DE102020111130B4 - Optoelectronic system and optoelectronic sensor - Google Patents

Abstract

Optoelectronic system (1) with at least one circuit board (2) with several light transmitters (3) and/or several light receivers (4) which are arranged at least in one row and with at least one one-piece optical component (5) made of plastic for the several light transmitters (3) and/or light receivers (4), wherein at least one lens (6) is provided in the optical component (5) for each light transmitter (3) and/or light receiver (4), wherein the optical component (5) is mechanically fixed to the circuit board (2) at least at one point, characterized in that the circuit board (2) has a first positive thermal linear expansion coefficient and the optical component (5) has a second positive thermal linear expansion coefficient, wherein the second positive thermal linear expansion coefficient is greater than the first positive thermal linear expansion coefficient, wherein particles (7) made of a secondary material (8) are mixed into the optical component (5), which are made of a different material than a primary material of the Optical component (5), wherein the secondary material (8) of the particles (7) has a smaller thermal linear expansion coefficient than the second thermal linear expansion coefficient of the primary material of the optical component, so that the resulting second positive linear expansion coefficient of the optical component (5) is reduced, wherein an elongated at least two-part housing (11) is provided, wherein the two-part housing (11) has at least two housing parts (12, 13), wherein the first housing part (12) has the optical component (5) and the second housing part (13) has the circuit board (2).

Description

The present invention relates to an optoelectronic system according to the preamble of claim 1 and an optoelectronic sensor according to the preamble of claim 13.

The problem with such optoelectronic systems or optoelectronic sensors is that, due to the expansion coefficients of the materials used, an optic expands differently when the temperature changes than the materials used in a circuit board on which the light transmitters and/or light receivers are arranged.

Thermal expansion is the change in the geometric dimensions (length, area, volume) of a body caused by a change in its temperature.

The coefficient of expansion or thermal expansion coefficient, colloquially also known as the expansion factor, is a characteristic value that describes the behavior of a material with regard to changes in its dimensions when the temperature changes, which is why it is often also called the thermal expansion coefficient. The effect responsible for this is thermal expansion. Thermal expansion depends on the material used, so it is a material-specific or substance-specific material constant. Since thermal expansion in many materials does not occur evenly across all temperature ranges, the thermal expansion coefficient itself is also temperature-dependent and is therefore specified for a specific reference temperature or a specific temperature range.

In this case, the coefficient of thermal expansion (also known as linear thermal expansion coefficient) is relevant.

For example, polycarbonate (PC) has a thermal expansion coefficient of approx. 70 ppm/K. Polyamide (PA) has a thermal expansion coefficient of approx. 110 ppm/K.

For example, electrical circuit boards, which are made of non-conductive material such as FR-4, expand due to an increase in temperature. This also shifts the position of components mounted on the circuit board. A shift of optoelectronic components relative to other components such as lenses can have a very detrimental effect on the behavior and availability of a sensor.

FR-4 or FR4 refers to a class of flame-retardant and flame-retardant composite materials consisting of epoxy resin and glass fiber fabric. The abbreviation FR stands for flame retardant and meets the requirements of UL94V-0. FR-4 is available in various versions on the market. To improve flame retardancy, the composite material is mixed with chemical substances such as polybrominated diphenyl ethers based on bromine; this additive is omitted in the halogen-free version. The properties of the FR-4 composite material were defined by the National Electrical Manufacturers Association (NEMA) in the NEMA LI1 specification.

Epoxy resins (EP resins) are synthetic resins that contain epoxy groups. They are hardenable resins (reaction resins) that can be converted into a thermosetting plastic with a hardener and possibly other additives. The epoxy resins are polyethers with usually two terminal epoxy groups. The hardeners are reaction partners and together with the resin form the macromolecular plastic.

The thermosets produced by cross-linking have good mechanical properties as well as good temperature and chemical resistance and are considered high-quality plastics. The composite materials for the circuit boards are then formed in conjunction with the glass fiber fabric. FR4, for example, has a thermal expansion coefficient of 12 to 17 ppm/K. The thermal expansion coefficients also differ depending on the direction.

