WO1996026023A1

WO1996026023A1 - Hydraulic actuator for punches and suchlike movable members for working sheet metal, and hydraulic system incorporating this actuator

Info

Publication number: WO1996026023A1
Application number: PCT/EP1996/000663
Authority: WO
Inventors: Antonio Codatto
Original assignee: Sapim Amada SpA; Amada Co Ltd
Current assignee: Sapim Amada SpA; Amada Co Ltd
Priority date: 1995-02-24
Filing date: 1996-02-16
Publication date: 1996-08-29
Anticipated expiration: 1997-08-24
Also published as: IT1278959B1; ITTO950136A0; ITTO950136A1; JPH11501870A

Abstract

The cylinder (10) of the actuator comprises, in its head part (12), a fixed annular dividing wall (28) extending towards the piston (14). This dividing wall (28) defines in its interior a head chamber (20) and, around its exterior, a blind annular chamber forming a power chamber (30). The piston (14) comprises a projection (34) that slides inside the power chamber (30). The dividing wall (28) comprises at least one transverse passage (36) for communication between the head chamber (20) and the power chamber (30). This passage (36) is closed by the annular projection (34) in all positions of the piston (14) between the rest end-of-stroke position and a mid-stroke position in order to prevent the hydraulic pressure from being applied from the head chamber (20) to the power chamber (30). The passage (36) is opened by the annular projection (34) in all positions of the piston (14) between the abovementioned mid-stroke position and the working end-of-stroke position. The abovementioned power chamber (30) is preferably a low-power chamber. Between the annular projection (34) and the rod (16), the piston (14) comprises a cylindrical collar (38) whose diameter is greater than the diameter of the annular projection (34). The cylinder (10) comprises a cylindrical cavity in which the collar slides and this cavity forms a high-power chamber (40) which can selectively receive the pressurized hydraulic fluid on the side of the collar (38) nearest the head part (12) of the cylinder (10).

Description

Hydraulic actuator for punches and suchlike movable members for working sheet metal, and hydraulic system incorporating this actuator

The present invention relates to a hydraulic actuator for punches and suchlike movable members for working sheet metal, of the type comprising a fixed hydraulic cylinder, with a head part, in which slides a piston having a rod passing out through the opposite end of the cylinder from the head part and forming a ram for driving a punch or suchlike member, wherein, between the piston and the head part of the cylinder, is a head chamber for receiving the pressurized hydraulic fluid in order to cause the piston and its ram to execute a forward stroke between a rest end- of-stroke position and a working end-of-stroke position, and wherein the cylinder comprises, around the rod,, a return chamber for receiving the pressurized hydraulic fluid in order to cause the piston and its ram to execute a reverse stroke from the working end-of-stroke position to the rest end-of-stroke position.

The invention has been conceived in terms of its application to multiple-punch punching presses.

These machines comprise two opposing bodies, an upper and a lower, of which the upper body contains a plurality of movable punches while the lower body contains a corresponding plurality of dies, each associated with a corresponding punch. The two bodies may be in the form of blocks in which the punches and the dies are arranged in rows and columns, or in the form of turrets in which the punches and the dies are arranged in circular rings .

The upper body has a hydraulic actuator associated thereto, of the kind defined above, the rod or ram of which, gergally called "tamper", selectively drives, as and when required, one of the punches, in order to perform a particular punching, blanking, drawing or other operation. In a recent development, in the upper and lower bodies of a multiple-punch punching press, one or more punch-die pairs can be replaced by a bending unit comprising two blocks, the upper block being movably mounted in the place of a punch and the lower block being fixed in the place of a die. These two blocks incorporate, respectively, blankholders and at least one bending blade cooperating with an opposing bending blade, in which the working movement of the blade is produced from the same ram as is used to actuate the punches . Details of these bending units are described and illustrated in three Italian patent applications filed by the Applicant company on 6 February 1995 under numbers TO95A000071, TO95A000072 and TO95A000073.

The known actuators used for punching, blanking or drawing operations, and used also for bending operations, are in practice double-acting actuators in which the head chamber, of invariable section, is the only working chamber. The only function of the hydraulic fluid injected into this chamber from a constant-pressure source is to move the ram on its forward stroke, between a rest end-of- stroke position and a working end-of-stroke position, there being no means of controlling the speed of the stroke or the force exerted.

