Title of Invention	METHOD FOR CONTROLLING DRAFT DEVICE IN SPINNING MACHINE AND CONTROLLER FOR DRAFT DEVICE IN SPINNING MACHINE
Abstract	This invention relates to a method of controlling a draft device 11 in a spinning machine and a controller 21 for draft device 11 in a spinning machine. The purpose to providing the method of controlling the draft device 11 and the controller 21 is to prevent yarn from becoming uneven in starting the spinning machine. The draft device comprises a front bottom roller 12, a middle bottom roller 13 and a back bottom roller 14 which are individually driven by motors 15, 16a, 16b, 17a, 17b. The method comprising the step of: changing a break draft ratio at least during a process of stopping the spinning machine from a predetermined value at a steady operation of the spinning machine such that a load torque of the draft device 11 is reduced.

Title of Invention

METHOD FOR CONTROLLING DRAFT DEVICE IN SPINNING MACHINE AND CONTROLLER FOR DRAFT DEVICE IN SPINNING MACHINE

Abstract

This invention relates to a method of controlling a draft device 11 in a spinning machine and a controller 21 for draft device 11 in a spinning machine. The purpose to providing the method of controlling the draft device 11 and the controller 21 is to prevent yarn from becoming uneven in starting the spinning machine. The draft device comprises a front bottom roller 12, a middle bottom roller 13 and a back bottom roller 14 which are individually driven by motors 15, 16a, 16b, 17a, 17b. The method comprising the step of: changing a break draft ratio at least during a process of stopping the spinning machine from a predetermined value at a steady operation of the spinning machine such that a load torque of the draft device 11 is reduced.

