In the specific industrial field where use is made of assembly lines carrying a plurality of platforms supporting members to be assembled, it has been remarked that the pneumatically-operated device acting at each operating station for the purpose of timely stopping a platform operates too abruptly, thus causing a displacement of the members resting on the platform, with resulting work troubles. Moreover, excessive wear is often noticed on the parts acting as an abutment, with resultant necessity of replacing said parts, or the like.

As a consequence, assuming obviously as obsolete the early rigid stop devices with a simple pneumatic retraction control, lacking of any dampening effect, and as conventional the more recent devices with control and dampening means of only pneumatic nature, the need has been felt to improve the action, i.e. to achieve a softer action, of the devices used to stop said platforms and to modify their constructional details so as to reduce friction, to increase their shock-absorbing features, and to improve the possibility of adjusting their dampening effect. Data collected during a careful study have enabled various improvements which, by taking advantage of the adjustment possibilities resulting from a hydraulic system coupled with a pneumatic control system, have shown capable of eliminating all the disadvantages heretofore experienced, while ensuring important advantages. Substantially, said exploitation of hydraulics coupled with a pneumatic control has enabled a very wide range of values in the dampening effect during the stopping action against platforms, and a shock-absorbing capability much higher than normally possible, the inventive system being thoroughly incorporated in a containing block which is entirely similar to the usual containing blocks.

The accompanying drawings show, as a non-limiting example, a preferred

embodiment of the invention. In the drawings:

Fig. 1 is a vertical axial sectional view of a stopping block according to the invention, improved by incorporating therein a hydraulic shock- absorbing or dampening system, wherein the abutment catch is in the retracted position, i.e. subsequent to the stopping action, and the movable assembly carrying said catch and comprising the hydraulic system, in the upper operative position.

Fig. 2 is an enlarged view of a detail of Fig. 1 , showing the parts producing the first progressive dampening stage of the stopping stroke of the abutment catch.

Fig. 3 is a view similar to Fig. 1 , with said movable assembly in the retracted position, i.e. in the lowered position allowing a platform to travel thereover unhindered, and ready for resetting, i.e. to be moved pneumatically to the protruding upper position for the catching action. Fig. 4 is a view similar to Fig. 2, but showing the operational stage of Fig. 3.

As shown in the Figures of the drawings, the stop device of the invention comprises a parallelepipedal body 1 with fixing holes 2,3 and a union 4 for connection to a source of compressed air as provided on similar traditional devices. In the device according to the present invention, however, the interior of the body 1 comprises several particular features developped as a result of the study mentioned in the preamble.

Substantially, the block comprises, starting from the top downwards, a recessed rectangular seat 5 with a two-diametre through-hole 6 formed off- center therein and opening at its lower end into the bottom of a cylindrical chamber 7 wherein a disc 8 is slidable axially in piston-like fashion. A supporting member 9 is slidable axially in the top seat 5 and is provided with an off-center stem 10 designed to be movable in the hole 6. The lower end of said stem is provided with an axial threaded hole for securing the disc/piston 8 thereto, and the stem has threaded thereon a coil spring 11 required to reset the device, as explained below. The slidable member 9, which is forced by its stem 10 to follow the movements

of the disc/piston 8 which is actuated by the pulses of compressed air reaching the chamber 7 via the duct 12 and its branch, houses within suitable recesses a catch or abutment member 13 which is movably mounted in piston-like manner and is provided with annular seals, within a suitable cylindrical seat 14 which is closed at the bottom by an insert or disc 15 in the form of a washer with a central hole to connect the seat 14 to a hydraulic shock-absorbing or dampening system arranged therebehind and housed partly in an inserted smaller block 16 which is provided with suitable communication ducts through which the oil or operative fluid flows in a closed-circuit manner. The travel of the catch 13 outwards is limited by a stop 13A.

