USRE25956E - Tool location in automatically controlled machine tools - Google Patents

Description

Feb. 22, 1966 WILLIAMSON Re. 25,956

TOOL LOCATION IN AUTOMATICALLY CONTROLLED MACHINE TOOLS Original Filed July 22, 1963 3 Sheets-Sheet 1 Indian.

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TOOL LOCATION IN AUTOMATICALLY CONTROLLED MACHINE TOOLS Original Filed July 22, 1963 3 Sheets-Sheet z INVEAJHL I 90m ism/244,, 9

5 Sheets-Sheet 3 D. T. N. WILLIAMSON Feb. 22, 1966 TOOL LOCATION IN AUTOMATICALLY CONTROLLED MACHINE TOOLS Original Filed July 22,

United States Patent 25,956 TOOL LOCATION IN AUTOMATICALLY CONTROLLED MACHINE TOOLS David Theodore Nelson Williamson, London, England, assignor to The Molins Organisation Limited, a British company Original No. 3,171,327, dated Mar. 2, 1965, Ser. No.

296,763, July 22, 1963. Application for reissue July 22,

1965, Ser. No. 475,626 Claims priority, application Great Britain, July 27, 1962,

28,962/62 6 Claims. (CI. 90-11) Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

This invention concerns improvements in or relating to a method of and apparatus for selecting and locating a cutting tool in a cutter head of a numerically controlled machine tool.

Present day practice in the engineering industry tends to lead to the production of components on a large scale. Where such components are made from metal which is to be machined, cut or fashioned to the required shape, it has become usual to perform successive operations on different machines, each of which has been tooled and set up for that one particular operation. The workpiece may be transferred from machine to machine after each operation, either manually or automatically, until the whole machining or fashioning process has been completed. The machine tools may be numerically or programme controlled since this has led to cost economies due to reduced machining time.

Whilst this practice is suitable for components to be produced in large batches, it may prove uneconomic if the required quantity is small or relatively small, since then the setting-up time becomes large in relation to the total machining time. It might in some cases be possible to revert to manually controlled multi-purpose machine tools for small batches but usually this increases costs due to increased machining time and, possibly, to additional inspection requirements. It has, therefore been proposed to use a multi-purpose numerically controlled machine tool capable of carrying out as many machining operations as possible and it is believed that this may help to reduce costs for batches of. components to be produced in small quantities or even singly. Accordingly, the setting-up time should be as short as possible. It, therefore, becomes desirable to have the machine tool designed to be able to change cutting or other types of tool as quickly as possible when desired either during machining operation or on completion of one batch and before starting another, and to be able to locate the selected tool accurately within the machine tools cutter head.

The accurate location of the cutting tool within the cutter head presents f-ew difficulties in two dimensions, i.e. those dimensions in a plane transverse to the axis of the cutting tool since it is gripped within a chuck or collet. The location in the third dimension i.e. along its own axis, does cause difficulties since the length of the tool itself is only nominal whilst the act of being gripped may cause it to move. Whilst small differences in the location of the tool end in this direction along its own axis may not be of any great importance for rough machining such as is involved in cleaning up the face of a casting, for contour milling such differences cannot be allowed except with the design limits of the machine tool itself. Consequently it is desirable to be able to locate the tool cutting end with a high degree of accuracy in a direction along its axis, to say .0005 or better.

According to the present invention there is provided Reissued Feb. 22, 1966 a method of gripping a selected tool from a plurality of tools and of locating it in a spindle of the cutter head of a numerically controlled machine tool, comprising the successive steps of: positioning the cutter head and the plurality of tools so that the longitudinal axes of the spindle and the selected tool are aligned with the shank of the selected tool directed towards the cutter head; reducing the distance between the cutter head and the plurality of tools until the shank of the selected tool is inserted into the spindle; causing the shank to be gripped in the spindle; withdrawing the selected tool by moving apart the cutter head and the plurality of tools; repositioning the cutter head opposite a surface of the machine tool; causing the shank to be free to move in the spindle; reducing the distance between the cutter head and the surface to a desired value whereby the cutting end of the tool is abutting the surface; and causing the shank to be gripped in the spindle with its cutting end the same distance from the cutter head as the said desired value.

