Variable Speed Drive

The speed of the motor depends on the applied frequency, as well as the winding arrangement and the load. Therefore in order to control the motor speed it is easy to control the frequency of the supply. Therefore in order to control the speed of a standard AC motor, the applied frequency and voltage can be controlled using inverters. Although it is difficult to control voltage and frequencies at these high powers, the use of a standard induction motor allows a cost effective speed control system to be built. For reason of energy savings, reduction of operating costs, reduction of machine down time, maximizing productivity and the ability to provide adjustable speed control with standard squirrel cage induction motors, Variable Speed Drives are becoming the essential components in every modern automation system.
In earlier time DC motors are used in applications were speed control is necessary. Now a days Induction motors are used because of above advantages than DC motors. VSD not only facilitates the variation of speed, but also provides several other facilities. The acceleration, Deceleration, High speed, Low speed, Forward/reverse operation, Preset speed, jogging can be programmed by the VSD.
VSD is an intelligent machine in now a days, it has feedback path and also PLC use to control. Now come inbuilt PLC has VSD. Normally, we use Telemecanique band under this Altiva type VSD. 0.18kw-500kw motors can run using this machine. Most of VSD can control remote operate. And they have communication cable (RS485) we can connect the PLC and run. Then can run slave mode. Basically, VSD consist of following sources.

• Power control board: Power board is used to in put & out put power handling.
• Control card and display unit: Control card used mainly measuring the in put &
out put current and voltage, calculation, the heart, RPM, etc., display unit,
inbuilt memory, and other controlling buttons are in the card.

• IGBT unit (Inter Grated Bipolar Transistor): IGBT is the main control part and
important part of the VSD. This IGBT has two type of models single phase & there
phase one. It has diode unit in the left side and IGBT unit in the right side.
Diodes are uses to convert alternative current (A/C) into direct current (D/C),
which act as a converter. The IGBT unit is use to convert direct current (D/C)
into alternative current (A/C), which act as an inverter. It can be shown the
diagram of control card as follows. When it works as an inverter, it changes the
frequency of the out put line’s current into design value using IGBT firing system.
And also, there can be use thyrister unit to the inverter.

The Inverters

An electronic converter which converts Direct Current (DC) into Alternating Current (AC) is known as an inverter. Electronic speed controllers for AC motors usually convert the AC supply into DC using a rectifier unit, and then convert it back to a variable frequency, variable voltage AC supply using an inverter unit. The connection between the rectifier and inverter is called the DC link. The diagram of a speed controller, (normally called an inverter) can also be shown as above.
The supply, which can be single phase (usually at low power) or three phases is fed to a full wave rectifier which supplies the DC link capacitors. The capacitors reduce the voltage ripple (especially on single phase supplies) and supply energy for short mains breaks. The voltage on the capacitors is uncontrolled and depends on the peak AC supply voltage. The DC voltage is converted back to AC using Pulse Width Modulation (PWM). The desired waveform is built up by switching the IGBT (Insulated Gate Bipolar Transistors) or Thyristers. By varying the firing time of the IGBT or Thyristers the desired current can be generated. But the output voltage is still a series of square wave pulses. Pulse Width Modulation (PWM) wave form can be shown as follows.
The control system to calculate the PWM requirements is very complex and specially designed integrated circuits (ASICs) are needed. The output current must be carefully monitored to protect the inverter and the motor during overload and short circuit. At first switch on the DC link capacitors are discharged, and the inrush current must be limited, usually using a resistor which is bypassed by a relay after a few seconds. The inverter, especially the IGBT or Thyristers and rectifier diodes, produce heat which must be dissipated using a fan and heat sink.

PROGRAMMING LOGIC CONTROLLERS (PLC)

There are many types of PLC software used in the world, such as Siemens, Hitachi, Mitsubishi, etc…In the CNC systems that we are retrofit, used siemens PLC software. But I learn write the PLC program and test it using Hitachi software. In the Hitachi PLC unit has input/output cards and device to run the program. There are 16 slots in the one card which means, we can in/out 16 signals by using one card. But it is vary according to the PLC unit that we are used. Each slot has individual address number. If it is an input card, the address number is begins at zero and varies as follows according to the card number

• 0 to 15 1st card

• 20 to 35 2nd card

• 40 to 55 3rd card...

If it is an output card, the address number begins at 200 and varies as follows according to the card number.


• 200 to 215 1st card
• 220 to 235 2nd card
• 240 to 255 3rd card...


1 PLC Programming languages

There are three types of PLC languages which mainly used for programming.

