Methods of and apparatus for controlling the thickness of an annular extrusion

Abstract

A cable core advances through an extruder head and then past an ultrasonic test set. In the extruder head, an annular plastic jacket is formed about the core. The test set generates four signals which correspond in magnitude to the jacket thickness in orthogonally spaced quadrants of the jacket. The signals are then applied to apparatus for centering the core with respect to the extruder head. Additional apparatus generates control signals in response to the signals from the test set. The control signals are applied to a mechanism for adjusting the jacket thickness in diametrically opposite quadrants with respect to the thickness in the quadrants adjacent thereto to control the uniformity of the jacket thickness. The control signals are also applied to a mechanism for controlling the overall jacket thickness. The signals give priority to the function of controlling the uniformity of the jacket thickness before the overall jacket thickness is reduced to a predetermined thickness range. A special control signal overrides other signals for controlling the jacket thickness and causes an increase in the overall jacket thickness whenever the jacket thickness in any of the quadrants falls below a predetermined minimum thickness.

What is claimed is: 
     
       1. A method of extruding an elongated annular article, wherein a first mechanism controls the uniformity of the wall thickness of diametrically opposite quadrants of the article with respect to the wall thickness of the quadrants adjacent thereto, and a second mechanism controls the average value of the wall thickness of the four quadrants of the article, the method comprising: generating first and second signals indicative, respectively, of a. an increase of the average value of the wall thickness in diametrically opposite quadrants of the article with respect to the average value of the wall thickness in the other two quadrants beyond a predetermined acceptable range, and   b. a deviation of the average value of the wall thickness from a predetermined thickness range;   applying the first signals to the first mechanism to increase the uniformity of the wall thickness; applying the second signals to the second mechanism to change the average thickness of the article to a value within the thickness range; and     blocking the second signals from being applied to the second mechanism upon the average wall thickness exceeding the predetermined thickness range while the first signals are being applied to the first mechanism.   
     
     
       2. A method of claim 1 further comprising: generating third signals indicative of the wall thickness having a value less than a predetermined minimum value in at least one of the quadrants;   blocking the second signals from being applied to the second mechanism upon the average wall thickness exceeding the values of the predetermined thickness range, while the third signals indicate that the wall thickness in at least one of the quadrants has a value less than the minimum value; and   applying the third signals to the second mechanism to further increase the average wall thickness of the article.   
     
     
       3. A method according to claim 2, wherein generating the first signals comprises; generating positive and negative signals corresponding to upper and lower limits of the predetermined acceptable range of values of the average wall thickness of any two diametrically opposite quadrants of the article with respect to the average wall thickness of the other two quadrants;   subtracting the average value of signals corresponding to the wall thickness of the article in two quadrants diametrically opposite one another from the average value of signals corresponding to the wall thickness in the other two mutually opposite quadrants;   comparing the difference between the average value of such signals to the signals corresponding to the upper and lower limits to determine the value of the difference in relation to such limits; and   generating pulsed signals of a first polarity when the value of the difference is more positive than the upper limit, and of a second polarity when such value is more negative than the lower limit.   
     
     
       4. A method according to claim 3, wherein the article is a jacket extruded about a cable core, wherein the first mechanism includes two pairs of rounding rollers, each pair engaging opposite sides of the core along an axis perpendicular to the longitudinal axis of the core and perpendicular to the axis along which the other pair of rollers engages the core, and wherein applying the first signals to the first mechanism comprises: applying the pulsed signals to at least one stepping motor mounted to move one pair of rounding rollers toward the core and the other pair away from the core; and altering the cross-sectional shape of the core with respect to an extrusion orifice to increase the jacket thickness in quadrants along a first axis of a cross section through the jacket with respect to the jacket thickness in quadrants along a second axis of the cross section perpendicular to the first axis in response to the signals of the first polarity, and to decrease the jacket thickness in quadrants along the first axis with respect to the jacket thickness in quadrants along the second axis in response to the signals of the second polarity.   
     
