JP3308463B2 - Control method of die cushion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of controlling a die cushion using a hydraulic servo used in a press machine, and more particularly to a method of accurately controlling a cushion force without delay irrespective of a vertical stand-by position of a cushion pad. Control
It is effective when pressing various products and can be retrofitted to existing press machines.

[0002]

2. Description of the Related Art In order to draw a sheet material by a press machine, a hydraulic cylinder for generating a cushion force is provided in opposition to the lowering of a slide. Cushioning force is generated to sandwich the plate material and prevent wrinkles of the plate material.

[0003] As an example of a conventional technique for controlling the die cushion, a magazine "Hydraulic Pneumatic", August, 1994, 22-
There is a “simulation of a mechanical press die cushion pressure control system” on page 26, and the concept of this device, a block diagram of the pressure control system, and a block diagram of the die cushion pressure control are as shown in FIGS. 5 and 6. .

In FIGS. 5 and 6, when the press machine is not loaded and the load is lowered, the cushion pad 37 stands by at the upper limit position of the cushion stroke.
(P) / integral (I) controller 39 for detecting the oil pressure of the pressure sensor 46 by a pressure detector 46 and feedback-controlling the output to the servo valve 43 in accordance with the deviation between the pressure and the pressure command value.
(Hereinafter referred to as PI controller)
A constant bias voltage Eb corresponding to the rotation speed of the press machine is input from the bias circuit 49 to the servo valve 43, and a surge occurs in the hydraulic cylinder 36 when the upper mold 32 collides with the cushion pin 30 (hereinafter referred to as pin touch). A certain degree of opening (hereinafter referred to as standby opening) is given so that pressure is not generated.

[0005] When the processing is started and the oil is discharged from the hydraulic cylinder 36 by the pin touch and the pressure is generated, the generation of the pressure is detected by the pin touch detection circuit 48.
The operation of the I controller 39 is validated, and the feedback control is started so that the cushion pressure Pr matches the pressure command value. After the feedback control is started, a pressure command is given in a pattern set in advance according to the crank angle of the crank angle detector 40, and the servo valve 43 is controlled to follow the pressure command, and the change in the cushion pressure Pr that follows the pressure command is detected. Can be obtained.

[0006]

In the conventional apparatus shown in FIGS. 5 and 6, since the standby position of the cushion pad 37 is limited to the upper limit, a cushion which is always effective for various products having different heights. Lack of freedom to operate with stroke. Further, when the pin is touched, the bias voltage Eb is applied to the servo valve 43 to suppress the pressure surge of the cushion cylinder 36, while the pressure control is started by detecting the surge (the pressure detector 46), so that the start of the pressure control is delayed. . Further, since the target value of the pressure control is set based on the crank angle, a crank angle detector 40 is required, and a detector of the set stroke number for obtaining the bias voltage Eb according to the operating speed is also required. Therefore, it was difficult to retrofit this control system to an existing press machine.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, to set a standby position of a cushion pad arbitrarily, to reduce a control delay from switching from pin touch to pressure control, and to obtain an initial bias voltage. An object of the present invention is to provide a method of controlling a die cushion which does not require connection with a press machine and can be retrofitted to an existing press machine.

[0008]

In order to solve the above-mentioned problems, the present invention obtains a cushion force current value from a pressure signal on the head side and a cap side of a cushion cylinder, and obtains a cushion force prepared in advance from a stroke of a die cushion. A target cushion force value for the current position of the die cushion is determined based on the diagram.

First, at the time of machining, a pin touch ON detected when the die cushion starts descending from the standby position.
The cushion force target value is output by a signal, and the output voltage to the servo valve is adjusted based on the deviation between the target value and the cushion force current value so that the deviation becomes zero (hereinafter, this control is referred to as axial force). Feedback control). In addition, by memorizing the change of the cushion stroke in this processing process, by folding it back on the time axis,
Generate a position target curve when the cushion is raised.

Next, the axial force feedback control is performed based on the deviation between the position target curve and the current position by a pin touch OFF signal detected when the die cushion starts to move up with the end of the processing. Is switched to control for adjusting the output voltage to the servo valve so that is zero (hereinafter, this control is referred to as position feedback control). This switching is specifically realized by switching the axial force command for the axial force feedback control from the cushion target value to the axial force command for the position control.