Full Text	METHOD OF CONTROLLING DRAFT DEVICE IN SPINNING MACHINE AND CONTROLLER FOR DRAFT DEVICE IN SPINNING MACHINE BACKGROUND OF THE INVENTION The present invention relates to a method of controlling a draft device in a spinning machine and a controller for a draft device in a spinning machine. In a spinning machine such as a ring spinning machine and a roving frame, a large number of spinning spindles are arranged in the longitudinal direction of the machine. The spinning machine has a draft device including a plurality of bottom rollers which are driven at one end (gear end) of the machine. The bottom rollers are very long in length, so that they are twisted and delayed at an out end of the spinning machine opposite to the gear end in starting the spinning machine. Especially, a bottom apron roller (or a middle bottom roller) on which an apron is wound at each spindle is substantially twisted, and unevenness and breakage of yarn may occur due to the delay by this twist. The yarn unevenness may occur not only due to the delay of the bottom rollers by their twist in starting the spinning machine but also due to twisting back of the bottom rollers during a stop period of the spinning machine. Recently, in a high-speed ring spinning machine, the spindles are driven at a speed of about 25,000 rpm. There nave deen proposed methods of controlling the operation of spinning machines, for preventing trouble such as yarn breakage during a period from start of winding to 20-30 percentage of bundle wound, or for preventing yarn spun at high speed from becoming thinner than desired counts of yarn (cf. Japanese Patent Application Publication No. 2-269814). Japanese Patent Application Publication No. 2-269814 discloses a control method, in which an amount of yarn being spun and wound is detected. The rotation speed of the spindles are changed according to the detected amount of yarn, and total draft ratio is changed according to the change of rotation speed of the spindles, thus preventing counts of spun yarn from varying. Japanese Patent Application Publication No. 2-269814 discloses that during spinning operation, the draft ratio of the draft device is changed to a draft ratio value that is different from a usual value corresponding to yarn counts. However, this change is made to change the total draft ratio according to the change of the rotation speed of the spindles, for preventing yarn counts from varying in the same cop. Therefore, it is not considered that unevenness of yarn occurs due to the twist of the bottom rollers of the draft device. The present invention is directed to a method of controlling a draft device in a spinning machine and a controller for a draft device in a spinning machine, both of which prevent yarn from becoming uneven in starting the spinning machine. SUMMARY OF THE INVENTION According to the present invention, a method of controlling a draft device in a spinning machine is provided. The draft device includes a front bottom roller, a middle bottom roller and a back bottom roller which are individually driven by motors. The method includes the step of changing a break draft ratio at least during a process of stopping the spinning machine from a predetermined value at a steady operation of the spinning machine such that a load torque of the draft device is reduced. The present invention also provides a controller for a draft device in a spinning machine. The draft device includes a front bottom roller, a middle bottom roller and a back bottom roller which are individually driven by motors. The controller includes a break draft ratio changing means operable to change a break draft ratio at least during a process of stopping the spinning machine from a predetermined value such that a load torque of the draft device is reduced. Other aspects and advantages of the 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 The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. 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 view of draft devices according to a preferred embodiment of the present invention, in which a top roller is omitted; FIG. 2 is a graph showing a relation between a break draft ratio and a torque required for break draft; FIG. 3 is a graph showing change of rotation speeds of bottom rollers during the operation of a ring spinning machine; and FIG. 4 is a graph showing change of speeds of bottom rollers during the operation of a ring spinning machine according to an alternative embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe a preferred embodiment with reference to FIGS. 1 through 3. In the preferred embodiment, the present invention is applied to a ring spinning machine which has a pair of draft devices arranged along the longitudinal direction of the spinning machine and on both sides thereof. FIG. 1 is a schematic plan view showing draft devices in which a top roller is omitted. FIG. 2 is a graph showing a relation between a break draft ratio and a torque required for break draft. FIG. 3 is a graph showing change of speeds of bottom rollers during the operation of the ring spinning machine. It is noted that the upper and lower sides in FIG. 1 correspond to the left and right sides of the ring spinning machine. Referring to FIG., 1, each of the draft devices 11 is of a three-roller type including a front bottom roller 12, a middle bottom roller 13 and a back bottom roller 14. The front bottom roller 12 is supported by a roller stand (not shown) at a certain location. The middle and back bottom rollers 13 and 14 are supported by the roller stand through a support bracket (not shown) which is fixed to the roller stand in such a manner that the position thereof is adjustable in the lateral direction of the ring spinning machine or the vertical direction in FIG. 1. The middle bottom roller 13 has an apron (not shown). A front top roller (not shown), a middle top roller (not shown) and a back top roller (not shown) are provided in a known structure corresponding to the bottom rollers 12 through 14, respectively. Each of the front bottom rollers 12 is formed of a roller shaft 12a extending for the entire longitudinal length of the ring spinning machine. Each of the middle bottom rollers 13 is divided into two roller shafts 13a and 13b coaxially arranged. Each of the back bottom rollers 14 is divided into two roller shafts 14a and 14b coaxially arranged. In the preferred embodiment, each of the middle bottom rollers 13 and each of the back bottom rollers 14 are divided at the center in the longitudinal direction of the ring spinning machine. The roller shafts 13a and 13b are symmetrical to each other, and the roller shafts 14a and 14b are symmetrical to each other. The front bottom rollers 12 are driven by a front roller drive motor 15 at one end or a gear end of the ring spinning machine which is on the left side in FIG. 1. The rotation of the front roller drive motor 15 is transmitted to the roller shaft 12a through gear train (not shown). The roller shaft 13a of each middle bottom roller 13, which is located on the left side in FIG. 1, is driven by a first middle roller drive motor 16a at the gear end of the ring spinning machine. The roller shaft 13b of each middle bottom roller 13, which is located on the right side in FIG. 1, is driven by a second middle roller drive motor 16b at an out end of the ring spinning machine opposite to the gear end. The rotation of the first middle roller drive motor 16a is transmitted to the roller shafts 13a through gear train (not shown), and the rotation of the second middle roller drive motor 16b is transmitted to the roller shafts 13b through gear train (not shown). The roller shaft 14a of each back bottom roller 14, which is located on the left side in FIG. 1, is driven by a first back roller drive motor 17a at the gear end of the ring spinning machine. The roller shaft 14b of each back bottom roller 14, which is located on the right side in FIG. 1, is driven by a second back roller drive motor 17b at the out end of the ring spinning machine. The rotation of the first back roller drive motor 17a is transmitted to the roller shafts 14a through gear train (not shown), and the rotation of the second back roller drive motor 17b is transmitted to the roller shafts 14b through gear train (not shown). Servomotors are used as the drive motors 15, 16a, 16b, 17a and 17b. The drive motors 15,16a, 16b, 17a and 17b have rotary encoders 15r, 16ar, 16br, 17ar and 17br, respectively. The drive motors 15, 16a, 16b, 17a and 17b are connected to servo drivers 18, 19a, 19b, 20a and 20b, respectively. The drive motors 15, 16a, 16b, 17a and 17b are controlled by a controller 21 through the servo drivers 18, 19a, 19b, 20a and 20b, respectively. The controller 21 includes a central processing unit (CPU) 22, a program memory 23, an operation memory 24, an input device 25, an input interface (not shown), an output interface (not shown) and a motor drive circuit (not shown). The CPU 22 is connected to the rotary encoders 15r, 16ar, 16br, 17ar and 17br through the input interface. The CPU 22 is also connected to the servo drivers 18, 19a, 19b, 20a and 20b through the output interface and the motor drive circuit. The CPU 22 serves to control drive motors (not shown) for lifting drive and spindle drive. The controller 21 also serves