Magnetic position marker

A magnetic marker, comprising a first fabric base sheet, a plurality of magnetized fibers attached to a surface of the first fabric base sheet by bonding means, and a second fabric base sheet secured to the surface of the first fabric base sheet so as to interpose the magnetized fibers between the first and second fabric base sheets. The magnetic marker using magnetized fibers can withstand repeated piercing which is encountered in the application for detecting the position of the ground fabric during the process of needling for the production of felt. The magnetized fibers are firmly secured between the two fabric base sheets, optionally reinforced by a multiplicity of perpendicularly arranged yarn, that the magnetized fibers can retain the capability to generate magnetic flux even after repeated use.

TECHNICAL FIELD 
The present invention relates to a magnetic position marker, and in 
particular to a magnetic position marker which is suitable for use in 
controlling the process of producing press felt intended for use in paper 
making machines. 
BACKGROUND OF THE INVENTION 
In a paper making machine, water is removed from a wet web of paper fibers 
between a series of mutually opposing rolls by compressing the paper fiber 
web, and press felt in the form of an endless belt having a relatively 
large width is wrapped around such rollers. The press felt is fabricated 
by passing woven ground fabric in the form of an endless belt around rolls 
including a motor driven roll and guide rolls, and entangling fibers of 
fiber web consisting of layers of woollen or synthetic fiber web with the 
ground fabric by needling as the ground fabric is passed under a needle 
head along with the fiber web placed thereon. 
During the process of needling, for the fibers to be favorably entangled 
with the ground fabric, it is necessary to adjust the stroke of needling, 
the density of needling and the feed speed of the ground fabric according 
to the number of turns which the ground fabric has made around the feed 
and guide rolls. Since the press felt must be highly smooth along the 
circumferential direction thereof without any steps or local 
irregularities, it is difficult to determine how many turns the press felt 
has made at any particular given time. Furthermore, since the time point 
of adjustment must coincide with the point of transition from one layer of 
fiber web to another, the detection of the rotation of the drive roll 
would not allow a sufficiently accurate detection of the position of the 
press felt during the process of needling. 
Conventionally, the operator placed a red thread or made a red mark with 
dye or ink in the ground fabric to identify a reference point on the press 
felt, and manually made necessary adjustments by visually determining the 
number of turns the ground fabric had made. Therefore, the operator was 
required to count the number of turns the press web had made and quickly 
make necessary adjustments upon detection of such a marker. This required 
a high level of concentration, and the quality of the press felt was 
highly dependent on the quality of the operator. Therefore, there has been 
a strong demand to automate the process of felt fabrication by needling. 
For automating the process of needling, it is preferable to be able to use 
a marker which can be easily detected with a sensor. However, 
conventionally known markers were inadequate because they tended to be 
quickly damaged by the process of needling in which the entire press felt 
including the sensor is repeatedly pierced by needles, and were rendered 
useless in a very short time. 
In Japanese patent laid open publication No. 03-124866 filed jointly by the 
applicant of this application and two other applicants, it is proposed to 
prepare a magnetic marker by arranging a plurality of magnetized fibers 
parallel to each other on a two-sided adhesive tape, and securing it to a 
lateral fringe of the ground fabric of press felt so that the movement of 
the ground fabric may be detected with a magnetic sensor during the 
process of needling, and the process of needling can be automated by using 
an output signal from the magnetic sensor which accurately indicates the 
movement of the ground fabric. Further, since the marker basically 
consists of magnetized fibers, the needling process is not hampered by the 
presence of the magnetic marker, and the marker can withstand the repeated 
piercing by the needles. 
However, since the magnetized fibers tended to be integrally combined with 
the ground fabric along with the fibers of fiber web as a result of the 
process of needling, the marker was not suitable for repeated use. Since 
the magnetized fibers typically consisting of amorphous alloy are highly 
expensive, it is more desirable if the magnetic marker can be used 
repeatedly. 
BRIEF SUMMARY OF THE INVENTION 
In view of such problems of the prior art, a primary object of the present 
invention is to provide a magnetic marker for an object such as an endless 
belt of such material as press felt which can retain its function as a 
marker even after being repeatedly pierced by needles, and is suitable for 
repeated use. 
