OPTICAL SENSOR

Description

[0001] The invention relates to a sensor arrangement comprising an optical sensor for detecting at least one object in a monitoring area, a transmitter emitting light beams, a receiver receiving light beams, and an evaluation device for generating an object detection signal depending on received signals at an output of the receiver, and comprising a transmitting optic and a receiving optic, wherein the transmitting optic serves to collimate the transmitted light beams and the receiving optic serves to focus the received light beams on the receiver, according to the preamble of claim 1.

[0002] Optical sensors for detecting objects, which can be designed as reflective photoelectric sensors or distance sensors, consist of a light source for emitting visible or invisible light and a detector for receiving light emitted by the light source. Examples of light sources or transmitters include LEDs, laser diodes, or IR diodes. The transmitter or light source can be pulsed or clocked. It can also be advantageous to polarize the light or to focus it into a beam using apertures, lenses, or collimators.

[0003] In the optical sensors to which the invention relates, a retroreflector limiting the monitoring area is generally provided as a cooperative target.

[0004] All the transmitted light rays guided via the retroreflector are reflected back onto the optical sensor in a narrow scattering cone, so that the transmitted light is essentially reflected back at the retroreflector in the same direction in which it struck it.

[0005] The advantage here is that object detection, and especially distance measurement, becomes possible even over long distances. However, a disadvantage is that problems arise with object detection or distance measurements at close range, because the retroreflector's reflective properties result in too little transmitted light reaching the optical sensor's receiver.

[0006] To address this problem, separate near-field optics can be provided, but this leads to increased design effort and also increased space requirements.

[0007] EP 3 546 980 A1 relates to an optical sensor for detecting objects in a monitoring area of ​​the sensor, comprising a light transmitter with transmitting optics for emitting light beams, a receiver with receiving optics for receiving light beams, and an evaluation unit for generating an object detection signal depending on received signals at an output of the receiver, wherein the transmitting optics and the receiving optics have different optical axes.In order to be able to use light emitted from an object, which is directed towards a transition area between transmitting optics and receiving optics, for the generation of received signals, and in particular to be able to use light from the near area to the receiving optics, it is provided that the optical sensor has a device for collimating light beams onto the receiving optics, which is arranged in the transition area between the transmitting optics and the receiving optics and directs light from the transition area onto the receiving optics.

[0008] EP 0 170 008 A2 relates to a photoelectric sensor or photoelectric barrier with a light transmitter and a light receiver, both housed in the same casing, and with a plano-convex lens for focusing the light from the transmitter into a beam, focusing the reflected light, and means for directing the reflected light to the receiver. The plano-convex lens surface is inclined to a plane perpendicular to the axis of the light beam.

[0009] CH 378 420 A1 relates to a photoelectric device comprising a light source, a photosensitive element, and a reflector. The device includes means for blocking a portion of the cross-section of the beam emanating from the light source that surrounds the optical axis. Furthermore, a converging optical system is provided between the light source and the reflector, influencing the beam. The zone of this optical system corresponding to a blocked zone, which influences the reflected light component, has a different focal length than the zone surrounding this zone.

[0010] EP 1 512 992 A1 relates to an optical sensor for detecting objects in a monitoring area, comprising a transmitter emitting light beams, a receiver receiving light beams, and an evaluation unit for assessing the received signals at the receiver's output. The transmitter is equipped with a transmitting optic in the form of a plano-convex lens. The receiver consists of a multiple array of receiving elements. In a learning process, the transmitter's light beams illuminate a background object that defines the monitoring area. The levels of the received signals from the receiving elements, generated by the light beams reflected back from the background object to the receiver, are then used as a reference signal profile in the evaluation unit.After the learning process has been completed, an object message is generated in the evaluation unit if the signal curve of the levels of the received signals of the receiving elements deviates from the reference signal curve.

[0011] EP 2 362 237 A1 relates to a laser radar sensor with a light-emitting transmitter and a light-receiving receiver. To generate a light beam with a diverging beam profile, the transmitter is associated with a transmitting optic in the form of a rotating cylindrical lens.

