US 3836017 A
The conveyor is disposed on a predetermined level. The height of the stack is changed by the transfer of articles by said apparatus. Pivotal mounting means are vertically movably mounted on a frame and define a horizontal axis. A rocker arm assembly is pivoted to said mounting means on said axis for a rocking movement through substantially 180 DEG and has an outer end which is remote from said pivotal axis. A gripper is carried by said rocker arm assembly at said outer end and adapted to hold articles. Vertical drive means are provided to adjust said pivotal axis in height during a rocking movement of said rocker arm assembly. Rocking drive means cooperate with said pivotal mounting means to impart to said rocker arm assembly a pivotal movement through 180 DEG . connecting means are connected between said vertical drive means and said rocking drive means and serve to impart to said rocker arm assembly a rocking movement in dependence on the vertical movement of said pivotal mounting means. Means are provided to define a reference level which is spaced a predetermined vertical distance above said stack.
Claims available in
Description (OCR text may contain errors)
United States Patent [1 1 Bargstedt 1 Sept. 17, 1974 1 APPARATUS FOR TRANSFERRING ARTICLES BETWEEN A CONVEYOR AND A STACK  Inventor: Gerd Bargstedt,Wischhafenersand 91, 2161 Drochtersen, Germany  Filed: June 13, 1972  App]. N0.: 262,285
 Foreign Application Priority Data June 15, 1971 Germany 2129576  US. Cl 214/6 FS, 214/1 BV, 214/8.5 D  Int. Cl. B65g 57/04  Field of Search 214/6 FS, 6 A, 6 P, 6 G, 214/6 DK, 309, 1 BD. 1 EV, 8.5 C, 8.5 D, 8.5 H
 References Cited UNITED STATES PATENTS 2,832,478 4/1958 Malewicz et al. 214/1 BD 3,095,082 6/1963 Allgeyer 214/1 BD 3,178,041 4/1965 Wheat 214/6 FS X 3,587,888 6/1971 Warren 214/1 BV 3,617,054 11/1971 Schilling.... 214/1 BD 3,675,790 7/1972 Avril 214/6 G X Primary ExaminerRobert J. Spar Attorney, Agent, or FirmToren, McGeady and Stanger  ABSTRACT The conveyor is disposed on a predetermined level. The height of the stack is changed by the transfer of articles by said apparatus. Pivotal mounting means are vertically movably mounted on a frame and define a horizontal axis. A rocker arm assembly is pivoted to said mounting means on said axis for a rocking movement through substantially 180 and has an outer end which is remote from said pivotal axis. A gripper is carried by said rocker arm assembly at said outer end and adapted to hold articles. Vertical drive means are provided to adjust said pivotal axis in height during a rocking movement of said rocker arm assembly. Rocking drive means cooperate with said pivotal mounting means to impart to said rocker arm assembly a pivotal movement through 180. connecting means are connected between said vertical drive means and said rocking drive means and serve to impart to said rocker arm assembly a rocking movement in dependence on the vertical movement of said pivotal mounting means. Means are provided to define a reference level which is spaced a predetermined vertical distance above said stack.
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APPARATUS FOR TRANSFERRING ARTICLES BETWEEN A CONVEYOR AND A STACK This invention relates to an apparatus for stacking or unstacking articles, which apparatus provides for a transfer of articles between a conveyor disposed on a predetermined level, and the top of a stack which changes ih height, and which apparatus comprises a rocker arm assembly, which is pivotally movable through substantially 180 and which is movable in height and at one end carries a gripper, and in which apparatus a vertical drive cooperates with a rocking drive.
An application of the invention is found in the stacking of plates. The gripper may consist, e.g., of vacuum cups.
A rocker arm assembly consists, e.g., of two parallel rocker arms, between which a cross-beam is provided, which carries the vacuum cups. That cross-beam is rotatably mounted and driven so that the vacuum cups always face downwardly.
