JP2000214377A - Lens drive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the focusing time in a lens drive device where a stepping motor is employed as a drive source and which has many lens setting steps. SOLUTION: The rotation of the stepping motor 3 is transmitted to a lens drive means 2 through a coupling means 4 and a photographing lens is driven to a focusing position. At the time of starting the motor 3, a start control means 7a drives the motor with pulses in a self-start region and then an acceleration control means 7b increases the pulse frequency from the self-start region to a through-region. After reaching the through-region, a constant-speed control means 7c drives the motor in terms of constant speed. When the lens reaches the vicinity of a target focusing position, a deceleration control means 7d decelerates the pulse frequency from the through-region to the self-start region and a stop control means 7e stops the motor at the time of attaining the target focusing position. At the time of starting and at the time of stooping, the motor is driven in the self-drive region but the drive of the lens is mostly performed in the through-region, so that the time required for focusing is shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lens driving device for a still camera using a stepping motor as a driving source.

[0002]

2. Description of the Related Art Conventionally, a stepping motor has been widely used as a driving source of a lens driving device in a still camera. Basically, the rotation of a stepping motor serving as a driving source is transmitted through a power transmission train such as a gear train. By doing so, the lens is driven, and the amount of drive of the lens is controlled by the amount of rotation of the step motor.

[0003]

In recent years, lenses for still cameras have tended to increase the number of lens stop stages with the increase in the number of focal points and zooming of lenses. A conventionally known control method of a lens driving device using a stepping motor as a driving source generally supplies a forward rotation pulse in a frequency band within a self-starting range to the stepping motor, and this forward rotation pulse A relatively simple method of stepping a preset counter whose set value is determined in accordance with the subject distance and stopping the motor when the preset counter counts up is adopted. When driving a camera lens with multiple lens stop stages, there is a problem that the time required for focusing becomes extremely long.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and it is an object of the present invention to reduce the time required for focusing in a recent still camera in which the number of lens stops is increased. It is an object to provide a possible lens drive. In summary, the lens driving device of the present invention includes: a step motor capable of normal rotation and reverse rotation; a motor control means for controlling the driving of the step motor; and a photographing lens for forming a subject image on a predetermined image plane. : Lens driving means for driving the photographing lens; and connecting the step motor and the lens driving means to transmit the forward rotation of the step motor to drive the photographing lens from the initial position to the in-focus position. And a coupling means for transmitting the reverse rotation of the step motor to drive the photographing lens from the in-focus position to the initial position. The motor control means stops at the initial position. Start control means for supplying a forward rotation pulse in a frequency band within the self-starting region to the stepping motor to start the stepping motor forward; Acceleration control means for increasing the forward rotation pulse frequency to the through region for the step motor placed in the forward rotation state by the start control means; and for the step motor placed in the forward rotation state in the through region by the acceleration control means. Constant-speed drive control means for maintaining the frequency of the forward rotation pulse to be applied to the vicinity of a desired focus position; and a forward rotation pulse applied to the step motor driven to the vicinity of the focus position by the constant-speed drive control means. It has deceleration control means for reducing the frequency band again within the self-starting area and stop control means for stopping the step motor driven to a desired focusing position by the deceleration control means. In addition, the lens driving device of the present invention: if desired: on the basis of the above: for operating each of the start control means, the acceleration control means, the constant speed drive control means, the deceleration control means and the stop control means Memory means for readable storage of the control data according to the target in-focus position: the start control means, the acceleration control means, and the constant speed drive control based on the control data read from the memory means. Means, the deceleration control means and the stop control means are operated. or,
The lens driving device of the present invention includes: biasing means for biasing the lens driving means from an initial position toward a focus position: if desired: on the basis of the above: Further, the lens driving device of the present invention is characterized in that: an initial position of the photographing lens is set at a long-distance photographing position: Further, the lens driving device of the present invention includes: if desired: the motor control means supplies a reverse rotation pulse in a frequency band within a self-starting region to the step motor moving from the in-focus position to the initial position to control the step motor. It is provided with reverse rotation control means for returning to the initial position.

