JPH0474684B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a camera system comprising a plurality of photographic lens structures and a camera body.

Conventionally, one driving method for the photographing lens of an automatic focusing device is to drive the photographing lens at high speed when the subject is relatively out of focus.
It has been proposed to solve the conflicting problems of response speed and braking of the photographing lens in relation to the time to focus by driving the photographing lens to the in-focus position at low speed when the object is close to being in focus. .
For this reason, methods have been used to lower the driving voltage of the photographing lens driving motor near the focal point, or to drive the motor intermittently using pulses to lower the driving speed. An example of the latter is the applicant's Japanese Patent Application Laid-Open No. 1983-
There is a specific example in the working example of 46216. There is also a method in which a photographing lens moving motor is driven based on the amount of deviation of the image plane from the in-focus position by the photographing lens to move the photographing lens to the in-focus position. However, these methods take into account that the gear ratio of the transmission gear used to drive the lens, the friction generated along the way, and the weight and moment of inertia of the mechanical system vary depending on the lens structure used. Therefore, as mentioned above, even if the drive circuit is controlled using the same drive voltage and drive pulse, the drive speed and control characteristics will differ depending on the lens, that is, the drive characteristics of the photographic lens will differ, and the optimal drive will be determined for each photographic lens used. The drawback was that no method was available. For example, if the moving speed of the photographic lens is too fast, even the brakes will not be able to control it sufficiently, and there is a risk that the photographic lens will pass through the in-focus point. If the braking force of the brake is insufficient, hunting may occur repeatedly. On the other hand, if the moving speed of the lens is too slow, the lens will not pass the in-focus point or hunt, but it will take a long time to focus, resulting in poor responsiveness.

In order to solve these drawbacks, the present invention drives the taking lens moving motor with a motor drive current that is changed according to the driving characteristics of the taking lens, thereby increasing the response speed of the taking lens in each taking lens assembly. The objective is to obtain a camera system with appropriate braking characteristics.

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

FIG. 1 is an overall diagram of a servo system of an embodiment of an automatic focusing device, and each function is represented by blocks. An outline of its operation will be explained below.

Light passing through the photographing lens 1 in the photographing lens assembly passes through the optical system of an automatic focusing device (not shown) and forms an image on a sensor 2 constituted by a CCD or the like. Sensor 2 decomposes this optical image into pixels, detects them, and sends them to A/D.
Output to converter 3. The A/D converted pixel output is read into the arithmetic unit 4, and the distance of the photographing lens 1 from the in-focus position is calculated by known means. This calculation result is output to the control device 5, and based on this, the device 5 outputs a control output to the drive circuit 6 to control the photographing lens 1 to be driven to the in-focus position. The photographic lens 1 has a drive motor 7
The photographic lens 1 is moved to the in-focus position by
The amount of movement is detected by a movement amount sensor 8 and fed back to the control device 5. Movement amount sensor 8
is a light emitter 8a, a light receiver 8b, and a rotating plate 8 between them.
This rotating plate 8c is composed of a motor 7
, and slit-shaped light transmitting portions and light blocking portions are alternately formed along the outer circumference. As the motor 7 rotates, the movement sensor 8 generates a number of pulse signals corresponding to the rotation amount and sends them to the control device 5. This pulse signal is called a feedback pulse signal.

The number of pulses of this feedback pulse signal corresponds to the amount of rotation of the motor and the amount of movement of the photographing lens, so it ultimately corresponds to the amount of movement of the subject image due to the movement of the photographing lens. .

The control device 5 outputs a control output to the drive circuit 6 so as to apply a brake to the drive motor 7 which detects that the above calculation result and the number of feedback pulses have a predetermined relationship, and releases the brake after a certain period of time. to end the servo. This fixed time is the time necessary for the motor to stop reliably by the brake. After one servo operation is completed, the same operation is repeated from the first distance measurement operation.

In addition, in this embodiment with the above configuration, the device 2,
3, 4, 5 are inside the camera body, devices 6, 7, 8
a, 8b, 8c, and the photographing lens 1 are respectively arranged in an exchangeable photographing lens structure.

FIG. 2 shows a specific example of the configuration of the control circuit.

