CA1147436A - Arrangement for presses - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The invention relates to a press arrangement of the kind in which forming depends on hydraulic pressure which varies during a pressing operation, comprising a pair of relatively mov-able components which are made to carry out a relative movement during the pressing operation, means for sensing the said movement and generating a control signal which, according to a functional relationship relevant to the pressing operation, depends on the sensed movement, and a hydraulic system for regulating by means of the control signal the hydraulic pressure during the pressing operation according to said functional relationship. Such a press arrangement is described in British Patent Specification No.
1,491,237. The invention provides a press arrangement which is characterised in that the said means comprise a manually program-mable electrical function generator which has a large number of contact points arranged in rows and columns for reproducing in an electrically readable form pairwise associated pressure and move-ment values constituting points in the relevant functional rela-tionship (p = f(s)), and which at its output is connected to the hydraulic system, while its input side is operatively connected via a measurement transducer to one of the said components for receiving a measurement signal (s) which is a measure of the move-ments covered and which makes the function generator read off in turn and in sequence and issue at its output the said pressure values as the movement values are reached.

Description

An Arrangement for Presses .
The present invention relates to an arrangement for presses, preferably intended for forming sheet metal blanks, and with which the forming depends on hydraulic pressure which varies during a pressing operation, and which comprise a pair of rela-tively movable components which are made to carry out a relative movement during the pressing operation, means for sensing the said movement and generating a control signal which, according to a functional relationship which is relevant to the pressing opera-tion, depends on the sensed movement, and a hydra~lic system forregulating by means of the control signals the hydraulic pressure so that this may be varied during the pressing operation according to the functional relationship. More specifically, the invention relates to an improved arrangement for controlling the hydraulic working pressure which acts in such a press during a pressing oper-ation and which thereby controls, either directly or indirectly, the course of the operation.
Pressure control of this kind in a press may be con-sidered necessary so that satisfactory working results may be obtained when carrying out deep drawing and similar pressing operations when sheet metal blanks are to be given a complicated form. For this purpose, various solutions may be found on the market, based on drawing a curve which represents on a specific scale the relationship between the hydraulic pressure and the movements carried out which has been found to be suitable for a pressing operation. A template is then produced from plate or another rigid mater:ial so that the contour of this corresponds accurately with the curve and this template is fixed to a movable ~ means appertaining to the press which detect the movements involved, in a mechanical way. A template sensor, the sensing part of which follows the contour of the template and is movable in the lateral direction relative to the displacement direction : , , :

of the template, transmits during the pressing operation the lateral movements obtained from the displacements of -the template to a signal generator in the form of a pressure control valve or a potentiometer which controls an electro-hydraulic valve via an amplifier. The latter arra~gement is described in more detail in Br-tish Patent Specification No. 1491237.
To establish the relationship between the relative move-ment and the working pressure which the contour of the template represents generally calls for a very comprehensive sampling proves, particularly for parts with a high drawing depth ratio, and it is not unusual before starting series-production for 20 samples to have to be made, with adjustments inbetween at different points over the contour of the template before a satisfactory work-piece is obtained. Obviously, a template cut out of plate is less suitable, but even if a cam plate is used, the contour of which is formed by a steel strip which is adjustable by means of a number of positioning screws connected to the steel strip, such adjustment work is still time-consuming and troublesome and can-not be carried out without tools.

2~ Furthermore, it is d~fficult to carry out a purely mech-anical template-sensing which is very accurate without the trans-mitted movement varying from one run to the next due to mechanlcal imperfections in the signal generating control valve.
- A template-sensing arrangement for hydraulic presses which works with photocells is known from Swedish Patent Specifica-tion No. 322 193. The template which, as in the above-described arrangement is displaced by one of the moving components of the press, can be made in this instance from a piece of paper which is cut so that it gives the desired pressure curve and which is then inserted in a holder so that depending on its movement, light from a light source located on one side of the template is screened from or reaches a row of photo-cells arrangPd on the other side.

