Workpiece guides

Description

[0001] This invention relates to workpiece guides particularly for use in machine tools such as grinding machines in which an elongate rotary workpiece is supported on an intermediate position in its length and/or at its end for a machining operation.

[0002] Presently most cam grinding machines utilise workpiece steady rests which have contact shoes which are either set at fixed position set to support a main bearing at the maximum outer diameter tolerance in which case smaller diameter bearings are loose in the steady rest while camshafts having over tolerance main bearings are marked due to excessive gripping pressure or two fixed tips may be provided with one spring loaded grip to ensure a clearance free support. However, as main journals may have diametral tolerances of 0.015 mm to 0.02 mm, whilst maintaining shake free support of the journal, the journal centre-line will vary by plus or minus 0.01 mm relative to the axis about which the cams are ground. Thus although the problem of excessive gripping pressure which can arise with a case of three fixed support points is overcome, another problem, that is supporting the journal off-centre from the correct centre-line is introduced.

[0003] US-A-4276723 discloses a steady rest for supporting a workpiece to be ground comprising three contact shoes which are simultaneously movable towards and away from the workpiece centre-line so that workpieces of varying diameter can be supported and maintained on a fixed centre-line of rotation. The top contact shoe is mounted for pivotal movement to a position clear of the work area to facilitate loading and unloading of the workpiece, one hydraulic operator being provided for pivoting the top contact shoe into and out of its operative position and a second operator being provided for moving the two lower non-pivoting contact shoes towards or away from a workpiece.

[0004] Whilst provision is made for adjusting the three point support to suit bearings of different diameters, no provision is made for ensuring that the supports hold the bearing on the required centre-line axis whilst at the same time avoiding excessive gripping pressure to the bearing.

[0005] GB-A-764493 also discloses a guide for supporting a rotary workpiece including a base with three jaw members movably mounted on the base to embrace and support a workpiece for rotation about a closing axis defined by the position of the jaw members. Drive means drivably connected to the three jaw members for moving the jaw members towards the closing axis thereof for closing the jaw members to grip a workpiece and for moving the jaw members away from the closing axis to release the jaw members by a predetermined amount. Whilst the jaw members are individually adjustable, no provision is made for adjusting the closing axis of the jaw members to suit the machine tool on which the guide is to be mounted.

[0006] This invention provides a workpiece guide for supporting a rotary workpiece on a machine tool for rotation about an axis of the machine tool comprising a base, three jaw members movably mounted on the base to embrace and support a workpiece for rotation about an axis defined by the closed positions of the jaw members, drive means drivably connected to the three jaw members for moving the jaw members toward the closing axis thereof for closing the jaw members to grip the workpiece and for moving the jaw members away from the closing axis to release the jaw members by a predetermined amount; wherein means are provided for the adjustment of the drive means and the jaw members drivably connected thereto as a unit relative to the base and transversely relative to the machine tool axis, to adjust the closing axis to coincide with the axis of the machine tool on which the guide is to be used whereby a workpiece supported by the guide may have the axis thereof made coincident with the machine tool axis whatever the workpiece diameter.

[0007] In one construction according to the invention the drive means for the jaw members may comprise a hub in which a drive shaft drivably connected to the jaw members is supported for rotation, the hub being mounted on the base for adjustment transversely to the shaft axis to adjust the closing axis of the jaw members and rotation of the shaft opening or closing the jaw members with respect to the axis according to the direction of rotation of the shaft.

[0008] More specifically the base may comprise a spaced pair of parallel walls having aligned apertures through which the hub extends with clearance to permit the hub to be adjusted radially in said apertures and releasable clamping means are provided for clamping the hub to each of the walls in a required position of adjustment of the closing access of the jaw members drivably connected to the shaft supported in the hub.

[0009] Further the adjustable clamping means for the hub may comprise two pairs of spaced collars encircling the hub, each pair of collars engaging opposite sides of a respective wall of the base and means being provided for clamping the collars to the wall to secure the hub in a required position of adjustment with respect to the walls. One collar of one of the pairs may be secured to the hub whereby clamping of collar to the respective sidewall of the base to secure the hub transversely with respect to the shaft axis extending through the hub also secures the hub in the axial direction.

[0010] In any of the preceding arrangements the drive shaft within the hub may include cam means and cam follower means may be mounted in the hub engageable with the cam means of the shaft and drivably connected to the jaw members to close and release the jaw members with rotation of the cam means by the shaft.

