Camera system, method of positioning a lens group relative to an image sensor, and control unit

Abstract

The present application relates to an optical system comprising a probe for image sensor detection. The invention relates generally to an optical system comprising: a lens system comprising at least one movable lens; a lens housing accommodating the lens system and comprising an opening, the lens housing being attachable to an image sensor housing for an image sensor such that the at least one lens, the opening and the image sensor are arrangeable along an axis, the opening being between the at least one lens and the image sensor; a probe extending towards the opening and being fixed relative to the at least one lens; an actuation system configured to move the at least one lens along the axis relative to the opening and to move the probe parallel to the axis such that the probe reaches through the opening to a position where the image sensor is arrangeable; and a control system configured to control the actuation system to move the at least one lens and the probe and to detect that a movement of the at least one lens and the probe is stopped due to the probe hitting a surface that is fixed relative to the image sensor.

Description

TECHNICAL FIELD

[0001] The present invention relates generally to the field of camera surveillance, and in particular to optical systems comprising movable lenses. BACKGROUND

[0002] A typical camera system comprises an objective with several lenses that focus light onto an image sensor. The distance between the lenses and the image sensor can be varied to change the imaging focus or zoom setting of the camera system. This implies that it is important to have sufficient resolution in the movement of the lenses and to know the relative position between the lenses and the image sensor.

[0003] However, the distance between the lenses and the image sensor is often unknown or deviates during use of the camera system. This is due to, for example, manufacturing tolerances related to the production method used to produce the camera system, and / or due to distance changes caused by temperature variations. This can lead to various problems, such as focus deviation and inability to calibrate the lenses.

[0004] Therefore, there is a need for improvements in calibrating the position of lenses relative to the corresponding image sensor. SUMMARY

[0005] In view of the above and other drawbacks of the prior art, it is an object of the present invention to provide an improved optical system that at least alleviates some of the drawbacks of the prior art.

[0006] According to a first aspect of the present invention, there is provided an optical system comprising: a lens system comprising at least one movable lens; a lens housing accommodating the lens system and comprising an opening, the lens housing being attachable to an image sensor housing for an image sensor such that the at least one lens, the opening and the image sensor are arrangeable along an axis, the opening being between the at least one lens and the image sensor; a probe extending towards the opening and being fixed relative to the at least one lens; an actuation system configured to move the at least one lens along the axis relative to the opening and to move the probe parallel to the axis such that the probe reaches a position of the arrangeable image sensor through the opening; and a control system configured to control the actuation system to move the at least one lens and the probe and to detect that the movement of the at least one lens and the probe is stopped due to the probe hitting a surface fixed relative to the image sensor.

[0007] The present invention is based on the realization to mount the probe such that it moves together with the at least one lens and can reach and touch a surface fixed relative to the image sensor. By means of the probe, a relatively cost-effective and precise way of calibrating the position of the at least one lens is obtained.

[0008] The axis along which the at least one lens, the opening and the image sensor can be arranged is a virtual axis and is generally referred to as the optical axis, i.e. the axis along which light passes through the at least one lens and is focused onto the image sensor.

[0009] The image sensor generally comprises a matrix of light-sensitive pixels configured to sense light and convert it into a voltage signal. Image sensors are considered to be known per se and their operation will not be discussed herein. A surface fixed with respect to the image sensor should be interpreted as a surface fixed with respect to the active part of the sensor, which is the part comprising the pixels.

[0010] In one embodiment, the control system can be configured to infer that the position of the image sensor has been found when it is detected that the motion of the probe is stopped, and to move the at least one lens relative to the found position according to the predetermined distance between the at least one lens and the image sensor, thereby achieving the desired imaging setup. Thus, as soon as the probe hits the surface, the control system detects that the actuation system cannot move the at least one lens further and can infer that the probe has reached the surface. The position of the at least one lens is considered to be a known position relative to the image sensor from which the at least one lens can be moved according to the desired setup.

[0011] In one embodiment, the optical system can comprise a lens holder attached to the at least one lens, wherein the probe is attached to the lens holder. The lens holder is fixed relative to the respective lens and thus provides a suitable position to attach the probe.

