JPS6346401B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lens motor drive device for an autofocus camera.

Focusing in an autofocus camera is performed by controlling a lens drive motor according to the output of a focus detection circuit. Some driving methods for this lens, such as those seen in simple autofocus cameras, extend the lens to a close distance, then retract it in response to a focus detection signal and stop it at the in-focus position. The present invention is directed to a system in which the lens, which has been extended to an arbitrary position, is brought into focus by being retracted or extended. Therefore, the lens drive motor is rotated in forward and reverse directions.

Here, the focus detection signal is the signal shown in Figure 1.
It is a signal such as Vf that has a larger value on one side and a smaller value on the other side around the focal point. This is because in the case of a camera with interchangeable lenses, it is necessary to minimize the number of contacts for transmitting and receiving signals due to space limitations of the lens mount.

The present invention has been made with these points in mind, and comprises a device that drives a lens motor in forward and reverse directions by receiving a focus detection signal from a camera body.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows the basic configuration of an embodiment of the present invention. This circuit is built into the lens side,
The lens motor M is driven in forward and reverse directions by receiving a focus detection signal Vf from the camera body side. The focus detection signal Vf is, for example, a distance ∞
The value changes continuously from 0 to 0, and becomes a constant value Vs within a certain range including the in-focus point. The constant value near this focal point has the same meaning as a dead zone in servo control.

When this focus detection signal Vf is applied to the input terminal Vin, the voltage amplification circuit AMP provides a signal Vf' inverted with respect to the reference voltage to the absolute value conversion circuit AV and the comparator COMP. The absolute value circuit AV converts the signal
For example, the near-distance side signal is inverted with Vf′ as the center of the in-focus point, thereby forming a signal in which the far-distance side and the near-distance side are symmetrical about the in-focus point, that is, an absolute value signal |Vf|, and VF conversion is performed. Give to circuit V/F. The VF conversion circuit V/F is an intermittent signal whose duty amplitude is constant according to the amplitude of the absolute value signal |Vf|
Vp is formed and given to the lens motor drive circuit MD. The lens motor drive circuit MD controls the rotational speed using this intermittent signal Vp.

On the other hand, the comparator CM compares the level of the signal Vf' with the reference signal and supplies one of the two output signals to the lens motor drive circuit MD. These two output signals determine whether the lens motor M is rotated in the forward direction or in the reverse direction. For example, forward rotation causes the lens to advance, and reverse rotation causes the lens to retract.

FIG. 2 shows a concrete example of FIG. 1, and FIG. 3 shows waveforms of various parts thereof.
The voltage amplification circuit AMP is constituted by an operational amplifier _OA1 , and a focus detection signal Vf is applied to its inverting input terminal from an input terminal Vin. Focus detection signal Vf (third
As mentioned above, the figure is a voltage signal whose value changes continuously according to the lens position with the in-focus point as the reference value, and when it passes through the voltage amplification circuit AMP, it becomes an inverted signal with respect to the reference voltage (the third Figure b).

This signal is given to the absolute value conversion circuit AV. The absolute value conversion circuit AV includes an inverting amplifier circuit with a gain of 1 configured by an operational amplifier OA ₂ , a diode D ₁ for extracting a part of the output of this amplifier circuit, and a part of the output of the voltage amplifier circuit AMP. and a butt circuit consisting of a diode _D2 for.
The output of the inversion circuit (Figure 3) is a voltage amplification circuit.
It is a signal with the opposite characteristics and the same magnitude as the output of the AMP (Fig. 3), and when these two outputs are brought together via diodes D ₁ and D ₂ , a symmetrical waveform signal centered on the focused point, that is, an absolute value signal |
Vf | (Figure 3).

This absolute value signal |Vf| is given to the VF conversion circuit V/F. This conversion circuit has an integration circuit using an operational amplifier OA ₃ , a mono-multivibrator using an operational amplifier OA ₄ , and a duty control circuit using a transistor _Q1 . Among these, the integrating circuit forms an integrated output by receiving the absolute value signal |Vf|, and provides it to the mono multivibrator. The mono-multivibrator is triggered when the integral output falls to a predetermined value, forming a pulsed signal (FIG. 3). A duty control circuit changes the duty of this pulsed signal. The pulsed signal thus formed is given to the control circuit of the lens motor drive circuit MD.