In a known design disclosed in Opened German Application 1,907,763 the pivotal mounting means for the rocker arm assembly is repeatedly moved in height by a drive chain as far as to the upper reversing sprocket of the chain and the rocker arm assembly when it has reached its uppermost position is pivotally moved through 180. This results in a sudden, high acceleration of the gripper at the outer end of the rocker arm assembly.
Regardless of the height of the conveyor or the top of the stack, the rocker arm assembly is moved always to its uppermost position before it is pivotally moved and there is no vertical movement during the pivotal movement. After the pivotal movement, the vertical movement in the other sense is continued by the oneway coupling to the drive chain.
That design has the disadvantage that the velocity of the pivotal movement is suddenly increased and that it involves long and changing times of operation because the lifting and lowering movements along the stack take different times in dependence on the height of the stack.
it is an object of the invention to provide an apparatus which is of the kind stated above and which when used in conjunction with a stack placed on the floor and changing in height depending on the nature of its processing ensures that the transfer path from the top of the stack to the conveyor and vice versa is as short as possible.
This object is accomplished according to the invention in that the pivot bearings or the rocking shaft for the rocker arm assembly is adjustable in height during the rocking movement and the uppermost position of the pivot bearings or the rocking shaft is variable in dependence on a changing reference level above the stack. It will be of special advantage if the pivotal movement and the vertical movement begin and terminate substantially at the same time.
In the apparatus according to the invention the rocker arm assembly is lifted only to the level which is required in view of the instantaneous height of the stack so that excessive vertical movements are avoided. The speed of operation is further increased in that the vertical movement and pivotal movement overlap in time. A high speed of operation is also enabled in that the velocity changes in accordance with a sine function resulting in a gradual acceleration to the highest speed and a subsequent deceleration. important features of the invention reside in the coupling of the vertical drive with the drive means and in the variability of the vertical drive. In practice, the change of the vertical drive results in a change of the are along which the gripper is pivotally moved and in a change of the length of the transfer path thereof so that the gripper actually travels only over the distance which is required in each case.
The vertical drive consists desirably of a crank member and the length of the crank member is variable in dependence on the height of the stack. As a result, the length of the crank member can be selected so that the crank member when moving between two end positions determines the uppermost and lowermost positions of the rocker arm assembly. The effective length of the crank member is adjustable in dependence on the change of the height of the stack.
The crank arm comprises suitably a screw or rack along which a nut or pinion, respectively, is movable. This nut or pinion is connected to a drive motor and provides an adjustable stop defining the effective length of the crank member.
In a preferred arrangement, the nut or pinion is provided with a chain sprocket, which is preferably freely rotatable and around which a vertical drive chain is trained, one end of which is connected to a vertically movable bearing plate for the rocker arm assembly whereas the other end of the chain is connected to that end of the crank member which serves as a permanent point of reference for the change of the length of the crank member. This permanent point of reference ensures that there will always be a fixed reference point for one end position in dependence on the change in length of the crank member. This one end position may be, e.g., the end position for the conveyor, which has a certain overall height. The other end position of the pivotal movement is adjusted in dependence on the changing height of the stack.
It is also preferred to provide the crank member in the form of a double crank, which extends from its axis 7 of rotation on both sides. This feature enables the provision of a 1:2 transmission ratio regarding the speed and the travel of the rocker arm assembly so that the machine can be designed more economically. Besides, the mass distribution is improved. The double crank has further advantages, which will be explained hereinafter, in special applications.
In a desirable embodiment, the double crank carries at one end the drive motor for a rotation of the screw and the chain is secured to that end. That end is the point of reference for the fixation of the drive chain.
In a particularly desirable embodiment the drive means consist of a crank mechanism and are arranged so that the rocker arm assembly is in one end position of its path of travel when a connecting rod and/or rack which is driven by the crank mechanism and operatively connected to the shaft of the rocker arm assembly is aligned with the crank. This arrangement will result in a change in speed according to a sine function resulting in an automatic deceleration or braking of the movement before each end position.
