its a matter of nor open / nor closed contacts. 2 get deeper seal in circuits might help but not on this level. please feel free 2 hit me back 4 further info & besure 2 give more info on mach. peace out!

What is your question?

You need a mechanical flip-flop. Have the first switch (NO, full travel past) latch a parallel relay which the second switch (NC) unlatches. Use debouncing if needed.

Not enough information here to correctly answer the missing question

Please provide more details, possibly a sketch.

Also clearly state your question, you know the one ending with a "?"

No only kidding, we will most definitely answer any question you have, just give us a bit more to go on please.

Did you know you can post a photograph as well? Just load you picture on your computers desktop and click the camera icon above in your reply box. You can then browse for your photo and include it in your next post.

Regards,

If you go with limit switches, you need at least two, serially connected, in case one breaks.

I personally would advise never to use mechanical switches in the first place.....or if its a must, have current monitoring for the motors to shut them down if a switch is missed or over ridden.....

What you are doing in this manner is old fashioned and dangerous to my mind......

Dear Andy,

Limit switches are still widely used in many areas of industry.

They are cheap, easy to fit and relatively easy to design and wire up. Any replacement for the limit switch can also fail and it is not the switch that should prevent that, it should be the application. You can wire up any limit switch in a "fail safe" mode and as such the humble mechanical switch becomes safe.

I have seen brand new hydraulic equipment with mechanical limit switches and in some industries they are even in the standards to adhere to. Elevators use mechanical limit switches and so do the safe guards on most operator interactive machines.

Look here for proof. All these products can be used for mechanical switches and if applied correctly will make a safe system.

Sorry I had to disagree with you my friend

Sadly you are correct, I knew that too, but it is a completely old fashioned method that should have gone out with the Dinos....that was my point!!!

No need to disagree on this.....

We have had chips around for many years to allow such systems to be built, and work far more effectively, without resorting to mechanical devices like limit switches.

I worked for a company that designed all its equipment from about 1981 onward without limit switches......and other companies STILL use them.....they will never ever learn....

Hopefully, in the 21st Century, younger Engineers will come with modern designs. I am ever hopeful.....

The reason why it has not yet gone out with the Dino's is cost.

When your project is big enough the cost is already in your profibus, plc or direct local bus systems. The cost for a safety system incorporated in that is nihil.

The cost for a chip for safety, including the design and the hardware around it, for a singular application is astronomical compared to the good old trusty switches.

We make stages for microscopes and they have normally 2 axis, third for the focus direction and maybe a shutter, filterwheel or a secondairy light. The limits for any of these are micro switches and cost pennies for each product. The other advantage is that if correctly designed you can make them so you can move them for your own purposes, a feature that costs very little extra.

I also think people still like the idea of a phisical stop instead of some invisible code. Strictly speaking we do not need limit switches as we drive the stage with stepper motors with a dedicated controller. So easy to limit the stage in the software but the customers will not have it, they want a switch for initialisation as well. Run the thing to switch and set zero point

At the end of the day, the cost will always drive the consumers choice.

With a microscope, you are hardly likely to kill someone if it does not work correctly. I was talking about industrial robots that would not even notice if they had taken your head off, or similar......with people's lives, you cannot take chances......sorry, that should have read - should not take chances......!!!

I know I am on a losing argument, everybody wants cheap cheap cheap.....not good good or better!!

Physical limit switches are and always will be the eyes and ears of any PLC--They even when hard wired are essential to production and not just for cost cutting. I work with 200 people and they(limit switches) still help keep my colleagues heads where they belong. Check the other thread for 8 pin relay wiring and I may have helped answer the control wiring question.

My bad--It wasn't me it was the Freon talking. We use a lot of photo eyes and there are so many applications that physical switches out preform them and it isn't because we design with cave paintings. I apologize.

My personal hate with regard to limit switches, is the fact that they generally speaking only provide protection at the ends of the arc of movement. Anything that happens between limit switches is often completely ignored.

Whereas a properly designed movement, watched over by motor current and an optical system attached to the motor shaft, can be very fine incrementally and the Robot (mechanism) can speed up and slow down substantially, that is to be far more dynamic, as the mechanism ALWAYS knows where it is and what speed it can best use.....

To do that using micro switches (still possible of course) must actually take a lot more switches to be done properly....as well as programming to qualify the inputs from the switches.....but I have to be careful here as I personally have not been a user of micro switches since the early 80s and methods improve and change!!!