DE102019210508A1 - Optical sensor module and method - Google Patents

Abstract

The invention relates to an optical sensor module (1), in particular for a vehicle, comprising, inter alia, a housing (1b), an objective, an imager (7), a diaphragm, a control unit and a lens arrangement (1a) with an adjustable lens element (2 ), wherein a diopter number of the adjustable lens element (2) can be adjusted by means of the control unit.

Description

The invention relates to an optical sensor module with an adjustable lens element and a method for adapting an adjustable lens element.

From the prior art, for example, from the publication DE102015205076A1 a distance detection device with a camera lens and a camera sensor is known. The camera lens has a variably adjustable focal length. Something similar is from the publication DE102015205077B4 known. This document also discloses a camera lens with a variably adjustable focal length, the distance detection device additionally being configured to synchronize the provision of image signals for the processing unit with a focal length variation of the camera lens.

In the cited publications, the focal plane of the camera is changed in order to adapt to different object widths. The systems mentioned are also actively designed.

A disadvantage of these systems is that active systems constantly require computing power, since these systems adapt each time the scene in front of the camera changes.

It is also known to increase the range of an increase in the depth of field of an image, in particular when the imager moves out of the focal plane of the lens, by selecting a smaller aperture or a larger f-number of the lens.

The disadvantage here is that the light transmission of the entire lens system is reduced by the selection of a smaller aperture. Due to the smaller aperture, the size of the diffraction disk is increased, which reduces the theoretically achievable maximum sharpness of the lens system.

It is accordingly an object of the present invention to provide an optical sensor module and a method which ensures a constant image quality.

This object is achieved by the subject matter of independent claims 1 and 7.

Advantageous configurations and embodiments are the subject of the subclaims.

In the course of the invention, it was found that temperature changes in particular can lead to undesired effects in a sensor module, which can worsen the image quality. Further considerations were that to compensate for the deteriorated image quality, for example, certain parameters of the sensor module must be adapted

According to the invention, therefore, an optical sensor module, in particular for a vehicle, is proposed, comprising, inter alia, a housing, an objective, an imager, a diaphragm, a control unit and a lens arrangement with an adjustable lens element, the dioptric number of the adjustable lens element being adjustable by means of the control unit .

The optical sensor module can in particular be a front camera or a surround view camera of a vehicle.

The control unit includes, among other things, a computing unit and control electronics. The computing unit can be used to process and monitor data.

The control electronics of the control unit controls the applied voltage and / or the applied current to the adjustable lens element in order to adjust the number of diopters accordingly, depending on the lens element. By adapting the number of dioptres, refractive errors or image position errors that occur can be compensated for in an advantageous manner and thus good image quality can be guaranteed.

The adjustable lens element is an additional element which is introduced into the lens arrangement.

Basically, the aperture of the lens via the depth of focus determines the temperature range in which the camera module still delivers an acceptably sharp image. The following applies in a simplified manner: the smaller the aperture, the larger the temperature range of acceptable sharpness, but also the smaller the transmitted light energy per time. An enlargement of the aperture would increase the transmission of the light energy per time and thus allow shorter integration times with the same signal-to-noise, but at the same time also reduce the temperature range of acceptable sharpness. With the adjustable lens element, however, an optimal point spreading function can advantageously be achieved for each temperature range, regardless of how the size of the aperture was selected. Furthermore, the adjustable lens element increases and simplifies the optical design freedom in the module, for example the optimization of a camera module for low light, which is one of the most critical use cases in the automotive sector.

Furthermore, the control unit is particularly preferably designed to receive and monitor temperature data of the optical sensor module from a temperature sensor. It would also be conceivable that the image data and their image sharpness or their change is monitored. This could result in an indirect temperature measurement based on the image blurring induced by the temperature.

This is advantageous because the sensor module is produced at a certain temperature. If the ambient temperature changes during operation, mechanical changes will occur in or on the module when this specific temperature is exceeded or not reached, as a result of which the position of the imager relative to the focal plane changes.