There are cases in which, in order to reduce processing times, it would be desirable to have an actuator in which the total stroke of the ram could be divided up, when desired, into a first portion, in which the punch is rapidly approached to the work, and a second or power part, in which the ram develops the full force required for the punching, blanking, drawing or bending operation in question.

It is an object of the invention to provide an actuator having this desirable characteristic.

According to the invention this object is achieved by means of a hydraulic actuator of the type described at the outset, characterized in that in the head part, the cylinder comprises a fixed annular dividing wall extending towards the piston, which wall defines in its interior the abovementioned head chamber and which together with the cylinder defines around its exterior a blind annular chamber forming a power chamber, in that the piston com¬ prises an annular projection that slides inside the power chamber, in that the dividing wall comprises at least one transverse passage for communication between the head chamber and the power chamber, which passage is closed by the annular projection in all positions of the piston between the rest end-of-stroke position and a mid-stroke position in order to prevent the hydraulic pressure from being applied from the head chamber to the power chamber, and is opened by the annular projection in all positions of the piston between the abovementioned mid-stroke position and the working end-of-stroke position.

By virtue of this idea of solution, when the fluid under pressure is admitted into the head chamber, the pressure of this fluid acts only on the relatively small area presented by the piston inside the head chamber, thus causing the piston and its ram to execute a rapid first portion of the stroke, or prestroke of approach. When the piston reaches the mid-stroke position in which the annular projection of the piston opens the transverse passage or passages through the annular dividing wall, the pressure bursts from the head chamber into the power chamber, whose cross section is greater than that of the head chamber, with the result that the movement of the piston is continued with the working force necessary to perform the desired punching, blanking, drawing or bending operation.

In known actuators, the hydraulic fluid admitted into the head chamber from a constant-pressure source merely causes the rod of the actuator to perform a stroke under constant pressure and the working force exerted on the punch or other working member, such as the movable block of a bending unit, is always the same, no matter what kind of operation is being carried out (punching, blanking, drawing or bending) and irrespective of the area of the workpiece on which this operation is being carried out .

It is a further object of the invention to provide a versatile actuator whose working force can be selected or controlled to suit the kind of operation being performed.

According to the invention, this object is achieved by means of an actuator characterized in that the abovementioned power chamber is a low-power chamber and in that, between the annular projection and the rod, the piston comprises a cylindrical collar whose diameter is greater than the diameter of the annular projection, the cylinder comprises a cylindrical cavity in which the collar slides and this cavity forms a high-power chamber which can selectively receive the pressurized hydraulic fluid on the side of the collar nearest the head part of the cylinder.

Between the annular projection and the rod, the piston may comprise cylindrical collars of increasing diameters greater than the diameter of the annular projection, and the cylinder may then comprise corresponding cylindrical cavities in which the respective collars slide, these cavities forming a corresponding number of chambers of increasingly high power which can selectively receive the pressurized hydraulic fluid on the side of the respective collars nearest the head part of the cylinder.

It is thus possible to provide an actuator capable of functioning, throughout its stroke or for part of its stroke following a stroke of approach, with a working force controlled to suit the conditions of the job to be carried out, for example with increasing forces for increasing thicknesses of the sheet metal and/or for increasing areas of a surface to be punched or bent. The invention also relates to a hydraulic system incorporating an actuator according to the invention and equipped with valve means for selecting low- and high-power strokes and for selecting whether or not the job requires a prestroke of approach.

A clearer understanding of the invention will be obtained by reading the following detailed description, which refers to the accompanying drawings provided by way of non-restricting example, wherein:

Figure 1 is a schematic longitudinal section through a hydraulic actuator for punches and suchlike movable members for working sheet metal, in its rest condition,

Figure 2 illustrates a hydraulic system for the actuator of Figure 1, in a condition corresponding to a prestroke of approach which will be followed by a low-power working stroke,

Figure 3 is a section on a smaller scale through the actuator of Figure 2 in the same prestroke condition as Figure 2 ,

Figure 4 shows the same hydraulic system as in Figure

2 in the condition corresponding to a low-power working stroke,

Figure 5 is a longitudinal section similar to Figure

3 and corresponding to the low-power working stroke,

Figure 6 shows the same hydraulic system set up for a prestroke prior to a high-power working stroke,

