[Emc-users] Spindle Servo Soft Start
I've just configured my first emc project, a 9x20 lathe conversion. I'm using a large servo for the spindle - I'm hoping to be able to use it as a 4th axis for some light engraving down the track. My problem - I've set up the servo for the spindle, but like a servo, it responds imediately to change requests. I haven't put a chuck on it yet, but it I'm sure it will break the belt when it tries to stop from 1000rpm to 0, instantly. Any ideas on how I can soft start and stop it? At the moment, my configuration is to take the motion.spindle-speed-out, into pid.command, and let it work itself out. I'm thinking if I reduce the Pgain that might do it, but then it would make it mushy under load. Any ideas? -- The NEW KODAK i700 Series Scanners deliver under ANY circumstances! Your production scanning environment may not be a perfect world - but thanks to Kodak, there's a perfect scanner to get the job done! With the NEW KODAK i700 Series Scanner you'll get full speed at 300 dpi even with all image processing features enabled. http://p.sf.net/sfu/kodak-com ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Spindle Servo Soft Start
On Wed, May 06, 2009 at 04:37:07PM +1000, Frank Tkalcevic wrote: I've just configured my first emc project, a 9x20 lathe conversion. I'm using a large servo for the spindle - I'm hoping to be able to use it as a 4th axis for some light engraving down the track. My problem - I've set up the servo for the spindle, but like a servo, it responds imediately to change requests. I haven't put a chuck on it yet, but it I'm sure it will break the belt when it tries to stop from 1000rpm to 0, instantly. Any ideas on how I can soft start and stop it? Send the commanded spindle speed through a limiter before pid, so that the pid 'command' value varies slowly. limit2, limit3, and lowpass are three built-in components that limit a signal: limit2 limits the range and first derivative of a signal. limit3 limits the range, first and second derivatives of a signal. lowpass uses an exponentially-weighted moving average to track an input signal. Here's a standalone hal setup I wrote to show the behavior of each of these limiters when fed a step signal: loadrt threads period1=100 name1=thread loadrt siggen loadrt lowpass loadrt limit2 loadrt limit3 net square siggen.0.square = lowpass.0.in limit2.0.in limit3.0.in net lowpass = lowpass.0.out net limit2 = limit2.0.out net limit3 = limit3.0.out setp siggen.0.frequency .1 setp lowpass.0.gain .9 setp limit2.0.maxv 2 setp limit3.0.maxv 2 setp limit3.0.maxa 10 addf siggen.0.update thread addf lowpass.0 thread addf limit2.0 thread addf limit3.0 thread start loadusr halscope .. run it with 'halrun -I limiters.hal' at the terminal. In halscope, I selected the signals 'square', 'limit2', 'limit3' and 'lowpass' and captured a trace: http://emergent.unpy.net/files/sandbox/limiters.png Jeff -- The NEW KODAK i700 Series Scanners deliver under ANY circumstances! Your production scanning environment may not be a perfect world - but thanks to Kodak, there's a perfect scanner to get the job done! With the NEW KODAK i700 Series Scanner you'll get full speed at 300 dpi even with all image processing features enabled. http://p.sf.net/sfu/kodak-com ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Spindle Servo Soft Start
Frank Tkalcevic wrote: I've just configured my first emc project, a 9x20 lathe conversion. I'm using a large servo for the spindle - I'm hoping to be able to use it as a 4th axis for some light engraving down the track. My problem - I've set up the servo for the spindle, but like a servo, it responds imediately to change requests. I haven't put a chuck on it yet, but it I'm sure it will break the belt when it tries to stop from 1000rpm to 0, instantly. Any ideas on how I can soft start and stop it? At the moment, my configuration is to take the motion.spindle-speed-out, into pid.command, and let it work itself out. I'm thinking if I reduce the Pgain that might do it, but then it would make it mushy under load. What you need to do is put motion.spindle-speed-out through a filter to round off the sharp edges before feeding it to whatever is trying to follow it. Since spindle-speed-out is already velocity, I send it directly to the servo drive without PID. That won't work for a positioning axis, but is OK for a velocity-only axis, ie. a spindle. The constant .0009018 is the speed calibration factor. This is using my Universal PWM Controller and PWM servo amps to drive the axes as well as the spindle in this system. Here's the relevant code : # set up 4th PWM generator as a spindle speed control newsig spindle-speed float newsig spindle-pwm-cmd float newsig spindle-pwm-filt float linkps motion.spindle-speed-out = spindle-speed linksp spindle-speed = mult2.1.in0 setp mult2.1.in1 0.0009018 linkps mult2.1.out = spindle-pwm-cmd linksp spindle-pwm-cmd = lowpass.0.in linkps lowpass.0.out = spindle-pwm-filt linksp spindle-pwm-filt = ppmc.0.pwm.03.value setp lowpass.0.gain 0.01 -- The NEW KODAK i700 Series Scanners deliver under ANY circumstances! Your production scanning environment may not be a perfect world - but thanks to Kodak, there's a perfect scanner to get the job done! With the NEW KODAK i700 Series Scanner you'll get full speed at 300 dpi even with all image processing features enabled. http://p.sf.net/sfu/kodak-com ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
