Patent Application
20190120962
The invention relates to a transmission/reception module for an optoelectronic sensor that has a light transmitter having a transmission optics and that has a light receiver having a reception optics, wherein an irradiation angle of transmitted light of the light transmitter is smaller than a reception angle of received light incident on the light receiver; the light transmitter and the light receiver are arranged coaxially; and the transmission optics and the reception optics are formed as a common optics. The invention further relates to a method of detecting objects in a monitored zone in which a light transmitter transmits transmitted light through a transmission optics into the monitored zone and a light receiver receives received light remitted with the transmitted light in the monitored zone by a reception optics, wherein an angle of irradiation of the transmitted light is smaller than an angle of reception of the received light; wherein the light transmitter and the light receiver are arranged coaxially; and wherein the transmission optics and the reception optics are configured as a common optics.
Many optoelectronic sensors work in accordance with the sensing principle in which a light beam is transmitted into the monitored zone and the light beam reflected by objects is received again in order then to electronically evaluate the received signal. The time of flight is here often measured using a known phase method or pulse method to determine the distance of a sensed object. This type of distance measurement is also called TOF (time of flight) or LIDAR (light detection and ranging).
To expand the measured zone, the scanning beam can be moved, as is the case in a laser scanner. A light beam generated by a laser there periodically sweeps over the monitored zone with the help of a deflection unit. In addition to the measured distance information, a conclusion is drawn on the angular location of the object from the angular position of the deflection unit and the site of an object in the monitored zone is thus detected in two-dimensional polar coordinates. The scanning movement is achieved by a rotating mirror in most laser scanners. It is, however, also known to instead have the total measurement head with light transmitters and light receivers rotate, such as is described in DE 197 57 849 B4.
The detection in said optoelectronic sensors and in a large number of further optoelectronic sensors is based on a light transmitter and a light receiver with which a transmission optics and a reception optics are associated in most cases by which the transmitted light is collimated or the remitted received light is focused and thus the range and the spatial resolution are increased. The light receiver is here designed as very small to detect as little extraneous light as possible beside its own light and to achieve a fast electronic reaction time. Typical measurements of the light sensitive area of the light receiver are in the range of some hundred micrometers.
It is accordingly necessary to position said components mechanically with respect to one another. This adjustment can relate to a plurality of degrees of freedom. The desired collimated transmitted beam is set via the distance from the light transmitter to the transmission lens. This direction is called the Z direction here. The transverse position of at least one participating component furthermore has to be adjusted such that the received light spot is incident on the light receiver as exactly as possible. Such an XY adjustment can selectively take place at the light transmitter or at the light receiver. The absolute direction in which the transmitted beam exits the sensor, that is so-to-say the line of sight of the unit or its squint angle, can be determined by an additional adjustment of a further participating component in the transverse direction.
Conventional sensors utilize different geometrical arrangements that each have their own advantages and disadvantages with respect to the adjustment demands. Biaxial and coaxial arrangements must first be distinguished here.
In a biaxial arrangement, the geometrical axis of the transmitted light is different to that of the received light. There are variants having separate transmission lenses and reception lenses and those having a dual lens as a common component here. In the case of separate lenses, the complete above-presented adjustment program is required. In addition, the light sensitive area of the light receiver is often kept larger than the dimension of the light spot, that is very small per se, would permit to have tolerances available for adhesion distortion of the fixing of the adjustment, for lateral displacements due to temperature changes or to influencing forces. More extraneous light is incident on the larger light sensitive area with the consequence of a worse signal-to-noise ratio and thereby a reduced range with the same transmission power. In addition, a larger reception element has a slower response time and therefore manages less well with high frequencies, in particular short pulses or steep flanks.
The above-explained XY adjustment could theoretically be omitted with a common dual lens. It is actually, however, mostly required, albeit to a reduced extent, since the positioning on the mounting of the light transmitter and the light receiver has tolerances in the range of a hundred micrometers and is often performed with respect to a housing element that is in turn only imprecisely positioned and has tolerances. The light sensitive area is therefore also kept larger with this model than the light spot itself would allow.
