Indexing Question

[J_Stalman 0]

So I'm working on a project and I'm not sure what the best way to index a dial is. The indexer is a 3 position camco with one position prox.  I have 3 stations,  one the operator loads 3 items which are verified by prox sensors, the next torques two screws and the third offloads the final part on to a conveyor, or if the part failed position two skips the off load and returns the part to the operator.  I need to verify all the parts are there before I index, and if the screw torque fails track the part back to the operator.  I have never done an index like this so I am looking for ideas.  Thanks for any thoughts. 

[JRoss 84]

I recently helped program a similar system, though with more stations. I wrote a sequence for each station, with the end of the sequence turning on a bit that indicated the sequence was complete. The sequence would not reset and run again until the dial indexed. The dial itself didn't need a full sequence, but had a similar principle. I would wait until every station was complete, then start the dial index. When the index was complete, this would restart all the station sequences.

For status tracking, I used an array of integers, where each position in the array corresponded with a station (Status[1] for station 1, Status[2] for station 2, etc.). The integer value indicated status in each station (0-empty, 1-good, 2-failed, etc.). The sequence code for each station would interact with the status value for that station. Skip actions if part failed or not present. Set status to failed if torque not met, etc. Then whenever the dial indexed, I would use a word shift instruction to shift all the array values so the status would move with the part from station to station.

[J_Stalman 0]

Thank's JRoss.  I have the sequences programmed like you stated, I'm mainly stuck on tracking the dial, knowing which station is in front of the operator so I know which nest sensors to check and tracking the status.  So I'll give this a try and see how I do sounds like a reasonable solution.  

[JRoss 84]

In my case all the sensors etc. were fixed at the appropriate station. The dial didn't have anything except a series of metal flags that triggered a single position to indicate the dial was in position.

You can use a variation on the array and word shift to track which nest is at which station. Or you could go even simpler and just increment a counter with each index and reset the counter when it gets to 3. Then use that to know which orientation the dial is in. Of course, you'll need a procedure to "home" the dial in case it gets out of sync.

If I were you I'd consider adding something to external to track the dial position. One idea is a single turn absolute encoder. Or since you only have three positions, use three in position sensors, one at each station, with one flag on the dial. Then based on which sensor is made you know the orientation of the dial, and therefore which nest is wear. Either method would ensure you won't get out of sync.

[J_Stalman 0]

I thought about adding some additional sensors to track the position.  The only other indexing dial I did we had 4 sensors which were setup as a BCD type thing that told the pic which station was at the operator.  I think I'll add three sensors with flags to make things simple. 

[JRoss 84]

Sounds good to me. It should save much headache.