Patent Publication Number: US-10786882-B2

Title: Machine tool, in particular multi-spindle turning machine

Description:
The present disclosure related to a machine tool, in particular a multi-spindle turninh machine. 
     BACKGROUND 
     In the prior art, machine tools, in particular multi-spindle turning machines, are known, including multiple workpiece spindles supported on a rotary drum (turret or turret body), wherein the rotary drum/turret body is configured to rotate/index the rotary drum/turret body around a longitudinal axis thereof. 
     For example, in EP 2 163 334 B2, a multi-spindle turning machine is described that has multiple workpiece spindles supported on a rotary drum, wherein the rotary drum is configured to rotate/index the rotary drum around a longitudinal axis thereof, and, for each workpiece spindle there is provided a tool assembly holding one or more tools. For relative movement between the workpieces received at the workpiece spindles and the tools of the tool assemblies, the spindles are movable in a Z-direction being axially arranged with the respective spindle axis. Further, each of the tool assemblies is configured to move in a radial X-direction with respect to the longitudinal rotation axis of the drum and in a tangential Y-direction with respect to the longitudinal rotation axis of the drum. 
     A drive mechanism for indexing a drum/turret of a multi-spindle turning machine using a torque motor is described in US 2013/0025408 A1. However, in US 2013/0025408 A1 the torque motor is arranged in a center portion of a full body turret, so that heat generated by the torque motor is easily dissipated through the turret body and thermal effects may affect the achievable level of accuracy in the machining processes on the turret side facing the workspace. Furthermore, the torque motor is described to not only drive the rotation of the drum/turret, but is further described to be used to lock the drum position during the actual machining of workpieces when the drum is held in a machining position during the machining of workpieces, however, this may actually lead to further increased thermal effects due to heat generated by the torque motor being kept energized during the machining operations. 
     It is an object of the present disclosure to further develop the concept of the multi-spindle turning machine of EP 2 163 334 B2, taking into account the above, and particularly to enhance the machining options of the multi-spindle turning machine, to provide a compact machine concept, allowing for more flexible, accurate, efficient and reliable machining operations, and/or to improve accuracy and/or stability of the machine tool. 
     SUMMARY 
     In view of one or more of the above objects, there is proposed a machine tool, in particular multi-spindle turning machine, according to claim  1 . The dependent claims relate to preferred exemplary embodiments. 
     According to some aspects, there may be provided a machine tool, in particular multi-spindle turning machine, comprising a machine frame, a turret body being rotatably supported by the machine frame, a plurality of workpiece spindles being arranged on the turret body, each of the workpiece spindles having a workpiece receiving portion for receiving a respective workpiece on one side of the turret body facing a working space of the machine tool. 
     In some exemplary aspects, each of the workpiece spindles may preferably be movable and/or slidable in a longitudinal direction (Z-direction), e.g. in parallel with the longitudinal rotational axis of the turret body and/or in parallel with the respective spindle axis. Accordingly, an advantageously compact design with independent accurate spindle movement in spindle axis direction can be provided. 
     Furthermore, in some exemplary aspects, there may be provided, for each workpiece spindle, a respective tool post assembly for holding one or more tools. The tool post assembly may preferably be movable in one or more, preferably two directions (X- and/or Y-directions), transversely or perpendicularly to the longitudinal direction. Accordingly, an advantageously compact design with independent accurate tool movement relative to the spindle axis, in particular in one or more directions transversely or perpendicularly to the respective spindle axis, can be provided. 
     In some preferred aspects, the machine tool may include a torque motor for driving a rotation of the turret body. Accordingly, a compact, efficient, precise and reliable drive mechanism for driving the rotation of the turret body can be provided. 
     In some preferred aspects, the torque motor may be arranged at a back end portion of the turret body, e.g. opposite to the side of the turret body facing the working space of the machine tool. Advantageously, such exemplary aspect allows to provide the torque motor on an opposite side as the working space area having the tool holder assemblies and other equipment, such that a balanced compact overall design can be provided, and the potential heat generating drive (torque motor) is provided at a distance to the working space area so that heat generation has minimal or almost no influence on equipment and assemblies at the side of the working space area, where high machining precision is required. 
     In some preferred aspects, a position locking mechanism for locking a rotational position of the turret body may be arranged at a front end portion of the turret body, e.g. on the side of the turret body facing the working space of the machine tool. Accordingly, the position locking mechanism is provided close (adjacent) to the working space area, where high machining precision is required, and therefore the position locking mechanism can lock positions very accurately and precisely to enable optimal exact spindle positioning during the machining operations. 
     In some preferred aspects, a position detecting mechanism for determining the rotational position of the turret body may be arranged at the front end portion of the turret body on the side of the turret body facing the working space of the machine tool. Accordingly, the position detecting mechanism is provided close (adjacent) to the working space area, where high machining precision is required, and therefore the position locking mechanism can lock positions very accurately and precisely based on the accurate and precise output of the position detecting mechanism to enable optimal exact spindle positioning during the machining operations. 
     In some preferred aspects, the position detecting mechanism may include an absolute encoder, in particular, wherein the absolute encoder may preferably be arranged around the whole circumference of the front end portion of the turret body. Accordingly, very accurate and precise position detection is provided. 
     In some preferred aspects, the position locking mechanism may include one or more hydraulic, pneumatic and/or electric brakes. 
     In some preferred aspects, the position locking mechanism may be arranged around the whole circumference of the front end portion of the turret body, e.g. by arranging brake mechanisms, particularly hydraulic, pneumatic and/or electric brakes, at circumferentially arranged positions. 
     In some preferred aspects, the machine frame may include a back frame portion rotatably supporting the back end portion of the turret body and/or a front frame portion rotatably supporting the front end portion of the turret body. 
     In some preferred aspects, a stator of the torque motor may be supported by the back frame portion of the machine frame, and/or a rotor of the torque motor may be arranged on the back end portion of the turret body. 
     In some preferred aspects, the position locking mechanism and/or a position detecting mechanism may be mounted to the front frame portion of the machine frame. 
     In some preferred aspects, a space may be provided between the back frame portion and the front end portion. 
     In some preferred aspects, the turret body has, preferably for each workpiece spindle, a longitudinally extending groove portion for receiving the workpiece spindle, the grooves preferably opening to the space provided between the back frame portion and the front end portion. 
     In some preferred aspects, the turret body supports, preferably for each workpiece spindle, a slide being guided on longitudinal slides extending longitudinally with respect to the turret body and/or being arranged on an outer side of the turret body adjacent to the respective groove. 
     In some preferred aspects, the turret body may support, preferably for each workpiece spindle, a drive mechanism for driving a longitudinal linear movement of the respective slide of the respective workpiece spindle. 
     In some preferred aspects, the drive mechanism may be arranged on a front end portion of the turret body and/or on a back end portion of the turret body, and/or a housing of the drive mechanism may extend radially with respect to the turret body into the space provided between the back frame portion and the front end portion. 
     In some preferred aspects, the turret body may be rotatably supported by two bearings, one bearing being preferably arranged on the back frame portion of the machine frame and another bearing being preferably arranged on the front frame portion of the machine frame. 
     In some preferred aspects, a safety brake system may be arranged on the back frame portion of the machine frame, wherein, exemplarily, the safety brake system may be including one or more electrically, pneumatically and/or hydraulically actuated brakes configured to brake a rotational movement of the turret body, wherein in particular the safety brake system may include one or more normally closed brakes being biased into a closing state by a biasing mechanism. 
     In some preferred aspects, a controller may be provided for controlling a machining of one or more workpieces received at the plurality of workpiece spindles, when the workpiece spindles are positioned at respective machining positions. 
     In some preferred aspects, the controller may be further configured to control the torque motor for controlling a rotational movement of the turret body for indexing the workpiece spindles between the respective machining positions and/or to control the position locking mechanism for locking the position of the workpiece spindles in the machining positions during the machining of the one or more workpieces. 
     In some preferred aspects, the controller may be configured to cut a control current of a control signal to the torque motor after a driven rotation of the turret body between the respective machining positions and to actuate the locking position locking mechanism before controlling the machining of the one or more workpieces; and/or the controller may be configured to loosen the locked position locking mechanism and to activate a control current of a control signal to the torque motor for driving a rotation of the turret body to the next respective machining positions after machining of the one or more workpieces at the current machining positions. 
     In addition or alternative to the above, independently or separately, the present invention further proposes a bar loader (or a combination of a machine tool with a bar loader, wherein the machine tool may be a single-spindle, double-spindle or multi-spindle lathe or turning machine). The bar loader may be configured to supply elongated workpieces, e.g. bars, from the rear side of the machine tool into the respective workpiece spindles of the one or more workpiece spindles of the machine tool. A main aspect of such bar loader may be that a bar loader guiding system is provided that includes three portions, including a fixed guide portion, a slidable middle guide portion and a slidable end guide portion. The slidable portions being arranged to have individual guides for each associated spindle which are respectively slidable into a direction of a spindle axis of its respective associated workpiece spindle. Such aspects may be provided for single-spindle, double-spindle or multi-spindle lathe or turning machines, in case of multi-spindle machines with or without rotary turret body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  exemplarily illustrates a schematic perspective view of a multi-spindle turning machine according to an exemplary embodiment; 
         FIGS. 2A and 2B  exemplarily illustrate schematic perspective views of a tool post assembly of the multi-spindle turning machine of  FIG. 1 ; 
         FIGS. 3A and 3B  exemplarily illustrate schematic perspective views of tool posts of the multi-spindle turning machine of  FIG. 1 ; 
         FIGS. 4A and 4B  exemplarily illustrate schematic perspective views of a tool post system of the multi-spindle turning machine of  FIG. 1 ; 
         FIG. 5  exemplarily illustrates a schematic perspective view of a chip conveyor for use at the multi-spindle turning machine of  FIG. 1 ; 
         FIGS. 6A and 6B  exemplary illustrate schematic perspective views of a multi-spindle turning machine according to another exemplary embodiment; 
         FIGS. 7A and 7B  exemplarily illustrate schematic perspective views of a drum of the multi-spindle turning machines of  FIGS. 1, 6A and 6B ; 
         FIGS. 8A to 8C  exemplary illustrate schematic perspective views of a multi-spindle turning machine according to yet another exemplary embodiment; 
         FIG. 9  exemplary illustrates a schematic perspective view of a multi-spindle turning machine according to yet another exemplary embodiment; 
         FIGS. 10A to 10D  exemplary illustrate schematic perspective views of a multi-spindle turning machine according to yet another exemplary embodiment; 
         FIGS. 11A and 11B  exemplary illustrate schematic perspective views of a counter-spindle assembly of the multi-spindle turning machines according to  FIGS. 10A to 10D ; 
         FIG. 12  exemplary illustrates a schematic perspective view of a multi-spindle turning machine according to yet another exemplary embodiment; 
         FIGS. 13A to 13C  exemplary illustrate schematic perspective views of a bar loader for use at a multi-spindle turning machine and of parts thereof; 
         FIGS. 14A and 14B  exemplary illustrate schematic perspective views of a machine frame for use at a multi-spindle turning machine according to yet another exemplary embodiment; 
         FIGS. 15A and 15B  exemplarily illustrate schematic perspective views of a drum of the multi-spindle turning machine frame of  FIGS. 14A and 14B ; 
         FIGS. 16A to 16C  exemplarily illustrate schematic views of a drum of the multi-spindle turning machine frame and detail views thereof for illustrating a drive mechanism thereof; and 
         FIG. 17  exemplary illustrates a schematic perspective view of an emergency brake system at a multi-spindle turning machine according to yet another exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS AND DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     In the following, preferred aspects and embodiments will be described in more detail with reference to the accompanying figures. Same or similar features in different drawings and embodiments are referred to by similar reference numerals. It is to be understood that the detailed description below relating to various preferred aspects and preferred embodiments are not to be meant as limiting the scope of the present invention. 
       FIG. 1  exemplarily illustrates a schematic perspective view of a multi-spindle turning machine  100  according to an exemplary embodiment. 
     The multi-spindle turning machine  100  of  FIG. 1  comprises a machine frame  10  which includes a machine bed  11 , a first machine frame upright  12  (front frame portion) and a second machine frame upright  13  (back frame portion), wherein the first machine frame upright  12  and the second machine frame upright  13  are arranged on the machine bed  11 . 
     A turret body  20  (spindle drum) is rotatably supported by the first machine frame upright  12  and the second machine frame upright  13  of the machine frame  10  of the multi-spindle turning machine  100 . The turret body  20  supports a plurality of workpiece spindles  30 , exemplarily arranged such that a respective spindle axis of the workpiece spindles  30  is arranged in parallel with the rotational axis (longitudinal axis) of the turret body  20 . Specifically, the workpiece spindles  30  are exemplarily arranged around the rotational axis (longitudinal axis) of the turret body  20 , exemplarily with equiangular distance. 
     The turret body  20  is rotatably supported by each of the first and second machine frame uprights  12  and  13 , and a free space is provided between the first and second machine frame uprights  12  and  13 , so that exemplarily the turret body  20  is only supported by the two machine frame uprights  12  and  13 . Specifically, exemplarily a front end portion of the turret body  20  is rotatably supported by the first machine frame upright  12  (front frame portion) and a back end portion of the turret body  20  is rotatably supported by the second machine frame upright  13  (back frame portion). 
     In  FIG. 1 , the turret body  20  exemplarily carries six workpiece spindles  30 , but the invention is not limited to configurations with six workpiece spindles  30  arranged on the turret body  20 , but the number of spindles can be also less or more than six, e.g. a turret body carrying four, five, seven, eight or more workpiece spindles. Exemplarily, for six workpiece spindles  30 , the equiangular distance between the respective adjacent workpiece spindles is ⅙ of 360°, i.e. exemplarily 60°. 
     Further exemplarily, the first machine frame upright  12  (front frame portion) supports, for each of the workpiece spindles  30 , a respective tool post assembly  40  for carrying tools for processing/machining workpieces received at the respective workpiece spindles  30 . Accordingly, in the present example, the first machine frame upright  12  (front frame portion) supports six tool post assemblies  40 , exemplarily at the similar equiangular distance between adjacent tool post assemblies as the equiangular distance between adjacent workpiece spindles  30 . 
     By such configuration, in a machining position of the turret body, each of the tool post assemblies  40  is positioned so as to be enabled to process a workpiece held by the currently associated workpiece spindle  30 , and by indexing (rotating) the turret body  20 , each of the workpiece spindles  30  can be moved to the next position of the next tool post assembly  40 . Accordingly, the turret body  20  is configured to index/rotate the workpiece spindles  40  between the multiple machining positions of the respective tool post assemblies  40 . Such rotation (indexing) of the turret body  20  can be made in clockwise and/or anti-clockwise direction. 
     Regarding the movement kinematics of the multi-spindle turning machine  100 , exemplarily, the one or more tools held by each of the tool post assemblies  40  can exemplarily be moved relative to the workpiece received at a respective workpiece spindle  30  in three translational directions (three linear degrees of freedom). Exemplarily, this is achieved in that each workpiece spindle  30  is moveable in a longitudinal direction which is axially arranged with respect to the respective spindle axis (referred to as “Z-direction”; Z-axis), and in that each tool post assembly  40  can be moved independently in two linear directions which are exemplarily perpendicular to each other and perpendicular to the longitudinal direction (Z-direction). Such directions are exemplarily referred to as “X-direction” (X axis) and “Y-direction” (Y axis). 
     Exemplarily, for each tool post assembly  40  the respective X-direction is arranged radially with respect to the rotational axis of the turret body  20  (i.e. the respective tool post assembly  40  can be moved in the X-direction perpendicular to and radially with respect to the rotational axis of the turret body  20 ), i.e. exemplarily perpendicular to the Z-direction of the respective workpiece spindle  30 . 
     Exemplarily, for each tool post assembly  40  the respective Y-direction is arranged tangentially with respect to the rotational axis of the turret body  20  (i.e. the respective tool post assembly  40  can be moved in the Y-direction perpendicular to and tangentially with respect to the rotational axis of the turret body  20 ), i.e. exemplarily preferably perpendicular to the Z-direction of the respective workpiece spindle  30  and perpendicular to the respective X-direction of said respective tool post assembly  40 . 
     On the side of the first machine frame upright  12  (front frame portion) opposite to the second machine frame upright  13  (back frame portion), a workspace is provided, on which side thereof the tool post assemblies  40  are provided on the first machine frame upright  12 . 
     Below the tool post assemblies  40 , exemplarily, a chip fall opening is provided in the machine bed  11  of the machine frame  10 , and a conveyor opening  11 A is provided in the machine bed  11  of the machine frame  10  on a front side thereof, and the conveyor opening  11 A is provided to insert a chip conveyor (see exemplary embodiments below). An advantage is that chips being created by the machining processes of machining workpieces received at the workpiece spindles  30  by tools held by the tool post assemblies  40  can fall freely downwards from the spindle positions to fall through the chip fall opening into a chip collector portion of a chip conveyor inserted through the conveyor opening  11 A. 
       FIGS. 2A and 2B  exemplarily illustrate schematic perspective views of a tool post assembly  40  of the multi-spindle turning machine of  FIG. 1 . 
