Grinding machine and method for operating a grinding machine

Abstract

The invention relates to a grinding machine (1) with a machine bed (10) on which a workpiece spindle (20) with a workpiece holder (21) and a tool spindle (40) with a tool holder (41) are arranged such that a workpiece (100) held in the workpiece spindle (20) can be moved or rotated along several axes relative to a tool (45) held in the tool holder (40), wherein a cabin (30) is arranged on the machine bed (10) which defines a working area (31) in which, in particular, the tool spindle (40) and the workpiece spindle (20) are arranged for machining workpieces (100). wherein the grinding machine (1) has a robot (60) for workpiece changing which is arranged outside the working area (31) in an automation cabin (61), wherein the workpiece spindle (20) can be moved on the X-axis towards or into the automation cabin (61) for a workpiece change, so that the robot (60) does not interfere with the working area (31) during workpiece changing, characterized in that the grinding machine (1) has a light barrier (90) encompassing the X-axis with a transmitter (91) and at least one receiver (92) for determining the clamping length of the workpiece (100) in the workpiece spindle (20) when the workpiece spindle (20) is retracted from the automation cabin (61) after the workpiece change, and a method for operating such a grinding machine (1).

Description

[0001] The invention relates to a grinding machine having the features of the preamble of claim 1 and a method for operating such a grinding machine.

[0002] Grinding machines, such as those known from EP 2 915 622 B1, enable workpiece machining characterized by the ability to produce complex surface geometries with high precision. Precisely because this high-precision manufacturing process often requires a considerable amount of processing time, it is particularly important to achieve the highest possible throughput of workpieces in order to manufacture cost-effectively and profitably.

[0003] DE 10 2022 112 353 A1 discloses a grinding machine in which a cabin is arranged on the machine bed, defining a work space in which, in particular, the tool spindle and the workpiece spindle for machining workpieces are arranged. The grinding machine has a robot for changing workpieces, which is arranged outside the work space in an automation cabin. The workpiece spindle can be moved on the X-axis towards or into the automation cabin for a workpiece change, so that the robot arm does not intervene in the work space during the workpiece change. After a workpiece change, the clamping length of the corresponding workpiece must be determined before each machining of the workpiece in order to ensure high machining accuracy.It is known to scan the clamped workpiece with a mechanical probe as soon as the workpiece spindle has returned to a machining position after a workpiece change to determine the clamping length. The clamping length can be defined in particular as the length of the workpiece that protrudes beyond the workpiece holder or the distance between the support surface of the workpiece spindle and the free end of the workpiece held in the workpiece spindle.

[0004] Further prior art documents cited are DE 10 2019 120 681 A1 and CN 1 12 894 377 A.

[0005] The object of the invention is to further develop a grinding machine and a method for operating a grinding machine in such a way that the throughput achievable with the grinding machine is increased.

[0006] This object is achieved by a grinding machine having the features of patent claim 1 and a method for operating a grinding machine having the features of patent claim 11.

[0007] Advantageous embodiments and further developments of the invention are the subject of the respective dependent claims.

[0008] The grinding machine according to the invention has a machine bed on which a workpiece spindle with a workpiece holder and a tool spindle with a tool holder are arranged in such a way that a workpiece received in the workpiece spindle can be rotated relative to a tool received in the tool holder, preferably a grinding tool, which can in particular be formed by a grinding wheel package, - is movable along an X-axis, which is an axis running in a first direction parallel to the surface of the machine bed, - is movable along a Y-axis, which is an axis running in a second direction parallel to the surface of the machine bed, - can be moved along a Z-axis, which is an axis perpendicular to the surface of the machine bed, - is rotatable about an A-axis, which is an axis parallel to the surface of the machine bed, and - is rotatable around a C-axis, which is an axis perpendicular to the surface of the machine bed.

[0009] The grinding machine further comprises a cabin arranged on the machine bed, which defines a working space in which in particular the tool spindle and the workpiece spindle for machining workpieces are arranged.

[0010] Finally, the grinding machine has a robot, which can be designed in particular as a robot arm, for changing the workpiece, which robot is arranged outside the work area in an automation cabin, which can, however, be opened at least temporarily, in particular in the direction of the work area, in particular for changing the workpiece, wherein the workpiece spindle can be moved on the X-axis towards the automation cabin or into the automation cabin, so that the robot does not have to intervene in the work area when changing the workpiece.

[0011] Essential to the invention is that a light barrier with a transmitter and at least one receiver is provided for determining the unclamping length of the workpiece in the workpiece spindle when the workpiece spindle retracts from the automation cabin after the workpiece change. The light barrier, in particular the light beam of the light barrier, traverses in particular the X-axis and is particularly preferably arranged perpendicular to it. Firstly, such an optical measuring method enables contactless measurement of the workpiece. Furthermore, this light barrier enables a simple determination of the unclamping length directly by moving the workpiece spindle along the feed path from the position of the workpiece spindle at which the workpiece change takes place to the machining position in the work area.The additional time required to determine the unclamping length once the workpiece spindle has moved to the machining position in the work area is thus completely eliminated, as the unclamping length is determined during the time already required to move the workpiece spindle from the change position to the machining position. This significantly increases the throughput achievable with the grinding machine.

[0012] Preferably, the transmitter is designed as a laser, which allows a high degree of accuracy in determining the position at which the light barrier is released.

[0013] A particularly advantageous embodiment of the invention provides for the transmitter and receiver to be arranged on a measuring bridge that encompasses the X-axis. By using such a measuring bridge, the transmitter and receiver are already aligned and adjusted relative to each other, which can simplify installation. The transmitter and receiver can be mounted on the measuring bridge so that they can be slidably aligned or finely adjusted relative to each other as needed.

[0014] Preferably, the measuring bridge is arranged so that it can be moved perpendicular to the X-axis. This allows for easy adjustment if workpieces of different geometries are to be machined in the grinding machine.

[0015] The grinding machine advantageously comprises means for electro-optical distance measurement and / or geometric measurement. The means can be laser-based, for example, and can be based on a time-of-flight measurement, a phase position measurement, or the principle of laser triangulation. The means are arranged in particular such that the measurement or measurement can take place at the change position or on the feed path from the change position to the machining position. Such means enable the determination of further geometric features of the workpiece, for example the measurement of the diameter or width of the workpiece, but also the measurement of the conicity or crowning or other geometric features of the workpiece or of the workpiece spindle relative to the workpiece, in particular on the feed path from the change position to the machining position and thus without any loss of time.

[0016] The means can be designed as a separate measuring unit in addition to the light barrier. However, a particularly advantageous development of the invention provides for the light barrier to have two receivers, with the second receiver, in particular, being arranged on the transmitter side and thus capable of detecting the laser beam reflected from the workpiece if the workpiece interrupts the laser beam. This makes it possible to measure not only the workpiece's clamping length, but also other geometric features such as the diameter or width of the workpiece with the smallest possible number of components.

[0017] The X-axis is advantageously guided through a lockable hatch between the cabin and the automation cabin, and the measuring bridge is arranged on the wall between the cabin and the automation cabin, particularly inside the automation cabin. The lockable hatch allows the work area and automation area to be separated as effectively as possible, so that the robot can be protected as much as possible from contamination. The smaller the hatch, the faster it can be opened and closed, thus further increasing the throughput achievable with the grinding machine. The hatch is therefore preferably only slightly wider than the workpiece spindle. The arrangement of the measuring bridge on the wall between the cabin and the automation cabin enables reliable and stable fixation. This arrangement can also enable alignment or adjustment of the measuring bridge if necessary.Within the automation cabin, the measuring bridge can also be largely protected from contamination.

