GB2219669A

GB2219669A - Press brake with a displacement sensor

Info

Publication number: GB2219669A
Application number: GB8813447A
Authority: GB
Inventors: Hiroshi Sato
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-06-07
Filing date: 1988-06-07
Publication date: 1989-12-13
Also published as: GB8813447D0

Abstract

A press brake e.g. for bending sheet metal has a base distance portion (70); an electrical displacement sensor (71) such as a differential transformer opposite the base distance portion (70); a pair of molds (11, 12), one of the molds being provided with either the base distance portion (70) or the displacement sensor (71), the other mold being provided with a linear actuator (50) to which the remaining one of the base distance portion or the displacement sensor is attached; a servo valve (60) controlled by the output of the sensor (71) via a servo amplifier (80); and a cylinder (40) controlled by the servo valve (60) and adapted to actuate either one of the pair of molds (11, 12). When the sensor (71) is lowered by the actuator (50) the mold (11) actuated by the cylinder (40) is moved to keep the distance d constant. <IMAGE>

Description

TITLE OF THE INVENTION PRESS BRAKE WITH A .DISPLAC#IENT SENSOR OF ELECTRIC SIGNAL OUTPUT BACKGROUND OF THE INVENTION This invention relates to a mechanical press in a broad sense.

and particularly to a press brake having a linear actuator.

More particularly. the present invention relates to a press brake comprising a displacement sensor having an electric signal output and adapted to detect the position of a ram plate.

In general. a press brake used for bending a sheet metal or the like is required a very high accuracy In controlling the position of its ram plate.

For example. as is shown in a side view of Fig. 2 (Fig. 1 shows the present invention and will therefore be described afterward). a plate such as a metal plate 20 or the like is interposed between an upper mold 11 and a lower mold 12 and pressed In a manner as shown in Figs. 2(A) and 2(B). in which the plate is usually bent at an angle of 90#. However. since the accuracy required for the press brake is so high that errors remained within +0.5 with respect to a target angle of 90' are rejected.

Therefore. the control of the pressing position of the upper mold 11 is required to be so accurate that the errors must usually remain within l,'lOOmm. approximately. Besides. a large power is required for bending a wide plate member. To this end. it is usuallY practiced that a pressure is applied to both sides of a ram plate 30 by a hydraulic cylinder 40 (of course. it is also practiced that the upper mold 11 is held stationary and the lower mold 12 is pushed up).

Right and left cYlinders 41 and 42 are required to be synchronously driven in high accuracy. However. when a workpiece is interposed between the upper mold 11 and the lower mold 12. it is often displaced leftward or rishtward. and when displaced. It becomes a one-sided load. Since a load is not equally applied to the right and left cylinders 41 and 42. it is very difficult for them to be driven in synchronism (control of the position).

The plate as the worpiece is not always required to be bent at equal angle. Sometimes. it is required that the bending angle of the left side of the plate is different from that of the right side as shown in the perspective view of Fig. 4. In this case. the pressure must be applied to the ram 30 held in its inclined state as shown in Fig.5 (synchronous drive of the cylinders 41 and 42).

Such control is generally obtainable by detecting the movement (displacement) of the ram plate 30 by a linear scale and feeding it back to a servo valve or a proportional control valve for controi#ing the cylinders 41 and 42. if this is carried out according to an analog system. a satisfactory control can be obtained. However. ;t lSi not easy to obtain an accuracy of l;lDOmm over the whole stroke. On the other band. if a digital system is adopted. the detection of the displacement and the control of cylinder are usually made by a microcomputer. In this case. if the displacement Is to be read to the limit of discrimination of the linear scale by computer.It taxes too much time for reading and controlling. and the acting speed of the cylinder is proportionately lowered. If some data from the linear scale are intendedly not read in order to same time. the result is the same as that the discrimination of the linear scale is made rough. This means that the synchronous drive of the right and left cylinders becomes insufficient.

