ABSTRACT

An Automatic Tool Changer is equipment 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.

CNC machines are in general, more expensive than general purpose man-

operated machine tools, special attention is given to the design of the NC

machines and production tooling in order to reduce the time spent in both

work and machine set up. Tooling systems for NC are designed to

eliminate operator error and maximize productive machine hours. CNC

tool changers allow a machine to perform more than one function without

requiring an operator to change the tooling. A CNC tool changer can

quickly change the end effectors without the requirement of multiple

robots. Tool changers can be a manual tool changers or automatic tool

changers. A CNC tool changer fulfills the requirement of multiple tooling

for a wide variety of machine tools. A CNC machine tool raises the

productivity by automatically translating designs into instructions for a

computer controller on a machine tool. The spindle axis of a CNC machine

tool fixes the chucks which is integral to the lathes functioning. A CNC

tool storage system is an organized, efficient, and secure method of

storing tools at all stages and time. The main component of a CNC tool

storage system is a CNC tool holder. A CNC tool holder is suitable for

vertically storing all types of preset tools.

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Index1. Automation and requirement of Automation

Automation in production system Automated manufacturing Systems Fixed Automation, Programmable Automation and Flexible Automation Automation Principles and strategies USA principle, Automation Migration Theory, Ten strategies for automation Reasons for Automation

2. Toolings For Numerical ControlToolings for Numerical Control Alternatives for Automatic tool changing semiautomatic tool changing preset tooling

3. Automatic Tool Changer An IdeaAutomatic Tool Changer What is automatic Tool Changer Why Automatic Tool Changer is needed Types of Automatic tool Changer tool Change system with gripper Arm Description of gripper arm - Tool Change system with Chain Magazine Tool Change system with Disc Magazine

4. Project DetailsProject Concept Description of Parts Construction of Parts Degrees of Freedom Details About main Parts Rack and Pinion Mechanism For gripper Arm - Relay what is Relay and How it works Relay Specifications How an electric motor works Specifications of Gear motors Idea about circuit Circuit Diagram and description of Circuit Diagram

5. NC SystemsBrief introduction about NC and CNC systems and NC controllers

6. Conclusion7. References

2

Automation and Requirements of Automation

AUTOMATION IN PRODUCTION SYSTEMSSome elements of the production systems are likely to be automated,

where as the others will be operated manually or clerically. For our

purposes here, automation can be defined as a technology concerned

with the application of mechanical, electronic and computer based

systems to operate and control production.

In modern production systems, the two categories overlap to some

extent, because the automated manufacturing systems operating on the

factory floor are themselves often implemented by computer systems and

connected to the computerized manufacturing support systems and

management information system operating at the plant and enterprise

levels. The term computer integrated manufacturing is used to indicate

this extensive use of computers in production systems.

Opportunities of automation and computerization in production system

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ManufacturingSupport systems

Potential computerization

applications

Facilities:Factory

Equipment

Potential Automation applications

AUTOMATED MANUFACTURING SYSTEMS

Automated manufacturing systems operate in the factory on the physical

product. They perform operations such as processing, assembly,

inspection, or material handling in some cases accomplishing more than

one of these operations in the same system. They are called automated

because they perform their operations with a reduced level of human

participation compared with the corresponding manual process. In some

highly automated systems, there is virtually no human participation.

Examples of automated manufacturing systems includes:

Automated machine tools that process machine parts

Transfer lines that perform a series of machining operations

Automated assembly systems

Manufacturing systems that use industrial robots to perform

processing or assembly operations

Automatic material handling and storage systems to integrate

manufacturing operations

Automatic inspection system for quality control

Automated manufacturing systems can be classified into three basic types

1. Fixed automation

2. Programmable automation

3. Flexible automation

All the three types of automation differ in certain specific ways as per

their characteristics. They are discussed in detail below.

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1. Fixed Automation

Fixed automation is a system in which the sequence of processing

operations is fixed by the equipment configuration. Each of the operations

in the sequence is usually simple, involving perhaps a plain linear or

rotational motion or an uncomplicated combination of the two; for

example, the feeding of a rotating spindle. It is the integration and

coordination of many such operations into one piece of equipment that

makes the system complex. Typical features of fixed automation are:

High initial investment for custom-engineered equipment

High production rates

Relatively inflexible in accommodation product variety

The economic justification for fixed automation is found in products that

are produced in very large quantities and at high production rates. The

high initial cost of the equipment can be spread over a very large number

of units, thus making unit cost attractive compared with alternative

methods of production. Example of fixed automation includes machining

transfer lines and automated assembly machines.

