Linkages Lesson 4 – Linkages

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

Plan In this lesson we shall discuss Linkages

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

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.

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° https://www.google.com/url?sa=i&source=images&cd=&ved=2ahUKEwjptqGjieLkAhWBTt8KHSVaCgcQjRx6BAgBEAQ&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FRadial_engine&psig=AOvVaw0pnfTSkQMkt1Ijmz4YQtnG&ust=1569160688385287 Here’s a 7-cylinder radial: https://www.google.com/search?q=radial+engine+images&rlz=1C1CHBF_enUS814US814&sxsrf=ACYBGNSfoVTPRa1fzTfRMKuVKJfQhNuTwA:1569074275021&tbm=isch&source=iu&ictx=1&fir=zfHt0JwJSpH3uM%253A%252CedFEExRiLEwE7M%252C_&vet=1&usg=AI4_-kQRxEksPzoK0TtZ4bextb77lcdBkg&sa=X&ved=2ahUKEwiIuKeWieLkAhWImOAKHS77BpYQ9QEwAHoECAYQBA#imgrc=0AwtbG-yMvWhJM:&vet=1

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: https://en.wikipedia.org/wiki/Scotch_yoke

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

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:

Toggle mechanism Another application would be for clamping something

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

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.

Thompson coupling – an improved CV joint This video shows a Thompson coupling, which avoids many problems of a CV joint: https://www.youtube.com/watch?v=UEvaOg7glKk

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

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 https://en.wikipedia.org/wiki/Escapement

Ratchet mechanism This mechanism ensures one-way rotation Pawl See a video of this at: Pawl https://www.youtube.com/watch?v=EpVPG2fZrHE Ratchet

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

End of Lesson 4