The linear actuator is widely used in the industrial and aerospace arenas. The application of the linear actuator varies. The ball screw type linear actuator or ball screw system is one design. The ball screw is a mechanical system that converts rotation motion into a linear motion. The ball screw linear actuator, compared with other linear actuators, has better efficiency, higher speed, less noise, and higher load capacity. Ball screw linear actuators are used in a number of areas, such as coordinated measuring machines, 3D printers, and aerospace actuators. In this research, the industrial sponsor provided a ball screw linear actuator, and they required its accuracy to be improved. The linear actuator suffers from an accuracy problem due to various reasons. One of the major problems is nonlinear friction, which makes it difficult to estimate using the simple friction model. In this thesis, a LuGre friction model is introduced and applied to the ball screw system. The sponsor’s ball screw system includes the ball screw sliding table, AC servo drive, AC servo motor, and a linear encoder sensor. The hardware control system for the ball screw system needs to be built. Therefore, this thesis describes how a custom ball screw control system was built. The control hardware ball screw system includes a microcontroller and a custom-made digital-to-analog converter. The linear encoder position sensor’s reading methods were tested and implemented in the microcontroller. A custom digital-to-analog converter was made and tested. The control algorithms based on the LuGre friction compensator are discussed and were simulated in the Matlab Simulink environment. Then, the physical implementation of the control algorithms on ball screw system hardware were made. Finally, a new proposed control method based on the LuGre friction model performed best in terms of accuracy consistence and tracking compare to the other mentioned controllers. / Thesis / Master of Applied Science (MASc)

Aujourd'hui, le soudage par friction-malaxage (FSW) a attiré beaucoup d'attention dans les secteurs universitaires et industriels. Malgré ses avantages importants par rapport aux techniques de soudage par fusion, il n'est pas largement utilisé dans l'industrie actuelle, principalement en raison des coûts d'équipement élevés et des redevances. Certaines autres raisons sont les forces de processus élevées, le besoin d'un serrage puissant, le manque de directives concernant la fenêtre de travail efficace des paramètres du processus et l'effet du traitement thermique après soudage. En outre, il est nécessaire d'avoir une conception d'outils appropriée pour différentes applications, géométries et configurations de soudage. Pour surmonter ces problèmes, une technique FSW rentable appelée FSW à angle droit(RAFSW) a récemment été introduite par l'équipe PI2/ REGAL de l'Université Laval. Il est essentiel de développer et d'étudier ses différents aspects pour rendre la technique fiable pour une large utilisation industrielle. Dans cette thèse, l'objectif est de fournir aux utilisateurs potentiels des directives et des fenêtres de travail efficaces pour les paramètres du processus de soudage à des vitesses de soudage élevées applicables à différentes configurations et géométries. Une conception d'outils appropriée pour différentes applications est également un autre aspect à explorer. De plus l'effet du traitement thermique après soudage sera étudié. Enfin, la technique sera adaptée pour être mise en œuvre sur des routeurs CNC de grande taille et à faible coût afin d'assembler de grands panneaux en aluminium à de faibles forces de soudage sans avoir besoin d'un serrage solide. / Today, friction stir welding (FSW) has attracted much attention in both academic and industrial sectors. In spite of its prominent advantages over fusion welding techniques, it is not widely used intoday's industry mainly due to high equipment costs and royalties. Some other reasons are high process forces, need for powerful clamping, lack of guidelines regarding efficient working window of process parameters and the effect of post weld heat treatment. Furthermore, it is needed to have aproper tool design for different applications, geometries, and welding configurations. To overcome these issues, a cost-effective FSW technique called FSW at right angle (RAFSW) has been recently introduced by PI2/REGAL team at Laval University. It is essential to develop and study its different aspects to make the technique reliable for widespread industrial use. In this thesis, the aim is to provide potential users with guidelines and efficient working windows for welding process parameters at high welding speeds applicable for different configurations and geometries. Proper tool design for different applications is another aspect to be explored, as well. Moreover, the effect of postweld heat treatment will be studied. Finally, the technique will be adapted to implement on big-size,low-cost CNC routers to assemble large aluminum panels at low welding forces without the need forsturdy clamping.

This work treats dual-plane automatic ball balancing of elastically-mounted cylindrical rotors. The application is primarily to systems with a vertically-oriented single-bearing support, but extension is also made to horizontally-oriented single-bearing support as typically found in a vehicle wheel. The rotor elastic mounting includes three translational degrees of freedom for the body geometric center and three rotational degrees of freedom. Damping is included for each of these six degrees of freedom. The model for the automatic ball balancer consists of up to two arbitrarily-located hollow circumferential races, each of which contains up to two sliding particles. The friction model for the particles includes both viscous and Coulomb friction forces. Of considerable complexity is the logic path for the individual particles being either in motion or stationary relative to the rotor. The exact equations of motion for the overall system are derived via a Newtonian approach. Numerical-integration results show that the balancer performance depends strongly on the friction levels as well as the operating speed of the body. Simulations conducted with a pure static imbalance show that ideal automatic balancing is possible only for vertical-axis rotors that have zero Coulomb friction levels between the balancing particles and the races. Simulations with a horizontal-axis statically-imbalanced rotor show that an automatic balancer can improve performance for certain operating speeds and non-zero Coulomb friction levels in the presence of gravitational forces. Simulations conducted with a pure dynamic imbalance show that there is no inherent mechanism to counteract rotational displacements of the rotor about its geometric center. As a result, the balancing particles exhibit several phenomena described in previous works such as synchronous motion and oscillatory behaviors within their respective races. Simulations for an arbitrarily located imbalance show that rotor performance can be improved using dual-plane balancing techniques for certain operating speeds and Coulomb friction levels. Due to the inherent complexity in eliminating an arbitrarily located mass imbalance, the system is generally unable to reach a perfectly balanced configuration, but performance can be improved for carefully-selected initial conditions. / Ph. D.

