Sophisticated Programme Able Industrial Robotic Arm

Introduction

SOPHISTICATED PROGRAMMABLE INDUSTRIAL ROBOTIC ARM INTRODUCTION

“Necessity is the mother of all inventions”. Since the time of evolution of man, his demands and needs have compelled him to invent new and sophisticated things. The exploration process never comes to an end, everyday thousands of people work day & night to bring various utilities to us. Man during the age of his evolution found & made new and different items which helped him in his daily activities. After stone age, copper age & bronze age, came the Industrial Age,in which various innovations started taking place. To ease out the labour work, new improved material handling equipments were being made. Automation was, and is the goal & motive of industry today. In order to reduce the stress on the labour & for

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Introduction

efficient working of the machines & increased production, it was very necessary for a sophisticated & intelligent material handling equipment to be developed. Thus began the evolution of what is called as a ROBOT.

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Robots

ROBOT ROBOT is a general term which stands for an automated unit which does have some kind of human symbolization in its operation or physical structure. It may not look human but it seems to be able to perform human type function and action. The term ROBOT comes from a CZECH word which means “forced labour”. A brief progress of the Industrial Revolution that began in the world two centuries ago is given as follows : 1) Construction of simple production machine in 1770. 2) Fixed automatic machine & transfer line machine for mass production came along as the second step at the turn of this century. 3) Numerical Control (NC) of machine tools in 1952 opened a new era in automation. 4) The logical extension of NC was computerized.

Numeric control of machine tool (1970) in which

minicomputer is included as an integral part of the control system was achieved . 5) Flexibility is the key word , which characterizes the new era in industrial automation.

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Robots

Robots and manufacturing systems are becoming more and more flexible with progress in computer technology and programming techniques. Advantages of Robots.: 

Flexibility of operation .



Increased Productivity.



Better quality of production.



Improved quality of human life by performing the tedious and repetitive jobs.



High precision.

Classification and Structure of Robotic systems: The classification of Robotics systems can be done in three ways: 1) According to the type of system : - Point to point versus continuous path. 2) According to the type of control loop :- Open loop versus closed loop. 3) According to the structure of manipulators:- Cartesian, Cylindrical, Spherical or Articulated.

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Robots

The selection of the type of system , control loop and manipulator depends on the particular application. In addition , an appropriate wrist and end effector should be selected to fit the required application.

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Selection Criteria For the Motors

SELECTION CRITERION FOR THE MOTORS . a) The motor must provide the required torque. b) It should have high torque to weight ratio. In other words the motor weight should be low. This is necessary as heavy motor will reduce the dynamic response of manipulator. c) The motor should rotate in steps. This is necessary to avoid need of the feedback circuits. This facilitates the exact position control with reduced hardware difficulties. d) The motor should have instantaneous start & stop characteristics. This is necessary to avoid the positional error due to the inertia of load. e) It must be easily and quickly reversible. Since the motion of manipulator is not unidirectional , this characteristic is necessary. f) The size of motor must be sufficiently small. This will make it possible to locate motor, in the minimum area and hence will reduce the overall manipulator size. The D.C. stepper motor possesses all such characteristics. Thus they are used.

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Stepper Motors

STEPPER MOTORS : Stepper motor is an electromagnetic device. Stepper motor converts electrical pulses received by its excitation windings into discrete angular displacements – known as steps. They perform as decoders , transforming the digital information into steps of angular position. As the no. of discrete angular steps taken by stepper motors are directly proportional to no. of pulses, there as no need for of feedback. Stepper motors can be programmed in three parameters , viz . , a) Direction b) Speed c)

Number of steps

Advantages of stepper motors : 1) The rotation angle of the motor is proportional to the input pulses. 2) The motor has full torque at standstill (if windings are energized).

