Optoelectronic sensor

Abstract

Optoelectronic sensor (10) of the type of a photoelectric sensor, with at least one measuring light source (12) for emitting measuring light beams (14) in the infrared wavelength range into a monitoring area (34), at least one pilot light source (20) for emitting pilot light beams (22) in the visible wavelength range into the monitoring area (34), an optical element for coaxially superimposing measuring light beams (14) and pilot light beams (22), a light receiver (44) for receiving measuring light beams (38) remitted or reflected from the monitoring area (34) and generating corresponding received signals, a control and evaluation unit (46) for controlling the light receiver (44), the measuring light source (12) and / or the pilot light source (20) and for evaluating the received signals, characterized in that the optical element is designed as an optical waveguide (18).

Description

The invention relates to an optoelectronic sensor for detecting an object in a monitoring area according to the preamble of claim 1. Many optoelectronic sensors operate on the touch principle, in which a light beam is emitted into the detection area and the light beam reflected by an object is received. The received signal is then electronically evaluated, for example, for distance measurement. Often, the time of flight of light is measured using a known phase or pulse method to determine the distance to a touched object. Optoelectronic sensors that use this method are frequently referred to as optical sensors, TOF (Time-of-Flight) sensors, or LIDAR (Light Detection and Ranging) sensors. In the following, the term optical sensor will be used as a general term. Photoelectric sensors of the type mentioned above can operate with visible light as well as with light in the infrared wavelength range. The use of infrared light has the advantage that the measurement is not perceived as disruptive. Furthermore, light sources that emit infrared light, such as vertical-cavity surface-emitting lasers (VCSELs), are available in smaller sizes than laser diodes that emit visible light. Therefore, a sensor can be built correspondingly smaller. However, an infrared light signal has the disadvantage that the detection range, in particular the specific location of the distance measurement on the respective surface, cannot be detected by the human eye without additional aids, which makes the mounting and adjustment of the sensor particularly difficult. In the prior art, a visible pilot or target beam is superimposed on the infrared measuring beam, usually with a dichroic mirror, as described, for example, in US 2004 0070745 A1. However, such systems are relatively large, and the alignment of the measuring beam and pilot beam is complex and prone to misalignment. US patent 2019 / 0025407 A1 discloses a laser-based distance measuring device (LADAR sensor). The LADAR sensor features an internal alignment laser for closed-loop control of scan mirrors that deflect a measuring light beam into a monitoring area. CN 207586421 U describes a laser rangefinder with a measuring beam source and a pilot beam source, wherein the beam sources are alternately activated and deactivated. Whether and how the measuring beam and pilot beam are superimposed is not disclosed. US Patent 5436757 A relates to an optical wavelength conversion device in which light of different wavelengths is coupled into a nonlinear optical waveguide. Wavelength mixing within the waveguide transforms the wavelength of the coupled light. US Patent 5222163 A discloses an optical node with a channel optical waveguide formed on a substrate for connecting data transmission lines of an optical network. A transmitting section of the optical node comprises several laser diodes that emit light beams of different wavelengths, which are combined using a Y-coupler (wavelength multiplexing for data transmission). US 5030321 A discloses a manufacturing process for optical waveguide couplers used in optical network technology. The waveguide couplers can be designed as symmetrical or asymmetrical Y-couplers. Based on this state of the art, the object of the invention is to provide an improved sensor in the form of a light switch, which has a compact and robust design. This problem is solved by an optoelectronic sensor having the features of claim 1. The optoelectronic sensor according to the invention is a photoelectric sensor with at least one measuring light source for emitting at least one measuring light beam in the infrared wavelength range. These light beams are not to be understood as rays in the sense of ray optics within a larger beam of light, but rather as beams of light that, upon striking an object in the monitored area, generate corresponding spots of light. An associated light receiver is capable of generating received signals from reflected or remitted measuring light beams. A control and evaluation unit controls the light sources and the light receiver and can evaluate the received signals from the light receiver to obtain information about the object, such as its distance to the sensor. To align the infrared measuring light beam, which is invisible to the human eye, at least one pilot light beam emitted by a pilot light source in the visible wavelength range is provided, as well as an optical element for superimposing the measuring light beam and the pilot light beam, so that they produce essentially overlapping light spots in the monitored area. The invention is based on the fundamental idea of ​​using an optical waveguide as the optical element for superimposing the measuring light beam and the pilot light beam. This has the advantage that the superposition of the light beams in the optical waveguide can be achieved largely without adjustment. To superimpose