1. Abstract

Dan ChenA, Tomotada AkutsuB, Masaki AndoC , Shuichi SatoD, Seiji KawamuraE , Masa-Katsu FujimotoA B,DPF WG

Department of Astronomy, Univ. of TokyoA, National Astronomical Obsevatory of JapanB, Kyoto Univ.C, Housei Univ.D, Institute for Cosmic Ray Research, Univ. of TokyoE

4. Control of Test Mass with Capacitive sensors and Electrostatic actuators

2. DECIGO Pathfinder (DPF)

2012/05/21-25 LISA Symposium @Paris

1V 2V

3V4V

1V 2V

3V4V

4.2 Experiment system

3.Control

X

θ

X

θ

d1 d2

d3 d4

F F

V(d2-d1)

V(d4-d3)

Matrix

xV

V

*30

0

*30

0

*30

0

*30

0

Differen

tial C

urren

t circuit

F.P. cavity

~

V

5. Conclusion

We have controlled the translational and yaw motions of a suspended test mass which is the same size as a test mass of DPF. We could suppress the fluctuation of the test mass under 0.1Hz.

4.3 Two DOFs control

We could suppress two DOFs fluctuations of the test mass

via our feedback control system.

Test Mass (50mm squares)

Electrodes

No

ise

Tran

sfer

Fu

nct

ion

Transitional motion (X) Yaw motion (θ)

Suppressed Suppressed

Phase margin~45 degrees

UGF~0.2Hz UGF~0.2Hz

Frequency [Hz] Frequency [Hz]

Frequency [Hz] Frequency [Hz]

Dis

pla

cem

ent

no

ise

[m/r

tHz]

An

gle

no

ise

[rad

/rtH

z]

Gai

n

Gai

n

Ph

ase

[deg

]

Ph

ase

[deg

]

The noise of the transitional motion and that of the yaw motion were suppressed in the same time period.

These transfer functions (transitional motion and yaw motion) have gains under 0.2Hz.The phase margins are approximately 45 degrees.

This article reports on the development of inertial sensors for DECIGO Pathfinder (DPF), which is the precursor of DECIGO, spaceborne gravitational-wave (GW) antenna of Japan in future. To achieve drag-free control, DPF will have micro thrusters and inertial sensors which sense external force on the satellite structure. The inertial sensor comprises a proof mass (test mass : T.M.) and position controllers which consist of capacitive sensors and electrostatic actuators. The position controller will sense the relative position between the proof mass and its housing, and control the proof mass motion with the actuator. We achieved the control of translational motion and yaw motion. We will report on the feedback.

Purpose Technology demonstration for DECIGO Gravitational‐wave detection (0.1‐1Hz) Earth gravity monitoring

Main Interferometer

Test Mass

Test Mass

Concept of design Test mass module ×2

Capacitive sensors Electrostatic actuators

Capacitive sensor T.M. Electrostatic actuator

Thruster Satellite

Filter

This part is tested.

There two loops: Signal from capacitive sensors will 1. feed back to T.M. with electrostatic actuators. 2. feed back to Satellite with thrusters. We will report the loop which feed back to T.M.

~

V ＋＋＋

＋＋＋

－ －

－ －

＋ ＋

＋ ＋

－ －

－ －

－ －

－ －

C1

C2 electrostatic induction

＋ ＋

＋ ＋

ー

ー

ー

ー

ー

ー

Differential current

C1 C2

C3 C4

V1 V2

V3 V4

Te

st Ma

ss

1V 2V

3V4V

1V 2V

3V4V

4.1 Principle

Capacitive sensor

Electrostatic actuator

We can sense the displacement of the T.M. as the difference of the capacitance.

We can actuate the T.M.’s DOFs by charging the electric filed around the T.M.

Lo

ck in

Phase margin~45 degrees