Low-power MEMS Accelerometer with Passive Binary Output
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Solution Overview
Problem
MEMS accelerometers face high power consumption due to the use of analog components for measuring capacitance, and designing springs with precise stiffness ratios in MEMS technology is challenging, especially for binary output accelerometers that require electrostatic actuators for operation.
Innovation Solution
A unary code accelerometer design featuring proof-masses suspended by springs with identical stiffness and weight, where each proof-mass has two conductive stops that intercept in opposite directions, allowing for discrete acceleration measurements without electrical contact until the proof-mass rests on both, thus eliminating the need for active power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If analog components are used to measure capacitance in MEMS accelerometers, then measurement precision is improved, but power consumption increases significantly
Solution Approach 1:
The patent replaces the analog capacitive measurement system with a purely mechanical binary output system. Proof masses are equipped with mechanical contacts that directly close electrical circuits when displaced by acceleration, eliminating the need for analog capacitive sensing components and their associated high power consumption while maintaining acceleration detection capability.
Solution Approach 2:
The proof masses themselves serve dual functions: they are both the sensing elements that respond to acceleration and the switching elements that directly close the electrical contacts. This self-service approach eliminates the need for separate actuation mechanisms and reduces overall system power consumption.
2Measurement precision
If electrostatic actuators are added to proof-masses for binary output, then measurement precision is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent extracts and eliminates the electrostatic actuator components from the system. Instead of using active actuators to move proof masses, the design relies on passive mechanical displacement of proof masses under acceleration, with mechanical contacts directly closing circuits to produce binary output.
Solution Approach 2:
Instead of using actuators to actively move proof masses to detect acceleration, the system inverts the approach by allowing proof masses to passively move under acceleration and use their own motion to close mechanical contacts, thereby generating the binary signal without active actuation.
3Measurement precision
If springs with geometric progression stiffness are used in binary accelerometer, then measurement precision is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs multiple proof masses with identical or homogeneous mechanical properties (mass, spring stiffness) rather than requiring progressively different stiffness values. This homogenization simplifies manufacturing by allowing standardization of spring components while maintaining the ability to generate binary output through sequential activation of mechanical contacts.
Solution Approach 2:
The system segments the acceleration measurement range into discrete thresholds by positioning mechanical contacts at different locations along the acceleration axis. Each proof mass with identical springs activates a specific contact at a specific acceleration threshold, creating binary output without requiring varying spring stiffnesses.
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 accelerometer provides reliable, fully passive acceleration measurements without power consumption, with the ability to filter transient contacts and offer flexible code configurations, simplifying design and production by using identical proof-masses and springs.
Implementation Method 1
a respective spring attached to each proof-mass, configured to exert an elastic return on the proof-mass along the measurement axis
Implementation Method 2
The stop and the proof-mass are metal-coated, so that the pressure of the proof-mass on the stop closes an electrical contact to represent a binary '1'
Implementation Method 3
A plurality of proof-masses movable along a measurement axis; a respective spring attached to each proof-mass, configured to exert an elastic return on the proof-mass along the measurement axis
Data Source
AI summary
An accelerometer comprising a plurality of proof-masses moveable along a measurement axis; a respective spring rigidly attached to each proof-mass, configured to exert an elastic recall on the proof-mass in the measurement axis; and a fixed stop associated with each proof-mass, arranged to intercept the proof-mass when the acceleration in the measurement axis increases by a step. The proof-masses are suspended in series with respect to one another by springs in the measurement axis, the stops being arranged to successively intercept the respective proof-masses for increasing thresholds of acceleration.