WO2002079722A1

WO2002079722A1 - Method and device for determining a relative length change

Info

Publication number: WO2002079722A1
Application number: PCT/DE2002/001052
Authority: WO
Inventors: Thomas KÄMPER; Thomas Elbel; Ingo Niewidok; Matthias Wetzel
Original assignee: Forbo International S.A.
Priority date: 2001-04-02
Filing date: 2002-03-22
Publication date: 2002-10-10
Also published as: DE10116233A1

Abstract

The invention relates to a method and to a device (1) for determining a relative length change of a drive or conveyor belt (2) by dilatation. To this end, a light beam is directed to a surface area of the drive or conveyor belt (2) by means of an illumination unit (5), in which area two reference marks (3, 4) are applied. The light reflected by the reference marks (3, 4) is detected by an optical detector configured as a CCD sensor (9) having two sections (7, 8) that are associated with respective reference marks (3, 4) linked with the drive or conveyor belt (2). The reflected light is transmitted by a linear optics (6) that transmits the light reflected by the reference marks (3, 4) to the associated section of the CCD sensor (9). The invention provides a transportable device (1) that is easy to handle and that requires no error of measurement-prone focusing.

Description

Method and device for determining a relative change in length

The invention relates to a method for the contactless determination of a relative change in length of a drive or conveyor belt by stretching, in which a surface area of the drive or conveyor belt exposes, the reflected light is detected and a changed relative position of the surface area is determined therefrom. Furthermore, the invention relates to a device for performing the method.

For measuring the elongation of conveyor belts or drive belts, a system with a camera is known from EP 06 94 756 A 3, for example, which detects reflections of a laser beam that is directed onto a small surface area. The laser beam is reflected differently due to the irregular surface properties of the drive or conveyor belt, which is provided with structuring that is particularly related to production. A characteristic reflection pattern of the belt is created from the reflected light before and after the stretching of the drive or conveyor belt. Using a mathematical method, individual sections can be identified by comparing the surface images and the relative elongation can be determined from the difference in distance. The method can therefore be used with any drive or conveyor belt.

The high outlay for the measuring method working with the laser beam has a disadvantageous effect, in which particularly cumbersome protective measures have to be observed in order to rule out any danger to the operating personnel. Furthermore, it has so far not been possible to implement a device which operates using this method and which can be transported without problems table and can therefore also be used on site. Furthermore, even slight deformations caused by stretching lead to an undesirable displacement, which deteriorates the measuring accuracy.

For this reason, one still helps to set the desired pretension, in particular when tensioning high-strength drive belts on corresponding running elements, in practice to check the correct tension, mostly with simple means. For example, before stretching, the belt is provided with two line markings spaced apart from one another, the changed distance of which is recorded manually on a scale in the stretched state of the drive or conveyor belt. The quality of the measurement result depends crucially on the care taken when carrying out the measurement and can therefore vary depending on the operating personnel.

In another technical field, according to DE 40 29 013 A1, it is also known to use an optical measuring method for strain measurement in connection with tensile tests of material samples, in which a previously applied measuring grid is monitored by a camera during the stretching. The greatest distance between adjacent grid lines is recorded and used as the basis for the calculation of the maximum elongation.

It proves to be disadvantageous here that an exact measurement result requires precise focusing of the optical system. For this purpose, the optical system has a lens arrangement which has a high aperture in order to achieve a contrast of the reference mark which is sufficient for the CCD camera. However, this requires an exact maintenance of the distance between the camera and the tensile specimen, which is unaffected by the elongation, which can only be achieved under laboratory conditions. In addition, the surface coordinates of the raster line change due to deformation, so that a permanent correction of the focus is necessary. For this reason, this method cannot be used for measuring the elongation of drive belts or conveyor belts, since such precise focusing requires both the transportation and the CCD camera to be fixed. In particular, an adjustable support for the band would have to be created in order to avoid the change in the height of the slightly sagging band associated with the tightening of the band. However, due to the wide variety of embodiments of the conventional drive or conveyor belts, it is not possible in practice, within an economically justifiable framework, to provide such necessary aids for the reliable reproducibility of the measurement results. The invention has for its object to provide a way that allows a simple and reliable determination of the elongation of a drive or conveyor belt. The method should in particular be carried out with little effort. Furthermore, a device for carrying out the method is to be created which, in particular, should be able to be carried along and thus permits problem-free use.

