Journal of Robotics, Networking and Artificial Life, Vol. 2, No. 4 (March 2016), 213-216

MEMS Microrobot Controlled by Mounted Neural Networks IC with Two Types Actuators
Kei Iwata, Hirozumi Oku, Yuki Okane, Yohei Asano, Masaki Tatani, Yuki Ishihara, Kazuki Sugita,Precision Machinery Engineering, Graduate school of Science and Technology, Nihon University,
7-24-1, Narashinodai, Funabashi, Chiba, 274-8501, Japan
Satohiro Chiba, Satoko Ono, Mizuki Abe, Minami Takato, Ken Saito, Fumio Uchikoba

Department of Precision Machinery Engineering, College of Science and Technology, Nihon University,
7-24-1, Narashinodai, Funabashi, Chiba, 274-8501, Japan
E-mail: takato@eme.cst.nihon-u.ac.jp, kensaito@eme.cst.nihon-u.ac.jp, uchikoba@eme.cst.nihon-u.ac.jp

Abstract
We report the hexapod microrobot controlled by the bare chip IC of hardware neural networks. MEMS (microelectro mechanical systems) technology is used for fabrication of the microrobot. Lead zirconium titanate (PZT)
and shape memory alloy (SMA) are used in each actuator, respectively. As the result, PZT type is realized thewalking motion by bare chip IC. Moreover, SMA type shows the hexapod walking locomotion with mounted barechip IC. The walking speed is 2.4mm / min and the step width was 0.083mm.
Keywords: Microrobot, Artificial Neural Networks, MEMS, PZT, SMA.

1. Introduction
Insects have small sophisticated motion mechanisms
controlled by flexible brain neural networks. Therefore,
fully understanding how insects move is among theultimate goals of microrobotic studies.
Many researches that mimic the flexible motion
mechanism of insects have been reported1. Especially,walking is a typical movement mechanism of insects.
The robot mimicking walking mechanism by using legs
has been reported2. However, most cases of them arelarge body compared with the insects. Realization of thesmall walking mechanism as large as the insect isdifficult in conventional process. Therefore, the demand
for micro electro mechanical systems (MEMS)
technology that can create miniature components withhigh degrees of accuracy is increasing2. In addition, thebig feature of the insects is flexible thinking circuit.

The robots that introduce the model of the neuralnetworks as the control system are reported3. However,the small size robot controlled by neural networks israre. Therefore, robots that are perfectly mimicked theinsects have not been realized.
Previously, we reported on an insect-type MEMS
microrobot that fits within 5-mm-cubed driven by apulsed hardware neural networks (P-HNN)4. However,the P-HNN circuit, which was constructed from discreet
components, was found to be too big to be mounted on
the microrobot. We then developed a P-HNN integrated
circuit (IC) using a bare chip IC and peripheral
amplifying circuits, but the resulting control system wasstill too big5. To solve the problem, the bare chip IC for
SMA (shape memory alloy)-type microrobot was newly
developed6.
In this paper, we report on the development of insecttype microrobots controlled by bare chip IC of artificial
neural networks. Actuators of the microrobots are usedpiezoelectric element composed of lead zirconium

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K. Iwata et al.

titanate (PZT) and artificial muscle wires composed ofshape memory alloy. The bare chip ICs for each type ofmicrorobot were newly developed.
2. Mechanism
Insect-type microrobot has hexapod legs like insects andfalls within 5-mm-cubic. The designs of the two-typemicrorobot are shown in figure 1. The components ofthe microrobot are the frame, rotary actuator, and thelink mechanisms. PZT and SMA are easy to downsize
because the material itself has the function of theactuator. Almost all of the component are fabricatedfrom silicon wafer using MEMS machining technology.

2.2. SMA-type microrobot
SMA which shrinks at high temperatures and expands at
low temperatures is used for the rotary actuator. The
SMA displacement can be changed by applying
electrical energy to create heat. We used 0.05 mm
diameter wire to create the SMA with a coil diameter of0.2 mm. A standard drive current from 50 to 120 mA
was used, and a maximum displacement of 50 % of theoriginal length was achieved. Figure 3 shows the designof SMA-type rotary actuator.

Fig. 3. Mechanism of the SMA-type actuator.

Four SMAs and a ground (GND) wire are connected tothe rotor. Rotational motion of the actuator is generatedby passing an electric current through the SMA inrotation.

Fig. 1. Microrobot designs.

