JP3475383B2 - Lens device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a lens device which is used in a camera, a video camera, a copying machine or the like and has an actuator for moving a predetermined lens.

[0002]

2. Description of the Related Art Generally, a lens apparatus includes actuators such as a zoom motor for driving a zoom lens group for zooming and a focus motor for driving a focusing lens group for focusing. It is fixed to the lens barrel that forms the outer shell of the lens device.

All of these actuators are accompanied by vibrations during driving, and the vibrations are transmitted to the lens barrel, and the transmitted vibrations cause a problem that the lens device emits noise.

Particularly in recent years, stepping motors convenient for position control are often used for these actuators, and since stepping motors in principle always have periodic vibrations, noise countermeasures for them are an extremely important problem. is there.

First, these vibrations will be considered by considering a model of forced vibration of a one-degree-of-freedom system as shown in FIG.

In the figure, a mass m is connected to the solid wall 41 with a spring stiffness k and a damping coefficient c. In this example, the mass m can be considered as a motor and the solid wall 41 can be considered as a lens barrel, and the spring stiffness k and the damping coefficient c are values determined by the material and shape of the lens barrel.

The equation of motion when the arbitrary excitation force f (t) acts on this mass m can be expressed by the following equation.

(M · d ² x / dt ² ) + (c · dx / dt) + kx = f (t) ... Both sides are multiplied by exp [−iωt] (where ω is an angular frequency). Then, the relationship is ω = 2πf with the actual frequency f (Hz).) When integrated in the range of time −∞ <t <+ ∞ (Fourier transform), the formula is transformed into the following formula. .

(−ω ² m + iωc + k) X = F ... Here, G (ω) = X / F ... Is called compliance, and represents the frequency response of the displacement X to the force F.

An example of compliance is shown in FIG.

Here, f _n (Hz) (= ω _n / 2π) is a natural frequency and can be expressed by an equation.

F _n = (k / m) ^1/2 / 2π ... Further, the damping ratio ζ can be expressed by an equation.

Ζ = c / {2 (mk) ^1/2 } ... Looking at this FIG. 2, the compliance is very large at frequencies near the natural frequency f _n (Hz). I understand. Its frequency f _f of the maximum value is almost the same as the natural frequency f _n, the difference between f _f and f _n is the damping ratio ζ
However, since the difference is very small, it can be considered that the peak of the compliance occurs almost in the vicinity of f _n . The size of the peak changes depending on the damping ratio ζ, and the smaller the damping ratio ζ, the larger the size of the peak. Further, when the damping ratio ζ is 1/2 ^1/2 or more, no peak occurs even at f _n .

That is, when the excitation frequency applied to the motor having the mass m approaches the natural frequency of the system, a resonance phenomenon occurs in which the vibration displacement of the mass m becomes very large, and the vibration occurs.
It is considered that the motion propagates through the spring stiffness k and the damping coefficient c, and causes the lens barrel, which is the solid wall 41, to quiver and generate noise.

The degree of transmission of this vibration is called the transmissibility,
As shown in FIG. The horizontal axis represents the ratio ω / ω _n (= f /) of the frequency ω (= 2πf) used and the natural frequency ω _n (= 2πf _n ).
f _n ), the vertical axis is the degree to which the vibration of mass m is transmitted to the solid wall. The degree of the transmission becomes maximum when the frequency ω used matches the natural frequency ω _n . The smaller the damping ratio ζ, the larger the magnitude. Also, use ω
_{When n} is 2 ^1/2 or more, the degree of transmission is 1 or less, that is, smaller than that which is transmitted as it is, that is, it is transmitted with attenuation. The smaller the damping ratio ζ, the greater the degree of damping, that is, the lesser the degree of transmission.

As a countermeasure against this, first, the motor is not used in the vicinity of the natural frequency of the system, and the frequency is always higher than the natural frequency, to be precise, it is 2 ^1/2 times or more of the natural frequency, and moreover, Use at the highest frequency possible.

Therefore, conversely, the natural frequency is often moved to a lower frequency.

In order to lower the natural frequency fn (Hz), as shown in the equation, first, the spring stiffness k is reduced. This is to make the lens barrel fixing the motor soft, but there is a problem of strength as the lens barrel, and there is a limit naturally.

It is also conceivable that the motor is not directly fixed to the lens barrel but can be mounted via a soft material, but this also has a limit in its softness because the mounting position of the motor is not fixed. Is exactly the same as above.

