JPH03219203A - Automatic focus adjusting device - Google Patents

Abstract

PURPOSE:To shorten the time of movement of an automatic focusing lens to its focusing position by making a reverse brake before a short brake is started while a motor rotates at a constant speed. CONSTITUTION:The position of the automatic focusing lens is controlled by a motor 12 to put the lens in focus. Then the short brake which is made by the short circuit of a motor circuit 11 or the reverse brake which is made by the voltage application of a motor circuit 11 in the motor reversing direction is selected to brake the motor 12. Namely, transistors A - D are applied with a voltage for a specific time so that the motor 12 rotates in the opposite direction from current rotation, and the reverse brake is made for the specific time in the beginning of the braking of the motor 12. Consequently, the time from the start of the speed reduction of the motor to its stop is shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device that is provided in an autofocus camera and that controls the movement and stop operation of a focusing lens during a focusing operation.

[Conventional technology]

In an autofocus camera, the autofocus lens is configured to be driven by a motor, and the motor is rotationally controlled according to the amount of defocus obtained by distance measurement, thereby controlling the lens to the in-focus position. . Stop position control of the autofocus lens in this focus control is started when the lens comes a predetermined distance from the focus position.

Motor deceleration control is performed by PWM control that repeats energization and short-circuiting of the motor circuit, and when the motor is decelerated to the target rotational speed due to the short brake generated by this, this target rotational speed is further increased to 1. is set to the lowest value and the motor is decelerated again.

-The lens then stops at the in-focus position with a predetermined accuracy.

[Problem to be solved by the invention] Therefore, the time required for stop control of the autofocus lens is
It is determined by the amount of motor braking caused by a short circuit in the motor circuit. However, there is a limit to the magnitude of this braking, and conventionally it has not been possible to sufficiently shorten the braking time. Therefore, when the amount of defocus is large,
It takes a long time to focus, which poses a problem in speeding up automatic focus control.

In view of the above points, the present invention has been made with the object of providing an automatic focusing device in which the time required for moving the focusing lens to the in-focus position is shortened. ] The automatic focus adjustment device according to the present invention includes a distance measuring device that detects a defocus amount for a subject, and a lens movement amount that calculates an amount by which the lens should be moved for focusing based on the defocus amount. a calculation means, a motor circuit for driving the motor to move the lens by the amount of movement obtained by the lens movement amount calculation means, and a movement amount detection means for detecting the amount of movement of the lens from an initial position. The motor is braked by selecting either a short brake caused by a short circuit in the motor circuit or a reverse brake caused by applying a voltage in the motor circuit in the reverse rotation direction, depending on the amount of movement obtained by the movement amount detection means. The invention is characterized by comprising a speed control means for controlling the speed.

〔Example〕

The present invention will be explained below with reference to illustrated embodiments.

FIG. 1 shows a control device for an autofocus camera to which an embodiment of the present invention is applied. The autofocus lens is positionally controlled by a lens drive unit 11 provided within the camera body, and is moved forward and backward by rotation of a DC motor 12, thereby changing the focal plane.

The lens driving section 11 includes a DC motor 12 and a motor circuit 20.
The motor circuit 20 has a motor interface 1
3 to the CPU 14.

The distance measurement sensor 15 is connected to the CPU 14 via the distance measurement interface 16, and the CPU 14 calculates the amount of defocus for the subject based on the distance measurement data input from the distance measurement sensor 15. The lens drive unit 11 moves the autofocus lens according to this defocus amount to the in-focus position.

The AF pulser part 7 is connected to the output shaft of the motor 12 and outputs a number of pulses corresponding to the rotation angle of the output shaft, and these pulses are input to the CPU 14. The event counter 18 counts pulses from the AF pulser part 7 in order for the CPU 14 to detect the position of the autofocus lens.

The distance measurement switch S1 is turned on by pressing the shutter button halfway, and at this time, the CPU 14 receives the defocus amount from the distance measurement sensor 15. The release switch SWR is turned on by fully pressing the shutter button, and at this time the shutter is released by the CPU 14.

Note that the CPU 14 is connected to a ROM 19 that is provided in the autofocus lens and stores various information about the lens in advance.

The motor circuit 20 rotates the motor 12 to move the autofocus lens for autofocus control, and includes first to fourth transistors A, B, C, and D, and a battery 2.
1. The collectors of the first and third transistors A and C are connected to the positive terminal of the motor 12, and the collectors of the second and fourth transistors B and D are connected to the negative terminal of the motor 12. . The emitter of each transistor is connected to the battery 21 and the base to the motor interface 13.