Also, a bias signal corresponding to the cushion speed obtained by differentiating the current position signal of the die cushion is obtained, and the bias signal is subtracted from the output of the cushion force controller. (Hereinafter, this control is referred to as feedforward control).

[0012]

1 to 4 show an embodiment of a method for controlling a die cushion according to the present invention. FIG. 1 shows a concept of a die cushion device and a configuration diagram of a pressure control system. When the upper die 2 attached to the slide 1 descends and the plate material 5 is drawn between the lower die 4 attached to the bed 3,
The peripheral portion of the plate member 5 is pressed between the upper die 4 via the cushion pad 7 by the upward cushioning force of the cushion cylinder 6 to prevent wrinkles. The cushion pad 7 detects the position in the vertical direction by a position detector 8, for example,
The output signal is input to the control 9 by the linear scale, and the cushion cylinder 6 detects the pressure in the upper cylinder chamber, that is, the head side pressure detector 10 that detects the pressure in the head side, and the lower cylinder chamber, that is, the pressure in the cap side. A cap-side pressure detector 11 is provided, and these output signals are input to the controller 9.

When the upper die 2 descends along with the slide 1 and collides with the cushion pad 7, that is, when it comes down from the standby position by pin-touching, oil is discharged from the cap side of the cushion cylinder 6, and oil flows into the head side. , Pressure is generated. Output signals from the position detector 8 and the pressure detectors 10 and 11 are processed by the controller 9, and the controller 9
The output of the cushion force controller is
, And controls the electric / hydraulic servo valve 13 to control the pressure of the cushion cylinder 6 so that the cushion force is optimally controlled for drawing.

FIG. 2 is a control block diagram of the controller 9. The output signal of the position detector 8 is input as a cushion position signal 14 as a signal of the current position of the cushion pad 7. In addition, the aforementioned cushion cylinder 6
Head-side pressure detector 10 and cap-side pressure detector 11
Are output as a head-side pressure signal 15 and a cap-side pressure signal 16.

From the head side pressure signal 15 and the cap side pressure signal 16, an axial force calculator 17 calculates and outputs a cushion force currently acting on the cushion pad 7.
When the cushion pad 7 starts lowering from the standby position by the pin touch and the cushion position signal 14 indicates the lowering start, the pin touch detector 18 sends an ON signal, and the position control / axial force control switch 19 is switched from the position control. Switch to axial force control. That is, the cushion force controller 2
The control of the cushion force is started by switching the axial force command value to the cushion force controller 4 from the axial force command from the cushion position controller 22 to the axial force command from the cushion target value generator 20.

When the descending stroke advances and the cushion pad 7 starts to move upward through the bottom dead center, the cushion position signal 14 is inverted, and the pin touch detector 18 is turned off by the inversion of this signal.
An F signal is transmitted to switch the switch 19 from the axial force control to the position control. That is, position control for returning to the cushion standby position is started.

The cushion force target value generator 20 stores a pattern of the stroke of the cushion cylinder 6 and the cushion force target value created in advance as shown in FIG. 3 and stores a cushion corresponding to the input of the cushion position signal 14. A force target value is output, and is transmitted as an axial force command while the switch 19 is switching to the axial force control. As a method of continuously generating the target values, as shown by the dots in FIG. 3, the target values at some stroke representative points are stored in the form of a table (MAP), and other arbitrary values are stored. The target value at the position can be obtained by various main interpolation calculations from the target values at adjacent representative points.

As shown in FIG. 4, the position control target value generator 21 stores the stroke diagram ab of the die cushion with respect to the time from the pin touch a to the bottom dead center b by monitoring the cushion position signal 14. After that, a stroke curve cd obtained by folding ab with respect to time after the elapse of the bottom dead center stop time of bc is output as a position target value with respect to time. Note that be shown by a dotted line in FIG. 4 is a slide motion.