That is, according to the lens driving device of the present invention,
The drive is in the self-starting area only at the time of rising and stopping,
Since the through area occupies most of the lens driving, the time required for focusing can be sufficiently reduced even if the number of lens stop steps is increased. In particular, the control data for operating each of the start control means, the acceleration control means, the constant speed drive control means, the deceleration control means and the stop control means is read out according to the target in-focus position. The start control unit, the acceleration control unit, the constant speed drive control unit, the deceleration control unit, and the stop control unit according to control data read from the memory unit. In the case of operating, optimal control can be easily performed in consideration of torque fluctuation and the like due to the lens driving position.

Further, when the lens driving means is provided with an urging means for urging the lens driving means from the initial position to the in-focus position, the torque required for the step motor can be reduced. Thus, the frequency of the self-starting area and the through area can be further increased, and the time required for focusing can be further reduced. In the case of an active focus adjustment type automatic focus adjustment mechanism, it is known that the distance measurement accuracy decreases as the distance increases, and the distance measurement accuracy decreases by performing a plurality of distance measurement operations at a long distance. Is generally compensated for, so that the total time from distance measurement to focusing tends to increase particularly on the long distance side. However, when the initial position of the photographing lens is set at a long-distance photographing position, the focusing time at a long distance can be shortened, and the total time from distance measurement to focusing can be shortened. Averaging can be performed regardless of the shooting distance.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. First, FIG. 1 is a block diagram showing the principle of a lens driving device according to the present invention, wherein 1 is for photographing for forming a subject image on a predetermined image plane, and 2 is for driving a photographing lens. Lens driving means such as a cam member, 3 is a step motor serving as a driving source, and 4 is connecting means for transmitting the rotation of the step motor 3 to the lens driving means 2, and generally a gear train or the like is assumed. . Reference numeral 5 denotes a switch for executing a distance measuring operation and a focusing operation in conjunction with operation of a shutter button or the like, and 6 denotes a distance measuring device for measuring an object distance by an active distance measuring method or another known method.

Reference numeral 7 denotes a motor control means for controlling a drive pulse supplied to the step motor 3 by program control, and reference numeral 8 denotes a memory means for storing various control data. The control means 7 supplies a forward rotation pulse in a frequency band within the self-starting range to the step motor stopped at the initial position to start the step motor 3 in the forward direction, and a start control means. The acceleration control means 7b for increasing the forward rotation pulse frequency to the through region with respect to the step motor 3 placed in the forward rotation state by 7a, and the step motor 3 placed in the forward rotation state in the through region by the acceleration control means 7b. Constant-speed drive control means 7c for maintaining the forward rotation pulse frequency applied to the vicinity of a desired in-focus position
A deceleration control unit 7d for reducing the forward rotation pulse applied to the step motor 3 driven to the vicinity of the in-focus position by the constant speed drive control unit 7c to a frequency band in the self-starting region again; and a deceleration control unit 7d. And a stop control means 7e for stopping the step motor 3 driven to the desired in-focus position, and supplying a reverse rotation pulse in a frequency band within the self-starting range to the step motor 3 from the in-focus position to the initial position. A reverse rotation control means 7f for returning the step motor 3 to the initial position by operating the control means 7f operates in accordance with control data prepared in advance in the memory means 8.

FIG. 2 shows the pulse frequency torque characteristic of the stepping motor. The area below the starting characteristic curve indicates the self-starting area (the area where the start-stop reverse rotation can be performed in synchronization with the input pulse). The area above the singing characteristic curve and below the slewing characteristic curve is the through area (the pulse frequency is increased beyond the self-starting area,
Or, a region where response can be achieved without losing synchronization even when the load torque is increased). As is clear from FIG. 2, the self-starting area and the through area vary with the variation of the load torque even with the same step motor. Further, when a step motor is used as a drive source of a lens for a still camera, the load torque applied to the step motor also varies depending on the lens extension position and the like. Therefore, these control data are prepared in the memory means 8 for each target in-focus position, and when the subject distance is input from the distance measuring device 6, various control data are stored in the memory means 8 according to the subject distance. Is read out, and the control means below the activation control means 7a operate.

