阅读说明：本技术 用于监测机床的方法、监测装置、机床和计算机程序产品 (Method for monitoring a machine tool, monitoring device, machine tool and computer program product ) 是由 M·茨威格 于 2019-07-25 设计创作，主要内容包括：描述了一种用于监测机床的方法,其中借助于控制计算机对工具的运动进行数控。所述方法包括以下方法步骤：-在由参考目标值曲线(37)控制的工具的参考运动期间,记录与所述工具的运动有关的监测被测变量的参考测量曲线(38),-在由加工目标值曲线(22)控制的工具(3)的加工运动期间,记录所述监测被测变量的加工测量曲线(32),其中由工具通过所述加工运动来对工件进行加工,-基于参考目标值曲线(37)和加工目标值曲线(22)使参考测量曲线(38)和加工测量曲线(32)在时间上相关,以及-形成参考测量曲线(38)和加工测量曲线(32)的差曲线(39)并监测差曲线(39)是否超出预定的极限值。所述方法可以借助于相应地配置的监测装置或机床来执行并且可以以计算机程序产品的形式实施。(A method for monitoring a machine tool is described, in which the movement of the tool is numerically controlled by means of a control computer. The method comprises the following method steps: -recording a reference measurement curve (38) of a monitored measurand related to the motion of a tool controlled by a reference target value curve (37), -recording a machining measurement curve (32) of the monitored measurand during a machining motion of the tool (3) controlled by a machining target value curve (22), wherein a workpiece is machined by the tool by the machining motion, -correlating the reference measurement curve (38) and the machining measurement curve (32) in time on the basis of the reference target value curve (37) and the machining target value curve (22), and-forming a difference curve (39) of the reference measurement curve (38) and the machining measurement curve (32) and monitoring whether the difference curve (39) exceeds a predetermined limit value. The method can be carried out by means of a correspondingly configured monitoring device or machine tool and can be implemented in the form of a computer program product.)

1. A method for monitoring a machine tool (1), wherein the movement of a tool (3) is numerically controlled by means of a control computer (10), the method comprising the method steps of:

-recording a reference measurement curve (38) of the monitored measurand in relation to the movement of the tool (3), said recording being performed during a reference movement of the tool (3) controlled by a reference target value curve (37),

-recording a machining measurement curve (32) of the monitored measurand during a machining movement of the tool (3) controlled by the machining target value curve (22), the machining movement being used by the tool (3) to machine the workpiece (2),

-bringing the reference measurement curve (38) and the machining measurement curve (32) into a time relationship based on the reference target value curve (37) and the machining target value curve (22), and

-forming a difference curve (39) of the reference measurement curve (38) and the machining measurement curve (32) and monitoring the difference curve (39) to check whether a predetermined limit value (40, 41) is exceeded.

2. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

wherein the difference curve (39) is divided into functional sections in which different functional areas of the tool (3) are used, and wherein different limit values (40, 41) are established for the different functional sections.

3. The method according to claim 1 or 2,

wherein the reference measurement curve (38) and the machining measurement curve (32) are brought into a time relationship by subjecting the assigned reference target value curve (37) and the machining target value curve (22) to an adjustment in which the relative time interval between the reference target value curve (37) and the machining target value curve (22) is used as a free parameter to be determined and the error norm describing the deviation between the reference target value curve (37) and the machining target value curve (22) is minimized.

4. The method of claim 3, wherein the first and second light sources are selected from the group consisting of,

wherein the sum of the squared deviations between the reference target value curve (37) and the machining target value curve (22) is used as the error norm.

5. The method according to claim 3 or 4,

wherein, before the adjustment of the reference target value curve (37) and the machining target value curve (22), corresponding sections of the reference target value curve (37) and the machining target value curve (22) are determined, and at least one transition section (42) between the sections is removed in the reference target value curve (37) and in the assigned reference measurement curve (38) and/or at least one transition section (42) is removed in the machining target value curve (22) and in the assigned machining measurement curve (32).

6. Method according to one of claims 1 to 5,

wherein the reference movement is performed without contacting the workpiece (2).

7. Method according to one of claims 1 to 5,

wherein the reference motion is performed in contact with the workpiece without material removal.

