Abstract:
A tool changing device for a machine tool with at least one tool carrier is proposed, which comprises at least one transit station, into which a tool is introducable in an inward transit direction and is extractable in an outward transit direction, wherein, at the transit station, the tool is at least one of detachable from the assigned tool carrier and fixable to the tool carrier provided.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of international application PCT/EP2004/008237, filed on Jul. 23, 2004, and also claims the benefit of German Application No. 103 37 547.3, filed Aug. 5, 2003, both of which are incorporated herein by reference in their entirety and for all purposes. 

   BACKGROUND OF THE INVENTION 
   The invention relates to a tool changing device for a machine tool with at least one tool carrier and to a machine tool, which is provided with a tool changing device. The invention also relates to a method for changing tools on a machine tool with at least one tool carrier, in which detached tools are deposited in a tool storing apparatus and tools to be fixed are supplied from the tool storing apparatus. 
   In the case of a machine tool and in particular a machining center, as described, for example in EP 0 614 724 B1, a plurality of various tools may be used, in order to be able to carry out different machining processes on one or more workpieces. Irrespective of this, tools have to be exchanged because of wear. 
   It should be possible to carry out a tool exchange on a tool carrier with a minimized stoppage time for the machine tool. 
   SUMMARY OF THE INVENTION 
   In accordance with the invention, a tool changing device is provided, which is configured in a simple manner and with which a tool exchange can be carried out in a simple manner. In accordance with the invention, the tool changing device comprises at least one transit or pass-through station, into which a tool can be introduced in an inward transit direction and can be extracted in an outward transit direction, wherein, at the transit station, the tool can be detached from the assigned tool carrier and/or can be fixed to the tool carrier provided. 
   A simple tool exchange can be carried out by means of the solution in accordance with the invention. The transit station can be arranged, for example, rigidly or linearly displaceably with respect to a machine frame. It is no longer necessary for a gripper, for example, to have to fetch a tool from the tool carrier or bring it to it. The tool carrier, which is generally itself configured to be movable, can move to the transit station, to deliver a tool or to fetch a tool. The transit station can therefore be arranged in a defined position or with a small room for movement with respect to the machine tool, and in particular be arranged such that it is free of collision with respect to the tool carrier(s). In the case of a transit station of this type, depositing of tools in a tool storing apparatus or fetching from the tool storing apparatus can also easily be achieved, as a corresponding transporting apparatus can be arranged outside the room for movement of the tool carrier(s). 
   Owing to a defined inward transit direction and a defined outward transit direction, a tool can easily be fetched from a tool carrier and supplied to a tool storing apparatus or a tool can be fetched from the tool storing apparatus and supplied to the tool carrier. 
   Owing to the provision of a plurality of transit stations, it is also possible, for example, to provide fetching stations for supplying tools to the tool carrier(s) and bringing stations for delivering tools from the corresponding tool carriers. Stoppage times for the machine tool can thus be minimized during the tool exchange, as a new tool can be held in readiness when an old tool is detached from a tool carrier. 
   Preferably, in this case, at least one transit station is assigned to the at least one tool carrier. Fetching of a tool by the tool carrier and bringing of a tool by the tool carrier can then therefore be controlled thereby in a simple manner, as the latter only has to approach the assigned transit station or assigned transit stations. 
   In particular, at least one transit station is assigned to each tool carrier. A tool change can then be carried out in a defined manner for each tool carrier in a machine tool with a plurality of tool carriers, for example a multi-spindle machine tool. 
   It is favorable if the inward transit direction, when introducing a tool into the at least one transit station to detach the tool from the assigned tool carrier, and the outward transit direction, when extracting a tool fixed to a tool carrier from the transit station or a further transit station, are substantially oriented in opposite directions. There are then defined directions at the machine tool, with it being possible to implement the corresponding inward transit or outward transit of the tool by means of linear movements. 
   For the same reason, it is advantageous if the outward transit direction, when extracting a tool detached from a tool carrier from the at least one transit station, and the inward transit direction, when introducing a tool for fixing to the tool carrier provided into the transit station or a further transit station, are substantially oriented in opposite directions. 
   It is quite particularly advantageous, when a first transit station for detaching a tool from the tool carrier and a second transit station for fixing a tool to the tool carrier are assigned to the at least one tool carrier. Stoppage times during a tool change can thus be minimized, as a new tool can be held in readiness in the second transit station when the old tool at the first transit station is detached from the corresponding tool carrier. The first transit station and the second transit station, in this case, are preferably arranged adjacently, so the travel movement of the tool carrier is minimized, once the tool carrier has delivered its old tool and is to receive a new tool at the second transit station. 
   It is favorable when the inward transit direction and the outward transit direction at the at least one transit station form a transit direction (pass-through direction). The inward transit direction and the outward transit direction can coincide in this case or be spaced apart from one another in parallel, when the position of the transit station in an inward transit position and an outward transit position differs. A tool can then be pushed to a certain extent through the corresponding transit station, in order to deposit it in this manner after detachment from the tool carrier or, after supply from a tool storing apparatus, to fix it to a tool carrier and to guide it away with the tool carrier. 
