NASA CASE NO. I AR 14879 - 1 - CU 

PRINT FIG. 1 

NOTlCE 

The invention disclosed in this document resulted from research in aeronautical and 

space activities performed under programs of the National Aeronautics and Space 

Administration. The invention is owned by NASA and is, therefore, available for 

licensing in accordance with the NASA Patent Licensing Regulation (14 Code of 

Federal Regulations 1 245.2). 

To encourage commercial utilization of NASA-owned inventions, it is NASA policy to 

grant licenses to commercial concerns. Although NASA encourages nonexclusive 

licensing to promote competition and achieve the widest possible utilization, NASA 

will provide the necessary incentive to the licensee to achieve early practical 

application of the invention. 

Address inquiries and all applications for license for this invention to NASA Patent 

Counsel, Langley Research Center, Code 21 2, Hampton, Virginia 23681-0001. 

Serial No.: 0813 1 6,708 

09/29/94 LaRC 

(NASA-Cdse-LAR-14879-1-CU) N95-20616 

APPARATUS AYO METHOD FOR ' l i' 

OETERMINING THE MASS DENSITY OF A 

FILAMENT Patent Appl icat ion (hASA. Uncl as 3 

Langley Research Center) 17 p 
LAR 14879-1 -CU AWARDS ABSTRACT 

APPARATUS AND METHOD FOR DETERMINING 

THE MASS DENSITY OF A FILAMENT 

The invention is an apparatus and method for determining mass density of a 

moving filament in a manufacturing process. The apparatus has two filament 

supports, one fixed and mounted to a base, the other mounted on a transducer 

and moveable in a transverse direction to the moving filament. Typically the 

filament or fiber is coated with resin prior to reaching the mass density apparatus. 

Control of density is necessary to insure the proper amount of resin is applied. 

The transducer includes a transverse vibrational pulse or continuous jiggle in the 

filament producing either a free vibration and decay or a continuous resonant 

vibration. This vibration is used to determine the mass density, m, using the well 

known relationship 

m = T 

4(~0* 

where T is the tension, L is the vibrational length, and f, the fundamental 

frequency of vibration. A production version of the apparatus can be used for 

continuous, real-time control of such fiber manufacturing processes as coating and 

impregnation without interrupting the manufacturing process. 

Inventor: Jeffrey A. Hinkley 

Address: 604 Tabb Lakes Drive 

York 3693 

SS#: 

Employer: NASA Langley Research Center 

Inventor: Joseph M. Marchello 

Address: 6 Rhoda Court 

Hampton, Virginia 23664 

SS#: 

Employer: Old Dominion University 

Initial Evaluator: Terry L. St. Clair 

Serial No.: 0813 1 6,708 

Filed: September 29, 1994 
LAR 14879- 1 -CU -1- PATENT APPLICATION 

APPARATUS AND METHOD FOR DETERMINING 

THE MASS DENSITY OF A FILAMENT 

n of the Inv~ntum 

5 

The invention described herein was joingtly made in the performance of 

work under NASA Grant No. NAG-1 -1 067 and an employee of the United 

States Government. In accordance with 35 USC 202, the Grantee elected 

not to retain title. 

10 

of the lnventlon 

The invention relates to testing and measurement, and more 

particularly to mass measurement of filaments using vibrational dynamics. 

15 In the preparation of impregnated yarns or fiber tows to be used, for 

example, in the manufacture of fiber-re-inforced composites, it is necessary 

to know the amount of resin being applied. The prior method for 

determining the resin content was to cut a known length of the yarn and 

weigh it. Obviously, this method required interrupting the production 

20 process. Other known methods, such as capacitance and radiation 

measurements, for determining resin content for quality control also have 

drawbacks. Capacitance gauges require close tolerances (difficult to 

achieve with non-uniform yarn) and are sensitive to EM interference, 

necessitating extensive filtering and long settling times. Various radiation 

25 gauges (beta, gamma) may work, but are expensive and contain potentially 

hazardous radioisotopes. More recent prior art has been directed toward 

evaluating mechanical properties by determining vibrational response of a 

section of fiber. U.S. Patent 5,269,181, December 14, 1993 by Gibson et 

al provide for testing of a fiber by inducing a longitudinal pulse into section 
LAR 14879- 1 -CU - 2- PATENT APPLICATION 

of fiber to which a weight has been attached. 

