Developing a Terrain Sensitive Flexible Simulation Platform For Mobile Vehicles Abdullah ÇAVUŞOĞLU1, Baha ŞEN1, Ferhat ATASOY1 1
Karabuk University, Faculty of Engineering, Computer Engineering Department E-mail addresses:
[email protected],
[email protected],
[email protected] ABSTRACT – 3D Virtual Reality platforms developed on computers can be used in several applications where avoiding the possible risks of real physical environments is essential. In expensive professional systems, such as the Stewart Platform, generally several graphics and physics software libraries are used for mechanical simulation systems providing six degrees of freedom. Less sophisticated systems offer fewer degrees of freedoms. In this study, an inexpensive system has been developed. In the system open source graphics and physics libraries, (PCI) I/O cards are used for controlling a mechanical platform providing five degrees of freedom. In this virtual reality application, positions of various mobile vehicles with different characteristics on a selectively chosen height maps are simulated. In addition the behaviour of the vehicle motions are transferred electronically onto the mechanical systems, that has been constructed, in real time. Since the simulator provides tangible outcomes, the users have the feeling of the real atmosphere of the vehicle. Here, we put emphasize on the integration issues between computer and mechanical system. Keywords: Vehicle simulation, simulation platforms, Delta3D, OpenSceneGraph, OpenDynamicsEngine
I.
INTRODUCTION
It is impossible that people can experience everything. Thus, virtual worlds and virtual models based on mathematical infrastructure became necessity for virtual reality applications. Virtual reality applications are one of the fields that simulating dangerous, hard to reach and hard to understand situations of real world by modelling with using computer technology and multi-media components. Recently VR applications are used in many fields, from entertainment industry to complex medical applications. The users feel as living the situations or moment in VR applications. Generally there is interaction between users and simulating objects in VR applications. Without a doubt, such simulators have had a very positive effect on training, reducing cost and at the same time allowing training in situations that would be too dangerous to execute in real world. At military side, most military simulators simulate weapons and vehicles such as plane, truck and helicopter. On the other hand vehicles, science experiments, flight simulators for entertainment, multidimensional cinema and etc are used as civil simulators. In this study, integration of virtual reality application, PCI I/O cards and mechanic simulator platform is emphasized. Delta3D game engine is used for simulating world and vehicles. Advantech 1711 and 1716 PCI I/O cards are used for data communication between virtual world on computer and mechanic platform. Five degree freedom mechanic platform simulates suspension system of vehicle.
II. VEHICLE SIMULATORS AROUND THE WORLD Vehicle simulations are a genre of video games that provide the player with a realistic interpretation. The prominent ones consist of flight simulators and driving simulators, also this genre includes simulations of driving trains, spacecraft, boats, tanks, and other combat vehicles. Various kinds of vehicle simulations are used for different purposes. Most popular vehicle simulators, FlightGear, Microsoft Flight Simulator, X-Plane, Indycar, NASCAR, Formula 1, 18 Wheels of Steel, Euro Truck Simulator the Wing Commander series, Orbiter, Microsoft Space Simulator, Space Shuttle Mission 2007, Lock-On are from foreign countries and Pedestal Mounted Stinger (PMS) System Training Simulator, Economic Driving Training Simulator (ESES) and Trafikent are from Turkey [1, 2, 3]. At the basic level, users drive car by keyboard or steer on home PCs or entertainment centers. Car racing games and drive training programs are good examples for basic level. Currently, most of the advanced driving simulators have the following features [4]: 1. Uses six degree of freedom Stewart platform for driver platform, 2. Multi-image generators for high resolution graphic projection, 3. High performance parallel-processed computers or group of server for real-time graphics, 3D sound and dynamics.
Special driving simulators include driver cabin on hexapod stewart motion platform. Some of them, including the throttle and brake pedal, steering and manual transmissions, etc. are important to a successful driving simulation [4]. More advanced driving simulators offer more than these. Engineers at Mazda, try to develop cars focusing on the sensory aspects of individual people. It is called as Kansei Engineering as a technology to transfer human perceptions, feelings and mental images into a tangible product [5]. Also Toyota has used a more advanced simulator, 360 degree visual simulation with 12 degrees of freedom. The simulator allows engineers and researchers to reproduce accidents and dangerous driving conditions [6]. Many automotive producers and research institutions have developed and applied their simulators for various purposes. New product design, safety researching, vehicle behaviour investigation are some of the purposes. Such as IOWA Driving Simulator (IDS) and National Advanced Driving Simulator (NADS) developed by the National Highway Traffic Safety Administration in United States [4, 7]. Less sophisticated simulators such as this study are used for education and entertainment industry. It allows user to drive and feel heights of roads. Accelerating simulation is possible but not enough good. Actually, these types of simulators are good at simulating heavy vehicles that can not accelerate as fast as automobiles. III. STRUCTURE OF SIMULATORS Simulator can be analyzed into three parts.
