OPTICAL TRIANGULATION BUTTON

Description

[0001] The invention relates to an optical triangulation probe according to the preamble of claim 1.

[0002] Such optical triangulation sensors operate according to the triangulation principle. Accordingly, the transmitter and receiver array of the optical triangulation sensor form a triangulation array. In this triangulation array, the receivers of the receiver array are arranged next to each other in a triangulation direction, spaced apart from the transmitter. The triangulation direction runs transversely, preferably perpendicularly, to the beam axis of the transmitted light beams emitted by the transmitter.

[0003] To detect an object in the surveillance area, the transmitter's transmitted light beams strike the object and are then returned to the receiver array as received light beams. The point of incidence of the light spot of the received light beams on the receiver array depends on the distance of the object from the optical triangulation sensor. At short distances, the received light beams primarily strike a first receiver in the receiver array, forming a near element. At long distances, the received light beams primarily strike the second receiver in the receiver array, forming a far element.

[0004] An object detection signal is generated in the control and evaluation unit from the ratio of the receiver signals.

[0005] Typically, the difference between the received signals of the receivers, i.e., the near and far elements, is calculated, and the object detection signal is generated from this difference. Typically, the difference between the received signals is evaluated using a threshold value that forms a switching threshold. This defines a sensing range, i.e., a detection distance that delimits a sensing area.

[0006] If the light spot of the received light beams primarily hits the near element, the object is within the sensing range. If the light spot of the received light beams primarily hits the far element, the object is located outside the sensing range in a background area.

[0007] Figure 3shows, as an example, the difference signals of an optical triangulation probe depending on the object distance, whereby the curve a shown originates from the detection of a bright, highly reflective object and the curve b shown originates from a weakly reflective object.

[0008] The same factor, namely the ratio of the object remissions, exists between the two curves at every distance. The zero crossing of the difference signal occurs at the same distance for both curves. At this point, regardless of the total amount of light collected, the near element and the far element deliver the same signal. If the received signals of the near and far elements are amplified equally, the light spot of the received light rays is centered on the dividing line between the near and far elements.

[0009] This type of evaluation has the significant advantage that objects located farther away from the optical triangulation sensor always generate a light spot centered on the far element, thus the difference signal is always negative. This allows objects in the background to be reliably suppressed, regardless of the object reflectance, i.e., background suppression occurs.

[0010] If there is no object in the monitoring area, i.e. no light hits the receivers, the evaluated difference signal is 0. In order to detect an object in the monitoring area without ambiguity, the threshold value used to generate the object detection signal is generally not at the zero point of the difference signal.

[0011] The threshold value, ie the switching threshold, is in Figure 3 designated thr.

[0012] This choice of switching threshold results in a slightly different detection distance for light and dark objects. This deviation in the detection distance is called the black-white error and is Figure 3 denoted by e.

[0013] Ideally, the black-white error is as small as possible, since then all objects, regardless of their remission, are detected up to the same detection distance. Figure 3 As can be seen, a prerequisite for this is the steepest possible course of the distance characteristic in the area of ​​the switching threshold.

[0014] For sensors with background suppression, it is advantageous to ensure robust switching behavior with minimal black-white error if the gap between the near and far elements is as small as possible. In this case, the transition between the near and far ranges is sharpest, as the light spot of the received light beams moves most quickly from the near to the far element, or vice versa. This results in robust switching behavior of the optical triangulation sensor and minimal black-white error.

[0015] Receivers typically consist of multi-pixel arrays or dual photodiodes. In these components, the individual photodiodes are physically housed on the same semiconductor substrate and only electrically separated. This allows for distances of just a few micrometers between the individual receivers.

[0016] These receiver components are very expensive compared to standard photodiodes due to the more complex semiconductor processes and lower production volumes. The components are also significantly larger than standard photodiodes. This can be an obstacle to the miniaturization of such sensors.

[0017] When using inexpensive standard photodiodes for the near and far elements, the problem arises that the gap between the elements becomes significantly larger than with the aforementioned state-of-the-art solutions. When using SMD photodiodes, the distance between the receiving surfaces can increase to >1 mm due to the distances to the housing edge. Even when the photodiodes are directly contacted on the circuit board (chip-on-board technology), distances of several hundred µm between the diodes must be expected.

