Proc. of International Workshop on Microfactories, Tsukuba/Japan,(1998)pp.145-156
Abstract
>This paper describes several small robots with accurate versatility
in microscopic range. Our small robot, size of which is approximately
1 cubic inch, is composed of piezo elements for the source of
micro locomotion and electromagnets for clamping on the surface.
This simple mechanism can provide good accurate mobility and design
modularity. In the several experiments, it is demonstrated that
they can provide unique microscopic machining and measuring performances.
Also some small robots can collaborate in making micro through-holes
on the sample plate and pattern control of thin film in the deposition
process. These experimental results indicate the potential capabilities
of micro robots to the promising industrial applications.
Keywords: miniature robot, micro tool, piezo element,
electromagnet, collaboration, micro indentation, capillary probe,
fine grating, thin film pattern, micro drill, desktop production.
1. Introduction
>One of the major problem in high precision production for small
size products is how to make and assemble them with both microscopic
resolution and low cost. The demand for machine tools with much
higher accuracy causes the development of ultra-precision mechanisms
although traditional top-down approaches, such special machine frame
design, actuator error compensation and temperature control need
much of cost and energy consumption. For these year, many new microfabrication
techniques based on IC process and deep X-ray have been also developed
and succeeded in providing micro mechanical parts with complex features.
However they still need much of cost for constructing and maintaining
the facilities. Alternative approach to this problem, several small
robots with useful versatilities of manipulating, tooling and gauging
in microscopic range have been developed by our group[1]. Each small
robot, size of which is approximately 1 cubic inch, is composed
of piezo elements for micro locomotion and electromagnets for fixing
itself on the surface. This simple arrangement can allow the small
robot to move on not only the horizontal plane but on the wall and
the ceiling without any special guideways. And it can also provide
good design modularity so that the optional facilities such as micro
hammer for indentation, micro grating tool and dust capturing probe
can be implemented on each robot in order to offer unique microscopic
tasks. These small robots motion and tool actuation can be controlled
automatically by the PCs with the help of visual monitoring system.
The central PC which is linked to parallel the sub-PC system with
share memory bus interfaces is responsible to negotiate for the
initial planning with the operator and to care the sub-PCs for the
command interpretation and the arbitration among the robots. In
the practical experiments, it is demonstrated that several small
robots, one of them has a micro drill shaft with reduction gear
and the other have which is driven micro DC motors and pinion gears,
can collaboration in making micro through-holes on the target sample
with much of flexibility and cost saving benefit. Another experiment
shows that small robots with the mask can make the micro thin film
patterns of deposition metal in the vacuum chamber. These experimental
results indicate the potential capabilities of micro robots to the
promising applications with low cost and much of flexibility. Finally
the current status of our development toward "Desktop Micro Robot
Factory" and the future work are described.
2. Miniature Robot for Micro Locomotion
>There have been reported many types of self-walking miniature
robots or mechanisms. Some of them have the main body where on
board CPUs, electronics, motor, sensors and battery are packaged,
and manipulator is equipped if necessary[2]. Generally they are
assembled by using off the shelf components at the time. The others
types are more smaller in size but have rather primitive morphology
due to actuator for propelling. Principle of almost these mechanisms
for locomotion are based on "an inchworm principle[3]" or "impact
inertia[4]", namely synchronous sequence of clamping action and
cyclic elasticity action. This type of micro mechanism is able
to be easily missioned into very narrow space such as in-pipe
environment although control signal and energy power are supplied
with wire. Understanding that there seems to be a lot of technical
problems for packaging every devices into complete autonomous
micro and miniature robots a few functionalities have been prioritized
in our small robots as to be applicable to scientific and industrial
fields at first. In our motivation, they should have locomotion
capability to move not only on plane surface but also on the wall
and the ceiling with less than sub-micron positioning resolution.
Furthermore they must be dispatched into the hazard environment
such as high temperature room and ultrahigh vacuum chamber. And
also micro operation capability is required to be implemented
rather than built-in sensing, computing and communicating capabilities
since it is important to provide practical accurate skills in
micro domain where conventional macro size robot and mechanism
are hard to take access. Thus our small robots is specialized
and simplified for performing the requirements mentioned above.
 [Fig.1] Mechanical
structure with piezo element and electromagnets for micro locomotion
on any curved surface of steel with no special guides
Figure 1 shows the basic structure which is developed as a locomotion
platform of our small robot. The basic design for keeping small
body as small as one cubic inch but size enough to load another
micro tool, and mechanical joint with no backlash was considered
carefully in order to satisfy the requirements[5],[6]. This robot
is composed of a pair of stacked type piezo elements for microscopic
locomotion and U shaped electromagnets for clamping to the target
surface. The main chassis which hold the piezo elements and electromagnets
is machined from a monolithic block of aluminum. It can move with
micro steps without any special guideways when synchronizing the
magnetic attraction, and the expansion/contraction of piezo elements.
