JP4713263B2 - Mobile tracking optical space communication system - Google Patents

Description

  The present invention transmits a relative position and orientation between a transmitting terminal and a receiving terminal in an optical space communication system in which laser light is propagated in space between a transmitting terminal and a receiving terminal in which the relative position and orientation can change greatly. A movement tracking type capable of stably maintaining the coincidence of the optical axes by adjusting the feedback control law for optical axis alignment according to the estimated value by estimating based only on the information inside the terminal and the receiving terminal The present invention relates to an optical space communication system.

  For example, in a normal optical space communication such as a building-to-building optical space communication, a mechanism is adopted in which two transmitters / receivers are fixedly arranged opposite to each other to correct the influence of a small axis shift caused by wind or vibration. On the other hand, in optical space communication involving movement of a terminal, an optical axis adjustment mechanism that corresponds to an axial shift accompanying a wide range of relative position changes is indispensable (see, for example, Non-Patent Document 1). In this case, it is important to accurately reflect the change in the distance and direction between the transceivers in the optical axis adjustment servo system in order to maintain the alignment accuracy. This is apparent from the fact that if the change in the relative direction of 180 degrees of the transmitter / receiver is ignored, the feedback of the optical axis adjustment acts in the reverse direction and does not use the servo mechanism. It is conceivable that such relative position / attitude information is provided by the principle of triangulation by preparing a plurality of fixed stations for one mobile station, for example. Surveying is not always possible. Further, when the deviation of the optical axis due to the movement of the terminal is suppressed by feedback, there arises a problem that an offset from the reference position according to the moving speed or the like occurs.

Koichi Yoshida, Tatsuro Yano, and Takeshi Tsujimura: “Automatic Optical Axis Alignment for Active Free Space Optics”, SICE Annual Conference in Sapporo, August 4-6, 2004, Hokkaido Institute of Tecnology, Japan, p.2035-2040

  The present invention has been made in view of the above circumstances, and estimates the relative position and orientation between a transmitting terminal and a receiving terminal that change dynamically based only on information inside the transceiver without using a new external device or the like. It is an object of the present invention to provide a mobile tracking optical space communication system that can adjust a feedback control law for optical axis alignment online to stably maintain optical axis coincidence.

In order to achieve the above object, a mobile tracking optical space communication system according to the present invention is an optical space communication system that performs communication by propagating laser light in space between a mobile terminal and a stationary terminal whose relative position can change. Of these terminals, a terminal on the transmitting side is provided with a first movable reflector having two degrees of freedom so that the laser beam emission direction (pan / tilt angle) by the laser beam source for transmission can be adjusted. , the receiving side comprising a second movable reflecting mirror 2 degrees of freedom to adjust the orientation of the laser light arriving from said a transmitting terminal to a terminal leading to two beam splitters arranged in series and the first beam splitter Two PSDs (Position Sensing Devices) that detect the irradiation position of one of the split beams divided into two by the next beam splitter and further divided into two by the next beam splitter. In capable space optical communication system by receiving a split light by the receiving PD (Photo Detector),
Wherein the three-dimensional position vector of the mobile terminal as viewed from a stationary terminal, a 7-dimensional relative position and orientation vector relative posture by combining the vector expressed in quaternion norm first mobile terminal as viewed from the stationary terminal, are each A 19-dimensional state vector, which is expressed in three dimensions, is defined by adding the relative velocity of the mobile terminal viewed from the stationary terminal , the angular velocity of the mobile terminal , the acceleration, and the angular acceleration vector,
Regarded as the first and second movable mirror angle and the observed two sets of data adjacent on at the time the time-series data of the captured beam spot position by PSD at the same relative position and orientation data and equality and, an extended Kalman filter based on an observation equation that the equations and quaternion norm concerning the acceleration and angular velocity obtained by the installed inertial sensors on the mobile terminal is derived from the equations to be bound to 1 Construct and estimate the state vector;
Said prepared by feeding back an error from the reference position of the beam spot position in order to perform optical axis alignment, a beam spot position captured by the said first and second angles of movable mirror PSD The control law represented by the associated Jacobian matrix is sequentially updated with the relative position and orientation vector included in the state vector estimated by the extended Kalman filter .

