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FIELD OF THE INVENTION

The present invention relates to a method for controlling the weft insertion system of a gripper loom. In particular, the invention relates to such a controlling method which is apt to continuously monitor the wear and the working conditions of the various components of the weft insertion system, on the basis of predetermined parameters, and to suggest corrective measures for setting the weft insertion system and/or replacing any system component subject to wear, when these parameters are not being fulfilled .

BACKGROUND OF THE PRIOR ART

As known to the experts in the art, and as schematically shown in Fig. 1, the weft insertion system of gripper weaving looms includes a pair of grippers, the carrying gripper and the drawing gripper, respectively, which move from the opposite sides of the loom, and provide for the insertion of the weft into the shed through a mutual weft exchange which occurs at the middle of the shed. The reciprocating movement of the carrying gripper and of the drawing gripper is symmetrically controlled by two flexible straps B, at one end of which a respective gripper is fixed. The reciprocating movement to each of the two straps is imparted by a respective toothed wheel W, whose teeth engage within a continuous series of slots F formed along the central portion of the straps B. The reciprocating rotary movement to the toothed wheels W is imparted by the loom electrical main motor, whose continuous rotary movement is conveniently converted into a reciprocating rotary movement through different types of kinematic mechanisms, which structure is not relevant for the purposes of the present invention.

The correct meshing between each toothed wheel W and its respective flexible strap B - a gripper being fixed at one end of each strap - is provided by two guide slides S for each toothed wheel. As a matter of fact, the guide slides S, being conveniently radially adjusted with respect to the rotational axis of the relative toothed wheel W, keep the strap B bended and wrapped in adherence to the toothed wheel, in the geometrically correct meshing position among the slots F of strap B and the teeth of the toothed wheel W, around an engagement sector of the toothed wheel having a predetermined angular width. The angular width of such an engagement sector is calculated so that the force imparted by the wheel W to the strap B does not cause excessively high local stresses on the teeth of the wheel W and, furthermore, so that the free end of the straps B is directed towards an area below the loom, when the grippers are outside the shed.

In the contact area between the surface of the bended strap B and a corresponding sliding surface of the guide slide S, a centrifugal radial force thus is caused, which force is comprised of a static component, due to the bending rigidity of the strap B which tends to recover its original rectilinear shape, and of a dynamic component due to the high speed rotation of the strap B around the axis of the toothed wheel W. Such a centrifugal force gives rise to a corresponding frictional force - which is a function of the friction coefficient of the materials forming the straps B and the guide slides S, of the setting position of the guide slides S relative to the wheel W axis, and of the sliding speed - which frictional force leads to a progressive heating of the guide slide S and strap B surfaces in mutual contact. Further sliding phenomena, which themselves contribute to the overheating of the straps B, occur between the lateral edges of straps B and metal guide hooks arranged along the shed, which enable to bring back and keep the straps B in their rectilinear configuration, by guiding them through the shed in the desired direction.

As the loom operation speed increases, or otherwise due to an incorrect adjustment position of the guide slides S, the heat energy to be dissipated increases, consequently causing rising temperatures of both the straps B and the guide slides S. A too high temperature of the guide slides S leads to a faster aging of the polymeric material the straps are made of, drastically reducing their service life due to early wear or breakage. Straps B wear, in turn, causes adverse impact on the other components of the weft insertion system, both upstream and downstream the straps. Upstream, strap wear leads in fact to a less accurate matching with the teeth of the toothed wheel W, and thus to setting up of plays which trigger impact events against the toothed wheel W at each reversal of the direction of rotation of the same. Downstream, on the other hand, strap wear implies a less accurate guide of the grippers and therefore causes an increased number of errors in the weft exchange between the carrying gripper and the drawing gripper, as well as to an accelerated wear of the grippers themselves .

The current methods for controlling the weft insertion system in gripper looms do not take into any account the above said interdependence among the individual components of the system, and therefore they merely monitor, both statistically and through direct observation, the wear conditions of the various components subject to wear indicated above, namely the toothed wheels W, the flexible straps B and the grippers, in order to provide for their replacement when their service life is assessed to be ended.

However, the wear of the various components of the weft insertion system is not a regular phenomenon, nor is homogeneous among said components since it is determined by several concurrent factors. According to the prior art, the evaluation of the right time wherein to replace an excessively worn component is therefore a very delicate process which requires the intervention of a specialized and long-experienced textile operator, who is able to evaluate the residual service life of the various components of the weft insertion system, on the basis of their external appearance and of the type and frequency of occurred weaving errors. An early replacement of a component of the weft insertion system obviously entails a waste of resources and an economic damage, while a prolonged use under excessive wear conditions entails serious risks of breakage with consequent possible damage to the textile articles being processed and to the loom members themselves.

