Device for transporting hollow plastic blow moldings

A device is provided for transporting hollow plastic blow moldings having at least one opening thereinto which device is particularly useful for removing hollow moldings from the cavities of blow molds. The device includes at least one gripper unit supported for axial movement toward and away from a blow mold, which unit has gripping means movable between a normal, retracted position and an expanded position. The gripping means are insertable within the opening of a hollow molding disposed in the mold cavity and are expanded to engage and grip the interior walls thereof. The device also includes means for adjusting the degree of expansion of the gripping means to ensure precise position control and to minimize damage to the hollow molding during gripping and transport.

This invention relates to a device for transporting hollow plastic 
blow-moldings which have at least one opening which is especially useful 
for removing such moldings from the blow-mold nest, or cavity, of a 
blow-mold. More particularly, it relates to such a device comprising a 
separate gripper unit for each molding cavity with expandable gripping 
means which are adapted to be introduced through the opening into the 
interior of the hollow molding and expanded therein to engage with the 
inner wall of the molding. 
Blow-molding transport devices of this type are well known. Typically, the 
gripper units are introduced into the hollow molding while the blow-mold 
is closed, whereupon the gripping means are expanded to engage with, and 
hold the molding firmly attached to the gripper unit so that, 
subsequently, the mold may be opened and the molding transported to 
another station by displacement of the gripper unit. In these conventional 
devices, the gripping means are mostly designed for dynamic co-action with 
the inner wall surfaces of the hollow molding, e.g. in the form of 
expanding spring clips or other elements which expand in the interior of 
the molding to a diameter, or cross section larger than the opening in the 
molding, which enables them to hold the molding attached to the gripper 
unit. While this form of engagement between gripper device and hollow 
molding is sufficient to permit the molding to follow the transporting 
movements of the gripper unit, it can by no means ensure that the hollow 
molding will in fact be transported to, and subsequently occupy the new 
position with a sufficient degree of accuracy for the precise application 
thereto of further processing means associated with such new position, 
e.g. for deburring, printing, density testing etc. 
In other words, if such positional precision is required, a device is 
needed which allows the hollow molding to be precisely located relative to 
the gripper unit and subsequently to be released, still preserving the 
precisely located position, as soon as the new station has been reached to 
which the molding is required to be transported from the mold or from any 
other, earlier occupied position. The provision of such a device is the 
principal objective of the present invention. 
Moreover, particularly for hollow blow-moldings which are made to high 
precision standards, it is desirable that the gripper device should in no 
way cause damage to the molding. In the case of previously known devices 
of this kind, the gripping means were designed to apply an uncontrolled 
engagement pressure to the interior molding walls which could produce 
notches or indentations in these walls. Accordingly, it is a further aim 
of this invention to ensure extremely gentle and careful handling of the 
hollow moldings, inspite of the high degree of precision engagement 
between the gripper and the molding. More particularly, the invention aims 
to ensure that the gripper device will engage with the hollow blow-molding 
with a high degree of precision without, however, applying any more 
pressure to the interior molding wall than essentially needed for safe and 
substantially form-fitting, i.e. positive engagement with the gripper. 
Furthermore, the parts of the gripper device which extend into the inside 
of the hollow blow-molding must predictably and reliably assume a safe 
non-expanded position so that they will not cause any damage when the 
grippers are withdrawn from the moldings. Lastly, in order to achieve and 
sustain optimal functional results, the effective application of the 
gripping means to the hollow molding should be adjustable and controllable 
at all times. 
According to this invention, these and other related objects are attained 
by virtue of the fact that the position occupied by the gripping means in 
expanded condition is precisely predetermined by selectively variable 
adjusting means. 
Since the device according to this invention is primarily designed for the 
manufacture of high-quality hollow moldings, the moldings in question will 
most probably have a calibrated opening, e.g. in the form of a bottleneck, 
adhering to strictly defined interior cross-sections, with a precision 
finished, outwardly-directed rim or edge zone. In an advantageous 
embodiment of the invention for application to hollow blow-moldings of 
this type, the gripping means are arranged in such a way that when 
expanded they will be applied to the inner wall face of the calibrated 
part of the opening in the molding. Advantageously, the gripper device 
comprises a stop-face which is directed towards the free end of the 
gripper, extending normal to the direction of gripper-introduction into 
the opening of the molding and adapted to co-act with the rim or edge of 
the opening in such a way that the latter engages therewith when the 
device has been introduced into the molding. 
The advantage of the arrangement according to this invention resides in 
that the gripper device can be adjusted irrespectively of the necessary 
distance of expansion displacement thereof in such a way that the gripping 
means are always applied to the inner wall of the hollow molding with 
precisely the right, or optimum amount of pressure. The correct end 
position of the device for effective and optimum gripping engagement with 
the molding can be easily ascertained by sight, that is to say, by setting 
the gripper-adjusting means to the appropriate position which is 
ascertained empirically with the aid of the gripper-traces on a few test 
pieces of the moldings to be handled in each case. 
