Theory of machines

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Theory of machines

  1. 1. Ken Youssefi UC Berkeley 1 Mechanism Machines are mechanical devices used to accomplish work. A mechanism is a heart of a machine. It is the mechanical portion of the machine that has the function of transferring motion and forces from a power source to an output. Mechanism is a system of rigid elements (linkages) arranged and connected to transmit motion in a predetermined fashion. Mechanism consists of linkages and joints.
  2. 2. Ken Youssefi UC Berkeley 2 Example of Mechanism Can crusher Simple press Rear-window wiper
  3. 3. Ken Youssefi UC Berkeley 3 Example of Mechanisms Moves packages from an assembly bench to a conveyor Lift platform Microwave carrier to assist people on wheelchair
  4. 4. Ken Youssefi UC Berkeley 4 Example of Mechanisms Lift platform Front loader Device to close the top flap of boxes
  5. 5. Ken Youssefi UC Berkeley 5 Example of Mechanisms Conceptual design for an exercise machine Rowing type exercise machine
  6. 6. Ken Youssefi UC Berkeley 6 Example of Mechanisms Six-bar linkage prosthetic knee mechanism Extension position Flexed position
  7. 7. Ken Youssefi UC Berkeley 7 Four-Bar Linkage
  8. 8. Ken Youssefi UC Berkeley 8 Four-Bar Linkage Categories
  9. 9. Ken Youssefi UC Berkeley 9 Four-Bar Linkage Categories
  10. 10. Ken Youssefi UC Berkeley 10 4-Bar mechanisms
  11. 11. Ken Youssefi UC Berkeley 11 4-Bar mechanisms S + l > p + q 4 double rocker mechanisms
  12. 12. Ken Youssefi UC Berkeley 12 The Slider-Crank Mechanism
  13. 13. Ken Youssefi UC Berkeley 13 The Slider-Crank Mechanism
  14. 14. Ken Youssefi UC Berkeley 14 Slider-Crank Mechanism - Inversion
  15. 15. Ken Youssefi UC Berkeley 15 Mechanism Categories Function Generation Mechanisms A function generator is a linkage in which the relative motion between links connected to the ground is of interest. A four-bar hand actuated wheelchair brake mechanism
  16. 16. Ken Youssefi UC Berkeley 16 Mechanism Categories Function Generation Mechanisms A four-bar drive linkage for a lawn sprinkler
  17. 17. Ken Youssefi UC Berkeley 17 Mechanism Categories Motion Generation Mechanisms In motion generation, the entire motion of the coupler link is of interest (rigid body guidance). New Rollerblade brake system
  18. 18. Ken Youssefi UC Berkeley 18 Mechanism Categories Motion Generation Mechanisms Four-bar automobile hood linkage design
  19. 19. Ken Youssefi UC Berkeley 19 Mechanism Categories Path Generation Mechanisms In path generation, we are concerned only with the path of a tracer point and not with the motion (rotation) of the coupler link. Crane – straight line motion
  20. 20. Ken Youssefi UC Berkeley 20 Primary Joints
  21. 21. Ken Youssefi UC Berkeley 21 Higher Order Joints
  22. 22. Ken Youssefi UC Berkeley 22 Motion Generation Mechanisms Rotating a monitor into a storage position Moving a storage bin from an accessible position to a stored position
  23. 23. Ken Youssefi UC Berkeley 23 Motion Generation Mechanisms Lifting a boat out of water Moving a trash pan from the floor up over a trash bin and into a dump position
  24. 24. Ken Youssefi UC Berkeley 24 Function Generation Mechanisms Graphical Solution Two position synthesis – Design a four-bar crank and rocker mechanism to give 45o of rocker rotation with equal time forward and back, from a constant speed motor input. 1 – Draw the rocker O4B in both extreme positions, B1and B2 in any convenient location with angle θ4 = 45o . 2 – select a convenient point O2 on line B1B2 extended. 3 – Bisect line B1B2 , and draw a circle with that radius about O2. 4 – Label the two intersection of the circle with B1B2 extended, A1 and A2. 5 – Measure O2A (crank, link2) and AB (coupler, link3).
  25. 25. Ken Youssefi UC Berkeley 25 Function Generation Mechanisms Graphical Solution
  26. 26. Ken Youssefi UC Berkeley 26 Crank-Rocker Mechanism