2. Programmable Automation

In programmable automation, the production equipment is designed with

the capability to change the sequence of operations to accommodate

different product configurations. The operation sequence is controlled by

a program which is a set of instructions coded so that they can be read

and interpreted by the system. New programs can be prepared and

entered in to the equipment to produce new products. Some of the

features that characterize programmable automation include:

High investment in general purpose equipment

Lower production rates than fixed automation

Flexibility to deal with variations and changes in product

configuration

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Most suitable for batch production

Programmable automated systems are used in low and medium volume

production. The parts or products are typically made in batches. To

produce each new batch of a different product, the system must be

reprogrammed with the set of machine instructions that correspond to

the new product.

3. Flexible Automation

Flexible automation is an extension of programmable automation. A

flexible automation system is capable of producing a variety of parts with

virtually no time lost for changeovers from one part style to the next.

There is no lost production time while reprogramming the system and

altering the physical setup (tooling, fixture, machine settings). It is a case

of soft variety, so that the amount of changeover required between styles

is minimal. The features of flexible automation can be summarized as

follows:

High investment for a custom engineered system

Continuous production of variable mixture of products

Medium production rates

Flexibility to deal with product design variations

Examples of flexible automation are the flexible manufacturing systems

for performing machining operations that date back to the late 1960s.

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AUTOMATION PRINCIPLES AND STRATEGIES

There are mainly three approaches for dealing with automation projects

1. The USA principle

2. Ten strategies for automation

3. Automation migration strategy

The USA principle

The USA principle is a common sense approach to automation projects.

Similar procedures have been suggested in manufacturing and

automation trade literature, but none has a more captivating title than

this one. USA stands for:

Understand the existing process

Simplify the process

Automate the process

A statement of the USA principle appeared in the APICS (American

Production and Inventory Control Society) article. The article was

concerned with implementation of enterprise resource planning but the

USA approach is so general that it is applicable to nearly any automation

project.

1. Understand the existing processThe obvious purpose of the first step in the USA approach is to

comprehend the current process in all of its details. What are the

inputs? What are the outputs? What exactly happens to the work unit

between input and output? What is the function of the process? How

does it add value to the product? What are the upstream and

downstream operations in the production sequenced, and can they be

combined with the process under consideration?

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Mathematical models of the process may also be useful to indicate

relationships between input parameters and output variables. What are

the important output variables? How are these output variables

affected by inputs to the process, such as raw material properties,

process settings, operating parameters, and environmental conditions?

This information may be valuable in identifying what output variables

need to be measured for feedback purposes and in formulating

algorithms for automatic process control.

2. Simplify the process

Once the existing process is understood, then the search can begin for

ways to simplify. This often involves a checklist of questions about the

existing process. What is the purpose of this step or this transport? Is this

step necessary? Can this step be eliminated? Is the most appropriate

technology being used in this step? How can this step be simplified? Are

there necessary steps in the process that might be eliminated without

detracting from function?

Some of the ten strategies of automation and production systems are

applicable to try to simplify the process. Can steps be integrated into a

manually operated production line?

3. Automate the process

Once the process has been reduced to its simplest form, then automation

can be considered. The possible forms of automation include those listed

in ten strategies discussed in the following section. An automation

migration strategy might be implemented for a new product that has not

yet proven itself.

Ten strategies for automation

Following the USA principle is a good first step in any automation project.

As suggested previously, it may turn out that automation of the process

is unnecessary or cannot be cost justified after it has been simplified.

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If automation seems a feasible solution to improve productivity, quality or

other measure of performance, then the following strategies provide a

road map to search for these improvements. These strategies are as

relevant and appropriate today as they did in 80s. They are referred as

strategies for automation because some of them are applicable whether

the process is a candidate for automation or just for simplification.

1. Specialization of operation

The first strategy involves the use of special purpose equipment designed

to perform one operation with the greatest possible efficiency. This is

analogous to the concept of labor specialization, which is employed to

improve the labor productivity.

2. Combined operations

Production occurs as a sequence of operations. Complex parts may

require dozens, or even hundreds of processing steps. The strategy of

combined operation involves reducing the number of distinct production

machines or work stations through which the part must be routed. This is

accomplished by performing more than one operation at a given machine,

thereby reducing the number of separate machines needed. Since each

machine typically involves a setup, setup time can usually be saved as a

consequence of this strategy. Material handling effort and non operation

time are also reduced. Manufacturing lead time is reduced for better

customer service.

3. Simultaneous operations

A logical extension of the combined operations strategy is to

simultaneously perform the operations that are combined at one

workstation.

4. Integration of operationsAnother strategy is to link several workstations together into a single

integrated mechanism, using automated work handling devices to

transfer parts between stations.

