Closed-Loop Lens Drive Layout for Fast, Precise Autofocus
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Solution Overview
Problem
Existing lens drive devices for automatic focusing cameras in mobile phones are time-consuming and lack precision due to inertia and stabilization issues, leading to inaccuracies in focusing.
Innovation Solution
A closed-loop lens drive device with elongated driving magnets, a Hall magnet position detection unit, and a screening can to enhance focusing accuracy and speed, utilizing four-pole magnetization and a stainless steel Hall magnet back gasket to improve magnetic flux intensity and prevent magnetic interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional lens drive device with coil and magnets is used, then the lens can be driven to move to achieve focusing, but the focusing process is time-consuming and the lens shakes at the expected position due to inertia
Solution Approach 1:
The patent implements a closed-loop feedback control system using a Hall sensor to detect the lens support position and feed back to the control circuit. This real-time position feedback enables the system to adjust the coil current dynamically, allowing the lens to stop precisely at the target position without overshooting or shaking, thereby reducing stabilization time and improving focusing speed.
Solution Approach 2:
The patent uses a spring to elastically support the lens support in advance, creating a pre-compressed elastic force that counteracts the inertia of the moving lens. This preliminary mechanical support system helps the lens stabilize faster at the target position by providing continuous restoring force during and after the electromagnetic driving action.
2Speed
If the lens is moved quickly to the target position, then focusing speed is improved, but the actual position stayed does not coincide with the specified position due to inertia
Solution Approach 1:
The Hall sensor continuously monitors the actual position of the lens support and feeds back to the control circuit. The control circuit compares the actual position with the target position and adjusts the coil current in real-time to compensate for inertia effects, ensuring the lens stops precisely at the specified position even when moved quickly.
Solution Approach 2:
The patent replaces pure mechanical positioning with an electromagnetic control system combined with electronic feedback. Instead of relying solely on mechanical stopping mechanisms that cannot account for inertia, the system uses electromagnetic forces controlled by feedback signals to achieve precise positional control.
3Force
If multiple magnets are arranged in the screening can, then the magnetic field intensity is improved, but magnetic field interference between magnets occurs
Solution Approach 1:
The patent extracts the Hall magnet from the screening can structure and places it on the lens support instead. This separation removes the source of magnetic interference from the screening can, allowing multiple driving magnets to be arranged in the screening can to improve magnetic field intensity without causing interference to the position detection system.
Solution Approach 2:
The patent introduces a non-magnetic gasket between the driving magnets and the screening can wall, and uses the lens support as an intermediary structure to carry the Hall magnet. These non-magnetic intermediaries prevent magnetic field interference while maintaining the structural integrity and magnetic field intensity benefits of multiple driving magnets.
4Measurement precision
If the Hall magnet is placed close to the driving magnets to improve detection sensitivity, then position detection precision is improved, but magnetic field interference affects the Hall chip operation
Solution Approach 1:
The Hall magnet is extracted from the screening can structure and relocated to the lens support, physically separating it from the driving magnets in the screening can. This spatial separation eliminates magnetic field interference on the Hall chip while maintaining position detection precision through the closed-loop feedback control system.
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
The device achieves faster and more accurate focusing with lower power consumption, improved anti-interference capacity, and reduced delay and shaking issues, enabling better imaging even in insufficient light conditions.
Implementation Method 1
By powering on the coil, the magnets and the coil are interacted to generate an electromagnetic force, so that the lens support is driven to move to an optical axis direction
Implementation Method 2
a Hall chip is provided on the PCB board; a Hall magnet back gasket and a Hall magnet are provided at corresponding positions of the lens support; spatially, the Hall magnet and the Hall chip are spaced to each other and are configured oppositely
Data Source
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AI summary
A lens drive device, comprising a lens support (1), a coil (2) winded at a periphery of the lens support (1), an upper cover (3) arranged above the lens support (1), and a lower cover (4) arranged below the lens support (1); a screening can (5) is covered outside the lens support (1); a driving magnets (9) is respectively provided on opposite two inner sidewalls of the screening can (5); a Printed Circuit Board board (PCB board) (10) is provided on a sidewall at another side of the screening can (5); a Hall chip (11) is provided on the PCB board (10); a Hall magnet back gasket (12) and a Hall magnet (13) are provided at corresponding positions of the lens support (1); spatially, the Hall magnet (13) and the Hall chip (11) are spaced to each other and are configured oppositely; and the PCB board (10) and the Hall chip (11) thereon and the Hall magnet (13) form a lens position detection unit. Since the driving magnets (9) and the Hall magnet (13) are not hindered to each other in a configuration structure, no obstacle is produced to assembly work, and the further miniaturization and thinning of the lens drive device also become possible.