DE102014105312B3 - detection device - Google Patents

Abstract

Detecting device for detecting contaminants on a monitoring surface (11) comprising a disc (13) having a front surface (19) and a rear surface (21), the front surface (19) or part of which forms the monitoring surface (11), one behind Disc (13) arranged light emitter (15) for illuminating the monitoring surface (11) from the rear surface (21) of the disc (13) and a behind the disc (13) arranged light receiver (17) for receiving received light and for issuing a receiving light based contaminant signal, characterized in that the monitoring surface (11) has a light scattering fine structure (35), due to which the light receiver (17) in the absence of contaminants on the monitoring surface (11) a base signal, with existing dry impurities on the monitoring surface (11 ) an impurity signal which is increased in relation to the base signal and in the presence of liquid Contaminants on the monitoring surface (11) outputs a relation to the base signal lowered impurity signal.

Description

The present invention relates to a detection device for detecting contaminants on a monitoring surface comprising a disk having a front surface and a back surface, the front surface or a part of which forms the monitoring surface, a light emitter disposed behind the disk for illuminating the monitoring surface from the back surface of the disk and a light receiver disposed behind the disk for receiving received light and for outputting an impurity signal based on the received light.

Such a detection device is for example in the DE 10 2011 112 212 A1 disclosed. In various fields of technology, it is desirable to automatically detect contaminants from transparent or partially transparent panes. For example, optical sensors such as buttons or light barriers usually have a windshield through which the transmitted light or the received light can pass. In particular, when used in an industrial environment can lead to contamination of this windscreen, which may affect a proper sensor function. Monitoring the degree of contamination of the windscreen is therefore desirable. Even in the case of window panes, windshields or cover plates of solar systems, it may be desirable to monitor the impurity level of the pane surface. In principle, a "disk" in the sense of the invention means any flat-shaped component which is at least partially transparent to electromagnetic radiation in the visible, infrared and / or ultraviolet spectral range.

Depending on the application, impurities of various kinds can deposit on the front surface of a pane. In particular, in addition to solid particles such as dust or chips, liquids such as oil, water or cleaning agents can reach the surface of the pane. If the disc is outdoors, it is also likely to be contaminated by rain, snow, ice, soot and pollens. In general, detection devices of the type mentioned above are designed such that the light receiver detects the scattered light generated by dirt particles on the disc. However, this measurement principle largely fails when liquid contaminants are present.

It is an object of the invention to provide a more accurate and reliable detection of contaminants on disc surfaces.

The solution of the invention is achieved by a detection device having the features of claim 1.

According to the invention, the monitoring surface has a light-scattering fine structure, due to which the light receiver outputs a base signal in the absence of contaminants on the monitoring surface, impurity signal increased with respect to the base signal in the presence of impurities present on the monitoring surface and impurity signal lowered in the monitoring surface with existing liquid impurities on the monitoring surface , By suitable structuring of the monitoring area, it is thus ensured that stray light strikes the light receiver even without impurities on the front surface of the pane, and thus a measuring signal different from zero is produced. If dry impurities, such as solid particles, are deposited in the area of the fine structure, additional scattered light results, so that the measuring signal increases accordingly. On the other hand, if liquid impurities such as water or oil settle in the area of the fine structure, filling their depressions smooths the fine structure and thus reduces the scattered light generated by the fine structure. The measurement signal thus decreases with respect to the base signal if a liquid with a similar refractive index as that of the disk material deposits in the region of the fine structure. Thus, due to the fine structure, it is possible to distinguish between dry impurities on the one hand and liquid impurities on the other hand. This expands the possible uses of a generic detection device and enables a more reliable and differentiated detection of contaminants of different types.

Preferably, an evaluation unit is provided, which is designed to generate a first warning signal indicative of dry impurities on the monitoring surface when the impurity signal exceeds a positive threshold value relative to the base signal and a second indicative of liquid impurities at the monitoring surface Warning signal to produce when the impurity signal below - based on the base signal negative - threshold. The warning signals may, for example, indicate to the user of an optical sensor that a cleaning of the front screen of the sensor is required. By defining a positive and a negative threshold, a distinction can be made in the evaluation of the contamination signal between dry impurities and liquid impurities. Dry contaminants and liquid contaminants can thus be evaluated independently of each other, so to characterize the degree of soiling of a disc more accurately.