Sensitivity analysis is one of the most prominent gradient based optimization techniques for mechanical systems. Model sensitivities are the derivatives of the generalized coordinates defining the motion of the system in time with respect to the system design parameters. These sensitivities can be calculated using finite differences, but the accuracy and computational inefficiency of this method limits its use. Hence, the methodologies of direct and adjoint sensitivity analysis have gained prominence. Recent research has presented computationally efficient methodologies for both direct and adjoint sensitivity analysis of complex multibody dynamic systems. Multibody formulations with joint friction were developed in the recent years and these systems have to be modeled by highly non-linear differential algebraic equations (DAEs) that are difficult to solve using numerical methods. The sensitivity analysis of such systems and the subsequent design optimization is a novel area of research that has been explored in this work. The contribution of this work is in the development of the analytical methods for computation of sensitivities for the most commonly used multibody formulations incorporated with joint friction. Two different friction models have been studied, capable of emulating behaviors of stiction (static friction), sliding friction and viscous drag. A case study has been conducted on a spatial slider-crank mechanism to illustrate the application of this methodology to real-world systems. The Brown and McPhee friction model has been implemented using an index-1 formulation for computation of the dynamics and sensitivities in this case study. The effect of friction on the dynamics and model sensitivities has been analyzed by comparing the sensitivities of slider velocity with respect to the design parameters of crank length, rod length, and the parameters defining the friction model. Due to the highly non-linear nature of friction, it can be concluded that the model dynamics are more sensitive during the transition phases, where the friction coefficient changes from static to dynamic and vice versa. / Master of Science / Mechanisms have been in existence since the earliest days of technology and are more relevant than ever in this age of robotics, artificial intelligence and space exploration. Innovations like myoelectric and neural prosthetics, legged robotics, robotic surgeries, advanced manufacturing, extra-terrestrial vehicles and so on are the modern day manifestations of the traditional mechanisms that formed the backbone of the industrial revolution. All of these innovations implement precision controlled multibody dynamic systems as part of their function. This thesis explores the modelling of such dynamic systems using different mathematical formulations. The contribution of this work is the incorporation of friction in the formulation of such systems. The performance of any dynamical system depends on certain parameters, which can be optimized to meet a certain objective criteria. This is achieved by performing a sensitivity analysis with respect to those parameters on the mathematical formulation of the mechanism. The derivation of this approach has been explored in this thesis. For the benefit of the reader, the application of this method has been discussed using a case study of a simple 3-dimensional slider crank mechanism.

A small shear sensor utilizing an array of carbon nanotubes to support a sensor head was developed for use in steady, high speed, 2D flow. The sensor is a non-intrusive, direct measurement device with a 2 x 2 mm square sensor head surrounded by a small gap on each side (~0.004 inches). The translation of the sensing element is due to the nanotubes bending when a shear force is applied to the sensor head. Displacements are measured by an interferometric technique using fiber-optics to measure the distance the sensor head travels by viewing a polished side of the head. The fiber-optical displacement sensor is bonded to a stationary substrate so that all measurements are relative to a fixed position. Arrays of carbon nanotubes were grown on bare 2 x 2 mm square silicon chips. The nanotubes were grown to heights of 75 microns with a thin layer of amorphous carbon on top. The silicon chips were then flipped, and the amorphous layer of carbon was bonded to bare 1 x 1 cm silicon substrates, making the bottom of 2 x 2 mm silicon chip the sensor head. The sensors were calibrated at Luna Innovations using a point-load technique. Four of the six sensors could not be successfully calibrated because they were fatally damaged during the last step of the calibration process. Wind tunnel tests were conducted on the one sensor that survived the calibration. An arrangement was designed and built from aluminum to test the performance of the sensor in the Virginia Tech Supersonic Wind Tunnel. Seven test runs were conducted in this cold-flow facility at a nominal Mach number of 2.4 and stagnation pressures ranging from 50 - 90 psia. Two test runs gave skin friction values 3 - 20% lower than those values predicted by indirect measurement techniques before the sensor was damaged. While these first results are encouraging, further studies are clearly needed. Due to distinct anomalies in the displacement data during test run 3, it was concluded that the sensor was damaged during this run. Possible explanations of the failure of this sensor are offered along with suggestions for future work. / Master of Science