[0012] In one embodiment, the probe and the lens holder can be made in a single piece. This advantageously eliminates tolerance errors that can occur if a separate probe is attached to a separate lens holder. For example, the probe and the lens holder can be formed in a single mold. As another example, the probe and the lens holder can be made from a single 3D printing process, or from a single workpiece in a milling process. Thus, the probe and the lens holder are preferably made from the same material.

[0013] In one embodiment, the surface can be a surface of the image sensor, wherein the probe is configured to hit the surface of the sensor when the image sensor housing is attached to the lens housing and the probe is moved to the image sensor position. In order to further eliminate error sources when determining the relative position between the at least one lens and the image sensor, it is advantageous if this surface is part of the image sensor itself.

[0014] In an embodiment, the surface can be an inactive part of the image sensor, wherein the probe is configured to reach the inactive part of the image sensor when the image sensor housing is attached to the lens housing and the probe is moved to the image sensor position. The inactive part of the image sensor can be located on a chip or die of the image sensor, adjacent to the pixels of the image sensor. The surface can be on a printed circuit board supporting the image sensor. In a possible implementation, the surface is an outer surface of a cover glass of the image sensor.

[0015] In an embodiment, the actuation system can comprise a motor for moving the at least one lens and an axle attached to the lens holder. The motor can be a stepper motor rotating the axle around its longitudinal axis. The connection between the axle and the lens holder is configured such that when the axle is rotated around the longitudinal axis, the lens holder is moved along the longitudinal axis of the axle.

[0016] In an embodiment, the probe can be elongated, wherein one end is configured to reach the position where the image sensor can be arranged when the at least one lens is moved towards the opening.

[0017] In an embodiment, the control system can be configured to receive an indication that the current imaging performance has deviated from a desired imaging setting, and in response, control the actuation system to move the at least one lens, and the control system can be configured to conclude that the position of the image sensor is found when a movement of the probe is detected to be impeded, and to move the at least one lens relative to the found position, thereby achieving the desired imaging setting. Thus, the optical system can advantageously be configured to actively recalibrate the position of the lens in response to a detected deviation.

[0018] In an embodiment, the optical system can comprise a plurality of lens groups and one probe for each lens group. Each lens group comprises at least one lens, and the respective actuation system moves the entire group as a single unit. Thus, all lenses of the group and the probe of the group are moved as one unit, fixed relative to each other. Advantageously, the position of each group can be calibrated individually.

[0019] According to a second aspect of the invention, there is provided a camera system comprising an optical system according to any one of the embodiments described herein, and an image sensor arranged in an image sensor housing removably attached to the lens housing. The camera system can further comprise the image sensor housing.

[0020] In an embodiment, the control system can be configured to find the position of the at least one lens relative to the image sensor by controlling the movement of the at least one lens to perform a calibration of the lens position when the camera system is started, and to use the position to achieve a desired imaging setting.

[0021] Further embodiments and effects obtained by the second aspect of the application are largely analogous to the above described first aspect of the application.

[0022] According to a third aspect of the application, there is provided a method for positioning a lens group relative to an image sensor, comprising moving at least one lens and a probe fixed relative to the at least one lens along an axis towards the image sensor, moving the probe out through an opening of a lens housing accommodating the at least one lens and the probe, detecting that movement of the at least one lens and the probe is stopped due to the probe hitting a surface fixed relative to the image sensor, and inferring that a position of the image sensor is found, and moving the at least one lens relative to the found position according to a predetermined distance between the at least one lens and the image sensor, thereby achieving a desired imaging setup.

[0023] Further embodiments and effects obtained by the third aspect of the application are largely analogous to the above description for the first and second aspects of the application.

[0024] According to a fourth aspect of the application, there is provided a control unit for controlling an actuation system of a moving lens group, and for performing steps of the method described herein.

[0025] Further embodiments and effects obtained by the fourth aspect of the application are largely analogous to the above described first, second and third aspects of the application.

