Adhesion state detection by vision and its application to automatic
micro manipulation
Tetsuyou Watanabe and Yutaka Serita

Abstract— In our previous paper, we proposed a method for
reducing adhesion forces by oscillation. However, the following
problems have not been still resolved: (1) Since adhesion state
was checked by analyzing the data obtained by laser
displacement meter, this method is available in only limited
situations. (2) Automatic checking system for adhesion state was
not developed. (3) Automatic micro manipulation system was
not developed. Considering the above, in this paper, we propose
a method to automatically check adhesion state by vision.
Firstly, we develop a method to estimate the amplitude of theoscillation using the blur resulted from the oscillation. We callthe estimated amplitude AIV (amplitude indicating value).
Then, we develop a method for checking adhesion state by AIV.
Based on the checking method, we develop a automatic micro
manipulation system for pick and place operation. The validityof our method is shown by experiments.

R

I. INTRODUCTIONECENTLY, there has been a growing interest in amanipulation of a micro/nano sized object. It is thetechnology
requiredtoassembleormaintainmicrocomputers, micro electronics parts, a micro medical
equipment, and so on. Different from a manipulation in amacro range, we cannot neglect an adhesion force between amicro object and an endeffector. In a macro range, the van der
Waals, capillary, and electrostatic forces (proportional tosurface area) become more significant than the inertial andgravitational forces (proportional to volume), because of ascale effect[1], [2]. These adhesion forces (van der Waals,
capillary, and electrostatic forces) cause the adhesion
between a micro object and an endeffector. Therefore, even abasic operation such as a pick and place operation is very hard
to complete. Especially, a release of an object from an
endeffector is very difficult.
In order to resolve the releasing problem, many methods
have been developed, including the adhesion-type micro
endeffector[3], the vacuum gripping tool[4], releasing byslopping and oscillating an endeffector[5]-[7], releasing bycontrol of electrostatic force[8], and releasing strategy basedon environment information[9]. However, the problems suchas the hardness of control after the release[3]-[8], thehardness of practical use due to the harness of acquisition of
all required information[9] were not resolved.
Recently, we developed a new strategy to cope with theadhesion force[10]. When bringing an oscillated endeffector

T. Watanabe and Y. Serita are with Graduate School of Natural Science &Technology, Kanazawa University, Kanazawa, 920-1192, Japan (e-mail:te-watanabe@ieee.org).

close to a micro object on a substrate and contacting theendeffector with the object, the adhesion force between theobject and the endeffector becomes smaller than that between
the object and the substrate. Then, it is easy to remove theendeffector from the object. Using this strategy, we canaccurately manipulate micro object like macro manipulation.
But, this strategy is not always available. When the amountof pushing the object by endeffector is large, the oscillation
becomes small, and then the adhesion force is not reduced
enough. To investigate the phenomenon, laser displacement
meter was used in the previous paper[10]. When lower mode
frequencies (than the frequency of the input oscillation) are
excited, adhesion force is reduced enough. When lower
frequencies are not exited, adhesion force is not reduced
enough. However, this method is available in only limited
situations since the laser displacement meter must be fixedand can measure only limited area/point. If something blocks
the light/laser or the target leaves measuring point, the laser
displacement meter can not measure the target. Therefore, it
is hard to check the adhesion state by this method in micro
manipulation. Also, the method for automatically checking
adhesion state was not developed. Applying FFT to themeasured data by the laser displacement meter, we search anddetect the lower mode frequencies manually. Since thismethod takes much time, it is not easy to check adhesion
force on-line. Also, controlling method to keep adhesion
force reduced was not developed. Hence, micro manipulation
was not atomized.
Considering the above, we propose a novel method forchecking adhesion force by vision. we also develop an
automatic micro manipulation system. The oscillation ofendeffector can not be perfectly caught by camera. Instead,the blur of the oscillation appears in the captured image. The
amount of the blur is associated with the amplitude of theoscillation. Then, we develop a method to estimate theamplitude of oscillation by the blur. Subsequently, we focus
that lower mode frequencies have very large amplitudes
comparing with higher mode frequencies or no-resonancefrequencies. Utilizing this findings, we develop a method for
detecting lower mode frequencies by a blur. The adhesion
state can be detected by checking whether or not lower mode
frequencies are excited. Then, based on this findings and themethod for detecting lower mode frequencies, we propose themethod for checking adhesion state by vision. This method
can be applied to any areas in the captured image and used all
the time during manipulation. Its computational load is low.
Since vision sensor is usually used in micro manipulation andsubstrate
Micro objectyendeffector
subendeffector

