EP0724500B1

EP0724500B1 - Improvements in and relating to grinding machines

Info

Publication number: EP0724500B1
Application number: EP94930282A
Authority: EP
Inventors: Michael Laycock
Original assignee: Unova UK Ltd
Current assignee: Intermec Europe Ltd
Priority date: 1993-10-20
Filing date: 1994-10-20
Publication date: 2000-10-11
Anticipated expiration: 2014-10-20
Also published as: GB9321639D0; DE69426125D1; WO1995011110A1; AU7944494A; EP0724500A1; ES2150995T3; DE69426125T2

Description

Field of the invention

This invention concerns a grinding machine as per the preamble of Claim 1. An example of such a machine is disclosed by US 5103596 A.

Background to the invention

Historically grinding machines have tended to be set up to grind large numbers of one particular component such as a cam shaft for a motor car engine. With the trend towards a greater variety of engines the need to be able to produce smaller runs of different cam shafts and other ground components has arisen.

Rather than provide different machines for grinding the different components thereby occupying valuable workshop space and increasing the overhead component of a business, the present invention provides an alternative solution to this problem.

In document FR-A-2614226 there is disclosed a grinding machine having a table or frame and a grinding wheel relative to which the table is moveable. The table carries firstly a headstock and a tailstock upon which a workpiece is rotationally mounted, and which are relatively adjustable in spacing on the table, and secondly an adjustable workrest. However, since all such movements and adjustments require to be performed under mechanical control, this known machine is not sufficiently flexible to enable smaller runs of different components to be rapidly machined.

Similarly, US-A-5103596 discloses a grinding machine having a worktable and a grinding wheel relative to which the worktable is movable, the latter carrying firstly a headstock and a tailstock adjustable in spacing and secondly a movable workrest or deflection-supressing device, wherein the workrest and at least one of the headstock and tailstock are adjustable relative to the worktable. Such a machine is particularly suited to the accurate grinding of slender cylindrical workpieces.

Document JP 5031667A discloses an automated grinding system in which a storage medium containing tooling data is physically associated with a workpiece to be ground, and an NC device reads this data and thus controls workpiece engagement elements including a grinding wheel, headstock, tailstock, workrests and measuring parts. However, this known system does not disclose any means for obviating possible errors in the lateral positioning of the workpiece.

It is an object of the present invention to provide an improved computer controlled grinding machine in which such lateral positioning errors can be corrected.

Summary of the invention

According to the present invention there is provided a grinding machine having a worktable and a grinding wheel relative to which the worktable is movable, the worktable carrying firstly a headstock and tailstock adjustable in spacing and secondly an adjustable workrest, at least one of the headstock and tailstock and additionally the workrest being adjustable relative to the worktable, characterised in that the relative movements and adjustments are computer controlled independently of the relative position of the grinding wheel and worktable by programmable drive means programmed at least in part with respect to a lateral reference, which serves to determine the relative position of the grinding wheel and the worktable in a direction parallel to an axis extending between the headstock and the tailstock, thereby to position the headstock and/or the tailstock and/or the workrest, enabling different workpieces and parts thereof to be positioned in their precise position in front of the grinding wheel for grinding.

Other features of the invention are defined in the appended claims.

Description of embodiment

The invention is further described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a general view of a grinding machine incorporating the invention;

Figure 2 is a close-up view showing the probe engaging a radial face of the workpiece;

Figure 3 is a close-up view showing the grinding wheel and workrests;

Figure 4 is an interior view of the machine showing the workhead mounted on the machine base;

Figure 5 shows the drive means for rotating the wheelhead about a vertical axis:

In Figure 1 the main machine bed 10 supports a wheelhead not visible, within the slidable enclosure 12 which can be opened to enable workpieces to be inserted and removed and includes an inspection window 14. A computer based control system 16 stands adjacent the machine and can be manually adjusted to control the machine so as to receive and grind different workpieces according to pre-programmed information.

There is shown in Figure 2 a probe 18 which can be seen engaging the radial shoulder 20 of a pre-machined section of the workpiece 22. The probe is adapted to be driven into engagement with the machine diameter of the segment 22 and then moved radially until it engages the radial shoulder it is seeking. Positional information is derived therefrom and sent to the computer control centre 16.

The workpiece is also visible in Figure 2 and is denoted by reference numeral 24.

Workrests are also visible at 26 and 28 and drive means within the workrests adjust them perpendicularly to the workpiece and if required laterally relative to the workpiece.

Signals for controlling the drives for the

workrests

26 and 28 are derived from the control centre 16.

Figure 3 shows the same part of the machine as viewed from a more distant point showing the beginning of the headstock assembly 30 and the tailstock at 32. Figure 3 also shows the additional workrests at 34 and 36. Each of the latter includes drives similar to those for

workrests

26 and 28 and is operable in the same way from the control centre 16.

Also in Figure 3 can be seen the grinding wheel 38.

In order to provide a further degree of workpiece customisation, the wheelhead assembly of the grinding machine is mounted on a pivotable platform. Figure 4 shows the wheelhead assembly at 40 mounted on a base 42 which itself is pivotable relative to a sub-base 44 carried on the machine bed 46. By moving the base 42 about a pivot axis (not shown in Figure 4) but preferably orthogonal to the axis of rotation of the grinding wheel, so the angle of attack of the wheel to the workpiece can be adjusted.

