GB2154163A

GB2154163A - Cylindrical grinding machine having position detection probe

Info

Publication number: GB2154163A
Application number: GB08502965A
Authority: GB
Inventors: Alan Chalmers Stephen; John Noel Tittle
Original assignee: TI MATRIX Ltd
Current assignee: TI MATRIX Ltd
Priority date: 1984-02-14
Filing date: 1985-02-06
Publication date: 1985-09-04
Also published as: DE3504944A1; GB8403877D0; GB8502965D0

Abstract

A positioning probe 25, for a cylindrical grinding machine is mounted relative to the grinding wheel 18 for movement in directions axially and radially relative to the workpiece 14, with the grinding wheel, said probe 25 being mounted on a pivotable arm 26 so as to be movable between an operable position in which it may be moved into radial overlap with a radially extending portion of the workpiece 14 and a retracted position in which it will be radially clear of the workpiece during a grinding operation, so that in its operable position it may be moved into engagement with a datum point (shoulder) on the workpiece by relative movement of the grinding wheel and workpiece. The probe may also be used to determine radial dimensions of the workpiece at desired locations along the workpiece. <IMAGE>

Description

SPECIFICATION Cylindrical grinding machine This invention relates to cylindrical grinding machines and in particular a probe for positioning the grinding wheel relative to a workpiece.

With numerical controlled (NC) or computer numerical controlled (CNC) grinding machines it is necessary to accurately position the grinding wheel relative to the workpiece before the programmed grinding operation is commenced. There is no problem in positioning the grinding wheel axially and radially with respect to the worktable. However, the centre depth on the workpiece is not normally accurately controlled and consequently it is probable that there will be some axial misalignment between shoulders on the workpiece and the grinding wheel. It is consequently necessary to either measure the misalignment of shoulders on the workpiece, so that the position of the workpiece relative to the grinding wheel may be corrected before the shoulders are ground or reposition the workpiece relative to the worktable.

According to one aspect of the present invention a cylindrical grinding machine comprises a worktable on which a workpiece may be mounted and rotated about an axis, and a grinding wheel; means being provided for movement of the grinding wheel relative to the workpiece, separately in two directions, one direction parallel to the axis of rotation of the workpiece and the other direction having at least a component perpendicular to the axis of rotation of the workpiece; programmable means are provided to control relative movement of the grinding wheel and workpiece in each direction relative to a programmed starting point; a probe is mounted for movement with the grinding wheel, said probe being movable between an operable position in which it may be moved into radial overlap with a radially extending portion of the workpiece, and a retracted position in which it will be radially clear of the workpiece during a grinding operation, so that in its operable position it may be moved into engagement with a datum point on the workpiece by relative movement of the grinding wheel and workpiece, to determine the location of the datum point and correct for any axial misalignment of the workpiece.

The means to the control the movement of the grinding wheel relative to the workpiece, in two directions may conveniently be numerically programmed drives which control the velocity and positioning for each direction. This means may permit separate movement in each direction for the purpose of probing the workpiece and separate or simultaneous movement for the main grinding operation, so that the diameters and shoulders of the workpiece may be ground in a single cycle.

The correction for any axial misalignment of the workpiece may be achieved by re-positioning the workpiece relative to the programmed starting point. Alternatively, the control programme may be updated to take account of the misalignment.

The probe used in the present invention may conveniently be a contact sensing probe, which produces a signal the instant the probe touches the workpiece. With this form of probe, the probe will initially be moved from a programmed starting point, radially relative to the workpiece until it is aligned with a datum point on a radial surface of a shoulder of the workpiece. The probe will then be moved axially relative to the workpiece under the control of the numerical programme until it contacts the datum point. In this manner the location of the datum point may be determined and correction made for any misalignment of the workpiece.

Alternatively, an analog probe which produces a signal proportional to the degree of deflection of the probe, may be used.

With this form of probe, the grinding wheel will be moved relative to the workpiece to a preprogrammed position in which the probe is in contact with a datum point on a radial surface of the workpiece. The analog signal from the probe would then provide a measure of any axial misalignment of the workpiece.

The probes used in the present invention are intended primarily for measuring axial misalignment of the workpiece. These probes must consequently be arranged to operate in the direction of the axis of rotation of the workpiece. However, as a single axis probe would require accurate alignment with the workpiece, it is convenient to use multi-axial probes.

In addition to measuring axial misalignment of the work piece, if the probe functions in the radial direction as well as axial direction, the apparatus according to the present invention may also be used to measure radial dimensions at positions along the workpiece. By measuring such dimensions at various locations and comparing them with theoretical values, the apparatus may also be used to ensure that the correct workpiece has been loaded or that the workpiece has been loaded the correct way round. As a further aid to workpiece recognition or to establish further datum points, the endwise positioning operation may also be carried out at various locations, where there are several shoulders on the workpiece.

