Q on How Closed Loop System Works

[aussiegazza]

I have a closed loop board. In simple language, how does it know that the actual position is different to what Mach3 thinks is the position?

eg if the CNC gets stuck (cannot cut and steppers try to keep it moving) - how does it know that it is not moving and getting out of step?

Am I misunderstanding the intent of the closed loop? Am I overstating its ability?

Romaxx's description of the interface card:

About Encoder Interface:

Interfaces a second PCI parallel port card from a PC running Mach software with up to 4
individual encoder/Gecko drive inputs. 4 2-channel encoder inputs in total. The data is
displayed on the "Settings" screen within Mach3. Giving the user, real time data count feedback
from each encoder thereby displaying the actual position of each axis. Used in conjunction with
the available "Rogers" plug-in for Mach3, which will be included with purchase, will trigger a
software "Reset" alerting that a count discrepancy has occurred, if position is lost. No special
screensets for Mach3 are required. Making operation almost seamless with Mach3. A following
error of any size can be set for each axis within the Rogers plug-in.


Garry

[Al_The_Man]

Is this for use with steppers or servo's, as it is that Gecko usually closes the servo loop via encoders?
When true closed loop servo boards are used, the PID servo loop is done in the card, so there would be a conflict if Gecko attempted the PID loop also.
Unless the card just operates as closed loop monitor and compares the Mach command to the actual position within the PC.
Normally with Mach and Gecko/encoder drives, Mach does not know of any position error that might occur.
The board could also be used to monitor stepper error and advise mach through the PCI interface of excess following error?
Just guessing?
Al.

[ger21]

eg if the CNC gets stuck (cannot cut and steppers try to keep it moving) - how does it know that it is not moving and getting out of step?

Am I misunderstanding the intent of the closed loop? Am I overstating its ability?

What that board does, is send signals from encoders to mach3 (by using the plugin). The plugin compares the commanded position with the position from the encoders, and stops the machine if it's out of position.

Imo, it's not needed with stepper systems, even though that's what it was designed for.

A properly designed stepper system should not be losing steps. If it is, than most likely you're trying to go faster than your motors are capable of going.

I'd rather cut a little slower and have the machine be 100% reliable, rather than run it on the edge of losing steps and have the board stop it every time it loses steps.
Just my opinion.