Quote:
Originally Posted by kenavt
I've played around with the excellent Excel spreadsheet-simulators on the previous page, but I still have a couple more questions. Namely, in the way Paul proposed of designing a motion profile (the "double filter" scheme), how do the filters work, exactly? I see that the parameters T1 and T2 modify the filters, and I see that the filters' role appears to be to shape the motion profile (defining the acceleration and deceleration especially).
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F1 is a low-pass FIR filter that imposes a rate limit on the input (where the input in this case is a "go full speed ahead" speed command). As a result, an acceleration limit is put on the output. The T1 parameter of F1 is the amount of time it takes to accelerate from 0 to full speed.
F2 is another low-pass FIR filter that imposes a rate limit on its input (which is the output of F1). As a result, a jerk (derivative of acceleration) limit is put on the output. The T2 parameter of F2 is the amount of time it takes to increase acceleration from 0 to the maximum defined by T1.
You could in theory add an F3 or even more successive FIR filters and achieve smoothness down to an arbitrary order.
Here are some examples...
If T1 is equal to 400ms and T2 is equal to 0 (use 1ms in the spreadsheet to avoid divide by zero), you get an acceleration-limited velocity, but there are no limits on the jerk (you immediately go to maximum acceleration).
If T1 is equal to 400ms and T2 is equal to 400ms, it takes the same amount of time to reach the maximum acceleration as velocity, so you get a triangular profile (as soon as you hit maximum acceleration it is immediately time to reduce acceleration)
If T1 is equal to 400ms and T2 is equal to 200ms (or any number 0 < T2 < 400ms), you spend a non-zero amount of time at your maximum acceleration before reducing acceleration.