[0011] More specifically the hub may have three radial bores at spaced locations along its length, and the cam follower means. include three push rods, respectively contained in said bores for acting on the three jaw members and the rotary cam means comprise three annular cam surfaces provided on the shaft within the hub for engaging the three push rods respectively to displace the push rods and thereby the jaw members in accordance with the rotational position of the shaft and thereby to close and release the jaw members.

[0012] In any of the preceding arrangements the shaft may be drivably connected to a reversible stepper motor for rotating the shaft to open and close the jaw members.

[0013] The jaw members may be pivotally mounted about parallel axes on the base. For example, two of the jaw members may be mounted to rotate on a common axis and the third jaw member may be mounted to rotate about a further axis.

[0014] In a specific embodiment of the invention a carrier may be movably mounted on the base, the third jaw member being mounted on the carrier, and means are provided for locking the carrier in an operative position in which the third jaw member can embrace and support a workpiece with the other two jaw members and an inoperative position in which the third jaw member is disposed away from the first two jaw members to permit a workpiece to be removed laterally from between the jaw members or inserted between the jaw members. Further, the carrier may comprise an arm movably mounted on the base, the third jaw member being pivotally mounted on the arm, for movement towards and along the closing axis, and means are provided for displacing the arm with respect to the base to move the third jaw member between said operative and inoperative positions.

[0015] The following is a description of a specific embodiment of the invention, reference being made to the accompanying drawings in which:

Figure 1 is a side elevation of a workpiece guide taken from one side of the guide;

Figure 2 is a side elevation of a workpiece guide looking at the opposite side;

Figure 3 is a front elevation of the workpiece guide;

Figure 4 is a section on the line 4-4 on Figure 3;

Figure 5 is a section on the line 5-5 on Figure 4;

Figure 6 is a section on the line 6-6 on Figure 4; and

Figure 7 is a section on the line 7-7 on Figure 4.

[0016] The drawings illustrate a workpiece guide for a machine tool for supporting an elongate workpiece to be rotated at an intermediate position along the length of the workpiece and/or at an end of the workpiece to ensure that the workpiece axis coincides with the axis of rotation of the machine tool. The workpiece guide is, by way of example, particularly applicable to grinding machines for grinding the cam lobes on motor vehicle camshafts. Examples of such machines are described and illustrated in GB-A-1596635 and U.K. Patent Application No. 8217890.

[0017] Referring now to Figures 1 to 4 of the drawings, there is shown a workpiece guide for use on a machine tool having a bed formed with a slideway on which centres or chucks are mounted to support a workpiece for rotation about a fixed axis extending parallel to the slideway. The workpiece guide comprises a housing indicated generally by the reference numeral 10 to be mounted on the slideway of the machine tool bed. The fixed axis of rotation of the machine tool is indicated at 11 and the housing has an open front 12 from which three workpiece guides 13, 14 and 15 project to encircle the axis 11 and support a workpiece for rotation on the axis as described below.

[0018] The housing comprises a base member 16 to which two upstanding parallel side walls 17, 18 are attached. The housing is completed by a top wall 19 and rear walls 20, 21 and 22 all secured to the side walls by screws 23. The front side of the housing is left open as indicated above for the guide members 13 to 15 to project from.

[0019] In use the housing is mounted with the base member 16 on the upper surface of the slide of a machine tool bed which is not illustrated. The slideway is of dovetail cross-section and to lock the housing to the base the lower ends of the side walls 17, 18 at the front of the housing have downwardly projecting lugs 24 extending below the base-member 16 which are undercut as indicated at 25 on the sides thereof facing across the base to engage one side of the dovetail section slideway. The clamp 26 extends across the other side of the base member 16 and is undercut as indicated at 27 to engage the other side of the dovetail section slideway. The clamp 26 is secured to the base 16 by means of screw threaded studs 28 projecting from the base member 16 through the clamp 26 to receive nuts 29 for tightening the clamp 26 against the side of the slideway to lock the housing to the slideway.

