Vibration Isolator with Co-Axial Spring for Vacuum Pumps
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Solution Overview
Problem
Existing vibration isolators for vacuum pumps are ineffective in minimizing vibration transmission to sensitive apparatus during evacuation due to increasing axial stiffness and limited freedom in selecting conductance, which affects the resolution of instruments like electron microscopes and manufacturing precision in process tools.
Innovation Solution
A vibration isolator design featuring a steel bellows with a co-axial, pre-tensioned helical tension spring as a resilient element, orthogonal connectors, and optional damping elements like plastics or elastomeric sleeves to reduce axial, shear, and tilt stiffness, along with an auxiliary mass to resist compression, providing a simpler structure with lower stiffness and higher conductance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an elastomeric cylinder is used to provide damping and prevent bellows collapse, then the isolator can withstand compression forces, but the axial stiffness increases progressively during evacuation, reducing vibration isolation effectiveness
Solution Approach 1:
The patent changes the mechanical parameter of the resilient element by using a pre-tensioned helical spring instead of an elastomeric cylinder. The pre-tensioning ensures the spring remains under tension throughout operation, maintaining consistent stiffness characteristics and preventing the progressive stiffening that occurs with elastomeric materials under compression.
Solution Approach 2:
The patent combines the steel bellows with a helical tension spring made of elastic material to create a composite resilient element. This composite structure leverages the high strength and dimensional stability of steel while incorporating the elasticity and damping characteristics of the spring material, achieving both compression resistance and consistent vibration isolation.
2Reliability
If the bellows has low inherent axial stiffness to minimize vibration transmission, then vibration isolation is improved, but the isolator cannot withstand compression forces when fluid is at sub-atmospheric pressure
Solution Approach 1:
The patent merges the bellows structure with the helical tension spring into a single integrated resilient element. The bellows provides the flow path and structural framework, while the pre-tensioned spring provides both the compression resistance and the low-stiffness characteristic needed for vibration isolation. This merging eliminates the need for separate components like elastomeric cylinders.
Solution Approach 2:
The spring is pre-tensioned during assembly to establish a predetermined tension force before operation. This preliminary action ensures that the spring remains under tension throughout the evacuation process, providing consistent compression resistance and maintaining optimal vibration isolation characteristics without progressive stiffening.
3Device complexity
If orthogonal connectors are used to attach the resilient element to flanges, then the structure is simplified and conductance is increased, but the attachment geometry must accommodate non-parallel connection points
Solution Approach 1:
The patent transitions from a planar attachment geometry to a three-dimensional orthogonal configuration. By using connectors that extend perpendicular to the flange surfaces, the design accommodates the spatial separation between connection points while maintaining structural simplicity. This dimensional change allows the resilient element to be attached to non-parallel surfaces without complex angled connectors.
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 significantly reduces vibration transmission to sensitive apparatus by lowering axial, shear, and tilt stiffness, maintaining high conductance and preventing vibration-induced errors in precision instruments and manufacturing processes.
Implementation Method 1
a resilient element substantially co-axial with and surrounded by the bellows, the resilient element having a first end located proximate to the first flange and connected to the second flange, and a second end located proximate to the second flange and connected to the first flange
Implementation Method 2
a steel bellows with a co-axial, pre-tensioned helical tension spring as a resilient element
Implementation Method 3
optional damping elements like plastics or elastomeric sleeves to reduce axial, shear, and tilt stiffness
Data Source
Figure 1~2
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AI summary
A vibration isolator is described for inhibiting transfer of vibration to an apparatus during evacuation thereof by a pump. The isolator comprising a bellows for isolating from the ambient atmosphere fluid drawn from the apparatus by the pump. A first flange is connected to one end of the bellows for mounting the isolators the apparatus, and a second flange is connected to the other end of the bellows for mounting the isolator to the pump. The bellows surrounds a resilient element, preferably a helical tension spring, which is substantially co-axial with the bellows. The resilient element has a first end located proximate to the first flange and connected to the second flange, and a second end located proximate to the second flange and connected to the first flange.