U.S. patent application number 09/725880 was filed with the patent office on 2001-05-31 for distance measuring apparatus.
Invention is credited to Miwa, Yasuhiro.
Application Number | 20010002148 09/725880 |
Document ID | / |
Family ID | 18337746 |
Filed Date | 2001-05-31 |
United States Patent
Application |
20010002148 |
Kind Code |
A1 |
Miwa, Yasuhiro |
May 31, 2001 |
Distance measuring apparatus
Abstract
A distance measuring apparatus is constructed to project light
toward an object to be measured, receive reflected light thereof at
a position according to the distance to the object to output a
position signal, generate a distance computation value based on the
position signal, integrate the distance computation value with an
integrating capacitor, detect the distance, based on distance data
corresponding to the integral result, charge the integrating
capacitor by letting a constant current flow for a predetermined
time, and calculate a voltage of the integrating capacitor. In the
distance measuring apparatus, the distance to the object is
detected, based on a correction voltage being the voltage
calculated in a ranging routine, a reference voltage of the
integrating capacitor preliminarily calculated before the ranging
routine, and the distance data. Then the apparatus can reduce a
ranging error due to change in the capacitance of the integrating
capacitor.
Inventors: |
Miwa, Yasuhiro; (Saitama,
JP) |
Correspondence
Address: |
LEYDIG VOIT & MAYER, LTD
700 THIRTEENTH ST. NW
SUITE 300
WASHINGTON
DC
20005-3960
US
|
Family ID: |
18337746 |
Appl. No.: |
09/725880 |
Filed: |
November 30, 2000 |
Current U.S.
Class: |
356/3.04 ;
396/106 |
Current CPC
Class: |
G01C 3/085 20130101 |
Class at
Publication: |
356/3.04 ;
396/106 |
International
Class: |
G01C 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 1999 |
JP |
1999-340517 |
Claims
What is claimed is:
1. A distance measuring apparatus comprising: light projecting
means for projecting a beam toward an object to be measured; light
receiving means for receiving reflected light of said beam
projected toward said object, at a reception position according to
a distance to said object and outputting a position signal
according to the reception position; computing means for performing
a predetermined operation based on said position signal from said
light receiving means to generate a distance computation value
according to the distance to said object; integrating means
comprising an integrating capacitor, said integrating means
charging or discharging said integrating capacitor according to
said distance computation value generated by said computing means
to integrate said distance computation value; detecting means for
detecting the distance to said object, based on distance data
corresponding to the result of integral in said integrating means;
charging means for charging said integrating capacitor by letting a
constant current flow for a predetermined time; and voltage
calculating means for calculating a voltage of said integrating
capacitor charged by said charging means, wherein said detecting
means detects the distance to said object, based on a correction
voltage being said voltage calculated by said voltage calculating
means in a ranging routine, a reference voltage of said integrating
capacitor preliminarily calculated before the ranging routine, and
said distance data.
2. The distance measuring apparatus according to claim 1, wherein
said detecting means detects the distance to said object, based on
corrected distance data Ra determined by the following equation:
Ra(.alpha.1/.beta.1).times.D (where D is said distance data,
.alpha.1 said reference voltage, and .beta.1 said correction
voltage).
3. The distance measuring apparatus according to claim 1, wherein
said detecting means detects the distance to said object, based on
corrected distance data Rb determined by the following equation:
Rb=[.alpha.1/{(.beta.1-.alpha.1).times.A+.alpha.1}].times.D+(.beta.1-.alp-
ha.1).times.B (where D is said distance data, .alpha.1 said
reference voltage, .beta.1 said correction voltage, and A and B
correction coefficients).
4. The distance measuring apparatus according to claim 1, wherein
when a difference between said correction voltage and said
reference voltage is smaller than a predetermined value, said
detecting means detects the distance to said object, based on
corrected distance data Ra determined by the following equation:
Ra=(.alpha.1/.beta.1).times.D (where D is said distance data,
.alpha.1 said reference voltage, and .beta.1 said correction
voltage), and wherein when the difference between said correction
voltage and said reference voltage is not less than the
predetermined value, said detecting means detects the distance to
said object, based on corrected distance data Rb determined by the
following equation:
Rb=[.alpha.1/{(.beta.1-.alpha.1).times.A+.alpha.1}].times.D+(.b-
eta.1-.alpha.1).times.B (where D is said distance data, .alpha.1
said reference voltage, .beta.1 said correction voltage, and A and
B correction coefficients).
5. The distance measuring apparatus according to claim 1, wherein
said voltage calculating means calculates said correction voltage
before ranging.
6. The distance measuring apparatus according to claim 1, wherein
said voltage calculating means calculates said correction voltage
after ranging.
7. The distance measuring apparatus according to claim 1, wherein
said voltage calculating means calculates the voltage of said
integrating capacitor before and after ranging, and wherein said
detecting means determines an average of said voltage before
ranging and said voltage after ranging and detects the distance to
said object, using the average as said correction voltage.
8. A distance measuring apparatus comprising: light projecting
means for projecting a beam toward an object to be measured; light
receiving means for receiving reflected light of said beam
projected toward said object, at a reception position according to
a distance to said object and outputting a position signal
according to the reception position; computing means for performing
a predetermined operation based on said position signal outputted
from said light receiving means to generate a distance computation
value according to the distance to said object; integrating means
comprising an integrating capacitor, said integrating means
charging or discharging said integrating capacitor according to
said distance computation value generated by said computing means
to integrate said distance computation value; detecting means for
detecting the distance to said object, based on distance data
corresponding to the result of integral in said integrating means;
charging means for charging said integrating capacitor by letting a
constant current flow for a predetermined time; and capacitance
calculating means for calculating a capacitance of said integrating
capacitor charged by said charging means, wherein said detecting
means detects the distance to said object, based on a correction
capacitance being said capacitance calculated by said capacitance
calculating means in a ranging routine, a reference capacitance of
said integrating capacitor preliminarily calculated before the
ranging routine, and said distance data.
9. The distance measuring apparatus according to claim 8, wherein
said detecting means detects the distance to said object, based on
corrected distance data Rc determined by the following equation:
Rc=(.beta.2/.alpha.2).times.D (where D is said distance data,
.alpha.2 said reference capacitance, and .beta.2 said correction
capacitance).
10. The distance measuring apparatus according to claim 8, wherein
said detecting means detects the distance to said object, based on
corrected distance data Rd determined by the following equation:
Rd=[.beta.2/{(.alpha.2-.beta.2).times.A+.beta.2}].times.D+(.alpha.2-.beta-
.2).times.B (where D is said distance data, .alpha.2 said reference
capacitance, .beta.2 said correction capacitance, and A and B
correction coefficients).
11. The distance measuring apparatus according to claim 8, wherein
when a difference between said correction capacitance and said
reference capacitance is smaller than a predetermined value, said
detecting means detects the distance to said object, based on
corrected distance data Rc determined by the following equation:
Rc=(.beta.2/.alpha.2).times.D (where D is said distance data,
.alpha.2 said reference capacitance, and .beta.2 said correction
capacitance), and wherein when the difference between said
correction capacitance and said reference capacitance is not less
than the predetermined value, said detecting means detects the
distance to said object, based on corrected distance data Rd
determined by the following equation:
Rd=[.beta.2/{(.alpha.2-.beta.2).times.A+.beta.-
2}].times.D+(.alpha.2-.beta.2).times.B (where D is said distance
data, .alpha.2 said reference capacitance, .beta.2 said correction
capacitance, and A and B correction coefficients).
12. The distance measuring apparatus according to claim 8, wherein
said capacitance calculating means calculates said correction
capacitance before ranging.
13. The distance measuring apparatus according to claim 8, wherein
said capacitance calculating means calculates said correction
capacitance after ranging.
14. The distance measuring apparatus according to claim 8, wherein
said capacitance calculating means calculates the capacitance of
said integrating capacitor before and after ranging, and wherein
said detecting means determines an average of said capacitance
before ranging and said capacitance after ranging and detects the
distance to said object, using the average as said correction
capacitance.
15. A distance measuring apparatus comprising: light projecting
means for projecting a beam toward an object to be measured; light
receiving means for receiving reflected light of said beam
projected toward said object, at a reception position according to
a distance to said object and outputting a position signal
according to the reception position; computing means for performing
a predetermined operation based on said position signal outputted
from said light receiving means to generate a distance computation
value according to the distance to said object; integrating means
comprising an integrating capacitor, said integrating means
charging or discharging said integrating capacitor according to
said distance computation value generated by said computing means
to integrate said distance computation value; detecting means for
detecting the distance to said object, based on distance data
corresponding to the result of integral in said integrating means;
charging means for charging said integrating capacitor to a
predetermined voltage by letting a constant current flow; and
charge time calculating means for calculating a time that elapses
before a voltage of said integrating capacitor reaches said
predetermined voltage, wherein said detecting means detects the
distance to said object, based on a correction charge time being
said charge time calculated by said charge time calculating means
in a ranging routine, a reference charge time of said integrating
capacitor preliminarily calculated before the ranging routine, and
said distance data.
16. The distance measuring apparatus according to claim 15, wherein
said detecting means detects the distance to said object, based on
corrected distance data Re determined by the following equation:
Re=(.alpha.3/.beta.3).times.D (where D is said distance data,
.alpha.3 said reference charge time, and .beta.3 said correction
charge time).
17. The distance measuring apparatus according to claim 15, wherein
said detecting means detects the distance to said object, based on
corrected distance data Rf determined by the following equation:
Rf=[.alpha.3/{(.beta.3-.alpha.3).times.A+.alpha.3}].times.D+(.beta.3-.alp-
ha.3).times.B (where D is said distance data, .alpha.3 said
reference charge time, .beta.3 said correction charge time, and A
and B correction coefficients).
