Four Bar Geometry Lift Mechanism design for maximum articulation

[MMcCawley]

I'm brainstorming different potential layouts to lift a load from the ground to a platform (see attached). In this particular layout, the mechanism would see more than 180 degrees of articulation and as a result the four-bar linkage becomes unstable when the four pivot axes become coplanar (bottom left image). I'm curious if anything has been done from a design perspective to mitigate this or is it just an inherent limitation of the four-bar linkage design? The attached picture should help to detail the problem.

 

[desertfox]

Hi

Where is the driver for this linkage? Motor? Cylinder or ?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[MMcCawley]

It would still need to be determined. Likely a cylinder with some sort of linkage to provide control over the 210 or so degrees.

 

[desertfox]

Hi

Well my thinking is that depending on where the prime mover is positioned might have a bearing on the linkages stability, four bar linkages can move through 360 degrees ( reciprocating cylinder for example). You need to do a loci plot of the mechanism you have with the prime mover included.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[TheTick]

Are you familiar with relative pole method for 4-bar design? Works great with CAD sketches. You can try a full range of possibile solutions based on two positions of a 4-bar linkage.

 

[drawoh]

MMcCawley,

What are you trying to accomplish? Minimum motor power and torque? Minimum current and power consumption? Accuracy?

Pick an arrangement. Do the analysis. Study the results. You will learn something and you will do better on the next try. This is what spreadsheets are for.

--
JHG

 

[rb1957]

I wonder if you'll need two drives, with the links moving through more than 180deg ?

How does the upper link travel from the initial position to the final position ? (answering my own question … 'cause the grey lug is outbd of the load, the link is outbd of the grey lug, the blur (fixed) lug is outbd of the link) … and the double link is outbd of all of this ??
which brings back to what are the constraints ? Possibly now, none, just get a mechanism that'll work, then we'll add constraints.

another day in paradise, or is paradise one day closer ?