1. Linkages
Lesson 4 – Linkages

2. Plan In this lesson we shall discuss Linkages
Four-bar – different types
Slider-crank mechanism
Scotch yoke
Quick return – how to speed up a manufacturing operation
Toggle mechanisms
Joints to transmit torque and motion around a corner
Geneva wheel
Rachet

3. Plan
In this lesson we shall discuss
Linkages

4. Drag-link mechanism
Here’s a picture of a drag-link mechanism that I found on-line

5. Slider-crank mechanism
This mechanism is very important for reciprocating engines, in that it converts the linear motion of the piston into rotational motion that eventually winds up at the wheels
Note: Often images show the slider-crank as a horizontal-bore machine. That is old-fashioned. Usually the bore is vertical or angled slightly off vertical.

6. Aircraft radial engine
An aircraft radial engine is shown in the link below. There you’ll see five cylinders oriented in a plane, the bore of each offset from its neighbor by 72°
Here’s a 7-cylinder radial:

7. Scotch-yoke mechanism
This mechanism turns rotary motion into oscillatory motion
The motion of the follower is harmonic, i.e. a sinusoid
The piston of a slider crank has sinusoidal-like motion, but it is not a true sinusoid
See a video of this at:

8. Quick-return mechanism
The purpose of this mechanism is to have a working stroke that is slow, and then a return stroke that is faster
Thus, in a manufacturing situation, time is save by shortening the return stroke

9. Toggle mechanism
A toggle mechanism is used to generate a large force over a small distance
At right a toggle mechanism is shown in an application for crushing rocks
Another application would be for clamping something:

10. Toggle mechanism
Another application would be for clamping something

11. Universal joint This is a very common component in a drive train
Inner part, the “cross”

12. Constant-velocity (CV) joint
CV joints are commonly used on cars to accommodate the movement of the wheels up and down relative to the fixed rotation of the drive shaft
They have the advantage over U-joints in that the driven shaft stays at a constant velocity, which is not so in a U-joint
The trick here is that these indentations are slots, so the ball can move longitudinally (in direction of shaft axis) as angle between driver and driven shaft changes.

13. Thompson coupling – an improved CV joint
This video shows a Thompson coupling, which avoids many problems of a CV joint:

14. Geneva mechanism
A Geneva wheel or mechanism converts steady, rotational motion into intermittent rotary motion

15. The pendulum bob is down below
Clock escapement mechanism
A clock escapement mechanism is used in conjunction with a pendulum to keep time.
As the pendulum swings back and forth, the anchor alternately stops and releases the escapement wheel.
Anchor
The escapement wheel is driven usually by a weight.
Escapement wheel
See a video of this at:
The pendulum bob is down below

16. Ratchet mechanism This mechanism ensures one-way rotation
Pawl
See a video of this at:
Pawl
Ratchet

17. Other mechanisms
I’ve left off some mechanisms, especially those related to manual drafting, because nowadays most drawing is done on the computer
Also, nowadays with cheap and accurate stepper motors, it is possible to coordinate multi-axis motion or any kind of motion with multi-axis controllers
Things that used to be mechanically linked can now be programmatically linked using stepper motors and electronic controllers

18. End of Lesson 4