GB2140335A - Transfer means for a machine tool - Google Patents

Abstract

In a machine tool of the kind comprising a rotatable workholding chuck (14) and a tool turret (24) having a plurality of tool stations (70), selectively indexable to bring each tool station (70) into a first turret position proximate to the workholding chuck (14) and a second turret position distal to the workholding chuck, workpieces are transferred to and from the workholding chuck by the use of gripping mechanism (32, 33) mounted in two of the tool stations. Each of the gripping mechanisms comprises a housing (49) having a central mounting axis and which is adapted to be mounted in a pocket at the tool station, and compliant means (62) to permit limited movement of the housing (49) relative to the pocket in said axial direction. A plurality of jaws (37) are mounted for movement under actuating means radially of said axis. A robot transfer means (28) transfers a rough workpiece (15A) to a work present position at which it is grasped by one of the grippers (33), whilst the other gripper (32) grasps a machined workpiece (15) held by the workholding chuck. <IMAGE>

Description

SPECIFICATION Improvements relating to machine tools This invention relates generally to machine tools of the kind comprising a plurality of tools mounted on an indexable tool turret, the tools being selectively indexed to a work zone and being powered into operation on a workpiece by appropriate slides of generally coordinate compound slide systems, for example turning.

The several automatic part loading systems which are employed presently in the art use a part loader which is completely external to the machine slide system. For example, a robot manipulator may be employed and is typically situated in front of the machine to take parts from a conveyor and insert them into the workholding chuck of the machine, and reverse motion when the operation is finished.

Similarly, the robot manipulator may be positioned at the rear of the machine where it reaches through rear guarding to accomplish the interchange of workpieces between the workholding chuck and the conveyor system.

In order to speed up the transfer of workpieces, the robot end effector is typically fitted with two grippers, one for holding "green", or rough, workpieces and one for holding finished workpieces. At the extension of the robot manipulator arm into the working zone area, the end effector is actuated to exchange the two pieces with the workholding chuck.

A main difficulty inherent in this prior art device is that the payload size is reduced; i.e.

since two workpieces must be held at the arm extension, the size of the workpiece is far more limited than if the robot had to hold only one workpiece. Further, the reach of the robot arm into the working zone can cause intrusion with working slides and interference with workholding chucks. In addition, when a rear robot manipulator is utilised on a machine having a slant bed for supporting the turret slides, the slant bed area may inhibit the reach of the articulatable arm into the working zone.

According to this invention there is provided gripping mechanism for a machine tool comprising: (a) a housing having a central mounting axis and which is adapted to be mounted in a tool pocket of the machine; (b) compliant means to permit limited movement of the housing relative to the pocket in said axial direction; (c) a plurality of jaws mounted for movement radially of said axis; and (d) actuating means for moving the jaws relative to the housing between open and closed positions.

Preferably said compliant means is afforded by a compression spring operative to urge the housing to an outer position but which permits limited movement of the housing from said outer position. In this manner, damage to a workpiece which may have tolerance variations for positional inaccuracies, which would otherwise occur by the gripping mechanism being forced against the workpiece, is avoided.

Preferably the gripping mechanism comprises a carrier member adapted to be fixedly secured in said tool pocket of the machine, the carrier member comprising means co-operative with the housing to limit movement of the housing in said axial direction.

Preferably the actuating means comprises a rotary drive member operative to cause movement of the jaws between their open and closed positions, and at least one linear actuator operative to cause rotation of the drive member. Thus, conveniently rack and pinion formations are provided which are operative between the linear actuator and the drive member.

Advantageously the drive member is rotational about the central mounting axis of the housing, which is parallel to the axis of rotation of the machine spindle.

According to this invention, there is also provided a part gripper for a turning machine having a tool turret with multiple tool pockets, the part gripper comprising a gripper housing having a central mounting axis and adapted to mount in a tool pocket, a plurality of jaws movable radially on said housing normal to said central mounting axis, compliant means mounting said gripper housing to said tool turret pocket, thus providing for relative movement between said housing and turret along said mounting axis, and means for actuating said jaws between open and closed positions.

