Vibrating device and image equipment having the same

1. A vibrating device comprising: a dust-screening member which is shaped like a plate as a whole and has at least one side that is symmetric with respect to a symmetry axis; a vibrating member secured to the dust-screening member and configured to produce, at the dust-screening member, vibration having a vibrational amplitude perpendicular to a surface of the dust-screening member; and a drive unit configured to drive the vibrating member to produce vibration Z(x,y) at the dust-screening member, the vibration being expressed as follows:

Z ( x,y )= W mn ( x,y )·cos(γ)+ W nm ( x,y )·sin(γ)

where Z(x,y) is vibration at a given point P(x,y) on the dust-screening member; m and n are positive integers including 0, indicating the order of natural vibration corresponding to a vibrational mode;

W

mn

⁡

(

x

,

y

)

=

sin

⁡

(

n

⁢

⁢

π

·

x

+

π

2

)

·

sin

⁡

(

m

⁢

⁢

π

·

y

+

π

2

)

;

W

nm

⁡

(

x

,

y

)

=

sin

⁡

(

m

⁢

⁢

π

·

x

+

π

2

)

·

sin

⁡

(

n

⁢

⁢

π

·

y

+

π

2

)

;

and

γ is +π/4 or ranges from −π/8 to −π/4, wherein the device has such a size that LP/LF is 0.5 or more, but less than 1, where LF is the length of the sides to which the vibrating member is arranged in a virtual rectangle having the same area as the surface of the dust-screening member and sides including the one side, and LP is the longitudinal length of the vibrating member of the sides parallel to the one side.

2. The device according to claim 1 , wherein the dust-screening member coincides with the virtual rectangle when the dust-screening member is rectangular.

3. The device according to claim 1 , wherein the dust-screening member has such a size that the ratio of the length of the short sides to the length of the long sides in the virtual rectangle is 0.9 or more, but less than 1.

4. The device according to claim 1 , wherein

γ is +π/4, and

the vibration produced at the dust-screening member by the drive unit is vibration such that peak ridges of the vibration having a vibrational amplitude perpendicular to the surface of the dust-screening member form closed loops.

5. The device according to claim 1 , wherein

γ ranges from −π/8 to −π/4, and

the vibration produced at the dust-screening member by the drive unit is vibration such that peak ridges of the vibration having a vibrational amplitude perpendicular to the surface of the dust-screening member form curves around a midpoint of the side which the dust-screening member has.

6. The device according to claim 1 , wherein

the vibrating member includes a piezoelectric element, and

the drive unit configured to supply a signal to the piezoelectric element to produce the vibration at the dust-screening member, the signal having a frequency that accords with a size and material of the dust-screening member.

7. The device according to claim 6 , wherein the drive unit configured to supply a signal to the piezoelectric element at prescribed time intervals, the signal changing in frequency, from a drive-start frequency to a drive-end frequency in increments of a given transmutation frequency, including the frequency that accords with the with size and material of the dust-screening member.

8. The device according to claim 1 , wherein a plurality of vibrating members are provided on the dust-screening member.

9. An image equipment comprising: an image forming element having an image surface on which an optical image is formed; a dust-screening member which is shaped like a plate as a whole, has at least one side that is symmetric with respect to a symmetry axis, and has a light-transmitting region flaring in a radial direction from the center, facing the image surface and spaced therefrom by a predetermined distance; a vibrating member configured to produce vibration having an amplitude perpendicular to a surface of the dust-screening member, the vibrating member being provided on the dust-screening member, outside the light-transmitting region through which a light beam forming an optical image on the image surface passes; a sealing structure for surrounding the image forming element and the dust-screening member, thereby providing a closed space in which the image forming element and the dust-screening member that face each other; and a drive unit configured to drive the vibrating member to produce vibration Z(x,y) at the dust-screening member, the vibration being expressed as follows:

Z ( x,y )= W mn ( x,y )·cos(γ)+ W nm ( x,y )·sin(γ)

where Z(x,y) is vibration at a given point P(x,y) on the dust-screening member; m and n are positive integers including 0, indicating the order of natural vibration corresponding to a vibrational mode;

W

mn

⁡

(

x

,

y

)

=

sin

⁡

(

n

⁢

⁢

π

·

x

+

π

2

)

·

sin

⁡

(

m

⁢

⁢

π

·

y

+

π

2

)

;

W

nm

⁡

(

x

,

y

)

=

sin

⁡

(

m

⁢

⁢

π

·

x

+

π

2

)

·

sin

⁡

(

n

⁢

⁢

π

·

y

+

π

2

)

;

A

⁢

nd

γ is +π/4 or range from −π/8 to −π/4, wherein the equipment has such a size that LP/LF is 0.5 or more, but less than 1, where LF is the length of the sides to which the vibrating member is arranged in a virtual rectangle having the same area as the surface of the dust-screening member and sides including the one side, and LP is the longitudinal length of the vibrating member of the sides parallel to the one side.

10. The equipment according to claim 9 , wherein the dust-screening member coincides with the virtual rectangle when the dust-screening member is rectangular.

11. The equipment according to claim 9 , wherein the dust-screening member has such a size that the ratio of the length of the short sides to the length of the long sides in the virtual rectangle is 0.9 or more, but less than 1.

12. The equipment according to claim 9 , wherein

γ is +π/4, and

the drive unit produces at the dust-screening member vibration such that peak ridges of the vibration having a vibrational amplitude perpendicular to the surface of the dust-screening member form closed loops around an optical axis that passes the image surface of the image forming element.

13. The equipment according to claim 12 , wherein the sealing structure includes:

a holder arranged so as to achieve airtight sealing between the image forming element and the dust-screening member; and

a support member configured to secure the dust-screening member to the holder, the support member being arranged in a node region that has almost no vibrational amplitude perpendicular to a surface of the dust-screening member.

14. The equipment according to claim 9 , wherein

γ is −π/8 to −π/4, and

the drive unit produces at the dust-screening member vibration such that peak ridges of the vibration having a vibrational amplitude perpendicular to the surface of the dust-screening member form curves surrounding a midpoint of the side which the dust-screening member has.

15. The equipment according to claim 14 , wherein the sealing structure includes:

a holder arranged so as to achieve airtight sealing between the image forming element and the dust-screening member; and

a support member configured to secure the dust-screening member to the holder, the support member being arranged in a node region that has almost no vibrational amplitude perpendicular to a surface of the dust-screening member.

16. The equipment according to claim 9 , wherein

the vibrating member includes a piezoelectric element, and

the drive unit configured to supply a signal to the piezoelectric element to produce the vibration at the dust-screening member, the signal having a frequency that accords with a size and material of the dust-screening member.

17. The equipment according to claim 16 , wherein the drive unit configured to supply a signal to the piezoelectric element at prescribed time intervals, the signal changing in frequency, from a drive-start frequency to a drive-end frequency in increments of a given transmutation frequency, including the frequency that accords with the with size and material of the dust-screening member.

18. The equipment according to claim 9 , wherein vibrating members including the vibrating member are opposed across a transmission region of the dust-screening member, through which light passes.