Photoelectric sensors

Abstract

The present application relates to a photoelectric sensor. A photoelectric sensor, in particular a laser scanner, for detecting objects in a monitoring area is proposed. The sensor comprises: a light emitter for emitting emission light; a drive having a fixed part and a rotating part; a scanning unit movable by means of the rotating part for periodically scanning the monitoring area using the emission light; a light receiver for generating a received signal from light diffusely reflected by objects in the monitoring area; a control and evaluation unit for detecting information about the objects in the monitoring area based on the received signal; and a base housing having a cover. The base housing and the cover have at least one interface for mechanical connection to each other, and the cover includes at least one first bearing for accommodating the scanning unit, wherein the scanning unit is rotatably supported in the first bearing by means of the rotating part.

Description

[0001] The present invention relates to a photoelectric sensor for detecting objects in a surveillance area.

[0002] Optoelectronic systems, particularly laser scanners, are suitable for distance measurements requiring a large horizontal angular range of the measuring system. In laser scanners, a light beam generated by a laser is periodically scanned across the monitoring area using a deflection unit. The light beam is diffusely reflected by objects in the monitoring area and evaluated in the scanner. The angular position of the object is inferred from the angular position of the deflection unit, and the distance of the object from the laser scanner is also inferred from the time of flight of the light using the speed of light.

[0003] Using the angle and distance information, the position of objects in the monitoring area is recorded in two-dimensional polar coordinates. This allows the position of an object to be determined, or its contour to be determined by scanning the same object multiple times at different positions. A third spatial coordinate can also be determined through relative motion in the transverse direction, for example by providing additional degrees of freedom of movement in the deflection unit of the laser scanner or by transporting the object relative to the laser scanner. This allows the measurement of three-dimensional contours.

[0004] In addition to these measurement applications, laser scanners are also used in safety technology to monitor hazardous sources, such as dangerous machines. A safety laser scanner of this type is known from DE 43 40 756 A1. Here, a protective field, which an operator is not permitted to enter, is monitored while the machine is operating. If the laser scanner detects an unauthorized interference with the protective field, such as an operator's leg, it triggers an emergency stop of the machine. Sensors used in safety technology must operate extremely reliably and therefore meet high safety requirements, such as those in the EN 13849 standard for machine safety and the EN 61496 standard for non-contact guards (BWS).

[0005] In laser scanners, scanning of the monitoring surface is typically achieved by directing the transmitted light beam onto a rotating deflecting mirror. The light transmitter, light receiver, and associated electronics and optics are fixedly mounted in the device and do not follow the rotational movement. However, it is also known to replace the deflecting mirror with a co-moving scanning unit. For example, in DE 197 57 849 B4, the entire measuring head rotates together with the light transmitter and light receiver. EP 2 388 619 A1 also provides a rotatable transmitter / receiver unit. This scanning unit is supplied with energy, for example, based on the transducer principle, from a rotationally fixed area of ​​the sensor.

[0006] Figure 1A schematic cross-sectional view of a conventional laser scanner 100 is shown with such a rotatable scanning unit 102. The rotational movement is generated by the scanning unit 102 being located on an axis 104 of a drive 106. The laser scanner 100 is protected by a housing 108, the upper part of which is formed by a cover 110.

[0007] The numerous components (housing, housing, drive, scanning unit) and the numerous interfaces between them make assembly and adjustment very complex, especially when the sensor must have a very high scanning field flatness. If the scanning unit also moves, additional interfaces for energy and data transmission must be provided on the rotating part of the sensor. This requires additional components or assemblies, which in turn increases the complexity of the sensor and its installation and adjustment.

[0008] It is therefore an object of the present invention to provide such a sensor having a simplified structure.

[0009] This object is achieved by a photoelectric sensor for detecting objects in a monitoring area and by a method for supporting a scanning unit as part of the photoelectric sensor.

[0010] The sensor includes a light emitter and a light receiver for scanning a monitoring area. A drive having a fixed part and a rotating part, and a scanning unit moved by the rotating part, provide a periodic scanning motion. The sensor includes a base housing with a cover, wherein the base housing and the cover have at least one interface for mechanical connection to each other. The cover includes at least one first bearing for accommodating the scanning unit, wherein the scanning unit is rotatably supported in the first bearing by the rotating part. Preferably, the first bearing can be arranged on the side of the cover facing the base housing.

