DE10238075A1 - Optical sensor for recording objects uses receptor line arrays to measure distance from two light sources with selection of highest signal for processing - Google Patents

Abstract

An optical sensor (1) recording objects (2) in a monitored area has two CMOS (Complementary Metal Oxide Silicon) or CCD (Charge Coupled Device) receptor line arrays (6, 6) measuring the distance from the light sources (5, 5) on an integrated chip by two modulated elliptical (4, 4) with a processor (8) to detect objects above a set threshold and give analogue distance, speed, counter or digital switch signal outputs (12).

Description

Optical sensor

The invention relates to an optical Sensor.

Such optical sensors are used for the detection of objects in a surveillance area. Are these optical sensors are preferably designed as distance sensors, by means of which the distances of an object in the surveillance area are determined can be.

From the DE 19850 270 A1 a distance sensor working according to the triangulation principle is known. This distance sensor has at least one transmitter light beam emitted and a receiver receiving receiver view beam connected to an evaluation unit, which is designed as a CCD line with a plurality of linearly arranged photosensitive elements. The received signals generated by an object O to the receiver at the outputs of the photosensitive elements are evaluated with regard to their signal amplitude, the photosensitive element E _{max is} determined, which delivers the maximum signal amplitude S _max . On both sides of this photosensitive element E _max , a predetermined number of further photosensitive elements up to a lower and an upper limit value E _U , E _{O are used} for determining the distance of the object O, in which the area of the section of the course of the signal amplitude along the CCD line between the lower one and upper limit element E _U , E _O and above a threshold value S _{mi n} derived from the signal amplitude of the lower and / or upper limit element E _U , E _{O is} calculated. The distance is determined by the position of the centroid within the interval delimited by E _U and E _O.

With this optical sensor you can Distances of objects are extremely precise be determined.

However, the distance measurement is in undesirable Whose dependent from the surface structures of objects. Due to inhomogeneities the object surface, especially due to high contrast differences such as edges at light-dark transitions adversely affects the triangulation measurement, because the location and shape of the mapped on the receiving elements of the recipient Light spots from this surface texture of the Object dependent is.

The invention is based on the object an optical sensor of the type mentioned with an extended functionality a high detection sensitivity and high immunity to interference.

To solve this task are the Features of claim 1 provided. Advantageous embodiments and appropriate further training the invention are described in the subclaims.

The optical sensor according to the invention is used for Detection of objects in a surveillance area and has two transmitting light beams emitting at a distance Sender and two receiver lines on. One recipient line each is one of the transmitters to carry out assigned to a distance measurement. In an evaluation unit, the output signals of the receiver lines generates an object detection signal.

Each sender and the recipient line assigned to it form a distance sensor element. With these distance sensor elements can two distance values are determined simultaneously. This will make one extended functionality of the optical according to the invention Sensor opposite usual receive optical sensors with a distance sensor element.

The functionality of the optical sensor can through suitable links the output signals of both receiver lines further increased become. For example, by evaluating the course over time the output signals of both receiver lines the speed and the direction of movement of an object in the surveillance area be recorded.

Is particularly advantageous in the evaluation unit of an amplitude evaluation of the output signals the recipient lines, for this purpose the output signals in particular with suitable threshold values be rated.

Using the threshold values, in particular binary Switch signals are generated, which as object detection signals can be output on the optical sensor.

By comparing the amplitudes of the output signals of the two receiver sides can inhomogeneities object surface and in particular contrast fluctuations are detected on the object surface become.

This information can in turn be used to eliminate interference factors in the distance measurement. For example, by comparing the output signals of the receiver lines, it can be determined whether the amplitudes or output signals of one receiver line are increased or reduced compared to the other. Typically, the amplitudes of the output signals are reduced by interference such as inhomogeneities on the object surface. In order to minimize the interference, only the receiver line for distance measurement is preferably used, which delivers the output signals with the higher amplitude values. With such evaluation methods, in particular special so-called black and white errors can also be eliminated. These are falsifications of the distance measurement, which are caused by the light spot of the transmitted light rays of a transmitter hitting a contrast edge. As a result, part of the light spot becomes strong, the other part of the light spot weakly reflects back to the receiver line, as a result of which a displacement of the light spot imaged on the receiver line with respect to detection of a homogeneous surface is obtained. This shift in turn leads to an error in the distance measurement.

