Principles Of Operation Of Dc Motor Information Technology Essay

The idea of a machine is very old about 2000 years. Hephaestus the God of fire according to Greek mythology constructed artificial women from gold. These were able to walk, talk and also able to think.

A robot is a mechanical device that can perform programmed physical tasks. The present disclosure generally relates to robotic systems,. Robots and other remote control devices are becoming more popular. At present

This motor generates torque using the DC power supplied to the motor through commutators, permanent and electrical magnets. While permanent magnets are stationary and electrical magnets are rotating. Lorentz force principal states that any current-carrying conductor placed in thel magnetic field experiences a force which is known as Lorentz force. Using brushed DC motor has several advantages that it has low cost, high dependability and easy control of speed. But here are some disadvantages that it requires high maintenance and has low life-span. In maintenance we have to change the commutators brushes and springs regularly. Rotor inside of the motor gets power from these components which are outside of the motor. So these are very important components of a DC motor.

2.1.2 Synchronous

These motors are also known as brushless motors. These motors generate the torque through the external commutation. These are similar to the AC synchronous motors.

2.2 Principles of Operation of DC Motor

The principle due to which the motor works is known as electromagnetism. When a current carrying conductor is placed in an external magnetic field then it experiences a force that is directly proportional to the current in conductor and to the strength of external magnetic field. Due to this force rotational motion is produced by the motor.

2.3 Parts of a DC Motor

Dc motor consists of six different parts described as follows.

Axle

Rotor or Rotator

Commutator

Brushes

Stator

Field Magnets

FIG 2.1Electric Motor Construction [2]

In DC motors the permanent high strength magnets produce the external magnetic field. The stationary part of the DC motor is stator. Motor casing and two or more permanent magnet pole pieces makes the stator. Stator is used by the rotor. It means that it rotate with respect to the stator. For this purpose it uses the axel and the attached commutator. Windings are electrically connected to the commutator to make rotor. To align the rotor with the stator’s field magnet it is rotated. When the rotator is in alignment with the brushes it moves the next commutator contacts and energizes the winding. The use of an iron core armature is very common. Iron core has a number of advantages which are given as follows.

Strong rigid and powerful support for the winding is given by the iron core. This is important for high torque motors. The core works as a heat sink for rotator windings; due to it we can drive the motor harder. The one more advantage is the iron core construction is cheap as compared to others types of construction. There are also other advantages that iron core have and these are given as follows.

“Iron armature has high inertia because of which the acceleration of the DC motor becomes restricted. It causes high winding inductances which limit the life of brushes and the commutator”.

In small motors a different design is used depends upon the wire used in the coil. This is done for the structural integrity purpose .This result in a hollow armature and in this way we can mount the permanent magnet inside the rotor coil. If coreless DC motor armature inductance is low as compared to others. Such a coreless design allows the manufacturers to make a motor of smaller size. Therefore such a design is generally used for small and low power motors. In other DC motors windings produce the external field. But modern DC motors are more efficient because the permanent magnets are used in them .These use the low power and reduce the external heating. In the above diagram you can see that there are two magnets in the motor. The field magnet is permanent magnet while the armature or rotor is an electromagnet. An electromagnet can also be used as a field magnet but in most cases it is not able to save the power.

The motor showed here is a simple electric motor that is typically used in a toy:

FIG 2.2 View of DC Motor [2]

FIG 2.3 Connection Views [2]

FIG 2.4 Back View Connections [2]

“The nylon end cape is held in place by two tabs that are part of the steel can. By bending the tabs back, you can free the end cape and remove it, Inside the end cape are the motor’s brushes. These brushes transfer power from the battery to the commutator as the motor spin” [2]

FIG 2.5 Brushes View [2]

FIG 2.6 Brushes connection view [2]

2.4 H-Bridge

For the graphical representation of a circuit H-Bridge term is used. Four switches (S1, S2, S3, and S4) are used in an H-Bridge as shown in the figure below. These switches are made mechanically or of the solid state. When switches S1 & S4 are closed then a positive voltage is applied to the motor. When the switches S2 & S3 are closed then a reverse voltage is applied to the motor to do the reverse operation. During the reverse operation the S1 & S4 are in open state.

