Note: Descriptions are shown in the official language in which they were submitted.
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M~NUALLY CO~JTROLLA~LL LATHE
RAC~G~OUND OF THE INVENTIG~
Field of the Invention
This invention relates to a manually controll-
able lathe comprising a machine bed provided with guideways
for guiding a tool carriage, ~hich comprises at least one
lonoitudinal slide and at least one cross-slide, a main drive
for the ~lork spindle, a longitudinal feed drive comprising a
lead screw and a feed screw for the longitudinal slide, a
eross-feed drive comprising a cross-scre~ far the cross-
slide, and two handwheels, which are mounted on the tool car-
riage and operable to control the movements of the longitu-
dinal slide and the cross-slide, respectively, along the asso-
eiated screws.
Deseription of the Prior Art
In the conventional lathes whieh can be manu-
ally controlled the work spindle is driven by a multiple-
speed main transmission, which is adapted to be driven at a
eonstant speed by a three-phase a.c. motor and the drive for
the tool carriage is derived from that main drive via a se-
eandary transmission, which is operatively connected to the
lead and feed screw for the lonyitudinal slide of the tool
earriage. An apron is connected ta the longitudinal slide and
is operable to drive a cross-screw for imparting a cross-
Feed movement to the cross slide. P manually shiftable trans-
mission is pravided for the longitudinal and cross-feed move-
ments. In addition to said feed dri\/es which are provided on
the tool carriage and driven by the main transmissian, hand-
wheels may be provided, which are meehanically connected to
the longitudinal slide and cross-slide and operable to drive
said slides. It is apparent that the feed drives with their
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tr3nsmissions,clutches, brakes and shiftable gears involve a
very high structural expenditure, particularly because close
tol-rances must be complied with.
In addition to such manually controllable lathes,
numerically controlled lathes are in operatian, in which the
feed drives for the tool carriage are constituted by variable-
speed reversible three-phase a.c. motors, which are controlled
by a suitably programmed computer whereas there is no need
for transmissions, clutches and brakes involving a substantial
structural expenditure. Such computer-controlled lathes can
hardly be used to machine individual workpieces but are used
in series production because the control program mu3t be al-
tered to conform to changing machining requirements and skilled
operators are required for such alteration.
Summary oF the Invention
It is an object of the invention so to improve
a lathe which is of the kind described first hereinbeforz that
the advantages of numerically controlled lathes as regards
simolicity of structure and infinite control of the feed drives
can be utilized whereas the conventional simple control which
is desirable for the machining of individual workpieces is re-
tained.
That object is accomplished in accordance with
the invention in that the feed drives for the longitudinal
slide and the cross-slide consist of respective variable-speed
reversible three-phase a.c. motors, which serve to drive the
associatzd screws, which consist of ball screws, the hand-
wheels for contralling the movementa of the tool carriage are
operable to adjust respective electric synchro generators, each
of which is connected to a controller for the associated three-
phase a.c. motor7 and z control unit is preferably mounted on
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the tool carriage and comprises manual data input means for
input data indicating ~he preselectable transmission ratio
between the rotation of each handwheel and the rotation of
the assaciated screw or the assDciated three-ohase a.c. motor
and display means for indicating the input data and data re-
presenting the actual positions of the slides.
In that arrangement the handwheels for con-
trolling the movement of the carriage in the longitLJdinal and
transverse directions serve to adjust a synchro generator,
which indicates to the control unit the desired value for the
finite angular movement to be performed hy the associated
screw and the associated three-phase a.c. motor can properly
be operated in consideration of the preselected transmission
ratio between the rotation of the handwheel and the rotation
of the screw so that the slide that is to be moved is adjusted
in response to an angular movement of the handwheel by a
manual control which is similar to that reauired in conven-
tional carriage control means comprising manually operable
drive wheels. The actual position of each slide will be dis-
played by the cantrol unit, which for that purpose is desirab-
ly mounted on the tool carri2ge. The handwheels for controll-
inq the movements of the slides may be mounted on the tool
carriage at the same locations as in conventional lathes of
the present kind so that the requirements for manual operation
are the same. For instance it will be desirable to mount the
handwheel for controllinq the adjustment of the cross-slide
at a location which is axially aligned with the transverse
screw provided for that purpose so that the lathe operator
gets a visual indication that that handwheel controls the ad-
justment of the cross-slide. The operational requirements
differ from those of conventional lathes only in that the se-
veral feed rates are not selected by associated transmissions
but are preselected by the input data for the contrcl unit.
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Special program~ing knowledoe is not required for inputt-
ing such data, particularly because the data which have been
input can be read from the display.
A relatively small torque will be sufficient
for adjusting a synchro generatDr. In order to ensure that
the rotation of the handwheels wheel is opposed by the re-
sistances which customarily oppose the adjustment of the
tool carriage in the longitudinal and transverse directions,
a brake for controlling the resistance opposing the rotation
of each handwheel may be provided so that conditions regard-
ing the operation of the handwheels are also comparable to
those arising in conventional lathes.