[0010]

FIG. 3 shows a specific example of the construction of the stepping motor 3. Reference numeral 10 denotes a base plate having an exposed opening 10a formed in the center. Reference numeral 3a denotes a rotor in which S poles and N poles are alternately arranged at intervals of 90 degrees. Reference numerals 3b and 3c denote stators symmetrically arranged with the magnetic poles facing the rotor 3a. Each stator is basically in a horseshoe shape, but is formed in a substantially concentric arc centered on the exposure opening 10a in order to improve the overall fit, and the tip of the magnetic pole thereof is
45 degrees -90 degrees -135-90 around the rotation axis of a
They are arranged at intervals of degrees. Each stator 3b, 3
The coils 3d and 3e are wound around c, respectively. When a pulse signal having a phase shift is applied to each of the coils 3d and 3e, the rotor 3a rotates stepwise in a direction corresponding to the phase order of the pulse signal.

The rotation of the rotor 3a is transmitted via a gear train which is an example of the connecting means shown in FIGS. FIG. 4 is a plan view as seen from the subject side, and FIG. 5 is a sectional view. First, reference numeral 11 denotes an output pinion coaxial with the rotor 3a.
Also, 12a and 12b, 13a and 13b, 14a and 14b
Indicates a large-diameter wheel and a small-diameter wheel, respectively, and each constitutes a two-stage gear. The rotation of the output pinion 11 is a large-diameter wheel 12a.
To rotate the small-diameter wheel 12b coaxially. Small diameter car 1
The rotation of 2b is transmitted to the large-diameter wheel 13a to rotate the small-diameter wheel 13b. The rotation of the small diameter wheel 13b is transmitted to the small diameter wheel 14b, and rotates the large diameter wheel 14a. Reference numeral 15 denotes a lens drive ring which is an example of lens drive means having a rack 15a formed over substantially the entire circumference.
5 is supported rotatably about the exposure opening 10a, and the rack 15a meshes with the large-diameter wheel 14a. A lens frame, which will be described later, is connected to the convex piece 15b formed on the lens driving ring 15. When the lens driving ring 15 turns rightward from the state shown in FIG. 4 around the exposure opening 10a, the lens frame approaches from infinity. It is extended toward the shooting position. Reference numeral 16 denotes a stopper for regulating the initial position of the lens driving ring 15. Reference numeral 17 denotes an extension gear which is a feature of the present embodiment. The extension gear 17 meshes with the rack 15a and is provided with a left turning property by a spring 18. In the drawings, the spring 18 shows only the biasing direction by an arrow, but the specific configuration of the spring is not limited as long as the spring 18 can provide a biasing force in this direction. Therefore, the lens extension gear 18 exerts a right-handed biasing force on the lens drive ring 15 to reduce the load torque applied to the step motor 3 when the lens is extended, and shift the self-starting area and the through area to the high-speed side. To make things possible. Note that the biasing force given by the spring 18 is a limit that does not rotate the step motor in a non-energized state.

Reference numeral 19 denotes a blade opening / closing lever for opening and closing a shutter blade described later.
9 is rotatably supported by a shaft 19a and is given a right-turning property by a spring 20. still,
The spring 20 also shows only the urging direction by an arrow. The pin 19b on the back surface of the tip of the blade opening / closing lever 19 is engaged with a shutter blade described later. When the blade opening / closing lever 19 is turned clockwise from the state shown in the drawing, the shutter blade described later is exposed to the exposure opening 1.
0a is opened. Reference numeral 21 denotes a blade drive motor for driving the blade open / close lever, and its drive pin 21a swings within a predetermined angle range by energizing the motor 21.
An arm 19c at the other end of the blade opening / closing lever 19 is engaged with the output pin 21a. When the output pin 21a turns left, the blade opening / closing lever 19 turns clockwise by the urging force of the spring 20. Reference numerals 22 and 23 denote stoppers for regulating the swing range of the output pin 21a.