as a controller for the ring spinning machine. The program memory 23 stores program data and various data required for executing the program data. The various data include spinning conditions, such as various fibrous raw materials, counts of spun yarn, counts of twist and the like, and data corresponding to rotation speed of the spindles at the steady operation of the ring spinning machine and rotation speeds of the drive motors for the draft drive and the lifting drive. The program memory 23 stores a change value, to which a break draft ratio is changed during a process of stopping the ring spinning machine, corresponding to the spinning conditions. The program memory 23 also stores the speeds of the middle and back bottom rollers 13 and 14 corresponding to the break draft ratio during the stopping process of the ring spinning machine. The operation memory 24 is operable to temporarily store data inputted from the input device 25 and the result of processing at the CPU 22. The input device 25 is used to input data of spinning conditions such as counts of spun yarn, a kind of fiber (raw material), a maximum rotation speed of spindles during spinning operation, spinning length, lift length, chase length, length of bobbin used and the like. The operation memory 24 has a backup power supply (not shown). The CPU 22 controls the drive motors 15, 16a, 16b, 17a and 17b to rotationally drive the front bottom rollers 12, the middle bottom rollers 13 and the back bottom rollers 14 at the stored speeds thereof such that a break draft ratio and a total draft ratio become preset values corresponding to the spinning conditions. During the stopping process of the ring spinning machine, the CPU 22 changes the break draft ratio of the draft devices 11 from a predetermined value at the steady operation of the ring spinning machine such that a load torque of the draft devices 11 is reduced. It is noted that the predetermined value at the steady operation of the ring spinning machine means a value of the break draft ratio which is set according to the counts of yarn as the spinning conditions without considering twist of the bottom rollers. The relation between the break draft ratio of the draft devices 11 and the torque required for break draft does not exhibit simple proportional relationship, but it is shown by a curve in FIG. 2 with a peak value (or maximum value) of the torque which is determined based on the spinning conditions. If the break draft ratio is greater than a value Bp of the break draft ratio as a first value corresponding to the torque peak value, the load torque decreases as the break draft ratio increases. On the other hand, if the break draft ratio is smaller than the break draft ratio value Bp corresponding to the torque peak value, the load torque decreases as the break draft ratio decreases. Thus, the CPU 22 increases the break draft ratio when the predetermined value of the break draft ratio at the steady operation of the ring spinning machine is greater than the break draft ratio value Bp corresponding to the torque peak value. The CPU 22 decreases the break draft ratio when the predetermined value of the break draft ratio at the steady operation of the ring spinning machine is smaller than the break draft ratio value Bp corresponding to the torque peak value. In the preferred embodiment, the predetermined value of the break draft ratio at the steady operation of the ring spinning machine is 1.25 which is greater than the break draft ratio value Bp corresponding to the torque peak value. Thus, the CPU 22 increases the break draft ratio, for example, to 1.6. In other words, the CPU 22 constitutes a break draft changing means operable to change the break draft ratio of the draft devices 11 at least during the stopping process of the ring spinning machine from the predetermined value such that the load torque of the draft devices 11 is reduced. The CPU 22 is operable to control the drive motors 16a, 16b, 17a and 17b for the middle and back bottom rollers 13 and 14 such that the middle and back bottom rollers 13 and 14 are driven at the stored speeds thereof. The break draft ratio is changed by changing the speed of the middle bottom rollers 13. The change of the break draft ratio is carried out during deceleration after starting speed change or deceleration of the bottom rollers in stopping the ring spinning machine. The time of changing the break draft ratio is set such that a period of time required for replacing the fiber between the back rollers and the middle rollers with fiber which is drafted at the changed draft ratio is ensured until the ring spinning machine is completely stopped. The following will describe the operation of the ring spinning machine as constructed above. Prior to the operation of the ring spinning machine, the spinning conditions such as fibrous raw material, counts of spun yarn, counts of twist and the like is inputted to the controller 21 by way of the input device 25. When the operation of the ring spinning machine is started, the drive motors 15, 16a, 16b, 17a and 17b are controlled based on command from the controller 21 such that they rotate at rotation speeds which provide preset values of the total draft ratio and the break draft ratio corresponding to the spinning conditions. The drive motors (not shown) for the spindle drive and the lifting drive are controlled to rotate at predetermined rotation speeds. When the ring spinning machine is operated, yarn is wound on bobbin which is rotated with the spindle at a winding section (not shown) after drafted by passing through the back rollers, the middle rollers and the front rollers of the draft devices 11. In stopping the ring spinning machine for doffing or suspension of operation, the break draft ratio is changed from the predetermined value (e.g. 1.25) at the steady operation of the ring spinning machine to a value (e.g. 1.6) which reduces the load torque from the load torque at the predetermine value of the break draft ratio. More specifically, the CPU 22 reduces a deceleration rate of the middle bottom rollers 13 such that the break draft ratio becomes 1.6, or such that the rotation speed of the middle bottom rollers 13 becomes larger than the usual rotation speed. After the break draft ratio has reached to 1.6, the middle bottom rollers 13 is decelerated such that the break draft ratio is maintained. More specifically, as shown in FIG. 3, in decelerating the middle bottom rollers 13 during the stopping process of the ring spinning machine, the middle bottom rollers 13 are initially decelerated at a constant deceleration rate such that the usual break draft ratio (1.25) is maintained, and then the deceleration rate is reduced. After the break draft ratio has reached to 1.6, the middle bottom rollers 13 are decelerated at a constant deceleration rate which is higher than that when the break draft ratio is maintained at 1.25 until the ring spinning machine is completely stopped. It is noted that in FIG. 3 the part indicated by the chain double-dashed line shows a state of deceleration in the prior art. The front and back bottom rollers 12 and 14 are decelerated at a constant deceleration rate during a period from start of deceleration to the complete stop. Thus, the total draft ratio is unchanged. During a process of restarting the ring spinning machine, the middle and back bottom rollers 13 and 14 are initially driven or accelerated such that the break draft ratio becomes 1.6 which is the same as that in stopping the ring spinning machine. And then, during the acceleration of the middle bottom rollers 13, an acceleration rate of the middle bottom rollers 13 is changed such that the break draft ratio becomes 1.25 which is the usual value. In other words, the acceleration rate is reduced after the middle bottom rollers 13 are accelerated at an acceleration rate which is higher than the acceleration rate of the prior art indicated by the chain double-dashed line in FIG. 3. After the break draft ratio has reached to the predetermined value (1.25), the middle bottom rollers 13 are accelerated to a predetermined rotation speed such that this break draft ratio is maintained. During deceleration for stopping the ring spinning machine, torque for driving the middle bottom rollers 13 is reduced. Thus, after the first and second middle roller drive motors 16a and 16b are stopped, the middle bottom rollers 13 or the roller shafts 13a and 13b are less twisted back. As a result, yarn is substantially prevented from being excessively fed due to the twisting back of the middle bottom rollers 13 during a period when the ring spinning machine is completely stopped, and hence unevenness of yarn is substantially prevented in restarting the ring spinning machine. During the restarting process of the ring spinning machine, the middle and back bottom rollers 13 and 14 are driven such that the break draft ratio becomes 1.6, to which the break draft ratio is changed in stopping the ring spinning machine. In other words, after the middle and back bottom rollers 13 and 14 are driven in a state that the torque for driving the bottom rollers is reduced, the break draft ratio is changed to the predetermined value (1.25) at which the ring spinning machine is in the steady operation. Therefore, the bottom rollers are substantially