Split Flow Vacuum Pump Shaft Stiffness and Weight Optimization
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Solution Overview
Problem
Existing split-flow vacuum pumps face challenges in designing long shafts with reduced weight and maintained rigidity, while also requiring cost-effective stiffening at one shaft end, and struggle with modal behavior and natural vibration frequencies.
Innovation Solution
The integration of a sleeve on the shaft with grooves, bores, or constrictions, made of metal or composite materials, which changes natural vibration frequencies and increases rigidity without increasing the starting material size, allowing for cost-effective stiffening and reduced weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the shaft is made longer to accommodate multiple pump stages, then the pumping capacity increases, but the rotor's natural frequency decreases and modal behavior deteriorates
Solution Approach 1:
The shaft is divided into multiple sections with different diameters along its length. Each section is optimized for its specific function: larger diameter sections provide stiffness where needed, while smaller diameter sections reduce mass. This segmentation allows the long shaft to maintain adequate natural frequency despite its extended length required for multiple pump stages.
Solution Approach 2:
Different sections of the shaft have different local properties (diameters) tailored to their specific requirements. Areas requiring high stiffness have larger diameters, while areas where mass reduction is critical have smaller diameters. This local optimization enables the shaft to achieve the necessary modal behavior for long configurations without sacrificing pumping capacity.
2Strength
If the shaft diameter is increased to stiffen the motor end, then the stiffness improves, but the cost increases due to larger drive magnets and motor stators
Solution Approach 1:
The shaft uses varying diameters along its length, with larger diameters only where locally required for stiffness (such as the motor end), and smaller diameters in other sections. This localized stiffening approach provides the necessary strength where critical while avoiding the cost increase that would result from uniformly increasing the entire shaft diameter, which would require larger drive magnets and motor stators.
Solution Approach 2:
The shaft is segmented into sections with different diameters, allowing the motor end section to have sufficient stiffness without requiring the entire shaft to be oversized. This segmentation enables cost-effective design by concentrating material only where structurally necessary.
3Weight of moving object
If the shaft is made hollow to reduce mass, then the weight decreases, but the stiffness of the shaft and rotor elements decreases
Solution Approach 1:
Rather than making the entire shaft hollow, the invention uses a solid shaft with segmented varying diameters. This approach maintains the stiffness benefits of solid material where needed while reducing mass through the tapered design, avoiding the stiffness problems that would result from a completely hollow shaft.
Solution Approach 2:
The shaft uses solid material distributed in a varying diameter configuration, providing stiffness where the larger diameter sections are located while reducing overall mass compared to a uniform solid shaft. This local optimization of material distribution achieves mass reduction without compromising stiffness.
4Adaptability or versatility
If multiple individual vacuum pumps are used to evacuate multiple chambers, then each chamber can be evacuated independently, but the space requirement and cost increase
Solution Approach 1:
Multiple pump stages are merged into a single integrated rotor assembly with multiple radial inlets, allowing one physical pump to evacuate multiple vacuum chambers simultaneously. This combining approach provides independent evacuation capability for each chamber (through separate inlets) while occupying the space of only one pump unit rather than multiple separate pumps.
Solution Approach 2:
The single vacuum pump is designed with multi-functionality, incorporating multiple radial inlets and multiple pump stages that can service multiple different vacuum chambers. This universal design allows one pump to perform the work of multiple pumps, reducing space requirements while maintaining the ability to evacuate each chamber independently.
Data Source
Figure 1
Figure 2~4
Figure 5~7
AI summary
The invention relates to a split-flow vacuum pump (1) with at least two radial inlets (23-27), wherein the vacuum pump has stator disks and rotor disks (21, 22, 24) arranged on a shaft (13). The shaft (13) further comprises at least one sleeve (59). The sleeve (59) makes it possible to reduce the weight of the shaft (13) while maintaining its stiffness, for example by means of a constriction (102) or a bore (109). The arrangement of the sleeve (59) also allows the natural frequencies of the rotor to be changed and the bearing forces to be reduced. Furthermore, the sleeve (59) can have a bore (83) through which enclosed cavities (102, 109) can be evacuated. The sleeve (59) can also be used in the area of the motor magnets (101) or to connect two separate shaft elements (107, 108).