An abrasion detector for a rapier band on a rapier loom

Abstract: In detection of abrasion on a rapier band (2) controlled in reciprocation by a rapier guide (3), the principal of detection is closely related to the critical abrasion (α ) of the rapier band and the system calls for no substantial modification in construction of the rapier band in production. In the first invention, a longitudinal channel (32) of a depth greater then the critical abrasion is formed in the guide face (31) of the rapier guide so that an abrasion sensor (4) attached to the rapier guide detects the dimension of a non-abraded region on the rapier guide projecting into the channel. In the second invention, a photoelectric sensor (5a,5b) is attached to the rapier guide so that its detection beam passes through the rapier band at a distance of β from the guide face, β being equal to a sum of the critical abrasion (α ) and the initial gap between the rapier band and the guide face of the rapier guide. The critical abrasion (α ) of the rapier band can be easily and freely adjusted by end users only by changing the position of the sensor or sensors.

Description: Background of the invention The present invention relates to a rapier guide for a rapier band on a rapier loom, said rapier guide being provided with a sensor for detecting a critical abrasion of width regions of the rapier band. 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 EP-A-0 341 522 relates to a type of rapier band 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 whilst 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 occurence 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 basic concept of the present invention, the rapier guide according to the preamble of claim 1 has a guide face on which said width regions of the rapier band can be in sliding contact, a longitudinal channel is formed in the guide face and has a depth greater than a prescribed critical abrasion of the rapier band, such that a non-abraded region of the rapier band can project into the channel when said width regions contact the guide face, and the sensor is attached to the rapier guide and detects presence of said non-abraded region projecting into the channel at a depth equal to or greater than the prescribed critical abrasion. 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. Brief description of the drawings Fig. 1 is a side view, partly in section, of a rapier band in cooperation with a rapier guide, Fig. 2 is a transverse cross sectional view of one embodiment of the rapier guide in accordance with the present invention, Figs. 3A and 3B are transverse cross sectional views for showing the operation of the rapier guide shown in Fig. 2, Fig. 4 is a transverse cross sectional view of another embodiment of the rapier guide in accordance with the present invention, Fig. 5 is a perspective view of one example of abrasion advanced on a rapier band, Description of the preferred embodiments As shown in Fig. 1, a rapier band 2 is driven for reciprocation 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 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 (α) of the rapier band, and a critical abrasion sensor is attached to the rapier guide 3 or 8. One embodiment of the abrasion sensor 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 α (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. Since the rapier band 2 is liable to slide near one end "a" of the rapier guide 3, the pressure sensor 4 is preferably arranged near this end "a" of sliding contact. 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 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 region 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 (α), 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 occurence 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 α, 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). Before current abrasion of the rapier band 2 reaches the critical abrasion in the regions corresponding to the guide face 31 of the rapier guide 3, the height of the non-abraded region 21 falls short of the critical abrasion (α) and, as a consequence, the detection beam travels from the light projector 5a to the light receiver 5b without any interception. As the current abrasion reaches the critical abrasion, the detection beam is intercepted by the higher non-abraded region 21 for detection of occurence 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 31 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 (α) 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 31 reaches the critical abrasion. 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.

Claims: A rapier guide (3, 8) for a rapier band (2) on a rapier loom, said rapier guide being provided with a sensor (4, 5a, 5b) for detecting a critical abrasion of width regions (22) of the rapier band, characterized in that : the rapier guide (3, 8) has a guide face (31) on which said width regions (22) of the rapier band (2) can be in sliding contact, a longitudinal channel (32) is formed in the guide face (31) and has a depth greater than a prescribed critical abrasion (α) of the rapier band, such that a non-abraded region (21) of the rapier band can project into the channel (32) when said width regions (22) contact the guide face (31), and the sensor (4, 5a, 5b) is attached to the rapier guide (3, 8) and detects presence of said non-abraded region (21) projecting into the channel at a depth equal to or greater than the prescribed critical abrasion (α). A rapier guide according to claim 1, characterized in that the sensor is a pressure sensor (4) which is inserted into the channel (32) and has a detection head located at a distance equal to the prescribed critical abrasion (α) from the guide face (31) of the rapier guide (3, 8). A rapier guide according to claim 1, characterized in that the sensor is a photoelectric sensor (5a, 5b) which is attached to the rapier guide (3, 8) in an arrangement such that a detection beam of the sensor is positioned in the longitudinal channel (31) at a distance equal to the prescribed critical abrasion (α) from the guide face (31) of the rapier guide (3, 8). A rapier guide according to claim 1, characterized in that the sensor is a distance sensor which is attached to the rapier guide atop the rapier band (2) in an arrangement such that a detection head of the sensor is positioned at a distance larger than the prescribed critical abrasion (α) from the guide face (31) of the rapier guide (3, 8). A rapier guide according to claim 1, characterized in that the sensor is located near one end (a, b) of said rapier guide (3, 8).

Inventors: YAMASHITA RYOJI C O TSUDAKOMA, YAMASHITA, RYOJI, C/O TSUDAKOMA KOGYO K.K.
Applicants: TSUDAKOMA IND CO LTD, TSUDAKOMA KOGYO KABUSHIKI KAISHA
Application year: 1992
Main classification: D03D47
IPC codes: D03D51, D03D47, G01B7, G01B21