The objects of the Gibson device is to evaluate longitudinal oscillatory 

response in order to determine mechanical properties such as dynamic 

modulus and damping. Fiber reinforced materials are increasingly used in 

5 automotive and aerospace applications. During production of the reinforcing 

fibers, resin is added to the fiber during production line operations. 

Typically, a continuous filament moving a high speed is brought in contact 

with the resin applicator and thereafter continues to a fabricating device 

where the fiber is wound around a nose cone or structure. In order to 

10 maintain optimized strength-to-weight and stiffness-to-weight ratios 

accurate control of the resin content must be established. It is preferable 

to control resin content without stopping the production line and without 

removing the fiber from the line process. 

15 Summary of the Lnv& 

Accordingly, it is an object of the present invention to provide an 

apparatus and method for measuring mass density of a filament, yarn, tape, 

wire or wire material. 

2 0 It is another object of the invention to provide a means of measuring 

mass density on a continuous filament. 

It is yet another object of the invention to provide a means of 

measuring mass density of a moving filament. 

The method of the invention comprises the steps of: providing two 

25 supports for a filament to be tested; leading a filament across the supports; 

tensioning the filament; inducing a transverse vibration into the filament; 

detecting the frequency of vibration; amplifying the frequency; feeding the 

amplified signal back to further excite filament vibration; and displaying the 

vibrational signal. The apparatus comprises a base having a fixed filament 
LAR 14879-1 -CU -3- PATENT APPLICATION 

support attached thereto and having a transducer attached thereto. A 

moveable filament support is attached to the free side of the transducer and 

this support is vibrated in a plane transverse to the path of the filament 

thereby inducing transverse vibrations in the filament. A light source and 

5 a photodetector are mounted on the base on either side of the path of the 

moving filament. An optical mask is mounted between the light source and 

the photodetector to allow detecting of the filament vibrational movement. 

The signal generated by the photodetector is amplified and used to provide 

feedback to the transducer thereby producing an augmented resonance 

10 response from the filament. This signal is then displayed to use a measure 

of filament density. 

15 For a more complete understanding of the present invention and for 

further objects and advantages thereof, reference is now made to the 

following description taken in conjunction with the accompanying drawings 

in which: 

FIG. 1 is a perspective view of the mass measurement apparatus; 

20 FIG. 2 is a block diagram of a self-tuning closed loop system; 

FIG. 3 is a block diagram of a pulsed excitationlfree decay system; 

FIG. 4 is a block diagram of a phase-locked loop detector; 

FIG. 5 is a block diagram of a variable input open loop detector; 

FIG. 6 is a flow chart delineating the steps in the process of the 

25 invention; and 

FIG. 7 is a graph of vibrational amplitude versus frequency produced 

by the variable input open-loop system. 
LAR 14879- 1 -CU -4- PATENT APPLICATION 

Referring now to FIG. 1, the apparatus for measuring filament 

density, designated generally by the reference numeral 10, is shown with 

5 its major components. The apparatus 10 has a fixed filament support I1 

and a transducer 13 attached to a base 14. A moveable filament support 

15 is attached to the transducer to provide a driver for inducing transverse 

vibrations into a filament 16. A light source 17 and photodetector 18 are 

mounted on base 14 and positioned with the suspended filament 16 passing 

10 between the light source and photodetector. An optical mask 19 is 

positioned between photodetector 18 and the moving filament 16 in order 

to provide a discrete signal to the photodetector during filament vibrations. 

A tensioning device 8 1 is affixed to base 14 to provide a uniform tension 

on filament 16. Weight 82 is suspended on filament 16 which is routed 

15 through pulleys 85 and 87. Although tension is normally on the filament 

during any manufacturing process, the tensioning device allows a uniform 

tension to be maintained. In some manufacturing processes where the 

tension in the filament is fairly uniform, the tensioning device may not be 

required. 