There is also disclosed a press brake having a mechanical feed back mechanism as shown in the front view of Fig. 6. In this conventional press brake. a plunger of a 4-port switch valve 60 is pushed by a linear actuator 50 (e.g.. a combination of a rotary encoder, a servo motor. ball screw. etc.# for switching the port.

thereby to actuate a hydraulic cylinder 40 to follow the ram plate 30. In other words. the ram plate 20 is caused to follow the movement of the linear actuator 50 by using a mechanical feed back system.

However. this system has the shortcoming in that it is very difficult to switch the port by a minor displacement of the plunger.

In order to respond to the minor dhsplacement. the mechanical accuracy of the spool and port must be extremely good or the movement of the linear actuator must be increased ac#ording to the principle of lever. However. if a lever mechanism is introduced into such place. It becomes very unstable In the area such as initial adjustment. aged change. or the like.

In the case of a mechanical feed back servo control. the feed back loop gain cannot be adjuster during the operation test Even if a mecnanical system is taken into consideration. it becomes complicated and always faces with such problems as aged change or the like. When a plate member is bent by actually applying pressure thereto. since the,Jaw portion of a frame S shown in a side view of FIg.7 is opened. the cylinder 40 must be pushed down to that extent.

This means that in order to-accurate!Y control the actual distance D between the upper. mold 11 and the lower mold 12. it is necessary to know the way of opening of the frame 6 as data beforehand. This always accompanies difficulties in control.

The present invention has been accomplished in order to overcome the above-mentioned problems.

SUMMARY OF THE INVENTION It is therefore a general object of the present invention to provide a press brake with a displacement sensor of an electric signal output. wherein a pair of right and left cylinders are perfectly synchronously driven the synchronous drive is not adversely affected even if a ram plate is held in its inclined state.

and the control speed is enhanced.

More specifically, in a press brake, in order to accurately bend a plate member. the distance between the upper mold and the lower mold must be accurately controlled. To this end. the lower mold is provided with a linear actuator. The distance between a movable front end portion of the linear actuator and the upper mold is measured by a displacement sensor. The minor change. if occurred. of the distance is output as an electric signal by a converter so as to control a hydraulic cylinder via an amplifier. thereby to maintain the distance between the upper mold and the lower mold constant.

A concrete structure of a press brake with a displacement sensor of an electric signal output according to the present invention will be described in detail.

It has a base distance portion. It also has a displacement sensor having an electric signal output. The displacement sensor having an electric signal output is located opposite the base distance Portion. It further has a pair of molds. One of the pair of molds is provided with either the base distance portion or the displacement sensor.

The other of the pair of molds is provided with the remaining one of the base distance portion or the displacement sensor. It further has a servo amplifier for inputting an output of an electric signal coming from the displacement sensor. It further has a servo valve controlled by an output signal coming from the servo amplifier.

Lastly. it has a cylinder controlled by the servo valve. The cylinder is connected as such that one of the pair of molds is actuated.

Since a press brake with a displacement sensor of an electric signal output according to the present invention is constructed In the manner as mentioned above. it has the following effects.

The base distance portion mounted on either one of the pair of molds and the displacement sensor having an electric signal output mounted on the other mold find out the correctness of the distance between the pair of molds. The displacement sensor outputs an electric signal in accordance with the result of finding. The electric signal output bY the displacement sensor controls the servo valve through the servo amplifier. This. in turn, controls the cylinder. The cylinder is connected to either one of the pair of molds so as to move the latter in the vertical direction.

The base distance portion or the displacement sensor is connected to either one of the pair of molds. whereas the linear actuator is mounted on the other one of the pair of molds. The other one of the pair of molds is provided with the remaining one of the base distance portion or the displacement sensor. Accordingly, the distance between the pair of molds can be controlled by actuating the linear actuator.

