EP0902891A1 - Use of load measurements for quality control of joints during assembly - Google Patents
Use of load measurements for quality control of joints during assemblyInfo
- Publication number
- EP0902891A1 EP0902891A1 EP97927860A EP97927860A EP0902891A1 EP 0902891 A1 EP0902891 A1 EP 0902891A1 EP 97927860 A EP97927860 A EP 97927860A EP 97927860 A EP97927860 A EP 97927860A EP 0902891 A1 EP0902891 A1 EP 0902891A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- load
- longitudinal
- measured
- waves
- shear
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/04—Analysing solids
- G01N29/07—Analysing solids by measuring propagation velocity or propagation time of acoustic waves
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
- G01L5/24—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for determining value of torque or twisting moment for tightening a nut or other member which is similarly stressed
- G01L5/246—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for determining value of torque or twisting moment for tightening a nut or other member which is similarly stressed using acoustic waves
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/34—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor
- G01N29/348—Generating the ultrasonic, sonic or infrasonic waves, e.g. electronic circuits specially adapted therefor with frequency characteristics, e.g. single frequency signals, chirp signals
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/02—Indexing codes associated with the analysed material
- G01N2291/028—Material parameters
- G01N2291/02827—Elastic parameters, strength or force
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/04—Wave modes and trajectories
- G01N2291/044—Internal reflections (echoes), e.g. on walls or defects
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/04—Wave modes and trajectories
- G01N2291/048—Transmission, i.e. analysed material between transmitter and receiver
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/26—Scanned objects
- G01N2291/269—Various geometry objects
- G01N2291/2691—Bolts, screws, heads
Definitions
- This invention relates to a method for measuring the load applied to a fastener during assembly and, more specifically, to a method of using direct load measurement methods—such as those measuring load with ultrasonic waves or the rate of change in direct load measurement methods using ultrasonic waves with time--to provide reliable and accurate assembly of a joint.
- direct load measurement methods such as those measuring load with ultrasonic waves or the rate of change in direct load measurement methods using ultrasonic waves with time--to provide reliable and accurate assembly of a joint.
- ultrasonic waves can be used to provide a precise measure of the tensile load in a fastener (such as a bolt) during installation, or subsequently for purposes of inspection. These techniques are well documented in the prior art. In addition, techniques have been documented which use ultrasonic waves to detect flaws and for other nondestructive evaluation purposes in fasteners and other load-bearing members. The success of all of these techniques depends upon reliably detecting echo signals from within the load- bearing member under evaluation.
- U.S. Patent No. 4,602,511 teaches a method of determining stress by using the times-of-flight of both longitudinal and shear waves without taking a time-of- flight measurement at zero load in a bolt. This method allows one to measure the tensile load in a previously installed fastener. The time-of-flight for each of the waves is measured and then used to calculate the tensile stress in the fastener using the formula:
- U.S. Patent No. 4,846,001 (issued to Kibblewhite and assigned to SPS Technologies, Inc.) teaches the use of a thin piezoelectric polymer film which is bonded to the upper surface of a load-bearing member, fasteners incorporating such films, and fastener tightening apparatuses for use with such fasteners.
- the method determines the length, tensile load, stress, and other tensile load-dependent characteristics of the member by ultrasonic techniques.
- the '001 patent discloses using a contact pin engaged with the piezoelectric polymer film and disposed in a fastener tightening tool which is electrically connected to an electronic control device.
- the electronic control device transmits and receives electronic signals from the piezoelectric polymer sensor to provide ultrasonic measurement of the tensile load, stress, or elongation of the shank of the fastener.
- U.S. Patent No. 5,131,276 (issued to Kibblewhite and assigned to Ultrafast, Inc.) teaches a load-indicating fastener having an ultrasonic transducer, including an acoustoelectric film, grown directly on the fastener surface. By growing the acoustoelectric film directly on the fastener, the film is mechanically, electrically, and acoustically interconnected to the surface.
- This advance not only allows a precise pulse- echo load measurement technique to be used during a production assembly operation but also significantly improves load measurement accuracy by eliminating errors that would result from axial and radial movement of the transducer relative to the bolt and from variations in the coupling media.
