PowerHap from TDK makes AR/VR experiences more immersive

Augmented and Virtual Reality (AR/VR) is one of the next big things. It creates entirely new experiences for consumers and commercial users. However, many of these devices focus solely on the visual dimension. With tactile feedback, AR/VR becomes more immersive by addressing other sensory experiences. TDK's multilayer piezo ceramic PowerHap actuators can render surface textures crisply, as demonstrated impressively by WEART's TouchDIVER.

What if staff could train realistically on equipment that has yet to be installed or in a hazardous environment without actual physical risk? What if a doctor could practice a complicated surgery vividly before performing it on an actual patient? What if car designers could touch and explore their new model before building a physical prototype?

For such tasks, more than the visual dimension is required. It needs to be augmented with haptic feedback. This helps staff feel more comfortable with new equipment or in risky situations. Doctors become more confident, while patients feel safer with well-trained surgeons. And car designers can optimize their models without needing one or more expensive physical prototypes. These are just three of the many applications where haptic feedback makes AR/VR more natural and immersive.

Human fingers combine at least three types of tactile sensations. First, when grasping an object, they feel a cutaneous pressure force. This is different whether grasping a solid object or a soft donut. Second, fingertips can distinguish texture, whether it is suede leather or a smooth surface. And third, fingertips are sensitive to temperature. This means that a metal object with its high thermal conductivity can be distinguished from a plastic object with the same dimensions. Finally, to make the experience immersive, the feedback loop with the visual system must be closed. To do this, the movement of the fingers in the virtual world must be tracked and fed back.

More than a decade of research

The challenge is to create a lightweight system that integrates tactile sensations with the visual system in real-time. WEART, an Italian company, has developed TouchDIVER, a haptic glove that provides lifelike interaction in VR, AR, and MR (Mixed Reality). The glove offers comprehensive haptic feedback such as pressure force, texture, and temperature sensations, enabling natural interaction with virtual elements and environments. For this, the glove has precise sensors that track hand and finger movements. One of the key elements of this glove is PowerHap from TDK. These multilayer piezo ceramic actuators render surface textures in a very natural way.

WEART’s foundation goes back to the EU research project WEARHAP (WEARable HAPtics for Humans and Robots), started in 2013 and coordinated by the University of Siena. There, Guido Gioioso and Giovanni Spagnoletti met during their Ph.D. studies at the Robotics and Automation Lab at the University of Siena, supervised by Prof. Domenico Prattichizzo. Eventually, these three founded the company in 2018 with the engineering and industrial partner e-Novia.

TouchDIVER haptic glove is designed with three touch points on the fingers, based on neuroscience that highlights the importance of the thumb, index finger, and middle finger for stability and manipulation (Fig. 1). This choice simplifies wearability and cost while maintaining performance.

Figure 1:

TouchDIVER haptic glove is designed with three touch points on the fingers that simplify wearability and cost while maintaining performance. (source: WEART)

A wired version is available for continuous usage while a wireless version connects via Bluetooth Low Energy (BLE) and lasts 40 to 60 minutes with one battery charge. The VR glove includes an SDK (software development kit) for integration with major development platforms to ensure unified tracking across platforms.

Combining three tactile sensations

To emulate contact forces, TouchDIVER uses servomotors that apply the prescribed pressure to the user's fingertips, creating the required tactile sensation. The system can render cutaneous forces up to 5 N with a resolution of 0.02 N. This allows users to feel variations in virtual object stiffness and perceive three-dimensional surface shapes. This includes simulating bumps on wavy textures. Content developers don’t need to become experts in biomechanics; in fact, the SDK calculates the amount of force to be applied automatically.

Thermal feedback enriches the extended reality experiences by delivering authentic sensations of heat and cold, heightening immersion by replicating temperature-related sensations on the user’s skin. The intensity of these sensations is influenced by the virtual materials involved. TouchDIVER spans a temperature range from +15 °C to +42 °C with a resolution of 0.1 °C and swift response times. This is invaluable in contexts like safety training and industrial use, where precise thermal feedback is crucial. It also improves material identification by recreating variations in thermal conductivity – for instance, how metal feels cooler than wood due to their distinct heat conduction properties.

Textures are rendered at world-class levels in TouchDIVER glove by fine-tuning vibrations using TDK's piezoelectric PowerHap actuator. It effectively converts electrical signals into mechanical displacements with remarkable speed and accuracy by tracking the user's hand speed and movement in real-time. To achieve this level of realism, WEART developed an extensive tactile library included in the SDK with over 20 different materials, allowing developers to create countless roughness variations using three parameters.

The WEART team learned about PowerHap at the AsiaHaptics 2018 conference in Songdo, South Korea, where TDK's Dr. Andreas Pentscher-Stani gave a presentation on PowerHap. The features that captured the attention include the actuator's resolution, vibration amplitude, and bandwidth. These specifications are pivotal in meeting the requirements for rendering the finishing of different materials. Moreover, PowerHap’s ability to generate a significant amplitude, even under a load of up to 5 N, stands out as a key factor. This attribute plays a crucial role in advancing WEART’s core technology, enabling the stacking, and rendering of three distinct tactile sensations on the same portion of the skin.

The actuator proves to be the ideal choice for several compelling reasons. Firstly, its wide bandwidth is crucial for accurately rendering various material roughness levels. Additionally, PowerHap‘s dimensions align seamlessly with the fingertip area, ensuring compatibility and facilitating optimal mechanical integration. The specified thickness is instrumental in achieving the best mechanical synergy.

Crisp vibrations with PowerHap

Figure 2:

PowerHap uses cymbals/bows on both sides to amplify the contraction caused by the piezo effect by a factor of 15 along the z-axis. It can generate a wider range of haptic feedback than traditional solutions such as eccentric rotary motors and linear resonant actuators between 1 Hz and 1000 Hz. (source: TDK Electronics AG)

PowerHap is based on multilayer piezo plates with migration-free copper inner electrodes that can be driven with relatively low operating voltages in a range from 0 V up to 120 V depending of the PowerHap design. The components use cymbals/bows on both sides to amplify the contraction caused by the piezo effect by a factor of 15 along the z-axis (Fig. 2).

PowerHap can generate a wider range of haptic feedback than traditional solutions such as eccentric rotary motors (ERMs) and linear resonant actuators (LRAs). PowerHap can generate the entire stimulation range between 1 Hz and 1000 Hz, allowing for more customized and crisp haptic feedback to be delivered to the key human mechanoreceptors.

PowerHap 1919 for instance reaches a high acceleration of the cymbals/bows of up to 16.0 g with a load mass of 500 g and up to 52 g with a 100 g load mass. At the same time, it generates a high force of up to 20 N combined with low insertion height and response times of less than 1 ms. This technology is not limited by any significant frequency or amplitude constraints, making it a versatile and effective solution for various applications.

Other haptic applications with PowerHap

PowerHap offers a high-performance haptic actuator for the most demanding and trending applications that require high acceleration with a long bandwidth frequency in compact dimensions with quite low power consumption. With PowerHap designers can develop buttons, modules, automotive systems (Haptic Display/Steering Wheel/Trackpad), VR, smartphones (solid state button), gaming (Controller/Ring/Wristband), or medical devices, and stylus, among others.

Conclusion

Tactile feedback is taking AR/VR to the next level. Equipped with TDK’s PowerHap, the TouchDIVER haptic glove from WEART AR/VR makes applications like industrial and medical training, virtual prototyping, and virtual showrooms more natural and immersive.