Patent Document

CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of PCT Application No. PCT/EP2004/ 010791, filed Sep. 25, 2004, the disclosure of which is herein incorporated by reference in its entirety. 
     The invention relates to devices for machining gear wheels in an indexing method and to methods for the indexing machining of gear wheels. 
     BACKGROUND OF THE INVENTION 
     There are various devices, such as for example gear milling machines or gear grinding machines, which are configured specifically for the machining of gear wheels. As the very names of these machines suggest, the first type of machine operates with milling tools and the second type of machine with grinding tools. 
     One basically draws a distinction between machines which operate in an indexing method and machines which operate continuously. In the indexing method, there is machined a tooth gap, then there is carried out a movement of relative displacement to extract the tool from a tooth gap and what is known as an indexing movement (indexing rotation), in which the gear wheel rotates relative to the tool before the subsequent tooth gap is then machined. A gear wheel is thus manufactured step by step or gap by gap. A gear cutting machine  10 , as indicated in  FIG. 1 , which operates in an indexing method, is typically provided with an indexing apparatus which rotates the workpiece  15  with teeth  16  by one or more pitches about the workpiece axis  12  at the moment at which the tool  13  is disengaged. In order to ensure that the tool  13  (in the present case, a grinding wheel indicated schematically in  FIG. 1 ) is disengaged, there is carried out a relative movement in which the tool  13  is moved out of the tooth gap parallel to the tool axis  14  (parallel to the x-axis). If the  14  (parallel to the x-axis). If the tooth  16  has a tooth depth H, the tool  13  has to be moved by a distance HA to ensure that the tool  13  and one of the teeth  15  do not collide when the indexing rotation is carried out. 
     The individual movement sequences in machines  10  of this type are mechanically coordinated with one another and use is made of drives which transmit motor rotations, using worm gears and other means, to the workpiece  15  to be machined and the tool  13 . 
     In more modern machines, a CNC control is employed instead of the indexing apparatus, which is configured to allow all the indexing movement to be carried out at the appropriate moment. Modern CNC machines typically use what are known as direct drives. 
     The continuous method, also sometimes referred to as the continuous indexing method, is based on relatively complex movement sequences in which the tool and the workpiece to be machined carry out a continuous indexing movement relative to each other. The indexing movement results from the coordinated driving of a plurality of axle drives. 
     The indexing method has the drawback that it is slower that the continuous method. Nowadays, in the industrial manufacture of larger batches, particular importance is attached to the time required for carrying out the indexing movement. In the manufacture of a gear wheel with n=20 teeth, n=20 tooth gaps have to be machined individually and n−1=19 indexing movements are required. If each indexing movement is reckoned to take 1 second, the indexing process alone takes approx. 19 seconds. 
     The object of the invention is therefore to provide an approach allowing the indexing method to be sped up. 
     The object is achieved by a device according to the present invention. 
     According to the invention, this object is achieved in that use is made of a device which is equipped with a workpiece spindle for receiving a gear wheel, a tool spindle for receiving a tool and with a plurality of drives for machining the gear wheel in an indexing process. In this indexing process, a tooth gap in the gear wheel is machined, then the tool is moved relative to the gear wheel to remove the tool from the tooth gap, then the gear wheel carries out an indexing rotation and the tool is advanced to machine a further tooth gap. According to the invention, one of the drives is activated via a control means in such a way that the relative movement includes a tilting movement by means of which a relative change of angle between the tool and the gear wheel is achieved, the tilting movement being coordinated with the indexing rotation. 
     According to the invention, this object was achieved in that for machining a gear wheel, use is made of a specific device comprising a workpiece spindle for receiving the gear wheel, a tool spindle for receiving a tool and a plurality of drives for machining the gear wheel using the tool. The device carries out the following steps:
         machining a tooth gap in the gear wheel using the tool by carrying out a machining movement,   carrying out a relative movement between the tool and the workpiece to remove the tool from the tooth gap,   carrying out an indexing rotation to transfer the gear wheel into a different angular position,   machining a further tooth gap in the gear wheel using the tool by repeated carrying out of a machining movement.