The principle is to reduce Interference also an averaging of the output signals of both receiver lines is conceivable.

In an advantageous embodiment According to the invention, the optical sensor for edge detection, i.e. can be used to detect contrast edges of an object. Here too, an amplitude evaluation of the output signals of the receiver line performed. There is an edge when the amplitudes, preferably the maximum amplitude of a receiver line are significantly larger than the amplitudes of the output signals of the other receiver line.

This evaluation method can also for object counting especially for counting scales in superimposed sheets of paper be used in printing presses or the like.

With such scale counts the edge of a sheet of paper, which is on a underlying second sheet of paper. The capture of a such scaling is due to a distance measurement the small thickness of the sheets of paper often not possible. However, the scaling provides a contrast difference in the form of a Contrast edge that can be detected with the optical sensor according to the invention is. Will the sheets of paper moved under the optical sensor, so the individual scaling in optical sensor can be recorded and counted one after the other.

The two transmitters of the optical according to the invention Sensors are preferred from two leaser diodes integrated on one chip educated. An advantage of this arrangement is that the chip is a has a small size, so that the laser diodes integrated on it are extremely small Distance from each other. It can be used with the optical sensor Distance measurements at two closely spaced measuring points be carried out.

The receiver lines of the optical sensor can in principle be formed by two discrete CMOS lines or CCD lines.

In a particularly advantageous embodiment The receiver lines are part of the invention one flat CMOS or CCD arrays. The evaluation unit prefers this the contents of two individual lines of this array running in parallel read out, these lines forming the recipient lines.

A major advantage of this arrangement is in that the location of the recipient lines relative to each other alone the selection of the rows of the array can be specified in the evaluation unit is and therefore requires no adjustment. In addition, the CMOS or CCD array simply related of the chip can be aligned with the two laser diodes.

The invention is as follows explained using the drawings. Show it:

1 : Block diagram of an embodiment of the optical sensor according to the invention.

2 : First example of a transmitter-receiver arrangement according to the optical sensor 1 ,

3 : Second example of a transmitter-receiver arrangement according to the optical sensor 1 ,

4 : First example of output signals of the receiver lines of the optical sensor according to 1 ,

5 : Second example of output signals of the receiver lines of the optical sensor according to 1 ,

1 shows the basic structure of the optical sensor according to the invention 1 for the detection of objects 2 in a surveillance area.

The optical sensor 1 is in one case 3 integrated and has two transmitted light beams 4 . 4 ' emitting transmitter 5 . 5 ' on, which is preferably each formed by a laser diode. In addition, the optical sensor 1 two recipient lines 6 . 6 ' on, each transmitter 5 . 5 ' a recipient line 6 . 6 ' is assigned so that from that transmitter 5 . 5 ' emitted, and on an object 2 reflected transmitted light rays 4 . 4 ' as received light rays 7 . 7 ' on the associated recipient line 6 . 6 ' are led. Each recipient line 6 . 6 ' consists of a linear arrangement of receiving elements, which are preferably designed as CCD or CMOS elements. The longitudinal axes of the recipient lines 6 . 6 ' preferably run parallel to one another at a distance.

Any transmitter 5 . 5 ' and the recipient line assigned to it 6 . 6 ' form a distance sensor element that works according to the triangulation principle. As a result, every transmitter lies 5 . 5 ' at a predefined basic distance from the assigned recipient line 6 . 6 ' , the transmitter 5 . 5 ' each lies at least approximately on a straight line through which the longitudinal axis of the receiver line 6 . 6 ' runs.

To carry out the distance measurement, one of the receiver lines 6 . 6 ' connected evaluation unit 8th the position of the light spots of the received light beams 7 . 7 ' on the recipient lines 6 . 6 ' evaluated. The evaluation unit 8th is preferably formed by a signal processor. Furthermore, the transmitters are also 5 . 5 ' to the evaluation unit 8th connected. The evaluation unit 8th thus controls the operation of the transmitters 5 . 5 ' , The transmit light beams are used to suppress the influence of extraneous light 4 . 4 ' the transmitter 5 . 5 ' modulated with a predetermined modulation frequency. Alternatively, the transmitter 5 . 5 ' are operated in pulse mode, so that they each transmit light beams 4 . 4 ' emit in the form of sequences of transmitted light pulses.

