtained from the CAD model. . . 38

4.1 Model parameters obtained from the subject under analysis. . . 56

4.2 Angle sets ranges. . . 56

4.3 Euler parameters (ZXZ) for the transversal clavicle variant of the proposed exoskeletal system. . . 58

4.4 Raw Volume Data . . . 62

4.5 Workspaces Intersections . . . 64

5.1 Error data series summary: recording trial, Standard Deviation (STD, degrees), variance (VAR), Mean Squared Error (MSE), mean, and phase delay (seconds). . . 85

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List of Abbreviations

The following table describes the significance or various abbreviations and acronyms used throughout the thesis, also including the page of first use or mention of the corresponding element. Product names and standard units are not included in this table.

Abbreviation Meaning Page

3D Three Dimensional 29

AC Alternate Current 10

ADC Analog to Digital Converter 71

CAD Computer-Aided Design 29

CR Center of Rotation 13

DARPA Defense Advance Research Project Agency 9

DoF Degrees of Freedom 9

EMG Electromyogram / Electromyography 12

FDA Food and Drug Administration 10

GPS Global Positioning System 70

I²C Inter-Integrated Circuit 73

NASA National Aeronautics and Space Administration 18

PET-G Polyethylene Terephthalate Glycol 46

ROM Range Of Motion 18

SPI Serial Peripheral Interface 73

STL Standard Triangle Language 61

TRIZ Theory to Resolve Invention Problems 21 UART Universal Asynchronous Receiver-Transmitter 73

US United States 71

USB Universal Serial Bus 72

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List of Variables

The following table summarizes the variables that are used in this thesis work. Together with the variable, a brief description of the concept or element they were assigned to is made.

Variable Description

α Angle variable β Angle variable γ Angle variable

A_i Axis of rotation of the anatomic joint i

~a Local axis Z as seen from a global reference frame B_i Labeling of the VICON back markers

d_i Anatomic dimensional parameter dx x element of the ~vi vector

d_y y element of the ~v_i vector d_z z element of the ~v_i vector

Eⁱ Homogeneous transform matrix (Euler ZXZ) that transforms the local frame i-1 to the local frame i

F_i Labeling of the VICON forearm/wrist markers

k Weighting index variable of the performance evaluation

L_i Reference line over the anatomic canvas used during the design process Mi Homogeneous matrix that transforms the global reference frame to a local

frame i

MT Homogeneous matrix that expresses the exoskeleton end-effector

~

n Local axis X as seen from a reference frame

N^T Variant of M^T considering a horizontal clavicle contribution

~

o Local axis Y as seen from a reference frame

0O~ Variant of the ⁰P considering no clavicle contribution~ Oac Matrix representing an accelerometer pose in space O^mp Matrix representing the markers plate pose in space

0P~ Global position vector that represents the position of a point in a local reference frame

iP~ Local position vector placed with its origin in frame i P_i Reference point over the anatomic canvas

P (k) Performance index based on mobility and matching workspaces

P_v Virtual point on the 3D space signaling the center of the wrist markers plate

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Variable Description

P~_v Global position vector of point P_v

oP~_x x element of vector ⁰P~

oP~_y y element of vector⁰P~

oP~_z z element of vector ⁰P~

0Q~ Variant of ⁰P considering a horizontal clavicle contribution~ R Limit value of ri

r_i Circumspheres radius of tetrahedra analyzed by the concave Hull mesh algorithm

Ri Regions over the subject anatomy Ri Homogeneous rotation matrix

~

v_i Position vector that translates the origin of local frame i − 1 to that of local frame i

X_i Orthogonal axis of the local frame i Y_i Orthogonal axis of the local frame i Zi Orthogonal axis of the local frame i

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Chapter 1 Introduction

It is change, continuing change, inevitable change, that is the dominant factor in society today. No sensible decision can be made any longer without taking into account not only the world as it is, but the world as it will be.

Isaac Asimov

Over the past decades, Robotics has been seen as one of the main tools to replace the human labour in the work field. Generally, the reason for this becomes evident when the replaced tasks comprise hard labour, repetitive work, or even activities in hazardous environments, where the main goal is to avoid tasks that held a low cost- benefit ratio with safety and health. However, the industrialization and the growing adoption of Robotics in the manufacturing line have highly boosted productivity and thus the income of these adopting companies. As a result, the Robotics field has rapidly evolved to adapt to almost every work area, with important developments in miniatur- ization, autonomous and adaptable systems, and artificial intelligence, stimulated by the economic support of the private initiative.

This adoption and usage growth have generated an everlasting debate, where the consistent cornerstone is if whether or not should Robotics be considered a threat to human labour, where the main concern lays in the fact that, over the years, factories are seen to have more robots and less humans in their manufacturing areas. Typically, robots have remained isolated in factories in order to avoid unintended harm to nearby individuals or facilities. This becomes an important issue due to the lack of advanced awareness from the robotic system to sudden changes in its surroundings. As a result, most robotic systems demand areas where humans are not an environmental factor, handing stronger arguments to maintain this debate growing.

