4. Ultrasonic Tactile Display: Theory of Operation
• Ultrasound waves at 40Khz interfere constructively to
produce a focal point in order to achieve higher acoustic
pressure level.
• Even at very high acoustic pressure levels, vibrations
above 1000Hz cannot be detected by cutaneous
mechanoreceptors on the hands. Thus the ultrasound
must be modulated with a low frequency signal in order
to achieve tactile stimulation.
• Different modulation frequencies and schemes result in
different tactile sensations.
14. Consider N transducers with position vectors 𝑟𝑖 = 𝑥𝑖, 𝑦𝑖, 0 where
(𝑖 = 1,2, … 𝑁). To achieve focusing at an arbitrary location 𝑟 =
𝑥, 𝑦, 𝑧 , the phase shift (in seconds) of transducer 𝑖 relative to a
particular reference transducer 𝑖 = k must satisfy
Δ𝑇𝑖 =
𝑟 − 𝑟𝑖 − 𝑟 − 𝑟𝑘
𝑉𝑠𝑜𝑢𝑛𝑑 𝑖𝑛 𝑎𝑖𝑟
=
𝑥 − 𝑥𝑖
2 + 𝑦 − 𝑦𝑖
2 + 𝑧2 − 𝑥 − 𝑥 𝑘
2 + 𝑦 − 𝑦 𝑘
2 + 𝑧2
331.4 + 0.6∗Temperature(°𝐶)
To ensure that all offsets are delays and not advances, all offsets must
be in reference to the transducer for which Δ𝑇 = min Δ𝑇𝑖 . This is
achieved by modifying the above equation to
Δ𝑇𝑖 =
𝑟 − 𝑟𝑖 − 𝑟 − 𝑟𝑘
𝑉𝑠𝑜𝑢𝑛𝑑 𝑖𝑛 𝑎𝑖𝑟
+ min
𝑟 − 𝑟𝑖 − 𝑟 − 𝑟𝑘
𝑉𝑠𝑜𝑢𝑛𝑑 𝑖𝑛 𝑎𝑖𝑟
Phase Delay Calculation Algorithm
16. Stepper Motors
EasyDriver Boards
Photointerruptor
Sensors
Arduino UNO NI USB-6009
Ultrasonic
Receiver
PC running
LabVIew
Design of Field Characterization Robot
Setup Block Scanning Block
Read input parameters
Move probe to desired
initial scanning position
Sweep 2D perimeter of
volume to be scanned
Scan one
(Z) column
Move probe toward the
sensors at X=0,Y=0,Z=0 Make a step
along X
Change X
direction
Make a step
along Y
Change Z
direction
Xend
reached?
No
Yes
No
Yes
Halt
Yend
reached?
17.
18. Stepper Motors
EasyDriver Boards
Photointerruptor
Sensors
Arduino UNO NI USB-6009
Ultrasonic
Receiver
PC running
LabVIew
Design of Field Characterization Robot
Setup Block Scanning Block
Read input parameters
Move probe to desired
initial scanning position
Sweep 2D perimeter of
volume to be scanned
Scan one
(Z) column
Move probe toward the
sensors at X=0,Y=0,Z=0 Make a step
along X
Change X
direction
Make a step
along Y
Change Z
direction
Xend
reached?
No
Yes
No
Yes
Halt
Yend
reached?
19. • Offset Distance (X,Y,Z)
• Dimensions of volume to scan (X,Y,Z)
• Resolution along (X,Y,Z) in terms of data points per distance
• Acquisition time per data point
• Delay time for vibrations to die out (~0.1s for Z; ~0.3s for X and Y)
• Sweep the edges of the 3D volume to be scanned (yes/no)
Setup Block Scanning Block
Read input parameters
Move probe to desired
initial scanning position
Sweep 2D perimeter of
volume to be scanned
Scan one
(Z) column
Move probe toward the
sensors at X=0,Y=0,Z=0 Make a step
along X
Change X
direction
Make a step
along Y
Change Z
direction
Xend
reached?
No
Yes
No
Yes
Halt
Yend
reached?
Design of Field Characterization Robot
Driver Software
20. Design of Field Characterization Robot
Data Acquisition Software
• User must specify number of columns and data points per column.
• The software calculates Elapsed Time, Total Time, and Remaining Time.
• Upon completion, a CSV file is generated containing the data points.
21. Design of Field Characterization Robot
Data Analysis Software
• User specifies data points in the X, Y, and Z planes.
• Software outputs color plots in 2D and 3D views.
