1 UDP ON “AUTOMATIC TOOL CHANGER (ATC)” A PROJECT REPORT In the partial fulfillment of the requirements for the award of the degree of DIPLOMA IN ENGINEERING OF MECHATRONICS Submitted By AGHERA HARDIK (002) BHADESIA DHAVAL (003) SINROJA NANDAN (014) THESIYA SAGAR (021) CHAUHAN SWAPNIL (038) Guided By: Jatin P. Patel Lecturer in B.S. Patel Polytechnic, Mehsana
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1
UDP ON
“AUTOMATIC TOOL CHANGER (ATC)”
A PROJECT REPORT
In the partial fulfillment of the requirements for the award of the degree of
DIPLOMA IN ENGINEERING
OF
MECHATRONICS
Submitted By
AGHERA HARDIK (002)
BHADESIA DHAVAL (003)
SINROJA NANDAN (014)
THESIYA SAGAR (021)
CHAUHAN SWAPNIL (038)
Guided By: Jatin P. Patel
Lecturer in B.S. Patel Polytechnic, Mehsana
2
CERTIFICATE
This is to certify that the Project report entitled “AUTOMATIC TOOL CHANGER
(ATC)” has been carried out by AGHERA HARDIK (106440320002), BHADESIA DHAVAL (106440320003), SINROJA NANDAN (106440320014), THESIYA SAGAR (106440320021), CHAUHAN SWAPNIL (106440320038) under my guidance in fulfillment of the degree of Diploma of Engineering in Mechatronics Engineering (6th Semester) of Gujarat Technological University, Ahmedabad during the academic year 2012 - 2013.
Mr. K.P PATEL (H.O.D MECHANICAL)
Mr. J.P. PATEL
(Internal Guide Teacher)
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ACKNOWLEDGMENT
Any accomplishment requires the effort of many people and this work is not different. And it is my prime duty to acknowledge the person who directly or indirectly helped us during completion of this project report. So I take opportunity to heartily thank our internal in charge Prof. JATIN P. PATEL for his valuable guidance and touch of inspiration and motivation throughout the project work without whose help the work would not have been in the shape what it is.
I am also heartily thank our H.O.D Mr. KALPESH P. PATEL who greatly helped us in our project work without whose help the work would not have been in the shape what it is.
We are also thankful to other relevant staff of workshop, library and department for their co-operation, help and guidance.
We are also thankful to our co-colleagues for a good team work to make the project successful.
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ABSTRACT
This research focuses on the automatic tool changing system in CNC machines. Most CNC parts are
controlled by hydro pneumatic or electronics, but this research represents with electronic system
only. In this research, two Stepper motors are used to control the spindle. The four limit switches are
used to start/stop operation of the two st motors. A unipolar stepping motor is used to rotate the
desired angle when the operator calls the required tool to operate. And the keypad is used as the user
input. PIC 16F877A microcontroller is used to interface the user input through the driver circuits.
And it also drives the two stepper motors and the stepper motor to operate correctly. This research
mainly concentrates on control logic program and simulation software for automatic tool changing
system. By using Proteus 7.7 simulation software, the required angle of stepper motor control and
directions of stepper motors control are simulated.
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INDEX
SR NO. CONTENTS PG NO.
Ch -1 1.1 Introduction. 6
1.2 Tools Changers fig. 7
Ch -2 2.1 Defination of ATC. 8
2.2 Working Principle of ATC. 8
2.3 Types of ATC and Magazines. 9
2.4 Classification of ATC 10
2.5 Working of Work Tables. 11
2.6 Technical Consideration of Influence the ATC. 11
2.7 Programming of ATC. 13
2.8 Requirement of Tool Magazine. 14
2.9 Characteristics of Tool Magazine. 14
Ch -3 3.1 Concept of ATC. 15
Ch -4 4.1 Stepper Motor Basics. 16
4.2 Stepper Motor Introduction. 18
4.3 Types of Stepper Motor. 19
4.4 Types of Stepper Motor Modes. 23
4.5 Stepper Motor Enviromental Considerations. 24
4.6 General Safety Considerations for Stepper Motor Applications. 25
4.7 Particulars of Model we have to Prepare. 25
4.8 Summary. 26
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Chapter - 1
INTRODUCTION
Computer numerical control is the process of manufacturing machined parts using a computerized
controller to command motors which drive each machine axis. In order to achieve high precision
machining, many efforts have been made to develop more accurate computerized numerical control
(CNC) systems. CNC systems are commonly used in industrial and commercial applications for its
compact size, high power-to-weight ratio, reliability, and low maintenance. CNC System includes a
PC, motion board, servo motor drive and motors, spindle drive and motor, automatic tool-changer
and general I/O card. A tool magazine is an indexable storage used on a machining center to store
tools not in use.