In coaxial arrangements, the geometrical axes of the transmitted light and the received light coincide. This is achieved most directly in that the light transmitter is arranged in front of the light receiver. With different models, the beam paths are merged by a deflection mirror or by a beam splitter. Different variants of the transmission and reception optics provide a central aperture of the reception lens for the passage of the transmitted light, a transmission lens arranged centrally in the reception lens, or a separate transmission lens.
The coaxial arrangements likewise require the total named adjustment program. Even a single-piece reception lens having a transmission lens at its center does not replace the XY adjustment because, as already explained, the positioning of the light transmitter and the light receiver is not accurate enough. There may even be adjustment steps in arrangements having an additional mirror. The light sensitive area is again increased for tolerance compensation.
An approach has become known from the white paper by M. Schillgalies “Micro-Hole Chip Technology For Next Level of Integrated Optical Detector Systems”, Mar. 30, 2011, having a combined electronic assembly in which the light transmitter is seated in a hole of the light receiver. However no more than vague application proposals are given; there is no practicable optical transmission/reception unit having a specific optics on this basis. At first glance, it can also not be sufficient to arrange a common transmission and reception lens in front of the electronic assembly. For the optical path in every lens is reversible. It should consequently be expected that such a common lens always images all the light emanating from the light transmitter back into the light transmitter. However, the total useful light portion of the received light would then be imaged into the hole and no detection could take place at all. In addition, a diameter is proposed for dimensions of the hole of 500 mm, which is disadvantageously larger.
EP 2 860 497 B1 discloses an optoelectronic sensor for the detection of an angle of rotation in which transmitted light is reflected at a standard, is received again, and is then evaluated. The light transmitter is seated behind a hole of the light receiver that serves as a diaphragm for beam shaping. No additional optics is provided here and would only disturb the measurement principle.
In a further optoelectronic sensor in accordance with EP 2 312 919 A1, the light transmitter is located in a coaxial arrangement on a first circuit board section in the optical path of the light receiver on a second circuit board section. A reception lens having a transmission lens at is center is supported by pins through holes of the first circuit board section on the second circuit board section and thus provides the desired spacings in the Z direction and a certain lateral orientation. However, the spacings between the light transmitter and the light receiver, for example, are still in the range of centimeters. The mechanical fixing by the reception lens provides a coarse preadjustment on this dimensional scale. A highly precise positioning is, however, only reached if this is refined by an adjustment having the above-named steps.
It is therefore the object of the invention to provide an improved transmission/reception module.
This object is satisfied by a transmission/reception module for an optoelectronic sensor and by a method of detecting objects in a monitored zone in accordance with the respective independent claim. The transmission/reception module is an optical transmission/reception assembly having a coaxial light transmitter and light receiver, and indeed in a direct coaxial arrangement without beam folding by beam splitters or the like. Coaxial means that the transmission/reception module at least outwardly behaves as a coaxial transmission/reception module; the arrangement itself is preferably already coaxial. A common optics acts as a transmission optics for at least approximately collimated transmitted light and as a reception optics for at least approximately focused received light. The angle of divergence of the light transmitter and thus the angle of irradiation of the transmitted light are here smaller than the angle of the received light.
The invention starts from the basic idea that the light transmitter and the light receiver are held from the outset in a well-defined spatial arrangement with respect to one another. They are at least indirectly micromechanically connected to one another for this purpose. The light transmitter and the light receiver can practically be considered as a single component with the precision of the mutual arrangement typical in microsystem technology. At least indirectly means that the light transmitter and the light receiver are either micromechanically connected to one another or that there is at least one intermediate part that is micromechanically connected to the light transmitter and to the light receiver, that is there is an indirect micromechanical connection of the light transmitter and the light receiver.