• User can progress through consecutive Z planes
48. Technical Specifications
Specs for the Display Desired Tech. Specs from Survey Current Progress
Price: $500-$1000 Current Cost = $974.67
Portability: Approx. weight and size of textbook Meets weight and size requirements
Daily Usage: 4 hours or less per day Multi-day tests are frequently run
Temperature: 19-23°C (or 66.2-73.4°F) Device functions in these temperatures
Specs for the Robot Desired Tech. Specs from Survey Current Progress
Price: Approx. $150 Current Cost without a DAQ = $87.47
Measurement Resolution: 1mm Resolution down to 5 µm increments
Points per Volume Test: 2000 points within test volume Completed tests with > 200,000 points
Time vs. Resolution: 4 hours for a 2 mm resolution test ~14,400 points in 4 hours at 2mm resolution
Size of Volume to Test: 12" x 12" x 12" volume Current Test Volume = 12" x 16" x 12"
49. Bill of Materials for the Ultrasonic Tactile Display
Part Description Supplier Unit Price Quantity Total Price
Spartan 3 Starter Kit (Obsolete) Ted 199.00$ 1 199.00$
Ultrasonic Transducers Mouser 3.68$ 100 368.00$
Custom PCB Advanced Circuits 40.50$ 2 81.00$
LM7171 Op Amp Digikey 2.21$ 100 221.00$
0.33 uF 1206 Capacitor Digikey 0.86$ 1 0.86$
0.1 uF 1206 Capacitor Digikey 0.05$ 1 0.05$
Power Jack Connector Digikey 1.18$ 1 1.18$
Mezzanine Connector Female Digikey 4.98$ 6 29.88$
40 Position Header Connector Digikey 4.95$ 3 14.85$
40 Position Ribbon Cable Interconnect Digikey 2.18$ 6 13.08$
Mezzanine Connector Male Digikey 4.83$ 6 28.98$
Approx. 6" of 26 Position Ribbon Cable N/A 2.00$ 2 4.00$
24V AC Adapter Mouser 11.61$ 1 11.61$
20V Linear Regulator Digikey 1.18$ 1 1.18$
Subtotal: 974.67$
In House: (203.00)$
Total: 771.67$
50. Subtotal: 386.74$
In House: (299.00)$
Total: 87.74$
Bill of Materials for the Field Characterization Robot
Part Description Supplier Unit Price Quantity Total Price
EasyDriver Motor Control Board SparkFun 14.95$ 3 44.85$
Arduino Uno Amazon 24.95$ 1 24.95$
Recycled Scanner Motors N/A -$ 3 -$
Recycled Photo Interrupter Sensors N/A -$ 3 -$
Ultrasonic Transducer, (Used for Reception) Mouser 4.48$ 1 4.48$
Recycled Aluminum Rails N/A -$ 2 -$
Recycled Cables, Connectors, and Power Cord N/A -$ 6 -$
LabVIEW USB-6009 DAQ Ted 299.00$ 1 299.00$
Screws Fastenall 0.25$ 16 4.00$
Balsa Wood Stick Hobbytown USA 0.10$ 1 0.10$
Right Angle Shelf Brackets Lowes 4.18$ 2 8.36$
Super Glue Hobbytown USA 1.00$ 1 1.00$
51. Future Goals
• Provide a seamless integration between the GUI and the FPGA.
• Create a new driver board that also supports amplitude modulation.
• Develop a graphical user interface for focal point steering.
• Miniaturize the display to achieve more localized focusing.
• Conduct additional experiments with different modulation schemes to
determine the optimal conditions for tactile stimulation.
• Conduct experiments with multiple focal points.
For the past year, we have been working the research project that is summarized in this picture. The main project is an ultrasonic tactile display that is uses modulated, focused, nonpenetrative, 40kHz ultrasound to produce tactile sensation on the user’s hands by exciting the exterior cutaneous mechanoreceptors.
Motivation for Ultrasonic Tactile Display
The motivation for the tactile display came from the fact that while visual displays have become pervasive in modern society, displays that transmit information via the sense of touch are nearly nonexistent. Currently, nearly all intelligent information we receive from the external world is either visual or auditory. This means that there is a tremendous opportunity for innovation at this time, because of the three primary senses (audition, sight, and touch) only two are being exploited for the transmission of intelligent information. Thus there is a 33% opportunity for innovation.
This research aims to demonstrate how nonpenetrative, focused ultrasound, modulated at low frequencies, could be exploited to produce tactile sensations on a user hands; and how a tactile display could be built using commercially available, 40kHz, ultrasonic transducers.
@
Soon after we began the research for the ultrasonic tactile display, we realized that we would need an affordable, high-resolution, field measuring device that would aid us in developing algorithms for the tactile display by enabling us to visualize the field profile generated by the display. Commercial solutions were priced over $2000, thus we built our own robot for less than $90 by constructing the hardware from recycled flatbed scanners.
@ We will now describe how each of the two projects works and how each was designed, starting with the Ultrasonic Tactile Display.
We have a 2D array of ultrasonic transducers that produce 40Khz ultrasound at a relatively low sound pressure level, which cannot be felt by any sensory organs.
