automatic actuator control through speed

1

Introduction

1.1 Purpose:

Its utility is in UNDERGROUND MINE VENTILATION to regulate the wind

speed inside the mines. If the wind speed exceeds a certain limit then the

actuator gets activated. In this way we can avoid the high speed wind entering

the mines.

Moreover, it can be used in garbage dumpers to dump industrial wastes.

1.2 Objective:

The main objective of our project work is to activate/deactivate the actuator after certain threshold speed.

In our project we consider the speed limit to be 20kmph. So, once the speed

limit cross 20kmph , the actuator gets automatically activated and once the

speed is decreased to below /or 20kmph the actuator gets deactivated

spontaneously.

1.3 ACTUATOR

An actuator is a type of motor that is responsible for moving or controlling a

mechanism or a system. It is operated by a source of energy, typically electric

current, hydraulic fluid pressure, or pneumatic pressure, and converts that

energy into motion.

In our project we are using an electric source of energy. An electric actuator is

powered by a motor that converts electrical energy to mechanical torque. The

electrical energy is used to actuate equipment such as multi-turn valves. It is one

of the cleanest and most readily available forms of actuator because it does not

involve oil. It also eliminates the complications like

1. The cost and bulk associated with hydraulic systems

2. Environmentally hazardous oil and risk of leakage

3. The high energy consumption of hydraulic systems

4. Costly hydraulic reliability issues (contamination)

5. The cost and hassle associated with fluid maintenance

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1.4 Why Go Electric?

Simpler, smaller installation

Easier control

Lower energy costs

Higher Accuracy

Less maintenance

Less noise

1.5 Need of automation:

In industrial field we need automation because of its various advantages. The

highlighted aspects are as follow:

1. High performance together with power efficiency

2. Rugged environmental design to resist water, dust, moisture and extreme

temperature

3. Advanced, yet cost effective human machine interface features

4. Support for high speed, wired and wireless communication

5. It saves manpower and hence time with more effective use

6. Repeatability, tighter quality control, waste reduction and increased

productivity

7. Increased emphasis on flexibility and convertibility in manufacturing process

3

APPROACH 1

USING TACHOMETER & RELAY:

2.1 TACHOMETER:

A tachometer (revolution-counter, tach, rev-counter, RPM gauge) is an

instrument measuring the rotation speed of a shaft or disk, as in a motor or other

machine. The device usually displays the revolutions per minute (RPM) on a

calibrated analogue dial, but digital displays are increasingly common.

2.1.1 Working of Tachometer:

Electronic tachometers work by counting pulses generated by the ignition

system, alternator, tach signal generator, or magnetic pickup sender. The tach is

hooked up to + 12VDC, Ground, and one of the signal sources. By selecting the

right tach and setting the switch on the back to the correct position, the

tachometer knows how many pulses are sent per each engine revolution. From

this information, the tach displays the correct engine speed.

2.2 RELAY:

The term Relay generally refers to a device that provides an electrical

connection between two or more points in response to the application of a

control signal. It is an electronic component - a form of switch.Basically it is a

binary actuator as it has two stable states

1. Energized and latched.

2. De-energized and unlatched.

http://en.wikipedia.org/wiki/File:ACRelay.jpg

4

Relays are used where it is necessary to control a circuit by a low-power signal

(with complete electrical isolation between control and controlled circuits), or

where several circuits must be controlled by one signal.

A type of relay that can handle the high power required to directly control an

electric motor or other loads is called a contactor.

Electrical Relays can also be distinguished as:

1. Electromechanical Relays- use an electromagnet to mechanically operate a

switch

2. Solid State Relays [or SSRs] - use semiconductor transistors, thyristors,

triacs etc. as their switching device.

2.2.1THE ELECTROMECHANICAL RELAY:

Electromechanical relays are electro-magnetic devices that convert a magnetic

flux generated by the application of a low voltage electrical control signal either

AC or DC across the relay terminals, into a pulling mechanical force which

operates the electrical contacts within the relay. The most common form of

electromechanical relay consists of an energizing coil called the primary

circuit wound around a permeable iron core.

WORKING:

An input voltage is applied to the coil mechanism. The input voltage

magnetizes the core which pulls the arm towards it. This action causes the

output contacts to touch, closing the load circuit. When the input voltage is

removed, the spring lever will push the contacts away from each other, breaking

the load circuit connection.

Inherent in its design, the EMR must make mechanical contacts in order to

switch a load. At the point of these contacts, oxidation breakdown occurs over

extended life cycling (typically 106 operations), and the relay will need to be

replaced. When an EMR is activated, bounce occurs at the contact site. Bounce

creates a window of time where the load circuit is flickering between open and

closed, a condition which may need to be considered in load design. Because

there are internal mechanical components with physical dimension restraints,

the package size of an EMR can limit the size of a PCB design. Isolation

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voltage is another area where EMRs are limited. Most EMRs are typically rated

for minimum input to output isolation voltages of 1500 to 2000 VAC.

2.2.2 The Solid State Relay:

The solid state relay being a purely electronic device has no moving parts

within its design as the mechanical contacts have been replaced by power

transistors, thyristors or triacs. The electrical separation between the input

control signal and the output load voltage is accomplished with the aid of an

opto-coupler type Light Sensor.