[0011] The advantage of the present invention is that, by supporting the scanning unit in the housing, the number of interfaces subject to tolerances is reduced, which simplifies assembly and / or adjustment efforts and, consequently, reduces manufacturing costs. Furthermore, supporting the scanning unit in the housing results in an optimal support arrangement (with the center of mass located between the support points), which significantly improves vibration and / or impact resistance. At the same time, the entire sensor becomes more robust in the field, with higher shock and vibration resistance. This significantly increases the potential for outdoor use or applications in demanding environments where the sensor cannot be protected from mechanical stress. Failures due to defective devices are significantly less likely.

[0012] In one embodiment of the present invention, the light emitter and light receiver can be arranged in a base housing. The scanning unit then has a deflection mirror for deflecting the emitted light into the monitoring area and for deflecting light diffusely reflected by objects in the monitoring area onto the light receiver. Preferably, the associated transmitting and receiving optics, transmitting and receiving electronics, and possibly at least part of the evaluation unit are also located in the base housing along with the light emitter and light receiver. This embodiment has the advantage that the system's motion mass is kept low, since only the deflection mirror moves with the rotating element of the drive.

[0013] In one embodiment of the present invention, the scanning unit can include a light emitter and / or a light receiver. This makes the scanning unit a rotating measuring head. With the light emitter and light receiver, the associated transmitting and receiving optics, the transmitting and receiving electronics, and possibly at least part of the evaluation unit are preferably also located in the scanning unit.

[0014] The fixed element of the drive can be arranged in the base housing or in the cover. If the fixed element and the rotating element are arranged in the cover, tolerances in the mechanical interface between the cover and the base housing, which are related to the alignment of the rotating element and the fixed element relative to each other, are eliminated. Arrangement in the base housing can be advantageous if the scanning unit is designed as a deflecting mirror and the remaining components of the sensor are arranged in the base housing, as electrical connections to the cover are not required.

[0015] The cover can include a second bearing for rotatably supporting the scanning unit, with the first bearing being arranged on the side of the cover facing the base housing, and the second bearing being arranged on the side of the cover facing away from the base housing. This improves the sensor's shock and vibration resistance. The dimensions of the bearings can optionally be adapted to the shape of the cover. For example, the second bearing can have a smaller diameter than the first bearing.

[0016] The housing can have a mechanical receptacle for the first and / or second bearing, which is advantageously an integral component of the housing. This virtually eliminates any tolerances between the housing and the scanning unit. For example, the receptacle for the first and / or second bearing can be fixed in the housing during the injection molding process used to manufacture the housing.

[0017] The cover can be designed as a solid of revolution with side walls and a cover area. For example, the side walls can form a cylindrical, truncated cone, or spherical segment, but more complex contours, such as a cup, are also conceivable. The cover is then closed at the top by the cover area, which can be circular but can also have a curvature.

[0018] The cover can have a front panel as an exit area for the emitted light and an entrance area for the diffusely reflected light. The front panel is preferably an integral component of the cover, in particular of the side wall.

[0019] The cover is preferably made of a plastic that is transparent to the emitted light. Therefore, the transparency also applies to the diffusely reflected received light, which has the same wavelength. Thus, the cover also functions as a front panel. However, the cover does not necessarily need to be transparent to the naked eye, but rather, for example, black and opaque, since the emitted light often uses spectral regions outside the visible range, particularly infrared light.

[0020] Preferably, the cover is a single component, rather than an assembly of multiple elements, in order to simplify the manufacture of the cover and its handling during assembly of the sensor.

[0021] A support element can be provided which supports the cover in the center. In this case, the support area on the cover is particularly located approximately in the middle of the cover area. Suitable support elements and arrangements are described, for example, in EP 3 293 546 B1.

[0022] The sensor is preferably a distance measuring sensor, in which the evaluation unit determines the light flight time between the emitted light signal and the received diffusely reflected light and thereby determines the distance to the object. This allows significantly more accurate object information to be obtained than simply by determining the presence of the object.

[0023] An angle measuring unit is preferably provided for detecting the angular position of the scanning unit. Overall, complete two-dimensional position coordinates are available for the detected object. In the case of a spatially expanded monitoring area by moving the scanning unit along two axes, the corresponding tilt angle of the scanning unit is preferably also detected, thereby subsequently obtaining overall three-dimensional spherical coordinates that also completely describe the position of the object within the monitoring area.

