Allen bradley help1

I have a motor which is controlled by a three way switch.Basically middle position the motor does nothing,and the other 2 posotions are forward and reverse.You have to keep your hand on the switch for it to go forward/reverse.
The motor has a flag which sits between 2 sensors.These 2 sensors are its limits,one sensor tells it its reached its maximum forward position and the other its maximum reverse position.
Sorry i don't know how to write ladder diagrams when posting(can anybody help me with that issue?).
Picture the motor forward output being in the same rung as the forward switch and the forward sensor(this is normally closed). The same set up goes for the reverse.
As soon as the motor forward/reverse sees its sensor the nc contact of the sensor opens and it can't go any further.
Last week the motor was connected the wrong way round with the result it fell off the end of its screw.I was thinking of putting another normally closed condition before the output which would open when the and condition of forward switch on and reverse sensor on was true(this condition tells us the motor is going in the wrong direction).
However it won't work because when the motor has reached the forward flag and you then press reverse to bring it back this is the condition for wrong direction. My solution was to use a switch which you can momentary press to bring the flag away from the sensor thereby allowing the motoe to move again. Sorry if i haven't explained it well but if i knew how to post using ladder it would have been easier to explain

thanks

three ways to skin a cat ...

but if i knew how to post using ladder it would have been easier to explain

Click to expand...

see if this post or this post or this post will help you out with your "posting" problems ...

sorry that I don't have time to dig into your problem right now ... but I'm sure that the other guys here can offer all of the help you'll need ...

Hopefully your normal forward and reverse stops are before the absolute ends of the screw. It sounds like you need a switch at each end which is beyond the normal stop and which will cut off the movement regardless of direction. If it does hit this then you will have to manually move it off this added switch and correct the motor's direction before continuing. I wouldn't try to do a timed bypass of the normal end switch as you may just get into more trouble.

How about if you're moving forward, and you see a oneshot rising of the reverse limit then it's going the wrong way? Set a bit to inhibit the motor. A vice versa of course. That's if the limits are NO. If they're normally closed then look for an falling edge. No extra hardware or wiring.

pp

Have the forward and the reverse limit switches each trigger a one-shot. If the forward command and the reverse one-shot or the reverse command and the forward one-shot are true simultaneously, latch up a 'Direction Fault' bit. Use the Direction Fault to kill both the forward and reverse commands. I'll leave it up to you to decide how and when to reset 'Direction Fault'.

Forward  Reverse    Direction

Command    OS         Fault

--] [------] [---+-----(S)-

                 |

Reverse  Forward |

Command    OS    |

--] [------] [---+



                    Direction

  Reset               Fault

--] [------------------(R)-





Forward  Forward  Direction  Forward

Command    LS       Fault    Starter

--] [------]/[-------]/[------( )-



Reverse  Reverse  Direction  Forward

Command    LS       Fault    Starter

--] [------]/[-------]/[------( )-

what about motor starter inputs?

I'm thinking there must be motor starters. If a little wiring work is not a problem, just run inputs from aux contacts in FWD/REV motor starters, if they are not already in there. Set up your logic so that if you see the motor FWD starter input and the motor full reverse sensor, the coil drops out. Than set up for the motor REV starter the same way. This way if the leads get reverse, and the FWD button is pushed, the motor will only go as far as the reverse sensor. You would just simply reverse the leads, and the motor would work normally.