CA1069414A - Pneumatically braked blade assembly for a clipper machine - Google Patents

Abstract

ABSTRACT

A machine for clipping strip material including a blade operated in a cyclic manner having a cutting stroke and a return stroke. A toggle linkage includes a toggle bar which moves in a longthwise direction to reciprocate the blade by toggle linkages. The toggle bar is coupled to an actuating piston rod of a pneumatic cylinder. End caps of the cylinder are recessed to receive piston exten-sions during final stages of piston travel for cushioning purposes. Seal means engage each piston extension during the later stage of piston travel to trap air between the advancing piston and the end cap to dissipate blade and linkage inertia. Exhaust ports within each of said end caps a?e valve controlled to release cylinder pressure at a desired pressure prior to completion of piston travel.
A modified cylinder includes exhaust poppet valves each subject to a valve regulated, poppet closing pressure as in the first form of cylinder and additionally having a surface area thereon against which a secondary supplement-ary source of air may act to hold the poppet closed against extremely high piston actuating pressures. The modified cylinder further includes end caps each having a port served by an end cap mounted valve to admit a piston impinging charge and a remaining port admitting a second-ary flow into the cylinder and controlled by an end cap mounted valve.

Description

SPECIFICATION
The present invention relates generally to clip-ping machines and particularly to such a machine having a pneumatically powered blaae with the pneumatic compon~
ent including integral braking means for the blade.
In clipping machines, such as those used to clip lengths of wood veneer ribbon into sections for use in '' plywood, a blade is intermittently reciprocated. Such '','~ - ' blades and their supporting linkage move at gre~t speed during the cutting stroke and in view of the ro resulting inertia res~llt in a rebound problem. Substan- -tial inertia is developed during the blade stroke which must be dissipated to avoid rebound. Ideally, blade ,~ ;
inertia would be dissipated immediately prior to or at ~' the blade reaching its raised, static position. Blade : . :
rebound is undesirable for the reason that when clipper blades are actuated in a rapid, consecutive manner precise cutting of the~ veneer material is adversely af~ected, The cycling time of a rebounding blade versus , ', . .
that of a static blade at rest will vary in milliseconds by reason of the blade being out of position at the start of the cutting stroke which stroke will hence be of an indefinite length. As clipper blades are commonly operated in conjunction with electronic scanner systems and high linear ribbon speeds it is essential that ~-clips be precise for avoidance of waste, The present invention is embodied within a clipper blade and its supportlng linkage with pressure respon- ' sive means in the form of an air cylinder wherein the ,, -1- " ' ' ' . ~ .

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cylinder accomplishes blade actuation and also brak-ing of cylinder associated components~
The present assembly includes a base attachable '' to the frame of a clipper machine which may be incor-porated as a modification thereto. Suspended ~rom said base is a toqgle linkage attached to an intermed-iate toggle bar adapted for linear motion during a cutting cycle. A blade assembly is carried by the toggles and accordingly is driven through one cycle ~o of operation by uni-directional movement of said toggle bar past a dead center position. The' air cylinder is ' disposed on said base so as to impart lengthwise move- ', ment to the toggle bar with a cutting stroke' being completed with movement of the toggle bar from a retrac-ted to an extended position and conversely,, a second cycle is completed by subsequent, opposite tra~el of ,~
the toggle bar. During one cutting cycle the blade edge is driven through 'the clipped material supported ', on an anvil which normally is of cylindrical config-uration and of resilient mater'ial. The air cylinder means may be generally described as a double rod, double acting type. Included within said cylinder means is a valve arrangement to dissipate blade and linkage inertia to avoid blade rebound from an upper-most position of rest. Said valve arrangement is biased by a regulated medium to permit unsea'ting at a selected pressure value. The pressure value is reached prior to the piston completing its stroke and subse-quent to cuttlng action of the blade so as to not slow the blade downstroke.

