Screws belong to the basic machine elements and are present in practically every machine and plant. They serve both as fastening elements as well as functional components. However, it does not always make sense to monitor them all.
In (highly) dynamically stressed connections, different challenges arise.
Screws are pack animals, they rarely come alone. Several dozen screws are frequently used in robot foundation screw connections. During assembly, the machines are aligned using the screws and subsequently fastened to the ground. The state of the art in this field is assembly with torque wrenches. Generally, it is not ensured that the pretensioning force actually present in the screw is the same across all screws. Both the geometry of the foundation and the tightening strategy (crosswise, sequentially, etc...) have a great influence on the actual preload distribution of the entire assembly. It can happen, for example, that 19 of 20 screws are fixed - but one has come loose during assembly or due to subsequent dynamic loading. As a result, the machine bed or robot foundation attached to the floor can deform under load and adversely affect the manufacturing process. The result is workpieces that are not dimensionally accurate or broken screw connections.
This is why screw connections are frequently checked in practice. Various solutions exist, from colour markings to the retightening of screw connections. As a rule, they are not satisfactory, because colour markings on the screw and nut can only be traced back to relative rotation - a fracture of the screw or loss of pretension due to other influences cannot be detected. The retightening of screw connections is extremely critical, especially with HV screw connections, and should be avoided. In addition, it is expensive: Screw maintenance is usually only possible with the machine at a standstill and therefore always means a loss of productivity.
The situation is similar with screw connections in steel structures. These are subject to a monitoring obligation - up to an annual 100% inspection. This is particularly the case when dynamic loads are exerted on a building by machines and systems such as cranes.
With the Sensorise Smart Screw System S4, both steel-steel and steel-concrete connections can be permanently and continuously monitored. Visitors to the Sensorise stand were able to experience for themselves the sensitivity of the system: Even tightening the nut of a M24 threaded rod without tools is clearly measurable. The same applies to the loss of preload occurring during rotating assembly processes.
What would metal processing be without machine tools... In fact, numerous suppliers presented themselves in the halls, from presses to machining centres to hand tools, the complete range of technology was represented.
The recording of machining forces was also in high demand this time. There were two main areas of application:
On the one hand, the forces on the individual axes of a machine are required for process control. The result is faster machining while maintaining high quality and reducing tool wear.
On the other hand, the machining forces can be used for quality control. Each process has its own force-time curve and thus an individual "fingerprint" from which process and quality changes can be immediately seen.
A high resolution of the measuring system is of central importance for both applications. For example, the process forces in micromachining are small, but the machines are also very rigid. This leads to problems because a compromise has to be found for monitoring: Either the sensor system can provide very fine resolution in a limited range or does not offer enough resolution over a large range for the smallest process forces.
With its Smart Linear Profile Rail System, Sensorise has demonstrated what is technically possible: a guide rail (Schaeffler, type TKVD25-U with carriage KWVE25-B with a static load rating of 37,000 N) achieves a resolution of 1 N with integrated sensor technology. This corresponds to a bar of chocolate on two fully packed VW Golf!
Threads are not only found in classic screws. Couplings, tensioners, motion threads... mechanical engineering is full of threads in various forms. In addition to pure load measurement, dielectric properties of surrounding materials can also be measured with thread-integrated sensors. The screw thus becomes a robust capacitive sensor. Visitor interest in sensor integration was therefore very high. So we are eager to see which products we will see at the next EMO in Milan. The course has been set!