[0001] This invention refers to a machine for programmed sheet bending of the general type
known in the art as panel bender.
[0002] These panel benders are able to automatically move a sheet metal blank on a horizontal
surface placed in front of a bending press provided with a bending unit with one or
two bending blades, which is able to perform a number of bends of variable size, angle
and direction on each side of the blank. The bending press also comprises a fixed
counter-blade and a blank-holder of variable size which cooperates with the counter-blade
for clamping the blank near the edge to be bent. The bending unit and the blank-holder
are activated by controlled hydraulic actuators consisting of hydraulic cylinders.
An example of this state of the art is given by the European patent EP-A-0293964.
[0003] The advantages of this machine reside in the constant production rate and the production
and programming flexibility. A few drawbacks, however, are encountered.
[0004] In particular, a drawback consists in low energetic efficiency due to the great quantity
of hydraulic energy dispersed in heat and cooled by an appropriate chiller. In fact,
the controlled actuators of the bending unit receive the energy from a constant power
hydraulic pump, which derives the power from a hydraulic circuit with a pressure limiting
device and a flow rate regulator. The inertia of the operation of the hydraulic pump
becomes dispersed energy transformed in heat.
[0005] The object of the present invention is to provide a sheet metal bending machine with
programmable reduced energy if maximum production rate is not required.
[0006] According to the present invention this object is reached by a bending machine comprising
a bending unit which is moved by hydraulic actuators controlled by a hydraulic pump,
characterised in that the hydraulic pump is a variable displacement pump provided
with an electronic closed-loop flow rate, pressure and power control system including
an electrically controlled proportional valve.
[0007] The use of this kind of pump with electronic control allows to program the hydraulic
power for the actuators according to the desired production rate. The new panel bender
according to the invention will thus have a reduced consumption of energy with respect
to the present panel benders provided with a constant power hydraulic pump.
[0008] An embodiment of the present invention is shown by way of nonlimiting example in
the accompanying drawings, in which:
Fig 1 shows the mechanical part of a bending press provided with a hydraulically controlled
bending unit;
Fig. 2 shows a control system for hydraulic actuators of a bending unit as shown in
Fig. 1.
[0009] The bending press shown in Fig. 1 comprises a fixed base 1, which supports a counter-blade
2 on which a lateral edge of a sheet metal blank 3 moved by a manipulator (not shown)
rests.
[0010] A blank-holder 4 cooperates with the counter-blade 3 to clamp the sheet metal edge.
The blank-holder is attached to the front end of a movable support 5, which has a
front end hinged at 6 on a rear part of the fixed base 1. The support 5 is moved up
and down by a plurality of hydraulic cylinders 7.
[0011] A bending unit 8 comprises a common support 9 for two bending blades 10 and 11 which
cooperate with the counter-blade 2 to cause bending of the clamped edge of the sheet
metal. The bending unit is subjected to combined horizontal and vertical movements
by hydraulic actuators consisting of hydraulic cylinders 12 interposed between the
rear part of the base 1 and a lever 13 having a fixed hinge 14 and a mobile hinge
100, and of further hydraulic cylinders 15 interposed between the blade support 9
and the fixed base 1.
[0012] The hydraulic actuators 12 and 15 are controlled by a control system schematically
shown in Fig. 2 (where S indicates a fluid tank) and including a variable displacement
hydraulic pump 16.
[0013] The variable displacement pump 16 is driven by an electric motor 17 and comprises,
as usual, a pump body 18 and a rotatable tiltable swashplate 19 acting on axial pistons
(not shown) to cause fluid displacement with a flow rate depending on the swivel angle
of the swashplate 19. This angle is forced to a maximum value by a piston 20 slidingly
housed in a hydraulic cylinder 21 subjected to the pump pressure and pushed by a spring
22 and can be reduced by the action of a control piston 23 which is slidingly housed
in a hydraulic cylinder 24 controlled by an electrically controlled proportional valve
25 included in a closed loop control system.
