WO2001010597A1

WO2001010597A1 - Grinding machines

Info

Publication number: WO2001010597A1
Application number: PCT/GB2000/002990
Authority: WO
Inventors: Robert Christopher Clarke
Original assignee: Robert Christopher Clarke
Priority date: 1999-08-04
Filing date: 2000-08-01
Publication date: 2001-02-15
Also published as: GB9918211D0; AU6305100A

Abstract

The invention describes a wheel head (10) for a grinding machine, the wheel head having a base (15) which is displaceable, in the conventional manner, toward the machine axis (13) on which is mounted a rotating work piece to be ground. The novelty resides in the fact that the grinding wheel (11) is mounted for movement along an arcuate path (16), and can thus follow the profile of the rotating work piece without having to reposition the main bulk of the wheel head (10). The grinding wheel (11) is preferably incorporated in a wheel spindle unit (17) which is suspended from an axis lying above the base (15), the movement of the wheel spindle unit (17) being counterbalance either by drive motor (22) or by a separate balance weight.

Description

GRINDING MACHINES

Field of the Invention

This invention relates to grinding machines and in particular, though not necessarily solely, to grinding machines for grinding rotating components such as crankshafts and camshafts.

Background to the Invention

When grinding round profiles rotating on an eccentric path, such as a crankpin or a cam type profile, current methods involve moving the wheel head of the grinding machine in and out in a straight linear path, the movement of the wheel head being synchronised with the rotation of the component. An alternative involves rocking the machine table to bring the grinding wheel into and out of contact with the rotating work piece, again in synch with the rotation of the component, but apparatus involving rocking of the machine table is currently limited to cam type profiles.

Moving the wheel head in and out allows a greater range of components to be ground but, due to the weight of the wheel head and the need to do rapid reversals of the wheel head, the accuracy and quality of the ground profile is often compromised. Rapid reversals can also cause wear on the mechanisms for moving the wheel head in and out. It is an object of this invention to address the problems of prior art grinding machines as outlined above; or to at least provide a novel and useful choice.

Swnmary of the Invention

Accordingly, in one aspect, the invention provides a grinding machine for grinding a work piece rotating about a machine axis, said grinding machine including a wheel head displaceable toward and away from said machine axis; and

a grinding wheel mounted for rotation, about a grinding wheel axis, on said wheel head,

said grinding machine being characterised in that said grinding wheel is mounted so that said grinding wheel axis moves through a path which is arcuate with respect to said wheel head.

Preferably said grinding machine further includes first displacement means to displace said wheel head with respect to said machine axis; and second displacement means to displace said grinding wheel with respect to said wheel head.

Preferably said grinding machine further includes balance means to substantially balance the movement of said grinding wheel.

The grinding wheel is preferably mounted in a wheel spindle unit, said wheel spindle unit being pivotally mounted on said wheel head. The pivot point of said wheel spindle unit lies above the main wheel head assembly, allowing said wheel spindle unit to hang down and said grinding wheel to move in an arc. To this end, said wheel head unit has two spaced columns or uprights which extend upwardly therefrom, said wheel spindle unit being mounted between the upper ends of said spaced columns or uprights.

Said wheel spindle unit preferably further includes a drive motor to rotate said grinding wheel. Said drive motor is preferably mounted on said wheel spindle unit but on the opposite side of the pivot point, to said grinding wheel. By mounting the motor on the opposite side of the pivot to the grinding wheel, the motor acts as a counterbalance to the wheel spindle/grinding wheel assembly. The position of said drive motor may be adjusted toward and away from said pivot to allow almost perfect balance to be achieved.

As an alternative, the drive motor could be mounted in said wheel spindle unit, on the same side of the pivot as said grinding wheel; and a separate balance weight then be provided, on the opposite side of the pivot, to counterbalance the wheel spindle/grinding wheel/ drive motor assembly.

Said second displacement means may comprise a ball screw/nut unit and servo drive motor or, alternatively, a linear motor, the chosen drive being be connected to said wheel spindle unit by a suitable linkage. Said first displacement means may comprise a ball screw and nut linked to a servo motor, or a linear motor.

In a second aspect the invention provides a wheel head unit for a grinding machine, said grinding machine being operable to grind work pieces mounted for rotation on a machine axis, said wheel head including:

a base mountable for movement toward and away from said machine axis when said wheel head is mounted on a machine; and

a grinding wheel mounted on said wheel head for movement along a path which is arcuate with respect to said base.