Figure 7 shows the same hydraulic circuit in the condition corresponding to a high-power working stroke,

Figure 8 is another section similar to Figures 3 and 5, in which the actuator is shown in a condition corresponding to a high-power working stroke,

Figure 9 shows the hydraulic system in the condition in which the actuator as shown in Figure 5 is performing a complete low-power working stroke with no prestroke,

Figure 10 again shows the same hydraulic system in the condition in which the actuator as shown in Figure 8 is performing a complete high-power working stroke with no prestroke,

Figure 11 again shows the same hydraulic system in the condition of withdrawal of the rod from the working end-of- stroke position to the rest end-of-stroke position, and

Figure 12 is another section through the actuator corresponding to the condition of the system shown in Figure 11.

In Figures 3, 5, 8 and 12 various lines, chambers and other internal spaces of the actuator that are under the delivery pressure of a source of hydraulic fluid are densely dotted, while lines, chambers and other spaces that are under zero pressure or discharge pressure are lightly dotted.

Likewise in Figures 2, 4, 6, 7, 9, 10 and 11, those lines of the system that are under the pressure of the source are shown in solid lines, while those that are under zero pressure or discharge pressure are shown in dashes .

Referring to Figure 1, a hydraulic actuator comprises a fixed hydraulic cylinder 10 with a head part 12.

A piston 14 having a rod 16 slides inside the cylinder 10.

The rod 16 passes out through the opposite end 18 of the cylinder 10 from the head part 12 and forms a ram for driving a punch or suchlike member.

Between the piston 14 and the head part 12 is a head chamber 20 for receiving pressurized hydraulic fluid from an injection/discharge manifold line 22.

The cylinder 10 comprises, around the rod 16, a return chamber 24 that constantly receives the pressurized hydraulic fluid through a manifold line 26.

The head chamber 20 has a cross section or diameter greater than the cross section or diameter of the return chamber 24. Consequently, when the pressure in the head chamber is equal to the delivery pressure, the same pressure in the return chamber 24 does not oppose the forward stroke of the piston 14 corresponding to the advancing of the ram 16.

However, when the head chamber 20 is discharging, the pressure in the delivery chamber 24 causes the piston 14 and its ram 16 to return to the rest end-of-stroke position shown in Figure 1.

In the head part 12, the cylinder 10 has a fixed annular dividing wall 28 attached threto. This annular dividing wall 28, which extends towards the piston 14, defines in its interior the head chamber 20 and, together with the cylinder 10, defines around its exterior a blind annular chamber 30.

As will be understood more clearly later, the annular chamber 30 is a power chamber.

The power chamber 30 can be put in direct com¬ munication with the pressure source, under certain conditions, through an extra line 32, which for the moment will be assumed to be closed.

As to the piston 14, this has an annular projection 34 that slides inside the power chamber. Adjacent to this annular projection 34, the annular dividing wall 28 comprises at least one transverse passage and preferably a plurality of transverse passages 36 for communication between the head chamber 20 and the power chamber 30.

The arrangement is such that the passages 36 are closed by the annular projection 34 in all positions of the piston 14 between the rest end-of-stroke position of Figure 1 and a mid-stroke position (see e.g. Figure 3) in order to prevent the hydraulic pressure from being applied from the head chamber 20 to the power chamber 30.

The passage or passages 36 are opened by the annular projection 34 when the piston advances past the position shown in Figure 3 and for the remainder of the piston stroke, as far as the working end-of-stroke position (see e.g. Figure 5) .

With the arrangement described above, it is possible to produce a rapid forward stroke of the piston 14 from the rest end-of-stroke position shown in Figure 1 to the mid- stroke position shown in Figure 3 at very low power, followed by a working or power stroke when the pressure, from the condition shown in Figure 3 onwards, has reached the power chamber 30, whose diameter is greater than that of the head chamber 20.

In order to produce a working stroke with still greater power or force, between the annular projection 34 and the rod 16 the piston comprises a cylindrical collar 38 whose diameter is greater than that of the annular projection 34. Adjacent to this collar 38, the cylinder 10 has a cylindrical cavity 40 in which the collar 38 slides. This cavity forms a high-power chamber, also marked 40, which can selectively receive the pressurized hydraulic fluid on the side of the collar 38 nearest the head part 12 of the cylinder 10.

