GB2067931A - Chucks - Google Patents

Abstract

A self-centering chuck for machine tools such as lathes includes jaw members (3) opened and closed by an electric motor (10-11) associated with an epicyclical reducing unit (19-20-21) which acts via a rotating nut (22) and rotationally fixed but axially moving screwsleeve (25) to operate wedge means (6a, 33) and radially move the jaws (3). The clamping force or torque on the workpiece, or bar, is obtained from the torque provided by the locked-rotor motor and is transmitted to the clamping jaws (3) by means of elastic means (27-28-29) disposed between the nut (25) and cylindrical wedge member 32, the value of the clamping force being held constant by means of an electromagnetic brake (14-15-16) acting on the rotor as this latter has achieved the desired clamping torque or by means of mechanical torque limiting means. <IMAGE>

Description

SPECIFICATION Controlled clamping electrically operated selfcentering chuck for tool machines The present invention relates to a self-centering chuck for supporting the workpiece in tool machines, in which the clamping of the workpiece is electrically obtained and is held constant by elastic or resilient means.

Well known are the difficulties associated to the use of electrically driven self-centering chuck units for holding the workpieces in tool machines or the like. For example, in the case of lathes with bar passage into the mandrel, in which the mandrel closing and opening movements are to be carried out automatically, it occurs that, in the known types of self-centering units, the workpiece clamping pressure cannot be adjusted depending on the strength of the workpiece itself and it does not remain constant during the workpiece machining, thereby slip sometimes occurs during important cutting operations, with consequent losses of reference marks on the workpiece or waste.

Thus, the tool machine has to be continuously monitored, with related servicing by the operator, and a great increase of the production costs and the overall machining time.

Accordingly the present invention sets out to eliminate the thereinabove mentioned drawbacks, by providing a self-centering chuck effective to permit the workpiece clamping pressure to be easily adjusted and maintained constant through the overall machining of the workpiece.

According to one aspect of the present invention, there is provided a self-centering chuck, in which the clamping chuck members are electrically driven for closing to clamp the workpiece and opening to release said workpiece, characterized in that it comprises an inner electric motor the rotor whereof is rigid with the gear train holder of an epicyclical coaxial reducing unit, said train-holder rotatably supporting planetary gears, consisting of elongated gears, which simultaneously mesh with two end parallel coaxial wheels, one whereof being fixed and rigid with the gear box of said self-centering chuck, the coupling of said fixed wheel to said check gear box being of a direct type or through the interposition of adjusting holding means, and the other whereof is effective to rotate and rigid with a nut screw, said nut screw extending coaxially and being effective to rotate and restrained from translating, said nut screw being coupled to a sleeve type of screw effective to be axially moved and restrained from rotating, said screw being coupled, by means of resilient interposed means, to an axially sliding cylindrical member provided with wedge-like portions, effective to act upon radially sliding clamping elements, said clamping elements being rigid with said clamping chuck members for supporting the workpiece, the clamping force, as determined by the maximum torque produced by said rotor, being effective to be limited and adjusted by electric and mechanic means thereby obtaining the desired clamping on said workpiece.

According to a further aspect of the present invention said electric means for adjusting the clamping force of said clamping elements on the workpiece act on the supply voltage value and this latter may be preset in such a way that a comparator element cuts off said supply voltage as a predetermined threshold value is exceeded, thereby ending the movement. Furthermore, that same rotor is associated with an electromagnetic type of brake, preferably of the tooth arrangement or the like, effective to lock at the reached torque the rotor thereby holding constant the torque during the overall machining operation of the workpiece. Said brake is driven on or off, respectively, as the rotor stops and at the starting of the clamping movement, in association with the related electric controls.

According to yet another aspect of the present invention, as the rotor is rotated, also the gear train holder rigid therewith and the planetary gears mounted on said train holder are rotated; however, since the planetary gears mesh, on one side thereof, with a fixed end wheel (rigid with the self-centering chuck gear box) they will rotate, by means of the other side whereof, the movable end wheel, rigid with said nut screw, of different tooth number. Accordingly said sleeve screw is axially moved which, in turn, acts on the workpiece clamping members, through interposed resilient means and sliding elements.

At the predetermined clamping torque, the rotor stops and, at this same time, said electromagnetic brake locks the rotor, and hence the pressing on the resilient or elastic means, at the reached value, while the clamping force, as transmitted to the clamping members by said resilient means, may automatically fit the conditions of the workpiece, in such a way as to allow for the elastic variations required thereby.

As thereinabove indicated, the clamping or locking torque provided by the motor and hence, through the interposed resilient means, the clamping force of said clamping elements, may be adjusted in its value by providing an electric comparator circuit, of any known types, the operating voltage whereof may be changed in any known ways, thereby, by indicating or displaying this operating voltage on a display graduated device or the like, it is possible to directly read the clamping force on the clamping elements on the workpiece.

According to a further aspect of the present invention, the supply to the electric motor is provided through the mandrel itself by means of slip rings which are actuated only-as the workpiece clamping chuck members are driven to open or close, whereas said slip rings do not operate during the machining of the workpiece, since, as thereinabove stated, the clamping force exerted on the workpiece is a predetermined one and furthermore it is held constant by the locking of the rotor.

As a variation, it is provided for adjusting the clamping force on the workpiece by mechanical means, by acting through a torque limiting device on the end wheel of the reducing unit, which wheel would be a fixed one. In this case this end wheel is coupled to the self-centering chuck box by means of said limiting device which may consist, for example, by balls engaged with conical recesses and pressed by adjustable spring members, in such a way that, as the predetermined torque is exceeded, said balls are ejected from the recesses thereof and the end wheel is then able of rotating thereby locking or stopping the other end wheel coupled to the nut screw and hence ending the pushing action of the related screw on resilient means.

Brief Description of the Drawings These and other characteristics will become more evident from the following detailed description of an embodiment of an electrically operated self-centering chuck, being illustrated in the accompanying drawings, where: Fig. 1 is an overall view of the self-centering chuck with the complete mandrel; Fig. 2 is an axial cross-section of a half of the self-centering chuck; Fig. 3 illustrates, on an enlarged scale, a detail of the current supplying circuit between the mandrel and the self-centering chuck; Fig. 4 illustrates an enlarged detail view illustrating the electrical radially extending contacts indicated at IV in fig. 1; Fig. 5 illustrates a variation of axially extending electric contacts, a) in the open position thereof, and b) in the closed position thereof.

Referring now to figure 1, it is an overall view illustrating the complete self-centering chuck or unit provided for a lathe head or any tool machines having a rotating head, and comprising the mandrel 1 , supported for carrying out its working rotating movement on an axle x-x thereon there is mounted, in any known ways, the self-centering chuck or unit, generally indicated at 2, and provided with radially moving clamping chuck members 3 which are to be simultaneously moved away from one another or brought together thereby maintaining an equal spacing from the pivoting axle x-x.

As it is shown in fig. 1, the mandrel is provided with an axially extending cylindrical hole 4, which extends through the overall length of said mandrel, to permit the workpiece to pass through, as this latter is of great length or continuous, such as a continuous bar or the like, and it is axially perforated through the thickness thereof by a hole 5 for the passage of the electric wires, as it will be described in a more detailed way thereinafter.

Referring now to fig. 2, it is a simplified axial cross-section of the sole self-centering chuck 2, the clamping chuck members 3 whereof are applied, in known way, to the chuck clamping elements 6, which clamping chuck members 3 have to be radially moved in both directions, as it is indicated by the Arrow A. The self-centering chuck 2 comprises a cylindrical outside box, generally indicated at 7 formed, for facilitating the mounting procedure, by several portions 7a, 7b, 7c, and held together by screws 8, and by an inner cylindrical body 9, provided with a front flange member 9a, as rigidly coupled, in a not shown known way, with the outside box 7. The box 7-inner cylindrical body 9 assembly is, as thereinabove mentioned, rigidly rotatively connected to the mandrel 1.

In the inside of the box 7 there is located, rigid therewith, the stator 10 of an electric motor, energized by the coil 1 Oa, and the rotor 11 thereof, rigidly mounted on a flanged ring 12, is able of rotating with respect to the cylindrical inner body 9, by means of revolving bearings 13 or the like. Said flanged ring 12, rigid with the rotor 11 is provided, on the flange portion thereof and axially, teeth 12a of known type, which are effective to mesh with corresponding teeth 14a of a disc 14 axially movable on the pins 15 and biassed against the flange 12 by a plurality of springs 1 5a, thereby the teeth 1 2a-1 4a normally mutually engage or mesh to make the rotor 11 rigid with the outside box 7.

An electromagnet forming coil 1 6 is located in front of the disc 14 in such a way that as said coil is energized it draws the disc 14 thereby causing the teeth 14a to move away from the teeth 12a rigid with the rotor and permitting said rotor to rotate.

Rigid with the rotor 11 there is provided a gear train holder 17 which, by means a set of pins 18 supports a set of elongated gears 19 to provide, jointly to two end gear wheels meshing with said gears 19, an epicyclical reducing unit. Said end wheels are formed by internal gears; the fixed end wheel, indicated at 20 is rigid with the portion 7b of the outside box 7 and the rotating end wheel, indicated at 21, is rigid with an inner cylinder 22 coaxially extending with respect to the x-x axis and rotatably supported with respect to the elements 7b-7c of the box 7, by means of thrust bearings 23-24 coaxially extending to the x-x axis.Said inner cylinder 22, forms, by being suitably threaded, a nut screw 22a for a screw 25 formed on a sleeve member 25a, provided, at one side whereof, with a shoulder 25b and, at the other side whereof, with a stop ring member 26, therebetween a plurality of elastic means 27-28-29 are located, placed between two flanged rings 30-31 which are axially restrained, with a clearance, on a cylindrical member 32 whereon two shoulders 32a-32b are formed, said cylindrical member terminating with a plurality of wedge-shaped portions, more specifically ofT-shape, slanted with respect to the x-x axis. Said cylindrical member 32 may axially slide according to the arrows B on the cylindrical inner body 9, within the limits of the radial movement of the parts connected thereto.

The T-shaped wedge like portion 33 of said cylindrical member 32 is inserted into a like slanted portion 6a, also having a T-shape, of a clamping element 6 guided through the box shaped body 7 by means of T-shaped guides 34, or the like, radially extending, thereby to each axial movement of the cylindrical member 32 there occurs a like radial movement, according to the corresponding direction, of the clamping element 6 and accordingly of the clamping chuck member connected thereto, or rigid therewith.

Referring now to fig. 3, there is represented a box-shaped body 7a which, on portions of the contour thereof, is provided with a plurality of insulating elements 35 on each whereof there is mounted a fixed contact member 36, parallelly extending with respect to the x-x axis and thereagainst a movable contact member 37 abuts which is biassed in this direction by the spring 38 and thereto the electric current is supplied by means of a strap 40 from a conductor wire 39 housed on the hole 5 of the mandrel 1. The movable contact 37 is mounted on an electrically insulating flange member 41 coaxial with the insulating members 35 and rigid with the mandrel 1, in such a way that each movable contact member 37 is located in front of the related fixed contact member 36 of the self-centering chuck.

In the embodiment of fig. 3, the conductor or wire 39 and the contact members 37-36 supply with electric current the coil or winding 1 Oa on the stator 10 of said electric motor by means of the wire or cable 36a.

Referring to fig. 4, there is represented the rear portion of the mandrel 1, thereon there are mounted a plurality of slip rings 42a-42b... 42n, located on an electrically insulating sleeve member 44 and connected by clamps 44a to the electric wires 39. On these rings there abut the front contact members 43a 43n of a contact assembly 45 effective to bring, in due time, the front contact members 43.... 43n against said slip rings .2.... 42n by means of a radial movement as carried out by electric, magnetic, hydraulic or the like means (not shown).

In figs. 5a-5b those same contact means, for the controls effective to cause the chuck parts to open, are axially located instead of radially, and they are formed by a plurality of disc-shaped collecting members 46a ..... . 46n, mounted on an electrically insulating sleeve 47 rigid with the mandrel 1 and connected by clamps 47a to the electric wires 39 leading to the movable contact 37 at the other end of the mandrel 1.

The disc-shaped collectors 46a-46n are effective to contact a plurality of asymmetrical blade contact members 48a-48n mounted on a sliding and rotating element 49 which, as it is shown in fig. Sb, by means of a rotation through 900 and an axial displacement as determined, for example by a cam slot 50 and a pin 51, or the like, causes said contact opening and closing movements to occur.

The operation is as follows: starting from the rest position whereat all of the elements are stopped and the front contact members .3.... 43n, or the asymmetrical blade contact members 48a-48n are raised with respect to the related rings thereby there is not supplied any currents. (Obviously electrical locks can be provided, not shown since they are of known type, effective to prevent said contact members from closing if the mandrel, and hence the chuck, are rotating.) More specifically the operator has to preliminarily set a limit for the short current to be supplied to the electric motor, said limit value corresponding to the maximum driving torque which can be obtained with the rotor tending to stop.

Upon having set this current maximum limit which, in a suitable Table, can be expressed directly in clamping Kf, the operator, by operating a known type of voltage controller (not shown) supplies with current the stator 10 thereby simultaneously energizing the electromagnet 16 of the tooth brake; thus the movable disc 14 is drawn or pulled and the teeth 14a are moved away from the teeth 12a rigid with the flanged ring 12 of the rotor.

Under these conditions, the rotor 11 is free of rotating, thereby entraining in its rotation the train holder 17 with the related elongated gears 19.