The US 2015/0362585 A1 discloses a proximity sensing device comprising an optical source comprising a plurality of VCSELs configured in a 2D spatial arrangement such that one or more objects arranged within a physical space can be fully or partially illuminated by an incident beam of rays from the plurality of VCSELs, a radiation detection device arranged together with the optical source in at least one plane and separated in an orthogonal plane in the physical space, the radiation detection device being arranged at a predetermined angle relative to the optical source, the radiation detection device generating one or more electrical signals proportional to the reflected radiation received from the one or more objects.

The US6 979 704B1 discloses an optical polymer mixture. This optical polymer mixture contains subwavelength particles to modify the refractive index of a polymer to match the refractive index of microparticles added to adjust the volume coefficient of thermal expansion of the blend. A relatively large amount of material can be added to the resin to adjust the volume coefficient of thermal expansion without excessively increasing the viscosity of the blend prior to curing. In some applications, optical polymer blends are used for molded or extruded optical elements; in other applications, optical polymer blends are used for optical adhesives with low thermal expansion coefficients.

An object of the invention is to provide an optoelectronic system or an optoelectronic sensor which is more available during temperature changes and is cheaper to manufacture.

The object is achieved according to claim 1 by an optoelectronic system with at least one circuit board with several light emitters and/or several light receivers which are arranged at least in one row and with at least one one-piece optical component made of plastic for the several light emitters and/or light receivers, wherein at least one lens is provided in the optical component per light emitter and/or per light receiver, wherein the optical component is mechanically fixed to the circuit board at least at one point, wherein the circuit board has a first positive thermal linear expansion coefficient and the optical component has a second positive thermal linear expansion coefficient, wherein the second positive thermal linear expansion coefficient is greater than the first positive thermal linear expansion coefficient, wherein particles made of a secondary material which are made of a different material than a primary material of the optical component are mixed into the optical component, wherein the secondary material of the particles has a smaller thermal linear expansion coefficient than the second thermal linear expansion coefficient of the primary material of the optical component, so that the resulting second positive coefficient of linear expansion of the optical component is reduced.

The object is further achieved with an optoelectronic sensor with an optical system according to claim 13.

The secondary material of the particles has a positive or negative coefficient of thermal expansion, so that the resulting second positive coefficient of thermal expansion of the optical component is reduced. In the case of a positive coefficient of thermal expansion of the secondary material, the coefficient of thermal expansion of the secondary material is smaller than the second coefficient of thermal expansion of the primary material of the optical component.

According to the invention, the first thermal linear expansion coefficient of the optical component is reduced by the added particles. The optical component consists of at least a portion of primary material and a portion of secondary material. This minimizes the different linear expansion of the optical component and the circuit board when there are temperature fluctuations. This means that the optical axes that run from the light transmitters or from the light receivers through the center of the respective associated lens are each more directionally stable within a required tolerance range. For example, light axes that are parallel to one another remain almost parallel to one another even when there are temperature fluctuations, since the circuit board and the optical component expand or contract to the same extent, depending on the temperature change.

The optical component and the circuit board are referenced to each other by mechanically fixing the optical component to the circuit board at least at one location. For example, the circuit board and the optical component are connected to each other at a single end of an elongated shape. However, the optical component and the circuit board can be connected to each other at any location.

For example, the first thermal expansion coefficient of the circuit board is less than 17 ppm/K.

The resulting second positive coefficient of linear expansion of the optical component is, for example, less than 40 ppm/K. Preferably, the resulting second positive coefficient of linear expansion of the optical component is less than 20 ppm/K.

Particularly preferably, the difference between the first coefficient of thermal expansion and the second coefficient of thermal expansion is less than 5 ppm/K, particularly preferably less than 2 ppm/K.

The optical component, for example, has a proportion of 5 to 30 percent by volume of secondary material. In particular, the optical component has a proportion of 5 to 20 percent by volume and, in particular, a proportion of 5 to 10 percent by volume of secondary material.

In a further development of the invention, the particles for the secondary material are glass particles and/or crystal particles. These materials each have negative thermal linear expansion coefficients.

In a further development of the invention, the particles are smaller than 50 nm in diameter.

Particles with a diameter of less than 50 nm are particularly effective in reducing the expansion of the optical component. The very small particles have little impact on the optical properties of the optical component. This means that homogeneous materials can be produced for the optical component. Glass particles and/or crystal particles are also advantageously transparent, so that the optical properties of the optical component are hardly affected by the secondary materials.

