Method and arrangement for force measurement in connection with a manufacturing machine

Abstract

 The invention relates to a method for force measurement in connection with a manufacturing machine (10). In the method an indirect measurement is done by measuring deformation of at least one a frame part (21, 22, 23, 24, 25) or corresponding support structure in connection or near the force measurement target (N) of the manufacturing machine (10) by at least two strain gauges (31, 32, 33, 34, 35) or corresponding measuring devices with lower exactness and measurement value is given a weighting coefficient to get the force value (NF) of the measurement target (N).The invention also relates to an arrangement for force measurement in connection with a manufacturing machine (10). The arrangement comprises at least two strain gauges (31, 32, 33, 34, 35) or corresponding measuring devices with lower exactness for an indirect measurement by measuring deformation of at least one a frame part (21, 22, 23, 24, 25) or corresponding support structure in connection or near the force measurement target (N) of the manufacturing machine (10).

Description

[0001] The invention relates to a method and an arrangement for force measurement in connection with a manufacturing machine, in particular in connection with a device, especially a finishing device such as a calender, of a fiber web production line. More especially the invention relates to a method according to the preamble part of claim 1 and to an arrangement according to the preamble part of claim 9 and to a calender according to the preamble part of claim 14.

[0002] In prior art force measurement has been mainly based on a sensor for force measurement located near a loading point of a measuring target, for example a force sensor located under a bearing housing of a roll or on a connection part of a cylinder. Sensors for force measurement are usually of a large size and their mounting possibilities are limited, their measurement principles require that effecting force is conveyed through them such as in weight scales. Due these reasons the measurement arrangements are sensible of breakage in over load situations and to minimize this disadvantage the arrangement will be complicated and expensive but of course very exact measurement results are received. In situations of exact, mounting possibility limited and expensive measurements only one measurement for each measuring point is used or measurement is omitted.

[0003] In US patent 4991499 a roll arrangement is disclosed which arrangement comprises a hydraulically supported bottom roller having rotating hollow cylinder and a stationary crosshead extending lengthwise through the cylinder to form a clearance space therewith. The ends of the crossheads are supported by force exerting devices. The forces producing the line pressure of the roll are transferred through a hydraulic supporting device, such as a hydraulic fluid contained within a longitudinal pressure chamber in the crosshead, to inner circumference of the hollow cylinder. When a quick release action is desired to separate the bottom roller from its counter roll, the pressure in the longitudinal chamber is suddenly lowered by opening a quick release valve connected to a return tank. A corresponding reduction of the pressure in the force exerting devices to permit separation of the rollers occurs only after a sensor, such as dynamometer, has determined that the load on the crosshead has been substantially removed. In this arrangement a sensor is provided for detecting the bending or deflection of the crosshead. The deflection and loading of the crossheads are directly related. For example, when the deflection equals zero, then the load also equals zero. A control system operable in response to a sensor that detects the deflection of the crosshead is disclosed. The sensor may comprise a position encoder or a strain gauge arrangement.

[0004] In US patent 3331313 a calender stack having transverse pressure sensing and adjustment means is disclosed which calender stack is constructed for automatic operation of the adjusting mechanism for each adjustably mounted intermediate roll in response to the action of a strain gauge sensing the thrust forces on the associated intermediate roll in directions generally transverse of the plane defined by the axes of the two immediately adjacent rolls. In this prior art arrangement a direct measurement manually with one sensor for compensating the lateral thrust forces is provided such that strain gauges have neither tension nor compression.

[0005] An object of the present invention is to created a method and an arrangement for force measurement in which the disadvantages of prior art are eliminated or at least minimized.

[0006] A further object of the invention is to provide created a method and an arrangement for force measurement in which the problems relating to over load situations will create neither problems nor the sensor is sensible of breakage.

