Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to a linear driying
arrangement having two motors, one motor driving a nut and the
other ~otor driving a screw spindle. Compared with a driving
arrangement operating with only one motor, which, for example,
drives the spindle, the present arrangement has the advantage
of a much larger adjustment range for the feed rate.
A slugyish, very slow feed can be attained when
the ~wo motors have the same sense of rotation but are run
with a small difference in speed. A fast feed can be attained
when only one motor is operated and the other motor is at a
standstill. Finally a very fast feed can be attained when the
motors are oppositely run.
US Patent 2,630,022 discloses a linear driving
arrangement with two motors in an open-type construction. The
motor axles extend at right angles to the spindle axle and
drive each of the spindle and the nut via a separate worm gear.
The constructional expenditure thus is relatively high and a
clean compact construction of the device cannot be attained.
In this patent the use of this driving arrangement in air-
craft is proposed and the fact that even when one of the two
motors fails the driving arrangement still remains operable
is emphasized as a special advantage. Of course this applies
to any of these linear driving arrangements when they are
operated with two motors.
US Patent 2,481,477 (Peery) discloses a two-motor
linear driying arrangement, in which one motor drives the
spindle directly. The motor driving the nut lies next to the
spindle and drives the spindle via a toothed-wheel gearing.
The present invention provides a linear driving
arrangement w~th two motors which has a mechanically clear and
simple construction and thus is inexpensive to produce.
According to the present invention there is pro-
vided a linear driving arrangement having two motors, one motordriying a nut and the other motor driying a screw spindle,
the motors being attached to the outer end of two tubular casing
members which are telescopically slidable into one another and
are secured against rotation about their axis, the nut and the
screw spindle being disposed on the inside of said casing mem-
bers.
Thus in the present invention the motors are
attached to the outer end of two tubular casing members which
are telescopically slidable with respect to each other and
are secured against rotation about their axis and the nut and
the screw spindle are disposed on the inside of these casing
members.
The present invention will be further illustrated
by way of the accompanying drawings, in which:-
Figure 1 is a longitudinal section through a lineardriving arrangement according to one embodiment of the present
invention;
Figure 2 is a lateral view of the rotary ball nut
with a portion of a spindle according to Figure l;
Figure 3 is a section along the line III-III in
Figure l;
Figure ~ is a section through the casing members
which are telescopically slidable with respect to each other
and are secured with nut and spring against rotation;
Figures 5 and 6 are variants of Figure ~; and
FIgure 7 is a diagrammatic section through a
lineax driving arrangement for extremely slow feed or extremely
small feed steps according to anoth.er embodiment of the
present invention.
2 -
Refer~ing to the accompanying drawings, the
linear drlving axrangement c~prises two tubular casing
members 1 and 2 whXch are telescopi~cally slidable with
respect to each other the outer ends being reinforced at
11 and at 21. ~ motor Ml and a motor M2 are fastened to
said ends. A journal ~ox 22 on the inner casing member 2
and a journal box 12 installed in the outer casing member 1
prov~de precise guldance of the members.
Pegs 13, 23 by means of which the driving
arrangement can be connected to the-members to be actuated
are installed on the reinforced ends 11, 21.
It is evident from Figure 3 that the reinforced
end 21 is provided with recesses 24 for receiving screws
with hexagonal recessed holes 25 with which the motor M2
is fastened to the tubular casing member end. The motor
is fastened to the reinforced end 11 by means of screws
on the inside of the tubular casiny member 1. (The screws
are not shown for the sake of clarity.) The motor flanges
of the two motors M1 and M2 have a tie 16 and 26, respectively,
by means of which they are exactly centered in the reinforced
casing ends 11 and 21 respectively.
The casing members 1 and 2 must be additionally
secured against rotation. For this purpose as shown in
Figure ~, two longitudinal grooves are provided in the outer
member 1 and two slide wedges 200 are provided in the inner
member 2. Figures 5 and 6 show other structures for such
purpose. ~n thR stxucture according to Figure 5~paths in
which balls 201 run are provi.ded in the outer member 1' and
in the member 2' extending parallelly to the member axis.