In a further development of the invention, the lenses are plano-convex, biconvex or convex-planar.

Such lenses are converging lenses, whereby received light is bundled onto the light receiver and/or transmitted light from a light transmitter leads to a directed beam.

A collecting lens, also called a collimator lens, convex lens or positive lens, is a cast lens with positive refractive power. Parallel incident light is collected in its focal plane. In particular, light that is incident parallel to the optical axis is focused at the focal point.

With the lens shapes plano-convex, biconvex or convex-plan, for example, only a single lens is necessary per light transmitter or per light receiver.

In a further development of the invention, the surface shape of the lens is spherical, aspherical or a free-form surface.

In contrast to a spherical lens, an aspherical lens is a lens with at least one refractive surface that deviates from the spherical or flat shape. The largely freely formable surface allows imaging errors that are unavoidable with spherical lenses to be avoided or reduced. In particular, spherical aberration can be corrected.

Using a freeform surface, the lens can be adapted very specifically to the optical requirements and the required geometry.

In a further development of the invention, the light transmitters and/or the light receivers are arranged in a matrix with several rows and several columns.

This makes it possible to create large-scale lighting with light transmitters and large-scale surveillance areas with light receivers.
Any flat geometry can be created using the selected number of rows and columns and the distances between the respective light transmitters or light receivers.

In a further development of the invention, an elongated housing comprising at least two parts is provided, the two-part housing having at least two housing parts, the first housing part comprising the optical component and the second housing part comprising the circuit board. The circuit board is inserted into the second housing part.

The housing parts are each open along one long side. This means that necessary components, namely the optical component and the circuit board, can be inserted directly via the respective open long side. This simplifies assembly.

The two housing parts each have similar or almost identical positive thermal expansion coefficients.

In a further development of the invention, the optical component is integrated in the first housing part, so that the first housing part and the optical component are a one-piece component. The first housing part is transparent to the light used. The one-piece first housing part with the integrated optical component eliminates assembly steps. Furthermore, the first housing part and the optical component are already aligned with each other in terms of production technology.

The first housing part with the integrated optical component can be made of two different materials or of a single material.

In a further development of the invention, the first housing part and the second housing part are connected by means of mechanical clip fasteners, by means of an adhesive connection, by means of an ultrasonic weld seam or by means of a laser weld seam.

Clip fasteners have the advantage that they can be installed very easily without additional devices. The clip fasteners are, for example, integrated into the respective housing parts.

A tight connection between the housing parts can be easily created using an adhesive bond, ultrasonic welding seam or laser welding seam. This makes it easy to create a tight housing.

In a further development of the invention, the first housing part is manufactured as a plastic injection molding using a plastic injection molding process. Using a plastic injection molding process, precise lens shapes of high quality can also be manufactured inexpensively. Using a plastic injection molding process, high-quality parts with a limited length, for example less than 500 mm, can be manufactured. These parts can be connected to form a longer housing part. Another plastic injection molding process is "exjection", with which long components < 3 m can be manufactured in one step.

The first housing part and the optical component can be manufactured in a two-component injection molding process using different materials. However, the first housing part and the optical component can also be manufactured in a one-component injection molding process using a single material.

In a further development of the invention, the second housing part is manufactured using an extrusion process. The mechanical accuracy requirements for the second housing part are lower than for the first housing part, since the second housing part does not have any optical components such as lenses. This means that the second housing part can be manufactured more cheaply using an extrusion process. The only requirement here is that there is a uniform contour in the cross section.

In a further development of the invention, the second housing part has a larger volume than the first housing part. Since the second housing part is cheaper to manufacture than the first housing part and the materials used for the second housing part are cheaper than for the first housing part, it is provided that the second housing part has a larger volume than the first housing part, thereby reducing the costs for the entire housing.

According to the invention, an optoelectronic sensor is provided with an optical system.

For example, a first housing with the light transmitters and a second housing with the light receivers form an optoelectronic sensor, such as a light barrier, a reflection light barrier, a light sensor, a camera system with lighting, or for example a solid state laser scanner with a plurality of light transmitters and light receivers, wherein no moving parts, such as a rotating deflection unit, are provided.