[0014] The proportional valve 25 is provided with a valve spool 26 pushed in the position
of Fig. 2 by a spring 41 and controlled by a proportional control solenoid 27 which
receives a control signal 28 from an electronic programmed control unit 29 provided
with command values provided by an operator or a programmed electronic control system,
such as a pressure value 30, a power value 31 and a flow rate value 32 and provided
with an amplifier stage 33 having input signals consisting of a valve spool position
signal 34 coming from an inductive position transducer 35 associated with the valve
spool 26, a swivel angle signal 36 coming from a swivel angle transducer 37 associated
with the control piston 23 and a pump pressure signal 38 coming from a pressure transducer
39 arranged on the pump delivery.
[0015] A pressure limiting device 40 is finally provided between the pump delivery and the
fluid tank S.
[0016] When the pump 16 is at rest and the control system is pressure-less, the swashplate
19 is held in the maximum tilted position by the spring 22.
[0017] When the pump 16 is driven to rotate and the proportional solenoid 27 is de-energized,
the control system regulates to zero stroke pressure as the valve spool 26 is pushed
to the position of Fig. 2 by the spring 41 and therefore the pump pressure is applied
to the control piston 23. A balance between the pump pressure and the force of the
spring 22 is obtained between 8 and 10 bar. This basic setting is taken on with inactive
electronic control unit 29.
[0018] When the electronic control unit 29 is active, the actual pressure value (signal
38), the valve spool position (signal 34) and the pump swivel angle (signal 36) are
compared with the command values 30, 31, 32 by the electronic control unit 29. Any
detected control deviations are processed further and generate a control signal 28
for the proportional solenoid 27, which moves the valve spool 26 from a central position
corresponding to detected values 28, 36, 38 equal to the command values 30, 31, 32
according to said deviations.
[0019] If the programmed control unit 29 demands an increase of the swivel angle in order
to increase the fluid flow rate from the pump 16 to the actuators 12, 15, the control
signal 28 causes the electric current through the solenoid 27 to increase in order
to move the valve spool 26 from the central position to the left until the swivel
angle has reached the required value. On the contrary, a reduction of the solenoid
current causes the valve spool 26 to move to the right to reduce the swivel angle
and therefore the fluid flow rate to the actuators 12, 15.
[0020] Particularly, by acting on the power command value 31 it is thus possible to vary
the hydraulic power delivered by the pump 16 to the actuators 12, 15.
[0021] In this way the hydraulic power supplied to the actuators may be programmed according
to the desired production rate so as to obtain a reduced energy consumption.
1. Bending machine comprising a bending unit (8) which is moved by hydraulic actuators
(12, 15) controlled by a hydraulic pump (16), characterised in that the hydraulic pump (16) is a variable displacement pump provided with an electronic
closed-loop flow rate, pressure and power control system (25, 29, 35, 37, 39) including
an electrically controlled proportional valve (25).
2. Bending machine according to claim 1, characterized in that said valve (25) includes a valve spool (26) for the control of the swivel angle of
the pump (16) and a proportional solenoid (27) for moving the valve spool (26) to
a position corresponding to a desired swivel angle of the pump (16).
3. Bending machine according to claim 2, characterized in that said control system (25, 29, 35, 37, 39) includes an inductive position transducer
(35) associated with the valve spool (26) for detecting the position thereof, a swivel
angle transducer (37) associated with the pump (16) for detecting the swivel angle
thereof, a pressure transducer (39) arranged on the pump delivery for detecting thereof
and a programmed electronic control unit (29) which receives position, swivel angle
and pressure signals (34, 36, 38) from said transducers (35, 37, 39) and predefined
pressure, power and flow rate commands (30, 31, 32) and supplies a control signal
(28) to said proportional solenoid (27).
4. Bending machine according to claim 1, characterized in that the power delivered by the pump (16) is adjustable by acting on the power command
(31).