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Stepper Motors

3) Precise positioning and repeatability of movement since good stepper motors have an accuracy of 3-5% of a step and this error is non cumulative from one step to the next. 4) Excellent response to starting / stopping / reversing. 5) Very reliable , since there are no contact brushes in the motor. Therefore the life of the motor is simply dependent on the life of the bearing. 6) The motor response to digital input pulses provides one loop control making the motor simpler and less costly to control. 7) It is possible to achieve very low speed synchronous rotation with a load that is directly coupled to the shaft. 8) A wide range of rotational speeds can be realized as the speed is proportional to the frequency of input pulses. Stepper motors are used for various robot applications where low torques are required. And the control system is operating as an open loop. Stepper motors allow a digital electrical signal to be converted directly into

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Stepper Motors

an incremented angular positioning movement. The stepper motor is synchronous, so there is a correlation between the input command and the resulting position. There are three categories of stepper motors : 1. Motor with permanent magnet rotors. 2. Motor with variable reluctance. 3. Hybrid motors ( also known as polarized reluctance motors), which combine the properties of the other two types. Permanent Magnet Motor. The principle of operation of a Permanent Magnet stepper motor is as follows: Coils

Stator

Permanent magnet rotor

Stepper Motor with permanent Magnet

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Stepper Motors

The polarity of the magnets in the stator poles is changed when electrical currents are pulsed into the stator windings. When one stator pole is turned off , this turning on and off of stator poles, and the resulting change in the polarity of each stator pole from north to south, causes the rotor to be attracted from one pole to the next thus causing the rotor to rotate. Each step is precise and the number of steps, or angular increments, for one complete revolution is dependent on the number of stator windings; usually the range is between 1.80 & 90O. Stepping motors supply : Torque of stepping motor depends almost exclusively on the current at a given position. Thus it is important to be able to control the current accurately. As for all electrical motors torque is controlled by current and voltage can be used to control speed. As in the d.c system performance is limited with respect to torque as speed increases because the emf induced is in fact the emtf relative to the direction of the current. The problem becomes complex in stepping motor, because apart from excess speed operation, a succession of electrical and mechanical phenomena are involved. Establishing, a current involves dI/dt, and so voltages are induced in other phases by mutual inductance between the coils. If these coils are close together, even with an ancillary control system, a current will be produced and will create a generally opposing torque.

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Stepper Motors

Moreover the current will not be produced and cancelled out instantly. Torque will depend on both position & time. The phenomenon will be all the more important because the electrical time constant will be of the same order of magnitude as the time of movement from one stable position to another. The supply must fulfill certain conditions: 1. The current is capable of being established & cancelled out according to the i/p commands of the control system. This involves power transistors, either bipolar or MOSEFET. Thyristors require a complex circuit for blocking & the response time is often inadequate. 2. The current is established rapidly and all available techniques must be used to decrease the apparent time constant. 3. The commutation of the current from its normal value to zero is also rapid, and does not involve any over voltages that could harm the transistors. 4. The current is controlled and maintained at a value imposed by the control system. 5. No current flows through coils that are not in use.

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Some Definitions

SOME DEFINITIONS.  Nominal current is the maximum current permissible in steady operation to conform with the maximum

temperature level of the motor.  Resolution of angular step is the angle of minimum movement, which is the inverse of the number of

steps for a rotation of 20. Resolution depends on the method of supply.  Positional precision is the error between the real position and the theoretical position. Errors are not

cumulative but depend on the dry viscous friction coefficients.  Static torque or maintenance torque is the torque obtained with constant current at rest, sometimes

torque. This depends on the position of the rotor. It also refers to the load torque that can be applied without any rotor movement. It is a function of the method of supply.  Residual torque is the torque in the absence of any current with all coils open.  Dynamic torque is the rotating motor torque that depends on the method of supply and is not a

characteristic of the motor but of the motor and supply with the load taken into account.

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Some Definitions

 Maximum reversible frequency is the maximum frequency of commutation of supply, allowing the

direction of rotation to change without missing a step.  Maximum unidirectional frequency or maximum, stop-short frequency is the maximum frequency of

commutation allowing a start up speed increase followed by stopping without any loss of step, for a motor from rest.

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Stepper Motor Characteristics

STEPPER MOTOR CHARACTERISTICS. The characteristics are classified as i)

Static characteristics

ii)

Dynamic characteristics

The static are at the stationary position of the motor while the dynamic are under running conditions of the motor. Static characteristics. These characteristics include: i)

Torque – displacement characteristics

ii)

Torque – current characteristics.

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Stepper Motor Characteristics

i)

Torque displacement characteristics This gives the relationship between an electromagnetic torque developed and displacement angle θ from steady state position. Initially static torque increases with angular displacement reaching a maximum value at θ = θm is called holding torque.

