I am trying to use a photoeye to stop a motor on a conveyor with a motor with no break. The problem I am having is that the conveyor continues to roll past the photoeye and then starts the motor back up on the conveyor. Is there a way to write the ladder logic so that the motor doesn't start up again?
Ladder Logic question
- Thread starter DamianMI
- Start date
Simplest way would be to add another PE in series or parallel depending on how its wired
(N.
r N.C.) This would need no change in logic. If you want to write logic make the
PE fire a latch and whatever is to start it back up fire the unlatch.
(N.
r N.C.) This would need no change in logic. If you want to write logic make the PE fire a latch and whatever is to start it back up fire the unlatch.
Welcome to the Forum!!
Instead of using the photoeye bit directly in the stop logic of the motor, create a bit that would seal in when the photoeye is detected, and use THAT bit in the stop logic. That way, even if the photoeye no longer sees the object, the sealed-in bit will continue to stop the motor.
The question then for you is -- what breaks the seal-in?
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on another note if the stop area that PE controls is not critical and the objects are
not to small you can angle the PE so it stays in contact with the object longer, if you use 2 PE's I would suggest angling the second.
not to small you can angle the PE so it stays in contact with the object longer, if you use 2 PE's I would suggest angling the second.
Firejo
Member
Hmm... Smells like homework. That's a real basic problem to solve, what have you tried so far?
janner_10
Lifetime Supporting Member
Fit a brake.
Fit a 2nd photoeye, to act a slow command before it gets to the stopping photo-eye
Decrease Decel to suit.
Fit a 2nd photoeye, to act a slow command before it gets to the stopping photo-eye
Decrease Decel to suit.
Tom Jenkins
Lifetime Supporting Member
You could always move the photoswitch further "upstream" and stop sooner.
mendonsy
Member
How much range does your photocell have?? If you can set it to scan diagonally across the conveyor then one photocell might work.
Firejo
Member
OK, gotta chime in.
How about simply having the photo eye latch the bit that is stopping the drive and then put in a "Restart" bit (from a switch, or timer, or?) that unlatches the bit?
How about simply having the photo eye latch the bit that is stopping the drive and then put in a "Restart" bit (from a switch, or timer, or?) that unlatches the bit?
GaryS
Member
Are you using a VFD to run the motor
if so try setting it ramp to stop and maybe add a braking resister
if so try setting it ramp to stop and maybe add a braking resister
milldrone
Member
Plus 1 to Parky's suggestion
waterbottle
Member
Let me see if I understood correctly....
You are trying to set a backup stop for a conveyor. If thats the case the PE will need to be set somewhere upstream where you want to trigger the stop. Regarding the over-travel situation since you dont have a brake you will need to set your decel to be as low as you can without tripping the drive for overvoltage since the inertia of the conveyor moving will regenerate feed to the drive. (In this case a brake resistor will be needed in the drive). Setting a timer(TON) timer will be needed in the logic to latch the bit for the trigger the stop and Unlatch when its clear. Otherwise every item that passes by will ramp down your drive. The drive should have parameter for how to react when a stop signal is trigger Should be set to coast this will allow your motor to ramp down for quick stop.
You are trying to set a backup stop for a conveyor. If thats the case the PE will need to be set somewhere upstream where you want to trigger the stop. Regarding the over-travel situation since you dont have a brake you will need to set your decel to be as low as you can without tripping the drive for overvoltage since the inertia of the conveyor moving will regenerate feed to the drive. (In this case a brake resistor will be needed in the drive). Setting a timer(TON) timer will be needed in the logic to latch the bit for the trigger the stop and Unlatch when its clear. Otherwise every item that passes by will ramp down your drive. The drive should have parameter for how to react when a stop signal is trigger Should be set to coast this will allow your motor to ramp down for quick stop.
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