Sensor for e.g. satellite, has light sensitive detector connected to readout circuit for processing electrical signal, indicating position of light incident on detector, to sensor signal that indicates position of sensor

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Patent Center

Netherlands © 2000789 © C PA TENT²⁰ © Application number: 2000789 © Submitted: 30.07.2007 lnt.CI .:

G01S3 / 784 (2006.01) G01B11 / 27 (2006.01)

B60P7 / 12 (2006.01)

<td> ©</td><td>Signed up: 02.02.2009</td><td> ©</td><td>Patent holder (s): Delft University of Technology in Delft. Dutch Organization for Technical</td>

<td> ©</td><td>Granted: 02.02.2009</td><td></td><td>Natural Science Research, TNO in Delft.</td>

<td> ©</td><td>Issued: 01.04.2009</td><td> ©</td><td>Inventor (s): Reinoud Felix Wolffenbuttel in Leidschendam. Ger de Graaf in Delft. Johannes Adrianus Petrus Leijtens in Bleiswijk.</td>

<td></td><td></td><td> ©</td><td>Authorized representative: Drs. A. Kupecz et al. At 1000 HB Amsterdam.</td>

© Position sensor.

The invention relates to a sensor for position determination, comprising at least a photosensitive detector which emits an electrical signal or signals depending on a position of light incident on the detector, and a read-out circuit connected to the photosensitive detect or for processing the electrical signal or signals up to a sensor signal indicative of the sensor position, which readout circuit is provided with an electrical supply, the photosensitive detector constituting the electrical supply.

NL C 2000789

This patent has been granted regardless of the enclosed result of the prior art research and written opinion. The patent corresponds to the documents originally filed.

The Netherlands Patent Center is an agency of the Ministry of Economic Affairs.

Position sensor

The invention relates to a sensor for position determination comprising at least a photosensitive detector which emits an electrical signal or signals depending on a position of light incident on the detector, and a read-out circuit connected to the photosensitive detector for processing the electrical signal or signals into a sensor signal that is indicative of the sensor position, which read-out circuit is provided with an electrical supply.

Such a sensor is known, for example, from space travel and is used therein for position control of a satellite, for position control of a solar panel, and for position control of antennas. Incidentally, the use of such a sensor is not limited to these applications.

The sensor known from the prior art has at least one, but usually more optical detectors placed on a platform of a satellite, the position of which has to be determined with respect to the sun. The position determination of the sensor thus also yields the position of the satellite in relation to the sun.

The sensor further comprises a readout circuit in the form of, for example, a measuring amplifier which is provided with a separate power supply. In the prior art, this power supply is provided by a separate solar panel. This solar panel can be a central solar panel of a satellite or a solar panel that is placed independently on the housing of the sensor.

For some time now, there has been a need to achieve further miniaturization of the sensor according to the preamble, in order to achieve a weight saving, which makes it possible that the satellite in combination with which the sensor can be used can be made smaller and that in the overall costs can be saved with regard to the mission to be carried out with such a satellite.

These and other objects of the invention are achieved with a sensor characterized by one or more of the appended patent claims.

In a first aspect, the sensor according to the invention is based on the surprising insight that savings in components, dimensions and weight can be made by designing the sensor such that the photosensitive detector also forms the electrical supply.

Within the scope of the invention, essentially a suitable detector is suitable for the photosensitive detector, in particular a detector selected from the group comprising a series connection of two diodes, and an array of at least two photodiodes arranged by two. With such an array comprising two by two placed photodiodes, a position determination in two dimensions can be performed.

When using a sensor that is equipped with a series connection of two diodes, position determination in one dimension is thus possible.

A further aspect of the sensor according to the invention relates to the preferred embodiment, characterized in that the photosensitive detector is a 2x2 array of photodiodes, which lie in a flat plane, and that a protrusion is arranged on the plane of the photodiodes. The projection has the function of casting a shadow spot on the array of photodiodes when the sensor is exposed by the sun, so that these photodiodes receive a respective exposure depending on the position the sensor takes with respect to the sun. This does not affect the aforementioned function of the photosensitive detector formed by the photodiodes, that is to say that the photodiodes also form the electrical supply to which they produce a potential difference independently of the position of the sensor upon exposure.

Determining the sensor position on the basis of the exposure of the photodiodes is easiest if the protrusion is placed upright on the plane of the photodiodes. It is also preferred that the protrusion is placed midway between the photodiodes.

The sensor according to the invention is then further preferably designed such that the readout circuit is adapted to measure differential currents between photodiodes from the 2x2 array, and that the readout circuit derives the sensor signal indicative of the sensor position from these differential currents.

A simple and very suitable embodiment of the sensor according to the invention is that in which the photodiodes from the 2x2 array are connected in two groups of photodiodes, each group comprising two series-connected photodiodes, and in which at least one group of photodiodes is feed-coupled to the readout circuit.

