Mechanisms and Devices: A Guide to Function and Application

1. Q. 8 Mechanisms & Devices

2. Devices • Flow Control Valve – To control the operating speed in a pneumatic circuit. • Thermocouple- To detect changes in temperature electronically. • Turbine- To transform the kinetic energy of water into electrical energy. • Shock Absorber- To slow down the action of a suspension spring. • Transformer- To change the voltage of AC without changing it’s frequency.

3. The energy conversation that occurs in a car battery: Chemical energy to electrical energy. • Ratchet and pawl mechanism A ratchet and pawl is used to allow a shaft, axle or pin to rotate in one direction only. The teeth on the ratchet wheel 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. A ratchet and pawl can be used in ratchet spanners, fishing reels, ratchet screwdrivers, micrometers and winding machines etc.

4. Idler gear An additional gear that is inserted between two other gears with the purpose of changing the direction of gear rotation. 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.

5. 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. • 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.

6. 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. • 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.

7. 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.

8. Light dependent resistor (LDR): An electronic sensing component that can be set up to sense the presence or absence of light. • The functions of the electronic transistor: Can be used as an electronic switch or an amplifier.

9. Devices • Mechanical Clutch- To make and break the drive between two shafts. • Rectifier- To conver AC to DC (incl. A diagram) • Universal Joint- To allow motion to be transmitted between two shafts which are not in line. • Electrical Relay- Allows a small current and voltage to turn on a circuit which operates at a higher voltage and current.

10. Devices • Heat Pipe- Transfers heat from one place to another. • Bimetallic Contact Breaker. A bimetallic strip acting as a switch. (different metals expand at different rates when heated) • Light Dependant Resistor -LDR- Resistance changes with light intensity. • Flow Regulator- To control air flow in a pneumatic circuit.

11. Devices • Sensor- Detects changes in the environment (LDR). • Motor- Changes electrical energy into mechanical energy. • Thermistor- Resistance cahnges with changes in temperature. • Bevel Gears- To connect shafts which move at right angles. • Solar Cell- Converts light energy into electrical energy.

12. Devices • Differential Gears- Allows wheels on the same axel to rotate at different speeds. • Thermostat- Measures temperature • Strain Gauge- To measure the distance between points on a component. • Non-Return Valve- Allows air/fuel to flow in one direction only. • Intregated Circuit (IC)- An electronic circuit containing components produced intregrally in a small piece of semi-conducting material. (chip)

13. Devices • Heat Pump- Used to extract heat from a body at one temperature and transfer it to a body at a higher temperature. Used in heating systems and air conditioning. • Flywheel- Absorbs all the up and down forces of the pistons and by means of a crankshaft smoothens out the forces into a smooth balanced rotary motion.

25. (a) (i) Universal joint: The drive rotates the spline shaft of the universal joint which transmits motion through to the output shaft. This allows motion to be transmitted in a line or at an angle. It is commonly used on tractor machinery. (ii) Simple helical 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. 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.

28. (i) Universal joint Allows motion to be transmitted in a line or at an angle. (ii) Overhead cam and valve As the camshaft rotates, the cams open and close valves in sequence.

29. (i) Name: Ratchet and pawl. Ratchet is used to allow the socket to turn and lock in either direction due to the design of the locking pawl. (ii) Name: Toothed belt and pulley. Toothed pulley and belt gives an effective grip drive for car timing belts, motorcycle drive and CNC lathes.

30. (i) Bevel gear system: used transfer motion at right angles, applications include hand drill. (ii) Ball thrust bearing system: allows an axial load on a rotating shaft, used in robotic control, transmission systems, turntables, rotating stools, etc.

31. (i) Rack and pinion converts rotary motion to linear motion. As the pinion rotates, the gear teeth mesh with those on the rack. This allows the rack to be moved in a line. Applications of the rack and pinion include raising and lowering the table of a pillar drill and steering in a car. (ii) 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.

32. (i) The operation of the toothed belt and pulley system ensures that there is no slippage between the driver and driven pulley. Therefore the driven shaft rotates at a consistent rate in sequence. This gives a quite, positive drive. Applications include, driving the camshaft of an engine, used for accurate movement of the pen of a graphic plotter. (ii) 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. This is an obvious drawback with this mechanism. When rotating for one complete revolution the follower stays level for approximately the first 120°. The follower then rises slowly and then suddenly drops when it passes its peak. Applications include, toys where sudden up and down movement is essential, clock and watch mechanisms, automated lifting mechanisms.

33. (i) Operation: Bell-crank mechanism Application: Bicycle brakes (ii) Operation: Ratchet an pawl mechanism Application: Used in wire tensioning devices e.g. tennis nets.

34. (i) Name: Worm and worm wheel. Application: Used in the dividing head. (ii) Name: Bevel gears (sometimes called mitre gears) Application: Connection of two moving shafts which meet at right angles and shafts that do not have parallel access.

35. (i) Vee pulley and V-belt: Used in lathes and drills, to transmit motion from motor to spindle. (ii) Chain and sprocket: Used on bicycles, motorcycles, go-karts and the camshaft drives, of some engines.

36. The mechanism at (i) is rack and pinion and may be used in steering mechanisms. The universal coupling is shown at (ii) where drive shafts are not in alignment.