The above and other objects and attendant advantages of the present invention will be apparent to those skilled in the art from a reading of the following description and claims in conjunction with the- accompanying drawings which constitute part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. I Is a side view of one embodiment of a press brake with a displacement sensor having an electric signal output according to the present invention: Fig. 2 is a side view of a generally known pair of molds.

wherein Fig. 2(A) shows the molds before pressing a workpiece.

whereas Fig. 2(B) shows the molds pressing a workpiece; Fits. 3 is a front view of a generally known ram plate: Fig. 4 is a perspective view of one embodiment of a plate member already pressed: Fig. 5 is a front view of one embodiment of a generallY known ram plate; Fig. 6 is a front view of one. embodiment of a control portion o: a conventional press brake: and Fig. 7 is a side view of one embodiment of a conventional press brake.

DETAILED DESCRIPTION OF THE EMBODIMENT A press brake with a displacement sensor having an electric signal output according to the present invention will be described in a form of a preferred embodiment in detail with reference to the accompanying drawings.

Fig. 1 is a side view of one embodiment Of a press brake with a displacement sensor having an electric signal output according to the present invention.

In Fig. 1. reference numerals II and 12 denote a pair of molds.

The upper mold 11 is provided with a bar 70 as a base distance portion. The lower mold 12 is held by a holding table 31. The holding table 31 is connected to a linear actuator 50. A front end 51 of a movable portion of the linear actuator 50 is provided with a displacement sensor 71 having an electric signal output. The displacement sensor 71 having an electric signal output is located opposite the bar 70. An output of the electric signal coming from the displacement sensor 71 is input in a converter 72 and then input in a servo amplifier 80. Reference numeral 60 denotes a servo valve. The servo valve 60 is controlled by an output signal coming from the servo amplifier ao. Reference numeral 40 denotes a cylinder assembly.

The cylinder assembly 40 is controlled by the servo amplifier 80. The cylinder assembly 40 is connected to the upper mold II so as to actuate the latter through a ram plate 30.

Although the bar 70 is mounted on the upper mold 1I in the illustrated embodiment. it may be mounted on the front end 51 of the movable portion of the linear actuator 50 and the displacement sensor 71 having an electric signal output may be mounted on the upper mold 11.

The operation of a Press brake with a displacement sensor having an electric signal output according to the present Invention will now be described.

A differential transformer type displacement gage 71 is mounted on the movable end Portion 51 of the linear actuator 50. The differential transformer 71 is moved in the vertical direction by the linear actuator 50. The bar 70 as a projection is mounted on the ram plate 30 or the upper mold 11 so that the front end of a probe of the differential transformer 71 hits it. The output of the differential transformer 71 is converted to a direct current signal by the converter 72 and the servo valve 60 is driven through the servo amplifier 80 for moving the hydraulic cylinder assembly 40 in the vertical direction. When the differential transformer 71 is pushed up by the linear actuator 50. it hits the bar 70.The distance d shortened is detected by the differential transformer 71. the servo valve SO is actuated by the signal coming from the differential transformer 71 and the ram plate 30 is pulled up through the hydraulic cylinder assembly 40. When the differential transformer 71 is descended. the ram plate 30 is also descended following the movement of the differential transformer 71. therefore. the distance d is always maintained constant.

Because of the foregoing, the distance D between the upper mold 11 and the lower mold 12 is changed in synchronism with the movement of the differential transformer 71. If a pair of the above-mentioned arrangements are provided. it is easy for the current control art to electrically drive the right and left linear actuators in suchronism. Accordingly. the hydraulic cylinder assembly. which is actuated following the movement of the right and left actuators is also driven in synchronism. This means that. in the electric control portion of a microcomputer or the like. the accurate and rapid control of only the linear actuator 50 suffice without taking into consideration the oil pressure portion of the servo valve 60 or the like. The oil pressure portion merely follows the movement of the linear actuator 50 in such a manner as to maintain the distance d between the linear actuator 50 and the bar 70 always constant by the differential transformer 71. In the construction as just mentioned.

the opening of the jaw portion of the frame 6(see Fig. 6). which is caused when a large pressure is applied. is automatically offset and the distance D between the upper mold li and the lower mold 12 can be always well controlled.

