Method and device for transferring a measurement signal from a revolving roll used in a paper making machine

A method and device for transferring a measurement signal from a revolving roll used in a paper making machine, in which detectors are arranged in the transverse direction of the roll, preferably uniformly spaced. Measurement signals generated by the detectors are passed to a measurement signal reading unit for reading the measurement of the detectors which is installed preferably at the end of the roll. From the measurement signal reading unit, the signals are transmitted wirelessly further as telemeter signals to a reading unit which is placed outside the roll and connected to a PC or equivalent computer. In the measurement signal reading unit for reading the measurement of the detectors, a transponder is arranged into which an unique code is coded for each detector. The signals are processed in the entire measurement process as analog signals. In the transfer of the telemeter signals between the unit for reading and measurement of the detectors and the reading unit placed outside the roll, a substantially low transfer frequency of an order of from about 100 kHz to about 150 kHz is employed.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for transferring a measurement 
signal from a revolving roll used in a paper making machine, in which 
detectors are arranged in the roll. The detectors are preferably uniformly 
spaced over a desired width of the roll in a transverse direction thereof. 
Measurement signals received from the detectors are passed to a 
measurement signal reading unit for reading and measuring the measurements 
signals generated by the detectors. The measurement unit is preferably 
installed at one end of the roll and transmits signals wirelessly as 
telemeter signals to a transponder reading unit which is placed outside 
the roll and is connected to a control unit, e.g., a PC or to an 
equivalent computer. 
The present invention also relates to a device for transferring measurement 
signals from a revolving roll used in a paper making machine. The device 
comprises detectors arranged in connection with the roll, and which are 
preferably uniformly spaced in the transverse direction of the roll. A 
measurement signal reading unit for reading measurement signals generated 
by the detectors is preferably installed at an end of the roll. Signals 
received from the measurement detectors are passed to the measurement 
unit. The device further includes a reading unit placed outside and 
exterior to the roll. The measurement signal reading unit for reading 
measurement signals from the detectors is arranged to transfer the 
measurement signals to the outside reading unit as telemeter signals, as 
well as a PC or an equivalent computer unit which is connected to the 
reading unit. 
In a number of different stages in the manufacture of paper, various nips 
are used through which the paper web is passed. Examples of such nips 
include roll nips and so-called extended nips in the dewatering presses in 
a paper machine, calendaring nips, and the nips in paper reels. The 
transverse distribution of the nip pressure in a dewatering press, i.e., 
the distribution of the nip pressure in the axial direction of the nip 
rolls, affects the transverse moisture profile of the web that is being 
pressed. 
In the prior art, it is possible to use adjustable-crown rolls or 
variable-crown rolls (so-called Kusters rolls) as the press rolls. 
Transverse distribution of the linear load in the press nip can be 
controlled by means of hydraulic loading members (in adjustable-crown 
rolls) or by means of a chamber or a series of chambers pressurized by 
means of hydraulic fluid (in variable-crown rolls). The hydraulic loading 
members that are used in adjustable-crown rolls are usually regulated on 
the basis of regulation signals given by moisture and/or grammage 
detectors. However, in view of overall control and regulation of the 
process, it would also be extremely important to determine and ascertain 
the factual values and distributions of the nip pressure both in the 
transverse direction and in the machine direction. An additional piece of 
information which is important in view of the control of the nip process 
is the width of the nip in the running direction of the web, i.e., in the 
machine direction, on whose basis it is possible to optimize the pressing 
process. This information is also a significant factor in the regulation 
of the calender and reel nips. As an exemplifying embodiment of a system 
of regulation of press nips, reference is made to the assignee's Finnish 
Patent No. 76,872 (corresponding to U.S. Pat. No. 4,791,863, the 
specification of which is hereby incorporated by reference herein). A 
measurement system similar to the present invention may be used in the 
environment of the sort described in this reference. 
Recently, various so-called extended-nip presses based on press shoes 
and/or on press bands have been introduced. In these extended nips, the 
width of the press zone in the machine direction is substantially larger 
than in roll nips proper. Also in extended-nip presses, the distribution 
of the nip pressure in the shoe and/or band nips both in the machine 
direction and in the transverse direction is an important parameter in 
view of the control of the pressing process. As an example with respect to 
extended-nip presses, reference is made to the assignee's Finnish Patent 
No. 82,092 (corresponding to U.S. Pat. No. 5,043,046, the specification of 
which is hereby incorporated by reference herein). 
