HairTouch: Providing Stiffness, Roughness and Surface Height Differences Using Reconfigurable Brush Hairs on a VR Controller

Title of the Paper

HairTouch: Providing Stiffness, Roughness and Surface Height Differences Using Reconfigurable Brush Hairs on a VR Controller

Paper Information

• Research Area: Haptic feedback design in virtual reality
• Keywords: haptic feedback, stiffness, roughness, handheld device, brush hairs, virtual reality

Research Background and Problem Statement

• Identified Issues or Challenges:

  • Many current virtual reality (VR) haptic devices face limitations in simulating the stiffness, roughness, and surface height differences of virtual objects.
  • Simulation devices using actuators (e.g., motors, vibration modules) experience latency, which restricts the realism of feedback.
  • There is a lack of devices capable of providing realistic and multifunctional haptic feedback while integrating multidimensional characteristics.

• Importance of the Research:

  • Stiffness and roughness are critical haptic cues when interacting with virtual objects, especially in scenarios such as touching virtual animals, fabrics, and furniture materials.
  • Creating realistic haptic experiences for users in VR is essential to attract more users and expand VR's application scope.

• Motivation and Related Work:

  • Previous studies proposed solutions based on haptic illusions or physical texture switching, but these approaches lacked flexibility or realism.
  • Devices such as snake-like arms and vibration modules provide certain haptic feedback but fail to integrate stiffness, roughness, and surface height characteristics simultaneously.

Proposed Solution

• Proposed Approach:

  • Developed a handheld device named HairTouch, which utilizes a reconfigurable brush hair structure combined with pin-based design to provide multi-level stiffness, roughness, and surface height differences.
  • Stiffness and roughness differences are achieved by controlling the length and bending direction of the brush hairs, while surface height differences are rendered by adjusting the pin height.

• Innovative Features:

  • Real-time adjustment of stiffness and roughness based on the physical properties of brush hairs (length, density, bending direction), avoiding latency caused by traditional actuator simulations.
  • Two pin structures independently provide haptic feedback to the two joints of the fingertip.
  • Dynamic switching and combination of different feedback types enable multifunctional haptic output.

• Implementation Steps:

  1. Design and Hardware Implementation: The device includes two brush hair components, two pins, and two rails, equipped with motors to control the length, bending angle of the brush hairs, and pin height.
  2. Software Control: A PID control algorithm dynamically adjusts the position of brush hairs and pins to match the haptic requirements of virtual scenes.
  3. User Perception Testing: Tests were conducted to evaluate users' ability to distinguish different levels of stiffness and roughness, optimizing brush hair parameters.
  4. Application Testing: Two practical VR applications (virtual pet and virtual shopping) were used to validate the haptic effects of HairTouch.

Research Outcomes

• Specific Results:

  • HairTouch achieved four levels of stiffness differentiation (31mm, 21mm, 11mm, 4mm) and four levels of roughness differentiation (based on varying angles between brush hairs and sliding direction, ranging from 45° to 135°).
  • Surface height differences were effectively rendered by controlling the elevation of the pins.

• Advantages Compared to Existing Solutions:

  • Provides realistic physical feedback without relying on actuator simulations, significantly reducing latency.
  • Compact and portable design (total weight: 320g).
  • In VR applications such as virtual pet and virtual shopping, user ratings for "realism," "recognizability," "pleasure," and "preference" were significantly higher than traditional vibration feedback devices.

• Experimental or Evaluation Results:

  • Users demonstrated significant ability to distinguish stiffness levels (p < 0.01), while roughness differentiation improved notably at larger angles (>90°).
  • HairTouch's feedback was proven to enhance user immersion and interaction experience compared to vibration feedback.

• Limitations and Future Directions:

  • Stiffness Range Limitation: The maximum stiffness level does not fully simulate rigid objects; future research suggests using harder materials like rubber.
  • Simultaneous Rendering of Stiffness and Roughness: Exploration of other brush hair properties, such as density, is needed to address this issue.
  • Dynamic Switching Latency: Optimization is required, potentially through hand trajectory prediction methods.
  • Small Haptic Perception Area: Expanding the brush hair surface area could improve user experience.

In summary, HairTouch successfully provides an innovative haptic solution, achieving a balance between realism and multifunctionality in multidimensional haptic feedback. This research offers significant insights for the advancement of haptic technology in virtual reality.