proceedings of the 1999 IEEWASME InternationalConference on Advanced IntelligentMechatronics September 19-23, 1999 Atlanta, USA ●

Remote controlled tele-nanomanipulation Jean-Michel 1

FRIEDTl,

Laboratoire

Moussa

de Physique

Centre

National

32, avenue 2

HOUMMADYl,

et Mt%rologie

Ecole D4partement

Normale

tele-manipulation,

\ TCP/IP

server

D/A converter I L

/

II

IEEE

France

atomic-

Piezoresistive AFM cantilever

L

Sample

43 Piezo tube

(XYZ)

PI positioning table I

I

Fig. 1. General setup of the tele-nanomanipulat ion system

of a Wheatstone bridge. Signal processing circuits have been reduced to the bare minimum and allow high integration of the full AFM as well as high adaptability depending on the working conditions and combination with other sensors. Data acquisition and position control by a commercial (Physik Instrument, PI) positioner as well aa by a piezoelectric tube (allowing 3 axis fast positioning) are controlled by an IBM compatible personal computer. The use of such a common computer allows easy adaptability of the software and associated hardware (analog to digital (A/D) and digital to analog (D/A) as well as parallel and serial communication (RS-232) ) to our requirements. High integration of the manipulation system is obtained by the use of a piezoresistive cantilever by avoiding the need for an optical deflection sensor. The lack of optical deflection detection method offers the possibility to combine optical detection methods (surface pla.smon resonance (SPR) [5], [6], fluorescence) which would otherwise be disturbed by the laaer beam of the deflection detector.

A commercial (Park Scientific Instruments) piezoresistive AFM cantilever is used as a manipulation tool. The deflection of the cantilever due to external forces is monitored as a variation of the value of one of the resistors @ 1999

(DMI)

Parallel port

THE HARDWARE

10.00

Lyon,

(

Recent trends in the development of local probe microscopy includes the use of the nanometric-sized sensors not only for detection but also for environment control (etching, particle manipulation). Applications include biological cells precise position control, high density data storage ancl highly integrated nano-manufacturing processes [1], [2], [3]. The very specific equipment required for nanomanipulation, and the related high costs, prompted for the development of a multiple-user, remote nano-manipulation system in which any number of users connected to a network can use the facilities installed in a laboratory for telemanipulation [4]. The high precision work of moving micrometric and nanometric sized particles is eased by the use of force feedback, informing the manipulators (“clients” ) on the force exerted by the atomic force microscope (AFM) tip on the sample. The general setup of such a system will here be described from the hardware and software points of view. We name “server’ the part of the hardware and software located in the laboratory in which the nano-manipulation equipment is located. We name “client” the software used to display the microscope output (magnification: x 30 to x 1500), and “control” the part of the software used on the remote computer to control the devices on the server side.

0-7803-5038-3/99/$

de Lyon,

RS232

1. INTRODUCTION

II.

France

et Informatique

69007

Abstract— We have successfully developed a remote forcefeedback tele-nanomanipulation system aimed at allowing any number of computers connected to a TCP/IP network to control a positioning stage supporting a sample and to receive a feedback on the deflection of the AFM tip used as manipulation tool as well as a microscope image for visual feedback of the operation. Force feedback information are sent back to the manipulator at a rate arbitrarily set to about 10 Hz.

(LPMO),

(CINRS)

Besanqon,

Sup4rieure

d’Italic,

CERVELLE2

Oscillateurs

Scientifique

25000

de Math4matiques 46, all~e

Keywords-Nano-manipulation, force microscopy (AFM).

des

de la Recherche

de l’observatoire,

Julien

III.

THE SERVER

The server is located in the laboratory in which the nano-manipulator haa been developed. From a hardware 9

2

point of view, it is composed of an optical microscope fitted with a CCD camera, an AFM cantilever deflection sen-

in fact are the exposure time, CCD A/D converter offset and amplification factors) and the sample position relative

sor (piezoresistive cantilever and signal pre-processing electronics), data acquisition system (analog to digital converter) and a nanometric scale resolution positioner. All this equipment is controlled by an IBM-PC compatible computer. This same computer hosts the server software

to the cantilever (3 axis). A third kind of request, the so called “force” request, asks the server to send back the torsion of the cantilever when no request from the user is

used to send information to the client(s) and control softwares on the remote computers. Later development of our instrument

will separate

the data acquisition

and control

aspect (relegated to an Hitachi H8 microcontroller based system) from the server and microscope image acquisition aspect and should sent to the client.

allow higher frame

rate of the images

The server side is highly hardware dependent due to custom made acquisition (A/D) and control (D/A) extension cards as well as due to the use of a camera (Connectix Quickcam, framerate < 5 fps) connected to the parallel port. as opposed

pending. Feedback to the user is limited by the network bandwidth and the load on the remote computer (control program). The force feedback rate has been arbitrarily set to 10 Hz, and can be increased up to 17 kHz, The control program continuously requests A/D conversions from the server on the Wheatstone bridge and displays the reading at a much greater rate than the information sent by the user, hence a feeling of continuous feedback on the state of the cantilever. The result of these readings feedback joystick. VI.

