- Email: [email protected]
On-Line Seam Qualification and Control in a Sewing Machine
IFAC
Copyright 1; IFAC Manufacturing. Modelling. Management and Control. Prague. Czech Republic. 200 I
c:
0
C>
Publications www.elsevier.com/locate.ifac
ON-LINE SEAM QUALIFICATION AND CONTROL IN A SEWING MACHINE M.A. Carvalho· and F.B.N. Ferreira
2
J University ofMinho. Textile Engineering Department. A::lIrem. 480() GlIimariies Tel: + 351 ]53510]80, Fax: + 351 ]53 510]93. email: [email protected]
.,
- University of Minho. Textile Engineering Department. A::urem. 4800 Guimariies Tel: + 351 ]53510280, Fax: + 351 253510]93. [email protected]
Abstract: This paper presents part of the results achieved with the use of a system and electronic equipment on an overlock sewing machine, to acquire, monitor and storage the variations of the thread tensions during the stitch formation . The correct balancing of the stitch, as well as the amount of the overall pre-tension given to the threads are of the highest importance to a quality stitch formation. The system developed allows the establishment of relationships between thread tension on the three threads involved in the stitch formation of stitch type 504 and its consumption and the evaluation of the quality of the seams. The knowledge of the absolute reference values of each variable on different sewing conditions, are the first step for the development of a control device to guarantee the on-line set-up of the sewing machine . Another application of the system used is the possibility to compare on-line the "sewability" of different materials. Copyright([) 20011FAC Keywords: Thread Tensions, Thread Consumption, Monitoring, Control.
This research project is being carried by a team at University of Minho, namely the Departments of Textile, Electronics and Mechanical Engineering (Carvalho, 1996; Ferreira, 1991; Rocha, 1996; H. Carvalho, 1998; Silva, et aI., 1999; Carvalho and Ferreira, 2000).
I. INTRODUCTION In order to obtain balanced stitch's and therefore quality seams in the apparel industry, the setting up of the machines is one of the most important tasks and more time consuming. The need to have these machines constantly being adjusted is a consequence of the market demands for short quantities per order and with higher level of quality required. Sewing machines must be reliable and flexible to these changes.
2. OVERVIEW OF THE SYSTEM As to the parameters discussed here, an overlock sewing machine was equipped with devices in order to acquire, store and analyse data reflecting the behaviour of the tensions in the threads involved in the formation of one of the most common sewing stitch type, the 504.
The pre-tensions applied on each thread and its consumption will determine the quality of the sewing process.
The system consists of data collection devices, namely sensors cantilever beams strain gauges, encoders customspecified for the precision needed and hardware for signal conditioning and processing. These devices are connected to a data acquisition board installed in a normal Pc.
By defining the ideal pre-tension values for each thread according to the type of material being sewn, an important step will be done to shorten the setting times of these machines. But if these values can be automatically adjusted, by determining the ideal relations between real thread consumption and the tension generated on each sewing thread during the stitch cycle, this problem no longer exists.
A software program allows the on-line graphical display and signal processing functions for the thread tensions
103
four peaks where analysed and three peaks for the upper looper thread . Based on the analysis of the position of the elements invol\'ed in stitch formation during each one of the four peaks in the needle and lower looper and the three peaks in upper looper, peaks importance was e\aluated, as \\ell as the role of each thread in stitch formation.
and thread consumption ·s. The program includes also an on-line presentation of the quality result for each seam, basic statistical facilities are also a\'ailablc for more detailed evaluation of the results (H. Carvalho, et aI. , 1997; H. Carvalho, et aI., 1998). Furthermore, the program \\'ill include a feed-back to the machine in order be able to adjust automaticall) the machine .
3. RESULTS AND DISCUSSION For all the experiments carried on in this project. the materials used where selected to represent normal types of knitting fabrics (more common for the overlock sewing machines) used in the apparel industry . To represent the thread tension variation during the stitch cycle , the software develops a curve, where different peaks of tension occur, reflecting the behaviour of the elements involved in stitch formation and its absolute value for the pre-tension adjusted in the threads, in order to obtain a balanced stitch. The curves obtained for each one are presented next.
Fig. 2. Position of the elements directly involved in stitch formation during peak I and peak 2 in the needle thread. Different correlation's were performed between each one of the peaks in order to establish the best situation to allow the characterisation of stitch qual ity.