Static torque Holding torque

O

θm Displacement from an equilibrium position

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θ

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Stepper Motor Characteristics

ii)

Torque – current characteristics. The holding torque of the motor increases with the exciting current. The relation between the

holding torque and the current is called as torque – current characteristics. holding torque (Nm)

variable reluctance motor permanent magnet motor

detent torque

O Current ( A) In variable reluctance motor, torque is zero when current is zero. Initially it increases according to palabolic nature and later on becomes linear. In permanent magnet motor, the static torque occurs – though motor is unexcited called as decent torque. Further it increases linearly with the current.

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Stepper Motor Characteristics

Dynamic Characteristics :-

This includes torque – stepping rate curves for a stopper motor. The curve 1 shows the start and synchronization of motor while the curve 2 corresponds to loss of synchronism. f1 = definite stepping late corresponding to given load torque at which motor can start & synchronize without loosing step. f2 = Once started stepping rate can be increased upto f2 after which motor starts loosing the steps. The stepper motor is not used at very law stepping rate indicated as A-B and A-B dotted, because of the oscillations.

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Torque Generation

TORQUE GENERATION. The torque produced by stepper motor depends, on several factors a. The step rate b. The drives current in the windings. c. The drives design or type. In the stepper motor a torque is developed when magnetic fluxes of the rotor and stator are displaced from each other. The stator is made up of a high permeability magnetic material. The presence of this high permeability material causes the magnetic flux to be confined for the most part to the paths defined by the stator structure in the same fashion that currents are confined to the conductors of an electronic ckt. This serves to concentrate the flux at the stator poles. The torque o/p produced by the motor is proportional to the intensity of the magnetic flux generated when the winding is energized. The basic relationship which defines the intensity of magnetic flux is defined by

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Torque Generation

H=(NxI)/L Where N = No. of windings turns I = Current H = Magnetic field intensity L = Magnetic flux path length. This relationship shows that the magnetic flux intensity and consequent the torque is proportional to the no. of winding turns and the current and inversely proportional to the length of magnetic flux path. From this basic relationship we can see that the same frame size. Stepper motor could have very different torque o/p capabilities simply by changing the winding parameters.

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Control of Stepping Motors

CONTROL OF STEPPING MOTORS

Torque as a function of pulse repetition frequency in the stepping motor.(1-3) Start & Stop zones (2) Unstable operating zones (4) Excessive speed zone (5) limit are corresponding to an excessive frequency. The methods of supply described before provide currents similar in form to the theoretically ideal current described at the start of the chapter. The approximate time constant values have been defined. If the frequency

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Control of Stepping Motors

of commutation is too great the current cannot reach normal value and there is a reduction in torque. There are the stopping and starting zones, the excessive speed zone and the unstable operating zone. The graphs provided by manufacturers are valid for a given supply and specific inertial load. Open-loop control of the stepping motor must satisfy a number of conditions 1. movement from one position to another is carried out in minimum time. 2. Operation is synchronous to avoid any loss of steps. 3. the final position is reached without oscillation. The load has a direct effect on the response of the system, and this must be taken into account in the control method. Bang – bang control can be described in general terms and the operational sequence broken down into four phases. 1. acceleration phase. 2. Excess speed operation. 3. Braking in order to return to the start – stop zone, 4. Stopping.

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Control of Stepping Motors

Frequency

f Excess speed

Braking Acceleration stop f0 t time Frequency variation method of stepping motor control Variation in linear pulse frequency is often used. Much research have been devoted to reducing time of motion and in creating strategies for increasing and decreasing speed. Problems can arise when the load is variable, both for inertia and load torque, and for this reason it is important to plan an adaptable method of control. A microprocessor can be used to consolidate all the information and form an overall view of stepping motor operation. Dynamic instability can be counteracted by : 1. damping using mechanical methods ( all of liquid )

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Control of Stepping Motors

2. damping using electrical devices ( short circuit coil) on the stator or rotor and introducing extra resistances, 3. Rapid self – adjustment of the current. The last method involves connecting the commutation from one phase to another to a single current source. Because of the emf induced during rotor movement the current is modulated to the frequency of the oscillations. Other singularities can be used to find the position of the rotor, such as current for one phase, or zero total current or the point of inflexion. The current is plotted and then processed before being fed to a microprocessor.