2.3. Walking mechanism

2.1. PZT-type microrobot
The PZT distorts by applying a voltage. In this study, amultilayer piezoelectric element composed of PZT isused for low voltage driving. The PZT has advantage oflow electricity consumption and fast response time.
However, it is difficult to use PZT as direct driven
actuator because of small displacement. Therefore, theimpact mechanism is adopted for the actuator of themicrorobot. The design of the PZT-type actuator, which
has side, end, and height dimensions of 1.0, 4.4, and 3.2mm, respectively, is shown in figure 2. The
displacements of a multilayer piezoelectric element are
110nm at applied 6V. The impact head is attached to thePZT and adjusted to contact to the impact head. The
PZT impacts the rotor to generate rotary motion.

Insects perform a stable hexapod walking by grounding
the three legs. In this paper, link mechanisms areadopted for realizing hexapod walking like insects.
Rotary motion of the actuator is converted into walking
motion by link mechanisms via a shaft shown in figure
4. The locomotion pattern uses a 180° phase shift oneach side.

Fig. 4. Walking mechanism of the microrobot.

3. Control system

Fig. 2. Mechanism of the PZT-type rotary actuator.

Insects function by using the neural networks in theirown brains. In this study, we mimic those neural circuits
using an analog system that allows the microrobot tofunction in an insect-like manner.

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MEMS Microrobot Controlled by3.1 Cell body model
The PZT-type microrobot is controlled by the cell bodymodel shown in figure 5. The cell body model has
refractory period, analog characteristic of the output
pulse and time varying negative resistance characteristic.
Driving frequencies of the PZT-type microrobot is 25
kHz. The amplifier circuit is added to obtain the output
voltage 20V.
icin

MC4

CG

MC2
MC1
MC3

Vcout

Fig. 7. Circuit diagram of the neuron.

4. Results

CMVA

Fig. 5. Cell body model circuit diagram.

3.2 CPG model
It is well known that locomotion rhythms of livingorganisms are generated by central pattern generator(CPG). The SMA-type microrobot is controlled by theCPG model. CPG model can be formed by inhibitory
synaptic connection of four neurons shown in Figure 6.

The bare chip IC of the neural networks made it
possible for the control system to be mounted on themicrorobot. Figure 8 shows the fabricated microrobot
mounted the bare chip IC. The side, the end, and height
dimensions of the fabricated PZT-type microrobot were4.0, 4.6, and 3.6 mm, respectively. The weight of therobot was 0.04 g. The length and the width dimensionsof the control circuit were 2.0, 3.0mm, respectively. Theside, the end, and height dimensions of the SMA-type
microrobot were 4.0, 2.7, and 2.5 mm, respectively. The
weight of the robot was 0.02 g. The length, width, andweight of the control circuit were 4.0mm, 4.0mm, and0.059g, respectively.

Fig. 8. Fabricated microrobot mounted control system. (a)PZT-type (b) SMA-type.

Fig. 6. Artificial neuron circuit connection diagram.

Figure 7 shows the circuit diagram of the neuron
composed the cell body model and inhibitory synaptic
model. The inhibitory synaptic model has
spatiotemporal summation characteristics similar toliving organisms. This sums the pulse waveforms
outputted by other bonded cell body models.

PZT-type microrobot could generate the walking motion
by the bare chip IC. However, the robot could notachieve locomotion by itself. Because, the bare chip IC
is insufficient of the output voltage for moving legs.
However, the bare chip IC for the PZT-type microrobot
could drive the rotary actuator. Figure 9 shows therotary motion of 1 s intervals.

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K. Iwata et al.

Acknowledgements

Fig. 9. Rotational motion of PZT-type actuator.

On the other hand, hexapod walking locomotion of theSMA-type microrobot, as shown in figure 10, wassuccessfully achieved. The walking speed was 2.4
mm/min and the step size was 0.083 mm. Power sourceof the control circuit is externally connected.

Fig. 10. Walking locomotion of the microrobot controlled bythe bare chip IC. The figure show microrobot transitions at 10s intervals.

5. Conclusion
In this paper, the control system of the neural networks
was mounted the fabricated insect-type microrobot. Itwas possible to reduce the control system within a 4mm
square by using a bare chip IC. In the PZT-type
microrobot, the bare chip IC could actuate the rotaryactuator. Moreover, hexapod walking locomotion of theSMA-type microrobot was achieved. The walking speed
was 2.4 mm/min and the step size was 0.083 mm. The
only external wire connections to the microrobot are tothe power source.

The MEMS microrobot fabrication was supportedby the Research Center for Micro Functional
Devices, Nihon University. This study wassupported by Nihon University College of Scienceand Technology Project Research and JSPS
KAKENHI (25420226). We appreciate the above
support. The very large scale integration (VLSI)
chip used in this study was fabricated by DigianTechnology, Inc. This work was supported by theVLSI Design and Education Center (VDEC) of theUniversity of Tokyo in collaboration with Synopsys,Inc., Cadence Design Systems, Inc. and Mentor
Graphics, Inc.
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