Single-axis actuator with internal ball return
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Solution Overview
Problem
Conventional single-axis actuators with circulating tubes face issues of increased cross-sectional shape and production costs due to protrusion from the slider, which affects load capacity and mechanical strength.
Innovation Solution
A single-axis actuator design with a nut and circulating parts arranged at both ends of the threaded shaft, utilizing a spacer between the nut and end cap for secure positioning, allowing the entire spiral groove length to serve as a ball raceway and eliminating the need for protrusions on the slider's top or bottom, thus maintaining a smaller cross-sectional shape and enhancing load capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a circulating tube is used for the ball returning passage, then the balls can be returned from the end point to the start point of the raceway, but the cross-sectional shape of the slider becomes larger and production cost increases
Solution Approach 1:
The circulating parts are nested within the slider body by forming through holes that penetrate the slider in the longitudinal direction of the threaded shaft. The circulating parts are positioned inside these through holes, eliminating the need for external circulating tubes that would increase the cross-sectional shape. This nesting approach maintains the ball returning function while keeping the slider compact.
Solution Approach 2:
The ball returning passage is reconfigured from an external circulating tube to internal through holes penetrating the slider body. By changing the dimensional arrangement from external protrusion to internal penetration, the solution maintains the returning function while reducing the external cross-sectional footprint of the slider.
2Reliability
If the circulating tube protrudes from the slider, then the balls can be returned, but the load capacity and mechanical strength are reduced
Solution Approach 1:
The circulating parts are nested within the slider body rather than protruding externally. This nesting eliminates stress concentration points that would occur at protrusions, thereby maintaining the structural integrity and load capacity of the slider while still enabling the ball returning function through the internal through holes.
Solution Approach 2:
The circulating tube is extracted from the external structure and repositioned as internal through holes within the slider body. This extraction from the external protruding form eliminates the weakening effect on mechanical strength while preserving the essential ball returning capability.
3Strength
If the area of the threaded shaft is increased, then the load capacity is improved, but the compact size is reduced
Solution Approach 1:
The design optimizes the arrangement of the threaded shaft and circulating parts in the longitudinal direction by forming through holes that penetrate the slider. This dimensional reorganization allows for a more efficient space utilization, enabling a larger threaded shaft area for improved load capacity without proportionally increasing the overall cross-sectional area of the slider.
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 achieves a larger load capacity and smaller cross-sectional shape perpendicular to the threaded shaft while maintaining mechanical strength, facilitating easier assembly and attachment of components.
Implementation Method 1
the spacer is arranged in a shrinking state by elastic deformation between the circulating part and the end cap
Implementation Method 2
the rolling elements circulate in the circulating passage while rolling in the rolling passage in a loaded state
Implementation Method 3
a ball screw mechanism and a linear guide mechanism are combined together
Implementation Method 4
the rolling elements are allocated in a circulating passage implemented by the rolling passage, the returning passage, and the direction changing passage
Data Source
Figure 1~2
Figure 3
Figure 4A~5
AI summary
As compared to a single-axis actuator in which a ball returning passage of a ball screw mechanism is made of a circulating tube, the cross-sectional shape perpendicular to the longitudinal direction of a threaded shaft of a slider can be made small, when the diameter of the outer circumferential circle of the threaded shaft of the present invention is same as that of the circulating tube type, and the load capacity can be made large, when the size in the longitudinal direction of the threaded shaft of the slider of the present invention is same as that of the circulating tube type.. The ball returning passage for returning the balls (4) of a ball screw mechanism from an end point to a start point of a raceway encompasses: a through hole (24) penetrating through a slider (2) in a longitudinal direction of a threaded shaft (3) ; and end deflectors (6). Each of the end deflector (6) has a direction changing passage to be connected with the through hole (24). A main body (61) of the end deflector (6) is fit into a notch part (26) arranged on each of both ends in the longitudinal direction of the threaded shaft (3) of a slider body (2A).