SUPPLY DEVICE AND PROCEDURE FOR PRESS DRIVE WITH RECOVERING THE LIFTING ENERGY

Supply device and procedure for press actuators, with recovery of the raising energy

The present invention relates to a supply device, with recovery of the raising energy, for press actuators, and the associated automatic operating procedure.

For certain operations and manufacturing processes, pneumatic actuators are used to perform pressing functions in which part of the pressing stroke, known as the approach stroke or the idle stroke, is completed without encountering any specific resistance, while the remainder of the stroke, described hereafter as the active stroke, requires a particular predetermined thrust force.

A specific case of this kind is that of internal mixers for rubber and elastomers, in which a pressing weight has to be raised by a corresponding pneumatic actuator, to make it possible to open the loading hatch for the material to be processed, and then lowered until it comes into contact with the loaded material and then presses it into the mixing chamber with a predetermined degree of pressure to permit complete processing of all the material. In this case a large amount of compressed air, supplied to the upper chamber of the actuator, is required to complete a stroke, part of which is necessary only to lower the weight connected to the actuator after it has been raised to open the access hatch of the mixing chamber, while the part of the stroke in which active pressure is required is limited.Since the necessity of supplying large volumes of compressed air entails high costs for the pneumatic equipment and high energy consumption by this equipment, the need arises to make savings in the compressed air required for a manufacturing cycle by limiting the quantity required from the compressor.

A further requirement arises from the reduction of the actuator movement times, which enables output to be increased.

These results are obtained by the present invention, which specifies a supply device with recovery of the raising energy, for press actuators having a cylinder inside which a piston delimits two chambers, namely an upper and a lower chamber, with a pneumatic power supply, and provided with corresponding supply and discharge valves, in which the supply lines to the actuator chambers pass through an economizer unit which is interposed between the control unit and the actuator, and which includes a servocontrolled valve which intercepts the supply line to the upper chamber, a servocontrolled valve intercepting the supply line to the lower chamber, and a connecting pipe between the supply line of the lower chamber and that of the upper chamber, downstream from the interception valves of these lines, provided with a servocontrolled interception valve, with detectors of the position of the actuator piston present, these being functionally connected to the servocontrolled valves and capable of bringing about the opening and closing of the valves in successive phases of the piston movement. The detectors of the position of the actuator piston include at least one detector of the actuator piston position, located at an intermediate point of the piston stroke and capable of bringing about, when actuated in the descending phase of the piston, the closing of the valve intercepting the connection line between the supply units of the piston chambers and the opening of the interception valves of the chamber supply lines, connected with the corresponding supply and discharge lines of the control unit.

The control unit includes pneumatic means of braking the descending stroke of the actuator piston and means of detecting the position of the actuator piston, comprising a detector of the piston position located at a level above the lowest level of descent and capable of controlling the activation of the braking means.

The economizer unit is located at a short distance from the actuator and includes pipes and valves with a wide passage section which induce negligible pressure drops in the pneumatic flow.

The servocontrolled valves may conveniently be spherical valves, each provided with a servocontrol actuator, supplied from a corresponding electromagnetic valve, in connection with external means of monitoring and control.

According to the invention, there is a procedure for supplying power, with recovery of the raising energy, to press actuators having a cylinder inside which a piston delimits two chambers, namely an upper and a lower chamber, with a pneumatic power supply, which includes at least a phase of raising the actuator piston, with a supply to the lower chamber of the cylinder at the maximum system pressure, an idle descending phase of the piston, with energy recovery, comprising the direct connection between the lower and the upper chambers of the piston and the the interception of the external supply and discharge lines of the chambers of the actuator, and an active descending phase of the piston, comprising at least the interception of the direct connection between the chambers of the actuator and the discharge of the lower chamber of the actuator.

The active descending phase includes the connection of the upper chamber of the actuator with a pneumatic supply source at predetermined pressure, or alternatively includes the expansion of the intercepted air inside the upper chamber of the piston.

The active descending phase may conveniently include a terminal braking phase which is automatically activated, and in which the discharge line from the lower chamber of the actuator to the atmosphere is throttled.

Additional details may be obtained from the following description, with reference to the attached drawings, which show: in Figure 1, a internal mixer of a type suitable for the application of the device according to the invention; in Figure 2, an pneumatic diagram of the supply device for the press actuator for the mixer according to the invention, in the phase of raising the pressing weight; in Figure 3, the device in Figure 2, in the phase of preparation for the descent of the weight; in Figure 4, the phase of descent of the weight with energy recovery; in Figure 5, the final phase of the descent with energy recovery; in Figure 6, the phase of compression of the material being mixed; in Figure 7, the phase of braking the descent; in Figure 8, the phase of compression of the material being mixed at reduced pressure, with energy recovery.

