The present invention relates to a machine tool arrangement and to
a method of operating a machine tool arrangement.
In a known machine tool, shown schematically in Figure 1, a ram 1
is able to reciprocate in a vertical direction within a housing 2 and, within the
ram 1, a torque tube 3 is able to rotate relative to the ram and is constrained
to move with the ram. The bottom of the torque tube is able to be connected to
a machine tool unit and a drive shaft 4 extending through the torque tube is able
to rotate relative to the ram and torque tube in order to rotate a tool of the
tool unit. Such a construction is expensive and complicated to manufacture, as
it is necessary to provide a linear guide for the ram and then, within the ram,
to also provide separately for the rotational mounting of the torque tube. Furthermore,
because the drive shaft is surrounded by the torque tube, and because the torque
shaft is surrounded by the ram, the unit has a large cross-sectional area which
prevents the ram from entering openings in workpieces which are smaller than the
cross-sectional area of the ram.
European Patent publication number 0 074 452 (Line) discloses a milling
head having an outer housing, a sleeve within the housing and a tool spindle within
the sleeve. The spindle is able to move translationally relative to the housing
to a limited extent, and also rotationally relative to the housing in order to
connect and disconnect an accessory automatically. However, the translational
movement of the spindle is to facilitate the connection and disconnection only.
When the head has an attachment connected to it for a machining operation the attachment
cooperates with the outer housing to prevent relative rotation of those parts
and the spindle does not move translationally relative to the housing.
DE-B-1 194 226 and DE-B-1 295 980, respectively, against which claims
1 and 8 are delimited show a rotatable ram that can move translationally to advance
or retract the operative position of a tool.
It is an object of the present invention to attempt to overcome at
least some of the above disclosed disadvantages.
According to one aspect of the present invention, a machine tool
arrangement includes a housing, a ram and a drive shaft, the drive shaft extending
through the ram and being rotatable relative to the ram, the ram being movable
translationally and pivotally relative to the housing, with relative translational
movement of the ram and the housing being arranged to cause the operative position
of a tool of the tool unit to advance to or retract, at least a part of the ram
including a cylindrical outer surface and at least a part of the housing including
an inwardly facing cylindrical surface (54), the cylindrical surfaces of the ram
and the housing comprising co-operating portions which enable the ram to move
translationally and pivotally relative to the housing, characterised in that the
ram includes tool unit engaging means which enable the ram to be connected to a
tool unit whereby when the ram is connected to a tool unit, pivotal movement of
the ran relative to the housing is arranged to alter the orientation of the rotational
axis of a tool in the tool unit relative to the rotational axis of the drive shaft,
and rotational movement of the drive shaft is arranged to cause a tool of the tool
unit to rotate about the axis of the tool, the ram being connected to an intermediate
portion which intermediate portion is slidably mounted on the housing, the intermediate
portion including drive means arranged to cause the ram to rotate relative to
the housing with the drive shaft being arranged to be driven by further drive means
arranged to move with the intermediate portion.
The housing may include clamping means selectively operable to clamp
the ram in the housing to ensure that the axis of rotation is not deflected. The
clamping means may be arranged to cooperate with the ram at two spaced locations.
The connection of the ram with the intermediate portion may be located
on the opposite side of the cooperating portions of the ram and housing to that
on which the output of the drive shaft is located.
The intermediate portion and the ram may include locking means, operable
to prevent rotation of the ram relative to the intermediate portion.
The drive shaft may extend beyond one or both ends of the ram.
The end of the ram may be provided with tool unit engaging means
which enable the ram to be connected to a tool unit. Control means which may include
hydraulic or electric means, may be provided via the intermediate portion to control
the tool unit engaging means at the end of the ram.
The housing may be movable about at least one axis extending transversely
to the direction in which the ram is movable translationally relative to the housing.
