A Novel Obstacle Avoidance Approach For Nonholonomic Ground Vehicle Autonomy

Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2012Thesis (PhD) -- İstanbul Technical University, Institute of Science and Technology, 2012Bu çalışmada, holonom olmayan bir kara taşıtı için, “Boşluğu Takip Et” (BTE) isimli yeni bir engelden kaçma ve çarpışma önleme metodu geliştirilmiştir. Bu metod, probleme yeni bir çözüm getirmektedir ve diğer metodlara göre çeşitli avantajlara sahiptir. Geliştirilen metodun, benzer metodlarla yapılan karşılaştırılmalar sonucunda, daha güvenli güzergahlarla sonuçlandığı gösterilmiştir. Ayrıca BTE, yapay potansiyel alanlar (YPA) metodu ve bu tabanda çalışan diğer tüm metodların ortak problemi olan lokal minimum probleminden bağımsızdır. BTE’nin bir diğer özelliği, aracın holonom olmayan kısıtlarını ve sensörlerin görüş açısı kısıtlarını da göz önünde bulundurabilmesidir. BTE’nin tamamen reaktif yapısı sayesinde, yalnızca durağan engellerden değil, hareketli engellerden de rahatlıkla sıyrıldığı da tez içerisinde gösterilmiştir. Son olarak, sadece bir ayar parametresine sahip olduğu için, kullanımı da oldukça kolaydır. Engelden kaçınmak için, yalnızca aracın yönelim açısının belirlenmesinin yetmeyeceği düşüncesinden hareketle, aracın engelli bir ortamda hız planlaması için de yeni bir metod geliştirilmiştir. İki adet bulanık çıkarım sisteminin (BÇS) tasarlanmasıyla oluşturulan bu yeni yapı, engellerin oluşturduğu risk durumuna ve aracın yönelim açısına bağlı olarak çalışır. Planlanan hızın takip edilmesi için de yine bulanık mantık kullanılarak yeni bir alt seviye hız kontrolörü tasarlanmıştır. Tasarlanan tüm metodlar, literatürdeki bezerleriyle simülasyon ortamında karşılaştırılmış ve sonuçları gösterilmiştir. Geliştirilen her üç yeni metod, tam otonom kara taşıtı (OKT) üzerinde deneysel olarak da test edilerek sonuçların başarılı olduğu gösterilmiştir. Simülasyonlarda kullanılan araç modelleri ve deneysel düzeneğin tasarımı da tez içerisinde ayrı bölümler halinde anlatılmıştır.In this study, a new obstacle avoidance algorithm “Follow the Gap Method” (FGM) is designed for nonholonomic ground vehicle autonomy. The proposed method brings a new solution to the problem and has several advantages compared to previous methods. Fisrstly, the FGM results in safer trajectories than other compared approaches. This new method is free from local minima which is a big problem for Artificial Potential Fields (APF) and similar methods. Taking into consideration the field of view and the nonholonomic constraints of the vehicle is another advantage of the FGM. Through the purely reactive nature of the FGM, it is shown that not only the static but also the dynamic obstacles are avoided. Besides these, it is easy to tune the algorithm with only one tuning parameter. Vehicle speed is as important as the appropriate steering angle for obstacle avoidance. From this view point, a new speed planning method is designed for the vehicle. Two fuzzy inference systems operate depending on the danger level of the obstacles and the steering angle. In order to track the speed commands from the speed planner, a new low level speed controller is designed based on fuzzy rules. All designed methods are simulated and compared with other methods in literature. The designed methods are also tested experimentally using the real unmanned ground vehicle (UGV) platform and it is shown that experimental results are successful too. The used models for the simulations and designed experimental platform are illustrated in separated sections throughout the thesis.DoktoraPh

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