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Autonomous cars, or cars that run without a human driver, have been in development for over the past few decades, starting from the late 70’s and extending towards the present date and even beyond. During the early stages, the autonomous vehicles were slow in speed and even in reaction time. Nowadays, with technological advancement, coupled with better research knowledge and funding towards further development, product improvement has clearly been observed. From the early days of mechanical feedback systems to modern software incorporation, numerous improvements have been made.
2. Advantages of Autonomous Vehicles
Finding from the World health Organization (WHO) several years ago regarding automobile accidents:
“Accidents expenditure in the United States reached $230 billion; with over $30 billion going into health care. Such will only increase, because the road accidents are expected to be the third largest killer worldwide by 2020”.
There are two possible approaches to make cars safer. Systems can be implemented to make a car accident less lethal or to prevent accidents.
Also, from an energy and efficiency point of view, in general, people are not able to drive the best as well. Having computers to do the driving is going to save energy significantly. However, since vehicles are networked and with traffic flow synchronized, it is an apples-to-orange comparison.
Autonomous cars won’t have to tackle congestion and stop-and-go traffic, as is present today. Road travel will speed up, more predictability, and passengers will have ample space to focus on other things while travelling.
The vehicles will be a lot less heavy. There will be a reduced need for designs to deal with impacts, as the heavy vehicles of today are driven by error prone humans, nor a need to be equipped with protection instruments to protect drivers (e.g. crumple zones, airbags, or even seatbelts).
Further advantages of driverless vehicles, aside from the significant safety and energy benefits that would be presented with their use, will be an increase in transportation access. Aged, restricted mobility, poor, and even the language illiterate individuals can safely travel. It will be like having a chauffeur at all times.
3. Integrating technology to make an autonomous vehicle
For vehicles to be made autonomous will require advanced sensors and actuators to coordinate hand in hand.
Definition of sensor and actuator
Sensor – A device that detects or measures a physical property and records, indicates, or otherwise responds to it
Actuator – An actuator is a mechanism responsible for the movement or control of a machine, apparatus or system. It utilizes energy, commonly transported by air, electrical current, or fluid, and translates that into a type of motion.
3.1. Sensors in an autonomous car
In an autonomous vehicle, apart from speed sensors, sensors are used for lane position tracking as well as front obstruction detection. This comes in the form of radars. If lane positioning or safety distance is not within safety parameters, the sensor will send signals to the microcontroller. From there, the microcontroller will coordinate the various actuators such as throttle, steering and brakes to enable the vehicle to stay within the parameter.
Various sensors used in the mobilization operation of autonomous cars includes a radar reflective stripe system with a vision based system for lane location sensing, a radar system and a scanning laser range finding system for the detection of obstacles ahead of the autonomous car, and various assisting sensors including off-centre looking radars and one angular rate gyroscope. Figure 1 shows a sketch of an autonomous car with the various sensors, actuators and operating devices.
3.2. Actuators in an autonomous car
Coordinate car speed with the sensors and/or user’s pre-input. Used for slowing down the car when there is a need to.
The steering actuator is a motor controlled by the car in-built microprocessor. The microcontroller takes in signals from the various sensors to steer the car which is done by directing the motor for controlling the angle of the wheels.
Used for controlling the output of the car’s engine based on the sensor or user’s pre-input. This will increase and reduce the speed of the vehicle as well as maintain.
3.3. Current technologies, design and construction concept used to realize various sensors and actuators in an autonomous vehicle
3.3.1. Electronic Scanning Radar
Electronic Scanning Radar is an inexpensive effective object-detection system that utilizes electromagnetic waves, specifically radio waves, to determine the range, direction, or speed of both mobilized and stationary objects. Radio waves or microwaves transition from the radar sensor bounces off any object in their path. The object will then return a tiny portion of the wave’s energy to the antenna which is normally located at the same spot as the transmitter.
Radar technology has the ability to measure positions and speed vectors of multiple targets at the same time, with precise accuracy, within a short time frame. Detection and tracking algorithms are normally given in a one-box-design and some manufacturers allow space for vehicle/customer/application specific code in the radar systems.
