JPH04180008A - Lens barrel for zoom lens - Google Patents

Abstract

PURPOSE:To make a lens barrel compact and to reduce noise caused by the movement of a lens by changing the rate of the driving pulse and the exciting voltage of a stepping motor according to the position of a movable lens group. CONSTITUTION:The stepping motor 501 is made to cooperate with a lead screw 502 for driving a variator. Next, a stepping motor 701 is made to cooperate with a lead screw 702 for driving a master lens group. Then, the drastic change of the rotation of the motors 501 and 701 is smoothed by fly wheels 504 and 704 so as to eliminate an excessive phenomenon. Besides, looseness is eliminated by pressing a lens frame 401 in one direction by a coil spring 1006. Then, a variator 2 is slowly moved at a telephoto end (near a tele-position) and quickly moved on a wide end side at a zooming time. Thus, excellent control is executed by the lens barrel nevertheless it is inexpensively constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improvements in zoom lens barrels that are combined with various cameras.

[Conventional technology]

First, in order to facilitate understanding of the present invention, an example of the configuration of a conventional zoom lens barrel for use on a boat will be described with reference to FIG.

A zoom lens system Z′ of this conventional zoom lens barrel 10
In this case, the front lens group L1 and the third lens group L3 are configured as fixed lenses, and the second lens group LX (hereinafter referred to as a variator) and the fourth lens group LX (hereinafter referred to as a variator) are configured as fixed lenses. The fourth lens group (hereinafter referred to as master lens) is configured as a movable lens group.

When changing the magnification, the variator L2 moves forward and backward along the optical axis O to change the magnification ratio, and the master lens group L4 follows and corrects the focus in order to eliminate the focus deviation caused by the magnification change. I do. The positional relationship between the variator L2 and the master lens group L4 at this time, as shown in FIG. 9, has a characteristic in which the movement range of the master lens group L4 rapidly expands particularly near the teleposition.

In this case, the variator L2 is driven by the zoom motor 51 so that the position on the optical axis at that time is digitally detected by the encoder 61, and the master lens L4 is driven by the stepping motor 71.
The configuration is such that the position on the optical axis at that time is detected as the number of pulses from the reference position detected by the reference position detection device 81.

In an actual zoom lens, the above-mentioned relative movement characteristics are replaced in advance with the number of divisions of the encoder 61 and the number of pulses from the above-mentioned reference position and created in a table, which is stored in the variable magnification control system. It is configured to control the movement of L2 and master lens L4.

On the other hand, in the case of focusing, the master lens L4
By making a micro-vibration in the optical axis direction, changes in the level of high-frequency components are detected from an image sensor (not shown) placed on the focal plane side, and front focus and rear focus are determined. Master lens L4 until the peak is obtained.
The camera is configured to perform focusing by moving the .

Now, the lens barrel that ultimately holds the four lens groups L1 to L4 described above is the fixed barrel 1 that constitutes the front half of the lens barrel.
2 and a seat member 13 that forms the rear half of the lens barrel.

In this case, a holding ring 4a is provided at the front end of the fixed cylinder 12, and the group of lune is directly fixed to the fixed cylinder 12 by this holding ring 4a.

Further, a cam cylinder 11 is rotatably mounted on the inner circumferential surface of the fixed cylinder 2 between the intermediate wall 12a of the fixed cylinder 12 and the retaining ring 4b fixed to the rear end portion, and the cam cylinder 11 is arranged rotatably in the optical axis direction. It is set up so that it does not move.

A variator cam groove 11a for moving the variator L2 according to a predetermined movement characteristic diagram is formed on the peripheral wall of the cam cylinder 11, and the rear end meshes with the drive gear 52 of the zoom motor 51. A drive gear portion 11b is formed.

In addition, in the internal space of this cam cylinder 12, the fixed cylinder 12
A zoom guide rod 14 and a rotation movement prevention rod 15 are arranged between the inner peripheral intermediate wall 12a and the retaining ring 4b so as to be parallel to the optical axis 0.

By the way, the variator L2, which is one of the movable lens groups, is configured to be held by the variator holding frame 21.