The first-mentioned object is achieved according to the invention with a method according to the features of patent claim 1. The further development of the method can be found in subclaims 1 to 5.

According to the invention, a method is therefore provided in which the drive or conveyor belt equipped with two reference marks is detected by a region of a CCD sensor assigned to the reference marks. This creates a method with which the distance from two reference marks attached for this purpose on the drive or conveyor belt can be detected with comparatively little effort, in that the brightness contrast of the reference mark is detected with pixel accuracy by the CCD sensor. The resolution that can be achieved thereby allows the distance of the pixels assigned to the respective reference marks to be converted by means of a controller into the distance of the pixels from one another and thus of the reference marks from one another. In particular, no complex focusing of the optical beam is required because the CCD sensor can be directly assigned to the reference marks at a very short distance, so that deformations of the drive or conveyor belt transversely to the direction of elongation cannot be noticed during the elongation measurement. Furthermore, errors in the implementation of the method are essentially ruled out because exact positioning and alignment in the method are omitted. In addition, the high computational effort required to identify such characteristic surface areas, which serve as reference marks, is reduced. In addition, the use of the laser beam can be dispensed with by the method according to the invention, which places comparatively high demands on the operating personnel and can easily lead to operating errors.

A particularly advantageous embodiment of the method according to the invention is also achieved if the exposure is set as a function of the intensity of the light reflected by the reference marks, as detected by the CCD sensor. As a result, the required contrast of the reference mark is set by direct control of the exposure as a function of the detected intensity and does not require any manual correction. In this case, it can be of particular advantage, depending on the design, if the exposure is carried out by means of flash light, in order in this way to produce a sufficient contrast between adjacent areas of the CCD sensor and to minimize influences from the ambient light.

Furthermore, it is also particularly favorable if the edge region of the reference marks is grasped and centered. As a result, a large number of different reference marks can be used by the method, the exact width of the reference mark in particular being irrelevant for determining the distance. The geometric center and, in a subsequent step, the spacing of the reference marks from one another are determined from the detected edge regions by means of a control unit. Depending on the nature of the drive or conveyor belt, reference marks with different dimensions can therefore be used. Furthermore, the undesirable influence of the stretch on the reference marks, which are also subjected to stretching or deformation depending on the design of the fixation, can thereby be reduced.

A further development of the method is particularly practical in which the measurement is carried out essentially continuously and a signal is generated when a predetermined change in length is reached. As a result, the drive or conveyor belt can be subjected to the desired stretching while the measurement is running and a signal can be generated when the set value is reached. Furthermore, safety-relevant values of the elongation can be taken into account, thereby preventing the operating personnel from being endangered.

The second-mentioned task of creating a device for determining a relative change in length of a drive or conveyor belt, with an exposure unit and an optical detector for detecting the light reflected from the drive or conveyor belt for carrying out the method, is performed according to the invention by a CCD - Sensor designed optical detector with two areas, each associated with a reference mark connected to the drive or conveyor belt, and a linear optic through which the light reflected by the reference marks can be transmitted to the assigned area of the CCD sensor. As a result, the distance between the reference marks from one another can be detected in a simple manner by the contrast generated by the reference marks being detected by the CCD sensor. The pixels of the CCD sensor assigned to the respective reference marks can be determined with high accuracy, from which the distance between the reference marks can be deduced. For this purpose, the linear optics transmit a linear image of the same size to the CCD sensor, whose distance from the reference mark is therefore in a predetermined range without affecting the accuracy of the measurement result is variable. The device therefore only needs to be positioned in the area of the reference marks on the drive or conveyor belt for measuring the strain. The distance between the reference marks is then automatically detected and the stretch is calculated. Incorrect handling is therefore largely ruled out, so that the effects of errors caused by improper operation are avoided.

The CCD sensor could extend over the entire area of both assigned reference marks. However, it is also particularly favorable if the device has a further CCD sensor and that an area is assigned to each of the CCD sensors. As a result, two comparatively small CCD sensors can be used, which are arranged at a certain distance from one another on the device, as a result of which the production outlay can be reduced. The distance between the CCD sensors is essentially determined by the intended use, and in principle the accuracy of the detection of the relative change in length can be improved by a large distance.

