WO2024200414A1 - Electromechanical shutter device for a thermal imaging camera with a rocker as shutter blade - Google Patents

Abstract

The invention relates to an electromechanical shutter device for a thermal imaging camera, comprising a carrier (2) having an opening (21) with a fixed electric motor (3) having a motor shaft (31) and a shutter blade (51) assigned to the opening (21), which forms a rocker (5) with a shaft (52), wherein the rocker (5) is mounted on a first rotation axis (53) arranged parallel to the motor shaft (31) on the carrier (2), is pivotable about the first axis of rotation (53) over a pivot angle range by means of a crank with a pin (4), and has an elongated hole (521) in the shaft (52) located opposite the shutter blade (51), with which the pin (4) is engaged, wherein a first spur gear (6) is attached to the motor shaft (31), the crank is formed by a second spur gear (7), the second spur gear (7) is mounted on a second axis of rotation (8) arranged parallel to the motor shaft (31) in the carrier (2), is rotatable over a defined rotation angle range and meshes with the first spur gear (6).

Description

Electromechanical shutter device for a thermal imaging camera with a swing arm as shutter blade

The invention relates to an electromechanical shutter device for a camera, in particular a thermal imaging camera, for use in various types of photography 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.

In conjunction with cameras, shutter devices are used to interrupt the optical beam path when necessary. A major challenge in the design of such shutter devices is the progressive miniaturization of cameras with increasing requirements in terms of the lowest possible heat development, the setting time, the service life, the operating temperature range, the manufacturing costs and the like. Known solutions include iris diaphragms, focal plane shutters or pivoting or guided shutter blades which are driven electromagnetically or by a motor.

In infrared or thermal imaging applications, it is necessary to carry out a so-called "dark frame calibration" at certain intervals to correct the temporal drifts of the individual pixel signal values that often occur during operation of the camera. This involves closing a shutter device, with a shutter blade positioned in front of the image sensor so that its receiving surface is completely shielded from the thermal radiation coming from the scene and all sensor pixels face the shutter blade. The shutter blade must have a homogeneous temperature and also have 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 correct the individual pixel signal values. In radiometric cameras, such a shutter device also serves as a temperature reference to improve measurement accuracy.

From WO2017/204946 A1, a camera shutter device is known with a motor, a spur gear connected to the motor and a shutter blade which is firmly connected to a spur gear segment which, meshing with the spur gear, pivots the shutter blade between two end positions (release position and closed position) over an angular range. The rotary motion 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 rotated depending on the angle of rotation over which the motor shaft rotates with changing direction of rotation, moves over an angular range from one end position to the other end position.

A thermal imaging camera with a fast electromechanical shutter device is known from DE 10 2010 023 167 B4. Here, a motor is connected to a shutter blade via a crank. The crank sits on the motor shaft of the motor and has a pin at its free end that engages in an elongated hole formed on the shaft of the shutter blade (hereinafter also referred to as the shutter blade). The shutter blade with the shaft represents a rocker. The crank and the rocker together form a crank loop. The pin and the elongated hole form a sliding joint.

The crank slider can be designed as a rotating gear so that the crank can complete full revolutions and the motor shaft alternates between the two angular positions in which the locking trowel is in one end position while the motor remains in the same direction of rotation. The swing arm is pivoted back and forth between the two end positions over the pivot angle, with the motor shaft being rotated through two different angles of rotation.

The crank slider can also be designed as a non-rotating gear, so that it has two dead center positions that are used as end positions, or the rotation of the crank is limited by stops. The direction of rotation of the motor must then be changed in order to swing the locking blade from one end position to the other. It is advantageous for the kinematics of the locking blade if the motor shaft always covers the same angle of rotation.

Stopping in the end positions can be achieved by controlling the motor alone or can be supported by additional dampening stops.

The dimensioning of the shutter device is determined by 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 swing arm must be so that the beams can pass freely in one end position and the sensor can fill the format 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 with which the shutter blade is pivoted between the end positions and thus the pivoting time of the shutter blade is only set via the angular speed or the speed of the motor. Normally, a certain maximum swivel time should be observed for the swiveling of the locking blade and at the same time there are certain minimum requirements for the torque of the locking blade associated with swiveling so that a sufficiently reliable function of the locking device can be guaranteed. This sets very strict framework conditions for 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 guarantee sufficient angular speeds but cannot provide sufficient drive torque. With regard to miniaturization efforts (and correspondingly small motors), this can be a disadvantage.

