Furthermore, the invention relates to an apparatus for picking up and releasing shims in appropriate seats in the cylinder head of an internal combustion engine, comprising a support body and a plurality of pneumatic pick up devices coupled to the support body.

Background Art There are known pneumatic devices for picking up and transporting objects substantially without there being any physical contact between the object and the device. Similar devices exploit the"Venturi tube"effect. As known, the <BR> <BR> <BR> -"Venturi tube"is an instrument for measuring the velocity of a fluid in a conduit, that consists of a tube with two truncated cones joined together at the minor bases. A fluid, flowing through the instrument, increases its velocity in the portion with converging cross-section and decreases it in the portion with diverging cross-section and in consideration of the fact that the pressure is inversely proportional to the square of velocity (as stated

in the Bernoulli principle), the velocity variation generates an opposite variation in pressure, that is higher at the input and at the output of the tube and is lower at the choke defined by the area of conjunction between the two truncated cones. The devices that exploit this principle and are mainly utilized for picking up and transporting flat, delicate and light weight objects, generally comprise an element with a substantially plane surface and a centrally located hole connected to a conduit for blowing compressed air. The device is moved towards the object to be picked up so that the plane surface faces a surface of the object, thereby creating, by means of the two surfaces, a choke like the one in the"Venturi tube".

The air flows out of the hole and into the choke at a high velocity, thus, according to the Bernoulli principle, the increase of the air velocity between the surface of the device and that of the object induces a depression between the two surfaces with respect to the atmospheric air pressure on the opposite surface of the object. When the pressure differential between the two surfaces becomes sufficiently high to overcome the force of gravity, the object can be picked up by the device, and released by the latter when the air flow is cut off.

U. S. patent 4,969,676 describes a manually operated device of the above described type for transporting silicon wafers for integrated circuits, that comprises a disc with a flat surface and a central air passage, and centering elements coupled at the periphery of the disc.

Pneumatic devices of this type are also utilized in the automotive industry, more specifically in apparatuses operating in automatic assembly lines for picking up and transporting appropriately thick shims and inserting them in respective recesses at the valve side of bucket type tappets of internal combustion engines, thus attaining the required amount of clearance between the cams of the camshaft and the valves. Similar apparatuses comprise a certain number of devices, or"pneumatic heads", that pick

up the shims-in the formerly described manner-at a selection station, transport and release them in the recesses of the associated bucket type tappets at the valve side. The heads are equipped with lateral limiting devices that have the purpose of centering the shims, hence permitting their correct insertion in the associated bucket type tappets. In some cases, more specifically if the head is not properly centered in the recess of the bucket type tappet, there may occur-during the insertion and release phases-that the lateral limiting devices apply transversal forces to the shim thereby causing, when the head retracts, the at least partial displacement of the shim out of the bucket type tappet recess.

The problems that may arise owing to improper positioning, or lack of shims are evident, in particular in automatic assembly lines. In fact, a defective assembly may not be detected, and thus cause malfunctions and damage to the engine, and even when it is detected, for example by an operator specifically dedicated to perform this task, the manual intervention may be considerably expensive in terms of involved time and costs.

Disclosure of Invention Object of the present invention is to provide a pneumatic pick up and release device that overcomes the limits of the known apparatuses, and in particular ensures a proper release of the objects that have been picked up.

This and other objects are achieved by a device according to claim 1 and an apparatus according to claim 5.

Brief Description of the Drawings The invention is now described in more detail with reference to the enclosed sheets of drawings, given by way of non limiting example, wherein:

figure 1 schematically shows an apparatus utilizing pneumatic devices according to the invention ; figure 2 is a longitudinal cross-sectional view of the end portion of a pneumatic device according to the invention, shown in a first operating condition and in an enlarged scale with respect to that of figure 1; figure 3 is a longitudinal cross-sectional view of the pneumatic device shown in figure 2, according to a second operating condition; and figure 4 is a transversal cross-sectional view of the device shown in figures 2 and 3, taken along line IV-IV in figure 3.

Best Mode for Carrying Out the Invention Figure 1 schematically shows an apparatus 1 for inserting a series of shims 3 in appropriate seats at the valve side of associated bucket type tappets of a cylinder head of an internal combustion engine, not shown in the figures. These shims 3, as already known, are specifically selected in order to define the proper amount of clearance between each cam of the camshaft and its associated valve.

The apparatus 1 comprises a support body 5 and a set of pneumatic pick up devices, or pneumatic heads, 7 coupled thereto for picking up, transporting and inserting shims 3 in the seats of the associated bucket type tappets.

Each head 7 defines a longitudinal geometric axis and is coupled with body 5 by means of a resilient type coupling, featured in a known way that is schematically shown and identified by reference number 4 in figure 1, that allows limited reciprocal longitudinal displacements, in the range of a few millimeters, according to the direction indicated by arrows 6.

Moreover, body 5 may have guides and slides, also per se known and not illustrated in the drawings, that enable the set of heads 7 to perform the displacements required for transporting the shims 3 from the pick up area to the seats

where they are released, for example according to the directions indicated by arrows 8.

As the pneumatic heads 7 are identical, only one will be detailedly described with reference to figures 2,3 and 4.

Each pneumatic head 7 has a casing 9, of a substantially cylindrical shape, with a larger terminal portion 11 that comprises a closure plate 37 for defining a transversal, substantially plane, end surface 47.

The terminal portion 11, i. e. specifically the end surface 47 has a rim 13 and a certain number of longitudinal centering overhangs, or teeth, 14 arranged along rim 13 (as an example only, the device shown in the figures has four teeth).

