JPH03261804A - Three-dimensional measuring instrument - Google Patents

Abstract

PURPOSE:To easily measure three-dimensional coordinates by performing operations to a local area including an edge part of an object to be measured within an image, and determining the position of the edge with not larger than the resolving power of pixels. CONSTITUTION:An image of an edge of an object to be measured is adjusted to be within a local area. While a lens barrel is moved in a direction of the Z axis, the variance of the luminance of the image is detected. In other words, when the luminance of the image is expressed by f(x,y), formulae I-III hold. In the formulae, N is the total number of pixels within the local processing area. A point where N is a maxi mum is regarded as the focusing position, so that the position of the local processing area in the Z direction is obtained from the moved distance. Thereafter, the focused positions m1, m2 and m3 (formula IV) are obtained. If one regards that the ideal edge for which the obtained first, second and third order moments become equal is the desired edge, it is given by formula V, in which P1+P2=1 and P1 and P2 are the ratios of occupation of h1 and h2 repectively, in the entirety. When equation V is solved, formulae VI, VII and VIII are obtained, and the position of the edge is deter mined from P1. Accordingly, three-dimensional coordinates can be measured in a simple manner without considering a threshold value or the change of the illumination.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to the structure of a measuring device used in three-dimensional shape measurement.

``Prior art'' Up until now, dimension measuring devices that apply image processing technology have compressed the brightness of an image into a black and white binary image (hereinafter referred to as a binary image), and determined the boundary position between white and black on that image. By this,
I was taking measurements.

However, measurement using binary images has the following drawbacks.

(1) It is necessary to determine the brightness level that separates white and black (hereinafter referred to as the threshold). This value is an important value that is closely related to accuracy, and must be finely adjusted depending on lighting conditions, etc. It is necessary and a burden.

(2) The measurement resolution of binary images is limited by the number of pixels, and when attempting to perform highly accurate measurements with current industrial video cameras, the field of view becomes significantly smaller.

These drawbacks result in difficulty in handling the device. Therefore, at present, it has been limited to use as an automated device in which an expert first sets various parameters, and then there is little need to do so.

"Means for Solving the Problems" Accordingly, in the present invention, by performing measurement in consideration of gradation information without binarizing the image, (1) eliminating the troublesomeness of threshold setting; (2) A measurement resolution lower than the pixel resolution was obtained to enable measurement over a wide field of view.

In order to easily measure various locations within that wide field of view, we decided to create a structure that allows the measurement area to be easily specified using a pointing device.

"Function" By doing this, (1) Anyone can easily use it without having to be proficient in handling it, that is, be an expert, and (2) It can be used not only as an automation device but also as an interactive measuring instrument. I have also become able to tolerate it.

``Example'' An example of the present invention will be described below with reference to FIG. 1 and the following figures. On the monitor 2, an image from a video camera 5 attached to a microscope 6 is displayed through the device of the main body of the present invention. A local processing area 1 is simultaneously displayed on the monitor 2, and this local processing area can be moved to any position on the image using a trackball 3. The axis in the focusing direction of the microscope 6 (hereinafter referred to as the Z axis) is
A motor is attached and is controlled by a controller 7 based on signals from the main body. Also, the X on the microscope 6
Encoders are attached to the Y table and the Z axis, and the amount of movement on the XY table and the Z axis is accurately transmitted to the main body via the decoder 8.

First, the local processing area is moved to a position where the image of the edge of the test object is located inside the local processing area. Start measurement by pressing the button. First, while moving the lens barrel in the Z-axis direction, the brightness dispersion of the image within the local processing area is determined.

That is, if the brightness of the image is expressed by f (x, y), then N is the number of all pixels within the local processing area.

Generally, the larger the dispersion, the better the in-focus state, so the point with the maximum value is detected and set as the in-focus position. The position of the local processing area in two directions can be determined from the movement distance. Next, m□, m2 and 1 m, (3rd moment>-Σf'<x, y+ are determined at the in-focus position.

The ideal edge is considered to be represented by two luminances as shown in FIG. If we want to find an ideal edge where the obtained first, second, and third moments are equal, then Σ P)h'j==mt (i=1.2.3)J=1 Here, P , 10P2=1 (Pi, P2 are hl and h
By solving this equation, σ2 =7712-ml is obtained, and the edge position can be determined from this P□. This value is obtained as a real value, that is, with an accuracy less than the pixel resolution.

Since the focusing algorithm is an intermediate value of the edge detection algorithm, it is possible to use the same hardware, which is advantageous for speeding up.

"Effects of the Invention" According to the present invention, three-dimensional coordinates can be easily measured without worrying about threshold values or illumination fluctuations. In addition, it can have a field of view 42 to 102 times larger than the conventional one for the required accuracy, and can easily measure any position within the field of view, so it is expected to greatly improve work efficiency.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining one embodiment of the present invention, and FIG.
The figure shows an ideal edge. 1: Local processing area 2: Monitor 3 Nidrak ball 4: Device body 5; Video camera 6; Microscope 7; Controller 8: Decoder

Claims (1)

[Claims] In a device that images the external shape of a test object with a video camera and measures the external dimensions of the test object in a non-contact manner by digital image processing from the obtained image, Perform calculations on the area,
Determine the edge position below the pixel resolution, and determine the position of the focal point by calculating the dispersion of the histogram within the local area while changing the distance between the optical lens and the test object. A three-dimensional measuring device having a function of determining three-dimensional coordinates of one point above, and the local area can be moved to an arbitrary position within an image using a pointing device.