Whats so good about a closed loop system?
In IBIS, the design of the head fetures a separate, dedicated force sensor. The output from the force sensor is compared to the user set-point and the difference is fed back to the pzt actuator. This is a closed-loop system. In IBIS, this happens in real-time in the electronics, and is not simulated digitally. The advantage is that the load is kept at the requested set point no matter what the indenter is doing – this is particularly important for creep and scratch testing. In standard nanoindentation tests, the closed loop system ensures that repeated tests are performed at exactly the same load increments in a precise and repeatable manner. In some competitor systems, the situation is quite different. One popular instrument uses the current in the coil as a measure of the force applied to the indenter. The problem with this system is that the current in the coil is also used to deflect the indenter shaft support springs. The current that is used for this deflection has to be subtract
