Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to method and apparatus for measuring a pitch of a stranded cable, and more particularly to method and apparatus capable of measuring a pitch for a spirally stranded structure of a cable in real time at a low cost. 
     1. Description of the Related Art 
     A communication cable is generally manufactured by stranding at least two wires. At this time, it is important to strand the wires at regular pitches along a longitudinal direction in order to improve transition characteristics especially Near End Cross-Talk (NEXT) and Return Loss (RL). 
       FIG. 1  is a schematic view showing a conventional apparatus for manufacturing a stranded cable  2 . 
     Referring to  FIG. 1 , the apparatus for manufacturing a stranded cable includes a wire pay-off  10  having a wire bobbin  11  for supplying at least two wires  1 , a capstan  25  for drawing the wires  1  at a regular velocity, a guide die  15  and a rotation body  20  positioned between the wire pay-off  10  and the capstan  25 , and a take-up device  30  for taking up the stranded cable  2 . 
     The wires  1  continuously supplied from the wire pay-off  10  by drawing of the capstan  25  is transmitted to the take-up device  30  after being stranded through the rotation body  20  in a state of being collected by the guide die  15 . 
     A method for manufacturing a stranded cable by using the conventional apparatus may be classified into, for example, single twister method, double twister method, triple twister method and so on according to the number of pitches per one rotation of the rotation body  20 . 
     Here, it is important to accurately monitor a length of pitch in real time during the stranding process so as to generate regular pitchs along a longitudinal direction of the cable. However, since a means for measuring a pitch of a cable by an in-line method has not been provided in the past, a pitch was generally measured off-line after all processes are finished. 
     In the off-line method, since the pitch is measured with the naked eye by using a length measurement means such as a micrometer or a vernier calipers, the method has disadvantages that measurement time is too long, and a measurement value error is apt to be generated depending on persons in charge of the measurement. 
     On the other hand, since inferiority of the pitch generated during stranding process cannot be detected in real time, the conventional method has a disadvantage that operating conditions affecting on the pitch state cannot be adequately set. For example, in the fact that a pitch of the cable is continuously changed by a change of tensile force acted on the wire and a change of a ratio of wire-velocity to the rotation body frequency caused by a slip of the wire in the capstan  25 , and so on, the conventional method cannot monitor these changes in real time. 
     SUMMARY OF THE INVENTION 
     The present invention is designed to solve the problems of the prior art, and therefore an object of the present invention is to provide method and apparatus for rapidly measuring a pitch of a spirally stranded cable in real time at a low cost. 
     In order to accomplish the object, the present invention provides a method for measuring a pitch of a stranded cable according to one embodiment of the present invention, which includes the steps of (A) manufacturing a stranded cable by stranding at least two wires; (B) irradiating a parallel ray on one side of the stranded cable moving at a regular velocity, and receiving the parallel ray at the opposed side of the stranded cable; and (C) determining a stranded cycle of the cable on the basis of a light-receiving quantity pattern on the opposed side corresponding to a stranded pattern of the cable, and then measuring a stranded pitch of the cable by calculating a moved distance of the cable during the stranded cycle. 
     At this time, a width of the parallel ray irradiated on one side of the cable should be set at least wider than a diameter of the cable. 
     In addition, the step (C) includes the steps of (a) generating a light-receiving signal in a shape of non-sinusoidal periodic wave corresponding to a light-receiving quantity on the opposed side; (b) converting the light-receiving signal into a square wave signal; (c) dividing the square wave signal into two parts; and (d) measuring a moved distance of the cable by using the divided square wave signal as a trigger signal. 
     Futhermore, the step (c) may include the steps of preparing a guide roller rotating in accordance with movement of the cable and an encoder for counting the rotation of the guide roller; counting the number of pulses output from the encoder by using the divided square wave signal as a trigger signal; and calculating a pitch P using the following equation, 
     
       
         
           
             P 
             = 
             
               
                 
                   π 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   D 
                 
                 n 
               
               × 
               N 
             
           
         