WORKING:

An input current is applied to the LED, which in most cases is a Gallium

Arsenide (GaAs) infrared LED. The emitted light is reflected within an optical

dome, generally constructed of a gel- like lensing material, onto a series of

photo diodes. The photodiodes generate a resulting voltage which, through

driver circuitry, is used to control the gates of two MOSFETs. Because there are

no moving parts, solid state relays have established switching lives of more than

1010 cycles, and exhibit bounce-free operation. The input LEDs require low

signal levels (

6

2.2.3APPLICATION OF RELAY:

A relay allows circuits to be switched by electrical equipment. For example, a

timer circuit with a relay could switch power at a preset time. For many years

relays were the standard method of controlling industrial electronic systems. A

number of relays could be used together to carry out complex functions (relay

logic). The principle of relay logic is based on relays which energize and de-

energize associated contacts. Relay logic is the predecessor of ladder logic,

which is commonly used in programmable logic controllers.

Relays are used for:

Amplifying a digital signal, switching a large amount of power with a

small operating power.

Detecting and isolating faults on transmission and distribution lines by

opening and closing circuit breakers (protection relays).

Time delay functions. Relays can be modified to delay opening or delay

closing a set of contacts.

Switching to a standby power supply.

2.3 PROBLEM ENCOUNTERD:

1. DIFFICULT TO GET THE OUTPUT CURRENT FROM TACHOMETER.

2. DIFFICULT TO INTERFACE THE ACTUATOR WITH TACHOMETER.

7

APPROACH 2:

USING INDUCTIVE PROXIMITY SWITCH, COUNTER, 555 TIMER

AND RELAY:

In this Approach we replaced the Tachometer with the Proximity Switch which

produces a pulse each time when any metallic substance comes near it. The

counter is used to count the no of pulses.

3.1 Proximity Sensors:

Proximity Sensors are available in models using high-frequency oscillation to

detect ferrous and non-ferrous metal objects and in capacitive models to detect

non-metal objects. Models are available with environment resistance, heat

resistance, resistance to chemicals, and resistance to water. "Proximity Sensor"

includes all sensors that perform non-contact detection in comparison to

sensors, such as limit switches, that detect objects by physically contacting

them. Proximity Sensors convert information on the movement or presence of

an object into an electrical signal. There are three types of detection systems

that do this conversion: systems that use the eddy currents that are generated in

metallic sensing objects by electromagnetic induction, systems that detect

changes in electrical capacity when approaching the sensing object, and systems

that use magnets and reed switches.

3.2 Counter:

In digital logic and computing, a counter is a device which stores (and

sometimes displays) the number of times a particular event or process has

occurred, often in relationship to a clock signal.

In electronics, counters can be implemented quite easily using register-type

circuits such as the flip-flop, and a wide variety of classifications exist:

Asynchronous (ripple) counter changing state bits are used as clocks to

subsequent state flip-flops

Synchronous counter all state bits change under control of a single

clock

Decade counter counts through ten states per stage

Up/down counter counts both up and down, under command of a

control input

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Ring counter formed by a shift register with feedback connection in a

ring

Johnson counter a twisted ring counter

Cascaded counter

Modulus counter.

Each is useful for different applications. Usually, counter circuits are digital in

nature, and count in natural binary. Many types of counter circuits are available

as digital building blocks, for example a number of chips in the 4000

series implement different counters.

Occasionally there are advantages to using a counting sequence other than the

natural binary sequencesuch as the binary coded decimal counter, a linear

feedback shift register counter, or a Gray-code counter.

Counters are useful for digital clocks and timers, and in oven timers, VCR

clocks, etc.

3.2.1Counter Used: - 4017 Decade Counter (5 Stage Johnson Counter)

The 4017 decade counter has ten outputs which go HIGH in sequence when a

source of pulses is connected to the CLOCK input and when suitable logic

levels are applied to the RESET and ENABLE inputs. Just one of the individual

outputs is HIGH at a time. Internally, the 4017 contains five bi-stable subunits.

These are interconnected in a pattern known as a Johnson counter. The outputs

of the bi-stables are decoded to give the ten individual outputs. The 4017 is

designed to drive higher current loads.

It is a CMOS decade counter cum decoder circuit which can work out of the

box for most of our low range counting applications. It can count from zero to

ten and its outputs are decoded.

This saves a lot of board space and time required to build our circuits when our

application demands using a counter followed by a decoder IC. This IC also

simplifies the design and makes debugging easy.

9

It has 16 pins and the functionality of each pin is explained as follows:

Pin-1: It is the output 5. It goes high when the counter reads 5 counts.







Pin-8: It is the Ground pin which should be connected to a LOW voltage (0V).




Pin-12: This is divided by 10 output which is used to cascade the IC with

another counter so as to enable counting greater than the range supported by a

single IC 4017. By cascading with another 4017 IC, we can count up to 20

numbers. We can increase and increase the range of counting by cascading it

with more and more IC 4017s. Each additional cascaded IC will increase the

counting range by 10. However, it is not advisable to cascade more than 3 ICs

as it may reduce the reliability of the count due to the occurrence glitches. If

10

you need a counting range more than twenty or thirty, I advise you to go with

conventional procedure of using a binary counter followed by a corresponding

decoder.

Pin-13: This pin is the disable pin. In normal mode of operation, this is

connected to ground or logic LOW voltage. If this pin is connected to logic

HIGH voltage, then the circuit will stop receiving pulses and so it will not

advance the count irrespective of number of pulses received from the clock.

Pin-14: This pin is the clock input. This is the pin from where we need to give

the input clock pulses to the IC in order to advance the count. The count

advances on the rising edge of the clock.

Pin-15: This is the reset pin which should be kept LOW for normal operation. If

you need to reset the IC, then you can connect this pin to HIGH voltage.

