Haptic Feedback Systems for Touchscreens – Using Touch Applications without Visual Contact

07/06/2022 Knowledge

Touchscreens 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. This can be dangerous at high speeds and in dense urban traffic. Haptic feedback systems provide a solution here. If a touchscreen is fitted with active haptic feedback, it provides the operator with a similar feedback to a mechanical key. There are three types of actuators for such haptic feedback systems: piezo elements, vibration motors and linear haptic actuators.

Linear Haptic Actuators: Enough Power Even for Large Displays

Linear haptic actuators are defined by the very strong feedback that they provide. This enables them to provide very noticeable haptic feedback even with large touchscreens or displays comparable with a keypress. The feedback is provided quickly with a trigger delay of no more than 3 to 5 milliseconds.

Linear haptic feedback actuators work with an operating voltage of between 9 and 16 V, and their only drawback is their installation height of 16 mm.

Vishay offers such an actuator based on a solenoid coil the 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, enabling it to simulate a keypress on a touch display, for instance. Its standard connectors have been immersed in 100% solder, and customized connectors are also possible on request. The IHPT-1411 has also been available with AEC-Q qualification since recently.

Vibration Motors: 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, which makes the feedback seem somewhat artificial. 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, however. This is because, for example, a display that is as large as a tablet and is screwed to the vehicle would have to have a vibration motor that is very large and respond with a great deal of lag.

Piezo Elements: Flat and Pressure-Sensitive

At 0.25 mm, piezo elements are extremely flat. They are also pressure-sensitive, which means that greater pressure on a given position of the display generates a greater voltage than lighter pressure. The feedback from the piezo element varies depending on the voltage, and the actuator can also trigger different types of feedback within different waveforms. This opens up other control opportunities for example, you could have the volume of a sound system increase faster the harder you press. However, the feedback is less pronounced than with the other two technologies.

Piezo elements have no moving parts whatsoever and this makes them very long lasting. However, they do have the disadvantage of a high trigger voltage of at least 24 V.

The PiezoHapt-L (PHUA8060-35A-33-000) from TDK is a suitable solution for providing a small element such as a single button with haptic feedback. It uses a multi-layer piezo element, which means it can handle a minimum voltage of 24 V, and can generate greater oscillation than a single-layer element of the same thickness.

The PiezoHapt actuator has a unimorph structure in other words, it 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 piezoelectric element alternately expands and contracts, which causes the bonded metal plate to move accordingly (Figure 5). The alternating current creates alternating peaks and troughs that produce a vibration. This is done very efficiently thanks to the unimorph structure.

Depending on the amplitude and frequency of the applied voltage, the PiezoHapt-L can generate a variety of vibration patterns; it is incredibly responsive with a reaction time of 4 ms. The vibration plate on which the piezo element is mounted measures 80 mm × 60 mm and is barely 0.35 mm tall.

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. The IHPT-1411 actuator from Vishay is ideal for this. In addition, with this, there is absolutely no excuse not to keep your eyes on the road!


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