18. The distance measuring apparatus according to claim 15, wherein
when a difference between said correction charge time and said
reference charge time is smaller than a predetermined value, said
detecting means detects the distance to said object, based on
corrected distance data Re determined by the following equation:
Re=(.alpha.3/.beta.3).times.D (where D is said distance data,
.alpha.3 said reference charge time, and .beta.3 said correction
charge time), and wherein when the difference between said
correction charge time and said reference charge time is not less
than the predetermined value, said detecting means detects the
distance to said object, based on corrected distance data Rf
determined by the following equation:
Rf=[.alpha.3/{(.beta.3-.alpha.3).times.A+.alph-
a.3}].times.D+(.beta.3-.alpha.3).times.B (where D is said distance
data, .alpha.3 said reference charge time, .beta.3 said correction
charge time, and A and B correction coefficients).
19. The distance measuring apparatus according to claim 15, wherein
said charge time calculating means calculates said correction
charge time before ranging.
20. The distance measuring apparatus according to claim 15, wherein
said charge time calculating means calculates said correction
charge time after ranging.
21. The distance measuring apparatus according to claim 15, wherein
said charge time calculating means calculates the charge time of
said integrating capacitor before and after ranging, and wherein
said detecting means determines an average of said charge time
before ranging and said charge time after ranging and detects the
distance to said object, using the average as said correction
charge time.
22. The distance measuring apparatus according to claim 1, wherein
said integrating means integrates said distance computation value,
based on a predetermined timing signal, and wherein said charging
means charges said integrating capacitor at timing equal to said
timing signal.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a distance measuring
apparatus for measuring the distance to an object to be measured
and, more particularly, to a distance measuring apparatus of an
active type used in cameras and the like.
[0003] 2. Related Background Art
[0004] The distance measuring apparatus of the active type used in
the cameras and the like is normally constructed to detect the
distance to the object in the following manner. First, an infrared
emitting diode (hereinafter referred to as "IRED") projects a light
beam toward the object and a position sensitive detector
(hereinafter referred to as "PSD") receives reflected light of the
thus projected beam. Output signals from this PSD are processed by
signal processing circuits and a computing circuit and the
computing circuit outputs the result of computation as distance
data to a CPU. Then the CPU detects the distance to the object,
based on this distance data.
[0005] Since there is the possibility of causing an error in
distance measurement (ranging) based on only one light projection,
it is conventional practice to employ a method of carrying out the
light projection multiple times to generate a plurality of distance
computation values and integrating the plurality of distance
computation values by an integrating circuit provided with an
integrating capacitor to effect averaging, as in the distance
measuring apparatus described in Japanese Patent Application
Laid-Open No. H10-281758. Then the CPU detects the distance to the
object, based on distance data corresponding to the integral result
in the integrating circuit.
[0006] The distance measuring apparatus constructed to integrate
the distance computation values by use of the integrating
capacitor, including the distance measuring apparatus described in
the above Japanese application, however, had the following problem.
Since the capacitor changes its capacitance with change in ambient
temperature, it posed the problem of ranging error. In addition, a
capacitor has such characteristics as to change its capacitance
with a lapse of time even under the storage condition without being
used, which was also the cause of the ranging error.
SUMMARY OF THE INVENTION
[0007] The present invention has been accomplished under such
circumstances and an object of the invention is to provide a
distance measuring apparatus that can reduce the ranging error due
to the variation in the capacitance of the integrating
capacitor.
[0008] (1) In order to achieve the above object, a distance
measuring apparatus according to the present invention is an
apparatus comprising light projecting means for projecting a beam
toward an object to be measured; light receiving means for
receiving reflected light of the beam projected toward the object,
at a reception position according to a distance to the object and
outputting a position signal according to the reception position;
computing means for carrying out a predetermined operation based on
the position signal from the light receiving means to generate a
distance computation value according to the distance to the object;
integrating means comprising an integrating capacitor, the
integrating means charging or discharging the integrating capacitor
according to the distance computation value generated by the
computing means to integrate the distance computation value;
detecting means for detecting the distance to the object, based on
distance data corresponding to the result of integral in the
integrating means; charging means for charging the integrating
capacitor by letting a constant current flow for a predetermined
time; and voltage calculating means for calculating a voltage of
the integrating capacitor charged by the charging means, wherein
the detecting means detects the distance to the object, based on a
correction voltage being the voltage calculated by the voltage
calculating means in a ranging routine, a reference voltage of the
integrating capacitor preliminarily calculated before the ranging
routine, and the distance data.
[0009] In the distance measuring apparatus according to the present
invention, the charging means charges the integrating capacitor by
letting the constant current flow for the predetermined time in the
ranging routine and the voltage calculating means calculates the
correction voltage being the voltage of the integrating capacitor
thus charged. The detecting means calculates the distance to the
object, based on (1) this correction voltage, (2) the reference
voltage of the integrating capacitor preliminarily calculated
before the ranging routine, e.g., immediately after manufacturing
of the distance measuring apparatus, and (3) the distance data
corresponding to the integral result in the integrating means. The
voltage after the flow of the constant current for the constant
time in the integrating capacitor is related to the capacitance of
the capacitor. Namely, the ranging error due to change in the
capacitance of the integrating capacitor can be reduced, because
the distance to the object is calculated with also considering the
reference voltage, e.g., the voltage immediately after
manufacturing and the correction voltage in actual ranging, in
addition to the distance data.
[0010] It is preferable that the detecting means detect the
distance to the object, based on corrected distance data Ra given
by Ra=(.alpha.1/.beta.1).times.D (where D is the distance data,
.alpha.1 the reference voltage, and .beta.1 the correction
voltage).
[0011] In this case, the detecting means detects the distance to
the object, based on the corrected distance data Ra obtained by
converting the distance data to data upon calculation of the
reference voltage, for example, upon manufacturing of the distance
measuring apparatus, which can reduce the ranging error due to the
change in the capacitance of the integrating capacitor.
[0012] In the distance measuring apparatus according to the present
invention, it is also preferable that the detecting means detect
the distance to the object, based on corrected distance data Rb
given by Rb=
[.alpha.1/{(.beta.1-.alpha.1).times.A+.alpha.1}].times.D+(.beta.1-.alpha.-
1).times.B (where D is the distance data, .alpha.1 the reference
voltage, .beta.1 the correction voltage, and A and B correction
coefficients).
[0013] The various members and housing constituting the distance
measuring apparatus sometimes undergo distortion with change in
ambient temperature. The distortion of the housing etc. will cause
distortion of the optical system of the distance measuring
apparatus, which can be the cause of degradation of ranging
accuracy. In such cases, it is difficult to improve the ranging
accuracy by simply making use of the value of the ratio of the
reference voltage to the correction voltage. It thus becomes
feasible to improve the ranging accuracy by employing such a
configuration that the correction coefficient A and correction
coefficient B of the distance measuring apparatus are preliminarily
calculated and the detecting means detects the distance to the
object, based on the above corrected distance data Rb.
[0014] Further, in the distance measuring apparatus according to
the present invention, it is preferable that the detecting means
detect the distance to the object, based on corrected distance data
Ra given by Ra=n(.alpha.1/.beta.1).times.D (where D is the distance
data, .alpha.1 the reference voltage, and .beta.1 the correction
voltage), when a difference between the correction voltage and the
reference voltage is smaller than a predetermined value and that
the detecting means detect the distance to the object, based on
corrected distance data Rb given by
Rb=[.alpha.1/{(.beta.1-.alpha.1).times.A+.alpha.1}].times.D+(.beta.1-.alp-
ha.1).times.B (where D is the distance data, .alpha.1 the reference
voltage, .beta.1 the correction voltage, and A and B correction
coefficients), when the difference between the correction voltage
and the reference voltage is not less than the predetermined
value.
[0015] In this case, when the difference between the correction
voltage and the reference voltage is smaller than the predetermined
value, the detecting means detects the distance to the object,
based on the corrected distance data Ra without use of the
correction coefficients, while assuming that the distortion is
small in the housing etc. of the distance measuring apparatus with
change in temperature. On the other hand, when the difference
between the correction voltage and the reference voltage is not
less than the predetermined value, the detecting means detects the
distance to the object, based on the corrected distance data Rb
with also utilizing the correction coefficient A and the correction
coefficient B, while assuming that the distortion is large in the
housing etc. of the distance measuring apparatus with change in
temperature. Since the detecting means detects the distance to the
object by use of the proper corrected distance data according to
the degree of the distortion of the housing etc. as described, the
ranging accuracy can be further improved.
[0016] In the distance measuring apparatus according to the present
invention, the voltage calculating means may calculate the
correction voltage before ranging in the ranging routine or may
calculate the correction voltage after ranging in the ranging
routine.
[0017] Further, it is preferable that the voltage calculating means
calculate the voltage of the integrating capacitor before and after
ranging in the ranging routine and that the detecting means detect
the distance to the object, using an average of the voltage before
the ranging and the voltage after the ranging as the correction
voltage.
[0018] In this case, since the average of the voltage before the
ranging and the voltage after the ranging is used as the correction
voltage, when compared with the case wherein the correction voltage
is calculated only either before the ranging or after the ranging,
the distance is detected using the voltage corresponding to a
capacitance closer to the capacitance of the integrating capacitor
in actual ranging, which can further improve the ranging
accuracy.
[0019] (2) Another distance measuring apparatus according to the
present invention is an apparatus comprising light projecting means
for projecting a beam toward an object to be measured; light
receiving means for receiving reflected light of the beam projected
toward the object, at a reception position according to a distance
to the object and outputting a position signal according to the
reception position; computing means for performing a predetermined
operation based on the position signal outputted from the light
receiving means to generate a distance computation value according
to the distance to the object; integrating means comprising an
integrating capacitor, the integrating means charging or
discharging the integrating capacitor according to the distance
computation value generated by the computing means to integrate the
distance computation value; detecting means for detecting the
distance to the object, based on distance data corresponding to the
result of integral in the integrating means; charging means for
charging the integrating capacitor by letting a constant current
flow for a predetermined time; and capacitance calculating means
for calculating a capacitance of the integrating capacitor charged
by the charging means, wherein the detecting means detects the
distance to the object, based on a correction capacitance being the
capacitance calculated by the capacitance calculating means in a
ranging routine, a reference capacitance of the integrating
capacitor preliminarily calculated before the ranging routine, and
the distance data.
