Dynamic stability is commonly defined as the ability to maintain balance through center of mass control during locomotion. Patients with locomotor impairments are especially challenged when walking over uneven surfaces (Richardson 2004). We studied dynamic stability margins in young healthy adults and in adults with unilateral traumatic trans-tibial amputations (TTA). To date, studies have not controlled for walking speed over an uneven surface in a patient population. We hypothesized that: 1) DSMs would increase over the uneven rocky surface (URS) for both groups, 2) DSMs would be greater on the involved side at faster walking speeds for subjects with TTA and, 3) DSMs would increase more for the involved limb when on the URS. 17 (4 females, 13 males) young healthy military service members (22.8 ± 6.4 years) and 12 (1 female, 11 males) service members (27.2 ± 4.7 years) with traumatic unilateral trans-tibial amputations participated in two study designs. A 15-segment model was used to estimate whole body COM motions. All subjects walked at 5 dimensionless speeds over a flat level surface (FLS) and an URS. Subjects completed 6-10 trials over each surface at each speed. Minimum frontal plane DSM values were extracted for each stride for statistical analyses. For young healthy subjects a two factor (speed x surface) ANOVA was used to test significance (p<.05). The DSMs were not greater over the URS (p=.307), but a main effect due to speed was found (p<.001) for young healthy subjects. In contrast, DSMs were significantly larger when subjects with TTA walked on the URS compared to the FLS (p = 0.011). For subjects with unilateral TTA, a three-factor ANCOVA ((amputation) side x speed x surface) with residual limb length (p=.029) and time in prosthesis (p=.741) as covariates was used for hypothesis testing. When limb length and time in prosthesis were accounted for there was no significant within subjects effect due to speed (p=.656). There were no significant differences between involved and uninvolved limbs (p = 0.211). There were no significant interaction effects. In conclusion, there was a difference in DSMs due to speed in unimpaired subjects and due to surface and residual limb length in subjects with unilateral TTAs. In subjects with unilateral TTA side-to-side symmetry was found for DSM measures, which was in contrast to an earlier study of subjects with unilateral trans-femoral amputations (Hof 2006). It appears that symmetry and dynamic stability are reasonable expectations for young adults with isolated TTAs. / text

This report documents our work in exploring active balance for dynamic legged systems for the period from September 1985 through September 1989. The purpose of this research is to build a foundation of knowledge that can lead both to the construction of useful legged vehicles and to a better understanding of animal locomotion. In this report we focus on the control of biped locomotion, the use of terrain footholds, running at high speed, biped gymnastics, symmetry in running, and the mechanical design of articulated legs.

Road and rail vehicles and aircraft rely mainly or solely on friction brakes. These brakes pose several problems, especially in hybrid vehicles: significant wear, fading, complex and slow actuation, lack of fail-safe features, increased fuel consumption due to power assistance, and requirement for anti-lock controls. To solve these problems, a contactless magnetic brake has been developed. This concept includes a novel flux-shunting structure to control the excitation flux generated by permanent magnets. This brake is wear-free, less-sensitive to temperature than friction brakes, has fast and simple actuation, and has a reduced sensitivity to wheel-lock. The present dissertation includes an introduction to friction braking, a theory of eddy-current braking, analytical and numerical models of the eddy-current brake, its excitation and power generation, record of experimental validation, investigation and simulation of the integration of the brake in conventional and hybrid vehicles.

The purpose of this thesis is to investigate the reaction to a purely unexpected slip during gait termination and subsequent experiences stopping on the slippery surface in participants who are young and healthy, older and healthy and who have Parkinson’s disease while on traditional dopamine-replacement medication. Gait termination requires control of the forward momentum of the body’s centre of mass (COM). This forward momentum must be dissipated and the COM held within a newly formed base of support. The challenge of stopping on a slippery surface involves maintaining stability while transitioning from steady-state locomotion to steady-state stance. Experience with a slippery surface changes postural and gait characteristics to diminish the perturbing effect of the slip. The magnitude of the slip response diminishes quickly as the movement becomes more efficient. Our investigations revealed a typical slip response to a purely unexpected slip during gait termination including a lowering of the COM, an increased muscular response to support the body, a shortened step and an arm raise. Knowledge of and experience with the slippery surface quickly changed the slip response to reduce the perturbing effect of the slip and also to increase the efficiency of the response while smoothly transitioning from steady-state locomotion to gait termination. Parkinson’s disease impairs balance control, the ability to switch between motor tasks and also to stop within two steps. The need for a voluntary change in motor programs along with difficulty stopping and increased instability makes gait termination a potentially difficult task for someone with Parkinson’s disease (PD). The participants with PD used a slower, safer strategy to stop on non-slippery surfaces to compensate for their instability compared to age-matched controls. When a slip was first introduced during gait termination, the participants with PD continued to be less stable in the plane of progression than the control group. Despite the instability, the PD group was still able to integrate a balance-correcting response into a voluntary gait termination program. The ability to generate adaptive strategies to integrate the balance-correcting response into a voluntary gait termination program over multiple trials does not appear to be affected by PD; both the control group and PD group showed behavioural modifications according to repeated exposures to the slippery surface. Although participants with PD seemed slightly less stable and walked slower, their behavioural adaptations were similar to the control group.

