Mechanisms

1. Mechanisms

2. What is a Mechanism? In a machine - one part causing another to move Used to transfer or change speed, torque, force, type of motion and / or direction of motion.

3. Mechanisms - Change Direction • Meshed gears in a gear train always turn in opposite directions

4. Mechanisms - Change Movement Rotary Oscillating • Linear • Reciprocating

5. Mechanisms - Change Speed • Gear ratios compare the output (or driven gear) to the input (or drive gear) • Output : Input • Gear Ratios can be determined using number (n) of teeth on the gear or diameter (d) of the gear • If the output gear is larger than the input gear the speed will decrease • If the output gear is smaller than the input gear the speed will increase

6. Mechanisms – Change Force or Torque A force is a push or pull in a straight line. Torque is a push or pull in a circular direction or twisting motion

7. Simple Gear Train Driven / Output Input and Output Shafts parallel (A & B) A – Ratio 1:1 [Output to Input] • Speed is constant • Torque is constant B – Ratio 3:5 [Output to Input] 36 teeth : 60 teeth • Speed is increased • Torque is decreased Flow of power - reversible Motion - rotational to rotational Direction – opposite Drive / Input A. Driven / output Drive / Input B.

8. Where Do You Find a Simple Gear Train? Found in: • Watch • Sewing Machine • Motor Watch gears Two meshed gears will rotate in opposite directions

9. Simple Gear Train with Idler Input and Output Shafts parallel Ratio 1:1 [Output to Input] • Speed is constant • Torque is constant Flow of power - reversible Motion - rotational to rotational to rotational Direction – same Drive / Input Idler Driven / Output

10. Where Do You Find a Simple Gear Train with Idler? Two meshed gears will rotate in opposite directions. An Idler Gear allows the drive and driven gears to rotate in the same direction. 7. Found in - Paper Transport Rollers / Car Transmission

11. Bevel Gear Input and Output Shafts 90 degrees Ratio 1:1 [Output to Input] • Speed is constant • Torque is constant Flow of power - reversible Motion - rotational to rotational Direction – same

12. Where Can You Find a Bevel Gear? Found in: • Hand drill • Car Differential • The bevel gear is used to change rotational motion at a 90˚ angle.

13. Differential Gear • Gears used – Bevel • Used in – rear end of rear wheel drive vehicles • Purpose – Wheels spin at different speeds when turning http://auto.howstuffworks.com/differential.htm

14. Worm and Wheel Wheel Input and Output Shafts 90 Degrees Ratio 1:24 [Output to Input] • Speed is decreased • Torque is increased Flow of power – not reversible Motion - rotational to rotational Direction – same & reversible Worm

15. Where Do You Find a Worm and Wheel? • A worm is used to reduce speed and increase torque. • Found in: • Tuning mechanism on string instruments • Electric motors • Winch

16. Leadscrew Speed is decreased Force is increased Revolutions 4.75 (per design) Flow of power – notreversible Motion - rotational to linear Direction – reversible

17. Where Do You Find a Lead Screw? • Changes rotary movement into linear movement • Significantly increases force • A person can put a little force into turning the handle to lift a heavy car • Jack • Vice

18. Rack and Pinion Force increased Input Movement rotary Output Movement linear With a Larger Pinion Gear - the rack will move a longer distance Flow of power - reversible Motion - rotational to linear Direction – same & Reversible Pinion Rack

19. Where Do You Find a Rack and Pinion? Used in steering systems of cars to convert rotary motion of steering wheel to the side to side motion in the wheels. • Used to convert between rotary and linear motion. • Provides gear reduction to make it easier to turn the wheels. Pinion Rack

20. Universal Joint Angular Range > 90˚ and < 270˚ Ratio 1:1 • Speed is constant • Torque is constant Flow of power - reversible Motion - rotational to rotational Direction – same

21. Where Can You Find a Universal Joint? • Drive shaft of vehicles • Power take-off Universal joints are used to transmit rotary movement at an angle that is not 90°.

22. Chain Drive Driven / Output A A - Shafts are parallel Ratio 30:18 or 5:3 [Output to Input] • Speed is increased • Torque is decreased B –Shafts are parallel Ratio 18:30 or 3:5 [Output to Input] • Speed is decreased • Torque is increased Flow of power - reversible Motion - rotational to rotational Direction – same Drive / Input Drive / Input Driven / Output B

23. Where Do You Find a Chain and Sprocket? Advantage of Chain and Sprocket over spur gears: Transfer torque and speed over long distances • Found in: • Bicycle • Motorcycle

24. Belt Drive Input and Output Shafts parallel Ratio 1:1 [Output to Input] • Speed is constant • Torque is constant Flow of power - reversible Motion - rotational to rotational to rotational Direction – open belt same - crossed belt opposite Drive Driven

25. Where Do You Find a Pulley and Belt? • Found in: • Lawn mower • Car engine BELTS • Belts instead of chains: • Quieter /Less expensive • Less durable / slip

26. Crank and Slider Speed / Force – N/A Input Movement rotary Output Movement reciprocating Slider moves- diameter of the crank Flow of power – not reversible Direction – same & reversible Crank Slider

27. Where Do You Find a Crank and Slider? Found in: • Steam train • Internal combustion engine

28. Cam and Follower Speed & Force N/A Input Movement rotary Output Movement reciprocating Follower moves up and down 1 time for every revolution of the crank Flow of Powernot reversible Direction of Travelnot reversible FOLLOWER CAM

29. Where Do You Find a Cam and Follower? • Found in: • Cam shaft • As a cam rotates, the flat follower is raised and lowered, converting rotary motion to reciprocating (back and forth) motion. • The cam pictured here would be reversible, as it is symmetrical.