System Level Design Description
Sensors This section is a classification of the sensor-systems to be placed on-board the vehicle. The robotic vehicle will require equipment that will allow it to gain information about itself and its surroundings in order to make intelligent decisions. These sensors take their inputs from their surroundings and output raw, unprocessed data. Proximity Sensor: Provides proximity information about any objects in the area around the sensor. Vision Sensor: Provides visual information of the area around the sensor. Directional Sensor: Provides absolute directions relative to the Magnetic North. Differential Speed Sensors: Provides reading of speed from the individual wheels, i.e. the differential speed of the vehicle. Differential GPS Unit: A GPS unit that relies on military-standard differential error correction technology to give measurements that are measurably far more accurate than regular GPS units. This type of a GPS unit is a competition requirement.
Guidance, Navigation and Control System This section is a classification of sub-systems that will undertake the necessary tasks and calculations in order to determine the vehicle’s current state and surroundings (maintaining a log of this information) and determine its desired state. Collision and Lane Avoidance System This sub-system contains modules that will acquire raw input data regarding the vehicle’s surroundings from the Proximity and Vision Sensors, will manipulate that information and perform computations on it in order to present this information to the Simultaneous Localization and Mapping sub-system. Obstacle Detection: This module acquires raw input data from the proximity sensor(s) and computes the distances and directions of all objects within a certain distance (this distance depends on the accuracy and range relationship of the proximity sensors). The output of this module will be object information presented in a format that understandable by the Mapping & History module. Computer Vision: This module acquires raw input data from the vision sensor(s), performs image manipulation and transformation in order to extract important information from it, and computes the distances and directions of all lane-markings, potholes and simulated pot-holes on the ground. The output of this module will consist of lane and pothole information presented in a format that understandable by the Mapping & History module. In the Navigation Challenge of the IGVC, the role of Computer Vision is significantly reduced as staying within lane boundaries is no longer required. Furthermore, for the Navigation Challenge, Computer Vision will have to be switched-off, bypassed or modified to ensure that waypoint-markings are not confused as lane-markings, thus hindering the robotic vehicle in achieving the requirements of this challenge. Simultaneous Localization and Mapping This sub-system contains modules that will acquire processed data from the Collision and Lane Avoidance System as well as raw data from the Directional, Differential Speed and Differential GPS Sensors. The sub-system will determine and provide, as an output, the current position, speed and direction of the robotic vehicle as well as the combined positions of visual and physical obstacles. Localization: This module acquires raw input information from the Differential GPS Unit, the Differential Speed Sensor(s) and the Directional Sensor(s). It then determines the true position, speed and direction of the robotic vehicle and outputs this information to the Mapping & History and Navigation modules. Mapping & History: This module acquires processed information regarding visual and physical obstacles from the Computer Vision and Obstacle Detection modules, as well as positional data from the Localization module, and logs the information onto a map. In the Autonomous Challenge, only the History sub-module of this module will be required in order to determine the correct direction of travel. The Mapping sub-module is not required for operation, but will be useful for simulation and testing. Navigation and Control System This sub-system contains modules that will acquire information regarding the position, speed, direction and recent history of the robotic vehicle as well as the positions of the combined visual and physical obstacle data from the Simultaneous Localization and Mapping sub-system. The output of this sub-system will be specific control commands to be sent to a motor-controlling Microcontroller. Navigation: This module acquires processed information about the true position, speed and direction of the robotic vehicle from the Localization module and combines it with the combined obstacle data from the Mapping & History module. It then determines the robotic vehicle’s desired path in order to avoid any and all obstacles while, ideally, taking the optimal path towards the next waypoint or in the forward direction. The output of this module will be the desired speed and direction of travel of the robot. Autonomous Challenge Navigation: In this challenge, the Navigation module is responsible for determining the forward direction (by looking at the robotic vehicle’s recent history), and ensuring that robot avoids all obstacles while staying within lane boundaries. Navigation Challenge: In this challenge, the Navigation module is responsible for traversing the waypoints in the optimal order while avoiding all obstacles. It would be ideal if the Navigation module could make decisions regarding the optimal path in real-time as it gathers newer information regarding the obstacles. Control: This module will acquire the desired speed and directional information from the Navigation module and convert it into commands that are understandable by the motor-controlling microcontroller’s firmware.
Microcontroller The firmware onboard this microcontroller will govern the driving motors. The firmware will determine the required differential motor-speed in order to achieve the desired direction of travel while maintaining the desired speed.
Emergency Stop The competition rules require the implementation of a push-button and wireless Emergency Stop (or E-Stop). The E-stops must be hardware-governed and must not rely on software. Therefore, the E-stop will be placed in a manner such that all power to the motor-drives is cut-off immediately, while the rest of the robotic system remains powered. The E-stop will also send a command to the Control module informing it that the vehicle has been stopped. |
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