[0020] Referring to Figure 7 of the drawings, the sidewalls 17, 18 of the housing are formed with oppositely facing coaxial circular apertures 30, 31, respectively. The inner sides of the side walls around the apertures 30, 31 are rebated as indicated at 32 and 33 respectively to receive annular plates 34, 35 respectively which project into the apertures 30, 31 and are secured in the rebates by set screws 36. A hollow cylindrical hub 37 extends through the annular plates 34, 35 with clearance between the outer surface of the hub and the inner peripheries of the plates to permit radial adjustment of the hub in the plates. One end of the hub located in the aperture in plate 17 is closed and is formed with an outwardly projecting integral flange 38 in the form of a collar which bears on one side of the annular plate 34. A separate collar 39 freely slidable along the hub engages the other side of the plate 34. Set screws 40 countersunk into the flange 38 extend through the flange, with clearance through openings 41 in the plate 34 and into screw threaded bores 42 in the collar 39. With the screws 40 slackened to release the clamping pressure of the flange 38 and collar 39 to the ring 34, the end of the hub can be adjusted radially with respect to the annular plate 34. The screws 40 can then be tightened to lock the end of the hub in the required position of adjustment. At the other end of the hub in the aperture in plate 35 two separate collars 39 encircle the hub on either side of plate 35 to support the hub radially and are locked together by screws 40 countersunk into the outer flange 39 and extending through openings 41 in the annular plate 35 into screw threaded bores 42 in the inner collar 39. Thus when the screws 40 are slackened, the hub can be adjusted radially in any direction as required and can then be locked into place by tightening the screws 40 to clamp the flange 38, collar 39 and annular plate 34 at one end of the hub together and to clamp the collar 39 and annular plate 35 at the other end of the hub together.

[0021] The hub 37 has a central bore 43 in which a shaft 44 is mounted on bearings 45 and 46. The shaft 44 has an enlarged diameter portion 47 and the inner races of the bearings 45, 46 are lodged against the shoulders at the ends of the enlarged diameter portion. The outer race of bearing 45 lies against the end of the bore 43 in the hub and the outer race of the bearing 46 is held in place by a sleeve 48 located in the hub and itself locked in place by an end cap 49 secured to the end of the hub by set screws 50. The end cap 49 has a central bore 51 through which the shaft 44 extends with clearance.

[0022] The end of the shaft 44 projecting from the end cap 49 carries a toothed pulley 52 secured in place by a screw 53. Set screws 50 also serve to secure an elongate plate 54 to the end cap, the plate extending to the rear of the housing. At the rear of the housing a stepper motor 55 is mounted on the plate 54 and has a toothed output pulley 56 with a tooth belt drive 57 to the tooth pulley 52 to rotate the shaft 44 as described later.

[0023] The enlarged portion 47 of the shaft 44 carries three annular eccentric cams 58, 59 and 60 locked to rotate with the shaft 44 by keys 61. The hub 37 encircling the eccentric cams 58 to 60 has three radial bushes 64 disposed at spaced locations around the hub and in line with the three respective cams and three push rods 64a are mounted in the respective bushes to bear against the three respective cam surfaces 58 to 60. Referring to Figures 4 and 6 of the drawings, the shaft 65 extends between and is mounted in bearings 66 secured in the side walls 17,18 of the housing. The shaft 65 supports a rocker arm 67 one end of which carries a pressure pad 68 which bears on the pushrod 64a acting on eccentric cam 58. The other end of the lever arm projects from the forward end of the housing and carries the guide element 15 secured to the arm by a set screw 69. The central part of the lever arm 67 around the shaft 65 is cut away as indicated at 70 in Figure 6 to provide a recess in which a further rocker arm 71 is pivotally mounted on the shaft 65 on a needle roller bearing 72. The rocker arm 71 extends upwardly from the arm 67 towards the front end of the housing and the guide element 14 is secured to one side of the arm by a set screw 73 to project from the forward side of the housing. The other side of the arm has a pressure pad 74 let into the arm against which the push rod 64a acting on the eccentric cam 59 bears. In the upper part of the housing a further lever arm 75 is pivotally mounted by means of needle roller bearings 76 on a spindle 77 supported at its ends in a double walled arm 78 one end of the arm 75 carries the guide element 13 secured thereto by set screw 79 and the other end of the arm has a pressure pad 80 let into the end of the arm which bears against a final pushrod 64a acting on the eccentric cam 60.

[0024] Each of the guide elements 13, 14 and 15 is provided with a small rectangular section steady tip 82 to engage the workpiece to be supported by the guide and by rotation of the shaft 44 and with it the eccentric cams 58 to 60, the guide elements are moved into engagement with the workpiece to support the workpiece for rotation about the axis 11 as will be described below. The radial position of the hub 37 in which the shaft 44 is supported is adjusted by slackening the clamping collars 39 securing the hub to the annular plates 34, 35. Adjustment of the shaft 44 enables the axis 11 to which the guide elements 13, 14 and 15 close to be adjusted for alignment with the axis of rotation of the machine tool.