20 The apparatus 10 provides a means of monitoring resin content or 

other coatings and impregnations in continuous fiber tows. The ability to 

provide continuous monitoring of both stationary and moving filaments 

ensures a uniform product when combining thermoplastic (powder coating) 

with continuous moving fibers. The determination of fiber or filament mass, 

25 and therefore the quantity of powder or resin applied, is accomplished by 

evaluating the vibrational characteristics of the fiber according to the 

following equation: 
LAR 14879- 1 -CU -5- PATENT APPLICATION 

f = fundamental frequency (hz) 

L = length (cm) 

T = Tension (dyne) 

m = mass density (glcm) 

Given a length of fiber under a known tension, the mass density can then 

be calculated based on the frequency response. More generally, if the 

string is moving axially in its lengthwise direction at a constant velocity v, 

then its resonant frequencies f, are given by 

The Doppler shift given by the last term in parenthesis is significant when 

10 the velocity is large, as it may be in some manufacturing processes. 

Furthermore, if the vibrating element is thick or stiff, modifications to these 

equations can be made to reflect beamlike in addition to stringlike behavior. 

Referring now to FIG. 2, the circuitry for collecting and processing 

data on the vibrating string of the preferred embodiment is shown by block 

15 diagram. The motion of the vibrating string 21 is detected by an optical 

sensor 22 or other means of detecting vibrational response. The signal from 

the optical sensor 22 is processed by amplifier 23. The amplified signal 

then drives transducer 25 at the natural resonance already occurring in the 

vibrating fiber. A part of the signal is directed to a display, in the preferred 

20 embodiment, a frequency meter 27 and to a frequency-to-voltage convertor 

29 for control use. 

Typically during the manufacturing of an impregnated or coated fiber, 

the high speed running of the fiber through the manufacturing devices will 
LAR 14879-1 -CU - 6- PATENT APPLICATION 

result in a natural vibration. Using the circuit of FIG. 2, the natural 

frequency will be amplified through the feedback circuit providing a selftuned resonant response, thereby providing a resonantly vibrating string. 

It is also possible to produce a single-pulsed system wherein the fiber 

5 is transversely displaced by the single pulse thereby setting up a natural 

vibration followed by a gradual decay in amplitude. In this embodiment, 

shown in FIG. 3, the pulse generator 31 sends a driving pulse through 

power amplifier 32 to transducer 33 which in turn drives the vibrating string 

34. As in the preferred embodiment, an optical sensor 35 detects the 

10 movement providing a signal to the amplifier 37. The output of amplifier 37 

is then analyzed by the fast fourier transform analyzer 39 to determine the 

fundamental frequency. 

FIG. 4 depicts a further embodiment wherein the frequency of 

vibrating string 41 is detected by optical sensor 42 which feeds amplifier 43 

15 to a phase locking component 44. This circuit provides feedback through 

power amplifier 45 to transducer 47 which in turn drives the vibrating string 

41. DC output 49 provides a signal conditioned by the vibrational 

frequency. 

Another variant of the invention, shown in FIG. 5, provides for a 

20 short duration excitation of the vibrating string over a specified frequency 

range. In this configuration, the variable frequency sine wave oscillator 51 

provides a signal to a power amplifier 52 which drives the transducer 53. 

The signal provided causes the transducer 53 to initially vibrate at a 

frequency well below the resonant frequency of vibrating string 59. The 

25 vibrating frequency rapidly increases to a frequency well above the resonant 

frequency. During this frequency range sweep, the optical sensor 57 

detects the vibrating string 59 response and provides a signal to 

oscilloscope 55 where the amplitude of the response identifies the resonant 

frequency. 
LAR 1 4879- 1 -CU -7- PATENT APPLICATION 

The method of the preferred embodiment is depicted in FIG. 6. The 

primary steps include providing two supports 61 for the filament or fiber; 

leading the filament across the supports 62; tensioning the filament 63; 

inducing vibrations into the filament 64; detecting the frequency of vibration 

5 65; amplifying that frequency 66; feeding back the detected signal 67 to 

further excite the vibrational mode; and displaying the vibrational frequency 

69. It is often necessary to perform every step specifically as some of the 

above-listed requirements may be provided by the underlying manufacturing 

process. For example, line tension may be sufficient without any additional 

10 tensioning from the invention. Likewise, there may be present, a natural 

vibration in a running fiber which can be amplified without the need to 

initially induce the vibration. 

