Essay: Mechanical Design Engineering – lifting devices

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1. INTRODUCTION
In machine tool applications like centre lathes, milling machines , CNC turning lathes , Vertical machining centres , vertical turret lathes, etc. it is often required to lift heavy work-pieces using conventional winches or chain blocks which may require assistance from two or more workers for loading the work-piece on the machine which is rather contradictory to one man-multi machine concept. Hence there is a need of compact lifting device which will be operated by the machine operator himself without any others assistance.
Problem in hand is to develop a compact lifting device to be operated using 12 Volt DC power system, to be button operated with easy loading and unloading facility so that operator can single handed load or unload the work-piece onto the machine.
Material handling equipment: Material handling equipment’s (MHE) are used for the movement and storage of material within a facility or at a site. MHE can be classified into the following five major categories:
Transport Equipment: Equipment used to move material from one location to another (e.g., between workplaces, between a loading dock and a storage area, etc.). The major subcategories of transport equipment are conveyors, cranes, and industrial trucks. Material can also be transported manually using no equipment.
Positioning Equipment: Equipment used to handle material at a single location so that it is in the correct position for subsequent handling, machining, transport, or storage. Unlike transport equipment, positioning equipment is usually used for handling at a single workplace. Material can also be positioned manually using no equipment.
Unit Load Formation Equipment: Equipment used to restrict materials so that they maintain their integrity when handled as a single load during transport and for storage. If materials are self-restraining (e.g., a single part or interlocking parts), then they can be formed into a unit load with no equipment.
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Storage Equipment: Equipment used for holding or buffering materials over a period of time. Some storage equipment may include the transport of materials (e.g., the S/R machines of an AS/RS, or storage carousels). If materials are block stacked directly on the floor, then no storage equipment is required.
Identification and Control Equipment: Equipment used to collect and communicate the information that is used to coordinate the flow of materials within a facility and between a facility and its suppliers and customers. The identification of materials and associated control can be performed manually with no specialized equipment. Lifting equipment, also known as lifting gear, is a general term for any equipment that can be used to lift loads. This includes jacks, block and tackle, hoists, rotating screws, lifting harnesses, fork lifts, hydraulic lifting pads, air lift bags, and cranes. Lifting equipment can be dangerous to use, and is the subject of safety regulations in most countries.
Material handling and storage: Handling and storing materials involves diverse operations such as hoisting tons of steel with a crane, driving a truck loaded with concrete blocks, manually carrying bags and material, and stacking drums, kegs, lumber, or loose bricks.
The efficient handling and storing of materials is vital to industry. These operations provide a continuous flow of raw materials, parts, and assemblies through the workplace, and ensure that materials are available when needed. Improper storage and improper handling of materials can cause costly injuries.
Workers frequently cite the weight and bulkiness of objects being lifted as major contributing factors to their injuries. In 1999, back injuries resulted in 420,000 workplace accidents. The second factor frequently cited by workers as contributing to their injuries was body movement. Bending, followed by twisting and turning, were the more commonly cited movements that caused back injuries. Back injuries accounted for more than 20% of all occupational illnesses, according to data from the National Safety Council. In addition, workers can be injured by falling objects,
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improperly stacked materials, or by various types of equipment. When manually moving materials, however, workers should be aware of potential injuries, including the following:
Strains and sprains from improperly lifting loads, or from carrying loads that are either too large or too heavy fractures or bruises caused by being struck by materials, or by being caught in pinch points. Cuts and bruises caused by falling materials that have been improperly stored, or by incorrectly cutting ties or other securing devices.
Since numerous injuries can result from improperly handling and storing materials, it is important to be aware of accidents that may occur from unsafe or improperly handled equipment and improper work practices, and to recognize the methods for eliminating, or at least minimizing, the occurrence of those accidents. Consequently, employers and employees can and should examine their workplaces to detect any unsafe or unhealthful conditions, practices, or equipment and take the necessary steps to correct them.[2]
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1.1 Problem statement at customer end
The term self-locking as applied to gear systems denotes a drive which gives the input gear the freedom to rotate the output gear in either directions but the output gear locks with input when an outside torque attempts to rotate the output in either direction. This characteristics is often sought after by designers who want to be sure that the loads on the output side of the system cannot affect the position of the gears. Worm gears are one of the few gear systems that can be made self-locking, but at the expense of efficiency, they seldom exceed 45% efficiency, when made self-locking.[7,8]
Fig. 1. Conventional method using Worm Gear box.
Worm gear box
Load drum
load
motor
Disadvantages:
1. Efficiency of self-locking gear box is less than 50%.Hence more than 60% power is lost in friction, hence large horse power is required.
2. Large space required.
3. Large cost of production.
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But if worm gear drives when used for lifting applications with self-locking as the primary objective for safety considerations the drives are extremely in-efficient. Hence there is a need of special purpose drive that will provide better transmission efficiency in self- locking condition so as to reduce power consumed by the device …i.e. lowering the running cost of device.
Problem statement at Sponsor end
Sponsor Details : (Third party development )
M/s Paramount Industries. A-62 , H-block MIDC ROAD, Morwadi Pimpri Pune -18
Proprietor : MR. C K George.
Company produces special purpose machinery, Jigs Fixtures etc for small scale Industry. A certain Vertical Turret lathe requires a compact lifting device with lifting capacity of 100 kg maximum , presently the loading of work-pieces is done using a Chain Winch , which requires two or more labour to handle the system.
