Abrasion detector for a rapier band

In detention of abrasion on a rapier band controlled in reciprocation by a rapier guide, the principal of detection is closely related to the critical abrasion (.alpha.) of the rapier band and the system calls for no substantial modification in construction of the rapier band in production. In a first embodiment, a longitudinal channel of a depth greater then the critical abrasion is formed in the guide face of the rapier guide so that an abrasion sensor attached to the rapier guide detects the dimension of a non-abraded region on the rapier guide projecting into the channel. In a second embodiment, a photoelectric sensor is attached to the rapier guide so that its detection beam passes through the rapier band at a distance of .beta. from the guide face, .beta. being equal to a sum of the critical abrasion (.alpha.) and the initial gap between the rapier band and the guide face of the rapier guide. The critical abrasion (.alpha.) of the rapier band can be easily and freely adjusted by end users only by changing the position of the sensor or sensors.

BACKGROUND OF THE INVENTION 
The present invention relates to an abrasion detector for a rapier band on 
a rapier loom, and more particularly relates to an improvement in 
detection of abrasion of a rapier band used for reciprocation of a rapier 
head on a rapier loom. 
In general on a rapier loom, each weft is inserted into an open shed by 
means of a rapier head, i.e. an weft gripper, reciprocating in the weft 
direction. The rapier head is driven for reciprocation by a rapier band, 
i.e. a tape, which cooperates with an oscillating band wheel, i.e. a 
driving wheel. 
In the following description, the term "critical abrasion" refers to a 
limit of abrasion of a rapier band beyond which the rapier band cannot 
exhibit its expected function. Generally, the critical abrasion of a 
rapier band is 1 mm or smaller. In practice, however, the critical 
abrasion of a rapier band is not fixed but more or less varies depending 
upon process conditions and/or user's requirements. The term "guide face" 
refers to the face of a rapier guide which causes abrasion of a rapier 
band through its direct surface contact. 
A wide variety of systems have been developed for detection of abrasion of 
rapier bands. In most cases, some modifications are applied to rapier 
bands. One typical example disclosed in Japanese Patent Laid-open Hei. 
2-14045 on "A strap for controlling movement of an weft gripper on a 
shuttleless loom. In the case of this prior art system, a strap is 
embedded in a rapier band while extending in the longitudinal direction of 
the latter. The strap is made of a material which allows transmission of 
optical, electric or magnetic signals. The system further includes a 
detection head which is arranged in a face to face relationship to the 
rapier band incorporating the above-described strap. The depth of the 
strap embedded in the rapier band is chosen so that the strap is exposed 
on the surface of the rapier band when abrasion of the latter exceeds the 
prescribed critical abrasion. Surface exposure of the strap is sensed by 
the detection head and translated into accurance of excessive abrasion. 
In the case of this prior art system, incorporation of the separate strap 
into the rapier band causes significant rise in cost due to its 
complicated construction. Since a rapier band is a sort of consumative 
product, its high production cost is a serious disadvantage in marketing. 
Further, since the critical abrasion is in general very small in 
dimension, accuracy in detection is greatly swayed by accuracy in 
production of the strap and/or accuracy in incorporation of the strap in 
the rapier band. As a result, no high degree of reliability in detection 
is in general expected. The strap is embedded into the rapier band during 
production of the latter. Stated otherwise, the critical abrasion of the 
rapier band is fixed at the stage of production and no free adjustment by 
users is accepted. 
SUMMARY OF THE INVENTION 
It is the basic object of the present invention to enable detection of 
rapier band abrasion with high degree of reliability and no substantial 
modification in construction of a rapier band itself. 
It is another object of the present invention to enable free adjustment in 
critical abrasion of a rapier band even by users. 
In accordance with the first basic concept of the present invention, a 
longitudinal channel is formed in the guide face of a rapier guide facing 
an associated rapier guide, the depth of the channel is set greater than 
the prescribed critical abrasion of the rapier band, and a critical 
abrasion sensor is attached to the rapier guide. The channel is most 
generally defined by a pair of side walls and a bottom wall. The channel 
may be defined by a side wall and a bottom wall. The channel may further 
has a bottomless construction. It is only required that the guide face of 
a rapier guide should have a width region not contacting an associated 
rapier band. 
In the case of the above-described construction, abrasion of the rapier 
band advances during long use in a width region or regions in contact with 
the guide face of the rapier guide but no abrasion starts in the width 
region corresponding in position to the channel in the guide face of the 
rapier guide. As a result, a longitudinal crest is developed on the second 
width region of the rapier band which projects into the channel in the 
guide face of the rapier guide. When the height of the longitudinal crest 
equals the critical abrasion, presence of such a longitudinal crest is 
detected by the critical abrasion sensor. The channel in the guide face of 
the rapier guide spans a prescribed distance in the longitudinal direction 
of the rapier guide so that a longitudinal crest is developed on the 
rapier band in the width region corresponding to the channel. It is not 
always required that the channel should span the entire length of the 
rapier guide. At acceleration of a rapier band, only one part of the 
rapier band comes into sliding contact with the guide face of an 
associated rapier guide. When the channel in the guide face spans the 
entire length of the sliding contact, absence of the guide face in the 
region of the channel develops a longitudinal crest on the surface of the 
rapier band. 
