User:Samvijay

DUAL OPERATED SCISSOR LIFTER 1. INTRODUCTION Lift tables can come in a vast array of configurations and can be built to suit various highly specialized industrial processes. The most common lift table design incorporates hydraulic cylinders and an electrical motor to actuate the scissor lifting mechanism. Lift tables can also be driven by pneumatic sources or by hydraulic foot pump when the load is not heavy. Lift tables can be mounted in a pit for floor-level loading can include rotating tops, tilting mechanisms, and other various features to ensure operator safety and ease of use. Dual scissor Lifts are used for indoor and warehouse applications because they are relatively quiet. There’s also the added benefit of not having to worry about emissions, as one would with fuel-powered lifts. The maneuverability of electric Scissor Lifts provides a distinct advantage in tight and compact work spaces because it’s perfectly suited for making tight turns. There is also the convenient option of powering the scissor lift from an electrical outlet, should the charge in the battery run out. There are many benefits associated with using a scissor lift in warehouse and indoor environments.

2. DESCRIPTION OF PARTS: Upper table Lower table Scissor leg Cotter pin Height support Lead screw Wheel Sensor unit Motor Relay Bearing Bush 2.1 UPPER TABLE: Upper table is placed on top of the scissor leg. It is made up of mild steel. It bottom side of the frame is used to sliding for scissor legs with bearings. It is used to support the materials while lifting. Top of the frame consist of ribs for loading materials.

Fig.1 Upper table 2.2 LOWER TABLE: Lower table is act as a base of the lift. It is made up of mild steel. It’s having provisions for lead screw attachment. Its top of the frame is used to slide the scissor lift with the help of bearing.

Fig.2 Lower table 2.3 SCISSOR LEG: Scissor leg is looks like an x type frame. It is made of steel. Its lower leg is connected to the lead screw. Upper leg is connected to the upper table sliding guide ways.

Fig.3 Scissor leg 2.4 COTTER PIN: Cotter pin used to connect the scissor leg and it has bearing for sliding of the scissor leg. It also acts as a support of the upper table. It is also made up of mild steel.

Fig.4 Cotter pin 2.5 HEIGHT SUPPORT: Height support is attached to the bottom side of the lower table. It is made up of mild steel angle. The roller wheel is connected at the lower side of the height support.

Fig.5 Height support

2.6. LEAD SCREW: A lead screws also known as a power screw or translation screw. It is used to translate Rotary motion of the motor into linear motion of the scissor leg. One end of the lead screw is connected to the hand wheel by the use of bearing for manual operation and another end is coupled with motor.

Fig. 6 Lead screw 2.7 WHEEL: Wheel is connected to the bottom of the height support. It is a roller type wheel. The main purpose of wheel is to rotate and also move the lift from one place to another place.

Fig.7 Wheel 2.8 SENSOR UNIT: Light sensor as its name suggests, is a mechanical or electronic apparatus that detects light. It has transmitter and receiver, the transmitter is attached to the upper table of the scissor lift and the receiver is attached to the machine table (fixed). The transmitter emits light, the receiver is attached on the machine table where the materials to be lifted. Whenever the receiver detects the light source it trips the power supply by the use of relay.

2.9 MOTOR:

          Motor is connected to the one end of the lead screw to serve electrical operated lift function. The motor and lead screw is coupled by using of coupling. Three phase induction motor is used to deliver high initial torque for high load lifting capacity.

2.10 RELAY: A relay is an electrically operated switch. When the three phase supply is given to the circuit, the relay is in normally open condition and when the receiver receives the light rays and the relay switches off the motor.

2.11 BEARING A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bush is used for easy sliding of scissor legs on the frame. The right side scissor legs are attached with bearing. This bearing and leg is arrested by using of cotter pin.

Fig.8 Bearing 2.12 BUSH Bush is welded at the lower frame. Lead screw is freely rotates in the bush it function is almost same as bearing.

