Improved optical feeler for monitoring a reserve of thread in weft feeders and weft feeder comprising said feeler

Abstract: A feeler for monitoring a thread reserve in weft feeders, comprising a light-emitting device constituted by a light source (21) which directs light rays (R) onto a thread (F) wound in spaced turns on the drum (11) of the feeder (10), and a receiver means (27-28-40), which collects the light rays and converts them into electrical signals that indicate the presence or absence of turns of thread. A first focused optical transmission system forms a first pointlike luminous image (A) of the light source (21) on the turn being monitored and, in the absence of the turn, a second pointlike luminous image (B) of the light source located on a screen surface (23) which is arranged below the turns. A second focused optical projection system (26) selectively projects the first or second luminous image (A-B), along respective differentiated optical paths (CO1-CO2), onto at least one optical sensor (27-28-40) which emits discriminated signals that correspond to the length of the corresponding optical paths.

Description: The present invention relates to an optical feeler for monitoring the reserve of thread in devices for feeding weft to looms and textile machines in general, and to the weft feeder that includes such device. More particularly, the present invention relates to conventional weft feeders comprising a fixed drum on which a windmilling arm, actuated by an electric motor, winds a plurality of spaced turns of thread which constitute a weft reserve, wherein the turns of the reserve are unwound from the drum in a preset amount at each beat of the loom and wherein optical feeler means are provided and are suitable to start and stop the motor that actuates the windmilling arm when the weft reserve drops below a preset number of turns and respectively when the reserve is fully replenished or if the thread breaks. Conventional optical devices for monitoring and detecting the presence of the turns of reserve thread are based on the use of one or more light-emitting devices which direct the light rays onto the thread wound on the drum and of one or more receivers which collect the rays and convert them into electric signals used to indicate the presence or absence of the spaced turns of thread. In the disclosure, the expression "light rays" refers both to rays within the visible-light spectrum and rays within the invisible-light spectrum, for example infrared rays. EP 0 624 674 A discloses an optical feeler comprising the features of the preamble of claim 1 and a weft feeder comprising such an optical feeler. EP 0 327.973 A discloses a device for monitoring the weft reserve which is based on the use of a pair of photoelectric cells which send respective rays of light, concentrated by lenses, onto a reflective surface of the drum on which the turns of the reserve are wound. The cells generate electrical signals which are produced by the reflection of said rays. The electrical signals have different durations depending on whether the turns of thread that intersect the incident and/or reflected light rays unwind from the drum by being requested by the loom or advance along the drum by being wound by the windmilling arm in order to form the weft reserve. An electronic circuit, connected to the photoelectric cells, is provided in order to discriminate the signals produced by the advancement of the turns that form the reserve from the signals produced by the unwinding of the turns that leave the drum by being requested by the loom, so that the signals are correctly used to control the actuation motor. It is also known to perform the optical detection of the presence of the turns of thread of the weft reserve by detecting, by means of a photosensor suitable to provide a useful electrical signal, the light rays reflected by the thread and emitted by a light source which is constituted by a photodiode or the like. Another known method, disclosed for example in prior Application WO 91/18818 A uses an array of sensors, for example optical sensors, arranged on the drum at respective turns of the reserve and suitable to provide signals which are processed by electronic circuits in order to provide various information, including information regarding the presence or absence of the turns of thread. The above-mentioned conventional monitoring systems entail some drawbacks which limit their use and diffusion. Generally speaking, the systems in fact are all relatively complicated and expensive, and those based on optical reflection entail the drawback that their functional characteristics change over time, due both to the accumulation of dust, lint and the like and to the possible variation of the reflection coefficients of the reflective surfaces, caused by wear and/or microstructural alteration of the materials. All the above-mentioned conventional systems further have, to varying extents, a sensitivity to ambient light which can bias the monitoring signals and thus requires the use of sophisticated electronic circuits for processing such signals. The aim of the present invention, is substantially to eliminate the above-mentioned drawbacks, and within the scope of this general aim the invention has the following important particular objects: to provide an improved optical feeler having an extremely simplified structure and capable of supplying a direct and discriminated signal indicating the presence or absence of the turns of thread of the weft reserve; to provide an improved optical feeler having a very compact structure and which can be easily associated with the weft feeder, particularly without requiring significant variations in the geometric profile of the drum of the devices; to provide an improved optical feeler comprising standard components and not requiring complicated