This document summarizes the development of an ultra sensitive mechanical force sensor capable of measuring forces at the milli-Newton and nano-Newton level. It describes the initial concepts considered, including using air curtains, water floatation, and electrostatic levitation to reduce contact friction. Prototypes were developed using acrylic and PDMS materials. The best concept selected was water floatation, but this had limitations due to vibrations. The final sensors developed include a nano-Newton sensor using water floatation and a micro-Newton sensor that can measure forces without additional support. Both sensors were manufactured using techniques like laser cutting, milling, and molding. The sensors are integrated into a computer interface to provide real-time force measurements

1. Ultra Sensitive Mechanical Force Sensor
Under
Prof. G.K. Ananthasuresh
By
Harshala//Ashveen
Major Project Presentation
1

2. 2
The
product
http://www.cense.iisc.ernet.in/people/g-k-ananthasuresh/->Gallery

3. Recap
• So far
– Prior art
– Establishment of need and need
statement
– Issues
– Ideas for Solution
– Concept Generation
– First mock up for a mili-newton force sensor
– Computer Interface and Matlab programming
3

4. Preliminary Ideas – Handling of mechanism
Electrostatic Levitation Air Curtain Contact area
reduction
Vibrating Platform Free fall measurement 4

5. Preliminary Ideas – Handling of mechanism
Unidirectional Stiff skin
Liquid bath levitation String suspensions
Elastic members 5

6. Preliminary Ideas – Initial Detailing
Air Curtain
Water
Floatation
Contact
Reduction
Electrostatic
Levitation
6

7. • First Mock up
– First trial was done in
acrylic, as a proof of
concept
Initial Trials
7

8. • Second mock up
Initial Trials
Image @230x
LoadedUnloaded
8

9. Initial Trials
2.108gm
From here we could
conclude that we can make a
milli-newton force sensor
with acrylic as material
(thickness 1.8mm)
9

10. Image Analysis
Loaded TipUnloaded Tip
Results Plotted
Edge DetectedEdge Detected
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11. First Mechanism
Material : Acrylic
Thickness= 1mm
Load = 2µN = 2x e-6 N
Output displacement = 0.002007 µm = 2x -9m
= 2 nm
COMSOL analysis – software**
Material : PDMS
Thickness = 1mm
Load = 2µN = 2x e-6 N
Output displacement = 4.014078 µm
Experimental Method:
Material: Acrylic
Thickness = 1.8mm
Load = 1.922 gms
= 18.85 x e-3 N
= 18.85mN
Output displacement =
51.61 µm*
*manufacturer ‘s E not
specified
Software analysis:
Material: Acrylic
Thickness = 1.8mm
Load = 1.922 gms
= 18.85 x e-3 N
= 18.85mN
Output displacement =
10.50 µm
**All analysis shown Nonlinear analysis with large deformations taken into account
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12. Trials With Different Mechanisms
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13. The best one – COMSOL analysis
Material: PDMS
Load= 3e-7 µN = 300nN
Thickness=0.003m= 3mm
Output Displacement= 5.064407 µm
13

14. • Boric powder (friction reduction)
• The mechanism is kept on a flat surface and boric powder is applied between the
surfaces to reduce the friction.
• Observations:
• The mechanism experiences friction from the flat surface even though boric
powder was applied.
• The mechanism does not come back to original position when the load is removed
in both horizontal as well as vertical position
• Lubricating oil (friction reduction):
• The lubricating oil is applied to one of the surfaces of the mechanism and is kept
on a flat surface.
• Observation:
• The mechanism experiences large amount of frictional forces that the mechanism
does not move.
• The mechanism actually sticks to the surface after application of the oil.
14
Trials and Mock-up

15. • Semi- solid lubricant (friction reduction):
• A semi-solid lubricant is applied on one of the surfaces of the mechanism and is
kept on a flat surface and it behaves similar to the above case of lubricating oil
• Rollers (point contact/ line contact)
• The mechanism is kept on rollers.
• Observations:
• The mechanism does not move smoothly when force is applied and experiences
frictional forces
• The mechanism does not come back to the original position
15
Trials and Mock-up