prevented from being twisted and hence delayed in restarting the ring spinning machine, thus more reliably preventing yarn unevenness. The following advantageous effects are achieved according to the preferred embodiment. (1) In the draft devices 11, the front bottom rollers 12, the middle bottom rollers 13 and the back bottom rollers 14 are individually driven by the drive motors 15, 16a, 16b, 17a and 17b, respectively. During the stopping process of the ring spinning machine, the break draft ratio of the draft devices 11 is changed from the predetermined value at the steady operation of the ring spinning machine such that the load torque of the draft devices 11 is reduced. Thus, in a state that each drive motor for the bottom rollers is stopped, the bottom rollers are less twisted back. As a result, yarn is substantially prevented from being excessively fed due to the twisting back of the middle bottom rollers 13 during the stopped period of the ring spinning machine, and hence yarn unevenness is substantially prevented in restarting the ring spinning machine. (2) In the draft devices 11, the front bottom rollers 12, the middle bottom rollers 13 and the back bottom rollers 14 are individually driven by the drive motors 15, 16a, 16b, 17a and 17b, respectively. During the stopping process of the ring spinning machine, the break draft ratio of the draft devices 11 is changed from the predetermined value at the steady operation of the ring spinning machine such that the load torque of the draft devices 11 is reduced. During the restarting process of the ring spinning machine, the break draft ratio which is changed in stopping the ring spinning machine is returned to the original value or the predetermined value at the steady operation of the ring spinning machine. Thus, during the initial period of restarting the ring spinning machine, the bottom rollers are driven in a state that the torque for driving the bottom rollers is smaller than that in case of driving the bottom rollers at the original break draft ratio. And then, the break draft ratio is changed to the predetermined value at which the ring spinning machine is in the steady operation. As a result, the bottom rollers are substantially prevented from being twisted and hence delayed in restarting the ring spinning machine, and hence yarn unevenness is more reliably prevented. (3) When the predetermined value of the break draft ratio at the steady operation of the ring spinning machine is larger than the break draft ratio value Bp corresponding to the torque peak value in the curve which is shown in the graph in which the horizontal axis indicates the break draft ratio and the vertical axis indicates the torque required for break draft, the break draft ratio is increased during the stopping process of the ring spinning machine. When the predetermined value of the break draft ratio at the steady operation of the ring spinning machine is smaller than the break draft ratio value Bp corresponding to the torque peak value, the break draft ratio is decreased during the stopping process of the ring spinning machine. Thus, during the stopping process of the ring spinning machine, the break draft ratio is changed such that the torque for driving the bottom rollers is certainly reduced. (4) The break draft ratio is changed by changing the speed of the middle bottom rollers 13. The other manner of changing the break draft ratio is to change the speed of the back bottom rollers 14 or to change the speeds of the middle and back bottom rollers 13 and 14. In the case of changing the speed of the back bottom rollers 14, the speed of the front bottom rollers 12 have to be correspondingly changed, otherwise the total draft ratio will be changed. However, in the preferred embodiment, the speed of the back bottom roller 14 is the same as the usual speed and only the speed of the middle bottom rollers 13 is changed for changing the break draft ratio. Thus, the break draft ratio is changed but the total draft ratio is maintained constant, so that the control is made easier. The present invention is not limited to the preferred embodiment described above but may be modified as exemplified below. As long as the break draft ratio of the draft devices 11 is changed during the stopping process of the ring spinning machine from the predetermined value at the steady operation of the ring spinning machine such that the load torque of the draft devices 11 is reduced, the draft devices 11 do not have to be initially driven during the restarting process of the ring spinning machine at the break draft ratio which is changed during the stopping process of the ring spinning machine. For example, in restarting the ring spinning machine, the draft device 11 may be initially driven such that the break draft ratio becomes the predetermined value at the steady operation of the ring spinning machine. Alternatively, the draft device 11 may be initially driven such that the break draft ratio becomes an intermediate value between the value to which the break draft ratio is changed during the stopping process of the ring spinning machine and the predetermined value at the steady operation of the ring spinning machine. The break draft ratio may be changed by changing the speed of the back bottom rollers 14, instead of by changing the speed of the middle bottom rollers 13. In this case, the back bottom rollers 14 are decelerated for increasing the break draft ratio, while the back bottom rollers 14 are accelerated for decreasing the break draft ratio. The speed of the front bottom rollers 14 need be changed in response to the speed change of the back bottom rollers 14 for maintaining the total draft ratio constant. FIG. 4 shows change of the speed of each bottom roller when the speed of the back bottom rollers 14 is changed for changing the break draft ratio. In FIG. 4, the part indicated by the chain double-dashed line shows change of the rotation speed in the case of acceleration and deceleration in the prior art. Both speeds of the middle and back bottom rollers 13 and 14 may be changed for changing the break draft ratio. The predetermined value of break draft ratio at the steady operation of the ring spinning machine is not limited to be greater than the break draft ratio value Bp corresponding to the torque peak value in the curve that is shown in the graph in which the horizontal axis indicates the break draft ratio and the vertical axis indicates the torque required for break draft, and it may be smaller than the break draft ratio value Bp. In this case, the break draft ratio is decreased during the stopping process of the ring spinning machine. During the stopping process of the ring spinning machine, the time of changing the break draft ratio is not limited to the time during the deceleration of each bottom roller. For example, the changing of the break draft ratio may be started simultaneously with starting deceleration of each bottom roller. Alternatively, the changing of the brake drat ratio may be completed before the deceleration of each bottom roller, and each bottom roller may be decelerated at constant break draft ratio after this changing. The value of the break draft ratio after changing during the stopping process of the ring spinning machine may be inputted by way of the input device 25 in inputting the spinning conditions of the ring spinning machine, instead of using the value which is previously stored in the program memory 23. The drive motors for the front, middle and back bottom rollers 12, 13 and 14 are not limited to the servomotors, and they may be motors whose rotation speed is controllable. For example, inverter-controlled induction motors may be used. The draft device is not limited to the three-roller draft devices 11 and it may be of four-roller type. In the four-roller draft device, second and third bottom rollers on which aprons are respectively wound correspond to the middle bottom roller. If an apron is wound on only the second bottom roller in the four-roller draft device, the second and third bottom roller corresponds to the middle bottom roller and the back bottom roller, respectively. The middle and back bottom rollers 13 and 14 are driven by the drive motors 16a, 16b, 17a and 17b at both ends of the ring spinning machine in the preferred embodiment. However, only a part of bottom rollers (i.e. the middle bottom rollers 13) may be driven by drive motors at both ends of the ring spinning machine, and the back bottom rollers 14 may be driven by a drive motor at one end of the ring spinning machine. The front, middle and back bottom rollers 12, 13 and 14 may be driven by drive motors at only one end of the ring spinning machine depending on the number of spindles in the ring spinning machine. The application of the present invention is not limited to the ring spinning machine which spins from roving. The present invention may be applied to a ring spinning machine which drafts and spins sliver directly into fine-spun yarn not via roving, and other spinning machines, such as an air jet spinning machine, a roving frame and the like, having a draft device in which the roller shafts of the bottom rollers are long and an apron is wound on the middle bottom roller. 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 of the appended claims.

