Optical sensor

Abstract

Optical sensor (1) for detecting objects (15) in a monitoring area with a transmitter (5) emitting light beams (4), with a receiver (8) receiving light beams (7), with a deflection unit (11) by means of which the transmitted light beams (4) are periodically guided within a scanning area, and with an evaluation unit (10) in which received signals from the receiver (8) are evaluated and an object detection signal is generated depending on this, characterized in that at least one optical element is connected to the deflection unit (11).

Description

The invention relates to an optical sensor for detecting objects in a monitored area. The optical sensor comprises a housing that integrates a transmitter emitting light beams, a receiver receiving light beams, and an evaluation unit that generates an object detection signal based on the receiver's received signals. An exit disc, through which the transmitted and received light beams are guided, is located in one wall of the housing. The housing also contains a deflection unit, for example, a motor-driven deflecting mirror rotating around an axis. This deflection unit periodically guides the transmitted light beams within a plane of the scanning area. In particular, the optical sensor can be designed as an area distance sensor, i.e., a scanning distance sensor, with which positions of objects in the monitored area can be determined. Such optical sensors can be designed as safety sensors and used for monitoring hazardous areas at facilities that pose a risk to people. In this case, the optical sensor effectively monitors a protective field within its scanning range. The evaluation of the receiver's received signals is then carried out in such a way that a binary object detection signal is generated, the switching states of which indicate whether an object is located within the protective field. This object detection signal is sent to a controller that operates the system. If an object detection signal is sent indicating that no object is present in the protective field, the system is enabled to operate. If the optical sensor generates an object detection signal with a switching state corresponding to an object detection in the protective field, this signal shuts down the system via the controller to prevent hazardous situations. One problem with such optical sensors is to reliably detect objects at both small and large distances from the optical sensor. The invention is based on the objective of providing an optical sensor with high functionality. The features of claim 1 are provided to solve this problem. Advantageous embodiments and expedient further developments of the invention are described in the dependent claims. The invention relates to an optical sensor for detecting objects in a monitoring area, comprising a transmitter emitting light beams, a receiver receiving light beams, and a deflection unit by which the transmitted light beams are periodically guided within a scanning area. An evaluation unit analyzes the received signals from the receiver. Based on this analysis, an object detection signal is generated. At least one optical element is connected to the deflection unit. The optical sensor according to the invention forms a scanning sensor in which transmitted light beams emitted by the transmitter are periodically guided within a scanning area by means of a deflection unit. The optical sensor generally works according to a light-tap principle such that transmitted light rays emitted by the transmitter are directed onto an object to be detected and from there are directed back to the receiver as received light rays, advantageously also being guided via the deflection unit. The components of the optical sensor are conveniently integrated into a housing. A section of the housing wall is formed by an exit disk through which the transmitting and receiving light beams are guided. The exit disc is transparent to the transmitting and receiving light rays, while the rest of the housing is opaque. The optical sensor is particularly advantageous as an area distance sensor, i.e., designed as a scanning distance sensor, which can be used to determine the positions of objects in the scanning area. The optical sensor according to the invention, particularly in its configuration as an area distance sensor, can be designed as a safety sensor suitable for use in safety-relevant applications. For this purpose, the safety sensor has a fail-safe design, for example with a fail-safe evaluation unit in the form of a multi-channel computer architecture. In particular, the safety sensor can be used to detect obstacles or collisions. Furthermore, the security sensor can be used for person detection. The optical sensor can be used, in particular, for monitoring the protective field. A binary object detection signal is then generated in the evaluation