The present invention, in the mobile tracking type optical wireless communication system, wherein included in the state vector estimated by extended Kalman filter, wherein the required tracking the relative velocity and the mobile terminal velocity of the mobile terminal as viewed from the stationary terminal back to find the rotational speed of the first and second movable mirror, with a rotational speed this calculated as the bias value of the rotational speed instruction value of the first and second movable mirror, the mobile terminal It is characterized in that the offset amount of the beam spot position at the receiving terminal with respect to the preset reference position accompanying the movement is corrected.

  According to the present invention, it is possible to detect the relative position / attitude between the transmitting terminal and the receiving terminal of an optical space communication system involving movement only by internal information of the transmitting terminal and the receiving terminal without adding a new external device or the like. is there.

  In particular, by defining a state vector by combining quaternions representing the posture of the terminal and applying an extended Kalman filter, it is possible to smoothly estimate the relative position and posture with excellent noise resistance. As a result, the optical axis adjustment servo system can be properly operated, and the value added such as providing useful information for the user based on the current position information of the mobile station and prompting the switch to the most appropriate fixed station. There is an effect that the creation can be expected.

Embodiments of the present invention will be described below in detail with reference to the drawings.
FIG. 1 is an explanatory diagram illustrating a mobile tracking optical space communication system targeted by the present invention. In FIG. 1, the transmission terminal side moves, and the transmission terminal 11 is provided with a transmission LD (Laser Diode) that emits a laser beam L, and the rotation of the motor D1 is positioned at the laser beam irradiation position from the transmission LD. A mirror (reflecting mirror) M1 attached to the shaft is provided. A mirror M2 is provided on the rotation axis of the motor D2 in which the rotation axis is arranged so as to be orthogonal to the rotation axis of the motor D1. The mirror M2 is provided at a position where the reflected light from the mirror M1 is irradiated. In this case, it arrange | positions so that the emission direction of the laser beam L from LD for transmission may turn into the rotating shaft direction of the motor D2. The laser beam L is emitted from the transmitting LD to a position corresponding to the rotation axis of the motor D1 on the mirror M1, and is transmitted to the receiving side after being reflected by the mirror M1 and the mirror M2, which are two-degree-of-freedom movable reflectors. To do. The emitting direction (pan / tilt angle) of the laser beam by the transmission LD can be adjusted by rotating the motors D1 and D2 to change the angles of the mirrors M1 and M2. The transmission terminal 11 is provided with an inertial sensor 13, and the inertial sensor 13 includes an acceleration sensor 14 that detects acceleration accompanying movement of the transmission terminal 11 and an angular velocity sensor 15 that detects angular velocity.

  The laser light L reaching the receiving terminal 12 from the transmission side is incident on a mirror M3 attached to the rotation shaft of the motor D3. A mirror M4 is provided on the rotation axis of the motor D4, the rotation axis of which is arranged so as to be orthogonal to the rotation axis of the motor D3. The mirror M4 is provided at a position where the reflected light from the mirror M3 is irradiated. Two beam splitters S1 and S2 arranged in series are provided at a position where the reflected light from the mirror M4 is irradiated. The mirrors M3 and M4, which are two-degree-of-freedom movable reflectors, adjust the direction of the laser light L that has arrived from the transmission side and guide it to two beam splitters S1 and S2 arranged in series. Two PSDs (Position Sensing Devices) 1 and PSD2 are provided at the irradiation positions of the laser light L, which is obtained by dividing one branched light divided by the first beam splitter S1 and further divided into two by the next beam splitter S2. Each PSD 2 detects the laser beam L. A receiving PD (Photo Detector) is provided at a position where the other branched light from the first beam splitter S1 is received.

  The transmission terminal 11 and the reception terminal 12 are provided with control units C1 and C2, respectively, and have interfaces that can exchange information with each other by a normal wireless LAN using radio waves or infrared rays.

