Optical sensor

Abstract

Optical sensor (1) for detecting objects, each having at least one electronic component and one sensor component, wherein the electronic component generates an output signal as a function of sensor signals from the one or more sensor components, characterized in that the sensor component and an optical system arranged upstream of the sensor component are mounted in a tube (6) at a distance from one another in the longitudinal direction thereof, that the tube (6) has a compensation region (15) consisting of a material with a high thermal expansion coefficient and located between the sensor component and the optical system, that the optical system has at least one optical element made of plastic, wherein a temperature-related change in optical properties of the optical element is compensated for by a temperature-related change in length of the compensation region (15) of the tube (6).

Description

[0001] The invention relates to an optical sensor.

[0002] Such optical sensors are generally used to detect objects. For this purpose, the optical sensor incorporates sensor components and electronic components integrated into a housing.

[0003] Typically, the optical sensor has a transmitter unit that emits light rays and a receiver unit that receives light rays reflected back from an object.

[0004] At least one electronic component forms an evaluation unit in which an output signal is generated depending on sensor signals from the sensor components.

[0005] The optical sensor can be used to detect objects in a surveillance area. In this case, the optical sensor generates an object detection signal as an output signal, which indicates whether or not an object is present in the surveillance area.

[0006] The optical sensor can also be used, in particular, to detect codes such as barcodes or 2D codes, i.e., the optical sensor then functions as a code reader. In this case, the code information contained in the sensor signals from the sensor components is decoded in the evaluation unit, so that the detected code can be output as an output signal.

[0007] Particularly in an embodiment in the form of a code reader, the receiver unit is designed in the form of an image sensor, i.e., an imager. Advantageously, the image sensor is associated with a transmitter unit in the form of a lighting unit, which, for example, comprises a multiple arrangement of light-emitting diodes.

[0008] The image sensor is typically preceded by a lens which is mounted in a tube.

[0009] The image sensor is located on one side of a circuit board, with the tube also being attached to this side of the circuit board.

[0010] Due to external environmental influences and also heat development in the optical sensor, in particular heat generated by sensor components or electronic components in the optical sensor, temperature-related changes in the optical properties of optical elements in the optical sensor can occur. The optical elements can form the optics, in particular the lens of the optical sensor. Specifically, temperature changes in the optical sensor can change the refractive index of optical elements such as lenses, which can result in, for example, changes in the focus positions of optics such as lenses, which impairs object detection with the optical sensor. For example, with code readers, codes to be read are imaged blurry, which makes code detection difficult or even impossible.This problem occurs particularly when optical elements made of plastic are used, which, although inexpensive to produce, exhibit a strong temperature drift in their optical properties, particularly the refractive index.

[0011] To address this problem, conventional optical sensors utilize optical elements in the form of glass lenses, which exhibit significantly lower temperature drift in their optical properties. However, the disadvantage is that glass lenses are very expensive. Another disadvantage is that they are predominantly only available as spherical lenses, which, for example, requires the use of a relatively large number of glass lenses when designing lenses.

[0012] The invention is based on the object of providing an optical sensor of the type mentioned above, with which reliable object detection is possible even at changing temperatures.

[0013] To achieve this object, the features of claim 1 are provided. Advantageous embodiments and expedient developments of the invention are described in the dependent claims.

[0014] The invention relates to an optical sensor for detecting objects, each comprising at least one electronic component and one sensor component. The electronic component generates an output signal depending on sensor signals from the sensor component(s). The sensor component and an optical system arranged upstream of the sensor component are mounted in a tube at a distance from one another in the longitudinal direction of the tube. The tube has a compensation region consisting of a material with a high thermal expansion coefficient located between the sensor component and the optical system. The optical system has at least one plastic optical element, wherein a temperature-related change in the optical properties of the optical element is compensated by a temperature-related change in the length of the compensation region of the tube.

[0015] The optical sensor according to the invention generally serves to detect objects and, for this purpose, preferably comprises electronic components and sensor components integrated in a single housing. Sensor components can be provided on the transmitting side, which emit light beams into a detection area. Furthermore, receiving-side sensor components are advantageously provided, which receive light beams reflected from objects to be detected. At least one electronic component forms an evaluation unit in which sensor signals are evaluated to generate an output signal.

[0016] The optical sensor is particularly advantageously designed as a code reader, with which codes in the form of barcodes or 2D codes can be detected.