FIG. 2 shows a flowchart of the main routine of automatic focus control.

In step 50, it is checked whether the distance measuring switch S1 is on, and if it is not on yet, step 50 is repeated. Distance switch S1
When turned on, distance measurement data measured by the distance measurement sensor 15 is input to the CPU 14 in step 51 . In step 52, the amount of defocus to the in-focus position is calculated based on the distance measurement data. Next, in step 53, the driving amount P of the lens to the in-focus position is determined based on the lens information data obtained from the ROM 19 of the lens and the defocus amount calculated in step 52.
cal is calculated as the number of pulses. This number of pulses corresponds to the amount of movement of the lens, that is, the rotation angle of the motor 12. The number of pulses corresponding to the drive amount Pcal, that is, the number of drive pulses, is determined by the event counter 18 in step 54.
is set to Note that this event counter 18 is a down counter, and when the count value reaches 0, the lens is at the in-focus position.

In step 55, a voltage is applied to predetermined transistors A, B, C, and D of the motor circuit 20, thereby energizing the motor 12 to rotate and begin moving the autofocus lens. The direction of movement of the lens differs depending on whether the lens is on the far side or near side of the in-focus position, and the amount of movement differs depending on the amount of defocus. The moving direction of the lens changes depending on the energization state of the transistors A, B, C, and D. When the lens is on the distant view side, as shown in (1) in FIG. 3, the first and fourth transistors A, A voltage is applied to the base of transistor D, which causes current to flow from transistor A to transistor D, causing motor 12 to rotate in a predetermined direction. When the lens is on the foreground side, voltage is applied to the bases of the second and third transistors B and C, as shown in (2) in FIG. ) rotates in the opposite direction.

When a short brake is applied to the motor 12, each transistor is set to the energized state as shown in (3) in FIG. 3, and as a result, the positive terminal and negative terminal of the motor 12 are short-circuited. The motor is forced to slow down. Note that (4) in FIG. 3 shows the energization state of each transistor when the motor 12 is in a free state, and no voltage is applied to the base of each transistor.

Step 56 is to control the speed of motor drive to stop the lens at the in-focus position, and this will be described later.

Step 57 is executed when the value of the event counter 18 becomes O in the control at step 56, and the motor 12 is thereby stopped.

In step 58, it is checked whether or not the image is in focus, and if it is not in focus, the process returns to step 51 and the process returns to step 51.
The processes from 57 to 57 are repeated, but if the image is in focus, the process advances to step 59, where it is checked whether the release switch SWR is turned on. When the release switch SWR is turned on, a release process is performed in step 60 to release the shutter, and this routine ends.

FIG. 4 shows the relationship between the rotational speed of the motor 12 and the value IVT of the event counter 18 in focus control, and the example shown in the second figure shows the case where the speed control in this embodiment, that is, the control in step 56 is not performed. It is.

In this figure, when the motor starts, the event counter value IVT is set to the drive amount Pcal to the lens focus position. As the motor accelerates, the event counter value IVT decreases as shown by the solid line 1, and when the motor reaches a predetermined speed, it rotates at a constant speed as shown by the solid line I2.

When the number of remaining pulses until the event counter value IVT reaches O reaches a predetermined value, that is, the event counter value IVT
When P3 reaches P3, only the first and second transistors A and B or only the third and fourth transistors C and D are turned on (the third
(3) in the figure, the motor circuit 20 is short-circuited, a short brake occurs, and the motor decelerates as shown by the solid line 3. When the motor speed reaches a predetermined value, the motor will move to the solid line ■4
As shown in , it rotates at a constant speed until the event counter value IVT reaches P2. Event counter value IVT is P
When it decreases to 2, the motor is decelerated again by the short brake determined by PWM control as shown by the solid line I. Below, by similar control, the event counter value I
When VT becomes 0, a short brake is applied and the motor stops.

Furthermore, since the motor is stopped only after the event counter value IVT reaches O, strictly speaking, it will stop at a position slightly beyond the original stop position, but this amount is sufficiently small and within the allowable range. .

Thus, the motor repeatedly decelerates to a predetermined target speed, and the lens stops at the position where the event counter value fVT becomes approximately O, that is, at the in-focus position. If the brake of the motor is ended at -degree, the lens can be moved to the in-focus position in a shorter time, but it becomes difficult to control the stopping position of the lens with high precision. This is because in the case of an eye reflex camera, the braking load differs depending on the lens, and the performance of the battery changes, so a brake operation of only -degrees causes an error in the stopping position. Braking of the motor must therefore be done in stages.

