Machine tools abstract
A clamping device for connecting a toolhead and a toolholder on
machine tools using a cylindrical or at least partly conical location
hole with corresponding shank, wherein a rotatable clamping bolt
with spiral guides is used, in clamping to move clamping members
outwards from within, thus providing a positive and non-positive
locking of the toolhead and the toolholder. The clamping bolt has
at least one stop to limit the angle of rotation in clamping. The
retainer for the clamping members is spring mounted in the toolholder.
Machine tools claims
We claim:
1. A chucking fixture for connecting a tool body to a machine tool,
comprising:
an elongated tool holder having a longitudinal axis, a shaft at
one end receivable in a machine tool and a location hole formed
in said tool holder, centered on said axis and open at an opposite
end of said tool holder, said location hole being at least partly
of conical configuration, whereby a centering pin of a tool body
is receivable in and centered in said hole;
a plurality of chucking elements in said tool holder engageable
with said tool body for locking said tool body in said tool holder;
a retainer in said tool holder and in which said chucking elements
are received, said retainer being axially movable in said tool holder
toward and away from a mouth of said location hole;
means in said tool holder for elastically prestressing said retainer
relative to axial movement in said tool holder;
a chucking shaft extending radially of said longitudinal axis in
said tool holder and into said retainer for engagement with said
chucking elements, said chucking shaft being rotatable about a radial
axis of said tool holder and having spiral guide surfaces for camming
said chucking elements outwardly with respect to said longitudinal
axis to lock said tool body in said tool holder; and
stop means for limiting rotation of said chucking shaft about said
radial axis.
2. The chucking fixture defined in claim 1 wherein said means in
said tool holder for elastically prestressing said retainer relative
to axial movement in said tool holder includes a stack of Belleville
spring washers acting upon said retainer.
3. The chucking fixture defined in claim 2 wherein said chucking
elements are balls.
4. The chucking fixture defined in claim 3 wherein said chucking
shaft has a chucking shaft head, said stop means including an arcuate
groove formed in said chucking shaft head and a pin projecting from
said tool holder into said arcuate groove.
5. The chucking fixture defined in claim 4 further comprising
an ejector movably received in said retainer and engageable against
said tool body upon rotation of said chucking shaft to release said
tool body.
6. The chucking fixture defined in claim 4 wherein said arcuate
groove is constructed and arranged to permit rotation of said chucking
shaft through 20.degree. to 160.degree..
7. The chucking fixture defined in clam 6 wherein said chucking
shaft has a pair of spiral camming surfaces separated by recesses
receiving said balls for release of said tool body from said tool
holder.
Machine tools description
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a national phase of PCT/DE 94 01 337 filed
8 Nov. 1994 and based, in turn, upon German national application
P43 38 953.8 of 15 Nov. 1993 under the International Convention.
The invention relates to a chucking fixture for connecting a tool
head and a tool holder to a machine tool via a cylindrical or at
least partially conical location hole and a correspondingly shaped
centering pin, wherein chucking elements can be moved from the inside
to the outside of recesses during the chucking process by means
of a rotatable chucking shaft equipped with helical guides, whereby
the tool head and the tool holder can be secured by means of friction
and positive interlocks.
BACKGROUND OF THE INVENTION
A chucking fixture of the type described is disclosed in EP 0 369
211 B1. Only a very short chuck travel is required for chucking,
whereby the travel of the chucking elements is initially relatively
large due to a steep inclination of the chucking cams, while the
high chucking forces required are applied in a second, substantially
flatter portion of the chuck cam.
DE 35 24 739 A1 discloses a chucking fixture with a conical shank
for a tool holder, which tool holder is detachably arranged in a
conical location hole of a tapered socket fastened in a chucking
cylinder. The location hole has a groove into which balls can be
inserted as chucking elements by means of a pull ring to which an
axial pressure can be applied, this ring being arranged slidably
in a tapered socket. A stop ring is located at the back section
of the tapered socket so that the rear position of the pull ring
can be fixed by means of a stud. Between this stop ring and an additional
stop ring for the back section of the tie rod, there is a pressure
spring for moving the pull ring and the tie rod in axial direction.
A ring through which the tie rod can pass and against which the
pressure spring is braced serves this purpose. The disadvantage
of the above-described fixture is its costly and complex design.
OBJECT OF THE INVENTION
The object of the present invention is to provide a chucking fixture
of the type described in the introduction so that even with short
chuck travel and a compact design, secure chucking is possible even
when the parts of the chucking fixture have dimensions which deviate
significantly from the nominal dimensions for which the device is
intended.
