OPTOELECTRONIC SENSOR

Description

[0001] The present invention relates to an optoelectronic sensor for detecting objects according to the triangulation principle, having a transmitting arrangement for emitting transmitted light signals along a transmitting axis, wherein the transmitting arrangement comprises at least one light source and a transmitting optics which is configured to focus the transmitted signals generated by the at least one light source at a focal point, and having a receiving arrangement having a receiving axis, which comprises a receiving optics for shaping received light signals which are generated by an object by remission of incident transmitted light signals, and a spatially resolving light receiver for receiving the shaped received light signals.

[0002] In such an optoelectronic sensor, which can also be referred to as a triangulation light sensor or generally as a triangulation sensor, the light source and the light receiver on the one hand, and the transmitting optics and receiving optics on the other, are each laterally offset from each other in the so-called triangulation direction, so that the transmitting axis and the receiving axis do not coincide. This type of optoelectronic sensor configuration is also referred to as a biaxial arrangement.

[0003] In an optoelectronic sensor operating according to the triangulation principle, the light receiver consists of at least two photosensitive receiving elements or is designed as a so-called line sensor with at least one line of photosensitive elements.

[0004] Depending on the distance between the sensor and a remitting object, the position of a received light spot, which is generated by the receiving optics by shaping the remitted light—i.e., the light diffusely or specularly reflected from the object—on the light receiver, changes in the triangulation direction. There is a clear geometric relationship between the point of incidence of the received light spot on the light receiver and the distance to the detected object. By evaluating the light distribution on the light receiver, the distance between the sensor and the object can be determined, or it can be established whether or not a detected object is within a specified distance from the optoelectronic sensor.

[0005] Such sensors are used to detect any objects present in a monitoring area detectable by the sensor, taking into account the distance of an object from the sensor. For this purpose, a corresponding evaluation unit can be provided, which is connected at least to the light receiver and is configured to process electrical received signals generated by the light receiver by converting detected received light signals into electrical signals, and to generate a corresponding object detection signal based on the electrical received signals. Such an object detection signal can, for example, include information about the aforementioned distance of the object or it can be generated based on a comparison with a distance threshold.Such a comparison may, for example, include checking whether a determined object distance is greater or smaller than a predefined distance threshold or whether the determined object distance lies within or outside a predefined distance range.

[0006] For reliable object detection, it is desirable for the transmitted light signals to be as focused as possible on the object to be detected, i.e. that the transmitted light spot generated on the object by the transmitted light signals has the smallest possible diameter. This ensures that the received light spot generated by the receiving optics on the light receiver has a high local energy density, which increases the switching point precision, and also minimizes errors in object detection caused by objects that do not reflect homogeneously. The location at which the light spot has a minimum diameter is called the focal point. The location on the receiving axis closest to the focal point is also called the operating point.The distance of the operating point from the optoelectronic sensor can also be referred to as the working distance, where the working distance essentially corresponds to the focal length of the focal point or is trigonometrically related to it. By changing the distance between the light source and the transmitting optics, the focal length and thus the working distance can be changed.

[0007] The focal length should not be confused with the focal length of the transmitting optics, and the focal point is therefore not the same as the focal point of the transmitting optics. Rather, the focal length corresponds to the image distance, if the creation of a light spot on an object to be captured at the focal point is understood as an image of a light source on the object to be captured.

[0008] Depending on the specific application situation for a triangulation sensor, it is desirable to be able to adjust the working distance or focal length so that the sensor can be used not only at a fixed working distance, but also within a specified working distance range. Such a working distance range can, for example, extend from a few millimeters or centimeters to several decimeters or meters, or even to infinity.

[0009] A disadvantage of many conventional triangulation sensors is that a change in the working distance or focal length of the transmitting arrangement not only changes the position of the focal point along the direction of the receiving axis, but also in the triangulation direction perpendicular to the receiving axis. This shifts the position of the received light spot on the light receiver in the triangulation direction as well. To ensure the largest possible working distance range with such triangulation sensors, correspondingly long light receivers must be used to ensure reliable detection of the received light spot in all circumstances. This increases the cost of the sensor and also increases the space required for the sensor components.

[0010] Various approaches to adjusting the working distance are described in the state of the art, but these do not solve the described problem or only partially solve it, or they cause considerable effort.

[0011] Thus, DE 29 24 685 A1 discloses a sensor arrangement in which the transmitting arrangement and the receiving arrangement can be adjusted synchronously with respect to their angular position by means of a gear device, so that the intersection point of the transmitting axis and the receiving axis lies on a straight line of symmetry.

[0012] DE 100 06 321 A1 describes a method for producing an optical monitoring device, in which the transmitter and / or the receiver or the transmitting optics and / or the receiving optics are aligned in a plane perpendicular to the optical axis to a maximum transmitting power in the target area or a maximum receiving power at the receiver and are then fixed in this position.

[0013] DE 198 21 112 C1 discloses a light sensor according to the triangulation method with button width adjustment, in which the transmitting lens and the receiving lens are coupled via a gear so that during an adjustment the transmitting lens is moved linearly and the receiving lens is pivoted synchronously.

[0014] In the optical proximity switch disclosed in DE 10 2015 009 619 A1, the light receiver can be moved in the triangulation direction by means of an adjustment unit.

