JPS63182634A - Automatic focus adjusting device - Google Patents

Abstract

PURPOSE:To improve the accuracy of a stop position to a focusing position by stopping the operation of a driving means for an optical system when a deviation detected by a focusing decision means is smaller than a set value, and updating the set value to a 2nd smaller value at a specific time after the deviation reaches the set value. CONSTITUTION:When the deviation detected by the focusing decision means JM becomes smaller than the set value, the operation of the driving means M is stopped and the means is put in a stand-by state for a specific time, so that the optical system OS almost stops or stops completely. Then the set value is updated into the 2nd smaller value. The operation quantity of the driving means M is not large from the restart of the operation of the driving means M to the restopping of the operation of the driving means when the detected deviation of the focusing decision means JM decreases below the 2nd set value. Consequently, the inertia and dead zone width of the optical system decrease and the optical system is not driven until it passes through the dead zone, so that the optical system is stopped at a position closer to the focusing position.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to driving and moving a photographing lens in a camera to a focusing position for an object, or to moving a projection lens in a projection device to a screen, which is an object. The present invention relates to an automatic focusing device that is driven and moved to a focusing position.

More specifically, it includes a light projecting means for projecting measurement light onto an object, a light receiving means for receiving the measurement light reflected from the object, and an optical system for adjusting the optical system for the object based on the intensity of light received by the light receiving means. a focus determining means for detecting a deviation from the focus position; a driving means for driving the optical system toward the in-focus position based on a detection result by the focus determining means;
The present invention relates to an automatic focus adjustment device comprising: a control means for stopping the operation of the drive means when a detected deviation by the focus determination means is less than a set value.

[Conventional technology]

In the automatic focus adjustment device described above, even if a stop signal is given to a drive means such as a motor, the optical system does not stop immediately due to the inertia of itself or the motor, so the detection deviation by the focus determination means is By comparing the detected deviation with the set value and stopping the operation of the driving means when the detected deviation is less than the set value, that is, when the optical system reaches the vicinity of the in-focus position, the optical system malfunction near the in-focus position can be avoided. Prevents stable movement. That is, the area between the positive and negative set values is a dead zone for the operation of the driving means based on the detected deviation by the focus determining means.

Conventionally, the above-mentioned setting values have been fixed, for example, when comparing voltage signals, the output voltage from a constant voltage circuit is used (for example,
(See Japanese Unexamined Patent Publication No. 54-51556).

[Problem that the invention seeks to solve]

However, in the conventional configuration described above, the setting values are fixed, so even if the inertia is large, such as when driving an optical system located far from the focus position, the focus can be focused without passing through the dead zone. In order to reliably stop near the position, the set value must be set to a relatively large value.
Therefore, it has been difficult to improve the accuracy of the stop position relative to the focal position of the optical system.

In view of the above-mentioned circumstances, an object of the present invention is to prevent unstable operation of an optical system near the in-focus position and to improve the accuracy of the stop position relative to the in-focus position.

[Means for solving problems]

A characteristic configuration of the automatic focus adjustment device according to the present invention is that the control means for stopping the operation of the drive means for the optical system when the detected deviation by the focus determining means is equal to or less than a set value, A set value updating means is provided for updating the set value to a second set value smaller than the set value after a predetermined period of time from when the set value is reached.

[For production]

That is, when the detected deviation by the focus determining means becomes less than or equal to the set value, the operation of the driving means is stopped, and by waiting for a predetermined period of time from this point on, the optical system almost or completely stops. Thereafter, by updating the set value to a smaller second set value, that is, by reducing the dead zone width, the driving means can be operated again to drive the optical system toward the in-focus position.

At this time, since the amount of operation of the drive means is not large, the amount of operation of the drive means is not large during the period from when the drive means resumes operation until the detected deviation by the focus determination means becomes equal to or less than the second set value and the operation of the drive means is stopped again. Although the inertia of the system is small and the width of the dead zone is small, the optical system is not driven until it passes through this dead zone, and moreover, the optical system is stopped at a position closer to the in-focus position.