[0020] In the distance measuring apparatus according to the present
invention, the charging means charges the integrating capacitor by
letting the constant current flow for the predetermined time in the
ranging routine and the capacitance calculating means calculates
the correction capacitance, based on the voltage of the integrating
capacitor thus charged. Then the detecting means calculates the
distance to the object, based on (1) this correction capacitance,
(2) the reference capacitance of the integrating capacitor
preliminarily calculated before the ranging routine, e.g.,
immediately after manufacturing of the distance measuring
apparatus, and (3) the distance data corresponding to the integral
result in the integrating means. Namely, the ranging error due to
change in the capacitance of the integrating capacitor can be
reduced, because the distance to the object is calculated with also
considering the reference capacitance, e.g., the capacitance
immediately after manufacturing and the correction capacitance in
actual ranging, in addition to the distance data.
[0021] It is also preferable that the detecting means detect the
distance to the object, based on corrected distance data Rc given
by Rc=(.beta.2/.alpha.2).times.D (where D is the distance data,
.alpha.2 the reference capacitance, and .beta.2 the correction
capacitance).
[0022] In this case, the ranging error due to change in the
capacitance of the integrating capacitor can be reduced, because
the detecting means detects the distance to the object, based on
the corrected distance data Rc obtained by converting the distance
data to data upon calculation of the reference capacitance, e.g.,
upon manufacturing of the distance measuring apparatus.
[0023] In the distance measuring apparatus according to the present
invention, it is also preferable that the detecting means detect
the distance to the object, based on corrected distance data Rd
given by
Rd=[.beta.2/{(.alpha.2-.beta.2).times.A+.beta.2}].times.D+(.alpha.2-.beta-
.2).times.B (where D is the distance data, .alpha.2 the reference
capacitance, .beta.2 the correction capacitance, and A and B the
correction coefficients).
[0024] With distortion of the housing etc. of the distance
measuring apparatus due to the change in ambient temperature, the
optical system of the distance measuring apparatus will be
distorted, which can increase the possibility of degrading the
ranging accuracy. In such cases, it is difficult to improve the
ranging accuracy by simply making use of the value of the ratio of
the reference capacitance to the correction capacitance. It thus
becomes feasible to improve the ranging accuracy by employing such
a configuration that the correction coefficient A and correction
coefficient B of the distance measuring apparatus are preliminarily
calculated and the detecting means detects the distance to the
object, based on the above corrected distance data Rd.
[0025] Further, in the distance measuring apparatus according to
the present invention, it is preferable that the detecting means
detect the distance to the object, based on corrected distance data
Rc given by Rc=(.beta.2/.alpha.2).times.D (where D is the distance
data, .alpha.2 the reference capacitance, and .beta.2 the
correction capacitance), when a difference between the correction
capacitance and the reference capacitance is smaller than a
predetermined value and that the detecting means detect the
distance to the object, based on corrected distance data Rd given
by Rd=[.beta.2/{(.alpha.2-.beta.2).times.A+
.beta.2}].times.D+(.alpha.2-.beta.2).times.B (where D is the
distance data, .alpha.2 the reference capacitance, .beta.2 the
correction capacitance, and A and B correction coefficients), when
the difference between the correction capacitance and the reference
capacitance is not less than the predetermined value.
[0026] In this case, when the difference between the correction
capacitance and the reference capacitance is smaller than the
predetermined value, the detecting means detects the distance to
the object, based on the corrected distance data Rc without using
the correction coefficients, while assuming that the distortion is
small in the housing etc. of the distance measuring apparatus with
change in temperature. On the other hand, when the difference
between the correction capacitance and the reference capacitance is
not less than the predetermined value, the detecting means detects
the distance to the object, based on the corrected distance data Rd
with also utilizing the correction coefficient A and correction
coefficient B, while assuming that the distortion is large in the
housing etc. of the distance measuring apparatus with change in
temperature. Since the detecting means detects the distance to the
object with use of the proper corrected distance data according to
the degree of distortion of the housing etc. as described, the
ranging accuracy can be further improved.
[0027] In the distance measuring apparatus according to the present
invention, the capacitance calculating means may calculate the
correction capacitance before ranging in the ranging routine or may
calculate the correction capacitance after ranging in the ranging
routine.
[0028] Further, it is preferable that the capacitance calculating
means calculate the capacitance of the integrating capacitor before
and after ranging in the ranging routine and that the detecting
means detect the distance to the object, using an average of the
capacitance before the ranging and the capacitance after the
ranging as the correction capacitance.
[0029] In this case, since the average of the capacitance before
the ranging and the capacitance after the ranging is used as the
correction capacitance, when compared with the case wherein the
correction capacitance is calculated only either before the ranging
or after the ranging, the distance is detected using the
capacitance closer to the capacitance of the integrating capacitor
in actual ranging, which can further improve the ranging
accuracy.
[0030] (3) Still another distance measuring apparatus according to
the present invention is an apparatus comprising light projecting
means for projecting a beam toward an object to be measured; light
receiving means for receiving reflected light of the beam projected
toward the object, at a reception position according to a distance
to the object and outputting a position signal according to the
reception position; computing means for performing a predetermined
operation based on the position signal outputted from the light
receiving means to generate a distance computation value according
to the distance to the object; integrating means comprising an
integrating capacitor, the integrating means charging or
discharging the integrating capacitor according to the distance
computation value generated by the computing means to integrate the
distance computation value; detecting means for detecting the
distance to the object, based on distance data corresponding to the
result of integral in the integrating means; charging means for
charging the integrating capacitor to a predetermined voltage by
letting a constant current flow; and charge time calculating means
for calculating a time that elapses before a voltage of the
integrating capacitor reaches the predetermined voltage, wherein
the detecting means detects the distance to the object, based on a
correction charge time being the charge time calculated by the
charge time calculating means in a ranging routine, a reference
charge time of the integrating capacitor preliminarily calculated
before the ranging routine, and the distance data.
[0031] In the distance measuring apparatus according to the present
invention, the charging means charges the integrating capacitor up
to the predetermined voltage by letting the constant current flow
in the ranging routine and the charge time calculating means
calculates the correction charge time being the time that elapses
before the integrating capacitor reaches the predetermined voltage.
Then the detecting means calculates the distance to the object,
based on (1) this correction charge time, (2) the reference charge
time of the integrating capacitor preliminarily calculated before
the ranging routine, e.g., immediately after manufacturing of the
distance measuring apparatus, and (3) the distance data
corresponding to the integral result in the integrating means. The
time up to the predetermined voltage with flow of the constant
current to the integrating capacitor is related to the capacitance
of the capacitor. Namely, the ranging error due to the change in
the capacitance of the integrating capacitor can be reduced,
because the distance to the object is calculated, also considering
the reference charge time, e.g., the charge time immediately after
manufacturing and the correction charge in actual ranging, in
addition to the distance data.
[0032] It is also preferable that the detecting means detect the
distance to the object, based on corrected distance data Re given
by Re=(.alpha.3/.beta.3).times.D (where D is the distance data,
.alpha.3 the reference charge time, and .beta.3 the correction
charge time).
[0033] In this case, the ranging error due to the change in the
capacitance of the integrating capacitor can be reduced, because
the detecting means detects the distance to the object, based on
the corrected distance data Re obtained by converting the distance
data to that upon calculation of the reference charge time, e.g.,
upon manufacturing of the distance measuring apparatus.
[0034] In the distance measuring apparatus according to the present
invention, it is also preferable that the detecting means detect
the distance to the object, based on corrected distance data Rf
given by
Rf=[.alpha.3/{(.beta.3-.alpha.3).times.A+.alpha.3}].times.D+(.beta.3-.alp-
ha.3).times.B (where D is the distance data, a3 the reference
charge time, .beta.3 the correction charge time, and A and B
correction coefficients).
[0035] With distortion of the housing etc. of the distance
measuring apparatus due to the change in ambient temperature, the
optical system of the distance measuring apparatus will be
distorted, which can increase the possibility of degrading the
ranging accuracy. In such cases, it is difficult to improve the
ranging accuracy by simply making use of the value of the ratio of
the reference charge time to the correction charge time. It thus
becomes feasible to improve the ranging accuracy by employing such
a configuration that the correction coefficient A and the
correction coefficient B of the distance measuring apparatus are
preliminarily calculated and the detecting means detects the
distance to the object, based on the above corrected distance data
Rf.
[0036] Further, in the distance measuring apparatus according to
the present invention, it is preferable that the detecting means
detect the distance to the object, based on corrected distance data
Re given by Re=(.alpha.3/.beta.3).times.D (where D is the distance
data, .alpha.3 the reference charge time, and .beta.3 the
correction charge time), when a difference between the correction
charge time and the reference charge time is smaller than a
predetermined value and that the detecting means detect the
distance to the object, based on corrected distance data Rf given
by Rf=[.alpha.3/{(.beta.3-.alpha.3).times.A+.alpha.3}].times.D+
(.beta.3-.alpha.3).times.B (where D is the distance data, .alpha.3
the reference charge time, .beta.3 the correction charge time, and
A and B correction coefficients), when the difference between the
correction charge time and the reference charge time is not less
than the predetermined value.
