Optical sensor for detecting articles in a monitored region and method for operating the same

• US 5,250,801 A
• Filed: 07/02/1992
• Issued: 10/05/1993
• Est. Priority Date: 10/02/1990
• Status: Expired due to Fees

• Current Assignee: Erwin SICK GmbH Optik-Elektronik
• Original Assignee: Erwin SICK GmbH Optik-Elektronik
• Inventors: Kuhn, Fritz, Krickl, Herbert, Kappeler, Ottmar, Grozinger, Roland
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): SHAMI, KHALED
• Application Number:
  US07/867,239
• Time in Patent Office: 460 Days
• Field of Search: 250/222.1, 250/223 R, 250/223 B, 250/214 B, 340/555, 340/556, 340/557
• US Class Current: 250/223.00B
• CPC Class Codes: G01S 17/04 Systems determining the presence of a target
• CPC Class Codes: H03K 17/941 using an optical detector H03K17/968 takes precedence

Abstract

An optical sensor device for detecting reflecting objects (11) has a light pulse emitter (12) and a light receiver (13) connected to an evaluation circuit (14) having a pulse generator (17) and a reception signal processing stage (24) which only emits an object detection signal when the light pulses or light pulse sequences received by the light receiver (13) lie above a switching threshold. The evaluation circuit (14) has a pulse emission influencing and triggering stage (15) connected in parallel to the reception signal processing stage (24) which triggers the emission of the following light pulse by the pulse generator (17) only when a detected variable disturbing signal has disappeared.

Claims

1. Method for the operation of an optical sensor arrangement for the detection of articles present in a monitored region with a pulsed light transmitter which transmits light pulses with a time spacing one after the other into the monitored region and with a light receiver which in the absence of articles to be detected receives substantially no light from the light receiver, but which on the presence of an article to be detected in the monitored region receives so much light from the light transmitter by reflection or transmission that a received signal processing stage connected to the light receiver transmits an article detection signal, characterised in that after transmitting a transmitted light pulse the received signal processing stage (24) is switched off and the output signal of the light receiver (13) is investigated, at least in the end region of the subsequent pause until the next transmitted pulse (45), as to whether a varying disturbing signal is present;

and in that on finding a varying disturbing signal the transmission of the next transmitted pulse is shifted timewise by an amount such that on transmitting the next transmitted pulse the disturbing signal has sunk at least with a certain probability below the response threshold of the received signal processing circuit (24).

2. Method in accordance with claim 1, characterised in that the result of a transmitted light pulse is temporarily stored and an article detection signals is only then triggered when an article was recognised and at the same time no variable disturbing signal was determined not only prior to but also after transmission of the transmitted light pulse.

3. Method in accordance with claim 2, characterised in that the durations of the time intervals investigated for the presence of a variable disturbing signal prior to and after transmission of the transmitted light pulse are of the same size.

4. Method in accordance with claim 1, characterised in that a specific transmitted pulse is only then transmitted a predetermined time after the preceding transmitted pulses when no disturbing signal is present shortly before the intended time of transmission;

and in that in the presence of such a disturbing signal the transmission of the transmitted pulse is shifted by a predetermined time which preferably corresponds to the fixed time interval present between two transmitted pulses in the disturbance-free case; and

in that the transmission of the transmitted pulse after even this time only then takes place when a disturbing signal has not been found shortly before it, etc.

5. Method in accordance with claim 1, characterised in that a transmitted pulse is first transmitted when no disturbing signals were found in several time intervals which respectively correspond to the normal time interval between two transmitted pulses shortly before the expiry of these times.

6. Method in accordance with claim 1, characterised in that on detecting a disturbance with periodic character during the disturbed light receiving periods between the transmitted light pulses the transmission of the light pulses is effected such that it takes place in the center region of the disturbance-free periods.

7. Method in accordance with claim 1, characterised in that the change of the disturbing signal is determined with respect to its amount and direction in that the changing disturbing signal is preferably investigated with respect to two different thresholds (29, 30;

53;

     56), or by means of a differentiation element (35), with the transmission of a transmitted pulse only then taking place when the disturbing signal reduces, with that value of the disturbing signal preferably being extrapolated where the disturbing signal should reduce to zero, and with the transmission of the transmitted pulse first taking place after this value.

8. Method in accordance with claim 1, characterised in that the received signal of the light receiver is time-averaged over a long time after a transmitted pulse and in that the next transmitted pulse is only triggered when after a predetermined time since the last transmitted pulse this signal falls beneath a predetermined value.

9. Method in accordance with claim 1, characterised in that the response threshold for the detection of a disturbing signal lies substantially lower than the response threshold of the received signal processing stage (24).