The crank mechanism is provided with a capstan head, to which the rack is linked. That feature will be adopted if predetermined larger distances are to be traveled.
In an arrangement which comprises a frame having columns in which bearing plates carrying the rocker arms are guided for vertical movement, a particularly desirable feature resides in that the drive shaft for the crank mechanism and the crank member or double crank of the vertical drive extend vertically and are provided on a cross-member between the vertical guides, and the bearing plates are provided with a drive chain for the crank member or double crank. The resulting arrangementis relatively light in weight and is economically composed of several parts.
In a desirable embodiment, an abutment of the chain is adjustable at a bearing plate to enable a selection of the reference height over the conveyor means. A handwheel may be provided for this adjustment. It is also preferred to provide for an automatic adjustment of the adjustable abutment in step with the cyclic operation of the machine and for this purpose to provide the adjustable abutment'in the form of a pneumatic or hydraulic actuator, which imparts to the gripper an initial or final stroke when the rocker arms have reached their end positions. In conjunction with the above-mentioned manual adjustment, the actuator would then be adjustable at the bearing plate in a vertical direction.
It is also pointed out that particularly desirable conditions will be obtained if a crank of the crank mechanism and the crank member or double crank of the vertical drive are parallel to each other. As a result, the rocking drive and vertical drive are synchronized, as is essential for the invention.
The crank mechanisfn suitably drives a square shaft, which constitutes a drive element for a bevel gearing provided on the stub shaft of the rocker arm assembly, and a drive gear is slidably mounted on the square shaft. In such an arrangement, a torque-transmitting member comprising four rollers is preferably provided between the square shaft and a housing for the driving bevel gear, which housing carries a stub shaft of the rocker arm assembly, and said four rollers roll on re spective side faces of the square shaft. This results in a particularly low-friction driving connection.
In another embodiment the double crank is provided on a horizontal stub shaft and provided with a cam slot, and a sliding block guided in said cam slot is connected by a pivoted rod to a vertically guided member, which is adjustable in height in dependence on the height of the stack. This arrangement is disclosed to show that the embodiments described and shown by way of example are not the only ways to carry out the invention. For
the same reason it is pointed out that in'another suitable arrangement the double crank non-rotatably secured to the rocker arm assembly is connected by a linkage to a drive shaft on which the drive motor is provided and the drive shaft is in mesh with a rack to change the distance from the rocker arm assembly, the vertical drive being connected to a drive wheel in the double crank.
In another embodiment, the double crank comprises a rack, which meshes with a pinion connected to a drive motor for changing the effective length of the double crank. This pinion meshes also with a rack which is pivoted to the frame.
In the described arrangement, the vertically movable rocker arm assembly is provided with a counterweight, which is guided in the columns and connected by a rope to at least one bearing plate of the rocker arm assembly. This embodiment is characterized according to the invention in that the rope is connected to the rocker arm assembly at a point which is spaced from the pivot bearing thereof and exerts an opposing torque so that the drive power is utilized in a particularly desirable manner.
The invention will now be explained with reference to embodiments shown by way of example in the drawing, in which FIG. 1 is a front elevation showing an apparatus according to the invention,
FIG. 2 is a side elevation of FIG. 1,
FIG. 3 is a fragmentary top plan view showing the left-hand half of FIG. 1,
FIG. 4 is a fragmentary top plan view showing the right-hand half of FIG. 1,
FIG. 5 is a top plan view of FIG. 1, partly in a section taken on line VV in FIG. 1, and shows only the parts intended to drive the rocker arm assembly,
FIGS. 6 and 7 are enlarged fragmentary end views of FIG. 1,
FIGS. 8 to 8e are diagrammatic representations of the sequence of motion in another embodiment,
FIG. 9 is an enlarged view showing essential elements of the embodiment of FIG. 8, and
FIG. 10 is a diagrammatic side elevation showing the apparatus provided with the elements of FIGS. 8 and 9.
