US3106119A

US3106119A - Automatic product remover for paper cutting machine

Info

Publication number: US3106119A
Application number: US42571A
Authority: US
Inventors: Rothman Henry; Raskin Archie
Original assignee: ROTHMAN
Current assignee: ROTHMAN
Priority date: 1960-07-13
Filing date: 1960-07-13
Publication date: 1963-10-08
Anticipated expiration: 1980-10-08

Description

Oct. 8, 1963 RQTHMAN f 3,106,119

AUTOMATIC PRODUCT REMOVER FOR PAPER CUTTING MACHINE- Filed July 13. 1960 3 Sheets-Sheet 1 I N V EN TORS l/ewev lfiJf/IMAIY BY 14 cm: $4547 AUTOMATIC PRODUCT REMOVER FOR PAPER CUTTING MACHINE Filed July 15, 1.960

Oct. 8, 1963 H. ROTHMAN ETAL 3 Sheets-Sheet 2 INVENTORS Hemqy POrWMA Y By Age/we- Pas/rm W, %M, Wz izfi Oct. 8, 1963 RQTHMAN ETAL 3,106,119

AUTOMATIC PRODUCT REMOVER FOR PAPER CUTTING MACHINE Filed July 13, 1960 5 Sheets-Sheet 3 INVENTORS H6119) forum-w BY flew/E Pas/ m 7 71/1 4, @z/V? a 47 NEYS United States Patent 3,106,119 AUTOMATIC PRODUT REMOVER FOR PAPER CUTTING MACHTNE Henry Rothman, Larchrnont, N.Y., and Archie Raskin, Englewood, NJ; said Raskin assignor to said Rothman Filed Italy 13, 1961), Ser. No. 42,571 Claims. (Cl. (SS-82) This application relates to a paper cutter having means for automatic ejection of the paper after it has been cut and automatic control of the pressure bar that clamps the paper in place to be cut.

Commercial paper cutters used to cut or trim stacks of paper are, by their very nature, dangerous devices to operate. The extent of the danger involved in using them is indicated by the fact that it has been hound necessary to pass strict legislation requiring that certain standards of safety be met in the design of these devices. One of the most critical times in each cycle of operation of such cutters is after the paper has been cut or trimmed when it is necessary to unclamp the remaining paper and to remove it from the cutter. This requires the operator to place his hands directly beneath the blade and the pressure bar in order to grasp the paper.

One of the Objects of the present invention is to provide for automatic ejection of paper after it has been trimmed or out. In addition, the invention provides a controlled sequence of clamping and ejecting the paper under the control of interconnected limit switches.

The invention comprises basically a paper cutter having a horizontal base or bed, a vertically movable pressure bar suspended over the bed and guided by vertical posts at the side of the bed, a suitable knife blade, and a horizontally slidable back gauge mounted on the bed in such a way that it can be positioned at any desired distance behind the pres-sure bar. The front face of the back gauge is serrated and the teeth of a rakelike ram lit within the serrations. The ram is provided with a handle which extends to the rear of the bed and is moved horizontally back and forth between certain limits by means of an actuator. At the rearward limit, the teeth of the ram are completely within the serrations of the back gauge, so that only the front surface of the serrations is contacted by the paper to be cut. After the paper has been cut, the ram is moved forwa-ud to the other limit, at which the teeth are beyond the location of the knife so that the paper may be removed from the cutter without the necessity of the operators ever placing his hands beneath the knife.

At or near the limits of travel of the ram, limit switches are engaged which control the actuator. These limit switches are interconnected in a circuit with additional limit switches that make contact with the pres-sure bar, the whole operation being such as to permit the ram to move forward toward the pressure bar at the forward end of the cutter only when the pressure bar is in its upward position. I

The invention will be described in greater detail in connection with the drawings, in which:

FIG. 1 shows a partial perspective view of the top of part of a paper cutter constructed according to the invention;

FIG. 2 shows the circuit incorporating the limit switches that control the operation of the pressure bar and the ram; 7

FIG. 3 is a partial side view of the paper cutter 0 FIG. 1 with the ram in the extended forward position.

FIG. 4 shows a ditierent embodiment of the actuator for the paper cutter of FIG. 1; and

FIG. 5 shows still another form of actuator.