Robotics have not stayed still while this debate develops. Latest advances in Robotics have been directed to bring an improved awareness to industrial robots, aiming to create intelligent and adaptable systems that have the ability to sense sudden changes and act accordingly in order to avoid harm. However, since automated manufacturing

1

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2 2 areas are highly dependent on synchronization, emergency actions due to unintended or accidental human interaction could lead to manufacturing delays. Furthermore, the latest trends in manufacturing are being directed to customization and rapid product evolution, where the need of flexible, adaptable and intelligent manufacturing lines grows considerably. Thus, later trends in Robotics aim to create a symbiotic relation between robotic systems and humans. This ideal partnership offers the exponential growth of both systems qualities, while minimizing their limits for almost any kind of task.

Notwithstanding that, over the latest years, important advancements on robot- human interactions have been achieved, there is still a long path to cover concerning the popular opinion that robots are still dangerous, stiff and blind. However, Robotics incursions to everyday activities are currently closing this adoption gap with developments in diverse areas such as assistive Robotics, medical Robotics, the growing area of entertainment Robotics, and the younger generations that have grown habituated with computing devices, and therefore interact more readily with new high technology systems.

For this reason, research has been developed to reach a synchronous behaviour between the robot and its user, trying to improve the efficacy of robots by means of the cooperation with a highly versatile and adaptable system (the human), and improving at the same time the human efficiency by the use of a highly repetitive and precise tool (the robot). Hence, assistive Robotics have been the main field of interest in recent years, developing important advances in humanoid robots, artificial intelligence and haptic interfaces that ease the interaction process between the human and the machine.

This advances have shockingly improved the general perception to the robotic systems by showcasing developments that look, move and act as humans, while withstanding an important strength and, at the same time, hold a docile behaviour.

The pursuit of the ultimate blending between the human and the machine, able to make an impact in the human and robot labour debate, has seen a promising solution in the exoskeleton robots and wearable systems. Devices that are able to move as one with the user, providing their strength and precision to the variety of tasks that its user is able to make. These exoskeletal devices promise to create the perfect symbiotic relationship, offering intuitive natural control systems and transparent mechanics to create the most versatile tool.

Robotic exoskeletons have acquired an important interest since the 1990’s, when these devices started to be seen as an important tool to enhance the capabilities of the human worker (human augmentation). Since then, and given the high versatility that these novel devices bring, robotic exoskeletons and wearable robots have raised interest due to their potential application in areas such as military, industry, health, care giving, entertainment and training. Military and industrial applications of these devices focus mainly in the ability to enhance the human capabilities, while maintaining the reasoning and judgment from the user, bringing the possibility to endure harder or longer work while reducing tiredness and abiding efficiency. On the other hand, health

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1.1. Statement of the Problem 3 and care give applications focus on the goal of returning the physical abilities that are lost in patients due to trauma, illness, or aging, also importantly improving the quality of life of these subjects.

Entertainment and training applications of exoskeletons refer to their ability to interact with secondary systems, while obtaining data from the user and its movements such as position and its derivatives. This characteristic brings a wide opportunity in rapidly growing fields, for example virtual or augmented reality, and the so called industry 4.0. Besides, exoskeletons applied to these areas open the chance to be used as enhanced user interfaces, where the interaction to the wearer can be extended not only to visual and auditory stimuli, but also to tactile and muscular by the use of a variety of actuators.

It is certain that robotic exoskeletons promise a wide variety of applications, industrial and socially focused, where they could be ideally considered the zenith of the human and machine integration. Nevertheless, there are several constraints that have to be overcome to reach these goals, which are pushing the technology boundaries and encouraging research in materials, sensory systems, actuators and mechanics, among others.

1.1 Statement of the Problem

Ideally, robotic exoskeletons represent an external projection of the skeletal structure of the user, which drives its motion by the force applied by muscles. Thus, these external mechanisms transparently emulate the biomechanics of the wearer body in order to comply its most basic function, mobility.

This necessity to recreate the users mobility represents one of the main challenges in the exoskeletons mechanical design, mainly due to the high complexity that the biomechanics withholds. It has to be highlighted that, among all complex and evolved creatures on earth, the human being has evolved to an outstanding versatility when compared to almost any other creature, not only considering cognitive capabilities, but also mechanical, where the human being has demonstrated to be able to create marvels with its bare hands by combining these evolutionary upgrades.

2014 will be remembered as the year in which the first exoskeleton got clearance for its sales in the United States. Since then, over four other similar devices have reached the same instance to date. However, they have an interesting characteristic in common, they all are lower limb exoskeletons.

The lower limb is the structure responsible of our ability to translate from one place to another and give us our primary physical characteristic, being erect. Also, holding a standing position aids the body regulation and the correct performance of our main body functions. However, it generally does not drive one of the abilities that is considered to make us humans and that is related mainly to the upper limb. The ability to create.

The human upper limb allows us to translate, position and actuate our hands,

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4 4 one of the most complex tools of nature. In order to achieve this, the biomechanics of the upper limb have evolved to a high complexity that leads an enhanced reachable workspace for the hands, mostly driven by the shoulder complex and importantly more intricate than the lower limb biomechanics. This behaviour complicates greatly the application of a proficient exoskeletal mechanism, which has to emulate the shoulder enhanced mobility while avoiding interference with the wearer, resulting in poorly effective devices with limited mobility and, therefore, limited usage capabilities.

In order to achieve a proper emulated mobility, exoskeletal mechanisms must align its rotational axes with those of the user, due to the highly dependent biomechanics of the shoulder. This means that the various joints that conform the shoulder complex work in close collaboration to be able to perform almost any movement. Hence, axes misalignment between an exoskeleton and its wearer could lead to important ill effects and possible tissue damage.