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5. Increased flexibilityThis strategy attempts to achieve maximum utilization of equipment for

job shop and medium volume situations by using the same equipment for

a variety of parts or products. It involves the use of the flexible

automation concepts.

6. Improved material handling and storageA great opportunity for reducing nonproductive time exists in the use of

automated material handling and storage systems. Typical benefits

include reduced work in progress and shorter manufacturing lead times.

7. Online inspectionInspection for quality of work is traditionally performed after the process

is completed. This means that any poor quality product has already been

produced by the time it is inspected. Incorporating inspection into the

manufacturing process permits corrections to the process as the product

is being made.

8. Process control and optimizationThis includes a wide range of control schemes intended to operate the

individual processes and associated equipment more efficiently. By this

strategy, the individual process times can be reduced and product quality

improved.

9. Plant operations controlWhereas the previous strategy was concerned with the control of the

individual manufacturing process, this strategy is concerned with control

at the plant level.

10. Computer integrated manufacturing

Taking the previous strategy one level higher, we have the integration of

factory operations with engineering design and the business functions of

the firm. CIM involves extensive use of computer applications, computer

data bases, and computer networking throughout the enterprise.

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The ten strategies constitute a checklist of the possibilities for improving

the production system through automation or simplification.

They should not be considered as mutually exclusive. For most situations,

multiple strategies can be implemented in one improvement project.

Automation migration strategy

Owing to competitive marketplace, a company often needs to introduce a

new product in the shortest possible time. As mentioned previously, the

easiest and least expensive way to accomplish this objective is to design

a manual production method, using a sequence of workstations operating

independently. If the product turns out to be successful, and high future

demand is anticipated, then it makes sense for the company to automate

production. A typical automation migration strategy is the following:

Phase 1: manual production using single station manned cells operating

independently. This is used for introduction of the new

product for reasons already mentioned: quick and low cost

tooling to get started.

Phase 2: Automated production using single station automated cells

operating independently. As demand for the product grows,

and it becomes clear that automation can be justified, then

the single stations are automated to reduce labor and

increase production rate.

Phase 3: Automated integrated production using a multistation

automated system with serial operations and automated

transfer of work units between stations.

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REASONS OF AUTOMATING

Companies undertake projects in manufacturing automation and

computer integrated manufacturing for a variety of good reasons. Some

of the reasons used to justify automation are the following:

1. To increase labor productivityAutomating a manufacturing operation usually increases production rate

and labor productivity. This means greater output per hour of labor

input.

2. To reduce labor cost

Ever increasing labor cost has been and continuous to be the trend in the

worlds industrialized societies. Consequently, higher investment in

automation has become economically justifiable to replace manual

operations.

3. To mitigate the effects of labor shortages

There is a general shortage of labor in many advanced nations, and this

has stimulated the development of automated operations as a substitute

for labor.

4. To reduce or eliminate routine manual and clerical tasks

An argument can be put forth that there is social value in automating

operations that are routine, boring, fatiguing, and possibly irksome.

5. To improve worker safety

By automating a given operation, and transferring the worker from

active participation in the process to a supervisory role, the work is made

safer.

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6. To improve product quality

Automation not only results in higher production rates than manual

operations; it also performs the manufacturing process with greater

uniformity and conformity to quality specifications.

7. To reduce manufacturing lead time

Automation helps to reduce the elapsed time between customer order

and product delivery, providing a competitive advantage to the

manufacturer for future orders.

8. To accomplish processes that cannot be done manuallyCertain operations cannot be accomplished without the aid of a machine.

These processes have requirements for precision, miniaturization, or

complexity of geometry that cannot be achieved manually.

9. To avoid the high cost of not automating

There is a significant competitive advantage gained in automating a

manufacturing plant. The advantage cannot easily be demonstrated on a

companys project authorization form. The benefits of automation often

show up in unexpected and intangible ways, such as an improved quality,

higher sales, better labor relations, and better company image.

Companies that do not automate are likely to find themselves at a

competitive disadvantage with their customers, their employees and the

general public.

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Tooling for Numerical Control

TOOLING FOR NUMERICAL CONTROLSince NC machines are in general, more expensive than general purpose

man-operated machine tools, special attention is given to the design of

the NC machines and production tooling in order to reduce the time spent

in both work and machine set up.

Tooling systems for NC are designed to eliminate operator error and

maximize productive machine hours. They do this in one or more of the

following ways:

1. Using quick change tool holders

2. Automatic tool selection

3. Automatic tool Changer

4. Presetting of tool

5. Facilitating tool selection and tool changing through the numerical

control program

While tooling for NC machines might appear to be specialized, the actual

components and principles involved have much in common with what

would be considered proper practice for conventional machine tools.