[0015] EP 2 159 599 B1 discloses a triangulation sensor in which the transmitting axis and the receiving axis extend diagonally and symmetrically with respect to an apparent optical axis. The transmitting arrangement comprises a plurality of light sources arranged at different distances from the transmitting lens and the apparent optical axis, with one of the light sources being activated to set a desired working distance. Since, in this arrangement, the transmitted light spot is always imaged onto the apparent optical axis, the received light spot moves on the light receiver due to the angle between the receiving axis and the apparent optical axis when the working distance changes.

[0016] It is the object of the invention to provide an optoelectronic sensor for detecting objects according to the triangulation principle, in which the focal length of the transmitting arrangement can be adjusted with little effort in such a way that the point of incidence of a received light spot generated on the light receiver is as independent as possible or, at least substantially, independent of the selected focal length.

[0017] The object is achieved by an optoelectronic sensor having the features of claim 1. According to the invention, it is provided that a relative position of an exit location of the transmitted light signals from the at least one light source relative to the transmitting optics can be selected such that the focal length, which corresponds to the distance of a focal point from the transmitting optics, can be set to a desired value, wherein the various relative positions are located on a positioning curve which is selected such that respective focal points assigned to the positioning curve for different focal lengths lie on a focal point line, wherein the distance of the focal point line from the receiving axis is minimized at least within a predetermined working distance range.

[0018] The at least one light source can, for example, be a point light source with a small light emission area and a divergent light emission. The use of cost-intensive laser light sources can be avoided.

[0019] A light receiver with a relatively low spatial resolution can be used as the light receiver, for example, a so-called dual-element sensor or a differential sensor with only two light-sensitive elements. Furthermore, a line sensor with relatively few light-sensitive elements or a short overall length can also be used. This also reduces the effort required for downstream signal processing of the electronic received signals.

[0020] As already explained, the aforementioned focal length at least essentially defines an operating point of the sensor, which can also be defined as the location in the range of the set focal length or in the range of the focal point where an object to be detected is expected. The focal point line describes the positions of the focal points for different focal lengths and can therefore also be somewhat inaccurately referred to as an operating point line. The aforementioned relative position can be illustratively understood as a position in a two-dimensional coordinate system, for example a Cartesian coordinate system, one axis of which runs in the triangulation direction and the other axis in a direction perpendicular to it, essentially parallel to the receiving axis. The origin of this coordinate system can be placed either in the light source or in the transmitting optics.The relative position then specifies the coordinates in this coordinate system for the position of the other element, i.e., the transmitting optics or the light source, and thus describes the distance between the light source or the light exit point and the transmitting optics in the direction of the receiving axis, as well as the lateral offset in the triangulation direction. The coordinates of different relative positions therefore differ in at least one, usually in both, dimensions.

[0021] Selecting or changing the relative position is achieved, in particular, by changing the position of the transmitting optics at a fixed light exit location of the light source, or by changing the position of the light exit location of the light source at a fixed transmitting optics, which will be explained in more detail below. The term "stationary" can be understood, for example, as "fixed relative to a housing of the sensor arrangement" or as "fixed relative to a supporting structure that is not necessarily fixed with respect to a housing of the sensor arrangement." Changing or selecting the relative position between the exit location of the transmitted light signals and the transmitting optics can be done both continuously and in discrete steps. By changing the relative position both in the direction of the receiving axis and in a direction transverse to it, i.e.in the triangulation direction, the relative angle between the transmitting axis and the receiving axis can be changed such that the focal point is kept on or near the receiving axis, so that the point of incidence of the received light spot on the light receiver remains essentially unchanged when the focal length is changed, at least within the working distance range.

[0022] This effect is achieved according to the present invention by minimizing the distance of the focus point line from the reception axis over the largest possible working distance range. This can be achieved in particular by calculating the positioning curve in a mathematically exact manner, taking into account the various geometric parameters. Alternatively, a simplified approximate solution for the positioning curve can also be calculated, for example by applying a mathematical optimization method or other known approximation methods. Thus, the focus point line can coincide with the reception axis at least within the predetermined working distance range, i.e. the distance between the focus point line and the reception axis is zero, or at least a certain predetermined maximum distance between the focus point line and the reception axis is not exceeded.In both cases, a specific focal length range or working distance range may be excluded from minimization, for example, an extremely close range for which minimization is no longer feasible due to technical and / or geometric limitations. Thus, the specified working distance range may be smaller than a maximum possible working distance range, which may be limited, for example, by the outermost adjustment positions of the light source or the transmitting optics, e.g., a range between the endpoints of the positioning curve.

[0023] Since in the sensor according to the invention at least a large proportion of all possible focal points lie on or close to the reception axis, after the sensor has been set to a respective desired operating point, at which the focal length is set that at least approximately corresponds to the desired operating point, a received light spot generated by an object located at the set operating point always strikes the light receiver at approximately the same location. Therefore, a comparatively compact light receiver, in particular even a two-element receiver, can be used. Without the inventive adjustment of the relative position between the light exit point and the transmitting lens when the focal length changes, the point of incidence of the received light spot on the light receiver would shift along the triangulation direction, relative to an object located at the operating point defined by the set focal length.

