Customizable Capacitive Sensor System Using Printed Electronics on Window Glass

Printed electronics offer new possibilities in the design of footprints and integrated mechatronic systems. Fast and uncomplicated customization and cost-efficient fabrication are further benefits of this technology. In combination with other production processes like pick-and-place systems or fused filament fabrication (FFF), functional applications like communication or sensing devices can be produced in a very flexible way. The authors demonstrate how to produce a capacitive sensor system on three millimeter window glass by combining the piezo-jet technology and a pick-and-place system within a single five-axis CNC machine. The piezo-jet system is used to produce the circuitry by printing silver micro paste onto the glass plate. The process is maskless, works with a standoff-distance between one and ten millimeters and can process inks and pastes with a viscosity from 50 mPas to 200,000 mPas. The pick-and-place system puts all necessary surface mounted devices (SMD) directly onto the liquid paste which contains adhesives. The only process that takes place outside the machine is the sintering. However, by integrating an ultra violet (UV) or near infrared (NIR) curing system this process step could also be carried out within the machine. After the sintering the system is fully functional and does not require any further post-processing. The system consists of a micro-controller, two capacitive proximity detection ICs, resistors and capacitors. The digital outputs of the sensors could be used to control any given application, for reasons of illustration the functionality of the system is shown by an additionally mounted LED-strip. The system is easy to design and quick to adapt since the electronic layout is based on the standard layout of the IC-provider and the used software uncomplicated and open-source. Due to the placement at the back of the glass the system is perfectly protected against mechanical and chemical influences. It detects all kind of materials so the sensors can be triggered while wearing gloves or by people with a hand prosthesis. Moreover, the sensitivity can be easily adjusted over the software of the microcontroller which makes the application easy adaptable to several conditions. By recognizing different touch patterns, different operating modes can be performed. Currently the sensor system works as a touch switch, but it could also be adapted to realize a low-cost distance sensor. The flexibility of the used five axis system in combination with the high standoff-distance of the piezo-jet print head offers the possibility to print such systems on a wide spectrum of three-dimensional bodies. Even printing around or into corners is possible. With this method existing components can be functionalized electronically without having to redesign them. The produced demonstrator shows the possibility to extend a component by operating elements, but the capabilities go much further. Existing components can not only be extended by numerous sensor functions, communication elements such as Bluetooth or W-Lan antennas can also be realized in this way.