Pin-16: This is the power supply (Vcc) pin. This should be given a HIGH

voltage of 3V to 15V for the IC to function. This IC is very useful and also user

friendly. To use the IC, just connect it according the specifications described

above in the pin configuration and give the pulses you need to count to the pin-

14 of the IC. Then you can collect the outputs at the output pins. When the

count is zero, Pin-3 is HIGH. When the count is 1, Pin-2 is HIGH and so on as

described above.

3.2.2 Inside the 4017 (Johnson/Twisted-Ring Counters):

The Johnson counter works in the following way: Take the initial state of the

counter to be 000. On the first clock pulse, the inverse of the last flip-flop will

be fed into the first flip-flop, producing the state 100. On the second clock

pulse, since the last flip-flop is still at level 0, another 1 will be fed into the first

11

flip-flop, giving the state 110. On the third clock pulse, the state 111 is

produced. On the fourth clock pulse, the inverse of the last flip-flop, now a 0,

will be shifted to the first flip-flop, giving the state 011. On the fifth and sixth

clock pulse, using the same reasoning, we will get the states 001 and 000, which

is the initial state again. Hence, this Johnson counter has six distinct states: 000,

100, 110, 111, 011 and 001, and the sequence is repeated so long as there is

input pulse. Thus this is a MOD-6 Johnson counter.

The MOD number of a Johnson counter is twice the number of flip-flops. In the

example above, three flip-flops were used to create the MOD-6 Johnson

counter. So for a given MOD number, a Johnson counter requires only half the

number of flip-flops needed for a ring counter. However, a Johnson counter

requires decoding gates whereas a ring counter doesn't. As with the binary

counter, one logic gate (AND gate) is required to decode each state, but with the

Johnson counter, each gate requires only two inputs, regardless of the number of

flip-flops in the counter. Note that we are comparing with the binary counter

using the speed up technique discussed above. The reason for this is that for

each state, two of the N flip-flops used will be in a unique combination of

states. In the example above, the combination Q2 = Q1 = 0 occurs only once in

the counting sequence, at the count of 0. The state 010 does not occur. Thus, an

AND gate with inputs (not Q2) and (not Q2) can be used to decode for this state.

The same characteristic is shared by all the other states in the sequence.

A Johnson counters represent a middle ground between ring counters and binary

counters. A Johnson counter requires fewer flip-flops than a ring counter but

generally more than a binary counter; it has more decoding circuitry than a ring

counter but less than a binary counter. Thus, it sometimes represents a logical

choice for certain applications.

3.3 555 Timer:

The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse

generation, and oscillator applications. The 555 can be used to provide time

delays, as an oscillator, and as a flip-flop element. Derivatives provide up to

four timing circuits in one package.

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Introduced in 1971 by Signetics, the 555 is still in widespread use due to its ease

of use, low price, and stability. It is now made by many companies in the

original bipolar and also in low-power CMOS types. As of 2003, it was

estimated that 1 billion units are manufactured every year.

Depending on the manufacturer, the standard 555 package includes

25 transistors, 2 diodes and 15 resistors on a silicon chip installed in an 8-pin

mini dual-in-line package (DIP-8).

3.3.1 Pins:

13

The connection of the pins for a DIP package is as follows:

Pin Name Purpose

1 GND Ground reference voltage, low level (0 V)

2 TRIG

The OUT pin goes high and a timing interval starts when this input

falls below 1/2 of CTRL voltage (which is typically 1/3 of VCC,

when CTRL is open).

3 OUT This output is driven to approximately 1.7 V below +VCC or GND.

4 RESET

A timing interval may be reset by driving this input to GND, but

the timing does not begin again until RESET rises above

approximately 0.7 volts. Overrides TRIG which overrides THR.

5 CTRL Provides "control" access to the internal voltage divider (by

default, 2/3 VCC).

6 THR The timing (OUT high) interval ends when the voltage at THR is

greater than that at CTRL (2/3 VCC if CTRL is open).

7 DIS Open collector output which may discharge a capacitor between

intervals. In phase with output.

8 VCC Positive supply voltage, which is usually between 3 and 15 V

depending on the variation.

Pin 5 is also sometimes called the CONTROL VOLTAGE pin. By applying a

voltage to the CONTROL VOLTAGE input one can alter the timing

characteristics of the device. In most applications, the CONTROL VOLTAGE

input is not used. It is usual to connect a 10 nF capacitor between pin 5 and 0 V

to prevent interference. The CONTROL VOLTAGE input can be used to build

an astable with a frequency modulated output.

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3.3.2 Modes:

The 555 has three operating modes:

Monostable Mode: In this mode, the 555 functions as a "one-shot" pulse

generator. Applications include timers, missing pulse detection, bounce

free switches, touch switches, frequency divider, capacitance

measurement, pulse-width modulation (PWM) and so on.

The output pulse width of time t, which is the time it takes to charge C to

2/3 of the supply voltage, is given by

Where t is in seconds, R is in ohms (resistance) and C is in farads

(capacitance).

While using the timer IC in monostable mode, the main disadvantage is

that the time span between any two triggering pulses must be greater than

the RC time constant.

Astable (free-running) mode: The 555 can operate as an oscillator. Uses

include LED and lamp flashers, pulse generation, logic clocks, tone

generation, security alarms, pulse position modulation and so on. The 555

can be used as a simple ADC, converting an analog value to a pulse

length. E.g. selecting a thermistor as timing resistor allows the use of the

555 in a temperature sensor: the period of the output pulse is determined

by the temperature. The use of a microprocessor based circuit can then

convert the pulse period to temperature, linearize it and even provide

calibration means.

