Abstract-- A car that controls its self is a marvel. Naturally, one of the best ways to control the car is with a control system. The car is driven by differential steering meaning that there is a motor on each of the two driving wheels. The first step to analyze what the system needs to control the car; research was done on sensors, cameras, and power systems. Then research was done to determine how various sensors, cameras, and motor controllers worked and which combination would work best for the requirements of the project. After thorough research and a few design matrixes the best setup turned out to be ultrasonic sensors and cameras combined with an expensive motor controller. This gave us the best response time limiting the amount of overshoot occurs during turning.
Manâ„¢s Sixth Sense
M.E. Husson, Senior Student at Calvin College
A.D.D. â€œ Automated Designated Driver
ABS â€œ Antilock Braking System
team of four electrical engineers and one computer science major are designing and building an automated vehicle. The name of their group is A.D.D. (Automated Designated Driver). In this paper they will be referred to as either A.D.D. or the design team. The Team goal is to enter into the IGVC (Intelligent Ground Vehicle Competition) and win. The paper contains how the team determined the design and parts of their control system that would control their automated car. The team has a budget that is near to $4500 dollars. Fig. 1 shows the team budget and how much money is available for some of the parts that are introduced in this paper. However, some of the items on the budget will not be talked about in this paper, but they give a general idea of where the money for the team is going to go. The first section will consist of a general analysis of how the main control system will work and what parts are necessary. The second part will consist of research done on the various parts needed and a comparison between the same groups of parts. The third section will be comparisons between the various combinations of parts from varying categories and the determination of the parts used. The fourth section will draw the selected parts together and explain in detail how they relate and how the system will interact.
III. SYSTEM OVERVIEW
The control system used to design the car is fairly simple. The loop that I am concerned with in this paper is how the camera, proximity sensor, and PC will be combined to determine the output to the motor controller. This control system has some hardware, but the output is essentially derived from software driven PC. Fig. 1 shows the basic control system for the project. This control system will be expanded later in order to provide a higher level of detail.
Fig. 1. Original block diagram for the control system.
IV. PROXIMITY SENSORS
A. Proximity Sensor Uses
Proximity Sensors are needed for the automated car design because they will allow the car to detect obstacles. The price of these sensors are usually proportional to the distance they detect obstacles. Therefore, the sensors for this project will be quite expensive because moving at five mph the sensor must detect obstacles at a minimum of twenty feet in order for the car to have an adequate amount of time to react or turn.
B. Proximity Sensor Types
The search for a proximity sensor turned up three major results. The first result was the laser proximity sensor. These sensors are very effective. Right now they are made so that when someone buys them the software actually can show you a 3D image of what is all around it. This is very effective in determining where obstacles are and what the best path is between them. The downfall of these sensors is they are extremely expensive. They are on the order of 10â„¢s of thousands of dollars. Due to the fact that the project does not have that big of a budget this sensor is excluded.
The next sensor that was researched was an infrared proximity sensor. These sensors are very good. Most of these sensors can only detect obstacles at a maximum of five to ten feet away. However, this is enough space to meet the requirements of our project. The cost of the PIR (Proximity Infrared) sensors is also within the allotted budget. This makes the PIRâ„¢s a competitor for the spot on the car.
The last sensor that was researched was an ultrasonic sensor. These sensors are very good at longer distances. They reach maximum distances of 50 to 100 feet. These sensors are acceptable for the range specified in the requirements of our project. The cost of the ultrasonic sensors is also within the allotted budget. This makes the ultrasonic sensors a viable alternative to the PIR sensors.
C. Proximity Sensor Comparisons
The laser sensors are not even going to be compared to the PIR and ultrasonic sensors because the laser sensor is automatically rejected due to its extreme costs that do not meet the allotted money for the project. The PIR sensor has a lower cost compared to the ultrasonic sensor. However, the ultrasonic sensor has a wider range of detection area then the PIR sensor. The PIR sensor essentially shoots one beam of infrared light like a common laser pointer, whereas the ultrasonic sensors shoot a sound wave comparable to the one shown in Fig. 1. The PIR laser is shown in Fig. 2. During testing if the PIR sensor was moved or touched the PIR would trigger detections. The ultrasonic sensor did not incorrectly trigger detections as it moved, only when there was something to detect did it trigger detections.