It is preferred that the monitoring surface extends only over a portion of the front surface of the disc, wherein the light emitter is associated with a transmitting optics to limit the illumination of the front surface of the disc by the transmitted light at least substantially on the monitoring surface. In general, it is sufficient to monitor a comparatively small portion of the disk, as is generally assumed that an approximately uniform contamination of a disk surface. Particularly in the case of window panes or windshields, it is desirable to limit the monitoring area with the light-scattering fine structure to an inconspicuous small subarea. In order to suitably limit the transmitted light beam impinging on the disc, the transmitting optics may comprise one or more lenses, apertures and the like. Preferably, the transmitting optics is designed to generate an at least approximately collimated transmitted light bundle. If necessary, optics can also be assigned to the light receiver, so that the light receiver preferably receives light emitted by the monitoring surface. In the case of an optical sensor, the region of the windshield which is not part of the monitoring surface can be used for a passage of sensor light, ie for the regular sensor operation.

An embodiment of the invention provides that the light-scattering fine structure extends over the entire monitoring surface. In this embodiment, the light emitter can be assigned a transmitting optics which limits the transmitted light bundle at least essentially to the light-scattering fine structure. The shift of the base signal with respect to a zero signal is maximum in this embodiment.

Alternatively, it can be provided that the monitoring area comprises a structured area over which the light-scattering fine structure extends and an unstructured area, the light receiver having two separate receiving channels for receiving received light from the structured area on the one hand and from the unstructured area on the other hand , Such a two-channel design allows completely independent detection of dry impurities on the one hand and liquid impurities on the other hand. In this way, for example, suspensions such as turbid waste water can be reliably detected. To provide two separate receiving channels, the light receiver does not necessarily have to be provided with two individual receiver components. Rather, it is possible, if necessary, to provide for the provision of the two separate receiving channels, for example, a single double receiving diode with two separate segments.

An embodiment of the invention provides here that the light emitter comprises a first light source for illuminating only the structured area and a separate second light source for illuminating exclusively the unstructured area for this purpose. If required, the separate light sources can have different spectral emission characteristics and / or be controlled alternately so as to enable a sharper channel separation.

Alternatively, the light emitter may comprise a single light source which illuminates both the structured area and the unstructured area. A suitable transmission optics can ensure that both areas are illuminated equally. Since only a single light source is needed, so manufacturing costs can be saved.

The light-scattering fine structure can be produced by reworking an unstructured front surface of the pane, for example by sandblasting, etching, embossing or brushing. Such post-treatment steps are relatively easy and inexpensive to carry out.

The light-scattering fine structure can also be formed directly on a, executed in particular as an injection molded part, basic body of the disc. There is then no post-treatment steps required to produce the light-scattering fine structure.

The pane can also comprise a main body and a structural element applied thereto, in particular adhered thereto, wherein the light-scattering fine structure is provided on a front surface of the structural element. For example, a textured film could be adhered to the front surface of the disk.

According to a specific embodiment of the invention, a main transmitter direction of the light transmitter and a main receiver direction of the light receiver are arranged symmetrically with respect to a surface normal of the back surface of the disc. Specifically, it is preferable that the incident angle of the transmitted light beams is equal to the angle of reflection of the received light beams. In this symmetrical arrangement results in the maximum Streulichtsensitivität.

In order to reduce influences of the measurement signal due to surface reflections, an embodiment of the invention provides that means for polarizing the transmitted light are provided and the angle of incidence of the on the back surface the disc meeting transmitted light at least approximately corresponds to the Brewster angle. An undesirable overdriving the scattered light measurement by surface reflections can be avoided in this way.