The same effects are obtainable even if the linear actuator 50 is mounted on the upper mold 11 and the bar 70 is mounted on the lower mold 12. The present invention is of course not limited to these. Instead. various other combinations can be made by those skilled in the art. Although the differential transformer 71 is employed in the present embodiment In order to measure the distance d. a noncontact type displacement gage. in which light. air. etc. are applied. may be employed instead of a contact type displacement gage.

According to the controlling system of the present invention. in the electric controlling portion. the linear actuator 50 mounted on the upper mold 11 or the lower mold 12 is accurately and rapidly actuated, the distance d between the linear actuator 50 and the projection for the use of measurement mounted on the remaining upper mold 11 or lower mold 12 is measured. and the hydraulic cylinder assembly is operated as such that the distance is always maintained constant.

The linear actuator 50 employed in the embodiment generally comprises a servo motor 53 with a pulse encoder 52 and a ball screw 54 combined with the servo motor 53. However, the present invention is not limited to the above. Any other type of linear actuator maY be employed as long as it moves linearly and has generally the same accuracy as a linear scale.

Since a press brake with a displacement sensor of an electric signal output according to the present invention is constituted as such as described in the foregoing, the power cylinder can be controlled rapidly and accurately.

As for the electric control thereof, it suffices the purpose only if the linear actuator is accurately and rapidly controlled and the oil pressure portion may be disregarded for this purpose. Accordingly, the electric portion and the oil pressure portion can be separately adjusted. Thus, much time and labour can be saved in manufacturing.

Although the present invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and arrangement of parts may be resorted to without departing from the spirit and the scope of the present invention as hereinafter claimed.

Claims

1. A press brake with a displacement sensor of electric signal output comprising a base distance portion; a displacement sensor disposed opposite said base distance portion and having an electric signal output; a pair of molds, one of said molds being provided with either said base distance portion or said displacexent sensor, the other being provided with the remaining one of said base distance portion or said displacement sensor through a linear actuator; a servo amplifier for inputting an electric signal output coming from said displacement sensor; a servo valve controlled by an output signal coming from said servo amplifier; and a cylinder controlled by said servo valve and adapted to actuate either one of said pair of molds.

2. A press brake with a displacement sensor of an electric signal output as claimed in Claim 1, wherein said base distance portion is a bar.

3. A press brake with a displacement sensor of an electric signal output as claimed in Claim 1 or Claim 2, wherein said base distance portion is formed on an upper mold of said pair of molds.

4. A press brake with a displacement sensor of an electric signal output as claimed in Claim 3, wherein said base distance portion is mounted on said upper mold of said pair of molds through a ram plate.

5. A press brake with a displacement sensor of an electric signal output as c # ai claimed in any of Claims 1 - 4, wherein said displacement sensor having an electric signal output is a contact type.

6. A press brake with a displacement sensor of an electric signal output as claimed in claim 5 wherein said displacement sensor having an electric signal output is a differential transformer.

7. A press brake with a displacement sensor of an electric signal output as claimed in any of Claims 1 - 4, wherein said displacement sensor having an electric signal output is a non-contact type.

8. A press brake with a displacement sensor of an electric signal output as claimed in Claim 7, wherein said displacement sensor having an electric signal output is an optical type.

9, A press brake with a displacement sensor of an electric signal output as claimed in Claim 7, wherein said displacement sensor having an electric signal output is a magnetic type.

10. A press brake with a displacement sensor of an electric signal output as claimed in any of Claims 1 - 9, wherein said linear actuator is mounted on a lower mold of said pair of molds.

11. A press brake with a displacement sensor of an electric signal output as claimed in Claim 10, wherein said linear actuator is indirectly mounted on a lower mold of said pair of molds through a holding table.

12. A press brake with a displacement sensor of an electric signal output as claimed in any of Claims 1 - 11, wherein said linear actuator comprises a combination of a servo motor with a pulse encoder and a ball screw.

13. A press brake substantially as hereinbefore described with reference to, and as illustrated in, Figure 1 of the accompanying drawings.