unit, the switching states of which indicate whether an object is located within the protective field or not. A key requirement for this is that the optical sensor can reliably detect objects across the entire scanning range. According to the invention, this is achieved by connecting at least one optical element to the deflection unit. The optical element preferably forms an additional element to a transmitting optics directly downstream of the transmitter and a receiving optics directly upstream of the receiver. The optical element according to the invention makes it possible to selectively increase the detection reliability in a specific area of ​​the scanning range. The optical element can influence the transmitted light rays and / or the received light rays. The optical element is particularly advantageous as a near-range element, improving the detection of objects at close range, i.e., at small distances from the optical sensor. In this case, the optical element favorably influences the received light rays. Furthermore, the optical element can be used to block out contamination of the housing's exit lens. Blocking out contamination here means that the stray light caused by contamination on the lens cannot reach the receiver, or only to a very limited extent. It is advantageous if the optical element is positioned directly in front of the housing's exit disc. This is ensured by the fact that the optical element is rigidly connected to the deflection unit and is therefore automatically located close to the exit disc. The optical element can, in particular, generate a suitable selection of the received light rays to increase the detection of objects in the immediate vicinity and to suppress contamination of the exit lens. This is fundamentally possible because the received light rays from objects in the immediate vicinity strike the optical element from different distances and directions than the scattered light from contamination on the exit lens. According to an advantageous embodiment, the optical element is a deflecting prism or a deflecting mirror. According to a further advantageous embodiment, the optical element is a spherical or aspherical lens. Furthermore, the optical element can be a diffractive optical element. Finally, the optical element can be a multifocal optic, with which different focus areas can be realized. According to a beneficial further training, several optical elements with different optical properties are present. For example, the optical elements are used to select different imaging areas of objects within the received light beams. The optical elements thus allow the detection sensitivity to be specifically increased in different zones in front of the optical sensor. According to an advantageous embodiment of the optical sensor, the transmitter and the receiver are arranged in a stationary position. A deflection unit rotating about an axis of rotation is provided, by which the transmitted light beams are deflected. Advantageously, the deflection unit deflects both the transmitted and received light rays. The deflection unit is generally driven by an electric drive and thus set into a rotary motion around the axis of rotation. The deflection unit can have a polygon mirror wheel that can be rotated about an axis of rotation. The polygon mirror wheel has several mirror surfaces on which the transmitting and receiving light rays are deflected one after the other by the rotational movement of the polygon mirror wheel. The deflection unit features a particularly advantageous deflecting mirror that can be rotated around a pivot axis. The transmitted and received light rays are then deflected at the mirror surface of the deflecting mirror and guided in the scanning area by its rotational movement. In this embodiment, it is advantageous if the optical element or elements are located in the edge region of the deflecting mirror. This means that each optical element is located close to the exit disc and can thus block out contamination of the exit disc, since the angles of incidence of backscattered light from objects outside the scanner differ greatly from those of scattered light from contamination on the scanner hood. The optical element(s) can be mounted on a bracket projecting above the deflecting mirror and rotating with the deflection unit. In particular, each optical element is mounted on the deflecting mirror. According to an advantageous embodiment, the scanning area is a flat surface. Alternatively, the scanning area can be a conical surface. According to an advantageous further development, a control unit is provided by means of which the deflection of the transmitted light beams at the deflection unit can be varied. This allows a three-dimensional scanning area to be scanned using the transmitted light beams. According to an advantageous further development, sensor means are provided