The light transmitter may comprise a semiconductor light source applied to a printed circuit board and a transmitting optical waveguide associated therewith. Alternatively or additionally, the light receiver may comprise a semiconductor light detector mounted on a circuit board and a receiving optical waveguide associated therewith. This embodiment allows a particularly cost-effective production and also requires little space. The optical waveguides can be used for beam shaping and for defining the main transmission direction and the main reception direction, so that complex additional optics can be dispensed with. Preferably, the light emitter and the light receiver are housed on a common board. Instead of optical waveguides, deflecting mirrors, deflecting prisms, molded interconnect devices (MID), angled LEDs (sidelooker) or the like can also be assigned to the light emitter and / or the light receiver.

The invention also relates to an optical sensor comprising a sensor housing with a front screen, which is provided for a passage of transmitted light and / or received light.

Optical sensors are used in a variety of ways for the contactless detection of objects present in the field of vision of the sensor. For example, light scanners are used to determine the distance of an object surface from a reference plane of the sensor. By means of light barriers or light grids, for example, persons who penetrate into a secured area can be recognized or danger areas of a machine, eg a machine, can be detected. As a press, are monitored. Another field of application of optical sensors is the determination of certain properties of objects, for example in the form of a color detection or the identification of object-side markings or marks.

For a reliable sensor operation, it is necessary that the windscreen is as free of contamination as possible. The term "windshield" is intended to mean not only a disc arranged on the front side of the sensor housing, but generally the transparent component of a sensor permitting the passage of light, which, for example, can also be arranged laterally on an elongated housing. The front panel of an optical sensor is often exposed to various contaminants such as dust, chips, water or oil during sensor operation.

In order to prevent incorrect measurements due to contamination of the windshield - which may have serious consequences - a detection device according to the invention as described above is integrated into the sensor housing, wherein the disc of the detection device forms the front window of the sensor housing. The optical sensor can thus be continuously monitored for contaminating the windscreen by evaluating the contamination signal. As contamination progresses, a corresponding warning signal can be output. This allows a user to make a needs-based cleaning of the windscreen. In particular, the safety and the efficiency of a complete system provided with optical sensors can be improved in the context of condition monitoring.

Further developments of the invention are set forth in the dependent claims, the description and the accompanying drawings.

The invention will now be described by way of example with reference to the drawings.

1 is a simplified representation of a detection device according to a first embodiment of the invention.

2 is a simplified illustration of a detection device according to a second embodiment of the invention.

In the 1 Detection device shown for detecting contaminants on a monitoring surface 11 includes a z. B. made of glass or plastic disc 13 , a light transmitter 15 as well as a light receiver 17 , The at least partially transparent pane 13 has a front surface 19 and a back surface 21 and separates accordingly a front room 23 from a back room 25 , For example, it may be at the disc 13 to act around the windshield of an optical sensor, in which case the front space 23 the outside space and the rear room 25 the interior of a sensor housing is. Part of the front surface 19 the disc 13 is transmitted by transmitted light from the light transmitter 15 illuminated. This part of the front surface 19 the disc 13 forms the surveillance area 11 ,

The light transmitter 15 includes a light source 27 , For example, a semiconductor light source such as a light emitting diode or a semiconductor laser, as well as a transmission optics 29 for beam shaping. The transmission optics 29 is exemplified here as a single lens, but it may, if necessary, comprise a plurality of lenses and optionally mirrors, prisms and diaphragms. The transmission optics 29 is at the in 1 illustrated embodiment designed such that a collimated transmission beam 30 is produced. The transmission beam 30 could also be slightly divergent. A polarizer 31 ensures that the light of the transmitted beam 30 polarized in the plane of incidence. Furthermore, the light transmitter 15 arranged such that the angle of incidence W1 of the rear surface 21 the disc 13 meeting broadcast beam 30 at least approximately corresponds to the relevant Brewster angle for this interface. Thus, on the back surface 21 the disc 13 no transmitted light reflected. The transmission beam 30 crosses the window 13 and impinges on the front surface at impingement angle W2, which also corresponds to the associated Brewster angle 19 on.

