Ball Screw Nut Retention Structure for Compact High-Load Assembly
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Solution Overview
Problem
Conventional ball screw devices face issues with increased size and reduced load capacity due to the need for larger pistons to prevent axial displacement between the nut and piston, and potential interference or weak joint strength from differing thermal expansion coefficients or welding, leading to higher manufacturing costs.
Innovation Solution
A ball screw device design that uses a fitting cylinder with retaining ring grooves to prevent axial displacement, allowing the fitting cylinder's outer diameter to match the nut's, and incorporates a rotation-locking member to prevent rotation, without increasing manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the piston is externally fitted over the entire nut to prevent axial displacement, then axial displacement prevention is improved, but the device size increases and load capacity decreases
Solution Approach 1:
The piston is divided into two separate components: a fitting cylinder that fits into the nut, and a separate retaining ring. This segmentation allows the fitting cylinder to have a smaller diameter (matching the nut's inner diameter) while the retaining ring provides the axial displacement prevention function, thus reducing overall device size while maintaining reliability
Solution Approach 2:
A retaining ring is introduced as an intermediary component between the fitting cylinder and the nut. The retaining ring engages with retaining ring grooves to prevent axial displacement, allowing the fitting cylinder to be smaller in diameter while still achieving the displacement prevention function through the combined action of the retaining ring and grooves
2Reliability
If the piston is externally fitted over the entire nut to prevent axial displacement, then axial displacement prevention is improved, but the load capacity decreases
Solution Approach 1:
By segmenting the piston into a fitting cylinder and retaining ring, the fitting cylinder can have a smaller diameter that matches the nut's inner diameter, allowing the nut's outer diameter to be maximized for load capacity while the retaining ring handles the displacement prevention function
Solution Approach 2:
The retaining ring acts as an intermediary that prevents axial displacement without requiring the fitting cylinder to extend over the entire nut, thereby preserving the nut's full load-bearing capacity while achieving displacement prevention through the retaining ring's engagement with the grooves
3Adaptability or versatility
If different metals are used for the nut and piston, then manufacturing flexibility is improved, but thermal expansion differences cause interference or weak joint strength
Solution Approach 1:
Dividing the piston into a fitting cylinder and retaining ring allows each component to be optimized for its specific function and material properties, reducing the impact of thermal expansion differences on joint strength while maintaining manufacturing flexibility
Solution Approach 2:
The retaining ring serves as an intermediary component that can be designed with appropriate material properties to accommodate thermal expansion differences between the nut and fitting cylinder, maintaining reliable engagement across temperature variations
Data Source
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AI summary
[Problem] To provide a ball screw device capable of effectively preventing relative displacement in an axial direction of a nut and fitting cylinder, as well as reducing the size of the entire device and increasing load capacity without increasing manufacturing costs. [Solution] A nut 3 has a first fitting surface 17 at an end portion on an other side in the axial direction, the first fitting surface 17 being provided with a first retaining ring groove 20, and a fitting cylinder 5 has a second fitting surface 27 at an end portion on one side in the axial direction, the second fitting surface 27 being provided with a second retaining ring groove 29 at a portion facing the first retaining ring groove 20 in the radial direction.