SUMMARY OF THE INVENTION
This object is achieved by means of a chucking fixture of the type
generally described above, but wherein the chucking shaft has at
least one stop to limit the angle of rotation during chucking and
the holder for the chucking elements is elastically prestressed
in the tool holder. Due to this preliminary stress, the holder can
deflect axially during chucking, compensating for dimensional irregularities
of the parts of the chucking fixture. The stop is a simple means
to prevent damaging of the chucking elements, which is always a
risk when chucking a tool without the use of a torque wrench or
if excessive chucking force is applied.
The holder for the chucking elements is preferably prestressed
by means of a tension spring, in particular a Belleville spring
washer or packet of Belleville spring washers. Because of their
low friction, balls are well-suited for use as chucking elements,
which are arranged in a canister as a holder. A compact design can
be achieved, when the chucking shaft is located in a bore in the
tool holder, oriented radially with respect to the common longitudinal
axis of the location hole and the centering pivot in the tool holder.
There are a number of possibilities for the limit stop. The chucking
shaft can have a head having a semicircular groove cut into its
outside surface, in which groove the pin of the tool holder is guided
so that the end faces of the groove represent stops to define the
angle of rotation of the chucking shaft. Alternately, the guide
of the chucking shaft for the chucking elements can have a dome-shaped
trough or troughs whose radius/radii has/have been modified to correspond
to the shapes of the chucking elements. As soon as a certain angle
of rotation is reached, the ball falls into such a trough, which
occurrence can easily be detected by the operator. Under these conditions
it is impossible to inadvertently overtorque the chucking shaft.
It is preferable and is also known in principle from the prior
art that the holder for the chucking elements can be secured against
rotation relative to the tool holder. In one particular embodiment
of the invention a pin is used as protection against rotation.
Because tool heads often remain stuck in the tool holder after
machining a workpiece, or are fitted in a self-locking manner in
the tool holder by means of the design of a conical recess in the
centering pivot, it is necessary to use an ejector to remove the
tool head. The invention includes a chucking shaft configuration
with a second helical guide by means of which the ejector can be
actuated.
To reduce chucking time, the guides are restricted to an angle
of rotation of 20.degree. to 160.degree.. The angle of rotation
is understood as the angle by which the chucking shaft must be rotated
to chuck or release the tool head. The guides are appropriately
located along the outer surface of the chucking shaft, preferably
with an angle of rotation of 115.degree..
According to another embodiment of the invention, the guides describe
a continuous second order or higher three-dimensional curve, whose
slope--in relation to the tool chucking process or ejection--steadily
decreases, preferably hyperbolically, exponentially or logarithmically.
The mentioned embodiments can be used so that by means of a relatively
steep inclination of the chucking cam, a slight movement of the
chuck at the beginning results in a correspondingly large amount
of travel of the chucking elements and the requisite high chucking
forces can increase sharply in a subsequent, significantly flatter
section. The same applies to ejection, where high forces are required
initially, before there is significantly greater chuck travel after
overcoming the static friction.
Finally, the recess for the centering pivot of the tool head is
realized as a bore or an annular groove for the chucking balls and/or
one side surface is realized as a bevel.
According to another embodiment of the invention, the guides have
an apex point (dead point) whereby until this point is reached during
the chucking process, the chucking elements are displaced increasingly
radially outward and when this point is passed, the balls move into
chucking position.
BRIEF DESCRIPTION OF THE DRAWING
The above and other objects, features, and advantages will become
more readily apparent from the following description, reference
being made to the accompanying drawing in which:
FIG. 1 is a cross section through the tool holder;
FIG. 1a is a side new partly in section through a tool holder and
a tool head;
FIG. 2 is a side view of a chucking shaft;
FIG. 3 is a cross section along the line III--III of FIG. 2; and
FIG. 4 is a cross section through a tool holder with elastic molded
elements.