[0018] If a receiving optics is used in such a system that images the received light as sharply as possible in the receiver plane, this can lead to undefined switching behavior, since the received light falls completely into the gap between the receiving elements when transitioning from one receiving element to the other and thus no defined received signal is generated.

[0019] In order to compensate for the gap between the receiving diodes and still maintain the functionality of an optical triangulation sensor with background suppression, it is conceivable to defocus the receiving light spot and thus enlarge it in the receiver plane so that during the transition from near to far element (or vice versa) both receivers are irradiated by a part of the light spot.

[0020] Increasing the size of the received light spot when there is a gap between the receivers results in less robust switching behavior and increased black-white error, as the transition of the received light spot from the near to the far element, or vice versa, occurs significantly more slowly. Furthermore, the maximum range of the optical triangulation sensor is reduced, as a large portion of the light collected by the receiving optics ends up in the gap between the receivers and does not contribute to signal generation.

[0021] DE 10 2015 119 668 B3 discloses an optoelectronic sensor based on the principle of triangulation for detecting an object in a surveillance area. The sensor comprises a light transmitter for emitting a light beam and a spatially resolving light receiver arranged offset from the light transmitter by a base distance for receiving the light beam remitted by the object. A receiving optical system and an optical element are arranged upstream of the light receiver. The optical element has a converging sub-region and a diverging sub-region and is arranged such that a remitted light beam from an object in a near area of ​​the surveillance area passes through the converging sub-region, and a remitted light beam from a far area of ​​the surveillance area passes through the diverging sub-region.

[0022] DE 10 2005 033 349 B4 relates to an optical sensor for detecting objects in a monitoring area delimited by a reflector, comprising at least one transmitter emitting transmitted light beams, wherein the transmitted light beams are guided to the reflector when the monitoring area is free, comprising two receivers receiving received light beams, wherein a first receiver is arranged in a zone close to the transmitter at a shorter distance from the transmitter than the second receiver located in a zone remote from the transmitter, and comprising an evaluation unit for generating a binary switching signal, the switching states of which indicate whether an object is located in the monitoring area or not, wherein the received signals of the receivers are each amplified with an adjustable amplification factor such thatthat upon detection of the reflector, the amplified reception signals U E1 of the receiver in the zone close to the transmitter are greater than the amplified reception signals U E2 of the receiver in the zone far from the transmitter, and the switching signal assumes the switching state "object detected" if either U E2 > U E1 or if the condition U E1 + U E2 < U min is met, where U min is a predetermined threshold value, and otherwise the switching signal assumes the switching state "free monitoring area".

[0023] DE 20 2009 002 340 U1 relates to a triangulation sensor for detecting objects in a surveillance area, comprising a transmitter unit for emitting transmitted light into the surveillance area, a detector unit for detecting detection light reflected by objects in the surveillance area, the detector unit comprising at least one near element, at least one far element, and a differential amplifier for amplifying a difference between a detection signal of the near element and a detection signal of the far element and for outputting a differential signal, and a control and evaluation unit for controlling the transmitter unit, evaluating the differential signal, and outputting switching signals to the outside. The detector unit comprises a separate amplifier for separately amplifying the detection signal of the near element.The control and evaluation unit is configured to evaluate the differential signal together with an output signal of the separate amplifier and to generate a switching signal "object detected" based on this evaluation.

[0024] US 10 634 785 B2 relates to an optoelectronic sensor for detecting object information from a surveillance area, comprising a light receiver, a receiving optics associated with the light receiver for generating a light spot on the light receiver, and an evaluation unit for generating the object information from a received signal of the light receiver, wherein a manipulation unit is provided for varying the receiving optics, light receivers, and / or elements of the receiving optics in such a way that the proportion of the light spot emerging from the light receivers changes.The manipulation unit is designed for targeted misalignment, which causes a change in the position, size and / or geometry of the light spot, so that a change in the position of the light spot hits the light receiver to a certain extent and the rest does not, whereby a change in the size ensures a more or less pronounced over-exposure of the light receiver and / or a change in the geometry of the light spot no longer fits on the light receiver even with the same surface area.