3. WORKING OPERATION: When the three phase supply is given to the input terminal, the supply will flow to the sensor unit and contactor. The motor is connected to the output terminal block and the motor is attached on the lower frame by plate welded on the lower table. The lead screw is attached on the lower table, one end of the lead screw is connected to the motor and another end is connected with lead screw. When the motor rotate clockwise direction, the lead screw also rotate in same direction and the lift moves upward. The lift attains a prescribed level, the receiver receives the light rays and it trips the power supply and switches off the motor. After the loading and unloading of materials should be done the power supply will again on and the supply reversed so the lead screw rotates in counter clockwise direction the lift moves downward. If there is absence of electric supply, the lift will operated by hand wheel.

4. ELECTRIC MOTOR An electric motor converts electrical energy into mechanical energy. Most electric motors operate through interacting magnetic fields and current-carrying conductors to generate force, although a few use electrostatic forces. The reverse process, producing electrical energy from mechanical energy, is done by generators such as an alternator or a dynamo. Many types of electric motors can be run as generators, and vice versa. For example a starter/generator for a gas turbine, or traction motors used on vehicles, often perform both tasks. Electric motors and generators are commonly referred to as electric machines.

Fig.9 Electric motor Electric motors are found in applications as diverse as industrial fans, blowers and pumps, machine tools, household appliances, power tools, and disk drives. They may be powered by direct current (e.g., a battery powered portable device or motor vehicle), or by alternating current from a central electrical distribution grid. The smallest motors may be found in electric wristwatches. Medium-size motors of highly standardized dimensions and characteristics provide convenient mechanical power for industrial uses. The very largest electric motors are used for propulsion of ships, pipeline compressors, and water pumps with ratings in the millions of watts. Electric motors may be classified by the source of electric power, by their internal construction, by their application, or by the type of motion they give. The physical principle of production of mechanical force by the interactions of an electric current and a magnetic field was known as early as 1821. Electric motors of increasing efficiency were constructed throughout the 19th century, but commercial exploitation of electric motors on a large scale required efficient electrical generators and electrical distribution networks. Some devices, such as magnetic solenoids and loudspeakers, although they generate some mechanical power, are not generally referred to as electric motors, and are usually termed actuators and transducers respectively.

4.1 THREE PHASE ELECTRIC MOTORS Three phase electricity powers large industrial loads more efficiently than single-phase electricity. When single-phase electricity is needed, it is available between any two phases of a three-phase system, or in some systems, between one of the phases and ground. By the use of three conductors a 3 phase system can provide 173% more power than the two conductors of a single-phase system. Three-phase power allows heavy duty industrial equipment to operate more smoothly and efficiently. 3 phase power can be transmitted over long distances with smaller conductor size. Most electric power is distributed in the form of 3-phase AC. Therefore, before proceeding any further you should understand what is meant by 3 phase power. Basically, the power company generators produce electricity by rotating (3) coils or windings through a magnetic field within the generator. These coils or windings are spaced 120 degrees apart. As they rotate through the magnetic field they generate power which is then sent out on three (3) lines as in three-phase power. 3 phase transformers must have (3) coils or windings connected in the proper sequence in order to match the incoming power and therefore transform the power company voltage to the level of voltage we need and maintain the proper phasing or polarity. The most common type of 3 phase electrical load is the 3 phase electric motor. A 3 phase motor is more compact and less costly than a 1-phase motor of the same voltage class and rating; also 1-phase AC motors above 10 HP (7.5 kw) are not as efficient and thus not usually manufactured. A 3 phase induction motor has a simple design, inherently high starting torque, and high efficiency. Such motors are applied in industry for 3 phase pumps, fans, blowers, compressors, conveyor drives, and many other types of 3 phase motor-driven equipment. There are a lot of benefits to using a 3 phase electric motor over a single phase electric motor. Large air conditioning equipment (for example, most air conditioning units above 2.5 tons (8.8 kw) cooling capacity) use 3 phase motors for reasons of economy and efficiency.

