08-01-2013, 03:50 PM
TRAINING REPORT OF SIX WEEKS INDUSTRIAL TRAINING, UNDERTAKEN
AT PPIN TECHNOLOGY LAB
INDUSTRIAL TRAINING,.docx (Size: 1.12 MB / Downloads: 48)
INTRODUCTION
The robots of the movies, such as C-3PO and the Terminator are portrayed as fantastic, intelligent, even dangerous forms of artificial life. However, robots of today are not exactly the walking, talking intelligent machines of movies, stories and our dreams. In the 1970’s scientists proposed that in the year 2000 we would have created artificial life forms, almost perfect in terms of intelligence and capabilities. The dream of free and efficient labor made the researchers of the time go on day and night to bring the dream to existence. But the task was futile due to the lack of compact processors to carry out the calculations which were oh so necessary. Now in the year 2000, the microprocessor
Technology is thousands of times more advanced than what existed back then.
But still the robots of today are no way close to what our movies portray them to be. This is not only due to drawbacks in processor technology, but also in various other fields such
as vision, motor control so and so forth .Robots may never make it to our kitchens or living rooms as personal slaves, but
they certainly have made their way to the manufacturing industry, aero-space industry, and yes to the work benches of robotic hobbyists. Robots are now working in dangerous
places, such as nuclear disposal, space explorers, fire fighting, etc.
DESCRIPTION
The line following robot, operates on the specified path. It is programmes to follow a dark line on a white background or vice-versa and detects turns or deviations and modifies the motors appropriately. The optional sensor is an array of commercially available IR reflective type sensors. The core of the robot is PHILIPSNXP P89V51RD2FN micro -controller. We can also use Atmel Microcontroller but Philips being more efficient and long lasting it is preferably used. The speed control of the robot is achieved by two 100rpm geared motors. The direction control is provided by two I/O pins. To run these motors, IC L293DNE is being used that take the signals and translates it into current direction entering the motor armature. The motors require separate supply for operation. The differential steering system is used to turn the robot. In this system, each back wheel has a dedicated motor while instead of front wheel a caster wheel has been used for free rotation. To move in a straight line, both the motors are given the same voltage (same polarity). The sensor is an array of 3 IR LED-Phototransistor pairs arranged in parallel on a separate PCB. The arrangement of IR LED sensors can be arranged in many different forms depending upon the type of work to be performed. The output of each sensor is fed into an analog comparator with the threshold voltage. These 3 signals (from each photo-reflective sensor) is given to a priority encoder, the output of which to the microcontroller. The control has 6 modes of operation, turn left/right, move left/right, pivot motion and straight motion. The actual action is caused by controlling the direction/speed of the two motor (the two back wheels)
SCOPE OF STUDY
The robot can be further enhanced to let the user decide whether it is a dark line on a white background or a white line on a dark background. The robot can also be programmed to decide what kind of line it is, instead of a user interface. The motor control could be modified to steer a convectional vehicle, and not require a differential steering system. The robot could be modified to be a four wheel drive. Extra sensors could be attached to allow the robot to detect obstacles, and if possible bypass it and get back to the line. In other words, it must be capable predicting the line beyond the obstacle. Speed control could also be incorporated. Position and distance sensing devices could also be built in which can transmit information to a mother station, which would be useful in tracking a lost carrier.
METHODOLOGY
The first idea was to use optical imaging (CCD cameras) to see the line. This was later given up due to various reasons including complexity and unavailability of components. Later a choice was made to use an array of sensors which solved most of the problems pertaining to complexity.
The resistor values used in the sensor array were experimentally determined rather than theoretical mathematical design calculations. This was done as the data sheets of the proximity sensor was not available anywhere and most of the parameters had to be determined experimentally.
The L293D chip is used as it was a much better option than forming an H-Bridge out of discrete transistors, which would make the design unstable and prone to risk of damage.
The 8051 microcontroller was used as the core of the robot.Few more IC’s has been that are LM324N and HEF40106 with there functionality described further.
THEORY
THE DIFFERENTIAL STEERING SYSTEM
The differential steering system is familiar from ordinary life because it is the arrangement used in a wheelchair. Two wheels mounted on a single axis are independently powered and controlled, thus providing both drive and steering. Additional passive wheels (usually casters) are provided for support. Most of us have an intuitive grasp of the basic behavior of a differential steering system. If both drive wheels turn in tandem, the robot moves in a straight line. If one wheel turns faster than the other, the robot follows a curved path. If the wheels turn at equal speed, but in opposite directions, the robot pivots.
IR- SENSING ABILITY
The IR sensors used are two LED’s attached together, one being the Receiver and the other one as Transmitter. As the name suggests receiver receives the signal(color code) and send the output to the controller and transmitter transmits the signal(color code).
The ability to sense the color or the nature of the surface depends upon the comparator frequency. It can be changed for different colors by just moving the button on top of the comparator. Earlier comparators were only designed for detecting black and white colors. But now they can detect any color.
The distance from the surface to the IR sensor chip also plays an important role. Lesser the distance, more easily the sensors will detect the color code and will do the pre-defined job. In case we change the color coding through comparator we also have to change the program code before burning it into the controller.
8051 MICROCONTROLLER:
8051 has a hardware architecture and based on CISC(complex instruction set computer).The 8051 has separate addresses for program and data memory.
The logical separation of both the memories allows the data memory to be accessed by the 8 bit addresses, that can be quickly stored and manipulated by an 8 bit cpu. The 16 bit data memory addresses can be generated through the data pointer register(dptr).The program memory (rom,eprom) can only be read. Thus there can be 64k bytes of memory and the programs upto 4k can be stored on chip. There is read strobe for external program memory called PSEN(program store enable).
RAM occupies a separate space from program memory. There are 128 bytes on chip memory for the ram and upto 64k bytes of external ram can be addressed in external data memory space. The cpu generates the read and write signals as needed during the external data memory access.
EXTERNAL CODE MEMORY
Code memory is the memory that holds the actual program that is to be run. The code memory can be on-chip or can be burnt in controller as ROM or EPROM and this could be completely off chip as external rom. Flash ram is another popular method of storing a program. The storage capacity of a memory depends on the version of the chip that is being used each version has its own specific capabilities and the amount of memory they are going to use.
EXTERNAL RAM
8051 is capable storing an external ram. The external ram is not as flexible in terms of accessing and is slower .e.g:-an internal ram requires only 1 instruction and 1 cycle to increment any number where as an external ram requires 4 instructions and 7 instruction cycles to do the same, thus it is 7 times slower than the internal ram. But it gains in quantity that means an internal ram is restricted to only 128 bytes but an external ram can offer you 64k of memory.
VOLTAGE REGULATOR:
It has been shown that practically all electronic devices need DC supply. A direct voltage of constant magnitude requires to be supplied, for the smooth and efficient functioning of these devices. A properly designed voltage regulator ensures that, irrespective of change in supply voltage, load impedance or temperature, the DC supply is maintained at a constant level. This is achieved by incorporating some type of feedback in the regulator circuit. An IC voltage regulator unit contains all the circuitry required in a single IC. Thus there are no discrete components and the circuitry needed for the reference source, the
comparator and control elements are fabricated on a single chip. Even the over load and short-circuit protection mechanism is integrated into the IC. IC voltage regulators are designed to provide either a fixed positive or negative voltage, or an adjustable voltage which can be set for any value ranging between two voltage levels.