Although for reasons of greater descriptive simplicity reference will be made to preforms of thermoplastic material used in the production of containers in the following description, the present invention shall of course to be understood as applying also to other cylindrical bodies used in different applications, as far as they do not depart from the scope of the appended claims.

Grippers for seizing and holding firmly preforms are known which comprise a handling arm, a pair of symmetrical, elastically diverging members, and connecting means between said arm and said symmetrical members. The latter are shaped so as to form a concavity whose opposite arms are arranged and sized in such a manner as to enable a cylindrical portion of the collar of a preform to be inserted therein by means of a simple pressure of said collar against the outer portions of said concavity, which, owing to the action of such a pressure, are caused to be enlarged by such an extent as adequate to enable the collar of the preform to slip into said concavity in which it is then retained.

However, such an operation and the particular type of gripper used to carry it

out, have following drawbacks: -the preform may be subjected to both axial and transversal stresses; in order to be able to withstand such stresses, said symmetrical members must possess a considerable elastic strength.

However, the required extent of said elastic strength brings about a considerable friction between said arms and the outer surface of the preform, which therefore undergoes a slight abrasion, considering that it is made of thermoplastic material that is only slightly heated up. In a situation of large-scale series production, this fact practically causes tiny particles, ie. the so-called"flour" of the plastic material involved to be produced, which then contaminates the adjacent parts of the plant and disturbs the regular flow of the subsequent process operations and makes them inaccurate.

If on the other hand such an undesired effect has to be reduced, the need arises for the elastic gripping force of said arms to be reduced. Such a constraint, however, is largely known to all those skilled in the art to bring about corresponding inaccuracies in the positioning of the preform, with clear handling difficulties resulting therefrom.

Moreover, making grippers provided with holding arms having a considerable elastic strength implies a production that requires a far higher extent of accuracy and, therefore, is much more expensive.

It is therefore a main purpose of the present invention to provide a gripper for handling cylindrical bodies, and in particular plastic preforms, which does away with the above described drawbacks and, at the same time, is compact, safe and reliable in its operation, and requires a simple, reliable construction based on the use of readily available techniques.

Such a type of gripper is obtained and implemented with the characteristics that are substantially described with particular reference to the appended claims.

Anyway, features and advantages of the present invention can more readily be understood from the description that is given below by way of non-limiting example with reference to the accompanying drawings, in which: -Figure 1 is a perspective view of a gripper according to the present invention; -Figure 2 is a similar perspective view of a component part of the same gripper illustrated in Figure 1; -Figure 3 is a top plan view of the same component part illustrated in Figure 2; -Figure 4 is a view along the A-A section of the component part illustrated in Figure 3; -Figure 5 is a view along the B-B section of the gripper illustrated in Figure 1; -Figure 6 is a view along the A-A section of the gripper illustrated in Figure 5 ; -Figure 7 is a perspective view of a partial assembly of some component parts of the gripper illustrated in Figure 1; -Figure 8 is a top plan view of the assembly illustrated in Figure 7.

With reference to the above Figures, the gripper according to the present inventioncomprises: -a handling arm 1, -a plate 2 for seizing and support the preform 3, -an interconnection means 4 provided between said arm and said plate and firmly joined thereto,

-two symmetrical side gripping members 5 and 6, -a cylindrical spring 8 provided between corresponding extremities of said gripping members 5 and 6.

Said plate 2 is provided, at an extremity thereof, with a semi-circular aperture 7 having such a diameter as adequate to enable it to accommodate a part of a cylindrical portion 28 of the collar of the preform 3.

It is however possible for said aperture to be given a non-circular shape, and to be for instance in the shape of an even non-circular arc instead, as far as it proves anyway capable of getting coupled with an adequate portion of the collar of the preform.

It is furthermore provided, in correspondence of the opposite side edges thereof, with two grooves 9 and 10 adapted to accommodate a respective side gripping member 5 and 6.

