Servo Compensating Accelerometer with Dual Housing
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Solution Overview
Problem
Conventional accelerometers face issues with temperature-dependent zero bias drift, vulnerability to shock and vibration, and complex installation due to single base mounting surface, as well as reduced accuracy from external magnetic fields and limited maximum voltage output.
Innovation Solution
A servo compensating accelerometer design with a top and bottom housing half rigidly connected, featuring coaxial threaded openings, a metallic sensing element with a proof mass and flexible suspension, and a feedback circuit including a preamplifier, demodulator, and high frequency generator, which allows for mechanical and electrical tuning to reduce zero bias drift and improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a bridge circuit with strain resistors is used to sense angular displacement, then the accelerometer can measure acceleration, but the zero bias drift increases due to temperature changes
Solution Approach 1:
The patent employs a feedback circuit that uses a second set of coils to generate a compensating force opposite to the gravitational force acting on the proof mass. This feedback mechanism actively counteracts temperature-induced zero bias drift by sensing the drift and applying an equal and opposite force, thereby maintaining measurement accuracy despite temperature changes.
Solution Approach 2:
The patent changes the physical state of the proof mass by transitioning it from a static position to a dynamically controlled position using electromagnetic forces. By adjusting the current through the second set of coils based on temperature conditions, the system compensates for parameter changes in the strain resistors and maintains stable zero bias across temperature variations.
2Device complexity
If the proof mass is flexibly attached to the frame using a single silicon monocrystalline wafer, then the accelerometer structure is simplified, but the device becomes more vulnerable to shock and vibration
Solution Approach 1:
The patent uses a composite structure combining silicon monocrystalline wafer with additional support elements and damping components. The flexible suspension is integrated with vibration damping features and protected by the housing structure, creating a composite system that maintains simplicity while reducing vulnerability to shock and vibration through multi-material design.
Solution Approach 2:
The patent incorporates vibration damping elements and shock absorption features into the flexible suspension structure before external shocks or vibrations occur. The housing design and suspension geometry are pre-configured to absorb and dissipate vibrational energy, protecting the proof mass from harmful effects before they can cause measurement errors.
3Device complexity
If the accelerometer uses a single base mounting surface, then the device structure is simplified, but installation becomes more difficult and less versatile
Solution Approach 1:
The patent divides the base mounting structure into multiple separate mounting surfaces or attachment points on the housing. This segmentation allows the accelerometer to be mounted in different orientations and positions while maintaining structural simplicity, thereby improving installation ease and versatility without adding complex mounting mechanisms.
4Power
If permanent magnets with cup-like magnetic conductors are used in the momentum sensor, then the compensating force can be generated, but external magnetic fields interfere with measurement accuracy
Solution Approach 1:
The patent introduces a magnetic shielding layer or mu-metal screen between the permanent magnets and the external environment. This intermediary shielding structure blocks external magnetic fields from reaching the proof mass and sensing elements, while allowing the internal magnetic fields necessary for generating compensating force to function normally, thus protecting against interference.
Solution Approach 2:
The patent utilizes the magnetic field generated by the permanent magnets in a controlled manner to create the compensating force, while simultaneously designing the magnetic circuit to minimize leakage fields that could be affected by external magnets. The magnetic conductors are shaped and positioned to concentrate fields where needed while shielding against external interference, converting potential vulnerability into a controlled magnetic field system.
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 effectively reduces temperature-dependent zero bias drift, enhances resistance to shock and vibration, simplifies installation with dual base mounting surfaces, and increases the maximum allowed voltage output, thereby improving measurement accuracy and reliability.
Implementation Method 1
a proof mass (PM) that is flexibly attached to a frame
Implementation Method 2
Current that flows through each coil creates a magnetic field, which interacts with the magnetic field of the corresponding magnetic stator, forming a compensating force which is applied to the proof mass
Implementation Method 3
The motion of the proof mass relative to the housing leads to a change in the differential resistance of the angular sensing element
Data Source
AI summary
A servo compensating accelerometer includes a top housing half and a bottom housing half rigidly connected together, and each having coaxial threaded openings. A sensing element is positioned between the top and bottom halves and affixed to the bottom half. Top and bottom magnetic systems, each of which has a magnetic conductor, a permanent magnet and a field concentrator, the magnetic systems being mounted within the respective top and bottom halves of the housing using the threaded openings. A momentum sensor includes the top and bottom magnetic systems, and also includes two movable coils mounted on a plate and positioned within the magnetic systems. A differential angle sensor includes toroidal excitation coils located on the permanent magnets, the magnetic systems and the coils of the momentum sensor. Zero bias of the accelerometer's angular displacement sensor is tuned by adjusting the position of the magnetic systems by moving them in the threaded openings. Stop screws can be used to fix position of the magnetic systems relative to the top and bottom halves of the housing. Two perpendicular mounting surfaces are located on the bottom half of the housing. An electrical circuit that includes a preamplifier, a demodulator, a correcting element, a high frequency generator, an amplifier, the excitation coils and the movable coils, which collectively form a feedback circuit, and generate an output of the accelerometer using an inductor, a resistor, a capacitor and a filter. The sensing element, in one embodiment, can be metallic.