Stuart: Didn't Cradek just do this?? ... the tach simulation with some Mesa controls on his Mori Jr mill?
So your drives do not require the commutation signals that on some Fanuc systems was derrived from the encoder on the motor via the controls?? I never really fully understood the Fanuc commutation dilemma as I don't have any Fanuc equipped machines. Skyko used to sell a little converter board that would make the commutation signals for a Fanuc drive based on the rotor position that was detected by the motor encoder. I know that was an issue on some retrofits. Dave On 9/15/2010 9:22 AM, Stuart Stevenson wrote: > On Wed, Sep 15, 2010 at 12:07 AM, Jon Elson<el...@pico-systems.com> wrote: > > >> 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. >> >> > once again pictures trump words - my explanation was not correct as you will > see > the acce/decel look the same but the beginning and ending phases of each are > not balanced > and the trace is the axis following error not the PID.output - I should have > said PID.error and axis following error - I had looked at the output trace > so that must have been stuck in one of the holes in my head > > >> 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. >> >> > so far in my world a Fanuc servo system is about as real as you can get > I don't think it is any better than what EMC can do and maybe not as good > and certainly not (by me) as adjustable. > I have no way of adjusting any parameters on these amps. There are some pots > and jumpers. > Does anyone know how to change the parameters without using a Fanuc control? > Does anyone have the information explaining the jumpers and pots? I have > some information about the pots but nothing about the jumpers. > > > >>> 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 >> >> > This Fanuc servo system has a servo amp that accepts: > an analog velocity signal from the control > digital signals to close the loop from the motor - an encoder on the motor > sends pulses to the servo and the control > The Fanuc servo motor has no tach. > > I propose using an ADC to convert the analog velocity signal to a pseudo > encoder pulse to replace the motor feedback. > I think this would remove the tuning from the servo amp as the amp would see > the motor as perfectly following the velocity signal at all times. > Even better would be to shunt the velocity signal directly to the tach > signal the chip on the control generates. > Even better would be to disable the internal tuning by shifting jumpers. > Maybe (I am not sure) better would be to have a procedure to tune the amps > and motors as a unit. This may be better but I don't like it as well as any > of my other thoughts. > > 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. >> >> > pictures are here > http://www.mpm1.com:8080/machines/enshu > > there are pictures of all three axes both positive and negative moves > thanks > Stuart > > ------------------------------------------------------------------------------ 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
