Orientation tracking device and orientation tracking method

Abstract

To avoid the occurrence of a dead angle caused by a delay in the rotation around an azimuth axis.SOLUTION: An orientation tracking device according to the present disclosure includes: an arm-type support structure which is connected rotatably around an azimuth axis to a base structure; a barrel which has an aperture being a transmitting / receiving port for laser beams and is held by the arm-type support structure rotatably around an elevation axis with respect to the arm-type support structure; a prism which has an optical axis inclined relative to the central axis of the aperture and is attached to the barrel rotatably around the central axis of the aperture; and a control processing device which controls the rotation angles of the arm-type support structure, the barrel, and the prism so that the laser beam passing through the prism tracks the trajectory of a target object in the sky.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a pointing and tracking device and a pointing and tracking method for controlling the irradiation direction of a laser beam. [Background technology]

[0002] As a conventional directional tracking device, Patent Document 1 discloses a device for directional tracking of a geostationary satellite from an orbiting satellite, which includes a gimbal having an azimuth axis and an elevation axis that are perpendicular to each other, and the gimbal is provided so that the azimuth axis is parallel to a direction tilted toward the center of the Earth at a predetermined angle from the normal direction of the orbital plane of the orbiting satellite and toward a direction in which there is no tracking target. As a result, the directional tracking device described in Patent Document 1 avoids gimbal lock by aligning the direction of an elevation angle of +90 degrees, which is a phenomenon in which tracking cannot be continued due to a sudden change in azimuth, with a direction in which there is no tracking target. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 5-108159 Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned directional tracking device had a problem that, if it was not possible to identify an area where no tracking target existed, a blind spot would occur due to a delay in rotation around the azimuth axis when the satellite approached the direction in which gimbal lock occurred (hereinafter, the peculiar direction). [Means for solving the problem]

[0005] The directional tracking device of the present disclosure is an arm-type support structure connected to the base structure so as to be rotatable about an azimuth axis; a lens barrel having an opening for transmitting and receiving a laser beam and held by the arm-type support structure so as to be rotatable around an elevation axis relative to the arm-type support structure; a prism having an optical axis inclined from a central axis of the opening and attached to the lens barrel so as to be rotatable around the central axis of the opening; a control processing device that controls the rotation angles of the arm-type support structure, the lens barrel, and the prism so that the laser beam passing through the prism follows the trajectory of a target object in the sky; A directional tracking device comprising: Effect of the Invention

[0006] The directional tracking device disclosed herein can avoid blind spots caused by rotation delay around the azimuth axis. [Brief description of the drawings]

[0007] [Figure 1] 1 is a block diagram of an optical space communications device using a directional tracking device according to a first embodiment. [Diagram 2] 2 is a cross-sectional view of a prism rotation device in the directional tracking device according to the first embodiment. [Diagram 3] 2 is a diagram showing a coordinate system that defines the positional relationship between the directional tracking device according to the first embodiment and a target object. [Figure 4] FIG. 4 is a diagram showing a coordinate system definition of a prism according to the first embodiment. [Diagram 5] This is a diagram showing a state in which the coordinate axis p is oriented parallel to the trajectory, as viewed from the Z-axis direction in Figure 3. [Figure 6] 6 is a diagram showing a blind spot in FIG. 5 and a possible direction range of the optical axis of a prism. FIG. [Figure 7] FIG. 6 is a diagram showing a range that can be tracked by the directional tracking device in FIG. 5. [Figure 8] FIG. 13 is a diagram showing a state in which the coordinate axis p is oriented parallel to the trajectory of a target object when the trajectory is not parallel to the X-axis. [Figure 9] 9 is a diagram showing a blind spot and the optical axis of a prism rotation device in FIG. 8. [Figure 10]FIG. 9 is a diagram showing a range that can be tracked by the directional tracking device in FIG. 8. [Figure 11] 11 is a diagram showing the relationship between a rotational positioning error of a prism rotation device and a pointing control error. FIG. [Figure 12] 11 is a diagram showing the relationship between a rotation axis runout error of a prism rotation device and a pointing control error. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] A directional tracking device is an optical mechanical device used in distance measuring devices that detect the distance to a target object by detecting a laser received from the target object with a photodetector, or in optical space communication devices that perform long-distance communication by the spatial propagation of a laser beam. The target object, or the other station, is located up to tens of thousands of kilometers away.

[0009] In addition, many directional tracking devices use a gimbal with two movable axes to control the line of sight of the telescope (i.e., the laser transmission and reception aperture). Hereinafter, such gimbals are called AZ-EL type gimbals. AZ-EL type gimbals have an azimuth axis that rotates on a horizontal plane, and an elevation axis that rotates on a vertical plane and is rotated by the rotation of the azimuth axis.

[0010] Pointing trackers using AZ-EL gimbals have a characteristic called gimbal lock, which is a state in which one rotational degree of freedom is lost when the telescope is pointed in the azimuth axis direction (hereafter, the singular direction).

[0011] Assume that a target object is located in a specific direction of the directional tracking device at a certain time, and the telescope is pointed at the target object. In order to track a moving target object in this state, the telescope must rotate around the azimuth axis at an infinite angular velocity. However, at this time, the telescope can only track in directions that can be tracked by driving around the elevation axis alone, and one degree of freedom of tracking is reduced. In other words, this is a gimbal lock state. Also, the closer the target object is to the specific direction, the higher the required angular velocity of rotation around the azimuth axis to continue tracking.

