zForce AIR Touch Sensor can be used for different purposes, such as detecting touches on a surface or objects in mid-air. Assembly requirements differ depending on what purpose the Touch Sensor fulfills. In addition, different industries have different standards and demands to fulfill. Mid-air detection applications generally require lower mounting tolerances.
Means of Integration
zForce AIR Touch Sensor comes in two types: one is designed to be integrated horizontally and the other vertically. This allows different types of assembly possibilities and better adaptation of the available space in the host system. The two sensor designs are built on the same concept, but use two different front light pipes. One light path is unaffected; the other bent 90°.
The front optical surface is not allowed to be blocked by the host system.
The short sides of the sensor should be protected from light of high intensity. If there is a risk for exposure to strong light, covering the short sides with, for example, black tape might improve performance.
Light is sent straight out and enables an active area in front of the module, in the same plane as the light path.
When integrating zForce AIR Touch Sensor into a host system make sure not to interfere with the light path. For horizontal integration, the opening for the sensors light path must be minimum 1.4 mm.
If the host system have large tolerances, opening must be adjusted to always be minimum 1.4 mm.
Light is bent 90 degrees within the Touch Sensor. This allows the sensor to be assembled vertically but still have an active area in the horizontal plane.
To make sure not to interfere with the sensor light path, the opening must be minimum 1.6 mm. If the host system has large tolerances, the opening must always be adjusted to be minimum 1.6 mm. Also note that it is not allowed to mount, glue or in any other way affect the sensor's optical surfaces since it will affect the performance. This applies to both the sensor's visible optical surface and the back of the mirror surface that bends the light path 90°.
Options for Guiding and Fastening
- Double adhesive tape – for smaller sizes this can be used alone to hold the zForce AIR Touch Sensor. The host system geometry needs to provide a flat supporting surface.
- Snaps – Host system geometry provides some sort of snap features holding the zForce AIR Touch Sensor in place. These must be developed for each case to fit the host System cover and the surrounding.
- Sandwiched – the zForce AIR Touch Sensor is mounted by pressing the Touch Sensor between host system exterior cover and display. A structure (ribs, foam gasket or adhesive) is needed to make sure the Touch Sensor cannot move.
The zForce AIR Touch Sensor needs to be protected from outer pressure and forces that can bend the sensor and by that change the direction of the sensor light. The most common cause of bending is when a Touch Sensor is mounted on a non-flat surface, so the host system supporting structure needs to be flat. High point load on the PCBA side of the sensor can also affect touch performance. If any kind of clamp or similar setup is used for fastening, make sure that the contact surface with the sensor is as large as possible.
An external window is something placed between the sensor and the desired touch active area, usually in form of a plastic or glass “window”. It is of high importance for the function that these surfaces fulfill the optical demands stated in Optical Requirements on External Window. It is important to know that each window the light passes through will reduce the sensors received signal levels, even though the requirements are fulfilled, which in some applications might reduce the maximum detection range.
External Reflective Surface
An external reflective surface is a surface located outside the active area, but close enough to be reached by the IR light emitted by the sensor. Depending on the angle and the reflectance of the surface, reflected light can enter the sensor and interfere with touch object detection. If the external reflective surface is close to the touch active area, it is recommended to make sure it has a low reflectance in the direction back towards the sensor.
Lower reflectance can be achieved by
- Using a color on the reflective material which has low reflectance in the IR spectrum, e.g. black plastic or black paint.
- Using an angle of the reflective surface to divert the reflective light away from the sensor, meaning that the surface can not be perpendicular to the sensor's optical axis. It need to differ with at least 3 degrees compared to the perpendicular angle.
The sections below describe integration aspects specific for touch applications and do not concern mid-air applications.
Mechanical integration of zForce AIR Touch Sensor and assembly tolerances has a direct impact on touch accuracy. For this reason relaxed assembly tolerances might in some applications have an impact on the perceived touch performance. The best user experience is achieved when the projected touch Active Area from the zForce AIR Touch Sensor perfectly overlaps the intended touch sensitive area on the host device, for example, the active area on a display.
Touch active area of host system and zForce AIR Touch Sensor needs to be well aligned. Translational tolerances in x and y directions and rotational tolerances will affect accuracy. See Translational Tolerances (x and y direction) and Rotational Tolerances (angle "b").
Hovering touch means that the Touch Sensor reports a touch event before the object reaches the surface. The basic principle of the Touch Sensor is that light is sent above the surface. To provide a good user experience the Touch Sensor software adjusts the signal and reports a touch first when the object reaches the surface.
Hovering touches is also direct linked to how the zForce AIR Touch Sensor is integrated in the host system. It’s important that the mounting surface has the correct angle compared to the intended touch surface. Twisting and tilting of zForce AIR Touch Sensor should always be avoided. Relaxed tolerances can lead to missed touches and increased hovering. See Translational Tolerances (z direction) and Rotational Tolerances (angle "a").
Furthermore, host system active area surface need to be flat or slightly concave. A convex surface can give false touches.
Recommended Tolerances for Touch Applications
0 mm to +0.5 mm
Translational tolerances affects the overlap between the display active area and the touch active area. For example, if the Touch Sensor is translated 0.5 mm in x-direction there will be a systematic touch offset of 0.5 mm for the complete sensor in x-direction.
A 0 mm translation in z-direction means that the host system active area surface is positioned exactly at the edge of the light path. A positive translation means that zForce AIR Touch Sensor, and therefore the light path, is translated up from the host system active area surface. This will not affect the touch accuracy in the sensor, but it can affect the perceived touch performance, since it leads to increased hovering. A negative translation in z-direction should be avoided since parts of the light will be blocked which leads to no or reduced touch performance.
There are two types of rotations that can affect the performance; defined as the angles "a" and "b". Angle "a" affects the hovering and angle "b" affects the overlap between the intended active area and the Touch Sensor active area. Both these issues will grow with larger display sizes. The angles are exaggerated in the pictures to better illustrate the problem. For any uncertainty regarding rotational tolerances for a specific application, contact Neonode for recommendations.
The angle "a" is defined as shown in the images below.
The example below illustrates how the problem increases with larger active areas.
The angle "b" is defined as shown in the image below. How sensitive zForce AIR Touch Sensor is for assembly rotations is directly linked to the size. At any given angle b, the touch AA will be tilted twice as much at 200 mm compared to at 100 mm.
Models and Drawings
3D-models and 2D-drawings for the zForce AIR Touch Sensor can be downloaded at https://support.neonode.com/docs/display/Downloads.