- the tensile load indication in the load measuring device may be combined with other parameters monitored by the fastener tightening tool, such as torque and angle, to determine when the tightening cycle is complete or to detect irregularities in the joint.
- Stick/slip conditions occur where an increased friction between the fastener and the medium into which the fastener is being inserted causes an erroneous load measurement due to the increased torque that must be applied to overcome the friction and to the sudden decrease in torque required to tighten the fastener after the friction has been overcome.
- Each upward spike and downward spike in the graph of torque versus angle, shown in Figure 1 indicates an increased or decreased, respectively, friction condition and the increase or decrease in torque associated with that condition. It is known that by measuring both torque and angle, joint irregularities or irregular friction conditions such as stick/slip can be detected.
- joint irregularities occur due to damaged or dirty threads, incorrectly tapped holes, out-of-tolerance joint components or incorrect joint materials or surface treatments.
- the present invention provides a method which uses a combination of ultrasonic load measurements, or the rate of change of an ultrasonic load measurement with time, to accurately and reliably measure the load applied to a load-bearing member.
- the present invention may be used to detect material yield, to detect errors in ultrasonic load measurements, and to detect irregularities in fasteners or joints during assembly and quality control operations.
- One object of the present invention is to detect joint and assembly irregularities using ultrasonic measurement alone without the need for expensive torque and angle transducers.
- the present invention provides a method for detecting an error in measuring a load on a load-bearing member comprising measuring a load on the load-bearing member with a first load measurement method and simultaneously measuring a load on the load-bearing member with a second load measurement method. The two load measurements are then compared and a relationship is determined between the two. Then, an error is identified in the load measurement made with the first or second method using the relationship.
- the present invention also provides a method for correcting an erroneous load measurement by compensating for the error.
- the first method uses longitudinal and shear waves, and the second method uses longitudinal waves.
- the error is determined using changes in load measured with longitudinal waves alone, load measured with shear waves alone, or load measured using longitudinal and shear waves, versus time.
- the first method uses longitudinal and shear waves and the second method uses shear waves.
- Fig. 1 is a graph showing torque versus angle and illustrating a slip/stick condition
- Fig. 2 is a graph, for a first error condition, showing load measured using longitudinal and shear waves (L LS ) versus load measured with longitudinal waves (LJ only or load measured with shear waves (Ls) only;
- Fig. 3 is a graph, for a second error condition, showing load measured with longitudinal waves (LjJ only or load measured with shear waves (Lj) only versus load measured with longitudinal and shear waves (L LS );
- Fig. 4 is a graph, for a third error condition, showing load measured with longitudinal and shear waves (L LS ) versus load measured with longitudinal waves (LJ only or load measured with shear waves (Lj) only;
- Fig. 5 is a graph, for a fourth error condition, showing load measured with longitudinal and shear waves (L LS ) versus load measured with longitudinal waves (LJ only or load measured with shear waves (Lg) only;
- Fig. 6 is a graph, for the third error condition, showing load measured with longitudinal waves (LJ only versus time measured during tightening;
- Fig. 7 is a graph, for the fourth error condition, showing load measured with longitudinal waves (L L ) only versus time measured during tightening
- Fig. 8 is a graph, for the third error condition, showing load measured with longitudinal and shear waves (L LS ) versus time measured during tightening
- Fig. 9 is a graph, for the fourth error condition, showing load measured with longitudinal and shear waves (L ⁇ ) versus time measured during tightening;
- Fig. 10 is a graph, for a fifth error condition, showing load measured using longitudinal waves (LjJ only, load measured with shear waves only (Ls), or load measured with longitudinal and shear waves (L s) versus time measured during tightening
- Fig. 11 is a graph, for the second error condition, showing load measured with longitudinal waves (L L ) only, load measured with shear waves only (Ls), or load measured with longitudinal and shear waves (L LS ) versus time measured during tightening
- Fig. 12 is a graph, for the first error condition, showing the use of load measured with longitudinal waves (L L ) only or load measured with shear waves (Lg) only to correct the erroneous load measurement made with longitudinal and shear waves (L LS ).
