The present invention relates to grinding machines, and more specifically
to systems to rotate wheelheads on grinding machines.
BACKGROUND OF THE INVENTION
Grinding machines are known that have the possibility of turning
the wheelhead to vary the angle of the grinder in relation to the piece to be ground.
US 4,897,964 describes a grinding machine where the wheelhead is
turned by a worm transmission. This type of transmission systems obtain a high
reduction, but at the expense of very low performance and not very good positioning
accuracy, unless components of very high mechanical quality and therefore very
costly are used.
There are also grinding machines that include a rotating plate on
which the wheelhead is supported. There are rotating plates which use frontal notching
for positioning the head. In such cases, the accuracy obtained is good, but the
number of possible positions is limited by the number of teeth in the frontal
notching. There are systems using frontal notching which, to increase the number
of possible positions, add a further drive limited to the angle between consecutive
teeth, which increases the complexity and cost of the plate.
On the other hand, there are also rotating plates with continuous
positioning. The drawback of this type of plates is its elevated cost.
DESCRIPTION OF THE INVENTION
The object of the invention is to provide a rotating machining unit
for a grinding machine, as defined in the claims.
The rotary unit of the invention comprises a base, a body rotating
on said base in relation to a rotating shaft, at least one wheelhead arranged on
said body, means for turning said body by the rotation of a motor, means for fixing
the body to the base, and a rotary encoder to detect the angular position of said
body. Said rotary encoder is placed concentrically to the rotating shaft of the
body, thus providing great precision in the measurement of the angular position
of the body and so of the wheelhead attached to said body.
The means for the rotation of the body include a ball spindle that
turns together with the motor, a threaded nut on said ball spindle fixed to a second
rotation shaft linked to the body with the possibility of turning, and a third
rotation shaft by which the ball spindle is linked to the base with the possibility
In the rotary unit of the invention, the distance between the rotation
shaft of the body and the nut threaded on to the ball spindle is greater than the
radius of the surface on which the body turns, so ensuring that the rotation is
extremely precise, because the greater the distance between the rotation shaft
of the body and the nut, the greater the linear displacement of the nut corresponding
to the same angular displacement. Thus, for example, for the same angular displacement
of the body, the rotation of the ball spindle is greater than the rotation that
would correspond to a worm using a crown with that radius.
On the other hand, because of the large distance between the rotation
shaft of the body and the nut, the surface for the support of the body on the base
is greater and, in addition, the means for securing the body to the base can be
further from the rotation shaft, so enhancing the fixing.
The three rotating shafts of the rotating unit of the invention include
pre-loaded angular contact bearings. This ensures that there is no play, and helps
to ensure that the transmission system is very accurate. Therefore, the rotating
unit of the invention guarantees the precision of the positioning of the grinder,
providing a solution that is significantly cheaper than systems using rotating
These and other features of the invention will become apparent in
the detailed disclosure of one embodiment of the invention.
DESCRIPTION OF THE DRAWINGS
DETAILED DISCLOSURE OF THE INVENTION
- FIG. 1 is an elevated view of one embodiment of the invention.
- FIG. 2 is a plan view of the embodiment of FIG. 1.
- FIG. 3 is a plan view of the embodiment of FIG. 1, turned through a given angle.
- FIG. 4 is a detail of the system of transmission of the turn in the embodiment
of FIG. 1.
With references to figures 1, 2 and 3, the rotating machining unit
of the invention comprises a base 1, a body 2 turning on said base 1 in relation
to a rotating shaft 3, at least one wheelhead 4 placed on said body 2, means for
turning said body 2 by the rotation of a motor 5, means for fixing the body 2 to
the base 1, and a rotary encoder 6 to detect the angular position of the body
2. Said rotary encoder 6 is placed concentrically to the rotation shaft 3, so
making the measurement of the angular precision extremely accurate.
The means for turning the body 2, shown in detail in figure 4, include
a ball spindle 7 that turns together with the motor 5, a nut 8 threaded on said
ball spindle 7 and fixed to a rotation shaft 9 which is linked, with possibility
of turning, to the body 2, and a rotation shaft 10 by which the ball spindle 7
is linked to the base 1 with the possibility of turning.
As shown in figure 3, the distance between the rotating shaft 3 and
the nut 8 is greater than the radius of the surface on which the body 2 turns.
Therefore, for the same angular displacement of the body 2, there is a rotation
of the ball spindle 7 that is greater than the one that would correspond to a
worm using a crown with that radius.
The rotating shafts 9 and 10 allow the ball spindle 7 and motor 5
to adapt to the rotating movement of the body 2. As the body 2 turns in relation
to the rotating shaft 3, the nut 8 turns in relation to the body 2 by means of
the rotating shaft 9, displacing the ball spindle 7 with it, said ball spindle
7 turning, with the motor 5, in relation to the rotating shaft 10 linked to the
base 1. Figures 2 and 3 show how this movement is performed.
The rotating shafts 3, 9 and 10 on the rotating unit of the invention
include pre-loaded angular contact bearings 11, 12 and 13, which ensure there is
no play in said rotating shafts. On the other hand, the ball spindle 7 is linked
to motor 5 by means of an elastic coupling 14.
The means for fixing the body 2 to the base 1 include a plurality
of mooring braces 15 on the base 1, whose ends 16 are housed in concentric grooves
17 (shown in figure 3) in the body 2. Said mooring braces 15 hold the body 2 on
the base 1 when pressure is not supplied to sealed chambers 18 on the opposite
ends of said mooring braces 15. When pressure is supplied to said chambers 18,
the mooring braces 15 are displaced vertically, so releasing the body 2. This embodiment
includes three mooring braces 15, with their three corresponding concentric grooves
In general, base 1 of the rotating unit is placed on two carriages
(not shown in the figures), perpendicular to each other and fixed, so that the
body 2 has the following movements: a linear displacement together with the base
1 in a direction X on one of the said carriages, a linear displacement together
with the base 1 in a direction Z on the second of said carriages, and an angular
displacement on base 1 in relation to the rotating shaft 3.
Therefore, because the perpendicular carriages do not turn, the reference axes
X and Z remain fixed at all times.