Full Text

METHOD OF CONTROLLING DRAFT DEVICE IN SPINNING MACHINE AND CONTROLLER FOR DRAFT DEVICE IN SPINNING MACHINE
BACKGROUND OF THE INVENTION
The present invention relates to a method of controlling a draft device in a spinning machine and a controller for a draft device in a spinning machine.
In a spinning machine such as a ring spinning machine and a roving frame, a large number of spinning spindles are arranged in the longitudinal direction of the machine. The spinning machine has a draft device including a plurality of bottom rollers which are driven at one end (gear end) of the machine. The bottom rollers are very long in length, so that they are twisted and delayed at an out end of the spinning machine opposite to the gear end in starting the spinning machine. Especially, a bottom apron roller (or a middle bottom roller) on which an apron is wound at each spindle is substantially twisted, and unevenness and breakage of yarn may occur due to the delay by this twist. The yarn unevenness may occur not only due to the delay of the bottom rollers by their twist in starting the spinning machine but also due to twisting back of the bottom rollers during a stop period of the spinning machine.
Recently, in a high-speed ring spinning machine, the spindles are driven

at a speed of about 25,000 rpm. There nave deen proposed methods of controlling the operation of spinning machines, for preventing trouble such as yarn breakage during a period from start of winding to 20-30 percentage of bundle wound, or for preventing yarn spun at high speed from becoming thinner than desired counts of yarn (cf. Japanese Patent Application Publication No. 2-269814). Japanese Patent Application Publication No. 2-269814 discloses a control method, in which an amount of yarn being spun and wound is detected. The rotation speed of the spindles are changed according to the detected amount of yarn, and total draft ratio is changed according to the change of rotation speed of the spindles, thus preventing counts of spun yarn from varying.
Japanese Patent Application Publication No. 2-269814 discloses that during spinning operation, the draft ratio of the draft device is changed to a draft ratio value that is different from a usual value corresponding to yarn counts. However, this change is made to change the total draft ratio according to the change of the rotation speed of the spindles, for preventing yarn counts from varying in the same cop. Therefore, it is not considered that unevenness of yarn occurs due to the twist of the bottom rollers of the draft device.
The present invention is directed to a method of controlling a draft device in a spinning machine and a controller for a draft device in a spinning machine, both of which prevent yarn from becoming uneven in starting the spinning

machine.
SUMMARY OF THE INVENTION
According to the present invention, a method of controlling a draft device in a spinning machine is provided. The draft device includes a front bottom roller, a middle bottom roller and a back bottom roller which are individually driven by motors. The method includes the step of changing a break draft ratio at least during a process of stopping the spinning machine from a predetermined value at a steady operation of the spinning machine such that a load torque of the draft device is reduced.
The present invention also provides a controller for a draft device in a spinning machine. The draft device includes a front bottom roller, a middle bottom roller and a back bottom roller which are individually driven by motors. The controller includes a break draft ratio changing means operable to change a break draft ratio at least during a process of stopping the spinning machine from a predetermined value such that a load torque of the draft device is reduced.
Other aspects and advantages of the 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
The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. 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 view of draft devices according to a preferred embodiment of the present invention, in which a top roller is omitted;
FIG. 2 is a graph showing a relation between a break draft ratio and a torque required for break draft;
FIG. 3 is a graph showing change of rotation speeds of bottom rollers during the operation of a ring spinning machine; and
FIG. 4 is a graph showing change of speeds of bottom rollers during the operation of a ring spinning machine according to an alternative embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following will describe a preferred embodiment with reference to FIGS. 1 through 3. In the preferred embodiment, the present invention is applied to a ring spinning machine which has a pair of draft devices arranged along the longitudinal direction of the spinning machine and on both sides thereof. FIG. 1 is a schematic plan view showing draft devices in which a top roller is omitted. FIG. 2 is a graph showing a relation between a break draft ratio and a torque required for break draft. FIG. 3 is a graph showing change of speeds of bottom rollers during the operation of the ring spinning machine. It is noted that the upper and lower sides in FIG. 1 correspond to the left and right sides of the ring spinning machine.
Referring to FIG., 1, each of the draft devices 11 is of a three-roller type including a front bottom roller 12, a middle bottom roller 13 and a back bottom roller 14. The front bottom roller 12 is supported by a roller stand (not shown) at a certain location. The middle and back bottom rollers 13 and 14 are supported by the roller stand through a support bracket (not shown) which is fixed to the roller stand in such a manner that the position thereof is adjustable in the lateral direction of the ring spinning machine or the vertical direction in FIG. 1. The middle bottom roller 13 has an apron (not shown). A front top roller (not shown), a middle top roller (not shown) and a back top roller (not shown) are provided in a

known structure corresponding to the bottom rollers 12 through 14, respectively.
Each of the front bottom rollers 12 is formed of a roller shaft 12a extending for the entire longitudinal length of the ring spinning machine. Each of the middle bottom rollers 13 is divided into two roller shafts 13a and 13b coaxially arranged. Each of the back bottom rollers 14 is divided into two roller shafts 14a and 14b coaxially arranged. In the preferred embodiment, each of the middle bottom rollers 13 and each of the back bottom rollers 14 are divided at the center in the longitudinal direction of the ring spinning machine. The roller shafts 13a and 13b are symmetrical to each other, and the roller shafts 14a and 14b are symmetrical to each other.
The front bottom rollers 12 are driven by a front roller drive motor 15 at one end or a gear end of the ring spinning machine which is on the left side in FIG. 1. The rotation of the front roller drive motor 15 is transmitted to the roller shaft 12a through gear train (not shown).
The roller shaft 13a of each middle bottom roller 13, which is located on the left side in FIG. 1, is driven by a first middle roller drive motor 16a at the gear end of the ring spinning machine. The roller shaft 13b of each middle bottom roller 13, which is located on the right side in FIG. 1, is driven by a second middle roller drive motor 16b at an out end of the ring spinning machine opposite to the gear