- load measurement techniques based on torque (rotational force applied to the bolt), angle (number of degrees the bolt is rotated), and time (period of time the bolt is rotated) have been used to measure and control the load applied to load- bearing members (such as fasteners) and to bolted joints. Load measurement accuracy with these techniques varies from ⁇ 10% to ⁇ 30% . Torque, independently, may also be used to measure load during tightening of a threaded fastener. Ultrasonic measurement of load is accurate and provides a way to inspect a tightened bolt but, until recently, was impractical for use in automated assembly operations. The technology developed by Ultrafast and described in U.S. Patent No. 5,131,276 (to Kibblewhite) allows the use of ultrasonic waves to measure and control load applied to a load-bearing member with power and hand tools. This technology is particularly useful in high volume production assembly operations in the automotive, aerospace, construction, and other industries.
- more than one ultrasonic measurement method can be used simultaneously, or the rate of change with time of load measured with one or more ultrasonic load measurement methods may be used to improve the accuracy and reliability of ultrasonic load measurements and to detect undesirable joint irregularities during assembly operations.
- load measured with longitudinal and shear ultrasonic waves can be used with load measured with longitudinal ultrasonic waves alone or shear ultrasonic waves alone—or rate of change of load measured with longitudinal and shear waves, longitudinal waves alone, or shear ultrasonic waves alone versus time may be used to improve the accuracy and reliability of load measurement.
- the first uses pulse-echo time-of-flight measurements of longitudinal ultrasonic waves only. This method is very accurate ( ⁇ 3 %) but generally requires a zero load measurement and, furthermore, cannot be used to measure loads at yield. That is, ultrasonic techniques using longitudinal waves alone cannot be used to measure load where there is plastic deformation of the fastener material.
- the present invention is discussed using the reference variable L L , which refers to load measured using longitudinal ultrasonic waves only; Ls, which refers to load measured with shear ultrasonic waves only; and the reference variable L ⁇ , which refers to load measured using both longitudinal and shear ultrasonic waves.
- L L refers to load measured using longitudinal ultrasonic waves only
- Ls which refers to load measured with shear ultrasonic waves only
- L ⁇ which refers to load measured using both longitudinal and shear ultrasonic waves.
- the present invention uses load measured using longitudinal waves or load measured with shear waves in combination with load measured using longitudinal and shear waves; or uses the rate of change of these load measurements with time to detect errors in load measurement.
- time-of-flight measurements of the longitudinal waves, shear waves, or both could be used, or the rate of change of these time-of-flight measurements with time could be used, to detect, for example, erroneous load measurements, material variations, or material yield as set forth below, rather than using the load calculated with these time-of-flight measurements to identify the errors or conditions.
- the present invention can detect the following errors and conditions: 1. Detect errors in load measured with longitudinal and shear waves
- LL S LL S using load measured at zero load with longitudinal waves (LjJ or shear waves (Ls) prior to or during tightening of the fastener. Errors in load caused from bolt-to-bolt variations (as discussed above) may be detected and removed in this way.
- Yield occurs when the load on the fastener causes the fastener material to make a transition from elastic deformation to plastic deformation.
- the onset of yield is detected as a gradual change in slope of the curve of load measured with one ultrasonic method versus load measured with another ultrasonic method, or rate of change of load measured using one ultrasonic method with time.
- Detection techniques can be used to measure change in slope of load measured with one method plotted against the load measured with a second method or one method plotted against time, which can indicate onset of yield.
- Table 1 shows which of the five above-described conditions can be detected using load measured with ultrasonic longitudinal waves (L L ) or ultrasonic shear waves (Ls), load measured with ultrasonic longitudinal and shear waves (L LS ), and rate of change of load measured with these direct load measurements with time.
- the above load measurement methods can be combined to accurately measure and monitor the load on a load-bearing member during, for example, an assembly operation. Note that, in Table 1, the upper right hand diagonal of the table is a mirror image of the lower left hand diagonal of the table.
- Table 1 describes load conditions that can be detected reliably during tightening and quahty control steps in an assembly operation.
- Figs. 2 through 12 show the relationship between possible load measuring methods during an assembly operation and how the different methods may be used to show the five above-listed conditions.
