Patent Description:
Conventionally, as a method for detecting such a double blank, there is a method described in <CIT> (PTL <NUM>).

In a case where a blank material (workpiece) is formed by using a linear motion type press machine of a system for driving an oil hydraulic cylinder for vertically moving a slide by a servo valve, when a slide position is detected at a time of rapid rising of a press load signal (calculated from a pressure signal for lowering and a pressure signal for rising of the oil hydraulic cylinder) at a forming start time point, and the detected slide position is outside a plate thickness allowable range (plate thickness allowable range set according to a reference plate thickness position for a single workpiece), a die protecting device of a linear motion type press described in PTL <NUM> determines that a double blank is generated, and moves the slide in a direction opposite to a direction at the time of pressurizing work. A die cushion device is not attached to the linear motion type press described in PTL <NUM>.

As a widely and generally used double blank detection system, there is a system in which a double blank detecting mechanism is provided in a die (upper die) such that a limit switch is turned on only at a time of double blank generation.

Document <CIT> discloses a die cushion device according to the preamble of claim <NUM>, which comprises a double blank detecting device.

In the method for detecting a double blank described in PTL <NUM>, a press load and a slide position are detected. And, when a slide position is detected at a time of a rapid rising of the press load at a forming start time point, and the detected slide position is outside a plate thickness allowable range, then it is determined that the double blank is generated. However, the change range (variation) of the detected slide position is large, the slide position exceeds the plate thickness of a single blank material to be changed, and therefore there is a problem that the double blank cannot be accurately detected.

It is considered that this reason is because the press machine is heavy, thick, long and large relative to the die cushion device attached thereto, resolution in detection of a press load, or slide position detection is low, or the press load is generated in accordance with a forming load or state change (such as linear expansion of a column) of a press machine secondarily (without control).

In a case where the double blank detecting mechanism is provided in the die such that the limit switch is turned on only at the time of double blank generation, there are a plurality of problems described below.

Firstly, it is time-consuming to perform fine adjustment for each die. Much time is required for the fine adjustment for each die since the limit switch is not tuned on when the blank number is normal, namely one, but the limit switch is tuned on when the blank number is two.

Secondly, detection accuracy is low. At the forming start time point at which a double blank is detected (to be detected), a machine is often brought into an excessive state accompanied by vibration. Thus, it is difficult that the limit switch having a mechanical detecting mechanism accurately (stably) performs detection of about <NUM>.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a double blank detecting device for a press machine, and a die protecting device for a press machine capable of reliably detecting a double blank in a case where the double blank is supplied to a press machine.

In order to achieve the above object, a die cusion device according to the invention is defined in claim <NUM>.

According to the aspect of the present invention, in place of detection of the slide position and the press load described in PTL <NUM>, the position of the cushion pad and the die cushion load are detected, and the double blank is detected based on the die cushion position signal indicating the position of the cushion pad and the die cushion load signal indicating the die cushion load.

In a press cycle of the press machine that automatically and repeatedly forms the blank materials one by one, in a case where the thicknesses of the blank materials are constant (normal), the cushion pad position signal and the die cushion load signal have higher responsiveness and higher accuracy, and more stable than a slide position signal and a press load signal.

For example, in a case where a thin plate (blank material) having a plate thickness of about <NUM> is formed, it is important that stability of the cushion pad position signal and the die cushion load signal at a normal time, namely, a change range is small, in order to reliably detect an abnormality (double blank) of changing the thickness to about <NUM>.

In the press cycle of the press machine, the double blank is detected by using the cushion pad position signal and the die cushion load signal which are more stable than the slide position signal and the press load signal, and therefore it is possible to reliably detect the double blank.

The die cushion position signal holding value at the time point of rising to the constant die cushion load signal (predetermined value) is stable at the normal time, and therefore it is possible to reliably detect the abnormality (double blank) from the change of the die cushion position signal holding value.

In a die cushion device attachable to a press machine according to yet another aspect of the present invention, it is preferable that in a case where die cushion load control by the die cushion device is started with a position of a slide of the press machine at a time of indirect collision of the slide with the single blank material as a reference, where the abnormality identification value is designated by Y, an average value of the die cushion position signal holding values obtained by repeatedly forming the single blank material a plurality of number of times is designated by XAVE, and a plate thickness of the blank material is designated by T, the abnormality identification value Y be set to a value satisfying a condition as follows: <MAT> and
the double blank detecting unit detect, as the double blank, a state where the holding value of the held die cushion position signal is smaller than the abnormality identification value Y.

In a case where the die cushion load control start time point is the slide position reference (time point when the slide position reaches a predetermined die cushion start slide position), when the double blank is detected, the die cushion load control start time point of the slide position reference is at a die cushion position smaller by the single blank material (pressed by the slide) than that at the normal time, and therefore the die cushion position signal holding value is smaller than the average value XAVE. The case where the die cushion position signal holding value is smaller than the above abnormality identification value Y is detected as the double blank, so that it is possible to reliably detect the double blank (two or more blank materials).

In a die cushion device attachable to a press machine according to yet another aspect of the present invention, it is preferable that in a case where die cushion control by the die cushion device is started with a position of a slide of the press machine at a time of indirect collision of the slide with the single blank material as a reference, where the abnormality identification value is designated by Y, a die cushion position signal holding value obtained in a case where double blank materials are tried is designated by X', and a plate thickness of the blank material is designated by T, the abnormality identification value Y be set to a value satisfying a condition as follows: <MAT> and
the double blank detecting unit detect, as the double blank, a state where the holding value of the held die cushion position signal is smaller than the abnormality identification value Y.

The abnormality identification value Y is set in the range of the value obtained by adding the change amount (<NUM> to <NUM>% of the plate thickness T of the blank material) to the die cushion position signal holding value X', and the case where the die cushion position signal holding value is smaller than the above abnormality identification value Y is detected as the double blank, so that it is possible to reliably detect the double blank. The change amount is mainly influenced by natural vibration of a machine at the moment of indirect contact of the slide with the cushion pad to be changed, and the degree is <NUM> to <NUM>% of the plate thickness T empirically.

In a die cushion device attachable to a press machine according to yet another aspect of the present invention, it is preferable that in a case where die cushion load control by the die cushion device is started with die cushion load change generated in the cushion pad due to indirect collision of a slide of the press machine with the cushion pad as a reference, where the abnormality identification value is designated by Y, an average value of the die cushion position signal holding values obtained by repeatedly forming the single blank material a plurality of number of times is designated by XAVE, and a plate thickness of the blank material is designated by T, the abnormality identification value Y be set to a value satisfying a condition as follows: <MAT> and
the double blank detecting unit detect, as the double blank, a state where the holding value of the held die cushion position signal is larger than the abnormality identification value Y.

in a case where the die cushion load control start time point is the die cushion load generation reference (at the moment of indirect contact of the slide with the cushion pad), when the double blank is detected, contact is caused at a die cushion position larger than that at the normal time by the single blank material, and die cushion load starts rising, and therefore the die cushion position signal holding value becomes larger than the average value XAVE. The case where the die cushion position signal holding value is larger than the above abnormality identification value Y is detected as the double blank, so that it is possible to reliably detect the double blank.

