Development Of A Flexible Position-Sensing Detector For Touch Control

With the ever growing developments of inter-disciplinary study, wearable electronic products have come into being. Wearable electronic products can be easily attached to garments. They provide people many services such as entertainment, health monitor and communication while not disable people activities, in other words, free our hands to the full extent. Many studies have been conducted to develop flexible touch pads as controlling unit of wearable electronic products. In this study a flexible position-sensing detector is developed. The detector consists of a flexible touch pad with conductive carbon films, a position detection circuit and a personal computer to display the reading data. The flexible detector can be used to read the coordinate information of the pressing position on the touch pad.As a kind of wearable electronics, it is important that the touch devices should be of excellent flexibility and working stability. At present many related studies focus on fabric switches and flexible sensor arrays. To increase the number of controlling positions embedded in smart clothes results always in the increase of connection wires, causing possible signals disturbances and reduction in flexibility of the detector. For the control unit, touch-control devices by calculating voltage distribution are more advanced. But relative research is rare and some techniques are still kept confidentially. Following the working principle of 4-wire resistive touch screen, a flexible touch pad made of conductive carbon films is developed, after testing several conductive films made of other methods. Characterized by uniform and suitable resistance, the conductive carbon film is designed to a proper size according to practical applications. Then a position detection circuit of coordinates is developed. After that, tests are conducted to evaluate the working properties of the developed touch pad. Finally selected application cases are used to verify the performances of the developed sensing detector.The develop of the flexible position-sensing detector includes the following four parts.(1) According to the requirements of touch pad's conductive films, we try several methods such as weaving, vapor deposition and screen printing to obtain a conductive fabric. After comparing the conductive performances of these fabrics, a carbon film is finally selected.(2) Following the wording principle 4-wire resistive touch screen, the formation structure of the flexible position-sensitive detector, as well as the constituent materials, is determined. The detector and computer used for information display are connected by the means of a 4-wire controller. Touch information display can be realized with a 4-point calibration software and Vb program.(3) As a multi-sensing-points flexible touch pad, accuracy of position sensing is tested. Considering the applying environments, the accuracy is also analyzed when the touch pad is small deformed with bending and stretching. Application cases are designed to simulate the detector's applications such as lights-control panel, flexible keypad and tablet. (4) The detector's switch performance is tested to evaluate its on-off properties. Tests include sensitivity, contact resistance change during one touch access and repeatability when the device is loaded continuously.On the basis of the 4-wire resistive touch screen's principle, this study consentrated on the development of a flexible position-sensitive detector by using carbon film as conductive layer and applying central layer to conductive layers. Thanks to carbon film's good uniformity, the detector shows excellent location-sensing accuracy. Central layer's well elasticity ensures the detector's on-off property. Through 4-wire controller, the touch pad is connected to the computer. By designing a program, simulation of the detector's application is performed. The simulation involves a lights-control panel, a flexible keypad and a tablet. The performance of the detector in the simulation manifests its good controlling properties. It would be suitable as the control part of a wearable electronic product.