[0007] In order to achieve the objects mentioned above and those explained in the following the method according to the invention is mainly characterized by the features of characterizing part of claim 1. The arrangement according to the invention is mainly characterized by the features of characterizing part of claim 9. The arrangement according to the invention is mainly characterized by the features of characterizing part of claim 14.

[0008] According to the invention force measurement data is created by at least two measurement of lower exactness and / or by process information data for example by pressure of a hydraulic cylinder. When the structure of the measurement target is know a mechanical model is created and by measurement data from different locations of the measurement target measured advantageously by strain gauges, the force is determined continuously. The mechanical model is for example based on FEM-model, in which the critical deformation areas and other sensitive areas are shown.

[0009] According to the invention based on deformation of supporting structures and corresponding machine parts force measurement in target loading point is provided. Also the condition of machine parts can be monitored since the measurement results also give information of a crack growth for diagnostic purposes.

[0010] By the force measurement according to the invention also vibration information is received when measuring and the resonance areas of vibration can be avoided, since the strikes can be noted based when measurement results are combined with history data of deformations.

[0011] According to an advantageous embodiment of the invention indirect force measurement is achieved by at least two strain gauges whose state varies under varying loading situations as the structures will be in different deformation state and thus the stain gauges are either under tension or under compression and by measurement result of the strain gauges located in connection with frame parts or corresponding structures of the force measurement target. Force is determined by using weighting by predictive optimization.

[0012] In the arrangement according to the invention at least two or advantageously more strain gauges, preferably at least three strain gauges are used. By advantageous arrangement with more strain gauges and thus more measurement result, a robust system and more exactness in results is achieved. Even accuracy of 0, 5 % can be achieved. The weighting coefficient for each strain gauge can be determined by calculation for example based on earlier date and reliable force measurement value is achieved. Also a measurement sensor can be used for calibrating the weighting coefficients.

[0013] Strain gauges are of small size and they do not have special requirements for space in mounting points. Measurement of strain gauges is based on the deformation of the target to be loaded and on the measurement of that. In such the principles of measurement by strain gauges are known. One major advantage is that the sensor is not sensible of over load situations, since the force to be measured does not focus directly on it.

[0014] By calculation and I/O-connections further advantageous utilizing possibilities for the force measurement are created according to further advantageous features of the invention. By using data of several measuring points and by providing with help of so called measurement fusion algorithms significantly more exact result than by one measurement indication.

[0015] According to an advantageous feature of the invention measuring by strain gauges is continuous and the measurement results are transmitted to diagnostics and control part of the machine for controlling the loading operation, controlling the operation such that vibration resonance points are avoided and machine parts of lower condition will be replaced.

[0016] Advantageously the invention is used in connection with force measurement of fiber web machine, especially in connection with a calender of a fiber web machine in continuous measurement of nip forces with help of loading cylinders. The invention is also well suited to be used in connection with crushing devices. In the following the invention is explained in more detail by reference to the accompanying drawing in which

[0017] Figure 1 discloses schematically in connection with a calender an example of force measurement arrangement according to the invention.

[0018] In the example of figure 1 the calender 10 of a fiber web machine comprises two calender rolls 11, 12 in between of which rolls 11, 12 is calendering nip N. In the calendering nip N the calendering force, i.e. the nips force NF is provided for calendering a fiber web. The frame parts of the calender 10 are indicated by reference numerals 21, 22, 23, 24, 25, 26. The frame parts comprise an upper support arm 21 for the upper calender roll 11, a top frame part 23 for supporting the upper support arm 21, a vertical frame part 24 for vertical support of the calender 10, a bottom frame plate 25 for horizontal support of the calender 10, a lower support arm 22 for the lower calender roll 12, and a support arm 26 for supporting the lower support arm 22.