There will now be given a detailed description, to be read with reference to the accompanying drawings, of a turning machine which is a preferred embodiment of this invention and which has been selected to illustrated the invention by way of example.

In the accompanying drawings: Figure 1 is a front view of the turning machine which is the preferred embodiment of the present invention; Figure 2 is a left end view of the preferred embodiment, taken in the direction of the arrow 2 of Fig. 1; Figure 3 is a front elevational view of gripping mechanism of the preferred embodiment, taken along the line 3-3 of Fig. 1; Figure 4 is an axial section through the gripping mechanism taken along the line 4-4 of Fig. 3; and Figure 5 is a section through pistons of the gripping mechanism taken along the line 5-5 of Fig. 4.

Referring to the drawings, and in particular to Fig. 1 thereof, there is shown a turning machine 10 having a base 11 and a headstock portion 12. The headstock portion 12 houses a rotatable spindle 13 and spindle workholding chuck 14 which is adapted to support and drive a workpiece 15 of revolution during a machining operation. The turning machine 10 has a slanted bed portion 16 which rises up to avoid any chips which fall from the workpiece during machining, and the slant bed portion 16 has ways 17 which carry a tool slide assembly 18.The tool slide assembly 18 in the machine described has coordinately movable upper and lower slides 19, 20 wherein the lower slide 20 is carried along the slant bed ways 17 in a direction parallel to the longitudinal axis of the workpiece 15, and a lower slide 20 has a way system 21 supporting the upper slide 19 which is movable in a radial direction relative to the workpiece 15.

Suitable slide drives 22, 23 are carried respectively on the slant bed portion 16 for moving the lower slide 20, and on the lower slide 20 for moving the upper slide 19. The upper slide 19 carries a rotatable tool turret 24, which is a multistation assembly indexable to present individual tools 25 to the workpiece 15 at desired machining times.

Certain details of the turret assembly are omitted, but reference may be made to U.S.

Patent No. 3,943,802 for an example of an indexable assembly which might utilise a plurality of boring bars, for example. It is sufficient to understand that an indexing prime mover 26 and gear train 27 are driven under automatic control in a manner well understood in the machine tool art.

A robot manipulator 28, of the type disclosed in U.S. Patent No. 3,909,600 or any of other similar types well known in robot art, is utilised at the rear of the machine 10 having its arm 29 extending over the headstock portion 12 of the machine 10 with an end effector comprising a robot chuck 30 which may hold a workpiece 1 spa. The robot chuck 30 is brought to a constant part present" station 31 above the spindle chuck 14, so that an interchange may occur between the robot chuck 30 and the spindle chuck 14 at a prescribed interchange time.

The turret 24 is fitted with two part grippers 32, 33 which take the place of tools at two respective tool stations 34, 35 so that the slides 19, 20 may be advanced to a point where the first gripper 32 is in a first position proximal to the workholding zone and may be engaged with a workpiece 15 chucked in the spindle chuck 14, and the second gripper 33 is thereby located at a second, or distal position relative to the spindle workholding chuck 14, which corresponds to the part present station 31.By advancing the slides 19, 20 to the respective workpieces 15, 15 a, and actuating the part grippers 32, 33, the parts 15, 15a may be gripped and removed from the respective robot chuck 30 and spindle workholding chuck 14, and exchanged positionfor-position, so that a rough part 15a may be loaded from the robot chuck 30 to the workholding spindle 13 and a finished part 15 may be taken from the spindle workholding chuck 14 back to the robot chuck 30, simultaneously.

