If several groups of mechanisms or machines are organised on one shaft and driven or actuated by one motor, the system is called a group drive or shaft drive. The various mechanisms connected may have different speeds. Hence the shaft is equipped with multi stepped pulleys and belts for connection to individual loads. In this type of drive a single machine whose rating is smaller than the sum total of all connected loads may be used, because all the loads may not appear at the same time. This makes the drive economical, even though the cost of the shaft with stepped pulleys may seem to be high.
This method is rarely used in modern drive systems and has become of historical interest, because of the following disadvantages:
- The efficiency of the drive is low, because of the losses occurring in several transmitting mechanisms.
- The complete drive system requires shutdown if the motor requires servicing or repair
- The location of the mechanical equipment being driven depends on the shaft and there is little flexibility in its arrangement.
- The system is not very safe to operate.
- The noise level at the work spot is high.
If a single motor is used to drive or actuate a given mechanism and it does all the jobs connected with this load, the drive is called an individual drive. For example, all the operations connected with operating a lathe may be performed by a single machine. If these operations have to be performed at different speeds, transmission devices may be required. The efficiency may become poor over several operations, due to power loss. In some cases it is possible to have the drive motor and driven load in one unit.
In a multimotor drive each operation of the mechanism is taken care of by a separate drive motor. The system contains several individual drives, each of which is used to operate its own mechanism. This type of drive finds application in complicated machine tools, travelling cranes, rolling mills, etc. Automatic control methods can be employed and each operation can be executed under optimum conditions.