Apparatus and method for the electrohydraulic control of parallelism in a bending machine for working metal products

Abstract

An apparatus for the electrohydraulic control of the parallelism of a roller in a bending machine for working metal pieces, has a first and second pumps for supplying with an operating fluid a first and second actuators, position transducers and a first and second proportional valves to adjust the flow of the operating fluid into the first and second actuators according to signals of the position transducers.

Claims

1. Method of operating an apparatus for the electrohydraulic control of the parallelism of a roller of a bending machine for processing metal pieces, the apparatus comprising: pump means for feeding with an operating fluid first actuating means and second actuating means arranged for moving respectively a first end and a second end of said roller; position transducer means operatively connected to an electronic control unit and suitable for detecting the positions of said first and second end; first and second proportional valve means that are operatively controllable by said electronic control unit to adjust the flow of said operating fluid into said first and second actuating means according to signals of said position transducer means wherein: said pump means comprises a first pump and a second pump operatively connected to each other, which are arranged for supplying in a dedicated manner said first and second actuating means respectively by means of a first and a second hydraulic circuit that are independent of one another, said first and second proportional valve means being located, according to a parallel configuration, along a first and a second ducts that are connected in a branched manner to a first and second delivery portion of said first and second hydraulic circuits respectively, said first and second proportional valve means being so configured as to be able to draw operating fluid from said first and second delivery portion to reduce the volumetric flowrate thereof to said first and/or second actuating means, said method comprising: a) activating said first pump and second pump for feeding in a dedicated manner said first actuating means and second actuating means through respectively said first and second hydraulic circuits in order to move the first and second ends of said roller; b) detecting, by said position-transducer-means, the positions of said first and second end of said roller to check the parallelism condition of said roller; c) processing through said electronic control unit the position-signals provided by said position-transducer-means and d) controlling, through said electronic control unit, said first and second proportional valve means to adjust the flow of said operating fluid into said first and second actuating means according to said position-signals, said first and second proportional valve means being opened for drawing operating fluid through said first and second ducts connected in a branched manner to the first and second delivery portions of said first and second hydraulic circuits respectively so as to reduce the volumetric flowrate of the operating fluid to the first and/or second actuating means.

Description

(1) The invention can be better understood and implemented with reference to the attached drawings, which illustrate an embodiment thereof by way of non-limiting example, in which:

(2) FIGS. 1 and 2 are schematic views respectively of a bending machine with four rollers and of a bending machine with two rollers, for bending metal pieces, in which the control apparatus according to the invention can be provided to control the parallelism of one or more rollers;

(3) FIG. 3 shows schematically the prior-art control apparatus disclosed above;

(4) FIG. 4 shows schematically an apparatus, according to the present invention, for the electrohydraulic control of the parallelism in a bending machine, as shown in FIG. 1 or 2, for working metal pieces, such as sheet metals, section bars and the like.

(5) With reference to FIGS. 1 and 2, there are respectively shown a bending machine 1 of the four-roller type, and a bending machine 10 of the two-roller type for working metal products, in particular for bending L-shaped sheet metal, metal profiled sections or other similar products.

(6) Both the bending machine 1 and the bending machine 10 each comprise a supporting frame 2 supporting one or more dragging rollers for the advancement of the piece of sheet metal L to be bent that are connected to respective reduction gears. In FIGS. 1 and 2, for the sake of simplicity, there is shown only one dragging roller 3. There is also provided a movable roller 4 for pinching the piece of sheet metal L, the movable roller 4 being configured for being brought near, and moved away from the aforesaid dragging roller 3. The movable roller 4 is supported by hydraulic actuators C1, C2, of the dual-effect type, that are drivable for raising and lowering the movable roller 4. At the two ends of the movable roller 4 respective slides 50 are provided that are arranged for guiding the ascent and descent movement of the movable roller 4.

(7) The dragging roller 3, in a non-limiting manner, can be supported by an overturnable arm that enables a workpiece to be removed once it has been bent. The bending machine 1 is further provided with a first 30 and a second 31 idle roller supported by respective oscillating arms pivoted on side pivots.

