DE10308148A1 - Optoelectronic detector for monitoring presence of objects in monitored region has outputs from rectifiers fed to summer which forms sum or difference based on clock phase shifts for near and far signals - Google Patents

Abstract

The detector has a light pulse transmitter, and a receiver that outputs near signals and far signals, which are used to generate an object detection signal. The near signals and the far signals are fed to respective rectifiers (11,12), which are controlled by respective clock signals derived from the transmission clock of the light pulses. The rectified signals are fed to a summer (13) which forms the sum or difference based on the phase shift of the clock signals. The output from the summer is fed to an evaluation unit (9) which generates the object detection signal.

Description

The invention relates to an optoelectronic device according to the Preamble of claim 1.

Such an optoelectronic device is known from DE 199 74 487 A1 known. This has a transmitter emitting light rays, a Receiving light beams, emitting a near and far signal spatially resolving receiver and an evaluation unit in which the Quotient of the near and far signal is formed. The quotient is when the sum of the near and far signals is controlled at a constant value Difference formed between the near and far signal. The totalization of the Local and remote signals are carried out in an adder. The difference formation of the near and remote signal is done in a subtractor. The differences so formed are read directly into the evaluation unit. The sums are over a controller unit in which the regulation of the sum to the constant Setpoint is regulated, read into the evaluation unit.

Since the sum and difference formation in different electronic Components, the signal evaluation is due to the system Inaccuracies due to the signals generated in the adder and subtractor different fluctuations and drifts due to different Component tolerances and temperature dependencies of the components are subject.

The invention has for its object an optoelectronic device to provide the type mentioned above, by means of which at low constructive effort enables safe and reliable object detection becomes.

The features of claim 1 are provided to achieve this object. Advantageous embodiments and expedient developments of the Invention are described in the subclaims.

The optoelectronic device according to the invention is used to detect Objects in a surveillance area and assigns one in one predetermined transmission clock transmitter light pulse emitting transmitter, a Receiving light pulses receiving, near signals and remote signals emitting receiver and with an evaluation unit for generating an object detection signal depending on the near and far signals. The near signals and the Remote signals are each fed to a rectifier unit, both of which Rectifier units each with a clock signal derived from the transmit clock are controlled. The rectified and rectified in the rectifier units Remote signals are fed to a summing element, in which depending the phase shift of the clock signals the sum or the difference of the Hub signals and remote signals is formed. The sums and differences on The output of the summing element is used in the evaluation unit for generation the object detection signal read.

A major advantage of the optoelectronic according to the invention The device consists in that for generating the object detection signal required sums and differences of the near and far signals of the receiver can be generated in the same component. The influence of drifts and Fluctuations in the component thus affect the same Sum and differences of the near and far signals. So that becomes a generation of the. largely insensitive to third parties and fluctuations Object detection signal guaranteed.

By controlling the rectifier units with clock signals whose Phase differences between one another and relative to the transmission clock can be set, can the summing element in a simple manner both for summation can also be used to form the difference between local and remote signals.

To form the sums of the near and far signals, the Rectifier units driven with in-phase clock signals. Particularly advantageous both positive and negative sums of the clock signals are formed, in which the clock signals are in phase in the first case and in the second case be selected in phase opposition to the transmission clock.

By forming the difference between the positive and negative sums Generated sum signals, in which the effects of signal drifts and Fluctuations are largely eliminated. Likewise, with rectifier units driven in opposite phase clock signals positive and negative Differences in the near and far signals obtained, from which by Difference formation Differential signals are derived.

By alternately determining these sum and difference signals an interference-free signal evaluation guaranteed.

In the simplest case, the difference signals are used for object detection at least one threshold for generating a binary Object detection signal evaluated.

The sum signals to predetermined ones are particularly advantageous Setpoint ranges are regulated, causing an overload of the receiver, which leads to Signal corruption would be avoided.

In an advantageous variant, in addition to the difference signals the sum signals are also evaluated with at least one threshold value which further increases the detection reliability of the optoelectronic device is increased.

The invention is explained below with reference to the drawings. It demonstrate:

Fig. 1 block diagram of an embodiment of the optoelectronic device for detecting objects in a monitoring area.

FIG. 2 shows timing diagrams for signal evaluation during object detection by means of the optoelectronic device according to FIG. 1.

Fig. 3 First exemplary embodiment of a control of the received signal level of the optoelectronic device of FIG. 1.

