Patent Application
20250073775
The art presented here is a Bucking Bar System (BBS), sometimes referred to as an “end effector”, and more specifically to a BBS having a slender body shape or form factor generally comprised of an anvil face, an elongated shaft, and a handle. The background art generally relates to bucking bar equipment used to set the ubiquitous solid core rivet fasteners or rivets when joining a plurality of work pieces to each other during the aero framing assembly process of aircraft manufacturing. When setting rivets, a pneumatic rivet gun impacts on the rivet manufactured head while the anvil face of the bucking bar is held against the rivet shank end face—this plastically deforms the rivet shank end into a button head to clinch or join the work pieces to each other.
Now to provide more background on prior art bucking bars. When backing the rivet the bucking bar technician must maintain coplanar alignment of the bucking bar anvil face with the rivet shank end face; however, this often requires holding the bucking bar mass an near arm's length distance from their torso and due to the mass of the bar and applied force, this causes worker fatigue. To reduce this fatigue, the technician often positions their body closer to the work; however, this results in poor working ergonomics and sometimes adversely affects the technician's balance.
Bucking bar tools bounce or “buck” from each rivet gun impact and are notorious for causing vibration injury. The technician's fingers, hands, arms, and body damp the bucking vibration which often causes technician injury, sometimes referred to as “white-finger injury”. Further, the bar resonances, producing a high decibel audible noise that causes hearing damage.
Due to bar's “buck” nature a high degree of skill is needed to maintain coplanar orientation of the anvil face to the rivet shank end face because non-coplanar alignment causes the rivet being set a skew angle and rivets set incorrectly require factory rework. Factory rework decreases productivity and can reduce the sales value of the airframe.
The new art presented here optionally incorporates PRIOR ART described in U.S. Pat. No. 9,764,376 and also described in preceding U.S. Pat. Nos. 8,316,524; 8,850,677; 8,978,231 and subsequently awarded international Pats. FR 2,344,234; BR 1,120,150,120,300; CA 2,892,774; and JP 6,177,341. Referencing U.S. Pat. No. 9,764,376 a rivet set tool is provided having an anvil body, a first end of an anvil body, first raised cylinder diameter having a captive shoulder, a second end having an anvil face, and other equipment operative to measure a protruding shank length, to monitor the forming shank length into a button head, and to control the rivet set process including enabling and disabling the rivet gun. This prior art provides automation capability to automatically control the button head formation and it's optional use is presented later.
The new art presented here also optionally incorporates PRIOR ART back riveting rivet set equipment viewable at website: www.aircraft-tool.com or found using web search key terms “back rivet set”. Features of this PRIOR ART back riveting rivet set equipment include an anvil body, a universal size (e.g. a “401” size) shank at a first end of the anvil body, an anvil face at the second end of the anvil body, located along the length of the anvil body a first raised cylinder diameter having a capture shoulder, a slotted plunger retained on anvil body by a pin, and spring or load source used to urge plunger nominally away from the anvil face. This equipment is conventionally installed in the rivet gun to backset rivets (deforming the shank end into a button head) while the manufactured rivet head is “backed” by a “back riveting plate”. This back rivet set equipment is referred to as PRIOR ART back riveting rivet set subsystem and it's optional use is presented later.
Those skilled in the art will readily recognize that the new BBS provided here offers many new benefits over prior art by use of a handle, an elongated shaft, and an anvil face to plastically deform the rivet shank into a button head. The elongated shaft provides a long moment arm to aid tool alignment and provide better working ergonomics. This configuration provides improved coaxial alignment of the BBS centroid between the anvil face and the handle and also moves the mass centroid closer to the handle to improve technician ergonomics. The PRIOR ART disclosures described above, of which are incorporated by reference as if fully set forth herein.
PRIOR ART bucking bar equipment inadequately prevents bucking bar vibration and does not allow for good working ergonomics or tool control resulting in worker fatigue and requiring a high level of skill to set rivets. Tool vibration and the bucking nature of the bucking bar makes it difficult to control, to maintain coplanar alignment, and causes worker injury. However, given the teachings provided here, those skilled in the art will recognize the new embodiment teachings as alternative improved ways to reduce technician fatigue, reduce injury, improve working ergonomics, improve rivet set quality, damp vibration, and avoid rivet set errors.
