The world-wide patented backlash-free ROBA®-DS shaft couplings produced by mayr® Antriebstechnik transmit the torque with high torsional rigidity and com-pensate for axial, angular and radial shaft misalignments. They have proved themselves as the ideal couplings for many direct-powered servo axes and are constantly being tried out with success on new applications, for example in the drive unit of a driving simulator.
In the Formula 1 driving simulator produced by the British company Ball Racing Developments (BRD), the driver sits in an original F1 racing car and drives down a fictional track which they view on the flat screens positioned in front of them. As when driving a real car, certain forces affect the driver when they accelerate, brake or drive round corners. In order to generate the centrifugal forces which occur when driving round corners, the vehicle is moved quickly to the left or the right in the area of both axes. If the vehicle is moved backwards or forwards along the longitudinal axis, the driver is pressed into the seat or against the safety belt just as when carrying out real braking and accelerating manoeuvres.
Spindles are used to generate the left-right movement in the area of the vehicle axes. These spindles are driven by servo motors via toothed belts. A direct-powered spindle axis pushes the vehicle along the longitudinal axis. A mayr® Antriebstechnik backlash-free, torsionally rigid disk pack coupling from the ROBA®-DS series is located between the servomotor and the spindle. This compensates for angular and axial shaft misalignments such as those caused by heat expansion. The ROBA®-DS servo coupling in single-joint design has an extremely compact form and impresses customers with its exceptionally low mass moment of inertia. This makes it ideal for this application and for many other servo technology applications. The world-wide patented, backlash-free ROBA®-DS shaft couplings are torsionally rigid but bend-flexible, and compensate for axial, angular and radial shaft misalignments. Their range of application is constantly increasing due to consistent extension of the size and variant possibilities. This series, conceived especially for servo technology, comes in sizes 3, 6, 10 and 15 in a diameter range of 45 to 79 mm to cater for torques from 35 to 150 Nm. Their characteristics are as follows: low mass moment of inertia due to compact assembly and the use of aluminium instead of steel as well as shaft-hub connections specially adapted for servo applications.
The series of “big ones”, the ROBA®-DS all-steel couplings, is also expanding constantly. They are currently being offered in 12 different sizes for nominal torques ranging from 300 to 24,000 Nm. An alternative, reinforced disk pack is also available for the sizes 16 to 160, which has further improved the coupling’s performance density. Dependent on the application, packs with high misalignment compensation capabilities or high performance densities can be selected and used. In order to keep up with the improved performance density on the coupling, the “normal” shrink disk hub has been supplemented by a shrink disk hub for large bores. Here, the outer diameter of the shrink disks used has been enlarged as much as possible so that the frictionally-locking transmittable torques can be substantially increased.
Intermediate sleeves made out of carbon fibre-reinforced plastics (CFP) allow high speeds even on long couplings. In comparison to steel sleeves, the CFP variants have a far higher bend-critical speed. Not only that, but CFP sleeves are up to 80 % lighter. This quality is particularly useful for large construction sizes and long sleeves. A further advantage of the plastic material is its resistance against corrosion. If additional insulation is required with reference to leakage current or voltage breakdown, glass fibre-reinforced plastics (GFP) are used. They reduce the achievable bend-critical speeds slightly but the advantages with reference to mass and resistance to corrosion remain. Spring steel disk couplings are robust and reliable. They are predestined for applications in extreme ambient conditions. Their temperature resistance and performance density can hardly be equalled by other shaft couplings. If correctly dimensioned and used, they have an almost unlimited lifetime. Spring steel disk couplings are wear and maintenance-free and transmit torques with extremely high rigidity.
Many spring steel couplings available on the market today transfer only a proportion of the nominal torque defined in the catalogues (50 to 80 %) via frictional locking. The remainder is transmitted via positive locking using fitting bolts. Minimal displacements are caused by loads over the backlash-free frictional locking torque in the area of the disk pack connection. Various disadvantages result from this. Depending on the amount of load and the load direction, the individual components shift position, leading to an unstable balance condition in the coupling.
The constant relative motion in the area of the disk pack connection means that the screw pre-tensioning force drops. The bend components to be adsorbed by the screw increase. This leads to screw breakage caused by excessive operating forces. In order to avoid this, manufacturers are forced to place appropriate limitation on such couplings with reference to alternating torques or applied operating factors. To sum up: in spite of the extremely high values stated in catalogues, a coupling in the next size up or two sizes up often has to be selected.
mayr® Antriebstechnik has trodden a new, unconventional path in the development of its ROBA®-DS all-steel couplings sizes 16 to 2,200. In order to unite high performance density with no backlash, the disks in the clamping area are treated in a special process. Specially shaped collar bushings are used for continued backlash-free torque transmission from the disk pack onto the hubs or the intermediate part which, due to the screw pre-tensioning forces available, allow absolutely backlash-free connection to the hubs. This has produced a backlash-free flow of force with excellent force flow density between the input and the output of a shaft coupling. Comparatively small screws have been used. Limitation of the compensation capability due to short free bending lengths could be avoided. The nominal values defined in the catalogue can be used without any limitations, and reductions due to misalignment, overall load configuration or balance requirements is not necessary.
Every drive has its own special features and places very different requirements on the couplings which transfer the torque and which may have to compensate for any shaft misalignments. On high-speed, dynamic or reversing drives, it is usually only backlash-free couplings which are capable of fulfilling these requirements. With its disk pack couplings, steel bellows couplings and elastomer couplings, mayr® Antriebstechnik has included three of the most common and attractive backlash-free shaft couplings in its program, thus offering the ideal solution for many different drives.