Fig. 4 shows a schematic representation of the characteristic of the received signal level as a function of light incident on the light intensity for the receiver of FIG. 3 conducted scheme.

Fig. 5 second embodiment of a control of the received signal level of the optoelectronic device of FIG. 1.

Fig. 1 shows the structure of an optoelectronic device 1 for detecting objects in a surveillance area 2. The optoelectronic device 1 is integrated in a housing 3 and has a transmitter 5 emitting light pulse 4 and a position-resolving receiver 7 receiving light pulse 6 .

The emitted from the transmitter S transmitted light pulses 4 and reflected back from an object 2 in the direction of the receiver 7 receiving light pulses 6 are guided by a front plate 8 in the housing wall.

In the present case, the transmitter 5 is formed by a laser diode. The spatially resolving receiver 7 arranged at a distance from the transmitter 5 is formed by a PSD element or a double photodiode. As can be seen from FIG. 1, the spatially resolving receiver 7 has two outputs for outputting two received signals. A local signal I _{A is} output as the first received signal via the first output. A remote signal I _{B is} output as the second received signal via the second output.

Depending on the distance of the object 2 to the optoelectronic device 1 , the received light pulses 6 are reflected back in different steel angles from the object 2 to the receiver 7 , so that the point of incidence of the received light pulses 6 on the light-sensitive surface of the receiver 7 varies accordingly. Depending on the position of the light spots of the received light pulses 6 on the receiver 7 , the ratio of the amplitudes of the near and far signals also varies. With small object distances, the amplitudes of the near signals are considerably larger than the amplitudes of the remote signals. The greater the object distance, the greater the amplitudes of the fine signals in relation to the amplitudes of the near signals. The ratio of the near and far signals thus provides a measure of the object distance.

The optoelectronic device 1 has an evaluation unit 9 , which serves on the one hand to control the transmitter 5 . Furthermore, the reception signals for generating a binary object detection signal are evaluated in the evaluation unit 9 , the switching states of the object detection signal indicating whether or not an object 2 is within a predetermined zone of the monitoring area. The object detection signal is output via a switching output 10 connected to the evaluation unit 9 .

The evaluation unit 9 , which is formed by a microprocessor or the like, has a clock oscillator (not shown), by means of which a transmission clock is generated to control the transmitter 5 . The duty cycle of the transmit clock is typically in the range 0.2 to 0.6 and is preferably 0.5. According to the transmission clock specified by the evaluation unit 9, the transmitter 5 emits transmission light pulses 4 with a specified pulse-pause ratio.

The local and remote signals present at the outputs of the receiver 7 are each fed to a rectifier unit 11 , 12 , which is in each case formed by a synchronous rectifier. The local and remote signals rectifying in the rectifier units 11 , 12 are fed to a summing element 13 , to the output of which a low-pass filter 14 is connected. The output signals of the low pass 14 are read into the evaluation unit 9 via an analog-digital converter (not shown).

The rectifier units 11 , 12 are driven with clock signals T _A , T _B , which are generated in a switching logic 15 . The switching logic 15 consists, for example, of two exclusive OR gates. In order to generate the clock signal T _A for the rectifier unit 11 for rectifying the near signals I _A , a first control signal M _{A is} output to the switching logic 15 in the evaluation unit 9 . Accordingly, in order to generate the clock signal T _B for the rectifier unit 12 for rectifying the remote signals I _B in the evaluation unit 9, a second control signal M _{B is} output to the switching logic 15 .

The clock signals T _A , T _B are derived from the transmission clock and have the same pulse frequency as the transmission clock. The phase differences between the clock signals and between the clock signals and the transmit clock can be set by the control signals.

The time course of the signal evaluation in the optoelectronic device 1 is shown schematically in FIG. 2. The time profiles of the binary control signals M _A, M _B are shown in Fig. 2, which has two switching states "low" and "high" have uni through which the phase differences of the clock signals relative to the transmit clock, which is also shown in Fig. 2, be specified. Furthermore, the time course of the output signal U _a at the output of the low pass 14 is shown in FIG. 2, which is obtained as a function of the control signals M _A , M _B.

As can be seen from FIG. 2, in the time interval T ₁ between t0 and t1, the control signal M _A assumes a "low" switching state, as a result of which the clock signal T _{A has} a phase difference of 0 ° with respect to the transmission clock. Likewise, the control signal M _B assumes a switching state "low" in the time interval T _{1, as} a result of which the clock signal T _{B has} a phase difference of 0 ° with respect to the transmission clock.