The invention has the advantage that no adjustment, or at best a still simple and coarse lateral or XY adjustment, is required so that the received light spot is incident on the light receiver. This adjustment step namely more precisely already takes place in the production of the electronic subassembly that at least indirectly micromechanically connects the light transmitter and the light receiver to one another. Unlike macroscopic mass production of a sensor or of an optical transmission/reception optics where a precision of 100 μm is already only successful with complex and/or expensive and error-prone methods, a positioning accuracy of 1 μm is a standard that can be achieved completely without problem in microsystem technology. Investment costs for auxiliary production means and care costs for a complex and/or expensive adjustment process that is prone to error are thus saved. Tolerances for transverse position fluctuations, for instance due to deformation on the fixing in the still remaining Z adjustment, due to temperature changes, due to acting forces and the like do not have to be available because they no longer influence the relative positioning of the light transmitter and the light receiver. The light spot can thus also be increased in size to utilize the total light sensitive area of the light receiver; and this improves the signal-to-noise ratio and the radio frequency behavior.
The common optics is preferably configured as a common lens. A particularly simple and inexpensive optics is thus used and not, for instance, an objective comprising a plurality of lenses or the like. There is also in particular no separate transmission lens present.
The light transmitter is preferably arranged at the focal point of the common lens. A sharp and small transmitted light spot is thereby produced. In many arrangements in accordance with the invention, the light transmitter and the light receiver are arranged offset from one another along the optical axis, that is in the Z direction. The light receiver is then at the same time easily displaced from the focal plane so that the received light spot is increased by defocusing. This in turn leads to the advantageous effect that a larger portion of the reflected transmission light is not again incident on the light transmitter and thus more useful light is detected.
The common lens is preferably configured as a multi-zone lens having a transmission zone and a reception zone. There is thereby the possibility of optimizing the lens properties for the transmitted light and the received light separately. The additional degrees of design freedom can be utilized to lose as little received light as possible on the light transmitter and nevertheless to maintain a small transmitted light spot to the extent these goals are compatible with one another at all.
Even more preferably, the transmission zone is arranged centrally and the reception zone is arranged surrounding the transmission zone. This is particularly well adapted to the coaxial arrangement of the light transmitter and the light receiver with a smaller angle of divergence of the light transmitter.
The transmission zone preferably has a smaller focal length than the reception lens. Even more preferably, the light transmitter is at the same time arranged in the focal plane. The larger focal length of the reception zone then produces a defocusing and thus, from a conventional viewpoint, an atypically large received light spot. This is not problematic due to the highly precise XY positioning in accordance with the invention because the larger received light spot is also reliably received without providing tolerances. The areal portion of the useful light that is lost due to the incidence on the light transmitter is thus particularly small.
The reception zone preferably has a conical component. An aberration is deliberately introduced by this that has the effect that object points are imaged on an annulus. A possible lens shape is a lens that is planoconvex starting from its base shape, but with the planar side being provided with an additional conical component in the region of the reception zone. Alternatively, the aspherical side is modified in that odd polynomial coefficients of the aspherical parameters are also used.
An annular beam profile produced by the conical component preferably has a central region of a size that corresponds to the light receiver. The size characterizes a characteristic geometrical size such as the radius or the area. The conical component is therefore adapted such that the ring produced from the received light spot surrounds the light transmitter as exactly as possible. The received light is thus practically completely deflected from the central region in which it would be lost in the light transmitter onto the light receiver. This preferably applies to received light from infinity and received light of a closer object will then no longer be able to completely avoid the light transmitter. The received light portion that is incident through the transmission zone would still have to be considered separately. This portion is, however, comparatively small due to the divergence properties of the transmitted light and the received light.
The light transmitter and the light receiver are preferably spaced apart from one another by at most 300 μm. Even more preferably, the spacing even amounts to at most 200 μm or at most 100 μm. They are orders of magnitude for microsystems that, as a reminder, would already be achieved in the sensor production simply with the typical tolerances. The spacing even more preferably relates to the Z direction. In a projection in the Z direction onto the XY direction, the light transmitter in a number of embodiments is directly next to or substantially centered in the light receiver with practically as good as no remaining spacing. In alternative embodiments, larger spacings of at most 500 μm or more are also conceivable.
