Touch me – feel me!

Touch me – feel me!
Feature articles |
Whether for smartphones, vehicles, industrial controls, domestic appliances or gaming consoles, the future belongs to piezo-based push-button solutions with haptic feedback.
By Julien Happich

Share:

As a result of the demand for greater convenience and safety, multi-functional human-machine interfaces (HMIs) such as touchscreens and other touch-sensitive surfaces can now be found almost everywhere. Existing solutions for haptic feedback such as eccentric rotary mass (ERM) or linear resonant actuators (LRA) have a number of drawbacks. These include their relatively large dimensions, the insertion height being particularly relevant for display controllers, and a high demand for power in battery-operated devices such as smartphones or tablets. Furthermore, the frequency or the strength of the feedback are at best only variable within very narrow limits, and they do not have any sensory capabilities.

Fig. 1: At no more than 35 mm, the TDK PiezoHapt types
are extremely thin and are suitable for smartphones,
tablets and vehicle displays.

A considerably better alternative is offered by TDK’s PowerHap and PiezoHapt families of piezo-based actuators. These components are a combination of pressure-sensitive sensor and actuator in one. With the two product families, TDK offers the widest range of actuators for haptic feedback.

TDK has developed the L8060 and L3015 types specially for use in vehicle and smartphone displays. They have impressively low-profile insertion heights of just 0.35mm and 0.3mm with areas of 80x60mm (L8060) or 30x15mm (L3015). The unimorph design of the PiezoHapt is based on a flat multilayer piezo element that is connected to a vibration plate on one side and can be mounted directly underneath displays.

The actuators are designed for operating voltages of ≤24 V (L8060) or ≤12 V (L3015). Depending on the amplitude and frequency of the applied voltage, a wide range of vibration patterns can be generated with PiezoHapt. These types are especially well-suited for OLED displays.


Acceleration, force and response time

Fig. 2: Design of square PowerHap actuators.
This family of products includes four types with
edge lengths of between 9.0 mm and 26.0 mm
and insertion heights from 1.1 mm to 2.3 mm.
Thanks to the multilayer technology, forces
in excess of 25 N and displacements of 230 µm
can be achieved.

The actuators of the PowerHap family are based on multilayer piezo plates with copper inner electrodes. Figure 2 illustrates the basic design.  If a voltage is applied to the piezo plate, it only expands minimally in the z axis, but due to the constant volume of the piezo effect it contracts simultaneously in both the x and y axes.

Two titanium cymbals bonded to either side of the plate amplify this contraction by a factor of 15 in the z-axis, achieving a large displacement of up to 230 µm for the largest 2626H023V120 type. The high level of linearity between applied voltage and displacement is advantageous. For this type it is 1.8 µm/V, enabling precise and, at the same time, variable control of both amplitude and signal form.

Fig. 3: Typical acceleration g as a function of the voltage
when a mass of 100 grams is applied. The voltage signal
here is a half-sine with a peak of 120 V and a pulse length
of 5 ms, corresponding to a frequency of 200 Hz.

Thanks to the multilayer piezo technology PowerHap offers unprecedented performance in terms of response time and acceleration. For example, with a rise time of just 1 ms the acceleration of the cymbals is already 15.0 g and attains a maximum value of 35 g when a mass of 100 grams is applied, generating a very large force of up to 25 N. Comparable values cannot be achieved using conventional solutions. Figure 3 illustrates the response time and acceleration for type 2626H023V120.


PowerHap actuators are suitable for a wide stimulation range from 1 Hz to 500 Hz with variable amplitudes, durations and signal shapes, such as sine, triangle or rectangle. Depending on the type, the drive voltage is between -20 V and 120 V or -10 V and 60 V. These actuators are therefore able to generate a customized haptic feedback to human mechanoreceptors.

Correspondingly, these actuators enable designers to create specific, high-definition haptic feedback profiles that users expect from cutting-edge HMIs in automotive and industrial applications. The combination of low-profile designs no more than 2.3 mm thick and strong feedback allows these actuators not only to be integrated in displays, but also to be placed directly below flat surfaces. This enables solutions with a high degree of leak-tightness which is just as necessary in harsh industrial environments as in applications with stringent hygiene requirements, such as in the food industry or medical technology.

