Electromechanical shutter device for a thermal imaging camera with a rocker as shutter blade
Patent Information
- Application Number
- EP2024715523
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-03-29
- Filing Date
- 2024-03-26
- Publication Date
- 2026-02-11
AI Technical Summary
Existing shutter devices for thermal imaging cameras face challenges in miniaturization due to requirements for low heat generation, long operating time, wide temperature range, and sufficient drive torque, particularly when using motors with low drive torque, which limits their compatibility with miniaturization efforts.
An electromechanical shutter device with a rocker-shaped shutter blade, featuring a motor shaft, a first spur gear, and a second spur gear that pivots the rocker arm between release and closed positions, allowing for efficient operation with motors of relatively low drive torque, and is designed to be compact and lightweight.
The solution enables reliable operation of the shutter device with low drive torque motors, enhancing compatibility with miniaturization efforts while maintaining the necessary angular speed and torque for reliable function, and ensures the closure sheet has uniform temperature and emissivity for accurate dark frame calibration.
Smart Images
Figure EP2024058067_03102024_PF_FP_ABST
Abstract
Description
[0001] Electromechanical shutter device for a thermal imaging camera with a swing arm as shutter blade
[0002] The invention relates to an electromechanical shutter device for a camera, in particular a thermal imaging camera, for use in various types of photographic and thermal imaging devices, as well as devices for measuring the image quality of lenses and for calibrating image sensors. The invention also relates to a thermal imaging camera with an electromechanical shutter device.
[0003] Shutter devices are used in conjunction with cameras to interrupt the optical beam path when necessary. A major challenge in the design of such shutter devices is the ongoing miniaturization of cameras, coupled with increasing requirements regarding minimal heat generation, operating time, service life, operating temperature range, manufacturing costs, and so on. Common solutions include iris diaphragms, focal plane shutters, or pivoting or guided shutter blades driven electromagnetically or by a motor.
[0004] In infrared or thermal imaging applications, it is necessary to perform a so-called "dark frame calibration" at specific intervals to correct the temporal drift of the individual pixel signal values that often occurs during camera operation. This involves closing a shutter device and positioning a shutter blade in front of the image sensor so that its receiving surface is completely shielded from the thermal radiation emanating from the scene and all sensor pixels face the shutter blade. The shutter blade must have a homogeneous temperature and a homogeneous emissivity that is as close to one as possible. The "dark" image provided by the image sensor during this time is then used to offset the individual pixel signal values. In radiometric cameras, such a shutter device also serves as a temperature reference to improve measurement accuracy.
[0005] WO2017 / 204946 A1 discloses a camera shutter device comprising a motor, a spur gear connected to the motor, and a shutter blade rigidly connected to a spur gear segment. The spur gear segment meshes with the spur gear to pivot the shutter blade between two end positions (release position and closed position) over an angular range. The rotational movement of the motor is transmitted to the shutter blade in the transmission ratio of the spur gear formed by the spur gear and the spur gear segment. The shutter blade is moved over an angular range from one end position to the other depending on the angle of rotation through which the motor shaft is rotated in alternating directions.
[0006] DE 10 2010 023 167 B4 discloses a thermal imaging camera with a fast electromechanical shutter device. Here, a motor is connected to a shutter blade via a crank. The crank is mounted on the motor shaft and has a pin at its free end that engages a slotted hole in the shaft of the shutter blade (hereinafter also referred to as the shutter blade). The shutter blade and the shaft form a rocker. The crank and the rocker together form a crank loop. The pin and the slot form a sliding joint.
[0007] The crank slider can be designed as a rotating gear, allowing the crank to complete full rotations, and the motor shaft, while maintaining the same direction of rotation of the motor, alternately assumes the two angular positions in which the locking blade is in one of the end positions. The rocker is pivoted back and forth across the pivot angle between the two end positions, with the motor shaft being rotated through two different angles.
