> Analog outputs is the same as DAC and analog inputs is the same as ADC?
Yes. > And step/dir is input to a stepper motor, right? Most stepper drives, but also some servo drives (both DC and AC) accept step/dir signals. > Can it also do torque control (I think this is the same as velocity > control)? Will it output faster than every millisecond? If you want to control the position of your machine, then the outermost feedback loop is always going to be a position control loop. Within that loop you may have speed or torque loops, but I'm not sure what the benefit those are. The update rate depends on your hardware, so try setting TRAJ_PERIOD lower and lower and see what happens, a few kHz should be possible, but I don't think much beyond 10kHz is realistic. > Let me make sure I understand: there are three cases: > > 1) DAC: IO card gets a digital number representing voltage from EMC. IO > card uses onboard DAC to convert to voltage. Voltage comes out of card, > gets amplified by external amp, then goes to motor. The servo amp is probably not as simple as a voltage amplifier, but otherwise this sounds about right. > 2) PWM-card: IO card gets a digital number representing voltage from > EMC. IO card converts to PWM signal using PWM generator. Then gets > amplified somehow...? What's the difference between a PWM generator and > a PWM amplifier? A PWM generator outputs logic-level signals (0 or 5V), varying the duty cycle depending on the digital number you input. A PWM amplifier uses this signal to drive a motor. So the motor sees the full DC-bus voltage (+24 V for example) for a while, then 0 V, then 24 V again etc. This is called a D-class power amplifier, and since the voltage drop across the amplifier is never very big it is much more efficient than a linear amplifier. Because the PWM frequency is high (15-30 kHz or more) it really does not matter for the motor that the voltage(and current) come in short pulses. > 3) PWM-EMC: IO card gets pwm signal from EMC, then gets amplified... Not sure what you mean here. It's possible to generate a PWM signal without a hardware PWM generator. You would use a general purpose IO pin (like the parallel port), and let EMC generate the PWM for you in software. This works for low PWM frequencies, maybe up to 10 kHz? > I heard that linear amplifiers are "smoother" than PWM amplifiers. > Thoughts? Since smoothness is important to haptics, I think I should go > the DAC route. Is my reasoning reasonable or am I completely misinformed? I bet most servo amps that accept +/- 10V analog control signals are not really linear amplifiers, since the waste of power due to the low efficiency is huge for a linear amp. PWM amps might certainly be electrically (and sometimes acoustically?) more noisier than linear amps. But if the PWM frequency is 50 kHz then you would not notice any mechanical noise or torque ripple unless the motion of your motors and machine was at frequencies approaching this frequency (I guess cnc-machines typically won't move at even 100 Hz ??) hth, AW ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
