Help Math reminder / calculating encoder cnts per unit

[drbitboy]

I would like to see an example. Your picture of a scissors lift is not linear. Close but not quite.

Oh for Pete's sake, try reading. That post with picture of a scissors lift was me pulling teeth by wondering if it was more complex than a simple right triangle, actuator as hypotenuse, system.

I hope you would agree that, if

• the base leg of the right triangle is horizontal and fixed in length ("a" in my model), and
• the vertical leg of the right triangle is the line along which the platform moves, and the height of the platform, measured from the base leg to the top of the actuator, is the variable length ("H" in my model), and
• the hypotenuse of the right triangle is the linear actuator, connected to the other end of the base leg and the top of the vertical leg, and is of controlled, variable length ("L = m * X + k" in my model, where X is the encoder count value, and m and k are the coefficients of the linear model),

then the angle of the actuator (hypotenuse) will change with changing X values?

 

[drbitboy]

Your picture of a scissors lift is not linear. Close but not quite.

Nobody is saying the scissors lift in that picture has a linear characteristic.

Neither is anyone saying that it is related to OP's system (which we still don't know much about, and they have not come back with any info).

By simple inspection it is obvious that, for it to have a linear characteristic, the actuators would need to be, and would remain, vertical.

The only differences in the models between that picture, and the fixed right triangle that we have been assuming the OP has, are that

• the cosine term can be non-zero in the picture, but in the fixed right triangle the cosine term is 0 and ignored.
• how the height is measured - for both it is linear with the vertical extent of the actuator i.e. it is non-linear with the length of the actuator.

 

[drbitboy]

I would like to see an example.

Provided more than a dozen posts ago: https://www.plctalk.net/qanda/showthread.php?p=954566#post954566

 

[Peter Nachtwey]

Yes you have an example
I have solution.

 

[drbitboy]

I have solution.

1) I doubt that. You don't even know OP's system; none of us do. I'm not saying you could not provide a solution, just that we don't have enough information to definitively state a solution.

2) You may have solution, but you have provided diddly; all OP has asked for is non-linear count per inch. OP has not explicitly requested advanced motion control.

3) I provided possible solution* to OP in Post #5, including requested count per inch formula, which you have not provided. @lfe also suggested another approach to same result. It would be great if someone had time, ability, and inclination to validate my math (or correct it).

Yes you have an example

4) I referenced example to you because is all you asked for.

* Solution assumes OP's lift moves vertically and based on right triangle with horizontal base; if that is not case and actual geometry of OP's system is unknown, then no one can provide OP with anything.