I need help on develping PLC logic to use a PE(photoeye) to detect and calculate the lenght of parts and gap between parts on a conveyor. Conveyor speed is controlled by VFD and vary according to line speed. Thanks.
Part length and gap between parts also change during production
Agree with @jayden regarding speed feedback directly on the conveyor.
And if your accuracy needs are moderate, like you need to detect the difference between a box that is 6 inches long or a box that is 12 inches long, using the VFD output frequency and calculating through the gearbox to get belt speed, like @mad4x4 suggested, should work.
Just a general comment - the more info you give us, the more we can help. Vague requirements can only get you guesses, and vague solutions.
For example, if you posted the following, it would be AWESOME:
- I'd like to measure gaps between objects, and the length of objects, on a conveyor plus or minus 1/8 inch.
- the belt is running 3 - 6 feet per second and is running on a VFD with an encoder on the motor
- the gearbox is enclosed and we can't put feedback on the final drive gear
- the belt is not enclosed, so we can add a rubber wheel that is driven directly off the bottom of the belt for speed feedback
I realize that you would have to have a solution in mind to include a lot of these details ... but with this information many of us could provide specific recommendations on photo eyes, perhaps some programming suggestions, encoder/rubber wheel mounting ideas, etc