Method of energy transmission using coherent electromagnetic radiation

The invention relates to a method for energy transmission and alignment of a mobile receiver on a spacecraft and a transmission unit, wherein the energy is transmitted in the form of coherent electromagnetic radiation which is sent as a directed, regulated laser beam from a transmitter unit to the receiver.

Methods and devices of this kind, which operate without direct mechanical and / or electrical contact, are already known; you can find so far, however, mainly for power transmission over short distances and for small amounts of energy use. In addition, from the US-B1-6 534 705 a device for power transmission is described in a high-flying platform that uses a method of the type mentioned. Finding the platform as well as the rough alignment of the laser beam take place in this known method using external aids, such as radar, infrared scanners and the like. The actual power transmission is ensured by means of bundled, separate single laser, while for tracking the receiving station as well as for fine alignment of the laser beam in this known process, a separate laser is used, the return radiation is detected and measured by the reflectors at the receiving platform.

For alignment, a separate unit is required in the form of a radar, in which a energy transmission beam is switched off if the receiver is not identified.

Starting from this known arrangement and with their unrealized method object of the invention to provide such method and apparatus for performing this method for spacecraft such a way that it a simple manner and with the least possible expenditure on equipment, a wireless power transmission for the automatic supply distant mobile unit with energy and an alignment with the same means and allows the same time is easy, safe and flexible. Furthermore, a device as simple as possible built to be provided for the implementation of such a method by the invention.

For performing the method is provided that the receiver is a part of the incident, the energy-transmitting laser beam is reflected back to the transmitter unit and derived from this reflected beam information for alignment of the transmitter unit and transmitted to one with a alignment unit for the transmitting unit connected control unit, whereby movements of the receiver about its instantaneous position are detected and the laser beam by means of a predeterminable algorithm passes over a arranged at the receiver solar cell and thereby a part of the beam is tangent to a arranged around the solar cell retroreflector as well as the alignment in two mutually perpendicular directions is effected by the two Movement is carried out modulation and evaluation at different frequencies.

The apparatus for performing the method is that the transmission unit comprises a control unit and actuators controllable mirror for deflecting the beam, and that the receiving unit has an annularly surrounding a photocell arrangement reflector.

In an advantageous embodiment of the invention, an automatic alignment unit is provided to align the energy received field optimally to the incoming beam of energy at the receiver. Manual intervention in this regulation is not necessary, so that no external media are required for the alignment and fine adjustment.

The planned in an advantageous development of the invention, modulating the laser beam, the movement of the receiver is analyzed and the beam is tracked via the transmitter device. The inventively provided control based on a measurement of the intensity of the reflected radiation, thereby enabling the effects of the beam with a movement of the receiver, both in the horizontal and in the vertical direction.

The invention will be described in greater detail with reference to embodiments shown in the drawing. Show it:<dl id="dl0001" compact="compact"><dt>Fig. 1</dt><dd>the construction of a transmission unit,</dd><dt>FIG. 2</dt><dd>a detail of the arrangement according to FIG. 1,</dd><dt>Fig. 3</dt><dd>a schematic representation of a receiver in front view,</dd><dt>Fig. 4</dt><dd>a rear view of the receiver of FIG. 3,</dd><dt>Fig. 5</dt><dd>a schematic representation of an adjustment mechanism of the arrangement according to FIG. 3 and 4,</dd><dt>Fig. 6</dt><dd>a schematic representation of the procedure for finding a reflector,</dd><dt>Fig. 7</dt><dd>a schematic representation of the process for detecting the reflector ring,</dd><dt>Fig. 8</dt><dd>a schematic representation of a method for tracking the laser beam,</dd><dt>Fig. 9:</dt><dd>a schematic representation of a further Nachführmethode,</dd><dt>Fig. 10</dt><dd>the occurrence of the fundamental and the first harmonic of the modulation frequency as a function of the spatial detuning</dd></dl>

In the apparatus shown in the figures, a laser unit 1 serves as an energy source. The beam of this laser is widened by an integrated in the laser unit 1 diverging optic, prior to entering a deflection unit. This consists of three rotatable members 9, 10a and 10b. The unit 9, on which the units 10a and 10b and the drive unit 3 are fixed, is rotated via the drive unit 2 and the drive ring 6 about the axis a. The axis A is identical with the optical axis of the light emitted from the laser light beam. In the unit 9 is fixed to the axis a of the deflection mirror 4 at an angle of 45 °, which deflects the laser beam in the direction b, which thus is perpendicular to the axis a. The axis b, which can be selected by rotating the unit 9 and the axis A in either direction is the optical axis of the laser beam between the mirrors 4 and the axis of rotation units 10a and 10b as they travel through the drive unit 3 and the drive rings 7 and 8 are rotated relatively with respect to the unit. 9