In a die cushion device attachable to a press machine according to yet another aspect of the present invention, it is preferable that in a case where die cushion load control by the die cushion device is started with die cushion load change generated in the cushion pad due to indirect collision of a slide of the press machine with the cushion pad as a reference, where the abnormality identification value is designated by Y, a die cushion position signal holding value obtained in a case where double blank materials are tried is designated by X', and a plate thickness of the blank material is designated by T, the abnormality identification value Y be set to a value satisfying a condition as follows: <MAT> and
the double blank detecting unit detect, as the double blank, a state where the holding value of the held die cushion position signal is larger than the abnormality identification value Y.

The abnormality identification value Y is set in the range of the value obtained by subtracting the change amount (<NUM> to <NUM>% of the plate thickness T of the blank material) from the die cushion position signal holding value X', and the case where the die cushion position signal holding value is larger than the above abnormality identification value Y is detected as the double blank, so that it is possible to reliably detect the double blank.

A die cushion device attachable to a press machine according to yet another aspect of the present invention preferably further includes a first manual setter that manually sets the abnormality identification value, or a first automatic setter that automatically calculates and sets the abnormality identification value.

In a die cushion device attachable to a press machine according to yet another aspect of the present invention, it is preferable that a predetermined value of the die cushion load signal be a value within a range of not less than <NUM>% and not more than <NUM>% of a maximum die cushion load of the die cushion device.

A die cushion device attachable to a press machine according to yet another aspect of the present invention preferably further includes a second manual setter that manually sets a predetermined value of the die cushion load signal, or a second automatic setter that automatically calculates and sets the predetermined value of the die cushion load signal based on the maximum die cushion load of the die cushion device.

The cushion pad position signal and the die cushion load signal can be acquired from the die cushion device, and addition of a detector dedicated for detection of these signals is unnecessary, and therefore an inexpensive device can be obtained.

When the double blank detecting unit detects the double blank, the braking device starts quick braking of the slide. In a case of a servo motor driven press machine, maximum torque is caused to act on the servo motor in the braking direction, and applies quick braking. Even when the quick braking is started, stopping of the slide requires limited time by inertia of the slide or the like, forming advances during the limited time, and the risk of breaking the die increases. Therefore, the quick braking is started, and the hydraulic cylinder incorporated in the slide is immediately depressurized, so that the one portion including the die mounting surface of the slide is relatively movable in the elevating direction. Consequently, the slide (die) is safely stopped before forming is started, and the breakage of the die is prevented (die is protected).

In a die cushion device attachable to a press machine according to yet another aspect of the present invention, it is preferable that the die cushion device include: a die cushion driving unit that supports the cushion pad, elevates and lowers the cushion pad, and generates a die cushion load in the cushion pad; a die cushion load command device that outputs a die cushion load command; and a die cushion load controller that controls the die cushion driving unit based on the die cushion load command output from the die cushion load command device, and generates a die cushion load corresponding to the die cushion load command in the cushion pad, wherein the die cushion load command device outputs a predetermined die cushion load command, causes the hydraulic cylinder to contract by a die cushion load generated in the cushion pad in response to the die cushion load command, and to relatively move one portion including a die mounting surface of the slide in an elevating direction, in a period when the slide reaches a stop, only in a region where forming is not started among a region where the cushion pad moves, when the double blank detecting unit detects the double blank.

Contraction action of the hydraulic cylinder is facilitated by the die cushion load added from the cushion pad, and the hydraulic cylinder incorporated in the slide is contracted, and the one portion including the die mounting surface of the slide relatively moves in the elevating direction with the contraction of the hydraulic cylinder. The predetermined die cushion load command is output in a period when the slide reaches a stop, only in the region where forming is not started. On the contrary, in the forming region at the time of double blank detection being the state extremely dangerous for the die, the die cushion load basically is not caused to act. In the forming region, in other case, for example, in a case where a light beam type safety device is shielded, at the time of press machine emergency stop with operation, a cope is different from a cope in a situation where the predetermined die cushion load acts in order to suppress damage of the die due to generation of drawing wrinkle until the slide is stopped.

In a die cushion device attachable to a press machine according to yet another aspect of the present invention, it is preferable that the die cushion device include: a die cushion position command device that outputs a die cushion position command; and a die cushion position controller that controls the die cushion driving unit based on the die cushion position command output from the die cushion position command device after termination of die cushion load control by the die cushion load controller, and raises the cushion pad to move the cushion pad to a predetermined die cushion standby position, wherein the predetermined die cushion standby position is a position obtained by movement in the elevating direction from a forming start position by a predetermined amount. This is because a stop period of the slide until the forming is started (lowering amount of the die mounting surface of the slide) is secured, in a case where the double blank is detected.

In a die cushion device attachable to a press machine according to yet another aspect of the present invention, the region where the forming is not started is a region between the predetermined die cushion standby position, and a position at which the forming is started.

In a die cushion device attachable to a press machine according to yet another aspect of the present invention, it is preferable that when the double blank detecting unit detects the double blank, the die cushion load command device automatically output a maximum die cushion load command as the predetermined die cushion load command.

When the double blank is detected, the maximum die cushion load is caused to act on the slide with the hydraulic cylinder incorporated therein, and the hydraulic cylinder is contracted as fast as possible, so that formed is not started.

According to the die cushion device attachable to a press machine according to the present invention, the position of the cushion pad, and the die cushion load having high detection accuracy are used for the detection of the double blank, and therefore in a case where the double blank is supplied to the press machine, it is possible to reliably detect this.

According to a preferred embodiment of the present invention, when the above double blank detecting device detects the double blank, quick braking of the slide is started by the braking device, the hydraulic cylinder incorporated in the slide is depressurized, and the one portion including the die mounting surface of the slide is relatively moved in the elevating direction, and therefore the slide (die) can be safely stopped before forming is started, and it is possible to prevent breakage of the die (protection of the die).

Hereinafter, embodiments of a die cushion device attachable to a press machine according to the present invention is described with reference to the attached drawings.

<FIG> is a schematic configuration diagram illustrating an embodiment of an entire device including a press machine, a die cushion device, and a die protecting device.

As illustrated in <FIG>, this entire device includes a press machine <NUM>, and a die cushion device <NUM>, and the press machine <NUM> includes a press controller <NUM>, an overload removal device <NUM>, and a press driving device <NUM>.

The die cushion device <NUM> includes a cushion pad <NUM>, oil hydraulic cylinders 130R, <NUM>, die cushion driving devices 160R, <NUM>, a die cushion controller <NUM>, and the like.

In this example, a die protecting device <NUM> (<FIG>) for a press machine is constituted in the die cushion controller <NUM>, a double blank detecting device <NUM> is constituted in the die protecting device <NUM>.

<FIG> is a diagram illustrating a mechanism portion of the press machine <NUM> and the die cushion device <NUM> illustrated in <FIG>.

In the press machine <NUM> illustrated in <FIG>, a flame is composed of a crown <NUM>, a bed <NUM>, and a plurality of columns <NUM> disposed between the crown <NUM> and the bed <NUM>, and a slide <NUM> is movably guided in the vertical direction by sliding members <NUM> provided in the columns <NUM>.

This press machine <NUM> is a so-called mechanical servo press in which the slide <NUM> is driven by a servo motor described below through a crank shaft <NUM>, and connecting rods <NUM>, and performs drawing of a large thin plate such as a body forming of a vehicle in this example.

Rotational driving force from the press driving device <NUM> is transmitted to the crank shaft <NUM>, and an encoder <NUM> for detecting the angle and the angular velocity of the crank shaft <NUM> is provided.