The BBS provided herein aids technicians when setting solid core rivets during the assembly of aircraft components. The BBS departs from all conventional bucking bars by its slender body shape or form factor (characterized particularly by an elongated shaft member). The BBS also has a handle and an anvil face. Optionally the PRIOR ART referenced above can be coupled to a shaft end to provide automated rivet setting and/or in the case of the back-set prior art, to provide a shroud to prevent the anvil face from slipping off the rivet shank end face. The plunger shrouds prevent the anvil face from slipping of the rivet shank end face while the rivet is being set.
In a first object of the preferred embodiment the BBS is comprised of a handle, an elongated shaft, and an anvil face; this configuration is a slender body. In this preferred embodiment, a coupler subsystem is used to coaxially join the PRIOR ART automated rivet set tool subsystem and to join the elongated shaft and handle subsystem to each other. This arrangement comprises the handle, elongated shaft, and anvil face; however, the PRIOR ART subsystem provides automated rivet setting capability. This configuration provides the following advantages over all PRIOR ART bucking bars.
First, with the subsystems coupled together the BBS has rivet setting automation capability. Automation in factory assembly areas is critical to remaining competitive.
Second, this configuration makes the BBS take a slender body shape or form factor and moves the BBS center-of-mass or centroid away from the anvil face and towards the handle. Also, by the nature of the slender body shape, the BBS mass is coaxially aligned between the anvil face and the handle. This mass location reduces angular moment forces in the BBS, as a kinematic response from rivet gun impact blows and makes the tool easier to control and maintain proper alignment.
Third, by moving the BBS centroid closer to the handle, the mass also gets closer to the worker's torso feature. This allows the technician to position most of the bucking bar mass near their torso to reduce worker fatigue and serves to improve worker body posture or ergonomics.
Fourth, the slender body form factor of the BBS resulting from the elongated shaft is a configuration that aids maintaining coplanar alignment of the BBS anvil face and the rivet shank end face, to each other—while driving a rivet. When in use the technician holds the handle with one hand and supports the anvil with the other hand. The elongated form factor of the BBS provides a geometry that requires a large angular position change at the handle end to create small misalignments between the anvil face and the rivet shank end face. This is a key advantage and distinguishing feature of this invention over prior art.
The elongated configuration of the BBS requires a technician to move the handle a large angle distance with respect to the rivet shank axis to produce a small misalignment between the planes of the anvil face and the rivet shank end face. This further improves the measurement accuracy of the PRIOR ART rivet set tool subsystem when measuring the forming button head height because non-coplanar alignment of these surfaces also can produce non-coplanar mating of the plunger distal end and the aircraft surface, nominally the aircraft surface should and the distal end of the plunger should be maintained in flush contact with each other when the rivet is being set.
Fifth, the co-axial alignment of the BBS shaft and handle and BBS mass with the rivet shank requires bucking forces to move the entire BBS mass as a result of each hammer blow. This configuration reduces vibration from the hammer blow impulse forces, specifically reducing vibration amplitude.
Sixth, the co-axial alignment also reduces angular vibration response forces which aids tool position control. In conventional bucking bar tools this co-axial alignment is not as pronounced which causes a rotational bucking motion in conventional bucking bars that produces rivet set errors. Further by eliminating the described rotational response motion, this configuration also ensures the entire BBS mass is used to buck the rivet and consequently fewer rivet gun impact blows are used to set the rivet, resulting in an installed rivet having improved rivet fastener material strength properties because the rivet shank undergoes fewer hammer blow fatigue cycles during the plastic deformation rivet set process. The set rivet using the BBS is a higher quality rivet.
Seventh, the elongated shaft configuration and centroid mass location damps resonance vibration better than conventional bucking bar tools to improve worker safety. Common technician injuries from bucking bar tools includes hearing loss from bucking bar acoustic noise (bucking bars often “ring like bell”) and vibration injury to fingers, hands, arms, and joints often referred to as “white-finger injury”.
Eighth, the elongated shaft configuration allows vibration damp equipment to be installed on the tool to reduce the fundamental frequency caused by the rivet gun impact blows and the resonance vibration, caused by anvil chatter on the rivet shank end face, between impact blows, and caused by resonance vibration of the BBS. This reduces injury and aids the technician when maintaining proper bucking bar position/alignment during the rivet driving or rivet set phase.
In a second object and alternated embodiment of the BBS, the PRIOR ART automated rivet setting subsystem is replaced with the PRIOR ART back set apparatus. Except for the automation capability this is the same as the first object, presented above.