Referring to FIG. 1, the cutter has a fiat bed or base 11 with a pair of vertical guide posts 12. and13, one on each side of the base. A pressure bar 14 slides in grooves 16 and 17 in the

guide posts

12 and 13, respectively, and is provided with a number of projections 18 extending toward the rear of the cutter to distribute pressure over a Wider area of the paper. The paper itself is inserted into the cutter in stacks, as indicated by reference character 1?, and is pushed toward the rear of the cutter until it comes up against a back gauge 21.

The back gauge 21 is a substantial member with a serrated fnont surface 22 perfectly aligned with the knife blade 23 of the cutter so that the stack of paper 19 may be cut perfectly square. The knife blade 23 may be supported and operated in nny conventional fashion. As shown here, it moves in a pair of

grooves

24 and 26 in the

guide posts

12 and 13, respectively, and operates in the manner of a guillotine.

The elements which have been described so far are standard elements, found in more or less the same form in commercial paper cutters presently available. In addition to these elements, the present invention includes further means to make possible automatic operation of the paper cutter, particularly the ejection of stacks of cut paper. These means provide for automatic interrelated operation of the pressure bar 14 together with automatic ejection of the paper.

The pressure bar 14 is raised and lowered by means of a fluid-operated cylinder 27. The fluid to operate the cylinder may be either hydraulic fluid or air and is supplied to the cylinder through one or the other of two fluid lines 2.9 and 31. This is a conventional fluidoperated cylinder with an internal piston (not shown) connected by a connecting rod 32 to the pressure bar 14. The valve means for controlling the fluid flow to one or the other of the

lines

29 and 31 may be conventional and need not be described in detail. It is sufiicient to note that when it is desired to raise the pressure bar 14, the fluid is admitted through the line 31 to the lower side of the enclosed piston within the cylinder 27 and withdrawn from the upper side of the cylinder 27 by way of the upper line 29. Conversely, when it is desired to push the pressure bar 14 down against a stack of paper 19, the fluid is admitted via line '29 to the upper portion of the cylinder 2''] and withdrawn through the line 31 of the lower portion. The degree of pressure applied to the pressure bar 14 by the fluid-operated cylinder 27 is quite suificient to hold a stack of paper 19 in place and may be varied as desired. When the pressure bar 14- is at the upper limit of its field of travel, it actuates the arm of a limit switch 33, and when it is at the lower end of its range of travel and down against a stack of paper 19, it actuates a lower limit switch 34. As a matter of fact, the limit switch 33 may be located where it can be actuated by either of the veitically moving members, the knife blade 23 or the pressure bar 14, at the upper part of the range of travel of the vertically moving member. These switches are interconnected in a circuit which will be described hereinafter.

The means for ejecting a stack of paper 19 from the cutter after the paper has been cut or trimmed includes a ram 36 which is somewhat similar to a garden rake and is provided with downwardly extending teeth 37 that fit into the serrations in the front side 22 of the back gauge 21. The cam 36 has a handle, or pusher, 38 extending to the rear and supported in two journals 39' and 41. Motive power to force the ram forward in order to eject a stack of paper 19 from the cutter is supplied by means of a ram actuator 42 which may be an electric motor or, as will be described hereinafter, other suitable motive means. In the case of an electric motor, the actuator 42 has an output shaft 43 which is connected through a crank arm 44 to a connecting rod 46. The connecting rod 46, in turn, is connected by means of a pivot block 47 to the pusher rod 38, so as to supply force to move the ram 36 back and forth. At the forward end of its range of travel the block 47, which is rigidly attached to the bar 38, actuates a forward limit switch 48 and at the rear extreme of its range of travel the block 47 actuates another limit switch 49. The journals 39 and 41 in which the bar 38 rides and the actuator 42, together with the

limit switches

43 and 49, are all mounted on a support bracket or plate 51 which is attached by means of

bolts

52 and 53 to the back gauge 21 to move therewith. In this way, it may be assured that the ram 35 will, at the rear of its range of travel, always be retracted sufiiciently to make the teeth 37 come within the serrations in the front side of the back gauge 21. As a result, only the front surface 22 of the back gauge 21 will be in contact with the paper 19' during the time that the paper is in the cutter, and the teeth 37 of the ram 36 will contact the paper 19 only during such time as the paper is being ejected from the cutter. This permits the location of cut to be determined very accurately by the precise distance between the knife blade 23 and the front surface 22 of the back gauge 21, and there is no need to be as accurate in the manufacture of the ram 36 or the insertion of its teeth 37.

