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Fuzzy based Wireless Speed Limiter

AbstractDifferent types of vehicle speed limiters are in current use for regulating traffic especially across roads near populated areas such as hospitals, malls, and schools. Motivated by statistics showing high traffic death rates occurring near these areas, a project aimed at implementing a wirelessly controlled speed limiting system is presented here. The proposed system is based on microcontroller technology for collecting data related to speed and transmitting it through a transceiver to a base station that analyzes the transmitted data and takes appropriate decisions related to speed limit and control requirements. The transmitting/receiving base station is to be located strategically at the entrance of populated areas where speed is to be maintained. Upon entry to these areas, the speed control is switched from the car driver to the speed limiting system. A model of the actual system is designed and built. Although this model is based on an electric car driven by a DC motor, it can be equally applied to a throttle valve controlled gasoline engine.

I.INTRODUCTION According to government estimates, India accounts for about 10 percent of the total 1.2 million fatal accidents in the world. An average of 365 accidents a day and more than 100000 fatalities a year. According to the ministry of shipping, road transport and highways, at least 129994 cases of road accidents were reported from the national highways in 2005, while the figure was 130265 in 2004. In 2003, a total of 127834 such cases were registered. All these fatal accidents are speed related. There is overwhelming evidence that lower speeds result both in fewer collisions and in reduced severity of collisions. A used method for speed management is cruise control. It is a system which allows the vehicle to maintain a steady speed without the driver using either the accelerator or the brakes. Cruise control systems are comprised of electronic and mechanical subsystems. The vehicle's speed sensor, mounted on the drive shaft of the transmission, sends electrical pulses generated by a magnet to the computer thus, when the vehicle's speed increases, the frequency of the pulses increases. For any given speed of the vehicle there is a corresponding pulse frequency. It is this pulse frequency which the cruise control tries to maintain as a constant. Disadvantages of Cruise control It works very effectively to control the speed of the vehicle but when it fails, it can be difficult to diagnose and fix. Driving over "rolling" terrain, with gentle up and down portions, can usually be done more economically (using less fuel) by a skilled driver viewing the approaching terrain, by

the vehicle to accelerate on the downgrades and decelerate on upgrades, while reducing power when cresting a rise and adding a bit before an upgrade is reached. Cruise control will tend to over throttle on the upgrades and retard on the downgrades, wasting the energy storage capabilities available from the inertia of the vehicle. The inefficiencies from cruise control can be overcome by using Wireless speed limiter system. This paper presents a new method by which vehicle speed is controlled externally rather than internally. The speed measurement and control is accomplished via two PIC microcontrollers with the signals being transmitted and received wirelessly by two transceivers. The master microcontroller is connected to a PC station in which fuzzy logic control software using Lab View is implemented to receive speed data from a shaft encoder implemented on a vehicle and then make appropriate decisions for controlling the speed to keep it below a certain limit. The motor speed control is carried out by controlling a PWM signal from the slave microcontroller installed on the vehicle. If the vehicle enters a speed-controlled zone, the control is shifted from the user to the speed limiting system that takes care of the PWM signal which controls the car speed to keep it in the desired range. All this process is activated when the vehicle passes through a certain populated area such as a school or a shopping area.

II. BLOCK DIAGRAM The first transceiver is installed near the base station while the other is implemented on the vehicle itself thus establishing a wireless link between the user interface near the computer and the microcontroller- H bridge-encoder system on the vehicle as shown in figure 1 below.

Figure 1: The overall system communication and control diagram

maintaining a relatively constant throttle position and allowing

III.SYSTEM COMPONENTS The proposed system is composed of a number of integrated subsystems namely: PWM motor controller, Fuzzy logic control, wireless serial communication and speed measurement. A brief description of each subsystem follows. A.PWM motor controller The PIC microcontroller is capable of generating a pulsewidth-modulated signal of specific duty cycle (see figure 3) controlled by programming several registers of the MCU. This PWM signal generates a varying output DC voltage to drive the DC motor through an H-bridge which transforms the PWM signal into an output voltage proportional to the duty cycle of the PWM signal.

Figure 4: Schematic of the L298

Fig 5 shows a bidirectional DC motor control Schematic diagram for which only one bridge is needed. The external bridge of diodes D1 to D4 is made by four fast recovery elements (trr = 200 nsec) that must be chosen of a VF as low as possible at the worst case of the load current. The sense output voltage can be used to control the current amplitude by chopping the inputs, or to provide over current protection by switching low the enable input. The brake function (Fast motor stop) requires that the absolute maximum rating of 2 Amps must never be overcome.

Figure 2: Pin diagram of PIC microcontroller

Figure 5: Bidirectional DC motor control

Figure 3: The pattern of the PWM signal

Vout = Duty Cycle (in %)*supply voltage Where Duty Cycle= (a/a+b)*100 The importance of the H-bridge circuit lies in the fact that it can drive the motor forward or backward at any speed through the use of an independent power source which provides the circuit with increased protection and isolation. In this paper, it is decided to use a common H bridge that can handle up to 2 A of current and about 40 V of supply voltage for driving the motors. In addition, it can drive up to 2 DC or stepper motors at the same time. Figure 4 below shows a schematic of the L298.

