CA1274878A - Method and device for measuring the distance between the discs of a refiner - Google Patents

Method and device for measuring the distance between the discs of a refiner

Info

Publication number
CA1274878A
CA1274878A CA000549576A CA549576A CA1274878A CA 1274878 A CA1274878 A CA 1274878A CA 000549576 A CA000549576 A CA 000549576A CA 549576 A CA549576 A CA 549576A CA 1274878 A CA1274878 A CA 1274878A
Authority
CA
Canada
Prior art keywords
coil
disc
magnetic field
refiner
discs
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
CA000549576A
Other languages
French (fr)
Inventor
Juhani Karna
Heikki Pahlman
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Sunds Defibrator Jylha OY
Original Assignee
Sunds Defibrator Jylha OY
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sunds Defibrator Jylha OY filed Critical Sunds Defibrator Jylha OY
Application granted granted Critical
Publication of CA1274878A publication Critical patent/CA1274878A/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

Links

Classifications

    • DTEXTILES; PAPER
    • D21PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21DTREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
    • D21D1/00Methods of beating or refining; Beaters of the Hollander type
    • D21D1/20Methods of refining
    • D21D1/30Disc mills
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B02CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
    • B02CCRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
    • B02C7/00Crushing or disintegrating by disc mills
    • B02C7/11Details
    • B02C7/14Adjusting, applying pressure to, or controlling distance between, discs
    • DTEXTILES; PAPER
    • D21PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21DTREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
    • D21D1/00Methods of beating or refining; Beaters of the Hollander type
    • D21D1/002Control devices
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01BMEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/14Measuring arrangements characterised by the use of electric or magnetic techniques for measuring distance or clearance between spaced objects or spaced apertures

Abstract

ABSTRACT

This invention is related to a method and device for measuring the distance(?)between the discs of a refiner, in which method a magnetic field is generated by means of a coil (5) placed at one disc (4), which magnetic field is allowed to run at least partly through the other disc (3). According to the invention the measuring is carried out by using the actual distance between the refiner discs as the object of measuring in that the magnetic flux over the distance between the discs caused by the coil (5), which is formed at least at one refiner-disc tooth (7) or comparable element, is measured by that the flux running over the distance between two opposite teeth (7,8) is detected by means of another coil (6), such as is formed round at least either of said teeth, the signal induced in the coil being interpreted as a quantity that expresses the distance (?) between the teeth.

Fig. 1

Description

~ ? 9~ ~7 ~

METHOD AND DEVICE FO~ ~EASU~IMG THE ~ISTANCE ~ETWEE~ TUE ~ISCS OF
A ~EFlNER

This invention is related to h method and device for measuring the distance between the discs of a re~iner, in which method a magnetic field is g~ne~ated by means of a coil placed at one di~c, which magnetic field is allowed to run at le~st partly through the other disc.

~easuring the distance between fo~ instance the discs of a disc refiner has chiefly two purposes. Firstly, the aim i~ tc prevent the discs f~om accidentally getting closer to each other and ~inally colliding, which is caused by the yielding of the refiner, its wearing and other facto~s, because this way the valuable discs wear quickly and might also easily get destroyed altogether. Secondly, measuring the distanre between the discs provides valuable information about the process itself, and it is possible to see tor instance what distance between the discs gives the desired final result and adjust the distance according to the quality of the final p~oduct already at the beginning of the process. This way costly experiments are a~oided.

In each case the equipment for measuring the distance between the discs has to meet high requi~ements because it has to work under great pressure and reliably measure distances no bigger than fractions of a millimeter in a vibrating machine. Known devices ~, i`;

., ' ' .:,; ' ' .. ::: ' ' . , '7 fk~78 for measu~in~ the distance between the discs are based either on indirect measu~ing, 4~ on the use of senso~s for detecting the distance between the discs9 or on capacitatiYe mea~uring One example of lndirec~ measuring is the measuring of the a~ial movement of the discs. The a~ial movement o~ the discs is in principle p~oportional to changes in the distance between the discs in a disc refiner, and the same rule applies also to a cone refiner. The yielding of the refine~ under varying forces and pressures and the wea~ing of all parts between ~he discs mutual distance and the indirect measuring point~ however, make the results of the measurement unreliable. Besides7 this kind of measuring does not provide information about the wearing of the disc surfaces themselves, in other words their condition.

