Abstract

In this work, an auto-focus actuator moving lens in mobile phone cameras is developed by applying a rotary VCM (voice coil motor). A novel inclined cam structure is used to convert the rotational motion by the VCM by into the linear motion of the focusing lens. The new focusing design enables the zero holding current required to maintain the lens module in the focusing position as well as the reduction of the module thickness. This paper presents the theoretical analysis and optimal design for the VCM actuator, cam structure and preload spring. We manufacture a prototype module with the size of 9.9×9.9×5.9 mm3. The experimental results agree with the theoretical predictions and meet the required specifications for mobile camera applications.

© 2009 Optical Society of America

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References

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  1. K. Tatsuno, "Current trends in digital cameras and camera-phones," Quarterly review 18, 35-44 (2006).
  2. C.-S. Liu and P. D. Lin, "A miniaturized low-power VCM actuator for auto-focusing applications," Opt. Express 16, 2533-2540 (2008).
    [CrossRef] [PubMed]
  3. H.-P. Ko, H. Jeong, and B. Koc, "Piezoelectric actuator for mobile auto focus camera applications," J. Electroceram. 20, (to be published).
  4. M.-J. Chung and S.-Y. Son, "Development of compact auto focus actuator for camera phone by applying new electromagnetic configuration," J. Mech. Sci. Technol. (KSME Int. J.) 20, 2087-2093 (2006).
  5. H. Ren and S. T. Wu, "Variable-focus liquid lens," Opt. Express 15, 5931-5936 (2007).
    [CrossRef] [PubMed]
  6. S. Kuiper and B. H. W. Hendriks, "Variable-focus liquid lens for miniature cameras," Appl. Phys. Lett. 85, 1128-1130 (2004).
    [CrossRef]
  7. F. Jorgensen, The Complete Handbook of Magnetic Recording, (MacGraw-Hill, 1995).

2008

2007

2006

K. Tatsuno, "Current trends in digital cameras and camera-phones," Quarterly review 18, 35-44 (2006).

2004

S. Kuiper and B. H. W. Hendriks, "Variable-focus liquid lens for miniature cameras," Appl. Phys. Lett. 85, 1128-1130 (2004).
[CrossRef]

Chung, M.-J.

M.-J. Chung and S.-Y. Son, "Development of compact auto focus actuator for camera phone by applying new electromagnetic configuration," J. Mech. Sci. Technol. (KSME Int. J.) 20, 2087-2093 (2006).

Hendriks, B. H. W.

S. Kuiper and B. H. W. Hendriks, "Variable-focus liquid lens for miniature cameras," Appl. Phys. Lett. 85, 1128-1130 (2004).
[CrossRef]

Jeong, H.

H.-P. Ko, H. Jeong, and B. Koc, "Piezoelectric actuator for mobile auto focus camera applications," J. Electroceram. 20, (to be published).

Ko, H.-P.

H.-P. Ko, H. Jeong, and B. Koc, "Piezoelectric actuator for mobile auto focus camera applications," J. Electroceram. 20, (to be published).

Koc, B.

H.-P. Ko, H. Jeong, and B. Koc, "Piezoelectric actuator for mobile auto focus camera applications," J. Electroceram. 20, (to be published).

Kuiper, S.

S. Kuiper and B. H. W. Hendriks, "Variable-focus liquid lens for miniature cameras," Appl. Phys. Lett. 85, 1128-1130 (2004).
[CrossRef]

Lin, P. D.

Liu, C.-S.

Ren, H.

Son, S.-Y.

M.-J. Chung and S.-Y. Son, "Development of compact auto focus actuator for camera phone by applying new electromagnetic configuration," J. Mech. Sci. Technol. (KSME Int. J.) 20, 2087-2093 (2006).

Tatsuno, K.

K. Tatsuno, "Current trends in digital cameras and camera-phones," Quarterly review 18, 35-44 (2006).

Wu, S. T.

Appl. Phys. Lett.

S. Kuiper and B. H. W. Hendriks, "Variable-focus liquid lens for miniature cameras," Appl. Phys. Lett. 85, 1128-1130 (2004).
[CrossRef]

Opt. Express

Quarterly review

K. Tatsuno, "Current trends in digital cameras and camera-phones," Quarterly review 18, 35-44 (2006).

Other

H.-P. Ko, H. Jeong, and B. Koc, "Piezoelectric actuator for mobile auto focus camera applications," J. Electroceram. 20, (to be published).

M.-J. Chung and S.-Y. Son, "Development of compact auto focus actuator for camera phone by applying new electromagnetic configuration," J. Mech. Sci. Technol. (KSME Int. J.) 20, 2087-2093 (2006).

F. Jorgensen, The Complete Handbook of Magnetic Recording, (MacGraw-Hill, 1995).

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Figures (7)

Fig. 1.
Fig. 1.

Structures of two types of VCM focusing actuators; (a) conventional structure with the large holding current [2]; (b) Structure of a proposed VCM actuator with zero holding current.

Fig. 2.
Fig. 2.

(a). Electro-magnetic simulation for the distribution of magnetic flux of air gap between the yoke and magnet; (b). magnetic flux density as a function of rotation angle.

Fig. 3.
Fig. 3.

(a). Torque of VCM actuator; (b) the deflection at various lengths and widths

Fig. 4.
Fig. 4.

Simulation result of spring deflection

Fig. 5.
Fig. 5.

Force diagrams by the cam structure

Fig. 6.
Fig. 6.

(a). Photograph of the proposed auto-focusing actuator; (b) operation test - initial condition; (b) lens moving by input voltage.

Fig. 7.
Fig. 7.

(a). Experimental set-up for testing auto-focusing performance; (b) auto-focusing performance test using a sector star target without auto-focus; (c) with auto-focus

Tables (2)

Tables Icon

Table 1. Input parameters for VCM electromagnetic simulation

Tables Icon

Table 2. Input parameters of the minimum torque

Equations (3)

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F t = q n ( f · cos λ + sin λ ) = 0 , F a = w n ( f · sin λ cos λ ) = 0
T u = F d m 2 ( L + 2 π 9 d m 2 π 9 d m fL ) T d = F d m 2 ( 2 π 9 d m L 2 π 9 d m fL )
2 π 9 f · d m > L

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