New caliper brakes for safety critical applications
17 March 2011
Specialist brake manufacturer INTORQ GmbH offers energise-to-release caliper brakes for safety critical applications with large masses or falling loads. Effectively these caliper designs are developed from disc brakes and their kidney shape allows the creation of compact assemblies with disc diameters from 150 to 850mm. Interruption of the dc supply voltage results in full clamping force being applied to the brake disc.
Depending on dimensions and the number of calipers, the brake torque can be from 100 to 10,000Nm.
The main caliper brake model, the BFK466, is robustly constructed for safety critical applications. Multiple helical springs apply force to a floating armature plate which clamps onto a rotating brake disc, normally part of the machine construction. High stability friction material between the brake and the rotating disc increases the resulting torque. To release the brake a DC voltage is applied to typically four electromagnetic coils inside the brake which pull back the armature plate to a released position leaving no residual torque. INTORQ ‘cold brake’ technology applies over-excitation of the coils for the fast release and then a lower holding current. This reduces energy consumption, the heat generated and also speeds the brake re-engagement when the DC supply is interrupted.
As well as the reliable design concept of multiple springs and coils, INTORQ give high priority to long service life and safety. B10d lifetime data is available to allow evaluations of the performance level of machine braking systems; for the BFK466 it is 12 million hours. The concept of a “redundant calliper” is normally used in safety critical applications so that if one caliper fails there is another available to stop the load. This is most effective where there are several calipers. For example, a brake with five active calipers would only require one more to be added for redundant safety – on the basis that only one caliper would ever fail at one time. Thus costs are minimised and the redundant caliper only adds and extra 20% torque, avoiding over-braking of lighter loads. INTORQ also fit microswitch detection of brake actuation so a fault is immediately identified.
INTORQ spring applied caliper brakes are described on the Techdrives website. The BFK463, a new model, suits smaller drives with typical braking torques of 100Nm. There is an intermediate model BFK456 and the larger BFK466 which can deliver around 1500Nm per caliper. These brakes are aimed at lifts and hoists, particularly where the motor is a direct drive without gearbox. They also suit general braking duties for high loads, for example where safety integrity requires braking at the low speed output rather than through a gearbox.
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