Cable Actuator Force Sensing via Nut Position Deviation
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Solution Overview
Problem
Force sensors for cable actuators are often bulky, expensive, and lack accuracy due to their susceptibility to impacts and vibrations, making it difficult to provide effective force control, which restricts their widespread use.
Innovation Solution
A cable actuator system that uses position measurement means, such as linear magnetic cores or distance sensors, to determine the actual position of the nut relative to the frame, allowing for the calculation of force applied to the output by comparing actual and theoretical positions, and utilizing anti-rotation cables to prevent nut rotation, thereby enhancing measurement reliability and reducing sensitivity to vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If force sensors are mounted directly on the output of the actuator, then force measurement is achieved, but the sensors become bulky, expensive, and less accurate due to impacts and vibrations
Solution Approach 1:
The patent introduces an intermediary measurement approach by measuring the position of the nut on the screw instead of directly measuring force. This intermediary position measurement, combined with the known mechanical relationship between the screw-nut system and the output, allows indirect force calculation without exposing sensors to harsh mechanical environments. The position sensor can be mounted on the stationary frame rather than on moving components, reducing vibration and impact exposure.
Solution Approach 2:
The patent replaces direct mechanical force sensing with a combination of position measurement and mechanical calculation. Instead of using force sensors that directly contact the output, the system uses position sensors to measure nut displacement along the screw, then calculates force based on the known screw pitch and mechanical advantage. This substitution of mechanical force measurement with positional measurement and calculation reduces the complexity and improves the reliability of the sensing system.
2Reliability
If force sensors are mounted directly on the output, then force control can be provided, but the sensors are subjected to impacts and vibrations which reduces their reliability
Solution Approach 1:
The patent uses position measurement as an intermediary that is less susceptible to vibration and impact effects. By measuring the position of the nut on the screw through magnetic or optical fields rather than direct mechanical contact, the sensing system achieves better reliability in the presence of harmful mechanical factors.
Solution Approach 2:
The patent extracts the sensing function from the high-vibration output area and relocates it to the stationary frame or to components experiencing less vibration. The position sensor measures the nut's position without being directly subjected to the same impact and vibration forces that would affect a force sensor mounted on the output.
3Reliability
If over-dimensioned sensors are used to avoid fragility, then sensor durability is improved, but volume increases and sensitivity reduces
Solution Approach 1:
The patent replaces mechanical force sensing with positional measurement and calculation, allowing the use of smaller, more sensitive position sensors instead of large, robust force sensors. The calculation based on screw mechanics provides the force information without requiring physically large sensing elements.
Solution Approach 2:
The patent changes the measurement parameter from force to position. This parameter change allows the use of more sensitive measurement technologies (such as magnetic or optical position sensors) that can detect smaller displacements, thereby improving sensitivity while maintaining durability through proper sensor placement.
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 system provides a cost-effective and accurate method for measuring forces applied to the output of cable actuators, improving their sensitivity and reliability while reducing the impact of vibrations and ambient light interference.
Implementation Method 1
the means for determining the actual position of the nut relative to the frame comprise a linear magnetic core secured to the frame and magnetic field induction means connected to the nut
Implementation Method 2
the distance sensor comprises a wave transceiver
Implementation Method 3
a screw rotatably mounted on the frame and extending along a first axis, a nut co-operating with the screw... rotation of the screw or of the nut under drive from the motor causes the nut to move along the screw
Data Source
AI summary
An actuator having a nut (4) co-operating with a screw (2); a first cable (6) coupled to the nut and functionally connected to an output (16, 17, 22.4) of the actuator (100); and a motor (3) arranged to drive the screw (2) in rotation. The actuator also has a mechanism (92) for comparing the actual position of the nut relative to the frame (10) with a theoretical position for the nut relative to the frame (10) in order to obtain a position deviation (δang4, δlin4) of the nut; and a mechanism (93) for determining a force applied to the output (22.4) of the cable actuator (100) as a function of the position deviation of the nut. Also disclosed is a method of measuring a force applied to an output (16, 17, 24.1) of an actuator (100), and to a method of determining prior loading (t6,9) of a cable actuator (100).