: :

~1~7~
The arrangement requires that every time a new part is to be pro-duced a template must be made or -the pressure curve adjusted on an existing one, if i-t is not desired to file all the templates used for future use, and the procedure for trimming a pressure curve into shape is basically just as labour and time-consuming as with a conventional template made of plate, for in this case as well the template must be removed from the machine for each modification of the pressure values and after aajustment, which can be effected by cutting away or sticking on a piece of paper along the contour of the pattern, this must be inserted again in its place in the holder.
With the known pressure regulating arrangements there is also no flexibility auring series-production, which might be desired bearing in mind the variations which may arise concerning the hardness of the basic material or other characteristics which are significant for the choice of working pressure. Neither does any one of the arrangements allow a simple and quick adjustment of the pressure curve in oraer to compensate for temperature aif-ferences in the pressure medium while pressing is being effected, and for the rises or reductions in pressure occasioned thereby, which in certain circumstances can result in an interruption of ~: work several times a day.
It is therefore an object of the present invention to : :
provide a pressure-regulating arrangement for use in presses which operate with hydraulic pressure which is to be varied during a pressing operation, which arrangement is not encumbered with the disadvantages which the known arrangements display, as mentioned :: :
above, but which enables the~functional relationship which should :;; exist during a pressing operation between the hydraulic pressure and the forming movements to be lnserted in a press quickly and :
with few manipulations, and which:has such flexibility that a relationship inserted in the press will be simple to alter and

- 3 - : -.

adjust subsequently without any appreciable interruption in a continuous production process.
Another object which the invention seeks to achieve is to generate the control signal which represents the working pres-sure in such a way that it is not sub~ect to errors on the grounds of inaccurate movement sensing, mechanical wear, etc., that the course of a pressing operation can be followed visually, and thus the movement and pressure values prevailing at any given moment according to the relevant relationship can be observed, and that the latter can be reproduced for filing, when applied, without preventing the same relationship being used in the production process.
According to the invention, an arrangement for presses as discussed hereinbefore is characterised in that the means for sensing movement and generating a control signal comprise a manu-ally programmable electric function generator which has a large number of contact points arranged in rows and columns for repro-ducing in electrically readable form pairwise associated pressure and movement values constituting points in the relevant functional relationship, and which at its output is connected to the hydraulic system, while its input side is operatively connected via an electrical measurement transducer to either of the said components for receiving a measurement signal which is a measure of the move~
ment covered and which makes the function generator in turn and in sequ~nce read of:E and issue at its output the said pressure values as the movement values are reached.
The function generator consists preferably of a pro~
gramming panel, the electrical parts of which comprise in a known way two crossing sy~stems of parallel conductors situated in dif-ferent planes, which are separately assigned to the pressure or --movement values respectively which increase stepwise and gradually within each system, from a common starting point. The panel also ~,:

- 4 - , ~
~ 1 ~ ~7436 has in a known way a perforated board covering the conductor systems, the holes in which are located right at the intersection points of the system, and suitable plug contacts for fitting in the holes.
For programming the pressure and movement relationship the p_ocedure is to insert for each of the movement values, a plug contact in the hole which corresponds w-ith a selected required demand pressure value so that the plug contact positions on the panel depict as a whole the pressure curve believed to be suitable for a certain pressing operation. If the working results are not satisfactory, it is possible with a few manipulations to adjust the curve rapidly, by moving one or more of the plugs so that the demand value of the hydraulic pressure for a specific relative position of the movable components of the press or during a cer- ;
tain part of the total forming movement is raised or lowered compared with the former value.
Each functional relationship progràmmed in this way can be recorded easily and rapidly for flling by providing the pro-gramming panel with a diagram sheet which is pierced by the plug contacts as they are inserted in the holes in the panel. ~ ;~
It is also of great practical importance that, accord-ing to a further characteristic of the invention, the function generator has a row of lamps or the like which are lit in turn in ~ ~
time with the sensed movement values. In this way, the operat~r ~ ;
can easily check the progress of a pressing operation.
The invention will be explained in more detail in the Iollowing with reference to the attached:Drawing, in which Flgure l, is an axial section through a hydraulic press with the arrange~
ment according to the invention, Figure 2 is an electrical circult diagram of the arrangement, and Figure 3 illustrates a programmed ;
relationship between the forming movements and the pressure.
Although the invention can be used~on any type of press , -- 5 - ~ i ~7~36 in which the forming depends on hydraulic pressure which is con-trolled during the forming process, thus also on a hydraulically driven press wherein the forming part works mechanically, and like-wise in a press which is driven purely mechanically and has a hydraulic forming chamber in which the hydraulic pressure which is effective during the forming process is controlled by altering the volume of the chamber, for the sa]ce of simplicity only its use in a hydraulic press constructed according to Figure 1 in British Patent Specification No. 1491~37 will be described here, and reference should be made thereto concerning any details which are not described below.
In Figure 1, 1 designates a stand which bears at the top a unit 2 which is specially designed for forming sheet metal blanks 3 and has a membrane 4 which defines the bottom of a closed chamber 5 containing a constant volume of fluid.
On its lower section the stand 1 bears a hydraulic assembly 6 comprising a cylinder 7 in which an outer pressing piston 8 is inserted, which passes at the top via an intermediate base 9 into a draw ring 10 on which the sheet metal blank 3 is 2Q placed when the press is in the open position. Running in the outer piston 8, the hydraulic assembly also has an inner piston -11 which bears a central tool component, in~this instance con-structed as a die 12. The chambers 13 and 14 underneath the outer and inner pistons respectively are filled with hydraulic fluid and are connected via pressure lines 15 and 16 to a hydraulic system comprising a pump assembly 17. The hydraulic system is designed to effect all the fluid transportation which is required for : closing the press, whereby during the expansion of the fluid cham-~ ber 13 the outer piston 8 moves upwards into the position shown in the Figure, bringing the inner piStOll 11 with it; similarly, for opening the press, pressure medium is introduced into the two~