The light receiver preferably has an aperture in which the light transmitter is arranged. The light transmitter then transmits the transmitted light from the light receiver, with substantially the same plane for transmission and reception. The aperture initially only relates to the light sensitive area. The light transmitter can therefore be arranged on the circuit board of the light receiver in the light sensitive area. A separate circuit board is, however, also conceivable. In this embodiment, the light transmitter and the light receiver are disposed on one plane, which facilitates the production and further processing.
The light receiver preferably has an aperture behind which the light transmitter is arranged. In this embodiment, the light transmitter transmits the transmitted light through the light transmitter so that the transmission source is set back in the Z direction with respect to the light reception. This can also initially only relate to the light sensitive area. The light transmitter then has a smaller construction height so that it disappears in the aperture, which can also be achieved by a pedestal of the light receiver. Other possibilities of an arrangement of the light transmitter behind an aperture of the light receiver provide an aperture also in the circuit board of the light receiver. An aperture of the size of the purely light emitting surface is sufficient here; the remaining light transmitter can project behind the light receiver beyond the aperture. A smaller aperture can thus be implemented than in the case in which the light transmitter is seated in the aperture.
The aperture is preferably at most 300 μm in size. Even more preferably, the aperture is even at most 200 μm or at most 100 μm in size. The size again relates to a characteristic geometrical dimension such as the diameter, the area, or an edge length. The central region of the light receiver that cannot register any received light, and thus the useful light loss, remains correspondingly small. In alternative embodiments, the aperture can, however, also be larger, that is, for example, at most 500 mm or even more. A SPAD detector can in particular easily bring along the order of magnitude of the extent of 1 mm and more required for this purpose.
On an arrangement of the light transmitter behind the aperture, a light guide element that guides the transmitted light into the aperture so that the aperture is the actual light source is preferably arranged between the light transmitter and the light receiver. Such embodiments represent an example for an only indirect micromechanical connection between the light transmitter and the light receiver with a certain spacing therebetween. The light of the light transmitter is conducted into the aperture by the light guide element so that practically all the transmitted light exits an actual, virtual light source in the aperture or in its direct proximity despite the spacing between the light transmitter and the light receiver. In this connection, the term virtual should not be confused with a virtual image of an optical image. It is rather important that the transmission/reception module behaves for all practical purposes like one in which the light transmitter is arranged in the aperture or at least very closely behind it.
A number of advantages are achieved by the greater spacing of the light transmitter from the aperture. The aperture itself can be smaller. Less reception area is therefore lost, which improves the signal-to-noise ratio and the range. In addition, light transmitters with greater dimensions can be used, for example also edge emitters. The problem of the dimensions is typically smaller with a VCSEL light transmitter that is likewise possible. Optical crosstalk is furthermore reduced and thus inter alia a better near zone detection is achieved. For transmitted light portions that would, for example, not reach the monitored zone due to flat angles of irradiation are already intercepted by the light guide element and the aperture so that they never reach the reception element.
The light guide element preferably has an optical fiber element. An optical fiber can be manufactured from solid material and can be based on total internal reflection, or it an additionally be internally mirror coated or can be configured as a hollow optical waveguide having an internal mirror coating. Alternatively, the light guide elements generates an image of the light source in or in front of the aperture. A lens, in particular a microlens, is preferably provided for this purpose. The (real) image of the light source in the aperture is the actual origin of the transmitted light viewed from the outside.
The light transmitter is preferably arranged on the light receiver. This is an alternative arrangement if the light receiver has no aperture. A small pedestal is, for example, provided on the light receiver for the light transmitter. The spacings are in turn only on a scale of microsystem technology in the range from some tens to at most some hundreds of micrometers.
A field aperture is preferably associated with the common optics. This field aperture is preferably arranged between the common lens and the light transmitter or light receiver. Lateral extraneous light that cannot be remitted useful light and only degrades the signal-to-noise ratio is screened by the field aperture. Extraneous light reductions that can easily amount to a factor of ten and more are achieved here. Apart from the improved extraneous light robustnesss and range, extraneous light generates an unnecessary power consumption and heat development in some light receivers, for example in SPADs (single photon avalanche diodes), which is likewise prevented by the field aperture. In embodiments having a light guide element, the transmitted light cannot only be guided into the aperture, but rather further through the field aperture to optimize its use even more. A real image of the light source is in particular generated in the region of the aperture opening.