 
According to the invention, the relative movement includes in this case a tilting movement which changes the relative angle between the tool and the gear wheel.
       

     Further advantageous embodiments may be inferred from the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention be described hereinafter in greater detail with reference to the drawings. 
         FIG. 1  is a schematic view of a portion of a conventional device; 
         FIG. 2A  is a schematic view of a portion of a device according to the invention in a first position; 
         FIG. 2B  is a schematic view of a portion of a device according to the invention in a second position; 
         FIG. 3  is a perspective view of a device according to the invention; 
         FIG. 4  is a schematic block diagram of a device according to the invention; 
         FIG. 5  is a schematic view of a portion of a further device according to the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present description uses concepts also used in relevant publications and patents. It should, however, be noted that the use of these concepts is intended merely for improved understanding. The specific choice of the terms is not intended to restrict the interpretation of the inventive idea and the scope of protection of the claims. The invention can readily be transferred to other conceptual systems and/or specialist fields. In other specialist fields, the concepts are to be used analogously. 
     A first device  20  according to the invention is shown in  FIGS. 2A and 2B . The principle of the invention will be described with reference to these figures which have deliberately been designed for ease of comparison with the conventional approach shown in  FIG. 1 . There is shown a device  20  for what is known as plunge grinding. The device  20  comprises a workpiece spindle  21  for receiving a gear wheel  25 . Also provided is a tool spindle (not shown) for receiving a tool  23 . The tool spindle defines an axis  24  (A 1 -axis) about which the tool  23  rotates. There are provided a plurality of drives for machining the gear wheel in an indexing process. These drives are not shown in  FIGS. 2A and 2B . 
     In accordance with the invention, a tooth gap in the gear wheel  25  is machined after an in-feed movement. This state, called the machining state, is shown in  FIG. 2B . Then a relative movement takes place between tool  23  and workpiece  25  to remove the tool  23  from the tooth gap. In accordance with the invention, the relative movement is a tilting movement or a combined movement composed of a translatory movement and a tilting movement. Due to the relative movement, a relative change in angle between the tool  23  and the gear wheel  25  is achieved. In  FIG. 2A , the angle a 2  between a tool plane  28 , extending parallel to the y-axis, and the axis of rotation  22  of the workpiece spindle is larger than the angle a 1  in  FIG. 2B . The change in angle is denoted by Δ and a 2 =a 1 +Δ applies. The relative change in angle occurs about a pivot point  27  (rotation about the C-axis). Due to this change in angle the size of the angle a 1  which is set during the machining of a tooth gap between the tool plane  28  and the axis of rotation  22  of the workpiece spindle  21 , increases. Due to the change in angle Δ an effective translational displacement HA eff  of the tool  23  relative to the tooth  26  of the workpiece  25  results, as shown in  FIG. 2A . In  FIG. 2A , the position of the tooth  26  prior to the change in angle is indicated by a dotted line and the tooth is denoted in this position by  26 ′. 
     According to the prior art, there previously occurred in none of the machines a change in angle when removing the tool  13  from a tooth gap. Conventional machines are not configured to carry out such a movement from the point of view of the arrangement of the axes either. In the case of conventional machines  10 , see  FIG. 1 , the tool  13  therefore has to perform a translatory withdrawal movement, corresponding to the tooth depth H plus a safety amount, to withdraw completely from the teeth. Only in this way is it possible to ensure, in the case of conventional machines  10 , that a flank of the tooth  16  and the tool  13  do not collide during the subsequent indexing rotation about the axes  12 . 
     In accordance with the invention, the change in angle Δ is abruptly carried out before the gear wheel  25  carries out an indexing rotation about the axis  22  and the tool  23  is advanced again. It is important that the corresponding tilting movement is coordinated with the indexing rotation. In the case of machines  20  comprising a mechanical drive, this coordination of the movements can be carried out using mechanical couplings. In the case of machines  20  equipped with a CNC control, the coupling is carried out “electronically”, i.e. by appropriate mutual adaptation of the individual movement sequences. 
