APPARATUS AND METHOD FOR MEASURING THE TENSION OF SPOKES MOUNTED IN A WHEEL AND APPARATUS AND METHOD FOR STRAIGHTENING SPOKED WHEELS

Abstract: The invention relates to an apparatus for measuring the tension of spokes mounted in a wheel, comprising a holder for securing the wheel such that it is rotatable, tapping means for generating the vibration characteristically occurring in tensed spokes moving along a path, and sensor means. The sensor means are able to detect the vibration of a spoke moving past said sensor means.

Description: Apparatus and method for measuring the tension of spokes mounted in a wheel and apparatus and method for straightening spoked wheels The invention relates to an apparatus for measuring the tension of spokes mounted in a wheel, comprising a holder for securing the wheel such that it is rotatable, tapping means for generating a vibration characteristically occurring in tensed spokes moving along a path, and sensor means. Such an apparatus is known from US 5103414, whereby the vibrations of the spokes are measured at the holder in which the wheel is secured. The disadvantage of the known apparatus is that the rim, the hub and the holder greatly influence the detected vibration, making the measurement inaccurate. The object of the invention is to improve the accu¬ racy of the measurement of the tension in the spokes and to this end the apparatus is equipped with sensor means able to detect the vibration of a spoke moving past said sensor means. By measuring the vibration by means of a sensor in the direct vicinity of the spoke, there is no effect from the vibration properties of the holder and the hub, so that only the vibration of the respective spoke is measured. According to a further improvement of the invention, the sensor means comprise a sensor placed next to the path of the spokes. This achieves that the vibration of a spoke is always directly measured, which increases accuracy. According to a further improvement of the invention the sensor is an inductive electromechanical element that is able to convert a vibration of a magnetizable material into an electric current. Such a sensor is simple and little sensitive to interference, being unaffected by noise and variations of the ambient temperature. According to a further improvement of the invention the sensor means are suitable for the detection of low- frequency vibrations, for instance between 1 Hz and 2,000 Hz. This limited range, which coincides with the natural frequency of the spokes' vibration, permits uncomplicated sensor means. According to a further improvement of the invention the sensor means are exclusively capable of detecting vibrations in the direct vicinity of the sensor. Consequently, only vibrations are detected from spokes moving very close to the sensor and spokes at, for instance, the other side of the wheel, do not influence the measurement . Surrounding influences are also not detected. According to another preferred embodiment of the invention the sensor means are connected with a computer via an analog-to-digital converter. By converting the measured vibration data into digital values, the data can easily be analyzed. According to a further improvement the computer is provided with a memory in which the digital measuring data may be stored for further analysis. This allows quick pro¬ cessing of the measuring data obtained from the spokes. According to a preferred embodiment of the invention the vibration measurement of a spoke can be carried out blank contact, such that preferably within 40 msec enough data are available. In this way a few seconds suffice to measure the tension state of all spokes in a wheel . The computer is preferably also equipped with means for recording the dimensions of the spokes and/or the wheel. According to a further preferred embodiment of the invention, detection means are provided for the identification of the detected spokes. The advantage being, that always the tension of a particular spoke can be recorded by the memory, which could be important for subsequent processing. These detection means comprise preferably a sensor for recognizing a position on the rim. It is then possible, for instance, that the valve hole is recognized, so that the spokes can be identified in relation to said valve hole. The invention also relates to a method of measuring the tension of spokes mounted in a wheel by means of a sensor, wherein the wheel is placed in a holder and is rotated so that the spokes move toward a sensor detecting in each spoke the spoke tension-dependent properties, which properties are subsequently recorded together with the spoke's position in the wheel. By placing the wheel in a holder and moving the spokes toward a sensor and by linking the spoke tension- dependent properties to the spoke's position in the wheel and subsequently recording these data, the