The total optics, in particular its reception zone, is preferably configured to only focus the received light up to an extent of an aperture opening of the field aperture. A field aperture has the advantages just explained. With a near object, however, the field aperture can practically only allow central light to pass that is focused on the light transmitter and is lost for the detection. The transmission/reception module in accordance with the invention having a field aperture in the near zone would thus be blind. This can be counteracted by defocusing the common optics or the reception zone. The reception optical path then has a wider waist, preferably just corresponding to the aperture opening, and no sharp focus is formed on the plane of the light receiver, but rather a larger light spot of which a sufficient portion is incident on the light sensitive area and not on the light transmitter.
The common optics preferably has beam deflection properties to compensate a tilt of the reception optical path with respect to the transmission optical path. This is suitable for embodiments in which the light transmitter or the actual-light source and the light receiver itself are not arranged coaxially, but rather next to one another. The transmission/reception module then behaves coaxially toward the outside since a tilt of the reception optical path toward the transmission optical path that is caused by the arrangement next to one another and is anyway only slight is compensated by the common optics. The common optics, more precisely its reception zone, has, for example, a wedge shape or prismatic properties for this purpose so that the focusing properties have a tilt of the reception optical path superposed that compensates the tilt toward the transmission optical path.
A transmission tube is preferably arranged between the light transmitter and the common optics. Optical crosstalk is thereby prevented in the transmission/reception optics. The transmission tube admittedly simultaneously also screens the portion of the received light that is incident on the common optics in the region of the transmission tube. Such light would then, however, anyway be almost completely incident on the light transmitter and would thus not contribute to the detection.
An optical element that deflects received light incident in the direction toward the light transmitter onto the light receiver is preferably arranged in front of the light transmitter. The optical element does not cause interference on the irradiation of transmitted light due to its angle of divergence. Received light beams that would be laterally outwardly incident on the light transmitter are again deflected back outwardly and thus onto the light receiver. This is therefore a further possibility of increasing the detectable portion of the received light.
In a preferred further development, an optoelectronic sensor is provided having at least one transmission/reception module in accordance with the invention. The sensor preferably has an evaluation unit that is configured to determine a time of flight and from this a spacing from a detected object from a received signal of the light receiver. Such a time of flight measuring system or TOF system is used, for example as a laser sensor or as a laser scanner. Alternatively, however, the time of flight measurement can also be dispensed with such as in simple light sensors, light barriers, light grids, or laser scanners that only have angular resolution and no distance resolution.
A plurality of transmission/reception modules can also advantageously be used in such a sensor to form a multi-beam system. Examples for this are light grids or laser scanners having a plurality of scanning planes as an approach to a 3D sampling. A plurality of transmission/reception modules can in particular be associated with the same common optics to thus save components and production effort and/or cost.
The method in accordance with the invention can be further developed in a similar manner and shows similar advantages in so doing. Such advantageous features are described in an exemplary, but not exclusive manner in the subordinate claims dependent on the independent claims.
The invention will be explained in more detail in the following also with respect to further features and advantages by way of example with reference to embodiments and to the enclosed drawing. The Figures of the drawing show in:
A transmission/reception module 12 has a light transmitter 14 that transmits a transmitted light beam 18 via a common transmission and reception optics 16 into a monitored zone 20. If the transmitted light beam 18 is there incident on an object 22, some of the light returns back to the transmission/reception module 12 as a remitted received light beam 24 and is there bundled onto a light receiver 26 by the common transmission/reception optics 16. The light receiver 26 in this embodiment has a central aperture 28 or a hole behind which the light transmitter 14 is seated and through which the transmitted light beam 18 is transmitted. This is varied in other embodiments. The light transmitter 14 and the light receiver 26 are at least in direct spatial proximity with one another and are micromechanically fastened to one another. The two-part representation of the light receiver 26 is due to the sectional view; it would be recognized in a plan view that the light receiver 26 is contiguous and has the central aperture 28. Embodiments are, however, also conceivable in which the light receiver 26 is not contiguous. Two or more separated light sensitive areas then surround the aperture 28 that can, but do not have to, almost contact one another at least at corners or edges. The arrangement of the transmission/reception module 12 is coaxial; the light transmitter 14 and the light receiver 26 are therefore disposed on the same optical axis. The irradiation path is not folded; there are in particular no beam splitters or deflection mirrors that establish the coaxial arrangement at all, with a common deflection mirror that relates both to the transmission path and to the reception path generally remaining conceivable, for example to optimize the construction space or the installation.