3. J Thread Tensions Thread tensions are measured by positioning three highsensitivity semiconductor strain gauge sensors in the path of the threads. These sensors were specifically developed to dynamically measure and track quick variations of the thread tensions (H . Carvalho, et aI., 1998). 1if;coIIIIo .. _
Tension
t:JI!I,D
(eN)
tlO.(l
....
Peak 1 Pull. 3
,
,
,,..-
..... . ,""
.,..,
..
.
~
Peak 1
~ I
,
I
; /1
11
~
Peak 1 \
1\
\
~eedl,e- f - -
(eN)
P •• k .f
, i,r P~alr: J l,-{,ealr:
,
, :\
Tension Peak 2 Lower Looper
If\. Peak 4 I
11 V
,..,
Figure 3 represents the relation in terms of peak 2 for the needle and lower looper threads for a jersey sewn in the different thread tension adjustments on the three threads.
"..f- i J( r'1I v i' " 11 1-
Pe.
'/ '
~~VI
!
\,~::pe;f-
,V
1
I Pea~y ~l
\\
UPP"" _
1\ \ loope.
, , J, \.\ .J--1 iJ , \~ ~l--i-LL~-.-l--+- i -- . :-.-L-L -1-1.-~
tOOUO"4t,*,UO'200::::tl2"')2I(olSlO3003:0..JIC3Kl_400
Angle
Peak 2 TenSion Needle (eN )
IDeg'ees )
Le gend : BA LANCED - Balanced stitch; NLT - Needle thread low tension; N HT . Needle thread highly tensioned; ULL T - Upper looper thread low tension; ULHT - Upper looper thread highly tensioned; LLL T - Lower looper thread low tension ; LLHT - Lower looper thread highly tensioned.
Fig. I. Needle, Lower and Upper Loopers thread tension variation in one complete stitch cycle. (Interlock, Ne24, K 14).
Fig. 3. Relationship bet\veen the second peaks of tension of the needle and lower looper threads for a jersey sewn in different thread tension adjustments on the three threads. (Jersey, Ne24, KI4).
Figure I shows the typical tension vanatlons during a complete stitch cycle on each thread (needle, lower and upper looper). For the needle and lower looper threads,
104
the border of the fabrics being sev,rn and the needle thread holds the looper's threads without "puckering" the fabric and being almost invi sible when observed by the lower looper thread 's side (Carvalho e Ferreira, 1996).
In figure 4 it is possible to sec how the variation of the pre-tension in the needle thread affects the tension in the lower looper thread. The relation betv..een the lower looper and the needle threads is shown here. When pre-tension varies in onc of the threads there is an influence in the other thread. This can be explained by observing the positioning of each thread in the construction of the stitch type 504. The \\ay that both threads are crossing in the bottom of the seam, holding each other, justities this influence.
It means that the amount of pre-tension on each thread is responsible for the geometry of the stitch and therefore tor the thread consumption of the three different thread s. A prope r relation of the consumption between these threads will guarantee a quality seam. This is managed by adjusting properly the threads pre-tension.
This relationship between these t\>,'o threads was studied in detail and was visible that they haw an important contact during the stitch formation .
The graphical representation of thread consumption for eac h acquisition of stitches is represented in the tollowing figure.
Lower Looper
t~EEDLE
24 .0-.-----.----__r--._-~-__r--._-
Thread TenslOO
Peak 1 (eN)
22.0-1---+---+---+-
Cons
20.0-
(cm)
1 8.0---+--__r-="""'+--+-+i-~~ 1II'!i'1'!~+16.0-r---+-----,f-t-.;-'~~\_+-..yo:~::.n~'F__+-
14,0 -,---+-::=:£--:I0Il 12.0-f---+-+1iiiIIi lOW 10.08.0-
6.0-1---+- . , . + - - - + - - - t - - + -- - + - 4.0-, 0.0
zO.o
, 40.0
60'.0
•
I
I
80.0
100.0
120 0
Cons
I
140
(cm)
Needle Thr ead TensIOn Peak 1
(eN)
Fig. 4. Needle thread tension vs Lower Looper tension in terms of pcak I for a balanced stitch and for stitches with high and low pre-tension in needle 's thread. (Jersey, Ne24, KI4).
UPPER LOOPER
Cons
On the other side, when pre-tension varies in the upper looper thread, there is no significant influence in the other two threads. Upper looper thread is not as much important as the other threads, behaving more as a follower thread .