     It is important that the indexing rotation is carried out with time delay but in part simultaneously with the tilting movement. The fact that the two movements take place at least in part simultaneously allows a huge amount of time to be saved. 
     If the machine  20  is provided with a CNC control, the coupling takes place “electronically”, i.e. by appropriate mutual adaptation of the individual movement sequences. The electronic coupling can be brought about by the control itself (for example, control  40  in  FIG. 4 ) or by a specific software module (for example, software module  42  in  FIG. 4 ). 
     In accordance with the invention, relatively high accelerations are required to be able to carry out the tilting movement so quickly that only a small amount of time elapses before the indexing rotation can be initiated. Machines  20  with a CNC control and direct drives are therefore particularly preferred, as the direct drives can convert a control command from the CNC control into the desired tilting movement quasi abruptly. 
     A control means according to the invention can be programmed in such a way that the gear wheel  25  and the tool  23  currently in use do not collide when the indexing rotation is carried out. Data about the dimensions of the gear wheel  25  and the tool  23  is taken into account when programming the control. 
     Particularly preferred is an embodiment in which the CNC control comprises a software module (for example, software module  42  in  FIG. 4 ) which allows there to be carried out, in conjunction with the fitting to the device  20  of a gear wheel  25  to be machined and a tool  23 , a so-called collision calculation to prevent a collision between teeth  26  and the tool  23 . To carry out the collision calculation, the software module preferably takes over data already defined in the device  20  in conjunction with the machining of the gear wheel  25 . On the basis of this data, it is then established three-dimensionally, taking account of the movement sequences, whether there is a risk of collision. 
     If the carrying-out of the collision calculation reveals that a collision may occur, the movement sequences are adapted accordingly. For example, the tilting movement carried out in accordance with the invention can be implemented with a more rapid ascent. Or the indexing rotation can start slightly later. 
     A CNC control according to the invention is programmed in such a way that the indexing rotation of the gear wheel and the movement (tilting movement or combined translatory movement and tilting movement) of the gear wheel  25  relative to the tool  23  take place in a coordinated manner. This means that the movement sequences are adapted to each other with respect to time. Thus, for example, the indexing rotation only starts delayed by a time Δt once the tilting movement has been initiated. 
     A particularly preferred embodiment of the invention is illustrated in  FIG. 3 . A new type of device  20  with a workpiece spindle  21  for receiving a gear wheel and a tool spindle  29  for receiving a tool is shown. The device  20  comprises a plurality of drives for machining the gear wheel in an indexing process. The drives are concealed behind linings of the device  20 . The device  20  further comprises a machine bed  30  with a region  31  for collecting chips. Provided on a stand  33 , extending in the X-Y-plane, a carriage  32  is provided which is displaceable along horizontally extending rails  34  parallel to the Y-axis. The carriage  32  carries the tool spindle  29  and can carry out translatory movements in the X and Z-directions. 
     This type of arrangement shown in  FIG. 3  differs from conventional machines. A basic difference to be highlighted is that the workpiece spindle  21  is rotatable about a C-axis. Unlike in conventional machines, a tilting movement of the workpiece relative to the tool can thus be carried out to separate the two with sufficient space from each other. Only after this spatial separation has been carried out, as described in conjunction with  FIGS. 2A and 2B , is the tool incrementally rotated about the B axis. In the embodiment shown in  FIG. 3 , at least the C-axis to drive is a direct drive controlled by a CNC control. This direct drive allows instantaneous rotation of the workpiece. 
     In accordance with the invention, there is machined on the device  20  shown a tooth gap in a gear wheel fastened to the workpiece spindle  21 . Then a relative movement between tool and workpiece is carried out to remove the tool from the tooth gap. For this purpose, one of the drives is activated via the CNC control in such a way that the relative movement includes a tilting movement about the C-axis which changes the relative angle between the tool and the gear wheel. The gear wheel then carries out an indexing rotation about the B-axis and the tool is advanced again to machine a further tooth gap. The described tilting movement is coordinated with the indexing rotation via the CNC control to prevent collisions. 