Drive means for effecting this sliding and thereby pivoting or tilting of the wheelhead assembly 40 is shown in Figure 5. This comprises a hydraulic or pneumatic ram 48 acting between the platform 42 and pivotally mounted at 50 to the sub-base 44. Mounted thereon at 52 is a control device for the ram to enable the latter to be advanced and retracted under control signals from the control centre 16.

In more detail dimensions taken from a component engineering drawing are directly used as input data to the control via a component part programme.

The dimensions required to manufacture a component are:-

1. The lateral positions of cam lobes or plain diameters from a defined lateral reference position (ABSZ).

2. In the case of a cam lobe, the profile shape of each cam lobe specified as "lift" distances above a specified cam minimum radius (base radius) at specified angles for a specified radius of cam follower and the angle of each cam lobe from a defined angular reference position (PROFILE).

3. In the case of a plain diameter, the diameter.

4. The angle of inclination of the surface of each cam lobe or plain diameter is specified with reference to the centre-line of rotation of the camshaft (ANGLE).

5. The lateral position of the work support bearing diameters from the above mentioned defined lateral reference position (ABSZ2, ABSZ3).

6. The lateral position of a measurement reference face that is perpendicular to the axis of rotation, from the above mentioned defined lateral reference position (ABSZ).

7. The length of the component (ABSZO).

Several radial work supports (workrests) and an axial work support (tailstock or footstock) are carried upon the worktable and each is independently positioned by the computer, laterally with respect to the worktable. The headstock can be fixed relative to the worktable, but this is not necessarily the case.

The worktable can also be positioned by the computer, laterally with respect to the grinding wheel on the wheelhead. It is apparent that, if the worktable is moved, the workrests, footstock and headstock that are mounted upon the worktable also move. The adjusted position of the worktable defines a lateral reference position.

The control system uses length information relating to the component to automatically position the footstock upon the worktable, so as to provide the necessary end thrust to properly constrain the component.

The control system uses the work support diameter lateral position information to automatically position the workrests upon the worktable, so that they laterally align with the component work support diameters.

The control system uses the lateral positions of the cam lobes and plain diameters to automatically position the worktable so that the cam lobes and plain diameters are sequentially brought in front of the grinding wheel so that they may be ground.

Variation in lateral position of the cam lobes/plain diameters and work support diameters due to component tolerance variation, e.g. variation in centre depth, is eliminated by use of the electronic measurement probe. The probe is automatically advanced, under computer control, at the start of each cycle, after the footstock is positioned to support the component. The worktable is positioned so as to place a measurement reference face at its theoretically correct position with respect to the probe. The probe is advanced onto the measurement face and measures the error in lateral position of the measurement reference face. The measured error is then algebraically summed with the programmed lateral positions of the cam lobes/plain diameters and work support diameters taken from the component drawing so correcting any possible error in lateral position.

The angle of inclination of each cam lobe or plain diameter is used automatically to swivel the grinding wheel axis of rotation about a vertical axis to the specified angle before each grind so that the specified surface incline is achieved on the finished component.

The cam profile data is used to grind non-round shapes at the specified angular positions.

Claims

A grinding machine having a worktable and a grinding wheel (38) relative to which the worktable is movable, the worktable carrying firstly a headstock (30) and tailstock (32) adjustable in spacing and secondly an adjustable workrest (26), at least one of the headstock (30) and tailstock (32) and additionally the workrest (26) being adjustable relative to the worktable, characterised in that the relative movements and adjustments are computer controlled independently of the relative position of the grinding wheel (38) and worktable by programmable drive means programmed at least in part with respect to a lateral reference (18), which serves to determine the relative position of the grinding wheel (38) and the worktable in a direction parallel to an axis extending between the headstock (30) and the tailstock (32), thereby to position the headstock (30) and/or the tailstock and/or the workrest (26), enabling different workpieces (24) and parts thereof to be positioned in their precise position in front of the grinding wheel (38) for grinding.
A grinding machine according to claim 1, in which the computer (16) is programmed with positional and dimensional information relating to the workpiece (24) and parts thereof to be ground.
A grinding machine according to any one preceding claim, in which said lateral reference is provided by a probe (18) adapted to be relatively movable towards and away from the workpiece (24) and in a direction parallel to the axis of the workpiece (24) in order to enable a part of the workpiece (24) to be located by said probe (18).
A grinding machine according to any one preceding claim, in which the computer (16) utilises the relative lateral positions of radial faces (20) of the workpiece (24) automatically to position the worktable so that parts to be ground are sequentially located for grinding by the grinding wheel (38).
A grinding machine according to any one preceding claim, in which the computer (16) utilises information relating to the length of a workpiece (24) automatically to position the tailstock (32) relative to the worktable.
A grinding machine according to any one preceding claim, in which the computer (16) utilises workpiece (24) diameter information automatically to position one or more workrests (26) relative to the worktable.
A grinding machine according to any one preceding claim, in which the axis of the grinding wheel (38) can be swivelled under control of the computer (16) for the inclined grinding of the workpiece (24).