Read width of part travelling on conveyor feed

[markn 0]

Hi Folks, We are retrofitting an old automatic spray machine. The machine has a conveyor feed system, an electric eye, Hall efferct sensor to read the speed of the conveyor, and a PLc to control the timing of the spray gun on-off operation. Presently the spray gun assembly reciprocates across the width of the conveyor via a rodless air cylinder, you manual set the width of the reciprocation by positioning pairs of proximity sensors. We would like to retrofit the machine to adjust the width of the spray travel automatically. My thoughts were to have a pair of laser sensors on the right and left sides of the infeed to read the position and width of the part being fed and send that info to a servo or stepper connected to the spray head with a timing belt outside the spray enclosure. Any suggestions on where to start?

[TimWilborne 108]

First what type of PLC are your using? You may have already determined the replacement for the rodless air cylinder but just in case you don't know you can get a rodless servo driven actuator to go in place of it. I would go with a timing belt and not a screw style since you should not need the accuracy of the screw. I would definitely use a servo and not a stepper. There are many different measurement systems you can use but knowing your PLC will also help on that. Also do you know what type of accuracy you will need? Will the paint overspray on the sensors be a problem?

[markn 0]

The existing PLC is a Mitusbishi about 15 years old. I would like to replace it with AB, as far as accuracy, +- 1/8" would probally be OK. The sensing takes place outside the spray cabinet, so overspray is not an issue. Edited 9 Jul 2006 by markn

[Spedley 0]

Would it not be possible to put at a proximity switch on the spray head. When an object is detected (by the proximity switch) then turn the spray on. It would not reduce the travel of the spray gun much but it would save paint (?) and it is a very cheap, simple and effective solution ... unless you specifically want to decrease the spray head travel i.e. to increase the coveyor speed. It may also help if you can push the part to one side of the conveyor, then you only have to measure the distance to one side of the part or, use the proxy I suggested above to detect the edge with the spray head if that is any use. What are the actual goals are you trying to achieve (e.g. increase conveyor speed - not measure width of part)

[markn 0]

I like the proxi idea, but I think the proxi would interfere with the spray pattern ( assuming the the proximity sensor has t be close to the wood part inorder to work. What we are trying to improve is the setup time involved with running the machine, we will be running different width parts, the machine is now configured such that each width must be adjusted manually.

[BobLfoot 302]

Sounds like you are running a planer or similiar machine and then a spray application. Have you considered a 4 servo application as follows: Servo 1 = Product Feed Servo - controls the spped of the board thur the machine. Servo 2 = Left side cutter positon servo Servo 3 = Right Side cutter position servo Servo 4 = Spray head control servo. This type of setup would allow you to actually possibly change widths on the fly and all synchronized servos would change as appropriate. You'd probably want to use SERCOS Drives and ControlLogx CPU's. Jsut a thought.

[markn 0]

Hi Bob, Yes that about sums up what we are trying to accomplish, however there is no planing involved. We are simply trying to improve the existing machine. I am not familiar with Contrologix, how would that differ from RSlogix 500? Is this something which I can learn or is it beyond a novices' skill level?

[gravitar 3]

If you don't already have an installed base of SLC/micrologix PLCs, I think the ControlLogix idea is a good one. ControlLogix is A-B's latest/greatest PLC family. The SLC 500 was designed in the 80s and is a capable PLC family to be sure, but probably not where you want to start in 2006 if you aren't heavily invested in them already. If you've been learning RSLogix 500, you'll find RSLogix 5000 (which is what you use for the ControlLogix) very similar. Many things are done exactly the same way, but the ControlLogix gives you more flexibility over a lot of things. It doesn't require more advanced knowledge, just some "different" knowledge!

[BobLfoot 302]

Definitely not beyond the learning curve of most novices who make a living in our field. My local AB rep had an AB sponsored demo called Kinetix on Tour. It demonstrated the Kinetix motion drives and the newest Flexlogic and Controllogix PLC's. it was 8 hours well spent and came with a "free" lunch. Check with your local AB rep for a Kinetix / Logix demo presentation and make up your own mind is my reccommendation.

[TimWilborne 108]

I second BobLfoot. Controllogix is extremely easy to learn in my opinion. The hardest thing to learn is the Tags. The motion is easy. Also the Compactlogix may be an option for you. It uses a SERCOS setup which is what Bob is talking about.

[TConnolly 13]

My first ControlLogix project had 4 axis motion control - There was a small, but not steep, learning curve. With the CLX's excellent motion control instruction set it was probably less work than trying to do it in a SLC despite the learning curve. Take the time to read the manuals. There is a new model CompactLogix now out which supports a Sercos card, though for this kind of app DeviceNet would probably be more than adequate for interfacing with the drives. The CompactLogix family is more economical than the SLC family as well. Edited 12 Jul 2006 by Alaric

[markn 0]

Hi Guys, Thanks for the responses. From what I have seen on different posts related to Controllogix, it appears that tere exists ready made functions to setup motion control projects. Where could I find more info about Controllogix?

[TimWilborne 108]

I would suggest you download the RsLogix 5000 demo. It is good for 90 days. You can find a link to it and other useful links HERE at the AB Faq

[markn 0]

Hi Guys, I took a look at RS5000. Wow, to think for the past for years I have been trying to write motion code from scratch in BASIC. Could anyone send me an example of a simple motion program? Thanks