[0012] DE 10 2015 115 101 A1 relates to a sensor system with a 3D camera that determines distance values ​​using a time-of-flight method, and with a light source. The light source is associated with a transmitting optic for dispersing the emitted light.

[0013] CN 108 415 148 A relates to a device with a light-emitting transmitter and a light-receiving receiver. Optical elements in the form of deflecting mirrors and lenses are provided in the light beam path.

[0014] Based on this state of the art, the invention is based on the objective of specifying a sensor arrangement with an optical sensor whose lower limit of the measuring range is minimized while at least maintaining its far-range properties and its emission performance.

[0015] The problem is solved with an optical sensor having the features of claim 1.

[0016] The invention relates to a sensor arrangement comprising an optical sensor for detecting at least one object within a monitoring area and a retroreflector defining the monitoring area. The optical sensor includes a transmitter emitting light beams, a receiver receiving light beams, and an evaluation unit for generating an object detection signal based on received signals at an output of the receiver, as well as transmitting optics and receiving optics. The transmitting optics collimate the transmitted light beams, and the receiving optics focus the received light beams onto the receiver. The transmitting optics include a collimating lens for increasing the power density of the transmitted light beams at at least one edge region of a light spot generated by the transmitting optics on the retroreflector. The collimating lens has a first refractive surface facing the transmitter.The device is characterized by a defined concave, rotationally symmetrical shape tapering to a point at a center, with respect to an axis of the transmitted light rays. The first refractive surface spreads the transmitted light rays away from the axis, guiding them through the collimator lens and onto a second refractive surface that forms a convex ring surface relative to the incoming transmitted light rays. The second refractive surface focuses the transmitted light rays, which then exit as an annular beam with increased power density.

[0017] In the event that the optical sensor is a distance sensor, the retroreflector itself forms the object to be detected, the distance of which is to be determined.

[0018] Preferred embodiments result from the dependent claims.

[0019] By incorporating a device in the transmitting optics to increase the power density of the transmitted light beams at at least one edge region of the light spot projected onto an object or reflector, a technical measure is implemented to provide more light to the receiving optics in the near field, because a higher proportion of the transmitted light follows the path that the receiving optics can detect. Conversely, the proportion of the transmitted light in the center of the light spot, which falls completely back into the transmitter after reflection and is lost in the near field, is reduced.

[0020] The geometric shape of the edge of the transmitted light spot on the retroreflector can be arbitrary and adapted to the receiving optics. It is predefined.

[0021] The boundary region with increased power density of the transmitted light beams can be formed from two boundary surface regions diametrically opposed to each other along an axis of the transmitted light beams. The boundary surface regions can be touching or separate from each other.

[0022] The edge area can also have a partial or complete ring shape.

[0023] The advantage is that the entire transmitted light power is directed towards the edge area, whereby the energy distribution can be predetermined.

[0024] According to the invention, the transmitting optics comprise a collimator lens which has a first refractive surface facing the light source. This surface spreads the transmitted light rays from the light source away from the axis. A second refractive surface of the collimator lens collimates the light rays into a ring shape, in which they are then emitted to the retroreflector or the object. This increases both the transmitted light power per unit area of ​​the ring shape and results in a compact ring shape with respect to its diameter and width.

[0025] The collimator lens is preferably manufactured from plastic using an injection molding process. This offers cost advantages and can simplify the arrangement of mounting elements for the collimator lens.

[0026] A collimator lens made of glass offers advantages in terms of mechanical properties such as expansion, as well as in terms of optical properties such as the temperature dependence of the refractive index.

[0027] In any case, the relative received power is increased by the device according to the invention for increasing the power density of the transmitted light beams in a

[0028] Object distance of approximately 0.7 m and less is significantly increased compared to state-of-the-art optical sensors.

[0029] The transmitting and receiving optics preferably form a unit that includes the described collimator lens.

[0030] It can also be advantageous to achieve the described beam shape of the transmitted light rays with an increase in optical power in a peripheral region using a Cassegrain optic consisting of several individual components. The desired beam shaping can also be achieved using a diffractive optical element.

