Optoelectronic sensor and method for the measurement of distances in accordance with light transit time principle

• US 8,625,080 B2
• Filed: 11/13/2009
• Issued: 01/07/2014
• Est. Priority Date: 11/21/2008
• Status: Active Grant

• Current Assignee: Sick AG (Sick)
• Original Assignee: Sick AG (Sick)
• Inventors: Heizmann, Reinhard, Hug, Gottfried, Marra, Martin, Torabi, Bahram
• Primary Examiner(s): RATCLIFFE, LUKE D
• Application Number:
  US12/591,257
• Publication Number:
  US 20100128248A1
• Time in Patent Office: 1,516 Days
• Field of Search: 356 301- 315, 356 401- 41, 356 501- 515, 356 6- 22, 356/28, 356/28.5
• US Class Current: 356/5.01
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 7/484 Transmitters
• CPC Class Codes: G01S 7/487 Extracting wanted echo signals , e.g. pulse detection
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

An optoelectronic sensor (10) for the measurement of distances in accordance with the light transit time principle is provided having a light transmitter (12) for the transmission of a light signal, having a light receiver (16) for the reception of a remitted or reflected received signal and having an evaluation unit (18) which is made to satisfy a transition condition for the received signal by systematic selection of a transmission delay time for the transmission of the light signal at an observation time and to calculate the light transit time from the transmission delay time required for this. In this respect, a regulator (44) is provided which is made to adjust the transmission delay time such that the transition condition is satisfied at the observation time.

Claims

1. An optoelectronic sensor for the measurement of distances in accordance with the light transit time principle, comprising:

a light transmitter configured to transmit a light signal;

a light receiver configured to receive at least one of a remitted and a reflected received signal;

an evaluation unit configured to satisfy a transition condition for the received signal by systematic selection of a transmission delay time for transmission of the light signal at an observation time and configured to calculate the light transit time from the transmission delay time; and

a regulator configured to adjust the transmission delay time such that the transition condition is satisfied at the observation time.

2. The sensor of claim 1, wherein the evaluation unit is further configured:

to trigger transmission of the light signal at a transmission time preset via the transmission delay time in a respective measurement period by the regulator;

to sample the received light signal; and

to accumulate a histogram of received light signals over a plurality of measurement periods to determine reception time from the histogram and the light transit time,

wherein a check of the transition condition for the received signal takes place in the histogram.

3. The sensor of claim 1, further comprising a filter element provided in a reception path between the light receiver and the evaluation unit, the filter element configured to convert a unipolar received signal into a bipolar signal,

wherein the transition condition includes a zero crossing from a first maximum to a first minimum of the bipolar signal.

4. The sensor of claim 1, wherein the regulator is further configured to:

check the transition condition within a first regulation time interval and adjust the transmission delay time to correspond to a partial measurement range of the sensor; and

to check periodically a time at which the received signal is received and, if the checked time is outside the first regulation time interval, to set a new regulation time interval for the regulator.

5. The sensor of claim 4, wherein the regulator is further configured to recognize the received signal with reference to an alternating change from maxima to minima and vice versa.

6. The sensor of claim 4, wherein the regulator is further configured to store a statistical history of any regulation time intervals which are set to a new regulation time interval on a periodic check.

7. The sensor of claim 4, further comprising an agent independent of the regulator and configured to locate a valid regulation time interval and to set the valid regulation time interval for the regulator as a time in which the received light signal is actually received.

8. The sensor of claim 1, wherein the evaluation unit is further configured to provide the regulator with at least one transmission delay time which corresponds to a multiple of a sampling period for the received light signal.

9. The sensor of claim 1, further comprising a time base unit configured to:

derive at least one transmission delay time from a first time signal with a first frequency (f1) and a second time signal with a second frequency (f2) different from the first frequency (f1); and

provide the at least one transmission delay time to the regulator with a time resolution given by a difference period belonging to the first and second frequencies (f1, f2).

10. The sensor of claim 9, further comprising

an adjustment unit configured for fine setting of the at least one transmission delay time by shifting transmission time within at least one of the plurality of measurement periods by an offset, and

wherein a plurality of offsets form a distribution whose center of mass forms a desired transmission time selectable with a time resolution better than a sampling period and the difference period.

11. The sensor of claim 10, further comprising an adjustment unit memory table which holds at least one offset distribution for a plurality of time increments,

wherein the at least one offset distribution is selected from the group consisting of a unimodal distribution, a triangular distribution, a parabolic distribution, and a Gaussian function distribution.

12. A method for measuring distances in accordance with the light transit time principle, comprising:

transmitting a light signal;

receiving at least one of a remitted and a reflected light signal;

satisfying a transition condition for the received signal by systematic selection of a transmission delay time for transmission of the light signal at an observation time;

adjusting the transmission delay time such that the transition period is satisfied at the observation time; and

calculating a light transit time from the transmission delay time.

13. The method of claim 12, further comprising the steps of:

checking the transition condition with a first regulation time interval;

adjusting the transmission delay time to correspond to a partial measurement range of the sensor;

periodically checking a time at which the received signal is received; and

setting a new regulation time interval if the checked time is outside the first regulation time interval.

14. The method of claim 12, further comprising the step of storing a statistical history of any regulation time intervals which are reset on a periodic check.

15. The method of claim 12, wherein the periodic check either constantly or at regular assigned time slots independent of the time regulation.

16. An optoelectronic sensor for the measurement of distances in accordance with the light transit time principle, comprising:

a light transmitter configured to transmit a light signal;

a light receiver configured to receive at least one of a remitted and a reflected received signal;

an evaluation unit configured to satisfy a transition condition for the received signal which fixes the reception time based on a characteristic by systematic selection of a transmission delay time for transmission of the light signal at an observation time and configured to calculate the light transit time from the transmission delay time; and

a regulator configured to adjust the transmission delay time such that the transition condition is satisfied at the observation time.

17. The sensor of claim 16, wherein the characteristic comprises at least one of a zero crossing, an extremum, and a point of inflection.