Autofocus Projection Lens Fine Adjustment via Segmented Group Movement
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Solution Overview
Problem
Existing autofocus systems in projection display and camera applications face challenges with bulky designs due to the need for large motors to move entire lens bodies for focusing adjustments, leading to slow adjustment times and image quality degradation, especially with thermal defocus issues in aspheric plastic lenses.
Innovation Solution
A compact autofocus projection apparatus that only moves a single group of lenses, utilizing a small stepper motor and time-of-flight distance measurement with infrared laser for rapid autofocus and thermal defocus compensation, allowing for quick and precise adjustments without moving the entire lens body.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the entire projection lens body is moved back and forth for focusing adjustment, then focusing accuracy is improved, but the device volume becomes bulky due to the mass of the projection lens requiring a big motor
Solution Approach 1:
The projection lens system is divided into multiple lens groups (first, second, third, and fourth lens groups). Instead of moving the entire lens body, only the second lens group is moved along the optical axis by a small stepper motor to achieve focusing adjustment. This segmentation allows a small motor to suffice, reducing device volume while maintaining focusing accuracy.
Solution Approach 2:
The focusing function is extracted from the entire lens body and assigned to a specific movable lens group (second lens group). This extraction enables the use of a small motor to move only the necessary component, avoiding the need to move the heavy entire lens assembly, thus reducing device volume.
2Extent of automation
If the entire projection lens body is moved for autofocus adjustment, then autofocus capability is achieved, but the adjustment time becomes long (over 1 second) due to the mass of the projection lens
Solution Approach 1:
The lens system is segmented into movable and stationary parts, with only the second lens group being movable. This reduces the mass that needs to be accelerated and decelerated during autofocus adjustments, significantly reducing adjustment time while maintaining automated focusing capability.
Solution Approach 2:
The patent replaces contrast detection autofocus control methods with time-of-flight (TOF) auto focus method using an infrared laser. The TOF method calculates distance directly by measuring light travel time, enabling faster control of the stepper motor and reducing adjustment time from over 1 second to under 0.3 seconds.
3Ease of operation
If a fixed focal-length lens body is moved for focusing adjustment, then focusing is achieved, but image quality degrades significantly when moving too close or too far
Solution Approach 1:
The projection lens system is divided into multiple lens groups with different functions. The second lens group is specifically designed to be movable for focusing adjustment, while other lens groups remain stationary. This segmentation allows optimized positioning of each group to maintain image quality across various distances.
Solution Approach 2:
The patent implements focal-length fine adjustment by moving the second lens group, which changes the effective focal length of the projection lens system. This allows maintaining optimal image quality across different projection distances by dynamically adjusting the focal length parameter rather than using a fixed focal-length lens.
4Volume of moving object
If an aspheric plastic lens is used in projection lens system, then compact design is achieved, but thermal defocus occurs when the projector runs for a while
Solution Approach 1:
The lens system is segmented into multiple groups, with the second lens group being movable. This allows independent adjustment of the second lens group to compensate for thermal defocus in aspheric plastic lenses without moving the entire lens system, maintaining compact design while improving focus stability.
Solution Approach 2:
The patent uses time-of-flight (TOF) distance measurement module to provide feedback on projection distance and focus status. This feedback enables the control system to detect thermal defocus and automatically adjust the second lens group position to compensate, maintaining focus stability during prolonged operation.
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
Enables rapid autofocus adjustments in under 0.3 seconds and automatic thermal defocus compensation, reducing the size and weight of the projection module while maintaining high image quality across various distances and temperatures.
Implementation Method 1
time-of-flight distance measurement module, wherein said stepper motor is connected to said second group lens through an adjustment level and only moves said second lens group for autofocus control based on projection distances measured by the TOF distance measurement module
Implementation Method 2
time-of-flight (TOF) auto focus using infrared laser
Implementation Method 3
stepper motor connected to said second group lens through an adjustment level
Data Source
AI summary
An autofocus projection apparatus having focal-length fine adjustment is disclosed. A projection light engine including the same is also disclosed. The autofocus projection apparatus comprises a projection lens system, which comprises a first lens group, a second lens group, an aperture stop, a third lens group and a forth lens group arranged from a long conjugate side to a short conjugate side; a stepper motor, a control board, and a time-of-flight (TOF) distance measurement module; wherein the stepper motor is connected to an inner barrel for enclosing the second group lens through an adjustment level and only moves the second lens group for autofocus adjustment based on projection distances measured by the TOF distance measurement module. A 3D TOF module which includes a modulated flash light emitter and a CMOS camera sensor, can be used for automatic keystone correction as well as autofocus distance detection in the projection light engine.