circuits for processing the emitted signal, highly sensitive and substantially immune from changes in the signal produced by wear, presence of dust and lack of maintenance in general. According to the present invention, this aim, these important objects and others which will become apparent from the detailed description that follows are achieved with an optical feeler having the specific features as set forth in the appended claims. Substantially, the present invention is based, in order to achieve said aim and objects, on an optical feeler comprising the features of claim 1 and on a weft feeder comprising the features of claim 14. According to a preferred embodiment of the invention, the first and second sensors are unified in a single photodiode with two outputs, of the PSD type, which is capable of generating corresponding and discriminated output signals in terms of current which are proportional to the positions in which the first and second pointlike images of the light source are projected onto the active surface of the photodiode and are therefore proportional to the length of the optical paths that separate the pointlike images from the photodiode. Further characteristics and advantages of the improved optical feeler according to the present invention will become apparent from the following detailed description and with reference to the accompanying drawings, provided merely by way of non-limitative example and wherein: Figure 1 is a schematic view of a weft feeder with the improved optical feeler according to the present invention; Figures 2 and 2a are schematic sectional views of the optical receiver of the optical feeler of Figure 1, according to a first preferred embodiment of the invention; Figure 3 is a schematic view, similar to Figure 1, of a second constructive embodiment of the device according to the invention. In the drawings, the reference numeral 10 generally designates a conventional weft feeder comprising a fixed drum 11 on which a windmilling rotating arm 12, actuated by an electric motor 13, winds a plurality of turns of thread F which constitute a weft reserve RT for a loom T or another textile machine. In a per se known manner, the turns of thread F of the weft reserve RT unwind from the drum 11 at each beat of the loom T and an optical feeler 20 monitors the weft reserve, starting the motor 13 of the windmilling arm 12 when the reserve drops below a preset number of turns and stopping the motor 13 when the reserve is fully replenished. According to the invention, and in order to achieve the specified aim and objects, the feeler 20 comprises a light source 21, constituted by a diode which emits visible or invisible (for example infrared) rays, or by a laser emitter or other high-intensity light source, which is located outside the drum 11 and directs a beam of rays R towards the drum. The rays R are focused by a first optical transmission system, constituted for example by a lens 22 of a kind which is not spherical or in any case has a very limited spherical aberration. In the presence of turns of thread F of the weft reserve RT, the optical system forms, on a generic turn being monitored, a first pointlike image A of the light source 21 and, in the absence of turns, a second pointlike image B arranged on a screen surface 23 which is located below the turns and sufficiently spaced from the cylindrical surface on which the turns wind. The surface 23 can be reflective or non-reflective and is constituted by the bottom of a channel-shaped recess 24 provided on the surface of the fixed drum 11 at a radial plane that contains the optical axis of the lens 22. The recess 24 is preferably closed by a plate 25 made of glass (or other transparent material), on which the turns rest. The plate 25 also protects the channel 24 from trapping dust and other foreign objects. The depth p of the channel 24 is preferably chosen so that with respect to the radius r of the drum 11 p/r = 0.15 - 0.45. By means of a second focused optical projection system, constituted for example by a lens 26 which is also of the non-spherical type, the first or second pointlike luminous images A-B are selectively projected onto corresponding optical sensors 27-28 arranged respectively on a first optical path CO1 and on a second optical path CO2, which have discriminated lengths. The first optical path CO1 joins the first pointlike image A to the sensor 27 and the second optical path CO2 joins the second pointlike image B to the sensor 28. Correspondingly, in the presence of the turns of thread the first image A is projected onto the sensor 27, which emits a turn presence signal "pr", and in the absence of turns the second image B is projected onto the sensor 28, which emits a turn absence signal "as". An electronic circuit 30, which is operatively connected to the motor 13 by means of an interface 31, processes the signals "pr" and "as" and emits respective signals for stopping and starting the motor 13. According to a preferred embodiment of the invention, the sensors 27-28 are unified in a single photodiode 40 of the known type termed PSD and manufactured for example by the SHARP company and marketed under the designation PD 311F. The known photodiode, shown schematically in Figures 2 and 2a, has two outputs U1-U2 which are affected by current signals I1-I2, the intensities whereof are proportional to the position in which the luminous image is projected onto the active surface 41 of the photodiode. According to the present invention, the first image A of the light source 21 strikes the active surface 41 of the photodiode 40 in a point A1 (Figure 2) so that I1 = L-X/ L I I1 = L-X/ L I I2 = X/L I and the second image B strikes the surface 41 in a point B1 (Figure 2a) so that I'1 = L-Y/L I I'2 = Y/L I As an alterative to the PSD diode described above, it is possible to use a sensor of the known