Automatic focus control system

This specification discloses an energizing control of a drive element for driving a motor or the like which drives a focusing lens. The energization is controlled on the basis of the detection of whether or not the position of the focusing lens is within the quasi-in-focus state, and when the continuation of the quasi-in-focus state for a predetermined time period or more is detected, energization of the driving element is stopped.

BACKGROUND OF THE INVENTION 
1. Technical Field of the Invention 
The present invention relates to an automatic focus control system for a 
camera or the like, and more particularly to an energizing control of 
drive means for driving a focusing lens. 
2. Prior Art of the Invention 
In the conventional automatic focusing control system, in-focus ranges are 
generally set to be fairly narrow for better focusing precision. However, 
if the is-focus range in narrow, and the focus adjustment is to be 
performed manually, it may be difficult to fix the lens position within 
the in-focus range, degrading the operability of the camera. To solve the 
problem, there has been already proposed a system in which a 
quasi-in-focus range which is wider than the in-focus range is defined and 
when the lens is displaced into the quasi-in-focus range, an indicator 
indicates such state. On one hand, there has also been conventionally 
proposed a system in which once the lens position has been fixed within 
the in-focus range, further focus adjustment is not executed even if the 
lens position becomes out of the in-focus range thereafter. However, in 
these systems, the focus adjustment is not terminated until the lens 
position is fixed into the narrow in-focus range, therefore, it requires 
much time to fix the lens position within the in-focus range, due to 
camera shake or the like. In such a case, even if the lens is in the 
quasi-in-focus state, the focus adjustment operation is not completed. 
Therefore, the lens driving operation is continued, which leads to poor 
operability of the camera. 
SUMMARY OF THE INVENTION 
A first object of the present invention is to provide a focus control 
system in which, when a focusing lens is at a position within the 
quasi-in-focus range, or when it is moved to a position in such a state, 
driving of the focusing lens is stopped, and in which particularly when 
the focusing lens is continuously in the quasi-in-focus state for a 
predetermined period of time or more, energization of the drive means is 
stopped, thereby preventing unnecessary lens driving operation. 
A second object of the present invention is to provide an automatic focus 
control system wherein, when a signal is detected which signal represents 
that the focusing state of an object to be photographed through a focusing 
lens is within the quasi-in-focus state(which is near the in-focus state 
so that no trouble will be practicably caused in taking a picture), and 
when this quasi-in-focus state continues for a predetermined period of 
time or more, power supply to the drive means is stopped and energization 
to the motor is also stopped. 
A third object of the present invention is to provide an automatic focus 
control system in which the energization time for the drive means such as 
a motor or the like can be minimized, whereby the consumption of power 
energy is suppressed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1A and 1B show a first embodiment of the present invention. A 
reference numeral 1 denotes a distance detecting unit which outputs a 
distance detection signal P.sub.1 and a data confirmation signal P.sub.2. 
As shown in FIG. 1B, the distance detection signal P.sub.1 put out from 
the distance detecting unit 1 is a signal corresponding to the location of 
the focusing lens. The data confirmation signal P.sub.2 is a strobe signal 
indicative of the completion of one cycle of the distance detecting 
operation of the distance detecting unit 1. 
The distance detection signal P.sub.1 shown in FIG. 1B may be obtained by: 
focusing an image of an object to be photographed on an image sensor such 
as a CCD or the like; extracting electric charge accumulation signals at 
two points on the image sensor; performing the signal processing such as 
waveform shaping or the like for these two electric signals; and computing 
a differential signal between those two signals. The extraction of the 
distance detection signal P.sub.1 may be executed by a well-known method 
which is disclosed, for example, in Japanese patent application Laid-open 
No. 76312/1980 or the like. 
A reference numeral 100 denotes a comparison signal generating means 
including resistors 4, 5, 6, 7, and 8, and reference voltage signal 
sources +V.sub.cc and -V.sub.cc. An output signal +V.sub.1 represents a 
voltage level for setting a quasi-in-focus range on the near-focus side 
and is put out from a connection point between the resistors 4 and 5. An 
output signal +V.sub.2 represents a voltage level for setting an in-focus 
range on the near-focus side and is put out from a connection point 
between the resistors 5 and 6. An output signal -V.sub.2 represents a 
voltage level for setting an in-focus range on the far-focus side and is 
put out from a connection point between the resistors 6 and 7. An output 
signal -V.sub.1 represents a voltage level for setting a quasi-in-focus 
range on the far-focus side and is put out from a connection point between 
the resistors 7 and 8. 
