METHOD FOR CONTROLLING DRAFTING DEVICE OF SPINNING FRAME

Abstract

 In a method for controlling a drafting device of a spinning frame, the drafting device includes a front bottom roller 12, a middle bottom roller 13, a back bottom roller 14, and motors (15, 16a, 16b, 17a, 17b) that independently drive the bottom rollers. The method includes changing a break draft ratio of the drafting device in a deactivation process of the spinning frame so that a load torque of the drafting device is smaller than when the break draft ratio is set to a value for normal operation to limit untwisting of the bottom rollers. The method further includes changing a main draft ratio when a fiber bundle, which has passed by the middle bottom roller 13 during a period the break draft ratio is changed, passes by the front bottom roller 12, to cancel influence on the fiber bundle of the changing in the break draft ratio.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method for controlling a drafting device of a spinning frame.

[0002] A spinning frame, such as a ring-spinning frame and a roving frame, includes spindles, which are arranged in the longitudinal direction of the spinning frame, and a drafting device. The drafting device drives bottom rollers at one end (gear end) of the spinning frame. The bottom rollers are extremely long. Thus, when the spinning frame is activated and twisting occurs in each bottom roller, the twisting is delayed when transmitted from the gear end to the opposite end (outer end) of the bottom roller. Twisting is especially large in a bottom apron roller (middle bottom roller), around which an apron is wound for each spindle. Thus, in portions where twisting occur, delayed twisting may result in yarn unevenness and yarn breakage. In addition to delayed twisting that occurs when the spinning frame is activated, yarn unevenness may be caused by untwisting of the bottom roller when the spinning frame stops operating.

[0003] Japanese Laid-Open Patent Publication No. 2007-23435 describes a method for reducing uneven yarns when the spinning frame is activated. In this method, at least in a deactivation process of the spinning frame, a break draft ratio of the drafting device is changed so that the load torque of the drafting device is smaller than that when the break draft ratio is set for normal operation of the spinning frame. The break draft ratio that has been changed in the deactivation process of the spinning frame is returned to its original value during a reactivation process of the spinning frame.

[0004] In the above method, for example, as shown in Fig. 6, during a deactivation of the spinning frame, a middle roller (middle bottom roller) is decelerated at a constant deceleration rate to maintain the original break draft ratio. Then, the deceleration rate of the middle roller is changed so that the break draft ratio increases from where the break draft is changed during deceleration. Then, the middle roller is decelerated at the changed deceleration ratio until the middle roller stops. In Fig. 6, the section shown by the broken line represents original deceleration of the middle roller. Afront roller (front bottom roller) and a back roller (back bottom roller) are decelerated at a constant deceleration rate from when the rollers start to decelerate until when the rollers stop so that the total draft ratio remains unchanged. However, the main draft ratio (i.e., draft ratio of middle roller and front roller) changes when the deceleration rate of the middle roller is changed.

[0005] Further, Japanese Laid-Open Patent Publication No. 2007-23435 describes a method for varying the deceleration rate of the back bottom roller in a break draft changed section during deceleration to change the break draft ratio during a deactivation process of the spinning frame. In this method, the deceleration rate of the front bottom roller is changed to maintain a constant total draft ratio.

[0006] In the above publication, the break draft ratio and the main draft ratio are changed. However, the influence on spun yarns caused by the change is not taken into account. This results in the occurrence of yarn unevenness. Yarn unevenness that occurs when changing the deceleration rate of the middle bottom roller to change the break draft ratio will now be described with reference to Fig. 7. Fig. 7 shows changes that occur when the spinning frame is deactivated and when the spinning frame is reactivated. More specifically, Fig. 7 sequentially shows, from the upper section, changes in the speed of the front roller, the middle roller, and the back roller, changes in the break draft ratio, changes in the main draft ratio, changes in the total draft ratio, and changes in the thickness of the spun yarn Y relative to the spun yarn length.