At the front surface 19 is a light-scattering fine structure 35 provided, which may be produced for example by sandblasting, etching, embossing or brushing. The fine structure 35 but could in principle already in the production of the disc 13 be molded directly into this. Furthermore, the fine structure could 35 also be incorporated in a separate element which on the disc 13 is glued on. At the in 1 illustrated embodiment, the light-scattering fine structure extends 35 over the entire surveillance area 11 time. That at the surveillance area 11 resulting stray light 37 is through a receiving optics 39 of the light receiver 17 on a light detector 40 such as a photodiode bundled. One of the receiving optics 39 upstream polarizer 41 is intended to increase the measuring sensitivity. As shown, the light emitter 15 and the light receiver 17 aligned in reflection arrangement, that is, a main transmitting direction S of the light emitter and a main receiving direction E of the light receiver are with respect to a surface normal N of the rear surface 21 the disc 13 symmetrically arranged and located in the plane of incidence. In this way, with respect to a detection of the scattered light 37 achieved a particularly high sensitivity.

The area in front of the front surface 19 the disc 13 in which the transmission beam is 30 with the receiving beam 32 intersects, defines an uncertainty area 50 in which, for example, objects to be detected by an optical sensor can be misinterpreted as impurities. In general, large incidence and angle of reflection are preferable for the optical arrangement, hence the range of uncertainty 50 as small as possible and the illuminated surveillance area 11 as big as possible. In practice, an angle of incidence between 45 ° and 65 ° at symmetrical angle of emergence has proven to be particularly favorable.

In the absence of any contaminants on the surveillance area 11 generates the light receiver 17 a base signal, which is different from zero and from the reception of the at the structural elements of the fine structure 35 generated stray light 37 results. As far as the fine structure 35 the surveillance area 11 depositing dry impurities, is generated by this additional stray light, so that of the light receiver 17 output impurity signal from the base signal increases. In contrast, when liquid impurities such as water or oil on the fine structure 35 the surveillance area 11 deposit, the pits of the fine structure fill 35 with liquid, which generally has a similar index of refraction as the glass or plastic of the disk 13 having. The fine structure 35 is therefore smoothed so that the stray light generated by them 37 decreases and thus that of the light receiver 17 output impurity signal from the base signal decreases.

One to the light receiver 17 downstream evaluation unit (not shown), it is thus possible, based on the level of the contaminant signal compared to the known level of the base signal between dry contaminants and liquid contaminants on the monitoring surface 11 to distinguish. Specifically, such an evaluation unit can be designed to provide a first, for dry contaminants on the monitoring surface 11 indicative warning signal when the contaminant signal exceeds a positive threshold based on the base signal, and a second, liquid contaminant at the monitored surface 11 indicative warning signal when the contaminant signal falls below a negative threshold relative to the base signal. The evaluation unit can transmit the warning signals via a wired or wireless communication connection to a suitable control device.

2 shows an alternative embodiment of a detection device according to the invention, which is designed in principle similar to that in 1 Detection device shown. Accordingly, the same components are designated by the same reference numerals. At the in 2 The detection device shown are the light source 27 the light transmitter 15 and the light detector 40 of the light receiver 17 on a common board 45 applied. Furthermore, the light emitter 15 as well as the light receiver 17 respective optical fibers 47 associated with the transmit light and the received light along a desired path. Thus, expensive beam deflection elements such as prisms or mirrors can be dispensed with. By means of apertures 49 , which, if necessary, in retaining elements of the optical waveguide 47 can be integrated, the angle of incidence and the angle of the arrangement are defined. The irises 49 could in principle also affect the back surface 21 the disc 13 applied, z. B. printed, be. In the detection device according to 2 is the transmission beam 30 ' divergent and the receive beam 32 ' convergent.

An embodiment, not shown, provides for two separate receiving channels and optionally also two separate transmitting channels, which are the fine structure 35 on the one hand and an unstructured area of the front surface 19 the disc 13 assigned on the other. As a result, a completely independent detection of dry impurities on the one hand and liquid contaminants on the other hand possible.

A detection device as described above can be integrated in particular in the sensor housing of an optical sensor, wherein the disc 13 the windscreen of the sensor housing forms. In this way, the windscreen of an optical sensor can be continuously monitored. If the impurities are too strong, a warning signal can be output, so that an operator of the sensor can initiate an appropriate cleaning.