end. The rotation of the first middle roller drive motor 16a is transmitted to the roller shafts 13a through gear train (not shown), and the rotation of the second middle roller drive motor 16b is transmitted to the roller shafts 13b through gear train (not shown).
The roller shaft 14a of each back bottom roller 14, which is located on the left side in FIG. 1, is driven by a first back roller drive motor 17a at the gear end of the ring spinning machine. The roller shaft 14b of each back bottom roller 14, which is located on the right side in FIG. 1, is driven by a second back roller drive motor 17b at the out end of the ring spinning machine. The rotation of the first back roller drive motor 17a is transmitted to the roller shafts 14a through gear train (not shown), and the rotation of the second back roller drive motor 17b is transmitted to the roller shafts 14b through gear train (not shown).
Servomotors are used as the drive motors 15, 16a, 16b, 17a and 17b. The drive motors 15,16a, 16b, 17a and 17b have rotary encoders 15r, 16ar, 16br, 17ar and 17br, respectively. The drive motors 15, 16a, 16b, 17a and 17b are connected to servo drivers 18, 19a, 19b, 20a and 20b, respectively. The drive motors 15, 16a, 16b, 17a and 17b are controlled by a controller 21 through the servo drivers 18, 19a, 19b, 20a and 20b, respectively.
The controller 21 includes a central processing unit (CPU) 22, a program

memory 23, an operation memory 24, an input device 25, an input interface (not shown), an output interface (not shown) and a motor drive circuit (not shown). The CPU 22 is connected to the rotary encoders 15r, 16ar, 16br, 17ar and 17br through the input interface. The CPU 22 is also connected to the servo drivers 18, 19a, 19b, 20a and 20b through the output interface and the motor drive circuit.
The CPU 22 serves to control drive motors (not shown) for lifting drive and spindle drive. The controller 21 also serves as a controller for the ring spinning machine. The program memory 23 stores program data and various data required for executing the program data. The various data include spinning conditions, such as various fibrous raw materials, counts of spun yarn, counts of twist and the like, and data corresponding to rotation speed of the spindles at the steady operation of the ring spinning machine and rotation speeds of the drive motors for the draft drive and the lifting drive. The program memory 23 stores a change value, to which a break draft ratio is changed during a process of stopping the ring spinning machine, corresponding to the spinning conditions. The program memory 23 also stores the speeds of the middle and back bottom rollers 13 and 14 corresponding to the break draft ratio during the stopping process of the ring spinning machine.
The operation memory 24 is operable to temporarily store data inputted from the input device 25 and the result of processing at the CPU 22. The input

device 25 is used to input data of spinning conditions such as counts of spun yarn, a kind of fiber (raw material), a maximum rotation speed of spindles during spinning operation, spinning length, lift length, chase length, length of bobbin used and the like. The operation memory 24 has a backup power supply (not shown).
The CPU 22 controls the drive motors 15, 16a, 16b, 17a and 17b to rotationally drive the front bottom rollers 12, the middle bottom rollers 13 and the back bottom rollers 14 at the stored speeds thereof such that a break draft ratio and a total draft ratio become preset values corresponding to the spinning conditions.
During the stopping process of the ring spinning machine, the CPU 22 changes the break draft ratio of the draft devices 11 from a predetermined value at the steady operation of the ring spinning machine such that a load torque of the draft devices 11 is reduced. It is noted that the predetermined value at the steady operation of the ring spinning machine means a value of the break draft ratio which is set according to the counts of yarn as the spinning conditions without considering twist of the bottom rollers. The relation between the break draft ratio of the draft devices 11 and the torque required for break draft does not exhibit simple proportional relationship, but it is shown by a curve in FIG. 2 with a peak value (or maximum value) of the torque which is determined based on the

spinning conditions. If the break draft ratio is greater than a value Bp of the break draft ratio as a first value corresponding to the torque peak value, the load torque decreases as the break draft ratio increases. On the other hand, if the break draft ratio is smaller than the break draft ratio value Bp corresponding to the torque peak value, the load torque decreases as the break draft ratio decreases. Thus, the CPU 22 increases the break draft ratio when the predetermined value of the break draft ratio at the steady operation of the ring spinning machine is greater than the break draft ratio value Bp corresponding to the torque peak value. The CPU 22 decreases the break draft ratio when the predetermined value of the break draft ratio at the steady operation of the ring spinning machine is smaller than the break draft ratio value Bp corresponding to the torque peak value. In the preferred embodiment, the predetermined value of the break draft ratio at the steady operation of the ring spinning machine is 1.25 which is greater than the break draft ratio value Bp corresponding to the torque peak value. Thus, the CPU 22 increases the break draft ratio, for example, to 1.6. In other words, the CPU 22 constitutes a break draft changing means operable to change the break draft ratio of the draft devices 11 at least during the stopping process of the ring spinning machine from the predetermined value such that the load torque of the draft devices 11 is reduced. The CPU 22 is operable to control the drive motors 16a, 16b, 17a and 17b for the middle and back bottom rollers 13 and 14 such that the middle and back bottom rollers 13 and 14 are driven at the stored speeds thereof.

The break draft ratio is changed by changing the speed of the middle bottom rollers 13. The change of the break draft ratio is carried out during deceleration after starting speed change or deceleration of the bottom rollers in stopping the ring spinning machine. The time of changing the break draft ratio is set such that a period of time required for replacing the fiber between the back rollers and the middle rollers with fiber which is drafted at the changed draft ratio is ensured until the ring spinning machine is completely stopped.
The following will describe the operation of the ring spinning machine as constructed above. Prior to the operation of the ring spinning machine, the spinning conditions such as fibrous raw material, counts of spun yarn, counts of twist and the like is inputted to the controller 21 by way of the input device 25. When the operation of the ring spinning machine is started, the drive motors 15, 16a, 16b, 17a and 17b are controlled based on command from the controller 21 such that they rotate at rotation speeds which provide preset values of the total draft ratio and the break draft ratio corresponding to the spinning conditions. The drive motors (not shown) for the spindle drive and the lifting drive are controlled to rotate at predetermined rotation speeds.
When the ring spinning machine is operated, yarn is wound on bobbin which is rotated with the spindle at a winding section (not shown) after drafted by passing through the back rollers, the middle rollers and the front rollers of the

