This article is about STOPRE Sinumerik 840D program command.
Siemens Sinumerik 840D is an advance cnc control.
One of the ability of Sinumerik 840D cnc control is that Sinumerik 840D Pre-Process part program commands before executing them.
In simple words Sinumerik 840D reads faster than the cnc machine.
Meaning that sinumerik 840D read-ahead the cnc program. You press the cycle start and the cnc machine start running, but the sinumerik 840D cnc control now might have read the whole cnc program, but actual cnc machine is behind.
This all mean that sinumerik 840D is running faster than the actual cnc machine.
This strategy has its advantages and disadvantages.
Sinumerik 840D read-ahead Advantages
Now almost sinumerik 840D has read the cnc program or it is far forward the actual the cnc machine, so now cnc machine can run more smoothly. Now the cnc control already knows what to do next, or if there is any complex calculation the cnc control has already solved that, and the cnc machine can run in a smooth way. Now the complex profiles can be machined more smoothly.
Sinumerik 840D read-ahead Disadvantages
But there are some shortcomings to this strategy. The cnc machine is behind and the cnc control is far forward.
So there might be a danger of reading a wrong value if we are using variables (R parameters) in our cnc program. Suppose you have initialized a local variable with some value and later in the cnc program you update the same local variable with some other value.
So if the cnc machine is behind and have not read the first local variable value yet, and the cnc control is running faster and has crossed the cnc blocks which have updated the local variable value. What will happen. Now when the cnc machine will read the local variable value this will be the wrong value, because the cnc control first initialized the value and then updated the value. But because the cnc machine was behind it can read the first value and got the updated value.
This might explain more http://www.automation.siemens.com/forum/guests/PostShow.aspx?PostID=246454&Language=en&PageIndex=1
The Siemens Sinumerik 840D has a part program command STOPRE (Stop Read).
The STOPRE Siemens Sinumerik command clears all the read-ahead data.
So whenever the cnc machine execute the STOPRE command the Sinumerik 840D cnc control clears all the read-ahead data. So now the cnc machine and the cnc control are on the same point in the cnc program.
As long as the STOPRE command completes the Sinumerik 840D again starts reading-ahead until the cnc program ends or cnc machine executes the STOPRE again.
STOPRE Siemens Sinumerik command Usage
STOPRE Siemens Sinumerik command is very vital, this solves the above local variable problem in a very simple way.
Another use of STOPRE Siemens Sinumerik command is when we are interacting with cnc machine hardware parts like chuck, tailstock etc.