Patent Publication Number: US-6339943-B2

Title: Device and method for adjusting hosiery tension in circular textile machines

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a device and a method for adjusting hosiery tension in circular textile machines. 
     It is known that one of the most important controls that can be performed during the knitting of a hosiery item is control of the force with which the hosiery item is drawn into the circular textile machine, in order to determine the quality of its fabric. 
     Conventional hosiery tensioning methods are of the pneumatic or mechanical type and are characterized by rigid and inaccurate adjustments. Moreover, the tension applied to the fabric being knit which is designed to constitute the hosiery item cannot be adjusted dynamically throughout the knitting; it is instead necessary to perform mechanical adjustments of the tensioning device, 
     This clearly does not facilitate chances in the force applied to the fabric that the operator might want to perform. 
     Moreover, changes in the tension performed manually by the operator by acting on pneumatic or mechanical devices cannot be easily repeated and therefore the changes made in one operating step, seldom, are unlikely to be reproduced with accuracy and repeatability in the knitting of a different batch of hosiery items. 
     Moreover, pneumatic and mechanical adjustment devices do not allow to apply low-modulus forces and therefore tension adjustment tension is not very precise. 
     SUMMARY OF THE INVENTION 
     The aim of the present invention is to provide a device and a method for adjusting hosiery tension in circular textile machines, which allow dynamic adjustment throughout knitting. 
     Within the scope of this aim, an object of the present invention is to provide a device and a method for adjusting hosiery tension, which allow to easily modify the force applied to the fabric of the hosiery item during its production without any kind of constraint. 
     Another object of the present invention is to provide a device and a method for adjusting hosiery tension, which allow to include tension among the data that describe, from the textile point of view, the hosiery item to be manufactured. 
     Another object of the present invention is to provide a device and a method for adjusting hosiery tension in circular textile machines, which are highly reliable, relatively simple to manufacture and at competitive costs. 
     This aim and these and other objects which will become better apparent hereinafter are achieved by a device for the electronic adjustment of hosiery tension in circular textile machines, characterized in that it comprises actuation means which are adapted to move a carriage, which is in turn adapted to perform a translatory motion along an axis being parallel to a diametrical axis of said circular textile machine, said carriage supporting, at least one transducer connected to a hosiery advancement device, said transducer being adapted to detect a contrasting force due to the advancement of said hosiery item, said contrasting force being processed in controller means which are suitable to emit a speed signal for said actuation means, in order to adjust the movement speed of said carriage in contrast with said contrasting force. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further characteristics and advantages of the invention will become better apparent from the description of a preferred embodiment of the device and method according to the invention, illustrated only by way of non-limitative example in the accompanying drawings, wherein: 
     FIG. 1 is a schematic view of the tension adjustment device according to the present invention; 
     FIG. 2 is a block diagram of the control method according to the present invention; and 
     FIG. 3 is a schematic view of the tension adjustment device implemented in a circular textile machine. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the figures, the control device according to the present invention, generally designated by the reference numeral  1  and designed to be arranged below the needle cylinder or cylinders, comprises actuation means  2  which are adapted to actuate, with a translatory motion along the axis of the needle cylinders (for example, as shown in FIG. 3, respectively the upper cylinder  21  and the lower cylinder  22 ), a carriage  3  being kept guided on a guide  4  which is parallel to the axis of the needle cylinder or cylinders. 
     Conveniently, the actuation means  2  comprise a motor which moves the carriage  3  by way of a belt  5  and a pair of pulleys  6  and  7 . 
     The carriage  3  is counted to the belt  5  by way of engagement means  8 . 
     The carriage  3  is conveniently provided with at least one load cell  9 , connected to supporting means  10  which are adapted to support a rod-like element  11  whereto the hosiery item being knit is attached 
     The movement of the hosiery item during knitting occurs upward, i.e., in the opposite direction with respect to the arrow  127  which accordingly indicates the contrasting force that the hosiery item applies to the supporting element  10 . 
