Force Platform Calibration Using 3D Grid Matrices
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Solution Overview
Problem
Force platforms suffer from crosstalk errors due to off-axis sensitivity, leading to inaccurate measurements, and existing calibration methods do not adequately reduce these errors to less than 1% across the surface area.
Innovation Solution
A method and system for calibrating force platforms using a 3D grid with nXm points, applying known loads along the X, Y, and Z axes, and deriving position and load-specific calibration matrices to correct for crosstalk, with verification using NIST traceable dead weights and a correction algorithm for accurate measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional single-point calibration is used, then the calibration process is simple and quick, but crosstalk errors remain high (greater than 1%) across the force platform surface
Solution Approach 1:
The calibration process is segmented into multiple discrete calibration points arranged in a 3D grid pattern across the force platform surface. Instead of using a single calibration point, the system divides the measurement space into multiple segments (n x m grid points), each calibrated independently with known loads applied at each position. This segmentation allows the system to capture and correct for spatially varying crosstalk errors across different locations on the platform, reducing overall measurement error to less than 1%.
2Measurement precision
If multiple calibration points are used, then measurement accuracy improves, but the time required for calibration increases
Solution Approach 1:
The system performs preliminary characterization of the force platform by pre-calculating and storing ideal calibration data for multiple known load positions and magnitudes. During the actual calibration process, the system retrieves this pre-computed data from lookup tables rather than performing real-time complex calculations. This preliminary preparation significantly reduces the time required for calibration while maintaining high measurement accuracy across all grid points.
Solution Approach 2:
The system uses ideal, pre-determined calibration data as templates or copies for each calibration point in the grid. Instead of performing independent complex calibration procedures at each of the n x m points, the system applies copied calibration patterns from ideal reference data, adjusting only for the specific position and load magnitude. This copying approach maintains measurement accuracy while dramatically reducing calibration time.
3Measurement precision
If off-axis sensitivity is not corrected, then the force platform structure remains simple, but crosstalk errors cause inaccurate measurements
Solution Approach 1:
The system introduces an intermediary calibration layer between the raw force platform measurements and the final results. This intermediary consists of position-specific calibration matrices and lookup tables that mediate the transformation from raw sensor outputs to corrected force measurements. The calibration system acts as an intermediary that compensates for off-axis sensitivity and crosstalk errors without requiring physical modifications to the force platform structure, thereby maintaining structural simplicity while achieving high measurement accuracy.
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 calibration process significantly reduces crosstalk errors to less than 1% and improves measurement accuracy, with typical load errors less than 0.1% and average Center of Pressure errors less than 0.2 mm.
Implementation Method 1
multi-axis spring members upon which a series of strain gauges are fixed for sensing loads along multiple axes
Implementation Method 2
an amplifier or signal conditioner, either connected to or embedded in the force plate or platform, and a computer for data collcction. Electrical signals from the strain gauges arc transmitted to the amplifier which amplifies the signals to a sufficient voltage for processing in the computer
Implementation Method 3
piezoelectric sensors, Hall effect sensors, optical sensors, capacitors or mechanical sensors are used to measure loads along multiple axes of the platform
Implementation Method 4
piezoelectric sensors, Hall effect sensors, optical sensors, capacitors or mechanical sensors are used to measure loads along multiple axes of the platform
Data Source
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Figure 3A
AI summary
A method for calibrating a force platform includes, providing a force platform and applying an nXm grid on a top surface of the force platform via a computing device. Next, applying p known loads on each of the nXm grid points of the top surface along a Z-axis being perpendicular to the X and Y axes and along the X and Y axes. Next, taking multipoint measurements at each grid point and for each applied known load along the X,Y and Z axes and generating six measured output signals, exact position coordinates and applied known load magnitude for each grid point. Next, assembling an array of nXmXp of six equations with six unknown for each grid point and applied known load and then solving the assembled equations and deriving a position and load specific calibration matrix for each grid point.