In this variator holding frame 21, a bush 22 provided on the upper part of the variator holding frame 21 is slidably fitted into the zoom guide support 14, and a U-shaped groove 23 formed on the lower part is engaged with the rotation movement blocking rod 15. Furthermore, a cam follower 24 formed on the upper part of the bushing 22 is connected to the variator cam rod 12 described above.
configured for precision engagement within.

Therefore, when the cam cylinder 11 rotates during zooming,
Due to the cam action of the variator cam groove 11a generated by this rotational movement, the variator holding frame 21 (variator t-
z) moves in the optical axis direction without rotating.

The position information of the variator holding frame 21 on the optical axis at this time is configured to be detected as digital rotation speed (rotation angle) information by the encoder 61 connected to the gear portion 11b of the cam barrel 11. ing. Note that the encoder 61 and the gear portion 11b of the cam cylinder 11 are connected to each other via appropriate intermediate gear trains 62, 63.

On the other hand, the mounting seat member 13 that constitutes the rear half of the lens barrel is
A suitable auto-iris (automatic aperture means) 91 is connected to the fixed barrel 12 with a group of diaphragm blades 92 in between, and the third lens group L3 is directly fixed to the seat member 13.

The master holding frame 41 that holds the master lens L4 has a bushing 42 provided on the lower part of the master holding frame 41 that is attached to the master lens L4, which is installed in parallel between the front wall 13a and the rear wall 13b of the seat member 13. By fitting into the guide rod 31, it is configured to be guided so as to be able to move straight along the optical axis 0.

In addition, the retaining pin 43 provided on the upper part of the master holding frame 41 is attached to the master holding frame 41 by precisely engaging with the U-shaped groove 34 formed in the upper wall portion 13C of the seat member 13. is configured to prevent pivoting movement of the

As described above, this master holding frame 41 is configured to be moved in the optical axis direction by the rotational operation of an appropriate stepping motor 7I.

That is, a nut 73 is screwed onto a lead screw 72 formed on the output shaft of the stepping motor 71, and a protrusion 73a formed on the outer periphery of this nut 73 is engaged with a rubber engagement provided on the master holding frame 41. It fits into the groove 33 of the member and prevents the nut 73 from rotating. Further, an arm 44 formed protrudingly on the lower part of the master holding frame 41 is biased in the direction of the arrow by the coil spring 35.
It is configured so that it is always pressed against the end face of the NAND 73.

Therefore, when the stepping motor 71 rotates the lead screw 72, the nut 73 moves straight in the optical axis direction.

Incidentally, the coil spring 35 in this case is connected to the lead screw 7.
It also functions to eliminate backlash between the screw 2 and the nut 73 and axial play between the stepping motor 71 and the lead screw 72.

Now, since the master holding frame 41 is moved by the stepping motor 71 that rotates under numerical control, it is necessary to set a reference position during numerical control. In order to detect this reference position, a reference position detection device 81 (for example, a photo ink club) having an appropriate structure is provided on the upper wall portion 13c of the seat member 13.

The conventional zoom lens barrel configured in this manner has many problems as described below.

[Problem to be solved by the invention]

That is, in the above-mentioned conventional zoom lens barrel, near the teleposition (hereinafter referred to as the telephoto end), the master lens group must move steeply to follow changes in the position of the variator lens group over a wide range of focus areas. . However,
The method of combining a high-output DC motor with a nonlinear cam and reducing the movement speed near the telephoto end has various problems, such as a complicated control system and difficult machining of the cam cylinder. .

Therefore, it is desirable to use a stepping motor that can be easily controlled by open loop control to move these lens groups. However, although stepping motors have the advantage of being easy to control, they also have problems such as increasing the size of the device and generating noise. That is, in order to stabilize the movement of the variator lens group,
A large (large diameter) stepping motor with high torque is required, but on the other hand, in order to make the main body of the lens barrel more compact and quiet, the trade-off is that a small, low torque motor is desirable. .

In view of the above points, it is an object of the present invention to provide a zoom lens barrel that is compact and equipped with a means for moving the lens with low noise while maximizing the advantage of the stepping motor, which is open-loop control using pulsed current. It is an object.

[Means to solve problems]

To achieve the above object, the present invention provides a zoom lens barrel equipped with a moving lens group driven by a stepping motor via a lead screw, in which the driving pulse of the stepping motor is adjusted according to the position of the moving lens group. The variator is configured to change the rate, and the moving speed of the variator can be adjusted appropriately without using a non-linear cam or the like.