     The hosiery item is engaged, by means of the thread, with the needles of needle cylinder or cylinders. 
     The contrasting force, indicated by the arrow  12 , thus contrasts the advancement of the carriage  3 , which moves in the opposite direction with respect to the arrow  12 , as shown by the arrow  13 . 
     FIG. 2 is a block diagram of the hosiery tension adjustment device, in which reference numeral  2  designates, as in FIG. 1, the electric motor, and reference numeral  9  designates a force transducer, for example the load cell  9  shown in FIG.  1 . 
     The load cell  9  is arranged so as to be coupled to the movable carriage  3 . The reference numeral  14  instead designates a generic control system which performs the following functions: 
     analog-to-digital conversion of the signal that arrives from a signal amplifier  15  which is feedback-connected between the force sensor  9  and the control system  14 ; 
     signal sampling; 
     processing of the information by way of appropriate algorithms (comparison with a reference force signal  18 ); 
     driving of the electric motor  2 . 
     The force sensor or transducer  9  emits in output an electric signal  16  which is proportional to the force applied to the sensor  9 . The amplifier  15  amplifies and cancels out any offset of the signal  16 . 
     In practice, the operation of the device according to the invention is as follows. 
     A reference force  18 , which must cause the advancement of the hosiery item during the various steps of its manufacture, is defined by way of an operator interface. 
     When hosiery tensioning is active, the load cell (force transducer)  9  measures a certain contrasting force  12 . Said measurement varies substantially instantaneously as the stresses to which the fabric that constitutes the hosiery item vary. 
     The signal  16  of the load cell is conveniently amplified in the amplifier means  15  and is then sampled at the appropriate rates by the control system  14 , which converts it into digital form and filters it. 
     The comparison between the signal thus amplified and filtered and the reference force signal  18  generates an error which is identified as the difference between the reference force signal  18  and the signal in output from the amplifier  15 . 
     A speed reference signal  20  for the motor  2  that moves the carriage  3  along the guide  4 , in the direction of the arrow  13 , is generated according to a control algorithm, for example of the PID (proportional-integral-derivative) type. 
     By varying the speed of the cantage  3 , the force applied to the hosiery item during its manufacture (knitting) is controlled. 
     The reference value for the force, constituted by the signal  18 , thus becomes a parameter which depends both on the type of thread being processed and on the textile characteristics of the product. 
     In practice, therefore, it is possible to introduce tension among the data that describe, from the point of view of the textile characteristics, the hosiery item to be manufactured. The tension can be changed dynamically during such knitting, without any kind of constraint dictated by a device of the pneumatic or mechanical type. 
     This further allows greater precision and repeatability of the force is applied to the fabric. 
     Electronic adjustment of the tension of the hosiery item during its knitting thus provides for the presence of a control unit which is suitable to drive, with a given speed, the motor, which in turn drives the carriage to which the force transducer that measures the contrasting force applied by the hosiery item being knit is fixed. 
     The speed signal for the carriage actuation motor is obtained directly according to the reference force signal and to the signal emitted by the force transducer. 
     In practice it has been observed that the device and the method for adjusting hosiery tension according to the present invention, particularly for circular textile machines, fully achieve the intended aim and objects, since they allow to electronically control hosiery tension, with the possibility to dynamically vary the force applied to the fabric during knitting. 
     The device and the method thus conceived are susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. 
     Thus, for example, the motor  2  can be a motor of the stepper type, with the corresponding power electronic systems, or it is possible to use, for example, a motor of the brushless type. 
     It is further possible to use a transducer other than the force sensor  9 , such as for example a torque meter. 
     In practice, the materials employed, so long as they are compatible with the specific use, as well as the dimensions, may be any according to requirements and to the state of the art. 
     The disclosures in Italian Patent Application No. MI2000A000149 from which this application claims priority are incorporated herein by reference.