No description available.

Many of the undesirable side effects that occur during orthodontic treatment can be attributed directly to a lack of understanding of the physics involved in a given adjustment of an orthodontic appliance. A large number of variables in orthodontic treatment are not within our control, such as growth and tissue response to appliances. However, the force placed on the tooth should be a controllable variable (1), and careful study of the physics underlying our clinical application, can help in reducing those undesirable side effects. If researchers and clinicians can quantify the force systems applied to the teeth, they can better understand clinical and histologic responses. Orthodontic force systems used in everyday orthodontic mechanics are considered indeterminate force systems, in other words, there are too many unknowns to determine the different components of these force systems. Until recently, much of the literature was restricted to experimental two-dimensional analyses of the biomechanical aspects of orthodontic force systems, and computer modeling of three-dimensional analyses. Very little evidence exists in the literature regarding three dimensional experimental measurement and analysis of orthodontic force systems (2). Force system measurements were made on one or two tooth models, however in order for us to understand the orthodontic force systems we need to simultaneously, measure in 3D, the forces being applied on every tooth in the dental arch. With the very recent technological advances in force/torque sensors technology, data acquisition and data representation, it became possible to measure those forces and reveal the force systems we are applying to the dentition. The purpose of this PhD research study is the design and construction of an experimental device that is capable of revealing the details of the force systems used in modern day orthodontic mechano-therapy of continuous arch technique. / Orthodontics

Vibration exposure can occur at work, commuting between home and work, and in leisure activities. Any form of transportation will expose humans to some degree of vibration. Exposure to vibration can cause health problems, but more likely comfort problems. Health problems are normally related to back pain. Comfort on the other hand is related to both physiological and psychological factors, which can have a wide range of effects from a general annoyance to a reduced work capability. The standard ISO 2631-1 (1997) provides a guidance, which can be used to measure, evaluate and assess effects of whole-body vibration to discomfort. The standard allows several interpretations, which can lead to different results, as the standard does not provide an explicit guidance for selecting which axes and locations to measure and which averaging method to use for evaluating the axes. The suggested averaging method is the root mean square (r.m.s.) method, but additionally vibration dose value (VDV) can be used. This can lead to different results, as VDV emphasises shocks more than the r.m.s. method. The standard guides to measure and evaluate at least the seat translational axes, but the additional nine axes from the seat, backrest and floor are not mandatory. However, this can result in a different comfort value, as the values from the measured axes are combined. So taking into account all possible interpretations the assessment can vary significantly for the same environment. The selection of the averaging method is not a technical issue, as both methods are supported by all commercial equipment. However, it is rare that more than three axes are possible to be measured with typical whole-body vibration measurement equipment, thus the majority of studies have published results based on only the seat translational axes. Especially the rotational axes have been missing in most studies. The full method (i.e. using all possible axes to calculate the comfort value) of ISO 2631-1 (1997) has been rarely used and there is very little information on how accurate the method is for assessing discomfort in a multi-axis environment. There are only a few studies that have used the full method, but there are no known studies which have actually validated the full ISO 2631-1 method. The objective of the thesis was to validate and, if necessary, to improve the full method of the ISO 2631-1 standard for evaluating discomfort from whole-body vibration in a multi-axis environment. It was assumed that the ISO 2631-1 method can be used to predict discomfort in practice, but there are a relatively low number of studies to confirm this. Frequency weightings have been the focus of many published studies and it was assumed that these are broadly correct. Other aspects of the ISO 2631-1 method are the focus of this thesis. The goal was to keep a backward compatibility to previous studies and the current commercial equipment, thus several limitations were defined for the improvement of the standard. Several laboratory experiments, field measurements, and field and laboratory trials were conducted to validate the standard method. At first it was concluded that practical equipment for measuring 12-axis data was needed as there was no commercial system available. The equipment and software was validated in two experiments, which showed that simple and affordable components could be used to develop equipment for the full method. Even though the standard does not include information about a six-axis sensor for measuring both translational and rotational axes, there was a method to validate the sensor. The first field study included measuring several machines using all twelve axes. The analysis showed that the seat and backrest translational axes will contribute about 90 % of the overall vibration total value of the standard method, thus very little justification was found for including the seat rotational and floor translational axes. Similar results were found based on the data from the previous 12-axis studies. It was also found that the neglected axes could be compensated with a factor for estimating the overall vibration total value including all twelve axes. As the overall vibration total value is directly related to the number of used axes, the compensating factors can be used to compare results which used different axes. The laboratory trial confirmed the results from the field study, and it was concluded that sufficient accuracy to predict discomfort can be achieved using just the seat translational axes, even though the correlation improved when more axes were included. It was found that the evaluation of discomfort was improved by the use of the frequency weighting curves and the r.m.s. averaging method. However, as the multiplying factors degraded correlation, it was concluded that a new set of factors should be calculated. The new factors showed that a higher emphasis on the seat horizontal axes should be given (x=2.7, y=1.8 and z=1.0). The new factors improved the correlation systematically for all subjects. The field trial showed a similar trend, where optimised multiplying factors improved the correlation, but it was also noted that different multiplying factors are required for different environments, thus a procedure to optimise the standard method to different environments was developed. The trial showed systematic behaviour and the optimised multiplying factors were best for all subjects and groups. Keywords: Discomfort, whole-body vibration, standard, ISO 2631-1, multi-axis, multiplying factors