[0008] The crank slider can also be designed as a non-rotating gear, so that it has two dead center positions that serve as end positions, or the rotation of the crank is limited by stops. The direction of rotation of the motor must then be reversed to pivot the locking blade from one end position to the other. It is advantageous for the kinematics of the locking blade if the motor shaft covers the same angle of rotation at all times.
[0009] Stopping in the end positions can be achieved by controlling the motor alone or can be supported by additional damping stops.
[0010] The dimensioning of the shutter device is dependent on the space provided for it in the thermal imaging camera and the cross-sectional size of the beams reaching the sensor in the plane in which the shutter blade is pivoted into the beam path. The smaller the distance between the motor shaft and the pivot axis, the greater the angle of rotation of the crank and the pivot angle of the rocker must be so that the beams have a free passage in one end position and the sensor has a full-frame view of the shutter blade in the other end position. In a shutter device according to the aforementioned DE 10 2010 023 167 B4, the angular speed at which the shutter blade is pivoted between the end positions, and thus the pivoting duration of the shutter blade, are adjusted solely via the angular speed or the speed of the motor.Normally, a certain maximum swivel duration must be maintained for the swiveling of the locking blade, and at the same time, certain minimum requirements apply to the torque associated with the swiveling of the locking blade to ensure sufficiently reliable operation of the locking device. This places quite strict constraints on the selection of a suitable motor. In particular, the locking device according to DE 10 2010 023 167 B4 cannot be operated with a motor that can ensure sufficient angular velocities but cannot provide sufficient drive torque. This can be a disadvantage with regard to miniaturization efforts (and correspondingly small motors).
[0011] It is the object of the invention to provide a shutter device for a thermal imaging camera which can be reliably operated with motors having a relatively low drive torque and is thus also more compatible with miniaturization.
[0012] It is also the object of the invention to provide a thermal imaging camera with a camera shutter device that can be reliably operated with motors with a relatively low drive torque and is thus also more compatible with miniaturization.
[0013] The object is achieved according to the invention for a thermal imaging camera by an electromechanical shutter device, comprising a carrier having an opening, an electric motor having a motor shaft and being fixed to the carrier, and a shutter blade associated with the opening, which shutter blade forms a rocker with a shaft formed thereon, wherein the rocker is mounted on a first axis of rotation fixed to the carrier parallel to the motor shaft, is pivotable by means of a crank having a pin about the first axis of rotation over a pivot angle range between a release position and a closed position of the shutter blade, and has an elongated hole in the shaft arranged opposite the shutter blade with respect to the first axis of rotation, with which the pin is engaged, wherein a first spur gear is fastened to the motor shaft, the crank is formed by a second spur gear,which is mounted on a second axis of rotation arranged parallel to the motor shaft in the carrier, the second spur gear is rotatable about the second axis of rotation over a defined angle of rotation range and the first spur gear is arranged in meshing engagement with the second spur gear.
[0014] In a preferred aspect, the opening has a rectangular shape and the elongated hole is a straight elongated hole which, in the release position and the closing position, runs longitudinally parallel to an edge of the opening.
[0015] Advantageously, the first rotation axis is arranged at a corner of the opening. Particularly advantageously, the closure leaf has a rectangular shape. Alternatively, it is advantageous if the closure leaf, deviating from a rectangular shape, has a circular-arc-shaped body edge and a circular-arc-shaped slideway is provided on the carrier, along which the closure leaf slides when pivoting between the closed position and the release position. In both cases, the pivot angle is preferably 90°.
[0016] Ideally, the rotation angle range is 270° or 90°, just like the swivel angle range.
[0017] To reduce weight, it may be advantageous for the second spur gear to be reduced to a spur gear segment with teeth extending over an angular range of 270° or 90°. Optionally, the first spur gear may also be reduced to a spur gear segment with teeth extending over an angular range of 270° or 90°, if a 1:1 gear ratio is present between the first and second spur gears. With a reduction ratio, the angular range of the teeth must be adjusted accordingly, or the segmentation may be omitted.