[0007] In the above publication, the break draft ratio is changed by changing the deceleration rate of the middle roller, and the deceleration rate of the middle roller is decreased during a predetermined time when deactivating the spinning frame. When reactivating the spinning frame, the middle roller is accelerated at an acceleration rate corresponding to the deceleration rate when deactivating the spinning frame. As a result, the break draft ratios when deactivating the spinning frame and when reactivating the spinning frame are changed to a tentative break draft ratio (hereinafter referred to as "tentative BD ratio"), which is higher than a predetermined break draft ratio (hereinafter referred to as "initial BD ratio"). Further, the main draft ratio is changed to a tentative main draft ratio (hereinafter referred to as "tentative MD ratio"), which is lower than a predetermined break main ratio (hereinafter referred to as "initial MD ratio").

[0008] A change in the main draft ratio from the initial MD ratio immediately affects the thickness of the spun yarn Y, which is fed from the front roller. When the main draft ratio is changed to the tentative MD ratio, which is lower than the initial MD ratio, the thickness of the spun yarn Y is increased. When the break draft ratio is changed from the initial BD ratio to the tentative BD ratio, the influence on the thickness of the spun yarn Y appears after a delay. When the break draft ratio is changed to be higher than the initial BD ratio, the thickness of the spun yarn Y decreases.

[0009] As a result, as shown in Fig. 7, the change in the main draft ratio immediately affects the spun yarn Y and forms a thick yarn Ya. Further, a change in the break draft ratio forms a thin yarn Yb behind the thick yarn Ya.

SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to provide a method for controlling a drafting device of a spinning frame that reduces the occurrence of yarn unevenness when changing the break draft ratio.

[0011] In a method for controlling a drafting device of a spinning frame, the drafting device includes a front bottom roller, a middle bottom roller, a back bottom roller, and motors that independently drive the bottom rollers. The method includes changing a break draft ratio of the drafting device in a deactivation process of the spinning frame so that a load torque of the drafting device is smaller than when the break draft ratio is set to a value for normal operation to limit untwisting of the bottom rollers. The method further includes changing a main draft ratio when a fiber bundle, which has passed by the middle bottom roller during a period the break draft ratio is changed, passes by the front bottom roller, to cancel influence on the fiber bundle of the changing in the break draft ratio.

[0012] Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

Fig. 1 is a schematic plan diagram showing a first embodiment of a drafting device without a top roller;

Fig. 2 is a graph showing the relationship of changes in the speed of bottom rollers, changes in the break draft ratio, changes in the main draft ratio, changes in the total draft ratio, and the thickness of a spun yarn relative to the spun yarn length in the first embodiment;

Fig. 3 is a graph showing speed changes in the bottom rollers during operation of the spinning frame;

Fig. 4 is a graph showing speed changes in the bottom rollers relative to time during operation of the spinning frame in a second embodiment;

Fig. 5 is a graph showing the relationship of changes in the speed of the bottom rollers, changes in the break draft ratio, changes in the main draft ratio, changes in the total draft ratio, and the thicknesses of spun yarns of bottom rollers relative to the spun yarn length;

Fig. 6 is a graph showing speed changes in the bottom rollers in the prior art; and

Fig. 7 is a graph showing the relationship of changes in the speed of the bottom rollers, changes in the break draft ratio, changes in the main draft ratio, changes in the total draft ratio, and the thickness of a spun yarn relative to the spun yarn length.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

[0014] A first embodiment of the present invention will now be described with reference to Figs. 1 to 3 using a ring-spinning frame as an example.

[0015] Fig. 1 shows one of two drafting devices 11, which are located at two sides of a spinning frame and extend in the longitudinal direction of the spinning frame. The drafting device 11 has a three-line structure that includes two front bottom rollers 12, two middle bottom rollers 13, and two back bottom rollers 14. Each of the front bottom rollers 12 is supported by roller stands (not shown) at predetermined locations. Each of the middle bottom rollers 13 and each of the back bottom rollers 14 are supported by support brackets (not shown). The support brackets are fixed to the roller stands so that the positions of the support brackets are adjustable in the front and rear directions. Each middle bottom roller 13 includes aprons (not shown). Further, the drafting device 11 includes front top rollers (not shown), middle top rollers (not shown), and back top rollers (not shown) that have known structures and correspond to the bottom rollers 12 to 14, respectively.

