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Sveriges samlade skogsindustriföretag förutspår en förlust av marknadsandelar, eftersom man inte lyckas hålla samma tempo på produktionen som många andra länder. En orsak till detta är att skogsmaskinerna är för långsamma. Skotarna, vars uppgift är att förflytta virket från avverkningsplatsen till en uppsamlingsplats, bär en stor del av skulden. De hinner inte transportera virket tillräckligt snabbt. För att råda bot på detta ska en ny typ av skotare utvecklas, vars plattform inspireras av försvarsteknologi. Tack vare sin långa erfarenhet av banddrivna fordon har BAE Systems Hägglunds i Örnsköldsvik fått i uppdrag att konstruera en prototyp, som baseras på deras framgångsrika bandvagn, BvS10.[A]   Skotaren går under namnet Hybrid Forestry Truck (HFT), och är en banddriven skotare med fyra larvband. Framdrivningen är av seriehybridtyp, vilket betyder att en generator drivs av en dieselmotor. Dieselmotorn förser sedan fyra elmotorer, en i varje bandställ, med ström.   Detta examensarbete går ut på att utveckla länken mellan elmotorn och drivhjulen till banden. Tre designkoncept presenteras och analyseras. Den, i författarens åsikt, mest ideala lösningen utvecklas sedan vidare mer detaljerat. Många andra examensjobb, samt interna analyser av Hägglunds själva, har gjorts på HFT. Detta innebär att många kraftsituationer och belastningsfall redan är uträknade, samt att de flesta komponenterna till slutväxeln är utvalda.

A multi-unit tracked vehicle such as a continuous haulage system is widely used in underground mining applications due to its high mobility and payload capacity on rugged and soft terrain. To automate such a system, a high fidelity model of a tracked vehicle is essential in designing a controller for each tracked vehicle in the system, and a system model is required to simulate its response to input commands. This thesis presents the 2-D mathematical models of a tracked vehicle and a multi-unit tracked vehicle. All existing track-terrain interaction models are investigated and modified. By employing the modified track-terrain interaction model and applying Newton's second law of motion, the equations of motion of both single and multi-unit tracked vehicles can be derived. Computer programs for simulating the motions of these tracked vehicles on level ground have been implemented on a digital computer based on the derived system of differential equations. The fourth-order Runge-Kutta and Keun's methods are adopted to numerically integrate these differential equations. The simulation results clearly show that the programs can accurately predict the motion of a tracked vehicle maneuvered on horizontal plane, and closely predict the response of a multi-unit tracked vehicle operated on level ground its command inputs. / Master of Science