Fig. 3 Experimental set up for checking adhesion state by laser
displacement meterx
Fig. 1 Target System

Fig. 2 Overview of the experimental setup

any other sensors are not needed, the total system is very
simple and low cost. Applying this method to micro
manipulation, we develop an automatic control system for
micro manipulation.
II. TARGET SYSTEM
Fig. 1 shows the target system. we consider to pick andplace an micro object on the substrate by endeffector andsubendeffector. For the simplicity, we assume that: (1) the
manipulation is done in a planner space and a gravity force
doesn't work, (2) the object is a sphere, (3) the endeffector,
the subendeffector, and the substrate are made of a samematerial, (4) the endeffector, the subendeffector, and thesubstrate are grounded for preventing an extra charge at theinitial state. Fig. 2 shows the experimental set up. This system
consists of the manipulation system, the image-capturingsystem, and the finger-oscillating system. The manipulation
system consists of the endeffector, the subendeffector, thesubstrate, and the object. The endeffector and thesubendeffector are cantilever beams made of copper in size of
3x40x0.3[mm]. 5[mm] from the edge is used for clamping.
The beams are rolled coppers, and any surface treatments
such as grinding are not conducted. Young's modulus ofcupper is 1.02x1011[N/m2], Poisson's ratio is 0.35, and density
is 8900[kg/m3]. On the endeffector the piezocell (Fujiceramics, Z0.2T50x50x50S-W C6) of 5x3x0.3[mm] isbonded at the position of 1[mm] from the clamped end foroscillating the endeffector. The surface of substrate is a
cupper cut bonded on stainless board. The endeffector and thesubendeffector are attached on XYZ stage (Surugaseiki,
PMZG413) which can be controlled by PC. Note that theorientation of the endeffector can be slightly adjusted at theclamping area. The object is a glass sphere (Union, unibeads)
with a radius of 50[10-6m]. Young's modulus of glass is
7.05x1010[N/m2], Poisson's ratio is 0.17, and density is2500[kg/m3]. The image-capturing system consists ofVideo-microscope (Surugaseiki, VMU-V) with objective
lens (Mitsutoyo S72M-5), CCD camera (Lumenera, LU135),
and PC. The overview of the manipulation is captured by the
CCD camera through the microscope and sent to PC. We use
maximum illumination of light source (Schott
MegaLight100-ROHS) whose maximum illumination is
24000[Lx] at the 100[mm] from the tip of the lighting system.

The endeffector is oscillated by oscillating the piezocell by afunction generator (NF, DF1906) through a power amplifier.
the power amplifier is handmade circuit and its amplification
ratio is set to 3.2.
III. REDUCING ADHESION FORCE BY OSCILLATION
Here, we introduce the method[10] for reducing adhesion
force by oscillation. In a micro range, due to the scale effect,adhesion causes and makes manipulation hard. In the target
system, the effect of capillary force among adhesion forces islargest. Here, we reduce such kind of adhesion force by
oscillation. When the oscillated endeffector is brought close
to the object on the substrate and contacts with it, theadhesion force between the object and the endeffector
becomes smaller than the adhesion force between the object
and the subendeffector. Then, the endeffector can be easily
removed from the object while the object adheres to thesubstrate. However, this method can not be always available.
When the amount/force of pushing the object by theendeffector is large, the effect of the oscillation decreases.
Then, the adhesion force is not reduced enough, and theobject sometimes adheres to the endeffector. Therefore,
adhesion state has to be checked. Here, we show theexperiment for the check. Fig. 3 shows the experimental set
up constructed by removing the subendeffector and adding
the laser displacement meter (Sony, VL10) in the system
shown in Fig. 2. y denotes the distance between the object andthe endeffector. We move the oscillated endeffector along y
positive direction in Fig. 3 with the step of 1[μm] until ybecomes 8[μm]. The endeffector contacts with the object at
y=0[μm]. We measure the oscillation of the endeffector by
the laser displacement meter. The input signal for theoscillation is sine curve whose amplitude is 5[V], and whose
frequency is 4th mode frequency 3.171[kHz]. Fig .4 shows
the results. The left figures show the movement of theendeffector and the right figures show the results obtained byapplying FFT to the movement data. y=3[μm] is the casewhen the adhesion force is reduced while y=8[μm] is the casewhen the adhesion force is not reduced. From Fig. 4, it can beseen that lower mode frequencies are excited at y=3[μm]while they are not excited at y=8[μm]. It indicates that we canestimate whether or not adhesion force is reduced bychecking the excitation of the lower mode frequencies.