[0016] Each front bottom roller 12 is formed by a roller shaft 12a, which extends over the entire length of the spinning frame. Each middle bottom roller 13 is divided into two roller shafts 13a and 13b. Each back bottom roller 14 is divided into two roller shafts 14a and 14b. The two roller shafts 13a and 13b are coaxial. The two roller shafts 14a and 14b are coaxial. In the present embodiment, the middle bottom rollers 13 and the back bottom rollers 14 are each divided at the longitudinally middle portion. The two roller shafts 13a and 13b are symmetrical, and the two roller shafts 14a and 14b are symmetrical.

[0017] Each front bottom roller 12 is driven by a front roller motor 15 located at the first end, or gear end, of the spinning frame (left end in Fig. 1). The rotation produced by the front roller motor 15 is transmitted to each roller shaft 12a by a gear train (not shown).

[0018] The two roller shafts 13a located at the left side as viewed in Fig. 1 of the two middle bottom rollers 13 are driven by a first middle roller motor 16a located at the first end of the spinning frame. The two roller shafts 13b located at the right side as viewed in Fig. 1 of the two middle bottom rollers 13 are driven by a second middle roller motor 16b located at the second end (outer end) of the spinning frame. The rotation produced by the first middle roller motor 16a is transmitted to each roller shaft 13a by a gear train (not shown). The rotation produced by the second middle roller motor 16b is transmitted to each roller shaft 13b by a gear train (not shown).

[0019] The two roller shafts 14a located at the left side as viewed in Fig. 1 of the two back bottom rollers 14 are driven by a first back roller motor 17a located at the first end of the spinning frame. The two roller shafts 14b located at the right side as viewed in Fig. 1 of the two back bottom rollers 14 are driven by a second back roller motor 17b located at the second end of the spinning frame. The rotation produced by the first back roller motor 17a is transmitted to each roller shaft 14a by a gear train (not shown). The rotation produced by the second back roller motor 17ba is transmitted to each roller shaft 14b by a gear train (not shown).

[0020] Servomotors are used as the front roller motor 15, the first middle roller motor 16a, the second middle roller motor 16b, the first back roller motor 17a, and the second back roller motor 17b. The motors 15, 16a, 16b, 17a, and 17b are respectively driven and controlled by independent servo drivers 19, 20a, 20b, 21 a, and 21 b, which are controlled based on the instructions from a controller 18.

[0021] The controller 18, which includes a microcomputer, functions as a control unit. The controller 18 is operated based on predetermined program data stored in a memory to control the motors 15, 16a, 16b, 17a, and 17b with the servo drivers 19, 20a, 20b, 21a, and 21b. The controller 18 controls each of the motors 15, 16a, 16b, 17a, and 17b to produce rotation at a speed that obtains a total draft ratio and a break draft ratio that have been set in advance in correspondence with spinning conditions input by an input device 22.

[0022] At least in a deactivation process of the spinning frame, the controller 18 controls the drafting device 11 to change a break draft ratio of the drafting device 11 so that the load torque of the drafting device 11 is lower than that when the break draft ratio of the drafting device 11 is set for normal operation of the spinning frame. The controller 18 further controls the drafting device 11 to correct unevenness when a fiber bundle, which has passed by the middle bottom roller 13 during a period the break draft ratio is changed, passes by the front bottom roller 12. Further, the controller 18 is configured to calculate the timing at which the fiber bundle passes by the front bottom roller 12 using a roller gauge between the front bottom roller 12 and the middle bottom roller 13, roller speeds of the front bottom roller 12 and the middle bottom roller 13, and the break draft ratio prior to changing.

[0023] The operation of the above drafting device 11 will now be described. Before operating the spinning frame, the input device 22 is used to input spinning conditions, such as the fiber material, the spun yarn count, and the number of twists, to the controller 18. When the operation of the spinning frame is started, the motors 15, 16, 16a, 16b, 17a, and 17b are controlled by the servo drivers 19, 20a, 20b, 21a, and 21b based on instructions from the controller 18. More specifically, the motors 15, 16, 16a, 16b, 17a, and 17b are controlled so as to produce rotation at a speed that obtains the total draft ratio and the break draft ratio that have been set in correspondence with the spinning conditions. Further, drive motors of a spindle system and a lifting system (not shown) are controlled so as to produce rotation at a predetermined speed.

