Rangefinder apparatus

Details Rangefinder apparatus Rangefinder apparatus

1999-10-26

2001-07-10

Buczinski, Stephen C. (Department: 3662)

Optics: measuring and testing

Range or remote distance finding

Triangulation ranging to a point with one projected beam

C396S098000, C396S106000, C396S120000, C396S625000

Reexamination Certificate

active

06259514

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rangefinder apparatus for measuring the distance to an object, and, in particular, to an active rangefinder apparatus suitably used in a camera or the like.
2. Related Background Art
In active type rangefinder apparatus used in cameras and the like, an infrared light-emitting diode (IRED) projects a luminous flux toward an object to be measured, the reflected light of thus projected luminous flux is received by a position sensitive detector (PSD), a signal outputted from the PSD is arithmetically processed by a signal processing circuit and an arithmetic circuit and then is outputted as distance information, and the distance to the object is detected by a CPU. In general, since errors may occur when the distance is measured upon a single light-projecting operation, light is projected a plurality of times so as to obtain a plurality of distance information items, which are then integrated by an integrating circuit and averaged.
As such an active type rangefinder apparatus, one shown in
FIG. 1
has conventionally been known.
FIG. 1
is a configurational view of the rangefinder apparatus in accordance with first prior art.
In the rangefinder apparatus shown in this drawing, under the control of a CPU
110
, a driver
112
drives an IRED
114
so as to make it output infrared light, which is then projected through a light-projecting lens
201
to an object to be measured. The infrared light reflected by the object is collected by a PSD
116
by way of a light-receiving lens
202
, and the PSD
116
outputs two signals I
1
and I
2
according to the position at which the reflected light of the infrared light is received. A first signal processing circuit
118
eliminates a steady-state light component contained in the signal I
1
which becomes a noise, whereas a second signal processing circuit
120
eliminates a steady-state light component contained in the signal I
2
which becomes a noise.
According to the signals I
1
and I
2
from which the steady-state light components have been eliminated, an arithmetic circuit
132
determines an output ratio (I
1
/(I
1
+I
2
)) by an arithmetic operation, and outputs an output ratio signal corresponding to the distance to the object. An integrating circuit
134
integrates the output ratio signals thus outputted from the arithmetic circuit
132
a plurality of times, thereby improving the S/N ratio. The signal outputted from this integrating circuit
134
(hereinafter referred to as “AF signal”) corresponds to the distance to the object. Then, according to the AF signal outputted from the integrating circuit
134
, the CPU
110
determines a distance signal by carrying out a predetermined arithmetic operation, and controls a lens driving circuit
136
according to this distance signal, so as to move a lens
138
to an in-focus position.
FIG. 2
is a graph showing the relationship between the AF signal outputted from the integrating circuit
134
in this first prior art and the distance to the object. In this graph, the abscissa indicates the reciprocal (1/L) of the distance L to the object, whereas the ordinate indicates the output ratio (I
1
/(I
1
+I
2
)), i.e., AF signal. As shown in this graph, the output ratio has substantially a linear relationship with respect to the reciprocal (1/L) of the distance L at a certain distance L
4
or less, such that the output ratio decreases as the distance L is longer (1/L is smaller). At the distance L
4
or greater, by contrast, the influence of the noise component increases as the distance L is greater. Letting I
n
(I
n
0) be the noise component, the output ratio is (I
1
+I
n
)/(I
1
+I
n
+I
2
+I
n
), whereby the output ratio would shift so as to increase (toward an output ratio of 50%) at the distance L
4
or greater. Also, since I
n
occurs randomly, it becomes unstable depending on the distance measuring condition. It is due to the fact that, as the distance L increases, the intensity of reflected light received by the PSD
116
decreases, whereby the noise component I
n
becomes relatively greater. If such a phenomenon occurs, the distance to the object L cannot be determined uniquely from the output ratio.
Therefore, as shown in
FIG. 3
, a clamping circuit
13
which outputs a clamp signal I
c
if the far-side signal I
2
outputted from the second signal processing circuit
120
is lower than the clamp signal I
c
is disposed between the second signal processing circuit
120
and the arithmetic circuit
132
. Even in this case, however, as shown in
FIG. 4
which will be explained later, the distance output is fixed at a certain constant distance on the far distance side, whereby the deviation from the designed value may become greater.
Hence, as a rangefinder apparatus overcoming such a problem, the following one has been known.
FIG. 5
is a configurational view of the rangefinder apparatus in accordance with the second prior art. This drawings shows the light-receiving side alone. In the rangefinder apparatus shown in this drawing, the signals I
1
and I
2
outputted from a PSD
140
, having their steady-state light components eliminated therefrom by their respective steady-state light eliminating circuits
142
and
144
, are inputted to both of arithmetic circuits
146
and
148
. According to the signals I
1
and I
2
with no steady-state light components, the arithmetic circuit
146
carries out an arithmetic operation of I
1
/(I
1
+I
2
), so as to determine the output ratio, and an integrating circuit
152
integrates this output ratio. On the other hand, an arithmetic circuit
148
carries out an arithmetic operation of I
1
+I
2
, so as to determine the quantity of light, and an integrating circuit
152
integrates this quantity of light. Then, a selecting unit
160
selects one of the output ratio and the quantity of light, and determines, based thereon, the distance to the object to be measured. Here, the selecting unit
160
is a processing operation in a CPU.
FIG. 6
is a configurational view of the rangefinder apparatus in accordance with the third prior art. This drawings shows the light-receiving side alone. In the rangefinder apparatus shown in this drawing, the signals I
1
and I
2
outputted from a PSD
170
, having their steady-state light components eliminated therefrom by their respective steady-state light eliminating circuits
172
and
174
, are inputted to one end of a switch
176
. The switch
176
is controlled by a CPU, and inputs one of the outputs of the steady-state light eliminating circuits
172
and
174
to an integrating circuit
178
. The integrating circuit
178
integrates one of the inputted signals I
1
and I
2
, whereas an arithmetic unit
180
carries out an arithmetic operation of I
1
/(I
1
+I
2
) according to the result of integration, so as to determine the output ratio. On the other hand, an arithmetic unit
182
carries out an arithmetic operation of I
1
+I
2
, so as to determine the quantity of light. Then, a selecting unit
184
selects one of the output ratio and the quantity of light, and determines, based thereon, the distance to the object to be measured. Here, the arithmetic units
180
,
182
and the selecting unit
184
are processing operations in the CPU.
In both of the rangefinder apparatus in accordance with the second and third prior art examples (FIGS.
5
and
6
), the distance L to the object to be measured is determined according to the output ratio (I
1
/(I
1
+I
2
)) and the light quantity (I
1
+I
2
) when the distance L is shorter and longer, respectively. Such a configuration makes it possible to uniquely determine the distance L.
SUMMARY OF THE INVENTION
As explained in the foregoing, both of the rangefinder apparatus in accordance with the second and third prior art examples (
FIGS. 5 and 6
) overcome the problem of the rangefinder apparatus in accordance with the first prior art (FIGS.
1
and
3
). However, two sets of arithmetic circuits and two sets of integrating circ

Affiliated with

Also associated with

Rating

Rangefinder apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Rangefinder apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rangefinder apparatus will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2501589