The abovementioned power chamber 30 will hereinafter be called the low-power chamber to indicate that the force developed on the collar 38 is greater than that developed on the annular projection 34.

As will be understood later, the high-power chamber 40 can be filled selectively from the low-power chamber 30 via external valve means forming part of the circuit of the hydraulic system illustrated in Figures 2, 4, 6, 7, 9, 10 and 11.

In an alternative which has not been illustrated, between the annular projection 34 and the rod 16 the piston 14 could comprise a plurality of cylindrical collars like the collar 38, but of increasing diameters greater than the diameter of the annular projection 34, and the cylinder 10 would comprise corresponding cylindrical cavities in which the respective collars would slide. These cavities would then form a corresponding number of chambers of increasingly high power which can selectively receive the pressurized hydraulic fluid on the side of the collar nearest the head part 12 of the cylinder 10.

According to the invention, this would give a hydraulic actuator with many power increments.

An actuator such as that illustrated in Figure 1 lends itself to incorporation in a numerical-control system.

For its application in a numerical-control system, the actuator comprises a position transducer indicated by the general reference 44, for sending an electrical signal corresponding to the position of the piston 14 in the cylinder 10 to a control apparatus.

Preferably, as illustrated, the transducer 44 comprises a known type of encoder 46 fixed to the head part 12 and comprising in turn a transducer rod 48 extending down a cavity inside the centre of the piston 14. The transducer rod 48 is surrounded by a magnet 50 in the form of a sleeve fixed to the piston 14 inside the head chamber 20.

The position transducer 44 makes it possible, through the numerical-control system, to program the working stroke of the piston 14 and its ram 16 to suit the operations to be carried out. For example, the piston 14 can be programmed to return to the rest end-of-stroke position before the working end-of-stroke position is reached.

Visible in Figures 1, 3, 5, 8 and 12 are many seals incorporated in the actuator, but these do not require detailed description as they are familiar to those skilled in the art .

A brief description will now be given of the system illustrated in Figures 2, 4, 6, 7, 9, 10 and 11, after which its various modes of operation will be described.

In all these figures the incoming line from the pressure source is marked P and the discharge line T.

The system comprises principal switching valve means for selectively connecting the head chamber 20 to the source P of pressurized hydraulic fluid.

In particular, these switching valve means include a two-position solenoid valve V_ and a two-position hydraulic valve V₂.

In all the conditions shown in Figures 2, 4, 6, 7, 9 and 10, valve V. allows the pressure to be transmitted to the head chamber 20, while the pressure transmitted to the return chamber 24 is taken from the line P upstream of valve V₁.

In the condition represented in Figures 2, 4, 6, 9 and 10, solenoid valve V_x connects to the discharge T the hydraulic actuator of valve V₂, which remains in the position illustrated in these same figures .

For the return of the piston 14 to the rest end-of- stroke position, the position of solenoid valve V. is changed as illustrated in Figure 11, removing the pressure from the head chamber 20 and applying pressure to the actuator of hydraulic valve V,. The latter then changes position, as illustrated in Figure 11, thereby removing the pressure from the entire system except in the line supplying the return chamber 24.

The system also comprises valve means able to select the low-power stroke, which are in the form of a solenoid valve V₃, and valve means able to select a high-power stroke, which are in the form of a solenoid valve V₄.

Lastly, the circuit includes two automatic hydraulically-controlled valves V₅, V₆ whose functions will be obvious to those skilled in the art.

A cycle of operation at low power with a prestroke will now be described.

Initially, the system is in the condition represented in Figure 2 with valve V. set to pass the pressurized fluid into the head chamber 20. Solenoid valve V₃ is closed and prevents the pressurized fluid from passing through it and into the other chambers of the actuator and in particular the low-power chamber 30.

This situation is reflected in Figure 3 in which the piston 14 is shown having descended to a mid-stroke position in which the annular wall 34 is about to open the passages 36.

As soon as the passages 36 have been opened, the pressure is transmitted to the low-power chamber 30 and the working stroke commences .

As can be seen in Figure 4 , the pressure in the low- power chamber 30 is transmitted to a number of system lines but with no particular effect since valve V₄ is closed.