Problem in hand is to develop Prototype of a compact lifting device to be operated using 12 Volt DC power , system to be button operated with easy loading and unloading facility so that operator can single handed load or unload the work-piece onto the machine. The proposed model is to be developed to demonstrate the load lifting system , and self-locking ability . The PMDC motor is to be used to demonstrate the load raising and lowering ability of the device by reversing the polarity of the motor by use of 2-pole 2-way motor. Point to point position control of device to be done using a NO-NC push button.
1.2 Objectives
1.2.1 Design of mathematical model of twin worm system with internal threaded ring system for optimal load lifting capacity
1.2.2 Optimal factor of safety and optimal efficiency for reduced power consumption.
1.2.3 Derivation of optimal power for the PMDC motor.
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1.2.4 Selection of PMDC motor for application so as to make device compact.
1.2.5 Development of theoretical model of system of forces, determination of forces and utilizing system of forces to determine the worm and internal threaded ring dimensions of drive.
1.3 Scope
The prototype model must lift the load and lower the load with self-locking. The device should exhibit increase in efficiency with the increase in load for which it has been designed.
1.4 Methodology
1.4.1 To make a detail study of the existing system and its drawbacks.
1.4.2 Studying all the available research related to the self-locking lifting device.
1.4.3 Designing the mathematical model of the worm and the ring gear system.
1.4.4 To determine the linakge dimensions of following parts:
a) Worm Shaft
b) Left hand threaded ring gear
c) Lifter drum
d) Lifter drum shaft
e) Right hand worm
f) Motor mounting bracket system
g) Ring gear cage
1.4.5 Mechanical design of above components using theroretical theories of failure after selection of appropriate materials.
1.4.6 3-D modeling of set-up using Unigraphix Nx-8.0
1.4.7 CAE of critical component and meshing using ANSYS –i.e. the preprocessing part.
1.4.8 Mechanical design validation using ANSYS ‘critical components of the system will be designed and validated.
1.4.9 Validation of strength calculations of critical components using ANSYS.–i.e. the post processing part for all the parts mentioned above.
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1.4.10 Creation of Prototype: The selected mechanism and machine will be designed.
1.4.11 Experimental validation
The experimental validation part of lifting force developed by the twin worm system be validated using test-rig developed . Following characteristics will be plotted.
a) Torque Vs Speed.
b) Power Vs speed.
c) Efficiency of system Vs speed.
1.4.12 Compare the results of analysis and experimental setup.
1.4.13 Conclusion.
1.4.13 Report writing.
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2 LITERATURE REVIEW
Neil Scalter has been discussed which would increase the efficiency, make the system compact and reduce the cost of the system. It focuses on the fact that an old invention can be, Nicholas P. Chironis [1] The book explains in detail the different mechanical elements such as gears, levers, clutches, cam , lead screws, springs, motors, etc. their use in advanced products so that it will perform valuable functions, making it more simple and likely so that they will continue to be included in the new and different products to be developed in the future. Design of different mechanisms carried further modification perhaps by changing the materials and the manufacturing methods as well. Many of the mechanisms illustrated in this book were invented by artisans, instrument makers and Mechanics over the past centuries. They left behind the sketches, formal drawings and even the working models on which many of the illustrations in this book are based. It is worth noting that many of the invention in the field of airplane, steam engine, influential machines from the water pump were invented by self-trained engineers, scientists and technicians. Many of the mechanisms and devices in this book are just mechanical curiosities.But when integrated by creative minds with others they can perform new and different functions.
William Martin,James Walters [2] The book explains the different material handling equipments, its use according to its lifting capacity, purpose of material handling equipment. General safety principles are discussed that can help reduce workplace accidents. These include work practices, ergonomic principles, and training and education. Whether moving materials manually or mechanically, employees should be aware of the potential hazards associated with the task at hand and know how to exercise control over their workplaces to minimize the danger. When manually moving materials, employees should seek help when a load is so bulky that it cannot be properly grasped or lifted. When an employee is placing blocks under raised loads, the employee should ensure that the load is not released until his or her hands are clearly removed from the load. All essentials measures of safety should be taken into
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consideration in companies to avoid accidental hazards.
R.S Khurmi, J. K Gupta [3] The book describes design as the creation of new and better and improving the existing ones. It focuses on the fact that it is time consuming to design a new one. But if the existing design is taken into consideration a new idea is conceived earlier. The classification of machine design, its various steps have been elaborated. Different mechanical components, different types of joints, couplings, shafts, levers, screws, different types of drives are designed considering all types of loads acting on it. The manufacturing processes required for a particular material have been discussed. Different types of stresses and strains are calculated. All types of gears, their tooth profile, their efficiency are calculated. Terminology used in gears, forces acting on it are calculated.
Kalaikathir Achchagam [4] This book focuses on the use of different materials, its properties are explained which makes selection of material easier. The strength of the materials are tabulated, its designation, its composition are elaborated. Fits and tolerances are explained. The selection of materials according to their applications becomes simple through this book. Alloy steel, Carbon steel their chemical composition, mechanical properties, different treatments undergone by it are elaborated.