The cushion position controller 22 receives the position command output from the position control target value generator 21 obtained by the adder / subtractor 23 and the position deviation of the cushion position signal 14 to match the cushion position with the target value. Proportional (P) that outputs the axial force command and supplies it to the switch 19
-Integral (I)-Differential (D) controller (hereinafter PID)
Controller).

The cushion force controller 24 calculates the cushion force from the axial force command output from the switch 19 and the axial force deviation output from the axial force calculator 17 calculated by the adder / subtractor 25. Is a PI controller which calculates and outputs a controller output 26, that is, a servo valve command voltage, so as to match with a target value.

The controller output 26, that is, the command voltage to the electrohydraulic servo valve 13, is supplied from an output of the cushion controller 24 by an adder / subtracter 27 to suppress a disturbance due to a change in cushion speed.
Is obtained by subtracting the bias signal output in accordance with the speed by the bias signal generation circuit 29 from the speed signal obtained by differentiating by the differentiating circuit 28.

The above is one embodiment of the present invention. Based on the detected value of the position of the cushion pad and the detected value of the pressure of the cushion cylinder, the cushion force is set when the die cushion is lowered and the cushion position is set when the die cushion is raised. A die cushion control method for controlling the axial force and controlling the position so as to match the values may be used.

[0023]

As is apparent from the above description, according to the present invention, the standby position of the cushion pad is not limited to the upper limit and can be arbitrarily selected. Therefore, a stroke of the die cushion corresponding to various products having different heights can be obtained.
In addition, pressure control is started immediately upon lowering of the cushion cylinder due to pin touch, and control delay is extremely small. In addition, disturbance can be suppressed by feeding forward a bias signal corresponding to the speed signal obtained by differentiating the position signal. Furthermore, since the die cushion device can be controlled independently, it is easy to retrofit a ready-made press machine.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a die cushion device and a configuration diagram of a pressure control system according to an embodiment of the present invention.

FIG. 2 is a control block diagram of a controller.

[FIG. 3] Similarly, a cushion stroke and a cushion force target value diagram.

FIG. 4 is also a cushion stroke diagram showing time and a cushion target position.

FIG. 5 is a conceptual view of a conventional die cushion device and a configuration diagram of a pressure control system.

FIG. 6 is also a pressure control block diagram of a die cushion device.

[Description of References] 1 is a slide, 2 is an upper mold, 3 is a bed, 4 is a lower mold, 5 is a plate material, 6 is a cushion cylinder, 7 is a cushion pad, 8 is a position detector, 9 is a controller, and 10 is a head. Side pressure detector, 11 is a cap side pressure detector, 12 is a servo amplifier, 13 is an electric / hydraulic servo valve, 14 is a cushion position signal, 15 is a head side pressure signal, 16 is a cap side pressure signal, and 17 is an axial force. Calculator, 18 is a pin touch detector, 19 is a switch, 20 is a cushion force target value generator, 21 is a position control target generator, 22 is a cushion position controller, 23, 25, and 27 are adder / subtractors, and 24 is a cushion force. Controller, 26 is a controller output,
28 is a differentiating circuit, 29 is a bias signal generating circuit.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B21D 24/02 B30B 15/02

Claims (2)

(57) [Claims] 1. A method of controlling a die cushion using a hydraulic servo used in a press machine, comprising the steps of: (a) obtaining a current cushion force value from a pressure signal of a cushion cylinder; (B) A cushion force target value for the current position of the die cushion is obtained based on a cushion force diagram created in advance from the stroke of the die cushion. (C) A feedback control of the cushion force based on the cushion force target value and the cushion force current value is started by a pin touch ON signal detected when the die cushion starts descending from the standby position. (D) Based on the stroke diagram of the die cushion obtained in the cushion lowering stroke, the position target value of the die cushion in the cushion rising stroke is obtained. (E) The feedback control of the cushion position based on the target position value of the die cushion and the cushion current position is started by the pin touch OFF signal detected when the die cushion starts to move upward. A die cushion control method characterized by the above. 2. A die cushion according to claim 1, wherein a bias signal corresponding to a cushion speed obtained by differentiating a position signal of a current position of the die cushion is fed forward to said cushion force controller output. Control method.