Sheet bending machine

A sheet bending machine wherein a sheet of metal is fixed between a clamping beam and a lower beam mounted with interchangeable folding rails and wherein the bending is performed by a bending beam being swung against the projecting part of the sheet metal. The interchangeable folding rails have markings, for example, protrusions or recesses on the rear edge which cooperate with a set of members for establishment of a steering code which determines the maximum permissible bending angle for the folding rail. The code may be in the nature of a series of contacts which are opened or closed, dependent on the folding rail being used, having a recess opposite them or not. The state of the contacts may, for example, be sensed by a cam disc which curves synchronically with the swing movement of the bending beam and successively opens the contacts which are connected in parallel above them, so that a current circuit is switched when both corresponding pair of contacts are opened.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a sheet bending machine of the type wherein the 
bending of a sheet of metal is performed by swinging a bending beam 
against a projecting part of the sheet metal fixed between a lower beam 
and a clamping beam. Such a sheet bending machine is e.g. described in 
DE-AS No. 1 076 608. The bending beam can be driven by electromotors or it 
can be moved hydraulically. 
2. Description of Background Art 
To be able to make various bendings, the clamping beam is usually provided 
with interchangeable folding rails with profiles permitting sharp bendings 
of e.g. 135.degree. or profiles permitting a rounded bending of up to 
180.degree. which means that the bending beam also must be able to be 
swung or curved 180.degree.. 
To be able to adjust the bending angle in accordance with a certain working 
plan, the sheet bending machines are usually provided with members which 
can be programmed to switch off the current to the driving motors or to 
stop the supply of liquid to the hydraulic punch operating the bending 
beam. These members can as proposed in the above mentioned publication 
consist of discs or rolls with manually adjustable protrusion of cams 
which co-operate with contact rails so that being moved a length by the 
bending beam corresponding to a desired angle they actuate an electrical 
switch. For every working operation said discs or rolls are turned a step, 
so that the new protrusion activates the switching off of the movement of 
the bending beam. The angle movement of the bending beam can naturally 
also be operated electronically. Electronical operation on angle movements 
after an input program is well known and is not going to be described more 
closely. 
Whether the input of the bending machine is performed in one way or 
another, it may be necessary to switch the program operation off. If after 
having switched off the automatical operation, the machine is 
unintentionally adjusted to a bending curve which is greater than the 
folding rail permits, it can result in damage to the machine. The same 
thing may take place if the input program and the folding rail used do not 
correspond. The object of the invention is to indicate such operating 
members for a sheet bending machine that is secured against fault 
programming as well as fault operation, so that curving of the bending 
beam beyond the angle a given folding rail permits is not possible. 
SUMMARY OF THE INVENTION 
According to the invention each folding rail is provided with markings 
which co-operate with a set of members fixedly connected with the clamping 
beam for establishment of a code which determines the maximum curving 
angle of the bending beam. 
The invention can be realized in several ways. The markings can be 
protrusions on the rear edge of the folding rail or a recess therein. The 
protrusions or recesses actuate one or more of a series of breakers fixed 
to the clamping beam. A part of the rear edge of the folding rail may be 
formed as a leit actuating operating levers for a system of hydraulic 
valves, or in the folding rail a plate of insulation material may be 
embedded carrying contact pieces which co-operate with corresponding 
contact pieces in the clamping beam. The code may be a single selection of 
a single core, electric and hydraulic, or it may be a selection of a 
combination of cores. The number of codes must naturally correspond with 
the number of various folding rails. 
If there are only two types of rails, opening and closing of a single 
circuit will be sufficient to determine the permitted maximum bending 
angle for each of them. With three circuits e.g. eight angles may be 
determined. Binary codes will first and foremost be important if the sheet 
bending machine is operated electronically. By applying voltage to a 
combination of canals leading to the electronic steering equiment, this 
can convert the voltage combination to a steering order hindering the 
exceeding of a certain bending angle though the incoded program is 
providing a steering order hereto. 
The greatest security against fault operation is obtained by using a closed 
circuit, which independent of the automatic and/or manual steering, 
switches off the supply of energy to the power of the bending machine, and 
in this closed circuit a number of switches are inserted and connected in 
series which separately or in succession are opened by a member being 
moved synchronously with the bending beam. The switches separately, except 
for the last in the series, are shunted with one or more switches 
co-operating with the marking on one or more of the rails. The no-signal 
current in the closed circuit will be switched off when the bending beam 
is curved in such an angle that the member opening the switches arrives at 
the contact where the shunted contact is opened by the marking on the 
folding rail at the moment fixed on the clamping beam.

DETAILED DESCRIPTION OF THE INVENTION 
In FIG. 1 the outlines of the parts of a bending machine are shown as 
stippled, which are necessary for the understanding of the invention, such 
as they look seen from one end side of the machine. A lower beam 1 is 
fixed to the machine frame, 2 indicates a clamping beam which manually or 
automatically e.g. hydraulically can be moved up and down in order to make 
space for insertion of the sheet metal and fixing the same during the 
working operation. 
