In KSS, the instructions for waiting conditions only include the basic instructions WAIT FOR and WAIT SEC for waiting time.
A program for waiting for a signal timeout is designed to handle situations where a system or process is anticipating a specific signal but it fails to arrive within a predefined time limit. This kind of program is crucial in many applications. For example, in a communication system, if a device is waiting for a response signal from another device and it doesn’t come in time, the waiting signal timeout program will take over. It might trigger an error message, log the event, or initiate a backup plan. This helps to prevent the system from getting stuck in an indefinite waiting state, ensuring the overall stability and reliability of the application. It allows the system to gracefully handle unexpected delays and continue to function effectively without being overly disrupted by the absence of the expected signal.
If you want to wait for a certain signal or condition, and do timeout processing if the waiting time exceeds a certain period, you can only expand on the basis of the basic instructions and then encapsulate it into a general function to call.
First, let’s temporarily implement this function, a simple version that can be used.
First wait for a period of time, and then use IF to determine whether a certain condition is in place. If not, do error processing.
For example, the signal of a vacuum or cylinder is usually in place in a few tenths of a second, so there is no big problem with a timeout of 1s. If the waiting timeout is longer, each time the program is executed, regardless of whether the signal is in place, it must wait, which will cause a waste of beats.
So what should we do next? You must have thought of the timer. Taking the timer No. 11 as an example, we need to use the timer’s start, stop, reset, and status operations. The waiting condition is input terminal 1, so the initial waiting timeout function is almost there. If the condition is not met, it will wait in the loop until the timeout period ends.
If the condition is met during the waiting timeout process, the loop will be exited and the execution will continue.
It is not realistic to copy and paste so many lines of code to modify the timeout time and waiting condition everywhere, so the next step is to encapsulate it into a function call form.
First, the timeout time is an integer type and can be used as the input parameter 1 of the function. Referring to the waiting timeout instruction of ABB, a flag is required to record whether it has timed out, so a Boolean input parameter 2 is also required, or the function can return a Boolean value for judgment.
The next step is the waiting condition. After all, there is no condition type in the data type, so how to pass this condition to the function?
Combined with the known system variables, my idea is to use CYCFLAG. Taking the function returning a Boolean value as an example, CYCFLAG No. 11 is used to implement the characteristics based on CYCFLAG. We can use AND and OR to arbitrarily combine the waiting conditions, as long as the result of the combination is TRUE.