Device for simultaneously driving the screws of two parallel screw-and-nut systems

The invention relates to a device for clamping the rolls (5 and 6) of a rolling mill. It comprises two screw-and-nut systems (1 and 2) controlled by two epicyclic planetary gear trains (7 and 8) coupled to each other and to a first motor (18) for controlling the screws in opposite directions via a respective one of their two sun shafts (9 and 10), and coupled to each other and the gear wheel of a motor (13) for screwing or unscrewing the two screws in the same direction via their planet carriers (7e, 8e).

BACKGROUND OF THE INVENTION 
There exist numerous mechanical devices which require simultaneous and 
parallel displacement of two points through the same amplitude. This 
applies, in particular, to top rolls in a rolling mill which must be moved 
parallel to themselves along fixed axes in order to take account of the 
thicknesses of sheet metal to be obtained and in order to ensure that said 
thicknesses correspond to set values. Rolls must also be capable of being 
tilted in order to adjust thickness or to overcome variations in thickness 
from one edge to another of a rolled strip. It is known that a strip which 
is thinner along one edge than the other by virtue of the metal being 
clamped more tightly at one axial end of the rolls in the mill presents a 
"long edge" on said side and this needs to be eliminated quickly by 
suitably tilting the top rolls. 
These prior devices are essentially of two types, namely: hydraulic systems 
of the actuator type with hydraulic chambers being fed from servo-valves 
controlled by electronic servo-control circuits; or else mechanical 
systems (screw-and-nut systems, wheel and endless screw systems, . . . ) 
in which each of the systems is driven by a separate motor with the 
desired servo-control being obtained by an electronic system coupling the 
motors. 
The drawbacks of such prior devices lie in their complexity, in the need 
for a high level of maintenance, in reliability which depends on the 
reliability of the electronic components, and in very high cost. 
The present invention seeks to remedy these drawbacks by proposing robust 
mechanical equipment which is simple and which avoids the need for 
expensive, fragile and complex servocontrol, while nevertheless being 
easily controlled either manually or automatically or by a combination of 
both. 
SUMMARY OF THE INVENTION 
To this end, the present invention provides a device for simultaneously 
driving the two screws of two parallel fixed-nut screw-and-nut systems in 
equal amplitude translation in the same direction or in opposite 
directions, the device comprising two planetary gear trains each having 
two sun wheels, and each having an outlet coupled to a respective one of 
the two screws, wherein each screw is coupled to rotate with one of the 
sun wheels of the corresponding planetary gear train, with the planet 
carrier of each of the planetary gear trains being coupled to the outlet 
shaft of a first motor in such a manner as to provide equal amplitude and 
same-direction rotation, and with the other sun wheel of the planetary 
gear trains being coupled to each other to rotate through the same 
amplitude in opposite directions under the effect of a second motor for 
driving one of them. 
In a preferred embodiment, the axes of rotation of the sun wheels, of the 
planet carriers, and of the drive motors are parallel to one another and 
to the screws, with the coupling between each of the planet carriers and 
the shaft of the first motor being provided by means of identical toothed 
wheels carried by each planet carrier and meshing with a gear wheel fixed 
to the shaft of the first motor, while the coupling between the two shafts 
of the said other sun wheels being provided by meshing between two 
identical toothed wheels fixed to each of said shafts, with one of said 
identical toothed wheels being driven by meshing with a gear wheel fixed 
to the shaft of the second motor. 
Each planetary gear train is carried by the screw to which it is coupled. 
During opposite-direction displacement of the screws, in order to avoid 
losing meshing between the toothed wheels providing coupling between the 
planet carriers themselves, between the planet carriers and the 
corresponding motor, and between the wheels coupling the other planetary 
shafts, each wheel and gear wheel involved in said couplings is of 
sufficient thickness to take account of the differences in height of the 
gear trains. 
Advantageously, use will be made of planetary trains whose coaxial sun 
shafts are also concentric. 
Finally, each of the motors used may be controlled either manually by an 
operator or else automatically in a rolling mill as a function of 
parameters measured from the sheet leaving the rolling mill. It may be 
observed that the main advantage of the device in accordance with the 
invention lies in the complete decoupling between the command for 
displacing the screw ends in the same direction, and the 
opposite-direction command of said ends which is symmetrical relative to a 
fixed point. This gives rise to an extremely simple servocontrol system 
which is much more reliable than those that have been used heretofore.

