Distance measurement system

• US 6,415,241 B1
• Filed: 09/21/1999
• Issued: 07/02/2002
• Est. Priority Date: 09/21/1998
• Status: Expired due to Fees

• Current Assignee: Fuji Photo Optical Co. Ltd (Fujifilm Holdings Corporation)
• Original Assignee: Fuji Photo Optical Co. Ltd (Fujifilm Holdings Corporation)
• Inventors: Yoshida, Hideo
• Primary Examiner(s): Bui, Bryan
• Application Number:
  US09/400,430
• Time in Patent Office: 1,015 Days
• Field of Search: 702/135, 702/149, 702/158, 702/159, 396/104, 396/106, 396/120, 396/123, 396/125, 356/3.04, 356/3.08, 356/4.01
• US Class Current: 702/159
• 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 7/4912 Receivers
• CPC Class Codes: G01S 7/493 Extracting wanted echo signals
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

In a distance measure system, an autofocus integrated circuit is furnished with a power source voltage and an integrating capacitor is preliminarily charged to a reference voltage V_REF. A temperature sensor detects ambient temperature. Thereafter, under the control of a CPU, an infrared emitting diode emits pulsed infrared light and the integrating capacitor discharges by a voltage level corresponding to a distance to an object to be measured. On the occasion of integration by an integrating unit of a signal output from an arithmetic unit, discharging of the integrating capacitor is performed multiple times, corresponding to the ambient temperature measured by a temperature sensor.

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 sensing detector for detecting the light pulses 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 outputting signals corresponding to the distance to the object in response to the signals output from said position sensing detector;

an integrating capacitor set to a reference voltage before emission of the series of light pulses, said capacitor being charged or discharged by signals output from said arithmetic unit;

a distance detection unit for detecting the distance to the object based on a voltage of said capacitor present after emission of the series of light pulses;

a temperature sensing unit for measuring ambient temperature; and

a control unit for controlling said distance measurement system to adjust charging and discharging operations of said capacitor by said arithmetic unit in response to the ambient temperature measured by said temperature sensing unit to offset a temperature dependency of the voltage of said capacitor present after emission of the series of light pulses.

2. The distance measurement system according to claim 1, wherein said control unit adjusts at least one of number and period of the charging and discharging operations of said capacitor by said arithmetic unit.

3. The distance measurement system according to claim 2, wherein said control unit adjusts at least one of number of the charging and discharging operations of said capacitor, relative to a reference number, by said arithmetic unit.

4. The distance measurement system according to claim 2, wherein said control unit adjusts the period of the charging and discharging operations of said capacitor to be shorter than a reference period in response to a change in ambient temperature relative to a reference temperature.

5. The distance measurement system according to claim 1, wherein said control unit adjusts the signals output from said arithmetic unit in response to the ambient temperature measured by said temperature sensing unit to adjust the charging and discharging operations of said capacitor.

6. 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 sensing detector for detecting the light pulses reflected from the object and outputting signals, each signal corresponding to a light pulse and a position on the position sensing detector where a light pulse reflected from the object is detected;

an integrating capacitor set to a reference voltage before emission of the series of light pulses, said capacitor being charged or discharged in a first integration by signals output from said position sensing detector and respectively corresponding to the light pulses;

a distance detection unit detecting the distance to the object by discharging or charging said capacitor at a constant rate to the reference voltage, after emission of the series of light pulses;

a temperature sensing unit for measuring ambient temperature before emission of the series of light pulses; and

a control unit receiving the ambient temperature measured and controlling said distance measurement system by changing at least one of the number of the light pulses emitted in the series of light pulses, duration of the light pulses emitted in the series of light pulses, and the constant rate of discharging or charging of said capacitor, after emission of the series of light pulses, in response to the ambient temperature measured.