Mechanism Machines are mechanical devices used to accomplish

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 and joints. Ken Youssefi Mechanical Engineering Dept. 1

Example of Mechanism Can crusher Simple press Rear-window wiper Ken Youssefi Mechanical Engineering Dept. 2

Example of Mechanisms Moves packages from an assembly bench to a conveyor Microwave carrier to assist people on wheelchair Lift platform Ken Youssefi Mechanical Engineering Dept. 3

Example of Mechanisms Lift platform Front loader Device to close the top flap of boxes Ken Youssefi Mechanical Engineering Dept. 4

Stair climbing mechanism Example of Mechanisms A box that turns itself off Airplane landing gear mechanism Ken Youssefi Mechanical Engineering Dept. 5

Example of Mechanisms Rowing type exercise machine Conceptual design for an exercise machine Ken Youssefi Mechanical Engineering Dept. 6

Example of Mechanisms Ken Youssefi Mechanical Engineering Dept. 7

Example of Mechanisms Extension position Flexed position Six-bar linkage prosthetic knee mechanism Ken Youssefi Mechanical Engineering Dept. 8

Four-Bar Linkage Ken Youssefi Mechanical Engineering Dept. 9

Four-Bar Linkage Categories Case I shortest link + longest link < summation of the other two links s+l < p+q a) Shortest link is the driver with either one of the intermediate 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) Ken Youssefi Mechanical Engineering Dept. 10

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. Ken Youssefi Mechanical Engineering Dept. 11

Four-Bar Linkage Categories Case I shortest link + longest link < summation of the other two links 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 Ken Youssefi Mechanical Engineering Dept. 12

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). Ken Youssefi Mechanical Engineering Dept. 13

4 -Bar mechanisms Ken Youssefi Mechanical Engineering Dept. 14

4 -Bar mechanisms S+l>p+q 4 double rocker mechanisms Ken Youssefi Mechanical Engineering Dept. 15

The Slider-Crank Mechanism Input link, crank Coupler link, connecting rod Output link, piston (slider) Ken Youssefi Mechanical Engineering Dept. 16

Slider-Crank Mechanism Offset slider-crank mechanism Ken Youssefi Mechanical Engineering Dept. 17

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 In-line slider crank mechanism Ken Youssefi Mechanical Engineering Dept. 18

The Slider-Crank Mechanism Ken Youssefi Mechanical Engineering Dept. 19

Slider-Crank Mechanism - Inversion Ken Youssefi Mechanical Engineering Dept. 20

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 Ken Youssefi Mechanical Engineering Dept. 21

Mechanism Categories Function Generation Mechanisms A four-bar drive linkage for a lawn sprinkler Ken Youssefi Mechanical Engineering Dept. 22

Mechanism Categories Function Generation Mechanisms A four-bar function generation mechanism to lower an attic stairway. A four-bar function generation mechanism to operate an artificial hand used for gripping. Ken Youssefi Mechanical Engineering Dept. 23

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 Ken Youssefi Mechanical Engineering Dept. 24

Mechanism Categories Motion Generation Mechanisms Four-bar automobile hood linkage design Ken Youssefi Mechanical Engineering Dept. 25

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 Ken Youssefi Mechanical Engineering Dept. 26

Mechanism Categories Path Generation Mechanisms Ken Youssefi A four-bar path generation mechanism to guide a thread in an automatic sewing machine A four-bar path generation mechanism as part of an arm-actuated propulsion system for a wheelchair Mechanical Engineering Dept. 27

Primary Joints Ken Youssefi Mechanical Engineering Dept. 28

Higher Order Joints Ken Youssefi Mechanical Engineering Dept. 29

Motion Generation Mechanisms Rotating a monitor into a storage position Ken Youssefi Moving a storage bin from an accessible position to a stored position Mechanical Engineering Dept. 30

Motion Generation Mechanisms Moving a trash pan from the floor up over a trash bin and into a dump position Ken Youssefi Mechanical Engineering Dept. Lifting a boat out of water 31

Straight line Mechanisms Ken Youssefi Mechanical Engineering Dept. 32

Straight line Mechanisms Ken Youssefi Mechanical Engineering Dept. 33

Straight Line Mechanism Ken Youssefi Mechanical Engineering Dept. 34

Straight Line Mechanism - Application Straight line mechanism with dwell Ken Youssefi Mechanical Engineering Dept. 35

Scotch Yoke Mechanism Example – car window Ken Youssefi Mechanical Engineering Dept. 36

Geneva Mechanism Ken Youssefi Mechanical Engineering Dept. 37

Linear Geneva Mechanism Ken Youssefi Mechanical Engineering Dept. 38

Ratchet Mechanism Ken Youssefi Mechanical Engineering Dept. 39

Straight Beam Walking Mechanism Ken Youssefi Mechanical Engineering Dept. 40

Ken Youssefi Mechanical Engineering Dept. 41

Roller and Flat Follower Cams Ken Youssefi Mechanical Engineering Dept. 42

Cylindrical Cam Mechanism Ken Youssefi Mechanical Engineering Dept. 43

Gears – Rack and Pinion Ken Youssefi Mechanical Engineering Dept. 44

Gears Worm Gear Sets Ken Youssefi Bevel gears Mechanical Engineering Dept. Planetary Gear set 45

V-8 Engine Ken Youssefi Mechanical Engineering Dept. 46

Type of Motion and Mechanisms 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. Translation to Translation Ken Youssefi Mechanical Engineering Dept. 47

Type of Motion and Mechanisms Rotational to Rotational Ken Youssefi Mechanical Engineering Dept. 48

Type of Motion and Mechanisms Rotation to Translation Ken Youssefi Mechanical Engineering Dept. 49

References • Mechanism Design, Analysis and Synthesis by Erdman and sander, fourth edition, Prentice-Hall, 2003, • Machines and Mechanisms by Uicker, Pennock and Shigley, third edition, Oxford, 2002. • Machines and Mechanisms by Myszka, Prentice. Hall, 2003 Ken Youssefi Mechanical Engineering Dept. 50