US3089393A

US3089393A - Drive mechanism for folding box machines of the plunger and die type

Info

Publication number: US3089393A
Application number: US179300A
Authority: US
Inventors: Richard V Pagendarm
Original assignee: Atlas General Industries Inc
Current assignee: Atlas General Industries Inc
Priority date: 1962-03-13
Filing date: 1962-03-13
Publication date: 1963-05-14
Anticipated expiration: 1980-05-14
Also published as: GB955132A

Description

May 14, 1963 R. v. PAGENDARM DRIVE MECHANISM FOR FOLDING BOX MACHINES OF THE PLUNGER AND DIE TYPE 4 Sheets-Sheet 1 Filed March 13, 1962 INVENTOR. ichard 1/. ihgendarm ATTORNEY May 14, 1963 R. v. PAGENDARM 3,089,393

DRIVE MECHANISM FOR FOLDING BOX MACHINES OF THE PLUNGER AND DIE TYPE Filed March 13, 1962 4 Sheets-Sheet 2 INVENTOR. Richard V. Pagendarm QM A TTORNEY y-1 1963 R. v. PAGENDARM 3,039,393

DRIVE MECHANISM FOR FOLDING BOX MACHINES OF THE PLUNGER AND DIE TYPE Filed March 13, 1962 4 Sheets-Sheet 3 Fig. 3 INVENTOR.

Richard V. Pagendarm BY W W ATTORNEY May 14, 1963 R. v. PAGENDARM 3,039,393

DRIVE MECHANISM FOR FOLDING BOX MACHINES OF THE PLUNGER AND DIE TYPE Filed March 13, 1962 4 Sheets-Sheet 4 i 1 l i 1 |I l l i I I I 5/ 9 I .9! h I I, 9)

v 1 1 j'lol I 39 105' m 107 I 69 95 "7 6,5 93 i 94- 92 I 73 i t r 86 7/ E 1 1 66 I E E F5 4 INVENTOR.

Ric/Yard V. Pagendarm BY W '5. W

a 4M ATTORNEY United States Patent DRIVE MECHANISM FOR FOLDING BOX MA- CHINES OF THE PLUNGER AND DIE TYPE Richard V. Pagendarln, Hillsborough, Calif., assiguor to Atlas Genera. Industries, Inc., New York, N.Y., a corporation of Massachusetts Filed Mar. 13, 1962, Ser. No. 179,300 Claims. (Cl. 9351) This invention relates to improvements in folding box forming machines of the type in which a box forming plunger folds a box blank into box shape by forcing it into a folding die. If the box is of the glued type, the folding die is momentarily contracted to exert a compressive force on the glued box which is internally supported by the plunger. During the period of compression the plunger must be at rest, but it is desirable to maintain other portions of the machine, for example the blank feeder, in continuous operation.

The patent to l-loyrup 2,997,928, dated August 29, 1961, discloses a drive mechanism for a box forming machine of the aforementioned kind in which a force and motion transmitting coupling is installed between the plunger and a continuously operating driving member. The coupling permits the plunger to come to rest during the box compression period, while the remanider of the machine continues in motion. In addition, the coupling imparts desirable motion and velocity characteristics to the plunger which differ from those of the continuously oscillating drive bar and which are particularly desirable, if the box blank consists of tough paperboard requiring temporarily a relatively high peak energy for folding the fiat blank.

The Hoyrup coupling disclosed in the aforementioned patent employs the compressive force of air both for the work stroke during which the plunger moves into the die, as Well as for the return stroke during which the plunger is withdrawn from the die.

In box machines of the universal type, i.e, built to form boxes of a variety of sizes, as distinguished from machines built to form one size or a narrow range of box sizes only, it is necessary to install a heavy plunger at one time, and a light plunger at another time. The weight of the plunger determines its momentum and the momentum, in turn, affects the motion characteristics. Assuming, for example, that a heavy plunger is employed, an unusually high air pressure is created in the air cylinder which operates to withdraw the plunger from the die. The pressure is particularly high if the machine is operated at a high rate of speed. As a result, high temperatures are experienced and chattering may occur evidenced by uneven and non-uniform acceleration of the plunger. To correct such behavior an adjustment of the air feeder passages of the pneumatic system is required which, although routine to a mechanic familiar with the characteristics of the machine, may require time consuming experimentation by personnel in a box makers plant less intimately familiar with machines of this type.

