Torsionally Compliant Actuator End Stop for Torque Spike Absorption
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Solution Overview
Problem
Existing ball screw actuators lack effective mechanisms to absorb energy at end stops, leading to potential damage from torque spikes and fatigue due to excessive loads, especially when high-speed motors are used.
Innovation Solution
A linear actuator with a radially compliant outer portion and a cam roller mechanism that converts rotary motion into radial loads, absorbing energy through elastic deformation of a compliant cam sleeve and a spring, preventing torque spikes and axial loads from reaching the gear train.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rigid end stop is used to limit actuator travel, then the actuator travel is effectively limited, but torque spikes and excessive loads occur that can damage the motor, ball screw or mechanical connections
Solution Approach 1:
The patent applies beforehand cushioning by incorporating a compliant element between the rigid end stop and the ball screw nut. This compliant element acts as a pre-positioned energy absorber that deforms elastically during impact, cushioning the blow before it reaches the rigid end stop and protecting against torque spikes that would otherwise damage the motor or mechanical connections.
Solution Approach 2:
The compliant element serves as an intermediary between the rigid end stop and the moving ball screw nut. It mediates the interaction by absorbing impact energy through elastic deformation, preventing direct transmission of high-force impulses to the rigid end stop and protecting the system from damaging torque spikes.
2Force
If a compliant end stop is used to absorb energy, then torque spikes are reduced, but the complexity of the end stop structure increases
Solution Approach 1:
The end stop is segmented into two distinct functional parts: a rigid end stop portion that provides structural support and travel limitation, and a compliant element that absorbs impact energy. This segmentation allows each component to be optimized for its specific function while keeping the overall design relatively simple.
Solution Approach 2:
The patent applies local quality by making only the specific portion of the end stop that contacts the ball screw nut compliant, while keeping the rest of the end stop structure rigid. This localized compliance provides the necessary shock absorption without requiring the entire end stop assembly to be complex or overly engineered.
3Productivity
If high-speed motors are used to increase productivity, then the actuator speed increases, but the kinetic energy at impact increases causing greater fatigue and potential damage
Solution Approach 1:
The patent converts the harmful high-velocity impact from high-speed operation into a beneficial elastic deformation process. The compliant element is designed to absorb the increased kinetic energy generated by high-speed motors through controlled elastic deformation, transforming what would be damaging impact energy into stored and then dissipated elastic energy, thereby protecting the system while maintaining high productivity.
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 solution effectively absorbs kinetic energy, preventing damage to the actuator components by reducing torque spikes and fatigue, ensuring smooth operation even with high-speed motors and frequent impacts.
Implementation Method 1
absorbing energy through elastic deformation of a compliant cam sleeve
Implementation Method 2
a cam roller mechanism that converts rotary motion into radial loads
Implementation Method 3
absorbing energy through elastic deformation of a compliant cam sleeve and a spring
Data Source
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AI summary
A linear actuator comprising a shaft and a nut that translates within a linear range of motion in response to relative rotation between the nut and shaft, a stop positioned at a travel limiting position and having an inner portion connected to the shaft, a radially compliant outer portion axially overlapping the inner portion and configured to rotate relative to the inner portion, and a cam roller portion disposed radially between the inner and outer portions and configured to move relative to a neutral orientation in response to relative rotation between the inner and outer portions, and the outer portion configured to radially bias the cam roller portion towards the neutral orientation; wherein rotation of the outer portion caused by the nut rotating into the outer portion provides an outward radial load at the cam roller portion on the outer portion that is absorbed by the outer portion.