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Capacitive Sensor System Using Printed Electronics on Window Glass



Capacitive Sensor System Using Printed Electronics on Window Glass
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.
Production Floor

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Authored By:


Jan Fröhlich, Daniel Gräf, Jörg Franke
Institute for Factory Automation and Production System
Friedrich-Alexander University Erlangen-Nuremberg
Erlangen, Germany
Jan.Froehlich@faps.fau.de

Johannes Hörber, Martin Hedges
Neotech AMT GmbH
Nuremberg, Germany

Summary


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 ICprovider and the used software uncomplicated and opensource.

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.

Conclusions


In this paper the authors described the production of a low cost capacitive sensor system within a five axis CNC machine. The system was designed as a basic concept. The needed components are easy to obtain, the manufacturing is almost fully automated and the software is open source.

Main issues were the connection of the LED strip as well as the connection of the power source. The latter could be solved by developing a frame with integrated spring probe pins. The connection of the RGB LEDs has to be simplified. Replacing the RGB LEDs by either LEDs with an upside down mounting option or by a completely different indication system should be considered in future works.

Another way to improve the manufacturing process would be the installation of a curing system in form of a ultraviolet (UV) or near infrared (NIR) curing system [10]. Thus the manual process of transferring the assembled glass plate into the convection oven could be replaced and a fully functional demonstrator could be produced in a single machine.

Despite some challenges during the production, the demonstrator shows proper functionality and high reliability. The sensor is intuitive and ergonomic to operate. It detects the touch of a finger as well as the approach of a dielectric rod. Therefore, the system can also be used while wearing gloves or by people with a prosthesis. Moreover, the system is perfectly protected against environmental influences, since it is situated behind the glass. Various applications of such a sensor system are conceivable.

Initially Published in the SMTA Proceedings

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