Embedded Permanent Magnet Rotor Mid-Plane Balance Correction

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Solution Overview

Problem

Current permanent magnet rotor assemblies do not allow for mid-plane balance correction without disassembling the rotor, making it difficult and costly to rebalance if balance changes occur during use, posing a safety risk due to the handling of powerful magnets.

Innovation Solution

A method involving machining axial slots in the rotor's recessed slots to insert balance weights and locating rods, allowing for mid-plane balance correction without disassembly, using trapezoidal slots and retainer plates to secure the balance weights and rods, ensuring they remain in place during operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If permanent magnets, lamination stacks and cradles are tightly packed axially to maximize power per unit length, then power density is improved, but mid-plane balance correction becomes impossible without disassembly

Engineering Contradiction:

Improvepower per unit axial lengthVSAvoidaccess to mid-plane for balance correction

Core Design Contradiction:

PowerVSEase of operation

Solution Approach 1:

The rotor assembly is segmented to include discrete axial slots within the recessed slots that are specifically designed to accommodate balance weights. This segmentation allows the balance correction function to be separated from the main rotor structure, enabling mid-plane balance adjustment without affecting the tight axial packing of permanent magnets and lamination stacks.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The balance weights are nested within the existing recessed slots of the rotor assembly, which themselves are integrated among the permanent magnets and lamination stacks. This nested configuration allows the balance correction mechanism to be housed within the already-packaged rotor structure, maintaining maximum power density while providing access for balance correction through the slot openings.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Manufacturing precision

If the rotor is disassembled to make mid-plane balance correction, then balance accuracy is improved, but time consumption and cost increase

Engineering Contradiction:

Improvebalance correction accuracyVSAvoidtime to disassemble and reassemble rotor

Core Design Contradiction:

Manufacturing precisionVSLoss of time

Solution Approach 1:

The axial slots for balance weight insertion are pre-machined into the rotor structure during manufacturing, and the balance weights are designed to be insertable through these slots. This preliminary preparation enables balance correction to be performed quickly by simply inserting or removing weights from the slots, eliminating the need for time-consuming disassembly and reassembly operations.

Inventive Principle:

Principle #10Preliminary action

3Ease of repair

If permanent magnets are handled for disassembly and reassembly, then mid-plane balance correction is possible, but safety risks increase due to powerful magnets

Engineering Contradiction:

Improveability to make balance correctionVSAvoidsafety risk from handling powerful magnets

Core Design Contradiction:

Ease of repairVSObject-affected harmful factors

Solution Approach 1:

The balance correction function is extracted from the main rotor assembly by using separate, removable balance weights that can be independently inserted or removed from the axial slots. This extraction allows balance correction to be performed without handling the powerful permanent magnets, cradles, or lamination stacks, thereby eliminating the safety risks associated with manipulating these components.

Inventive Principle:

Principle #2Taking out (Extraction)

4Manufacturing precision

If end planes and mid-span material removal method is used for balancing, then initial balancing is achieved, but rebalancing becomes difficult if balance changes during use

Engineering Contradiction:

Improveinitial balanceVSAvoidability to rebalance after bearing area or shaft end repair

Core Design Contradiction:

Manufacturing precisionVSAdaptability or versatility

Solution Approach 1:

The balance correction system is made dynamic by providing adjustable balance weights that can be inserted or removed from the axial slots to change the balance configuration. Unlike fixed material removal methods, this dynamic system allows the rotor to be rebalanced multiple times throughout its service life by simply adjusting the balance weights, adapting to changes in bearing area or shaft end conditions without requiring permanent modifications or disassembly.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS7626309B2Method of balancing an embedded permanent magnet motor rotor

Publication Date: 2009.12.01 ELLIOTT CO

AI summary

A method of balancing an embedded permanent magnet motor rotor includes the steps of: a) providing a non-magnetic cylindrical shaft having an axis of rotation and a generally cylindrical surface with an even number of recessed slots defining an even number of ribs therebetween; b) machining an axial slot having a cross-section with a top opening, a bottom and two sides in a center portion of each of the recessed slots; c) sliding at least one balance weight into at least one of the axial slots; and d) inserting locating rods into the axial slot on each side of the at least one balance weight.