After the interchange takes place, the turret 24 is indexed to present workholding tools 25 as needed to complete machining operations on a workpiece 15a. During the machining cycle, the robot arm 29 takes the finished workpiece 15 which has been deposited in its robot chuck 30, and transfers it to a remote location (not shown). The remote location could be a conveyor system passing at the rear of the machine 10 or a batch location for workpieces, such as a wooden flat. After depositing the finished workpiece 15 at the remote location, another rough workpiece 15a is picked up and moved back to the part present position 31 for a subsequent interchange by the turret 24.

Since it is not known in turning machines to carry workpieces in a part gripper, or chuck, mounted to an indexable tool turret 24 while indexing, the partial cut-away section of the turret assembly, Fig. 1 illustrates how such grippers 32, 33 may be implemented.

The grippers 32, 33 are moved between clamped and unclamped conditions by fluid pressure applied to an internal linear actuator afforded by a piston/cylinder. These details of gripper construction are explained further in the details of Figs. 3, 4 and 5. The fluid pressure lines 38a, 386 and 39a, 39b are internal ports in the rotatable turret spindle 40, and the lines communicate with respective annular grooves 41 a, 41 b and 42a, 42b in a non-rotatable end cap 43 to establish a rotary fluid coupling. External hose lines 44a, 44b and 45a, 45b serve to connect the annular grooves 41 a, 41 b and 42a, 42b to a pair of solenoid operated, spring return, fluid control valves 46, 47 (symbolically depicted).

Pressurised fluid 'P' may be ported to the grippers 32, 33 when a part unclamping" mode is signalled by the machine control (not shown) which energises the solenoid operated valves 46, 47. Thereafter when the valves 46, 47 are de-energized, the grippers 32, 33 are reclamped by fluid pressure.

Fig. 2 depicts an end view of the machine of Fig. 1, where it is seen that the rearmounted robot manipulator 28 has its arm 29 extended over the headstock portion 12 of the machine 10, to establish the part present position 31. Workpieces 15 are interchanged with the machine spindle workholding chuck 14 by means of the indexable turret 24 carrying the part grippers 32, 33 mounted thereon. In actual operation, the machine slides 19, 20 are movable automatically by means of electronic control well known in the art. One control which might be used, for example, is the numerical control system de scribed in U.S. Patent No. 3,703,112 which illustrates, in principle, how co-ordinate slide assemblies of a turning machine may be moved with respect to a spindle held workpiece under the coded commands of an N.C.

control.

The view shown in Fig. 3 depicts the part gripper 33, or chuck, shown at the top of the turret of Fig. 1. The lower gripper 32 is identical to the upper gripper 33. Each gripper is basically a three jaw chuck, having three equally spaced jaws 37 which are radially movable in respective guide slots 48 in the gripper housing 49. Hold down plates 50 are provided to prevent the slidable jaws 37 from falling out of the assembly. Each jaw 37 has a jaw slide 51, with a rack portion 52 extending inwardly, in mesh with a central drive pinion 53. The drive pinion 53, when rotated, causes the radial positions of the jaws 37 to vary, thus permitting the clamping and unclamping of a workpiece.

The section shown in Fig. 4 is a partial broken away axial section through the gripper 33 of Fig. 3, illustrating that the central drive pinion 53 is integral with a rotatable central shaft 54, and the midspan portion of the journalled shaft 54 is provided with an integral gear 55 which is in mesh with a pair of racks 56, 57 oppositely disposed in the gripper housing 49.

The jaw slides 51 are shown with a grooved top surface 58, for locating repositionable top jaws 59, in a manner well known in the workholding art. The gripper housing 49 has a rearwardly extending shaft portion 60 which has a counterbore 61 to receive a stiff spring 62. The shaft portion 60 is received in the bore 63 of a gripper adaptor 64, which is secured to the face 65 of the turret spindle 40 by threaded studs 66 and nuts 67 retaining an adaptor flange 68. The adaptor 64 has a cylindrical diameter 69 received in a pocket 70 in the turret spindle 40.