[0019] According to the invention at least two strain gauges 31, 32, 33, 34, 35 are located in connection with frame parts of the calender 10. One strain gauge 31 is located in connection with the top frame part 23, one strain gauge 32 is located in the connection area of the top frame part 23 and the vertical frame part 24, one strain gauge 33 is located in connection with the vertical frame part 24, one strain gauge 34 is located in connection with the lower support arm 22 and one strain gauge 35 is located in connection area of the lower support arm 22 and the bottom frame plate 25. The strain gauges 31, 32, 33, 34, 35 give the indication and measurement values m1...m5 of any deformation in the respective frame part / frame parts.

[0020] The nip force NF is calculated based on the measurement values m1...m5

[0021] NF= f1m1 +f2m2+f3m3+f4m4+f5m5

[0022] Coefficients f1...f5 take into account scaling and reliability of each measurement.

[0023] In the above the invention has been described with reference to one example to which the invention is not to be narrowly limited. Many modifications and variations are clear to one skilled in the art. For example the number of strain gauges is at least two but with more strain gauges more exact results are achieved. Also it is possible to use not all of the strain gauges at the same time and also the locations of strain gauges can be varied.

Claims

1. Method for force measurement in connection with a manufacturing machine (10), characterized in, that in the method an indirect measurement is done by measuring deformation of at least one a frame part (21, 22, 23, 24, 25) or corresponding support structure in connection or near the force measurement target (N) of the manufacturing machine (10) by at least two strain gauges (31, 32, 33, 34, 35) or corresponding measuring devices with lower exactness and that measurement value is given a weighting coefficient to get the force value (NF) of the measurement target (N).

2. Method according to claim 1, characterized in, that force measurement data is created by at least two measurements of lower exactness and / or by process information data.

3. Method according to claim 1, characterized in, that based the structure of the measurement target a mechanical model is created and by measurement data from different locations (21, 22, 23, 24, 25) in the frame parts or corresponding support structures near the measurement target (N) measured by strain gauges(31, 32, 33, 34, 35).

4. Method according to claim 1, characterized in, that the condition of machine parts is monitored by the measurement results for diagnostic purposes.

5. Method according to claim 1, characterized in, that vibration information is received when measurement results are combined with history data of deformations.

6. Method according to claim 1, characterized in, that force is determined by using weighting by predictive optimization.

7. Method according to claim 1, characterized in, that weighting coefficient for each strain gauge is determined by calculation for example based on earlier data.

8. Method according to claim 1, characterized in, that by strain gauges is continuous measured and the measurement results are transmitted to diagnostics and control part of the machine for controlling the loading operation, controlling the operation such that vibration resonance points are avoided and machine parts of lower condition will be replaced.

9. Arrangement for force measurement in connection with a manufacturing machine (10), characterized in, that the arrangement comprises at least two strain gauges (31, 32, 33, 34, 35) or corresponding measuring devices with lower exactness for an indirect measurement by measuring deformation of at least one a frame part (21, 22, 23, 24, 25) or corresponding support structure in connection or near the force measurement target (N) of the manufacturing machine (10).

10. Arrangement according to claim 9, characterized in, that at least two, preferably at least three strain gauges are used.

11. Arrangement according to claim 9, characterized in, that the arrangement further comprises a measurement sensor for calibrating.

12. Use of the method or the arrangement according to previous claims in connection with force measurement of fiber web machine, especially in connection with nip force measurement of a calender of a fiber web machine in continuous measurement of nip forces.

13. Use of the method or the arrangement according to previous claims in connection with force measurement of crushing devices.

14. Calender of a fiber web machine comprising at least two calender rolls (11, 12) between of which a calendering nip (N) is located, in which calendering nip (N) nip force (NF) is focused on the fiber web, which calender (10) further comprises frame parts or corresponding supporting structures (21, 22, 23, 24, 25), characterized in, that calender (10) further comprises at least two strain gauges (31, 32, 33, 34, 35) or corresponding measuring devices with lower exactness for an indirect measurement by measuring deformation of at least one a frame part (21, 22, 23, 24, 25) or corresponding support structure in connection or near the nip (N) of calender (10).

Drawing