A. Camera Uses
The automated car uses cameras as an integral part of the control system. This type of sensor can and will be used in obstacle detection. Two cameras will be used. They will be positioned above the car at approximately five to seven feet high. They will be positioned on the sides of the car with at the same angle in degrees so they both point to the same spot in front of the car. This will allow the cameras to view the whole track in which the car will drive.
A PC will be used to filter the color out of these pictures leaving only lines of obstacles that need to be avoided. These filtered pictures are shown below in Fig. 2. As you can see, the color picture is of the track and the filtered pictures show precisely where the obstacles are. The software that is implementing the filtering of the pictures will only be able to filter a certain number of images a second. Therefore, a camera for this project does not necessarily have to take over five or six pictures per second. Given the overview of how the cameras will be used the next step is to determine the types of cameras that the team may possibly use.
Fig. 2. Pre-filtered color pictures are shown and their corresponding filtered pictures.
B. Camera Types
The team did extensive research on many different types of digital cameras and concluded that there are three viable options that need to be compared and researched further. The three types are security, commercial, and web cameras.
The team researched security cameras. The security cameras are fairly large. They are also durable. Most of the security cameras can be dropped from varying distances without breaking. The cost of these cameras can range anywhere from 200 dollars to 2000 dollars. The refresh rate is proportional to the cost of the camera. If the camera costs 200 dollars then the refresh rate is slow. If the cost is around 2000 dollars then the camera refreshes fairly quickly.
Research was done on commercial digital cameras. The cameras that meet the requirements of the project without going excessively over cost at most 200 dollars. These cameras have varying picture qualities. If the car would need a higher quality picture this is one way to go. However, the car does not need that. The commercial cameras have a very slow refresh rate. They can literally only take a picture a second at the fastest times. This is mainly due to the auto focus and replay features of the digital camera. While these two features are activated the camera does not take a new picture.
Research was also done on web cameras. It was determined that the web cameras cost approximately 50 dollars. These cameras have a refresh rate of approximately 10 frames per second, which meets the requirement of the project. The speed does not need to be any faster because the computer can not process more then five two or three per second. These cameras are very small, but they are not very durable. If this camera is dropped there is a good possibility that it will break.
Seeing as all these cameras have benefits and drawbacks it is time to determine which camera is the best fit for the current project. The team does not want to get a camera with functionality they will not use, but they want to get a camera with all of the features they will need.
C. Camera Comparison
Looking back at the three cameras above we know that we can exclude the security cameras because in order to meet the requirements and meet the budget the least expensive camera with the least amount of capability would need to be chosen. With the least expensive set of security cameras the purchaser would need to build a case for it and also write some extra software in order for it to work. The purchaser would also have to build or order the wires and connectors in order to connect it to anything. This seems like excessive work considering that if the team gets any of the other two their labor hours will be cut down dramatically. So, security cameras are excluded from the list. Commercial cameras are also excluded automatically because there are no cameras that have a quick enough refresh rate that can run continuously. The quality of the camera creates too much of a delay between pictures at this time. That will change over the next few years so they might be compatible, but for now they are not. So, looking back over the comparisons it is obvious that the choice of cameras will be two web cameras. They are relatively inexpensive. They have a quick enough but do not have an excessive refresh rate. They are also durable enough to withstand the shaking of the car.
A. Processor Uses
A processor is needed in our design because the signals coming from the proximity sensor and the cameras will not go directly to the motor control to determine the speed. The processor will accept these sensors as inputs and produce an output that the motor controller will be able to interpret. The design calls for a processor that will be capable of filtering the images, doing the triangulation of images to determine the distance of obstacles, and convert the input signals to the appropriate output signals for motor controls all in real time. The processor must also have many serial connectors available because that is how the data will be passed from the sensors to the PC and then from the PC to the motor controllers.
B. Processor Types
The first type of processor the team researched was a prototype board processor. This process gave the team the accurate speed of processing that was needed, but did not allow the team to easily receive drivers to install and use the cameras effectively. The amount of time the team would need to spend on recreate drivers that were already created was considered a waste of man hours and deemed unnecessary. This option also does not allow for a sturdy connection of the serial cables running from the various devices.