     
       5. A method according to claim 3, wherein generating the second signals comprises: generating signals corresponding to upper and lower limits of the thickness range;   averaging the values of the signals corresponding to the wall thickness of the article in each of the quadrants thereof;   comparing the resulting average value of such thickness signals to the values of the signals of the upper and lower limits of the thickness range;   applying pulses to a counter to increase the count of the counter when the average value of the thickness signals exceeds the value of the upper limit, and to decrease the count of the counter when the average value of the thickness signals is less than the value of the lower limit; and   converting the count of the counter to analog signals corresponding to the second signals.   
     
     
       6. A method of controlling the wall thickness of an annular extruded article, including controlling the uniformity of the wall thickness of the article by a first mechanism, and controlling the average wall thickness of the article by a second mechanism, the method comprising: generating first control signals in response to a disparity between .Iadd.the average value of the wall thickness in diametrically opposite quadrants of the article and the average value of .Iaddend.the wall thickness in .Iadd.the .Iaddend.adjacent .Iadd.two .Iaddend.quadrants of the article, the disparity exceeding a predetermined tolerance range;   generating second control signals of a first type in response to an increase of the average wall thickness of the article above a predetermined thickness range and of a second type in response to a decrease of the average wall thickness below the thickness range;   applying the first control signals to the first mechanism to render the first mechanism effective to reduce the disparity between .Iadd.the average value of the thickness in diametrically opposite quadrants and the average value of .Iaddend.the wall thickness in adjacent quadrants and thereby increase the uniformity of the article;   applying the second signals to the second mechanism to render the second mechanism effective to change the average wall thickness to a value within the predetermined thickness range; and   blocking the second signals of the first type from being applied to the second mechanism while the first signals are being applied to the first mechanism, whereby the average wall thickness is prevented from being decreased while the uniformity of the wall thickness is outside of the predetermined tolerance range.   
     
     
       7. A method according to claim 6, further comprising: generating a timing cycle including first and second timing periods;   generating first and second intermediate signals indicative, respectively of a. a disparity between the wall thickness in the adjacent quadrants of the article,   b. an increase or decrease of the average wall thickness beyond the predetermined thickness range;     updating first and second data memories by storing the first and second intermediate signals in the first and secnd data memories, respectively during each of the first timing periods; and   generating the first and second control signals from the first and second intermediate signals, respectively, and applying such generated control signals to the respective mechanisms during each of the second timing periods.   
     
     
       8. A method according to claim 7, further comprising: generating third intermediate signals upon the wall thickness in any of the quadrants becoming less than a predetermined minimum thickness;   increasing, in response to the presence of third intermediate signals, the frequency of the timing cycle; and   overriding, in response to the presence of the third intermediate signals, the second intermediate signals, and storing in the second data memory signals which are indicative of the average wall thickness being less than the predetermined thickness range.   
     
     
       9. Apparatus for extruding an elongated annular article, including a means for mechanically controlling the uniformity of the wall thickness of diametrically opposite quadrants of the article with respect to the wall thickness of the quadrants adjacent thereto, and means for mechanically controlling the average value of the wall thickness of the four quadrants of the article, wherein an improvement comprises: means for generating first and second signals indicative respectively, of a. an increase of the average value of the wall thickness in diametrically opposite quadrants of the article with respect to the average value of the wall thickness in the other two quadrants beyond a predetermined acceptable range of values, and   b. a deviation of the average value of the wall thickness from a predetermined thickness range;     means, coupled to the means for mechanically controlling the uniformity of the wall thickness, for translating the first signals into mechanical motion;   means for applying the first signals to the signal translating means to increase the uniformity of the wall thickness;   means for applying the second signals to the means for controlling the average wall thickness to alter the operation thereof and to change the average thickness of the article to a value within the thickness range; and   means rendered effective upon the average wall thickness exceeding the values of the thickness range while the first signals are being applied to the signal translating means for blocking the second signals from being applied to the means for controlling the average wall thickness.   
     
     
       10. An improvement according to claim 9 further comprising: means for generating third signals indicative of the wall thickness having a value less than a predetermined mined minimum value in at least one of the quadrants;   means rendered effective upon the average wall thickness exceeding the values of the thickness range while the third signals are indicating that the wall thickness in at least one of the quadrants has a value less than the minimum value for blocking the second signals from being applied to the means for controlling the average wall thickness.   
     