[0037] In this case, when the difference between the correction
charge time and the reference charge time is smaller than the
predetermined value, the detecting means detects the distance to
the object, based on the corrected distance data Re without using
the correction coefficients, while assuming that the distortion is
small in the housing etc. of the distance measuring apparatus with
change in temperature. On the other hand, when the difference
between the correction charge time and the reference charge time is
not less than the predetermined value, the detecting means detects
the distance to the object, based on the corrected distance data Rf
with also utilizing the correction coefficient A and the correction
coefficient B, while assuming that the distortion is large in the
housing etc. of the distance measuring apparatus with change of
temperature. Since the detecting means detects the distance to the
object with use of the proper corrected distance data according to
the degree of distortion of the housing etc. as described, the
ranging accuracy can be further improved.
[0038] In the distance measuring apparatus according to the present
invention, the charge time calculating means may calculate the
correction charge time before ranging in the ranging routine or may
calculate the correction charge time after ranging in the ranging
routine.
[0039] Further, it is preferable that the charge time calculating
means calculate the charge time of the integrating capacitor before
and after ranging in the ranging routine and that the detecting
means detect the distance to the object, using an average of the
charge time before the ranging and the charge time after the
ranging as the correction charge time.
[0040] In this case, since the average of the charge time before
the ranging and the charge time after the ranging is used as the
correction charge time, when compared with the case wherein the
correction charge time is calculated only either before the ranging
or after the ranging, the distance is detected using the charge
time corresponding to a capacitance closer to the capacitance of
the integrating capacitor in actual ranging, which can further
improve the ranging accuracy.
[0041] Further, in the distance measuring apparatus of above (1)
and (2), it is preferable that the integrating means integrate the
distance computation value, based on a predetermined timing signal,
and that the charging means charge the integrating capacitor at the
timing equal to the timing signal.
[0042] When this configuration is employed, the correction voltage
or the correction capacitance is calculated under circumstances
closer to those during actual ranging, which can thus further
improve the ranging accuracy.
[0043] The present invention will be more fully understood from the
detailed description given hereinbelow and the accompanying
drawings, which are given by way of illustration only and are not
to be considered as limiting the present invention.
[0044] Further scope of applicability of the present invention will
become apparent from the detailed description given hereinafter.
However, it should be understood that the detailed description and
specific examples, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the
invention will be apparent to those skilled in the art from this
detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] FIG. 1 is a block diagram to show the distance measuring
apparatus of the first embodiment of the present invention;
[0046] FIG. 2 is a circuit diagram of a first signal processing
circuit and an output circuit in the distance measuring apparatus
illustrated in FIG. 1;
[0047] FIG. 3 is a timing chart to show the operation of the
distance measuring apparatus in the first embodiment and in the
ninth embodiment;
[0048] FIG. 4 is a graph to show the relationship between ambient
temperature of the distance measuring apparatus and deviation of
the distance signal;
[0049] FIG. 5 is a timing chart to show the operation of the
distance measuring apparatus in the fourth embodiment;
[0050] FIG. 6 is a timing chart to show the operation of the
distance measuring apparatus in the fifth embodiment;
[0051] FIG. 7 is a timing chart to show the operation of the
distance measuring apparatus in the ninth embodiment;
[0052] FIG. 8 is a timing chart to show the operation of the
distance measuring apparatus in the twelfth embodiment;
[0053] FIG. 9 is a timing chart to show the operation of the
distance measuring apparatus in the thirteenth embodiment; and
[0054] FIG. 10 is a timing chart to show the operation of the
distance measuring apparatus in the fourteenth embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0055] The preferred embodiments of the distance measuring
apparatus according to the present invention will be described
below in detail with reference to the accompanying drawings. The
same elements will be denoted by the same reference symbols and
redundant description will be omitted.
First Embodiment
[0056] FIG. 1 is a block diagram to show the distance measuring
apparatus 100 of the present embodiment. A CPU 1 is a unit for
controlling the entire camera in which this distance measuring
apparatus 100 is mounted and for controlling the entire camera
including this distance measuring apparatus 100, based on programs
and parameters preliminarily stored in an EEPROM 2. In this
distance measuring apparatus 100, the CPU 1 controls a driver 3 to
control emission of infrared light from an IRED (infrared emitting
diode) 4. The CPU 1 also controls the operation of autofocusing IC
(hereinafter referred to as "AFIC") 10 and receives an AF signal
(distance data) from the AFIC 10.
[0057] The infrared light emitted from the IRED 4 is projected
through a projection lens (not illustrated) placed in front of the
IRED 4, toward an object to be measured, and is reflected in part.
The reflected light travels through a receiving lens (not
illustrated) placed in front of a PSD (position sensitive detector)
5 to be received somewhere on a photoreceptive surface of the PSD
5. This reception position is a position according to the distance
to the object.
[0058] The PSD 5 outputs two signals I.sub.1 and I.sub.2 according
to the reception position. The signal I.sub.1 is a near signal,
which increases with decrease in the distance to the object if the
quantity of received light is constant. The signal I.sub.2 is a far
signal, which increases with increase in the distance to the object
if the quantity of received light is constant. The sum of the
signal I.sub.1 and the signal I.sub.2 represents the quantity of
reflected light received by the PSD 5. The near signal I.sub.1 is
supplied to a PSDN terminal 31 of the AFIC 10 and the far signal
I.sub.2 to a PSDF terminal 32 of the AFIC 10. It is, however, noted
that the AFIC 10 actually receives signals resulting from addition
of a stationary light component I.sub.0 to the near signal I.sub.1
and to the far signal I.sub.2 according to the outside
conditions.
[0059] The AFIC 10 is an integrated circuit (IC) and is comprised
of a first signal processing circuit 11, a second signal processing
circuit 12, a computing circuit 14, and an output circuit 15. The
first signal processing circuit 11 accepts input of the signal
I.sub.1+I.sub.0 from the PSD 5, eliminates the stationary light
component I.sub.0 from the signal, and outputs the near signal
I.sub.1. The second signal processing circuit 12 also accepts input
of the signal I.sub.2+I.sub.0 from the PSD 5, eliminates the
stationary light component I.sub.0 from the signal, and outputs the
far signal I.sub.2.
[0060] The computing circuit 14 accepts input of the near signal
I.sub.1 from the first signal processing circuit 11 and the far
signal I.sub.2 from the second signal processing circuit 12,
calculates an output ratio (I.sub.1/(I.sub.1+I.sub.2)), and outputs
an output ratio signal (distance computation value) indicating the
result of computation. This output ratio
(I.sub.1/(I.sub.1+I.sub.2)) represents the reception position on
the photoreceptive surface of the PSD 5, i.e., the distance to the
object.
[0061] The output circuit 15 accepts input of this output ratio
signal (distance computation value) and accumulates multiple output
ratios in cooperation with an integrating capacitor 6 connected to
a CINT terminal 33 of the AFIC 10, thereby improving S/N ratios.
Then the CPU 1 receives the thus accumulated output ratio as an AF
signal (distance data). Receiving the AF signal from the AFIC 10,
the CPU 1 performs a predetermined operation to transform the AF
signal to a distance signal and sends the distance signal to a lens
driving circuit 7. The lens driving circuit 7 performs the focusing
operation of taking lens 8, based on the distance signal.
[0062] The first signal processing circuit 11 and output circuit 15
of the AFIC 10 will be described below in further detail with
reference to FIG. 2.
[0063] FIG. 2 is a circuit diagram of the first signal processing
circuit 11 and output circuit 15. The configuration of the second
signal processing circuit 12 is also similar to that of the first
signal processing circuit 11. As described above, the first signal
processing circuit 11 is a circuit receiving the near signal
I.sub.1 plus the stationary light component I.sub.0 from the PSD 5,
eliminating the stationary light component I.sub.0 from the signal,
and outputting the near signal I.sub.1. Namely, the near range
terminal of the PSD 5 is connected through the PSDN terminal 31 of
the AFIC 10 to the negative input terminal of operational amplifier
20 of the first signal processing circuit 11.
[0064] The output terminal of the operational amplifier 20 is
connected to the base terminal of transistor 21 and the collector
terminal of the transistor 21 is connected to the base terminal of
transistor 22. The collector terminal of the transistor 22 is
connected to the negative input terminal of operational amplifier
23 and also connected to the computing circuit 14. Further, the
cathode terminal of compressing diode 24 is connected to the
collector terminal of the transistor 22 and the cathode terminal of
compressing diode 25 is connected to the positive input terminal of
the operational amplifier 23. A power supply 26 is connected to the
anode terminals of these respective compressing diodes 24 and
25.
[0065] A stationary light eliminating capacitor 27 is externally
connected to a CHF terminal 35 of the AFIC 10 and this stationary
light eliminating capacitor 27 is connected to the base terminal of
stationary light eliminating transistor 28 in the first signal
processing circuit 11. The stationary light eliminating capacitor
27 and the operational amplifier 23 are connected through a switch
29 to each other and the CPU 1 controls on/off of this switch 29.
The collector terminal of the stationary light eliminating
transistor 28 is connected to the negative input terminal of the
operational amplifier 20 and the emitter terminal of the transistor
28 is grounded through a resistor 30.
[0066] The output circuit 15 has the following configuration. The
integrating capacitor 6 externally connected to the C.sub.INT
terminal 33 of the AFIC 10 is connected through a switch 60 to the
output terminal of the computing circuit 14, is connected through a
switch 62 to a constant current source 63, and is grounded through
switch 64. The potential of the integrating capacitor 6 is read out
by the CPU 1 as described above. The switch 60, switch 62, and
switch 64 are controlled by a control signal from the CPU 1.
[0067] Next, the action of this AFIC 10 will be schematically
described referring to FIG. 1 and FIG. 2.