[0012] However, the azimuth axis angular velocity has an upper limit due to mechanical constraints. Therefore, due to delays in the rotation of the telescope and, in turn, the telescope barrel, there is a range in which the laser beam does not reach the target object and tracking becomes impossible, i.e., communication is cut off. Hereinafter, such an angular range in which a directional tracking device cannot track is called a blind spot.

[0013] Once the other station enters a blind spot, communication cannot be resumed immediately even if the other station exits the blind spot, and it takes additional time to resume directional tracking control. The directional tracking device of the present disclosure avoids such problems and enables directional tracking without blind spots in a hemispherical field of view. Hereinafter, an embodiment of the present disclosure will be described in detail using the drawings. In the following description, similar components are illustrated with the same reference numerals, and their names and functions are the same or similar. Therefore, detailed description of them may be omitted.

[0014] Embodiment 1 1 is a block diagram of an optical space communications device 900 using a directional tracking device 100 according to the first embodiment. The optical space communications device 900 includes the directional tracking device 100 and an optical transmitting / receiving device 200.

[0015] The directional tracking device 100 includes a main body 110, a prism rotation device 130, and a control processing device 140. The main body 110 further includes a telescope 1, an arm-type support structure 2, a first rotation drive unit 3, a second rotation drive unit 4, and a base structure 5.

[0016] The telescope 1 serves as an antenna section of the optical space communications device 900. The telescope 1 includes a primary mirror 1a, a secondary mirror 1b, a third mirror 1c, and a lens barrel 1d. The primary mirror 1a, the secondary mirror 1b, and the third mirror 1c are mirrors that reflect a laser beam, and form an optical path for the laser beam that is sent to or received from a target object. The primary mirror 1a, the secondary mirror 1b, and the third mirror 1c are supported by a support member attached to the lens barrel 1d.

[0017] The primary mirror 1a is supported on the inner surface of the lens barrel 1d so as to face the opening 1e. Here, the opening 1e is a transmission / reception port for a laser beam that is sent to a target object or received from the target object. In the directional tracking device 100 of the first embodiment, the size of the mirror surface of the primary mirror 1a is approximately the same as the size of the opening of the opening 1e of the lens barrel 1d.

[0018] The secondary mirror 1b is provided between the opening 1e of the lens barrel 1d and the primary mirror 1a. The mirror surface of the secondary mirror 1b faces the mirror surface of the primary mirror 1a. The size of the mirror surface of the secondary mirror 1b is smaller than that of the primary mirror 1a, and in the directional tracking device 100, it is about one-third the size of the primary mirror 1a.

[0019] The third mirror 1c is provided between the primary mirror 1a and the secondary mirror 1b inside the mirror tube 1d. The mirror surface of the third mirror 1c is tilted from facing the mirror surface of the secondary mirror 1b toward the plane mirror 2a inside the arm-type support structure 2, which will be described later. In other words, the third mirror 1c is installed at an angle such that the laser beam received from the secondary mirror 1b enters the plane mirror 2a.

[0020] The arm-type support structure 2 is a structure having a U-shaped arm section 2d that supports the telescope 1, and a pillar section 2e that is fixed to the center of the bottom of the arm section 2d or is formed integrally with the arm section 2d. The arm-type support structure 2 holds the telescope tube 1d so that it can be rotated around an elevation axis 3a via a bearing 2d. In addition, the pillar section 2e is connected to a second rotation drive section 4 via a bearing so that it can be rotated around an azimuth axis 4a relative to a base structure 5.

[0021] The arm-type support structure 2 is hollow inside and incorporates a coude-path optical system. The coude-path optical system is an optical system made up of multiple mirrors. In the directional tracking device 100 of the first embodiment, the coude-path optical system is made up of plane mirrors 2a, 2b, and 2c. The plane mirrors 2a, 2b, and 2c are supported and fixed by support members attached to the arm-type support structure 2.

[0022] The mirror surface directions of the plane mirrors 2a, 2b, and 2c are determined so as to bend the incident laser beam in the direction connected to the second rotary drive unit 4, i.e., downward in the plane of the drawing. Here, the plane mirror 2a is provided at the same height as the third mirror 1c when viewed from the ground surface of the directional tracking device 100. The plane mirror 2b is located below the plane mirror 2a and near the bending point of the arm unit 2d. Furthermore, the plane mirror 2c is provided at the same height as the plane mirror 2b when viewed from the ground surface of the directional tracking device 100, and above the pillar unit 2e.

[0023] The first rotation drive unit 3 is fixed to the arm-type support structure 2. The first rotation drive unit 3 is composed of, for example, an electrically or hydraulically driven rotary motor and a rotary encoder that measures the rotation angle of the lens barrel 1d. The first rotation drive unit 3 is connected to the lens barrel 1d of the telescope 1 directly or via a transmission.

[0024] The first rotation drive unit 3 receives a control command signal including information related to the target angle of the telescope tube 1d from the control processing device 140. The control command signal is, for example, a voltage pulse of a rotary motor, and the angle is set according to a pulse pattern. The first rotation drive unit 3 then drives the rotary motor while measuring the rotation angle of the telescope tube 1d with a rotary encoder, and rotates the telescope tube 1d by the target angle around the elevation axis 3a relative to the arm-type support structure 2.

[0025] The second rotary drive unit 4 holds the arm-type support structure unit 2 via a rotary bearing. Furthermore, the second rotary drive unit 4 is fixed to a base structure 5. Here, the base structure 5 is a structural interface between the optical space communications device 900 and a support structure (not shown). The support structure is, for example, a reinforced concrete foundation structure laid on the ground surface. Moreover, the second rotary drive unit 4 and the base structure 5 are hollow structures, and the laser light propagates inside.

