Machining center

A machining center for the machining of workpieces (26). It comprises at least one work unit (22) with a rotary tool (24) for machining a workpiece (26) arranged in a machining zone (28). The workpiece (26) is secured to a workpiece carrier (15), which for this purpose possesses a holding device (25). The workpiece carrier (15) may be moved into a workpiece change station (25), wherein workpiece change may take place. During workpiece change the workpieces (26) are picked up and put down from above by the holding device (25). During machining the workpiece (26) is hangingly held on the workpiece carrier (15). The machining center ensures high productivity and minimum complexity for operation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a machining center for machining workpieces, 
comprising at least one work unit having at least one work spindle able to 
be driven in rotation and adapted to be fitted with a machining tool, with 
which tool at least one workpiece arranged in the machining zone may be 
machined, a workpiece carrier on which the workpiece may be releasably 
held by means of a holding device arranged on the workpiece carrier, the 
work unit and the workpiece carrier being able to be shifted in relation 
to one another, a conveying and positioning device for the workpiece 
carrier by which the workpiece carrier is able to be shifted between the 
machining zone and a workpiece change station located outside the 
machining zone, and a gripper for the change over a from workpieces to be 
machined to workpieces already machined, the gripper receiving the 
workpiece from above or from the side, lifting the same and conveying it 
into the machining zone and, after machining, depositing it at a workpiece 
deposit site in the workpiece change station from above or from the side. 
2. Prior Art 
A machining center of this type is constituted by the machine tool 
described in the European patent publication 0 088 645 A1. Such a machine 
tool additionally possesses further machine parts permitting the use 
thereof as a vertical lathe with a rotating workpiece and a stationary 
tool. To the extent that it is relevant for the machining center of the 
type initially mentioned, this known machine comprises a workpiece carrier 
formed by an indexing head and a workpiece change station arranged 
adjacent to it and constituted by a magazine. A gripper changes over the 
unmachined and machined workpieces between the workpiece change station 
and the workpiece carrier. The tool employed for machining is held on the 
rotating working spindle of one work unit. 
During the machining of a workpiece the gripper assumes a standby position 
outside the machining zone. It must consequently, for each workpiece 
change, be shifted, directly before and after machining engagement of the 
tool, between the standby position and the machining zone. The time spent 
for this has an unfavorable effect on workpiece re-tooling times and 
accordingly on the overall workpiece machining times. Furthermore, it is a 
relatively complex matter to free the workpiece carrier, constantly 
remaining in the machining zone, of shavings, something which results in 
an increase in the time expended. 
OBJECT ONE SUMMARY OF THE INVENTION 
Accordingly one object of the present invention to create a machining 
center of the type initially mentioned, which while possessing a simpler 
structure leads to shorter workpiece machining times also simplifies 
removal of shavings. 
In order to attain this object a holding device on the workpiece carrier is 
provided which constitutes the gripper and the gripper moves the workpiece 
into machining engagement. The workpiece, which is respectively to be 
machined, remains constantly on the gripper from pickup until renewed 
deposit in the workpiece change station and accordingly also during 
intermediate machining by the machining tool which is arranged on the at 
least one rotating work spindle of the work unit. The workpiece carrier is 
arranged replaceably on the positioning device jointly with the holding 
device. 
It is in this manner that a separate gripper as in the prior art for moving 
the workpieces between the workpiece change station and the machining zone 
is no longer needed. The holding device on the workpiece carrier has a 
double function since it serves both for handling during conveyance of the 
workpieces into and out of the machining zone and also for holding the 
workpiece during machining. The gripper constituted by the holding device 
itself collects the workpieces to be machined and itself also returns same 
after machining, it moving same into machining engagement in the meantime. 
Since no idle travel of the gripper is involved, as a whole the workpiece 
machining time can be generally reduced. 
This accordingly alone leads to high workpiece machining rates and a 
correspondingly high productivity using but one single workpiece carrier. 
Since the workpieces may now also be machined while hanging, a large 
proportion of the shaving produced may fall down freely under their own 
weight without fouling the holding device or, respectively, the gripper 
and the holding and support surface adjacent to same. 
This renders possible a simplified disposal of shavings while 
simultaneously reducing the effort involved in cleaning prior to clamping 
a new workpiece in place. All in all the invention provides a "pickup" 
system since the workpiece carrier using its holding device itself 
collects and takes up the workpiece to be machined. 
