Optoelectronic sensor

Abstract

Optoelectronic sensor with a light transmitter (1) for emitting a light signal through a collimator (2) into an object area (3) on a first optical axis (4), with a receiver (5) and a receiver lens (6) for receiving the light signal reflected by an object on a second optical axis (7), wherein the receiver lens (6) contains a main lens (8) for imaging the object area (3) and an additional lens (9) for detecting the near range, wherein the additional lens (9) has a two-dimensionally parameterizable freeform surface which directs the light more strongly in the direction of the second optical axis (7), the closer a reflecting object is to the sensor, characterized in that the additional lens (9) is arranged downstream of the main lens (8) in the beam path and is raised with respect to a surface of the main lens (8) facing the receiver (5).a biconic surface (10) refracting rays from the near field with two different focal lengths f1 and f2, and a surface (11) reflecting rays from the near field, wherein the receiver lens (6) is penetrated by rays reflected from the surface (11) in such a way that the rays reflected from the surface (11) are refracted at the biconic surface (10) and directed onto the receiver (5).

Description

[0001] The invention relates to an optoelectronic sensor with a light transmitter for emitting a light signal into an object area on a first optical axis, with a receiver and a receiver lens for receiving the light signal reflected by an object on a second optical axis, wherein the receiver lens has a main lens for imaging the object area and an additional lens for reducing the blind zone in the near range caused by the axial distance, wherein the additional lens directs the light more strongly in the direction of the second optical axis the closer the object is to the sensor.

[0002] Optoelectronic sensors, especially diffuse reflection sensors, are used in many areas of everyday life, recently in automotive applications, but also in automation technology. Due to their comparatively long range, these simple, energetic photoelectric sensors can easily be interfered with by reflective background objects. Furthermore, objects with different reflection coefficients lead to different switching distances. To avoid this, triangulation photoelectric sensors with two adjacent optical axes were initially developed. Due to the axial spacing, this inevitably leads to a blind zone directly in front of the sensor.

[0003] The later developed time-of-flight sensors (TOF = Time Of Flight), which are preferably designed as phase measuring devices, in particular as photonic mixing detectors (PMD) due to the short light travel time, cannot provide a remedy here even with coaxial optics with a split pupil, because the extremely short light travel times can no longer be evaluated at close range.

[0004] Therefore, DE 10 2004 037 137 A1 proposes a line-shaped arrangement with several TOF detectors, whose signals in the near range are additionally evaluated triangulatorily, which also leads to the blind zone mentioned above.

[0005] In order to keep this as low as possible, DE 20 2006 004 240 U1 discloses an auxiliary optic in the form of a wedge or a cylindrical lens, which directs light near the optical axis of the receiver, but without focusing the light in the image plane.

[0006] DE 10 2009 047 662 A1 describes a triangulation sensor in which the lack of focus at close range is compensated by forming the geometric center of gravity of the light spot. However, this requires a high-resolution CCD camera as the receiver.

[0007] DE 20 2013 102 370 U9 describes a laser rangefinder with a collimated measuring beam and a receiver lens. The receiver lens has a first curved surface (main lens) and a second curved surface (additional lens). It also shows a recess with a reflective and light-scattering effect, although the recess in particular is considered disadvantageous from a manufacturing perspective.

[0008] CN 102 313 882 B shows an arrangement with a main lens and an additional lens, whereby the additional lens is not suitable for reflecting short-range rays.

[0009] DE 102 20 037 A1 shows a main lens and a separate additional lens that must be mounted and adjusted separately, which is considered to be disadvantageous.

[0010] DE 102014 116 254 A1 shows an optical sensor with a receiver lens that is flattened at the edge toward the optical axis, so that short-range rays that have previously penetrated the front surface are directed to the receiver, but this reduces the receiving area. An additional lens for short-range rays is not provided.

[0011] DE 698 05 598 T2 shows a proximity switch with a receiving lens and a prism arranged next to it with a separate light entry surface that occupies a considerable part of the light entry surface, which is considered a disadvantage.

[0012] DE 100 26 625 C1 shows an optical triangulation sensor with a receiver lens inclined to the transmitter axis, which can be configured as a conventional converging lens, a Fresnel lens with two different focal lengths, or a stepped parabolic mirror. An additional lens as defined by the invention is not present and is probably not necessary here either.

[0013] DE 102014 114 314 A1 discloses a triangulation light sensor with a polymer-coated aspherical receiver lens featuring a two-dimensionally parameterized freeform surface that refracts the light striking the lens's inner edge area toward the optical axis of the receiver more strongly the closer the remitting object is to the detection zone. A disadvantage is that the large edge area of ​​the modified receiver lens cannot contribute to the received signal.

[0014] Another disadvantage is the rather complicated manufacturing process for the receiver lens.

[0015] The object of the invention is to at least partially eliminate the above-mentioned disadvantages and to provide a receiver lens which is simple and inexpensive to manufacture and which reduces the blind zone for objects in the near range.

[0016] This object is achieved by the characterizing features of patent claim 1. Claims 2 to 5 relate to the advantageous embodiment, and claim 6 relates to the receiver lens.