4.2 INDUCTION MOTOR An induction motor or asynchronous motor is a type of alternating current motor where power is supplied to the rotor by means of electromagnetic induction. An electric motor turns because of magnetic force exerted between a stationary electromagnet called the stator and a rotating electromagnet called the rotor. Different types of electric motors are distinguished by how electric current is supplied to the moving rotor. In a DC motor and a slip-ring AC motor, current is provided to the rotor directly through sliding electrical contacts called commutators and slip rings. In an induction motor, by contrast, the current is induced in the rotor without contacts by the magnetic field of the stator, through electromagnetic induction.

Fig.10 Induction motor An induction motor is sometimes called a rotating transformer because the stator (stationary part) is essentially the primary side of the transformer and the rotor (rotating part) is the secondary side. Unlike the normal transformer which changes the current by using time varying flux, induction motors use rotating magnetic fields to transform the voltage. The current in the primary side creates an electromagnetic field which interacts with the electromagnetic field of the secondary side to produce a resultant torque, thereby transforming the electrical energy into mechanical energy. Induction motors are widely used, especially poly phase induction motors, which are frequently used in industrial drives. Induction motors are now the preferred choice for industrial motors due to their rugged construction, absence of brushes (which are required in most DC motors) and—thanks to modern power electronics—the ability to control the speed of the motor. 4.3 CONSTRUCTION OF INDUCTION MOTOR The stator consists of wound 'poles' that carry the supply current to induce a magnetic field that penetrates the rotor. In a very simple motor, there would be a single projecting piece of the stator (a salient pole) for each pole, with windings around it; in fact, to optimize the distribution of the magnetic field, the windings are distributed in many slots located around the stator, but the magnetic field still has the same number of north-south alternations. The number of 'poles' can vary between motor types but the poles are always in pairs (i.e. 2, 4, 6, etc.).

Fig.11 Construction of Induction motor Induction motors are most commonly built to run on single-phase or three-phase power, but two-phase motors also exist. In theory, two-phase and more than three phase induction motors are possible; many single-phase motors having two windings and requiring a capacitor can actually be viewed as two-phase motors, since the capacitor generates a second power phase 90 degrees from the single-phase supply and feeds it to a separate motor winding. Single-phase power is more widely available in residential buildings, but cannot produce a rotating field in the motor (the field merely oscillates back and forth), so single-phase induction motors must incorporate some kind of starting mechanism to produce a rotating field. They would, using the simplified analogy of salient poles, have one salient pole per pole number; a four-pole motor would have four salient poles. Three-phase motors have three salient poles per pole number, so a four-pole motor would have twelve salient poles. This allows the motor to produce a rotating field, allowing the motor to start with no extra equipment and run more efficiently than a similar single-phase motor.

4.4 PRINCIPLE OF OPERATION

When the stator or primary winding of 3-phase induction motor is connected to a 3-phase ac supply, a rotating magnetic field is established which rotates at synchronous speed. The direction of revolution of this field will depend upon the phase sequence of the primary currents and, therefore, will depend upon the order of connection of the primary terminals to the supply. The direction of rotation of the field can be reversed by interchanging the connection to the supply of any two leads of a 3-phase induction motor.

Fig.12 Rotating Magnetic Field in an Induction motor The number of magnetic poles of the revolving field will be the same as the number of poles for which each phase of the primary or stator winding is wound. The speed at which the field produced by the primary currents will revolve is called the synchronous speed of the motor and is given by an expression, Ns = 120f/P Where,

	f is supply frequency and P is the number poles on stator.