[0026] The second rotation drive unit 4 is composed of, for example, an electrically or hydraulically driven rotation motor and a rotary encoder that measures the rotation angle of the arm-type support structure 2. The second rotation drive unit 4 receives a control command signal including information related to the target angle of the arm-type support structure 2 from the control processing device 140. The control command signal is, for example, a voltage pulse of the rotation motor, and the angle is set according to the pulse pattern.

[0027] The second rotation drive unit 4 drives the rotation motor while measuring the rotation angle of the arm-type support structure 2 with a rotary encoder, and rotates the arm-type support structure 2 around the azimuth axis 4a by that rotation angle. In other words, the arm-type support structure 2 rotates around the azimuth axis 4a relative to the base structure 5. Due to this rotation, the second rotation drive unit 4 rotates the telescope tube 1d around the azimuth axis 4a.

[0028] Prism rotation device 130 is provided at opening 1e of barrel 1d. Prism rotation device 130 also includes prism 34 rotatably provided at opening 1e of barrel 1d, as described below. The traveling direction of the laser beam transmitted and received by directional tracking device 100 coincides with the traveling direction of light passing through prism 34. Prism rotation device 130 rotates prism 34 based on a control command from control processing device 140, and controls the traveling direction of the laser beam transmitted and received by directional tracking device 100.

[0029] The control processing device 140 calculates the orbit of the remote station or satellite to be tracked using the time obtained from an internal clock circuit. The control processing device 140 also transmits a control command signal to the drive unit of the directional tracking device 100 so that the direction of the laser beam passing through the prism 34, i.e., the directional direction of the directional tracking device 100, coincides with the direction in which the remote station exists at any time. Here, the drive unit of the directional tracking device 100 refers to the first rotation drive unit 3, the second rotation drive unit 4, or the prism rotation device 20. As a result, the control processing device 140 controls the rotation angles of the arm-type support structure 2, the telescope tube 1d, and the prism 34 so that the laser beam passing through the prism 34 follows the orbit of the target object.

[0030] The control and processing device 140 may also include, for example, a display and a keyboard or a touch screen, in which case the operator of the directional tracking device 100 operates the keyboard, touch screen, or other input device to input information to be used by the control and processing device 140.

[0031] The orbit information 42 is orbit information required for the control processing device 140 to perform orbit calculations, and is input by the operator to the input device of the control processing device 140 in, for example, TLE (Two Line Elements) format. Here, TLE is one of the formats for expressing orbit information, and is a two-line text format including Keplerian orbital elements of the artificial satellite.

[0032] Fig. 2 is a cross-sectional view of prism rotation device 130 in directional tracking device 100 according to embodiment 1. In Fig. 2, the same numbers and symbols as in Fig. 1 indicate the same parts, and their explanations will be omitted. Fig. 2(a) is a top cross-sectional view of prism rotation device 130 as seen from the optical axis direction. Fig. 2(b) is a side cross-sectional view as seen from a direction perpendicular to the optical axis.

[0033] The prism rotation device 130 includes a bearing 32, a stator 33, and a prism 34. The bearing 32 has an inner ring 32a and an outer ring 32b. The inner ring 32a rotates relative to the outer ring 32b around a rotation axis 35. Here, the rotation axis 35 approximately coincides with the central axis of the opening 1e of the telescope 1. The bearing 32 is, for example, a ball bearing.

[0034] The inner ring 32a and the stator 33 constitute a stepping motor. The inner ring 32a becomes the rotor of the stepping motor. The stator 33 also incorporates a rotary encoder (not shown) that measures the rotation angle of the inner ring 32a. The stepping motor then performs feedback control to rotate the inner ring 32a so as to eliminate the difference between the rotation angle measured by the rotary encoder and the rotation angle control command from the control command device 40. Additionally, the stator 33 is fixed integrally with the outer ring 32b, and is further fixed to the lens barrel 1d of the telescope 1.

[0035] The prism 34 is a glass plate whose front and back surfaces are processed to be optically flat and transmits a laser beam. In the directional tracking device 100 of the first embodiment, the prism 34 is a wedge prism. As shown in FIG. 2(a), the prism 34 is fixed to the inner cylindrical surface of the inner ring 32a and has an outer shape of a cylinder. In addition, the cross section of the prism 34 is wedge-shaped as shown in FIG. 2(b).

[0036] The optical axis 36 is the trajectory of the laser beam passing through the prism 34, and is inclined at a predetermined angle from the rotation axis 35, which is the central axis of the opening 1e, in the direction in which the inclination angle between the two planes is maximum (i.e., in the direction of the apex angle of the prism). The predetermined angle is here defined as the deviation angle δ. The deviation angle δ is set so that the aforementioned blind spot is included in the circle that the optical axis 36 describes on the hemispherical field of view when the prism 34 and the optical axis 36 rotate with the rotation of the inner ring 32a. The absolute value of the deviation angle δ is constant.

[0037] In general, the larger the deviation angle δ, the larger the movement of the optical axis 36 relative to the rotation of the prism 34. Also, the larger the deviation angle δ, the more elliptical the laser beam becomes. Therefore, it is desirable to minimize the deviation angle δ so that the blind spot is included in the circle drawn by the optical axis 36 on the hemispherical field of view. In other words, the smaller the apex angle of the prism 34, the better, and a wedge prism is more suitable than a triangular prism for the prism 34 employed in the directional tracking device 100.

[0038] Returning to FIG. 1, the optical transmitter / receiver 200 includes an optical angle correction device 6, a reflecting mirror 7, optical branching devices 8a and 8b, a laser tracking photodetector 9, an optical communication photodetector 10, and an optical transmitter 11.