[0024] According to a preferred embodiment of the invention, the positioning curve runs along a straight line. Such a straight-line course of the positioning curve is an example of a simplified approximate solution. Alternatively, the positioning curve can also have a curved course and be defined, for example, by a second- or higher-order polynomial.

[0025] According to a further preferred embodiment of the invention, the transmitting optics have an optical plane, the positioning curve of the relative positions runs in a transmitting plane, the receiving axis and / or the focal point line run in a receiving plane, and the transmitting plane, the optical plane, and the receiving plane intersect in a common intersection line. In this context, the optical plane is understood to be a main extension plane or main plane of the transmitting optics. In this embodiment, the optical plane, the transmitting plane, and the receiving plane satisfy the conditions of Scheimpflug's rule. With such a configuration, by definition, the light exit locations of the transmitted light signals for the various relative positions are located in the transmitting plane, which can also be referred to as the focal plane.Accordingly, the light source(s) are sharply imaged into the receiving plane, regardless of their position in the transmitting plane; the receiving plane can also be referred to as the image plane. With such a Scheimpflug arrangement, only one relative position needs to be selected for a desired focal length or working distance. Configuring the sensor according to Scheimpflug's rule then automatically ensures that the corresponding focus points are always located on the receiving axis or at least on the focus point line that is essentially identical to the receiving axis. Preferably, the receiving axis and the focus point line run in a receiving plane, which can thus also be referred to as a common receiving plane.

[0026] According to a further preferred embodiment of the invention, the transmitted light arrangement comprises a light source that is displaceable along the positioning curve, or the transmitted light arrangement comprises a transmitting optic that is displaceable along the positioning curve. The positioning curve is, so to speak, a trajectory along which the light source or the transmitting optic can be displaced. As already explained at the beginning, the displaceability of the light source or the transmitting optic can relate to a housing of the optoelectronic sensor or to a supporting structure provided within the housing, in which or on which, in the first case, the transmitting optics and, in the second case, the light source and, in both cases, optionally also the light receiver and / or the receiving optics can be arranged in a stationary manner. The at least one light source is preferably located in the transmitting plane. Particularly preferably, exactly one light source is provided.

[0027] According to the invention, the light source and the light receiver are arranged on a common carrier module, spaced apart from each other in a triangulation direction. Said carrier module can be, for example, a printed circuit board or electronics card. By combining the two electrical components mentioned on a common carrier module, the manufacturing and assembly costs can be significantly reduced compared to a solution with two separate carrier modules or printed circuit boards.

[0028] According to a further preferred embodiment of the invention, the carrier module is displaceable along the positioning curve. Thus, the light source is displaced along the positioning curve or trajectory together with the light receiver.

[0029] According to a further preferred embodiment of the invention, the receiving optics are coupled to the carrier module in such a way that the angular position of the receiving axis does not change when the carrier module is moved. In other words, the receiving axis is merely displaced parallel and not tilted. The receiving optics are thus displaced parallel to the positioning curve. However, the receiving optics need not be rigidly connected to the carrier module; rather, the receiving optics can be displaceable in the direction of the receiving axis, for example, in order to adjust the focus for the received light spot on the light receiver if necessary.

[0030] According to a further advantageous embodiment of the invention, the positioning curve is defined by a linear or nonlinear approximation function, which preferably tangentially touches an ideal positioning curve at a contact point, wherein the ideal positioning curve is defined by those relative positions for which the focal point line coincides with the receiving axis. If, for the desired application, it is not necessary for the focal point line to coincide exactly with the receiving axis, but rather a deviation of the focal point line from the receiving axis can be tolerated within certain limits, which does not exceed a predetermined maximum value, it may be desirable to simplify the course of the actual positioning curve or trajectory for design or manufacturing reasons.The said linear or non-linear approximation function can be determined, for example, by a series expansion of a function which describes the ideal positioning curve, for example in the form of a Taylor series or a Laurent series. Preferably, the positioning curve described by a linear approximation function, i.e. the real positioning curve, has the form of a tangent to the ideal positioning curve. Alternatively, the real positioning curve described by the linear or non-linear approximation function can be defined by a curve which intersects the ideal positioning curve at two points, in particular by a secant of the ideal positioning curve. If the real positioning curve is to be described by a non-linear approximation function, this can be done, for example, by a polynomial function ora series expansion whose order is smaller than the order of the function that describes the ideal positioning curve.

[0031] In this context, it is preferred if the point of contact is selected for the relative position for which the focal length is infinity or corresponds to a predetermined reference working point. The focal length for the said reference working point is less than infinity. The selection of the reference working point is related to the desired predetermined working distance range. While for a reference working point that is close to or at infinity, the working distance range is more optimized for a long-distance range, i.e. the distance between the focal point line and the reception axis is minimized, in particular for larger focal lengths, with a reference working point provided relatively close to the sensor, a particularly good approximation for the close-up range can be achieved, so that the distance between the focal point line and the reception axis is minimized, in particular for smaller focal lengths.

