Apparatus for thermomechanical testing of fibers

The invention provides a fiber testing device for thermomechanical testing of fibers which preferably includes a linear step motor coupled to a first fiber gripping jaw. A second fiber gripping jaw is positioned in linear relation to the first gripping jaw and is coupled to a load cell. Advantageously, the apparatus includes a chamber for maintaining a fiber test specimen in a substantially thermally isolated environment during testing of the fiber. A heating means and a cooling means are connected to the chamber. The heating means and cooling means are controlled by a control means which also controls the position of the linear step motor. The fiber testing device of the invention is capable of performing complicated mechanical and thermal fiber testing protocals without operator involvement except for initiation of the testing sequence.

FIELD OF THE INVENTION 
The invention is directed to an apparatus for testing of fibers to 
determine various mechanical properties of the fibers. More specifically, 
the invention is directed to an apparatus for testing fibers which is 
capable of varying parameters and temperature conditions for fiber testing 
during separate different tests and/or during a single fiber testing 
protocol including varied thermal conditions and/or mechanical stress 
conditions. 
BACKGROUND OF THE INVENTION 
Testing devices which measure tensile stresses on various materials by 
stretching and/or compressing these materials are used in numerous 
industries. Essentially, these devices include various means for mounting 
of the material to be tested such that the material is attached to the 
testing device at different portions of the material. The material is then 
stretched or compressed by the device and, for example, the load during 
stretching or compression is recorded. Known stress/strain testing 
instruments of this type are marketed by Instron Corporation. 
Stress/strain testing devices are used extensively by fiber manufacturers 
and fiber end users. By carefully stretching, relaxing or otherwise 
manipulating fibers under controlled conditions, substantial information 
relating to fiber strength and expected performance can be determined. For 
example, measurements can be made on fiber strength such as fiber tenacity 
which is the force required to break a yarn or filament expressed in grams 
per denier; fiber elongation including the load exerted by the fiber at a 
certain specified elongation; fiber shrinkage at various temperatures and 
the like. 
Particularly with industrial fibers which are to be used in various highly 
demanding environments, such as high temperature environments, it is 
desirable to measure the response of the fibers to various stress/strain 
conditions under various thermal conditions. Accordingly, various known 
testing devices such as devices sold by Instron Corporation can optionally 
include heating and/or cooled environmental testing chambers for 
conducting tests on the materials, including fibers. 
A testing apparatus for the thermal testing of tire cord is disclosed in 
U.S. Pat. No. 4,998,825 to Hublikar, et al. This device includes a heating 
cavity which is constructed to receive a sample of tire cord and wherein 
heating elements surrounding the cavity are controlled by a computerized 
temperature recorder. A plurality of weights are used to stress the tire 
cord under various temperature conditions. 
U.S. Pat. No. 4,841,779 to Mitsuhashi, et al. discloses a tension tester 
which includes a central processing unit for controlling a motor which 
applies test loads to a specimen. The specimen can be retained within a 
thermostatic chamber including a cooling coil. Video cameras are used to 
measure the amount of elongation experienced by a specimen and a load cell 
measures a tensile load applied to the specimen. 
U.S. Pat. No. 4,335,615 to Kalfa, et al. discloses a device for testing 
materials for stress corrosion cracking in which a pair of rotary stepping 
motors are used to impart a tensile load to a test sample. The rotary 
stepping motors are connected via a planetary gear system to the test 
sample for the application of controlled stress to the sample. 
U.S. Pat. No. 3,813,919 to Taniguchi, et al. discloses a testing apparatus 
for measuring thermal behaviors of filament yarn. This apparatus includes 
a tube heater which encloses a test specimen. A spiral resistor and air 
cooling blower are employed for maintaining the specimen at a 
predetermined temperature. The temperature of the specimen is said to be 
capable of being increased or decreased rapidly by an electronic 
temperature controller. 
Although these and other known testing apparatus provide the capability for 
performing various controlled tests on fibers, the known devices can 
include various drawbacks including the requirement for multiple testing 
devices in order to perform various different tests. Many of the devices 
are large and complex. For example, those systems which are highly 
accurate can typically include gearing systems, mounting systems and the 
like such that the apparatus can be extremely large. Similarly, with those 
systems that the test parameters can be varied as chosen by the user of 
the system, the various parts and portions of the system result in a 
complete system which is highly complex. Systems are not readily available 
which are highly accurate, of relatively small size and are capable of 
varying mechanical testing parameters and temperature conditions during a 
single test at the option of the user or according to one or more sets of 
predetermined instructions. 
