Ball-on-Disc Friction Calibration at Pure Rolling Contact
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Solution Overview
Problem
Existing friction and traction measurement apparatuses suffer from inaccuracies due to internal friction, differential thermal expansion, elastic deflections, and manufacturing tolerances, leading to variations in measured forces.
Innovation Solution
A method and apparatus that calibrate traction or friction measurements by accounting for extraneous forces, using a disc and spherical ball setup with independent drives and elastic support structures to measure forces at pure rolling, and adjust the disc track radius based on known ball track radius, employing dry or lubricated contacts to eliminate offset drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional friction measurement apparatus are used, then measurement can be performed, but measurement precision deteriorates due to internal friction, differential thermal expansion, elastic deflections, and manufacturing tolerances
Solution Approach 1:
The patent extracts and eliminates extraneous forces from the measurement system by using a magnetic coupling mechanism that transfers torque without mechanical contact, thereby removing internal friction and elastic deflection sources from the force measurement path
Solution Approach 2:
The patent introduces a magnetic field as an intermediary to transmit torque from the drive motor to the disc, eliminating the need for direct mechanical contact and associated friction and deflection errors in the force transmission path
2Measurement precision
If apparatus with fixed dimensions are used, then manufacturing is simplified, but measurement precision deteriorates due to variations in disc track radius from manufacturing tolerances
Solution Approach 1:
The patent makes the disc track radius dynamic and adjustable, allowing the disc to be positioned at different radial locations to optimize the measurement track radius and compensate for manufacturing tolerances in the ball and disc components
Solution Approach 2:
The patent changes the geometric parameters of the measurement system by allowing adjustment of the disc track radius, enabling optimization of the measurement configuration to achieve higher precision despite fixed manufacturing tolerances
3Measurement precision
If complex calibration procedures are used to eliminate extraneous forces, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent extracts the force measurement function from the torque transmission path by using magnetic coupling, thereby eliminating the need for complex mechanical force sensors and calibration procedures while maintaining high measurement precision
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
Achieves highly accurate traction and friction force measurements by eliminating the effects of extraneous forces and variations, ensuring direct proportionality to actual forces.
Implementation Method 1
The disc is driven by a motor whose drive shaft is magnetically coupled to the disc
Implementation Method 2
The ball traction surface is mounted on elastic flexures which allow elastic deflection of the ball traction surface in the direction of any resulting traction force but not in orthogonal directions
Data Source
AI summary
The invention relates to a traction or friction measuring apparatus and method of calibration. The apparatus comprising a flat disc traction surface; a spherical ball traction surface constructed and arranged to, in use, contact said disc traction surface; a support structure constructed and arranged to support said disc and ball traction surfaces with respect to one another whilst allowing relative rotational movement therebetween; about an axis, the disc drive means and ball drive operable to effect the relative movement between said disc and ball traction surfaces and include disc speed measuring means and ball speed measuring means, and thereby to generate a traction or friction force therebetween; and force measuring means associated with at least said disc and ball traction surfaces to provide a force measurement arising from said traction or friction force and that measurement of the ball speed and the disc speed can be made at a point of pure rolling between the ball and disc in order to accurately determine the disc track radius based on the known ball track radius. The method comprises the following steps: a. steadily increasing the disc speed and reduce the ball speed (or vice versa) in such a way as to ensure that at some point the speeds pass through a point where the disc and ball are in pure rolling, b. plotting traction force against the slide/roll ratio (SRR), c. observing and recording the values of the motor speeds that correspond to the point of transition from positive to negative (or negative to positive) traction force as the contact passes through pure rolling contact, and, d. determining the disc track radius (DTR) based on the formula: DTR=Ball speed×ball track radius/Disc speed.