Due to the fact that these latter mesh with the fixed end wheel 20, the rotating end wheel 21, of different tooth number, will rotate entraining therewith the nut screw, which latter is free of rotating, being on the contrary restrained from axially moving, on the thrust bearings 23-24.

Accordingly the screw 25, being free of axially moving and being restrained from rotating, is axially displaced according to either direction of the other of the arrow C, thereby biassing the cup springs 27-28-29 by means of the shoulder 25b or 26, according to the movement direction, in the axial direction.

In turn, said springs 27-28-29, by resting against either one or the other of said shoulders 32a, 32b of the cylindrical member 32, push this latter in one direction or in the other, as it is indicated by the arrows B, thereby displacing the slanted portions 33 and hence the portions 6a associated thereto of the clamping elements 6, in the radial direction. Thus, the clamping chuck members 3, being rigid with the clamping elements 6 are biassed radially, according to the arrows A, to move closer or further to/from the x-x axis.

This movement brings said clamping chuck members to contact a workpiece, as gripped from the outside or the inside, to be machined. Upon having stopped the approaching movement, the operator, by actuating said voltage controller, causes the voltage to increase as far as to obtain the maximum set value thereof, thereby the rotor will continue to rotate as far as to stop at the corresponding predetermined maximum torque value.

The screw 25 will energize, by continuing its axial movement, the resilient means 27-28-29 and the related clamping elements connected thereto, with a clamping force corresponding to the locking motor torque, this latter being predetermined by the operator.

Said elastic or resilient means 27 and 29 are so designed as not to lock even with the maximum clamping torque which can be obtained with the electric motor provided for each self-centering chuck, thereby the clamping force of the clamping chuck members on the workpiece is exerted always under a resilient action thereby providing an efficient and calibrated gripping of the selfcentering chuck on the workpiece.

Simultaneously to the achieving of the maximum predetermined torque, a known type of current comparator (not shown) operates and disenergizes both the motor 10 and the electromagnet 16 of the tooth brake, thereby the movable disc 14 is pushed by the springs 15a to recover the locked condition of the rotor 11 and, accordingly, through the described kinematic system, the pushing on the resilient means 27, 28 and 29 and the clamping force of the clamping chuck members 3.

In the same time, the movable contacts 43a-n, 48a-n are moved away thereby the tool machine can be operated to carry out the provided machining operations.

According to the invention, the described selfcentering chuck may also be automatically driven, for example on digitally controlled tool machines and the like, in particular for turning operations starting from bar materials. In this case a card or tape or the like will be provided for controlling the tool machine, which latter can be preset for carrying out all of the movements thereinabove indicated, thereby eliminating, in this case, the approaching stroke of the clamping chuck members and only holding the maximum clamping torque on the clamping elements, as originally adjusted by the maximum voltage to be reached and the related current comparator.

To prevent the comparator device from accidentally operating due to current peaks, for example during the electric starting step, it may be possible to provide for the use of a suitable timer effective to momentarily disenergize said current comparator at the start of the operating cycle.

For opening the clamping elements the above operations are carried out in a reverse way, and in each case there is eliminated the double adjusting of the supply voltage to the electric motor and the operation of the current comparator, since they are not necessary.

Referring now to fig. 6, a variation is herein illustrated in which a mechanical type of torque limiting device is used thereby the maximum value of the clamping torque and hence of the force exerted by the clamping chuck members on the workpiece is adjusted by means of elastic or resilient friction means, or snap sliding means or the like.

In the example illustrated in fig. 6 the fixed end wheel 20, meshing with the planetary gears 19 formed by the elongated gears 19, and which was rigid with the box 7, is now rigid with a rotating sleeve 52, axially resting, at one side, on the thrust member 24 against the inner cylinder 22 and, at the other side, on the thrust member 53, against the fixed box 7, being restrained from rotating by one or more balls 54, as pressed in conical seats 55 by springs 56, adjustably preloaded by screws 57.

With this arrangement, as the train holder 17 is rotated, the elongated gears 19, by acting on the fixed end wheel 20 restrained from rotating, cause the end wheel 21 to rotate, as well as the inner cylinder 22, as far as the desired torque is obtained.

As the pressure against the plurality of balls 54, as produced by the preloaded spring 56, is exceeded by the ejection action from the seat 55 of said balls 54, the rotating sleeve 52 is caused, to rotate by the fixed end wheel 20 which, in this manner, is able of moving thereby stopping the movement of the other rotating end wheel 21, rigid with the inner cylinder 22.