     Exemplarily, each of the tool post assemblies  40  of the multi-spindle turning machine of  FIG. 1  are configured similarly, only that they are mounted to the first machine frame upright  12  (front frame portion) on the face side facing the workspace such that the respective X- and Y-axes, which exemplarily are arranged perpendicularly with respect to each other, are arranged depending on the longitudinal axis of the turret body, e.g. in that the plane spanned by the respective X- and Y-axes is arranged perpendicular to the longitudinal axis of the turret body  20  (i.e. that each of the respective X- and Y-axes is arranged perpendicular to the longitudinal axis of the turret body  20 ), and in that the respective X-axis is arranged radially with respect to the longitudinal axis (rotational axis) of the turret body  20 . 
     For providing the X- and Y-axes, the tool post assembly  40  exemplarily comprises a cross slide assembly including a first slide  45  (X-slide) movable in the X-direction and a second slide  47  (Y-slide) movable in the Y-direction, wherein the first slide  45  (X-slide) is arranged on the second slide  47  (Y-slide) as exemplarily shown in  FIGS. 2A and 2B . 
     The tool post assemblies  40  further exemplarily comprise respective drives  46  and  48 , wherein the drive  46  (e.g. drive motor) is configured to drive the linear movement of the first slide  45  (X-slide) into the X-direction and the drive  48  (e.g. drive motor) is configured to drive the linear movement of the second slide  47  (Y-slide) into the Y-direction. 
     The X- and Y-direction movements can be independently driven and by simultaneously driving the X- and Y-direction movements, the tool post can be moved in any direction within the plane of the X- and Y-directions, perpendicularly to the longitudinal axis of the turret body  20  and perpendicular to the respective spindle axis of a respective workpiece spindle  30 . 
     The guide elements  49 , along which guides of the second slide  47  (Y-slide) are guided, are mountable to the first machine frame upright  12  (front frame portion) at the respective positions as shown in  FIG. 1 , for example. 
     Exemplarily, each of the tool post assemblies  40  of the multi-spindle turning machine of  FIG. 1 , as exemplarily shown in  FIGS. 2A and 2B , comprises a tool post  41  which has a plurality (exemplarily three) tool receiving openings  41 A,  41 B and  41 C for receiving tools. Exemplarily, the tool receiving openings  41 A,  41 B and  41 C are arranged adjacent to each other and are arranged along the Y-direction. 
     This has the advantage that, by moving the tool post  41  into the Y-direction, the respective tool, which actually engages the workpiece received at the respective workpiece spindle, can be changed among the tools received in the tool receiving openings  41 A,  41 B and  41 C. Accordingly, without actually inserting a new tool into the tool post  41 , the tools engaging into the machining operation at a respective workpiece spindle  30  can be quickly, efficiently and reliably changed by merely moving the tool post  41  into the Y-direction. 
     Also, the tool post assembly  40  is configured to drive tools received in the tool receiving openings  41 A,  41 B and  41 C (so-called live tools) by way of the optional drive mechanism including the drive  43  (e.g. a drive motor in a drive housing) and the gearbox  42 . Specifically, the gearbox  42  may include a gear mechanism, which may be configured to allow for one or more gear changes for different gear ratios, and the gear mechanism may be driven by the drive  43  so as to drive one or more of the tools received in the tool receiving openings  41 A,  41 B and  41 C. 
     For example, the gearbox may be configured to include a gear mechanism which may be set to (or switched between) one or more gear settings, which may be provided for driving one or more of the tools received in the tool receiving openings  41 A,  41 B and  41 C at high revolution speeds and/or high torque, e.g. depending on the intended machining condition and/or depending on the used live tool. 
       FIGS. 3A and 3B  exemplarily illustrate schematic perspective views of tool posts of the multi-spindle turning machine of  FIG. 1 . 
     Exemplarily,  FIG. 3A  illustrates a tool post  41  with the mounting portion  44  on which the drive  43  (exemplarily including a housing and a drive motor being arranged in the housing) and the gearbox  42  are mounted, and  FIG. 3B  illustrates a tool post  41  with the mounting portion  44  from which the drive  43  and the gearbox  42  are detached. 
     That is, the drive  43  (e.g. drive motor) and the gearbox  42  may be optional in the sense that the tool post assembly  40  may be configured to detachably mount the drive unit including the drive  43  and the gearbox  42  to the tool post  41 , e.g., on a mounting portion  44  which is exemplarily arranged on the first slide  45  (X-slide) and which exemplarily supports the tool post  41 . Accordingly, if no live tools are intended to be used or required, the drive unit including the drive  43  and the gearbox  42  may be demounted or detached from the tool post  41 , e.g. if only fixed tools (e.g. fixed cutter blades) are inserted to the tool receiving openings  41 A,  41 B and  41 C. 
     Exemplarily, in  FIGS. 3A and 3B , the drive  43  and the gearbox  42  may be mechanically fixed to the mounting portion  44 , e.g., by way of screws or the like. In other exemplary embodiments, the drive  43  and the gearbox  42  may be mechanically fixed to the tool post  41  directly. In yet further exemplary embodiments, the drive  43  and the gearbox  42  may be mounted to the mounting portion  44  and/or the tool post  41  and locked mechanically and/or by electric, pneumatic and/or hydraulic locking mechanisms. 
       FIGS. 4A and 4B  exemplarily illustrate schematic perspective views of a tool post system of the multi-spindle turning machine of  FIG. 1 . Exemplarily, according to  FIGS. 4A and 4B , the tool post system has a configuration that the tool receiving openings  41 A,  41 B and  41 C of the tool post  41  are adapted to receive detachable, replaceable and interchangeable tool holder cartridges TC which are configured to hold respective tools. 
     For example,  FIG. 4A  exemplarily illustrates a plurality of interchangeable tool holder cartridges TC, each of which can be inserted into the tool receiving openings  41 A,  41 B and  41 C of the tool post  41  which may, depending on the intended machining operations and the used tools, be optionally augmented with the optionally added drive  43  and the gearbox  42  to be detachably mounted to the mounting portion  44  (and/or the tool post  41 ), as exemplarily described above. 
     The plural tool holder cartridges TC, having the interchangeable cartridge design to be fitted into the fitting tool receiving openings  41 A,  41 B and  41 C (as cartridge-receiving openings), are adapted to hold a variety of different tools such as fixed tools FT in  FIG. 4A  (e.g. fixed blades, fixed cutters, etc.) or live tools (i.e. drivable tools) such as boring tools, milling tools, drill bits, etc. For such live tools, some of the cartridges TC are adapted to hold axially arranged live tools ALT which are rotationally driven about a tool axis arranged axially with a longitudinal axis of the respective cartridge TC, the longitudinal axis of the respective cartridge TC being the axis of the insertion direction into the tool receiving openings  41 A,  41 B and  41 C (as cartridge-receiving openings). 
     Exemplarily, some of the cartridges TC are adapted to hold vertically/perpendicularly arranged live tools PLT which are rotationally driven about a tool axis arranged perpendicularly with respect to the longitudinal axis of the respective cartridge TC. Further exemplarily, one of the cartridges TC is adapted to hold a vertically/perpendicularly arranged double live tool DPLT with two tools which are rotationally driven about a tool axis arranged perpendicularly with respect to the longitudinal axis of the respective cartridge TC. 
     Accordingly, while each of the plural tool cartridges TC has the same interface fitting end portion to fit into the tool receiving openings  41 A,  41 B and  41 C (as cartridge-receiving openings), a front portion of the plural tool cartridges TC may be adapted according to different types of tools, e.g. to receive/hold one or more fixed tools FT, to receive/hold an axially drivable tool ALT, to receive/hold a perpendicularly drivable tool PLT (perpendicular live tool) or even to receive/hold one or more drivable tools, such as axially drivable double tools and perpendicularly drivable double tools, etc. 
     Whenever it is intended to use at least one live tool (drivable tool) at the tool post  41 , the optionally available drive unit including the gear box  42  and the drive  43  can be detachably mounted as exemplarily illustrated in  FIG. 4A . 
     Exemplarily,  FIG. 4B  illustrates such situation in which a tool cartridge TC holding an axially drivable tool ALT (axial live tool) is exemplarily inserted into the tool receiving opening  41 B of the tool post  41 , and, for driving the axially drivable tool ALT, the gear box  42  and the drive  43  are exemplarily mounted to the mounting portion  44  (and/or to the tool post  41 ). 
     For fixedly holding the tool cartridges in the tool receiving openings  41 A,  41 B and  41 C (as cartridge-receiving openings), the tool post  41  may be configured to enable mechanical fixing or locking the received cartridges TC, e.g. by means of screws and/or a clamping or other mechanical locking mechanism, e.g. also including quick-acting fasteners or quick clamps. 