  Now, the rotation angle of the motors D3 and D4 is such that the light reaching the receiving terminal 12 is reflected by the mirror M3 and the laser light reflected by the mirror M4 passes through the two beam splitters S1 and S2 arranged in series. It shall be adjusted. At this time, when the mirror image of the receiving PD with respect to the prism slope P1 of the beam splitter S1 is PD 'and the mirror image of PSD2 with respect to the prism slope P2 of the beam splitter S2 is PSD2', the PSD1 and PSD2 'are arranged so as not to overlap. For example, the relationship between the reflected light from the mirror M4 and the optical axis of PD ′ is parametrized by the coordinates of the intersection of the reflected light from the mirror M4 and the PSD1 and PSD2 ′ light receiving surfaces. Accordingly, if the laser spot coordinates on the two PSDs 1 and PDS2 when the reflected light from the mirror M4 coincides with the optical axis of the PD are used as reference points, the relative positions of the transmission terminal 11 and the reception terminal 12 change and the light Even when the axis is off, the optical axes can always be matched by adjusting the rotation angles of the motors M3 and M4 so that the laser spots on the PSD1 and PDS2 return to the reference point.

The first embodiment of the present invention is as follows.
In the optical space communication system as shown in FIG. 1, the relative velocity is set to a 7-dimensional position / orientation vector obtained by combining the position vector of the receiving terminal 12 viewed from the transmission terminal 11 with the relative attitude represented by the quaternion of the norm 1. A 19-dimensional state vector is defined by adding angular velocity, acceleration, and angular acceleration vector, and the time of the time series data on the angle of the mirrors M1 to M4, which are movable reflectors, and the beam spot position captured by PSD1 and PSD2 That are considered to be observed simultaneously at a certain time, equations for the outputs of the acceleration sensor 14 and the angular velocity sensor 15 of the inertial sensor 13 installed on the mobile terminal 11, and the norm of the quaternion The state vector is estimated by constructing an extended Kalman filter based on the observation equation derived from the equation for It is possible to provide a mobile tracking type optical wireless communication system for adjusting the estimated relative position and orientation of the control law for performing optical axis alignment by feeding back the error from reference position. The control units C1 and C2 execute the extended Kalman filter to estimate the state vector. Further, the control law is calculated in the control units C1 and C2, and its parameters change according to the result of state estimation.

That is, the rotation angle of the motors D1 to D4 of the transmission terminal 11 and the reception terminal 12 is Θ (= [θ ₁ ... Θ ₄ ] ^T ), and the relative position and orientation of the translational 3 degrees of freedom rotation 3 degrees of freedom is X∈R ⁶ . The beam spot position Y = [y ₁ y ₂ ] ^T on the two PSD1 and PSD2 is expressed as follows.
Y = h (X, Θ) (1)

If the influence on the Y due to the change of the relative position and posture is negligible compared to the change of the beam spot due to the change of the motor rotation angle, the relationship between the motor rotation speed and the time derivative of Y is Can be described as follows.

ただし、κ_ｐは比例ゲイン、Ｙ_０は光軸が一致している場合の基準となるＰＳＤ１、ＰＳＤ２出力値ベクトルを表している。具体的なＪの計算法は非特許文献１に記述されている。一方、制御則中のＪは送信端末１１及び受信端末１２の相対位置姿勢Ｘの関数となっておりこれが変化していく場合にはその適切な推定値をオンラインで得る必要がある。２つのＰＳＤ１、ＰＳＤ２出力の瞬時値データだけではミラーＭ２からミラーＭ３へ至る光線方向の距離とその周りの回転角を決定することはできないが、送信端末１１側モーターＤ１，Ｄ２の微小変化に対応するＰＳＤ１、ＰＳＤ２上のビームスポットの微小変化に対応させることができればその距離と回転角が求められ従って送信端末１１及び受信端末１２の相対位置姿勢が決定できることになる。この概念的な推定法は拡張カルマンフィルタを用いることによってシステマティックに実現できる。 At this time, the control law for the motor to obtain the coincidence of the optical axes can be designed as follows.

However, kappa _p is a proportional gain, _{Y 0} represents the PSD1, PSD2 output value vector as a reference when the optical axes are coincident. A specific calculation method of J is described in Non-Patent Document 1. On the other hand, J in the control law is a function of the relative position and orientation X of the transmitting terminal 11 and the receiving terminal 12, and when this changes, it is necessary to obtain an appropriate estimated value online. Although only the instantaneous value data of the PSD1 and PSD2 outputs cannot determine the distance in the direction of the light beam from the mirror M2 to the mirror M3 and the rotation angle around it, it corresponds to the minute change of the motor D1 and D2 on the transmission terminal 11 side. If the beam spot on PSD1 and PSD2 can be made to cope with a minute change, the distance and the rotation angle can be obtained. Therefore, the relative position and orientation of the transmission terminal 11 and the reception terminal 12 can be determined. This conceptual estimation method can be systematically realized by using an extended Kalman filter.

