CA1094191A - Device for measuring axial displacement of rotating machine parts especially for measurement during operation of the plate clearance in a disc refiner - Google Patents
Device for measuring axial displacement of rotating machine parts especially for measurement during operation of the plate clearance in a disc refinerInfo
- Publication number
- CA1094191A CA1094191A CA298,603A CA298603A CA1094191A CA 1094191 A CA1094191 A CA 1094191A CA 298603 A CA298603 A CA 298603A CA 1094191 A CA1094191 A CA 1094191A
- Authority
- CA
- Canada
- Prior art keywords
- disc
- indicia
- pair
- sensing means
- sensing
- 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
Links
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
- D21D1/00—Methods of beating or refining; Beaters of the Hollander type
- D21D1/20—Methods of refining
- D21D1/30—Disc mills
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/14—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring distance or clearance between spaced objects or spaced apertures
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
- G01D5/244—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing characteristics of pulses or pulse trains; generating pulses or pulse trains
- G01D5/247—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing characteristics of pulses or pulse trains; generating pulses or pulse trains using time shifts of pulses
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Length Measuring Devices With Unspecified Measuring Means (AREA)
- Crushing And Grinding (AREA)
Abstract
TITLE OF THE INVENTION:
DEVICE FOR MEASURING AXIAL DISPLACEMENT
OF ROTATING MACHINE PARTS, ESPECIALLY FOR
MEASUREMENT DURING OPERATION OF THE PLATE
CLEARANCE IN A DISC REFINER
ABSTRACT OF THE DISCLOSURE
A device for the measurement of the axial position of a rotating body comprises a sensor fixed near a preferably cylindrical surface of the body, coaxial with its rotational axis. The cylindrical surface comprises markings which may be two lines together forming an angle. The two lines are successively detected by the sensor when the body rotates.
The time difference between two successive detections will vary with axial displacement of the body a making such displace-ment measurable.
DEVICE FOR MEASURING AXIAL DISPLACEMENT
OF ROTATING MACHINE PARTS, ESPECIALLY FOR
MEASUREMENT DURING OPERATION OF THE PLATE
CLEARANCE IN A DISC REFINER
ABSTRACT OF THE DISCLOSURE
A device for the measurement of the axial position of a rotating body comprises a sensor fixed near a preferably cylindrical surface of the body, coaxial with its rotational axis. The cylindrical surface comprises markings which may be two lines together forming an angle. The two lines are successively detected by the sensor when the body rotates.
The time difference between two successive detections will vary with axial displacement of the body a making such displace-ment measurable.
Description
The invention rela-~es to the measurement of axial positions and displacements for rotating bodies, especially but not exclusively, to the measurement and control of the size of the disc clearance in a chip refiner.
In refining devices of this type there is a clearance be.ween two refining plates mounted on discs. Either one of the discs is stationary and the other rotates around a shaft perpendicular to the plate, or both of the discs rotate in opposite directions. The plates are provided with suitable patterns on their sides facing one another and the material which is to be ground up is usually fed in through a hole in the middle of one of the plates and after refining is taken out at the periphery of the concentrically rotating plates. The size of the clearance between the two plates is of course crucial to the refining results, and therefore there is as a rule some ~orm of device for controlling the same. The problem is complicated by the great forces involved, both in the form of centrifugal forces and in the form of pressure on the material which is being refined. One must also consider the effect of varying temperature on the unit, making it di~ficult to maintain a set clearance. Depending on the device~ the usual desired clearance is from one or two millimeters down to some tenths of a milli-meter. Because o F the forces involved, it can happen that the operating position for the plates corresponds to what is called "negative clearance", meaning tha-t the plates have been displaced so far towards one another that the positions of the rotating shafts have passed -the point at which the plates at rest would make metallic contact with one another.
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One purpose of the invention is now to ~chieve a device with wllich the clearance can be measured during operation.
Another problem encountered in clearances of this type ls wllat is usually called "out of tram", meaning that the plates are not parallel, so that the clearance varies along the periphery.
This is usually caused by one or both of the rotating shafts changing orientation, e.g. because of temperature gradients in the frame in which the shafts are journalled. If such an error, whiGll c.an be seen from the refining results, is corrected by movltlg tlle reining plates closer to one another, the plates can easily be brought into metal]ic contact so that they are damaged.
Therefore it is another purpose of the invention to achieve a device for measurement of clearance during operation, W]liC]l can be arranged so that the clearance can be measured at several points along the periphery.