In a third object of the preferred embodiment of the BBS, a carbon fiber shaft is used to further move the centroid mass closer (as near as possible) to the handle. The carbon fiber shaft material properties also serve to additionally damp vibration forces from the rivet gun to help technicians control the “bucking” tool while the rivet is being set and to further improve safety through less vibration, less acoustic noise, and improved technician body position and working ergonomics.
In a fourth object and alternate embodiment of the BBS, shaft and/or handle surfaces (possibly including the shaft cavity) can be coated or filled with materials having properties that passively damp vibration.
In a fifth object and alternate embodiment an elongated slender body BBS is provided comprising an anvil face at a first end of an elongated shaft and a handle at a second end of the elongated shaft. Optionally, the anvil face may include a recess or pocket to prevent the rivet shank end from slipping off the anvil face as the rivet is being set. Preferably, the pocket depth is less than the height of the desired set button height, to prevent damage to the aircraft surface. In use the technician supports and positions the BBS with respect to a rivet to be set by locating the anvil face onto the shank end of the rivet and orientating the handle into a position that orthogonally positions the anvil face to the rivet shank end. The technician applies coaxial force through the BBS so that the applied force passes through the rivet shank axis.
In a sixth object and alternate embodiment, a tuned mass damper (TMD) device consisting of a mass, a spring or load source, and a damper is attached to the BBS in order to attenuate three vibration frequency responses produced by a pneumatic hammer blow: In the first case, a first TMD is used to attenuate a first frequency dynamic response formed by BBS's resonance natural frequency. In the second case, a second TMD is used to attenuate a second frequency dynamic response of the BBS's bouncing or “bucking” frequency as the BBS's anvil face returns to rest upon the rivet shank end. In the third case, a third TMD is tuned to match the rivet gun hammering frequency to attenuate a third frequency dynamic response of the BBS from the rivet gun impact blows (though not limiting pneumatic rivet guns impact rate ranges from about 20 to 50 Hz). All three described frequencies are excited by the impulse force of hammer blows.
Returning to the first case: The impulse energy from each hammer blow causes the BBS to vibrate at or near the gun's impact frequency. In this case the frequency of a first TMD is tuned to match or to be similar to the structural resonant frequency of the BBS. Operatively when the BBS resonance first frequency is excited, the TDM will resonate out of phase with the first frequency. So, although the inertia force from a hammer blow causes the BBS to resonate, the TMD dissipates energy or damps the resonant first vibration of the BBS.
Now returning to the second case: The impulse energy from each hammer blow also “bucks” the BBS's anvil face off the shank end of the forming rivet head and prior to the next impact the anvil face bounces (vibrates) as it attempts to return to a steady-state rest on the shank end before the next hammer blow, as a result of the technician's applied force (load source) to the bucking bar. Operatively when the BBS bouncing second frequency is excited, the second TDM will resonate out of phase with the described bouncing frequency to damp the second frequency.
Now returning to the third case: When in use the rivet gun produces a burst of impact blows that correspond to the hammering rate (gun frequency) and impact force (frequency amplitude) are dominantly a function of the gun size and BBS mass. The third TMD will resonate to the natural frequency of the BBS. To damp the BBS vibrations described as first, second, and third vibration frequencies enables technicians to better control the tool position and reduces vibration injury. Those skilled in the art will recognize that TMD devices can be attached to the BBS's elongated shaft, to the shaft outside diameter or preferably to the shaft inside cavity, or alternately to the handle. TMD concepts have been applied since 1909 to reduce the rolling motion of ships at seas and have many other well-known applications.
Those skilled in the art will recognize the many benefits of the slender body BBS configuration also distinctly differentiated it from conventional bucking bars. Upon assembly of the preferred embodiment, the PRIOR ART set tool subsystem, coupling subsystem, and bucking bar subsystem are coaxially joined together. In use the technician positions the BBS anvil face on the rivet shank end, nominally forming a coplanar alignment of these surfaces to each other; the technician orbits the handle above the rivet until coplanar alignment is achieved and then applies coaxial force through the BBS so that the applied force passes through the shank end and rivet shank axis while the rivet is being set.
As used herein, the following terms and variations thereof have the meanings given below, unless a different meaning is clearly intended by the context in which such term is used:
“Anvil face” means a rivet impacting surface of an anvil on a bucking bar or a set tool.
