Capstan Rotary Actuator With Cable Torque Sensing
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Solution Overview
Problem
Existing actuator designs for robotic systems face challenges in achieving low friction, low backlash, high-power density, and cost-effective torque control, especially for pivoting angles less than 360 degrees, due to the high cost and added mass of strain gauge sensors and elastic elements used for torque measurement.
Innovation Solution
A rotary actuator assembly with a capstan drive and integrated absolute torque sensor device using strain gauge load cells, coupled to the drive pulley, allows for accurate torque measurement and control through force feedback, utilizing steel wire ropes for transmission and a spur gear for increased torque levels, minimizing backlash and friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strain gauge sensors are used for torque measurement, then torque control precision is improved, but cost and mass increase significantly
Solution Approach 1:
The patent replaces traditional strain gauge sensors with a capstan drive mechanism that uses cable tension measurement to determine torque. This substitution eliminates the need for expensive and heavy strain gauges while maintaining torque measurement capability through the relationship between cable force and torque on the pulley.
Solution Approach 2:
The patent introduces a capstan drive system with cables as an intermediary mechanism between the motor and the load. The cables transmit both motion and force information, allowing torque to be inferred from cable tension measurements rather than direct strain gauge readings on the shaft.
2Measurement precision
If elastic elements are integrated into the drive train for torque detection, then torque measurement capability is improved, but actuator controllability deteriorates due to increased elasticity
Solution Approach 1:
The patent replaces elastic elements used for torque detection with a rigid capstan drive system. The torque measurement is achieved through cable tension sensing rather than elastic deformation, eliminating the compromise between measurement capability and controllability.
3Adaptability or versatility
If high-performance gears are used to meet multiple technical constraints, then actuator performance is improved, but cost increases significantly
Solution Approach 1:
The patent segments the drive train into distinct functional modules: a capstan drive for motion transmission, separate cable tension sensing for torque measurement, and a hollow shaft for cable routing. This modular segmentation allows each component to be optimized independently and manufactured cost-effectively while meeting overall system requirements.
Solution Approach 2:
The capstan drive system serves multiple functions simultaneously: it transmits rotational motion, provides torque measurement through cable tension, and allows for hollow shaft configuration. This multi-functionality eliminates the need for separate expensive high-performance gears that would be required to meet all constraints individually.
4Measurement precision
If strain gauge-based torque sensors are used, then torque measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex strain gauge-based torque sensors with a simpler capstan drive system where torque is derived from cable tension measurements. This substitution reduces device complexity by eliminating the need for strain gauge installation, calibration, and signal conditioning circuits.
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 provides a robust, cost-effective, and compact actuator design with improved control and accuracy for robotic kinematics, achieving high torque levels with reduced mass and volume, suitable for applications requiring precise actuation within limited rotational ranges.
Implementation Method 1
each cable transmitting the drive pulley's pivoting motion to the main pulley by tensile forces applied to the lateral area of the main pulley
Implementation Method 2
the absolute torque sensor device exhibits at least one force sensor, especially at least one strain gauge load cell, which is coupled to the capstan drive
Data Source
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AI summary
The present invention relates to an actuator assembly (30) for rotary actuation around a pivot axis, comprising: a motor (19); a drive train with a capstan drive comprising a drive pulley (2) and a main pulley (1) and transmission means (3) for interconnecting the pulleys, and comprising an absolute torque sensor device (12); wherein the transmission means (3) are provided by at least one cable transmitting the drive pulley's pivoting motion to the main pulley (1) by tensile forces applied to the lateral area of the main pulley, and wherein the absolute torque sensor device (12) exhibits at least one force sensor (12.2) coupled to the capstan drive, for absolute torque measurement via force measurement. Further, the present invention also relates to a method for exerting a respective rotary actuation around a pivot axis, as well as to use of such an actuator assembly for actuating robotic kinematics.