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Chapter 1 Introduction Walking is the most basic form of human locomotion which is considered a learned activity that defines a certain attribute of human life. There are however millions of people with gait disabilities and unable to experience a normal walking pattern. These patients require rehabilitation or assistive devices such as orthosis or prosthesis to improve their walking patterns [1]. In 2002, a statistical study conducted by Nielsen C. for National Commission on Orthotic and Prosthetic Education, indicated that two million individuals in North America suffer from complete or partial paralysis of extremities. Approximately 20.3 percent of this population use orthoses [2].

Drop foot is a neuromuscular disorder that deteriorates patients' walking ability by preventing them from raising their feet during the swing [3]. This issue happens due to paralysis of the muscles and/or their malfunction at the ankle joint [4]. This issue causes two main problems during walking which include: uncontrolled falling of the forefoot after heel strike which consequently makes foot slap and dragging of the toes when the affected leg starts swinging [5].

Drop foot might be a temporary or permanent weakness in the affected limb. Without treatment, it may develop into a severe disorder, damaging other limbs and causing a permanent abnormal gait. There are several treatment options including physical therapy, assistive devices and surgery. Each of these techniques could be a temporary or permanent solution depending on the specific conditions of the patient [6]. Orthotic devices are the most common treatment for drop foot patients, in which a controlled force prevents the foot drop and foot slap during the stance and swing phases of the gait, respectively these devices are intended to improve patients’ walking pattern and normalize the gait [7, 8].

1.1 Ankle foot orthosis An Ankle Foot Orthosis (AFO) is a mechanical device used by drop foot patients with paretic ankle dorsiflexor muscles, to support and improve the functionality of the foot and ankle joint [9]. Although, the aim of AFO is preventing the forefoot to drop in swing by inhibiting the ankle movement, it also improves the ankle capability to support body weight, provides progression and secures push-off ability during stance phase of walking [10]. Many current AFO designs used for foot drop treatment while capable of controlling the foot during swing, restrict the ankle motion during the stance phase of gait. This restriction of movement causes abnormal gait pattern, disuse atrophy of the ankle flexor muscles, harmful effect on other joints and ligaments and further energy consumption [11, 12]. AFOs are mainly divided in three groups: passive, semi-active, and active. Passive AFOs include a mechanical element such as spring or damper to provide motion control of the ankle joint during gait. Semi-active AFOs may consist of a control system to adjust joint compliance or damping. In fully active devices, an actuator connected to a source of power provides motion at the joint [13].

1.1.1 Passive ankle foot orthosis

A passive AFO assists the patient by preventing undesirable foot motion during the swing phase of the gait. Essentially, acts like a torsional spring, limiting the foot deflection by providing an external torque. Passive AFOs are commercially available devices commonly used by patient in daily walking. Commercialized AFOs must be lightweight, durable, compact, and relatively inexpensive. For commercial success and acceptance, AFOs could be either articulated or non-articulated devices

and are also categorized based on their constituent material which might be metal, leather, thermoplastic, composite, or a combination of materials in hybrid AFOs [14, 15].

Thermoplastic AFOs, as shown in Figure 1-1, are the most common and are made as L-shaped polypropylene plastic braces, with the upright portion behind the calf and the lower portion under the foot. It is attached to the calf with a strap, and is made to fit inside the accommodative shoes. In a thermoplastic AFO also called posterior leaf spring AFO, motion control characteristics is specified by the material properties and the geometry [16, 17].

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Figure 1-1: Passive thermoplastic AFOs: (a) Plastic solid ankle AFO, (b) Plastic articulating AFO [17] Rigid AFOs, although control motion during swing and inhibit the drop foot, they disturb normal motion behavior in stance phase when foot is to plantar flex. Articulated thermoplastic and carbon fiber AFOs with commercial hinge joints such as Tamarack Flexure Joint (Figure 1-2), are introduced to address this issue. It is worth noting that some joints such as Tamarack also provide self co-aligning characteristics of the medial and lateral joint axes [18].

Figure 1-2: Tamarack Flexure Joint for thermoplastic and carbon laminate bracing [18]

Hybrid AFOs are developed in order to provide motion control in swing without unrestricted range of motion during stance. These devices consist of lightweight thermoplastic or carbon braces with articulated joints and passive elements aimed at storing and releasing for motion control [14]. A passive hybrid AFO called Dorsiflexion Assist Controlled by Spring (DACS) [19] is developed at University of Health and Welfare in Japan for drop foot patients (Figure 1-3 (a)). Also another hybrid device developed in Japan by researchers at Osaka University[20], employing a passive pneumatic element to control the ankle joint (Figure 1-3 (b)). These hybrid AFOs enable the patient to use a variety of shoes, and also provide biomechanical options for adjustability of the ankle joint.

