Linear Stepper Motor Rotor Shaft Composite Design
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Solution Overview
Problem
Existing linear stepper motors face challenges in achieving a hard-wearing, low-tolerance, and cost-efficient rotor shaft with minimal play and smooth operation, especially in miniaturized designs, while maintaining high actuating forces and avoiding maintenance and lubrication requirements.
Innovation Solution
A flexurally and torsionally rigid plastic threaded spindle with coaxial metallic plain bearing journals at both ends, supported in plain bearings, and a trapezoidal thread made of hard-wearing plastic, allowing for independent design of the plain bearing journal and rotor shaft, with optional metallic or separate insert-moulded journals and a rotation-locked connection for enhanced efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a steel core with plastic thread is used for the rotor shaft, then high strength and hard-wearing properties are achieved, but manufacturing complexity and cost increase due to composite material processing
Solution Approach 1:
The rotor shaft combines a plastic core with a metallic thread layer, creating a composite structure that leverages the advantages of both materials: the plastic provides flexibility and corrosion resistance, while the metallic thread delivers high strength and wear resistance. This composite approach resolves the contradiction by achieving superior mechanical properties without requiring complex steel-plastic composite processing.
Solution Approach 2:
The rotor shaft is segmented into distinct functional layers: a plastic core providing structural support and a separate metallic thread layer providing mechanical engagement. This segmentation allows each material to be optimized for its specific function and simplifies manufacturing compared to creating a monolithic steel-plastic composite.
2Volume of moving object
If the rotor shaft is miniaturized to reduce device size, then compactness is improved, but the ability to transmit high actuating forces without jamming or bending deteriorates
Solution Approach 1:
The metallic thread layer wrapped around the plastic core creates a high-strength, low-weight structure that maintains excellent force transmission capabilities even in miniaturized configurations. The composite construction prevents jamming through the plastic's flexibility while the metallic thread ensures sufficient mechanical strength for high actuating forces.
Solution Approach 2:
The rotor shaft design allows optimization of thread geometry, material properties, and dimensional parameters to maintain high force transmission capability in miniaturized versions. By adjusting these parameters, the shaft can transmit proportionally high forces relative to its reduced size without jamming or bending.
3Device complexity
If plain bearing journals are integrated into the rotor shaft, then structural simplicity is improved, but bearing precision and smooth operation deteriorate due to plastic material limitations
Solution Approach 1:
The rotor shaft incorporates metallic plain bearing journals within the plastic structure, creating a composite design where the metallic journals provide precise bearing surfaces while the plastic body maintains structural simplicity. This resolves the contradiction by achieving both simplicity and precision through material combination.
Solution Approach 2:
The rotor shaft exhibits local quality differentiation: the bulk of the shaft is made of plastic for simplicity and flexibility, while the bearing journal regions are made of metal for precision and smooth operation. This localized material selection allows each region to have the optimal properties for its specific function.
4Power
If a rotation-locked connection is implemented between rotor shaft and actuating rod, then mechanical efficiency is improved, but device complexity increases due to additional connection mechanisms
Solution Approach 1:
The rotation-locked connection utilizes the composite structure of the rotor shaft, where the metallic thread layer is mechanically engaged with the actuating rod while the plastic core provides structural support. This integrated approach achieves rotation locking without requiring separate complex connection mechanisms, thereby maintaining mechanical efficiency while minimizing additional complexity.
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 solution enables a maintenance-free, low-friction, and high-force transmission capability without jamming or bending, adaptable to various applications with reduced eccentricity and improved motor efficiency.
Implementation Method 1
The plain bearing journals are guided both radially and axially in plain bearings of the bearing shields
Implementation Method 2
low-friction axial support can be implemented by means of balls holding the pointed tips
Data Source
Figure 1
Figure 2
AI summary
A linear stepper motor includes a rotor, two plain bearings (13, 15; 14, 16), two motor bearing shields (2, 3), a spindle nut (9), and a fork-shaped actuating rod (8). The rotor has a rotor shaft (6) that includes a motive thread (7) and is used to drive a linearly guided actuator. The rotor shaft (6) includes plain bearing journals (11, 12) at ends thereof, which each comprise an end radially and axially enclosed in the plain bearings (13, 15; 14, 16) seated in the motor bearing shields (2, 3), and, by the motive thread (7), axially drives the spindle nut (9) connected with the fork-shaped actuating rod (8) in a rotation-proof manner. The rotor shaft (6) includes a flexurally and torsionally rigid plastic threaded spindle with coaxially arranged metallic shaft ends so as to act as metallic journals on opposite ends for concurrent plain bearing support and axial support.