I want to motorize window blinds such that they cover upto the percentage of window I specify each time.

So, how do I achieve this if every time I roll or unroll the roller tube its outer radius changes?

kumbhrageri:

I am using stepper motor. So I want to calculate the angle of rotation. Or is there any other simple method to implement?

kumbhrageri:

So, how do I achieve this if every time I roll or unroll the roller tube its outer radius changes?

Are you referring to the fact that the roll diameter reduces as the blind pays out? Or are you finding that it does not roll up the same way every time?

If the former I suggest you do some experiments and note the number of steps required for different settings.

...R

Robin2:

Are you referring to the fact that the roll diameter reduces as the blind pays out? Or are you finding that it does not roll up the same way every time?If the former I suggest you do some experiments and note the number of steps required for different settings.

...R

I was talking about the changing diameter

kumbhrageri:

I was talking about the changing diameter

So was I. But I was wondering if your problem is that the diameter changes in an unpredictable way because the blind does not roll up the same each time (I admit that seems unlikely but I imagined you might have already figured out how to deal with regular changes in diameter).

...R

The method I could think of involves a lot of calculations like measurement of final radius, initial radius, number of layers on the roll, etc.

kumbhrageri:

The method I could think of involves a lot of calculations like measurement of final radius, initial radius, number of layers on the roll, etc.

Did you read the 2nd paragraph in Reply #2? Is there some reason why that would not be suitable?

...R

Yes I did read! The reason I mentioned the theoretical method was because you said you assumed I figured how to deal with a constant change. And I think for accurate results, I need to find it experimentally.

Thank you for your inputs.

first, test. even if you do the math, the changing diameter is not going to effect the height very much.

unless you have some very specific needs, a hight difference of a few percent will be unnoticable to the observer.

you know that as the blind rolls up, the circumference will be chaning constantly. but, you assume it will be in steps, with each revolution adding the thickness of the material. at full extension, the circumference will be the smallest, and rolled all the way up, the largest.

since you should have absolution postion, ie: a device to show revolutions, such as an encoder, you can just add or subtract one thickeness for each revolution.

in order to have a place to start, you need the diamter with the blind fully extended, the diameter with it full coiled on the shaft, how many rotations of the shaft. I suspect distance traveled would help for the basic calculations.

however, in the end, I would think that just adding a value for each revolution will suffice for a blind that only has humans observing movement.