A second object of the present invention is to provide a magnetic marker 
which is capable of producing and retaining a high level of magnetic flux 
even after being pierced by needles a large number of times. 
These and other objects of the present invention can be accomplished by 
providing a magnetic marker, comprising: a first fabric base sheet; a 
plurality of magnetized fibers attached to a surface of the first fabric 
base sheet by bonding means such as a two-sided adhesive tape; and a 
second fabric base sheet secured to the surface of the first fabric base 
sheet so as to interpose the magnetized fibers between the first and 
second fabric base sheets. Preferably, the magnetized fibers consist of 
amorphous metal or alloy which can produce a large magnetic flux. 
Since the magnetized fibers are firmly secured between the first and second 
fabric base sheets, the magnetized fibers can be retained at their 
original positions between the two fabric base sheets even after being 
repeatedly pierced by needles. In particular, because the magnetized 
fibers are prevented from being displaced and entangled with the ground 
fabric of the felt, the magnetic marker can be easily detached from the 
completed felt, and can be used again. Thus, the magnetized fibers can 
continue to generate a high level of magnetic flux even after repeated use 
without requiring any replacement for the magnetized fibers, and economy 
and reliability can be achieved at the same time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 1 and 2 generally show a press felt fabricating device 1 according to 
the present invention. The press felt which is produced by this device 1 
is used for removing water from wet paper in a paper making machine. 
Ground fabric 2 consisting of an endless belt of woven fabric having a 
relatively large width is passed around a plurality of rolls in a main 
body of a needle machine 3 so as to travel around them in clockwise 
direction as illustrated in FIG. 1. More specifically, the ground fabric 2 
is fed in the direction indicated by arrow A in FIG. 1 by being held 
between a drive roll 4 and a touch roll 5, and, after being fed out of the 
touch roll 5 and stored in a lower part of the device 1, is guided upward 
by a guide roll 6 to a brake roll 7 which, located above the guide roll 6, 
deflects the ground fabric 2 into a horizontal path extending between the 
brake roll 7 and a delivery roll 8 provided in an upper right part of the 
needle machine main body 3. The ground fabric 2 is fed along this 
horizontal path in the direction indicated by arrow B in FIG. 1, and, 
after being deflected downward by the delivery roll 8, is deflected 
horizontally toward the drive roll 4 by a guide roll 9 located under the 
delivery roll 8. In this way, the ground fabric 2 forms a complete loop 
which is passed around the rolls 4 through 9. 
Layers of fiber web 11 are individually placed over the upper surface of 
the ground fabric 2 near the brake roll 7, and are each conveyed jointly 
with the ground fabric 2 as it is conveyed between the brake roll 7 and 
the delivery roll 8. The fiber web 11 is prepared from wool or synthetic 
fibers by a card machine not shown in the drawing, and is typically folded 
over into several layers before it is placed over the ground fabric 2 as a 
single fiber web. 
An upper part of the main body of the needle machine 3 is provided with a 
needle punch unit 12 for entangling the fibers of the fiber web 11 with 
the ground fabric 2. This needle punch unit 12 is of a known structure, 
and comprises a needle head 13 having, on its lower surface, a 
multiplicity of needles arranged in a dense staggered arrangement and 
directed toward the upper surface of the ground fabric 2, a stripper plate 
14 interposed between the needle head 13 and the ground fabric 2 and 
provided with a multiplicity of through holes corresponding to the needles 
of the needle head 13, and a bed plate 15 guiding the lower surface of the 
ground fabric 2 and provided with holes similar to the holes of the 
stripper plate 14. 
A pair of sensor blocks 16 are provided each adjacent to either fringe of 
the ground fabric 3 as it is conveyed downward between the delivery roll 8 
and the guide roll 9 along a vertical path. As illustrated in FIG. 2, each 
of the sensor blocks 16 is guided by a guide rail 17 fixedly secured to 
one side of the main body of the needle machine 3 so as to be moveable in 
a lengthwise direction or in a direction perpendicular to the feeding 
direction of the ground fabric 2 along the reverse surface of the ground 
fabric 2. 