 

Fig 4: When functioning as a sensor, the output voltage of
PowerHap is to a great extent proportional to the force applied.

Excellent sensory properties

Apart from the excellent actuator performance, the PowerHap components also feature outstanding sensor functionality thanks to the multilayered piezo technology. In contrast to conventional switches or pushbuttons that, as is well known, can only provide the On and Off switching states, PowerHap delivers an output voltage that is proportional to the pressure applied. Figure 4 illustrates this behavior. As a result, and unlike conventional mechanical push-buttons, it is even possible to create solutions based on PowerHap that trigger different actions and haptic feedback, depending on the force applied.


Slim design for lateral installation

Fig. 5: Rectangular PowerHap types are suitable for the lateral
control of displays. Typical applications are vehicle displays.

In addition to the square PowerHap types that are particularly suitable for use under flat surfaces, TDK has also developed four slim, rectangular PowerHap types that are designed to provide lateral haptic feedback in addition to vertical haptic feedback. The two smallest versions only 9mm or 12mm long, are particularly suitable for handheld-held devices.

The two larger versions with side lengths of 60 mm are currently the most powerful PowerHap types, as they enable forces of up to 50 N to be generated, enabling masses of up to 1 kg to be moved. These powerful packages can, for example, be installed at the side of displays in order to achieve a horizontal haptic feedback, as shown in Figure 5.

To enable users to gain initial impression of the varied possibilities of haptic feedback with PowerHap actuators, TDK offers two evaluation kits. The BOS1901Kit development board is designed for the 60 V actuators that are contained in the kit (0909H011V060, 0904H014V060 and 1204H018V060). The board is based on the haptic driver architecture from Boréas Technologies. The main features are the compact dimensions, low current consumption and fast response times. In addition, the board offers extensive adjustment options with regard to the voltage amplitude, frequency, pulse repetition rate, signal shape and sensor functionality. The second evaluation kit is suitable for both 60 V and 120 V PowerHap types and is available in two versions: A driver for one actuator and a driver for up to 5 actuators. These kits contain PowerHap actuators of the types 0909H011V060, 1313H018V120 and 2626H023V120.


Competent design support through cooperative ventures

Systems with haptic feedback are relatively new technologies. Accordingly, no standard solutions yet exist which can be drawn upon. In order to enable customers from every industry to complete a fast and cost-efficient design-in of haptic solutions, TDK has entered into joint ventures with three leading touch response companies. Aito (www.aito-touch.com) offers controller solutions with its HapticTouch hardware and software, which convert piezo actuators into precise touch sensors with haptic feedback. These enable tactile switches or pushbuttons to be simulated on smooth surfaces. Using the combined haptic technologies of TDK and Aito, touch response solutions can be implemented on smartphone touchscreens, or conventional switches and pushbuttons in vehicles can be replaced.

Fig. 6: The evaluation kits provide an initial impression
of haptic feedback with PowerHap actuators and allow
users to evaluate design possibilities.

Boréas Technologies (www.boreas.ca) has developed the BOS1901 driver IC on the basis of its patented CapDrive technology. It is particularly energy efficient, also offering sensor functions, and is especially suitable for controlling TDK PowerHap actuators with an operating voltage of up to 60 V. In a further stage of development, Boréas will develop the first low-power piezo driver IC for the larger TDK PowerHap models with a maximum driver voltage of 120 V.

Immersion (www.immersion.com) is a leading developer and licensor for touch -feedback technologies. TDK has struck a co-marketing agreement with this company for its PowerHap and PiezoHapt actuators. Immersion certifies these actuators for use with its software products and also includes the actuators in its reference designs. This enables customers to implement advanced haptic solutions with the world’s thinnest and most powerful actuators.

About the author:

Christoph Jehle is Manager Technology & Product Communications at TDK Electronics – www.tdk-electronics.tdk.com

 

Related articles:

Haptics is ready for standardization

Surface haptics render textures, dials: on-the-fly

French startup promises meaningful haptics

Automotive multi-touch display comes with programmable textures and haptics

Linked Articles
eeNews Europe
10s