   It is basically possible for the inward transit direction and the outward transit direction to lie transversely with respect to one another and, for example, to lie at an angle of 90° with respect to one another. If they form a single transit direction, i.e., if they lie in parallel or coincide, then it is also possible to achieve holding of the tool for detachment from the tool carrier or fixing to the tool carrier in a simple manner with respect to design. It is also favorable then, if the transit direction is a vertical direction, to configure the device in conjunction with a tool storing apparatus and a transporting apparatus for transportation of tools between the tool storing device and the at least one transit station in a space saving manner. 
   A space saving configuration can also be achieved when the transit direction for detaching a tool and passing it to a tool storing apparatus and the transit direction for introducing a tool from the tool storing apparatus and fixing the tool to the tool carrier provided are substantially oriented in opposite directions. This ensures that a tool carrier for a tool change in the region of the transit stations substantially only has to carry out a linear movement in the transit direction. This also applies to a transporting apparatus that delivers tools from the tool storing apparatus or fetches them from the corresponding transit station in order to supply them to the tool storing apparatus. 
   Advantageously, the at least one transit station is arranged in a movement space, or preferably at the edge of a movement space, of the at least one tool carrier. This makes it possible for the tool carrier to be able to deliver a tool to the transit station or fetch it therefrom. The transit station itself then no longer needs to be movable as a whole in order to be able to fetch a tool. However, it may be movable for removing a tool from the tool carrier or for inserting a tool on the tool carrier. As a result of this, a transporting apparatus for transporting tools between the tool storing apparatus and the transit station(s) can in turn be configured separately and, in particular, can be arranged outside the movement space. This ensures freedom from collisions. Moreover, the provision of tools and the detachment or fixing of tools can be at least partially decoupled with respect to tool carriers and this allows machine stoppages during a tool change to be reduced. 
   In a variant of an embodiment, the at least one transit station is rigidly arranged relative to a machine frame of the machine tool. A separation can thus be implemented between a movement space of the tool carrier(s) and a transporting space, in which a transporting apparatus moves and transports tools between the transit station(s) and a tool storing apparatus. The at least one tool carrier is movable, in this case, preferably transversely to the inward transit direction and outward transit direction, so a tool can be removed from the tool carrier by movement thereof or can be inserted on it by movement thereof. 
   In an alternative embodiment, the at least one transit station is movably arranged with respect to a machine frame of the machine tool. This embodiment is particularly advantageous when the at least one tool carrier has no mobility in a removal direction or insertion direction of the tool on the tool carrier. By means of a movement of the transit station, depending on the movement direction, a tool can then be removed from the tool carrier or a tool inserted on the assigned tool carrier. 
   The at least one transit station is then preferably displaceable transversely to the inward transit direction and outward transit direction, and, in particular, vertically displaceable with respect to these directions. By means of a movement of the transit station, a tool can then be removed from the tool carrier or a tool can be inserted in the assigned tool carrier. The tool changing device in accordance with the invention can then also be used, for example, on a tool machine, in which no mobility in the Z-direction is provided for the tool spindle or tool spindles, for example when the tool spindle or tool spindles are not configured as spindle sleeves. 
   It may be provided that the at least one transit station is arranged on a movable slide, the movement space of this slide preferably lying outside the movement space of the at least one tool carrier. The relative position between the at least one transit station and the at least one tool carrier can be changed by means of a movement of the slide. In this manner, a fixing apparatus and detachment apparatus for tools can be formed in the tool carrier. The movement space of the slide can be limited in this case, as only the mode of functioning of tool removal or tool insertion has to be ensured. The slide is preferably driven and, in this case, driven in a synchronized manner with a tool changing process, in order to now be able to carry out a tool change. 
   In particular, the at least one transit station is movable between an inward transit position and an outward transit position, in order to thus be able to fetch tools from the assigned tool carrier or deliver them thereto. 
   A tool is held by the assigned transit station, in particular, during the movement between the inward transit position and the outward transit position. An intermediate location, at which a tool is held, is thereby movably configured. 
   The at least one transit station is, in particular, connected to a tool storing apparatus, so tools can be supplied from the tool storing apparatus to the transit station and tools can be supplied from the transit station to the tool storing apparatus. 
   A supply location or delivery location for tools with respect to a tool carrier is provided by the at least one transit station. In order to connect this supply location or delivery location to a tool storing apparatus, a transporting apparatus advantageously moves for the transportation of tools between the at least one transit station and the tool storing apparatus outside a movement space of the at least one tool carrier. This transporting space for tools, which corresponds to the movement space of the transporting apparatus, is then decoupled from the actual working space of the machine tool, in which the tool carriers are movable. The transporting apparatus can then be configured in a simple manner as it can fetch the tools at defined locations, namely the transit station(s) or the tool storing apparatus, or can deliver them at such defined and spatially fixed locations. The degrees of freedom with respect to the mobility of the transporting apparatus can thus be reduced, so the latter can in turn be configured more simply in terms of design. The transporting apparatus comprises, for example, a cross slide, which can be moved by corresponding guides in directions lying transversely with respect to one another. 