Furthermore, an effective robotic exoskeleton could be considered so once its usage does not implies en extra effort to its user. This important aspect should be fulfilled in order to achieve the main objective of an exoskeletal device, to bring support or enhancement. Attributes such as weight, volume and mobility extend, mechanically, the key points to design a compelling device, which by means of applying adequate actuation and control systems could integrate an ideal robotic exoskeleton.

Moreover, designs that lack interest in these key points have lead to bulky devices that are too big and heavy to be portable (wearable), or mechanisms with limited mobility that are secluded to a minimum of tasks and therefore a low cost benefit ratio. At the same time, the nonexistence of methods to assess an exoskeletal mechanism performance in terms of a proper mobility complicates an appropriate standard comparison between devices.

1.2 Aims and Objectives

The general objective of this work is to propose, construct and test an upper limb exoskeletal mechanism. This exoskeletal structure is intended to have a biomimetic architecture, such that is able to emulate the mobility of the human upper limb. More- over, this mechanism should be constructed based on a design method that allows ergonomic links and an adequate axes placing. While the focus of these project lays on the mobility characteristic that these devices should have, the scope of this development is to construct a passive prototype (not actuated). Also, an assessment method for robotic exoskeletons should be developed, with the ability to perform a quantitative analysis of mechanical performance against the biomechanics of the user, while appropriate to a variety of mechanical structures intended for similar applications.

Alongside the general objectives, more specific targets are defined in the following lines.

• To propose a biomimetic exoskeletal structure for the human upper limb, based

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1.3. Methodology 5 on a novel design method intended to reach ergonomics and enhanced human like mobility.

• Establish the mathematical model of the proposed architecture to obtain the pose and position of the system (forward kinematics).

• To apply vision systems in order to develop an assessment method based on mobility.

• Test the constructed device in gross motion tracking tasks.

1.3 Methodology

Being an ergonomic and biomimetic focused project, this thesis work path comprehends greatly of biomechanics and anatomic analysis efforts, which can be later applied from the design to the construction and tests processes. Therefore, this development is composed of four main stages: study of literature, anatomic and biomechanics review of the human shoulder, biomimetic design and construction of the exoskeletal system, and performance assessment. Additionally, an usage case is to be studied and tested with the resulting device.

The first stage of the project consists in a thorough study of the state of the art concerning robotic exoskeletons and exoskeletal devices, including their classification, recent developments in upper limb devices and future challenges. This review process is based in research published in various scientific journals focused in Robotics, Ergonomics and Mechanics, among others.

As this project second stage, the theoretical background concerning the human shoulder anatomy is studied, focused on the biomechanics of its bone structure and the constraints presented by its interaction with the related muscle and ligaments. This stage is intended to bring clarity to the exoskeleton design process, and to propose a convenient assessment method that can be directly related to the user anatomy and mobility.

The development of the exoskeletal device takes part in this thesis work third stage. This task consists on the development of a biomimetic design method, and the analysis and selection of proper tools to perform the design and construction of an upper limb exoskeleton. This process is mainly based on digital vision systems, able to obtain proper anatomic data to be used as foundations for the construction of a prototype. Also, additive manufacturing technologies are extensively used in order to create functional and ergonomic links to assemble the final prototype.

Finally, the fourth stage of this project represents the application of a performance assessment method to the exoskeleton functional prototype. This performance test consist in mobility comparisons between the device and its wearer. As used in the third stage, vision systems represent the main tool to obtain position and translation data of the anatomic system, thus bringing the proper information to analyze its mobility.

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1.4 Organization of the Thesis

This thesis describes the construction process and assessment of a biomimetic upper limb exoskeleton, which is intended to emulate the complex mobility of the human shoulder, able to extend its usage capabilities. This development includes the development of a biomimetic design method and a vision based assessment method for the mechanical performance of exoskeleton mechanisms. All of these developments are the result of a thorough review and observation of the human shoulder biomechanics. Also, a gross motion tracking is analyzed as use case of the resulting prototype.

Chapter 2 presents the literature review concerning relevant developments around exoskeletons. General information about robotic exoskeletons is shown while narrowing the research advances to upper limb devices and studies over their mobility. Research papers on these topics, including future challenges and novel developments, are reviewed and analyzed.

Chapter 3 describes the proposed construction process of an upper limb exoskeleton, including the biomimetic design methodology applied, and the followed prototyping and manufacturing tasks. The anatomic foundations in which this work is developed is hereby shown, creating a proper theoretical background of the human upper limb anatomy and biomechanics, also stating the foundations of a novel assessment method based on mobility. This background is then used to describe the design process, including the basic model obtainment and the proper axes placement in order to mimic the drifting behaviour of the shoulder joint center of rotation. Based on this methodology and the resulting architecture, the mathematical model to obtain position and orienta- tion of the kinematic chain is shown and tested. Furthermore, this chapter depict the construction and refinement process of the exoskeletal mechanism.

Chapter 4 presents the followed steps to apply the proposed assessment test. This chapter establishes the needed tools and processes to obtain normalized and comparable data from both exoskeletal and anatomic systems.

Chapter 5 analyzes the final functional prototype by its ability to perform gross motion tracking tasks. Here, the instrumentation of the exoskeleton is described together with the corresponding data processing. Also, the assessment of this use case is presented by its comparison with a gold standard tool based on vision systems.

