JP2002048521A - Instrument and method for measuring shape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate an influence of disturbance light such as peripheral illumination to exclude a measured data including an error caused by the disturbance light, in a free-scanning type shape measuring instrument for measuring a complicated shape by holding a measuring head by the hand to be moved freely around a measuring object. SOLUTION: In the first solution means, three-dimensional motion information of the measuring head measured by two cameras is held time-serially, and erroneous extraction of a marker is excluded by monitoring abrupt motion of the measuring head generated by the erroneous extraction of the marker. A positional change (velocity) and an angle change (angular velocity) of the magnetic measuring head from the last measurement are calculated to determine the presence of the marker erroneous extraction caused by the disturbance light based on whether the changes exceed set threshold values or not. In the second solution means, one maker out of the four markers fixed onto the measuring head is arranged in a center-of-gravity position of all the markers to eliminate the marker erroneous extraction cauced by the distutrbance light based on positional information therein. The center of gravity in images of the plural markers extracted from the images is calculated to determine the presence of the marker erroneous extraction by the disturbance light, based on whether the marker exists in the center of gravity or not.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a shape measuring device.

[0002]

2. Description of the Related Art Conventionally, there has been known an active stereo type shape measuring apparatus which irradiates spot light or slit light to an object to be measured and restores a shape from a position of an optical image observed on a surface.

As an active stereo shape measuring device, there is one that scans slit light with a rotating mirror.
In a shape measuring device provided with such a scanning mechanism,
Although the shape of the surface of the measured object observed from the measuring instrument can be measured, the shape of the entire measured object cannot be measured.

On the other hand, in order to measure the shape of the whole object to be measured, a rotary stage is used to move the object to be measured in 360.
An active stereo shape measuring device for observing from all around the degree has been developed. However, when the object to be measured has a complicated shape, there is an area that cannot be observed even by using the rotary stage, and therefore, the shape of the entire object to be measured cannot be measured.

In order to solve the above problem, the applicant of the present application first grasps a compact measuring head in a hand and performs measurement by moving the measuring head around an object to be measured, thereby obtaining a complicated shape. Japanese Patent Application No. Hei 10-20686 for a free scan shape measuring device that can measure even the whole object to be measured
Filed as 4.

This apparatus (hereinafter, referred to as a free scan shape measuring apparatus) is composed of a measuring head for measuring an object to be measured, and a stereo camera head for three-dimensionally measuring the position of a marker fixed to the measuring head. ) Optical cutting measurement of the surface shape of the object to be measured by the portable measuring head, 2) Three-dimensional stereo measurement of the measuring head position by two fixed cameras, and two-stage image measurement are performed simultaneously. The measurement results are reconstructed three-dimensionally.

This device will be described in more detail.

FIG. 1 shows the configuration of a free scan shape measuring apparatus.

The device under test 100 is placed on a table 201. The support 201 is attached to the base 201. A horizontal bar 203 is attached to an upper part of the support column 202.

The free-scan shape measuring apparatus includes a measuring head 10 which can be freely moved by a measurer, a marker provided on the measuring head 10, and stereo cameras 21 and 22 attached to both ends of a horizontal bar 203. A band pass filter 23 having a pass frequency designed to pass only the marker light is provided, and a control device 30 including a personal computer for controlling the band pass filter 23 and performing various calculations is provided.

FIG. 2 shows the structure of the measuring head 10.

The measuring head 10 includes one CCD camera 1
2 and a slit light source 13 and six LED light sources 14 provided on the upper surface of the measuring head. Slit light source 1
As 3, a semiconductor laser is used.

FIG. 3 shows the principle of measurement.

The coordinates of a measurement point A are measured using a measurement head 10 which can be freely moved by a measurer.
The measured coordinates are converted to a coordinate system (Xc, Y
c, Zc). This coordinate system is a coordinate system that moves as the measuring head 10 moves.

On the other hand, the shape of the DUT 100 is represented by a fixed coordinate system, and this coordinate system is called world coordinates. The world coordinates of the measurement point measured by the measurement head 10 are defined as (Xw, Yw, Zw). Since the shape of the measured object needs to be described in the world coordinate system, the measuring head 10
The coordinates (Xc, Yc, Zc) of the center of the measurement head of the measurement point A measured by the above are converted into world coordinates (Xw, Yw,
Zw). This conversion is performed by using the rotation matrix R representing the movement of the measuring head 10 and the translation vector t,
It is performed based on.

[0016]

(Equation 1)

Therefore, the position and direction of the measuring head 10 in the world coordinate system are obtained as a rotation matrix R and a translation vector t, so that the coordinates (X
c, Yc, Zc) are converted to world coordinates (Xw, Yw, Z
w).

