Autofocus Driving Unit Segmentation for Lens Precision
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Solution Overview
Problem
Existing autofocus driving units in photographing apparatuses face a trade-off between lens position precision and driving speed, with increased pitch for higher speed reducing precision and increased steps per revolution in step motors leading to noise and vibration.
Innovation Solution
Incorporating a second driving source, such as a variable member made of piezoelectric, magnetostrictive, or shape memory alloy materials, to move the lead screw and rotor in a different direction, allowing for improved lens movement speed and precision without increasing the revolutions of the first driving source, thus reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the pitch of the screw threads is increased to provide a high driving speed, then the driving speed is improved, but position precision decreases
Solution Approach 1:
The patent divides the driving function into two independent driving sources: a first driving source (step motor) that rotates the lead screw to move the lens holder by integer multiples of a first distance, and a second driving source that moves the lead screw and rotor in the optical axis direction to achieve a second distance different from the first distance. This segmentation allows each driving source to operate optimally without compromising the other, resolving the contradiction between driving speed and position precision.
2Measurement precision
If the pitch of the screw threads is reduced to improve position precision, then the position precision is improved, but the number of revolutions of the step motor increases causing noise or vibration
Solution Approach 1:
By segmenting the driving function into two independent sources, the system can use a moderate pitch that avoids excessive step motor revolutions while still achieving high position precision through the combined action of both driving sources. The second driving source compensates for the reduced precision that would result from a moderate pitch, eliminating the need for high-speed motor operation.
3Measurement precision
If a step motor having a relatively high number of steps per revolution is used to improve position precision, then the position precision is improved, but the effective magnetic surface area in the motor is reduced, resulting in a decrease in driving efficiency and driving torque
Solution Approach 1:
The patent segments the precision control function from the torque generation function by using two separate driving sources. The first driving source (step motor) operates with a moderate number of steps per revolution, maintaining adequate driving torque and efficiency. The second driving source supplements the position precision, allowing the step motor to operate in its optimal torque range without requiring excessive steps per revolution.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances both the moving speed and position precision of the lens while minimizing noise, as the second driving source compensates for precision decreases without requiring more steps from the first driving source.
Implementation Method 1
The variable member may include at least one selected from a piezoelectric material, a magnetostrictive material, and a shape memory alloy
Implementation Method 2
The variable member may include at least one selected from a piezoelectric material, a magnetostrictive material, and a shape memory alloy
Implementation Method 3
The variable member may include at least one selected from a piezoelectric material, a magnetostrictive material, and a shape memory alloy
Data Source
AI summary
An autofocus driving unit for moving a lens holder supporting at least one lens in an optical axis direction with respect to an image sensor. The autofocus driving unit includes: a lead screw that has a length in a direction parallel to an optical axis and rotates to move the lens holder in the optical axis direction; a first driving source that rotates the lead screw so that the lead screw moves in multiple integers of a first distance in the optical axis direction and that comprises a rotor mounted in an outer circumference of the lead screw and a stator that is spaced apart from the rotor and rotates the rotor; and a second driving source that moves the lead screw and the rotor in a first direction that is parallel to the optical axis with respect to the stator so that the lens holder is moved by a second distance that is different from the first distance in the optical axis direction.