30
MAS836 – Sensor Technologies for Interactive Environments Original images © source unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse. Lecture 4 – Pressure Sensors Pt. 1

Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

  • Upload
    others

  • View
    4

  • Download
    0

Embed Size (px)

Citation preview

Page 1: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

MAS836 – Sensor Technologies for Interactive Environments

Original images © source unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.

Lecture 4 – Pressure Sensors Pt. 1

Page 2: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

2

JAP2/04

Very Basic Digital Noise Reduction • Remove outliers • Average the signals

– Summing N signals results in a resolution improvement of a factor N

– Provided that measurements are uncorrelated and exhibit Gaussian statistics

– Must not be quantization limited • I.e., you *need* some noise to start with! • Note that this is *not* usually true for pickup, which

is from a correlated source! • Pickup noise can add in phase

– Linearly!!!

• L3 BGO story...

Page 3: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

4

JAP2/04

Position Encoders • Displacement

– Rotary or Linear Potentiometer – Linear encoder

• Optical • Magneto-Acoustic

– Shaft encoders • Rotary into Linear w. screw

(L) Incremental and (R) optical encoding disks. Courtesy of FABRA Inc. Used with permission. Image by MIT OpenCourseWare.

Incremental (A) and absolute (B) optical encoding disks.

A B

Page 4: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

JAP2/04

2 photodetectors

2 emitters

Holes at 90° and different r

Rotating Disk Rotating Disk

One Hole

Photodetectors

Emitters

Quadrature Encoders Determine Direction

2 Holes and 1 dual optical sensor 1 hole and 2 single optical sensors

One sensor measures “I” and the other measures “Q” -> Direction determined by whether I leads Q in time or vice-versa

Can be spaced more closely, for rapid direction determination 5

Page 5: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

7

JAP2/04

Linear Encoders Optical encoders - Track micro marks - 100 nm accuracy! - Film encoders are in cheap printers

Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due to copyright restrictions. See: Heidenhain.

Page 6: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

10

2/04 JAP

Magneto-Acoustic Linear Encoders

• 1 mil per sample, 9 kHz updates

• Must measure T too! • MTS Sensors

Images relating to magnetostriction removed due to copyright restrictions. See: MTS Sensors.

Page 7: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

11

JAP2/04

Pressure

• Displacement into pressure – E.g., F = -kx, and P = F/A (force per area)

• Strain into Force – Strain is defined by s = ΔL/L

• Piezoresistivity

Expansion (longer)

Compression (shorter)

Applied Force

Page 8: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

JAP2/04

Membrane Switch

A membrane switch being used as a tactile sensor.

• Commercial – can be printed and snap-assembled – Made by ALPS among others (switch floor too) – Typically polled in row-column fashion (e.g., drive columns, read rows)

12

Multiplexer

Output

+5V

4.7k

Spacer

Image by MIT OpenCourseWare.

Page 9: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

How a MIDI Keyboard Works

Counter Start (On low)

Stop (On high)

(typically in ASIC or μP)

+V

• Velocity – Measure time difference between key transitions

• Aftertouch – FSR underneath keys

• FSRs were developed for this purpose (Interlink) – Poly aftertouch has FSR under each key – Mono aftertouch has FSR under key bank

Count ~ Velocity

Page 10: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

Thunder 1 - with capacitance

14

JAP2/04

The Buchla Thunder

• Thunder 2 Tracks multipoint finger position optically using reflective back of mylar drumhead.

• Thunder 1 used capacitance

US Patent 5,913,260 - June 15, 1999 Donald F. Buchla

System and method for detecting deformation of a membrane

Courtesy of Buchla. Used with permission.

Page 11: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

15

JAP2/04

Optical Pressure Sensors

• Pressure Profile of deformable dot-matrix fingertip (Hristu, Ferrier & Brockett)

Housing

Lighting

Camera Window

Gel

Membrane

© Unknonwn. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.