(8) The aforesaid bending machines 1 and 10 represent two possible apparatuses in which a control apparatus 20 according to the invention, which will be disclosed below, can be incorporated and which is used to vary the tilt of the or of each movable roller, for example to correct bending defects or to make conical bends, whilst maintaining always control of the parallelism of the roller with respect to the axis thereof or according to a preset axis.

(9) It remains understood that the control apparatus 20 according to the inventionwhich will be disclosed in detail belowcan be applied for controlling parallelism both in bending machines with rollers that are movable along linear guides and vertical or horizontal axes and in bending machines provided with rollers moving along planetary guides or supported by oscillating arms pivoted on side pivots.

(10) In the description that follows that is provided by way of example, for the sake of clarity, a case is disclosed in which the control apparatus 20 is configured for controlling the parallelism of the only movable roller 4, in the bending machine 1 or 10 shown In FIGS. 1 and 2. Obviously, parallelism control can also be applied to several or all the moving rollers of a bending machine, providing several respective control apparatuses 20 or a single control apparatus 20 that is suitably configured for controlling all the aforesaid moving rollers.

(11) With reference to FIG. 4, at a first end 11 and at an opposite second end 12 of the movable roller 4, in the bending machine 1 or in the bending machine 10, a first hydraulic actuator C1 and a second hydraulic actuator C2 are provided respectively for moving the movable roller 4 towards or away from the dragging roller 3. The first C1 and second C2 hydraulic actuator are suppliable with an operating fluid, in particular oil, each by a respective pump and a dedicated hydraulic circuit. In particular, the first C1 and the second C2 hydraulic actuator are suppliable respectively with a first pump P1 and a second pump P2, through a first hydraulic circuit 5 and a second hydraulic circuit 6 that are independent of one another. The first pump P1 and the second pump P2 are operationally connected to one another. In particular, the first pump P1 and the second pump P2 are substantially similar to one another, of the same volumetric flowrate, and are mechanically connected to one another via a mechanical transmission shaft 7 as can be seen in schematized form in FIG. 4. The mechanical transmission shaft 7 that is common to the first P1 and to the second pump P2, is arranged for synchronizing the motion of the two aforesaid pumps at the same rotation speed, such as to supply the same oil volumetric flowrate values to the first C1 and second C2 hydraulic actuator. In other words, owing to this configuration and constructional condition, dispensing of identical quantities of oil to the first C1 and second C2 hydraulic actuator is ensured.

(12) As can be seen in FIG. 4, the first hydraulic circuit 5 comprises a first delivery portion 8 that connects the first pump P1 to a first directional valve VD1. The first directional valve VD1 is connected by two connecting conduits to two respective fluid dynamic chambers of the first hydraulic actuator C1. The first directional valve VD1 acts to control the flow direction of the oil inside the first hydraulic actuator C1, such as to fill one chamber by emptying the other, depending on whether the first end 11 of the movable roller 4 has to be moved towards or away from the dragging roller 3.

(13) The first hydraulic circuit 5 further comprises a first return portion 9 through which the oil that is evacuated from the first hydraulic actuator C1, passing through the first directional valve VD1, returns to a collecting and storage tank 21.

(14) Similarly, the second hydraulic circuit 6 comprises a second delivery portion 18 that connects the second pump P2 to a second directional valve VD2, that has a function that is similar to what has been disclosed for the first directional valve VD1. The second directional valve VD2 is connected by two further connecting conduits to two respective further fluid dynamic chambers of the second hydraulic actuator C2. The second hydraulic circuit 6 comprises a second return portion 19 through which the oil that is evacuated from the second hydraulic actuator C2, passing through the second directional valve VD2, returns to the oil collecting and storage tank 21.

(15) The control apparatus 20 comprises a first proportional flow valve VP1 and a second proportional valve VP2, associated respectively with the first hydraulic circuit 5 and with the second hydraulic circuit 6. The first proportional flow valve VP1 and the second proportional valve VP2 are connected according to a parallel configuration with respect to the first delivery portion 8 and to the second delivery portion 18. More precisely, the first proportional flow valve VP1 is placed along a first branch conduit 13 connected, in derivation, to the first delivery conduit 8 and extending as far as the tank 21.

(16) Similarly, the second proportional valve VP2 is placed along a second branch conduit 14, connected, in derivation, to the second delivery conduit 18 and extending as far as the tank 21.