MORE DETAILED DESCRIPTION 
With reference to the figures, two parallel screw-and-nut systems 1 and 2 
can be seen, with each screw 1a and 2a rotating in a corresponding fixed 
nut 1b and 2b belonging to a frame (not shown). It can be seen in FIG. 2, 
that the ends of the screws 1a and 2a are coupled to bearings 3 and 4 
which are vertically movable in a frame (not shown) and which support the 
top roll 5 of a rolling mill whose bottom roll 6 rotates about a fixed 
axis. It can thus be seen that by screwing or unscrewing the screws 1a and 
2a in the nuts 1b and 2b, the bearings 3 and 4 are displaced. The screws 
are assumed to be of the same size and to have the same pitch, such that 
simultaneous screwing or unscrewing thereof through the same amplitude 
causes the roll 5 to move parallel to itself. In contrast, screwing only 
one of them while simultaneously unscrewing the other through the same 
amplitude causes the roll 5 to pivot about an axis O running through the 
middle of the roll perpendicularly to its axis of rotation. 
Each of the screws 1a and 2a is coupled to one of the sun wheels 7a or 8a 
of a corresponding planetary gear train 7 or 8 having two sun wheels. The 
other sun wheels are referenced 7b and 8b, and the planet wheels are 
referenced 7c, 7d, 8c and 8d, and they are carried by planet carriers 7e 
and 8e. The planetary trains 7 and 8 have the special feature of their sun 
wheel shafts being concentric. Thus one of the sun shafts is constituted 
by the screws 1a or 2a and the other sun shaft coupled to the wheels 7b 
and 8b is constituted by a sleeve 9 or 10 which surrounds the screw. These 
special gear trains are known and have been sold for many years by the 
French Firm REDEX as an epicyclic or a differential module. 
When used in accordance with the invention, each planet carrier 7e or 8e of 
a differential module is fitted with an identical toothed wheel 11 or 12 
which co-operates directly with an outlet gear wheel 13 of a motor and 
step-down gear unit 14. In addition, each sun shaft sleeve 9 or 10 is 
fitted with an identical toothed wheel 15 or 16 which meshes with the 
other toothed wheel 16 or 15, and with one of these wheels, in this case 
wheel 16, being driven by the outlet gear wheel 17 of a second motor or 
motor and step-down gear unit 18. 
The device in accordance with the invention operates as follows: 
When the two screws 1a and 2a are to be screwed simultaneously in the nuts 
1b and 2b, the gear wheel 13 is caused to rotate in the appropriate 
direction by powering the motor unit 14. This rotation causes the two 
planet carriers 7e and 8e to rotate in the same direction. Since the unit 
18 is unpowered, the gear wheel 17 is stationary as are the wheels 15 and 
16 and the corresponding sun wheels 7b and 8b. Under these conditions, 
rotation of the planet carrier 7e, 8e causes the sun wheel 7a and 8a to 
rotate giving rise to corresponding screwing or unscrewing of the screws 
1a and 2a in their nuts, with said operations taking place at the same 
speed and thus at the same amplitude as can be shown by simple 
calculation. In the application shown in FIG. 2, this causes the roll 5 to 
move parallel to itself relative to the roll 6. It will be understood that 
simple servo-control of the position of the roll 5 relative to the roll 6 
can be obtained using a sensor for sensing the thickness of the rolled 
product being obtained. 
However, if it is necessary to adjust the inclination of the axis of the 
roll 5 relative to the roll 6, for example to correct a long edge along 
metal strip, the motor 18 may be rotated in one direction or the other, 
since when it rotates its outlet wheel 17 causes the wheels 15 and 16 to 
rotate in opposite directions. Assuming that the planet carriers 7e and 8e 
are prevented from rotating, then rotation of the wheels 15 and 16, and 
thus of the sun wheels 7b and 8b, gives rise to rotation of the sun wheels 
7a and 8a with a step-down ratio which is defined by the step-down ratio 
firstly between the wheels 7b, 7d, or 8b, 8d and secondly between the 
wheels 7c, 7a or 8c, 8a. The screws are thus caused to rotate in opposite 
directions with one of them screwing by the same amplitude as the other 
one of them unscrews, as can also be shown by calculation. In this case, 
the roll 15 pivots about an axis centered on O in FIG. 2. At this point, 
the thickness (or the distance) between the two rolls is conserved as 
defined by the first servo-controlled adjustment using the motor 14. Use 
of the motor 18 therefore gives rise to differential rocking of the 
clamping between the rolls about a predetermined average value because of 
the mechanical independence of the two screw-controlling motors. It is 
recalled that this could not be obtained in the prior art where adjusting 
the inclination of the top roll gives rise to a reaction on the thickness 
adjustment. It can thus be seen that complex servo-control is required to 
obtain an appropriate reaction when varying one or other of the monitored 
parameters (thickness or long edge, for example), can thus be seen. 
In contrast, with the present invention, there is no need to couple the 
motor 14 and the motor 18 in order to obtain a fully satisfactory device. 
The motor 18 may, for example, be controlled by an operator who visually 
monitors the product coming from the rolling mill and who causes clamping 
corrections to be applied as a function of the quality of the product as 
perceived by the operator. Simultaneously, the motor 14 is controlled by a 
measuring apparatus which compares the real thickness of the product with 
the reference thickness value. Servo-control may also be provided for the 
motor 18 by using sensors to detect a difference in thickness occuring at 
the edges of the product, with said difference being maintained in the 
vicinity of a zero over a given range of tolerance. 
Finally, it may be observed that the amplitudes of the displacements when 
performing adjusting by means of the motor 18 are very small. Since, by 
construction, the gear trains 7 and 8 are supported solely by the screws 
1a and 2a, a vertical offset may occur between them when the motor 18 is 
used. In order to avoid a loss of meshing between the gear wheels and the 
toothed wheels, it is necessary to ensure that the various thicknesses 
E.sub.1, E.sub.2, E.sub.3, and E.sub.4 of these members are always 
sufficient to ensure that the teeth always mesh over an adequate length 
for properly transmitting the torques involved. The motors 14 and 18 could 
alternatively be fixed to a frame with the assemblies 7 and 8 moving 
vertically relative thereto. In this case, the gear wheels 13 and 17 need 
to have toothed lengths E.sub.2 and E.sub.4 which are sufficient (in the 
axial direction) to ensure that they mesh at all times with the wheels 
which are axially displaceable by virtue of the two possible motions of 
the screws (together or in opposite directions). The motors may also be 
supported on a frame which moves together with the point O of the roll 5. 
The invention is applicable throughout the field of mechanical 
construction, and in particular in rolling mills.