1. Mechanical Actuation System Lecture 6 (Chapter 8)

2. SME 3252: Mechatronics Lecture 6 Introduction Mechanisms are devices which can be considered to be motion converters Transform motion from one form to another 3 common motion transmission mechanism: 1.Rotary-to-rotary motion transmission mechanism – gears, belt and pulley 2.Rotary-to-translational motion transmission mechanism – lead-screw, rack-pinion, belt-pulley 3.Cyclic motion transmission mechanism – linkages and cams

3. SME 3252: Mechatronics Lecture 6 8.2: Types of motion Motion of rigid bodies – combination of translational and rotational Kinematics of rigid bodies (Dynamics SME1213) Translational motion – one or more of 3 axes Rotational motion – one or more of 3 axes

4. SME 3252: Mechatronics Lecture 6 x y z

5. Exercise Analyse the motion of the following mechanisms and state whether they are pure translation, pure rotation or a mixed of translation and rotation: 1.The keys on a computer keyboard 2.The pen in an XY plotter 3.The hour hand of a clock 4.The pointer on a moving coil ammeter 5.An automatic screwdriver

6. SME 3252: Mechatronics Lecture 6 6.2.1: Freedom and constraints No. of degree of freedom – no. of components to motion that are required to generate motion Problem in design – reduce d.o.f requires orientation constrains

7. SME 3252: Mechatronics Lecture 6 How any dof?

8. SME 3252: Mechatronics Lecture 6 How any dof? SamsulSamsul Tongaji, PSM 2006/2007

9. SME 3252: Mechatronics Lecture 6 Exercises By examining the following mechanisms, state the number of degree of freedom each has: 1.A car hood hinge mechanism 2.A windscreen wiper mechanism 3.Your knee 4.Your ankle

10. SME 3252: Mechatronics Lecture 6 8.2.2: Loading Mechanisms are structures and transmit and support loads Analysis – determine loads to be carried by individual elements

11. SME 3252: Mechatronics Lecture 6 0.125kg Torque Required force, F v Friction force, f v 0.08m From total weight, M; M = Body weight + battery weight + servo motor weight + leg weight + others M = 1 kg + 0.5 kg + 0.055 kg (8 motors) + 0.1 kg (4 legs) + 0.5 kg = 2.84 kg m = M/4= 0.947kg Thus, F = 0.3 x 0.947kg x 9.81 m/s 2 = 2.786N The minimum required torque, T = n(Fv.r) Where; n = Safety factor, 1.5 r = Turning radius, 0.08 Thus, T = 1.5 × 2.786N × 0.08m = 0.3343 Nm From the calculation, the minimum required torque to perform the vertical leg movement is 0.3343Nm. From static friction theory, Fv = fvand Fv = μN Fv = μ(mg) Where; Fv = Force min for actuation, N μ = Static friction coefficient, 0.3 m = Robot weight imposed on each leg, kg g = Gravity, 9.81m/s2 By: Lim Kim Fung, PSM 2006/2007

12. SME 3252: Mechatronics Lecture 6 Rotary-to-rotary motion transmission mechanism Examples are: 1.Gears 2.Belt 3.Pulley

13. SME 3252: Mechatronics Lecture 6

14. Gear System Observed variables: torque , acceleration , velocity  and displacement  for input and output gear System parameters: number of teeth or radius which gives gear ratio:

15. SME 3252: Mechatronics Lecture 6 No slipping occurs:r a  a = r b  b Differentiate with respect to time: Orr a  a = r b  b In gear ratio: Force acting on both teeth: Therefore:

16. SME 3252: Mechatronics Lecture 6 8.5: Gear trains Gear trains – a series of intermeshed gear wheels A compound gear train where the two central gears revolve together at the same speed on the same shaft

17. SME 3252: Mechatronics Lecture 6 Gear types – bevel, spur, worm, helical

18. SME 3252: Mechatronics Lecture 6 6.6: Ratchet and paw The ratchet is the toothed wheel, the pawl is the arm that locks it in position The purpose - to limit rotation to one direction only It is often used as a safety device to prevent reverse running of a winch or as part of the wrench in a socket set

19. SME 3252: Mechatronics Lecture 6

20. 6.7: Belt and chain drives A typical Vee belt drive system is shown below In this eg. the driver pulley is larger, the driven pulley will run much faster. Driver / Driven = Speed of Driven / Speed of Driver

21. SME 3252: Mechatronics Lecture 6 www.co-design.co.uk/dpg/bel/bel8.gif 6.7.1: Types of belts

22. SME 3252: Mechatronics Lecture 6 www.co-design.co.uk/dpg/bel/bel8.gif

23. SME 3252: Mechatronics Lecture 6 6.7.2: Chains Use of chain – to prevent slip, lock into teeth on rotating cylinders Component of chain drives. Eg of chain drive - bicycle

24. SME 3252: Mechatronics Lecture 6 Sprocket and chain

25. SME 3252: Mechatronics Lecture 6 Robot power chair http://www.fatnfast.com/robot/ The objective was/is to evaluate: The practicalities of 4x4 steering

26. SME 3252: Mechatronics Lecture 6

27. End of Lecture 6