The purpose of this thesis is to investigate the reaction to a purely unexpected slip during gait termination and subsequent experiences stopping on the slippery surface in participants who are young and healthy, older and healthy and who have Parkinson’s disease while on traditional dopamine-replacement medication. Gait termination requires control of the forward momentum of the body’s centre of mass (COM). This forward momentum must be dissipated and the COM held within a newly formed base of support. The challenge of stopping on a slippery surface involves maintaining stability while transitioning from steady-state locomotion to steady-state stance. Experience with a slippery surface changes postural and gait characteristics to diminish the perturbing effect of the slip. The magnitude of the slip response diminishes quickly as the movement becomes more efficient. Our investigations revealed a typical slip response to a purely unexpected slip during gait termination including a lowering of the COM, an increased muscular response to support the body, a shortened step and an arm raise. Knowledge of and experience with the slippery surface quickly changed the slip response to reduce the perturbing effect of the slip and also to increase the efficiency of the response while smoothly transitioning from steady-state locomotion to gait termination. Parkinson’s disease impairs balance control, the ability to switch between motor tasks and also to stop within two steps. The need for a voluntary change in motor programs along with difficulty stopping and increased instability makes gait termination a potentially difficult task for someone with Parkinson’s disease (PD). The participants with PD used a slower, safer strategy to stop on non-slippery surfaces to compensate for their instability compared to age-matched controls. When a slip was first introduced during gait termination, the participants with PD continued to be less stable in the plane of progression than the control group. Despite the instability, the PD group was still able to integrate a balance-correcting response into a voluntary gait termination program. The ability to generate adaptive strategies to integrate the balance-correcting response into a voluntary gait termination program over multiple trials does not appear to be affected by PD; both the control group and PD group showed behavioural modifications according to repeated exposures to the slippery surface. Although participants with PD seemed slightly less stable and walked slower, their behavioural adaptations were similar to the control group.

The high incidence of falls and fall-related injuries among Canadians over the age of 65 continues to be a key public health issue. As the current proportion of individuals within this cohort of the population is predicted to double by the year 2031, the absolute number of individuals experiencing falls, fall-related injuries and subsequent hospitalization will increase dramatically. While a fall in any direction can lead to injury and reduced quality of life, lateral falls have been shown to be prevalent and can be particularly devastating because of the increased probability of hip fracture. Forward stepping tasks, whether initiated volitionally or by external perturbation, pose a challenge to stability, as they require the precise regulation of the spatial and temporal characteristics of the whole body centre of mass (COM) in relation to a changing base of support (BOS). Despite our understanding of both proactive and reactive mechanisms for balance control at movement initiation during such stepping tasks, there appears to be little understanding or consensus regarding the origins of age-related decline in mediolateral stability, which can manifest during the restabilisation phase, at movement termination. From this, the global objective of this thesis was to develop further understanding regarding such age-related differences in mediolateral dynamic stability control during the restabilisation phase of forward stepping. Notwithstanding the well documented differences between volitional and perturbation-evoked stepping until the time of foot-contact, we have proposed the control of the COM during the restabilisation phase of such stepping tasks to be a central determinant of age-related differences in mediolateral dynamic stability, common to both forms of stepping. We quantified the COM kinematics during the restabilisation phase and calculated the magnitude of incongruity between the peak and final, stable, COM position, in addition to the intertrial variability of this incongruity. Further, we analysed the orientation of the net ground reaction force (GRF) with respect to the COM, which allowed us to draw conclusions regarding the mechanisms that may be responsible for the age-related differences in the COM kinematics. To vary the challenge to control, we included conditions in which individuals were required to step with altered step width. In addition, we attempted to probe the extent and means by which individuals could alter the dynamics of stepping over time, with trial repetition. In general, we found that overshoots of the final COM position were common to all forms of stepping and may serve the functional role of simplifying reactive control during the restabilisation phase. The magnitude and intertrial variability of incongruity, however, were greater among the older adults during all forms of stepping. We believe such increased COM incongruity is likely indicative of greater instability within this group, which may be associated with the increased time required to reorient the net GRF in a manner necessary to oppose the total body angular momentum that developed during the swing phase. Particularly interesting was the use of proactive strategies by older adults, which may have the potential to offset instability that arises due to difficulty with reactive control during the restabilisation phase. The present work provides support for previous studies, which have suggested that the control of mediolateral stability may be particularly challenging for older adults. Further, our work provides evidence that the challenges associated with mediolateral stability control have important links to the restabilisation phase and are common to both volitional and reactive stepping. This work highlights the need to further explore the control of mediolateral stability and develop therapeutic interventions to reduce such incidence of instability among older adults.

