Measurement of Feed Dog Motion and Dynamic Torque in Sewing

Measurement
of Feed
Machines
Dog Motion
by means
By Masanori
Osawa
and Dynamic
of an Optical
and Hiroshi
Saito,
Torque
Lever
Members,
in Sewing
Device
TMSJ
Osaka Kyoiku University, Osaka Pref.
Based on the Journal of the Textile Machinery Society of Japan, Proceedings, Vol. 34, No. 9, P419-P423 (1981-9)
Abstract
This article describes the application of an opto-mechanical lever apparatus in the education and
research of the mechanism of sewing machines.
One device is a projector which produces feed dog motion profiles. The device displays on a screen
magnified pofilesof feed dog motion measured by contacting a lever with thefeed dog. For a better visualization of the feed dog motion profile, angular displacements of the arm shaft at regular intervals are
indicated on the profile as bright spots by using two polaroid discs combined as a light beam modulator. The other is a projector for displaying dynamic torque profiles. The projector displays torque
profiles on polar coordinates by making the inclination of a mirror attached to the arm shaft proportional to the torque.
These apparatuses are easily attachable to and removable from regular household and industrial
sewing machines to make them useful not only as teaching aids but also as service tools for lockstitch
sewing machines.
1. Introduction
The mechanism of sewing machines is so complex that it
takes considerable training to perform fine tuning required in
their assemblage and maintenance. On the other hand sewing
machine has been a common teaching material in Japanese
junior high shools for the instruction of general mechanism
and machine maintenance but the complexity of sewing machine has always been an obstacle for effective teaching. In
view of this, the present authors developed direct visual apparatuses to teach the mechanism: a projector for feed dog
motion profiles«~, a synchronized flash lamp to indicate
angular displacement of the arm shaft (arm shaft angle) at
regular intervals~2~ and a projector for dynamic torque
profiles~3'. In developing these apparatuses mainly used
as teaching aids, we placed emphasis on low cost by using
easily obtainable materials and modified mass produced
parts. For example, an incandescent lamp was first tried as
an optical source but it presented some disadvantages. The
incandescent light, therefore, was replaced by a laser light
source plus a polaroid type modulator to eliminate most of
these disadvantages.
2. Apparatus
Apparatuses used in previous works~l~-c3~were improved optically and mechanically as below. The use of a tiny
(1 mW) He-Ne laser made the projected profile clearly visible
66
even in a well illuminated classroom eliminated the need of
lens system and enabled a readily adjustable magnification
rate. A polaroid type laser beam modulator accurately synchronized to arm shaft revolution was made to provide
bright spot marks on projected profiles indicating arm shaft
angles at regular intervals to enable quantitative analysis.
2.1 Projector for Feed Dog Motion Profiles
The movement of the feed dog is two-dimensional and the
amplitude of its movement (several millimeters) is very small
compared to those of the needle bar and the thread take-up
lever. But, as is well known, the movement must be well adjusted to obtain good seams. This is the reason for the need of
magnified feed dog motion profile. The two-dimensional
movement of the feed dog consists of horizontal displacement X and vertical displacement Y. To measure a series of
displacements ((X1, Yl), (X2, Y2). ....(X, Yn)) at many different angular positions of the arm shaft to produce the motion profile is quite time consuming.
To overcome the drawback a new apparatus was developed, which displays magnified feed dog motion profiles
without the need of point by point measurement and hand
drawing. The apparatus is shown in Fig. 1. Measuring lever
consists of a steel needle ~'i)(0.2 mm in thickness), an aluminum tube lever ® (2 mm in outside diameter, 35 mm in length),
a cantilever steel spring 3` (0.6 mm in diameter, 5 mm in
length) and a glass mirror ~4:~
(8 x 6 x 0.5 mm) with an inclination adjuster (5~. The measuring lever is positioned perJournal
of The Textile Machinery
Society
of Japan
Fig.
1
Projector for feed dog motion profiles
pendicular to the plane of feed dog motion, and the needle ii
is pressed against the feed dog by means of two clamps (a
vertical and a horizontal positioner) ;;c and (7i which enable
an independent and continuous shifting of vertical and horizontal fulcrum positions. The fulcrum positions must be set
to keep the needle firmly pressed against the feed dog even
at the lowest position.
