1

UDP ON

“AUTOMATIC TOOL CHANGER (ATC)”

A PROJECT REPORT

In the partial fulfillment of the requirements for the award of the degree of

DIPLOMA IN ENGINEERING

OF

MECHATRONICS

Submitted By

AGHERA HARDIK (002)

BHADESIA DHAVAL (003)

SINROJA NANDAN (014)

THESIYA SAGAR (021)

CHAUHAN SWAPNIL (038)

Guided By: Jatin P. Patel

Lecturer in B.S. Patel Polytechnic, Mehsana

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CERTIFICATE

This is to certify that the Project report entitled “AUTOMATIC TOOL CHANGER

(ATC)” has been carried out by AGHERA HARDIK (106440320002), BHADESIA DHAVAL (106440320003), SINROJA NANDAN (106440320014), THESIYA SAGAR (106440320021), CHAUHAN SWAPNIL (106440320038) under my guidance in fulfillment of the degree of Diploma of Engineering in Mechatronics Engineering (6th Semester) of Gujarat Technological University, Ahmedabad during the academic year 2012 - 2013.

Mr. K.P PATEL (H.O.D MECHANICAL)

Mr. J.P. PATEL

(Internal Guide Teacher)

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ACKNOWLEDGMENT

Any accomplishment requires the effort of many people and this work is not different. And it is my prime duty to acknowledge the person who directly or indirectly helped us during completion of this project report. So I take opportunity to heartily thank our internal in charge Prof. JATIN P. PATEL for his valuable guidance and touch of inspiration and motivation throughout the project work without whose help the work would not have been in the shape what it is.

I am also heartily thank our H.O.D Mr. KALPESH P. PATEL who greatly helped us in our project work without whose help the work would not have been in the shape what it is.

We are also thankful to other relevant staff of workshop, library and department for their co-operation, help and guidance.

We are also thankful to our co-colleagues for a good team work to make the project successful.

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ABSTRACT

This research focuses on the automatic tool changing system in CNC machines. Most CNC parts are

controlled by hydro pneumatic or electronics, but this research represents with electronic system

only. In this research, two Stepper motors are used to control the spindle. The four limit switches are

used to start/stop operation of the two st motors. A unipolar stepping motor is used to rotate the

desired angle when the operator calls the required tool to operate. And the keypad is used as the user

input. PIC 16F877A microcontroller is used to interface the user input through the driver circuits.

And it also drives the two stepper motors and the stepper motor to operate correctly. This research

mainly concentrates on control logic program and simulation software for automatic tool changing

system. By using Proteus 7.7 simulation software, the required angle of stepper motor control and

directions of stepper motors control are simulated.

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INDEX

SR NO. CONTENTS PG NO.

Ch -1 1.1 Introduction. 6

1.2 Tools Changers fig. 7

Ch -2 2.1 Defination of ATC. 8

2.2 Working Principle of ATC. 8

2.3 Types of ATC and Magazines. 9

2.4 Classification of ATC 10

2.5 Working of Work Tables. 11

2.6 Technical Consideration of Influence the ATC. 11

2.7 Programming of ATC. 13

2.8 Requirement of Tool Magazine. 14

2.9 Characteristics of Tool Magazine. 14

Ch -3 3.1 Concept of ATC. 15

Ch -4 4.1 Stepper Motor Basics. 16

4.2 Stepper Motor Introduction. 18

4.3 Types of Stepper Motor. 19

4.4 Types of Stepper Motor Modes. 23

4.5 Stepper Motor Enviromental Considerations. 24

4.6 General Safety Considerations for Stepper Motor Applications. 25

4.7 Particulars of Model we have to Prepare. 25

4.8 Summary. 26

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Chapter - 1

INTRODUCTION

Computer numerical control is the process of manufacturing machined parts using a computerized

controller to command motors which drive each machine axis. In order to achieve high precision

machining, many efforts have been made to develop more accurate computerized numerical control

(CNC) systems. CNC systems are commonly used in industrial and commercial applications for its

compact size, high power-to-weight ratio, reliability, and low maintenance. CNC System includes a

PC, motion board, servo motor drive and motors, spindle drive and motor, automatic tool-changer

and general I/O card. A tool magazine is an indexable storage used on a machining center to store

tools not in use.

The tool magazines are available.

1) Rotary Drum type ATC.

2) Chain type ATC.

3) Turret Head type ATC.