This kind o~ ~u~dance is precise and nevertheless of easy
motion.
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In ~i~ure 6 the outer casin~ ~e~ber 1" is
pr~vided with a plurality of longitudinal graoves which form
a type of internal gear~ng 2Q2 and the inner member 2ll is
provided with. a corresponding external gearing 203, This type
of guidance can absorb la~ge forces.
Instead of using tubular casing members which
are telescopically slidable with respect to each other the
casing members 1 and 2 can also have a polygonal cross
section, for example, a tetragonal or a hexagonal cross
section. Special means of securing against rotation can thus
be dispensed with.
The motor Ml drives a rotary ball nut 31 by
means of a hollow coupling element 3. One end 32 of the
coupling element 3 is connected to the shaft of the motor M
and the other end is widened in a bell-shaped manner so
that the rotary ball nut 31 can be received therein~ It is
pressed into this end, secured against rotation by a wedge 34
and additionally secured against slidiny by a retaining ring
35. In the tubular member 36 between the two ends the end
of the screw spindle is slidably and rotatably supported.
The mo-tor M2 drives the screw spindle 4. For
this purpose the shaft of the motor M2 is connected to one
end of the spindle by means of a muff coupling 41. The screw
spindle 4 h.as a thread corresponding to the balls of the rotary
ball nut 31 as is evident from Figure 2. The free end of the
screw spindle is provided with a journal box 42 which is
rotatab~e on the spindle end and is held axially by a retaining
ring 43~ The external diameter of the journal box .is so
dimensioned that it is slidingly displaceable in the tubular
member 36 of the coupling elements. This addit.ional support
at the free end o~ the screw spindle is very important since it
prevents the screw spindle f~om oscillating at high numbers
of rotation.
The driving arrangement can be operated with one
or two motors ~1 and M2. Correspondingly a sluggish, an
averaye or a very fast feed can be attained. By feed is
meant both an increase of the distance X and a reduction of
the distance x.For example, it is possible to carry out the
feed in a direction of increase of the distance X sluggishly
(by operating the two motors but with a smaller difference in
the number of revolutions) or the feed can be carried out
very rapidly in the opposite direction (by operating the two
motors with opposite directions of rotation). This has
already been mentioned.
The guide journal boxes 12, 22 of the casing
members 1 and 2, the length of the spindle and the axial
length of the nut limit the maximal feed length, i.e., the
stroke to the extent H (Figure 1).
When using a rotary ball nut with corresponding
screw spindle high-precision linear feed devices which
operate withou-t play can be produced. Of course, the
motor shafts must be supported so as to be free from play
axially as well as radially. In cases in which precision is
not so important and more attention is paid to the price a
simple bronze nut can be used.
Instead of using radial pegs 13, 23 as surface
for transmission of power many other structures are possible.
For example, the outer beariny pla-tes of the motors Ml, M2
can be provided with eyelets for the transmission of force.
~ ith this linear driving arranyement a slow
feed motion can be achieved in a simple and inexpensi~e manner
in that the two motors are operated at a slight difference in
speed. However, when precisel~ measured Eeed steps of 1OO mm
or less are requixed, then stepping motors must he used
~ small constant ;Eeed steps are to ~e attained
with the linear dri~ving axrangement according to Figure 1, a
SteppIng ~otor, for example, motor Ml and a motor M2 braked
to a standstill can be used. IE, for example, the stepping
motor M1 indicates 1000 steps per rotation and only this motor
is started so that it makes one step, then at a spindle pitch
of 2 mm Eeed steps of 1OOO x 2 = O.002 mm can be attained.