[0032] According to a preferred embodiment of the invention, the contact point of the approximation function is selected such that, for the selected contact point, a maximum distance of the assigned focus point line from the receiving axis is minimized within the specified working distance range. This implements an optimization method in which, for a specified or desired working distance range for which the optoelectronic sensor is to be optimized, the contact point between the approximation function and the ideal positioning curve is determined at which the maximum distance between the assigned focus point line and the receiving axis assumes the smallest possible value. In other words, the focus point line and the receiving axis are optimally adapted to each other.

[0033] According to a further preferred embodiment of the invention, the distance of the focus point line from the reception axis is additionally minimized by shifting and / or tilting the reception axis. As will be explained in more detail below, the focus point line can have a hyperbolic-like course, particularly for a reference operating point which lies at infinity. With such a course, the distance between the focus point line and the reception axis increases continuously towards smaller focal lengths. By shifting and / or tilting the spatial position of the reception axis, the absolute deviations of the various focus points from the reception axis can be minimized even further, whereby the adjustment can be carried out, for example, by a compensation calculation.

[0034] According to a non-claimed embodiment, the transmitting arrangement comprises a plurality of light sources arranged at a distance from one another along the positioning curve, wherein the selection of a respective relative position is carried out in such a way that only the light source arranged at this relative position is activated and the remaining light sources are deactivated. The plurality of light sources are arranged in a fixed location, preferably in a transmitting plane. This eliminates the need for mechanical displacement of the light source or the transmitting optics. In this context, it has proven advantageous if, for this embodiment as well, the transmitting plane, the optics plane, and the receiving plane intersect in a common intersection line. The aforementioned planes, which have already been defined above, thus fulfill the conditions of Scheimpflug's rule.

[0035] Further advantages are evident from the following description of the drawings. The drawings illustrate exemplary embodiments. The drawings, the description, and the claims contain numerous features in combination. Those skilled in the art will also expediently consider the features individually and combine them into further meaningful combinations.

[0036] They show: Fig. 1 shows a schematic cross-sectional view of an optoelectronic sensor according to a first embodiment not claimed; Fig. 2 shows a schematic cross-sectional view of an optoelectronic sensor according to a second embodiment not claimed; Figs. 3 and 4 show schematic cross-sectional views of an optoelectronic sensor according to a third embodiment corresponding to an inventive configuration in different operating states; Figs. 5 to 7 show schematic cross-sectional views of an optoelectronic sensor according to a fourth embodiment corresponding to another inventive configuration in different operating states; and Figs. 8 to 12 show various schematic views of beam paths.

[0037] In the following, the same reference numerals are used for identical or similar elements or components. In the figures, the dimensions and spacing of the various elements and components are not to scale and are sometimes shown several times larger to illustrate the effects of the invention.

[0038] In Fig. 11 shows an optoelectronic sensor 110 operating according to the triangulation principle according to a first exemplary embodiment not claimed. The sensor 110 comprises a light source 10, which emits divergent transmitted light 14 and is displaceable along a positioning curve P. The positioning curve P is defined by a plurality of discrete relative positions or a continuously variable relative position. Depending on the relative position at which the light source 10 is located, the transmitted light 14 is focused by a transmitting optics 12 into a respective focal point FP. Depending on the selected relative position on the positioning curve P, the transmitted light 14 propagates along a respective transmitted light axis S1 to S4. Each transmitted axis S1 to S4 is assigned a respective focal point FP1 to FP4 according to the index, wherein the focal points FP3 and FP4 are located outside the drawing area and therefore in Fig. 1 are not shown.

[0039] The sensor 110 further comprises a light receiver 20, which in this and all other exemplary embodiments is shown as a two-element light receiver with a long-range element 26.1 and a short-range element 26.2. Instead of such a two-element receiver, a line receiver extending in the triangulation direction T can also be used. The light receiver 20 and an associated receiving optics 22 define a receiving arrangement with a receiving axis E, which can be referred to as the optical axis or main axis of the receiving arrangement. When the transmitted light 14 strikes an object located in the region of the receiving axis E, it is remitted as received light and formed by the receiving optics 22 into a received light spot on the light receiver 20.

[0040] The transmitting optics 12 has a main plane or optical plane OE, which in the exemplary embodiment coincides only coincidentally with the main plane of the receiving optics 22. The positioning curve P is selected here in a transmitting plane SE and the receiving axis E runs in a receiving plane EE. The receiving plane EE, the optical plane OE and the transmitting plane SE intersect in a straight line SG, whereby due to the sectional representation of Fig. 1the aforementioned planes EE, OE, SE are recognizable as straight lines and the intersection line SG as a point. The receiving plane EE, the optical plane OE, and the transmitting plane SE thus satisfy Scheimpflug's condition. This means that the point light source 10, regardless of its relative position in the transmitting plane SE, is always sharply imaged into a focal point FP1,...., FP4 located on the receiving plane EE or the receiving axis E. The distance between the transmitting optics 12 and a respective focal point FP1 to FP4 is referred to as the focal length. The distance between the focal points FP1 to FP4 and the receiving optics 22 is referred to as the working distance, whereby the working distance can be derived from the focal length according to the underlying trigonometric relationships.