The tool magazines are available.
1) Rotary Drum type ATC.
2) Chain type ATC.
3) Turret Head type ATC.
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Chapter - 2
A) Definition:
A common mill feature that reduces cycle times by automatically changing tools
between cuts. Automatic tool changers are differentiated by tool-to-tool time and the number of tools
they can hold
B) Working Principle of ATC:
The desired tool is collected from one end of magazine of the spindle arm. At the
position of tool change, the empty end of the arm grips the tool in the spindle, removes it, indexes to
180˙ and inserts the new tool into the spindle.
There are no. of variations on the double arm. It is due to design of arm and
variation in the relative movement between the arm and spindle during tool change. Quill – type
spindles generally move at towards the stationary (after rotation) arm to accept a new tool or replace
the existing tool. For non – type spindles, the double – end arm incorporates an in – out motion to
insert or extract the tool from the spindle taper. Its function are;
1) Transports the tool magazine during storage.
2) Keep the tool clean.
3) It avoids the tool change.
A part from these, the ATC also do the function that, keeps the tracks of tools.
This may be done by coding the tools physically either on the tool itself or in the magazine adjacent
to the tool, when the pocket is loaded. Alternatively, to use the NC program itself. A tooling
instruction sheet is given to the operator with every tape and part setup sheet with the manual data
entry system, this problem becomes easy by operator keying both the tool number and corresponding
pocket number.
The NC does the data handling and retrieving tool position and also the
reviewing the tool position from the CRT control is possible at any time. When it is time directional
magazine clockwise or anti - clockwise to get the proper pocket to its pick point, and gives
instruction to the magazine – drive motor.
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C) Types of ATC and Magazine:
For automatic selection and changing (positioning) we need the variety of tools
for a specific job to be complete. ATC can be
1) Turret Head Type:
- Used in drilling machines.
- Semi – ATC
2) Drum Type:
- For holding small number of tools, these are used.
- Stored the periphery of the drum.
- Tool search speed is faster.
3) Chain Type:
- For holding more number of tools, these are used.
- Tool search speed is comparatively slow.
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D) CLASSIFICATION OF ATC:
There are several ways are available to classify ATC. They may be;
1) As per type of Cutting tool:
- ATC for single tool.
- ATC for multi tool heads.
- ATC for special type of tool like micro – borers.
2) As per Tool Changing system.
- Tool – change without arm
- Tool – change with arm.
- With tool parking position.
3) As per Tool Position:
- With Horizontal tool position.
- With Vertical tool position.
4) As per Axis of Tool and Spindle.
- With parallel axis.
- With intersecting axis.
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E) Working of Work Tables:
Work tables can be titled to any position for machining a new surface. Table tilting is
usually done by hinges in the cse of horizontal machining center. Hinges are provided at the side of
the table are to the spindles column and the tables is lifed from the other side by means of aball
screw. One innovative rotations,the unit present work at compound angles to the spindles.
For simple indexing of work table, Geneva mechanism may be used .But for typical
rotary table indexing such as DC servomotors connected to a worm drive that rotates the table on
preloaded ball bearings, are sometimes supplemented with air bearins. In worm drive system,
backlash is the major problem occurs through the double – lead method, in which pre – loaded worm
drives are combined with double pinions to the drive gear rim. Alternatively, anti – backlash systems
may be used to avoid backlash effect which consists of a special flexure spring. Rotation is stopped
at the end of indexing and the table is clamped hydro – mechanically at that position. Positioning
measures the ability of the table to stop in the same location time after time.
The work clamp table is usually of squre type with rounded corners provided with
necessary T – slots, center holes, tapped holes at the top of table for fixure location and clamping the
workpiece. The table is either designed to have a continuous rotary motion or indexing facility. The
normally available indexing facility are 90, 5, 2.5 and 1 and is achieved by means of a
coupling(hurth or curvic type). The maximum table load depends on the size of the machine, the
design of table and related elements.
F) Technical Consideration Influence the ATC:
The following technical factor area influenced in the tool change of CNC
programming control system. These factors are related mostly related to physical characteristics of
cutting tool. They will be:
i. Maximum tool diameter.
ii. Maximum tool length.
iii. Maximum tool weight.
1) Maximum Tool Diameter :
If there is any necessary to use maximum size of tool in the pocket of a tool
magazine, then it can be used without any special consideration. But it may affect the adjacent
pocket. In this situation it is necessary to empty the two adjacent pockets of the magazine.
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The adjacent pockets must be empty for a large tool diameter.
Let assume the machine is in a position to hold tool with diameter and adjacent pocket diameter is
100mm. If the both adjacent pockets are emptied then the maximum size of the tool can be increased
to 150 mm. But there is a decrease in actual capacity tool placed in the tool magazine.