According to the present invention there is provided a device for use in making out-of-tram and clearance measurements in C]lip refiners having first and second normally parallel and spaced apart coaxial discs~ at least said first disc being ~0 rotatable with a coaxial shaft having a longitudinally extending - a~is of rotation, comprising a pair of linear converging and cliverging indicia located on the periphery of said first disc d ~ositioned so that a plane normal to said axis of rotation intersects both indicia of said pair of indicia~ first sensing means positioned at a first stationary location substantially adjacent to the periphery of said first disc for sensing the passage of said pair of indicia past said first sensing means and generating a signal whenever one of said pair of indicia
In refining devices of this type there is a clearance be.ween two refining plates mounted on discs. Either one of the discs is stationary and the other rotates around a shaft perpendicular to the plate, or both of the discs rotate in opposite directions. The plates are provided with suitable patterns on their sides facing one another and the material which is to be ground up is usually fed in through a hole in the middle of one of the plates and after refining is taken out at the periphery of the concentrically rotating plates. The size of the clearance between the two plates is of course crucial to the refining results, and therefore there is as a rule some ~orm of device for controlling the same. The problem is complicated by the great forces involved, both in the form of centrifugal forces and in the form of pressure on the material which is being refined. One must also consider the effect of varying temperature on the unit, making it di~ficult to maintain a set clearance. Depending on the device~ the usual desired clearance is from one or two millimeters down to some tenths of a milli-meter. Because o F the forces involved, it can happen that the operating position for the plates corresponds to what is called "negative clearance", meaning tha-t the plates have been displaced so far towards one another that the positions of the rotating shafts have passed -the point at which the plates at rest would make metallic contact with one another.
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One purpose of the invention is now to ~chieve a device with wllich the clearance can be measured during operation.
Another problem encountered in clearances of this type ls wllat is usually called "out of tram", meaning that the plates are not parallel, so that the clearance varies along the periphery.
This is usually caused by one or both of the rotating shafts changing orientation, e.g. because of temperature gradients in the frame in which the shafts are journalled. If such an error, whiGll c.an be seen from the refining results, is corrected by movltlg tlle reining plates closer to one another, the plates can easily be brought into metal]ic contact so that they are damaged.
Therefore it is another purpose of the invention to achieve a device for measurement of clearance during operation, W]liC]l can be arranged so that the clearance can be measured at several points along the periphery.
According to the present invention there is provided a device for use in making out-of-tram and clearance measurements in C]lip refiners having first and second normally parallel and spaced apart coaxial discs~ at least said first disc being ~0 rotatable with a coaxial shaft having a longitudinally extending - a~is of rotation, comprising a pair of linear converging and cliverging indicia located on the periphery of said first disc d ~ositioned so that a plane normal to said axis of rotation intersects both indicia of said pair of indicia~ first sensing means positioned at a first stationary location substantially adjacent to the periphery of said first disc for sensing the passage of said pair of indicia past said first sensing means and generating a signal whenever one of said pair of indicia
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passes thereby and second sensing means positioned at a second stationary location, different from said first stationary loca-tion, substantially adjacent to the periphery of said first disc for sensing the passage of said pair of indicia past said second sensing means and generating a signal whenever one of said pair of indicia passes thereby, whereby the time interval between ; successive signals produced by said first and second sensing mcans can be used in making the out-of-tram and clearance measure-mcnts .
t0 Although the invention will now be described in connec-`tiOIl with an application with two discs rotating in opposite directions, it will be obvious to the skilled art worker that the same inventive idea is also applicable without major modifi-cations to measurement of a clearanceJ where one of the plates is stationary~ and the measurement according to the - 2a -`~
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invention is done on the rotating plate. The skilled art worker will see that the posi-tion of the second plate can in this case be determined in a number of different ways, and that the problem is thus greatly simplified since the stationary plate, although it can be deformed~ is at least standing still.
A non-limi-ting embodiment of -the invention will now be described with reference to the drawings.
Fig. 1 shows a portion of a chip refiner, showing the placement of a pair of sensors.
Fig. 2 is a sketch showing portions o~ the peripheral surfaces ofthe two discs, which are provided with line members to be sensed, preferably by magnetic sensors.
Fig. 3 shows an example of a simple circuit for determina-tion of clearance.
The example shown is based on a reiner of known type, e.g.
the model RSA 1300 manufactured b~ Sunds AB. Although the following description relates particularly to such a machine, it is obvious that the invention can be applied to many different types of units where de-termination of the axial position ~f rotating objects is desired. Although the inven-tion was developed in connection wi-th work relating to refining machines in the cellulose industry, it is obvious -that the principle of the invention is applicable to many other machine parts, in turbines for example.
