On Fri, 2008-06-06 at 23:32 -0500, Jon Elson wrote: ... snip > My guess is the Pluto is using synchronous antiphase modulation, > where the bridge is switching the transistors on 50% of the time > at idle. This provides full DC supply voltage across the > inductor at the PWM frequency, and heating of the inductors is > guaranteed, over a wide frequency range. > > Have you looked at the control waveforms with a scope? If it is > synchronous antiphase, then you would lock the PWM optocoupler > on by just hooking a resistor to the 5 V power, and drive the > amp completely with only one signal to the direction input. > Above 50 V or so, however, the output filters will overheat for > sure.
I haven't looked at the control signals with a scope. One inductor was much hotter than the other. I assumed because it was because I was driving the motor mostly one direction. I was planning on using 110 Volts for the motor supply. > These amps are designed for sign-magnitude PWM. At idle, there > should be no current in the PWM optocoupler, and the high-side > transistors will be off. The low-side transistors will be on, > shorting the motor. As the servo jitters, it will send very > short pulses of current to the PWM optocoupler, which will turn > one of the high-side transistors on for a short pulse. > > Briefly looking at the Altera datasheet it looks like the output pins > > are good for 25mA? > > > > I'd appreciate any comments on using Pluto's with PCI cards and how to > > keep the Pico amp inductors cool(er). > If the Pluto tests out to actually be putting out the right > sign/magnitude signals, then you must have a subharmonic > oscillation that is reversing the inductor current on every nth > cycle. With the low frequency of the Pluto's PWM, these > oscillations should be audible. Proper tuning should get rid of > this, and you should be able to see the PWM output command using > Halscope. > > Jon I am not sure what you mean, but I get the impression that you are saying that for synchronous anti-phase, the PWM signal and the direction signal are both modulated to control motor speed? I did put a voltmeter on the direction signal and got 0 and 3.3 Volts DC with a direction change. The PWM signal went between 0 to 3.3 Volts DC dependent on the speed setting. There was never any audible noise from the motor other than bearings and brushes, which actually was kind of strange. I am feeding the spindle command straight into the Pluto PWM input, so, I believe, there is no PID or anything else that could be tuned. I am a little surprised the Pluto PWM frequency isn't higher. -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC/EMC CNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending Craftsman AA 109 restoration Shizuoka ST-N/EMC CNC) ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://sourceforge.net/services/buy/index.php _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