In addition, the excitation voltage of the stepping motor is configured to vary according to the pulse rate, so that the external size of the stepping motor serving as the driving source can be reduced and the desired driving torque can be obtained with low noise. This is what I did.

〔Example〕

Before explaining the embodiments, general characteristics regarding torque, pulse rate, noise, etc. in a stepping motor will be described.

-i, the stepping motor has a property that its output torque decreases as the pulse rate increases, as shown in FIG.

Now, let T o (-n
2, three types of stepping motors with wire diameters a, b, and c (a>b>c), an outer diameter of φ10, and a wire diameter of d,
Let us examine the characteristics of three types of stepping motors, e and f (d>e>f).

First, the pulse rate fluctuation range is f, -f2.1! :
Then, under a constant voltage condition, the required torque T0 can be achieved with an outer diameter of φ12 and wire diameters a and b.

It is only the stepping motor of C. Here, the wire diameter a,
The torque generated by motor b is the required torque T.

Since there is too much leeway, the noise becomes louder. Therefore, when the voltage is constant, the outer diameter = φ12, the wire diameter -
It follows that motor C is optimal.

By the way, if we look at a stepping motor with a wire diameter of d, although it is slightly below the required torque T0 near the pulse rate f2, the outer diameter is small at φ10, which is large enough to contribute to the compactness of the lens barrel body. I understand that.

Therefore, in the embodiment of the present application, in a stepping motor having a wire diameter of -d, the driving voltage is increased near the pulse rate fz to increase the generated torque. That is, if torque = T, voltage -■, and pulse rate -F, then the stepping motor torque T is T = A・V −B −F
-C------■ (A, B, and C are constants). Here, the voltage (■) is V=B/A-F+V according to the pulse rate P.

When changed by the formula, the above ⑐ becomes T=AV. -C, making it possible to keep the torque T constant (C is the detent torque, which corresponds to the minimum torque required to start the motor).

Therefore, by varying the drive voltage, the torque T=T over the entire pulse rate range.

It can be done.

Note that the coefficients A, B, and C are constants specific to the motor that can be measured, and the net load TL can be calculated from the minimum drive voltage and the pulse rate at that time.

The stepping motors 501 and 701, which will be described later, have their sizes determined by the method described above, and the drive pulse rate is appropriately changed according to the position of the movable lens groups, so that the moving speed of these lens groups can be adjusted as appropriate. .

Next, regarding the variator lens group and the master lens group having the characteristics as shown in FIG. 9, conditions for the master lens group to follow the movement of the variator lens group without causing blurring will be clarified.

First, variator lens group: Amount of movement per pulse = ε1 Pulse rate = p1 Master lens group: Amount of movement per pulse = ε2 Pulse rate = 22, and the position of the master lens corresponding to the variator position X is y ( x). At this time, the follow-up conditions for the master lens group with respect to the variator lens group, and the time required for the master lens group to shift IJI for one pulse, must be shorter than that of the variator lens group, so the following should be satisfied. . Here, if y (x) is approximated by a quadratic function, the condition of formula ■ is ε z Pz □≧b'−a' χ −−−−−−−−−−
It can be expressed as −■ε I p I . From now on, when x'=O, that is,
It is clear from the equation that the behavior near the telephoto end, where the right side is maximum, is important.

Therefore, first of all, if you make the value on the left side as large as possible, you should have some margin, but increasing the unit movement amount ε2 of the master lens group means that the unit step width (position This is undesirable because visible blur will occur due to the minute vibrations of the master lens in the optical axis direction mentioned above.Therefore, there is a reasonable upper limit value for ε2. .

Next, increasing the pulse rate p2 may be considered, but as explained in the general characteristic diagram above, the torque of the stepping motor decreases in proportion to the increase in the pulse rate. Therefore, in order to guarantee the accuracy of the moving position during open-loop control, it is necessary to ensure the output of the stepping motor, which leads to an increase in the size of the motor, that is, an increase in the size of the entire lens barrel. Therefore, p2 also has a reasonable upper limit.