The control unit is particularly preferably further designed to determine a value for an offset of an objective focus plane and an image sensor plane based on the temperature data.

A very high or a very low temperature results in an expansion or contraction of the entire sensor module. This creates an offset between the lens focus plane and the image sensor plane, which in turn leads to image position errors and a blurred image.

The control unit can calculate the offset based on the temperature data and material data, etc., for example. It would also be conceivable that the control unit retrieves a value for the offset from a look-up table, a value for the offset being assigned to each temperature or a specific temperature range. This solution is particularly advantageous because it is particularly power-saving and not very computationally intensive.

In a further preferred embodiment, the offset of the lens focus plane and the image sensor plane can be compensated for by the adjustable number of diopters of the adjustable lens element.

A suitable number of dioptres is calculated accordingly, which can compensate for the offset and thus also compensate for the image position error in order to obtain the desired image quality or image sharpness. After calculating the number of diopters, the adjustable lens element is activated accordingly by the control electronics.

The adjustable lens element is preferably a liquid lens, a polymer lens, a liquid crystal lens or a mechanically movable lens.

In the case of a liquid crystal lens, the alignment of the liquid crystals can be changed, for example, by applying a voltage. This allows the refractive power of the lens to be changed, for example. Liquid lenses usually consist of two different liquids which cannot be mixed with one another, but which have the same density as possible but different refractive indices. By applying a voltage, the contact angle of a drop on a chamber window of the lens and thus the focal length can be changed via the effect of electrowetting. A polymer lens consists of an elastic polymer membrane in which an optical liquid is located. The focal area of the lens can be changed by adding or removing the liquid.

Furthermore, the adjustable lens element can preferably be introduced into a diaphragm opening. The adjustable lens element is introduced into the lens system in the position of the diaphragm along the optical axis. Furthermore, the adjustable lens element can preferably be introduced into the plane of the aperture stop of the lens system. The position of the diaphragm plane is advantageous because here changes in the focal length of the adjustable lens element have little or no effect on the image size.

• - Erfassen von Temperaturdaten eines optischen Sensormoduls mittels eines Temperatursensors,
• - Bestimmen eines Versatzes einer Objektivfokusebene und einer Bildsensorebene mittels einer Steuereinheit basierend auf den Temperaturdaten,
• - Anpassen einer Dioptrienzahl des einstellbaren Linsenelements mittels der Steuereinheit zum Ausgleich des Versatzes.

According to the invention, a method for adapting an adjustable lens element for an optical sensor module with the following steps is also proposed:

• - Acquisition of temperature data from an optical sensor module using a temperature sensor,
• - Determination of an offset of an objective focus plane and an image sensor plane by means of a control unit based on the temperature data,
• Adaptation of a diopter number of the adjustable lens element by means of the control unit to compensate for the offset.

In a preferred embodiment of the method, after the offset of the lens focus plane and the image sensor plane has been calculated, the number of diopters suitable for compensating for the offset is determined by means of the control unit. For this, algorithms are used which examine the edge transitions for their sharpness and thus draw conclusions about the sharpness of the image. By making small adjustments to the liquid lens, these transitions become sharper or softer, which the computing unit serves as an indication of the control direction. The algorithm regulates until an optimal sharpness of the transitions is achieved.

In a further preferred embodiment, the number of diopters is determined by analyzing the image data.

Further advantageous configurations du embodiments emerge from the drawings. For the sake of clarity, the same features or components have only been given the respective reference symbols once.

• 1 eine schematische Darstellung einer Linsenanordnung gemäß einer Ausführungsform des Sensormoduls;
• 2 eine weitere schematische Darstellung einer Linsenanordnung gemäß einer Ausführungsform des Sensormoduls;
• 3 eine schematische Darstellung einer Ausführungsform des Sensormoduls,
• 4 ein schematisches Ablaufdiagramm einer Ausführungsform des Verfahrens.