If extremely small feed steps are to be
attained with the linear driving arrangement according to
Figure 1, it is advantageous to use two di~ferent stepping
motors, for example, a motor M1 which makes 1000 steps per
rotation and a motor M2 making 999 steps per rotation. If
the two motors are so started that they make one step in the
same direction of rotation and if the thread pitch of the
spindle is two millimetres, then a feed step of
1 1 x 2 = 2 x 10 mm
can be attained.
These stepping motors with 1000 steps or with
999 steps are very costly.
The modification o~ a linear driving arrangement
represented diagrammatically in Figure 7 provides a struc-ture
with which extremely small feed steps can be realized, using
relatively inexpensive stepping motors.
When the two motors Ml and M2 make a full
rotation in the same direction, a ~eed of approximately
l/lOOQ mm results, as will be described hereaEter.
In Ftguxe 7 similar parts have the same reEerence
numbers as in ~igure 1. In the two casin~ memhers 1, 2, which
are telescopically slidable with xespect to one another,
there are disposed a hollow coupling element 3 and a screw
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spindle 4, In the portion 33 which is widened in a bell-
shaped ~anner there is disposed a high-precision rotary
ball nut interacting with the screw spindle 4, which operates
precisel~ and ~ree ~ro~ play.
The di~fe~ence between the linear driving
arrangement shown in E'igure 7 and that according to
Figure 1 lies in that ~oth the coupling element 3 and the
screw spindle 4 are not longer connected directly to the motor
shafts but they are separately so supported at 50 and 51
respectively in the casing members Gl,G2 that they are
axially and radially free from play.
Toothed-belt transmission gearings 500,501,502 and
600,601,602 are disposed in t~e casing members Gl and G2.
Each of said belt-transmission gearings comprises a toothed-
belt wheel 500 and 600, respectively, a toothed belt pinion 502
and 602, respectively, and a toothed-belt 501 and 502
respectively. The pinions 502 and 602 are driven by the
motors Ml and M2 respectively. The motors are laterally
flanged to the casing members Gl and G2. The gear ratios of
the two toothed-belt gearings differ slightly from each other.
For the example shown it holds true that
wheel 600 has 44 teeth and pinion 602 has 15 teeth. This
results in a year ratio
U = 145 - 0.340909
and
wheel 500 has 41 teeth and pinion 502 has 14 teeth. This
results in a gear ratio
U = 144 = 0.3414634
~hen the two motors Ml,M2 make a rotation in the
same direction, the nut makes Q.340909 rotation and the spindle
~.3414634 Xotation. Since the direction of rotation is the
same, th~s corresponds to a 0.34]4634 - 0.34n9Q9 = 0.0006524
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rotation ~f the spindle relati~e to the nut. At a ptich o~
the spindle thread o~ 2 mm this corresponds to a ~eed of
O.OQ13048 ~. When the two motor~ make a complete rotation
through 3~Q the ~eed thus is slightly more than l~lOQO
millimetre.
When using stepping motors they can be so con-
trolled that the linear driving arrangement, for example,
upon pressing a button, moves one machine member at a time,
` for example, a cross-table Tl,T2 by 1/1000 millimetre.
With such small Eeed steps it is of course
important that all the members operate so that they are free
from play. This can be attained by using slightly prestressed
antifriction bearings, by a rotary ball nut operating free
from play and having a ground spindle and by toothed-belts
operating free from play. When using the linear driving
arrangement Eor adjusting a cross-table having the members
Tl,T2, which, as mentioned hereinbefore, permits a feed with
extremely small steps, the possibility of rapid adjustment is
maintained nevertheless. When only one motor is driven
while the other motor is at a standstill this results in a
fast feed. When the second motor is run in the opposite
direction the rate of feed even doubles. The gear ratio of
the intermediate gearings - which only is approximately 1 to
3 - is not very important in the present case.
In addition to the descrihed use of the linear
driving arrangement for the gradual drive of a cross-table
involving feed and standstill the linear driving arrangement
can be used for a continuous, extremel~ slow feed. This kind
of use i5 suitable, for example, for solar energy plants in
which mirrors must be readjusted corresponding to the
position of the sun.
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