Fig. 1 shows an outline of the basic arrangement of a chip refiner with two discs 3 and 4~ mounted on coaxial shafts 5 journa]led in bearings 6. Material to be refined is fed in through a screw device 7. Since this belongs to prior art~ it . , "
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will not be dealt with in more detail here. The present invention rela-tes to the measurement of the clearance between the plates on the discs 3 and 4. Two sensors 1 and 2 are arranged for this measurement, and they are disposed to sense special line members arranged on the peripheral edges of the discs.
Fig. 2 shows said line members on the peripheral edges of the discs. The lines consist of ferromagnetic bars which are attached to the peripheral casing or to the discs of non-magnetic material, possibly sunk into the same, at angles to theaxis of rotation, preferably about 4S~ although other angles are possible. T~e sensors are indicated as small circles in this figure which only shows portions of the peripheral casing surfaces of the discs. The directions of rotation are indicated lS by arrows. When the discs rotate, they will be sensed by the sensors 1 and 2 along the dash-do-t lines 20 and 21 respectively.
If, for example, disc 4 is moved axially a certain distance a, the sensing would now be done along the line 22.
Now observation of -this displacement is possible according to the invention, in spite of the fact that the disc is rotating, by virtue of the fact tha-t, as is shown in the figureg -the distance along the sensed peripheral line between the bars 12 and 13 is in this case smaller. ~The bars can of cour6e be placed so that the distance becomes greater ins-tead.) In the example shown, with undiminished speed, the -time interval between the respective detections of the two bars will be reduced, so that the displacement a i6 immediately calculable, if the angles of the bars in relation to the axis of ro-tation .
~ ~ , and the peripheral speed of the disc are known, Since the discs are usually made of austenitic and non-~agnetic stainless steel, it is easy to sense the passage of the ferromagnetic bars with magnetic sensors. Even lf the discs were magnetic it would of course be possible to sense the passage of the bars, if they are raised and the distance-dependence of the sensors is sufficiently great. As a rule, this does not present any problem, since most sensors of this type have characteristics which decrease by a factor lying somewhat between the square and the cube of the distance. In the embodiment which has been tested, a Phillips PR 9262 electro-magnetic sensor was used~ which worked excellently.
In the presently preferred embodiment there are two bars on each disc, which are screwed fast to the peripheral s~rfaces.
These surfaces are cylindrical with their axes coinciding with the axis of rotation, In view of the high rotational speed of the discs, it is of course necessary after screwing the bars down to rebalance the discs. The bars are rectangular and have the dimensions 5 x 10 x 75 mm. The circumference o the discs is approximately 4,~ mm, and the bars have a space between them of about 150 mm, measured from their centers. It is also possible to mount more than two bars around the circumference if desired, In order to be able to measure the clearance at several different poin-ts along the periphery, pairs of sensors 1,2 are 2S arranged at three different places, namely a-t the location shown in Fig. 1~ and at 90 therefrom in either direction. This is in order to be able to measure "out of tram" (not shown in the figure~, Other placements are of course conceivable, according ,, " ., ,:
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Pairs of sensors are arranged in holes in covers screwed onto -the casing around the discs (not shown). By vir~ue of the fact that the sensors are screwed into threaded holes in the covers, it is possible by screwing in or screwing out to adjust their position as to depth and thereby their distance to the respective rotating disc. The sensors are adjusted in this way to lie several millimeters above the bars (with the above-mentioned sensor from Phillips) a-t most 8-10 mm *rom the bars.
The bars should be protected from corrosion in a suitable manner, e.g. by treatment with an appropriate plastic lacquer.
One should also ~alvanically insulate between the disc and the bar, since galvanic corrosion can occur in this use.
The functional principle of the invention can best be seen from Fig. 2 partially showing the peripheral surfaces of the discs 3 and 4, with ferromagnetic bars 10 and 11, and 12 and 13 respectively. When the discs rotate, the sensors 1 and 2 will sense the bars along the circles 20 and 21, drawn with dash-dot lines. It will be assumed that the discs ro-tate at a constant r.p.m. and that the time intervals between the sensing of the two pairs of bars are tl and t2 respectively. It is obvious that if the right-hand disc 4 in the figur~ were to be moved to the left the distance a~ -the sensor 2 would instead sense along the line 22. It i5 immediately evident from the figure -tnat -the distance between the pair of bars along this line is shorter than the distance along line 21, so that the time interval for their passage in front of the sensor 2 is reduced. It is also immediately evident that the time difference is a linear :' :
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function of the displacement a. If the new time interval between the passage of the bars is now t4 instead of t2, it is easily seen that the dis-tance a can be calculated from the equation a = k(t2 - t4), where the constant k is only dependen-t on s constant geometric conditions.