Road and rail vehicles and aircraft rely mainly or solely on friction brakes. These brakes pose several problems, especially in hybrid vehicles: significant wear, fading, complex and slow actuation, lack of fail-safe features, increased fuel consumption due to power assistance, and requirement for anti-lock controls. To solve these problems, a contactless magnetic brake has been developed. This concept includes a novel flux-shunting structure to control the excitation flux generated by permanent magnets. This brake is wear-free, less-sensitive to temperature than friction brakes, has fast and simple actuation, and has a reduced sensitivity to wheel-lock. The present dissertation includes an introduction to friction braking, a theory of eddy-current braking, analytical and numerical models of the eddy-current brake, its excitation and power generation, record of experimental validation, investigation and simulation of the integration of the brake in conventional and hybrid vehicles.

The high incidence of falls and fall-related injuries among Canadians over the age of 65 continues to be a key public health issue. As the current proportion of individuals within this cohort of the population is predicted to double by the year 2031, the absolute number of individuals experiencing falls, fall-related injuries and subsequent hospitalization will increase dramatically. While a fall in any direction can lead to injury and reduced quality of life, lateral falls have been shown to be prevalent and can be particularly devastating because of the increased probability of hip fracture. Forward stepping tasks, whether initiated volitionally or by external perturbation, pose a challenge to stability, as they require the precise regulation of the spatial and temporal characteristics of the whole body centre of mass (COM) in relation to a changing base of support (BOS). Despite our understanding of both proactive and reactive mechanisms for balance control at movement initiation during such stepping tasks, there appears to be little understanding or consensus regarding the origins of age-related decline in mediolateral stability, which can manifest during the restabilisation phase, at movement termination. From this, the global objective of this thesis was to develop further understanding regarding such age-related differences in mediolateral dynamic stability control during the restabilisation phase of forward stepping. Notwithstanding the well documented differences between volitional and perturbation-evoked stepping until the time of foot-contact, we have proposed the control of the COM during the restabilisation phase of such stepping tasks to be a central determinant of age-related differences in mediolateral dynamic stability, common to both forms of stepping. We quantified the COM kinematics during the restabilisation phase and calculated the magnitude of incongruity between the peak and final, stable, COM position, in addition to the intertrial variability of this incongruity. Further, we analysed the orientation of the net ground reaction force (GRF) with respect to the COM, which allowed us to draw conclusions regarding the mechanisms that may be responsible for the age-related differences in the COM kinematics. To vary the challenge to control, we included conditions in which individuals were required to step with altered step width. In addition, we attempted to probe the extent and means by which individuals could alter the dynamics of stepping over time, with trial repetition. In general, we found that overshoots of the final COM position were common to all forms of stepping and may serve the functional role of simplifying reactive control during the restabilisation phase. The magnitude and intertrial variability of incongruity, however, were greater among the older adults during all forms of stepping. We believe such increased COM incongruity is likely indicative of greater instability within this group, which may be associated with the increased time required to reorient the net GRF in a manner necessary to oppose the total body angular momentum that developed during the swing phase. Particularly interesting was the use of proactive strategies by older adults, which may have the potential to offset instability that arises due to difficulty with reactive control during the restabilisation phase. The present work provides support for previous studies, which have suggested that the control of mediolateral stability may be particularly challenging for older adults. Further, our work provides evidence that the challenges associated with mediolateral stability control have important links to the restabilisation phase and are common to both volitional and reactive stepping. This work highlights the need to further explore the control of mediolateral stability and develop therapeutic interventions to reduce such incidence of instability among older adults.

