[cncsnw]

Another forum participant sent me the following inquiry in a private message:

Last year about this time I had a cquired a V2XT. I wanted to get it running with a centroid all in one unit. Guys from ajax refused to sell to me because they wanted me to buy their everything included ready to bolt on cabinet.

I can only speculate that there is more to that story. In general, the point of the Ajax DIY division is to sell component-level controls to qualified DIY builders.

I went with a MACH system that has left a very bad taste in my mouth. Loop only closed between driver and servo, limit switches sensitive to VFD, drivers sensitive to VFD, Lost steps during rapid, Homing relies 100% on switch and not on index off of encoder, need to tune servo motors.

A Centroid control would address most of those concerns. You do still need to tune the servo loop, but it is not as tedious a process as it is with analog drives.

In addition my motors seem to lightly buzz after moving in certain directions. One person told me bad bearings, armature needs to be skimmed and rebalanced.

The depends on what "lightly buzz" means. We commonly tolerate a low level of buzz or whine, as a tradeoff in performance and accuracy. It is usually possible to silence the motors when sitting still, but at the cost of backing off on all the PID gains and accepting higher error spikes at the beginning and end of each move.

If your motors buzz, or don't buzz, depending on what move was just done, that is probably just due to friction in the ways. Sometimes when the motor comes to a stop there may be more tension in the drive train, sometimes less.

Will this give me 300 IPM Rapids, .0005 tolerances, ...

Probably not, but it depends on your belt ratios. If your axes are direct coupled or belted 1:1, then yes, you can probably exceed 300 in/min. If your axes are belted 2:1 (common on many Bridgeport knee mills) then your rapids will be around 180 in/min.

Whether you can maintain 0.0005" tolerances has less to do with the control system, and more to do with the machine, the tooling, and the fixturing. If your machine has negligible mechanical backlash, low static friction (stick/slip), and ideally 2:1 belting, then you should be able to maintain 0.0005" or better fairly easily.

If you have 0.001" backlash, sticky ways, binding gibs, sloppy fixtures and dull cutters, then the best control in the world won't get you within 0.002".

... is teh all in one sensitive to interference from my VFD in the cabinet?

Maybe. It depends on how noisy your VFD is, and how careful you are with your wiring procedures.

In general, using good quality inverters (e.g. Yaskawa, but also the Delta drives from Automation Direct), and using reasonable care in wiring (e.g. ensuring that encoder cables and input signal cables are shielded, that the shields are properly grounded, and that such cables are kept away from the outgoing spindle motor power wiring), I have not had many noise problems.

On the systems where I have had noise problems, it has generally shown up as one of two things:
1) Distortion of the analog spindle speed command (0-10V from the PLC to the VFD) on some OEM machines where there was a speed meter on the head, wired to an analog output from a Delta inverter, with said analog wiring routed alongside the spindle motor power wiring; or
2) Encoder quadrature errors, due to encoder cabling (even though shielded) routed too close to spindle motor power wiring in retrofits of machines with older spindle drives (ca. 1996 Yaskawa G3 in two cases, ca. 1987 Fanuc -6055 drive in another case).

I also have a macro and brain combination that stops my programs and tells me when I need to change spindle gears according to commanded speed. Will centroid system do that?

It will if you write custom M3 and M4 macros to make it do that.

For example, assuming you have a range detect switch wired to INP7, closed in low gear, and you want to use low gear for anything below 350 RPM, you might put something like this in an M3 macro (file named mfunc3.mac):

M95/1/2
IF [#4119 < 350 && #50007==0] THEN M200 "Shift to low gear and press Cycle Start"
IF [#4119 >= 350 && #50007==1] THEN M200 "Shift to high gear and press Cycle Start"
M94/1

I would also like to put a servo on my knee for tool length offsets and use that axis for axial DOC steps. Can I get a plug in or macro for TLO on a kne servo?

In short, no.

The control is inherently a G code interpreter. It moves the axes that your CNC program tells it to move. There can be only one Z axis. If you want to set up a W axis as well, you can command W to move any way you want, using the appropriate G code commands in your program. The control, however, is not going to decide to move W sometimes when you command Z, and not other times.

See the comments and suggestions in this thread: http://www.cnczone.com/forums/ajaxcn...ml#post1070854

[Johns tool room]

MY servso are rated at 4000RPM, so theroretically if they are giving out full power thery should reach 400IPM ( I don't expect that). Originally machine was giving 250 IPM. Does the all in one use differential step and direction signals? I suspect that while currently using single ended signals for step and dir I am losing a bit here and there and especially after rapids on extreme cases can be off by as much as .010" I see that on that link you had a possible macro for M6 where W would be used for the knee and TLO. I would basically have to program teh axial DOC w/ a W command. Right nwo I have decided that maybe my current hardware is part of my reliability problem instead of the software.

You ever worked with Mach, can you pint out any serious reliabaility issues of mach compared to CNC11? I understand that both Ajax and machmotion have a plug in for mach that make it closed loop. It seems to me that mach is more friendly for customizing. Custom screen, make your own VB macros, brains etc etc. Maybe thsi is the beast that I (kinda) know. I appreciate your reply, it has been EXTREMELY helpful. BTW, my VFD is an automation direct Gs2 and I will try some of the suggestions you pointed out. There is a strong possibility that this is where I am losing most of my accuracy. I already have input and poutput line reactors and EMI/RFI filter on teh VFD. My grounded RJ45 cables for input and step/dir are not yet grounded and my encoder cabling can be grounded and shielded in a much better fashion.

[cncsnw]

At what voltage do your motors turn 4000 RPM?

Do you really have that high a voltage coming out of your rectifier assembly?

The All-in-one DC unit, like all Centroid DC drives, is a torque-mode control (current regulator). The position loop is closed on the motion board. Actual encoder position vs. target position feeds back into the current control loop.

I have never used Mach software, so I cannot comment on how it may be more or less reliable than any other software.

[Al_The_Man]

A previous link to VFD's and ground problems.
http://www.cnczone.com/forums/phase_...se_issues.html
Al.

[Johns tool room]

At what voltage do your motors turn 4000 RPM?

I suspect at 96VDC because it saeems to be 24 VDC /1000 rpm? Its SEM motors. I have 110 VDC coming out of my power supply. My instruction manual said I should be getting 130VDC coming out, so I suspect that my transformer has the wrong leads plugged in.

Do you really have that high a voltage coming out of your rectifier assembly?

The All-in-one DC unit, like all Centroid DC drives, is a torque-mode control (current regulator). The position loop is closed on the motion board. Actual encoder position vs. target position feeds back into the current control loop.

I have never used Mach software, so I cannot comment on how it may be more or less reliable than any other software.

[Al_The_Man]

The power supply voltage value does not concisely decide the motor rpm, it depends on the back EMF of the motors and what the maximum the safe manufacturers maximum rpm rating is for the motor in question and where the torque curve start to drop off.
Normally the maximum power supply voltage is never sized at the motor rated RPM, the design for power supply voltage is usually at at least 10% above the max motor voltage.
The reasoning behind this is that not only is there not a direct connection between supply and motor (drive in between) with the associated voltage drop, but the drive is, or should be capable of controlling both max rpm (voltage) and the max rated current.
Al.