[0025] EP 1 916 545 B1 relates to an optoelectronic sensor with a radiation source for emitting light into a monitored area and with a detector for detecting light reflected and / or scattered by a target object to be detected and / or a reflector. The detector has a plurality of detector segments, the total of which forms a detector base area. The detector is segmented in an x-direction and in a y-direction running transversely thereto, the detector segments being formed symmetrically with respect to a central axis of the detector running in the x-direction. The detector has switching elements assigned to the detector segments, with which the detector segments can be connected together to form an active area or switched away from the active area. The position and two-dimensional shape of the active area within the detector base area can be variably adjusted.The detector outputs a detection signal integrated across the active area. The detector segments, which are symmetrical to each other with respect to the detector's center axis, can be interconnected in pairs, with the segment height in the y-direction of the detector segments increasing with increasing distance from the center axis.

[0026] DE 199 07 547 B4 relates to an optoelectronic device for detecting objects in a surveillance area, comprising a transmitter emitting transmitted light beams and a receiver element receiving received light beams. The receiver element has a near element and a far element. The received light beams reflected by the object first strike the near element and then the far element as the distance to the object increases. A binary switching signal is generated in an evaluation unit depending on the received signals at the outputs of the near and far elements. The receiver element, consisting of the near element and the far element, is constructed from a number of individual segments, which are first selected by the evaluation unit and, based on this selection, are combined to form a near element and the remaining part to form a far element.

[0027] The invention is based on the object of providing an optical triangulation sensor with high functionality while using inexpensive standard components.

[0028] To achieve this object, the features of claim 1 are provided. Advantageous embodiments and expedient developments of the invention are described in the dependent claims.

[0029] The optical triangulation sensor according to the invention is used to detect objects in a surveillance area and comprises a transmitter emitting transmitted light beams and a receiver arrangement with at least two receivers arranged next to one another in a triangulation direction at a distance from the transmitter. Transmitted light beams from the transmitter are reflected by an object in the surveillance area and guided to the receiver arrangement as received light beams. The optical triangulation sensor comprises a control and evaluation unit in which an object detection signal is generated depending on the receiver signals from the receiver. A gap exists between the receivers. A receiving optics is arranged upstream of the receiver arrangement, by means of which the received light beams are split into two received light beams, the spacing of the received light beams being adapted to the size of the gap.

[0030] The optical triangulation sensor according to the invention enables reliable, safe object detection regardless of the remission of the objects to be detected, ie only a small black-white error occurs in the object detections.

[0031] This is achieved according to the invention in that the at least two receivers of the receiver arrangement are arranged in a fixed position relative to one another in the optical triangulation sensor such that a defined gap exists between them. According to the invention, a receiving optics adapted for this purpose is provided, which splits the received light beams reflected back from an object into two received light beams, the spacing of which is adapted to the size of the gap between the two receivers.

[0032] Advantageously, the distance between the received light beams at the location of the receiver arrangement corresponds at least approximately to the size of the gap.

[0033] This ensures that, at any object distance, the light spot of at least one received light beam always hits at least one receiver, which is an essential prerequisite for a low black-and-white error.

[0034] In addition, the receiving optics adapted to the receiver arrangement make it possible to select small light spots of the received light beams, thus further keeping the black-white error of the optical triangulation sensor low.

[0035] Another significant advantage of the optical triangulation sensor according to the invention is that the receivers can be arranged so that there is a gap between them without significantly degrading the black-and-white error. This is because the gap between the receivers is largely compensated for by the receiving optics, which splits the received light beams into two received light beams.

[0036] The receiver arrangement according to the invention can then be formed by receivers in the form of photodiodes, as standard receiving elements that are available at low cost, which contributes to a reduction in the manufacturing costs of the optical triangulation sensor.

[0037] Advantageously, the components of the optical triangulation sensor are accommodated in a housing in which there is a circuit board on which the receivers, which can be designed as photodiodes, are arranged.

[0038] The circuit board can advantageously be assembled using a conventional SMD (surface mounted device) process.

[0039] A particularly efficient manufacturing process and compact design of the optical triangulation sensor results when the transmitter is also arranged on the circuit board.

[0040] The transmitter can be a light-emitting diode or a laser diode.

[0041] According to a structurally advantageous design, a diaphragm is provided in the area of ​​the gap between the receivers.

[0042] The aperture can conveniently cover edge areas of the receiver arrangement.

