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Mechanisms

Leaving cert Engineering HL Q8

QuestionAnswer
Explain the function of a thermostat A thermostat is a component of a control system which senses the temperature of a system so that the system's temperature is maintained near a desired set-point. The thermostat does this by switching heating or cooling devices on or off
Advantages of roller bearings Roller bearings typically have higher load capacity than ball bearings - Gives a smoother drive - Are generally easy to replace and maintain - Are designed in a range of sizes in both length and diameter
Suggest one application of a DPDT switch A Double Pole Double Throw switch may be used to turn a circuit on or off. DPDT switches are commonly used to operate a motor both forward and reverse.
State two advantages of helical gears over spur gears • Allow a number of teeth to mesh at the same time providing a strong drive • Shafts need not be parallel for transferring power• Quieter in operation then straight spur gears.
Explain the operation of a pneumatic double-acting cylinder. A double acting cylinder needs compressed air to move the piston but will stay in this position if the air is turned off. It needs air to return the piston to its original position.
Describe, with the aid of a diagram, the principle of operation of a relay. A relay is an electromagnetic device that changes switching contacts when it receives an electric signal. It consists of a wire coil with a soft iron core. The relay is a switch and changes electrical energy into mechanical energy.
Explain the operation of a pneumatic single-acting cylinder. A single acting cylinder is a pneumatic output device that requires compressed air to make the piston move. If the air is removed the piston will return. A spring can be used to push is back to its starting position
Explain the operation and application of a rack and pinion system. In a rack and pinion mechanism, the rotational motion of the pinion is translated into the linear motion of the rack. Applications include steering racks in cars, drilling machine tables, carriage on lathe etc.
Explain one application of reciprocating motion Cutting with a saw, sliding door, piston in an engine, etc.
Describe a toggle mechanism This linkage is widely used as a clamping mechanism, it is used in a ‘vice grips’ as it holds very firmly and is quick to use.
Explain the function of idler gears An additional gear that is inserted between two other gears. Idler gears do not have an influence on the gear ratio of the system. They allow the input gear and output gear shafts to rotate in the same direction.
Explain the operation of a universal joint This allows rotary motion to be transmitted in a line or at an angle. The drive rotates the spline shaft of the universal joint which transmits motion through to the output shaft. It is commonly used on tractor machinery.
Explain the advantages of helical gears The helical teeth on the gears allow a number of teeth on each gear to be in contact at the same time, this gives a smoother and stronger drive. These gear systems may be used on gear driven drills.
Explain a simple gear train Two shafts are driven in opposite directions by a simple gear train. When there is no difference in gear size, both rotate at the same speed. Speeds can be varied by using different sized gears
Explain the advantages of toothed pulley belts; Toothed belts are much less prone to slippage. Can be used as a drive for timing engines giving a quieter operation than chain drives.
Explain the operation and one application of a solenoid a coil of wire, wound around a soft iron core, is energised. The magnetic force induced by the current pulls the bar towards the centre. A solenoid spring will return the bar to its original position. Used for controlled entry door locks.
Explain one application for a resistor A resistor will limit current flow and is used to protect electronic components. It is often used to protect LED's
Suggest a mechanical device used to convert rotary motion into linear motion Crank and slider. Rack and pinion.
Explain the operation of a pneumatic flow regulator. This restricts, or regulates, the flow of air in one direction only in a pneumatic circuit.
Explain the operation of a ball bearing Allows a shaft to rotate in the centre of the bearing while it is held in a machine or structure. This reduces friction, promotes free running of the shaft and reduces the build-up of heat.
Expliain the operation of a poly vee belt and pulley Motor drives belt to an output pulley which can increase or decrease speeds depending on the size of the pulleys. Has more grip than an ordinary vee belt
Name the energy conversation that occurs in a car battery Chemical energy to electrical energy
Explain the operation of a ratchet and pawl mechanism used to allow a shaft rotate in one direction only. teeth on the ratchet are so shaped that the pawl slides over them in one direction and engages with them so as to restrict movement in the other direction. used in ratchet spanners and clothes lines
Explain the operation of a heat sink A heat sink is used in electronics to conduct away heat generated by a component. These heat sinks are normally corrugated or finned to dissipate heat to the surrounding air and protect components such as transistors.
Explain the benefits of using solar panels Solar panels are used to harness the free energy from the sun and use it to generate electrical energy or to provide hot water and heating for buildings
Explain the operation of bevel gears Allows motion from the output shaft to be transmitted at 90o to the input movement.
Explain the operation of a roller bearing A roller bearing gives a greater area of contact than a ball bearing system, this allows greater loads to be carried. Tapered roller bearings can cope with radial and axial loads and are used for wheel bearings in most vehicles.
Explain the advantages of using vee pulley belts over flat belts Gives a greater area of contact with the pulley wheel. Provides a stronger grip. Reduces slip. Can drive larger forces
Explain the operation of a chain and sprocket A chain is used to transmit motion from one toothed wheel to another. This eliminates slip and is in common use on bicycles and motor cycles. A chain and sprocket gives a strong drive.
Explain the operation of an LDR Light Dependent Resistor. An electronic sensing component that can be set up to sense the presence or absence of light.
Outline the functions of the electronic transistor Can be used as an electronic switch or an amplifier.
Explain the operation of an overhead cam and valve As the camshaft rotates, the cams open and close valves in sequence
Outline the operation of a clutch It is used in a transmission system to break and make the drive between the engine and wheels. When the clutch engages, the pressure plate and friction plate are pushed together.
Explain the operation of a capacitor It is used to store charge, it can discharge through a circuit so that the stored charge can be used. Capacitors are commonly used in timer circuits
Explain the operation of a crank and slider A mechanism used to convert rotary movement to reciprocating movement or vice versa In a 4 stroke engine, the piston moves up and down. The connecting rod and crankshaft convert this to rotary motion that is then transmitted to the wheel
Explain the operation of an Integrated circuit An electronic circuit containing components such as transistors, resistors, capacitors, etc. which is produced onto a small piece of semi-conducting material. Commonly known as a ‘silicon chip’, these circuits are used to control electrical appliances
Explain the operation of a ball thrust bearing allows an axial load on a rotating shaft, used in robotic control, transmission systems, turntables, rotating stools, etc.
Explain the operation of a shuttle valve controls a single-acting pneumatic cylinder from two positions. An air signal from one side of the valve closes the opposite side.
Explain the operation of a worm and wormwheel Worm and worm wheel transmit motion at right angles. For every complete turn of the worm shaft, the worm wheel advances only one tooth of its gear. Worm and wheels are commonly used to reduce the speed of electric motors.
Explain the operation of a snail or drop cam A snail or drop cam is used where drop or fall of the follower must be sudden. The system shown rotates in an anticlockwise direction as clockwise rotation would lead to the entire mechanism jamming.
Explain the function of a compound gear train A compound gear train is a gearing system that uses more than one pair of gears combined together on a common axis. The gear ratios for each individual gear pair are multiplied together to compute the overall gear ratio for the gear train.
Explain the operation of a dividing head This is used when machining around the periphery of a component e.g. splines on shafts. A worm and wormwheel is used to index the component accurately so that it may be machined the required number of times
Outline the function of a quick return mechanism It is used on a shaping machine, to return the ram on the idle stroke at a faster speed than the cutting stroke.
Created by: todd.ciaran