2) Maximum Tool Length :
The tool length is nothing but the projection of cutting from the spindle gauge
line towards the part of the automatic tool changer. If the length of the tool is more, then it is
necessary to give more attention to the clearance on Z – axis during tool change. Any physical
contact of tool with a machines or fixture will create undesirable damage and the condition will be
highiy danger. This difficulties can be overcome by emergency switch on the CNC machine.
3) Maximum Tool Weight :
The tool weight is also one of the important factor to be considered but it does
not make any difference in programming, because most of the tools are lighter weight to compare
with recommended weight. The ATC is a larger mechanical device therefore it contains limitations.
The weight of the tool is always combined weight of cutting tool holder, including collets, screws,
pull studs and similar parts.
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For example given CNC machining centre may have to be recommended tool weight specified about
10 kg. If even a slightly heavier is used 11 kg. The automatic tool changer should not be used over
weight at all.
G) Programming the ATC:
There are many possibilities exist in relatation to the automatic tool changer. The
important parameters to be considered are number of tools, tool size, tool number and type of change
required initially.
If the programmer want to program the ATC successfully some conditions must be
adopted. For example a tool changer with three tools, each tool number will represent one of the
available formats,that is four tool number be used. The fourth one is dummy tool.
T01 – Tool designation represents the first tool used in the CNC
program.
T02 - Tool designation represents any tool used in the CNC
program between the first and last tool.
T03 - Tool designation represents the last tool used in the CNC
program.
T99 - Tool designation represents empty tool(dummy – tool) as a
empty tool pocket identification.
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H) Requirements of Tool Magazines:
The characteristics of tool magazines should be such that, it should fulfil the
following requirements:
1) Tool magazine must be capable of holding enough tools needed for
performing complete operations to finish the workpiece on machining centres.
2) Magazine should be as compact as possible.
3) Construction has to be simple.
4) Interchange of tool should not interfere with the workpiece space and tool
space.
5) Easier and safer manual exchanges of tool should be facilitated in the tool
magazine during loading and unloading.
6) All preparatory works for tool exchanges should be made during machining.
I) CHARACTERISTICS OF TOOL MAGAZINES:
1. Magazine should be capable of storing required numbers of tools to carry out all the
operations on a machining center.
2. It should be compact and simple to reduce its cost and space requirement.
3. It should not be protruding the working space of the machine for preventing it from
disturbing tool space at the time of tool changing.
4. It should allow manual transfer of tool easily and safely at the time of loading and the tools.
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Chapter - 3
CONCEPT OF ATC:
ATC means Automatic Tool Changer. This is important part of CNC machine. ATC
select the tool from the magazine. Magazine stores the tool and replace the Cutting tool from the
spindle. Time of tool changing 3 to 7 seconds. ATC is playing an important role in reducing
operation time. The required to is brought to the end of a special type of arm at the time of tool
changing free end of the arm holds the tool in the spindle, removes it and it’s indexing is done by
180˙ and new tool is replaced in the spindle. There are many differences in the various double ended
arms. For replacing new tool, quill type spindle is generally coming out towards stationary arm. In
non-quill spindle for fixing and removing tool, in – out moment of double ended arm is done. Tool
magazine is used for storing tool and preventing damage to the tools. It also keeps track of the tool
location. For this tools are coded or the coding is provided on the tool pocket instead of the
magazine. NC program is also used to keep track of tools.
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Chapter – 4
Stepper Motor:
A) Stepper Motor Basic:
- A stepper motor is a digital device. Digital information is processed by the stepper motor
to accomplish an end result, in this case, controlled motion. One may assume that a
stepper motor will dependably follow digital instructions just as a computer is expected.
This is the distinguishing feature of a stepper motor.
- The stepper motor is an electrical motor that is driven by digital pulses rather than a
continuously applied voltage. Inherent in this concept is open-loop control, wherein a
train of pulses translates into so many shaft revolutions, with each revolution requiring a
given number of pulses.
- Each pulse equals one rotary increment, or step (hence named, stepper, stepping, or step
motor), which is only a portion of one complete rotation. Therefore, counting pulses can
be applied in the stepper motor to achieve a desired amount of shaft rotation.
- The count automatically represents how much movement has been achieved, without the
need for feedback information, as would be the case in servo systems, and other
technologies. Although not required, most stepper motors can accommodate an encoder
when it is desired.
- A stepper motor is an electromechanical device which converts electrical pulses into
discrete mechanical movements. The shaft or spindle of a stepper motor rotates indiscrete
step increments when electrical command pulses are applied to it in the proper sequence.
The motors rotation has several direct relationships to these applied input pulses.
- The stepper used in this research has 200 steps per revolution. The relationship between
steps per revolution and step angle is given by the following formula: