GB2068791A - Chucks - Google Patents

Abstract

A chuck for a machine tool includes a body 10 with a number of jaws 11 movable in radial slots 13, movement of the jaws 11 being by means of respective lead screws 17 engageable with a drive mechanism incorporating a main clutch 52, 53 and the individual lead screws being engageable or disengageable with the drive mechanism main clutch through respective further clutches 31, 32, the main and further clutches being fluid pressure actuated. <IMAGE>

Description

SPECIFICATION Chucks This invention relates to chucks for machine tools, such as lathes and of the kind having a body on which are mounted, two, three, four or more jaws, which are connected to a driving mechanism whereby they may be moved in or out for the purpose of gripping a workpiece.

The movements of the jaws are carried out through respective lead screws, which may be individually actuated, or they may be capable of simultaneous actuation. Individual actuation enables the workpiece to be centred about the axis of rotation of the chuck, and it also enables non-symmetrical workpiece to be gripped. Chucks are conventionally either of the type in which the jaws can be moved individually or in which they are moved simultaneously.

The conventional arrangement of a chuck with individual jaw adjustment has means at the outer end of each lead screw for manual actuation, as by means of a spanner or key.

The operator will rotate the chuck from one position to the next making adjustments each time. The centering or other adjustment of the workpiece is, by this means, slow and furthermore adjustments must be followed by measurement at each stage. Manual adjustment moreover is not compatible with the automatic actuation of most other functions of modern machines.

Simultaneous actuation of the lead screws in an automatic chuck is carried out by a mechanical mechanism, which may be hydraulically actuated, such mechanism being usually housed in the centre of the chuck.

Since space in this area of a machine is very limited, it is desirable that such mechanisms are compact, within the limits set by the need for accessibility and assembly methods, as well as strength.

It is the object of this invention to provide a chuck for a machine tool in which individual or simultaneous adjustment of jaws can be conveniently carried out without the need for manual actuation and in which the mechanism for jaw actuation is compact.

According to the present invention a chuck for a machine tool comprises a body with a number of movable jaws thereon, movement of the jaws being controlled by respective lead screws, the lead screws being drivingly enga gable with a drive mechanism which incorporates a releasable main clutch, the lead screws being disconnectably engageable from said drive mechanism through respective further clutches and the drive mechanism including fluid pressure actuated means for selectively engaging and disengaging said drive mechanism main clutch and each of said further clutches.

Preferably the main clutch is situated between a drive motor and a bevel drive to the respective lead screws, the further clutches being situated between the bevel drive and said lead screws respectively.

Conveniently, positional sensing means are provided to sense the correct actuation at least of the main clutch.

Preferably also, the lead screws are engaged by nuts on which the jaws are carried, the lead screws being arranged to accommodate the whole of the possible travel of the respective jaws. This is therefore unusual on power operated chucks in that the jaws are usually adjustably mounted on shoes which are mounted for movement through relatively short travel lead screws.

Advantageously the adjustment of the jaws controls a device which is arranged to transmit signals related to the positions of the jaws.

By this means automatic trueing of a component, or part of a component, may be carried out, involving incremental adjustment of the jaws in turn. This is preferably carried out in accordance with a predetermined programme.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a rotary workpiece support having jaws arranged to be driven in accordance with the invention; Figure 2 is a plan view thereof; Figure 3 is an enlarged cross-sectional view of actuating mechanism for the jaws shown in Figs. 1 and 2; Figure 4 is a plan view of the mechanism shown in Fig. 3, Figure 5 is an end view on the arrow 5 in Fig. 4, Figure 6 is a cross-sectional view on the line 6-6 in Fig. 3, and Figure 7 is a cross-sectional view on the line 7-7 in Fig. 3.

The chuck assembly illustrated is intended for use on lathes or other machine tools having rotary work tables and in which workpieces are located and gripped by jaws adjustably mounted on the table. Selective actuation of the individual jaws or simultaneous operation thereof can be carried out and provision is made for automatic chuck operation in accordance with a predetermined programme.

Referring to Figs. 1 and 2 there is shown a work table in the form of a workpiece support disc member 10. Provision is made for rotating this workpiece support through gears.

These are not illustrated. On the face of the workpiece support 10 there are a number of slots which extend radially or chordally. Four of these slots which extend radially receive workpiece gripping jaws, two of which are shown in the drawings at 11 and 12 respectively. The slots for these are items 13 and 14 respectively. Each such slot is of inverted T shape to engage a correspondingly shaped foot of the jaw.