The above processing is performed while moving the measuring head 10 around the measured object 100, and the shape of the measured object 100 is described as a set of (Xc, Yc, Zc) obtained each time.

The shape measurement by the free scan shape measuring apparatus is executed according to the following processing procedure.

First step: Using the measuring head 10,
The coordinates of the measurement point on the measured object in the coordinate system of the center of the measurement head are obtained.

Second step: Information on the position of the measuring head 10 in the world coordinate system, that is, a rotation matrix R representing the movement of the measuring head 10 in the world coordinate system and a translation vector t are provided on the measuring head. The marker 11 is obtained by measuring a stereo image with the stereo cameras 21 and 22.

Third step: Based on the rotation matrix R and the translation vector t obtained in the second step, the coordinates of the measuring point on the object to be measured in the coordinate system of the measuring head center obtained in the first step are Convert to world coordinates.

Next, the stereo image measurement in the second step will be described with reference to FIG.

In step S1, images from the cameras 21 and 22 are input.

In S2-1 to S2-4, the camera 21
Are binarized and noise-removed to obtain an image including only the marker. After that, labeling is performed to obtain the CCD image coordinates of each marker.

In S3-1 to S3-4, the camera 22
Similarly, the CCD image coordinates of each marker are obtained for the image of.

In step S4, the three-dimensional coordinates of the marker are obtained by performing stereo calculation from the correspondence of the CCD coordinates of the marker between the cameras 21 and 22.

[0028]

As described above, in the free scan shape measuring apparatus, the position of the measurement head is specified by measuring the image of the marker fixed to the measurement head with two fixed cameras. ing. At the time of this image measurement, reflected light of the laser used for ambient light and light cutting, etc.
Incorrect measurement may be made as a marker. At this time, the position and orientation of the measuring head are erroneously measured, and as a result, there is a problem that a large error is included in the reconstructed measurement result of the measurement target.

FIG. 5 shows a state of measurement when the laser reflected on the object to be measured is erroneously recognized as the marker 11.
The slit laser hitting the measurement object 100 is reflected,
It is incident on the camera 21. If the light from the laser is erroneously recognized as the marker 11, the position and orientation of the measuring head 10 are erroneously determined.

A similar phenomenon can occur when ambient light such as illumination is reflected on the cameras 21 and 22.

An object of the present invention is to obtain a measurement result free from errors by effectively eliminating disturbance light and improving the stability of marker extraction.

[0032]

According to the first embodiment of the present invention, there is provided means for eliminating marker erroneous extraction due to disturbance light.
Three-dimensional motion information of the measurement head measured by two cameras is stored in chronological order, and erroneous extraction of markers is eliminated by monitoring the rapid movement of the measurement head caused by erroneous extraction of markers. And

The position change (speed) and angle change (angular speed) of the measurement head from the previous measurement are calculated, and it is determined whether or not a marker is erroneously extracted due to disturbance light based on whether the set threshold value is exceeded. .

The disturbance light elimination means according to the second embodiment is provided with four or more markers fixed to the measuring head.
One marker is placed at the center of gravity of all markers, and erroneous extraction of markers due to disturbance light is eliminated based on this position information.

The center of gravity of a plurality of markers extracted from the image is calculated in the image, and the presence or absence of the marker at the position of the center of gravity is used to determine the presence or absence of erroneous marker extraction due to disturbance light.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described.

FIG. 6 shows a moving trajectory of the measuring head on the three-dimensional world coordinate system.

The position and direction of the measuring head are determined by the cameras 21 and
2 is measured. When the movement of the measurement head is recorded in a time series, the movement trajectory and direction change of the measurement head are gentle within the range where the marker is normally extracted. (Does not exceed the hand movement expected at the measurement interval (about 100 msec).) In this state, if disturbance light is erroneously extracted, the calculated position and direction of the measurement head will change significantly, which will have a large effect on the measurement results. give. From this, it is possible to determine that an erroneous extraction has occurred when the movement of the measuring head in time series is recorded, and the change in position and angle with time is obtained.

FIG. 7 shows a flowchart for eliminating erroneous measurement due to disturbance light by monitoring the time series movement of the measuring head.

At T1, the images of the cameras 21 and 22 are input.

At T2, for each image,
Six markers are extracted.

At T3, the position and orientation of the measuring head in world coordinates are calculated by three-dimensional stereo calculation based on the information of T2.

At T4, the calculation result is stored as time-series data.