In a third aspect the invention provides a wheel head unit for a grinding machine, said wheel head unit including:

a grinding wheel mounted on said wheel head unit for movement along an arcuate path with respect to said wheel head unit; and

counterbalance means operable to counterbalance the movement of said grinding wheel.

Many variations in the way the present invention can be performed will present themselves to those skilled in the art. The description which follows is intended as an illustration only of one means of performing the invention and the lack of description of variants or equivalents should not be regarded as limiting. Wherever possible, a description of a specific element should be deemed to include any and all equivalents thereof whether in existence now or in the future. The scope of the mvention should be limited by the appended claims alone. Brief Description of the Drawings

One example of a grinding machine including a wheel head embodying the invention will now be described with reference to the following drawings in which:

Figure 1 : shows a side view of a wheel head assembly embodying the invention;

Figure 2: shows a plan view of the wheel head assembly shown in Figure 1 ;

Figure 3: shows an isometric view of a wheel spindle unit structure with the moving parts omitted for clarity ;

Figure 4: shows an isometric view of the main wheel head unit structure with the moving parts omitted for clarity;

Figure 5: shows an isometric view of a typical crankshaft ;

Figure 6: shows an isometric view of a typical camshaft, in a larger scale than Figure 4; and

Figure 7: shows an example of the relationship between a typical crankshaft and the grinding wheel during grinding of a crank pin using the wheel head unit shown in Figure 1. Detailed Description of Working Embodiment

Referring to the drawings, the invention provides a wheel head assembly 10 having a grinding wheel 1 1 mounted thereon, the grinding wheel 11 being displaced into and out of contact with a rotating work piece 12, such as, for example, a crankshaft or camshaft, mounted between the rotating centres (not shown) of a grinding machine, so as to rotate about machine axis 13.

In the conventional manner the wheel head assembly 10 is adapted for movement toward and away from the machine axis 13, i.e. in the directions of arrows 14. However, rather than the grinding wheel 1 1 being simply displaced with the wheel head assembly, the present invention provides for the grinding wheel to move in an arcuate path with respect to the wheel head base 15, which allows the grinding wheel to stay in contact with the rotating work piece, without having to displace the entire bulk of the wheel head assembly through the entire movement cycle of the rotating work piece 12. As will become apparent from the description which follows, the movement of the grinding wheel 11 along its arcuate path, as indicated by arrow 16, is preferably counterbalanced. This allows the grinding wheel to be positioned with little effort, in consequence of which fast and accurate grinding operations can be performed.

As can be seen, the grinding wheel 11 is incorporated in a wheel spindle unit 17, the unit 17 including a chassis 18 which is pivotally mounted at 19 between a pair of columns or uprights 20 extending upwardly from the wheel head base 15. The grinding wheel 1 1 is mounted at the lower end of the chassis 18 so as to rotate about axis 21. It will thus be appreciated that the grinding wheel is suspended and moves through an arc whose centre is axis 19, while rotating about its own axis.

A drive motor 22 is incorporated in the wheel spindle unit 17 to rotate the grinding wheel 11. In the form shown, the motor 22 is located on the opposite side of pivot axis 19, to the grinding wheel 11 , and can thus counterbalance the movement of that part of the wheel spindle unit 17 on the opposite side of pivot axis 19. The position of the motor 22 in relation to the pivot 19 may be varied to adjust the counterbalance effect. Alternatively, the motor may be mounted in the wheel spindle unit, on the same side of pivot axis 19 as the grinding wheel 1 1 , in which case a separate counterbalance weight is preferably provided to counterbalance the mass of the chassis 18, grinding wheel 11 , and drive motor about the pivot axis 19.

The drive is transmitted from the motor 22 to the grinding wheel 11 by drive belt 23 supported on two pulleys 24a, 24b concentric with the drive motor axis and grinding axis respectively.

The main wheel head base 15 is displaced in the direction of arrows 14 by first displacement means. In the form shown, the first displacement means comprises a ball screw and nut arrangement 25 in combination with a servo drive 26. As but one alternative, the first displacement means could comprise a linear motor which, it will be appreciated, could conveniently be mounted under the wheel head.

Second displacement means is provided to displace the grinding wheel 11 through its arcuate path as indicated by arrow 16. In the particular form depicted, the second displacement means comprises servo motor 27 and ball screw/nut 28. The components 27 and 28 could, for example, be replaced by a linear motor. Whichever precise form of drive is chosen, it is connected to the linkage unit 29 which, in turn, is connected to chassis 18.