In the prior art, various drum reels are known, in which, besides the reel 
drums, belt-support units have also been used. When reeling a paper web, 
it is also important to know the values of the nip pressure and its 
distributions both in the machine direction and in the transverse 
direction. As some examples of the reels that have been developed by the 
assignee, in connection with which it is possible to use the method and 
the device of the present invention, reference is made to the assignee's 
Finnish Patent Nos. 81,768 and 81,770 (corresponding to U.S. Pat. Nos. 
4,921,183 and 4,883,233, respectively, the specifications of which are 
hereby incorporated by reference herein). 
By means of the prior art methods and devices, it has been practically 
almost impossible to measure the distribution of the nip force both in the 
machine direction and in the transverse direction during production 
operation. However, this distribution is important in view of the 
regulation and control of the paper making process. Measurement of the nip 
forces from a revolving roll has been carried out under laboratory 
conditions, in which respect reference is made to the paper in the journal 
Paperi ja Puu --Paper and Timber 73 (1991): 5, by J. Koriseva, T. Kiema 
and M. Tervonen: "Soft Calender Nip: an Interesting Subject for Research 
and Measurement". In the method described in this paper, a number of 
detectors are installed on the roll, each of which detectors requires a 
telemetric equipment of its own and amplifiers of its own. Since the 
weight of the measurement system mainly consists of the weight of the 
telemetric equipment (about 1 kilogram per channel), this, together with 
the high cost of such equipment, sets a limit on the number of measurement 
channels and detectors in a roll of a factual paper machine or a paper 
finishing machine. Moreover, owing to the limited space, it is very 
difficult to install a large number of telemetric equipments on a 
revolving roll in a paper machine or finishing machine without changes in 
the construction of the machines. 
With respect to the prior art related to the present invention, reference 
is also made to published International Patent Application No. WO 91/13337 
(in the name of Beloit Corp.). 
In the prior art methods and devices for measuring nip forces, problems 
have also been encountered in the calibration of the detectors and in the 
transfer of the signal from a revolving roll. In the prior art, for the 
transfer of the signal, glide rings and similar arrangements have been 
used, and also telemetric equipments. However, it is a drawback that such 
arrangements are complicated and susceptible to interference. 
In order to eliminate the drawbacks of the prior art methods and device 
described above, in the assignee's Finnish Patent Application No. 914829 
(corresponding to published Finnish Patent No. 86,771 and U.S. Ser. No. 
07/960,725 issued as U.S. Pat. No. 5,383,371, the specification of which 
is hereby incorporated by reference herein), a method and device closely 
related to the present invention are described in which the measurement 
signals received from the different detectors are passed to a switching 
unit. Connectors in the switching unit are controlled based on the 
rotation of the roll, or equivalent, by means of a pulse generator or 
equivalent so that, through the switching unit, the signal of each 
measurement detector is alternatingly connected to a telemeter transmitter 
placed in connection with the revolving roll or equivalent. By means of 
the telemeter transmitter, the series of measurement signals are 
transmitted wirelessly to a stationary telemeter receiver placed outside 
the revolving roll or equivalent. 
One of the objects of the invention described in Finnish Patent Application 
No. 914829 is to provide a method and a device for measurement of the nip 
forces and nip pressures and the distribution of the same in roll and/or 
band nips that are used in the manufacture of paper so that the drawbacks 
discussed above can be substantially avoided. The measurement method and 
device of FI 914829 is suitable for on-line measurement of nip forces 
and/or nip pressures during production operation, and the transfer of 
signals from the revolving roll is solved in a simpler and more economical 
way so that the method is suitable for an environment of paper 
manufacture, which environment is quite demanding in this respect. 
Further, in the method and device of FI 914829, the problems related to 
the placing of the detectors on a nip roll and/or on a nip band are 
substantially solved. 
Even though the prior art methods and devices described above have proved 
quite good and operable in comparison with earlier systems, some unsolved 
problems have however remained. One particular problem consists of the 
high frequencies employed in the transfer of signals from the detectors to 
the measuring and reading units. Owing to the high frequencies, the signal 
transfer distance may have to be quite long, but the long transfer 
distance results in a relatively high susceptibility to interference. In 
the earlier telemeter systems, the signal to be transmitted was already 
converted to digital form at the roll-side end, the signal being then 
transferred in the digital form (see, e.g., the assignee's Finnish Patent 
Application No. 924138 of earlier date). Such a system has required a 
relatively high number of complex electronic components which are arranged 
on the roll. This has the consequence of the construction of the equipment 
having a large size and high weight, frequently even a few hundred grams, 
for which reason the roll has to be balanced separately for this purpose. 
