Lens driving apparatus and method

Patent metadata

Field	Value
Publication number	US-9500838-B2
Application number	US-201514670449-A
Country	US
Kind code	B2
Filing date	Mar 27, 2015
Priority date	Sep 28, 2012
Publication date	Nov 22, 2016
Grant date	Nov 22, 2016

Abstract

A lens driving apparatus for a lens includes a voice coil motor. A coil position of a coil is detected. A table memory stores a correction factor for each one of plural values of the coil position according to flux density distribution. The correction factor is read from the table memory according to the detected coil position. A coil current is corrected by use of the correction factor for each coil position. The corrected coil current is caused to flow through the coil, with which the lens is moved together along an optical axis. Consequently, changes in a moving speed of the lens can be prevented.

First claim

What is claimed is:

1. A lens driving apparatus for a lens supported in a lens holder movable in an optical axis direction, comprising:
a voice coil motor, having a magnet extending in said optical axis direction, and a coil disposed in a magnetic field of said magnet and coupled to said lens holder, for generating electro-magnetic force by flow of a coil current, to move said lens holder together in said optical axis direction;
a position detector for detecting a coil position of said coil relative to said magnet in said optical axis direction;
a first table memory for storing a first correction factor for compensating for a low level area in flux density distribution of said magnet in said optical axis direction in relation to respectively said coil position;
an initial flux density memory for storing initial flux density of said magnet set in a reference position;
a flux density measurer for measuring monitored flux density of said magnet in said reference position;
a flux density ratio determiner for determining a flux density ratio between said initial flux density and said monitored flux density being measured by said flux density measurer;
a factor modification unit for modifying said first correction factor stored in said first table memory by use of said flux density ratio in relation to respectively said coil position;
a controller for correcting said coil current according to said first correction factor read out from said first table memory according to said coil position detected by said position detector.

2. A lens driving apparatus as defined in claim 1 , wherein said flux density measurer measures said monitored flux density upon powering up.

3. A lens driving apparatus as defined in claim 1 , wherein said flux density measurer measures said monitored flux density at each time that a predetermined period elapses;
further comprising a first update unit for updating said first table memory for respectively said coil position according to a new value of said first correction modified by use of said flux density ratio.

4. A lens driving apparatus as defined in claim 1 , further comprising:
an angle detector for detecting an elevation/depression angle of a lens barrel containing said lens holder;
a second table memory for storing a second correction factor for compensating for a low force area in said electro-magnetic force changeable according to a change in said elevation/depression angle in relation to respectively said elevation/depression angle;
wherein said controller corrects said coil current by use of said second correction factor read out from said second table memory according to said elevation/depression angle being detected by said angle detector.

5. A lens driving method for a lens supported in a lens holder movable in an optical axis direction, comprising steps of:
using a voice coil motor, having a magnet extending in said optical axis direction, and a coil disposed in a magnetic field of said magnet and coupled to said lens holder, for generating electro-magnetic force by flow of a coil current, to move said lens holder together in said optical axis direction;
detecting a coil position of said coil relative to said magnet in said optical axis direction;
acquiring a first correction factor from a first table memory according to said coil position being detected, said first table memory storing said first correction factor for compensating for a low level area in flux density distribution of said magnet in said optical axis direction in relation to respectively said coil position;
measuring monitored flux density of said magnet;
determining a flux density ratio between initial flux density of said magnet being stored and said monitored flux density being measured;
modifying said first correction factor by use of said flux density ratio in relation to respectively said coil position;
correcting said coil current according to said first correction factor.

6. A lens driving method as defined in claim 5 , further comprising steps of:
detecting an elevation/depression angle of a lens barrel containing said lens holder;
storing a second correction factor in a second table memory for compensating for a low force area in said electro-magnetic force changeable according to a change in said elevation/depression angle in relation to respectively said elevation/depression angle;
wherein in said current correcting step, said coil current is corrected by use of said second correction factor readout from said second table memory according to said elevation/depression angle being detected.

Assignees

• Fujifilm Corp

Inventors

• Shimotsu Shinichi

Classifications

• G02B7/04 Primary

  with mechanism for focusing or varying magnification · CPC title

• H02K41/0356

  moving along a straight path · CPC title

• G02B7/023

  permitting adjustment · CPC title

• H02P25/034

  Voice coil motors (voice coil motors driven by DC H02P7/025) · CPC title

• G02B7/08 Primary

  adapted to co-operate with a remote control mechanism · CPC title