I~ in the case aceording to Fig. 2 there is a cer-tain clearance Mdo, for which the time intervals tl and t2 respectively are measured, and then the time intervals t3 and t4 respectively~ the new clearance can be computed from the equation Md MdO ~ (kl(tl - t3) + k2( ~ 4 (1) or ~ d K + klt3 + k2t4 t2) if the constant K is determined from the computed values ~orthe case where the clearance is zero. If the geome-try is otherwise, for example if the angles ~etween the bars are in the opposite directions, then the signs in the equations will be reversed.
A relatively simple device for treating the signals from the sensors 1 and 2 is shown in Fig. 3. The sensors are each coupled to an individual means for measuring the time interval between the successive passages of the bars and giving off analog voltage signals which are proportional to the respective time intervals. These voltages are coupled to a precision resistor in such a manner that the two analog voltages are summed. The resistance is a potentiome-ter and one end of the resistance and the slidable contact are coupled to a digital voltmeter. By adjusting the setting of the slidable contact of the potentiometer it is possible to produce a value which :`
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differs from the magnitude of the clearance by a constant ~ac-tor.
This presupposes that the constants kl and k2 are equal, which is the case if in Fig. 2 the con~igurations of the bars are mirror images of one another. If this is not the case, the units 15 and 16 must be made adjustable to include the appropriate calibration constan-ts, Even the constant K in Equation (2) can be adjustable either in units lS and 16 or in uni-t 18.
The skilled art worker will see that this trea-tment of -the signals can be done in many different ways, either digitally or by analog. In the embodiment shown there was used ~or units 15 and 16 the Hewlett Packard 5300 A measurement system. This comprises a crystal-controlled oscillator and a scaler, which is turned on at the sensing o~ he first bar and is shut off at the sensîng of the second. During the intervening time interval, lS pulses are counted from the oscillator~ and the resulting counted number is presented at the ou-tput in the form of an analog voltage signal. The potentiometer 17 is a wire-wound precision potentiometer of Helipot manufacture, which provides an accurate setting of a calibration constant, e.g. so that the ~ readings on the voltmeter 18 are in millimeter units for variations in the clearance.
In the embodiment shown here the refiner motors are synchronous motors, as is usually the case to assure that ~e power factor in the load on -the electricity supply system will remain constant and not be too reactive. This means tha-t after the motors have been started and brought in-to synchronous operation with the mains frequency~ -then no special correction is required for varying r.p.m.'s. O-therwise it is necessary to .
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make a special correction for varying rotational speeds, suitably with a tachome~er on the motor shafts. The skilled art worker will see how such a correction can be carried ou-t.
As disclosed previously, in the arrangement described there are three different pairs of sensors with accompanying measure-ment equipment. This makes it possible to determine ~he size of the clearance at three different locations around the periphery and to thereby diagnose any obliqueness or "out of tram".
The described measuring device provides a measurement of the clearance during operation. This makes it possible, in addition to manual control, to automatically control the size of the clearance by return couplin~ to the means, which are known per se, by which the clearance is normally adjusted during operation. Previously it was necessary to control -the clearance based on the sensing of the axial positions of the shafts in relation to the machine frame. This causes obvious problems if one notes that the clearance should be set with an accuracy of better than one tenth of a mîllimeter~ that -the distance be-tween the points of measurement is on the order of two meters, and that the temperatures Oll the order of 100C are present in certain parts of the refiner at the same -time as other parts are possibly a-t room temperature. Therefore the -temperature gradients can cause considerable difficultiesj even if a-ttempts are made to solve these problems by careful temperature control of the machine frame. Measuring the clearance in situ elimina-tes most of these problems. Even a distortion of the machine frame, causing the disc shafts to be out of parallel, can be brought under control by arranging several pairs of sensors around the " : "
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discs in the manner described above.
It was mentioned in ~he introduction tha-t ~he plates~
primarily due to the ef~ect of the centrifugal force and the pressure o~ the ma-terial between the plates, do not have the same form as in the machine at rest. ~owever refining discs oi the type intended here usually have concave surfaces so that the clearance is least at t~le periphery. This means that chan~es are re~lected in a relevant manner when the clearance is measured according to the principle of the invention, since wha-t is measured .is the clearance at the periphery. This means tha-t -the problem occurring in many refiners according to the prior art, namely that one must work with a so-called negative clearance, is eliminated. ~ change in the pressure on the fed-in material or in its composition, which af~ects the size of the clearance in spite of the fact that the motor shafts do not move axially, .is thus measurable and controllable.