Further, if the spring stiffness k is reduced, the natural frequency fn (Hz) is lowered, but the damping ratio ζ is increased as can be seen from the equation. 2 ^1/2 fn as shown in FIG.
At frequencies above (Hz), the smaller the damping ratio ζ, the harder it is for the vibration to propagate, so it is not a good idea to reduce the spring stiffness k.

In order to reduce the damping ratio ζ, the damping coefficient c
However, the attenuation coefficient c is a physical property value determined by the material of the lens barrel used,
Its value cannot be moved freely.

However, it can be seen from the equations and expressions that not only can the natural frequency fn (Hz) be reduced by increasing the mass m, but also the damping ratio ζ can be reduced.

Therefore, generally, the noise countermeasures for the lens barrel are
A weight such as lead is often attached to the vibrating portion of the lens barrel.

In addition to being directly attached to the motor, it is often applied to the vibrating member of the lens barrel.

This is because the above theory holds true not only for the model as shown in FIG. 1 in which the mass is concentrated like a motor, but also for the distributed constant model of a plate or beam.

[0026]

However, in the explanation of the preceding paragraph, the actual lens drive of recent years often covers a wide frequency range only when the frequency to be used is one point, and further, the range is continuous. Often used. Therefore, the natural frequency may be included in the frequency domain.

The countermeasure when the natural frequency is in the frequency range to be used is completely opposite to the explanation of the damping ratio ζ in the previous section. As can be seen from FIG. When the excitation frequency of is close to the natural frequency, it resonates and a large noise is generated.

The actual lens barrel is not a one-degree-of-freedom system shown in FIG. 1, but a multi-degree-of-freedom system having a plurality of natural frequencies (vibration modes). As a result, there are frequencies that generate large noises in places to be used.

As a countermeasure for this, the spring stiffness k or the mass m is changed according to each vibration mode to make a fine adjustment of the mode. In order to use even in the vicinity, after all, it is not a drastic measure unless the damping ratio ζ is increased.

However, it is extremely difficult to change the damping coefficient c which governs the damping ratio ζ, because the value depends on the physical properties of the material.

Therefore, various methods of damping the magnitude of vibration at resonance depending on the structure have been studied.

However, as shown in FIG. 4, what is practically used at present is only a vibration damping steel plate in which a viscoelastic material 51 is sandwiched between two metal plates 52, and the vibration damping steel plate is manufactured by a manufacturing process. Is complicated and the quality is not stable, which makes it extremely expensive and difficult to use for low-cost products such as lens barrels. Also, the effect was not very good.

In view of the above problems, it is an object of the present invention to propose a lens device having a simple and low-cost structure and a vibration damping effect in which resonance damping performance is extremely effective.

[0034]

SUMMARY OF THE INVENTION The above object, the with the lens apparatus having an actuator for moving the predetermined lens, the lens barrel constituting an outer shell of said lens device is formed by a first resin material A predetermined hole is formed in a part of the lens barrel, and the hole is formed in the second resin material.
Are embedded in a member which is more formed by the lens apparatus, wherein the Young's modulus of the second resin <br/> material is smaller than the Young's modulus of the first resin material, it is achieved It

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION One embodiment of a lens device of the present invention is shown in FIG.

A guide shaft 1 is provided inside the lens barrel 10.
The movable lens group frames 12 and 14 and the fixed lens group frame 13 are supported with the optical axes aligned with each other via 5 and 16, and the guide shafts 15 and 16 are fixed to the lens barrel 10 by pressing members 17 and 18. . The fixed lens group 11 is directly fixed to the lens barrel 10. Reference numeral 19 is a lid that covers the opening of the lens barrel 10.

Furthermore, a stepping motor unit 21 for driving the moving lens group frame 12 and a stepping motor unit 22 for driving the moving lens group frame 14.
Is fixed directly to the lens barrel.

Besides this, the lens barrel 10 is provided with an auto iris, a lens position sensor, etc., but these are not shown in the drawing because they are not related to the present invention.

In this embodiment, the lens barrel 10 is a glass fiber 15 which is an engineering plastic (hereinafter referred to as engineering plastic) material having sufficient impact resistance.
% Injection polycarbonate part (hereinafter referred to as PCG). As the physical properties of this material, Young's modulus: E = 4.6 (GPa), Poisson's ratio: γ = 0.
It is 3.

