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The rotary high performance direct drive series RKI from Idam offers previously unreachable features. An increase in speed of more than 400% and an approximately 30% higher torque make the series extremely attractive for use in machine tools. But also downsizing options are convincing: With the same power, engine sizes can be adjusted and costs for converter and motor can be reduced. In combination with the Axial angular contact ball bearing generation ZKLDF..B RKI torque motors worldwide represent the upcoming peak performance for rotary table bearings.

Direct drives have evolved over the last 20 years from the special motor for single applications to the series product. The technology has been optimized step by step, and today's commercially available engines have reached a technical level that is difficult to improve in big throws. The achieved force or moment density is now sufficient for most applications. The only notable limit is the speed limitation due to eddy current losses in the motor. Whenever a magnet passes a coil or a current flows through the coil, the magnetic field generates a current that counteracts its cause. Specifically, this means that the iron parts of the engine are warming up. This is comparable to the eddy current brake of a tram. Kinetic energy is converted into heat. The engine is thereby additionally charged thermally. Rough basic values ​​are 150 Hz for conventional motors and 300 to 700 Hz for high-speed systems. This value is calculated using the number of revolutions per second (n) and the number of pole pairs (2p) of the motor (f = n * 2p).

Construction of direct drives

Idam2Looking at a RI standard motor and comparing it to the RKI series, it is noticeable that the surface magnets still used in the standard version have disappeared on the rotor. The new RKI rotor consists of a laminated steel package in which many magnets are embedded. This is also called a magnet system. This bundles the magnetic flux (B) and produces about 30% more "B" than comparable surface magnets. The formula that calculates the generated force in a motor shows that the 30% more magnetic flux (B) is directly proportional to the force generated. One can assume the same ampacity (I) and coil length (L).

=> F = B * I * l

It turns out that only by replacing the rotor up to 30% more torque can be generated from a motor (stator + rotor). This additional torque, in turn, has an influence on the reverse voltage and thus on the speed adaptation of the overall system.

Whenever a magnet moves past a coil, the magnetic field induces a voltage in the coil. The amount of this voltage depends on the speed of the magnet. The higher the relative velocity between the two, ie the faster the field changes, the greater the induced voltage becomes. The problem with this effect is that with high reverse voltages it is no longer possible to impress a current in the motor. It usually comes in this case to strong vibrations before the axis falls out of the scheme.

The point in time at which this effect takes effect depends largely on two values: the intermediate circuit voltage of the converter and the inductance / negative voltage constant of the motor. The DC link voltage is usually dependent on 540 to 600 V in Europe and the inverter manufacturer. This means that the only way to change the speed of a motor is by winding. By processing a stronger wire, the inductance of the motor decreases. To the extent that the inductance decreases, the required current strength of the motor increases (half the inductance corresponds to approximately twice the current).

Tests: Moment, Lastpulsation and cogging forces

idam3Each system is designed for specific current densities in the winding. In order to continue to ensure the working principle, for example, 1 A is not sent through 50 turns with 1 mm², but 2 A is sent through 25 turns 2 mm². Thus, the current density within the motor remains the same.

In direct comparison one sees an RI standard with WL winding, RKI with the same winding and a RKI with high current winding Zx. Here it is clearly recognizable, as with the same winding WL, the speed in the RKI variant goes back. The RKI series provides more torque and significantly more speed. With the winding adaptation, the mechanical power can be quintupled. Considering only the efficiency and thus the heat loss at a given moment, you can see another significant improvement. The direct comparison is possible with the aid of the motor constant. The motor constant Km (unit in Nm / √W) indicates how much heat is generated at a given moment.

Power loss in W: Pv = (M / Km) ²

ie at half kilometer constant there is a fourfold loss. A direct comparison of the RI and RKI series shows that up to 60% of the power loss can be saved at the same torque output. There is less heat. Accordingly, less cooling is required, which is an advantage that is directly reflected in the operating costs.

Applications in the machine tool

All these advantages make the RKI series ideal for use in slow and fast rotating rotary axes and spindle applications with high performance. Increasing performance allows downsizing or upgrading the application without fundamentally changing the design. The advantages of the RKI motor series in the machine tool, especially for slow and fast rotating rotary axes, are convincing at a glance:

* Moment: increase + 30%
* RPM: increase + 400%
* mechanical: increase + 400%
* Total Cost of Ownersphip: Cost reduction by up to 60%
* Installation space: outside diameter same
* Costs: same for the same performance.

With the combination of RKI direct drive and the Schaeffler ZKLDF..B axial angular contact ball bearing, the manufacturers of machine tools and their subsystems have the option to build the most powerful rotary axis in the world.

Five-year view

Marko Pfeiffer, Head of Sales at INA Drives & Mechatronics GmbH & Co. oHG, gives an outlook on the development possibilities of the RKI engine series in the next 4 to 6 years:

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