U.S. patent application number 09/835977 was filed with the patent office on 2002-10-17 for most accurate method of tensioning threaded fasteners in assembled units.
Invention is credited to Leong, Irving.
Application Number | 20020148299 09/835977 |
Document ID | / |
Family ID | 25270928 |
Filed Date | 2002-10-17 |
United States Patent
Application |
20020148299 |
Kind Code |
A1 |
Leong, Irving |
October 17, 2002 |
MOST ACCURATE METHOD OF TENSIONING THREADED FASTENERS IN ASSEMBLED
UNITS
Abstract
A highly accurate method of tensioning threaded fasteners into
assembled units is presented. A mechanical process for locating the
initial point that a threaded male fastening unit enters into the
female fastening unit provides a definite reference point from
which angular movement of the fastener can be digitally measured
with the greatest accuracy. Accurate measurement of angular
rotation of a threaded unit into a receiving unit provides a direct
relationship to allow an accurate measurement of the tension
applied to the fastener inside the recess. Multiple fasteners can
be randomly indexed to start at the zero point and be driven into
the receiving unit with equal tension in each fastener in timed
increments of rotation during the entire process of driving the
fasteners into the fastened unit. A digital printout of the process
certifies the reference numbers of all components assembled and
timed movement activity of each of the assembled components.
Inventors: |
Leong, Irving; (Taylors,
SC) |
Correspondence
Address: |
Flint & Kim, P.A.
P.O. Box 10823
Greenville
SC
29603-0827
US
|
Family ID: |
25270928 |
Appl. No.: |
09/835977 |
Filed: |
April 16, 2001 |
Current U.S.
Class: |
73/761 |
Current CPC
Class: |
B23P 19/042 20130101;
B23P 19/066 20130101; B23P 19/069 20130101 |
Class at
Publication: |
73/761 |
International
Class: |
F16B 031/02 |
Claims
What is claimed is:
1. A basic unit for accurately tensioning threaded fasteners in a
threaded recess comprising: a. means for locating the initial zero
starting point of a threaded fastener when positioned at the
opening of a threaded recess; b. a motor for driving a chucked
threaded fastener in a clockwise direction; c. a magnetic notched
wheel having evenly divided number of segments of teeth and notches
within the 360 degrees of a circle, said notched wheel having
substantially no permanentmagnetic qualities, each tooth being
provided with a coil therearound; d. an electromagnet rotation
sensor comprising an iron core and solenoid, a pole of said
electromagnet being disposed for passing across the notch of the
magnetic notched wheel; e. means for converting the threshold
signal generated as a tooth of the wheel passes the electromagnet
into a discrete binary "1" signal; f. means for counting the
digital signals as they are transmitted to an axial position sensor
for a fastener as it is driven and for converting the signal into a
measurement of the driven axial distance of the bolt; g. sensor as
a function thereby determining the threaded fastener's stretched
length inside the threaded recess after the fastener is fully
driven home.
2. The basic unit of claim 1 wherein the magnetic notched wheel and
said electromagnet are components of a slipper motor.
3. A destructive test unit comprising the Basic Unit of claim 1;
and, including a. means for stretching the threaded fastener inside
of the threaded recess to the destruction of the threaded fastener;
b. means for recording the failure length of the fastener; and, c.
means for calculating the design percentage of the threaded
fastener as the discrete elongated design length and as the
percentage of elongation to failure.
4. A multiple gang wrench unit comprising two or more Basic Units
of claim 1 and further comprising; a. means for enacting random
axial placement of identical fasteners in assigned threaded
recesses in a unit to be assembled; b. means for randomly locating
each threaded fastener to the zero reference engagement point; c. a
controller for activating the clockwise rotation of each driving
motor in unison; d. means for sending a binary digital signal to
the controller, such controller allowing each driving motor to move
one angular increment in unison but preventing any one motor from
proceeding to the next angular increment, until all threaded
fasteners have moved to the same last axial increment.