Another way to measure the distance between the discs is to use built-in approach sensors which~ installed in one disc, measure the distance between the opposite disc and themselves, as described in Finnish patent application no. 801748. ~Ottl in the invention presented by means of that patent application and in the description of prior art, the point of departure is the measuring of the distance between smooth surfaces, which measuring is problematic. In the case of said invention further problems are the discs wearing and the resultant changes in their mutual distance. As the sensors do not wear in the same way as the disc material, if at all, they are ce~tainly not able to take into considerati4n the wearing of the disc in which they are mounted.

-: , ~ - 3 - ~ ~t7~7~

A third way ~f measuring referred t~ is t~ measure the capacitance between the discs and its changes, on the basis of which for instance in a disc refiner the average distance between the rotor disc and the stator disc can be determined. Yet the capacitance measurQd is also in~luenced by several other factors7 such as the chemical propertie~ of the woc.dpulp t~ be ground and of the diluti~n water. Thus the results are very easily distortedi consequently, no practical applications o4 this method are known to be in the ma~ket. ~esides7 it i5 impossible to measure the angle ~etween the discs with this method only.

In addition to the above-mentione~ problems7 all above-mentioned methods are burdened by difficulties ~f calibration because the absolute locati~n of the measuring points needed for calibration or their l~caticn in relation to the discs is constantly changing as time ~oes ~n~

The object of this inventi~n is to create a method and device for measurinQ the distance t~etween the discs of a re-finer without the above-menti~ned drawbacks~ To achieve this, a method accordin~
to the invention is characteri2ed by that the measuring i5 carried out by using the actual distance ~etween the refiner discs as the object of measuring in that the magnetic flux over the distance ~etween the discs caused by the coil, which i~

,: - . . . . , .::

7~i~78 fo~med at least at one refiner-disc tooth or comparable element~
i5 measured by that the ~lux running over the distance between two opposite teeth is detected by means of a coil~ such as i5 formed round at least either cf said teeth, the signal induced in the coil being inte~p~eted as a quantity that e~presses the distance between the teeth.

The most si~nificant advantages of the inventi~n a~e the following:
- The actual critical pa~ts of the discs a~e used fo~ the measuring of the distance between the discs, which gives the ~eal value ir~esFective of the discs wearing and the refiner s yieldings. The accurate measuring method also c~eates opportunities for a soundly utilizable multi-point measuring, with which the obliquity of the positions of the discs in respect to each cthe~ can be determined.
- It is to be noted that because the measuring in the invention 15 ~ased on the measuring oF a magnetic field the materials between the discs (water, wood chips)~ being magnetically not conductive, do not influence the ~esults.

An advantayeous application of the invention is characte~i2ed by that three-wave voltage is fed into the coil that generates the magnetic field~

- 5 ~

F~om this kind of amplitude of an easily modifiable signal it is possi~le to read the distance between the discs as a quantity reversely proportial to the amplitude.

Another advantageous application of the invention i5 characteri7ed by that the calibration of the measuring device is carried out by ~easuring the corresponding signal levels with the discs in the extrem~ positions in relation to each o$her and by reco~ding said signal levels into a memory.

The difficulty of calibration which burdens devices based on prior art are eliminated fFom a solution pro~ided by the invention partly through the absolute method of measurement and partly through the uliti2ation of such electronic equipment as i5 in agreement with the application described above.

Other advantageous applications of the invention are characteri~ed by what is stated in the patent claims presented below.

In the following, the invention is explained in more detail by means of an example with reference to the enclosed drawings, in which Fig. 1 shows an advantageous application of the invention.

7~7~

~ig. 2 shows the field lines of the most import~nt r4utes of the magnetic flux in a case like that in F19. i.

Fig. 3 show~ another adv~ntageous application of the invention.

Fig. 4 shows as a block diagram the control electronic~
of a device according to the invention~

Fig. 5 shows the position of a coil according to the invention at a disc o~ a disc re~iner as seen from line V-V of Fig. 1.

Figure 1 shows a cross-section along the outer circles of the discs of a disc r~finer. In a situation like that in the figure, the teeth of the two discs are positioned opposite each othera The base plates of the rotor and of the stator a~e denoted with numbers 1 and 2 respectively~ Likewise, the rotor ~nd stator discs are denoted with numbers 3 ~nd 4 respectively. In one disc~ in this case the stator disc 4, cavities 7a and 7b have been machined surrounding one tooth 7. Round the tooth 7 has then been formed a coil S, and into that coil is fed sawtooth voltage.
~he coil compels the magnetic ~lux caused by it to run as effectively as possible through the magnetic body in the field, in this case the refiner-disc tooth 7 in the coil~

If the wearing properties of the ~a~e plates 1,2 of the rotor and o~ the stator respectively are close enough to the wearin~

_ 7 _ ~ '7~

pr~perties of the actual di~c material, the coils can also be placed a~ the locations A or ~ of the base plates~ which form the outer circles of ~he respective ref iner discs. This has the ~dvantage that the coil5 ~re readily ac~essible for instance for maintenance.