[0025] The double arm 78 supporting the lever 75 is supported in the housing for movement between the operative position indicated in Figure 4 in a retracted position in which the lever arm 75 is retracted into the housing (as shown in Figure 1) to permit the workpiece to be located in or removed from the guide by a mechanism which will now be described. The double arm 78 is formed with a short L-section slot 85 in both parts of the arm in which a pin 86 is located. The ends of the pin locate in horizontal slots 87 formed in the side walls 17, 18 of the housing. The pin is thus constrained to slide horizontally in the slots in the housing. A pivotal link 88 is connected at one end to the pin 86 between the two parts of the arm 78 and the other end of the link is connected by a further pin 89 to an arcuate link 90 as shown in Figure 4 which extends downwardly through the housing behind the hub assembly 37. The lower end of the arm 90 is supported on a shaft 91 mounted in bearings 90a in the side walls 17 and 18 of the housing as shown in Figure 6. A pin 90b is mounted on the arcuate arm 90 approximately halfway down the arm and projects laterally of the arm through arcuate slot 92 in the side wall 17 of the housing. A pneumatic ram 93 is mounted on the side wall 17 of the housing towards the upper end thereof and acting in a downwardly inclined direction and the piston rod 94 of the ram is connected to the pin 90b on the arm 90. When the ram 93 is extended, the arcuate arm 90 is pressed towards the rear of the housing and, in so doing, retracts the lever arm 75 into the housing to allow a workpiece to be moved into or out of the position by engagement by the guide element. When the ram 93 is retracted, the arm 90 is drawn forwardly to extend the lever arm 75 into the operative position around the axis 11 to support a workpiece coaxial with the axis. When the ram 93 is initially extended to retract the arm 75 the pin 86 travels along the short horizontal part of the dog-leg slot 85 in the arm 78 without causing any movement of the arm 75. When the pin comes to the downwardly inclined section of the dog-leg slot the arm 78 starts to move with the pin and the arm is raised and retracted into the housing as the pin runs down the slot until it reaches the bottom of the slot when the ram is fully extended and the rocker arm 75 is raised and almost fully retracted into the housing as shown in Figure 1. Since the rocker arm 75 cannot retract until the pin 86 has reached the downwardly inclined section 85 of the dog-leg slot, the lever arm cannot be forced backwardly into the housing from its extended position by force alone on the lever arm itself. Thus, whatever load is applied to the lever arm, the arm will remain in its extended position until retracted by the pneumatic ram 93.

[0026] The workpiece guide is set up with a master component in the machine tool the axis of which coincides with the required degree of accuracy with the machine axis 11. The workpiece steady tips are then closed on to the master component with the fixing screws securing the hub 37 to the annular plates 34, 35 sufficiently slack to allow the hub to adjust automatically to the position required to hold the workpiece guides gripping the master component. The hub is then locked in position and the guide is then ready for use.

[0027] As indicated earlier, tha shaft 44 is driven by a stepper motor to contract and expand the workpiece guides 13, 14 and 15 around the workpiece to be supported in the guide. This enables the guide to be operated through an automatic cycle of the following steps initiated by operation of a cycle start button.

1. A solenoid valve operates to extend the ram 93 to advance arm 75 to the extended position.

1.1 By a switch or timer (allowing arm 75 to reach its extended position, the stepper motor is energised to advance 400 steps (equivalent to two full revolutions). 1.2 The steady tips 82 should contact the component and align it with the axis 11 and stall the stepper motor before 400 steps have been completed.

1.3 From its stall condition, the motor is reversed 10 steps to retract the steady tips slightly from the workpiece and allow a running clearance for the workpiece.

N.B. If the motor completes 400 steps then there is a "steady fault" which should be signalled and the machine cycle should be stopped at that point.

1.4 At completion of reversal, the motor is held stationary at maximum torque and should signal the start of rotation of the workhead of the workpiece and the start of the machining operation on the workpiece, e.g. a grinding cycle.

1.5 At the completion of the machining operation, the stepper motor is re-started in the reverse direction and run for -60 steps to retract the steady tips from the workpiece and the solenoid valve for the ram 93 is operated to retract the ram and thereby retract the upper rocker arm 75.