       FIG. 4  shows the corresponding block diagram of a device  20  according to the invention. The device  20  has six drives X, Y, Z, B, C and A 1  which are shown in  FIG. 4  as functional units. Each of these drives is activated from a CNC control  40 . In the example shown, the connections between the CNC control  40  and the drives are illustrated by double-headed arrows; this is intended to indicate that the drives can provide feedback to the control means  40 . The rotary drives B, C, A 1  can, for example, provide feedback concerning the torque, or angle encoders can be used to send the angular position to the control means  40 . The drives X, Y, Z can, for example, send information back to the control means via displacement or position transmitters. In the embodiment shown, the control means  40  is connected to a software module  41 . This software module  41  can, for example, allow access to a data memory. Stored information concerning the composition (shape, material, etc.) of a workpiece to be machined can be extracted from this data memory. Information concerning the tool used can also be stored in the data memory. A double-headed arrow between the control means  40  and the software module  41  indicates, in this case, that the control means is able to send information back to the software module  41 . 
     In accordance with the invention, there can be provided a software module  42  which allows there to be carried out, in conjunction with the fitting to the device  20  of a gear wheel  25  to be machined and a tool  23 , a so-called collision calculation to prevent a collision between teeth  26  and the tool  23 . To carry out the collision calculation, the software module  42  preferably takes over already defined data from the software module  41 , as indicated by the arrow  44 . On the basis of this data, the software module  42  then establishes three-dimensionally, taking account of the movement sequences, whether there is a risk of collision. If there is a risk of collision, the software module  42  of the control means  40  can define other parameters for activating the drive C (tilting movement) and the drive B (indexing rotation). 
     It should be noted that the illustration shown in  FIG. 4  is merely a block diagram representing a specific embodiment. There are also other approaches for integrating the principle of the invention into a CNC control, or for expanding a control means by software modules. 
     The functional units  41  and  42  can pertain to the scope of application software which is typically installed and run on an (external) computer which is connected to the control means  40  via a network connection. The control means  40  is typically implemented in a device  20 . 
     The invention provides a method for machining a gear wheel using a device comprising a workpiece spindle  21  for receiving the gear wheel, a tool spindle  29  for receiving a tool and a plurality of drives for machining the gear wheel using the tool. This method includes the following steps:
         machining a tooth gap in the gear wheel using the tool by carrying out a machining movement,   carrying out a relative movement between the tool and the workpiece to remove the tool from the tooth gap, the relative movement being a tilting movement about the C-axis which changes the relative angle between the tool and the gear wheel,   carrying out an indexing rotation about the B-axis to transfer the gear wheel into a different angular position,   machining a further tooth gap of the gear wheel using the tool by carrying out once more a machining movement.       

     In an advantageous embodiment of the machine according to the invention shown schematically in  FIG. 5 , the pivot axis C is located at the point of the pitch cone apex K 1  of the pitch cone of the workpiece  25 , or in proximity to this point K 1 . This allows the majority of the tilting movement about the point K 1  to point in the direction of the X-axis and thus assists the removal of the tool  23  from the tooth gap in the workpiece  25 . If the pivot axis C were located at a point K 2 , the tool  23  would carry out a tilting movement about this point K 2 , as indicated in  FIG. 5 . In the event of a tilting movement about the point K 2 , the component of the tilting movement that points in the X-direction is smaller than in the aforementioned case, in which the pivot axis C is located at or in proximity to the point K 1 . Choosing the position of the pivot axis C appropriately provides, for the same tilting angle, a larger movement in the X-direction and a smaller movement in the Y-direction, as illustrated schematically in  FIG. 5 . 
     The invention can also be used with machines  20  comprising mechanical drives, although less time can be saved, as a mechanical drive allows only lower accelerations. A drawback of the application of the invention in a machine comprising a mechanical drive is the wear that can occur if the axles are accelerated too fast. 
     The invention can be used not only in plunged-cut grinding, as described, but also in milling or honing. 
     The invention is particularly suitable for the machining of bevel gear tooth systems or spur gear couplings in an immersion process.

Technology Category: b