DEVICE FOR MEASURING MECHANICAL TENSION, EXTENSION AND BENDING

Abstract: Device for measuring mechanical tension, extension and bending based on longitudinal changes of an object, comprising a base plate (1) which at one end is adapted to be secured in two points to the object, a measuring part (13) being displaceable in relation to the rest of the base plate (1), however connected yieldingly with the base plate (1), and being adapted to be secured at a third point of the object, and that a sensor (12) being arranged between the measuring part (13) and the rest of the base plate (1), whereby a processor is adapted to compute the signals from the sensors (11, 12) to provide measuring data for respectively mechanical tension, extension and bending related to physical changes of the material.

Description: Device for measuring mechanical tension, extension and bending The present invention is related to a device for measuring mechanical tension, extension and bending. Measuring of extension in structures and parts thereof traditionally has been accomplished by gluing tension strips on the structure. To secure such tension strips, the material must be cleaned very thoroughly to ensure that the tension strip has good contact with the base material. Thereafter a resistant wire is secured. Resistant wires normally used have a size like a post stamp or such. The resistant wire is connected electrically with a measuring device which is registrating changes in the electri- cal resistance based on the extension or possibly the compression of the base material caused by a load, as the resistant wire likewise is exposed to the same influence. Use of tension strips is time consuming and the demand large to the highest purity and accuracy, also to the surroun- dings. Another disadvantage with existing methods is that tension strips only can be used once. Measurements also have been made optically, especially in laboratories and partly based on polarised light and the interference occurrence. It furthermore is well known to use devices which are secured by bolts to the structure to be measured, whereby the measurement as such is provided by means of tension strips. Here the measuring device is used as a mechanical shunt as it has a relatively large mechanical rigidity. In this way the devices as such may influence the structure on which measurements are to take part and therefore also influence the measurements. From prior art, reference is made to DE 3 504 872 and GB 1 286 993 as examples of prior art devices. The devices used today to measure tension, extension and bending in a structure all have disadvantages. Such measure¬ ments take a long time, the preparation of the structure as such is time consuming as material to be measured must be clean thoroughly and therefore possible painting or other surface treatment, must be removed. The measuring device furthermore very commonly have an extension coefficient different from the material to be measured, a fact what makes the measuring results depending on temperature fluctuations. This is also concerned with the tension strength as the electrical conductivity likewise is dependent on the temperature. The measuring device according to the present invention avoids the above mentioned disadvantages. Additionally further advantages are achieved, together with a substantially increased measuring accuracy and small dimensions. The device according to the present invention is distinguished above the prior embodi¬ ments also in that handling is very easy and quick and the device does have no influence on the material to be measured. The above mentioned advantages and special effects are achieved with the device according to the present invention as defined with the features stated in the claims. The drawing discloses in figure 1 a ground view of the base plate of the device fully equipped, figure 2 discloses only the base plate in figure 1, and figure 3 discloses one embodiment of the device according to the invention in a version built into a housing disclosing the base plate of providing figures as a house base. The base plate 1 is manufactured preferably in an aluminium alloy having a known and uniform texture. In the base plate a pattern is cut out with small tolerances by means of laser cutting, in such way that a measuring part 13 is provided, being displaceable within the slots made by the cutting. The measuring part 13 is connected with the rest of a base plate 1 by a number of bridges 14 which act like plate springs and which maintain the measuring part 13 centralized in an unloaded condition. The base plate 1 is secured to the structure to be measured by means of for example magnets which can be used for measuring ferric materials. For measuring other materials, such as tree, concrete etc. screws, double sided tape or such are used. The figures disclose one embodiment having three magnets 4. One magnet 4 is secured to the measuring part 13 and two magnets 2 and 3 are secured to one end of the base plate 1. A sensor 12 is secured between the measuring part 13 and the rest 3 of the base plate 1, preferably a highly sensitive magnet sensor. A change of the material length between the magnets 2, 3 and magnet 4 therefore will immediately be registrated by the sensor 12. A further sensor 11, corresponding to the first mention, is secured between the base plate 1 and the opposite end in the longitudinal direction of the measuring part 13. This sensor 11 abuts a part 15 of the base plate 1 which is movable in the longitudinal direction by means of an eccentric disc 5 with the purpose of calibrating the measuring device. The part 15 is, like the measuring part 13, connected with the base plate by bridges 14. With such a device, calibration can be made all along the entire range of the measuring scale. The device according to the present invention may be displaced by pressure from both sides against cams 6. The cams 6 thereby press against the middle of the base plate 1 and thereby displace flexible movable wedges 9 and 10 into correspon¬ ding recesses in the measuring part 13. With such a constant pressure the device is locked in such a way that the calibration is maintained even when moving the device to another place. Figure 3 discloses one embodiment of the device accor¬ ding to the present invention, built into a housing having a display 8, a plug 7 for connection of a serial interface and a push bottom set for operation of different functions computed and possibly to be disclosed in the display 8. The device furthermore suitably may have a securement against overloading. Signals from the sensors 11 and 12 are transmitted to an electronical part for computing the signals which thereafter may be disclosed in the display and/or transmitted to a computer by means of an interface. The device is suitable to measure stress as a function of a load as this is expressed as a relative change of the length, compression or extension. The device, however, also can measure bending expressed by the bending radius. Furthermore the change of the length may be measured and disclosed directly as a function of the load measuring length units, such as in μm. With knowledge of the material of the structure, the cross section, the module of elasticity etc., the readings may be expressed directly in kN in such a way that the device according to the invention principally also can be used as a dynamometer. By measurement during short periods of time, the differences between the extension coefficient based on the temperature, of the material and of the measuring device will be without significance. In case of permanent installation of the device for surveillance, however, a compensation is made as the unit microprocessor comprises constant values for the specific material which may be stored in advance or selected when activating the device, depending of the material onto which the device is secured. In this way a device is provided, the measuring results of which are completely compensated for changes due to temperature variations.