   Advantageously, a detachment apparatus for detaching a tool from a tool carrier is provided for the at least one transit station. For the same reason, it is favorable if a fixing apparatus for fixing a tool to a tool carrier is provided for the at least one transit station. A tool change can then be carried out, in this case, during transit through the corresponding transit station, in a simple manner. The detachment apparatus and the fixing apparatus can be formed by means of a movement apparatus for the at least one transit station. 
   In this context, it is advantageous if a tool is held in an intermediate location at the at least one transit station. This intermediate location, which is, in particular, spatially defined and may be rigid or movable, is used to detach a tool from a tool carrier or to fix it to a tool carrier. Holding of this type can be achieved in a simple manner in terms of design if the tool is positively held at the intermediate location. Corresponding gripper elements then grip the tool in such a manner that it does not fall from this intermediate location. A holding apparatus is provided, in particular, for this purpose, in order to hold the tool at an intermediate location. 
   It is favorable when, during a movement of the tool into an intermediate location, a movement of the tool in the opposite direction can be blocked. Falling out is thus prevented, in particular, for as long as the tool is not yet positively held in the intermediate location. This blocking may be brought about, for example, in that the tool is still held on the tool carrier, when it is pushed into the intermediate location or is held on a transporting apparatus such as a cross slide, when it is pushed into the intermediate location. 
   It is quite particularly advantageous when at least one separate bringing location (delivery or supply location) and fetching location are provided for the tool as intermediate locations. A tool, which has been delivered by a tool carrier for exchange can be held via a bringing location. A tool which has been delivered from the tool storing apparatus for tool change to a tool carrier can be held via a fetching location. Machine stoppage times for the tool change can be minimized by the provision of separate bringing locations and fetching locations. 
   A tool change can be carried out in a simple manner in terms of design when the holding apparatus comprises opposing corresponding gripper elements, by means of which a tool can be positively held. These gripper elements then hold the tool in order to be able to detach it from the assigned tool carrier or in order to be able to fix it to the tool carrier provided. If a tool is positively held between the corresponding gripper elements, the tool carrier can then be guided away. The gripper elements are, in this case, in particular, configured to be movable in such a way that introduction into an intermediate space is made possible and extraction is also made possible. 
   The gripper elements are, in particular, arranged to be rotatable for this purpose. It can be achieved, by means of a corresponding rotary movement or pivoting movement of the gripper elements, that a tool can be passed through the corresponding transit station. In specific rotary positions, inward or outward transit is possible and in other specific rotary positions, positive holding is possible. 
   It is favorable if a blocking apparatus is provided for blocking the rotary movement. It can be achieved during blocked rotary movement that a position of the gripper elements, in which the latter hold a tool in a positive manner, is secured. 
   For example, the blocking apparatus comprises a spring-loaded pawl, which can be immersed in a blocking receiver of a gripper element. The rotary movement of a gripper element can thus be blocked in a simple manner in terms of design. The pawl is adapted to the assigned gripper element, for example, in such a manner that a rotary movement is only allowed in one direction of rotation. This allows a transit station to be produced, in which a tool can only be passed through in one transit direction. For example, a blocking position is adjusted such that a specific application of force is necessary in order to release it. This application of force may then be applied, for example, via a tool carrier (tool spindle) during entry. 
   The gripper elements are, in particular, configured such that a rotary movement can be initiated via a movement of the tool. The movement of the tool in turn takes place via a tool carrier or via a transporting apparatus for tools. This allows automatic grasping of tools by the gripper elements. It is quite particularly advantageous if the shaping of the gripper elements is adapted to the tool to be held, in order to thus make positive holding possible. 
   In one embodiment, the gripper elements can be rotated in an angle range, which is a partial angle of 360°. In particular, the gripper elements can then be fork-shaped and arranged in a pivotable manner. The space requirement for such fork elements is relatively small. 
   In a further embodiment, the gripper elements can be rotated in a full angle range and are, in particular, rotatable. Transit including positive holding in an intermediate location can then be obtained via a corresponding peripheral rotary movement of the gripper elements. A corresponding rotary movement in the case of gripper elements of this type can be initiated in a simple manner in terms of design via a tool movement. 
   The axis of rotation of the gripper elements is preferably transverse and in particular vertical to the transit direction, in order to thus make a transit with positive holding possible in an intermediate location. The gripper elements can be configured as gripper forks. It is also possible for the gripper elements to have a plurality of receivers for a tool, in each case. By rotating the gripper elements, positive holding can thus be achieved at an intermediate location. In particular, adjacent receivers are separated, in this case, by an arm. The gripper elements are then preferably star-shaped. 
   It is also advantageous if the directions of rotation of the opposing corresponding gripper elements are oriented in opposite directions. The spacing between corresponding points of the corresponding gripper elements can thus be changed, i.e., increased and reduced. This allows positive holding in one or more specific rotary positions of the gripper elements and, in other rotary positions, a release of this positive holding position, in order to thus be able to in turn transit a tool inwardly or outwardly. 
   A machine tool, for which a tool storing apparatus is provided, in particular, can be provided with the tool changing device in accordance with the invention. In accordance with the invention, a method is provided with which the machine stoppage times during tool change are minimized. 
