JPH052906Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic film drive device for a camera, and more particularly to an overload detection control circuit for the drive device.

In recent years, with the advancement of automation in cameras, it has become easier to wind and rewind the film by using a drive source such as a motor to automatically wind the film along with the related operations of the shutter and release member. Some products have already been commercialized in which film rewinding is automatically achieved by switching a switch.

In such automated cameras, if the entire amount of film is completed during the film winding operation, or if a failure occurs in the automatic film drive device, the motor is overloaded and an overcurrent occurs. In order to prevent the motor from being destroyed or the power to be wasted if the camera operator leaves it unattended without noticing, the system detects the overcurrent and automatically switches off the power supply to the motor. There have also been proposals to stop it.

Conventionally, this type of overcurrent detection has been done by detecting voltage fluctuations appearing across a resistor connected in series with the motor, or by detecting the emitter voltage of a motor drive transistor connected in series with the motor.
Methods such as detecting the voltage between the collectors have been used. However, the former has the disadvantage that a resistor is connected in series with the motor, which consumes a large amount of power. In the latter case, a comparator or the like is used as a means for detecting the voltage to compare it with a reference voltage, which has the disadvantage that the circuit becomes complicated and expensive. Furthermore, in a device that uses a transistor for detection and applies a voltage between the emitter and collector of the drive transistor to its base, the voltage between the emitter and collector of the drive transistor is the same as that of the detection transistor. Since detection control cannot be performed until the threshold level is reached, the difference between the normal motor drive current level and the overcurrent detection level cannot be very large. When winding a large film, there is a risk that even a slight torque fluctuation will cause overcurrent detection to occur, causing the motor to stop and resulting in unsatisfactory film winding.

The present invention has been developed in consideration of the above, and is a method for detecting and controlling voltage fluctuations occurring between the emitter and collector of a drive transistor connected in series with a motor using a detection transistor. By connecting a diode and a resistor to the emitter of the detection transistor, the detection level of the detection transistor is lowered, thereby increasing the current that can flow to the motor, making it possible to use small motors and small capacity power supplies. Another object of the present invention is to provide an automatic film drive device for a camera having a circuit that reduces fluctuations in detection level due to temperature fluctuations and improves detection accuracy.

The present invention will be explained in detail below using the drawings.

FIG. 1 is a circuit diagram showing an example of a conventional overcurrent detection control circuit. 1 is a PNP type transistor for driving the motor, its base is connected to the output terminal of the motor drive control circuit 3 via the resistor 2, and the connection point (point a) between the collector and the motor M is connected to the detection transistor 4. connected to the base. The detection transistor 4 is of PNP type, and its collector is connected to the resistor 5 and the input terminal of the motor drive control circuit 3. Note that E represents a power source and S represents a power switch.

Here, when the power switch S is turned on, for example, by the return operation of the release member, a base current is supplied from the motor drive control circuit 3, the drive transistor 1 is turned on, and the motor starts rotating.
When the film has been wound by one frame, the power switch S is turned off by a known method, the motor is deenergized, and one frame feeding is completed. However, if the motor is overloaded due to the reasons listed above while the film is being fed one frame, the back electromotive force generated by the motor decreases.
Also, since an overcurrent occurs, the voltage at point a decreases and the detection transistor 4 is turned on, and the motor drive control circuit 3 cuts off the base current of the drive transistor 1, so the motor is deenergized. be. This relationship is expressed as follows: V _E is the power supply voltage, V _CE(1) is the voltage between the emitter and collector of driving transistor 1, V M is the voltage at point a, and V _M is the voltage between the base and emitter of detection transistor 4. Assuming that V _BE(4) and the threshold level of this detection transistor are V _S(4) , the condition for stopping power supply to the motor is V _CE(1) = V _BE(4) > V _{S(4). )} , and therefore V _M
=V _E −V _CE(1) <V _E −V _S(4) . Furthermore, if the internal resistance of the motor is _RM , then the current _IM that can flow through the motor in this circuit is _IM = ( _VE - _VS(4) )/ _RM ... For this reason, for example, in the case of a film that requires a large amount of pulling force, there is a fear that the current value required for winding the film may not actually be much different from this I _M.
Due to torque fluctuations in the hoisting mechanism, the current value supplied to the motor during hoisting may exceed the I _M level, causing the motor to stop and making it impossible to perform the desired hoisting operation. . The present invention was developed with one purpose of solving this problem, and the basic circuit of the present invention shown in FIG. 2 will be explained next.

