Ball-Bearing Actuator Decoupling for Jam Recovery
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Solution Overview
Problem
Existing actuators in aircraft and other applications face issues with jamming, particularly in electromechanical actuators, where a jammed actuator can lock a surface in position, and existing solutions like shear pins are single-use and cannot be re-engaged if the jam is resolved, such as through deicing.
Innovation Solution
The actuator design features a spline with a sloping edge and ball bearings that can be moved between a top surface and a recessed portion, allowing for repeated engagement and disengagement without mechanical damage, using a control mechanism to manage relative rotation and linear motion between the control rod and output shaft, enabling the actuator to be re-engaged after disengagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a shear pin is used to mechanically fail when torque reaches a threshold, then the backup actuator can take over operation, but the shear pin is single-use and must be replaced during servicing and cannot be re-engaged if the jam is removed
Solution Approach 1:
The patent applies the dynamics principle by making the coupling between the control rod and output shaft reversible rather than permanent. The splined connection with engagement/disengagement capability allows the system to dynamically adapt - remaining engaged during normal operation for efficient torque transmission, and becoming disengaged when jamming occurs, enabling backup actuator operation without permanent damage to components
Solution Approach 2:
The patent implements discarding and recovering by allowing the ball bearing to be temporarily discarded from the engagement position during jamming events, then recovered and re-engaged when the jam is resolved. The ball bearing can move between the groove (engaged state) and recessed portion (disengaged state), enabling repeated use without replacement
2Adaptability or versatility
If an electromechanical actuator is used to replace hydraulic/mechanical systems, then electric controls increase in aircraft, but the risk of jamming increases which can lock the surface in position
Solution Approach 1:
The patent applies beforehand cushioning by designing a mechanical failure protection mechanism that activates before complete system failure. The ball bearing-spline-groove mechanism is pre-configured to detect jamming conditions through torque buildup and automatically disengage, preventing the actuator from locking the control surface in a dangerous position
3Adaptability or versatility
If a reversible decoupling device with ball bearing in groove and recessed portion is used, then the actuator can be disengaged and re-engaged, but the device complexity increases with control mechanism requirements
Solution Approach 1:
The patent applies self-service by designing a mechanism that automatically responds to jamming conditions without requiring external control system intervention. When torque exceeds the threshold during jamming, the ball bearing is naturally pushed from the groove to the recessed portion through the mechanical action itself, enabling automatic disengagement and reengagement based on operational conditions
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 allows for the actuator to be repeatedly engaged and disengaged without mechanical damage, enabling continued operation even if the primary actuator jams, as the backup actuator can take over, and the actuator can be re-engaged if the jam is resolved, improving reliability and reducing maintenance needs.
Implementation Method 1
The actuator comprises a control rod with a spline having a top surface, a cylinder coaxial with the control rod, the cylinder having a circumferential groove formed in an inner surface and an output shaft which is held against rotation by engagement with the housing as it slides in and out of the housing. The cylinder is arranged to be driven axially within the actuator and the output shaft is coaxial with the control rod. The output shaft has a hole extending therethrough. The actuator comprises further a ball bearing located in the hole of the output shaft.
Data Source
Figure 1
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AI summary
An actuator is provided with means for controlling whether or not forces are transferred between a cylinder 12 (controlled by a motor of the actuator) and an output shaft 14. The output shaft 14 is located between the cylinder 12 and the control rod 18, 38. The cylinder 12 coaxially surrounds the output shaft 14, and the output shaft 14in turn coaxially surrounds the control rod 18, 38. The control rod 18, 38 has one or more splines 20 on its outer surface facing the output shaft 12. The output shaft 14 has one or more holes 15, each containing a ball bearing 16. In the engaged state, the output shaft 14 holds each ball bearing 16 on the top 22 of a spline 20 of the control shaft 18, 38, such that the ball bearing is held in engagement with a groove 13 formed in the inner surface of the cylinder, for transferring axial forces between the cylinder 12 and output shaft 14. To disengage the actuator the control rod 18, 38 is moved relative to the output shaft 14 so that each ball bearing 16 no longer sits atop a spline 20, but instead may sit in a recessed portion 26, so that the ball bearing 16 does not engage a groove 13 and thus forces are no longer transmitted between the cylinder 12 and the output shaft 14.