[0018] Preferably, the tool spindle is completely kinematically separated from the workpiece spindle, with movements along the X-axis, around the A-axis, and around the C-axis being performed by the workpiece spindle (whose axis of rotation is usually defined by the A-axis or forms the A-axis), and movements along the Y-axis and along the Z-axis being performed by the tool spindle. This type of kinematic separation not only improves positioning precision by avoiding an arrangement with three linear axes stacked on top of each other, but also allows the workpiece and tool to be changed simultaneously, thus increasing the workpiece throughput achievable with the grinding machine, because the movements required for the tool change or workpiece change to the change positions to be approached by the tool spindle or workpiece spindle can be performed simultaneously.

[0019] For this purpose, it can be particularly useful to extend the X-axis. This can be achieved particularly advantageously by installing an add-on module on the machine bed that extends the X-axis and supports the automation cabin. However, the add-on module can also be designed as a single piece, extending the machine bed beyond the cabin.

[0020] According to an advantageous development of the invention, a palletizing system or a pallet storage system is provided from which the robot can remove workpiece blanks and in which the robot can deposit finished workpieces.

[0021] In the method according to the invention for operating a grinding machine according to the invention, workpieces clamped in the workpiece spindle are machined one after the other with one or more grinding tools clamped to the tool spindle. A workpiece change is performed by a robot located outside the work area in an automation booth. The workpiece spindle, with the workpiece holder, which is designed, for example, as a clamping system, is moved along the X-axis toward or into the automation booth. Especially when using linear motors and a direct position measuring system, this is faster and more precise than the movement of the robot, which is also protected in this way.

[0022] According to the invention, after the workpiece change, when the workpiece spindle is returned from the automation cabin, the clamping length of the workpiece in the workpiece spindle is determined by means of a light barrier with a transmitter and a receiver, in that - when changing the workpiece, the workpiece is inserted into the workpiece spindle in such a way that in a change position the workpiece inserted into the workpiece spindle interrupts the light barrier, - when the workpiece spindle is retracted, the position of the workpiece spindle at which the light barrier is no longer interrupted is determined - and this position is set in relation to the position of the workpiece spindle in the change position.

[0023] The light barrier is arranged in particular in such a way that the light beam of the light barrier crosses the X-axis and is particularly preferably arranged perpendicular to it.

[0024] Such a method enables the unclamping length to be determined in a simple manner directly while the workpiece spindle is moving along the feed path from the workpiece spindle position where the workpiece change takes place to the machining position in the work area. Additional time required to determine the unclamping length once the workpiece spindle has moved to the machining position in the work area is thus completely eliminated, as the unclamping length is determined during the time already required to move the workpiece spindle from the change position to the machining position. This significantly increases the throughput achievable with the grinding machine.

[0025] Advantageously, an electro-optical distance measurement and / or geometric measurement is performed after the workpiece change, particularly when the workpiece spindle returns from the automation cabin. The electro-optical measurement or measurement can be laser-based, for example, particularly based on a time-of-flight measurement, a phase position measurement, or the principle of laser triangulation. This enables the determination of further geometric features of the workpiece, for example, the measurement of the diameter or width of the workpiece, but also the measurement of the conicity or crowning or other geometric features of the workpiece or of the workpiece spindle relative to the workpiece, particularly on the feed path from the change position to the machining position, thus avoiding any loss of time.

[0026] The measurement or calibration can be performed using a measuring unit installed in addition to the light barrier. Preferably, however, after the workpiece change, when the workpiece spindle is retracted from the automation cabin, another geometric feature, such as the diameter or width of the workpiece, the conicity or crown of the workpiece, or the relative position of the cooling channel of the workpiece spindle to the workpiece, is determined using the light barrier. With the light barrier interrupted by the workpiece, the runtime, phase position, and / or angle of the laser beam reflected by the workpiece are determined. This allows for additional measurement of the workpiece during the feed path.