The CCD sensor can have a matrix by means of which a two-dimensional image of the reference mark can be acquired and in particular several parallel measurements can be carried out simultaneously, a shift between successive measurements being recorded and corrected by the control. In contrast, a modification in which the CCD sensor is designed as a line sensor is particularly simple. As a result, the outlay for producing the device can be reduced further because only one line is required. For this purpose, the reference marks extend essentially transversely to the direction of expansion and can therefore be reliably detected without the exact positioning or orientation of the device on the drive or conveyor belt being required for this.

A particularly advantageous modification of the invention is also created in that the linear optics have a plurality of gradient index lenses arranged next to one another, in order thereby to enable imaging of the same size and thus reliable measurement value acquisition.

Another particularly practical embodiment of the invention is also created in that the reference marks can be fixed on the drive or conveyor belt by means of an adhesive connection. As a result, the reference marks can also be attached to an already existing drive or conveyor belt without this requiring substantial intervention on the drive or conveyor belt or without a corresponding appropriate reference mark must be provided. The reference marks are glued on at a suitable point and can then be removed again after the measurement.

It is furthermore particularly simple if the reference marks for fixing to the drive or conveyor belt are fixed at a predetermined distance from one another by a holding means. As a result, the reference marks are already fixed in their relative position to one another by the holding means and can thus be easily fixed to the drive or conveyor belt. The holding means can then be removed and, if necessary, reused. For example, the holding means can also be designed as an adhesive surface from which the reference marks can be detached as soon as they are fixed to the drive or conveyor belt with their surface facing away from the holding means.

A further particularly promising modification of the invention is achieved if the reference marks are equipped with two sections with a different reflectivity, in order in this way to be able to clearly identify the reference marks based on the contrast. Therefore, the reference marks can also be attached to drive belts or conveyor belts that are equipped with patterns or have an irregular light reflection behavior due to their surface properties.

The distance between the reference mark and the CCD sensor is essentially determined by the required exposure, with inadequate exposure in particular precluding reliable measured value acquisition. Another particularly advantageous development of the invention is achieved, however, in that the reference marks are self-luminous or luminescent. As a result, the exposure need not take place immediately before the detection of the reference marks by means of the CCD sensor, because the reference mark temporarily emits sufficient brightness for the measurement value acquisition. The reference marks can be passive or luminescent or can also be designed as a self-illuminating reference mark in the form of a luminescent film.

Another particularly practical embodiment of the invention is achieved if the device has means for shielding the reference marks from the ambient light. In this way, the undesired influence of the ambient brightness can be avoided and errors in the measurement value acquisition can be prevented. The agent can also serve as a contact surface for placing the device on the drive or conveyor belt. The invention allows various embodiments. To further clarify its basic principle, one of these is shown in the drawing and is described below. This shows in

1 shows a schematic diagram of a device according to the invention;

2 shows a side view of the device;

3 shows the reference marks shown in FIG. 1 in a top view;

4 shows a holding means provided for fixing the reference marks shown in FIG. 3.

FIG. 1 shows a device 1 according to the invention for determining a relative change in length of a drive or conveyor belt 2. The drive or conveyor belt 2 is equipped with two reference marks 3, 4, which are aligned essentially parallel to one another. The reference marks 3, 4 are exposed for a short time in particular by means of an exposure unit 5 and the reflected light is fed to a respective region 7, 8 of a CCD sensor 9 by means of a linear optic 6. Taking into account the known distance of the areas 7, 8 from one another, a precise determination of a distance A of the exposed pixel of the CCD sensor 9 (not shown further) and thus the distance A of the reference marks 3, 4 is determined by means of a controller 10 designed as evaluation electronics. The controller 10 uses this to produce a display 11, by means of which, in a desired form of representation, the operator is given the relative elongation as a result of a measurement by an elongation.