for monitoring the contamination of the exit disc. This allows the contamination of the outlet disc to be monitored. In particular, an error message can be generated if the contamination exceeds a certain level. The invention is explained below with reference to the drawings. They show: Fig. 1: Schematic representation of a first embodiment of the optical sensor according to the invention a) when detecting an object in the far range. b) when detecting an object in the near range. c) when detecting scattered light from contaminants on the scanner hood. Fig. 2: Optical arrangement for the optical sensor according to Fig. 1. Fig. 3: Variant of the embodiment according to Fig. 1. Fig. 4: Variant of the embodiment according to Fig. 1 with a first configuration of window monitoring. Fig. 5: Variant of the embodiment according to Fig. 1 with a second configuration of window monitoring. Figures 1a, 1b, and 1c show a highly schematic embodiment of the optical sensor 1 according to the invention. The components of the optical sensor 1 are integrated into a housing 2. One wall of the housing 2 is formed by a translucent exit disk 3 extending circumferentially around the housing 2. The optical sensor 1 comprises a transmitter 5 emitting light beams 4 and a transmitting optic 6 positioned downstream of the light beams, as well as a receiver 8 receiving light beams 7 and a receiving optic 9 positioned upstream. The transmitter 5 is, for example, a laser diode, and the receiver 8 is an avalanche photodiode or the like. The transmitting / receiving unit thus configured is stationary within the housing 2. Furthermore, an evaluation unit 10 is present, which may be a microcontroller or the like. The evaluation unit 10 controls the transmitter 5 and evaluates received signals from the receiver 8 to generate an object detection signal. The optical sensor 1 also has a deflection unit 11, by means of which the transmitted light beams 4 are periodically guided within a planar scanning area. The deflection unit 11 has an electric drive 12 arranged in a base 2a of the housing 2 which stands on a support, which drives a drive shaft 13, thereby setting a deflecting mirror 14 into a rotational movement about a rotational axis. The axis of rotation runs along the drive shaft 13 in a vertical direction. The plane of the deflecting mirror is inclined at 45° to the horizontal. This guides the transmitted light beams 4 by means of the deflection unit 11 into a scanning area that lies in a horizontal plane. The optical sensor 1, as in all other embodiments, is designed as an area distance sensor. The transmitter 5 and the receiver 8 form a distance sensor that advantageously operates according to a pulse time-of-flight method. For this purpose, the transmitter 5 emits transmit light beams 4 in the form of light pulses. These are guided across the reflective surface of the deflecting mirror 14 and pass through the exit disk 3. From an object 15 to be detected, the transmit light beams 4 are reflected back as received light beams 7, pass through the exit disk 3, and are guided via the deflecting mirror 14 to the receiver 8. The object distance is determined from the measured light time of the light pulses. Together with the current deflection position of the deflection unit 11, which is detected by a measuring encoder, the object position within the scanning area is obtained. The optical sensor 1 is advantageously a safety sensor designed for use in safety-related applications and has a fail-safe design, which can be implemented, for example, with an evaluation unit 10 in the form of a multi-channel computer structure. Advantageously, the optical sensor 1 monitors a protective field within the scanning range. The optical sensor 1 then generates a binary object detection signal, the switching states of which indicate whether an object 15 is located in the protective field or not. The illustrations in Figs. 1a and 1b are highly schematic, particularly with regard to the beam path of the transmitting light rays 4 and receiving light rays 7. Fig. 1 shows a transmitting / receiving unit with which a coaxial beam path of the transmitting light rays 4 and receiving light rays 7 can be realized. According to the invention, the optical sensor 1 of Fig. 1a, Fig. 1b, Fig. 1c has an optical element connected to the deflection unit 11, which in the present case is designed as a near-range element 16. In the present case, the near-area element 16 is mounted on the reflective surface of the deflecting mirror 14 in its edge region. As can be seen from Fig. 1a , Fig. 1b, the near-range element 16 improves the detection of objects 15 in the near range, i.e. at small distances to the optical sensor 1. For an object 15 in the far range, i.e. at large distances from the optical sensor 1, the received light rays 7 are guided directly to the receiver 8 via the deflecting