Processor

interface

supply

motor

load

servocontrol Diagram showing stepping motor servocontrol

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Control of Stepping Motors

The stepper motor can be actuated by i)

A microprocessor

ii)

A Computer (pc)

There are two ways of open loop control. a)Software intensive :- A microprocessor of a PC produces the phase control signals, the program is responsible for timing and sequencing the signals to move the motor to the required position. b) Hardware intensive :- The programme merely feeds the target position information and a start command to the hardware controller, which generates the phase control signals for the motor drive circuits and a finish signals for the controller when the target is reached. A P C is used to actuate the stepper motor. A software intensive approach is used to control the motor. The use of PC has following advantages i)

Higher level programming languages can be used.

ii)

The uses oriented software package can be developed.

iii)

It improves the versatility of the whole system.

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Control of Stepping Motors

iv)

The software intensive approach makes it easier to implement more sophisticated control schemes dimed at maximizing motor performance.

Interfacing. Designing logic circuits to enable the computer to communicate with the stepper motors is called Interfacing.

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Losses in the Stepping Motors

LOSSES IN THE STEPPING MOTOR. Losses in the stepping motor are similar to those in the standard d.c. motor. The Joule losses are easily calculated if the currents in the phases being supplied are known. An equivalent effective current can be used often. Mechanical and electro-magnetic losses all more difficult to find. They cannot be measured except during steady operation at constant speed, and so far no way of forming a valid model for transient operation has been found. The stator teeth are subjected to variable flux of frequency f/p. The rotor is subjected to the same variation in flux when the angular speed is less than the frequency, that is in the motor with a large number of teeth on the rotor. In motors with rotating magnets, however, the electro-magnetic losses at the rotor are negligible.

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Losses in the Stepping Motors

Total losses can be expressed thus ∑pi = ∑ RI2 ( t) + a ω + b ω2 Where I is the index of a phase being supplied, It is the corresponding current, W is the angular speed and a & b all constants. The thermal model has one node because the construction is homogeneous. The time constants vary between several minutes and tens of minutes.

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Robot Languages and Programming

ROBOT LANGUAGES AND PROGRAMMING. Robot languages have been developed for case of control of motion of robots having different structures and geometrical capabilities. Programming languages have been developed by the pioneering efforts of various researchers at Standard Artificial Intelligence Laboratory. Research Laboratories of IBM corporation, under U.S. Air force sponsorship, General Electric Co., Unimation and many other robot manufacturers.

Computers Control and Robot Software For performing a specific task, a robot is required to move in proper sequence. The robot can be taught & programmed through teach pendant teaching.. So textual programming is attempted and the computer instructions are given following the syntax of a certain robot languages, the program and control methods are actuated through software running on an operating system in which manipulation of data takes place. Monitors are used to activate control functions.

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Robot Languages and Programming

In a robot, there are three basic modes of operation. 1. Monitor mode. 2. Editor mode. 3. Run or execute mode. The above modes constitute the operation system. Monitor mode :In the monitor mode, the programmes can define locations load a particulars piece of a information in a particular register, store information in the memory, save, transfer programs storage into computer control memory, enable or disable and move back & forth into its edit and run mode. Edit mode :In the edit mode, the programmer can edit or change a set of instructions of existing programs or introduce new set of information. The user can erase some instruction and can replace them by new lines. In this mode, any error if shown on the monitor can be corrected. However, to come out of the edit mode, an end command say(E) should be given.

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Robot Languages and Programming

Run or Execute Mode :The program to carry out a predefined task can be executed in the run mode. The sequential steps as written by the programmer are followed during the run mode. Sometimes dry run can be tested by making the switch disable. After dry run, the switch may be made. Operational by the instruction enable. A program can be tested in run mode and debugging, the errors in the program can be rectified. The operating system for implementing robot language program uses either an interpreter or a compiles. An interpreter tabs the source program one line at a time and generates equivalent code that is understood by the controller. Any mistake in the source program, will be indicated to the uses. The uses can correct the source program and the line is reinterpreted. Every line is executed by the interpreter as and when it is written. So an interpreter works slowly while executing the program as it may reinterpret the same instruction repeatedly appearing at different lines of source program. But it is flexible. C is a language and the source of codes are instructions are processed by an interpreter. Compiler is a software in the operating system that converts source code into the object code ( m/c code ) after compilation of the whole program. The robot controller can then read and processes the machine codes. The compiles

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Robot Languages and Programming

passes through the entire program several times and checks all the variables, addresses, constants etc and produces equivalent machine codes. As it passes several times, the process is lengthy one. A computer does not repeat the process similar programs appearing several times, but it only recopies those parts. Execution time for a complied program is fast while editing of an interpreted program is very fast.

