EP1702716A1

EP1702716A1 - Grinding machine

Info

Publication number: EP1702716A1
Application number: EP05425152A
Authority: EP
Inventors: Claudio Tacchella
Original assignee: TACCHELLA MACCHINE SpA
Current assignee: TACCHELLA MACCHINE SpA
Priority date: 2005-03-14
Filing date: 2005-03-14
Publication date: 2006-09-20

Abstract

There is described an adjustable grinding tool-holder assembly (1; 1') having a fixed base (10); a movable supporting member (2); at least one dual tool-holder spindle or at least one pair of spindles (4, 6; 4a', 4b', 4c') carried by the supporting member (2) and for supporting respective grinding tools (5, 7; 5a', 5b', 5c') cooperating sequentially with a workpiece; and a drive member (3) for moving the supporting member (2), with respect to the base (10) and about an axis (A), between at least two predetermined angular work positions.

Description

The present invention relates to an adjustable grinding tool-holder assembly.
Grinding is performed on a grinding machine by producing relative motion between a tool - fitted to the machine and having a highly abrasive work surface - and an inner or outer surface of a workpiece from which material is to be removed.
Grinding machines normally comprise tool-holder assemblies for positioning the tool correctly with respect to the workpiece, and are arranged in production lines, along which various grinding operations on respective surfaces of the workpiece are performed successively.
In grinding plants, a demand exists for short production lines and compact grinding machines capable of performing highly repeatable, precise movements of the tool-holder assembly with respect to the workpiece.
It is an object of the present invention to provide an adjustable grinding tool-holder assembly designed to meet the above demand.
According to the present invention, there is provided an adjustable grinding tool-holder assembly, as claimed in Claim 1.
A number of preferred, non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows a top plan view of a grinding machine adjustable tool-holder assembly in accordance with the present invention;
Figure 2 shows a larger-scale section, with parts removed for clarity, along line II-II in Figure 1;
Figure 3 shows a section along line III-III in Figure 2;
Figure 4 shows a top plan view of a further embodiment of the adjustable tool-holder assembly in Figure 1.