Padmanabhan. S.,Chandrasekaran.M., Srinivasa Raman.V [5] The paper focuses on the gear optimization . Gears are used in almost all mechanical devices and its main aim is to provide gear reduction. At the same time it has to provide maximum power with minimum weight. Gears are machine elements used to transmit rotary motion between two shafts, normally with a constant ratio. Worm and worm wheel drives are mostly used for nonparallel, non-intersecting, right angle gear drive system with high gear reduction ratios are concerned, still they are also engaged with low to medium speed reducers in many engineering applications. The design optimization of worm gear drive is complicated to resolve since the consideration of multiple objectives and
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more number of design variables. Therefore more consistent and robust design optimization technique is considered. In this paper an attempt has been made to obtain optimal solution of worm gear drive design problem. Within the various design variables available for the worm and worm wheel design, the power, weight, efficiency and center distance have been considered as objective functions and bending stress, compressive stress as vital constraints to get an efficient compact and high power transmitting drive.
Alex Kapelevich and Elias Taye [6] In most gear drives, when driving torque is suddenly reduced as a result of power off, torsional vibration, power outage, or any mechanical failure at the transmission input side, then gears will be rotating either in the same direction driven by the system inertia , or in the opposite direction driven by the resistant output load due to gravity, spring load, etc. The latter condition is known as backdriving. During inertial motion or back driving, the driven output shaft (load) becomes the driving one and the driving input shaft (load) becomes the driven one. There are many gear drive applications where output shaft driving is undesirable. This paper explains the principle of the self-locking process for the parallel axis gears with symmetric and asymmetric teeth profile, and shows their suitability for different applications. The self-locking gears finds many applications in various industries. For example in a control systems where position stability is very important (such as Automotive, aerospace, medical, robotics, agricultural, etc). The self-locking will allow to achieve regard performance. Similar to the worm self-locking gears, the parallel axis self-locking gears are sensitive to operating conditions. The locking reliability is affected by lubrication, vibrations, misalignments, etc. Implementation of these gears should be done with caution and requires comprehensive testing in all possible operating conditions.
R.D. Ankush, P.D.Darade [7] The paper presents the fact that in most material handling equipments , gear drives are used. In these systems when the driving torque is suddenly decreased due to power cut off or any other mechanical failure at the
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input shaft of the system then the gears will be rotating either in the same direction driven by the system inertia or in the opposite direction driven by the resistant output load due to gravity. Self-locking is the ability of gear system which constitute a drive which gives the input gear the freedom to rotate the output gear in either directions but the output gear locks with input when an outside torque attempts to rotate the output in either direction. The load on output side of the system cannot affect
the position of the gears due to self-locking. The paper focuses on the fact that worm gears are one of the few gear systems that can be made self-locking but at the expense of efficiency they seldom exceed 40% efficiency when made self-locking. The worm pair drive discussed in this paper consist of two threaded rods or worm screws. They are meshed together. Each worm is wound in a different direction and has a different lead angle. For proper mesh the worm axes are not parallel but slightly skewed.
Prof. P. B. Kadam, Prof M. R. Todkar [8] Has presented the mating worm self-locking system which is a simple dual worm system that not only provided self-locking with maximum efficiency but also exhibited a new phenomenon called deceleration locking. In this system both the worms are wound in different directions and has a different pitch angle. For proper mesh the worm axes are not parallel but slightly skewed. The design procedure of Twin worm gear self-locking system has been discussed in detail. The right hand worm gear is the input gear of the system having module 2 and helix angle of 2 degrees. The left hand worm with module 2 and helix angle 5 degrees forms the output gear of the system. Both the worms and the load drum are checked for shearing .Finally the efficiency of the drive is calculated which comes out to be 89.30%.
Faydor L. Litvin, Alessandro Nava, Qi Fan, and Alfonso Fuentes [9] New geometry of face worm gear drives with conical and cylindrical worms is proposed. The generation of the face worm-gear is based on application of a tilted head-cutter. A predesigned parabolic function of transmission errors for reduction of noise and vibration is provided. The stress analysis of the gear drive is performed using a three-
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dimensional finite element analysis. The contacting model is automatically generated. The new geometry proposed in this paper is based on application of head-cutters or head grinding tools that have higher precision and larger dimensions in comparison and enable to provide a higher productivity of the process of generation. The gear drives of new geometry may be generated similar to the generation of spiral bevel gears and hypoid gears. The proposed new face worm gear drives are provided with a bearing contact and predesigned parabolic function of transmission errors of low level. Therefore vibrations and noise of gear drives might be reduced.
Feng Li, Shenzhen (CN), jing Ning Ta,Hong Kong (CN)[10] The present invention provides a self-locking worm gear drive which has a simple and efficient structure. In the invention, to achieve self-locking of the gear train, the design of the worm and worm wheel has to be modified from ideal or optimal from an efficiency view point. The gear train consists of a worm fitted to a motor shaft and in mesh with a worm wheel which drives the output. The motor shaft extends between two thrust bearings having faces which contacts respective axial ends of the motor shaft. The contact between at least one of the thrust bearings and the shaft is adapted to provide a high frictional force. Worm gear drives are speed step down gear boxes and as such increase the torque developed by the motor driving the shaft. The lead angle is made low, so that the helical thread of the worm has a greater number of turns per unit length. The surface texture of the worm and worm wheel is made rough to increase friction between the two gears thus making it harder for the worm wheel to drive the worm. This is highly appreciated in certain applications such as for lifting heavy loads or for security issues such as for doors and windows, specially windows in vehicle, where to prevent theft the windows cannot be pulled down to gain access. These can use a smaller lighter motor. These designs can have a separate clutch mechanism to prevent back drive but they are usually complex, prone to failure and add weight and cost to the final assembly.