• Ladder diagram
• Instruction list
• Function block diagram

But normally, engineers are using ladder diagram for PLC programming. Because it is
very easy to construct the logic, and trouble shooting. There are four basic symbols
used to programming by using ladder diagram.

• Normally open (N/O) input
• Normally close (N/C) input
• Normally open (N/O) output
• Normally close (N/C) output

By using these basic symbols, we can build some basic logics which are used in the PLC
programming

Pneumatic Actuators for power, motion and control

Introduction

» Pneumatic actuators include linear cylinders and rotary actuators.
» They are devices providing power and motion to automated systems,
machinesand processes.
» A pneumatic cylinder is a simple, low cost, easy to install device that is
ideal for producing powerful linear movement.
» Speed can be adjusted over a wide range.
» A cylinder can be stalled without damage.
» Adverse conditions can be easily tolerated such as high humidity, dry and
dusty environments and cleaning down with a hose.
» The bore of a cylinder determines the maximum force that it can exert.
» The stroke of a cylinder determines the maximum linear movement that it
can produce.
» The maximum working pressure depends on the cylinder design. VDMA cylinders work
up to 16 bar.
» Thrust is controllable through a pressure regulator.

Fundamental designs

» Pneumatic actuators are made in a wide variety of sizes, styles and types
including the following
» Single acting with and without spring return
» Double acting
» Rodless
» Rotary

Single acting spring return

Single acting cylinders have a power stroke in one direction only

Single acting no spring

Gravity or other external force to return the rod

Double acting

» Double acting cylinders use compressed air to power both the outstroke
and instroke.
» Superior speed control is possible
» There are
 Non-cushioned types
 Fixed cushioned types
 Adjustable cushioned types

Double acting non-cushioned

» Non cushioned cylinders are suitable for full stroke working at slow speed.
» Higher speeds with external cushion

Programmable Relay

Programmable Relay is a device that control logics as PLC, but it has limitations. This gives small number of input outputs and don’t have many functions as PLC. This is very useful in small applications. The main feature that programmable relay has is it has real calendar. So is can set to function using calendar. We used OMRON ZEN-10C1DR-D programmable relay in our training. It can program on the device, it has supplied a small display that can write the ladder diagram and run it.

Inverter


Inverter is a device that can control a 3phase induction motor in many ways. Within a very little period I learnt have to quick read the manuals and get the maximum usage of the device. As example driving foreword & reverse, electronic starting method, range of rpm, adjustable acceleration functions and adjustable breaking functions. I could drive a 3phase induction motor many ways that our engineer needs

Cylinders and Motors

These devices are used as output devices for automation system. Especial feature of cylinder is output motion in various ways .But many type of motors give only circular motion and we should change it into liner or other types by using mechanical devices. Main disadvantage of cylinders over motors is can not apply for very high power applications. In economically cylinders are cheaper than motors. Not only that it is very easy to install and more reliable.

Final control element

1 Solenoid valves

Solenoid valve is a device which connects electrical and pneumatic side. There is a coil in solenoid valve and it can be operated by applying relevant voltage. Then coil becomes magnetic and valve can be closed or opened. So pneumatic system can be controlled according to that.

2 Contactors

This device is widely used for power circuit of high power induction motors. By using this can be controlled three phase line according to control signals. When contactor is working that signal can be taken through normally open point of contactor. For some kind of contactors control signal points can be expanded through auxiliary cards.

Signal Processing Elements

Relay

We can think of a relay as an electromagnetic switch. Apply a voltage to the coil and a magnetic field is generated. This magnetic field sucks the contacts of the relay in, causing them to make a connection. These contacts can be considered to be a switch. They allow current to flow between 2 points thereby closing the circuit. The most important feature of relay is self holding. There are different types of relays according to the application. They are differ by coil supply as 24 DCV, 220ACV, 110ACV or number of contact points as 2 or 4 n/c - n/o points or shape of pins as LY, MY.

“Self holding” and “Interlocking”

In automatons m/c the signals to control cct is given by sensors or switches and as they operate in real time they give pulse to cct as signals. So it is needed to memories them in the cct. This feature can develop using self-holding method.
In some cases until one action stopped other action should not activate. That means if two actions want to be prevented operate at same time we can use interlocking method.

Contractors

Contractor is a scale up device of relay. Using contactor we can drive any load according to their rating. But relay can only drive few amperes. So relay is used to drive contractor and contractor can drive higher load (motor). For small power applications (solenoid valve) relays can directly use to drive them. Using contractors only it can be developed a control cct so there are auxiliary devices to increase the number of contact points. Using this method we can drive motor forward and reverse with star to delta manual changing. I practiced induction motor control with star delta changing, forward reverse driving using contactors.