8. Method according to one of claims 1 to 5,

wherein the reference movement is performed with a new tool (3) on the workpiece (2).

9. Method according to one of claims 1 to 8,

wherein the reference movement is repeated after a number of machining movements have been performed.

10. Method according to one of claims 1 to 9,

wherein the reference movement and the machining movement comprise a rotational movement and/or a translational movement of the tool (3).

11. Method according to one of claims 1 to 10,

wherein the monitored measurand is a torque or a translational force.

12. Method according to one of claims 1 to 11,

wherein the target values of the machining target value curve (22) and the reference target value curve (37) are positions of the tool (3) along a predetermined path of the tool (3) along which the tool (3) is moved during the machining movement and the reference movement.

13. Method according to one of claims 1 to 12,

wherein the rotational movement generated by the drive motor (9) is converted by the machine tool (1) into a translational movement of the tool (3), and the torque of the drive motor (9) is used as a monitoring variable, and the difference curve (39) is used to monitor the force acting on the tool (3) in the translational direction.

14. Method according to one of claims 1 to 13,

wherein the values of the difference curve (39) are converted from torque values into force values and monitoring is performed using the force values.

15. Method according to one of claims 1 to 14,

wherein, when a preset limit value (40, 41) is exceeded, a user-recognizable alarm and/or a movement of the intervention tool (3) is triggered.

16. Method according to one of claims 1 to 15,

wherein the tool (3) is designed for drilling, thread cutting, milling, turning or grinding.

17. A monitoring device for monitoring a machine tool (1), the drive (9) of which acting on a tool (3) is numerically controlled by means of a sensor (16) and a control computer (10), the monitoring device being arranged for

Capturing the monitored measurand, and

-capturing a target value that has been generated by the control computer (10) and used for controlling the movement of the tool (3), and

-performing the method according to one of claims 1 to 16 based on the captured monitored measurand and target values.

18. A machine tool having a tool (3) for machining a workpiece (2), the drive (9) of which acting on the tool (3) is numerically controlled by means of a sensor (16) and a control computer (10), the control computer (10) of which is arranged for

Capturing the monitored measurand, and

-capturing target values that have been generated by the control computer (10) and are used for controlling the movement of the tool (3), and for

-performing the method according to one of claims 1 to 16 based on the captured monitored measurand and target values.

19. A computer program product for monitoring a machine tool (1), said product containing instructions which, when executed on a computer (19), cause the computer to carry out the method according to one of claims 1 to 16.

Technical Field

The invention relates to a method for monitoring a machine tool, wherein the movement of the tool is numerically controlled by means of a control computer.

The invention also relates to a device for monitoring a machine tool, a machine tool and a computer program product for carrying out the method.

Background

A method for producing a thread in an assembly is known from DE 102016114631 a 1. In the known method, a thread forming tool is used, which has a groove generating area at its end facing the assembly, which groove generating area contributes to the formation of at least one helical groove in the wall of the core hole when the tool is introduced into the core hole. Behind the groove generating region, a plurality of thread generating regions are formed on the tool, which are twisted about the tool axis, and are introduced into the groove when the groove is formed, that is to say during the groove generating movement. After the tool is inserted into the core hole, the tool is rotated in the direction opposite to the groove generating motion and simultaneously slowly moved backward. During this thread cutting movement, the thread-generating region leaves the groove and forms a thread in the wall of the core hole adjacent to the groove. The thread cutting motion may be stopped when the thread producing area reaches one groove or the next. In a subsequent shearing movement, the tool is again passed through the groove into the core hole in order to shear off any chips that may have occurred when cutting the thread and extending into the groove. The tool is then moved back again in a resetting motion and the produced thread is re-cut in a re-cutting motion. The re-cutting movement is performed in the opposite direction to the thread-cutting movement. The re-cutting movement therefore takes place in the opposite rotational direction with respect to the thread-cutting movement, while moving slowly forwards. When the thread cutting area of the tool reaches one or said grooves again, the re-cutting movement can be ended and the tool can be withdrawn from the core hole by a retracting movement. The groove cutting zone and the thread cutting zone are guided to the outside by the groove.