[0017] In this case in particular, the optical sensor has an image sensor as the receiving-side sensor component, which is designed, for example, in the form of a matrix-shaped CCD or CMOS array.

[0018] In the optical sensor according to the invention, at least one sensor component with an upstream optics system is mounted in a tube made of opaque material and having a substantially hollow-cylindrical shape. The tube rests with its underside on a base, which is preferably formed into a printed circuit board, on which the sensor component in the tube also rests. The optics system is arranged in the longitudinal direction of the tube, i.e., in the direction of its longitudinal axis, at a distance from the sensor component.

[0019] The sensor component mounted in the tube can be a transmitting sensor component that emits light beams. In this case, the optics mounted in the tube serve to shape the light beams.

[0020] Particularly advantageous is the sensor component mounted in the tube, which is a receiving-side sensor component designed to receive light beams. The optics then serve to focus the light beams onto the receiver. Especially when the optical sensor is a code reader and the sensor component is an image sensor, the optics are designed as a lens.

[0021] The lens is advantageously mounted in the tube using a lens holder.

[0022] According to the invention, the optics mounted in the tube consist of optical elements made of plastic. Such optical elements are more cost-effective than optical elements made of glass. By manufacturing the optical elements as plastic injection-molded parts, virtually any shape of the optical elements is possible, with the optical elements also being designed, in particular, as aspherical lenses, optionally with freeform surfaces. This allows the optical properties of the optics to be precisely and precisely specified with just a few optical elements.

[0023] In the event that the optics is a lens arranged in front of an image sensor, this can consist of plastic lenses, whereby the lens advantageously consists of only two lenses, so that it has a simple and cost-effective construction.

[0024] Due to external temperature influences and / or heat generated by sensor components and electronic components in the housing, temperature fluctuations can occur that change the optical properties, in particular the refractive index of the plastic optical elements, thereby changing the focus position of the optics in the tube.

[0025] This can lead to impairments in object detection. Temperature fluctuations, in particular, can cause a lens to no longer capture objects, especially codes, clearly on the image sensor.

[0026] According to the invention, such temperature-related changes in optical properties of the optics in the tube are compensated for by the tube having a compensation region located between the sensor component and the optics, which compensation region consists of a material with a high thermal expansion coefficient.

[0027] Advantageously, the compensation area of ​​the tube is made of a material whose thermal expansion coefficient is greater than 120 ppm / K.

[0028] The tube is preferably made of a plastic that has a correspondingly high thermal expansion coefficient.

[0029] When temperature changes occur in the optical sensor, a change in the length of the compensation area, i.e. a change in its extension in the longitudinal direction of the tube, is obtained, which leads to a corresponding change in the distance between the optics and the sensor component, with which the temperature-related changes in the optical properties of the optical elements are compensated.

[0030] Advantageously, a temperature-related change in the refractive index of the optical element(s) is compensated by a temperature-related change in the length of the compensation area of ​​the tube.

[0031] A temperature-related change in the refractive index of the optical element(s) causes a change in the focal position of the optics, which is compensated by a temperature-related change in the length of the compensation area of ​​the tube.

[0032] By changing the length of the compensation area, the change in the focus position can be precisely compensated. To ensure this compensation over the widest possible temperature range, the material, geometry, and extent of the compensation area are selected appropriately. This selection can be precisely specified by calculating the respective influencing factors.

[0033] In order to achieve a homogeneous, uniform change in the length of the tube when the temperature changes, it is advantageous if the compensation area extends over the entire circumference of the tube.

[0034] According to a first variant, the entire tube is made of a material with a high thermal expansion coefficient.

[0035] In particular, the tube is made of HDPE (high density polyethylene).

[0036] In this variant, the sensor component is mounted stationary within the tube. The optics within the tube are adjustable in its longitudinal direction, with the part of the tube located between the sensor component and the optics forming the compensation area.

[0037] By adjusting the position of the optics, its distance from the sensor component is adjusted. The resulting adjustment of the tube area between the optics and the sensor components then forms the compensation area, since only this area causes a change in the distance between the optics and the sensor components when the temperature changes, thus contributing to compensating for temperature-related changes in the optical properties of the optics' optical elements.

[0038] It is advantageous to adjust the position of the optics in a calibration operation.

[0039] This allows the size of the compensation range to be specified that is optimized for compensating the optical properties of the optical elements.

[0040] In the event that an image sensor with a lens in front is mounted in the tube, it is advantageous to have a lens holder with the lens mounted in the tube so that its position can be adjusted.