〔Example〕

Hereinafter, the present invention will be described in detail based on the drawings.

FIG. 2 schematically shows an Overherad projector equipped with an automatic focusing device according to the invention.

The optical system (O3) of this Overherad projector is
It is composed of three lenses (la) to (lc), and these three lenses are held in a lens barrel (2). There is a helicoid screw part (2a) on the outer peripheral surface of the lens barrel (2).
is formed, and this helicoid threaded portion (2a) is
It engages with a helicoid threaded portion (3a) formed on the inner peripheral surface of the fixed outer cylinder (3).

A gear part (2b) is formed on the outer peripheral surface of the rear end of the lens barrel (2), and a drive gear (4) interlocked with the motor (M) is engaged with this gear part (2b). It matches. That is, by rotating this motor (M), the lens barrel (
2) is rotated around the optical axis (L), and its helicoid threaded part (2a) is guided by the helicoid threaded part (3a) of the fixed outer cylinder (3), so that it rotates in the direction of the optical axis (L). It is configured to move back and forth in a straight line.

On the front edge of the lens barrel (2), there is a pin (5a) implanted in one arm of an operating lever (5) that is rotatable around the axis (X).
) are in contact. Moreover, the pin (5b) implanted in the other arm of this operating lever (5) is connected to a two-segment photodiode (6
) is fitted into a long hole (7a) in the optical axis (L) direction formed in a diode holder (7) that holds the diode holder (7).

This diode holder (7) is urged to move rightward in the drawing by a spring (8), and thereby the operating lever (5) is also urged to rotate clockwise in the drawing.

When the lens barrel (2) is extended forward in the optical axis (L) direction, the operating lever (5) is rotated counterclockwise in the figure.
The diode holder (7) is pressed by the operating lever (5) and moves to the left in the figure against the biasing force of the spring (8). On the other hand, when the lens barrel (2) is retracted to the rear side in the direction of the optical axis (L), the pressure from the operating lever (5) is removed, and the diode holder (7) is moved to the right in the figure by the biasing force of the spring (8). Moving.

On the opposite side of the two-part photodiode (6) across the optical axis (L), a light emitting diode (9), which is a light emitting means constituting an automatic focus adjustment device, is provided. Also,
Two-part photodiode (6) and light emitting diode (9)
), respectively, there are condenser lenses (10) and (11
) is provided.

The light from the light emitting diode (9) is passed through the condensing lens (11)
The light is focused and projected onto the screen (12) which is the object of projection by the projector. The light reflected from the screen (12) is condensed by a condensing lens (10) and reaches the two-split photodiode (6).

When the screen (12) is in the position shown by the solid line in the figure, the reflected light from the screen (12) is condensed by the condenser lens (10) and proceeds with the solid line in the figure as the principal ray. Then, the light emitting diode image (I) formed by the condensing lens (10) is formed by the two photodiodes (6^), ( 6B).

At this time, the optical system (
O3) is located at the position shown by the solid line in the figure (12
) so that it is in focus on the diode holder (7)
, the operating lever (5), and the lens barrel (2).

With the optical system (O3) in the same position, the screen (
The imaging position of the reflected light from the screen (12) by the condenser lens (10) changes depending on the position of the screen (12) in the optical axis (L) direction. That is, when the screen (12) is closer to the position shown by the two-dot chain line in the figure, this screen (
12) is also focused with the two-dot chain line in the figure as the principal ray, and the light emitting diode image (1) is biased toward one photodiode (6A), as shown in Figure 3 (II). ing.

Furthermore, although not shown in FIG. 2, when the screen (12) is located further away than the position indicated by the solid line, the screen (12)
12), that is, the light emitting diode image (I) is biased toward the other photodiode (6B), as shown in FIG. 3(c).