[0041] The transmitting optics 12 generates a focused transmitted light spot on an object (not shown), which is located, for example, exactly at a working distance defined by the focal point FP1, exactly at the intersection point between the transmitting axis S1 and the receiving axis E, i.e., at the focal point FP1, so that the received light spot generated by the receiving optics 22 as an image of the transmitted light spot falls directly on the boundary between the far element 26.1 and the near element 26.2. If the distance of the object from the receiving optics 22 is further than the working distance for the focal point FP1, the transmitted light spot migrates downwards on the object (relative to the plane of the drawing), so that the received light spot on the light receiver 20 migrates upwards in the direction of the far element 26.1.If, however, the object is closer to the receiving optics 22 than the working distance, the transmitted light spot strikes the object above the receiving axis E, so that the received light spot on the light receiver 20 migrates downward toward the near element 26.2. The direction in which the received light spot migrates on the light receiver 20 depending on the distance of the object is referred to as the triangulation direction T. Here, this direction runs perpendicular to the receiving axis E in the plane of the figure.

[0042] In Fig. 2 an optoelectronic sensor 210 according to a second embodiment not claimed is shown, which corresponds to the optoelectronic sensor 110 of Fig. 1 similar, so only the main differences are explained below.

[0043] Instead of the sensor 110 ( Fig. 1) provided single light source 10, which is arranged displaceably along the positioning curve P, are in the sensor 210 ( Fig. 2 ) A total of four point light sources 10.1 to 10.4 are arranged in a fixed position along the positioning curve P, distributed on a common circuit board or a common carrier module 16. According to the index number, each light source 10.1 to 10.4 is assigned a transmission axis S1 to S4 and a focus point FP1 to FP4, with the focus points FP3 and FP4 again lying outside the plane of the drawing. To set a desired focal length or a desired working distance, one of the light sources 10.1 to 10.4 is activated, while all other light sources remain deactivated.

[0044] An advantage of the sensor 210 over the sensor 110 is that no mechanical components are required to carry out the displacement, but the adjustment of the working distance can be done exclusively electronically.

[0045] According to a modification, the light sources 10.1 to 10.4 can be mounted on the carrier module 16 at an angle toward the receiving axis E. This allows the proportion of the transmitted light 14 captured by the transmitting optics 12 to be increased.

[0046] In Fig. 3 and 41 shows an optoelectronic sensor arrangement 310 according to a third exemplary embodiment corresponding to an embodiment of the invention. In the optoelectronic sensor 310, the light transmitter 10 and the light receiver 20 are arranged on a common carrier module 16 at a fixed base distance from one another in the triangulation direction T. The receiving optics 22 can also be rigidly connected to the carrier module 16, either directly or indirectly via a housing (not shown) or a supporting structure (also not shown) provided within the housing, which does not necessarily have to be stationary relative to the housing. If necessary, the receiving optics 22 can be displaceable along the receiving axis E in order to be able to adjust the focus of the received light spot. However, the orientation in the triangulation direction T is fixed, so that the angular orientation of the receiving axis E cannot be changed.The transmitting optics 12, however, are arranged to be displaceable relative to the light source 10 along a positioning curve P, which is inclined to the receiving axis E and to the triangulation direction T. In . Fig. 3 the transmitting optics 12 is shown in two different relative positions, which each represent maximum positions and thus define end points of the positioning curve P.

[0047] In Fig. 4 The transmitting optics 12 are additionally shown in an intermediate position between these two maximum positions. Depending on the selected relative position, the transmitted light propagates along one of the three Fig. 3 and 4illustrated transmission axes S1 to S3, wherein each transmission axis S1 to S3 is again assigned a respective focus point FP1 to FP3 according to the index. The focus point FP3 assigned to the transmission axis S3 is at an infinite distance and is therefore not shown in the drawing. While the focus point FP3 defines a maximum working distance, the focus point FP1 defines a minimum working distance. In the present exemplary embodiment, the minimum working distance is determined by a collision limit KG shown with a dash-dotted line. As long as the transmission optics 12 is located completely below the collision limit KG, there is no overlap between the beam paths of the reception optics 22 and the transmission optics 12 in the triangulation direction T, viewed in the direction of the reception axis E.

[0048] The exact determination of the position and orientation of the positioning curve P is described in more detail below.

[0049] In Fig. 5 to 7 An optoelectronic sensor 410 according to a fourth embodiment of the invention is shown. The arrangement of the components of the sensor 410 is similar to the arrangement of the sensor 310 ( Fig. 3 and 4 ), which is why only the main differences are discussed below.

[0050] While the optoelectronic sensor 310 ( Fig. 3 and 4 ) only the transmitting optics 12 is designed to be displaceable along the positioning curve P and the remaining components of the transmitting and receiving arrangement are stationary, the optoelectronic sensor 410 ( Fig. 5 to 7 ) is exactly the opposite. Thus, the transmitting optics 12 are arranged in a fixed position, while the carrier module 16 with the light source 10 and the light receiver 20 as well as the receiving optics 22 are designed to be movable. Fig. 5The carrier module 16 and the transmitting optics 22 are shown in their respective end positions. The displacement of the light source 10 takes place along the positioning curve P, whereby due to the mechanical coupling a positioning curve P' results for the displacement of the light receiver 20 and a positioning curve P" results for the displacement of the receiving optics 22, which for better understanding are also shown in Fig. 5 are shown. The trajectories or positioning curves P, P', P" have the same length and orientation and differ only in their position.

