Sensory zero-point clamping system for condition and process monitoring

Abstract

Zero-point clamping systems are used for safe and reproducible clamping of workpieces and workpiece pallets in machine tools. Due to the high geometric repeatability of the clamping process, re-clamping errors are avoided and thus high accuracy is achieved when machining workpieces on multiple machine tools. In order to avoid errors during clamping, e.g. due to chips between the clamping surfaces, the clamping force as well as the clamping condition must be checked manually. However, this time-consuming work cannot be carried out simultaneously. In order to reduce non-productive times and to increase the process reliability, a sensory zero-point clamping system was developed. The use of sensory zero-point clamping systems enables process-parallel measurement of clamping and process forces as well as the evaluation of the clamping condition. In this paper, a method for the design and integration of strain sensors in zero-point clamping systems is presented and evaluated. For the experimental validation, four sensory zero-point clamping systems are used to clamp a workpiece pallet. The sensory zero-point clamping system is used for process as well as condition monitoring. As an example of process monitoring, the determination of clamping and process forces that occur during milling is presented. Within the scope of the experimental investigations, a clamping force resolution of 32 N and a process forces resolution of 2 N was achieved. Furthermore, the monitoring of different clamping conditions is shown on the basis of the detection of erroneously missing pallets in the machine tool and the existence of foreign objects between the clamping surfaces. It is shown that deviations from the target states of these conditions can be detected. This offers potential to avoid non-productive times and geometry errors of the workpieces.