In addition, the output of the voltage amplification circuit AMP is connected to a comparator.
Given to CM. This comparator CM has two comparators CM ₁ and CM ₂ , one of which produces an output when the signal Vf' exceeds (1.5 + V _U ), and the other does not produce an output when it is smaller than (1.5 - V _L ). (Figure 3,). These two outputs are given to transistors Q ₂ and Q ₃ respectively, and their characteristics are inverted.
As a result, an output that occurs when the signal Vf' exceeds (1.5+V _U ) and an output that occurs when the signal Vf' is less than (1.5-V _L ) are formed (FIG. 3). Both of these outputs are given to the control circuit of the lens motor drive circuit MD.

Lens motor control circuit MD is transistor _Q4 ~
_Q7 energizes motor M in the forward or reverse direction, and the comparator determines this direction.
This is the output of the CM, and the output of the VE conversion circuit V/F determines the rotational speed, that is, the number of rotations.

FIG. 4 shows a modification of the VF conversion circuit V/F, and this circuit consists of an integrating circuit using an operational amplifier OA ₁₁ , an operational amplifier OA ₁₂ , and a transistor Q _10.
It is composed of an oscillation circuit and an oscillation circuit. Similar to the circuit shown in FIG. 2, this circuit also forms an output whose frequency and duty change in response to changes in input voltage.

Figure 5 shows a modification of the absolute value converting circuit AV, and this circuit is composed of a characteristic inverting circuit using an operational amplifier OA ₂₁ and a differential amplifying circuit using transistors Q ₂₁ and Q ₂₂ . . In this case, the characteristic inverting circuit is the same as that shown in FIG. 2, and the differential circuit is replaced by the matching circuit of diodes D ₁ and D ₂ shown in FIG.

6 to 9 are configuration examples in which the focus detection signal is given as a current signal, and FIG. 6 shows the overall configuration. In this case, the focus detection signal is not a characteristic signal like a voltage signal, but
It is characterized by a signal that changes over + and -, and also that the absolute value conversion circuit AV has a current-voltage conversion function, and that the current-voltage conversion circuit I/V is inserted before the comparator CM. is different from the configuration shown in FIG. Utilizing a focus detection signal as a current signal has the advantage that when the camera body and lens are powered by separate power supplies, even if the power supply voltage on the lens side drops, the effect on the in-focus range is reduced.

Figure 7 shows an example of the configuration of the current-voltage converter I/V, in which a feedback resistor is connected between the inverting input terminal and the output terminal of the operational amplifier OA ₃₀ , and a reference voltage source is connected to the non-inverting input terminal. Voltage output can be obtained by connecting and applying current input Iin to the inverting input terminal.

FIG. 8 shows the absolute value conversion circuit AV in the overall configuration of FIG. 6. In this circuit,
The focus detection signal If is double-wave rectified by a diode bridge circuit made up of diodes D ₃₁ to _{D 34} via input terminals Iina and Iinb, and is applied to a current-voltage conversion circuit I/V made up of an operational amplifier OA ₃₁ to be converted into a voltage signal. . The characteristics of this voltage signal are inverted with respect to the reference voltage by a characteristic inverting circuit including an operational amplifier OA ₃₂ , and the voltage signal is used as a signal to be applied to the VF conversion circuit V/F. Note that the current signal applied to the input terminal Iina is applied to the current-voltage conversion circuit I/V to form a signal to be applied to the comparator CM (FIG. 6).

Figure 9 shows the focus detection signal as a current signal as well.
This is an example of a circuit configuration in which If is given. In this case, the absolute value conversion circuit AV is assumed to form a current output, and this current signal is directly formed into a pulse-like signal by the I/F conversion circuit I/F. ing. Therefore, the absolute value converting circuit AV consists of diodes D ₄₁ to _{D 44}
The IF conversion circuit I/F consists of a current integration circuit using an operational amplifier _OA41 , a mono multivibrator using an operational amplifier _OA42 , and a duty control circuit using a transistor _Q41 . ing.
The output of this IF conversion circuit I/F is then given to the lens motor drive circuit MD (FIGS. 1 and 2) via the transistor _Q42 .

FIG. 10 shows another example of the configuration of the VF conversion circuit V/F. In this case, an output voltage is obtained in which the output frequency is constant and only the duty varies. In other words, transistors Q ₅₁ and Q ₅₂ constitute a mono multivibrator, and the absolute value signal |Vf| of the collector of transistor Q ₅₁ is given, and the mono multivibrator changes depending on the magnitude of this absolute value signal |Vf|. Duty control is performed. and,
This mono multivibrator is a transistor
A trigger is performed by applying a constant frequency pulse generated by an astable multivibrator formed by Q ₅₃ and Q ₅₄ via a differential amplifier circuit formed by a transistor Q ₅₅ . Therefore, the output of the mono multivibrator has a constant frequency and a duty controlled by the absolute value signal |Vf|.