Outcomes from the development and experimental processes are correspondingly presented at the end of the aforementioned chapters, comprising results from the design and construction processes, and mainly focusing on those obtained from the performance assessment applied to the final exoskeleton prototype.

Finally, Chapter 6 summarizes this thesis work, presents conclusions, establishes the contributions to the state of the art, and recommends future work that could be fit to emerging trends in this research field.

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Chapter 2 Literature Review

It is paradoxical, yet true, to say, that the more we know, the more ignorant we become in the absolute sense, for it is only through enlight- enment that we become conscious of our limitations. Precisely one of the most gratifying results of intellectual evolution is the continuous opening up of new and greater prospects.

Nikola Tesla

This Chapter contents are focused in the clarification of the exoskeleton developments in research and of those who have reached the market, aiming to clarify their definitions and usage over the last years, in which these devices have evolved. In Section 2.1 a concise inspection to the development history of exoskeletons is presented, narrowing this Chapter to the studies in upper limb exoskeletons in Section 2.2. Later in this chapter, a thorough analysis of the common exoskeleton architectures is displayed in Section 2.3, citing recent research made in the Robotics field. Ultimately, a more specific review of studies based on exoskeletons performance is presented in Section 2.4.

The definition of the exoskeleton concept has been clarified earlier. However, robotic exoskeletons should hold their own definition, mostly considering their intended use in humans and the main characteristics that these devices maintain. These robotic systems can be specified as mechanisms whose joints and links correspond to those of the human body and mimic their users movements [1]. Even though the same outcome from this definition can be fulfilled with common end effector devices, matching links and joints to those of the wearer enables full posture control and the application of torques to each joint separately [2] as seen in Figure 2.1.

Although the first approaches to exoskeletal devices were documented in the late 1800’s [3], the first serious research development in this area can be awarded to the Gen- eral Electric’s Hardiman system [4] in the early 1970’s, notwithstanding the resulting size of these device and the little to no usage it permitted (see Figure 2.2). Exoskele- tons have been widely defined as mechanisms that are capable of bringing mobility to

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Figure 2.1: End effector mechanism (left) and exoskeleton mechanism (right).

their wearers [5], reason that has directed their usage mainly to augmentation tasks such as human performance enhancers and rehabilitation tools. Considering changes in the control algorithms of these devices, their main applications could also include physiotherapy, haptic interfaces, and control devices for virtual environments or remote systems [1, 6].

1890 1971

Figure 2.2: Timeline representation of the exoskeletons field development from the work in [3] to the development of the Hardiman Exoskeleton [4].

2.1 Brief Review of Exoskeletons

From the Yagn’s patent to the Hardiman’s prototype, exoskeletons were considered just as science fiction devices, given mostly that technology was not advanced in order to create such complex devices in small sizes, needed to bring portability. However,

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2.1. Brief Review of Exoskeletons 9 after the later development, exoskeletons gained an important interest in more serious projects and applications, where military interest has to be highlighted.

In the early 2000’s, the Defense Advance Research Project Agency (DARPA) founded a project to develop a series of robotic exoskeletons intended to augment, mainly, the human strength and endurance during locomotion [7]. These project leaded to the Berkeley lower extremity exoskeleton, commonly referred as BLEEX (Figure 2.3.a), a 14 degrees of freedom (DoF) device intended to allow its wearer to carry higher loads in a backpack, as in common military drills. Being these developments founded by military initiatives, later advances mainly remained of private access, thus not appearing in the State of the Art.

LOWER LIMB EXOSKELETON

UPPER LIMB EXOSKELETON

a) b)

Figure 2.3: Exoskeleton robots developed at U.C., Berkeley by [7] for both lower limb (a) and upper limb (b).

Although the aforementioned project produced upper limb exoskeletons, they where dimmed by the lower limb device due to the promising application directly on the field from the later, and the limiting size and weight of the former (Figure 2.3.b).

This situation led to research works that consisted in designing and constructing novel devices, mostly lower limb, to be used in various fields with an increasing interest in physiotherapy [8].

The human lower limb entails straightforward mechanics, which directed the focus of novel developments to research in control and actuation systems. Furthermore, these two branches established a serious interest given the continuous concern in constructing more portable devices and with a more intuitive and user friendly behaviour.

Research on novel control and actuation systems have consistently been constructed simplifying the exoskeletal structure mechanics. Work has been done considering one DoF such as the presented in [9]. Here, authors developed a novel actuated

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10 10 device for the ankle. The principal focus of this research was to analyze the influence in the muscular activity of the user when external forces are applied to the ankle joint.

In this case, the forces were exerted by a one DoF robotic ankle exoskeleton.

Another example of research done with one DoF exoskeleton is the presented in [10], where authors highlight that exoskeletons must have the ability to decrease the metabolic consumption of the user while performing mobility tasks, but most devices perform the opposite way. The research presented by this group focuses on the implementation of admittance and inertia compensation controls for a single servo AC motor that actuates the knee joint, trying to proficiently emulate the user mobility.

This device is presented fixed to a chair, and its functionality is limited to leg swing exercises.

