Scissor Jack(How does it really work?)

[cadstudent]

I am designing a Scissor Jack. I have been doing a lot of investigating. I would like to ask by what means of design are there already for transmitting the screw thread to actual lift in the arms. I have seen the use of a collar being used. I would like to know how that exactly works please. (Is the threaded collar connected to one end of the threaded screw rod. Preventing the screw rod from disconnecting. At the end is a nut. Thus allowing when turned by means of say a "z" shaped crank, obtaining lift. Also my design does not have gear teeth on the end of my four "C" shaped Support members. Does that matter in actual lift? As well they do not close into each other.

http://www.scribd.com/koanakist/d/23191468-Design-of-the-Toggle-Jack

I need this design explained regarding how this collar works please.

Regards & Thanks

A Student

 

[OldEngr63]

The threaded collar you speak of is nothing more than an nut, incorporated into the pin at one end of the horizontal extremes, while there is a simple collar (no thread) as a bearing at the other horizontal extreme. It is not absolutely essential that the two lower levers be geared together, but it is a good design practice for safety sake.

The whole idea is that by pulling the two extreme points together, the upper and lower parallelograms are forced to gain height due to shortening their common base (the screw length).

Be sure you work through the kinematics first and understand the motion thoroughly. Then do an analysis of the forces so that you can find the joint forces and thus the link forces for design purposes. Then you will be in a position to do the design.