The frontal, abutting engagement between the end-stop on the gripper unit 
and the edge, or rim aroung the opening in the hollow molding provides 
additional stability for the molding which ensures precise movements when 
the molding is transported by the device from one given position to 
another, even under considerable acceleration. 
In a particularly advantageous embodiment of the invention, the operative 
movement of the gripper from the normal to the expanded position and vice 
versa is positively controlled and guided by means of a curve which is 
associated with the gripper. Most desirably, a separate guide curve of 
this kind is provided for actuation of each gripper device. According to a 
further advantageous embodiment, the gripper movements are appropriately 
adjusted by means of an adjustable endstop which is associated with he 
guide curves. 
According to another advantageous embodiment of the invention, the gripper 
unit comprises gripping levers which are mounted pivotally on the gripper 
in such a way as to permit variations in the radial distance between the 
operative gripping end of each lever and an axis extending in the 
direction of operative gripper movement into and out of the opening of the 
hollow molding. The levers are adapted to co-act with an actuating link 
which is displaceable relative to the gripper unit and precisely 
adjustable with regard to its end position, which corresponds to the 
expanded gripper position, with the aid of precision adjusting or setting 
means. 
According to yet another advantageous embodiment, the actuating link is 
mounted on the gripper unit for displacement in the direction of the 
gripper axis. Preferably, the guide curve is provided in a tapering 
annular space concentric with the gripper axis which accomodates the end 
portions of the two-armed gripping levers which are on the opposite side 
to their gripping ends. 
In a preferred embodiment, employed in conjunction with multiple molds, 
provision is made for a common driving member for displacing the gripping 
means of all of the gripper units provided. Most desirably, the adjusting 
means are sited in the vicinity of this common driving member. 
In further advantageous embodiment, the actuating links have 
positive-form-fitting engagement with a common cross-beam which is adapted 
to be displaced in the direction of the gripper axes by an associated 
drive unit. In a particularly convenient arrangement of this kind, the 
drive unit is an actuating or servo-cylinder driving one of a pair of 
parallel guides which are interconnected by the cross beam. The cross beam 
is longitudinally slidably engaged with the actuating links, and one of 
the guides is associated with an adjustable endstop to limit guide 
defelection during the gripper-expansion process. 
Other objects and features of the present invention will become apparent 
from the following detailed description considered in connection with the 
accompanying drawing which discloses the embodiments of the invention. It 
is to be understood, however, that the drawing is designed for the purpose 
of illustration only and not as a definition of the limits of the 
invention.

Referring now in detail to the drawings, the device according to this 
invention is mounted in a basic frame 10 which is adapted to be connected 
with suitable means, not shown, for transporting the hollow blow-moldings 
which are engaged by the device. This basic frame 10 is generally U-shaped 
and open on its underside, and the lower ends of the lateral frame limbs 
10a, 10b are suitably prepared or adapted to receive a supporting beam 12. 
Beam 12 is adapted to be slid into the basic frame 10 in a direction 
perpendicular to the drawing plane of FIG. 1, i.e., in a horizontal 
direction and to be secured in position by means of clamping screws 
14a,14b. As a result of this arrangement, griper units of relatively 
different design can be easily fitten in the device to suit varying shapes 
of hollow moldings to be handled. 
The gripper units, which will be more specifically described below, are 
generally designated 16a, 16b and 16c. All three of these gripper unites 
are identical, for which reason only gripping unit 16a will be hereinafter 
described in detail. In the illustrated example it has been assumed that 
the device is designed for association with a blow-mold which comprises 
three mold-nests or cavities, and consequently the device is provided with 
three gripper units. It has been mentioned that the gripper units may be 
adapted to the given shape and configuration of the hollow moldings to be 
handled and for this reason the gripper units which are shown in elevation 
in FIG. 1 are of slightly different form to those shown in FIGS. 2 and 3. 
However, in all FIGURES like reference signs have been used for like parts 
in all gripper units. 
By way of actual gripping means, each gripper unit 16a to 16c comprises 
three levers 18 spaced equi-angularly at intervals of 120.degree. around 
the vertical longitudinal gripper unit axis. The drawings showing the 
levers occupying a position wherein they are adjacent, and substantially 
parallel, to the longitudinal axis. In this position, the levers 18 can be 
readily introduced into the interior of the hollow molding to be handled, 
as will be observed from FIG. 2, where the upper region of this molding is 
outlined in dot-and-dash lines. 
Levers 18 are actuated by means of vertically displaceable actuating links 
20 which are concentric with the gripper unit axis. Each of these 
actuating links 20 is slidable in a multi-part gripper unit housing 22 
which is connected to the supporting beam 12, and the upper lever end 
which projects out of housing 22 is formed with notch or recess 24 (FIG. 
3). In the event of beams 12 being equipped with gripper units of 
different design these notches 24 are always arranged at the same vertical 
level so that, when the beam 12 is changed for another, correctly aligned 
operational engagement with a drive unit mounted on the basic frame 10 is 
always ensured by notches 24. 
