If we dig deep enough, i guess something technically correct is something just a little bit different:Quote
Dala.horse
Ohms law never plays a direct role in deciding the current through the motor. The chopper circuits always limits the current to the set level.
"Ohms law never plays a direct role in deciding the peak current through the motor. The chopper circuits always limits the current to the peak set level."
Why it matters, because if the driver would just leave things go naturally, then the current would eventually settle at the value of I(final)=V/R. This means the V/R is the final point in the *rise time formula*. The rise time formula is tought i believe in first year of any EE class or something like that. Ok, so the rise time formula can be in several forms, here i would put it like Fcurrent(t) = initial value * e^-t/tau + final value * (1 - e^-t/tau) , and we can set the initial value to zero then only the second part remains. So the Fcurrent(time) = V/R * (1 - e^-time/tau), where tau is the time constant ofc. This shows current as continuous function of time. This is the function which will tell us current=.... for any point of time, and in reverse will tell how many nanoseconds it takes for the current to grow to 1A or 2A or w/e we set the peak or limit. Put this in an math software like wxmaxima or even a spreadsheet, and see how much time it takes to get to 1A with different values of V/R. So V/R matters that way, because a high value of V/R will get at 1A in short time of nanoseconds, while a small value of V/R will need much much more time to get to same set point. And we are interested to get to 1A as fast as possible <=> e.g. to energize the coils as fast as possible.
What is unrelated to V/R, is the peak, that is simply something we manually set. Ofc that controlling the peak means we sort of control the average, this is the purpose. But to say that ohms law does not apply or that there is a region that is "outside" of ohms law - anybody with an elementary course in electronics can not say that. Imagine that there was a time when ppls only knew about current and voltage. And then a guy came and introduced a totally knew concept, it named it resistance and he said this resistance = V/I. At first didnt belived him, but ultimately ppls accepted this new concept of "resistance". So ohms law is not just a law, its much more, its the very definition of resistance. Without ohms law, we count not even measure the resistance of the coil, we could not have resistance as a concept. Probably we could not do anything and we could not understand anything without the concept of resistance and hence without ohms law. So its not a question if ohms law is there or not, the question is only how deep you need to dig for it, coz at the lowest level its always there, one way or another.
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Dala.horse
The drivers in printers are mixed analogue/digital/mechanical control systems with feedback. Ohms law is never used to describe such systems.
The fact that is not used to describe something, does not mean ohms law is not there. It just means the explanation is one abstraction layer above.
I guess its like that because the ones reading the subject are supposed to already know and understand things like ohms law, rise time formulas, inductor element law, and things like that, which again are the basics of ee. Then it does suffice to say we get an average current, and we deal with this average current and thats all. And there is no need to get too deep into the matter of exactly how that average current is obtained, which is a separate matter to itself, not specific to a certain system, but rather something too generic to be repeated over and over. Talking about same thing at different abstraction levels is confusing, and sometimes a thing that is true at some level turns out to be false/different at another level. Or sometimes its just semantics. But anyway the abstraction process is a tool we need today, because how things grow in complexity. Anyhow, its wise to just be aware these abstractions exist and sometimes they can have their "traps" or contexts or at very least their semantics.