In a further development of the invention, the optoelectronic sensor is a light grid.

Light grids comprise a large number of light transmitters or transmitting elements and associated light receivers or receiving elements, so that a pair of a transmitting element and a receiving element forms a light barrier that detects whether or not the light beam spanned between the transmitting element and the receiving element is interrupted by an object. The transmitting elements and receiving elements are each combined in a transmitting unit and a receiving unit, which are mounted opposite each other.

There are also light grids in which the light transmitter and light receiver are housed in two mixed transmitting and receiving units facing each other. There are also known reflection light grids in which the transmitting and receiving units are mounted on one side of a monitoring area and a retroreflector on the opposite side.

An important field of application for light grids is automation technology for measuring items and objects or for dimensional control but also for object detection and especially for object counting.

Another important application area for light grids is safety technology. The parallel light beams serve as a kind of virtual wall, and if they are interrupted by an object, for example, a source of danger is secured. In automation technology, light grids are used to measure the size of objects based on the number of interrupted beams. For example, the height of objects moving on a conveyor belt can be determined in this way, with an accuracy that is determined by the distance between the light beams.

The idea of a light beam from the individual transmitting elements is idealized. In fact, depending on the opening angles of the beam-forming optics, transmitting and receiving lobes are created. With normal distances between the transmitting unit and the receiving unit, it is often unavoidable that, due to the transmitting beam divergence, a receiving element receives transmitted light not only from the assigned transmitting element, but also from its neighbors. In order to avoid incorrect evaluations, the transmitting elements are therefore activated cyclically. In this process, one after the other, each transmitting element receives element sends out individual light pulses or packets, and for a certain time window only the corresponding receiving element is activated to determine whether there is an object in the respective channel.

The invention is explained below with regard to further advantages and features with reference to the accompanying drawings using exemplary embodiments.

• 1 bis 4 jeweils ein optoelektronisches System;
• 5 ein zweiteiliges Gehäuse;
• 6 ein erstes Gehäuseteil;
• 7 einen optoelektronischen Sensor;
• 8 ein optoelektronisches System nach dem Stand der Technik.

The figures in the drawing show:

• 1 until 4 one optoelectronic system each;
• 5 a two-part housing;
• 6 a first housing part;
• 7 an optoelectronic sensor;
• 8 an optoelectronic system according to the state of the art.

In the following figures, identical parts are provided with identical reference symbols.

8 shows an optoelectronic system according to the state of the art. In such optoelectronic systems or optoelectronic sensors, an optic 16 expands differently in the event of temperature changes due to the expansion coefficients of the materials used than the materials used in a circuit board 2 on which light transmitters 3 and/or light receivers 4 are arranged. As a result, the optical axes 17 are arranged according to 8 are no longer aligned parallel to each other, but are disadvantageously positioned at an acute angle to each other.

1 shows an optoelectronic system 1 according to the invention with a circuit board 2 with several light transmitters 3 and/or several light receivers 4, which are arranged at least in one row and with at least one one-piece optical component 5 made of plastic for the several light transmitters 3 and/or light receivers 4, wherein in the optical component 5 at least one lens 6 is provided per light transmitter 3 and/or per light receiver 4, wherein the optical component 5 is mechanically fixed at least at one point to the circuit board 2, wherein the circuit board 2 has a first positive thermal linear expansion coefficient and the optical component 5 has a second positive thermal linear expansion coefficient, wherein the second positive thermal linear expansion coefficient is greater than the first positive thermal linear expansion coefficient, wherein the optical component 5 is mixed with particles 7 made of a secondary material 8, which are made of a different material than the optical component 5, wherein the secondary material 8 of the particles 7 has a negative thermal linear expansion coefficient, so that the resulting second positive linear expansion coefficient of the optical component 5 is reduced.

According to 1 the first thermal linear expansion coefficient of the optical component 5 is reduced by the added particles 7. The optical component 5 consists of at least a portion of primary material 9 and a portion of secondary material 8. This minimizes the different linear expansion of the optical component 5 and the circuit board 2 in the event of temperature fluctuations. This means that the optical axes 17, which run from the light transmitters 3 and from the light receivers 4 through the center of the respective associated lens 6, are each more directionally stable within a required tolerance range. For example, light axes that are parallel to one another remain almost parallel to one another even in the event of temperature fluctuations, since the circuit board 2 and the optical component 5 expand or contract to the same extent, depending on the temperature change.

