Basic kowledge Electric drive systems - basics and design

Drive systems are essential means for providing the mechanical kinetic energy required for running industrial processes.

The various technological processes require targeted solutions that are to implement the necessary motion sequences. There are several different drive media, e.g. combustion, hydraulic, pneumatic or electric motors.

Due to its many advantages, the electric drive has conquered a large field of applications. Environmental friendliness, good transportability of the necessary energy even over long distances, good efficiency in the conversion of electrical into mechanical energy, high availability as well as simple recirculation and use of braking energy are just a few of the advantages.

But even if the motion is realized by hydraulic or pneumatic drives, it often starts with an electric motor, which converts the primary energy into mechanical energy. A transformation at the place of operation is therefore no longer necessary.

The electric motor: Conversion of energy

The electric drive uses an electric motor to convert electrical into mechanical energy. With regard to the type of motion, to motor principles can be distinguished:

• Rotary motors for generating rotary motions

• Linear motors for generating linear motions

In the case of the rotary motor, the mechanical power available on the motor shaft is determined by the torque M it generates and its speed n.

The mechanical power of linear motors results from the force F and the velocity v generated by the equivalent parameters.

Basics about linear motors

The linear motor: The "unwound" rotary motor

The actuator: Rotational speed and velocity control

With one exception, the speed of the electric motor cannot be controlled without external circuitry or additional equipment. In the simplest case, it is directly connected to the supply network via switching mechanisms as well as protective devices against short circuits and overloads.

If the motor and thus also the process are to be operated at variable speeds, there are different controls available - depending on the electromagnetic motor principle.

The speed of asynchronous and synchronous motors depends, among other things, on the frequency of supplied voltage. The alternating voltage of the power grid has a constant frequency. Thus, the engine speed is also constant.

Frequency converters, inserted between the mains supply and the motor, first convert this "rigid" mains voltage into a constant DC voltage and then generate a variable output voltage for the motor. Both their level and frequency, and thus the rotary speed and velocity, are continuously adjustable.

The speed of DC motors depends, among other things, on the level of the DC voltage supplying them. For variable-speed operation, power converters are inserted between the supply grid and the motor. They convert the AC voltage of the supply grid into a variable DC voltage and thus generate a continuously adjustable speed.

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The transmission element: Adaptation of the motion variables

The speed required at the output element or for the application is in most cases lower than that provided by the rotary motor. Due to their electromagnetic principle, motors can only be manufactured in certain speed gradations at economically justifiable expense. In order to be able to optimally adapt to the variety of speed requirements, a wide variety of transmission elements such as gear, wedge, flat or toothed belt drives are available. They convert the torque M1 provided by the motor and the speed n1 on the input side into the torque M2 and the speed n2 on the output side.

The output element: Conversion of the motion type

The type of motion to be realized in a machine can be either rotary or linear. Fans, pumps or drills, for example, require a rotary input motion. In these applications, the motion of the rotary motor can be used. If, however, the desired output motion is linear, for example in the winch of a crane or the drive of a trolley, an output element is required to convert a rotary motor motion into a linear output motion. This can be a rope drum, a wheel or a roller. It converts the torque M into a force F and the velocity n into a velocity v.

Linear motors are generally used for the direct use of the type of motion they generate. Further mechanical conversion into other types of motions is rare.

This article was first published by MaschinenMarkt.

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