Yakov Fleytman [11] A worm differential gear mechanism is provided utilizing a
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double enveloping worm/worm gear transmission. The double enveloping transmission has an increased torque capacity in comparison with standard worm differential gear mechanisms. This invention provides a worm differential unit including a differential case adapted to be driven rotationally. Pair of worm gears are supported by a differential case with each worm gear adapted for connection to a corresponding axle shaft. The worm gears are arranged co-axially and are independently rotatable. Furthermore, the present invention also enables heavy duty worm differentials to be made with little or no more increase in comparison with conventional differential worms. There could be two different types of operations. When the worm/worm gear transmission does not incorporate the self-lock feature, the motion could be provided from the drive shaft through enveloping worm and enveloping type worm gear to an output shaft or back from the output shaft to the drive shaft. The same operation is applicable for motion from the drive shaft to the driven shaft or from the driven shaft to drive shaft of the various other embodiments shown. Alternatively, when the worm/worm gear transmission does include the self-lock feature, rotary motion can be provided only from the drive shaft to the enveloping worm and through the enveloping type worm gear to the output shaft.
Jalchin Bons Popper,Kiryat Motzkin,Isrnel [12] The present invention relates in its broader aspects to cooperating wedges, and includes mating worms. The invention in one aspect includes self-locking in one way motion gears in which the function of the driving and the driven gear is not interchangeable. The purpose of this invention is to provide self-locking gears which has higher efficiency. It also provides self-locking without large reduction ratios. The Patent describes a worm drive consisting of two mating worms place almost parallel to each other, and also explains that the pitch angles of the two worms must be chosen according to certain rules inorder to obtain a worm drive which possesses self-locking and at the same time operates with a high efficiency. The invention of the above Patent is described and analysed. A motion transmitting device comprising: an input worm having worm threads on its circumferential surface, an output worm mounted with some axial play and having
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worm threads on its circumferential surface which are constantly in mesh with the worm threads on the input worm and establishing a coefficient of friction between them; the tangent of the pitch angle of the worm threads on the input worm being less than said coefficient of friction; and the pitch angle of the worm threads on the output worm being greater than the pitch angle of the worm threads on the input worm by an amount not exceeding 10 degrees; an antifriction bearing transmitting the axial thrust of the input worm; a second anti-friction bearing transmitting the axial thrust of the output worm; a spring member taking up said axial play of the output worm and exerting an axial force which opposes the axial thrust generated by the output worm when the input worm is being turned against the load; and a thrust surface mounted at a distance from the edge of the output worm sufficient to prevent contact with the output worm when the input worm is being turned against the load, but permitting contact with the output worm when the input worm is being turned with the load.
Wikto w. Panjuchin, Wladimir[13] A self-locking dual worm with parallel axes and linear contact for the worm with involute herringbone gears is characterised by the fact that the cross-section for curvature radii and the longitudinal section for the curvature radii of the worm profile are always determined at the contact. One special feature of such gears is the very large tooth inclination angle which makes it possible to use the production method used for helical toothed gears, spinning machines or worms to cut these gears. The invention is designed to provide a self-locking dual worm gear that is simple to produce and furthermore, to provide a simple tool, designed to produce in a simple and reproducible method.
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3. CONSTRUCTION OF COMPACT LIFTER MECHANISM
Fig 2. Schematic diagram of the Compact lifter
The compact lifter comprises of the following parts :
Load Drum : The load drum is the component on which the rope is wound with the object to lift the load. One end of the rope is fixed to the drum where as the other end is connected to the load.
Base plate
load
pinion
Internal ring gear cage
LH internal threaded ring
Load drum
RH worm
Gear
PMDC motor
Motor housing bracket
Bearing housing
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Bearing housing Bracket : The bearing housing bracket holds the bearing 6020 with 100 mm internal diameter and 150 mm outer diameter and 24 mm width. The bearing housing is mounted on MS channel supports .
Internal threaded Lifter ring : The internal threaded ring is left hand threaded with trapezoidal threads of 10 mm pitch and lead angle of 1.5 degree .
Ring gear cage : This element is the holder bracket for the internal threaded link that mounts it on the output shaft of the load drum.
Gear : The spur gear with 2 module 44 teeth is mounted on the threaded worm shaft to transmit power from the motor pinion to the threaded worm to drive the ring gear.
RH threaded worm : This is the input worm with 1 degree lead angle 10 mm pitch grooves . This enables the threaded ring to drive internal gear but at the same time acts as a self-lock as the internal ring gear cannot drive the input worm.
PMDC geared motor : The PMDC geared motor is with 5 watt power 92 rpm as output and with an integral 9 teeth 2 module pinion on the output shaft of the motor.
Electrical control circuit : The control circuit consists of 2-pole 2-way switch that controls the direction of motor thereby facilitating the raising or lowering of the load where as the push button is used to control the position of load.
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3.1 Working of compact lifter:
The power supply to the motor is 12 V Dc which is routed to the poles either to rotate motor clockwise to raise the load or counter clockwise to lower the load. The 2-pole 2-way switch controls the direction where as the push button controls the position.
The input from the motor is given to the input right hand threaded worm via spur gear pair. The pinion of 2 module 14 teeth mounted on the motor shaft where as the gear with 44 teeth 2-module mounted on the rh worm shaft. The RH worm shaft is held in ball bearings 6004 and 6003 zz respectively. The motion of the RH wom shaft is imparted to the threaded internal ring which there by rotates the load drum via the ring gear cage.
