A study on a tactile display drive system using SPI communication and a piezoelectric driver IC

With the advancement of the Metaverse, the need for haptic devices is increasing. Piezoelectric haptic devices require a piezoelectric amplifier to drive them, and the large size of the power supply has hindered wearable applications. In this research, we developed a driving circuit that compactly realizes 25 channels of haptic sensation by utilizing a small 12V boost power supply and a multi-channel piezoelectric IC, and developed software to control the haptic sensation in multiple gradations, and confirmed its effectiveness.

Tactile displays have the function of presenting the shape, surface roughness, and texture of objects to humans. Humans have layers under the skin: epidermis, dermis, and subcutaneous tissue. To sense touch, the skin has seven types of mechanoreceptors and four types of pain receptors. The characteristics of each receptor show that in order to stimulate these mechanoreceptors and obtain a sense of touch, it is effective to first provide a 200–300 Hz instructional stimulus.

Our group is also developing tactile devices, controlling such multi-point tactile sensations requires a lot of wiring. However, to achieve compactness, it is necessary to reduce the amount of wiring. To achieve this, it is advantageous to transmit control signals from the PC via serial communication [33]. And the piezoelectric amplifiers normally used PIEZO DRIVER / AMPLIFIER. Our group use a Trek MODEL PZD 350, but it is large and can only drive one channel. To achieve wearable, to install the driving circuit close to the device, we use high voltage output Integrated Circuit (IC). Here, Serial Peripheral Interface (SPI) is used for communication, and Microchip's 8-Channel Serial-to-Parallel Converter with High-Voltage Push-Pull Outputs: HV513 is used as the driving IC, which can control voltage up to 250V and drive piezoelectric devices. We also developed a control system on a PC that generates tactile patterns for each of the 25 tactile presentation points and changes the tactile patterns over time. We also implemented a function to control the frequency at double the frequency so that dithering [34] can be performed, focusing on the strength of the tactile sensation.

The tactile device developed in this study uses silicone rubber and fluorinated ethylene propylene (FEP) film as main structural materials, with Titanium (Ti) electrodes deposited on top for a flexible, durable structure by sputter.

The device structure features 25 vibration generation points within a 2 cm × 2 cm area. Each tactile generation point is independently controlled, allowing for different types of tactile patterns.

The control hardware of the tactile device primarily comprises a high-voltage push-pull output driver (HV513) with serial-to-parallel conversion and an Arduino. The Arduino transfers tactile generation data from a PC to the HV513 using SPI communication. HV513 converts serial data to parallel data and, with high-voltage push-pull output drivers that support up to eight output channels, it drives the piezoelectric control of the device, generating tactile sensations. Using two DC-DC converters, MHV12-300S10P, a stable high voltage of 200V is supplied to the HV513 from 12 V source power.

This drive circuit is controlled by communicating control signals from a PC using an Arduino Mega 2560 to control the four HV513 (total 32 channel control).

Tactile presentation involves physical vibrations, pressure, shape and slippage to deliver tactile feedback to users. Quality depends on vibration parameters like frequency, amplitude, and duration, which, when controlled appropriately, produce diverse and complex tactile effects.  Human touch sensitivity ranges from approximately 5 Hz to 500 Hz, with peak sensitivity between 200–300 Hz. Adjusting these factors enhances realism and precision in tactile presentations in VR. First tactile stimulation, subjects’ ability to identify changes in stimulus positions on the tactile device is evaluated. The second stimulation method presents the direction of movement to the subject on the tactile device. This method controls the direction of movement along a column or a row. Third, binary dithering methods produce a continuous intensity gradation. This experiment uses binary dithering to achieve different intensity levels on the tactile device.

For verification, the experiment involved four subjects who placed their fingers on a haptic device and conducted four types of experiments. From these experiments, both the normal 200 Hz signal and the weak 400 Hz signal were recognized 100% of the time, and the difference in position was also recognized, verifying the effectiveness of the tactile presentation ability of this system.

We conducted control experiments on the piezoelectric driver and confirmed that it was capable of responding at the required frequency and outputting multiple tones. This will enable the control of tactile devices with different frequencies and complex vibration patterns.
This paper ”A study on a tactile display drive system using SPI communication and a piezoelectric driver IC” was published in Electronics and Signal Processing.

Zheng J, Otahara Y, Sone J. A study on a tactile display drive system using SPI communication and a piezoelectric driver IC. Electron. Signal Process. 2025(1):0001