Cobots are characterized, among other things, by their lightweight design and their freedom of movement in terms of multi-axis movements and at the same time maximum safety for humans, realized for example by laser scanners or camera systems. To ensure that the flexible movement and lightness can also be implemented in practice, it makes sense to integrate disk slip rings (pancake slip rings) into the gripper system for electrically controlled grippers that grip various workpieces, objects or weights at the end of the robot arm. These disk slip rings can be used to transmit loads and signals and thus supply the gripping system.

Of course, cables can also be used to transmit the load and signals. However, the main disadvantage of using cables is the limited movement of the robot arm. Continuous rotary movement, for example, is not possible with cables. And even in swivel mode, conventional cables are exposed to such high mechanical loads that they are often the weakest link in the chain.

The disk slip ring from Kübler transmits load and signals and can therefore replace cables in the robot arm.

© Kübler

Using disk slip rings, such as those offered by Kübler, the load and signal can be reliably transferred from a stationary platform to the rotating platform - in this case the gripper system at the end of the robot arm.
The weight and length of the robot arm are the main factors that determine its dynamics. In this respect, disk slip rings score highly in terms of installation depth - the slip ring from Kübler, for example, measures 10 to 15 mm in the axial direction and weighs just a few grams in the double-digit range. The shorter the robot arm, the faster movements are possible for the robot, allowing work processes to take place in short cycle times.

Long service life

Combined with a rotary encoder, the disk slip ring handles positioning as well as signal and load transmission.

© Kübler

Fault-free transmission of load and signals is essential for high system availability. To ensure this, the disk slip rings from Kübler are equipped with a multiple redundant system that offers a high level of transmission reliability. In concrete terms, this means that several contacts are implemented per transmission path, each of which in turn has several contact points. An example to illustrate this: there are at least four contacts (brushes) on the circumference of the disk slip ring. Each individual contact uses micro-springs to ensure reliable transmission of load and signal.
The transmission takes place by lightly pressing the two plates or disks together. The slip ring module is usually integrated into the gripper housing. Due to the many contact points, very low contact pressures are sufficient to transmit the load and signals without interference. Thanks to the low contact pressure of the two disks, the disk slip rings are maintenance-free and have a long service life. Common variants currently provide up to 5 A/60 V(AC), 48 V(DC) and are available with up to 20 channels. The disk slip rings are suitable for common fieldbuses or Industrial Ethernet up to 100 Mbit/s and operate in a temperature range between -40 and +75 °C.

Positioning and transmission combined

Manfred Hick is Business Development Manager/Product Manager Slip Rings at Kübler in Villingen-Schwenningen.

© Kübler

In addition to the pure disk slip ring range, there is also the option of a compact slip ring solution that can take on positioning tasks as well as transmitting loads and signals. For this purpose, the slip ring is combined with an absolute rotary encoder. Such an encoder/slip ring combination can be used in gyrocompasses for navigating ocean-going vessels, for example. The power supply and industrial bus-supported data feedback are reliably secured.