The next option is to use an older laptop with a minimum of a 2 GHz processor. This option would work effectively too. The laptop would be approximately eight hundred dollars. The laptop would allow the camera drivers to be installed and interfacing the laptop and the camera would take hardly any man hour at all. There are at most two serial connections on the back of a laptop.
The final option is for the team to build a desktop computer. This option gives the team great flexibility because they can purchase the exact components and pieces that they need in order to complete the project. With the team building their own desktop they can put as many serial connections in as needed.
C. Processor Comparison
Looking back at the three processor options above it is easy to exclude the prototype board processor due to the lack of expansion slots available. The man hours required to design this system and actually incorporate it into the overall system would be hard to justify. The cost of man hours exceeds the costs saved by buying this type of processor.
The closest comparison is between using a laptop or a self-built desktop. The laptop has the advantage of containing its own battery, which would mean that no AC voltage would be needed on the moving car. For a desktop PC the team would either need to buy a generator or a power supply with a back up voltage supply. The back up voltage supply is relatively inexpensive compared to the generator. The back up voltage supply also weighs less, which is also a consideration for this project since the heavier the car is the more powerful the motors need to be.
The laptop also lacks in the ability to be configured exactly the way the team wants it to be done. The team needs to have many serial connections, which can easily and affordably be incorporated into the design of their desktop PC.
So, it is fairly obvious now that the team should build a desktop PC in order to save money and have the flexibility to add or take away features they deem necessary and unnecessary respectably.
VII. SYSTEM DECISIONS
So far this paper has given the sensors and processors that the team will use for this project. The general consensus is that the team will use ultrasonic proximity sensors in order to detect obstacles directly in front of the vehicle. The Cameras will be used in parallel with these ultrasonic sensors to ensure that if one sensor fails to detect a target the other sensor will detect it. The sensors will communicate their data to a desktop PC built by the team with the correct number of serial ports and various other components it will need. This concludes the decision part of the paper and now the paper will shift to an analysis of the chosen system.
VIII. ABS BRAKING SYSTEM OVERVIEW
While I was researching a possible breaking system for the car I cam across many sources saying that anti lock breaks are good. Now, antilock or ABS breaks are overkill for the senior design project, but they are a very effect control system that saves many lives and prevents crashes daily. The rest of this paper will focus primarily on the control system involved in the design of ABS breaks.
A. ABS Introduction
Stopping a car in a hurry on a slippery surface can be very difficult or nearly impossible. ABS brakes can take much of the difficulty out of this scary situation. This is a nerve racking event that no one enjoys going through. ABS does so well that an average driver can stop faster with ABS brakes then a professional drive can without them. Therefore, it is pretty clear that ABS breaks definitely have a clear place in the car industry today and in the future. Many accidents can possibly be avoided.
B. ABS Concept
ABS breaks actually have quite a simple concept. The skidding wheel (where the tire patch is sliding relative to the road) has less traction then a non skidding wheel. Therefore ABS tries to eliminate the skidding of any of the wheels. ABS breaks will not only allow the driver to slow down quicker when the wheels are not sliding, but the driver will also have the ability to steer the car instead of sliding out of control.
C. ABS Components
There are four main components in the ABS system. There are speed sensors, valves, pumps, and a controller.
In order for the ABS system to prevent the wheels from locking up ABS must be able to determine when the wheel is about to lock up or stop moving. The speed sensor is used to determine if the wheel is about to stop. Think of it this way. A car has a certain amount of inertia as it is moving forward. When a driver tries to stop the car there is a certain amount of time (usually approximately five seconds) that it takes the car to actually stop. However, the drivers tire can stop in less then one second if the brakes are applied hard enough. The speed controllers measure the speed on the wheels so that the controller can process that information and determine if the wheel is about to slide or not.
The valves determine how the break should respond given the circumstances. There are usually three positions that the valve has. The first position allows all of the pressure from the master cylinder to pass through. This means that the valve does not limit the braking of the driver at all. The second position blocks the line to the mater cylinder. This keeps the pressure on the break, but if the driver pushes the break pedal harder no more pressure is applied on the break. The third position releases some of the pressure from the break. This allows the car to experience a slight reacceleration. Refer to Fig. 3 to see the valves hooked up to the pump .