[0027] According to an advantageous development of the invention, during a workpiece change, it is monitored whether the workpiece inserted into the workpiece spindle interrupts the light barrier in the change position. An alarm signal or error message is issued if the light barrier is not interrupted. This makes it easy to check whether the workpiece change is being carried out correctly and whether the workpiece is inserted into the workpiece holder.

[0028] Preferably, in order to carry out a workpiece change and / or to carry out a tool change, the workpiece spindle and / or the tool spindle are moved kinematically decoupled from one another, thereby making it possible to send both the workpiece spindle and the tool spindle simultaneously to their respective setup position at which they are loaded or their loading is adjusted.

[0029] In particular, the robot and the workpiece spindle can be pre-positioned so that only a single movement along the X-axis is required to specify the machined workpiece and / or to accept the new workpiece, especially as a blank. This allows the workpiece spindle, together with the clamping system that forms the workpiece holder, and the workpiece to be moved into the automation cabin immediately after machining. The A-axis can be aligned parallel or at a defined angle to the X-axis by rotating around the C-axis before reaching the automation cabin.

[0030] Because the control of the X-axis operates with high precision and greater precision than that of the robot, it is particularly advantageous if, when picking up the next workpiece to be machined, the movement in the direction of the X-axis required to remove the workpiece from the clamping system that forms the workpiece holder of the workpiece spindle and / or to insert the next workpiece into the clamping system that forms the workpiece holder of the workpiece spindle is carried out by moving the workpiece spindle along the X-axis, in particular after the robot has assumed the correct position relative to the X-axis.

[0031] An embodiment of the invention is explained in more detail below with reference to the following figures. Fig. 1 a side view of an embodiment of a grinding machine according to the invention, in which a side wall is hidden, with a workpiece spindle in a machining position, Fig. 2 a perspective view of the grinding machine according to Fig. 1, Fig. 3 a side view of an embodiment of a grinding machine according to the invention, in which a side wall is hidden, with the workpiece spindle in a change position, Fig. 4 a perspective view of the grinding machine according to Fig. 3, Fig. 5 a view along the X-axis of the workpiece spindle of the grinding machine according to Fig. 3, Fig. 6 another perspective view of the grinding machine according to Fig. 3, Fig. 7 a view of one of the grinding machine according to Fig. 1 with remote cabin, remote automation cabin and remote workpiece holder and Fig. 8 a plan view of components of the grinding machine according to Fig. 1.

[0032] The Fig. 1 to 8 show various views of an embodiment of a grinding machine 1 according to the invention, wherein the same reference numerals designate the same or functionally identical parts, but for the sake of clarity not all reference numerals are indicated in all figures.

[0033] The grinding machine 1 comprises a machine bed 10, which, in the interest of high precision, can be manufactured using molding technology using mineral casting for improved vibration damping. The machine bed 10 supports a workpiece spindle 20 with a workpiece holder 21 and a tool spindle 40 with a tool holder 41. The machine bed 10 can further include integrated cable ducts, a gravity-driven drain with an outlet, on which an optional screen is arranged, for coolant and lubricant, integrated lines for lubrication, motor cooling, process cooling, and grounding, as well as an integrated level monitor. These, however, are not visible in the illustration of the figures because they are concealed by other components.

[0034] The workpiece spindle 20, whose workpiece holder 21 defines the horizontally extending A-axis of the grinding machine 1, can be integrated into a T-slot table 22, which can be designed to be rotatable about the vertically extending C-axis and horizontally movable along the X-axis on a carriage 23. The carriage 23 runs in particular on rails that are arranged on the machine bed 10, but which are in Fig. 7 as well as the linear motor that drives the carriage 23 and the direct, absolute measuring system that monitors its position are located under a cover 24 and are therefore not visible.

