Creating a safety interlock on an enclosure with PWNCNC vfd

Spindle/VFD (Aftermarket)
4

Hey Andrew,

  1. on VFDs controlled by Modbus communication over a RS-485 serial line, most cheaper VFDs do not support the START/STOP function on the VFD keypad or by a switch wired to one of the input terminals at the same time, so the CNC controller has to send the STOP command via Modbus. There however is the possibility to enter a ‘ModBus Override Mode’ on Omron MX2 (PDF Manual) or Hitachi WJ200 (PDF Manual) (which are practically nearly identical) or on Hitachi S1 VFDs. With these, you can temporaraly override the ModBus control by CNC controller at any time by a switch “Modbus override” wired to the VFD and another switch at same time serving as “STOP” switch, and this way stop the spindle. This is described here and here.

  2. On VFDs that run on controllers like the Masso which is incapable of Modbus communication, speed is controlled by an analog voltage and START/STOP is controlled via an input terminal by a hi/lo state change from a digital output from the VFD, or by a switch. This input can also be used to simply trigger STOP on these VFDs.

As far as I know, PwnCNC offers their VFD in both configurations, Modbus for the Onefinity Standard series, control lines for the Elite (Masso) Series. Is your model controlled by Modbus or by control lines? If the first, I would ask Daniel @PwnCNC if your model supports Modbus override.

Note that industrial VFDs like Omron MX2 have Intelligent Terminals which you can program to serve as ISO 13849-1 Safety Inputs, and support safety wiring with a safety relay like Omron G9SE. A CNC controller would be integrated into this safety circuit, including door sensor. However the limitation that the Onefinity controller cannot pause and resume by a hardware input remains, it’s only ‘estopped’ mode that is available.

However, if you stop the spindle, but not the g-code program, the bit is likely to break, which can be dangerous too.

:warning: In any case, never interrupt the spindle power between spindle and VFD! Your VFD may get damaged. A spindle must only be stopped by the STOP function of the VFD. Also a VFD must only be powered off when the spindle is stopped.

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