Claims: P a t e n t C l a i m s 1. Device for measuring mechanical tension, extension 5 and bending based on longitudinal changes of an object, CHARAC¬ TERIZED IN comprising a base plate ( 1 ) which at one end is adapted to be secured in two points to the object, a measuring part (13) being displaceable in relation to the rest of the base plate (1 ), however connected yieldingly with the base plate ( 1 ), o and being adapted to be secured at a third point of the object, and that a sensor (12) being arranged between the measuring part (13) and the rest of the base plate (1), whereby a processor is adapted to compute the signals from the sensors (11, 12) to provide measuring data for respectively mechanical tension, s extension and bending related to physical changes of the material. 2. Device according to preceding claims, CHARACTERIZED IN the measuring part (13) being connected with the rest of the base plate with at least two blade spring like connections ( 14) . o 3. Device according to preceding claims, CHARACTERIZED IN a sensor (11, 12) being arranged on two opposite sides of the measuring part (13) and that a calibrating device ( 5 ) being adapted to allow changing the pressure against the measuring part ( 13 ) from the rest of the base plate ( 1 ) thereby to make a 5 calibration of the device possible. 4. Device according to preceding claims, CHARACTERIZED IN that outer cams (6) being adapted to, by pressure towards each other, to press wedges (9, 10) towards recesses in the measuring parts ( 13 ) thereby to secure the measuring part and thereby o maintaining the calibration of the device, when the device is removed locally, the device thereby being lifted and removed with the pressure against the cams (6) maintained. 5. Device according to preceding claims, CHARACTERIZED IN the base plate ( 1 ) being manufactured in a aluminium alloy 5 having uniformally and known texture. 6. Device according to preceding claims, CHARACTERIZED IN two magnets (2, 3) being secured to one end of the base plate ( 1 ) and that a third magnet (4 ) being secured to the measuring part (13), to secure the measuring device to the object.

Inventors: BURMANN BJOERN, BURMANN, BJOERN
Applicants: BURMANN BJOERN, SCAN SENSE A S, BURMANN, BJOERN, SCAN-SENSE A/S
Application year: 1995
Main classification: G01B7
IPC codes: G01B7