[0035] The tool spindle 40, which is shown, for example, with a tool 45 accommodated therein in the form of a grinding wheel package, can be supported by a carriage 42, which can be arranged on a rail system arranged vertically on another carriage 43, which defines a vertical Z-axis, and can be linearly movable along this Z-axis in the vertical direction. This rail system, as well as the drive and position monitoring of the carriage 43, are also not visible in the figures because they are arranged under a cover 44.

[0036] The additional carriage 43, in turn, runs on rails arranged on the machine bed 10. However, in the figures, these rails, like the linear motor that drives the additional carriage 43 and the direct, absolute measuring system that monitors its position, are located under the cover 46 and are therefore not visible. These rails define the Y-axis, which runs perpendicular to the X-axis and is also horizontal.

[0037] In this way, in the grinding machine 1, the tool spindle 20 is completely kinematically separated from the workpiece spindle 40, with movements along the X-axis, around the A-axis and around the C-axis being performed by the workpiece spindle 20 and movements along the Y-axis and along the Z-axis being performed by the tool spindle 40.

[0038] Also carried by the carriage 42 is a tool changer 50, which in this case is designed for a total of four tools, of which, however, only the tool 45 which is currently mounted in the tool spindle 40 is shown in the figures in order to illustrate the structure of the tool changer 50 in the figures more precisely.

[0039] The tool changer 50, which is therefore moved together with the tool spindle 40 in the direction of the Y-axis and in the direction of the Z-axis, has in this case a carrier plate 51 with four cross-shaped, equally long arms, at the end of each of which a gripper 52 can be arranged, which, when loaded, carries a tool 45, in particular a grinding wheel package. The carrier plate 51 is in particular rotatable about a driven BY axis running parallel to the Y-axis; moreover, it can be rotated in the direction parallel to this axis into the Fig. 7 can be moved in a direction towards and back from the viewer.

[0040] This allows the tool 45 held by the tool spindle 40 during grinding to be gripped with the associated gripper 52 when a tool change is necessary and, after releasing the spindle clamp, to be moved by a linear movement which Fig. 7 in the direction towards the viewer, parallel to the BY axis. The tool changer 50 can then be rotated, for example, by 90°, so that the next tool 45 held by the gripper 52 of the next arm is positioned in such a way that it is possible to move the tool 45 by a linear movement which is Fig. 1 in the direction away from the viewer, parallel to the BY axis into the tool holder 41 of the tool spindle 40, activate the spindle clamp, and then release the gripper 52 to continue machining. This gripper 52 thus remains in a position during machining where it only needs to be closed during the next tool change to grasp the tool 45 to be replaced. This allows for a very fast tool change because only minimal travel distances need to be covered.

[0041] A cabin 30 is arranged on the machine bed 10, which encloses a working space 31 in which in particular the tool spindle 40 and the workpiece spindle 20 are arranged.

[0042] Fig. 8 shows a plan view of components of the grinding machine according to Fig. 7 in combination with automation by a robot 60 and a palletizing system 70. The entire structure supporting the tool spindle 40 and the tool changer 50, as well as the covers 24, 44 and 45, has been omitted so that additional details of the machine bed 10, in particular the rails defining the X-axis and the Y-axis, can be seen.

[0043] The robot 60, which is particularly designed as a robot arm, is arranged outside the workspace 31 in an automation cabin 61. In this exemplary embodiment, the automation cabin 61 and the robot 60 are supported by an add-on module 80 arranged on the machine bed 10, which, in particular, extends the X-axis or the rail system defining it, as can be deduced from the position of the workpiece spindle 20 shown in the workpiece change position and the T-slot table 22 supporting it, as well as the slide 23.

