Rigid and elastic are 2 often used types of mechanical connection between 2 motors.
As their name says, the rigid connection is the type of connection where motor shafts are firmly connected together or connected via a gearbox (e.g with cogged wheels). In other words, saying, in a rigid connection, the motors have to have the same speed. It is not possible at any time for one motor to rotate faster than the other.
On the other hand elastic connection is the type of connection where motors are not directly linked together, but they are linked via elastic belt or load material. For example belt conveyor that has one motor on one side and other motors on the other side is linked by the conveyor belt. In this case, it is possible that one motor has greater speed than the other, either temporarily (belt can prolong or shrink) or continuously (if the belt slips at least on one side possible).
In some applications, it is required to synchronize the speed of 2 motors even if the motors do not have any mechanical linkage (or the linkage is very flexible). For example 2 independent conveyors. Here we speak about the function "speed follower" but the setting will be done in the same way as elastic connection and with direct speed control.

The reason why direct speed control in rigid connection is not available is the fact that both motors in rigid connection must have the same speed which is done naturally by rigid mechanics. So it would be useless to regulate the speed of each motor individually. On the contrary, the target is to balance the load (torque) between 2 motors with rigid coupling.
In elastic connection, it is possible to choose speed or torque control. The torque control makes sense if the mechanical connection between 2 motors can naturally balance the same speed. But if the mechanical connection is very weak or too elastic, you have to use a speed follower (sped control).
Few pictures in the attachment.

Diterbitkan untuk: Schneider Electric Indonesia