[0024] The sensor is preferably designed as a safety sensor and has a safety output, wherein the evaluation unit is designed to determine whether an object is located in the protective field within the monitoring area and then output a safety-related disconnection signal via the safety output. The safety sensor is safe within the meaning of the safety standards mentioned at the outset and can therefore be used in particular for protecting people at a hazardous source. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The following will exemplarily describe other features and advantages of the present invention in more detail based on embodiments and with reference to the accompanying drawings. Here, the same reference numerals represent the same or similar features. In the accompanying drawings:

[0026] Figure 1 shows a schematic cross-sectional view of a conventional laser scanner;

[0027] Figure 2 A schematic sectional view shows an embodiment of a laser scanner according to the invention having a scanning unit designed as a deflecting mirror;

[0028] Figure 3 Shows something like Figure 2 A schematic cross-sectional view of an embodiment of a laser scanner according to the present invention;

[0029] Figure 4 Shows something like Figure 2 A schematic cross-sectional view of another embodiment of a laser scanner according to the present invention;

[0030] Figure 5 A schematic sectional view shows an embodiment of a laser scanner according to the invention having a scanning unit comprising a light emitter and a light receiver;

[0031] Figure 6 Shows something like Figure 5 Schematic cross-sectional view of another embodiment of the laser scanner according to the present invention.

[0032] Figure 2 A schematic cross-sectional view of a photoelectric sensor according to the present invention, in an embodiment as a laser scanner 10, is shown. Roughly speaking, the laser scanner 10 comprises a movable scanning unit 12, a base housing 14, and a cover 16. The base housing 14 and the cover 16 are mechanically connected to each other via at least one interface 18. The cover 16 has a side wall 50, which is cylindrical in form, typically as a solid of revolution formed from a suitable profile. The side wall 50 serves as a front panel through which the emitted light 30 is emitted or through which light 36 diffusely reflected from the monitoring area 32 enters. Accordingly, the front panel is made of a material that is transparent to the emitted light 30 generated by the light emitter 26. The cover 16 is closed at the top by a cover region 52, which is connected to the side wall 50 and preferably formed integrally with the side wall. For example, the cover 16 is a single plastic component that can be manufactured using an injection molding process. The housing 16 includes at least one first bearing 20 for accommodating the scanning unit 12. The first bearing 20 is arranged on the side of the housing 16 facing the base housing 14, and the scanning unit 12 is rotatably supported in the first bearing 20. Furthermore, the scanning unit 12 has at least one rotating element 22, which, in conjunction with at least one fixed element 24 arranged in the base housing 14, enables the scanning unit to perform an oscillating or rotational movement. Thus, the rotating element 22 and the fixed element 24 together form a drive for the scanning unit 12.

[0033] In this embodiment, the scanning unit 12 includes a deflecting mirror 25, while the other components of the laser scanner 10 are arranged in a base housing 14. A light transmitter 26 generates emission light 30 using a transmission lens 28. This emission light is emitted via the deflecting mirror 25 of the scanning unit 12 into a monitoring area 32. If the emission light 30 strikes an object 34 in the monitoring area 32, corresponding diffusely reflected light 36 returns to the laser scanner 10. The diffusely reflected light 36 is directed via the deflecting mirror 25 of the scanning unit 12 to a receiving lens 38 in the base housing 14, where it is focused onto a light receiver 40 and converted into an electrical receive signal. The light transmitter 26 and the light receiver 40 are located together on a printed circuit board 42.

[0034] The control and evaluation unit 44 controls the fixture 24 and the light transmitter 26 of the drive of the scanning unit, evaluates the received signals of the light receiver 40, and obtains a signal from the angle measuring unit 46, which determines the corresponding angular position of the scanning unit 12. The control and evaluation functions can be largely freely distributed between the printed circuit board 42 and the evaluation unit 44, but are described as if the evaluation unit 44 alone is responsible.

[0035] For evaluation, the distance to the scanned object 34 is preferably measured using the light time-of-flight method. To this end, in a phase-based system, the emitted light of the light transmitter 26 is modulated and the phase relationship with the received signal of the light receiver 40 is evaluated. Alternatively, in a pulse-based system, a short light pulse is emitted at the time of emission, and its reception time is determined from the received signal. In this case, both a single-pulse method, in which the distance is determined from a single transmitted pulse, and a pulse averaging method, in which the received signal is collected after a plurality of consecutive transmitted pulses and statistically evaluated, are conceivable. The corresponding angular position of the emitted light 30 is also known by the angle measuring unit. Therefore, after each scanning cycle, i.e., after one rotation of the scanning unit 12, the two-dimensional polar coordinates of all object points in the scanning plane can be obtained via angles and distances.