The revolving magnetic field produced by the primary currents sweeps across the rotor conductors and thereby induces an emf in these conductors. Since the rotor winding is either directly shorted or closed through some external resistance, the emf induced in the secondary by the revolving field causes a current to flow in the rotor conductors whose direction is such as to oppose the cause which is producing it. Because the cause producing the induced currents is the relative speed between the rotating magnetic field and the stationary rotor conductors, therefore, they circulate in such a way that a torque is produced in the rotor tending to cause it to follow the rotating magnetic field and thus reducing the relative speed. An induction motor cannot run at synchronous speed. If it were possible, by some means, for the rotor to attain synchronous speed, the rotor would then be standstill with the respect to the rotating flux. Then no emf would be induced in the rotor, no rotor current would flow, and therefore, there would be no torque developed. An introduction motor running on no-load will have a speed very close to synchronous speed and, therefore, emf induced in the rotor winding will be very small. As the mechanical load is applied to the motor shaft, the motor slows down, the relative motion between the rotating magnetic field and the rotor increases causing increase in rotor emf, rotor current and so in the torque developed. Thus the motor meets the increased load.

5. TYPES OF 3-PHASE INDUCTION MOTORS: 5.1 SQUIRREL-CAGE ROTOR The most common rotor is a squirrel-cage rotor. It is made up of bars of either solid copper (most common) or aluminum that span the length of the rotor, and those solid copper or aluminum strips can be shorted or connected by a ring or sometimes not, i.e. the rotor can be closed or semi closed type. The rotor bars in squirrel-cage induction motors are not straight, but have some skew to reduce noise and harmonics.

5.2 SLIP RING ROTOR A slip ring rotor replaces the bars of the squirrel-cage rotor with windings that are connected to slip rings. When these slip rings are shorted, the rotor behaves similarly to a squirrel-cage rotor; they can also be connected to resistors to produce a high-resistance rotor circuit, which can be beneficial in starting 5.3 SOLID CORE ROTOR A rotor can be made from solid mild steel. The induced current causes the rotation.

6. PURPOSE OF SELECTING INDUCTION MOTOR Medium construction complexity, multiple fields on stator, cage on rotor High reliability (no brush wear), even at very high achievable speeds Medium efficiency at low speed, high efficiency at high speed Driven by multi-phase Inverter controllers Motor EMI good but…terrible EMI from Inverter Sensor less speed control possible Low cost per horsepower, though higher than for 1-ph AC induction motor Higher start torque than for 1-ph, easy to reverse motor Inverter ‘shoot-through’ possible, requires ‘dead-time’ circuits & compensation

7. RELAY A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays were used extensively in telephone exchanges and early computers to perform logical operations. A type of relay that can handle the high power required to directly drive an electric motor is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protective relays". 7.1 DESIGN AND OPERATION OF RELAY A simple electromagnetic relay consists of a coil of wire surrounding a soft iron core, an iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature, and one or more sets of contacts (there are two in the relay pictured). The armature is hinged to the yoke and mechanically linked to one or more sets of moving contacts. It is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open. Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke. This ensures continuity of the circuit between the moving contacts on the armature, and the circuit track on the printed circuit board (PCB) via the yoke, which is soldered to the PCB.

Fig.13 Relay When an electric current is passed through the coil it generates a magnetic field that attracts the armature and the consequent movement of the movable contact either makes or breaks (depending upon construction) a connection with a fixed contact. If the set of contacts was closed when the relay was de-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low-voltage application this reduces noise; in a high voltage or current application it reduces arcing. When the coil is energized with direct current, a diode is often placed across the coil to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a voltage spike dangerous to semiconductor circuit components. Some automotive relays include a diode inside the relay case. Alternatively, a contact protection network consisting of a capacitor and resistor in series may absorb the surge. If the coil is designed to be energized with alternating current (AC), a small copper "shading ring" can be crimped to the end of the solenoid, creating a small out-of-phase current which increases the minimum pull on the armature during the AC cycle. A solid-state relay uses a thyristor or other solid-state switching device, activated by the control signal, to switch the controlled load, instead of a solenoid. An opto coupler (a light-emitting diode (LED) coupled with a photo transistor) can be used to isolate control and controlled circuits.