An advantage of the known method is that a lot of time can be saved in the thread cutting. However, no method has been found that can reliably monitor tool quality and thus the quality of the cut thread.

Similar problems occur with other numerically controlled machines such as numerically controlled milling machines, drilling machines, lathes and grinding machines.

However, in automated manufacturing, it is important to be able to reliably monitor the manufacturing process.

Disclosure of Invention

Starting from this prior art, the invention is therefore based on the following objects: a reliable method for monitoring a machine tool is established, wherein the movement of the tool is numerically controlled by means of a control computer. The invention is also based on the following object: an apparatus for monitoring a machine tool, a machine tool and a computer program product for performing the method are established.

This object is achieved by a method, a monitoring device, a machine tool and a computer program product having the features of the independent claims. Advantageous configurations and developments are specified in the dependent claims.

In a method for monitoring a machine tool, a reference measurement profile of a monitored measured variable related to the movement of a tool is recorded during a reference movement of the tool controlled by a reference target value profile. Furthermore, a machining measurement curve of the monitored measured variable is recorded during a machining movement of the tool, wherein the workpiece is machined by the tool by means of the machining movement. The reference measurement curve and the machining measurement curve are brought into a time relationship based on the reference target value curve and the machining target value curve. A difference curve is then formed from the reference measurement curve and the machining measurement curve, and it is monitored whether the difference curve exceeds a predetermined limit value. Since the difference curve is essentially determined by the forces acting on the tool, the function of the tool can be reliably monitored using the difference curve.

In one embodiment of the method, the difference curve is divided into functional segments in which different functional areas of the tool are used, and different limit values are established for the different functional segments. In this way, the various functional areas of the tool can be reliably monitored.

The reference measurement curve and the machining measurement curve are brought into a time relationship by subjecting the assigned reference target value curve and the machining target value curve to an adjustment in which a relative time distance between the reference target value curve and the machining target value curve is used as a free parameter to be determined and an error norm describing a deviation between the reference target value curve and the machining target value curve is minimized. Since the target value curve is generally executed in the same manner, the time relationship can be reliably determined using the target value curve.

In general, the sum of the squared deviations between the reference target value curve and the machining target value curve is used as the error norm.

In order to take account of time delays from the target value curves in the processing of the machining program, respective sections of the reference target value curves and of the machining target value curves are determined before the adjustment in the reference target value curves and in the machining target value curves, and at least one transition section between the sections is removed in the reference target value curves and in the assigned reference measurement curves and/or at least one transition section is removed in the machining target value curves and in the associated machining measurement curves, so that different delays do not impair the adjustment.

The reference movement may be performed outside the workpiece. In this case, the difference curve is determined solely by the forces acting on the tool and the function of the tool can be monitored easily and reliably.

In addition, the reference movement can also be performed on the workpiece by means of a new tool. In this case, the difference curve represents the change in the force acting on the tool.

After a large number of machining movements have been performed, the reference movement may be repeated to repeatedly record the reference target value curve, so that gradual changes in the machine tool do not affect the monitoring and to ensure that the difference curve is a measure of the current force acting on the tool.

Depending on the machine tool, the reference movement and the machining movement may comprise a rotational movement and/or a translational movement of the tool.

Thus, the monitored measurand may be a torque or a translational force.

The target values of the machining target value curve and the reference target value curve may each indicate a position of the tool along a predetermined path along which the tool is moved during the machining movement and the reference movement. This is because the motion performed by the tool follows a precisely defined path. When moving along the path, the external force loads the tool in some way. The respective position of the tool is therefore particularly suitable for bringing the reference measurement curve and the machining measurement curve into a temporal relationship.

In particular, the rotary motion generated by the drive motor can be converted into a translational motion of the tool by the machine tool, and the torque of the drive motor can be used as a monitoring measurand. The difference curve can then be used to monitor the force acting on the tool in the direction of translation. This is a particularly suitable measure for monitoring the function of the tool.

In order to make it easier for the user to grasp the physical meaning of the values of the difference curve, the values of the difference curve may be converted from torque values to force values and monitoring may be performed based on the force values.

