Cable Actuator Force Sensing via Nut Position Deflection
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Solution Overview
Problem
Cable actuators face challenges with cumbersome, expensive, and inaccurate force sensors that are prone to fragility due to shock and vibrations, making them difficult and costly to control, especially in compact applications.
Innovation Solution
A cable actuator design that uses position measurement means, such as linear and angular displacement sensors, to determine the effective position of the nut relative to the chassis, allowing for reliable force measurement by calculating the deviation and applying an anti-rotation mechanism through cables, thereby reducing the need for traditional force sensors and enhancing sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional force sensors are mounted directly on the actuator outlet, then force measurement is achieved, but the sensors become cumbersome, expensive, inaccurate, and fragile due to shocks and vibrations
Solution Approach 1:
The patent introduces an intermediary measurement approach by mounting force sensors on the screw instead of directly on the actuator outlet. The screw acts as a mediator that transmits force information to the sensors in a more stable location, reducing direct exposure to shocks and vibrations from the load. This intermediary positioning maintains measurement capability while improving sensor reliability.
Solution Approach 2:
The patent replaces direct mechanical force sensing at the outlet with an indirect measurement system using position sensors on the screw combined with knowledge of the screw pitch. By measuring the linear position of the screw along its axis and using the known pitch relationship, the system calculates force without requiring traditional mechanical force sensors to be positioned where vibrations are most severe.
2Measurement precision
If traditional force sensors are mounted directly on the actuator outlet, then force measurement is achieved, but manufacturing and maintenance costs increase
Solution Approach 1:
The patent substitutes expensive mechanical force sensors with more economical position sensing systems. By using linear position sensors on the screw combined with the known screw pitch geometry, the system derives force information through calculation rather than direct mechanical measurement. This substitution significantly reduces manufacturing and maintenance costs while maintaining measurement capability.
Solution Approach 2:
The patent creates a virtual model of the force measurement system by using position data from the screw and applying the known pitch relationship. Instead of physically measuring force directly, the system copies the positional information and transforms it into force data through mathematical relationships, eliminating the need for expensive physical force sensors.
3Reliability
If oversized force sensors are used to withstand shocks and vibrations, then sensor durability is improved, but volume increases and sensitivity decreases
Solution Approach 1:
The patent uses the screw as an intermediary structure that naturally isolates the sensing system from direct shock and vibration exposure. By measuring position on the screw rather than force directly at the outlet, the system achieves durability without requiring oversized sensors, as the screw's rigid structure and distance from the load provide natural protection.
Solution Approach 2:
The patent replaces mechanical force sensing with position sensing, allowing for the use of small, sensitive position sensors on the screw rather than large, robust force sensors at the outlet. The position sensors can be miniaturized and positioned in a stable location, achieving both high sensitivity and durability through the substitution of measurement methodology.
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 approach improves the accuracy and reduces the manufacturing and maintenance costs of cable actuators by using position measurement methods to determine applied forces, enhancing their sensitivity and robustness against vibrations.
Implementation Method 1
a plurality of magnetized poles attached to the nut and a magnetic sensor
Implementation Method 2
means of determining an effective position of the nut relative to the chassis, means of comparing the effective position of the nut relative to the chassis with a theoretical position
Implementation Method 3
a rotating rotary encoder attached to the third shaft
Implementation Method 4
the distance sensor includes a wave transmitter/receiver
Data Source
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AI summary
The invention relates to an actuator comprising: - a nut (4) cooperating with a screw (2); - a first cable (6) attached to the nut (4) and functionally connected to an output (16, 17, 22.4) of the actuator (100); - a motor (3) arranged to drive the screw (2) in rotation; - the actuator also comprising: - means of comparing (92) an effective position of the nut (4) relative to the frame (10) with a theoretical position of the nut (4) relative to the frame (10) in order to obtain a position deflection (δang4, δlin4) of the nut (4); and - means of determining (93) a force applied to the output (22.4) of the cable actuator (100) as a function of the position deflection of the nut (4). - Method for measuring the force applied to an output (16, 17, 24.1) of an actuator (100). The invention also relates to a method for determining a preload (t6,9) of a cable actuator (100).