[0024] In a deactivation process of the spinning frame, the controller 18 changes the break draft ratio of the drafting device 11 so that the load torque of the drafting device 11 is lower than that when the break draft ratio of the drafting device 11 is set for normal operation. This limits untwisting of the back bottom roller 14. As shown in Fig. 3, the controller 18 changes the break draft ratio of the deactivation process of the spinning frame only by changing the deceleration rate of the back bottom roller 14 (back roller) so that the break draft ratio when the spinning frame is in the deactivation process is lower than an initial break draft ratio, that is, the break draft ratio for normal operation. Although not illustrated in the drawings, the torque for drafting is not simply proportional to the break draft ratio of the drafting device 11 and has a peak value (maximum value), which is determined by spinning conditions. If the value of the break draft ratio corresponding to the peak value of the torque is set to a boundary value and the boundary value is higher than the break draft ratio, the load torque of the drafting device 11 decreases as the break draft ratio increases. When the boundary value is lower than the break draft ratio, the load torque of the drafting device 11 decreases as the break draft ratio decreases. The controller 18 increases the break draft ratio when the break draft ratio for normal operation of the spinning frame is higher than the value of the break draft corresponding to the peak value of the torque. The controller 18 decreases the break draft ratio when the break draft ratio for normal operation of the spinning frame is lower than the value of the break draft corresponding to the peak value of the torque. The break draft ratio in the deactivation process of the spinning frame is changed by changing the speed of the back bottom roller 14 to be higher than the speed (shown by dotted line in Fig. 3) that allows the break draft ratio for normal operation of the spinning frame to be obtained.

[0025] In a reactivation process of the spinning frame, the controller 18 starts activation at the break draft ratio that is used when the spinning frame stopped operating. After the break draft ratio reaches the break shaft ratio for normal operation, the controller 18 controls the middle roller motors 16a and 16b and the back roller motors 17a and 17b to change only the main draft ratio without changing the break draft ratio. Then, the controller 18 changes the acceleration rates of the middle bottom rollers 13 (middle rollers) and the back bottom rollers 14.

[0026] More specifically, as shown in Fig. 2, in the deactivation process of the spinning frame, the controller 18 receives a deactivation signal and then changes the deceleration rate of the back bottom roller 14 after a predetermined time elapses so that the break draft ratio decreases from the break draft ratio for normal operation of the spinning frame (hereinafter referred to as "initial BD ratio") to a tentative break draft ratio (hereinafter referred to as "tentative BD ratio"). As a result, the break draft ratio gradually decreases from during the deactivation process of the spinning frame and reaches the tentative BD ratio before the spinning frame completely stops. During this period, the main draft ratio remains unchanged from the main draft ratio of for normal operation of the spinning frame (hereinafter referred to as "initial MD ratio").

[0027] After the break draft ratio reaches the tentative BD ratio and the spinning frame is stopped, in the reactivation process of the spinning frame, the driving of the back bottom roller 14 starts when the break draft ratio is set at the tentative BD ratio, which is lower than the initial BD ratio in break draft ratio. Then, the break draft ratio reaches the initial BD ratio.

[0028] The yarns of the fiber bundle that are fed from the middle bottom roller 13 when the break draft ratio is changed from the initial BD ratio are thick if the fiber bundle is spun without changing the main draft ratio from the initial MD ratio. However, in the present embodiment, the main draft ratio is changed to correct unevenness when the fiber bundle, which has passed by the middle roller (middle bottom roller 13) during the period the break draft ratio changes from the initial BD ratio, passes by the front roller (front bottom roller 12). That is, in the present embodiment, the main draft ratio is changed to cancel the influence on the fiber bundle of the change in the break draft ratio.