[0036] The object position or object contour is thus known and can be output via the sensor interface 48. The sensor interface 48 or another port (not shown) can in turn be used as a parameterization interface. In applications in safety technology, the protective field that can be configured in the monitoring area 32 is monitored for unauthorized interference and, if necessary, a safety-related shutdown signal is output via a safely configured interface 48 (e.g., OSSD, Output Signal Switching Device).

[0037] Figure 3 Shown Figure 21 . The present invention relates to a variant embodiment of the laser scanner 10 . Here, the housing 16 has a second bearing 54 for rotatably mounting the scanning unit 12 with a stabilizing element 56 , wherein the second bearing 54 is arranged on the side of the housing 16 facing away from the base housing 14 . The second bearing 54 has a smaller diameter than the first bearing 20 .

[0038] Figure 4 Shown Figure 2 Another variant of the embodiment of the laser scanner 10, wherein Figure 2 The embodiment differs from that of in that the cover 16 comprises the rotating part 22 and the fixed part 24 of the drive of the scanning unit 12. This eliminates tolerances of the mechanical interface 18 between the cover 16 and the base housing 14, which relate to the alignment of the rotating part 22 and the fixed part 24 relative to one another.

[0039] Figure 5 An alternative embodiment of the sensor according to the invention is shown. Figure 2-Figure 4 As in the embodiment shown in FIG, the photoelectric sensor implemented as a laser scanner 60 roughly comprises a movable scanning unit 62, a base housing 14, and a cover 16. The base housing 14 and the cover 16 are mechanically connected to each other via at least one interface 18. The cover 16 has a side wall 50, which is in the form of a cylinder, typically as a rotational body formed with a suitable profile. The side wall 50 serves as a front panel through which the emitted light 30 is emitted or through which the light 36 diffusely reflected from the monitoring area 32 enters. Accordingly, the front panel is made of a material that is transparent to the emitted light 30 generated by the light emitter 26. The cover 16 is closed at the top by a cover area 52, which is connected to the side wall 50 and is preferably formed together with the side wall. For example, the cover 16 is a single plastic component that can be manufactured using an injection molding process. The housing 16 includes at least one first bearing 20 for accommodating the scanning unit 62, wherein the first bearing 20 is arranged on the side of the housing 16 facing the base housing 14, and the scanning unit 62 is rotatably supported in the first bearing 20. Furthermore, the scanning unit 62 has at least one rotating element 22, which, in conjunction with at least one fixed element 24 arranged in the base housing 14, enables the scanning unit 62 to perform an oscillating or rotating motion to periodically scan the monitoring area 32. Thus, the rotating element 22 and the fixed element 24 together form a drive for the scanning unit 62.

[0040] With Figure 2-Figure 4Unlike the embodiment shown in FIG, scanning unit 62 is configured as an optical measuring head, in which a light transmitter 26 emits transmission light 30 into a monitoring area 32 using transmission optics 28. If the transmission light 30 strikes an object 34 in monitoring area 32, corresponding diffusely reflected light 36 returns to laser scanner 60. The diffusely reflected light 36 is guided by receiving optics 38 to a light receiver 40, where it is converted into an electrical receive signal. Here, light transmitter 26 and light receiver 40 are located together on a first printed circuit board 42. Scanning unit 62 also includes a first energy transmission module 64 and a first data transmission module 66.

[0041] The arrangement in scanning unit 62 is to be understood as purely exemplary. Thus, light emitter 26 and light receiver 40 can each be located on their own printed circuit board, and overall, more or fewer printed circuit boards can be provided in various arrangements. In principle, any other arrangement known per se for single-beam photoelectric sensors or laser scanners is possible, such as a double lens with a transmitting lens in the center of a receiving lens, or the use of beam-splitting mirrors. It is not even absolutely necessary to construct a scanning system consisting of light emitter 26 and light receiver 40; alternatively, another sensor or a combination of multiple sensors can be rotated, for example, to achieve multiple scans in multiple planes, as described, for example, in DE 10 2013 111547 A1.