In order to render possible rapid re-tooling of the machining center for 
handling other workpieces, the workpiece carrier is preferably arranged in 
a replaceable fashion on the positioning device. It may then be exchanged 
jointly with the holding device provided on it and replaced by a workpiece 
carrier with a differently designed holding device. 
Although in the machine tool of the said European patent publication 0 088 
645 A1, in the case of use as a vertical lathe, the respective workpiece 
to be machined is taken from the magazine by the chuck itself after 
machining is returned, this application is however restricted to lathe 
operation with the chuck rotating and the tool stationary. In the case of 
use as a machining center of the type initially mentioned recourse is had 
to an additional gripper for handling the workpieces. 
The same applies for the machine tool disclosed in the German patent 
publication 4,022,458 A1. Here the workpiece carrier, rotating during use, 
is arranged underneath the stationary machining tool and is supplied with 
a workpiece with the aid of a gripper. Although the time required for such 
supply is shorter than in the case of the said European patent publication 
0 088 645 A1, since two grippers are present, the greater technical 
complexity of the machine does lead to a substantial increase in the costs 
of such machine tool. 
Furthermore the German patent publication 3,416,660 A1 had also made a 
proposal to collect the workpieces in a single clamping operation from the 
workpiece magazine, to machine them and to replace them. Again it is a 
question however only of a lathe, which grips the workpieces with the 
chuck connected with the operating spindle. A further point is that in 
this lathe there is no provision of the possibility of replacement of a 
workpiece carrier necessary for machining centers together with the 
holding device. 
The workpiece get-ready site in the workpiece change station, from which 
the workpiece carrier takes the respective workpiece to the worked, can be 
identical with the workpiece deposit site. 
It is convenient for the workpiece carrier to also comprise a chuck plate 
also termed a palette, which is arranged hangingly on the conveying and 
positioning device, the holding device being located on the lower side 
thereof. In order to ensure optimum removal of shavings it is preferred to 
provide a shavings receiving passage underneath the machining zone, such 
passage opening if, desired, into a conveying device conveying away the 
shavings as same are produced. 
The at least one work unit present may have a single spindle or a multiple 
spindle design. A single spindle design is more particularly employed for 
high speed machining, a system preferably being employed, in which the 
spindle and the motor are collected together as a single unit. It is more 
especially in the case of single spindle designs to provide several and 
more particularly two such work units for simultaneous operation, which 
are more particularly arranged in one horizontal plane adjacent to one 
another and work independently of each other. Thus for example the one 
work unit may perform a machining operation, whereas as regards the work 
unit not presently in use a tool change is carried out. 
In order to facilitate re-tooling, it is to be recommended to carry out 
re-tooling with a workpiece carrier and exchange device, which has a 
workpiece carrier magazine associated with it. The exchange of the 
workpiece carriers between the workpiece exchange device and the workpiece 
carrier magazine may for example be carried out by hand or with a suitable 
auxiliary device. 
In order to render possible rapid re-tooling of the machining center for 
handling other workpieces, the workpiece carrier is preferably arranged in 
a replaceable fashion on the positioning device. It may then be exchanged 
jointly with the holding device provided on it and replaced by a workpiece 
carrier with a differently designed holding device. In order to facilitate 
re-tooling, it is to be recommended to carry out re-tooling with a 
workpiece carrier and exchange device, which has a workpiece carrier 
magazine associated with it. The exchange of the workpiece carriers 
between the workpiece exchange device and the workpiece carrier magazine 
may for example be carried out by hand or with a suitable auxiliary 
device. 
A preferred embodiment of the invention provides the workpiece carrier 
arranged on a boom-like portion of the positioning device in order to 
offer as much space as possible for movement of the workpiece carrier.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) OF THE INVENTION 
All figures are diagrammatic. More particularly, no attempt has been made 
to represent the necessary drive and control means, which as such are 
known and may be provided by the man in the art as desired. 
The machining center depicted in FIGS. 1 through 5 comprises a table or 
base 1 at whose rear side an upwardly extending carrier 2 is provided. In 
the top part of the carrier and at a vertical distance from the top side 3 
of the base there is a first horizontal guide 4, which is for example 
rail-like. On it a vertical guide 5 is mounted for horizontal linear 
movement, the corresponding first horizontal direction of movement being 
indicated by a double arrow 6. 