5. A certification quality control unit for assembled components
comprising; a. means for recording the unique bar coded identifying
number of each component to be assembled; b. a binary digital
storage means that records the real time performance of each
component as a function of axial position, fastener stretched
length, and pertinent environmental parameters as selected.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to a method and apparatus
for tightening a series of threaded fasteners so that all the
fasteners are under the same tension forces. Specifically, the
invention relates, in one embodiment, to a method for tightening
the cylinder head bolts in an internal combustion engine to the
same degree of tension.
BACKGROUND OF THE INVENTION
[0002] The present invention departs from prior art practices and
provides an exceedingly accurate method of tensioning threaded
bolts which are used to fasten or attach one element to another
using bolts, technically referred to as cap screws. The tensioning
system eliminates the margin of error associated with current
torque wrenches and torque application systems which are based on
the measurement of "torque" or fastener tensioning through the
frictional intermediate interface of the bolt and threads of the
fastener receptacle. Further, the present invention allows real
time equal starting, running in, and tensioning of fasteners and
computer certified automated quality control of the assembly
process.
[0003] To better understand the significance of the present
invention, a brief description of prior art practices follows. When
threaded fasteners are tightened, they are actually stretched not
unlike a rubber band holding together two blocks of wood. The
current method of tensioning fasteners is referred to as applying
torque to the fastener. Current torque wrenches measure the force
of tension applied to a lever arm at a unit radius distance away
from the center axis of the fastener. In the United States the
current common measurement is the foot pound. In the current
method, inaccuracy is created by the friction between the threaded
fastener and the threaded receptacle into which the fastener is
driven. Fasteners and the threaded receptacles are most commonly
alloys but may also be ceramics, cermets, plastics, or combinations
of these. Alloys, which are crystalline structures, and cermet
matrices are almost never homogeneous and have highly variable
frictional characteristics. Forming threads in these materials not
only exposes unknown surfaces, but the tools used to form the
threads, further imparts unknown frictional characteristics unique
to the tool marks or striae created by each unique tool. Given to
the large number of variables in the materials and the screw thread
forming process, measurement of fastener tensioning through the
frictional interface used by current art torque wrenches will
always provide a sizable percentage of error and preclude
reliability in regard to definite repeated uniform tensioning of
the fastener and the fastened unit.
[0004] Angular torque has been adopted virtually universally as the
measure of measuring tension strain. Accuracy has increased, but
the current angular torquing method still starts with a low initial
starting torque value, from which torque angles are later measured
and inaccuracies due to friction irregularities have not been
eliminated.
[0005] Presently used torque wrenches, either hand or machine
operated, are frictional compression or tension loaded devices that
release when the set threshold setting is reached. These are
referred to in the industry as torque limiting devices. Since these
devices are based on springs and friction, they are subjected to
increased inaccuracy due to repeated use and must be re-calibrated
and compared to a reference which is, currently, an analog,
frictional spring loaded unit.
[0006] The current method of setting up a multiple fastener
assembled unit such as an engine block, a gasket and a cylinder
head requires tightening individual fasteners in a spiral pattern
in steps of lesser that the ultimate desired torque value, either
measured by a torque wrench or an angular torque device. This
method requires that the components be over designed in strength to
prevent displacement or warping during the assembly process.
[0007] The current method of quality control is to have an operator
place a paint mark of each fastener that he or she has securely
tightened. Thus, another object of the present invention is to
provide a method whereby all bolts can be tightened simultaneously
and uniformity to the same tension.