The calculation device 4 determines the front and rear focus and the amount of image plane deviation (the amount of deviation between the actual subject image position and the planned focal plane).
is output to the latch circuit 51. The circuit 51 sends an image plane shift amount signal to digital comparators 52 and 53, and sends a front and back pin signal (a signal for rotating the motor forward or reverse) to OR gates 54 and 55. Specifically, L level and H level signals are sent to gates 54 and 55 as front pin signals, and H level and L level signals are sent to gates 54 and 55, respectively, as rear pin signals. When control is started, counter 56 counts feedback pulses from terminal _T1 . As described above, the number of pulses of this feedback pulse signal represents the amount of movement of the subject image by the photographing lens (hereinafter referred to as the amount of image plane movement) accompanying the movement of the photographing lens. The digital comparator 52 compares the image plane shift amount signal of the latch circuit 51 with the count value of the counter 56, and when the count value, that is, the image plane movement amount approaches the image plane shift amount to a predetermined value, the image plane shift amount is determined as the image plane shift amount. When the difference from the image plane movement amount reaches a predetermined amount, it is assumed that the photographing lens 1 has been moved to a predetermined vicinity of the in-focus position, and an H level output is output to the NAND gate 57.

Digital comparator 52 is NAND gate 5
When an H level output is output to the pulse generator 7, the pulse output of the pulse generator 58 is inverted through the NAND gate 57 and applied to the OR gate 59.

On the other hand, when the count value of the counter 56, that is, the amount of image plane movement matches the image plane shift amount signal, the digital comparator 53 detects this and outputs an H level output indicating that the photographing lens has reached the in-focus position. This is output to OR gates 54, 55, 59 and also triggers monostable multi 60. The monostable multi 60 outputs a signal that becomes L level for the braking time _t3 to the AND gates 61 and 62, and
AND gates 61 and 62 each have an OR gate 5
4, 59, and the outputs of OR gates 55 and 59 are input.

Because of the above, the output of the digital comparator 53 is at L level outside the vicinity of the in-focus point.
OR gates 54 and 55 are set to H depending on the front and rear pins, respectively.
On the other hand, since the output of digital comparator 52 is L level, both NAND gate 57 and OR gate 59 output H level, and monostable multi 60 also outputs H level. Therefore, the outputs of the OR gates 54 and 55 are output as they are to the terminals T ₂ and T ₃ .

Next, as mentioned above, NAND
A pulse output is output from the gate 57 to the OR gate 59, and on the other hand, since the output of the digital comparator 53 is at L level, the OR gate 59 receives this pulse.
Inform AND gates 61 and 62. Moreover, the monostable multi 60 outputs H level, and the OR gate 54,
Since one of the gates 55 outputs an H level depending on the front and rear pins, a pulse is output from either of the AND gates 61 and 62 to which this H level output is input. Therefore, pulse driving is performed during this period.

When the focus is finally focused, the output of the digital comparator 53 becomes H level, and therefore the OR gate 54,
The outputs of 55 and 59 are all at H level. Therefore, the focused direct brake pulse (L level)
is monostable multi 60 to AND gate 61, 62
L level is applied to terminals T 2 and T ₃ during the period when T ₂ and T 3 are applied to apply the brake, but after that, H level output is output from the monostable multi 60 and terminals T 2 and T 3 are applied with a brake.
Both T ₂ and T ₃ become H level and the servo ends.

The above situation is shown in the time chart of FIG.

FIG. 4 shows a specific example of a drive circuit 6 that uses the control signal from the control device 5 shown in FIG. 2 as is without correction. It is provided in the structure 6. The operation will be explained below.

Terminals T ₂ and T ₃ are input terminals for control signals from the control device 5 of FIG. Here, the control signal is assumed to be input as a digital signal, and the L level corresponds to OV (GND), and the H level corresponds to a voltage higher than V _CC +V _BE (V _BE is the base-emitter voltage of the transistor). Approximately 0.6V at normal potential between
V _CC is the supply voltage).

The operation modes will be explained for each type of control signal applied to the control terminals T ₂ and T ₃ .