Show in it:

• 1 a schematic representation of a lens arrangement according to an embodiment of the sensor module;
• 2 a further schematic representation of a lens arrangement according to an embodiment of the sensor module;
• 3 a schematic representation of an embodiment of the sensor module,
• 4th a schematic flow diagram of an embodiment of the method.

1 shows a schematic representation of a lens arrangement 1a according to one embodiment of the sensor module 1 . The lens arrangement 1a has a front part 3 as well as a rear part 4th the lens assembly. Between the front part 3 and the rear part 4th is an adjustable lens element 2 arranged. The front part 3 is the part where the light rays 6th hit first. These rays of light 6th move through the front part 3 via the adjustable lens element 2 and the back part 4th towards the imager 7th .

In 1 are three representations of the lens arrangement 1a for different scenarios I-III shown. The first scenario I. describes the operation of the sensor module 1 at one temperature T = T_0, where T_0 corresponds to an ambient temperature at which the sensor module 1 was made. The adjustable lens element 2 is in this scenario I. not active or does not have to be active and no diopter number is adjusted. Depending on the lens system, it may be necessary that the adjustable lens element 2 has a specific focal length. In the second scenario II the temperature has increased and thus an expansion of the sensor module or, as shown here, the lens arrangement 1a evoked. The lens image also changes due to the temperature. These include, among other things, refractive indices, lens radii, lens thicknesses and / or lens positions. This results in an offset 5 between the lens focus plane OE and the image sensor plane BE , with the distance between the lens focus plane OE and image sensor plane BE is enlarged. The adjustable lens element 2 is in this scenario II also not active or no diopter number is adjusted. This results in a focus deviation on the imager 7th which leads to poor image quality or a blurred image. In the third scenario III an appropriate number of diopters of the adjustable lens element was set, thereby reducing the offset 5 has been balanced and the rays of light 6th thus again focused on the imager 7th hit.

2 shows the same components as 1 and also three different scenarios I-III . The first scenario I. is identical to the one from 1 . In the second scenario II the 2 the temperature has decreased which leads to a contraction of the sensor module. This results in an offset 5 between lens focus plane OE and image sensor plane BE , where, due to the contraction, the distance between the lens focus plane OE and image sensor plane BE is reduced. In this scenario II is the adjustable lens element 2 not active or the dioptre number is not adjusted. This leads to a defocused impact of the light rays 6th on the imager 7th . In the third scenario III an appropriate number of diopters of the adjustable lens element was set, thereby reducing the offset 5 has been balanced and the rays of light 6th thus again focused on the imager 7th hit.

3 shows a schematic representation of an embodiment of the sensor module 1 . The sensor module 1 consists of a lens arrangement 1a and a housing 1b . Furthermore is the image sensor plane BE shown. Here is the entire sensor module 1 with changing temperature T in three different versions A. , B. and C. shown. Furthermore, so-called point spread functions (PSF) 8th for the respective variants AC shown. The values 8a the point spread functions 8th change due to imaging errors, for example. The lower the value 8a is, the blurrier the image. The higher the value 8a on the PSF 8th the sharper the image. The reference number 9 describes a value at which the sharpness of the image is still acceptable.

In the first variant A. became the sensor module 1 so focused that at one temperature T = T_0, i.e. the temperature during the production of the sensor module the best image sharpness is achieved. If the temperature changes now T , the respective value also changes 8a the point spread function 8th . In variant A. reaches the value 8a at T = T_0 the highest value and the best sharpness. At a lower temperature T <T_0, the value becomes 8a the PSF 8th lower and the sensor module 1 provides a blurred image. This is due to the contraction of the sensor module 1 and the displacement of the image sensor plane BE traced back. Will the temperature T greater than T_0, i.e. T> T_0, the value decreases 8a the PSF 8th also starting, resulting in a very blurry Image leads. The value 8a for T> T_0 is also below the value 9 for acceptable sharpness.