A pair of left and right oil hydraulic cylinders (hydraulic cylinders) <NUM>, 107R are incorporated in (fixed to) the slide <NUM>, and leading ends of the connecting rods <NUM> are rotatably fixed to pistons <NUM> of the oil hydraulic cylinders <NUM>, 107R.

<FIG> illustrates the oil hydraulic cylinder 107R illustrated on the right, the oil hydraulic cylinder 107R being in a state where the piston <NUM> moves to an upper end, and illustrates the oil hydraulic cylinder <NUM> illustrated on the left, the oil hydraulic cylinder <NUM> being in a state where the piston moves to a lower end.

These oil hydraulic cylinders <NUM>, 107R expand and contract, so that relative positions between leading end positions of the connecting rods <NUM> and a die mounting surface (lower surface) of the slide <NUM> are changed. That is, the oil hydraulic cylinders <NUM>, 107R can relatively move the die mounting surface of the slide <NUM> by extension and contraction of the oil hydraulic cylinders <NUM>, 107R with respect to movement of the slide <NUM> driven by the crank shaft <NUM> and the connecting rods <NUM>.

A pair of balancer cylinders <NUM> that apply upward force to the slide <NUM> are disposed between the slide <NUM> and the crown <NUM>.

An upper die <NUM> is mounted on the die mounting surface of the slide <NUM>, and a lower die <NUM> is mounted on an upper surface of a bolster <NUM> on the bed <NUM>.

The die cushion device <NUM> presses a peripheral edge of material (blank material) formed by the press machine <NUM> from a lower side, and mainly includes a blank holder (wrinkle pressing plate) <NUM>, the cushion pad <NUM>, and a pair of left and right oil hydraulic cylinders <NUM>, 130R.

The cushion pad <NUM> supports blank holders <NUM> through a plurality of cushion pins <NUM>.

The oil hydraulic cylinders <NUM>, 130R function as die cushion driving units for supporting the cushion pad <NUM>, elevating and lowering the cushion pad <NUM>, and generating a die cushion load to the cushion pad <NUM>.

Die cushion position detectors <NUM>, 133R that detect positions in the extending and contracting direction of the piston rods as positions in the elevating and lowering direction of the cushion pad <NUM> (die cushion positions) are provided near the oil hydraulic cylinders <NUM>, 130R, respectively.

The material (blank material) <NUM> is set on (brought into contact with) upper sides of the blank holders <NUM> by a carrier device (not illustrated).

When the upper die <NUM> mounted on the die mounting surface of the slide <NUM> collides with the cushion pad <NUM> through the blank material <NUM>, the blank holders <NUM>, and the cushion pins <NUM> with lowering operation of the slide <NUM>, thereafter the blank material <NUM> is formed between the upper die <NUM> and the lower die <NUM> while the peripheral edge of the blank material <NUM> is pressurized and held between the blank holders <NUM> to which die cushion loads are applied from the oil hydraulic cylinders <NUM>, 130R, and the upper die <NUM>.

The maximum die cushion load of the die cushion device <NUM> of this example is <NUM> kN, the die cushion load set value is <NUM> kN, and the die cushion stroke is <NUM>. However, in a die cushion stroke of <NUM>, <NUM> is a non-forming stroke ΔZ (ΔZ = <NUM>) from when the upper die <NUM> comes into contact with the blank material <NUM> until when the blank material <NUM> comes into contact with the lower die <NUM>. That is, standby positions of the blank holders <NUM> are each set to a position (Z2) larger than a forming start position (position Z1 at which the blank material <NUM> comes into contact with the lower die <NUM>), and forming is not started during the stroke ΔZ (=Z2 - Z1) before forming start at which the position of the slide lower surface is larger than Z1. In this example, the plate thickness of the blank material <NUM> is <NUM>.

<FIG> is a configuration diagram illustrating an example of the press driving device <NUM> illustrated in <FIG>.

The press driving device <NUM> functions as a driving device and a braking device of the press machine <NUM> (slide <NUM>), and includes a servo motor <NUM>, a reduction gear <NUM> that transmits rotational driving force of the servo motor <NUM> to the crank shaft <NUM>, and a braking device <NUM>.

A driving electric power corresponding to a torque command signal <NUM> is supplied from a servo amplifier <NUM> to the servo motor <NUM>, and the servo motor <NUM> is driven and controlled such that the speed becomes a predetermined (set) sliding speed or crank shaft angular velocity. Power is supplied from a DC (Direct Current) power supply <NUM> with a regenerator to the servo amplifier <NUM>, and electric power generated by a driving torque of the servo motor <NUM> acting in the braking direction at the time of braking of the press machine <NUM> (slide <NUM>) is regenerated to an AC power supply <NUM> through the servo amplifier <NUM> and the DC power supply <NUM>.

An encoder <NUM> is mounted on a rotating shaft of the servo motor <NUM>, an encoder signal output from the encoder <NUM> is converted to a servo motor angular velocity signal <NUM> by a signal converter <NUM>.

The braking device <NUM> has a solenoid valve <NUM> for brake release to which compressed air is supplied from an air pressure source <NUM> through a reducing valve <NUM>, a brake mechanism <NUM>, and a silencer <NUM>.

A driving signal is added from the press controller <NUM> to the solenoid valve <NUM> for brake release, and ON/OFF control of the solenoid valve <NUM> for brake release is performed.

At a normal time (operation with no abnormality), the solenoid valve <NUM> for brake release of the braking device <NUM> is turned on, a brake is released, and when (various) abnormality occurs, a torque command signal <NUM> of the direction opposite to the slide operation direction is given to the servo amplifier <NUM>, so that the slide <NUM> is braked, and after stopping (at almost the same time as stopping), the solenoid valve <NUM> for brake release is turned off, and the brake is caused to act.

<FIG> is a configuration diagram illustrating an example of the overload removal device <NUM> illustrated in <FIG>.

As illustrated in <FIG>, the overload removal device <NUM> includes an oil hydraulic pump <NUM> axially connected to an induction motor <NUM>, an accumulator <NUM>, a check valve <NUM> disposed on a discharge port side of the oil hydraulic pump <NUM>, relief valves <NUM>, <NUM>, a pressure detector <NUM>, and a solenoid (depressurizing) valve <NUM>.

A high pressure line where the pressure detector <NUM> is disposed is connected to head-side hydraulic chambers <NUM> of the oil hydraulic cylinders 107R, <NUM> incorporated in the slide <NUM>, and a low pressure line connected to the accumulator <NUM> is connected to rod-side hydraulic chambers of the oil hydraulic cylinders 107R, <NUM> (<FIG>).

At a normal time, pressure of initial pressure P0 (about <NUM>/cm<NUM>) acts on the head-side hydraulic chambers <NUM>, and the oil hydraulic cylinders 107R, <NUM> are most extended in a no-load state (state in which load does not act on the slide <NUM> from outside) (state on the right in <FIG>).

In a case where the head-side hydraulic chambers <NUM> are pressurized, in a state where the slide <NUM> is at a top dead center (at least no-load state), a contactor <NUM> is turned on (is turned off after P0 is confirmed) until the initial pressure P0 is confirmed by the pressure detector <NUM>.

The setting pressure of the relief valve <NUM> that acts on the discharge port of the oil hydraulic pump <NUM> is set slightly larger than the initial pressure P0, and therefore it is possible to control the almost constant initial pressure P0 regardless of OFF delay time of the contactor <NUM>.