[0068] The CPU 1 keeps the switch 29 of the first signal processing
circuit 11 on while the IRED 4 emits no light. The stationary light
component I.sub.0 outputted from the PSD 5 during this period is
supplied to the first signal processing circuit 11, is subjected to
current amplification in a current amplifier consisting of the
operational amplifier 20, transistor 21, and transistor 22, and is
converted into a voltage signal by logarithmic compression in the
compressing diode 24. This voltage signal is supplied to the
negative input terminal of the operational amplifier 23. When the
signal entered into the operational amplifier 20 is large, the
cathode potential of the compressing diode 24 becomes large and
thus the signal from the operational amplifier 23 becomes large to
charge the stationary light eliminating capacitor 27. Then the base
current is supplied to the transistor 28, so that the collector
current flows in the transistor 28, so as to decrease the signal
entered into the operational amplifier 20 out of the signal I.sub.0
supplied to the first signal processing circuit 11. After the
operation of this closed loop becomes stable, all the signal
I.sub.0 supplied to the first signal processing circuit 11 flows to
the transistor 28 and a charge corresponding to the base current at
that time is stored in the stationary light eliminating capacitor
27.
[0069] When the CPU 1 switches the switch 29 off in synchronism
with light emission of the IRED 4, the stationary light component
I.sub.0 in the signal I.sub.1+I.sub.0 from the PSD 5 at this time
flows as a collector current to the transistor 28 to which the base
potential is applied because of the charge stored in the stationary
light eliminating capacitor 27. The near signal I.sub.1 is
current-amplified by the current amplifier consisting of the
operational amplifier 20 and the transistors 21 and 22, and is
converted into the voltage signal by logarithmic compression in the
compressing diode 24 to be outputted. Namely, the first signal
processing circuit 11 eliminates the stationary light component
I.sub.0 and outputs only the near signal I.sub.1, and the near
signal I.sub.1 is supplied to the computing circuit 14. On the
other hand, the second signal processing circuit 12 also eliminates
the stationary light component I.sub.0 and outputs only the far
signal I.sub.2 as the first signal processing circuit 11 does. The
far signal I.sub.2 is supplied to the computing circuit 14.
[0070] The near signal I.sub.1 outputted from the first signal
processing circuit 11 and the far signal I.sub.2 outputted from the
second signal processing circuit 12 are entered into the computing
circuit 14, and the computing circuit 14 calculates the output
ratio (I.sub.1/(I.sub.1+I.sub.- 2)) and outputs it. The output
ratio is supplied to the output circuit 15. During emission of a
predetermined number of pulses from the IRED 4, the switch 60 of
the output circuit 16 is on and the switch 62 and switch 64 are
off. Then the output ratio signal (distance computation value) from
the computing circuit 14 is stored in the integrating capacitor 6,
so as to perform the integral operation of the output ratio signal.
Namely, the integrating means is composed of the output circuit 15,
integrating capacitor 6, and CPU 1 in the present embodiment.
[0071] The voltage of the integrating capacitor 6 at this time,
i.e., the integral result is read out as an AF signal (distance
data) by the CPU as described above. Receiving the AF signal from
the AFIC 10, the CPU 1 detects the distance to the object, based on
this AF signal and information etc. stored in the EEPROM 2. Namely,
the CPU 1 also functions as the detecting means for detecting the
distance to the object in the present embodiment. A feature of the
distance measuring apparatus of the present embodiment is this
distance detection process and this point will be described in the
following description of the operation.
[0072] The operation of the distance measuring apparatus of the
present embodiment will be described referring to FIG. 1 to FIG.
3.
[0073] In the timing chart of FIG. 3, FIG. 3(a) shows the control
signal from the CPU 1, FIG. 3(b) the operation of the switch 62,
and FIG. 3(c) the charge voltage of the integrating capacitor
6.
[0074] When the release button of the camera is depressed by a half
stroke to-go into a ranging routine, the CPU 1 outputs the control
signal, as illustrated in FIG. 3(a), to the AFIC 10. Then the
switch 62 in the output circuit 15 is switched on at the timing of
the fall of pulse P3, as illustrated in FIG. 3(b). This causes the
integrating capacitor 6 to be charged at a constant speed
determined by the rating of the constant current source 63 in the
output circuit 15, as illustrated in FIG. 3(c). Namely, the CPU 1
and output circuit 15 compose the charging means. Then the switch
62 is turned off at the timing of the fall of pulse P4 to terminate
the charging of the integrating capacitor 6. After that, the CPU 1,
as the voltage calculating means, calculates the voltage of the
integrating capacitor 6 before the timing of the fall of pulse P5.
The voltage of the integrating capacitor 6 on this occasion will be
referred to hereinafter as a correction voltage. The CPU 1 turns
the switch 64 on at the timing of the fall of pulse P5 to discharge
the integrating capacitor 6 to the potential of the ground. In the
present embodiment, as illustrated in FIG. 3(a) to FIG. 3(c), the
charging of the integrating capacitor 6 for the calculation of the
correction voltage is carried out before the ranging operation (or
during the pulses P1 to P6) in the ranging routine, i.e., before
the integration of distance computation value described
hereinafter.
[0075] A reference voltage of the integrating capacitor 6 is
preliminarily stored in the EEPROM 2 (see FIG. 1). This reference
voltage is a voltage measured when the integrating capacitor 6 was
charged by the constant current source 63 for the same time as the
period between the fall of the pulse P3 and the fall of the pulse
P4 illustrated in FIG. 3(a), before the ranging routine, e.g.,
immediately after manufacturing of the distance measuring apparatus
100. The capacitance of the integrating capacitor 6 can vary
because of influence of ambient temperature or the like, but the
reference voltage is the voltage measured before the change of the
capacitance of the integrating capacitor 6.
[0076] After the calculation of the correction voltage as described
above, the driver 3 is actuated by a signal from the CPU 1, whereby
the IRED 4 emits pulses of infrared light. The infrared light
emitted from the IRED 4 is reflected by the object and thereafter
is received by the PSD 5. On the other hand, at the same time as
the emission from the IRED 4, the switch 29 (see FIG. 2) of the
first signal processing circuit 11 is turned off to enter the near
signal I.sub.1 without the stationary light component I.sub.0 into
the computing circuit 14. Similarly, the second signal processing
circuit 12 supplies the far signal I.sub.2 without the stationary
light component I.sub.0 to the computing circuit 14. The computing
circuit 14 outputs data (distance computation value) of the output
ratio I.sub.1/(I.sub.1+I.sub.2), based on the near signal I.sub.1
and the far signal I.sub.2.
[0077] Then, during the period between the fall of the pulse P7 and
the rise of the pulse P8 illustrated in FIG. 3(a), the switch 60 of
the output circuit 15 is kept on, whereby a positive voltage
corresponding to the output ratio from the computing circuit 14 is
entered into the integrating capacitor 6. The IRED 4 is turned off
at the timing of the rise of the pulse P8. After a lapse of a
signal error time, the switch 29 of the first signal processing
circuit 11 is turned on to start accumulation of the stationary
light component I.sub.0 of the output signal from the PSD 5 into
the stationary light eliminating capacitor 27.
[0078] The integrating capacitor 6 of the output circuit 15 accepts
the output ratio from the computing circuit 14, i.e., the distance
computation value to be charged by a voltage according to the level
of the distance computation value. According to this operation, the
voltage of the integrating capacitor 6 increases stepwise with
input of the distance computation value every emission of the IRED
4, as illustrated in FIG. 3(c). An amount of voltage increase of
each step itself is distance information corresponding to the
distance to the object, but the distance information in the present
embodiment is the sum of voltage increase amounts resulting from
the emission of pulses from the IRED 4.
[0079] After completion of input of distance computation values in
the predetermined emission number into the integrating capacitor 6,
the CPU 1 reads the integral result of distance computation values
by the integrating capacitor 6, as an AF signal (distance data).
The CPU 1 also reads the reference voltage of the integrating
capacitor 6 preliminarily stored in the EEPROM 2.
[0080] Then the CPU 1 detects the distance to the object, based on
a corrected AF signal (corrected distance data) Ra given by Eq. (1)
below.
Ra=(.alpha.1/.beta.1).times.D Eq. (1)
[0081] (where D is the AF signal (distance data), .alpha.1 the
reference voltage, and .beta.1 the correction voltage.)
[0082] The voltage of the integrating capacitor 6 after flow of a
constant current for a fixed time is associated with the
capacitance of the integrating capacitor 6. Therefore, the distance
measuring apparatus 100 of the present embodiment is constructed to
detect the distance to the object, based on the corrected AF signal
Ra obtained by converting the AF signal to that upon calculation of
the reference voltage, e.g., upon manufacturing of the distance
measuring apparatus, as seen from above Eq. (1). This can reduce
the ranging error due to the change in the capacitance of the
integrating capacitor 6.
[0083] When the release button is fully depressed thereafter, the
CPU 1 controls the lens driving circuit 7, based on the distance
thus obtained, to perform appropriate focusing operation of the
taking lens 8, and opens the shutter (not illustrated) to effect
exposure. The sequential photographing operations of calculation of
the correction voltage, ranging, focusing, and exposure are carried
out as described above in conjunction with manipulation on the
release button.
Second Embodiment
[0084] Next, the second embodiment of the distance measuring
apparatus according to the present invention will be described
below. The present embodiment is different in the detection process
of distance in the CPU 1 from the first embodiment.
[0085] The various members and housing (mechanical parts)
constituting the distance measuring apparatus 100 can undergo
distortion with change in ambient temperature. With the distortion
of the housing etc., the optical system of the distance measuring
apparatus 100 will be distorted, which can be the cause of
degradation of ranging accuracy. In such cases, the ranging
accuracy is hardly improved by simply making use of the value of
the ratio of the reference voltage to the correction voltage as in
the first embodiment.