According to the present embodiment, a marker 18 is secured to a lateral 
fringe part of the ground fabric 2 for detecting the movement of the 
ground fabric 2, and another similar marker is secured to an opposite 
fringe part of the ground fabric 2 so that the two markers 18 may be 
substantially aligned with each other in the lateral direction. As 
illustrated in FIG. 3, each of the markers 18 consists of two parts, each 
part comprising a fabric base sheet 18a, a two-sided adhesive tape 18b 
securely attached to a surface of the fabric sheet 18a, and a layer of 
magnetized fibers 18c secured to the other surface of the adhesive tape 
18b. The two parts are joined together by bringing the surfaces of the 
adhesive tapes 18b carrying the magnetized fibers 18c together. The 
magnetized fibers 18c may consist of amorphous alloy fibers sold under the 
tradename of Sency by Unitika KK of Tokyo, Japan. The diameter of each of 
the magnetized fibers 18c may generally range between 15 micrometers to 
125 micrometers, and may be in the order of 30 micrometers when #32 or #36 
needles having a triangular crosss section are used. Further, in the 
present embodiment, the magnetized fibers are arranged in mutually 
parallel relationship. 
The marker 18 constructed in this manner may be secured adjacent and along 
a lateral edge of the ground fabric 2 by passing threads through the 
fringe of the ground fabric 2 and the marker 18. The movement of the 
ground fabric 2 can be detected by magnetically detecting the presence of 
the layer of the magnetized fibers 18c. 
Referring to FIG. 6, the guide rail 17 is fixedly secured, via mounting 
block 23, to a support plate 22 fixedly secured to the side portion of the 
main body of the needle machine 3 as mentioned earlier, and a rack 24 is 
fixedly secured to the support plate 22 parallel to and vertically spaced 
apart from the guide rail 17. A slider 26 which is guided by the guide 
rail 17 is provided with a sensor mounting plate 25 for integrally 
carrying the sensor block 16, and the sensor mounting plate 25 carries 
magnetic sensors 27 for magnetically detecting the marker 18. As 
illustrated in FIG. 5, there are four such magnetic sensors 27 arranged in 
a row extending perpendicularly to the feed direction of the ground fabric 
2 on each lateral side thereof. A part of the sensor mounting plate 25 
corresponding to the outer edge of the ground fabric 2 is provided with a 
proximity sensor 28 for measuring the width of the ground fabric 2, and a 
pair of photoelectric sensors 29 are arranged under the proximity switch 
28 and the magnetic sensors 27 for the tracking control of the sensor 
block 16 by photoelectrically detecting the edge of the ground fabric 2. 
The upper end of the sensor mounting plate 25 is integrally connected to a 
motor unit 31 incorporating a motor 32. The output shaft of the motor 32 
is connected to a pinion gear 33 via reduction gear unit, and the pinion 
gear 33 in turn meshes with the rack 24 which is fixedly secured to the 
mounting plate 22. Therefore, by driving the motor 32 in either direction, 
the sensor block 16 can be moved in a desired direction along the guide 
rail 17. The pinion gear 33 is coaxially connected to a slit disk 34 so 
that the travel of the sensor block 16 can be measured by 
photoelectrically counting radial slits provided in the slit disk 34 with 
a photoelectric rotation sensor 35. The sensors 27 through 29, the motor 
32 and the rotation sensor 35 are electrically connected to a control unit 
36 (FIG. 1) which controls the operation of the drive means for the needle 
punch unit 12 and the drive roll 4, and the brake torque of the brake roll 
7 for applying an appropriate tension to the ground fabric 2. 
Now the operation of the above described apparatus for fabricating press 
felt is described in the following. 
First of all, ground fabric 2 in the form of an endless belt is passed 
around the rolls 4 through 9, and a pair of markers 18 are attached to 
reference points on the side fringes of the ground fabric 2. The ground 
fabric 2 is then driven in the direction indicated by arrow A in FIG. 1 
with the drive roll 4 so that the needling of fiber web 11 into the ground 
fabric 2 may be carried out over the entire area of the ground fabric 2. 
Prior to this needling process, the sensor blocks 16 are positioned at 
their respective initial positions located on either side end of the main 
body of the needle machine 3. 