The probe is preferably mounted on an arm which is pivoted to the wheelhead. This arm may thus be pivoted to move the probe from the retracted to the operable position and vice versa, by suitable means, for example a hydraulic ram. The means for moving the probe between its operable and retracted position may conveniently be controlled by the numerical programme and thus the endwise positioning operation or operations and workpiece recognition operation if used, may be included at the start of each grinding operation.

An embodiment of the invention is now described, by way of example, with reference to the accompanying drawings, in which Figure 1 shows a partial plan view of a cylindrical grinding machine formed in accordance with the present invention; and Figure 2 shows a sectional end elevation of the probe assembly used in the machine illustrated in Figure 1.

The cylindrical grinding machine illustrated in the accompanying drawings comprises a worktable 10 having a headstock 11 and tailstock 12 mounted thereon. The headstock 11 and tailstock 12 are provided with centres 13 between which a workpiece 14 may be mounted. The headstock 11 is provided with a driving ring 15 having a spigot 16 which engages a ring 17 clamped to the workpiece 14, by which the workpiece 14 may be rotated.

The worktable 10 is mounted on slides (not shown) which move along a track (not shown) running parallel to the longitudinal axis of the workpiece 14 when it is supported between the centres 13. A grinding wheel 18 is mounted upon a slide 19 which moves along a track 20, this track 20 being transverse to the longitudinal axis of the workpiece 14 when it is supported between the centres 13. The grinding wheel 18 is mounted on the slide 19, so that it rotates in a plane inclined to the axis of rotation of the workpiece 14.The edge of the grinding wheel 18 is dressed so as to provide adjacent surfaces 21 and 22, at right angles to one another, one surface 21 being parallel to the longitudinal axis of the wforkpiece 14 and the other surface 22 being perpencicular to the longitudinal axis of the workpiece 14.

Separate drive means (i'oL shown) are provided for the slides supportin' lis worktable 10 and the slide 19, so that relative ongitudinal movement and transverse movermei. of the grinding wheel 18 and workpiece 14 may 133 controlled separately.

Each of the drive means is controlled numerically in known manner, so thai ."e slides supporting the worktable 10 and slide 19 may be moved either individually or simuìtaneously.

A touch sensitive probe 25 is mounted upon an arm 26 which is pivotail- secured to the wheelhead 27 so as to permit movement of the arm 26 in a vertical plane. A double acting ram 28 is mounted between the wheelhead 27 and arm 26, for movement of the arm 26 beqa.^lGcn a position (shown in broken line in Figure 2. in which the probe 25 is retracted and a position (shown in full line in Figure 2) in which the arm 2u abutts a stop 29 and the probe is in an operable position. Actuation of the ram 28 to move the probe 25 from its retracted to its operable position and vice versa, is controlled by the same system controlling movement of the slides upon which the grinding wheel 18 and worktable 10 are mounted.

The touch sensitive probe 25 is provided with a stylus 30 which is mounted so that it is free to deflect in all directions and also move axially. Means is provided in the probe 25 to detect any such movement of the stylus 30 and provide a signal the instant the stylus 30 moves.

In a typical grinding operation, the workpiece 14 is loaded between the centres 13 of the headstock 11 and the tailstock 12. Under the control of a numerical programme, the probe 25 is then moved to its operable position as indicated in Figure 1 and in full line in Figure 2, so that the stylus 30 is forward of the cutting edge of the grinding wheel 18. In this position, the coordinates of the head of the stylus 30 are fixed according to the programme. Again, under the control of the programme, the slide 19 is driven to move the wheelhead 27 and probe 25 radially towards the workpiece 14, until it is within the radius of the large diameter portion 31 of the workpiece 14 but clear of the adjacent smaller diameter portion.The programme then drives the slide supporting the worktable 10, so that the workpiece 14 moves axially to a programmed position at which point the axial speed is reduced until the shoulder of the large diameter portion 31 engages the stylus 30.

The instant the stylus 30 touches the shoulder of the workpiece 14, a signal is produced thus indicating to the control system the exact position of the workpiece 14. Alternatively, in order to achieve rapid positioning of the stylus 30, the worktable 10 may initially be driven to provide a fast approach so that when the stylus 30 touches the shoulder there will be some overrun before the signal from the probe 25 can stop movement of the workpiece 14. The workpiece 14 is then backed off until it is clear of the stylus 30 and a final slow approach may be made to accurately locate the stylus 30 on the workpiece 14.

The control system can thus determine the location of the shoulder relative to the programmed starting point and the position of the workpiece 14 corrected by updating the programmed position of the worktable 10 by an appropriate amount to allow for any misalignment. Finally, the probe 25 is moved to its retracted position as shown in broken line in Figure 2 where it is clear of the cutting surfaces of the grinding wheel 18 and the grinding process can commence.

