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    Automated ppt Automated ppt Presentation Transcript

    • Building Automated Robots Sagar N & Sanjay R III year ECE
    • What is an automated robot? A machine which can accomplish a predefined task without external control. It must possess sufficient intelligence to take decisions. It must not receive any kind of aid from an external agent. It should have an on-board power source. Micromouse video.
    • Structure Of a Simple Robot A robot designed to accomplish a fairly difficult task must necessarily have a microcontroller. Input devices are interfaced to microcontroller through circuit elements which convert analog signals to digital signals. Output of the microcontroller is interfaced to actuators through buffers and drivers. Feedback can be used for efficient control. Power unit is essential to supply power to the various blocks.
    • A line follower… Sensors act as inputs to the microcontroller. Sensor outputs are given to the microcontroller after analog to digital conversion. Microcontroller is the basic intelligence unit which processes the input and controls the actuators – motors in this case. Motor drivers are either current amplifiers or pulse sequencers or both. They are used to drive the motors and prevent the microcontroller from getting burnt. A power supply unit is designed so as to provide proper voltage levels to microcontrollers, drivers and motors. Stabilized power to the microcontroller is an absolute necessity.
    • Sensors A LED is diode which emits light when forward biased by sufficient voltage. LDR: Its resistance varies with incident light intensity. Phototransistor is a transistor in which, the base current is proportional to IR Rays and, to a certain extent, visible light incident on it. IR LED: This emits infrared rays when forward biased. Commonly used reflective sensors: -LDR and LED pair -Phototransistor and IR LED pair
    • LDR and LED pair LDR has two terminals similar to a normal resistor but the resistance varies inversely with the light intensity. Its response is most significant in the visible region of spectrum. White LEDs give better performance as compared to other types. A small bulb can be used instead of LED but it consumes more power and dissipates a lot of heat. This sensor pair is better suited for light sensing bots and not for reflective sensing.
    • Phototransistor and IR LED Pair IR LED is similar to normal LED except that it emits IR Rays. Phototransistor generally has two terminals- collector and emitter –base drive is proportional to light intensity. IR LED emission strength increases by decreasing the series resistance and phototransistor sensitivity increases by increasing the collector resistance. Phototransistor response is best for IR radiation.
    • Spectral distribution of IR LED and phototransistor sensitivities
    • Circuit Connections
    • Interface to microcontroller Microcontrollers do not recognize voltages other than standard TTL levels. Comparators are used to convert the input analog signals to digital. Op amps LM324 can be used as comparators; LM339 is an IC designed as a comparator-they can be used for higher frequency operations.
    • Complete circuit diagram for IR LED - phototransistor sensor
    • Power Supply to Microcontrollers (µC) For proper functioning of µC a constant power supply is necessary. A Voltage regulator is used to give a constant 5V to the microcontroller. IC 7805 is generally used as a voltage regulator.
    • Circuit Connections
    • Motors Two types of motors are generally used : -DC Motors -Stepper Motors DC Motors:-Advantages: Small and light, cheap, consumes less power. Disadvantages: Inaccurate, Complicated closed loop control, needs gear boxes. Stepper Motors:- Advantages: Very easy to control (Open loop), very accurate. Disadvantages: Heavy, costly setup, consumes more power.
    • DC Motors-General It has two terminals. Voltage is applied to the terminals and the motor begins to rotate. Induced voltage opposes the current. Applying more load to the dc motors drops the speed & increases current, thus increasing the power consumption. Stall torque- A load just sufficient to stop the dc motor from turning.
    • DC Motors-Working Structure: Rotating armature-electromagnet. Armature enclosed between a set of permanent magnets. Commuter – Rotary switch which reverses the direction of electric current twice every cycle.
    • DC Motors-Torque and R.P.M Two important parameters-Torque, R.P.M. Torque is the amount of turning force. T=Kt*I I: Current through armature. R.P.M is rotations per minute and is proportional to the voltage applied. E=Ke*w w: Angular velocity • V=Rin*I + Ke*w
    • DC Motors-Gear Box DC Motors generally have thousands of R.P.M. Torque is very less without gears. Gears are used to decrease the R.P.M and in effect increase the torque. No gears and don’t expect your robot to move. Choose gears appropriately.