Image concentration

500(a). y = freeConcentration
gradient

50

Oscillation is not excited

40
0

40

Oscillation is excited(b). y = 3

Fig. 5 Image concentration gradient(c). y = 8

grey-scaled

Fig. 4 Oscillation of endeffector measured by laser displacement meter

IV. ADHESION STATE ESTIMATION BY VISION
A. Amplitude estimation by vision
In this paper, we develop a method for detecting lower
mode frequencies by vision in order to automatically control
to keep adhesion force reduced. For the purpose, we firstly
develop a method for estimating amplitude of oscillation
using only vision information.
Oscillation is too fast to be perfectly caught by camera.
However, a blur resulted from the oscillation appears in thecaptured image. Then, we try to estimate the amplitude of theoscillation using the blur. When oscillation is not excited, theimage concentration gradient (see Fig. 5) around the edge ofthe endeffector is large. On the other hand, when oscillation is
excited, it is small due to a blur. Using the concentration
gradient, we estimate the amplitude of the oscillation. We callthe estimated amplitude AIV (amplitude indicating value).
The procedure for deriving AIV is shown in Fig. 6. First, thecaptured image is grey-scaled. Next, it is smoothed andbinarized. Previously, we prepare the tip area image of theendeffector as a template image. By template matching
technique[12] which find the part in the binarized image
which matches the template image, we detect the position ofendeffector. On the other hand, we search suitable points for
tracking, p, around the edge of the endeffector in the firstly
grey-scaled image. Here, we pick up p’s located around theupper side (area of 10 pixel (about 10μm) from the upperedge), and let Pu be a set of the picked up points (see Fig. 7).
Similarly, we pick up p’s located around the bottom side and
let Pb be a set of the picked up points. Also, let pk-i be ith p
contained in Pk ( k ∈ {u, b} ), let n be the number of pu −i ∈ Pu ,and let m be the number of pb−i ∈ Pb . We calculate lk-i which is
the length between pk-i and its nearest side/edge. Then, we
derive the maximum value of lk-i:(1)
lmax = max lk − ii,kUsing lmax, we define the following region Xk-i for pk-i:

smoothed and binarized
search suitable points for
tracking
detect the position ofendeffector using templatemaching

set Pu and Pb(tracking points around upperand bottom sides)

set the region x u −i and x b− ifor every pu − i and pb −iderive cui-max and cbi-max(the maximum concentration
gradients in the x u−i and x b− i )derive cu-avg and cb-avg(the averages of cui-max, cbi-max)

a = c u − avg - c b − avg(derive AIV )Fig. 6 Flowchart for deriving AIV (amplitude indicating value)p k - ix − 0.6 *l max ≤ x ≤ p k - ix + 0.6 * l max ⎫⎧X k − i = ⎨(x , y )⎬p k - iy − 1.4 *l max ≤ y ≤ p k - iy + 1.4 *l max ⎭⎩(2)where pk-ix and pk-iy are, respectively, x and y components of
pk-i. Here, 0.6 and 1.4 is set by trial and error so that the

90

AIV

Upper side

AIV

120

60
30

y

Bottom sidex

Fig. 7 Upper and bottom sides of theendeffector

1st mode

0
0

2.5

5

7.5

Input voltage[V]m

3rd mode

4th modenonresonanceFig. 9 AIV for 1-4th mode frequency

Fig. 8 Relation between the input
voltage and AIVnc b− avg = (∑i =1c bi −max ) / m

2nd mode10

nearest side/edge can be contained in Xk-i and the variation of
the maximum image concentration gradient in the Xk-i can besmall. Let cki-max be the maximum concentration gradient in
the Xk-i. We compute cki-max for every pk-i (Xk-i) and derive its
average value ck-avg :c u − avg = (∑i =1c ui − max ) / n

100
80
60
40
20
0

(3)