Thus, in-phase clock signals T _A and T _B are obtained within the time interval T ₁ , which are also in phase with the transmission clock. Through this in-phase control of the rectifier units 11 , 12 , which is effected with the clock signals T _A and T _B , the positive sum of the rectified local and remote signals is formed in the summing element 13 . The duration of the time interval T ₁ between t0 and t1 is, like the other time intervals shown in FIG. 2, of the same length of time between t1 and t2 (T ₂ ), t2 and t3 (T ₃ ), and t3 and t4 (T ₄ ) selected so that that they are greater than the settling time of the output signal U _a at the output of the low pass 14 . The duration of a time interval T ₁ , T ₂ , T ₃ or T ₄ is typically in the range between 100 μs and 2 ms and is preferably 1 ms. Thus, the maximum value of U _a at the end of the interval T ₁ provides the positive sum of the near and far signals.

In the time interval T ₂ between t1 and t2, the control signal M _A assumes a "high" switching state, as a result of which the clock signal T _{A has} a phase difference of 180 ° with respect to the transmission clock. Likewise, the control signal M _B assumes a "high" switching state, as a result of which the clock signal T _{B has} a phase difference of 180 ° with respect to the transmission clock.

Thus, in-phase clock signals T _A and T _B are obtained within the time interval T ₂ , but both are 180 ° out of phase with the transmission clock. By activating the rectifier units 11 , 12 in phase with the clock signals T _A , T _B , the negative sum of the rectified local and remote signals is formed in the summing element 13, which sum from the extreme value of U _a at the end of T ₂ after the output signal U has settled _{a of} the low pass 14 is formed.

The differences are formed in the evaluation unit 9 from the positive and negative sums, whereby the sum signal U _s shown in FIG. 2 is obtained.

During the time intervals T ₃ and T ₄ , the control signals M _A and M _{B are of} opposite phase. In the time interval T ₃ , the control signal M _A assumes the switching state "low", so that the clock signals T _A and the transmission clock are in phase. In contrast, the switching signal M _B assumes the "high" switching state, so that the clock signals T _B are out of phase with the clock signal T _A and also with the transmission clock by 1800.

By controlling the rectifier units 11 , 12 with the clock signals T _A , T _B in phase opposition, positive differences of the near and far signals are formed in the summing element 13 . The steady-state output signal U _a at the end of the time interval T ₃ provides the end value for the positive difference.

During the time interval T ₄ , the switching states of the control signals M _A , M _B are inverted with respect to the switching states in the time interval T ₃ . Accordingly, the clock signals T _B are now in phase with the transmission clock and the clock signals T _A are 180 ° out of phase for this purpose.

Thus, the phase-shifted control of the rectifier units 11 , 12 in the time interval T _{4 forms} negative differences in the near and far signals.

Analogous to the generation of the sum signals U _s , difference signals U _{d are} formed in the evaluation unit 9 by forming the difference between the positive and negative differences of the near and far signals as shown in FIG. 2.

The binary object detection signal is then generated in the evaluation unit 9 from the difference signals U _d and possibly from the sum signals U _s by means of a threshold value evaluation.

In the simplest case, only the difference signals U _d , which provide a measure of the distance of an object 2 from the optoelectronic device, are evaluated with two threshold values that define a threshold value hysteresis. The switching states of the binary object detection signal generated thereby indicate whether an object 2 is located within a zone of the monitoring area that is limited by a scanning distance. The optoelectronic device 1 is preferably designed as a light scanner with so-called background suppression. The binary object detection signal assumes the "object detected" switching state if the measured object distance is smaller than the cycle width defined by the threshold values. With larger object distances, the object detection signal assumes the switching state "free beam path".

To increase the reliability of detection, the sum signal U _s can also be evaluated with two threshold values forming a threshold value hysteresis. As an additional requirement for object detection, it is then required that the amplitude of the sum signal lies above the higher of the two threshold values.

In an advantageous embodiment of the invention, the level of the sum signal U _{s is} regulated to a predetermined desired value or desired value range in order to avoid, in particular, overdriving of the receiver 7 when the light intensities are too high.

Fig. 3 shows a first embodiment of such a control. Here, in Fig. 3, the time courses of the transmit clock and the clock signals T _A, T _B with an in-phase control of the rectifier units 11, 12.