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Chapter - 2

A) Definition:

A common mill feature that reduces cycle times by automatically changing tools

between cuts. Automatic tool changers are differentiated by tool-to-tool time and the number of tools

they can hold

B) Working Principle of ATC:

The desired tool is collected from one end of magazine of the spindle arm. At the

position of tool change, the empty end of the arm grips the tool in the spindle, removes it, indexes to

180˙ and inserts the new tool into the spindle.

There are no. of variations on the double arm. It is due to design of arm and

variation in the relative movement between the arm and spindle during tool change. Quill – type

spindles generally move at towards the stationary (after rotation) arm to accept a new tool or replace

the existing tool. For non – type spindles, the double – end arm incorporates an in – out motion to

insert or extract the tool from the spindle taper. Its function are;

1) Transports the tool magazine during storage.

2) Keep the tool clean.

3) It avoids the tool change.

A part from these, the ATC also do the function that, keeps the tracks of tools.

This may be done by coding the tools physically either on the tool itself or in the magazine adjacent

to the tool, when the pocket is loaded. Alternatively, to use the NC program itself. A tooling

instruction sheet is given to the operator with every tape and part setup sheet with the manual data

entry system, this problem becomes easy by operator keying both the tool number and corresponding

pocket number.

The NC does the data handling and retrieving tool position and also the

reviewing the tool position from the CRT control is possible at any time. When it is time directional

magazine clockwise or anti - clockwise to get the proper pocket to its pick point, and gives

instruction to the magazine – drive motor.

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C) Types of ATC and Magazine:

For automatic selection and changing (positioning) we need the variety of tools

for a specific job to be complete. ATC can be

1) Turret Head Type:

- Used in drilling machines.

- Semi – ATC

2) Drum Type:

- For holding small number of tools, these are used.

- Stored the periphery of the drum.

- Tool search speed is faster.

3) Chain Type:

- For holding more number of tools, these are used.

- Tool search speed is comparatively slow.

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D) CLASSIFICATION OF ATC:

There are several ways are available to classify ATC. They may be;

1) As per type of Cutting tool:

- ATC for single tool.

- ATC for multi tool heads.

- ATC for special type of tool like micro – borers.

2) As per Tool Changing system.

- Tool – change without arm

- Tool – change with arm.

- With tool parking position.

3) As per Tool Position:

- With Horizontal tool position.

- With Vertical tool position.

4) As per Axis of Tool and Spindle.

- With parallel axis.

- With intersecting axis.

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E) Working of Work Tables:

Work tables can be titled to any position for machining a new surface. Table tilting is

usually done by hinges in the cse of horizontal machining center. Hinges are provided at the side of

the table are to the spindles column and the tables is lifed from the other side by means of aball

screw. One innovative rotations,the unit present work at compound angles to the spindles.

For simple indexing of work table, Geneva mechanism may be used .But for typical

rotary table indexing such as DC servomotors connected to a worm drive that rotates the table on

preloaded ball bearings, are sometimes supplemented with air bearins. In worm drive system,

backlash is the major problem occurs through the double – lead method, in which pre – loaded worm

drives are combined with double pinions to the drive gear rim. Alternatively, anti – backlash systems

may be used to avoid backlash effect which consists of a special flexure spring. Rotation is stopped

at the end of indexing and the table is clamped hydro – mechanically at that position. Positioning

measures the ability of the table to stop in the same location time after time.

The work clamp table is usually of squre type with rounded corners provided with

necessary T – slots, center holes, tapped holes at the top of table for fixure location and clamping the

workpiece. The table is either designed to have a continuous rotary motion or indexing facility. The

normally available indexing facility are 90, 5, 2.5 and 1 and is achieved by means of a

coupling(hurth or curvic type). The maximum table load depends on the size of the machine, the

design of table and related elements.

F) Technical Consideration Influence the ATC:

The following technical factor area influenced in the tool change of CNC

programming control system. These factors are related mostly related to physical characteristics of

cutting tool. They will be:

i. Maximum tool diameter.

ii. Maximum tool length.

iii. Maximum tool weight.

1) Maximum Tool Diameter :

If there is any necessary to use maximum size of tool in the pocket of a tool

magazine, then it can be used without any special consideration. But it may affect the adjacent

pocket. In this situation it is necessary to empty the two adjacent pockets of the magazine.

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The adjacent pockets must be empty for a large tool diameter.

Let assume the machine is in a position to hold tool with diameter and adjacent pocket diameter is

100mm. If the both adjacent pockets are emptied then the maximum size of the tool can be increased

to 150 mm. But there is a decrease in actual capacity tool placed in the tool magazine.

