Cell Analysis System Using Two-fingered Micro Hand -Fine adjustment mechanism for end-effector-
Izumi HATTA 8, Kenichi OHARA *, Tatsuo ARAI*, Yasushi MAE*, Tomohito TAKUBO*,
Kenji INOUE**
* Department of Systems Innovation Graduate School of Engineering Science Osaka University 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan TEL/FAX: 06-6850-6367 ** Department of Bio-System and Engineering Graduate School of Science and Engineering Yamagata University 4-3-16 Jonan, Yonezawa, Yamagata, 992-8510, Japan
hatta(darai-1ab.sys.es.osaka-uacj
Abstract: A two-fingered micro hand has been developed for years and it allows dexterous manipulation of a single cell: grabbing, positioning, rotation and releasing. The end-effector of this
micro hand consists of two glass needles. Before grabbing an object, the glass needles need to be approached to each other
manually (initial setup). However, this operation requires high skill manual control, so that it is very difficult and a time-consuming. This paper discusses improvement of the original micro hand mechanism to achieve its fine adjustment of two glass needles. For the easy initial setup, movement of the glass tips should be divided into three directions (horizontal, translational, vertical) and have the resolution of several micro
meter order. Three piezoelectric devices are used to realize the fine movement for three directions. Moreover the workspace of
the end-effector can be widened by applying the principle of leverage to glass and piezoelectric device. Based on these ideas, we prototyped a new shape of end-effector which enables fine movement along three axes. Using this end-effector design, the initial setup of micro hand is easier than the previous model. As a result, the micro hand can achieve more efficient manipulation.
elasticity at the surface of single microbial cell [7]. Even tracking dynamic changes in the stiffness of the cortex of adherent cultured cells along a single scan-line during M phase, from metaphase to cytokinesis was done [8]. On the '
ohe hd, smpeasysem whaich inot so exesive has developed to measure mechanical properties of cells[9].
These research results are expected to lead to diagnosis and
therapeutic approaches of diseases. S.E.Cross et al [10]
studied the stiffness of cancer cells and shows the mechanical analysis can distinguish cancerous cell from normal one even when they show similar shapes. The micro manipulation is becoming more and more important technology in these biotechnology fields. inti fi,om
devices,w
ae
to s
re
operation in micro environment, are expected. We are e
developing a two-fingered micro hand which adopts parallel mechanisms and piezoelectric devices as actuators modeling chopstick usage. This has six degrees of freedom for motion
and high positioning accuracy in each finger and this allows dexterous manipulation of a single cell: grabbing, positioning, rotation and releasing in the size of micrometers [1 1][12]. Utlzn Utilizing this micro hand, Tanikawa et.al .1]1] thsmcohn,Tnkw'ta Keywords - Micro-manipulation, Two-fingered micro hand,' M icmademonstrated a micro assembly with adhesive bonding Keywordsg technique [13]. Another function including image to enable auto-focus and calibration, user processing 1. INTRODUCTION interface for tele-operation and auto manipulation also has been developing.[14][15][16] In recent years technical development of biotechnology The end-effector of this micro hand consists of two glass is remarkable. For example, nuclear transportation technique needles which have sharpened ends with less than 1 um is in the limelight with high availability for a broad field curvature. And, these needles are attached to the micro hand such as regenerative medical, pharmacy, stockbreeding, using holding parts and screws so that they can be fertility treatment and so on. And, researchers have great exchanged to new one when they break, become wor and interests in knowing how the cell behaves when various are adhered by dust. Before grabbing an object, the glass mechanical signals are input and measuring the mechanical needles need to be approached to each other in the property (e.g. shear stress, cytoskeletal tension stiffness) Of mirsoi vie mauly oee,ti prto a single cell. Such mechanical properties have been studied onavreyo* el usn th tehiqe of cel poki1] requires high skill manual control, so that it is very difficult mic~~~~~~~~~~~~~roppet apraton oflclcl ufc ae[] h and takes a lot of time. As a solution of this problem, we * . . to o~~~~~~~~roto yed a new shape of end-effector holding parts which atomic force microscope (AFM)[3] .has .been applied l tyl enable fine movement about three axis using three std bilgia materis[] Mirmcaia boes5 an eptela cels6 are stuie using 1AsFM piezoelectric devices. In this paper, the principle of the en-fctrsm haimspooed Moreover, AFM are used to distinguish regions Of different
