Double-acting pneumatic cylinder with hydraulic damper

Abstract

 A handling equipment of the swingable lever type comprises a driving double acting cylinder (5) having a chamber (18) in which a main piston (15) is sealingly mounted. The main piston (15) is connected to a rod (10) having a driving end (10a) which projects from the cylinder (5) and is associated with a movable arm (7). The equipment (1) is provided with a device for dampening the oscillation of the arm (7), which comprises an axial cavity (27) formed in the rod (10) and containing a service fluid, in which a stem (30) rigidly connected to the cylinder (5) and provided with orifice means (31,31a) for the service fluid is sealingly and slidably mounted in such a cavity (27).

Description

[0001] The present invention refers in general to handling equipments of the so-called swingable lever type.

[0002] More particularly, the invention relates to a device for dampening the oscillation of the arm of a handling equipment of the swingable lever type, which equipment comprises 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 associated with said arm.

[0003] In known equipments of the type defined above, for example in pneumatic handling equipments also called "tilter devices", anomalous conditions of delivery of fluid under pressure to the chamber of the cylinder can take place, which may involve on the one hand risks to the integrity of the structure of such equipments and of the equipment associated with them, and on the other hand risks to the safety of operators who may be close to the equipments.

[0004] These anomalous conditions are essentially of two kinds.

[0005] 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 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 with the feeding of the fluid under pressure while the other end freely communicates with the outer environment. When, in such conditions, the fluid under pressure is fed only to one of the cylinder ends, the piston moves violently against the cylinder end which is in communication with the outer environment, causing the arm of the equipment to fall down sharply to an end-of-travel position.

[0006] Another anomalous condition occurs in the case of a pressure drop in the feeding line of 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 associated with the rod makes irreversible its movement in the cylinder. 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.

[0007] In order to avoid the latter 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 example, to this purpose 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 sheet member 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 member is perpendicular to the axis of the rod, whereby the rod can slide axially through it. In the case of pressure drop, the sheet member is placed in a configuration inclined with respect to the rod axis, so that an interference take place between the edges of its through hole and the radial surface of the rod, which causes the axial locking of the latter.

[0008] 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 their good operation, as well 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 when the locking of the motion of the rod in both its shifting directions is desired. 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 of the shifting directions of the rod, while if pierced sheet members are used for locking the rod, two sheet members, one for each shifting direction of the rod, will have to be provided.

[0009] 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 close to 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 the fluid under pressure to the cylinder.

[0010] The main object of the present invention is therefore to provide a dampening device intended to fit out a handling equipment of the swingable lever type, which is able to prevent that malfunctions may occur in the case in which the anomalous feeding conditions mentioned above take place.

[0011] This object is attained thanks to the fact that an axial cavity separated from the cylinder chamber and containing a service fluid is formed inside the rod, a stem rigidly connected with the cylinder and provided with orifice means for the service fluid being sealingly and slidably mounted in such a cavity, so that the movement of the rod with respect to the stem is slowed down as a consequence of the flowing of the service fluid through the orifice means, if the sliding speed of the main piston inside the cylinder exceeds a threshold speed set by the cross-section of the orifice means.

[0012] Thanks to these characteristics, the dampening device of the invention is marked by a simple and compact structure allowing to obtain an effective slowing down of the arm towards the end-of-travel positions, in the case in which an anomaly in the feeding of the cylinder takes place, keeping at the same time the hindrance and the weight of the equipment small, and allowing to limit its production costs.

[0013] Further characteristics and advantages of the invention will become more clearly evident from the reading of the detailed description which follows, given purely by way of a non limiting example and referred to the attached drawings, in which:

figure 1 is a schematic elevational side view of a swingable lever handling equipment provided with a dampening device according to the invention,

figure 2 is an enlarged cross-sectional view of a detail of the equipment indicated by the arrow II in figure 1, and

figure 3 is a view similar to figure 2, showing a different working condition of the device.

[0014] With reference to the figures, 1 indicates as a whole a handling equipment of the swingable lever type, which is operated by means of fluid under pressure, typically air.

