Time for the Specialists

Boom in adapted safety brakes based on sophisticated product platforms

Safety brakes of the first generations were universally applicable in many different branches. Nowadays, the dominating trend is for application-optimised solutions with very high demands on safety and reliability. This is a task which can only be solved with extensive professi onalcompetenceinthe development and production of safety brakes.

Spring-applied electromagnetic safety brakes have a long tradition. mayr power transmission launched the first ROBA-stop-safety brake onto the market more than 40 years ago. Since then, new models and designs have constantly been added. The increasing demands from very different application branches further accelerated the development. Nowadays, the regulated drive motors drive the machines or systems predominantly into the required position. In most cases the brakes only have a holding function. At the beginning of the ROBA-stop era, this was different. Back then, the unregulated three-phase asynchronous motor was the dominant drive machine in many branches. The brakes had to slow down the motors in such a way that the system came to a standstill in the required position.

ROBA-stop-safety brakes of the first generations were equipped with a central wear adjustment and individually adjustable springs, in order to influence the brake behaviour or the position accuracy sensitively.

This is a demanding task, since different factors influence the braking torque and therefore also the retardation time. When operated for a longer period of time, the brake behaviour can change slightly. The linings are subject to wear, and the working air gap widens. As a result, the spring force, which generates the braking torque, decreases. Fluctuations in temperature and humidity may also influence the friction lining behaviour. All of this may lead to a decrease in position accuracy.

In order to counteract this effect, the first ROBA-stop -brakes were already equipped with several special modifications. A central adjustment device compensates for the friction lining wear and restores the working nominal air gap. The braking force is generated by several helical compression springs, which can be individually and sensitively pretensioned. Nowadays, working brakes are hardly ever used for positioning, as this is carried out by regulated drives with holding brakes.

Working and holding brakes of the first ROBA-stop generations were universally applicable in many different branches. Further development was generated by general demands, for example the request to attach a tacho generator to the brake rear side. Other designs were optimised to tolerate extreme thermic loads, caused by high friction work in emergency STOPsituations.

As a general rule, both the brakes and the motors were designed according to Protection IP 54. When brakes with a higher protection were required for applications in harbour crane systems, the first attempt was to seal a standard brake by slipping a housing over it and upgrading it to IP 67. The terminal box for the electrical supply screwed onto the housing was susceptible to  mechanical damage, the installation was complicated and complex and the sealing procedure was difficult. Due to these experiences, mayr power transmission developed a completely new brake, which is specially designed for the specific demands of harbour crane systems. The housing and the terminal box are cast from the same mold, and the number of sealing surfaces are reduced to a minimum. A typical branch-optimised safety brake was born.