(i) When H level control signals are applied to both terminals T ₂ and T ₃ - (standby state) PNP transistors Q ₁ , Q ₂ and Q ₇ , Q ₈ have resistors R ₁ , R ₂ , H level voltage is applied through R ₃ , R ₆ , R ₇ , and R ₈ , so all are OFF.
becomes. Therefore, the PNP transistors Q ₃ , Q ₅ and the base of the bridge are each resistor.
NPN transistors Q ₄ , Q ₆ also connected to the collectors of transistors Q ₇ , Q ₂ via R ₅ , R ₄
It is turned OFF and motor M is not supplied with power and remains stationary. In this case, all of the transistors in the circuit are
It is OFF, the current consumption of the circuit is 0, and the servo is in standby mode.

(ii) When an L level control signal is applied to terminal T ₂ and an H level control signal is applied to terminal T ₃ (forward rotation drive), current is supplied to the base of transistor Q ₂ via resistor R ₃ and transistor Q ₂ turns on.
As a result, transistors Q ₃ and Q ₆ are turned on, and current flows to motor M in the direction of arrow A, driving motor M. On the other hand, transistors Q ₇ and Q ₈
is OFF, so transistors Q ₄ and Q ₅ are OFF
are doing. Also, at this time, transistor _Q1 is turned on, but since transistors _Q5 and _Q7 are turned off, there is no effect on the circuit operation.

(ii) When an H level control signal is applied to terminal T ₂ and an L level control signal is applied to terminal T ₃ - (reverse rotation drive) The circuit operation is opposite to case (ii), and transistors Q ₄ and Q ₅ , Q ₇ , and Q ₈ are turned on, and all other transistors are turned off, in the direction of arrow B, i.e. (ii)
The motor drive current flows in the opposite direction to that in case (ii), and the motor M is driven to rotate in the opposite direction to that in case (ii).

(iv) When L level control signals are applied to both terminals T ₂ and T ₃ - (brake operation) Transistors Q ₂ and Q ₇ turn on, but at the same time transistors Q ₁ and Q ₈ also turn on, so transistor Q ₇ The emitter current of transistor Q 2 is supplied entirely from transistor Q ₁ and the emitter current of transistor Q ₂ is supplied from transistor Q ₈ . Also, transistors Q ₁ and Q ₈
Since the V _CE saturation voltage is smaller than _the V _BE required to turn on transistors Q ₅ and Q ₃ ,
_Q5 is turned off, and only transistors _Q4 and _Q6 are turned on.
A loop consisting of transistors _Q4 and _Q6 and motor M acts to brake and control motor M while it is being driven. This is because after the motor drive current is cut off, the motor M, which is rotating due to inertia, temporarily becomes a generator and current flows through the short circuit loop, and the rotational energy is released as thermal energy, causing the motor M to rotate due to inertia.
A brake is applied to the rotation of the At this time, due to the rotation of the motor M, one of the transistors Q ₄ and Q ₆ is in reverse transistor mode (the roles of the emitter and collector are reversed, and in the case of an NPN transistor, current flows from the emitter to the collector). It's working.

On the other hand, the light emitting diode LED ₁ and the phototransistor Q ₁₀ constitute a light emitter 8a and a light receiver 8b in FIG. 1, respectively.

If at least one of terminals T ₂ and T ₃ is at L level, the mode base of (ii), (iii), and (iv) above is the resistance R ₉
The transistor Q ₉ connected to _the terminal T ₃ via the diode D 3 and to the terminal T ₂ via the resistor R ₉ and the diode D ₄ is turned on, so current flows through the resistor R ₁₀ and the light emitting diode LED ₁ emits light. do. Therefore, while the motor is being driven, the amount of movement of the photographic lens 1 is detected by a photointerrupter composed of a light emitting diode LED ₁ and a phototransistor _Q10 , and a terminal T connected to ground via a resistor _R11 is detected. A feedback pulse signal appears at ₁ .
This terminal _T1 is an output terminal for sending a feedback pulse signal to the control device 5.

The static control mode has been explained above, but when the taking lens is within the vicinity of the in-focus position, it is necessary to reduce the driving speed of the taking lens to improve braking at the in-focus point. There is a dynamic mode.

