logic for monitoring the change of position of a carriage

[dingomex3]

Hello, anyone know how to make a logic that monitors the change in position of a carriage through some rails ?. In my application I measure the position of the carriage by means of a laser sensor and I have to detect if the laser beam is interrupted when the carriage is stationary or moving. I have implemented a logic as the adjunct file, but doesn't work. the carriage has 15 positions.

 

[realolman]

what would cause the laser beam to be interrupted? Are you wanting something that tells when the laser is interrupted or something that tells where the carriage is located?

 

[osmanmom]

carriage move by motor?

any picture can post?

 

[widelto]

If your application is motion control you can get that info from plc, you need no laser.

 

[dingomex3]

the carriage is moved by electric motor, and I want to monitor its position to know when the car loses its position. I don't use encoder for this application, I use laser sensor and I wanna know when the carriage lost his position because of an interruption in the laser beam or a sudden change in accounts analog signal.

 

[Lancie1]

...because of an interruption in the laser beam or a sudden change in accounts analog signal.

Usually this type of error-finding means you need to use some timers, and decide for HOW LONG the interruption has to be before action is taken, and for HOW LONG a sudden change is.

 

[dingomex3]

someone had recommended me to program a logic that monitors the position of the carriage every so often (perhaps every two seconds) and when it detects that there was a change in position from the previous scan, then generate the error bit in the laser. Go storing the position from time to time and compare it with the previous, could be something ?, but I have doubts of how to implement it.

Thanks

 

[Lancie1]

Yes, you could check for a change every scan of the PLC. That would most likely be in the 10 to 20 miliseconds range.

You could activate this logic all the time, but it seems it would be most useful when the carriage is supposed to be stationary.

 

[dingomex3]

and how I could do it when the carriage is moving and there is a very large sudden change?

 

[Lancie1]

Normally, a change in value is detected by saving the value (or carriage Current Position in your case) on every scan to a memory location called something like "Old Position".

Then on the next scan you compare the value of the saved Old Position with the read-in Current Position. If different (or greater, or less, or the difference is greater than some "X" value), then you take some action, then as the last step, again save the Current Position to the Old Position.

You may not want to do the above steps on every scan. You could do them every 2 seconds, or something like that, whatever makes sense for the process.

The details will depend on which brand of PLC, and which version of software you are using.