Conventional lathes for manual control comprise
a control switch, which is provided adjacent to the apron
and consists of a four-way intermediate switch, which via
associated clutches controls the feed drives for the move-
ments alon~ the longitudinal and transverse axes in both di-
rections of movement in dependence on the position of the
switch. The tool carriage of the lathe in accordance with the
invention may also be provided with such a control switch for
controlling the two feed drives by means of the control unit.
If the control unit is provided with desired-
sDeed input means for the contral of the main drive and with
a control signal output for the main drive consisting of a
controllable three-phase a.c. motor and a manually shiftable
two-speed transmission, the control unit can also be used to
control the drive of the work spindle so that the control of
the feed drives in dependence on the drive of the work spindle
will be simplified. In that case, conventional operating re-
quirements will have to be met in that respect iF the tool
carriage carries for the control of the energization of the
main drive a switch which i9 operatively connected to the control
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unit and can be operated to initiate an ooeration of the
work spindle in one sense or the other after an input of
data which determine the speed desired for the work spindle.
Brief Description of the nrawina
The drawing is a diagrammatic top plan view
showing an illustrative embodiment of a manually controllable
lathe in accordance with the invention and i9 also a block
circuit diagram representing the control system.
Detailed Descriotion of the Preferred Embodiment
The illustrated lathe comprises a machine bed
1, hich in the usual manner carries a~headstock 2, a ~ork
spindle 3 mounted in the headstock, a tailstock 4 and a tool
carriage 5. The tool carriage 5 comprises a longitudinal
slide 7, which is movable alonq longitudinal guideways 6 of
the machine bed 1, and a cross-slide B, which is movably
mounted on transverse guideways on the longitudinal slide 7.
The work spindle 3 is driven by a variable-speed reversible
three-ohase a.c. motor 9, which together with a manually
shiftable two-speed transmission 10 constitutes the main
drive of the lathe. The longitudinal feed drive for the longi-
tudinal slide 7 consists of a variable-speed reversible three-
phase a.c. motor 11 for driving a lead and feed screw 1Z,
which consists of a ball screw that is provided with a bia-
sed nut 13 for moving the longitudinal slide 7 without a
backlash. Similarly, the cross-feed drive far the cross-slide
3 consists of a variable-speed reversible three-phase a.c.
motor 14 for driving the cross-feed screw 13, which again con-
sists of a ball screw provided with a biased nut 16.
~ or the control of the three-phase a.c. motors
9, 11 and 14 the tool carriage 5 is provided with a control
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unit 17, which is provided with data input means 1~ for a
manual input of data indicating the desired feed rates and
transmission ratio, and with a display 19 for indicating the
selected desired values anr! the instantaneous actual positions
of the slides of the tool carriage 5. The manual control of
the three-phase a.c. motors 9, 11 and 14 is effected by means
of manual contrDls which are Drovided on the tool carriage 5
and are operable under conventional conditions. For instance,
the main drive is controlled by means of a control switch Z1,
which is operable by a handle 20 and delivers suitabla con-
tral commands to the control unit 17 for the operation of
the work spindle 3 at the speed which has been selected by
the data input means 13. The actual speed of the work s,oindle
3 is detected by an incremental angle encoder Z2, by which
corresponding feedback data are delivered to the control unit
17. The sense of rotation of the work spindle is determined
by the sense of the rotation which is imparted to the handle
Z0, which is mounted for rotation about an axis which is pa-
rallel to the axis of the work spindle 3.
The energization of the feed drives for the
movements along the longitudinal axis and the transverse axis
can similarly be controlled by a contral switch 23, which
consists of a four-way intermediate switch and which in res~
ponse to an actuation in a direction which is parallel to
the lead and feed screw 12 will cause the control unit 17 to
energ,ize the three-~h~se a.c. motor 11 for a rotation in a
sense dependino on the direction of the movement of the con-
trol switch 23 and for effecting a feed movement at the in-
stantaneously selected feed rate or at a rapid feed rate. An
actuation of the control switch Z3 in a plane which is at
right angles ta the lead and feed screw 1Z will similarly
control the energizatian of the three-phase a.c. motor 14
for the movement along the transverse axis.
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In addition, the longitudinal slide 7 and the
cross-slide a can be moved under the control of handwheels
24 and Z5, respectively, each of which is connected for that
purpose to an associated electric synchro generator 25 so
that a desired value of the angular movement to be imparted
to each of the screws 1Z and 15 can be indicated to the con-
trol unit hy the synchro generators 26 in dependence on the
preselected transmission ratio between the rotation of the
handwheel and the rotation of the screw. In this manner the
handwheels 24 and 25 can control the movements of the tool
carriage 5 along the longitudinal and transverse axes and the
actual positions of the resoective slides will be fed back
to the control unit 17 by incremental angle encoders, which
are associated with the three-phase a.c. motors 11 and 14 or
the screws 1Z and 15, and will be indicated by the display 19.
It is aoparent that the illustrated lathe can
be used for all machining operations which can be performed
by conventional lathes and the operational requirements are
the same as usual and the advantases are afforded which are
due to the use of variable-speed reversible three-phase a.c.
motors in the feed drives. This will not only result in a
higher economy but also in a higher accuracy of the machining
operation, e.g., because the drives can infinitely be con-
trolled.