This will be explained using the time chart shown in FIG. In the period _t1 in the figure, the static mode (ii) or (iii) is mentioned above, and one of the terminals _T2 and _T3 is at H level and the other is at L level, and the motor rotates at full speed. However, when the control device 5 detects from the feedback pulse count that the photographing lens has been driven near the in-focus point, the control becomes the pulse drive mode indicated by the period _t2 . In other words, one of terminals T ₂ and T ₃ remains at L level, and the other terminal goes to H level and L.
Repeat levels periodically. Therefore, when this other terminal is at L level, the motor is braked, and when this other terminal is at H level, the motor is driven. In other words, since the static modes (i) and (iv) described above are repeated alternately, the motor energization time is reduced compared to cases (ii) and (iii), and the lens driving speed is slower than during period _t1 . .
When the photographic lens is driven to the in-focus point, terminal T ₂
The application of the L level signal to _T3 continues for a braking period _t3 , and the motor is controlled and suddenly stops. Since one control input is at L level during all periods t ₁ , t ₂ , and t ₃ , the light emitting diode is not activated while the photographic lens is being driven.
The generation of the feedback pulse with LED ₁ ON is guaranteed (the motor is stopped during time _t3 , so it has no practical meaning).

In the above description of dynamic drive mode _t2 , the motor is decelerated by repeating braking and driving in a pulsed manner, but there is also a method of repeating driving and stopping in a pulsed manner without using the brake. At this time, one control input is at H level between _t1 and _t2 , the other is at L level during _t1 , and pulsed during _t2 . In this case, the above-mentioned modes (i) and (ii) or (iii) are repeated in a pulsed manner. However, in this case, in the circuit shown in Figure 4, the light emitting diode
Since LED ₁ turns ON and OFF during t ₂ , which interferes with the generation of feedback pulses, an appropriate time constant circuit is added to keep the light emitting diode from turning ON and OFF during t ₂ .
You need to make sure that LED ₁ stays ON. Here, the following explanation will be given by taking a control signal as shown in FIG. 3 as an example. Further, the duty of the pulse during t ₂ is assumed to be 50%.

As described above, in the drive circuit 6 of FIG. 4 provided in the lens assembly having a photographing lens with a relatively short focal length, the control signal during the pulse drive period is generated from the pulse generator 58 of FIG. The motor is controlled using pulses with a duty of 50%. However, in a lens structure where the driving characteristics of the photographing lens are different, even if the motor is driven by the same control input as shown in Fig. 3, the control characteristics of the photographing lens will be different, so it is necessary to compensate for this. It is necessary to consider a control method. For this reason, the duty ratio of the drive pulse at t ₂ in Figure 3 is changed in the lens drive circuit according to the drive characteristics of the lens used, and the moving speed of the lens near the focal point, more precisely, the image of the imaging plane. One possible method is to adjust the surface movement speed to an appropriate level. In general, it is possible to raise or lower the pulse deuter at _t2 , but here we will consider a lens structure with a large lens such as a long focal length lens, and increase the driving time at _t2 and reduce the braking time. Do it like this. This is because a large lens such as a long focal length lens generally has a large mechanical load, so that the speed is significantly lower with 50% duty pulse drive at _t2 than the speed with continuous drive at _t1 .

FIG. 5 shows an example of a drive circuit that includes a function of changing the duty of input pulses and is provided within a lens assembly having a large lens. The circuit in Figure 5 has a configuration in which a circuit for changing the pulse duty (encircled by a broken line in the diagram) is added to the circuit in Figure 4, so the explanation of this added circuit is shown in the time chart in Figure 6. Do it together. When terminal _T2 rises from L level to H level, transistor _Q11
immediately turns on, instantly discharging capacitor _C1 and turning off transistor _Q12 .
Therefore, the base of transistor _Q12 is a resistor
R ₁₄ brings it to ground potential and the transistor
_Q13 is turned OFF as shown by the lower line in Figure 6.
For diode _D7 , the H level input of terminal _T2 is V _CC +
This is to prevent the voltage from rising above V _D (conducting voltage of the diode), thereby preventing the terminal T ₂
By clamping the unnecessarily high H level voltage of
When an H level is applied to the terminal _T2 , the capacitor _C1 is reversely charged to prevent the base of the transistor _Q12 from becoming higher than V _CC as shown by the line in FIG. However, terminal T ₂ (T ₃ )
When is at H level, it is assumed that there is a signal impedance of an appropriate magnitude. Next, when the terminal T ₂ rises to the L level, the transistor Q ₁₁ is turned off, and the capacitor C ₁ begins to be charged through the diode D ₅ and the resistor R ₁₂ . The time when terminal _T2 becomes L level is t
= 0, and the voltage V _B at the base of the transistor Q ₁₂ is determined as follows.

