The present invention refers in general to handling equipments of the so-called swingable lever type.
More particularly the invention relates to a device for controlling the oscillation of the arm of such an equipment comprising a driving double acting cylinder having a chamber in which a main piston is sealingly mounted, which is slidable as a result of the selective delivery of fluid under pressure at opposite zones of the chamber of the cylinder, the main piston being connected to a rod having a driving end which projects from the cylinder and is connected to said arm by a toggle joint.
In the equipments of the type defined above, for example in pneumatic handling equipments also known as tilter devices, anomalous conditions can take place during delivery of fluid under pressure to the chamber of the cylinder, which may involve risks for the integrity of the equipments themselves and for the apparatuses which are associated to them, or for possible operators which may be close to such equipments.
These anomalous conditions are essentially of two types.
A first anomalous condition can take place in the case in which, for example after a maintenance operation carried out on the equipment, the feeding and the exhaust lines of the fluid under pressure are not correctly connected to the opposite ends of the cylinder, in particular if an end of the cylinder is connected to the feeding of the fluid under pressure while the other end freely communicates with the outside environment. When, in such conditions, the fluid under pressure is only fed to one of the cylinder ends, the piston is moved violently against the cylinder end in communication with the outside environment, causing the arm of the equipment to fall down suddenly to an end-of-travel position.
Another anomalous condition occurs in the case of a pressure drop in the line for feeding the fluid under pressure to the cylinder, in particular if the oscillation axis of the arm of the equipment is not arranged vertically and if the piston has not reached as yet the end-of-stroke position in which the toggle joint makes its movement irreversible. In this case in fact, owing to the lack of pressure and under the weight of the apparatuses associated with the arm, it can fall down violently towards its lower end-of-travel position.
In order to overcome the aforesaid anomalous condition, devices for controlling the motion of the piston rod have been proposed which operate on the basis of the principle to apply a friction force against the outside surface of the rod in the case of a pressure drop. For this purpose, for example, brake devices may be used which include planes inclined with respect to the cylinder axis, to which rollers or balls are associated which are intended to interfere with the peripheral surface of the rod when a pressure drop below a predetermined threshold occurs. Other braking devices employ a laminar element having a through circular hole in which the rod is inserted, whose diameter is little greater than that of the rod. In the latter devices, in the operation with the fluid fed under normal pressure, the sheet element is perpendicular to the axis of the rod, whereby the rod can slide axially through it. In the case of pressure drop, the sheet element is placed in a configuration inclined with respect to the rod axis, in order to cause interference between the edges of its through hole and the radial surface of the rod, which causes the axial locking of the latter.
At any rate, the devices mentioned above for controlling the movement of the rod, and therefore the oscillation of the arm, may turn out to be not very practical or not very reliable in use. In fact, their operation can be affected by the dimensions of the mechanical members involved in the operation, so that the wear of one of the members of the device can jeopardize its good operation, such as the presence of foreign bodies, also if they are very small, in the fluid fed to the cylinder.
Moreover, such devices allow to lock the rod when it is moving along only one of its shifting directions and require therefore to be doubled in order to lock the motion of the rod in both its shifting directions. In practice, if inclined planes with rollers or balls are used, it will be necessary to provide inclined planes with respective rollers or balls for each shifting direction of the rod, while if pierced laminar elements are used for locking the rod, two laminar elements, one for each shifting direction of the rod will have to be provided.
In both the anomalous feeding conditions of the cylinder considered above, the traditional swingable lever handling equipments risk to endure serious damages which could jeopardize their operation and that of the apparatuses carried by their swingable arm, as well as to cause damages to possible people standing in proximity of the equipments, if they are not equipped with devices adapted to prevent the arm to fall down in the event of an anomaly in the feeding of fluid under pressure to the cylinder.
The main object of the present invention is therefore to provide a handling equipment of the swingable lever type, whose structure is fitted with a device for controlling the oscillation of the arm, said device being able to prevent that malfunctions may take place as a consequence of the anomalous conditions of feeding mentioned above.
This object is attained thanks to the fact that the device comprises:
an axial cavity formed in the rod, in which a nut screw is arranged,
a screw member comprising a threaded shank so arranged as to engage the nut screw of the rod, and a head portion opposite to the rod and mounted rotatably but not axially slidable with respect to the cylinder, and
control means for controlling the rotating movement of the screw member, which are associated to the head portion of the screw member and are adapted to perform a braking action of its rotation when an anomalous condition occurs in the feeding of the fluid under pressure to the cylinder chamber.