07-08-2012, 04:59 PM
POWER TRANSMISSION
1POWER TRANSMISSION.ppt (Size: 6.07 MB / Downloads: 294)
ROTARY TO LINEAR
motion convertion is concerned with taking the rotational motion and torque from an actguator and producing a linear motion and force on the output
Lead screw
Rack and pinion
Slider cranks
Cams
Lead screws
Screw is fixed with its ends free to rotate: as the screw is turned, the nut moves along the shaft with the payload attached
A rotary displacement of the input shaft θ1 causes a linear motion of the payload x
X= θ·P (P pitch of the screw mm/rev)
This equation may be differentiated any number of times in order to obtain the relationship among linear velocity, acceleration and jerk and rotational relative quantities
How a load on th output is seen by the input? i.e. Equivalent torque-inertia system
For linear motion of the payload mass the kinetic energy is: Ek = ½ MVL²
The corresponding kinetic energy of a torque-inertia system Ek = ½ Jeqω²
Solving for the inertia, after relating rotary and linear velocity with the pitch
SLIDER CRANKS
The slider-crank mechanism is an extremely cost-effective means of converting rotary to linear motion.
The crank portion is the wheel that rotates about its center and has a rod of fixed lenght mounted to a point on its circumference; the other end of the connecting rod is attached to a linear stage which is constrained to move in only one dimension on a relatively frictionless surface.
At both its location the connecting rod is free to rotate thus the angle formed with the horizontal will change as a function of the disk’s position.
As the disk travels from 0 to 180° in the counterclockwise direction, the linear stage moves a distance equal to 2r: if the disk continues to travle from 180° back to 0° - still in counterclockwise direction, the load will move in the opposite direction over exactly the same linear distance.