With reference to Figures 1 to 3, number 1 indicates a tool-holder assembly in accordance with the invention for a known grinding machine (not shown in the accompanying drawings).
Assembly 1 substantially comprises a base 10 fixed in known manner, e.g. by screws, to the supporting structure of the grinding machine; and a supporting member 2, to which are fitted two or more grinding tools (described in detail below), and which rotates, with respect to base 10 and about an axis A, between a number of tool angular work positions.
More specifically, supporting member 2 is located vertically over base 10, and has a plane of symmetry P containing axis A.
Supporting member 2 is moved between the angular work positions by a motor 3 fitted to supporting member 2; and by a transmission 12 fitted partly to supporting member 2 and partly to base 10.
In the example shown, supporting member 2 is fitted with two external-grinding tools 5, and one internal-grinding tool 7, which are fitted integrally to respective spindles 4, 6, in turn fitted to supporting member 2.
Spindles 4 - which are two in number in the example shown - are advantageously fitted to supporting member 2 in axially-fixed positions, and so as to rotate about respective diverging axes B equidistant angularly from plane P and perpendicular to axis A.
More specifically, external-grinding tools 5 are fitted to corresponding adjacent end portions of respective spindles 4, coaxially with respective axes B.
Axes B of spindles 4 advantageously diverge towards the portions of spindles 4 fitted with external-grinding tools 5, so as to reduce total inertia of assembly 1 and the total adjustment angle of sequentially-operated grinding tools 5, 7 with respect to axis A.
Spindle 6 is fitted to supporting member 2 in an axially-fixed position, and so as to rotate about an axis C perpendicular to plane P.
More specifically, with respect to external-grinding tools 5, spindle 6 is located at the converging end of axes B, and internal-grinding tool 7 is fitted to and projects from one end of spindle 6.
With particular reference to Figure 2, base 10 comprises a first annular plate 15 fitted releasably to a supporting structure of the grinding machine and for axially supporting supporting member 2, and a second annular plate 16 for axially securing supporting member 2, as described in detail below, and connected elastically to plate 15.
More specifically, plate 15 has a first and a second axial end 20, 21 opposite each other, and which respectively secure assembly 1 to the supporting structure, and support supporting member 2 in a direction parallel to axis A.
More specifically, axial end 21 comprises a radial first surface 22 facing plate 16; a second surface 23 radially outwards with respect to surface 22 and for statically supporting supporting member 2; and an axial portion 17 connecting surfaces 22 and 23.
Surface 23 cooperates in sliding manner with supporting member 2, as supporting member 2 moves between the various angular work positions.
To reduce the friction caused by supporting member 2 sliding on base 10, surface 23 advantageously has a layer 35 of plastic antifriction surfacing material, which also acts as a damper between the two parts.
Plate 16 comprises an axial end 24 loosely facing surface 22 of plate 15; and a radial end 25 opposite axis A and defining a shoulder 26 cooperating with supporting member 2.
Shoulder 26 is defined by a radial first portion 27, and by an axial second portion 28 radially inwards with respect to radial portion 27, and which joins radial portion 27 to end 24.
Shoulder 26 and surface 23 of plate 15 define an annular recess 14 for axially securing supporting member 2.
Supporting member 2 rotates spindles 4, 6 (in known manner not shown) by means of motor 3 and transmission 12, is supported axially with respect to axis A on surface 23 of plate 15, and is secured axially with respect to axis A inside recess 14 defined by plates 15 and 16.
More specifically, supporting member 2 is bounded, at one annular axial end 34, by a surface 52 extending radially with respect to axis A, resting on surface 23 of plate 15, and cooperating in sliding manner with surface 23 as supporting member 2 moves between the various angular work positions.
At axial end 34, supporting member 2 comprises an annular, radially inner projection 33, which engages recess 14 of plate 16 to lock supporting member 2 axially with respect to base 10.
More specifically, projection 33 is bounded axially at opposite ends by a radial surface 36 and by surface 52, and is bounded radially by an axial surface 38 connecting surfaces 36 and 52.
Projection 33 engages recess 14 by radial portion 27 of shoulder 26 pressing on radial surface 36, so that surface 23 of plate 15 contacts surface 52 of supporting member 2, leaving a radial clearance between axial surface 38 and axial portion 28 of shoulder 26.
Engagement of projection 33 of supporting member 2 inside recess 14 of plate 16 therefore secures supporting member 2 to base 10 in axially-fixed manner and, depending on the contact pressure exerted by radial portion 27 of shoulder 26 on radial surface 36 of projection 33, in rotary manner with respect to axis A.
Supporting member 2 comprises a through first annular cavity 30, of axis A, and a second annular cavity 31, parallel to cavity 30, which house transmission 12 and permit interaction between transmission 12 and supporting member 2 and motor 3 respectively.
More specifically, motor 3 is fixed to and projects vertically from an axial end of supporting member 2 opposite base 10, and comprises an output shaft 32 engaging cavity 31 of supporting member 2, rotating about an axis parallel to axis A, and connected angularly to supporting member 2 by transmission 12, as explained in detail below.