The light transmitter 14 can be configured as an LED or as a laser, in particular as a VCSEL laser or as an edge emitting laser diode. The light receiver 26 is, for example, a PIN diode, an APD (avalanche photo diode), or a single photon APD (SPAD), or a multiple arrangement. An advantage of a SPAD beside its exceptionally high sensitivity is also the possibility of quickly switching it to sensitive or non-sensitive (“active quenching”, time gating, time windows, adaptation of the bias voltage). Interference portions that arise due to optical or electrical crosstalk can thereby be very effectively masked in that the sensitive time windows are set such that the crosstalk signal has already dropped, but the measurement signal has not yet returned, not even from near distances. In addition, SPAD arrangements can easily be used in a construction size of 1 mm and more, which provides advantages in some of the embodiments still to be explained for large received light spots.
An evaluation unit 30 controls the light transmitter 14 and evaluates the received signal of the light receiver 26 to detect the object 22. The evaluation can, for example, include a time of flight method to measure the distance from the object 22; for instance, a single pulse method, multi-pulse method, or phase method known per se. The evaluation unit 30 is also representative for further possible electronic components of the sensor 10 that will not be looked at in any more detail.
The common optics 16 is illustrated as a common lens in
The angle of divergence αs of the light transmitter 14 and thus of the transmitted light beam 18 is smaller than the angle αE of the received light bundle 24. This has the result that sufficient received light is incident on the light receiver 26 even though a portion thereof is lost in the aperture and thus on the light transmitter 14 or, in other embodiments, also by a shading of the light transmitter 14. This can be easily understood using the schematic beam progressions and the two angles αs, αE in
In addition, a numerical example should be given at this point. A common lens is assumed as the reception optics 16 by way of example for this. Unlike many examples following below, this lens has unchanging properties at the center, where the transmitted light beam exits as outside, for instance a focal length that is the same everywhere. The lens is designed as a plano-asphere from glass having a center thickness of 13 mm, a refractive index of n=1.515, a focal length of f=30 mm, and a useful aperture of 35 mm, wherein the radius r, the cone k, and the two straight polynomial coefficients a4 and a6 of the asphere parameters being used. The irradiation angle αs of the light transmitter 14 amounts to ±15° and the maximum angle αE of the received light beam 24 amounts to ±38°. The light transmitter 14 is arranged at the focal point of the lens. The aperture 28 in the light receiver 26 has a diameter of 130 μm, with a mechanical thickness of the chip of the light receiver 26 of 150 μm that also determines the depth of the aperture 28. The light transmitter 14 has dimensions of 300 μm, with 50 μm thereof comprising the light emitting area. The required hole diameter also results from this in another respect: 50 μm+2*tan(15°*150 μm=130 μm. The resulting size of the received light spot on the light receiver 25 is then 2*tan(38°*150 μm=235 μm. Consequently, a portion of approximately (2352−1302)/2352=70% of the received light beam 24 is not incident on the aperture 28 and is detected. The spot size can be further increased and an even greater reception efficiency of more than 70% can be achieved by as light defocusing of the transmitted light beam 18.