A multi-axis compact positioner is designed and implemented in this thesis. The single-moving-part positioner is designed to move in the magnetic field generated by a superimposed concentrated-field permanent magnet matrix. The compact positioner is primarily for the stepping and scanning applications that require 3-DOF planar motions. In which, the travel ranges in two orthogonal directions are on the order of 100 mm. The moving platen, which has the size of 185.4 mm x 157.9 mm and weighs 0.64 kg, mainly comprises of a plastic frame and six copper coils. It is actuated in the horizontal plane by flowing six independent electric currents into the coils. The platen is supported against gravity by three air bearings. Force calculation is based on the Lorentz force law. With a current-carrying rectangular coil placed in the magnetic field of the supper-imposed Hallbach magnet matrix, the force acting on the coil is calculated by volume integration. The distances between the longer sides and between the shorter sides of the rectangular coil are designed to fit a half pitch and one pitch of the Hallbach magnet array, respectively. Therefore, the volume integration is simplified considerably. The force-current relation for the entire platen with six coils is derived. Three Hall-effect sensors are attached to the moving platen to measure the magnetic flux densities at the center points of the sensors. The position of the moving platen is determined by the field solution of the magnet matrix and the magnetic flux densities sensed by the Hall-effect sensors. A new discrete PID-like controller is proposed and tested. For the step responses with the step sizes within 1000 micrometers, the overshoots and the steady state errors are negligible. The achieved velocity in x is 10.50 cm/s and in y is 16.25 cm/s, respectively. The achieved acceleration in x is 43.75 cm/s^2 and in y is 95.59 cm/s^2, respectively. The achieved travel ranges are 15.24 cm in x, 20.32 cm in y, and 0.21 rad in the rotational motions about the vertical axis. The positioning resolution in x and y is 8 micrometers with the rms positioning error of 6 micrometers. The positioning resolution in rotation about the vertical axis is 130 microrad.

Sequential single-axis vibration testing strategies often produce over-testing when qualifying system hardware. Multi-axis excitation techniques can simulate realistic service environments, but the hardware and testing strategies needed to do so tend to be costly and complex. Test engineers instead must execute sequential tests on single-axis shaker tables to excite each degree of freedom, which the previous two decades of vibration testing literature have shown to cause extensive over-testing when considering cross-axis responses in assessing the severity of the applied test environments. Traditional assessments assume that the test article responds only in the axis of excitation, but often significant response occurs in the off-axes as well. This paper proposes a method to address the over-testing problem by approximating a simultaneous multi-axis test using readily-available, single-axis shaker tables. By optimizing the angle of excitation and the boundary condition through dynamic test fixture design, the test article can be tested using a Single-Input, Multiple-Output (SIMO) test in a way that approximates a Multiple-Input, Multiple-Output (MIMO) test. This paper shows the proposed method in simulation with a 2D finite element box assembly with removable component (BARC) model attached to springs with variable stiffness. The results include quantified test quality assessment metrics with comparison to standard sequential testing. The proposed method enables access to rapid, approximate, multi-axis testing using existing hardware, thereby reducing the over-conservatism of sequential single-axis tests and requisite over-design of systems.