15

In astable mode, the 555 timer puts out a continuous stream of

rectangular pulses having a specified frequency. Resistor R1 is connected

between VCC and the discharge pin (pin 7) and another resistor (R2) is

connected between the discharge pin (pin 7), and the trigger (pin 2) and

threshold (pin 6) pins that share a common node. Hence the capacitor is

charged through R1 and R2, and discharged only through R2, since pin 7

has low impedance to ground during output low intervals of the cycle,

therefore discharging the capacitor.

In the astable mode, the frequency of the pulse stream depends on the

values of R1, R2 and C:

The high time from each pulse is given by:

and the low time from each pulse is given by:

Where R1 and R2 are the values of the resistors in ohms and C is the value

of the capacitor in farads.

The power capability of R1 must be greater than .

16

Particularly with bipolar 555s, low values of must be avoided so that

the output stays saturated near zero volts during discharge, as assumed by

the above equation. Otherwise the output low time will be greater than

calculated above. The first cycle will take appreciably longer than the

calculated time, as the capacitor must charge from 0V to 2/3 of VCC from

power-up, but only from 1/3 of VCC to 2/3 of VCC on subsequent cycles.

To achieve a duty cycle of less than 50% a small diode (that is fast

enough for the application) can be placed in parallel with R2, with the

cathode on the capacitor side. This bypasses R2 during the high part of the

cycle so that the high interval depends approximately only on R1 and C.

The presence of the diode is a voltage drop that slows charging on the

capacitor so that the high time is longer than the expected and often-cited

ln(2)*R1C = 0.693 R1C. The low time will be the same as without the

diode as shown above. With a diode, the high time is

Where Vdiode is when the diode has a current of 1/2 of Vcc/R1 which can

be determined from its datasheet or by testing. As an extreme example,

when Vcc= 5 and Vdiode= 0.7, high time = 1.00 R1C which is 45% longer

than the "expected" 0.693 R1C. At the other extreme, when Vcc= 15 and

Vdiode= 0.3, the high time = 0.725 R1C which is closer to the expected

0.693 R1C. The equation reduces to the expected 0.693 R1C if Vdiode= 0.

The operation of RESET in this mode is not well defined, some

manufacturers' parts will hold the output state to what it was when

RESET is taken low, others will send the output either high or low.

Bistable mode or Schmitt trigger: The 555 can operate as a flip-flop, if

the DIS pin is not connected and no capacitor is used. Uses include

bounce-free latched switches.

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In bistable (also called Schmitt trigger) mode, the 555 timer acts as a

basic flip-flop. The trigger and reset inputs (pins 2 and 4 respectively on a

555) are held high via Pull-up resistors while the threshold input (pin 6) is

simply floating. Thus configured, pulling the trigger momentarily to

ground acts as a 'set' and transitions the output pin (pin 3) to Vcc (high

state). Pulling the reset input to ground acts as a 'reset' and transitions the

output pin to ground (low state). No timing capacitors are required in a

bistable configuration. Pin 5 (control voltage) is connected to ground via

a small-value capacitor (usually 0.01 to 0.1 uF); pin 7 (discharge) is left

floating.

3.3.3 Specifications:

These specifications apply to the NE555. Other 555 timers can have different

specifications depending on the grade (military, medical, etc.).

Supply voltage (VCC) 4.5 to 15 V

Supply current (VCC = +5 V) 3 to 6 mA

Supply current (VCC = +15 V) 10 to 15 mA

Output current (maximum) 200 mA

Maximum Power dissipation 600 mW

Power consumption (minimum operating) 30 mW@5V, 225 mW@15V

Operating temperature 0 to 70 C

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3.4 CIRCUIT DIAGRAM:

3.5 CIRCUIT DESCRIPTION:

In the above used circuit the output from the proximity switch is fed to the

CLOCK IN pin of the counter (IC 4017). Proximity switch generates one pulse

for each rotation. Counter counts number of pulse input at CLK IN pin. To

activate the actuator the threshold speed is 20 km/h. For speed of 20 km/h there

are 5 rotations thus the proximity switch will generate 5 pulses. The Relay is

connected to the pin1 which is the output for 5 counts. As the counter output is

5 relay is immediately activated which activates the actuator. One 555 timer (IC

NE555) is used to provide a pulse of 1 Hz frequency which resets the counter

after each second. For every second counter circuit monitors the proximity

switch output and activates the actuator for 5 counts.

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3.6 PROBLEM ENCOUNTERED:

1. IT IS DIFFICULT TO GET RESET SIGNAL FOR VERY SMALL TIME

INTERVAL.

2. FOR VERY FIRST TIME INTERVAL THE 555 TIMER CIRCUIT

PROVIDES PULSE OF TIME INTERVAL MORE THAN 1S.

3. THIS CIRCUIT IS ABLE TO ACTIVATE OR DEACTIVATE THE

MOTOR (ACTUATOR) BUT CANNOT ROTATE IT IN OPPOSITE

DIRECTION.

4. THIS CIRCUIT WORKS ONLY FOR THE LIMITED RANGE I.E. 20

KM/H. IF THE THRESHOLD SPEED IS CHANGED THE WHOLE

CIRCUIT HAS TO BE REPLACED.

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APPROACH 3

USING PROXIMITY SWITCH, DARLINGTON PAIR (ULN2003A) AND

MICROCONTROLLER (PIC16F877A).