Other projects have oriented their focus on constructing more autonomous systems that enable the user in practical activities. For this, work has been done concerning two legged lower limb exoskeletons with 4 DoF (two hips and two knees). In [11], authors describe the use of the Vanderbilt powered orthosis, an exoskeleton intended for its use in walk assistance activities. This research work highlights the compact size and weight of the resulting device, and its high torque capability of about 40 Nm. This device is later analyzed in [12] to assess its gait assistance capabilities, while applying gait phase detection and active compensation for passive dynamics, concluding that this exoskeleton is able to aid gait without affecting the natural gait dynamics of the user. Advances concerning the Vanderbilt device were later performed in [13], where the exoskeleton ability to climb and descent stairs was evaluated.

Furthermore, a device with similar dynamics is later presented in [14], where the main contribution lays in the use of serial elastic actuators and a set of force and position sensors for each joint capable of a biomimetic functionality. Here, authors claim that the use of actuators that emulate the mechanics of tendons, muscles, and ligaments could provide a more intuitive experience to the user.

Developments on control architectures have been applied and evaluated mostly for lower limb devices. In [15], a novel gait control is presented, which encloses an adaptive trajectory control and an admittance control. Hence, this device gains the ability to actively comply to the wearer gait. The work presented in this project is applied by the use of a 6 DoF two legged exoskeleton (2 hips, 2 knees and 2 ankles).

Consistently, exoskeletons have gained complexity, reaching a milestone where their usage seems to justify the high number of researches done over them. In the year 2014, the United States Food and Drug Administration (FDA) provided clearance for marketing to the first powered lower limb exoskeleton [16]. In that year, the clearance was granted to the ReWalk Personal Exoskeleton (see Figure 2.4) as a Class II medical device with special controls. Later, the Indego from Parker Hannifin and the Ekso from Ekso Bionics followed in the clearance granting. This situation represented an important turning point for exoskeletons, opening a new market opportunity, thus encouraging founded research. It becomes important to establish that all of these devices are intended for their use as walk assistance, mostly for patients with different stages of

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2.1. Brief Review of Exoskeletons 11

Hip

Knee

Ankle

Figure 2.4: ReWalk lower limb exoskeleton, first device to obtain FDA commercial clearance, admit three DoF per leg (hip, knee and ankle).

paraplegia. Moreover, other regional markets saw the introduction of these devices in an early stage, such as the Walk Assist devices, from Honda [17] (for walking rehabilitation); the Lokomat and Armeo, from Hocoma (walking and post stroke rehabilitation);

and the HAL full body exoskeleton, from Cyberdyne (for physical rehabilitation and human augmentation), these last two being the only devices considering upper limb mobility assistance.

Although the aforementioned developments could be considered as the most representative turning points on this research field, other projects have developed important technological advances concerning exoskeletal devices between the BLEEX appearance and the FDA clearance granting. Such is the case of advances related to actuators for their use in these devices, where hybrid passive-active actuators have been developed to reduce the actuation energy consumption and stiffness [18], and the evaluation of linear and pneumatic motors have been performed in order to emulate muscle contraction as actuators for exoskeleton joints, in [19] and [20] respectively.

It is important to notice that research over the mechanical architecture of lower limb devices have been developed in considerably lower numbers than the developments on control or actuation, such as in [21] and [22]. Nonetheless, research applied to the development of upper limb exoskeletons has been raised in the last years, were a persistent topic is the kinematic interaction between the exoskeletal device and the anatomic system, these research is further reviewed and cited in 2.2.

Notwithstanding the shared characteristics between most novel exoskeleton robots, it is completely evident the important differences that they share. Despite of that, these devices and their current trends appear to point to shared objectives, having the medical and assistive applications as constants as stated in [23]. However, these differences bring the necessity to establish a classification method for them considering their different constraints, capabilities and usage intentions.

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2.2 Upper Limb Exoskeletons

It is remarkable that most research fields developing around exoskeletons can be suc- cessfully exemplified with lower limb exoskeleton projects. Nevertheless, the research environment of exoskeletal devices enclose a considerably bigger variability.

Exoskeletons are typically classified considering the anatomic part they are intended to assist or enhance. This classification separates devices in two main families:

lower limb, and upper limb exoskeletons [7]. At the same time, exoskeletons can also be classified by their kind of actuation, or the lack of it, as active and passive exoskeletons. These two classifications are commonly used altogether in order to bring a better understanding of the device and the challenges it has to tackle.

Lower limb exoskeletons, as seen in Section 2.1, have been thoroughly analyzed in the last years. Considering their characteristic mechanics and their intended usage, the main problems their research environment is trying to tackle include: their high torque necessity, enhancement of their autonomy, gait process adaptation throughout users, and equilibrium control among others. A complete review on the history, state of the art, and challenges concerning these devices can be seen in [5] and [24].

On the other hand, upper limb exoskeletons have demonstrated to have different challenges such as overall weight, actuators size, and its autonomy from lower limb devices. However, these challenges are commonly overshadowed by the upper limb demand on complex mobility, which is given by the human upper limb biomechanics and specially by the shoulder complex [25]. Furthermore, upper limb exoskeletons have been commonly seen as promising tools for their use as power augmentation and rehabilitation devices [2], such as their lower limb complementary devices. However, the interest on their applications as haptic interfaces, that enable proprioception in virtual environments, is currently opening the opportunity for novel upper limb exoskeleton studies [6].

