Various drive concepts have taken root, depending on the complexity and require­ments of a posi­tioning task. The most common include AC servos, DC motors – either with brushes or no brushes with elec­tronic commu­ta­tion (BLDC) – and stepper motors. All of them have typical fields of appli­ca­tion in which they can offer their own func­tional advan­tages.

AC servo­motor or stepper motor

AC servo­mo­tors are consid­ered partic­u­larly powerful and respon­sive. Due to their high dynamics, they are used in rapid pick-and-place machines, for example. For many posi­tioning tasks, their perfor­mance exceeds the require­ments and the drives are there­fore over­priced for these appli­ca­tions. There­fore, stepper motors are often used in ‘more simple’ appli­ca­tions. These work with either an open or closed control loop. When the control circuit is open, there is no posi­tion feed­back. The motor then usually ends up being over­sized to meet the torque require­ments at all times and to ensure that no steps are lost.

Although this saves on sensors, users cannot clearly iden­tify whether the motor has actu­ally been brought to the desired posi­tion, and the over­sized motors require a lot of energy. If stepper motors are in a closed control loop, i.e. with posi­tion feed­back via an encoder, the torque margin can be reduced, less energy is required and the motors are able to be much smaller. However, stepper motors whose perfor­mance is adapted to the appli­ca­tion cannot with­stand over­load.

They cannot work with alter­nating loads, e.g. when pack­ages of different weights are trans­ported on a conveyor belt. These drives can be absolutely the right choice for a robot or swivel arm that always grabs parts of approx­i­mately the same weight. In some areas, however, the noise that stepper motors make – and that cannot be avoided – are intol­er­able from an occu­pa­tional safety perspec­tive.

Fig. 1: Posi­tioning drives from the modular drive system: the internal rotor motors are at the heart of this with power outputs of 30 to 750 watts. Depending on the appli­ca­tion, they can be indi­vid­u­ally combined with control elec­tronics and various trans­mis­sion, brake, and encoder modules. (Graphic | ebm-papst)

DC servo­mo­tors from the modular drive system

DC servo­mo­tors are also frequently used in posi­tioning appli­ca­tions. The elec­tron­i­cally commu­tated vari­ants expe­ri­ence almost no wear and are very durable. Due to the safety extra-low voltage (24 VDC or 48 VDC), there are much fewer training require­ments for the personnel installing this type of drive and the user does not need to spend nearly as much effort on docu­men­ta­tion as with the AC servo­mo­tors mentioned above. The drives are also smaller. Their posi­tioning is much more precise than stepper motors, and they are more dynamic, extremely quiet and energy effi­cient. In addi­tion, drive systems that are suit­able for a wide range of posi­tioning tasks can be found “off the shelf”, which keeps the costs of the high-perfor­mance drives down. Motor specialist ebm-papst proves this with its modular ECI drive system.

Fig. 2: Equipped with an inte­grated elec­tronics module, many intel­li­gent func­tions can be imple­mented in the drive itself; the PLC required previ­ously is freed up or, in an ideal scenario, can be completely omitted. (Graphic | ebm-papst)

The internal rotor motors are at the heart of the series with power outputs of 30 to 750 watts (Fig. 1). Depending on the appli­ca­tion, they can be indi­vid­u­ally combined with control elec­tronics and various trans­mis­sion, brake, and encoder modules. A lot of appli­ca­tion exper­tise went into devel­oping this modular system. The experts know what users in a wide range of sectors need, from automa­tion tech­nology and logis­tics right through to medical tech­nology. This enables precise move­ments at low speeds as possible as a rapid change to a dynamic oper­a­tion. The drives are highly effi­cient and can even be easily accom­mo­dated in confined instal­la­tion condi­tions.

The active compo­nents (wound stator and rotor equipped with magnets) are short at only 20, 40 or, in the most powerful variant, 60 mm. Equipped with an inte­grated elec­tronics module, many intel­li­gent func­tions can be imple­mented directly in the drive (Fig. 2). The PLC required previ­ously is freed up or can, in an ideal scenario, be completely omitted. They can be controlled with digital and analog inputs and outputs. There is nothing standing in the way of them being inte­grated into Industry 4.0 concepts.

Wide range of appli­ca­tions

Fig. 3: Work­piece carrier trans­porta­tion systems are a typical appli­ca­tion for ECI drives. They move parts quickly and effi­ciently in produc­tion from one assembly step to the next. (Photo | ebm-papst)

There are many typical posi­tioning appli­ca­tions for ECI drives. One example is work­piece carrier trans­porta­tion systems, which quickly and effi­ciently move parts in produc­tion from one assembly step to the next. It is impor­tant that nothing jolts or wobbles to ensure that sensi­tive prod­ucts do not get damaged. Fig. 3 shows an appli­ca­tion in which ECI motors with inte­grated elec­tronics and worm gears have replaced the AC gear motors used previ­ously. As a result, users can save up to 80% of energy.

Fig. 4: The drives can be installed easily and can save space, and they can make complex pneu­matic solu­tions at diverts or lifting equip­ment unnec­es­sary. (Graphic | ebm-papst)

ECI motors also feature torque control and high over­load capacity. Since the motor regu­lates torque and current, work­pieces of different weights can be trans­ported at constant speed. For post-sorting in large logis­tics centers, the compact brush­less DC drives on the belts, gates and diverts have also replaced the AC motors that used to be common with their large control cabi­nets for controllers. ECI drives can be installed easily and can save space (Fig. 4), and they can make complex pneu­matic solu­tions at diverts or lifting equip­ment unnec­es­sary.

The indus­trial-grade drives are suit­able for count­less other posi­tioning appli­ca­tions, for example in medical tech­nology: they meet the require­ments for dental chairs, which include compact dimen­sions, high holding force, EMC, fail-safe oper­a­tion and oper­a­tion with as little noise as possible (Fig. 5).

Fig. 5: The ECI motors meet the require­ments for dental chairs, including compact dimen­sions, a high holding force and an oper­a­tion that is as quiet as possible. (Graphic | ebm-papst)

And the right drive can be found quickly. Thanks to defined preferred types, selected drive config­u­ra­tions can be deliv­ered within 48 hours, which means that sampling, for example, can be done very quickly.