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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
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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
3
ManufacturingSupport systems
Potential computerization
applications
Facilities:Factory
Equipment
Potential Automation applications
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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.
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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
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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
29
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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).
30
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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.
31
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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
32
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,
33
-
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.
34
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.
35
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
36
-
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.
37
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.
38
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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.
39
-
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.
40
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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
[email protected]
www.controldevices.com
Magazines
Electronics 4 you
41
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