The speed (and/or position) control of an electric motor is often the ultimate aim of its control. The industrial applications of this device are countless: for machine tools, for robots and for special machines. Each time a production machine works, the motor is fulfilling this task. We talk about an “axis” for these applications, because a robot has “six axes”, when it can set a tool in a certain point of the space (three dimensions) with a certain direction (three other dimensions). One motor per axis is necessary. A special machine can gather tens of axes, and a production factory, hundreds or even thousands: each operation has its axis. The motors in charge of this operation must quickly and efficiently move the tools. Figure 4.1 shows an example of a “multi-axis” control system. In this chapter, we will mainly take a look at the speed control, with a short presentation of the position control.

Indeed, the industry of equipment goods‘ production supplies “electronic speed variators”, comprising the motor, its supply (the static converter) and its speed control: traditionally, with the help of a high level decision-making element, the user supplies the speed reference, frequently coming from a position control.

Figure 4.1. Example of an industrial multi-axis control (see [JOU 02])