Distance measuring method and distance measuring system

Patent metadata

Field	Value
Publication number	US-9778361-B2
Application number	US-201514789184-A
Country	US
Kind code	B2
Filing date	Jul 1, 2015
Priority date	Jan 31, 2013
Publication date	Oct 3, 2017
Grant date	Oct 3, 2017

Abstract

In a TOF distance measurement employing light, the accuracy of distance measurement is improved without a significant increase in cost. A light source emits light to an object during an emission period. A sensor converts received reflected light (delay time τ) into an electrical signal during a plurality of signal accumulation periods, and accommodates the electrical signal. The signal accumulation period is set so that an accumulated signal amount varies depending on a distance to the object. The emission intensity of the light source is changed during the emission period so that the accumulated signal amount and the distance to the object has a nonlinear relationship.

First claim

What is claimed is:

1. In a time-of-flight (TOF) distance measuring system including a light source for emitting light, a sensor for operating in synchronization with the light source to convert received reflected light into an electrical signal and accumulate the electrical signal, and a calculation device, a method for measuring a distance to an object comprising:
emitting light to the object during a predetermined emission period using the light source;
accumulating signal amounts during a plurality of signal accumulation periods different from each other in at least one of a start time and an end time in the sensor; and
calculating the distance to the object based on the signal amounts accumulated in the plurality of signal accumulation periods using the calculation device,
wherein
a first signal accumulation period that is at least one of the plurality of signal accumulation periods is set so that a first accumulated signal amount that is a signal amount accumulated during the first signal accumulation period varies depending on the distance to the object,
emission intensity of the light source during the emission period is changed so that the first accumulated signal amount and the distance to the object have a nonlinear relationship within a distance measurement range, and
the emission intensity of the light source is higher during an initial portion of the emission period than during the other portion of the emission period so that the proportion of a change in the distance to the object to a change in the first accumulated signal amount is smaller in the vicinity of an upper limit of the distance measurement range than in the other portion of the distance measurement range.

2. The method of claim 1 , wherein the first signal accumulation period is set so that the first accumulated signal amount is maximized when the object is located in the vicinity of the upper limit of the distance measurement range.

3. In a time-of-flight (TOF) distance measuring system including a light source for emitting light, a sensor for operating in synchronization with the light source to convert received reflected light into an electrical signal and accumulate the electrical signal, and a calculation device, a method for measuring a distance to an object comprising:
emitting light to the object during a predetermined emission period using the light source;
accumulating signal amounts during a plurality of signal accumulation periods different from each other in at least one of a start time and an end time in the sensor; and
calculating the distance to the object based on the signal amounts accumulated in the plurality of signal accumulation periods using the calculation device,
wherein
a first signal accumulation period that is at least one of the plurality of signal accumulation periods is set so that a first accumulated signal amount that is a signal amount accumulated during the first signal accumulation period varies depending on the distance to the object,
emission intensity of the light source during the emission period is changed so that the first accumulated signal amount and the distance to the object have a nonlinear relationship within a distance measurement range, and
the emission intensity of the light source is higher during an end portion of the emission period than during the other portion of the emission period so that the proportion of a change in the distance to the object to a change in the first accumulated signal amount is smaller in the vicinity of a lower limit of the distance measurement range than in the other portion of the distance measurement range.

4. The method of claim 3 , wherein the first signal accumulation period is set so that the first accumulated signal amount is maximized when the object is located in the vicinity of the lower limit of the distance measurement range.

5. The method of claim 1 , wherein the emission intensity of the light source is higher during a middle portion of the emission period than during the other portion of the emission period so that the proportion of a change in the distance to the object to a change in the first accumulated signal amount is smaller in the vicinity of a middle of the distance measurement range than in the other portion of the distance measurement range.

6. The method of claim 5 , wherein the first signal accumulation period is set so that the first accumulated signal amount is maximized when the object is located in the vicinity of the middle of the distance measurement range.

7. The method of claim 1 , wherein
the distance measuring system has a camera, or the sensor has a camera function, and
the calculation device specifies a main object to be measured, based on an image captured by the camera or the sensor.

8. In a time-of-flight (TOF) distance measuring system including a light source for emitting light, a sensor for operating in synchronization with the light source to convert received reflected light into an electrical signal and accumulate the electrical signal, and a calculation device, a method for measuring a distance to an object comprising:
emitting light to the object during a predetermined emission period using the light source;
accumulating signal amounts during a plurality of signal accumulation periods different from each other in at least one of a start time and an end time in the sensor; and
calculating the distance to the object based on the signal amounts accumulated in the plurality of signal accumulation periods using the calculation device,
wherein
a first signal accumulation period that is at least one of the plurality of signal accumulation periods is set so that a first accumulated signal amount that is a signal amount accumulated during the first signal accumulation period varies depending on the distance to the object,
emission intensity of the light source during the emission period is changed so that the first accumulated signal amount and the distance to the object have a nonlinear relationship within a distance measurement range, and
a portion of the emission period during which the emission intensity of the light source is higher than during the other portion of the emission period, is adjusted, depending on a predetermined distance within the distance measurement range, so that the proportion of a change in the distance to the object to a change in the first accumulated signal amount is smaller at the predetermined distance within the distance measurement range than in the other portion of the distance measurement range.

9. The method of claim 8 , wherein the first signal accumulation period is adjusted, depending on the predetermined distance, so that the first accumulated signal amount is maximized when the object is located at the predetermined distance within the distance measurement range.

10. The method of claim 8 , wherein
a first distance to the object is calculated by performing first distance measurement where the predetermined distance is set as an initial value,
a portion of the emission period during which the emission intensity of the light source is higher than during the other portion of the emission period, is adjusted, depending on the first distance, so that the proportion of a change in the distance to the object to a change in the first accumulated signal amount is smaller at the calculated first distance than in the other portion of the distance measurement range, and
a second distance to the object is obtained by performing second distance measurement using the adjusted emission intensity.

11. The method of claim 10 , wherein the first signal accumulation period is adjusted, depending on the first distance, before the second distance measurement i

Assignees

• Panasonic Ip Man Co Ltd

Inventors

• Tsukamoto Akira
• Shiraki Hirokazu

Classifications

• G01S7/4863

  Detector arrays, e.g. charge-transfer gates · CPC title

• G01S7/4865

  Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak (peak detection in noise, signal conditioning G01S7/487) · CPC title

• G01S7/4868

  Controlling received signal intensity or exposure of sensor · CPC title

• G01S7/484

  Transmitters · CPC title

• G01S17/10 Primary

  using transmission of interrupted, pulse-modulated waves (determination of distance by phase measurements G01S17/32) · CPC title