Servo drivers and spindle

HI every one,

I am new to servos until now I used steppers, and I have a question after I browsed different forum and did not find the information I was looking for.
So hier I am.

I saw arround people using servo motors and drivers for the spindle, I am in the process of converting my lathe.

The big question is:
to my understanding servo drivers work in 3 different mode 1) vilocity +-10, 2) torque +-10, 3) possition step dir.

After browsing the net I did not find servo drivers that do vilocity in step dir, if there is could u refer one to me?

Did I miss somthing, and no one is using servo drivers and are using vfd for there spindles

Or I could use a servo driver in possition mode and linuxcnc in vilocity mode?

I must add that I have a Mesa 7i95 witch dosen 't have a +- 10 but I could add a pwm pin and convert it to 0-10v for a vfd.

Any idea and clarification would be welcome and highly appreciated.

Thanks for you reply

I am not sure I understand,
you are saying that the servo drive exist in stp dir vilocity mode if so could u give ma a brand doing this pls.

To come back to my original question, the drive I found is only doing vilocity in +-10 witch I don't have on my contrôler.

So can I use the driver in portion mode step dir, connect the encoder output of the driver to my contrôler encoder input and use linuxcnc in vilocity

I am just asking to be sure, but I suppose that in possition it will créât a conflict as the driver is counting pulses I suppose it can not go indefeniviely?

Thanks in advance

This thread is right on a topic I am trying to wrap my head around at the moment. A few questions if I may and hopefully you can sort me out.

tommylight wrote:

The new servo drives that use step/dir for control are position mode drives, not velocity mode. Linuxcnc can use those drives in position mode for axis, but it can also use them in velocity mode for spindle.

So ... when you say linuxcnc can use them in velocity mode are you referring to the Stepgen control-type=1? Where (if I have this correct) you are telling Stepgen the velocity-cmd in position units per sec? So its not the driver that is creating a velocity mode it is linuxcnc via the Stepgen part of hostmot2?

If you found drives that use +-10V, those are velocity mode drives, so wiring the encoder to Linuxcnc makes them position mode control.
And i like +-10V mode a lot so i try to use them whenever i can as this way Linuxcnc has full control.

Now this is interesting. I have a 7i76 card and from what I have read and understand the built in isolated spindle pins can only do 0 to +10v. So how do you manage to control in a range of +/-10v?

From what I can see in the manual of the servo driver I can use the Stepgen path, I have +/-10v control over velocity mode and torque mode. This servo will be used as an upgrade to the spindle motor on a small mill. So I "think" I am interested in velocity and/or torque mode. Any advice on which of those two is most desirable would also be gratefully received. But the "magic" of getting access to that +/-10V analogue control range would be REALLY helpful.

Oh, I can see from the manual in the servo driver I can do some parameter adjustment to get control of full speed from +/-5v but that does (I presume) reduce the resolution of that adjustment band and might not be that desirable.

Cheers, and thanks,
James.

Cheers Andy. Thanks re the VFD angle. Confirms my suspicion.
On rigid tapping, yes that is a strong reason for improving the existing motors capabilities. So reverse really is on the "must have" list.

Okay more research and reading of the manual. I think this might be a viable path and would be interested if anyone has seen this approach used. I am still operating on trying to do this all with the 7i76 card and not have to get a serial add on card like the 7i83.
This approach looks valid (per the manual) for either Velocity(Speed) or Torque control which both use under default setup +/-10V analogue input.
[1] I can configure the internal +/-10V "curve" such that it will only react/register to 0-10V. This is done by setting the lower and upper limit values that drive to 0. Lower = -1000, Upper = 0. Net effect it now works on a 0-10v band (unipolar). I presume that I am then only dealing with 0-10V+ and that the spindle block on the 7i76 should be ok? Obviously not doing anything else means forward direction only.
[2] I now need way to be able to reverse the spindle direction while under the 0-10v+ band control. Same as I would if using a VFD. From the manual I see I can assign different functions to the 4 digital input signals. I can assign one of these the function called "CINV - Instructions in Reverse". This says it will do the following: "The speed or torque control mode, take the speed or torque of the instruction. OFF: The normal order; ON: in reverse". It's not great english. But I interpret that as being able to switch the 0-10V+ as being interpreted as 0-10V- when the pin is driven ON.

The other angle I could investigate and again any advice on if this would be worth while, is that the driver has modbus comms (either RS-232 or RS-485). I could look to utilise those capabilities to drive some of the behaviour. It seems to support RTU and ASCII modes.

Cheers,
James.