- Figs. 2-5 are graphs comparing load measured with longitudinal and shear waves against the load measured with longitudinal or shear waves alone.
- Fig. 2 is a graph showing that load measured with longitudinal or shear waves alone can be used to detect erroneous load measurements made with longitudinal and shear waves (Condition 1).
- the graph indicates that, with no load applied to the load-bearing member, the load measured with longitudinal and shear waves (L LS ) was not zero. This "error” is indicated by an offset load "a. " Because the load measured with longitudinal waves (L L ) or shear waves (Lg) alone requires an initial load measurement at zero load, the graph can be used to show that the load measured with longitudinal and shear waves is erroneously offset by load "a. " The L L or Ls measurement can be used, therefore, to detect and correct the erroneous L measurement.
- Fig. 3 is a graph showing that load measured with longitudinal and shear waves can be used to detect erroneous load measurements made with longitudinal or shear waves alone (Condition 2).
- the graph shows that, at load "b," the load measured with longitudinal or shear waves erroneously indicated that the load on the fastener was increasing. This "error” can be detected by using the load measured with longitudinal and shear waves which indicates that the load on the fastener is not increasing or increasing by load "b.
- Fig. 4 is a graph showing that load measured with longitudinal and shear waves can be used to detect yield in a bolt. In the region of yield, the load measured with longitudinal and shear waves begins to increase at a lower rate than the load measured with longitudinal or shear waves alone (Condition 3).
- Yield occurs where the fastener material goes through a transition from elastic deformation to plastic deformation.
- the load measured with longitudinal or shear waves shows that the load continues to increase.
- Load measured with longitudinal and shear waves shows, however, that the load has not increased.
- Measuring load by longitudinal or shear waves alone erroneously shows increasing load because the fastener length is increasing due to plastic deformation which causes the time-of-flight of the longitudinal and shear waves to increase. If the load had been measured by longitudinal or shear waves alone, the onset of yield would not have been detected.
- Fig. 5 is also a graph showing that load measured with longitudinal and shear waves can be used to detect the constant load at yield in a bolt whereas load measured with longitudinal or shear waves alone indicates that load continues to increase with tightening.
- the load measured with longitudinal and shear waves is used to detect variations in the fastener material such as grade or hardness (Condition 4).
- the load at which the fastener undergoes yield is indicated by the flattening of the curve.
- Fig. 5 shows that load measured by longitudinal and shear waves falls below the minimum expected yield load, load "c" (dotted line). This condition would not have been detected if load had been measured by longitudinal or shear waves alone.
- Figs. 6-11 are graphs showing changes in load measured with longitudinal and/or shear waves versus time.
- Fig. 6 is a graph showing load measured with longitudinal waves versus time to detect erroneous load measurements due, for example, to the onset of yield (Condition 3). The load measurements show that, in the region of yield, the load measured with longitudinal waves is increasing but at a decreasing rate.
- Fig. 7 is also a graph showing that load measured with longitudinal waves versus time can be used to detect yield in a bolt.
- the load measured with longitudinal waves is used to detect variations in fastener material such as grade or hardness (Condition 4).
- the load at which the fastener experiences yield is indicated by the change of slope of the curve.
- Fig. 7 shows that the load at which the fastener experienced yield falls below the minimum expected yield load, load "d" (dotted line).
- the premature occurrence of yield indicates that there is some fault condition related either to the fastener material or to other factors in the load-bearing member or the joint.
- Fig. 8 is a graph showing that load measured using longitudinal and shear waves versus time can be used to detect, for example, the onset of yield (Condition 3). The flattening of the curve indicates that, while the bolt is still mrning, the load measured with longitudinal and shear waves is not increasing.
- Fig. 9 is also a graph showing that load measured using longitudinal and shear waves versus time can be used to detect premature yield in a fastener when used in conjunction with time. In this graph, the load measured with longitudinal and shear waves is used to detect variations in the fastener material such as grade or hardness (Condition 4).
- Fig. 9 shows that load measured by longitudinal and shear waves versus time detects that the fastener falls below the minimum required yield load "e. "
- Fig. 10 is a graph showing that load measured with longitudinal waves (L L ) only, load measured with shear waves only (Lg), or load measured with longitudinal and shear waves (L LS ) versus time can be used to detect a stick/slip condition (condition 5 above).