The time signal waveforms of the transmit clock and the clock signals T _A , T _B according to FIG. 3 correspond to the signal relationships in the time interval T ₁ in FIG. 2.

To regulate the sum voltage U _s to a predetermined setpoint U _s, the clock signals T _A , T _B are shifted by a time interval d _t with respect to the transmission clock. The larger the time interval dt is selected, the more the level of U _{s is} reduced.

The result of such a regulation is shown schematically in FIG. 4. The amplitude profile of the sum signal U _{s is shown there} as a function of the received light intensity I incident on the receiver 7 . A determination of U _s and thus object detection is not possible below a predetermined minimum intensity I _min . Up to an intensity I ₀ , the value for U _{s is} still below the target value U _s , so that the regulation of U _s does not yet begin in its range between I _min and I ₀ . In this unregulated area, the value for U _s increases in proportion to the received light intensity. At the value I ₀ , the sum signal U _{s reaches} the target value U _{s, soll} . By the control according to FIG. 3 for values I ≥ I ₀ U, the sum signal _s to the desired value U _{s intended regulated.}

FIG. 5 schematically shows a second embodiment for regulating the sum signal U _s to a predetermined target value U _{s, soll} . The upper diagram shows the time course of the output signal U _{a of} the low pass 14 during a first measurement cycle of the control process. The lower diagram shows the course of U _a during a subsequent measuring cycle. Here, in Fig. 5, the waveform _of V corresponding to FIG. 2 for the time intervals T _1, T _2, T ₃ and T ₄ for the different controls of the rectifier units 11, 12 with equal or opposite-phase clock signals T _A, T _B ,

In the uncontrolled operation of the optoelectronic device 1 for received light intensities I <I ₀ according to FIG. 4, the regulation of the sum signal U _s does not yet start. In this case, the signal is evaluated in accordance with FIG. 2. Accordingly, the rectifier units 11 , 12 are driven with the clock signals T _A , T _{B of} different phases within the identical time intervals T ₁ , T ₂ , T ₃ and T ₄ as shown in FIG. 2 ,

As soon as the sum signals U _{s reach} the target value U _{s, soll} , the control system starts as illustrated in FIG. 4.

In the control operation shown in FIG. 5 for the control of the sum signal, the lengths of the time intervals T _1, T ₂ are appropriately changed, whereby the lengths of the time intervals T _3, T _4, in which the difference signals determined constant at their initial values become.

The basic principle of the control according to FIG. 5 is to shorten the time intervals T ₁ and T ₂ in order to limit the sum signal U _s to a predetermined desired value U _s . For this purpose, the time constant of the low-pass filter 14 is reduced to such an extent that the output signals U _a can no longer settle to their maximum values in these time intervals. The upper diagram shows the signal curve of U _a in a given measuring cycle without control. During the control, the level of U _{a is} compared within the time interval T ₁ with a predetermined threshold value S1. If the level of U _a exceeds the threshold S1, as is the case for U ₁ in the upper diagram in FIG. 5, the time interval T ₁ is shortened in the next measuring cycle of the control process so that the output signal U _{a then} during the shortened time interval T. ₁ no longer settles and is therefore safely below the threshold value S1. This case is shown in the lower diagram of FIG. 5. The amount of the reduction in T ₁ is preferably calculated from the extent to which the threshold value S1 has been exceeded by the level U _a , ie by the difference U ₁ - S ₁ . T ₁ is preferably reduced in several substeps until the maximum level of U _{a is} below S1 within the reduced time interval. The length of the time interval T ₂ is preferably calculated from the current length of T ₁ . It has proven expedient to choose the length of T ₂ greater than the length of T ₁ . The length of T ₂ is particularly preferably approximately twice the width of T ₁ . REFERENCE SIGN LIST ( 1 ) Optoelectronic device
( 2 ) object
( 3 ) housing
( 4 ) transmitted light pulses
( 5 ) transmitter
( 6 ) received light pulses
( 7 ) Receiver
( 8 ) windscreen
( 9 ) Evaluation unit
( 10 ) switching output
( 11 ) Rectifier unit.
( 12 ) Rectifier unit
( 13 ) summer
( 14 ) low pass
( 15 ) switching logic

Claims (20)