Claims

1. A workpiece guide for supporting a rotary workpiece on a machine tool for rotation about an axis (11) of the machine tool comprising a base, three jaw members (13,14,15) movably mounted on the base to embrace and support a workpiece for rotation about an axis defined by the closed positions of the jaw members, drive means (55 to 60) drivably connected to the three jaw members for moving the jaw members toward the closing axis thereof for closing the jaw members to grip the workpiece and for moving the jaw members away from the closing axis to release the jaw members by a predetermined amount;
characterised in that means (38, 39, 40) are provided for the adjustment of the drive means and the jaw members drivably connected thereto as a unit relative to the base and transversely relative to the machine tool axis (11), to adjust the closing axis to coincide with the axis of the machine tool on which the guide is to be used whereby a workpiece supported by the guide may have the axis thereof made coincident with the machine tool axis whatever the workpiece diameter.

2. A workpiece guide as claimed in Claim 1, characterised in that the drive means for the jaw members comprise a hub (37) in which a drive shaft (44) driveably connected to the jaw members is supported for rotation, the hub being mounted on the base for adjustment transversely to the shaft axis to adjust the closing axis of the jaw members and rotation of the shaft opening or closing the jaw members with respect to the axis according to the direction of rotation of the shaft.

3. A workpiece guide as claimed in Claim 2, characterised in that the base comprises a spaced pair of parallel walls (17, 18) having aligned apertures through which the hub (37) extends with clearance to permit the hub to be adjusted radially in said apertures and releasable clamping means (38, 39, 40) are provided for clamping the hub to each of the walls in a required position of adjustment of the closing access of the jaw members driveably connected to the shaft supported in the hub.

4. A workpiece guide as claimed in Claim 3, characterised in that the adjustable clamping means for the hub comprise two pairs of spaced collars (38, 39) encircling the hub, each pair of collars engaging opposite sides of a respective wall (34, 35) of the base and means (40) being provided for clamping the collars to the wall to secure the hub in a required position of adjustment with respect to the walls.

5. A workpiece guide as claimed in Claim 4, characterised in that in one collar (38) of one of the pairs is secured to the hub (37) whereby clamping of collar to the respective sidewall of the base to secure the hub transversely with respect to the shaft axis extending through the hub also secures the hub in the axial direction.

6. A workpiece guide as claimed in any of Claims 2 to 5, characterised in that the drive shaft (44) within the hub (37) includes cam means (58, 59, 60) and cam follower means (64a) are mounted in the hub engageable with the cam means of the shaft and driveably connected to the jaw members to close and release the jaw members with rotation of the cam means by the shaft.

7. A workpiece guide as claimed in Claim 6, characterised in that the hub (37) has three radial bores (64) at spaced locations along its length, and the cam follower means include three push rods, (64a) respectively contained in said bores for acting on the three jaw members (13, 14, 15) and the rotary cam means comprise three annular cam surfaces (58, 59, 60) provided on the shaft (44) within the hub for engaging the three push rods respectively to displace the push rods and thereby the jaw members in accordance with the rotational position of the shaft and thereby to close and release the jaw members.

8. A workpiece guide as claimed in any of the Claims 2to 7, characterised in that the shaft (44) is driveably connected to a reversible stepper motor (55) for rotating the shaft to open and close the jaw members.

9. A workpiece guide as claimed in any of claims 1 to 8, characterised in that jaw members (13, 14, 15) are pivotally mounted about parallel axes on the base (10).

10. A workpiece guide as claimed in claim 9, characterised in that two of the jaw members (14, 15) are mounted to rotate on a common axis and the third jaw member (13) is mounted to rotate about a further axis.

11. A workpiece guide as claimed in claim 10 characterised in that a carrier (78) is movably mounted on the base, the third jaw member (13) being mounted on the carrier, and means are provided for locking the carrier in an operative position in which the third jaw member can embrace and support a workpiece with the other two jaw members and an inoperative position in which the third jaw member is disposed away from the first two jaw members to permit a workpiece to be removed laterally from between the jaw members or inserted betweem the jaw members.

12. A workpiece guide as claimed in claim 11 wherein the carrier comprises an arm (78) moveably mounted on the base, the third jaw member (13) being pivotally mounted on the arm, for movement towards and along from the closing axis, and means (90, 93, 94) are provided for displacing the arm (78) with respect to the base to move the third jaw member (13) between said operative and inoperative positions.

13. A workpiece guide as claimed in claim 12, characterised in that the means for moving the arm comprises a double acting ram (93, 94).

14. A workpiece guide as claimed in any of the preceding claims, characterised in that the base (10) is provided with a clamp (24) for fixing the base to a work table of a machine tool.