(cm)
3.2 Thread Consumption Legend : BAL . Balanced sti tch : NL T • Needle thread low tension: NHT • Needle thread hi ghly tensioned; ULL T . Upper looper thread 10\, tension: UL HT . Upper looper thread highly tensioned: LLL T • Lo"er looper thread 10" tension: LLHT . Lower looper thread highly tensioned.
The knowledge of the thread consumption becomes an important parameter for the seam qualification, once to he able to quantify a balanced stitch, it is not enough the acquisition and analysis of thread tension and its relationship To measure the thread consumption of the three threads, three encoders were introduced in the path of each thread. This way it is possible to acquire for each experiment the total amount of thread used in the seam and compare it with other parameters.
Fig. 5. Variation of thread consumption in one complete acquisition for the needle, lower and upper looper threads for the different pre-tension adjustments on eac h thread . (Jersey, Ne24, KI4). Figure 6 shows the effect of the pre-tension variation in the needle thread tension , Thi s same experiment was done in the looper threads ,
A balanced stitch (type 504) is produced when the upper and lower looper's threads are crossed in the middle of
105
Tension (eN)
..."
~,,-~
I
...."
.... ,
f'fNll
>Cl"
""'"
-.... ,.."
" -"
"'" 00jl
E"
"'"
\ \
J ~
1\
/.
V
r.-- ..,..
1 .\/, I. II! r lY
1\ \
"" 1\':~
The following figure shows the representation of Stitcheck obtained on a jersey fabric produced with yarn Ne 24 and tightness factor 14, on seams with two plies.
,
;
1\"
N
I
{
I I HIGH
I1
1/11/ Ill'
.....
uo"
.... , r",
J
,
\
BAtANaO
c~
c:=:
t lOW
Cc
!
( ..,
~"
c
I Li.'HT
)
""'"
N~T
c
/'
\
~ f?\: ~I-"
DO·: ~
,
f--..
yLLT:
J
"
~ 1\
I- ~
BALANCED ~'i>
NHT
Angle (Degrees)
u~
V- t - 1\ 'V
I'>t:'~
\le.: D J LI,LT
Fig. 6. Needle thread tensions variation in one complete stitch cycle for a balanced stitch and for stitches with high and low pre-tension in needle's thread. (Jersey, Ne24, KI4).
Legend: LLHT - Lower looper thread highly tensioned; NL T Needle thread low tension; ULL T - Upper looper thread low tension; BALANCED - Balanced stitch; ULHT - Upper looper thread highly tensioned; NHT - Needle thread highly tensioned; LLL T - Lower looper thread low tension.
Each different stitch adjustment was analysed in distinct structures of knitted fabrics (jersey, rib and interlock), produced with different yarns (Ne 20, 24 and 30) and in various tightness factors (K ).
Fig. 7. Stitcheck representation for a jersey sewn in different thread tension adjustments on the three threads. (Jersey, Ne24, KI4).
3.3 General Discussion
Here it is possible to see that a balanced stitch always occurs in the same area, which represents an ideal thread tension on the three threads. When pre-tension varies on each thread also varies the positioning of Stitcheck.
As it was shown on the previous graphics, it is possible to perform accurate signal acquisition and to detect on the various measured variables, the effect of different sewing conditions.
With the definition of each possible position of Stitcheck for each type of not balanced stitch, we intend to develop a control system to balance automatically the sewing process.
This system shows a high potential to be used as a testing equipment. Another possible use of this system is to detect defects in the stitch formation (Carvalho e Ferreira, 1999).
4. CONCLUSION
Nevertheless, the purpose of this investigation is to find a way to control on-line the quality of each seam as operator is performing his job.
At this moment, studies are being carried out in order to further understand the phenomenon that are happening during stitch formation, namely the relationship between thread tensions and thread consumption.
3.4 Automatic Seam Qualification - Stitcheck
We believe that through the relationship between these parameters it will be possible to establish the correct combination between them, in order to obtain always a balanced stitch and consequently also be able to control the sewing machine in an automatic mode.
A factor was defined to evaluate the quality of the seams and designated as Stitcheck. Stitcheck is obtained with a defined relationship of peaks of tension on the three threads in the x axis and thread consumption on the y axis.
The equipment developed has proven to be an important tool for testing the "sewability" of any fabric, regarding thread tension and thread consumption.
The amount of tension that occurs when the stitch is being formed was chosen to control the quality of the seams, together with its thread consumption.