The read-out circuit is preferably arranged for measuring the differential current between the two photodiodes of a group of series-connected photodiodes.

The invention will be explained in more detail below with reference to the drawing, with reference to a specific exemplary embodiment which is not restrictive with regard to the attached patent claims.

In the drawing shows:

fig. 1 shows a schematic representation of the sensor according to the prior art;

fig. 2 shows a schematic representation of the circuit of the sensor according to the invention;

fig. 3 and fig. 4 schematically show some usage situations of a preferred embodiment of the sensor according to the invention, together with an electrical circuit diagram of a part of the sensor.

Like reference numerals used in the figures refer to like parts.

Referring first to Fig. 1, reference numeral 1 designates the prior art sensor which comprises a photosensitive detector 2 which emits an electrical signal 3 depending on a position of light incident on the detector 2. Furthermore, a reading circuit 4 is connected to the detector 2 for processing the electrical signal 3 into a sensor signal 5 which is indicative of the position of the sensor 1 relative to the light source used, usually the sun.

For the supply of the readout circuit 4, a separate electrical supply 6 is provided, in which use is generally made of a series connection of photodiodes 7 which are coupled to the readout circuit 4 in a feeding manner.

Referring now to Figure 2, the sensor 1 according to the invention is shown. This sensor 1 also comprises a photosensitive detector 2 which emits an electrical signal 3 depending on a position of light incident on the detector 2. Furthermore, as in the prior art, the photosensitive detector 2 is connected with a readout circuit 4 for processing the electrical signal 3 to a sensor signal 5 indicative of the position of the sensor 1.

According to the invention, the electrical supply of the readout circuit 4 is provided in that the photosensitive detector 2 also forms the electrical supply 6.

Hereinafter, the invention will be further elucidated on the basis of a preferred embodiment selected from the group comprising a series arrangement of two diodes, and an array of at least two photodiodes arranged by two. The preferred embodiment concerns the embodiment of the photosensitive detector 2 as an array of at least two photodiodes placed by two.

Figure 3 and Figure 4 show in Figure 3A and Figure 4A such a photosensitive detector 2 with photodiodes 8, 9,

10, 11 which lie in a flat plane corresponding to the plane of the drawing. The electrical circuit diagram of these photodiodes 8, 9, 10, 11 is shown very schematically in Figures 3C and 4C and is indicated by the reference numerals 8 ', 9', 10 'and 11'.

Figure 3A shows the photodiodes 8, 9, 10 and 11 lying in the plane of the drawing together with a spot 12, which represents an exposure of these photodiodes 8, 9, 10 and 11 in a first (neutral) position of the detector 2 In Fig. 3B this illumination is shown in side view and it is also clearly visible that a protrusion 13 is placed on the detector 2, at least on the plane of the photodiodes 8, 9, 10 and 11. This projection 13 is shown in the preferred position in which it is placed upright on the plane of the photodiodes 8, 9, 10 and 11 and occupies a central position therebetween. This central position means that the projection 13 is placed midway between the photodiodes 8, 9, 10 and 11, which is also clearly visible in Figure 3A.

In the neutral first position of the detector 2 as shown in figure 3A and figure 3B, an equal exposure of the photodiodes 8, 9, 10 and 11 takes place, so that the difference currents II and 12 (see figure 3C) between the photodiodes 8 'and 10 'and 9' and 11 'are 0 respectively.

Another position of the sensor of which the detector 2 forms part also includes a different exposure of the photodiodes 8, 9, 10 and 11 as shown schematically in Figs. 4A and 4B.

Figure 4B shows a clear skew of detector 2, in which photodiode 9 receives less light than the other photodiodes 8, 10 and 11.

In the electrical diagram of these photodiodes shown in Figure 4C, this is shown because a difference current 12 deviating from 0 arises between the photodiodes 9 'and 11'. The difference current II between the diodes 8 'and 10' is still 0, since these two photodiodes receive an equal amount of light.

The differential currents II and 12 just referred to, the development of which has been explained above with reference to Figures 3 and 4, are processed in a readout circuit 4 as shown in Figure 2, for which purpose this readout circuit 4 is adapted for measuring the difference currents II and 12 between the photodiodes 8, 9, 10 and 11 from the 2x2 array to form the sensor signal 5 (see figure 2) which is indicative of the position of the sensor 1 of which detector 2 is a part.

Figures 3 and 4 further show that the photodiodes

8, 9, 10 and 11 from the 2x2 array shown are connected in two groups of photodiodes 8, 10 and 9, 11 respectively, each group comprising two series-connected photodiodes. The photo diodes 8, 10 or the photo diodes 9, 11 or both groups of photo diodes are coupled to the readout circuit 4 shown in Figure 2.