Hinge Angle Sensing with Sensor Fusion and Axis Alignment
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Solution Overview
Problem
Conventional methods for determining hinge angle using accelerometer-based information suffer from noise, susceptibility to shaking motions, saturation during large accelerations, and inability to sense rotation about the gravity vector, leading to inaccurate hinge angle estimates.
Innovation Solution
Employ a system with integrated three-axis accelerometers and gyroscopes in each device portion, performing six-axis sensor fusion to relate the portions to a world frame, and aligning the determined axes of the sensor assemblies based on known mechanical hinge relationships to compensate for accumulating sensor measurement errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If accelerometer-based information is used to determine hinge angle, then the system can operate with simpler sensors, but the measurement precision deteriorates due to noise and susceptibility to shaking motions
Solution Approach 1:
The patent combines data from both accelerometers and gyroscopes in a sensor fusion algorithm. The gyroscope measures angular velocity which is integrated to obtain angular orientation, while the accelerometer provides gravity reference. By merging these complementary measurements, the system achieves accurate hinge angle estimation that overcomes the weaknesses of either sensor used alone.
Solution Approach 2:
The sensor assembly is designed to perform multiple functions: the gyroscope measures rotation about all three axes including the hinge axis, while the accelerometer measures gravity vector orientation. This multi-functional sensor system can determine hinge angle in all device orientations, not just when the hinge is perpendicular to gravity.
2Device complexity
If accelerometers are used to sense hinge angle, then the device can remain simple, but reliability worsens due to saturation during large accelerations
Solution Approach 1:
The gyroscope acts as an intermediary sensor that measures angular velocity without being affected by linear acceleration. By integrating gyroscope measurements, the system obtains reliable angular orientation information even during large accelerations when the accelerometer would saturate. The accelerometer then serves to correct drift in the integrated gyroscope data.
3Device complexity
If accelerometer-based determination is used, then the system architecture remains simple, but adaptability worsens due to inability to sense rotation about the gravity vector
Solution Approach 1:
The system transitions from relying solely on accelerometer data in the gravity-aligned coordinate system to incorporating gyroscope data that provides rotation information about all three axes. This dimensional expansion allows the system to determine hinge angle regardless of how the device is oriented in space, including when the hinge axis is aligned with gravity.
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
Accurately determines hinge angle in various orientations, including when the hinge is aligned with gravity, by constraining sensor axes, thereby improving estimation accuracy and tracking hinge angle changes over time.
Implementation Method 1
inertial motion sensors include gyroscopes that measure angular velocity
Implementation Method 2
accelerometers that measure specific forces along one or more orthogonal axes
Data Source
AI summary
Described herein are methods and systems for determining a relative position of different portions of a hinged device. Motion sensor data from sensor assemblies of each portion is fused to relate the device portions to a world frame. An angular orientation between the device portions is determined with respect to the hinge axis and accumulating sensor measurement errors are compensated by constraining determined axes of the sensor assemblies using the motion sensor data and known relationships between physical axes of the sensor assemblies and the mechanical hinge, such that the determined axes of the sensor assemblies are aligned along the hinge axis.