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Figure 1-3: Passive hybrid AFOs: (a) The DACS’s hybrid AFO, (b) The Osaka University AFO [19, 20] Dynamic and Smart Systems Laboratory at University of Toledo proposed a novel design for passive AFOs based on shape memory alloy materials. This device consists of parallel superelastic wires subjected to tensile loading. In this design, SMA wires elongate during the powered plantarflexion, which assist the foot in dorsiflexion in swing phase. Although, this design is able to provide the required motion during a gait cycle and successfully prevents the drop foot, some problems such as structure durability, oversized wires architecture and noise of the actuation mechanism existed. The first generation of passive SMA AFOs, was proposed and fabricated by Bhadane M. [10] as shown in the Figure 1-4 (a), which consists of a combination of eight parallel superelastic wires wrapped around fourteen plastic freely rotating pulleys and the arrangement is

assembled on a polypropylene hinged AFO. Deberg L. [21] developed the second generation of these AFOs by modifying the arrangements of the wires and designing a

guide and carriage mechanism to transfer the linear motion to the hind-foot of the AFO structure. This is shown in the Figure 1-4 (b).

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Figure 1-4: University of Toledo SMA AFOs with superelastic wires: (a) Bhadane’s SMA AFO, (b) Deberg’s SMA AFO [10, 21]

1.1.2 Active ankle foot orthosis

As discussed in the previous section, passive AFOs produce excessive resistance to plantarflexion in stance phase. Thus, ankle motion becomes restricted through loading response and the stability of the leg during walking is affected. Due to this fact, passive AFOs are unable to completely normalize the entire gait functionality.

Therefore researchers have been interested in active AFOs, intended to adjust impedance of the orthotic joint for various portions of the gait cycle. Active AFOs are equipped with powered actuators to adapt the orthosis characteristics with the changes in the walking conditions. 7

Blaya et al. at Massachusetts Institute of Technology developed a powered ankle-foot orthosis based on Series Elastic Actuators [22]. This device was aimed at changing the orthosis impedance (stiffness) actively, thus eliminates the foot slap. The MIT group developed a Series Elastic Actuator (SEA) for the active AFO to realize variable stiffness. This SEA is comprised of a DC motor, a helical spring and a ball screw mechanism. Compliance of the system is controlled by driving the lead screw and adjusting the spring height. Additionally a control algorithm was developed for the actuator to provide proper stiffness for different events during the walking cycle. Although this active AFO shows promising results in a lab environment, the actuator is not practical for daily-wear application as it weighs 2.6 kg and has a bulky structure [23]. In the Human Neuromechanics Laboratory at the University of Michigan an active AFO was developed with pneumatically powered actuators called artificial pneumatic muscles (McKibben Muscles) which are providing both dorsiflexion and plantar flexion motion. Also in this device a control algorithm adjusts air pressure of each actuator. The total weight of the device excluding the off-board computer and air compressor is 1.6 kg [24]. At Arizona State University, researchers proposed and fabricated another active AFO with highly compliant actuator knows as robotic tendon. This device also includes a motor and screw mechanism and an adjustable spring. Robotic tendon act as SEA in harvesting energy from the gait cycle by utilizing increased elasticity. The modified version of this AFO weighs 1.75 [25-27].

All the aforementioned active AFOs (Figure 1-5), need to be connected to the external power supplies and computers for operation. Therefore, the applicability of these

orthoses is currently limited to laboratory studies. A portable powered ankle-foot orthosis (PPAFO) was developed at the University of Illinois [14], using a pneumatic actuator, a CO 2 power source, and an onboard controller. Although, this AFO presents an untethered controllable device, performance of the device as a sustained rehabilitation tool for daily wearing depends on future studies and improving the endurance of the AFO.

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Figure 1-5: Active AFOs: (a) MIT’s SEA active AFO; (b) The University of Michigan AFO powered by pneumatic muscles; (c) The Arizona State University robotic tendon AFO; (d) The University of Champaign Illinois PPAFO [14, 22-27]

SMA based active AFOs have been studied by several research groups recently [10, 28-30]. Two generations of innovative actuation design based on thermo-mechanical properties of shape memory alloys was proposed at the University of Toledo [10, 21, 28]. Combinations of superelastic and shape memory wires were investigated to develop an active actuator for AFOs. The designed SMA AFO although could provide motion requirements, was not successful in practice. The limitation of the first generation design was heating and cooling of the shape memory element due to the limited response time of the actuator in comparison to the walking cycle time. The second generation solved some of the issues of the previous generation by using superelastic elements to store and release energy.

1.2 Problem statement Drop foot patients suffer from paralysis of their muscles in the anterior portion of the lower leg which disable them to lift their foot at ankle. This prevents proper dorsiflexion in swing and makes foot slap or toes drag during walking. This problem also causes instability in walking and leads to an abnormal gait.

Conventional passive AFOs as the most common treatment option for drop foot patients although could prevent the drop foot in swing, they restrict the ankle movement. Also they do not produce normal ankle stiffness behavior during the whole gait cycle. Additionally passive AFOs are unable to provide adaption to various walking conditions.