1. Tool Holders

Quick change tool holders are designed so that cutting tools can be

readily positioned with respect to the spindle axis of the machine. This

requires that tolerances on length and/or diameter be held on all tools

used in the machine.

Arbor type cutters such as face mills and shell end mills are held in arbor

type tool holders. Shank type mills are held in positive lock holder. Drills,

reamers and boring tools are held in a straight shank collet type holder.

Taps are held in a tension and compression collet type holders.

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2. Automatic tool selection

Automatic tool selectors in NC make all the tool changes required to

complete a predetermined sequence of machining operations on a

part.

There are two basic approaches to automatic tool selection:

When relatively small number of different tools is required,

automatic tool selector is the turret type. The turret is rotated

under program control to bring the proper tool into position. The

tools are held in preset tool holder adapters which are mounted into

turret spindles.

An automatic tool changer and magazine of tools is frequently used

in preference to the turret approach, when the number of tools to

be used is large. Each tool is inserted in a common spindle as

required. The tools which are mounted in uniform holders, are

automatically picked up, placed into the spindle and locked in place.

When the operations using that tool are completed it is returned to

the tool storage magazine.

For changing tools rapidly it is better to place tool in magazine or turret in

the order in which they will be used.

3. Automatic Tool Changer

For three axis machines which perform a wide variety of operations tool

changes a programmed into the tape for fully automatic selection and

replacement.

The automatic tool change system may consist of following elements:

Rotary tool storage magazine for numerous tools.

Automatic tool changer to remove tool holders from the

machine spindle and replace them with tape programmed

tools.

15

Basic tool holders adaptable to a multiplicity of cutting tool

types and work specifications.

Tool coding rings and system for selection of proper tools in

accordance with tape signals.

In operation, the automatic tool change is accomplished in four steps:

By tape command (and from any location the magazine) the

tool magazine rotates to proper position to bring the pre

selected tool into place for particular operation. One end of the

tool change your arm then grasps the tool while the opposite

end grasps the tool to be replaced in the spindle.

The tool changer arm moves out away from the spindle

removing one tool from the magazine and other tool from the

spindle.

4. Preset Tooling

In machining relatively small batches of work very considerable

savings can be made by reducing the machine down time during

the period needed for the initial machine tool setup i.e. when

preparing two machines a batch of different components. This

reduction in setup time favourabaly influences the breakeven

point towards the use of NC machine tool.

Since the cost per minute of maintaining an NC machine in

production is much greater than the cost of a tool setter working

on a bench with special tool setting equipment there arises the

necessity for presetting the tools to be used by NC machines.

In other word the advantage of presetting tool in the tool room on

precision tool presetting machine can readily be seen by

calculating the cost of operator mistakes and machine down time

on jobs which require continuous machine cycling. The time and

costs for any interruption for trial cuts or to adjust tooling would

be prohibitive.

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AUTOMATIC TOOL CHANGER

AUTOMATIC TOOL CHANGERAn Automatic Tool Changer is equipment 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.

CNC tool changers allow a machine to perform more than one function

without requiring an operator to change the tooling. A CNC tool changer

can quickly change the end effectors without the requirement of multiple

robots. Tool changers can be a manual tool changers or automatic tool

changers. A CNC tool changer fulfills the requirement of multiple tooling

for a wide variety of machine tools.

Why Tool Changer is needed?

Tool changer is equipment which is used in CNC machines to reduce the

cycle time.

The term applies to a wide variety of tooling, from indexable insert, single

point tools to coded, preset tool holders for use in automatic tool

changers. It includes power-actuated, cross-slide tooling and turret tool

holders for single spindle chuckers, interchangeable-block boring tools.

A number of basic types of tool holders are available that accommodate

most face mills, end mills, drills, reamers, taps, boring tools,

counterbores, countersinks, and spot facers.

Arbor type cutters such as face mills and shell end mills are held in an

arbor type tool holders. Shank type mills are held in positive lock holder.

Drills, reamers and boring tools are held in a straight shank collet type

holder. Taps are held in a tension and compression collet type holders.

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TYPES OF AUTOMATIC TOOL CHANGERThere are mainly three kinds of tool changers available in market

according to the tool magazine arrangements provided.

1. Tool change system with gripper arm

2. Tool change system with chain magazine

3. Tool change system with disc magazine

1. Tool Change system with gripper Arm

In this system, there are mainly two elements

Disc with magazine

Gripper arm

In this system, a disc is provided with magazine, in which different types

of tools are loaded. It can hold maximum 32 tools.

In magazines, all the tools which are required are fixed in the magazines.