A reference numeral 102 denotes quasi-in-focus state detecting means which 
comprises comparators 9 and 10 and a NOR gate 11. The level signal 
+V.sub.1 of the quasi-in-focus range on the near-focus side is supplied to 
the inversion input terminal (-) of the comparator 9. The distance 
detection signal P.sub.1 is applied to the non-inversion input terminal 
(+) thereof. 
The distance detection signal P.sub.1 is applied to the inversion input 
terminal (-) of the comparator 10 and the level signal -V.sub.1 of the 
quasi-in-focus range on the far-focus side is applied to the non-inversion 
input terminal (+) thereof. Output signals from the comparators 9 and 10 
are applied to the NOR gate 11, and its output terminal is connected to 
quasi-in-focus state continuation detecting means which will be described 
hereinlater. 
A reference numeral 104 denotes in-focus state detecting means comprising 
comparators 12 and 13 and a NOR gate 14. The output level signal +V.sub.2 
representative of the in-focus range on the near-focus side is applied to 
the inversion input terminal (-) of the comparator 12, and the distance 
detection signal P.sub.1 is applied to the non-inversion input terminal 
(+) thereof. The distance detection signal P.sub.1 is input to the 
inversion input terminal (-) of the comparator 13, and the output level 
signal -V.sub.2 indicating the in-focus range on the far-focus side is 
input to the non-inversion input terminal (+) thereof. Output signals from 
the comparators 12 and 13 are applied to the NOR gate 14, and its output 
terminal is connected to the above-mentioned quasi-in-focus state 
continuation detecting means. 
The quasi-in-focus state continuation detecting means is designated by a 
numeral 106, which comprises a D-type flip flop 15 and an AND gate 16. 
A circuit 108 for indicating the focusing state comprises inverters 21, 22 
and 23, light emitting diodes 17, 18 and 19, a resistor 20, and a constant 
voltage power supply Vc. This circuit 108 functions to indicate three 
kinds of states, i.e., near-side deviation, quasi-in-focus and far-side 
deviation, respectively, in accordance with the outputs Q.sub.1, Q.sub.2 
and Q.sub.3 from the quasi-in-focus state continuation detecting means 
106. The above-mentioned three states imply, respectively, that the 
focusing lens is positioned on the near-focus side with respect to the 
in-focus point, that it is in the quasi-in-focus state, and that it is on 
the far-focus side of the in-focus point. 
The distance detection signal P.sub.1 is also applied from the distance 
detecting unit 1 to an amplifier 2. As shown in FIG. 1B, for example, when 
the focusing lens is in a position A.sub.2 on the near-focus side and out 
of a range A.sub.1 of the in-focus state, the voltage signal +V.sub.1 
corresponding to the position A.sub.2 is applied, so that the energization 
voltage to be applied to a motor M for driving the focusing lens is 
amplified through the amplifier 2, thereby controlling the energization. 
Reference numerals 3 and 24 show OR gates, respectively. The OR gate 3 is 
connected to the amplifier 2. The OR gates 24 and 3 constitute operating 
control means for the amplifier 2. The OR gates 24 and 3 and the amplifier 
2 provide drive control means for performing the drive control of the 
motor M. 
Reference numeral 110 denotes auto-focus mode selecting means, which serves 
to select either of the two modes; a one-shot auto-focus mode, for 
example, an operational mode in which the distance detecting operation is 
performed once, in association with the release operation of a camera and 
the focusing lens is driven in accordance with the distance detecting 
operation; and a so-called servo-focus mode in which, if an object to be 
photographed moves continuously, in-focus signals are put out or the 
location of the object to be photographed is intermittently detected at 
predetermined timing to follow the movement of the object, thereby driving 
the focusing lens to the "in-focus" position. A switch 27 is connected 
between a reference signal level V.sub.b and a resistor 26, and a 
set-reset flip flop 25 is connected to the output terminal of the OR gate 
24. The Q output terminal of the flip flop 25 is connected to the OR gate 
3. 
