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This project is a continuation and amalgamation of a number of previous student dissertations and research work. The purpose of this project is to implement an optical communication channel between two points in an x-y co-ordinate scanning/lock/acquisition mode using separate controlled pan/tilt positioning units. Each end of the system needs to incorporate some form of data communication capability. To facilitate the data transfer the transmitter must be able to locate the receiver as it does not know where the receiver is located and this is where the XY scanning comes in.
This is a system integration project which follows the work in integrating various pieces of hardware and software, into a complete system.
The transmitter scans the area in a set pattern to locate the receiver, when it locates the receiver, it is said to have ‘Locked On’. It is at this point that data is transmitted to the receiver which then acknowledges to the transmitter that it has received the data. Data is to be transmitted optically using components such as laser diodes and infrared light emitting diodes.
The target application is data transfer between two small mobile robots within a wider context of covert communications between autonomous vehicles. In these scenarios the likely data transfer will be co-ordinate data.
Previous research work has been completed in developing an underwater communications link using a closed loop feedback controller to maintain the link. Bosman, N. (1999)[i] had developed on this idea to construct dual XY laser scanners able to lock on and communicate. This project builds on this previous work.
The main goal is to demonstrate the concept developed in prior work as it has been a number of years since the research was carried out. The project is limited in terms of cost and development time as is was part of an MEng Dissertation, therefore it is unlikely that major components such as Galvanometers and Laser Modules could be used. A normal BEng dissertation is four modules over a year whereas the MEng is only two modules, cutting the time and effort by half.
The desired final outcome should be a system capable of achieving the specified objectives of this project within set controlled experimental conditions, building on the previous work and allowing continuation of this project by another student in future years.
The main objectives of this project are:
- Develop a Pan/Tilt head for the transmitter
- Develop a transmitter
- Develop a receiver
- Develop a communications channel
- Develop a way for the transmitter to locate the receiver
- Develop control software under control of a host PC
- Achieve Lock-On and data transfer (Both objects stationary)
- Achieve Lock-On and data transfer (Receiver Moving)
In order to achieve these objectives it was decided to initially set the range between transmitter and receiver to a distance of 1 meter and perform the experiments in a controlled environment where the light conditions can be set.
This project was tackled by first researching all the previous work completed in this area and finding out what the outcomes were.
Initially each part of the project was considered individually and within each section research was carried out on potential methods and also further problems caused by each method. A mind map was drawn up to illustrate the different parts of the project.
Figure 1 - Top Down Design
At each stage parts of the system were constructed and continually tested, and during these stages some initial decisions were changed in light of knowledge gained. The project evolved at each stage. This is known as stepwise refinement or top-down design.
In order to determine how to proceed with the project, at the beginning research was carried out to fully understand the project. A brainstorm diagram was then created to try to identify the different parts of the system and all the problems created. Solutions were when considered to each problem. The main parts of the system were identified as the following:
Figure 2 - System Brainstorm Diagram
As the system requires the ability to scan the area some form of positional control is required. This could be achieved with two distinct options, a pan and tilt head or a moving mirror arrangement from previous work. Whatever method chosen will require a controller to drive the movement stage and also make the system respond to user/computer input. Since the receiver is in an unknown position, the transmitter needs to know when it has found it, or a way to locate it. The final most important stage is the communications channel between the transmitter and receiver. This is a key part of the system and it needs to be able to pass low rate data optically.
Figure 3 - Main System Parts
Initially the projects main application is low rate data communication between mobile robots. By using this system it will give them the ability to locate and communicate to other robots in the immediate vicinity. One of the uses of the channel could be to pass co-ordinate data between robots so that they are all aware of the current location of each other. This would give them the ability to take avoidance action if another robot comes near them or create a wide mesh network enabling data to be passed from robot to robot, via other robots.
Another application presented in previous research work is the communication between underwater autonomous vehicles, such as pipeline inspection robots, this could for instance enable a large ‘pack’ of autonomous robots to coordinate their actions and movements, potentially improving commercial efficiency and reliability of gathered data.
Previous project work also developed an optical link which was primarily intended to be used between a remotely operated vehicle (ROV) underwater and a surface vessel. This link could be used to provide video streams and data from onboard equipment to the controller on board the boat.
Using an optical communications channel is much more covert than acoustic methods such as sonar, therefore the applications could extend to military work. In particular underwater vehicles where communication by acoustic methods would be dangerous, as it could signal to an enemy the presence of their enemy or automatically trigger an explosive device. Acoustic energy is much easier to detect than optical energy, meaning optics would give added stealth to the system.
A further application of this work could extend to a communications link to a teams racing car in formula one and other racing sports. This link could be used to pass telemetry and other data from the cars on board sensors remotely back to the teams base enabling them to make changes in real time to the cars ECU and other variable settings.
An additional application could be in observation systems tracking the position and status of a number of objects in close proximity (line of sight) to the system. By equipping each of the systems with a receiver and beacon, the observation system could routinely ‘speak’ to each object, determine if its position has changed, and also determine if any alarms or flags have been raised by the object. This could be used for asset tracking or security.
Effective time management is crucial to the success of any project and this one is no different. In order to ensure deadlines were met a project time plan was drew up at the start of the project in the form of a Gantt Chart.
Figure 4 - Initial Gantt chart
Initially it was planned that semester 1 would be mainly spent researching and developing options for the system. Construction of the circuit and parts would take place towards the end of semester 1. This left semester 2 free for designing and programming the software. This would likely take up a large amount of time. Leaving the rest of semester 2 allocated for testing, and writing this report.
A major factor in planning the project was the exam times, due to the fact that preparation for the exams was as important as working on this project. The final few weeks before the exams were planned to be project free.
However this planning hadn’t accounted for the level of work required from other modules with assignments and reports. To speed up, some initial work on developing the pan and tilt head was carried out during the research stage.
It was found as well that at the initial planning stage there were still a lot of unknowns with regard to which direction the project would go. Also due to the stepwise refinement method used, much of the final outcome of the project was not initially accounted for in the plan. By incorporating the image processing part to the project meant much less programming as a whole however resulted in development time being spent on the image processing side.
Figure 5 - Actual Gantt chart
Towards the middle of semester 2 it was decided to finish up the practical side of the project and begin writing this report. This was decided on the basis of needing more time at the end to revise for the exams; and also to allow enough time to work on assignments and reports for the other 3 modules.
In hindsight by spending the time in the holidays and working on the project in the late evenings it was found that a great deal more could be achieved and also allowing more time can be spent at the end dedicated to the exams. Therefore avoiding the ‘last minute rush’ and producing substandard work while exams, revision and assignments are all looming.
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