DE202014102451U1 - Opto-electronic sensor for detecting objects - Google Patents

Abstract

Optoelectronic sensor (10) for detecting objects in a surveillance area (20), in particular a laser scanner, having a light transmitter (28) for emitting a transmitted light beam (32), a light receiver (38) for generating a reception signal from that in the surveillance area ( 20) remitted light (34), a base unit (14) having a circumferential windshield (26), a relative to the base unit (14) movable scanning unit (12) for periodically scanning the monitoring area (20) and an evaluation unit (46) for detecting Information about objects in the surveillance area (20) based on the received signal, wherein the scanning unit (12) comprises a first optical data transmission unit (42) and the base unit (14) has a second optical data transmission unit (44) to transfer data between the socket unit (12) and the scanning unit (14) via an optical signal, characterized in that the data transmission unit en (42, 44) for data exchange via a light guide (26, 52) are formed, which is arranged on the windscreen (26).

Description

The invention relates to an optoelectronic sensor for detecting objects according to the preamble of claim 1.

For distance measurements that require a large horizontal angle range of the measuring system, optoelectronic systems and especially laser scanners are suitable. In a laser scanner, a laser beam generated by a laser periodically sweeps over a monitoring area by means of a deflection unit. The light is remitted to objects in the surveillance area and evaluated in the scanner. From the angular position of the deflection is on the angular position of the object and from the light transit time using the speed of light in addition to the removal of the object from the laser scanner closed.

With the angle and distance indications, the location of an object in the surveillance area is recorded in two-dimensional polar coordinates. Thus, the positions of objects can be determined or determined by multiple probing the same object at different points whose contour. The third spatial coordinate can also be detected by a relative movement in the transverse direction, for example by a further degree of freedom of movement of the deflection unit in the laser scanner or by the object being conveyed relative to the laser scanner. Thus, even three-dimensional contours can be measured.

In addition to such measuring applications, laser scanners are also used in security technology to monitor a source of danger, such as a dangerous machine. Such a safety laser scanner is from the DE 43 40 756 A1 known. A protective field is monitored, which must not be entered by the operating personnel during operation of the machine. If the laser scanner detects an inadmissible protective field intervention, for example a leg of an operator, it triggers an emergency stop of the machine. Sensors used in safety technology must work very reliably and therefore meet high safety requirements, such as the Standard EN13849 for machine safety and the device standard EN61496 for non-contact protective devices (ESPE).

The scanning of the monitoring level in a laser scanner is usually achieved by the transmission beam impinging on a rotating rotating mirror. The light transmitter, light receiver as well as the associated electronics and optics are permanently mounted in the device and do not carry out the rotary movement. Due to the mirror very high demands are made on the alignment of the light emitter and light receiver to the axis of rotation. Deviations from this lead to a bent surveillance level. In addition, such optical units are large in size, because always a part of the object width extends over the mirror to the receiving optics in the device. Stray light effects on the windscreen by the windscreen itself or their contamination lead to a deterioration of the sensor function.

It is also known to replace the rotating mirror by a co-moving scanning unit. For example, rotates in the DE 197 57 849 B4 the entire measuring head with light transmitter and light receiver. The EP 2 388 619 A1 also provides a rotatable transmitter / receiver unit. This scanning unit is powered, for example, according to the transformation principle of the non-rotatable regions of the sensor with energy, while the data transmission is wirelessly by radio or by optical means. However, these wireless interfaces are not more detailed.

In the EP 2 645 125 A1 are provided in the rotating deflection light guides, which redirect the light from a stationary light emitter or to a stationary light receiver. This is not optical data transmission, because the light signal is transmitted directly to the measurement.

The US 7,187,823 B2 describes a system for transmitting power and an optical signal between components of a monitor. In this case, two ring cores rotate to each other, while the optical transmission takes place through openings in the center. This system requires a special drive with hollow shaft.

Therefore, an object of the invention to provide an optoelectronic sensor with improved optical data communication between stationary and rotating part.

This object is achieved by an optoelectronic sensor for detecting objects according to claim 1. The sensor, in particular a laser scanner, has a movable scanning unit and a base unit, each with an optical data transmission unit. The invention is based on the basic idea of using a light guide for data exchange, which is arranged on a circumferential windscreen of the sensor. Such a windscreen is customary for protection of the sensor and circumferentially formed, d. H. a panoramic window with an angle range up to 360 ° for the rotating scanning beam. Via the light guide unidirectional or bi-directional communication is possible.

The invention has the advantage that the light guide on the windshield a significant distance creates to the rotating scanning unit. There is therefore a clear spatial separation without a mutual mechanical or optical interference between the actual measuring system and the data transmission between the scanning unit and base unit. A special drive for the movement of the scanning unit, such as with a hollow shaft or the like, is not required.