This invention and improvement is based on the discovery that a pneumatic variable volume chamber device in combination with a hydraulic variable volume chamber device disposes of the existing difficulties and makes it unnecessary to adjust the force and motion transmitting device or coupling for different plunger weights.

Variable volume chamber devices may assume different forms, the most suitable forms being basically the bellows type and the cylinder and piston type. Use of a bellows or of multiple diaphragm capsules is generally only advisable where the stroke is relatively small. A short multiple diaphragm or bellows stroke may, of course, be multiplied by suitable lever devices.

The cylinder and piston type may have the form of ICC the familiar straight line cylinder and piston arrangement, but may also be of the rotary design in which a pivoted vane-piston divides a substantially sector shaped cylinder into two chambers.

The choice of the specific form of cylinder and piston arrangement depends on the construction of the machine and the availability of space. The invention will be illustrated as applied to a box machine in which the straight line cylinder and piston is the most convenient form of motion and force transmitting device.

The various objects, features and advantages of this invention will appear more fully from the detailed description which follows accompanied by drawings snowing, for the purpose of illustration, a preferred embodiment of the invention. The invention also resides in certain new and original features of construction and a combination of elements hereinafter set forth and claimed.

Although the characteristic features of this invention which are believed to be novel will be particularly pointed out in the claims appended hereto, the invention itself, its objects and advantages, and the manner in which it may be carried out may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part of it, in which:

FIG. 1 is a diagrammatic drawing illustrating certain portions of the plunger and die mechanism and portions of the drive;

FIG. 2 is a perspective view of the plunger drive incorporating the invention;

FIG. 3 is a perspective view of the mechanism during a different phase of its operation; and

FIG. 4 is a vertical cross sectional view of the pneumatic and the hydraulic portions of the mechanism.

In the following description and in the claims various details will be identified by specific names for convenience. The names, however, are intended to be generic in their application. Corresponding reference characters refer to corresponding parts in the several figures of the drawmgs.

The drawings accompanying, and forming part of, this specification disclose certain specific details of construction of the invention for the purpose of explanation of broader aspects, but it is understood that constructional details may be modified in various respects without departure from the principles of the invention and that the invention may be incorporated in other structural form than shown.

FIG. 1 shows a box blank 11 having a main panel M, end panels E, side panels S and glue flaps F underneath a plunger 12 and above a die 13. The die is a combined folding and compression die and comprises front and rear blank folding elements 14 and 15 adapted to engage the side panels S and fold the side panels against the sides 18 and 19 of the plunger 12.

Further blank folding elements 16 and 17 are adapted to engage the end panels E to fold these against the

end surfaces

20 and 21 of the plunger 12. Glue applicators 22 and 23 are provided at the four corners of, and slightly above, the die 13. The two glue applicators nearest the observer are omitted for the sake of clarity.

The glue applicators prefold the flaps F at an angle to the side panels S and apply adhesive to the outside of the flaps so that upon entry of the blank into the die the flaps F overlie the

end surfaces

20 and 21 of the plunger and the end panels E lie thereover and become adhesively secured thereto.

A pair of pressure plates 24 and 25 are linked to power levers 26 and 27 at 28 and 29. One end of the levers is pivotally supported at 30 and 31 and a hydraulic servo-motor 32 is pivotally connected to the opposite end of the power levers at 33 and 34. The piston 35 of the servo-motor subdivides the servo-motor cylinder 36 into a left chamber 37 and a right chamber 38. Pressure lines 39 and 40 lead to the chambers of the servo-motor. Fluid under pressure entering the left chamber 37 through the line 39 causes the power levers 26- and 27 to be drawn together and the plates 24 and 25 to exert compressive force on a folded box moved into the die by the plunger 12.

FIG. 1 also shows in simplified form the major elements of the drive mechanism comprising an electric motor 41 having a pulley 42 which drives a gear 43 on a pinion shaft 44 through a chain 45. A pinion 46 on shaft 44 meshes with a gear 47 on a crank shaft 48 carrying a crank 49. The crank is linked to an oscillating arm 50 by a connecting rod 51. The oscillating lever oscillates about a fixed pivot 52 and the free end of the arm 50 is linked to a reciprocating cross head 53 by a further connecting rod 54. The cross head is slidably supported on a column 55 and supports one end of a drive bar 56 whose other end is supported in a similar cross head 57 on the opposite side of the machine. The drive bar supports the plunger 12 in a manner later to be described.