The ESR enables a wide coverage at mid-range and high-resolution long range using stand-alone radar. Wide and mid-range coverage not only enables vehicles cutting in from adjacent lanes to be detected, but also determines vehicles and pedestrians along the width of the vehicle. Long-range coverage gives accurate range and speed data, with great object discrimination that can identify as much as 64 targets in the vehicle’s path.
The ESR also allows powerful functionality which includes the following:
-adaptive cruise control
-forward collision warning
3.3.2. Brake actuator
One method of braking widely used by autonomous vehicles, although also widely used in contemporary vehicles, is the disc braking system.
The main components of disc brakes comprise the following:
Caliper containing a piston
Rotor that is mounted to the hub
The disc brake is quite similar to the brakes on a bicycle. Bicycle brakes use a caliper, which forces the brake pads against the wheel. In a disc brake, the pads forces on the rotor instead of the wheel, and with the force being transmitted hydraulically instead of a cable. Friction between each pad and the disc slows the vehicle down.
A moving car contains kinetic energy and by stopping the car, the brakes are actually removing this energy. The brakes do this by converting the kinetic energy into that of heat. Therefore, in most cars, ventilation is provided for the brakes.
3.3.3. Adaptive Cruise Control
Adaptive cruise control utilizes forward-looking radar with its installation located at the back of the grill of a vehicle, to identify the speed and distance of the vehicle in front of it.
Adaptive cruise control is of the same principal as conventional cruise control in that it maintains the vehicle pre-set speed. However, unlike the contemporary cruise control, this implementation can automatically adjust the speed to maintain a safe distance from vehicles along the same lane. This is performed through a radar headway sensor, digital signal processor as well as a longitudinal controller. If the front vehicle slows down, or should another object get detected, the system will send a signal to the engine or braking system to slow down. Subsequently, when the road gets cleared, the system will increase the vehicle speed back to the set value. Cruise control is an example of a closed-loop control system
Closed and Open Loop Explained
In a closed-loop configuration, a feedback component is being sent together with the input. The difference in the input and feedback signals is sent to the controller. In response to the difference, the controller acts on the process forcing the output to change in a direction that will cause reduction in the difference of the input signal and the feedback component.
A closed-loop system has the ability to regulate itself in the midst of disturbances or variations in its own characteristics. Hence, a closed-loop system has an advantage over that of an open-loop
Likewise, a cruise control has an input signal of a desired velocity. This goes through any number of amplifiers in the mode of transfer functions and gains, and then, outputs a signal which the motor utilizes to modify its power. Disturbances in the system may include wind speed, bumps on the road, etc. When these obstacles affect the speed of the car, data passes through from the end of the control system in the form of velocity data to the beginning, where it makes appropriate changes to the input signals so it can then properly adjust the speed of the car.
Closed loop control systems has its output compared with the desired parameter settings and the process is varied in order for the output to satisfy the requirement.
The accelerator of a conventional man-driven vehicle, on the other hand, is an example for an open-loop control. This is a simple link between the gas pedal and the car engine. When stepped on, the engine propels the car, and this does not stop until you remove the input signal (Pedal stepped on with continued pressure). Should there be obstacles along the way, this will affect the speed of the vehicle so long as pedal is being stepped on to a certain particular extend.
Open-loop systems provides an output according to the desired set point irrespective to the changes that occur due to certain disturbances in the process.
An open-loop control system is influenced directly, and only, by an input signal, without the beneficial use of a feedback.
3.3.4. Oxygen Sensor
A vehicle oxygen sensor, also known as a lambda sensor, is a small sensor installed into the exhaust system of a petrol engine for the measurement of the oxygen concentration that remains in the exhaust gas to enable an electronic control unit (ECU) to control the efficiency of the engine combustion process. In majority of all modern automobiles, including autonomous ones, these sensors are installed at the engine’s exhaust manifold to identify whether the mixture of air together with gasoline going into the engine is rich or lean. That means too much or too little fuel respectively.
