Machine tool

A machine tool comprising a portal stand having a number of, preferably four, screw pillars and a moveable yoke driven and guided along the screw pillars by means of nuts preferably roller nuts, in the yoke. Tools, machining devices or the like can be attached to the yoke. The nuts are driven simultaneously by a drive motor through a drive shaft extending therefrom. A very good parallel guiding of the yoke is achieved despite uneven loads. When the power demand is high, for example during heavy pressings, an auxiliary cylinder is provided, the piston rod of which is fixed to the yoke.

FIELD OF THE INVENTION 
The present invention relates to a machine tool for performing pressing 
and/or cutting tooling operations during motion, said machine comprising a 
portal stand comprising at least three pillars and at least one yoke 
moveable along the pillars for supporting tools and the like for said 
tooling operations. 
DESCRIPTION OF THE PRIOR ART 
There exists today a great need for a flexible production apparatus that 
can be used for a number of different machine tool operations. Thus it is 
desirable to have one and the same machining unit able to carry out a 
plastic forming operation for example pressing, deep drawing, etc., as 
well as drilling, thread cutting, cutting, punching, milling, turning etc. 
The conventional mechanical equipment available within this field today 
comprises hydraulic and eccentric presses and machine tools for cutting 
tooling. However presses cannot perform a cutting tooling and cutting 
machines are not adapted to perform pressing operations. Thus the 
workpiece has to be moved several times to different machines and the 
repeated chucking work requires a lot more time than the work operation 
itself. 
The production modules existing today for the above mentioned purposes are 
either enormously large machines, such as eccentric type presses, which 
have the required stiffness and the capability of withstanding eccentric 
loads, or machines, which cannot withstand any eccentric loads, because of 
too great a flexibility when fully loaded etc. 
Such a machine is shown in e.g. the German "Offenlegungsschrift" No. 
1.477.622. It comprises a portal stand consisting of two or more pillars 
which form a guide for as many tubes, which are displaceable along the 
pillars. Two yokes are fixed on the arms at a certain distance from each 
other. Between the yokes a machining device is supported, which may 
comprise a press, a rotary body, a heat treating device etc. Screws, which 
are turned by a motor mounted above the yoke, make the yokes and thereby 
the machining apparatus move along the pillars. 
This device provides a very good guide for the machining apparatus, but the 
yoke height is very large. The device works only as a power supplier to 
the machining apparatus and not as a paralleling means. The screws are 
self-braking and cannot eliminate moment of force caused by possible 
uneven loads. These moments of force must instead be carried by the 
control pillars and can cause their deformation. 
Another known construction is shown in the U.S. Pat. No. 2,896,529, 
disclosing a screw press working with two bolt attachments, whereby the 
one bolt attachment forms resistance during the lifting movement, so that 
the other bolt attachment is relieved and can be screwed a distance 
corresponding to the lift height. The bolts cannot work in loaded state. 
There is no parallel guide of the machining plate and the arrangement is 
therefore very sensitive to uneven loads. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide a machine tool, which is so 
constructed that it can perform both a pressing and cutting tooling, and 
which provides: 
(a) a very good parallel holding and guide of the machine tool along the 
pillars, 
(b) non-sensitivity to uneven loads, retaining its good parallel holding, 
(c) a very small flexibility even when heavily loaded, 
(d) a very high repeating exactness, 
(e) a very favourable relationship between machine weight and machine 
volume, and 
(f) a large length of stroke despite a limited height. 
It is a further object of the invention to provide a machine tool which is 
easy to mechanize and automate so that it can easily form a part of a 
manufacturing line. 
The objects have according to the invention been solved by the fact that 
the pillars comprise screw spindles that are fixedly mounted in the axial 
direction in the stand and that non self-braking nuts in the form of 
roller- or ball nuts cooperating with the screw spindles are rotatably but 
axially undisplaceably mounted in or at the yoke, the nuts being arranged 
to carry axial tractive and compressive forces, said nuts and/or the screw 
spindles being arranged to be simultaneously and syncronously driven by at 
least one driving means, so that the yoke is loadable and displaceable 
along the pillars with a stepless, adjustable speed.