The head-side hydraulic chambers <NUM> are connected to the accumulator <NUM> composing the low pressure line equivalent to a tank function, through the relief valve <NUM> and the solenoid valve <NUM>, and in a case where abnormal cylinder pressure PU (about <NUM>/cm<NUM>) equivalent to pressure when an abnormal load acts on the slide <NUM> (for example, <NUM>,<NUM> kN equivalent to <NUM>% of maximum permissible load <NUM>,<NUM> kN of the press machine <NUM> in this example) acts, the relief valve <NUM> operates, the pressure detector <NUM> detects the operation of the relief valve, the solenoid valve <NUM> is turned on, and the head-side hydraulic chambers <NUM> is depressurized.

In this example, the cylinder stroke of each of the oil hydraulic cylinders 107R, <NUM> is <NUM>.

<FIG> is a configuration diagram illustrating an example of the die cushion driving device 160R illustrated in <FIG>.

The die cushion driving device 160R includes an oil hydraulic circuit that supplies hydraulic oil to the rod-side hydraulic chamber 130a, and the head-side hydraulic chamber 130b of the oil hydraulic cylinder 130R illustrated in <FIG>, and includes an accumulator <NUM>, an oil hydraulic pump/motor <NUM>, a servo motor <NUM> connected to a drive shaft of the oil hydraulic pump/motor <NUM>, an encoder <NUM> for detecting the angular velocity (servo motor angular velocity ω) of a drive shaft of the servo motor <NUM>, a relief valve <NUM>, a check valve <NUM>, and a pressure detector <NUM> equivalent to a die cushion load detector.

A die cushion driving device <NUM> that supplies hydraulic oil to the oil hydraulic cylinder <NUM> has the same configuration as the die cushion driving device 160R, and therefore the die cushion driving device 160R is hereinafter described.

The accumulator <NUM> is set to low gas pressure and plays a role as a tank, and also plays a role to supply substantially constant low pressure oil to the head-side hydraulic chamber 130b (cushion pressure generation side pressurizing chamber) of the oil hydraulic cylinder 130R through the check valve <NUM>, and to be likely to increase pressure at the time of die cushion load control.

One (discharge port) of ports of the oil hydraulic pump/motor <NUM> is connected to the head-side hydraulic chamber 130b of the oil hydraulic cylinder 130R, and the other port is connected to the accumulator <NUM>.

The relief valve <NUM> is provided as a device which operates at the time of abnormal pressure generation (when a die cushion load cannot be controlled, and sudden abnormal pressure is generated), and prevents breakage of hydraulic equipment. The rod-side hydraulic chamber 130a of the oil hydraulic cylinder 130R is connected to the accumulator <NUM>.

The pressure detector <NUM> detects the pressure that acts on the head-side hydraulic chamber 130b of the oil hydraulic cylinder 130R, a die cushion pressure signal 171R that indicates the detected pressure is output, an encoder signal that is output from the encoder <NUM> mounted on the drive shaft of the servo motor <NUM> is converted to a servo motor angular velocity signal 175R by a signal converter <NUM>.

The die cushion driving device 160R outputs a torque command signal 177R input from the die cushion controller <NUM> described below to the servo motor <NUM> through a servo amplifier <NUM>, and drives the oil hydraulic pump/motor <NUM>. Consequently, the oil hydraulic cylinder 130R is driven, and die cushion pressure (load) control and die cushion position control are performed.

The die cushion load (force) may be represented by a product of the pressure of the head-side hydraulic chamber of the oil hydraulic cylinder that supports the cushion pad, and a cylinder area. Thus, control of the die cushion load means control of the pressure of the head-side hydraulic chamber of the oil hydraulic cylinder.

Where oil hydraulic cylinder/die cushion pressure generation side cross-sectional area: a;.

static behavior can be expressed by Expressions (<NUM>) and (<NUM>). <MAT> <MAT>.

Additionally, dynamic behavior can be expressed by Expression (<NUM>) and (<NUM>) in addition to Expressions (<NUM>) and (<NUM>). <MAT>
<MAT>.

What the above Expressions (<NUM>) to (<NUM>) means, namely, force transmitted from the slide <NUM> to the oil hydraulic cylinders <NUM>, 130R through the cushion pad <NUM> compresses the head-side hydraulic chambers 130b of the oil hydraulic cylinders <NUM>, 130R to generate die cushion pressure. At the same time, the oil hydraulic pump/motor <NUM> is caused to perform oil hydraulic motor action by die cushion pressure, and when rotating shaft torque generated in this oil hydraulic pump/motor <NUM> becomes against driving torque of the servo motor <NUM>, the servo motor <NUM> is rotated, and rise of the pressure is suppressed. At last, the die cushion pressure (die cushion load) is determined in accordance with the driving torque of the servo motor <NUM>.

The die cushion pressure signal 171R output from the pressure detector <NUM>, and the servo motor angular velocity signal 175R output from the signal converter <NUM> are used to generate the torque command signal 177R in the die cushion controller <NUM>.

The torque command signal 177R is output to the servo motor <NUM> through the servo amplifier <NUM>, the driving torque of the servo motor <NUM> is controlled, and pressure applied to the head-side hydraulic chamber 130b of the oil hydraulic cylinder 130R from the oil hydraulic pump/motor <NUM> having the drive shaft connected to the servo motor <NUM> is controlled, so that a die cushion load generated from the oil hydraulic cylinder 130R is controlled.

Power from a DC power supply <NUM> with a regenerator is supplied to the servo amplifier <NUM>, and electric power generated by the servo motor <NUM> driven by driving force from the oil hydraulic pump/motor <NUM> that acts as an oil hydraulic motor is regenerated in the AC (Alternating Current) power supply <NUM> through the servo amplifier <NUM> and the DC power supply <NUM>, during die cushion load (pressure) control.

<FIG> is a configuration diagram mainly illustrating an embodiment of the die cushion controller <NUM> illustrated in <FIG>.

The die cushion controller <NUM> illustrated in <FIG> includes the die protecting device <NUM> in addition to a pressure controller (die cushion load controller) <NUM> and a position controller <NUM>.

To the pressure controller <NUM>, the die cushion pressure signals 171R, <NUM>, the servo motor angular velocity signals 175R, <NUM>, a crank angle signal <NUM>, a crank angular velocity signal <NUM>, and a switching command (switching command for causing a die cushion load at maximum capacity to act at the time of double blank detection) of a die cushion load from a safety processing device <NUM> described below are added. The crank angle signal <NUM> and the crank angular velocity signal <NUM> are signals that indicate the angle and the angular velocity of the crank shaft <NUM>, and are converted by a signal converter <NUM> that inputs an encoder signal output from the encoder <NUM> mounted on the crank shaft <NUM>.

The pressure controller <NUM> includes a die cushion pressure command device (die cushion load command device) that outputs a preset die cushion pressure (load) command, and inputs the die cushion pressure signals 171R, <NUM> in order to control die cushion pressure based on the die cushion pressure command.

The pressure controller <NUM> mainly inputs the servo motor angular velocity signals 175R, <NUM> as angular velocity feedback signals for securing dynamic stability in die cushion pressure (load) control and position control, and further inputs the crank angular velocity signal <NUM> indicating the crank angular velocity in order to use for compensation for securing pressure control accuracy in the die cushion pressure (load) control.

Furthermore, the pressure controller <NUM> inputs the (changeable) crank angle signal <NUM> corresponding to a position of the slide <NUM> in order to obtain start timing of a die cushion function, starts or ends the die cushion pressure (load) control based on the input crank angle signal <NUM> (slide position), and the die cushion pressure (load) command device in the pressure controller <NUM> outputs a corresponding die cushion pressure (load) command based on the crank angle signal <NUM>.