In this basic circuit, compared to the conventional example shown in Fig. 1, an npn type is used for the detection transistor 7, its emitter is connected to the connection point (point b) between the diode 8 and the variable resistor 9, and the collector is connected to the motor drive. Characteristically, they are connected to the input terminals of the control circuit 3'. In this circuit configuration, when the motor is overloaded and an overcurrent flows, the detection transistor 7 is turned off and the drive control circuit 3' turns off the motor by cutting off the power supply to the base of the drive transistor 1. It has become a powerful structure. Here, the base of the detection transistor 7
Assuming that the voltage between the emitters is V _BE(7) , the threshold level is V _S(7) , and the voltage generated across diode 8 is V _D , the conditions for the motor power supply to be cut off in this circuit are is: V _BE(7) = V _D −V _CE(1) ＜V _S(7) ∴V _M ＜V _E −V _D ＋V _S(7) Therefore, the current I that can be passed through the motor in this circuit is _M is I _M = (V _E − V _D + V _S(7) )/R _M ……. Here, adjust the variable resistor 9 to make V _D and V _S
By setting the difference small, it is possible to increase the current that can be passed through the motor.
For example, assuming that V _E =2.5 volts, V _S(4) = V _S(7) =0.6 volts, and R _M =1 ohm, I _M =1.9 amps in the conventional example, whereas in the present invention, I M =1.9 amps. By setting V _D to 0.9 volts, I _M can be set to 22 amperes, and the output torque of the motor can be increased. In addition, since the diodes are connected in parallel to set the detection level of the detection transistor, specific changes in the element due to temperature cancel each other out, and the voltage detection level is not affected by temperature fluctuations. Therefore, detection accuracy is improved.

FIG. 3 is a circuit diagram of an automatic film drive device showing a specific embodiment of the basic form of the present invention shown in FIG. 2.

SW ₁ is a back cover switch that prevents overload detection due to incorrect operation or careless loading of the film drive system when the back cover is opened.It turns on when the back cover is opened and turns off when it is closed. . SW ₂ is a winding switch that is switched to the c side when the shutter has finished operating, and to the d side when the film has been fed one frame, but is forcibly connected to the e side when the film is rewound. SW ₃
For example, a film detection switch installed near the film rail surface of a camera is turned on when film is present and turned off when film is absent, and is involved in automatic stopping at the end of film rewinding. SW ₄ is a changeover switch that is connected to the f side when winding and to the g side when rewinding. C ₃ is the starting capacitor, and winding switch SW ₂ is d
By being switched from the side to the e side, a self-holding circuit consisting of transistors Q ₄ and Q ₅ following the capacitor C ₃ is turned on, and thereby a driving transistor Q whose base is connected to the collector of the transistor Q ₅ is turned on. ₆ turns on and the motor starts rotating. Even after the charging of the starting capacitor _C3 is completed, the self-holding circuit remains on and winding of the film continues, but the charge in the capacitor _C3 is transferred to the discharging diode _D1 and the transistor Q while the motor is rotating. ₅ to prepare for the next activation. Q ₆ is a detection transistor. Its base is connected to the collector of the driving transistor Q ₆ , and its emitter is connected to the connection point between the diode D ₂ and the resistor R ₁₁ . Here, the resistor _R11 is set in advance to appropriately determine the overcurrent detection level of the detection transistor _Q8 . Transistors Q ₁ and Q ₂ and resistors R ₂ and R ₃ constitute a control circuit, and resistor R ₄ and capacitor C ₁ constitute an integrating circuit. That is, when the detection transistor Q ₈ is on, the transistors Q ₁ and Q ₂
are both turned on and shoot both ends of capacitor _C1 , so the following transistor _Q3 is turned off and the self-holding circuit remains on. When the detection transistor Q ₆ is turned off, the transistor
_Q1 and _Q2 are turned off, and when the capacitor _C1 of the integrating circuit is charged to a predetermined amount, transistor _Q3 is turned on and transistor _Q5 is turned off, so the self-holding circuit is reset and the entire circuit is turned off. be. Incidentally, capacitor _C2 acts as a low-pass filter and prevents malfunction due to noise. On the other hand, transistor _Q7 is a driving transistor for film rewinding.

Next, the operation will be explained.