The load drum thus will either raise or lower the load depending upon its direction of rotation.
3.2 Selection of coefficient of friction
Self-locking characteristic of the system is given by the relation
Tan �� = �� / s
Where ;
��: Pitch angle of the driver screw ( normally less that 20)
s : Factor safety selected by designer as per application ranging between 1 to 2.
�� : Coefficient of friction between the two materials of worms in out case steel to steel. [3]
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Table 1. Coefficient of friction for a range of material combinations [3]
combination
Static
Dry (��)
lubricated
steel-steel
0.05…00.6
0.015
Considering factor of safety (s) = 1.8
tan �� = �� / s
�� = tan-1( 0.05 / 1.8) =1.5 degree
Thus adopting fllowing specifications of thread angle for screw :
Lead angle on ouput threaded ring = 1. Degree
Module =pitch = 10 mm
Lead angle on input worm = 1 degree
Module = 10 mm
3.3 Selection of the motor
Effort to be applied to lift load of 100kg = Wtan(�� +��)
9.81x 100 x tan (1.5+0.05 ) = 26.5 N
Torque required by motor = Force x radius of pinion
= 26.5 x(18/2)
Torque required by motor = N-mm = 2.43 kg-cm
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Thus selecting motor as follows:
3.4 Construction of motor
Fig 3. Motor construction
1. Motor
2. Connector
3. Gear
4. Hall effect switch no. 1
5. Hall effect switch no. 2
6. Shaft
7. Magnet
Specifications of motor selected for study
12V PMDC Motor
Key Specifications/Special Features:
‘ Six mounting-hole positions
‘ Various output-shaft shapes are available
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‘ Motor with Japanese technology
‘ Working voltage: 12V DC
‘ No-load speed: 92rpm
‘ No-load current: 1.30A
‘ Stall torque: 2-N-m
‘ Power = 5 watt
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3.5 Design of spur pinion and gear for drive from motor to the main shaft
Stage 1: Drive as GEAR and pinion arrangement
Maximum load =Maximum torque / Radius of gear
Maximum torque = 2 N-m
No of teeth on pinion= 9
No of teeth on gear = 44
Module = 2 mm
Radius of gear by geometry = ( 44 x 2 ) /2 = 44 mm
Maximum load = Torque /radius of gear =2 x 103 /44 = 45.45 N
b = 10 m
Material of spur gear and pinion = EN24
Sult pinion = Sult gear = 800 N/mm2
Service factor (Cs) = 1.5
‘Pt =( W x Cs) =68.2N.
Peff = 68.2 N (as Cv =1 due to low speed of operation)
Peff = 68.2N ——–(A)
Lewis Strength equation
WT = Sbym
Where ;
y = 0.484 ‘ 2.86
Z
‘ y = 0.484 – 2.86 = 0.166
9
‘ Syp = 132.8
As Syp < Sys ‘ as pinion is weaker than the gear in mesh with it Page 22 WT = (Syp ) x b x m =132.8x 10m x m WT= 1328m2———-(B) By equation (A) & (B) 1328 m2 = 68.2 ‘m=0.71 mm selecting standard module = 2 mm —-for ease of construction as we go for single stage gear box’making size compact ‘achieving maximum strength and proper mesh. Hence gear pair dimensions are as follows, Pinion : 9 teeth . 2 module . 3.6 Design of worm shaft Fig 4. Geometry of worm shaft Page 23 Table 2. Material selection for worm shaft[4] DESIGNATION ULTIMATE TENSILE STRENGTH N/mm2 YEILD STRENGTH N/mm2 EN 24 800 680 ‘ fs max = uts/fos = 800/2 = 400 N/mm This is the allowable valve of shear stress that can be induced in the shaft material for safe operation. Assuming 100 % efficiency of transmission ‘ T design = 0.4 X GEAR RATIO = 0.4 X (44/9) =1.95 N-m CHECK FOR TORSIONAL SHEAR FAILURE OF SHAFT. Torque is applied at the driven gear mounting point on the shaft which 16mm in diameter Td = ‘/16 x fs act x d3 ‘ fs act = 16 x Td ‘ x d 3 = 16 x 1.95X10 3 ‘ x 16 3 ‘ fs act = 2.42 N/mm2 As fs act < fall ‘ WORM SHAFT is safe under torsional load. Page 24 Analysis of worm shaft Fig 4.1 Meshing of worm shaft Fig 4.2. Boundary conditions of worm shaft Page 25 Fig 4.3. Loading on worm shaft Fig 4.4. Equivalent stresses in worm shaft Page 26 Fig 4.5. Total deformation of worm shaft Table 3. Result and discussion of worm shaft Part Name Maximum theoretical stress N/mm2 Von-mises stress N/mm2 Maximum deformation mm Result RH WORM SHAFT 2.42 6.266 0.00156 safe 1. Maximum stress by theoretical method and Von-mises stress are well below the allowable limit, hence the RH worm shaft is safe. 2. Worm shaft shows negligible deformation under the action of system of forces Page 27 3.7 Design of RH worm Fig 5. Geometry of right hand worm Table 4. Material selection for RH worm[3] DESIGNATION ULTIMATE TENSILE STRENGTH N/mm2 YEILD STRENGTH N/mm2 