[0043] With the aperture, the gap between the receivers can be precisely specified, regardless of the mounting tolerances of the receivers in the receiver arrangement.

[0044] According to an advantageous embodiment, the receiving optics has two partial lenses with different optical axes.

[0045] According to an alternative embodiment, the receiving optics has optical surfaces tilted relative to one another.

[0046] Furthermore, the receiving optics can have an arrangement of microlenses or microprisms.

[0047] Finally, the receiving optics can form a diffractive element.

[0048] The optical triangulation sensor according to the invention can generally have more than two receivers, with two adjacent receivers always being separated by a gap, with the gaps advantageously being at least approximately equal in size. For these embodiments, it is also sufficient if the receiving optics split the received light beams into two received light beams, the spacing of which is adapted to the size of the gap.

[0049] In this embodiment, multiple receivers can be interconnected together to form a near element, to which received light from an object in the near range is directed. Likewise, multiple receivers can be interconnected to form a far element.

[0050] According to an advantageous embodiment, the object detection signal is formed from a ratio of the received signals of the receivers.

[0051] This evaluation generally enables object detection within a scanning range limited by a certain scanning distance. Background suppression is also implemented in such a way that objects at distances greater than the scanning distance are not detected.

[0052] For example, the ratio is the quotient of the received signals of the near and far elements, whereby both the near element and the far element can consist of one or more receivers.

[0053] Alternatively, the object detection signal is formed from the difference between the received signals of the receivers.

[0054] Both variants are particularly suitable if the receiver arrangement has exactly two receivers.

[0055] Advantageously, the difference between the received signals is evaluated with a threshold value.

[0056] The threshold defines the sensing distance that limits the sensing area within which objects are detected and separates it from a background area.

[0057] By dividing the received light beams into two received light beams by means of the receiving optics according to the invention and by adapting the distance of the received light beams to the gap between the receivers, a high steepness of the difference signal in the area adjacent to the zero crossing is obtained despite the gap, thereby reducing the black-white error of the optical triangulation probe.

[0058] The invention is explained below with reference to the drawings: Figure 1: Schematic representation of a prior art optical triangulation sensor for an object in close range. Figure 2: Arrangement according to Figure 1for an object in a distant area. Figure 3: Distance dependence of the differential signal of the receiving elements of the optical triangulation sensor according to the Figure 1 and 2 for two objects with different remissions. Figure 4: First embodiment of the optical triangulation sensor according to the invention. Figure 5: Second embodiment of the optical triangulation sensor according to the invention. Figure 6: Light spot distribution of two received light beams on the receiver arrangement of the optical triangulation sensor according to Figure 4 or 5. Figure 7: Variant of the embodiment according to Figure 4 .

[0059] The Figure 1 and 2 show a prior art optical triangulation sensor 1. The components of the optical triangulation sensor 1 are integrated in a housing 2 with opaque walls. A translucent front panel 3 is located in the front wall of the housing 2.

[0060] A circuit board 4 is fixedly arranged in the housing 2. A transmitter 6 emitting transmitted light beams 5 is mounted on the circuit board 4, followed by a beam-shaping optics 7. A receiver arrangement with two receiving elements 8a, 9a is also arranged on the circuit board 4. The receiving elements 8a, 9a form a double diode arranged on a semiconductor substrate. The receiving elements 8a, 9a are connected to one another almost seamlessly.

[0061] The receiver arrangement forms a triangulation arrangement such that the receiving elements 8a, 9a are arranged next to one another and at a distance from the transmitter 6 in a triangulation direction running transversely to the beam axis of the transmitted light beams 5.

[0062] Components of a control and evaluation unit are integrated on circuit board 4 or another circuit board. The control and evaluation unit serves to control the transmitter 6 and the receiving elements 8a, 9a. Furthermore, the control and evaluation unit evaluates received signals from the receiving elements 8a, 9a to generate an object detection signal.

[0063] The receiver arrangement is assigned a receiving optics 10a in the form of a lens.

[0064] To detect an object 11 in a surveillance area, the transmitter 6 emits transmitted light beams 5, which are guided through the front window 3 into the surveillance area. The transmitted light beams 5 are diffusely reflected by the object 11 and are guided back to the optical triangulation sensor 1 as received light beams 12.

