Distance measuring apparatus

• US 6,819,407 B2
• Filed: 02/05/2003
• Issued: 11/16/2004
• Est. Priority Date: 02/08/2002
• Status: Expired due to Fees

• Current Assignee: Omron Corporation
• Original Assignee: Omron Corporation
• Inventors: Ishio, Wataru, Arita, Satoru
• Primary Examiner(s): Gregory, Bernarr E.
• Assistant Examiner(s): ANDREA, BRIAN K
• Application Number:
  US10/361,801
• Publication Number:
  US 20030218919A1
• Time in Patent Office: 650 Days
• Field of Search: 356/4-1-, 356/141.1, 180/167-169
• US Class Current: 356/4.01
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 7/4873 by deriving and controlling a threshold value
• CPC Class Codes: G01S 7/489 Gain of receiver varied automatically during pulse-recurrence period

Abstract

A distance measuring apparatus includes components for transmitting electromagnetic waves such as laser light to scan a detection area, and receiving reflected waves. The detection area is partitioned into standard areas of a fixed width and signals corresponding to waves received from different standard areas are stored separately. Mutually adjacent standard areas are combined to form a single combined area, if the corresponding signals each fail to exceed a specified threshold value, and these signals are cumulatively added. Conditions of a target object, such as its presence and its position, may be judged on the basis of combined areas thus created such that the detection can be made with increased sensitivity although the resolving power is adversely affected. An upper limit may be introduced for the number of standard areas over which cumulative addition of signals may be made. The threshold value may be made variable according to an average of signal values to be used for detection judgment or the noise component, or time-dependent so as to decrease as the delay time until the reflected waves are received increases.

Claims

1. A distant measuring apparatus comprising:

light-transmitting means for transmitting electromagnetic waves to scan in a specified scan direction a specified detection area which is partitioned into a plurality of standard areas of a fixed width;

light-receiving means for receiving reflection of said electromagnetic waves transmitted from said light-transmitting means and reflected by a target object in said detection area;

memory means for storing signals from said light-receiving means individually corresponding to said standard areas;

area-combining means for carrying out cumulative addition of the signals stored in said memory means corresponding to a set of those of said standard areas which are mutually adjacent in said scan direction to obtain a combined signal associated with a single combined area consisting of said set of standard areas if the signals corresponding to said set of standard areas do not exceed a threshold value, those of said standard areas, the signals from which are not cumulatively added, being each defined as a different one of combined areas and the signals therefrom being each defined as a different combined signal associated therewith; and

judging means for judging presence and position of a target object from the combined signals from the combined areas obtained by said area-combining means.

2. The distance measuring apparatus of claim 1 wherein, if neither added result over a set of mutually adjacent ones of standard areas nor the signal from the next one of the standard areas after said set of standard areas in said scan direction exceeds said threshold value, said area-combining means repeats the cumulative addition including the signal from the next standard area and includes the next standard area in the single combined area corresponding to said set of standard areas, thereby sequentially increasing the number of standard areas combined in said single combined area.

3. The distance measuring apparatus of claim 2 wherein, if said cumulative addition has been repeated and the number of standard areas combined in said cumulative addition has reached a specified upper limit number but if the combined signal does not exceed said threshold value, said area-combining means defines said upper limit number of combined standard areas as one combined area.

4. The distance measuring apparatus of claim 1 wherein said judgment means invalidates judgment result corresponding to a combined area if the size of said target object in said scan direction estimated from the width of said combined area is considered abnormally large according to a specified criterion and concludes that there is no target object for detection in said combined area although the signal corresponding to said combined area exceeds said threshold value.

5. The distance measuring apparatus of claim 1 wherein said judgment means validates judgment result thereby corresponding to a combined area in a situation where the signal corresponding to said combined area exceeds said threshold value, the size of said target object in said scan direction estimated from the width of said combined area is considered abnormally large according to a specified criterion, if time rate change of the size of said target object estimated by said judgment means remains smaller than a specified maximum value over a specified length of time, said judgment means invalidating judgment result thereby if otherwise.

6. The distance measuring apparatus of claim 1 wherein said judgment means validates judgment result thereby corresponding to a combined area in a situation where the signal corresponding to said combined area exceeds said threshold value, the size of said target object in said scan direction estimated from the width of said combined area is considered abnormally large according to a specified criterion, if time rate change of the position of said target object estimated by said judgment means remains smaller than a specified maximum value over a specified length of time, said judgment means invalidating judgment result thereby if otherwise.

7. The distance measuring apparatus of claim 1 wherein said threshold value is set according to a time average of those of said signals on which said judging means judges said target object.

8. The distance measuring apparatus of claim 1 wherein said threshold value is set according to those of said signals received while said electromagnetic waves are not being transmitted.

9. The distance measuring apparatus of claim 1 wherein said threshold value is set to be time-dependent, decreasing as the delay time increases until said electromagnetic waves are received by said light-receiving means.