POSITIONING

will be later sent to a force-

OF MICROMETER

SIZED PARTICLES

Data structures are Intel processor oriented, to the client and control sides which are sim-

ple greyscale image display and Xl 1 graphic user interface programs that should be easily portable to any kind of architecture and operating systems. IV.

THE

CLIENT

The client is used to display the image viewed from the microscope on the server side to any number of hosts. Such a system allows several people connected to the network to view the work in progress without being allowed to act on the manipulator itself. The framerate

of the 320x240

greyscale

(6 bpp) images

is determined by a compromise between network speed and compression time on the server. Using the standard Z1 lb 1 .0.4 compression library (variation of the LZ77 algorithm), a factor two compression rate is available without major speed loss on the server side, resulting on a local network (10 Mbit ethernet ) to a framerate of about 2 images/second, mainly limited by the speed of the parallel port to which the camera V.

THE

is connected.

CONTROL

PROGRAM

Although visually less remarkable than the client, the control program is the central part of the remote manipulation system. It is mainly composed of a graphic interface easing the emission of orders to the sender via a TCP/IP (telnet) connection, and a continuous request for information on the force applied on the cantilever. This force information is for now simply displayed on the control panel and might later be used to control force-feedback joystick. Reactivity

the force applied

on a Fig. 2.

by the bandwidth of the PI positioner (30 Hz) which is usually much lower than the network bandwidth (at least on a local network), Better reactivity will be achieved with the use of a piezo tube as positioner. The control program is able to send two kinds of commands to the server : information brightness,

regarding the CCD camera contrast and white-balance

settings (so called parameters which

Sticking of small particles during lateral motion of the canis 60 um.

tilever. The width of the cantilever

of the system to the user control is determined

The main problem

with nanomanipulation

under room

conditions (high moisture) is the liquid bonding between the manipulated particles and the cantilever [7]. While large dust particles (characteristic size: 20 pm) do not stick to the cantilever but seem to roll on the surface, aggregates of smaller particles (characteristic size: 3 to 7 pm,

10

‘

3

Fig. 4. Cantilever after manipulating 3-7 pm calibrated Ni particles. Note the particles still attached to the cantilever near the tip.

VII.

FORCE

FEEDBACK

INFORMATION

Contact of the cantilever with the surface is observed as a large shift in the Wheatstone bridge output. Although our latest electronic processing circuit lacks resolution for attractive-region observation in the force-distance curve, a visible shift is observed at the Wheatstone bridge output during

particle

particles observed output

-. Fig. 3. Effect of the wedge-shape of the cantilever during forward motion. Particles are moved to the side of the tip rather than precisely pushed in the displacement direction.

calibrated Ni particles) tend to stick to the cantilever even when the distance between the cantilever and the sample is increased. Steps for particle removal by shaking the cantilever lower the resolution of the manipulation device. Solutions include work in liquid medium (as required for biological applications) or under low moisture environment (such as vacuum conditions), or hydrophobic preprocessing of the sample’s surface and of the particles when possible. Current experiments have been made on surfaceacoustic wave (SAW) device electrodes (for distance reference) and seem to be an efficient way of modulating friction forces: lateral motion, orthogonal to the electrodes direction, helps the particles displaced to come off the cantilever when sticking occurs. It is expected that applying an oscillating acoustic

voltage to the electrodes in order to generate the waves will reduce sticking forces between the par-

ticles and the sample’s

increasing

with the load of

far from the sample and after contact. VIII.

CONCLUSION

We have successfully developed an experimental version of the software and hardware aspects necessary for telemanipulation of micrometric and nanometric sized objects with force feedback. The very modular aspect of this instrument allows easy adaptability ditions (contact/dynamic modes,

to many kinds of conair/liquid medium) and

easy combination with other sensors. Further developments include task oriented

manipula-

tion (rather than step by step control), tapping mode AFM implementation in order to be able to use the AFM cantilever not only as a manipulation tool in contact mode but also as an imaging tool in non-contact dynamic mode. Reduction in the size of the manipulated particles will require to adapt our manipulator for work under liquid medium. AFM cantilevers are not ideal manipulation tools due to their wedge shape and lack of grasping capability. More appropriate tools (tweezers for micro-manipulation, combined multiple under development.

AFM

tips for nano-manipulation)

are

REFERENCES

surface.

Liquid medium nano-manipulation will be first developed on inorganic particles in de-ionized water in order to avoid liquid conductivity disturbances on the data acquisition circuit. Such a device working in liquid medium will later be adapted for work in ionic liquid medium, for biological applications.

displacement,

attached to the cantilever. This shift has been to be about 10 ?10 that of the shift between the

necessary

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