The distance between the cutter head and the plurality of tools may be reduced to a figure whereby the distance of the cutting end of the selected tool from the cutter head exceeds the said desired value.

Further according to the invention there is provided a numerically controlled machine tool comprising a cutter head, a surface to which is fixed a workpiece, opposed to the cutter head, and a magazine adjacent the surface containing a plurality of cutting tools having their shanks directed towards the cutter head, the cutter head having a spindle in which is located a collet actuated to grip the shank of a selected cutting tool and the surface having a datum pad against which the cutting end of the selected cutting tool is capable of being abutted. The collet may be actuated to close by the application of a force acting in the direction of the longitudinal axis of the selected cutting tool, the said force being transformed by the collet into a gripping force acting normally to the shank of the selected cutting tool which is thereby maintained in a stationary position relative to the spindle.

Thus, it can be seen that the arrangement of the present invention is such that the selected cutting tool and the workpiece are mounted in opposed relationship to each other such that relative rotation between the same is provided to eficct the desired machining operation.

The magazine may comprise a series of openings, into each of which a holster fits, each holster being adapted to grip the cutting end of a cutting tool, and may be fixed to the said surface and the holsters form an array in which shanks of the cutting tools housed therein project parallel to each other.

The cutter head may be movable in a horizontal plane and the surface is movable in a vertical plane.

Apparatus in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which:

FIGURE 1 is a perspective view of a numerically controlled machine tool,

FIGURE 2 is a section through the tool magazine shown in FIGURE 1,

FIGURE 3 is a section through a cutter head of the machine tool of FIGURE 1, and

FIGURE 4 is a section on the line IVIV of FIG- URE 3.

The numerically controlled machine tool shown in FIGURE 1 consists of a slide table 101 carrying acutter head 102 and of avertical member 103 to which is attached a work surface, in this case a pallet, 104. Thecutter head 102 possesses two degrees of freedom of movement, a traversingslide 105 for movement across the slide table 101 and afeed slide 106 which moves on and at right angles to the traversingslide 105. The

cutter head 102 is integral with the feed slide 1.06 and is adapted to hold twocutting tools 107 and T which are inserted and gripped in a manner to be described hereinafter inquills 109 and 2. Thepallet 104 possesses one degree of freedom of movement, i.e. in a vertical direction, and is attached to a vertical slide table 113 provided with tenopenings 114 facing towards thecutter head 102. Twoworkpieces 115 and 116 are fixed to the work surface of the pallet 104 [and] so that saidtools 107, T and saidworkpieces 115, 116 are mounted in p- POA't'd rcl't'ltionship to each other such that relative rotation between the some is provided to effect the desired machining operation. Also mounted on thepallet 104 in a position lower down and to the right of the workpieces there are twopads 117 and 118. The spacing between the twoworkpieces 115 and 116 and between the twopads 117 and 118 is the same as that between the twoquills 109 and 2. Thus the machine shown in FIG- URE l is suitable for machining two workpieces simultaneously. The spacing of theopenings 114 is similarly arranged. The space between the first opening and the sixth opening (numbering the openings consecutively from one side or the other) is the same as that between the twoquills 109 and 2 and is identical with that between the second and seventh openings, the third and eighth, the fourth and ninth and between the fifth and tenth openings.

Automatic control mechanism is not shown in FIG-URE 1, although a control panel is indicated at 119. It is, however, of known design operating on known principles embodying, for example, a punched or magnetic tape containing operating instructions. In FIGURE 3 thequill 2 is fixed to the casting l. A rotating spindle 3 is positioned within thequill 2, from which it is separated by twoangular contact bearings 4 and 5 and a plain ball bearing 6. A locating ring 7 is fixed to the bore of thequill 2 by means ofdowels 8. Concave-convex washers 9, known as Belleville washers, separate an outer race 10 of the angular contact bearing 5 and the locating ring '7, and being compressed supply the force necessary to preload the balls of the bearing 5 between the outer race 10 and an inner race 11 machined around the spindle 3 and thus to prevent axial play. Tile bearing 4 has anouter race 12 which fits into the bore of thequill 2. An inner race 13 is machined around the spindle 3. A lock nut 14 is threaded over thequill 2 and bears against theouter race 12, thus supplying the force necessary to pro-load the balls of thebearing 4. Thebearing 4 is fitted to take away any forward axial thrust and the bearing 5 to take backward axial thrust. Oil mist lubrication is supplied to bothbearings 4 and 5 through a hole 15 and a circumferential channel 16 in thequill 2. A guard ring 17 is threaded on the spindle 3 and provides a labyrinthine passage 18 between it and the lock nut 14, thus preventing the entry of foreign matter without allowing excessive escape of oil.