As Figure 1 shows, an internal mixer for the preparation of rubber, elastomer, and similar mixes includes a body 1 containing rotors 2, capable of mixing the material inside a chamber 3; a discharge hatch 4 allows the material to be removed after processing, while a loading port, 5, permits the ingress of the materials to be mixed, these materials being impelled into the chamber 3 by means of a pressing weight 6, represented by a solid line in its completely lowered position and by a broken line in its raised position.

The pressing weight 6 is connected by a shaft 7 to a piston 8 which can slide inside a cylinder 9, in which it delimits an upper and a lower chamber; by means of the piston 8, the weight 6 may be raised for loading and lowered for the compression of the material to be processed.

The piston 8 and the cylinder 9 form an actuator, indicated in its entirety by the number 10, which is supplied with pneumatic power to perform the above operations of raising and pressing.

For the supply of the actuator 10, a pneumatic circuit is provided, a diagram of which is shown in Figure 2 in the phase of raising the weight and is shown in Figures 3 to 8 in successive phases of descent and pressing

According to this diagram, the pneumatic actuator 10 is supplied from the pneumatic main supply 11 through a master control unit 12, of a known type, including a lubrication and condensation separation unit 13, downstream from which the supply line to the lower chamber of the cylinder includes an electromagnetic valve 14, a valve 15 which is pneumatically controlled by the electromagnetic valve 16, a non-return valve 17, and a throttle, 18; in the supply line to the upper chamber of the cylinder there is a pressure reducer 19, operated by a selector 20 at the desired pressure level, and an electromagnetic valve 21.

The economizer unit 22 is supplied from the control unit 12 and includes a valve 23, located in the supply line to the upper chamber of the cylinder and controlled through a pneumatic servocontroller 24 by an electromagnetic valve 25; a valve 26, located in the supply line to the lower chamber of the cylinder and controlled through a pneumatic servocontroller 27 by an electromagnetic valve 28; and a valve 29, interconnecting the supply lines to the chambers of the cylinder, and controlled through a pneumatic servocontroller 30 by an electromagnetic valve 31.

For operation without the use of the economizer unit, valves 23, 26 and 29 are set in the configuration shown in Figure 2, namely with valves 23 and 26 open and valve 29 closed: in this way the control unit 12 supplies the actuator directly, as if it were directly connected to it, without the intervention of the unit 22.

The system is kept in this configuration, as shown in Figure 2, during the raising of the piston 8 and the weight 6.

By energizing the electromagnetic valve 14 and thus opening it, air is supplied through unit 12 to the lower chamber of the cylinder, while the upper chamber is connected through valve 21 to the discharge pipe, so that the piston 8 begins to rise and is then maintained in the raised position at the top of its stroke.

The piston 8 may rise at the maximum speed permitted by the available pressure, since there is a free flow through valves 15 and 17 and the throttle 18.

To initiate the descent of the piston 8 with recovery of the energy, the electromagnetic valves 25 and 28 are energized to close valves 23 and 26, as shown in Figure 3; when this has taken place, the position indicators 32 and 33, relating to valves 23 and 26 respectively, permit the energizing of the electromagnetic valve 31, which causes the valve 29 to open, thus bringing the unit into the configuration shown in Figure 4, while the electromagnetic valve 14 returns to its de-energized position, connected to the discharge pipe 34, and the electromagnetic valve 21 is energized, thus connecting the supply pipe to the upper chamber of the cylinder to the pneumatic mains, and consequently preparing the control unit 12 for the initiation of the active descent of the weight.

In these conditions, the compressed air contained in the lower chamber of the cylinder 9, having been previously isolated from the mains pressure, is transferred to the upper chamber of the cylinder, as shown by the arrows in Figure 4, by means of the kinetic energy of the descending weight and the positive difference between the forces acting on the opposing surfaces of the piston.

In this phase, it is possible to arrest the descent of the weight in any intermediate position by de-energizing the electromagnetic valve 31, thus closing valve 29 and consequently interrupting the transfer of air from one chamber of the cylinder to the other.

Having passed through a predetermined section of the descending stroke, the piston 8 actuates the end-of-travel device 35, which causes the electromagnetic valve 31 to be de-energized and valve 29 to be closed.

