Extract encoder count from driver

[CNCChris]

Hi.
I have a servo spindle and belt drive bt30 on its way to hook up to a mill.

To do rigid tapping what is the best way to control the spindle? 0-10v? Can you get the encoder value from the driver that runs the spindle or do you need a seperate encoder?
Thanks

[cncsnw]

The only straightforward way to control a spindle with Acorn is relay-closure run signals (two of them in your case, because you want to run both forward and reverse); plus a 0-10VDC analog speed reference.

Most closed-loop drive systems provide some way to get the encoder position from the drive, as a differential quadrature signal (as required by Acorn). As long as your motor drives the spindle at exactly 1:1, you can use that for rigid tapping.

Since you have not shared the make or model of your servo/spindle drive unit, no one here can guess whether your particular drive provides that feature, nor tell you anything about how to wire it.

[CNCChris]

This is the manual for the driver. Does acorn support modbus?

[tblough]

Acorn does not support MODBUS. The manual did mention encoder feedback which you would need for the Acorn if your motor is belted 1:1, but it looks like you need a special expansion card for your drive.

[Richards]

I've used ModBus indirectly with my Acorn. A PLC (AutomationDirect P1-540 with I/O module) is connected to the output's of the Acorn. Then, the PLC's ladder logic monitors the Acorn. When the proper condition occurs, the P1-540 sends RS-485 or TCP/IP ModBus data to whatever it is controlling (AutomationDirect G1 VFD or intelligent I/O external to the PLC). Depending on how you configure ModBus, there can be significant delay in message transfer. In the case of the Acorn, the output relays might take 10mS to 25mS to change state, then, unless the ModBus PLC is interrupt driven, no ModBus data is transferred until the next ModBus transfer cycle. Those delays could wreak havoc with rigid tapping cycles.