Stepping Motor Rotor Magnet Variable Wall Thickness
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Solution Overview
Problem
Conventional PM type stepping motors face challenges in achieving desired driving torque due to reduced magnetic force when magnet wall thickness is minimized for weight reduction, and increased inertia mass when wall thickness is maximized, leading to low drive responsiveness.
Innovation Solution
A PM type stepping motor design featuring a rotor with a cylindrical magnet having a variable wall thickness distribution along the axial direction, where the central portions of the magnet are thicker than the sides, and the inner peripheral surface is concavo-convex to enhance magnetic force and reduce inertia mass.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the magnet wall thickness is made small to reduce weight, then the weight of the rotor is reduced, but the magnetic force becomes small and desired driving torque cannot be obtained
Solution Approach 1:
The magnet is designed with non-uniform wall thickness where the central portion (corresponding to the central portion of the coil) has a larger wall thickness than the end portions. This local quality variation ensures that the region generating the most effective magnetic force has sufficient thickness, while other regions can be thinner to reduce overall weight.
Solution Approach 2:
Instead of varying wall thickness uniformly, the invention introduces axial dimension variation by making the inner peripheral surface bulge inward at the central portion. This creates a three-dimensional thickness distribution that optimizes magnetic force where needed while minimizing weight overall.
2Force
If the magnet wall thickness is made large to increase magnetic force, then the driving torque is sufficient, but the weight of the magnet becomes heavy and drive responsiveness becomes low due to increase in inertia mass
Solution Approach 1:
The magnet wall thickness is optimized locally rather than uniformly. The central portion has sufficient thickness to generate strong magnetic force for driving torque, while the end portions have reduced thickness to minimize inertia mass and improve responsiveness.
Solution Approach 2:
The wall thickness parameter is varied along the axial direction of the magnet. By changing this geometric parameter from a constant value to a variable value (thicker at center, thinner at ends), the design achieves both sufficient magnetic force and reduced inertia mass.
3Ease of manufacture
If the magnet wall thickness is made small to reduce cost, then the production cost is reduced, but the magnetic performance with respect to stator deteriorates
Solution Approach 1:
The magnet is designed with different wall thicknesses at different axial locations. The central portion maintains sufficient thickness to ensure adequate magnetic performance and driving torque, while end portions can be thinner to reduce material usage and cost.
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 design secures desired driving torque with strong magnetic force at the coil central portions and reduces rotor inertia mass, improving responsiveness and durability while maintaining accurate gap alignment with stators.
Implementation Method 1
a cylindrical magnet integrally provided on an outer periphery of the rotor body and magnetized to form multipoles in a circumferential direction
Implementation Method 2
By switching the direction of the electric current which is passed through the coils 62A and 62B of the respective phases, polarity of the poles is changed, so that the rotor 52 including the magnet is synchronously rotated
Data Source
AI summary
A stepping motor is disclosed which is capable of obtaining desired driving torque without sacrificing magnetic properties of a magnet with respect to a stator, reducing inertia mass of a rotor by decreasing a use amount of a magnet material, and thereby, can enhance driving performance including control responsiveness. In a stepping motor in which a plurality of stators (20A, 20B) around which coils (21) are wound are placed in an axial direction of a motor shaft (31), a rotor (30) is rotatably provided with a space at inner periphery sides of these stators (20A, 20B), the motor shaft (31) is placed in a center of the rotor (30), and the rotor (30) includes a rotor body (33) placed at an outer periphery of the motor shaft and a cylindrical magnet (32) integrally provided on an outer periphery of the rotor body and magnetized to form multipoles in a circumferential direction, the stepping motor is characterized in that the cylindrical magnet (32) has at least its inner peripheral surface bulged inward in a diameter direction so that a portion corresponding to a central portion in the above described axial direction of each of the coils (21) becomes thicker than the other portions.