The automatic focus adjustment device moves the lens barrel (2) in the optical axis (L) direction and moves the two-segment photodiode (6) in the horizontal direction in the figure in conjunction with the lens barrel (2) to move the screen (12).
By aligning the optical system (O8) with the screen (1) so that the image formation position of the reflected light from the
2).

Next, the configuration and operation of this automatic focus adjustment device will be explained using FIGS. 1, 4, and 5.

FIG. 1 shows a schematic circuit of an automatic focus adjustment device.

Figure 4 is a time chart showing the automatic focus adjustment operation from the state where the optical system (O8) is focused in front of the screen (12) as shown in Figure 3 (C); 3 is a time chart showing an automatic focus adjustment operation from a state where the optical system (O3) is focused on a point farther than the screen (12) as shown in FIG. 3(B).

In addition, in FIGS. 4 and 5, [Δy] indicates the deviation from the in-focus position, and [Δym], [Δym'],
[−Δym] and [−Δym′] are deviation values of regions corresponding to dead zones, which will be described later.

In FIG. 1, (6A) and (6B) are two photodiodes of the two-part photodiode (6) which is the light receiving means described earlier.

Each of the photodiodes (6A) and (6B) outputs a photocurrent according to the received light intensity, and the photocurrent is converted into a voltage signal and amplified by separate amplifiers (AMPI) and (AMP2). , differential amplifier (O
AMP) outputs a differential voltage [DVS].

That is, two amplifiers (AMPI), (AMP2),
And a light receiving means (6) from a differential amplifier (DAMP), etc.
The target object, the screen (1
2) constitutes a focus determining means (JM) that detects the deviation of the optical system (O8) from the in-focus position.

The above differential voltage [DVS] is input to the control means (CM) that controls the operation of the motor (formerly known as the drive means). The motor (M) is configured to be stopped when .

In this control means (CM), the differential voltage [DVS] is controlled by a pair of window comparators (WCI), (WC
2), it is input to one positive side input terminal and the other negative side input terminal. One window comparator (
Four resistors (R1
) ~ (R4) Positive side reference voltage [+Viv]
is entered. In addition, the positive terminal of the other window comparator (WC2) also has four resistors (R
1) - (R4) The negative side reference voltage [-Vw
] has been entered.

The voltage [Va] on the lower side (point 81 in the figure) of one of the window comparators (WCI) shows a negative value while the differential voltage [DVS] is smaller than the plus side reference voltage [+Vwl]. Also, the other window comparator (WC2)
The voltage [Vbl] on the downstream side (point [b] in the figure) takes a negative value while the differential voltage [DVS] is larger than the negative side reference voltage [-Vw].

As shown in Fig. 4, when the optical system (O3) is driven when the focusing position of the optical system (O3) is in front of the screen (12), the voltage [Va] is always When the differential voltage [DVS] reaches the negative reference voltage [-Vi1], the voltage [Vbl] changes from a positive value to a negative value.

In addition, as shown in FIG. 5, when the focus position of the optical system (O3) is farther than the screen (12),
O3) is driven, the voltage [Vbl] always shows a negative value, and when the differential voltage [DVS] reaches the positive reference voltage [+Vw], the voltage [νa] changes from the positive value. Changes to a negative value.

And this pair of window comparators (WCI)
, (WC2) output voltage [Va] , [Vbl
(7) The operation of the motor (M) is controlled according to the combination.

When the output voltage [Va] takes a positive value, that is, when the differential voltage [DVS] is larger than the positive reference voltage [+Vw], the motor (M) has a current [+■]. I and] are supplied, and the motor (M) is rotated in a direction to retract the lens barrel (2) backward.

Furthermore, when the output voltage [Vbl] takes a positive value, that is, the differential voltage [DVS] is the negative reference voltage [-
If the motor (M) is smaller than [-■]
A current [IM] is supplied, and the motor (M) is rotated in a direction to move the lens barrel (2) forward.