Figure 1 – Parts of simulator. A.
Simulator Software Developers and researchers from companies and universities have created visual and mathematical models. Some of them are developed for special purposes or specific fields. Others are used as a part of any simulation. Such as OpenGL, OpenSceneGraph, OpenSG, Direct3D graphic libraries are used for visualization and such as Open Dynamics Engine, Newton Game Dynamics and Havok are used for physical rules [8 - 12]. Additionally game engines include graphic libraries, physics libraries and moreover as 3D sounds. A game engine is a software system that designed for video games. Game engines offer reusable components, loading, displaying, animating models, collision detection between objects, physics, input, graphical user interface and etc [13]. There are lots of game engines such as Delta3D, id Tech, CryEngine and etc [14]. B.
Control Systems Control system consists of driver circuit and piston height control unit. Computer output voltages and currents are not enough or safe to drive loads such as valve, motor
and etc. Computer outputs are isolated from valve/motor etc. by using driver circuit. Piston height control unit controls pistons whether piston is at setting position. Task of closed loop control system is comparing reference input amplitude and output amplitude of feedback on measurement component and generating appropriate control signal according to own control effect and error value that consist of comparing result. Traditionally four control methods are used. The methods are following [15, 16]: 1. On-Off Control Method 2. Proportional Control Method 3. Integral Control Method 4. Derivative Control Method Various control methods consist of the methods or combination of the methods as following [15, 16]: Proportional Control (P Type) Proportional Integral Control (PI Type) Proportional Derivative Control (PD Type) Proportional Integral Derivative Control (PID Type) The proportional value determines the reaction to the current error. The integral value determines the reaction based on the sum of recent errors and the derivative value determines the reaction based on the rate at which the error has been changing. The weighted sum of these three values is used to adjust the process via a control element such as the position of a control valve [15, 16]. Simple PID algorithm is shown in Figure 2. Fuzzy logic is a new method for control applications. Basically, measurements in a fuzzy logic can be partly true. Although commonly true = 1 and false = 0, a fuzzy measurement can be between 0 and 1. The disadvantages of fuzzy logic, required prior knowledge and may not generate definite result [18]. Fuzzy logic controller block schema is shown in Figure 3.
has more than six degrees of freedom, uses Stewart platform, too. Additionally they are not fixed anywhere, their motions are dynamic, such as used by Mazda, Toyota(12 degrees of freedom) and Iowa State University(13 degrees of freedom)[5, 6, 7]. The most advanced systems are used for researching.
Figure 5 – Most advanced simulators and platforms [5, 6]. IV. DEVELOPED SIMULATOR
Figure 2 – Basic PID algorithm [17].
Figure 3 – Fuzzy inference system [19]. C.
Mechanic Platforms In space dot has six degrees freedom, motion or rotation on each of axis is one degree freedom. Figure 4 shows freedom degrees of dot.
Figure 6 – Physical configuration of designed system. A.
Computer Side Delta3D game engine is used for creating virtual reality. It uses opensource products such as OpenSceneGraph, Open Dynamics Engine and OpenAL and more [21].
Figure 4 – Freedom degrees of dot in space. Figure 7 – Delta3D architecture [21]. Mechanic platforms are not mandatory requirement but it is very important feature. Various types of platforms are used according to purpose and necessity. At entertainment centers, two degrees of freedom (z and roll) platforms that can are used. Generally motion intensity is not based on mathematical calculating. More advanced platforms, five degrees of freedom with three pistons are used for training [3, 20]. More sophisticated platforms are six degree of freedom Stewart platform and most advanced platforms
Delta3D offer almost everything to make game and simulations. It allows developers to design virtual world with tools and wide model libraries. Additionally developers can use their model files too. Thus, numerous organizations, companies and institutions, such as CogPit(DARPA effort project), Nemesis (from Applied Research Associates), VIRTHUALIS(The largest European Research Project on Industrial Safety) use Delta3D [22].
B.