Master of Science / Material extrusion is a common form of 3D printing that has historically been limited to producing prototypes, models, and low load-bearing parts. This is primarily because parts are manufactured layer-by-layer, resulting in poor adhesion along the build direction, and machines struggle to print with high-strength polymers, which tend to shrink significantly as they cool. However, one way to address these limitations is to use fiber-reinforced materials in combination with multi-axis deposition strategies. In material extrusion, embedded fibers will align themselves along the deposition path, providing structural, thermal, and chemical improvements. Multi-axis toolpathing can enable the deposition of this fiber-filled material in full 3D along a part's expected stress paths. This is possible using a complex kinematic system like an industrial robot arm that can rotate the angle of the tool relative to the part as it is printing. The objective of this work was to develop and test a tool capable of multi-axis continuous carbon fiber reinforcement, which required a dedicated cutting mechanism to shear the fiber at the end of each deposition path, control over the amount of fiber used, and a slender tool profile to avoid collisions during multi-axis printing. The findings of this work revealed that while the use of continuous carbon fiber further reduced the adhesion between deposition paths, it substantially improved the strength of the part along them. To validate the multi-axis capability of the system, a toolpath was generated for a curved tensile bar. The results showed that the continuous carbon fiber multi-axis toolpath resisted a load 820.57% higher than an XY-planar sliced part printed with traditional filament, confirming the effectiveness of the presented approach. Multi-axis motion can also be used for avoiding support material requirements. In traditional 3-axis material extrusion, steep overhanging features often require additional, sacrificial material to be printed underneath. This leads to longer print times, more material waste, and a poor surface finish left behind on the final part. To minimize the amount of support material required, various techniques have been explored, including changing the toolpath, part geometry, or material processing parameters. However, none of these techniques have been successful in eliminating the need for supports entirely. A promising approach to address this issue is multi-axis material extrusion, where the angle of the printing tool and the direction of the layers can be precisely controlled during the printing process. This technique can be used to ensure that the tool is always extruding material onto a well-supported surface, rather than over thin air. However, research to date has not yet fully explored how the range of achievable overhang features changes as the tool is rotated. To address this knowledge gap, this work used an industrial robot arm equipped for material extrusion to investigate the relationship between tool angle, build direction, and achievable overhang threshold. The results showed that the same overhang limitations that exist in the XY plane will rotate with the tool and are unaffected by gravitational forces. These findings provide valuable insights for advancing the use of multi-axis material extrusion in the production of complex and intricate 3D objects without the need of supports.

It is believed that structures and actuation systems should be tightly integrated together in the future to create fast moving, efficient, lightweight dynamic machines. Such actuated structures could be used for morphing aircraft wings, lightweight actuated space structures, or in robotics. This requires actuators to be distributed through the structure. A tensegrity structure is a very promising candidate for this future integration due to its potentially excellent stiffness and strength-to-weight ratio, and the inherent advantage of being a multi-element structure into which actuators can be embedded. Development of these machines will utilise expertise in several fields, involving kinematics, dynamics, actuation and multi-axis motion control. The research presented in this thesis concerns the study of multi-axis actuated tensegrity structures. A form-finding method has been developed to find stable geometries and determine stiffness properties of the type of tensegrity structure proposed. It has been shown that a tensegrity structure, with practical nodes of finite size, can be designed with actuated members to give shape-changing properties while potentially allowing a good stiffness to mass ratio. An antagonistic multi-axis control scheme has been developed for the tensegrity structure. The describing function technique has been used to analyse the dead band controller in the control scheme, giving a stability criterion. An experimental actuated tensegrity system has been designed and built incorporating pneumatic muscles controlled by switching valves. Mathematical models for the experimental actuated tensegrity system have been developed in detail, including the pneumatic actuation system and the structure geometry. The dynamic behaviour of the tensegrity system has been investigated via several simulation studies, using the developed models and the proposed control scheme. Experimental validation has been successfully conducted. The multi-axis control scheme can accurately control the tensegrity structure to achieve shape changes while maintaining a desired level of internal pre-load. The mathematical models can be used as a basis for further development.