[0051] For a first end position, where the working distance is minimal, a transmission axis S1 results, which intersects the corresponding reception axis E1 at the focal point FP1. For the opposite end position, the transmission axis S2 runs parallel to the corresponding reception axis E2, so that the resulting focal point FP2 lies at infinity and thus in Fig. 5is not shown.

[0052] As in Fig. 5 and also in Fig. 7 can be clearly seen, in contrast to the third embodiment ( Fig. 3 and 4 ) the receiving axis E between the extreme positions E1 and E2. However, this shift is acceptable in practical operation.

[0053] For a better overview, Figs. 6 and 7 The carrier module 16 with the light source 10 and the light receiver 20 as well as the receiving optics 22 are shown separately in their respective extreme positions including the associated axes. In Fig. 6 the configuration for the case with infinite working distance is shown, while Fig. 7 the configuration for the case with minimum working distance is shown, whereby the transmitting axis S2 and the receiving axis E2 for an infinite working distance are also shown here.

[0054] For the optoelectronic sensors 310, 410, particularly when using a two-element light receiver, the adjustment to a desired working distance by changing the relative position between the light source 10 and the transmitting optics 12 is, for practical reasons, not carried out with the aim of generating a transmitted light spot with a minimal diameter on a test object arranged at the working distance. Rather, a test object is positioned at the desired working distance, and then the relative position between the light source 10 and the transmitting optics 12 is shifted until the received light spot generates a defined energy distribution on the light receiver. For the two-element receiver 20 used as an example, this would typically be the case if 50% of the intensity impinges on the far element 26.1 and the remaining 50% impinges on the near element 26.2.If the focus points are not exactly on the receiving axis, this adjustment procedure may result in a slight defocusing of the transmitted light spot, which is, however, acceptable.

[0055] The following are based on Fig. 8 to 12 Calculations are explained to determine, for given optical and geometric parameters, an exact function describing the ideal positioning curve P, as well as approximate functions AF1, AF2 describing a simplified or real positioning curve. For the sake of simplicity, it is assumed that the transmitting optics is a thin lens, which is why it is also referred to as a transmitting lens.

[0056] In Fig. 8 to 12Various positions and components of the optoelectronic sensor as well as corresponding axes, auxiliary lines and curves are shown, which are explained in detail below. Three different cases are distinguished, which are Fig. 8 are designated by a respective index, where a "short working distance" case is designated by the index A, a "medium working distance" case is designated by the index B, and a "infinite working distance" case is designated by the index C. The light source is located at a point LQ, the light receiver at a point LE, and the movable transmitting optics or transmitting lens, depending on the set working distance, is located at a point LA, LB, or LC. Furthermore, the receiving axis E and the respective transmitting axes SA to SC are shown.

[0057] For all three cases A to C, straight lines are obtained between the respective auxiliary points HP AC and L AC , which run parallel to the line LE - LQ, whereby the auxiliary points HP AC represent the intersection points of this straight line with the receiving axis E. The straight lines HP AC - L AC represent a respective triangulation basis and have a respective length b A , b B and b C . Furthermore, in Fig. 8 respective auxiliary lines between the light source LQ and the auxiliary points HP AC are drawn, whereby the distance between these auxiliary lines and the associated lens positions L AC measured parallel to the receiving axis E corresponds to the focal length f of the transmitting lens.

[0058] The following describes the derivation of an ideal positioning curve P for case B. The relevant intersection points are shown in Fig. 8marked by corresponding circles for this case. The distance b B is denoted by b for simplification. The designation n is used for the distance between the points LE and HP B and the designation r for the distance between the points LE and LQ, i.e. the distance between the light receiver and the light source. Finally, as a further reference point, there is an intersection point of the transmitting axis SB, which is relevant for the case under consideration, with the receiving axis E, which is the operating point of the sensor. Although this operating point AP B is actually outside the drawing area, for the sake of illustration it is located at an actually incorrect location in Fig. 8 The distance between the auxiliary point HP B and the working point AP B is denoted by d.

[0059] According to the ray theorem, the following equation applies: f / b = n / r

[0060] Also following the ray theorem, the following equation results: b / d = r / n + d

[0061] Equations (1a) and (2a) initially describe purely geometric length ratios. First, we will show that such an arrangement achieves a sharp image of the light source at the operating point. For this purpose, equations (1a) and (2a) are first transformed: b / r = f / n b / r = d / n + d

[0062] By equating and transforming, the following equations result: f / n = d / n + d 1 / f = n + d / d ⋅ n 1 / f = 1 / d + 1 / n

[0063] Equation (3c) thus corresponds to the imaging equation or lens equation of geometric optics for a thin lens. Thus, a light source whose distance from a lens with focal length f is exactly n will be sharply imaged at a distance d.

[0064] Even though these geometric considerations were only made for case B as an example, the corresponding equations apply to every position of the transmitting lens on the positioning curve P.