Subsequently the electromagnetic valves 25 and 28 are de-energized, thus causing valves 23 and 26 to open as shown in Figure 5.

This again connects the actuator 10 to the control unit 12, and permits the actuator to be activated with the maximum specified thrust, depending on the available pressure level, to compress the material within the chamber 3 of the mixer.

The compression, represented in the diagram in Figure 6, is obtained by supplying compressed air from the mains to the upper chamber of the cylinder 9 through the electromagnetic valve 21 and the valve 23 which is open; the air contained in the lower chamber of the cylinder is discharged to the atmosphere through the controlled valve 15, the electromagnetic valve 14, and the discharge pipe 34.

When the piston 8 reaches the end-of-travel device 36, as shown in Figure 7, this device activates the electromagnetic valve 16, which causes the valve 15 to close; the outflow of air through the lower chamber of the cylinder 9 is then permitted only through the throttle 18, which thus brakes the descent for the remaining part of the stroke to the position of complete lowering of the weight.

On reaching the lowest position, the piston is kept in place, with valve 21 energized, for the time necessary for the completion of mixing; after this, the electromagnetic valve 21 is de-energized, permitting the air contained in the upper chamber of the cylinder to be discharged to the atmosphere through the pipe 34, and a new cycle may then be initiated, with the complete raising of the piston 8 and of the weight 6, as described previously.

From the above description it may be seen that for each cycle during the raising phase a certain volume of compressed air contained in the cylinder is discharged to the atmosphere, while during the lowering phase a volume of compressed air equal to approximately a third of the previous amount is discharged into the atmosphere.

This makes it possible to save 70% of the air for each descent and approximately 33% of the compressed air for the whole cycle as compared with operation without the economizer unit.

If the descent of the weight is controlled in its active phase at a pressure less than the maximum mains pressure at which the raising is performed, it is possible also to obtain a saving of compressed air in the active section of the piston stroke below the end-of-travel device 35, by making use of the expansion of the compressed air present in the upper chamber of cylinder 9 throughout the piston stroke.

For this purpose, as shown in Figure 8, when the end-of-travel device 35 is activated the electromagnetic valve 31 is de-energized, causing the valve 29 to close; when the valve 29 is closed, the position indicator 37 associated with the shutter of the valve 29 permits the energizing of the electromagnetic valve 28, which causes valve 26 to open, thus discharging to the atmosphere, through the pipe 34, the remaining air contained in the lower chamber of the cylinder.

In this way the air pressure present in the upper chamber of the cylinder is no longer opposed and enables the remainder of the descending stroke to be completed.

On completion of the descent, with its braking phase as described previously, the end-of-travel device 38 is activated, and this causes the electromagnetic valve 25 to be energized, which opens the valve 29, thus restoring the configuration shown in Figure 2.

In both the possible modes of operation described, that is either with active descent in connection with the pneumatic mains or with active descent with expansion of the air in the upper chamber, a time-delay relay is provided in parallel with the end-of-travel device 35, and operates to initiate the active phase of descent after a predetermined time, even if the position corresponding to the activation of the end-of-travel device 35 has not yet been reached by the piston, or in any other case in which the end-of-travel device 35 fails to operate.

The device according to the invention is also advantageous with respect to the descent time of the weight, since the circuit through which the air passes in the first part of the descent of the weight, in other words the communication between the upper and the lower chamber of the cylinder through the valve 29, is quite short and presents insignificant resistance, permitting a descent velocity in this phase which is considerably greater than that which would be obtained if air were supplied at the mains pressure through the electromagnetic valve 21 and the valve 23 and the air were discharged from the lower chamber through the valve 15 and the pipe 34.

The gain in time in the descending stroke is of the order of 25%. Consequently, as a result of the saving of compressed air which is achieved, the device according to the invention, and its automatic operating procedure, can be used to reduce the capacity of the compressors, to reduce the consumption of electrical energy, and to reduce the initial installation costs, since equipment of smaller dimensions can be installed; the presence of the economizer group also makes it possible, by closing the valves 23, 26, 29, to reliably lock the piston at any intermediate point of its descent, thus enabling cleaning and maintenance operations to be performed in safe conditions.

The economizer device according to the invention, described in detail in relation to a particular control unit, may also be applied to different control units while remaining within the ambit of the present invention.

The economizer unit may also be realized in a different form, for example with the use of multiple-acting valves, and other variations may be made in accordance with specific applications, while still remaining within the ambit of the invention in its general characteristics.