[0029] The main draft ratio is changed by changing the acceleration rate of the middle bottom roller 13. The break draft ratio is maintained at the initial BD ratio even when the speed of the middle bottom roller 13 is changed. Thus, the acceleration rate of the back bottom roller 14 is changed synchronously with when the acceleration rate of the middle bottom roller 13 is changed. The main draft ratio is changed to a yarn unevenness correction main draft ratio, which is higher than the initial MD ratio, to avoid situations in which the yarns of the fiber bundle fed from the middle bottom roller at the tentative BD ratio become thick.

[0030] More specifically, in the present embodiment, during the deactivation process of the spinning frame, the main draft ratio is not changed until the break draft ratio is changed from the initial BD ratio to the tentative BD ratio and the spinning frame stops operating. This avoids the formation of yarns having unevenness thickness in the fiber bundle when changing the main draft ratio. The main draft ratio is changed in conformance with the timing at which the thickness becomes uneven in the fiber bundle when changing the main draft ratio. This reduces the yarn unevenness of the spun yarn Y.

[0031] The present embodiment has the advantages described below.

(1) The ring-spinning frame, which serves as a spinning frame, includes the drafting device 11 that includes the front rollers (front bottom rollers 12), the middle rollers (middle bottom rollers 13), the back rollers (back bottom rollers 14), and the motors 15, 16a, 16b, 17a, and 17b that independently drive the bottom rollers. In the deactivation process of the spinning frame, the break draft ratio of the drafting device 11 is changed so that the load torque of the drafting device 11 is lower than when the break draft ratio is set to a value for normal operation of the spinning frame. Thus, when the motors 15, 16a, 16b, 17a, and 17b that drive the bottom rollers 12, 13, and 14 are stopped, untwisting of the bottom rollers is limited. This reduces fibers that are overfed when a bottom roller is untwisted during the deactivation period of the spinning frame. Further, uneven yarns are reduced when reactivating the spinning frame.
In the reactivation process of the spinning frame, when the bundle that has passed by the middle roller during the period the break draft ratio is changed, passes by the front roller, the main draft ratio is changed to cancel the influence on the fiber bundle of the change in the break draft ratio. This reduces uneven yarns that would be formed when changing the break draft ratio.

(2) The break draft ratio is changed only by changing the speed of the back bottom roller 14 from the speed that allows the break draft ratio for normal operation of the spinning frame to be obtained. The changing of the break draft ratio is not limited to changing only the deceleration rate of the back bottom roller 14 and may also be performed by changing only the deceleration rate of the middle bottom roller 13 or by changing the deceleration rates of the back bottom roller 14 and the middle bottom roller 13. When the deceleration rate of the middle bottom roller 13 is changed, the main draft ratio can be changed in addition to the break draft ratio. When a change in the deceleration rate of the middle bottom roller 13 is combined with a change in the front bottom roller 12, a change of the main draft ratio can be inhibited. However, when changing the break draft ratio without changing the main draft ratio, the control would be easier when changing only the deceleration rate of the back bottom roller 14 than when a change in the deceleration rate of the middle bottom roller 13 is combined with a change in the deceleration rate of the front bottom roller 12.

(3) The break draft ratio in the deactivation process of the spinning frame is changed by changing the speed of the back bottom roller 14 to be higher than the speed that obtains the break draft ratio for normal operation of the spinning frame. This improves the response for changing the break draft ratio.

(4) In the reactivation process of the spinning frame, after starting activation at the break draft ratio that is used when the spinning frame stopped operating, the break draft ratio is returned to the value for normal operation of the spinning frame. When a delay in the twisting of the bottom roller is small, the occurrence of yarn unevenness is limited even when each of the bottom rollers 12, 13, and 14 is immediately driven to obtain the predetermined break draft ratio when reactivating the spinning frame. Nevertheless, spinning conditions for when a twisting delay is small need to be checked in advance. However, after starting activation of the spinning frame at the break draft ratio that is used when the spinning frame stopped operating, the occurrence of yarn unevenness is reduced regardless of the spinning condition by driving each of the bottom rollers 12, 13, and 14 so that the break draft ratio is returned to the value for normal operation of the spinning frame.