[0065] The following explains how to determine an ideal positioning curve P. First, a Cartesian coordinate system is defined, whose origin lies at point LE and whose positive x-direction runs in the direction of the auxiliary point HP B , i.e., in the direction of the receiving axis E, and whose positive y-direction runs in the direction of the straight line LE - LQ. Thus, a respective position of the transmitting lens LB has the following coordinates: x , y = n , b

[0066] First, b is determined as a function of r, f, and d. Rearranging equation (2b) yields: n = d ⋅ r / b − 1

[0067] By inserting equation (2c) into equation (1b) we get: b / r = f / d * r / b − 1 b / r ⋅ d ⋅ r / b − 1 = f d ⋅ 1 − b / r = f 1 − b / r = f / d 1 − f / d = b / r b = r ⋅ 1 − f / d

[0068] Equation (1b) can be rearranged to: n = r ⋅ f / b which together with equation (5f) immediately results in: n = r ⋅ f / r ⋅ 1 − f / d n = f / 1 − f / d

[0069] This results in the ideal positioning curve within the framework of the described boundary conditions: x y = f ∗ d d − f r − r ∗ f d x y = f ∗ 1 1 − f d r − r ∗ f d

[0070] This function is in Fig. 8 shown as positioning curve P.

[0071] With reference to Fig. 9 to 12The determination of approximation functions for the ideal positioning curve P is now described in order to obtain a simplified trajectory or positioning curve. Two different cases will be considered as examples. In the first case, an approximation function is to be determined for a working distance d = ∞, which can also be described by the condition f / d << 1. For the second case, an approximation function is to be determined for a given reference operating point d Ref (d Ref < ∞).

[0072] The first case considered here corresponds to case A according to Fig. 8 . In this case (f / d << 1) the term 1 1 − f d for example, as a geometric series, a Taylor series, or a Laurent series. In all cases, such a series expansion for this term yields, in the lowest order, 1 + f / d + O((f / d) 2< ). The approximate positioning curve in the case f / d << 1 is thus: x y ≈ f ∗ 1 + f d r − r ∗ f d = f r + f d ∗ f − r

[0073] This approximation function for the first case is in Figs. 9 and 10 and labeled AF1. For a clearer visualization, the operating point AP underlying the series expansion is again drawn at a finite distance, not entirely accurate.

[0074] To illustrate, equation (7c) defines a straight line with a reference point at the coordinates (f, r) and a direction vector ( f − r ). The factor in front of the direction vector maintains the reciprocal dependence on the working distance d, which is typical for triangulation.

[0075] In Fig. 9For the use of the approximation function AF1 as a positioning curve, a corresponding focus point line FL1 is shown, which illustrates the positions of the various focus points as a function of d. The focus point line FL1 has an asymptotic curve and approaches the receiving axis E for an infinite working distance, while the deviation increases at shorter working distances.

[0076] As in Fig. 9 As can be clearly seen, by changing the positioning of the light receiver or the receiving optics, an optimized receiving axis E' shown as a dashed line can be created, which is closer to the focus point line FL1 determined for the first approximation function AF1 and thus - with respect to a selected working distance range - has a smaller maximum deviation from the focus point line FL1. Fig. 9It is also evident that a further improved adaptation of an optimized receiving axis E' to the focal point line FL1 can be achieved by slightly tilting the receiving axis E'. The parallel shift and / or tilting of the receiving axis E' is preferably performed statically in order to minimize the number of degrees of freedom during adjustment.

[0077] Out of Fig. 8 It can be deduced that the receiving axis E defines a receiving plane, the line HP A - LA an optical plane or principal plane of the transmitting lens and the line HP A - LQ a transmitting plane or object plane, which is vertical to the drawing plane of Fig. 8 and intersect in a common straight line, which is aligned with the drawing plane of Fig. 8 forms the intersection point HP A.

[0078] This means that the levels mentioned in Fig. 8represented by the lines E, HP A - LA and HP A - LQ, satisfy Scheimpflug's condition. Thus, the approximation function AF1 can be regarded as a parallel to the object plane referenced by the line HP A - LQ. The line HP A - LQ can also be regarded as a straight line with the reference point (r, 0) and the same direction vector ( n − r ) as the function AF1. The approximation function AF1 therefore corresponds to an object plane or line HP A - LQ shifted by the amount f in the x-direction. Therefore, the function with reference to Fig. 8 and 9 The determination of the approximation function AF1 described above represents at least indirectly an application of the Scheimpflug condition as it is defined with reference to Fig. 1 and 2 was described.

[0079] When determining an approximation function for the second case, a series expansion around the specified working distance d Ref must be performed. The corresponding approximation function is then: x y ≈ f ∗ d Ref d Ref − f r − f ∗ r d Ref + d − d Ref ∗ f ∗ − f d Ref − f 2 r d Ref 2

[0080] In equation (7d), the first vector defines the reference point on the ideal positioning curve and the second vector the direction angle of the tangent. The corresponding approximation function AF2 is given in Figs. 11 and 12 shown. In Fig. 11 The reference operating point AP Ref for the selected working distance d Ref is also shown. A comparison with Figs. 9 and 10 shows that the use of an approximation function AF2 determined for an average working distance d Ref as a positioning curve results in a focus point line FL2 that is somewhat closer to the reception axis E.

