Actuator with Preloaded Nuts Eliminates Axial Clearance
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Solution Overview
Problem
Existing actuators for operating tables and treatment chairs often cause jerky movements due to axial clearance, especially when tilting, which compromises comfort and require additional braking mechanisms.
Innovation Solution
An actuator design featuring a threaded spindle and multiple nuts with opposing forces, minimizing axial clearance through deep groove ball bearings and a self-locking mechanism, allowing for comfortable and cost-effective movement with reduced jerking during longitudinal or lateral tilting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional actuators with axial clearance are used, then the construction is simple, but jerky movements occur during tilting which compromises comfort
Solution Approach 1:
The actuator is segmented into multiple independent nuts (first nut and second nut) that can be preloaded separately. Each nut is equipped with deep groove ball bearings that are preloaded in the radial direction, creating multiple contact points between the threaded spindle and nuts. This segmentation allows the system to eliminate axial clearance through combined preload effects while maintaining operational simplicity.
Solution Approach 2:
The deep groove ball bearings are preloaded in the radial direction before operation, and the nuts are preloaded axially to eliminate clearance. This preliminary action of preloading creates optimal contact conditions between the threaded spindle and nuts, ensuring that no axial clearance exists before the actuator begins its tilting operation, thereby preventing jerky movements from the outset.
2Reliability
If axial clearance is minimized through preloading, then jerky movements are prevented, but the device complexity increases
Solution Approach 1:
The invention merges the functions of multiple nuts and deep groove ball bearings into a compact arrangement where the bearings are integrated between the housing and nuts. The first and second nuts work together with their respective bearings to collectively eliminate axial clearance, combining multiple clearance-reduction mechanisms into a unified structure that does not proportionally increase complexity.
Solution Approach 2:
The deep groove ball bearings serve multiple functions: they support radial loads, provide preload in the radial direction, and contribute to eliminating axial clearance when combined with the nut preload. This multi-functionality reduces the need for separate components for each function, thereby limiting the increase in device complexity while achieving reliable clearance minimization.
3Reliability
If multiple nuts with opposing forces are used, then axial clearance is reduced, but the manufacturing cost increases
Solution Approach 1:
The first and second nuts are designed to be screwed onto the threaded spindle in a clearance-free manner, with the system's own components (the nuts and preloaded bearings) providing the necessary preload forces. The actuator uses its structural elements to generate and maintain the preload without requiring external adjustment mechanisms or additional expensive components, making the clearance-free operation self-sustaining and cost-effective.
Solution Approach 2:
The invention uses standard deep groove ball bearings and conventional nuts that can be manufactured cost-effectively. These components are designed to maintain their preload and clearance-free characteristics throughout their service life without requiring expensive specialized materials or complex assembly procedures, achieving reliable clearance minimization at reasonable manufacturing 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
The actuator provides a compact, high-stiffness, and cost-effective solution that minimizes jerky movements, ensuring increased comfort and reliability by maintaining a small axial clearance over a long service life without the need for additional braking.
Implementation Method 1
The two rolling-element bearings are configured as deep groove ball bearings
Implementation Method 2
A threaded spindle (14) is screwed into the two nuts (10, 12) in a clearance-free manner
Implementation Method 3
The first rolling-element bearing (16) is disposed axially between the housing (32) and a part of the nut (10)
Data Source
AI summary
An actuator includes a housing, a first nut in the housing, a second nut in the housing, and a threaded spindle screwed into the first nut and the second nut. The first nut exerts a first force in a first direction on the threaded spindle, and the second nut exerts a second force in a second direction on the threaded spindle, the first direction being different than the second direction.