properties*of
978-1 -4244-291 9-6/08/$25OO0 ©2008 IEEE
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2. SYSTEM CONFIGURATION
PiR
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Figure 1 shows the configuration of cell analysis system using two-fingered micro hand (Fig.2). The micro hand has
a two 3DOF modules to drive two fingers adopting parallel LQWer Upper UMo duled Mod_. mechanism. Parallel mechanism has merits of high speed, high accuracy and high rigidity in addition to its simple configuration. Joint of the micro hand consist of thin plate, which is punched some holes and bent, and this mechanism P monitor E Proesmn enables it to be low costs, small size, and good benefits. Three piezoelectric actuators (NEC TOKIN, AE0203D16) are arranged on the base-plate and another three on the L Pianlio or middle plate. Their extensional direction is vertical to the plate. Each finger has a glass needle with one millimeter in MWnPpulr conttrl, diameter sharpened at the end. Each module is controlled by Fig. 1 System Configuration the PC (Dell, XPS600, Pentium 4, 3.80GHz) through D/A board (Contec, AIO AD1 6-1 6(PCI)E) and drive amp(MATSUSADA, HJPZ-0. 15Px3). The displacements are measured by strain gauge attached on the piezoelectric devices and sent to the PC through A/D board (Contec, AIO DA12-16(PCI)) for PI control. The micro hand and object are put on the optical microscope stage. The image of the end-effector tips are captured by the CCD camera (Point Gray Research, Flea) and displayed on the PC monitor. The motor is attached on the microscope and controls the motion of the objective lens for focusing. It is basically controlled...................... by human operator in tele-operation with operation device, e.g. joystick, PHANToM omni device, and GUI.
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3. IMPROVEMENT OF END-EFFECTOR HOLDING PARTS
3.1 Structures of current end-effector The present micro hand's end-effector unit consists of two glass needles and holding parts which enable fix and change positions and directions of glasses. The holding part consists of lower and upper parts shown in Fig.3. The glass needles are inserted in triangular incision on the each holding part of the lower and the upper and fixed with a screw. Using the ball joint and the screw A an operator brings two glass needle tips close. These movements are shown by the white arrows in Fig.3. The screw B fixes the ball joint. The end-effector(glass needle) needs to be
replaced to new one frequently because the thinned tips are easy to break by careless contact, adhere garbage and wear-out etc. When setting a new glass needle, it is necessary to make both tips of two glass needles appear to aet.wh oweveralt
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b
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Fig.2 Two-fingered Micro Hand 3.2 Idea of improvements The approaching work (glass setup) can be divided into following three tasks. (i) Bring glass tips close on the x-y plane. (ii) Arranging length of glass tips.
(iii) Matching glass tips height.
It is difficult to meet these 3 conditions at the same time. For example, when the distance between two glasses are less than several um on the x-y plane and length of tips are almost same, their heights are far more than 100um. There are three reasons why it is difficult to adjust the tips by hand. First reason is that the ball joint which have two
these ajset
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n micrometer order,
To solve these problems fine adjusting mechanism should realize the glass needle movement in an accuracy of several micro meters along following direction; (1) horizontal (2) translational (3) vertical as shown by the arrows in Fig.3. It is possible to move in the three directions by using three piezoelectric devices as an actuator. Because the displacement of the piezoelectric device is about several ten um, the range of displacement will be expanded by using the principle of the leverage.