     In further exemplary embodiments, in alternative or in addition, the tool post  41  may be equipped with automatically actuated locking/unlocking mechanisms to automatically lock/unlock tool cartridges TC received in the tool receiving openings  41 A,  41 B and  41 C (as cartridge-receiving openings) of the tool post  41 . Specifically, such automatically actuated locking/unlocking mechanisms may be including mechanical, pneumatic, hydraulic and/or electric locking/unlocking mechanisms. Accordingly, locking/unlocking tool cartridges TC received in the tool receiving openings  41 A,  41 B and  41 C (as cartridge-receiving openings) of the tool post  41  may be actuated automatically by way of mechanical, pneumatic, hydraulic and/or electric actuators. 
     This would exemplarily advantageously allow for a possibility of an automatic tool change function to be provided at the multi-spindle turning machine. While automatic tool change mechanisms are well known in the field of machine tools with tool-carrying spindles, such as milling machines or milling machining centers, efficient and reliable automatic tool change mechanisms are not yet realized in the field of turning machines/lathes, specifically for multi-spindle turning machine, and therefore such automatic tool change system at a turning machine, such as a multi-spindle turning machine, is highly beneficial and significantly improves the versatility of the respective turning machine. 
     For example, in case of equipping a multiple-spindle turning machine with handing robots, such robots could be used to handle workpieces at the workpiece spindles (e.g. for workpiece removal after the machining process) and/or tools to be removed from or inserted to the tool post  41  of one of the tool post assemblies  40  (see below exemplary embodiments). 
     Even without automatically actuated locking/unlocking mechanisms, the highly flexible and efficiently usable tool cartridge system with plural interchangeable tool holding cartridges fitted to the tool receiving openings  41 A,  41 B, and  41 C of the tool post  41  makes it advantageously possible to efficiently, more quickly and accurately enable tool exchanges, be it made manually, automatically or semi-automatically, at the turning machine, such as the multi-spindle turning machine. 
       FIG. 5  exemplarily illustrates a schematic perspective view of a chip conveyor  200  for use at the multi-spindle turning machine  100  of  FIG. 1 . 
     Exemplarily, the chip conveyor  200  (chip conveyor apparatus) includes a chip collector portion  210  which is opened to the upper side. The chip collector portion  210  may be inserted into the chip conveyor opening  11 A of the machine bed  11  of the machine frame  10  of the multi-spindle turning machine, e.g. as illustrated in  FIG. 1 . Accordingly, when inserted in the conveyor opening  11 A, the chips created by the machining operations of workpieces received at the workpiece spindles  30  being machined by the tools of the tool post assemblies  40  will advantageously be enabled to fall straight down into the chip collector portion  210  of the chip conveyor  200 . 
     The chip conveyor  200  exemplarily further includes an inclined conveying portion  230  which internally has a conveyor system for conveying chips collected in the chip collector portion  210  upwards towards the chip output portion  240 , which has a lower opening to output conveyed chips, e.g. into a collector container that may be placed under the chip output portion  240 . For driving the conveyor system, the chip conveyor  200  further includes a conveyor drive  220 . 
       FIGS. 6A and 6B  exemplary illustrate schematic perspective views of a multi-spindle turning machine  100  according to another exemplary embodiment. 
     The principle configuration of the multi-spindle turning machine  100  of  FIGS. 6A and 6B  is similar to the exemplary embodiments discussed above in connection with  FIG. 1 . However, the chip conveyor  200  is exemplarily inserted into the conveyor opening  11 A of the machine bed  11  of the machine frame  10 . 
     Further exemplarily, the multi-spindle turning machine  100  of  FIGS. 6A and 6B  is exemplarily equipped with two automatically controlled robots  301  and  302  (exemplarily, six-axis robots). For example, the first robot  301  is mounted to an upper portion of the workspace facing side of the first machine frame upright  12  (front frame portion) of the machine frame  10 . The second robot  302  is exemplarily mounted to a portion of the machine bed  11  of the machine frame  10  opposite to the first machine frame upright  12  with respect to the workspace (i.e. a region above the chip fall opening formed in the machine bed  11  of the machine frame  10 ). 
     Exemplarily, both of the robots  301  and  302  include grippers G adapted to pick up workpieces from the workpiece spindles  30  (e.g. to remove workpieces after completion of the machining process) and/or adapted to pick up (and/or insert) tool cartridges TC at the tool posts  41  of the tool post assemblies  41 , e.g. for automated tool exchanges. The exemplary embodiments are not limited to configurations having two robots but also only one of the robots  301  or  302  may be provided, or additional robots may be provided in yet further exemplary embodiments. 
       FIGS. 7A and 7B  exemplarily illustrate schematic perspective views of a drum (turret body  20 ) of the multi-spindle turning machines  100  of  FIGS. 1, 6A and 6B . 
     Exemplarily, only the turret body  20  is shown with one exemplary spindle slide mechanism of a respective workpiece spindle  30 , wherein the spindle slide mechanism includes a spindle slide  31  which supports a spindle body  32  which includes an integrated spindle drive (built-in spindle motor) and a actuated locking mechanism (e.g. a mechanically, hydraulically, pneumatically and/or electrically actuated locking mechanism) to automatically lock received workpieces (such as e.g. bars) in the spindle to rotatively drive the received and locked workpieces by the spindle drive. 
     The turret body  20  exemplarily includes a front end portion  22  and a back end portion  21  which are the portions respectively supported rotatably by the front frame portion  12  and the back frame portion  13  of the machine frame  10 . The front end portion  22  of the turret body  20  includes openings  25  to receive the workpiece spindles  30  (specifically the front portions thereof), and the back end portion  21  of the turret body  20  includes openings  26  through which each of the spindles  30  may be supplied with workpieces (such as e.g. bars) from a backside of the multi-spindle turning machine  100 . This has the advantage that workpieces, such as e.g. long bars, do not need to be inserted from a workspace side but may be supplied/inserted by a bar loader or bar feeder from a backside of the machine, where more space may be available. Then, workpieces only may need to be removed after machining from a front side at the working space, when such workpieces may be easier to be handled, e.g. automatically by external handling robots or additionally integrated robots such as e.g. in  FIGS. 6A and 6B . 
     However, as can be seen from  FIGS. 7A and 7B , exemplarily, the turret body  20  does not have through holes from the front side to the backside of the turret body  20  for each of the spindles  30 , as typically known from known multi-spindle turning machines, but the turret body  20  has, for each of the workpiece spindles  20 , a respective longitudinal groove  23  extending longitudinally (Z-direction/longitudinal direction of the turret body  20 ) from the front end portion  22  of the turret body  20  to the back end portion  21  of the turret body  20 . The longitudinal grooves  23  are exemplarily opened to the outer circumferential side of the turret body  20  so as to open to the space between the front frame portion  12  and the back frame portion  13  of the machine frame  10 . 
     Exemplarily, the turret body  20  has, between each pair of adjacent grooves  23 , a respective ledge portion  24  extending longitudinally (Z-direction/longitudinal direction of the turret body  20 ) from the front end portion  22  of the turret body  20  to the back end portion  21  of the turret body  20 . Exemplarily, the number of grooves  23  is the same as the number of longitudinal ledge portions  24 . 
     The spindle body  32  of the workpiece spindle  30  is exemplarily guided in the respective longitudinal groove  23  and supported by the spindle slide  31  which is arranged at an outer circumferential side of the turret body  20 . Specifically, each spindle slide  31  is exemplarily guided, with guide elements  35 , on the longitudinal ledge portions  24  formed on the sides of the respective grooves  23 . 
     Such configuration has the advantage that the slides  31  and their drive mechanisms may be provided outside on an outer circumferential side of the turret body  20 , so that the turret body  20  can be made efficiently compact and light-weight, since the radiating profile of the turret body  20  having the groove-ledge arrangement gives very high stability and stiffness even at relatively low ledge thickness, and the spindles can be arranged more compactly since the spindle slides and their drive mechanisms can be arranged circumferentially outside of the turret body  20 , efficiently using the space between the front and back frame portions  12  and  13 , and the size of the slides and their drive mechanism does not need to be compactified, even though the turret body  20  is very compact. 
     Exemplarily, the slide drive mechanism includes a thread shaft  34  driven by a drive  33  (drive motor). In  FIGS. 7A and 7B , the drive  33  is not mounted to the spindle slide  31  but may itself be mounted to a mount structure of (or attached to) the back portion the turret body  20 . 
     When rotatively driving the thread shaft  34  by way of the drive  33 , the respective spindle slide  31  is driven in the longitudinal direction (Z-direction, axially with respect to the respective spindle axis) along the guiding ledges  24  so as to move the spindle body  32  of the respective workpiece spindle  30  in the longitudinal Z-direction (e.g. towards or away from the workspace) within the respective longitudinal groove  23 . 