The mirror 5 is disposed in the unit 10 in the normal position at an angle of 45 ° to the axis b and directs the laser beam to the direction from under it leaves the transmitting unit. About two electromechanical control elements 11 and 12, for example, piezoelectric actuators, the mirror 5 is tilted about two axes perpendicular to the axis b. This tilting movement has a smaller control range but a shorter correction time as the rotation about the axes a and b. Thus, slow movements of the laser beam to large deflection angle by the rotation about the axes a and b can be realized; fast but small movements by the actuators 11 and 12. The angle of rotation about the axes a and b can be 360 ​​° or larger. In synchronism with the unit 10 a is rotated about the axis b and the unit 10 b. b on the unit 10, the detector unit, installed for example consisting of a parabolic mirror 28 and a radiation detector 29 for receiving the back-reflected light from the receiver. The synchronous turning of the units 10a and 10b ensures that the detector unit is always aligned with the direction at which the laser beam leaves the transmitting unit.

The structure of such fine actuator based on a piezoelectric crystal drive is shown schematically in detail in FIGS. 2. As can be seen, each of the mirrors is 4 or 5 at a point A pivotally supported. In this illustration, for simplicity only a piezoelectric crystal 9 is shown. The piezoelectric crystal is arranged between two lever arms 13,14, wherein the one lever arm 13 deflects the mirror directly, while the other lever 14 via an adjusting device 15, the entire piezo element can be adjusted and preloaded. The entire suspension for both piezo crystals for a mirror is housed in a separate low-distortion housing 16th

The mobile receiver which is arranged as in the case of the embodiment described here on a reconnaissance vehicle 17 such as a spacecraft or,, is located at any distance from the transmitter, but in the direct field of view. This receiver has, as is apparent from Figures 3 and 4, a rotatable and adjustable attachment 18, which is for receiving the laser beam. The beam receiver 18 is composed of a solar panel 19 and set up a surrounding, the laser beam back to the transmitter reflective surface 20th The solar cells convert the incident light of the laser beam into electricity, which is used to power the receiver. Due to the beam profile of the laser beam always hits a part on the surrounding reflector ring 20, so that it is not on the solar cells 19 impinging part of the light to the transmission unit is reflected back by that the. The size of the laser beam is chosen so that it is smaller than the diameter of the solar cell 19, to ensure that the major portion of the available light energy for conversion into electrical energy is used and only a very small portion is reflected.

Furthermore, in the exemplary embodiment described here and as shown in Figures 4 and 5, integrated in the beam receiver 18 is an alignment unit which ensures that the beam receiver, with its two transverse axes always stands normal to the incident beam. The heart of this alignment is a behind a small hole 21 19 arranged in the center of the solar cell device sensitive sensor 22 which is shown in detail in Fig. 5 and comprises arranged at the ends of jet 23 Photo diodes 24. By means of this sensor 22 can always be measured whether the article 18 is still vertical, with its two axes from the beam. Once in a downstream evaluation unit 25, a deviation is detected, is adjusted by a built in this control electronics via motors 26 and drive elements 27 of the top 18 in its orientation.

The receiver from the return reflected portion of the light is collected in the transmitter unit on a parabolic mirror 28 and converted by a central sensor 29, and specific filters into an information signal relative to the position of the beam on the surface of the solar receiver. This signal is used in a control unit 30 of the transmitter, 4 and 5 to adjust and readjust the optimal alignment of the mirrors.

The control computer 30 then controls on the basis of the collected reflection signal in a cascaded control both the engines 2 and 3 for the coarse movement and the piezoelectric crystals 9,10 and 11,12 for the fine motor movements of both mirrors 4 and 5 at their respective pivot point A to and controls in this way to the overall system.

In addition to transmitting and receiving units further includes a control program which includes the entire procedural sequence of the automatic power transmission from a transmitting unit to a mobile receiver unit to the device. This control program essentially consists of two parts: a search algorithm that allows you to find and locate the receiver unit in a large area, and a tracking system, which ensures that a receiver unit found tracked accurately over long periods and thus constantly supplied with energy can.

In search mode, the motor-gear units of the sending unit are initially used extensively of scanning with an attenuated laser beam to the target area line by line for a return reflection. If such a reflection is detected, in a sub-mode, the surrounding area of ​​the last reflecting position is scanned accurately and thereby independently of the center circle R_m the reflector ring 20 is determined. Here, the beam on the fine-tuning means of piezoelectric crystals is positioned 9,10 and 11,12. This is done in a two-step approach in that in a first step, a search pattern in the form of a 3 × 3 matrix is ​​measured and is determined the brightest position and elected as the new starting point, as illustrated in Fig. 6. This process is repeated several times. In a subsequent second step, the shape of the ring and thus the central position of the solar panels 19 is detected. This algorithm is illustrated with reference to Fig. 7. From the starting point, several search steps, exemplarily shown here on 3 steps, carried out in a similar direction in which every step in the reflection signal intensity is measured. The step direction with the strongest signal value is taken as a new main analysis direction, and the process repeated until the contour of the ring reflector is fully recorded. On the basis of the individual items can now with a center of gravity calculation of the area spanned the middle of this area can be determined and the transmission beam are thus accurately guided to the solar cell 19 in the middle of the ring 20th This method is oriented so that the search and capture of the solar cells, the receiving unit does not necessarily already have to be oriented normal to the beam direction, but also inclinations be reliably detected and measured.