“Resilient member” means a “load source” and may be understood as a force applying system or component; for example a spring.
“Tuned Mass Damper” or “TMD” means a harmonic resonance absorber or damper and is an attached device to reduce mechanical vibrations, generally consisting of a mass mounted on one or more damped springs or damped load sources.
“Slender body” is also an “elongated body” and means a mechanical body that is substantially longer than it is wide and by definition a slender body has a high slenderness ration (L/r), where L is the nominal length and r is the nominal radius of the BBS. Though not limiting and for purposes of illustration to help distinguish this new art from prior art, the slenderness ratio of the new art may range from 6 to 45 while the slenderness ratio of conventional bucking bars may range from 1 to 6.
“Neutral axis” means the line nominally formed by the elongated central axis or axial axis of a slender body.
The BBS in these teaching used to set a solid core rivet fastener that has a rivet manufactured head, a shank, a shank face, and a shank neutral axis. When fastened the shank end rivet plasticly deforms into a button head to join a plurality of work pieces to each other. The BBS equipment is comprised of an elongated shaft having a first end and a second end with an anvil face located at the first end the shaft and an anvil located at said second end of said shaft.
The BBS is long, forming a slender body with a length to radius (L/r) slenderness ratio greater than six. This geometry operatively places mass centroid of the bucking bar system toward the handle and away from the anvil face; this aids colinear alignment of said bucking bar system with said rivet shank and ergonomics. The arrangement also requires a large angular pivot rotation of said handle over said rivet to substantially misalign the anvil face relative to the rivet shank face. This prevents rivet setting errors due to skew alignment. In addition, the arrangement also substantially (i.e. predominately) coaxially aligns the mass of the BBS with the rivet shank. This reduces vibration because the impact force from the rivet gun must displace the entire BBS.
The BBS preferably has a tubular shaft this is operative to damp vibration from rivet tool impact blows and to position the mass centroid proximal to the handle.
In the preferred embodiment a coupler subsystem is used to join a PRIOR ART subsystem comprised an automated rivet set tool subsystem or a back set tool subsystem to a shaft/handle subsystem. The shaft of the shaft/handle subsystem mates with the shaft of the PRIOR ART subsystem in a coaxial arrangement to form a rigid body between these subsystems.
The BBS is always comprised of an elongated shaft and an anvil face at the first end and a handle at the second end. Operatively this locates the BBS's mass centroid proximal to said handle and away from said anvil face to coaxially align the said rivet shank with said elongated shaft. This geometric arrangement requires a large angular motion the handle with respect to the neutral axis of the rivet shank, when positioning the BBS over a rivet; therefore, improper coplanar misalignment between the shank end and the anvil face becomes less probable.
A coupler subsystem is used to coaxially join the PRIOR ART subsystem(s) to the shaft/handle subsystem. In this case the PRIOR ART subsystem can comprised of a set tool having a set tool shoulder and a first distal end and an anvil face located at a second distal end of said set tool. Further the shaft/handle subsystem is further comprised of a shaft with a first end and a second end, a handle that is affixed to the first end of the shaft, and a pocket is located proximal to the second end of the shaft. Also, a set of external threads are also located proximal to the second end of the shaft. Next the coupler also has internal through hole cavity, a group of internal threads, and a coupler shoulder for joining the PRIOR ART subsystem to the shaft/handle subsystem. Upon coupling assembly, the described internal and external threads are engaged which urges a set tool shoulder and a coupler shoulder toward other until the first end of the set tool seats into the pocket located at the end of the shaft. When the PRIOR ART subsystem shaft and the shaft/handle subsystem shaft become coaxially coupled or joined to each other forming a rigid body BBS.
Further aspects of the invention will become apparent from consideration of the drawings and the ensuing description of preferred embodiments of the invention. A person skilled in the art will realize that other embodiments of the invention are possible and that the details of the invention can be modified in a number of respects, all without departing from the disclosed concepts. Thus, the following drawings and description are to be regarded as illustrative in nature and not restrictive.
