Light sensor with evaluation of the light transit time

• US 6,100,539 A
• Filed: 01/20/1998
• Issued: 08/08/2000
• Est. Priority Date: 01/20/1997
• Status: Expired due to Term

• Current Assignee: Sick AG (Sick)
• Original Assignee: Sick AG (Sick)
• Inventors: Blumcke, Thomas, Breisacher, Hans-Joachim
• Primary Examiner(s): Le, Que T.
• Assistant Examiner(s): PYO, KEVIN K
• Application Number:
  US09/008,937
• Time in Patent Office: 931 Days
• Field of Search: 250/559.38, 250/559.29, 250/221, 356/5.01, 356/5.05, 356/5.07, 356/4.01, 356/4.07, 356/375, 359/154, 359/155, 359/161
• US Class Current: 250/559.38
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: G01S 17/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 17/87 Combinations of systems using electromagnetic waves other than radio waves

Abstract

The invention relates to a light sensor comprising a light transmitter for transmitting a light signal (T_x, T_xd) into a region to be monitored, a light receiver for receiving a reflected light signal (R_x) from an object present in the monitored region, at least one signal generator for producing a first signal (T_x) to energize the light transmitter and also for producing a second signal (L₀) standing in a defined phase relationship to the first signal (T_x), but with a different signal shape in comparison to the first signal (T_x), and also a correlation stage for producing the correlation function (KKF) between the received light signal (R_x) and the second signal (L₀, L_0d) as well as an evaluation stage following the correlation stage for determining information related to the distance between the light sensor and the object.

Claims

1. A light sensor comprising a light transmitter for transmitting a light signal (T_x, T_xd) into a region to be monitored;

a light receiver for receiving a reflected light signal (R_x) from an object present in the monitored region, at least one signal generator for producing a first signal (T_x) to energize the light transmitter and also for producing a second signal (L₀) standing in a defined phase relationship to the first signal (T_x), but with a different signal shape in comparison to the first signal (T_x), and also a correlator for producing a correlation function (KKF) between the reflected light signal (R_x) and the second signal (L₀) as well as an evaluation unit following the correlator for determining information related to the distance between the light sensor and the object.

2. A light sensor in accordance with claim 1, wherein the first signal (T_x) and the second signal (L₀) have the same period length T (L₀, T_x).

3. A light sensor in accordance with claim 1, wherein the correlation function (KKF) has an amplitude step in the range of one period, which is larger and/or steeper than all further amplitude steps which occur during one period.

4. A light sensor in accordance with claim 1, wherein both signals (T_x, L₀) each have only two amplitude steps different from one another.

5. A light sensor in accordance with claim 4, wherein both signals (T_x, L₀) are built up of sequential individual signals, each of the same length (T_CLK), with the individual signals each having the first or the second amplitude step.

6. A light sensor in accordance with claim 4, wherein both amplitude steps of the second signal (L₀) are arranged symmetrically about zero.

7. A light sensor in accordance with claim 4, wherein the correlation function (KKF) has an amplitude step in the range of one period which is larger and/or steeper than all further amplitude steps which occur during one period and the amplitude step is so steep that its extent timewise lies approximately in the range of the length (T_CLK) of an individual signal or below.

8. A light sensor in accordance with claim 3, wherein the values of the correlation function (KKF) before the amplitude step lie above or below an upper or lower threshold (S₀, S_u) respectively, and lie below or above a lower or upper respective threshold (S_u,S₀) after the amplitude step.

9. A light sensor in accordance with claim 1, wherein the signal shapes to the two signals (T_x, L₀) are found by computer-aided search and subsequent analysis of the respective correlation function (KKF) is performed.

10. A light sensor in accordance with claim 1, wherein the values of the correlation function (KKF) fluctuate about the amplitude value zero and/or wherein the correlation function (KKF) has no DC component.

11. A light sensor in accordance with claim 3, wherein the correlation function (KKF) has an amplitude step in the range of one period, which is larger and/or steeper than all further amplitude steps which occur during one period and the time position of the amplitude step can be shifted by an adjustment process which can be effected by the user of the light sensor within one period of the correlation function (KKF), whereby the light sensor can be matched to different sensing distances.

12. A light sensor in accordance with claim 1, wherein two signals (T_x, L₀) arranged without phase shift have values which differ from one another within one period, at least in a range of 50% of the period.

13. A light sensor in accordance with claim 1, wherein an adjustable delay element is inserted between the signal generator generating the first signal (T_x) and the light transmitter to produce a delayed signal (T_xd) which energizes the light transmitter.

14. A light sensor in accordance with claim 1, wherein an adjustable delay element is inserted between the signal generator generating the second signal (L₀) and the correlator to produce a delayed signal (L_0d).