the measuring light beam and the pilot light beam, the optical waveguide has a first section with a first coupling point for coupling in the measuring light beam, a second section with a second coupling point for coupling in the pilot light beam, and a third section for superimposing the measuring light beam and the pilot light beam with an output coupling point for outputting the superimposed light beams, wherein the sections can be discrete elements of a multi-part optical waveguide or areas of a single-part optical waveguide. In one embodiment of the invention, the optical waveguide for superimposing the measuring light beam and the pilot light beam can be designed like an optical fork coupler or Y-coupler. Such couplers are known from the prior art, for example, from optical data transmission, wherein the first section and the second section are each arranged at an angle to the third section. The angles are chosen to be as small as possible for high coupling efficiency, preferably less than 10 degrees. The smallest possible angle is generally determined by the geometry of the components, in particular the size of the light sources. The measuring light beam coupled into the first section and the pilot light beam coupled into the second section are combined at the interface of the three sections and superimposed in the third section. In an alternative embodiment of the invention, the optical waveguide for superimposing the measuring light beam and the pilot light beam is designed such that the first and third sections are arranged coaxially, and the second section is arranged at an angle to the first and third sections. The measuring light beam coupled into the first section thus travels along a straight line through the optical waveguide. Compared to the previously described embodiment, this embodiment exhibits improved coupling efficiency between the measuring light beam and the pilot light beam. As in the embodiment described above, the angle is chosen to be as small as possible for high coupling efficiency, preferably less than 10 degrees. The smallest possible angle is generally determined by the geometry of the components, in particular the size of the light sources. The optical waveguides are preferably integrated into an electro-optical circuit board, which can be produced using photolithographic methods. The light sources and / or the control and evaluation unit can also be arranged on the electro-optical circuit board. This enables a highly integrated sensor design with minimal space requirements. To improve light mixing, the third section of the optical waveguide can have a beam homogenizer in the form of a light guide rod with a square or hexagonal cross-section. The third section of the optical waveguide can have a coupling point with the smallest possible cross-section for extracting the superimposed light beams, in order to generate a small measurement light spot in the monitored area. The cross-section is preferably less than 100 µm, and particularly preferably less than 50 µm. For this purpose, the beam homogenizer or optical waveguide in the third section can be tapered, i.e., the optical waveguide cross-section can be narrowed towards the coupling point. The first section of the optical waveguide can have an enlarged cross-section at the coupling point for the measurement beam to allow the coupling of measurement beams with a larger beam diameter or multiple parallel measurement beams. Thus, the coupled light power can be increased by using a multi-emitter VCSEL. This compensates for lower coupling efficiencies, especially those of planar optical waveguides. The electro-optical circuit board can have mirror elements at the ends of the optical waveguide for coupling the light rays in and out. Alternatively, coupling prisms, which are either mirrored or operate on the principle of total internal reflection, can be arranged at the ends of the optical waveguide. The coupling of the measuring and pilot light beam can take place at an end face of the circuit board, so that beam deflection can be dispensed with. The pilot light source can emit pilot light beams with a wavelength adapted to the light sensitivity of the human eye. For example, green light with a wavelength of 550 nm is perceived by the human eye as 31 times brighter than red light with a wavelength of 670 nm. Therefore, when using green light, a lower-power pilot light source can be used. An optical filter can be placed upstream of the light receiver to suppress stray light, especially reflected or remitted pilot light beams. The sensor's control and evaluation unit can be configured to provide various operating modes. One operating mode, for example, could be an adjustment mode in which the measuring light beam and pilot light beam are activated simultaneously. Another operating mode could be a measurement mode in which the pilot light beam is deactivated, thus reducing the amount of stray light generated by the pilot beam that reaches the light receiver. According to a further development, the photoelectric sensor is designed to determine the distance between a given surface and the sensor itself from the travel time of a pulsed light signal to the surface and back, or from the phase shift of a modulated light signal emitted by the sensor compared to the light signal reflected from the surface. The photoelectric sensor can therefore operate, in particular, according to the Time-of-Flight (ToF) principle. The invention will now be explained in detail using an exemplary embodiment with reference to the drawing. In the drawing: Fig. 1 shows a schematic representation of the sensor according to the invention; Fig. 2a shows a schematic representation of an optical waveguide configured as a Y-coupler; Fig. 2b shows a schematic representation