Vibrations caused by rough road excitations influence tracked vehicle dynamic performance. Good capabilities of such vehicles like high mobility, manoeuvrability and comfort are guaranteed by optimal suspension systems. The suspension systems of tracked vehicles are exposed to extreme operating conditions. This creates a conflict between ride comfort and handling that is even greater than the conflict between ride comfort and handling for general road vehicles. Tracked vehicles must be able to traverse not only rough roads but also smooth terrains. The challenges in developing an optimized suspension system for tracked vehicles include the high and changeable damping forces required for tracked vehicles crossing rough terrains. The use of active or semi-active suspension systems overcomes the limitations inherent in the conventional passive suspension. However, active suspension systems are expensive, complicated to design and have high power demand. Thus, semi-active suspension systems have emerged as a good compromise between active and passive suspension system. There is considerable current research on the applications of magnetorheological (MR) fluid dampers for semi-active suspensions of executive brand of some cars. However, there is very little research on semi-active devices for tracked vehicle suspension. In fact, currently, there is no commercially available large scale MR dampers in the market that produce the high damping force to suit such applications. In response to these requirements, this research proposes a novel semi-active tracked vehicle suspension system that uses MR dampers to improve the ride comfort and handling characteristics of tracked vehicles. It also assesses the dynamics of the new suspension with various semi-active control methods. This study is conducted in four phases. The first phase provides a numerical investigation on the dynamic performance of a seven-degrees-of-freedom (7-DOF) passive suspension model of the armour personnel carrier (APC) M113 tracked vehicle. The numerical investigation considers the influence of variation of five suspension design parameters on the vehicle dynamic performance. These parameters include number, locations of hydraulic shock absorber, damping coefficient, suspension and wheel stiffnesses. The results indicate that the optimal suspension performance is attained by using two or three dampers. The best locations for these dampers are at the extreme road wheels i.e. the first, second and last road wheel stations. Moreover, the vehicle performance is reduced when the damping coefficient is increased. Additionally, low suspension stiffness offers better vehicle ride while high wheel stiffness degrades the vehicle performance. These results identify the limitations inherent in the conventional passive suspension. For the second phase, the dynamic characteristics of the hydraulic, hydro-gas and MR dampers are experimentally measured and fitted using the Chebyshev orthogonal functions to produce the restoring force surfaces for each damper, which are compared. On one hand, the restoring force surfaces of the hydraulic and hydro-gas dampers show fixed properties at specified frequencies. On the other hand, the restoring force surfaces of the MR dampers show properties that can be controlled at the same specified frequencies by the variation of the applied current levels. Thus, the potential and the effectiveness of the controllable properties of MR dampers for semi-active vibration control is demonstrated. Also, in this phase, the best set of parameters to use in the modified Bouc-Wen model to characterise the MR dampers, has been derived. The third phase of the project is also experimentally based. A new and novel test rig which represents the 7-DOF scaled suspension model of the tracked vehicle is designed and fabricated. The primary purpose of the test rig is to evaluate the performance of the proposed suspension with MR dampers. Furthermore, experiments are conducted on the test rig to evaluate some semi-active control methods and their effectiveness in reducing suspension vibration. The results show that the use of two or three MR dampers at the extreme wheels offers optimal suspension performance. This confirms the numerical results that are derived from the full scale passive suspension system with hydraulic dampers. The experimental results also show that skyhook control and hybrid control (which combines groundhook and skyhook controls) of the semi-active suspension are more effective in reducing the road-induced vibration and improving the suspension dynamic behaviours. Also, validations of the predicted responses of the semi-active scaled MR suspension model with the measured responses have been presented. The fourth and final phase provides a numerical simulation on the development and evaluation of the semi-active control methods for a full scale tracked vehicle suspension with MR dampers using the validated suspension model. Three semi-active control strategies are proposed. The first two controllers are the skyhook and hybrid controls which provide better suspension performance. In addition, the third controller, which is an intelligent fuzzy-hybrid control system, is used to optimize the suspension performance. The results from this intelligent system are compared with the two traditional control methods (skyhook and hybrid controls) under bump, sinusoidal and random excitations. It is shown that the proposed controller can enhance simultaneously the vehicle ride and handling characteristics.

Wearing a virtual reality head-mounted display (VR-HMD) disconnects users from the real- world context that they are physically in. While one solution is to have everyone in the room wear VR-HMDs, this is not inclusive for all users. For example, children are not recommended to wear VR-HMDs due to eyesight concerns, and individuals with cybersickness, make-up, or thick hair texture may not want to wear them. In this thesis, we investigated the effects of using motion-tracked tablets as a window through which people can see the virtual world and understand how we can offer a more inclusive and social VR experience. Finally, we explore our in-lab user study to evaluate the usability of such a system, and we compare it against watching the VR-HMD user's egocentric view on a computer screen. Our results show that the tablet-based VR system is highly usable. Because of its agency, the participants felt more present and preferred the tablet-based system over the baseline method. / Master of Science / Wearing a VR-HMD (Virtual Reality Head Mounted Display) to enter VR (Virtual reality) usually cuts the user off from the real-world context around them. One possible solution to this problem is to let everyone wear VR-HMDs. But it is not feasible for everyone. Some individuals experience cybersickness or physical constraints such as glasses, thick hair, or makeup. Additionally, children are not allowed to wear VR-HMD as it may affect their eyesight. We propose a solution to this problem by enabling users to use motion-tracked tablets. Motion-tracked tablets refer to tablets such as iPad, Galaxy Tab, etc., that are tracked inside a Virtual Environment (VE) using trackers such as Vive Tracker. The trackers track the relative location of the tablet inside the VE. We believe motion-tracked tablets will give the users a window to the VE. In this thesis, we investigated the effects of using motion-tracked tablets in VR to understand how we can offer a more inclusive and social VR experience. We explored how useful the users found the system, how situationally aware they were about the VE, and how present they felt in the VE. Our results show a preference for motion-tracked tablets over the egocentric view of the VR-HMD user through a computer screen.