Further, the prior art systems of have involved the problem related to the 
calibration of the measurement detectors. In the earlier systems, viz., 
the computer connected with the system, such as a PC or equivalent, had to 
include an extensive and complex calibration program, which in most cases 
was tailored for the specific case, in order that it was possible to 
calibrate the detectors. The special required tailoring of a program also 
constitutes an important cost factor. 
OBJECTS AND SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a method 
and device more advanced than the methods and devices described in the 
assignee's Finnish Patent Applications of earlier dates (Nos. 914829 and 
924138), so that, compared with the methods and device of these earlier 
patent applications, the method and device of the present invention are 
simpler, easier to operate, more reliable in operation, and more 
versatile. In particular with respect to the electronics, in the present 
invention, attempts have been made to provide an embodiment that is 
simpler and also involves lower costs in comparison with the assignee's 
earlier inventions. 
It is a further object of the present invention to provide a new and 
improved measurement system that can be controlled in a simple way during 
operation of the machine from outside the revolving roll so that, if 
necessary, measurement data and calibration data can be supplied to the 
measurement system from outside the roll and measurement data can be 
transferred from the roll wirelessly to the outside system in this manner, 
it is favorably possible to feed the measurement data into the regulation 
system of the roll so that, in some cases, a closed regulation circuit can 
be formed. 
It is another object of the present invention to provide a new and improved 
method and device for transferring measurement signals from detectors 
arranged on a roll to a remote control unit in which a low transfer 
frequency is used. 
In view of achieving the objects stated above and others, in the method in 
accordance with the present invention, a transponder is arranged in a 
measurement signal reading unit which reads and processes the measurements 
signal generated by the detectors. The transponder is provided with a code 
representing each of the detectors. Signals from the detectors are 
processed in the entire measurement process as analog signals. During the 
transfer of the telemeter signals between the measurement signal reading 
unit for reading the measurements of the detectors and a transponder 
reading unit placed outside the roll, a substantially low transfer 
frequency of an order of from about 100 kHz to about 150 kHz is employed. 
The device in accordance with the present invention comprises a transponder 
in itself known which is coded and arranged in the unit for reading and 
measurement of the detectors. The transponder comprises means to process 
the signals received from the measurement detectors as analog signals, and 
in pulse form, the signals being transmitted in pulse form from the 
transponder to an antenna of the transponder reading unit situated 
exterior to the roll. The frequency of transfer of the telemeter signals 
between the measurement signal reading unit for reading the measurements 
of the detectors and the transponder reading unit placed outside the roll 
is arranged to be substantially low, e.g., of an order of from about 100 
kHz to about 150 kHz. The transponder comprise means to transmit the 
telemeter signals at these low frequencies. Although the specified range 
of frequencies is preferred,other transfer frequencies may also be used in 
connection with the transponder herein. 
By means of the present invention, compared with the prior art devices, a 
number of advantages are obtained, of which the following advantages are 
expressly stated. Compared with the prior art, the components included in 
the system of the present invention are very small and have a low weight 
so that they can also be fitted easily at the roll-side end without having 
to balance the roll on their account. The power requirement of the system 
is very little. The supply of current can be accomplished by means of a 
very small battery because the system is not active all the same time. The 
system is not activated until a separate command for this purpose is given 
from the receiving end, i.e., the reading unit or the control means via 
the reading unit. The measurement unit otherwise remains in a passive 
state conserving electricity. 
The measurement signal is transferred in the system in accordance with the 
present invention as an analog signal and at a very low frequency (the 
transfer frequency is of an order of from about 100 kHz to about 150 kHz, 
preferably 130 about kHz). The signal to be transferred is FSK-modulated 
(FSK=Frequency Shift Keying), in which case the transfer of the signal 
takes place as an analog signal and in pulse form. By means of this 
arrangement, the transfer of information can be made substantially free of 
interference. When the signal is converted to pulse form in the 
measurement unit, any interference can be easily filtered out, in which 
case it is possible to read the main frequency alone. 
