Capacitive Washer for Remote Bolt Tension Monitoring
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Solution Overview
Problem
Current methods for monitoring bolt tension in large anchor bolts, such as those used in luminaire and traffic signal structures, are inadequate, leading to incorrect installation and potential catastrophic failures due to loose nuts, and require labor-intensive maintenance inspections.
Innovation Solution
A sensor assembly is integrated into the anchor bolt system that includes a capacitive sensing washer with a resilient material, allowing for direct measurement of bolt tension and remote monitoring using a radio frequency identification (RFID) system, enabling accurate tension measurement and long-term monitoring without the need for battery power or manual inspection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional torque-based installation methods are used for anchor bolts, then the installation process is simple and quick, but the measurement precision of bolt tension is insufficient leading to incorrect installation
Solution Approach 1:
The patent replaces traditional mechanical torque-based tension measurement with a capacitive sensing system. The capacitive washer contains conductive plates that form a capacitor, where changes in capacitance directly correlate to bolt tension. This substitution enables precise electrical measurement of tension forces without relying on mechanical torque estimation, resolving the contradiction between measurement precision and system complexity.
Solution Approach 2:
The patent introduces a capacitive washer as an intermediary component between the bolt and the monitoring system. This washer contains conductive plates that convert mechanical tension into electrical capacitance signals, which can then be read by RFID tags and external monitoring devices. The intermediary enables accurate tension measurement while keeping the overall system relatively simple through wireless communication.
2Productivity
If manual inspection methods are used for monitoring anchor bolts, then the monitoring system is simple, but the productivity and coverage of inspections are limited
Solution Approach 1:
The patent implements a self-monitoring system where the capacitive washer continuously measures bolt tension and stores data in RFID tags without requiring constant human intervention. The system automatically detects tension changes and can alert authorities when threshold values are exceeded, enabling the infrastructure to monitor itself and significantly improving inspection productivity.
Solution Approach 2:
The patent replaces manual physical inspection with an automated electronic monitoring system. Capacitive sensors continuously measure tension, RFID tags store the data, and wireless communication enables remote reading. This substitution transforms labor-intensive manual inspections into an automated system that can monitor multiple bolts simultaneously, dramatically improving productivity while managing complexity through standardized components.
3Reliability
If frequent manual inspections are conducted to ensure safety, then the reliability of the structure is maintained, but the loss of time and labor resources increases
Solution Approach 1:
The patent implements continuous monitoring through the capacitive washer that constantly measures bolt tension and updates RFID tags with current status data. This continuous action eliminates the need for periodic manual inspections, maintaining structure safety without the time loss associated with repeated human inspections. The system provides uninterrupted surveillance of bolt integrity.
Solution Approach 2:
The monitoring system operates autonomously without requiring continuous human presence or intervention. The capacitive sensor continuously monitors tension, the RFID tag continuously stores data, and the system automatically detects and reports issues. This self-service capability maintains high reliability while eliminating the time burden of manual inspection scheduling and execution.
4Measurement precision
If direct tension measurement devices are installed on anchor bolts, then the measurement precision is improved, but the ease of manufacture and installation deteriorates
Solution Approach 1:
The patent merges the tension measurement function with the existing washer component that is already part of the anchor bolt assembly. The capacitive plates are integrated into the washer, which is a standard component in bolted connections. This merging allows precise tension measurement to be achieved without adding separate complex devices, maintaining ease of manufacture and installation while improving measurement precision.
Solution Approach 2:
The capacitive washer serves multiple functions: it acts as both a standard structural washer and a tension sensor. The same component that provides mechanical support also contains conductive plates for capacitance measurement. This multi-functionality eliminates the need for separate measurement devices, simplifying manufacture and installation while achieving precise tension measurement.
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 accurate, real-time, and cost-effective monitoring of bolt tension, reducing the risk of failures and minimizing maintenance costs by allowing for remote sensing and efficient tracking of bolt tension over time.
Implementation Method 1
The compression sensor is on a washer assembly and includes two capacitor plates spaced apart along the direction of the bolt axis and encapsulated in an elastomeric material which urges the capacitor plates apart. The compression sensor is configured to transduce a capacitance value between the two capacitor plates.
Implementation Method 2
an elastomeric material which urges the capacitor plates apart
Implementation Method 3
The RFRD is in electrical communication with the compression sensor and is configured to transduce the capacitance value into a radio frequency signal for stand-off remote sensing by a reader.
Data Source
AI summary
A method, apparatus, and system to quantify tension forces of the anchor bolts for, e.g., SLTS support structures. A sensing assembly comprising one or more washers is installed along an anchor bolt. The sensing assembly comprises two spaced-apart surfaces between which a capacitance can be measured if electrical potential is created between the surfaces. The capacitance between the surfaces can be calibrated to bolt tension based on the relative distance between the surfaces. An RFRD circuit is connected to the two surfaces. An RF interrogation signal can supply the electrical potential and allow a reading of the responsive capacitance between surfaces to convert the capacitance reading into a bolt tension. Additionally, the introduction of the battery-free RFRD allows data to be acquired wirelessly from a distance, enabling an entirely new method of inspection. With minimum additional hardware cost, it provides a cost-effective way to replace traditional bolt installation and inspection methods.