Said side gripping members 5 and 6 are hinged on said interconnection means 4 by means of appropriate pivotally connecting means (pivots, pins and the like) and, since said interconnecting means 4 is firmly joined with said plate 2, it ensues that said side gripping members 5 and 6 are substantially attached to said plate, while however being able to slightly rotate with respect to said plate thanks to said pivotally connecting means getting engaged into respective appropriate holes 11 and 12 provided in said side gripping members.

These members are provided at the respective extremities 13 and 14 located in correspondence of said semi-circular aperture 7, with two respective arcs of a circle 15 and 16.

On the opposite side of said extremities 13 and 14 there is provided a cylindrical compression spring 8 which, as such, tends therefore to keep said

extremities 13 and 14 closed, or at least approached to each other, said extremities being anyway limited in their separation gap by the fact that the inner sides 17,18, respectively, of said extremities 13 and 14 are adapted to abut against the outer edges of a central relief 20 of said support plate 2, as this is illustrated in particular in Figures 1 and 5.

Said side members are adapted to move into at least a resting position and at least a working position; the resting position is determined by the action of the spring 8 that tends to move said extremities 13 and 14 closer to each other up to the point at which the stopping action of said central relief 20 comes into play.

In this resting position, said arcs of a circle 15 and 16 move into an arrangement as illustrated symbolically in Figures 7 and 8, ie.: -they identify a circle whose diameter D is slightly smaller than the diameter H of the semi-circular aperture 7, and -the outer edges 21 and 22, respectively, of said arcs of a circle 15 and 16 are located at a distance M that is smaller than said diameter D and also smaller than the outside diameter of the preform.

The working position is illustrated in Figures 1,5 and 6: it can be noticed that the preform is inserted within said semi-circular aperture 7, where it is retained by said arcs of a circle 15 and 16 which are pressed against a cylindrical portion of the collar of said preform by the effect of the elastic action of the spring 8 and also owing to the fact that the diameter of said collar is greater than the diameter D of said arcs of a circle in the resting position thereof, so that, when the preform is so inserted, said arcs of a circle are deflected outwardly, thereby causing the preform to be held firmly.

In an advantageous manner, said preform retaining action can be further improved if said central relief 20 is provided, in correspondence of the edge thereof which is adjacent to said semi-circular aperture 7, with abutting means in

the shape of an arc of circle 23, as illustrated in particular in Figure 2, which are adapted to get fittingly into coupling with a cylindrical portion of the collar of the preform, as illustrated in Figures 1,5 and 6.

In this way, the combined effect of said side members 5 and 6 so closing elastically and said abutting means 23 moving so into coupling against the collar of the preform causes the latter to be held firmly, in an elastically releasable manner, against the described gripper.

It is in fact sufficient for an appropriate portion of the collar of the preform to be pressed in an axial direction into said semi-circular aperture in order to cause said side gripping members to move apart by an adequate extent, thereby allowing for the preform to slide into said semi-circular aperture. When said side gripping members are then so moved into such a position, they tend to move back into their resting position, owing to the action of the spring 8, thereby causing the collar of the preform to be held firmly.

It should be particularly noticed that, with such an embodiment, the side stresses on the preform are easily neutralized by the resistance of the arms of the semi-circular aperture 7, without any consequence on the capability thereof to grip and hold the preform in a firm and efficient manner. On the other hand, the axial stresses determined by the preform being inserted in and released from the gripper may be limited to any desired extent by simply adjusting the characteristics of the spring 8 accordingly, without anyway impairing the stability and, above all, the precision of the position in which the preform is held, owing to the effect of the abutting means 23 getting so coupled.

A further improvement in the way in which the preform is inserted is easily obtained if said two side gripping members 5 and 6 are provided, at the respective extremities 13 and 14, with respective edges 31,32 with an appropriate flared shape and arranged so as to define a V-shaped or funnel-shaped configuration in view of facilitating the preform to move into self-positioning and said extremities 13, 14 to move apart under the action of even a moderate axial pressure exerted by the

preform.

It shall be appreciated that the description and illustrations given above with reference to the accompanying drawings have been given by mere way of exemplification of the present invention, and that a number of variants and modifications can therefore introduced thereto without departing from the scope of the present invention.