[0015] The equipment 1 comprises a body 3 to which a double acting fluid cylinder 5 is associated for driving a fork lever arm 7 by means of a toggle joint unit of a type known per se and not illustrated in the figures, which is contained inside the body 3 of the equipment 1. In brief, the toggle joint unit allows to set in an oscillation motion a pair of coaxial crank pins 11 on which the branches 13 of the fork arm 7 are fitted, as from the reciprocating motion of a driving end 10a of a rod 10 which is slidable with respect to the cylinder 5. Then, an attachment plate 13a is fastened to the branches 13, which is provided with holes and/or openings in order to allow to connect apparatuses (not shown in the figures) to be moved by the equipment 1.

[0016] A main piston 15 which is connected to the rod 10, is slidably and sealingly mounted by annular seals 16, inside a chamber 18 defined by the body of the cylinder 5. The two opposite faces of the piston 15 have each an axial sleeve portion 15a, 15b, whose diameter is slightly wider than that of the rod 10.

[0017] The chamber 18 is axially defined by a pair of heads 20a and 20b, respectively higher and lower with reference to the figures. Respective feeding and exhaust lines 21a, 21b and 22a, 22b for the fluid under pressure are formed in each of the heads 27a and 27b. The lines 21a and 21b or 22a and 22b are selectively connected, by a switching device of a type known per se, with a source of fluid under pressure, in order to produce alternatively over-pressure conditions on one of the faces of the piston 15, so as to cause the reciprocating motion of the piston 15 inside the chamber 18 between the heads 20a and 20b. Each of the lines 21a, 21b has preferably a pair of branch lines one of which ends in the chamber 18 facing a respective face of piston 15, the other one ending into a seat 25a, 25b for receiving a respective sleeve portion 15a, 15b of the piston 15 when the piston is in an end-of-stroke position.

[0018] In the rod 10 a cylindrical cavity 27 is formed axially, in which an enlarged head 29 of a sliding stem 30 is slidably and sealingly mounted. The head 29 is provided with an outer seal 32 bearing on the sidewall of the cavity 27. The end of the stem 30 opposite to that supporting the head 29 is rigidly connected to a support plate 34 anchored to the bottom of the cylinder 5, for example by means of a plurality of axial screws (not illustrated in the figures).

[0019] The cavity 27 is filled up with a service fluid, typically oil, and is separated with respect to the outer environment in order to prevent the discharge of such a liquid. To this end, a bored plug 36 which is screwed at the end of the rod 10 opposite to its driving end 10a, is arranged on the side of the chamber 18. The plug 36 is crossed centrally by the stem 30, a ring-like seal 37 being interposed between the stem 30 and the plug 36.

[0020] On the side of the rod 10 close to the drive end 10a, an auxiliary piston 38 which will be considered in further detail in the following, is inserted in the axial cavity 27. The piston 38 is provided with a ring-like seal 39 similar to the seal 37 of the bored plug 36.

[0021] Moreover, the stem 30 is provided with orifice means for the service fluid, which are conveniently arranged at its end provided with the head 29. These orifice means can consist of a longitudinal hole 31 opening at the end of the stem 30 facing the auxiliary piston 38 and is connected with a calibrated transversal hole 31a opening on the side of the enlarged head 29 facing the plug 36.

[0022] As a result of the sliding of the piston 15 inside of the chamber 18, and therefore of the rod 10 with respect to the head 20a, the enlarged head 29 of the stem 30 slides inside of the cylindrical cavity 27 forcing the service fluid to run through the orifice means constituted by the holes 31 and 31a, so as to pass from a side to the other of the head 29. The hole having the smaller cross-section of the orifice means, that is the hole 31a in the case illustrated in the figures but which could be otherwise the hole 31, is dimensioned in such a way that, in the normal operation of the equipment 1, the rod does not endure any appreciable slowing down. However, its cross-section is such as to involve a slowing down of the rod 10 if the movement speed of the rod exceeds a prefixed threshold, owing to the viscous friction caused by the passage of the service fluid through the holes 31 and 31a. In particular, in the case in which a condition of anomaly of one of the kinds considered above, in connection with the feeding of the cylinder 5, had to be taken place, the excessive movement speed of the rod 10 is slowed down owing to the passage of the service fluid through the holes 31 and 31a of the stem 30 which causes a dampening of the oscillation of the arm 13 of the equipment 1.

