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Ken Youssefi Mechanical Engineering Dept. 1 Mechanism Machines are mechanical devices used to accomplish work. A mechanism is a heart of a machine. It.

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Presentation on theme: "Ken Youssefi Mechanical Engineering Dept. 1 Mechanism Machines are mechanical devices used to accomplish work. A mechanism is a heart of a machine. It."— Presentation transcript:

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2 Ken Youssefi Mechanical Engineering Dept. 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 and/or force in a predetermined fashion. Mechanism consists of linkages (rigid bars, gears, belts & pulleys, chains & sprockets and cams) and joints.

3 Mechanism Synthesis and Analysis Synthesis – design a mechanism to perform a desired function Analysis – given a mechanism, perform kinematics and kinetics analysis Graphical techniques Analytical methods

4 Ken Youssefi Mechanical Engineering Dept. 3 Four-Bar Linkage θ2θ2 θ3θ3 θ4θ4

5 Ken Youssefi Mechanical Engineering Dept. 4 The Slider-Crank Mechanism Input link, crank Coupler link, connecting rod Output link, piston (slider) Member 4 is converted to a slider

6 Ken Youssefi Mechanical Engineering Dept. 5 Example of Mechanism Can crusher Simple press Rear-window wiper

7 Ken Youssefi Mechanical Engineering Dept. 6 Example of Mechanisms Moves packages from an assembly bench to a conveyor Six bar Lift platform Six bar Microwave carrier to assist people on wheelchair Six bar

8 Ken Youssefi Mechanical Engineering Dept. 7 Example of Mechanisms Lift platform Front loader Device to close the top flap of boxes

9 Ken Youssefi Mechanical Engineering Dept. 8 Example of Mechanisms Stair climbing mechanism A box that turns itself off Airplane landing gear mechanism

10 Ken Youssefi Mechanical Engineering Dept. 9 Example of Mechanisms Conceptual design for an exercise machine Rowing type exercise machine

11 Ken Youssefi Mechanical Engineering Dept. 10 Example of Mechanisms 6-Bar mechanism, automatic spoiler

12 Ken Youssefi Mechanical Engineering Dept. 11 Example of Mechanisms Six-bar linkage prosthetic knee mechanism Extension position Flexed position

13 Ken Youssefi Mechanical Engineering Dept. 12 Four-Bar Linkage Categories Case I shortest link + longest link < summation of the other two links a)Shortest link is the driver with either one of the adjacent links as the ground link (fixed). The result is two different types of crank-rocker mechanisms, input link rotates 360 (crank) and output link oscillates (rocker) fixed l = longest link p and q = intermediate links s = longest link

14 Ken Youssefi Mechanical Engineering Dept. 13 Four-Bar Linkage Categories Case I shortest link + longest link < summation of the other two links b)Shortest link is fixed. The result is a double-crank mechanism. Both, input and output links rotate 360.

15 Ken Youssefi Mechanical Engineering Dept. 14 Four-Bar Linkage Categories c)The longest link is fixed and either one of the intermediate links is the driver. The result is a double-rocker mechanism. Both, input and output links oscillate. Grashof condition – one link rotates 360 Case I shortest link + longest link < summation of the other two links

16 Ken Youssefi Mechanical Engineering Dept. 15 Four-Bar Linkage Categories Case II shortest link + longest link > summation of the other two links There are four possible mechanisms depending on which link is fixed. All mechanisms are double-rockers. Case III shortest link + longest link = summation of the other two links Same mechanisms as in case I with the addition of a branching point (all links become collinear).

17 Ken Youssefi Mechanical Engineering Dept Bar mechanisms Case I: s + l < p + q

18 Ken Youssefi Mechanical Engineering Dept Bar mechanisms S + l > p + q 4 double rocker mechanisms

19 Ken Youssefi Mechanical Engineering Dept. 18 The Slider-Crank Mechanism Input link, crank Coupler link, connecting rod Output link, piston (slider) Member 4 is converted to a slider

20 Ken Youssefi Mechanical Engineering Dept. 19 Slider-Crank Mechanism Offset slider-crank mechanism

21 Ken Youssefi Mechanical Engineering Dept. 20 Slider-Crank Mechanism In-line slider crank mechanism The mechanism has a stroke B 1 B 2 equal twice the crank length r 2. Locations B 1 and B 2 are called the extreme positions (limiting) of the slider