tension distribution of the spokes in the wheel is measured quickly, while the individual tension of each spoke is also known. According to a further embodiment of the method the sensor detects the spokes' vibrations generated by tapping the spokes after which the vibrations are converted into spoke tensions on the basis of, for instance, the spoke and/ or wheel dimensions stored in the computer. The conversion of the vibrations into spoke tensions allows their subsequent use in the presentation concerning the quality of the wheel and, for instance, for final work on the wheel such as straightening. According to a further improvement the vibrations of the spokes are analyzed and split into one or more har¬ monic vibrations approximately in the range from 0 to 500 Hertz. By analysing the signal and by recording the first harmonics thereof, the spoke tension can be calculated. According to the invention the measured vibrations are also a means for determining which spokes are loose. This makes it possible, even in situations where there is hardly any vibration in a spoke due to its being loose, that this is indicated so that measures may be taken. The invention also comprises an apparatus for straightening spoked wheels, comprising sensors for the determination of the lateral deviation and vertical devi¬ ation of a rim in relation to the hub, straightening means for tightening or loosening nipples on the spokes and control means for the control of the straightening means, using the above-mentioned apparatus according to the invention. The invention also comprises a method of straightening the spoked wheels in which the lateral deviation and the vertical deviation of a rim in relation to a hub are measured and the nipples on the spokes can be tightened or loosened with the aid of straightening means under influence of the control means, wherein the control means use one of the methods for the measurement of spoke tensions in accordance with the invention. By using the accurate spoke tension measurements, straightening can proceed more quickly and more efficiently. According to a further improvement of the invention the spokes having a tension above an adjustable value are loosened first of all and/or the loose spokes are tightened to a minimum spoke tension, after which all spoke tensions are measured anew and straightening commences. In this manner an even spoke tension in the straightened wheel is obtained in a short time. According to a further improvement the correction to be made by means of the straightening means is calculated, based on the measured lateral deviation, vertical deviation and spoke tension, such that it does not come above or below the adjustable values. By immediately incorporating the measured data in a calculation, there will be fewer corrections ensuing from subsequent measurements, which affords an extra time gain. The invention will now be elucidated by means of a drawing with reference to a few embodiments. In the drawing Fig. 1 shows a schematic cross-section of an apparatus for measuring the spoke tension and for straightening a wheel; Fig. 2 shows a partial side view of the apparatus according to Fig. 1; Fig. 3 shows a front view of a sensor for measuring the vibrations in a spoke; Fig. 4 shows a side view of the sensor according to Fig. 3 ; and Fig. 5 shows a graph illustrating the strength of a measuring signal of the sensor subject to the distance between sensor and spoke. In the Figure identical parts are indicated by identical reference numbers whenever possible. Through of a group of spokes 4, a rim 1 is fastened to a side of a hub 2 and through a second group of spokes 5 to another side of the hub 2. The axle of the hub 2 is fastened in a holder 3. On rotation of the wheel in a direction A, the first spokes 4 and the second spokes 5 each move in a conical plane past the sensors 7. While rotating, the spokes are tapped by a plectrum 6 causing the spokes which are under sufficient tension, i.e. the spoke tension, to vibrate. This vibration is detected by the sensor 7. The sensor 7 may, for instance, be a sensor element capable of detecting the vibrating movements of a magnetizable element such as a steel spoke, at frequencies ranging from 1 Hz to 2000 Hz. Such elements are known and are used to detect the vibrations of the strings, for instance, of a bass guitar. The sensor 7 consists of a sensor core 8 surrounded by a coil. In the coil a tension is created which cor¬ responds with the vibrating movement cauβed by the vibration produced by the spoke 4 moving in a direction B past the sensor core 8. Such sensors may, for instance, have a length of 40 mm and a width b of 10 mm. For the sensor an operational area 9 may be indicated. The distance between the spoke 4 and the sensor 7 is c, while the graph of Figure 5 shows how the signal intensity P, indicated on