Upper limb devices have constantly been around the exoskeletons research environment. [26], for instance, developed an elbow exoskeleton (one DoF) to create an assistive device able to move as its user intents. By reading skin surface electromyogram signals (EMG) from the user, this device was able to exert torque to the elbow joint with its motor by detecting the wearer intention. Another work related to this same joint is presented in [27], where authors developed a curved pneumatic actuator looking forward for its use in rehabilitation and teleoperation, given its force feedback capabilities. It can be seen that research endeavours concerning actuators are usually focusing in the muscle-like behaviour, as the work presented in [28], but many other studies are also focusing on the design of control strategies in order to reach this goal, such as the minimal assist as needed control for actuators presented in [29]. Further analysis of control strategies for upper limb exoskeletons are presented in [30].

Other developments in upper limb exoskeletons have generally focused in the mobility characteristics of the arm, consistently researching and constructing mechanisms around the wrist joint and the shoulder complex given their high mobility. Although

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2.2. Upper Limb Exoskeletons 13 the wrist is composed by a conjunction of bones, its mobility can be represented by three rotational DoF (it can also be constructed as 2 rotations directly in the wrist and a third one coming from the elbow). However, the shoulder complex allows a wider mobility to the arm when compared to the wrist, which depends on at least four DoF as stated in [25]. In the cited work, authors established that these complexity arises from the interaction between the clavicle, scapula, and humerus bones, which create a drifting Center of Rotation (CR). Hence, upper limb exoskeletons should follow this CR in order to minimize ill effects. Nevertheless, research has been done where the shoulder is presented as sole spherical joints. In [1, 31], authors design an upper limb powered exoskeleton consisting on shoulder, elbow and wrist. This development implements a rotational DoF to the elbow, a spherical joint at the wrist, and also a spherical joint at the shoulder, thus representing the shoulder complex as a stationary CR. This work was applied by means of vision systems in [32], where daily motion tasks were thoroughly analyzed.

Figure 2.5: Exoskeleton presented in [33]. This device is cable driven and fixed to a wheelchair.

Shoulder CR mobility represents a topic of interest in upper limb exoskeletons design, where most applications require optimal motion tracking that considers the drifting CR characteristic of the shoulder. For these applications, at least one DoF exerted by the clavicle is required, supplementary to the three DoF that are commonly considered at the shoulder joint. In [34] and [35], for instance, authors present an exoskeleton with mechanisms to allow a mobile CR of the shoulder. Here, a three DoF device is developed where only two of them exerts directly to the shoulder joint and arm mobility, while a third one is intended for the vertical displacement of the shoulder CR. The resulting device actuation is cable driven, which creates a bulky system that is fixed to a wheelchair, thus not portable (see Figure 2.5). Authors extend this work

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14 14 in [36], where elbow and wrist joints are added to create a seven DoF device. Neuro fuzzy networks are used in these developments as control systems, while joints torque are estimated by the use of EMG signals [33]. Exoskeletons with similar mechanics are analyzed in [37], where the main focus is to establish the importance of the shoulder CR mobility in the vertical axis. The ARMin devices are analyzed and the common CR translation is shown. These devices are fixed to a mobile platform, and are intended for their use while the wearer sits in front of them (see Figure 2.6).

Figure 2.6: ARMin II upper limb exoskeleton. Device with a vertical DoF to allow shoulder CR mobility.

Upper body exoskeletons with variant CR have also been patented. For example, an upper-limb design implements a parallel robot with seven linkages that drive a platform over the shoulder, where six links are attached to the user’s torso and the remaining link connects the platform to the arm [38] as shown in Figure 2.7. This configuration enables mobility assistance to the arm, but further work is required to implement such concept in a device that exerts the necessary forces and protects the user from unsafe postures.

Coupled with the multiple research that has been done over upper limb exoskeletons mechanics, a rising need on control systems for these complex mechanisms is gaining importance in the upper limb exoskeletons environment, as it is established in [2]. Also, these characteristics constantly bring a redundancy problem which has also been tackled in [39] and [40]. Thanks to the aforementioned advances in exoskeleton robots, its application has been studied in motion assistance and rehabilitation tasks, where post-stroke robot-assisted therapy has improved patient recovery outcomes [41], encouraging further exoskeleton developments.

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2.3. Exoskeletons Design and Architecture 15

Shoulder Platform

Figure 2.7: Shoulder exoskeleton patented. Allows shoulder pose and translation by the use of parallel mechanisms.

2.3 Exoskeletons Design and Architecture

As it was earlier mentioned in Section 2.1 and overall exemplified in Section 2.2, exoskeletons must mimic the biomechanics of their wearers. This brings a nascent necessity on biomimetic design methods to be applied in the development of exoskeletal structures. The work presented in this thesis is based on the earlier published project based on the use of vision systems to create a biomimetic design of exoskeletal joints [42].

This work proposed a biomimetic architecture of the knee joint, to latter apply reverse engineering by means of motion tracking tools in order to particularize the proposed architecture. This Section presents different architectures of exoskeletal mechanisms, which were intended to mimic the biomechanics of the user.

Originally, exoskeletons were based on industrial robot architectures, adopting similar actuators, mechanisms and materials [23]. This approach however, is sub- optimal for exoskeletons that try to mimic the human body mobility. Joint complexity and the dimensional variability between individuals limit the effectiveness of industrial robot architectures and, therefore, new exoskeleton designs have been proposed in the past years to tackle these challenges. In the case of lower limb exoskeletons, architectures have been well established and remained with little to no change since the earlier developments, as seen in [7]. This architecture includes three DoF at the hip (ball and socket joint), one rotational DoF at the knee, and three DoF at the ankle (ball and socket joint) for each leg (see Figure 2.8). However, and as it was mentioned earlier, some developed devices neglect DoF mainly at the hip and ankle for simplicity, and due to the remaining usability of the resulting architecture.