With this instrumented sewing machine, it will be possible to test new materials, to prevent defects and to guaranty better and more reliable quality in production.
106
The same approach is being done on another type of sewing machines.
5. REFERENCES Carvalho, M.A . (1996) "Estudo das Tensoes nas Linhas na Maquina de Costura Corta-e-cose", Msc thesis; University of Minho, Guimaraes. Ferreira, F.B.N. (1991), "A Study of Thread Tensions on a Lockstitch Sewing Machine", PhD thesis; University of Leeds. Rocha A.M . (1996), "Contribution to the Automatic Control of Sewing Parameters: Study of Needle Penetration and Feeding Dynamics", PhD thesis; University of Minho, Guimaraes. Carvalho H. (1998), "Medic;ao e Analise de Parametros em Maquina de Costura Industrial", Msc thesis; University of Minho, Guimariies. Carvalho M .A. and F.B.N. Ferreira (1996), "Study of Thread Tensions on an Overlock Sewing Machine", in Proceedings of the 3rd International Conference on Mechatronics and Machine Vision in Practice, pp 223-226; University of Minho, Guimaraes. Carvalho H., F.B.N . Ferreira and 1. Monteiro (1997), "Measurements and Feature Extraction in High-Speed Sewing", Proceedings of the ISI£'97, pp 961966;University ofMinho, Guimaraes. Carvalho H., J. Monteiro, F.B.N. Ferreira and A. Rocha (1998), "A sewing rig with automatic feature extraction"; Proceedings of the 6th UK Mechatronics Forum International Conference (Mechatronics'98), pp 727-732, Skovde. Silva L.F., M. Lima, F.B.N . Ferreira, 1. Coelho and C. Couto (1999), "Development of a Mechatronic Controlled Actuation on the Presser Foot of an Overlock Sewing Machine", Proceedings of the 44th International Scientific Colloquium (44.1WK.99), Vo\. 2, pp. 116-121, Technical University of Ilmenau. Carvalho M.A. and F.B.N. Ferreira (2000), "Seam Qualification and Control of Parameters in an Overlock Sewing Machine", in Proceedings of the SPRING 2000 Meeting, "Sustainability And Recycling Of Textile Materials", The Fiber Society, University of Minho, Guimaraes.
107
Copyright 1; IFAC Manufacturing. Modelling. Management and Control. Prague. Czech Republic. 200 I
c:
0
C>
Publications www.elsevier.com/locate.ifac
ON-LINE SEAM QUALIFICATION AND CONTROL IN A SEWING MACHINE M.A. Carvalho· and F.B.N. Ferreira
2
J University ofMinho. Textile Engineering Department. A::lIrem. 480() GlIimariies Tel: + 351 ]53510]80, Fax: + 351 ]53 510]93. email: [email protected]
.,
- University of Minho. Textile Engineering Department. A::urem. 4800 Guimariies Tel: + 351 ]53510280, Fax: + 351 253510]93. [email protected]
Abstract: This paper presents part of the results achieved with the use of a system and electronic equipment on an overlock sewing machine, to acquire, monitor and storage the variations of the thread tensions during the stitch formation . The correct balancing of the stitch, as well as the amount of the overall pre-tension given to the threads are of the highest importance to a quality stitch formation. The system developed allows the establishment of relationships between thread tension on the three threads involved in the stitch formation of stitch type 504 and its consumption and the evaluation of the quality of the seams. The knowledge of the absolute reference values of each variable on different sewing conditions, are the first step for the development of a control device to guarantee the on-line set-up of the sewing machine . Another application of the system used is the possibility to compare on-line the "sewability" of different materials. Copyright([) 20011FAC Keywords: Thread Tensions, Thread Consumption, Monitoring, Control.
This research project is being carried by a team at University of Minho, namely the Departments of Textile, Electronics and Mechanical Engineering (Carvalho, 1996; Ferreira, 1991; Rocha, 1996; H. Carvalho, 1998; Silva, et aI., 1999; Carvalho and Ferreira, 2000).
I. INTRODUCTION In order to obtain balanced stitch's and therefore quality seams in the apparel industry, the setting up of the machines is one of the most important tasks and more time consuming. The need to have these machines constantly being adjusted is a consequence of the market demands for short quantities per order and with higher level of quality required. Sewing machines must be reliable and flexible to these changes.