In T5 and T6, if any one of the position movement amount (or speed) and the angle change (or angular speed) from the previous measurement exceeds the thresholds Th1 and Th2, the marker is erroneously extracted. For this reason, the processing T8 at the time of erroneous marker measurement is performed without performing three-dimensional measurement of the measurement target.

At T7, if neither of them exceeds the threshold value, it is determined that marker extraction has been performed normally, and three-dimensional measurement of the object to be measured is performed.

Next, a second embodiment of the present invention will be described.

FIG. 8 is a schematic diagram for eliminating disturbance light using a marker arranged at the position of the center of gravity.

The figure shows an image that has been binarized and labeled after image input. When the marker is correctly extracted, the positions of the centers of gravity of the six extracted labels coincide with the positions of one of the six labels. When disturbance light is erroneously extracted as a marker, 6
There is no label at the position of the center of gravity of the extracted labels (the probability is high). This makes it possible to know the erroneous extraction of disturbance light.

FIG. 9 shows a flowchart for eliminating disturbance light using a marker arranged at the position of the center of gravity.

At U1, first, an image is fetched.

At U2, binarization is performed.

At U3, labeling is performed.

At U4, six marker candidate labels are extracted using the label area, luminance, shape information, and the like.

At U5, the center of gravity of the extracted marker candidate label is calculated.

At U6, it is checked whether or not the label exists within a radius r centered on the obtained position of the center of gravity.

At U7, if a label exists, it is determined that normal extraction has been performed, and the position of the measuring head is calculated.

In U8, if there is no label,
The position calculation of the measuring head is not performed because the erroneous extraction is performed.

When extracting marker candidate labels from a plurality of labels, a marker candidate label may be selected such that one label exists on the center of gravity of all labels.

When confirming the coincidence between the position of the center of gravity and the label, the label position is compared with an area having a radius r centered on the position of the center of gravity in consideration of image input and fluctuation during binarization. From this, in marker arrangement on the measuring head, one marker only needs to be arranged near the center of gravity, and it is not necessary to be strictly arranged at the center of gravity of all markers.

[0060]

According to the present invention, erroneous measurement of the measurement head position and direction due to the influence of ambient light can be eliminated, and erroneous measurement data due to erroneous marker extraction can be eliminated.

In particular, in the first embodiment, it is not necessary to provide a special mechanism or circuit, and erroneous measurement data can be eliminated only by improving the software.

In the second embodiment, it is not necessary to store past measurement results, and it is possible to determine erroneous measurement independently for each image measurement.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a conventional free scan shape measuring apparatus.

FIG. 2 is a plan view showing a conventional measuring head.

FIG. 3 is an explanatory diagram for explaining a conventional measurement principle.

FIG. 4 is a flowchart showing a processing sequence of a conventional stereo image measurement.

FIG. 5 is a schematic diagram showing a state of measurement when a conventional laser reflected light is erroneously recognized as a marker.

FIG. 6 is a schematic diagram illustrating a method for eliminating disturbance light according to the first embodiment of the present invention.

FIG. 7 is a flowchart of a disturbance light elimination method according to the first embodiment of the present invention.

FIG. 8 is a schematic diagram illustrating a method for eliminating disturbance light according to a second embodiment of the present invention.

FIG. 9 is a flowchart of a disturbance light elimination method according to the second embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 10 measuring head 11 marker 12 CCD camera 13 slit light source 21, 22 stereo camera 23 band limiting filter

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Hiroaki Yoshida 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. F-term (reference) 2F065 AA04 AA53 BB05 BB29 DD03 DD04 DD11 FF05 FF42 JJ03 JJ05 JJ26 MM23 QQ04 QQ08 QQ17 QQ21 QQ24 QQ32 QQ34

Claims (4)

[Claims] 1. A measuring head which is freely moved by a measurer, a marker attached to the measuring head,
A measuring device configured to measure the position of the measurement head by measuring the marker position, and to measure the three-dimensional shape of the surface of the target object. A shape measurement method for determining that there is an error in marker extraction when there is a movement change exceeding the threshold value of (1). 2. The shape measuring method according to claim 1, wherein the motion information of the measuring head is a three-dimensional position and a head orientation. 3. A measuring head which is freely moved by a measurer, four or more markers attached to the measuring head, and a camera which measures a position of the measuring head by measuring a marker position, A measuring device for measuring a three-dimensional shape of a surface of a target object, wherein one marker among four or more markers is arranged at the center of gravity of all markers. 4. A shape measuring apparatus according to claim 1, wherein candidate markers are extracted from an image of a camera for measuring the position of the measuring head, and whether one marker exists at the center of gravity of all the extracted markers. A disturbance light exclusion method that determines erroneous extraction due to disturbance light depending on whether or not.