The pump is used to put pressure back in the brakes once the valve is set to position three. Otherwise, the pressure would be released and no more pressure would be added. Therefore without the pump the system would not work correctly. Refer to Fig. 3 to see the pump hooked up with the valves .
Fig. 3. Anti-lock brake pump and valves
The controller does the computing work. It looks at the outputs from the speed sensors and first determines if the wheels are going to lock up. If they are going to lock up the controller changes the valve positions and controls the pump accordingly.
Below is a picture of the position of all of these parts on a car . This will allow you to view and get a better perception of how these components work together.
Fig. 3. Location of anti-lock brake components
D. ABS at Work
There are many different types of ABS algorithms that are present today. The more complicated algorithms usually work more efficiently then the easier algorithms. However, in this paper I will focus on one of the easier algorithms so that the readers will easily understand the methods presented.
As mentioned before the controller is watching the speed sensors constantly looking for the wheel to make any rapid decelerations that are impossible for the car to keep up with.
The controller knows with the current braking pressure it is impossible for the car to stop as fast as the wheel. So the controller moves the valve so that some of the pressure is released from the break. The pressure is released until the car is able to accelerate and then the pressure is put back in. However as the pressure is put back in it is quickly taken out again when the tire is about to lock or begin to slide. This process is done in such a short amount of time that the tire will not necessarily change speed during this process. A good ABS system can pulse the pressure fifteen times per second.
During this pulsing process the driver can feel it as his foot pushes the break pedal. The pedal itself will pulse with the ABS system.
E. Types of ABS Braking
Anti-lock breaks use several different setups and channels depending up the car and other features. Here is an excerpt off of the howstuffworks.com page that shows the various setups.
Four-channel, four-sensor ABS - This is the best scheme. There is a speed sensor on all four wheels and a separate valve for all four wheels. With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force.
Three-channel, three-sensor ABS - This scheme, commonly found on pickup trucks with four-wheel ABS, has a speed sensor and a valve for each of the front wheels, with one valve and one sensor for both rear wheels. The speed sensor for the rear wheels is located in the rear axle.
This system provides individual control of the front wheels, so they can both achieve maximum braking force. The rear wheels, however, are monitored together; they both have to start to lock up before the ABS will activate on the rear. With this system, it is possible that one of the rear wheels will lock during a stop, reducing brake effectiveness.
One-channel, one-sensor ABS - This system is commonly found on pickup trucks with rear-wheel ABS. It has one valve, which controls both rear wheels, and one speed sensor, located in the rear axle.
This system operates the same as the rear end of a three-channel system. The rear wheels are monitored together and they both have to start to lock up before the ABS kicks in. In this system it is also possible that one of the rear wheels will lock, reducing brake effectiveness.
This system is easy to identify. Usually there will be one brake line going through a T-fitting to both rear wheels. You can locate the speed sensor by looking for an electrical connection near the differential on the rear-axle housing.
IX. ABS CONTROL SYSTEM
Below in Fig. 4 you can see the ABS control system . It is fairly complex and has many different functions to go through.
Fig. 4. ABS Control System Model in Simulink
X. STABILITY CONTROL SYSTEM
A. Stability Enhancements
One major enhancement that might need to be done is implementing a stability control system. This system would reduce the chance of the vehicle skidding out of control during a turn.
B. Implementation Today
Ford is beginning to implement a new stability control system in 2005 and 2006 as standard equipment on SUVâ„¢s to prevent harmful rollovers and other accidents. The system uses a gyroscope to sense when a vehicle starts to roll over. Other systems measure rollover propensity in two dimensions but the new Ford system measures in three dimensions, said Ford spokesman Jon Harmon. Ford showed the enhanced system to journalists Thursday in Romeo. In one demonstration, Ford strapped a refrigerator to the top of an Explorer and failed to roll the vehicle over despite aggressive handling. In order for this system to effectively work the gyroscope is the main sensor. Then there are various control loops for each brake and the accelerator.