In this approach we kept on using proximity switch to generate pulse for each

rotation. But replaced the Counter IC with a Microcontroller to monitor speed

and provide more accurate as well as fast output. In this Circuit motor which is

working as actuator is interfaced with Microcontroller using Darlington pair

(IC ULN2003A)

4.1 MICROCONTROLLER

Microcontroller is a highly integrated chip that contains all the components

comprising a controller. Typically this includes a CPU, RAM, some form of

ROM, I/O ports, and timers. Unlike a general-purpose computer, which also

includes all of these components, a microcontroller is designed for a very

specific task - to control a particular system. A microcontroller differs from a

microprocessor, which is a general-purpose chip that is used to create a

multifunction computer or device and requires multiple chips to handle various

tasks. A microcontroller is meant to be more self-contained and independent,

and functions as a tiny, dedicated computer. The great advantage of

microcontrollers, as opposed to using larger microprocessors, is that the parts-

count and design costs of the item being controlled can be kept to a minimum.

They are typically designed using CMOS (complementary metal oxide

semiconductor) technology, an efficient fabrication technique that uses less

power and is more immune to power spikes than other techniques.

4.1.1 PIC16F877A MICROCONTROLLER:

28/40-Pin 8-Bit CMOS FLASH Microcontrollers

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Microcontroller Core Features:

High performance RISC CPU

Only 35 single word instructions to learn

All single cycle instructions except for program branches which are two cycle

Operating speed: DC - 20 MHz clock input DC - 200 ns instruction cycle

Up to 8K x 14 words of FLASH Program Memory, Up to 368 x 8 bytes of

Data Memory RAM) Up to 256 x 8 bytes of EEPROM Data Memory

Pin out compatible to the PIC16C73B/74B/76/77

Interrupt capability (up to 14 sources)

Eight level deep hardware stack

Direct, indirect and relative addressing modes

Power-on Reset (POR)

Power-up Timer (PWRT) and Oscillator Start-up Timer (OST)

Watchdog Timer (WDT) with its own on-chip RC oscillator for reliable

operation

Programmable code protection

Power saving SLEEP mode

Selectable oscillator options

Low power, high speed CMOS FLASH/EEPROM technology

Fully static design

In-

Single 5V In-Circuit Serial Programming capability

In-Circuit Debugging via two pins

Processor read/write access to program memory

Wide operating voltage range: 2.0V to 5.5V

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High Sink/Source Current: 25 mA

Commercial, Industrial and Extended temperature ranges

Low-power consumption:

- < 0.6 mA typical @ 3V, 4 MHz

- 20 A typical @ 3V, 32 kHz

- < 1 A typical standby current

4.1.2 Peripheral Features:

Timer0: 8-bit timer/counter with 8-bit prescaler

Timer1: 16-bit timer/counter with prescaler, can be incremented during

SLEEP via external Crystal/clock

Timer2: 8-bit timer/counter with 8-bit period register, prescaler and postscaler

Two Capture, Compare, PWM modules

- Capture is 16-bit, max resolution is 12.5 ns

- Compare is 16-bit, max resolution is 200 ns

- PWM max resolution is 10-bit

10-bit multi-channel Analog-to-Digital converter

Synchronous Serial Port (SSP)

(Master/Slave)

Universal Synchronous Asynchronous Receiver Transmitter (USART/SCI)

with 9-bit address detection

Parallel Slave Port (PSP) 8-bits wide, with external RD, WR and CS controls

(40/44-pin only)

Brown-out detection circuitry for Brown-out Reset (BOR)

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4.1.3 PIN DIAGRAM:

27

4.1.4 Block representation:

4.2 PROXIMITY SWITCH :

A proximity sensor is a sensor able to detect the presence of nearby objects

without any physical contact.

A proximity sensor often emits an electromagnetic field or a beam of

electromagnetic radiation (infrared, for instance), and looks for changes in the

field or return signal. The object being sensed is often referred to as the

proximity sensor's target.

The maximum distance that this sensor can detect is defined "nominal range".

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4.2.1 Features:

1) Proximity Sensors detect an object without touching it, and they therefore

do not cause abrasion or damage to the object. Devices such as limit

switches detect an object by contacting it, but Proximity Sensors are able

to detect the presence of the object electrically, without having to touch it.

2) No contacts are used for output, so the Sensor has a longer service life

(excluding sensors that use magnets). Proximity Sensors use

semiconductor outputs, so there are no contacts to affect the service life.

3) Unlike optical detection methods, Proximity Sensors are suitable for use

in locations where water or oil is used. Detection takes place with almost

no effect from dirt, oil, or water on the object being detected. Models

with fluororesin cases are also available for excellent chemical resistance.

4) Proximity Sensors provide high-speed response, compared with switches

that require physical contact. For information on high-speed response,

refer to Explanation of Terms.

5) Proximity Sensors can be used in a wide temperature range. Proximity

Sensors can be used in temperatures ranging from -40 to 200C.

6) Proximity Sensors are not affected by colors. Proximity Sensors detect

the physical changes of an object, so they are almost completely

unaffected by the object's surface color.

7) Unlike switches, which rely on physical contact, Proximity Sensors are

affected by ambient temperatures, surrounding objects, and other Sensors.

Both Inductive and Capacitive Proximity Sensors are affected by

interaction with other Sensors. Because of this, care must be taken when

installing them to prevent mutual interference. Care must also be taken to

prevent the effects of surrounding metallic objects on Inductive Proximity

Sensors, and to prevent the effects of all surrounding objects on

Capacitive Proximity Sensors.

8) There are Two-wire Sensors. The power line and signal line are

combined. This reduces wiring work to 2/3 of that require for Three-wire

Sensors. If only the power line is wired, internal elements may be

damaged. Always insert a load.