[0018] A stepper motor is preferably used as the motor.
[0019] The object is further achieved by a thermal imaging camera which contains an electromechanical locking device according to the invention.
[0020] Advantageously, the thermal imaging camera comprises a housing on which the carrier of the closure device represents a front plate, the opening of the closure device represents a first beam passage opening, and a front cover covering the front plate with a second beam passage opening arranged coaxially to the first beam passage opening is provided, wherein the first spur gear, the second spur gear and the rocker of the closure device are arranged between the front plate and the front cover.
[0021] It is very advantageous that the second axis of rotation is fixed in the front cover and the motor shaft is mounted.
[0022] For a particularly small design, the front panel is rectangular and the motor shaft, the second rotation axis and the first rotation axis are arranged along a diagonal of the front panel.
[0023] The invention will be explained in more detail below using exemplary embodiments and drawings. These show: Fig. 1 a shows an exemplary embodiment of a closure device in which the closure leaf is in a closed position,
[0024] Fig. 1 b shows the closure device according to Fig. 1 a, in which the closure leaf is in an intermediate position,
[0025] Fig. 1c shows the closure device according to Fig. 1 a, in which the closure leaf is in a release position,
[0026] Fig. 2 a thermal imaging camera with a shutter device according to Fig. 1 a-1c without front cover,
[0027] Fig. 3 a thermal imaging camera with a shutter device according to Fig. 1 a-1c with front cover and
[0028] Fig. 4 shows a thermal imaging camera with a shutter device according to a second embodiment, without a front cover.
[0029] A camera shutter device according to the invention, as shown in Figs. 1a-1c, essentially contains in all embodiments a carrier 2 with an opening 21, an electric motor 3 fixed to the carrier 2 with a motor shaft 31, a spur gear 6 seated on the motor shaft 31, a crank designed as a second spur gear 7 with a pin 4, and a shutter blade 51 which forms a rocker 5 with a shaft 52 formed thereon opposite a first axis of rotation 53. Furthermore, the camera shutter device contains a second axis of rotation 8 which is fixedly arranged in the carrier 2 parallel to the motor shaft 31 and rotatably supports the second spur gear 7 with the pin 4.
[0030] The rocker arm 5 is mounted on the first pivot axis 53 and can pivot over a pivot angle range between a release position (see Fig. 1c) and a closed position (see Fig. 1a). The second spur gear 7 is rotatably mounted on the second pivot axis 8 over a defined pivot angle range.
[0031] In the shaft 52 of the rocker 5, more precisely, in a region of the shaft 52 opposite the shutter blade 51 with respect to the first rotation axis 53, an elongated hole 521 is formed, angled to the center of the surface of the shutter blade 51, with which the pin 4 of the second spur gear 7 engages. The shaft 52 is preferably aligned to surround the elongated hole 521 in the same way as the shutter blade 51. The first spur gear 6 and the second spur gear 7 are arranged to mesh with one another. All of the following exemplary embodiments of a camera shutter device according to the invention have the aforementioned features.
[0032] The geometric shape and size of the opening 21 are adapted to the operating conditions of the camera shutter device. This means that it is tied to the shape and size of a beam of rays that is to pass through the opening 21 at the position of the opening 21 and that is to be shaded in the shutter position of the shutter blade 51. In the case of the arrangement directly in front of the receiving surface of an image sensor 11 (only shown in Fig. 4), the opening 21 corresponds to the shape and size of the receiving surface of the image sensor 11.
[0033] Image sensors are typically rectangular, which is why the opening 21 is also typically rectangular. Therefore, in order to completely cover the opening 21, the closure leaf 51 must circumferentially cover the opening 21 in the closed position, at least with a slight oversize. Advantageously, the closure leaf 51 is also rectangular, with a slight oversize relative to the opening 21, and thus has the smallest possible weight for a given thickness. In a special embodiment, the shape of the closure leaf 51 can also deviate from the rectangular shape, as described later in relation to Fig. 4.