[0039] The optical angle corrector 6 is a steering mirror equipped with an electric actuator. The optical angle corrector 6 variably controls the angle of the reflecting mirror 7 by driving the electric actuator based on a laser angle signal (described later) from the laser tracking detector 9.

[0040] The optical splitters 8a and 8b are, for example, polarizing beam splitters, and reflect or transmit light. For example, the optical splitter 8a transmits a laser beam incident from the left side of the paper to the right side, i.e., toward the optical angle correction device 6. The optical splitter 8a also reflects a laser beam incident from the right side of the paper downward, i.e., toward the laser tracking photodetector 9.

[0041] The optical branching device 8b transmits a laser beam incident from, for example, the right side of the paper to the left side, i.e., to the optical communication photodetector 11. The optical branching device 8b also reflects a laser beam incident from below the paper to the right side, i.e., in the direction of the optical branching device 8a.

[0042] The laser tracking detector 9 has a signal processing unit that calculates the incident angle of the laser beam reflected by the optical branching device 8a, a lens that collects the incident laser beam, and an image pickup element that captures the laser beam collected on the lens. The laser tracking detector 9 also transmits a laser beam angle signal indicating the incident angle calculated by the signal processing unit to the optical angle correction means 6.

[0043] When a laser beam is incident on the optical communication photodetector 10, the optical communication photodetector 10 converts the laser beam into an electrical signal and demodulates it to a communication format determined by an operator.

[0044] The optical transmitter 11 converts an electrical signal representing voice, image, or digital data to be transmitted to a target object into an optical signal. The optical transmitter 11 also modulates the optical signal into a communication format determined by an operator and transmits a laser beam. In modulating the optical signal, the optical transmitter 11 performs, for example, intensity modulation.

[0045] The directional tracking device 100 may include a wave plate and a polarizer in the lens barrel 1d in order to block the reflected light reflected by the prism 34 toward the primary mirror 1a. For example, the laser beam output by the optical transmitter 11 may be linearly polarized, and a polarizer and a quarter-wave plate may be disposed in the optical transmitter / receiver unit 200 so that the polarization direction of the reflected light is perpendicular to the polarization direction of the laser beam, thereby blocking the reflected light of the prism 34 with the polarizer.

[0046] Next, the receiving operation of the optical space communication device 900 will be described with reference to FIG. 1. An optical communication signal from a remote station, which is a target object, passes through the prism rotation device 130 from the upper direction of the paper, becomes a laser beam, and enters the lens barrel 1d of the telescope 1. The parallel light beam of the laser beam that entered the lens barrel 1d advances in the order of the primary mirror 1a, the secondary mirror 1b, and the third mirror 1c, and the beam diameter is converged. At this time, the spatial optical axis of the light beam passing between the primary mirror 1a and the secondary mirror 1b and between the secondary mirror 1b and the third mirror 1c coincides with the optical axis of the primary mirror 1a and the secondary mirror 1b (i.e., the vertical direction of the paper). In addition, the optical axis of the light beam emitted from the third mirror 1c coincides with the direction perpendicular to the optical axis of the primary mirror 1a and the secondary mirror 1b (i.e., the horizontal direction of the paper).

[0047] The collimated light beam with a converged beam diameter is then emitted to the coude-path optical system of the arm-type support structure 2 located to the right of the page. The light beam is bent by the plane mirrors 2a, 2b, and 2c that make up the coude-path optical system, in that order, and heads toward the second rotation drive unit 4 located below the page. The light beam incident on the second rotation drive unit 4 further heads toward the optical space communications device 200. At this time, the optical axis of the light beam is approximately parallel to the azimuth axis 4a.

[0048] The light beam incident on the optical space communications device 200 is reflected by the optical angle correction device 6 and reaches the optical branching device 8a. A part of the received laser beam is reflected by the optical branching device 8a and enters the laser tracking photodetector 9. A part of the received laser beam passes through the optical branching device 8a and travels in the direction of the optical branching device 8b.

[0049] The laser tracking photodetector 9 detects the angle of incidence when the received laser beam is incident. The photodetector 9 also calculates an appropriate reflection angle in the optical angle corrector 6 from the incident angle, and transmits this as a reflection angle control signal to the optical angle corrector 6. The appropriate reflection angle is a reflection angle at which the received laser beam is reflected by the optical branching device 8a. Upon receiving the reflection angle control signal, the optical angle corrector 6 controls the angle of the reflecting mirror 7 to the reflection angle.

[0050] On the other hand, the received laser beam that reaches the optical branching device 8b passes through the optical branching device 8b and reaches the optical communication photodetector 10. The optical communication photodetector 10 converts the received laser beam into an electrical signal using a photodiode or the like, and further demodulates it into a signal in a communication format specified by the operator.

[0051] Next, the transmission operation will be described. The optical transmitter 11 converts the electrical signal of the data to be transmitted to the target object into an optical signal, and modulates it to a communication method determined by the operator to transmit a transmission laser beam. The transmission laser beam is reflected by the reflecting mirror 7 toward the upper side of the paper and enters the optical branching device 8b. After being reflected by the optical branching device 8b, the laser beam passes through the optical branching device 8a. The laser beam is further reflected by the optical angle correction device 6 and bent toward the second rotary drive unit 4 located toward the upper side of the paper.

[0052] The laser beam that enters the second rotary drive unit 4 is reflected in turn by the plane mirrors 2c, 2b, 2a, the third mirror 1c, the secondary mirror 1b, and the primary mirror 1a, and the beam diameter is expanded. The laser beam then passes through the prism rotation device 130 and is transmitted to the target station, which is the remote station.

