L6470: max acceleration register too low

[markmunte9]

Posted on November 12, 2011 at 20:20

Hello, we have been testing the L6470 and are quite pleased with it. Very simple to use IC.

But for fast movements the max acceleration value of 

59.590 step/s2 is just too low.

Small stepper motors (1.5 Amp) can easily be accelerated at 800.000 steps/s2.Is there any trick around this limitation?Regardsmark

[Enrico Poli]

Posted on November 14, 2011 at 08:37

Dear Mark,

for this kind of stepper motors you can use the infinite acceleration mode (see section 6.6.1 of the datasheet).In this way you can directly impose the motor speed skipping the acceleration and deceleration phases.Best regardsEnrico

[markmunte9]

Posted on November 14, 2011 at 12:32

Hello Enrico,

thanks for the reply, but I don't see how infinite acceleration can help.For example: we are using a 0.9degree stepper with 0.22 Nm holding torque, max 1.5A, very little load. Our aim is to move 18 degrees - 20 full steps - below 15ms.This can be easily done with a profile with start velocity 100 steps/s, max velocity 3100 steps/s, acceleration/deceleration 800.000 steps/s^2. The motor has enough torque to set the start velocity to higher values, say 800 steps/s, but above 1200 steps/s the initial acceleration is just to high and the motor loses steps. My understanding of infinite acceleration is that it has pretty much the same effect as a very high min velocity, it leads to a quite high instantaneous acceleration, one that can easily exceed motor torque and lead to step loss.Probably 90% of stepper motors till 3A can easily exceed the ICs max acceleration of 

59.590 step/s^2.

Best regardsMark