20MnCr1 1000 880 ‘ fs max = uts/fos = 1000/2 = 500 N/mm2 This is the allowable valve of shear stress that can be induced in the shaft material for safe operation. Assuming 100 % efficiency of transmission Page 28 ‘ T design = 0.4 X GEAR RATIO = 0.4 X (44/9) =1.95 N-m CHECK FOR TORSIONAL SHEAR FAILURE OF SHAFT. Torque is applied at the RH worm minimum section being the root area that is 11mm in diameter Td = ‘/16 x fs act x d3 ‘ fs act = 16 x Td ‘ x d 3 = 16 x 1.95X10 3 ‘ x 113 ‘ fs act = 7.46 N/mm2 As fs act < fs all ‘ RH WORM is safe under torsional load. Page 29 Analysis of RH worm Fig 5.1 Meshing of RH worm Fig 5.2 Boundary conditions of RH worm Page 30 Fig 5.3 Loading on RH worm Fig 5.4 Equivalent sressses in RH worm Page 31 Fig 5.5 Total deformation of RH worm Table 5 Result and discussion of RH worm Part Name Maximum theoretical stress N/mm2 Von-mises stress N/mm2 Maximum deformation mm Result RH WORM 7.46 14.738 0.002 safe 1. Maximum stress by theoretical method and Von-mises stress are well below the allowable limit, hence the RH worm is safe. 2. RH Worm shows negligible deformation under the action of system of forces Page 32 3.8 Design of Load drum Fig 6 Geometry of load drum Table 6. Material selection for load drum[3] Designation Ultimate Tensile strength N/mm2 Yield strength N/mm2 EN 9 600 480 ‘ fs max = uts/fos = 600/2 = 300 N/mm2 This is the allowable valve of shear stress that can be induced in the load drum material for safe operation. Check for torsional shear failure:- Tdesign= ‘ x fs act x Do 4 ‘ Di 4 16 Do 1.95 x 103 = ‘ x fs act x 994 ‘ 86 4 16 99 Page 33 ‘ fs act = 0.023 N/mm2 As; fs act < fs all ‘ Drum is safe under torsional load Fig 6.1 Meshing of Load drum Fig 6.2 Boundary conditions of load drum Page 34 Fig 6.3 Loading on load drum Fig 6.4 Equivalent stresses in load drum Page 35 Fig 6.5 Total deformation of load drum Table 7 Result and discussion of load drum Part Name Maximum theoretical stress N/mm2 Von-mises stress N/mm2 Maximum deformation mm Result LOAD DRUM 0.023 1.9726 0.00038 safe 1. Maximum stress by theoretical method and Von-mises stress are well below the allowable limit, hence the load drum is safe 2. Load drum shows negligible deformation under the action of system of forces Page 36 3.9 Design of internal threaded left hand ring gear Fig 7. Geometry of Internal threaded LH worm gear Table 8. Material selection for internal threaded LH ring gear[3] DESIGNATION ULTIMATE TENSILE STRENGTH N/mm2 YEILD STRENGTH N/mm2 20 MnCr1 1000 800 ‘ fs max = uts/fos = 1000/2 = 300 N/mm2 This is the allowable valve of shear stress that can be induced in the load drum material for safe operation. ‘ T design = 1.95 N-m Page 37 CHECK FOR TORSIONAL SHEAR FAILURE Td = ‘/16 x fs act x( D4- d4) /D ‘ fs act = 16 x Td ‘ x ( D4- d4) /D = 16 x1.95 x 10 3 x 148 ‘ x ( 1484- 1204) ‘ fs act = 0.00539 N/mm2 As fs act < fs all ‘ Internal threaded ring is safe under torsional load. Analysis of internal threaded LH ring gear Fig 7.1 Meshing of Internal threaded LH ring gear Page 38 Fig 7.2 Boundary conditions of Internal threaded LH ring gear LOADING Fig 7.3 Loading on Internal threaded LH ring gear Page 39 Fig 7.4 Equivalent stresses in Internal threaded LH ring gear Fig 7.5 Total deformation in Internal threaded LH ring gear Page 40 Table 9. Result and discussion of Internal threaded LH ring gear Part Name Maximum theoretical stress N/mm2 Von-mises stress N/mm2 Deformation mm Result LOAD DRUM 0.00539 0.04856 2.83 x10-6 safe 1. Maximum stress by theoretical method and Von-mises stress are well below the allowable limit, hence the internal thread ring is safe 2. Internal threaded ring shows negligible deformation. 3.10 Design of Ring gear cage Fig 8 Geometry of Ring gear cage Page 41 Table 10 Material selection for Ring gear cage[3] DESIGNATION ULTIMATE TENSILE STRENGTH N/mm2 YEILD STRENGTH N/mm2 En9 600 400 ‘ fs max = uts/fos = 600/2 = 300 N/mm2 This is the allowable valve of shear stress that can be induced in the load drum material for safe operation. ‘ T design = 1.95 N-m CHECK FOR TORSIONAL SHEAR FAILURE . Td = ‘/16 x fs act x( D4- d4) /D ‘ fs act = 16 x Td ‘ x ( D4- d4) /D = 16 x1.95 x 10 3 x 38 ‘ x ( 384- 204) ‘ fs act = 0.196 N/mm2 As fs act < fs all ‘ Ring cage is safe under torsional load. Page 42 Analysis of Ring gear cage Fig 8.1 Meshing of Ring gear cage Fig 8.2 Boundary conditions of Ring gear cage Page 43 Fig 8.3 Loading of Ring gear cage