GB2041802A

GB2041802A - Control arrangement for a press or free bending machine

Info

Publication number: GB2041802A
Application number: GB8000899A
Authority: GB
Original assignee: Mengele and Soehne Maschinenfabriken Karl GmbH
Current assignee: Mengele and Soehne Maschinenfabriken Karl GmbH
Priority date: 1979-01-15
Filing date: 1980-01-10
Publication date: 1980-09-17
Also published as: FR2446138A1; GB2041802B; DE2901376A1; CH620610A5; DE2901376B2; NL7909223A; FR2446138B1

Abstract

A control arrangement for a press or free bending machine wherein the length of travel of one tool relative to another tool is adjusted in accordance with the thickness of a workpiece interposed between them comprises sensing means (22) arranged to monitor the actual thickness of the workpiece (21), and means for adjusting the length of travel of said one tool (11) relative to the other tool (10) in accordance with the thickness sensed by the sensing means. The control arrangement has an electrical circuit fed with signals indicative of the nominal thickness of the workpiece and the actual thickness monitored by the sensing means, the deviation of the actual thickness being arranged to provide an output signal for controlling the length of travel of said one tool relative to the other tool. <IMAGE>

Description

SPECIFICATION Control arrangement for a press or free bending machine TECHNICAL FIELD OF THE INVENTION The invention relates to a control arrangement for a press or free bending machine, wherein the length of travel in a movement of one, usually an upper, tool is adjusted according to the nominal thickness of a workpiece and/or the groove width of the other lower, tool and the desired bending angle.

The limit of the downward stroke of the upper tool (depth of travel) can be manually adjusted by reference to tables of sample values; but the travel depth can albo be adjusted by means of a position control according to values fed into a computer of a control arrangement. Furthermore, the upper tool can be manually brought to the reference value when performing free bending of a given workpiece, and operations can then be carried out based on this derived value.

BACKGROUND ART A control arrangement for free bending machines is already known, wherein the downstroke depth of the upper tool into the lower tool is automatically adjusted by feeding into a programming arrangement the groove width of the lower tool and the thickness of the workpiece together with the desired bending angle, whereafter the position control is set into operation by a position and switching instruction store.

Notwithstanding the capital expense involved, recourse is still had to measuring the actual bending angle produced in the workpiece, for which purpose the production line must be interrupted and the workpiece set aside.

Dependent on the dimensions of the bending angle it is then necessary to carry out a suitable correction of the adjustment of the downstroke of the upper tool. Those workpieces which had already been produced with a faulty bending angle then have had to be subjected to an additional bending operation, if the inaccuracies of the workpieces were unacceptable.

It has therefore been the practice to wait and see how the bending angle turns-out and not to pay attention to the fact that the tolerances in the thickness of the workpiece, which are in any case unavoidable, could often cause considerable variation in the bending angle. However the dimensional accuracy of the wçorkplece must be suited in each case to the further uses of the workpiece, for example for industrial manufacture, since otherwise the individual parts will not match each other, as a result of which the production cycle could be disturbed or the products scrapped.

An object of the invention is to provide a control arrangement for a press or free bending machine which can compensate for variation in the thickness of the workpiece.

DISCLOSURE OF THE INVENTION According to the present invention, in a control arrangement for a press or free bending machine wherein the length of travel of one tool relative to another tool is adjusted in accordance with the nominal thickness of a workpiece interposed between them, there is provided sensing means arranged to monitor the actual thickness of the workpiece, and means for adjusting the length of travel of said one tool relative to the other tool in accordance with the thickness sensed by the sensing means.

The sensing means may comprise a plurality of sensing heads located at or near to the deformation zone of the workpiece, and the length of travel of said one tool relative to the other tool may be adjusted in accordance with the means value of the thickness monitored by the plurality of sensing heads.

In carrying out the invention a machine control drive may be interrupted until an initial position of said one tool relative to the other tool has been adjusted to provide a length of travel in accordance with the thickness sensed by the sensing means.

Preferably, the said one tool is an upper tool in the form of a die which travels downwards relative to a lower tool having a groove with which the die cooperates, and the relative downward movement of said upper tool is modified in accordance with the width of the groove.

The length of travel of said one tool relative to the other tool may also be adjusted in accordance with the desired bending angle of the workpiece and/or the recovery factor of the material of the workpiece.

The sensing means may have sensing surfaces located above and below the workpiece, the lower sensing surface being fixed and the upper sensing surface being urged downwards into contact with the workpiece. Alternatively, the upper sensing surface may be fixed and the lower sensing surface urged upwards into contact with the workpiece.

The movable sensing surface may be urged in contact with the workpiece by a pneumatic piston and cylinder unit or by spring means.

The control arrangement may also have electrical circuit means arranged to be fed with signals indicative of the nominal thickness of the workpiece and the actual thickness monitored by the sensing means, the deviation of the actual thickness from the nominal thickness being arranges to provide an output signal for controlling the length of travel of said one tool relative to the other tool.