annular chambers 18 and 19 which are located between the cylinder : `' , 7 and the outer piston, and between the outer piston and the inner piston respectively, at the same time as the chamber 13 is com-pressed.
The forming operation itself is effected, as is known in this kind of press, in that the inner piston 11 together with the die 12 is made to move upwards by the supply of pressure fluid from the pumping assembly 17 via the line 16 into the chamber 14, so that the sheet metal blank 3 is drawn over the die and deformed.
During this process a high fluid pressure arises in the forming chamber 5, which leads to the result that under the influence of themembrane 4 the sheetmetal blank is pressed a~ainst all sides of the die and assumes the shape thereof, and in addition the cas-ing of the unit 2, the draw ring 10 which rests thereon and the outer piston 8 also move downwards during the draining of fluid from the chamber 13 via the line 15 to the hydraulic system. As explained in British Patent Specification No. 1491237, with so-called matrix-forming, these relative movements of the two tool ~ ' components is the reverse of what is described here.
With this type of pressing operation the specific pres-sure in the forming chamber 5 is of great importance for the work-ing results and it has been found that this pressure should be ;;
controlled so that it varies in a specific way with the mutual movement of the tool components, that it, as a function of the~
relative movements between the outer piston 8 and the inner piston 11, which parts are hereinafter called the two movable components of the press. One way proposed to accomplish this pressure con-trol is to allow the fluid-which is drained from the hydraulic assembly 6 during forming to pass through a valve arrangement 20 ;~

~ whi~ch ensures that the pressure upstream from the valve arrange-ment and therefore the pressure in the fluid chamber which is com-pressed during forming (i.e. the chamber 13 in the example of die-forming) corresponds to a demand value which varies depending on - 7~-:

74~6 ~he mutual displacement of the two movable components of the press.
Accordingly, the valve arrangement indirectly controls the fluid pressure which is effective in the forming chamber 5. The fluid drained off in this way can either go to a tank 21 or as described in British Patent Specification No. 1491237, it can be returned to the fluid chamber which is expanding (in the example this is chamber 14) so as to co-operate in this way in the work which the upwards-moving tool component is carrying out, and thereby reduc-ing the consumption of energy.
According to the present invention, the hydraulic pres-sure which controls the forming, this being either the pressure which acts directly on the blank during the forming process or the indirectly acting pressure _ which, in a press of the kind des- `
cribed above, prevails in a fluid chamber, appertaining to a hydraulic assembly and being compressed during the forming pro-cess, is regulated with the aid of an arrangement which consists basically of a measurement transducer 22 for sensing the mutual displacement s of the two movable components 8 and 11 of the press, ~ `
and an electrical function generator 23 for manual programming of the functional relationship p = f(s) between the said pressure p - and the displacement s, which should apply for a forming operation and for producing, according to the development of the sensed dis-placement movement, a control signal 15 which varies according to the programmed relationship and is supplied to the valve arrange-ment 2Q.
The measurement transducer 22, which is assumed to be the type of optical absolute position transducer which produces a digitally coded measurement signal, comprises a grid disc 24 which is attached rotatably but not displaceably to the inter- ~
~ediate base 9, and a rod 25 which rotates round the grid disc and which is attached to the inner piston 11 by means of a bracket 26.
This projects out laterally through a slit 27 in the draw ring 10 - , - , , . ~ : ~

