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Without visual contact: Haptic feedback systems for touchscreens
By Edgar Schäfer, FAE Automotive Business Unit at Rutronik T
ouchscreens have already replaced many switches and dials in the car. But the sleek, flat surface is also the problem—controls cannot be felt, so the driver has to look. To avoid this danger, haptic feedback systems provide a solution here. If a touchscreen is fitted with active haptic feedback, it provides the operator with similar feedback to a mechanical key. There are three types of actuators for such haptic feedback systems:
Enough power even for large displays
Linear haptic actuators are defined by the very strong feedback that they provide; even with large touchscreens or displays. It is provided quickly with a trigger delay of no more than 3 to 5 ms. Linear haptic feedback actuators work with an operating voltage of between 9 and 16 V. Vishay’s IHPT-1411 combines very compact construction with powerful oscillation of 6 g with a mass of 0.5 kg and a trigger voltage of 12 V. Which enables it to simulate a keypress on a touch display, for instance.
Figure 2: Compact and powerful: the IHPT-1411 actuator from Vishay.
Easy to control
Vibration motors move a weight, such that they vibrate instead of emitting the “click” feedback of actuators. However, they suffer from relatively substantial lag with a trigger delay of between 20 and 50 ms. They require a trigger voltage of under 12 V - most models can run with just 3 V - and are easy to trigger. Vibration motors are only suitable for smaller displays.
Flat and pressure-sensitive Piezo elements are extremely flat (0.25 mm) and pressure-sensitive. The feedback from the piezo element varies depending on the voltage, and the actuator can trigger different types of feedback within different waveforms. This opens up other control opportunities, like increasing the volume of a sound system faster by pressing harder. However, they do have the disadvantage of a high trigger voltage of at least 24 V. The PiezoHapt-L from TDK is a solution for a haptic feedback system with a high reaction time of 4 ms. It uses a multi-layer piezo element, so it can handle a minimum voltage of 24 V, and generate greater oscillation
30 May 2022 Components in Electronics
Figure 1: Construction of a touchscreen with haptic feedback actuator.
Figure 3: A comparison with vibration motors shows that piezo elements respond much more quickly and flexibly.
than a single-layer element of the same thickness. Its unimorph structure consists of an active and a non-active layer. The active, piezoelectric element with electrodes on both sides is bonded onside to a non-active metal plate. If an alternating current is applied to the electrode, the element alternately expands and contracts causing the bonded metal plate
to move accordingly - produce a vibration. Surfaces with feeling
Touch displays are not the only thing that can be fitted with haptic feedback - any smooth surface can become a touch-sensitive solution that replaces conventional buttons and switches on the dashboard and in the door panel.
Figure 4: The PiezoHapt-L from TDK is just 0.35 mm thin and is ideal for adding haptic feed- back to a single button.
www.cieonline.co.uk
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