The light guide is preferably attached to the windscreen. Thus, the light guide in this embodiment is a separate component, in particular a light guide rod, which is glued to the front pane, clipped there or otherwise secured. The light guide is preferably so narrow and transparent to the scanning beam that the measurement is not disturbed. Alternatively, in a sensor having a scanning angle range smaller than 360 °, the optical fiber is mounted in an unused angular range where usually internal reference targets for checking the light emitter and the sensor function and the like are accommodated.

In a preferred embodiment, the windscreen itself acts as a light guide. The optical signal is forwarded here by total internal reflection in the windscreen. On a separate component as a light guide can be dispensed with. Preferably, structures or coatings of the windscreen are provided to hold the optical signal on a predetermined light path.

The windshield preferably forms a hood, and the coupling of the optical signal occurs in a center of the hood. The scanning unit and the base unit are usually arranged one above the other on the axis of rotation of the scanning unit, and the hood serves as a dome-like conclusion. According to this embodiment, the optical signal from the scanning unit is now first emitted in the opposite direction of the base unit, namely to the hood and then deflected in the hood to the base unit. In this case, the hood belongs to the base unit, as it also does not follow the movement of the scanning unit, but the evaluation electronics of the base unit is usually not in the hood. In embodiments with a separate light guide instead of a windshield as a hood and a non-transparent housing part, the windscreen dome-shaped complete, since the light-conducting properties of the windscreen are not needed here.

The evaluation unit is preferably designed to evaluate a degree of contamination of the windshield on the basis of the optical signal. Fouling of the windshield is a common problem of opto-electronic sensors, and many conventional laser scanners have their own measuring units for checking the light transmission. When the optical signal is transmitted by total internal reflection in the windscreen, light is swallowed or may leak out of contaminants of the windscreen. Therefore, the optical signal actually arriving in the socket unit offers the possibility to evaluate the contamination of the front screen. This provides additional important information without the need for additional components.

The evaluation preferably includes an error rate of the transmission. In any case, the communication protocol of the optical data transmission usually offers options for evaluating the quality of the transmission, for example a bit error rate. This embodiment makes use of such an evaluation in order to be able to evaluate the contamination of the windscreen without separate evaluation of its own. However, it is also conceivable to evaluate the optical signal differently and in particular independently of the information encoded therein, for example on the basis of a signal amplitude.

The first data transmission unit and the second data transmission unit are preferably designed for wavelength division multiplexing. This allows data to be transmitted in both directions without interfering with each other, and allows bidirectional full-duplex communication.

The data transmission units preferably exchange optical signals with a different wavelength than that of the transmitted light beam. Due to the optical waveguide and the spatial separation of the optical data communication by arrangement on the windscreen, the problem of optical crosstalk has already been largely reduced. By different wavelengths but the mutual influence can be suppressed by stray light even more effective.

The invention will be explained below with regard to further advantages and features with reference to the accompanying drawings with reference to embodiments. The figures of the drawing show in:

1 a schematic sectional view through a laser scanner;

2 a schematic sectional view through a further embodiment of a laser scanner.

1 shows a schematic sectional view through an optoelectronic sensor in one embodiment as a laser scanner 10 , Of the laser scanner 10 comprises in rough division a movable scanning unit 12 and a socket unit 14 , The scanning unit 12 is the optical probe while in the socket unit 14 other elements such as a supply, evaluation electronics, connections and the like are housed. In operation, with the help of a drive 16 the base unit 14 the scanning unit 12 in a rotational movement about a rotation axis 18 offset so as to provide a surveillance area 20 to periodically scan. The laser scanner 10 is in a housing 22 accommodated, which upwards a hood 24 with one around the axis of rotation 18 circumferential windscreen 26 is completed. casing 22 and hood 24 could be different than shown as part of the socket unit 14 be understood as they are like the socket unit 14 rest.

In the scanning unit 12 creates a light transmitter 28 with the help of a transmission optics 30 a transmitted light beam 32 in the surveillance area 20 is sent out. Meets the transmitted light beam 32 in the surveillance area 20 on an object, then a corresponding ray of light returns as a remitted light 34 to the laser scanner 10 back. The remitted light 34 is from a receiving optics 36 on a light receiver 38 guided and converted there into an electrical received signal. The received signal is sent to a preprocessing unit 40 passed and amplified there for example, filtered, digitized and the like. The preprocessing unit 40 can also do other functions like controlling the light transmitter 28 take over or be absent in other embodiments.