the vertical axis, decreases as the distance c increases. As soon as c becomes greater than a distance d, d being for instance 5 mm, the signal has become insignificantly low which means that, for instance, the vibrations of the second spokes 5 do not influence the signal that the first spokes 4 induce in the sensor 7 near the path of the first spokes 4. The spoke tension is measured as follows: the wheel is made to rotate either by hand or by means of a motor. The spokes are made to vibrate with the aid of the plectrum 6 and the vibrating movement of the spokes is measured by means of the sensors 7. The analogous signals recorded by the sensors are converted into digital values with the aid of an analog-to-digital converter, which converter can use a sample-frequency from 1 to 4 kHz. These digital values are stored in a memory of a computer (not shown), or, for instance on its hard disk. This digital value is then analyzed per spoke, for instance, by a Fourier transformation, and one or more first harmonics are determined in the 0-500 Hz frequency range. Using the computer data about the dimensions of the spoke and/or the wheel, the tensions in the spoke are calculated. If a wheel comprises spokes that are in contact, then two harmonics are measured in a spoke, which corresponds with the partial restraint of the spoke where it is in contact with the other spoke. After a spoke tension has been calculated, it is stored as pertaining to one particular spoke. To that end the position of the spoke in relation to the rim of the wheel is determined, for instance in relation to a valve hole 13 or another detectable characteristic. For the detection of the valve hole 13 a sensor (not shown) may be used. The measurement of the spoke tension may be carried out in a special measuring bench, the wheel being introduced and rotated by hand, first measuring one side of the wheel and after turning the wheel by hand, measuring the other side of the wheel. The measuring results may be visualized on a screen of the computer, if desired a measuring report is printed out, or the results may be stored in a data file for future analysis. Tension measurement may also be carried out in an apparatus in which the wheel is straightened which means that after the lateral deviation is measured by means of a lateral deviation sensor 10 and the vertical deviation by means of a vertical deviation sensor 11, said lateral and vertical deviations are reduced to acceptable values by means of straightening means (not shown) . The straightening means consist of rotation means for turning the nipples screwed onto the spokes, the amount of turning being controlled on the basis of the sensor measurements. When straightening, use is also made of the information obtained from the spoke tension measurement. One of the first steps during straightening may be the detection, by means of the spoke tension measurement, of loose spokes which will then be tightened to a minimum tension. Tensions may also be found to be too high and are first reduced to acceptable values before continuing the straightening process. The method hereby is that the wheel is clamped in the holder 3 and by means of a drive 12, is rotated, for instance, in about 1-2 seconds around its axle. The spokes are made to vibrate by means of the plectrum 6 and the vibrations are measured by the sensor 7. The spoke tensions for each spoke are calculated in a computer (not shown) . Thus these are known after about 2 seconds. Subsequently spokes that are too loose are tightened and spokes that are too tight are loosened. Then the straightening process commences, whereby the lateral deviation and the vertical deviation are measured, and the spoke tensions are possibly measured anew. Based on the values measured for lateral deviation, vertical deviation and spoke tension, the rotations of the nipples to be applied to the spokes are calculated and carried out. The wheel is now straightened, although it is also possible that one or more measurements need to be carried out anew. The calculation also entails that the spoke tension must not be above a maximum value and not below a minimum value. Should it become apparent from the calculation that a particular minimum of lateral deviation or vertical deviation is not attainable, then the minimum and maximum values of the spoke tensions are adjusted. It is also con¬ ceivable that the range of minimum and maximum value in the spoke tension is laid down, so that possibly the maximum of allowable vertical deviation and/or lateral deviation may be increased. During straightening on the basis of the calcula¬ tions, the spokes to be straightened will first be loosened after which the spokes that are too tight will be dealt with, in order to avoid that even only temporarily the spoke tension becomes too high, which could cause permanent deformation.

