Thank you for your response.
Actually, I have found out that setAdditionalForceControl() works in smartServoLIN (linear)mode. but I cannot understand the actual procedure behind this command
addingConstantForceMode = new CartesianLinImpedanceControlMode();
addingConstantForceMode.setDestination(Frame); //just angular displacement
I applied a geayer torque(10Nm) in an example to see the result better. actually, when it comes to setAdd... it shows an angular displacement with respect to Stiffness( before an unlimited position hold command ); but when I used this command in the for loop it does not change anything at all. And I want to know why KUKA works like this in this situation?