Then it essential that the magnetic force should be controlled
critically so that the resulting friction force at the each leg
could be large enough to move without slipping and to hold its
body even on the inclined surface. And the different of step width
between two piezo elements gives the small robot steerage motion
in the right or the left orientation. This arrangement allowed
the small robot to move even on curved surface and typical moving
speed is approximately 2mm/sec when exciting the piezo element
at 100Hz with a 20 micron step width, although the working environment
is unfortunately limited on the ferromagnetic materials. One of
the most interesting feature of this small robot is the possibility
of climbing up and down on even curved surface. For instance,
the typical result performed on the surface of 4cm curvature is
demonstrated in Fig.2
 [Fig.2] Typical performance:
the small robot can climb up and down on S-curved surface with
sub-micron resolution
3. Simple Precision Task by Single Small Robot
3.1 Surface Micro Indentation
>Figure 3 shows a miniature robot with a micro hammer which is
actuated by a small electromagnetic coil[7],[8]. A single diamond
tip with the radius of 5 micron is attached at the end of the
hammer and driven to make an indentation motion to the sample
material when an impulse signal is applied. Two degrees of freedom
of the hammer motion, in the direction of impact motion and in
the lateral direction are to be controlled with the closed loop
circuit so that microscopic indentation within the range of 1mm2
could be provided.
 [Fig.3] Small robot
with a micro hammer actuated by the voice coil positioner with
2 degrees for surface indentation
 [Fig.3'] Photo of
small robot with a micro hammer
A typical experimental result is shown in Fig.4, which demonstrates
the performance of an automatic serial indentation with only a
simple step count based path control. The Japanese characters
of 16 x16 dot matrix in 100 micron square on the metal sample
were achieved. It should be possible to exchange the tip end tool
for producing a various feature of micro indentations with low
cost.
 [Fig.4] Accurate indentation:well-aligned
micro dents of Japanese characters on the sample plate
3.2 Capillary Probe for Micro Capturing
>We have also succeeded in making other small robot with capillary
probe for capturing minute objects[9]. It is well-known that micro
grasping mechanism, electrostatic force and vacuum nozzle are
able to pick up small objects. Such tools, however, need one more
actuator to transport them close to the objects due to the lack
of working distance. Otherwise they need the high voltage electric
source and air tube which are rather expensive and too heavy to
connect the small robot. So news mall facility which has the capability
of approaching to the micro object, capturing it and retracting
quickly is anxious as shown in Fig.5.
 [Fig.5]Capillary
probe can push and pull the small water drop dynamically with
the help of the magnet solenoid piston to capture the small object
Water in the capillary is pushed and pulled by the small permanent
magnet piston and the solenoid coil. Then the water drop can be
extended and capture the small object with the help of the surface
tension force. Figure 6 shows the photograph of the developed
capturing probe. Small object of metal ball of 0.8mm in diameter,
2.4mg in weight is successfully picked up. This probe is based
on the surface tension force between the micro object and the
water drop of the capillary. Then it is obvious that the feature
of the water drop is dynamically deformed to long and narrow.
 [Fig.6] Photograph
shows a sequencial motion of the water drop which is extending
to the object and retracting quickly
In the experiments, this capillary probe is incorporated in
one of our small robot as shown in Fig.7, in order to clear several
small objects on the working area without no damage to the surface.
 [Fig.7] Capillary
probe is attached on the tiny robot to make the surface clearing
operation
4. Fine Grating by Two Small Robots Cooperation
>In order to guarantee the accuracy of motion, two small robots
have been developed to cooperate each other with the help of the
local closed loop control technique. Figure 8 shows the schematics
of the miniaturized robots for micro surface grating task[10].
 [Fig.8] Miniature
robot with a single diamond tool which is driven by the micro
stepping motor and positioned by piezostack for fine surface grating
This small robot has a single diamond tool of 0.5 micron radius
which is mounted on the rotating disk and driven by a micro stepping
motor fixed on another piezo stack on the body. So this arrangement
can provide both micro tool positioning and microgrooves scratching
perpendicular to the moving direction. Furthermore a small reference
mirror is attached on the frame of the machining unit in order
to monitor the tool position precisely by the optical fiber probe
on another robot mentioned later.
