Clutches protect against machine tool collisions

Edited by the Engineeringtalk editorial team Feb 27, 2008

When a collision occurs the torque increases so rapidly in modern machine tools that the electronic monitoring systems can no longer react in time.

Mechanical torque limiting clutches are indispensable protective elements in dynamic servo axes when collisions occur in applications like machine tools.

This is so even if the control unit is equipped with a monitoring function.

EAS-smartic torque limiting clutches are optimally adapted to the requirements of such axes.

No machine is safe from collisions.

They occur even on machines with the most intelligent control and monitoring systems.

The results for the user are high costs for repairs and replacement parts, downtimes and a damaged image due to late delivery.

However, quite often the consequences for the machine manufacturer are ignored.

Collisions can cause hidden damage which can result in the loss of accuracy.

Some servo controls manufacturers are still of the opinion that mechanical torque limiting clutches are no longer necessary.

The collision monitoring in the machine controls is intended to take over the protective function.

Collision monitoring systems recognise an increase in torque and activate countermeasures.

However, this only works under certain conditions and can only provide effective protection in applications with low dynamics and soft collisions.

The technical development in the field of machine tools has always taken the opposite direction.

Reliable mechanical torque limiting clutches are used as protection against expensive overload damage.

Machines are no longer designed to produce the same part over and over again for their entire service lifetime.

The increased complexity with several, simultaneously moving axes multiplies the risk of collision.

The increased productivity requires faster axis movements and stronger motors which possess a higher inertia.

Higher speeds and larger mass moments of inertia make sure that the kinetic energy constantly increases.

The demands for higher accuracy require stiffer frame and drive axis designs.

In case of a collision, the torque increases so rapidly in modern machine tools that the electronic monitoring systems can no longer react in time.

Mechanical torque limiting clutches, however, separate the drive line within milliseconds after the preset torque is reached and uncouple the majority of the destructive kinetic energy.

The EAS-smartic range of Mayr torque limiting clutches have been specially adapted to the requirements of machine tool axes.

The outer diameter equals that of a standard shaft coupling and it is only 10 to 15mm longer.

This results in a moment of inertia which is lower than for a steel servo coupling.

Hardened components with the tried and tested ball-detent principle and special cup springs provide extremely high torsional rigidity.

All components have been dimensioned so that reliability and lifetime do not have to be compromised despite the high-performance density.

If no specific value is required, the clutch is pre-set manufacturer-side to approximately 75% of the maximum torque and delivered.

A reference marking and torque indication on the clutch show the set value directly.

In only a few simple steps, the torque can be changed to another required value.

The clutch is mounted onto the shaft by tightening a single screw.

The EAS-smartic clamping hub is designed so that it transmits even the maximum torque safely and reliably.

During failure-free operation, the EAS-smartic transmits the torque from the drive shaft onto a drive element or, in combination with an elastic coupling, onto an output shaft.

The torque is transmitted backlash-free over the entire clutch service lifetime.

If the pre-set torque is exceeded, the clutch disengages.

The torque immediately drops.

A mounted limit switch registers the disengagement movement and switches off the drive.

After the cause of the malfunction has been removed, the clutch re-engages automatically and is ready for operation immediately.