[0053] In order for the laser beam to reach the remote station or to be received from the remote station, the directional tracking device 100 performs a tracking operation, which will be described later. The tracking operation is performed by adjusting the azimuth angle and elevation angle of the telescope 1 and the bending angle of the prism rotation device 130.

[0054] Hereinafter, the tracking operation of the directional tracking device 100 will be described. First, the coordinate system used in this description will be described with reference to Fig. 3 and Fig. 4. Fig. 3 is a diagram showing a coordinate system that defines the positional relationship between the directional tracking device 100 of the first embodiment and a target object. In Fig. 3, the same numbers and symbols as Fig. 1 and Fig. 2 indicate the same parts, and their description will be omitted.

[0055] 3 shows the directional tracking device 100, the X-axis 51, the Z-axis 52, the blind spot 53 of the AZ-EL gimbal, the target object 54, the orbit 55 of the target object, and the celestial sphere 56. The directional tracking device 100 is fixedly installed on the ground surface. The X-axis 51 is a coordinate axis defined on a horizontal plane, and the Z-axis 52 is a coordinate axis defined in the zenith direction perpendicular to the X-axis 51. The Z-axis 52 also approximately coincides with the azimuth axis 4a of the directional tracking device 100.

[0056] Here, assuming a directional tracking device without the prism rotation device 130, a blind spot will be generated, which is an area where the laser beam does not reach the target object when the lens barrel 1d is directed toward the zenith, just like a conventional directional tracking device using an AZ-EL gimbal. The blind spot 53 of the AZ-EL gimbal is the blind spot that occurs under this assumption. The blind spot 53 is also defined as an angular range of less than half angle φ from the Z axis 52.

[0057] The target object 54 is, for example, an artificial satellite in an orbit, and moves on an orbit 55 that is nearly a straight line in the field of view of the directional tracking device 100.

[0058] Celestial sphere 56 is a conceptual hemisphere used in astronomical observation. Celestial sphere 56 also shows a schematic representation of a hemispherical viewing angle. In FIG. 3, blind spots 53 are the hatched portions of the circles on celestial sphere 56.

[0059] Fig. 4 is a diagram showing the definition of the coordinate system of the prism 34 of the present embodiment 1. In Fig. 4, the same numbers and symbols as in Figs. 1 to 3 indicate the same parts. Fig. 4 shows a coordinate axis q61, a coordinate axis p62 perpendicular to the coordinate axis q61, a coordinate axis r63 coinciding with the direction of the rotation axis 35, a virtual plane 64, and a virtual circle 65.

[0060] The coordinate axis q61 is defined in a direction coinciding with the elevation axis 3a on the virtual plane 64. The elevation axis 3a rotates around the azimuth axis 4a, that is, around the Z axis 52. In other words, the coordinate axis q61 rotates around the Z axis 52 on the virtual plane 64.

[0061] The coordinate axis p62 is defined to be on the imaginary plane 64 and to be perpendicular to the coordinate axis q61. The coordinate axes q61 and p62 rotate on the imaginary plane 64 in synchronization with the rotation of the elevation axis 3a.

[0062] The coordinate axis r63 coincides with the rotation axis of the prism rotation device 130, i.e., the rotation axis 35 of the optical axis 36. Moreover, the coordinate axis r63 rotates around the elevation axis 3a, i.e., around the coordinate axis q61, in synchronization with the rotation axis 35. An imaginary circle 65 represents the locus of the optical axis 36 of the prism 34 when it rotates around the coordinate axis r63.

[0063] Next, the tracking operation will be explained using the coordinate systems of Figures 3 and 4. Figure 5 is a diagram showing a state in which coordinate axis p62 is oriented parallel to trajectory 53, as viewed from the direction of Z axis 52 in Figure 3. Figure 6 is a diagram showing blind spots 53 in Figure 5 and the tracking range of optical axis 36 of prism 34. In Figures 5 and 6, the same numbers and symbols as in Figures 1 to 4 indicate the same parts.

[0064] First, the directional tracking device 100 judges whether or not the trajectory 55 passes through the blind spot 53 based on the trajectory information 42. If it is judged that the trajectory 55 passes through the blind spot 53, the directional tracking device 100 controls the second rotation drive unit 4 to rotate the coordinate axis p62 to be approximately parallel to the trajectory 55 before the target object 54 enters the celestial sphere 54. As a result, as shown in FIG. 5, the coordinate q61 (i.e., the elevation axis 3a) becomes perpendicular to the trajectory 55, and the lens barrel 1d of the telescope 1 can be rotationally driven in the direction of the trajectory 55. After this, the directional tracking device 100 fixes the azimuth axis and does not use it for directional tracking control.

[0065] Next, the control processing device 140 of the directional tracking device 100 calculates the direction of the target object 54 at each time based on the trajectory information 42. The directional tracking device 100 also tracks the target object 54 by controlling the elevation axis 3a by the first rotation drive unit 3 and aligning the optical axis 36 with the direction of the target object 54 by rotating the prism rotation device 130.

[0066] When the target object 54 moves along the trajectory 55 toward the blind spot 53, the directional tracking device 100 rotates the prism rotation device 130 and controls the bent optical axis 36 to point to a point on the trajectory 55, as shown in Fig. 6. Here, it is assumed that the blind spot 53 has been adjusted in advance to be within the imaginary circle 65. Other conditions that enable tracking when the trajectory 55 passes through the blind spot 53 will be described later.