More specifically, with an elastic preload system, shaft 32 rotates about axis A a sleeve 41 housed inside cavity 31 of supporting member 2, and both are fitted on their axial ends with a gear 54, which meshes with a tubular body 39 housed in a fixed position with respect to axis A inside cavity 30 of supporting member 2.
More specifically, sleeve 41 is supported inside supporting member 2 on a number of bearings 42 enabling sleeve 41 to rotate with respect to supporting member 2 at a different angular speed from that of supporting member 2.
Tubular body 39 receives a torque, having a component along axis A, from shaft 32 via gear 54, is fixed by screws to plate 15 of base 10, and supports supporting member 2 in rotary manner with respect to axis A.
More specifically, the radially outermost surface of tubular body 39 has teeth 40, which mesh with gear 54 on shaft 32.
Tubular body 39 supports supporting member 2, in rotary manner about axis A, by means of two bearings 43 interposed between supporting member 2 and tubular body 39.
Consequently, when a torque having a component along axis A is applied, tubular body 39 is subject to torsional stress, which is transmitted by bearings 43 from tubular body 39 to supporting member 2, which, being movable angularly with respect to axis A, is rotated about axis A.
Base 10 advantageously comprises a fluidic assembly 19 to reduce the contact pressure between radial portion 27 of shoulder 26 and radial surface 36 of projection 33 as supporting member 2 moves from one work position to another, and to facilitate rotation of supporting member 2 with respect to axis A.
More specifically, fluidic assembly 19 comprises an annular cavity 18 formed in fluidtight manner between plates 15 and 16; and a feed conduit 37 for feeding fluid into cavity 18.
Cavity 18 is defined by the axial clearance between surface 22 of plate 15 and end 24 of plate 16, and is bounded radially by axial portion 17 connecting surfaces 22 and 23.
Feed conduit 37 extends axially inside plate 15, and provides, with a given timing, for feeding external fluid into cavity 18 to produce axial thrust on plate 16 in the detachment direction of plate 16 from projection 33 of supporting member 2, and so reduce the contact pressure between radial portion 27 of shoulder 26 and radial surface 36 of projection 33.
Plates 15 and 16 are advantageously preloaded elastically to each other, so as to rapidly grip projection 33 of supporting member 2 between plates 15 and 16 when cavity 18 is emptied of fluid, and so immediately lock supporting member 2 in the desired angular work position, when the fluid pressure in cavity 18 is released.
More specifically, plates 15 and 16 are connected by a number of bolts 29 having axes parallel to axis A, and by respective numbers of Belleville washers 13; and each number of Belleville washers 13 surrounds a relative bolt 29, and is housed inside a relative cavity in plate 16, between a bottom surface of plate 16 and the end of respective bolt 29.
Assembly 1 advantageously also comprises a balancing device 46 housed inside plate 15.
More specifically, with reference to Figures 2 and 3, balancing device 46 comprises a number of axial conduits 47 for feeding fluid, e.g. air, to device 46; a circumferential groove 48 formed in the radially innermost edge of surface 23, and a number of fluid chambers 49 spaced angularly and preferably equally spaced about axis A along surface 23.
Balancing device 46 also comprises a number of shutters 50 activatable selectively from outside, and each interposed between a respective chamber 49 and circumferential groove 48 to enable/disable fluid supply to respective chamber 49, and so adjust the centre of gravity, and achieve balanced dynamic performance, of assembly 1.
Assembly 1 advantageously also comprises a known encoder 44 for measuring angular displacement of supporting member 2 with respect to a fixed direction.
Encoder 44 comprises a fixed shaft 45, of axis A, fitted to the supporting structure of the grinding machine and housed radially loosely, and therefore subjected to no torsional stress, inside tubular body 39; and a movable member 53 fitted to the axial end of supporting member 2 opposite base 10, and projecting from supporting member 2 for easy access from the outside.
Finally, assembly 1 is immersed completely in an oil bath to lubricate supporting member 2 as it rotates about axis A with respect to base 10.
In actual use, assembly 1 provides for performing a number of successive external and internal grinding operations.
More specifically, assembly 1 can be set to three different angular work positions with respect to axis A: two for performing respective external grinding operations on a workpiece, and one for performing an internal grinding operation on the workpiece.
More specifically, in the external-grinding angular work positions of assembly 1, one of external-grinding tools 5 is positioned contacting the outer surface of the workpiece, and, in the internal-grinding angular work position of assembly 1, internal-grinding tool 7 is positioned contacting the inner surface of the workpiece.
The switch from one to another of the angular work positions is made by feeding fluid along feed conduit 37 into cavity 18. The pressure exerted by the fluid on end 24 of plate 16 subjects plate 16 to thrust parallel to axis A and in the detachment direction of plate 16 from plate 15 and projection 33 of supporting member 2.
