Device and method for machining gear wheels in an indexing method with a reduced indexing time

The invention relates to a device (20) comprising a workpiece spindle (21) for receiving a gear wheel (25), a tool spindle (29) for receiving a tool and several drives (X, Y, Z, B, C, A1) for machining the gear wheel in individual divisions. According to the invention, one tooth gap of the gear wheel is machined and then the tool is displaced in relation to the gear wheel in order to remove the tool from the tooth gap. The gear wheel is then rotated by a division and the tool is placed against the wheel again to machine another tooth gap. One of the drives (C) can be controlled in such a way that the relative displacement involves a tilting displacement, which modifies the relative angle between the tool and the gear wheel, the tilting displacement being co-ordinated with the displacement of a division.

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 machine10, as indicated inFIG. 1, which operates in an indexing method, is typically provided with an indexing apparatus which rotates the workpiece15with teeth16by one or more pitches about the workpiece axis12at the moment at which the tool13is disengaged. In order to ensure that the tool13(in the present case, a grinding wheel indicated schematically inFIG. 1) is disengaged, there is carried out a relative movement in which the tool13is moved out of the tooth gap parallel to the tool axis14(parallel to the x-axis). If the14(parallel to the x-axis). If the tooth16has a tooth depth H, the tool13has to be moved by a distance HA to ensure that the tool13and one of the teeth15do not collide when the indexing rotation is carried out.

The individual movement sequences in machines10of 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 workpiece15to be machined and the tool13.

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.

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 device20according to the invention is shown inFIGS. 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 inFIG. 1. There is shown a device20for what is known as plunge grinding. The device20comprises a workpiece spindle21for receiving a gear wheel25. Also provided is a tool spindle (not shown) for receiving a tool23. The tool spindle defines an axis24(A1-axis) about which the tool23rotates. There are provided a plurality of drives for machining the gear wheel in an indexing process. These drives are not shown inFIGS. 2A and 2B.

In accordance with the invention, a tooth gap in the gear wheel25is machined after an in-feed movement. This state, called the machining state, is shown inFIG. 2B. Then a relative movement takes place between tool23and workpiece25to remove the tool23from 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 tool23and the gear wheel25is achieved. InFIG. 2A, the angle a2between a tool plane28, extending parallel to the y-axis, and the axis of rotation22of the workpiece spindle is larger than the angle a1inFIG. 2B. The change in angle is denoted by Δ and a2=a1+Δ applies. The relative change in angle occurs about a pivot point27(rotation about the C-axis). Due to this change in angle the size of the angle a1which is set during the machining of a tooth gap between the tool plane28and the axis of rotation22of the workpiece spindle21, increases. Due to the change in angle Δ an effective translational displacement HAeffof the tool23relative to the tooth26of the workpiece25results, as shown inFIG. 2A. InFIG. 2A, the position of the tooth26prior to the change in angle is indicated by a dotted line and the tooth is denoted in this position by26′.

According to the prior art, there previously occurred in none of the machines a change in angle when removing the tool13from 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 machines10, seeFIG. 1, the tool13therefore 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 machines10, that a flank of the tooth16and the tool13do not collide during the subsequent indexing rotation about the axes12.

In accordance with the invention, the change in angle Δ is abruptly carried out before the gear wheel25carries out an indexing rotation about the axis22and the tool23is advanced again. It is important that the corresponding tilting movement is coordinated with the indexing rotation. In the case of machines20comprising a mechanical drive, this coordination of the movements can be carried out using mechanical couplings. In the case of machines20equipped 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 machine20is 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, control40inFIG. 4) or by a specific software module (for example, software module42inFIG. 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. Machines20with 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 wheel25and the tool23currently in use do not collide when the indexing rotation is carried out. Data about the dimensions of the gear wheel25and the tool23is taken into account when programming the control.

Particularly preferred is an embodiment in which the CNC control comprises a software module (for example, software module42inFIG. 4) which allows there to be carried out, in conjunction with the fitting to the device20of a gear wheel25to be machined and a tool23, a so-called collision calculation to prevent a collision between teeth26and the tool23. To carry out the collision calculation, the software module preferably takes over data already defined in the device20in conjunction with the machining of the gear wheel25. 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 wheel25relative to the tool23take 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 inFIG. 3. A new type of device20with a workpiece spindle21for receiving a gear wheel and a tool spindle29for receiving a tool is shown. The device20comprises a plurality of drives for machining the gear wheel in an indexing process. The drives are concealed behind linings of the device20. The device20further comprises a machine bed30with a region31for collecting chips. Provided on a stand33, extending in the X-Y-plane, a carriage32is provided which is displaceable along horizontally extending rails34parallel to the Y-axis. The carriage32carries the tool spindle29and can carry out translatory movements in the X and Z-directions.

This type of arrangement shown inFIG. 3differs from conventional machines. A basic difference to be highlighted is that the workpiece spindle21is 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 withFIGS. 2A and 2B, is the tool incrementally rotated about the B axis. In the embodiment shown inFIG. 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 device20shown a tooth gap in a gear wheel fastened to the workpiece spindle21. 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. 4shows the corresponding block diagram of a device20according to the invention. The device20has six drives X, Y, Z, B, C and A1which are shown inFIG. 4as functional units. Each of these drives is activated from a CNC control40. In the example shown, the connections between the CNC control40and the drives are illustrated by double-headed arrows; this is intended to indicate that the drives can provide feedback to the control means40. The rotary drives B, C, A1can, for example, provide feedback concerning the torque, or angle encoders can be used to send the angular position to the control means40. 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 means40is connected to a software module41. This software module41can, 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 means40and the software module41indicates, in this case, that the control means is able to send information back to the software module41.

In accordance with the invention, there can be provided a software module42which allows there to be carried out, in conjunction with the fitting to the device20of a gear wheel25to be machined and a tool23, a so-called collision calculation to prevent a collision between teeth26and the tool23. To carry out the collision calculation, the software module42preferably takes over already defined data from the software module41, as indicated by the arrow44. On the basis of this data, the software module42then 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 module42of the control means40can define other parameters for activating the drive C (tilting movement) and the drive B (indexing rotation).

It should be noted that the illustration shown inFIG. 4is 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 units41and42can pertain to the scope of application software which is typically installed and run on an (external) computer which is connected to the control means40via a network connection. The control means40is typically implemented in a device20.

The invention provides a method for machining a gear wheel using a device comprising a workpiece spindle21for receiving the gear wheel, a tool spindle29for 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 inFIG. 5, the pivot axis C is located at the point of the pitch cone apex K1of the pitch cone of the workpiece25, or in proximity to this point K1. This allows the majority of the tilting movement about the point K1to point in the direction of the X-axis and thus assists the removal of the tool23from the tooth gap in the workpiece25. If the pivot axis C were located at a point K2, the tool23would carry out a tilting movement about this point K2, as indicated inFIG. 5. In the event of a tilting movement about the point K2, 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 K1. 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 inFIG. 5.

The invention can also be used with machines20comprising 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.