WO2002031436A1

WO2002031436A1 - Method and system for measuring objects

Info

Publication number: WO2002031436A1
Application number: PCT/SE2001/002226
Authority: WO
Inventors: Björn Larsson
Original assignee: Latronix Ab
Priority date: 2000-10-12
Filing date: 2001-10-12
Publication date: 2002-04-18
Also published as: SE520060C2; SE0003693D0; AU2001294492A1; SE0003693L

Abstract

A contour meter, for example comprising a light source generating a laser line, and an accompanying registering device, for example a comaera, suchas a CCD camera or a CMOS camera, are arranged to measure the shape of a section throught the object, for example a cylinder. This section shape is obtained by a number of three-dimensional points on the enveloping surface determined bz the of the camera registered laser light line reflected bz the object. Then, these tree-dimensional points are adapted to the previously known shape of the object. By continuously repeating the measuring, a measure is obtained of a number or parameters of the object, including the size, the position in two dimensions, and the direction. It is also possible to only adapt the measuring data to a selection of these parameters. Thus, in a number of applications, it is possible to assume a fixed direction of the object when moving. If such an assumption is possible, a more robust measuring can be obtained. By using the system and the method of the invention a number of advantages compared to tprior art are obtained. Thus, only one contour meter is needed, provididng a measuring system that is inexpensive to manufacture and, further, eacy to assemble and calibrate. Other advantages achieved include a high accuracy and the possibly to measure objects with a varying position.

Description

Method and system for measuring objects

TECHNICAL FIELD

The present invention relates to a method and a system for measuring the size, position and direction of an object, using contact-free measuring, especially of objects having a constant cross-section in space, but with a size, position and direction varying in time.

PRIOR ART

At paper manufacturing, the paper is rolled up on big cylinders, called tambour rollers. During this rolling-up it is of vital importance to continuously determine, among other things, the position, diameter and growth of these tambour rollers. This is both for the delivering of the correct amount of paper on the tambour rollers and for accurate control of the rolls in the paper machine manufacturing the paper, in order to avoid paper breakage .

In other applications, too, there is a need to continuously measure the size of an object varying in time. Exemplary applications include steel processing, aluminium production, etc .

One possible method of measuring the diameter of a roll is having a gauge located up against the roll, whereby a measurement of the diameter during the roll-on is obtained. One problem with this type of measuring is, however, a resulting wear of the paper and that the measuring device itself has a limited lifetime since it includes movable parts. Another problem arising is that some paper types are soft and that the paper is compressed by the measuring gauge, resulting in an incorrect measurement .

Thus, in many cases it is advantageous to arrange a contact- free measuring arrangement for measuring in such cases . One way of arranging a contact-free measuring is to measure the distance to one or more points on the cylinder. This method provides, in most cases, a satisfactory result, since the axis of the cylinder is fixed during the rolling-up. However, this is not always the case. Thus, in many applications the peripheral part of the roller is located up against a fixed roll, while the growth on the roller forces the cylinder axis away from the fixed roll. In some applications, this movement takes place rectilinearly, while in other applications a more complex movement is described. It is, in principle, possible to measure the diameter on a moving roll by using three or more point meters. However, it has proven to be very difficult to align and calibrate such a system.

Furthermore, WO 00/29809 discloses a laser-based system for measuring objects having a cylindrical shape. The purpose of the system described in WO 00/29809 is to determine whether a cylindrical object fulfils existing demands on roundness or the like. The system uses a number of laser beams for measuring the distance to an object having properties to be determined.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and a system for measuring the size of an object, in particular an object with a size that varies in time and in particular an object having a cylindrical shape, i.e. an object with a shape corresponding to a surface being rectilinearly translated through space.

These and other purposes are achieved by a contour meter, for example consisting of a light source generating a laser line and an accompanying registering device, for example a camera, such as a CCD camera or a CMOS camera, arranged to measure the shape of a cross-section of the object, e.g. a cylinder. This cross-sectional shape is obtained by determining a number of three-dimensional points on the enveloping surface by the laser light line registered by the camera and reflected by the object. Thereafter, these three-dimensional points are adapted to the previously known shape of the object. By continuously repeating the measuring, a measure of a number of parameters of the object is obtained, including the size, the position in two dimensions, and the direction. It is also possible to only adapt measuring data to a selection of these parameters. Thus, in a number of applications it is possible to assume a fixed direction of the object during movement. If such an assumption is possible, a more robust measuring can be obtained.

By using the system and method according to the invention a number of advantages are obtained as compared to prior art . Thus, only one contour meter is needed, giving a measuring system, which is inexpensive to manufacture and, furthermore, easy to assemble and to calibrate. Other advantages achieved include a high accuracy and a possibility to measure objects with a varying position.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described in more detail, by means of non-limiting embodiments and with reference to the enclosed drawings, of which:

Fig. 1 shows a tambourroller, suspended in a lever.

Fig. 2 shows a laser measuring system for measuring a cylinder-shaped body.

Fig. 3 shows more closely the measuring of a contour of the cylinder body according to figure 2. Fig. 4a and 4b illustrate a flowchart showing the steps performed when determining the size and position of a cylindrical body.