[0017] The essential idea of ​​the invention is to design the inner edge area of ​​the receiver lens in such a way that, in addition to the known area which refracts rays from the near field, a second area which reflects rays from the near field is created, which also directs light coming from the immediate near field onto the receiver.

[0018] This is achieved by an aspherical structure which, in an advantageous design, directs light to the receiver by total reflection.

[0019] A further advantageous embodiment of the invention consists in producing the receiver lens entirely from plastic in a single injection molding process, which reduces manufacturing time and costs.

[0020] The invention is explained in more detail with reference to the drawing. Fig. 1 shows a time-of-flight diffuse sensor according to the invention with a PMD receiver. Fig. 2 shows a receiver lens according to the invention with a Fresnel structure.

[0021] The Fig. 1 shows a laser diode as a light transmitter 1, whose diverging beam is directed by a collimator 2 into an object region 3. A diffusely reflecting object with an approximately Lambertian radiation characteristic located on this first optical axis 4 directs light onto a receiver lens 6, which is located on a second optical axis 7 arranged at a distance d from the first optical axis 4.

[0022] The receiver lens 6 is aspherical and has, in addition to a main lens 8, an additional lens 9 on its inner edge, which has a surface 10 which refracts rays from the near field and a surface 11 which reflects rays from the near field.

[0023] The refracting surface 10 is advantageously biconical, which leads to an astigmatic beam path with two different focal lengths in the x- and y-direction, whereby the term focal length here is merely intended to express that the light is directed specifically onto the receiver 5, creating an approximately elliptical light spot.

[0024] The coordinated interaction of the two surfaces 10 and 11 not only reduces the blind zone but also smooths the signal path. Reflection at the reflecting surface 11 can be caused by a reflective coating or by total internal reflection.

[0025] The receiver 5 is a photo-mixing detector (PMD receiver) suitable for evaluating the time of flight (TOF), which, like the transmitter 1, is connected in a known manner to a control and evaluation unit 20 symbolically represented as µC.

[0026] The Fig.2 shows a receiver lens 6 with a main lens 8 and an additional lens 9, wherein the main lens 8 has a Fresnel structure 12 on its front side.

[0027] The dimensions of the main lens 8 are 10 x 20 mm, and those of the auxiliary lens 9 are approximately 6 x 8 mm. The axial distance d is approximately 15 mm.

[0028] The receiver lens 6 has a further additional lens with a second biconical surface 102, which serves to smooth the signal curve so that a nearly linear relationship between the object distance and the received signal is achieved between 30 and 500 mm.

[0029] The contour of the additional lens 9 is described by a free-form surface, which can be specified in a known manner by a two-dimensional parameter representation or also in a table.

[0030] In an advantageous embodiment, the contour of the free-form surface is designed taking into account the lens material used, preferably plastic (polycarbonate or Plexiglas), the surface 11 such that total reflection occurs for certain angles of incidence.

[0031] In a further advantageous embodiment, the lens 6 can be manufactured from the aforementioned plastics or any other material suitable for optical components in one piece by injection molding or injection-compression molding.

[0032] The receiver lens 6 according to the invention is suitable for use both in a diffuse reflection sensor measuring the time of flight (TOF) and in a triangulation light sensor. List of reference symbols 1 light transmitter 2 Collimator 3 Object area 4 First optical axis 5 recipients 6 Receiver lens 7 Second optical axis 8 Main lens 9 First additional lens 10 Refractive biconical surface on the additional lens 9 11 Reflective surface on the additional lens 9 12 Fresnel structure on the main lens 8 20 Control and evaluation unit 102 Second biconical surface

Claims

[1] Optoelectronic sensor with a light transmitter (1) for emitting a light signal through a collimator (2) into an object area (3) on a first optical axis (4), with a receiver (5) and a receiver lens (6) for receiving the light signal reflected by an object on a second optical axis (7), wherein the receiver lens (6) contains a main lens (8) for imaging the object area (3) and an additional lens (9) for detecting the near range, wherein the additional lens (9) has a two-dimensionally parameterizable free-form surface which directs the light more strongly in the direction of the second optical axis (7), the closer a reflecting object is to the sensor, characterized bythat the additional lens (9) is arranged downstream of the main lens (8) in the beam path and is raised with respect to a surface of the main lens (8) facing the receiver (5), has a biconic surface (10) refracting rays from the close range with two different focal lengths f1 and f2, and a surface (11) reflecting rays from the close range, wherein the receiver lens (6) is penetrated by rays reflected at the surface (11) in such a way that the rays reflected by the surface (11) are refracted at the biconic surface (10) and directed onto the receiver (5). [2] Optoelectronic sensor according to claim 1, characterized by that rays coming from the near area at the reflecting surface (11) are directed to the receiver (5) by total reflection. [3] Optoelectronic sensor according to claim 1 to 2, characterized by that the receiver lens (6) is made of one piece and is made of plastic. [4] Optoelectronic sensor according to one of the preceding claims, characterized by that the main lens (8) has a Fresnel structure (12). [5] Optoelectronic sensor according to one of the preceding claims, characterized by that the receiver lens (6) has a further additional lens with a second biconic surface (102) which serves to smooth the signal curve. [6] Receiver lens (6) for an optoelectronic sensor according to one of the preceding claims.

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