[0044] The palletizing system 70 is located on the side of the robot 60 opposite the T-slot table 22. Accordingly, the robot 60 can place machined workpieces 100 in the palletizing system 70 by a simple pivoting movement, grip a new workpiece blank to continue machining, and feed it to the workpiece spindle 20 without intervening in the work space 31.It is particularly advantageous if the movement of the robot 60 is designed in such a way that the robot 60 is pre-positioned with its workpiece gripper in such a way that when the finished workpiece 100 is transferred, the carriage 23 moves a section of the workpiece 100 still held in the workpiece holder 21 into the open workpiece gripper of the robot 60, which then grips it before it is released, and when the next workpiece blank is transferred to the workpiece spindle 20, the carriage 23 moves a section of the workpiece 100 still held in the workpiece gripper of the robot 60 into the open workpiece holder 21 of the workpiece spindle 20, which then fixes it, for example with an expansion chuck, before the workpiece gripper of the robot 60 releases it.Since the movement of the carriage 23 along the X-axis is faster and controlled with high precision than that of the robot 60, not only is time saved, but transfer errors are also effectively avoided.

[0045] In the Fig. 1 and Fig. 2, the workpiece spindle 20 is shown with the workpiece 100 in a machining position in which the machining of the workpiece 100 can be carried out by the tool 45. In the Fig. 3 to 6, the workpiece spindle 20 with the workpiece 100 is shown in a change position in which the robot 60 can remove the machined workpiece 100 and insert a new workpiece 100 to be machined.

[0046] A wall 36 is arranged between the cabin 30 and the automation cabin 61, separating the interior spaces of the cabin 30 and the automation cabin 61. The wall 36 merely has a closable hatch 35, through which, in particular, the X-axis is guided, so that the workpiece can be changed through the hatch 35 by moving the workpiece spindle 20 along the X-axis toward the automation cabin 61 or, in particular, through the hatch 35 into it, so that the robot 60 does not intervene in the work space 31 during the workpiece change.

[0047] The grinding machine 1 has a light barrier 90 with a transmitter 91 and a receiver 92, with which the unclamping length of the workpiece 100 in the workpiece spindle 20 can be determined when the workpiece spindle 20 retracts from the automation cabin 61 after the workpiece change. For this purpose, the light barrier 90 is arranged on the X-axis, in particular such that a light beam from the light barrier 90 crosses the X-axis, in particular perpendicularly. The transmitter 91 and the receiver 92 are arranged, in particular, on opposite sides of the X-axis. The positions of the transmitter 91 and the receiver 92 shown in the figures can, of course, be interchanged.

[0048] The clamping length is determined by inserting the workpiece 100 into the workpiece spindle 20 during the workpiece change in such a way that, in the change position of the workpiece spindle 20, the workpiece 100 inserted into the workpiece spindle 20 interrupts the light barrier 90. An interruption is achieved by the workpiece 100 being arranged between the transmitter 91 and the receiver 92 and the receiver 92 being unable to detect any signal from the transmitter 91 (see Fig. 3 to 6). The change position is detected in particular by detecting the position of the carriage 23 along the X-axis using the direct, absolute measuring system. When the workpiece spindle 20 is retracted, it is determined at which position of the workpiece spindle 20, in particular of the carriage 23 along the X-axis, the light barrier 90 is no longer interrupted, i.e. a signal is detected in the receiver 92. This position is then related to the position of the workpiece spindle 20 in the change position, whereby - if necessary taking into account the relative position between the workpiece spindle 20 and the light barrier 90 in the change position - the clamping length of the workpiece 100 is determined. This thus takes place directly on the feed path of the workpiece 100, so that time-consuming measuring of the workpiece 100 at the machining position (cf. Fig. 1 and Fig. 2) the workpiece spindle 20 can be omitted.

[0049] During the workpiece change, it can be monitored whether the workpiece 100 inserted into the workpiece spindle 20 interrupts the light barrier 90 in the change position, and an alarm signal can be issued if the light barrier 90 is not interrupted in order to obtain information about whether the workpiece change was carried out correctly.