The tool which is programmed in controller according to the program will

be indexed in front of the gripper arm and then the gripper arm grips the

tool and performs the operation. After completion of the operation by

each tool, the gripper arm places the tool back in to the magazine.

Description of the gripper arm

The tool changer gripper arm consists of a central aluminum structure

with terminal tool grippers of hardened steel.

Tool gripping and release are obtained by means of a spring-operated

mechanism actuated by the rotation of the arm. The latter, in turning,

engages or disengages the grippers from the tools when these are in

exchange position.

2. Tool Change system with chain magazine

In this kind of system, a chain is provided with magazines for tool

holding. This chain can hold numerous tools so it is used in heavy

machineries. Starting from 32 it can hold more than 100 tools.

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These chain is indexed in front of the head stock directly as per the tool

programmed position.

Tool Change system with chain magazine

19

In this kind of system there is no arrangement like gripper arm. The

chain itself is indexed and the machining is done while keeping the tool in

the chain only.

3. Tool change system with Disc magazine

In this system, the tools are held in a big disc. This disc is not similar to

the disc provided in gripper arm mechanism. In this disc, there are tool

grippers provided separately for each magazine these grippers holds the

tool and performs machining operation as well.

Tool change system with disc magazine

This system disc can hold 32 to maximum of 64 tools. These type of tool

changers are used in medium capacity machineries.

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Project Details

CONCEPTDuring training, we have seen huge CNC units equipped with automatic

tool changers. From there we have got the idea to replicate the same as

our project. CNC machines are widely used in industries these days. For

saving time consumed in loading and unloading the tools, almost all the

CNC machines are equipped with automatic tool changers.

DESCRIPTION OF THE PARTSHere, we have selected the gripper arm type arrangement for our project.

We have made the model of gripper arm automatic tool changer.

Main Components

The main components of the gripper arm arrangement are:

1. Base

2. Griper arm

3. Tool holder

4. Support arm

5. Horizontal rib

Description of all the parts used and its function is discussed here. The

main parts are base, tool holder, support arm and gripper arm

1. Base:

We have provided 400x600x20 mm wooden base. This base holds the

whole arrangement as well as supports it.

2. Gripper Arm:

An aluminum strip is provided on which the gripper arm is fixed. The

gripper arm rotates 360 degree and performs the machining operation as

per our requirement.

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The aluminum strip can oscillate about the support arm and gripper

arm rotates 360 degree about the pivot point and also reciprocates

due to the rack and pinion arrangement provided in the gripper arm.

So the machining operation can be performed.

The tool gripper mechanism also rotates 360 degree which is provided

at the end of gripper arm.

So mainly there are three motions

1. Tool gripper rotation 360 degree

2. Whole rack and pinion mechanism disc rotates 360

degree

3. Gripper arm reciprocates due to rack and pinion

mechanism

These motions facilitate machining operations in all directions

very easily.

4. Tool holder

Tool holder can be any disc or block type arrangement in which the

tools can be held. Here, we have provided wooden block with metal

strip at the bottom for holding the tools. We have fixed a metal strip

with the bottom strip so after putting the tool back into the tool holder,

the tool is locked. So basically it is a locking and unlocking mechanism

for all the four tools.

5. Support arm

Support arm does not perform any kind of specific function; it just

supports the whole assembly mainly, the gripper arm and the

horizontal rib. It is a mild steel hollow shaft of 150 mm diameter. It is

kept hollow so that all the wires can be passed inside the shaft.

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Motors

There are mainly three motors are used all of different RPM ranging

from 15 rpm to 45 rpm. Motors used here are the simple gear motors

used for electrical purposes. These motors have the capacity to carry

load upto 4-5 kg. and then it can give torque of

The motors are called gear motors which are directly available in

market. The supply to the motors is given by 9 watts battery.

The electric motor is a standard DC electric motor.

DC Electric Motor

On the end of the motor is a small 6-tooth gear. This gear fits into the

center of the planetary gear system, as shown here:

A gear attached to the motor fits in the middle of the three smaller

gears

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This gear system is the heart of any electric screwdriver. An electric

motor by itself is a pretty weak device. You can grab the axle and stop

a small motor's rotation very easily. This means that the chuck moves

very slowly relative to the motor, but that the chuck has a great deal

of torque (it takes 56 times more strength to stop the motor from

spinning because of the gear ratio).

Parts of an electric motor

You can see that this is a small motor, about as big around as a dime.

From the outside you can see the steel can that forms the body of the

motor, an axle, a nylon end cap and two battery leads. If you hook the

battery leads of the motor up to a flashlight battery, the axle will spin.