Image by MIT OpenCourseWare.

Page 12: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

16

JAP2/04

GelForce (U. Tokyo – Kamiyama et al)

Dual layers resolve both See: YouTube normal and shear forces

– Derive pressure vector

Courtesy of TachiLab. Used with permission.

Page 13: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

17

JAP2/04

he Carbon Microphone – Sonic FSR T

1878 1929

1628 N-1 Type Carbon Microphone Microphone Characteristics A. Minimum Sensitivity @ 1 kHz with 85 mA(DC) Applied Current: 38 dBmV B. Impedance Range: 15-60 ohms

© Unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.

Page 14: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

18

JAP2/04

Conductive Foam

Metalized

Photo courtesy of Collin Mel on Flickr. CC-BY-NC-SA

Photo courtesy of Jurvetson on Flickr. CC-BY© Unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information , see http://ocw.mit.edu/fairuse.

Standard (3D!)

0.1

0.00

0.06

0.04

0.02

0 0% 10% 20% 30% 40% 50% 60% 70%

0

1

2

3

4

5

6

7

8

9

10

% Compression

Res

ista

nce

(ohm

s/10 c

m len

gth

)

Forc

e (K

g/1

0 c

m len

gth

)

Competitive conductive foam LT conductive foam Wrapped FOF

Image by MIT OpenCourseWare.

Page 15: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

19

JAP2/04

Resistive (conductive) Elastomers

Early Z-Tiles from the University of Limerick McElligott, L., et al, 'ForSe FIElds' - Force Sensors for Interactive Environments,” in UbiComp 2002

• Carbon or silver-loaded silicone rubber • Dynamic range limits, hysteresis, longevity… • Commercial conductive rubber from:

– “Zoflex” from Xilor, inc. (rfmicrolink.com) See: Koehly et al, “Paper FSRs and Latex/Fabric Traction Sensors: Methods for the

Development of Home-Made Touch Sensors,” Proc. Of NIME 06

Image of a freshly made polymer sensor removed due to copyright restrictions. See 'ForSE FIElds' - Force Sensors For Interactive Environments.

Page 16: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

20

JAP2/04

Force Sensitive Resistors

• Composite structure – Top, ink, electrodes

• Flat, but can be fragile to shear force (delamination) and sensitive to bend

Active area

Spacer opening

Tail

Vent

Semi-conductor printed on a flexible substrate

Adhesive spacer

Interdigitating diodes printed on a flexible

substrate

FSR Construction

Image by MIT OpenCourseWare.

Page 17: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

21

JAP2/04

Conductive Polymers and FSR’s

• Microphotograph, showing conductive ink and metalization from Interlink FSR

© unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.

Page 18: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

22

JAP2/04

FSR Characteristics

• 3-4 decades of sensitivity, 0.01 - 100 PSI, hundreds of Ω to 10 Meg Ω – Depending on device & Manufacturer – “---” is part-part repeatability bound

• Typically ±15% - ±25% for Interlink – Sensitive to temperature, humidity...

© Interlink Electronics. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.

Page 19: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

23

JAP2/04

FSR Interface Circuits

• Voltage Divider – Very nonlinear; switch

characteristic – Only buffer needed

• Current Mode – Smoother range but

(Less headroom) – Transimpedance amp

Voltage Divider

Current-to-Voltage © Unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.

Page 20: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

25

JAP2/04

The FSR Potentiometer

Force and pressure

R ?

Can also inject voltage into W and have transimpedance amplifiers at A and B Position is: (VA-VB)/(VA+VB) and Force becomes: VA+VB

atiometric? From Rob Poor Oscillator

(+V)

VB

-

+ -+VA

© Unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.

Page 21: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

26

JAP2/04

The FlexiForce (from TekScan)

Courtesy of TekScan. Used with permission.

Page 22: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

29

JAP2/04

Tekscan Specs

Robustness? Courtesy of TekScan. Used with permission.