 [Fig.9] Miniature
robot has the optical elements of fibers, LED and PFD for measuring
the distance precisely
Figure 9 also gives another small robot which has an optical
fiber displacement sensor on its head. The simple displacement
sensor which is based on the well-known technique that the reflected
light from the target is sensitive relative to the distance between
the target and the probe end, is implemented. This type of displacement
sensor has good robustness to electromagnetic disturbances. So
some optical devices such a light emitted diode and a photo diode
are packed on the body. One fiber for light transmitting and two
for reflected light receiving are also composed. Indeed, we obtained
the static measuring range up to 1200 micron on the test bench.
Difference signal between two receiving fibers means the orientation
of the robot to the target. We can conceive that precise operation
over the wide working range by using such miniature robots system
should be achieved by multilayered feedback loops with the help
of precise measuring instruments and micro computers. In fact,
short feed-back loop between two small robots in local area as
shown in Fig. 10 allows higher positioning resolution with good
response but poor dynamic range, although the long loop including
such a laser interferometer and vision monitoring system with
sufficient low-pass filtering technique provides wide working
range for global positioning.
 [Fig.10] Schimatics
shows the simple short closed loop system between two robots to
offer the fine-positioing control for micro grating in local
So we believe that the combination of these feedback loops should
give good compatibility of microscopic operation over wide dynamic
range. In the primary setup, it was considered that two miniature
robots can approach to the specified working area and there they
can collaborate in precision machining performed by the flexible
local feed-back loop between two robots, which includes a single
diamond tool driver, displacement sensor and tool positioner on
the robots in Fig.11.
 [Fig.11] The combination
of two robots which are well controlled to get a serial formation
can provide easy-microscopic operation with much of flexibility
anywhere with low cost
As the result of Fig.12, we succeeded in micro-grating by position-controlled
single diamond cutting tool on the small robot. Excellent resolution
of line spacing approximately less than 0.5 micron have been achieved.
 [Fig.12] Typical results
of micro grooves with the separation of 0.5 micron was achieved
on the glass plate
5. Several Small Robots for Complex Micro Tasks
5.1 Thin Film Control in Metal Deposition Process
>Another advantage of our small robot is that they can be easily
missioned to the hazard environment such high vacuum chamber and
high temperature condition where the performance of normal robots
can meet the serious problems. So we attempt to design the small
robot to work in high vacuum chamber and to control the deposition
process precisely [11],[12]. With respect to micro surface modification,
it should be valuable that several small robots with micro mechanical
tools could collaborate with another robot capable of controlling
the local deposition process within a single vacuum operation
although conventional facilities such as turning machine tool
never coexists with the physical deposition process.
 [Fig.13] Small robots
were enhanced to work in the high vacuum chamber to control the
thin film pattern in the metal deposition process
Figure 13 shows the experimental set-up that three tiny robots
with a mask, a substrate and a small manipulator can work to control
the local deposition process in the vacuum chamber. Each small
robot is required to work there and controlled remotely by the
responsible computer . There are two stages in the chamber, the
upper stage for two small robots which are responsible for overlapping
the mask and the substrate and for controlling the positions of
them precisely while the lower one is for the robot which will
supply the metal grains into the heat pot as illustrated in Fig.14.
 [Fig.14] Simple sequence
for small three robots to get the thin film deposition patterns
with much of flexibility
At first, the mask and the substrate can be overlaid and positioned
at the initial point by two micro robots' collaboration so that
they can move incrementally with sub-micron resolution. At the
center of bottom stage ,there is the heating pot for metal deposition
and evaporated metal can go through the mask to the substrate.
This arrangement provides local deposition patterns at any location
of the substrate easily although the uncertainty of the pattern
edge is determined by the layout of the deposition source, the
mask and the substrate. On the bottom stage, another robot stands
by for supplying different metal grains, for example Cu, Au and
Al into the heat pot on demand so that the small amount of metal
can be evaporated quickly. This process of small three robots
cooperation can be repeated to make the micro patterns anywhere
as illustrated in Fig.15
 [Fig.15] Unique thin
film pattern of different metals of cooer and aluminum given by
the combination of small robots and the physical deposition process
5.2 Flexible Micro Through-Hole Tooling
>In another experiment, it is demonstrated that several small
robots, one of them has a micro drill shaft with reduction gear
and the others have a micro DC motors and pinion gears, can cooperate
to make a micro through-hole on the sample plate which is also
transported by the small robot. Figure 16 shows small robots with
the unique facilities.
 [Fig.16] Isometric
view shows a micro through hole tooling performed by the cooperation
of many small robots with the specified tools of micro drill and
micro DC motor.