If you reverse the leads, it will spin in the opposite direction. Here are

two other views of the same motor. (Note the two slots in the side of

the steel can in the second shot - their purpose will become more

evident in a moment.)

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Nylon cap

The nylon end cap is held in place by two tabs that are part of the

steel can. By bending the tabs back, you can free the end cap and

remove it. Inside the end cap are the motor's brushes. These brushes

transfer power from the battery to the commutator as the motor spins.

Rack and pinion mechanism for gripper arm

Rack and pinion mechanism is provided for gripper arm for

reciprocating movement of gripper arm. The mechanism is fixed in a

plate kind of arrangement and in this arrangement, gripper arm is

fixed. Due to up and down motion of rack and pinion, the gripper arm

moves up and down and the whole mechanism rotates 360 degree for

performing the required task. The gripper arm used here is of screw

driver kind of arrangement. It is available readily in market with

different arrangements for different kinds of screw heads.

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DEGREES OF FREEDOMMain aspect of this project is its degrees of freedom. It has mainly 10

degrees of freedom.

There are mainly

1. Rotational motion of horizontal arm

2. Rotational motion of Rack and pinion disc

3. Reciprocating motion of gripper arm

4. Rotational motion of gripper

5. Reciprocating motion of tool holder lock unlock mechanism

Rotational Motion of Horizontal Arm

The horizontal arm is pivoted about the main arm and it can rotate,

clockwise as well as anticlockwise about the main arm. This motion

facilitates machining in any direction.

Rotational Motion of Rack and Pinion Disc

The rack and pinion disc is provided at the end of the horizontal arm.

It is pivoted about the upper middle side. It can rotate about the pivot

point. This motion facilitates movement of tool gripper in any direction.

Reciprocating Motion of Gripper Arm

Rack and pinion arrangement is provided for gripper arm. Gripper arm

is fixed with pinion. So reciprocating motion of the gripper arm can be

obtained and machining can be done accordingly.Rotational Motion of Gripper

The tool gripper which is almost cylindrical in shape and provided at

the end of gripper arm for actually holding the tools can have circular

motion. This motion facilitates the tasks like fastening or loosening a

screw.

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CONSTRUCTION

We have carried out the construction of the tool changer equipment in

following manner.

Firstly, we have attached the main arm (which is of 65 mm

diameter) to the base. As mentioned above the base is wooden

board of 400x600x20 mm.

On this wooden board, the hollow arm is fixed with two bolts.

The arm is kept hollow so that the wirings can be passed inside

the hollow arm. On the arm, a motor is fixed. Motor is of 20rpm

and it can carry maximum of 4kgs. load.

After fixing the horizontal arm to the main arm, at the end of the

horizontal arm, the disc of rack and pinion arrangements is

attached. This attachment is also fixed with motor. So the whole

rack and pinion disc can rotate 360 degree.

In the rack and pinion arrangement, a gripper arm is attached.

Gripper arm is attached so that up and down movement of the

gripper arm can be achieved by rack and pinion mechanism.

The gripper arm used here is of screw driver kind of

arrangement. It is available readily in market with different

arrangements for different kinds of screw heads. This kind of tool

gripper arrangement is used. The all four tools are arranged in

tool holder, and the tool gripper comes down, grips the tool and

goes to the required location.

A circuit with eight relays is used for four different tools holding

and un-holding. A relay is an electrical switch that opens and

closes under the control of another electrical circuit.

The circuit diagram is very simple and it is explained in next

page.

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Description of the Circuit

Circuit diagram is shown in previous page. It is a very simple circuit. It

consists of transistors, Relays and motors.

The detail about relay is given in next pages. Relay is an

electromagnetic switch which is used to convert AC to DC. The motors

and all the other parts used in circuit can be run through DC supply.

So for converting AC current into DC we have used Relay.

P Total

P total is maximum total power which can be generated in a transistor.

The Specifications

All the specifications of the BC547 PNP transistor, we have used, is

described in next page.

RELAYA relay is a simple electro mechanical switch made up of an electro

magnet and a set of contacts A relay is an electrical switch that opens

and closes under the control of another electrical circuit. In the original

form, the switch is operated by an electromagnet to open or close one

or many sets of contacts. Relays are found hidden in all sorts of

devices.

Parts of a relay

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A simple electromagnetic relay, such as the one taken from a car in

the first picture, is an adaptation of an electromagnet. It consists of a

coil of wire surrounding a soft iron core, an iron yoke, which provides a

low reluctance path for magnetic flux, a moveable iron armature, and

a set, or sets, of contacts; two in the relay pictured. The armature is

hinged to the yoke and mechanically linked to a moving contact or

contacts. It is held in place by a spring so that when the relay is de-

energized there is an air gap in the magnetic circuit.