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According to the present invention, there is provided a pneumatic cylinder of the double acting type comprising in combination, a piston within said cylinder having axial extensions of reduced diameter, a piston rod, end caps closing the cylinder and each defining a central recess to alternately receive said piston extensions, each end cap recess in communica-tion with a valve controlled pressurized source of air, and cylinder exhaust means within each of said J~ end caps and including pressurized air biased valve members alternately operable to vent a non-constant flow of air from ahead oE the moving piston from the cylinder interior at a predetermined pressure value to prevent piston rebound.
In the accompanying drawings:
Figure 1 is a front elevational view o a machine for clipping elongate material into sections~ and Figure 2 is a sectional view of a pneumatic cylin-der comprising part of the present blade assembly.
With continuing reference to the accompanying drawings wherein applied reference numerals indicate parts similarly identified in the follo~ing specifi-cation, the reference numeral 10 indicates generally a ;
machine hereinafter termed a clipper of the type common-ly used for severing bands of peeled wood veneer used in the manufacture of plywood. Such clippers conven-tionally include pairs of leg members 2 and 3 support-ing at their upper ends a machine base 4 all of welded plate construction. Indicated~ generally at 10 is a - :
blade assembly including an elongate member 11 suitably '~.
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seeured to the underside of base ~. One form of such s~curement may be by means of bolt m~n~ers 12 which permit detachable installation of member ll to machine base 4. A clipper blade 13 is detaehably mounted on a blade bar 14 which bar also is provided with cylin-drical guides 15. Posts at 16 depend ~rom elongate member 11 to guide the blaae bar and assure vertieal reciprocal movement of blade 13 during each cycle of operation.
A toggle assembly ineludes a toggle bar 17 which pivotally mounts the opposing ends of upper and lower sets of toggle links 18 and 19 eonnected at ~heir outer ends respeetively to member ll and blade bar 14.
Passage of the links to an oppositely inclined posi-tion upon lengthwise displaeement of toggle bar 17 in one direction will eause blade 13 to be moved downwardly through a cutting stroke and thence upwardly through a return stroke constituting one cyele of blade opera-tlon. The blads and its supporting gu1de means is not unlike that general arrangement found on existing elipping machines.
Driving blade 13 in a cyelic manner is a pneumatie eylinder 20 which is in end mounted relationship to ~ .
toggle bar 17 and eonneeted thereto by a pivotally mounted linkage 21. Cylinder 20 is mounted on member 11 - .
by means of a ~raeket 22. In existing clippers, end ( :-mounted eylinders for aetuatin~ ~oggle linkage and a eutter blade supported thereby are eommon, however sueh ~ ~
eylinders are not beli~eved to embody means for dampen- ~ .
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- ~O lng blade rebound. ~ .

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With ~ttention now to Figure 2, the pneumatic cylinder 20 is of the double rod, double acting type with equal displacement from a chamber 20A on both sides o~ a piston 23. Piston surfaces are indicated at S~ Cylinder 20 is closed by end caps 24, 25 each centrally recessed a~ 24A, 25A to receive oppositely directed piston extensions 23A and 23B. A piston rod ', 26 is slidably journalled and sealed at 27A, 28A with- , , in aligned openings at 27 and 28 in the end caps. Uni-/0 directional seal means at 30 and 3I in end caps 24 and 25 sealingly engage th~e piston extensions to prevent the subsequent escapement of air co~lpressed by an advancing surface S of piston 23. Serving each end of cylinder 20 are end cap bores 32 and 33 with 'airflow therethrough being controlled by a four way, two posi-tion valve 34 permitting eithe'r end of the cylinder to be pressurized and the opposite end vented via lines , ,~
45, 46. The seal means at 30 and 31 permit air entry into cylinder chamber 20A in one direction to actuate - ~0 piston 23 but:prevent escaping airflow in an opposite direction for the' purpose of sealing chamber 20A once a-piston extension ~23A, 23B) has engaged its respect-ive seal. Close tolerances between piston extensions :
and the cap internal walls deifining recesses 24A,25A ~. .
may dispense with the need for seals 30 and 31. '', ' : Valve 34 is in communication with a source of air '' '' pressure via a line 47 and vented to the atmosphere ~; at 48. In most installations valve 34 will be solenoid '~
actuated in cirOuit with an electronic scanning system ~o~