Furthermore, those two output voltages [Va] and [Vbl
When both take negative values, that is, when the differential voltage [DVS] is smaller than the positive reference voltage [+Vw] and larger than the negative reference voltage [-Vw], the motor (M ) is not supplied with current to the motor (
M) is configured to be held in a stopped state.

In other words, the plus/minus reference voltage [+Vwl].

The absolute value of [-Vw] is the set value, and the difference between the positive reference voltage [+Vw] and the negative reference voltage [-Vw] is the difference detected by the focus discrimination mechanism (JM). This is a dead zone for the operation of the motor (M) based on the voltage [DVS].

When moving the optical system (O8) to perform automatic focus adjustment, the optical system (O5) may overrun due to inertia.
In order to reliably stop the lens near the in-focus position, it is necessary to increase the width of the dead zone, that is, to increase the set value. In this case, the accuracy with which the optical system (O3) stops at the in-focus position deteriorates.

Therefore, in addition to the control mechanism (CM) described above, a focus determination mechanism (
After a predetermined period of time has elapsed since the differential voltage [DVS], which is the detection deviation detected by A setting value updating means (RM) for updating the setting value to two setting values is provided. Next, this setting value updating means (RM) will be explained.

A pair of window comparators (MCI), (WO2
) output voltages [Vdl, [Vb] are divided by two resistors (R7) and (R8) of equal resistance value,
The voltage [Vc] is applied to the base of the transistor (06). The collector voltage [Vdl] of this transistor (O6) is the differential voltage [DVS] mentioned above.
It becomes "H" level when it is within the dead zone, and becomes "L" level when it is outside the dead zone.

This collector voltage [Vdl is input to the first monostable multi-by-break (OSMI). This monostable multi-by-break (OSMI) is caused by the rise of the collector voltage [Vdl], which will be described later.
O3? The trigger is applied via a differential circuit (DIF) having a time constant longer than the pulse width [t2] of I2), and the pulse width of [t1] (for example, 1
sec) is output.

Furthermore, this one-shot pulse signal [νe]
input to the monostable multi-by-break (OSM2). This monostable multi-by-break (05M2) is triggered by the falling edge of the one-shot pulse signal [Ve], and accordingly, a one-shot signal with a pulse width of [t2] (for example, Q, about 2 seconds) is triggered. Outputs a pulse signal [Vf].

This one-shot pulse signal [νf] is applied to F ET (O5) as a switching element.

This FET (O5) is connected to one of the negative input terminals of the window comparator (MCI) to which the above-mentioned positive reference voltage [+Vw] is input, and the other to which the negative reference voltage [-νw] is input. A variable resistor (R
It is interposed with ゛).

When the one-shot pulse signal [Vf] is at the "L" level, FET (O5) is in an inactive state, and one window comparator (MCI) receives the positive reference voltage [+C], and the other window comparator The negative side reference voltage [-Vei] is input to (WO2), respectively.

Furthermore, when the one-shot pulse signal [Vf] is at the kHII level, the FET (O5) is activated, and the pair of window comparators (IIcI) and (WO2) each have a resistance value of a variable resistor (R゛). The second reference voltage [+V
w'] and [-Vw'] are input.

The second reference voltage [+Viv', [-Vw'] has an absolute value equal to the reference voltage [+Vw], [-Vw].
] and, as described above, a pair of window comparators (WCIs).

By updating the reference voltage input to (WO2), the width of the fuwaza band becomes narrower during [t2].

As a result, the motor (M) is controlled by the control means (CM) again.
operation is started, and the optical system (O3) begins to move. While the one-shot pulse signal [Ve] described above continues [t1], the optical system (O8
) has almost or completely ended its inertial movement.

Therefore, from this point on, the motor (M) is driven again to move the optical system (O3) so that the differential voltage [DVS] reaches the second reference voltage [+S] [-Vw°], which is either plus or minus.
Even if the motor (M) is stopped when the motor (M) reaches the limit, the inertia is small and the dead zone is narrow, but it can be stopped reliably without overrun, preventing unstable movement of the optical system (O3). At the same time, it is possible to improve the accuracy of stopping at the in-focus position.