How out 1 the transmission light rays are visible 4 . 4 ' and received light beams 7 . 7 ' through a window 9 led in the front wall.

Furthermore, the transmitters 5 . 5 ' a collimation lens 10 downstream. With the collimation lens 10 become collimated light beams 4 . 4 ' generated on the surface of an object 2 be mapped. The surveillance area within whose objects 2 with the transmitted light beams 4 . 4 ' are detectable is essentially through the collimation lens 10 specified. It is essential here that with the transmitted light beams 4 . 4 ' two separate transmission light spots are generated within the monitoring area on an object surface.

The recipient lines 6 . 6 ' is a common receiver lens 11 upstream, by means of which the received light beams 7 . 7 ' to the respective recipient line 6 . 6 ' be mapped.

From the in the evaluation unit 8th determined distance values for the two distance sensor elements, an object detection signal is generated, which via a sensor output 12 can be spent. Via the sensor output 12 digital and / or analog object detection signals can be output. A multiple arrangement of sensor outputs is also possible.

2 shows a first example of a transmitter-receiver arrangement of the optical sensor 1 according to 1 , This has two discrete transmitters 5 . 5 ' on, which are arranged next to each other at a distance d. Furthermore, the arrangement according to 2 two discrete receiver lines 6 . 6 ' which are preferably formed by CCD or CMOS lines. The longitudinal axes of the recipient lines 6 . 6 ' run parallel to each other, with the recipient lines 6 . 6 ' are at a distance d 'from each other. The ratio of the distances d and d 'is essentially due to the design of the collimation lens 10 and the receiver optics predetermined and chosen so that the from a transmitter 5 . 5 ' emitted and as reception light beams 7 . 7 ' from the object 2 reflected transmitted light rays 4 . 4 ' to the assigned recipient line 6 . 6 ' of the respective distance sensor element are guided.

3 shows a second example of a transmitter-receiver arrangement of the optical sensor 1 according to 1 , In this case, the transmitters 5 . 5 ' formed by two laser diodes on a chip 13 are integrated. The transmitters 5 . 5 ' are again at a distance d from one another. In this case, they are assigned by the transmitters 5 . 5 ' emitted light beams 4 . 4 ' , as in 3 indicated an elliptical beam cross-section.

The large semiaxes of the ellipses of the beam cross sections of the transmitted light rays run 4 . 4 ' parallel to each other and in the direction of the longitudinal axes of the assigned receiver lines 6 . 6 '.

The recipient lines 6 . 6 ' are part of a flat receiver array in the present case 14 , in particular a CCD or CMOS array. Every recipient line 6 . 6 ' in this case is from one row of the receiver array 14 educated. These lines are about the evaluation unit 8th selectable. Only the contents of these lines are in the evaluation unit 8th read in to carry out the distance determinations. The selection of the rows of the receiver array 14 takes place in the evaluation unit 8th such that the recipient lines 6 . 6 ' again analogous to the embodiment according to 2 are at a distance d 'from each other. Because the recipient lines 6 . 6 ' of different rows of a receiver array 14 in this case there is no alignment of the recipient lines 6 . 6 ' ,

With the optical sensor according to the invention 1 two distance measurements are carried out at closely adjacent measuring points on the surface of an object 2 performed in the surveillance area.

In the simplest case, both Distance measurement values as object detection signal one after the other or in parallel over one or more sensor outputs output.

In a further advantageous embodiment, the evaluation unit takes place 8th , a link between the output signals of the two receiver lines 6 . 6 ' to derive a suitable object detection signal.

On the one hand, the determined distance values can be in the evaluation unit 8th be linked. This takes place particularly advantageously in the evaluation unit 8th an amplitude evaluation of the output signals of the receiver line 6 . 6 ' , for which purpose the output signals are evaluated with suitable threshold values. Then takes place in the evaluation unit 8th a connection of the amplitude profiles evaluated in this way on the individual receiver lines 6 . 6 ' ,

By linking the output signals of the receiver lines 6 . 6 ' For example, speed signals or generally motion detection signals can be generated as the object detection signal.