The procedure for the projection of motion profile is as
follows. Attach a projector mount s to the presser bar and
lower the bar to position. Care must be taken in this operation to insure all the three legs c of the mount contact the
bed of the machine. By adjusting the vertical and horizontal
positioners, the needle should be made to press against the
feed dog with a force of approximately 30 gf. Then project
He-Ne laser beam on the mirror and adjust mirror angle to
make the reflected beam form a light spot on the screen.
When the feed dog motion is started at an arm shaft speed of
6 rev/s (360 rpm) or more the light spot displays a feed dog
motion profile on the screen. The magnification of the projector is 2D/l, where D is the distance between the mirror and
the screen and 1is the effective length of the measuring lever,
approximately 38 mm.
In the course of planning and assembling this apparatus
emphasis was placed on precision and good visibility of the
projected profile. For a high accuracy the moment of inertia
of the measuring lever was made as small as possible. As a
result, the needle under the contact force of 30 gf correctly
followed the feed dog motion at the high shaft speed of 1,000
Vol. 29 No. 3 (1983)
rpm. The intense light beam produced by laser source produces clearly visible light spot on the screen even when the
illumination of screen surface is 100 to 2001ux.
It is highly desirable to mark arm shaft angle on projected
motion profiles. In previous experiments~2J, light beam was
modulated to indicate the arm shaft angle in the following
way. The light source (an incandescent light) was connected
to an interrupter (a micro-switch and an eccentric cam, or a
photo-sensitive SCR and a sector, where the cam or the sector rotates with the arm shaft). When the interrupter is activated, light beam is modulated to produce bright spots on
the motion profile indicating arm shaft angles. These interrupters were simple but there were some mechanical and optical troubles. Mechanical troubles were due to the bouncing
of the cam and to the friction in the flexible joint. On the
other hand, the incandescent light source caused optical
troubles, namely, insufficient brightness of projected profiles
and slow response of electric current to modulation.
In the present experiment, by use of a polaroid type modulator driven directly by the arm shaft as shown in Fig. 2,
most of these disadvantages are removed. The modulator
consists of two polaroid discs, disc 1 O and disc 2 2® both
180 mm in diameter and 1 mm in thickness. Disc 1 having
2 mm wide slits (4 at 75 mm radial position and at an angular interval of 30° is attached to the stop motion clamp screw
(clamp screw) ~3). Disc 2 is attached to disc 1.
Fig.
2
Polaroid
type modulator
Transparency
varies
with
of the
relative
Fig. 3. When
overlaid
angular
the light
disc 2 the transparency
the
broken
line
slits to produce
passes
increases
in Fig. 3. Thus
bright
spots
discs
position
beam
and
for feed dog motion
the
marking
to He-Ne
profiles
laser
beam
of two discs as shown
through
to the
beam
a slit on
level shown
is intensified
angular
position.
in
disc
1
by
at the
Visi-
67
was approximately 30, the screen being placed at 530 mm
from the mirror. The numerals in Fig. 5 indicate the arm
shaft angle starting at the upper dead point of the needle bar.
In the profile shown in Fig. 5 (a) the feed dog descends as it
moves forward. This profile can be improved by adjusting the
position of the feed cam so that the feed dog properly feeds
the cloth. The profile after adjustment (the feed cam is shifted approximately 30°) is shown in Fig. 5 (b).
An alternative optical system configuration in which the
laser beam is projected to the mirror directly is possible as
mentioned in previous papers~1>,~2~.However, this configuration leaves some difficulties since it requires transmission between modulating disc and the arm shaft.
Fig.
3 Characteristics
of polaroid
type modulator
bility was best when bright marking spots were about three
times brighter than the loop profile. So, the angular displacement between discs is fixed at approximately 35°.
The optical system for the projection of feed dog motion
profiles is shown in Fig. 4. The laser source is set above the
hand wheel and the beam travels horizontally passing
through the modulator. The beam is reflected by two rectangular prisms and led to the mirror which in turn projects motion profiles on the screen.
The feed dog motion profiles with the arm shaft angle
marked by this projector are shown in Fig. 5. These profiles
projected on a semitransparent screen ruled in 10 mm squares
were those of a HL type (JIS classification) sewing machine
running at 400 rpm. The magnification in this configuration
Fig.