2) Maximum Tool Length :

The tool length is nothing but the projection of cutting from the spindle gauge

line towards the part of the automatic tool changer. If the length of the tool is more, then it is

necessary to give more attention to the clearance on Z – axis during tool change. Any physical

contact of tool with a machines or fixture will create undesirable damage and the condition will be

highiy danger. This difficulties can be overcome by emergency switch on the CNC machine.

3) Maximum Tool Weight :

The tool weight is also one of the important factor to be considered but it does

not make any difference in programming, because most of the tools are lighter weight to compare

with recommended weight. The ATC is a larger mechanical device therefore it contains limitations.

The weight of the tool is always combined weight of cutting tool holder, including collets, screws,

pull studs and similar parts.

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For example given CNC machining centre may have to be recommended tool weight specified about

10 kg. If even a slightly heavier is used 11 kg. The automatic tool changer should not be used over

weight at all.

G) Programming the ATC:

There are many possibilities exist in relatation to the automatic tool changer. The

important parameters to be considered are number of tools, tool size, tool number and type of change

required initially.

If the programmer want to program the ATC successfully some conditions must be

adopted. For example a tool changer with three tools, each tool number will represent one of the

available formats,that is four tool number be used. The fourth one is dummy tool.

T01 – Tool designation represents the first tool used in the CNC

program.

T02 - Tool designation represents any tool used in the CNC

program between the first and last tool.

T03 - Tool designation represents the last tool used in the CNC

program.

T99 - Tool designation represents empty tool(dummy – tool) as a

empty tool pocket identification.

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H) Requirements of Tool Magazines:

The characteristics of tool magazines should be such that, it should fulfil the

following requirements:

1) Tool magazine must be capable of holding enough tools needed for

performing complete operations to finish the workpiece on machining centres.

2) Magazine should be as compact as possible.

3) Construction has to be simple.

4) Interchange of tool should not interfere with the workpiece space and tool

space.

5) Easier and safer manual exchanges of tool should be facilitated in the tool

magazine during loading and unloading.

6) All preparatory works for tool exchanges should be made during machining.

I) CHARACTERISTICS OF TOOL MAGAZINES:

1. Magazine should be capable of storing required numbers of tools to carry out all the

operations on a machining center.

2. It should be compact and simple to reduce its cost and space requirement.

3. It should not be protruding the working space of the machine for preventing it from

disturbing tool space at the time of tool changing.

4. It should allow manual transfer of tool easily and safely at the time of loading and the tools.

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Chapter - 3

CONCEPT OF ATC:

ATC means Automatic Tool Changer. This is important part of CNC machine. ATC

select the tool from the magazine. Magazine stores the tool and replace the Cutting tool from the

spindle. Time of tool changing 3 to 7 seconds. ATC is playing an important role in reducing

operation time. The required to is brought to the end of a special type of arm at the time of tool

changing free end of the arm holds the tool in the spindle, removes it and it’s indexing is done by

180˙ and new tool is replaced in the spindle. There are many differences in the various double ended

arms. For replacing new tool, quill type spindle is generally coming out towards stationary arm. In

non-quill spindle for fixing and removing tool, in – out moment of double ended arm is done. Tool

magazine is used for storing tool and preventing damage to the tools. It also keeps track of the tool

location. For this tools are coded or the coding is provided on the tool pocket instead of the

magazine. NC program is also used to keep track of tools.

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Chapter – 4

Stepper Motor:

A) Stepper Motor Basic:

- A stepper motor is a digital device. Digital information is processed by the stepper motor

to accomplish an end result, in this case, controlled motion. One may assume that a

stepper motor will dependably follow digital instructions just as a computer is expected.

This is the distinguishing feature of a stepper motor.

- The stepper motor is an electrical motor that is driven by digital pulses rather than a

continuously applied voltage. Inherent in this concept is open-loop control, wherein a

train of pulses translates into so many shaft revolutions, with each revolution requiring a

given number of pulses.

- Each pulse equals one rotary increment, or step (hence named, stepper, stepping, or step

motor), which is only a portion of one complete rotation. Therefore, counting pulses can

be applied in the stepper motor to achieve a desired amount of shaft rotation.

- The count automatically represents how much movement has been achieved, without the

need for feedback information, as would be the case in servo systems, and other

technologies. Although not required, most stepper motors can accommodate an encoder

when it is desired.

- A stepper motor is an electromechanical device which converts electrical pulses into

discrete mechanical movements. The shaft or spindle of a stepper motor rotates indiscrete

step increments when electrical command pulses are applied to it in the proper sequence.