[0067] As described above, the directional tracking device 100 tracks the target object 54 through the following steps: an azimuth determination step of determining whether the target object 54 will pass through the blind spot 53; an azimuth rotation step of rotating the arm-type support structure 2 around the azimuth axis 4a by the first rotation drive unit 3 when it is determined that the target object 54 will pass through the blind spot 53, so that the azimuth component of the pointing direction of the telescope tube 1d is approximately parallel to the trajectory 55 of the target object 54; and a tracking step of fixing the elevation 3 azimuth axis and then tracking the target object 54 by rotating the telescope tube 1d around the elevation axis 3a and rotating the prism 34.

[0068] Note that the trajectory 55 of the target object 54 is just an example, and even if the target object 54 moves along a different trajectory, it is possible to track the target object 54 by fixing the azimuth axis 4a and combining the rotation of the elevation axis 3a by the first rotation drive unit 3 with the control of the prism rotation device 130.

[0069] Fig. 7 is a diagram showing a range that can be tracked by directional tracking device 100 under the condition that coordinate axis p is fixed to coincide with the direction of X-axis 51. In Fig. 7, range 55a is the range that can be tracked by directional tracking device 100. In other words, directional tracking device 100 can track all trajectories that pass through blind spots 53 and are parallel to coordinate axis p within range 55a. Here, trajectory 55 in Fig. 6 is assumed to be included in range 55a.

[0070] Moreover, range 55a is determined based on the range of blind spot 53. Range 55a is a band-like region perpendicular to azimuth axis 4a, with a width approximately equal to the maximum width of blind spot 53 expressed using φ as described above (i.e., the diameter if blind spot 53 is circular).

[0071] In addition, by appropriately controlling the prism rotation device 130 during tracking based on the trajectory information 42, the directional tracking device 100 can also track a trajectory that is not parallel to the coordinate axis p62 or a curved trajectory, as long as the trajectory falls within the range 55a.

[0072] Next, another tracking operation of the directional tracking device 100 when the trajectory 55 of the target object 54 passes through the blind spot 53 will be described with reference to Figs. 8 to 10. Fig. 8 is a diagram showing a state in which the coordinate axis p61 is oriented parallel to the trajectory 55 of the target object 54 when the trajectory 55 is not parallel to the X-axis 51. Fig. 9 is a diagram showing the blind spot 53 in Fig. 8 and the optical axis 36 of the prism rotation device 130. In Figs. 8 and 9, the same numbers and symbols as in Figs. 5 to 7 indicate the same parts, and their explanation will be omitted.

[0073] As described above, the directional tracking device 100 judges whether or not the trajectory 55 passes through the blind spot 53 based on the trajectory information 42. If it is judged that the trajectory 55 passes through the blind spot 53, the directional tracking device 100 controls the second rotation drive unit 4 to rotate the coordinate axis p62 so that it is approximately parallel to the trajectory 55 before the target object 54 enters the celestial sphere 54. After this, the directional tracking device 100 fixes the azimuth axis and does not use it for directional tracking control.

[0074] Next, the directional tracking device 100 tracks the target object 54 by controlling the elevation axis using the prism rotation device 130 and the first rotation drive unit 3.

[0075] When the target object 54 moves on the orbit 55 toward the blind spot 53, the directional tracking device 100 rotates the prism rotation device 130 via the control processing device 140, controlling the optical axis 36 to point to a point on the orbit 55, as shown in FIG. 9.

[0076] In this way, after fixing the azimuth axis 4a, the directional tracking device 100 performs directional tracking of the entire trajectory 55 by controlling the rotation angle about the elevation axis 3a and controlling the optical axis 36 by the rotation of the prism rotation device 130. Also, as long as the trajectory 55 falls within the range 55a shown in Fig. 10, it is possible to track an trajectory that is not parallel to the coordinate axis p or a curved trajectory.

[0077] The above describes the tracking operation when it is determined that the trajectory 55 of the target object 54 passes through the blind spot 53. Next, the tracking operation when the trajectory 55 does not pass through the blind spot 53 will be described. When it is determined that the trajectory 55 does not pass through the blind spot 53, the directional tracking device 100 controls and fixes the rotation angle of the prism 34 so that the direction of the bent optical axis 36 coincides with the direction of the X-axis 51. Next, the directional tracking device 100 rotates the telescope barrel 1b using the first drive control unit 3 and the second drive control unit 4, in the same way as a directional tracking device using a conventional AZ-EL type gimbal, to track the target object 54.

[0078] The conditions under which the directional tracking device 100 of the first embodiment can track the target object 54 passing through the trajectory 55 that crosses the blind spot 53 will be described below.

[0079] First, it is necessary to be able to calculate trajectory 55 in advance based on trajectory information 42. Second, it is necessary that deviation angle δ (see FIG. 4) of prism 34 is equal to or greater than half angle φ (see FIG. 3) of blind spot 53. Third, trajectory 55 must not pass outside range 55a (see FIG. 7 and FIG. 10). In optical space communications, where the target object, a satellite, is fixed, the above-mentioned conditions can be satisfied by designing and operating based on foresight information.

[0080] In this way, the directional tracking device 100 includes an arm-type support structure 2 rotatably connected to the base structure 5 around the azimuth axis 4a, a telescope 1d having an opening 1e which is a transmission / reception port for the laser beam and held on the arm-type support structure 2 so as to be rotatable around the elevation axis 3a relative to the arm-type support structure 2, a prism 34 having an optical axis 36 tilted from the central axis of the opening 1e and attached to the telescope 1d so as to be rotatable around the central axis of the opening 1e, and a control processing device 140 which controls the rotation angles of the arm-type support structure 2, the telescope 1d, and the prism 34 so that the laser beam passing through the prism 34 follows the trajectory 55 of the target object 54 in the sky. By controlling the direction of the telescope 1d using the first rotation drive unit 3 and the second rotation drive unit 4, the directional tracking device 100 tracks a target object in an area excluding the blind spot 53 in a hemispherical field of view.