The invention has been described with re~erence to an application within the cellulose indus-tryO It can also be applied generally in order to solve problems relating to similar axial displacemen-ts o~ moving machine parts where it is not suf~icien-t to read the positions at res-t. The sk~led worker in the ~ield in question will see that the application in a particula~ case will require modifications of the application descr:ibed here. It is intended that -the following claims will also cover applica-tions which are similar and obvious to the skilled art worker. For example, it is not necessary that the line members be ferromagne-tic, with magnetic sensors. In many cases it is possible to use optical means instead, as the ,:.
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skilled art worker will see. Thus the sensing can be done for example by directing a light from a light-emitting diode against a line member and is reflected against a phototransistor, which then gives off a pulse every time a line member passes. Thus there are qui-te a number of conceivable detecting principles, for example capacitive sensing, sensing of the Foucault effect in line members with lower resistivity -than the machine parts on which they are mounted, etc~ Thus innumerable variations of the present inventive idea are possible, and it is impossible to mention more than a few ill~strative examples here.
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passes thereby and second sensing means positioned at a second stationary location, different from said first stationary loca-tion, substantially adjacent to the periphery of said first disc for sensing the passage of said pair of indicia past said second sensing means and generating a signal whenever one of said pair of indicia passes thereby, whereby the time interval between ; successive signals produced by said first and second sensing mcans can be used in making the out-of-tram and clearance measure-mcnts .
t0 Although the invention will now be described in connec-`tiOIl with an application with two discs rotating in opposite directions, it will be obvious to the skilled art worker that the same inventive idea is also applicable without major modifi-cations to measurement of a clearanceJ where one of the plates is stationary~ and the measurement according to the - 2a -`~
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invention is done on the rotating plate. The skilled art worker will see that the posi-tion of the second plate can in this case be determined in a number of different ways, and that the problem is thus greatly simplified since the stationary plate, although it can be deformed~ is at least standing still.
A non-limi-ting embodiment of -the invention will now be described with reference to the drawings.
Fig. 1 shows a portion of a chip refiner, showing the placement of a pair of sensors.
Fig. 2 is a sketch showing portions o~ the peripheral surfaces ofthe two discs, which are provided with line members to be sensed, preferably by magnetic sensors.
Fig. 3 shows an example of a simple circuit for determina-tion of clearance.
The example shown is based on a reiner of known type, e.g.
the model RSA 1300 manufactured b~ Sunds AB. Although the following description relates particularly to such a machine, it is obvious that the invention can be applied to many different types of units where de-termination of the axial position ~f rotating objects is desired. Although the inven-tion was developed in connection wi-th work relating to refining machines in the cellulose industry, it is obvious -that the principle of the invention is applicable to many other machine parts, in turbines for example.
Fig. 1 shows an outline of the basic arrangement of a chip refiner with two discs 3 and 4~ mounted on coaxial shafts 5 journa]led in bearings 6. Material to be refined is fed in through a screw device 7. Since this belongs to prior art~ it . , "
:
: . . : ~, . - ~ :
will not be dealt with in more detail here. The present invention rela-tes to the measurement of the clearance between the plates on the discs 3 and 4. Two sensors 1 and 2 are arranged for this measurement, and they are disposed to sense special line members arranged on the peripheral edges of the discs.
Fig. 2 shows said line members on the peripheral edges of the discs. The lines consist of ferromagnetic bars which are attached to the peripheral casing or to the discs of non-magnetic material, possibly sunk into the same, at angles to theaxis of rotation, preferably about 4S~ although other angles are possible. T~e sensors are indicated as small circles in this figure which only shows portions of the peripheral casing surfaces of the discs. The directions of rotation are indicated lS by arrows. When the discs rotate, they will be sensed by the sensors 1 and 2 along the dash-do-t lines 20 and 21 respectively.
If, for example, disc 4 is moved axially a certain distance a, the sensing would now be done along the line 22.
Now observation of -this displacement is possible according to the invention, in spite of the fact that the disc is rotating, by virtue of the fact tha-t, as is shown in the figureg -the distance along the sensed peripheral line between the bars 12 and 13 is in this case smaller. ~The bars can of cour6e be placed so that the distance becomes greater ins-tead.) In the example shown, with undiminished speed, the -time interval between the respective detections of the two bars will be reduced, so that the displacement a i6 immediately calculable, if the angles of the bars in relation to the axis of ro-tation .