It estimated using an extended Kalman filter from the time series measurements of beam trajectories captured by PSD1, PSD2 on position and receiving the attitude terminal 12 of the receiving terminal sigma _R as viewed from the transmitting terminal sigma _T. However, the rotation (posture) matrix is expressed by a quaternion q = [q ₁ q ₂ q ₃ q ₄ ] ^T (q ^T q = 1) of the norm 1. The quaternion of norm 1 can represent a three-dimensional rotation so that the complex number of norm 1 represents a two-dimensional rotation, and the following relational expression holds between the rotation matrix and the quaternion.

Here, the state vector χ related to the position and orientation to be estimated including r = [xyz] ^T is redefined as follows.

Furthermore, sigma _T a moving velocity vector of the viewed from _{Σ R υ = [υ x υ} y υ z] T, Σ acceleration defined on _R, angular velocity, respectively the angular acceleration vector _{α = [α 1 α 2 α} 3 ^T , ω = [ω ₁ ω ₂ ω ₃ ] ^T , Ω = [Ω ₁ Ω ₂ Ω ₃ ] ^T, and a state vector obtained by combining these is represented by Χ.

At this time, the time derivative of q is connected to ω by the following relational expression.

各変数の添え字κは時系列上のサンプリング数を示す。ミラーＭ１〜Ｍ４の回転角とＰＳＤ１、ＰＳＤ２上のビームスポット位置それぞれの微小変化量を対応させるため、１サンプリング時間でのΧ_κの変化は微小であると仮定し連続する２サンプルの観測データ（Ｙ_κ−１，Θ_κ−１），（Ｙ_κ，Θ_κ）はΧ_κのときに同時に観測されたデータとみなす。また、移動端末は加速度と角速度を検出可能であるものとすれば観測方程式は次のように構成される。

Here, considering that χ is discretized with a sufficiently small sampling time dt, a dynamic state transition model relating to a change in position and orientation is introduced as follows.

The subscript κ of each variable indicates the number of samplings in time series. To correspond to the rotation angle and PSD1, each small variation beam spot position on PSD2 mirror M1 to M4, 2 samples of observation data assuming continuous with changes in the chi _kappa at 1 sampling time is small ( _{Y κ-1, Θ κ-} 1), (Y κ, Θ κ) is regarded as the same time observed data when the chi _kappa. If the mobile terminal can detect acceleration and angular velocity, the observation equation is constructed as follows.

  The last element of the observation vector corresponds to the norm of the quaternion q representing the posture being 1. w and ν represent system noise and observation noise vector, respectively.

Here, if w _κ and ν _κ are independent of each other by the mean value vector 0 and their covariance matrices are given by Σ _w and Σ _υ , respectively, state estimation can be performed by applying the following extended Kalman filter. It becomes.

Therefore, since the position and orientation χ of the mobile terminal 11 can be estimated online, this estimated value can be used for the calculation of the Jacob matrix J of Equation (3). Here, the acceleration sensor 14 and the angular velocity sensor 15 are used for the estimation by the extended Kalman filter. However, even if the acceleration sensor 14 and the angular velocity sensor 15 are replaced with other inertial sensors (systems), the same estimation can be performed by rewriting the observation equation accordingly. . For example, r ₁ to the position of the two acceleration sensors viewed from when sigma _R using a plurality of acceleration _sensors, r _2, the respective sensor output alpha _1, when the alpha _2,
Since R (q) (α ₂ −α ₁ ) = Ω × (r ₂ −r ₁ ) + ω × (ω × (r ₂ −r ₁ )) holds, the acceleration sensor necessary for estimating ω and Ω What is necessary is just to comprise an observation equation in consideration of arrangement and output components.

Next, a second embodiment of the present invention will be described.
In the mobile tracking optical space communication system according to the first embodiment of the present invention, the rotational speeds of the movable reflectors M1 to M4 required for tracking are calculated from the relative speed and angular speed of the mobile terminal 11 estimated by the extended Kalman filter. Provided is a mobile tracking optical space communication system that reversely calculates and corrects an offset of a beam spot from a reference position associated with movement of a terminal 11 using a bias value of a rotational speed command value of the movable reflectors M1 to M4. Can do.