(5) The timing when the fiber bundle, which has passed by the middle roller, passes by the front roller during the period in which the break draft ratio is changed, is calculated using the roller gauge between the front bottom roller 12 and the middle bottom roller 13, the roller speeds of the front bottom roller 12 and the middle bottom roller 13, and the break draft ratio prior to changing. This allows for accurate calculation of the timing when the fiber bundle, which has passed by the middle roller (middle bottom roller 13) during the period the break draft ratio is changed, passes by the front roller (front bottom roller 12). Thus, unevenness correction is performed in a preferred manner.

Second Embodiment

[0032] A second embodiment will now be described with reference to Figs. 4 and 5. The second embodiment differs from the first embodiment in that the break draft ratio of the drafting device is changed in the deactivation process of the spinning frame so that the speed of the back bottom roller 14 is lower than the speed that obtains the break draft ratio for normal operation of the spinning frame. Like or same reference numerals are given to those components that are like or same as the corresponding components of the first embodiment, and detailed explanations are omitted.

[0033] In the deactivation process of the spinning frame, after a predetermined time elapses from when a stop signal is received, the controller 18 changes the deceleration rate of the back bottom roller 14 so that the break draft ratio increases from the initial BD ratio to the tentative BD ratio. As a result, the break draft ratio gradually increases during the deactivation process of the spinning frame and reaches the tentative BD ratio before the spinning frame completely stops operating. Thus, when the break draft ratio is changed to the tentative BD ratio, thin yarns are formed from the fiber bundle. During the deactivation process of the spinning frame, the main draft ratio remains unchanged from the initial MD ratio.

[0034] After the break draft ratio reaches the tentative BD ratio and the spinning frame stops operating, in the reactivation process of the spinning frame, driving of the back bottom roller 14 starts when the break draft ratio is the tentative BD ratio, which is higher than the initial BD. As a result, the break draft ratio reaches the initial BD ratio.

[0035] After the break draft ratio reaches the initial BD ratio, the main draft ratio is changed to perform unevenness correction when the fiber bundle, which has passed by the middle roller (middle bottom roller 13) during the period in which the break draft ratio is changed from the initial BD ratio, passes by the front roller (front bottom roller 12). That is, the main draft ratio is changed to cancel the influence on the fiber bundle of the change in the break draft ratio. The main draft ratio is changed by changing the acceleration rate of the middle bottom roller 13.

[0036] The main draft ratio is changed so that the yarns become thick, that is, so that the main draft ratio becomes lower than the initial MD ratio. The break draft ratio is maintained at the initial BD ratio even when changing the acceleration rate of the middle bottom roller 13. Thus, the acceleration rate of the back bottom roller 14 is changed synchronously with when changing the acceleration rate of the middle bottom roller 13.

[0037] As described above, in the deactivation process of the spinning frame, even when the break draft ratio is changed to be higher than the initial BD ratio, the main draft ratio is changed to be lower than the initial MD ratio. This avoids situations in which the yarns of the fiber bundle become thin. Thus, the occurrence of yarn unevenness in the spun yarn Y is limited.

[0038] It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.

[0039] In each of the above embodiments, the break draft ratio may be changed by changing the deceleration rate of the middle bottom roller 13. In this case, the break draft ratio can be changed without changing the deceleration rate of the back bottom roller 14. However, the deceleration rate of the front bottom roller 12 needs to be changed in combination with a change in the deceleration rate of the back bottom roller 14 so that the main draft ratio is not changed when changing the deceleration rate of the back bottom roller 14.

[0040] In the first embodiment, when a twisting delay of the bottom roller is small, in the reactivation process of the spinning frame, activation may be immediately performed at the BD ratio for normal operation without returning the break draft ratio from the tentative BD ratio to the BD ratio for normal operation.

[0041] In each of the above embodiments, the break draft ratio prior to changing does not have to be used to calculate the timing when the fiber bundle, which has passed by the middle roller during the period in which the break draft ratio is changed, passes by the front roller. For example, the timing when the fiber bundle passes by the front roller may be calculated using only the roller gauge between the front bottom roller 12 and the middle bottom roller 13 and the roller speeds of the front bottom roller 12 and the middle bottom roller 13.