[0034] In the case of the rectangular shape of the opening 21, but independent of the shape of the closure leaf 51, the elongated hole 521 is designed in a first exemplary embodiment as a straight elongated hole 521 in the shaft 52, which in the release position and the closed position runs longitudinally parallel to one of the edges 211 of the opening 21. The pin 4 guided in the elongated hole 521 therefore has a particularly good locking effect in the release position and the closed position, where the elongated hole 521 forms a locking mechanism with the pin 4. In a conventional spatial arrangement of the closure device, the elongated hole 521 is arranged perpendicularly in the release position and orthogonally thereto in the closed position. The closure leaf 51 does not have to be held in the release position or the closed position by the drive torque of the electric motor 3 or other measures.However, an additional current supply to the electric motor 3 during the closure time and possibly also during the release time increases the shock resistance, ie the closure blade 51 is held securely in the release position or the closed position even if vibrations or shocks act on the closure device.
[0035] By arranging the first pivot axis 53 at a corner of the opening 21 and mounting it in the rocker arm 5 adjacent to the closure blade 51 in the transition to the shaft 52, the shape and size of the closure blade 51 can be adapted to the opening 21 such that it is only marginally larger than the opening 21. With this arrangement of the first pivot axis 53, the pivoting path between the release position and the closed position is minimal, and the space required for the closure blade 51 in the release position is also minimal, both of which facilitate miniaturization.
[0036] In a special second embodiment of the closure leaf 51, as shown in Fig. 4, the closure leaf 51, deviating from a rectangular shape, has a circular-arc-shaped body edge 511. This lies outside a rectangular surface area which corresponds to the opening 21 with a slight oversize. In this embodiment, a circular-arc-shaped slideway 22 is provided on the carrier 2, on which the closure leaf 51 slides with its circular-arc-shaped body edge 511 when pivoting between the closed position and the release position. The closure leaf 51 is thus given lateral support, whereby the closure leaf 51 can be designed to be less rigid and thus thinner than if it were only connected to the first rotation axis 53.
[0037] The first spur gear 6 and the second spur gear 7 are dimensioned such that the angular velocity of the electric motor 3 and thus of the first spur gear 6 is transmitted to the second spur gear 7 with a selected reduction ratio, for example with a reduction ratio of 1:2. A further reduction of the angular velocity of the electric motor 3 takes place by converting the rotation angle range of the second spur gear 7 of 270° around the second rotation axis 8 into a 90° pivot angle range of the rocker arm 5 around the first rotation axis 53, for example with an average reduction ratio of 1:3.
[0038] Alternatively, the reduction ratio can also be transmitted to the rocker 5 by the second spur gear 7 with an (averaged) 1:1 transmission ratio. In this case, for the same pivoting movement of the rocker 5 from the closed position to the release position, the rotation - in contrast to the drive diagram in Fig. 1 a to 1 c - is brought about by a negative direction of rotation of the second spur gear 7 (clockwise rotation), as shown in Fig. 2. As a result, the pivoting angle range of 90° is already established on the locking leaf 51 after the rotation of the second spur gear 7 over a rotation angle range of 90°.
[0039] In the first and second embodiments of the closure blade 51, the second spur gear 7 can therefore have a rotation angle range of 270° or 90° in order to set the pivot angle range of 90° in the same way for the closure blade 51.
[0040] In further embodiments, in order to reduce the mass of the closure device, the second spur gear 7 is reduced to a spur gear segment which has a toothing over an angular range of 270° (not shown) or 90° (only shown in Fig. 2), and optionally also the first spur gear 6 is reduced to a spur gear segment which then also has a toothing over an angular range of 270° or 90° if a 1:1 ratio is present between the first spur gear 6 and the second spur gear 7.