16. • Water floatation
• The mechanism was made to float on
water.
• Observations:
• The mechanism moved smoothly when
force was applied. Seems like no
frictional forces were acting or very
less frictional forces are experienced
• The mechanism comes back to its
original position once the force is
removed.
• Vibrations are experienced caused by
the environment and the mechanism is
very sensitive to the external
environment which leads to
unexpected movement of the reading
16
Trials and Mock-up

17. • Air flotation
• The mechanism is kept on a surface
which has lot of small holes. The
mechanism floats on the air passed from
the mechanism.
• Observations:
• The mechanism is lifted off the flat
surface due to the air curtain created
• The mechanism moves smoothly over
the air curtain
• The mechanism comes back to its
original position when the load is
removed
• The mechanism experiences lot of
vibrations due to the air flow.
• It does not stop at one position.
17
Trials and Mock-up

18. • Magnetic flotation
• Magnets were attached to one surface of
the mechanism and magnets were
attached to a flat surface. The mechanism
was tried to float on the magnets on the
flat surface.
• Observations:
• The mechanism could not float with
magnets. The magnets on the mechanism
would tend to turn and twist to get
attracted to the magnets on the flat
surface.
• The mechanism would get flipped and get
stuck on the flat surface.
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Trials and Mock-up

19. • The concept is chosen on the basis of the observations made and the best one of
the above is selected for the detailed design.
• Hence, the water floatation method is used to float the mechanism.
• Some of the issues with the water floatation method are as follows:
• The water surface is prone to vibrations.
• Also there are issues related to the leakage that might be there with it.
• Camera set up that is to come will have to be water-proof here.
• Also the major requirement that is there for this is the device has to be horizontal
for the measurements to take place.
• This suggests that though this is an optimistic design that may allow us to go for
nanoNewton measurements but has limitations of its own.
• That is why it was pertinent for us to look for an alternate that might be little more
robust than this. This is why we led to develop two designs and prototypes
subsequently. The second design was with a mechanism that will offer us micro
Newton range measurements and is small in size. Smaller size allows it to sustain
its weight on its own and the need for supports is reduced.
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The chosen concept

20. Detailed design phase of nano Newton force sensor:
20
Detailed Design Phase

21. • The final complete design of the nano newton sensor is shown above. The working
of the sensor will be explained in the subsequent paragraphs.
• The product consists of the following assemblies which fit together to complete
the embodiment.
• The mechanism
• Camera assembly
• Probe holder
• Mechanism holder
• Embodiment
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Components of the sensor

22. 22
• The camera is a digital microscope.
• This camera is held exactly on top of the
mechanism output pointer end.
• The camera captures the images when the
mechanism is loaded and when it is
unloaded. After analysing and computing
we get the unknown force by image
processing.
• Design of camera holder such that focusing
of pointer possible by use of rack and
pinion.
• The camera can be locked by a small locking
system provided at the shaft so that once
the pointer is focused we can fix the camera
in position for image capturing.
Camera Assembly

23. • The probe is the part attached at the
input point of the mechanism. The
probe is used to poke the subject like a
bio cell to compute the forces exerted by
the subject.
• The probe in our case is a glass pipette.
• Breakage problem of probe.
• Our probe assembly is a snap fit kind of
part. The probe is permanently stuck on
one of the snap part and other part of
the snap part is stuck on the mechanism
input end.
• The two parts are then snap fitted. This
probe is weight balanced so that it can
be held in position while in operation.
23
Probe holder

24. • Mechanism holder
• The mechanism is to be floated on
water.
• When the water drains away the
mechanism will sag and the
corners of the mechanism will
break.
• Mechanism can break during
Transportation and handling
Therefore for the safety of the
mechanism, two plates held by
springs and opened by a
mechanism will be used.
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Mechanism holder

25. Embodiment
25
Water barriers
The water barriers are provided to reduce the vibrations which may occur due to the
external environment.
Embodiment of the mechanism