mirror 14 ( Fig. 1a). When an object 15 is in close proximity, the receiving light rays 7 are not guided, or only insufficiently guided, to the receiver 8 via the deflecting mirror 14. According to the invention, objects 15 in close proximity can be detected by guiding the receiving light rays 7 to the receiver 8 via the close-range element 16 (Fig. 1b). It is also advantageous that the near-field element 16 is located directly in front of the exit disk 3. The focus area of ​​the near-field element 16 is then set such that as little light as possible from contaminants on the exit disk 3 is directed to the receiver 8. The closer the near-field element 16 is to the exit disk 3, the better the stray light from contaminants can be separated from the received light 7 by the near-field element 16. As outlined in Fig. 1c, rays of scattered light originating from contaminants 15´ on the inner and / or outer surface of the exit disk 3, after passing the near-field element 16, exhibit a targeted strong tilt towards the axis of the receiver 8 compared to received light from external objects in the far and / or near field (see Fig. 1a, Fig. 1b) and can thus be effectively reduced or suppressed spatially. The optical element can advantageously be a deflecting prism or a deflecting mirror. Furthermore, the optical element can be a spherical or aspherical lens. Furthermore, the optical element can be a diffractive optical element. Finally, any optical element can be a multifocal optic. In the present case, the optical element designed as a near-field element 16 only influences the received light rays 7. Alternatively or additionally, the optical element can also influence the transmitted light rays 4. Fig. 3 shows an extension of the embodiment according to Fig. 1a , Fig. 1b in that two near-area elements 16, 16´ are present on the deflecting mirror 14 in its edge region. According to the embodiment shown in Fig. 1a, Fig. 1b, and Fig. 1c, the first near-range element 16 serves to improve the detection of objects 15 at close range. The second near-range element 16' improves the detection of objects 15 at greater distances. Advantageously, different focus areas 17, 17' are realized using the near-range elements 16, 16', which define different sensitivity ranges within the scanning range. As sketched in Fig. 3, a focus area 17, 17' is intended to mark the distance range from which the received light is focused most narrowly and thus most efficiently onto the receiver. The sensitivity ranges can be set so that contamination on the exit disc 3 is not detected or only detected to a limited extent. Interfering objects in the vicinity of the optical sensor 1 can also be filtered out. In the embodiments of Fig. 1a, Fig. 1b, Fig. 1c, Fig. 3, the scanning area extends in a horizontal plane. By modifying the deflection unit 11, a conical scanning area can also be scanned, in which, for example, the deflecting mirror 14 or the measuring head has different orientations. In general, it is also possible to dynamically tilt components of the deflection unit 11 by means of an actuating unit in order to scan a three-dimensional scanning area. The embodiments shown in Fig. 4 and Fig. 5 represent further developments of the embodiment shown in Fig. 1a, Fig. 1b, Fig. 1c, in that they include sensor means for monitoring the contamination of the exit disc 3. In the embodiment of Fig. 4, window monitoring is provided such that a transmitting element 19 in the upper part of the housing 2 emits light beams 20 which are guided through the exit disk 3 to a receiving element 21 in the base 2a of the housing 2. The greater the contamination of the exit disk 3, the lower the amount of light from the light rays 20 registered at the receiving element 21. To measure the entire exit disk 3, several transmitting elements 19 and receiving elements 21 can be provided in the circumferential direction of the exit disk 3. Fig. 5 shows a variant of the window monitoring system. In this case, the transmitter 19 and the receiver 21 are located in the upper part of the housing 2. A reflector 22 is located in the base 2a. To perform the window monitoring, the light beams 20 pass through the transmitter 19, first through the exit disc 3, then reach the reflector 22, are reflected by it, then pass through the exit disc 3 a second time, and then reach the receiver 21. If the window monitoring system detects that a critical level of contamination has been exceeded on the exit pane 3, an error message is generated. The arrangement described here for contamination control represents only one possible embodiment; other arrangements for stationary or rotating transmitter and receiver elements for implementing contamination control are possible. Reference symbol list 1 Optical sensor 2 Housing 2a Base 3 Exit disc 4 Transmitting light beam 5 Transmitter 6 Transmitting optics 7 Receiving light beam 8 Receiver 9 Receiving optics 10 Evaluation unit 11 Deflection unit 12 Drive 13 Drive shaft 14 Deflection mirror 15 Object 15' Contamination on the exit disc 16, 16' Near-range element 17, 17' Focus area 19 Transmitting element 20 Light beam 21 Receiving element 22 Reflector

