Tuning and Calibrating Spindle Speed with a VFD (inverter)
Posted: Mon Mar 19, 2018 9:24 am
Posted by CNCKeith:
The Acorn outputs 0-10 vdc. 0 vdc = 0 RPM, 10 VDC = max rpm that you choose.
if you set max RPM of 3000
then
M3 S1500 yields 5 VDC on the analog output terminals
M3 S3000 yields 10 VDC on the analog output terminals
M3 S1000 yields 3.33 VDC on the analog output terminals etc...etc..
its up to YOU to set up the inverter (VFD) so that the inverter (VFD) puts out the correct HZ (or DC volts, if using a DC spindle motor) so that 3.33 volts = 1000 RPM, 5 vdc = 1500 rpm etc..
The Encoder allows CNC12 to display actual spindle speed so you can use the encoder to setup the inverter (VFD) properly.
The Encoder gives positional feedback to CNC12 so for example... using G98 on a Lathe the FEEDRATE of the X and Z axis will increase or decrease as necessary to keep the tool chip load the same as the spindle speed changes... or as another example to make good threads etc..
here is how to "tune" the VFD for exact rpm functionality.
1. Enter in the desired maximum spindle speed in the Wizard, write settings to CNC config.
2. Following the instructions in the inverter manual and set the inverter maximum frequency to 120hz.
3. Using the Virtual Control Panel switch to MANUAL SPINDLE MODE and turn the SPINDLE Speed OVERRIDE all the way down.
4. Turn the spindle on CW and make sure it is turning the correct direction. If it is turning the wrong direction correct this by turning off power and swapping 2 legs of the 3 phase cable between the inverter and the motor.
5. Repeat step 3 and 4.
6. Monitor the actual spindle speed on the screen and slowly increase the SPINDLE OVERRIDE until the correct maximum spindle speed is reached. If the maximum speed cannot be reached turn the spindle off and restart at step 2 with a higher maximum frequency.
7. Write down the actual frequency that the inverter is outputting (from the control panel on the front inverter) and then turn off the spindle.
8. Then following the instructions in the inverter manual set the inverter maximum frequency to the frequency in step recorded in step 7.
9. Using the VCP turn on AUTO SPINDLE MODE; and with the Spindle speed OVERRIDE at 100%, in MDI turn on the spindle at 640 RPM (use this command “M3 S640”) Now with the spindle running. Adjust the maximum frequency of the VFD so the actual spindle speed is within 1 rpm of 640 RPM.
10. Spot check the spindle speed across the full speed range commanded vs. acutal reported by the spindle encoder.
11. It is more critical for the spindle speed to be exact at lower speeds and it is normal for the actual spindle speed to be correct at low speeds and up to 50 rpm slower at max rpm then the commanded speed.
The Acorn outputs 0-10 vdc. 0 vdc = 0 RPM, 10 VDC = max rpm that you choose.
if you set max RPM of 3000
then
M3 S1500 yields 5 VDC on the analog output terminals
M3 S3000 yields 10 VDC on the analog output terminals
M3 S1000 yields 3.33 VDC on the analog output terminals etc...etc..
its up to YOU to set up the inverter (VFD) so that the inverter (VFD) puts out the correct HZ (or DC volts, if using a DC spindle motor) so that 3.33 volts = 1000 RPM, 5 vdc = 1500 rpm etc..
The Encoder allows CNC12 to display actual spindle speed so you can use the encoder to setup the inverter (VFD) properly.
The Encoder gives positional feedback to CNC12 so for example... using G98 on a Lathe the FEEDRATE of the X and Z axis will increase or decrease as necessary to keep the tool chip load the same as the spindle speed changes... or as another example to make good threads etc..
here is how to "tune" the VFD for exact rpm functionality.
1. Enter in the desired maximum spindle speed in the Wizard, write settings to CNC config.
2. Following the instructions in the inverter manual and set the inverter maximum frequency to 120hz.
3. Using the Virtual Control Panel switch to MANUAL SPINDLE MODE and turn the SPINDLE Speed OVERRIDE all the way down.
4. Turn the spindle on CW and make sure it is turning the correct direction. If it is turning the wrong direction correct this by turning off power and swapping 2 legs of the 3 phase cable between the inverter and the motor.
5. Repeat step 3 and 4.
6. Monitor the actual spindle speed on the screen and slowly increase the SPINDLE OVERRIDE until the correct maximum spindle speed is reached. If the maximum speed cannot be reached turn the spindle off and restart at step 2 with a higher maximum frequency.
7. Write down the actual frequency that the inverter is outputting (from the control panel on the front inverter) and then turn off the spindle.
8. Then following the instructions in the inverter manual set the inverter maximum frequency to the frequency in step recorded in step 7.
9. Using the VCP turn on AUTO SPINDLE MODE; and with the Spindle speed OVERRIDE at 100%, in MDI turn on the spindle at 640 RPM (use this command “M3 S640”) Now with the spindle running. Adjust the maximum frequency of the VFD so the actual spindle speed is within 1 rpm of 640 RPM.
10. Spot check the spindle speed across the full speed range commanded vs. acutal reported by the spindle encoder.
11. It is more critical for the spindle speed to be exact at lower speeds and it is normal for the actual spindle speed to be correct at low speeds and up to 50 rpm slower at max rpm then the commanded speed.