A preferred embodiment is shown in FIGS. 1 to 7, wherein like parts are designated with like reference characters.
As is particularly apparent from FIGS. 1 and 2, two columns 3, 4 are provided beside a support for a stack 2. This support consists of a roller conveyor 1. Bearing plates 5, 6 are vertically movably guided on the columns 3, 4. The bearing plate 5 is provided, e.g., with the guide rollers 7, 8, 9, 10, which roll on different sides of a flange 11. The rollers 7, 8 are shown by way of example in FIG. 5.
The rollers 13, 14 of the bearing plate 6 roll on the corresponding flange 12 of column 4.
The columns are connected at the top by a crossbeam 15.
In the rocking drive means of the invention, the bearing plates 5, 6 are provided with pivot bearings 16, 17 for the rocker arm assembly which comprises the rocker arms 18, 19, which are connected by a crossbeam 20 carrying the vacuum cups 21, 22.
A parallel-holding shaft 23 is rotatably mounted in the bearing plates 5, 6 and is provided at its ends with pinions 24, 25, which mesh with racks 26, 27 of the columns 3, 4. As a result, the two bearing plates 5, 6 are constrained to move parallel to each other.
A stub shaft 28 extending through the pivot bearing 17 is rotatably mounted in a bevel gear housing 29 and connected to a bevel wheel 30, which meshes with a bevel wheel 31 in the housing 29. The bevel wheel 31 is slidably and nonrotatably mounted on a square shaft 32, which is parallel to the column 4. The bevel wheel 31 is connected to a torquetransmitting member, which is generally designated 33 and by means of a swivel member 34 is mounted on the housing 29 and imparts rotation to the bevel wheel 31 and the square shaft 32.
It is apparent from FIG. 5 that the torquetransmitting member 33 comprises a capstan head, in which four rollers 35, 36, 37, 38 are rotatably mounted, which roll on the sides of the square shaft 32 so that the rotational adjustment of the square shaft is transmitted to the bevel wheel 31 with relatively low friction. The square shaft 32 is rotatably suspended at its upper end in an end journal bearing 39 on the cross-beam and carries a pinion 40 in mesh with a rack 41 (see also FIG. 4), which is held in mesh by means of a backing roller 42. The rack itself is pivoted on a pivot pin 43 in a capstan head 44, which is slidably guided on the cross-beam 15.
A cranked connecting rod 45 is also connected to the pivot pin 43 and is rotatably mounted on the pin 46 of a crank 47. By means of the reversible drive motor 48 and a rope or chain 49 trained around a rope pulley or chain sprocket 50 the crank 47 is pivotally movable through steps of 180 along an arc of a circle 51 shown in FIG. 3.
Together with the crank 47, the vertical drive means of the invention are shown to include a double crank generally designated 53 which is mounted on the same drive shaft 52 carrying the sprocket 50. The double crank extends, e.g., equal distances from the drive shaft 52 on both sides. In the embodiment shown by way of example, a screw 55 is rotatably mounted in the double crank and connected to a gearmotor 56, which is operated in dependence on the height of the stack to move a traveling nut 57 from the opposite end 58 as the stack decreases in height. A chain sprocket 59 is freely rotatably mounted on the traveling nut beside an element 60 for guiding the chain to ensure a constant engagement. During a pivotal movement of the crank through 180", the end designated 58 moves along the arc of a circle 61. The chain sprocket 59 may be displaced beyond the shaft 52 to that end of the double crank at which the gearmotor 56 is disposed. The drive chain 62 is trained around the chain sprocket 59 and is secured at 63 to that end toward which the chain sprocket 59 is moved. As a result, a fixed reference level over the conveyor 64 (FIG. 2) is provided for the vertical adjustment of the rocker arms. It should be taken into account that this reference position is established in that the end provided with the fixing means 63 is pivotally moved outwardly relative to the cross-beam whereas the double crank 53 is aligned with the cross-beam. A closer approach of the fixing means 63 to the other abutment of the chain 105 is not possible.