[0042] In addition to the fixing element 24, the base housing 14 of the laser scanner 60 also includes a control and evaluation unit 44 and a sensor interface 48 as well as a second energy transmission module 68 and a second data transmission module 70. The energy supply of the scanning unit 62, in particular the light transmitter 26 and the light receiver 40, can be realized via the first energy transmission module 64 and the second energy transmission module 68. The first and second data transmission modules are used for wireless, bidirectional data transmission of control signals from the control and evaluation unit 44 to the scanning unit 62 and electrical reception signals from the light receiver 40 to the control and evaluation unit 44. The control and evaluation unit 44 evaluates the reception signals, controls the drives and obtains signals from the angle measurement unit 46, which determines the corresponding angular position of the scanning unit 62. The control and evaluation functions can be largely freely distributed between the scanning unit 62 (in particular the printed circuit board 42) and the evaluation unit 44. The evaluation of the received signals is similar to that of the control and evaluation unit 44. Figure 2 Description in .

[0043] Figure 6 Shown Figure 5This embodiment shows a variant of the embodiment of the laser scanner 60. In this embodiment, the cover 16 is supported centrally in the cover area 52 by a support element 72. The support element 72 can have a simple shape and can be designed as a pin or a rod, for example. The connection between the cover 16 and the support element 72 is preferably fixed. A rotatable bearing is not provided and is not required because the support element 72 does not move with the scanning unit 62. Rather, the support element 72 extends through the recess in the scanning unit 62 to the base housing 14. The cover 16 is thus fixedly connected to the base housing at the interface 18 and also in the cover area 52.

Claims

1. A photoelectric sensor (10, 60) for detecting an object (34) in a monitoring area (32), wherein: The sensor (10, 60) comprises: a light emitter (26) for emitting emission light (30); a drive having a fixed part (24) and a rotating part (22); a scanning unit (12, 62) movable by means of the rotating part (22) for periodically scanning the monitoring area (32) using the emission light (30); a light receiver (40) for generating a reception signal from light (36) diffusely reflected by an object (34) in the monitoring area (32); a control and evaluation unit (44) for detecting information about the object (34) in the monitoring area (32) based on the reception signal; and a base housing (14) having a cover (16). The base housing (14) and the cover (16) have at least one interface (18) for mechanical connection to each other, and the cover (16) is configured as a rotating body with side walls (50) and a cover area (52), and the cover (16) has a front panel as an exit area for the emitted light (30) and an entrance area for the diffusely reflected light (36), wherein the front panel is an integral component of the side walls (50) of the cover (16), The cover (16) includes at least one first bearing (20), which is arranged on a side of the cover (16) facing the base housing (14) for accommodating the scanning unit (12, 62), wherein the scanning unit (12, 62) is rotatably supported in the first bearing (20) by means of the rotating member (22), and the side wall (50) of the cover (16) includes the first bearing (20).

2. The photoelectric sensor (10, 60) according to claim 1, characterized in that The fixing element (24) is arranged in the base housing (14).

3. The photoelectric sensor (10, 60) according to claim 1, characterized in that The fixing element (24) is arranged in the cover (16).

4. The photoelectric sensor (10, 60) according to claim 1, characterized in that The photoelectric sensor (10, 60) is a laser scanner.

5. The photoelectric sensor (10, 60) according to claim 1, characterized in that The cover (16) has a second bearing (54) for rotatably supporting the scanning unit (12, 62), wherein the second bearing (54) is arranged on a side of the cover (16) facing away from the base housing (14).

6. The photoelectric sensor (10, 60) according to any one of the preceding claims, characterized in that The cover (16) is made of plastic that is transparent to the emitted light (30).

7. The photoelectric sensor (10) according to any one of claims 1 to 5, characterized in that The light emitter (26) and the light receiver (40) are arranged in the base housing (14), and the scanning unit (12) has a deflection mirror (25) for deflecting the emitted light (30) into the monitoring area (32) and deflecting light (36) diffusely reflected by an object (34) in the monitoring area (32) onto the light receiver (40).

8. The photoelectric sensor (60) according to any one of claims 1 to 5, characterized in that The scanning unit (62) has the light transmitter (26) and / or the light receiver (40).

9. The photoelectric sensor (60) according to claim 8, characterized in that The sensor (60) has a support element (72) for centrally supporting the cover (16).

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