Figure 5 reflects the situation in which the piston 14 and its ram 16 are driven to the bottom of the working stroke by the pressure in the low-power chamber 30.

Under these conditions the ram 16 can exert, for example, a working force of 9 tonnes.

A cycle of operation at high power with a prestroke will now be described.

In Figure 6 the system is in the conditions represented in Figure 2, except as regards valve V₄, which is open.

During the prestroke the conditions of the pressures in the actuator 10 are still as illustrated in Figure 3.

However, when the low-power chamber 30 receives the pressure through the passages 36, the situation that occurs is that shown in Figure 7. The pressure is transmitted from the low-power chamber 30 through solenoid valve V₄ and reaches the high-power chamber 40, producing in the actuator 10 the situation illustrated in Figure 8, in which the piston 14 and its ram 16 execute the working stroke under the force of the pressurized fluid present in the high-power chamber 40. Under these conditions the ram 16 can exert, for example, a working force of 20 tonnes.

The hydraulic system illustrated also offers the possibility of having the piston 14 and its ram 16 execute a stroke at working pressure throughout, beginning at its rest end-of-stroke position.

Figure 9 illustrates the case of a working stroke with no prestroke and at low power. As compared with the situation shown in Figure 2, the circuit differs in that solenoid valve V₃ is open, with the result that the opening of solenoid valve V₁ puts the pressure source in communication simultaneously with both the head chamber 20 and the low-power chamber 30.

The distribution of pressures in the actuator 10 for the entire working stroke is that shown in Figure 5.

In Figure 10 the system is set up for a working stroke with no prestroke and at high power.

Whilst in the situation of Figure 9 only valve V, was open, in the situation of Figure 10 valve V₄ is open as well. Thus the pressurized fluid simultaneously reaches all the chambers 20, 30 and 40, producing in the actuator 10 the condition of pressure shown in Figure 8 and in particular causing the piston 14 and its ram 16 to descend under the force of the pressurized fluid present in all the chambers 20, 30 and 40.

In the case (not illustrated) of an actuator having a plurality of increasingly high-power chambers, the execution of working cycles at the different powers, with or without prestroke, can be achieved by using selective valve means for placing these high-power chambers in communication with a low-power chamber such as 30 as soon as the latter is in receipt of pressure through the passages 36, to give a working cycle with a prestroke; on the other hand, in order to execute a working cycle with no prestroke, the valve means will be set in such a way as to transmit the pressure immediately to the chambers corresponding to the desired power.

After a working cycle has been executed in any of the modes described above, the piston 14 and its ram 16 are returned to the rest position by setting the system to the condition shown in Figure 11.

As can be observed in Figure 11, solenoid valve V₁ has been switched and the pressure of the source P is no longer being transmitted to the head chamber 12 of the actuator, which instead is in communication with the discharge T as usual . The pressure is applied to the return chamber 24 and, via valve V\, is also applied to the operating means of hydraulic valve V₂. The position of valve V₂ is then such as to connect the power chambers 30 and 40 of the actuator to the discharge, thus allowing the pressure in the return chamber 24 to act .

This situation is illustrated in Figure 12.

Claims

CLAIMS 1. Hydraulic actuator for punches and suchlike movable members for working sheet metal, of the type comprising a fixed hydraulic cylinder (10) with a head part (12) , in which slides a piston (14) having a rod passing out through the opposite end of the cylinder (10) from the head part (12) and forming a ram (16) for driving a punch or suchlike member, wherein, between the piston (14) and the head part (12) of the cylinder (10) , is a head chamber (20) for receiving the pressurized hydraulic fluid in order to cause the piston (14) and its ram (16) to execute a forward stroke between a rest end-of-stroke position and a working end-of-stroke position, and wherein the cylinder (10) com¬ prises, around the ram (16) , a return chamber (24) for receiving the pressurized hydraulic fluid in order to cause the piston (14) and its ram (16) to execute a reverse stroke from the working end-of-stroke position to the rest end-of-stroke position, characterized in that in the head part (12) , the cylinder (10) comprises a fixed annular dividing wall (28) extending towards the piston (14) , which wall (28) defines in its interior the abovementioned head chamber (20) and which together with the cylinder (10) defines around its exterior a blind annular chamber (30) forming a power chamber, in that the piston (14) comprises an annular projection (34) that slides inside the power chamber (30) , in that the dividing wall (28) comprises at least one transverse passage (36) for communication between the head chamber (20) and the power chamber (30) , which passage is closed by the annular projection (34) in all positions of the piston (14) between the rest end-of-stroke position and a mid-stroke position in order to prevent the hydraulic pressure from being applied from the head chamber (20) to the power chamber (30) , and is opened by the annular projection (34) in all positions of the piston (14) between the abovementioned mid-stroke position and the working end- of-stroke position.