According to another aspect of the present invention, a method of
operating a machine tool arrangement including a housing, a ram and a drive shaft
extending through the ram comprising rotating the drive shaft relative to the
ram to cause a tool of a tool unit to rotate about the axis of the tool and moving
the ram translationally and pivotally relative to the housing, with relative translational
movement of the ram and the housing advancing or retracting a tool of the tool
unit whereby an outwardly facing cylindrical surface of the ram co-operates with
an inwardly facing cylindrical surface of the housing during both relative translational
and pivotal movement, is characterised in that when the ram is moved pivotally
relative to the housing the orientation of the axis of rotation of the tool is
altered relative to the rotational axis of the drive shaft and rotational movement
of the drive shaft causes the tool of the tool unit to rotate about the axis of
the tool, with an intermediate portion being connected to the ram and being slidably
mounted on the housing with drive means on the intermediate portion causing the
ram to rotate relative to the housing, the drive shaft being driven by further
drive means that move with the intermediate portion.
The method may comprise the ram moving simultaneously translationally
and pivotally relative to the housing.
The method may comprise causing a surface of the ram to slide and
pivot against a surface of the housing.
The method may comprise applying a clamping means to increase stiffness
between the ram and the housing.
The method may comprise causing rotation of a tool with the drive
shaft and simultaneously causing translational or pivotal movement or both of the
same whilst a workpiece is being machined with a tool.
The present invention may be carried into practice in various ways
but one embodiment will now be described by way of example and with reference to
the accompanying drawings in which:
- Figure 2 is a schematic perspective view of a machine tool showing schematically
the rotational provision for the ram, and
- Figure 3 is a detailed cross-sectional view showing the means for effecting
rotation of the ram.
As shown schematically in Figure 2, the machine tool 10 includes
a cast housing 12 which includes a pair of spaced, parallel vertical rails 14 on
which a main transmission carriage 16 may slide up and down in the vertical or
Z direction and which is constrained against any rotation.
The housing 12 is able to move in the horizontal x and y directions
The housing 12 is mounted on parallel rails 18 which extend in the
y direction and which are secured to their related structure 28 over the full length.
A motor 20 mounted on the housing drives, via a belt 22, a ring 24 which threadably
engages a ball screw 26 which extends parallel with the rails 18. The ring is rotatable
relative to the housing but is otherwise constrained to move with the housing,
whereby rotation of the ring causes the housing to be driven along the ball screw
in the y direction with the housing sliding on the rails. The direction of movement
in the y direction of the housing can be altered by changing the direction of rotation
of the ring.
Each side of the structure 28 (only one of which is shown) is slidably
mounted on spaced parallel rails 30 which extend in the x direction. Driving means
32 (shown schematically) cause the structure to be slid along the rails 30 in
the required direction.
The carriage 16 is driven up and down in the z direction by a motor
34 mounted on the housing which rotates a ball screw shaft 35 via a belt 38 in
the required direction. The carriage 16 is suspended on the shaft 36 and threadably
engages that shaft which, by rotation, causes the carriage to slide on the rails
The carriage 16 supports, and carries with it in the vertical direction,
a drive shaft 40 and a ram 42 through which the shaft 40 extends. The shaft 40
is rotatably driven by a motor 44 mounted on the carriage which drives a pulley
46 connected to the top of the shaft 40.
In order to enable the ram, carriage and shaft to move up and down
relative to the housing, the upper part of the housing is in the form of an arch
having upwardly extending spaced sides 47 connected at their upper ends by a top
The lower end of the housing includes a cylindrical guide passage
54 within which the ram is able to slide up and down in the vertical direction
and within which the ram can rotate as described later. The cylindrical guide
passage is lined with a layer including at least some plastics. The ram is hardened
and precision ground.
Figure 3 is a detailed cross-sectional view through the ram 42 and
the shaft 40 in the region of their co-extent with the carriage. All of the components
shown in Figure 3 are constrained to move together with the carriage in the z
The pulley 46 which drives the shaft 40 is shown at the top of the
figure. The shaft 40 is rotatably supported in bearings 56 mounted in the carriage
and the cylindrical shaft 40 extends downwardly through the ram 42 and is rotatably
supported by further bearings (not shown) towards the bottom of the ram.
The ram 42 is itself rotatable, separate from the shaft 40, upon
operation of a motor 60 (shown schematically in Figure 2) which drives a worm 62,
as shown in Figure 3. The worm 62 engages a worm wheel 64 which surrounds the
ram 42 and is fast therewith in order to cause the ram to rotate about the z axis.