The electrical circuit means may comprise a programming device of a computer arranged to be fed with signals indicative of the desired bending angle of the workpiece and/or the recovery factor of the material of the workpiece, the computer being arranged tokeceive signals indicative of the nominal thickness of the workpiece and the actual thickness monitored by the sensing means, the computer also having a switching instruction store and a comparator arranged to control a tool adjusting device in accordance with all the received signals.

The electrical circuit means may be connected to the electrical circuit of the machine control device so that actuation of the press or free bending machine operates the electrical circuit means.

The workpiece may be in the form of metal sheet or strip and for the purpose of enabling the sheet or strip thickness tolerances to be sensed in the immediate vicinity of the deformation zone of the workpiece the sensing means can be of various designs.

The sensing means can be provided with a flexible cable and can be set down from above onto the workpiece, but for the same purpose the sensing means can be pressed automatically against the sheet or strip from below, for example by a pneumatic operating cylinder, a spring or an analogous device.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side elevation of a drop bending press incorporating a control arrangement according to the invention; Figure 2 is a plan view of the lower tool of the bending press shown in Figure 1; Figure 3 is a section taken on the line Il-Il in Figure 2 and showing a more detailed arrangement of the sensing head; and Figure 4 is a block schematic circuit diagram of the control arrangement.

BEST MODE FOR CARRYING OUT THE INVENTION Referring in the first instance to Figures 1 to 3, the control arrangement is shown in a free bending machine (drop bending press) comprising a lower tool 10 having a groove 18, an upper tool 11 secured at the lower end of a press plunger 16, and a ram cylinder 13 having a ram piston 12. The free bending machine also has a press table 15 and a C-shaped frame member 14. The workpiece 21, is in the form of a metal sheet or strip which is to be bent in the groove 18.

In accordance wihh the invention a thickness measuring device comprising a support 23 with a measured value transmitter or sensing head 22 is arranged adjacent the lower tool 10 and has operating parts situated both above and below the press table 15 which provides sensing surfaces arranged to cooperate with the upper and lower surfaces of the workpiece 21. One of the sensing surfaces of the sensing head 22 is fixed and the other sensing surface is movable in accordance with the actual thickness of workpiece 21 . The support 23 is secured to the top of an adjusting piston 26, which is slidably mounted in a guide member 25. The adjusting piston 26 is operated by a pneumatic working cylinder 27 arranged so that when the working cylinder 27 is charged the movable sensing surface of the sensing head 22 is lightly pressed against the workpiece 21.

Referring in particular to Figure 3 the thickness measuring device is shown in more detail, a nonrotatable pin 29 is threaded into the guide member 25 and engages in a longitudinal slot 28 of the adjusting piston 26. Furthermore, the measured value transmitter or sensing head 22 is replaceably held in the support 23 by a clamping screw 30. The connecting cable to the control arrangement is shown at 24.

The mode of operation of the control arrangement will now be explained with reference to the block schematic circuit diagram shown in Figure 4.

Prior to the operation of the free bending machine, the reference value of the bending angle, the width of the groove 1 8, as well as the values of other machine functions such as the spring response of the frame and the expected spring recovery value for the bend in the workpiece, are fed into a programming device A and these are stored in a reference value store and a constant value store B1 and B2 respectively.

The actually existing thickness of the workpiece 21 is measured by the measured value transmitter or sensing head 22 of the thickness measuring device and, together with the other values which have been fed into the programming stores, is taken to a computer C, and the downstroke travel thus determined is fed into a switching instruction store D.

The thickness measurement, which is effected by the measuring value transmitter or sensing head 22, is initiated upon the operation of the ram cylinder 13.

In accordance with the measured thickness of the workpiece 21, the position control, which is derived in dependence upon a comparator E, a control circuit F, an actual value position store G and an actual value transmitter H, is switched into effect, and thereby the mechanical or hydraulic means for limiting the downward stroke (travel depth) of the press plunger 1 6 of the upper tool 11 are actuated.

Any existing deviation of the bending angle from its reference value is fed as a correction factor into the programming device; the device then operates fully automatically.

Without necessarily limiting the scope of the invention claimed, preferred embodiments of the invention may be summarised as follows.

1. A control arrangement for free bending machines, wherein the depth of travel in the downstroke of the upper tool (die) is adjusted according to the existing thickness of the workpiece and/or the groove width of the lower tool (matrix) characterized in that the existing workpiece (sheet) (21) thickness is sensed by means of at least one measured value transmitter (22) belonging to a thickness measuring device located in the immediate vicinity of the deformation zone of the workpiece, and the machine control drive (12,13) is interrupted for such period until the upper tool (11) has been adjusted by position control means to a downstroke depth corresponding to a reference value stored in advance in a programme carrier.

2. A control arrangement according to Summary 1, characterized in that the thickness of the workpiece to be deformed is fed into the programming device and, by means of the thickness measuring device, the deviations from the prescribed thickness are measured and fed into the position control which, by means of the upper tool adjustment device, effects a corresponding correction of the downstroke depth of travel.

