Linear Actuator Torque Sensing for End-of-Travel Detection
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Solution Overview
Problem
In the space field, adding sensors to mini linear actuators to measure failure, position, and stroke information is complicated, costly, and often results in inaccurate and unreliable data due to size and weight constraints, as seen in prior art like US 2002/074866, which requires additional sensors increasing bulk and weight.
Innovation Solution
A mechanical linear actuator utilizing strain gauges interconnected to form a Wheatstone bridge, coupled with a reduction device and elastic mechanical stops, allows for reliable position and abnormal operation detection without increasing size or weight, using strain gauges to generate signals for start and end of travel detection and anomaly monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional sensors are added to measure actuator position and detect failures, then measurement precision and reliability improve, but device complexity, size, and weight increase
Solution Approach 1:
The actuator structure itself serves as the sensing element. The flexible element with embedded strain gauges directly measures the forces and positions within the actuator, eliminating the need for separate external sensors. The structure provides its own measurement capability through the strain gauges integrated into the flexible element.
Solution Approach 2:
The flexible element serves multiple functions simultaneously: it provides mechanical support, enables motion transformation, and acts as a sensing element through the embedded strain gauges. This multi-functionality reduces the need for separate dedicated sensing components, thereby reducing overall device complexity and weight.
2Reliability
If additional sensors are added to detect actuator state, then reliability improves, but weight increases
Solution Approach 1:
The actuator's flexible element with strain gauges provides self-monitoring capability, detecting forces and positions inherent to its operation. This self-service approach to reliability monitoring eliminates the need for additional weight-bearing sensor components while maintaining continuous surveillance of actuator health and position.
3Reliability
If mechanical stops are made elastic to prevent damage, then reliability improves, but manufacturing precision requirements increase
Solution Approach 1:
The mechanical stops are made elastic, changing their physical parameter from rigid to flexible. This elasticity allows the stops to deform under load, providing a cushioning effect that prevents damage from abrupt impacts while still maintaining precise positioning control through the strain gauge measurements.
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 provides a compact, reliable, and cost-effective means to improve actuator reliability by reducing the number of sensors needed, enabling accurate position sensing and anomaly detection, while preventing damage by cutting off power supply before maximum torque is reached, thus maintaining actuator integrity.
Implementation Method 1
a group of at least one strain gauge (21) placed on a force path (30) of the actuator and connected to a control module (15), said strain gauge group (21) being configured to generate a signal representative of a detected torque or force
Implementation Method 2
the strain gauge group comprises at least four strain gauges, said gauges being connected together so as to form at least one Wheatstone bridge
Implementation Method 3
at least one mechanical stop is made of an elastic material
Data Source
Figure 1~2a
Figure 2b~3
Figure 4a
AI summary
The present invention relates to a control device for a linear actuator, comprising a motor (11) coupled to a device for transforming a rotational motion into a translational motion (13) configured to move a movable part (14) in translation. The actuator includes at least one mechanical stop (132) located on a fixed part of said actuator, the group of at least one mechanical stop being configured to prevent the relative helical movement of a pin (22) of the moving part in translation when the pin reaches at least one predetermined position, the contact of said pin with a stop generating a torque.The control device further includes a control module connected to at least one strain gauge (21) configured to generate a signal representative of the detected torque, the control module being configured to compare the amplitude of the signal generated by the group of at least one strain gauge to at least one predetermined value.