In the variant B. became the PSF 8th optimized for cold temperatures. The values 8a for T = T_0 and T <T_0 are above the value 9 for acceptable sharpness, with the value 8a is highest at T <T_0 due to the optimization for cold temperatures. The value 8a for T> T_0 is still below the value 9 . The sensor module would therefore also deliver a blurred image here at high temperatures.

In variant C. the PSF was optimized for warm temperatures. With this variant it can be determined that with T = T_0, T <T_0 and T> T_0 the associated values 8a all above the value 9 an acceptable sharpness. Depending on the module behavior, it can be very difficult or even impossible, especially with a low f-number of the lens, to compensate for the temperature-dependent module behavior (e.g. shift of the image plane, material expansion) simply by changing the BFL (back focal length) of the lens system. It would then not be possible to guarantee the target values for image sharpness for all operating temperatures. The use of an adjustable lens element is a possible solution here.

4th shows a schematic flow diagram of an embodiment of the method. In step S1 of the method, temperature data of an optical sensor module are recorded by means of a temperature sensor. In a second step S2, an offset of an objective focus plane and an image sensor plane is calculated by means of a control unit based on the temperature data or, alternatively, based on the image data. In a further step S3, a diopter number of the adjustable lens element is adjusted by means of control electronics to compensate for the offset.

List of reference symbols

1

Sensor module

1a

Lens assembly

1b

casing

2

adjustable lens element

3

front part of the lens assembly

4th

rear part of the lens assembly

5

Offset

6th

Rays of light

7th

Imager

8th

Point spread function PSF

8a

Value of the point spread function PSF

9

Value for acceptable sharpness

BE

Image sensor level

OE

Lens focus plane

T

temperature

I-III

Scenarios

A-C

variants

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102015205076 A1 [0002]
• DE 102015205077 B4 [0002]

Claims (9)

Optical sensor module (1), in particular for a vehicle, comprising, inter alia, a housing (1b), an objective, an imager (7), an aperture, a control unit and a lens arrangement (1a) with an adjustable lens element (2), wherein a The number of diopters of the adjustable lens element (2) can be adjusted by means of the control unit. Optical sensor module (1) according to Claim 1 , characterized in that the control unit is designed to receive and monitor temperature data of the optical sensor module (1) from a temperature sensor. Optical sensor module (1) according to Claim 2 , characterized in that the control unit is further designed to determine a value for an offset (5) of an objective focus plane (OE) and an image sensor plane (BE) based on the temperature data. Optical sensor module (1) according to one of the Claims 1 - 3 , characterized in that a diopter number of the adjustable lens element (2) can be determined by means of the control unit, by means of which the offset (5) of the lens focus plane (OE) and the image sensor plane (BE) can be compensated. Optical sensor module (1) according to one of the preceding claims, characterized in that the adjustable lens element (2) is a liquid lens, a polymer lens, a liquid crystal lens or a mechanically movable lens. Optical sensor module (1) according to one of the preceding claims, characterized in that the adjustable lens element (2) can be introduced into a plane of the aperture stop. Method for adapting an adjustable lens element (2) for an optical sensor module (1) with the following steps: - Acquisition (S1) of temperature data from an optical sensor module (1) by means of a temperature sensor, - Calculation (S2) of an offset (5) of an objective focus plane (OE) and an image sensor plane (BE) by means of a control unit based on the temperature data, - Adaptation (S3) of a diopter number of the adjustable lens element (2) by means of the control unit to compensate for the offset (5). Procedure according to Claim 7 , characterized in that after the calculation of the offset (5) of the lens focus plane (OE) and the image sensor plane (BE) a suitable number of dioptres to compensate for the offset (5) is determined by means of the control unit. Procedure according to Claim 7 , characterized in that the number of diopters is determined by analyzing image data from the sensor module.

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