[0023] In the case in which, as illustrated in the figures, the change of position of the enlarged head 29 inside the cavity 27 involves a different extension of the stem 30 inside such a cavity, it is necessary to provide a device for compensating the longitudinal extension of the cavity 27, in view of the fact that the working volume for the service fluid must remain constant. To this end, the auxiliary piston 38 is mounted floating in the cavity 27 and it can be associated with elastic thrust means 40, constituted by a coil spring, biasing it towards the stem 30. However, it has been surprisingly found that the spring 40 can be eliminated without jeopardize the operation of the device, and concurring to reduce the number of the parts of the equipment and, consequently, its total cost.

[0024] Moreover, the auxiliary piston 38 is associated with guide means of its axial movement in the cavity 27, comprising a pin 42 an end of which is fixed to the auxiliary piston 38, while the opposite end is slidable in a corresponding seat 46 formed in proximity of the driving end 10a of the rod 10. Preferably, the seat 46 communicates with the outer environment with respect to the cylinder 5, by means of a vent hole 48.

[0025] In the case in which it is desirable to adjust the operating threshold of the dampening device, that is of the threshold speed of the main piston 15 beyond which its sliding within the chamber 18 has to be slowed down, adjusting means of the cross-section of the orifice means in which the service fluid passes, can be arranged. For example, a spindle (not illustrated in the figures) can be arranged in a coaxial hole inside the stem 30 and associated with the base of the stem 30 in proximity of the plate 34 by means of a threaded connection, which has a conical tip at his end facing the driving end of the rod 10, in order to cooperate with a corresponding seat formed in a position adjacent to the hole 31, for allowing the section of the hole is changed as a result of the control of such a spindle by means of a tool which can be driven from the outside of the cylinder 5.

Claims

1. Device for dampening the oscillation of the arm of a handling equipment of the swingable lever type, which equipment (1) comprises a driving double acting cylinder (5) having a chamber (18) in which a main piston (15) is sealingly mounted, which is slidable as a result of the selective delivery of fluid under pressure at opposite zones of the chamber (18) of the cylinder (5), the main piston (15) being connected to a rod (10) having a driving end (10a) which projects from the cylinder (5) and is associated with said arm(7),
   characterized in that an axial cavity (27) separated from the chamber (18) of the cylinder (5) and containing a service fluid is formed inside the rod (10), a stem (30) rigidly connected with the cylinder (5) and provided with orifice means (31, 31a) for the service fluid being sealingly and slidably mounted in such a cavity (27), so that the movement of the rod (10) with respect to the stem (30) is slowed down as a consequence of the flowing of the service fluid through the orifice means (31, 31a), if the sliding speed of the main piston (15) inside the cylinder (5) exceeds a threshold speed set by the cross-section of the orifice means (31, 31a).

2. Device according to claim 1, characterized in that the stem (30) has an enlarged head (29) in proximity of which orifice means (31, 31a) for the service fluid are arranged.

3. Device according to claim 2, characterized in that a seal (32) is interposed between the enlarged head (29) of the stem (30) and the wall delimiting the axial cavity (27) of the rod (30).

4. Device according to anyone of claims 1 to 3, characterized in that the stem (30) has an end fixed to a support plate (34) anchored to the bottom of the cylinder (5) .

5. Device according to anyone of claims 1 to 4, characterized in that the axial cavity (27) of the rod (30) has a variable longitudinal extension for allowing to compensate the variation of the extension of the stem (30) received inside it.

6. Device according to claim 5, characterized in that a floating auxiliary piston (38) is arranged in proximity of the end of the axial cavity (27) opposed to the stem (30).

7. Device according to claim 6, characterized in that the floating auxiliary piston (38) is associated with guide means (42, 46) for its axial movement.

8. Device according to claim 7, characterized in that the guide means of the axial movement of the auxiliary piston (38) comprise a pin (42) one end of which is connected to the auxiliary piston (38) while the opposite end is slidably mounted in a corresponding seat (46) formed in proximity of the driving end (10a) of the rod (10).

9. Device according to claim 8, characterized in that said seat (46) communicates with the outer environment with respect to the cylinder (5) by means of a vent hole (48).

10. Device according to anyone of claims 1 to 9, characterized in that the cross-section of the orifice means (31, 31a) is variable as a result of the movement of an adjustment member which can be controlled from the outside of the equipment (1).

Drawing