Motion Control The driver circuits make computer outputs suitable for valve unit and control pistons’ heights. Hydraulic pomp provides fluid to pistons. It has nitrogen tank that provides stable pressure. Measurement data from linear encoders are fed back driver circuit unit and driver circuit unit generates suitable signal to control valves and piston heights. Here, different control methods can be used for controlling mechanic platform such as PID and fuzzy logic. Each of techniques has advantages and disadvantages. The most suitable technique can be found after experiments. It will be future work. C.
Figure 8 – Architecture of system software. The Core of simulation software based on Delta3D is the Game Manager (GM), and it owns all the Actors, Components and Messages. All the active objects such as driving vehicle and the inactive objects including the static terrain, lights, sounds, etc., are induced into the simulation software as Actors. Components receive all the Messages from the GM and deciding whether processing these Messages or just sending them to a specific Actor. Messages are user defined data used for the communication between Actors and Components. The overall architecture of the driving simulation software is described in Figure 7. The HUD Component provides the graphic user interface (GUI) to the user. The Physical Component performs collision detection among all the Actors in the virtual world. The Input Component receives data and drive vehicle according to user inputs. Our vehicles have four wheels and height data are based on terrain heights. The relations of calculated heights are based on minimum height of wheels. After that, calculated height relations of wheels are sent to driver circuit through Advantech PCI 1711 and 1716 cards. Working of the system is based on four wheeled vehicle and height maps, so terrains and vehicles can be changed and system can be used without problem. The important things are scaling and calibration.
Figure 9 – Screenshot of the simulation.
Mechanic Platform Mechanic platform is designed with four hydraulic cylinders. Its motion talent is five degrees freedom. It can move on x, y, z axis and rotate x and y axis (roll and pitch). Hydraulic cylinders are simulated map heights and platform has own suspension system like car.
Figure 10 – The designed platform V. CONCLUSIONS As a result of the study, vehicle acts according to ode physical rules in created virtual world and heights data are calculated to send mechanical system through pci i/o cards, Advantech 1711 and 1716. System is flexible that various type vehicle and supported height maps can be used, also generated (Digital Terrain Elevation Data) DTED maps from other applications as “3D Virtual City Generations on Digital Geographical Maps for Simulation Systems” are useful [23]. It can be used as training simulator for heavy vehicles because they can’t accelerate rapidly and users feel height easily. Delta3D game engine is preferred because it is opensource, free, support open-source graphic and physic libraries and more. It has already been developed US Naval Postgraduate School Moves Institute and many developers. Stability and fast system respond are very important for control applications. Different control techniques and comparing them are future work.
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sarımı ve Gerçekleştirilmesi. Master's thesis, Gazi University, Ankara. [19] Chang, Y.; Liao, C.; and Chieng, W. 2009. Optimal motion cueing for 5-DOF motion simulations via a 3DOF motion simulator. Control Engineering Practice 17: 170-184. [20] Darken, R.; McDowell, P.; and Johnson, E. 2005. The Delta3D Open Source Game Engine. IEEE Computer Graphics and Applications, 25(3): 10-12. [21] Delta3D, Retrieved February 25 , 2010 from the World Wide Web: http://www.delta3d.org/index.php?topic=projects. [22] Şen, B.2006. 3 Boyutlu Sanal Şehirler İçin Zeki Bir Platformun Sayısal Coğrafik Haritalar Üzerinde Geliştirilmesi, Gazi University, Ankara. BIOGRAPHIES (The names, the vitae and the research interests of the authors should be given at the end of the paper.) Abdullah ÇAVUŞOĞLU – was born in Konya, 1964. He graduated from Gazi University in 1985. He received his M.Sc. degree from the same university in 1988, and his D. Phil degree from University of Sussex in 1993 from the School of Engineering. He interests neural network applications, computer graphics and algorithms. Prof. Dr. Cavusoglu still works for Karabuk University, Department of Computer Engineering as Faculty of Engineering Dean and Department Chair of Computer Engineering. Baha ŞEN – was born in Mersin, 1974. He graduated from Gazi University in 1996. He received his M.Sc. degree from the same university in 1999, and his D. Phil degree in 2006. He works for Logo Business Solutions and Havelsan A.Ş. as software engineer and Ministry of National Defense as Project Officer. He interests 3D graphics and algorithms, database systems, expert systems, data mining. Asist. Prof. Dr. Sen still works for Karabuk University, Department of Computer Engineering as Assistant Department Chair of Computer Engineering. Ferhat ATASOY – was born in Ankara, 1984. He graduated from Gazi University in 2008. He still continues his master degree at Karabuk University. He interests 3D graphics and algorithms, embedded systems, computer controlled applications. Research Assistant Atasoy still works for Karabuk University, Department of Computer Engineering.