Main points to select proper relay are as follows
(1) Points for contact

1) Forms and number of contact combinations
2) States of contact load AC or DC?; resistive or inductive or capacitive
or lamp?; occurrence of back electromotive force or inrush current?
3) Level of contact load Large or small current?; Switch on or
not for current load?; Switch off or not for current load?
4) Frequency in switching operation
5) Demand for life in switching operation

(2) Points for coil

1) Coil power source DC or AC?
2) Fluctuation in supply voltage
3) Energizing method and circuit Necessity of special energizing circuit
4) Coil resistance
5) Operate and release voltages
6) Operate time and release time

(3)Insulation

1) Dielectric strength
2) Insulation resistance
3) Surge strength

(4) Environment

1) Range of ambient temperature or humidity
2) Environmental atmosphere
3) Vibration and shock

(5) Mounting

1) Outside dimensions
2) Fixing and soldering of terminals
3) Mounting method

(6) Others

1) Safety standards and other standards
2) Special specifications or conditions

Timers and Counters

We could study about the timers and counters used in automation systems. Timers used to get time interval and switch signals to control cct. User can adjust this time and when supply given the timer count time and switch the points after set time. There are two types of timers called delay ON and delay OFF timers. In delay ON timers after set time normally open points will be closed and normally closed points will be opened. In delay off timers, just after supplies given normally open points will be closed and normally open points will be closed. Then after the set time, normally open points will be opened and normally closed points will be closed. Timers used in many applications. When motor wants to auto-change to star – delta timer used to get time interval. Auto-change over in generator uses timers.

Signal Input Devices

Proximity sensors

These are in three types. They are capacitive, inductive and optical. Capacitive sensors are used to sense according to material property. To operate inductive sensors is used magnet. Inductive types are widely used with actuators. Because permanent magnets are included in one side of cylinders. Optical type is more familiar to us. It is sensitive to light intensity.

Push buttons and limit switches

Push buttons are widely used to give signals for control systems. Mainly push buttons are two types which are normally open and Close buttons. These are applying to switch panels of control circuits. By using normally open type push button can be given start signals for systems. Similarly close button can be used to stop purposes.

Limit switches are applied to instead of sensors. It works by touching its roller or relevant part. Accuracy is depending on limit switch types. Some one works micrometer distances. Reliability of limit switches are more higher than sensors. Because sensors may be week in dust areas but limits switch are not like that they can apply very robust areas in industry.

Signal Input Devices

Sensors

Sensors can be used to detect the position of mechanisms or other moving parts. It is similar to human eyes. Mainly input which are needed to control systems is taken through sensors.

Programmable Logic Solutions for automation

Programmable logic solutions have the following characteristics:
•They provide more flexible solutions.
•They need a combination of hardware and software to solve the automation problems.
•They are good for complex and frequent change systems.


In this fast changing world, the product cycles are short, the manufacturing
lines need to change their manufacturing processes very often.
Programmable logic solutions have been widely accepted as the vital control
solutions in the modern automation systems.

Hard-wired Logic Solutions for automation

Hard-wired logic solutions have the following characteristics:
•They are strictly single purpose.
•They need to connect up discrete components, such as relays, timers, etc.
to perform the required control functions.
•They are good for small and rugged systems.

Automation elements

Output Elements
ELECTRO-PNEUMATICS
• Cylinders
• Vacuum generators
• Rotary Actuators
ELECTRICAL
• Electrical Motors
• Linear Motors
• (Read-outs & displays)

Final control elements
ELECTOR-PNEUMATICS
• Directional control solenoid valve
ELECTRICAL
• Contactors

Automating the process

As industrial automation is aimed at reduction of human involvement in controlling a machine or process,its implementation necessarily entails the following steps.

Step 1: Replacement of human's muscles(hand)by some out put devices,
eg-The electrical motors,pneumatic actuators or hydraulic cylinders.

Step 2: replacement of human's brain by a logic signal processing devices
such as a computer,micro-controller or programmable controller.

Step 3: Replacement of human's senses(eyes,ears,etc.)by input devices such as
limit switches and sensors.

Step 4: The use of signal conversions means to match the out put element with the
signal processing layer.

Introduction to Automation Engineering

Automation is a process of technological development,which is aimed at reducing human involvement in performing a task.specifically,industrial automation is concentrated with the application of mechanical,Electrical,Electronic,networking and computer based systems to operate and control the automatic manufacturing of goods