- L L load measured with longitudinal waves
- Lg load measured with shear waves only
- L LS load measured with longitudinal and shear waves
- Fig. 11 is graph showing load measured with longitudinal and shear waves, or load measured with either longitudinal or shear waves alone, versus time. The time measurement will be identical to the angle measurement if the fastener is rotated at a constant speed.
- Fig. 11 is a graph showing that discrete changes in load measurements made with longitudinal and shear waves, or with either longitudinal or shear waves alone, versus time (Condition 2) can be used to detect erroneous load measurements. The graph shows that, at load "f," the load measured with longitudinal and shear waves, or with either longitudinal or shear waves alone, erroneously indicated that the load on the fastener was increasing. This "error" can be detected by using a time measurement which shows that the load on the fastener could not have increased instantaneously.
- the sudden increase in load indicates that there has been an error in the time-of-flight measurement of the longitudinal and shear waves or of either the longitudinal or shear waves alone.
- the use of direct load measurements in combination with one another may also be used to correct enoneous load measurements. For example, as shown in Fig. 12, load measured with longitudinal or shear waves may be used to correct an erroneous load measurement made with longitudinal and shear waves.
- Fig. 12 shows that, with zero load applied to a load-bearing member, the load measured with longitudinal and shear waves is not zero. Rather, the load is offset by load "g" which is identical to load offset "a” described above with reference to Fig. 2. Because the load measured with longitudinal or shear waves alone requires an initial load measurement at zero load, the graph can be used to show that the load measured with longitudinal and shear waves is erroneously offset by load "g. " In addition, because the offset is a known value (load "g"), the load measured with longitudinal and shear waves may be corrected by this offset value such that the load measured using longitudinal and shear waves coincides with the load measured using longitudinal or shear waves.
- the load measured with longitudinal or shear waves alone can be used to detect and correct the erroneous load measurement made with longitudinal and shear waves.
- rates of change of load measurements, or the slope or gradient of the load versus time graph can be measured simply by taking the difference in load measurement over an interval of time and dividing by that interval of time.
- the applicability of these techniques is independent of how each load measurement is made. They could be used with direct load measurement technology other than ultrasonic load measurement methods should such methods be developed in the future.
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- General Health & Medical Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Health & Medical Sciences (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Acoustics & Sound (AREA)
- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
- Force Measurement Appropriate To Specific Purposes (AREA)
Abstract
Description
Claims
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US1885996P | 1996-05-31 | 1996-05-31 | |
US18859P | 1996-05-31 | ||
US86688697A | 1997-05-30 | 1997-05-30 | |
US866886 | 1997-05-30 | ||
PCT/US1997/009271 WO1997045725A1 (en) | 1996-05-31 | 1997-06-02 | Use of load measurements for quality control of joints during assembly |
Publications (1)
Publication Number | Publication Date |
---|---|
EP0902891A1 true EP0902891A1 (en) | 1999-03-24 |
Family
ID=26691600
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP97927860A Withdrawn EP0902891A1 (en) | 1996-05-31 | 1997-06-02 | Use of load measurements for quality control of joints during assembly |
Country Status (2)
Country | Link |
---|---|
EP (1) | EP0902891A1 (en) |
WO (1) | WO1997045725A1 (en) |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4846001A (en) * | 1987-09-11 | 1989-07-11 | Sps Technologies, Inc. | Ultrasonic load indicating member |
US5131276A (en) * | 1990-08-27 | 1992-07-21 | Ultrafast, Inc. | Ultrasonic load indicating member with transducer |
US5150620A (en) * | 1991-06-19 | 1992-09-29 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Method of recertifying a loaded bearing member |
-
1997
- 1997-06-02 WO PCT/US1997/009271 patent/WO1997045725A1/en not_active Application Discontinuation
- 1997-06-02 EP EP97927860A patent/EP0902891A1/en not_active Withdrawn
Non-Patent Citations (1)
Title |
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See references of WO9745725A1 * |
Also Published As
Publication number | Publication date |
---|---|
WO1997045725A1 (en) | 1997-12-04 |
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