Page 23: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

30

JAP2/04

Force Imaging

They do chair seats and beds too...

Car driving over force imaging plate

Hong Tan, Purdue

Ken Perlin/NYU make transparent “interpolating” FSRs

Courtesy of Hong Tan. Used with permission.

Pressure images by Ken Perlin have been removed due to copyright restrictions.

Page 24: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

31

JAP2/04

QTC Pressure Sensors • Made by Peratech in the UK • Quantum Tunneling Composites

Metal-filled polymers, no direct conductive path – Current flows via quantum tunneling (AC readout w. capacitance?) – More tunneling (hence current) with more pressure

– No zero-point deadband, smoother response, more durability (maybe)

Many form factors (buttons, cables, etc.)

See: QTC – the discovery of a novel material | Practical Physics

© Peratech Limited. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.

Page 25: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

JAP2/04

FSR Bendy Sensors

Available from the Images Co. (for PowerGlove - made by “Abrams-Gentile)

High-end versions made by Immersion for their CyberGlove - 0.5° resolution, 1° repeatability, 0.6% max nonlinearity, 2-cm min bend radius These only measure bend in one dimension (expanding the FSR’s on surface) - Conduction saturates quickly when contracted - Can measure bidirectional bend with 2 FSR’s back-to-back (and diff amp) 33

Courtesy of Images SI Inc. Used with permission.

Page 26: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

34

JAP2/04

Resolution and Calibration Tests (from Stacy Morris ‘04)

Bend Sensor calibration Pin Bendy Sensor with Batteries and bend according to printed protractor

FSR calibration Apply known pressure via rubber bumper with materials tester

Images removed due to copyright restrictions.

Page 27: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

2/04 JAP

Abrams-Gentile (used) Bend Sensor Pairs into differential amp for bidirectional bend sensing b i l

Angl e [degrees] © Unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.

35-80 -60 -40 -20 0 20 40 60-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

t

t Poor response (age or tape?)

Better response

Right Ankle Bend, midpt pivot

1/4 pt pivo

3/4 pt pivo

Left Ankle Bend, midpt pivot

1/4 pt pivot

3/4 pt pivot

B e n d

S e n s o r

O u t p u t

[ u n c a

Two pairs of sensors tested Each pair tested around 3 different pivot points Hysteresis from tape?

Page 28: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

37

JAP2/04

Stretchy FSR “strain sensors”

“A novel strain sensor was used which was developed by EMPA, Switzerland [12]. The sensor thread consists of a commercial thermoplastic elastomer (TPE) filled with 50wt-% carbon black powder and changes resistivity with length. It is fiber-shaped with a diameter of 0.3mm and has, therefore, the potential to be fully integrated into textile. In this prototype setup, the sensor was attached with a silicone film (see Fig. 2) which enables a measurement range of 100% strain. The length of the sensor was chosen to be 2cm.”

Recognizing Upper Body Postures using Textile Strain Sensors Corinne Mattmann, Oliver Amft, Holger Harms, Gerhard Tröster, and Frank Clemens (ETH Zurich) - Proc. Of ISWC 2007

TMS International - breathing belts (resistive) http://www.tmsi.com

More on fabric-compatible sensors in Bio Lecture…

Courtesy of TMS International. Used with permission.

© ETH Zurich Wearable Computing Lab. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.

Page 29: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

38

JAP2/04

Merlin Stretch Sensors…

http://www.merlinrobotics.co.uk

Comercial stretchy resistive sensor

Courtesy of Merlin Robotics. Used with permission.

Page 30: Lecture 4 – Pressure Sensors Pt. 1 · cheap printers Screen shot of the webpage for Heidenhain Linear Encoders—sealed linear encoders and exposed linear encoders, removed due

MIT OpenCourseWarehttp://ocw.mit.edu

MAS.836 Sensor Technologies for Interactive Environments Spring 2011

For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms.