Safety system for contactless measurement of paths and/or speeds

• US 7,995,192 B2
• Filed: 12/29/2008
• Issued: 08/09/2011
• Est. Priority Date: 01/28/2008
• Status: Active Grant

• Current Assignee: Sick AG (Sick)
• Original Assignee: Sick AG (Sick)
• Inventors: Wüstefeld, Martin
• Primary Examiner(s): NGUYEN, SANG H
• Application Number:
  US12/318,382
• Publication Number:
  US 20090190120A1
• Time in Patent Office: 953 Days
• Field of Search: 356 27- 28, 356/5.01, 250/206.1, 250/221, 250/206.2, 340/679, 340/680, 340/686.6, 340/552, 340/557
• US Class Current: 356/27
• CPC Class Codes: F16P 3/144 using light grids
• CPC Class Codes: G01D 3/08 with provision for safeguarding the apparatus, e.g. against abnormal operation, against breakdown
• CPC Class Codes: G01D 5/30 the beams of light being detected by photocells
• CPC Class Codes: G01P 21/02 of speedometers
• CPC Class Codes: G01P 3/68 using optical means, i.e. using infrared, visible, or ultraviolet light G01P3/80 takes precedence ; by reflection of waves G01S17/58
• CPC Class Codes: G01P 3/806 in devices of the type to be classified in G01P3/68
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 2207/30232 Surveillance
• CPC Class Codes: G06T 2207/30236 Traffic on road, railway or crossing
• CPC Class Codes: G06T 2207/30261 Obstacle
• CPC Class Codes: G06T 7/20 Analysis of motion motion estimation for coding, decoding, compressing or decompressing digital video signals H04N19/43, H04N19/51

Abstract

An optoelectronic safety sensor (10) is set forth for the contactless measurement of paths and/or speeds of the safety sensor (10) or of a first object connected in a fixed position to the safety sensor (10) with respect to a second object (12) moved relatively to the first object, which form a potential source of danger, wherein the safety sensor (10) has a light source (20), a light receiver (16) with a plurality of light reception elements and has an evaluation unit (22), with the evaluation unit (22) being configured to determine by means of an optical correlation process and/or by evaluation of the optical flow the path and/or the speed from at least two images of a surface structure (18, 18a, 18b) of the second object (12) taken sequentially by the light receiver (22). In this respect, the evaluation unit (22) is further configured to evaluate the quality of the determined path and/or of the determined speed, and a safety output (24) is provided via which the evaluation signal (22) can output a shutdown signal or brake signal to secure the danger source when a required quality is not reached.

Claims

1. An optoelectronic safety sensor for the contactless measurement of paths and/or speeds of the safety sensor or of a first object connected in a fixed position to the safety sensor with respect to a second object moved relative to the first object wherein the objects form a potential source of danger on movement, the optoelectric safety sensor comprising:

a light source;

a light receiver having a plurality of light reception elements;

an evaluation unit configured to determine at least one of a path and a speed of a surface structure with respect to a second object, using at least one of an optical correlation process and an evaluation of an optical flow from at least two images of the surface structure taken sequentially by the light receiver, wherein;

the evaluation unit is further configured to evaluate a quality of the at least one determined path and determined speed; and

the evaluation unit is operably connected to a safety output via which the evaluation unit is configured to output a shutdown signal or brake signal when an evaluated quality falls below a predetermined threshold.

2. A safety sensor in accordance with claim 1, wherein the evaluation unit is configured to check an image of the second object for whether a sufficient spatial change of intensity is present over the plurality of light reception elements.

3. A safety sensor in accordance with claim 2, wherein the evaluation unit is configured to calculate a reliability measure for sufficient structure which takes account of at least one of a number of extremes of intensity, an extent of the extremes, a scattering of spatial position, and a distribution of the extremes.

4. A safety sensor in accordance with claim 1, wherein the evaluation unit is configured to define a maximum time interval within which the quality or part criteria of the quality can be evaluated as insufficient without outputting a shutdown signal or a brake signal.

5. A safety sensor in accordance with claim 1, wherein:

an optical element is connected before the light receiver and is configured to impose a regular base structure on the image;

at least one of the evaluation unit and the light receiver is configured to generate the regular base structure virtually by changing the brightness signal of selected light reception elements; and

the evaluation unit is configured to take account at least one of the regular and the virtual base structure as a reference signal in an evaluation of a structure of the second object.

6. A safety sensor in accordance with claim 1, wherein the safety output is selected from the group consisting of two channels, at least one redundant evaluation unit, and a plurality of evaluation units.

7. A safety sensor in accordance with claim 6, wherein the safety output is configured to evaluate the quality of the at least one determined path and determined speed.

8. A safety sensor in accordance with claim 1, wherein the second object has an amplified optical structure of differently colored pigments and/or patterns.

9. A safety sensor in accordance with claim 1, wherein the evaluation unit is configured:

to calculate an absolute position of the safety sensor, of at least one of the first object and the second object from at least one of the path and speed of the at least one first and second object by means of a starting reference; and

to monitor at least one of the speed and absolute position of the at least one first object and second object; and

to output the shutdown or brake signal if at least one predetermined specific absolute position is reached or at least one predetermined specific speed is exceeded, or if at least one predetermined specific speed is exceeded at at least one predetermined specific absolute position.

10. A safety sensor in accordance with claim 1, wherein the safety sensor is stationary and the second object is part of a machine tool, a conveyor belt or a robot.

11. A safety sensor in accordance with claim 1, wherein the safety output acts on the danger source via a higher ranking connected safety control.

12. A safety sensor in accordance with claim 1, further comprising at least one of a second sensor of the same construction as the first sensor and a laser scanner.

13. A safety sensor in accordance with claim 1, wherein the safety sensor is mobile and the first object is a vehicle, an elevator or a robot and the second object is part of a floor, of a wall, of a work surface or of a rail.

14. A safety method for the optical contactless measurement of paths and/or speeds of a safety sensor or of a first object with respect to a second object moved relative to the first object wherein the objects form a potential source of danger on movement, the method comprising the steps of:

illuminating the second object by a light source;

imaging a surface structure of the second object on a light receiver having a plurality of light reception elements; and

determining at least one of a path and a speed of the first object using at least one of an optical correlation process and an evaluation of an optical flow;

evaluating a quality of the at least one determined path and determined speed; and

outputting a shutdown signal or brake signal via a safety output when an evaluated quality falls below a predetermined threshold.

15. A safety method in accordance with claim 14, wherein the image of the second object is checked for whether a sufficient spatial intensity change is present over the plurality of light receivers.

16. A safety method in accordance with claim 15, wherein a reliability measure is determined for sufficient structure which takes account of at least one of extremes of intensity, control of spatial position, and distribution of extremes.

17. A safety method in accordance with claim 14, further comprising the steps of:

imposing a regular base structure on the image by an optical grating connected before the light receiver;

virtually generating the regular base structure by changing a brightness signal of selected light reception elements; and

taking into account at least one of the virtually generated and the regular base structure as a reference signal in the evaluation of the structure of the second object.

18. A safety method in accordance with claim 14, wherein an absolute position of the at least one safety sensor, first object, and second object is determined on the basis of the at least one determined path and speed while taking account of at least one of a start position, an intermediate position, and a safe navigation of the first object and/or of the second object by means of two-fold determination of path and/or speed.