Hallo,

I`m working on a project in which i have to make some movements based on timing. I`m using IEC timers on/off/tp to make delay and give an impuls for movement. When i make a slow/long movement then the value is changed on time but when i make few after each other and they are short or quick +/- 1-2s then the value of the movement is 1 step behind. 

When i make it like in nw2, i have the problem with quick steps,so i found a sollution with adding extra timers - first timer to change value and then 2nd to execute it like in nw1 but...it`s not a good solution because i got so much timers that is not clear anymore.

Is there a solution to use the timers and first change the value and then execute the movement.

PLC - S7 1214C; values can be changed also on the HMI(ktp400) - reaction time changed from 1s to 100ms.

Thanks

Bart

Every timer call needs to be a unique instance.

The code can be written as a sequence:

step1 AND condition1 ----> RESET(step1)
                     ----> SET(step2)

step1 --- TON ---> condition1

Thanks, i`m gonna try to  make it with set/reset

Gr

Bart

Hello my friend. I hope you are doing well. 

mopS04

hi,

the problem with timers is that it depends on where you are calling them. You don´t know when the time is up until you call the function which is using the timer. The higher the time between two calls, the more inaccurate is the timer.

regards,

What you say is true but I am of the opinion that this is not the actual challenge to solve. Movement takes time to get to speed. The distance travel when speeding up is less than when at speed -- for the same time the difference is x2 or more. The same can be said when bringing movement to a stop.

It is several short start-stop movements vs one long movement for the same distance. The total travel time will look different. The trick is to develop code that calculate travel distance according to time and which movement phase (accel / const / decel). It does not use the timer directly but it pushes the time value through formulas to get the travel at that moment.

It is not a trial exercise. It is mathematically possible.

The stumble-block is that you cannot be sure exactly how long it takes to get to constant speed and the progress curve used to do so.

A more accurate way would be to use an analog speed feedback (from variable speed drive for example). Moment speed can be processed to give travel distance between every PLC scan. This can be added up to give a much more accurate result .. provided the speed measurement is accurate.

Hallo,

I`ve tried with set/reset but it doesn`t work.

On the picture NW1 and NW2 are 2 sepatate examples. When i make it like in NW1, so first the signal(pulse) for changing data (MOVE blk) and then 200ms later execute the everything works fine: timing is good, data is good, movement is good but for 1 movement i need at least 3-4 timers.
Problem begins when i want to reduce the amount of the timers - NW2 example and at one moment i want to changing the value of a movement and execute it, then the PLC stays behind, because it execute first and then it change the value.and for short movement it is too late.

Maybe i`m gonna try with scl, if that does`nt work i leave this amount of timers.

Thanks for advice, have a nice day.

Gr

Bart

Hello barth87, 

barth87

[...]

Is there a solution to use the timers and first change the value and then execute the movement.

[...]

is it a requirement to assign "Execute" e.g. 100ms after changing the value or would it be an option to compare the value of the current cycle with the value of the last cycle  and then assign the Execute-bit?

What is the actual cycle time of the PLC?

Regards.

Frink