Mechanical Engineering Dept. 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. Ken Youssefi Mechanical Engineering Dept.

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

Mechanical Engineering Dept. Four-Bar Linkage θ3 θ2 θ4 Ken Youssefi Mechanical Engineering Dept.

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

Mechanical Engineering Dept. Example of Mechanism Can crusher 4 Simple press 5 3 4 2 1 6 2 3 1 Rear-window wiper 4 3 2 1 Ken Youssefi Mechanical Engineering Dept.

Mechanical Engineering Dept. Example of Mechanisms Moves packages from an assembly bench to a conveyor 6 5 4 2 3 Six bar 1 Microwave carrier to assist people on wheelchair Six bar 5 3 4 2 1 6 Lift platform Six bar 5 3 4 2 1 6 Ken Youssefi Mechanical Engineering Dept.

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

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

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

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

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

Four-Bar Linkage Categories l = longest link s = longest link p and q = intermediate links Case I shortest link + longest link < summation of the other two links 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 Ken Youssefi Mechanical Engineering Dept.

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

Four-Bar Linkage Categories Case I shortest link + longest link < summation of the other two links 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.

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.

Mechanical Engineering Dept. 4-Bar mechanisms Case I: s + l < p + q Ken Youssefi Mechanical Engineering Dept.

Mechanical Engineering Dept. 4-Bar mechanisms S + l > p + q 4 double rocker mechanisms 8/26 mon Ken Youssefi Mechanical Engineering Dept.

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

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

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

The Slider-Crank Mechanism Ken Youssefi Mechanical Engineering Dept.

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

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 Ken Youssefi Mechanical Engineering Dept.

Mechanical Engineering Dept. 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. 2 1 4 3 A four-bar hand actuated wheelchair brake mechanism Ken Youssefi Mechanical Engineering Dept.

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

Mechanical Engineering Dept. 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.

Mechanical Engineering Dept. Mechanism Categories Motion Generation Mechanisms In motion generation, the entire motion of the coupler link (3) is of interest (rigid body guidance). 2 Moving joints 3 Fixed pivot points 4 New Rollerblade brake system Ken Youssefi Mechanical Engineering Dept.

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

Mechanical Engineering Dept. Mechanism Categories Microwave carrier to assist people on wheelchair Six bar 5 3 4 2 1 6 Lift platform Six bar 5 3 4 2 1 6 Ken Youssefi Mechanical Engineering Dept.

Mechanical Engineering Dept. 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.

Mechanical Engineering Dept. Mechanism Categories Path Generation Mechanisms with timing 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 Ken Youssefi Mechanical Engineering Dept.

Primary Joints Lower Order Joints Ken Youssefi Mechanical Engineering Dept.

Mechanical Engineering Dept. Higher Order Joints Ken Youssefi Mechanical Engineering Dept.

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

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 Ken Youssefi Mechanical Engineering Dept.

Straight line Mechanisms Ken Youssefi Mechanical Engineering Dept.

Straight line Mechanisms Ken Youssefi Mechanical Engineering Dept.

Straight Line Mechanism Ken Youssefi Mechanical Engineering Dept.

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

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

Mechanical Engineering Dept. Geneva Mechanism Ken Youssefi Mechanical Engineering Dept.

Linear Geneva Mechanism Ken Youssefi Mechanical Engineering Dept.

Mechanical Engineering Dept. Ratchet Mechanism Ken Youssefi Mechanical Engineering Dept.

Straight Beam Walking Mechanism Ken Youssefi Mechanical Engineering Dept.

Mechanical Engineering Dept. Ken Youssefi Mechanical Engineering Dept.

Roller and Flat Follower Cams Ken Youssefi Mechanical Engineering Dept.

Cylindrical Cam Mechanism Ken Youssefi Mechanical Engineering Dept.

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

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

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

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.

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

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

Mechanical Engineering Dept. 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 Ken Youssefi Mechanical Engineering Dept.