Therefore, in this embodiment, in order to shorten the driving time of the lens, a voltage is applied to each transistor A, B, and C1D for a predetermined time so that the motor 12 rotates in the opposite direction to the current rotation. That is, this embodiment is configured to generate reverse braking for a predetermined period of time at the beginning of braking of the motor 12.

The fifth objective is to shorten the lens driving time by using this reverse brake.
This will be explained using FIG. 6 and FIG.

In FIG. 5, the solid line J indicates the same as that shown in FIG. 4, and the broken line indicates the relationship between the event counter value IVT and the motor speed in this embodiment. In this embodiment, when the event counter value IVT reaches P3', the predetermined time T
During this period, the reverse brake is applied, which causes the motor to
As shown by the symbols J1 in FIG. 5, the reverse brake is used only for a predetermined time to decelerate more rapidly than the conventional technology shown by J1, after which it is changed to a short brake, and the motor speed reaches the first target. P to become speed animal 'M3
WM! II IB is performed. Next, when the event counter value rVT reaches P2' after the motor speed reaches the first target speed PWM3, PWM ilJ control is performed so that the motor speed reaches the second target speed PWM2, and the short brake is activated. is applied. Similarly, when the event counter value IVT reaches P, ", a short brake is applied so that the motor speed reaches the third target speed PWMI, and when the event counter value IVT reaches O, the motor is stopped by the short brake. It will be done.

FIG. 6 shows the temporal change in the operation of the motor shown in FIG. 5, with the broken line representing the temporal change in motor speed in this embodiment, and the solid line representing the temporal change in motor speed in the prior art. It is indicated by M. As can be understood from this figure, according to this embodiment, by applying a reverse brake for a predetermined time T at the start of deceleration, the time (r-+) from the start of deceleration of the motor to the stop of the motor is shorter than that of the prior art. This is significantly shortened compared to the deceleration time (M, ).

In this embodiment, the slope of L changes as indicated by the broken line in FIGS. 5 and 6, depending on the length of time T during which a voltage is applied to the motor in a direction opposite to the current rotation. This time again T
Event counter value P1゛~P3' when the motor is reversed or short brake is applied depending on the length of
can be changed.

Now, in Figures 5 and 6, the amount of defocus is large and the amount of lens movement is large, that is, the motor is braked after the motor speed reaches a certain speed. is small and the amount of lens movement is small, if the reverse brake is applied at a motor speed lower than this constant speed E, the motor speed will drop too much and it will take a long time to stop the motor, as described below. There are cases where it is too much. This will be explained using FIGS. 7 and 8.

FIG. 7 shows the relationship between event counter value IVT and motor speed. The motor speed increases as shown by the dashed line F1,
The event counter value IVT is P3 when the speed is still relatively low.
When the reverse brake is applied when reaching the limit, -dotted chain line F2
As shown in , the motor speed becomes too low than the target rotational speed. Therefore, the motor speed is increased again under the control of the CPU 14 so as to approach the target rotation speed. Therefore, in this case, as shown by the dashed line G in FIG. 8, the time until the motor stops becomes longer. That is, in such a case, the reverse brake is not necessary, and the motor should be braked only by the short brake, as shown by the broken line F3 in FIG.

Symbols F3, Fz, and K shown in FIG. 8 indicate the time from the start of deceleration of the motor to the stop in the deceleration control shown by the dashed line F2, the broken line F3, and the solid line in FIG. 7. In addition, the solid line in Fig. 7 shows the braking operation using the reverse brake,
This is the same as the broken line in FIG. As clearly shown in Fig. 8, if the motor speed is decelerated too much by the reverse brake, the time until the motor stops will be too long (symbol F2), and if the motor speed is greater than a predetermined value, the reverse brake will reduce the motor speed too much. The time until the motor stops is significantly improved (symbol K).

On the other hand, if only the short brake is used as in the past, the lens will move to the focus position 0, as shown by the dotted line F4 in FIG.
The motor will stop at a position that is beyond the allowable range. Therefore, as shown by the symbol X in FIG. 7, there is a limit speed of the motor due to the short brake,
Reverse braking should only be used if the motor speed at the time of starting motor braking is greater than this limit speed X.