SUMMARY OF THE INVENTION 
The invention provides a highly precise and extremely variable fiber 
testing apparatus. The fiber testing apparatus of the invention can be 
provided in relatively small size and can be constructed in a relatively 
simple and straightforward manner while having a minimum of parts. 
Nevertheless, the fiber testing apparatus of the invention is capable of 
performing highly sophisticated conventional and unconventional testing 
protocols on fibers and can provide highly precise and accurate 
information on fiber properties. 
In one aspect, the invention provides a method and apparatus for fiber 
testing involving the use of linear step motor. The linear step motor 
includes a forcer arranged for controlled linear movement on a stationary 
platen. A first fiber gripping means, e.g. a fiber gripping jaw or clamp, 
is coupled to the forcer of the linear step motor and is arranged for 
linear motion along a predetermined path in correspondence with the linear 
motion of the forcer. A second fiber gripping means is positioned at a 
spaced location and in linear relation to the predetermined linear path of 
the first fiber gripping means. The second fiber gripping means is coupled 
to a force measuring means, such as a load cell so that force experienced 
by the second fiber gripping means is transmitted to the force measuring 
means. A control means, such as a microcomputer is coupled to the force 
transmitting means and to the linear step motor and controls the linear 
motion of the linear step motor according to a set of predetermined 
instructions. 
Because a linear step motor is used to move the first fiber gripping means, 
no sophisticated gearing system is needed to effect movement of the fiber 
gripping means or jaw thus simplifying the fiber testing apparatus as 
compared to conventional fiber testing devices. The linear step motor is 
additionally, high accurate and can be digitally controlled by the control 
system, such as a microcomputer so that highly precise tests can be 
conducted on the fiber and so that highly variable testing protocols as 
determined by the user or in accordance with standard fiber testing 
procedures, can be readily conducted on the fibers. 
In another aspect of the invention, the invention provides a fiber testing 
apparatus which includes a chamber arranged for containment of the fiber 
test specimen and the first and second fiber gripping means during testing 
of the fiber. A heating means and a cooling means are connected to the 
chamber for heating and cooling of the chamber. The heating means and 
cooling means are advantageously capable of rapidly changing the thermal 
conditions within the chamber and preferably supply a forced stream of 
heated air or a forced stream of cooled air to the chamber. The heating 
and cooling means are connected to the control means, such as a 
microcomputer, so that the temperature conditions within the chamber can 
rapidly be changed during testing of fibers. A temperature sensor in the 
chamber is also connected to the control means so that temperature changes 
effected by the heating means and cooling means can continuously be 
monitored and so that heating or cooling supplied to the chamber can be 
varied in response to signals from the temperature sensor. Preferably, the 
chamber provides a substantially thermally isolated environment for 
testing of the fiber. Preferably, the means used to mechanically 
manipulate the fiber within the chamber is a step motor, such as the 
linear step motor discussed previously. 
The testing device of the invention, in its various embodiments can provide 
numerous advantages and benefits. For example, fibers can be tested during 
a single testing protocol under a variety predetermined temperature 
conditions and under a variety of predetermined mechanical conditions so 
that the strength, elongation, shrinkage and like fiber properties which 
can change due to exposure of the fiber to various mechanical 
manipulations and temperature conditions can be measured and predicted. 
For example, in the tire manufacturing process, fibers in the tire are 
stretched and heated, then relaxed and heated, then stretched further 
while heated, and then cooled, while the molding and curing steps in the 
tire manufacturing process are accomplished. The fiber testing device of 
this invention can rapidly and readily provide information as to expected 
changes in fiber elongation and strength according to any given set of 
heating, stretching, relaxing, cooling and like conditions which the fiber 
is expected to experience during its incorporation into an end use 
product, such as a tire. In addition, the fiber testing device of the 
invention can readily perform conventional fiber test such as tests to 
determine tenacity, load at specified elongation, elongation at specified 
load and the like. Moreover, the fiber testing device of the repetitive 
tests such as the known test for determining work loss, without requiring 
operator involvement and concomitant operator error.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the following detailed description, there is described a preferred 
embodiment of the invention for testing of fibers. It will be recognized 
that although specific terms may be used in describing the perferred 
embodiment, these are used in the descriptive sense and not generically, 
and are used for the purposes of description and not of limitation. The 
invention is susceptible to numerous changes and variations within the 
spirit and scope of the teachings herein as will be apparent to the 
skilled artisan. 