In Figure 2 dashed lines show how the ma~netic fiux r~ns in a case like that in Figure 1. It is seen, that th~re arises at every tooth a closed magnetic field ~hich ~ecause o~ the shape of the discs has an air gap. Th~ total flux runs through the tooth that is e~uipped with the coil. The flux returns ~hrough all the other teeth in the magnetic circuit, of which the disc has a great number. The coil 5 corresponds to the primary coil of an iron-cored transformer and the flux induced by it creates a voltage in the other coil S, which in turn corresponds to the ~econdary coil of a ~ransformer. For ~easons expl~ined later on, the coils 5,S do not, however, operate as a transformer. The coils 5, S can be one and the same coil.

~agnetic flux 0 is proportional to the permeance of the magnetic circuit:
0 = N i ~o A = N i P
~1) in which 7~

N = number of revolutions of the primary coil i = cur~ent of the coil ~ = permea~ility of free space, defined as 4~ 10 H/M
A - area of the material permeated by the flux ~ = delta distance between the discs~(dn this case) P = permeance.

In a like that in Figure 1 the permeance of the circuit can be divided into two components:

P = ~0 _ + ~0 n h (2 in which A = area of one refiner-disc tooth.

The contribution of iron has been left out of the equation. The components represent the perme~nce of the air ~ap permeated by the main ~lux and he permeance of the air gaps of the flux that returns throu~h the other teeth ~n pcs). A5 permeance is the inverse of reluctance, we get p 1 1 ~rQm which ~ollows that P ~> R ~ when n -~

Thus, according to this only the air gap at the coil tooth 7 is decisive.

~ ~ Z74~87~

The flux received by the coil 6 is reversely proportional to the distance ~ between the refiner-disc teeth 7 and 8 bec~use an inc~ease in the distance also means an increase in magn~tic reluctanceg in other w4rds in the resistance in the closed circuit where the magnetic flux runsO The invention is based on the ve~y idea that utili2ation of refiner-disc teeth ~or creating a maqnetic circuit and the ~etection at a tooth 7 itself of the ~lux changes in one such magnetic circuit pr4vide such ~ field intensity and precision as can be measured without the drawbacks that ~ccur when measuring the distance between planar sur~aces.
Besides7 what is measured all the time is the actual distance between the discs, since the changes in the distance bet~een the refine~-disc teeth are directly reflected in the measurements, irrespective of why the changes occu~ ~inner yieldings of the refiner, wearing).

When the rotor 4f the refiner rotates in relation t~ the stator, the magnetic flux naturally changes cyclically because the magneti~ resistance between the teeth, in other words reluctance~
is at its lowest when the teeth are precisely opposite each ~ther, at which time the flux correspondingly is at its greatest.
This maximum value is the actual result ~f the measurement, and it can be easily discerned fo~ instance by filtering or with a peak-value detecto~.

Figure 3 shows another app1ic~tion of the invention1 in which a windin~ 9 is inst~lled 10ngitudina11y in ~ g~ve between two ~efine~-disc teeth~ The winding cau~es the s~me kind ~f magnetic circuit as in the forme~ c~se, as is shown by the flux line 10.
This f1ux can ~e detected and me~sured in the s~me w~y a~ th~t sh~.wn in Figure 1. As a new ~eature in Figure 3 i5 a so-c~1led short-ci~cuit coil 111 with which the f1UY~ is prevented from ~unning outside its area 4~ g~neration. ~ecause of the flux, in the c~i1 11 is induced a current which in turn ~educes the magnetic field that runs through the coil. It is furthermore seen in Figure 3 that the discs ~n also consist of separate segments 1~, 13, for inst~nce such as can be changed one by ~ne.

Figure 4 shows the control e1ectronics of a system according to the invention fo~ measuring the distan~e between the discs. As already stated above, into the generating coi1s 5,6 i5 ~ed sawtooth voltage. This is because the disc material is not a particularly good ferromagnetic material. Among other things, therefore, this means that it cannot be made crystal-oriented, which is what, for instance, cold-rolled transformer plates mostly are. Owing to this and with an appropriate number of windings of the coils, the flux, in practice, tendsto get quickly saturated, which causes the magnetic field to behave derivatively. Thus in this kind of situation, for instance, the coils 5 and 6 and the disc 4 become a derivator, not a transformer. If, in that case, the supply voltage is sawtoothed, the curve form of the output signal of the secondary side will advantageously, for further ~.~ 7~7~

pr~cessing,be ~hat o4 a square wave, the amplitude of which is reversely proportional to the distanee ~ between the discs~ As stated earlier, is is possible at the same time to both generate and detect a magnetic field ~ith the coil 57 in whi~h case a separate c~il 6 i5 not necessary. The circuit shown in Figure 4 i5 not essentially changed by this.