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4.2.2Operating Principles:

Inductive Proximity Sensors detect the presence of metal objects which come

within range of their oscillating field and provide target detection to zero

speed. Internally, an oscillator creates a high frequency electromagnetic field

(RF) which is radiated from the coil and out from the sensor face. When a metal

object enters this field, eddy currents are induced into the object. As the metal

moves closer to the sensor, these eddy currents increase and result in an

absorption of energy from the coil which dampens the oscillator amplitude until

it finally stops.

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4.2.3 Selection by Detection Method:

Items

Requiring

Confirmation

Inductive Proximity

Sensors

Capacitive Proximity

Sensors

Magnetic Proximity

Sensors

Sensing

object

Metallic objects (iron,

aluminum, brass, copper,

etc.)

Metallic objects, resins,

liquids, powders, etc. Magnets

Electrical

noise

Affected by positional relationship of power lines and

signal lines, grounding of cabinet, etc. CE Marking (EC

Directive compliance) Sensor covering material (metal,

resin). Easily affected by noise when the cable is long.

Almost no effect.

Power

supply

DC, AC, AC/DC, DC with no polarity, etc. Connection method, power supply

voltage.

Current

consumption

Depends on the power supply, i.e., DC 2-wire models, DC 3-wire models, AC,

etc.

DC 2-wire models are effective for suppressing current consumption.

Sensing

distance

The Sensing distance must be selected by considering the effects of factors such

as the temperature, the sensing object, surrounding objects, and the mounting

distance between Sensors. Refer to the set distance in the catalog specifications

to determine the proper distance. When high precision sensing is required, use a

Separate Amplifier model.

Ambient

environment

Temperature or humidity, or existence of water, oils, chemicals etc.

Confirm that the degree of protection matches the ambient environment.

Physical

vibration,

shock

An extra margin must be provided in the Sensing distance when selecting

Sensors for use in environments subject to vibration and shock.

To prevent Sensors from vibrating loose, refer to the catalog values for

tightening torque during assembly.

Assembly

Effects of tightening torque, Sensor size, number of wiring steps, cable length,

distance between Sensors, surrounding objects. Check the effects of

surrounding metallic and other objects, and the specifications for the mutual

interference between Sensors.

31

4.2.4 Interpreting Engineering Data:

Sensing Area Sensing Distance vs. Display

Characteristics

Effects of Sensing Object

Size and Material

E2E-X[]E[]/-X[]Y[]/

X[]F1

E2C-EDR6-F E2E-X3D[]/-X3T1

This graph shows

engineering data from

moving the sensing object

parallel to the sensing

surface of the Proximity

Sensor.

Refer to this graph for

Proximity Sensor

applications, such as

positioning. When a high

degree of precision is

required, use a Separate

Amplifier Proximity

Sensor.

This type of graph is used

with Separate

Amplifier Proximity

Sensors. It shows the values

when executing FP (Fine

Positioning) at specified

distances. FP settings are

possible at any desired

distance, with a digital value

of 1,500 as a reference for

the E2C-EDA.

The above graph shows

numerical examples when

Fine Positioning is executed

at the three points of 0.3, 0.6,

and 0.9 mm.

Here, the horizontal axis

indicates the size of the

sensing object, and the

vertical axis indicates the

Sensing. It shows changes in

the Sensing Distance due to

the size and material of the

sensing object. Refer to this

data when using the same

Sensor to detect various

different sensing objects, or

when confirming the

allowable leeway for

detection.

32

Leakage Current Characteristics Residual Voltage Characteristics

In contrast with contact-type limit

switches, which have physical contacts,

leakage current in a 2-wire Proximity

Sensor is related to an electrical switch that

consists of transistors and other

components.

This graph indicates the leakage current

characteristics caused by transistors in the

output section of the Sensor.

Generally speaking, the higher the

voltage, the larger the leakage current.

Because leakage current flows to the load

connected to the Proximity Sensor,

care must be taken to select a load that will

not cause the Sensor to operate from the

leakage current.

Be careful of this factor when replacing

a limit switch, micro-switch, or other

switch with a Proximity Sensor.

Similar to leakage current

characteristics, residual voltage is

something that occurs due to electrical

switches that are comprised of

transistors and other components. For

example, whereas the voltage in a

normally open switch should be 0 V in the

ON state, and the same as the power

supply voltage in the OFF state, residual

voltage refers to a certain level of voltage

remaining in the switch. Be careful of this

factor when replacing a limit switch,

micro-switch, or other switch with a

Proximity Sensor.

33

4.2.5 Explanation of Terms:

1. Standard Sensing Object

A sensing object that serves as a reference for measuring basic performance,

and that is made of specified materials and has a specified shape and

dimensions.

2. Sensing Distance

The distance from the reference position (reference surface) to the measured

operation (reset) when the standard sensing object is moved by the specified

method.

3. Set Distance

The distance from the reference surface that allows stable use, including the

effects of temperature and voltage, to the (standard) sensing object transit

position. This is approximately 70% to 80% of the normal (rated) sensing

distance.

34

4. Hysteresis (Differential Travel)

With respect to the distance between the standard sensing object and the Sensor,

the difference between the distance at which the Sensor operates and the

distance at which the Sensor resets.

5. Response Time

t1: The interval from the point when the standard sensing object moves into the

sensing area and the Sensor activates, to the point when the output turns ON.

t2: The interval from the point when the standard sensing object moves out of

the Sensor sensing area to the point when the Sensor output turns OFF.

35

6. Response Frequency

The number of detection repetitions that can be output per second when

the standard sensing object is repeatedly brought into proximity.