FIG. 11 shows signal waveforms at various parts of the circuit shown in FIG. 10. When the output of the astable multivibrator passes through the differential amplifier circuit, it becomes a trigger pulse and is applied to the monomultivibrator.
On the other hand, if the absolute value signal |Vf| gradually changes in value as shown _by It changes depending on the magnitude of the signal |Vf|, and as a result, the output of the mono multivibrator has a constant frequency but a duty that changes depending on the absolute value signal |Vf|.

FIG. 12 shows a configuration example of a VF conversion circuit V/F that can be replaced with the VF conversion circuit V/F in FIG. ₁₀ , in which the absolute value signal |Vf| Transistor Q ₆₁ ,
The output side of the mono multivibrator by Q ₆₂ is given to the base of the transistor Q ₆₂ .

FIG. 13 shows signal waveforms of various parts of the circuit in FIG. 12. Looking at the waveform corresponding to the waveform in FIG. 11, the falling voltage does not change, but the slope of the rising voltage changes as an absolute value signal |Vf| In other words, it can be seen that it changes depending on the waveform. As a result, the output voltage of the mono-multivibrator has a constant frequency and a duty that changes in accordance with the absolute value signal. In the figure, the waveform is, for example, a trigger pulse obtained by extracting a constant frequency signal given from an astable multivibrator through a differentiating circuit, and the waveform is an absolute value signal |Vf|, that is, a voltage signal obtained by inverting the waveform with respect to a reference voltage. It is.

As described above, the present invention is provided with a focus detection signal that is unipolar and takes a predetermined value at the focused point, and other values continuously change depending on the lens position. A pulse-like signal with a constant amplitude of duty corresponding to this absolute value signal is formed and used to control the rotational speed of the lens motor, and the value of the in-focus point of the focus detection signal is used as a reference. Since the level is detected and this detection signal is used to control the rotation direction of the lens motor, there is only one signal transmission path other than the ground between the camera body and the lens.
It is possible to provide an autofocus camera in which the number of contacts in a lens mount is minimized. In addition, the amplitude of the pulse signal for controlling the rotational speed of the lens motor is kept constant, and the rotational speed is changed by duty control, so power supply voltage can be applied to the lens motor even when starting it, which prevents it from being unable to start due to insufficient voltage. It can be prevented.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of the configuration of a device according to the present invention, Fig. 2 is a circuit diagram showing a more specific version of Fig. 1, and Fig. 3 is an explanation showing waveforms of various parts of the circuit in Fig. 2. Figures 4 and 4 are VFs in Figures 1 and 2.
Circuit diagram showing another configuration example of the conversion circuit V/F, No. 5
The figures are a circuit diagram showing another example of the configuration of the absolute value conversion circuit AV in FIGS. 1 and 2, FIG. 6 is a block diagram showing an example of the configuration when the focus detection signal is given as a current signal, and FIG. The figure is a circuit diagram showing an example of the configuration of a current-voltage conversion circuit, FIG. 8 is a circuit diagram showing an example of the configuration of an absolute value converting circuit when the focus detection signal is given as a current signal, and FIG. A circuit diagram showing a combination configuration of an absolute value converting circuit, a current frequency converting circuit, and a current-voltage converting circuit when a current signal is given as a current signal, and FIG. 10 is a VF converting circuit V/
11 is a signal waveform diagram of each part of the circuit in FIG. 10, FIG. 12 is a circuit diagram showing another configuration of the VF conversion circuit VF, and FIG. 13 is a diagram of FIG. 12. FIG. 3 is a signal waveform diagram of each part of the circuit. OA...Operation amplifier, Q...Transistor, D...Diode, Vf...Focus detection signal (voltage), |Vf|...
Absolute value signal, If...Focus detection signal (current).

Claims (1)

[Claims] 1. In the lens motor drive circuit of an autofocus camera, which drives the lens motor to perform focusing when a focus detection signal is given, a predetermined value is set at the focused point, and other values are continuously changed according to the lens position. A power supply voltage is unipolar when a focus detection signal is given, and an absolute value converting circuit converts the focus detection signal into an absolute value with reference to the value of the in-focus point. a conversion circuit that forms an intermittent signal with a constant amplitude of duty corresponding to the signal; and a comparator that detects the sign based on the value of the focused point of the focus detection signal and forms a signal for driving the lens motor forward or reverse. and a lens motor drive circuit for controlling the rotation speed according to the output of the conversion circuit and the rotation direction according to the output of the comparator.