The problem addressed by the present invention is therefore to provide an automatic control of the actual wear of the components of a weft insertion system of a gripper loom, with the purpose of promptly warn the operator about any possible malfunction of the weft insertion system, in order to carry out adjustments so as to avoid the onset of accelerated wear phenomena, or to replace components, so as to avoid accidental breakage of said components during weaving operations.

In the context of this problem, a first object of the invention is to define a control parameter which is particularly significant for evaluating the quality of the actual working conditions of the weft insertion system of a gripper loom and which can be effectively monitored with sufficiently simple and industrially feasible technical procedures.

A second object of the invention is then to provide a method for controlling the weft insertion system of a gripper loom which is apt to process the variations of the above said control parameter, in the different working conditions of the loom, in order to distinguish those malfunctions that require interventions to adjust the components of the weft insertion system, from those which require a replacement of one or more of the components of the weft insertion system which have reached limit wear conditions.

Lastly, a third object of the invention is to provide a controlling method which can be integrated with devices providing the direct detection of the degree of wear of the various components of the weft insertion system.

SUMMARY OF THE INVENTION

This problem is solved, and these objects achieved by means of a method for controlling the weft insertion system of a gripper loom having the features defined in claim 1. Other preferred features of said controlling method are defined in the secondary claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the method for controlling the weft insertion system of a gripper loom according to the present invention will however become more evident from the following detailed description of a preferred embodiment thereof, given as a mere and non-limiting example and illustrated in the attached drawings, wherein:

Fig. 1 is a schematic front view of a gripper weaving loom which illustrates the essential elements of the weft insertion system of a gripper loom, as described in the introductory part of the present description;

Fig. 2 is a perspective view of a guide slide of the gripper strap according to the invention;

Fig. 3 is a top and see-through view of the guide slide of Fig. 2 which shows an internal cooling coil thereof; and

Fig. 4 is a diagram of a cooling circuit which feeds the guide slides of the gripper straps in a gripper loom.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As a result of the studies and experimental assessments which have been carried out, the Applicant came to the conclusion that, for the variety of reasons already indicated in the introductory part of the present description, a critical element of the weft insertion system of a gripper loom can certainly be found in the flexible straps B which drive the gripper movements.

Furthermore, among the several possible parameters which characterize the actual conditions of use of the straps B, in the experimental tests made by the Applicant the surface temperature of said straps B was found to be as the most significant one, considering that such a surface temperature, as mentioned above, is directly related to the friction conditions of the straps B against the respective guide slides. Since the friction conditions under which the straps work are related in turn to the main variable working parameters of the loom, and in particular to:

- the loom operative speed;

- the working room temperature;

- the play among the straps and their guide slides; - an improper strap setting;

- an improper loom adjustment;

the Applicant had the insight that the surface temperature of the straps, as well as the gradient of such a surface temperature over time, when accurately and continuously monitored, could be ideal parameters to be used in solving the problem underlying the invention. Based on this insight, the present invention has then been conceived.

Straps surface temperature measurement

In order to use the surface temperature of the gripper straps as an evaluation parameter of the quality of the actual working conditions of the whole weft insertion system, it is firstly necessary to measure such a temperature in the direct proximity of each strap B, and preferably at a point of the strap path where there is the highest frictional force and therefore the resulting highest strap temperature increase. As a matter of fact, by measuring the strap temperature at a position as defined above, the actual maximum fluctuations in the local temperature of the strap can be detected, which fluctuations are the most significant for the purposes of the invention, rather than a strap average temperature, whose changes over the time would not be useful to provide as much information.

In this regard, a preferred position is where the strap B enters the upper guide slide S, i.e. where the strap switches from the curvilinear configuration in adherence to the control wheel W, to the rectilinear configuration assumed within the shed. For convenience, the temperature is measured on the wall of the guide slide S which is in contact with the running strap B, by placing on such wall a temperature sensor 1 as close as possible to the contact area of said wall with the strap B, therefore assuming that here the temperature of the slide guide S substantially equals the surface temperature of strap B at the same position, given the close mechanical sliding contact between the strap B and the guide slide S herein, and further considering that the guide slide S is made of metallic materials having a high thermal conductivity. These two combined observations lead therefore to believe that the difference of temperature between the strap B and the guide slide S, at the above said position, may be negligible.

Hence, the sensors 1 constantly detect the strap B surface temperature under friction conditions, hereinafter referred to as Tf, and the information they collect on said temperature Tf during the weaving operations, for each of the two straps B which simultaneously work in the loom, is then sent to and stored in the loom central control unit for further processing.