10. Optical sensor arrangement for detecting articles present in a monitored region comprising a pulsed light transmitter which transmits light pulses having a time spacing one after the other into the monitored region, and a light receiver which is so arranged relative to the light transmitter and the monitored region that in the absence of articles to be detected in the monitored region it receives at least substantially no light from the light receiver, but on the presence of an article to be detected in the monitored region receives so much light from the light transmitter through reflection or transmission that a received signal processing stage connected to the light receiver transmits an article detection signal, characterised in that a disturbance detection stage (16;

46) is also connected or connectable to the light receiver (13) and causes, on detecting reception of a variable disturbing signal, a subsequent transmitted pulse influencing or trigger stage (15) to trigger the transmission of the next transmitted pulse by the pulse generator (17) activated by the transmitted pulse influencing or trigger stage (15) only after the actual or probable end of the varying disturbing signal, and in that a controlled change-over switch (25) is inserted in the path between the light receiver (13) and the received signal processing stage (24) and is so switched, that it connects the light receiver (13) with the received signal processing stage (24) only on the transmission of a transmitted pulse by the pulse transducer (17) but in contrast, in the pause between two transmitted pulses connects the light receiver (13) at least shortly before the triggering of the next transmitted pulse, preferably however during the entire time interval between the sending of two sequential transmitted pulses, to the disturbance detection stage (16;

     46) or to the transmitted pulse influencing or trigger stage (15).

11. Optical sensor arrangement in accordance with claim 10, characterised in that a clock generator (23) with a frequency of a higher order of magnitude than the normal light pulse frequency digitises the received signal;

in that the individual received pulses formed in this way are investigated in the transmitted pulse influencing or trigger stage (15) for the presence or absence of a disturbance; and

in that the triggering of a transmitted pulse in the pulse transducer (17) is caused via the transmitted pulse influencing or trigger stage (15) when no disturbance has been found with a predetermined number of preferably sequential received pulses.

12. Optical sensor arrangement in accordance with claim 11, characterised in that the transmitted pulse influencing or trigger stage includes a pulse step down stage (42) connected to the clock generator (23) which first triggers a transmitted pulse only after a plurality of in particular 50 to 100 clock pulses;

and in that on the occurrence of only one disturbed received pulse the disturbance detection stage (16,

     46) prevents the initiation of a transmitted pulse through the pulse step down stage (42), or through the transmitted pulse influencing or trigger stage (15), until the predetermined number of undisturbed received pulses has been found.

13. Optical sensor arrangement in accordance with claim 11, characterised in that the clock generator (23) clocks a digital integrator (16) connected to the transmitted pulse influencing or trigger stage (15) representing the disturbance detection stage, with the clocked received signal which is evaluated in accordance with disturbance or non-disturbance being connected to the digital integrator and with the latter causing the transmitted pulse influencing or trigger stage (15) to initiate a transmitted pulse in the pulse transducer (17) only on the presence of a specific number of disturbance-free received pulses, with the digital integrator (16) in particular being reset to zero after the occurrence of only a single disturbed received pulse and with a transmitted pulse only then being triggered when the digital integrator (16) has counted a predetermined number (N) of undisturbed received pulses.

14. Optical sensor arrangement in accordance with claim 13, characterised in that the output signal of a likewise clocked comparator (48) with a fixed threshold (69) to which the received pulses are supplied is connected to the resetting input (I) of the digital integrator (16).

15. Optical sensor arrangement in accordance with claim 10, characterised in that the output signal of a preferably clocked comparator (48), to which a two stage threshold signal (58) is supplied from the disturbance detection stage (46), is applied to the disturbance detection stage (46) and switches to and fro between two threshold values (57, 62) when the disturbed signal only falls short of the upper threshold (53) and switches to the lower threshold value (62) when the signal also does not reach the lower threshold (56);

and in that the transmitted pulse (45) is only triggered thereafter, and indeed preferably that much later the longer the disturbing signal adopts a value between the two thresholds (53,

     56).

16. Optical sensor arrangement in accordance with claim 10, characterised in that the transmitted pulse trigger stage (15) has, following an amplifier (34) fed by the light receiver (13), two comparators (27, 28) with different thresholds (29, 30) and connected in parallel, wherein, when the received signal forms short of the upper threshold (30) an internal signal increase is triggered in a subsequent threshold time circuit (31) with an attached comparator (33) and wherein, on also falling short of the lower threshold (29), an external signal output to the comparator (33) is effected which continuously reduces from the achieved signal increase value, and in particular decreases linearly, and in that a transmitted pulse is triggered only when the external signal of the threshold timing circuit (31) falls short of the threshold (32) of the comparator (33).

17. Optical sensor arrangement in accordance with claim 10, characterised in that it has, following an amplifier (34) which is fed by the light receiver (13), a first comparator (36) with a first threshold (39) and connected in parallel with a differentiating circuit (35), the outputs of which are supplied to the two inputs of a sample and hold circuit (37) which follows a voltage current converter (61) with a subsequent charging element, in particular a capacitor (38), which, on achieving a predetermined voltage, causes, via a comparator (59) with a threshold (40), the transmission in the transmitted pulse influencing or trigger stage (15) of a transmitted pulse trigger signal to the pulse generator (17).

18. Optical sensor arrangement in accordance with claim 10, characterised in that the transmitted pulse influencing and trigger stage (15) is acted on by a mean value forming stage (41), for example in the form of a low pass filter, provided following an amplifier (34) fed by the light receiver (13), with the mean value forming stage triggering a transmitted pulse in the pulse generator (17) via the transmitted pulse influencing or trigger stage (15) when, after a specific time since the last transmitted pulse, the mean value falls below a predetermined threshold (43).

19. Optical sensor arrangement in accordance with claim 10, characterised in that a missing pulse detection stage (54) is provided which triggers an alarm device (55) in the absence of a transmitted pulse within a predetermined time interval after the transmission of the last transmitted pulse.