The Journal of the Acoustical Society of Korea (한국음향학회지)

The Acoustical Society of Korea (한국음향학회)
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Haptic recognition of the palm using ultrasound radiation force and its application

초음파 방사힘을 이용한 손바닥의 촉각 인식과 응용

  • 김선애 (대진대학교 전기 및 전자공학부) ;
  • 김태양 (대진대학교 전기 및 전자공학부) ;
  • 이열음 (대진대학교 전기 및 전자공학부) ;
  • 이수연 (대진대학교 전기 및 전자공학부) ;
  • 정목근 (대진대학교 전기 및 전자공학부) ;
  • 권성재 (대진대학교 휴먼IT융합학부)
  • Received : 2019.04.29
  • Accepted : 2019.07.01
  • Published : 2019.07.31
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Abstract

A high-intensity ultrasound wave generates acoustic streaming and acoustic radiation forces when propagating through a medium. An acoustic radiation force generated in a three-dimensional space can produce a solid tactile sensation, delivering spatial information directly to the human skin. We placed 154 ultrasound transmit elements with a frequency of 40 kHz on a concave circular dish, and generated an acoustic radiation force at the focal point by transmitting the ultrasound wave. To feel the tactile sensation better, the transmit elements were excited by sine waves whose amplitude was modulated by a 60 Hz square wave. As an application of ultrasonic tactile sensing, a region where tactile sense is formed in the air is used as an indicator for the position of the hand. We confirmed the utility of ultrasonic tactile feedback by implementing a system that provides the number of fingers to a machine by receiving the shape of the hand at the focal point where the tactile sense is detected.

고출력의 초음파는 매질을 진행하면 음향 흐름과 음향 방사힘을 만들어낸다. 공기를 매질로 하는 3차원 공간상에 음향 방사힘을 발생시키면 입체적인 촉감을 형성할 수 있으므로 공간적인 정보를 직접 피부에 촉각으로 전달할 수 있다. 본 논문은 40 kHz의 작은 초음파 송신자 154개를 묶어 오목한 형태로 배열시켜서 초음파를 송신하여 집속초점에서 음향 방사힘을 발생시켰다. 초음파 음장의 초점의 근처에서 음향 방사힘에 의한 촉각을 확인하였다. 촉각 감도를 올리기 위하여 송신 초음파를 60 Hz의 구형파로 진폭 변조를 하였다. 초음파 촉각의 응용으로 음향 방사힘이 형성되는 허공에 촉각이 감지되는 영역을 형성시켜서, 손의 위치를 지정하는 지시자로 사용하였다. 촉각이 감지되는 초점위치에 있는 손의 모양을 영상 입력으로 받아서 손가락의 개수를 기계에 피드백하는 시스템을 구현함으로써 초음파를 이용한 촉각의 유용성을 확인하였다.

Keywords

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Fig. 1. The overall system architecture.

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Fig. 2. The spatial field distribution of a single ultrasound transmit element.

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Fig. 3. The spatial field distribution of a concave ultrasound transmit module of diameter 24 cm.

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Fig. 4. The axial field distribution of a concave ultrasound transmit module.

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Fig. 5. The lateral field distribution of a concave ultrasound transmit module at focal depth.

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Fig. 6. Photograph of the concave ultrasound transmit module consisting of 154 ultrasound transmit elements connected in parallel, where a camera and an LED light source are placed in the center.

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Fig. 7. The paper is shown to be pushed upward by acoustic streaming.

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Fig. 8. Comparison of the relative sensitivity of the tactile sensation as a function of the modulation frequency with the dashed-line graph representing the curve-fitted result.

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Fig. 9. The left, middle, right images represent the process of finding the palm center, and are, respectively, the palm, its binary image showing the boundary, and the red dot marking its center of mass obtained using the distance transformation matrix, along with a circle drawn around the center.

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Fig. 10. Monitor screenshot where three fingers are recognized and the number 3 is displayed.

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Fig. 11. Photograph of the entire system.

Table 1. Measurement of weight (mg) as a function of the number of ultrasound transmit elements and depth (cm).

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Table 2. Measurement of weight (g) as a function of the number of ultrasound transmit elements at a depth of 20.3 cm.

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