[0065] The received light beams 12 are guided through the front panel 3 and guided by the lens to the receiver plane of the receiving elements 8a, 9a.

[0066] At a short object distance, the receiving light beams 12 focused by the receiving optics 10a predominantly hit the receiving element 8a forming a near element ( Figure 1 ). At a large object distance, the received light rays 12 predominantly hit the receiving element 9a, which forms a long-distance element ( Figure 2 ).

[0067] The difference between the received signals of the near and far elements is calculated in the evaluation unit. The dependence of the resulting difference signal D on the object distance z is shown in Figure 3 . This shows Figure 3 the difference signal D for the detection of an object 11 with high remission (curve a) and for the detection of an object 11 with low remission (curve b).

[0068] To generate the object detection signal, the differential signal D is evaluated in the evaluation unit with a threshold value thr, which forms a switching threshold. The position of the zero crossing of the differential signal D and the threshold value thr define a sensing distance (detection distance) that delimits a sensing area (detection range).

[0069] If the threshold evaluation results in a value of the difference signal D greater than thr, the object 11 is considered detected within the detection range. Values ​​of the difference signal D below the threshold thr are suppressed as background signals, i.e., background suppression occurs with the optical triangulation sensor 1.

[0070] Since the signal curves of the difference signal D are different for objects 11 with different remissions, the difference signals D reach the threshold value thr at different object distances, ie there is a black-and-white error in the object detection (in Figure 3 denoted by e).

[0071] The sensing range can be adjusted by changing the triangulation conditions, which shifts the object distance at which the zero crossing of the differential signal D occurs. This is advantageously achieved by mechanically shifting the position of the receiving optics or receiver arrangement in the triangulation direction.

[0072] Figure 4shows a first embodiment of the optical triangulation probe 1 according to the invention. This optical triangulation probe 1 according to the invention differs with regard to the design of the receiver arrangement and the receiving optics 10 from the optical triangulation probe 1 known from the prior art of Figure 1 and 2 .

[0073] The optical triangulation sensor 1 according to Figure 4 has a receiver arrangement with two receivers 8, 9, which are mounted on the circuit board 4 such that a defined gap 13 is present between them.

[0074] The receivers 8, 9 are designed in the form of photodiodes, ie in contrast to the receiving elements 8a, 9a of the optical triangulation sensor 1 according to the Figure 1 and 2The receivers 8, 9 of the optical triangulation sensor 1 according to the invention consist of cost-effective standard components. The receivers 8, 9 are advantageously mounted on the circuit board 4 using an SMD process.

[0075] Furthermore, the receiving optics 10 according to the invention is designed such that it splits the received light beams 12 into two received light bundles 14, 15.

[0076] The spacing of the received light beams 14, 15 is adapted to the size of the gap 13. Advantageously, the spacing of the received light beams 14, 15 in the receiver plane of the receiver arrangement corresponds at least approximately to the size of the gap 13. This ensures that, regardless of the object distance z, at least one received light beam 14, 15 always strikes at least one receiver 8, 9, thus ensuring reliable object detection for any object distance.

[0077] This is in Figure 6which shows the top view of the light-sensitive surfaces of the receivers 8, 9 with the light spots of the received light beams 12. As Figure 6 shows, the light spots of the received light beams 12 are smaller than the light-sensitive surfaces of the receivers 8, 9. This is an essential prerequisite for error-free, reliable object detection.

[0078] In particular, this improves the switching behavior of the optical triangulation sensor 1.

[0079] The difference signals D are again evaluated with the threshold value thr to generate the object detection signal. By means of the receiver arrangement according to the invention in combination with the receiving optics 10 according to the invention, a steep curve of the distance signals D is obtained in the upper limit range of the scanning range, which results in a comparably low black-white error e compared to the optical triangulation sensor 1 known from the prior art (as in Figure 3 illustrated).

[0080] In the receiving optics 10 of the optical triangulation sensor 1 according to Figure 4 The splitting of the received light beams 12 into two received light bundles 14, 15 occurs because this receiving optics 10 consists of two partial lenses 16, 17.

[0081] Figure 5 shows a variant of the embodiment according to Figure 4 , whereby this embodiment differs only in the design of the receiving optics 10. In the receiving optics 10 according to Figure 5 The splitting of the received light beams 12 into the two received light bundles 14, 15 takes place in that the receiving optics 10 has two light exit surfaces 18, 19 which run at an inclination to one another.