[0042] In each of the above embodiments, if the fiber bundle that passes by the middle roller during the period the break draft ratio is changed passes by the front roller before the spinning frame stops operating, the main draft ratio may be changed during a deactivation process of the spinning frame.

[0043] In each of the above embodiments, the break draft ratio in a deactivation process of the spinning frame does not necessarily have to be changed during deceleration of each of the bottom rollers 12, 13, and 14. For example, the break draft ratio may be started at the same time as when each of the bottom rollers 12, 13, and 14 starts decelerating.

[0044] In each of the above embodiments, instead of a value stored in advance in a program memory of the controller 18, a value received from the input device 22 may be used as the changed break draft ratio in the deactivation process of the spinning frame, that is, the tentative BD ratio, when inputting the spinning conditions of the spinning frame.

[0045] In each of the above embodiments, instead of the drafting device 11 that has a three-line structure, the present invention may be applied to a drafting device that has a structure of four or more lines.

[0046] In each of the above embodiments, the middle bottom roller 13 and the back bottom roller 14 do not have to be driven at the first end and the second end by the motors 16a, 16b, 17a, and 17b. For example, the middle bottom roller 13 may be driven at the first end and the second end of the spinning frame, and the back bottom roller 14 may be driven at either one of the first end and the second end of the spinning frame. Further, depending on the number of spindles of the spinning frame, the front bottom roller 12, the middle bottom roller 13, and the back bottom roller 14 may all be driven at either one of the first end and the second end of the spinning frame.

[0047] In each of the above embodiments, the present invention is applied to a ring-spinning frame that spins a spun yarn from a roving. Instead, the present invention may be applied to a ring-spinning frame that drafts a sliver without using a roving and directly spins a spun yarn. Further, the present invention may be applied to other spinning frames, such as a bundling spinning frame or a roving machine, that include a drafting device in which bottom rollers have long roller shafts and aprons are wound around a middle bottom roller.

[0048] Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.

[0049] In a method for controlling a drafting device of a spinning frame, the drafting device includes a front bottom roller, a middle bottom roller, a back bottom roller, and motors that independently drive the bottom rollers. The method includes changing a break draft ratio of the drafting device in a deactivation process of the spinning frame so that a load torque of the drafting device is smaller than when the break draft ratio is set to a value for normal operation to limit untwisting of the bottom rollers. The method further includes changing a main draft ratio when a fiber bundle, which has passed by the middle bottom roller during a period the break draft ratio is changed, passes by the front bottom roller, to cancel influence on the fiber bundle of the changing in the break draft ratio.

Claims

1. A method for controlling a drafting device of a spinning frame, wherein the drafting device includes a front bottom roller, a middle bottom roller, a back bottom roller, and motors that independently drive the bottom rollers, wherein the method comprises changing a break draft ratio of the drafting device in a deactivation process of the spinning frame so that a load torque of the drafting device is smaller than when the break draft ratio is set to a value for normal operation to limit untwisting of the bottom rollers,
characterized by further comprising changing a main draft ratio when a fiber bundle, which has passed by the middle bottom roller during a period the break draft ratio is changed, passes by the front bottom roller, to cancel influence on the fiber bundle of the changing in the break draft ratio.

2. The method according to claim 1, wherein the break draft ratio in the deactivation process of the spinning frame is changed only by changing a speed of the back bottom roller from a speed that allows the break draft ratio for normal operation to be obtained.

3. The method according to claim 1 or 2, further comprising returning the break draft ratio, in a reactivation period of the spinning frame, to the break draft ratio for normal operation after starting activation of the spinning frame at the break draft ratio that is used when the spinning frame stopped operating.

4. The method according to any one of claims 1 to 3, further comprising calculating a timing when the fiber bundle that has passed by the middle bottom roller during a period in which the break draft ratio is changed, passes by the front bottom roller using a roller gauge between the front bottom roller and the middle bottom roller, roller speeds of the front bottom roller and the middle bottom roller, and a break draft ratio prior to changing.

Drawing