See the accompanying diagram for the measuring method.

7. Shielded

With a Shielded Sensor, magnetic flux is concentrated in front of the Sensor and

the sides of the Sensor coil are covered with metal.

The Sensor can be mounted by embedding it into metal.

8. Unshielded

With an Unshielded Sensor, magnetic flux is spread widely in front of the

Sensor and the sides of the Sensor coil are not covered with metal.

This model is easily affected by surrounding metal objects (magnetic objects),

so care must be taken in selecting the mounting location.

36

Expressing the Sensing Distance

When measuring the Sensing Distance of a Proximity Sensor, the reference position

and the direction of approach of

the sensing object are determined as follows:

Cylindrical/Rectangular Sensors

Perpendicular sensing distance

Horizontal Sensing

Distance and sensing area

diagram

Expressed as the measured distance from the

reference surface when the standard sensing

object approaches from the radial direction

(perpendicular to the sensing surface).

Expressed as the measured

distance from the reference

axis when the standard sensing

object is moved parallel to the

reference surface (sensing

surface). This distance depends

on the transit position (distance

from the reference surface), so

it can be expressed as an

operating point track. (Sensing

Area Diagram)

37

Output Configuration

NPN transistor

output PNP transistor output

Non-polarity/non-contact

output

A general-use

transistor can

be directly

connected to a

Programmable

Controller or

Counter.

Primarily built into machines

exported to Europe and other

overseas destinations.

A 2-wire AC output that can

be used for both AC and DC

Sensors. Eliminates the need to

be concerned about reversing

the polarity.

Output Configuration

NO (normally open) NC (normally closed) NO/NC switchable

When there is an object

in the sensing area, the

output switching element

is turned ON.

When there is no object

in the sensing area, the

output switching element

is turned ON.

NO or NC operation can be

selected for the output

switching element by a switch

or other means.

38

4.3 STEPPER MOTOR :

A stepper motor (or step motor) is a brushless DC electric motor that divides a

full rotation into a number of equal steps. The motor's position can then be

commanded to move and hold at one of these steps without any feedback sensor

(an open-loop controller), as long as the motor is carefully sized to the

application.

It is an incremental drive (digital) actuator and is driven in fixed angular steps.

They are driven by pulses of electricity. Each pulse drives the shaft of the motor

a little bit. The more pulses that are fed to the motor, the more the shaft turns.

This mean that a digital signal is used to drive the motor and every time it

receives a digital pulse it rotates a specific number of degrees in rotation.

4.3.1 CALCULATION OF STEP ANGLE :

The step angle, the number of degrees a rotor will turn per step, is calculated as

follows:

4.3.2 Theory:

A step motor can be viewed as a synchronous AC motor with the number of

poles (on both rotor and stator) increased, taking care that they have no common

denominator. Additionally, soft magnetic material with many teeth on the rotor

and stator cheaply multiplies the number of poles (reluctance motor). Modern

steppers are of hybrid design, having both permanent magnets and soft iron

cores.

To achieve full rated torque, the coils in a stepper motor must reach their full

rated current during each step. Winding inductance and reverse EMF generated

by a moving rotor tend to resist changes in drive current, so that as the motor

speeds up, less and less time is spent at full current thus reducing motor

http://en.wikipedia.org/wiki/Brushless_DC_electric_motorhttp://en.wikipedia.org/wiki/Open-loop_controller

39

torque. As speeds further increase, the current will not reach the rated value, and

eventually the motor will cease to produce torque.

Stepper motor ratings and specifications :

A stepper's low speed torque will vary directly with current. How quickly the

torque falls off at faster speeds depends on the winding inductance and the drive

circuitry it is attached to, especially the driving voltage.

Steppers should be sized according to published torque curve, which is specified

by the manufacturer at particular drive voltages or using their own drive

circuitry.

Step motors adapted to harsh environments are often referred to as IP65 rated.

Motor used in project - Bipolar motor

Bipolar motors have a single winding per phase. The current in a winding needs

to be reversed in order to reverse a magnetic pole, so the driving circuit must be

more complicated, typically with an H-bridge arrangement (however there are

several off-the-shelf driver chips available to make this a simple affair). There

are two leads per phase, none are common.

Static friction effects using an H-bridge have been observed with certain drive

topologies.

Dithering the stepper signal at a higher frequency than the motor can respond to

will reduce this "static friction" effect.

Because windings are better utilized, they are more powerful than a unipolar

motor of the same weight. This is due to the physical space occupied by the

windings. A unipolar motor has twice the amount of wire in the same space, but

only half used at any point in time, hence is 50% efficient (or approximately

70% of the torque output available). Though a bipolar stepper motor is more

complicated to drive, the abundance of driver chips means this is much less

difficult to achieve.

An 8-lead stepper is wound like a unipolar stepper, but the leads are not joined

to common internally to the motor. This kind of motor can be wired in several

configurations:

Unipolar.

40

Bipolar with series windings. This gives higher inductance but lower

current per winding.

Bipolar with parallel windings. This requires higher current but can

perform better as the winding inductance is reduced.

Bipolar with a single winding per phase. This method will run the motor

on only half the available windings, which will reduce the available low

speed torque but require less current

Stepper motor driver circuits

Stepper motor performance is strongly dependent on the driver circuit. Torque curves

may be extended to greater speeds if the stator poles can be reversed more quickly, the

limiting factor being the winding inductance. To overcome the inductance and switch the

windings quickly, one must increase the drive voltage. This leads further to the necessity

of limiting the current that these high voltages may otherwise induce.