       FIGS. 8A to 8C  exemplary illustrate schematic perspective views of a multi-spindle turning machine  100  according to yet another exemplary embodiment. The principle configuration of the multi-spindle turning machine  100  of  FIGS. 8A to 8C  is similar to the exemplary embodiments discussed above in connection with  FIGS. 1, 6A and 6B . 
     Exemplarily, the  FIG. 8A  illustrates schematically a machine housing  110  of the multi-spindle turning machine  100 .  FIGS. 8B and 8C  illustrate the multi-spindle turning machine  100  without housing  110 . Such housing may also be provided for other described exemplary embodiments above and below. 
     Furthermore, the multi-spindle turning machine  100  of  FIGS. 8A to 8C  is exemplarily equipped with a chip conveyor  200  as exemplarily shown in  FIG. 5 , similar as the machine tool of  FIGS. 6A and 6B . 
     In addition, a bar loader  300  is exemplarily shown in  FIG. 8A , being arranged on the rear side of the multi-spindle turning machine  100  facing the back frame portion  13  of the machine frame  10 , which bar loader  300  is configured to supply elongated workpieces, e.g. bars (e.g. bars with a round or circular cross section or bars with an angled cross section such as e.g. a hexagonal cross section), from the rear side into the respective workpiece spindles  30  through the holes  26  formed in the back end portion  21  of the turret body  20  (see e.g.  FIG. 8C ). Such bar loader  300  may be used in other exemplary embodiments described above and below. 
     In addition, different to previously described exemplary embodiments, the multi-spindle turning machine  100  of  FIGS. 8A to 8C  exemplarily includes a pick-up spindle mechanism  50  which is mounted on a beam portion  14  of the machine frame  10  which is exemplarily arranged on the upper side of the front frame portion  12  and which exemplarily extends from the upper side of the front frame portion  12  into the working space. 
     The pick-up spindle mechanism  50  with its pick-up spindle  51  is exemplarily arranged in a hanging position being mounted to the beam portion  14  of the machine frame  10  from below and hanging from the beam portion  14  of the machine frame  10 . This has the advantage that the pickup-spindle mechanism does not obstruct the free space of chip fall below the spindles (including the pick-up spindle). 
     The pick-up spindle mechanism  50  includes a support portion  53  which is mounted, in the hanging position, to the bottom side of the beam portion  14  of the machine frame  10 , exemplarily by way of guide elements  54  which are guided along a longitudinal direction (Z-direction) in guides arranged on the bottom side of the beam portion  14 . The pick-up spindle mechanism  50  exemplarily further includes a drive  56  (drive motor) to drive movement of the support portion  53  (pickup-spindle slide) in the longitudinal direction (Z-direction) towards and away from the opposing workpiece spindles  30 . 
     The support portion  53  supports (holds) the pickup-spindle  51  which is driven by another drive  52  (drive motor), e.g. via a driving belt  55 . The pickup-spindle  51  and the drive  52  are arranged on (mounted to) the support portion  53 , and by moving the support portion  53  in the longitudinal direction (Z-direction), the pickup-spindle  51  can be moved towards and away from the opposing workpiece spindles  30  for picking up a workpiece received at one of the workpiece spindles  30  for rear machining purposes. 
     For such rear machining processing, the pickup-spindle may rotatively drive the picked up workpiece, which has a rear side, which was previously received in the respective workpiece spindle  30 , now openly facing the workspace for being machined on said rear side, and said rear side of the workpiece may be machined by using the tools of the tool post  40  associated with the respective workpiece spindle  30  opposite of the pickup spindle  51  and/or by way of additional tools (fixed tools or driven tools, i.e. live tools) which may be mounted to or arranged on the support portion  53  or on tool post assemblies mounted to or arranged on the support portion  53 . 
     The configuration advantageously allows for a very efficient and compact configuration allowing for additional rear machining of workpieces with optimized chip fall conditions. 
       FIG. 9  exemplary illustrates a schematic perspective view of a multi-spindle turning machine  100  according to yet another exemplary embodiment, similar to the exemplary embodiments of  FIGS. 8A to 8C . 
     In addition, similar to  FIGS. 6A and 6B , the multi-spindle turning machine  100  of  FIG. 9  is exemplarily equipped with a robot  302  (exemplarily a six-axis robot). The robot  302  is exemplarily mounted to a portion of the machine bed  11  of the machine frame  10  opposite to the first machine frame upright  12  with respect to the workspace (i.e. a region above the chip fall opening formed in the machine bed  11  of the machine frame  10 ). 
     Exemplarily, the robot  302  includes a gripper G adapted to pick up workpieces from the workpiece spindles  30  (e.g. to remove workpieces after completion of the machining process), to pick up workpieces from the pick-up spindle  53  (as exemplarily shown in  FIG. 9 ) and/or adapted to pick up (and/or insert) tool cartridges TC at the tool posts  41  of the tool post assemblies  41 , e.g. for automated tool exchanges. The exemplary embodiments are not limited to configurations having one robot but also two or more robots may be provided in yet further exemplary embodiments. 
       FIGS. 10A to 10D  exemplary illustrate schematic perspective views of a multi-spindle turning machine  100  according to yet another exemplary embodiment. 
     Furthermore, the multi-spindle turning machine  100  of  FIGS. 10A to 10D  is exemplarily equipped with a chip conveyor  200  as exemplarily shown in  FIG. 5 , similar as the machine tool of  FIGS. 6A and 6B  and  FIGS. 8A to 9 . 
     In addition, a bar loader  300  is exemplarily shown in  FIG. 10A  (similar to  FIG. 8A ), being arranged on the rear side of the multi-spindle turning machine  100  facing the back frame portion  13  of the machine frame  10 , which bar loader  300  is configured to supply elongated workpieces, e.g. bars, from the rear side into the respective workpiece spindles  30  through the holes  26  formed in the back end portion  21  of the turret body  20 . Such bar loader  300  may be used in other exemplary embodiments described above and below. 
     In addition, different to previously described exemplary embodiments, the multi-spindle turning machine  100  of  FIGS. 10A to 10D  exemplarily includes a counter-spindle mechanism  60  which is mounted on a beam portion  14  of the machine frame  10  which is exemplarily arranged between the upper side of the front frame portion  12  and an upper side of another (third) machine frame upright  15  (third machine frame portion) arranged opposite of the front frame portion  12  with respect to the workspace (opposite of the workpiece spindles  30 ), and which beam portion  14  exemplarily extends from the upper side of the front frame portion  12  into the working space. 
     The counter-spindle mechanism  60  exemplarily comprises two counter-spindles  61 , however, other exemplary embodiments with one or more than two counter-spindles are also possible in yet further exemplary embodiments. 
     The counter-spindle mechanism  60  with its counter-spindles  61  is exemplarily arranged in a hanging position being mounted to the beam portion  14  of the machine frame  10  from below and hanging from the beam portion  14  of the machine frame  10 . This has the advantage that the counter-spindle mechanism does not obstruct the free space of chip fall below the spindles (including the counter-spindles). Embodiments with two counter-spindles have an advantage that both of double cycle machining operations and double rear machining operations become possible (for double cycle machining operations and double rear machining operations, please see e.g. EP 2 163 334 B2). 
     Furthermore, as exemplarily shown in  FIG. 10A , e.g. for (double) rear machining operations performed on workpieces received at the counter-spindles  61 , the multi-spindle turning machine  100  exemplarily further comprises two additional tool posts  71  and  72 , which are exemplarily arranged in a hanging position mounted to the bottom side of the beam portion  14  between the counter-spindles  61  of the counter-spindle mechanism  60  and the workpiece spindles  30 . Each of the tool posts  71  and  72  is adapted to hold one or more tools (including fixed tools and/or drivable tools, e.g. live tools). 
     The exemplary embodiment exemplarily comprises two additional tool posts  71  and  72  for rear machining purposes of workpieces received at the counter-spindles  61 , however, other exemplary embodiments with one or more than two additional tool posts are also possible in yet further exemplary embodiments. 
       FIGS. 11A and 11B  exemplary illustrate schematic perspective views of a counter-spindle assembly of the counter-spindle mechanism  60  of the multi-spindle turning machines according to  FIGS. 10A to 10D . 
     For each counter-spindle  61 , the counter-spindle mechanism  60  includes a respective counter-spindle assembly which includes the respective counter-spindle  61  supported by a spindle slide  64  which is slidably supported by a cross slide assembly including a first slide  63  and a second slide  62 . The first slide  63  is slidably supported on the second slide  62 , and the second slide  62  is slidably supported on the bottom side of the beam portion  14 . 
