Hi Chris, Wiki defines Servo Motor as a motor that has closed the loop so it knows the position of the motor.
Years ago there were discussions about closed loop with linear scales. The trouble there is the amount the motor has to turn before the scales report data. That can cause oscillations that are hard to damp. There is no reason a stepper cannot be the drive part of the motor with an encoder feedback. Google TXM24C-1CG for example. And there are others. The current name for that type of drive is step-servo. The UHU Servo driver http://www.uhu-servo.de/servo_en/ explains how to use a DC motor with either a 0 to +/- 10V or PWM and DIR. One of the first electronic lead screws also used a DC motor on the lathe lead screw. Using counters connected to the spindle motor and the lead screw motor the difference between the counters is an error value that adjusts the DC voltage out to the motor. In each of these examples a varying DC voltage or PWM to a DC motor is the control. A brushless DC motor still essentially works the same way too. Supply a voltage or PWM and the motor turns. Not so with stepper motors. You essentially need to first create a driver that effectively turns the motor at a specific RPM based on a voltage input. Then you can close the loop with the desired number of steps in verses the encoder counts as an error that moves the motor in the correct direction for the required distance. John Dammeyer . > -----Original Message----- > From: Chris Albertson [mailto:albertson.ch...@gmail.com] > Sent: January-18-16 11:04 PM > To: Enhanced Machine Controller (EMC) > Subject: [Emc-users] Question about closed loop CNC > > > I've read that it is hard to use steppers for closed loop CNC. If this is > still true could some one explain the theory. > > I have a small mill with DRO scales that are good to about .001 inch and > I'd like to put them to use with my planned CNC conversion. I understand > software. I've worked in the field for 30 years and have experience with > Linux (and other OS) device drivers, embedded real time code and so on. > If the problem is simply that no one has bothered to write the code, I can > fix that. But if there is something of a mechanical nature I'm not > thinking of maybe some one can point me at what I need to read up on. > > At least I think I might be able too automatically measure backlash using > the DRO scale data. But my goal is to go closed loop if I can > > -- > > Chris Albertson > Redondo Beach, California > ---------------------------------------------------------------------------- -- > Site24x7 APM Insight: Get Deep Visibility into Application Performance > APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month > Monitor end-to-end web transactions and take corrective actions now > Troubleshoot faster and improve end-user experience. Signup Now! > http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