In use the wheel head 10, as described above, is mounted on a new grinding machine or in a retro fit application in place of a conventional wheel head on an existing grinding machine.

A typical component such as a crankshaft 30 as depicted in Figure 5 or a camshaft 31 as depicted in Figure 6 is supported in the grinding machine between rotating centres, or other suitable means of support, and is driven by a motor drive (not shown]. Some form of radial positioning arrangement (not shown) is also provided which firmly holds the component so that its radial position is retained and known during rotation. This allows accurate synchronisation with the wheel spindle unit 17 and grinding wheel 11 , to create the profile imparted to the work piece 12. The size of the component and the metal removal rate is determined by the overall movement of the wheel head 10 under the influence of the ball screw and nut 25, and servo motor 26.

Figure 7 shows an example of the positions of grinding wheel 1 1 during one revolution of a component being ground, in this case a crank pin 32 on crankshaft 30. As can be seen, the wheel spindle unit chassis 18 is displaced by drive motor 27, and ball screw and nut arrangement 28, to maintain the grinding wheel in contact with different surface parts of the crank pin 32. By keeping the wheel spindle unit 1 7 fixed in one position, diameters on centreline, as in a conventional grinder, can also be ground.

It will be appreciated that components with more than one crank pin, or more than one cam profile, can also be ground.

It is envisaged that the various drive functions will be powered by numerically controlled apparatus and that suitable software will be produced to control entire grinding cycles.

It will thus be appreciated that the present invention provides a relatively simple yet effective form of wheel head for a grinding machine, and a grinding machine which incorporates such a wheel head, in which the force required to position the grinding wheel so that it might follow the profile of the work piece, is substantially reduced. This allows faster and more accurate grinding and leads to less wear and tear on the grinding machine.

Claims

1) A grinding machine for grinding a work piece rotating about a machine axis, said grinding machine including a wheel head displaceable toward and away from said machine axis; and

2) A grinding machine as claimed in claim 1 further including first displacement means to displace said wheel head with respect to said machine axis; and second displacement means to displace said grinding wheel with respect to said wheel head.

3) A grinding machine as claimed in claim 1 or claim 2 further including counter-balance means to substantially counterbalance balance the movement of said grinding wheel.

4) A grinding machine as claimed in any one of claims 1 to 3 wherein said grinding wheel is rotatably mounted in a wheel spindle unit, said wheel spindle unit being pivotally mounted on said wheel head. 5) A grinding machine as claimed in claim 4 wherein the pivot point of said wheel spindle unit lies above the main wheel head assembly and wherein said wheel spindle unit is suspended from said pivot point.

6) A grinding machine as claimed in claim 5 wherein said wheel head unit includes two spaced columns or uprights which extend upwardly therefrom, said wheel spindle unit being mounted between the upper ends of said spaced columns or uprights.

7) A grinding machine as claimed in any one of claims 4 to 6 wherein said wheel spindle unit further includes a drive motor to rotate said grinding wheel.

8) A grinding machine as claimed in claim 7 wherein said drive motor is mounted on said wheel spindle unit but on the opposite side of the pivot point, to said grinding wheel to thereby serve as a counter-balance.

9) A grinding machine as claimed in claim 8 wherein the position of said drive motor is adjustable toward and away from said pivot to vary the counterbalance effect.

10) A grinding machine as claimed in claim 7 wherein said driv e motor is mounted in said wheel spindle unit, on the same side of the pivot as said grinding wheel; said wheel spindle unit further including a separate balance weight, on the opposite side of the pivot, to counterbalance the wheel spindle/grinding wheel/drive motor assembly. 11) A grinding machine as claimed in any one of claims 4 to 10 wherein said second displacement means comprises a ball screw/nut unit and servo drive motor, or a linear motor, said second displacement means being connected to said wheel spindle unit by a linkage.

12) A grinding machine as claimed in any one of claims 3 to 10 wherein said first displacement means comprises a ball screw and nut linked to a servo motor, or a linear motor.

13) A wheel head unit for a grinding machine, said grinding machine being operable to grind work pieces mounted for rotation on a machine axis, said wheel head including:

14) A wheel head as claimed in claim 12, for fitting to the grinding machine claimed in any one of claims 1 to 12.

15) A wheel head unit for a grinding machine, said wheel head unit including:

a grinding wheel mounted on said wheel head unit for movement along an arcuate path with respect to said wheel head unit; and counterbalance means operable to counterbalance the movement of said grinding wheel.