Fig 8.4 Equivalent stresses in Ring gear cage Page 44 Fig 8.5 Total deformation of Ring gear cage Table 11 Result and discussion of Ring gear cage Part Name Maximum theoretical stress N/mm2 Von-mises stress N/mm2 Deformation Result Ring cage 0.196 0.708 1.2×10-4 safe 1. Maximum stress by theoretical method and Von-mises stress are well below the allowable limit, hence the ring gearcage is safe 2. Ring gear cage shows negligible deformation. Page 45 3.11 Design of system bracket Fig 9. Geometry of system bracket Table 12 Material selection for system bracket[3] Designation Tensile Strength N/mm2 Yield Strength N/mm2 EN9 600 480 Direct Tensile or Compressive stress due to an axial load :- fc act = W A 2 Page 46 fc act = ‘ fc act = 2.45 N/mm2 As fc act < fc all ; System bracket is safe in compression. Analysis of system bracket Fig 9.1. Meshing of System bracket 100 x 9.81 (166-150) x25 Page 47 Fig 9.2 Boundary conditions of System bracket Fig 9.3 Loading on System bracket Page 48 Fig 9.4 Equivalent stresses in System bracket Fig 9.5 Total deformation of System bracket Page 49 Table13 Result and discussion of System bracket Part Name Maximum theoretical stress N/mm2 Von-mises stress N/mm2 Deformation mm Result System bracket 2.45 0.8537 0.0000425 safe ‘ Maximum stress by theoretical method and Von-mises stress are well below the allowable limit, hence the system bracket is safe ‘ System bracket shows negligible deformation. Page 50 4.EXPERIMENTAL VALIDATION OF THE LIFTER TEST & TRIAL of compact lifter internal worm type Aim: – To conduct trial a) Torque Vs Speed characteristics b) Power Vs Speed characteristics c) Efficiency Vs Speed characteristics In order to conduct trial , load drum, cord, weight pan are provided on the output shaft. Inptu data:- A) Drive Mo
tor 12 V dc 92 rpm OUTPUT Power = 5 watt B) Diameter (Effective ) of load drum = 100 mm. Procedure :- 1) Start motor 2) Let mechanism run & stabilize at certain speed (say 18 rpm) 3) Place the pulley cord on load drum and add 1 Kg weight into , the pan , note down the output speed for this load by means of tachometer. 4) Add another 1 Kg cut & take reading . 5) Tabulate the readings in the observation table 6) Plot the specified graphs Page 51 Table 14. Observation table SR NO LOADING UNLODING MEAN SPEED rpm WEIGHT (Kg) SPEED rpm WEIGHT (Kg) SPEED rpm 1. 1 18 1 18.2 18.1 2. 2 17.6 2 17.6 17.6 3. 3 17.2 3 17.4 17.3 4. 4 16.4 4 16.6 16.5 5. 5 15.6 5 15.4 15.3 6. 6 14.6 6 14.2 14.4 Sample calculations at 6 Kg load 1) Average Speed :- N= N1 + N2 = 14.6+14.4 2 2 N= 14.5 rpm 2) Output Torque:- To/p = Weight in pan x Radius of load drum Page 52 To/p= (6x 9.81) x 50 To/p=2943 N-mm To/p =2.943N-m 3) Input Power:- (Pi/p) = 5 WATT 4) OutPut Power:-(Po/p) Po/p = 2 ‘ NTo/p 60 = 2 x ‘ x 2.943 x 14.4 60 Po/p = 4.4watt 5) Efficiency:- �� = Out put power Input power Page 53 �� = 4.4 5 ‘ = 88 % ‘ Efficiency of transmission of gear drive at 6 kg load= 88% Table 15. Experimental validation result SR NO LOAD (Kg) SPEED (rpm) TORQUE (N-m) POWER (watt) Efficiency % 1. 1 18.1 0.4905 0.929828 18.59656 2. 2 17.6 0.981 1.808284 36.16568 3. 3 17.3 1.4715 2.666191 53.32382 4. 4 16.5 1.962 3.390532 67.81064 5. 5 15.3 2.4525 3.929935 78.5987 6. 6 14.4 2.943 4.438515 88.7703 Page 54 Fig 10. Graph of Torque Vs Speed The graph shows that there is increase in torque with increase in load and marginal drop in load speed. Fig 10.1. Graph of Power Vs Speed 0 0.5 1 1.5 2 2.5 3 3.5 18.1 17.6 17.3 16.5 15.3 14.4 SPEED (RPM) TORQUE (N-m) TORQUE (N-m) Page 55 The graph shows increase in power output with increase in load with marginal drop in load speed. Fig 10.2 Graph of Efficiency Vs Speed The graph shows increase in Transmission efficiency with increase in load with marginal drop in load speed. Page 56 Table 16. Bill of materials SR NO. PART CODE DESCRIPTION QTY MATERIAL 1. TWS-1 IP_RH_WORM 01 20MnCr1 2. TWS -2 OP_LH_WORM RING 01 20MnCr1 3. TWS -3 SYSTEM_ BRG_HOUSING 01 EN9 4. TWS -4 RH_WORM SHAFT BRG_HOUSING 01 EN9 5. TWS -5 BASE PLATE 01 EN9 6. TWS -6 LOAD DRUM 01 EN24 7. TWS -7 BRG 6020 ZZ 04 STD 8. TWS -8 RH WORM SHAFT 01 EN9 9. TWS -9 GEARED MOTOR 01 STD 10. TWS ’10 ROPE 01 STD 11. TWS ’11 MOTOR BRACKET 01 STD 12. TWS ’12 SUPPORT CHANNEL 02 MS 13. TWS-13 BRG 6004 ZZ 01 STD 14. TWS-14 BRG 6003 ZZ 01 STD Page 57 Raw material cost The total raw material cost as per the individual materials and their corresponding rates are as follows, Total