The arrangement within the scanning unit 12 is anyway purely exemplary to understand. As an alternative, any other arrangement known per se from single-beam optoelectronic sensors or laser scanners, such as a double lens with transmitting optics in the center of a receiving lens or the use of a beam splitter mirror, would be possible.

The invention is less concerned with the specific embodiment of the scanning unit 12 but rather with an optical data transmission to be explained between the scanning unit 12 and socket unit 14 , For this purpose, a first optical data transmission unit exchanges 42 the scanning unit 12 optical signals with a second optical data transmission unit 44 the base unit 14 out. The preprocessing unit is located above this communication channel 40 or, if this is not present, immediately light emitter 28 and / or light receiver 38 with an evaluation unit 46 the base unit 14 in connection. The control and evaluation functionality can be largely free between preprocessing unit 40 and evaluation unit 46 be distributed, but is described as if only the evaluation unit 46 responsible for.

The evaluation unit 46 evaluates the received signal, controls the drive 16 and receives the signal from an angle measuring unit 48 showing the respective angular position of the scanning unit 12 certainly. For evaluation, the distance to a touched object is preferably measured with a light transit time method. For this purpose, in a phase-based system, the transmitted light of the light transmitter 28 modulated and a phase relationship with the received signal of the light receiver 38 evaluated. Alternatively, in a pulse-based system, short light pulses are emitted at a transmission time as transmission light and the reception time is determined from the reception signal. In this case, both individual pulse methods, each of which determines a distance from a single transmission pulse, and pulse averaging methods are conceivable in which the received signal is collected after a multiplicity of successive transmission pulses and statistically evaluated. The respective angular position, under which the transmitted light beam 32 each emitted is from the angle measuring unit 48 also known. Thus, after each scan period, so turn the scanning unit 12 , two-dimensional polar coordinates of all object points in a scanning plane are available over the angle and the distance.

Thus, the object positions or object contours are known and can via a sensor interface 50 be issued. The sensor interface 50 or another, not shown connection vice versa serve as a parameterization interface. In safety applications, protective fields are used in the surveillance area 20 can be configured, monitored for improper interventions, and then, if necessary, a safety-related shutdown signal on the then securely trained interface 50 (eg OSSD, Output Signal Switching Device).

The light transmitter 28 can be constructed as a simple light source, such as in the form of a semiconductor diode, but also as, for example, row or matrix-shaped arrangement numerous light sources. Accordingly, it may be in the light receiver 38 a simple receiving surface, such as a photodiode, or act, for example, a line or matrix-shaped arrangement of light-receiving elements, such as a CCD or CMOS chip. This results in not only a single scanning beam, but a corresponding plurality for receiving two-dimensional image data or three-dimensional image data using a light transit time method. In principle, almost any sensor units in the scanning unit 12 rotate and so the surveillance area 20 Capture, for example, a plurality of sensor units in different angular positions, the one another with the same or different physical Complement measuring principles. There is also the option of the scanning unit 12 in addition to tilt or multiple superimposed light emitters 28 or light receiver 38 or to rotate a particular range-measuring camera line to scan a three-dimensional space area.

For communication between scanning unit 12 and socket unit 14 becomes an optical signal via the optical data transmission units 42 . 44 replaced. The more important direction of this communication is mostly from the scanning unit 12 to the base unit 14 because no measurement information can be output without the received signal or information obtained from the received signal. Often, bidirectional communication is also useful, such as the light transmitter 28 to drive or with the preprocessing unit 40 connect to. Also, the possibility of unidirectional communication from the socket unit 14 to the scanning unit 12 should not be excluded in principle. Depending on are in the optical data transmission units 42 . 44 each one not shown separately light emitter, light receiver or both provided.

In the embodiment according to 1 becomes the optical signal from the first data transmission unit 42 in the hood 24 coupled and then propagates with total internal reflection within the hood 24 or the windscreen 26 like in a light guide. Accordingly, the optical signal at any point of the hood 24 or the windscreen 26 from the second data transmission unit 44 be decoupled, in the example of 1 bottom of a support surface where the hood 24 on the rest of the housing 22 rests. The optical signal is therefore on the one hand, instead of freely within the laser scanner 10 to be emitted and thus to cause stray light, and on the other hand no additional component is needed, but the hood 24 or windscreen 26 used in an additional function.

That through the windshield 26 Guided optical signal can additionally be used to their degree of pollution and thus sufficient transparency for transmitted light beam 32 and remitted light 34 to rate. This is because pollution also dampens the optical signal, be it due to impaired light pipe properties or due to imperfections where light, instead of total internal reflection, can leak out and thus be lost. This attenuation can be detected directly from the signal amplitude or indirectly by degrading the data communication, such as increasing a bit error rate.

