Stuart Stevenson wrote: > Gentlemen, > The servo amps on the Enshu have different accel/decel shapes. The > PID.output trace has a sharp corner to it. The trace raises a little and > then turns almost straight up. The decel trace is MUCH more rounded. Does > this sound like an amplifier problem? > Not necessarily. It may just be a symptom of friction. During acceleration, the motor is not only accelerating the mass, it is also fighting the friction of the slide, both have the same mathematical sign. On deceleration, it must fight the mass of the table, which exactly mirrors the accel condition, BUT the friction is now of opposite sign, and is HELPING the deceleration. So, you can't perfectly optimize FF2 to cover both conditions.
I wouldn't look at the PID.output, but just at following error, and set FF2 to balance the error of the two situations. If you have large discontinuities at the accel/decel time, then you may have to reduce acceleration in the .ini file, you may be asking for too much accel. > I am thinking it would be possible to convert this Fanuc amp to a simple > amp by fooling the tach feedback. This servo amp accepts the encoder > feedback on two terminals and converts these two signals into a tach voltage > for comparison to the velocity signal. Would it be possible to do one of two > things to convert it to a simple amp with no tuning to the motor. > I think the best way would be to find where the chip ouputs the matching > tach voltage and connect the velocity signal voltage at that point. The amp > would think the motor is following the signal perfectly and require no > output adjustment. > Well, I happen to think a real velocity servo amp is just about unbeatable. It does require some more tuning than some other systems, but can be expected to perform better under a wide variety of conditions. > or > I could use an ADC to accept the velocity signal and generate an encoder > pulse to match what would be seen as feedback from the motor. > Either way this feedback would be perfectly matched to the input. > EMC2's tuning would then have complete and total control of the servo > motor (axis motion) Not sure how an analog-digital converter would be used here. More likely, you'd need a digital to analog converter to produce the simulated tach signal. But, most servo amps can be converted to torque mode, usually by pulling a jumper that bypasses the velocity error amp. But, I still feel that a velocity servo with a real tach should work well, and you need a VERY high resolution encoder to move smoothly without a tach. Maybe you could post the trace you are concerned about. Jon ------------------------------------------------------------------------------ Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