One of them has the micro drill and the reduction large gear.
The others have micro DC motor and the pinion gear of its head.
Another small one which can move down on the wall has the sample
holder.
[Fig.17] Experimental set-up for flexible through-hole drilling
organized by the multiple small robots on going development
As illustrated in Fig.17, small robots with the pinion gear
can approach to the another robot with the micro drill. Then the
reduction gear can be driven by the micro motor on several small
robots. This organization can provide the micro drill drive with
torque enough to make the through hole. On the wall, the small
robot with the sample can move down on the drill top and push
it to get the through-hole on the sample materials. In the experiment,
several through hole of 0.4mm diameter can be achieved under the
manual control while the appropriate automatic sequence control
is currently on going development.
6. Conclusions
>In this report, the basic structure and performance of small
robot which was composed with the piezo stack element and electromagnet
were described. And the examples of single task and more complex
tasks were demonstrated by several small robots with unique tools
and sensors. These experiments are not sophisticated yet because
the control properties are not established. Currently we keep
developing various small robots with unique micro facilities as
well as the multiple robots control system with the help of the
networked computers and the vision monitoring facility in global
area.
References
[1] Hisayuki Aoyama, Futoshi Iwata and Akira Sasaki: Desktop Flexible
Manufacturing System by Movable Miniature Robots with Micro Tool
and Sensor, Proc. of IEEE Int . Conf. on Robotics and Automation,
pp.660-665(Nagoya,1995).
[2] A.M.Flynn, R.A.Brooks,W.M.Wells and D.S.Barrett, "Intelligence
for Miniature Robots",Sensors and Actuators, Vol.20(1989)pp.187-196
[3] R.Curtis, C.Pearson, P.Gaard and E.Ganz, "A Compact Micropositioner
for Use in Ultrahigh Vacuum", Review of Scientific Instruments,
Vol.64, No.9(1993)pp.2687-2690
[4] K.Ikuta, A.Kawahara and S.Yamazumi,"Miniature Cybernetic Actuators
Using Piezoelectic Device", Proc. of IEEE Micro Electro Mechanical
Systems(1991)pp.131-136
[5] Hisayuki Aoyama, Takayuki Iwasaki, Akira Sasaki, Jisuke Fukaya
andAkira Shimokohbe: Micro Climber with Piezo Thrust and Magnetic
Lock,Proc. of Int. Symp. on Theory of Machines and Mechanisms,Vol.1,pp.282-287
(Nagoya, 1992).
[6] Hisayuki Aoyama,Hitoshi Nakano, Nariyasu Hayakawa, Akira Sasaki
and Akira Shimokohbe: Miniature Robots for Ultra Precision Measurement
and Machining, Proc. of 7th Int. Prec. Engg. Semr., pp.273-289(Kobe,
1993).
[7] Hidetake Kato, Hisayuki Aoyama, Futoshi Iwata and Akira Sasaki:
Micro Hammer Forming Performed by Miniature Robot, Proc. of 2nd
Int. Conf. on Prec. Engg., pp.680-683 (Singapore,1995).
[8] Hisayuki Aoyama, Akira Sasaki and Takahiro Kubo: Precision
Machining and Measurement Organized by Miniature Robots, Proc.
of 8th Annual Meeting of A.S.P.E., pp.126-129(Seattle,1993).
[9] Hisayuki Aoyama, Shinya Hiraiwa, Futoshi Iwata and Akira Sasaki:
Miniature Robot with Micro Capillary Probe, Proc. of IEEE 6th
Int. Conf. on Micro Machine and Human Science,pp.173-178(Nagoya,1995).
[10]Hisayuki Aoyama, Hitoshi Nakano, Akira Sasaki, Jisuke Fukaya
and Takahiro Kubo: Collaborative Precise Operation by Two Miniature
Robots-Single Diamond Cutting with Local Position Feedback, Proc.
of 9th Annual Meeting of A.S.P.E., pp.238-241(Cincinnati,1994).
[11]Hisayuki Aoyama, Futoshi Iwata and Akira Sasaki: Micro-Pattern
Control by Miniature Robots in Vapor Deposition Process, Proc.
of 10th Annual Meeting of A.S.P.E., pp.384-387(Austin,1995).
[12]Hisayuki Aoyama, Ken'ichiro Mizutani Tadahiro Miura, Kenji
Murakami and Futoshi Iwata: Micro Devices produced by Micro Robots,
Proc. of 12th Annual Meeting of A.S.P.E.,pp.529-532(Norfolk,1997)
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