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Source Code

PROGRAMME FOR OPERATION OF STEPPER MOTORS USED IN THE S.P.I.R.A. #include<stdio.h> #include<dos.h> #include void main() { char direction; int flag=0, motorno, count, i, de=200; clrscr(); printf("\n\n\t\t\Welcome To The Stepper Motor Program !\n"); st: { printf("\n\n\tPlease Enter The Motor Number\t--->\t"); scanf("%d", &motorno); if (motorno==1) { outportb(0x0378, 0x10); } else if (motorno==2) { outportb(0x0378, 0x20); } else if (motorno==3) { outportb(0x0378, 0x40); } else if (motorno==4) { outportb(0x0378, 0x80); } else goto st;} m:

{

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Source Code

printf("\n\Please Enter The Number Of Count\t"); scanf("%d", &count); while( flag == 0 ) { clrscr(); printf("\n\n\t\t\Select One Of The Following Options ....."); printf("\n\nEnter\n\t f ---> Forward Direction"); printf("\n\t r ---> Reverse Direction\n\t "); printf("\n\t c ---> To Enter New Count\n\t "); printf("\n\t q ---> Quit The Program\n\n"); printf("\n\tEnter Your Choice Carefully --->\t "); scanf("\n\n\t%c", &direction); printf("\n\n\t %c\n", direction); switch( direction ) { case 'f' : clrscr(); i = 0; while( i++ < count ) { printf("\n\t Forward Count = %d", i); delay( de ); if( (i%4) == 0 ) { outportb(0x0375, 0x088); } else if( (i%4) == 1 ) { outportb(0x0478, 0x75); }

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Source Code

else if( (i%4) == 2 ) { outportb(0x0398, 0x89); } else if( (i%4) == 3 ) { outportb(0x0358, 0x4a); } } printf("\n\n\n\n\t\a End Of Forward Count"); printf("\n\n\t Press Enter For Further Instruction ......"); getch(); break;

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Mechanical Design

MECHANICAL DESIGN . The SPIRA is built up in such a way so as to obtain maximum movement, ease of design and maximum use of standard parts available .SPIRA comprises of 3 arms, 2 of which are moving & the third one, stationary. Stepper motors are used which are programmable & signals are provided via a P.C. The design is simple. Arm 1 which has a provision for gripper arrangement has 270 0 rotation. It is provided motion via a chain drive mounted on sprockets on two parallel shafts. These sprockets are press fitted on the shaft & the rear shaft also has a gear wheel press fitted to it, which is driven by a stepper motor. Arm 2 also has 270° rotation and it carries a counter weight to reduce the load on the motors. Arm 2 is directly driven via a gear drives which derives its source from another stepper motor. Gear drive is used to reduce the torque requirement of the stepper motor. A large gear ratio is used for a better effect in the same. The sprockets in the chain wheel drive are of the same diameter as motion to be transferred is required to be in the ratio of 1:1. This makes the program easier & signals given in the form of pulses will be to scale 1:1. Arm 2 also has 2700 rotation and it carries is counter weight to reduces the load on the motors.

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Arm 3 is a fixed one,

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Mechanical Design

on which, the two stepper motors are mounted. .The shaft mounted on this arm is actually a disjoint one , which are synchronized by a brass bush. The motion (rotational)of these two shafts is entirely independent of each other. One is press fitted to the sprocket on which driver Arm 1 and the other is press fitted to arm 2 and provides motion to it. The whole assembly is mounted on a circular plate, which has gear teeth on its outside. It is actually a flywheel ring welded to a strong circular plate. A meshing gear with that of the teeth of this flywheel ring is mounted on the shaft of the 3rd stepper motor, which is mounted inside the box which is the base of SPIRA. This box also houses the circuits of the motors. The various parameters involved like size of the arms, dimensions of shafts, no. of teeth of gear, gear wheel dia., diameter of shafts, length of chain, dia. of sprocket, base design etc. were decided keeping in mind the design calculations accompanied by the practical consideration like availability etc. Slight compromise was adopted, as Production Engineering. is an art of not only making things work, but making things work in the most efficient & economic manner with optimization involved to the maximum.