The subject of this experimental investigation is to measure the dynamic stability derivatives in roll plane for an oscillating combat aircraft model by using forced oscillation technique. In forced oscillation technique the model is forced to oscillate around the center of gravity according to a harmonic motion of small amplitude and low frequency. The aerodynamic reactions are measured by an internal balance placed inside the model. The thesis presents a brief description of the test rig and the measurement system. The theory of dynamic stability derivatives and forced oscillation technique are also explained. The data is collected and analyzed by using a data acquisition system written with under the Labview programming language. Systematic analysis of the static and dynamic tests results and effect of various parameters (angle of attack, sideslip angle, oscillation frequency and amplitude, wind velocity) on these results are presented. Comparison of the present results with previous results obtained in other test facilities is also given. Design and manufacture process of a new angle of attack mechanism is also given in this thesis.

Inertial measurement units (IMUs) are being recognized as a portable and cost-effective alternative to motion analysis systems and have the potential to be introduced into clinical settings for the assessment of functional movement quality of the spine in patients with low back pain. However, uncertainties regarding sensor accuracy and reliability are limiting the widespread use and acceptance of IMU-based assessments into routine clinical practice. The objective of this work was to assess the performance of inexpensive wearable IMUs (Mbientlab MetaMotionR IMUs; Mbientlab Inc., San Francisco, USA; product specifications available in Appendix C) relative to conventional optical motion capture equipment (Vicon Motion Systems Ltd., Oxford, UK) in: 1) a controlled environment, and 2) an uncontrolled environment. The first study evaluated the performance of 2 IMUs in a controlled environment during simulated repetitive spine motion carried out by means of a motorized gimbal. Root mean square error (RMSE) and mean absolute measurement differences between cycle-to-cycle minimum, maximum, and range of motion values, as well as correlational analyses within IMUs and between IMUs and Vicon, in all movement directions (i.e., simulated flexion-extension (FE), lateral bending (LB), and axial twisting (AT)), were compared. Measurement error was low in all axes during all tests (i.e., ≤ 1.54°); however, low-to-moderate correlational results were found in one non-primary axis, and this axis changed depending on the direction of the movement (i.e., LB during FE-motion (0.244 ≤ R ≤ 0.515), AT during LB-motion (0.594 ≤ R ≤ 0.795), and FE during AT-motion (0.002 ≤ R ≤ 0.255)). The second study was designed to assess the performance of the IMUs in an uncontrolled environment during repetitive spine FE in human participants. Absolute angles and local dynamic stability were compared for individual IMUs (which were placed over T10-T12 spinous processes, and the pelvis) as well as for relative motion between IMUs. Maximum finite-time Lyapunov exponents (λmax) were used to quantify local dynamic stability and were calculated using both FE and the sum of squares (SS) from measured spine kinematics. It was found that the IMUs have acceptable performance in all axes when tracking motion (RMSE ≤ 2.43°); however, low-to-moderate correlational results were found in one non-primary axis (0.987 ≤ RFE ≤ 0.998; 0.746 ≤ RLB ≤ 0.978; 0.343 ≤ RAT ≤ 0.679). In addition, correlations between λmax estimates were high; therefore, local dynamic stability can be accurately estimated using both FE and SS data (0.807 ≤ 〖ICC〗_2,1^FE ≤ 0.919; 0.738 ≤ 〖ICC〗_2,1^SS ≤ 0.868). Correlation between λmax estimates was higher when using FE data for individual sensors/rigid-body marker clusters; however, correlation was higher when using SS data for relative motion. In general, the results of these studies show that the MetaMotionR IMUs have acceptable performance in all axes when considering absolute angle orientation and motion tracking, and measurement of local dynamic stability; however, there is low-to-moderate correlation in one non-primary axis, and that axis changes depending on the direction of motion. Future research will investigate how to optimize performance of the third axis for motion tracking; it will also focus on understanding the significance of the third axis performance when calculating specific outcome measures related to spine movement quality.