The terminal portion 11 comprises a cylindrical recess 21 and a pneumatic circuit including a conduit 19, housed in casing 9 and communicating with recess 21, and a source of compressed air, identified by reference number 20 in figure 1, connected to conduit 19. The closure plate 37 has a cylindrical through hole 45 communicating with the cylindrical recess 21 and substantially aligned along the longitudinal axis of head 7. A thrust mechanism includes a piston 25 that can longitudinally slide within the interior of cylindrical recess 21 and has cylindrical portions with different diameter that define transversal plane limit stop surfaces 32 and 40 for contacting internal plane surfaces 33 and 41 of recess 21 for limiting the stroke of piston 25 in either direction, and transversal, oppositely arranged, thrust surfaces 34 and 42.

A pin 35 is coupled to, for example screwed into, piston 25 and arranged substantially along the longitudinal axis of head 7. The diameter of pin 35 is smaller than that of the cylindrical hole 45 for the purpose of allowing the flow of compressed air through the formerly mentioned hole even when pin 35 is partially housed therein.

Furthermore, the thrust mechanism comprises a compression spring 31, arranged between the internal plane surface 33 of the cylindrical recess 21 and the transversal thrust

surface 34, that urges pin 35 towards the exterior of casing 9, by protruding from hole 45.

The compressed air, injected into the cylindrical recess 21 through conduit 19, acts upon the other transversal thrust surface 42 for urging piston 25, and thus pin 35, towards the interior, in a retracted position (as shown in figure 2). The same compressed air flows out of recess 21 by passing through hole 45.

The apparatus operates in the following way.

Body 5 of apparatus 1 is displaced towards a pick up area, not shown in the figures, where the shims 3 to be inserted in the seats of the bucket type tappets have been suitably arranged. The shims 3 have different thickness and are selected on the basis of previous checkings and measurement takings performed, for example, on the cylinder head and the camshaft, for determining the amount of clearance that it is desired to achieve between the cams and their associated valves. The end surfaces 47 of the pneumatic heads 7 are moved towards the shims 3 until contact is made. Then, ejection of compressed air from source 20 is started. In each head 7 the compressed air flows-by passing through conduit 19-into recess 21 and urges piston 25 towards the interior in the retracted position, opposing the thrust applied by compression spring 31 (figure 2).

Moreover, air flows through hole 45 of closure plate 37, comes out of the same hole 45 and moves in a path limited by end surface 47 and shim 3, thereby lifting head 7 with respect to shim 3 of an amount in the range of a tenth of a millimeter, thanks to the resilient type coupling 4 between head 7 and body 5, and flows, at a high velocity owing to the"Venturi tube"effect, substantially along radial directions, within the small amount of space existing between surface 47 and the surface of the shim 3 to be picked up. Within this space, there is formed a depression (Bernoulli pinciple) and shim 3 is urged-by the greater amount of atmospheric air pressure on the opposite surface-

towards surface 47 of head 7, thereby enabling head 7 to pick up and transport shim 3.

In the course of the pick up and the transporting operations, teeth 14 contribute to center shims 3 with respect to the associated end surfaces 47.

Once the set of heads 7 has picked up shims 3, it is displaced towards the cylinder head of the engine (not shown in the figures), and positioned, for example by means of mechanical references, in such a way so that heads 7 and shims 3 are at the seats of the bucket type tappets, schematically shown and identified by reference number 10 in figure 3.

The air flow ejected from source 20 is stopped, the pressure applied to the two faces of shims 3 is re-balanced and, by effect of the force of gravity, shims 3 are released in seats 10. The moment when the air flow is stopped, the thrust applied to the transversal surfaces 42 of pistons 25 stops too, and the latter, urged by their associated springs 31, switch from retracted positions (figure 2) to advanced thrust positions (figure 3) in which their associated pins 35 protrude from holes 45 and take part in the insertion of shims 3 in seats 10.

Moreover, when the heads 7 retract, pins 35 are urged by springs 31 to continue to exert their action on shims 3 for a short stroke, that is sufficient for keeping the shims 3 properly positioned in seats 10 and opposing the effect of possible undesired transversal forces among some of the teeth 14 and the associated shims 3, that could tend to displace the shims 3 out of seats 10, upon the retraction of the associated heads 7.

The release of the thrust applied by each pin 35 and the complete detachment of each head 7 from its associated shim 3 are events that occur-in the course of the retraction of the set of heads 7-subsequently to the contact of the transversal limit stop surface 40 of piston 25 against the internal surface 41 of the cylindrical recess 21 (at a time following the one referred to in figure 3).

Hence, the device according to the invention guarantees a proper and stable insertion of the shims 3 in their associated seats 10 of the bucket type tappets.

An embodiment like the one herein described and illustrated is particularly advantageous in that it enables to simultaneously perform-with just a single pneumatic circuit and a single control-both the pick up (and the release) of shims 3 by exploiting the Bernoulli principle and the retraction (and the release) of the thrust mechanism. More specifically, as described in the foregoing description, the same compressed air flow ejected from source 20 and that passes through conduit 19 induces both the depression-that enables to pick up the shims-and the release of piston 25. The stopping of the formerly mentioned air flow causes the release of the shims and simultaneously the actuation of the thrust mechanisms.

It will be apparent that a device according to the present invention may undergo variants with respect to what has been herein described and illustrated, for instance in so far as the shape, the proportions and the arrangement of the thrust mechanism, the recess for its housing and the pneumatic conduit are concerned. Spring 31 can be replaced, for example, with a different device or may even be left out, where the weight of piston 25 is sufficient to provoke, when the flow of compressed air stops, its displacement towards the advanced thrust position.

Moreover, one or more pneumatic devices according to the invention can be utilized in apparatuses that have an entirely different structure with respect to the one that has been illustrated in an extremely schematic way in figure 1 for picking up and releasing substantially flat pieces that may have an entirely different shape and function with respect to those of the herein described and illustrated shims.