In contrast, upper limb exoskeletons have been developed proposing different architectures, mainly for the shoulder complex. In [43] authors propose and develop an exoskeleton robot with a mobile shoulder CR. This architecture is integrated by a linear joint that allows the shoulder CR displacement over a vertical axis, where the

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Hip CR

Knee joint

Ankle CR

Figure 2.8: Common mechanical architecture for lower limb exoskeletons with 7 DoF for each leg.

exoskeletal mechanism is attached to a static platform. A similar architecture was earlier discussed from the work in [36].

Mobile shoulder CR architectures have also been proposed with translation over the horizontal plane. The work presented in [44] demonstrates an exoskeletal mechanism for the full arm, where two linear DoF are added to the shoulder CR as orthogonal axes over the horizontal plane (see Figure 2.9). This work also presents a mechanism that is fixed to a platform, thus not portable. Note that, since a ball and socket joint can be represented as three rotational joints whose axes intersect in a common point and are orthogonal to each other, the intersection point of these axes represents the CR. In the case of exoskeleton devices, these axes must be projected externally to the wearer, in order to maintain alignment with the user axes and avoid unwanted collisions between the exoskeleton links and the user body.

Additionally, a more complete architecture was proposed by [45] that considers the complex interaction between the clavicle and scapula to exert the complex shoulder CR mobility. This work adds three extra DoF solely for the shoulder CR translation in space, while maintaining the common arm architecture for the shoulder, elbow, and wrist joints as seen earlier (see Figure 2.10). This work represents one of the most promising and complete architectures in terms of biomimetic mobility. However, no further analysis nor assessment was performed for this device.

Drifting CR behaviours can be applied to most anatomic joints due to bone to bone interactions and common organic irregularities. Apart from the projects related to wide CR translations, namely the shoulder, simpler articulations have been studied to create self aligning exoskeletal joints [46] and biomimetic joints that emulate the

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2.4. Performance Studies on Exoskeletons 17

Figure 2.9: Upper limb exoskeleton architecture that allows shoulder CR translation over the X-Y plane [44].

bone to bone interaction [42, 47].

2.4 Performance Studies on Exoskeletons

Research in the Biomechanics and Robotics fields have found a common ground in the development of robotic exoskeletons. In the last years, these devices have reached important milestones and grow constant interest in both social and industrial endeavours.

Although this field have found different obstacles to tackle, and constraints given by the current technology state, solutions have been proposed presenting highly promising results.

Solutions regarding human-like mobility for exoskeletons have been numerously proposed, with the goal of developing novel mechanic architectures that are able to effectively mimic the biomechanics of the user. While developments of autonomous an- thropomorphic robots result relatively simple in their mechanics [48,49], the projection of this mobility to external structures, that do not collide with the internal structure (user), represents a challenging factor for exoskeleton developments. The research cited earlier in this thesis include a wide variety of mechanic architectures, however, almost any of them have been assessed in order to quantitatively evaluate their performance in terms of mobility.

In 2014, [50] introduced the concept of metabolic cost reduction to exoskeletons.

This work was based on earlier research applied to robotic prosthesis in [51], and es-

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Scapula-Clavicle mechanism

Figure 2.10: Upper limb exoskeleton with scapula and clavicle mobility at the Shoulder CR. Work presented in [45].

tablishes the fact that assistive devices must at least generate a positive cost reduction in order to be practical. This concept determines the effort of the wearer while developing an activity. A similar concept is also studied in [52] with the development of a hip exoskeleton for walk assistance of elderly users.

Metabolic cost reduction ability on exoskeletons depends considerably on the physical characteristics of the device. Weight, size and mobility can be considered as the critical factors to consider when developing a practical robotic exoskeleton, and could be used directly in order to develop proper assessment methods for the performance of these mechanisms. Note that the aforementioned studies on metabolic cost reduction were based in devices, whose similar characteristics include: lightness and reduced size, reaching portability; and mobility that mimics the joints they cover, which have fundamentally single rotational joints (see Figure 2.11).

Notwithstanding the previously established, most recent research have assessed performance by means of complex methods that measure directly the metabolic cost.

These methods include the measurement of oxygen consumption and hearth rate as shown in [53] and [54], and the direct measurement of interaction forces between the joint and the motor [55].

In contrast, a more promising assessment method is presented in [56], where the exoskeleton Harmony, from NASA, is presented (see Figure 2.12). Here, the exoskeletal structure design is based on the biomechanics of the human upper limb, and the assessment is performed taking the human arm mobility as comparison baseline. This work also includes an evaluation of the exoskeleton Range of Motion (ROM) while

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2.4. Performance Studies on Exoskeletons 19

Ankle Powered Exoskeleton (1 DoF) Hip Powered Exoskeleton (1 DoF)

a) b)

Figure 2.11: Exoskeletons tested by their metabolic cost reduction ability: ankle (a) and hips (b) powered exoskeletons presented in [50] and [52] respectively.

ROM

Figure 2.12: Harmony exoskeleton (NASA). This device was evaluated by means of its range of motion (ROM) when under use [56].

being on by the user. Accordingly, this thesis presents a novel architecture for the human shoulder based on a biomimetic design method, and implements an assessment method based on the ROM of the exoskeleton mechanism and the anatomic mechanism separately, which allows the acquisition of a quantitative comparison, used as a base to determine performance.