No / Z. W. Pylyshyn and R. W. Storm (1988) have shown that human observers can accurately track four to five items at a time. However, when a threshold paradigm is used, observers are unable to track more than a single trajectory accurately (S. P. Tripathy & B. T. Barrett, 2004). This difference between the two studies is examined systematically using substantially suprathreshold stimuli. The stimuli consisted of one (Experiment 1) or more (Experiments 2 and 3) bilinear target trajectories embedded among several linear distractor trajectories. The target trajectories deviated clockwise (CW) or counterclockwise (CCW) (by 19°, 38°, or 76° in Experiments 1 and 2 and by 19°, 38°, or 57° in Experiment 3), and observers reported the direction of deviation. From the percentage of correct responses, the ¿effective¿ number of tracked trajectories was estimated for each experimental condition. The total number of trajectories in the stimulus and the number of deviating trajectories had only a small effect on the effective number of tracked trajectories; the effective number tracked was primarily influenced by the angle of deviation of the targets and ranged from four to five trajectories for a ±76° deviation to only one to two trajectories for a ±19° deviation, regardless of whether the different magnitudes of deviation were blocked (Experiment 2) or interleaved (Experiment 3). Simple hypotheses based on ¿averaging of orientations,¿ ¿preallocation of resources,¿ or pop-out, crowding, or masking of the target trajectories are unlikely to explain the relationship between the effective number tracked and the angle of deviation of the target trajectories. This study reconciles the difference between the studies cited above in terms of the number of trajectories that can be tracked at a time.

<p> The movement of diamond drills by tracked vehicles and drill trailers in south Central Keewatin was studied during the summer of 1980. Tests of the physical ground strength showed that the ability of the terrain to resist disturbance from tracked vehicle operations depended on two main physical factors: the type of surficial material and the presence of water. Moisture contents varied throughout the summer so that the response of till and peat to compression and shear was not constant. As the summer proqressed, the increasing depth of thaw and gradual surface drying caused strengthening of both major types of surficial material. As a result, vehicle trafficability gradually increased throughout the summer. While surface rutting increased the depth of thaw compared to an undisturbed site, especially in peat, after the first few weeks of the thaw this had little apparent effect on vehicle trafficability. In many cases the vehicle disturbance was largely aesthetic giving the impression that the terrain disturbance was much more serious than it actually was.</p> <p> Although the load distribution of the vehicle tracks concentrated much of the longitudinal stress directly beneath the bogie wheels, in most cases the performance of the tracked vehicle itself was adequate. However, problems caused by the drill trailer wheels resulted in unnecessary mechanical strain on the vehicles and created marked increases in terrain disturbance.</p> / Thesis / Bachelor of Arts (BA)

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The use of robotics in hazardous environments is becoming more common, where autonomy can handle the dull, dirty and dangerous jobs that humans have previously supported. This thesis focuses on the design of a helicopter deployable unmanned ground vehicle for use in hazardous environments, and presents the benefits of heterogeneous unmanned vehicle teams for operation in beyond line-of-site hazardous environments. The design of a ground robot that is capable of being flown on the undercarriage of a Yamaha RMAX unmanned air vehicle is presented. The robot is size, weight, and power limited and must be capable of traversing rough, unstructured terrain. The results of testing show that the design criteria for size, weight, and mobility are met. A path planning algorithm is developed using the A* search algorithm for the planning of optimal paths through rough terrain. The algorithm makes use of a vehicle/terrain interaction model to compute the cost of path traversal. In the CONOPS, the terrain model is generated real-time during a mission through the use of a stereovision system carried on the helicopter, which station-keeps above the ground robot. The algorithm simulates the robot on the terrain and presents the best feasible path to the operator to aid in teleoperated robot navigation. Simulations of the planning algorithm provided feasible paths over a rough terrain environment. A user study was conducted that evaluates the abilities of both mono- and stereo-vision systems in providing the teleoperator with adequate situational awareness with the intent of proving that stereovision data is more effective at aiding the user in making timely navigation decisions. The results of the study showed that the helicopter-mounted stereovision system was more efficient than the monovision system with respect to navigation time, the number of invalid moves, and total moves required for navigation of a simulated rough terrain environment. / Master of Science

This diploma thesis deals with the use of powerful tractors with tracked chassis in agricultural primary production. For my work I chose Farma Pokorný Kmetiněves s. R. O., Which uses Challenger MT865E crawler tractor and BOTEP PLUS spol. s .r. o., which uses CASE IH STX 450 Quadtrac tracked tractors and CASE IH STX 480 Quadtrac. Literary review deals with the construction of wheeled and tracked bogies of tractors. The thesis describes the utilization of tracked tractors in given companies during the marketing year and analysis of the performance of individual tractors. The thesis is supplemented with characteristics of enterprises, description of technical parameters of individual machines and analysis of investment and operating costs.