2. OVERVIEW OF THE SYSTEM As to the parameters discussed here, an overlock sewing machine was equipped with devices in order to acquire, store and analyse data reflecting the behaviour of the tensions in the threads involved in the formation of one of the most common sewing stitch type, the 504.
The pre-tensions applied on each thread and its consumption will determine the quality of the sewing process.
The system consists of data collection devices, namely sensors cantilever beams strain gauges, encoders customspecified for the precision needed and hardware for signal conditioning and processing. These devices are connected to a data acquisition board installed in a normal Pc.
By defining the ideal pre-tension values for each thread according to the type of material being sewn, an important step will be done to shorten the setting times of these machines. But if these values can be automatically adjusted, by determining the ideal relations between real thread consumption and the tension generated on each sewing thread during the stitch cycle, this problem no longer exists.
A software program allows the on-line graphical display and signal processing functions for the thread tensions
103
four peaks where analysed and three peaks for the upper looper thread . Based on the analysis of the position of the elements invol\'ed in stitch formation during each one of the four peaks in the needle and lower looper and the three peaks in upper looper, peaks importance was e\aluated, as \\ell as the role of each thread in stitch formation.
and thread consumption ·s. The program includes also an on-line presentation of the quality result for each seam, basic statistical facilities are also a\'ailablc for more detailed evaluation of the results (H. Carvalho, et aI. , 1997; H. Carvalho, et aI., 1998). Furthermore, the program \\'ill include a feed-back to the machine in order be able to adjust automaticall) the machine .
3. RESULTS AND DISCUSSION For all the experiments carried on in this project. the materials used where selected to represent normal types of knitting fabrics (more common for the overlock sewing machines) used in the apparel industry . To represent the thread tension variation during the stitch cycle , the software develops a curve, where different peaks of tension occur, reflecting the behaviour of the elements involved in stitch formation and its absolute value for the pre-tension adjusted in the threads, in order to obtain a balanced stitch. The curves obtained for each one are presented next.
Fig. 2. Position of the elements directly involved in stitch formation during peak I and peak 2 in the needle thread. Different correlation's were performed between each one of the peaks in order to establish the best situation to allow the characterisation of stitch qual ity.
3. J Thread Tensions Thread tensions are measured by positioning three highsensitivity semiconductor strain gauge sensors in the path of the threads. These sensors were specifically developed to dynamically measure and track quick variations of the thread tensions (H . Carvalho, et aI., 1998). 1if;coIIIIo .. _
Tension
t:JI!I,D
(eN)
tlO.(l
....
Peak 1 Pull. 3
,
,
,,..-
..... . ,""
.,..,
..
.
~
Peak 1
~ I
,
I
; /1
11
~
Peak 1 \
1\
\
~eedl,e- f - -
(eN)
P •• k .f
, i,r P~alr: J l,-{,ealr:
,
, :\
Tension Peak 2 Lower Looper
If\. Peak 4 I
11 V
,..,
Figure 3 represents the relation in terms of peak 2 for the needle and lower looper threads for a jersey sewn in the different thread tension adjustments on the three threads.
"..f- i J( r'1I v i' " 11 1-
Pe.
'/ '
~~VI
!
\,~::pe;f-
,V
1
I Pea~y ~l
\\
UPP"" _
1\ \ loope.
, , J, \.\ .J--1 iJ , \~ ~l--i-LL~-.-l--+- i -- . :-.-L-L -1-1.-~
tOOUO"4t,*,UO'200::::tl2"')2I(olSlO3003:0..JIC3Kl_400
Angle
Peak 2 TenSion Needle (eN )
IDeg'ees )
Le gend : BA LANCED - Balanced stitch; NLT - Needle thread low tension; N HT . Needle thread highly tensioned; ULL T - Upper looper thread low tension; ULHT - Upper looper thread highly tensioned; LLL T - Lower looper thread low tension ; LLHT - Lower looper thread highly tensioned.
Fig. I. Needle, Lower and Upper Loopers thread tension variation in one complete stitch cycle. (Interlock, Ne24, K 14).
Fig. 3. Relationship bet\veen the second peaks of tension of the needle and lower looper threads for a jersey sewn in different thread tension adjustments on the three threads. (Jersey, Ne24, KI4).
Figure I shows the typical tension vanatlons during a complete stitch cycle on each thread (needle, lower and upper looper). For the needle and lower looper threads,
104
the border of the fabrics being sev,rn and the needle thread holds the looper's threads without "puckering" the fabric and being almost invi sible when observed by the lower looper thread 's side (Carvalho e Ferreira, 1996).