For reliable tracking of the transmission beam to the found and measured receiving unit four basic algorithms are alternatively provided, which will be described in greater detail below.

In the first method, which is also called a "random walk", the position of the laser beam from the starting position by a small step in any direction is changed and determined by means of light reflected back from the receiver light, whether this step was an improvement or deterioration , In case of deterioration jumps back to the start position; the new position is retained as the new start position at an improvement. Thereafter, the procedure continues with a new step in any direction. The decision whether a position change has led to an improvement or deterioration, for example, can be determined by the overall intensity of the back-reflected light, the closer is the position of the laser beam to the center of the solar cell 21, the less light strikes the reflector ring 20 and is reflected or it can be determined for example by the "modulation method" that is, by the detection of the double frequency, as is described later as a separate method.

In the second, the "main process" designated procedure, the current position of the laser beam is defined as the center. Now at least three vectors of the same length, but different directions are selected. The directions are preferably chosen so that they are axially symmetrical to the horizontal and vertical axes, as is illustrated in Fig. 8 for 4 vectors. Then the beam is positioned in each vector direction and determines the signal strength at each endpoint. After each position was measured once, the vectors are weighted by their signal strength to each other about a center of gravity calculation. As a result, there is a new vector, which points in the direction of the strongest intensity, and whose magnitude is a measure of the distance of the offset. Using this vector, the new center is determined. The process can be further optimized by a correction step of new and old vectors already determined after each measurement. This optimization increases on the one hand, the responsiveness of the system to another direction changes smoothly designed, as is easily corrected after each measurement and not only after a full cycle.

In the third, the so-called "circle method", a modulation frequency f and a modulation in the vertical direction at the same frequency but 90 degrees is phase shifted to the second in the beam direction mirror 5 in the horizontal direction, characterized. Thereby, the mirror performs 5 circular movements and the laser beam is modulated in this manner around the center. By measuring the reference voltage to the piezoelectric crystals, it is possible to determine the angle at which the mirror 5 is straight. Now a circular passage is long continuously measured accurately. The reflection signal describes the direction then a sinusoidal contour, as illustrated in Fig. 9. The larger the amplitude is, the more there is the beam off-center on the reflection film. By comparison with the reference signal, it is possible to assign each stage directions and it is regulated in the direction of the weakest intensity to be in the center of the solar panels.

In the fourth, the so-called "modulation method" is the position x of the laser beam at its center position x_M in function of time t with a modulation frequency f in accordance with x = x_M + x_O sin (2 nft) modulated. Since, as is apparent from Fig. 10, the laser beam always hits a part of the reflection ring 20, the back-reflected light with the frequency f and their higher harmonics will be modulated. 11 shows the back-reflected light intensity depending on the position of the laser beam to the receiver. Is x_M exact in the middle of the photocell 19 and x_O smaller than the radius of the photocell, so meet portions of the laser beam at an oscillation through both the right and left of the reflector ring 20. The reflected-back light is modulated at twice the frequency f 2. The more x_M is away from the center of the photocell, the lower the component in 2f, because on one side of the reflector ring 20 is always less made. Is x_M exactly on the edge of the photocell 20, as with a vibration process in half the time the photocell 19 and is swept in the other half the time, the reflector ring 20; the back-reflected is now modulated with the frequency f only and has practically no components at frequency 2 f. If the laser beam to the middle radius of the reflector ring 20 (r_M have slipped in Figure 6), as occurs in the back-reflected light again a strong component at the frequency f 2 on; this component is, however, relative to the position "x_M "Phase-shifted in the center of the photocell to 180 °, since the light beam is incident at the reversal points of the vibration at low reflective structures.

Thus, from the size and the phase of the component at frequency f 2 to deduce how well the position of the laser beam x_M coincides with the center of the photocell 20th For a control loop, a lock-in amplifier or a Fourier analysis can be consulted for example.

The modulation method is not limited to one dimension. The mirror 5, for example, in the horizontal and in the vertical direction with two different frequencies f₁ and f₂ be modulated. Preferably, both frequencies are chosen to be significantly different and in a non-rational ratio to one another in order to accurately detect the frequency analysis of the reflected light back to the way in which deviates the position of the laser beam from the center of the solar cell.

In this way, an optimal orientation of the arrangement is achieved at each of the methods described above, at the same time ensure maximum energy transfer.