     By movement of the respective second slide  62  with respect to the beam portion  14  along guides  67 , exemplarily arranged on the bottom side of the beam portion  14  so as to extend into a longitudinal direction (Z-direction), by the drive  65  (drive motor), the respective counter-spindle  61  can be moved into the longitudinal direction (Z-direction) which is exemplarily arranged in parallel with respect to the spindle axis of the respective counter-spindle  61  and the spindle axes of the workpiece spindles  30 . That is, by such movement in the Z-direction, i.e. towards or away from the opposing workpiece spindles  30 , a respective workpiece received at one of the workpiece spindles  30  may be picked up by the respective counter-spindle  61  for rear machining purposes. 
     Furthermore, by movement of the respective first slide  63  with respect to the second slide  62  along guides  68 , exemplarily arranged on the bottom side of the second slide  62  so as to extend into a horizontal direction (X-direction) perpendicular to the longitudinal direction (Z-direction), by another drive (drive motor, not shown), the respective counter-spindle  61  can be moved into the horizontal direction (X-direction) perpendicularly with respect to spindle axis of the respective counter-spindle  61  and the spindle axes of the workpiece spindles  30 . 
     Furthermore, by movement of the respective spindle slide  64  with respect to the first slide  63  along guides (not shown), exemplarily arranged on the first slide  63  so as to extend into a vertical direction (Y-direction) perpendicular to the longitudinal direction (Z-direction), by another drive  66  (drive motor), the respective counter-spindle  61  can be moved into the vertical direction (Y-direction) perpendicularly with respect to spindle axis of the respective counter-spindle  61  and the spindle axes of the workpiece spindles  30 . 
     By the above counter-spindle assemblies of the counter-spindle mechanism  60 , each of the counter-spindles can be moved independently in all three directions X, Y and Z, and highly flexible and accurate rear machining operations become possible. 
     For rear machining processing, a respective counter-spindle  61  (simultaneously with the other counter-spindle or asynchronously with the other counter-spindle) may rotatively drive the picked up workpiece, which has a rear side, which was previously received in the respective workpiece spindle  30 , now openly facing the workspace for being machined on said rear side, and said rear side of the workpiece may be machined by way of additional tools (fixed tools or driven tools, i.e. live tools) which may be held by the tool post  71  and  72 . 
     The configuration advantageously allows for a very efficient and compact configuration allowing for additional rear machining of workpieces with optimized chip fall conditions, specifically since the chips may fall downwards to and through the chip opening  11 B formed in the machine bed  11  of the machine frame without being obstructed by the counter-spindle mechanism  60  or the tool posts  71  and  72 . 
     Furthermore, the configuration having the beam portion  14  being supported on both sides, respectively by the upper portion of the front frame portion  12  and the outer frame portion  15 , has an advantage that a high stability and advantageous stiffness of the machine frame can be achieved. 
       FIG. 12  exemplary illustrates a schematic perspective view of a multi-spindle turning machine  100  according to yet another exemplary embodiment, similar to the exemplary embodiments of  FIGS. 10A to 10D . 
     In addition, similar to  FIGS. 6A and 6B and 9 , the multi-spindle turning machine  100  of  FIG. 12  is exemplarily equipped with a robot  302  (exemplarily a six-axis robot). The robot  302  is exemplarily mounted to a portion of the machine bed  11  of the machine frame  10  opposite to the first machine frame upright  12  with respect to the workspace (i.e. a region above the chip fall opening  11 B formed in the machine bed  11  of the machine frame  10 ). 
     Exemplarily, the robot  302  includes a gripper G adapted to pick up workpieces from the workpiece spindles  30  (e.g. to remove workpieces after completion of the machining process), to pick up workpieces from the counter-spindles  61  and/or adapted to pick up (and/or insert) tool cartridges TC at the tool posts  41  of the tool post assemblies  41 , e.g. for automated tool exchanges, and/or even to pick up (and/or insert) tool cartridges TC at the tool posts  71  and  72  hanging from the beam portion  14  (not shown in  FIG. 12 ). The exemplary embodiments are not limited to configurations having one robot but also two or more robots may be provided in yet further exemplary embodiments. 
       FIGS. 13A to 13C  exemplary illustrate schematic perspective views of a bar loader  300  for use at a multi-spindle turning machine  100  and of parts thereof. Such bar loader  300  may exemplarily be used at any of the machine tools of above or below exemplary embodiments. 
       FIG. 13A  exemplary illustrates the bar loader  300  with a housing  310  and a stand  320 . Through an opening on a side of the housing  310 , the bar loader includes a bar receiving portion  330  for receiving (being supplied) with unprocessed bars or other elongated workpieces to be machined at the multi-spindle turning machine  100 . Such elongated workpieces may have round profiles of various widths or other profiles. 
     On one side of the bar loader  300 , a turret fixture body  340  extends laterally from the bar loader  300 . The turret fixture body  340  is rotatably supported around a longitudinal axis to be axially arranged with the rotational longitudinal axis of the turret body  20  of the multi-spindle turning machine  100 . The turret fixture body  340  is configured to be fixed to the turret body  20  (e.g. by plural fixture rods) from a rear side of the multi-spindle turning machine  100  through a through hole of the back frame portion  13  (see e.g.  FIG. 8C ) so as to rotate together with the turret body  20  about the axially arranged longitudinal axes thereof. 
     Specifically, the turret body  20  and the turret fixture body  340  are exemplarily configured to be rigidly fixed to each other to rotate together about the common longitudinal axis. Accordingly, exemplarily the driven rotation of the guide system of the bar loader supported by the turret fixture body  340  is performed by mechanical connection of the turret fixture body  340  with the rear side of the turret body  20  through plural mechanical connections (e.g. by plural fixture rods) working on the external diameter of a rear flange of the machine. This mechanical connection of the turret fixture body  340  with the rear side of the turret body  20  assures the proper angular synchronisms with the spindles in the turret body  20  itself. Accordingly, the rotation of the bar loader guide system and the turret fixture body  340  of the bar loader  300  is exemplarily performed by the torque motor  80  described below. 
       FIG. 13B  exemplarily illustrates the bar loader  300  of  FIG. 13A  without housing  310  having an inner guide system, which is exemplarily shown in  FIG. 13C . 
     The bar loader guide system as a whole is, together with the turret fixture body  340 , rotatably supported about the longitudinal axis of the turret fixture body  340  (longitudinal axis of the guide system), and the guide system includes a fixed guide portion  360 , a slidable middle guide portion  350  and a slidable end guide portion  370 , wherein each of the fixed guide portion  360 , the slidable middle guide portion  350  and the slidable end guide portion  370  are, together, rotatably supported about the longitudinal axis of the turret fixture body  340  (longitudinal axis of the guide system). 
     Accordingly, when the turret body  20  of the multi-spindle turning machine  100  is rotated/indexed, the turret fixture body  340  of the bar loader  300 , being fixed to the turret body  20  of the multi-spindle turning machine  100 , rotates in a synchronous manner together with the turret body  20  of the multi-spindle turning machine  100 , and the guide system including the fixed guide portion  360 , the slidable middle guide portion  350  and the slidable end guide portion  370  is driven to be rotated together with the turret fixture body  340  of the bar loader  300  and the turret body  20  about the common longitudinal axis. 
     Preferably, the control of the driven rotation of the guide system is thereby performed by driving rotation of the turret  20  by control from the numerical control apparatus (NC) and/or the programmable logic controller (PLC) of the multi-spindle turning machine  100 . This has the advantage that the control of the rotation of the turret body  20  and the rotation of the guide system of the bar loader  300  is synchronously controlled. 
     In addition, preferably, the numerical control system of the multi-spindle turning machine  100  (including the NC and/or the PLC) may be communicably connected with the bar loader&#39;s control system according to a master/slave relationship. This has the advantage that the numerical control apparatus (NC) and/or the PLC of the machine is enabled to manage directly plural or all of the functionalities of the bar loader (e.g. the machine is the “master”, and the bar loader is the “slave”). Functionalities of the bar loader system may include at least one of: the selection and lifting of a new bar from a bar storage area into the guide system of the bar loader, the introduction of a new bar into a bar loader channel of the guide system, pushing of the bar for feeding new raw material for machining process (e.g. after receiving a specific signal, exemplarily indicating that a spindle collet is opened), and handling of a bar remnant. 
     The fixed guide portion  360  of the bar loader  300  exemplarily has plural fixed bar guide portions  361  arranged around the longitudinal axis, each fixed bar guide portion  361  being provided for receiving a bar/elongated workpiece for a respective one of the workpiece spindles  30  of the multi-spindle turning machine  100  so that the number of fixed bar guide portions  361  is the same as the number of workpiece spindles  30  of the multi-spindle turning machine  100 , at same angular distances corresponding to the angular distances of the workpiece spindles  30  of the multi-spindle turning machine  100  arranged on the turret body  20 . 
