Autoleveller in Drawframe: Types, Operation & Advantages of Autoleveling

Autoleveller

Alternative name for autolevelling include auto regulator, draft, leveller. Although these different names are used by different machinery manufacturers, the basic principle remains the same.

Rieter card leveling operates as medium-term to long-term leveling (closed-loop, produced by a proportional integral regulator) and is performed by a microprocessor. In the feed of the card the feed measuring device records the fluctuations in the cross-section of the batt feed. The speed of the feed roller of the card is changed electronically so that these fluctuations in the cross-section are leveled out. The chute is also included in the control loop.

However, the filling level is not used for regulating the feed rollers in the chute but is considered as an additional control parameter. In the delivery of the card a pair of disc rollers scan the cross-section of the carded sliver as it emerges. These readings are compared electronically with the preselected set value. Deviations in the set value are corrected electronically by altering the speed of the feed roller in the card.

Object of Autoleveling

The object of an autoleveller is to measure the sliver thickness variations and then continuously to after the draft accordingly so that more draft is applied to thick places & less to thin places with the result that the sliver delivered is less irregular than it, otherwise would have been. Besides an improvement in production appearance, autolevelling can also contribute to better productive efficiency, fewer end-breakages in subsequent process, less waste & constant process conditions.

Autoleveller may classified into two main groups according to the basic principle of operation :

• Open loop Autoleveller

The open loop control principle, which can be used for the correction of fairly short term variations, where the solid lines indicate the flow of fibers through the m/c & the broken lines represent to flow of information in the autoleveller unit. The control unit compares the measurement signal with the reference signal which in this case represents the mean output reqd. The control unit accordingly increases, leaves unaltered, or decreases the output of the regulatory which in turn provides a variable speed to the back of front rollers of the process to give the required draft when the measured material  has reached the point at which draft is applied. The magnitude & direction of each change in draft is determined by the magnitude of the change of count previously indicated by the measuring unit. Most of the drawframe autoleveller are open loop auto levellers.

If the direction of the arrows in (a) is followed from any starting point, it always leads out into the open from the diagram at the place marked material by the control unit. Measurement always takes place on the material prior to the material. Thus if measurement is made on the input material, the correction may be applied to either the back rollers or the front rollers.

• Closed loop Autoleveller

The closed loop principle is illustrated in (b); this system is used for the correction of long term & medium term variations. Again the measurement signal is compared with the reference signal by the control unit which then determines the output of the regulator which provides the variable speed to the process to give the required draft.

However, if the direction of the arrows in (b), is following from any starting point except the delivery, is always leads to a never-ending circuit of the loop which links the process & the control unit together, hence the name closed loop; measurement always takes place on the mtl after the point where corrective action is applied. Thus if measurement is made on the output, the correction may be applied to either the back rollers or the front rollers.

It is immediately apparent that the control unit continually cheeks the results of its own actions because measurement is taken from the product of the process. This may be regarded as a basic advantage of the closed loop system, but it is obtained at the price of increased complexity.

Because the flow of fibers in the process forms part of the control loop, this means that the amount of control which can be applied is restricted not only by the limitations of the control unit itself, but the characteristics of the process.

A closed loop system must be designed so as to avoid hunting, i.e. an unwanted oscillation in the output, in this case sliver thickness.

Advantages of Autolevelling

1. All variations are corrected.
2. Count c.v.% will be consistent & good, hence the yarn will be suitable for knitting.
3. Thin places in the sliver, hence in the yarn quality will be low.
4. Ring frame breaks will come down, hence pneumfil waste will be low.
5. Fluff in the department will be less, therefore Uster cuts will be less.
6. Fabric quality will be good because of lower number of fluff in the yarn.
7. Labour productivity will be more.
8. Machine productivity will be more.
9. Idle spindles will be less.
10. RKM c.v.% will be low, because of low number of thin places.
11. Workability in warping & weaving will be good, because of less no. of thin places & lower end breaks in spg & winding.
12. Low sliver U%, hence yarn U% will be good.
13. Production will be more accurate in autoleveller drawframe compared to non autoleveller drawdframe.
14. Variation in Blend percentage will be very less, if both the components are autolevelled before blending, hence fabric appearance after dyeing will be excellent.