Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION OF THE INVENTION.
MULTI BALL SELF-ADJUSTING SELF-CENTERING TOOL HOLDER (MBSSTH) and
MULTI BALL SELF- ADJUSTING SELF-CENTERING CLAMPING SYSTEM (MBSSCS).
FIELD OF THE INVENTION.
The present invention relates generally to tool holding systems for machine
tools, more
specifically, to a universal tool holder assembly that is used to center and
hold a range of cutting
tools, such as drill bits, reamers, and mills.
This invention is based on the following principals:
1. Ball self adjustment inside a closed space
2. Statically determinate system
3. Principal of equal distribution of base points uniformly on a tool surface
(a-spot)
4. Principal of a full force closure
5. Principal of independently centering every layer of balls along the
spindle's axis
The name for the new Tool Holder is Multi Ball Self adjusting Self centering
Tool Holder
(MBSSTH). The name for the new clamping system is Multi BaII Self adjusting
Self centering
Clamping System (MBSSCS). It is based on the same principles as MBSSTH; the
only difference is
that this clamping system can be used in any application where coaxial
centering and holding of two
parts is needed.
The main goal of any tool holder is to hold the tools as precisely as
possible, providing centering
accuracy (where the tool axis coincides with the axis of a spindle of a
Machine Tool), and holding
the tools with high rigidity during machining operations. In modern time,
manufacturing industry
progressively uses aluminium alloys. Aluminum is machined at very high speeds
(RPMs -
revolution per minute). In order to perform accurate machining, it is
especially important for the tool
to stay rigid and maintain very high precision at high speeds. Today, usual
machining speeds range
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between 10,000 to 20,000 RPM. Not many kinds of tool holders can handle such
high RPMs
without losing precision and rigidity.
A more traditional tool holder assembly (US Patent No 5,201,620) uses an
external collet system
(Fig. 1 and 2). In a traditional tool holder assembly, the axial movement of
the conical collet causes
the Inside Diameter of the collet to decrease due to its resiliency. This
accomplishes the locking of
the tool.
'The centering accuracy in such tool holder depends on the geometric precision
of every element
of the tool holder assembly and the tool itself. The top picture in Fig. 2
shows just a theoretical case,
where it is impossible to provide full conformity of external base conical
surface of the collet (EX),
with internal base conical surface of the tool holder's body (BIN),
simultaneously with conformity
of internal cylindrical base surface of the collet (IN), with cylindrical base
surface of the tool (T).
Any kind of precision has a tolerance. As a result, when the tool is locked,
it is locked only on one
side of the collet. However, on the other side of the tool, micro clearances
remain.
Therefore, the Tool Axis (TA) of the locked tool ends up in some indeterminate
position inside
the micro tapered angle (G).
The same happens in the plane perpendicular to the tool axis. The size (H), of
all petals of a
collet, slightly differs from one another due to machining tolerances. As a
result, the appearance of
micro clearance (C1) or (C2) occurs.
Theoretically, any solid body has 6 possible movements: translation along
three axes X, Y, Z and
rotation around the same three axes. To eliminate all 6 possible movements, 4
contact points and
clamping forces are needed. This condition provides a determinate position for
any solid body.
This theoretical statement is true in practice for a traditional collet. The
contact between the tool,
the petals of the collet and the tool holder, is possible by three petals on
one side and only one petal
on the other side. These 4 points (a-spot) are theoretically possible for
traditional tool holder
assembly, Fig. 2.
As we can see, even in static state, the tool is clamped just on one of the
sides of the collet along
its axis, and only three petals are in contact with the tool. This causes the
tool to lock in some
indeterminate position inside the micro tapered angle (G), thus the tool
cannot coincide with the
base surface of the tool holder body and spindle of a machine tool. The
presence of micro clearances
and imprecise positioning of the tool inside the micro tapered angle (G) is
especially noticeable at
high RPMs. In places where micro clearances exist, the collet expands due to
the centrifugal forces,
causing the tool to distort and thus creating even greater inaccuracy and
vibrations.
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Due to the fact that a traditional collet has only 4 contact points, the
contact surface area with a
tool is very small. Sometimes because of that, the tool slips inside the tool
holder at higher torque
caused by cutting forces. A slipped bit completely loses its setting position
inside the tool holder.
The presented invention, Multi Ball Self adjusting Self-centering Tool Holder
(MBSSTH), completely solves all of these problems.