[0081] Moreover, the directional tracking device 100 tracks a target object in the blind spot 53 by rotating the optical axis 36 of the prism rotation device 130. In other words, the target object can be tracked in all areas of the hemispherical field of view. This allows the directional tracking device 100 to prevent the occurrence of blind spots due to delays in rotation around the azimuth axis 4a, including cases where it is not possible to specify in advance an area where no target object exists.

[0082] Furthermore, by including the prism rotation device 130, the directional tracking device 100 is capable of high-precision tracking of a gimbal having three orthogonal movable axes for reasons that will be described below.

[0083] The angle control accuracy of the prism rotation device 130 will be described below using a specific design example. The refractive index of the glass constituting the prism 34 is n1, and the apex angle is α. Furthermore, if the normal vector of the first surface of the prism is N1, the normal vector of the second surface of the prism is N2, the laser beam vector that passed through the first surface of the prism is A1, the beam vector emitted from the prism is A2, and the refractive index of free space is n0 (=n2), the relationship between N1, N2, A1, and A2 can be expressed by formula (1).

[0084]

number

[0085] Here, the light beam incident on the first surface of the prism 34 is assumed to be perpendicular to the first surface. In this case, N2 can be expressed by the formula (2). Furthermore, A2 and δ can be expressed by the formulas (3) and (4), respectively.

[0086]

number

[0087] In the above relationship, assuming that n1 is the value shown in formula (5) and α is the value shown in formula (6), δ is calculated as shown in formula (7).

[0088]

number

[0089] As described above, the deviation angle δ needs to be larger than the half angle φ of the blind spot 53. To be on the safe side, it is assumed that tracking control is possible in the blind spot 53 of φ=4° under these conditions.

[0090] Fig. 11 is a diagram showing the results of calculating the relationship between the rotational positioning error (control error in the rotational direction) and the pointing control error (angle deviation from the theoretical value of the curved optical axis 36) of the prism rotation device 130 using the prism 34 under the above-mentioned conditions. As shown in Fig. 11, for example, when the rotational positioning error is 100 μrad, the pointing control error is about 8 μrad. In other words, the pointing control error is smaller than the rotational positioning error.

[0091] Fig. 12 is a diagram showing the results of calculating the relationship between the rotation axis runout error (tilt error of the rotation axis) and the pointing control error (angle deviation from the theoretical value of the curved optical axis 36) of the prism rotation device 130 using the prism 34 under the above-mentioned conditions. As shown in Fig. 12, for example, when the rotation axis runout error is 100 μrad, the pointing control error is about 1.75 μrad. In other words, the pointing control error is smaller than the rotation axis runout error.

[0092] From the above, it can be said that the pointing control error of the prism rotation device 130 has the property of mitigating the effect of the rotation control error of the prism 34. On the other hand, in the angle control of the gimbal used in the conventional directional tracking device, the rotational positioning error of each axis or the rotational axis runout error coincides with the pointing control error. For example, if the rotational positioning error or the rotational axis runout error is 100 μrad, the pointing control error will be 100 μrad.

[0093] Moreover, the directional tracking device 100 according to the first embodiment uses two axes simultaneously in one directional tracking. That is, it uses either a combination of rotation around the elevation axis by the second rotary drive unit 4 and rotation of the prism 34, or a combination of rotation around the azimuth axis by the first rotary drive unit 3 and the elevation axis. In general, the directional control error of a directional tracking device is the sum of the directional control errors of each movable axis. Therefore, compared to a directional tracking device that controls three axes, the directional tracking device 100 is capable of tracking with high accuracy.

[0094] Furthermore, the movement of the center of gravity when the prism 34 is rotated by the prism rotation device 130 is smaller than the movement of the center of gravity caused by rotation in a directional tracking device using three axes. This also contributes to the directional tracking accuracy of the directional tracking device 100.

[0095] In addition, since the directional tracking device 100 has two control axes, the amount of signal processing required for axis control is smaller than that of a directional tracking device that uses a three-axis gimbal, enabling high-speed tracking.

[0096] In addition, the prism rotation device 130 is lighter than a device with one gimbal axis, which makes it easier to make the directional tracking device 100 smaller and lighter than a directional tracking device that uses a three-axis gimbal.

[0097] As described above, the directional tracking device 100 has the following advantages over conventional directional tracking devices. First, directional tracking without blind spots is possible in a hemispherical field of view. Second, directional tracking with higher accuracy is possible than conventional directional tracking devices using orthogonal three-axis gimbals. Third, the amount of signal processing required for control of each axis is smaller than that of conventional directional tracking devices using orthogonal three-axis gimbals, enabling high-speed tracking control. Fourth, it is easier to reduce the size and weight compared to conventional directional tracking devices using orthogonal three-axis gimbals.

[0098] In addition, the prism rotation device 130 is not limited to a directional tracking device using a three-axis gimbal, but can provide higher control accuracy than a device that provides multiple rotatable mirrors near the opening 1e and tilts the optical axis by reflecting the laser beam with the mirrors. This is because the reflection angle of the optical axis changes twice as much as the drive angle of the mirror.