type termed CCD, or a sensor constituted by an array of photodiodes. The electronic circuit 30 is programmed to process the pairs of the above cited signals that are simultaneously present and to extract corresponding signals for stopping and starting the motor 13, and to extract a third signal I3 = f(I'1-I'2) which is a function of two signals which are simultaneously present and is suitable to provide information related to the operating condition of said screen surface 23 (presence of dust or other substances). The same result is achieved, if the differentiated sensors 27-28 of Figure 1 are used, with the double arrangement shown in Figure 3, in which the signals pr-as and pr'-as', which are simultaneously present, allow to obtain a signal I3 = f(pr-pr';as-as') for the specified purpose. The invention includes also the embodiment that uses an optical feeler (20), as described above, which is arranged on the front part of the feeder 10, downstream of the drum 11, to report the presence or the absence of the turns being unwound; the feeler 20 is arranged, in this case, at the diametrical plane that contains a generatrix of the solid of revolution, i.e., the so-called "balloon", which the unwinding turns generate downstream of the drum. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims: An optical feeler (20) for monitoring a thread reserve in weft feeders (10), comprising a light-emitting device constituted by a light source (21) which directs light rays onto a thread wound in spaced turns on a drum (11) of the feeder (10), and a receiver means (27, 28, 40), which collects said light rays and converts them into electrical signals (pr, as) which indicate presence or absence of turns of thread, characterized in that it comprises a first focused optical transmission system (22), which forms a first pointlike luminous image (A) of the light source (21) on the turn being monitored and, in the absence of the turn, a second pointlike luminous image (B) of the light source located on a screen surface (23) which is arranged below the turns, and a second focused optical projection system (26) which selectively projects the first or second luminous image (A, B), along respective differentiated optical paths (CO1, CO2), onto at least one optical sensor (27, 28, 40) capable of emitting discriminated signals (pr, as) which correspond to a discriminated length of the corresponding optical paths that separate said first and second pointlike images (A, B) from said optical sensor. An optical feeler according to claim 1, characterized in that it comprises a first optical sensor (27), arranged along a first optical path (CO1) that joins said first pointlike image (A) and said first sensor (27), and a second optical sensor (28), arranged along a second optical path (CO2) that joins the second pointlike image (B) to said second sensor (28), and in that said first and second sensors (27, 28) are activated selectively and respectively by the first and second images (A, B) to emit corresponding signals indicating the presence (pr) and the absence (as) of the turn. An optical feeler according to claim 1, characterized in that it comprises a single optical sensor (40) with two outputs (U1, U2), the active surface (41) whereof is intersected by both discriminated optical paths (CO1-CO2), which selectively project said first or second pointlike images (A, B) in correspondingly discriminated points (A1, B1) of said active surface (41), generating on said outputs (U1, U2) current signals (I1-I2, I'1-I'2) the intensity whereof depends on the position of said discriminated points (A1, B1) in relation to said active surface (41) of the sensor (40). An optical feeler according to claim 3, characterized in that said single optical sensor (40) is constituted by a PSD diode. An optical feeler according to claim 3, characterized in that said single sensor (40) is constituted by a CCD sensor. An optical feeler according to claim 3, characterized in that said single sensor (40) is constituted by an array of photodiodes. An optical feeler according to claim 1, characterized in that said screen surface (23) is constituted by a bottom of a channel-shaped recess (24) provided on a surface of the drum (11) of the feeder (10) at an optical axis of said first optical system (22). An optical feeler according to claim 7, characterized in that said channel-shaped recess is closed by a plate (25) made of transparent material, typically glass, on which the turns of the weft reserve (RT) rest. An optical feeler according to claim 1, characterized in that said first and second optical systems respectively comprise at least one lens (22, 26) of the nonspherical type. An optical feeler according to claim 1, characterized in that said screen surface (23) is opaque. An optical feeler according to claim 1, characterized in that said screen surface (23) is reflective. An optical feeler according to claim 1, characterized in that it comprises an electronic circuit (30) which is operatively connected to the motor (13) of the feeder (10) and is suitable to process the discriminated signals emitted by said optical sensors (27, 28, 40) and to emit corresponding signals for starting and stopping said motor (13). An optical feeler according to claim 1, characterized in that it comprises a double arrangement of said first and second optical systems. A weft feeder (10), characterized in that it comprises at least one optical feeler (20) according to claim 1. A weft feeder according to claim 14, characterized in that said optical feeler (20) is arranged at the drum (11) of the feeder (10) and monitors the weft reserve (RT) accumulated on said drum.

Inventors: ZENONI PIETRO, ZENONI, PIETRO
Applicants: LGL ELECTRONICS SPA, L.G.L. ELECTRONICS S.P.A.
Application year: 1998
Main classification: B65H51
IPC codes: G01N21, B65H51, D03D47, B65H63