DETAILED DESCRIPTION 
The machine tool according to FIG. 1 consists of a portal stand comprising 
four pillars 1, which are made up of four screw spindles 2, that are fixed 
to the bottom plate 3 of the stand. The screws 2 are at the top joined 
together by and fixed to the upper plate 4 of the stand. The screws 2 are 
arranged inside telescoping seals 5. 
A moveable yoke 6 is further arranged within the portal stand, said yoke 
being guided along the screws 2 by means of four nuts 7, which are 
rotatably but axially undisplaceably mounted in the yoke 6. The nuts 7 are 
simultaneously driven by a driving motor 8 (FIG. 2) arranged in the space 
below the bottom plate 3 of the stand. A drive shaft 9 extends from the 
motor 8 and up to the yoke 6, where via a belt, chain 10 or similar power 
coupling device (FIG. 3) it is connected to the nuts 7 for simultaneously 
driving them. The drive shaft 9 is arranged inside the telescoping sealing 
5 of one of the rear pillars 1. Hydraulic conduits, electrical wiring etc. 
are also housed inside the telescoping sealings of the rear pillars, which 
are larger than those of the front pillars. All four screws 2 are however 
of the same dimension. It is of course also possible to arrange the drive 
motor inside the top plate 4 or the yoke 6. Instead of driving the nuts 7 
it is of course possible to drive all screw spindles 2 by alternatively 
rotatably mounting them and fixing nuts 7 in the yoke (not shown). 
In the bottom and top plates 3 and 4 of the stand as well as in the yoke 6 
guides 11 for quick attachment of tools, machining equipment or similar 
device are arranged, for example for thread cutting, deep drawing, 
cutting, punching, turning and grinding tools. 
The nuts 7 are non-self-braking, namely ball- or roller nuts, preferably 
precision roller nuts, which can carry higher loads than ball nuts. In 
addition the nuts 7 at both end gables are provided with thrust bearings 
19. In roller nuts a number of rollers are running in an endless path. The 
nut has a correspondingly larger thread diameter than the screw and the 
rollers are provided with peripheral grooves, which cooperate with the 
threads in the nut and the screw respectively. Thus a roller nut has a 
very large number of effective points of contact, whereby it can carry 
high loads. 
The nuts 7 both guide and drive the yoke 6 and by simultaneous driving of 
all nuts a very good parallel guiding is maintained despite uneven loads. 
Possible moment forces are taken up as tensile and compressive forces 
respectively in the screws 2. The displacement of the yoke 6 along the 
screws 2 can continuously be controlled and measured. 
During machining operations demanding a relatively small power supply, for 
example cutting and light pressing operations, the yoke 6 with its roller 
nuts 7 make a single linearly guided and controlled driving means. 
When the power demand is higher, for example during heavy pressing, an 
auxiliary cylinder 12 is necessary for driving, whereby the yoke 6 is 
guided and controlled by means of the screws 2. This is shown in the 
embodiment according to FIG. 2. The cylinder 12, for example a hydraulic 
cylinder is fixed to the top plate 4 and its piston rod 13 is connected to 
the yoke 6. A machining member 14 for pressing against a pad 15 supported 
in the bottom plate 3 is attached to the yoke 6. Hydraulic conduits 16 to 
the cylinder 12 extend through the telescoping sealing 5 from a hydraulic 
assembly 17 arranged in the space below the bottom plate 3. In this space 
is also room for the control and other equipment. 
In the embodiment shown in FIG. 4 the drive shaft 9 is connected to the 
nuts 7 by a toothed wheel rim 18, which has a relatively large mass and 
thereby a high mass-moment of inertia. The toothed wheel rim 18 is rotated 
by the drive shaft 9 and the rotating movement is then used as a driving 
force during the machining operation. The drive shaft 9 is in this 
embodiment arranged substantially midway between two pillars and the drive 
motor is preferably placed in the yoke 6 itself. 
The machine tool according to FIG. 5 has a rectangular top-and bottom plate 
4, 3, as well as the yoke 6, which facilitates series connection and 
automization. The top- and bottom plates 4 and 3 are at their corners 
interconnected by means of profiles 20 having an L-shaped cross-section 
and the yoke 6 adjacent these profiles is provided with sliding blocks 21. 
The profiles 20 act as guides, against which the sliding blocks 21 bear, 
but they also stiffen the construction i.e. for enabling the support of 
great radial forces. 
Thus the machine tool according to the invention forms a basic unit, which 
can be complemented with different equipment for different machining 
operations. It is even possible to connect together a number of machine 
tools in production lines and for cooperative machining. A number of 
advantages with the machine tool according to the invention are: 
Less tied-up capital in special purpose machines; 
Fewer type restricted tools. 
Increased flexibility, when the same machine can be used for different 
machining functions; 
Quicker and cheaper establishment of production lines; and 
Increased possibilities for short series production in production lines. 
Better automation possibilities since uniform machines can be automated in 
the same way. 
Another advantage with the machine tool according to the invention is that 
it has a cutting impact dampening effect, since the recoil action that 
results when the cutting is completed is converted to kinetic energy in 
the nuts 7. 
The machining can even be done outside the portal stand by increasing the 
working surfaces of the bottom plate 3 and the yoke 6 with separate units 
extending outside the portal stand. 
The invention is of course not limited to the shown embodiments, but can be 
modified within the scope of the claims. A simplified embodiment of the 
machine tool can for example have a stand without any top plate, i.e. the 
pillars are only fixed to a bottom plate. The number of pillars is in all 
of the shown embodiments four. It is however possible to have only three 
pillars or even five or more pillars.