[0050] The transmitter 91 is designed as a laser to enable high measurement accuracy. As shown in the Fig. 1 to 6, the transmitter 91 and the receiver 92 can be arranged on a measuring bridge 94. In this way, the transmitter 91 and the receiver 92 can be fixed relative to one another and the assembly of the light barrier 90 can be carried out in a simple manner. It is possible for the transmitter 91 and the receiver 92 to be arranged displaceably on the measuring bridge 94 in order to be able to carry out a fine adjustment of the transmitter 91 and the receiver 92 relative to one another if necessary. The measuring bridge 94 is in particular U-shaped and encompasses the X-axis, so that the transmitter 91 and the receiver 92 are arranged on different sides of the X-axis, and in particular of the workpiece 100. The measuring bridge 94 is arranged in particular on the wall 36 between the cabin 30 and the automation cabin 61, in particular within the automation cabin 61 (cf. in particular Fig. 2, Fig. 4, Fig. 5 and Fig.6). The measuring bridge 94 can be arranged to be displaceable in the direction perpendicular to the X-axis, particularly in height, in order to be able to adjust it easily if necessary for different geometries of the workpiece 100.

[0051] It is possible for a second receiver 92 to be arranged next to the transmitter 91 on the side of the transmitter in order to detect the laser beam reflected from the workpiece 100 and in this way, in particular by determining the travel time of the laser beam from the transmitter 91 to the workpiece 100 and back to the second receiver 92 and, for example, converting this value into a length value which is subtracted from the distance between the axis of rotation of the tool spindle 20 and the transmitter 91, to be able to detect further geometric features of the workpiece 100, such as the diameter or the width of the workpiece 100, likewise when the workpiece spindle 20 moves back on the feed path of the workpiece 100. List of reference symbols 1 grinding machine 10 Machine bed 20 workpiece spindle 21 Workpiece holder 22 T-slot table 23 sleds 24 Cover 30 cabins 31 work space 35 Luke 36 wall 40 tool spindle 41 Tool holder 42 sleds 43 sleds 44 Cover 45 tools 46 Cover 50 tool changers 51 Carrier plate 52 grippers 60 robots 61 Automation cabin 70 palletizing system 80 add-on module 90 light barrier 91 channels 92 recipients 94 measuring bridge 100 workpieces