When the gyroscope is in a position that is about to result in the tires losing their adhesiveness to the road and sliding action is quickly taken to avoid this unnecessary risk. A brake is applied or the car is accelerated, whichever step will counter the sliding affect.
XI. SOCIAL BENEFITS
In order for any engineering project to be acceptable a team or individual must take into consideration the applicable design norms. The design norms that directly correspond to the A.D.D. project include cultural appropriateness, transparency, stewardship, integrity, caring and trust.
The first design norm is cultural appropriateness. This design norm deals primarily with the ability of the automated vehicle to fit into the culture in which it will be used (United States of America.) Currently the U.S. car industry is beginning to create cars that apply a greater level of automation and modern engineering breakthroughs, such as putting proximity sensors on cars so they stop before backing into an obstruction. The automated car that A.D.D is designing will implement this same technology as well as expand the scope to include steering around obstacles. Americaâ„¢s culture is not very receptive to change so the prototype being built will resemble a car. Due to this resemblance, more people will be receptive to the new driving mechanisms.
This design will be transparent in that documentation will be written for the main section and the subsections explaining what each component is responsible for. The documentation written for the whole design will accurately and reliably indicate, to any future teams or users, what the car will do and how it will respond. Furthermore, a simplified userâ„¢s manual and its accompanying software will be produced to help others understand how to operate the vehicle without understanding its inner workings. This considerable amount of documentation will give future teams entering the IGVC the ability to use and expand on the implemented design. It also serves as a safety feature. For instance, if disassembly of the car is ever necessary in future years, the disassembly person(s) can look at the documentation and avoid being injured in the process. Errors during execution of the teamâ„¢s software will invoke debugging processes in an attempt to display pertinent information pointing to the error. The design team cannot eliminate the problems stemming from the WindowsÃ‚Â© operating system, but the team will try to minimize them by adding debugging software. This debugging software will also store information on some medium that can be removed and then further processed.
The stewardship norm entails being conscious of eliminating excess strain on the environment. A major problem in the world today is the inefficient gas motors in modern cars. A.D.D. took this into consideration when choosing the motors to be implemented. The motors chosen for the automated car are two DC electric motors. With electric motors, the car will not burn fuels that are corrupting the ozone layer. A.D.D. also hopes to include many previously used parts in the design instead of buying all new parts. This is beneficial to the environment because computers and other sensors are not very recyclable and anytime they can be reused decreases the amount of unnecessary non-biodegradable materials.
A.D.D. cares about disabled people. There are people living in the U.S.A. that can not currently drive because of disabilities. These people are at a loss because it is harder for them to get from one place to the other. A current solution to this issue has been to outfit a car with equipment specially designed for a disabled person. However, such a car, which allows them to drive, is frequently very expensive and not as safe and efficient as other vehicles. Autonomous vehicles will allow these people to be able to travel from place to place without help or public transportation.
A.D.D. also cares about public safety. When autonomous ground travel becomes feasible on a grand scale, humans will not be in control of their car. This will reduce the number of traffic fatalities caused each year by human error. Drunk drivers, careless drivers, road rage, and other potential roadway hazards could be avoided if humans were eliminated from the driving equation. On a smaller scale the design team will make absolutely certain that all safety requirements of the project are met, and that no person or animal is injured in the design, testing, or use of the product.
The documentation written for the design will be accurate because A.D.D. wants to implement the integrity design norm. The written documentation will not be exaggerated to make the design look better, which could pose risks to any user or future designer. The design team will abstain from removing information that places the project in a negative light. The project can only be successful and effectively impact the United States of America if the general public can view the project in its unbiased form. If the documentation is lacking and/or if the documentation is inaccurate the general public will reject the project. This rejection will cause the appearance of automated cars into main stream markets of the United States of America to be delayed even further.
A.D.D. wants the public and future users to be able to trust their design. With this in mind A.D.D. designed the prototype with reliability as constant goal. Any unreliable sections are or will be clearly apparent so that every individual will know all risks that are possible. The parts chosen for the prototype are also of as high of quality as is feasible to ensure that they have the best chance of withstanding the physical abuse of competition.
actual Simulink model
Good for ABS â€œ Diagram included