22 Ken Youssefi Mechanical Engineering Dept. 21 The Slider-Crank Mechanism

23 Ken Youssefi Mechanical Engineering Dept. 22 Slider-Crank Mechanism - Inversion

24 Ken Youssefi Mechanical Engineering Dept. 23 Categories of Mechanisms  Function generation mechanisms Output is a specified function of input  Motion generation mechanisms The orientation of the object is important, rigid body guidance  Path generation mechanisms A point on a link moves on a specified path

25 Ken Youssefi Mechanical Engineering Dept. 24 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

26 Ken Youssefi Mechanical Engineering Dept. 25 Mechanism Categories Function Generation Mechanisms A four-bar linkage for a lawn sprinkler

27 Ken Youssefi Mechanical Engineering Dept. 26 Mechanism Categories Function Generation Mechanisms A four-bar function generation mechanism to operate an artificial hand used for gripping. A four-bar function generation mechanism to lower an attic stairway.

28 Ken Youssefi Mechanical Engineering Dept. 27 Mechanism Categories Motion Generation Mechanisms In motion generation, the entire motion of the coupler link (3) is of interest (rigid body guidance). New Rollerblade brake system Fixed pivot points Moving joints

29 Ken Youssefi Mechanical Engineering Dept. 28 Mechanism Categories Motion Generation Mechanisms Four-bar automobile hood linkage design

30 Mechanism Categories Ken Youssefi Mechanical Engineering Dept. 29 Lift platform Six bar Microwave carrier to assist people on wheelchair Six bar

31 Ken Youssefi Mechanical Engineering Dept. 30 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

32 Ken Youssefi Mechanical Engineering Dept. 31 Mechanism Categories Path Generation Mechanisms with timing A four-bar path generation mechanism as part of an arm-actuated propulsion system for a wheelchair A four-bar path generation mechanism to guide a thread in an automatic sewing machine

33 Ken Youssefi Mechanical Engineering Dept. 32 Primary Joints Lower Order Joints

34 Ken Youssefi Mechanical Engineering Dept. 33 Higher Order Joints

35 Ken Youssefi Mechanical Engineering Dept. 34 Motion Generation Mechanisms Rotating an object into a storage position Moving a storage bin from an accessible position to a stored position

36 Ken Youssefi Mechanical Engineering Dept. 35 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

37 Ken Youssefi Mechanical Engineering Dept. 36 Straight line Mechanisms

38 Ken Youssefi Mechanical Engineering Dept. 37 Straight line Mechanisms

39 Ken Youssefi Mechanical Engineering Dept. 38 Straight Line Mechanism

40 Ken Youssefi Mechanical Engineering Dept. 39 Straight Line Mechanism - Application Straight line mechanism with dwell

41 Ken Youssefi Mechanical Engineering Dept. 40 Scotch Yoke Mechanism Example – car window

42 Ken Youssefi Mechanical Engineering Dept. 41 Geneva Mechanism

43 Ken Youssefi Mechanical Engineering Dept. 42 Linear Geneva Mechanism

44 Ken Youssefi Mechanical Engineering Dept. 43 Ratchet Mechanism

45 Ken Youssefi Mechanical Engineering Dept. 44 Straight Beam Walking Mechanism

46 Ken Youssefi Mechanical Engineering Dept. 45

47 Ken Youssefi Mechanical Engineering Dept. 46 Roller and Flat Follower Cams

48 Ken Youssefi Mechanical Engineering Dept. 47 Cylindrical Cam Mechanism

49 Ken Youssefi Mechanical Engineering Dept. 48 Gears – Rack and Pinion

50 Ken Youssefi Mechanical Engineering Dept. 49 Gears Worm Gear SetsBevel gearsPlanetary Gear set

51 Ken Youssefi Mechanical Engineering Dept. 50 V-8 Engine

52 Ken Youssefi Mechanical Engineering Dept. 51 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, or linear actuators.

53 Ken Youssefi Mechanical Engineering Dept. 52 Type of Motion and Mechanisms Rotational to Rotational

54 Ken Youssefi Mechanical Engineering Dept. 53 Type of Motion and Mechanisms Rotation to Translation

55 Ken Youssefi Mechanical Engineering Dept. 54 References Mechanism Design, Analysis and Synthesis by Erdman and sander, fourth edition, Prentice-Hall, Machines and Mechanisms by Uicker, Pennock and Shigley, third edition, Oxford Machines and Mechanisms by Myszka, Prentice- Hall


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