FIG. 1 illustrates a perspective view of a preferred fiber testing 
apparatus according to the invention. A linear step motor 10, including a 
moving forcer 12 and a stationary platen 14, is provided for mechanical 
fiber manipulation. The movable forcer 12 is connected via a rigid 
connecting bar 16 to a first fiber gripping jaw 18 which grips the first 
end of a fiber 20 to be tested. It will be apparent that as forcer 12 is 
caused to move linearly upon platen 14, the fiber gripping jaw 18 is, in 
turn, caused to move in a corresponding linear motion along a 
predetermined linear path as determined by the linear path of forcer 12 
upon platen 14. An air hose 22 is attached to the forcer 12 for supply of 
air to a portion of the forcer 12 which, in turn, provides for an air 
bearing between the forcer 12 and the platen 14 as discussed in greater 
detail later. 
A second fiber gripping jaw 24 is provided at a location spaced from and in 
linear relation with the predetermined linear path of the first fiber 
gripping jaw 18. The second fiber gripping jaw 24 is coupled via a 
connecting linear bar 26 and a connecting pin 28 to the arm 30 of a 
conventional load cell 32. It will be apparent that the second fiber 
gripping jaw 20 is thus positioned at a substantially fixed location while 
the movement of jaw 18 can provide different degrees of stretching to the 
fiber 20. The force experienced by the second jaw 24 is then transmitted 
via bar 26 and arm 30 to load cell 32 for measurement. 
A thermally isolated chamber is provided by housing members 40 and 42, each 
of which define portions 44 and 46 of a cavity for containment of fiber 20 
and gripping jaws 18 and 24 when the upper housing member 42 is pivoted 
downwardly about hinge 50 for mating with the lower housing member 40 
thereby providing closure of the cavity formed by the cavity portions 44 
and 46. Advantageously, the walls of the housing members 40 and 42 are 
lined with a relatively thick insulation lining 52 and 54 so that the 
fiber and fiber gripping jaws are contained within an insulated thermal 
environment. 
A temperature sensor 56 is provided within the interior of the cavity for 
continuous measurement of the temperature within the cavity. In addition, 
there is port 58 for admitting forced heated air into the cavity and a 
port 60 for removing air from the cavity. A port 62 provides cooling air 
to the cavity via a cooling air "vortex" device which is cooling air 
device commercially from EXAIR and capable of providing cooling air at a 
rate of 2000 BTU/Hr. 
A heater 62 which includes a fan (not shown) and a heating element (not 
shown) is provided for supplying heated air to port 58. The heated air is 
rapidly moved through supply line 64 to port 58 so that the chamber can 
rapidly be heated. A return line 66 removes heated air via port 60 from 
the heated chamber. The use of a forced air heating means provides the 
capability for rapidly changing the temperature within the environmental 
chamber. For example, using a forced air heater as illustrated in FIG. 1, 
the temperature within the chamber can be rapidly changed at a rate of up 
to about 25.degree. C. per minute. Similarly, the use of the vortex 
cooling apparatus which supplies cooled air via port 62 allows for cooling 
of the chamber at a rate of up to -60.degree. C. per minute. 
FIG. 2 schematically illustrates the system for control of the fiber 
testing apparatus of the invention. As illustrated in FIG. 2 the chamber 
43, formed by upper and lower housing members 42 and 44, is shown to be in 
the closed position. As seen in FIG. 2, a control means 70 which can be a 
conventional microcomputer or a similar control device is connected via a 
conventional input/output means 72 to the various parts of the testing 
apparatus including load cell 32, linear step motor 10, the cooling means 
63, the heater 62, and the temperature sensor 56. The controller 70 is 
typically a digitally operated system and includes a set of predetermined 
instructions for periodically sampling signals received from load cell 32 
and from temperature sensor 56 and for operation of linear step motor 10, 
cooling means 63 and heating means 62. 
