Linear Scale Calibration Using Recessed Portion Edge Intersections

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Solution Overview

Problem

The calibration plates used in dimension measuring apparatuses with small hole radii suffer from significant errors when determining the center of reference circles from hole images, leading to inaccuracies in position coordinate correction.

Innovation Solution

A method utilizing a calibration plate with two-dimensionally arranged recessed or projecting portions, where the true position coordinates of intersection points are defined in a substrate coordinate system, and actual measured values are used to correct detected values by accounting for thermal expansion and misalignment, reducing error through clearer edge detection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If small radius holes are used as markers on the calibration plate, then the calibration plate can be made more compact and easier to handle, but the error in extracting the center of the reference circle from the hole image increases significantly

Engineering Contradiction:

Improvecalibration plate sizeVSAvoidcenter extraction accuracy

Core Design Contradiction:

Area of stationary objectVSMeasurement precision

Solution Approach 1:

Instead of using small holes and trying to extract their centers accurately, the invention inverts the approach by using large holes and extracting intersection points from the hole edges. The reference point is defined as the intersection of straight lines passing through opposite edges of the hole, which is more accurate than center extraction from small holes.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The invention transitions from one-dimensional center extraction (finding the center point of a small hole) to two-dimensional edge intersection (finding where lines through opposite edges intersect). This dimensional change in the measurement approach improves accuracy by utilizing more geometric information from the hole structure.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Measurement precision

If the calibration plate is made with larger holes, then the center extraction error is reduced, but the calibration plate size and complexity increase

Engineering Contradiction:

Improveposition coordinate accuracyVSAvoidcalibration plate area

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

The invention inverts the conventional approach by not trying to make small holes more measurable, but rather using larger holes with a different measurement methodology (edge intersection instead of center extraction). This resolves the contradiction by changing the measurement principle rather than simply scaling up the hole size.

Inventive Principle:

Principle #13The other way round (Inversion)

3Device complexity

If thermal expansion of the calibration plate is not compensated, then the correction process is simpler, but the position coordinate accuracy deteriorates when temperature differs from calibration conditions

Engineering Contradiction:

Improvecorrection process complexityVSAvoidposition coordinate accuracy under temperature variation

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The invention performs preliminary thermal expansion compensation calculations during the calibration process. By pre-calculating and storing correction factors for thermal expansion at different temperatures, the system prepares in advance for temperature variations, eliminating the need for complex real-time compensation during actual measurements.

Inventive Principle:

Principle #10Preliminary action

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

This method enables more accurate correction of position coordinates on an object by minimizing the effect of errors in linear scale measurements, improving the precision of position identification.

Implementation Method 1

the true value may be corrected by an amount of change caused by thermal expansion based on the difference in temperature

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS11333535B2Method for correcting values detected by linear scales

Publication Date: 2022.05.17 OMRON CORP

AI summary

Provided is a method for more accurately correcting position coordinates of a point on an object to be imaged, the coordinates being identified based on values detected by linear scales. A visual field is moved to a measurement point defined on a recessed portion formed on a calibration plate, and an image is captured (step S13-1), edges are detected from an image of sides of the recessed portion (step 313-2), an intersection of the edges is calculated (step S13-3), values of the intersection as actually measured by the linear scales are saved (step S13-4), and position coordinates of the point on the object to be imaged as detected by the linear scales are corrected by using a true value and a difference.