After the ground fabric 2 has started moving, either automatically or by 
manually operating a start switch of each sensor block 16 not shown in the 
drawings, each of the sensor blocks 16 is moved toward the corresponding 
edge of the ground fabric 2, and is thereafter made to follow the edge of 
the ground fabric 2 even in the presence of the lateral wiggling of the 
ground fabric owing to the tracking control of the sensor block 16 by the 
photoelectric sensors 29. Therefore, every time the ground fabric 2 makes 
a full turn around the series of rolls 4 through 9, the marker 18 passes 
near the corresponding magnetic sensors 27, and the reference point of the 
ground fabric 2 can be detected in a reliable fashion. Every time the 
magnetic sensors 27 have detected the marker 18 or every time the ground 
fabric has made a full turn, the sensor block 16 is moved inwardly so that 
the proximity sensor 28 may detect the edge of the ground fabric 2, and 
measure the width of the ground fabric 2 for the convenience of the 
evaluation of the quality of the press felt that is going to be produced. 
The fiber web 11 is integrally joined with the ground fabric 2 as the 
needles of the needle punch unit 12 are repeated pierced through the fiber 
web 11 and the ground fabric 2, and the fibers of the fiber web 11 get 
entangled with the ground fabric 2. Upon completion of the needling of the 
first layers of fiber web 11, second layers of fiber web 11 are placed 
thereon, and are likewise subjected to a similar needling process. This 
process is repeated 4 to 7 times before the final press felt is produced. 
During the process of needling, it is necessary to adjust the needling 
stroke and the needling density by the needle punch unit 12 according to 
the number of turns the ground fabric 2 has made and the different layers 
of the fiber web. According to the present invention, the number of turns 
the ground fabric 2 has made can be automatically detected by detecting 
the markers 18 with the magnetic sensors 27. The signals detected by the 
magnetic sensors 27 are supplied to the control unit 36 so that the drive 
means for the needle punch unit 12 and the drive roll 4 and the brake 
means for the brake roll 7 can be automatically controlled to optimum 
levels for each different turn which the ground fabric makes. 
Since the markers of the present embodiment consist of a plurality of 
extremely fine metallic fibers arranged in a mutually parallel 
relationship, the needles of the needle punch unit would not encounter any 
obstacle as they are pierced through the ground fabric, and, therefore, 
would not be damaged by the markers even after a long use. Further, since 
the metallic fibers of the markers 18 would also not be damaged or 
dispersed by the needles, they retain their capability as markers at all 
times. In particular, since the magnetized fibers 18c are firmly secured 
between the two fabric base sheets 18a via two-sided adhesive tapes 18b, 
the magnetized fibers 18c are prevented from being dislodged from the 
fabric base sheets 18a. 
In the case of the magnetic marker of the prior structure in which 
magnetized fibers are simply attached to the ground fabric of the felt via 
a two-sided adhesive tape, the magnetized fibers were required to be of a 
sufficiently small diameter because the magnetized fibers have a tendency 
to be detached from the marker during the process of needling and such 
loose magnetized fibers may cause undesirable irregularities on the 
surface of the fabricated felt unless the diameter of the magnetized 
fibers is extremely small. Obviously, magnetized fibers having an 
extremely small diameter require a special care in handling, and are 
relatively expensive to fabricate. 
However, according to the present invention, since the magnetized fibers 
are firmly secured between a pair of fabric base sheets, and would not be 
detached or otherwise exposed from the fabric base sheets, the magnetized 
fibers are prevented from being entangled with the ground fabric of the 
felt along with the fibers of the fiber web, and the quality of the 
produced felt would not be impaired in any way as a result of the use of 
such magnetic markers. Further, since the markers are magnetically 
detected, the markers may be detected even when the ground fabric is 
reversed for needling from the reverse surface of the ground fabric. 
According to the above described embodiments, since the magnetized fibers 
are initially secured to each of the surfaces of the two-sided adhesive 
tapes of the two halves of the magnetic marker before these two halves are 
combined, it is possible to secure a relatively large number of magnetized 
fibers within the magnetic marker, and to increase the magnetic flux 
produced therefrom as compared to the prior structure mentioned above. In 
this case, the magnetized fibers are 30 micrometers in diameter, and may 
be arranged at density of 15 to 70 fibers per cm, more preferably at the 
density of 34 fibers per cm. 