During the die cushion pressure (load) control, the pressure controller <NUM> outputs the torque command signals 177R, <NUM> calculated by using the input die cushion pressure command, die cushion pressure signals 171R, <NUM>, servo motor angular velocity signals 175R, <NUM>, and crank angular velocity signal <NUM> to the die cushion driving devices 160R, <NUM> through a selector <NUM>.

When a die cushion load switching command for automatically switching the die cushion load from the safety processing device <NUM> at the time of double blank detection is input, the pressure controller <NUM> outputs the torque command signals 177R, <NUM> corresponding to maximum pressurizing capacity (command for causing a general die cushion load of <NUM> kN to act in vehicle body forming use, in this example).

One the other hand, to the position controller <NUM>, die cushion position signals 173R, <NUM>, the servo motor angular velocity signals 175R, <NUM>, and the crank angle signal <NUM> are added.

The position controller <NUM> includes a die cushion position command device. The die cushion position signals 173R, <NUM> are added to the die cushion position command device in order to use for initial value generation in die cushion position command generation. After the slide <NUM> (cushion pad <NUM>) reaches a bottom dead center, and the die cushion pressure (load) control is terminated, the die cushion position command device performs product knockout operation, and outputs a common position command (die cushion position command) for controlling a die cushion position (position of the cushion pad <NUM>) in order to make the cushion pad <NUM> wait at a die cushion standby position which is an initial position.

In the case of a die cushion position control state, the position controller <NUM> generates the torque command signals 177R, <NUM> based on the common die cushion position command output from the die cushion position command device, and the die cushion position signals 173R, <NUM> detected by the die cushion position detectors <NUM>, 133R respectively, and outputs the generated torque command signals 177R, <NUM> to the selector <NUM>. It is preferable that the position controller <NUM> input the servo motor angular velocity signals 175R, <NUM>, and perform position control in the elevating and lowering direction of the cushion pad <NUM> based on the input servo motor angular velocity signals 175R, <NUM>, in order to secure dynamic stability in position control. Furthermore, it is preferable that the crank angle signal <NUM> be input, and position control be performed based on the input crank angle signal <NUM> at the time of knockout such that the cushion pad <NUM> does not collide with the slide <NUM> indirectly.

In the case of a die cushion pressure (load) control state, the selector <NUM> selects the torque command signals 177R, <NUM> input from the pressure controller <NUM> by a selection command input from the pressure controller <NUM>, and outputs the input torque command signals 177R, <NUM> to the die cushion driving devices 160R, <NUM>, and in the case of a die cushion position control state, the selector <NUM> selects the torque command signals 177R, <NUM> input from the position controller <NUM>, and outputs the input torque command signals 177R, <NUM> to the die cushion driving devices 160R, <NUM>.

The die cushion controller <NUM> outputs the torque command signals 177R, <NUM> generated as described above to the die cushion driving devices 160R, <NUM>, drives the servo motor <NUM> through the servo amplifier <NUM> inside the die cushion driving devices 160R, <NUM>, and performs die cushion pressure (load) control and die cushion position control.

The crank angle signal <NUM>, and the servo motor angular velocity signal <NUM> are added to the press controller <NUM>, the press controller <NUM> generates the torque command signal <NUM> such that the speed becomes a predetermined sliding speed or crank shaft angular velocity based on the input crank angle signal <NUM>, and servo motor angular velocity signal <NUM>, and outputs the generated torque command signal <NUM> to the press driving device <NUM> (servo amplifier <NUM>). The servo motor angular velocity signal <NUM> is used as the angular velocity feedback signal for securing the dynamic stability of the slide <NUM>.

The press controller <NUM> generates the torque command signal <NUM> for making maximum torque act on the press driving device <NUM> in the braking direction based on a braking command input from the die protecting device <NUM>, and outputs a signal for turning on/off the braking device <NUM> (solenoid valve <NUM> for brake release).

As illustrated in <FIG>, the die cushion controller <NUM> of this example is constituted by including the die protecting device <NUM>.

The die protecting device <NUM> may be constituted inside the die cushion controller <NUM>, since a die cushion load signal <NUM> and a die cushion position signal <NUM> are applied. The die protecting device <NUM> has a mission of quickly identifying and processing an abnormality, and higher speed calculation processing time is required, and therefore, for example, the calculation cycle of a controller in a configuration in which the die protecting device <NUM> is constituted inside the die cushion controller <NUM> that takes on die cushion load (die cushion pressure) control (power control) is generally faster than the calculation cycle (requires faster calculation cycle) of a controller in a configuration in which the die protecting device <NUM> is constituted inside the press controller <NUM> that takes on angle control (position control) of the slide (crank shaft), and therefore more effective. Furthermore, waste time accompanying input/output processes of both the signals can be omitted, and therefore the die cushion controller <NUM> is more effective, compared to a case where the die protecting device is separately provided.

The die protecting device <NUM> includes the double blank detecting device <NUM> and the safety processing device <NUM>.

<FIG> is a block diagram illustrating an embodiment of the double blank detecting device <NUM>.

As illustrated in <FIG>, the double blank detecting device <NUM> includes a load signal acquiring unit <NUM>, a position signal acquiring unit <NUM>, and a double blank detector <NUM>, and the double blank detector <NUM> further includes a predetermined value setter <NUM>, a first comparator <NUM>, a hold circuit <NUM>, a second comparator <NUM>, and an abnormality identification value setter <NUM>.

The load signal acquiring unit <NUM> is a component that acquires the die cushion load signal <NUM> indicating a die cushion load generated in the cushion pad <NUM> of the die cushion device <NUM>, and inputs the die cushion load signal <NUM> indicating the die cushion load calculated based on the die cushion pressure signals 171R, <NUM> by the pressure controller <NUM> of the die cushion controller <NUM>, from the pressure controller <NUM>. The load signal acquiring unit <NUM> may directly input the die cushion pressure signals 171R, <NUM> to acquire the die cushion load signal <NUM> indicating the die cushion load calculated based on these die cushion pressure signals 171R, <NUM>.

The position signal acquiring unit <NUM> is a component that acquires the die cushion position signal <NUM> indicating the position of the cushion pad <NUM> of the die cushion device <NUM>, and inputs the die cushion position signal <NUM> calculated as the average value of the die cushion position signals 173R, <NUM> by the position controller <NUM> of the die cushion controller <NUM>, from the position controller <NUM>. The position signal acquiring unit <NUM> may directly input the die cushion position signals 173R, <NUM> to acquire the die cushion position signal <NUM> calculated as the average value of these die cushion position signals 173R, <NUM>.

The die cushion load signal <NUM> acquired by the load signal acquiring unit <NUM> is output to the first comparator <NUM>. A predetermined value F is added as other input of the first comparator <NUM> from the predetermined value setter <NUM>, and the first comparator <NUM> compares these <NUM> inputs, and outputs a signal for enabling the hold circuit <NUM> to perform hold operation when the die cushion load signal <NUM> reaches the predetermined value F.

Herein, it is preferable that the predetermined value F set by the predetermined value setter <NUM> be in a range of not less than <NUM>% and not more than <NUM>% of the maximum die cushion load of the die cushion device <NUM>. In this example, the maximum die cushion load is set to <NUM> kN, and the predetermined value F is set to F = <NUM> kN. The predetermined value F may be manually set by a manual setter (second manual setter), or may be automatically calculated and set based on the maximum die cushion load of the die cushion device by an automatic setter (second automatic setter).

