Optical Deflector Mirror Reinforcement Rib Coupling
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Solution Overview
Problem
Existing optical deflectors used in scanners suffer from low rigidity leading to significant stress and deformation, which deteriorates optical scanning characteristics and can result in mirror breakdown, especially when driven at high speeds.
Innovation Solution
An optical deflector design featuring a mirror with protruded portions on the torsion bars and a reinforcement rib with extension portions that symmetrically couple to the torsion bars, concentrating stress at the protruded portions and preventing distortion of the mirror surface, thereby improving optical scanning characteristics and preventing rib peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the mirror is made thin to reduce moment of inertia and increase resonant frequency, then the mirror can be driven at higher speed, but the rigidity of the mirror becomes very small causing large stress spread and deformation
Solution Approach 1:
The patent applies local quality by making the mirror thin in most areas to reduce moment of inertia, but adding localized reinforcement ribs at specific positions (coupling portions with torsion bars) to concentrate strength where needed. This allows the mirror to be driven at high speed while preventing stress-induced deformation at critical locations.
Solution Approach 2:
The reinforcement structure is segmented into discrete reinforcement ribs positioned at specific locations rather than making the entire mirror thick. This segmentation allows selective strengthening at coupling portions while maintaining overall thinness for high-speed operation.
2Strength
If a ring-shaped reinforcement rib is added to increase rigidity, then stress spread is interrupted and deformation is reduced, but the portions of the mirror between the torsion bars and the reinforcement rib become distorted and the reinforcement rib peels off
Solution Approach 1:
Instead of placing the reinforcement rib far from the torsion bars (as in prior art), the patent inverts the approach by positioning the reinforcement rib directly at the coupling portion between the mirror and torsion bars. This reversed positioning ensures the reinforcement is exactly where stress is generated, preventing both mirror distortion and rib peeling.
Solution Approach 2:
The reinforcement rib is positioned in advance at the coupling portion to preemptively counteract stress concentration before it causes deformation or peeling. This preliminary reinforcement prevents the harmful effects from occurring in the first place.
3Strength
If the reinforcement rib is extended to couple to protruded portions of the torsion bar, then rigidity is increased and stress is concentrated at the protruded portions, but stress still spreads into portions of the mirror surrounded by the extension portions causing distortion
Solution Approach 1:
The patent employs asymmetric design by providing protruded portions only at specific locations (vicinity of coupling portions) rather than uniformly around the mirror. The reinforcement rib extends asymmetrically to couple to these specific protruded portions, concentrating stress control where it is most needed while avoiding unnecessary reinforcement elsewhere that could cause distortion.
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 design effectively concentrates stress at the torsion bar protrusions, preventing mirror distortion and rib peeling, thus enhancing the optical scanning performance and reliability of the deflector.
Implementation Method 1
The torsion bar has a pair of protruded portions arranged symmetrically with respect to the torsion bar in the vicinity of a coupling portion between the torsion bar and the mirror
Implementation Method 2
a relatively large stress as a repulsive force spread from the torsion bars into the mirror would be interrupted by the ring-shaped reinforcement rib
Data Source
AI summary
An optical deflector includes a mirror with a reflective layer on its front-side surface, a first support frame adapted to support the mirror, at least one torsion bar coupled between the first support frame and the mirror; and a reinforcement rib provided on a rear-side surface of the mirror. The torsion bar has a pair of protruded portions arranged symmetrically with respect to the torsion bar in the vicinity of a coupling portion between the torsion bar and the mirror. The reinforcement rib has a central portion and a pair of extension portions extended symmetrically from the central portion and coupled to the protruded portions, respectively, of the torsion bar.