When an electric current is passed through the coil, the resulting

magnetic field attracts the armature and the consequent movement of

the movable contact or contacts either makes or breaks a connection

with a fixed contact. If the set of contacts was closed when the relay

was de-energized, then the movement opens the contacts and breaks

the connection, and vice versa if the contacts were open.

If the coil is energized with DC, a diode is frequently installed across

the coil, to dissipate the energy from the collapsing magnetic field at

deactivation, which would otherwise generate a voltage spike

dangerous to circuit components. Some automotive relays already

include that diode inside the relay case.

CONSTRUCTION OF A RELAYRelays are amazingly simple devices. There are four parts in every

relay:

Electromagnet

Armature that can be attracted by the electromagnet

Spring

Set of electrical contacts

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Working principle of a relay

In this figure, you can see that a relay consists of two separate and

completely independent circuits. The first is at the bottom and drives

the electromagnet. In this circuit, a switch is controlling power to the

electromagnet. When the switch is on, the electromagnet is on, and it

attracts the armature (blue).

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NC System An Idea

NC SYSTEMMany of the achievements in computer-aided design and

manufacturing have a common origin in numerical control (abbreviated

as NC). The conceptual, framework established during the

development of numerical control is still undergoing further refinement

and enhancement in todays CAD/CAM technology.

Numerical control can be defined as a form of programmable

automation in which the process is controlled by numbers, letters and

symbols. In NC the numbers form a program of instructions designed

for a particular workparts or job.

NC technology has been applied to the wide variety of operations,

including drafting, assembly, inspection, sheet metal press working,

and spot welding. However, numerical control finds its principle

applications in metal machining processes. The machined work parts

are designed in various sizes and shapes, and most machined parts

that are produced in industry today are made in small to medium size

batches.

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BASIC COMPONENTS OF AN NC SYSTEM

An operational numerical control system consists of the following three

basic components.

1. Program of instructions

2. Controller unit, also called a machine control Unit

3. Machine tool or other controlled process

The general relationship among the three components is illustrated in

figure. The program of instructions serves as the input to the controller

unit, which in turn commands the machine tool or the other process to

be controlled.

In NC system you need to write the part programs required to run the

machine tool manually. Programs are listing of codes in a proper

sequence that as instructions for the machine. The program of

instructions is the detailed step by step set of directions which tell the

machine tool what to do.

It is a multifunction machine which incorporates several time saving

features into a single piece of automated production equipment. All the

components are explained in detail below.

NC system

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Part program Controller Machine Tool

1. Program of Instructions

The program of instructions is the detailed step by step set of

directions which tell the machine tool what to do. It is coded in

symbolic form on some type of input medium that can be interpreted

by the controller unit. The most common input medium today is 1 inch

wide punched tape. Over the years, other forms of input media have

been used, including punched cards, magnetic tapes, and even 35-mm

motion picture film.

2. Controller Unit

The second basic component of the NC system is the controller unit.

This consists of the electronics and hardware that read and interpret

the program of instructions and convert it into mechanical actions of

the machine tool. The typical elements of a conventional NC controller

unit include the tape reader, a data buffer, signal output channels to

the machine tool, feedback channels from the machine tool, and the

sequence control to co-ordinate the overall operation of the foregoing

elements.

Here, some systems are provided with Automatic Tool Changer so

there will be no operator required for changing the tools and the tool

changing time will also be reduced so the machining operation will be

performed fast.

3. Machine tool or other controlled process

The third basic component of an NC system is the machine tool or

other controlled process. It is the part of the NC system which

performs useful work. In the most common example of an NC system,

one designed to perform machining operations, the machine tool

consists of the work table and spindle as well as the motors and

controls necessary to drive them. It also includes the cutting tools,

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work fixtures and other auxiliary equipment needed in the machining

operation.

CNC SYSTEM

In a CNC system, a dedicated computer is used to perform all basic NC

functions. Part program of CNC is similar to part program of an NC

system. This program is entered only once, and it serves as input for

the computer. The CNC systems have more computational capability,

more reliable and are flexible compared to NC system.

CNC System

DEFINITION OF CNC

A system in which the actions are controlled by direct insertion of

numerical data at some point. The system automatically interprets at

least some portion of this data.

DNC SYSTEM

The DNC system uses a central computer, which sends control signals

to number of local CNC machines. Program is stored in the memory of

host computer, when a machine tool needs control commands, host

computer instantaneously communicates with it and perform

operation.

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Part program

Computer Machine Tool

DNC System[

NEED FOR CNC

In conventional machines, after loading the work piece, you have to

manually operate different hand wheels to feed the cutting tool into

the work piece.