The clamping beam has an interchangeable folding rail 3. The construction 
of the folding rail is essential for the invention and will therefore be 
described more closely in connection with FIGS. 3 and 4 in the drawing 
showing a part of the clamping beam and the folding rail in an enlarged 
scale. A bending beam 4 is provided which can be swung or curved around an 
axis indicated by the center of the circle 5 in FIG. 1. The bending beam 
can be worked electrically or hydraulically. The driving mechanism is not 
comprised by the invention and will therefore not be described here. A 
drive mechanism is disclosed in the German publication No. 1 076 608 
mentioned above dealing with a hydraulically driven sheet bending machine. 
It is obvious that the rack-and-pinion shown in this publication can be 
replaced by for example a worm drive which is driven by an electromotor. 
In FIGS. 3 and 4 a cross section of the clamping beam 2 in FIG. 1 is shown 
in an enlarged scale, so that the essential construction details for the 
invention can be seen clearly. The clamping beam comprises as can be seen 
a rigid front edge beam welded to a frame 7 of sheet iron. The front edge 
beam carries the folding rail 3 which in FIG. 3 is shown with a nose 8 of 
about 45.degree., and which thererfore permits a maximum bending of the 
edge of the sheet metal of 135.degree., in practice the bending angle is 
smaller. The folding rail in FIG. 4 is shown with a round nose 9 
permitting a bending of a whole 180.degree.. 
As illustrated in FIG. 3, in a space 10 under the beam a number of switches 
11 are disposed, so that the rear edge of the rail 3 will actuate a 
switch. As illustrated in FIG. 4, a recess in the rear edge will actuate a 
switch. The number of switches is determined by the number of types of 
rails as it shall be explained in connection with FIGS. 2 and 4. 
FIG. 2 is a flow sheet for a current circuit which can be used in 
connection with a bending machine constructed according to the invention. 
In a closed circuit for a control member, which in a simple form may be an 
electromagnetical switch or a magnetic valve, a number of switches 13 
connected in series are inserted which under the normal state are closed, 
so that a current runs throught the control member. Each of the switches 
13 except the last one in the series are shunted with the contacts in the 
switches 11 which are shown in FIGS. 3 and 4. These switches are closed 
except the one, for which the used folding rail 3 has a recess. A member 
which moves synchronically with the bending beam 4 during its curving 
movement and switches on the first contact in the direction of the 
horizontal arrow when the bending beam has curved a predeterminded angle 
V.sub.1, and then the next when the bending beam has curved another 
V.sub.2 and so on will not switch off the current unless the shunted 
contact 11 is switched off too, or when it has reached the last contact in 
the series. 
This current diagram gives, as it is a closed circuit, a greater security 
of the fact that the maximum bending angle, which is determined by the 
marking of the folding rail according to the invention--here a recess in 
the rear edge of the rail--cannot be exceeded by any operation resulting 
in a damaging to the machine. 
FIG. 5 shows a practical embodiment of the flow sheet, as shown in FIG. 2, 
S.sub.1, S.sub.2 and S.sub.3 indicate three types of rail which 
respectively permit the bending angles of 135.degree., 160.degree. and 
180.degree.. A cam disc 14 is connected to the shaft of the bending beam 
and has a single cam 15 which successively actuates three switches 13V1, 
13V2 and 13V3 disposed in a circuit around the disc 14, so that the cam 15 
actuates 13V1 when the disc has curved 135.degree., 13V2 when the disc has 
curved 160.degree. and 13V3 when it has curved 180.degree.. 
The switches 11S1 and 11S2 are connected via 13V1 and 13V2 respectively. As 
it will be seen 11S1 is switched off if a folding rail of the type S2 is 
in the machine. As it is seen the current is switched off from + to - by 
curving of the disc 14 of 135.degree.. This angle is passed without 
interruption of the current if S2 is in the machine, because 11S1 is not 
interrupted now, but 160.degree. cannot be passed without interruption of 
the current as 11S2 is open. If the rail S3 is in the machine, both 11S1 
and 11S2 are closed and the current is interrupted only by a curving angle 
of 180.degree. of the disc 14. 
The embodiment of the invention described is simple and efficient, but as 
mentioned above there is nothing to prevent from using the invention in 
connection with sheet bending machines, where the desired bending angle is 
determined automatically by an electronic steering system by means of 
input codes. If so a bit in a binary code system may be represented by the 
presence or the absence of a recess on a certain place of the folding rail 
or by a pattern of insulated or conducting areas. The folding rails may 
also be a part of an in itself well known code converter by giving a part 
of their rear edge a key profile which by inserting of the rail in the 
bending machine adjust a number of slideable bars disposed in the clamping 
beam, and which is their sliding in a well known manner permit one of a 
number of traversing bars to be slided.