FIG. 6 shows the structure around the shutter blade. The shutter blades 25 and 26 are basically left-right symmetrically shaped shutter blades.
A pin 19b, which is swingably supported by shafts 25a and 26a provided on the back surface of the shutter blades 25 and 26 and is formed on long holes 25b and 26b formed in the shutter blades 25 and 26, is provided on the back surface of the front end of the blade opening / closing lever 19. 10 and is engaged. The through holes in the base plate 10 are omitted to avoid complicating the drawing. Therefore, when the blade opening / closing lever 19 is turned clockwise from the state shown in the figure, the shutter blade 25
, And the shutter blade 26 turns left about the axis 26a to open the exposure opening 10a. Reference numeral 27 denotes a stopper for regulating the initial position of the shutter blade 25, and reference numeral 28 denotes a photoreflector for detecting the blade position.

FIG. 7 is a sectional view showing the relationship between the lens drive ring 15 and the lens frame 31.
Is held back by the spring 32. A convex piece 15b, which is formed to be bent from the lens driving ring 15 supported on the base plate 10 with the exposure opening at the center, is engaged with the lens frame 32.
The outer periphery of 1 is screwed with the helicoid screw 33. Therefore, when the lens drive ring 15 is rotated to rotate the lens frame 31, the lens frame 31 moves in the optical axis direction along the helicoid screw.

Next, the operation of the above embodiment will be described with reference to the above-mentioned matters, the state change of FIGS. 8 and 9, and the time chart of FIG. The motor control means is switch 5
Is turned on, data indicating the distance to the subject is read from the distance measuring device 6, various control data are read from the memory means 8 based on the read distance data, and the activation control means 7a and the acceleration control means are read based on the control data. 7b,
Necessary control data is set for each of the constant speed traveling control means 7c, the deceleration control means 7d, the stop control means 7e, and the reverse rotation control means 7f. In the initial state, the lens drive ring 15 is at the position shown in FIG. 4, and the motor control means 7 determines that the activation control means 7a has the normal rotation pulse (the phase of the pulse A is larger than the phase of the pulse B) (A pulse advanced by 90 degrees) is supplied to the step motor 3. More specifically, at the point “1” in the time chart, both the pulse A and the pulse B are maintained at, for example, 10 ms (millisecond) H level to stabilize the step motor 3 and then “2” in the time chart. From the timing of, a pulse having a frequency band of, for example, 2.5 ms in the frequency band in the self-starting region is applied to the stepping motor, and the fourth pulse is applied to the
maintain.

By supplying the normal rotation pulse in this manner, the rotor 3a of the step motor 3 rotates clockwise, and this rotation is transmitted through the gears 11 to 14 shown in FIG. , And the lens drive ring 15 rotates clockwise by four steps. At this time, the biasing force of the spring 18 is transmitted to the rack 15a of the lens drive ring 15 via the lens extension gear 17, so that the load torque of the step motor 3 required for turning the lens drive ring 15 clockwise is reduced. Thus, a faster self-starting frequency can be set. In this way, while the lens drive ring 15 rotates clockwise by four steps, the convex piece 15c of the lens drive ring 15 pushes down the tip of the blade opening / closing lever 19, and slightly rotates the blade opening / closing lever 15 clockwise. As a result, the shutter blade 25 shown in FIG.
5c shields the detection window 28a of the photo reflector 28. Therefore, the output of the photoreflector 28 is inverted at the timing "3" in the time chart, and if this output inversion is not recognized, it is determined that some error has occurred and error processing is performed.

On the other hand, the timing "3" in the time chart
When it is confirmed that the output of the photoreflector 28 is inverted, the motor control means 7 controls the acceleration control means 7b from timing "4" to timing "5" in the time chart.
Shifts to the control operation by. More specifically, the acceleration control means 7a supplies the stepping motor 3 with a forward rotation pulse whose pulse frequency is gradually accelerated from a pulse width of, for example, 2.5 ms in the self-starting region to a pulse width of, for example, 1.2 ms in the through region. Then, the step motor 3 rotates clockwise while being gradually accelerated. Accordingly, the lens drive ring 15 also performs a clockwise operation while gradually accelerating, and the convex piece 15b rotates the lens frame 31 to extend the photographing lens in the short distance direction. At this time, the spring 18 also reduces the load torque applied to the step motor 3, and thus contributes to setting a higher self-starting frequency and a through frequency.