On the vertical guide 5 a rider 8 guided for movement in a vertical 
direction as indicated by a double arrow 7. 
On the bottom side of the rider 8 a turntable 11 is arranged. It is able to 
be turned about a vertical axis 12 in relation to the rider 8. The 
direction of rotation is indicated by a double arrow 13. 
On the turntable 11, in the present case of the bottom side thereof, a 
workpiece carrier 15 is detachably attached with the aid of a coupling 
device 14. The turntable 11, the rider 8, the vertical guide 5 and the 
first horizontal guide 4 form a positioning device generally referenced 16 
for the workpiece carrier 15 coupled therewith. The latter may be 
consequently shifted in the directions 6, 7 and 13 as required in order to 
be brought into a desired position. A second horizontal guide 17 is 
provided on the base 1 adjacent to top side 3 of the base. Such horizontal 
guide extends, as seen in plan view, at a right angle to the first 
horizontal guide 4. The horizontal guide mounts a work unit 22 which is 
able to be reciprocated, as indicated by the double arrow 18, in its 
longitudinal direction in a second horizontal direction of movement. In 
the present example it is a question of a single spindle work unit, which 
possesses one work spindle 23, on which the desired machining tool 24 is 
mounted in a detachable manner. By means of a drive motor, not 
illustrated, which is integrated in the work unit 22 it is possible to 
drive the work spindle 23, and accordingly the machining tool 24, in a 
known manner to perform a rotary movement. In the present case the design 
of the motor permits high speed machining. 
Instead of the single spindle work unit 22 it is also possible to provide a 
multiple spindle work unit, which is able to be simultaneously fitted with 
a plurality of machining tools driven in rotation. 
The workpiece carrier 15 mounts a holding device 25 so that so that a 
workpiece 26 to be machined may be clamped in a predetermined position on 
the workpiece carrier 15. This position will be termed the carrier 
position. The above mentioned degrees 6, 7, and 13 18 of freedom render 
possible relative motion between the machining tool 24 and the workpiece 
26 located in the carrier position so that the workpiece can be worked in 
any desired manner by bringing the machining tool 24 into engagement with 
it in the appropriate fashion. 
The vertical guide 5 and the rider 8 are attached at the front on the first 
horizontal guide 4 with the result that the rider 8, together with the 
turntable 11 (preferably mounted thereon) protrudes like a boom to the 
front (FIG. 3). This means that the workpiece carrier 15, together with 
the workpiece 26 in the carrier position, is held with a clearance above 
the top side 3 of the base and in front of the carrier 2. Therefore the 
portion, which is located above the base 1 and represents the machining 
zone 28, is substantially accessible from the front side 27 and may be 
inspected. 
In the present example the arrangement is such that the first horizontal 
direction 6 of movement extends in the width direction of the base 1 and 
accordingly in terms of FIG. 2 from the left to the right. The second 
horizontal direction 18 of movement extends in the depth direction of the 
base 1 between the front side and the rear side. In the example the second 
horizontal guide 17 is arranged in the left hand marginal part of the base 
1 and the axis 32 of the rotation of the work spindle 23 extends in 
parallelism to the first horizontal direction 6 of motion. The machining 
zone 28, as considered in plan view in FIG. 2, is surrounded by the first 
and the second horizontal guide 4 and 17 and furthermore by the front and 
the right hand edge 33 and 34 of the base 1. 
The positioning device 16 serves not only for positioning the workpiece 26 
during machining, but also for changing the position of the coupled 
workpiece carrier 15 between the above mentioned machining zone 28 and a 
workpiece change station 35. The latter is located preferably clear of the 
machining zone 28 and in the present embodiment of the invention is, in 
terms of the plan view of FIG. 2, to the side of the right hand side edge 
34. In the workpiece change station 35 workpiece changing is possible with 
respect to the workpiece carrier 15, i.e. the workpiece previously located 
in the carrier position is replaced after machining by the next workpiece 
to be machined. There is an exchange of workpieces. 
The first horizontal guide 4 extends laterally beyond the right hand side 
edge 34 so that the vertical guide 5 is able to be moved, together with 
workpiece carrier 15, along this first horizontal guide 4 into the 
workpiece change station 35. The workpiece change position assumed in the 
workpiece change station 35 is indicated in FIGS. 1 and 2 in broken lines 
at 36. 
