IGF project 21173 N: Additive Manufacturing for the Integration of Sensor Technology in Mechatronic Systems [PrESens]
Although they rarely catch the eye, resistive sensors, which convert a mechanical load into an electrically measurable signal, have become indispensable in industry. They are used in weighing technology, in stress analysis, for example in structures such as bridges, or for torque measurement in machines. Another area of application is temperature measurement. The sensor is available as a finished component that still has to be integrated into the system to be monitored. Common designs are semiconductor-based sensors with high sensitivity for low loads or metal-based resistance sensors that are processed into foil strain gauges using lamination, lithography and etching processes. Disadvantages of the existing technology are a limited design freedom on 3D geometries and the typically required application of the sensors into the system in an additional (adhesive) assembly step.
The aim of the PrESens research project is to overcome these limitations by using digital printing technologies for sensor production, such as aerosoljet, piezojet and inkjet printing. On the one hand, the printing technologies enable the direct application of sensors to different carrier substrates and components. On the other hand, the sensors can be applied directly to 3D geometries in multi-axis printing systems, making it possible to map even complex sensor body geometries.
In order to qualify the feasibility and suitability of digital printing for the manufacture of resistive sensors (sensor production), comprehensive printing tests are being carried out for this purpose, and various media, substrate material systems and processes for compacting (sintering) sensing structures and for curing insulating or protective components are being researched. For comparison, established printing processes such as screen printing as well as novel hybrid approaches such as screen printing in combination with dispensing processes are investigated. The manufactured sensors (sensor production) will be characterized with respect to their sensor properties, such as accuracy, reliability and reproducibility, in order to determine suitable sensor applications. Strain gauges and temperature sensors on polymeric as well as metallic substrates are investigated as sensors.
The results obtained to date demonstrate the feasibility of printing production using different functional media, with process control and contacting of the printed sensors representing a highly important factor for precise results. The silver, copper and carbon functional materials investigated exhibit k-factors in the identical range as their chemically manufactured counterparts, whereby structure widths and sensor size are largely determined by the printing process. Surface roughness and surface energy have an influence on printability. Very rough and inhomogeneous surfaces can usually be compensated with layer thicknesses above 20 µm (e.g. by piezojet printing). Material adaptation in the form of pre-treatment (polishing, plasma) or coating of the substrate will probably be target-oriented, as fine structures could also be applied here via other printing processes.
The IGF project 21173 N of the Research Association for Mechatronic Integrated Devices is funded by the Federal Ministry of Economics and Climate Protection (BMWK) via the AiF within the framework of the program for the promotion of joint industrial research (IGF) on the basis of a resolution of the German Bundestag. The project is being carried out in collaboration with the Laboratory for Integrated Circuit Packaging Technology at Technical University Nuremberg. The project is accompanied by an extensive industry committee consisting of 14 companies with material and equipment manufacturers as well as users.