       
     
     where P: a stranded pitch, π: the ratio of the circumference of a circle to its diameter, D: a diameter of the guide roller, n: the number of pulses of the encoder per one rotation, and N: the number of pulses of the encoder. 
     In another embodiment of the present invention, an apparatus for measuring a pitch of a stranded cable includes a stranded cable in which at least two wires are stranded in a predetermined pitch, a light-emitting element and a light-receiving element positioned on both opposite sides of the stranded cable moving in a predetermined direction, a measurement sensor for sensing a moved distance of the cable, and a pitch calculator for calculating a pitch of the stranded cable on the basis of an output value of the measurement sensor by using periodical change of the output signal from the light-receiving element as a trigger signal. 
     The measurement sensor includes a guide roller contacted with the cable for rotating as much as a moved distance of the cable, and an encoder for counting the rotation of the guide roller. 
     In addition, the pitch calculator includes a comparator for converting a light quantity signal output from the light-receiving element into a square wave, a frequency divider for dividing the square wave output from the comparator into two parts, and a signal processor for calculating a pitch of the stranded cable by counting the number of pulses of the encoder until the divided square wave is triggered. 
     At this time, the signal processor calculates a pitch of the stranded cable on the basis of the following equation, 
     
       
         
           
             P 
             = 
             
               
                 
                   π 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   D 
                 
                 n 
               
               × 
               N 
             
           
         
       
     
     where P: a stranded pitch, π: the ratio of the circumference of a circle to its diameter, D: a diameter of the guide roller, n: the number of pulses of the encoder per one rotation, and N: the number of pulses of the encoder. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and aspects of the present invention will become apparent from the following description of embodiments with reference to the accompanying drawing in which: 
         FIG. 1  is a schematic view showing an apparatus for manufacturing a stranded cable according to a conventional art; 
         FIG. 2  is a schematic view showing an apparatus for measuring a pitch of a stranded cable according to a preferred embodiment of the present invention; 
         FIG. 3  is a sectional view showing that a light-receiving area is partially hidden by the cable in  FIG. 2 ; 
         FIG. 4  is a schematic diagram for illustrating a process of calculating a width hidden by the cable according to the present invention; 
         FIG. 5  is a schematic diagram showing a change of the area hidden by the cable in accordance with a rotation of a wire; 
         FIG. 6  is a block diagram showing functional components of the present invention; 
         FIG. 7  is a waveform diagram of an output signal of each component in  FIG. 6 ; and 
         FIG. 8  is a waveform diagram of a signal for calculating a pitch of a stranded cable by using a signal processor in  FIG. 6 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, preferred embodiments of the present invention will be described in detail referring to the accompanying drawings. Prior to the description, it should be understood that the terms used in the specification and appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present invention on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Therefore, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the invention. 
       FIG. 2  is a schematic view showing an apparatus for measuring a pitch of a stranded cable according to a preferred embodiment of the present invention. 
     Referring to  FIG. 2 , the pitch measuring apparatus of the present invention includes a light-emitting unit  100  and a light-receiving unit  115  positioned on both opposite sides of a stranded cable  2 , which is continuously progressed, a guide roller  120  and an encoder  125  operating in contact with the stranded cable  2 , and a signal processor  155  (see  FIG. 6 ) for calculating a pitch of the cable  2 . 
     Since the stranded cable  2  is moved between the light-emitting unit  100  and the light-receiving unit  115 , an irradiated ray emitted from the light-emitting unit  100  toward the light-receiving unit  115  reaches the light-receiving unit  115  in a state of being partially hidden as much as a portion corresponding to a spirally stranded structure of the cable  2 , as shown in  FIG. 3 . 
     Here, a width W hidden by the cable  2  may be represented as the following equation  1 , when referring to  FIG. 4 ,
 