DESCRIPTION OF PRIOR ART
[0008] Previous attempts to solve the problem of uniform tensioning
of threaded bolts have resulted in inventions that have addressed
methods of tightening threaded fasteners (bolts or cap screws) with
quantitative measurement of tightness and the certification of
tightened fasteners. None provide for the indexing of the actual
referenced starting point of a threaded fastener into the threaded
unit, the digital measurement of fastener elongation within the
threaded recess and the integrated "quality control" certification
of the assembled unit. For example, U.S. Pat. Nos. 3,970,155;
4,091,664; 4,328,709; 4,958,541; 5,172,616; 5,890;406; 5,911,801;
and 6,021,555 are all illustrative of prior art. On the other hand,
U.S. Pat. No. 6,021,555 granted to Applicant is helpful in
appreciating the current invention; however, the rest of the cited
art may be suitable for a particular purpose that each addresses
but none would be suitable for the intended purpose of the present
invention as herein described. Detailed discussion of these prior
art patents is set forth below:
[0009] U.S. Pat. No. 4,328,709
[0010] Inventor: Wayne E. Shramm
[0011] Issued: May 11, 1982
[0012] This patent discloses conventional beam displacement torque
wrench with an attachment that allows presetting a torque value,
wherein the attachment provides an audio and a visual signal to the
operator, when the preset torque is reached. The beam displacement
torque wrench is well known in the prior art and measures torque as
a factor of the bending of a wrench beam in relation to a reference
indicator to which no bending force is applied.
[0013] U.S. Pat. No. 4,958,541
[0014] Inventor: Jeffrey R. Annis et al.
[0015] Issued: Sept. 25, 1990
[0016] In this patent an analog torque limiting wrench is described
which registers torque as pressure imparted upon a piezoelectric
strain gauge. When a preset threshold level of strain imparted by
the wrench is reached, a signal is sent to a vibration creating
electric motor that provides the user with a tactile signal.
[0017] U.S. Pat. No. 5,172,616
[0018] Inventor: Masaki Negishi
[0019] Issued: Dec. 22, 1992
[0020] This patent describes a device that simultaneously measures
both "torque angle" and torque resistance of the threaded fastener
as it is tightened into an assembled threaded recess. While this
device provides a digital readout of the turning angle of the
fastener being turned, the unit's primary aim is to prevent over
tightening of bolts by measuring the relationship between the
torque applied and the angular displacement of the fastener.
[0021] U.S. Pat. No. 5,890,406
[0022] Inventor: Brent Thorn
[0023] Issued: Apr. 6,1999
[0024] The device disclosed is a torque wrench with an electro
mechanical torque limiting release mechanism. For quality control
purposes, when a preset torque is reached on the device, a felt tip
marker is used to mark the bolt head to certify that the particular
bolt has been correctly tightened.
[0025] U.S. Pat. No. 5,199,801
[0026] Inventor: Rene Michel Fravalo
[0027] Issued: Jun. 15, 1999
[0028] Described is a version of the well known and well used
spring loaded torque limiting wrench, which releases when a preset
torque level is reached. This particular device claims increased
accuracy over prior release mechanisms on the basis of its unique
design and components.
[0029] In these prior art devices the parameter being measured is
the angular force required to turn a bolt in a threaded recess.
Thus, a primary object of my invention is, instead, to measure a
bolt's longitudinal position.
[0030] U.S. Pat. No. 6,021,555
[0031] Inventor: Irving Leong
[0032] Issued: Feb. 8, 2000
[0033] The disclosure of the patent is incorporated herein by
reference and it provides for an automated method of starting
threaded fasteners into tapped recesses. In this invention the
process begins by precisely locating the initial "zero" entry point
of thread engagement. Having located the initial referenced "zero"
starting point, the number of turns or a purely angular torque
determines the position of the bolt. The error prone frictional
pre-load initial torque value is completely eliminated.
[0034] U.S. Pat. No. 6,167,788
[0035] Inventors: Heinz Schonberger et al.
[0036] Issued: Jan. 2, 2001
[0037] This invention represents the electronic duplication of the
current angular process that depends on an initial pre-loaded
torque, applied in a similar manner with a conventional torque
wrench. Recognition of a "zero" starting point is not
disclosed.
[0038] My invention and the improvements it introduces will be more
fully understood from the summary of the invention and detailed
description which follow.
SUMMARY OF THE INVENTION
[0039] In one aspect, the present invention involves inserting a
threaded fastener into a threaded element, locating the initial
zero starting point of the receptacle and fastener threads by
rotating the fastener clockwise and, digitally measuring the
angular degree of motion imparted upon the moving fastener to
provide assured definite elongation of the fastener into the tapped
hole thereby providing optimum fastening.
