kwkenyon wrote: ↑Wed Sep 11, 2019 12:19 pm
For Info:
My analog wires are all properly shielded. The results of my test are as follows: 0 RPM = 0.195V, 100 rpm = 1.195 Volts, 200 rpm = 2.196 Volts etc. All the way up ca. 0.195V +- a couple mV. I've worked with Stephen at DMM and I can set the deadzone in the servo to keep it from rotating at Acorn power up. The draw back is Acorn still sees this .195mV and when the M3/M4 are called it sets a rpm exactly minus the maxspeed setting of the servo because of this Acorn drift voltage. If the analog output was in fact 0V there would be no problem. Hence my question if it was possible to Adjust Acorns analog output through the parameters. Possibly A/C servos are to sensitive to this drift and a VFD is no problem? I found it an interesting project to use a Servo as a spindle. Maybe not?
Thank you for all your help and time.
Did you do the test with NOTHING but the meter connected to Acorn spindle analog output?
Acorn's analog voltage can not be adjusted.
Acorn was never inteneded to drive a servo motor.
I am currently testing DMM's DYN4 as a Spindle motor.
The issues as observed them as of this morning:
1) DYN4 needs an input for FORWARD and an input for REVERSE. DYN4 would then NOT rotate unless one of the inputs was called.
(Just like a VFD)
2) You CAN NOT stop the servo motor when its running at a high speed. (Call an M5) DYN4 will fault. There has to be a place for that energy to go. A VFD uses a braking resistor and has Accelleration and Decelleration settings.
3) DMMDRV does not have good way to set Accelleration and Decelleration settings. Try and rigid tap....
4) DMMDRV makes you jump through algebraic equations to come up with some of the settings. Quite simply they need an Accelleration and Decelleration field in the DMMDRV software that you enter seconds into.
5) PID Settings may need to be tweaked.
6) Motor speed is not exactly tracking with commanded speed. I have noted my spindle exhibiting a "quivering" behavior. What it appears to be doing is dithering between encoder marks. I have gotten this to get better by increasing the MAX GAIN in DMMDRV.
DYN4 and an AC Servo was designed to be a SERVO motor, NOT a spindle motor. I don't understand the infatuation with trying to use it as a spindle motor. Are you folks trying to do this simply trying to kill mulitple birds with one stone? I.E. a spindle motor (which MUST be belted to the spindle at 1:1 by means of a timng belt). And because there is an encoder output on DYN4, you are connecting it to Acorn's Encoder input, so you don't have install an encoder on the spindle? Lastly some of you are infatuated with trying to make your lathe have the motor double as a positional C axis.
You understand that you are asking the servo motor to hold position against tool cutting pressures? Drive can fault during such an operation, freeing the spindle and could lead to something ugly.....
While I give DMM credit for trying YOU guys need to understand their DYN4 and AC Servos were never designed to be spindle motors. They were designed to be servo motors.
VFD, 3 phase motor, line driver differential encoder mounted at 1:1 to the spindle is proven and the way to go. Everything else is just an experiment at this point.
My .02 on this issue, if anyone else has successfully made it work, share your recipie. (Keep in mind I am doing some testing on an EMCO PC 5 lathe, and testing the DYN4 and AC Servo as BOTH a Position (C Axis) and Spindle motor. I have NO interest in either other than many of you are attempting this. I will stick to VFD's and encoders.
Marty