The motors rotation has several direct relationships to these applied input pulses.

- The stepper used in this research has 200 steps per revolution. The relationship between

steps per revolution and step angle is given by the following formula:

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360˙

Step angle 360˙ = _______________________________________

Number of steps per revolution Step angle

360˙

Step angle 360˙ = __________

200 Steps

Step angle =1.8°

It is found that the step angle is 1.8 degree in a step. In this research, the number of tools in the tool

magazine is 25 tools. It is necessary to rotate 14.4 degree for one position of 25 tools. So, it needs to

rotate 80 steps for one position of tools.

For example, if the operator needs to operate the tool number 5, the stepper motor has to

rotate 72 degree.

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Introduction:

Motion Control, in electronic terms, means to accurately control the movement of an object

based on either speed, distance, load, inertia or a combination of all these factors. There are

numerous types of motion control systems, including; Stepper Motor, Linear Step Motor, DC Brush,

Brushless, Servo, Brushless Servo and more. This document will concentrate on Step Motor

technology.

In Theory, a Stepper motor is a marvel in simplicity. It has no brushes, or contacts. Basically

it's a synchronous motor with the magnetic field electronically switched to rotate the armature

magnet around.

A Stepping Motor System consists of three basic elements, often combined with some type of

user interface (Host Computer, PLC or Dumb Terminal):

The Indexer (or Controller) is a microprocessor capable of generating step pulses and

direction signals for the driver. In addition, the indexer is typically required to perform many other

sophisticated command functions.

The Driver (or Amplifier) converts the indexer command signals into the power necessary to

energize the motor windings. There are numerous types of drivers, with different current/amperage

ratings and construction technology. Not all drivers are suitable to run all motors, so when designing

a Motion Control System the driver selection process is critical.

The Step Motor is an electromagnetic device that converts digital pulses into mechanical

shaft rotation. Advantages of step motors are low cost, high reliability, high torque at low speeds and

a simple, rugged construction that operates in almost any environment. The main disadvantages in

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using a step motor is the resonance effect often exhibited at low speeds and decreasing torque with

increasing speed.

Types of Stepper Motor:

Stepper motor rotate the rotor with small equal angles and this small equal angle is known

as a “Step”.

There are three basic types of stepper motor. These stepper motor types vary by construction

and in how they function. Each stepper motor type offers a solution to an application in a different

way.

There are three types of Stepper Motor:

1) Variable Reluctance (VR) type of Stepper Motor.

2) Permanent magnet(PM) Stepper Motor.

3) Hybrid Stepper Motor.

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A) Variable Reluctance (VR) Stepper Motor:

- The variable reluctance motor in the above illustration has four "stator pole sets" (A, B,

C,), set 15 degrees apart. Current applied to pole A through the motor winding causes a

magnetic attraction that aligns the rotor (tooth) to pole A.

- Energizing stator pole B causes the rotor to rotate 15 degrees in alignment with pole B.

This process will continue with pole C and back to A in a clockwise direction. Reversing

the procedure (C to A) would result in a counterclockwise rotation.

- The Variable Reluctance stepper motor is known for having a soft iron multiple rotor and

a wound stator construction. The Variable Reluctance stepper motor generally operates in

step angles from 5 to 15 degrees at relatively high step rates.

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B) Permanent Magnet (PM) Stepper Motor:

- The permanent magnet motor, also referred to as a "Canstack" motor, has, as the name

implies, a permanent magnet rotor. It is a relatively low speed, low torque device with

large step angles of either 45 or 90 degrees.

- It's simple construction and low cost make it an ideal choice for non industrial

applications, such as a line printer print wheel positioner.

- The Permanent Magnet stepper motor differs from the Variable Reluctance stepper motor

by having permanent magnet rotors with no teeth. These rotors are magnetized

perpendicular to the axis. When the four phases are energized in sequence, the rotor

rotates as it is attracted to the magnetic poles.

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C) Hybrid Stepper Motor:

- Hybrid motors combine the best characteristics of the variable reluctance and permanent

magnet motors. They are constructed with multi-toothed stator poles and a permanent

magnet rotor. Standard hybrid motors have 200 rotor teeth and rotate at 1.80 step angles.

- Other hybrid motors are available in 0.9ºand 3.6º step angle configurations. Because they

exhibit high static and dynamic torque and run at very high step rates, hybrid motors are

used in a wide variety of industrial applications.