The die cushion position signal <NUM> acquired by the position signal acquiring unit <NUM> is output to the hold circuit <NUM>.

The hold circuit <NUM> holds the die cushion position signal <NUM> when the die cushion load signal <NUM> rises to the predetermined value (F) every cycle (when the signal is input from the first comparator <NUM>) with the start of die cushion load action.

The die cushion position signal holding value X held by the hold circuit <NUM> is output to the second comparator <NUM>. The abnormality identification value Y is added as other input of the second comparator <NUM> from the abnormality identification value setter <NUM>, and the second comparator <NUM> detects a state where the two (plurality of) blank materials <NUM> are overlapped, as a double blank, based on the comparison result of these <NUM> inputs.

<FIG> is a diagram illustrating an example of a die protecting device setting screen.

The double blank abnormality identification value Y for detecting a double blank in contrast to the die cushion position signal holding value X normally repeated (in a case of a single sheet is formed) a plurality of number of times is displayed as Y = <NUM> every forming (condition inherent to forming such as a die, a material, a die cushion load set value, and the speed setting and the die height setting of a press machine) on the die protecting device setting screen in this example. This is automatically calculated in the double blank detecting device.

In this example, as described below, a die cushion load control start time point is recognized by a slide position reference (time point when the slide position reaches a predetermined die cushion start slide position), the die cushion load control start time point of the slide position reference is at a die cushion position smaller by a single blank material (pressed by the slide <NUM>) than that at a normal time at the time of double blank detection, and therefore the die cushion position signal holding value X is smaller than an average value XAVE.

In this example, the latest value of the die cushion position signal holding value is X = <NUM>, and the average value of the die cushion position signal holding values is XAVE = <NUM>. The latest value is a value in a latest (last) cycle in production performed in the past, and is held just before a next die cushion load action start time point. The average value is the average value of a plurality of number of times (<NUM> times in this example) in normal production (with no abnormality) performed in the past. The calculation cycle of the die cushion controller <NUM> is <NUM>, left and right die cushion loads are controlled every <NUM> so as to follow a target die cushion load, and die cushion position signal hold process calculation is performed, and therefore change in the die cushion position signal holding value at a normal time is small. The latest value and the average value of the die cushion position signal holding value is always displayed on the die protecting device setting screen (<FIG>) of a die cushion operating unit.

A first embodiment of the double blank detection is applied to a case where die cushion load control according to the die cushion device <NUM> is started with a position of the slide <NUM> at the time of indirect collision of the slide <NUM> of the press machine <NUM> with the single blank material <NUM> as a reference, as described above.

An abnormality identification value Y of the first embodiment is a value obtained by subtracting a half of the plate thickness (<NUM>) from the average value of the die cushion position signal holding values X, namely, XAVE = <NUM> (where the plate thickness is designated by T, Y = XAVE - <NUM>. 5T = <NUM> - <NUM> × <NUM> = <NUM>).

The abnormality identification value Y may be manually set by a manual setter (first manual setter), or automatically calculated and set on the basis the average value XAVE of the die cushion position signal holding values X, and the plate thickness T by an automatic setter (first automatic setter).

The abnormality identification value Y set by the abnormality identification value setter <NUM> is not limited to <NUM> set as described above, and can be set to a value satisfying the following condition, where the average value of the die cushion position signal holding values X obtained by repeating forming of the single blank material a plurality of number of times is designated by XAVE, and the plate thickness of the blank material is designated by T, <MAT>.

The second comparator <NUM> that functions as a double blank detecting unit detects, as a double blank, a case where the die cushion position signal holding value X is smaller than the abnormality identification value Y which is set so as to satisfy the above Expression (<NUM>).

The reason why the abnormality identification value Y is set by the above Expression (<NUM>) is because prior to the die cushion load control start time point, the slide <NUM> indirectly comes into contact with the cushion pad <NUM>, and pressure (to restore a deviation between a die cushion position command equivalent to a standby position, and a die cushion position) acts on the head-side hydraulic chambers <NUM> of the oil hydraulic cylinders 130R, <NUM> being stopped at a die cushion standby position in a position control state, so that a pressure rising time point is advanced. Therefore, the abnormality identification value Y is even small, but is larger than at least (XAVE - T), and is smaller than at most (XAVE - <NUM>. 3T) in empirical consideration of robustness of position control (in empirical consideration of pressure rising rate in a case where position control is most robust).

The second embodiment is different from the first embodiment in a setting method of the abnormality identification value Y.

The double blank abnormality identification value Y may be determined by actually (experimentally) performing a double blank, and considering the result.

In this example, a die cushion position signal holding value X' at the time of double blank is X' ≈ <NUM>, and the abnormality identification value Y may be Y = <NUM> (Y = <NUM> + <NUM> × <NUM> = <NUM>) as a value obtained by adding a change amount (ΔX) of <NUM>% of the plate thickness to X'.

The abnormality identification value Y is determined by adding the change amount (ΔX) to the die cushion position signal holding value X' obtained in a case where a double blank is actually tried. ΔX is mainly influenced by natural vibration of a machine at the moment of indirect contact of the slide <NUM> with the cushion pad <NUM> to be changed, and the degree is <NUM> to <NUM>% of the plate thickness T empirically. Therefore, the abnormality identification value Y set by the abnormality identification value setter <NUM> can be set to a value satisfying the following condition, from the die cushion position signal holding value X' obtained in a case where double blank materials are tried, and the plate thickness T of the blank material, <MAT>.

The second comparator <NUM> detects, as a double blank, a case where the die cushion position signal holding value X is smaller than the abnormality identification value Y set by the above Expression (<NUM>).

A third embodiment of the double blank detection is applied to a case where die cushion load control according to the die cushion device <NUM> is started with die cushion load change generated in the cushion pad <NUM> by indirect collision of the slide <NUM> of the press machine <NUM> with the cushion pad <NUM> as a reference.

A die cushion control start time point is recognized by a die cushion load generation reference (time point of recognizing change with rise of pressure generated in the head-side hydraulic chambers <NUM> of the oil hydraulic cylinders 130R, <NUM> that generate a die cushion load at the moment of contact of the slide <NUM> with the cushion pad <NUM> through the upper die, the material, the blank holder, and the cushion pin), and is being stopped at a standby position in a position control state. In this case, when a double blank is detected, contact is caused at a die cushion position larger than that at a normal time by the single blank material, and pressure starts rising, and therefore the die cushion position signal holding value X becomes larger than the average value XAVE.

In this case, the abnormality identification value Y set by the abnormality identification value setter <NUM> can be set to a value satisfying the following condition, where the average value of the die cushion position signal holding values X is designated by XAVE, and the plate thickness of the blank material is designated by T, <MAT>.

The second comparator <NUM> detects, as a double blank, a case where the die cushion position signal holding value X is larger than the abnormality identification value Y which is set by the above Expression (<NUM>).

The reason why the abnormality identification value Y is set by the above Expression (<NUM>) is because the pressure rising degree is influenced by natural vibration of a machine in accordance with the robustness of position control, and variation is generated every cycle. Therefore, the abnormality identification value Y is smaller than at most (XAVE + T), and is at least (XAVE + <NUM>. 3T) or more in empirical consideration of variation of pressure change.

A fourth embodiment is different from the third embodiment in a setting method of the abnormality identification value Y.