The operation of the cutter of FIG. 1 will be de scribed with reference to the electrical circuit of FIG. 2. At the beginning of a cycle of operation the pressure bar 1 and the knife blade 23 are at the tops of their ranges of travel so as to leave space for a stack of paper to be inserted between the guide posts 12 and i3 and pushed against the back gauge 21. In order to permit the paper to be pushed all the way against the back gauge 21. In order to permit the paper to be pushed all the way against the front surface 2-2 of the back gauge, the ram must be at the rear of its range of travel which means that the block 47 will be against the limit switch 49. As indicated in FIG. 2, this limit switch is normally closed and, therefore, being actuated by the block 47 means that it is in the open state at the beginning of the cycle.

After the paper 19 has been pushed into place, the cylinder 27 is actuated to bring the pressure bar 14 down against the paper. This is accomplished by directing pressure fluid into the upper line 29' and withdrawing it from the lower line 31. In moving down the pressure bar 14 actuates the lower limit switch 34. This switch is of the normally-open type, and actuating it closes it.

The limit switch 34 is connected to one of a pair of

electrical supply lines

52 and 53 which may either be an ordinary single-phase line or two lines of a threephase circuit. The switch 34 is further connected in series with the coil of a relay 54. This relay is provided with a normally-closed contact 54a and a normally-open contact 54b. In the unenergized state of the relay the movable contact 54a is closed in series with the power supply line 53. The coil of the relay 54 is energized from the

lines

52 and 53 by way of the switch 34 and he normally-closed contacts Immediately upon being energized when the pressure bar closes the switch 34, the relay 54; moves the arms of the contact pairs 54a and 54b to their alternative positions. The alternative position of the arm of contacts 54a is against a contact S te which is connected to a line 56 which in turn is connected to one terminal of the coil of the relay 57 and to normally-closed contacts 58a of a relay 58. Relay 58 is, at this time, not energized, because the block 4'7 is pressing against the normally-closed switch 49, holding it open. In the unenergized state of the relay 58, the contacts 58a form a closed circuit with the power supply line 53. As a result, when the relay 54 is energized and the arm of contacts 54a moves to the energized position, the relay 54 remains energized because it then derives current from the line 53 by way of the line 56 and the normally-closed contacts 58a of the relay 58. Furthermore, the energized position of the normally-open contacts 54b completes a circuit directly to the power supply line 52. Since the movable arm of the contacts 54-12 is also connected to the junction between the switch 3 and the coil of the relay 54, the relay 54 remains energized even'after the pressure bar 14 moves up and out of contact with the switch 34.

The reason that the pressure bar 14 moves up away from the switch 34 and away from the paper 19 is that fluid in the cylinder 27 has been removed by way of the upper line 29 and has been supplied to the lower end of the cylinder by way of the line 31. Again, this part of the operation is standard and not part of the present invention.

As a result of the release of pressure on the stack of paper 19 when the pressure bar 14 moves up, the paper is free to be ejected from the cutter. This occurs when the pressure bar 14 moves up into contact with the arm of the upper limit switch 23. As shown in FIG. 2, the limit switch 33a is connected in series with the contacts 54!), which are now closed, so that the switch 33 is directly connected to the supply line 52. Thus, when the pressure bar 14 moves up and actuates the switch 33, the relay 57 is energized from

lines

52 and 53 via

switches

33 and 48 and the normally-closed contacts 58a. When the relay 57 is actuated it closes the normally open contacts 57b and 57c at the same time that it opens the normally closed contacts 57a. The contacts 57b and 57c are connected in series between the

power supply lines

52 and 53 and an actuator control 42 This control energizes the actuator 42 of FIG. 1 to cause it to push the ram 36 forward so as to eject the stack of paper 19 from the cutter. If the actuator 42 is a motor the control circuit 42f therefor may be simply the field windings of the motor connected so as to cause the motor to operate in one direction.