In the workpiece change position 36 the workpiece carrier 15 assumes a 
position vertically above a workpiece get-ready site 37 provided in the 
workpiece change station 35. In order to provide the empty workpiece 
carrier 15 with a workpiece 26, the corresponding workpiece 26 is arranged 
a get-ready position 42 at a get-ready site 37. After this the workpiece 
carrier 15 located in the workpiece change position 36 is moved from a 
standby site 43, at a distance above the workpiece 26, in a direction 7 of 
vertical movement downward into a receiving position 44; in which it grips 
the workpiece 26 with its holding device 25 and clamps it. The grasping of 
the workpiece 26 thus takes place in a downward direction directly by the 
holding device 25 which hence simultaneously performs a gripper function. 
In the position, in which the holding device 25 has the workpiece 26 
transferred to it from the get-ready position 42, the workpiece 26, 
remains clamped and held on the workpiece carrier 15- until, after 
machining has been completed, it is deposited in the workpiece change 
station 35. The workpiece 26 held in the get-ready position 42 is lifted 
by vertical upward motion of the rider 8 away from the workpiece get-ready 
site 37 and henceforward assumes a hanging position on the workpiece 
carrier 15 until it is returned to the workpiece change station 35. 
Such return is performed in the reverse order of movements, the workpiece 
carrier 15 firstly being moved back into the workpiece change position 36 
so that it is located in a standby position 43 above and clear of a 
workpiece deposit site 38 in the workpiece change station 35. This 
workpiece deposit site 38 is preferably identical with the workpiece 
get-ready site 37 so that by, lowering the workpiece carrier 15, the 
machined workpiece is deposited back in a position corresponding to the 
preceding get-ready position 42. 
It will be clear that the workpiece deposit site 38 does not necessarily 
have to be identical with the workpiece get-ready site 37. More 
particularly in the case of continuous supply of workpieces 26 and if the 
workpiece get-ready site 37 can not be always kept free during machining 
of the workpiece collected from it, it is recommended to select a 
different workpiece deposit site 38. This different site will then 
preferably be to the side of the workpiece get-ready site 37 or, however, 
given a suitable extension of the first horizontal guide 4, adjacent to 
the left hand side edge 45 of the base 1. It will be clear from this that 
the workpiece change station 35 does not necessarily have to be a single 
constructional unit and it may certainly be sub-divided into a plurality 
of station parts separated from each other in space. In one station part 
it is then possible for instance for the grasping of the workpiece, which 
might be referred to as a "pickup" function" to occur, whereas in the 
other station part the release of the machined workpiece takes place. 
The transfer of the workpiece 26 to be machined into the workpiece 
get-ready site 37 is preferably performed with the aid of a workpiece 
conveying device 45, which in the present working example of the invention 
in accordance with FIGS. 1 through 5 is designed in the form of a conveyor 
belt, which runs through the workpiece change station 35 and moves past 
the machining center to the side adjacent to right hand side edge 34. It 
is possible to arrange a plurality of the machining centers one after the 
other in the depth direction so that the conveyor belt moves past all of 
same and the workpieces to be machined may be removed by the respective 
machining center. The workpiece conveying device 45 may in this case 
practically represent a low-cost workpiece magazine, which makes do 
without expensive workpiece palettes equipped with holding devices. 
In the case of the embodiment of FIG. 6 a workpiece conveying device 45', 
designed in the form of a round indexing table, is provided, the 
workpieces 26 being able to be arranged on a turntable for running through 
the workpiece change station 35 in sequence. 
In order to ensure reliable acceptance of the workpieces 26 by the 
workpiece carrier 15 in the workpiece change station 35, it is recommended 
to get the workpiece 26 ready, respectively located at the workpiece 
get-ready site 37, using positioning means 46 to assume a predetermined 
alignment. In this respect it may be a question of positioning or locating 
pins, which set a certain angular alignment of the workpiece 26. If the 
workpieces 26 are supplied by means of a workpiece conveying device 45 and 
45', it is convenient to provide corresponding positioning means 46 at 
each workpiece site 49. 