Active AFOs are expected to provide more natural stiffness behavior. This is possible through adjusting the device compliance during walking which stabilizes the gait. However, developed active AFOs at the present time, are limited in their practice

Assistive applicability due to the design issues and the factors such as durability, efficiency and portability.

SMA based AFOs are studied as possible candidates capable of promoting sufficient ankle dorsiflexion and normalizing the gait. Although thermo-mechanical characteristics of SMA in active AFO leads to some limitations due to long cooling rate of the material, the SMA superelasticity provides appropriate stiffness and stability in ankle assistance. There is however a need to AFOs with smaller profile that would allow the patients to wear them on daily basis. Such as AFO should allow for wearing regular shoes and should have a single hinge for a minimalist profile.

1.3 Objective The main objective of this study is to design and develop an articulated portable ankle foot orthoses device based on superelastic characteristics of SMA to address drop foot neuromuscular disorder. The device is aimed to provide desired controlled dorsiflexion motion in the sagittal plane during leg swinging without disturbing the entire gait movement. Hinged joint provides flexibility in ankle movement and lateral loading response is controlled to inhibit hypermobility and improve lateral stability. The second goal of this study is investigating different concepts of active mechanism in order to control stiffness variations at the ankle joint due to the various walking conditions such as various walking speeds.

1.4 Approach

In this thesis, a novel compact design is proposed for an articulated passive AFO using the superelastic behavior of SMA. This design is aimed to provide a low weight, flexible and efficient device for daily walking rehabilitation purposes. This AFO secures desired motion in the regular direction and prevents unwanted motion in other directions. Several active concepts for the compliance adaptation have then investigated to extend the performance of SMA AFO in supporting various walking conditions. To achieve a reliable design for the proposed AFO, a comprehensive gait analysis is performed to extract and evaluate all the effects of loading components during a normal gait. Based on desired stiffness and motion requirements in the sagittal plane, a Finite Element Analysis (FEA) is developed for the proposed design of the passive SMA AFO. Lateral loading response is also evaluated by corresponding multi-axial loading simulation in 3D space. The design is optimized and updated several times to meet all stiffness, motion and loading requirements.

For the proposed active AFO concepts, numerical simulations are carried out to evaluate the stiffness properties of the active component under different walking speeds. It is been tried to achieve experimental ankle stiffness profiles by tuning the design variables during the simulation process. Since the SMA elements in both passive and active concepts are made of superelastic material, a particular simulation method is employed to assign the required material properties.

1.5 Contributions The main contributions of this dissertation include: Develop a concept of lightweight, comfortable and efficient one-sided SMA hinge for AFO, based on superelastic characteristics of shape memory alloy.  Simulation of the SMA hinge in both sagittal plane of motion and frontal/transverse planes by evaluating the behavior of the element in satisfying the uni-axial ankle rotation in the regular plane of motion and resisting against deflections in the 3D multi-axial loading model.  Gait analysis or extracting ankle-foot complex requirements during the whole gait.  Calculation of 3D loading components of the ground reaction on the defined foot plate during stance phase of the gait.  Estimate desired ankle stiffness and moment in various walking conditions during the swing phase of the gait.  Design and optimization of the SMA hinge for the passive AFO concept.  Develop the design of actuation techniques based on mechanical and structural stiffness adjustment of SMA element in order to control the stiffness of the ankle for various walking conditions.  Perform the simulation for the active element based on stiffness and rotation requirements in the main plan (sagittal plane) of motion.

1.6 Outline Chapter one of this thesis concludes with the outlines of the intended contributions. Chapter 2 provides required backgrounds on the special behavior of shape memory alloys. In Chapter 3, gait analysis parameters and techniques are presented at the beginning. Then, ankle stiffness behavior and range of motion are reviewed in Sections 3.3 and 3.4. Section 3.5, in particular focuses on multi axial loading of ankle-foot complex during the gait. Design and simulation of a novel passive AFO including one-sided superelastic hinge is presented in Chapter 4. In the first two sections of this chapter, concept development and design of the hinge are discussed. Detailed design study and simulation in the regular plane of the motion is demonstrated in Section 4.3. Simulation for multi axial loading with estimation of 3D loading conditions is developed in Section 4.4. Sections 4.5 and 4.6 concentrate on optimization process and mesh study for the proposed SMA hinge.

In Chapter 5, an investigation for active mechanism of AFO based on the adjustable compliance concept is presented. The basic concept is introduced in Section 5.1. Section 5.2 describes the actuation mechanisms. Design and development of the active elements for the proposed mechanically and structurally stiffness control techniques are discussed respectively in Sections 5.3 and 5.4. Section 5.5 provides information about the modeling and simulation method. Chapter 6 contains all the simulation results in comparison with experimental data and finally Chapter 7, summarizes the conclusions of this thesis and comprises recommendations for further research.

1.7Publications 1.8GorzinMataee, M., Taheri Andani, M. and Elahinia, M.,” A compliant ankle-foot orthoses based on multi-axial loading of superelastic shape memory alloys", ASME 2013 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, September 2013, Snowbird, Utah.