[0026] Further features and advantages of the present application will become apparent when considered in light of the following detailed description and accompanying drawings. It will be appreciated that different features of the application can be combined in different embodiments without departing from the scope of the application. BRIEF DESCRIPTION OF DRAWINGS

[0027] Various aspects of the application will become apparent when considered in light of the following detailed description and accompanying drawings, in which:

[0028] Figure 1 Conceptually illustrating a camera system comprising a lens housing and an image sensor housing according to embodiments of the application;

[0029] Figure 2A Conceptually illustrating an optical system in a first position according to embodiments of the application;

[0030] Figure 2B Conceptually illustrating an optical system in a second position according to embodiments of the application;

[0031] Figure 2C Conceptually illustrating an optical system in a third position according to embodiments of the application;

[0032] Figure 3 conceptually illustrating an optical system according to an embodiment of the application; and

[0033] Figure 4 is a flowchart of method steps according to an embodiment of the application. DETAILED DESCRIPTION

[0034] The present application will now be described more fully hereinafter with reference to the accompanying drawings, in which current preferred embodiments of the application are shown. The application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of thorough and complete disclosure of the application and completely and completely convey the scope of the application to those skilled in the art. Like reference numerals refer to like elements throughout.

[0035] Reference is now made to the drawings, and in particular the following figures: Figure 1 , shows a camera system 100. The camera system 100 comprises an optical system 1 comprising a housing, herein referred to as a lens housing 5. The optical system 1 further comprises a lens system 7 housed in the lens housing 5.

[0036] Furthermore, the camera system 100 comprises an image sensor 13 arranged in an image sensor housing 11, which can be removably attached to the lens housing 5. When the camera system 100 is imaging a scene, light enters through an aperture 12 in the lens housing 5, is redirected by the lens system 7 according to the desired imaging settings, e.g. zoom or focus settings, before being focused onto the image sensor 13. The light path through the lens system 7, via an opening 9 in the lens housing 5, and finally via an opening 10 in the image sensor housing 11 to the image sensor 13 is along an axis 15, which is often referred to as the optical axis of the camera system 100. The opening 9, the lens system 7 and the image sensor 13 are located on the optical axis 15, with the opening 9 located between the lens system 7 and the image sensor 13. The opening 10 of the image sensor housing 11 is located on the optical axis 15 between the lens system 7 and the image sensor 13.

[0037] A common problem in conventional cameras is that it is difficult to know the distance between the lens and the image sensor with high precision due to tolerances in the manufacturing or material expansion due to temperature fluctuations, for example. The distance between the lens surface closest to the image sensor and the image plane is referred to as the back focal length and is important for imaging settings such as focus and zoom. In order to more accurately determine or calibrate the distance between the image sensor and the lens, the inventors have come up with a probe, which will be discussed in more detail below.

[0038] Figure 2AAn embodiment of the optical lens system 7 of the optical system 1 is conceptually illustrated. The lens system 7 comprises at least one movable lens 3. As described with reference to Figure 1 The lens system 7 is housed in a lens housing 5 comprising an opening 9. The lens housing 5 is attachable to an image sensor housing 11 housing an image sensor 13, such that the at least one lens 3, the opening 9 and the image sensor 13 are arrangeable along an axis 15, the opening 9 being located between the at least one lens 3 and the image sensor 13.

[0039] The lens system 7 comprises a probe 17 extending towards the opening 9 and being fixed relative to the at least one lens 3. In this example embodiment, the lens 3 is attached to a lens holder 30 and the probe 17 is attached to the lens holder 30. This ensures that the relative position of the probe 17 relative to the lens 3 is fixed. In a preferred embodiment, the probe 17 and the lens holder 30 are made in a single piece. For example from the same workpiece in a milling process, in a single mold, or from a single 3D printing step or process. The probe 17 can for example be made of a plastic or metal material. The lens holder 30 is slidably arranged on a guide rod 36 guiding the movement of the lens holder 30.

[0040] Furthermore, the optical system 1 comprises an actuation system 19 configured to move the at least one lens 3 along the axis 15 relative to the opening 9 and to move the probe 17 parallel to the axis 15. The probe 17 can reach the position of the arrangeable image sensor 13 in its housing 11 through the opening 9. The probe 17 is preferably elongated, one end 37 of the probe 17 being configured to reach the position of the arrangeable image sensor 13 when the at least one lens 3 is moved towards the opening 9 and the probe 17 reaches the position of the image sensor 13 in its housing 11 through the opening 9.