In the case of the preferred embodiment the workpiece carrier 15 comprises 
a base plate, termed a chuck plate, which, with its top side foremost, is 
fixedly clamped on the turntable 11, the plane of the plate extending at a 
right angle to the vertical axis 12 of rotation. The holding device 25 is 
provided on the bottom plate face 48 which faces downward in the coupled 
position. The position is assumed by the workpiece carrier 15 also in the 
workpiece change position 36 so that for accepting a workpiece 26 one 
vertical movement is sufficient, the holding device 25 being laid 
downwardly on the workpiece 26 positioned in the workpiece get-ready site 
37. The holding device 25 itself may be fitted in a conventional fashion 
with suitable, for example hydraulic, holding mechanisms and comprise the 
necessary holding and abutment faces so that grasping and clamping of the 
workpiece 26 may take place in the course of automatic operation of the 
machining center. The necessary holding and, respectively, grasping 
movements are indicated in FIG. 1 by the double arrows 52. 
Since the workpiece 26 is worked hangingly in the machining zone, by far 
the greatest part of the resulting shavings will fall downward so that 
they will not foul the holding device 25. In the illustrated working 
embodiment the shavings are received in a shaving passage 53, which is 
located underneath the machining zone 28 and is preferably integrated in 
the base 1. The shavings receiving passage 53 may taper in a funnel-like 
manner downward and for instance open into a conveying device constituted 
by a conveyor belt, such device extending horizontally and clearing the 
shavings produced from the machining center. 
The machining center may furthermore be provided with a tool magazine 55 
holding ready a number of machining tools, with which the work unit 22 may 
be selectively fitted as desired. The fitting of the tools itself is then 
conveniently performed with the aid of a suitable tool changer 56. 
It will be clear from the embodiment in accordance with FIG. 6 that the 
machining center may readily be equipped with a plurality of work units 
22. As shown in FIG. 6 two such work units 22' and 22" are provided, which 
are each able to be changed in position as indicated by the double arrow 
18 on a second horizontal guide 17 like the arrangement in FIGS. 1 through 
5. In this case they are arranged in the front part of the front side 27 
of the base 1 so that they are opposite to the carrier 2 in the depth 
direction of the base 1. The axes of the rotation of the work units 22' 
and 22", which in the present case as well are single spindled, extend, 
unlike the case of the design in accordance with FIGS. 1 through 5, 
parallel to the second horizontal direction 18 of movement. 
The machining center in the present example is only equipped with one 
single workpiece carrier 15, which in sequence is loaded with the 
workpieces 26 to be machined. Since, owing to the acceptance and release 
of the workpiece taking place in vertical direction, workpiece change may 
be performed by the holding device 25 itself automatically, the workpiece 
change being extremely short so that it is possible to do without any 
further workpiece carriers and without any alternate shifting into the 
machining zone. This means that there is a reduction in costs, since per 
workpiece type only one single workpiece carrier is required. 
It is however an advantage if the workpiece carrier 15 of the machining 
center is replaceable or interchangeable. This renders possible an 
exchange for re-tooling the machining center for work on another type of 
workpiece to be machined. Therefore in the working embodiment the 
workpiece carrier 15 is detachably secured via the coupling device 14 to 
the turntable 11 and if required may be replaced by another workpiece 
carrier 15' which has a holding device adapted for other workpieces. 
Particulars will be seen from FIGS. 4 and 5. 
In accordance with this the machining center is preferably equipped with a 
workpiece carrier magazine 57, which is arranged at a suitable point 
adjacent to the base 1. In it workpiece carriers with a differently 
designed holding device 25 are held available for use. The changing of the 
workpiece carriers preferably takes place mechanically, for which reason 
the machining center given as an example herein is provided with a 
suitable workpiece carrier change device 58. It renders it possible to 
remove a workpiece carrier 15, arranged in a working position 61 and 
presently at the positioning device 16, from such working position 61 and 
in place thereof to couple up another workpiece carrier 15' with the 
position device 16, which is then loaded so that this new workpiece 
carrier 15' will assume the working position 61 indicated in FIGS. 1 
through 5. It is preferred for the workpiece carrier change device 58 also 
to at least partially perform the shifting of the workpiece carriers 15 
and 15' into and out of the workpiece carrier magazine 57. 