The remaining slots 15 in the face of the workpiece support 10 accommodate a lifting frame whereby workpieces may be loaded and unloaded on to the workpiece support. This assembly however forms no part of the present invention and is therefore omitted.

Each jaw 11, 12 has an integral lower internally threaded extension 16 forming an integral nut. Engaged within this nut is a lead screw 17.

To enclose the slot 13 or 14 to prevent entry of swarf and dirt into the region of the nut and lead screw 17, a flexible strip 18 is secured at its ends beyond the inner and outer extremities of the slot. As shown in Fig.

1 the jaw 11 has a hollow interior through which the strip 18 passes. Arcuate guides 19 and a bridge 21 within the jaw 11 guide the strip 18 as the jaw moves along the slot when the lead screw 17 is rotated. The arcuate guides 19 serve the purpose of guiding the raised portion of the strip 18 over the bridge 21 and then guiding the strip back again into the plane of the top of the slot 13.

The lead screw 17 is mounted by means of thrust and journal bearings in the workpiece support 10. At its outer end, thrust is accepted by discs 22 and radial loading is supported by means of the journal bearing 23. At said outer end the lead screw 17 has a square end 24 which is accommodated in a recess in the exterior of the workpiece support 10.

At its inner end the lead screw is supported against thrust loads by disc assembly 25 and radial loading is accommodated by the journal bearing 26. Between the bearing assembly and the inner end of the threaded portion of the lead screw, a pinion 27 is secured onto the lead screw.

The four radially extending lead screws are arranged to be driven by a bevel gear assembly in the centre of the workpiece support 10.

Pinions 27 on each of the lead screws engage respective gears 28 rotatably mounted on stub shafts 29. Each gear 28 has a set of dog teeth 31 engaging corresponding teeth 32 on a spool component 33. The dog teeth are axially presented but have inclined faces to assist inter-engagement by sliding of the spool component 33 along the stub shaft 29. The spool component is non-rotatably engaged on the stub shaft 29 by splines 34.

Also engaged on the splines on the stub shaft is a bevel gear 35.

There are four such bevel gears 35 associated with the lead screws 17 respectively and they mesh with a pair of bevel gears 36 mounted on a shaft 37 located in the centre of the workpiece support and co-axial therewith. The shaft 37 is keyed to a sleeve 38 which has four radial holes to accept bearings 39 for the respective inner ends of the stub shafts 29. Only the lower of the two bevel gears 36 transmits the drive, the upper one being provided for balancing inertia forces during starting and stopping of the rotation of the chuck.

The four clutches each formed by the interengagable teeth 31, 32 of the gear 28 and of the spool component 33 are actuated by respective sliding members 41. These are slidably mounted on short spindles 42 which are secured in the casing 43 housing the mechanism just described. Each sliding member 41 is spring loaded by spring means (not illustrated) in a direction to engage the teeth 32 with the teeth 31 on the gear 28. The spool component 33 has an annular groove in which is engaged a tooth formed on the sliding member 41.

To actuate the sliding members 41 there are four hydraulically controlled operating discs 44 respectively. Each such disc is mounted on a stem 45 carrying a piston 46 located within a cylinder 47 formed within a further housing 48. As shown in Fig. 1 there are two spring-loaded support posts 50 engaging the edge of the disc 44 at positions remote from the sliding member 41. The purpose of these is to prevent tilting of the disc in operation.

The discs 44 engage their respective sliding members 41 as shown in Fig. 1 in recesses in the underneath of the sliding member 41.

There are two such recesses, each having bevelled sides to engage the correspondingly bevelled sides of the disc 44, one recess 49 being longer than the other recess 51.

The lower of the two bevel gears 36 mounted on the centre shaft 37 has integral teeth 52 presented towards and engageable with teeth 53 on a part 54, shown particularly in Fig. 3, and non-rotatably mounted on the upper end of a shaft 55.

The actuating assembly shown in Fig. 3 includes provision for raising and lowering the whole of the upper part relatively to a fixed structure to engage and disengage the discs 44 with their respective sliding members and also the central drive through the teeth 52 and 53. This is accomplished hydraulically in a manner which will be described.

The part 54 is engaged on splines on the shaft 55 and is loaded by a compression spring 56 towards a position in which it can engage the teeth 52 on the bevel gear 36. An abutment ring 57 supports the spring 56 and is mounted on the inner race of a journal bearing 58 for the shaft 55. The teeth 53 are, as shown in Fig. 4, arcuate in form. There are two such teeth 53 engaging two teeth 52 of similar form.

