Firstly, not all manufacturing processes in which the dimensional control of the product is crucial, allow modification in real-time of the variables of the process itself. In other cases it is impossible for the nature of the line of production (line transfer versus machining centers) that he sacrifice flexibility for productivity. Finally we cannot forget that in most cases it is difficult to establish a direct relationship between the cause and the effect produced by a variation of the control parameters, either due to ignorance of the process itself or difficulty to describe / make this relationship.
There are specific applications that work satisfactorily closed control loops, where the sensor is a MMC. As a general rule the error signal acts on the program of machining of one machine numerical control, on the basis of the trend rather than the absolute value of the measurements. In short, we are compensating for the degradation of the machine or the wear of the cutting tool, action not insignificant if we take into account the savings in time (maintenance) and money (the cutting tool change) that this represents.