The present invention is to replace the part 10a of the lens barrel 10 with a member 20 made of a material having a Young's modulus lower than that of the material of the lens barrel 10.

In this embodiment, the member 20 is made of thermoplastic elastomer (hereinafter referred to as TPE). This material has E = 0.13 (GPa) and γ = 0.49, and the Young's modulus is about 1/35 of PCG.

Of course, the present invention is not limited to the combination of these materials, and various elastomers which are not thermoplastic may be used for the member 20, various rubber materials may be used instead of the elastomer, and further, the Young's modulus is low. Various engineering plastics are also acceptable. In addition, the material that forms the base of the lens barrel is PCG.
Besides, it may be ABS or the like. In short, the lens barrel 10
Is partly formed of a material having a lower Young's modulus.

As a manufacturing method thereof, as shown in FIG. 5, a hole may be preliminarily formed in a part 10a of the lens barrel 10 and a member 20 having a low Young's modulus may be embedded therein, or 2
You may process integrally by a color molding method.

Next, the basic principle of the present invention and its effect will be described.

FIG. 6A shows a flat plate corresponding to the wall of the lens barrel, and the material thereof is the above-mentioned PCG. The flat plate has a long side of 80 mm, a short side of 40 mm, and a plate thickness of 2 mm.
Due to the structure of the lens barrel, two short sides and one long side are fixed.

The simulation results of vibration analysis of this flat plate by FEM (finite element method) are shown below.

The model of FIG. 6 (A) is solid P
It is called a late model and is abbreviated as SPM hereinafter.

Under the above conditions, the problem of 500-
In the frequency region of 5000 (Hz), FIGS.
There are three vibration modes shown in (C).

In each vibration mode when an exciting force acts in the direction perpendicular to the plane of this flat plate, the vibration acceleration (Acceleration) at the point P which is the representative evaluation position.
Is shown in Table 1 together with the natural frequency (Frequency).

[0050]

[Table 1]

It can be seen from this calculation result that the vibration acceleration in Mode 3 is much larger than that in Mode 1, and in this example, the vibration force is applied in the direction perpendicular to the plane of the flat plate. One mode 2 is that it rarely appears.

Further, the magnitude of the vibration is evaluated not by the vibration displacement but by the vibration acceleration. In the lens device of this example, the noise generated by the vibration is more affected by the vibration acceleration than by the vibration displacement. Because I know that.

The frequency response of the vibration acceleration is called inertance, and when expressed by the compliance G, there is a relationship of -ω ² G (ω) in the one degree of freedom system.

Next, at the center of the model of FIG.
Make a hole in. This is FIG. 6 (B), which is Sol
id Plate Model with Center
It is referred to as rHole, and hereinafter abbreviated as SPM with CH.

The vibration mode is the same as that of SPM, but its natural frequency slightly changes. In each of the vibration modes, the vibration acceleration (Acceleration) at the point P is changed to the natural frequency (Fre) as described above.
It is Table 2 that is described together with the (qency).

[0056]

[Table 2]

Next, the hole of φ20 formed in the center of the flat plate of FIG. 6B is filled with TPE of the above-mentioned material. This is FIG. 6C, and this is Solid Plate Mo.
del with Elastomered Hole
Hereinafter, it is abbreviated as SPM with EH.

In the same manner as above, the vibration acceleration (Acceleration) at the point P is calculated from the natural frequency (Fr).
Table 3 is the one written together with "equency".

[0059]

[Table 3]

Based on the above calculation results, the SPM value is 100%.
Table 4 is a summary of only Mode 1 and Table 5 is a summary of Mode 3 only.

[0061]

[Table 4]

[0062]

[Table 5]

In mode 1 shown in Table 4, even if a hole is formed in the SPM or the hole is filled with TPE, neither the natural frequency nor the vibration acceleration changes so much.

However, looking at the mode 3 shown in Table 5, it was found that opening the hole had no effect.
By filling in with, both the natural frequency and the vibration acceleration are greatly reduced. It can be seen that the vibration acceleration that most affects noise is about half of SPM.

That is, the vibration of the flat plate whose three sides are fixed is
By replacing a certain part of the flat plate with a material having a smaller Young's modulus, it is possible to reduce the natural frequency of a certain mode, and at the same time, to significantly attenuate the vibration acceleration.

Table 6 shows a search for the principle of this effect.