Likewise, a temperature at rest of the straps B, hereinafter referred to as Ti, needs to be detected, which is used as a baseline to evaluate the temperature increase of straps B which is directly related to the weaving process frictions and not resulting from a general overheating of the individual loom or of the weaving room. However, it is practically impossible to detect such a temperature directly, since the limited areas of the straps B which are not directly affected by the friction phenomena against said strap guide slides are inevitably affected by the increased temperature of the surrounding areas under friction.

According to the invention, in order to achieve a reliable measurement of the surface temperature at rest Ti of the straps B, it was assumed that this temperature correspond, with reasonable approximation, to the room temperature near the straps working area. However, a direct measurement of the room temperature is not easy nor practical to be taken too, since it locally varies at a high extent depending on the greater or lesser proximity to the "hot" components of the loom, thus making it difficult to identify a correct position where this temperature could be significantly detected. According to a feature of the present invention, it was therefore considered more effective and convenient to measure the room temperature in an indirect manner, controlling its effect on the thermal regime of the loom, i.e. using the temperature of the lubricating oil contained in the tank of the loom, and its variations over time, as a direct indicator of the thermal regime of the machine and as an indirect indicator of the local room temperature.

Therefore, assuming as the initial room temperature, and thus as the surface temperature at rest Ti of the straps B, the lubricating oil temperature before starting the weaving operations, any subsequent change in the temperature of the lubricating oil in a running condition was considered to be a sufficiently accurate measurement of the corresponding changes in the room temperature, with reference to the individual machine taken into consideration, and therefore of the surface temperature at rest Ti of the straps B. By this choice, hence, the increased values of the straps B temperature can be automatically rectified from the effects caused by any change in the local room temperature.

The temperature data thus collected are then processed in the loom central control unit to provide significant parameters of the working conditions of the weft insertion system such as, for example, the following main parameters:

- Ti: surface temperature at rest of the straps;

- Tf : surface temperature under friction of the straps;

- DT = (Tf - Ti) : increase of the surface temperature under friction of the straps in the initial transitional phase;

- G: temperature increase gradient from Ti to Tf versus time in the initial transitional phase;

- ATd: DT value increase during daily processing;

- Gm: gradient of temperature Tf during an extended working period, wherein the temperature Tf is normalised at a predefined reference room temperature.

Reference baseline values and reference threshold values

The above parameters values are experimentally detected on a test loom wherein the weft insertion system is formed by new components, perfectly installed on the loom, after an initial running-in period during which a mechanical settling of the various components occurs. Theoretical reference baseline values are thus established, which are considered as optimal for each one of the above considered parameters.

Upon installation of the controlling method of the present invention on one single specific loom, these reference baseline values are refined through a self-learning process that takes place in an initial operative phase, also in this case by means of a weft insertion system including new components, after an initial running-in period, thus defining a series of actual reference baseline values which are specific to said specific loom.

Similarly, and on the basis of experimental data, a series of reference threshold values for said parameters are then defined, beyond which an action must be taken such as either replacing the components that show signs of marked wear or progressively reducing the weaving speed to such a value that the parameter under consideration drop under said threshold values .

Adjustment and replacement

Based on a comparison between the above indicated parameters and their relative reference baseline values and reference threshold values, the controlling method of the present invention can send alert messages to the user and/or direct instructions to the central control unit of the loom to modify its operation. For example, such messages can in a first phase simply advise the operator to progressively reduce the loom weaving speed step by step, or to replace worn out components, or even to check the mechanical adjustment of the different components. In case of advanced wear of the components, the central control unit of the loom can directly progressively limit the weaving speed or prevent the machine from restarting after a first stop due to other reasons, or even halt the loom.

In particular, according to another characteristic of the method of the present invention, when a first group of parameters relative to the surface temperature of straps B, such as Tf, DT and ATd exceed their threshold values, whilst a second group of parameters relative to the gradient of surface temperature of straps B over time, such as G and Gm, do not exceed their threshold values, this is regarded as an index of the achievement of the limit wear conditions of one or more components of the weft insertion system, and thus a message in this regard is sent to the operator.

On the contrary, when both the above groups of parameters exceed their threshold values, the malfunctioning is considered to depend from an incorrect mechanical adjustment of the components and therefore a corresponding message is sent to the operator .

The controlling method of the present invention can also be easily integrated with other information from one or more devices - preferably either optical, electrical, electronic, or electromagnetic devices - which directly monitor the wear conditions of the weft insertion system individual components. This additional information may be coordinated with those described above relating to the surface temperature of the grippers straps B, in order to provide more accurate information to the operator with regard to the specific components of the weft insertion system which need to be replaced having reached limit wear conditions.