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Designing

DESIGNING Material selected for fabrication owes its selection to its properties like – • Machineability • Weldability • Availability • Low cost • Strength etc. Various factors considered for designing the various components of S.P.I.R.A. are : 1. Arm 1 

Length

, thickness , wt.

2. Arm 2 

Length

, thickness , wt.

3. Arm 3 

Length

, thickness , wt.

4. Bearing  Inner φ

, Outer φ

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Designing

5. Bush 

Strength, diameter.

6. Welded Joints  Strength ( Electric Arc welding ) 7. Shaft  Torsional moment, Bending moment . 8. L – bracket  Length 9. Counter weight  Weight calculation 10. Gears  Spur, no of teeth 11. Flywheel  No. of teeth, diameter. 12. Torque requirement  wt. to be lifted, factors to reduce the torque.

(A factor of safety of 3and 6 was supposed.)

1). Shaft :- The shaft is acted on by Torsional and Bending moments. fs

=

T =

C. θ

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Designing

r

J

l

C = angle of twist in radians on length θ = modulus of rigidity. fs = Torsional shear stress r = radius of shaft T = Torque L = length of shaft .

J = Ixx + Iyy = π x d4 + 64 f = 2πNT 4500

π x d4 =

π

64

64

x d4

T = π fs d3 16

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Designing

Design of shaft 4  Shafts used are transmission shafts. There are 4 shafts used. 3 & 4 are aligned by a bush and are disjoint. These two shafts are free to move in the bush but shaft 3 is fixed to arm 3 via a bearing and to arm 2 via a bush which is press fitted to the arm 2. This shaft also has a gear press fitted to it.

Bending moment = 7 kgf .cm = M Torque = 18 kgf.cm = T Ultimate tensile stress = 0.7000 kgf/ cm2 Ultimate shear stress = 0.5000 kgf/cm2 Factor of safety = 6 allowable tensile stress , ft = F.S allowable shear stress , ft = F.S

ftu = 0.7 = 0.1166 kgf/cm2 6 ftu = 0.5 = 0.083 kgf/cm2 6

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Designing

Acc. to maximum shear stress theory , equivalent twisting moment Te = √ M2 + T2 = 19.31 kgf.cm

Te = 19.31 = π

fs x d3 = π x 0.083 x d3

16

16 19.31 = 0.016 d3 d = 0.93 cm

Acc. to maximum normal stress theory, Equivalent bending moment Me = ½ ( M + √ M2 + T2 ) = ½ ( M + Te) = ½ ( 7 + 19.31 ) = 13.2 kgf.cm Also,

Me = 13.2 = π x fb x d3 = 32

π x 13.2 x d3 = 1.3 d3 => d= 0.95 c.m. = 9.5 m.m.

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Designing

Taking larger value d = 0.95 cm or

d = 9.5 mm

2) Welding is Electric arc type. 3) Bearing  The bearings are used to provide free rotating motion of shaft is the arms. The bearings that matched the inner dia. of recess equivalent to shaft dia. ( Slightly less, for press fit ) and conforming to other stress calculations were found to be 6000 No. ( 4 No’s ). Another bearing was used for the base plate circulation was 6205 No.(1. No.) Grease was used for lubrication of these bearings. 4).Arm I : Material selection for fabrication. This material was selected due to its properties like: • Machinabitlity

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Designing

• Weldability • Availability • Low cost • Strength etc. It was constructed by using two plates parallel to each other. Shaft 1 is mounted using press fit bushes .It is a machine shaft. The following stresses could arise, as shaft is subjected to bending moment. It contains a provision for jaw which has not been implemented but a weight of 500 gms. for jaw of 500 gms. of workpiece are supposed. The shaft supports weight of 1 kg of weights on shaft 1 and is subject to twisting moment at points of press fit of bushes & sprocket. Thus total load on shaft 2 = load on Aim 1+ due to chain drive.