If the influence of wrinkle change cannot be ignored in the time differentiation of equation (1), it is necessary to consider the following equation instead of equation (2).

の影響を無視できない場合、式（１４）の第２項がＹ→Ｙ_０の収束にオフセットとして表れ軸ズレの要因となる。そこで、次の制御則を考える。

ただし、

は拡張カルマンフィルタによる推定値を用いればよい。また、

は式（１３）Ｈ_κの部分行列を用いることができる。式（１５）を式（１４）へ代入すれば、

の推定値が正しい場合、これによるオフセットの影響を相殺してＹ→Ｙ_０を得ることが分かる。 At this time, if Expression (3) is used,

If the influence of the above cannot be ignored, the second term of the equation (14) appears as an offset in the convergence of Y → Y ₀ and becomes a factor of axis deviation. Therefore, consider the following control law.

However,

The estimated value by the extended Kalman filter may be used. Also,

Can use the submatrix of Equation (13) H _κ . Substituting equation (15) into equation (14),

If the estimated value is correct, it can be seen that Y → Y ₀ is obtained by offsetting the influence of the offset.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiment examples may be appropriately combined.

It is a configuration explanatory view showing a mobile tracking optical space communication system targeted by the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Transmission terminal, 12 ... Reception terminal, 13 ... Inertial sensor, 14 ... Acceleration sensor, 15 ... Angular velocity sensor, LD ... Laser diode (laser light source), D1-D4 ... Motor, M1-M4 ... Mirror, PD ... Photo detector , PSD1, PSD2 ... position sense device, S1, S2 ... beam splitter, C1, C2 ... control unit.

Claims (2)

An optical spatial communication system that performs communication by propagating a laser beam in space between a mobile terminal and a stationary terminal whose relative position can change, and emitting a laser beam from a transmitting laser light source to a terminal serving as a transmission side A first movable reflector with two degrees of freedom is provided so that the direction (pan / tilt angle) can be adjusted, and the direction of the laser light reaching from the terminal serving as the transmitting side is adjusted in series to the terminal serving as the receiving side. Irradiation position of each of the laser beams obtained by dividing one split light divided into two by the second beam splitter into the second beam splitter and the second movable reflector having two degrees of freedom guided to the two beam splitters arranged in In an optical space communication system that has two PSDs (Position Sensing Devices) that detect light and can receive the other branched light from the first beam splitter by a receiving PD (Photo Detector) ,
Wherein the three-dimensional position vector of the mobile terminal as viewed from a stationary terminal, a 7-dimensional relative position and orientation vector relative posture by combining the vector expressed in quaternion norm first mobile terminal as viewed from the stationary terminal, are each A 19-dimensional state vector, which is expressed in three dimensions, is defined by adding the relative velocity of the mobile terminal viewed from the stationary terminal , the angular velocity of the mobile terminal , the acceleration, and the angular acceleration vector,
Regarded as the first and second movable mirror angle and the observed two sets of data adjacent on at the time the time-series data of the captured beam spot position by PSD at the same relative position and orientation data and equality and, an extended Kalman filter based on an observation equation that the equations and quaternion norm concerning the acceleration and angular velocity obtained by the installed inertial sensors on the mobile terminal is derived from the equations to be bound to 1 Construct and estimate the state vector;
Said prepared by feeding back an error from the reference position of the beam spot position in order to perform optical axis alignment, a beam spot position captured by the said first and second angles of movable mirror PSD A mobile tracking optical space communication system , wherein a control law represented by an associated Jacobian matrix is sequentially updated with a relative position and orientation vector included in a state vector estimated by the extended Kalman filter . The mobile tracking optical space communication system according to claim 1,
The included in the state vector estimated by extended Kalman filter, based on the angular velocity of the relative velocity and the mobile terminal of the mobile terminal as viewed from the stationary terminal, the rotation of the first and second movable reflectors required tracking Backward calculation of the speed, and using the calculated rotation speed as a bias value of the rotation speed command value of the first and second movable reflectors , the beam at the terminal on the receiving side accompanying the movement of the mobile terminal A mobile tracking optical space communication system characterized by correcting an offset amount of a spot position with respect to a preset reference position.

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