   With this method, a tool is introduced in an inward transit direction into a transit station, at which the tool is detached from the assigned tool carrier or the tool is fixed to the tool carrier provided, and is extracted in an outward transit direction. 
   The method in accordance with the invention has the advantage already described in conjunction with the device in accordance with the invention. Further advantageous configurations have also already been described in conjunction with the device in accordance with the invention. 
   In particular, the inward transit direction and the outward transit direction are rigidly predetermined and are fixed spatially with respect to the machine tool. A defined fetching from the transit station or a defined bringing of tools to the transit station can thus be achieved. The inward transit direction and the outward transit direction at a transit station advantageously form a transit direction. 
   The following description of preferred embodiments is used in conjunction with the drawings for a more detailed description of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to assist the understanding of embodiments of the invention, reference will now be made to the appended drawings, which are not necessarily drawn to scale, and wherein: 
       FIG. 1  shows a schematic front view of an embodiment of a machine tool, which is provided with an embodiment of a tool changing device in accordance with the invention; 
       FIG. 2  shows an enlarged view of part elements of the tool changing device from the region A according to  FIG. 1 ; 
       FIG. 3  shows a sectional view along the line  3 — 3  according to  FIG. 1 ; 
       FIG. 4  shows an enlarged sectional view of the region B according to  FIG. 1  with a transporting apparatus for tools; 
       FIG. 5  shows a,plan view in the direction C according to  FIG. 4  of the transporting apparatus; 
       FIG. 6  shows a schematic view of an embodiment of gripper elements for holding tools; 
       FIG. 7  shows a schematic view of an embodiment of a blocking apparatus for blocking the rotary movement of gripper elements in a non-blocking intermediate state; and 
       FIG. 8  shows a detailed view of the blocking apparatus according to  FIG. 7  in a blocking position. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention now will be described more fully hereinafter. However, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. As used in this specification and the claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. 
   The tool changing device in accordance with the invention, of which an embodiment is shown in  FIG. 1  and is designated there as a whole by  10 , is assigned to a machine tool designated as a whole by  12 . The tool changing device  10  may, in this case, be an integral component of the machine tool  12  or be fitted thereto retrospectively. In the embodiment shown in  FIG. 1 , the machine tool is a two-spindle tool, which, as tool carriers  14  and  16 , comprises tool spindles, in each case. 
   The tool changing device according to the invention can basically be used on all types of machine tools with movable tool carriers. The tool carriers  14  and  16  may be non-movable in the Z-direction (which lies transverse to the plane of the drawing in  FIG. 1 ) or be configured as spindle sleeves, which are displaceable along their longitudinal axis (the Z-direction). 
   The machine tool  12  comprises a machine frame  18  with a machine bed  20 . The machine frame  18  is erected in a fixed manner. The tool carriers  14 ,  16  are movably guided with respect to the machine frame  18  in the X-direction and Y-direction. For this purpose, in the embodiment shown in  FIG. 1 , a tool carrier slide  22  is provided, which holds the two tool carriers  14  and  16 . This tool carrier slide  22  is displaceably guided in turn, for example in the vertical direction, on a guide apparatus  24 . Further tool carrier slides  22  may be provided, in order to also ensure mobility of the tool carriers  14 ,  16  in a transverse direction. The guide apparatus  24  is rigidly arranged with respect to the machine frame  18 . 
   The tool carriers  14 ,  16  have a movement space  26 , which is determined by the mobility of the tool carrier slide(s)  22  and optionally of the tool carriers  14 ,  16  in the Z-direction. 
   A tool storing apparatus  28 , in which a plurality of tools are stored, is provided; these tools are indicated by the reference numeral  30  in  FIG. 1 . Tools can be changed on the tool carriers  14 ,  16  by the tool changing device  10 , with it being possible to supply tools for depositing to the tool storing apparatus  28  and it being possible to supply tools from the tool storing apparatus  28  for changing. 
   The tool changing device  10  has, in accordance with the invention, at least one transit station  32 , which may be arranged rigidly or movably with respect to the machine frame  18 . In the embodiment shown, the tool carriers  14  and  16  are assigned their own transit stations  34   a,    34   b  and  36   a,    36   b,  in each case, which sit on a slide  37  ( FIGS. 4 and 5 ). The two-spindle tool thus has four transit stations  32 . 
   For the tool carrier  14 , the transit station  34   a  is a fetching station, via which the tool carrier  14  can fetch a tool. The transit station  34   b  is configured as a bringing station (delivery or supply station), to which the tool carrier  14  can bring a tool, in order to carry out a tool change. The same circumstances apply to the tool carrier  16  with its assigned transit stations  36   a  and  36   b.    
   It is basically possible for a transit station  32  to be configured both as a fetching station and a bringing station, via which a tool can be supplied to the corresponding tool carrier and via which an exchanged tool can be guided away from the tool carrier. If separate transit stations  34   a,    34   b  or  36   a,    36   b  are provided for fetching and bringing, a tool exchange can be carried out more quickly, as, for example, during a bringing process, a new tool can already be waiting in the fetching station or can be delivered to the latter. Tool changing times can thus be shortened. 