Clay consolidation has generally been considered from a macro-scale perspective by measuring the macro-scale compression of a clay soil over time. Clay particles in consolidation tests experience shear and normal forces at the inter-particle level due to force applied to the soil at the macro-scale. These shear and normal forces cause the particles to slide at the micro-scale and produce macro-scale changes in soil volume and shape. By considering the inter-particle interactions at the micro-scale, the shear force - normal force - velocity relationship can be described by the Rate Process Theory (RPT). This research investigated the use of the RPT for analyzing sliding at individual clay particle contacts during secondary compression to describe macro-scale clay behavior. The novel micro-scale friction experiments conducted in this research demonstrated that an Atomic Force Microscope (AFM) can be used to obtain coefficient of friction (μ) measurements for montmorillonite. This method allows for the measurements to be performed over spatial scales of a few microns, can be done under dry conditions or a wide range of aqueous solutions, and requires no calibration beyond making a few microscopic measurements of the probe. Control tests of silica on mica (μ = 0.29 ± 0.02) agree with literature values where limits indicate one standard deviation.μ values for wet and dry sodium montmorillonite were determined to be 0.20 ± 0.03 and 0.72 ± 0.03, respectively. The micro-scale AFM and macro-scale triaxial shear, ring shear, and direct shear experimental data ofμ as a function of sliding velocity were found to match well with those calculated using common RPT parameter values. The activation energy for the macro-scale triaxial shear and corresponding micro-scale friction regime experiments fall within the expected range for pure montmorillonite of 84–109 kJ/mol. Additionally, the micro-scale and macro-scale experimental results fall within the expected range for the number of bonds per unit of normal force of 10^7–10^9 bonds/N. A discrete element method (DEM) model was developed to calculate thin, disk-shaped clay particle movement in three dimensions during compression using the RPT as a contact model. The DEM compression results were compared to macro-scale consolidation experiments conducted on the same reference clay as the micro-scale AFM experiments. The influences on the compression of the number of bonds at each clay contact per unit of normal contact force and the activation energy were quantified. Increasing the activation energy decreased the compression, as expected. Similarly, increasing the number of bonds per unit of normal force at the contacts decreased the compression, as expected. Realistic clay fabrics with varying particle sizes, particle size distributions, and aspect ratios led to a compression model with behavior similar to the macro-scale laboratory compression tests. This research provides evidence of the close correspondence between macro-scale and micro-scaleμ measurements and contributes to multi-disciplinary understanding of factors that control friction between clay particles and deformation of clay masses. The results from this work can be applied to a wide range of time-dependent phenomena such as clay secondary compression, shear deformation, and fault dynamics behavior. / Ph. D.

Pavement friction have become a characteristic of interest due to its impact on road safety. The demand of the transportation agencies for equipment to measure the friction of their pavements grew. Different companies developed in parallel way different devices to satisfy that demand. This generate that the different transportation agencies are using different devices to measure the same characteristic. In order to determine a threshold for the adequate friction levels, the need to compare those data was created. Several attempts to harmonize those measurements have been developed, but have demonstrate that not produce harmonious results among some devices. Also, there are new equipment like the Continuous Friction Measurement Equipment (CFME) that offer some advantages compared to the traditional Locked Wheel Trailer (LWST) that also generate the need to compare historical data to the collected with the new device. This thesis is proposing an interconversion method between the measurements from a CFME as the SCRIM and the LWST. / Master of Science

Yes / Results and analysis from investigations into the behaviour of the interfacial layer (Tribolayer) at the friction interface of a brake friction pair (resin bonded composite friction material and cast iron rotor) are presented in which the disc/pad interface temperature has been measured using thermocouple methods. Using a designed experiment approach, the interface temperature is shown to be affected by factors including the number of braking applications, the friction coefficient, sliding speed, braking load and friction material. The time-dependent nature of the Tribo-Iayer formation and the real contact area distribution are shown to be causes of variation in interface temperatures in friction braking. The work extends the scientific understanding of interface contact and temperature during friction braking.

No

yes / To investigate the heat partition on a vehicle disc brake, a small scale test rig with one contact interface was used. This allowed the disc/pad contact temperatures to be measured with fast-response foil thermocouples and a rubbing thermocouple. Based on the experimental conditions a 3D symmetric disc brake FE model has been created. Frictional heat generation was modelled using the ABAQUS finite element analysis software. The interface tribo-layer which affects heat partitioning was modelled using an equivalent thermal conductance value obtained from the authors¿ previous work. A 10 second drag braking was simulated and the history and distribution of temperature, heat flux multiplied by the nodal contact area, heat flux leaving the surface and contact pressure was recorded. Test rig and FE model temperatures were compared to evaluate the two methods. Results show that heat partitioning varies in space and time, and at the same time contact interface temperatures do not match. It is affected by the instantaneous contact pressure distribution, which tends to be higher on the pad leading edge at the inner radius side. They are also affected by the thermal contact resistance at the components contact interface. / IMechE