Claims: CLAIMS 1. An apparatus for measuring the tension of spokes (4,5) mounted in a wheel, comprising a holder (3) for securing the wheel such that it is rotatable, tapping means (6) for generating a vibration characteristically occurring in tensed spokes moving along a path, and sensor means (7) , characterized in that the sensor means (7) are able to detect the vibration of a spoke (4,5) moving past said sensor means. 2. An apparatus in accordance with claim 1, charac- terized in that the sensor means comprise a sensor (7) placed next to the path of the spokes (4,5) . 3. An apparatus in accordance with claim 2, charac¬ terized in that the sensor (7) is an inductive electromechanical element that is able to convert a vibration of a magnetizable material into an electric current. 4. An apparatus in accordance with any one of claims 1-3, characterized in that the sensor means are suitable for the detection of low-frequency vibrations, for instance between 1 Hz and 2,000 Hz. 5. An apparatus in accordance with any one of claims 1-4, characterized in that the sensor means are exclusively capable of detecting vibrations in the direct vicinity of said sensor means. 6. An apparatus in accordance with any one of claims 1-5, characterized in that the sensor means are connected with a computer via an analog-to-digital converter. 7. An apparatus in accordance with claim 6, charac- terized in that the computer is provided with a memory in which the digital measuring data may be stored for further analysis. 8. An apparatus in accordance with any one of the preceding claims, characterized in that the vibration measurement of a spoke can be carried out blank contact. 9. An apparatus in accordance with claim 8, charac¬ terized in that the sensor means are such that within 40 msec enough data about a spoke are available. 10. An apparatus in accordance with any one of claims 6-9, characterized in that the dimensions of the spokes and/or the wheel can be stored in the computer. 11. An apparatus in accordance with any one of the preceding claims, characterized in that detection means are present by means of which the detected spokes can be identified. 12. An apparatus in accordance with claim 11, char¬ acterized in that the detection means comprise a sensor for recognizing a position on the rim. 13. A method of measuring by means of a sensor the tension of spokes mounted in a wheel, wherein the wheel is placed in a holder and is rotated so that the spokes move toward a sensor detecting in each spoke the spoke tension- dependent properties, which properties are subsequently recorded together with the spoke's position in the wheel. 14. A method in accordance with claim 13, characterized in that the sensor detects the spokes' vibrations generated by tapping the spokes after which the vibrations are converted into spoke tensions on the basis of, for instance, the spoke and/ or wheel dimensions stored in the computer. 15. A method in accordance with claim 14, characterized in that the vibrations of the spokes are analyzed and split into one or more harmonic vibrations approximately in the range from 0 to 500 Hertz. 16. A method in accordance with any one of claims 12-15, characterized in that based on the measured vibrations it is determined which spokes are loose. 17. An apparatus for straightening spoked wheels, comprising sensors for the determination of the lateral deviation and vertical deviation of a rim in relation to the hub, straightening means for tightening or loosening nipples on the spokes and control means for the control of the straightening means, provided with an apparatus in accordance with any one of claims 1-12. 18. A method for straightening spoked wheels in which the lateral deviation and the vertical deviation of a rim in relation to a hub are measured and the nipples on the spokes can be tightened or loosened with the aid of straightening means under influence of the control means, wherein the control means use the spoke tension measurements obtained in accordance with any one of the methods according to claims 13-16. 19. A method in accordance with claim 18, characterized in that the spokes having a tension above an adjustable value are loosened first of all and/or the loose spokes are tightened to a minimum spoke tension, after which all spoke tensions are measured anew and straightening commences. 20. A method in accordance with claim 18, characterized in that the correction to be made by means of the straightening means is calculated, based on the measured lateral deviation, vertical deviation and spoke tension, such that it does not come above or below the adjustable values.

Inventors: ADMIRAAL ANTONIUS SIMON, VAN DIJK PETER, ADMIRAAL, ANTONIUS, SIMON, VAN DIJK, PETER
Applicants: ADMIRAAL ANTONIUS SIMON, DIJK PETER VAN, HOLLAND MECHANICS BV, ADMIRAAL, ANTONIUS, SIMON, HOLLAND MECHANICS B.V., VAN DIJK, PETER
Application year: 1997
Main classification: G01L5
IPC codes: B60B31, G01L5