SAW Sensor Arrangement for Large Shaft Torque Measurement
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Solution Overview
Problem
Conventional non-contact torque sensors are not suitable for large shafts like ship propeller or wind turbine shafts due to requirements for special magnetic materials, heavy transformers, or significant shaft modifications, and existing SAW sensor installations face challenges with bonding and hysteresis issues, especially in aftermarket installations.
Innovation Solution
The SAW sensor arrangement uses a clamp arrangement with friction raisers and a heat-cured adhesive bond to securely attach the SAW device to a curved measurement surface without machining, minimizing hysteresis and allowing for easy installation and calibration on large items like ship propeller or wind turbine shafts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a stiff bond with high curing temperature (150-200°C) is used to bond the SAW die to the shaft, then the bond stiffness and strain transfer quality are improved, but the installation time and thermal strain introduction are worsened due to long curing time (10-20 hours) and thermal expansion mismatch
Solution Approach 1:
The patent changes the bonding parameters by using room temperature curing adhesives instead of high temperature curing adhesives. This eliminates the need for long curing times and high temperature ovens, while still achieving sufficient bond stiffness for accurate strain transfer. The bonding process can be completed in minutes rather than hours, making it practical for field installation on large shafts.
2Measurement precision
If a stiff bond is used to transfer shear strain from the shaft surface to the quartz surface, then the strain transfer accuracy is improved, but the hysteresis and non-repeatability are worsened due to bonding imperfections and thermal strain
Solution Approach 1:
The patent changes the bonding temperature parameter to room temperature, which eliminates thermal expansion mismatch between the steel shaft and quartz die. This reduces hysteresis and non-repeatability in the strain transfer, improving measurement reliability while maintaining sufficient bond stiffness through optimized adhesive selection and application procedures.
3Measurement precision
If conventional torque sensors are used on large shafts, then torque measurement capability is achieved, but the device complexity and installation difficulty are worsened due to requirements for special magnetic materials, heavy transformers, or shaft modifications
Solution Approach 1:
The patent replaces complex mechanical and magnetic systems with a simplified SAW-based system. Instead of using heavy transformers, battery-powered transmitters, or shaft modifications required by conventional sensors, the invention uses a small SAW die bonded to the shaft surface that can be wirelessly interrogated. This dramatically reduces device complexity and installation difficulty while maintaining torque measurement capability on large shafts.
4Manufacturing precision
If the SAW die is firmly bonded to a flat spot on the shaft, then the strain transfer is improved, but the ease of installation is worsened due to the need for machining a flat spot on the shaft
Solution Approach 1:
The patent segments the bonding interface by using a small, self-contained SAW die with a standardized bonding surface. This allows the die to be bonded to a small prepared area on the shaft without requiring a large machined flat spot. The segmentation of the sensing element into a small, portable die makes installation practical while maintaining sufficient strain transfer quality through proper bonding technique.
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 enables accurate torque measurement with low hysteresis and no need for shaft modifications, facilitating easy installation and calibration, suitable for large shafts, and reducing thermal strain issues.
Implementation Method 1
Non-contact torque sensors based on SAW sensing elements have been disclosed in US 5585571
Implementation Method 2
The die 56 is made of a thin piezoelectric quartz substrate with an aluminium pattern formed on its top surface
Implementation Method 3
The sensor arrangement includes at least two spaced friction raisers, the sensor arrangement including a clamp arrangement which applies a clamping force to clamp the sensor arrangement to an item
Implementation Method 4
The aim of the stiff bond between the flat spot of the shaft 54 and the SAW die 56 is to transfer the shear strain from the shaft surface to the quartz surface
Data Source
Figure 1
Figure 2A~2C
Figure 3A~3D
AI summary
An SAW sensor arrangement(10)includes a transducer (11), the transducer (11)including a support (12)for supporting an SAW device(14). The support(12)includes a sensor location part (16)located between two oppositely extending attachment parts(18). The SAW device (14) is mountable to the sensor location part(16). The sensor arrangement (10) includes at least two spaced friction raisers(20). The sensor arrangement (10) includes a clamp arrangement (22) which applies a clamping force to clamp the sensor arrangement (10) to an item(24). The sensor arrangement (10) is arranged so that in use each of the friction raisers (20) is located between a different one of the attachment parts (18) and the item(24).