The next thing to consider is to always keep ε+p+, the denominator on the left side, small, but since this is nothing but a reduction in the amount of movement of the variator lens group per unit time, that is, the movement speed, T This means that the time required to go from (tele) to W (wide) becomes redundant, which is not desirable in terms of performance.

Therefore, in order to focus on the vicinity of the telephoto end, which is a problem in movement characteristics, even if the movement amount ε1 per pulse is kept constant, the pulse rate p1 is set near X = 0 (telephoto end). The configuration may be such that the pulse rate is low, and as X increases (on the wide side), the pulse rate P+ increases. That is, p+(x)−α×βx−′−′−”
Practical difficulties can be overcome by configuring it so that '-''■.The embodiment of the present application is configured in this way.

In the end, constants a' and b' may be determined so that the follow-up conditions of the master lens group with respect to the variator lens group are as follows.

Furthermore, in order to stabilize the movement of the master lens group, the drive pulse rate is configured to vary depending on the position, and if the density is high on the ω side and low on the close side, then equation , δ, it becomes α+βX (k-ε2/ε,).

Furthermore, if the case where the pulse rate is configured to change non-linearly is included, the general condition τ for P+ and P2 becomes p+(x) dx.

Hereinafter, the present invention will be described based on an embodiment shown in the accompanying drawings.

Fig. 1 is a side sectional view showing the overall configuration of the zoom lens barrel of the present application, Fig. 2 is a front sectional view, Fig. 3 is a horizontal sectional view showing the structure of the outer case, and Fig. 4 (a) is a front guide. A sectional view showing the support of the pin, (b) a sectional view showing the support of the rear guide pin, Fig. 5 a sectional view of the lid body, and Fig. 6 showing the relationship between pulse rate and torque in the stepping motor. FIG. 7 is a diagram showing the principle configuration of a PM type stamping motor, FIG. 8 is a comparison diagram of the principle of the excitation method of the same motor, and FIG. 9 is an explanatory diagram showing the movement characteristics of the variator and master lens.

In the figure, of the five lens groups 1.2.3.4.5 that make up the zoom lens system Z, 1.3.5 is a fixed lens group, 2 is a variator lens group that has a variable power function, and 4 is a composite lens group. This is the master lens group responsible for focusing and zoom correction.

Reference numeral 100 denotes an outer case constituting the lens barrel body, and the outer case 100 includes:
Instead of a cylindrical member like the conventional lens barrel, as shown in the fourth figure,
- Consists of a box-shaped member with a U-shaped cross section and an opening K formed on the side surface.

Reference numeral 101 denotes a lens frame provided on the outer front surface of the outer case 100. The fixed lens group 1 is assembled into the lens frame 101 by a conventional drop-in method, and is configured to be fixed by thermal caulking or the like. 105 is also a lens frame 10
1, the lens frame 105 is the outer case 100.
The fixed lens group 5 is provided on the inner rear surface of the lens, and is arranged so that the fixed lens group 5 can be fixed by the drop-in method. 1
Reference numeral 06 denotes a frame portion for accommodating the solid-state image sensor 7 and the crystal plate 6, and the frame portion 106 is also integrally formed at the rear of the outer case 100.

110.111.112.113 is movable lens group 2.4
Each of the supports 110 to 113 is a rod-shaped member that stands upright from the inner wall surface of the outer case 100 toward the opening K of the outer case 100. The tip is provided with a groove M having an r (J)-shaped cross section. That is, the guide pin 1003 (lower side) is provided in the U-shaped groove M.
, 1004 (lower side) and insert the lid body 109 into the opening from the side.
It can be sealed and fixed.

The variator lens group 2 is housed in a frame 201,
Further, the frame body 201 is provided with a bush 202 through which the guide pin 1004 is held and a U-shaped groove 203 into which the guide pin 1003 is fitted and held.

The master lens group 4 is housed in a frame 401, and the frame 401 includes a bush 402 and a U groove 403.
is provided. Similarly, the fixed lens group 3 also has a frame body 30.
1, and the frame body 301 is provided with a bush 302 and a U groove 303. Here, the U groove 303
．． 403 has a guide pin 1003, and a bush 302.
Guide pins 1004 pass through 402, respectively.