[0040] In one aspect, my invention is a Basic Unit for accurately
tensioning threaded fasteners comprising a means for locating the
initial zero starting point of a threaded unit in a threaded
recess, a motor for driving a chucked threaded fastener in a
clockwise direction a magnetic notched wheel having evenly divided
number of segments within the 360 degrees of a circle, such notched
wheel having no permanent magnetic qualities and preferably may be
the notched rotor of a stepper motor; an electromagnet axial
rotation sensor comprising an iron core and solenoid, such
electromagnet's pole being disposed to pass across a notch of the
magnetic notched wheel, and such electromagnet be part of a stepper
motor; means for converting the threshold magnetic signal generated
as the notch of the wheel passes over the electromagnet and
converting such signal to a binary "1" signal; a means for counting
the digital signal provided to an axial sensor provided for the
fastener as it is driven and for converting the signal into a
measurement of the driven axial distance of the fastener; and,
means for counting the digital signal provided to the axial sensor
as a function of the threaded fastener's stretched length inside
the threaded recess after the fastener is fully driven in.
[0041] Accordingly, one object of the invention is to totally
eliminate the measurement of torque or fastener tightening tension
through the unknown and irregular frictional interface as has been
the practice of the prior art.
[0042] Another object of the invention is to provide a digitally
readable system to determine the exact position of the fastener as
it is rotated and driven into a threaded receptacle. Thus, axial
position determines ultimate tensioned length to fully tighten the
fastener.
[0043] Another object of this invention is to provide a fully
digital method of measuring torque or tension applied to a fastener
and to eliminate the inaccuracy introduced by wear to torque
driving machine components.
[0044] Yet another object of the invention is to provide a method
of near perfect repeatability of inserting a fastener made with
equal specification tolerances into a receiving fastened unit of
equal specification tolerance.
[0045] A significant object of the invention is to provide
simultaneous, evenly distributed, micro incremental tightening of
multiple fasteners to establish a near perfect equally distributed
tightening of gasketed components in assembled units. Such units
can be made lighter due to minimized distortion of the components
to be assembled.
[0046] An additional object of the invention is to provide an
extremely accurate method of calculating the quantitative "design
safety margin" for assembled units.
[0047] Another object of the invention is to provide computer
certifiable quality control of the components assembled, without
manual human intervention.
[0048] The aggregate object of the invention provides for a fully
automated system of starting, running in, accurately tightening,
and quality control certification of the assembled unit in one
continuous operation.
[0049] By referring to the drawings and detailed description below
it will be understood how my invention accomplishes the foregoing
objects.
DESCRIPTION OF THE DRAWINGS
[0050] FIG. 1 is a perspective representation of the Basic Unit of
the invention showing the motors, control unit, and chuck
positioned to drive a bolt into a threaded recess;
[0051] FIG. 2 is an enlarged perspective representation of the
threaded recess of FIG. 1 viewed from lines 2-2;
[0052] FIG. 3 is a representation of a multiplicity of the Basic
Unit which forms the Gang Wrench of the invention in position to
tighten the cylinder head onto an engine block;
[0053] FIG. 4 is a plan view of the coils of a stepper motor with
the notched timing wheel; and
[0054] FIG. 4A is an enlarged section of the notched wheel of FIG.
4.
DETAILED DESCRIPTION
[0055] My invention comprises of a "basic" embodiment and
permutations or enhanced extended function units based on the Basic
Unit. The Basic Unit is a singular bolt tightening component. The
first enhanced unit is the Basic Unit constructed to provide
destructive testing of fasteners. This unit is called the "Test"
unit. The second enhanced unit is the "Gang Wrench" unit, which is
used to evenly tighten multiple bolts into an assembled unit in
unison by rotating all bolts with the same number of rotations from
the zero point. The third enhanced unit is the quality control or
"Certification" unit, which can be applied to both the Basic Unit
and the Gang Wrench unit. These units are explained in greater
detail below:
[0056] A. The Basic Unit
[0057] Referring now the FIG. 1, the Basic Unit 10 comprises high
torque drive motor 42 connected to a bipolar stepper motor 18 via a
clockwise engaging one way clutch 20, a vertical displacement
sensor 46, a chuck 16 for the bolt 12 and a controller 44. An axial
equally divided sensor 56 is connected to the controller 44 to
provide a digital discrete signal to the controller to register
angular position of the unit's chuck. The controller 44 is a
digital computer. These components can be readily assembled by
those skilled in the art upon seeing FIG. 1.
