It’s predicted that by 2020 almost 2.9 billion people will own a smartphone (source statstica), and thanks to the worldwide adoption of smart devices, such as tablets, e-readers and smartphones; almost everyone is familiar with, and embraces touchscreen technology.

In fact many people are so acquainted with smart devices they expect all touch sensors, regardless of size to operate in the same way, with the same functions. We’ve seen this most recently with the release of Apple touch, or “Force Sensing” which can differentiate between a soft and hard touch, allowing for different options to be selected using the correct software. Discover more about Zytronic’s multi-touch force sensing here

Another widely used function on small consumer touch devices is Tactile, or Haptic feedback.

Haptic feedback is the use of vibration patterns and wave forms to convey information or enhance user experience. At first glance this function would seem like a natural partner for touchscreen technology, as the word “Haptic” comes from the Greek phrase haptikós, literally meaning “I Touch”, and is used widely used on smart phones and tablets.

Tactile touch on consumer devices

Haptic feedback on small consumer devices such as tablets and smart phones, is widely accepted and allows the device to “communicate” with the user by creating a vibration to alert/ offer reassurance that an action has occurred as a response to a physical touch to the screen. Applying this function to the small touch surfaces of phones and tablets can be achieved relatively easily with the following:

1. An actuator is a machine component that is responsible for moving or controlling a mechanism or system. An actuator requires a control signal and energy source, the control signal required is moderately low energy and may be electric voltage or current, pneumatic or hydraulic pressure, or even human power. In the case of smart phones the actuator vibrates in a specific pattern and the sensation is felt through the touch glass.
2. The driver is part of the electrical design and is the connection between the controller and the actuator. The drivers can be simple analog or intelligent digital interfaces depending on the type of actuator
3. The software generates the haptic wave forms in response to a touch event, sending the information to the driver, then actuator to create the “buzz” or vibration to alert the user of the action.

Actuator Technologies

There are a number of actuator technologies which may offer a solution for touch sensors.

• Eccentric Rotating Mass (ERM)

Using a vibration method a motor with an off-centre mass that creates strong vibrations when spinning. While this method has been in use for a number of years, it lacks the precision to create high definition haptics.

• Linear Resonant Actuator (LRA)

Another vibration technology, LRA achieved a more enhanced vibration precision by using a spring mass system that oscillates in a linear motion. While the vibration pattern is advance, LRA is still unable to offer high definition haptics, but the system does save power.

• Piezo

Again Piezo achieve haptic feedback via vibration. Voltage is applied to a piezo-electric material which bends to create the vibration. This method is much more accurate, and high definition haptics can be achieved but the system is costly.

All of the technologies described above are well suited to small size touch sensors used in hand held consumer electronics, and generally very accurate through thin glass based sensors.

The challenges of achieving tactile touch in large format sensors

In theory achieving haptic, or tactile touch function in a large projective capacitive touchscreen could done in a similar way, however process is much more difficult….

To provide sufficient impact resistance and rigidity to protect the underlying display, typically glass thickness of mid to large sized touch sensors for self-service applications can be anywhere from 3mm  to10mm thick. This presents a major problem when trying to create a force strong enough to create a detectable vibration, but without causing damage to the system.

Furthermore any devices used to generate a force strong enough to be felt through thick glass would require both power and space, which could negatively affect the design of the touch sensor, and unit as a whole.

Another potential issue is the integration of the touch system. Usually self-service touch screens are integrated using very strong adhesive tape or silicone/epoxy adhesives to ensure there is no movement of the glass and to offer protection from contaminants penetrating the assembly – especially in outdoor applications. However when the glass physically needs to be able to move to provide feedback, such rigid mounting methods are not suitable as they inherently restrict  movement. Instead the touch sensor must be almost “suspended” in front of the display and attached with a much more flexible substance such as spongy neoprene gasket. However, these can cause potential problems with liquid and dust ingress, rendering the touch display vulnerable, and unsuitable for outdoor or heavy use applications.

While applying haptic feedback to large format touch sensors is not an impossible task, the issues highlighted above are currently making the technology very challenging to implement for most system integrators, but that being said, it is probably only a matter of time before advances in haptic technology enable increased levels of user feedback irrespective of the type of touchscreen, application and environment. In the meantime, as a glass processing specialist, Zytronic is able to incorporate permanent surface features on the front of their self-service optimised touch sensing products. These features can be raised ‘bumps’ or ridges printed onto the glass using ceramic inks, or CNC machined dimples and grooves. Both help to guide fingertips – especially in applications where the user may be partially sighted or the operator’s concentration and vision is not on the touchscreen. For more information on these glass customisations, please contact us.