The lens effect can therefore be set differently for the transmitted light bundle 18 and the received light bundle 24 due to the multi-zone lens. The focal length of the transmission zone 16a can in particular be selected as not the same as the focal length of the reception zone 16b. The selection of a smaller focal length in the transmission zone 16a is advantageous to increase the received light spot of the received light bundle 24 on the light receiver 26. The relative portion of the received light beam 24 that is lost in the aperture 28 or on the light transmitter 14 thereby becomes smaller. Due to the same consideration, the light receiver 26 should not be seated in the focus of the reception zone 16b to achieve the atypically large received light spot. Such a defocus and thus an increase in the received light spot would not be considered in a conventional observation. A sharp imaging with a small received light spot and surrounding free marginal regions on the reception surface of the light receiver 26 is rather aimed for there to maintain tolerances. In accordance with the invention, such tolerances are not required because the XY adjustment from the light transmitter 14 to the light receiver 26 with extremely high accuracy has already been reached in advance.
In the embodiments in accordance with
Currents or electromagnetic fields from the light receiver 14 can continue to pass into the light receiver 26 in direct spatial proximity of the light transmitter 14 and the light receiver 26, possibly even with a contact. Such an electrical crosstalk results in falsified received signals and in particular occurs at high frequencies in an order of magnitude of 1 GHz and more, that are, however, actually by all means desired in time of flight measurements.
A further aspect is the optical crosstalk. Some transmitted light is irradiated by the light transmitter 14 so that it cannot be used because it is, for example, irradiated at a large angle of divergence. This light portion practically does not disadvantageously impair the transmission power, but the light can rather enter into the light receiver 26 and can there falsify the actual received signal. An arrangement as in
In
The asphere formula is additionally shown in the following in this respect:
where: z is the sagittal height; r is the spacing perpendicular to the axis or to the height of incidence; p is the vertex curvature (vertex radius R=1/ρ9; k is the conical constant; a2i a2i+1 are even or odd coefficients of the correction polynomial; max(2n, 2m+1) is the degree of the polynomial.
It is achieved by introducing a conical component, whether on the plano side, via odd polynomial coefficients, or quite a different lens shape that an object point is no longer imaged on an image point on the light receiver 26, but rather on a small annulus. The lens having the conical component therefore generates an annular beam profile whose contour depends on the focal location.
This is illustrated for spot profiles in different focal locations in
The arrangement in accordance with
Let the value −0.005 be selected for a1 as a specific numerical example. It must again be mentioned that this only relates to the reception plane 16b; the odd polynomial coefficients preferably remain at the value 0 in the transmission zone 16a. Let the other dimensions and parameter including the other asphere parameters be the same as in the above numerical example with respect to
In an alternative numerical example, the value +0.01 is selected with otherwise the same values for a1. The circle diameter then becomes 2*30 mm*0.01*(1.5−1)=300 μm. This is just sufficient to surround the larger aperture 28 in
In these numerical examples, provision is made by the sign of a1 that not only objects 22 at infinity, but also objects 22 coming closer generate a light spot that is still incident on the light sensitive surface of the light receiver 26 and does not completely disappear in the aperture 28 or on the light transmitter 14. With an incorrect arrangement or sign selection, this could namely easily occur, with the consequence of a dead zone of several meters in size in the proximity of the transmission/reception module 12.
There is a conflict between two opposite interests here: To thread as much transmitted light 18 as possible through the field aperture 34, a large diaphragm aperture at great proximity is desirable. On the other hand, a small diaphragm having a certain spacing from the receiver is required for an effective reduction of the reception FOV. A compromise therefore has to be found here.
Embodiments having optical fibers as the light guide elements 29a-b in accordance with
This near zone problem can, however, also be solved by optimizations of the lens. The lens, in particular its reception zone 16b, is designed such that the minimal beam waist, so-to-say at the reception focus, no longer becomes very small, but rather intentionally only reaches a certain minimal diameter that just passes through the field aperture 34. The received light spot is therefore also no longer smaller than the aperture opening of the field aperture 34 with near objects so that sufficient light of the received light beam 24 remains on its suitable configuration that does not disappear in the aperture 28.