The motor is supplied with power from a source 58 and controlled by switches 59 and 60. The first switch 59 is operated by a cam 61 on the crank shaft 48. The shape of the cam is such that the switch 59 opens whenever the drive bar 56 approaches the lower end of the down stroke at which moment the plunger 12 enters the die 13. This would stop the machine were it not for the presence of a second switch which then closes and maintains the circuit unbroken. The second switch, as will later be seen, is operated by a cam 62 moving with the plunger 12. The purpose of this arrangement is to stop the machine if for any reason the plunger is prevented from entering the die.

The foregoing description covers the essential elements of the driving mechanism in a simplified combination of assembly. In actual practice the mechanism is somewhat more complex and refined and comprises, for example, means for varying the speed of the drive, relay control mechanisms in the electric circuit, and other details not essential to an understanding of the present invention. These details are disclosed in the patent to Edward J. Pagendarm.

The plunger drive bar 56 carries two

bracket

63 and 64 on which a common base plate 65 is mounted. The base plate carries two

vertical cylinders

66 and 67. The cylinder 66 is a pneumatic cylinder and contains a piston 68 whose piston rod 69 extends through the top of the cylinder to a piston plate 70.

The piston 68 divides the cylinder 66 into an upper chamber 71 and a lower chamber 72. The upper chamber 71 is vented to the atmosphere through a duct 73 and an air filter and silencer 74, and the lower chamber 72 comprises a passage 75 leading to a check valve 76. The check valve is so oriented as to seal the passage 75 while subatmospheric pressure exists in the chamber 72, but to open the passage to vent above atmospheric pressure in the chamber.

This arrangement limits the range of pressures which may exist Within the chamber 72 to a maximum of atmospheric pressure and a minimum approaching vacuum. If desired, a restricted passage may be provided parallel to the check valve 76. for example in the form of a needle valve as disclosed in the aforesaid Hoyrup patent. Such a by-pass operates to limit the degree of vacuum which may be created in the chamber 72.

The hydraulic cylinder 67 represents an enclosure within which an inner cylinder 77 is mounted. The upper end of the inner cylinder 77 is fitted with a guide bushing 78 of synthetic plastic such as nylon or tetrafluoroethylen polymer plastic also known by the name Teflon.

The lower end of the inner cylinder is normally closed by a check valve comprising an annular valve member 79 urged in an upward direction by a helical spring 80. The valve member 79 normally closes a plurality of passsages 81 leading to an annular space 82 between the inner and the

outer cylinders

77 and 67, respectively. This space 82 is filled with a hydraulic liquid extending to a level 83 controlled by a filler plug 84.

The piston cooperating with the cylinder 77 preferably has the form of a rod 85 having a lower portion 86 of reduced cross section. This may be accomplished by longitudinal flutes in a cylindrical lower portion, but is more conveniently accomplished by tapering the lower portion 86 slightly.

As the rod enters the bore 87, the liquid in the cylinder tries to escape and encounters a progressively increasing flow resistance as the escape passage between the rod portion 86 and the cylinder 77 becomes progressively longer and narrower. During entry of the rod piston 86 into the cylinder bore 87 the check valve remains closed.

The disk shaped valve member 79 has a central bore 88 and the liquid pressure acting on the underside of the valve member 79 keeps the valve tightly closed, supplementing the closing force of the spring 80.

The space of the cylinder 67 above the liquid level 83 is vented to the atmosphere. This may be accomplished by a vent passage 73.

The

rod piston

85, 86 is longitudinally adjustable in the piston plate. For this purpose the upper portion of the rod 85 is threaded at 89 and fitted with

knurled nuts

90 and 91.

The tops of the cylinders are connected by a tie plate 92 on which two

compressible buffers

93 and 94 are mounted composed of rubber or other suitable material. Butler 94 cooperates with the knurled adjustment nut 91 and a corresponding cylindrical element is mounted on the piston rod 69. The

buffers

93, 94 and

elements

91, 91 limit the extent to which the

pistons

68, 86 may be moved into the

cylinders

66 and 77.