Surrounding the housing 48 is a casing 59 within which the housing 48 is enclosed.

Columns 61 serve to raise and lower the whole assembly relative to fixed structure.

There are four columns as shown in Fig. 7 at eqi-angularly spaced positions and these are secured into the housing 48. At their lower ends the columns 61 are secured by nuts 62 to a ring 63. They also pass through a flanged ring 64 mounted on the top of the ring 63 and through respective washers 65.

The washers 65 engage the underneath of a part casing 66 of which the other part 67 engages the underneath of the casing 59.

Housed within the part casings 66, 67 is a reduction gear drive between the spindle 55 and a co-axial main drive spindle 68. To this main drive spindle is connected and electric motor 69 which is bolted to a sleeve 71 surrounded by a further sleeve 72. The latter sleeve, 72 is bolted into the part casing 66 by bolts 73.

The reduction gear drive system includes a gear 74 engaged on a splined lower end of the shaft 55. The gear 74 is journalled in bearings 75, 76 and meshes with a gear 77 on a short vertical shaft 78. On the lower end of this is mounted a gear 79 which, in turn, meshes with a gear 81 formed on the main drive spindle 68. The upper end of that spindle engages in a bearing 82 within the end of the gear 74 which is itself splined to the lower end of the shaft 55.

To the main drive spindle 68 below its integral gear 81 is fixed a gear 83 meshing with a small gear 84 on a short stub spindle 85 journalled at its upper end in the casing part 67 and at its lower end in the casing part 66. This spindle 85 carries a toothed disc 86 which is also shown in Fig. 6.

For convenience the reduction gear system just described may include two shafts 78 with gears 77 and 79 thereon running in parallel, this arrangement being generally indicated in Fig. 6.

The purpose of the disc 86 is to provide for electrical signals which indicate the positions of the lead screws. The disc 86 has ten teeth.

Adjacent to it are two proximity switches 87, 88 shown in Fig. 6 which provide electrical signals relating to the presence or absence of a tooth in front of the switch. The proximity switches provide different signals for approach and for exit of each tooth or each gap of the disc 86. The spacing of the switches 87, 88 is such that it is possible to produce forty signals providing recognition of the position of the disc. The disc is driven through the reduc ti/on gear system, the main clutch teeth 53, 52 the lead screw clutch teeth 32, 31 to the lead screws 17. The forty signals are produced with one revolution of the disc 86.

Each signal spacing is the equivalent of 1 /700th of the revolution of the lead screws 17. This is achieved by 5:1 ratio at the gear reduction system, giving the equivalent of 200 pulses. The 7:1 drive of the lead screws is reduced to 3.5:1 between the bevel gear 36 and the gear 27 on the lead screws, giving 200 X 3.5 = 700 pulses for each rotation of the lead screws. It is thus possible to produce a signal at the proximity switches indicative of each 1 /700th of a revolution of the lead screws 17 or each of them.

To raise and lower the assembly comprising the housing 48 and its contents, the casing 59, the pillars 61, the part casings 66, 67 and their internal mechanisms and the rings 63 and 64 there is hydraulic supply to chambers defined between the rings 63, 64 and the sleeve 72. These chambers are annular and are defined in Fig. 3 by numerals 89 and 91. These are fed through drillings 92, 93 which are supplied through an external connection 94. On an end plate 95 are valves 96 which control supply of hydraulic fluid preferably it is from the same source to the interiors of the columns 61. Fig. 3 shows a drilling 97 forming one of the entry ports into the interior of the column 61. This feeds into the inner tube of such column 61. An annular space between said inner tube and the exterior of the column is fed by a further drilling 98 communicating with the valve 96.

At the other end the inner and outer tubular spaces formed by the pillar 61 feed into drillings 99, 101 in the housing 48 and thence into the cylinder 47 for actuating the operating discs 44. The motor 69 may also be hydraulically operated in place of the electric motor previously referred to.

In order to actuate the jaws of the chuck it is necessary to engage the drive from the motor 69 to the lead screws 17. It may be desired to actuate all the lead screw simultaneously or individually. In order to connect the main drive the teeth 53 on the part 54 must first be engaged with the teeth 52 on the lower of the larger central bevel gears 36.

This is accomplished by providing pressurised supply into the drilling 93 and at the same time permitting exhaust from the drilling 92.

The whole assembly within the casing parts 66, 67 and the casing 59 will be lifted and this will have the effect of allowing engagement of the teeth 52 and 53 to take place.

