Mill device
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Solution Overview
Problem
Manual portable mill devices face issues with wear between the shaft portion and shaft hole leading to the operating handle being idled or coming off during rotary operation, limiting their compactness and portability.
Innovation Solution
A mill device with a rectangular shaft portion and corresponding rectangular shaft hole, featuring a predetermined twist around the shaft center, which reduces wear and prevents the operating handle from coming off by locking it in place during rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the operating handle is securely adhered with a screw to one end of the drive shaft and significantly protruded laterally, then the coupling strength is improved, but the device size increases and portability is reduced
Solution Approach 1:
The operating handle is inserted into a hollow cylindrical housing that forms part of the milling unit, allowing the handle to be nested within the overall device structure rather than protruding externally. This nesting approach maintains the coupling strength through the screw connection while significantly reducing the external dimensions of the device, enabling it to be easily carried in a bag.
2Ease of operation
If the shaft portion and shaft hole are displaced from the shaft center or relatively inclined during operation, then the ease of operation is improved, but wear between the shaft portion and shaft hole increases causing the operating handle to be idled or come off
Solution Approach 1:
A rectangular shaft portion with asymmetric cross-section is used instead of a circular shaft. The rectangular shape with specific side length ratios creates unequal clearance gaps when displaced from the center, generating restoring forces that guide the shaft back to the centered position. This asymmetric geometry maintains ease of operation while preventing excessive displacement and wear, ensuring reliable fitting between the shaft portion and shaft hole.
Data Source
AI summary
A coffee mill 1 to which the present invention is applied includes a milling unit 2 which mills, with an inner blade 8, coffee beans 5, a drive shaft 3 in which one end is cooperatively coupled to the inner blade 8 and in which on the shaft center 23 of the other end, a rectangular shaft portion 21 is formed that has a predetermined twist around at least part of the shaft center in a shaft center direction and that is rectangular in cross section and an operating handle 4 to which a rectangle shaft hole 22 that is rectangular in plan view is open and which is coupled to the drive shaft 3 by externally fitting the rectangular shaft hole 22 to the rectangular shaft portion 21.