The apparatus as described above may also be used to check the radial dimensions of the workpiece 14 at various points along its length. This may be achieved by moving the workpiece axially relative to the probe 25, by means of the slide supporting worktable 10, until the probe 25 is in line with an appropriate location. The probe 25 may then be moved radially towards the workpiece 14, by moving the wheelhead 27 on slide 19 until the stylus 30 engages the cylindrical surface of the workpiece 14. The position of the surface relative to the programmed starting point of the probe 25 may thus be determined and the dimensions of the workpiece 14 at that location calculated. This operation may be repeated at various positions along the length of the workpiece 14. The dimensions thus measured may be compared against theoretical values, to ensure that the correct workpiece 14 has been loaded or that the workpiece 14 has been loaded the correct way round. This workpiece recognition procedure may again be carried out under the control of the numerical programme and may be included at the beginning of a grinding programme together with the endwise positioning procedure.

Various modifications may be made without departing from the invention. For example, instead of mounting the worktable 10 on slides so that it may be moved in the direction of the axis of the workpiece 14, the worktable 10 may be fixed and the slide 19 may be mounted on a subslide which per mits movement of the wheelhead 27 axially as well as radially of the workpiece. Also, while in the apparatus described above the grinding wheel 18 is arranged to move in a direction perpendicular to the axis of rotation of the workpiece 14, it may be arranged to move in a direction inclined to the axis of rotation of the workpiece 14.

Furthermore, the centres 13 may be movable axially with respect to the headstock 11 and tailstock 12 and movement of the workpiece 14 axially with respect to the probe 25 to bring the probe into contact with the datum point may be achieved by movement of the centres 13. This means may also be used to reposition the workpiece relative to the programmed starting position.

Also rather than mounting the probe on an arm so that it may be moved between its operable and retracted positions, the grinding wheel may be arranged so that it may be moved away from the workpiece to leave the probe in its operable position. For example, the probe and grinding wheel may be mounted together in fixed relationship and the wheelhead arranged so that the grinding wheel can be swung away from the workpiece and the probe brought towards the workpiece.

Claims

1. A cylindrical grinding machine comprising a worktable on which a workpiece may be mounted and rotated about an axis and a grinding wheel; means being provided for movement of the grinding wheel relative to the workpiece, separately in two directions, one direction parallel to the axis of rotation of the workpiece and the other direction having at least a component perpendicular to the axis of rotation of the workpiece; programmable means are provided to control relative movement of the grinding wheel and workpiece in each direction relative to a programmed starting point; a probe is mounted for movement with the grinding wheel, said probe being movable between an operable position in which it may be moved into a- dial overlap with radially extending portion of the workpiece and a retracted position in which it will be radially clear of the workpiece during a grinding operation, so that in its operable position it may be moved into engagement with a datum point on the workpiece by relative movement of the grinding wheel and workpiece, to determine the location of the datum point and correct for any axial misalignment of the workpiece.

2. A cylindrical grinding machine according to Claim 1 in which the probe is a contact sensing probe which produces a signal when the probe touches the workpiece.

3. A cylindrical grinding machine according to Claim 1 in which the probe is an analog probe which produces a signal proportional to the degree of deflection of the probe.

4. A cylindrical grinding machine according to any one of the preceding claims in which the probe produces a signal in response to deflection along an axis parallel to the axis of rotation of the workpiece.

5. A cylindrical grinding machine according to Claim 4 in which the probe is multi-axial.

6. A cylindrical grinding machine according to any one of Claims 4 or 5 in which the probe produces a signal in response to movement in the direction radially of the workpiece axis.

7. A cylindrical grinding machine according to any one of the preceding claims in which the probe is mounted for movement with the grinding wheel on an arm pivoted for movement towards or away from the workpiece, means being provided to move the arm so that the probe may be moved between its operable and retracted positions.

8. A cylindrical grinding machine according to any one of the preceding claims in which the programmable means is arranged to: a) move the grinding wheel and probe to a predetermined starting position relative to the worktable; b) move the grinding wheel and probe relatively from the staining position, radially towards the workpiece so that the probe in its operable position is spaced from the workpiece but is aligned axially with a datum point or a radial surface of a shoulder of the workpiece, and then c) traverse the grinding wheel relative to the worn piece parallel to its axis of rotation until the probe makes contact with the shoulder of the workpiece, at the datum point; so that the location of the datum point may be determined and corrections made for any misalignment of the workpiece.

9. A cylindrical grinding machine according to Claim 8 in which the starting position is adjusted relative to the workpiece to allow for any misalignment, before commencing a grinding operation on the workpiece.

10. A cylindrical grinding machine according to Claim 8 in which the grinding control programme is updated to allow for any misalignment of the workpiece.

11. A cylindrical grinding machine according to any one of the preceding claims in which the programmable means is arranged to: a) move the grinding wheel and probe to a pre determined starting position; b) move the grinding wheel and probe axially relative to the workpiece until the probe is radially opposite a required location; and then c) move the grinding wheel and probe radially relative to the workpiece until the probe, in its operable position, engages the surface of the workpiece; so that the dimension of the workpiece at that location may be determined.

12. A 'cylindrical grinding machine according to any one of the preceding claims in which the programmable means controls movement of the probe from its operable to its retracted position and vice versa.

13. A cylindrical grinding machine substantially as described herein with reference to, and as shown in, Figures 1 and 2 of the accompanying drawings.