1. Optoelectronic device for detecting objects in a surveillance area with a transmitter emitting light pulse in a predetermined transmission clock, a receiver receiving light pulse, emitting near signals and remote signals and with an evaluation unit for generating an object detection signal as a function of the near and far signals, characterized in that the local signals and the remote signals are each fed to a rectifier unit ( 11 , 12 ), the two rectifier units ( 11 , 12 ) each being controlled by a clock signal derived from the transmission clock, that the local and remote signals rectified in the rectifier units ( 11 , 12 ) , A summing element ( 13 ) is supplied, in which the sum or difference of the near signals and remote signals is formed as a function of the phase shift of the clock signals, and that the sums and differences at the output of the summing element ( 13 ) are included in the evaluations Unit ( 9 ) for generating the object detection signal can be read. 2. Optoelectronic device according to claim 1, characterized in that a clock oscillator for specifying the transmit clock of the transmitter ( 5 ) is integrated in the evaluation unit ( 9 ). 3. Optoelectronic device according to one of claims 1 or 2, characterized in that a switching logic ( 15 ) is provided for generating the clock signals. 4. Optoelectronic device according to claim 3, characterized in that the switching logic ( 15 ) is formed by two exclusive OR gates. 5. Optoelectronic device according to one of claims 3 or 4, characterized in that in each case a control signal is generated by the evaluation unit ( 9 ) for specifying the phase relationships between the clock signals, the control signals being supplied to the switching logic ( 15 ). 6. Optoelectronic device according to claim 5 characterized in that the phase shifts between the Clock signals and the transmit clock are predetermined. 7. Optoelectronic device according to one of claims 1-6, characterized in that the rectifier units ( 11 , 12 ) are each formed by a synchronous rectifier. 8. Optoelectronic device according to one of claims 1-7, characterized in that a low-pass filter ( 14 ) is connected to the output of the summing element ( 13 ), the output signals of which are read into the evaluation unit ( 9 ) via an analog / digital converter. 9. Optoelectronic device according to claim 8, characterized in that in order to form sums of the near and far signals, in-phase clock signals are supplied to the rectifier units ( 11 , 12 ). 10. Optoelectronic device according to claim 9, characterized in that in order to form positive sums of the near and far signals, in-phase clock signals with a phase shift of 0 ° with respect to the transmission clock are supplied to the rectifier units ( 11 , 12 ). 11. Optoelectronic device according to one of claims 9 or 10, characterized in that in order to form negative sums of the near and far signals, in-phase clock signals with a phase shift of 180 ° with respect to the transmission clock are supplied to the rectifier units ( 11 , 12 ). 12. Optoelectronic device according to claim 11, characterized in that sum signals U _{s are} formed in the evaluation unit ( 9 ) by forming the difference between successive positive and negative sums of the near and far signals. 13. Optoelectronic device according to one of claims 8-12, characterized in that the rectifier units ( 11 , 12 ) are supplied to form differences in the near and far signals offset by 180 °, out-of-phase clock signals. 14. Optoelectronic device according to claim 13, characterized in that in order to form positive differences between the local and remote signals, the rectifier unit ( 11 ), to which the local signals are supplied, is driven with clock signals which are in phase with the transmission clock. 15. Optoelectronic device according to one of claims 13 or 14, characterized in that the rectifier unit ( 12 ), to which the remote signals are fed, is driven with clock signals which are in phase with the transmission clock, in order to form negative differences between the near and far signals. 16. Optoelectronic device according to claim 15, characterized in that in the evaluation unit ( 9 ). Difference formation of successive positive and negative differences of the near and far signals, difference signals U _{D are} formed. 17. Optoelectronic device according to claim 16, characterized in that in order to generate the object detection signal, the difference signals U _{D are} evaluated in the evaluation unit ( 9 ) with at least one threshold value. 18. Optoelectronic device according to one of claims 16 or 17, characterized in that to generate the object detection signal, the sum signals U _{s are} evaluated in the evaluation unit ( 9 ) with at least one threshold value. 19. Optoelectronic device according to one of claims 16 or 17, characterized in that the sum signals U _s are regulated to predetermined target values, in which the clock signals are delayed by a time interval dt compared to the transmission clock. 20. Optoelectronic device according to claim 16 or 17, characterized in that the sum signals U _s are regulated to predetermined target values, in which the time intervals T ₁ , T ₂ , within which the rectifier units 11 , 12 are supplied with in-phase clock signals, to limit the rule the sum of the near and far signals are reduced in duration.