Accelerometer Cartridge Mass-Spring-Damper Shock Isolation
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Solution Overview
Problem
MEMS accelerometers in inground devices, such as those used in horizontal directional drilling, fail due to exposure to high mechanical shock, and existing solutions like shock mounting the entire circuit board or using foam damping are inadequate, as they either increase the tool diameter or fail to effectively isolate the accelerometer from vibrations.
Innovation Solution
An accelerometer cartridge with a housing mass of at least 17.2 grams, configured to work with resilient damping foam to form a complex mass-spring-damper system, which reduces resonant frequency and enhances isolation from mechanical shock and vibration, allowing the accelerometer to operate effectively within the inground tool.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the accelerometer is shock mounted on the main printed circuit board, then the accelerometer is protected from mechanical shock, but the diameter of the transmitter increases
Solution Approach 1:
The accelerometer is extracted from the main printed circuit board and mounted on a separate accelerometer circuit board. This separation allows the accelerometer to be protected with shock mounting elements without requiring the entire main circuit board to be shock mounted, thereby reducing the overall transmitter diameter while still providing adequate protection.
Solution Approach 2:
The transmitter is segmented into multiple functional modules: the main printed circuit board and a separate accelerometer circuit board. This segmentation allows independent optimization of each module, enabling the accelerometer to receive enhanced shock protection without increasing the overall transmitter size, as each module can be compactly designed.
2Reliability
If the accelerometer is supported in a separate accelerometer housing with foam damping material, then the accelerometer is isolated from mechanical shock, but the device complexity increases
Solution Approach 1:
The accelerometer housing is merged with the accelerometer circuit board to form an integrated accelerometer cartridge assembly. This combination eliminates the need for separate foam damping materials and complex housing structures, as the circuit board itself serves as the mounting structure with integrated shock protection features.
Solution Approach 2:
The shock protection mechanism is changed from using foam damping material to using a rigid accelerometer housing with specific mass characteristics. By changing the protection parameter from soft damping to rigid structural protection with appropriate mass, the system achieves shock isolation without requiring complex foam-based damping structures.
3Reliability
If the mass of the accelerometer housing is increased to at least 17.2 grams, then the resonant frequency is reduced and isolation from mechanical shock is enhanced, but the weight of the transmitter increases
Solution Approach 1:
A heavy metal washer is introduced as an intermediary mass element between the accelerometer and the shock environment. This washer provides the necessary mass (at least 17.2 grams) to reduce resonant frequency and enhance shock isolation, while being a compact component that minimizes the overall weight increase of the transmitter.
Solution Approach 2:
The accelerometer housing assembly uses composite construction combining lightweight materials for the housing structure with a dense heavy metal washer for mass. This composite approach achieves the required 17.2 gram mass for shock isolation while keeping the overall transmitter weight increase minimal through efficient material selection.
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 significantly reduces accelerometer failure rates by at least an order of magnitude, providing enhanced reliability and allowing the accelerometer to accurately characterize the orientation of the inground device despite exposure to mechanical shock and vibration.
Implementation Method 1
An accelerometer housing is provided having an exterior periphery that is receivable in the interior passage of the transmitter housing and a mass of at least 17.2 grams. The accelerometer arrangement is thereby subject to enhanced isolation from the mechanical shock and vibration.
Implementation Method 2
cooperate with associated damping to control and lower resonant frequency response to the mechanical shock and vibration
Data Source
AI summary
An accelerometer module is supported within an interior passage of a transmitter housing of a transmitter that is itself receivable within an inground housing of an inground tool to perform an inground operation which subjects the transmitter to mechanical shock and vibration. An accelerometer housing of the module includes an exterior periphery that is receivable in the interior passage of the transmitter. A resilient damping foam can be supported to dispose the foam between the accelerometer housing and the transmitter housing such that the foam cooperates with the accelerometer housing to form a complex mass-spring-damper system that exhibits a resonant frequency which is controllable. An accelerometer cartridge of the module can include a mass that is at least five times the mass of an original accelerometer cartridge. In one feature, the accelerometer cartridge can include a mass of at least 20 grams for a one inch diameter transmitter housing.