The ram may rotate in either direction in dependence upon the direction of rotation
of the worm.
A thrust and journal bearing 65 is located just above the wormwheel
and the bearing acts on the periphery of the ram. The bearing 65 transfers the
thrust from the cutting tool through the ram up into the sledge and constrains
the ram to rotate about the required axis. The bearing 65 thereby imparts both
axial and rotational stiffness to the ram.
The lower end of the ram is arranged to engage a tool unit from a
tool unit store such as a carousel unit in a conventional manner. The downwardly
facing surface of the ram includes sockets into which studs from a tool unit can
enter and locations devices to accurately align and secure the tool unit to the
As shown in Figure 3, electrical services 64 and hydraulic fluid
services 66 are connected to the ram to enable operations of the ram, and in particular
the pick up and release of tool units from the bottom of the ram to be performed.
The shaft 40 is arranged to engage with a socket in a tool unit in order to be
able to cause a tool mounted on an output shaft of a tool unit to rotate. The
tool of the tool unit may rotate about an axis coincident with or parallel to the
axis of the ram 42 or may rotate about an axis extending at any angle to the axis
of rotation of the ram 42.
It will be appreciated that the precise angular position of the ram
42 relative to the housing will be important in certain circumstances such as when
the tool of the tool unit is rotating and being advanced in a direction in the
horizontal plane. In order to ensure the precise angular position of the ram, a
hirth ring 68 surrounds the ram 42 and is able to engage with downwardly extending
teeth 70 secure with the ram 42 in order to bring the ram into the required angular
position and maintain the ram in that position. The hirth ring 68 is connected
to a support 72 by a flexible arm 74. A piston 76 is connected to the hirth ring
and, upon pressurisation of a chamber 78, can move downwardly in order to disengage
the hirth ring 68 from the teeth of the ram (in which position the ram may rotate)
or, upon pressurisation of a chamber 80, can move upwardly to cause the hirth ring
68 to engage the teeth or the ram (to prevent the ram from rotating and to bring
the ram into the precise angular orientation required).
It can be seen from Figure 2 that the diameter of the bottom of the
ram is relatively very small as that portion of the ram extending beneath the housing
is caused to rotate and reciprocate by parts located away from the bottom region.
Thus the machine tool can be used to bore out a relatively small hole in a workpiece.
That machining may comprise mounting the tool unit on the end of the ram having
an output shaft extending in the horizontal or any other required direction. Rotation
of the shaft 40 then causes rotation of the cutting tool about its axis. At the
same time as the cutting tool is rotating about its axis and cutting into the walls
of the workpiece the ram can be rotated about its axis to cause the output shaft
of the tool unit to rotate in a horizontal plane. If required, the housing can
also be moved in the x and y directions, separately or together. Furthermore,
the ram can move downwardly into the feature being cut to enable the machine tool
to cut workpieces which are relatively deep in the z direction.
The ram can be clamped in the housing by hydraulically operating
clamps 82 located at either end of the passage way in the housing, as shown in
Figure 3 to provide maximum stiffness to the ram for instance during certain high
performance machining operations. When the ram is clamped it may still rotate but
the clamp ensures that the axis of rotation is not deflected.
The ram is that part of the device which carries the tool (either
directly or indirectly) towards and away from a workpiece and which also absorbs
or reacts against the forces tending to deflect a tool from the intended path of
milling or cutting.
The ram on a milling machine is a cantilevered structure which supports
the spindle and provides accurate location and support to a variety of attachable
auxiliary spindle heads on its forward face which are designed to satisfy a variety
of particular machining operations.
The ram is required to traverse the machine spindle such that its
axis follows a precise straight line perpendicular to the X Y Plane of the machine
tool with a feed mechanism of such stiffness as to provide for all of the machining
operations required, either from the machine spindle directly, or from the variety
of attachable auxiliary spindle heads which are supported by it.
The ram is also required to provide such axial, transverse and torsional
stiffness for all of the machining operations required, either from the machine
spindle, or from the variety of attachable auxiliary spindle heads which are supported
by it when fed in any required combination of Traverses X Y Z.