[0031] The invention is explained below with reference to the drawings. The drawings show: Figure 1: A schematic representation of the optical components of an optical sensor designed as a distance sensor according to the prior art; Figure 2: A schematic, perspective view of a longitudinally sectioned transmitting optic of an optical sensor according to the invention; Figure 3: A longitudinal section through a device according to the invention for increasing the power density of the transmitted light beams, which is represented as a collimator lens with a schematic beam path of the transmitted light beams; Figure 4: A perspective view of a collimator lens as shown in Figure 2 and 3 Figure 5a shows a view of a light spot generated by an optical sensor according to the prior art; and Figure 5b shows a view of a light spot generated by an optical sensor according to the invention.

[0032] In Figure 1A schematic diagram shows an optical sensor 1 for detecting the distance to an object 2, represented as a retroreflector 12, within a monitoring area 3. In the case shown, the retroreflector 12 is located in the immediate vicinity, i.e., at a short distance from the optical sensor 1. The optical sensor 1 generates an object detection signal with a downstream evaluation unit (not shown) and outputs this signal as a signal. The optical sensor 1 has a transmitter 5 emitting light beams 4 and a receiver 7 receiving light beams 6, which are connected to the common evaluation unit and integrated in a housing (also not shown). The transmitter 5 consists of a Figure 2The laser diode is shown in a schematic longitudinal section. The receiver 7 can be formed by an avalanche photodiode. The evaluation unit consists of a microprocessor and other peripheral components not shown.

[0033] Distance measurement is performed, for example, according to a phase measurement principle, whereby a modulation frequency is superimposed on the transmitted light beams 4. The phase shift of the received light beams 6 reflected back by the retroreflector 12 to the transmitted light beams 4 emitted by the transmitter 5 is evaluated in the evaluation unit as a measure of the object distance.

[0034] The transmitter 5 and the receiver 7 are not arranged coaxially. A transmitting optic 8 is positioned downstream of the transmitter 5, and a receiving optic 9 is positioned upstream of the receiver 7. The transmitted light beams 4 are guided through the transmitting optic 8 and collimated. In these optical sensors according to the prior art, the light spot 13 produced by the light source 5 is essentially round and homogeneous, as Figure 1 shown on the right in a view of light spot 13.

[0035] Located, as in Figure 1 As shown, the retroreflector 12 in the near field, only the portion 20 of the receiving optics 9 is used to receive the receiving light rays 6, since only this portion 20 of the receiving optics receives light, namely the edge area 11 of the light spot 13.

[0036] If, on the other hand, the retroreflector 12 is located in the far range, i.e. at large distances from the optical sensor 1, the entire receiving optics are illuminated by the light spot 13.

[0037] This disadvantage is overcome by the optical sensor 1 according to the invention, as for example in Figure 2 The transmitting optics 8 is shown with a device 10 for increasing the power density of the transmitted light beams 4 at at least one edge region 11 (cf. Figure 2 and Figure 3 ) of the light spot 13. This transforms significantly more of the optical light power of the transmitter 5 into components of the light spot 13 that can be detected by the receiving optics 9, thereby reducing the measurement range limit of the optical sensor 1 considerably further than is achieved in the prior art.

[0038] In return, the proportion of the transmitted light in the center of the light spot 13, that is, the central area 22 ( Figure 2), which falls completely back into the transmitter 5 after reflection. The range of the optical sensor 1 is not changed because, with the transmitting optics 8 according to the invention, only the spatial distribution of the transmitted light is changed at the same total transmit power. The shape of this spatial distribution no longer plays a role for large reflector distances, so the range of the optical sensor 1 remains unchanged.

[0039] The Figures 5a and 5b This illustrates that in Figure 5a a light spot 13 of an optical sensor 1 according to the prior art is shown, while in Figure 5b a light spot 13 of the optical sensor 1 according to the invention is shown, which assumes a ring shape.