The actuator control circuit 42f remains energized so long as the relay 57 is energized which in turn is governed by the normally closed limit switch 48. As soon as the ram reaches its forwardmost position at which the block 47 engages the limit switch 4-8, the latter opens up thereby opening the circuit through which the relay 57 is energized. As a result the relay 57 becomes deenergized and the normally open contacts 5% and 570 open up thereby de-energizing the forward actuator control circuit 42 At the time that the ram 36 starts forward the block 47 moves away from the rear limit switch 49 thereby allowing the latter to return to its normally closed condition. However, the relay 58 which is in series with the limit switch 49 is not immediately energized because at this time the relay 57 is energized and the normally closed contacts 57a are open. It is only after the block 47 engages the forward limit switch 48 and opens it up so as to allow the relay 57 to become de-energized that the normally closed contacts 57a can return to their closed state and permit the relay 58 to be energized by a circuit including the normally closed limit switch 49, and the normally closed contacts 57a. Energizing the relay 58 causes the normally open contacts 58b and 58c to close. These contacts are in series with the

power supply lines

52 and 53 and a reverse-control 421* for the actuator 42. Again, in the event that the actuator is an electric motor, the reverse-control 42r may simply be the field windings of the motor connected to cause the motor to rotate in the reverse direction. This places the circuit and the cutter back in its original condition ready to receive a new load of paper.

FIG. 3 shows a partial side view of the cutter of FIG. 1 with some of the parts broken away to show the interior. Part of the bed 11 is broken away to show a a feed arrangement for adjusting the position of the back gauge 21. This feed arrangement consists of a feed screw 61 cooperating with a threaded member 62. This threaded member rides upon a guide bar 63 and is actually the base of the back gauge 21. Rotating the feed screw 61 by means of a handle which is of the custom-ary type and is not shown, causes the threaded member 62, to move backward or forward depending upon the direction of rotation of the screw and thus bring the back gauge 21 closer to or farther from the knife blade 23.

FIG. 3 also shows the mounting of the plate 51 on the back gauge 21. In the condition shown in FIG. 3, the ram 36 is advanced to its forwardmost position and the connecting arm 46 is directly in line with the crankarm 44. As may be seen, in this condition the stack of paper 19 has been pushed completely out from under the knife blade 23 so that there is no necessity for the operators getting his hands under the blade or under the pressure arm 44 to the connecting rod 46 travels along a circular path indicated by the arc 66. Because of this inerrant oscillating motion, due to the circular path, it is not necessary for the direction of the rotation of the shaft 43 to be reversed; the actuator could simply be permitted to continue in one direction until the block 47 returned to the rear limit switch 49 arid de-energized the actuator.

FlG. 4 shows a different type of actuator. In this figure the actuator is a fluid-operated cylinder which may be either operated by air or by hydraulic pressure. The cylinder is indicated by reference character 142 and has

fluid lines

67 and 68 connected to opposite ends of the cylinder in the customary fashion to cause the piston (not shown) within the cylinder 142 to move either to the left or to the right. This piston is directly connected to the rod 138 which corresponds to the rod 38 of FIGS. 1 and 3 and so pushes the ram 36 or pulls it as required. The fluid pressure supplied to one or the other of the lines 67 andcfi is controlled by the customary solenoid operated valve 69. This is a four-way valve which either supplies fluid pressure to the lines 67 and withdraws it at the same time from the lines 68 so as to move the ram 36 to the left or reverses the foregoing condition and supplies pressure to the lines 68 and withdraws it from the lines 67 to cause the ram 36 to return to the right to its plam within the serrated portion of the b ack gauge 21. In the case of a solenoid operated valve system such as this the forward control circuit 42 of FIG. 2 may be one of the valve solenoids and the reverse oontrol circuit 42; may be the other since there are normally two.

FIG. 5 shows still another modification of the actuator arrangement. In this case a bracket 71 is mounted on the back gauge 21 and is provided with two threaded upright members 72 and 73. A long feed screw 74 which takes the place of the rod 38 of FIGS. 1 and 3, is threaded through the uprights 72 and 73 and is connected to the ram 36 at its forward end. A gear 76 is aifixed to the feed screw 74 so that when the gear rotates the feed screw rotates with it. The gear is connected by means of an internally toothed rfeed belt 77 to another gear '73 on the shaft of a motor 242.

When the motor 242 is energized by the forward control circuit 42 to turn in one direction, the gear 78 turns with the shaft of the motor causing the belt 77 to turn with it and thereby to turn the lower gear '76. This in turn rotates the feed screw 74 which moves forward in the threaded uprights 72 and 73 to push the ram 36 to the left. Conversely, when the direction of rotation of the motor 242 is reversed the gear 78 and the belt 77 are driven in a reversed direction driving the lower gear 76 in reverse direction and causing the feed screw 74 to return to its original position.