3. A control device according to Summary 1, characterized in that the width of the groove (18) together with correcting factors for the existing machine, if necessary also the spring recovery factor of the material and the desired bending angle a of the workpiece (21) to be deformed, are fed into a programming device (A) of a computer (C) with a store (D) and comparator (E), thereby controlling the upper tool adjusting device (J, K), whilst simultaneously the total sheet thickness (reference thickness + any tolerance value) is measured by a measured value transmitter (22) and fed into the computer (C), wherein is effected a suitable logical coupling of the values.

4. A control arrangement at least according to Summary 1, characterized in that the control arrangement is so connected in the electrical circuit of the machine control drive (12/13) that the pulse for effecting the measurement and for the position control is generated by the actuation of the press.

5. A control arrangement at least according to Summary 1, characterized in that several measured value transmitters (22) are provided and these are so connected that the position control of the downstroke depth is effected in dependence upon a mean value.

6. A control arrangement at least according to Summary 1, characterized in that the measured value transmitter (22) is provided with a flexible conductor (24) and can be set down upon the workpiece (21) from above.

7. A control arrangement as least according to Summary 1, characterized in that the measured value transmitter (22) can be pressed against the workpiece (21) by a pneumatic piston and cylinder unit (26/27).

8. A control arrangement at least according to Summary 1, characterized in that the measured value transmitter (22) can be pressed against the workpiece (21) by means of a spring or the like.

Claims

1. A control arrangement for a press or free bending machine wherein the length of travel of one tool relative to another tool is adjusted in accordance with the nominal thickness of a workpiece interposed between them, characterised by sensing means (22) arranged to monitor the actual thickness of the workpiece (21) and means for adjusting the length of travel of said one tool (11) relative to the other tool (10) in accordance with the thickness sensed by the sensing means.

2. A control arrangement as claimed in Claim 1, characterised in that the sensing means (22) comprises a plurality of sensing heads located at or near to the deformation zone of the workpiece (21) and the length of travel of said one tool (11) relative to the other tool (10) is adjusted in accordance with the mean value of the thicknesses monitored by the plurality of sensing heads.

3. A control arrangement as claimed in Claim 1 or Claim 2, characterised in that a machine control drive (12, 13) is interrupted until an initial position of said one tool (11) relative to the other tool (10) has been adjusted to provide a length of travel in accordance with the thickness sensed by the sensing means (22).

4. A control arrangement as claimed in any preceding claim, characterised in that said one tool (11) is an upper tool in the form of a die which travels downwards relative to a lower tool (10) having a groove (18) with which the die cooperates, and the relative downward movement of said upper tool is modified in accordance with the width of the groove.

5. A control arrangement as claimed in any preceding claim, characterised in that the length of travel of said one tool (11) relative to the other tool (10) is also adjusted in accordance with the desired bending angle of the workpiece (21) and/or the recovery factor of the material of the workpiece.

6. A control arrangement as claimed in any preceding claim, characterised in that the sensing means (22) has sensing surfaces located above and below the workpiece (21), the lower sensing surface being fixed and the upper sensing surface being urged downwards into contact with the workpiece.

7. A control arrangement as claimed in any one of claims 1 to 5, characterised in that the sensing means (22) has sensing surfaces located above and below the workpiece (21), the upper sensing surface fixed and the lower sensing surface being urged upwards into contact with the workpiece.

8. A control arrangement as claimed in any preceding claim, characterised in that a sensing surface of the sensing means (22) is urged into contact with the workpiece (21) by a pneumatic piston and cylinder unit (26, 27).

9. A control arrangement as claimed in any one of claims 1 to 7, characterised in that the sensing surface of the means (22) is urged into contact with the workpiece (21) by spring means.

10. A control arrangement as claimed in any preceding claim, characterised by electrical circuit means arranged to be fed with signals indicative of the nominal thickness of the workpiece and the actual thickness monitored by the sensing means, the deviation of the actual thickness from the nominal thickness being arranged to provide an output signal for controlling the length of travel of said one tool (11) relative to the other tool (10).

11. A control arrangement as claimed in Claim 10, characterised in that the electrical circuit means comprise a programming device (A) of a computer (C) arranged to be fed with signals indicative of the desired bending angle of the workpiece (21) and/or the recovery factor of the material of the workpiece, the computer also being arranged to receive signals indicative of the nominal thickness of the workpiece and the actual thickness monitored by the sensing means (22), the computer (C) having a switching instruction store (D) and a comparator (E) arranged to control a tool adjusting device (J, K), in accordance with all the received signals.

12. A control arrangement as claimed in Claim 11, characterised in that the electrical circuit means is connected to the electrical circuit of the machine control device (12, 13) so that actuation of the press or free bending machine operates the electrical circuit means.

13. A control arrangement for a press or free bending machine substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

14. A control arrangement as claimed in Claim 14, having an electrical circuit substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.