[0041] The optical system 1 further comprises a control system 21 configured to control the actuation system 19 to move the at least one lens 3 and the probe 17. The control system 21 is further configured to detect that the movement of the at least one lens 3 and the probe 17 is stopped due to the probe 17 hitting a surface 23, 25 fixed relative to the image sensor 13.

[0042] Once the control system 21 detects that the movement of the probe 17 is stopped, the control system 21 infers that the position of the image sensor 13 is found. The control system 21 can then move the at least one lens relative to the found position according to a predetermined distance between the at least one lens and the image sensor, thereby achieving the desired imaging setup. Even though the absolute distance between the lens 3 and the image sensor can be determined with the known length of the probe 17, it is more beneficial to find the relative distance and from this found position the lens 3 can be moved a known distance, thereby achieving the desired imaging setup.

[0043] When the control system 21 concludes that the position of the image sensor 13 is found, the distance between the image sensor and the lens surface closest to the image sensor can be determined from the known length of the probe and the position of the surface it touches. This measurement is referred to as a back focus measurement.

[0044] The at least one lens 3 can be moved in two different ranges. An optical range R1 and a mechanical range R2, which only differ in Figure 2A is conceptually illustrated and is not necessarily drawn to scale. The actual ranges will depend on the specific implementation at hand. The optical range R1 is the range for adjusting the camera optical settings. For example, the at least one lens 3 is movable within the optical range R1 to adjust settings such as focus and zoom. The mechanical range R2 is larger than the optical range R1 and is the sum of the optical range R1 and an additional distance, which is typically used to fill to make sure that the lens does not move into any physical wall within the housing. To allow movement of the probe 17 to reach the surface 23, 25, the mechanical range is advantageously increased by a small range, such as tens of millimeters. This additional range is used to move the probe so that it can touch the surface 23 or 25, depending on the implementation, so that a back focus measurement can be performed. The camera 100 is typically not used during the back focus measurement, because the lens is outside the optical range. However, the back focus measurement typically only takes a few seconds.

[0045] Thus, starting from the first position in Figure 2A , the control system 21 can control the actuator system 19 to move the at least one lens 3 and the probe to the second position shown in Figure 2B , where the probe has hit the surface 25, which is preferably the surface of the image sensor 13. Thus, when the image sensor housing 11 is attached to the lens housing 5 and the probe 17 is moved to the image sensor position, the end 37 of the probe is configured to hit the surface 25 of the image sensor 13. From this position, the control system 21 can move the at least one lens 3, which can be referred to as the lens group 3, to a position that realizes the desired imaging settings, as conceptually illustrated in Figure 2C .

[0046] Preferably, the surface 25 that the probe end 37 hits is an inactive portion 33 of the image sensor 13, not including any pixels 34a of the active portion 34. For example, a side frame, edge region or unused portion of the sensor die can be used as the inactive portion 33. Preferably, the surface 23 is a cover glass of the image sensor. However, it is also conceivable that the probe 17 is configured to reach and hit another surface that is fixed relative to the image sensor, such as a surface 23 of a printed circuit board 40 that supports the image sensor 13. The surface 25 of the inactive portion 33 can be in the same plane as the pixels 34a. For illustrative purposes, the pixels 34a are conceptually shown and denoted. The size of the pixels is not to scale.

[0047] The actuation system 19 can be an electric motor 19 connected to the wheel axle 35. For example, the wheel axle 35 is threaded, with the threads engaging threaded holes of the lens holder 30. The electric motor 19 is configured to cause the wheel axle 35 to rotate about its axis, whereby the threaded connection causes the at least one lens 3 to move along the optical axis 15 that is parallel to the axis of the wheel axle 35.

[0048] The electric motor 19 can be a stepper motor. Once the position of the image sensor has been found by using the probe 17, the control system 21 can be configured to operate the stepper motor to run a predefined number of steps, thereby achieving the desired imaging setting.