     The slidable middle guide portion  350  has plural slidable bar guide portions  351  arranged around the longitudinal axis, each slidable bar guide portion  351  being provided for receiving a bar/elongated workpiece for a respective one of the workpiece spindles  30  of the multi-spindle turning machine  100  so that the number of slidable bar guide portions  351  is the same as the number of workpiece spindles  30  of the multi-spindle turning machine  100 , at same angular distances corresponding to the angular distances of the workpiece spindles  30  of the multi-spindle turning machine  100  arranged on the turret body  20 . 
     Each slidable bar guide portion  351  of the slidable middle guide portion  350  is associated with a respective fixed bar guide portion  361  of the fixed guide portion  360 , and the respective slidable bar guide portion  351  is axially arranged with its associated fixed bar guide portion  361  in parallel with the longitudinal direction, so that the respective slidable bar guide portion  351  with its associated fixed bar guide portion  361  are configured to simultaneously receive a bar/elongated workpiece supplied through the bar receiving portion  330 . 
     Accordingly, both of the slidable bar guide portion  351  with its associated fixed bar guide portion  361  can be actuated to laterally open for laterally receiving the same bar/elongated workpiece supplied through the bar receiving portion  330 , and then to be actuated to be laterally closed for enclosing the bar and providing a longitudinally extending guide channel for the respective received bar. 
     A feeding mechanism of the fixed guide portion  360  is configured to feed bars/elongated workpieces, received in the slidable bar guide portion  351  with its associated fixed bar guide portion  361 , in the longitudinal direction towards the slidable end guide portion  370  and the turret fixture body  340 . 
     The slidable end guide portion  370  has plural slidable bar guide portions  371  arranged around the longitudinal axis, each slidable bar guide portion  371  being provided for receiving a bar/elongated workpiece for a respective one of the workpiece spindles  30  of the multi-spindle turning machine  100  so that the number of slidable bar guide portions  371  is the same as the number of workpiece spindles  30  of the multi-spindle turning machine  100 , at same angular distances corresponding to the angular distances of the workpiece spindles  30  of the multi-spindle turning machine  100  arranged on the turret body  20 . 
     Each slidable bar guide portion  371  of the slidable end guide portion  370  is associated with a respective slidable bar guide portion  351  of the slidable middle guide portion  370 , and the respective slidable bar guide portion  371  is axially arranged with its associated slidable bar guide portion  351  in parallel with the longitudinal direction, so that the respective slidable bar guide portion  371  with its associated respective slidable bar guide portion  351  are configured to simultaneously guide a bar/elongated workpiece, when the respective bar/elongated workpiece is fed from the fixed guide portion  360  towards the slidable end guide portion  370  and the turret fixture body  340 . 
     In addition, each slidable bar guide portion  371  of the slidable end guide portion  370  longitudinally extends though the turret fixture body  340  of the bar loader  300 , being fixed to the turret body  20  of the multi-spindle turning machine  100 , so as to extend through the openings  26  of the back end portion  21  of the turret body  20  of the multi-spindle turning machine  100 , so that each slidable bar guide portion  371  may be connected or fixed to a respective spindle body  32  of a respective workpiece spindle  30 , e.g. by one or more connection elements (e.g. connection rods or the like), preferably one or more per spindle, as exemplarily shown in  FIGS. 13A and 13B  (connection elements  380 ). 
     When the respective bar/elongated workpiece is fed through the respective slidable bar guide portion  371  to extend into the connected spindle body  32  of a respective workpiece spindle  30 , another optional feeding mechanism may be provided in the spindle body  32  of a respective workpiece spindle  30 , so that the slidable bar guide portions  351  and  371  may be provided without another feeding mechanism, and the slidable bar guide portions  351  and  371  may preferably provide a guide channel providing guiding support for long bars or other elongated workpieces. 
     Exemplarily, contrary to the fixed bar guide portion  361  of the fixed guide portion  360 , each slidable bar guide portion  371  with its respective associated slidable bar guide portion  351  is exemplarily configured to longitudinally slide together with the longitudinal movement of the respective workpiece spindle  30  in the longitudinal Z-direction. 
     Specifically, since the workpiece spindles  30  are configured to be driven independently from each other in the longitudinal Z-direction, each of the slidable bar guide portions  371  with its respective associated slidable bar guide portion  351  is adapted to longitudinally slide independent of the other slidable bar guide portions  371  with its respective associated slidable bar guide portion  351 . 
     This has the advantage that the bar loader  300  additionally provides a reliable and accurate guiding support for long bars or other elongated workpieces, which gives constant guiding support even when the workpiece spindles  30  are driven in the Z-direction. 
       FIGS. 14A and 14B  exemplary illustrate schematic perspective views of a machine frame  10  for use at a multi-spindle turning machine  100  according to yet another exemplary embodiment. 
     Different from the above exemplary embodiments, the machine frame  10  is adapted such that the upper side of the front frame portion  12  and the upper side of the back frame portion  13  are connected by an upper roof frame portion  16  which further increases and improves the stability and stiffness of the machine frame  10 , e.g. in addition to the optional beam portion  14  and the frame portion  15  on the other side of the workspace opposite to the front frame portion  12 . 
     In addition, as exemplarily described below for  FIGS. 15A and 15B , the configuration of  FIGS. 14A and 14B  has a modified turret configuration and spindle slide drive mechanism. 
       FIGS. 15A and 15B  exemplarily illustrate schematic perspective views of a drum/turret body  20  of the multi-spindle turning machine frame  10  of  FIGS. 14A and 14B . 
     The turret body  20  exemplarily has attached a front end portion  22  and a back end portion  21  which are the portions respectively supported rotatably by the front frame portion  12  and the back frame portion  13  of the machine frame  10 . The back end portion  21  attached to the turret body  20  includes openings  26  through which each of the spindles  30  may be supplied with workpieces (such as e.g. bars) from a backside of the multi-spindle turning machine  100 . 
     The turret body  20  has, for each of the workpiece spindles  20 , a respective longitudinal groove  23  extending longitudinally (Z-direction/longitudinal direction of the turret body  20 ) from the front end portion  22  to the back end portion  21 . The longitudinal grooves  23  are exemplarily opened to the outer circumferential side of the turret body  20  so as to open to the space between the front frame portion  12  and the back frame portion  13  of the machine frame  10 . 
     Exemplarily, the turret body  20  has, between each pair of adjacent grooves  23 , a respective ledge portion  24  extending longitudinally (Z-direction/longitudinal direction of the turret body  20 ) from the front end portion  22  to the back end portion  21 . Exemplarily, the number of grooves  23  is the same as the number of longitudinal ledge portions  24 . 
     The spindle bodies  32  of the workpiece spindles  30  are exemplarily guided in the respective longitudinal grooves  23  and supported by the respective spindle slide  31  which is arranged at an outer circumferential side of the turret body  20 . Specifically, each spindle slide  31  is exemplarily guided, with guide elements  35 , on the longitudinal ledge portions  24  formed on the sides of the respective grooves  23 . 
     Exemplarily, the slide drive mechanism includes a thread shaft  34  driven by a drive  33  (drive motor). In  FIGS. 15A and 15B , the drive  33  is not mounted to the spindle slide  31  but is mounted to the front end portion  22  or a front portion of the turret body  20 . 
     When rotatively driving the thread shaft  34  by way of the drive  33 , the respective spindle slide  31  is driven in the longitudinal direction (Z-direction, axially with respect to the respective spindle axis) along the guiding ledges  24  so as to move the spindle body  32  of the respective workpiece spindle  30  in the longitudinal Z-direction (e.g. towards or away from the workspace) within the respective longitudinal groove  23 . 
       FIGS. 16A to 16C  exemplarily illustrate schematic views of a drum (turret body  20 ) of the multi-spindle turning machine frame  10  and detail views thereof for illustrating a drive mechanism thereof. 
     As previously described, the turret body  22  is rotatably supported about the longitudinal rotational axis, in that a back-side end portion  21  of the turret body  20  (e.g. made as one piece with the turret body  20  or being attached to the turret body  20  at the back side) is rotatably supported at the back frame portion  13  of the machine frame  10  and a front-side end portion  22  of the turret body  20  (e.g. made as one piece with the turret body  20  or being attached to the turret body  20  at the front side facing the workspace) is rotatably supported at the front frame portion  12  of the machine frame  10 . 
     For driving the rotational movement of the turret body  20 , exemplarily a torque motor  80  is provided at the back frame portion  13  of the machine frame  10  (see e.g.  FIG. 16A ). The use of a torque motor has an advantage that the rotation between machining positions of the workpiece spindles  30  can be controlled efficiently, reliably, accurately and with quick response time by the numerical controller of the machine tool controlling the torque motor  80  as the drive for the rotational movement of the turret body  20 . 