 W=d ×(1+|sin θ|)   Equation 1
 
     where d: a diameter of the wire, θ a rotation angle of the wire. 
       FIG. 5  illustrates a value of W and a rotation mode of the wire which are changed in accordance with movement of the cable  2 , and calculated by the equation 1. 
     Referring to  FIG. 5 , when the stranded cable is interposed between the light-emitting unit  100  and the light-receiving unit  115  so as to make a value of W become d, a hidden area of a light-receiving element  115   a  is minimized. On the other hand, when the stranded cable is interposed between the light-emitting unit  100  and the light-receiving unit  115  so as to make a value of W become  2   d , the hidden area of the light-receiving element  115   a  is maximized. As a result, it would be known that the light-receiving quantity is changed according to a rotation angle. 
     In addition, a stranded structure of the cable  2  becomes one pitch when the wire substantially returns to its original position by rotating as much as 360 degrees. However, it would be noticed that the light-receving quantity is changed as much as two cycles in one pitch. 
     Preferably, a lens unit  105  having a collimator function is located between the light-emitting unit  100  and the stranded cable  2 . The lens unit  105  converts a ray radiated from the light-emitting unit  100  into a parallel ray, and irradiates the parallel ray toward the light-receiving unit  115 . A width of the parallel ray should be set at least wider than a diameter of the cable. 
     In addition, an optical slit  110  for controlling a changed degree of a light quantity sensed by the light-receiving element  115   a  is interposed between the stranded cable  2  and the light-receiving unit  115  so as to control a signal-to-noise ratio (or, a S/N ratio) of the signal output from the light-receiving element  115   a . For example, since a change of a light quantity reaching the light-receiving element  115   a  becomes larger as a width of the optical slit  110  is narrower than a predetermined critical value, the S/N ratio is improved and the signal is better detected. 
     An LED (Light Emitting Diode) having excellent optical characteristics and inexpensive than other elements, especially an infrared ray LED, is preferably adopted as a light-emitting element  100   a , which composes the light-emitting unit  100 . In addition, a photodiode is preferably adopted as the light-receiving element  115   a , which composes the light-receiving unit  115 . 
     The guide roller  120  rotates in accordance with the stranded cable  2  in a state that its circumsference is contacted with the stranded cable  2 . At this time, an encoder  125  syncronized with the guide roller  120  for generating a predetermined number of pulses per one rotation of the guide roller is preferably installed on one side of the guide roller  120  so as to count rotation of the guide roller  120 . For combination of the guide roller  120  and the encoder  125 , which substantially act for measuring a moved distance (or, a velocity) of the stranded cable  2 , a common tachometer or a rotary encoder may be adopted as it is. 
     The signal processor  155  plays a role of calculating a pitch of the spirally-stranded cable by processing a signal output from the light-receiving unit  115  and a signal related to a movement velocity of the cable, output from the encoder  125 . 
       FIG. 6  illustrates a functional configuration of a pitch calculator for such operation of the present invention. 
     Referring to  FIG. 6 , the pitch calculator of the present invention includes a common comparator  145  for converting an electrical signal output from the light-receiving unit  115  into a square wave, a frequency divider  150  for dividing the square wave signal into two parts, and a signal processor  155  for calculating a pitch of the stranded cable by using the divided square wave signal output from the frequency divider  150  and a pulse signal output from the encoder  125 . 
     In addition, in order to generate a square wave signal, a first amplifier  130  for amplifying the light-receiving signal in a predetermined level, a condenser  135  for extracting AC components from a signal at an output of the first amplifier  130 , and a second amplifier  140  for amplifying a signal at an output of the condenser  135  in a predetermined level are preferably interposed between an output of the light-receiving unit  115  and the comparator  145 . Output waveforms in each component are illustrated in  FIG. 7 . 
     The square wave signal output from the comparator  145  is divided so that the two-cyclic light-receiving pattern generated during one pitch of the cable is in correspondance to one-cyclic square wave with passing through the frequency divider  150 . 
     The signal processor  155  calculates a pitch of the stranded cable in a way of measuring a circumferential length of the guide roller  120 , which is rotated per one pitch of the stranded structure, by counting the number of pulses of the encoder  125  with using the divided square wave signal as a trigger signal, as shown in  FIG. 8 . Accordingly, the signal processor  155  calculates a pitch P of the cable using the following equation 2. 
     