ADVANTAGES OF CNC MACHINES With a CNC system you can:

Reduce non-production time

Achieve manufacturing flexibility

Increase in production rate

Produce parts with complex shapes

Improve quality

Achieve good surface finish and accuracy

In short, CNC offers ACCURACY, REPEATABILITY, RELIABILITY and

PRODUCTIVITY.

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Host computer

CNC Computer

CNC Computer

CNC Computer

M/c. Tool

M/c. Tool

M/C. Tool

TYPES OF CNC MACHINES1. Single spindle drilling machine

2. Turning center or CNC lathe

3. Milling center

4. Machining center

5. CNC Non conventional machines (EDM, AJM etc.)

COMPONENTS OF CNC SYSTEM

Part program

Computer

Machine control unit (MCU)

Processing machine

1. Part Program

Before making a part program, you need to understand the:

1. Given part drawing.

2. Different machining operations to be performed on

the job.

3. Sequence through which these operations are to be

performed.

4. Cutting conditions to be selected.

2. Machine Control Unit

It is a main part of CNC system. This unit interprets the program of

instructions and sends it to the next step in the process. All control

signals to the machine tool are generated here, based on the

instructions given in the part program. The MCU reads the part

program, and then sends the control signals to the control unit of the

machine tool in the form of electrical pulses. The drives in the machine

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tool convert these electrical pulses into the equivalent mechanical

motions.

Control signals

Inform of ele. Pulses

MCU

3. Processing Machines

Processing machines are designed to execute the metal machining

work as per the signals received from MCU. Different types of

machines are developed for different operations. These include

conventional and non-conventional machine tools. Conventional

machine tool includes lathe, milling, drilling etc. non-conventional

machines are machines that uses non-conventional energy, such as

thermal energy, chemical energy etc. Examples are, Electro Chemical

Grinding (ECG), Electro Discharge Machining (EDM) etc.

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MCU(Interpretation)

M/C. TOOL (Conversion)

CLASSIFICATION OF CNC SYSTEMS

1. TYPE OF MACHINE:

Point to point machining

Continuous path machining

2. PROGRAMING METHOD:

Incremental

Absolute

3. TYPE OF CONTROL LOOPS:

Open loop

Closed loop

DEVICES FOR DRIVING CNC SYSTEMS

Electrical devices

Hydraulic devices

Electric devices use different type of motors such as stepper motor or DC motor.

Hydraulic devices use actuator and other set up.

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CONCEPT OF PART PROGRAMMING

In CNC machine tools, the operations to be performed are given in a coded form, which is known as part program.

Manual part programming is a very tedious work. For manual programming a programmer must have sufficient knowledge of

machining processes and part programming techniques.

The programmer has to prepare a part program with a proper sequence of operations and appropriate selection of cutting

parameters such as feed and speed.

In such cases chances of committing errors are high while developing a part program. There for the concept of computer

assisted part programming came into existence so,

computational errors are eliminated.

Programming software does the calculations required to produce the component and the programmer communicates with this

system, through the system language, which is based on English

words.

TYPES OF PROGRAMMING LANGUAGES

APT (Automatically programmed tools)

COMPACT 2

ADAPT (Adaptation of APT)

EXAPT (Extended subset of APT)

AUTOSPOT

SPLIT

These languages are utilized as per type of machine, but APT is widely

used.

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CONCLUSION

An Automatic Tool Changer is equipment 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.

We have made the simplest model of an automatic tool changer. In

this model, there is scope of as many modifications as we want. By

more investment, it can be made more sophisticated as per our

requirement. For example, by using the disc instead of tool holder we

have used, more tools can be accommodated.

By using timers for operations, the time required for a particular

operation can be fixed and as per that time, the tool changing

procedure can be carried out.

So, in this way, more modifications can be done in the model we have

made.

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REFERENCES

Books

Automation principles and strategies by Mikell Groover

Production Technology Part II by O.P.Khanna

Computer Aided design and manufacturing by Mikell P. Groover & Emory W. Zimmers

Websites

www.ati-ia.com

www.howstuffworks.com

www.wikipedia.com

www.atc.cnc.in

www.industrialautomation.com

www.electronics@home.com

www.controldevices.com

Magazines

Electronics 4 you

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Machine CNC CNC CNC M/C. TOOL MCUTool changer is equipment which is used in CNC machines to reduce the cycle time.NC systemCNC SYSTEM

Definition Of CNC IncrementalDEVICES FOR DRIVING CNC SYSTEMSElectrical devicesHydraulic devicesTYPES OF PROGRAMMING LANGUAGES