   The transit station  34   a,  as a fetching station, has an inward transit direction  38 , in which a tool  40  can be introduced into the transit station  34   a.  The tool  40  is delivered from the tool storing apparatus  28  via a transporting apparatus  42 , which comprises, for example a cross slide  44 . During inward transit, this transporting apparatus  42  holds the tool  40 . 
   The tool  40  leaves the transit station  34   a  in an outward transit direction  46 . This outward transit direction  46  preferably coincides with the inward transit direction  38  or is parallel thereto, so the tool  40  can be passed through in a transit direction  48  through the transit station  34   a.  When the tool  40  is extracted from the transit station  34   a  in the outward transit direction  46 , it fits on the tool carrier  14 . In the transit station  34   a,  the tool  40  is fixed to the tool carrier  14 . For this purpose, a fixing device, designed as a whole by  50 , is provided. 
   As described in more detail below, the outward transit direction  46  and the inward transit direction  38  can be offset in parallel owing to a transverse movement of the transit station  34   a,  between the inward transit position and the outward transit position. 
   The adjacent transit station  34   b,  which is configured as a bringing station, has an inward transit direction  52 , which opposes the inward transit direction  38 . A tool  54 , which sits on the tool carrier  14 , can be introduced in this direction  52  into the transit station  34   b.    
   The tool  54  is detached from the tool carrier  14  in the transit station. A corresponding detachment apparatus  56  is provided for this purpose. 
   The detached tool  54  can be guided from the transit station  34   b  in an outward transit direction  58 , which opposes the outward transit direction  46 . The outward transit direction  58  preferably coincides with the inward transit direction  52  or is parallel thereto, so a transit direction  60  is present for the tool  54  through the transit station  34   b.  This transit direction  60  opposes the transit direction  58  of the fetching station  34   a.    
   As is described below in more detail, the outward transit direction  58  and the inward transit direction  52  can be offset in parallel owing to a transverse movement of the slide  37 , between the inward transit position and outward transit position. 
   During outward transit of the tool  54  in the outward transit direction  58 , the latter is held by the cross slide  44 . It is then supplied to the tool storing apparatus  28  for depositing. 
   The same circumstances apply correspondingly to the transit stations  36   a  and  36   b,  which are assigned to the tool carrier  16 . 
   In the embodiment shown, the transit directions  48  and  60  are parallel to the movement direction of the tool carrier slide  22  (in the Y-direction). Tools can thus be fetched or brought by movement of the tool carrier  14 ,  16  via the tool carrier slide  22 . 
   Each transit station  32  comprises a holding apparatus  62 , in order to hold a tool  30  or  54  in an intermediate location  64  or  66 . In the transit station  34   a,  the tool  40  is held in the intermediate location  64  by the assigned holding apparatus  62 , in order to be able to fix it to the tool carrier  14 . The tool  54  is held in the intermediate location  66  of the transit station  34   b,  in order to be able to detach it from the tool carrier  14  and to then hold it after detachment. The tool  40  is guided at the transit station  34   a  in the transit direction  48  through the intermediate location  64 . The tool  54  is guided in the transit station  34   b  in the transit direction  60  through the intermediate location  66 . 
   The holding apparatus  62 , in each case, comprises opposing gripper elements  68 ,  70 , which are forked-shaped in the embodiment shown in  FIG. 2 . The gripper elements  68 ,  70  are rotatably or pivotably mounted here, in each case. Their axes of rotation lie transversely and, in particular vertically, with respect to the transit direction  48 . 
   The gripper elements  68 ,  70 , in this case have directions of rotation or pivoting directions, which are opposed to one another. In a movement of the two gripper elements  68 ,  70  these then either move toward one another or away from one another. 
   Owing to the gripper elements  68 ,  70 , the tool  40  can be positively held at the intermediate location  64 . The gripper elements  68 ,  70  are adapted, in this case, with respect to their shaping, accordingly to the tool  40 . Together they form a receiver  72  which, to hold the tool  40  at the intermediate location  64 , blocks a movement of the tool  40  from the intermediate location  64 , i.e. blocks it with respect to the inward transit direction  38  and also in the outward transit direction  46 . This blocking is caused in that the tool  40  rests on corresponding walls of the gripper elements  68 ,  70  delimiting the receiver  72 . 
   In order to hold the tool  40  at the intermediate location  64  in this intermediate position, in which the tool  40  can be fixed to the tool carrier  14  via the fixing apparatus  50 , a blocking device designated as a whole by  74  is provided, which prevents the gripper elements  68 ,  70  of the holding apparatus  72  rotating out of the holding position. For example, the blocking device  74  comprises suitable stop elements  76 , in each case, for the gripper element  68  and the gripper element  70  which block a rotary movement of the gripper elements  68 ,  70 . The stop element  76  can thus be controlled or switched, in this case, in such a way that a rotary movement of the gripper elements  68 ,  70 , can be released, in order to be able to now guide the tool  40  fixed to the tool carrier  14  from the transit station  34   a.    