initiating cutting strokes at desired intervals and to clip out waste ri~on material.
Each end cap embodies exhaust means including bores at 35 and 36 in communication with cylinder chamber 20A via ports 3~A, 36A each normally closed by biased valve members 37, 38 shown as poppet valves.
sores 35, 36 are in communication, via pressure regu-la~ing means at 40, with a pressure source whereby the valves are biased to closed positions to close o~f ~o their respective ports 35A, 36A. A pair of vents at 41, 42 exhaust to the atmosphere. Air lines at 43, 44 communicate air under the desired pressure through suitable fittings into each bore 35, 36 to bias valve members 37, 38 closed. While shown as being air biased, mechanical biasing means could be utilized.
In operation, one cycle of blade operation will take place as piston 23 moves from one extreme to the other. The cut or clipping action occurs as toggle bar 17 is displaced lengthwise imparting vertical motion to the blade 13 by the over center travel of toggle links 18 and 19. For example, pressurized air entering bore 32 will travel past uni-directional seal means 30 to actuate piston 23 to the left (in Figure 2). Midway in its travel along cylinder 20, piston extension 23B
comes into sealing contact with uni-directional seal 31 to thereafter close chamber 20A ahead of the moving piston surface. Such closure takes place as blade 13 commences its return travel to its rest position. trhe -remaining tavel of piston 23 is resisted by increasing pressurization of ~hat portion oE chamber 20A ahead of said piston suriace. The dynamic energy of the piston, toggle linkage, blaae and blade holder is dissipated by compression with energy being converted into heating of the air compressed ahead of advancing piston 23. Valve 38 will unseat at a desired pressure value within cylinder 20A to permit piston 23 to come to rest in the broken line position of Figure 2 in a "cushioned" manner thus avoiding blade rebound.
J0 While cylinder 20 is shown and described in conjunction with the blade instrumentality of a veneer clipping machine, such i8 not intended to imply use of such a cylinder is limited to such a machine.

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suppLE~læNTAL DI SCLOSURE
~ modified form of the invention is ambodied in a cylinder having flow con~rolling valv~ closely disposed to the cylinder to minimize conduit volume between valves and the cylinder piston to reduce response time ~etween valve actuation and piston movement for preci~e clipper blade control. The modi~ied pneumatic cylinder has poppet valves biased to a closed position by a constant, re~ulatable fluid pressure, as in the firs~ described cylinder, with an additional provision made Eor bleeaing off pressure from the cylinder interior to supplement the constant pressure acting on the poppet to assure poppet valve clos-ure in the pxesence of very high cylinder actuating pres~
sures which heretofore would unseat the poppet valves resulting in lower piston speeds. The modified c~linder ~ - :
does not utilize troublesome seals or ball check valves.
Hence, extraordinary internal cylinder pressures and hiyh ~ :
piston speed~ are realized ~ithout . premature cylinder failure. - .
The modified cylinder is illustrated in the sectional view of Figure 3.
A modi~ied form of cylinde~ is indicated at 50 in . ~ ~:
Figure 3 and, in similarity to the first form oE cylinder : æhown in Figure 2, includes end caps 51-52 with the cyl~
inder being of th~ double acting, double rod type with ~-;
equal di~placement from a chamber SOA on both sides of a piston 53 having piston s~faces Sl. The end caps 51-52 are centrally recessed at 51A-52A and ra~eive in sur~acial s~aling 2nsagement (without ~eals) oppositely directed -.:

3~ axial piston extensions 53A-53B coaxial with a pis~on rod 56. ~aid rod is slidably journalled in each end cap by ' .
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rod seal equipped bushings 57-5~ and terminates in attach-ment to linkage 21 coupling a work performing instrumental-ity, At~entio~ is directed ~o the absence of air ~eals in the end caps ~or interm~ttent sealing engagement With piston components. The dispensing with o~ short lived air seals avoids operating pressure limitation~ and the most common cause of cylinder malfunction l~e., seal damage or wear and consequent blow by with loss o~ the cylin~er's inertia absorbing capability. The present cylinder ex-ten-sions 53A-53B are substantially net in fit to provide airtight, surfacial sealing engagement with the end cap . .
recesses 51A-52A.
Each end cap 51-52 defines a first port 61-62 termin- -~
ating in ~nward communication with end cap recess~s 51A-52A. A three way solenoid actuated valve at 63-64 is mounted within a threaded segment 61A-62A of each p~rt and functions to alternately control the entry of a supple .
mental air~low into the cylinder end and to exhaust the ~0 opposite cylinder end~ ~ir l~nes S9 serve said valves. ~ .
~ach end cap additionally defines a second port 66-67 extending through the cap and directing a pressurized .. ~ :
piston stroking ai~ charge or ~low in a direc~ion normal to piston surfaces Sl. ~ach end cap is adapted, as by a threaded segment 66AW67A of ports 66-67, to m~unt a two way :~
valve 68-69 served by a branched air line 70~ Mounting of valves 68-69 on end caps 51-52 in close proximity with th~
cylinder piston virtually eliminates the communicating -- -volume between valve and piston to provide substantially _ 9 _ :

instantaneous movement of piston 53 upon valve (68 or 69 actuation ~uring a firing stroke. An economy is also effected in the reduced use of compressed air from a plant compressor.
Valves 63-64 and 68-69 are preferably solenoid act-uated, the same having an arma-ture in circult wi~h an electronic scanning system which monitors the moving v~neer ribbon and triggers the valves at one side o~ th~ cylinder : :
to dri~e ~he piston and clipper ~lade linkage 21. Other :
applications of the present cylinder, of course, would include vaxious signal generating sources other than an : :
electronic scanning system.
Each end cap Sl-52 embodies cylinder exhaust means housed in end cap bores 70-71 ported at 70A-71A to the cylinder interior. Poppet valves 72-73 each include a --:
valve face 72A~73A which may seat against ports 70A-71A
to close same. Said poppet valves also include a pri-mary pilot air biased end surface 72B-73B responsive ~o pilot air pressure in chambers 74-75 within suitably at~ached end cap ~ittings 76-77. A primary pilot pressure line 78 is branched at a pressure regulator 80 to permit conYeni2nt, uniform adjustment of primary pilot pressure acting on both poppet valves. The poppet valves, end cap ::
; bores 70-71 and attached ~ittings are suitably sealed to prevent leakage~
A secondary air bia~ed sur~ace 81-82 on each poppet ; valve is of annular shape and is responsiv o air pres- :
sures within end ~ap chambers at 83-84 which, in turn~
~ - are in respective communication with end cap central :~ ;
30 recesses 51A-52A via air passageways ~6-87. Pressurss ~ :

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- applied to surface 81-82 supplement pilot air pressure to retain the poppet seated against all cylinder stroking pressures. The cylinder exhaust mean~ additionally include vents at 88-89 which serve, upon poppe~ valve opening, to exhaust a non-constant, uni~orm pressure flow ~rom the cyl- -inder interior.
In a typical uni-directional stroke of piston 53 and one full cycle of clipper blade operation, pressurized air is admitted, for example, via signal actuated valve 68 while valve 64 at the cylindex~s opposite end is simultane-ously actuated to an exhaust position venting the cylinder interior into the atmosphere. Valve 63 is actuated simul-taneously with valve 68 to contri~ute to piston stroking pressurization within one end of the cylinderO Air pres-sure flow from valve 63 via port 61, end cap recess SlA, ~ ;
passageway 86 and chamber 83 biases poppet valve 7~ to~- -hold same closed against port 70A and the piston stroking pressure in the cylinder. The bia~lng air pressure being ~-~
applied to poppet secondary air biased poppet surace 81 supplements the poppet d osing ~orce exerted by primary pilot pressure in chamber 74~
Desirably the valves 68-69 are solenoid actuated valves permitting the valve control circuit ~o include a timing component for ~pulsedl~ ox timed valve opening for a portion of the piston stroke to avoid excessive residual pressurization of the cylindex interior and consequent impedance of tha next or return stroke of the piston.
With attPntion back to a typical stroke sequence of piæton 53, two way valve 69 at one end o* the cylinder is closed throughout the stroke while valve 64 remains in a vent or . .. :.

