Drive technology manufacturers have been trying to operate motors without encoders for some time now. However, according to Günter Großmann, Head of Product Management Motors at Stöber Antriebstechnik, previous approaches have a serious disadvantage: In the zero to 1000 rpm range, the rotor no longer provides any evaluable position signals and one can only hope that it will turn. In other words: In this range, you always have to work in a controlled manner - in stepper motor mode, so to speak - meaning precise control is not possible."

Not so with the new LeanMotor. Its developers have given it an anisotropic process with regard to inductance. This means that, depending on the inductance, the motor has an assignable position that can be measured and therefore allows conclusions to be drawn at any time as to where the rotor is currently located. Based on this, speed and torque can be infinitely adjusted from standstill to maximum speed with full torque control, even without an encoder. Stöber specifies a speed deviation of less than 1% and a positioning accuracy of ±1°.

Günter Großmann, Stöber: "We save on everything with the LeanMotor, but not on performance!"

© Stöber drive technology

The motor is based on the so-called IPMSM technology (Interior Permanent Magnet Synchronous Motor) with 'buried' magnets. Positive characteristics of reluctance motors have also been incorporated into the motor design. "This has also enabled us to get more torque out of the motor despite using less permanent magnet material," says Großmann. This means that designers can design smaller drives or make the machine itself smaller, thereby saving installation space. And thanks to the greatly reduced inertia, the lean motor can also be controlled more dynamically and efficiently compared to the standard asynchronous motor with incremental encoder. With its efficiency of up to 96%, it also exceeds the energy efficiency values defined for IE4.

But that's not all: according to Großmann, the LeanMotor is also a 30% cheaper alternative to the versatile servomotors and is also significantly more robust in comparison, as neither sensors nor fans are installed. This makes it suitable for automation tasks that are exposed to high vibrations and oscillations, among other things. However, replacing a high-performance servo motor with a lean motor is still not the goal: "The measuring accuracy for position determination is not sufficient for this, i.e. we don't get 500,000 pieces of information per revolution out of the motor," Grossmann points out. "But it doesn't need an encoder for that either!"

Speaking of omission: Because the motor manages completely without sensors, only a standard power cable without additional wires or shielding is required for the connection to the controller. "I can't imagine an even simpler single-cable solution for a motor that provides position feedback," says Großmann. Other common encoder-based single-cable solutions would always require a special cable and special connectors.