[0049] The calibration of the lens position can be performed in different situations. For example, the control system 21 can be configured to, upon start-up of the camera system 100, find the position of the at least one lens 3 relative to the image sensor 13 by controlling the motion of the at least one lens 3 using the probe motion discussed herein to perform a calibration probe of the lens position, and use the position to achieve the desired imaging setting.

[0050] As another example, the control system 19 can be configured to receive an indication that the current imaging performance has deviated from the desired imaging setting. The deviation can be detected from feedback from the image sensor, i.e. that the acquired images are out of focus. In response, the control system 19 can control the actuation system 19 to move the at least one lens 3 towards the image sensor 13, and when it is detected that the motion of the probe 19 is stopped, it is inferred that the position of the image sensor has been found, and the at least one lens 3 is moved relative to the found position, thereby achieving the desired imaging setting.

[0051] As another example, if it is known that at the location of the camera system 100 a high temperature difference occurs that can cause a defocus, the control system 19 can in response control the actuation system 19 to move the at least one lens 3 towards the image sensor 13 to find the image sensor 13 and to move the at least one lens 3 relative to the found position to achieve the desired imaging setup. Material thermal expansion can be corrected this way. The control system 19 can receive a signal indicative of the temperature difference from an external sensing system or from a temperature sensing system of the camera 100 itself.

[0052] It will be appreciated that the at least one lens 3 can comprise a set of lenses.

[0053] Reference is now made to Figure 3 The optical system 1 can comprise a plurality of lens sets 3, 45 and one detector 17, 47 for each lens set. In the example embodiment, two lens sets are shown, but the present invention is equally applicable to any number of lens sets and one detector for each lens set.

[0054] In Figure 3 The second detector 47 is connected to a lens holder 49 of the second lens set 45. The second lens set is arranged further away from the opening 9 along the optical axis 15 in the lens housing 5 compared to the first lens set 3. The second detector 49 can be slidably passed through a through hole of the lens holder 30 of the first lens set 3. The movement of the second lens set 45 and the second detector 47 is controlled by the control system 21. The control system 21 is configured to control an actuation system, e.g. a motor 19, dedicated to the second lens set 45 and the detector 47. Thus, the second lens set 45 and the second detector 47 can be moved independently of the first lens set 3 and the first detector 17 and vice versa, thereby independently calibrating their positions. The control system 21 can be provided as a single control system comprising a single control unit or separate control systems 21 can be provided to control the respective actuation systems 19.

[0055] The control system 21 can be provided as a control unit for controlling the actuation system 19 for moving the lens set.

[0056] Figure 4 is a flowchart of method steps according to an embodiment of the present invention.

[0057] According to step S102, the control unit is configured to move the at least one lens 3 and the detector 17 fixed relative to the at least one lens 3 along the axis 15 towards the image sensor 13. The detector 17 is moved out through the opening 9 of the lens housing 5 accommodating the at least one lens 3 and the detector 17.

[0058] According to step S104, the control unit detects that the movement of the at least one lens 3 and the detector 17 is stopped due to the detector 17 hitting the surface 23, 25 which is fixed relative to the image sensor 13.

[0059] According to step S106, the control unit concludes that the position of the image sensor 13 is found.

[0060] According to step S108, the control unit controls the actuator system 19 to move the at least one lens 3 relative to the found position according to a predetermined distance between the at least one lens 3 and the image sensor 13, thereby achieving the desired imaging setting.

[0061] The control unit comprises a microprocessor, microcontroller, programmable digital signal processor or another programmable device. The control unit can also or instead comprise an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device, or a digital signal processor. Where the control unit comprises a programmable device such as the microprocessor, microcontroller or programmable digital signal processor mentioned above, the processor can further comprise computer executable code that controls operation of the programmable device.