While the invention has been described in terms of certain specific embodiments it will be recognized by those skilled in the art that modifications may be made therein which will still be within the scope of the following claims.

What is claimed is:

1. A paper cutter comprising a base; a pressure bar perpendicularly movable with respect to said base; a knife located adjacent to said pressure bar and movable to cut the paper disposed on said base, means to drive said pressure bar and knife substantially simultaneously through an upper and lower region of travel; a back gauge on said base; a ram; an actuator for said ram fixedly mounted with respect to said back gauge, said actuator having controllably movable means connected to said ram to move said ram longitudinally along said base from said back gauge to a more forward location and to return said ram to a rearward location adjacent to said back gauge; a first limit switch located to be actuated by said pressure bar when said pressure bar is at the upper region of its range of travel; a second limit switch located to be actuated by said pressure bar when said pressure bar is at its lower region of its range of travel; a third limit switch located to be actuated when said ram is in the forward portion of its range of travel; a fourth limit switch located to be actuated when said ram is in the rearward region of its range of travel, and a circuit connecting said limit switches and said ram actuator whereby said actuator is energized when said first limit switch is actuated after said second limit switch has been actuated so as to push the ram forward to eject paper from said cutter, and said third limit switch is actuated when said ram is in the forward position to reverse the movement of said actuator to return said ram to the rearward position.

2. A paper cutter comprising a base; a pressure bar perpendicularly movable with respect to saidbase; a knife located adjacent to said pressure bar and movable to cut the paper disposed on said base, means to drive said pressure bar and knife substantially simultaneously through an upper and lower region of travel; a back gauge movably mounted on said base; a ram; an electric motor actuator for said ram fixedly mounted with respect to said back gauge to move therewith; movable means connecting the shaft of said motor to said ram to move said ram longitudinally along said base fromsaid back gauge to a more forward location and to return said ram to a rearward location adjacent to said back gauge; a first limit switch located to be actuated by said pressure bar when said pressure bar is at the upper region of its range of travel; a second limit switch located to be actuated by said pressure bar when said pressure bar is at its lower region of its range of travel; a third limit switch located to be actuated when said ram is in the rearward region of its range of travel, and a circuit connecting said limit switches land said motor whereby said motor is energized when said first limit switch is actuated after said second limit switch has been actuated so as to push the ram forward to eject paper from said cutter, and said third limit switch is actuated when said ram is in the rearward position to halt the operation of said motor when said ram returns to the rearward position after ejecting the paper.

3. A paper cutter comprising a base; a pair oif vertically moving members, one of said members being a pressure bar perpendicularly movable with respect to said base, the other of said members being a knife located adjacent to said pressure bar and movable to cut the paper disposed on said base, means to drive said pressure bar and kru'fe substantially simultaneously through an upper and lower region of travel; :a back gauge movably mounted on said base; a ram; a reversible motor actuator for said ram fixedly mounted on said back gauge to move therewith; a crank arm and a connecting rod connecting the shaft of said motor to said ram to move said ram longitudinally along said base from said back gauge to a more forward location and to return said ram to a rearward location adjacent to said back gauge; a first limit switch located to be actuated by one of said vertically moving members when said one of said vertically moving members is at the upper region of its range of travel; a second iimit switch located to be actuated by said pressure bar when said pressure bar is at its lower region of its range of travel; a third limit switch located to be actuated when said rain is in the forward portion of its range of travel; a fourth limit switch located to be actuated when said ram is in the rearward region of its range of travel, and a circuit connecting said limit switches and said motor whereby said motor is energized when said first limit switch is actuated after said second limit switch hast been actuated so as to push the ram forward to eject paper from said cutter, and said third limit switch is, actuated when said ram is in the forward position to reverse said motor to return said ram to the rearward position.

4. A paper cutter comprising a base; a pressure bar perpendicularly movable with respect to said base; a knife located adjacent to said pressure bar and movable to cut the paper disposed on said base, means to drive said pressure bar and knife substantially simultaneously through an upper and lower region of travel; a back gauge movably mounted on said base and having a serrated face; a ram having a reversible motor actuator for said ram fixedly mounted with respect to said back gauge to move therewith; a crank arm and a connecting rod connecting the shaft of said motor to said ram to move said ram longitudinally along said base from said back gauge to a more forward location and to return said ram, to a rearward location with said I usher means fitting within said serrated face; a first limit switch located to be actuated by said pressure bar when said pressure bar is at the upper region of its range of travel; a second limit switch located to :be actuated by said pressure bar when said pressure bar is at its lower region of its range of travel; a third limit switch located to be actuated when said ram is in the forward portion of its range of travel; a fourth limit switch located to be actuated when said ram is in the rearward region of its range of travel, and a circuit connecting said limit switches and said motor whereby said motor is energized when said first limit switch is actuated after said second limit switch has been actuated so as to push the ram forward to eject paper from said cutter, and said third limit switch is actuated when said ram is in the forward position to reverse said motor to return said ram to the rearward position.