[0041] With a reduction ratio from the first spur gear 6 to the second spur gear 7, the toothed spur gear segment of the first spur gear 6 must be adapted to a larger angular range than the toothing of the second spur gear 7 - or the segmented toothing of the first spur gear 6 is omitted. An example segmentation of the spur gears 6 and 7 is shown in Fig. 2 for a reduction ratio of 1:2, whereby the spur gear segment of the second spur gear 7, which is toothed over an angular range of 90°, requires a gear segment over an angular range of 180° on the first spur gear 6. However, if the second spur gear 7 has a toothing in the angular range of 270° and / or the reduction ratio exceeds a ratio of 1:2 (neither shown), segmentation of the toothing of the first spur gear 6 would most likely be omitted.
[0042] All embodiments can advantageously incorporate a stepper motor as the electric motor 3. It is easier to operate than, for example, a servo motor, which must be adjusted to a desired position. Any stepping losses of the stepper motor are not detrimental here, since the crank pin 4 is rotated against a mechanical stop in each of the two end positions. Optionally, an additional end-position safety device, e.g., with permanent magnets, can be provided.
[0043] All of the aforementioned embodiments and combinations thereof can be part of a thermal imaging camera 1 or a thermal imaging camera module.
[0044] An exemplary embodiment of a thermal imaging camera 1 with a shutter device according to the invention is explained below with reference to Fig. 2 and Fig. 3.
[0045] The thermal imaging camera 1 comprises a housing 9, on which the carrier 2 of the closure device represents a front plate 91 and the opening 21 forms a first beam passage opening 911 (only clearly visible in Fig. 1b and 1c).
[0046] It further includes a front cover 92 covering the front plate 91 with a second beam passage opening (not shown) arranged coaxially with the first beam passage opening 911. The first spur gear 6, the second spur gear 7, and the rocker 5 are arranged between the front plate 91 and the front cover 92. Thus, the closure blade 51 is shielded from heat sources located inside and possibly also outside the housing 9, or at least not directly exposed to the heat in question. At the same time, in the release position, the closure blade 51 is located in a narrow space formed between the front plate 91 and the front cover 92, in which no or at most very slight local temperature gradients arise, thus preventing the closure blade 51 from experiencing any locally varying heating, which would severely impair its suitability for offset correction and possibly also its suitability as a temperature reference.
[0047] In an advantageous embodiment of the thermal imaging camera 1, as shown in Fig. 3, the second rotation axis 8 is fixed in the front cover 92, and the motor shaft 31 is mounted in the front cover 92. Due to the two-sided fixation of the rotation axis 8 and the two-sided mounting of the motor shaft 31, the locking device is better anchored within the thermal imaging camera 1 and can withstand greater mechanical loads.
[0048] A particularly advantageous embodiment for a thermal imaging camera 1 results from a substantially rectangular design of the front plate 91 according to Fig. 2, in which the arrangement of the motor shaft 31, the second axis of rotation 8 and the first axis of rotation 53 takes place along a diagonal 912 of the front plate 91. This type of arrangement of the axes of rotation is more clearly visible in Fig. 1c, because the axes of the shutter blade 51 (first axis of rotation 53), the second spur gear 7 (with second axis of rotation 8) and the first spur gear 6 (with motor shaft 31) are shown in a plan view positioned exactly along the diagonal 912. This makes the shutter device very compact and also ensures that its electric motor 3 is not only separated from the shutter blade 51, but is also arranged as far as possible away from the image sensor 11 (only shown in Fig. 4) when the maximum radial extension of the interior of the housing 9 is fully utilized.