26. • One more prototype is done which
gives us micro Newton force. Micro
Newton force sensor also has lot of
applications similar to the nano
Newton range.
• This design and prototype was done
as the mechanism for this is stiff in
the plane perpendicular to the plane
of the mechanism. This mechanism
can be held in any position and
angle and still it works. This
mechanism does not need any
floatation method as it remains in its
plane on its own.
26
Detailed design phase of micro Newton force
sensor

27. Form fector
• Form for the device was inspired by digital SLR
cameras.
– The theme completely syncs with the idea of using
vision based system for doing the force
measurement.
– The theme thus becomes “to see the force”.
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28. • The camera assembly remains same and only the mechanism holder parts differ
from the nano newton sensor.
28
Components of micro sensor

29. • The glass pipette which will be used
for probing has to be able to replace
the probe as and when neede like
when broken
• This probe holder is a snap fitment of
two parts which can be easily
removed and replaced by another
pipette
29
Components of micro sensor

30. • The manufacturing of both the sensors is carried out as follows. First the
manufacturing of the mechanism was carried out.
• Manufacturing of mechanism in PDMS:
• The procedure is as follows
• Make a mould from – acrylic or metal
• Pour the PDMS mixture of base and hardener
• Put in oven for curing (around 100oC for approx 2 hrs)
• Remove from oven and peel from the mould
– Mechanical properties of PDMS depend on curing time and temperature
– PDMS before curing spreads on surfaces very easily so it can seep into very
small gaps as well
30
Manufacturing

31. • First mould in PDMS
• PDMS got stuck inside and mechanism could
not be peeled off
• Second mould tried with acrylic material
• Breakage of mechanism at many corners
• Made mechanism in 1mm thickness
• Applied vaseline in thin section. Mechanism
could be peeled off easier than before.
31
Manufacturing

32. • The manufacturing of the two sensors
nano newton as well as micro newton
was done by the following
manufacturing processes and
methods:
 Laser cutting for plastic parts
 Turning operation
 Milling operation
 CNC machining for nano newton parts
 Wire EDM cutting for mould
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Embodiment Manufacturing

33. 33
Camera assembly -components

34. 34
Micro Newton mechanism holder componenets

35. 35
Nano newton -components

36. 36
Nano newton -components

37. • As has been discussed before that the
requirement for the device was to make it a stand
alone system and a plug and play device.
– This gave the rise to the computer interface that is
simple for the user and is very informative as well.
– Keeping simplicity in mind the sequence of operations
was defined.
– Format for the screen was selected to be a window
that acts like a preview tool as well as the information
provider.
– Sequence of operation was defined in easy toggle
buttons as the operations were reduced to two states.
37
Computer interface and image processing

38. The Screens
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39. • Steps were decided on the basis of functional
requirements and ease of use-
– The camera must focus on the measuring pointer
• This job was left as the first step for the user.
– Second is the data capture screen
• Present system was made to capture 20 frames with an
interval of 5 frames.
– Camera fps- measured to be ~10fps
• This screen allows the user to log the data while the
measurement is going on.
– Third screen allows the user to view results.
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The Screens

40. Scope for further work
• Development of the mechanism to
enhance the sensor resolution
• Development of image processing
algorithm to handle image noises
better
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41. Acknowledgment
• We express our sincere thanks to Prof. G.K. ANANTHASURESH, Mechanical
Department, IISc for his constant guidance, much needed moral support and
encouragement and for providing us help as and when needed at every stage of
our project.
• We owe special thanks to Mr. John , Mr. A.RaviKumar, Mr. Ramu and Mr.
Govindaraju for providing us help during the manufacturing of the prototype of
our project. We also owe thanks to Mr. Santosh and Mr. Sajeesh kumar for helping
us with materials and manufacturing of mechanisms.
• And last but not the least we thank the faculty of our department CPDM for their
support and encouragement.
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42. 42
Demo of the product

43. 43
Thank you !!!