    • DC Motors– Speed Control Speed is proportional to the voltage applied across the motor terminals. Pulse Width Modulation is used. Pulses of definite frequency is applied whose ‘ON’ Time and ‘OFF’ Time decide the average voltage applied. PWM is easy to achieve using a micro-controller.
    • DC Motors-Speed Measurement PWM varies the speed but exact speed control requires speed measurement. Some DC Motors come with built in encoders. For DC Motors without such a setup, sensors must be used to measure the R.P.M and thus the speed. !idea! –Make some notches on the wheel and keep track of number of notches per second.
    • DC Motors- Motor Drivers Microcontrollers can supply 5V but not the enormous current required by motors. DC Motor Drivers act as buffer and in this case – current amplifiers. H –Bridge. Motor Driver IC-L293D. Different voltage can be given to motors.
    • L293D Circuit Connections
    • Stepper Motors-General Stepper is used for its accurate and easy control. Stepper motor has 4 control wires. 4 independent pulse trains to each of the 4 control wires. Two types of stepper motors: - Unipolar, Bipolar.
    • Stepper Motors-Working Shaft is a permanent magnet. Imagine a compass needle surrounded by four electro- magnets. Magnetising the coils one after the other makes the shaft to rotate. Here the step angle is 90 deg.
    • Stepper Motors-Working If the number of electro- magnets are more, then step angle reduces. In commercial stepper motors step angle will be approx 1.8 to 7.2 deg. Computers are great at switching things on and off. Thus with 4 pins dedicated to a stepper, speed can be easily controlled without feedback.
    • Stepper Motors-Control Sequences Full Step Sequence –Type 1 A B C D comment 1 0 0 0 take a step clockwise 0 1 0 0 another step clockwise 0 0 1 0 another step clockwise 0 0 0 1 another step clockwise 0 0 0 1 Wait right here! 0 0 1 0 Take a step back. Winding A 1000100010001000100010001 Winding B 0100010001000100010001000 Winding C 0010001000100010001000100 Winding D 0001000100010001000100010
    • Stepper Motors-Control Sequences Full Step Sequence-Type 2:More torque A B C D comment 1 1 0 0 take a step clockwise 0 1 1 0 another step clockwise 0 0 1 1 another step clockwise 1 0 0 1 another step clockwise 1 0 0 1 Wait right here! 0 0 1 1 Take a step back. Winding A 1100110011001100110011001 Winding B 0110011001100110011001100 Winding C 0011001100110011001100110 Winding D 1001100110011001100110011 time --->
    • Stepper Motors-Control Sequences Half Step Sequence: More accuracy A B C D comment 1 0 0 0 start here 1 1 0 0 half a step clockwise 0 1 0 0 complete the first full step clockwise 0 1 1 0 another half step 0 0 1 0 complete that step 0 0 1 1 another half step 0 0 0 1 complete that step 1 0 0 1 final half step 1 0 0 0 back to the starting position
    • Stepper Motors-Types Two types: Unipolar and Bipolar. Unipolar was discussed till now. Bipolar gives more torque and size is less. Drivers are expensive.
    • Interface to Microcontrollers (Uni-Polar) Unipolar stepper has 5 or 6 terminals. 4 control terminals and two power terminals. To drive Unipolar steppers, current amplifiers which amplify current in only one direction will suffice. ULN2803 is an IC designed as a current amplifier.L293D can also be used.
    • ULN 2803
    • Interface to Microcontrollers (Bi-Polar) Current flows from one terminal to other. H-bridge must be used. Driver ICs:L293D,UCN5804B,SLA7024. Sequencing ICs which generate pulses are available(e.g.L297) but are costly. Sequencing can be done by microcontrollers.
    • Block Diagram Of L293D
    • Inside a microcontroller