Rotary Drive Apparatus Rotor Magnet Cracking Prevention
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Solution Overview
Problem
High-speed rotary drive apparatuses, such as those used in image formation and optical scan systems, face issues with rotor magnet cracking due to centrifugal force and thermal stress, leading to vibration and imbalance, especially at speeds above 30,000 rpm and temperatures above 80 degrees.
Innovation Solution
A rotary drive apparatus design with a support portion for the rotor magnet, where the Young's modulus of the rotor magnet is less than or equal to 75% of the support portion, and an outer diameter of 10 to 30 mm, using a rare-earth bond magnet and aluminum alloy, with press-fitting or adhesive attachment, to reduce centrifugal stress and thermal expansion mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the rotary body is rotated at high speed (30,000 rpm or more), then image formation speed and precision are improved, but the rotor magnet may crack due to centrifugal force and thermal stress
Solution Approach 1:
The patent changes the material parameters of the rotor magnet by specifying a Young's modulus ratio (E1/E2 ≤ 0.75) between the rotor magnet and support portion, and controlling the outer diameter (10-30 mm). These parameter changes optimize the mechanical properties to withstand centrifugal force at high rotation speeds while preventing cracks.
Solution Approach 2:
The patent employs composite material selection by specifying that the rotor magnet be made from a material with appropriate Young's modulus (such as rare-earth bond magnets) and the support portion from aluminum alloy or other materials with matching thermal expansion coefficients. This composite approach ensures both components can withstand high-speed rotation without cracking.
2Ease of manufacture
If the rotor magnet is fixed to the rotation axis with adhesive, then assembly is simplified, but thermal stress causes the fitted portions to move minutely
Solution Approach 1:
The patent addresses thermal stress by selecting materials with matched thermal expansion coefficients. The support portion is specified to have a linear expansion coefficient within 0.8-1.5 times that of the rotor magnet, ensuring both components expand and contract at similar rates during high-temperature operation, thereby maintaining adhesive bond stability.
3Manufacturing precision
If the rotation axis is processed to be perfectly circular, then sealing with rotor magnet is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies local quality by specifying that the support portion have a particular Young's modulus (E2) that is at least 1.33 times that of the rotor magnet. This localized material property enhancement at the support portion compensates for imperfections in the rotation axis circularity, ensuring proper contact and sealing without requiring perfect axis processing.
4Force
If the outer diameter of the rotor magnet is increased, then magnetic strength is improved, but centrifugal force increases causing cracks
Solution Approach 1:
The patent optimizes the outer diameter parameter within the range of 10-30 mm to achieve the desired magnetic force while maintaining resistance to centrifugal force. This parameter optimization ensures the rotor magnet generates sufficient magnetic field strength for high-speed operation without exceeding the mechanical strength limits under centrifugal loading.
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 prevents rotor magnet cracking, reduces vibration, and allows for cost-effective manufacturing while maintaining high-speed operation without significant thermal stress, ensuring reliable operation at speeds up to 40,000 rpm.
Implementation Method 1
the rotor magnet may have a crack due to centrifugal force
Implementation Method 2
The change of the balance of the rotary body due to the temperature increases occurs since components of the rotary body differ from each other in thermal expansion rate
Implementation Method 3
the fitted portions minutely moves. Especially, the above problems are conspicuous in the polygon mirror since it is rotated at the high speed of 30,000 rpm or more and exposed at the high temperature of 80 degrees or more
Data Source
AI summary
A rotary drive apparatus includes a rotary body with a support portion, a rotor magnet supported by the support portion of the rotary body, a fixation section facing the rotor magnet and rotatably supporting the rotary body, and a winding coil provided in the fixation section, in which an expression E1/E2≦0.75 is satisfied where Young's modulus of the rotor magnet is E1 [GPa], and Young's modulus of the support portion is E2 [GPa].