In this example, the die cushion position signal holding value X' at the time of double blank is X' ≈ <NUM>, and the abnormality identification value may be Y = <NUM> (Y = <NUM> - <NUM> × <NUM> = <NUM>) as a value obtained by subtracting a change amount (ΔX) of <NUM>% of the plate thickness from X'.

The abnormality identification value Y is determined by subtracting a change amount (ΔX) from a die cushion position signal holding value X' obtained in a case where a double blank is actually tried. ΔX is mainly influenced by natural vibration of a machine at the moment of indirect contact of the slide <NUM> with the cushion pad <NUM> to be changed, and the degree is <NUM> to <NUM>% of the plate thickness T empirically. Therefore, the abnormality identification value Y set by the abnormality identification value setter <NUM> can be set to a value satisfying the following condition, from the die cushion position signal holding value X' obtained in a case where double blank materials are tried, and the plate thickness T of the blank material, <MAT>.

The second comparator <NUM> detects, as a double blank, a case where the die cushion position signal holding value X is larger than the abnormality identification value Y set by the above Expression (<NUM>).

The safety processing device <NUM> illustrated in <FIG> outputs a command for quickly braking the slide <NUM> to the press controller <NUM> when a double blank is detected by the double blank detecting device <NUM>.

Upon receipt of this command, the press controller <NUM> outputs the torque command signal <NUM> in the direction opposite to the slide operation direction to the press driving device <NUM>, and starts quick braking of the slide <NUM>. Additionally, after the slide <NUM> is stopped (at the almost the same time as the stopping), the press controller <NUM> turns off the solenoid valve <NUM> for brake release of the braking device <NUM>, and actuates braking.

When the double blank detecting device <NUM> detects a double blank, the safety processing device <NUM> outputs the command for quickly braking the slide <NUM>, and a command for depressurizing the head-side hydraulic chambers <NUM> of the oil hydraulic cylinders 107R, <NUM> incorporated in the slide <NUM>, to the overload removal device <NUM> through a selector <NUM> at the same time.

Upon receipt of this command, the overload removal device <NUM> turns on the solenoid (depressurizing) valve <NUM>, the head-side hydraulic chambers <NUM> of the oil hydraulic cylinders 107R, <NUM> are connected to the low pressure accumulator <NUM> through the solenoid (depressurizing) valve <NUM>, and the head-side hydraulic chambers <NUM> are depressurized.

Furthermore, when the double blank detecting device <NUM> detects a double blank, the safety processing device <NUM> outputs a command for causing maximum capacity of <NUM>,<NUM> kN to act on the cushion pad <NUM> to the pressure controller <NUM> in order to quickly contract the depressurize head-side hydraulic chambers <NUM> of the oil hydraulic cylinders 107R, <NUM>.

Upon receipt of this command, the pressure controller <NUM> outputs the torque command signal <NUM>, 177R for causing maximum capacity of <NUM>,<NUM> kN to act on the cushion pad <NUM>.

<FIG> is a waveform chart illustrating a press machine-slide position, and a die cushion position with a lapse of time, and <FIG> is a waveform chart illustrating a press load, and a die cushion load, in a case where a thin plate having a thickness of <NUM>, and a sectional shape of about <NUM>,<NUM> × <NUM>,<NUM> is normally continuously (drawn) formed by using a press machine having maximum pressurizing capacity of <NUM>,<NUM> kN.

In each of <FIG>, waveforms of <NUM> cycles are illustrated, and waveforms (both positions, load) in the same form are repeatedly act between the cycles, at a glance.

<FIG> illustrate a die cushion position signal holding value at a rising time point of die cushion load signal <NUM> kN, a die cushion position signal holding value at a rising time point of press load signal <NUM>,<NUM> kN, a press/slide position signal holding value at a rising time point of die cushion load signal <NUM> kN, and a press/slide position signal holding value at a rising time point of press load signal <NUM>,<NUM> kN, respectively. These position signal holding values are obtained by performing a calculating process of data illustrated in <FIG>.

Change between the cycles in the position signal holding value illustrated in <FIG> is the smallest, and the change between the cycles becomes larger in the order of the position holding values illustrated in <FIG>, <FIG>.

The reason why the rise of the press load signal is <NUM>,<NUM> kN (twice the die cushion load) is because change at <NUM> kN identical with a die cushion load signal is large (due to resolution), and the position holding value largely changes.

As illustrated in <FIG>, in a case where the press load signal and the slide position holding value are used (a case of a double blank detection method described in PTL <NUM>), the change of the position signal holding value is the largest.

It is considered that this reason is because (lowering of resolution in load detection, or a position detection value with) a heavy, thick, long and large press machine relative to the die cushion device attached thereto, or a difference between both load generation mechanisms caused by secondarily generating a press load in accordance with a forming load or state change (such as linear expansion of a column) of a press machine (without control), and controlling the die cushion load (in the servo die cushion device) to a constant value, a difference of responsiveness and accuracy between the both, resulting from output of a press load signal from a press load detector dedicated for monitoring, and output of a die cushion load signal from a die cushion load detector dedicated for die cushion load control.

The press load signal and the die cushion load signal rise at a time point when the material (and an indirect member such as a die) is sandwiched, a press/slide position and a die cushion position coincide with each other. In a state where the thickness of the material is constant, when repeating action of a load signal and a position signal are stable every cycle, the position signal takes a substantially constant value every load value, and a position signal holding value at a time point of rising to be a constant load signal is stable at a normal time. In a case where the thickness of the material is changed by a double blank, for example, in a case where a thin plate having a plate thickness of about <NUM> is formed, at the time of an abnormality of changing the thickness of the material to about <NUM>, it is important that stability of the position signal holding value at a normal time, namely, a change range is small, in order to reliably detect a double blank from the change of the position signal holding value.

In a double blank detection method of PTL <NUM> using the press load signal and the press/slide position signal illustrated in <FIG>, double blank detection is impossible, since the change range of the position signal holding value becomes <NUM> larger than the thin plate thickness (<NUM>).

One the other hand, in a double blank detection method of the present invention using the die cushion load signal and the die cushion position signal, the change range of the position signal holding value becomes <NUM> sufficiently smaller than the thin plate thickness (<FIG>), and therefore it is possible to accurately detect a double blank.

<FIG> is a waveform chart illustrating a slide position and a die cushion position, and <FIG> is a waveform chart illustrating a predetermined value of a die cushion load signal, a die cushion load command, and a die cushion load.

<FIG> illustrates the pressure of the head-side hydraulic chamber of the oil hydraulic cylinders 107R, <NUM> with built-in slides, and <FIG> is a waveform chart illustrating a die cushion position signal holding value X, an abnormality identification value Y, and detection of a double blank.

In each of <FIG>, waveforms of <NUM> cycles are illustrated, and a first cycle, and a second cycle are normally function. During a die cushion load control step, the die cushion load is maintained at about <NUM>,<NUM> kN which tends to be slightly excessive at the time of start of die cushion load control in contrast to a command of <NUM>,<NUM> kN (<FIG>).

The pressure of the head-side hydraulic chamber of each of the oil hydraulic cylinders 107R, <NUM> increases in accordance with a press load value at the time of forming (die cushion load action) with respect to initial pressure of <NUM>/cm<NUM> (<FIG>).

The die cushion position signal holding value X shifts from <NUM> to <NUM> (<FIG>). These are held at the die cushion load control start time point, and the press/slide position is not held at a position of <NUM> by <NUM> above a next die cushion load control start slide position of <NUM>.