That is, as shown in Fig. 7, S is the number of pulses from when the motor is energized and starts driving until the motor speed reaches the limit speed χ, and the event when braking of the motor starts. If the counter value IVT is P3, the number of driving pulses Pc set in step 54 of FIG.
Regarding al, when there is a relationship of s+p, ≧Pcal, it is sufficient to use only the short brake, and when reverse C2, S0P:l<Pcal, it is sufficient to use the reverse brake.

FIG. 9 shows a flowchart of the speed control in step 5.6 of FIG. 2 when the speed of the motor is controlled in consideration of the limit speed X. In this flowchart, the symbols P+XPz and P3 correspond to the symbols P,'', P2'', and P3° in FIG. 5, respectively.

In FIG. 9, in step 61, it is checked whether the event counter value IVT is smaller than P3. When the event counter value IVT is larger than P3, that is, for example, in FIG.
3, step 61 is repeated and the motor is not braked. When the event counter value IVT becomes .JX smaller than P3, the process proceeds to step 62, where it is determined whether S+P3≧Pcal holds true. If this is true, the reverse brake should not be applied, so skip step 63 and proceed to Step 2/Pro 4. If this is not true, the reverse brake should be applied, so step 63 is executed. That is, in step 63, a voltage that rotates the motor 12 in the opposite direction to the current rotation direction is applied for only a time T (see FIGS. 5 and 6).
(see figure).

Note that this time T is determined depending on the characteristics of the motor 12, and is determined, for example, by experiment.

Step 64 and subsequent steps are normal braking control. First, in step 64, the short brake is applied for a predetermined time, and then in step 65, the short brake is applied by PWM control so that the motor reaches the first target rotational speed PWM3.

In step 66, it is determined whether the event counter value IVT becomes smaller than P2, and the event counter value IVT is determined to be smaller than P2.
When VT becomes smaller than P2, step 67 is executed. That is, the motor is at the second target rotational speed PWM2.
A short brake is applied by PWM control so that Similarly, when the event counter value IVT becomes smaller than P2 in step 68, step 6
9 is executed and the motor reaches the third target rotational speed PWMI.
A short brake is applied so that When the event counter value IVT becomes 0 in step 70, a short brake is applied in step 71 to stop the motor.

As described above, this embodiment is configured to apply reverse braking in accordance with the number of drive pulses Pcal before short braking by PWM control is started from a state in which the motor 12 is rotating at a constant speed. There is. Therefore, when the motor is being driven at a high speed higher than a predetermined value, the motor can be stopped quickly, the motor control time can be shortened, and automatic focus control can be performed at high speed.

[Effects of the Invention] As described above, according to the present invention, the travel time of the autofocus lens to the in-focus position is shortened, and the autofocus control can be performed at high speed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a control device for an autofocus camera having an autofocus adjustment device according to an embodiment of the present invention, FIG. 2 is a flowchart of the main routine of autofocus control, and FIG. 3 is a block diagram showing each of the motor circuits. A diagram showing the energization state of the transistor, and Fig. 4 shows the event counter value I in conventional focusing control.
A graph showing the relationship between VT and motor speed, FIG. 5 shows event counter values TVT in the embodiment of the present invention and in the prior art.
FIG. 6 is a graph showing the temporal change in motor speed in the embodiment of the present invention and the prior art. FIG. Figure 8 is a graph of the relationship between the event counter value rVT and the motor speed, which is shown in comparison with . FIG. 9 is a flowchart of a speed control routine in an automatic focusing device according to an embodiment of the present invention. ]1...Lens drive unit 12...Motor

Claims (2)

[Claims] (1) An automatic focus adjustment device that controls the position of an automatic focus lens using a motor to focus the image, and includes a distance measuring device that detects the amount of defocus for the subject, and a distance measuring device that detects the amount of defocus for the subject and adjusts the focus based on the amount of defocus. a lens movement amount calculation means for calculating the amount by which the lens should be moved; a motor circuit for driving the motor to move the lens by the movement amount obtained by the lens movement amount calculation means; A movement amount detection means for detecting the movement amount from the initial position, and a short brake caused by a short circuit in the motor circuit and a voltage in the motor reverse rotation direction of the motor circuit according to the movement amount obtained by the movement amount detection means. 1. An automatic focus adjustment device comprising speed control means for braking the motor by selecting a reverse brake produced by application of a reverse brake. (2) The automatic focus adjustment device according to claim 1, wherein the speed control means is capable of selecting the reverse brake when the speed of the motor at the time of starting braking is equal to or higher than a predetermined value. .