of an optical waveguide with lateral coupling of the pilot light beam; Fig. 2c shows a schematic representation of a further embodiment of the optical waveguide; Fig. 3 shows a schematic representation of an optical waveguide arranged in an electro-optical circuit board. Fig. 1 shows a schematic representation of an optoelectronic sensor 10 in an embodiment as a light sensor. The sensor 10 has a measuring light source 12, for example a laser diode or a vertical-cavity surface-emitting laser (VCSEL), which emits a measuring light beam 14 in the infrared wavelength range. This beam is coupled into the optical waveguide 18 at a first coupling point 62. The sensor 10 also has a pilot light source 20, for example a light-emitting diode (LED), which emits pilot light beams 22 in the visible wavelength range. The pilot light beams 22 are coupled into the optical waveguide 18 at a second coupling point 66. The measuring light beam 14 and the pilot light beam 22 are superimposed in the optical waveguide 18 and coupled out of the optical waveguide 18 at an output point 72.The superimposed measuring light and pilot light beams 26 can be collimated with a transmitting optic 28 and projected through a window 30 in the housing 32 of the sensor 10 into a monitoring area 34. The light reflected or remitted by an object 36 in the monitoring area 34 is directed as received light 38 via an optical filter 40 to suppress stray light and onto a receiving optic 42 and a light receiver 44. The light receiver 44 is preferably designed as a photodiode, APD (Avalanche Photo Diode), or SPAD (Single-Photon Avalanche Diode), or SPAD matrix (SPAD array). The sensor 10 also includes a control and evaluation unit 46, which is connected to the measuring light source 12, the pilot light source 20, and the light receiver 44. The control and evaluation unit 46 comprises a measuring light source control 48, a pilot light source control 50, a time-of-flight measurement unit 52, and an object distance estimation unit 54. These are initially only functional blocks that can also be implemented in the same hardware or in other functional units such as the light sources 12, 20, or the light receiver 44. The control and evaluation unit 46 can output measurement data and, conversely, receive control and parameterization instructions via an interface 56. The control and evaluation unit 46 can also be arranged as local evaluation structures on a chip of the light receiver 12 or interact as a partial implementation with the functions of a central evaluation unit (not shown). The control and evaluation unit 46 can be designed to activate and deactivate pilot light source 20 and measuring light source 12 independently of each other. Fig. 2a shows a schematic representation of an embodiment of the optical waveguide 18 for superimposing a measuring light beam 14 with a pilot light beam 22 in a design as a Y-coupler. The optical waveguide 18 has a first section 60 with a first coupling point 62 for coupling the measuring light beam 12, a second section 64 with a second coupling point 66 for coupling the pilot light beam 22, and a third section 68 for superimposing the measuring light beam 14 and the pilot light beam 22, the boundaries of the sections being indicated by dotted lines 70. The sections 60, 64, 68 can be discrete elements of a multi-part optical waveguide 18, for example, fiber elements joined together by a fusion bond, or regions of a single-part optical waveguide 18, which was produced, for example, by a photolithographic process in a printed circuit board. The first section 60 and the second section 64 are each arranged at a first angle α and a second angle β with respect to the third section 68. The measuring light beam 14 coupled into the first section 60 and the pilot light beam 22 coupled into the second section 64 are combined at the interface of the three sections and superimposed in the third section 68. The third section 68 has an output point 72 for extracting the superimposed light beams 26. Fig. 2b shows an alternative variant of an optical waveguide 18 for superimposing the measuring light beam 14 and the pilot light beam 22, which is designed such that the first section 60 and the third section 68 are arranged coaxially and the second section 64 is arranged at a third angle γ to the first section 60 and third section 68. The measuring light beam 14 coupled into the first section 60 thus travels through the optical waveguide 18 along a straight line 74. Fig. 2c shows an alternative variant of an optical waveguide 18 from Fig. 2b which is designed such that the first section 60 and the third section 68 are arranged coaxially and the second section 64 has a curvature 76 at the transition to the first and third sections. Figure 3 shows a schematic representation of an electro-optical circuit board 80 into which an optical waveguide 18 is integrated. A measuring light source 12 and a pilot light source 20 are arranged on the electro-optical circuit board 80, emitting measuring light beams 14 and pilot light beams 22 perpendicular to the circuit board plane 82 into the optical waveguide 18. The optical waveguide 18 has deflecting elements 86, 88 at the coupling points 62, 66, which deflect the light beams 14, 22 parallel to the circuit board plane 82. In the optical waveguide 18, the measuring light beam 14 and the pilot light beam 22 are superimposed and coupled out of the optical waveguide 18 at the coupling point 72 by a further deflecting element 90 perpendicular to the circuit board plane 82. A transmitting optic 28 collimates the coupled-out superimposed light beams 26.Alternatively, the coupling can also take place at an end face 92 of the circuit board 80, the further deflection element 90 at the coupling point 72 can then be omitted.