According to the present invention, the magnetized fibers are so firmly 
secured within the marker that the magnetized fibers would not spread out, 
and the magnetic flux would therefore not be reduced even after long use. 
Further, the structure of the present invention allows the use magnetized 
fibers having a wide range of diameter, and the cost of the magnetic 
marker can be reduced. When magnetized fibers of a relatively large 
diameter is used, it is possible to produced an accordingly large magnetic 
flux. 
As described above, the magnetic marker of the present invention can be 
detachably attached to the ground fabric with suitable means such as 
thread which would not hamper or get damaged by the process of needling 
without involving any substantial disintegration, it can be easily 
detached from the ground fabric for repeated use. 
The fabric base sheets 18a of the present embodiment measured 2 cm in 
width, 8 cm in length, and 3 mm in thickness, but may have other sizes and 
thicknesses for different applications. However, the thickness may be 
preferably between 0.8 and 4 mm, more preferably between 2 and 3 mm, for 
the process of fabricating press felt for paper making by needling. The 
fabric base sheets may be woven from durable fibers such as polyester 
using yarn of yarn number metric count 8 made by twisting a pair of yarns 
each of yarn number metric count 16. The weight of the fabric base sheets 
is typically 400 g/m.sup.2, and the magnetic marker is made by combining 
two of such fabric base sheets. The warp and weft of the fabric base 
sheets may consist of synthetic fiber yarns such as polyester and 
polyamide or natural fiber yarns such as cotton and wool, and may also be 
either woven, non-woven or knit fabric. 
When the magnetic marker is attached to a lateral edge of the ground fabric 
so as to be located externally of the edge as illustrated in FIG. 4, the 
fabric base sheet should have a relatively large weight so as to retain 
its shape. When the magnetic marker is attached to a lateral edge of 
ground fabric so as to be located internally of the edge, it is preferable 
to place fiber web over the ground fabric and secure the magnetic marker 
over the layer of the fiber web using thread along a lengthwise edge of 
the magnetic marker. In this case, the fabric base sheet should have a 
relatively small weight so as to able to pass through the gap between the 
stripper plate 14 and the felt which is being produced. When these 
possibilities a considered, the weight of the fabric base sheet should be 
between 150 and 800 g/m.sup.2, more preferably between 300 and 450 
g/m.sup.2. 
Optionally, as illustrated in FIG. 7, the magnetized fibers may be woven or 
otherwise combined with yarn, preferably spun yarn, extending 
perpendicularly to the orientation of the magnetized fibers. Preferably, 
the magnetized fibers may be woven with synthetic or natural spun fiber 
yarn using these two materials as weft and warp, respectively. This 
structure further increases the durability of the magnetic marker. 
Alternatively, the magnetized fibers may be combined with multi-filament 
yarn, mono-filament yarn, twisted matallic fiber yarn or metallic 
mono-filament yarn. The yarns may be combined not only by weaving but also 
by entangling them or otherwise combining them. For instance, polyester 
fibers may be placed perpendicularly over a multiplicity of magnetized 
fibers arranged in parallel orientation, and thermally welding the 
intersections of these fibers as illustrated in FIG. 7 in which like parts 
are denoted with like numerals. Alternatively, a bonding agent may be 
employed for joining such intersections. The use of perpendicularly 
extending fibers or yarn can even further improve the capability of the 
present invention to retain the magnetized fibers in the original 
arrangement without undesirable disturbances and spreading even after 
repeated use. 
According to the present invention, magnetized fibers are firmly secured 
between two fabric base sheets, optionally reinforced by a multiplicity of 
perpendicularly arranged yarn, the magnetized fibers can retain the 
capability to generate magnetic flux even after repeated use. 
Although the present invention has been described in terms of specific 
embodiments, it is possible to modify and alter details thereof without 
departing from the spirit of the present invention. For instance, the 
markers and the system for detecting the markers are useful not only in 
the production of press felt, but also in other production processes where 
detection of the position of an object is required.