DESCRIPTION OF PREFERRED EMBODIMENTS

In figure 1, a tambour roller 1 ids shown, suspended in a lever 2. During rolling-up of paper on the tambour roller, the roller is moving along an arc of a circle in the direction of the arrow 4. The lever, fixed in a position 3, determines the arc of the circle.

In figure 2, a laser measuring system 5 is shown for the measuring of a tambour roller 1. The system 5 includes a laser light source 6, a camera 7 and a device 8 for processing measuring data generated by the camera 7.

The laser light source 6 is adapted to emit a laser light line towards the enveloping surface of the cylindrically shaped tambour roller. The laser light line is reflected by the tambour roller and the reflected ray is registered by the camera 7. In a preferred embodiment, the camera is a CCD camera or a CMOS camera .

The camera 7 is continuously delivering measuring data corresponding to the reflected laser light line. Typically, the camera is registering hundreds of discrete measuring points on the enveloping surface of the cylinder, as disclosed in figure 3.

By knowing the cross-section of the cylindrical object, measuring values generated by the camera can be adapted to parameters of the object. By referring to a cylindrical object, cylindrical objects are addressed in a broad sense, i.e. a shape resulting from a surface being rectilinearly translated in space, for example a rectangular parallelepiped, a prism, a cylinder, etc. In this example, in which the object is a cylinder, the measuring data can be adjusted to parameters including position, size and direction. This adjustment can be performed by a suitable adjustment method, for example by minimising the sum of the squares between the measuring points and the cylinder.

In fig. 4a and 4b, a flow chart is shown comprising the steps performed by the device 8 in order to generate values describing a measured cylinder when measured by a system described above in connection with figures 1 - 3.

Accordingly, at first, in a step 21 and with reference to figure 4, a contour is measured of the object to be measured, on which the contour consist of a number of three-dimensional measuring points. Next, in a step 23, an adjustment is performed to the model cylinder, which closest corresponds to the measuring data. Finally, the result from step 23 is the output of step 25, and a new measuring is initiated in step 21.

Figure 4b more closely shows the substeps performed in the procedure step 23. At first, a set of parameters is selected for the model cylinder in a step 23a; in the case of a cylinder the parameters may comprise the radius, the position and the direction. Next, in a step 23b, a measure is calculated of the deviation between the contour measured in step 21 and the model cylinder, given the used parameters. In a preferred embodiment, the gradient of the measurement with respect to the parameters can be used as well. For example, the sum of the squares of the distances between each point of the measuring data and the model cylinder may be used. Finally, the procedure moves to step 25 if the optimisation is finished. Otherwise, an optimising logarithm is used in order to obtain an improved value of the parameters, providing a smaller value of the measurement. Exemplary optimising algorithms that may be used comprise Steepest Descent, DFP and BFGS.

By using the system and method as described herein, a number of advantages are achieved. Thus, only one contour meter is needed, which gives a measuring system that is inexpensive to manufacture. Further, a relatively large amount of measuring points are obtained, typically a few hundred, by which the system becomes more insensitive to noise, as compared to other types of meters using only a few measuring points, typically three or less.

Furthermore, the space available in the locations in which the type of meter described herein can be used, for example in paper- and steel machines, is relatively small. The measuring system, as described herein, only requires that a part of e.g. a cylinder is visible, from a single direction. In many cases it is enough that 10% of the circumference is visible for obtaining accurate measuring results. Furthermore, the system does not require that the object to be measured is held in a fixed position. Instead, a position and/or direction can be obtained as a part of the measurement .

According to the example above, the described measuring system is provided with a laser light source emitting a laser line. The measuring system may, however, be designed with other light sources emitting light beams, or with a system generating a shadow line. The system can be calibrated by an object having a known shape. Also, a scanning point meter may be used in order to obtain the measured contour, for example a scanning PSD meter time-of-flight meter.

Further, the system may use several light- or shadow lines and these may also be registered by plural cameras. By such an arrangement, the measuring accuracy can be improved.

Claims

1. A System for determining the size of an object having a previously known shape, characterised by a source arranged to emit a line towards the surface of the object, a registering device arranged to register the line reflected by the object, and a measuring data processing device connected to the registering device and arranged to receive output signals from the registering device, corresponding to the reflected line, and to adapt these output signals to the previously known shape, in order to generate data corresponding to the size of the object.

2. A System according to claim 1, characterised in that line- generating source is a laser light source arranged to generate a laser light line.

3. A System according to claim 1, characterised in that the line-generating source is a source arranged to generate a shadow line.

4. A System according to any of claims 1 - 3, characterised in that more than one line-generating source is arranged.

5. A System according to any of claims 1 - 4, characterised in that more than one registering device is arranged.

6. Method of determining the size of an object having a previously known shape, characterised by the steps of: - emitting a line towards the surface of the object, by using a registering device, registering the line reflected by the object, and in a measuring data processing device connected to the registering device, receiving output signals from the registering device corresponding to the reflected line, and adapting these output signals to the previously known shape in order to generate data corresponding to the size of the ob ect .

7. Method according to claim β, characterised in that the generated line is a laser light line.

8. Method according to claim 6, characterised in that the generated line is a shadow line.

9. Method according to claim any of claims 6 - 8, characterised in that more that one line are generated.

10. Method according to any of claims 6 - 9, characterised in that the lines are registered by more than one registering device .