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Designing

5). The chain drive is designed to transmit rotary motion from shaft 3 to shaft 2. On shaft 3, it is driven by a gear mounted on the same shaft and driven by a motor. The sprockets used have 25 teeth and both are of same size. Since ratio of sprocket teeth is 1:1, therefore the motion will also be transferred in 1:1 ratio. 6). Bush The I.D. of Bush should be such that it is a press fit on the shaft i.e. Internal Diameter = 9.4 mm (assumed) Now the 0.D of the Bush should be a press fit as the metal sheet forming the arm. The available bush in the market was found to have 12.5 mm O.D. which was press fitted in the arm by drilling a hole of 12.4 mm in the arm. Shaft 2 is subjected to both Twisting & Bending moment. Shaft 2 is required to transmit a torque of 28 kgf. This torque is provided to it by shaft 1 attached to a motor through gears via a chain drive. Engagement of the arms is done as follows : Arm 1 is press fitted via a bush Arm 2 is press fitted through a bearing to provide no nation when shaft 2 rotates.

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Designing

Length of Arm 2 = 14 cm center to center to transfer torque in ratio 1:1. When chain is driven, shaft 2 rotates and hence arm 1 moves. This shaft transmits torque of 28 kgf via a gear train of ratio 1:4 7). Gear : The gears used were having the following no. of teeth :No of teeth on larger gear = 64. No of teeth on smaller gear = 16. Two such sets were used on arm 3 and, the stepper motor 1 & 2 are engaged with the smaller gear. 8). Specifications of the motors used :  Type

: STM 602

Current

: 0.8 A AC

Input voltage

: 12 V

Torque

: 4 Kg cm

 Type

Current

: STM 902 : 3 A AC

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Designing

Input voltage

: 10 V

Torque

: 14 Kg cm

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College of Engg. & Tech., Akola.

Application of Robots

APPLICATION OF ROBOTS. Sophisticated technology, for a majority of manufacturing activities in fabrication, forming, machining, assembly facilities will be significant contribution to productively improvement with substantial gain in the quality of product in the face of tough challenge and competition. An organized approach is necessary to decide the right technology orientation, for productivity the end product with high level of disability reliability at the lowest possible price. It is expected that the flexible automation and robotics technology in particular, will play an important role in the revolutionizing process. First commercial application of Robots took place in the late fifties and early sixties for pick & place orientation in an unpleasant task like die casting. In the early stages Robots application were in areas like welding, painting & casting where many health hazards and monotonous manual labour existed . Currently, improved productivity, better quality, reasonably reduced cost and introduction of hazard-free safer environment to relief the workers from discomfort all some of the vital points in favour of using Robots. But the present day

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College of Engg. & Tech., Akola.

Application of Robots

Commercial Robots are stiff mechanical units with an elbow, a whist and usually two fingers without any mobility & no sense of feeling, hearty & seeing. The manipulators may comprise different geometric configuration such as Cartesian, cylindrical, spherical & anthropomorphic. They are controlled by microprocessors with simple internal positional senses. Though the fetch pendant, the gripper or end-of-arm feeling held by the Robot wrist can be manipulated so as to move though space to accomplish useful industrial tasks. Each task or movement can be recorded in the memory as a series of point in space. The programme can be simply re – run whenever the task is to be repeated. The simple Robots can however, perform, a great many repetitive industrial tasks in the area of manufacturing. Capabilities of Robots. In order to make the Robots useful in manufacturing activities, they should possess the skill of transportation and manipulation. The study of batch manufacturing production has revealed that an average part on a shop floor spends 95% of its line in moving is waiting and only about 5% of its production time an actual processing. So introduction of Robots technology will be justified in reducing the queue and more/time which

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College of Engg. & Tech., Akola.

Application of Robots

in turn will reduce work in process & load time. One of the important capabilities of the Robot is its ability to acquire a part or a tool, transport it through a programmed space and then either to release it to the proper location or manipulate to accomplish a certain task. Accordingly there are categories of Robots known as 1. Material transfer 2. Machine loading 3. Welding 4. Splay painting/coating 5. Processing Operations 6. Assembly 7. Inspection General Consideration in Robot Application. There are certain general characteristics of an industrial situation which tend to make the installation of Robot economical and practical. These are as follows. 1. Hazardous or Uncomfortable Working Conditions :-

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College of Engg. & Tech., Akola.