[0040] In principle, other geometric shapes 14 besides the ring shape are conceivable for the light spot 13. The device 10 for increasing the power density of the transmitted light rays 4 is part or an integrated component of the transmitting optics 8 and is advantageously represented by the shape of refractive or refracting lens surfaces 17 and 19 of a collimator lens 16.

[0041] The in the Figures 2 and 3 The collimator lens 16 shown is advantageously made of plastic, but can also be made of a glass material. It is shown in an exemplary view in Figure 4 in addition shown, whereby their surfaces 17 and 19 which act refractively on the transmitting light rays 4 can also be seen.

[0042] As mentioned, the collimator lens 16, representing the transmitting optics 8, has the first refractive surface 17 facing the light source 18, which, as shown in Figures 3 and 4, is characterized by a defined concave, rotationally symmetric shape tapering to a point 21 with respect to an axis 15 of the transmitting light rays 4.

[0043] The first refractive surface 17 spreads the transmitted light rays 4 away from the axis 15, guides them through the lens 16, and directs them to the second refractive surface 19, which is formed as a convex ring surface with respect to the incoming transmitted light rays 4. In the second refractive surface 19, the transmitted light rays 4 are focused and exit the second refractive surface 19 as a ring beam with increased optical power density towards the object 2 or retroreflector 12.

[0044] The calculation of the shape of the two refractive surfaces 17, 19 is based on an analytical method, whereby ray assignments and thus curve shapes of the refractive surfaces 17, 19 can be calculated by solving differential equations.

[0045] The transmitted light power of the inventive optical sensor 1 shown is increased by up to 30% compared to sensors according to the current state of the art, while still maintaining eye safety. Reference symbol list

[0046] (1) Optical sensor (2) Object (3) Monitoring area (4) Transmitting light beam (5) Transmitter (6) Receiving light beam (7) Receiver (8) Transmitting optics (9) Receiving optics (10) Device for increasing the power density of the transmitted light beams (11) Edge area (12) Retroreflector (13) Spot of light (14) Geometric shape (15) Axis (16) Collimator lens (17) First refractive area (18) Light source (19) Second refractive area (20) Proportion of 13 (21) Center (22) Central area

Claims

1. Sensor arrangement with an optical sensor (1) for detecting at least one object (2) in a monitoring area (3), and with a retroreflector (12) delimiting the monitoring area (3), wherein the optical sensor (1) has a transmitter (5) emitting light beams (4), a receiver (7) receiving light beams (6) and an evaluation device for generating an object detection signal as a function of reception signals at an output of the receiver (7), as well as a transmitting optic (8) and a receiving optic (9), wherein the transmitting optic (8) serving to collimate the transmitted light beams (4) and the receiving optics (9) serving to focus the received light beams (6) on the receiver (7), characterised in that the transmitting optics (8) have a collimator lens (16) for increasing the power density of the transmitted light beams (4) at at least one edge region (11) of a light spot (13) produced by the transmitting optics (8) on the retroreflector (12), wherein the collimator lens (16) has a first refractive surface (17) facing the transmitter (5) and is characterised by a defined concave, rotationally symmetrical shape tapering to a centre (21), characterised by a rotationally symmetrical shape with respect to an axis (15) of the transmitted light beams (4), wherein the transmitted light beams (4) are spread away from the axis (15) by the first refractive surface (17), wherein the transmitted light beams (4) are guided through the collimator lens (16) and guided to a second refractive surface (19) forming a ring surface that is convex with respect to the incoming transmission light beams (4), wherein the transmission light beams (4) are focused by the second refractive surface (19) and leave the second refractive surface (19) as a ring beam with increased power density.

2. Sensor arrangement according to claim 1, characterised in that the collimator lens (16) is made of glass or plastic.

3. Sensor arrangement according to one of claims 1 or 2, characterised in that the optical sensor (1) has a receiver (7) arranged coaxially with the transmitter (5), wherein the transmitter (5) and receiver (7) are assigned a collimator lens (16) forming transmitting and receiving optics (8, 9).

4. Sensor arrangement according to claim 1, characterised in that it is designed as a distance sensor.