A conventional linear step motor 10 is illustrated in FIG. 3. As is known 
to the skilled artisan, the linear step motor includes a forcer member 12 
and a stationary platen member 14. A motor control 80 is typically 
included as part of the step motor. The forcer includes two electromagnets 
82 and 84 including field windings 86 and 88. The two pole faces of each 
electromagnet are toothed to concentrate the magnetic flux. The teeth 90 
on the electromagnet are arranged so that only one set of teeth on each of 
the electromagnets can be aligned with corresponding platen teeth at a 
time. A strong rare earth permanent magnet is disposed between the two 
electromagnets. 
Linear stepping motors include bearings between the platen surface and the 
surface of the electromagnets. The bearings can be mechanical bearings or 
air bearings. An air bearing operates by floating the forcer on high 
pressure air introduced through orifices near the pole faces of the 
forcer. Thus, the forcer is continually disposed a small distance 96 (FIG. 
3) above the platen when the air bearing is operational. 
The operation of linear step motors is well known. In essence, when current 
is established in a field winding, the resulting mechanic field tends to 
reinforce the magnetic flux at one pole face and cancel it at the other. 
By reversing the current, the reinforcement and cancellation are 
exchanged. By selectively applying current, it is possible to concentrate 
flux at any of the forcer's four pole faces. The face receiving the 
highest flux concentration will attempt to align its teeth with the platen 
thus moving the forcer in one direction or another. 
Linear step motors are known in the art and are available from various 
sources including KER Compumotor Corp. of Rohnert Park, Calif. 
Returning to FIG. 2, the linear step motor 10 receives control input from 
controller 70. In addition, the linear step motor sends position signals 
via input/output device 72 to controller 70. Position signals sent from 
the linear step motor 10 to the controller 70 allow for calculation within 
controller 70 of the exact total amount of movement of the forcer 12 which 
in turn allows calculation of percent fiber extension or elongation. 
Various testing protocols for fibers are well known in the art and can be 
conducted using the system of the invention. For example, to determine 
load at specified elongation (LASE) wherein, for example a 5% elongation 
is specified, the fiber 20 to be tested is first clamped between jaws 18 
and 20. Operator input then is used to initiate the test. The controller 
70 sends signals to the forcer member 12 for movement in a left direction 
until the load cell 32 detects an increase in the load on fiber clamping 
jaw 24. The position of the forcer 12 is then determined by the controller 
and the forcer 12 is moved further to the left until the position, as 
calculated by the controller, is reached at which the fiber is elongated 
5%. The controller then measures the load on load cell 32 and displays the 
load via display 74 which can be a video screen and or a printer/plotter. 
FIG. 4 illustrates application of the measuring device of the invention to 
the industry standard testing protocol known as "simulated cure postcure 
inflation test". In this test, the fibers are subjected to conditions 
simulating the conditions which would be experienced by the fibers during 
a tire manufacturing process. Using prior systems, a testing technician 
performed certain of the testing steps manually and would spend 
approximately forty-five minutes conducting the test. With the system of 
this invention, the test is performed by the testing device. Operator 
involvement is limited to loading of the fiber in the system and 
initializing the test. 
Referring to FIG. 4, the test is initiated by the operator by loading a 
fiber sample having a length close to a predetermined amount, e.g. ten 
inches, into the fiber jaws. The operator then begins the test. In step 
100, (FIG. 4) the system is automatically initialized. Initialization of 
the system by the control means, e.g. the microcomputer, includes the 
following steps: 
determine load cell reading; 
move the forcer to the left one discrete step; 
measure load on load cell; 
move forcer one step to the left; and 
repeat load measuring step and forcer moving step until a threshold load is 
sensed by load cell. 
Following the above initializing subroutine, the fiber is assumed to be at 
zero percent elongation and the control sequence passes to step 110 for 
the initialization of the constant load subroutine which subjects the 
fiber to a constant load. This subroutine is conducted by the system as 
follows: 
move forcer to the left; 
measure load on load cell; 
compare load to predetermined value; 
if load is less than predetermined value then return to "move forcer" step; 
if load equals predetermined value return to immediately preceding "measure 
load" step. 