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Chapter 3 Biomimetic Design of an Upper-Limb Exoskeleton

I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection.

Charles Darwin

The development of exoskeleton robots has to be centered in the biomimetic design of all its parts, from the mechanics, to the actuation, sensory, and control systems.

In [57], the author established the raising importance that taking biological systems to current technology designs is having. Mechanisms such as actuators, sensors, and full robots can benefit from the application of a biomimetic design. Furthermore, general design methods that focus in innovation (e.g. TRIZ) have established the importance of the nature based inspiration since the late 90’s [58]. This thesis highlights the importance of biomimetic mechanics on a robotic exoskeleton, which would directly impact on the performance of such device, and subsequently, its usage capabilities.

This thesis presents the development of an upper limb exoskeleton with natural shoulder abduction/adduction movements. To fulfill this goal, it is necessary to formu- late the complex biomechanics of the human upper limb, also establishing its kinematic architecture for a better understanding of the mechanism. Notice that by acquiring this anatomic kinematic model, it becomes possible to construct a secondary mechanism such as an exoskeleton, however, reenacting this mobility in an external mechanism, which covers the anatomic links of the user and avoids self constraints while moving, represents an important problem to overcome in the design of these devices.

Section 3.1 presents a thorough analysis of the upper limb anatomy, clarifies the constraints that are representative of complex biological structures, and propose kinematics models that may ease the proper understanding of the arm mobility. Section 3.1.1 presents the musculoskeletal system related to the arm mobility, with a main focus on the shoulder complex. Section 3.1.2 demonstrate the kinematics of the anatomic

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22 22 systems in terms of its architecture. Finally, a model to obtain a quantitative measurement of performance of the exoskeleton is presented in Section 3.1.3, whose result depends directly on the mobility comparison between the exoskeletal structure and the user mobility.

Moreover, the following sections present the design and development of an exoskeletal mechanism. Section 3.2 presents the methodology to obtain a proper anatomic canvas over which the exoskeleton mechanism can be designed; Section 3.3 illustrates the steps to correctly allocate the rotational axes that effectively mimic the upper limb mobility; Section 3.4 then constructs the mathematical model that models the kinematic architecture, and the equivalent variables of this model with respect to the final wearer of the device; finally, Section 3.5 shows the manufacturing steps followed to construct and refine the final prototype.

3.1 Shoulder-Arm Anatomy and Mobility Analysis

This thesis targets the development of an upper limb exoskeleton mechanism with the ability to effectively mimic the human arm mobility (gross motion tasks). This ability represents one of the main challenges that exoskeleton devices need to overcome in order to reach a proficient level of practicality, given the raising promise of their application in different activities such as rehabilitation, motion assistance and human augmentation. Hence, a proper theoretical background of the upper limb anatomy, its biomechanics, and the constraints this system withholds has to be studied in order to propose adequate design methods that ease the development process.

The following sections present a thorough analysis of the upper limb anatomy, clarifies the constraints which are representative of complex biological structures, and propose kinematics models that may ease the proper understanding of the arm mobility.

3.1.1 Shoulder Complex Anatomy

The shoulder mobility is exerted by the shoulder complex. This musculoskeletal system is mainly conformed by four bones, and is actuated by a variety of external and inner muscles at the back, chest, and the shoulder itself. The shoulder mechanical structure includes the sternum, clavicle, scapula, and humerus bones and its mechanical interactions extend to the ribs and thorax, over which the system moves. Figure 3.1 shows a front view of the mechanical structure of the shoulder complex, and the four joints that produce its mobility: glenohumeral, acromioclavicular, sternoclavicular and scapulothoracic. Although the thorax and scapula interact physically, the scapulothoracic articulation cannot be considered an anatomical joint due to the lack of connective tissue between these two bones [59].

In general, anatomic articulations can be considered as synovial joints that glide.

However, the gliding effect of most joints in the human body is considerably small and is commonly neglected. In the case of the shoulder complex, joints have rather small

INSTITUTO TECNOL ´ OGICO Y DE ESTUDIOS SUPERIORES DE MONTERREY

INSTITUTO TECNOL ´ OGICO Y DE ESTUDIOS SUPERIORES DE MONTERREY

CAMPUS MONTERREY

DISSERTATION

Instituto Tecnol´ ogico y de Estudios Superiores de Monterrey

Campus Monterrey

School of Engineering and Sciences

Dissertation

Doctor of Philosophy in Engineering Science

Mechanical Design and Assessment of a Biomimetic Upper-Limb Exoskeleton with Shoulder Mobility

Enhancement

Dedication

Acknowledgements

Abstract

Contents

List of Figures

List of Tables

List of Abbreviations

List of Variables

Chapter 1 Introduction

1.1 Statement of the Problem

1.2 Aims and Objectives

1.3 Methodology

1.4 Organization of the Thesis

Chapter 2

Literature Review

2.1 Brief Review of Exoskeletons

2.2 Upper Limb Exoskeletons

2.3 Exoskeletons Design and Architecture

2.4 Performance Studies on Exoskeletons

ROM

Chapter 3

Biomimetic Design of an Upper-Limb Exoskeleton

3.1 Shoulder-Arm Anatomy and Mobility Analysis

3.1.1 Shoulder Complex Anatomy