Two

plunger rods

95 and 96 extend downwardly from the piston plate 70 and are guided in

slide bushings

97 and 98 in the tie plate 92. Similar bushings in the base plate 65 are not visible in the figures. The plunger rods terminate at a plunger plate 99. The plunger 12 is attached to the plunger plate by a bolt 100 and is aligned with respect to the plunger plate by appropriate dowel pins (not visible). In FIGS. 2 and 3 certain elements shown in FIG. 1 are removed from the die assembly 13 for the sake of clarity.

It was previously mentioned that the downward motion of the plunger 12 is arrested in the position in which compressive force is exerted on the folding box by the die 13.

A hydraulic snubber mechanism is provided for this purpose comprising a snubber 101 mounted on the framework on the machine and a striker pad 102 on the piston plate 70'.

The snubber comprises a cylinder 103 containing a piston 104 having a narrow groove or passage 105 through which fluid may pass from a lower chamber 106 of the body 107 into an upper chamber 108. The upper chamher 108 is a reservoir for the liquid 109. The piston 104 is under the action of a spring 110 tending to maintain the piston 104 raised. When the piston is depressed it otTers increasing resistance to displacement due to the fact that the flow resistance of the passage 105 between the lower chamber 106 and the upper chamber 108 increases. The increasing resistance offered by the snubber arrests the plunger gently.

When the plunger reaches its lowest position and is arrested, the pressure plates 24 and 25 are urged together. As a result the plunger is temporarily clamped between the plates and rendered immovable while compressive force is being exerted on the glued ends of the box carried by the plunger.

The drive bar 56 of the plunger may start its upward stroke without delay while the plunger proper stays in place until the compressive force of the plates 24 and 25 is released. During the upward motion of the bar 56 the

cylinders

66 and 67 move in an upward direction with respect to their pistons which are at rest by reason of being attached to the plunger. During the upward motion the rod piston 85 enters the inner cylinder 77 at about the moment the die 13 is expanded to release the plunger 12. Liquid pressure is being built up in the inner cylinder 77 from which the liquid is permitted to escape at a slow controlled rate past the tapered portion 86 of the rod piston 85. The force exerted by the upwardly moving cylinder 77 on the rod piston 85 drives the latter in an upward direction and at a gradually accelerating rate which towards the end of the upward return stroke becomes substantially equal to the rate of motion of the cylinder 77 and the drive bar 56.

During the return stroke the volume of the pneumatic chamber 72 is also reduced and excess air which may have entered it is expelled through the check valve 76.

When the drive bar 56 reaches the top of its stroke the plunger 12 and its

piston assembly

68, 85, 70, 95, 96 continues its upward motion for a certain short distance until the vacuum in the chamber 72 and the weight of the plunger become powerful enough to reverse the plunger. At the point of reversal of the plunger partial vacuum exists in the chamber 72 causing the plunger to be driven downwardly to perform its work stroke.

During the work stroke atmospheric pressure acting on the top side of the piston 68 drives the piston downward inside the cylinder 66. This downward motion is unrestrained during the initial portion of the stroke and is restrained or controlled as soon as the rod piston 86 enters the inner cylinder 77 of the hydraulic unit.

During the initial phase of the work stroke the rod piston 86, which immediately prior to this moment extended into the hydraulic inner cylinder 77, is being withdrawn therefrom. Liquid then enters the cylinder 77 through the

bottom check valve

79, 81 and is being withdrawn from the annular liquid storage space 82.

The plunger comes to rest at its lowest point when its striker pad 102 meets the snubber 101.

During the lower portion of the downstroke the plunger cam 62 actuates the switch 60 which closes and maintains the drive circuit unbroken during the phase of the operation during which the switch 59 opens.

If the downstroke of the plunger 12 is obstructed, for example by accidental feeding of several cohering blanks or some other obstacle in the path of the plunger, the pneumatic mechanism permits the drive bar 56 to continue moving until the entire drive mechanism is stopped immediately thereafter due to failure of the plunger switch 60 to close.

Obviously structural details of the yielding drive mechanism may be modified in various respects to fit the requirements of the individual installations.