It is apparent that the gearmotor 56 is connected by a chain drive 65 to the screw 55.
The use of the double crank with the chain sprocket 59 affords the advantage that a 1:2 transmission ratio is obtained for the movement and speed.
The chain 62 is guided in the capstan head by two guide sprockets 66, 67 to extend to a chain sprocket 68 disposed adjacent to the column 4. An intermediate chain fastener 69 is provided in an intermediate position and changes the orientation of the chain for meshing through 90 in accordance with the orientation of the guide sprocket 66, 67 and of the chain sprocket 68. The chain end 105 guided over the chain sprocket 68 is secured to an abutment, which in accordance with FIGS. 1 and 2 consists of an end portion of the piston rod 70 of a cylinder-piston unit 71, which is mounted in the bearing bracket 6. The cylinder-piston unit 71 is vertically adjustable along guide rods 72, 73 by means of a screw 74 and a handwheel 75. The height of the support provided by the cross-beam can be adjusted in the directions of the double arrow 76 in FIG. 2 in dependence on the vertical adjustment. This adjustment could also be effected by a corresponding vertical adjustment of a hooklike abutment. The cylinder-piston unit 71 also cooperates with a control means not shown in detail in such a manner that the last approximately 50 millimeters of the vertical movement are added in each end position to the movement of the rocker arm assembly so that a careful handling is enabled.
In the embodiment described thus far, the crossbeam 20 and the vacuum cups 77 can move along the dotted line 78 so that the vacuum cups are raised only to the extent required to lift a top plate from the stack 2 and as a result of the simultaneous displacement of the bearing plates 5, 6 are then moved downwardly and laterally and thereafter downwardly beyond the center of the top of the conveyor 64. This matching of the movements is accomplished in that the double crank 53 has the same drive imparted to it as the crank 47 for the pivotal movement of the rocker arms. The gearmotor 56 can be controlled by stack height sensing means such as photoelectric means 56a for detecting the height of the stack or, alternatively by a step-by-step switch, the steps of which correspond to the height of individual articles of the stack 2.
The motion curve 78 indicates that the transfer is effected along a path which is as short as possible.
As is apparent from FIG. 5, a drive chain 79 is connected between the rocking shaft and the cross-beam 20, which carries the vacuum cups 21, 22 and which is rotatably mounted in the rocker arms 18, 19. The drive chain 79 is trained around a chain sprocket 80 nonrotatably connected to the cross-beam 20 and at its other end is trained around a chain sprocket 81 fixed to the gearbox 29.
In this connection it is also pointed out that the connecting-rod 45 has an offset portion 82 so that it will not strike on the drive shaft 52 when an end position is assumed in which the crank member 47 is aligned with the cross-beam 15.
A counterweight 88 is guided by means of the rollers 84, 85 and the backing members 86, 87 on a flange 83 of the column 3 and is suspended from a rope 89, which is trained around deflecting pulleys 90, 91, 92 and connected to an abutment 93 in the intermediate portion of the rocker arms 18, 19. Because the abutment 93 is spaced from the pivot pins of the rocker arms, which pivot pins extend through the pivot bearings 16, 17, the counterweight 88 exerts a moment on the rocker arm assembly. That moment changes with the angle of the rocker arms relative to the vertical so that a relatively exact balancing of the forces acting on the loaded rocker arms can be accomplished.