3~

and has aver-tical extent such that the bracket can move freely relative to the draw ring, with the upwards displacement of the inner piston. The grid disc thereby rotates through an angle which exactly corresponds to the mutual displacement between the two moving components 8 and 11 and which is imambiguously repret sented by the digital measurement signal which is supplied to the input 28 of the function generator. There is nothing to prevent an analogue position transducer, for example, a contact-free potentiometer, from being used instead, when naturally another adaptation may be effected between the position transducer and the function generator.
The function generator, the electrical structure of which is shown in Figure 2, comprises advantageous1y a conventional programming panel 29 with two conducting systems which cross over each other, whieh are located in separate planes so that the con-ductors themselves do not provide any link between the systems.
Each system comprises a large number of equidistantly located conductors-(of which only a small number are shown in the Drawing), together forming a regular checked pattern,~ the rows 30 and columns 31 of which represent pressure and movement values respec-tively, all gradually increasing in smaIl steps from the lower left-hand corner 32 of the panel. As shown here, the conductors systems are eovered by a perforated sheet 33 which is made of `~
insulating material and in which there are holes located right at the interseetion points. By fitting a plug eontact 34 in a hole, the two row and column conductors which pass inside it are con~
nected to each other, thus allowing a point in a desired function ` relationship to be programmed in the function generator. On the board, the function value corresponding to the positions of the holes should be given, the pressure values expediently in percent~
of the maximum operating pressure of the press, and di;splacement values in appropriate units of length. The programming panel is _ g _ -~, ;

.

-~7436 also provided with an illuminated array 35, the lamps 36 of which are associated one by one with the columns on the panel and are connected to a decoder 37 which receives measurement si~nals from the position generator 22 and which is designed to light the lamps 36 in turn and in sequence when the movement values corresponding to a column are obtained.
At the input 28 the function generator has a second decoder 38 which is connected to each of the column conductors 31 via a gate 39, and which is designed so that, during a forming operation, it activates one of the column conductors with the aid of the measurement signals received which will occur in the same sequence and at the same moment as the corresponding lamp 36 is lit. This activation can be effected so that the conductor in question is connected to electrical earth by means of its gate while all the remaining column conductors remain inactive due to the fact that their gates have a high impedance to earth.
The output side of the function generator comprises a resistance chain 40 in which each separate resistance is connected between a pair of adjacent conductors in the rows 30, and has a ~20 resistance value such that the series resistance for the chain increases, preferably by the same amount at each step and calcu-lated rom the terminal point 41 according to the pressure values appertaining to the rows. A current generator 42 connected to the terminal point provides a current with constant current strength and while forming is being effected, this current can be con-ducted to earth only via the column conductor which is activated at that moment. Assuming that this is the conductor 31' which i9 :
connected to the plug contact 34, the current will accordingly pass through the two lower resistances in the chain 40, then via the horizontal conductor 30' to the contact plug, and then via the conductor 31' and its gate to earth, while at the same time all the other paths through the function generator are inter-, ", ~ .

7~36 rupted. The potential at the point 41 is gradually changed accord-ingly, in time with the ~orming movement and by the amount which obviously depends on the row in which the plug contact is inserted.
A voltage with such a characteristic is not, however, used directly for controlling the pressure, but is first modified, according to a characteristic feature of the invention, into a continuously varying signal, this be:;ng effected in a filter 43.
This can consist of a RC circuit with a variable condenser and by using this to adjust the filter time-constant in relation to the prevailing relative speed of the moving components in the press, it is possible to smooth, at least to a large extent, the stepwise variation in the direct current produced in the function generator at the transition from one column 31 to another.
If, as in the example shown, the valve arrangement 20 comprises a pressure regulating valve 44 the characteristic of which is such that the pressure is proportional to the current in a spool 45 in the valve, it can be expedient to process the filtered direct current signal in the following way. In an oscillator 46, an alternating current is produced which has a small amplitude compared with the direct current and which is superimposed on the latter in an operation amplifier 47 so that, in a known way, the mechanical hysteresis of the pressure control valve, or its tendency to stick, is eliminated. The summing sig-nal, the mean current value of which is unchanged compared with the current at the point 41, is applied to another operation amplifier 48 where it is compared with the voltage across a r~s~stor D resistance 49 with low ~ce, series-connected to the valve ;~
spool 45, this voltage, which is therefore a measure of the valve current, being fed back by means of the conductor 50. The result-ing control current is supplied~finally to an amplifier 51 which forms the drive fo:r the valve spool. The current to this will therefore be proportional to the current at the input of the :
~;
".,.:

