Orthogonal MEMS Accelerometer Axes for Shock Resistance
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Solution Overview
Problem
Consumer-grade MEMS triaxial accelerometers used in high mechanical shock and vibration environments, such as underground drilling, are prone to failures due to the susceptibility of their normal sensing axes to mechanical stress.
Innovation Solution
The use of dual MEMS triaxial accelerometers with their normal sensing axes oriented orthogonally to each other, allowing the processor to determine accelerations along three orthogonal axes without relying on the weaker normal sensing axes, thereby enhancing reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If consumer-grade MEMS triaxial accelerometers are used in high mechanical shock environments, then cost is reduced, but reliability deteriorates due to susceptibility of normal sensing axes to mechanical stress
Solution Approach 1:
The patent segments the accelerometer system into multiple independent sensing units. Instead of relying on a single triaxial accelerometer where all three axes share the same vulnerable normal axis, the system uses multiple accelerometers (e.g., two triaxial accelerometers) with orthogonally oriented normal axes. This segmentation isolates the vulnerability to specific axes, allowing the system to maintain reliability by excluding only the vulnerable normal axes from critical measurements while using the more robust in-plane axes.
Solution Approach 2:
The patent introduces an additional dimensional aspect to the problem by considering the orientation and redundancy of multiple accelerometer units. By orienting the normal sensing axes of multiple accelerometers orthogonally to each other, the system creates a multi-dimensional sensing architecture where the weakness of individual normal axes is compensated by the presence of multiple in-plane axes from different accelerometer units, effectively adding redundancy in the sensing dimension.
2Measurement precision
If the normal sensing axis is used for acceleration measurement, then complete triaxial measurement capability is achieved, but the risk of premature failure increases due to higher susceptibility to mechanical shock
Solution Approach 1:
The patent extracts and excludes the vulnerable normal sensing axes from the critical measurement pathway. By identifying which accelerometer normal axes are most susceptible to mechanical shock and excluding them from determining the final acceleration values along the three orthogonal axes, the system removes the source of premature failure while maintaining complete measurement capability through the use of in-plane axes from multiple accelerometer units.
Solution Approach 2:
The patent changes the measurement parameter strategy by shifting from relying on normal axes (which have high failure risk) to relying on in-plane axes (which have lower failure risk). This parameter change involves modifying which sensing axes are used for critical measurements, thereby changing the system's vulnerability profile while maintaining the ability to perform complete triaxial acceleration measurement.
Data Source
AI summary
An accelerometer arrangement and method are described for determining accelerations of an inground tool. First and second triaxial accelerometers are supported such that a normal sensing axis of the first triaxial accelerometer is at least generally orthogonal to the normal sensing axis of the second triaxial accelerometer for determining the accelerations along the three orthogonal axes based on a combination of sensing axis outputs from one or both of the triaxial accelerometers. A weaker sensing axis of one triaxial accelerometer can be supported at least approximately normal to a weaker sensing axis of another triaxial accelerometer such that the weaker axes are not used. The triaxial accelerometers can be supported such that one axis of one accelerometer can be redundant with respect to another axis of another accelerometer. One triaxial accelerometer can be mounted on a tilted plane with respect to another triaxial accelerometer.