Electric Linear Actuator Roller Contact Reliability
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Solution Overview
Problem
The existing electric linear motion actuators face issues with maintaining constant contact between planetary rollers and the rotary shaft due to the elastic C-shaped rings used for radial biasing, leading to loss of function when the rings radially shrink and fail to press the rollers against the shaft.
Innovation Solution
The electric linear motion actuator incorporates rotation stop means, such as engaging pieces or ring springs, to prevent the elastic rings from rotating and maintain constant radial biasing of the roller shafts, ensuring continuous contact and reliable transmission of rotation to the planetary rollers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If C-shaped elastic rings are used to radially bias the roller shafts, then the planetary rollers are pressed against the rotary shaft, but the C-shaped rings rotate with the roller shafts and eventually fit into the gap between their circumferentially separate ends, causing them to radially shrink and lose pressing capability
Solution Approach 1:
A rotation stop member is introduced as an intermediary component between the elastic ring and the roller shaft. This rotation stop member has a rotation stop protrusion that engages with a rotation stop groove on the roller shaft, preventing the elastic ring from rotating relative to the roller shaft. This intermediary component solves the problem of the elastic ring fitting into its own gap while maintaining the simple C-shaped ring structure for radial biasing.
2Ease of manufacture
If the elastic rings are allowed to rotate freely on the roller shafts, then the structure remains simple, but the rings eventually fit into the gap between their ends and radially shrink, causing loss of function
Solution Approach 1:
The rotation stop member serves as an intermediary that maintains the simplicity of the C-shaped elastic ring installation while preventing the harmful rotation that leads to functional loss. The rotation stop protrusion and groove engagement provides a simple mechanical constraint that prevents the elastic ring from fitting into its own gap, thereby maintaining both ease of manufacture and reliability.
3Reliability
If interference fit is used to mount planetary rollers between the rotary shaft and outer ring member, then the contact is secure, but the mounting process becomes troublesome and costly
Solution Approach 1:
Instead of using a static interference fit, the patent employs a dynamic elastic biasing mechanism where C-shaped elastic rings provide continuous radial pressing force on the roller shafts. This dynamic approach allows the planetary rollers to be mounted more easily without interference fit, while the elastic rings maintain secure contact by constantly pressing the rollers against the rotary shaft, thus improving ease of manufacture while maintaining reliability.
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 solution ensures that the planetary rollers remain elastically pressed against the rotary shaft at all times, preventing malfunction and ensuring reliable operation of the electric linear motion actuator.
Implementation Method 1
elastic rings each having circumferentially separate ends and each fitted around the roller shafts so as to contact the respective roller shafts from radially outside, thereby biasing the respective planetary rollers against the radially outer surface of the rotary shaft
Implementation Method 2
when the rotary shaft rotates, the planetary rollers are configured to rotate about center axes of the respective planetary rollers while revolving around the rotary shaft, due to frictional contact between the rotary shaft and the respective planetary rollers
Data Source
Figure 1
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AI summary
An electric linear motion actuator is provided comprising a housing (1), an outer ring member (5), a rotary shaft (10) driven by an electric motor (11), a carrier (14) supported on the rotary shaft (10) and planetary rollers (21) mounted between the rotary shaft (10) and the outer ring member (5). The outer ring member (5) has a helical rib (6) formed on the radially inner surface of the outer ring member (5) and in engagement with circumferential grooves (24) formed on a radially outer surface of each of the planetary rollers (21). When the rotary shaft (10) rotates, the planetary rollers (21) are configured to rotate due to a frictional contact between the rotary shaft (10) of the planetary rollers (21), thereby moving the outer ring member (5) in an axial direction. The electric linear motion actuator further comprises a friction coupling means which is configured to frictionally fixedly couple the carrier (14) to the rotary shaft (10) while an axial load applied to the outer ring member (5) in a push-in direction is small, and to uncouple the carrier (14) from the rotary shaft (10) under the axial load when the axial load is large.