B.Speed Measurement A rotary encoder is used to transform the mechanical rotational movement of the vehicle shaft into an electrical signal in the form of pulses and thus detect rotations of the rotating shaft. The shaft has brushes perpendicular to the axis. The number of brushes determines the resolution of the rotation. The used encoder generates 1024 pulses per revolution which indicates high resolution. As each brush passes the pickup sensor, the output voltage level reverses (from high to low) to indicate that a brush has passed. The number of output voltage changes, over a given period of time, gives angular velocity. Angular velocity= (no of voltage changes)/ (1024*time of measurement) The encoder is from the E40S series manufactured by

3 Autonics and is shown in figure 6 below. 10s and 200s for correct operation. A double layer board for each transceiver is implemented as shown in figure 8 taking into consideration two important elements: proper positioning of the whip antenna which must be connected to a 50 ohm line surrounded by ground and proper 12V power supply regulator since the device is very sensitive to voltage variations. The receiver antenna must get the transmitted signal from the transceiver antenna across the channel. When the wireless transceiver at the transmitter side is not transmitting, the transceiver at the receiving side will catch noise in the air by the receiver antenna and demodulate the signal as shown in figure 9.

Figure 6: The shaft encoder used for measuring speed

This encoder is characterized by the following features: First, it is easily installed at narrow space. Second, it has small inertia moment. Third, it has wide range of power source: 15~24VDC 5% and finally it is characterized by various output types. The output of the encoder is driven to one of the pins of the PIC through which a hardware interrupt is generated to count the number of changing edges (rising or falling) for a given period of time (90 ms in this case) to calculate the speed of the vehicle . The speed measurement is then processed to the speed control algorithm for proper action. C.Wireless Serial Communication One of the major tasks in this paper was to establish a reliable wireless serial link between the vehicle and the base station. The communication protocol used to establish the link is the Asynchronous Serial Protocol which is considered one of the most reliable protocols in serial telecommunications. In this protocol, logic 1 represents the idle state (marking state) of the communication channel, while logic 0 represents the non-idle state (spacing state) as shown in figure 7 below. The start bit of the sent data is the synchronization bit that indicates the transition from the idle state. The stop bit on the other hand, indicates that desired data is transferred which switches returns the link to the idle state

Figure 8: Schematic of the XTR 434 transceiver and its double layer board

The noise signal observed is around few MHz and the PIC microcontroller must be able to distinguish between valid data and noise from air in order to receive the desired data.

Figure 7: The idle and non-idle states of the UART Protocol

The transceiver chips used to establish the wireless link are the AUREL XTR 434 which operates at 100 kbps and 433.92 MHz The time between each two consecutive level transitions on the line of the serial signal must be comprised between

Figure 9: The signal pattern at the receiver side before and after data transmission

IV. FUZZY LOGIC CONTROL Fuzzy logic is a new promising technology used to find

solutions for complex non-linear control problems. Its significance lies in the fact that it does not require a mathematical model to solve the problem instead, it relies on human interaction and experimentation which reduces the complexity and produces more efficient results. Moreover, the implementation of the fuzzy logic control techniques on microcontrollers requires less space and is characterized by faster execution. A. The Fuzzy Logic Method The fuzzy logic analysis and control method is, therefore: Receiving of one, or a large number, of measurement or other assessment of conditions existing in some system we wish to analyze or control. Processing all these inputs according to human based, fuzzy "If-Then" rules, which can be expressed in plain language words, in combination with traditional non-fuzzy processing. Averaging and weighting the resulting outputs from all the individual rules into one single output decision or signal which decides what to do or tells a controlled system what to do. The output signal eventually arrived at is a precise appearing, defuzzified, "crisp" value. Please see the following Fuzzy Logic Control/Analysis Method diagram.

with the maximum speed value pre-set in the device. Based on this, it computes the command value for the pulse proportional valve (PPV) that controls the air pressure in the cylinder. The air stems from the vehicle's pressured air system. In a nonlinear but proportional ratio, the cylinder shortens the arm linking the accelerator pedal to the fuel pump so that the fuel pump is throttled.

Figure 11: Mechanical Design of the Speed Limiter

VI. CONCLUSION The new speed limiting system presented in this paper combines several pioneering techniques that integrate wireless and fuzzy logic technologies in order to implement a reliable speed control system. This proposed system can be easily implemented near different populated areas such as schools, malls etc. The power of the proposed system lies in its flexibility and capability of development with little hardware changes such as changing the speed limits and speed control methods using the software of the base station in negligible amount of time. REFERENCES1] 2] 3] 4] 5] 6] 7] 8] 9] Developments in Safer Motor Vehicles.16-17 March 1998 Parliament House, New South Wales. A. Smaili, F. Mrad, Mechatronics: Integrated Technologies for Intelligent machines, Future. Minds Publishers 2004 M. Predko, Programming and Customizing PIC Microcontrollers, McGraw Hill 2002. R. Stevens, Serial Communications Using PIC Microcontrollers, Square Publishers 2002. Pic16F87X Datasheet, Microchip.[Online]. Available: http:://www.microchip.com XTR 434 Transceiver Instruction Manual, Aurel2001. [Online]. Available: http:://www.aurel.it Hou, Cheung et al, "RoboCup: A systems engineering project", Thesis, Cornell University 2003. Ron Ng W.L, "Development of a Security System using Wireless FSK Communication", Thesis, University of Queensland, Australia 2003. Altrock, B. Krause, E. Nield, M.Lord, and A.Baker, "Truck Speed Limiter Control by Fuzzy Logic", Fuzzy Logic '94 Conference, San Francisco.

In this project three member functions for input and three for output were used representing low, medium, and high speeds where the output of the encoder is the input for the fuzzy logic controller while the final output from the controller is the duty cycle of the PWM signal. Figure 10 below shows the input/output characteristics of the implemented fuzzy controller.

Figure 10: The input/output characteristics of the fuzzy logic controller

V. MECHANICAL DESIGN OF THE SPEED LIMITER Figure.11 sketches the outline of the mechanical design of the speed limiter. An electronic control unit (ECU) compares the digital pulse signal from the speedometer or speed encoder