[0041] For this purpose, there is an external thread on the outer surface of the lens holder, which engages with an internal thread arranged on the inner wall of the tube.

[0042] By operating the threads, the position of the lens relative to the image sensor and thus the size of the compensation area can be precisely specified.

[0043] The height range in the tube, in which the internal thread and external thread mesh, structurally defines the area that is used for compensation.

[0044] According to a second variant, the compensation area is formed by a portion of the tube. The rest of the tube is made of a material with a low thermal expansion coefficient.

[0045] Silicone is an advantageous material forming the compensation area with a high thermal expansion coefficient.

[0046] The silicone can be used in liquid form to model the tube and then harden.

[0047] Another advantage is the material with a low thermal expansion coefficient, Macrolon or Ultem.

[0048] In general, this material has a thermal expansion coefficient that is significantly less than 120 ppm / K.

[0049] According to a first embodiment, the compensation region is formed by a lower portion of the tube. Adjoining the upper portion is a portion made of a material with a low thermal expansion coefficient.

[0050] Advantageously, locking structures are formed at the interfaces between the sub-areas, allowing the sub-areas to engage with each other in a form-fitting manner. The sub-areas can be manufactured using a two-component injection molding process, where they are fused together at the interfaces. Alternatively, the sub-areas can also be glued together.

[0051] This improves the grip between the sections.

[0052] According to a second embodiment, the compensation region is arranged between two partial regions of the tube which consist of a material with a low thermal expansion coefficient.

[0053] Advantageously, the sections of the tube on both sides of the compensation area are made of the same material.

[0054] Further advantageously, the compensation area has a height structure that varies periodically in the circumferential direction of the tube.

[0055] The periodically varying height structure, which can be sinusoidal or meander-shaped, for example, which stabilizes the flexible silicone of the compensation area.

[0056] In both embodiments, the entire or almost entire compensation range is advantageously located between the optics and the sensor component, so that changes in the length of the compensation range during temperature changes fully contribute to compensating the optical properties of the optical elements or the optics.

[0057] The invention is explained below with reference to the drawings. Fig. 1: Schematic representation of an embodiment of the optical sensor according to the invention. Fig. 2: First embodiment of a tube arrangement according to the invention for the optical sensor according to Fig. 1. Fig. 3: Second embodiment of a tube arrangement according to the invention for the optical sensor according to Fig. 1. Fig. 4: Third embodiment of a tube arrangement according to the invention for the optical sensor according to Fig. 1.

[0058] Fig. 1 shows, in a highly schematic and not to scale, an embodiment of the optical sensor 1 according to the invention. In the present case, the optical sensor 1 is designed as a code reader, by means of which barcodes and 2D codes can be detected.

[0059] The electronic components and sensor components of the optical sensor 1 are integrated in a housing 2 made of non-transparent material.

[0060] A circuit board 3, the central electronic component, is mounted in the housing 2. Mounted on one mounting side of the circuit board 3 are sensor components comprising an image sensor 4 and several LEDs 5 surrounding the image sensor 4. The image sensor 4 is formed, for example, by a matrix-shaped CCD or CMOS array. The LEDs 5, which emit light beams, form an illumination unit that illuminates the field of view of the image sensor 4.

[0061] The image sensor 4 is located in a substantially hollow-cylindrical tube 6 made of non-transparent material. Mounted in the tube 6 is a lens 7 arranged in front of the image sensor 4, which lens serves to focus light rays onto the image sensor 4.

[0062] In a front wall of the housing 2 there is mounted a disc 8 which is made of transparent material, i.e. material which is permeable to the light rays.

[0063] A microcontroller 9, which forms an evaluation unit, is mounted on a component side opposite the mounting side. Instead of a microcontroller 9, another computer unit can also be arranged.

[0064] The light beams emitted by the LEDs 5 are guided through the disc 8 into a detection zone. From a code applied to an object, light beams are guided across the disc 8 and the object to the image sensor 4. The sensor signals generated by the image sensor 4 are evaluated in the evaluation unit. The code is decoded in the evaluation unit based on the code information contained in the sensor signals, which is output as an output signal from the optical sensors 1.

[0065] The tube is attached to the mounting side of the circuit board with fasteners so that the image sensor is located inside the circuit board.

[0066] The image sensor 4 and the microcontroller 9 are located opposite each other on either side of the circuit boards 3. This allows the image sensor 4 and the microcontroller 9 to be connected via very short MIPI lines (not shown), allowing interference-free data transmission between the image sensor 4 and the microcontroller 9.