Another embodiment is diagrammatically indicated in FIGS. 8 and 9. In the diagrammatically shown end view, the rocker arm assembly is designated 94 and shown in various positions. In this embodiment, this rocker arm assembly is provided with a counterweight. The cross-beam carrying the vacuum cups is designated 95 and cooperates with a conveyor 96 having a constant height and a stack 97 having a changing height. In this embodiment, a double crank 99 is non-rotatably connected to the pivot bearing or the horizontal rocking shaft 98 of the rocker arm assembly 94 and a pinion 101 is mounted at the end of the rocker arm assembly 94 and in mesh with a rack 100. The pinion 101 is connected to a drive motor 102, to which it may be coupled by a worm gearing or bevel gearing, if desired. The pinion 101 is also in mesh with a rack 103, which is pivoted on an axis 104 to a column of the frame. Thus, a rotation of the pinion 101 will change its relation to the rack 103 and to the rack 100 of the double crank 99, so that the latter will be swung out and its effective length relative to the rocking shaft 98 will be changed. This effect is the same as that described with reference to the double crank 53 shown in FIGS. 1 to 5. This embodiment is described only to show that other arrangements may also be used.
FIG. 10 shows an embodiment comprising a rack 103, a pivot bearing 104 and a gearmotor 102. In the embodiment of FIG. 10, the vertical drive is effected in dependence on the rotation of the rocking shaft 98, which is driven by a crank mechanism whereas the gearmotor 102 is controlled in dependence on the changing height of the stack.
The control is particularly accomplished with limit switches. Two limit switches are associated with the rocker arms to define the positions over the stack and the conveyor. Two additional limit switches are associated with the bearing plates and the so-called double crank to define the upper and lower end positions. The cylinder-piston unit forming an abutment for the drive chain of the vertical drive is provided with another limit switch. To indicate that they are ready to receive an article, e.g., at vacuum cups, the grippers are provided for the stack 2 to indicate the presence of a stack. Additional limit switches serve to detect the condition of the conveyor.
The limit switches control the described motors and also control the vacuum pump for the vacuum cups to operate in the required sequence. Such control systems can readily be designed in view of the described sequence of motion of the mechanical system. It is pointed out that the drive motor for the vertical adjustment and for operating the rocker arm assembly is a reversible motor, just as the lift-setting motor provided on the double crank for adjustment to the stacking or unstacking operation.
What is claimed is:
1. Apparatus for transferring articles between a conveyor disposed on a predetermined level and a stack of articles in order to change the height of said stack, said appraratus comprising a frame, pivotal mounting means vertically movably mounted on said frame and defining a horizontal pivotal axis, a rocker arm assembly pivotally mounted to said mounting means on said axis for rocking movement through substantially 180 and having an outer end remote from said pivotal axis, a gripper carried by said rocker arm assembly at said outer end and adapted to hold articles, vertical drive means for reciprocally adjusting the vertical height of said pivotal axis during rocking movement of said rocker arm assembly, rocking drive means cooperating with said pivotal mounting means to impart to said rocker arm assembly pivotal movement through 180, connecting means arranged between said vertical drive means and said rocking drive means to impart to said rocker arm assembly a rocking movement in dependence upon the vertical reciprocal movement of said pivotal mounting means, means for sensing the height of said stack, and means associated with said vertical drive means for determining in response to said stack height sensing means the uppermost position of said pivotal mounting means at a level relative to the height of said stack, said vertical drive means and said rocking drive means being operatively positioned in a superposed arrangement relative to each other in such a manner that, as a result of said superposed arrangement, the vertical positioning of said pivotal axis is adjusted simultaneously during rocking movement of said rocker arm assembly with the vertical location of said pivotal axis being varied as a function of the sensed stack height.
2. Apparatus according to claim 1 wherein said vertical drive means comprise a crank member and a rectilinear drive mechanism including an elongated first drive element and a second drive element operatively connected to and movable along said first drive element, said crank member having a variable effective length one end of which is defined by said second drive element, and a drive motor connected to said first drive element and operable to move said second drive element along said first drive element.
3. Apparatus as set forth in claim 2, in which said first drive element comprises a screw and said second drive element comprises a nut threaded on said screw.