In the system in accordance with the present invention, at the roll-side 
end, a transponder is used, one of whose advantages over the earlier 
systems is the ease of calibration of the detectors. This is based on the 
fact that, in the transponder, it is possible to assign an individual and 
unique code for each detector, by means of which code it is then simple to 
compare the calibration of each detector. The possibility of coding also 
simplifies and facilitates the use of the system, by means of the computer 
or other control means, such as a PC (personal computer) or equivalent, 
connected to the system. Through the read/write unit of the transponder, 
it is possible to give the transponder a command to read a detector of a 
certain code alone. As the detectors in the system, it is possible to use 
PVDF-type film detectors or, for example, strain gauges or equivalent. 
Further advantages and characteristic features of the invention will come 
out from the following detailed description of the invention.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the accompanying drawings wherein like reference numerals 
refer to the same elements, FIG. 1 is a schematic side view of a press nip 
N in a dewatering press of a paper machine. The nip N is formed between 
the rolls 10 and 13. In the press nip N, water is removed out of a web W 
which is passed into the nip N on support of a press felt 12. The upper 
roll, roll 10, in the dewatering press has a smooth outer face 10' and is 
provided with an elastic coating 11. Onto the lower roll, roll 13, in the 
dewatering nip, a hollow face 13' has been formed, into which water can be 
removed out of the press felt 12. 
FIG. 2 is a schematic illustration of the distribution of the compression 
pressure P.sub.M in the press nip N in the machine direction l. The 
maximum value of the compression pressure P.sub.M is denoted by the 
reference P.sub.max. The nip N as shown in FIG. 1 may also represent a 
calendaring nip, in which case a press felt 12 is not used and in which 
case, e.g., the roll 13 is a hard-faced roll and the roll 10 is a 
calendaring roll provided with a soft coating, such as a polyurethane 
coating 11, so that the nip N is a so-called soft calendaring nip. 
FIG. 3 illustrates schematically the distribution of the compression 
pressure P.sub.T in the nip N in the transverse direction, i.e., in the 
axial direction of the rolls 10 and 13. The transverse width of the paper 
web W and of the nip N is denoted by reference L.sub.O. The transverse 
distribution of the compression pressure P.sub.T affects the dry solids 
content of the web in dewatering nips, the caliper and smoothness of the 
web in calendaring nips, and the uniformity and the hardness profile of 
the reel in reeling nips. These are important process quantities, so that 
the distributions P.sub.M and P.sub.T of the nip forces and nip pressures 
are important parameters for the regulation and control of the paper 
making process. 
FIG. 4 is a schematic illustration of the main principles of the 
measurement arrangement in accordance with the present invention as 
applied to one of the rolls 10 that form the press nip, the roll 20 being 
provided with an elastic coating 11, e.g., of polyurethane. A number of 
measurement detectors 5 are arranged inside the coating 11, and are 
preferably arranged to be uniformly spaced in the axial direction of the 
roll. By means of such a series of detectors 5 arranged at different 
circumferential positions on the roll, it is possible to measure both the 
distribution P.sub.M of the nip pressure in the machine direction and the 
transverse distribution P.sub.T of the nip pressure. The transverse nip 
pressure is measured at the points corresponding to the number of the 
detectors 5 in the transverse direction. The detectors 5 may be attached 
either directly to the body of the roll 10 or may be inlaid into the 
coating 11, e.g., between different layers in the coating. In some 
particular cases, it is possible to arrange the detectors 5 directly on 
the outer face of the roll. The detectors 5 may also be arranged in 
several positions along the circumference of the roll to provide 
measurements in the machine direction of the roll. 
Measurement signals are passed from the detectors 5 along cables 6 to a 
unit 2 for reading the measurement of the detectors, referred to as a 
measurement signal reading unit. Unit 2 is fixed to the end of the roll 
near the roll axle 18. As shown in FIG. 5, the measurement signal reading 
unit 2 for reading the measurement signals generated by the detectors 
includes a voltage/frequency converter 21, through which signals 
representative of, e.g., the pressure measurements from the detectors are 
transferred further to the signal processing/analyzing electronics unit 22 
integrated in the same unit 2. In the signal processing and analyzing 
electronics unit 22, the signal is modulated by means of a frequency 
modulator to FM-modulation into so-called FSK-modulated pulse form 
(FSK=Frequency Shift Keying). The signal, which has been converted to this 
form, is transferred further into the transponder 23, which is integrated 
in the same unit 2 and capable of processing the FSK-modulated 
pulse-formed signal. The transfer of the signal is constantly analogous, 
and it is at no stage converted to digital form. The analog signal is just 
converted to pulse form in the measurement signal reading unit 2 for 
reading the measurements from the detectors, in which case it is easy to 
filter off any interference so that the main frequency can be read. 