CAN Bus is a multiplexed wiring system commonly utilized in the connection of intelligent devices such as Electronic Control Units (ECU) on vehicles, allowing data to be transferred in reliable manner at a lower cost. This also reduces the need for massive amounts of cables In a vehicle. CAN stands for ‘Controller Area Network’ and it was development was by Bosch, in 1980. Majority of new vehicles utilizes this system and it is becoming more difficult to install after-market products without the use of a CAN Bus Interface. CAN bus is commonly used in autonomous vehicles.
4. Capabilities and Potentials as well as the limitation for the various telematic devices in an autonomous vehicle
4.1. Disc Brakes
Today, in almost all automobiles, both conventional and autonomous, disc brakes are the most found .They are better at stopping vehicles than many other type of brakes; which is why they are still in existence since 1902. High speed vehicles need better brakes to slow them down, so most probably a disc brake would be installed.
Heat retention is a common problem with disc brakes. Unfortunately, this causes brake fade. It is where the brake components have absorbed all the heat they can possibly withstand. This means they are unable to absorb more energy and thus, will not be able to slow the car further.
4.2. Cruise Control
It is definitely better to be in an autonomous vehicle. This makes life for the user easier as he do not need to drive. Also, with humans in control of the vehicle, a higher tendency of error occurs. In autonomous vehicles, one of the components that make the technology possible is the cruise control. The cruise control aids in automatically controlling the speed as well as maintaining a safe distance from the car in front. This makes travelling safer.
The cruise control of today’s autonomous vehicles can only track the car ahead of the equipped vehicle. This means safety is only taken in reference from the front, and not from the back. In the later part of this report, we will look into the intelligent cruise control.
4.3. Radar Sensor
Radar aids in making a vehicle autonomous. Current technology enables radar to accurately detect at greater distances, identify up to 64 targets and can be integrated to an autonomous vehicle to assist in many various operations such as cruise control, braking, collision warning and headway alert.
Current implementations do not permit collision avoidance when environment is obscured with smokes and dust.
With the huge reduction in wiring, this leads to the following:-
(i) Vast reduction in production cost; which also leads to lower retail cost.
(ii) Lighter weight for vehicle, thus leading to improved fuel consumption.
(b) Reduced number of interconnections, which leads to improved reliability.
Installation is relatively costly, and the requirement for specialised knowledge is needed for maintenance and repair of the vehicle.
5. Continued improvements for Sensors and Actuators in autonomous vehicles
The first segment in this section discusses about the improvement in intelligence provided in a sensor over the years and how it has brought about major improvements. Second section will talk about the future sensors and actuators development in autonomous vehicles.
5.1.1. Increased level of intelligence provided in sensors has and explanation to why enhancing the intelligence of a typical sensor may encourage improved performance.
This section discusses the details and describes the evolution of a critical sensor in the implementation of a safety critical active controller in passenger cars called ABS (Antilock Brake System).
ABS works on the principle of optimizing the wheels slips (for maximizing the brake force) in the car during the event of braking. Wheel slips are defined as below:
The critical task in controlling the braking wheels of the car boils down to evaluating the speed of the vehicle and hence estimating the deceleration desired and actually achieved. The difference of which triggers the actual hydraulic pressure build up in each wheel.
The complex task of vehicle velocity estimation is done through using wheel speed sensors in each wheel of the car as shown below:
Until the advent of active wheel speed sensors recently, global automotive industry was using the passive wheel speed sensors for calculating the wheel speeds.
126.96.36.199. Passive Sensors
Passive sensors operate with a steel tone ring application. These variable reluctance sensors are used to measure speed/position of the vehicles tone ring. As the magnetic flux through the coil of the sensor is changed, so does the resulting voltage which is then measured and used to calculate wheel speed. This technology is considered outdated and is typically bypassed for active intelligent sensors.
188.8.131.52. Active Sensors (Intelligent)
Standard active wheel speed sensors operate on the Hall Effect. They are able to be used with a magnetic encoder or steel tone ring application. As the magnetic flux changes (created by an internal magnet or the magnetic encoder), the hall sensor creates an output current which can be measured and converted into wheel speed. Standard WSS only measure wheel speed and do not have any additional signals for vehicle operation. A Hall element (square shaped semiconductor layer) is supplied by a permanent current (I const). Applying a magnetic field perpendicular to the current flow the electrons are deflected due to the Lorenz force. This deflection can be measured as Hall – voltage, which is perpendicular to the magnetic field (B) and the current flow (I const). The Hall voltage (V Hall) is directly proportional to the external magnetic field.
