Multi-Axis Capacitive Accelerometer with Decoupled Proof Masses
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Solution Overview
Problem
Conventional three-axis accelerometers suffer from poor cross-axis sensitivity and linearity due to interference between proof masses, particularly in designs with single sensing structures and non-decoupled springs, which affect the performance of modern consumer electronic devices requiring compact and cost-effective multi-axis acceleration sensing.
Innovation Solution
A multi-axis capacitive accelerometer design featuring multiple independent proof masses with asymmetric suspension and rotating axes, eliminating linear shift and interference by forming capacitive structures between proof masses and sensing electrodes, ensuring high sensitivity and linearity across orthogonal axes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a single sensing structure with proof masses is used to detect acceleration along three mutually orthogonal axes, then the size and cost are reduced, but the cross-axis sensitivity deteriorates due to interference between proof masses
Solution Approach 1:
The accelerometer is divided into three independent sensing structures, each dedicated to sensing acceleration along one of the three mutually orthogonal axes (X, Y, Z). Each sensing structure includes its own proof mass and elastic linkages, preventing interference between axes while maintaining a compact integrated design.
Solution Approach 2:
Each sensing structure is designed with specific local characteristics optimized for its designated axis. The elastic linkages are configured with specific orientations and stiffness properties tailored to each axis, ensuring that each local sensing element operates independently with high precision without affecting other axes.
2Device complexity
If non de-coupled springs are used for detecting acceleration of three axes with one proof mass, then the device complexity is reduced, but the cross-axis sensitivity performance deteriorates seriously
Solution Approach 1:
The spring system is segmented into three separate sets of elastic linkages, with each set dedicated to one axis. This segmentation decouples the sensing mechanisms for each axis, eliminating cross-axis interference while maintaining reasonable structural complexity through systematic arrangement.
Solution Approach 2:
Instead of using a single proof mass with non-decoupled springs as in conventional designs, the invention inverts the approach by using three independent proof masses, each with its own dedicated elastic linkages. This inversion fundamentally resolves the cross-axis sensitivity issue.
3Device complexity
If the motion of the proof mass for sensing Z-axis acceleration is a combination of rotation and translation, then the device structure is simplified, but the linearity of the accelerometer deteriorates
Solution Approach 1:
Each proof mass is equipped with elastic linkages having specific local stiffness characteristics tailored to its sensing axis. The Z-axis proof mass uses vertically oriented elastic linkages with appropriate stiffness to ensure purely vertical translational motion, while X and Y axis proof masses use horizontally oriented linkages, creating locally optimized motion characteristics for each axis.
Solution Approach 2:
The elastic linkages are designed with dynamic properties that constrain each proof mass to move only in its designated direction. The stiffness and geometric configuration of the linkages create restoring forces that prevent rotation and ensure purely translational motion along the sensing axis, improving linearity.
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 design achieves improved sensitivity and linearity by preventing mutual interference between acceleration sensing axes, providing high precision and accuracy for in-plane and out-of-plane acceleration measurements without cross-axis interference.
Implementation Method 1
a first capacitive structure is formed between each first fixed sensing block and the corresponding first proof mass or second proof mass... each second fixed sensing block forms a second capacitive structure with the second proof mass
Data Source
AI summary
A multi-axis accelerometer is consisted of a substrate with sensing electrodes and a structure layer. The structure layer includes anchor bases fixed on the substrate. A first proof mass is disposed over the substrate and has a first opening and a second opening symmetric to each other. The first proof mass is suspended to the anchor bases. Fixed sensing blocks are disposed on the substrate, and capacitors are formed between each fixed sensing block and the first proof mass for sensing acceleration along two in-plane directions. A second proof mass and a third proof mass are disposed in the first opening and the second opening and are asymmetrically suspended. Separate electrodes are disposed on the substrate and form two differential capacitors with the second proof mass and the third proof mass for sensing the out-of-plane acceleration.