~ ~ , and the peripheral speed of the disc are known, Since the discs are usually made of austenitic and non-~agnetic stainless steel, it is easy to sense the passage of the ferromagnetic bars with magnetic sensors. Even lf the discs were magnetic it would of course be possible to sense the passage of the bars, if they are raised and the distance-dependence of the sensors is sufficiently great. As a rule, this does not present any problem, since most sensors of this type have characteristics which decrease by a factor lying somewhat between the square and the cube of the distance. In the embodiment which has been tested, a Phillips PR 9262 electro-magnetic sensor was used~ which worked excellently.
In the presently preferred embodiment there are two bars on each disc, which are screwed fast to the peripheral s~rfaces.
These surfaces are cylindrical with their axes coinciding with the axis of rotation, In view of the high rotational speed of the discs, it is of course necessary after screwing the bars down to rebalance the discs. The bars are rectangular and have the dimensions 5 x 10 x 75 mm. The circumference o the discs is approximately 4,~ mm, and the bars have a space between them of about 150 mm, measured from their centers. It is also possible to mount more than two bars around the circumference if desired, In order to be able to measure the clearance at several different poin-ts along the periphery, pairs of sensors 1,2 are 2S arranged at three different places, namely a-t the location shown in Fig. 1~ and at 90 therefrom in either direction. This is in order to be able to measure "out of tram" (not shown in the figure~, Other placements are of course conceivable, according ,, " ., ,:
, , : ~, ; , :; , , to the suitability in the refiner which is to be equipped.
Pairs of sensors are arranged in holes in covers screwed onto -the casing around the discs (not shown). By vir~ue of the fact that the sensors are screwed into threaded holes in the covers, it is possible by screwing in or screwing out to adjust their position as to depth and thereby their distance to the respective rotating disc. The sensors are adjusted in this way to lie several millimeters above the bars (with the above-mentioned sensor from Phillips) a-t most 8-10 mm *rom the bars.
The bars should be protected from corrosion in a suitable manner, e.g. by treatment with an appropriate plastic lacquer.
One should also ~alvanically insulate between the disc and the bar, since galvanic corrosion can occur in this use.
The functional principle of the invention can best be seen from Fig. 2 partially showing the peripheral surfaces of the discs 3 and 4, with ferromagnetic bars 10 and 11, and 12 and 13 respectively. When the discs rotate, the sensors 1 and 2 will sense the bars along the circles 20 and 21, drawn with dash-dot lines. It will be assumed that the discs ro-tate at a constant r.p.m. and that the time intervals between the sensing of the two pairs of bars are tl and t2 respectively. It is obvious that if the right-hand disc 4 in the figur~ were to be moved to the left the distance a~ -the sensor 2 would instead sense along the line 22. It i5 immediately evident from the figure -tnat -the distance between the pair of bars along this line is shorter than the distance along line 21, so that the time interval for their passage in front of the sensor 2 is reduced. It is also immediately evident that the time difference is a linear :' :
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'.f-fl~
function of the displacement a. If the new time interval between the passage of the bars is now t4 instead of t2, it is easily seen that the dis-tance a can be calculated from the equation a = k(t2 - t4), where the constant k is only dependen-t on s constant geometric conditions.
I~ in the case aceording to Fig. 2 there is a cer-tain clearance Mdo, for which the time intervals tl and t2 respectively are measured, and then the time intervals t3 and t4 respectively~ the new clearance can be computed from the equation Md MdO ~ (kl(tl - t3) + k2( ~ 4 (1) or ~ d K + klt3 + k2t4 t2) if the constant K is determined from the computed values ~orthe case where the clearance is zero. If the geome-try is otherwise, for example if the angles ~etween the bars are in the opposite directions, then the signs in the equations will be reversed.
A relatively simple device for treating the signals from the sensors 1 and 2 is shown in Fig. 3. The sensors are each coupled to an individual means for measuring the time interval between the successive passages of the bars and giving off analog voltage signals which are proportional to the respective time intervals. These voltages are coupled to a precision resistor in such a manner that the two analog voltages are summed. The resistance is a potentiome-ter and one end of the resistance and the slidable contact are coupled to a digital voltmeter. By adjusting the setting of the slidable contact of the potentiometer it is possible to produce a value which :`
::: ., .
~o~
~~
differs from the magnitude of the clearance by a constant ~ac-tor.
This presupposes that the constants kl and k2 are equal, which is the case if in Fig. 2 the con~igurations of the bars are mirror images of one another. If this is not the case, the units 15 and 16 must be made adjustable to include the appropriate calibration constan-ts, Even the constant K in Equation (2) can be adjustable either in units lS and 16 or in uni-t 18.