In order to achieve perceptible tactile stimulation of the cutaneous mechanoreceptors there are two prerequisites:
We need stronger sound pressure levels, which we achieve by focusing the ultrasound at a particular focal point through constructive interference.
But even after achieving a strong amplitude, we still have one more problem to solve. Cutaneous mechanoreceptors on the hands are sensitive to frequencies from a few Hz to a couple hundred Hz. Most sources quote the upper frequency limit as 250Hz, but it varies for different people. The blind, for instance, have sensitivity to about 1kHz. The 40Khz operational frequency of the display is far above the detectable. Therefore, in order to enable tactile perception, we must play a trick. We modulate the ultrasound with a low frequency square wave.
These are the 2 prerequisites. And what is really interesting is that different modulation frequencies and different modulation schemes result in different tactile sensations. Thus by changing the modulation you change the texture you perceive.
Now we will discuss how each of these two systems was built and the specifications for each system. Let’s begin with the tactile display. What we see here is the high-level system representation of the ultrasonic tactile display.
This slide shows the high-level representation of the tactile display system.
This program was crated in java to calculate the phase delays for each transducer in order to achieve focusing at a particular point.
The user specified the desired location of the focal point, the room temperature, and the clock frequency of the FPGA.
The software then calculates the phase delays for each transducers and outputs a table of 100 values. The phase delays are calculated in terms of both microseconds, and also in terms of FPGA clock cycles. There is also a third option, which is to have the output in terms of Verilog code that you can directly copy and paste into Xilinx and then upload to the FPGA.
The program also shows a 2D plot of the locations of the transducers as well as the location of the focal point.
There is also the option to view this information in 3D, where we have the transducer array here and the focal point there.
If you wish, you can choose to display these cones, whose length is proportional to the phase delay at which you must drive each transducer.
And you can rotate this 3D graphs as you wish, so here is a picture from a different angle.
@Behind the G.U.I is there is quite a bit of mathematics for calculating the phase delays for each transdcuer, which is very briefly summarized in this slide. For the sake of time, I will skip the explanation and if you wish I can come back to this at the end and explain the algorithm by drawing a picture on the board.
@This concludes the design of the tactile display, and now we move on to explaining how the robot works.
@Here is the high-level representation of the design of the field characterization robot.
The hardware was constructed out of recycled flatbed scanners, as you can see on this picture.
And the control circuit is shown on the left. We have an Arduino board connected to 3 EasyDriver boards that power the stepper motors driving the 3 scanners.
@
The hardware platform for the field characterization robot was built from three recycled scanners which were obtained for free. The bottom two scanners allow motion in the x and y direction and the vertical scanner allows motion in the z direction. The motion is provided by stepper motors, which are controlled by the driver circuit in this box.
Here is a picture of what is inside this box. There is an Arduino board which is connected to three EasyDriver boards. Each EasyDriver board contains an H-Bridge which supplies up to 700mA to each stepper motor.
I wish I could demonstrate how the system works but I am not allowed to, so I would have to explain verbally. We have written about 300 lines of code which allows the user to specify a broad range of parameters about what the system can achieve. The next slide shows the parameter that one can specify:
@
Here is the high-level design of the field characterization robot.
@
To illustrate what these parameters mean, let’s suppose I want to scan the 3D region that is located over here (SHOW SOME REGION).
Then I would specify where that region begins by specifying the offset from the starting position along the x, y, and the z axis.
Then I would specify the dimensions of the volume I want to scan. I would also specify the resolution I want and the time needed for one data acquisition operation to complete.
There is also the option to add an additional delay which allows for vibrations to die out before taking a measurement.
Finally, there is the option to choose if you want the robot to sweep the edges of the 3D volume to be scanned to confirm that the parameters the user specified were correct.
Now we are going to show you the results from one of our latest focal point formation experiments. For this experiment we had 9 transducers constructively interfering to form a focal point at a height of exactly 15 cm.
The focal point is somewhere here (SHOW) and we are scanning 21 horizontal planes from here to here. So as we go up we will see how the focal point forms and then as we keep moving up we will see that it decreases in amplitude. Here we go.
We begin seeing regions of constructive and destructive interference forming. As we keep moving up, we begin to see a focal point forming at the center.
The is where the focal point is at its highest intensity (PLANE 11) – 15 centimeters above the display. As we keep moving up, we begin to see a decrease in the intensity.
We performed this experiment only two weeks ago, and last week we did another experiment where we characterized the field from a single transducer. Here is an animated gif of the results from that experiment. As we go higher from the transducer, the amplitude rapidly decreases.
So you can see how our focal point experiment compares to a single transducer.
@
The animations you saw were from last semester. This semester we performed experiments with all 36 transducers. But instead of making a high resolution 3D scan of the entire volume above the display, we decided to make 1Dimensional vertical scan of the columns above each transducer.
@
@
And now we make a full circle by returning to the slide you saw at the beginning of this presentation. But this time, you now understand everything that is on this poster.