8. THREE PHASE CONTACTOR A contactor is an electrically controlled switch used for switching a power circuit, similar to a relay except with higher current ratings. A contactor is controlled by a circuit which has a much lower power level than the switched circuit. Contactors come in many forms with varying capacities and features. Unlike a circuit breaker, a contactor is not intended to interrupt a short circuit current. Contactors range from those having a breaking current of several amps and 24 V DC to thousands of amps and many kilovolts. The physical size of contactors ranges from a device small enough to pick up with one hand, to large devices approximately a meter on a side. Contactors are used to control electric motors, lighting, heating, capacitor banks, and other electrical loads.

9. TRANSFORMER A transformer is a static device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the secondary winding. This effect is called mutual induction. 9.1 TYPES OF TRANSFORMER A wide variety of transformer designs are used for different applications, though they share several common features. 9.1.1 AUTOTRANSFORMER In an autotransformer portions of the same winding act as both the primary and secondary. The winding has at least three taps where electrical connections are made. An autotransformer can be smaller, lighter and cheaper than a standard dual-winding transformer however the autotransformer does not provide electrical isolation.

Fig.14 Auto transformer Autotransformers are often used to step up or down between voltages in the 110-117-120 volt range and voltages in the 220-230-240 volt range, e.g., to output either 110 or 120V (with taps) from 230V input, allowing equipment from a 100 or 120V region to be used in a 230V region. A variable autotransformer is made by exposing part of the winding coils and making the secondary connection through a sliding brush, giving a variable turns ratio. Such a device is often referred to by the trademark name variac. 9.1.2 POLYPHASE TRANSFORMERS For three-phase supplies, a bank of three individual single-phase transformers can be used, or all three phases can be incorporated as a single three-phase transformer. In this case, the magnetic circuits are connected together, the core thus containing a three-phase flow of flux.

Fig.15 poly phase Transformer A number of winding configurations are possible, giving rise to different attributes and phase shifts. One particular poly phase configuration is the zigzag transformer, used for grounding and in the suppression of harmonic currents. 9.1.3 LEAKAGE TRANSFORMERS A leakage transformer, also called a stray-field transformer, has a significantly higher leakage inductance than other transformers, sometimes increased by a magnetic bypass or shunt in its core between primary and secondary, which is sometimes adjustable with a set screw. This provides a transformer with an inherent current limitation due to the loose coupling between its primary and the secondary windings. The output and input currents are low enough to prevent thermal overload under all load conditions—even if the secondary is shorted. Leakage transformers are used for arc welding and high voltage discharge lamps (neon lights and cold cathode fluorescent lamps, which are series-connected up to 7.5 kV AC). It acts then both as a voltage transformer and as a magnetic ballast.

Fig.16 Leakage Transformer Other applications are short-circuit-proof extra-low voltage transformers for toys or doorbell installations.