4. Apparatus as set forth in claim 2, in which said first drive element comprises a rack and said second drive element comprises a pinion in mesh with said rack.
5. Apparatus as set forth in claim 2, which comprises a freely rotatable chain sprocket connected to the second drive element, and
a chain trained around said chain sprocket,
one end of said chain'being connected to said pivotal mounting means,
the other end of said chain being connected to said second end of said crank member.
6. Apparatus as set forth in claim 5, in which said crank member consists of a double crank,
a pivot pin is mounted in the frame,
said crank member is mounted on said pivot pin and consists of a double crank extending on both sides of said pivot pin,
a drive motor for driving said drive mechanism is carried by said crank member at one end, and
said chain is connected to the same end of said crank member.
7. Apparatus as set forth in claim 6, in which a square shaft is provided, which is operatively connected to said crank mechanism,
said pivotal mounting means comprise a stub shaft which is rotatable to rock said rocker arm assemy.
a bevel gearing is interconnected between said square shaft and said stub shaft and comprises an input bevel wheel, which is slidably mounted on said square shaft,
said input bevel wheel is mounted in a housing, which carries said stub shaft, and
a torque-transmitting member is connected between said square shaft and said housing and carries four rollers adapted to roll on respective sides of said square shaft.
8. Apparatus as set forth in claim 6, in which said frame carries a horizontal stub shaft,
said double crank is mounted on said stub shaft and carries a cam slot,
a slide block is guided in said cam slot,
a constraining member is vertically guided on said frame,
a rod is connected to said slide block and pivoted to said constraining member and said vertical drive means are connected to said constraining member and operable to adjust the same in a vertical direction.
9. Apparatus as set forth in claim 6, in which said double crank is provided with a rack,
a pinion is in mesh with said rack,
a drive motor is connected to said pinion to move the same along said rack in order to change the effective length of said double crank, and
a second rack is pivoted to said frame and in mesh with said pinion.
10. Apparatus as set forth in claim 1, in which said rocking drive means comprise a crank mechanism mounted in said frame and a drive shaft for said crank mechanism,
said drive shaft and said crank of said vertical drive means extend vertically,
said frame comprises vertical guides,
a cross-member is guided on said vertical guides and carries said drive shaft and said crank member,
a chain is connected to said crank member and operable to drive the same and connected to said pivotal mounting means, and
said pivotal mounting means comprise a rocking shaft which is rotatable to rock said rocker arm assembly,
a rod is connected to said rocking shaft and operable by said crank mechanism to rotate said rocking shaft, and
said crank mechanism is arranged so that said rocker arm assembly is in one end position of its rocking movement when said rod is aligned with said crank member.
11. Apparatus as set forth in claim 10, in which said crank mechanism comprises a capstan head and said rod consists of a rack which is pivoted to said capstan head.
12. Apparatus as set forth in claim 10, in which said chain is connected to an abutment,
said pivotal mounting means comprise a bearing plate vertically movably mounted on said frame, and
said abutment is adjustably mounted on said bearing plate for a selection of the reference height over said conveyor.
13. Apparatus as set forth in claim 12, which comprises an adjusting means connected between said frame and said abutment, and
means for intermittently adjusting said adjusting means in step with the movement of said rocker arm assembly,
said adjusting means being arranged to impart to said gripper initial and final strokes, respectively, when said rocker arm assembly reaches its two end positions.
14. Apparatus as set forth in claim 10, in which said crank mechanism comprises a crank which is parallel to the crank member of said vertical drive means.
15. Apparatus as set forth in claim 1, in which a rope pulley is mounted in an upper portion of said frame,
a rope is trained around said rope pulley and on one side of said pulley is connected to said vertically movable rocker arm assembly at a point disposed between said gripper and said pivotal axis and spaced from the latter, and
a counterweight is connected to said rope on the other side of said pulley to exert by means of said rope an opposing moment on said rocker arm assembly.