5. A paper cutter comprising a base; a pressure bar perpendicularly movable with respect to said base; a knife located adjacent to said pressure .bar and movable to cut the paper disposed on said base, means to drive said pres.- sure bar and knife substantially simultaneously through an upper and lower region of travel; a back gauge movably mounted on said base; a ram; a reversible motor actuator for said ram fixedly mounted on said back gauge to move therewith; a crank arm and a connecting rod connecting the shaft of said motor to said ram to move said ram longitudinal ly along said base from said back gauge to a more forward location and to return said rarn to a rearward location adjacent to said back gauge; a first limit switch located to be actuated by said knife when said knife is at the upper region of its range of travel; a second limit switch located to be actuated by said pressure bar when said pressure bar is at its lower region of its range of travel; a third limit switch located to be actuated when said ram is in the forward portion of its range of travel; a fourth limit switch located to be actuated when said ram is in the rearward region of its range of travel, and a circuit connecting said limit switches and said motor whereby said motor is energized when said first limit switch is actuated after said second limit switch has been actuated so as to push the ram forward to eject paper from said cutter, and said tird limit switch is actuated when said ram is in the forward position to reverse said motor to return said ram to the rearward position.

References Cited in the file of this patent UNITED STATES PATENTS 947,360 Wallenthin Ian. 25, 1910 1,653,303 Mulroney Dec. 20, 1927 2,009,487 Ernst July 30, 1935 2,259,576 MacMillin Oct. 21, 1941 2,613,592 Nemir Oct. 14, 1952 2,752,847 Vandenburgh July 3, 1956 FOREIGN PATENTS 13,398 Great Britain Oct. 4, 1887 838,740 Germany May 12, 1952

Claims

5. A PAPER CUTTER COMPRISING A BASE; A PRESSURE BAR PERPENDICULARLY MOVABLE WITH RESPECT TO SAID BASE; A KNIFE LOCATED ADJACENT TO SAID PRESSURE BAR AND MOVABLE TO CUT THE PAPER DISPOSED ON SAID BASE, MEANS TO DRIVE SAID PRESSURE BAR AND KNIFE SUBSTANTIALLY SIMULTANEOUSLY THROUGH AN UPPER AND LOWER REGION OF TRAVEL; A BACK GAUGE MOVABLY MOUNTED ON SAID BASE; A RAM; A REVERSIBLE MOTOR ACTUATOR FOR SAID RAM FIXEDLY MOUNTED ON SAID BACK GUAGE TO MOVE THEREWITH; A CRANK ARM AND A CONNECTING ROD CONNECTING THE SHAFT OF SAID MOTOR TO SAID RAM TO MOVE SAID RAM LONGITUDINALLY ALONG SAID BASE FROM SAID BACK GAUGE TO A MORE FORWARD LOCATION AND TO RETURN SAID RAM TO A REARWARD LOCATION ADJACENT TO SAID BACK GAUGE; A FIRST LIMIT SWITCH LOCATED TO BE ACTUATED BY SAID KNIFE WHEN SAID KNIFE IS AT THE UPPER REGION OF ITS RANGE OF TRAVEL; A SECOND LIMIT SWITCH LOCATED TO BE ACTUATED BY SAID PRESSURE BAR WHEN SAID PRESSURE BAR IS AT ITS LOWER REGION OF ITS RANGE OF TRAVEL; A THIRD LIMIT SWITCH LOCATED TO BE ACTUATED WHEN SAID RAM IS IN THE FORWARD PORTION OF ITS RANGE OF TRAVEL; A FORTH LIMIT SWITCH LOCATED TO BE ACTUATED WHEN SAID RAM IS IN THE REARWARD REGION OF ITS RANGE OF TRAVEL, AND A CIRCUIT CONNECTING SAID LIMIT SWITCHES AND SAID MOTOR WHEREBY SAID MOTOR IS ENER-