PLC program for index table

I am looking for some help on writing logic for an index table application. I haven't programmed a machine like this before and am looking for some advice.

This is a simplified description of the machine:

5 stations total.

Station 1 - parts are loaded and detected
Table indexes
Station 2 - part is tested to make sure all pieces are present
Table indexes
Station 3 - some additional pieces added manually by operator
Table indexes
Station 4 - part is tested
Table indexes
Station 5 - part is picked and placed onto conveyor or reject chute.

The logic for th individual stations should not be that difficult. I just am not sure on the best way to write the code for the index table.

The index table is controlled by a frequency drive and the PLC is an Omron CPM2A.

Your help is appreciated.

1.Release the locking pin and make sure it released (by sensor)
2.Run your VFD until you get signal from the index sensor, then stop
the VFD.Put the DCC on the VFD lowest you can.
3.Lock the table by the pin and make sure it locked {by the pin sensor)RUN YOUR CYCLE.
Some index tables dont have locking pin it make it more easy.

I you dont manage send me the details I will try to help.

A DC break is needed many times in order to get the table to stop close enough to a point so the pins can lock the table into place. Do you have an input and output chart yet? That would be the best place to start for designing your program.

ste1171,

For similar applications, I typically use a VFD to drive the table, an encoder on the table for positioning (tied directly back to the PLC), and an external brake either on the motor or directly on the table.

Each time the table is told to go to the next position, a predifined target position is loaded and the drive starts driving at some rate.

As the encoder sees it is "getting close" to the target position, the command speed to the VFD is lowered to a preset "approach" speed.

Then as the encoder sees it is "getting really close" to the target position, the command speed is lowered again to a preset "creep" speed.

Finally, when the encoder sees it has reached the target position, the command speed is sent to zero, the VFD is stopped, and the brake applied.

Everything is reset in preparation for the "go to the next position" command.

This technique allows you to use the VFD's acceleration and deceleration rates as needed and electronically adjust your individual targets rather than physically adjusting switches. You can also easily set the system to drive to any desired position by merely telling it a specific "target" position.

Steve

Automation Direct has had some really great pricing on encoders lately too.

If u are going to use an encoder on the index table might i sugget using an absolute encoder. The posistion will never be lost. See this tread FYI.
Absolut encoder to CPM PLC Thread