In Figure ~ a sawtooth voltage generator 14 fe~ds three-wave voltage into the coil 5. The output 5ignal of the secondary coil ~ of the transformer circuit is, as stated earlier~ square wave, and it i5 rectified in a rectifier 15. The rectified siqnal Ul is taken into a reduction element 16g in which the signal U2, the stray flux o~ the magnetic field ~nd the background noise o~ the rest o~ the circuit is subtracted from the signal Ul, the result being signal U3. Finally, this signal is corrected in the circuit 17 by means of a coefficient chosen on the basis of the disc material and design, in such a way that the output of the circuit directly represents the ~istance d between the discs. Said coe~ficient ~lso takes into consideration the dislinearity of the interdependence hetween the value d of the discs distance from each other and the amplitu~e o~ the correspondin~ square wave~ in such a way that the output J value is in a direct and linear ~ay dependent on the distance between the discs, which makes e~entual ~urther processing as easy as possible. The output signal can ~e binary or analog. In practice~ the circuit 17 can comprise a microproc~ssor, the ~.~'7~

advantages o~ which are easy modifiability of the corrective coefficients ~nd a wide range of possibilities of 4urther processing.

The definition of the background noise U2 ~nd ~t the same time the calibration o~ the device happen automatically ~no scaling or searching for reference points~ in such a way that the discs cf the refiner are moved far from each ~ther, for instance to the maintenance position, and the device is allowed to mea~ure the signal that corresponds to this 'indefinite' distance between the discs. The resultant signal 9 in other words the base v41tage U2, which mainly represents the stray ~lu~ of the m~gnetic field, is ~ecorded into a holding circuit 18, 50 that it in real measurements could be subtracted from the measured signalO
Finally, in the calibration the discs are moved together to zero distance9 by which means the circuit is informed about the ~ero position signal characteristic of the disc type~ It is thereby possible to form and check the correction coefficient stored in th~ circuit 17.

This way, a device according to thP invention can be advantageously scaled and cali~rated~ and because the measuring method is insen~itive to the reasons of the chanyes in the the discs' distance ~rom each other and to the quality and amount of the material between the discs, the calibration generally need not be carried out more than once, when installing the discs.

~ ~2~4~7~

Finally Figure 5 shows a cross-6ectional view taken along line V-of Fig. 1 of a real eituation where a part of a disc eection 19 has been provided around a geparate refiner-disc tooth 22 with machined grooves 20 and fastening plaaes 21 for the coils. The coils are fastened by screwing through point~ 21 ~crews that go through the disc, after which the coils are oovered by casting a solid plastic layer over them.

It is obvious to a person gkilled in the art that the invention is not restricted to the embodiments described abovet but can be varied within th~ scope of the following patent alaims.

Claims (19)

The embodiments of the invention in which an exclusive right or privilege is claimed are defined as follows:
1. A method for measuring the distance .delta. between discs in a refiner, each of said discs having at least one tooth, said method comprising:
generating a magnetic field by means of first coil means formed at least at one refiner-disc tooth of a first disc, said magnetic field being allowed to run at least partly through a second disc, the second disc comprising a tooth;
detecting, by means of a second coil means formed around the tooth of the first disc, the magnetic flux caused by the first coil means running over the distance between two opposite teeth of the first and second discs, respectively;
outputting a signal representing the detected magnetic flux; and interpreting the signal as a quantity that expresses distance .delta. between the teeth.
2. The method according to Claim 1, wherein the step of generating comprises the step of generating the magnetic field by a first coil wound around one disc tooth along at least part of its length and the step of detecting comprises the step of detecting the magnetic flux by a separate second coil wound around the one disc tooth.
3. The method according to Claim 1, wherein the step of generating comprises the step of generating the magnetic field by a coil which is wound to run through a groove between two teeth and through the rear side of the disc.
4. The method according to Claim 1, wherein the step of generating comprises the step of generating the magnetic field by a first coil wound around one disc tooth along at least part of its length and the step of detecting comprises the step of detecting the magnetic flux by a separate second coil wound around the same disc tooth.
5. The method according to Claim 1, wherein the steps of generating and detecting respectively comprise the steps of generating and detecting the magnetic field by separate coils which are wound around the same protruding part of a base plate of either disc along at least part of its length.
6. The method according to Claim 1, wherein the step of generating comprises the step of directing the course of the magnetic field generated by the magnetic coil with short-circuit coils installed at the disc.
7. The method according to Claim 1, further comprising the step of performing the above-listed steps of generating, detecting, outputting, and interpreting the distance .delta. between the discs of the refiner at more than one location.
8. The method according to Claim 1, wherein the step of generating comprises the step of feeding a saw-tooth voltage into the first coil means that generates the magnetic field.
9. The method according to Claim 1, wherein the step of outputting comprises the step of measuring, at the output of the second coil means that detects the magnetic field, the amplitude (U1) of a voltage signal that has the shape of a square wave.
10. The method according to Claim 1, further comprising the step of calibrating the measuring device comprising the steps of measuring the corresponding signal levels with the discs in the extreme positions in relation to each other and recording said signal levels into a memory.
11. A device for the implementation of Claim 1, said device comprises:

a first coil for the generation of a magnetic field said first coil being wound at one refiner-disc tooth of the refiner disc;
a second coil for the detection of the flux running over the distance between two opposite teeth wound to surround at least partly said refiner-disc tooth of said first coil;
an electronic circuit for the interpretation of the signal induced in said first coil.
12. The device according to Claim 11, wherein the first coil that generates the magnetic field and the second coil that detects the magnetic field are wound around the one refiner-disc tooth along at least part of its length.
13. The device according to Claim 11, the first coil that generates the magnetic field is wound to run through a groove between two teeth and through the rear side of the disc.
14. The device according to Claim 11, wherein the first coil that generates the magnetic field and the second coil that detects the magnetic field are wound around the same refiner-disc tooth along at least part of its length.
15. The device according to Claim 11, wherein the first coil that generates the magnetic field and the second coil that detects the magnetic field are wound around the same protruding part of a base plate of either disc along at least part of its length.
16. The device according to Claim 11, further comprising short-circuit coils installed at the refiner disc that direct the course of the magnetic-field.
17. The device according to Claim 11, further comprising several pairs of coils installed at the refiner disc that measure the distance (.delta.) between the discs of the refiner at more than one location.
18. The device according to Claim 11, further comprising a saw-tooth voltage generator for providing voltage to the first coil that generates the magnetic field.
19. The device according to Claim 11, wherein the electronic circuit comprises a rectifier, a reduction circuit, a modifying circuit, and a holding circuit for the background noise.
CA000549576A 1986-10-31 1987-10-19 Method and device for measuring the distance between the discs of a refiner Expired - Fee Related CA1274878A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI864443A FI80146C (en) 1986-10-31 1986-10-31 Method and apparatus for measuring the distance between the grinding wheels of a refiner
FI864443 1986-10-31

Publications (1)

Publication Number Publication Date
CA1274878A true CA1274878A (en) 1990-10-02

Family

ID=8523421

Family Applications (1)

Application Number Title Priority Date Filing Date
CA000549576A Expired - Fee Related CA1274878A (en) 1986-10-31 1987-10-19 Method and device for measuring the distance between the discs of a refiner

Country Status (10)

Country Link
US (1) US4878020A (en)
EP (1) EP0290487B1 (en)
JP (1) JPH01501093A (en)
AT (1) ATE67430T1 (en)
AU (1) AU597744B2 (en)
CA (1) CA1274878A (en)
DE (1) DE3773194D1 (en)
FI (1) FI80146C (en)
NO (1) NO172526C (en)
WO (1) WO1988003054A1 (en)

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Also Published As

Publication number Publication date
NO882906L (en) 1988-06-29
AU597744B2 (en) 1990-06-07
NO172526B (en) 1993-04-26
FI864443A (en) 1988-05-01
FI80146C (en) 1990-04-10
FI80146B (en) 1989-12-29
JPH01501093A (en) 1989-04-13
ATE67430T1 (en) 1991-10-15
AU8074687A (en) 1988-05-25
US4878020A (en) 1989-10-31
NO172526C (en) 1993-08-04
DE3773194D1 (en) 1991-10-24
EP0290487A1 (en) 1988-11-17
NO882906D0 (en) 1988-06-29
FI864443A0 (en) 1986-10-31
WO1988003054A1 (en) 1988-05-05
EP0290487B1 (en) 1991-09-18

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