Ansprüche

1. Werkstückführung zur Unterstützung eines sich drehenden Werkstückes auf einer Werkzeugmaschine zur Drehung um eine Achse (11) der Werkzeugmaschine mit einer Basis, drei beweglich auf der Basis befestigten Spannelementen (13, 14, 15) zum Umfassen.und Unterstützen eines Werkstückes zur Drehung um eine durch die geschlossenen Stellungen der Spannelemente definierte Achse, Antriebsmitteln (55-60), die antreibend mit den drei Spannelementen verbunden sind, zur Bewegung der Spannelemente in Richtung auf ihre Verschlußachse für das Schließen der Spannelemente zum Ergreifen des Werkstückes und für die Bewegung der Spannelemente von der Verschlußachse weg zum Freigeben der Spannelemente um einen vorgegebenen Betrag, dadurch gekennzeichnet, daß Mittel (38, 39, 40) vorgesehen sind für die Einstellung der Antriebsmittel und der antreibend mit ihnen verbundenen Spannelemente als eine Einheit, relativ zur Basis und quer relativ zu der Werkzeugmaschinenachse (11) zum Einstellen der Verschlußachse in Übereinstimmung mit der Achse der Werkzeugmaschine, auf der die Führung verwendet wird, wodurch die Achse eines durch die Führung unterstützten Werkstückes in Übereinstimmung mit der Werkzeugmaschinenachse gebracht werden kann, unabhängig vom Durchmesser des Werkstückes.

2. Werkstückführung nach Anspruch 1, dadurch gekennzeichnet, daß die Antriebsmittel für die Spannelemente eine Buchse (37) aufweisen, in der eine mit den Spannelementen antreibbar verbundene Antriebswelle (44) für eine Drehung gelagert ist, wobei die Buchse auf der Basis für eine Einstellung quer zur Wellenachse befestigt ist zum Einstellen der Verschlußachse der Spannelemente und wobei eine Drehung der Welle die Spannelemente bezüglich der Achse abhängig von der Drehrichtung der Welle öffnet oder schließt.

3. Werkstückführung nach Anspruch 2, dadurch gekennzeichnet, daß die Basis aufweist ein beabstandetes Paar von parallelen Wandungen (17, 18) mit fluchtenden Öffnungen, durch die sich die Buchse (37) mit Spiel erstreckt, so daß die Buchse radial in den Öffnungen eingestellt werden kann, und daß lösbare Klemmittel (38, 39, 40) vorgesehen sind zum Festklemmen der Buchse an jeder der Wandungen in einer erforderlichen Einstellposition für die Verschlußachse der antreibbar mit der in der Buchse gelagerten Welle verbundenen Spannelemente.

4. Werkstückführung nach Anspruch 3, dadurch gekennzeichnet, daß die einstellbaren Klemmmittel für die Buchse zwei Paare von beabstandeten Lochscheiben (38, 39) aufweisen, die die Buchse umfassen, wobei jedes Paar von Lochscheiben mit entgegengesetzten Seiten einer entsprechenden Wand (34, 35) der Basis in Eingriff steht, und Mittel (40) zum Festklemmen der Lochscheiben an der Wand vorgesehen sind zur Befestigung der Buchse in einer erforderlichen Einstell position bezüglich der Wand.

5. Werkstückführung nach Anspruch 4, dadurch gekennzeichnet, daß eine Lochscheibe (38) eines der Lochscheibenpaare an der Buchse (37) befestigt ist, wodurch das Festklemmen der Lochscheibe an der entsprechenden Seitenwand der Basis zum Sichern der Buchse in Querrichtung bezüglich der Achse der sich durch die Buchse erstreckenden Welle ebenso die Buchse in axialer Richtung sichert.

6. Werkstückführung nach einem der Ansprüche 2 bis 5, dadurch gekennzeichnet, daß die Antriebswelle (44) innerhalb der Buchse (37) Nokkenmittel (58, 59, 60) aufweist und daß nockenbetätigte Mittel (64a) in der Buchse befestigt sind, die in Eingriff bringbar sind mit den Nockenmitteln der Welle und die antreibbar mit den Spannelementen verbunden sind, zum Verschließen und Lösen der Spannelemente bei einer Drehung der Nockenmittel durch die Welle.

7. Werkstückführung nach Anspruch 6, dadurch gekennzeichnet, daß die Buchse (37) drei Radialbohrungen (64) an beabstandeten Positionen entlang ihrer Länge aufweist und daß die nockenbetätigten Mittel drei Stößelstangen (64a) aufweisen, die in den entsprechenden Bohrungen zur Wirkung auf die drei Spannelemente (13, 14, 15) aufgenommen sind, und daß die Drehnockenmittel drei ringförmige Nockenflächen (58, 59, 60) aufweisen, die auf der Welle (44) innerhalb der Buchse vorgesehen sind, zum Betätigen der entsprechenden drei Stößelstangen und zum Verschieben der Stößelstangen und damit der Spannelemente entsprechend der Drehstellung der Welle, wodurch die Spannelemente geschlossen bzw. gelöst werden.