SPECIFIC DESCRIPTION
The tool holder 10 shown in FIG. 1 has a conical shaft 11 for mounting
on a machine tool, a rotating disk or the like. The tool holder
has a conical seating bore, hole or socket 12 in which a correspondingly
shaped centering pin of a tool can be inserted. The ring-shaped
stop collar of the tool rests at 13 against the tool holder. The
chucking fixture consists of a radially oriented chucking shaft
14 which is shown in greater detail in FIGS. 2 and 3. This chucking
shaft has a head 15 into whose outer surface a groove 16 extending
over an angle of 115.degree. is cut. This groove serves as a guide
for a pin 17 connected to the tool holder, whereby the respective
end faces of the groove 16 serve as stops to limit the angle of
rotation of the chucking shaft 14. The chucking shaft which can
be rotated about its longitudinal axis 18 has a spiral chucking
and ejection path 19 on its surface, the course of which can be
seen in greater detail in FIG. 3. Due to these spiral guides 19
which are essentially second order or higher three-dimensional curves,
a short chucking motion will move the chuck a relatively long way
at the beginning of chucking, as a result of the relatively steep
inclination. 20 indicates the initial position wherein the locating
face of the holder is in contact with the corresponding ring-shaped
locating face of the tool head. The chucking ball reaches its highest
position 22 when the chucking shaft is rotated around the longitudinal
axis (see arrow 21) and moves past this point to the chucked position
23 whereby in the last part of the curve, i.e. from position 22
to position 23 the chucking distances are clearly shorter, so that
great force can be applied here. When loosened, the chucking balls
drop into the recesses 24. The chucking shaft can be actuated by
means of a key inserted into hex socket 25. The tool base holder
10 also has a holder, retainer or canister 26 for the chucking balls
(not shown), which holder is supported by means of a packet of Belleville
spring washers 27 braced on one side against a ring 28 and the
head 29 of a screw rigidly connected to the canister 26. The springs
27 exert a tensile force on the holder 26 in the direction of arrow
30.
Instead of a stop realized by means of a groove 16 in combination
with a pin 17 there can also be a dome-shaped recess 31 in the
chucking cam 19 as suggested in the left half of FIG. 3. During
chucking the operator notices a significant decrease in the force
counteracting the chucking movement as soon as the ball drops into
the chucking position in the dome. Therefore the operator can also
recognize (i.e. without stops) when the chucking position has been
reached.
The advantage of the current invention lies in the fact that the
holder 26 can deflect axially against the force of spring 27 during
chucking, so that the chucking fixture is protected against damage,
even in the event of manufacturing inaccuracies. The dimensional
tolerances can therefore be somewhat larger; in some cases, tolerances
of up to 5/10 mm are acceptable. By means of the holder 26 to which
prestress is applied by means of springs, together with insertion
of the chucking shaft 14 in the radial bore of the holder, a compact
structure with great stiffness can be accomplished. The spring resistance
used depends on the size of the tool holder and can be as high as
4 metric tons. Naturally, a coil spring which engages in a helical
groove in the holder 26 and whose free end is rigidly fastened to
the body of the tool base holder by means of a bolt or similar fastener,
can be used instead of the Belleville spring washers 27.
According to one embodiment of the invention, the chucking and
loosening/ejection process can be carried out with only one chucking
cam. This is possible only because of the special design of the
chucking cam on the chucking shaft and the spherical shape of the
ejector.
The axial compliance of the holder (canister) is primarily necessary
to ensure that the upper dead point of the chucking cam is reached
and passed. The axial displacement of the holder makes it possible
to avoid mechanical redundancy.
Also possible are flexible moldings (FIG. 4) which are rigidly
connected to the holder (canister) 26 or which form an integral
component with the holder.
To relieve the tension or eject the tool head, the chucking shaft
14 is rotated in the direction opposite to the direction indicated
by arrow 21 so that the chucking balls are relieved of pressure
due to the decreasing inclination of the chucking cams 19 until
reaching the end position, defined by a stop in the groove 16 of
the head 15 and the balls drop into the recesses 24.
During loosening a somewhat greater amount of torque (release moment)
must initially be applied to overcome the highest position of the
chucking cam 19. This greater torque simultaneously represents good
protection against unintentional loosening of the chuck, such as
due to vibrations.
The actual ejection of the tool head is achieved by means of the
interaction of the steep portion of the chucking cam 19 shown in
the lower left region of FIG. 3 with the spherical compression piece
33 of the ejector 32 when the chucking shaft 14 is rotated in the
direction opposite to the direction indicated by arrow 21. As soon
as the highest point 22 of the chucking cam 19 passes the compression
piece 32 at the spherically shaped end, the compression piece 32
achieves the maximum value for the direction of ejection 34 which
is sized so that the tool head is safely ejected.
The guides of the chucking shaft are described in detail in EP
0 369 211 B1 (see also U.S. Pat. No. 4981057), to which express
reference is made. |