At the top, the smaller block 16 comprises an adjustment or choke valve 17 to control the speed of the flow during the first step of the dampening action and a screw 18 to limit the travel of a spring-loaded ball valve 19 which permits a rapid reset flow. At their lower ends, the ducts of the circuit open into the bottom of a cylindrical chamber 20 where is floatingly slidable a small piston 21 which is provided on its back side with a short stem to limit its stroke. At the end opposite to the side provided with the mouth of the ducts of the hydraulic circuit, the chamber 20 is provided with the mouth of a smaller duct 22 which, through a protruding extension 23 (either integral or inserted) can be connected (Fig. 3) to a corresponding duct 24 provided with an annular seal having the function of a sealing abutment seat for an underlying ball valve 25 loaded by a coil spring housed in an underlying chamber communicating through its bottom with a duct 12 for inlet of the control compressed air, thus establishing the pneumatic servo-control connection for the hydraulic system described above. With reference to the last-mentioned system (Figs. 2 and 4), it is to be pointed out that in order to obtain a gradual dual dampening effect, according to the invention, the inner end of the piston- like member 13 is provided with an axial stud-like extension 26 adapted to co-operate with the disc-shaped insert 1 which is arranged and locked between the parts 9 and 16 in a suitable recess provided with a seal. The

insert 15 is provided centrally with a two-diametre through-hole communicating with the adjacent duct of the hydraulic system, said hole being closed in the end positions shown in Figs. 1 and 2. One side of the stud 26, as clearly shown in these Figures, is formed with an oblique longitudinal taper which reduces progressively its sectional area in the direction of its free end. As a result, upon the occurrence of the stopping and dampening stroke, wherein the member 13 moves from the position of Fig. 4 to the position of Fig. 2, an outflow occurs initially through the full section of the related duct, but when approaching the end of said stroke, the stud 26 begins penetrating the hole in the insert 15, i.e. said duct wherethrough oil flows, and gradually chokes it thanks to the progressive tapered cross section of said stud 26, thus obtaining in a simple manner the second effect of gradual dampening, whereas the first effect is obtained thanks to said adjustment and choke screw 17. Of course, the variable cross section of the stud 26 may also be obtained by means of a stepped or conical configuration.

The movable member 9 has a limited vertical operational stroke, and it can assume, as shown in the Figs. 1 and 3 of the drawing, an upper operative stop position and a lower rest position. The latter position is obtained by the compressed air which flows by means of known and suitable systems through the union 4, duct 12 and related branch, into the upper portion of the chamber 7, so that the movable member 9 overcomes the action of the reset coil spring 11 threaded around the stem 10 and is kept in its lower position, i.e. in the fully retracted position. At the same time, the tubular extension 23, integral with the member 9, has penetrated the seat for the ball valve 25 and is connected to the source of compressed air so that the latter enters the chamber 20 and causes the floating piston 21 to move and, thereby, it causes a flow into the hydraulic circuit and through the valve 19 and related duct to displace the member 13 in the cylinder 14 towards the position preparatory to the stoppage action, though in a still lowered position. As soon as, in the chamber 7, the action of the compressed air ceases because it has been interrupted upstream of the union

4, the reset spring pushes upwards the member 9 carrying the catch 13 and the entire hydraulic system. In this position the catch 13 is protruding and is ready to stop an incoming platforms (as indicated by the arrow) which will push it backwards to the position shown in Fig. 1 , i.e. the end of the dampened travel. The oil in the hydraulic circuit is caused to flow back into the chamber 20 through the two stages of the gradual dampening action, whereby the interconnecting floating piston 21 is returned to the starting position of Fig. 1. At the same time, as seen in this Figure, the tubular extension 23 is opened to give vent to the compressed air, and the underlying ball valve 25 is closed by its spring and is ready to receive the next pulse of air.

Summarizing, it is useful to point out the two substantial particular features which characterize the device of the invention with respect to the known devices, namely the combined pneumatic/hydraulic operation and the dual choking stage of the outflow of fluid during the dampening step, bearing in mind that, above all, said pneumatic/hydraulic combination enables a wide compliance with the requirements of the assembling operations on platforms even in case of high loads, while the dampening action by means of a co-ordinated hydraulic system enables to comply with the most various requirements of graduality in stopping the platforms. The device described and shown may undergo changes and improvements within the basic principle of the invention.