Students :Rabee odeh

Ahmad Anwarsupervisor:

Dr. Raed jaber

Angular position control of a dc motor

There are several industrial ,automatic ,and other processes that require the control of angular position of a motor (or translation position) the stepper motor achieve this purpose but the stepper motor lack the advantage of controlling the angular position at wide range of speeds; this aim is achieved by using dc motor which allow us to control the position at a wider range of speeds in both reverse and forward direction.

Introduction

Position control systems are an important component of many industrial products . Examples are found in disc drives ,automotive products ,robotics ,process control and many others.

Aim of a position control system

In all servomechanisms one of the most important components is the position sensor it measures the position of the servomotor and convert it to an electrical signal that the control system can interpret and use.

Digital optical position sensors are particularly important because they are non contact and thus not subject to the wear and noise of analog position controllers .

A further advantage of optical sensors is that

they can be used in severe environments where strong magnetic field exists.

General information and introduction

• We used a dc motor of parameters that will be studied and analyzed next,an optical shaft encoder that consist of a transmitter and a receiver will be studied and analyzed next,pic 16f877 4 MHZ it's cct and code will be analyzed next.

Generic block diagram of the project

Load information and parameters (DC-MOTOR)

Dc electric motor is used as a manipulative device in control systems ; dc motors are extremely versatile drives capable of reversible operation over a wide band of speeds ,with accurate control of the speed at all times ;they can be controlled from zero speed to full speed in both directions in this project our goal is to control the motor position at a specific speed in both directions but the advantage of range of speeds give the motor a great importance in position control systems.

Measurement of motor constantsAbout used DC motor.

-It is a DC motor (constant flux) ,12 volt rated , -We measure its parameters (Ra, La, Kp, J, B) as follows

:1st : armature resistance (Ra)

By an ohm meter we found that Ra =10.5 Ω•

•2nd :induced or back emf constant (Kb)•We applied a 12 v DC voltage to the terminals of the

motor and measured Va and the speed (rpm) and repeated for less voltages as in the following table:

Va Ia (mA) N(rpm) W=2*pi*N/60 (rad/s)

12 170 3000 314.16

10 145 2200 230.384

8 123 1700 178.024

6 115 1350 141.372

4 86 800 83.776

2 68 350 36.652

Now from the relation Va = e+RaIa +La(dIa/dt)

In steady state Ia is constant so Va =e + RaIa But e = Kb* Ф*w (Ф: is constant)

e= Kb*w (Va/Ia) = Kb (w/Ia) + Ra so we construct the following table:

Va/Ia Wm/Ia

70.58824 1848

68.96552 1588.855

65.04065 1447.35

52.17391 1229.322

46.51163 974.1395

29.41176 539

• We plot (Va/Ia ) vs. (Wm/Ia ) as follows :

Kb = slope = 0.033 v/rad/

Ra = intersection =12.28ΩRa = Ra avg =(10.5+12.28)/2 =11.2 Ω

rd : Armature reactance (La ) 3By applying a variable low AC voltage to the armature terminals and increasing the voltage until the motor start to move we measured the current (Ia) and the

rms voltage (Va) , we found that: The min AC voltage Va = 20 v

Then Ia = 1.7ARa = 1.1*11.66 =12.83 Ω we calculated La from the relation:

=26.8 mH

4th : J and B: Rotor mass = 50 gmRotor diameter = (shaft diameter+ Rotor diameter)/2

( = 0.002+0.02/)2=0.011 mJrotor = 0.125* mass*diameter^2

= 0.125*0.05(*0.011^)2= 8*10-^7Now for B :From the relation : (Kb*Ia) =B* (W)We construct the following table and plot (Kb*Ia) vs (W)

Kb*Ia W

0.00561 314.16

0.004785 230.384

0.004059 178.024

0.003795141.372

0.002838 83.776

0.002244 36.652

B = slope =1.1*10^-5Tind rated =Kb* Ia rated =0.0308*0.085 = 0.0056

OR:Tind rated =er*Iar/Wr=(Var-Iar*Ra)*Iar/Wr

( = 12-0.085*11.6*)0.085/335 =0.00542

This was the first section which describes the used dc motor

driving cct(H-BRIDGE)

An H-bridge is an electronic circuit which enables a voltage to be applied across a load in either direction. These circuits are often used to allow DC motors to run forwards and backwards. H-bridges are available as integrated circuits, or can be built from discrete components.