It is the object of the invention to provide a shutter device for a thermal imaging camera which can be reliably operated with motors with a rather low drive torque and is thus also better compatible with miniaturization.

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 better compatible with miniaturization.

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 with a motor shaft that is fixed to the carrier, and a shutter blade that is associated with the opening and forms a rocker with a shaft formed thereon, wherein the rocker is mounted on a first axis of rotation that is fixed to the carrier parallel to the motor shaft, can be pivoted about the first axis of rotation over a pivot angle range between a release position and a closed position of the shutter blade by means of a crank with a pin, and has an elongated hole in the shaft that is arranged opposite the shutter blade with respect to the first axis of rotation, with which the pin is in engagement, wherein a first spur gear is fastened to the motor shaft, the crank is formed by a second spur gear that is mounted on a second axis of rotation that is arranged in the carrier parallel to the motor shaft, 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 so as to mesh with the second spur gear.

In a preferred aspect, the opening has a rectangular shape and the elongated hole is a straight elongated hole which runs longitudinally parallel to an edge of the opening in the release position and the closing position, respectively.

Advantageously, the first axis of rotation is arranged at a corner of the opening. It is particularly advantageous if the closure leaf has a rectangular shape. Alternatively, it is advantageous if the closure leaf has a circular-arc-shaped body edge instead of a rectangular shape and if there is a circular-arc-shaped slideway on the carrier on which the closure leaf slides when pivoting between the closed position and the release position. In both cases, the pivot angle is preferably 90°.

Ideally, the rotation angle range is 270° or the same as the swivel angle range 90°.

To reduce weight, it can be advantageous for the second spur gear to be reduced to a spur gear segment that has a toothing over an angular range of 270° or 90°, and optionally also for the first spur gear to be reduced to a spur gear segment that has a toothing over an angular range of 270° or 90° if there is a 1:1 ratio between the first and second spur gear. In the case of a reduction ratio, the angular range of the toothing must be adapted accordingly or the segmentation must be dispensed with.

A stepper motor is preferably used as the motor.

The object is further achieved by a thermal imaging camera which contains an electromechanical locking device according to the invention.

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 present, 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.

Very advantageously, the second axis of rotation is fixed in the front cover and the motor shaft is mounted.

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.

The invention is explained in more detail below using exemplary embodiments and drawings. Fig. 1 a shows an embodiment of a closure device in which the closure leaf is in a closed position,

Fig. 1 b shows the closure device according to Fig. 1 a, in which the closure leaf is in an intermediate position,

Fig. 1c the closure device according to Fig. 1 a, in which the closure blade is in a release position,

Fig. 2 a thermal imaging camera with a shutter device according to Fig. 1 a-1c without front cover,

Fig. 3 a thermal imaging camera with a shutter device according to Fig. 1 a-1c with front cover and

Fig. 4 shows a thermal imaging camera with a shutter device according to a second embodiment, without a front cover.

A camera shutter device according to the invention, as shown in Figs. 1a-1c, essentially contains in all versions 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 sitting on the motor shaft 31, a crank which is 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.

The rocker arm 5 is mounted on the first rotation axis 53 and can be pivoted 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 rotation axis 8 over a defined rotation angle range.

In the shaft 52 of the rocker 5, more precisely, in a region of the shaft 52 opposite the closure blade 51 with respect to the first axis of rotation 53, an elongated hole 521 is formed which is angled to the center of the surface of the closure blade 51 and with which the pin 4 of the second spur gear 7 is in engagement. The shaft 52 is preferably aligned in the same way to the closure blade 51 as a surround of the elongated hole 521. The first spur gear 6 and the second spur gear 7 are arranged so as to mesh with one another. All of the following Embodiments of a camera shutter device according to the invention have the features mentioned.

The geometric shape and size of the opening 21 is 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 immediate arrangement in front of the receiver surface of an image sensor 11 (only shown in Fig. 4), the opening 21 corresponds to the shape and size of the receiver surface of the image sensor 11.

Image sensors are usually rectangular, which is why the opening 21 is also usually rectangular. In order to completely cover the opening 21, the closure leaf 51 must therefore cover the opening 21 in the closed position at least with a small excess. The closure leaf 51 is also advantageously rectangular with a small excess 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.