~7f~3~

amplifier and therefore to the potential at the point 41.
In applications where the pressure control calls for large amounts of through-flow, which is the case with presses working in the same way as or in a similar way to the example in Figure 1, the pressure control valve is operated as a pilot valve controlling a main valve 52. This is dimensioned in such a way that it is capable of taking over if all or most of the stream of fluid which is to be drained from the press into the tank 21 or is to circulate from one fluid chamber 13 in the press, through the valve to the other fluid chamber 14.
It will be seen that with the described arrangement an effective and expedient pressure control is obtained which follows accurately a given relationship p = f(s) which, by means of the arrangement, can be varied within wide limits according to the type of pressing work, and can be modified or adjusted easily and quickly during continuous production: A further advantage which characterises the arrangement according to the invention is that :
such a relationship can be reproduced with simple means in its form as inserted in the function generator. For this purpose, the programming panel is provided with a sheet of diagram paper 53 (see Figure 3) which can be provided with printed fitting marks 54 matching the corners of the panel and/or with a checked pattern 55 corresponding to the pattern of holes in the board 33. ~:
By means of holders which are not shown, the diagram paper is attached in the correct position on the board after which the ~ .:
actual pressure curve is transferred to the paper by the plug contacts 34 being pressed through the paper so that they make a series of holes 56 corresponding with the programmed points. In comparison with the filing of templates which are sensed mechan-ically or optically, the method affords the advantage that the ::
.. ..
pressure curve of a certain work-plece can be filed in easily handled form, or can be used for preparing a subsequent operation while the part involved is in production.

~ - 12 -

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An arrangement for presses with which forming depends on hydraulic pressure which varies during a pressing operation, comprising a pair of relatively movable components which are adapted to carry out a relative movement therebetween during the pressing operation, means for sensing the said movement and gen-erating a control signal which, according to a functional rela-tionship which is relevant to the pressing operation, depends on the sensed movement, and a hydraulic system for regulating by means of the control signal the hydraulic pressure so that this may be varied during the pressing operation according to the func-tional relationship, said means comprising a manually programmable electrical function generator which has a large number of contact points arranged in rows and columns for reproducing, in an elec-trically readable form, pairwise associated pressure and movement values constituting points in the relevant functional relation-ship (p = f(s)), between the pressure (p) and the movement (s) and which at its output is connected to the hydraulic system, while its input side is operatively connected via a measurement trans-ducer to one of the said components for receiving a measurement signal which is a measure of the movement covered and which makes the function generator read off in turn and in sequence and issue at its output the said pressure values as the movement values are reached.

2. A press arrangement according to claim 1, in which the function generator comprises a programming panel with a first system of parallel conductors representing the movement values, which conductors are adapted to be individually actuated by a device decoding the measurement signal from the press, a second conductor system representing the pressure values, which crosses over the first conductor system and has a chain of resis-tors each of which is connected between two of the conductors in the second system such that the series resistance of the chain increases towards the output thereof in small steps, and with plug contacts each of which may be inserted into an arbi-trary crossing point for mutually connecting two conductors re-presenting a movement value and a pressure value respectively.

3. A press arrangement according to claim 1, in which the function generator is provided with a row of lamps, one for each movement value which is representable on the function gen-erator, and arranged to be lit one by one by means of the mea-surement signals at the same time as the corresponding pressure value is read off.

4. A press arrangement according to claim 1 or 2, in which the function generator has at its output a circuit which is arranged to smooth the stepwise change in the pressure values read off, so that a continuously variable control signal is issued to the hydraulic system.

5. A press arrangement according to claim 2, in which, for filing the programmed functional relationship, diagram paper is provided which, with the aid of matching marks fitting the con-ductor system on the panel or checks, can be applied over the programming panel so that the programmed points can be recorded by pressing the plug contacts through the paper.

6. A press arrangement according to claim 1 or 2, in which the function generator has a circuit which is arranged to smooth the stepwise change in the pressure values read off and which operates with an adjustable time-constant so that the pres-sure value smoothing function of the circuit can be adapted to the relative speed of the moving components of the press during forming.