Forced cooling of the surface temperature of the straps

The controlling method according to the present invention additionally provides a direct cooling intervention when the surface temperature under friction Tf of the straps B approaches the reference threshold value, to reduce or limit the temperature of the guide slides S of the straps B, in the contact area with the strap, removing the heat generated by friction through a refrigerant fluid circulation inside the same guide slide, thus avoiding the onset of an accelerated damage to the straps B due to overheating.

Such forced cooling can be performed permanently when the temperature Tf rise is essentially due to a room temperature rise. On the contrary, the forced cooling can be a temporary one when the excessively high temperature Tf is due to problems of mechanical adjustment or to the use of worn components, and yet such adjustment/replacement must be postponed, e.g. in order to complete weaving operation of an article. In this way, the operation can in fact be completed without any interruption, maintaining the straps B under safe conditions precisely thanks to said forced cooling.

The diagram of Fig. 4 represents in a simplified way a possible cooling circuit of the guide slides S of a strap for a gripper weaving loom. A refrigerant fluid is circulated inside the guide slides S to remove part of the heat generated by friction between the strap external surface and the guide slide itself. A conveniently sized pump 2, placed downstream of a tank 3, pushes the refrigerant fluid into the guide slide S. The exchange of energy between the two elements in contact allows for the temperature of the guide slide S to lower, though resulting in an increased temperature of the refrigerant fluid. Before being re-entered into the tank, the refrigerant fluid is therefore conveyed through one or more static heatsinks 4 (or any other active device apt to dissipate heat) to lower its temperature .

The internal structure of a guide slide S equipped with such a cooling device is shown in Fig. 3 and includes one or more channels 5 for internal circulation where the refrigerant fluid flows. The metallic material of the body of the guide slide S further promotes heat dissipation to the external environment and heat exchange with the refrigerant fluid.

The refrigerant fluid can be specifically selected for this application, using a dedicated suitable cooling circuit or, otherwise, the circulation system of the loom lubricating oil can be used, if available, diverting part of the flow towards the guide slides to be cooled. The choice between these two cooling systems obviously also depends on the required cooling system performances .

In particular, when the temperature of the loom lubricating oil, on average usually of 55-65°C, is just too high to make such a cooling, i.e. when the reference threshold value of the surface temperature under friction Tf of the straps B is <55°C, it is still possible to use as a cooling source the main circuit of lubricating oil, by combining the guide slides S with Peltier cells, whose negative thermoelectric effect is exploited to lower the temperature of the guide slides S, leaving the cooling circuit in charge of lowering the temperature of the Peltier cells hot side.

As a matter of fact, by electrically powering a Peltier cell a heat flow is obtained from one side of the cell, which cools down, to the opposite side of the cell, which therefore heats up. The "cold side" of the cell is that brought into contact with the body of the guide slide S, in order to absorb part of the heat generated by friction against straps B, thus cooling down the guide slide side in contact with the strap. The heat removed from the cold side is conversely transferred to the "hot side", in addition to the heat generated by Joule effect by the Peltier cell itself.

Also in this case, therefore, the application of a thermal dissipation system is therefore needed, to ensure the integrity of the Peltier cell itself, which thermal dissipation system is just provided by a cooling circuit which uses the loom' s lubricating oil as a refrigerant fluid. As an advantage of this solution, it is possible to reach lower temperatures of the guide slide S, compared to those achievable with a traditional system, thanks to the cooling effect of the Peltier cells. Furthermore, since the generated heat is removed from the guide slide S at higher temperatures, the oil of the forced lubrication circuit of the loom can be used as a refrigerant fluid, despite its temperature being higher than usually desired for the surface temperature under friction Tf of the straps B.

From the preceding description it becomes evident how the present invention has fully achieved all its intended objects. The surface temperature of the straps in fact has proven to be an easy to be monitored parameter as a control parameter of the actual working conditions of straps B. This parameter is also particularly significant in efficiently and timely highlighting abnormal working conditions of the loom, whether they are caused by an incorrect adjustment or by using excessively worn components, thus fully achieving a first object of the invention .

Furthermore, processing additional control parameters relative to the gradient of variation over time of the basic control parameter mentioned above, and using such parameters in a controlling method, allows to select the type of intervention to be performed on the loom, by guiding the operator towards adjusting or towards replacing the components of the weft insertion system, giving him the specific indication of the component to be replaced when the controlling method is integrated by special devices for detecting said components wear. The second and third objects of the invention are thus fully achieved too.

However, it shall be understood that the invention is not to be considered as limited by the specific arrangements illustrated above, which are only exemplary embodiments thereof, but that several variants can be made, all within the reach of a person skilled in the art, without departing from the scope of the invention itself, which is only defined by the following claims .