(Normal winding) Load the film, close the back cover, and the switch will turn on.
SW ₁ is off and switch SW ₃ is on. Also, switch SW ₄ is on the f side. In this state, the camera operator operates a release member (not shown) to operate the shutter, and when the shutter operation is completed, a member that is displaced moves the winding switch SW ₂ to the e side, and the start capacitor C ₃ activates the shutter. In response to the pulse, a self-holding circuit (Q ₄ ,
Q ₅ ) is turned on, the motor starts rotating due to the power supplied by the drive transistor Q ₆ , and the film winding operation is performed. When starting the motor, a rush current may flow and the detection transistor _Q8 may turn off momentarily, but this is due to the integrator circuit ( _R4 ,
C ₁ ), preventing the self-holding circuit from resetting. Also, from this point on, the transistor
Since Q ₃ remains on, the integrator circuit is deactivated. When the film is advanced by one frame and the winding switch _SW2 is connected to the d side, the motor is shot and immediately stops, the self-holding circuit is also turned off, and the winding operation for one frame is completed. (When an overload occurs on the motor during film winding) The voltage between the emitter and collector of transistor _Q4 is V _CE(Q4) , the voltage appearing across diode _D2 is V _D2 , and the base of detection transistor _Q4 is vinegar·
If the voltage between the emitter and collector is V _BE(Q3) and the voltage between the emitter and collector of driving transistor _Q6 is V _CE(Q6) , then V _BE(Q3) = {V _CE(Q4) +V _D2 }−V _{CE (Q6)} There is a relationship between... If the motor is overloaded and an overcurrent occurs, V _{CE (Q6)} will increase, and V _{BE (Q3)} will fall below the threshold level of the detection transistor _Q8 according to the relational expression. ₈ is off. Then, transistors Q ₁ and Q ₂ of the control circuit turn off, the integrating circuit (R ₄ , C ₁ ) starts operating, and capacitor C ₁ is charged by a predetermined amount, which turns on transistor Q ₃ and activates the self-holding circuit. Since it resets, transistor Q ₆
is turned off, the power supply to the motor is cut off, and winding is automatically stopped. Since transistor Q ₄ is also turned off, the self-holding circuits of transistors Q ₄ and Q ₅ are also reset, and at the same time, transistor
The power supply to motor control circuits such as Q ₁ , Q ₂ , and Q ₃ is also cut off.

(When rewinding the film) To rewind the film, set changeover switch SW ₄ to G.
This is done by switching to the side. At this time, the winding switch _SW2 is forcibly switched to the e side in conjunction with the switching of the switch _SW4 . With this switching operation, the rewind drive transistor
When _Q7 is turned on, the motor starts to reverse rotation and the film is rewound. Then, the film is rewound, and the film detection switch _SW3 is turned off when it no longer detects the film, and when the transistor _Q7 is turned off, the rewinding is automatically completed.

In the above explanation, a pnp type transistor was used as the driving transistor (1 in Fig. 2, Q ₆ in Fig. 3), but it is not limited to the pnp type.
When using an npn type, the detection transistor
The same thing can be done if you use a pnp type and connect its emitter to the connection point between the anode side of the diode and the resistor. FIG. 4 shows the circuit of FIG. 2 modified in this way.

Now, as explained in detail above, according to the present invention, the detection voltage level of the detection transistor can be lowered, and the amount of current that can be passed through the motor can be increased, which can interfere with normal winding operation depending on the type of film. Since there is no change in the detection level due to temperature, a film drive device capable of good and highly accurate overload detection can be obtained. Furthermore, by increasing the amount of current that can be passed through the motor, sufficient torque can be output from the motor, making it possible to use a relatively small motor, which is also effective in making cameras smaller and lighter. It is something to play.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional overcurrent detection control circuit. Figure 2 is the basic circuit diagram of this invention.
FIG. 3 is a circuit diagram showing a specific embodiment of the present invention, and FIG. 4 is another basic circuit diagram of the present invention. Explanation of symbols of main parts, 1, Q ₆ ... Drive transistor, 4, 7, Q ₈ ... Detection transistor, 3, 3' ... Motor drive control circuit, 8,
D ₂ ... Diode, 9 ... Variable resistor, R ₁₁ ... Resistor, SW ₂ ... Winding switch, SW ₄ ... Changeover switch, C ₃ ... Starting capacitor, Q ₁ , Q ₂ ,
R ₂ , R ₃ ... Control circuit, R ₄ , C ₁ ... Integration circuit, D ₁
...discharge diode, Q ₄ , Q ₅ ... self-holding circuit,
M...Motor, E...Power battery.

Claims (1)

[Scope of utility model registration request] A film drive circuit formed by a film drive motor and a drive transistor connected in series to the motor, a detection transistor whose base is connected to the collector of the drive transistor, and an output of the detection transistor that drives the motor. an overload detection control circuit that has a motor drive control circuit that controls a drive circuit, detects an overcurrent that occurs when an overload is applied to the motor, and automatically stops the motor; 1. An automatic film drive device for a camera, comprising a diode having one terminal connected to an emitter of the diode, and a circuit for setting a detection level by flowing a current from an anode to a cathode of the diode.