[0082] Figure 7 shows a further development of the embodiment according to Figure 4 . The embodiment according to Figure 7 differs from the embodiment according to Figure 4only by covering the gap 13 with a cover 20. In this case, the cover 20 also covers the edge areas of the receivers 8, 9. With the cover 20, the size of the gap area between the receivers 8, 9 can be precisely specified, whereby the cover 20 can also compensate for mounting tolerances of the receivers 8, 9 on the circuit board 4. Of course, the design of the Figure 5 an aperture of 20 should be provided. List of reference symbols

[0083] (1)Optical triangulation sensor (2)Housing (3)Front screen (4)Printed circuit board (5)Transmitted light beams (6)Transmitter (7)Beam-forming optics (8)Receiver (8a)Receiving element (9)Receiver (9a)Receiving element (10)Receiving optics (10a)Receiving optics (11)Object (12)Received light beams (13)Gap (14)Received light beam (15)Received light beam (16)Partial lenses (17)Partial lenses (18)Light exit surface (19)Light exit surface (20)Aperture (D)Difference signal (e)Black-white error (thr)Threshold (z)Object distance

Claims

1. An optical triangulation probe (1) for detecting objects (11) in a monitoring area with a transmitter (6) emitting transmitted light beams (5), with a receiver arrangement with at least two receivers (8, 9), which are arranged side by side in a triangulation direction at a distance from the transmitter (6), wherein transmitted light beams (5) of the transmitter (6) are reflected at an object (11) in the monitored area and are guided as received light beams (12) to the receiver arrangement, and with a control and evaluation unit, in which, depending on the at least two receiver signals of the at least two receivers (8, 9), an object detection signal is generated which defines a scanning range which limits a scanning range, characterised in that a gap (13) between the receivers (8, 9), and in that a receiving optical system (10) is arranged upstream of the receiver arrangement, by means of which the received light beams (12) are divided into two received light beams (14, 15), the spacing of the received light beams (14, 15) being adapted to the size of the gap (13).

2. An optical triangulation probe (1) according to claim 1, characterised in that its components are integrated in a housing (2) in which there is a printed circuit board (4) on which the receivers (8, 9) of the receiver arrangement are arranged.

3. An optical triangulation probe (1) according to one of claims 1 or 2, characterised in that the receivers (8, 9) of the receiver arrangement are formed by photodiodes.

4. An optical triangulation probe (1) according to one of claims 2 or 3, characterised in that the receivers (8, 9) are assembled on the printed circuit board (4) by means of an SMD process.

5. An optical triangulation probe (1) according to one of claims 2 to 4, characterised in that the transmitter (6) is arranged on the printed circuit board (4).

6. An optical triangulation probe (1) according to one of claims 1 to 5, characterised in that a diaphragm (20) is present in the region of the gap (13) between the receivers (8, 9).

7. An optical triangulation probe (1) according to claim 6, characterised in that the diaphragm (20) covers edge regions of the receivers (8, 9).

8. An optical triangulation probe (1) according to one of claims 1 to 7, characterised in that the receiving optics (10) has two partial lenses (16, 17) with different optical axes.

9. An optical triangulation probe (1) according to one of claims 1 to 7, characterised in that the receiving optics (10) have optical surfaces which are tilted relative to one another.

10. An optical triangulation probe (1) according to one of claims 1 to 7, characterised in that the receiving optics (10) has an arrangement of microlenses or microprisms.

11. An optical triangulation probe (1) according to one of claims 1 to 7, characterised in that the receiving optics (10) form a diffractive element.

12. An optical triangulation probe (1) according to one of claims 1 to 11, characterised in that the spacing of the receiving light beams (14, 15) at the location of the receiver arrangement corresponds at least approximately to the size of the gap (13).

13. An optical triangulation probe (1) according to one of claims 1 to 12, characterised in that the object detection signal is formed from a ratio of the received signals of the receivers (8, 9).

14. An optical triangulation probe (1) according to claim 13, characterised in that the object detection signal is formed from the difference between the received signals of the receivers (8, 9).

15. An optical triangulation probe (1) according to claim 14, characterised in that the difference between the received signals is evaluated with a threshold value (thr).