What is claimed is:

1. In a folding box forming machine in which a reciprocating drive means moves a box shaping plunger into a forming die during a work stroke and out of the forming die during a return stroke, an improved force and motion transmitting coupling between the drive means and the plunger comprising: a pneumatic variable volume chamber means and a hydraulic variable volume chamber means including a charge of liquid therein, said pneumatic means comprising a passage to the atmosphere, and passage control means arranged to close said passage during the work stroke sufficiently to cause a difference in air pressure to build up in the chamber with respect to the atmosphere and to vent the chamber pressure to the atmosphere during the return stroke, said hydraulic means comprising a restricted liquid charge passage and being arranged to undergo compression and discharge of liquid during the return stroke.

2. In a folding box forming machine in which a reciprocating drive means moves a box shaping plunger into a forming die during a work stroke and out of the formingdie during a return stroke, an improved force and motion transmitting coupling between the drive means and the plunger comprising: a pneumatic variable volume chamber means and a hydraulic variable volume chamber means including a charge of liquid therein, said two chamber means being arranged in parallel, said pneumatic means comprising a passage to the atmosphere and a check valve in said passage arranged to close the passage during the work stroke to a degree suilicient to cause a difference in air pressure to build up in said chamber with respect to the atmosphere, and to vent the chamber to the atmosphere upon reversal of the pressure during the return stroke, said hydraulic means comprising a restricted liquid discharge passage and being arranged to experience compression during the return stroke and discharge of liquid through said restricted liquid passage.

3. In a folding box forming machine in which a reciproeating drive means moves a box shaping plunger into a forming die during a work stroke and out of the forming die during a return stroke, an improved force and motion transmitting coupling between the drive means and the plunger comprising: a pneumatic variable volume chamber means and a hydraulic variable volume chamber means including a charge of liquid therein, said pneumatic means comprising a passage to the atmosphere, and passage control means arranged to close said passage during the work stroke sufficiently to cause a diiference in air pressure to build up in the chamber with respect to the atmosphere and to vent the chamber pressure to the atmosphere during the return stroke, said hydraulic means comprising a restricted liquid discharge passage and being arranged to undergo compression and discharge of liquid during the return stroke of said plunger; and motion limiting stop means in parallel with said hydraulic means to become effective during the return stroke after displacement of a certain volume of liquid through said last named passage to render said hydraulic means ineffective during the remainder of the return stroke.

4. In a folding box forming machine in which a reciprocating drive means moves a box shaping plunger into a forming die during a work stroke, and out of the forming die during a return stroke, an improved force and motion transmitting coupling between the drive means and the plunger comprising: a pneumatic first cylinder; a first piston movable relatively to said first cylinder; a hydraulic second cylinder including a charge of liquid therein; a second piston movable relatively to said second cylinder, said first and said second cylinder and piston being arranged in parallel; first air flow control means for said first cylinder and piston, said first air flow control means including an air passage between said first cylinder and the atmosphere, said control means being arranged substantially to seal said air passage during the work stroke, and to open said passage during the return stroke; and second liquid flow control means for said second cylinder and piston, said second control means being arranged to provide low flow resistance to the liquid during the work stroke and high flow resistance during the return stroke.

5. The combination as set forth in the preceding claim 4 in which said second flow control means comprises means for gradually increasing the liquid flow resistance during the progress of the return stroke.

6. In a folding box forming machine in which a reciprocating drive means moves a box shaping plunger into a forming die during a work stroke, and out of the forming die during a return stroke, an improved force and motion transmitting coupling between the drive means and the plunger comprising: a pneumatic first cylinder; a first piston movable relatively to said first cylinder; a hydraulic second cylinder including a charge of liquid therein; a second piston movable relatively to said second cylinder, said first and said second cylinder and piston being arranged in parallel, the said first cylinder and piston defining a chamber in which vacum is created during the work stroke, said second cylinder and piston defining a chamber in which pressure is created during the -above atmospheric pressure; liquid flow control means for said second cylinder and piston, said liquid flow control means being arranged to provide low flow resistance to liquid into said second cylinder during the work stroke, and a higher flow resistance to liquid from said second cylinder during the return stroke, said second control means including means for varying the flow resistance in dependence on the position of said second piston relatively to said second plunger during the return stroke.