The switches S1 and S2 are never closed together and also the switches S3 and S4, because if it happens then the short circuit would happen on input voltage. The name of that condition is shoot-through.

The figure is shown below.

H-Bridge structure

S1

S2

S3

S4

Result

1

1

Moves right

1

1

Moves left

1

1

1

1

Motor runs freely

1

1

Motor is braked

1

1

Motor is braked

Truth Table of H-Bridge

2.4.1 Description

In a 15-lead Multi-Watt and PowerSO20 packages the L298 is an integrated monolithic circuit. It is designed to accept standard TTL logic level and drive inductive loads such as relay, solenoids, DC and stepping motors and is a high voltage high current dual full-bridge driver. To enable or disable the device independently of the input signals two enable inputs are provided. The emitter of each bridge is connected together and the external terminal can also be used for the connection of an external transistor which is a sensor. To work at lower logic level an additional supply input is provided

We used H-Bridge with the DC motor. The motors of 100 watt, 40 volts or 5 amps are driven through that device or circuit. The operation of the H-Bridge is very easy. 6 to 40 volts DC power of motor is required. A & B are used as two logic level inputs and two outputs. To make the output-A high and output B low input A is given high voltages and the motor moves in one direction. To make the output-A low and output B high input B is given high voltages or input A is given low voltages and the motor moves in opposite direction. If both the inputs are at low then motor do not run and freely coasts and no power is consumed by the circuit. When both the inputs are at high then braking occurs in the motor. In common H-bridge 0.05 amps are consumed.

In our project we used L298 as H-Bridge. The L298 is an advanced IC which is in lead multi-watt power SO20 packages. It is a dual bridge driver with high voltage and high current. It is designed to accept standard TTL logic levels to drive inductive loads such as relays, solenoids, DC and stepping motor. There are two enable Inputs in it. To enable or disable the device independently of input signals these inputs are used. The emitter in which lower transistors are used is connected together. Two powerful outputs are integrated by the use of L298.

FIG 2.7 Block Diagram of L298 [3]

2.4.2 Absolute Maximum Ratings of L298 [17]

Symbol

Parameters

Values

Units

Vs

Power Supply

50

V

Vss

Logic Supply Voltage

7

V

Vi, Ven

Input and Enable Voltage

-0.3 to 7

V

Io

Peak Output Current (Each Channel)

-Non Repetitive (t=100µs)

– Repetitive (80% on -20% off; ton = 10ms)

-DC Operation

3

2.5

2

A

A

A

Vsens

Sensing Voltage

-1 to 2.3

V

Ptot

Total Power Dissipation (Tcase =75°C)

25

W

Tstg, Tj

Storage & Junction Temperature

-40 to 150

°C

2.4.3 Pin Connection

FIG 2.8 Pin Connection of H-Bridge [3]

FIG 2.9 DC Motor Driving Circuit Testing Photo

2.5 Microcontroller

Microcontroller is a small computer on a single integrated circuit having a processor core, memory and programmable input or output. Program memory is included on the chip and it is in the form of NOR flashes or OTP ROM. Microcontroller is used in the embedded applications.

Microcontrollers are used to automate the products and devices such as home appliances, office machines, medical devices and remote controls etc. We use the microcontroller because due to it the cost and the size of the device is reduced, and the single microcontroller can control even more devices and processes.

2.5.1 Peripherals Features

Peripheral features are given below.

It consists of a timer0 module. It is an 8 bit pre-scalar with 8-bit timer.

It also has timer1 module which is 8 bit timer with pre-scalar. During SLEEP via external crystal It can be incremented or clock.

It has 8 bit timer with 8 bit period register along with pre-scalar and post-scalar with timer2 module.

Two capture, compare, PWM modules.

It has Master synchronous serial port module.

It has two modes of operation.

Supports all 4 SPI modes.

1^2 C Slave and Master Modes.

It has module of Addressable USART

On address bit it supports interrupt.

It has module 8 bit wide Parallel Slave Port (PSP).

It has Source current of 25 milli-amps and also the high sink. [5]

2.5.2 Analogue Features

10 bit 8-ch to digital converter.

