Magnetic Encoder Outer Diameter Expansion via Pressed Surface
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Solution Overview
Problem
Conventional inward flange-type magnetic encoders face issues with magnetic force leakage due to a limited magnetic force stable region, caused by a smaller outer diameter of the annular plastic magnet, which is constrained by molding limitations and thermal shock, leading to burrs and cracks.
Innovation Solution
The magnetic encoder is designed with a high form accuracy surface on the sensor-opposed surface, extending the outer diameter of the annular plastic magnet by forming a high form accuracy surface through press processes such as stepwise pressing, chamfering, or bead processing, allowing the magnet to be positioned on a larger metal mold matching surface, thereby increasing the magnetic force stable region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the outer diameter of the annular plastic magnet is increased to widen the magnetic force stable region, then the magnetic force distribution is improved, but the magnet cannot be surely stopped on the PL surface during injection molding, leading to occurrence of PL burrs or thermal shock cracks
Solution Approach 1:
A high form accuracy surface is formed on the annular fixing member before the injection molding process. This preliminary surface preparation ensures that when the annular plastic magnet is subsequently injected, it can be properly positioned and stopped on this high accuracy surface, preventing burrs and thermal shock cracks while allowing the magnet outer diameter to be increased for a wider magnetic force stable region
2Reliability
If the outer diameter of the annular plastic magnet is increased beyond the high form accuracy surface range, then the magnetic force stable region is widened, but the magnet outer diameter is constrained by the limited high form accuracy surface area
Solution Approach 1:
The high form accuracy surface is extended radially outward beyond the conventional limit of (d - 2·r) by applying additional press processing to the sensor-opposed surface of the annular fixing member. This dimensional extension in the radial direction provides a larger area for magnet positioning, allowing the magnet outer diameter to be increased while maintaining manufacturing precision
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
This configuration effectively widens the magnetic force stable region by positioning the annular plastic magnet on a high form accuracy surface, enhancing the magnetic force distribution and preventing molding-related issues like burrs and thermal shock cracks.
Implementation Method 1
an injection molding step of, while the annular fixing member is placed in an axial draw mold, injecting a dissolved annular plastic magnet material into the mold
Implementation Method 2
forming by a press process a high form accuracy surface on a sensor-opposed surface
Implementation Method 3
an annular magnet member that is fixed to the fixing member and has N and S poles magnetized circumferentially at regular intervals in a multipolar manner
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
Provided is a magnetic encoder in which the outer diameter of an annular plastic magnet is increased to widen a magnetic force stable region, and a manufacturing method thereof. An axial-type magnetic encoder 1 includes: an annular fixing member 2 that has a cylindrical part 2A attached to a rotating body and an inward flange part 2B extended radially inward from an end edge of the cylindrical part 2A and is fabricated by press molding; and an annular plastic magnet 3 that is attached by injection molding to a sensor-opposed surface of the annular fixing member 2. The magnetic encoder 1 has a high-form accuracy surface (outer diameter FD of a flat surface) on the sensor-opposed surface more radially outward than a range of a diameter (d - 2·r) determined by an inner diameter d of the cylindrical part 2A and a radius r of a corner between the cylindrical part 2A and the inward flange part 2B. An outer diameter MD of the annular plastic magnet 3 is positioned on the high-form accuracy surface.