9.1.4 RESONANT TRANSFORMERS A resonant transformer is a kind of leakage transformer. It uses the leakage inductance of its secondary windings in combination with external capacitors, to create one or more resonant circuits. Resonant transformers such as the Tesla coil can generate very high voltages, and are able to provide much higher current than electrostatic high-voltage generation machines such as the Van de Graaff generator. One of the applications of the resonant transformer is for the CCFL inverter. Another application of the resonant transformer is to couple between stages of a super heterodyne receiver, where the selectivity of the receiver is provided by tuned transformers in the intermediate-frequency amplifiers. 9.1.5 AUDIO TRANSFORMERS Audio transformers are those specifically designed for use in audio circuits. They can be used to block radio frequency interference or the DC component of an audio signal, to split or combine audio signals, or to provide impedance matching between high and low impedance circuits, such as between a high impedance tube (valve) amplifier output and a low impedance loudspeaker, or between a high impedance instrument output and the low impedance input of a mixing console. Such transformers were originally designed to connect different telephone systems to one another while keeping their respective power supplies isolated, and are still commonly used to interconnect professional audio systems or system components. Being magnetic devices, audio transformers are susceptible to external magnetic fields such as those generated by AC current-carrying conductors. "Hum" is a term commonly used to describe unwanted signals originating from the "mains" power supply (typically 50 or 60 Hz). Audio transformers used for low-level signals, such as those from microphones, often include shielding to protect against extraneous magnetically coupled signals. 9.1.6 INSTRUMENT TRANSFORMERS Instrument transformers are used for measuring voltage and current in electrical power systems, and for power system protection and control. Where a voltage or current is too large to be conveniently used by an instrument, it can be scaled down to a standardized, low value. Instrument transformers isolate measurement, protection and control circuitry from the high currents or voltages present on the circuits being measured or controller. A current transformer is a transformer designed to provide a current in its secondary coil proportional to the current flowing in its primary coil. Voltage transformers (vts), also referred to as "potential transformers" (pts), are designed to have an accurately known transformation ratio in both magnitude and phase, over a range of measuring circuit impedances. A voltage transformer is intended to present a negligible load to the supply being measured. The low secondary voltage allows protective relay equipment and measuring instruments to be operated at a lower voltage. Both current and voltage instrument transformers are designed to have predictable characteristics on overloads. Proper operation of over-current protective relays requires that current transformers provide a predictable transformation ratio even during a short-circuit. 9.2 STEP DOWN TRANSFORMER Step down transformers are designed to reduce electrical voltage. Their primary voltage is greater than their secondary voltage. This kind of transformer "steps down" the voltage applied to it. For instance, a step down transformer is needed to use a 110v product in a country with a 220v supply.

Fig.17 Step down Transformer Step down transformers convert electrical voltage from one level or phase configuration usually down to a lower level. They can include features for electrical isolation, power distribution, and control and instrumentation applications. Step down transformers typically rely on the principle of magnetic induction between coils to convert voltage and/or current levels. Step down transformers are made from two or more coils of insulated wire wound around a core made of iron. When voltage is applied to one coil (frequently called the primary or input) it magnetizes the iron core, which induces a voltage in the other coil, (frequently called the secondary or output). The turn’s ratio of the two sets of windings determines the amount of voltage transformation. Step down transformer is used because of the sensor circuits are working in 12 volts.

10. ELECTRONIC OSCILLATOR An electronic oscillator is an electronic circuit that produces a repetitive electronic signal, often a sine wave or a square wave. They are widely used in innumerable electronic devices. Common examples of signals generated by oscillators include signals broadcast by radio and television transmitters, clock signals that regulate computers and quartz clocks, and the sounds produced by electronic beepers and video games. A low-frequency oscillator (LFO) is an electronic oscillator that generates an AC waveform at a frequency below ≈20 Hz. This term is typically used in the field of audio synthesizers, to distinguish it from an audio frequency oscillator. Oscillators designed to produce a high-power AC output from a DC supply are usually called inverters.

11. POWER SCREWS Power Screws are used for providing linear motion in a smooth uniform manner. They are linear actuators that transform rotary motion into linear motion. Power screws are generally based on Acme, Square, and Buttress threads. Ball screws are a type of power screw. Efficiencies of between 30% and 70% are obtained with conventional power screws. Ball screws have efficiencies of above 90%.Power Screws are used for the following three reasons, To obtain high mechanical advantage in order to move large loads with minimum effort. E.g. Screw Jack. To generate large forces e.g. compactors press. To obtain precise axial movements e.g. machine tools lead screw. 12. TYPES OF SCREW THREAD

12.1 SQUARE FORM This form is used for power/force transmission i.e. linear jacks, clamps. The friction is low and there is no radial forces imposed on the mating nuts. The square thread is the most efficient conventional power screw form. It is the most difficult form to machine. It is not very compatible for using split nuts-as used on certain machine tool system for withdrawing the tool carriers 12.2 ACME FORM Used for power transmission i.e. Lathe lead screws. Is easier to manufacture compared to a square thread. It has superior root strength characteristics compared to a square thread. The acme screw thread has been developed for machine tool drives. They are easy to machine and can be used with split nuts. The thread has an optimum efficiency of about 70% for helix angles between 25o and 65o. Outside this range the efficiency falls away.