In order to enable bidirectional communication, either time-division multiplexing with time windows for the one and the other data direction or a full-duplex data link for example by wavelength division multiplexing is conceivable. Alternatively, another data channel may be independent of the optical data transmission units 42 . 44 be created. Although due to the light-conducting properties of the windscreen 26 Stray light can be largely avoided should preferably for the measuring transmitted light beam 32 and the optical signal of the data transmission units 42 . 44 a different wavelength can be selected, possibly additionally with corresponding band-limiting optical filters.

2 shows a further embodiment of a laser scanner 10 in a schematic sectional view. Structure, properties and design options largely correspond to the embodiment 1 and will not be described again.

In contrast to 1 will not be the windscreen 26 used as a light guide for optical data communication, but a separate light guide 52 or fiber optic rod on the windscreen 26 arranged or in the hood 24 integrated. The first optical data transmission unit 42 the scanning unit 12 and the top of the light pipe 52 are preferably located centrally on the axis of rotation 18 , so that their mutual arrangement of the rotation of the scanning unit 12 remains independent. The position of the second optical data transmission unit 44 in the socket unit 14 is hardly fixed, because the light guide 52 not rotated and the optical signal practically to every position of the base unit 14 could lead. In 2 is the second optical data transmission unit 44 exemplarily housed at an edge position.

The light guide 52 can be made for example of Plexiglas or as a molded part. Optionally, the light guide 52 in the hood 24 integrated, glued or clipped there. A thin light guide 52 interferes with the light paths of transmitted light beam 32 and remitted light 34 hardly and is reflected only in a low attenuation. But it is also conceivable, the light guide 52 in a dead zone of the laser scanner 10 accommodate, so an angle range in which is not scanned anyway and, for example, a reference target for an internal functional test is housed, behind which the light guide 52 then advantageously runs. As in the embodiment of 2 No internal total reflection is exploited, the hood can 24 in the area outside the windscreen 24 also be constructed of opaque housing material. Furthermore, with the same basic structure and an electrical instead of optical Data transmission possible, in which the light guide 52 replaced by an electrical conductor. The connection at the top of the hood 24 between rotating scanning unit 12 and resting pedestal unit 14 then takes place, for example, inductive or capacitive.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 4340756 A1 [0004]
• DE 19757849 B4 [0006]
• EP 2388619 A1 [0006]
• EP 2645125 A1 [0007]
• US 7187823 B2 [0008]

Cited non-patent literature

• Standard EN13849 [0004]
• EN61496 [0004]

Claims (8)

Optoelectronic sensor ( 10 ) for capturing objects in a surveillance area ( 20 ), in particular laser scanners, with a light transmitter ( 28 ) for emitting a transmitted light beam ( 32 ), a light receiver ( 38 ) for generating a received signal from that of objects in the surveillance area ( 20 ) remitted light ( 34 ), a base unit ( 14 ) with a circumferential windscreen ( 26 ), one opposite the base unit ( 14 ) movable scanning unit ( 12 ) for periodically scanning the monitoring area ( 20 ) and an evaluation unit ( 46 ) for collecting information about objects in the surveillance area ( 20 ) based on the received signal, wherein the scanning unit ( 12 ) a first optical data transmission unit ( 42 ) and the base unit ( 14 ) a second optical data transmission unit ( 44 ) to transfer data between socket unit ( 12 ) and scanning unit ( 14 ) via an optical signal, characterized in that the data transmission units ( 42 . 44 ) for data exchange via a light guide ( 26 . 52 ) formed on the windscreen ( 26 ) is arranged. Sensor ( 10 ) according to claim 1, wherein the light guide ( 52 ) on the windscreen ( 26 ) is attached. Sensor ( 10 ) according to claim 1, wherein the windscreen ( 26 ) itself acts as a light guide. Sensor ( 10 ) according to claim 3, wherein the windscreen ( 26 ) a hood ( 24 ) and the coupling of the optical signal in a center of the hood ( 24 ) he follows. Sensor ( 10 ) according to claim 3 or 4, wherein the evaluation unit ( 46 ) is designed for, based on the optical signal, a degree of contamination of the windscreen ( 26 ) to rate. Sensor ( 10 ) according to claim 5, wherein the evaluation includes an error rate of the transmission. Sensor ( 10 ) according to one of the preceding claims, wherein the first data transmission unit ( 42 ) and the second data transmission unit ( 44 ) are designed for wavelength division multiplexing. Sensor ( 10 ) according to one of the preceding claims, wherein the data transmission units ( 42 . 44 ) exchange optical signals with a different wavelength than that of the transmitted light beam ( 32 ).

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