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exhaust position throughout the stroke to vent the cylinder interior. The cutting action of the clipper blade occurs at the mid-point of piston travel with piston travel being therea~ter cushioned as piston extension 53B sealingly engages the end cap shoulder definin~ end cap recess 52A
thereby sealing the cyllnder interior ahead of advancing piston 53. Subsequent cylinder pressurization serves to dis~ipate the dynamic energy of pi~ton 53 and an~ driven component such as the clipper blade now on i~s return or upward ~al~ o~ a blade cutting cycle. Poppet valve 73 remains seated against port 71A in response to primary pilot pressure in chamber 75. Cylindex pressure buildup sventually un~eats poppet 73 with cylinder pressure above a certain value thereafter venting via ven-t 89~ During such cushioning of the piston, the secondary biasing surface 82 is inoperative as chamber 84 is vented, via passageway ~7, central end cap recess 52A and valve 64, to the atmosphere.
For retaining the piston 53 against end cap 52 and hence the clippar blade a~ a raised rest position, valve 63 i~ the present example, ramains open -to communicate a somewhat reduced pressure to the cylinder interiox~ A
regulator 90 in air line 59 may be used in such instances.
In one suitable emb~diment o~ the cylinder, piston diameter is approximately twenty-five centimeters with a .
stroke o twelve point five centimetersO Cylinder strok-in~ pressure, admitted by oppositely acting ~wo way valves . :-: ~ . -68-6g may for example be 115 p~i while a somewhat reduced pressure 30 ~si is admitted via three way valves 63-64. ~

Primary pilot æur~aces 72B-73B receive a continuou~ poppet ~ ;

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valve closin~ ~orce o:~ ~3 pounds w.ith opening and con~rolled ventin~ of cylinder ends occurriny upon piston eushioning pressure applying a somewhat greater force agains~ poppet valva faces 72A-73~ to unseat same and vent a non-constant cylinder dischar~e. Such discharge dissipates piston speed and constitutes a "cushioning" action for the piston and associated work instrumentalities.
To re~ain the poppet valves sea~ed in the presence of piston actuating or s~roking pressures, the in~ermi~tently 10 ap~lied biasing force, applied against poppet valve surfaces .
81-82, is approximately 47 pounds which, of course, i9 additional to the primary pilot biasing forc~ of 43 pounds.
~oth air pressure and component surface areas may of course vary to b~st suit each cylinder use.
It is to be undexstood tha~ the cylinder end cap arran~ement including the two way and three way valves thereon, the end cap multiple porting and the surfacial sealing engagement of the piston extensions with the end caps may all be somew~at less advantag20usly utiliz~d in a cylinder having exhaust means other than the poppet valve type presently disclosed~

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

A pneumatic cylinder of the double acting type comprising in combination, a piston within said cylinder having axial exten-sions of reduced diameter, a piston rod, end caps closing the cylinder and each defining a central recess to alternately receive said piston extensions, each end cap recess in communication with a valve controlled pressurized source of air, and cylinder exhaust means within each of said end caps and including pressurized air biased valve members alternately operable to vent a non-constant flow of air from ahead of the moving piston from the cylinder interior at a predetermined pressure value to prevent piston rebound.

The invention claimed in claim 1 wherein said biased valve members are in communication with a common pressure regulating means.

The invention claimed in claim 2 wherein said biased valve members are in the form of poppet valves.

In combination with a toggle assembly of a clipping machine, a reciprocally cyclical blade carried by said assembly with a cutting stroke and a return stroke coincident with lengthwise movement of a toggle bar and passage of toggle linkages through an upright position, the improvement comprising, a pneumatic cylinder of the double acting type imparting lengthwise movement to the toggle bar of the toggle assembly causing one reciprocal cycle of blade operation, a piston within said cylinder having axial extensions of reduced diameter, a piston rod, and caps closing the cylinder and each defining a central recess to alternatively receive said piston extensions, each end cap recess in communication with a valve controlled pressurized source of air for alternately powering the piston, and cylinder exhaust means within each of said end caps, said exhaust means including pressurized air biased valve members alter-nately opening to vent a non-constant flow of air from ahead of the moving piston from the cylinder interior at a predetermined cylinder pressure value the build-up of which pressure dissipating blade and toggle assembly inertia to prevent blade rebound from a blade rest position.

