Powerflex 4M and Micrologix 1400 communication

Hello,
I am pretty new to the PLC world and have a Micrologix 1400 PLC commanding several small Powerflex 4M VFDs on a bottle capping machine via RS485 and MODBUS protocol.

I am trying to understand how the VFD knows when it has met the requested torque from the program.

The user requests a maximum torque on the HMI, in this case "72" (on a scale of 0-100). The program scales with an SCP instruction the 72 to 180 and assigns it to an integer file. This data file address is then sent to the VFD through a read/write command to a MODBUS address on the assigned VFD.

When an encoder on a "table" housing the VFDs reads a certain position in degrees it toggles a bit to engage the VFD

Once the cap is tight the VFD stops turning. If the cap never becomes tightened the VFD keeps on spinning until the encoder on the "table" signals that it is in a certain position (degrees) and de-energizes the bit for the vfd.

The only feedback I can find from the VFD is a read command stating to the program whether the VFD is running or not.

My question is how can the VFD take the 180 figure from the integer file and convert that to a usable torque? Without an encoder how does the VFD know when to stop?

Thanks a lot

If you could tell us what the MODBUS address is we could provide insight on the torque control.

The 'encoder' (which can be anything which indicates multiple positions, not just an actual encoder) is probably connected to the PLC directly which then decides whether or not to enable or disable the VFD.

If you are allowed to zip and post the program we could help further but in many cases this is not allowed by company policies.

Thanks for the reply.

I doubt I am allowed to post the program, but here are screen shots of the write message and read message

Thanks

I'm having a hard time reading the Modbus address in the Write message. It looks like possibly '102' which wouldn't make sense. That would be the 'Motor Nameplate Voltage'. (102 Modbus = Parameter 101 in the drive)

The PowerFlex 4M's are fairly simple drives designed for speed control not torque control however your MicroLogix may be limiting the torque by reducing the current limit in the drive.

This is a bit of a guess but torque is more or less proportional to current therefore with reduced torque when the screw cap is tight the drive will stall, the MicroLogix can read back the fault status word to detect that the drive has stalled and signal the drive to stop.

If the drive runs for too long the MicroLogix can assume the cap has not tightened and also signal a stop then presumably reject the bottle.

Bernie it does say 102 for the MB data address. It lists the MODBUS address as 40102.

Even after the motor stalls the internal bit stays energized telling the VFD to come on, so the only thing I can figure out is the program limits the current to the VFD, and once it stalls it clears the error code before the spindle comes around to grab the next cap?

The only feedback to the PLC appears to be from address 8449, which is only error codes from my understanding.

I will have to hook to the PLC when it is running and see what the feedback is then, since this snapshot was taken when the machine was stopped.

Thanks for the help so far