[0049] List of reference symbols
[0050] 1 thermal imaging camera
[0051] 11 Image sensor
[0052] 2 carriers
[0053] 21 Opening
[0054] 211 Edge of the opening
[0055] 22 Slideway
[0056] 3 electric motor
[0057] 31 Motor shaft
[0058] 4 cones
[0059] 5 swingarm
[0060] 51 Cover sheet
[0061] 511 circular arc-shaped body edge (of the closure blade)
[0062] 52 shaft
[0063] 521 slot
[0064] 53 first axis of rotation
[0065] 6 first spur gear
[0066] 7 second spur gear
[0067] 8 second axis of rotation
[0068] 9 housings
[0069] 91 Front panel
[0070] 911 first jet passage opening
[0071] 912 diagonal
[0072] 92 front cover
Claims
Patent claims 1. An electromechanical shutter device for a thermal imaging camera, comprising a support (2) having an opening (21), an electric motor (3) fixedly arranged to the support (2) with a motor shaft (31), and a shutter blade (51) associated with the opening (21) and forming a rocker (5) with a shaft (52) formed thereon, wherein the rocker (5) is mounted on a first axis of rotation (53) fixedly arranged on the support (2) parallel to the motor shaft (31), is pivotable about the first axis of rotation (53) over a pivot angle range between a release position and a closed position of the shutter blade (51) by means of a crank with a pin (4), and has an elongated hole (521) in the shaft (52) opposite the shutter blade (51) with respect to the first axis of rotation (53), with which the pin (4) is engaged, characterized in that - a first spur gear (6) is mounted on the motor shaft (31), - the crank is formed by a second spur gear (7) which is mounted on a second axis of rotation (8) arranged parallel to the motor shaft (31) in the carrier (2), - the second spur gear (7) is rotatable about the second axis of rotation (8) over a defined angle of rotation range and - the first spur gear (6) is arranged to mesh with the second spur gear (7).
2. Electromechanical locking device according to claim 1, characterized in that the opening (21) has a rectangular shape and the elongated hole (521) is a straight elongated hole (521) which, in the release position and the closed position, runs in the longitudinal direction parallel to an edge (211) of the opening (21).
3. Electromechanical locking device according to claim 1 or 2, characterized in that the first axis of rotation (53) is arranged at a corner of the opening (21).
4. Electromechanical locking device according to claim 3, characterized in that the locking leaf (51) has a rectangular shape.
5. Electromechanical locking device according to claim 3, characterized in that the locking leaf (51) has a circular arc-shaped body edge, deviating from a rectangular shape, and a circular arc-shaped slideway (22) is provided on the carrier (2), on which the locking leaf (51) slides when pivoting between the closed position and the release position.
6. Electromechanical locking device according to one of claims 1 to 5, characterized in that the rotation angle range is 270° or 90° and the pivoting angle range is 90°.
7. Electromechanical locking device according to claim 6, characterized in that the second spur gear (7) is reduced to a spur gear segment which has a toothing over an angular range of 270°.
8. Electromechanical locking device according to claim 6, characterized in that the second spur gear (7) is reduced to a spur gear segment which has a toothing over an angular range of 90°.
9. Electromechanical locking device according to one of claims 1 to 8, characterized in that the motor is a stepper motor.
10. Thermal imaging camera with an electromechanical shutter device according to one of claims 1 to 9.
11. Thermal imaging camera according to claim 10, further comprising a housing (9), on which the carrier (2) represents a front plate (91) and the opening (21) forms a first beam passage opening (911), and a front cover (92) covering the front plate (91) with a second beam passage opening arranged coaxially to the first beam passage opening (911), wherein the first spur gear (6), the second spur gear (7) and the rocker (5) are arranged between the front plate (91) and the front cover (92).
12. Thermal imaging camera according to claim 11, characterized in that the second axis of rotation (8) is fixed in the front cover (92) and the motor shaft (31) is mounted in the front cover (92).
13. Thermal imaging camera according to claim 11 or 12, characterized in that the front plate (91) is rectangular and the motor shaft (31), the first axis of rotation (53) and the second axis of rotation (8) are arranged along a diagonal (912) of the front plate (91).