In the third cycle, a double blank is detected. The die cushion position signal holding value X is <NUM>, and smaller than the double blank abnormality identification value Y (= <NUM>), and therefore the double blank is detected by the double blank detecting device <NUM> (<FIG>).

Just before double blank detection, a time point when the blank holders <NUM> and the upper die <NUM> come into contact with each other through blank materials (two sheets) (time point just before die cushion load control start) is the state of the right half of the press machine illustrated in <FIG>. In this state, a distance between the blank material lower surface and the lower die <NUM> (punch) is <NUM>, and when the slide <NUM> (lower surface) further does not lower by <NUM>, forming is not started.

<FIG> each illustrate a cycle waveform of partially enlarged part of <FIG>, mainly at the time of double blank detection.

When the double blank detecting device <NUM> detects a double blank, the safety processing device <NUM> gives a command to the press controller <NUM> in order to quickly brake the slide <NUM>. Upon receipt of this command, a slide (connecting rod point) position depending on the crank shaft angle reaches an emergency stop (<FIG>).

However, the slide (connecting rod point) position lowers by about <NUM> by inertia due to inertia of an entire movable unit interlocked with the slide <NUM>, and stops at <NUM>.

At the same time, the safety processing device <NUM> gives a command to the solenoid (depressurizing) valve <NUM> through the selector <NUM> in order to depressurize the head-side hydraulic chambers of the oil hydraulic cylinders 107R, <NUM> with built-in slides. Upon receipt of this command, the head-side hydraulic chambers are quickly depressurized (<FIG>). In order to enhance quick depressurizing action, the solenoid valve <NUM> having large valve opening (flow coefficient), and enabling fast response is selected. Furthermore, in order to enhance response, an applied voltage at an ON (excitation) starting time point is instantaneously increased (improved in order to advance a phase of a substantially primary delay characteristic with solenoid force action of a solenoid valve).

At the same time, the safety processing device <NUM> gives a die cushion load command to the pressure controller <NUM>, so as to cause maximum capacity of <NUM>,<NUM> kN to act in order to quickly contract the depressurized head-side hydraulic chambers. Upon receipt of this command, the die cushion load command immediately changes to <NUM>,<NUM> kN (a broken line of <FIG>). The pressure of each of the head-side hydraulic chambers of the oil hydraulic cylinders with built-in slides lowers to about <NUM>/cm<NUM> at a time point when the slide (connecting rod point) position reaches about <NUM> after about <NUM> (vicinity of <NUM> of <FIG>).

After this, the oil hydraulic cylinders 107R, <NUM> start contracting, and a slide (lower surface) die mounting position interlocked with the above also reverses (turns to rise) (broken line of <FIG>). At this time, the die cushion load is influenced by lowering of the speed of the slide lower surface that presses the die cushion, and is fixed to about <NUM>,<NUM> kN smaller than a command of <NUM>,<NUM> kN once (<FIG>). At this time, the oil hydraulic cylinders 107R, <NUM> are indirectly pressed from below by a die cushion load, and continue to contract while discharging hydraulic oil.

About <NUM>/cm<NUM> which is a pressure loss generated when a discharging oil amount flows in the solenoid valve <NUM> acts on the head-side hydraulic chambers of the oil hydraulic cylinders 107R, <NUM>. In the vicinity of <NUM> to <NUM> illustrated in <FIG>, the oil hydraulic cylinders 107R, <NUM> each reach a contract (machine) limit, and the discharging oil amount is drawn up, and the pressure of each head-side hydraulic chamber lowers to almost <NUM>. Additionally, the speed of the slide lower surface is equal to a predetermined sliding speed, and therefore the die cushion load changes to <NUM>,<NUM> kN as commanded (<FIG>). At this stage, the slide (connecting rod point position) still slightly continues lowering operation (<FIG>), and the die cushion terminates load control (<FIG>).

In this series of operation, a minimum position of the slide (lower surface) die mounting position is about <NUM> (the vicinity of <NUM>, and the vicinity of <NUM> of <FIG>), and is equivalent to a left half state of the press machine illustrated in <FIG>. The left half state of the press machine illustrated in <FIG> illustrates a state just before a blank material comes into contact with the lower die <NUM> (punch), and forming is started. When the double blank is detected by this die protection function, a machine is safely stopped previously (before forming).

Thus, as long as the position of the slide lower surface in consideration of the influence of contraction of the oil hydraulic cylinders 107R, <NUM> exists in a region where forming is not started, the oil hydraulic cylinders 107R, <NUM> are quickly contracted, and a maximum die cushion load acts until the contraction is completed. In a forming region at the time of double blank detection being a double blank material state extremely dangerous for a die, a die cushion load basically does not act.

In the forming region, in other case, for example, in a case where a light beam type safety device is shielded, at the time of press machine emergency stop with operation, a cope is different from a cope in a situation where the predetermined die cushion load acts in order to suppress damage of the die due to generation of drawing wrinkle until the press/slide is stopped.

The die protecting device <NUM> including the double blank detecting device <NUM> and the safety processing device <NUM> is configured to be incorporated in the die cushion controller <NUM> in this embodiment, but the present invention is not limited to this, and the die protecting device <NUM> may be provided outside the die cushion controller <NUM>.

It goes without saying that the die cushion device according to the present invention can also detect a state where three or more blank materials are overlapped.

Additionally, it is preferable that a carrier device that sets the blank materials in the press machine <NUM> immediately stop, when the double blank detecting device <NUM> detects a double blank.

Furthermore, the cushion pad is supported by the two oil hydraulic cylinder in this embodiment, but the number of the oil hydraulic cylinders is not limited to two, and may be one, or more than two. Additionally, the die cushion driving unit is not limited to a unit that uses oil hydraulic cylinders, and any unit that supports a cushion pad, elevates and lowers the cushion pad, and generates a desired die cushion load in the cushion pad may be employed.

The oil hydraulic cylinder with a built-in slide uses oil as hydraulic fluid, but is not limited to this. It goes without saying that a hydraulic cylinder that uses water or other liquid can be used in the present invention.

Claim 1:
A die cushion device (<NUM>) attachable to a press machine (<NUM>) that automatically and repeatedly forms blank materials (<NUM>) one by one, the die cushion device (<NUM>) comprising a double blank detecting device (<NUM>), characterized in that, the die cushion device further comprises:
a die cushion position detector (<NUM>, 133R) configured to detect a position of a cushion pad (<NUM>) and output a die cushion position signal indicating the position of the cushion pad (<NUM>); and
a die cushion load detector (<NUM>) configured to detect a die cushion load generated in the cushion pad (<NUM>) and output a die cushion load signal indicating the die cushion load,
the double blank detecting device (<NUM>) comprising:
a position signal acquiring unit (<NUM>) configured to acquire the die cushion position signal from the die cushion position detector (<NUM>, 133R);
a load signal acquiring unit (<NUM>) configured to acquire the die cushion load signal from the die cushion load detector (<NUM>); and
a double blank detecting unit (<NUM>) configured to detect, as a double blank, a state where a plurality of the blank materials are overlapped, based on the die cushion position signal acquired by the position signal acquiring unit (<NUM>), and the die cushion load signal acquired by the load signal acquiring unit (<NUM>),
wherein the double blank detecting unit (<NUM>) holds the die cushion position signal at a time point when the die cushion load signal rises to a predetermined value, compares a holding value of the held die cushion position signal with an abnormality identification value, and detects the double blank.