Therefore, the variator lens group 2, fixed lens group 3, and master lens group 4 are connected to the guide pins 1003 and 1004.
It is configured to be movable in the optical axis 0 direction via. However, the fixed lens group 3 is attached to the guide pin 10 at the installation stage.
03.1004, and the frame body 301 after being charged and adjusted is fixed at a predetermined position in the outer case 100.

502 is a lead screw for driving the variator, 50
1 is a stepping motor linked to the lead screw 502. Similarly, 702 is a lead screw for driving the master lens group, and 701 is the lead screw 7.
This is a stepping motor linked to 02. 703 is
This is a nut screwed onto the lead screw 702.

Reference numeral 504.704 is a flywheel invented by the inventor of the present application, and the flywheel 504.704 drives the stamping motor 501 by its respective moment of inertia.
．． 701 is configured to smooth out steep rotational fluctuations and eliminate transient phenomena (Japanese Patent Laid-Open No. 1-20815).
. 505.705 is the flywheel 504.704
This is an O-ring that limits the axial position of the

Here, lead screws 502 and 702 are easy to process by rolling, etc., and can be produced at low cost and with high precision.Furthermore, product variations such as friction coefficients can be reduced, and high precision control is possible. becomes.

Reference numeral 404 denotes a protrusion provided on the lens frame 401 to prevent backlash, and the protrusion 404 is configured to always come into contact with the screw 703 screwed into the screw 702. That is, by fitting the protrusion 703a on the outer periphery of the nut 703 into the rubber groove 405 provided at the lower part of the lens frame 401, the protrusion 404 and the nut 703 can maintain a pressed state. In addition, the lens frame 401
is biased in one direction (in the direction of the arrow in FIG. 1) by a coil spring 1006 disposed coaxially on the outside of the guide pin 1003, and is configured so that the nut 703 can be brought into constant contact with the screw 702 via the protrusion 404. has been done. Furthermore, the coil spring 1006 causes the screw 70 to
2 to one side, and the stepping motor 701
This also eliminates the play of the screw 702 against the screw 702.

Note that the spring pressure of the coil spring 1006 is greater than the total weight of the master lens group 4, lens frame 401, nut 703, lead screw 702, etc.
Needless to say, the structure is such that the shaking can be eliminated regardless of the gripping posture of the camera equipped with the zoom lens barrel 1.

Now, when moving the variator 2, the master lens group 4
Similar to the moving mechanism, it is not possible to use a spring coaxial with the guide pin to shift the nut in one direction and eliminate the rattling of the drive screw system. This is because the movement range of the variator 2 is much larger than that of the master lens group 4, so there is a risk that the spring biasing force at the telephoto or wide end may become too large (minimum spring pressure is set at the wide end). When determining at the end, the load on the tele end side will be excessive)
. In this case, the lead screw 502 is driven by a stepping motor under open-loop control, so in order to counteract the excessive load on the screw and drive it stably, the stepping motor must be made larger, which in turn increases the size of the entire lens barrel. It will bring.

Therefore, in the embodiment of the present application, two nuts 503a and 50
The looseness is eliminated by using springs that urge the parts 3b in opposite directions. That is, the protrusion 204 protruding from the lens frame 201 of the variator lens group 2 is connected to one nut 503.
a and the washer 506, and a spring 1005 is inserted between the washer 506 and the other lug l-503b.
They are interposed so that they repel each other. According to this configuration, from the screw 502 to the nuts 503a, 503b,
Since the driving force transmission path leading to the protrusion 204 of the lens frame 201 is free from rattling due to the springs 1005, the lens frame 201 can be moved relative to the lead screw 502 while maintaining a state free of any bulges. Moreover, at this time, since the length of the blade 1005 is constant, there is no load variation in the drive system, and the blade pressure is applied to the moving object (lens frame 20).
1, lens 2, etc.). Therefore, the stepping motor 501 only needs to have a capacity that can generate the minimum necessary torque, and can be made smaller.

Note that the nuts 503a and 503b are the lead screws 5.
In order to prevent the lens from rotating with respect to the lens frame 201, protrusions 5033 and 5034 erected on the side surfaces thereof are fitted into the rubber grooves 205 of the lens frame 201. In addition, in order to eliminate the axial play of the lead screw, for example,
A known technique such as 814 may be used.