The structural design of the device 1 is also shown in addition in FIG. 2, which shows a side view of the device 1 shown only in sections. The drive or conveyor belt 2 can be seen, which has a reference mark 3 shown in FIG. The light reflected by the drive or conveyor belt 2 or the reference mark 3 is transmitted from the linear optics 6 spaced between the drive or conveyor belt 2 between 2 and 20 mm to an element 12 of the CCD sensor 9, through which an evaluable electrical signal is generated if a predefined, adjustable brightness value is reached. The linear optics 6 generate a linear image of the same size, so that focusing of the light beam for imaging and the associated time-consuming preparation of the measurement value recording can be dispensed with. The linear optics 6, like the CCD sensor 9, are attached to a common circuit board 14 by means of a fixation 13 arranged. This creates a compact design that can be easily accommodated in a portable handheld device.

Figure 3 shows two mutually spaced reference marks 3, 4 in a plan view. The reference marks 3, 4 each have a light section 15 and a narrower, dark section 16, which is attached centrally to the light section 15. The contrast generated in this way is reliably detected by means of the CCD sensor 9 shown in FIG. 1, it being possible, for example, to determine the geometric center 17 from the edge regions of the dark section 16. The reference marks 3, 4 are already spaced invariably apart from one another on a common holding means 18 designed as a self-adhesive surface and can thereby be fixed together on the drive or conveyor belt 2 shown in FIG. This further simplifies the attachment of the reference marks 3, 4. Depending on the area of application, these can also be luminescent or self-luminous.

FIG. 4 shows one of the reference marks 3 shown in FIG. 3 in a sectional side view. The reference mark 3, like the further reference mark 4 shown in FIG. 3, is detachably attached to the holding means 18 designed as an upper film. A side of the reference mark 3 facing away from the holding means 18 is provided with an adhesive layer 19, which is protected from use by a lower film 20 for protection against environmental influences. After removal of the lower film 20, the reference mark 3 can be fixed to the drive or conveyor belt 2 shown in FIG. 1 without any problems.

Claims

claims

1. A method for the contactless determination of a relative change in length of a drive or conveyor belt (2) by stretching, in which a surface area of the drive or conveyor belt (2) exposes, detects the reflected light and uses this to determine a changed relative position of the surface area characterized in that the drive or conveyor belt (2) equipped with two reference marks (3, 4) is detected by an area (7, 8) of a CCD sensor (9) assigned to the reference marks (3, 4).

2. The method according to claim 1, characterized in that the exposure is set depending on the detected by the CCD sensor (9) intensity of the light from the reference marks (3, 4) reflected.

3. The method according to claims 1 or 2, characterized in that the exposure takes place by means of flash light.

4. The method according to at least one of the preceding claims, characterized in that in each case the edge region of the reference marks (3, 4) is detected and centering is carried out.

5. The method according to at least one of the preceding claims, characterized in that the measurement is carried out essentially continuously and a signal is generated when a predetermined change in length is reached.

6. The device (1) for determining a relative change in length of a drive or conveyor belt (2), with an exposure unit (5) and an optical detector for detecting the light reflected from the drive or conveyor belt (2) for carrying out the method by an optical detector designed as a CCD sensor (9) with two areas (7, 8), each associated with a reference mark (3, 4) connected to the drive or conveyor belt (2), and a linear optics (6), through which the light reflected by the reference marks (3, 4) can be transmitted to the assigned area (7, 8) of the CCD sensor (9).

7. The device (1) according to claim 6, characterized in that the device (1) has a further CCD sensor and that in each case one of the CCD sensors (9) is assigned an area (7, 8).

8. Device (1) according to claims 6 or 7, characterized in that the CCD sensor (9) is designed as a line sensor.

9. The device (1) according to at least one of claims 6 to 8, characterized in that the linear optics (6) has a plurality of gradient index lenses arranged next to one another.

10. The device (1) according to at least one of claims 6 to 9, characterized in that the reference marks (3, 4) by means of an adhesive connection (19) on the drive or conveyor belt (2) can be fixed.

11. The device (1) according to at least one of claims 6 to 10, characterized in that the reference marks (3, 4) for fixing to the drive or conveyor belt (2) by a holding means (18) are fixed at a predetermined distance from each other ,

12. The device (1) according to at least one of claims 6 to 11, characterized in that the reference marks (3, 4) with two sections (15, 16) are equipped with a different reflectivity.

13. The device (1) according to at least one of claims 6 to 12, characterized in that the reference marks (3, 4) are self-luminous or afterglow.

14. The device (1) according to at least one of claims 6 to 13, characterized in that the device (1) has means for shielding the reference marks (3, 4) from the ambient light.