The back end of the spindle 3 has a reduceddiameter 19 and a shoulder 20. Aspacer 21 nips the inner race 22 of theball bearing 6 against the shoulder and is held in position by ahub 23 of apelton wheel 24. The individual buckets of thepelton wheel 24, which is a high speed wheel operated by an oil jet, are secured to thehub 23 by a lock washer 25, which in its turn is locked into position by a nut 26 threaded over a further reduceddiameter 27 of the spindle 3. Theouter race 28 of theball bearing 6 is held in position by a lockingring 29 secured to the quill. Lubrication for thebearing 6 is supplied by the oil mist pressure being transmitted through a clearance 30 between the spindle 3 and the bore of the Belleville washers 9.

The front end of the spindle 3 is bored to mate with the front end of a nose tub-e 34. The front peripheral end of thenose tube 34 forms a truncated cone, whilst internally it is provided with a shoulder 32 and ataper 33. Restraining means, a retaining ring 31 which for the sake of assembly is split into four quadrants, is interposed between the bore of the spindle 3 and the truncated cone of thenose tube 34. The function of the ring 31 is to cause thenose tube 34 to lock against the internal taper of the spindle 3. Thus thenose tube 34 cannot move forwards when a forward axial force is applied to it. The back periphery of thenose tube 34 is a sliding fit within the bore of the spindle 3. A compression tube 35 also forms a sliding fit within the bore of the spindle 3 and is provided with an internal taper, the slope of which opposes that of the taper of thenose tube 34. Acollet 36 fits within thenose tube 34 and the compression 35. Thecollet 36 has a front frustroconical end 37 which mates with the internal tapers of thenose tube 34, and has a back frustro-conical end 38, which mates with the internal taper of the compression tube 35. A sleeve 39, provided with slits 40, fits inside thecollet 36. The front end of the sleeve 39 is held against the shoulder 32 of thenose tube 34 by the action of a spring 41 bearing against ashoulder 42 of the compression tube 35.

A cutting tool T fits within the sleeve 39', its back end having a dog 43 which fits in a recess of a plunger 44. Apush rod 45 is attached to the plunger 44 by means of a pin 46. An enlarged portion of the plunger 44 is fixed against relative rotary movement to the compression tube 35 by a key 47. The plunger 44 is however, movable axially relative to the compression tube 35, since the key 47 is slidable within elongated keyways. The plunger 44 is held in its front position by a spring 48 bearing against apiston 49 which is slidable within the bore of the spindle 3. The space between the back of thepiston 49 and a shoulder 50 of the spindle 3 is occupied by Belleville washers 51. The assembly of the retaining ring 31, thenose tube 34, thecollet 36, the compression tube 35 and thepiston 49 is such that the Belleville washers 51 are in a state of compression and thus act to force the compression tube 35 forwards. Thepush rod 45 is slidable within a draw bar 52 which is integral with thepiston rod 49.

Both thepush rod 45 and the draw bar 52 extend beyond the back end of the spindle 3 into a recess 53 within a hydraulic piston 54 which is slidable within a composite cylinder 55. A throughpiston rod 56 is integral with the piston 54, with its front end drilled totake twopins 57 and 58 (see FIGURE 2). The heads of thepins 57 and 58 are slidable ingrooves 59 in afront cylinder head 60 of the cylinder 55. A bearing ring 61 is threaded onto the back end of the draw bar 52, along which its position is adjustable.

The cylinder comprises abarrel 62 to which is fixed the front cylinder head and aback cylinder head 63.End plates 64 and 65 are fixed respectively between theback cylinder head 63 and thebarrel 62 and between thefront cylinder head 60 and thebarrel 62. 0 rings 66 seal the cylinder area so that the hydraulic fluid is prevented from leaking to atmosphere. The front cylinder area is connected via a passage 67 in thebarrel 62 to a flexible hose 68 which communicates directly to a 1,500 psi. hydraulic main. The back cylinder area com municates via apassage 69 to aflexible hose 70 which can be connected through a three-way selector (not shown) to the 1,500 psi hydraulic main or to a tank.