From (3), we define the amplitude indicating value (AIV) a
as follows:(4)
a = c u −avg - c b−avg .
Here, we confirm the efficiency of AIV by experiment. We
oscillate the endeffector by oscillating PZT. The input
voltage for PZT is square wave whose peak to peak is from 0
to 0-10 [V], whose duty ratio is 50[%] , and whose frequency
is 1st mode frequency 0.18[kHz]. AIV is computed by the
program written by C++ language using OPEN CV library[12].
Fig. 8 shows the result. The horizontal axis expresses the
input peak voltage, and the vertical axis expresses thecomputed AIV. Note that the input peak voltage indicatesamplitude of oscillation (since the voltage is proportional tothe amplitude). By applying regression analysis, the relation
is expressed by v=85a-0.27 where v denotes the input peakvoltage. From the result, it can be seen that the amplitude ofoscillation can be estimated by AIV.
B. Discrimination between higher and lower mode
frequencies by AIVWhen bringing the oscillated endeffector with higher mode
frequency close to the object on the substrate and lower mode
frequencies are excited, the adhesion force between theendeffector and the object is reduced. Then, if discriminating
between higher and lower mode frequencies by AIV, we candetect the adhesion state by AIV. Here, we investigate
whether or not higher and lower mode frequencies can bediscriminated by AIV by experiment.
The input voltage for PZT is square wave whose peak topeak is from 0 to 24 [V], whose duty ratio is 50[%], andwhose frequency is 1st -4th mode frequency. Here, we selectfrom 1st to 4th mode frequencies, considering 4th mode
frequency is used in our previous paper[10]. For thecomparison, we also select non-resonance frequency of 2

[kHz].
Fig. 9 shows the results. From Fig. 9, it can be seen that thehigher the frequency mode is, the larger AIV is. It is thought
to come from that the higher frequency mode is, the smaller
the amplitude is. The difference between AIV’s for 1st modeand the other modes (including non-resonance frequency) isvery large, and then the 1st mode oscillation can be easily
detected. The 2nd mode can also be discriminated from theother higher mode oscillations by checking the difference of
AIV. On the other hand, the discriminations between 3rd and4th modes and between 4th mode and non-resonancefrequencies are not easy, although they are possible.
C. Detection of adhesion state by AIVIn this subsection, base on the previous subsection results,
we investigate whether adhesion state can be detected by
AIV.
We take the following way (see Fig. 10). First, we bring theoscillated endeffector close to the object and contact theendeffector with the object. Next, we move the endeffector in
the left and right directions of this page. If adhesion force isreduced, the endeffector slides on the object while the object
is at stationary state. If can not, the object rotates. In the casewhen the endeffector slides on the object, we increase theamount of pushing the object, and move the endeffector in theleft and right directions again. This procedure is repeateduntil the object rotates. The input voltage for the oscillation issquare wave whose peak to peak is from 0 to 24 [V], whose
duty ratio is 50[%] , and whose frequency is 4th mode
frequency 3.456 [kHz]. The experience was done 5 times.
The results are shown in Fig. 11. Free means theendeffector is oscillated without contacting with the object.
Note that in this experiment, the value of AIV when adhesion
force is reduced changes with the change of the amount ofpushing the object. Then, AIV in that case is shown by range.
From Fig. 11, it can be seen that AIV when adhesion force isreduced is smaller than or equal to AIV for free state. The
maximum difference is about 20. It is the reason why thelower mode frequencies (than the frequency of the input
oscillation) are excited. On the other hand, AIV whenadhesion force is not reduced is larger than AIV for free state.
It is the reason why if the amount of pushing the object islarge, the energy of oscillation decreases and then theamplitude of the oscillation becomes smaller than that in thefree state (refer to Fig. 4).
Note that AIV for 4th mode in Fig. 9 is different from AIV

variable range of AIV

100

AIV

80

find tip positions of the endeffector and the subendeffector, andgeometric center of the object by template matching

60
40

pinch the object between the endeffector and the subendeffector.

20
0
free

Fig. 10 Overview of the experimentfor checking whether adhesion state
can be detected by AIVAdhesionforce isreducedAdhesionforce is no
reducedFig. 11 AIV’s when adhesion force is reduced andnot reduced (AIV is shown by range because AIV
when adhesion force is reduced changes with thechange of amount of pushing the object)for free state in Fig. 11. It is due to the large difference of theendeffector position. The illumination or light intensity
differs from place to place. Then, if the endeffector positiondiffers largely, AIV also differs. Therefore, in order to checkadhesion state, we use the difference between AIV when theendeffector is freely oscillated around the target point andAIV when the endeffector contacts with the object. Note alsothat there is the case when AIV when adhesion force isreduced is almost same as AIV for free state. It is thought thatthe lower mode frequencies are excited but their amplitude issmall, and then AIV is large. In such a case, it is difficult to
detect adhesion state. However, a precious control for theamount of pushing the object is not need in the target
operation. Therefore, we only have to control endeffector sothat the difference between AIV’s for free and contacting
cases can be included in the appropriately defined range.
Then, we can keep adhesion force reduced, while pushing theobject with enough large force.

remove the object from the substrate by moving the endeffector andthe subendeffector.
remove the endeffector from the object.

