OLD UHU POSITION ERROR

[dfv]

Hi, i´m testing my mill (bf20 vario) with servos of 40V with the current limit set to 2.5A, the encoders have 90 lines, the controller is the old uhu board and i didn´t modificate the inicial PID parameters. After finding errors in some mechanized pieces i began to investigate where is the problem and i discovered the next thing:
-When the motor works without load it works perfect there is no position error and it works smoothly, the problems appear when the motor works under load because it works not smoothly at low speeds and always has position error (at low and at high speeds), in the board doesn´t appear the signal error.

I don´t know where is the problem? any suggestion?

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[H.O]

Sounds like you need to increase the gains. The following error trip limit is set to 2000 by default (IIRC) so with your 90 line encoder the motor shaft would have to be 2000° (5.5 revolutions) off position before the drice would error which is probably why you don't see the error signal.

There will always be a small a following error when the motor runs. The higher the speed is the larger the error, generally. Raising the H-gain greatly affects the amount of following error you get when the motor is running.

If the motor never reaches it target, ie. you have a remaineng error even when the motorshaft stops you need to increase the I-gain.

Also, if the motor is rated at 2.5A continous current you may want to raise the current limit to get better acceleration out of it. If it's rated continous current is less than 2.5A then perhaps the motor is too small for that machine. I'm not saying that is the case - I'm just thinking out loud here. Do you have any references to other BF20 builders, what size of motor are they using?

/Henrik.

[dfv]

ok thank you very much, i will try to tune the uhu increasing the I-gain to see if the motor reachs the target position under load. I will tell you the results.