V _B = V _CC・exp(-t/τ) (τ=C ₁・R ₁₂ ) Here, ignoring the conduction voltage of diode D ₅ , the signal source when terminal T ₂ (T ₃ ) is at L level Impedance was set to 0.

While V _B decreases with a time constant τ as shown by the line in FIG. 6, the time comes to turn on the transistor _Q12 . If the base-emitter voltage required to turn on transistor _Q12 is V _BE , then t ₀ = τlnV _CC /V _CC −V _BE After time from t ₂ o, transistor Q ₁₂ turns on.
and turns on transistor _Q13 . Therefore, during the pulse drive at _t2 in FIG. 3, the pulse signal from the control device 5 has an H level time _t0 extended and an L level time _t0 shortened. This situation is the 6th
They are drawn on the top and bottom lines of the diagram. The explanation so far has been about the pulse input of terminal _T2 , but
Since the circuit is left-right symmetrical, it is exactly the same when a pulse is input to terminal _T3 . Therefore, regarding the broken line portion on the right side of FIG. 5, each element is indicated by a reference numeral, and the explanation thereof will be omitted. However, the time constant τ'=C ₂ · R ₁₇ of the pulse expansion on the terminal T ₃ side must be equal to C ₁ ·R ₁₂ to eliminate the difference in speed depending on the driving direction.
Note that if the mechanical load on the motor differs depending on the driving direction due to the structure of the photographic lens structure, τ and τ' can be changed to compensate for this. If we consider that the transistors Q ₁₃ and Q ₁₄ in FIG. 5 control the terminals T ₂ and T ₃ in FIG.
Transistor Q ₁₃ due to pulse duty change
(Q ₁₄ )'s OFF time t ₀ is extended, the motor drive time becomes longer, and the braking time is shortened by that amount, which increases the average torque of the motor during pulse drive at t ₂ in Figure 6. Recognize.

The above explanation assumes the control signal shown in FIG. 3, but the pulse expansion circuit in the circuit shown in FIG. 5 operates in exactly the same way even with the aforementioned pulse drive without applying the brake. Furthermore, during full-speed operation at t ₁ and braking at t ₃ in FIG. 3, the circuit in FIG. 5 operates in the same way as the circuit in FIG. 4, if a slight time delay is ignored. Therefore, if the drive circuit shown in FIG. 5 is used in a lens structure having a lens with a large mechanical load, such as a long focal length lens, and the time constant τ is determined according to the magnitude of the load, etc.
It is possible to compensate for the fact that the driving speed becomes extremely slow during pulse driving near the focal point, resulting in poor servo responsiveness.

The circuit for extending the period of the H level of the pulse has been described above with reference to FIG.
A circuit for reducing the speed is also considered, and this can be used when it is necessary to reduce the driving speed during pulse driving.

In other words, if it is determined that pulse drive with a duty of 50% is to be performed for a standard lens as described above, then the duty must be increased for a lens assembly that has a photographic lens whose mechanical load on the lens drive system is sufficiently smaller than that of the standard lens. It is desirable to make it small. In this way, it is possible to avoid cases where braking becomes insufficient and the vehicle passes past the focal point or repeatedly hunts.

By the way, switch SW ₁ in Figures 4 and 5 is _a focus lock switch.
When turned on, the emitters of transistors Q ₄ and Q ₆ are connected to terminals T ₂ and T ₃ via diodes D ₁ and D ₂ , respectively, and enter the brake mode, and the photographing lens is fixed regardless of the signals from terminals T ₂ and T ₃ . .