All described above is rightly for positioning the Tool Holder itself inside
the nest of a spindle of
machine tool. The Multi Ball Self adjusting Self centering Clamping System
(MBSSCS) can be
used for positioning the Tool Holder itself inside the Spindle of machine
tool. MBSSCS can be used
even to directly position the Tool inside the Spindle of Machine Tool. In that
case, some of the
inaccuracies of the tool setting assemblies can be completely eliminated.
SUMMARY OF THE INVENTION
The most essential goal of current invention is to improve universal tool
holding system:
~ Significantly increase accuracy of the tool holder especially at high RPM.
~ Significantly increase rigidity of tool holders.
~ Create a Universal Tool Holding system for different applications.
~ Reduce accuracy requirements of tool's base surface. Accuracy requirement is
run-out only.
~ Increase the ability of the tool holder to work with wider range of tool
diameters.
~ Improve tool-setting procedures.
~ Significantly increase accuracy of positioning the tool holder inside
spindle of machine tool.
~ Creating a system where the tool is seated directly into the spindle of
machine tool, and
eliminating the whole bunch of inaccuracies inside the tool setting
assemblies.
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LIST OF FIGURES, WHICH ARE FORMING A PART OF THIS SPECIFICATION.
Fig. 1 is the photo of more traditional tool holder assembly that utilizes an
external collet system
(US Patent No 5,201,620).
Fig. 2 is an explanation of reasons of imperfection of a traditional tool
holder assembly (US Patent
No 5,201,620).
Fig. 3 is an explanation of main principal of the invention.
Fig. 4 is a primary design of the Multi Ball Self adjusting Self centering
Insert (MBSSI) with two
layers of balls.
Fig. 5 is a three-layer MBSSI where three different kinds of balls exist:
supporting balls (C),
intermediate balls (E) and clamping Balls (D).
Fig. 6 is the MBSSI where the balls in each layer are equal in size but
different from size of balls on
another layer. This design allows using a conical surface of the body as a
base surface.
Fig. 7 is a primary design of the Multi Ball Self adjusting Self centering
Tool Holder (MBSSTH).
Fig. 8 is a design of the Multi Ball Self adjusting Self centering Insert
(MBSSI) that is used to
position MBSSTH inside Spindle of Machine Tool.
DETAILED DESCRIPTION OF THE INVENTION.
NATURE OF THE INVENTION
~ The main principle of the invention is based on a principal of a ball's self
adjustment inside a
closed space.
~ Another principal of the invention is a distribution of base point (a-spot)
uniformly on a tool
surface.
~ Using the principals increases accuracy because of the use of mufti base
elements.
~ Statically determinate system with full force closure.
~ Using the principal of independently centering in line of tool's axis in
every layer of balls.
6
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CA 02488743 2004-12-08
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Theoretical background of the idea of the Multi Ball Self adjusting Self
centering Tool Holder
(MBSSTH) is presented in Fig. 3.
Supporting balls (SB), have to have equal size. Clamping balls (CB), have to
have equal size too.
Supporting and clamping balls can have equal or different sizes. Additional
requirements include:
the base surface (B) has to be perpendicular to the main base cylindrical
surface (M), and all
clamping balls (CB), have to lie in one geometrical plane that is parallel to
base surface (B). This
goal is achieved by using bushing (F). Base cylindrical surface of the bushing
(F) can slide along
base cylindrical surface (MO of the body. The end surface of the bushing (F)
is perpendicular to the
base cylindrical surface of the bushing. In this case, all clamping balls (CB)
will be in one
geometrical plane that is parallel to base surface (B). Every 'ball here has 4
base a-spots. Every
supporting ball (SB) has one a-spot with base surface (B), one a-spot with
base surface (M), and two
a-spots with two clamping balls (CB). Every clamping ball (CB) has two a-spots
with supporting
balls (SB), one a-spot with clamping bushing (F), and one a-spot with
cylindrical surface of the tool
(T). Due to self adjustment of the balls, all elements of a holder, even
theoretically, are completely
locked with full force closure and are in a position of stable equilibrium.
The tool is clamped by
multiple a-spots, which provides high accuracy and high rigidity. Many layers
of supporting and
clamping balls are used to hold the tool. Since every layer of balls
independently centers in line of
tool's axis, the tool holder can hold tools with small conical or wavy
surfaces. Only a run-out is
important to provide high accuracy.