[0086] FIG. 4 is a graph to show the relation between ambient
temperature of the distance measuring apparatus 100 and deviation
of the distance signal. In the figure, circular dots indicate the
results where the distance to the object was calculated based on
the AF signal without calculation of the corrected AF signal,
triangular dots the results where the distance was calculated based
on the corrected AF signal Ra obtained by Eq. (1) of the first
embodiment, and square dots the results where the distance was
calculated by the present embodiment. As seen from the same figure,
if the distance is calculated by the method of the first embodiment
without consideration to the distortion of the housing etc., there
can occur such an event that the ranging error is not reduced while
there is little change in the absolute value of deviation of the
distance signal with an opposite sign; e.g., as in the case of the
ambient temperature of -10.degree.C.
[0087] In the present embodiment, the CPU 1 detects the distance to
the object, based on a corrected AF signal (corrected distance
data) Rb given by Eq. (2) below accordingly.
Rb=[.alpha.1/{(.beta.1-.alpha.1).times.A+.alpha.1}].times.D+(.beta.1-.alph-
a.1).times.B Eq. (2)
[0088] (where D is the AF signal (distance data), .alpha.1 the
reference voltage, .beta.1 the correction voltage, and A and B
correction coefficients.)
[0089] The correction coefficients A, B are values inherent in each
distance measuring apparatus and proper values thereof are
preliminarily determined by experiment upon manufacturing of the
distance measuring apparatus. An example of how to determine the
correction coefficients A, B will be described below. When the
reference voltage .alpha.1 (A/D value) is the count of 600 and the
correction voltage .beta.1 the count of 500, the corrected AF
signal Ra at ordinary temperature can be determined by
Ra=600/500.times.D according to above Eq. (1). Now let us suppose
that there occurred the distortion of the housing due to influence
of temperature and it was verified by experiment that better
distance data was obtained with the count of 550 than with the
count of 600 for the reference voltage .alpha.1. In this case, the
correction coefficient A can be determined by equating Eq. (1) with
.alpha.1 of 550 and .beta.1 of 500 to Eq. (2) with .alpha.1 of 600
and .beta.1of 500, as presented below. Here the correction
coefficient B is assumed to be zero.
550/500=[600/{(500-600).times.A+600}]
[0090] From the above equation, A=0.545454 is determined. Then this
is substituted into Eq. (2) to obtain the corrected AF signal by
Rb=[600/{(500-600).times. 0.545454+600}].times.D. The correction
coefficients A, B are preliminarily stored in the EEPROM 2. FIG. 4
shows the results where the correction coefficient A is 0.7 and the
correction coefficient B is 0. As described above, the distance
measuring apparatus of the present embodiment can also reduce the
ranging error due to the distortion of the housing etc. of the
distance measuring apparatus by adjusting the values of the
correction coefficients A, B and thus improve the ranging
accuracy.
Third Embodiment
[0091] Next, the third embodiment of the distance measuring
apparatus according to the present invention will be described. The
present embodiment is different in the detection process of
distance in the CPU 1 from the first embodiment and the second
embodiment. As shown in FIG. 4, the ranging error is larger around
the ordinary temperature (25.degree. C.) when the distance is
detected based on the corrected AF signal (corrected distance data)
Rb using the correction coefficients A, B than when the distance is
detected based on the corrected AF signal Ra not using the
correction coefficients A, B. This is because the distance to the
object was detected based on Eq. (2) involving the premise of
existence of distortion of the housing etc., though there was
little distortion in the housing etc. of the distance measuring
apparatus due to change in temperature.
[0092] In the present embodiment, therefore, the CPU 1 detects the
distance to the object, based on the corrected AF signal Ra
determined by above Eq. (1), when the difference between the
correction voltage and the reference voltage is smaller than a
predetermined value, but the CPU detects the distance to the
object, based on the corrected AF signal Rb determined by above Eq.
(2), when the difference between the correction voltage and the
reference voltage is not less than the predetermined value.
[0093] Namely, when the difference between the correction voltage
and the reference voltage is smaller than the predetermined value,
the CPU 1 detects the distance to the object, based on the
corrected AF signal Ra without use of the correction coefficients,
while assuming that the distortion is small in the housing etc.
with change of temperature. On the other hand, when the difference
between the correction voltage and the reference voltage is not
less than the predetermined value, the CPU 1 detects the distance
to the object, based on the corrected AF signal Rb, with also
utilizing the correction coefficient A and correction coefficient
B, while assuming that the distortion is large in the housing etc.
with change of temperature. In this way the present embodiment can
further improve the ranging accuracy, because the CPU 1 detects the
distance to the object, using the appropriate corrected AF signal
according to the degree of distortion of the housing etc.
Fourth Embodiment
[0094] Next, the fourth embodiment of the distance measuring
apparatus according to the present invention will be described
referring to the timing chart of FIG. 5(a) to FIG. 5(c). The
present embodiment is different in the time of calculation of the
correction voltage from each of the above embodiments. As
illustrated in FIG. 5(a) to FIG. 5(c), in the present embodiment
the charging of the integrating capacitor 6 for the calculation of
the correction voltage is not carried out before the ranging
operation (the pulses P1 to P6) in the ranging routine, but is
carried out after the ranging operation, i.e., after the
integration of distance computation values.
[0095] Specifically, the switch 62 is turned on at the timing of
the fall of the pulse P8, whereby the integrating capacitor 6 is
charged at a fixed speed determined by the rating of the constant
current source 63, as illustrated in FIG. 5(c). Then the switch 62
is turned off at the timing of the fall of the pulse P9 to
terminate the charging of the integrating capacitor 6. After that,
the CPU 1 calculates the correction voltage of the integrating
capacitor 6 before the timing of the fall of the pulse P10. Then
the CPU 1 detects the distance to the object, based on the
correction voltage, the reference voltage, and the AF signal, as in
each of the above embodiments.
Fifth Embodiment
[0096] Next, the fifth embodiment of the distance measuring
apparatus according to the present invention will be described
referring to the timing chart of FIG. 6(a) to FIG. 6(c). The
present embodiment is different in the time of calculation of the
correction voltage from each of the above embodiments. As
illustrated in FIG. 6(a) to FIG. 6(c), in the present embodiment
the charging of the integrating capacitor 6 for the calculation of
the correction voltage is carried out before the ranging operation
(the pulses P6 to P11) and after the ranging operation in the
ranging routine, i.e., before and after the integration of distance
computation values.
[0097] Specifically, the switch 62 is turned on at the timing of
the fall of the pulse P2, whereby the integrating capacitor 6 is
charged at the fixed speed determined by the rating of the constant
current source 63, as illustrated in FIG. 6(c). Then the switch 62
is turned off at the timing of the fall of the pulse P3 to
terminate the charging of the integrated capacitor 6. After that,
the CPU 1 calculates the voltage of the integrating capacitor 6
before the timing of the fall of the pulse P4. Then the ranging is
carried out in synchronism with pulses P6 to P11 etc., then the
integrating capacitor 6 is charged by the fixed current from the
fall of pulse P13 to the fall of pulse P14, and the CPU 1 again
calculates the voltage of the integrating capacitor 6. Then the CPU
1 calculates an average of the voltage before the ranging and the
voltage after the ranging thus obtained, and uses the average as
the correction voltage. Then the CPU 1 detects the distance to the
object, based on the correction voltage obtained in this way, the
reference voltage, and the AF signal.
[0098] The integrating capacitor 6 can change its capacitance
before and after the ranging. Since the distance measuring
apparatus of the present embodiment is constructed to use the
average of the voltage before ranging and the voltage after ranging
as the correction value as described above, the distance is
detected using the voltage corresponding to the capacitance closer
to the capacitance of the integrating capacitor 6 in the actual
ranging, as compared with each of the above embodiments constructed
to calculate the correction voltage only either before the ranging
or after the ranging. Therefore, the present embodiment can further
improve the ranging accuracy.
Sixth Embodiment
[0099] Next, the sixth embodiment of the distance measuring
apparatus according to the present invention will be described
referring to FIG. 1 and FIG. 3. The structure of the distance
measuring apparatus of the present embodiment is similar to that of
the first embodiment and the present embodiment is different in the
way of detecting the distance by the CPU 1 of the detecting means,
from the first embodiment. The details are as follows.
[0100] First, as in the first embodiment, the integrating capacitor
6 is charged by the constant current from the constant current
source 63 during the period between the fall of the pulse P3 and
the fall of the pulse P4, as illustrated in FIG. 3(a) to FIG. 3(c).
After completion of the charging of the integrating capacitor 6,
the CPU 1 then reads the voltage of the integrating capacitor 6
thus charged and the CPU 1 further calculates the capacitance of
the integrating capacitor 6, based on this voltage and the charge
accumulated in the integrating capacitor 6. This capacitance will
be referred to hereinafter as a correction capacitance.
[0101] A reference capacitance of the integrating capacitor 6 is
preliminarily stored in the EEPROM 2 (see FIG. 1). This reference
capacitance is a capacitance measured when the integrating
capacitor 6 is charged by the constant current source 63 for the
same time as the period between the fall of pulse P3 and the fall
of pulse P4 illustrated in FIG. 3(a), before the ranging routine,
e.g., immediately after manufacturing of the distance measuring
apparatus 100. The integrating capacitor 6 can change its
capacitance because of the influence of the ambient temperature or
the like, but the reference capacitance is the one measured before
the capacitor is subjected to such influence.
[0102] After completion of the calculation of the correction
capacitance, the ranging is carried out in synchronism with the
pulses P7 to P12 and the like, as in the first embodiment. After
completion of entry of output ratio signals
(I.sub.1/(I.sub.1+I.sub.2)) corresponding to the predetermined
number of pulse emissions, into the integrating capacitor 6, i.e.,
after completion of entry of distance computation values, the CPU 1
then reads the integral result of distance computation values by
the integrating capacitor 6 as the AF signal (distance data). The
CPU 1 also reads the reference capacitance of the integrating
capacitor 6 preliminarily stored in the EEPROM 2.