(17) The first VP1 and second VP2 proportional valve, which are so positioned, are configured for being able to tap, i.e. draw, the oil respectively from the first 8 and second 18 delivery portion to reduce the volumetric flowrate of oil that flows respectively to the first C1 and second C2 hydraulic actuator. Substantially, unlike known prior art systems, in which the proportional valves are placed in series on the delivery portions of the oil to throttle the passage of the oil, in the control apparatus 20 according to the invention, the first VP1 and second VP2 proportional valvewhich are placed in a derivation position i.e. branched position with respect to the delivery paths of the oilare positioned for operating parallel to the work flow of the oil. As a result, the parallelism control of electronic type, obtained by acting on the first VP1 and second VP2 proportional valve, is an auxiliary or additional control to the inherent parallelism control already existing in the hydraulic circuit conformation of the control apparatus 20.

(18) As shown in FIG. 4, a maximum pressure valve Vmax is also provided that is connected to the first 8 and second 18 delivery portion, the function of which is to deliver the circulating oil directly to the tank 21 if the pressure reaches a maximum set value, thus avoiding undesired damage to the bending machine.

(19) Near the first end 11 and the second end 12 of the movable roller 4 a first T1 and a second T2 position transducer are respectively provided. The first T1 and the second T2 position transducer are arranged for detecting the positions of said first 11 and second 12 end.

(20) The control apparatus 20 comprises an electronic control unit U1 to which the first VP1 and second VP2 proportional valve, the first VD1 and second VD2 directional valve, and the first T1 and second T2 position transducer are operationally connected. As will be seen in greater detail below, the first VP1 and second VP2 proportional valve are driven, in case of need, by the electronic control unit U1, on the basis of position signals produced by the first T1 and second T2 position transducer, such as to regulate the oil volumetric flowrate that advances to the first C1 and second C2 hydraulic actuator. The electronic control unit U1 is able to check the parallelism of the movable roller 4, or of each movable roller, of the bending machine 1 or 10 through position signals that are provided by the position transducers T1 and T2 and are compared by an analogue comparing unit, which in turn supplies instructions to a logical processing unit (PLC). The logical processing unit (PLC) comprises a suitably programmed microprocessor for automatically correcting possible parallelism errors by commanding the first VP1 and/or second VP2 proportional valve, or solenoid valves, for supplying the pressurized oil to the hydraulic actuators C1, C2 for the translation movement of the roller. The proportional valves or solenoid valves VP1, VP2, are activatable by respective driving solenoids by means of suitable electric pulses or signals.

(21) The first T1 and second T2 position transducer can each comprise a linear potentiometric transducer that sends the position signals to a respective input of the control unit U1, which compares it with programmed reference data and then sends suitable instructions to the microprocessor, such as to intervene, if required, on the tilt of the movable roller 4.

(22) Also the first pump P1 and the second pump P2 can be connected operationally to the electronic control unit U1, which controls all the various steps of a work cycle. In particular, the electronic control unit U1 commands the first VD1 and second VD2 directional valve in such a manner that the oil flow in the first C1 and in the second C2 hydraulic actuator is enabled in an advancement direction or in an opposite direction, depending on whether the movable roller 4 has to be moved towards or away from the dragging roller 3. In the case described, the first VD1 and second VD2 directional valve are driven by the electronic control unit U1 to lower or raise the movable roller 4.

(23) During operation, in normal operating conditions, the first VP1 and second VP2 proportional valve are normally closed, i.e. they are not traversed by a flow of oil, which oil thus advances undisturbed along respectively the first 8 and second 18 delivery portion with identical volumetric flowrate values both in the first 5 and in the second 6 hydraulic circuit, thus ensuring perfectly balanced driving of the first C1 and second C2 hydraulic actuator. Essentially, owing to the particular structural configuration providing for a splitting of the circulation of the oil into two distinct and substantially identical hydraulic circuits, i.e. the first 5 and second 6 hydraulic circuit, a first control level, of hydraulic type, of the parallelism is defined that guarantees, with a satisfactory degree of precision, the parallelism of the movable roller 4, more precisely, the parallelism of a first longitudinal axis A1 of the movable roller 4 with respect to a second longitudinal axis A2 of the dragging roller 3, during raising or lowering, also in a non-centered loading operating situation, i.e. with a load acting near the first 11 or the second 12 end.