The optical component 5 and the circuit board 2 are referenced to each other by the optical component 5 being mechanically fixed to the circuit board 2 at least at one point. For example, the circuit board 2 and the optical component 5 are connected to each other at a single end of an elongated shape. However, the optical component 5 and the circuit board 2 can be connected to each other at any point.

For example, the first thermal expansion coefficient of the circuit board 2 is less than 17 ppm/K. The resulting second positive expansion coefficient of the optical component 5 is according to 1 for example less than 40 ppm/K, or less than 20 ppm/K.

The optical component 5 has, for example, a proportion of 5 to 20 volume percent of secondary material 8, with 95 to 80 volume percent being formed by the primary material 9.

According to 1 The particles 7 for the secondary material 8 are glass particles and/or crystal particles. These materials each have negative thermal expansion coefficients.

For example, particles 7 are smaller than 50 nm in diameter.

Due to the very small particles 7, the optical properties of the optical component 5 are hardly affected. This allows homogeneous materials to be produced for the optical component 5. Glass particles and/or crystal particles are also advantageously transparent, so that the optical properties of the optical component 5 are hardly affected by the secondary materials 8.

According to 1 the lenses 6 are plano-convex or convex-planar.

According to 1 the lenses 6 are converging lenses, whereby received light is bundled onto the light receiver 4 and/or transmitted light from a light transmitter 3 leads to a directed beam.

With the lens shape according to 1 For example, only a single lens 6 is required per light transmitter 3 or per light receiver 4.

According to 1 the surface shape of the lens 6 is spherical or aspherical.

According to an embodiment not shown, the light transmitters and/or the light receivers are arranged in a matrix with several rows and several columns.

2 shows a further embodiment according to the invention similar to 1 . 2 shows an optoelectronic system 1 with a circuit board 2 with several light transmitters 3 and/or several light receivers 4, which are arranged at least in one row and with at least one one-piece optical component 5 made of plastic for the several light transmitters 3 and/or light receivers 4, wherein in the optical component 5 at least one lens 6 is provided per light transmitter 3 and/or per light receiver 4, wherein the optical component 5 is mechanically fixed to the circuit board 2 at least at two points

According to 3 an elongated at least two-part housing 11 is provided, wherein the two-part housing 11 has at least two housing parts 12 and 13, wherein the first housing part 12 has the optical component 5 and the second housing part 13 has the circuit board 2.

The housing parts 12 and 13 are each open along one long side. This means that necessary components, namely at least the optical component 5 and the circuit board 2, can be inserted directly over the respective open long side. This simplifies assembly.

The two housing parts 12 and 13 each have similar or almost identical positive thermal expansion coefficients.

According to 3 the optical component 5 is integrated in the first housing part 12, so that the first housing part 12 and the optical component 5 are a one-piece component. The first housing part 12 is transparent to the light used. The one-piece first housing part 12 with the integrated optical component 5 eliminates assembly steps. Furthermore, the first housing part 12 and the optical component 5 are already aligned with each other in terms of production technology.

The first housing part 12 with the integrated optical component 5 can be made of two different materials or of a single material.

According to 4 the first housing part 12 and the second housing part 13 are connected by means of mechanical clip fasteners, by means of an adhesive connection, by means of an ultrasonic weld seam or by means of a laser weld seam.

The clip fasteners are, for example, integrated into the respective housing parts. A tight connection between the housing parts 12 and 13 can easily be created using an adhesive connection, ultrasonic welding seam or laser welding seam.

According to 3 the first housing part 12 is manufactured as a plastic injection molding using a plastic injection molding process. The first housing part 12 and the optical component 5 can be manufactured using different materials in a two-component injection molding process. However, the first housing part 12 and the optical component 5 can also be manufactured using a single material in a one-component injection molding process.

According to 3 the second housing part 13 is manufactured using an extrusion process. The mechanical accuracy requirements for the second housing part 13 are lower than for the first housing part 12, since the second housing part 13 does not have any optical components such as lenses. The only requirement here is that there is a uniform contour in the cross section.

According to 3 For example, the second housing part 13 has a larger volume than the first housing part 12.