LIST OF REFERENCE NUMBERS

11

monitoring area

13

disc

15

light source

17

light receiver

19

front surface

21

rear surface

23

front room

25

back room

27

light source

29

transmission optics

30, 30 '

Transmit beam

31

polarizer

32, 32 '

Receive beams

35

fine structure

37

scattered light

39

receiving optics

40

light detector

41

polarizer

45

circuit board

47

optical fiber

49

cover

50

uncertainty range

S

Main transmission direction

e

Main receiving direction

N

Surface normal of the back surface

W1

angle of incidence

W2

angle of impact

Claims (13)

Detection device for detecting contaminants on a monitoring surface ( 11 ) comprising a disk ( 13 ) with a front surface ( 19 ) and a back surface ( 21 ), the front surface ( 19 ) or part of it the surveillance area ( 11 ), one behind the disc ( 13 ) arranged light emitter ( 15 ) for illuminating the surveillance area ( 11 ) from the back surface ( 21 ) of the disc ( 13 ) and one behind the disc ( 13 ) arranged light receiver ( 17 ) for receiving receiving light and for outputting an impurity signal based on the received light, characterized in that the monitoring area ( 11 ) a light-scattering fine structure ( 35 ), due to which the light receiver ( 17 ) in the absence of contamination on the monitoring area ( 11 ) a base signal, in the presence of dry contaminants on the monitoring surface ( 11 ) an impurity signal which is increased in relation to the base signal and in the case of existing liquid impurities at the monitoring surface ( 11 ) outputs an impurity signal lowered from the base signal. Detection device according to claim 1, characterized by an evaluation unit, which is adapted to a first, for dry impurities on the monitoring surface ( 11 ) warning signal when the contaminant signal exceeds a positive threshold based on the base signal, and a second, at liquid contaminants at the monitor area (FIG. 11 ) warning signal when the contaminant signal falls below a negative threshold relative to the base signal. Detection device according to claim 1 or 2, characterized in that the monitoring surface ( 11 ) only over a portion of the front surface ( 19 ) of the disc ( 13 ), wherein the light emitter ( 15 ) a transmission optics ( 29 ) is assigned to the illumination of the front surface ( 19 ) of the disc ( 13 ) by the transmitted light on the surveillance surface ( 11 ). Detection device according to one of the preceding claims, characterized in that the light-scattering fine structure ( 35 ) over the entire surveillance area ( 11 ). Detection device according to one of Claims 1 to 3, characterized in that the monitoring surface is composed of a structured region over which the light-scattering fine structure extends and an unstructured region, the light receiver having two separate receiving channels for receiving Receiving light from the structured area on the one hand and from the unstructured area on the other hand. Detection device according to claim 5, characterized in that the light emitter comprises a first light source for illuminating only the structured area and a second light source separate therefrom for illuminating only the unstructured area. Detection device according to claim 5, characterized in that the light emitter comprises a single light source which illuminates both the structured area and the unstructured area. Detection device according to one of the preceding claims, characterized in that the light-scattering fine structure ( 35 ) by reworking an unstructured front surface of the disc ( 13 ) is generated. Detection device according to one of claims 1 to 7, characterized in that the light-scattering fine structure ( 35 ) directly to a main body of the disc ( 13 ) is formed. Detecting device according to one of claims 1 to 7, characterized in that the disc comprises a base body and a structural element applied thereto, wherein the light-scattering fine structure is provided on a front surface of the structural element. Detection device according to one of the preceding claims, characterized in that a main transmitter direction (S) of the light emitter ( 15 ) and a main receiving direction (E) of the light receiver ( 17 ) with respect to a surface normal (N) of the back surface ( 21 ) of the disc ( 13 ) are arranged symmetrically. Detection device according to one of the preceding claims, characterized in that means ( 41 ) are provided for polarizing the transmitted light and the angle of incidence (W1) of the on the back surface ( 21 ) of the disc ( 13 ) meeting the transmitted light at least approximately corresponds to the Brewster angle. Detection device according to one of the preceding claims, characterized in that the light emitter ( 15 ) one on a board ( 45 ) applied semiconductor light source and one of these associated transmit optical waveguide ( 47 ) and / or that the light receiver ( 17 ) one on a board ( 45 ) applied semiconductor light detector and a receiving optical waveguide associated therewith ( 47 ).

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