The operation of the circuit shown in FIG. 1A will be described 
hereinbelow. The distance detection signal P.sub.1 from the distance 
detecting unit 1 is applied to each of the comparators 9, 10, 12 and 13 of 
the quasi-in-focus state detecting means 102 and the in-focus state 
detecting means 104, where each signal is compared with each of the 
comparison signals from the comparison signal generating means 100. Now 
assuming that the focusing lens locates, for example, on the near-focusing 
side from the position of the in-focus point, the distance detection 
signal P.sub.1 indicating that the focus is in the near-focus side is 
output. Since the signal level of this distance detection signal P.sub.1 
is higher than the level signal +V.sub.1 representative of the 
quasi-in-focus range on the near-focus side, the output signals of the 
comparators 9 and 12 become higher levels, while the output signals of the 
comparators 10 and 13 become lower levels. Hence, the outputs of the NOR 
gates 11 and 14 become lower levels and the data confirmation signal 
P.sub.2 is applied to the quasi-in-focus state continuation detecting 
means 106, so that a higher-level signal is output to the output terminal 
Q.sub.1 of the D-type flip flop 15. Therefore, the light emitting diode 17 
lights up to indicate the near-side deviation in which the focus is 
deviated in the near-focus direction. 
In case of the above-mentioned near-side deviation, namely, in the case 
where the distance detection signal P.sub.1 is higher than the 
quasi-in-focus level +V.sub.1, the outputs of the NOR gates 11 and 14 
become lower levels. The input of the AND gate 16 is at a lower level, and 
therefore, the output of the AND gate 16 becomes lower level, so that the 
inputs of the OR gates 24 are also at lower levels. 
If the selection switch 27 of the auto-focus mode selecting means 110 is 
turned off (that is to say, the one-shot auto-focus mode is selected), the 
set-reset flip flop 25 is reset, so that both inputs of the OR gate 3 
become lower levels. Thus, the amplifier 2 amplifies the distance 
detection signal P.sub.1, thereby driving through a motor M, the focusing 
lens (not shown) to an in-focus position. In case of one-shot auto-focus 
mode, the quasi-in-focus state and in-focus state detecting operations are 
executed once at every computation cycle of the distance detection signal, 
that is to say, synchronously with the data confirmation signal P.sub.2. 
When the lens is in the quasi-in-focus range, or when the lens having its 
focus on the near-focus side is moved into the quasi-in-focus range by the 
above-mentioned operation, and if the quasi-in-focus range is on the 
near-focus side, for example, the output level of the distance detection 
signal P.sub.1 have a value between the level +V.sub.1 representative of 
the quasi-in-focus on the near-focus side and the level +V.sub.2 
representative of the in-focus range on the near-focus side, put out from 
the comparison siganl generating means 100. Therefore, both outputs of the 
comparators 9 and 10 become lower levels and the NOR gate 11 is inverted 
to a higher level. The output of the comparator 12 becomes higher level 
and the output of the comparator 13 becomes the lower level. As a result, 
the output of the NOR gate 14 becomes lower level. 
In response to the data confirmation signal P.sub.2 from the distance 
detecting unit 1, only the output terminal Q.sub.2 of the D-type flip flop 
15 becomes a higher-level, so that the light emitting diode 22 lights up. 
At the same time, a higher-level signal is applied to the input terminal 
D.sub.4 of the D-type flip flop 15. However, the output of the output 
terminal Q.sub.4 remains at a lower level, so that the focus adjustment is 
continued. 
If, due to the camera shake or the like, the lens is not fixed into the 
in-focus range but remains in the quasi-in-focus range even upon the 
succeeding quasi-in-focus and in-focus detecting operations, the 
higher-level signals are output from both output terminals Q.sub.2 and 
Q.sub.4 of the D flip flop 15 due to the input of the data confirmation 
signal P.sub.2, causing the output of the AND gate 16 to be inverted into 
higher level. This higher-level signal is transmitted through the OR gates 
24 and 3 to the amplifier 2, thereby inhibiting the output thereof. Hence, 
the operation of the lens driving motor M is stopped. In this case, when 
the selection switch 27 is turned off, the RS flip flop 25 is set due to 
the higher-level signal of the OR gate 24; so that the higher-level signal 
to be output from the output terminal Q of the RS flip flop 25 is 
effective to maintain the inhibition of output from the amplifier 2. If 
the selection switch 27 is turned on, the RS flip flop 25 is always reset 
and will not be set even if the output of OR gate 24 becomes higher level. 
Thus, if thereafter the lens deviates from the in-focus range, the 
focusing adjustment will be done again. 
When the lens moves into the in-focus range, the comparators 12 and 13 
output the lower-level signals and the output of the NOR gate 14 becomes 
higher level, so that the output of the amplifier 2 is inhibited and the 
lens driving operation is also stopped. 