5 shows a further embodiment of a two-part housing 11 in the assembled state in cross section. The second housing part 13 has further fastening receptacles.

6 shows a subassembly consisting of the circuit board 2 with the light transmitters 3 and/or the light receivers 4 and a tube 18, namely a light trap and the first housing part 12 with the lenses 6.

According to 7 An optoelectronic sensor 14 is provided with an optical system 1.

According to 7 A first housing with the light transmitters and a second housing with the light receivers form an optoelectronic sensor 14, such as a light barrier with several optical axes or light beams.

According to 7 the optoelectronic sensor 14 is a light grid 15. Light grids 15 comprise a plurality of light transmitters 3 or transmitting elements and associated light receivers 4 or receiving elements, so that a pair of a transmitting element and a receiving element forms a light barrier that detects whether or not the light beam spanned between the transmitting element and the receiving element is interrupted by an object. The transmitting elements and receiving elements are each combined in a transmitting unit and a receiving unit, which are mounted opposite one another.

Reference number:

1

Optoelectronic system

2

Circuit board

3

Light transmitter

4

Light receiver

5

Optical component

6

lens

7

Particles

8

Secondary material

9

Primary material

11

two-part housing

12

first housing part

13

second housing part

14

optoelectronic sensor

15

Light grid

16

optics

17

optical axis

18

Tube

Claims (13)

Optoelectronic system (1) with at least one circuit board (2) with several light transmitters (3) and/or several light receivers (4) which are arranged at least in one row and with at least one one-piece optical component (5) made of plastic for the several light transmitters (3) and/or light receivers (4), wherein at least one lens (6) is provided in the optical component (5) for each light transmitter (3) and/or light receiver (4), wherein the optical component (5) is mechanically fixed to the circuit board (2) at least at one point, characterized in that the circuit board (2) has a first positive thermal linear expansion coefficient and the optical component (5) has a second positive thermal linear expansion coefficient, wherein the second positive thermal linear expansion coefficient is greater than the first positive thermal linear expansion coefficient, wherein particles (7) made of a secondary material (8) are mixed into the optical component (5), which are made of a different material than a primary material of the Optical component (5), wherein the secondary material (8) of the particles (7) has a smaller thermal linear expansion coefficient than the second thermal linear expansion coefficient of the primary material of the optical component, so that the resulting second positive linear expansion coefficient of the optical component (5) is reduced, wherein an elongated at least two-part housing (11) is provided, wherein the two-part housing (11) has at least two housing parts (12, 13), wherein the first housing part (12) has the optical component (5) and the second housing part (13) has the circuit board (2). Optoelectronic system according to Claim 1 , characterized in that the particles (7) are glass particles and/or crystal particles. Optoelectronic system according to at least one of the preceding claims, characterized in that the particles (7) are smaller than 50 nm in diameter. Optoelectronic system according to at least one of the preceding claims, characterized in that the lens (6) is plano-convex, biconvex or convex-planar. Optoelectronic system according to at least one of the preceding claims, characterized in that the surface shape of the lens (6) is spherical, aspherical or a free-form surface. Optoelectronic system according to at least one of the preceding claims, characterized in that the light transmitters (3) and/or the light receivers (4) are arranged in a matrix with several rows and several columns. Optical system according to at least one of the preceding claims, characterized in that the optical component is integrated in the first housing part (12), so that the first housing part (12) and the optical component (5) are a one-piece component. Optical system according to at least one of the preceding claims, characterized in that the first housing part (12) and the second housing part (13) are connected by means of mechanical clip closures, by means of an adhesive connection, by means of an ultrasonic weld seam or by means of a laser weld seam. Optical system according to at least one of the preceding claims, characterized in that the first housing part (12) is manufactured as a plastic injection molding by means of a plastic injection molding process. Optical system according to at least one of the preceding claims, characterized in that the second housing part (13) is produced by means of an extrusion process. Optical system according to at least one of the preceding claims, characterized in that the second housing part (13) has a larger volume than the first housing part (12). Optolelectronic sensor (14) with an optoelectronic system (1) according to at least one of the aforementioned Claims 1 until 11 . Optolelectronic sensor (14) according to Claim 12 , characterized in that the optoelectronic sensor (14) is a light grid (15).

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