There are various possibilities of achieving this effect in the lens design. For example, aberrations are deliberately maintained that result in such a large received light spot. Alternatively, an asphere of the parameters a1 is used via which the minimal beam diameter in the focus can be set. The cross-section of the received light beam 24 then nowhere becomes smaller. The advantages of an annulus explained with respect to
Some numerical examples that are optimized for large object distances without restrictions thus implied should also be given for embodiments having a field aperture 34. In this respect, let in each case in large agreement with the previous examples, the irradiation angle at the transmission side be αs=±15°, the maximum angle at the reception side be αE=±30°, the chip thicknesses be 150 μm, the light emitting area be 50 μm, at a chip size of 300 μm of the light transmitter 14. Dimensions of 1 mm are used for the light transmitter 26, with this not playing any role for the calculations, but rather only sufficient space being available to receive the received light spot, with the aperture opening of the field aperture 34 in particular being smaller than the light receiver 26. The estimates of the reception spot sizes and as a consequence of the reception efficiencies start from the slightly simplifying assumption that the field aperture 34 is exactly positioned in the intermediate focus of the reception optical path.
In a first example for the situation of
In a second example for the situation of
In a third example for the situation of
A problem can result with optical crosstalk or also electrical crosstalk from the transmission path directly into the reception path by the direct spatial proximity in accordance with the invention of the light transmitter 14 and the light receiver 26. With a pulsed system, the active phase of the light transmitter 14 and thus the crosstalk is short, above all when a short pulse length of at most 1 ns is selected, for example. In the near zone, while the light transmitter 14 still generates the pulse, the detection of the light receiver 26 is, however, still disturbed, up to a practically complete loss of the detection ability.
To solve this, an additional light receiver 26a is provided for the near zone in the embodiment in accordance with
Another conceivable measure to prevent crosstalk or at least to limit its effects, is the already addresses gating or instead of the additional light receiver 26a, another complementary sensor is used for the near zone, for instance an inductive, capacitive or magnetic ultrasound sensor or radar sensor. A complete optoelectronic additional module having a design in accordance with the invention or having a conventional design or even a separate additional optoelectronic sensor are also conceivable.
The light transmitter 14 and the light receiver 26 are next to one another in
The lens of the common optics 16 is still coaxial in the sense that the transmission zone 16a is seated centrally, surrounded by the reception zone 16b; however, possibly displaced minimally from the center. Such a displacement has hardly any practical effect in view of the micrometer spacings between the light transmitter 14 and the light receiver 26 in comparison with the spacing from the lens.
The shape of the lens, however, preferably differs. It is no longer rotationally symmetrical in the region of the received zone 16b but has a wedge shape or prismatic properties there. Such modifications can be applied to the planar side or they are integrated in the curved side that was already explained above for an additionally conceivable conical component. The tilt is shown in greatly exaggerated form in
With such an arrangement and such a lens, the beam progression outside the transmission/reception module 12 is then both concentric and colinear because the slight tilt of the reception optical path to the transmission optical path within the transmission/reception module 12 is compensated by the wedge shape of the reception zone 16b; it is thus effectively coaxial, albeit not in the strict above-named understanding of the term because the light transmitter 14 and the light receiver 26 are next to one another.
The invention was described with reference to embodiments that are primarily directed to a specific advantageous modification, but sometimes also in specific combinations. The invention also comprises the variants with which the advantageous modifications are combined in a different manner. The arrangement of the light transmitter 14 behind the aperture 28, in the aperture 28, or in front of the light receiver 26 or the design of the lens with a plurality of zones, with a conical component and/or with aberrations can thus be selected largely independently of one another; the field aperture 34 can be added or omitted in various spacings and sizes of the diaphragm aperture; and an additional light receiver 26a, or an arrangement slightly differing from the ideal coaxial arrangement and with a correspondingly adapted reception optics 16, the transmission tube 38 and/or the optical element 40 can be added or omitted. In addition, transmission/reception modules 12a-c that are of the same type or also different in various embodiments can be combined as in
| Number | Date | Country | Kind |
|---|---|---|---|
| 102017124535.9 | Oct 2017 | DE | national |
| 18177007.4 | Jun 2018 | EP | regional |