   It is preferably provided that a rotary movement of the gripper elements  68 ,  70 , can be initiated, via a movement and, in particular a linear movement of the tool  40 . The gripper elements  68 ,  70  are configured accordingly. In the embodiment shown in  FIG. 2 , they have, in each case, surfaces  78 , located at an angle based on the transit direction  38 , in each case toward the transporting direction  42 , when they are rotated toward one another. When the tool  40  is moved via the cross slide  44  into an intermediate location between the opposing surfaces  78  of the respective gripper elements  68 ,  70 , this brings about a rotation away from one another of the gripper elements  68 ,  70  (when the blocking apparatus  74  is released). The tool  40  can thus be immersed in a trough-shaped region of the two gripper elements  68 ,  70 , which then forms the receiver  72 . When the tool  40  is located in the receiver  72 , it can be ensured, for example, via spring loading that the gripper elements  68 ,  70  rotate toward one another again. This rotary position is fixed via the blocking apparatus  74 . The tool  40  is now positively held in the intermediate location  64  in the receiver  72 . It can then be fixed to the tool carrier  14 , the tool carrier  14  being correspondingly brought to the tool  40 , in order to be able to implement this fixing. 
   After fixing the tool  40  to the tool carrier  14 , the blocking device  74  is released. The tool carrier  14  with the fixed tool  40  can then move away in the outward transit direction  46 . 
   The transit station  34   b  basically functions in the same manner, the tool  54  being detached from the tool carrier  14  at this bringing station at the intermediate location  66 . The detached tool  54  can then be moved away in the outward transit direction  58 . 
   The tool carrier  14 , which is then without a tool, is moved to the transit station  34   a  in order to be able to now receive the tool  40  there, as described above. 
   A sectional view is shown in  FIG. 3 , in which the gripper elements  68 ,  70  of the transit station  34   a  positively hold the tool  40 . In this position, the tool  40  can be detached from the tool carrier  14 ′. 
   Next to this, a situation is shown for the transit station  34   b,  in which corresponding gripper elements  80 ,  82  are in a rotary position such that the tool  54  can be extracted upwardly after detachment from the tool carrier  14 ″, upwardly in the outward transit direction  58 . As the transit stations  34   a  and  34   b  are assigned in the example to a single tool carrier  14 , the tool carrier, from which the tool  54  was detached, is designated  14 ′ and  14 ″ (i.e., the tool carriers  14 ′ and  14 ″ are the same tool carrier). 
   In the situation shown in  FIG. 3 , the tool carrier  14 ″ is prepared for receiving a new tool (for example the tool  40 ). A tool exchange is carried out at the tool carrier  14 ′. This now carries the tool  40 . 
   The transporting apparatus  42  with its cross slide  44  is movable outside the movement space  26  of the tool carriers  14 ,  16 , so there is no risk of collision between the transporting apparatus  42  and the tool carriers  14 ,  16 . The cross slide  44  is linearly displaceable, for example transversely in a direction  84  (parallel to the X-direction) and, in particular, vertically with respect to the transit directions  48 ,  60  and displaceable in a direction  86  (parallel to the Y-direction) parallel to the transit directions  48 ,  60  ( FIGS. 2 ,  4 ,  5 ). 
   The transporting apparatus  42  is the binding member between the transit stations  32  and the tool storing apparatus  28 . The cross slide  44  guides tools  30  from the tool storing apparatus  28  to the transit stations  32  and guides tools away from the transit stations  32  to the tool storing apparatus  28  for depositing. The tool changing device  10  is arranged with respect to the movement space of the tool carriers  14 ,  16  in such a way that the tool carriers  14 ,  16  can deliver tools or receive them. It is preferably arranged at the edge of the movement space  26 . The cross slide  44  is guided outside the movement space  26  and for example above the transit stations  32 . This is indicated in  FIG. 4 . The cross slide comprises a column  88 , which can be displaced in the direction  84 , on which a tool bringing/fetching slide  90  is guided in the direction  86 . 
   The column  88  and the tool bringing/fetching slide  90  form the cross slide  44 . The movement of the tool bringing/fetching slide  90  in the direction  86  is driven by a motor  91  arranged on the column  88 . To move the column  88 , a motor, which is arranged on the latter, is provided ( FIG. 1 ). The motor  92  drives a threaded rod  93 , which is oriented along the column  88 ; a pinion-toothed rack drive is provided for movement of the column  88 . The column  88  is oriented in the example shown ( FIG. 1 ) in the vertical direction (based on the direction of gravitational force). The tool-bringing/fetching slide  90  can be displaced with respect to height on the column  88  and can be displaced with the column  88  in the transverse direction  84 . Tools  30  can be deposited in specific height positions in the tool storing apparatus  28  via a movement along the column  88 . 
   Moreover, a guide  94  for the movement of the cross slide  44  along the direction  84  is provided by displacement of the column  88  ( FIG. 1 ). This guide  94  is rigidly arranged with respect to the machine frame  18  and with respect to the transit stations  32 . The guide plane for the guide  94 , in this case, lies transversely and, in particular, vertically with respect to the transit directions  48 ,  60 . The movement of the column  88  in the direction  84  is driven by means of the threaded rod  93 , which is driven in turn by the motor  92 . The threaded rod  93  is coupled accordingly to the guide  94  and the guide is configured in an adapted manner. The cross slide  44  can be brought into a respective defined position in the X-direction, via the movement in the direction  84 , in order to supply a corresponding tool to the transit station  32  or to guide it away therefrom. 