At the timing "5" of the time chart, the stepping motor is rotating forward with the forward rotation pulse of the frequency band in the through region, and the motor control means 7 changes the timing "5" of the time chart to the timing "5" of the time chart. 6 ", the control operation is shifted to the control operation by the constant speed traveling control means. More specifically, the constant speed traveling control means 7c continues to supply the stepping motor 3 with a pulse having a pulse width of, for example, 1.2 ms in the through region. Also makes a right turn at a constant speed. Then, when the timing reaches the timing "6" of the time chart, the motor control means 7 leaves the control operation to the deceleration control means 7d until the timing "7" of the time chart.
More specifically, the deceleration control means 7d supplies the stepping motor 3 with a forward rotation pulse whose pulse frequency is gradually reduced from a pulse width of, for example, 1.2 ms in the through area to a pulse width of, for example, 2.5 ms in the self-starting area. Then, the step motor 3 rotates clockwise while being gradually decelerated. Therefore,
The lens driving ring 15 also performs a clockwise operation while gradually decelerating, and extends the photographing lens to a target in-focus position.

At timing "7" in the time chart, the motor control means 7 entrusts control to the stop control means 7e. Specifically, the stop control unit 7e maintains the pulse state at the timing “7” for, for example, 10 ms, and after stabilizing the step motor 7, sets the timing “8”.
Then, the power supply to the step motor 7 is turned off. Therefore,
The taking lens stops at that position. FIG. 8 shows a state in which the lens driving ring 15 is turned clockwise as much as possible.

At the timing "8", the energization of the stepping motor 7 is turned off, and at the same time, the energization of the blade driving motor 21 is performed in the forward direction.
Turn a counterclockwise. Accordingly, the blade opening / closing lever 19 rotates clockwise by the biasing force of the spring 20, the shutter blade 25 rotates clockwise about the shaft 25a, and the shutter blade 26 rotates clockwise about the shaft 26a as shown in FIG. Open 10a. Further, when the convex piece 25c formed on the shutter blade 25 passes through the detection window 28a of the photoreflector 28 during the operation of the shutter blade 25 in this manner, the photoreflector 28 generates a pulse. The pulse rising edge of the timing “9” and the pulse falling edge of the timing “10” can be used as, for example, a delay timing for automatic exposure control and a delay timing for strobe tuning. Thereafter, at time "11" in the time chart, the blade drive motor 21 is energized in the reverse direction and the output pin 21a is turned clockwise toward the initial position, so that the blade open / close lever 19 turns counterclockwise against the spring 20 and is exposed. The opening 10a is closed.

At timing "12" after the end of the exposure operation, the motor control means 7 operates the reverse rotation control means 7f, and the reverse rotation control means 7f operates the reverse rotation pulses (pulse A and pulse A) in the self-start area. A pulse in which the phase order of B is reversed) is supplied to the stepping motor 7, the lens driving ring 15 is reversed toward the initial position, and once the lens driving ring 15 reaches the initial position, one photographing operation is performed. Complete. It is to be noted that the drive with the pulse in the self-starting area is performed at the time of the initial return of the lens because there is a margin in time, and the acceleration and deceleration may be performed even in the reverse rotation.
In the above description, the motor control means is divided into a plurality of control means. However, each of these control means is actually realized by using a single microprocessor. Further, in the above description, the case where the lens is extended to the maximum is described. However, when the extension amount is small in the long-distance shooting, the pulse in the self-start area is not sequentially increased to the in-focus position without performing the acceleration constant-speed deceleration. In addition, even when driving in the self-starting area as described above, if the amount of extension is small as in long-distance shooting, the time required for focusing can be reduced.