The skilled art worker will see that this trea-tment of -the signals can be done in many different ways, either digitally or by analog. In the embodiment shown there was used ~or units 15 and 16 the Hewlett Packard 5300 A measurement system. This comprises a crystal-controlled oscillator and a scaler, which is turned on at the sensing o~ he first bar and is shut off at the sensîng of the second. During the intervening time interval, lS pulses are counted from the oscillator~ and the resulting counted number is presented at the ou-tput in the form of an analog voltage signal. The potentiometer 17 is a wire-wound precision potentiometer of Helipot manufacture, which provides an accurate setting of a calibration constant, e.g. so that the ~ readings on the voltmeter 18 are in millimeter units for variations in the clearance.
In the embodiment shown here the refiner motors are synchronous motors, as is usually the case to assure that ~e power factor in the load on -the electricity supply system will remain constant and not be too reactive. This means tha-t after the motors have been started and brought in-to synchronous operation with the mains frequency~ -then no special correction is required for varying r.p.m.'s. O-therwise it is necessary to .
:;;
make a special correction for varying rotational speeds, suitably with a tachome~er on the motor shafts. The skilled art worker will see how such a correction can be carried ou-t.
As disclosed previously, in the arrangement described there are three different pairs of sensors with accompanying measure-ment equipment. This makes it possible to determine ~he size of the clearance at three different locations around the periphery and to thereby diagnose any obliqueness or "out of tram".
The described measuring device provides a measurement of the clearance during operation. This makes it possible, in addition to manual control, to automatically control the size of the clearance by return couplin~ to the means, which are known per se, by which the clearance is normally adjusted during operation. Previously it was necessary to control -the clearance based on the sensing of the axial positions of the shafts in relation to the machine frame. This causes obvious problems if one notes that the clearance should be set with an accuracy of better than one tenth of a mîllimeter~ that -the distance be-tween the points of measurement is on the order of two meters, and that the temperatures Oll the order of 100C are present in certain parts of the refiner at the same -time as other parts are possibly a-t room temperature. Therefore the -temperature gradients can cause considerable difficultiesj even if a-ttempts are made to solve these problems by careful temperature control of the machine frame. Measuring the clearance in situ elimina-tes most of these problems. Even a distortion of the machine frame, causing the disc shafts to be out of parallel, can be brought under control by arranging several pairs of sensors around the " : "
: ~: : . :
- . . ; . .. . .
, : . - ~ :
, .. .
,, : : .
9~
discs in the manner described above.
It was mentioned in ~he introduction tha-t ~he plates~
primarily due to the ef~ect of the centrifugal force and the pressure o~ the ma-terial between the plates, do not have the same form as in the machine at rest. ~owever refining discs oi the type intended here usually have concave surfaces so that the clearance is least at t~le periphery. This means that chan~es are re~lected in a relevant manner when the clearance is measured according to the principle of the invention, since wha-t is measured .is the clearance at the periphery. This means tha-t -the problem occurring in many refiners according to the prior art, namely that one must work with a so-called negative clearance, is eliminated. ~ change in the pressure on the fed-in material or in its composition, which af~ects the size of the clearance in spite of the fact that the motor shafts do not move axially, .is thus measurable and controllable.
The invention has been described with re~erence to an application within the cellulose indus-tryO It can also be applied generally in order to solve problems relating to similar axial displacemen-ts o~ moving machine parts where it is not suf~icien-t to read the positions at res-t. The sk~led worker in the ~ield in question will see that the application in a particula~ case will require modifications of the application descr:ibed here. It is intended that -the following claims will also cover applica-tions which are similar and obvious to the skilled art worker. For example, it is not necessary that the line members be ferromagne-tic, with magnetic sensors. In many cases it is possible to use optical means instead, as the ,:.
.
.
skilled art worker will see. Thus the sensing can be done for example by directing a light from a light-emitting diode against a line member and is reflected against a phototransistor, which then gives off a pulse every time a line member passes. Thus there are qui-te a number of conceivable detecting principles, for example capacitive sensing, sensing of the Foucault effect in line members with lower resistivity -than the machine parts on which they are mounted, etc~ Thus innumerable variations of the present inventive idea are possible, and it is impossible to mention more than a few ill~strative examples here.
~11~
; .
.