   It can basically be provided that the transit stations  32  are arranged rigidly and in particular non-movably with respect to the machine frame  80 . The tools are decoupled in the assigned tool carriers  14 ,  16  or the tools are coupled into the tool carriers  14 ,  16  when the corresponding tools are fixed in the assigned transit stations  32 , by means of a movement of the tool carriers  14 ,  16  in the Z-direction; for this purpose, a corresponding mobility of the tool carriers  14 ,  16  in the Z-direction must be permitted. If the tool carriers  14 ,  16  are for example spindle sleeves, these can be moved in the Z-direction. 
   It may also alternatively be provided, that the transit stations  32 , as shown in  FIGS. 4 and 5 , are arranged on a slide  37 , which can be moved in a direction  202  parallel to the Z-direction. The removal of the tools from the assigned tool carriers  14 ,  16  or insertion, does not then take place via a movement of the tool carriers  14 ,  16  themselves, but via a movement of the slide  37 . A movable slide  37  of this type is provided, in particular, when no Z-lift is provided for the tool carriers  14 ,  16 . 
   The slide  37  is guided on a guide  204 , which allows mobility in the direction  202 . The slide  37  holds the transit stations  32 ; in the embodiment shown, it holds the transit stations  34   a,    34   b  and  36   a  and  36   b.    
   The movement space of the slide  37  preferably lies outside the movement space of the tool carriers  14 ,  16 . 
   Provided for the movement of the slide  37  is a spindle motor  206  which drives a shaft  208 . The shaft  208  is configured, for example, in the manner of a crankshaft, on which eccentric elements  210  are arranged, via which a rotational movement of the shaft  208  can be converted into a translatory movement. The shaft  208  is rotatably mounted on the machine frame  18  via bearings  209  and in a non-translational manner with respect to the machine frame  18 . 
   The eccentric elements  210  are connected, for example, to a connecting rod  212 , in each case, the connecting rod being connected in turn via pivot bearings  214  to the slide  37 . By rotating the shaft  208 , the slide  37  can be moved in the Z-direction relative to a fixed beam  216 , on which the shaft  208  is mounted. The totality of the transit stations  32  can thereby be moved in turn relative to the tool carriers  14 ,  16  in the Z-direction. 
   If, for example, a tool is to be removed from the tool carrier  14 , the slide  37  moves with the transit station  34   b  toward the tool carrier  14 . When the tool is gripped in the transit station  34   b,  the slide  37  moves away from the tool carrier  14  and in the process decouples the corresponding tool from the tool carrier  14 . The tool can then be gripped by the cross slide  44 , in order to deposit it in the tool storing apparatus  28 . 
   In order to insert a tool on the tool carrier  14 , the corresponding tool is delivered from the tool storing apparatus  28  via the cross slide  44  to the transit station  34   a,  with it being gripped by the latter when the slide  37  is positioned away from the tool carrier  14 . The slide  37  then moves in the Z-direction toward the tool carrier  14 , which was previously brought into the corresponding X-Y-position. The tool is then inserted thereby in the tool carrier  14 . 
   The movement direction of the slide  37  to remove and insert the tools is, in this case, preferably transverse and, in particular, vertical with respect to the transit directions  48 ,  60 . When a slide  37 , which can be moved in the Z-direction, is provided for the transit station  32 , the inward transit position of a transit station and the outward transit position of a transit station are spaced apart from one another in the Z-direction. For example, the transit station  34   a  as a fetching station, has a greater spacing from the tool carrier  14  in the inward transit position, when a tool is coupled into the transit station  34   a  by the cross slide  44  from the tool storing apparatus  28 , than in the outward transit position. When the tool is decoupled from the transit station  34   a,  the transit station  34   a  then lies closer to the tool carrier  14 . 
   Accordingly, the transit station  34   b  as the bringing station lies closer to the tool carrier  14  when a tool is passed inwardly together with the tool carrier  14 . In the outward transit position, in which a tool is removed by the cross slide  44  in order to supply it to the tool storing apparatus  28 , the tool transit station  34   b,  in the Z-direction, is spaced apart from the inward transit position. 
   The fixing apparatus  50  for fixing a tool to a tool carrier and the detachment apparatus  56  for detaching a tool from a tool carrier comprise the movable slide  37  in order to thus allow feeding in and out. 
   In order to be able to carry out a tool change, the rotary movement of the shaft  208  is controlled. This control takes place in such a way that the slide  37  is accordingly provided when a tool or tools is or are delivered or provided from the tool storing apparatus  28  and when the tool carriers  14 ,  16  deliver tools to the tool changing device  10 . 
   In a further embodiment of a holding apparatus, which is shown schematically in a partial view in  FIG. 6  and is designated as a whole there by  94 , rotatable gripper elements  100 ,  102  are provided in each case at adjacent transit stations  96 ,  98 . The transit station  96  is configured, for example, as a fetching station for the tool carrier  14  and the transit station  98  is configured, for example, as a bringing station for this tool carrier  14 . (In  FIG. 6 , the same reference numerals are used for the elements of the machine tool as in  FIG. 1 .) 