The drive unit comprises an actuating- or servo- cylinder 26 wherein a 
piston (not shown) is reciprocable between two operative positions. The 
piston is connected with an actuating rod 28 which extends outwardly of 
the cylinder on both sides thereof. Actuating rod 28 is articulated at 
each end thereof, at 30 and 32, to one lever arm of bell-crank lever 34, 
36. The other lever arm or limb of lever 34, 36, is connected at 38 and 40 
respectively to an actuating bar or beam 42 which extends parallel to the 
rod 28 thereby completing an articulated parallelogram-linkage assembly. 
On actuation of the cylinder 26 the actuating bar 42 will be driven in a 
direction substantially parallel to its own extension and consequently it 
will be displaced in the horizontal as well as in the vertical direction. 
The actuating bar 42 consists of a box-profile of approximately square 
cross section with a laterally projecting strip or flange 42a (FIG. 3) 
which is adapted to engage in notches 24 of actuating links 20. When bar 
42 is driven by cylinder 26, the horizontal component of the movement will 
take the form of sliding in notches 24 and only the vertical component of 
the actuation movement is transmitted to links 20. 
The basic frame 10 further comprises a set screw 44 with a knurled 
operating grip 46. The opposite end of screw 44 represents an end stop 48 
for the bell-crank lever 34 thereby affording a means for precision 
adjustment with respect to upward displacement of actuating links 20. The 
knurled operating grip 46 of set screw 44 has a circumferential groove 48 
co-acting as a setting mark with a graduated scale arranged in the 
direction of set-screw adjustment on a scale-mounting 50. 
A downwardly tapering cone 52 is provided at the lower end of actuating 
link 20 in the interior of the gripper unit housing 22. Cone 52 is 
surrounded by a crown ring 58 arranged in suitably spaced relation 
therewith to define an annular conical chamber 54 between the outer 
surface of cone 52 and the inner wall face 56 of crown ring 58. The cone 
52 is secured in a rotationally rigid and axially non-slidable manner to 
link 20 by means of a bolt 60 which extends through a diametral bore 
through crown ring 58 and through link 20. One end of each lever 18 is 
formed with a knob or button 62 and extends into this annular chamber 54. 
The levers are each mounted in the gripper unit housing for pivotal 
movement about axes 64 which are normal to the direction of operative 
displacement of links 20 and tangential to an imagined inscribed circle of 
the pivot axes in one gripper unit. For simplified representation, FIG. 2 
only shows one lever 18 which is pivotable in the drawing plane. 
As a result of this construction, levers 18 are capable of pivotal movement 
in radial planes relative to the gripper unit axis. Within, and 
corresponding to this range of movability of the levers 18, the gripper 
unit housing 22 is provided with a radial slot 66. 
The other lever end, which is opposite to the end carrying the knob or 
button 62, is provided with a gripping beak or cam 68 which can be pivoted 
radially outwards as shown in FIG. 2, by an upwardly directed movement of 
the actuating link 20 owing to the fact that in the course of such upward 
displacement of the link 20 the smaller diameter region of the tapered 
annular chamber 54 approaches the knob 62. Since the arm of lever 18 which 
carries the knob 62 is considerably shorter than the other lever arm which 
carries the gripping beak 68, the lever ratio will be sufficiently high to 
ensure that even a minor axial displacement of the actuating link 20 can 
produce a significant outward swing of the beak 68. 
The drive mechanism is adjusted with the aid of the set screw 44 in such a 
way that the gripping beak or cam 68 is applied to the interior wall face 
70 of the hollow molding 72 without producing damage or indentations 
therein. The correct adjustment setting can be easily determined with the 
aid of a few experimental test pieces. The pressure applied by the beak 68 
to the surface 70 need only be sufficiently strong to hold the molding 72 
on the gripper unit. 
To allow the hollow molding to be transferred with great positional 
precision from an initial station to an end station, it is necessary- in 
addition to the appropriately precise displacement of the basic frame 10 
which can be readily obtained by the skilled man with the aid of suitable 
conventional means- that the hollow molding should be securely held on the 
gripper device during transport. For this reason the gripper unit is 
provided, preferably at the end thereof which faces the hollow molding 72, 
with a stop- or abutment face 74, which is adapted to co-act with the rim 
or edge of the opening in the molding. When the basic frame 10 is lowered 
towards the molding 72 for introduction of the gripping means into the 
latter, this stop or locating face 74 engages with the rim 76 around the 
opening in the molding, thereby preventing the molding from rocking or 
swinging about the gripper unit. This is particularly important in those 
cases of practical application where the moldings are transported at high 
speeds and consequently subjected to considerable accelerations and 
decelerations. Furthermore, the gripper unit housing 22 may also comprise 
a spike- or mandrel-like extension 76 which is adapted to engage in the 
opening of the hollow molding; the latter being made to constant internal 
dimensional specification by suitable calibration for the successful and 
advantageous application thereto of the gripper device according to this 
invention. 
While only a few embodiments of the present invention have been shown and 
described, it will be obvious that many changes and modifications may be 
made thereunto without departing from the spirit and scope of the 
invention.