Note that the setting value update described above is not limited to two stages, but may be performed over three or more stages. In the final stage, for example, in the case of the previous embodiment, the variable resistor (
By setting the resistance value of R') to zero, the set value can be set to zero,
That is, the width of the dead zone may be set to zero.

Furthermore, the duration time [tl] of the two one-shot pulse signals [Vel and [Vfl] explained in the previous embodiment.

The specific value of [t2] can be changed as appropriate to suit the load of the optical system (O8) and the performance of the motor. Alternatively, the one-shot pulse signal [Vfl may be output repeatedly.

FIG. 6 shows a pair of monostable multi-by-breaks (O3MI) described in the previous embodiment when the one-shot pulse signal [Vfl is repeatedly output.

(03M2) shows an oscillation circuit provided in place of (03M2).

Points [d] and [f] in the figure correspond to points in the circuit shown in FIG. 1 of the previous embodiment, respectively.

In the figure (RE) is a reset terminal used during initial setting.
(DIF) is a differential circuit that operates in the same way as in the previous embodiment.

This oscillation circuit consists of an oscillator (OSC), a 1/n frequency divider (D
EM), an OR circuit (OR), etc., and the seventh As shown in the figure, the pulse train signal [Vfl is outputted, and this output is stopped by inputting the reset node signal from the OR circuit (OR) to the reset input terminal (R). This results in F E T (O
5) is continuously activated for [t4] at time intervals of [t3], and the set value is updated as in the previous embodiment.

Although the above embodiment has been explained using an over-the-top projector as an example, the automatic focus adjustment device according to the present invention can also be applied to other projection devices such as slide projectors and microfilm leagues, and cameras such as still cameras and video cameras. It can be passed.

〔Effect of the invention〕

As described above, the automatic focus adjustment device according to the present invention adjusts the width of the dead zone with respect to the driving means for driving the optical system.
For example, after the driving means stops, the optical system is stopped for a period of time necessary to almost stop the optical system, and then the size is reduced so that the driving means can drive the optical system to a position closer to the in-focus position. While sufficiently preventing the movement of the optical system from becoming unstable due to passing through a dead zone due to inertia, etc., it is now possible to further increase the precision with which the optical system stops at the in-focus position.

[Brief explanation of the drawing]

The drawings show an embodiment of the automatic focus adjustment device according to the present invention, in which FIG. 1 is a schematic circuit diagram, FIG. 2 is a schematic configuration diagram of an overherad projector, and FIGS. These are front views showing the relative relationship between the split photodiode and the light emitting diode image. Figure 3 (A) shows the state where the optical system is focused on the screen, and Figure 3 (II) shows the state where the optical system is focused. Figure 3 (C) shows a state where the optical system's focus position is closer than the screen, and Figure 4 shows a state where the optical system's focus position is closer to the screen. A time chart showing a focus adjustment operation from a certain state. FIG. 5 is a time chart showing a focus adjustment operation from a state where the focusing position of the optical system is farther than the screen. FIG. 6 shows another example. Part of the circuit diagram, FIG. 7, is a time chart of output signals in the embodiment shown in FIG. (6)...Light receiving means, (9)...Light projecting means, (12)...Target, (OS)...
・・Optical system, (JM) ・・・Focus determination means, (M
)...Drive means, (CM)...Control means, (RM)...Setting value updating means.

Claims (1)

[Claims] A light projection means for projecting measurement light onto the object; a light reception means for receiving the measurement light reflected from the object; a focus discriminating means for detecting a deviation; a driving means for driving the optical system toward a focus position based on a detection result by the focus discriminating means; and a control means for stopping the operation of the drive means, the control means is configured to adjust the set value after a predetermined period of time from the time when the detected deviation by the focus determining means reaches the set value. An automatic focus adjustment device provided with a setting value updating means for updating the setting value to a second setting value smaller than the second setting value.