12.3 BUTTRESS FORM A strong low friction thread. However it is designed only to take large loads in on direction. For a given size this is the strongest of the thread forms. When taking heavy loads on the near vertical thread face this thread is almost as efficient as a square thread form. 12.4 RECIRCULATING BALL SCREW This type of power screw is used for high speed high efficiency duties. The ball screw is used for more and more applications previously completed by the conventional power screws.

           The ball screw assembly is as shown below and includes a circular shaped groove cut in a helix on the shaft.   The ball nut also includes an internal circular shaped groove which matches the shaft groove.   The nut is retained in position on the shaft by balls moving within the groove.  When the nut rotates relative to the shaft the balls move in one direction along the groove supporting any axial load.   When the balls reach one end of the nut they are directed back to the other end via ball guides.   The balls are therefore being continuously recirculated.

12.5 ROLLER SCREW A recent high specification power screw option is the roller screw. For this unit the nut includes a number of special threaded rollers arranged around the central screw. The rollers each take a part of the load. This system is efficient and can withstand high loads.

13. SCREW THREAD NOMENCLATURE 13.1 LEFT/RIGHT THREAD TYPES Threads are normally Right Handed and unless otherwise stated this is the norm. This means that the nut screws on with a CLOCKWISE rotation. Left Hand threads are of course the opposite. Left Handed Threads are used extensively in the Motor Industry to secure rotating parts such as Drive Shafts, Gears etc. Where the normal angular rotation would tend to tighten the nut. Left & Right Hand threads are used, as appropriate, on the Offside/Nearside of the Vehicle. When working on rotating parts always check the hand of the thread or consult the correct instruction manual. It is not uncommon for Wheel Nuts to be Left or Right handed. Use caution. 13.2 EFFECTIVE OR PITCH DIAMETER On a parallel thread it is the diameter of an imaginary cylinder which would pass through the threads at such a point that both male and female thread were the same width. This point is usually but not always 1/2 the thread depth. It is only at 1/2 depth when the root & crest radii are the same. 13.3 LAND (MAJOR) DIAMETER

	The outside diameter of the screw.

13.4 ROOT (MINOR) DIAMETER

           The diameter of the screw measured at the bottom of the thread.

13.5 PITCH

           The axial distance between threads. Pitch is equal to the lead in a single start screw.

13.6 LEAD

            The axial distance the nut advances in one revolution of the screw. The lead is equal to the pitch times the number of starts.

LEAD = PITCH x STARTS 13.7 THREAD INCLUDED ANGLE Apart from a number of specialist threads the included angles for the most common threads are as follows. BA 47½°. BSW, BSF 55°. UNF, UNC, ANF, ANC 60°. Metric or ISO 60°. British Standard Cycle Thread (BSC) 60°. Acme 29°. Do not be tempted to use male & female threads with differing V angles. The entire load is transferred to the thread crests and causes high stress levels, leading to slackening in service and premature failure. 13.8 SCREW STARTS The number of independent threads on the screw shaft; example one, two or four. (SEE FIG)

Fig.18 Screw starts 13.9 THREAD PITCH Usually expressed in threads per inch (tpi) or as an absolute dimension for one single pitch. I.e. 1mm. 0.2mm .75mm etc. Multi-start threads are basically the single start form, but with the pitch doubled etc. Very rare to come across these in model engineering.

