OPENI and CLOSEI

You shouldnt, i use normal SIGNAL for gripper functions.

OPENI and CLOSEI produce a break in CP motion, SIGNAL commands do not.

As to why you should choose one over the other, the answer is above, so you choose which suits your application requirements.

OPEN and CLOSE are relative to CLAMPS.

In the automotive world, these are clamps used to clamp down assemblies before the robot commences work relative to them.

These are just outputs though, but Kawasaki develop these commands to have specific characteristics associated with them which are clearly written in the AS Manual.

Look up OPENI and CLOSEI and SIGNAL commands, you will read the differences between them.

Again, as for how you use them, it is upto you and your application.

I use OPENI and CLOSEI in some applications, I use OPEN and CLOSE in other applications and use SIGNAL in other applications because of how the commands operate.