When do you need a servo clutch?

A coupling initially connects two shaft journals. However, even a minimal misalignment of the shafts or fluctuations in the ambient temperature can lead to uneven running, which is reflected in increased wear on the bearings, greater noise development or even damage to the entire drivetrain.

Bellows couplings are very torsionally rigid in the direction of rotation, i.e. they hardly twist on themselves. Laterally, on the other hand, they are flexible, which allows them to compensate for misalignments. Low restoring forces, absolutely backlash-free torque transmission and flexible application options make them an indispensable component in mechanical engineering today. Metal bellows couplings score particularly well for high speeds and precise applications.

Elastomer couplings have a damping effect on vibrations instead of passing them on to the next component. With this type of compensating coupling, it is also important to ensure the most precise alignment possible, but the risk of damage is much lower.

Safety couplings can be based on both bellows and elastomer couplings, but have a torque limiter as overload protection. It reliably prevents costly machine damage, repairs and downtime.

If the set torque is exceeded, the drive is mechanically disconnected.

With its extensive modular system, JAKOB Antriebstechnik GmbH offers an optimum variant for every application. Combinations of metal bellows couplings, safety couplings, elastomer couplings and spacer couplings are also possible.

Where do you need servo couplings?

Torque transmissions are a necessity in almost all technical systems. The more dynamically and precisely a system is to operate, the more attention must be paid to the drive with the shaft connection area - the couplings.
Servo couplings can be used in highly dynamic feed axes of machine tools or are suitable for demanding drives in general mechanical engineering. They can be found in industrial robots, servo and stepper motor applications. Due to the increased use of servo drives with their high dynamics, ever more perfect couplings are required. Even if the drive elements are manufactured with high precision, the unavoidable axial displacements in the hundredths of a millimeter range must be compensated for. Backlash-free metal bellows couplings, which are equipped with additional functions to protect the machine as safety brakes, are particularly suitable here.

What are servo (compensating) clutches?

Servo couplings are compensating couplings for backlash-free, angularly accurate transmission of torques with the highest possible torsional rigidity and the lowest possible mass moment of inertia. However, elastomer couplings with a flexible polyurethane core can also be a sensible alternative for a variety of applications due to their product-specific advantages. Common to all servo couplings is the absolute freedom from backlash (also shaft-hub connection) and the flexibility to compensate for shaft misalignment. As spacer couplings or cardan shafts, they can bridge distances of up to six meters without intermediate bearings. As miniature couplings, they are designed for the offset or axial displacement of two axes. Various versions are available for different applications such as NC axes, stepper motors, robot drives, linear units, handling devices, angle encoders or servo drives. They are available as bellows couplings, elastomer couplings or cross-slide couplings.

Equipped with an additional safety function, servo compensating couplings also serve as overload protection and torque limiters and protect expensive systems from costly machine damage. Stainless steel bellows with various designs, polyurethane stars with different Shore hardnesses or cross slide parts made of polyacetal are used as flexible compensating elements.

How to choose the right servo coupling

In order to find the right coupling for a drive train, a number of factors must be taken into account. The required torque range, the offset and the ambient temperatures of the coupling are particularly important. The distance to be bridged between the shafts, electrical conductivity or insulation, use in potentially explosive atmospheres, particularly high speeds or torques and many other factors also influence the choice of the right servo coupling.

First, the required maximum torque is determined. The coupling should be selected accordingly and should not be used permanently with an overload or in the absolute limit range.

The misalignment goes hand in hand with the possible service life, because the greater the misalignment, the shorter the life expectancy of the coupling. It is therefore essential to ensure that the alignment is as accurate as possible. The compensable lateral misalignment is in the range of approx. 0.15 - 0.3 mm. This also depends heavily on the number of bellows shafts. For example, a 4-shaft coupling achieves several times higher possible offset values than a 2-shaft coupling. In principle, however, the lateral displacement is one of the most important factors to be taken into account after the torque, as it has a major impact on the possible power transmission. A high misalignment can also lead to uneven running, which can be reflected in increased wear, greater noise development or even damage to the entire drivetrain.

When measuring the maximum operating temperature, it is also important to take into account any heat generated by the machine and its components during operation. The choice of clutch material is also important in this context. The lightweight aluminum that is often used is replaced by stainless steel components at very high maximum temperatures, for example. While steel or stainless steel couplings can be joined using a special micro-plasma welding process, this method is not suitable for combinations of aluminum and steel. Bonding methods can be used here, but these can fail under extreme operating conditions (chemicals, very high or low temperatures). Particularly in the case of couplings on the input side of a planetary gearbox, high temperatures can occur in critical applications, which could loosen the bonded joints.

The joining process developed and patented by JAKOB (crimping process), on the other hand, is ideal for connecting multi-layer stainless steel bellows to aluminum hubs without backlash. Here, operation is also safely possible in temperature ranges from -50°C to +350°C.