This is when an object penetrates 2 the time course of the output signals is registered in the monitoring area. In particular, it is registered for which distance sensor element a distance measurement value is registered first and in which subsequent time interval a distance measurement value is registered on the second distance sensor element.

By a suitable comparison of the amplitude profiles of the output signals of both receiver lines 6 . 6 ' interference can be compensated for the distance measurement. Such interferences can be caused, for example, by inhomogeneities in the object surface.

Such inhomogeneities can vary from local roughening of an otherwise smooth object surface his.

4 shows schematically the courses of the amplitudes of the output signals of both receiver lines 6 . 6 ' of the optical sensor 1 in the detection of such an object structure. The transmitted light beams 4 of the first transmitter 5 hit the area of the smooth object surface so that the received light rays reflected there 7 form a narrow bundle of rays and accordingly a small spot of light on the first line of the receiver 6 form. Accordingly, at the outputs of the first recipient line 6 those in the top diagrams of the 4 obtained amplitudes. The amplitude curve of the first receiver line 6 has a maximum with the amplitude U _max1 in the receiving _{element no} .

The transmitted light beams 4 ' of the second transmitter 5 ' meet the inhomogeneous, roughened area of the object surface. The received light rays reflected from it 7 ' are scattered accordingly, so that a significantly wider light spot on the second receiver line 6 ' is mapped. As a result, the second recipient line 6 ' receive a significantly broadened signal _peak , whose maximum value U _{max2 is} below the maximum value U _{max1 of} the signal _peak on the first receiver line 6 is. In addition, this is the position n _{0 of} the maximum of the signal peak on the first receiver line 6 postponed.

In the evaluation unit 8th the amplitudes of the output signals of both receiver lines are continuously compared 6 . 6 ' , If the comparison results in a signal curve impaired by interference, as is the case with the output signals of the second receiver line in the present exemplary embodiment 6 ' the case is, these results are discarded and only the output signals of the first receiver line 6 used to determine the distance and to generate the object detection signal.

5 shows a further example of an object detection with the optical sensor according to the invention 1 , In this case, an object surface with several surfaces of different reflectivity is detected. 5 shows the amplitude profiles of the output signals of the receiver lines 6 . 6 ' of the optical sensor 1 in the event that the transmitted light rays 4 of the first transmitter 5 hit a bright surface of the object surface, whereas the transmitted light rays 4 ' of the second transmitter 5 ' on a contrast edge, that is, the transition of this light area to a dark area. The output signals of the first receiver line accordingly 6 a signal _peak at n ₀ and with the maximum amplitude U _max1 . Because the transmitted light rays 4 ' of the second transmitter 5 ' meet the contrast edge, the part of the transmitted light rays hitting the bright surface 4 ' more reflected on the object surface than the part of the transmitted light rays 4 ' which hits the dark surface. Accordingly, there is a signal peak for the second receiver line 6 ' whose position n _{0 '} compared to the position of the signal n _{0 of} the first receiver line 6 is shifted and its maximum value U _{max2 is} smaller than the maximum value U _{max1 of} the signal _peak of the second receiver line 6 ' , This shift in the position of the light spot on the second receiver line 6 ' and the resulting distance measurement error is also referred to as a black and white error.

By continuously registering several successive measurements with both receiver lines 6 . 6 ' the single measurements with a black and white error can be eliminated.

The evaluation according to the embodiment according to 5 can also be modified such that with the optical sensor 1 the position of contrast edges on object surfaces is measured. The detection of an edge is in accordance with the exemplary embodiment 5 given when, for example, the transmitted light beams 4 of the first transmitter 5 completely onto a bright surface and the transmitted light beams 4 ' of the second transmitter 5 ' completely hit an adjacent dark surface. In this case, the recipient lines 6 . 6 ' each receive a signal peak whose maxima have the same position n ₀ . However, the signal peak points to the first receiver line 6 a higher maximum signal amplitude U _max1 than the maximum of the second receiver line 6 ' , The position of the contrast edge can be detected by evaluating the position and height of both signal peaks.

Finally, in the evaluation unit 8th also several contrast edges can be selected, so that via the sensor output 12 a corresponding count signal can be output.