Wave drive or Full step drive (one phase on)

In this drive method only a single phase is activated at a time. It has the same number of

steps as the full step drive, but the motor will have significantly less than rated torque. It

is rarely used. The animated figure shown above is a wave drive motor. In the animation,

rotor has 25 teeth and it takes 4 steps to rotate by one teeth position. So there will be

25*4 = 100 steps per full rotation and each step will be 360/100 = 3.6 degrees.

Full step drive (two phases on)

This is the usual method for full step driving the motor. Two phases are always on so the

motor will provide its maximum rated torque. As soon as one phase is turned off, another

one is turned on. Wave drive and single phase full step are both one and the same, with

same number of steps but difference in torque.

41

Half stepping

When half stepping, the drive alternates between two phases on and a single phase on.

This increases the angular resolution. The motor also has less torque (approx 70%) at

the full step position (where only a single phase is on). This may be mitigated by

increasing the current in the active winding to compensate. The advantage of half

stepping is that the drive electronics need not change to support it. In animated figure

shown above, if we change it to half stepping, then it will take 8 steps to rotate by 1 teeth

position. So there will be 25*8 = 200 steps per full rotation and each step will be 360/200

= 1.8 degrees. Its angle per step is half of the full step.

Microstepping

What is commonly referred to as microstepping is often "sine cosine microstepping" in

which the winding current approximates a sinusoidal AC waveform. Sine cosine

microstepping is the most common form, but other waveforms can be used. Regardless

of the waveform used, as the microsteps become smaller, motor operation becomes

more smooth, thereby greatly reducing resonance in any parts the motor may be

connected to, as well as the motor itself. Resolution will be limited by the

mechanical stiction, backlash, and other sources of error between the motor and the end

device. Gear reducers may be used to increase resolution of positioning.

Step size repeatability is an important step motor feature and a fundamental reason for

their use in positioning.

42

4.3.3 TWO-PHASE STEPPER MOTOR WIRING DIAGRAM :

43

4.4 CIRCUIT DIAGRAM :

Interfacing with Microcontroller

4.5 CIRCUIT DESCRIPTION :

Output of proximity switch is fed to the PORTB (RB0 Pin). PORTC is working

as output Port which provides the output signal as the program burnt in it. This

circuit works at a clock frequency of 1MHz. In this Circuit motor which is

working as actuator is interfaced directly with Microcontroller.

44

4.6 PROGRAM:

#include

void time_delay(unsigned int i)

{

unsigned int k;

for(k=0;k

45

{

PORTC=0x08;

time_delay(100);

PORTC=0x02;

time_delay(100);

PORTC=0x04;

time_delay(100);

PORTC=0x01;

time_delay(100);

temp=1;

}

if(count

46

}

4.7 PROGRAM DESCRIPTION :

For compilation of the program and generating .hex file we have used HI-TECH

C compiler integrated with MPLAB IDE.

In this Program PORTB is set to Input mode and PORTC is set to output mode.

The pulse_count() function is used to count the no of pulses in one second.

Pulse_count() function counts the no of times the RB0 pin goes from low to

high and returns the no of counts every second. Value of no of count from

pulse_count() function is returned to variable count of main() function. In the

main function when the value of count is greater than or equal to 5, which is the

corresponding value of pulse for speed of 20 km/h, the output value to operate

motor is send to PORTC i.e. actuator is activated. If the count is less than 5 the

actuator is not activated. Once the actuator is activated the value of variable

temp is changed to 1 from 0 and actuator is not activated again (i.e. motor does

not rotate) is count is more than 5. But if the count is less than 5 motor is rotated

in the opposite direction. Time_delay() function provides time delay in ms.

47

5 FUTURE SCOPE OF AUTOMATIC ACTUATION :

Following are the application of automatic actuation :

1.mining ventilation.

2.garbage dumpers.

3.openin and closing of doors automatically.

4.automation counting of industrial goods.

5.anti-collission security.

48

CONCLUSION

The project for Automatic actuator control with speed is very important

project for the mines safety and for high production. It reduces the human

involvement and increases man-machine interaction. For achieving our goal we

went through different approaches with different techniques. In our first

approach we were using tachometer and relay but after finding difficulties in

applying this technique we had to look for another one. In our second approach

we have used proximity switch, counter, relay, 555 timer and we almost

achieved our goal but this approach was unable to operate the actuator in

backward direction also a lot of hardware involvement increased the

complication thus we moved to new technique. This technique used the

Microcontroller (PIC16F877A). Use of microcontroller reduced the need for the

counter and separate control circuit. Program was burnt into the microcontroller

which counts the no of pulse generated by the proximity switch and operates the

actuator as per the requirement. To fulfill our task we have used different

equipment and learned to operate them. This project has vital role in our day to

day life not only inside the underground mines for ventilation but also in almost

every field where speed is concerned.

Through this project during our training we have learnt about many techniques

and ideas. Learnt about different type of ICs, switches and most importantly

programming for microcontroller. This project helped us to gain sufficient

knowledge from industrial training.

49

REFERENCES

WEBSITES:

1. http://www.electronicsproject.org

2. http://www.kitsrus.com

3. http://www.piclist.com

4. http://www.8051projects.net

5. http://www.arduino.cc

6. http://www.mikroe.com

7. http://www.extremeelectronics.co.in

8. http://www.mstracey.btinternet.co.uk

9. http://www.edaboard.com

10. http://www.freescale.com

11. http://www.rockwellautomation.com

BOOKS:

Mazidi A.Muhammad and Mazidi G.Janice, Microcontroller And

Embedded Systems

automatic actuator control through speed

Documents