In figure 4 it is possible to sec how the variation of the pre-tension in the needle thread affects the tension in the lower looper thread. The relation betv..een the lower looper and the needle threads is shown here. When pre-tension varies in onc of the threads there is an influence in the other thread. This can be explained by observing the positioning of each thread in the construction of the stitch type 504. The \\ay that both threads are crossing in the bottom of the seam, holding each other, justities this influence.
It means that the amount of pre-tension on each thread is responsible for the geometry of the stitch and therefore tor the thread consumption of the three different thread s. A prope r relation of the consumption between these threads will guarantee a quality seam. This is managed by adjusting properly the threads pre-tension.
This relationship between these t\>,'o threads was studied in detail and was visible that they haw an important contact during the stitch formation .
The graphical representation of thread consumption for eac h acquisition of stitches is represented in the tollowing figure.
Lower Looper
t~EEDLE
24 .0-.-----.----__r--._-~-__r--._-
Thread TenslOO
Peak 1 (eN)
22.0-1---+---+---+-
Cons
20.0-
(cm)
1 8.0---+--__r-="""'+--+-+i-~~ 1II'!i'1'!~+16.0-r---+-----,f-t-.;-'~~\_+-..yo:~::.n~'F__+-
14,0 -,---+-::=:£--:I0Il 12.0-f---+-+1iiiIIi lOW 10.08.0-
6.0-1---+- . , . + - - - + - - - t - - + -- - + - 4.0-, 0.0
zO.o
, 40.0
60'.0
•
I
I
80.0
100.0
120 0
Cons
I
140
(cm)
Needle Thr ead TensIOn Peak 1
(eN)
Fig. 4. Needle thread tension vs Lower Looper tension in terms of pcak I for a balanced stitch and for stitches with high and low pre-tension in needle 's thread. (Jersey, Ne24, KI4).
UPPER LOOPER
Cons
On the other side, when pre-tension varies in the upper looper thread, there is no significant influence in the other two threads. Upper looper thread is not as much important as the other threads, behaving more as a follower thread .
(cm)
3.2 Thread Consumption Legend : BAL . Balanced sti tch : NL T • Needle thread low tension: NHT • Needle thread hi ghly tensioned; ULL T . Upper looper thread 10\, tension: UL HT . Upper looper thread highly tensioned: LLL T • Lo"er looper thread 10" tension: LLHT . Lower looper thread highly tensioned.
The knowledge of the thread consumption becomes an important parameter for the seam qualification, once to he able to quantify a balanced stitch, it is not enough the acquisition and analysis of thread tension and its relationship To measure the thread consumption of the three threads, three encoders were introduced in the path of each thread. This way it is possible to acquire for each experiment the total amount of thread used in the seam and compare it with other parameters.
Fig. 5. Variation of thread consumption in one complete acquisition for the needle, lower and upper looper threads for the different pre-tension adjustments on eac h thread . (Jersey, Ne24, KI4). Figure 6 shows the effect of the pre-tension variation in the needle thread tension , Thi s same experiment was done in the looper threads ,
A balanced stitch (type 504) is produced when the upper and lower looper's threads are crossed in the middle of
105
Tension (eN)
..."
~,,-~
I
...."
.... ,
f'fNll
>Cl"
""'"
-.... ,.."
" -"
"'" 00jl
E"
"'"
\ \
J ~
1\
/.
V
r.-- ..,..
1 .\/, I. II! r lY
1\ \
"" 1\':~
The following figure shows the representation of Stitcheck obtained on a jersey fabric produced with yarn Ne 24 and tightness factor 14, on seams with two plies.
,
;
1\"
N
I
{
I I HIGH
I1
1/11/ Ill'
.....
uo"
.... , r",
J
,
\
BAtANaO
c~
c:=:
t lOW
Cc
!
( ..,
~"
c
I Li.'HT
)
""'"
N~T
c
/'
\
~ f?\: ~I-"
DO·: ~
,
f--..
yLLT:
J
"
~ 1\
I- ~
BALANCED ~'i>
NHT
Angle (Degrees)
u~
V- t - 1\ 'V
I'>t:'~
\le.: D J LI,LT
Fig. 6. Needle thread tensions variation in one complete stitch cycle for a balanced stitch and for stitches with high and low pre-tension in needle's thread. (Jersey, Ne24, KI4).