[0067] The lens 7 of the optical sensor 1 consists of plastic optical elements, in particular plastic lenses.

[0068] The Fig. 2 to 4 show embodiments of the tube arrangement according to the invention.

[0069] Fig. 2 shows an embodiment of a tube 6 with an objective 7 consisting of two lenses 10a, 10b, which are mounted on a lens holder 11, wherein the lens holder 11 is in turn mounted in the tube 6.

[0070] This optical design is also used in the tube arrangement of the Fig. 3 and Fig. 4 available.

[0071] On the underside of the tube 6 there is a locating pin 12, by means of which the tube 6 can be fixed to the circuit board 3, in particular by pressing. This locating pin 12 is also present in the embodiments of the Fig. 3 and Fig. 4 available.

[0072] In the embodiment according to Fig. 2, the entire tube 6 is made of a material with a high thermal expansion coefficient, which is advantageously greater than 120 ppm.

[0073] The tube 6 is advantageously made of a plastic, such as HDPE (high density polyethylene).

[0074] The lens holder 11 has an external thread 13 which engages with an internal thread 14 on the inner wall of the tube 6.

[0075] By adjusting the external thread 13 on the internal thread 14, the position of the lens holder 11 and thus the distance of the lens 7 to the image sensor 4 can be adjusted, which is advantageously done in a calibration operation.

[0076] This setting specifies a compensation area 15 which is formed by the part of the tube 6 which lies between the image sensor 4 and the lens 7.

[0077] According to the invention, a change in the refractive index of the lenses 10a, 10b and thus in the focus position of the objective 7 caused by temperature changes is compensated by a change in the length of the compensation region 15, wherein the position of the lens holder 11 with the objective 7 is suitably predetermined for a complete compensation of the focus position.

[0078] The Fig. 3 and Fig. 4 show further embodiments of the tube arrangement according to the invention.

[0079] In this case, the lens holder 11 with the lens 7 is mounted in a fixed position in the tube 6, ie the distance between the image sensor 4 and the lens 7 is constant.

[0080] In the embodiments of the Fig. 3 and Fig. 4, the tube 6 consists of several sub-areas. One sub-area forms the compensation area 15. This compensation area 15 is made of a material with a high thermal expansion coefficient, which is advantageously greater than 120 ppm / K. In particular, the compensation area 15 is made of silicone.

[0081] Furthermore, the tube 6 has sub-areas that form fixed areas 16, 16a, 16b, as they are made of a material with a very low thermal expansion coefficient. In particular, the fixed areas 16, 16a, 16b are made of Macrolon or Ultem.

[0082] Both the compensation area 15 and the fixed area(s) 16, 16a, 16b extend over the entire circumference of the tube 6.

[0083] In the embodiment according to Fig. 3, a lower portion of the tube 6 forms the compensation region 15, to the top of which a fixed region 16 is connected. A base, which also forms a fixed region, is connected to the underside of the compensation region 15.

[0084] On the upper side of the compensation area 15, projections 17 are provided that engage in recesses 18 on the underside of the fixed area 16, 16a, 16b. This creates locking structures that improve the grip between the compensation area 15 and the fixed area 16, 16a, 16b.

[0085] In the embodiment according to Fig. 4, the compensation region 15 forms a periodically varying, sinusoidal height structure which lies between two fixed regions 16a, 16b.

[0086] In both embodiments, the compensation area 15 is located between the lens 7 and its image sensor 4. Temperature-related changes in the length of the compensation area and thus of the tube 6 thus change the distance between the lens 7 and the image sensor 4, thereby compensating for the temperature-related change in the refractive index of the lenses 10a, 10b of the lens 7 and thus the focus position of the object.

[0087] By a suitable choice of material, geometry and size of the compensation area 15, compensation of the focus position can be achieved over a wide temperature range. List of reference symbols 1 optical sensor 2 housings 3 circuit board 4 image sensor 5 LEDs 6 tube 7 Lens 8 slices 9 microcontrollers 10a lens 10b lens 11 lens holders 12 Dowel pin 13 external threads 14 internal threads 15 Compensation range 16 Festive area 16a Festival area 16b Festival area 17 lead 18 recess