The constant load subroutine is continued until the predetermined load on 
the fiber has been achieved. Control of the system then passes to step 120 
in which the cavity heating subroutine is initiated. In this subroutine, 
the cavity is brought to and held at a predetermined temperature using the 
following steps: 
heat cavity with forced air at predetermined temperature; 
measure temperature in cavity; 
compare measured temperature to predetermined temperature; 
if temperature in cavity is less than predetermined temperature increase 
temperature of heated forced air; 
if temperature in cavity is greater than predetermined temperature, 
decrease temperature of heated air; 
if temperature in cavity is equal to predetermined temperature hold 
temperature of forced air constant; 
return to immediately preceding "measure temperature" step. 
When the cavity heating subroutine has achieved the predetermined 
temperature, the system control passes to step 130 wherein the elongation 
of the fiber is calculated in percent elongation and stored. Percent 
elongation is calculated by comparing the fiber length at zero load to the 
fiber length at the specified load. Fiber length is determined based on 
the position of the forcer. 
When the fiber elongation has been determined and stored, the system 
control passes to step 140. In step 140 the constant load subroutine and 
heating subroutine are continued for a predetermined time period. 
Upon completion of the predetermined time period as determined by the 
control system, the system control passes to step 150 wherein the fiber 
elongation is once again calculated. It will be apparent that during the 
previous step 140 the length of the fiber can change slightly while the 
fiber is maintained at a constant temperature and under a constant load. 
Thus, while the constant load subroutine is continued in step 140, the 
position of the forcer is periodically adjusted at, for example, about 20 
times per second, to maintain the load as sensed by the load cell at the 
predetermined constant value. 
Following step 150, control of the system passes to step 160 wherein the 
fiber is subjected to a zero load subroutine. In this subroutine, the 
position of the forcer is slowly adjusted to achieve a zero load on the 
fiber as follows: 
move forcer one position to the right; 
sense load reading from load cell; 
if reading is greater than zero, return to "move forcer" step; 
if reading is equal to zero, return to "sense load reading" step. 
When the system has achieved a zero load on the fiber, control is passed to 
step 170. In step 170, the zero load subroutine and the heat cavity 
subroutine are continued for a predetermined period of time. Following the 
predetermined period of time, control of the system passes to step 180. 
In step 180, the fiber elongation, based on initial fiber length, is 
calculated in the manner explained previously. It will be recognized that 
during the predetermined period of step 170, the fiber length may have 
decreased slightly as the fiber is maintained under a zero load for the 
predetermined time period. 
Control of the system is next passed to step 190 wherein the constant load 
subroutine, explained previously, is initiated using a greater 
predetermined load value than in step 110. In step 190, the constant load 
subroutine is continued until the system achieves the predetermined load 
on the fiber according to the predetermined instructions. Thereafter, 
control of the system is passed to step 200. 
In step 200, the system initiates a cooling subroutine to achieve a 
predetermined cooler temperature in the cavity. The cooling subroutine is 
comparable to the heating subroutine described previously in connection 
with step 120; however, the forced air cooling system is used to cool the 
cavity instead of the forced air heating system used in step 120. When the 
forced cool air has achieved the predetermined cooler temperature in the 
cavity, control of the system is passed to step 210. 
In step 210, the constant load subroutine and the cooling subroutine are 
continued for a predetermined period of time. Thereafter, control of the 
system is passed to step 220. 
In step 220, the system initiates the zero load subroutine as explained in 
connection with step 160. When zero load has been achieved on the fiber, 
control of the system is passed to step 230. 
In step 230, the fiber elongation is calculated, based on initial fiber 
length as explained in connection with step 130. When the elongation of 
the fiber has been calculated, control of the system passes to step 240 
wherein a written report is generated for the completed test. The written 
report may include reported values and/or data presented graphically in 
the form of plotted curves and the like as will be apparent to the skilled 
artisan. 
It will be apparent that stress/strain curves can be generated for various 
fibers in a similar manner to that discussed above. Following initiation 
of the system, the linear step motor is moved to the left at the rate 
specified by the testing protocol. The controller continuously samples the 
force signals received from load cell 32 and position signals from the 
forcer to obtain a substantially continuous stress/strain curve 
information which can be displayed graphically following the test. 
The system can also provide data as to, for example, elongation at 
specified load. Moreover the system can automatically perform the complex 
work loss test described in U.S. Pat. No. 4,101,525 to Davis et al. 
without requiring operator input and potential operator error. 
The invention has been described in considerable detail with reference to 
its preferred embodiments. However, variations and modifications can be 
made with in the spirit and scope of the invention as described in the 
foregoing specification and defined in the appended claims.