[0081] Also the Figs. 11 and 12The second approximation function AF2 shown can be interpreted as a parallel to the object plane of a Scheimpflug configuration defined by the auxiliary line HP - LQ. List of reference symbols

[0082] 110 - 410 optoelectronic sensor 10, 10.1 - 10.4, LQ light source 12, L, LA - LC transmitting optics 14 transmitting light 16 carrier module 20, LE light receiver 22 receiving optics 26.1 far element 26.2 near element AF1, AF2 Approximation function AP, AP B , AP Ref Working point E, E', E1, E2 Reception axis EE Reception plane FP, FP1 - FP4 Focus point FL1, FL2 Focus point line HP A - HP C Auxiliary point KG Collision limit P, P', P" Positioning curve OE Optical plane S, S1 - S4, SA - SC Transmission axis SES Transmission plane SG Intersection line TTriangulation direction

Claims

1. An optoelectronic sensor (110 - 410) for detecting objects in accordance with the triangulation principle, said optoelectronic sensor (110 - 410) comprising a transmission arrangement for transmitting transmission light signals along a transmission axis (S, S1 - S4, SA - SC), wherein the transmission arrangement comprises at least one light source (10, 10.1 - 10.4, LQ) and a transmission optics (12, L, LA - LC) which is configured for focusing the transmission light signals generated by the at least one light source (10, 10.1 - 10.4, LQ) at a focus point (FP, FP1 - FP4), and a reception arrangement which has a reception axis (E, E', E1, E2) and which comprises a reception optics (22) for forming reception light signals, which are generated by an object by a remission of incident transmission light signals, and a spatially resolving light receiver (20, LE) for receiving the formed reception light signals, wherein a relative position of an exit location of the transmission light signals from the at least one light source (10, 10.1 - 10.4, LQ) relative to the transmission optics (12, L, LA - LC) can be selected such that the focus width, which corresponds to the distance of a focus point (FP, FP1 - FP4) from the transmission optics (12, L, LA - LC), can be set to a desired value, wherein the different relative positions are located on a positioning curve (P) which is selected such that respective focus points (FP, FP1 - FP4) associated with the positioning curve (P) lie on a focus point line (FL1, FL2) for different focus widths, wherein the focus point line (FL1, FL2) has a distance from the reception axis (E, E', E1, E2) that is minimized at least within a predefined working distance range such that the focus point line (FL1, FL2) coincides with the reception axis (E, E', E1, E2) or at least a certain predefined maximum distance between the focus point line (FL1, FL2) and the reception axis (E, E', E1, E2) is not exceeded, characterized in that the light source (10, 10.1 - 10.4, LQ) and the light receiver (20, LE) are arranged spaced apart from one another in a triangulation direction (T) on a common carrier module (16) which is a circuit board or an electronic card.

2. An optoelectronic sensor (110 - 410) according to claim 1, characterized in that the positioning curve (P) extends along a straight line.

3. An optoelectronic sensor (110 - 410) according to one of the preceding claims, characterized in that the transmission optics (12, L, LA - LC) has an optics plane (OE), in that the positioning curve (P) of the relative positions extends in a transmission plane (SE), in that the reception axis (E, E', E1, E2) and / or the focus point line (FL1, FL2) extends / extend in a reception plane (EE), and in that the transmission plane (SE), the optics plane (OE) and the reception plane (EE) intersect in a common intersection line (SG).

4. An optoelectronic sensor (110 - 410) according to any one of the preceding claims, characterized in that the light source (10, 10.1 - 10.4, LQ) is displaceable along the positioning curve (P).

5. An optoelectronic sensor (110 - 410) according to claim 1 or 2, characterized in that the transmission optics (12, L, LA - LC) is displaceable along the positioning curve (P).

6. An optoelectronic sensor (110 - 410) according to any one of the preceding claims, characterized in that the carrier module (16) is displaceable along the positioning curve (P).

7. An optoelectronic sensor (110 - 410) according to claim 6, characterized in that the reception optics (22) is coupled to the carrier module (16) such that the angular position of the reception axis (E, E', E1, E2) does not change on a displacement of the carrier module (16).

8. An optoelectronic sensor (110 - 410) according to any one of the preceding claims, characterized in that the positioning curve (P) is defined by a linear or non-linear approximation function (AF1, AF2) which tangentially contacts an ideal positioning curve (P) at a contact point, with the ideal positioning curve (P) being defined by those relative positions for which the focus point line (FL1, FL2) coincides with the reception axis (E, E', E1, E2).

9. An optoelectronic sensor (110 - 410) according to claim 8, characterized in that the contact point is selected for that relative position for which the focus distance is infinite or corresponds to a predefined reference working point (AP, APB, APRef).

10. An optoelectronic sensor (110 - 410) according to claim 8, characterized in that the contact point of the approximation function (AF1, AF2) is selected such that, for the selected contact point, a maximum distance of the associated focus point line (FL1, FL2) from the reception axis (E, E', E1, E2) becomes minimal within the predefined working distance range.

11. An optoelectronic sensor (110 - 410) according to any one of the preceding claims, characterized in that the distance of the focus point line (FL1, FL2) from the reception axis (E) is additionally minimized by means of a displacement and / or a tilting of the reception axis (E), with an optimized reception axis (E'), which has a smaller maximum deviation from the focus point line (FL1, FL2) compared to the non-displaced or non-tilted reception axis (E), being provided by the displacement or tilting of the reception axis (E) that takes place by means of an adapted positioning of the light receiver (20, LE) or the reception optics (22).