However, if they are not aligned so as to be capable of meshing, the part 54 is pressed back against its spring 56. Rotation of the main shaft 55 will take the part 54 to a position in which the teeth will engage. In order to check the correct actuation of these mechanisms, there is a proximity switch 102 in the upper flange of the casing 59. When this reaches a position close to a bolt head 103 on the housing 43 an appropriate signal will be transmitted through the line 104 to a control device (not shown). If, however, the teeth are not in engagement, a further proximity switch 105 shown in Fig. 4 will fail to provide an appropriate signal. This signal will, however, be transmitted when the teeth become engaged.

Simultaneously with engagement or at tempted engagement of the teeth 52, 53, the operating discs 44 will rise into engagement with the recesses 49 or 51 in the sliding members 41 respectively. The sliding members 41 are spring loaded towards engagement between the teeth 31, 32 but are hydraulically disengaged by appropriate entry of hydraulic fluid from the drillings 99, 101 into the cylinders 47. A still further proximity switch 106 will provide a signal when the operating discs 44 are in positions for engagement between the teeth 31, 32.

It is therefore possible to select which one or more of the discs 44 is actuated to engage the teeth for the appropriate lead screw 17.

The control for actuation of the discs may incorporate a means for producing a sequence of movements of the respective jaws in turn, for the purpose of trueing the jaws with respect to a component to be gripped.

Different levels of gripping may be achieved for example for strong or weak workpieces by application of appropriate hydraulic pressure.

Conveniently two levels of gripping force may be available.

For a non-circular or unsymmetrical workpiece it is possible to bring the jaws into appropriate positions for clamping either in accordance with a predetermined programme or under manual control through the hydraulic apparatus.

The chuck described is therefore capable of individual jaw movement either under manual or under predetermined programme control.

Alternatively, the jaws may be brought in for gripping simultaneously under manual control of the hydraulics of automatically in accordance with the programme.

Claims (14)

1. A chuck for a machine tool comprising a body with a number of movable jaws thereon, movement of the jaws being controlled by respective lead screws, the lead screws being drivingly engageable with a drive mechanism which incorporates a releaseable main clutch, the lead screws being disconnectably engageable from said drive mechanism through respective further clutches and the drive mechanism including fluid pressure actuated means for selectively engaging and disengaging said drive mechanism main clutch and each of said further clutches.

2. A chuck as claimed in claim 1 wherein the drive mechanism includes a drive motor which is drivingly connectible with the lead screws through said main clutch and bevel drives between the main clutch and the further clutches, through which the lead screws are drivable.

3. A chuck as claimed in claim 1 or claim 2 in which the main and said further clutches are dog type clutches and are actuated by fluid under pressure.

4. A chuck as claimed in any one of the preceding claims in which positional sensing means are provided to sense the positions of parts of the main clutch in order to establish whether correct engagement thereof has taken place.

5. A chuck as claimed in claim 4 wherein said positional sensing means includes a proximity switch and means for receiving a signal therefrom, in accordance with the positions of said parts of the clutch.

6. A chuck as claimed in any one of the preceding claims wherein the main clutch includes a movable assembly, on which actuators for the further clutches are mounted, the further clutches being spring loaded into en- ' gagement and the actuators being arranged to actuate said clutches to disengage them respectively.

7. A chuck as claimed in claim 6 wherein each of the actuators for the further clutches comprises a fluid pressure actuated member arranged, upon movement of said movable assembly, engages with a spring loaded slidable member, sliding movement of which operates the clutch.

8. A chuck as claimed in any one of the preceding claims wherein the lead screws are engaged by respective nuts on which the respective jaws are carried.

9. A chuck as claimed in claim 8 which, for each jaw a flexible strip is slidably engaged in the jaw and serves to close a slot in the body along which the jaw can move, upon rotation of the lead screw.

10. A chuck as claimed in any one of the preceding claims wherein a device provides a signal related to the positions of the jaws relatively to the body, by means of the rotational position of the lead screw.

11. A chuck as claimed in claim 10 wherein said device is a slotted wheel, adjacent to which are two proximity switches, the slotted wheel being connectable, through step down gearing with the lead screws respectively.

12. A chuck as claimed in any one of the preceding claims including means for carrying out incremental adjustments to the lead screws in turn, to adjust the jaws individually.

13. A chuck as claimed in claim 12 wherein the incremental adjustments of the lead screws is carried out according to a predetermined programme, for trueing a workpiece in the chuck.

14. A chuck for a machine tool substantially as hereinbefore described with reference to and as shown in the accompanying drawings.