(1)

optical sensor

(2)

object

(3)

casing

(4, 4 ')

Transmitted light beams

(5, 5 ')

Channel

(6, 6 ')

receiver line

(7, 7 ')

Receiving light rays

(8th)

evaluation

(9)

window

(10)

Collimating lens

(11)

Receiver Lens

(12)

sensor output

(13)

chip

(14)

receiver array

Claims (19)

Optical sensor for the detection of objects ( 2 ) in a surveillance area with two transmitting light beams arranged at a distance ( 4 . 4 ' ) emitting transmitters ( 5 . 5 ' ) and two recipient lines ( 6 . 6 ' ), with one recipient line ( 6 . 6 ' ) the transmitter ( 5 . 5 ' ) for carrying out a distance measurement, and with an evaluation unit ( 8th ) in which the output signals of the receiver lines ( 6 . 6 ' ) an object detection signal is generated. Optical sensor according to claim 1, characterized in that the transmitter ( 5 . 5 ' ) are arranged at a distance d from one another and that the receiver lines ( 6 . 6 ' ) are arranged with parallel longitudinal axes at a distance d ', so that the object ( 2 ) as received light beams ( 7 . 7 ' ) reflected light rays ( 4 . 4 ' ) the transmitter ( 5 . 5 ' ) to the assigned recipient line ( 6 . 6 ' ) are performed. Optical sensor according to one of claims 1 or 2, characterized in that the transmitter ( 5 . 5 ' ) of two on one chip ( 13 ) integrated laser diodes are formed. Optical sensor according to claim 3, characterized in that the of the transmitters ( 5 . 5 ' ) emitted light beams ( 4 . 4 ' ) each have an elliptical beam cross section, the large semiaxes of the ellipses running parallel to one another. Optical sensor according to one of claims 1-4, characterized in that the transmitters ( 5 . 5 ' ) to generate collimated transmission light beams ( 4 . 4 ' ) a collimation lens ( 10 ) is subordinate. Optical sensor according to one of claims 1-5, characterized in that the transmitter ( 5 . 5 ' ) transmission light beams modulated with a predetermined modulation frequency ( 4 . 4 ' ) emit. Optical sensor according to one of claims 1-5, characterized in that the transmitter ( 5 . 5 ' ) Emit transmitted light pulses. Optical sensor according to one of claims 1-7, characterized in that each receiver line ( 6 . 6 ' ) has a linear arrangement of CMOS or CCD elements. Optical sensor according to one of claims 1-8, characterized in that the receiver lines ( 6 . 6 ' ) Part of a flat receiver array ( 14 ), in particular CMOS or CCD arrays. Optical sensor according to claim 9, characterized in that the receiver array ( 14 ) the contents of individual lines in the evaluation unit ( 8th ) can be read out, whereby one line each represents a recipient line ( 6 . 6 ' ) forms. Optical sensor according to one of claims 1-10, characterized in that the receiver lines ( 6 . 6 ' ) a receiver lens ( 11 ) is upstream. Optical sensor according to one of claims 1 - 11, characterized in that for generating the object detection signals, the output signals of the receiver lines ( 6 . 6 ' ) can be linked. Optical sensor according to one of claims 1-11, characterized in that in the evaluation unit ( 8th ) the output signals of a receiver line ( 6 . 6 ' ) are used to generate the object detection signal, the selection of the respective receiver line ( 6 . 6 ' ) by comparing the output signals of both receiver lines ( 6 . 6 ' ) he follows. Optical sensor according to one of claims 1-13, characterized in that the amplitudes of the output signals of the receiver lines ( 6 . 6 ' ) in the evaluation unit ( 8th ) at least one threshold value each. Optical sensor according to one of claims 1-14, characterized in that the object detection signal via a to the evaluation unit ( 8th ) connected sensor output ( 12 ) can be output. Optical sensor according to claim 15, characterized in that as object detection signal analog distance values via the sensor output ( 12 ) can be output. Optical sensor according to claim 15, characterized in that as object detection signal analog speed signals via the sensor output ( 12 ) can be output. Optical sensor according to claim 15, characterized in that as the object detection signal counting signals via the sensor output ( 12 ) can be output. Optical sensor according to claim 15, characterized in that as the object detection signal digital switching signals via the sensor output ( 12 ) can be output.