[0067]

[Table 6]

This is the maximum principal stress (M
Here, the ax Principal Stress and the maximum strain energy (Max Strain Energy) are summarized for the mode 3 with the SPM value set to 100% and the position showing the maximum value. The position symbols A to C are shown in FIG.

Looking at this, the maximum principal stress in SPM,
The position where the maximum strain energy occurs is near the fixed long side.

When a hole is drilled, the position where the maximum principal stress is generated moves to the periphery of the hole, and the position of maximum strain energy also becomes the periphery of the hole.

However, if this hole is filled with TPE, the position where the maximum principal stress occurs remains the same around the hole, but the position where the maximum strain energy occurs moves from the hole periphery to the center of the TPE. Will end up.

When the distribution of strain energy was examined in detail,
It was found that the strain energy is almost exclusively stored in TPE. That is, according to this structure, it can be construed that the energy causing the vibration is absorbed by the TPE having a low Young's modulus, so that the magnitude of resonance as a flat plate is relaxed. Since TPE has a smaller Young's modulus and a larger Poisson's ratio than PCG, the Poisson's ratio was changed in order to confirm the difference, but the calculation did not show a large difference.

Now, in the meaning of confirming the above calculation results,
The graph shown in FIG. 8 is obtained by actually making the flat plate model used for the calculation and conducting the experiment to confirm the effect.

The horizontal axis represents the frequency in the range of 0 to 5 kHz, the vertical axis represents the vibration acceleration, the upper figure is SPM, and the lower figure is S.
This is PM with EH.

First, the four resonance points in the above figure correspond to modes 1, 2, 3, and 4 in order of increasing frequency. Although not shown in FIG. 7 for mode 4, it corresponds to twice the harmonic vibration of mode 2.

As can be seen from the above, Mode 3 appears much larger than Mode 1 as calculated.

In addition, although mode 2 hardly appeared in the calculation result, this is because in the experiment, the vibration was applied in the direction perpendicular to the plane of the flat plate by the vibration exciter. It is difficult to vibrate on, and it makes a slight angle to the surface. Then, since a force in the twisting direction is applied to the flat plate, a mode 2 which is a vibration mode of torsional vibration appears.

On the other hand, the SPM with E shown in the figure below
Looking at H, it can be seen that mode 1 does not change much in frequency and size as calculated, and mode 3 has a low resonance frequency and a very small size.

The magnitude thereof is reduced to about 25% of SPM and is attenuated from 50% of the calculation result, but this includes the attenuation characteristic of the elastomer itself which is not included in the previous calculation process. It seems to be the body.

The above-mentioned application of these principles is shown in FIG. That is, the lens barrel 1 in which resonance occurs
A hole is made in the wall of No. 0, and the hole is filled with the TPE member 20.

According to this method, the structure is extremely simple and the weight is not increased as in the conventional case.
It is not difficult to manufacture like the vibration-damping steel plate, and it is possible to mold it integrally with the lens barrel by using the recent two-color molding method.

[0082]

According to the lens device of the first and second aspects, it is possible to provide a lens barrel having a simple and low-cost structure and a damping effect in which the damping performance of resonance is extremely effective. Even if the actuator is driven in a wide frequency range including the natural frequency, there is no fear of noise.

[Brief description of drawings]

FIG. 1 is a diagram of a forced vibration model of a one-degree-of-freedom system.

FIG. 2 is a graph of compliance and natural frequency.

FIG. 3 is a graph of transmissibility and frequency ratio.

FIG. 4 is a diagram of a damping steel plate.

FIG. 5 is a diagram of an embodiment of a lens device.

FIG. 6 is a diagram of an analytical model showing the principle of the present invention.

FIG. 7 is a diagram of vibration modes in this analysis model.

FIG. 8 is a graph of an experiment of a flat plate model.

[Explanation of symbols]

10 lens barrel 11 Fixed lens group 12, 14 Moving lens group frame 13 Fixed lens group frame 15, 16 Guide shaft 17, 18 Presser member 19 lid 20 members 21,22 Stepping motor unit

Claims (2)

(57) [Claims] 1. A lens apparatus having an actuator for moving a predetermined lens, wherein a lens barrel forming an outer shell of the lens apparatus is a first tree.
Some of the lens barrel while being formed by fat material
A predetermined hole is bored and the hole is made of a second resin material.
And a Young's modulus of the second resin material is smaller than that of the first resin material. 2. The lens device according to claim 1, wherein the lens barrel is molded by a two-color molding method using the first resin material and the second resin material.