Claims

Optical sensor (1) for detecting objects (15) in a monitoring area with a transmitter (5) emitting light beams (4), with a receiver (8) receiving light beams (7), with a deflection unit (11) by means of which the transmitted light beams (4) are periodically guided within a scanning area, and with an evaluation unit (10) in which received signals from the receiver (8) are evaluated and an object detection signal is generated depending on this, characterized in that at least one optical element is connected to the deflection unit (11). Optical sensor (1) according to claim 1 , characterized in that the optical element is a near-range element (16, 16'). Optical sensor (1) according to one of claims 1 or 2, characterized in that the optical element is a deflecting prism or a deflecting mirror. Optical sensor (1) according to one of claims 1 or 2, characterized in that the optical element is a spherical or aspherical lens. Optical sensor (1) according to one of claims 1 or 2, characterized in that the optical element is a diffractive optical element. Optical sensor (1) according to one of claims 1 to 5, characterized in that several optical elements with different optical properties are present. Optical sensor (1) according to claim 6, characterized in that different focus areas (17, 17') of the transmitting light rays (4) or receiving light rays (7) are generated with the optical elements. Optical sensor (1) according to one of claims 1 to 7, characterized in that the optical element or elements are a multifocal optic. Optical sensor (1) according to one of claims 1 to 8, characterized in that the optical element(s) influence the transmitting light rays (4) and / or receiving light rays (7). Optical sensor (1) according to claim 9, characterized in that the transmitter (5) and the receiver (8) are arranged in a stationary position, wherein a deflection unit (11) rotating about an axis of rotation is assigned to them, at which the transmitted light beams (4) are deflected. Optical sensor (1) according to claim 10, characterized in that the transmitting light rays (4) and receiving light rays (7) are deflected at the deflection unit (11). Optical sensor (1) according to one of claims 10 or 11, characterized in that the deflection unit (11) has a polygon mirror wheel rotatable about an axis of rotation. Optical sensor (1) according to one of claims 10 or 11, characterized in that the deflection unit (11) has a deflecting mirror (14) rotatable about an axis of rotation. Optical sensor (1) according to claim 13, characterized in that the optical element or elements are located in the edge region of the deflecting mirror (14). Optical sensor (1) according to claim 14, characterized in that the optical element or elements are mounted on a holder projecting beyond the deflecting mirror (14) and rotating with the deflection unit (11). Optical sensor (1) according to claim 14, characterized in that the optical element or elements are mounted on the deflecting mirror (14). Optical sensor (1) according to one of claims 1 to 16, characterized in that the scanning area is a flat surface. Optical sensor (1) according to one of claims 1 to 16, characterized in that the scanning area is a conical surface. Optical sensor (1) according to one of claims 1 to 16, characterized in that an actuating unit is provided by means of which the deflection of the transmitted light beams (4) at the deflection unit (11) can be varied. Optical sensor (1) according to one of claims 1 to 19, characterized in that its components are integrated in a housing (2), wherein at least one section of a housing wall is formed by an exit disk (3) through which the transmitting light rays (4) and receiving light rays (7) are guided. Optical sensor (1) according to claim 20, characterized in that the optical element or elements are located directly in front of the exit disk (3). Optical sensor (1) according to one of claims 20 or 21, characterized in that sensor means for monitoring the contamination of the exit disc (3) are provided. Optical sensor (1) according to one of claims 1 to 22, characterized in that it is an area distance sensor. Optical sensor (1) according to one of claims 1 to 23, characterized in that it is a safety sensor whose evaluation unit (10) has a fail-safe design. Optical sensor (1) according to claim 24, characterized in that it is used to perform obstacle or collision detection. Optical sensor (1) according to claim 24, characterized in that person detection is carried out with it.

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