[0058] Referring to both FIGS. 1 and 2, in operation, one method of
invention comprises the steps of:
[0059] 1. Placing the threaded tip portion 24 of the bolt 12
chucked in the unit 10 into the threaded recess 26 with light but
firm contact.
[0060] 2. Moving the bolt 12 counterclockwise or to the left.
Preferably, a stepper motor 18 is used to turn the bolt
counterclockwise. Thus, the bolt moves axially away from the
threaded recess.
[0061] 3. Locating the zero point of the threads of the threaded
recess. At some point from zero to 360 degrees of rotation, the
tips or terminal points of the threads 36 of the bolt 12 and the
threads 28 of the recess coincide. This is at point 40 where the
recess threads terminate. At this point, the axial direction
changes to clockwise "R."
[0062] 4. Disengaging the stepper motor 18. The drive motor 42 and
the axial movement sensor 56 is activated.
[0063] 5. Driving the bolt into the recess. The axial movement
sensor 56 provides a binary signal to the controller 44. The
controller counts the discrete angular movement of the chuck and
converts the angular movement into axial movement measurement into
the threaded recess. The values are specific for a particular
thread pitch.
[0064] 6. Elongating the length of the bolt within the recess upon
full insertion. The full insertion position is predetermined by
first driving a test bolt into a recess and counting the
revolutions from the zero point to contact the bolt head with the
surface. When the bolt head 22 reaches full contact with the
surface 14 around the opening of the recess further rotation
continues to elongate the length of the bolt within the recess.
However, the unit measures bolt tightening as a function of the
stretching of the bolt inside of the recess, i.e., rotation that
stretches the bolt within the recess after the bolt head contacts
the surface. The unit makes every bolt driven in as if it were
measured with a fully digital micrometer.
[0065] In a preferred embodiment, as shown in FIGS. 4 and 4A, the
axial sensor 56 is represented by the leads 56 in combination with
the driving coils 57 of the stepper motor, after its stepper motor
driving function is disengaged. As each individual tooth 58 of the
stepper motor passes by or across the particular coil 57, the
magnetic field strength, measured in either in miligauss or
microgauss, when reaching a threshold value, is registered as a
binary "1" to the digital controller which is incorporated in the
computer. It is important that the wheel 59 with the coils 57, have
no permanent magnet properties so that there is not induced or
residual magnetism in the wheel 59 to interfere with the generation
of current by teeth 58 as they move across or by the coils 57.
[0066] B. The Destructive Test Unit.
[0067] The destructive testing unit is used to determine the design
failure length of the "stretched" fastener or bolt. Using the
aforementioned Basic Unit the bolt is driven into the recess until
it "snaps" or fails. At the point of failure, the elongated length
of the particular bolt is recorded by the computer. Torque will no
longer be measured in units such as foot pounds or newton meters.
The term "percentage of elongation before failure" or "PEBF" is the
parameter that is appropriate. Accordingly, instead of the
customary 25% "overbuild" or structures, the percentage can be
decreased, due to the greater accuracy in bolt tightening of the
present invention.
[0068] C. The Gang Wrench Unit
[0069] Multiple basic units 10 can be arranged to tighten each bolt
incrementally at the same time in a closure assembly where a
plate-like member is bolted tight against a substrate surface. The
Gang Wrench or multiple basic unit array can be applied to two or
more basic units working together in unison. For the Gang Wrench
unit to function in the intended purpose of the invention, all
bolts driven by each basic unit for the same assembly must be
identical in material length and PEBF or ultimate failure stretched
length, aforementioned in the description of the test unit. The
distance that each bolt is driven before head contact is made with
the surface around the opening to the respective threaded recess of
the assembled unit is dependent upon the uniformity of the bolts
both in dimensions and in materials. Tolerances must be kept close.