7. In a folding box forming machine in which a reciprocating drive means moves a box shaping plunger into a forming die during a work stroke, and out of the forming die during a return stroke, an improved force and motion transmitting coupling between the drive means and the plunger comprising: a first end member; a second end member, one of said end members being adapted to be connected to said drive means, the other end member being adapted to be connected to the plunger; a pneumatic first cylinder mounted on said first end member; a first piston mounted on said second end member, said first piston being movable in said first cylinder and dividing the first cylinder into two chambers; air passage control means comprising means forming an air passage between one of said chambers and the atmosphere and a check valve therein to restrict flow of air between said chamber and the atmosphere to a greater degree in one direction than in the opposite direction; a second cylinder mounted on said first member and constituting an outer cylinder; an inner cylinder mounted within said outer cylinder; a charge of liquid in said outer cylinder, said liquid occupying the space between said inner and outer cylinders; a second piston mounted on said second end member in a position to be movable into and out of said inner cylinder, said second piston having a loose fit with respect to said inner cylinder to permit fluid to escape past said second piston when said second piston enters said inner cylinder; and a check valve between the interior space of said inner cylinder and the space between said inner and outer cylinder, said last named check valve being oriented to open when as a result of withdrawal of said second piston the pressure in said inner piston is reduced.

8. The combination as set forth in the preceding claim 7 in which said second piston has the form of a tapered rod for gradually increasing the flow resistance to liquid flowing from said inner cylinder as the rod passes into said inner cylinder.

9. In a folding box forming machine in which a reciprocating drive means moves a box shaping plunger into a forming die during a work stroke, and out of the forming die during a return stroke, an improved force and motion transmitting coupling between the drive means and the plunger comprising: a first cylinder and piston forming a pneumatic chamber and arranged to create vacuum in said chamber during the work stroke; a second cylinder and piston forming a hydraulic chamber; a charge of liquid in said hydraulic chamber, said second cylinder and piston being arranged to undergo compression during the return stroke; passage forming means through which liquid may flow from the hydraulic chamber during the return stroke, and into said hydraulic chamber during withdrawal of the second piston from the cylinder during the work stroke; and flow control means associated with said passage means for subjecting liquid flow from the hydraulic chamber to greater resistance than liquid flow into the chamber.

10. in a folding box forming machine in which a reciprocating drive means moves a box shaping plunger into a forming die during a work stroke, and out of the forming die during a return stroke, an improved force and motion transmitting coupling between the drive means and the plunger comprising: a first cylinder and piston forming a pneumatic chamber and arranged to create a difierence in pneumatic pressure within said chamber in relation to the atmosphere during the work stroke; a second cylinder and piston forming a hydraulic chamber; a charge of liquid in said hydraulic chamber, said second cylinder and piston being arranged to undergo compression during the return stroke; passage forming means through which liquid may flow from the hydraulic chamber during the return stroke, and into said hydraulic chamber during withdrawal of the second piston from its cylinder during the work stroke; and flow control means associated with said passage means for subjecting liquid flow from the hydraulic chamber to greater resistance than liquid flow into the chamber.

No references cited.

Claims

1. IN A FOLDING BOX FORMING MACHINE IN WHICH A RECIPROCATING DRIVE MEANS MOVES A BOX SHAPING PLUNGER INTO A FORMING DIE DURING A WORK STROKE AND OUT OF THE FORMING DIE DURING A RETURN STROKE, AN IMPROVED FORCE AND MOTION TRANSMITTING COUPLING BETWEEN THE DRIVE MEANS AND THE PLUNGER COMPRISING: A PNEUMATIC VARIABLE VOLUME CHAMBER MEANS AND A HYDRAULIC VARIABLE VOLUME CHAMBER MEANS INCLUDING A CHARGE LIQUID THEREIN, SAID PNEUMATIC MEANS COMPRISING A PASSAGE TO THE ATMOSPHERE, AND PASSAGE CONTROL MEANS ARRANGED TO CLOSE SAID PASSAGE DURING THE WORK STROKE SUFFICIENTLY TO CAUSE A DIFFERENCE IN AIR PRESSURE TO BUILD UP IN THE CHAMBER WITH RESPECT TO THE ATMOSPHERE AND TO VENT THE CHAMBER PRESSURE TO THE ATMOSPHERE DURING THE RETURN STROKE, SAID HYDRAULIC MEANS COMPRISING A RESTRICTED LIQUID CHARGE PASSAGE AND BEING ARRANGED TO UNDERGO COMPRESSION AND DISCHARGE OF LIQUID DURING THE RETURN STROKE.