Said thrust reduces the contact pressure between radial portion 27 of shoulder 26 of plate 16 and radial surface 36 of projection 33 of supporting member 2, thus facilitating rotation of supporting member 2 with respect to axis A, and compressing washers 13.
At the same time, motor 3 rotates shaft 32, which, by virtue of gear 54 meshing with teeth 40 on tubular body 39, subjects tubular body 39 to a torque having a nonzero component along axis A.
Being fitted to angularly-fixed base 10, tubular body 39 cannot be rotated by said torque, and therefore is subjected to torsional stress, which is transmitted by bearings 43 from tubular body 39 to supporting member 2, which, being angularly movable about axis A, is rotated to move spindles 4, 6 into the desired angular position.
As it rotates about axis A, supporting member 2 also rotates on sleeve 41 by means of bearings 42.
The vibration produced by rotation of the grinding tools is damped by layer 35 of antifriction and damping surfacing material.
Encoder 44 measures the angular displacement of supporting member 2 with respect to the supporting structure of the grinding machine, and, in known manner not shown, cuts off power to motor 3 when the desired angular work position is reached.
At the same time, the fluid is drained from cavity 18, so that radial portion 27 of shoulder 26 of plate 16 increases the contact pressure on radial surface 36 of projection 33 of supporting member 2 to brake supporting member 2 more or less instantaneously by means of washers 13.
Advantageously, the equilibrium of assembly 1 may be optimized easily, in various operating configuration, by means of device 46.
That is, circumferential groove 48 is fed with fluid along conduits 47. And, by acting externally on shutters 50, fluid supply from circumferential groove 48 to each chamber 49 can be enabled or disabled to selectively adjust the centre of gravity of assembly 1 with respect to the angular work position of supporting member 2 about axis A.
With reference to Figure 4, number 1' indicates as a whole a tool-holder assembly in accordance with a further embodiment of the present invention. Tool-holder assembly 1' is similar to tool-holder assembly 1, and is described below only as regards the differences between the two; and any corresponding or equivalent component parts of tool-holder assemblies 1 and 1' are indicated, where possible, using the same reference numbers.
More specifically, tool-holder assembly 1' comprises two external-grinding tools 5a' fitted to a spindle 4a' of axis C' parallel to plane P; a third external-grinding tool 5b' fitted to a spindle 4b' of axis D'; and a fourth external-grinding tool 5c' fitted to a spindle 4c' of axis F'.
More specifically, axes D' and F' diverge and are located on the opposite side of plane P to axis C'.
More specifically, external-grinding tools 5a' are fitted to and project from opposite axial ends of spindle 4a', coaxially with axis C'.
External-grinding tools 5b' and 5c' are fitted to and project from corresponding ends of respective spindles 4b' and 4c', coaxially with respective axes D' and F'. More specifically, axes D' and F' of spindles 4b' and 4c' converge towards the portions of spindles 4b', 4c' fitted with external-grinding tools 5b', 5c', so as to reduce the total inertia of assembly 1' with respect to axis A.
The advantages of tool-holder assemblies 1, 1' according to the present invention will be clear from the foregoing description.
In particular, tool-holder assemblies 1, 1' provide for achieving short production lines and, at the same time, compact grinding machines capable of performing highly repeatable, precise movements with respect to the workpiece.
That is, by featuring a number of external-grinding tools 5, 5a', 5b', 5c' and possibly an internal-grinding tool 7, tool-holder assemblies 1, 1' enable a number of internal and external grinding operations to be performed on the same grinding machine, thus enabling a reduction in production line length by not having to feed the workpiece through a succession of different grinding machines, each for performing internal or external grinding operations.
By featuring respective pairs of spindles (4; 4b', 4c') rotating about respective diverging axes (B; D', F'), each tool-holder assembly (1; 1') reduces the angular displacement and, therefore, the time taken to move from one angular work position to another.
Moreover, as stated, by virtue of the axes (B; D', F') of the spindles (4; 4b', 4c') diverging, or converging towards the portions of the spindles fitted with the external-grinding tools (5; 5b', 5c'), the inertia of each tool-holder assembly (1; 1') as regards rotation about axis A is reduced. As such, tool-holder assemblies 1, 1' pose few problems as regards wear of mutually contacting component parts, and are easier to move between the various work positions.
Tool-holder assemblies 1, 1' also have a high degree of positioning precision and repeatability, by encoder 44 measuring angular displacement between the supporting structure of the grinding machine and supporting member 2, so that deformation of tubular body 39 of transmission 12, caused by torsional stress when starting motor 3, has no effect on operation of encoder 44.
Given the absence of in-service heating sources in the locking, release, and adjusting technology employed, no thermal drift is produced, so that the stability of no part of the structure of tool-holder assembly 1, 1' is affected.
Clearly, changes may be made to tool-holder assemblies 1, 1' as described and illustrated herein without, however, departing from the protective scope as defined in the accompanying Claims.

