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

• US 20100128248A1
• Filed: 11/13/2009
• Published: 05/27/2010
• Est. Priority Date: 11/21/2008
• Status: Active Grant

• Current Assignee: Sick AG (Sick)
• Original Assignee: Sick AG (Sick)
• Inventors: Marra, Martin, Torabi, Bahram, Hug, Gottfried, Heizmann, Reinhard
• Granted Patent: US 8,625,080 B2
• Time in Patent Office: Days
• US Class Current: 356/5.10
• 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 (10) for the measurement of distances in accordance with the light transit time principle 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, wherein 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.

2. A sensor (10) in accordance with claim 1, wherein the evaluation unit (18) is made to trigger the transmission of a light signal at a transmission time preset via the transmission delay time in a respective measurement period (100) by the regulator (44) and to sample the received light signal and to accumulate a histogram (110) of such received light signals over a plurality of measurement periods (100) to determine the reception time from the histogram (110) and the light transit time from it, and wherein the check of the transition condition for the received signal takes place in the histogram (110).

3. A sensor (10) in accordance with claim 1, wherein a filter element (32) is provided in the reception path between the light receiver (16) and the evaluation unit (18) to convert the unipolar received signal into a bipolar signal, and wherein the transition condition in particular includes a zero crossing from the first maximum to the first minimum of the bipolar signal.

4. A sensor (10) in accordance with claim 1, wherein a regulation time interval (101) within which the regulator (44) can check the transition condition and can adjust the transmission delay corresponds only to a partial range of a measurement range of the sensor (10), and wherein a change of position monitoring unit (44) is provided to check periodically the time at which the received signal is received and, if this time is outside the regulation time interval (101), to set a new regulation time interval (101) for the regulator (44).

5. A sensor (10) in accordance with claim 4, wherein the change of position monitoring unit (44) is preferably made to recognize the received signal with reference to a signature, in particular to an alternating change from maxima to minima and vice versa which each form a falling envelope, in particular a logarithmic envelope.

6. A sensor (10) in accordance with claim 4, wherein change of position monitoring unit (44) is preferably made to store a history of which regulation time interval (101) it would in each case have preset for the regulator (44) at the periodical check to preset that regulation time interval (101) for the regulator (44) which is that of the received signal in accordance with a statistical evaluation of this history.

7. A sensor (10) in accordance with claim 4, wherein the change of position monitoring unit (44) has an agent, that is a process which is active constantly or in regular assigned time slots and which is independent of the regulator (44), wherein the agent has the aim of locating a valid regulation time interval (101) and of setting it for the regulator (44) in which the light signal is actually received.

8. A sensor (10) in accordance with claim 1, wherein the evaluation unit (18) is made to provide the regulator (44) with transmission time delays which correspond to a multiple of a sampling period for the received signal.

9. A sensor (10) in accordance with claim 1, wherein a time base unit (38) is provided which has a DDS or is made to derive transmission time delays 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 thus to provide transmission time delays to the regulator (44) with a time resolution given by the difference period belonging to the first and second frequencies (f1, f2).

10. A sensor (10) in accordance with claim 1;

wherein a unit (40) for the fine setting of a transmission time is provided which is made to shift the respective transmission time within the measurement periods (100) by an offset, and wherein the offsets form a distribution (56, 60) whose center of mass forms a desired transmission time and which can be selected with a time resolution which is better than both the sampling period and the difference period, in particular with a time resolution of fewer than ten picoseconds or even less than one picosecond.

11. A sensor (10) in accordance with claim 10, wherein the distribution (56, 60) of the offsets is unimodal, is in particular preset in accordance with a triangular, parabolic or Gaussian function, and wherein a memory is provided in which a table for the unit (40) for the fine setting of a transmission time is stored which holds an associated offset distribution for a plurality of time increments, in particular one respective offset distribution for evenly distributed time increments.

12. A method for the measurement of distances in accordance with the light transit time principle in which a light signal is transmitted and the remitted or reflected light signal is received, and in which a transition condition for the received signal is satisfied by systematic selection of a transmission delay time for the transmission of the light signal at an observation time and the light transit time is calculated from the transmission delay time required for this, wherein the transmission delay time is adjusted by means of a regulation (44) such that the transition period is satisfied at the observation time.

13. A method in accordance with claim 12, wherein a regulation time interval (101) within which the regulator (44) can check the transition condition and can adjust the transmission delay corresponds only to a partial range of a measurement range of the sensor (10), and wherein a check is made periodically of the time at which the received signal is received and, if this time is outside the regulation time interval (44), a new regulation time interval (101) is preset for the regulator (101).

14. A method in accordance with claim 12, wherein a history is saved of which regulation time interval (101) would be preset in each case on a periodic check of the regulation (44) to preset that regulation time interval (101) for the regulation (44) which is that of the received signal in accordance with a statistical evaluation of this history.

15. A method in accordance with claim 12, wherein the periodic check is carried out by an agent, that is by a process active constantly or at regular assigned time slots and independent of the regulation (44), wherein the agent has the goal of locating a regulation time interval (101) and of presetting it for the regulation (44) in which the light signal is received.