Mayr Antriebstechnik has with the "Roba guide stopThe redundant brake concept works very reliably thanks to two separate brake circuits.Very short switching times of the spring-actuated and hydraulically released holding brake increase process accuracy and cutting performance, and it relieves the load on the linear guides and ballscrews.
To the individual NC axes one machine tool To operate as energy-efficiently as possible, the axis movement as well as the axle stoppage must be optimized from an energy point of view. For example, standby losses can be reduced by shutting down unrelated axes and switching them back on when needed. This process can only be realized with a backlash-free holding brake.
Biggest challenge: rigidityThe specifications for the development of such a safety brake presented the drive specialists with so many challenges: they had to work fail-safe, that is to say be closed in the de-energized state. Since sufficient position accuracy can only be maintained with appropriate axial rigidity, this was specified with 100 N / μm. The requirements for the surface quality of the workpiece, which requires low-vibration machining, could also be implemented only with the stiffest possible axis. The holding power should be 20 kN and the lifetime was set at 1 million cycles over the entire runtime and 200.000 clocks per year.
Rotary brakes mounted on the drive were basically out of the question because they do not allow the required axle rigidity. Even linear braking systems, which act parallel to the carriage on a rod or a belt, do not meet the rigidity requirements. Rotary engine brakes can withstand comparison even less. They are usually subject to play and every element between the brake and the slide has a negative effect on the stiffness. The development engineers therefore rely on a braking system that acts directly on the profile rail guide. For example, the new profile rail brake with the product name Roba-guidestop is now at least 3 stiffer than, for example, bar or band brakes.
Two brake circuits better than oneThe integrated in a slide safety brake operates with two independent brake circuits and is therefore redundant. Prestressed disc springs press friction linings onto the "waist" of the profile rail. We hydraulically lift with a nominal pressure of 70 bar. The brake mechanism is designed for relatively large stroke paths. This allows the brake compensate for manufacturing tolerances in the rails without losing braking power.
By clamping directly onto the linear guide, ROBA-guidestop fulfills the current constructive requirement for safety reasons that brake and clamping units are to be attached directly to the masses to be braked or held. Drive elements between motor and moving mass such as spindle, spindle nut, shaft coupling or gearbox have no impact on safety. This advantage is particularly important for gravity-loaded axles if the risk of danger to persons should be minimized.
Keep full forceParticularly critical is the dynamic braking at full speed downwards, as required in the event of an emergency stop or power failure. A safe brake must be able to stop the load safely and quickly without being damaged. Motor brakes are only partially able to do so because they are often not adequately dimensioned due to limited space and very high temperatures within the engine. The ROBA-guidestop is equipped with special friction linings, which allows a variety of dynamic braking and brings the load safely to a halt. However, direct clamping to the profile rail offers even more advantages: The additional stiffening of the NC axis increases process accuracy, increases cutting performance and is also proven in heavy-duty machining. Here, machining takes place with lower vibration, which improves surface quality.
When the vertical axis is stationary, the ROBA-guidestop takes over the load, for example during machining. In this phase, the drive motor can be switched off and taken out of regulation. Switching off the motor eliminates the control movements and thus protects the ball screw. The closed brake absorbs axial forces and tilting moments and thus relieves the linear guide. Service life and maintenance intervals of the drive components are extended and energy consumption is slightly reduced.