Claims

An adjustable grinding tool-holder assembly (1, 1'), characterized by comprising:
- fixed supporting means (10);

- a movable supporting member (2);

- at least one pair of grinding tools (5, 7, 5a', 5b', 5c') carried by said movable supporting member (2) and cooperating sequentially with a workpiece; and

- a drive member (3) for moving said movable supporting member (2), with respect to said fixed supporting means (10) and about a first axis (A), between at least two predetermined angular work positions.
An assembly as claimed in Claim 1, characterized in that said movable supporting member (2) is fitted axially to said fixed supporting means (10) with a given contact pressure; and in that said assembly (1, 1') comprises first feed means (37) for feeding fluid between a first surface (22) and a second surface (24) to selectively reduce said contact pressure to facilitate rotation of said movable supporting member (2) with respect to said fixed supporting means (10).
An assembly as claimed in Claim 2, characterized in that said fixed supporting means (10) comprise a first and a second fixed supporting member (15, 16) contacting each other along said first and said second surface (22, 24); and in that said movable supporting member (2) comprises at least one portion (33) sandwiched, along said first axis (A), between said first and said second fixed supporting member (15, 16).
An assembly as claimed in Claim 3, characterized by comprising elastic means (13) interposed between said first and said second fixed supporting member (15, 16).
An assembly as claimed in any one of the foregoing Claims, characterized by comprising antifriction or damping means (35) interposed between said fixed supporting means (10) and said movable supporting member (2).
An assembly as claimed in Claim 5, characterized in that said fixed supporting means (10) and said movable supporting member (2) have respective contact surfaces (23, 52); and in that said antifriction means comprise a plastic layer (35) applied to one (23) of said contact surfaces (23, 52).
An assembly as claimed in any one of the foregoing Claims, characterized by comprising at least one chamber (49) formed between said fixed supporting means (10) and said movable supporting member (2); and second feed means (47, 48) for feeding fluid into said chamber (49) to adjust the centre of gravity of the assembly (1, 1').
An assembly as claimed in Claim 7, characterized by comprising shutter means (50) activatable selectively to disable fluid supply to said chamber (49).
An assembly as claimed in Claim 7 or 8,
characterized by comprising a number of said chambers (49) angularly and preferably equally spaced about said first axis (A).
An assembly as claimed in any one of the foregoing Claims, characterized in that said grinding tools (5, 5b', 5c') are carried by at least one pair of spindles (4; 4b', 4c') fitted to said movable supporting member (2) to rotate about respective diverging second axes (B; D', F') .