Application of Robots

In the job situations where there are potential dangers or health hazards due to heat, radiation, toxicity or achore the work place is uncomfortable and unpleasant, a Robot should be considered as a suitable for the human worker. 2. Repetitive Tasks :If the work cycle consists of a sequence of elements which do not vary from cycle to cycle, it is possible that a robot could be programmed to perform the task. Pick and place operation and machine loading are obvious example of repetitive basks. 3. Difficulty Handling :If the work-part or tool involved in the operation, it is awaked or heavy, it might be possible for a Robot to perform the task operation involving the handling of heavy work-part are good example of this case. 4. Multi-shift operation :If the initial investment cost of the Robot can be spread over two or three shifts the labour saving will result in a quicker payback.

Plastic injection molding and other processes which must be operated

mountainously are example of multi-shift of Robot applications.

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College of Engg. & Tech., Akola.

Application of Robots

Selecting the right application :Not all Robots installation have been successful.

So there will be the selection if the right

application. These are as follows :1. simple repetitive operation are needed. 2. cycle times are greater than 5 seconds. 3. port can be delivered in proper location and operation. 4. port weight is suitable ( 1100 lb is typically used or the upper part) 5. No inspection is used. 6. one as two persons can be replaced in a 24 hour period. 7. setups and change over are not frequent.

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College of Engg. & Tech., Akola.

Future of Robotics

FUTURE OF ROBOTICS The future of Robotics is extremely blight. The use of vision, tactile and voice communication is expected to increase the future. The Robots of the future expected to be smaller more mobile, multi arm machine with increased speed accuracy and repeatability. More often off line easier and faster means of programming are also expected. Cyborg :A biological type of Robot which has all capabilities of previous type of machines and also has some artificial intelligence or thanking capabilities. Cybert :Most advanced type of ROBOT responding to external stimulae and learning by its own experience. Industrial ROBOT are now beginning to revolutionize industries. These robots do not look or behave like human beings, but they do the work of humans. Inspection and assembly current research efforts focus on creating a smart ROBOT that can ‘see’, ‘heal’, ‘teach’ and make decisions.

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College of Engg. & Tech., Akola.

Future of Robotics

Robots, as other modern manufacturing systems, are advanced automation systems that utilize computers as an integral part of their control. Even more sophisticated are the new Robot that perform various automation of factories. Every operation in this factory of the future, from product design to manufacturing assembly and product inspection would be monitored and controlled by computers and performed by industrial robots and intelligent systems.

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College of Engg. & Tech., Akola.

Conclusion

CONCLUSION The technical details of the design have been speculated to some extent in order to put theory into practical. During the course of fabrication slight modifications were done repeatedly in the design and structure of the S.P.I.R.A. Though we have taken full care in compiling all the gathered information in making design calculations but there is always a first time. We encountered lot of problems and faced many complex situations while the fabrication, like gathering the required parts, fitting the economics of S.P.I.R.A. within reasonable limits etc., working as a team was a wonderful experience. We came to learn the application of the concepts of Production Engineering during this project period. All of us feel that S.P.I.R.A. not only made us feel proud of succeeding in the first trial, but also brought us a lot of invaluable experience.

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College of Engg. & Tech., Akola.

Conclusion

Development of Robotics has been paced up by lightening speed through out the globe, but the indigenous developments have been quite slow as compared to the rest. Inspite of having the various advantages which have been mentioned earlier, a robot can prove to be more than useful to make its presence felt. We would like to invite your valuable suggestions and comments in order to improve upon our first venture as an Engineer. Thanking you

The S.P.I.R.A. team

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College of Engg. & Tech., Akola.

Bibliography

BIBLIOGRAPHY 1. INDUSTRIAL ROBOTICS : BERNARD HODGES 2. A ROBOT COMPONENT AND WORK CELLS : AUSTIN LANGER & JACK HOUSTON 3. CAD/CAM : BY MIKELL GROOVER & ZIMMER 4. INTRODUCTION TO CAD/CAM : PAUL McKINSLEY 5. DESIGN OF MACHINE ELEMENT : R.S. KHURMI & J.K.GUPTA 6. DESIGN DATA HANDBOOK : V.S. SUBHRAMANYAM

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College of Engg. & Tech., Akola.