(24) During operation, in normal operating conditions, the piece of sheet metal L is appropriately bent by the interaction with the movable roller 4 and with the dragging roller 3, without the first VP1 and second VP2 proportional valve intervening, which remain normally closed.

(25) In other words, the parallelism condition is maintained through the effect of the hydraulic control level that derives from the particular hydraulic supply that is split and balanced in relation to the two hydraulic actuators C1 and C2. If factors intervene that have a strong influence on the parallelism condition, for example a noticeable decentring of the piece of sheet metal L with respect to the median zone of the rollers, or an irregularity of the thickness of the piece of sheet metal L or something else and the parallelism condition can no longer be assured by relying only on the duplicated hydraulic conformation disclosed above, the control unit U1 intervenes to open the first VP1 and/or second VP2 proportional valve. A second control level of electronic type thus intervenes, which is servo-assisted by the first hydraulic control level disclosed above, but is independent thereof. For example, if the first hydraulic actuator C1 advances faster upwards, the first proportional flow valve VP1 is opened (and not closed as would occur in a prior-art apparatus), to enable a calibrated passage of the derived oil, i.e. of the oil tapped, i.e. drawn, parallely from the first delivery portion 8, to the tank 21. Thus part of the oil, instead of continuing to advance to the first hydraulic actuator C1, is discharged freely (and thus at the working pressure of the piece of sheet metal L and not at maximum pressure as would occur in the prior-art apparatus) to the tank 21. This means that a smaller amount of oil reaches the first hydraulic actuator C1, thus slowing the first hydraulic actuator C1 and adapting the position and advancement speed thereof to those of the second hydraulic actuator C2. At this point, the first C1 and second C2 hydraulic actuator can continue advancement perfectly synchronized with one another. The control of the parallelism of the movable roller 4 can be carried out indifferently both during the ascent and the descent movement of the movable roller 4.

(26) Owing to the particular configuration of the control apparatus 20, the first VP1 and second VP2 proportional valves are thus not fatigued and are driven only when strictly necessary, i.e. with reduced frequency compared with what occurs in the prior art, as the parallelism is maintained in most of the operating circumstances by the hydraulic control level inherent to the hydraulic structural conformation of the control apparatus 20. Both the proportional valves VP1, VP2 and the first P1 and second pump P2 and all the other components of the apparatus operate subject to a pressure that is the one requested by the working of the piece of sheet metal L, and never at a higher pressure, this resulting in an extension to the working life of the hydraulic componentry of the bending machine. It is thus clear how the parallelism condition of the movable roller 4, owing to the control apparatus 20, can be ensured without the need to depend exclusively on the proportional valves VP1, VP2; i.e. in the event of a fault of the proportional valves VP1, VP2, the parallelism condition, in relation to non-exceptional operating conditions, is ensured by the hydraulic structural configuration of the apparatus 20. In other words, if the electronic componentry is faulty, the control apparatus 20 continues to maintain the movable roller 4 parallel to itself or to the dragging roller 3, up to a new load near the maximum permissible value, enabling the bending machine 1 to be used continuously.

(27) The parallelism obtained hydraulically proves to be tougher, more reliable, safer and simpler to maintain than what is obtainable by resorting only to electronics, as occurs in the prior art. The reduction of the probabilities of a fault in the electronic componentry obtained with the control apparatus 20 according to the invention enables the need to resort to interventions by expensive specialized personnel for repairing electronic faults to be significantly reduced or even eliminated. In all cases, even in the event of a fault to an electronic component, the bending machine, owing to the control apparatus 20, can continue to be used without causing machine downtime, in normal operating circumstances in which exceptional load conditions do not occur or in which no commanded variation is required of the tilt of the first longitudinal axis A1 with respect to the second longitudinal axis A2, for example for conical bending of the sheet metal, or for bending section bars, made on the outside of the rollers, on apposite shaping portions protruding from the latter.

(28) In conclusion, the control apparatus 20 according to the invention, including a first control level of hydraulic type, and a second control level of electronic type, make the bending machine 1 or 10 more reliable and efficient, drastically reducing machine downtime risks.