Legend: LLHT - Lower looper thread highly tensioned; NL T Needle thread low tension; ULL T - Upper looper thread low tension; BALANCED - Balanced stitch; ULHT - Upper looper thread highly tensioned; NHT - Needle thread highly tensioned; LLL T - Lower looper thread low tension.
Each different stitch adjustment was analysed in distinct structures of knitted fabrics (jersey, rib and interlock), produced with different yarns (Ne 20, 24 and 30) and in various tightness factors (K ).
Fig. 7. Stitcheck representation for a jersey sewn in different thread tension adjustments on the three threads. (Jersey, Ne24, KI4).
3.3 General Discussion
Here it is possible to see that a balanced stitch always occurs in the same area, which represents an ideal thread tension on the three threads. When pre-tension varies on each thread also varies the positioning of Stitcheck.
As it was shown on the previous graphics, it is possible to perform accurate signal acquisition and to detect on the various measured variables, the effect of different sewing conditions.
With the definition of each possible position of Stitcheck for each type of not balanced stitch, we intend to develop a control system to balance automatically the sewing process.
This system shows a high potential to be used as a testing equipment. Another possible use of this system is to detect defects in the stitch formation (Carvalho e Ferreira, 1999).
4. CONCLUSION
Nevertheless, the purpose of this investigation is to find a way to control on-line the quality of each seam as operator is performing his job.
At this moment, studies are being carried out in order to further understand the phenomenon that are happening during stitch formation, namely the relationship between thread tensions and thread consumption.
3.4 Automatic Seam Qualification - Stitcheck
We believe that through the relationship between these parameters it will be possible to establish the correct combination between them, in order to obtain always a balanced stitch and consequently also be able to control the sewing machine in an automatic mode.
A factor was defined to evaluate the quality of the seams and designated as Stitcheck. Stitcheck is obtained with a defined relationship of peaks of tension on the three threads in the x axis and thread consumption on the y axis.
The equipment developed has proven to be an important tool for testing the "sewability" of any fabric, regarding thread tension and thread consumption.
The amount of tension that occurs when the stitch is being formed was chosen to control the quality of the seams, together with its thread consumption.
With this instrumented sewing machine, it will be possible to test new materials, to prevent defects and to guaranty better and more reliable quality in production.
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The same approach is being done on another type of sewing machines.
5. REFERENCES Carvalho, M.A . (1996) "Estudo das Tensoes nas Linhas na Maquina de Costura Corta-e-cose", Msc thesis; University of Minho, Guimaraes. Ferreira, F.B.N. (1991), "A Study of Thread Tensions on a Lockstitch Sewing Machine", PhD thesis; University of Leeds. Rocha A.M . (1996), "Contribution to the Automatic Control of Sewing Parameters: Study of Needle Penetration and Feeding Dynamics", PhD thesis; University of Minho, Guimaraes. Carvalho H. (1998), "Medic;ao e Analise de Parametros em Maquina de Costura Industrial", Msc thesis; University of Minho, Guimariies. Carvalho M .A. and F.B.N. Ferreira (1996), "Study of Thread Tensions on an Overlock Sewing Machine", in Proceedings of the 3rd International Conference on Mechatronics and Machine Vision in Practice, pp 223-226; University of Minho, Guimaraes. Carvalho H., F.B.N . Ferreira and 1. Monteiro (1997), "Measurements and Feature Extraction in High-Speed Sewing", Proceedings of the ISI£'97, pp 961966;University ofMinho, Guimaraes. Carvalho H., J. Monteiro, F.B.N. Ferreira and A. Rocha (1998), "A sewing rig with automatic feature extraction"; Proceedings of the 6th UK Mechatronics Forum International Conference (Mechatronics'98), pp 727-732, Skovde. Silva L.F., M. Lima, F.B.N . Ferreira, 1. Coelho and C. Couto (1999), "Development of a Mechatronic Controlled Actuation on the Presser Foot of an Overlock Sewing Machine", Proceedings of the 44th International Scientific Colloquium (44.1WK.99), Vo\. 2, pp. 116-121, Technical University of Ilmenau. Carvalho M.A. and F.B.N. Ferreira (2000), "Seam Qualification and Control of Parameters in an Overlock Sewing Machine", in Proceedings of the SPRING 2000 Meeting, "Sustainability And Recycling Of Textile Materials", The Fiber Society, University of Minho, Guimaraes.
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