Centroid Community CNC Support Forum

I am leaning towards purchasing the CENTROID software as opposed to using MACH3 on my mill conversion. I am ok with MACH and use it on other tools but the more I play with the CENTROID DEMO the more I like the feel of it.

The big question for me is what is possible as far as having actual spindle speed shown and maintained within the software? My spindle is currently a 3phase /3hp motor running on 1phase 220V with a MITSUBISHI VFD. It does have a mechanical 2 speed gearbox for hi and low range (currently no switches to use as inputs to plc) . reduction is approx 6.3:1 The spindle doesn't currently have any sort of speed sensor so I am free to add what is required. Also I guess the question is do I need it at all? Can the software merely check the output frequency of the drive and interpolate the speed from that assuming the loads are relatively light and not slowing the rotation?

I wonder what others have done on their conversions

Gerald

Can the software merely check the output frequency of the drive and interpolate the speed from that assuming the loads are relatively light and not slowing the rotation?

Yes, more or less. Assuming you are using the Centroid PLC to control spindle speed, then the PLC already knows what fraction of the maximum speed it is requesting. It does not need to read the frequency back from the inverter.

To make this work, you enter the maximum spindle RPM for high gear range on the Control Configuration screen: i.e. given your current inverter programming, how fast will the spindle turn if the PLC commands 100% output (10V reference)? If you program a higher or lower maximum frequency in your inverter, then you need to go back and change the value on the Control Configuration screen to match.

To compensate for the gear range, you need to install a switch (wired to a PLC input) to detect when the head is in low gear. You then enter the ratio of low gear speed to high gear speed (e.g. 0.1587 for a 6.3:1 reduction) in Parameter 65. If the control sees that you are in low gear, then it will scale its speed commands and display using the value in Parameter 65.

The PLC can also reverse the motor direction when it sees you are in low gear, to compensate for Bridgeport-style back gear assemblies that rotate the opposite direction when shifted.

To compensate for the gear range, you need to install a switch (wired to a PLC input) to detect when the head is in low gear. You then enter the ratio of low gear speed to high gear speed (e.g. 0.1587 for a 6.3:1 reduction) in Parameter 65. If the control sees that you are in low gear, then it will scale its speed commands and display using the value in Parameter 65

Thanks for the comments, it all makes sense and sounds straight forward. I may actually do a switch or sensor right on the gearbox lever so that changing to low will automatically trigger the input on the PLC, it looks like a fairly easy task. I may attach a sensor of some sort to the spindle so that I can use an digital tach to measure the spindle speed precisely and be able to fine tune the software parameters to be quite close. The gearbox setting doesn't change the spindle rotation as far as I know but I will certainly verify this now that you mention it.

Gerald