[0103] Then the CPU 1 detects the distance to the object, based on
a corrected AF signal (corrected distance data) Rc determined by
Eq. (3) below.
Rc=(.beta.2/.alpha.2).times.D Eq. (3)
[0104] (where D is the AF signal (distance data), .alpha.2 the
reference capacitance, and .beta.2 the correction capacitance.)
[0105] As seen from above Eq. (3), the distance measuring apparatus
100 is constructed to detect the distance to the object, based on
the corrected AF signal Rc obtained by converting the AF signal to
that upon the calculation of the reference capacitance, e.g., upon
manufacturing of the distance measuring apparatus, and thus can
reduce the ranging error due to change in the capacitance of the
integrating capacitor 6. Since the capacitance of the capacitor is
in the relation of inverse proportion to the voltage, Eq. (3) has
the denominator of the reference capacitance .alpha.2 and the
numerator of the correction capacitance .beta.2, different from
above Eq. (1).
[0106] The present embodiment is arranged to calculate the
correction capacitance before the ranging operation in the ranging
routine, i.e., before the integration of distance computation
values, but the apparatus may also be modified to charge the
integrating capacitor after the ranging operation, i.e., after the
integration of distance computation values and then calculate the
correction capacitance of the integrating capacitor 6, as in the
fourth embodiment described above (see FIG. 5). Further, the
apparatus may also be modified so as to charge the integrating
capacitor 6 for calculation of the correction capacitance before
the ranging operation (the pulses P6 to P11) and after the ranging
operation in the ranging routine, i.e., before and after the
integration of distance computation values, as in the fifth
embodiment (see FIG. 6), and use the average of the capacitance
before the ranging and the capacitance after the ranging thus
obtained, as the correction capacitance. The integrating capacitor
6 can change its capacitance before and after the ranging. However,
since the average of the capacitance before ranging and the
capacitance after ranging is used as the correction capacitance,
the distance is detected based on the capacitance closer to the
capacitance of the integrating capacitor 6 in actual ranging, when
compared with the case wherein the correction capacitance is
calculated only either before the ranging or after the ranging.
Therefore, the ranging accuracy can be further improved.
Seventh Embodiment
[0107] Next, the seventh embodiment of the distance measuring
apparatus according to the present invention will be described. The
present embodiment is different in the detection process of
distance in the CPU 1 from the sixth embodiment.
[0108] The various members and housing constituting the distance
measuring apparatus 100 can undergo distortion with change in
ambient temperature. In this case, the ranging accuracy is hardly
improved by simply making use of the value of the ratio of the
reference capacitance to the correction capacitance as in the sixth
embodiment. In the present embodiment, employing the technique
similar to that in the second embodiment described above, the CPU 1
thus detects the distance to the object, based on a corrected AF
signal (corrected distance data) Rd determined by Eq. (4)
below.
Rd=[.beta.2/{(.alpha.2-.beta.2).times.A+.beta.2}].times.D+(.alpha.2-2).tim-
es.B Eq. (4)
[0109] (where D is the AF signal (distance data), .alpha.2 the
reference capacitance, .beta.2 the correction capacitance, and A
and B correction coefficients.)
[0110] The correction coefficients A, B are values inherent in each
distance measuring apparatus and appropriate values thereof are
preliminarily determined by experiment, for example, upon
manufacturing of the distance measuring apparatus. The correction
coefficients A, B are preliminarily stored in the EEPROM 2. As
described above, the distance measuring apparatus of the present
embodiment can also decrease the ranging error due to the
distortion of the housing etc. of the distance measuring apparatus
by adjusting the values of the correction coefficients A, B,
thereby achieving the improvement in the ranging accuracy.
Eighth Embodiment
[0111] Next, the eighth embodiment of the distance measuring
apparatus according to the present invention will be described. The
present embodiment is different in the detection process of
distance in the CPU 1 from the sixth embodiment and the seventh
embodiment. In certain cases the ranging error is larger when the
distance is detected based on the corrected AF signal Rd using the
correction coefficients A, B than when the distance is detected
based on the corrected AF signal Rc not using the correction
coefficients A, B, as described in the third embodiment. This is
because the distance to the object is detected based on above Eq.
(4) involving the premise of existence of distortion of the housing
etc. though there is little distortion in the housing etc. of the
distance measuring apparatus with change of temperature.
[0112] In the present embodiment, therefore, the CPU 1 detects the
distance to the object, based on the corrected AF signal Rc given
by above Eq. (3), when the difference between the correction
capacitance and the reference capacitance is smaller than a
predetermined value, but the CPU detects the distance to the
object, based on the corrected AF signal Rd given by above Eq. (4),
when the difference between the correction capacitance and the
reference capacitance is not less than the predetermined value.
[0113] Namely, when the difference between the correction
capacitance and the reference capacitance is smaller than the
predetermined value, the CPU 1 detects the distance to the object,
based on the corrected AF signal Rc without use of the correction
coefficients, while assuming that the distortion is small in the
housing etc. with change of temperature. On the other hand, when
the difference between the correction capacitance and the reference
capacitance is not less than the predetermined value, the CPU 1
detects the distance to the object, based on the corrected AF
signal Rd with also using the correction coefficient A and the
correction coefficient B, while assuming that the distortion is
large in the housing etc. with change of temperature. As described
above, the present embodiment can further improve the ranging
accuracy, because the CPU 1 detects the distance to the object,
using the appropriate corrected AF signal according to the degree
of distortion of the housing etc.
Ninth Embodiment
[0114] Next, the ninth embodiment of the distance measuring
apparatus according to the present invention will be described
referring to FIG. 1, FIG. 2, and FIG. 7. The structure of the
distance measuring apparatus of the present embodiment is similar
to that of the first embodiment and the present embodiment is
different in the way of detection of distance by the CPU 1 of the
detecting means, from the first embodiment. The details are as
follows.
[0115] First, the switch 62 is turned on at the timing of the fall
of the pulse P1 illustrated in FIG. 7(a). This causes the
integrating capacitor 6 to be charged at the constant speed
determined by the rating of the constant current source 63, as
illustrated in FIG. 7(c). Then the CPU 1 calculates a charge time
t1 that elapses before the integrating capacitor 6 reaches a
predetermined voltage V1. This charge time t1 will be referred to
hereinafter as a correction charge time. After the integrating
capacitor 6 reaches the predetermined voltage V1, the CPU 1 emits
the pulse P2 to switch the switch 62 off, thereby terminating the
charging of the integrating capacitor 6. Then the CPU 1 turns the
switch 64 on at the timing of the fall of the pulse P3 to discharge
the integrating capacitor 6, whereby the potential thereof becomes
that of the ground.
[0116] A reference charge time of the integrating capacitor 6 is
preliminarily stored in the EEPROM 2 (see FIG. 1). This reference
charge time is a time necessary for the charging of the integrating
capacitor 6 to the voltage V1 by the constant current source 63
before the ranging routine, e.g., immediately after manufacturing
of the distance measuring apparatus 100. The integrating capacitor
6 can change its charge time because of the influence of ambient
temperature or the like, but the reference charge time is the one
measured before change of the capacitance of the integrating
capacitor 6.
[0117] After completion of the calculation of the correction charge
time, the ranging is carried out in synchronism with the pulses P4
to P9 and the like, as in the first embodiment. After output ratio
signals (I.sub.1/(I.sub.1+I.sub.2)) corresponding to a
predetermined number of emissions, i.e., distance computation
values have been entered into the integrating capacitor 6, the CPU
1 then reads the integral result of distance computation values by
the integrating capacitor 6, as an AF signal (distance data). The
CPU 1 also reads the reference charge time of the integrating
capacitor 6 preliminarily stored in the EEPROM 2.
[0118] Then the CPU 1 detects the distance to the object, based on
a corrected AF signal (corrected distance data) Re determined by
Eq. (5) below.
Re=(.alpha.3/.beta.3).times.D Eq. (5)
[0119] (where D is the AF signal (distance data), .alpha.3 the
reference charge time, and .beta.3 the correction charge time.)
[0120] As seen from above Eq. (5), the distance measuring apparatus
of the present embodiment is constructed to detect the distance to
the object, based on the corrected AF signal Re obtained by
converting the AF signal to that upon calculation of the reference
charge time, e.g., upon manufacturing of the distance measuring
apparatus, and thus can reduce the ranging error due to change in
the capacitance of the integrating capacitor 6.
Tenth Embodiment
[0121] Next, the tenth embodiment of the distance measuring
apparatus according to the present invention will be described. The
present embodiment is different in the detection process of
distance in the CPU 1 from the ninth embodiment.
[0122] The various members and housing constituting the distance
measuring apparatus 100 can undergo distortion with change in the
ambient temperature. In such cases, it is difficult to improve the
ranging accuracy by simply making use of the value of the ratio of
the reference charge time to the correction charge time as in the
ninth embodiment. In the present embodiment, employing the
technique similar to those of the second embodiment and seventh
embodiment described above, the CPU 1 thus detects the distance to
the object, based on a corrected AF signal (corrected distance
data) Rf determined by Eq. (6) below.
Rf=[.alpha.3/{(.beta.3-.alpha.3).times.A+.alpha.3}].times.D+(.beta.3-.alph-
a.3).times.B Eq. (6)
[0123] (where D is the AF signal (distance data), .alpha.3 the
reference charge time, .beta.3 the correction charge time, and A
and B correction coefficients.)
[0124] The correction coefficients A, B are values inherent in each
distance measuring apparatus and appropriate values thereof are
preliminarily determined by experiment, for example, upon
manufacturing of the distance measuring apparatus. The correction
coefficients A, B are preliminarily stored in the EEPROM 2. As
described above, the distance measuring apparatus of the present
embodiment can also reduce the ranging error due to the distortion
of the housing etc. of the distance measuring apparatus by
adjusting the values of the correction coefficients A, B and thus
improve the ranging accuracy.