     
       11. An improvement according to claim 10, wherein the means for generating the first and second signals comprises; means for generating positive and negative signals corresponding to upper and lower limits of the predetermined acceptable range of values of the average wall thickness of any two diametrically opposite quadrants of the article with respect to the average wall thickness of the other two quadrants;   means for subtracting the average value of signals corresponding to the wall thickness of the article in two quadrants diametrically opposite one another from the average value of signals corresponding to the wall thickness in the other two mutually opposite quadrants;   means for comparing the difference between the average value of such signals to the signals corresponding to the upper and lower limits to determine the value of the difference in relation to such limits; and   means for generating the first signals of a first polarity when the value of the difference is more positive than the upper limit, and of a second polarity when such value is more negative than the lower limit.   
     
     
       12. An improvement according to claim 11, wherein the means for generating the first and second signals further comprises: means for generating signals corresponding to upper and lower limits of the thickness range;   means for averaging the values of the signals corresponding to the wall thickness of the article in each of the quadrants thereof;   means for comparing the resulting average value of such thickness signals to the values of the signals of the upper and lower limits of the thickness range;   a counter coupled to the thickness range comparing means;   means for increasing the count of the counter when the average value of the thickness signals exceeds the value of the upper limit, and for decreasing the count of the counter when the average value of the thickness signals is less than the value of the lower limit; and   means for converting the count of the counter-to-analog signals corresponding to the second signals.   
     
     
       13. Apparatus for controlling the wall thickness of an annular extruded article, including a first mechanism for controlling the uniformity of the wall thickness of the article, and a second mechanism for controlling the average wall thickness of the article, the apparatus comprising: means for generating first control signals in response to a disparity between .Iadd.the average value of the wall thickness in diametrically opposite quadrants of the article and the average value of .Iaddend.the wall thickness in .Iadd.the .Iaddend.adjacent .Iadd.two .Iaddend.quadrants of the article, the disparity exceeding a predetermined tolerance range;   .[.means for generating second control signals of a first type in response to an increase of the average wall thickness of the article above a predetermined tolerance range;.].   means for generating second control signals of a first type in response to an increase of the average wall thickness of the article above a predetermined thickness range and of a second type in response to a decrease of the average wall thickness below the thickness range;   means for applying the first control signals to the first mechanism to render the first mechanism effective to reduce the disparity between the .Iadd.average value of the .Iaddend.wall thickness .Iadd.in two opposite quadrants and the average value of the wall thickness .Iaddend.in adjacent quadrants to, thereby, increase the uniformity of the article;   means for applying the second signals to the second mechanism to render the second mechanism effective to change the average wall thickness to a value within the predetermined thickness range; and   means for blocking the second signals of the first type from being applied to the second mechanism while the first mechanism has been rendered effective, the blocking means preventing the average wall thickness from being decreased while the uniformity of the wall thickness is outside of the predetermined tolerance range.   
     
     
       14. Apparatus according to claim 13, further comprising: means for generating a timing cycle including first and second timing periods;   first and second data memories;   means for generating first and second intermediate signals indicative respectively of a. a disparity between the wall thickness in the adjacent quadrants of the article,   b. an increase or decrease of the average wall thickness beyond the predetermined thickness range;     means, rendered effective during each of the first timing periods, for updating first and second data memories with the first and second intermediate signals, respectively; and   means, rendered effective during each of the second timing perods, for generating the first and second control signals in response to the signals from the first and second memories, respectively, and for applying such generated control signals to the respective mechanisms during each of such second timing periods.   
     
     
       15. Apparatus according to claim 14, further comprising: means for generating third intermediate signals, rendered effective upon the wall thickness in any of the quadrants becoming less than a predetermined minimum thickness;   means, response to the third intermediate signals, for increasing the frequency of the timing cycle; and   means, response to the third intermediate signals, for overriding the second intermediate signals and for updating the second memory with signals indicative of the average wall thickness being less than the predetermined thickness range.