In the illustrated working embodiment the workpiece carrier change device 
58 is arranged adjacent to right hand edge 34 of the base 1. It possesses 
a holder 62, which using a horizontal carriage 63 on a carriage guide 64, 
extending horizontally and linearly, is able to be shifted as indicated by 
the double arrow 65 in parallelism to the second horizontal direction 18 
of motion. The carriage guide 64 is preferably arranged on the base 1. On 
the holder 62 two loading sites 66 and 67 are provided, which are 
respectively suitable for detachably accepting or, respectively, holding a 
workpiece carrier 15 and 15'. The holder 62, depicted by way of example, 
is bifurcated in design and possesses two adjacently placed recesses 
constituting the loading sites 66 and 67, which are open toward the front 
side of the holder. In order to hold a workpiece carrier in a loading site 
66 and 67 the said workpiece carrier 15 is inserted from the open front 
side into the respective loading site 66 as indicated by the arrow 72. The 
removal of a held workpiece carrier is performed by withdrawal from the 
respective loading site 67 in the oppositely direction as indicated by the 
arrow 73. The directions 72 and 73 of insertion and of withdrawal run in 
parallelism to the horizontal direction 65 of motion of the holder 62. 
The holder 62 is so arranged that the open front side of the loading sites 
66 and 67 is directed toward the rear side of the base. Workpiece carrier 
replacement takes place as follows: 
One of the loading sites 66 remains unoccupied, while the other loading 
site 67 is loaded with the new workpiece carrier 15'. Loading takes place 
in a home position 71, wherein the horizontal carriage 63 is arranged in 
the front base portion, as is generally shown in FIG. 4. Now the workpiece 
carrier 15, located in the work position 61, is so positioned by means of 
the positioning device 61 that it is horizontally directly opposite to the 
free loading site 66. This intermediate position is illustrated in FIG. 5. 
The next step is for the horizontal carriage 63 to be shifted toward the 
workpiece carrier 15 as indicated by the arrow 74 so that the workpiece 
carrier 15 is introduced into the free loading site 66. This intermediate 
position is as indicated in broken lines in FIG. 5 at 75. The new 
workpiece carrier held in the second loading site 67 is then in the 
horizontal direction 6 of motion alongside the workpiece carrier 15 to be 
removed. 
The coupling device 14 is now unlocked and the turntable 11 is shifted in 
the horizontal direction 6 of movement while keeping to the same height 
toward the new workpiece carrier 15', the workpiece carrier 15, located in 
the working position 61, remaining in the first carrier site 66. During 
this lateral movement the coupling engagement with the workpiece carrier 
so far used is gradually released, while simultaneously coupling 
engagement with the new workpiece carrier 15' is caused to come into being 
until same assumes the working position 61. Now the coupling device 14 is 
re-locked and the new workpiece carrier 15' is securely fixed on the 
turntable 11. 
In order to ensure that these movements take place in the illustrated 
working embodiment the coupling device 14 possesses a linear guide 76, 
which is made up of two complementary linear guide parts 77 and 77', which 
are able to be moved in relation to each other in the longitudinal 
direction while same are interlocked with each other. One of these linear 
guide parts 77 is provided on the turntable 11 and the other is provided 
on the clamping plate 47. The linear guide 76 may for example be designed 
in the form of a dovetail guide or, as illustrated, a T-section guide. The 
individual locking elements for locking the respective working position 61 
are not illustrated in the drawings. 
Once the new workpiece carrier 15' is locked in the working position 61, 
the holder 62 is moved back using horizontal carriage 63 from the 
intermediate position 75 into the home position 71. In this respect the 
new workpiece carrier 15' remains back on the turntable 11, while the old 
workpiece carrier 15 is kept in the associated loading site 66 and is also 
moved back as well. It is now possible for the machining center to start 
working the new type of workpiece using the new workpiece carrier 15'. 
In preferred design the holder 62, which for example has a bifurcated, 
E-like outline as illustrated, is able to be pivoted between a change 
position as indicated in continuous lines in FIG. 4, and a loading 
position 82 as indicated in broken lines, the pivot axis 78 preferably 
being a horizontal axis. In the change position 81 the holder 62 assumes 
the above described position, in which the loading sites 66 and 67 have 
their open front sides facing the rear side of the base. In order to 
ensure that there is no interference by the holder 62 and the workpiece 
carrier secured thereto, the holder 62 may be pivoted about the horizontal 
pivot axis 78 as indicated by the double arrow 83 into the loading 
position 82, the angle of pivot being for example 180 degrees. The holder 
62 is accordingly turned facing the workpiece carrier magazine 57 and the 
old workpiece carrier 15 can be placed in the workpiece carrier magazine 
57. Similarly in the loading position 83 the workpiece carrier to be used 
next, can be held at one of the loading sites 66 and 67. 