Claims

[1] Optical sensor (1) for detecting objects, each comprising at least one electronic component and one sensor component, wherein the electronic component generates an output signal depending on sensor signals from the one or more sensor components, characterized by that the sensor component and an optical system arranged upstream of it are mounted in a tube (6) at a distance from one another in the longitudinal direction thereof, that the tube (6) has a compensation region (15) consisting of a material with a high thermal expansion coefficient located between the sensor component and the optical system, that the optical system has at least one optical element made of plastic, wherein a temperature-related change in optical properties of the optical element is compensated by a temperature-related change in the length of the compensation region (15) of the tube (6). [2] Optical sensor (1) according to claim 1, characterized bythat the sensor component mounted in the tube (6) is an image sensor (4). [3] Optical sensor (1) according to claim 2, characterized by that the optics mounted in the tube (6) is a lens (7). [4] Optical sensor (1) according to claim 3, characterized by that the objective (7) has lenses (10a, 10b) made of plastic as optical elements. [5] Optical sensor (1) according to one of claims 3 or 4, characterized by that the object is mounted in the tube (6) by means of a lens holder (11). [6] Optical sensor (1) according to one of claims 1 to 5, characterized by that the tube (6) and the sensor component mounted therein are mounted on a circuit board (3). [7] Optical sensor (1) according to one of claims 1 to 6, characterized by that a temperature-related change in the refractive index of the optical element(s) is compensated by a temperature-related change in the length of the compensation region (15) of the tube (6). [8] Optical sensor (1) according to claim 7, characterized by that a temperature-related change in the refractive index of the optical element(s) causes a change in the focal position of the optics, which is compensated by a temperature-related change in the length of the compensation region (15) of the tube (6). [9] Optical sensor (1) according to one of claims 1 to 8, characterized by that the compensation area (15) of the tube (6) consists of a material whose thermal expansion coefficient is greater than 120 ppm / K. [10] Optical sensor (1) according to one of claims 1 to 9, characterized by that the compensation area (15) extends over the entire circumference of the tube (6). [11] Optical sensor (1) according to one of claims 1 to 10, characterized by that the compensation area (15) of the tube (6) is made of a plastic. [12] Optical sensor (1) according to one of claims 1 to 11, characterized bythat the entire tube (6) is made of a material with a high thermal expansion coefficient. [13] Optical sensor (1) according to claim 12, characterized by that the sensor component is arranged stationary in the tube (6) and the optics in the tube (6) are positionally adjustable in its longitudinal direction, wherein the part of the tube (6) lying between the sensor component and the optics forms the compensation area (15). [14] Optical sensor (1) according to claim 13, characterized by that the position adjustment of the optics takes place in a calibration mode. [15] Optical sensor (1) according to one of claims 13 or 14, characterized by that a lens holder (11) with the lens (7) is mounted in the tube (6) in an adjustable position. [16] Optical sensor (1) according to claim 15, characterized bythat as a means for adjusting the position on the outer surface of the lens holder (11) there is an external thread (13) which engages with an internal thread (14) arranged on the inner wall of the tube (6). [17] Optical sensor (1) according to one of claims 12 to 16, characterized by that the tube (6) is made of HDPE (High Density Polyethylene). [18] Optical sensor (1) according to one of claims 1 to 11, characterized by that the compensation region (15) is formed by a partial region of the tube (6), and that the remaining tube consists of a material with a low thermal expansion coefficient. [19] Optical sensor (1) according to claim 18, characterized by that the material forming the compensation area (15) with a high thermal expansion coefficient is silicone. [20] Optical sensor (1) according to one of claims 18 or 19, characterized bythat the material with low thermal expansion coefficient is Macrolon or Ultem. [21] Optical sensor (1) according to one of claims 18 to 20, characterized by that the compensation region (15) is formed by a lower partial region of the tube (6), wherein a partial region consisting of a material with a low thermal expansion coefficient adjoins the upper side thereof. [22] Optical sensor (1) according to claim 21, characterized by that locking structures are formed at the interfaces between the sub-areas, by means of which the sub-areas are locked. [23] Optical sensor (1) according to one of claims 18 to 20, characterized by that the compensation region (15) is arranged between two partial regions of the tube (6) which consist of a material with a low thermal expansion coefficient. [24] Optical sensor (1) according to claim 23, characterized bythat the sections of the tube (6) on both sides of the compensation area (15) are made of the same material. [25] Optical sensor (1) according to claim 24, characterized by that the compensation region (15) has a height structure that varies periodically in the circumferential direction of the tube (6). [26] Optical sensor (1) according to claims 1 to 25, characterized by that this is a code reader.

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