Fig. 12 Flowchart for picking operation

find tip positions of the endeffector and the subendeffector, geometric center ofthe object, and the position of the substrate by template matching

move the subendeffector to place the object on the substrate

move the endeffector to nearby the object

calculate AIV and set the AIV as a reference AIV

move the endeffector along y direction by small step so that the endeffector can
get closer to the object

calculate AIV and derive the difference from the reference AIV.

Is the difference is included in the range of from ω1 to ω2 ?

No

Yesremove the subendeffector from the object.

V. AUTOMATIC MICRO MANIPULATION SYSTEM
Using the developed method for detecting the adhesion
state by vision, we develop a system which automaticallypick and place a micro object. We use the experimental set up
shown in Fig. 1 and Fig. 2.
We show the procedure for picking operation in Fig. 12(refer to the real movement shown in Fig. 14). First, using
template matching technique, we find the tip positions of theendeffector and the subendeffector, and the geometric centerof the object. The endeffector is oscillated. Using the position
information, we pinch the object between them. Next, weremove the object from the substrate by moving (controlling)
the endeffector and the subendeffector. Subsequently, weremove the endeffector from the object. In this case, theoscillation of the endeffector can reduce the adhesion force
between the endeffector and the object (see [10] for detail).
We check the difference of AIV and judge the control ofendeffector (adhesion force) is not needed, and then the
checking and controlling procedure is not included in the
flowchart shown in Fig. 12. Next, placing operation shown in
Fig. 13 is done. First, using template matching technique, wefind the tip positions of the endeffector and theremove the endeffector from the object.

Fig. 13 Flowchart for placing operation

subendeffector, the geometric center of the object, and theposition of the substrate. Using the information, we place theobject on the substrate by moving (controlling) the
subendeffector. Next, we move the endeffector to nearby theobject so that the endeffector can contact with the object andpush it if moving the endeffector along y direction (refer to y
direction in Fig. 1). The endeffector is oscillated. Here, we
calculate AIV and set it as the reference AIV. Next, we movethe endeffector along y direction by small step so that theendeffector can get closer to the object. We calculate AIV andderive the difference from the reference AIV. If thedifference is not included in the range of from ω1 to ω2, wemove the endeffector along y direction by small step, andcalculate AIV and the difference from the reference AIV
again. If the difference is included in the range, we judge thatthe endeffector push the object by enough large force,
reducing the adhesion force. In this case, we stop moving thesubstrateobjectsubendeffector
endeffector
100μm

(1)

(2)

(3)

(4)

(5)

(6)

automatically check adhesion state, using only vision
information. Firstly, we have developed a method to estimate
the amplitude of the oscillation, using the blur resulted fromthe oscillation. We call the estimated amplitude AIV(amplitude indicating value). Using this method, we haveshowed lower mode oscillations can be discriminated fromhigher mode oscillations. Then, we have developed a method
for checking adhesion state by AIV. Based on the checking
method, we have developed a automatic micro manipulation
system for pick and place operation. The validity of our
method has been shown by experiments. The target
manipulation doesn’t need precious control of (adhesion)
force. Then, the proposed method is available. If applying
this method to another manipulation which needs more
precious force control, we need to develop a more robust
method including illumination (noise) effect. It’s our future
work.
REFERENCES
[1]

(8)

(7)

Fig. 14 Overview of the experiment for automatic pick and place micro
operation

endeffector and remove the subendeffector from the object.
Subsequently, we remove the endeffector from the object,and finish the operation.
The input voltage for PZT is square wave whose peak topeak is from 0 to 24 [V], whose duty ratio is 50[%], andwhose frequency is 4th mode frequency 3.456[kHz]. The
threshold value ω1 and ω2 are, respectively, set to 5 and 10 bytry and error so that the difference from the reference AIV canbe detected, while the endeffector can apply enough large
pushing force to the object.
The outline of the result is shown in Fig. 14. The number
denotes the order of the time line.
We did this operation 5 times, and all operations weresuccessfully done. These results indicates the validity of ourapproach.
VI. CONCLUSION
In our previous paper [10], we proposed a method for
reducing adhesion force by oscillation. However, thefollowing problems have not been still resolved: (1) Since
adhesion state was checked by analyzing the data obtained bylaser displacement meter, this method is available in only
limited situations. (2) Automatic checking system foradhesion state was not developed. (3) Automatic micro
manipulation system was not developed. Considering theabove, in this paper, we have proposed a method to

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