1. Role of a speed reducer

A power transmission is installed between a motor and a machine to be controlled.

A motor with a single operating speed and a single rated torque is used in the majority of cases, whether electric, thermal, hydraulic or pneumatic, as it is the economically acceptable solution. These two characteristics evolve between two close values: speed under load ( N _{m 0} ± ΔN _{m 0} ), torque under load ( C _m ± ΔC _m ), with accepted variations of between 2% and 10% depending on the type of motor and the desired energy efficiency.

The machine to be controlled generally operates at a single speed and torque known as the operating characteristics: ( N _...