Analog comparator module is programmable on-chip voltage reference module with two analog comparators. Programmable input multiplexing from devices inputs and internal voltage reference. The outputs of comparators are externally accessible.

2.5.3 Special Features

100,000 erase or write cycles enhanced flash memory program typical.

1, 00,000 erase or write cycles data EPROM memory typical.

Retention of data EPROM is greater than 40 years.

Under software control it is self reprogrammable.

Serial programming via two pins is done in circuit.

In-Circuit serial programming there is single voltage supply of 5 volts.

With its own on-chip RC oscillator for reliable operation it has Watch Dog Timer.

Programmable code protection.

Sleep mode of power saving.

Oscillator options are selectable. [5]

2.5.4 Advance Information about PIC16f877

PIC16f877 has program memory of 14.3K bytes. Single word is of 8192 bytes.

It has data SRAM of 368 bytes.

EPROM is of 256 bytes.

It has 33 I/O ports.

It has 2 comparators.

It has 2 PWM channels.

2.5.5 PORT A & TRIS A Register

Port A is bidirectional and 6 bit wide port. The register is named as TRIS A. Clearing a TRIS A bit=0 will make the port A an output. To make the port A pin an input it is set at 1. Reading a PORTA register reads the status of the pin whereas writing to it will write to the port latch. All write operations are read-modify-write operations. Therefore a write to the port implies that the port pins are read. The value is modified and then written to the port data latch. Pin RA4 is multiplexed with the timer 0 module clock input to become the RA4/T0CKI pin.

2.5.6 PORT B & TRIS B Register

PORTB is an 8 bit wide and bidirectional port. The corresponding data direction register is TRIS B. setting a TRIS B bit=1 will make corresponding port B pin an input. Clearing a TRIS B bit=0 will make the corresponding port B an output. Three pins of the PORTB are multiplexed with the low voltage programming functions.

2.5.7 PORT C & TRIS C Register

PORTC is an 8 bit wide and bidirectional port. The corresponding data direction register is TRIS C. Setting TRIS C bit=1 will make the corresponding port C pin an input. Clearing TRIS C bit=0 will make the corresponding port C an output. PORTC is multiplexed with several peripheral functions PORTC pins have Schmitt Trigger input buffers.

2.5.8 PORT D & TRIS D Register

PORTD and TRIS D are not implemented on the PIC16F873 or PIC16F876. PORTD is an 8 bit port with Schmitt Trigger input buffers. Each pin is individually configurable as an input or output.

2.5.9 PORT E & TRIS E Register

PORTE has three pins (RE0/RD/AN5, RE1/WR/AN6, and /CS/AN&) which are individually configurable as inputs or outputs. THESE pins have Schmitt Trigger input buffers.

2.6 Ultrasonic Module

2.6.1 Advantages of Ultrasonic Sensor

When used for sensing functions the ultrasonic method has unique advantages over conventional sensors given below.

Moving objects can be detected and measured from discrete distance.

Less effected by target material and surfaces, and not affected by color. Solid State units have virtually unlimited maintenance free life.

Can detect small objects over long operating distances.

Resistance to external disturbances such as vibration, infrared radiation, ambient noise and EMI radiation.

2.6.2 Types of Ultrasonic Sensors

Proximity Detection

An object passing anywhere within the present range will be detected and generate an output signal. The detect point is independent of target size, material or degree of reflectivity.

Ranging Measurements

Precise distance(s) of an object moving to and from the sensor are measured via time interval between transmitted and reflected bursts of ultrasonic sound. The example shows a target detected at six inches from sensor and moving to 10 inches. The distance change is continuously calculated and outputted.

2.6.2 Target Angle and Beam Spread

Terminology “Target Angle” refers to the “tilt response” limitation of a given sensor. Since ultrasonic sound waves off the target object target angles indicates acceptable amount of tilt for a given sensor. If an application requires a target angle beyond the capabilities of a single sensor two sensors can be teamed up to provide an even broader angle of tilt.

And the term “Beam Spread” is defined as the area in which a round wand will be sensed if passed through the target area. This is the maximum spreading of the ultrasonic sound as it leaves the transducer.