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A device for use in making out-of-tram and clearance measurements in chip refiners having first and second normally parallel and spaced apart coaxial discs, at least said first disc being rotatable with a coaxial shaft having a longitudinally extending axis of rotation, comprising a pair of linear converg-ing and diverging indicia located on the periphery of said first disc and positioned so that a plane normal to said axis of rota-tion intersects both indicia of said pair of indicia, first sensing means positioned at a first stationary location substan-tially adjacent to the periphery of said first disc for sensing the passage of said pair of indicia past said first sensing means and generating a signal whenever one of said pair of indicia passes thereby and second sensing means positioned at a second stationary location, different from said first stationary loca-tion, substantially adjacent to the periphery of said first disc for sensing the passage of said pair of indicia past said second sensing means and generating a signal whenever one of said pair of indicia passes thereby, whereby the time interval between successive signals produced by said first and second sensing means can be used in making the out-of-tram and clearance measurements.
2. A device according to claim 1, further comprising third sensing means positioned at a third stationary location, differ-ent from both of said first and second stationary locations, substantially adjacent to the periphery of said first disc for sensing the passage of said pair of indicia past said third sens-ing means and generating a signal whenever one of said pair of indicia passes thereby.
3. A device according to claim 1, further comprising measuring means for measuring the time interval between succes-sive signals generated by said first and second sensing means.
4. A device according to claim 3, further comprising calculating means for calculating the out-of-tram and clearance measurements from the time interval between successive signals generated by said first and second sensing means.
5. A device according to claim 1, wherein said pair of indicia is a pair of ferromagnetic bars, said first and second sensing means are electromagnetic sensors, and the signals generated by said first and second sensing means are electric signals.
6. A device according to claim 1, wherein said second disc is rotatable, said second disc also including a pair of linear converging and diverging indicia located on the periphery of said second disc and positioned so that a plane normal to said axis of rotation intersects both indicia of said pair of indicia of said second disc, first sensing means positioned at a first stationary location substantially adjacent to the periphery of said second disc for sensing the passage of said pair of indicia of said second disc past said first sensing means of said second disc and generating a signal whenever one of said pair of indicia of said second disc passes thereby and second sensing means positioned at a second stationary location, different from said first station-ary location of said first sensing means of said second disc, substantially adjacent to the periphery of said second disc for sensing the passage of said pair of indicia of said second disc past said second sensing means of said second disc and generating a signal whenever one of said pair of indicia of said second disc passes thereby, whereby the time intervals between successive signals produced by said first and second sensing means of said second disc can be used in making the out-of-tram and clearance measurements.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE7702843-9 | 1977-03-14 | ||
| SE7702843A SE404658B (en) | 1977-03-14 | 1977-03-14 | DEVICE FOR SATISFACTION OF SHAFT MOVEMENT IN ROTARY MACHINE ELEMENTS, SEPARATE FOR SATURATION WHILE GOING ON THE GRINDING COLOR IN A TILE REFINOR OR GRINDER |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1094191A true CA1094191A (en) | 1981-01-20 |
Family
ID=20330705
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA298,603A Expired CA1094191A (en) | 1977-03-14 | 1978-03-09 | Device for measuring axial displacement of rotating machine parts especially for measurement during operation of the plate clearance in a disc refiner |
Country Status (4)
| Country | Link |
|---|---|
| CA (1) | CA1094191A (en) |
| DE (1) | DE2810787C2 (en) |
| FI (1) | FI780680A (en) |
| SE (1) | SE404658B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2204693B (en) * | 1987-05-14 | 1991-02-13 | Rolls Royce Plc | Turbomachine tip clearance sensor |
| DE4311689C2 (en) * | 1993-04-08 | 1997-02-13 | Roesler Roland Oberflaechen | Centrifugal vibratory grinding machine with gap adjustment |
| DE19622545A1 (en) * | 1996-06-05 | 1997-12-11 | Teves Gmbh Alfred | Movement measuring device |
| EP1749193B1 (en) | 2004-05-26 | 2014-03-05 | Nsk Ltd. | Rolling bearing unit with load measuring unit |
| SE537929C2 (en) * | 2014-02-11 | 2015-11-24 | Daprox Ab | Refiner and a method for refining cellulose materials |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1303994A (en) * | 1969-04-01 | 1973-01-24 |
-
1977
- 1977-03-14 SE SE7702843A patent/SE404658B/en unknown
-
1978
- 1978-02-28 FI FI780680A patent/FI780680A/en not_active Application Discontinuation
- 1978-03-09 CA CA298,603A patent/CA1094191A/en not_active Expired
- 1978-03-13 DE DE2810787A patent/DE2810787C2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2810787A1 (en) | 1978-09-21 |
| DE2810787C2 (en) | 1981-10-15 |
| SE7702843L (en) | 1978-09-15 |
| FI780680A (en) | 1978-09-15 |
| SE404658B (en) | 1978-10-23 |
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