The positions of the variator 2 and the master lens group 4 are controlled by a simple open-loop control method using stepping motors 501 and 701 of the drive system, but in this case, detection of a reference position is essential.

Therefore, when starting up the device of the present application, the lens frame 201.401
The light shielding plates 206 and 406 fixedly attached to each are detected by photo ink clubters 1101 and 1201 to determine the reference position, and the subsequent pulse numbers are counted to determine the position.

By the way, driving by the stepping motor method is DC
Compared to the motor type, this has problems in that it consumes more power and is more likely to generate noise.

In the embodiment of the present application, a PM type stepping motor is employed as the stepping motor, and the PM type stepping motor is driven by an excitation method using detent torque (holding torque).

In Figure 8, which shows the three main types of excitation methods, ■The l-phase excitation method is simple as a control method, but is disadvantageous in terms of generated torque and stability, and is generally rarely used. Never.

(2) The two-phase excitation method has a large torque and (2) a large rotation angle of 18 degrees per pulse, but it has the drawbacks of high power consumption and high vibration and noise.

■Although the 1-2 phase excitation method has smaller torque than the 2-phase excitation method, it can achieve a rotation angle of 9 degrees per pulse, reduce vibration and noise, and is suitable for precision control. are doing.

Therefore, in the embodiment of the present application, this 1-2 phase excitation method is adopted, and in the control mode of ■ sequence - 8 steps, the motor is stopped only at the odd numbered steps of 1.3.5.7. It is composed. This is because, in odd-numbered steps, the positional relationship between the excitation side and the rotor is equal to the detent torque (holding torque) position when not energized, and the energization can be stopped when stopped to save power. This is to ensure that.

That is, in this 1-2 phase excitation method, if 2.4.6
．． If the power is turned off at an even numbered step of 8, the rotor will rotate forward or backward by one step = 9 degrees. Moreover,
Since this rotational deviation is a completely random phenomenon, in the case of open-loop control, the number of pulse counts from the reference position will deviate by ±1 every time the motor stops, making precise control impossible.

901 is an auto iris unit.

In the above embodiment, the U groove 203.303.403, the bunche 202.302.402, and the spring 1006 are
After passing through the guide pins 1003 and 1004 respectively, the lens frames 201 and 30 of the lens group 1.2.3.4.5
1.401 is loaded in one direction through the opening of the outer case 100, and further components such as the stepping motor 501.701 are sequentially assembled, the main setting of the zoom lens system Z is easily completed. That is, compared to the work of sequentially assembling lens groups into a cylindrical lens barrel as in conventional zoom lens barrels, assembly from one direction can be performed much more easily.

Further, the auto iris 901, the zoom photo interrupter 1101, the AF photo interrupter 1201, etc. can also be disposed on the inner surface of the outer case 100 by being assembled from one direction. Furthermore, the stepping motor 701 is also
03 can be hooked onto the arm 404 and fixed. Similarly, the stepping motor 501 moves the arm 204 of the variator frame to one zoom lens) 503a and the washer 50.
Two Nando's 503a, 5 while sandwiching between 6
The protrusions 5034 and 5033 of 03b are connected to the rubber engaging member 205.
After inserting the plate spring 1005 and the engaging element 503, the engagement member 503 may be set in a predetermined position. Furthermore, each U7 of the guide pin strut 110.111.112.113
If the guide pins 1003 and 1004 are held and sealed at 1 iM, all members of the optical system can be assembled while looking directly into the opening from the side. Therefore, even if there is a problem with the position of the lens group or the assembly of other members, it is easy to identify the cause and it is also extremely easy to adjust the problem. Once the assembly and adjustment have been completed, sealing of the outer case 100 can be completed by simply attaching the lid 109.

During zooming, when the stepping motor 501 is rotated while changing the pulse rate depending on the position of the variator 2, the variator 2 moves slowly at the tele end and quickly at the wide end, making it difficult for the master lens 4 to follow. Make it easy. At this time, as the pulse rate of the stepping motor 501 increases, the excitation voltage increases appropriately, and as the pulse rate decreases, the excitation voltage decreases as appropriate.
The generated torque will not fall below the required load, and vibrations and noise will not be generated due to excessive torque.