Eleventh Embodiment
[0125] Next, the eleventh embodiment of the distance measuring
apparatus according to the present invention will be described. The
present embodiment is different in the detection process of
distance in the CPU 1 from the ninth embodiment and the tenth
embodiment. In certain cases the ranging error is larger when the
distance is detected based on the corrected AF signal Rf using the
correction coefficients A, B than when the distance is detected
based on the corrected AF signal Rd without use of the correction
coefficients A, B, as described in the third embodiment. This is
because the distance to the object is detected based on above Eq.
(6) involving the premise of existence of distortion of the housing
etc. though there is little distortion in the housing etc. of the
distance measuring apparatus with change of temperature.
[0126] In the present embodiment, therefore, the CPU 1 detects the
distance to the object, based on the corrected AF signal Re
determined by above Eq. (5), when the difference between the
correction charge time and the reference charge time is smaller
than a predetermined value, but the CPU detects the distance to the
object, based on the corrected AF signal Rf determined by above Eq.
(6), when the difference between the correction charge time and the
reference charge time is not less than the predetermined value.
[0127] Namely, when the difference between the correction charge
time and the reference charge time is smaller than the
predetermined value, the CPU 1 detects the distance to the object,
based on the corrected AF signal Re without use of the correction
coefficients, while assuming that the distortion is small in the
housing etc. with change of temperature. On the other hand, when
the difference between the correction charge time and the reference
charge time is not less than the predetermined value, the CPU 1
detects the distance to the object, based on the corrected AF
signal Rf with also using the correction coefficient A and
correction coefficient B, while assuming that the distortion is
large in the housing etc. with change of temperature. Since the CPU
1 detects the distance to the object, using the appropriate
corrected AF signal according to the degree of distortion of the
housing etc. as described above, the present embodiment can further
improve the ranging accuracy.
Twelfth Embodiment
[0128] Next, the twelfth embodiment of the distance measuring
apparatus according to the present invention will be described
referring to the timing chart of FIG. 8(a) to FIG. 8(c). The
present embodiment is different in the timing of calculation of the
correction charge time from the ninth to eleventh embodiments. As
shown in FIG. 8(a) to FIG. 8(c), in the present embodiment the
charging of the integrating capacitor 6 for the calculation of the
correction charge time is not carried out before the ranging
operation (the pulses P1 to P6) in the ranging routine, but is
carried out after the ranging operation, i.e., after the
integration of distance computation values.
[0129] Specifically, the switch 62 is turned on at the timing of
the fall of the pulse P7, whereby the integrating capacitor 6 is
charged at the constant speed determined by the rating of the
constant current source 63, as illustrated in FIG. 8(c). Then the
CPU 1 calculates the correction charge time t2 that elapses before
the integrating capacitor 6 reaches the predetermined voltage V1.
After the integrating capacitor 6 reaches the predetermined voltage
V1, the CPU 1 emits the pulse P8 to switch the switch 62 off and
terminate the charging of the integrating capacitor 6. After that,
the CPU 1 detects the distance to the object, based on the
correction charge time t2, the reference charge time, and the AF
signal, as in the ninth to eleventh embodiments.
Thirteenth Embodiment
[0130] Next, the thirteenth embodiment of the distance measuring
apparatus according to the present invention will be described
referring to the timing chart of FIG. 9(a) to FIG. 9(c). The
present embodiment is different in the timing of calculation of the
correction charge time from the ninth to twelfth embodiments. As
illustrated in FIG. 9(a) to FIG. 9(c), in the present embodiment
the charging of the integrating capacitor 6 for the calculation of
the correction charge time is carried out before the ranging
operation (the pulses P4 to P9) and after the ranging operation in
the ranging routine, i.e., before and after the integration of
distance computation values.
[0131] Specifically, the switch 62 is turned on at the timing of
the fall of the pulse P1, whereby the integrating capacitor 6 is
charged at the constant speed determined by the rating of the
constant current source 63, as illustrated in FIG. 9(c). Then the
CPU 1 calculates the charge time t3 that elapses before the
integrating capacitor 6 reaches the predetermined voltage V1. After
the integrating capacitor 6 reaches the predetermined voltage V1,
the CPU 1 emits the pulse P2 to switch the switch 62 off and
terminate the charging of the integrating capacitor 6. Then the
ranging is carried out in synchronism with the pulses P4 to P9 and
the like, and thereafter the integrating capacitor 6 is again
charged by the constant current from the fall of the pulse P10. The
CPU 1 calculates the charge time t4 that elapses before the
integrating capacitor 6 reaches the voltage V1.
[0132] Then the CPU 1 calculates an average of the charge time t3
before the ranging and the charge time t4 after the ranging
obtained in this way and uses it as a correction charge time. Then
the CPU 1 detects the distance to the object, based on the
correction charge time obtained in this way, the reference charge
time, and the AF signal.
[0133] The integrating capacitor 6 can change its capacitance
before and after the ranging in certain cases. However, since the
distance measuring apparatus of the present embodiment uses the
average of the charge time t3 before ranging and the charge time t4
after ranging as the correction charge time, when compared with the
above ninth to twelfth embodiments wherein the correction charge
time is calculated only either before the ranging or after the
ranging, the apparatus detects the distance, using the charge time
corresponding to the capacitance closer to the capacitance of the
integrating capacitor 6 in actual ranging, and thus can further
improve the ranging accuracy.
Fourteenth Embodiment
[0134] Next, the fourteenth embodiment of the distance measuring
apparatus according to the present invention will be described
referring to FIG. 1, FIG. 2, and FIG. 10(a) to FIG. 10(c). The
present embodiment is different in the way of charging of the
integrating capacitor 6 for the calculation of the correction
voltage from the first embodiment.
[0135] As illustrated in FIG. 10(a), the switch 62 is turned on to
charge the integrating capacitor 6 by the constant current source
63 during the period from the fall of the pulse P1 to the rise of
the pulse P2, during the period from the fall of the pulse P3 to
the rise of the pulse P4, and during the period from the fall of
the pulse P5 to the rise of the pulse P6. Then the charging of the
integrating capacitor is terminated when the total charge time by
the constant current source 63 reaches a predetermined time. After
completion of the charging of the integrating capacitor 6, the CPU
1 calculates the correction voltage, which was described in the
first embodiment. Then the ranging is carried out in synchronism
with the pulses P7 to P12 and the like.
[0136] In the present embodiment the spacing ta between the pulses
P1 and P2, P3 and P4, P5 and P6, which determines the timing of the
charging for the calculation of the correction voltage, is equal to
the spacing Ta between the pulses P7 and P8, P9 and P10, P11 and
P12, which determines the integral timing in the ranging operation.
The spacing tb from the rise of the pulse P2 to the fall of the
pulse P3 is also equal to the spacing Tb from the rise of the pulse
P8 to the fall of the pulse P9.
[0137] After distance computation values corresponding to a
predetermined number of emissions have been entered into the
integrating capacitor 6, the CPU 1 reads the integral result of
distance computation values by the integrating capacitor 6, as an
AF signal. The CPU 1 also reads the reference voltage of the
integrating capacitor 6 preliminarily stored in the EEPROM 2. Then
the CPU 1 calculates the corrected AF signal Ra by substituting the
reference voltage, the correction voltage, and the AF signal into
above Eq. (1) and further detects the distance to the object, based
on this corrected AF signal Ra. Since the integrating capacitor 6
is charged by the constant current source 63 at the timing equal to
the integral timing in the ranging operation in the distance
measuring apparatus of the present embodiment, the CPU 1 calculates
the correction voltage under circumstances close to those in actual
ranging and thus can further improve the ranging accuracy.
[0138] It is noted that the spacing tb from the rise of the pulse
P2 to the fall of the pulse P3 can be set smaller than the spacing
Tb from the rise of the pulse P8 to the fall of the pulse P9. This
permits the ranging routine to be completed within shorter time. In
addition, since the integrating capacitor 6 is not charged during
the spacing tb, the accuracy is not degraded in detection of the
capacitance of the integrating capacitor 6.
[0139] This method of charging the integrating capacitor 6 at the
timing equal to the integral timing in the ranging operation can
also be applied to the second to eighth embodiments, without having
to be limited to the first embodiment.
[0140] The invention accomplished by the inventor was described
above in detail based on the embodiments thereof, but it is noted
that the present invention is by no means limited to each of the
above embodiments. For example, for the integration of distance
computation values, the distance computation values may also be
integrated by preliminarily storing charge in the integrating
capacitor and discharging the integrating capacitor with input of
distance computation values.
[0141] As detailed above, the distance measuring apparatus
according to the present invention can reduce the ranging error due
to the change in the capacitance of the integrating capacitor,
because the detecting means calculates the distance to the object
with also taking account of the reference voltage, e.g., that
immediately after manufacturing of the distance measuring apparatus
and the correction voltage in actual ranging, in addition to the
distance data.
[0142] Another distance measuring apparatus according to the
present invention can also reduce the ranging error due to the
change in the capacitance of the integrating capacitor, because the
distance to the object is calculated, also taking account of the
reference capacitance, e.g., that immediately after manufacturing
of the distance measuring apparatus and the correction capacitance
in actual ranging, in addition to the distance data.
[0143] Further, another distance measuring apparatus according to
the present invention can reduce the ranging error due to the
change in the capacitance of the integrating capacitor, because the
distance to the object is calculated, also taking account of the
reference charge time, e.g., that immediately after manufacturing
of the distance measuring apparatus and the correction charge time
in actual ranging, in addition to the distance data.
[0144] From the invention thus described, it will be obvious that
the invention may be varied in many ways. Such variations are not
to be regarded as a departure from the spirit and scope of the
invention, and all such modifications as would be obvious to one
skilled in the art are intended for inclusion within the scope of
the following claims.
* * * * *