The magnetic field is established either by a magnetic encoder or internal sensor magnet.
These active sensors offer benefits when compared to passive sensors. The dominant factors that took the stride towards active intelligent wheel speed sensors were:
Reduction in Cost but improvement in performance.
Low speed detection benefits. Passive sensors had the hurdle of building enough reluctance at low vehicle speeds but with active sensors wheel speeds can be detected with changing magnetic fields at as low as ~0.1 m/sec.
Direction detection. With developing ASICs and also the magnetic encoders thereby made wheel speed sensors smarter and hence has led to the advantage of vehicle motion direction detection in the sensors. It effectively has offloaded the software task of direction detection by many folds. With detection possible at such low vehicle speeds a new development of Hill Hold Controllers was triggered in the industry.
5.1.2. Intelligent sensor and the mechanism for transferring the measurement to a central data logger or processor.
Example is explained in the above question. The mechanism for transferring the measurement to a processor in this case it is ABS controller is here:
Pressure application on each wheel
With reference to the diagram above:
The data or pulses/signals from the wheel speed sensors are collected in the special ASICs designed for this purpose from there a SPI bus architecture is used to transfer it to the software layer (HSW box above). Filtering and certain algorithms regarding determination of data usability are made in the stat machine of the software layer. Usable and filtered data is further passed down to the ABS controller through the CAN bus. ABS determines the pressure targets for each wheel and hydraulic controller applies the set targets on the individual wheels for attaining the desired stopping distance of the car.
5.2 Future Development for Sensors and Actuators in autonomous vehicles
In the future, the hydraulic line may not ever again be needed in an automobile’s braking system. In fact, in a recent study performed by Frost & Sullivan, it is predicted that, after the year 2010, the automobile industry will begin to replace hydraulic-braking systems with that of brake-by-wire. The utilization of the brake-by-wire technologies like the electro-mechanical braking system and the electronic-wedge brake is predicted to be the norm for future vehicles.
This method of braking uses electronic signals instead of mechanical to achieve braking power. The electro mechanical barking system or EMB will not require hydraulic lines due to the activation of the brake being done within the wheel assembly itself. Instead of utilizing calipers, this system uses a wheel brake module. The module comprises of disc brakes and an electric motor which will be the one that activates the brakes during activation.
As it is, this method of braking is known as brake-by-wire. Certain automobile companies have almost already fully implemented this system into their automobiles, namely Toyota and Mercedes. However, a full brake-by-wire system has yet to come out and will only be out in the near future.
Future implementations will be the ‘autonomous vehicle navigation and obstacle detection sensor radar’. This device, currently being tested, will assist in reducing the quantity of separated components that is required to satisfy the needs of an autonomous vehicle. The navigation and obstacle detection can be done with just one component device. If being mounted on a suitable spot on a vehicle, this all-rounder obstacles detection and navigation radar will eliminate the need for multiple contemporary radars. This will reduce the weight of the vehicle and thus, saving on fuel cost.
Furthermore, future implementations will enable obstacle avoidance and prevent collision even when environment is obscured with smokes and dust.
5.2.3. Intelligent Cruise Control
In cars nowadays and in autonomous vehicles, the cruise control will only strive to maintain a safe distance from the front car. Unfortunately, this does not include the back car. With this new implementation, the spacing from the back vehicle will also be taken into consideration, together with the spacing from the front vehicle. This system also works and serves especially well when lane switching is being performed. This is due to the inadequate gap tendency between the front and back vehicle.
The earlier sections in this report has aimed to bring about the ideas of current technology implementations of an autonomous vehicle. As demonstrated, there are still flaws within the system. However, with the intelligence of sensors increasing constantly, it is almost sure that many of the problems faced by autonomous vehicle manufacturers will be solved in the near future.
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