To provide simple tool setup procedure and simplifying tool change operations,
all balls are
assembled in one Multi Ball Self adjusting Self centering Insert (MBSSI). 'The
MBSSI consist of
high precision balls assembled in a special order and kept together like one
flexible piece by flexible
stuff or a special separator.
Fig. 4, Fig. S, Fig. 6 and Fig. 7 show a possible design of MBSSI.
Fig. 4 is a primary design of MBSSI with two layers of balls.
Fig. 5 is a three-layer MBSSI where three different kinds of balls exist:
supporting balls (SB),
intermediate balls (IB) and clamping Balls (CB).
Fig. 6 is the MBSSI where the balls in each layer are equal in size but
different from size of
balls on another layer. This design allows the use of conical surface of the
body like a base surface.
Fig. 7 is a primary design of the Multi Ball Self adjusting Self centering
Tool Holder
(MB S STH).
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MBSSI can be designed in many different ways. ~"he main rule of design is very
simple. All balls inside system have to have four a-spots, and have to be
located in
position of stable equilibrium.
The primary design of MBSSTH is shown in Fig. 7. This tool holder includes a
body (O1),
supporting balls (02), clamping balls (03), clamping nut (04), and elastic
substance (05). The
washers (06) and (07), are on opposite sides of the insert assembly.
Supporting balls (02), clamping
balls (03), washers (06) and (07) are kept together by an elastic substance
(05) as one flexible piece -
Multi Ball Self adjusting Self centering Insert (MBSSI).
While tightening nut (04), up against body (0l), the distance (L) between butt-
end of the nut
(04), and base surface (B) of the body (01), decreases. That causes the space
between supporting
balls (02) to decrease, and clamping balls (03) to shift to the center and
clamp circular surface of
tool (06). Since all levels of balls work independently, centering is realized
in every level in-line
with the spindle's axis. That provides mufti-point contact with full force
closure. The screw (08) is
necessary for the tool's length setup.
The elastic substance (OS), which does not influence the accuracy of the tool
holder, keeps all the
balls together and returns the balls to their original position when the tool
is released from the tool
holder. In addition, it allows to keep all the balls together like one insert
(MBSSI), so it allows
changing MBSSI for different diameters of tools. Furthermore, the elastic
substance (05) creates a
great amount of additional torque between the body of the tool holder and the
tool's surface. That
helps to prevent the tool from slipping inside the tool holder.
Since the flexibility of the MBSSI is much higher than any kind of external
spring collet of a
traditional tool holder, the new design allows holding a very wide range of
tool diameters with a
single MBSSI.
Fig. 8 is a design of the Mufti Ball Self adjusting Self centering Insert
(MBSSI) that is used for
positioning MBSSTH inside Spindle of Machine Tool. Position O1 is a MBSSI for
holding a tool
inside tool holder. Position 02 is the body of a tool holder. Position 03 is a
MBSSI for holding tool
holder inside spindle O5. Position 04 is a pusher of spindle mechanism.
Activation of this pusher
causes the decreasing of distance between butt end of the pusher and tool
holder and shifting the
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clamping balls to the center. Due to this, the tool holder will be centered
and clamped inside the
spindle with high precision and rigidity.
ACHIEVEMENTS
1. Since the new Multi Ball Self adjusting Self centering Insert has all
elements in position of
stable equilibrium and the system is statically determinate with full force
closure, it is very
stable.
2. The Multi Ball Self adjusting Self centering Insert provides distribution
of base points
uniformly on a tool's surface (a-spot) with full force closure, because of
that, the MBSSTH
achieves a very high rigidity.
3. The MBSS Insert can hold tools with small conical or wavy surfaces, because
every layer of
balls independently centers in-line of the spindle's axis.
4. Because of multi point contact (a-spot) with full force closure,
centrifugal forces cannot change
position of balls or other elements of clamp. As a result, a high accuracy of
radial positioning of
a tool, even at high speed machining operations, is achieved.
5. Because MBSS Insert has mufti point contacts (a-spot) between all elements,
its accuracy
increases and makes the rigidity of the Tool Holder very high.
6. MBSSTH does not have any complicated details.
7. The MBSSI can be used for positioning the tool holder itself inside the
spindle of machine tool.
8. The MBSSI can be used for direct positioning of the tool inside the spindle
of machine tool and
eliminate the whole bunch of inaccuracies inside the tool setting assemblies.
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