draft devices 11.
In stopping the ring spinning machine for doffing or suspension of operation, the break draft ratio is changed from the predetermined value (e.g. 1.25) at the steady operation of the ring spinning machine to a value (e.g. 1.6) which reduces the load torque from the load torque at the predetermine value of the break draft ratio. More specifically, the CPU 22 reduces a deceleration rate of the middle bottom rollers 13 such that the break draft ratio becomes 1.6, or such that the rotation speed of the middle bottom rollers 13 becomes larger than the usual rotation speed. After the break draft ratio has reached to 1.6, the middle bottom rollers 13 is decelerated such that the break draft ratio is maintained. More specifically, as shown in FIG. 3, in decelerating the middle bottom rollers 13 during the stopping process of the ring spinning machine, the middle bottom rollers 13 are initially decelerated at a constant deceleration rate such that the usual break draft ratio (1.25) is maintained, and then the deceleration rate is reduced. After the break draft ratio has reached to 1.6, the middle bottom rollers 13 are decelerated at a constant deceleration rate which is higher than that when the break draft ratio is maintained at 1.25 until the ring spinning machine is completely stopped. It is noted that in FIG. 3 the part indicated by the chain double-dashed line shows a state of deceleration in the prior art. The front and back bottom rollers 12 and 14 are decelerated at a constant deceleration rate during a period from start of deceleration to the complete stop. Thus, the total

draft ratio is unchanged.
During a process of restarting the ring spinning machine, the middle and back bottom rollers 13 and 14 are initially driven or accelerated such that the break draft ratio becomes 1.6 which is the same as that in stopping the ring spinning machine. And then, during the acceleration of the middle bottom rollers 13, an acceleration rate of the middle bottom rollers 13 is changed such that the break draft ratio becomes 1.25 which is the usual value. In other words, the acceleration rate is reduced after the middle bottom rollers 13 are accelerated at an acceleration rate which is higher than the acceleration rate of the prior art indicated by the chain double-dashed line in FIG. 3. After the break draft ratio has reached to the predetermined value (1.25), the middle bottom rollers 13 are accelerated to a predetermined rotation speed such that this break draft ratio is maintained.
During deceleration for stopping the ring spinning machine, torque for driving the middle bottom rollers 13 is reduced. Thus, after the first and second middle roller drive motors 16a and 16b are stopped, the middle bottom rollers 13 or the roller shafts 13a and 13b are less twisted back. As a result, yarn is substantially prevented from being excessively fed due to the twisting back of the middle bottom rollers 13 during a period when the ring spinning machine is completely stopped, and hence unevenness of yarn is substantially prevented in

restarting the ring spinning machine.
During the restarting process of the ring spinning machine, the middle and back bottom rollers 13 and 14 are driven such that the break draft ratio becomes 1.6, to which the break draft ratio is changed in stopping the ring spinning machine. In other words, after the middle and back bottom rollers 13 and 14 are driven in a state that the torque for driving the bottom rollers is reduced, the break draft ratio is changed to the predetermined value (1.25) at which the ring spinning machine is in the steady operation. Therefore, the bottom rollers are substantially prevented from being twisted and hence delayed in restarting the ring spinning machine, thus more reliably preventing yarn unevenness.
The following advantageous effects are achieved according to the preferred embodiment.
(1) In the draft devices 11, the front bottom rollers 12, the middle bottom rollers 13 and the back bottom rollers 14 are individually driven by the drive motors 15, 16a, 16b, 17a and 17b, respectively. During the stopping process of the ring spinning machine, the break draft ratio of the draft devices 11 is changed from the predetermined value at the steady operation of the ring spinning machine such that the load torque of the draft devices 11 is reduced. Thus, in a state that each drive motor for the bottom rollers is stopped, the bottom rollers are

less twisted back. As a result, yarn is substantially prevented from being excessively fed due to the twisting back of the middle bottom rollers 13 during the stopped period of the ring spinning machine, and hence yarn unevenness is substantially prevented in restarting the ring spinning machine.
(2) In the draft devices 11, the front bottom rollers 12, the middle bottom rollers 13 and the back bottom rollers 14 are individually driven by the drive motors 15, 16a, 16b, 17a and 17b, respectively. During the stopping process of the ring spinning machine, the break draft ratio of the draft devices 11 is changed from the predetermined value at the steady operation of the ring spinning machine such that the load torque of the draft devices 11 is reduced. During the restarting process of the ring spinning machine, the break draft ratio which is changed in stopping the ring spinning machine is returned to the original value or the predetermined value at the steady operation of the ring spinning machine. Thus, during the initial period of restarting the ring spinning machine, the bottom rollers are driven in a state that the torque for driving the bottom rollers is smaller than that in case of driving the bottom rollers at the original break draft ratio. And then, the break draft ratio is changed to the predetermined value at which the ring spinning machine is in the steady operation. As a result, the bottom rollers are substantially prevented from being twisted and hence delayed in restarting the ring spinning machine, and hence yarn unevenness is more reliably prevented.

(3) When the predetermined value of the break draft ratio at the steady
operation of the ring spinning machine is larger than the break draft ratio value Bp
corresponding to the torque peak value in the curve which is shown in the graph
in which the horizontal axis indicates the break draft ratio and the vertical axis
indicates the torque required for break draft, the break draft ratio is increased
during the stopping process of the ring spinning machine. When the
predetermined value of the break draft ratio at the steady operation of the ring
spinning machine is smaller than the break draft ratio value Bp corresponding to
the torque peak value, the break draft ratio is decreased during the stopping
process of the ring spinning machine. Thus, during the stopping process of the
ring spinning machine, the break draft ratio is changed such that the torque for
driving the bottom rollers is certainly reduced.
(4) The break draft ratio is changed by changing the speed of the middle
bottom rollers 13. The other manner of changing the break draft ratio is to change
the speed of the back bottom rollers 14 or to change the speeds of the middle and
back bottom rollers 13 and 14. In the case of changing the speed of the back
bottom rollers 14, the speed of the front bottom rollers 12 have to be
correspondingly changed, otherwise the total draft ratio will be changed. However,
in the preferred embodiment, the speed of the back bottom roller 14 is the same
as the usual speed and only the speed of the middle bottom rollers 13 is changed
for changing the break draft ratio. Thus, the break draft ratio is changed but the