Claims

Optoelectronic sensor (10) of the type of a photoelectric sensor, with at least one measuring light source (12) for emitting measuring light beams (14) in the infrared wavelength range into a monitoring area (34), at least one pilot light source (20) for emitting pilot light beams (22) in the visible wavelength range into the monitoring area (34), an optical element for coaxially superimposing measuring light beams (14) and pilot light beams (22), a light receiver (44) for receiving measuring light beams (38) remitted or reflected from the monitoring area (34) and generating corresponding received signals, a control and evaluation unit (46) for controlling the light receiver (44), the measuring light source (12) and / or the pilot light source (20) and for evaluating the received signals, characterized in that the optical element is designed as an optical waveguide (18). Optoelectronic sensor (10) according to claim 1, wherein the optical waveguide (18) has a first section (60) with a first coupling point (62) for coupling in measuring light beams (14), a second section (64) with a second coupling point (66) for coupling in pilot light beams (22) and a third section (68) for superimposing the measuring light beams (14) and the pilot light beams (22) with an output coupling point (72) for coupling out the superimposed light beams (26) from the optical waveguide (18). Optoelectronic sensor (10) according to claim 2 wherein the optical waveguide (18) is multi-part, and the sections (60, 64, 68) are discrete elements of the multi-part optical waveguide (18). Optoelectronic sensor (10) according to claim 2 wherein the optical waveguide is made in one piece, and the sections (60, 64, 68) are regions of the one-piece optical waveguide (18). Optoelectronic sensor (10) according to one of claims 2 to 4, wherein the optical waveguide (18) is configured as a Y-coupler, wherein the first section (60) has a first angle (α) and the second section (64) has a second angle (β) to the third section (68). Optoelectronic sensor (10) according to one of claims 2 to 4, wherein the first section (60) and the third section (68) are arranged coaxially and the second section (64) is arranged at an angle (y) to the first section (60) and to the third section (68). Optoelectronic sensor (10) according to one of claims 2 to 6, wherein the third section comprises a beam homogenizer. Optoelectronic sensor (10) according to one of the preceding claims, wherein the optical waveguide (18) is arranged in an electro-optical circuit board (80). Optoelectronic sensor (10) according to claim 8, wherein the optical waveguide (18) has at least one deflecting element (86, 88, 90) for deflecting light rays (14, 22, 26) into and / or out of a printed circuit board plane (82) of the printed circuit board (80). Optoelectronic sensor (10) according to one of claims 2 to 9, wherein the optical waveguide (18) has a tapered section in the region of the coupling point (72). Optoelectronic sensor (10) according to one of claims 2 to 9, wherein the first section (60) of the optical waveguide (18) has an enlarged cross-section in the area of ​​the first coupling point (62) for coupling the measuring light beam (14). Optoelectronic sensor (10) according to one of the preceding claims, wherein the pilot light source (20) emits pilot light beams (22) in the wavelength range of 490 - 640 nm.

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