The rear, inward, end 71 of the adaptor 64 is fitted with a cap 72 which is bolted to the adaptor 64 to provide a reaction plate for the spring 62. The inner face 73 of the cap has a counterbore 74 to receive the spring 62. A transverse pin 75 extends radially from the shaft portion 60, and bears on the end 76 of an elongate slot 77 provided in the adaptor 64, so as to trap the gripper housing 49 from moving out of the adaptor 64, yet permit inward movement of the gripper housing 49 with respect to the adaptor 64. The purpose of the spring loading of the gripper housing 49 is to permit some axial compliance of the gripper jaws 37 when being forced against a workpiece which may have tolerance variations or positional inaccuracies, thereby avoiding hamming of the part.The central shaft 54 is entrapped from axial movement with respect to the gripper housing 49, by a split bushing 78 which is inserted in a groove 79 created by the pinion 53 and gear 55 of the shaft. The bushing 78 is fastened with screws 80 to the gripper housing 49.

Fig. 5 depicts a section through the gear 55 and oppositely disposed racks 56, 57 within the gripper housing 49. The racks 56, 57 are formed on identical pistons 81, 82 which are powered in respective cylinders 83, 84. The pistons 81, 82 have seal rings 85 provided thereon, and fluid ports 86, 87, 88, 89 are connected to the ends of the cylinders 83, 84.

Here it should be noted that the racks 56, 57 move in unison and in opposite directions, to create torque loading on the gear 55.

Therefore, the opposite ends of the racks 56, 57 are in fluid communication with each other and are connected by hoses 90, 91 to the turret spindle 40 to pick up respective fluid pressure lines 38a, 38b. The hoses 90, 91 or other flexible fluid connectors serve to permit the axial movement of the gripper housing 49 with respect to the turret spindle 40.

Whilst a preferred embodiment of the invention depicts a general robot manipulator 28 to convey parts between the part ready position 31 and the remote location, it may be appreciated that other types of conveyors may be used, such as a dedicated shuttle mechanism.

Claims (12)

1. Gripping mechanism for a machine tool comprising: (a) a housing having a central mounting axis and which is adapted to be mounted in a tool pocket of the machine; (b) compliant means to permit limited movement of the housing relative to the pocket in said axial direction; (c) a plurality of jaws mounted for movement radially of said axis; and (d) actuating means for moving the jaws relative to the housing between open and closed positions.

2. Gripping mechanism according to Claim 1 wherein said compliant means comprises a compression spring operative to urge the housing to an outer position but which permits limited movement of the housing from said outer position.

3. Gripping mechanism according to one of Claims 1 and 2 comprising a carrier member adapted to be fixedly secured in said tool pocket of the machine, the carrier member comprising means co-operative with the housing to limit movement of the housing in said axial direction.

4. Gripping mechanism according to any one of the preceding claims wherein the actuating means comprises a rotary drive member operative to cause movement of the jaws between their open and closed positions.

5. Gripping mechanism according to Claim 4 wherein the actuator means com prises at least one linear actuator operative to cause rotation of the drive member.

6. Gripping mechanism according to Claim 5 comprising rack and pinion formations operative between the linear actuator and the drive member.

7. Gripping mechanism according to any one of Claims 4 to 6 wherein the drive member is rotational about the central mounting axis of the housing.

8. Gripping mechanism according to any one of the preceding claims wherein the mounting axis is parallel to the axis of rotation of the machine spindle.

9. A part gripper for a turning machine having a tool turret with multiple tool pockets, the part gripper comprising a gripper housing having a central mounting axis and adapted to mount in a tool pocket, a plurality of jaws movable radially on said housing normal to said central mounting axis, compliant means mounting said gripper housing to said tool turret pocket, thus providing for relative movement between said housing and turret along said mounting axis, and means for actuating said jaws between open and closed positions.

10. A part gripper according to Claim 9 wherein the mounting axis is parallel to the machine rotary workholding spindle axis.

11. Gripping mechanism for a machine tool constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.

12. Any novel feature or novel combination of features disclosed herein and/or shown in the accompanying drawings.