The back end of thepiston rod 56 is provided with an extension 71 which projects through a bracket 72 attached to thecasting 1. A spring 73 urges thepiston rod 56 forwards and bears between the bracket 72 and a shoulder 74. Forward movement of the piston rod 54 is restricted by a circlip 75 in the extension 71 coming into contact with the bracket 72.

A second push rod 76 extends through thepiston rod 56 and is provided with a pusher face 77 at its back end. The pusher face is operable to move two arms, only one of which, 78, can be seen in FIGURE 1. The twoarms 78 swing aboutpivots 79 fixed to thecasting 1 and in moving anti-clockwise about theirpivots 79 trip microswitches 80, of which only one again can be seen in FIGURE 1. A stop 81 attached to theback cylinder head 63 prevents the second push rod 76 being moved forward beyond a preset position by aspring 82 held in tension between the bracket 72 and thearms 78, the object of thespring 82 being to keep thearms 78 and the pusher face 77 in contact.

FIGURE 2 shows a section through thevertical slide 113 which is provided withrails 146 to take amagazine 147. The back of themagazine 147 slides on therails 146 and its far end locks against an end stop for positive location on thevertical slide 113, the end stop and locking mechanism not being shown. Opposite each of the tenopenings 114 an aligned hole 148 in themagazine 147 is adapted to hold aholster 149. Theholster 149 is flanged at 150 to locate it against the back of themagazine 147 and is pinned (not shown in FIGURE 4) to prevent it moving against thevertical slide 113.

A tool-holder 151 has ashoulder 152 which is a snug fit in theholster 149. Between theshoulder 152 and alip 153 of theholster 149 is aspring 154 which holds the tool-holder 151 firmly against apin 155. The tool-holder 151 is provided with a thin-walled projection 156 into which the cutting end of the tool T is pushed. The bore of the thin-walled projection 156 is made to be an interference fit with the diameter of the tool T, say 0.004 smaller. Since the tool 108 has two cuttingflutes 157 only there will be two point contact in any plane at right angles to the tools longitudinal axis between the tool T and theprojection 156. The thin wall enables the projection to take up an appropriate set and thus to grip the tool T firmly. Thetool holder 151 is made from a suitable plastic.

Aguard 158 carried in aframe 159 is hinged to the top of thevertical slide 113 at 160. Theguard 158 has to be opened for changing or selecting a cutting tool, this opening being carried out automatically by a stationary ramp which lifts it when thevertical slide 113 is lowered to a position where the longitudinal axes of the cutting tools and thequills 109 and 2 are aligned. The ramp is not shown in FIGURE 2.

In operation, thepallet 104 containing twoworkpieces 115 and 116 and themagazine 147 containing a suitable quantity of cutting tools to carry out the requisite machining operations on the workpieces, are fed by hand to the machine and are located on the vertical slide table 113. Since the machine is provided withtwin quills 109 and 2 for operating simultaneously on the twoworkpieces 115 and 116 it will be seen that each operation must be duplicated. In the description following only onequill 2 and oneworkpiece 116 will be dealt with, it being understood that theother quill 109 duplicates all movements and operations. When thepallet 104 and themagazine 147 are in position the machine is ready to start its automatic operation.

Programmed instructions in the form of a tape are fed to the control console, which is not shown, detailing the first cutting tool T to be used on theworkpiece 116, its position in themagazine 147 and the nominal length of its cutting end. The actual length differs from the nominal length by the amount the cutting tool has been previously ground or by an amount representing normal manufacturers tolerances. Servo mechanisms which are not shown in the drawings, being of known design and application, operate to lower the vertical slide table 113 until the axes of the cutting tool T and of. thequill 2 are in the same horizontal plane, and to traverse thefeed slide 106 until the two axes are in the same vertical plane. By the time the cutter head and the magazine are in this position it is essential that the spindle 3 should have ceased to rotate. A brake of known design and not shown in any of the figures is incorporated to stop the spindle 3 and is actuated by a positional microswitch when the vertical slide table 113 has been lowered so that the axes of the cutting tool T and of thequill 2 are in the same horizontal plane. As the vertical slide table 113 is lowered the guard 158 (FIGURE 2) is raised by means of the ramp which is not shown.

