Motor controller

[gibby106141]

All,

After my last project the cow feeder i am now looking to make in roads into my next challenge with hopefully your help!

In the cow shed there are a set of scrapers if you can imagine a system of two pulleys with a continuous piece of chain and in the middle on each side of the pulleys a scraper would sit so when one goes forward the other goes back. A magnet is placed on the chain in two positions to tell the system when it is at each end of travel.
The proxy limit sits on one pulley only as there is only one switch which gives an input to the system.

I need a circuit that ultimately controls a forward and reverse set of relays.
The circuit should have a start button
A stop button and a reverse button.

There would be one say proxy type limit switch only which tells me when i am at the end of travel

The circuit should work as follows

If the scraper is in home position and on the limit it should not reverse but can go forward

It would continue going forward until the magnet on the reverse scraper hits the limit.

The sytem would then reverse the other way back to the home position and then stop.

However the circuit needs to be able to be started when its not in its home position just in case the system trips on overload etc.

This is a lot to take in but i am looking forward to hearing your responses i guess the circuit needs to be based on some form of flip flop?

I could probably build the basic flip flop but its the stopping with only one input that appears to be hard

Regards

Mark

 

[strantor]

1. is this prox already installed? Model number?
2. Is this control system to be AC or DC? What voltage?
3. Is your motor reversing scheme already in place, or does that need to be drawn in? - give all details; do you have contactors or what? what coil voltages?
4. motor, AC or DC motor? already existing? how many amps? What voltage are the motor/motors. The more info the better, part #s etc.

 

[ccurtis]

1. Will the magnet pass over the limit switch after the motor is turned off, or will the mechanism stop immediately when the motor is turned off so that the limit switch remains closed?
2. In one case, the blade must only move forward when the limit switch is closed, never backward. In another case, the blade must reverse direction, going backward when the limit which is also closed. Two different, and opposite, things must happen for the same state of the limit switch. This leads to ambiguity that must be resolvable, even after a power failure. The switch does not know from which direction the blade is approaching. Perhaps two limits switches would be better.

 

[gibby106141]

I agree two would be better but trying to do with one if at all possible

To answer other questions yes would expect the system to stop once the switch is activated and not run on the switch is a simple mag type which open circuits

The control voltage will Be 24 vdc and the electrical part of the circuit can be ignored as that is already in place so all i need is the relay direction outputsmfrom the control circuit

However the electrical part of the circuit is single phase ac

Regards

Mark

 

[alec_t]

I think the direction ambiguity when only one limit switch is used could be resolved by fitting an extra magnet close to an existing one, so that a double pulse could be obtained for one direction but only a single pulse for the other direction.

 

[mbarazeen]

check the attached circuit using 4017, the idea is to use three states of the IC and a clock during power up just after giving a start reset.

1) start switch is assumed to be NO so, inverted before U2C AND gate, will give an input high
2) so at start the IC will reset and reverse the motor if it wil be in a mid position until the limit switch gets high. then it will generate a clock high and change the state.
3) if the limit switch is already high at start then clock is given immediately and go to the same state as above
4) if the start is hit once (must be made bounce free) state will change and drive it forward and the limit switch again gives a clock high making a state change and reset the IC.
5) this state will reverse the motor till "home" and stops, waits for the next start

it came to my mind it would work, let me know if any problem...

Edit: i found one problem: if the motor trips at end positon or remain at end when power up the system will not recongize it. only way to work with one sensor for this situation is to modify my schematic to manually bring it to home at powerups. or manually trigger to return or manually select the system to tell where the present state os the system remains.

 

[strantor]

Ok sir,
I have been back and forth on this. I thought it would be simple, but every effort I make to keep it simple results in some unacceptable shortcoming. Trying to make it work with with only one prox input, I found to be totally impossible. Even with latching relays that save their state when power is lost. Even with 2 proxes, my solution is more complicated than I think it ought to be. If anybody can make a simpler solution that meets all the requirements, please let me know. I am eager to see it.

would expect the system to stop once the switch is activated and not run on the switch is a simple mag type which open circuits

You say it won't overshoot the prox, but unless it has brakes (good ones) I seriously doubt it. Because of this, I've designed the circuit so that if it overshoots, reverses, and crosses the prox again, it will not reverse again. Otherwise it would go to the end and gyrate back and for over the top of the prox.

here it is <shitscraper.jpg>

It works as follows:
You press start, the run relay latches, and this feeds power to the rest of the circuit. You can press stop at any time to break the latch and kill the circuit.
If the shitscraper is not in the home position or the end position, the home pos relay will latch, and it will take off towards the end position. If it is at the home position, same thing, it will take off toward the end position. If it is at the end position, the Edn Pos relay will latch, and it will take off toward the home position.
So, let's say the Home Pos relay is latched and it is heading toward the end position, once it gets to the end position, the End Pos relay will latch, and break the Home Pos latch and the shitscraper will head back toward the home position.
Once it gets back to the home position, (end pos relay is latched + end cycle relay engaged) it will trigger the shutdown relay, which will unlatch the run relay and kill the circuit.
If at any point while it's moving, you press the reverse button, if the home pos relay is latched and it is head toward the end position, it will reverse directio, and vise versa.

Unless I missed something, this satisfies every requirement you listed, except for using only one prox.
You would need to use 4PDT general purpose relays throughout. Your motor contactors coils would go in parallel with end pos and home pos relays.

 

[mbarazeen]

Unless I missed something, this satisfies every requirement you listed, except for using only one prox.

With two sensors its a piece of cake...