       
         
           
             
               
                 
                   P 
                   = 
                   
                     
                       
                         π 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         D 
                       
                       n 
                     
                     × 
                     N 
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
               
             
           
         
       
     
     where P: a stranded pitch, π: the ratio of the circumference of a circle to its diameter, D: a diameter of the guide roller, n: the number of pulses of the encoder per one rotation, and N: the number of pulses of the encoder. 
     By using the above equation 2, it is possible to calculate a pitch corresponding to the square wave corresponding to one cycle. If this process is repeatedly applied on each square wave, a pitch of each point of the stranded cable may be calculated in real time along a longitudinal direction of the stranded cable  2 . 
     Hereinafter, a process of calculating a pitch of the stranded cable by using the pitch measuring apparatus according to the present invention is described in detail. 
     First, a device for measuring a stranded cycle of the cable  2 , in which at least two wires  1  are stranded, and a device for measuring a moved distance of the cable  2  are positioned in a direction of the moving cable, as shown in  FIG. 2 . Here, the stranded cycle measuring device is defined to include the light-emitting unit  100  and the light-receiving unit  115  oppositely positioned with the cable interposed therebetween, and the moved distance measuring device represents the guide roller  120  and the encoder  125 . 
     A light radiated from the light-emitting unit  100  is converted in a parallel ray having larger width than a diameter of the cable by the lens  105 , and then shed on the stranded cable  2 . A light-receiving quantity of the light-receiving unit  115  shows periodic patterns according to a stranded shape (or, a rotation mode) of the cable, as shown in  FIG. 5 . 
     In other words, the stranded shape of the cable periodically changes according to movement of the cable  2  positioned between the light-receiving unit  100  and the light-receiving emitting unit  115 , and an output signal (i.e., the light-receiving signal) of the light-receiving receiving unit  115  accordingly has a shape of non-sinusoidal periodic wave (e.g., a full-wave rectified sinusoidal periodic wave) shown in {circle around (a)} of  FIG. 7 . The light-receiving signal illustrated in {circle around (a)} of  FIG. 7  represents an amplified state by the first amplifier  130  (see  FIG. 6 ). 
     The amplified light-receiving signal is input into the comparator  145  via the condensor  135  and the second amplifier  140 , and then converted into a square wave signal, as shown in {circle around (d)} of  FIG. 7 , by the comparator  145 . The square wave signal is then converted into a divided square wave signal, as shown in {circle around (e)} of  FIG. 7 , through the frequency divider  150 . 
     On the other hand, the guide roller  120  rotates as much as a moved distance of the cable as the stranded cable  2  moves, and the encoder  125  generates pulses corresponding to the rotated distance of the guide roller  120 , and inputs the pulses into the signal processor  155 . 
     Accordingly, the signal processor  155  counts the number N of pulses of the encoder during a trigger-cycle of divided square wave signal output from the frequency divider  150 , as shown in  FIG. 8 . A stranded pitch P of the cable may be calculated by inputting the counted pulse number N into the below equation. 
     
       
         
           
             P 
             = 
             
               
                 
                   π 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   D 
                 
                 n 
               
               × 
               N 
             
           
         
       
     
     where P: a stranded pitch, π: the ratio of the circumference of a circle to its diameter, D: a diameter of the guide roller, n: the number of pulses of the encoder per one rotation, and N: the number of pulses of the encoder. 
     APPLICABILITY TO THE INDUSTRY  
     As noted above, the present invention may compose an apparatus for measuring a pitch of a stranded cable by using an inexpensive LED, thereby saving manufacturing expenses. 
     In addition, since a pitch of each point of the stranded cable may be rapidly measured in real time as the stranded cable moves, it is possible to quickly deal with a stranded state of the cable. 
     Accordingly, if the apparatus of the present invention is used in a process for manufacturing a cable, there is an advantage that a cable having regular pitchs along a longitudinal direction may be more efficiently manufactured. 
     The present invention has been described in detail. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

Technology Category: g