[0062] The control functionality of the present disclosure can be implemented using existing computer processors, or through custom computer processors incorporated for this or another purpose for a suitable system, or through a hard-wired system. Embodiments within the scope of the present disclosure include program products comprising machine-readable media for carrying or having machine-executable instructions or data structures stored thereon. Such machine-readable media can be any available media that can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer or other machine with a processor. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a machine, the machine

[0063] Although the diagrams can show a sequential order, the order of the steps can differ from what is described. Also, two or more steps can be performed concurrently or with partial concurrence. Such variation will depend on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the disclosure. Likewise, software implementations could be accomplished with standard programming techniques with rule based logic and other logic to accomplish the various connection steps, processing steps, comparison steps and decision steps. Also, even though the description has been described with reference to particular embodiments, those skilled in the art will understand that various modifications can be made and equivalents can be substituted for elements thereof without departing from the scope of the disclosure.

[0064] Further, variations to the disclosed embodiments can become apparent to those of ordinary skill in the art, once the disclosure is fully appreciated and implemented. Further, in the claims, the phrase "comprising" does not exclude the presence of other elements or additional steps. Furthermore, the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

1. A camera system comprising: an image sensor arranged in an image sensor housing; a lens system comprising at least one movable lens; a lens housing accommodating the lens system and comprising an opening, the lens housing being removably attached to the image sensor housing such that the at least one lens, the opening and the image sensor are arranged along an optical axis, the opening being between the at least one lens and the image sensor; a probe extending towards the opening and being fixed relative to the at least one lens; characterized in that: an actuation system configured to move the at least one lens along the optical axis and to move the probe parallel to the optical axis relative to the opening such that the probe reaches a position where the image sensor is arranged through the opening; and a control system configured to control the actuation system to move the at least one lens and the probe and to detect that the motion of the probe is stopped due to the probe hitting a surface of the image sensor.

2. The camera system of claim 1, wherein, The control system is configured to conclude that the position of the image sensor is found when the motion of the probe is detected to be stopped and to move the at least one lens relative to the found position according to a predetermined distance between the at least one lens and the image sensor to a position where a desired imaging setting is achieved.

3. The camera system of claim 1, comprising a lens holder attached to at least one lens, wherein, The probe is attached to the lens holder.

4. The camera system of claim 3, wherein, The probe and the lens holder are made in one piece.

5. The camera system of claim 4, wherein, The probe and the lens holder are formed in a single mold.

6. The camera system of claim 1, wherein, The surface is an inactive part of the image sensor, wherein the probe is configured to reach the inactive part of the image sensor when the image sensor housing is attached to the lens housing and the probe is moved to the image sensor position.

7. The camera system of claim 1, wherein, The actuation system comprises a motor for moving the at least one lens and an axle attached to a lens holder.

8. The camera system of claim 1, wherein, The probe is elongated, wherein one end is configured to reach the position where the image sensor is arrangeable when the at least one lens is moved towards the opening.

9. The camera system of claim 1, wherein, The control system is configured to receive an indication that a current imaging performance has deviated from a desired imaging setting and in response to control the actuation system to move the at least one lens and to conclude that the position of the image sensor is found when the motion of the probe is detected to be stopped and to move the at least one lens relative to the found position according to a predetermined distance between the at least one lens and the image sensor to a position where a desired imaging setting is achieved.

10. The camera system according to claim 1, comprising a plurality of lens groups and one probe for each lens group.

11. The camera system of claim 1, wherein, The control system is configured to find the position of the at least one lens relative to the image sensor by controlling the movement of the at least one lens upon starting the camera system to perform a calibration of the lens position and to move the at least one lens to a position achieving a desired imaging setting relative to the found position according to a predetermined distance between the at least one lens and the image sensor.

12. A method for positioning a lens group relative to an image sensor, comprising: moving at least one lens along an optical axis and moving a probe fixed relative to the at least one lens parallel to the optical axis towards an image sensor, the probe being moved out through an opening of a lens housing accommodating the at least one lens and the probe; characterized in that: detecting that the movement of the at least one lens and the probe is stopped due to the probe hitting a surface of the image sensor, inferring that the position of the image sensor is found, and moving the at least one lens to a position achieving a desired imaging setting relative to the found position according to a predetermined distance between the at least one lens and the image sensor.

13. A control unit for controlling an actuation system for moving a lens group and for performing the steps according to claim 12.

Images