68
4
Optical system for the projection of feed dog motion
profiles
Feed regulator handle "4"
Height of feed dog "up"
Fig. 5 Projected profiles of feed dog motion with indices of arm
shaft angle
2.2 Projector for Dynamic Torque Profiles
It is important to measure driving torque in order to evaluate the conditions of machines. In sewing machines, static
measurement
of driving torque against arm shaft angle to
check mistakes in assembling is standardized
in JIS B 7014
and 7071. However, dynamic measurement
of driving torque
is more important in testing the machine for a high speed
operation. Because, inertia forces of reciprocating
parts and
unbalanced forces of rotating parts generate dynamic torque
which is proportional
to the square of speed.
Several methods to measure dynamic torque in relation to
the arm shaft angle are available : a torque dynamometer
Journal of The TextilC Machinery
Society
of Japan
attached
using
methods
time
to the
strain
arm
gagesC4J
require
too
for use in testing
shaft
or
detects
the
optically
torque
using
large-scale
by electrically
a mirror~5~.
equipments
and
too
and training.
Fig. 6 Polar
profile
of driving
torque
These
much
In view of above an optical lever type apparatus was developed by the authors for real time projection of dynamic torque profiles on a screen. The torque profile is displayed in
polar coordinates in which radial distance dr corresponds to
the torque T as shown in Fig. 6.
Schematic of the apparatus is shown in Fig. 7.Acoil spring
(1 is inserted between the hand wheel 2O and the clamp
screw 3. The clamp screw ( and the arm shaft are fixed by
two small screws 4) after removing the clamp stop motion
washer. Extension of the spring O is related linearly to shaft
torque. The extension causes a small angular displacement
between the hand wheel and the clamp screw. This angular
displacement is transformed linearly into inclination of a
mirror 5 (6 x 6 x 0.5 mm). The mirror is attached to the end
of a flat spring (s) (2.5 x 5 x 0.3 mm) placed on the center line
of the clamp screw. The spring is connected to the hand wheel
via a piano wire 7 (0.2 mm in diameter) and a small pulley 18 . A mount () attached to the flat spring is supported by
a pivot io and a set of azimuthal adjusters it . In order to
reduce the mirror motion hysteresis to a minimum the hand
wheel and the clamp stop motion flanged bushing were well
lubricated.
The optical system configuration is shown in Fig. 8. A rectangular prism is placed at the origin of the polar coordinates
(r, 0) on the screen. The screen is a semitransparent plastic
sheet. A polar coordinates scale (r, concentric circles at an
interval of 10 mm; 0, radial lines at an interval of 30°) is
drawn on the screen. The circle of r = 30 mm is defined as
the basic circle on which the beam displays the zero-torque
profile. A rotatory and an azimuthal adjuster are also attached to the prism. The optical system is adjusted as follows: 1) the incident beam upon the mirror coinsides with
the axis of the arm shaft and therefore is almost horizontal
(variable by means of the adjusters attached to the prism),
and 2) the reflected beam is at the coordinates of 0 = 0°
and T = 0° on the screen if the shaft is torque-free at 0 = 0°,
and when the shaft is loaded the beam swings in radial direc-
Fig.
Fig.
7
8 Optical system for the projection of dynamic torque
profiles
Projector for dynamic torque profiles
Vol. 29 No. 3 (1983)
69
tion in proportion to the torque (direction of the swing adjustable at the azimuthal adjusters).
The static characteristics of this apparatus are calibrated by
means of a specially prepared Prony dynamometer attached
to the arm shaft. In calibrating the shaft was freed of all mechanical parts except the dynamometer. The result is shown
in Fig. 9. The radial displacement of the spot is practically
proportional to the torque. The natural frequency of the optical system was also measured when the apparatus is attached to a ZDJ type (JIS) sewing machine without the driving
belt. The natural frequency was approximately 70 Hz. When
the belt was used, the frequency became slightly lower and
the vibration was strongly damped. At the present state the
upper limit of usable shaft speed is approximately 400 rpm
Fig.
10
Projected profiles of dynamic torque
and the maximum
tensions
of the top
thread
and 50gf,
respectively.
were
150gf
thread
and the bobbin
By comparing
these
profiles
with the motion
diagram
of the machine
used,
following
was found.
The first increase
in torque
at 0 =
is due to the tightening
of the top
up lever and the next increase
Fig. 9 Sensitivity of projector for dynamic torque profiles
which is about one-tenth of the natural frequency. However ,
the limit may become higher if the coil spring is made more
stiff and the screen placed correspondingly distant from the
mirror.
