Distance measurement system

• US 6,323,940 B1
• Filed: 09/24/1999
• Issued: 11/27/2001
• Est. Priority Date: 09/29/1998
• Status: Expired due to Fees

• Current Assignee: Fujinon Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fuji Photo Optical Co. Ltd (Fujifilm Holdings Corporation)
• Inventors: Yoshida, Hideo
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US09/405,174
• Time in Patent Office: 795 Days
• Field of Search: 396/106, 396/120, 356/3-4-
• US Class Current: 356/3.04
• CPC Class Codes: G01C 3/08 Use of electric radiation detectors
• CPC Class Codes: G01S 17/46 Indirect determination of position data
• 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

In a distance measuring system in a camera including an integrating unit having an integrating capacitor, if the period of a second integration exceeds a maximum period, a CPU stops the second integration. Furthermore, the CPU informs a photographer that the distance measurement has not performed successfully by issuing an alarm, urging the photographer to take proper action. As the CPU determines the distance to the object to be measured based on the maximum period of the second integration, error in the distance measurement may be minimized.

Claims

1. An active distance measurement system comprising:

a light source for emitting a series of light pulses toward an object at a distance to be measured;

a position sensitive detector for detecting light pulses emitted by said light source and reflected from the object and outputting signals, each signal corresponding to a position where a light pulse reflected from the object is detected;

an arithmetic unit for outputting signals, each signal corresponding to the distance to the object, in response to the signals output from said position sensitive detector;

an integrating unit including an integrating capacitor, and a comparator comparing a voltage on said capacitor with a reference voltage and outputting a compared signal representing a result of comparing, said integrating unit performing a first integration during which said integrating capacitor is discharged or charged in response to the signals output from said arithmetic unit, and a second integration during which said integrating capacitor is charged or discharged at a fixed speed, until the earlier of (i) the voltage on said integrating capacitor reaching a reference voltage and (ii) elapsing of a maximum time period; and

a distance detecting unit for detecting a measured distance to the object based on elapsed time of the second integration only when the elapsed time of the second integration does not exceed the maximum time period.

2. The distance measurement system according to claim 1, wherein said distance detection unit issues an alarm signal when the elapsed time of the second integration exceeds the maximum time period.

3. The distance measurement system according to claim 1, wherein when the elapsed time of the second integration exceeds the maximum time period, said distance detection unit detects, as the distance to the object, a distance based on the maximum time period.

4. The distance measurement system according to claim 1, wherein if the elapsed time of the second integration is shorter than a minimum time period, said distance detection unit detects, as the distance to the object, a distance based on the minimum time period.

5. The distance measurement system according to claim 1, said integrating unit further including a charging or discharging unit setting said integrating capacitor to the reference voltage before performing a succeeding first integration, when said distance detection unit has detected that the elapsed time period of the second integration immediately preceding the succeeding first integration has reached the maximum time period.

6. The distance measurement system according to claim 4, wherein said distance detection unit issues an alarm signal when the second integration is shorter than the minimum time period.