In the case of an arrangement of the work units 22, 22' and 22" as shown in 
FIG. 6, it may be useful if the workpiece carrier change device 58 is 
positioned adjacent to the opposite left hand side margin 31 of the base 
1. This is free here, since the work units 22' and 22" are arranged in the 
front portion of the machining center. In order to be able to implement an 
optimum workpiece carrier change in this case the first horizontal guide 4 
should however be extended so far to the left that the rider 8 can be 
positioned in the depth direction 18 in relation to the workpiece carrier 
change device 58. 
FIG. 8 indicates a further design structure of the machining center in a 
side elevation more or less looking in the same direction of the arrow III 
of FIG. 1, such design rendering possible a particularly low-cost 
workpiece carrier change method. The change operation is here undertaken 
in a workpiece carrier change station 92, through which a supply device 93 
runs, with which said supply device serving the workpiece carrier 
respectively no longer required 15 may be conveyed away and the workpiece 
carrier 15', which as the next one is to be secured in the working 
position on the positioning device 16 and, respectively, the turntable 11, 
is supplied. In accordance with the preferred embodiment of the working 
example the workpiece carrier change station 92 is identical to the 
workpiece change station 35 and the supply device 93 is the workpiece 
conveying device 45 and 45'. On the latter, in addition to the positioning 
means 46 for workpieces 26, several holding devices 94 are arranged, with 
which one respective workpiece carrier 15 and 15' may be so secured that 
when same moves through the workpiece carrier change station 92 it assumes 
an alignment which is suitable for the change. It is preferred for the 
workpiece carrier 15', secured in a holding device 94, to be so arranged 
and aligned that the holding device 25 is downwardly directed, the plane 
of the plate of the clamping plate 47 extending in a horizontal plane and 
the linear guide part 77' is preferably aligned in the advance direction 
95 of the supply device 93. The holding device 94 preferably cooperates 
with the holding device. 
In order to load the free positioning device 16 with a workpiece carrier 
15' the positioning device 16 is preferably so positioned in the workpiece 
carrier change station 92 that the linear guide part 77 provided thereon 
is at the same level as the linear guide part 77' of the workpiece carrier 
15', which is just arriving, and is also aligned in the advance direction 
95. Using its linear guide part 77' the moving supply device 93 then 
automatically thrusts the workpiece carrier 15', which is just arriving, 
onto the linear guide part 77 on the turntable 11. Once the desired 
working position has been reached, the coupling device 14, which is not 
illustrated in detail, is actuated and the workpiece carrier 15' is lifted 
by upward movement of the turntable 11 clear of the holding device 94. 
In like manner a workpiece carrier 15 no longer required in the workpiece 
carrier change station 92 may be passed on to a holding device 94. It is 
convenient for the positioning device 16 to directly place the workpiece 
carrier 15 in a holding device 94. Simultaneously the coupling device is 
released so that the moving supply device 93 draws the workpiece carrier 
15 off the linear guide part 77. Simultaneously it is possible in this 
case for the next workpiece carrier 15' to be already pushed off on to 
positioning device 16. 
It will be clear that the workpiece carrier change may be coordinated with 
other kinetic sequences, more particularly in a manner dependent on the 
design of the coupling device 14. It would for example be conceivable for 
the threading in and out of the linear guide system 77 and 77' to be 
undertake at a right angle to the advance direction 95, i.e. in the first 
horizontal direction of movement 6. In this case the workpiece carriers 15 
and 15' and the turntable 11 would have to be set with a 90.degree. offset 
about the vertical axis in relation to the positions shown in FIG. 8. The 
positioning device 16 would then best firstly deposit the workpiece 
carrier 15, which is no longer required, on the supply device 93 and then 
move back somewhat so that the "new" workpiece carrier 15' could arrive at 
the change site and could be received by the turntable. 
Given a corresponding design of the coupling device 14, for instance 
without the linear guide parts 77 and 77', the change operation could also 
readily be undertaken exclusively as part of a vertical movement of the 
turntable. The workpiece carrier 15, which is no longer required, is 
deposited at a change site from above on the supply device 93 and, after 
decoupling, conveyed away. Following this the next workpiece carrier 15' 
is conveyed to the change site, coupled from above by the positioning 
device 16 and lifted. 