[0099] Although the directional tracking device 100 according to the first embodiment is applied to the free space optical communication device 900, this is merely an example, and the same effect can be obtained in any application that transmits or receives a laser beam to an object moving in a substantially straight line. For example, the directional tracking device 100 can be applied to a satellite laser ranging (SLR) device that measures the distance to a satellite by the round trip time of a pulsed laser beam, or a device that removes space debris with a laser.

[0100] In addition, in the above embodiments described in this specification, the relative positional relationship of each component may be described, but these are examples in all aspects and are not limited to the embodiments described. Therefore, countless modifications not exemplified are expected within the scope of each embodiment. For example, this includes cases where any component is modified, added, or omitted, and further cases where at least one component in at least one embodiment is extracted and combined with a component in another embodiment. That is, each embodiment can be freely combined, or each embodiment can be modified or omitted as appropriate.

[0101] Unless inconsistent, a component described in each of the above embodiments as being provided with "one" may be provided with "one or more." Furthermore, each component is a conceptual unit, and includes cases where one component is composed of multiple structures and cases where one component corresponds to a part of a structure.

[0102] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) an arm-type support structure connected to the base structure so as to be rotatable about an azimuth axis; a lens barrel having an opening for transmitting and receiving a laser beam and held by the arm-type support structure so as to be rotatable around an elevation axis relative to the arm-type support structure; a prism having an optical axis inclined from a central axis of the opening and attached to the lens barrel so as to be rotatable around the central axis of the opening; a control processing device that controls the rotation angles of the arm-type support structure, the lens barrel, and the prism so that the laser beam passing through the prism follows the trajectory of a target object in the sky; A directional tracking device comprising: (Appendix 2) an angle at which the optical axis is inclined with respect to a central axis of the opening is greater than an angle between a point at which the optical axis becomes a blind spot due to a delay in rotation of the lens barrel and the central axis of the opening; 2. A directional tracking device as described in claim 1. (Appendix 3) an arm-type support structure rotatably connected to the base structure around an azimuth axis; a lens barrel having an opening for transmitting and receiving a laser beam and supported rotatably around an elevation axis with respect to the arm-type support structure; a prism having an optical axis inclined from a central axis of the opening, the prism being attached to the lens barrel so as to be rotatable around the central axis of the opening; and a trajectory determination step in which a control and processing device for controlling the rotation angle of the arm-type support structure, the telescope, and the prism is used to determine whether the target object passes through a blind spot where the laser beam does not reach due to a delay in the rotation of the telescope, so that the laser beam passing through the prism follows the target object in the sky. an azimuth rotation step of rotating the arm-type support structure when it is determined that the target object passes through the blind spot so that an azimuth component of the pointing direction of the opening becomes substantially parallel to a trajectory of the target object; a tracking step of tracking the target object by rotating the lens barrel and the prism around the elevation axis; A directional tracking method comprising: [Explanation of symbols]

[0103] 1 telescope, 1a primary mirror, 1b secondary mirror, 1c third mirror, 1d telescope tube, 1e opening, 2 arm-type support structure, 2a plane mirror, 2b plane mirror, 2c plane mirror, 2d arm section, 2e column section, 3 first rotation drive section, 3a elevation axis, 4 second rotation drive section, 4a azimuth axis, 5 base structure, 6 optical angle correction device, 7 reflecting mirror, (8a, 8b) optical branching device, 9 laser tracking photodetector, 10 optical communication photodetector, 11 optical transmission device, 32 bearing, 32a inner ring, 32b outer ring, 33 stator, 34 prism, 35 rotation axis, 36 optical axis, 42 orbit information, 51 X-axis, 52 Z-axis, 53 blind spot, 54 target object, 55 orbit, 56 celestial sphere, 61 Coordinate axis q, 62 coordinate axis p, 63 coordinate axis r, 64 virtual plane, 65 virtual circle, 55a range, 100 directional tracking device, 110 main body, 130 prism rotation device, 140 control processing device, 200 optical transmission / reception unit, 900 optical space communication device

Claims

1. an arm-type support structure connected to the base structure so as to be rotatable about an azimuth axis; a lens barrel having an opening for transmitting and receiving a laser beam and held by the arm-type support structure so as to be rotatable around an elevation axis relative to the arm-type support structure; a prism having an optical axis inclined from a central axis of the opening and attached to the lens barrel so as to be rotatable around the central axis of the opening; a control processing device that controls the rotation angles of the arm-type support structure, the lens barrel, and the prism so that the laser beam passing through the prism follows the trajectory of a target object in the sky; A directional tracking device comprising:

2. an angle at which the optical axis is inclined with respect to a central axis of the opening is greater than an angle between a point at which the optical axis becomes a blind spot due to a delay in rotation of the lens barrel and the central axis of the opening; 2. The directional tracking device according to claim 1.

3. an arm-type support structure rotatably connected to the base structure around an azimuth axis; a lens barrel having an opening for transmitting and receiving a laser beam and supported rotatably around an elevation axis with respect to the arm-type support structure; a prism having an optical axis inclined from a central axis of the opening, the prism being attached to the lens barrel so as to be rotatable around the central axis of the opening; and a trajectory determination step in which a control and processing device for controlling the rotation angle of the arm-type support structure, the telescope, and the prism is used to determine whether the target object passes through a blind spot where the laser beam does not reach due to a delay in the rotation of the telescope, so that the laser beam passing through the prism follows the target object in the sky. an azimuth rotation step of rotating the arm-type support structure when it is determined that the target object passes through the blind spot so that an azimuth component of the pointing direction of the opening becomes substantially parallel to a trajectory of the target object; a tracking step of tracking the target object by rotating the lens barrel and the prism around the elevation axis; A directional tracking method comprising:

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