Referring to FIG. 7, a plot of a typical response to a variable sine 

wave oscillator. The frequency 73 sweeps through the range of 500 to 540 

15 Hz and the amplitude 71 has a maximum, indicating the resonant frequency, 

at 520 Hz. 

The features and advantages of the invention are numerous. The 

mass density detector allows a variety of inputs to be used to excite 

vibration in the fiber to be tested. There is no requirement to stop the 

20 manufacturing process or remove the fiber from the manufacturing line. 

The fiber may be tested either running or in a stationary position. 

Although the invention has been described relative to a specific 

embodiment thereof, there are numerous variations and modifications that 

will be readily apparent to those skilled in the art in the light of the above 

25 teachings. It is therefore to be understood that, within the scope of the 

appended claims, the invention may be practiced other than as specifically 

described. 

What is claimed as new and desired to be secured by Letters Patent 

of the United States is: 
LAR 14879- I -CU 1?, PATENT APPLICATION 

APPARATUS AND METHOD FOR DETERMINING 

THE MASS DENSITY OF A FILAMENT 

act of the Invanlum 

5 

A method and apparatus for determining the mass density of a 

moving filament is provided. The method includes the steps of providing a 

filament across two supports, tensioning the filament, inducing a vibration 

into the filament segment between the supports, reinforcing the vibration 

10 using an amplified feedback signal, detecting the vibrational frequency data, 

processing the data using a fast-fourier transform analysis, and then 

displaying the frequency. The use of the feedback signal results in a selftuning resonant loop. Open loop versions may also be used. The apparatus 

includes a base supporting a fixed support and a transducer which in turn 

15 supports a moveable support. The transducer vibrates the moveable 

support transversely to the direction of travel of the filament, thereby 

inducing a transverse vibrational mode. The output of the transducer is 

amplified and used to drive a second amplifier to produce a self-tuning 

resonant loop. In the open loop version a signal generator is used to drive 

20 the transducer through a frequency range, during which the amplitude peak 

is identified. 
FIG. 1 
Block Diagram I 

Self-tuning Closed-Loop Resonant System 

\ 

transducer - I 

29 - 27 

/ 

uency-to-vol tage frequency met 

FIG. 2 
Block Diagram II 

Pulsed excitation/free decay System 

FIG. 3 

31 32 33 

\ 

pulse generator - transducer 

34 

t F 

Vibrating string 

-/ 

i9 . v 35 

fft signal amplifier - optical sensor 

analyzer A 

> 
Block Diagram Ill 

Phase locked loop detector 

. 43 

\ 

Vibrating string optic cat sensor amplifier 

47 44 

/ r/ 

phase 

transducer * 4 - locked 

\ 

DC output 

FIG. 4 
Block Diagram IV 

sdup used to produce figure 2 

\ 

variabie 

frequency 

sine wave 

oscillator 

FIG. 5 

I oscilloscope 

+ /- - transducer 

& 

optical sensor 4 Vibrating string A 1 
PROVIDE SUPPORTS FOR i FILAMENT TESTING 

m TENSION FILAMENT 

62\ 

INDUCE 

VIBUTION INTO 

LEAD FILAMENT 

ACROSS SUPPORTS r 

DETECT FREQUENCY 

1 AMPLIFY FREQUENCY 

I VIBRATION 1 

67 

6 9 

DISPLAY VIBRRTIONAL I 

FEZD AMF'LIFIED SIGNAL 

BACK TO EXCITE FILAMENT 

i S I GNAL 1 
\ 

amplitude, mV 

frequency, HZ /73 

FIG. 7