[0022]

As described above, according to the present invention, the driving in the self-starting region is performed only at the time of rising and stopping, and the through region occupies most of the lens driving. It is possible to sufficiently reduce the time required for focusing even if it is changed. In particular, there is provided a memory means for storing control data for operating each of the start control means, the acceleration control means, the constant speed drive control means, the deceleration control means, and the stop control means in a readable manner in accordance with a target focusing position. When each of the start control means, the acceleration control means, the constant speed drive control means, the deceleration control means and the stop control means is operated by control data read from the memory means, Optimal control can be easily performed in consideration of torque fluctuation and the like caused by the driving position of the motor. In addition, when an urging means for urging the lens driving means from the initial position to the in-focus position is provided, the torque required for the step motor can be reduced, and the frequency of the self-starting area and the through area is reduced. The speed can be further increased, and the time required for focusing can be further reduced. Furthermore, when the initial position of the photographic lens is set at a long-distance shooting position, it is possible to shorten the focusing time at a long distance, which requires time for the distance measurement operation, and the total time from the distance measurement to the focusing is obtained. Can be averaged regardless of the shooting distance.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the principle of a lens driving device according to the present invention.

FIG. 2 is a characteristic diagram showing pulse frequency torque characteristics of a step motor.

FIG. 3 is a plan view showing a configuration example of a step motor used in the lens driving device of the present invention.

FIG. 4 is a plan view showing an example of an initial state of a power transmission path used in the lens driving device of the present invention.

FIG. 5 is a sectional view of the power transmission path shown in FIG. 4;

FIG. 6 is a plan view showing an initial state of a blade opening / closing mechanism used in the embodiment of the present invention.

FIG. 7 is a cross-sectional view around a lens of the lens driving mechanism of the present invention.

FIG. 8 is a plan view showing a state where the power transmission path shown in FIG. 4 has been operated to the maximum.

FIG. 9 is a plan view showing a state where the blade opening / closing mechanism shown in FIG. 6 has reached a fully open position.

FIG. 10 is a time chart showing a control operation example of the present invention.

[Explanation of symbols]

1 (30) Shooting lens 2 Lens drive member 3 Step motor 4 Connecting means 6 Distance measuring device 7 Motor control means 7a Start control means 7b Acceleration control means 7c Constant speed drive control means 7d Deceleration control means 7e Stop control means 7f Reverse rotation control Means 11 Output pinion constituting the connecting means 12a, 12b, 13a, 13b, 14a, 14b Gear group constituting the connecting means 15 Lens driving ring 15b as a specific example of the lens driving member 15b Projecting piece 17 Feeding gear 18 Urging means An example spring

Claims (5)

[Claims] 1. A step motor capable of rotating forward and backward, a motor control means for controlling the drive of the step motor, a photographing lens for forming a subject image on a predetermined image plane, and a photographing lens. Driving the lens drive means, connecting the step motor and the lens drive means, and transmitting the forward rotation operation of the step motor to drive the photographing lens from an initial position to an in-focus position, A lens driving device comprising: a coupling unit for transmitting the reverse rotation operation to drive the photographing lens from the in-focus position to the initial position, wherein the motor control unit controls the stepping motor stopped at the initial position. A start control means for supplying a normal rotation pulse in a frequency band within the self-start area to start the step motor in the normal rotation; Control means for increasing the forward rotation pulse frequency to the through region for the step motor placed in the normal state, and the forward rotation pulse frequency applied to the step motor placed in the forward rotation state in the through region by the acceleration control means Constant-speed drive control means for maintaining near the desired in-focus position, and forward rotation pulses applied to the step motor driven to near the in-focus position by the constant-speed drive control means again within the self-start area. A lens driving device comprising: deceleration control means for reducing the frequency band to a frequency band; and stop control means for stopping a step motor driven to a desired focusing position by the deceleration control means. 2. The lens driving device according to claim 1, wherein
Control data for operating each of the start control unit, the acceleration control unit, the constant speed drive control unit, the deceleration control unit, and the stop control unit is stored in a readable manner according to a target focus position. A memory means for controlling activation of each of the activation control means, the acceleration control means, the constant speed drive control means, the deceleration control means, and the stop control means by control data read from the memory means. Characteristic lens driving device. 3. A lens driving device according to claim 1, further comprising: urging means for urging said lens driving means from an initial position toward a focus position. . 4. The lens driving device according to claim 1, wherein the initial position of the photographing lens is set at a long distance photographing position. 5. A lens driving device according to claim 1, wherein said motor control means is provided within a self-starting area for a step motor moving from an in-focus position to an initial position. A reverse rotation control means for supplying a reverse rotation pulse in the frequency band of (1) to return the step motor to the initial position.