In the case of the rectangular shape of the opening 21, but regardless of the shape of the closure leaf 51, the elongated hole 521 is designed in a first embodiment as a straight elongated hole 521 in the shaft 52, which in the release position and the closed position runs in the longitudinal direction parallel to one of the edges 21 1 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 arrangement of the locking device in space, the elongated hole 521 is arranged vertically 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, additional power supply to the electric motor 3 during the closure time and possibly also during the release time increases the shock resistance, i.e. the closure blade 51 is held securely in the release position or the closed position even if vibrations or impacts act on the closure device.

By arranging the first rotation axis 53 at a corner of the opening 21 and mounting it in the rocker 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 so that it is only marginally larger than the opening 21. The pivoting path between the release position and With this arrangement of the first rotary axis 53, the closing position is minimal and the space required for the locking blade 51 in the release position is also minimal, both of which facilitate miniaturization.

In a special second embodiment of the closure leaf 51, as shown in Fig. 4, the closure leaf 51 has a circular-arc-shaped body edge 511, which deviates from a rectangular shape. This edge lies outside a rectangular surface area which corresponds to the opening 21 with a slight oversize. In this embodiment, the carrier 2 has a circular-arc-shaped slideway 22 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, which means that the closure leaf 51 can be made less rigid and thus thinner than if it were only connected to the first axis of rotation 53.

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 with 270° around the second rotation axis 8 into a 90° swivel angle range of the swing arm 5 around the first rotation axis 53, e.g. with an average reduction ratio of 1:3.

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 set on the locking blade 51 after the rotation of the second spur gear 7 over a rotation angle range of 90°.

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.

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 the first spur gear 6 is also reduced to a spur gear segment which then also has a Toothing over an angular range of 270° or 90° when there is a 1:1 ratio between the first spur gear 6 and the second spur gear 7.

In the case of 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 for the toothing of the second spur gear 7 - or the segmented toothing of the first spur gear 6 is dispensed with. An example of 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 exceeds a ratio of 1:2 (neither shown), segmentation of the toothing on the first spur gear 6 would very likely be omitted.

All embodiments can advantageously have 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 step losses of the stepper motor do not have a detrimental effect here, since the crank pin 4 is rotated against a mechanical stop in each of the two end positions. Optionally, there can be an additional end position safety device, e.g. with permanent magnets.

All of the aforementioned embodiments and combinations thereof can be part of a thermal imaging camera 1 or a thermal imaging camera module.

An 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.

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).

It also contains a front cover 92 covering the front plate 91 with a second beam passage opening (not shown) arranged coaxially to 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. The closure blade 51 is thus 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, the closure blade 51 is located in the release position in a narrow space formed between the front plate 91 and the front cover 92, in which no or at most very little local Temperature gradients arise, whereby the shutter blade 51 does not experience any locally different heating, which would seriously impair its suitability for offset correction and possibly also its suitability as a temperature reference.

In an advantageous embodiment of the thermal imaging camera 1, as shown in Fig. 3, 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. Due to the two-sided fixation of the axis of rotation 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.

A particularly advantageous design 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 away as possible from the image sensor 11 (only shown in Fig. 4) when the maximum radial expansion of the interior of the housing 9 is fully utilized.

list of reference symbols

1 thermal imaging camera

11 image sensor

2 carriers

21 opening

211 edge of the opening

22 slideway

3 electric motors

31 Motor shaft

4 cones

5 swingarms

51 closure sheet

511 circular arc-shaped body edge (of the closure blade)

52 shaft

521 slot

53 first axis of rotation

6 first spur gear

7 second spur gear

8 second axis of rotation

9 housings

91 front panel

911 first jet passage opening

912 diagonal

92 front cover

Claims

patent claims 1. Electromechanical shutter device for a thermal imaging camera, comprising a carrier (2) having an opening (21), an electric motor (3) fixed to the carrier (2) with a motor shaft (31) and a shutter blade (51) associated with the opening (21), which forms a rocker (5) with a shaft (52) formed thereon, wherein the rocker (5) is mounted on a first axis of rotation (53) fixed to the carrier (2) parallel to the motor shaft (31), can be pivoted by means of a crank with a pin (4) 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) 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 in engagement, 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 closing 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 closure device according to claim 3, characterized in that the closure leaf (51) has a rectangular shape. 5. Electromechanical locking device according to claim 3, characterized in that the locking blade (51) has a circular arc-shaped body edge, deviating from a rectangular shape, and a circular arc-shaped slideway (22) is present on the carrier (2), on which the locking blade (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 pivot 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).