This also applies to the stepping motor 701 for driving the master lens 4.

Since the lead screw 502 connected to the stepping motor 501 drives the lens frame 201 via the nuts 503a and 503b which are urged in the repulsive direction by the spring 1005, play between the lead screw 502 and the lens frame 201 is always eliminated. Ru. Moreover, the play in the axial direction of the motor 501 and the lead screw 502 can be easily removed using a known technique, for example, Japanese Patent Application Laid-Open No. 2-20814.

On the other hand, since the lead screw 702 connected to the stepping motor 701 drives the lens frame 401 via the nut 703 that is biased in one direction by the spring 1006, the lead screw 702, the lens frame 401, and the lead screw 702 are driven. Play between the motors 701 is always eliminated.

In addition, both lens frames 201.401 have a light shielding plate 206.4.
06 by the photo interrupters 1101 and 1201, the reference position can be determined.
Since it stops only at steps using detent torque, accurate positioning can be achieved even with open-loop control.

〔Effect of the invention〕

As described above, in a zoom lens barrel equipped with a moving lens group driven by a stepping motor via a lead screw, the driving pulse rate of the stepping motor is changed depending on the position of the moving lens group. Since the present invention is characterized in that it is configured as follows, the moving speed of the variator and the master lens can be adjusted as appropriate without using a non-linear cam or the like.

As a result, although it is a lead screw driven movable lens group that enables a compact and inexpensive lens barrel configuration,
No blurring in all areas from tele to wide,
Moreover, the excellent effect is that the zoom lens system can be controlled so that the zoom speed does not become too slow.

Further, by configuring the excitation voltage of the stepping motor to vary according to the pulse rate,
The stepping motor that serves as the drive source can be made smaller in size,
It can also greatly contribute to making the entire lens barrel more compact. In addition, it is possible to avoid the generation of excessive torque with respect to the load, reduce noise, and provide an excellent effect of providing a zoom lens barrel with excellent quietness.

[Brief explanation of drawings]

Fig. 1 is a side sectional view showing the overall configuration of the zoom lens barrel of the present application, Fig. 2 is a front sectional view, Fig. 3 is a horizontal sectional view showing the structure of the outer case, and Fig. 4 (a) is a front guide. Figure 4(b) is a cross-sectional view showing the support of the pin, Figure 5 is a cross-sectional view of the lid, and Figure 6 shows the relationship between pulse rate and torque in the stepping motor. Figure 7 is a diagram showing the principle configuration of the PM type stepping motor, Figure 8 is a comparison diagram of the principle of the excitation method of the motor, and Figure 9 is a diagram showing the principle of the excitation method of the same motor.
The figure is an explanatory diagram showing the movement characteristics of the variator and the master lens, and FIG. 10 is a sectional view showing the structure of a conventional zoom lens barrel. l - Front fixed lens group 2 - Variator lens group 3 - Intermediate fixed lens group 4 - Master lens group 5 - Rear fixed lens group 6 - Solid-state image sensor 7 - Vibration generating means 11 - Cam cylinder 12 - Fixed cylinder 13 - Mounting Seat member 14 - Zoom rod 15 Rotating movement prevention rod 100 - Outer case 101.105 - Lens frame 106 - CCD frame 109 - Lid 110.111.112.113 - Guide pin holding member 1019.1091.1092.1093 - Guide pin holder 201.301.401 - Lens frame 202.302.40:) - Bush 203.303.403 - U groove 204.404 - Arm 205.405 - Rubber groove 206.406 - Light shielding plate 1003.1004 - Guide pin 501.701-Stepping motor 502.702-Lead screw 503a, 503b-Nand 703a-Nand 504.704-Flywheel 505.705--0 ring 1005.1006-Flip 901-Auto iris unit 1101.1201-Photoin Craft M-U-shaped groove〇One optical axis K -Aperture z, z'--Zoom lens system

Claims (2)

[Claims] (1) In a zoom lens barrel equipped with a moving lens group driven by a stepping motor via a lead screw, the drive pulse rate of the stepping motor is configured to be changed depending on the position of the moving lens group. A zoom lens barrel characterized by: (2) The zoom lens barrel according to claim 1, wherein the excitation voltage of the stepping motor is configured to change according to the pulse rate.