An embodiment of the present invention has been described above with reference to FIGS. 1 to 6. In this embodiment, a circuit for changing the power supply time of the lens drive motor in accordance with the drive characteristics of the photographic lens is installed on the lens structure side. Since it is included in the drive circuit installed on the camera body side, the control output of the control device installed on the camera body side can be standardized regardless of the type of photographic lens on the lens structure side, making it easy to convert the control device into an IC or unit. It will be advantageous.

Incidentally, in the above embodiment, the duty ratio is changed in accordance with the driving characteristics of the photographing lens so that the responsiveness and braking characteristics of the photographing lens are made appropriate, but a method of changing the voltage of the motor drive current may also be considered. In addition, an expansion or compression circuit was included in each lens structure (sometimes it was not included, as in the example lens structure shown in Figure 4), and the motor drive current was varied on each lens structure. A device with this function is installed on the camera body side, and the camera body side reads the type of photographic lens each time, changes the motor drive current on the camera body side based on its drive characteristics, and sends it to the lens body side. Another possible method is to control and drive the motor.

Conversely, the control device can also be provided on the lens assembly side, and the pulse generation means included therein can generate drive pulses that have already read the drive characteristics of the photographing lens.

Furthermore, in the above embodiment, as the focus adjustment state,
Detects the direction of deviation from the in-focus position, the amount of image plane deviation, and whether the photographic lens is within or outside a predetermined range near the in-focus position, and drives the photographic lens in the direction of the in-focus position within this range. The speed is reduced compared to that outside the range, and the photographing lens is moved to the in-focus position.
Then, within a predetermined nearby range, the motor was driven with a motor drive current that was changed according to the drive characteristics of the photographic lens, but the type of automatic focusing device is not limited to this; Any type of device may be used as long as it detects the focus and drives the focusing lens of the interchangeable lens.

As described above, according to the present invention, since the pulse generating means and the duty changing means are provided, even if the driving characteristics necessary to drive the photographing lens differ depending on the photographic lens structure, the pulse generation means and the duty changing means are provided, so that even if the driving characteristics necessary for driving the photographing lens differ depending on the photographic lens structure, the pulse generation means can be generated from the camera side. A drive pulse with a predetermined duty ratio can be changed to a drive pulse with a duty ratio corresponding to the drive characteristics of the lens structure, and each photographic lens can be moved to the in-focus position at the optimal speed, making it an excellent photographic lens. The responsiveness and braking characteristics can be obtained. In addition, since the pulse generation means is provided on the camera side and the duty changing means is provided on the photographic lens structure side, there is no need for the camera side to have a circuit for determining what kind of photographic lens structure is attached. Since there is no need to provide a circuit for generating drive pulses whose duty ratio is changed accordingly, the camera control device becomes extremely simple.

[Brief explanation of the drawing]

FIG. 1 is a schematic overall diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram of a specific example of the control device shown in FIG. 1, FIG. 3 is a time chart of control signals applied to terminals of the control device, and FIG. 4 is a circuit diagram of a specific example of the drive circuit in FIG. 1, FIG. 5 is a circuit diagram of another specific example of the drive circuit,
FIG. 6 is a time chart for explaining the operation of the expansion circuit shown in FIG. [Explanation of symbols of main parts], 1...Photographing lens,
5, 6...driving means, 7...motor.

Claims (1)

[Scope of Claims] 1. A plurality of photographic lens assemblies each having a built-in motor for driving a photographic lens, each of which has different drive characteristics necessary for driving the photographic lens with the motor, and each of the plurality of photographic lens assemblies It is removable and
A camera system comprising: a camera having a focus detection means for detecting a focus state from a light image of a subject that has passed through the photographing lens; a pulse generating means for generating a driving pulse having a predetermined duty ratio and driving the motor; and an output terminal for outputting the driving pulse generated by the pulse generating means to the photographing lens assembly. an input terminal connected to an output terminal of the camera; and duty changing means for changing the duty ratio of the driving pulse inputted through the input terminal in accordance with the driving characteristics of each of the photographic lens structures; A camera system comprising: motor drive means for driving the motor with a drive pulse whose duty ratio has been changed by a duty change means.