Claims

[1] Grinding machine (1) with a machine bed (10) on which a workpiece spindle (20) with a workpiece holder (21) and a tool spindle (40) with a tool holder (41) are arranged such that a workpiece (100) received in the workpiece spindle (20) can be rotated relative to a tool (45) received in the tool holder (40) - is movable along an X-axis, which is an axis running in a first direction parallel to the surface of the machine bed (10), - is movable along a Y-axis, which is an axis running in a second direction parallel to the surface of the machine bed (10), - is movable along a Z-axis, which is an axis perpendicular to the surface of the machine bed (10), - is rotatable about an A-axis, which is an axis parallel to the surface of the machine bed (10), and - is rotatable about a C-axis, which is an axis perpendicular to the surface of the machine bed (10), wherein a cabin (30) is arranged on the machine bed (10), which defines a working space (31) in which in particular the tool spindle (40) and the workpiece spindle (20) for machining workpieces (100) are arranged, wherein the grinding machine (1) has a robot (60) for changing the workpiece, which is arranged outside the working space (31) in an automation cabin (61), wherein the workpiece spindle (20) can be moved on the X-axis towards the automation cabin (61) or into the automation cabin (61) for a workpiece change, so that the robot (60) does not intervene in the working space (31) during the workpiece change, characterized bythat the grinding machine (1) has a light barrier (90) with a transmitter (91) and at least one receiver (92) for determining the clamping length of the workpiece (100) in the workpiece spindle (20) when the workpiece spindle (20) is moved back from the automation cabin (61) after the workpiece change. [2] Grinding machine (1) according to claim 1, characterized by that the transmitter (91) is designed as a laser. [3] Grinding machine (1) according to one of the preceding claims, characterized by that the transmitter (91) and the receiver (92) are arranged on a measuring bridge (94) which encompasses the X-axis. [4] Grinding machine (1) according to claim 3, characterized by that the measuring bridge (94) is arranged to be displaceable in the direction perpendicular to the X-axis. [5] Grinding machine (1) according to one of the preceding claims, characterized by that the grinding machine (1) comprises means for electro-optical distance measurement and / or geometric measurement. [6] Grinding machine (1) according to one of the preceding claims, characterized by that the light barrier (90) has two receivers (92). [7] Grinding machine (1) according to one of claims 3 to 6, characterized by that the X-axis is guided through a closable hatch (35) between the cabin (30) and the automation cabin (61) and the measuring bridge (94) is arranged on the wall (36) between the cabin (30) and the automation cabin (61), in particular within the automation cabin (61). [8] Grinding machine (1) according to one of the preceding claims, characterized by that the tool spindle (40) is completely kinematically separated from the workpiece spindle (20), whereby movements along the X-axis, around the A-axis and around the C-axis are carried out by the workpiece spindle (20) and movements along the Y-axis and along the Z-axis are carried out by the tool spindle (40). [9] Grinding machine (1) according to one of the preceding claims, characterized by that an add-on module (80) is arranged on the machine bed (10), which extends the X-axis and carries the automation cabin (61). [10] Grinding machine (1) according to one of the preceding claims, characterized by that a palletizing system (70) or a pallet storage area is provided adjacent to the automation cabin (61). [11] Method for operating a grinding machine (1) according to one of the preceding claims, in which workpieces (100) clamped one after the other in the workpiece spindle (20) are machined by grinding with one or more tools (45) clamped on the tool spindle (40), wherein a workpiece change is carried out with a robot (60) arranged outside the work space (31) in an automation cabin (61) by moving the workpiece spindle (20) with the workpiece holder (21) along the X-axis towards the automation cabin (61) or into the automation cabin (61), characterized by that after the workpiece change, when the workpiece spindle (20) is returned from the automation cabin (61), the clamping length of the workpiece (100) in the workpiece spindle (20) is determined by means of a light barrier (90) with a transmitter (91) and a receiver (92) by - during the workpiece change, the workpiece (100) is inserted into the workpiece spindle (20) in such a way that in a change position the workpiece (100) inserted into the workpiece spindle (20) interrupts the light barrier (90), - when the workpiece spindle (20) is moved back, it is determined at which position of the workpiece spindle (20) the light barrier (90) is no longer interrupted - and this position is set in relation to the position of the workpiece spindle (20) in the change position. [12] Method according to claim 11, characterized by that after the workpiece change, in particular when the workpiece spindle (20) returns from the automation cabin (61), an electro-optical distance measurement and / or geometric measurement is carried out. [13] Method according to claim 11 or 12, characterized bythat after the workpiece change, when the workpiece spindle (20) is moved back from the automation cabin (61), a further geometric feature of the workpiece (100) is determined by means of the light barrier (90) by determining the running time, the phase position and / or the angle of the laser beam reflected on the workpiece (100) when the light barrier (90) is interrupted by the workpiece (100). [14] Method according to one of claims 11 to 13, characterized by that when changing the workpiece, it is monitored whether, in the change position, the workpiece (100) inserted into the workpiece spindle (20) interrupts the light barrier (90) through the workpiece (100), and an alarm signal or an error message is output if the light barrier (90) is not interrupted. [15] Method according to one of claims 11 to 14, characterized bythat in order to carry out a workpiece change and / or to carry out a tool change, the workpiece spindle (20) and the tool spindle (40) are moved kinematically decoupled from one another. [16] Method according to one of claims 11 to 15, characterized by that when picking up the next workpiece (100) to be machined, the movement in the direction of the X-axis required to remove the workpiece (100) from the workpiece holder (21) of the workpiece spindle (20) and / or to insert the next workpiece into the tool holder (21) of the workpiece spindle (20) is carried out by moving the workpiece spindle (20) along the X-axis.

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