The invention claimed in claim 4 wherein said biased valve members are in communication with a common pressure regulating means.

The invention claimed in claim 5 wherein said biased valve members are in the form of poppet valves.

The invention claimed in claim 4 wherein engage-ment of a piston extension with an end cap occurs contemporaneously with the completion of the cutting stroke of the blade with subsequent cylinder pressur-ization ahead of the piston occurring during the return stroke of the blade.

Claims Supported by the Supplementary Disclosure A pneumatic cylinder of the double acting type com-prising in combination, a piston within said cylinder and having axial exten-sions of reduced diameter, a piston rod adapted at one end for linking to a work performing instrumentality, end caps of the cylinder each defining a central recess to alternately receive said piston extensions, each end cap also defining a first port communicating the cap central recess with a first air valve, each end cap also defining a second port communicating a second valve with the cylin-der interior, said second port in each cap intermittently directing a charge of piston actuating air against a piston surface, said first port in each end cap serves to exhaust cylinder air from ahead of an advancing piston until an axial extension sealingly engages an end cap and alternately serves to admit pressurized air to the cylinder behind an advancing piston, and cylinder exhaust means carried by each of said end caps, each exhaust means including a pressurized air biased valve member independently opening to vent a non-constant flow of cylinder air trapped ahead of the advanc-ing piston by sealing engagement of a piston extension with an end cap, cylinder venting by said biased valve members occurring at a predetermined cylinder pressure and serving to dissipate piston and work instrumentality inertia and hence rebound tendencies of same.

The pneumatic cylinder claimed in claim 8 wherein said end caps are each adapted to support one of said second air valves whereby the volume of air between each of said second valves and the cylinder interior is mini-mized to reduce piston response time to a valve controlled air flow.

The pneumatic cylinder claimed in claim 9 wherein each of said end caps is further adapted to support one of said first air valves.

The pneumatic cylinder claimed in claim 8 wherein each of said air biased valve members are poppet valves one each carried by an end cap, each poppet valve subject to a primary pilot pressure biasing the poppet valve toward a cylinder closing position and intermittently sub-ject to a supplementary valve closing pressure assuring poppet valve closure in the presence of piston actuating air pressure.

The pneumatic cylinder claimed in claim 11 wherein said end caps each define an air passageway communicating the central recess of the end cap with the end cap housed poppet valve, each poppet valve having a secondary air biased surface against which said supplementary pressure acts.

In a pneumatic cylinder of the double acting type having a piston and piston rod for coupling to a work performing instrumentality, said cylinder including exhaust means responsive to internal cylinder pressures for venting the cylinder chamber air above a pre-determined pressure, the improvement comprising, a piston having axial extensions, end caps closing the cylinder ends and each defining a central recess within which a piston extension is slid-ably received in surfacial sealing engagement to close the cylinder chamber, said end caps each defining multiple ports, one of said ports in each end cap extending through the end cap and serving to admit a valve controlled flow of piston stroking pressurized air for direct impingement against a piston surface, a remaining port in each end cap terminating in communication with said central recess of the cylinder and serving to admit a valve controlled flow of pressurized air to said cylinder behind the moving piston, said remaining port in each end cap additionally serving to communicate that portion of the cylinder chamber ahead of the moving piston with a cylinder exhaust until a piston extension sealingly engages an end cap whereafter the buildup of cylinder pressure dissipates piston momentum.

The improvement claimed in claim 13 additionally including a valve on each of said end caps controlling the admission of pressurized air through said one of said ports in each end cap.

The improvement claimed in claim 14 additionally in-cluding a valve on each of said end caps controlling the flow of pressurized air through said remaining port in each end cap.