- The Hybrid stepper motor combines qualities from the permanent magnet and variable

reluctance stepper motors. The Hybrid stepper motor has some of the desirable features of

each. This type of stepper motor has a high detent torque, excellent holding and dynamic

torque, and they can operate in high stepping speeds. Step angles of 0.9 to 5.0 degrees are

normally seen in the Hybrid stepper motor. Bi-filar windings are generally supplied to

this stepper motor, so that a single power supply can be used to power the stepper motor.

- The rotor will rotate in increments of 1.8 degrees if the phases are energized one at a time

in the order they are indicated at. This stepper motor can be driven in two phases at a time

to yield more torque. The Hybrid stepper motor can also be driven by one then two then

one phase to produce half-steps of 0.9 degree increments.

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Types of Stepper Motor Modes:

- There are three excitation modes that are commonly used with the stepper motor.

1) Full - Step.

2) Half - Step.

3) Micro Step.

1) Full Step:

- In full-step operation, the stepper motor steps through the normal step angle, e.g. 200

step/revolution motors take 1.8 steps, while in half-step operation 0.9 steps are taken.

There are two kinds of full-step modes. Single phase full-step excitation is where the

stepper motor is operated with only one phase energized at a time.

- This mode should only be used in applications where torque and speed performance are

not important, wherein the motor is operated at a fixed speed and load conditions are well

defined. Typically stepper motors are used in full-step mode as replacements in existing

motion systems, and not used in new developments.

- Problems with resonance can prohibit operation at some speeds. This type of mode

requires the least amount of power from the drive power supply of any of the excitation

modes. Dual phase full-step excitation is where the stepper motor is operated with two

phases energized at a time. This mode provides good torque and speed performance with

a minimum of resonance problems.

2) Half Step:

- Stepper motor half-step excitation is alternate single and dual phase operation resulting in

steps one half the normal step size. Therefore, this mode provides twice the resolution.

While the motor torque output varies on alternate steps, this is more than offset by the

need to step through only half the angle.

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3) Micro Step:

- In the stepper motor micro step mode, a stepper motor's natural step angle can be divided

into much smaller angles. For example, a standard 1.8 degree motor has 200

steps/revolution. If the motor is micro stepped with a 'divide-by-10', then each micro step

moves the motor 0.18 degrees, which is 2,000 steps/revolution.

- The micro steps are produced by proportioning the current in the two windings according

to sine and cosine functions. This mode is only used where smoother motion or more

resolution is required. Typically, micro step modes range from divide-by-10 to divide-by-

256 (51,200 steps/rev for a 1.8 degree motor).

- Some micro step drivers have a fixed divisor, while the more expensive micro step

drivers provide for selectable divisors.

Stepper Motor Environmental Considerations:

- The following environmental and safety considerations must be observed during all

phases of operation, service and repair of a stepper motor system. Failure to comply with

these precautions violates safety standards of design, manufacture and intended use of the

stepper motor and driver.

- Please note that even a well-built stepper motor products operated and installed

improperly, can be hazardous. Precaution must be observed by the user with respect to the

load and operating environment.

- The customer is ultimately responsible for the proper selection, installation, and operation

of the stepper motor system.

- The atmosphere in which a stepper motor is used must be conducive to good general

practices of electrical/electronic equipment. Do not operate the stepper motor in the

presence of flammable gases, dust, oil, vapor or moisture.

- It is wise to install the stepper motor and driver in an environment which is free from

condensation, dust, electrical noise, vibration and shock.

- Additionally, it is preferable to work with the stepper motor/driver /controller system in a

non-static protective environment.

- Exposed circuitry should always be properly guarded and/or enclosed to prevent

unauthorized human contact with live circuitry. No work should be performed while

power is applied. Don’t plug in or unplug the connectors when power is ON. Wait for at

least 5 minutes before

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General Safety Considerations for Stepper Motor Applications:

- The following safety considerations must be observed during all phases of operation,

service and repair.

- Failure to comply with these precautions violates safety standards of design, manufacture,

and intended use of the stepper motor, driver and controller.

Particulars of model we have to prepare:

Motor Used: Stepper Motor (4 step).

Type of ATC used: Turret Head Type.

Microcontroller based Indexing.

Wooden Turret with four tools.

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Summary:

- Use caution when handling, testing, and adjusting during installation, set-up and

operation.

- Service should not be performed with power applied.

- Exposed circuitry should be properly guarded or enclosed to prevent unauthorized human

contact with live circuitry.

- All products should be securely mounted and adequately grounded.

- Provide adequate air flow and heat dissipation.

- Do not operate in the presence of flammable gases, vapors, liquids or dust.