  27. 27. Ken Youssefi UC Berkeley 27 Motion Generation Mechanisms Graphical Solution Two position synthesis – C1D1 and C2D2 • Draw the link CD in its two desired positions, C1D1 and C2D2 • Connect C1 to C2 and D1 to D2. • Draw two lines perpendicular to C1 C2 and D1D2 at the midpoint (midnormals) • Select two fixed pivot points, O2 and O4, anywhere on the two midnormals.
  28. 28. Ken Youssefi UC Berkeley 28 Motion Generation Mechanisms Graphical Solution Two position synthesis (coupler output) – C1D1 and C2D2 The rigid body to be moved from position 1 to 2 is secured to link 3.
  29. 29. Ken Youssefi UC Berkeley 29 Motion Generation Mechanisms Graphical Solution Two position synthesis (coupler output) with Dyad added. 1 – Select any point B1 on link O2C1. Locate B2. 2 – Choose O6 anywhere on B1B2 extension. 3 – Draw a circle from O6 with radius B1B2/ 2. Mark the intersection with B1B2 extension as A1 and A2.
  30. 30. Ken Youssefi UC Berkeley 30 Motion Generation Mechanisms Graphical Solution Two position synthesis (coupler output) with Dyad added.
  31. 31. Ken Youssefi UC Berkeley 31 Motion Generation Mechanisms Graphical Solution Two position synthesis (rocker output) – C1D1 and C2D2
  32. 32. Ken Youssefi UC Berkeley 32 2 Position Motion – rocker output
  33. 33. Ken Youssefi UC Berkeley 33 Motion Generation Mechanisms Graphical Solution Three position synthesis – C1D1, C2D2 and C3D3 • Draw the link CD in its three desired positions. • Follow the same procedure,draw construction lines, C1C2, C1C3 and C2C3. Same for point D. • Draw three midnormals for each point. • Locate the intersection of the three midnormal, O2 and O4 are the two fixed pivot points.
  34. 34. Ken Youssefi UC Berkeley 34 Motion Generation Mechanisms Graphical Solution Three position synthesis – C1D1, C2D2 and C3D3
  35. 35. Ken Youssefi UC Berkeley 35 3 Position Motion
  36. 36. Ken Youssefi UC Berkeley 36 3 Position Motion
  37. 37. Ken Youssefi UC Berkeley 37 3 Position Motion
  38. 38. Ken Youssefi UC Berkeley 38 Slider-Crank Mechanism In-line slider crank mechanism The mechanism has a stroke B1B2 equal twice the crank length r2. Locations B1 and B2 are called the extreme positions (limiting) of the slider
  39. 39. Ken Youssefi UC Berkeley 39 Slider-Crank Mechanism Offset slider-crank mechanism
  40. 40. Ken Youssefi UC Berkeley 40 Straight line Mechanisms
  41. 41. Ken Youssefi UC Berkeley 41 Straight Line Mechanism
  42. 42. Ken Youssefi UC Berkeley 42 Scotch Yoke Mechanism
  43. 43. Ken Youssefi UC Berkeley 43 Geneva Mechanism
  44. 44. Ken Youssefi UC Berkeley 44 Linear Geneva Mechanism
  45. 45. Ken Youssefi UC Berkeley 45 Ratchet Mechanism
  46. 46. Ken Youssefi UC Berkeley 46 Straight Beam Walking Mechanism
  47. 47. Ken Youssefi UC Berkeley 47
  48. 48. Ken Youssefi UC Berkeley 48 Roller and Flat Follower Cams
  49. 49. Ken Youssefi UC Berkeley 49 Cylindrical Cam Mechanism
  50. 50. Ken Youssefi UC Berkeley 50 Gears – Rack and Pinion
  51. 51. Ken Youssefi UC Berkeley 51 Gears Worm Gear Sets Bevel gears Planetary Gear set
  52. 52. Ken Youssefi UC Berkeley 52 V-8 Engine
  53. 53. Ken Youssefi UC Berkeley 53 Type of Motion and Mechanisms Translation to Translation Most power sources that are readily available today are either of the pure rotational motion type, such as electric motor or hand crank, or of the pure translational type, such as pneumatic or hydraulic cylinder.
  54. 54. Ken Youssefi UC Berkeley 54 Type of Motion and Mechanisms Rotational to Rotational
  55. 55. Ken Youssefi UC Berkeley 55 Type of Motion and Mechanisms Rotation to Translation
  56. 56. Ken Youssefi UC Berkeley 56 References • Mechanism Design, Analysis and Synthesis by Erdman and sander, fourth edition, Prentice-Hall, 2001, • Machines and Mechanisms by Uicker, Pennock and Shigley, third edition, Oxford, 2002. • Machines and Mechanisms by Myszka, Prentice- Hall, 1999

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