13.10 ROOT & CREST FORM A major part of any thread is the crest & root form. Usually but not always this takes the form of a radius. Sometimes a flat. The root & crest form may also vary on the male & female threads. Production of a correct form is for the average modeler virtually impossible. The ISO Metric threads are however an exception. The standard allows for flat roots & crests (p/8 & p/4) It is possible to produce a "V" tool with a rounded root & let the crest remain as a flat. Where taps & dies are used the correct form is produced automatically.. When screw cutting it is now possible to buy ceramic tips that will automatically produce the correct root and crest radii. Since an insert is required for each form & pitch this puts their use outside the reach of most modelers due to cost. A 100% sharp "V" is undesirable as it may form the stress point for fracture and on bolts, cut fingers. Adding a small radius on the "V" tool with a stone is probably the best we can achieve. Another very good way is to use part of a new tap as a thread chaser & skim off the last few tenths & form the radii. Application of the correct root & crest radii does of course reduce the Actual thread depth compared to the full Theoretical Triangular "V" depth.

14. ASSEMBLY VIEW

Fig.19 Assembly View

15. SPECIFICATIONS Motor - 3Φ, 1 H.P Transformer – Step down ( 230v to 12v) Oscillator – 32 KHZ Contactor - 3Φ, 16 amps Terminal block - 3Φ, 30 amps, 440v IC chip – 311( opp-amp) Reference – 20 to 30 mm Maximum lifting height – 150 cm Minimum table level – 30 cm Lifting capacity – 1100 pounds

16. CALCULATIONS:

	For 30 mm nominal diameter,

Preferred Length = 1200 mm Major Diameter for lead screw = 30 mm Major Diameter for Nut = 30.5 mm Minor Diameter = 27 mm Pitch = 3 mm For single start thread, Lead = pitch Lead = 3 mm Pitch = 1/(no.of threads per unit length) No. of threads per unit length = 1/pitch No. of threads per unit length = 1/3 No. of threads per unit length = 0.333 No. of threads per unit length for 1200 mm length = 1200×0.333=400 threads Linear speed of the lift = RPM of the input shaft × lead Linear speed of the lift = 435 × 3 = 1300 mm/min Power = 1 H.P (or) 746 WATT Power = 2πNT/60 Torque = (p×60)/2πN Torque = (746×60)/(2π×1440) Torque = 4.95 Nm

17. COMPONENTS AND MATERIALS USED

Table.1 Components and materials used

Sl. No Component Material 1. L - Angle Mild Steel 2. Flat strip Mild Steel 3. Wheel Mild Steel 4. Shaft Mild Steel 5. Motor plate Mild Steel 6. Coupling Mild Steel

18. COST ESTIMATION Table.2 Cost estimation Sl. No Component Quantity Cost (Rs) 1. L - Angle 15 feet 820 2. Flat Strip 23 feet 300 3. Motor Support 1 210 4. Coupling 1 220 5. Bush 1 40 6. Shaft 10 feet 800 7. Motor 1 3000 8. Sensor Unit 1 2000 9. Fabrication - 2000 10. Others - 1000 Total 10390

19. APPLICATIONS: Loading or unloading of raw materials, bags, bricks, tiles. For elevating product placed on conveyors, into feeding hoppers, extruder. Maintenance of process and production equipment. Personnel lift. Mezzanine and between floor lifts. Order picking. Raised storage access.

20. ADVANTAGES: Duty cycle is high / highly reliable. Integrates well with electrical controls. Scissor lifts are inherently safe. Integrates well with robotic applications. Has no fluid or gas that can be use and create environmental contamination.

21. CONCLUSION:

Thus we have design and fabricated a “Dual Operated scissor Lifter” after facing lot of problems, from the project work. We have a chance to know the quality materials used in our project. At the same time, we are having the chance to know the prices of the materials, which are used in making this “Dual Operated scissor Lifter”. By doing this project work, we purchased materials from various shops, which help us to learn how to move the people in the market. We gain more knowledge. In the stage of our project felt very much because of its difficulty in design and fabricating. But the successful result treated as to hope that in future we can do any job by proper planning and designing. From using this “Dual Operated scissor Lifter” we are Lift the materials in workshop and department lab in successful.