8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

1/18

IOT

POLYENGINEERING4-09

MECHANICAL TECHNOLOGY

REVIEW OF MECHANISMS FOR QUIZ

ON TUESDAY 26 MAY 2009

TUE 5/26 - QUIZ ON MECHANISMS, BEGIN TEST REVIEWWED 5/27 - REVIEW LESSON FOR FINAL TEST

THU 5/28 - FINAL TEST (VECTORS , TRIGONOMETRY,

ELECTRICITY, MECHANISMS)

FRI 5/29 - EXTRA CREDIT WORK

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

2/18

IOT

POLYENGINEERING4-09

A 4-bar linkage mechanism has a crank that rotates at a

constant angular speed. The crank is connected to the

coupler which is connected to the follower. The frame does

not move.

crank

couplerfollower

frame

KINEMATICS is the branch of physics thatstudies the motion of a body or a system of

bodies without consideration given to its massor the forces acting on it.

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

3/18

IOT

POLYENGINEERING4-09

A Grashof linkage is a planar four-bar linkage with

S + L < P + Q

where S = length of the shortest link

L = length of longest linkP and Q are the lengths of the two remaining links.

1. Crank-Rocker : a Grashof linkage where the shortest link is the

input link (crank).

2. Double-Rocker: a Grashof linkage where the shortest link is the

floating link (coupler).

3. Rocker-Crank : a Grashof linkage where the shortest link is the

output link (follower).

4. Crank-Crank : a Grashof linkage where the shortest link is the

ground link (frame).

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

4/18

IOT

POLYENGINEERING4-09

1. Crank-Rocker : a Grashof linkage where the shortest link is the

input link (crank).

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

5/18

IOT

POLYENGINEERING4-09

2. Double-Rocker: a Grashof linkage where the shortest link is the

floating link (coupler).

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

6/18

IOT

POLYENGINEERING4-09

4. Crank-Crank : a Grashof linkage where the shortest link is the

ground link (frame).

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

7/18

IOT

POLYENGINEERING4-09

framecrank

couplerfollowerDoor Closer Mechanism

Folding Tableframecrank

couplerfollower

TWO COMMON EXAMPLES OF A 4-BAR MECHANISM

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

8/18

IOT

POLYENGINEERING4-09

Apantograph is a mechanism that is

used to create a drawing that is larger

or smaller than an original drawing.

Thepantograph simulation below creates a drawing that

is larger than the original drawing.

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

9/18

IOT

POLYENGINEERING4-09

Aparallel bar mechanism is a mechanism that

retains parallelism in its members.

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

10/18

IOT

POLYENGINEERING4-09

Two more examples of theparallel bar mechanism

are shown below. On the left is a scissors lift

which is used in the construction industry. On the

right is a scissors jack which is used when

changing an automobile tire.

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

11/18

IOT

POLYENGINEERING4-09

A straight line mechanism is a mechanism that is

used to create straight lines. The examples below

are Peaucellier mechanisms.

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

12/18

IOT

POLYENGINEERING4-09

Two more examples of a straight line mechanism are

shown below. These are the Tchebicheff mechanism.

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

13/18

IOT

POLYENGINEERING4-09

Another example of a straight line mechanism is

shown below. This is the Watt mechanism, invented

by James Watt of steam engine fame. If you look

closely, you will see that the path deviates from astraight line at the top and the bottom of motion.

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

14/18

IOT

POLYENGINEERING4-09

There is no end to the ingenuity of engineers who invent

various mechanisms for desired outcomes.

This is a CAM-FOLLOWER. The cam is red. As the cam

rotates, it causes the flat follower to rise and fall.

Thus, rotational motion has been converted to linear

motion.

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

15/18

IOT

POLYENGINEERING4-09

This is a SCOTCH YOKE. As the yellow knob rotates, itcauses the light gray yoke to move side to side.

Thus, rotational motion has been converted to linear

motion.

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

16/18

IOT

POLYENGINEERING4-09

This is a GENEVA MECHANISM. As the small black knob

rotates at a constant rate, it causes the dark gray mechanism

to rotate one-sixth of a turn and stop, rotate one-sixth of a

turn and stop, etc. The Geneva mechanism on the right side

causes one-fourth of a turn movements.

Rotational motion has been converted to sporadic rotational

motion.

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

17/18

IOT

POLYENGINEERING4-09

This is a PISTON & CRANK. As the crankshaft on the right

rotates at a constant rate, it causes the light blue connecting

rod to push and pull on the piston (two-tone gray).

Thus, rotational motion has been converted to reciprocating

motion.

8/2/2019 4-09 IOT - Review of Mechanisms _Fri May 22

18/18

IOT

POLY ENGINEERING4-09

TUE 5/26 - QUIZ ON MECHANISMS, BEGIN TEST REVIEWWED 5/27 - REVIEW LESSON FOR FINAL TEST

THU 5/28 - FINAL TEST (VECTORS , TRIGONOMETRY,

ELECTRICITY, MECHANISMS)

FRI 5/29 - EXTRA CREDIT WORK

REMINDER