2. Actuator according to Claim 1, characterized in that the abovementioned power chamber is a low-power chamber (30) and in that, between the annular projection (34) and the rod (16) , the piston (14) comprises a cylindrical collar (38) whose diameter is greater than the diameter of the annular projection (34) , the cylinder (10) comprises a cylindrical cavity (40) in which the collar (38) slides and this cavity (40) forms a high-power chamber which can selectively receive the pressurized hydraulic fluid on the side of the collar (38) nearest the head part (12) of the cylinder (10) .

3. Actuator according to Claim 2, characterized in that, between the annular projection and the rod, the piston comprises cylindrical collars of increasing diameters greater than the diameter of the annular projection, the cylinder comprises corresponding cylindrical cavities in which the respective collars slide, and these cavities form a corresponding number of chambers of increasingly high power which can selectively receive the pressurized hydraulic fluid on the side of the respective collar nearest the head part of the cylinder.

4. Actuator according to any one of the previous claims, characterized in that it comprises a position transducer (44) for sending an electrical signal corresponding to the position of the piston (14) in the cylinder (10) to a control apparatus .

5. Actuator according to Claim 4, characterized in that the transducer (44) comprises an encoder (46) with a transducer rod (48) fixed to the head part (12) of the cylinder (10) and extending down a cavity inside the centre of the piston (14) , and a magnet in the form of a sleeve

(50) fixed to the piston (14) inside the head chamber (20) and surrounding the transducer rod (48) .

6. Hydraulic system incorporating an actuator according to any one of Claims 1 to 5, characterized in that it comprises principal switching valve means (V.) for selectively connecting the head chamber (20) to a source of pressurized hydraulic fluid (P) or to a discharge (T) , and valve means able to select the low-power stroke (V₃) for selectively disconnecting and connecting the low-power chamber (30) to the head chamber, in such a way as to produce, selectively, a stroke of the rod (16) divided into an approach portion of the stroke and a low-power portion of the stroke when the head chamber and low-power chamber are not connected by the external valve means (V₃) , and a low-power stroke from one end-of-stroke position of the rod to the other when the head chamber (20) and the low-power chamber (30) are connected by the external valve means (V₃) .

7. Hydraulic system according to Claim 5, characterized in that it also comprises valve means (V₄) able to select the high-power stroke for selectively disconnecting and connecting the low-power chamber (20) and the high-power chamber (30) in such a way as to produce, selectively, a stroke of the rod (16) divided into an approach portion of the stroke and a high-power portion of the stroke when the head chamber (20) , low-power chamber (30) and high-power chamber (40) are not connected by the high-power stroke valve means (V₄) , and a high-power stroke from one end-of- stroke position of the rod to the other when the head chamber (20) , low-power chamber (30) and high-power chamber

(40) are connected by the high-power stroke valve means

(V₄) .

8. System according to Claim 6, characterized in that it comprises a plurality of valve means able to select the high-power stroke, corresponding to chambers of increas¬ ingly high power, for selectively disconnecting and connecting the low-power chamber and the respective chambers of increasingly high power, in such a way as to produce, selectively, a stroke of the rod divided into an approach portion of the stroke and a portion of the stroke of a respective high power when the head chamber, low-power chamber and respective high-power chamber are not connected by the respective high-power stroke valve means, and a stroke of a respective high power from one end-of-stroke position of the rod to the other when the head chamber, low-power chamber and high-power chamber respectively, are connected by the respective high-power stroke valve means.

9. System according to any one of Claims 6 to 8 , charac¬ terized in that the abovementioned external valve means comprise solenoid valves (V₃, V₄) suitable for incorporation in a numerical-control system.