It is an advantage in this design that there is no need for a complex, 
customized workpiece carrier change device 58, because workpiece carrier 
change may be implemented by means of the positioning device 16 itself 
using the workpiece conveying device 45 and 45', present in any case. For 
instance, following the last workpiece 26 to be machined it is merely 
necessary to arrange the next workpiece carrier 15 on the workpiece 
conveying device 45 and 45' so that following the last workpiece change, a 
workpiece carrier change may be undertaken, also in the pickup system. 
It is even possible to implement the workpiece carrier change with the 
workpiece secured in the holding device 25. In this case the workpiece 
carriers 15 are held over the respective workpiece 26 at the workpiece 
conveying device 45 and 45' and the holding devices 94 will be practically 
constituted by the positioning means 46, which directly, by way of the 
associated workpiece 26, also hold the respective workpiece carrier. 
The machining center taken as an example renders possible workpiece 
processing with only one single workpiece carrier and only one holding 
device arranged thereon, which is more particularly hydraulically or 
pneumatically operated. The workpieces not in the process of being 
machined do not have to be held in a complex and high-cost holding device, 
and same may be supplied to the workpiece change station using simple 
conveying means and removed from same again. It is sufficient to provide 
simple positioning means in order to ensure a certain basic alignment 
which in turn ensures that the workpieces arriving at the workpiece 
get-ready site 37 in each case possess the same alignment, which permits 
direct grasping by the holding device of the workpiece carrier 15, whose 
position is able to be changed in the vertical direction. The machining 
center renders possible fully automatic workpiece machining without human 
operators for workpiece change. The workpiece carrier itself picks up the 
workpieces to be machined and itself clamps them in the carrier position. 
It will be clear that the machining center may readily be provided with 
still further degrees of freedom or, respectively, axes. For instance it 
would be feasible to further subdivide the workpiece carrier 15 or the 
turntable 11 and to link the two parts with a transverse shaft extending 
at a right angle to the vertical shaft 12, it being possible for such 
transverse shaft to extend obliquely, that is to say not at a right angle 
to the vertical shaft 12. Accordingly the holding device 25 may, in case 
of need, also be so positioned in the course of machining so that it is 
not directed vertically downward but (also) laterally, the plate surface 
48, which during tool changing is directed downward, being directed to the 
side. 
FIG. 7 shows a modified arrangement of the workpiece carrier 15. In this 
case it is not set directly on the above mentioned turntable 11, but on a 
second turntable 85, which using an angle head 86 is secured on the said 
first turntable 11. The second turntable 85 is able to be rotated about a 
horizontal rotary shaft 87, extending rectangle to the vertical shaft 12, 
in relation to the angle head 86, which for its part is able to be rotated 
about the vertical shaft 12. By way of its clamping plate 47 via the 
coupling device 14 of the above mentioned type the workpiece carrier 15 is 
detachably secured to the second turntable 85, whereas the angle head 46 
is fixedly secured to the first turntable 11 by means of a corresponding 
coupling device 14. The workpiece carrier 15 may now be turned 
additionally as indicated by the double arrow 88 about the horizontal 
rotary shaft 87. This means that it is practically possible to machine to 
practically any angle in space and to carry out machining on five sides of 
the workpiece 26. 
In this respect the workpiece carrier 15 is so aligned that the plane of 
the clamping plate 47 is horizontally aligned and the plate surface 48, 
with the holding device 25 arranged thereon, is directed horizontally 
sideways. 
In order in the case of such an arrangement or alignment of the workpiece 
carrier 15 to receive a respective workpiece, which is to be machined, in 
the workpiece change station 35, the workpiece located at the workpiece 
get-ready site 37 is engaged from the side by the holding device 25. The 
workpiece carrier 15 is moved by the positioning device 16 into the 
workpiece change station 35, then lowered until it is arranged alongside 
the workpiece 26 to be picked up and then moved by a horizontal lateral 
movement toward the workpiece 26, which for its part is gripped by the 
holding device 25 itself. Now the workpiece carrier 15 is lifted by the 
positioning device 16 and the workpiece 26 is moved into the machining 
zone. Deposit of the workpiece 26 after machining is performed in a 
corresponding fashion.