While the cutter head is moving, instructions carried on a tape activate the chuck to open. The three-way selector (which is not shown) connects theflexible hose 70 to tank. The pressure difference between the front and back sides of the cylinder causes it to move forward until the front end of the front cylinder head comes to rest against the back end of the nut 26. During this last movement the force exerted by the spring 73 on thepiston rod 56 is sufficient to hold the piston 54 at rest and therefore to cause the cylinder 55 to move. As soon as the cylinder 55 comes to rest, the piston 54 starts to move backwards. As the piston 54 moves, thepins 57 and 58 move with it, until they come to bear against bearing ring 61 which then moves backwards. The total backward movement of the bearing ring 61, of the draw bar 52 and thepiston 49, which moves with it, is of the order of .020". This movement is sufficient to compress the Belleville washers 51 further and thus to remove the forward acting force exerted by thepiston 49 on the compression tube 35. As soon as this forward acting force is removed, its radial component acting through the frustro-conical ends 37 and 38 of thecollet 36 on the slit sleeve 39 is also removed. The sleeve 39 is thus allowed to expand to its uncompressed diameter and the chuck is open.

When the chuck is open and the spindle 3 and the tool shank are aligned to within .003", the cutting head moves forward i.e. towards themagazine 147 to a predetermined position. The predetermined position varies with the effective length of the cutting tool selected and is regulated by the taped instructions. As the cutting head moves forward the shank of the tool is inserted into the sleeve 39. The spindle 3 is rotated slowly by cracking the com trol value to the hydraulic fluid jet (neither of which are shown) operating thepelton wheel 24. As soon as the dog 43 engages in the corresponding recess in the plunger 44, the spindle 3 is brought to rest. The three-way selector then admits pressure to the flexible hose and thus to the position of the cylinder 55 behind the piston 54. Due to the greater cross-sectional area of the back portion of the piston 54, it moves forward until its front end comes to rest against thefront end plate 65. Forward movement of the piston 54 and thepiston rod 56 allows the draw bar 52 and thepiston 49 to move forward. By the time the piston 54 and the cylinder 55 come to rest due to the circlip coming into contact with the bracket 72, the Belleville washers 51 are again exerting the designed forward thrust on thepiston 49. This thrust is transmitted directly to the compression tube 35. Due to the back frusto-conical end 38 of thecollet 36 and the mating portion of the bore of the compression tube 35 this thrust is transferred into a skin force normal to the two surfaces. The normal force then has two components, a force directed radially inwards over the circumference of the back frustro-conical end 38 of thecollet 36 and a forward force directed over the cylindrical portion of thecollet 36. The forward force is similarly divided into two components due to the front frusto-conical end 37 and the mating portion of the bore of thenose tube 34, a radially inward force acting around the circumference of the front frusto-conical end 37 and a forward axial force. This latter forward axial force acts to wedge the front frusto-conical end 37 into thetaper 33 of thenose tube 34 and to wedge the retaining ring 31 between thenose tube 34 and the mating portion of the spindle 3. Thus there are two radially inward directed forces acting on the slit sleeve 39. These forces partially close up the slits 40 and reduce the diameter of the sleeve 39 so that the tool T is gripped sufficiently tightly to resist the torque necessary for cutting. The radial forces cannot move the sleeve 39 axially, whilst any axial movement due to frictional force between thecollet 36 and the sleeve 7 39 is resisted by the sleeve 39 being in contact with the shoulder 32 of thenose tube 34. The sleeve 39 thus remains stationary relative to the spindle 3 whilst gripping the tool T.