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3.3 Prototype of end-effector part Fig.4 and Fig.5 show the prototype of the lower and upper fine adjustment parts. Fig.6 shows the figure of whole end-effector part. The piezoelectric devices moving in each direction of 1, 2, and 3 mentioned by paragraph 3.2 are called each piezoelectric device (PZT) 1, 2, and 3. PZT 1 was arranged in lower fine adjustment part and PZT2 and 3 were arranged in upper fine adjustment part. These glass needle fine adjustment devices are made by dimension, 3D printer, and made of an acrylonitrile-butadiene-styrene resin. PZT 2 is fixed to the parts using glue. PZT 1 and 3 are fixed to the parts by screws to adjust their position because they touch directly to glass needles. 10 mm PZT (expand 10 um) was used for PZT1 that moved to the horizontal direction. The glass tip theoretically moves 120um by PZT1 according to the principle of the leverage. As for PZT2 of 40mm (expand 40um), PZT 3 of 20mm (expand 20 um) is used for the movement of the vertical direction, and the amount ofa the expectation movement is 195um for the direction3. The distance from the position of the piezoelectric device to the glass needle tip is assumed to be 65mm. The longer glass needle's length is the longer glass tip move.
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Fig.3 Present End-effector of Micro Hand
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Fig.4 Lower Module Part 4. EXPERIMENT
4.1 Experiment 1: measurement of working distance In this section, we measure the working distance in each direction, and compare them with the theoretical values. The result is shown in Tablel. It can be said that a satisfactory correspondence between theory and experiment is observed. During the experiment, glass tips sometimes didn't move even though voltages were applied on PZTs. This is because PZT didn't touch the glass needle well. PZT have to push the glass. The glass tip doesn't extend parallel to the glass needle when PZT2 was applied voltage because PZT2 was attached to the holding parts obliquely.
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Fig.5 Upper Module Part
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Fig.6 Prototype of new end-effector
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Fig.7 Picture of new end-effector Table I Maximum displacement of the end-effector Theoretical[um] Actual [um I
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PZTI 120 134.2
PZT2 40 42.9
PZT3
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4.2 Experiment 2: Approaching glass needle tips The glass setup was executed using the prototype and measured the time. Fig.7 shows the procedure for setting up the micro hand end-effector by using the fine adjustment parts and Fig.8 the microscopic image of the setup process. In the first step an operator sets the glass needles to the
microscopic view(480um
the ball joint and the Tlii-n
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Table 2 Result of approaching experiment manual setup piezo setup x T y | time x[um] y[um] z[um] time 18 136 12.5 13m30s 2.1 35.8 50s 35 96 27.6 5m 20 11.1 30s 88.1 171.9 112.8 16m 12.2 9.7 55s 21.4 85.7 90.8 18m35s 12.8 13 47s 7.1 137.1 73.6 8m40s 2.7 14.2 77s
tips and its time by hand, and the same one by using fine adjustment parts. Seeing the result, adjusting work ended within 30 minutes. Comparing . . . with . conventional ............ adjusting .. ..J work which took more than several hours it can be said that this fine adjustment unit enables to make the setup easier. Because the glass tips can be arranged with this before using micro hand, the working area of an upper module can be used effectively. The problem is that the expansion of glass needle in direction 2 is only 40 um which is shorter than another. So it takes most of the tome to match the glass length. Widening the working distance of direction 2 to 100-200 um will make the setup process easy. 5. CONCLUSION
[2]
[3] [4]
[5] [6]
[7]
[8]
The new shape of the end-effector holding parts was designed and built to solve the problem of the difficulty of glass setup work. This enables the movement in three directions by the micrometer order using three piezoelectric devices. It realized easy work to approach the point of the glass needle tips. The piezo setup needs to be done automatically to reduce operator's burden further more. This requires that the workspace of the fine adjustment parts which operators assume in their mind has to be calculated. As a future work, the model fine adjustment parts will be made. And connection mechanism between glass needle and piezoelectric device on the fine adjusting part also need to be improved.
[9]
[10]
[11]
6. ACKNOWLEDGMENT
[12]
This work was supported by MEXT under Grant-in-Aid for Scientific Research on Priority Areas (Project No. 17076010).
[13]
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