total draft ratio is maintained constant, so that the control is made easier.
The present invention is not limited to the preferred embodiment described above but may be modified as exemplified below.
As long as the break draft ratio of the draft devices 11 is changed during the stopping process of the ring spinning machine from the predetermined value at the steady operation of the ring spinning machine such that the load torque of the draft devices 11 is reduced, the draft devices 11 do not have to be initially driven during the restarting process of the ring spinning machine at the break draft ratio which is changed during the stopping process of the ring spinning machine. For example, in restarting the ring spinning machine, the draft device 11 may be initially driven such that the break draft ratio becomes the predetermined value at the steady operation of the ring spinning machine. Alternatively, the draft device 11 may be initially driven such that the break draft ratio becomes an intermediate value between the value to which the break draft ratio is changed during the stopping process of the ring spinning machine and the predetermined value at the steady operation of the ring spinning machine.
The break draft ratio may be changed by changing the speed of the back bottom rollers 14, instead of by changing the speed of the middle bottom rollers 13. In this case, the back bottom rollers 14 are decelerated for increasing the

break draft ratio, while the back bottom rollers 14 are accelerated for decreasing the break draft ratio. The speed of the front bottom rollers 14 need be changed in response to the speed change of the back bottom rollers 14 for maintaining the total draft ratio constant. FIG. 4 shows change of the speed of each bottom roller when the speed of the back bottom rollers 14 is changed for changing the break draft ratio. In FIG. 4, the part indicated by the chain double-dashed line shows change of the rotation speed in the case of acceleration and deceleration in the prior art.
Both speeds of the middle and back bottom rollers 13 and 14 may be changed for changing the break draft ratio. The predetermined value of break draft ratio at the steady operation of the ring spinning machine is not limited to be greater than the break draft ratio value Bp corresponding to the torque peak value in the curve that is shown in the graph in which the horizontal axis indicates the break draft ratio and the vertical axis indicates the torque required for break draft, and it may be smaller than the break draft ratio value Bp. In this case, the break draft ratio is decreased during the stopping process of the ring spinning machine.
During the stopping process of the ring spinning machine, the time of changing the break draft ratio is not limited to the time during the deceleration of each bottom roller. For example, the changing of the break draft ratio may be started simultaneously with starting deceleration of each bottom roller.

Alternatively, the changing of the brake drat ratio may be completed before the deceleration of each bottom roller, and each bottom roller may be decelerated at constant break draft ratio after this changing.
The value of the break draft ratio after changing during the stopping process of the ring spinning machine may be inputted by way of the input device 25 in inputting the spinning conditions of the ring spinning machine, instead of using the value which is previously stored in the program memory 23.
The drive motors for the front, middle and back bottom rollers 12, 13 and 14 are not limited to the servomotors, and they may be motors whose rotation speed is controllable. For example, inverter-controlled induction motors may be used.
The draft device is not limited to the three-roller draft devices 11 and it may be of four-roller type. In the four-roller draft device, second and third bottom rollers on which aprons are respectively wound correspond to the middle bottom roller. If an apron is wound on only the second bottom roller in the four-roller draft device, the second and third bottom roller corresponds to the middle bottom roller and the back bottom roller, respectively.
The middle and back bottom rollers 13 and 14 are driven by the drive

motors 16a, 16b, 17a and 17b at both ends of the ring spinning machine in the preferred embodiment. However, only a part of bottom rollers (i.e. the middle bottom rollers 13) may be driven by drive motors at both ends of the ring spinning machine, and the back bottom rollers 14 may be driven by a drive motor at one end of the ring spinning machine. The front, middle and back bottom rollers 12, 13 and 14 may be driven by drive motors at only one end of the ring spinning machine depending on the number of spindles in the ring spinning machine.
The application of the present invention is not limited to the ring spinning machine which spins from roving. The present invention may be applied to a ring spinning machine which drafts and spins sliver directly into fine-spun yarn not via roving, and other spinning machines, such as an air jet spinning machine, a roving frame and the like, having a draft device in which the roller shafts of the bottom rollers are long and an apron is wound on the middle bottom roller.
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 of the appended claims.

Documents:

1243-CHE-2006 CORRESPONDENCE OTHERS.pdf

1243-CHE-2006 CORRESPONDENCE PO.pdf

1243-che-2006-abstract.pdf

1243-che-2006-claims.pdf

1243-che-2006-correspondence-others.pdf

1243-che-2006-description-complete.pdf

1243-che-2006-drawings.pdf

1243-che-2006-form 1.pdf

1243-che-2006-form 18.pdf

1243-che-2006-form 3.pdf

1243-che-2006-form 5.pdf

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Patent Number

234073

Indian Patent Application Number

1243/CHE/2006

PG Journal Number

22/2009

Publication Date

29-May-2009

Grant Date

05-May-2009

Date of Filing

17-Jul-2006

Name of Patentee

KABUSHIKI KAISHA TOYOTA JIDOSHOKKI

Applicant Address

2-1, TOYOD-CHO, KARIYA-SHI, AICHI-KEN,

Inventors:

#	Inventor's Name	Inventor's Address
1	HAYASHI, HISAAKI	C/O KABUSHIKI KAISHA TOYOTA JIDOSHOKKI, 2-1, TOYODA-CH0, KARIYA-SHI, AICHI-KEN,
2	SHINOZAKI, YUTAKA	C/O KABUSHIKI KAISHA TOYOTA JIDOSHOKKI, 2-1, TOYODA-CH0, KARIYA-SHI, AICHI-KEN,
3	KOJIMA, NAOKI	C/O KABUSHIKI KAISHA TOYOTA JIDOSHOKKI, 2-1, TOYODA-CH0, KARIYA-SHI, AICHI-KEN,
4	FUJII, YOSHIMASA	C/O KABUSHIKI KAISHA TOYOTA JIDOSHOKKI, 2-1, TOYODA-CH0, KARIYA-SHI, AICHI-KEN,
5	NIIMI, KIWAMU	C/O KABUSHIKI KAISHA TOYOTA JIDOSHOKKI, 2-1, TOYODA-CH0, KARIYA-SHI, AICHI-KEN,

PCT International Classification Number

D01H1/20

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2005-209133	2005-07-19	Japan