The clamping axial pushings are equally transmitted to the box 7 through the thrust teeth, as in the preceding case, with the addition of the thrust member 53 thereinabove described. By adjusting the preloading of the spring 56 by means of the screw 57, it is thus possible to obtain the desired limiting on the clamping torque, in a mechanical way, owing to the ejection of the balls 54 from the seats whereof.

Upon having stopped the nut screw, the electric controls are disactuated, as thereinabove described.

According to the invention, moreover, the described self-centering chuck can be mounted on or removed from the mandrel without the necessity of carrying out any electrical connection operations, due to the elastic contact members 36-37 distributed all along the insulating flange 41 and so located as to assume the desired positions and connect the several electric portions by the slip rings 42a-42n or 46a-46n, for actuating said slip rings.

It should be noted that variations and modifications can be brought about to the device thereinabove described, without departing from the scope of the invention.

Claims (10)

1. A self-centering chuck, in which the clamping chuck members are electrically driven for closing to clamp the workpiece and opening to release said workpiece, characterized in that it comprises an inner electric motor the rotor whereof is rigid with the gear train holder of an epicyclical coaxial reducing unit, said train-holder rotatably supporting planetary gears, consisting of elongated gears, which simultaneously mesh with two end parallel coaxial wheels, one whereof being fixed and rigid with the gear box of said selfcentering chuck, the coupling of said fixed wheel to said chuck gear box being of a direct type or through the interposition of adjusting holding means, and the other whereof is effective to rotate and rigid with a nut screw, said nut screw extending coaxially and being effective to rotate and restrained from translating, said nut screw being coupled to a sleeve type of screw effective to be axially moved and restrained from rotating, said screw being coupled, by means of resilient interposed means, to an axially sliding cylindrical member provided with wedge-like portions, effective to act upon radially sliding clamping elements, said clamping elements being rigid with said clamping chuck members for supporting the workpiece, the clamping force, as determined by the maximum torque produced by said rotor, being effective to be limited and adjusted by electric and mechanic means thereby obtaining the desired clamping on said workpiece.

2. A self-centering chuck, according to claim 1, characterized in that said electric motor rotor is normally locked on the self-centering chuck gear box by a spring biassed electromagnetic brake, of the continuous engagement type, said brake being excluded only when said rotor is to be rotated for opening or closing said workpiece clamping chuck members.

3. A self-centering chuck according to claim 1, characterized in that said nut screw, being rotated by said planetary gears as said rotor is rotatably driven, rests against axial shoulders of the outside box by means of axial thrust bearings in such a way as to be able of rotating while being axially restrained.

4. A self-centering chuck, according to claim 1, characterized in that said screw associated with said nut screw is able of axially moving while being restrained from rotating and biasses, by two axially extending opposite shoulders, a plurality of coaxial resilient means resting at the other side whereof on said axially sliding cylindrical element the wedge-shaped portions thereof are of T-shape and act on corresponding portions of said clamping elements, as axially driven on said outside box, thereby, for each movement of said axially sliding element a radial movement occurs of said clamping elements and hence of said clamping chuck members.

5. A self-centering chuck, according to claim 4, characterized in that said resilient meons interposed between said screw and said cylindrical axially sliding element are effective to absorb or dampen the maximum axial thrust as produced by the rotation of said electric motor rotor and not to lock said rotor in order to permit a resilient adjusting of the clamping force on said workpiece.

6. A self-centering chuck, according to claim 1, characterized in that the electrical connections for supplying the inside elements are taken or derived from the chuck or mandrel and are transmitted by means of resilient contacts distributed on an insulating flange member opposite to the inner end of the self-centering chuck and rigid with said chuck or mandrel, said resilient contacts being provided at predetermined positions in such a way that, as the self-centering chuck is mounted on the mandrel, the related contacts are automatically closed.

7. A self-centering chuck according to claim 1, characterized in that the current supply to said self-centering chuck is made by contact assemblies and slip rings as located at the free end of the mandrel, said contact assemblies being in a normally open condition and being closed on the related slip rings only as the mandrel is at rest and said self-centering chuck is operated for opening or closing said clamping chuck members.

8. A self-centering chuck, according to claim 7, characterized in that said contact assemblies are effective to act, either radially or axially, on the related slip rings and to be operated or driven in any known ways in association with and prior to the drives to be imparted to said self-centering chuck.

9. A self-centering chuck, according to claim 1, characterized in that it comprises mechanical clamping torque limiting means, interposed between the first fixed end wheel meshing with said planetary gears and said outside box, said torque limiting means being effective to be adjusted from the outside and being formed by friction snap means or the like effective to yield as a predetermined torque is reached to permit said first end wheel to freely rotate and lock the other wheel associated with said clamping nut screw.

10. A self-centering chuck, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.