8. Werkstückführung nach einem der Ansprüche 2 bis 7, dadurch gekennzeichnet, daß die Welle (44) antreibbar mit einem umkehrbaren Schrittmotor (55) verbunden ist, um die Welle für das Öffnen oder das Schließen der Spannelemente zu drehen.

9. Werkstückführung nach einem der Ansprüche 1 bis 8, dadurch gekennzeichnet, daß die Spannelemente (13,14,15) schwenkbar um parallele Achsen auf der Basis (10) befestigt sind.

10. Werkstückführung nach Anspruch 9, dadurch gekennzeichnet, daß zwei der Spannelemente (14, 15) zur Drehung um eine gemeinsame Achse befestigt sind und daß das dritte Spannelement (13) zur Drehung um eine weitere Achse befestigt ist.

11. Werkstückführung nach Anspruch 10, dadurch gekennzeichnet, daß ein Träger (78) bewegbar auf der Basis befestigt ist, wobei das dritte Spannelement(13) auf dem Träger befestigt ist, und daß Mittel vorgesehen sind zum Verriegeln des Trägers in einer Betriebsstellung, in der das dritte Spannelement mit den anderen beiden Spannelementen ein Werkstück umfassen und unterstützen kann, und einer Ruhestellung, in das dritte Spannelement von den ersten beiden Spannelementen entfernt angeordnet ist, so daß es möglich ist, ein Werkstück aus einer Position zwischen den Spannelementen seitlich zu entnehmen oder es zwischen die Spannelemente einzufügen.

12. Werkstückführung nach Anspruch 11, dadurch gekennzeichnet, daß der Träger einen bewegbar auf der Basis befestigten Arm (78) aufweist, wobei das dritte Spannelement (13) schwenkbar auf dem Arm befestigt ist für eine Bewegung in Richtung auf oder weg von der Verschlußachse, und daß Mittel (90,93,94) vorgesehen sind für eine Verschiebung des Armes (78) bezüglich der Basis zum Bewegen des dritten Spannelementes (13) zwischen der Betriebsstellung und der Ruhestellung.

13. Werkstückführung nach Anspruch 12, dadurch gekennzeichnet, daß die Mittel zur Bewegung des Armes einen doppelt wirkenden Kolben (93, 94) aufweisen.

14. Werkstückführung nach einem der vorstehenden Ansprüche, dadurch gekennzeichnet, daß die Basis (10) mit Klemmitteln (24) zum Befestigen der Basis an einem Arbeitstisch der Werkzeugmaschine versehen ist.

Revendications

1. Guide-pièce pour supporter une pièce tournante sur une machine-outil afin qu'elle tourne autour d'un axe (11) de la machine-outil comprenant un socle, trois mâchoires (13, 14, 15) montées mobiles sur le socle pour embrasser et supporter une pièce en vue de sa rotation autour d'un axe défini par les positions de fermeture des mâchoires, des moyens d'entraînement (55 à 60) accouplés aux trois mâchoires pour les déplacer vers leur axe de fermeture afin de les fermer pour qu'elles agrippent la pièce et pour écarter les mâchoires de l'axe de fermeture afin de les relâcher dans une mesure déterminée, caractérisé en ce que des moyens (38, 39, 40) sont prévus pour ajuster les moyens d'entraînement et les mâchoires qui leur sont accouplées d'un seul tenant par rapport au socle et transversalement par rapport à l'axe (11) de la machine-outil, afin d'amener par adjustement l'axe de fermeture à coïncider avec l'axe de la machine-outil sur laquelle le guide doit servir de façon que l'axe d'une pièce supportée par le guide puisse être amené à coïncider avec l'axe de la machine-outil quel que soit le diamètre de la pièce.

2. Guide-pièce selon la revendication 1, caractérisé en ce que les moyens d'entraînement des mâchoires comprennent un moyeu (37) dans lequel tourillonne un arbre menant (44) accouplé aux mâchoires, le moyen étant monté sur le socle en sorte qu'on puisse l'ajuster transversalement à l'axe de l'arbre pour ajuster l'axe de fermeture des mâchoires et la rotation de l'arbre ouvrant ou fermant les mâchoires par rapport à l'axe suivant le sens de rotation de l'arbre.