In this project the first type is used ; a dual full bridge driver l298.

L298 is high current high voltage full bridge driver of a total dc current up to 4 ampere and of an operating supply voltage up to 46 volts .

The block diagram of the circuit is shown in the following figure:

From which we use two inputs connected to the microcontroller and two outputs connected to the motor(load).

• The alternative was to to build a full bridge using transistors which is cheaper , but for purposes of simplifying the work we use this chip (L298) .

• An H-bridge is built with four switches (solid-state or mechanical). When the switches S1 and S4 (according to the first figure) are closed (and S2 and S3 are open) a positive voltage will be applied across the motor. By opening S1 and S4 switches and closing S2 and S3 switches, this voltage is reversed, allowing reverse operation of the motor as shown below .

Forward direction

And in this case the applied voltage(Va) at the motor terminals equal to input voltage(Vi)-voltage drop on switch 1(VT1)-voltage drop on switch 2(Vt2)

shaft encoder and it's cct

• Sources and detectors • Source:• The light source for the optical encoder is either

light emitting diode (led ) or laser diode , the led is considerably less expensive than the laser and used for relatively slow speed or lower frequency communication application ,the light output from the led has a broad spectral bandwidth and emits from the led as a large cone!

• Detectors: • Optical receivers are critical components in such

systems ,their performance play a dominant role in determining the spacings and in the flexibility of the system in terms of its sensitivity.

• The received signal must be converted into an electrical signal , amplified and processed ; to give an estimate of the transmitted signal ;to use it in directing the motor in the desired direction .

Basic Light Detector

• The following cct features basic, visible light photo-detector circuit that can be used to detect trains or other light blocking objects.

• The sensor used for this circuit is silicon phototransistor this sensor allow less current to flow when they are dark. (Phototransistors change their 'conductance' ).

• The phototransistor would normally be placed between the rails in the circuit .

• The Photo-detector use LM339 voltage comparator, integrated circuits to detect the change in voltage across the sensor. the circuit is configured to have the LED's turn on when the sensor element is dark (covered by a train.) The LED's can also be made to turn off when a train is detected.

• The supply voltage for the circuit is specified as regulated 12 volts DC but this can be changed if needed. In some cases the values of some resistors may have to be adjusted to compensate(calibrate).

• In this circuit, when the light falling on the phototransistor (Q1) is blocked, its conductance will decrease and the voltage across Q1 will rise. When the voltage rises above 1/2 of the supply voltage the output of the comparator will turn ON and the LED will be lit.

• The only critical part of this circuit is the value of resistor R1 which in most cases can be 470K ohms but may have to be increase if the room is dark or decreased if the room is well lit.

• Increasing the value of R1 will cause the sensitivity of the sensor to decrease. This may be necessary when the light falling on the cell is not very strong or shadows can affect the phototransistor.

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• Pin Diagram For An LM339(Internal Circuitry For LM339)

pic16f877

While talking about the pic and it’s cct ,excuse me Dr. samer and please accept my maximum respect and all of you my classimates , dr.s.

Let me tell a joke about why using this pic(pic 16f877), When I decided to buy the microcontroller (pic) , we look

for the memory of the pic; what will the type which will fit the size of the project program , anyhow we decided to use pic18 you know it has a larger memory maybe 5 more size we need to control the position at different velocities , we need to do a lot of things anyhow students said “ مجنون انت .”... شو

By a childish behavior I switched back to pic 16 despite of my unconveniance .

Yes in the last month we learnned about the pic and exactly pic 18 but we haven't absorbed it yet in the matter which enables us to write a program .

However the connection of the basic circuit of the pic which we used is shown in the next slide the connection of the input output devices is shown next:

• The position control mode is the simplest and least expensive mode of control in which the controller output has only two possible values depending on the sign of of the error (in which a neutral zone is considered around the zero such that no action take place).

Such that SP: step pointen: nth sample of error.In: integral mode action.Pn: proportional mode action .Dn: derivative mode action.Delta: sample time used to compute the

derivative mode action.