Although in the embodiment shown in FIG. 1, the quasi-in-focus state 
continuation is detected on the basis of the number of times of the 
quasi-in-focus state detection, this continuation may be detected on the 
basis of the time period. In other words, it may be detected by detecting 
whether the quasi-in-focus state continues for a predetermined time 
period. A modification in such a case will be shown in FIG. 2. As the 
quasi-in-focus state continuation detecting means, a resistor 28, a diode 
29, a capacitor 30, division resistors 31 and 32, and a comparator 33 are 
used in place of the D flip flop 15 and the AND gate 16 of FIG. 1. When 
the lens is moved into the quasi-in-focus range, an output of the NOR gate 
11 is inverted to higher level and this higher-level signal is integrated 
by the resistor 28 and capacitor 30. When the quasi-in-focus state 
continues for a predetermined time period, the integrated voltage exceeds 
the potential of division voltage of the division resistors 31 and 32. 
Thus, the comparator 33 outputs a higher-level signal to stop the lens 
driving operation. The diode 29 serves to allow the accumulated charges of 
the capacitor 30 to be discharged promptly in the case where the lens 
deviates from the quasi-in-focus range before the predetermined time 
period elapses. 
FIG. 3 shows another embodiment of the present invention, in which similar 
parts and elements as those shown in FIG. 1 are designated by the same 
reference numerals. A distance detecting unit 34 is of a well-known type 
for outputting a distance signal P.sub.3 represented by a digital code. A 
lens position signal generator 35 acts to generate a lens position signal 
P.sub.4 which is represented by a digital code and corresponds to the 
distance or position of the lens. A subtracter 36 outputs both a focus 
state signal P.sub.5 indicating the sign (positive or negative) of the 
difference between the distance signal P.sub.3 and the lens position 
signal P.sub.4 and outputs a signal P.sub.6 representing an absolute value 
of the difference. A comparator 37 compares the signal P.sub.6 with the 
level corresponding to the quasi-in-focus range. A comparator 38 compares 
the signal P.sub.6 with the level corresponding to the in-focus range. 
Reference numerals 39 and 40 denote NAND gates, reference numerals 41 and 
42 denote inverters; reference numeral 43 denotes a clock pulse generator; 
and reference 44 represents a counter. The clock pulse generator 43 and 
the counter 44 constitute an example of the quasi-in-focus state 
continuation detecting means. 
Then, the operation of the circuit of FIG. 3 will be described. When the 
signal P.sub.6 is larger than the level corresponding to the 
quasi-in-focus range, the comparator 37 outputs a higher-level signal from 
the terminal G. This output signal is transmitted to the NAND gate 39 or 
40 which is opened or closed in accordance with the signal P.sub.5 to 
energize the light emitting diode 17 or 19. In case of the near-side 
deviation, the diode 17 lights up, while, in case of the far-side 
deviation, the diode 19 lightsup. At the same time, the amplifier 2 acts 
to drive the lens driving motor M, and to perform the focusing adjustment. 
When the signal P.sub.6 is lower than the level corresponding to the 
quasi-in-focus range, the comparator 37 outputs a higher-level signal from 
the terminal L for allowing the light emitting diode 18 to light up, and 
at the same time, the reset of the counter 44 is cancelled. Thus, the 
counter 44 starts counting clock pulses and when the number of pulses 
corresponding to a predetermined time period has been counted a carry 
signal is output from the terminal C. This carry signal is applied through 
the OR gates 24 and 3 to the amplifier 2 to inhibit the output thereof. 
This causes the lens driving operation to be stopped. 
In the embodiment shown in FIG. 3, the extent of the quasi-in-focus range 
for display is equal to that of the quasi-in-focus range for stopping the 
lens driving operation, but they may be different from each other. 
The quasi-in-focus detecting means and the in-focus dectecting means may be 
modified in accordance with the type of distance detecting unit. The 
display device is not limited to the light emitting diode. The lens is not 
necessarily driven by a DC motor. 
As described above, according to the present invention, when it is detected 
that the quasi-in-focus state continues for a predetermined time period or 
more, the quasi-in-focus state continuation detecting means functions to 
stop the lens driving operation, so that the stable focusing adjustment is 
ensured irrespective of camera shake or the like. Therefore, unnecessary 
lens driving operation can be prevented and the operability is improved.