3. Guide-pièce selon la revendication 2, caractérisé en ce que le socle présente deux parois parallèles espacées (17, 18) présentant des trous alignés que le moyeu (37) traverse avec jeu afin qu'on puisse l'ajuster radialement dans lesdits tours et des moyens de cramponnement temporaire (38, 39, 40) sont prévus pour cramponner le moyeu sur chacune des parois en position voulue d'ajustement de l'accès de fermeture des mâchoire accouplées à l'arbre supporté dans le moyeu.

4. Guide-pièce selon la revendication 3, caractérisé en ce que les moyens de cramponnement réglable du moyeu comprennent deux paires de colliers espacés (38, 39) encerclant le moyeu, chaque paire de colliers portant contre des côtés opposés d'une paroi respective (34, 35) du socle et des moyens (40) étant prévus pour cramponner les colliers sur la paroi afin d'immobiliser le moyeu en position voulue d'adjustement par rapport aux parois.

5. Guide-pièce selon la revendication 4, caractérisé en ce qu'une des colliers (38) de l'une des paires est fixé au moyeu (37) de sorte qu'en cramponnant le collier sur la paroi latérale respective du socle pour immobiliser le moyeu transversalement par rapport à l'axe de l'arbre traversant le moyeu on immobilise aussi le moyeu axialement.

6. Guide-pièce selon l'une quelconque des revendications 2 à 5, caractérisé en ce que l'arbre menant (44) intérieur au moyeu (37) comporte des cames (58, 59, 60) et des moyens palpeurs (64a) montés dans le moyeu peuvent porter contre les cames de l'arbre et sont accouplés aux mâchoires pour les fermer et les relâcher du fait de la rotation imprimée aux cames par l'arbre.

7. Guide-pièce selon la revendication 6, caractérisé en ce que le moyeu (37) présente trois alésages radiaux (64) en des endroits espacés sur sa longueur, et les moyens palpeurs de came comportent trois tiges-poussoirs (64a) respectivement contenues dans lesdits alésages pour agir sur les trois mâchoires (13, 14, 15) et les cames rotatives sont constituées par trois profils de came annulaires (58, 59, 60) prévus sur l'arbre (44) à l'intérieur du moyen pour porter respectivement contre les trois tiges-poussoirs afin de déplacer les tiges-poussoirs et par là les mâchoires en fonction de la position angulaire de l'arbre et de fermer et relâcher ainsi les mâchoires.

8. Guide-pièce selon l'une quelconque des revendications 2 à 7, caractérisé en ce que l'arbre (44) est accouplé à un moteur pas-à-pas réversible (55) destiné à le faire tourner pour ouvrir et fermer les mâchoires.

9. Guide-pièce selon l'une quelconque des revendication's 1 à 8, caractérisé en ce que les mâchoires (13, 14, 15) sont articulées autour d'axes parallèles portes par le socle (10).

10. Guide-pièce selon la revendication 9, caractérisé en ce que deux des mâchoires (14, 15) sont montées de façon à tourner autour d'un axe commun et la troisième mâchoire (13) est montée de façon à tourner autour d'un autre axe.

11. Guide-pièce selon la revendication 10, caractérisé en ce qu'un support (78) est monté mobile sur le socle, la troisième mâchoire (13) étant montée sur le support, et des moyens sont prévus pour verrouiller le support dans une position active dans laquelle la troisième mâchoire peut embrasser et supporter une pièce, les deux atures mâchoires occupant une position inactive dans laquelle la troisième mâchoire est écartée des deux premières mâchoires pour qu'une pièce puisse être retirée latéralement d'entre les mâchoires ou insérée entre les mâchoires.

12. Guide-pièce selon la revendication 11 dans lequel le support est constitué par un bras (78) monté mobile sur le socle, la troisième mâchoire (13) étant articulée sur le bras, pour pouvoir se rapprocher et s'écarter de l'axe de fermeture, et des moyens (90, 93, 94) sont prévus pour déplacer le bras (78) par rapport au socle afin de déplacer la troisième mâchoire (13) entre lesdites positions active et inactive.

13. Guide-pièce selon la revendication 12, caractérisé en ce que les moyens de déplacement du bras sont constitués par un vérin à double effet (93, 94).

14. Guide-pièce selon l'une quelconque des revendications précédentes, caractérisé en ce que le socle (10) est muni d'une bride (24) permettant de le fixer à la table de travail d'une machine-outil.

Drawing