No description available.

In modern manufacturing industries, many applications require precision motion control of multi-agent systems, like multi-joint robot arms and multi-axis machine tools. Cutter (end effector) should stay as close as possible to the reference trajectory to ensure the quality of the final products. In conventional computer numerical control (CNC), the control unit of each axis is independently designed to achieve the best individual tracking performance. However, this becomes less effective when dealing with multi-axis contour following tasks because of the lack of coordination among axes. This dissertation studies the control of multi-axis machine tools with focus on reducing the contour error. The proposed research explicitly addresses the minimization of contour error and treats the multi-axis machine tool as a multi-input-multi-output (MIMO) system instead of several decoupled single-input-single-output (SISO) systems. New control schemes are developed to achieve superior contour following performance even in the presence of disturbances. This study also extends the applications of the proposed control system from plane contours to regular contours in R3. The effectiveness of the developed control systems is experimentally verified on a micro milling machine.

Purpose/Hypothesis: Mal de Debarquement Syndrome (MdDS) is a rare condition in which those afflicted perceive a chronic rocking or swaying sensation, often relieved when in motion and symptomatic when still. Etiology is uncertain; therefore, treatment options are limited. While there is reported success with medication, optokinetic stimulation or transcutaneous magnetic stimulation, there is no single treatment that works for all patients. This retrospective chart review investigated rehabilitation outcomes following sensorimotor, multi-axis, rotational (SMART) training to address MdDS symptoms. Number of Subjects: Forty-nine Materials and Methods: Forty-nine patients participated in 10-20 sessions of SMART training, with integrated use of a visual targeting system and physical therapy. Between sessions, patients were instructed to perform mindfulness breathing, relaxation and grounding techniques. Pre- and post-training Dizziness Handicap Inventory (DHI), 4-item Dynamic Gait Index (DGI), and computerized posturography including Sensory Organization Test (SOT) were assessed. Subjective change following rehabilitation was tracked at discharge, 5 weeks, 3 months, 6 months and 1 year post-training. Results: Mean age (SD) of patients was 52.9 (12.6) years with the majority (n=47) being female. Mean time from onset of symptoms (SD) was 50.8 (87.8) months suggesting chronic symptoms. At discharge, 42 of 49 patients reported improvements, with nearly half (n=24, 48.9%) of all patients reporting marked or moderate improvement in symptoms; whereas, 14 (28.6%) reported minimal improvement in symptoms. Based on paired t-tests, all outcome measures – DHI, MdDS severity Visual Analog Scale (VAS), Motion VAS, 4-item DGI, and SOT - improved significantly (p < 0.001) from initial evaluation to discharge. Several personal factors were associated with rehabilitation outcomes based on bivariate correlations. With some variation, patients sustaining improvements at 1 week post-discharge, generally continued to sustain at 5 weeks, 3 months, 6 months and 1 year. Conclusions: SMART training plus physical therapy resulted in improved performance outcomes and in significant reduction or resolution in MdDS symptoms. This study provides early evidence that this method of training has promising potential to aid in the management or recovery of MdDS. Clinical Relevance: MdDS is disorder with no specific cure. Treatment is limited. SMART training may serve as an effective outcome to reduce or resolve symptoms associated with MdDS.