     As exemplarily illustrated in  FIGS. 16B and 16C , the torque motor includes a rotor  82  and a stator  81 , wherein the rotor  82  is mounted on a circumferential portion of the back-side end portion  21  of the turret body  20 , and the stator  81  is mounted to the back frame portion  13  of the machine frame  10 . The torque motor  80  is configured to drive the rotational movement of the turret body  20  for movement of the workpiece spindles  30  between machining positions of the workpiece spindles  30 . 
     By including the torque motor  80  into the rotatable support of the end portion of the turret body  20 , a compact and efficient, power saving drive mechanism can advantageously be provided. 
     Furthermore, any potential heat generated potentially by the drive mechanism is advantageously located far and separate from the front frame portion  12  and the front end portion  22 , in that the torque motor  80  is separated by the air space between the frame portions  12  and  13  and is located on the opposite end side portion of the turret body  20  with respect to the end side portion  22  of the turret body  20  facing the workspace. 
     Accordingly, an accuracy and precision of machining operations at the workspace side can be improved since the torque motor  80  as potential heat source, which might affect accuracy by thermal effects, is located on the opposite end side of the turret body  20  so that thermal effects at the side facing the workspace close to the workpiece receiving portions of the workpiece spindles  30  and the tool post assemblies  40  are advantageously minimized, while at the same time having the efficient, accurate and direct driving mechanism provided by the torque motor  80 . 
     To further enhance the accuracy of the machining operations and the movement control of the turret body  20 , exemplarily, a positioning system  90  is circumferentially arranged around the front end portion of the turret body  20  facing the workspace at the position of the rotatable support of the front frame portion  12 . 
     The positioning system  90  exemplarily includes a circumferentially arranged absolute encoder  91  for determining the rotational position of the turret body  20 . 
     By detecting a rotational position of the turret body  20  by way of the position signal from the absolute encoder, the driving control of the torque motor  80  can be based on accurate feedback-control to accurately and precisely drive the turret body  20  to the rotational position according to the intended machining position, for aligning the position of the workpiece spindles  30  with the respective tool post assemblies  40 . 
     Since the positioning system is provided at the front side of the turret body  10  at the front frame portion  12  facing directly the workspace and close to the tool post assemblies  40 , the accuracy and precision of the positioning system is advantageously improved. 
     While using an absolute encoder  91  is a very preferred exemplary embodiment, the present invention is not limited to the use of absolute encoders as positioning detecting device, and other positioning detecting devices may be used such as e.g. incremental encoders, e.g. measuring not the absolute position but the distance between the machining positions. 
     Furthermore, the positioning system  90  exemplarily includes plural brake mechanisms  92  (e.g. hydraulic, pneumatic and/or electric brakes) circumferentially arranged with respect to the front end portion of the turret body  20  facing the workspace at the position of the rotatable support of the front frame portion  12 . 
     Accordingly, when the rotational position of the turret body  20  by way of the position signal from the absolute encoder is detected to be accurately and precisely located at the intended machining position, the brake mechanisms  92  (position locking system) are actuated to fix and lock the rotational position of the turret body  20  in said intended machining position during the machining phase. 
     In some preferred aspects, a controller may be provided for controlling a machining of one or more workpieces received at the plurality of workpiece spindles  30 , when the workpiece spindles  30  are positioned at respective machining positions. 
     In some preferred aspects, the controller may be further configured to control the torque motor  80  for controlling a rotational movement of the turret body  20  for indexing the workpiece spindles  30  between the respective machining positions and/or to control the position locking mechanism (brake mechanisms  92 ) for locking the rotational position of the workpiece spindles in the machining positions during the machining of the one or more workpieces. 
     In some preferred aspects, the controller may be configured to cut a control current of a control signal to the torque motor  80  after a driven rotation of the turret body  20  between the respective machining positions and to actuate the locking position locking mechanism (brake mechanisms  92 ) before controlling the machining of the one or more workpieces; and/or the controller may be configured to loosen the locked position locking mechanism (brake mechanisms  92 ) and to activate a control current of a control signal to the torque motor  80  for driving a rotation of the turret body  20  to the next respective machining positions after machining of the one or more workpieces at the current machining positions. 
     At that time, during the machining phase, when workpieces are machined at the machining positions by the driven rotation of the workpieces spindles  30  and engaging the tools of the tool post assemblies  40 , when the rotational position of the turret body  20  is fixed and locked by way of the brake mechanisms  92 , the drive signal to the torque motor can be cut off and the torque motor is deenergized. 
     Accordingly, power can be saved and the heat generation by the torque motor  80  and potential negative thermal effects on accuracy and precision can be reduced even further. 
     Furthermore, as exemplarily shown in  FIGS. 16B and 16C , the turret body  20  is rotatably supported on the front and back frame portions  12  and  13  by way of circumferentially arranged bearings B 2  and B 1 , respectively. 
     As further shown in  FIGS. 16B and 16C , and as previously described, the spindle body  32  of the respective workpiece spindles  30  have an integrated drive  39  (built-in spindle motor) for driving the rotational movement of the respective workpiece spindle  30 . 
     Furthermore, the spindle body  32  of the respective workpiece spindles  30  further includes a clamping unit  38  configured to fixedly clamp a bar or other elongated workpiece received in the respective workpiece spindle  30 , wherein the clamping unit  38  exemplarily includes a hydraulic actuator for actuating the clamping and the unclamping of a bar or other elongated workpiece. In other exemplary embodiments, the clamping unit can be actuated by a hydraulic, pneumatic, mechanical, and/or electrical actuator. 
       FIG. 17  exemplary illustrates a schematic perspective view of an emergency brake system at a multi-spindle turning machine according to yet another exemplary embodiment. 
     It is to be noted that such emergency brake system (safety brake system) may exemplarily be provided at any of the above-mentioned embodiments of multi-spindle turning machines. 
       FIG. 17  exemplarily shows a back-side of the turret body  20  supported by the back frame portion  13  of the machine frame  10 . A rotational support system for rotationally supporting the back-side portion  21  of the turret body  20  includes a fixed support ring structure  13   a  attached to the back frame portion  13  of the machine frame  10  and rotationally supports a rotatable support ring structure  21   a  attached to the back-side portion  21  of the turret body  20 . The rotational support system may further include the torque motor  80  as described exemplarily above. 
     Exemplarily, a brake disc  900  is attached to the rotatable support ring structure  21   a  and exemplarily three electric brakes  901 ,  902  and  903  are attached to the fixed support ring structure  13   a , and each of the electric brakes  901 ,  902  and  903  includes a respective brake clamp  900   a  configured to engage with the brake disc  900  being attached to the rotatable support ring structure  21   a . The invention is however not limited to three brakes  901 ,  902  and  903  but may include one or more brakes, and the invention is not limited to electric brakes but may also include hydraulically, electrically and/or pneumatically actuated brakes. 
     In preferred embodiments, the brake(s)  901 ,  902  and  903  are configured as normally closed brakes, which are normally biased by a biasing mechanism (e.g. by respective spring mechanisms) into a closing direction to engage with the brake disc  900  such as to fixedly hold the brake disc  900  in the closed state. By electric (and/or pneumatic and/or hydraulic) actuation, the brakes  901 ,  902  and  903  can be opened to movably release the engagement with the brake disc  900  so as to allow the brake disc  900  and the turret body  20  to rotate about the longitudinal axis (e.g. during machining operations). 
     Advantageously, if needed e.g. in a failure or collapse or fall down of power supply, the normally closed brakes can again lock engagement with the brake disc  900  by closing the respective brake clamp  900   a  due to the normally-closing biasing force of the biasing mechanism. 
     Accordingly, in case of power supply failure or other emergency situation, the safety (emergency) brake system, which is exemplarily provided at the back portion of the turret body  20 , may act to initiate an emergency stop of the potentially rotating turret body  20 . 
     By exemplary embodiments as described above, there are proposed beneficial aspects and features to enhance the machining options of the multi-spindle turning machine, to provide a compact machine concept, allowing for more flexible, accurate, efficient and reliable machining operations, and/or to improve accuracy and/or stability of the machine tool. 
     While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and are not restrictive on the broad invention, and that the embodiments of invention are not limited to the specific constructions and arrangements shown and described, since various other changes, combinations, omissions, modifications and substitutions, in addition to those set forth in the above paragraphs, are possible. 
     Those skilled in the art will appreciate that various adaptations, modifications, and/or combination of the just described embodiments can be configured without departing from the scope of disclosure of the present invention. Those skilled in the art will also appreciate, in view of this disclosure, that different embodiments of the invention described herein may be combined to form other embodiments of the invention. Therefore, it is to be understood that, the invention may be practiced other than as specifically described herein.