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Motor spindle copes with crash and increases machine availability

(PresseBox) (Kleinwallstadt, ) Errors happen again and again in mechanical engineering. To prevent such damage to motor spindles, spindle bearings and other sensitive components during machining in machine tools, JAKOB Antriebstechnik has developed the motor spindle protection system MS³.

A variety of causes can be responsible for collisions in the engine room. In addition to programming errors, incorrectly defined tools, and extraneous contraindications that are not taken into account, inadvertent processing at rapid speeds can lead to massive impacts. The problem remains the same regardless of cause: force peaks of up to 100 kN acting on spindle bearings and other components.

Broken tools or destroyed tool holders are certainly even easier to handle in such a case than serious damage to the motor spindle, or deformations on the machine frame. Admittedly, the purchase of an MS³ system is initially not a very cheap investment. However, the installation may have more than paid for itself after a massive collision, because only the repair of machine tools and the higher-grade spindles installed in it after a serious collision quickly engulfs a five-figure amount; not to mention the costs of a weeks-long shutdown of a production machine.

Mechanical protection systems, which include the MS³ from JAKOB, have their effect even before the machine control can initiate measures such as braking, reversing and standstill of the feed axes of the machine tool for crash prevention via electronic process monitoring systems due to the reaction time. The system is adapted by the manufacturer to the respective application: the holding force of the magnets and the geometry of the system must be adapted to the motor spindle.

Due to the ingenious permanent magnet system and the resulting mobility, MS³ can react equally to axial and radial collisions. At the same time, the system ensures a high level of rigidity during machining and, following a crash and replacement of the damaged tool, usually allows further use of the machine. This is made possible not least by the self-centering design as a double flange system.

When the adhesive force at the separation point is exceeded, the magnet system effects a direct separation of the flanges installed on the machine tool and motor spindle side. With the detachment of the motor spindle side flange and increasing air gap, the magnetic force decreases rapidly. After separation take radially arranged and machine side anchored compression spring elements, the support and the floating guide of the flange of the motor side. The springs act counter to the deflection and allow the motor spindle to swing out by a pre-defined angle. The system is efficiently protected against dirt, lubricants and chips.

Proximity switches installed in the flanges permanently record the bearing position of the flanges and send an emergency stop signal to the machine control system in the event of a collision, whereby the axes of the machine tool are braked. Afterwards, the motor spindle can move freely from the collision location. Due to the compressive force of the springs and the self-centering separation point design, the system reliably and precisely (accuracy <0.01 mm) aligns itself to its origin, the spindle does not need to be readjusted even after an accident, machining can be continued in a timely manner.

The Institute for Production Management, Technology and Machine Tools (PTW) of the Technical University of Darmstadt installed the system in a reference application in a milling machine. After consultation with the manufacturer interested parties can examine the MS³ there.

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