In accordance with the second basic concept of the present invention, a 
photoelectric sensor is attached to a rapier guide in an arrangement such 
that the axis of a detection beam from the photoelectric sensor should 
pass an associated rapier band at a position of .beta. from the guide face 
of the rapier guide, .beta. being equal to the sum of the critical 
abrasion of the rapier band with the initial gap between the rapier band 
and the guide face of the rapier guide. 
In the case of this construction, the detection beam is intercepted by the 
rapier band as long as its abrasion falls short of the critical abrasion. 
Once its current abrasion exceeds the critical abrasion, interception by 
the rapier band disappears thereby enabling abrasion detection.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in FIG. 1, a rapier band 2 is driven for receiprocation through 
its engagement with a band wheel 1 arranged on one side of a loom for 
transportation of a rapier head in the weft direction. Curved and linear 
rapier guides 3 and 8 are arranged to properly control the reciprocation 
of the rapier band. For drive engagement with the rapier band 2, a number 
of teeth 11 project radially on the periphery of the band wheel 1 and a 
number of corresponding openings 23 (see FIG. 5) are formed in the rapier 
band 2 at substantially equal intervals along the length thereof. As the 
band wheel 1 rotates, teeth-opening engagement translates the wheel 
rotation into corresponding band reciprocation. 
In accordance with the above-described first concept of the present 
invention, a longitudinal channel is formed in the guide face of a rapier 
guide facing an associated rapier band, the depth of the longitudinal 
channel is set greater than the prescribed critical abrasion (.alpha.) of 
the rapier band, and a critical abrasion sensor is attached to the rapier 
guide 3 or 8. 
One embodiment of the abrasion detector in accordance with the present 
invention is shown in FIG. 2, in which a pressure sensor 4 is used for the 
critical abrasion sensor. A longitudinal channel 32 is formed in the guide 
face 31 of a rapier guide 3 about the middle of its width. In the case of 
the illustrated example, the channel 32 is formed through the entire 
thickness of the rapier guide 3 and the pressure sensor 4 is inserted 
firmly into the channel 32. The pressure sensor 4 is positioned such that 
its detection head is at a distance of .alpha. (the critical abrasion) 
from the guide face 31 of the rapier guide 3. In the case of the 
illustrated example, the channel 2 spans substantially the entire length 
of the rapier guide 3. Because the rapier band 2 is prone to sliding at 
end "a" of rapier guide 3, it is preferred to arrange a sensor 4 near end 
"a". 
During long use of the rapier band 2, abrasion gradually advances in the 
width regions in sliding contact with the guide face 31 of the rapier 
guide 3 and no abrasion starts in the other width region out of sliding 
contact with the guide face 31. As a result, the working surface of the 
rapier band 2 assumes a condition such as shown in FIG. 5. More 
specifically, a non-abraded center regions 21 and abraded side regions 22 
are present on the working surface of the rapier band 2 and the 
non-abraded region 21 takes the form of a longitudinal crest which 
projects into the channel 32 in the rapier guide 3. Development of such a 
longitudinal crest, i.e. the non-abraded region 21, is shown in FIGS. 3A 
and 3B. When the height of the crest, i.e. the non-abraded region 21, 
equals the critical abrasion (.alpha.), the top of the crest comes in 
contact with the detection head of the pressure sensor which thereupon 
detects the fact that abrasion of the rapier band has reached the critical 
level. 
The channel 32 may span a part of the length of the rapier guide 3. As 
stated above, the rapier band 2 is liable to perform sliding contact with 
the guide face 31 of the rapier guide 3 near the end "a" during 
acceleration. When the channel 32 spans only the longitudinal section near 
the end "a" in contact with the rapier band, a crest-like, non-abraded 
region 21 can be also developed on the working surface of the rapier band 
2. 
The pressure sensor 4, i.e. the critical abrasion sensor, is activated 
basically during running of the loom. It may be activated, however, once 
every prescribed number of picks or once every prescribed length of time. 
In particular, it is preferable to activate the critical abrasion sensor 
during acceleration of the rapier band 2 between a prescribed crank angles 
for reciprocation of the rapier band 2. 
Detection can be carried out when the loom is out of running too. In this 
case, a longitudinal channel is formed in the guide face of the rapier 
guide 8 and the pressure sensor 4 is arranged therein. A retractable 
roller is arranged below the rapier band 2. When the loom ceases its 
running, the roller projects to press the lower surface of the rapier band 
2. In addition to the one end "a" of the rapier guide 3, the rapier band 2 
tends to slide near the other end "b" of the rapier guide 3. An additional 
pressure sensor may be arranged near this end "b" of the rapier guide 3 so 
that at least one of the pressure sensors should alert occurance of the 
critical abrasion. 
As a substitute for the pressure sensor 4 in FIG. 2, a photoelectric sensor 
may be used for detection of abrasion. One embodiment of this type is 
shown in FIG. 4, in which the photoelectric sensor is made up of a light 
projector 5a and a light receiver 5b. In this case, the light projector 
and receiver are arranged so that the detection beam traveling between 
them should be positioned at a distance of .alpha., i.e. the critical 
abrasion, from the guide face 31 of the rapier guide 3. 
