Ball Screw End Stop Assembly for Torque Spike Absorption
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Solution Overview
Problem
Existing ball screw actuators face challenges in effectively absorbing shock and managing torsional and axial loads, particularly when equipped with high-speed motors, leading to potential damage from torque spikes and fatigue issues.
Innovation Solution
The implementation of a ball screw end stop assembly that includes a ball ramp assembly and a spring, which converts rotary motion and torsional loads into linear motion and axial loads, thereby absorbing energy and reducing stress on the ball screw and motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional rigid end stop is used to limit actuator travel, then the actuator travel is limited at fully retracted and extended positions, but torque spikes and shock loads cause damage to the motor, ball screw or mechanical connections
Solution Approach 1:
The patent applies beforehand cushioning by introducing a compliant member (spring or elastomer) between the end stop and the nut that absorbs shock energy before it can transmit damaging torque spikes to the motor and ball screw. The compliant member compresses during impact, cushioning the blow and preventing damage to mechanical connections.
Solution Approach 2:
The compliant member serves as an intermediary element between the rigid end stop and the ball screw nut. It mediates the interaction by transforming the rigid stop into a compliant interface that reduces peak forces while maintaining the travel limitation function, thereby protecting the motor and ball screw from damage.
2Reliability
If a compliant member is added to absorb shock, then torque spikes are reduced and damage is prevented, but the device complexity increases
Solution Approach 1:
The patent merges the end stop function with the compliant member into a single integrated assembly. Rather than adding a separate complex shock absorption system, the compliant member is incorporated directly into the end stop structure, combining the travel limitation and shock absorption functions in one compact unit that minimizes additional complexity.
3Productivity
If high-speed motors are used to increase productivity, then the actuator speed increases, but shock absorption becomes insufficient leading to fatigue issues
Solution Approach 1:
The compliant member provides beforehand cushioning that is particularly effective for high-speed applications. The spring or elastomer is pre-configured to absorb the higher impact energies generated by faster actuator speeds, cushioning blows before they can cause fatigue damage to the ball screw or motor components during rapid operation.
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 effectively reduces axial and torsional loads, preventing damage from torque spikes and minimizing fatigue, while ensuring smooth operation even with high-speed motors.
Implementation Method 1
The axially compliant member (19) may comprise a spring acting between the shaft (17) and the axial output portion (21)
Implementation Method 2
an axially compliant member (19) configured to bias the axial output portion (21) axially on the center axis (30) towards the travel limiting position
Data Source
AI summary
A linear actuator comprising a shaft and a nut in engagement with the shaft such that the nut translates within a linear range of motion axially on a center axis relative to the shaft in response to relative rotation between the nut and the shaft, a stop positioned at a travel limiting position and having a rotational input portion and an axial output portion, the rotational input portion configured to rotate about the center axis relative to the shaft, the axial output portion constrained from rotating about the center axis relative to the shaft and configured to translate axially on the center axis relative to the rotational input portion in response to relative rotation between the axial output portion and the rotational input portion, and an axially compliant member configured to bias the axial output portion towards the travel limiting position.