The features of the invention will be better understood by reference to the accompanying drawings which illustrate presently preferred embodiments of the invention. In the drawings:
The following reference numerals are used to indicate the parts and environment of the invention on the drawings:
The following description of the preferred embodiments of the invention is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
Referring to PRIOR ART
In operation of set tool 2, plunger 12 slides co-axially over anvil body 4 and after calibration, a sensor inside cap 20 measures axial displacement of plunger 12 relative to fixed frame cap 2 and housing 10 and more specifically measures distance between distal end 14 of plunger 12 and anvil face 16. Although not shown in
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A carbon fiber shaft 52 is preferred because it is lightweight, rigid or stiff, and has an inherit property of being able to passively damp vibration from pneumatic hammers. In an alternate embodiment, cylinder 54 can be filled with a vibration absorbing material such as foam or rubber to further attenuate system 50 vibration. These vibration damp approaches of subsystem 52 help protect technicians from vibration induced injury.
Further, lightweight shaft 52 (such as a carbon fiber tube shaft) also moves the assembled BBS's 50 center of mass or centroid towards handle 64. Notably, unlike all other bucking bars, this also moves the centroid away from the aircraft surface. The slender body BBS 50 has the advantage of allowing the technician to optionally hold the BBS 50 with the handle 64 near their body's torso, making it more ergonomic for technical posture and reducing technician fatigue. Further still, BBS 50 optionally allows the technician to coaxially align their forearm with shaft 54 to allow bucking bar motion and vibrations to be absorbed by a pivot motion from their shoulder.
Another advantage of BBS 50 is that the slender body system inherently requires a very large angular movement or pivot of handle 64 relative to the rivet surface to change the angle between the anvil face 16 and a rivet shank end face. This is highly beneficial because it helps prevent the technician from installing rivet sets at skew angles; a common type of rivet setting error when using conventional bucking bars because maintaining the proper bucking bar anvil face position when bucking is difficult, and rivets set at a skew angle to the rivet shank axis often require rework.
When using BBS 50, the technician preferably uses two hands. The first hand grasps handle 64 to support the BBS mass and coaxially align the slender body neutral axis of BBS 50 with the rivet shank axis while the second hand supports housing 10 to position anvil face 16 upon a rivet shank end, perhaps while optionally resting the back second hand against aircraft surface. The first hand orbits handle 64 about rivet location (a pivot point) until the described axes are colinear. The technician then applies axial force to handle 64 urging anvil face 16 against face of rivet shank end. When setting the rivet, cylindrical body of plunger 12 encircles the forming rivet prevents anvil face 16 from slipping off the rivet shank end face. This creates a stable and ergonomic work position for the technician.
To further contrast BBS 50 with conventional bucking bar equipment, technicians hold conventional bucking bar (a mass of several pounds) near arm's length to do work which causes fatigue or else they must move their body towards the airframe which produces poor body posture. Also, conventional bucking bars often require rivet gun forces imparted into bucking bars to be absorbed by the technician's fingers and wrists, often resulting in injury known as “white finger.” Further in contrast to conventional bucking bars, the elongated shaft 54 distinguishes itself as a slender body by functionally moving the BBS 50 centroid towards handle 64—though not limiting and for illustration purposes only, to further draw a distinct difference from all PRIOR ART bucking bars—the preferred embodiment BBS 50 forms a slender body that may have a length of about 18-inches.
Those skilled in the art will appreciate other embodiments. For example, without deviating from this invention subassembly 52 can be altered so that coupler mate 42, tubular member 54, and handle transition component 62 can be replaced with a solid shaft while still coupling to set tool 2 with coupler 32. Other embodiments are possible.
TMDs depicted in
A person having ordinary skill in the art would understand that the invention has applications in the rivet setting industries and in particular the aerospace assembly industry. This invention could be incorporated into other machines without limitation. Further, provided these teachings many variations of the invention will occur to those skilled in the art. Some variations include different lengths of BBSs, distinguished primarily by length changes to the tubular or shaft members while other variations include form factor changes; however, still other variations are allowed without limit. All such variations are intended to be within the scope and spirit of the invention. Further still, although some embodiments are shown to include certain features, the applicant specifically contemplates that any feature disclosed herein may be used together or in combination with any other feature on any embodiment of the invention. It is also contemplated that any feature may be specifically excluded from any embodiment of the invention.
This art may optionally incorporate PRIOR ART most clearly described in U.S. Pat. No. 9,764,376 but is also described preceding U.S. Pat. Nos. 8,316,524; 8,850,677; and 8,978,231 and subsequently international Pats. FR 2,344,234; BR 1,120,150,120,300; CA 2,892,774; and JP 6,177,341. The disclosures of which are incorporated by reference as if fully set forth herein.