   The transit station  96  has a transit direction  104 , which is opposed to the transit direction  106  for the transit station  98 . The transit directions  104 ,  106  are oriented, for example, parallel to the gravitational force direction. 
   The gripper elements  100 ,  102  are star-shaped in this example, with a plurality of receivers  108   a,    108   b,    108   c,    108   d  for the gripper element  108  and with a plurality of corresponding receivers  110   a,    110   b,    110   c,    110   d  for the gripper element  102 . In the embodiment shown, four receivers are provided. More or less receivers may also be provided. 
   Adjacent receivers, such as for example the receivers  108   a  and  108   b,  are separated by an intermediate arm  112 . They are trough-shaped at their respective intermediate arms  112 . 
   The gripper elements  100 ,  102  are in each case rotatably mounted with an axis of rotation which is vertical with respect to the transit directions  104 ,  106 . They can in this case, be rotated, in particular, about a full angle. The directions of rotation are opposing in each case, so corresponding intermediate arms  112  of the two gripper elements  100 ,  102 , either move away from one another or toward one another. 
   The corresponding receivers of the two gripper elements  100 ,  102 , for example the receivers  108   a  and  110   a,  are configured in such a way that the tool  40  is positively held at an intermediate location, in order to be able to fix the tool  40  to the tool carrier  14 . 
   The gripper elements for the transit station  98  are correspondingly configured in order to be able to detach the tool  54  held on the tool carrier  14  at the intermediate location. 
   In order to prevent further rotation of the assigned gripper elements  100 ,  102  when the tool  40  or  54  is positively held at an intermediate location, a blocking apparatus is provided as described above, which now blocks the rotary movement of the gripper elements  100 ,  102 . The tool  40  or  54  is then securely held. 
   An embodiment of a blocking apparatus, which is shown in  FIG. 7 and 8  and is designated as a whole by  120  there, comprises a pawl  124  rotatably mounted about an axis  122 . The axis  122  lies parallel to an axis of rotation  126  of the assigned gripper element (in  FIGS. 7 and 8 , of the gripper element  100 ). 
   The pawl is spring-loaded via a compression spring  128 . The spring force acts in a direction  130 , which, in the embodiment shown, is substantially parallel to the gravitational force direction. The compression spring  128  exerts a torque on the pawl  124 , via which the latter is pressed against a contact element  132 . 
   The compression spring  128  is supported for this purpose on a support element  134  with a holding pin  136  and is pushed on to a holding pin  138  of the pawl  124 . 
     FIG. 7  shows a position of the pawl  124 , in which the latter rests on the contact element  132 . In this position, a rotation of the gripper element  100  in a direction of rotation  140  is possible, and to be precise, until an immersion region  142  is immersed in a blocking receiver  144  of the gripper element  100  ( FIG. 8 ). The pawl  124  is pivoted via the gripper element  100  about the axis  122  in the direction counter to the direction of rotation  140  by means of the rotation of the gripper element  100  in the direction of rotation  140  and, in this case, the compression spring  128  is compressed. When the immersion region  142  is immersed in the blocking receiver  144 , the compression spring  128  presses this immersion region  142  into the assigned blocking receiver  144  and thus ensures (non-positive) fixing of the gripper element  100  in a specific rotary position. 
   The blocking can be eliminated in that a torque is exerted, in particular via a tool carrier such as a tool spindle, on the gripper element  100 , so the immersion region  142  is lifted from the blocking receiver  144 . The pawl  124  is configured at the immersion region  142  and in the vicinity thereof in such a way that such lifting out from the blocking receiver  144  is made possible. The blocking receiver  144  is also configured in a correspondingly adapted manner. 
   When the corresponding intermediate space  112 , at which the blocking receiver  144  is configured, is rotated beyond the region of the pawl  124 , the compression spring  128  then presses the pawl  124  in turn onto the contact element  132 ; a blocking of further rotation can then be achieved at the next rotary position to hold a tool. 
   Otherwise, the holding apparatus  94  functions as described above for the holding apparatus  62 . 
   According to the invention, a tool is passed through the respective transit station  32  for the tool change. The tool is supplied to the assigned transit station with respect to the movement space of the tool carriers  14 ,  16  by these tool carriers, or fetched therefrom. The transit stations  32  can be non-displaceably arranged with respect to the machine frame  18 , i.e. they do not move. 
   However, they may also be movable via a slide  37  which is movable in the Z-direction, as shown in  FIGS. 4 and 5 . Removal or insertion of the tools then takes place via a slide movement, when the tool carriers  14 ,  16  cannot themselves carry out a lifting movement in the Z-direction. In particular, no movement is provided inside the movement space  26 . 
   The tools are fetched from the transit station(s)  32  by the transporting apparatus  42 , which in particular comprises a cross slide  44  and supplied to the tool storing apparatus  28  for depositing, or tools provided for a tool change are fetched from the tool storing apparatus  28  by the cross slide  44  and supplied to the transit station(s)  32 . The transporting apparatus  42  moves, in this case, outside the movement space  26 , ensuring freedom from collision with the tool carriers  14 ,  16 . 
   Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing description. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.