As in the foregoing cases, a crest-like, non-abraded region 21 is developed 
on the working surface of the rapier band 2 after long use (see FIG. 5). 
As a rapier band 2 is abraded, but before the level of abrasion reaches a 
critical level, i.e. critical abrasion (a) the crest-like non-abraded 
region 21 of the rapier band remains too small to interrupt a detection 
beam traversing the longitudinal channel from light projector 5a to light 
receiver 5b. As the current abrasion reaches the critical abrasion, the 
detection beam is intercepted by the higher non-abraded region 21 for 
detection of occurance of the critical abrasion. 
As a further substitute for the pressure sensor 4 in FIG. 2, a distance 
sensor may be arranged directing the top face of the rapier band 2 in 
order to detect the distance between the top surface of the rapier band 2 
and the guide face 32 of the rapier guide 3 or 8. In this case, the 
detection head of the distance sensor is positioned at a distance larger 
then the critical abrasion (.alpha.) from the guide face 31 of the rapier 
guide 3. An alert is issued when the distance between the top surface of 
the rapier band 2 and the guide face 32 reaches the critical abrasion. 
In accordance with the second basic concept of the present invention, a 
photoelectric sensor 5 is attached to a rapier guide in an arrangement 
such that the axis of its detection beam should pass through an associated 
rapier band 2 at a distance of .beta. from the guide face 31 of the rapier 
guide 8. Here, .beta. is equal to a sum of the critical abrasion (.alpha.) 
of the rapier band 2 with an initial gap between the rapier band 2 and the 
guide face 31 of the rapier guide 8. One embodiment of the abrasion 
detector of this type is shown in FIG. 6, in which the photoelectric 
sensor 5 is made up of a pair of spaced and opposed light projector 5a and 
light receiver 5b. The light projector 5a and receiver 5b are mounted to 
the rapier guide 8 in an arrangement such that the axis X of the detection 
beam runs in parallel to the guide face 31 of the rapier guide 8 while 
passing, in the thickness direction, through an associated rapier band 2. 
In this case, the working surface of the rapier band 2 is taken on one of 
its lateral side surfaces. As long as the current abrasion on the working 
surface of the rapier band 2 falls short of the critical abrasion (.alpha. 
), the detection beam from the light projector 5a is intercepted by the 
rapier band 2 without arrival at the light receiver 5b. When the current 
abrasion equals the critical abrasion (.alpha.) of the rapier band 2, the 
detection beam arrives at the light receiver 5b without any interception 
and occurance of the critical abrasion is alerted. 
The working surface may be taken on the top or bottom surface of the rapier 
band 2 too. In this case, the photoelectric sensor is mounted to the 
rapier guide 8 in an arrangement such that the axis X of its detection 
beam passes, in parallel to the lower guide face 32, through the rapier 
band 2 at a distance of .beta. from the guide face 32 of the rapier guide 
8, .beta. being equal to a sum of the critical abrasion (.alpha.) of the 
rapier band 2 with an initial gap between the rapier band 2 and the guide 
face 31. 
A certain amount of initial gap is in general reserved between the rapier 
band 2 and the rapier guide 3. In the case of the present invention of the 
first basic concept, presence of such an initial gap need not be taken 
into consideration. This is because the extent of non-abrasion, i.e. the 
dimension of the non-abraded region 21, is used for detection. As a 
consequence, attention is focussed upon the critical abrasion (.alpha.) in 
the case of the invention of the first basic concept. In contrast to this, 
the extent of abrasion, i.e. the dimension of the abraded region 22, is 
used for detection in the present invention of the second basic concept. 
As a consequence, presence of the above-described initial gap must be 
taken into consideration and attention is focussed upon the 
above-described sum .beta.. 
In the case of the embodiment shown in FIG. 7, the light projector 5a and 
light receiver 5b are arranged so that the axis X of the detection beam 
runs aslant the guide face 31 of the rapier guide 8. In addition, the 
system is constructed so that the axis X of the detection beam should get 
into the rapier band 2 at a distance of the sum .beta. from the guide face 
31. With the system so designed, not only abrasion on one lateral side 
surface but also abrasion on top or bottom surface of the rapier band 2 
can be detected concurrently. 
In one modification of the arrangement shown in FIG. 7, two sets of like 
photoelectric sensors may be arranged on different lateral sides of the 
rapier band 2 so that an alert should be issued when one of the 
photoelectric sensors detects occurance of the critical abrasion. This 
arrangement is particularly advantageous when abrasion on the top or 
bottom surface of the rapier band is inclined in the width direction. 
In accordance with the present invention, no modification in construction 
needs to be made in production of rapier bands, which incurs no 
substantial rise in production cost. Accuracy in detection is not 
influenced at all by accuracy in production of rapier bands, thereby 
assuring high degree of accuracy in detection of abrasion. Adjustment in 
critical abrasion can be performed quite easily and freely even by end 
users through change in position of the critical abrasion sensor on a 
rapier guide.