raw material cost = Rs 12800 /- Total machining cost = Rs 7183 /- Table 17. Miscellaneous costs OPERATION COST(Rs) FABRICATION 1600 ASSEMBLY 1800 Bench Work 300 Total 3700 Table 18. Cost of purchased parts SR NO. DESCRIPTION QTY COST 1. MOTOR 01 3450 2. GEAR 01 610 3. BEARINGS 03 3600 4. CIRCLIPS 04 200 COST OF PURCHASED PARTS = 7860/- Page 58 TOTAL COST TOTAL COST = Raw Material Cost +Machine Cost + Miscellaneous Cost + cost of Purchased Parts +Overheads = Rs 32543/- Hence the total cost of machine = Rs 32500/- Page 59 5. CONCLUSION AND SCOPE FOR FUTURE WORK 5.1 Conclusion 5.1.1 The device exhibits load lifting ability in vertical upward direction with instantaneous self-locking. 5.1.2 The device exhibits load lowering ability in vertical downward direction with instantaneous self-locking. 5.1.3 There is marginal deceleration of the load drum with increase in load. 5.1.4 Device exhibits increase in power output with increase in load with marginal drop in load speed maximum power output being 4.4 watt. 5.1.5 Device exhibits increase in transmission efficiency with increase in load with marginal drop in load speed maximum efficiency being 88%. 5.1.6 Maximum power consumption of the input motor at 6 kg load is 5 watt. 5.2 Advantages 5.2.1 Compact lifter system offers high transmission efficiency close to 90 % efficiency 5.2.2 Lower power consumption 5.2.3 Compact in size 5.2.4 Low weight 5.2.5 Low production cost 5.2.6 Deceleration locking possible. Page 60 5.3 Applications 5.3.1 The mechanism can be effectively used in Hoists and lifts. 5.3.2 Cranes. 5.3.3 Propulsion lifts. 5.3.4 Power winches. 5.3.5 The mechanism can also be used in operating the doors and windows of a vehicle where self- locking is a must. 5.4 Further modifications 5.4.1 Present model is a prototype model hence the R H worm shaft is mounted on a separate bracket , instead it can be made integral with the system bracket for proper support and better performance. 5.4.2 The entire casing can be made closed to provide better lubrication and improve life of worm system. 5.4.3 Forged ring gear cage will give best result and better compactness as compared to the present fabricated one. Page 61 REFERENCES 1. Neil Scalter, Nicholas P. Ghironis., Mechanisms and Mechanical Devices Sourcebooks, 3rd edition, United states of America,2001. 2. William Martin,James Walters., ‘Safety and Health essentials’, British library of congress by cataloging-in-publication, 2001. 3. R.S Khurmi, J.K Gupta.,’ Machine Design’, 14th edition, New Delhi, 2005. 4. Kalaikathir Achchagam., ‘PSG Design Data book’, Coimbatore, India,2014. 5. Padmanabhan. S.,Chandrasekaran.M., Srinivasa Raman.V., ‘Design Optimization Of worm gear drive’, International Journal Of Mining, Metallurgy and Mechanical Engineering, Volume1 issue1 (2013). 6. Alex Kapelevich and Elias Taye,’Application for self-locking gears’,May 2012 7. R.D. Ankush, P.D.Darade.,’Design and Analysis of worm pair used in self-locking system with Development of manual clutch’., International Journal Of Research in Engineering and Technology,ISSN 2319-1163. 8. Prof. P. B. Kadam, Prof M. R. Todkar.,’ Improvement in the Design And Manufacturing Of Twin Worm Self-locking techniques and Applications’., IOSR Journal of Engineering ,Vol.2 (5), May2012. 9. Faydor L. Litvin, Alessandro Nava, Qi Fan, and Alfonso Fuentes,’ New Geometry of Worm Face Gear Drives With Conical and Cylindrical Worms: Generation,Simulation of Meshing, and Stress Analysis’, University of Illinois at Chicago, NASA/CR’2002-211895. 10. Feng Li , Shenzhen (CN), Jing Ning Ta, Hong Kong (CN),’United States Patent’,Patent No.US8,051,737B2,Date Nov,8,2011. 11. Yakov Fleytman, Orion.,MI US ‘United States Patent’, Patent No.US6,582,338 B1, Date June, 24,2003. 12. Jalchin Bons Popper,Kiryat Motzkin,Isrnel,’United States Patent Office’,Patented Sept.26,1967 Page 62 13. Wikto w. Panjuchin, Wladimir,’United States Patent’,Patent no.5,522,278,Patent date Jun 4,1996. Page 63 ANNEXURE Sr no. Drawing no. Title 1 Drawing no. 1 worm shaft 2 Drawing no. 2 Right hand worm 3 Drawing no.3 Load drum 4 Drawing no. 4 Internal threaded left hand ring gear 5 Drawing no. 5 Ring gear cage 6 Drawing no. 6 System bracket Drawing no.1 Worm shaft Page 64 Drawing no. 2 Right hand worm Drawing no. 3 Load drum Page 65 Drawing no. 4 Internal threaded left hand ring gear Page 66 Drwing no. 5 Ring gear cage Page 67 Drawing no. 6 System bracket..