The transponder 23 is of the read/write type and is arranged to both 
receive and transmit signals. From the transponder 23, the signal is 
transferred telemetrically to a transponder reading unit 3 by means of an 
antenna 4. 
As shown in FIG. 4, the transponder reading unit 3 is attached to the frame 
14 of the bearing housing of the roll 10. The antenna 4 may be attached to 
a face of the frame 14 of the bearing housing of the roll 10. In the 
telemetric signal transfer, a low transfer frequency is used, which is 
preferably of an order of about 130 kHz. The transponder reading unit 3 
includes the electronics necessary for data transfer and, e.g., a 
frequency/voltage converter, by whose means the transferred signal is 
converted back to voltage form. The signal is converted to voltage form 
because the PC computer 7 can process such a voltage form. From the 
transponder reading unit 3, the signal is transmitted to the PC 7 along a 
cable 8, so that the distance from the transponder reading unit 3 to the 
PC 7 does not constitute a limiting factor in the system. 
The transponder 23 is a commercially available component which has a very 
small size and low weight, and is manufactured and marketed, e.g., by 
Texas Instruments Corp. under the trade mark TIRIS. Such a transponder 23 
can be coded so that it is possible to code (assign a code to) consisting 
of a number of several digits, e.g., 20 digits, for each detector 5. In 
such a case, the calibration of the detectors 5 can be carried out easily 
and simply, because the calibration of each detector 5 can be compared 
with the number coded in the transponder 23. Thus, the PC 7 does not have 
to contain a large and complex calibration program for the detectors 5. 
It is another advantage of the present invention that the use of the system 
in accordance with the invention is very easy and simple, among other 
things, especially because of the fact that the transponder 23 can include 
a code of its own for each detector 5. Since both the measurement signal 
reading unit 2 for reading the measurements of the detectors and the 
transponder reading unit 3 are of the read/write type, from the PC 7, 
through the transponder reading unit 3, the transponder 23 can be given a 
command to read exclusively the detector 5 that has a certain code. In 
such a case, the PC 7 may include, e.g., a program that gives commands to 
read the detectors 5 in a certain sequence or at certain intervals. 
Two-way communications are thus provided. 
The power consumption of the measurement electronics is very little, 
because the system is not active all the time. The system is, viz., not 
activated until a separate command is given for activation from the 
signal-receiving end (the reading unit or the control means coupled to the 
receiving unit). Thus, the current supply can be arranged by means of a 
very small battery having a corresponding low weight, and which can be 
fixed in a simple manner to the roll end in connection with, or at the 
vicinity of, the measurement signal reading unit 2 for reading and 
measurement of the detectors. The detectors 5 can be made favorably out of 
a PVDF-film (PVDF=polyvinylidenedifluoride), which is a piezoelectric 
film. The PVDF-film is well suitable for a power or pressure detector 
especially because, by means of such a film, with a force of just tens of 
newtons an output voltage of the volt level is already obtained. As the 
detectors, it is indeed also possible to use, e.g., strain gauges or 
other, corresponding detectors of this type that are commonly used. 
Besides measuring pressures and forces, the system of the present invention 
can also be applied, e.g., to measure temperature at objects at which such 
information is needed. Some possible objects of this type of application 
are also, e.g., the headbox of a paper machine, in which the system can be 
used for measuring the uniformity of the lip profile. Further, the system 
can be applied, e.g., to monitoring the condition of bearings, in which 
case the measurement can be carried out, e.g., as measurement of the 
vibration level. The measurement system in accordance with the present 
invention can also be arranged to collect information constantly and at 
certain intervals. In such a case, when desired, it would be possible to 
look via the PC 7 what has happened in the object to be measured within a 
certain period of time. In such a case, the measurement system would 
operate in the way of a "black box". 
Thus, in accordance with the invention, individual codes for each detector 
can be stored in the transponder and each of the detectors can be 
calibrated based on the stored individual codes. Moreover, during 
measurement operations, specific ones of the detectors can be identified 
by means of the individual codes so that measurements signals from the 
identified detector can be read and processed. 
The examples provided above are not meant to be exclusive. Many other 
variations of the present invention would be obvious to those skilled in 
the art, and are contemplated to be within the scope of the appended 
claims.