After the tool T is gripped thecutter head 102 moves away from the magazine withdrawing the tool T from thetool holder 151. The vertical slide table 113 rises and theslide 105 traverses until the centre of the surface 118 is approximately aligned with the longitudinal axis of the cutting tool T when both movements stop. Thecutter head 102 then feeds forward on theslide 105 until it is a predetermined distance which is dependent on the nominal length of the cutting portion of the cutting tool T, from the surface 118 when it stops. Whilst it is moving towards the surface 118 the chuck opens as described hereinafter so that the tool T is movable along its axis relative to the spindle 3. The predetermined distance is dependent on taped instructions and differs for each nominal length of cutting tool. It is, however, always less than the nominal length so that as the cutting head approaches the predetermined position the front end of the tool comes to rest against the datum surface. Further forward movement of the cutting head leads to the tool moving backwards relative to the spindle 3 and to backward movement of the plunger 44 against the action of the spring 48 and of thepush rod 45. Since the chuck is open, the cylinder 55 is in its forward position thus reducing the gap between thepush rod 45 and the second push rod 76. Backward movement of thepush rod 45 is therefore transmitted to the second push rod 76 which in its turn moves thearms 78 in an anti-clockwise direction about theirpivots 79. The predetermined distance and the nominal length of the tool are chosen and calculated so that anti-clockwise movement of thearms 78 makes contact in one only of the microswitches 80. the wrong tool is selected either both microswitches make contact or neither do, the former in the case of a tool having too great a nominal length and the latter when the nominal length is too small. Only when the correct microswitch has made contact will the machine tool continue to accept and carry out subsequent taped instructions. Thus the possibility of damage is safeguarded should a tool of incorrect length be gripped.

After the completion of the machining operation the cutting head and the empty tool storage position on the pallet are again aligned. The cutting head moves forward in the Z plane, the chuck opens and the tool is inserted into the tool storage where it is gripped. The cutting head moves backwards, the tool is left behind, and plunger 44 moves forward under the action of the spring 48. The cutting head is now in readiness to pick up the next tool for the following machining operation.

Although a machine tool has been described as shown in FIGURE 1, the invention is equally applicable to other forms. For instance the vertical worktable might be rotatable while the cutter head might also be capable of being swivelled through 90. In this instance there would be, of course, only one quill and one workpiece.

What I claim as my invention and desire to secure by Letters Patent is:

l. A numerically controlled machine tool comprising a cutter head, a surface to which is fixed a workpiece ill opposed to the cutter head. and a magazine adjacent the surface containing a plurality of cutting tools having their shanks directed towards the cutter head, the cutter head having a spindle in which is located a collet actuated to close and to grip thereby the shank of a selected cutting tool and the surface having a datum pad against which the cutting end of the selected cutting tool is capable of being abutted so that the distance of the cutting end of the selected cutting tool is a predetermined distance from the cutter head.

2. A numerically controlled machine tool as claimed inclaim 1, in which the collet is actuated to close by the application of a force acting in the direction of the longitudinal axis of. the selected cutting tool, the said force being transformed by the collet into a gripping force acting normally to the shank of the selected cutting tool which is thereby maintained in a stationary position relative to the spindle.

3. A numerically controlled machine tool as claimed inclaim 1, in which the magazine comprises a series of openings, into each of which a holster fits, each holster being adapted to grip the cutting end of a cutting tool.

4. A numerically controlled machine tool as claimed in claim 3, in which the magazine is fixed to the said surface and the holsters form an array in which the shanks of the cutting tools housed therein project parallel to each other.

5. A numerically controlled machine tool as claimed inclaim 1, in which the cutter head is movable in a horizontal plane and the surface is movable in a vertical plane.

6. A numerically controlled machine tool comprising a tool-holding member, a workpiece opposed to raid toolholding member, a magazine containing a plurality of cutting tools having their shanks directed towards the too-I- hOlding mcmbcr the tool-holding member having toolgripping means adapted to be actuated to close and to grip thereby the shank of the selected cutting tool from among said plurulit ,v, means to provide relative rotation between said workpiece and said selected cutting tool to eflect the machining operation, and a datum surfacc against which the cutting curl of said selected cutting tool is capable of being abuttcd so that the distance of said cutting and of said selected cutting tool is a predetermined distance from the l0ol-holding member.

References Cited by the Examiner The following references, cited by the Examiner, are of record in the patented file of this patent or the original patent.

UNITED STATES PATENTS 1,208,852 l2/19l6 Sproul.

2,326,848 8/1943 Fanning.

2,901,927 9/1959 Morgan 774 2,927,703 3/1960 Raincy et al. 29568 3,064,502 l1/l962 Pittwood 29568 3,124,976 3/1964 Pittwood 77-4 \VILLIAM W. DYER, JR., Primary Examiner.

L. VLACl-IOS, Assistant Examiner.

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