Examples of torque profiles are shown in Fig. 10. A ZDJ
type (JIS) sewing machine was used in these experiments.
Fig. 10 (1) shows that 1) dynamic torque varies with arm
shaft angle, 2) it generally increases with rotational speed and
3) the ratio of increase depends markedly on the arm shaft
angle. It was found, however, that the torque decreased with
increasing rotational speed at fI = 150°. This may be due to
the inertia of the parts (e.g. the shuttle body) forced to decelerate. The torque profiles of the machine in idling (without
the threads and the cloths) and in sewing, at the same speed
(300 rpm), are shown respectively in (a) and (b) of Fig. 10 (2).
The sewing was done in the following manner. Two sheets of
cotton broad cloths were straightly sewed by use of X11 (JS)
needle and X60(JIS) cotton threads. Stitch-length was 2 mm
70
penetrating
d =
sheets
the cloths.
110° disappears
such
proves that
from stroke
as papers
the needle
to stroke.
The
when
thread
at 0 =
take-
110° is due to the needle
fluctuation
relatively
by the thread
the
60°
of torque
homogeneous
profile
at
or soft
or non-woven
fabrics
are sewed.
penetrating
resistance
tends
This
to vary
3. Conclusions
Optical lever type apparatuses for the direct projection of
feed dog motion profiles and dynamic torque profiles of lockstitch sewing machine had been developed by the authors.
In the present paper, improved version of these apparatuses
are described. One improvement is the use of a tiny laser
source in order to make the projected mark spots clearer and
brighter. The other is the use of a polaroid type modulator
in order to make the modulation of the beam adjustable and
accurate. These improvements made these apparatuses far
easier to use to extend the scope of their application. It is expected that these apparatuses are useful not only as teaching
aids but also as testing and analyzing devices for sewing
Journal
of The Textile Machinery
Society of Japan
[2] M. Osawa and H. Saito; ibid., 17, III-1,127 (1968).
[3] M. Osawa and H. Saito; ibid., 18, III, 81 (1969).
machines.
Currently
material
the improved
in our
apparatuses
university
with
great
are used
interest
as teaching
shown
by the
[4] Japan Sewing Machine Center; Sewing Machine (Part of
Technology), 28, 35 (1968).
[5] Y. Jimbo; J. Japan Soc. Prec. Engn., 31, 61 (1965).
students.
The
authors
M. Tanaka
would
for their
like to thank
critical
reading
Dr. I. Miura
of this
and
Prof.
manuscript.
Reference
[1] M. Osawa
University,
and
H.
16, V-2,
Saito; Memoirs
19 (1967).
of Osaka
Kyoiku
OBJECTIVE
SPECIFICATION
MECHANICAL
PROPERTIES
Edited
S. Kawabata
The proceedings
University)
of New South Wales)
Niwa (Nara Women's
of the Japan-Australia
Quality, Mechanical Properties
431 pages. English. Published
Science and Technology Center
Japan. 8,000 Yen plus shipping
by
(Kyoto
R. Postle (The University
Masako
OF FABRIC QUALITY,
AND PERFORMANCE
University)
Joint Symposium on Objective Specification
of Fabric
and Performance which was held in Kyoto, May 10-12, 1982.
by The Textile Machinery Society of Japan. Address: Osaka
Bldg., 8-4, Utsubo Honmachi 1-chome, Nishi-ku, Osaka, 550,
fee, Air: 3,500 Yen; Sea: 1,500 Yen.
During the last two decades, the application of the principles of textile technology
and textile engineering has resulted in increasingly higher speed production of
textiles, thus supplying the market place with a large quantity of textile products to
meet the rapidly growing demand for clothing materials. Having satisfied the basic
quality requirement for textile materials the next stage of innovation in engineering
is the design and large-scale production of high quality fabric to meet the demands
of the more discerning consumers of the future. The main aim of this symposium
was to exchange information and knowledge which had been developed in the two
countries in the field of fabric objective specification and characterization to attain
the next technological and engineering target-high-quality
fabric production. 103
participants from Australia, New Zealand,
U.K., U.S.A., West Germany,
People's Republic of China, South Africa and Japan gathered at the Kyoto International Conference Hall and 32 papers were presented. These papers are completely included in this book. We believe that this book will be useful for those
people who are looking forward to the next stage of innovation in textile technology.
Vol. 29 No. 3 (1983)
71
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