However, current manufacturing techniques provide such tolerances
for bolts. Also, if the assembled unit includes a gasket, and its
degree of compression the thickness of the gasket and its degree of
compression also must be kept uniform to achieve accurate
tightening of the completed assembled unit.
[0070] Turning to FIG. 3, a preferred method of operating the Gang
Wrench will be described:
[0071] 1. Identical bolts 24 are placed in the chuck 16 of each
basic unit of the Gang Wrench, with the axis of each chuck centered
over each threaded recess 26' in head 14' to receive the bolt. The
location of the tip of the threads within the 360 degree circle of
either the bolt or the threaded recess is random and need not be
oriented at the same cardinal compass position. The Gang Wrench is
placed with each bolt of the threaded recess with light but
sufficient contact.
[0072] 2. Each stepper motor 42 in each component basic unit 10 is
engaged to move it's basic unit independently in the counter
clockwise direction. As each basic unit is driven, the axial
displacement sensor will provide a signal to the controller 44,
when the movement of the driven fastener changes from and outward
movement and drops into the recess. This detent or change in
direction represents the zero reference engagement point of each
bolt. At this point of each basic unit, the stepper motor 42 holds
its position and is controlled by the computer controller C.
[0073] 3. When all of the basic units for each driven bolt reach
the zero position, all of the stepper motors are de-energized by
the computer controller 44.
[0074] 4. The torque driving motor in each basic unit is engaged as
well as each axial sensor 56. As each torque motor drives the bolt
in the tightening clockwise direction, the digital axial sensor
send a signal to the computer controller C. The computer controller
records both the actual discrete position of each bolt and assures
that no bolt will move to the next axial increment until each Basic
Unit has reached the previous same axial position from the zero
reference point.
[0075] 6. In equal incremental movement, all the bolts are driven
to the desired stretch length inside the threaded recess with equal
pressure.
[0076] D. The Quality Control Certification Unit
[0077] By bar coding each component and reading and imputing each
bar coded unit prior to assembly, the entire resultant assembled
unit can be certified for quality control purposes by either a
computer data file or a certification print out to be delivered to
the customer with the assembled unit. A desirable assembly record
can be recorded by the computer controller C. These factors, for
example, can be the actual time and the order that each bolt
reaches the zero reference point and the actual stretch length of
each bolt driven inside the threaded recess, in the case of the
Gang Wrench. No longer is it necessary to manually apply or to have
a system to apply a certifying mark to each bolt head. If this mark
was done by a person, fatigue from repetitive task would lead to a
high error rate.
[0078] E. Evaluation of A Previously Assembled Unit
[0079] This unit allows for the accurate measurement of torque
applied to an assembly fastened together by any other method of
torquing. This unit is a modification of the basic unit mentioned
above. It comprises a device that allows the fastener to be locked
to it as the fastener is withdrawn or loosened from the assembly.
Tension is applied to the chuck as the fastener is withdrawn. The
controller registers the fastener in its tightened assembled
position as the "zero" point. As the bolt is loosened, the degree
of angular movement, measured in incremental steps on the stepper
motor are recorded. At a terminal point, the tip of the fastener's
thread ridge will cross the tip of the tapped recess' tapped thread
ridge. This measurement of the degrees of rotation used to
calculate the original elongation of the fastener and the torque
applied to fasten the unit. That is, the length of the withdrawn
bolt or fastener can be compared to the original fastener length
and the elongation that has occurred can be related to the number
of turns.
[0080] Another method may be to apply the fastener in the
Destructive Testing Unit to study the design of an unknown
fastener. Data obtained from similar or known representative
samples of the withdrawn fastener can be used to obtain valuable
data of the previously assembled unit.
[0081] The foregoing description will enable those skilled in the
art to readily adapt my invention for various applications, as the
computers, motors and other described devices are all within the
skill of those in the art to obtain and arrange once they have read
my foregoing disclosure. However, my invention is limited only by
the scope of the following claims.
* * * * *