Midterm report

1
Midterm report

• Department Institute of NEMS
• Student ID?d9635808
• Report? Yen - Liang Lin

2
Outline

• Introduction of tactile system
• Abstract
• Operation principle
• Fabrication process
• Experimental results
• Conclusion
• Reference

3
Introduction

• The Braille system is a method that is widely
  used by blind people to read and write.
• Each Braille character or cell is made up of six
  dot positions, arranged in a rectangle containing
  two columns of three dots each.
• Today different Braille codes (or code pages)
  are used to map character sets of different
  languages to the six bit cells.
• Dot height is approximately 0.02 inches (0.5 mm)
  the horizontal and vertical spacing between dot
  centers within a Braille cell is approximately
  0.1 inches (2.5 mm).
• A standard Braille page is 11 inches by 11.5
  inches and typically has a maximum of 40 to 43
  Braille cells per line and 25 lines.

4
Introduction SMA

• The SMA (Shape-memory alloy spring) actuator is
  heated by supplying electrical current
• Palm-top sized tactile display
• 100 (10 x 10) pins array
• The pins are arranged at a pitch of 2.5 mm and
  move 2 mm up and down
• The tactile information are displayed
  sequentially every 0.3 sec and the pins are
  latched at 0.1 N by magnetic force

T. Matsumga et al., Transducer, 2005
5
Introduction SMA

• Maximum displacement of 30 µm under 4.2 mN load
• It can drastically reduce the volume of the
  system.
• However, it has to be improved the actuation
  method to generate a large force.

W. Yoshikawa et al., MEMS, 2006
6
Introduction - electrostatic
A. Yamamoto,et al., MEMS, 2006
L. Yobas,et al., MEMS, 2006
7
(No Transcript)
8
Abstract

• A chip-sized arrayed actuator device has been
  developed for application to a tactile display.
• Each actuator uses a liquidvapour phase change
  to drive a microneedle that stimulates receptors
  in a finger in contact with the array.
• The total size of the 3 3 arrayed actuator
  device is 15 15 1 mm.
• The device performance is experimentally
  evaluated and a large needle displacement (61 µm)
  is obtained with an input energy of 457 mJ.

9
Operation principle

• A change from the liquid to vapour phase yields a
  huge increase in volume. This means that one can
  obtain a relatively large stroke using a small
  amount of liquid.
• To transmit tactile information to the finger
  receptor, an electrical current is applied to the
  heater to generate a bubble on the surface, which
  causes the flexible embrane to deform upwards.

10
Specifications

• Needle heightThis graph shows that the threshold
  value for skin deformation for receptor
  recognition was around 100µm in the quasistatic
  mode. So we chose a needle height of 200 µm for
  our device design.
• Needle pitchThe value of the two-point
  discrimination threshold was also experimentally
  investigated, and a pitch value of 3 mm was
  obtained.
• Total device sizeWe designed the total size to
  be 15mm 15 mm 1.0 mm and arranged the elements
  in a 3 3 array

11
Fabrication three parts

• 40 KOHanisotropic wet etching
• PDMS resin was used as the membrane material. The
  size and thickness of the PDMS membrane were 2.5
  mm square and 20 µm,
• Si wafer thickness 200 µm
• Au/Cr heaterThe film thickness was 270 nm.
• sputtering and lift-off

12
Fabrication assembly

• Liquid sealing into chamber ? We chose fluorinert
  FC-72 (3M Chemicals), which has a low boiling
  point (56 ?C).

• Photocurable resin (TB3115B,Three Bond) for
  sealing .The final assembly process was performed
  in the driving liquid to avoid aeration,

• PDMS has high gas permeability, so the bonded
  structure were coated with the parylene-C
  film(23µm), which has excellent step-coverage
  properties.

13
Experimental Results

• The width and voltage of the applied pulse
  voltage were 5 ms and 31.25 V, respectively.
• The displacement reached a maximum of 27.7 µm
  after 330 ms and then fell to 2.5 µm. It did not
  return to the original value even after several
  seconds.

• A laser displacement sensor was placed over the
  needles and used to detect their displacement by
  the bubble actuation.

14
Experimental Results

• This picture was taken after 1 s. Several
  bubbles remained in the cavity. These bubbles
  finally coalesced into one large bubble after 3
  s. This single large bubble gradually shrank.

• Bubble generation at maximum displacement. A
  large number of tiny bubbles coming off the
  heater were observed.

• The state before the voltage was applied. No
  bubbles were observed in this state

? The coalesced bubble remained after the input
voltage was turned off, which makes the response
poor.
15
Experimental Results

• The needle displacement increases with input
  energy and does not depend on the pulse wave
  forms if the input energy is the same.
• A large displacement of 60.7µm was obtained for
  an input energy of 457 mJ (pulse width 15 ms
  amplitude 28.7 V).

• The response time did not depend on the input
  energy or pulse waveform. The value was 330 ms.

16
Results Periodic operation

• The applied pulse width, amplitude and frequency
  were 1 ms, 52.2 V and 1 Hz, respectively.
• The total displacement gradually increased to the
  range of 3048 µm as the number of the periodic
  motions increased. The motion reached the steady
  state (thermal equilibrium state) after 8 s from
  the onset of the driving.
• The base value of the periodic motion increased
  to 30 µm, and the amplitude became nearly 20 µm,
  in the steady state.
• The off-set value (30 µm in this case) must be
  considered at the device design stage if the
  device is operated at 1 Hz.

17
Conclusion

• The needle height and pitch were chosen to be 200
  µm and 3 mm, respectively, considering the skin
  deformation and two-point discrimination
  threshold.
• The needle displacement produced by bubble
  generation reached a maximum of 27.7 µm after 330
  ms, and then it fell to 2.5 µm. It did not return
  to the original value even after several seconds
  because the bubbles remained in the cavity.
• The needle displacement increased with input
  energy and did not depend on the pulse wave forms
  for the same input energy. A large displacement
  of 60.7 µm was obtained when the input energy was
  457 mJ (pulse width 15 ms amplitude 28.7 V).

18
Reference

• Mitsuhiro Shikida, Tsubasa Imamura, Shinji Ukai,
  Takaaki Miyaji and Kazuo Sato, Bubble Driven
  Arrayed Actuator Device for a Tactile Display,
  Transducer, 2007.
• Mitsuhiro Shikida, Tsubasa Imamura, Shinji Ukai,
  Takaaki Miyaji and Kazuo Sato, Fabrication of a
  bubble-driven arrayed actuator for a tactile
  display, J. of Micromech. Microeng., 18,
  065012(9pp), 2008.
• T. Matsumgal, W. Makishi, K. Totsu, M. Esashi and
  Y. Haga, 2-D and 3-D Tactile Pin Display Using
  SMA Micro-coil Actuator and Magnetic Latch,
  Transducer, 2007.
• W.Yoshikawa, A.Sasabe, K.Sugano, T.Tsuchiya,
  O.Tabata and A.Ishida, Vertical drive micro
  actuator using SMA thin film for a smart button,
  MEMS, 2006.
• L. Yobas, D. M. Durand, G. G. Skebe, F. J. Lisy,
  M.l A. Huff, A Novel Integrable Microvalve for
  Refreshable Braille Display System, Journal of
  microelectromechanical systems., 12 , pp252-263 ,
  2003.
• A. Yamamoto, T. Ishii, and T. Higuchi,
  Electrostatic tactile display for presenting
  surface roughness sensation, IClT , 2003.

19
Thank you for your attention !