In the method, when a preset limit value is exceeded, a warning which can be recognized by the user can be triggered and/or the movement of the tool can be intervened. For example, the movement of the tool may be stopped or reversed. In addition, the movement of the tool, for example the rotational movement of the tool or the movement of the tool along a predetermined path, can be slowed down and the energy input into the workpiece caused by the machining of the tool can be kept below a predetermined limit value.

The method is suitable for monitoring various processes using different tools. For example, the tool may be designed for drilling, thread cutting, milling, turning or grinding.

A monitoring device may be provided for performing the monitoring method, the monitoring device being arranged for

Capturing the monitored measurand, and

-capturing a target value that has been generated by the control computer and used for controlling the movement of the tool, and

-performing a monitoring process based on the captured monitored measurand and target values.

Existing machine tools can be retrofitted with such monitoring devices.

Furthermore, the machine tool may have a control computer arranged for performing the monitoring method.

The method may also be embodied in the form of a computer program product. The computer program product then contains commands which, when executed on a computer, cause the computer to carry out the monitoring method.

Drawings

Further advantages and features of the present invention will become apparent from the following description, which describes in detail exemplary embodiments of the present invention with reference to the attached drawings. Shown is that:

fig. 1 shows a numerically controlled machine tool for thread cutting, in which a tool is moved in the direction of the tool axis by means of a spindle which can be rotated by spindle drive;

FIG. 2 depicts a diagram of a target position along a tool axis direction and a time profile of a torque of a spindle drive during machining of a workpiece;

FIG. 3 shows a diagram of a conventional monitoring method;

fig. 4 shows a diagram of a time curve of a target position, a torque of a spindle drive when machining a workpiece, a torque during a reference process and a difference curve;

FIG. 5 is an enlarged representation of the difference curve;

FIG. 6 shows the adjustment of the target value curves for the machining process and the reference process;

FIG. 7 shows the preparation of a target value curve before adjustment;

FIG. 8 illustrates a gear roll grinding process;

fig. 9 shows a diagram of the target position, the torque when grinding a gear, the torque during a reference process and a time curve of the difference curve;

FIG. 10 illustrates an external cylindrical grinding process, such as a shaft;

fig. 11 shows a diagram of a target position, a torque when grinding a workpiece, a torque during a reference process and a time curve of a difference curve;

FIG. 12 shows a surface grinding process; and

fig. 13 shows a diagram of the target position, the torque when grinding the workpiece, the torque during the reference process and the time profile of the difference curve.

Detailed Description

Figure 1 shows a numerically controlled machine tool 1. The workpiece 2 is machined by means of the machine tool 1. For this purpose, the machine tool 1 has a tool 3, which may be, for example, a tool for cutting a thread in a workpiece 2. The tool 3 is driven by a tool motor 4 that rotates the tool 3. It should be noted that the tool 3 may also be a drill or a milling head.

In the exemplary embodiment shown in fig. 1, the tool motor 4 is mounted on a spindle block 5 which is attached to a spindle 7, for example via a recirculating ball bearing 6, and which is movable in the direction of the axis of the tool 3. The spindle 7 is driven via a gear 8 by a spindle motor 9, which rotates the spindle 7 and in this way translates the spindle block 5 along the spindle 7.

Both the tool motor 4 and the spindle motor 9 are connected to a control computer 10. The control computer 10 is a computer that typically includes at least one processor, various storage units, and output and input units. A program for controlling the machine tool 1 is executed on the control computer 10. In particular, the control computer 10 sends control signals to the tool motor 4 and the spindle motor 9 and evaluates sensor signals for monitoring the tool motor 4 and the spindle motor 9. To this end, the tool motor 4 may be connected to a control computer 10, for example via a control line 11 and a sensor line 12. The drive current for controlling the tool motor 4 can be transmitted via the control line 11. In the opposite direction, the measurement signal from the speed sensor 13 can be transmitted to the control computer 10, for example via a sensor line 12. The speed sensor 13 records the number of rotations performed by the tool motor 4 per unit time, and outputs the result as a rotation speed n (number of rotations/time). If the rotation speed n is known, the angular speed ω 2 n is also known. Since the power P delivered by the tool motor 4 is known from the voltage U applied to the tool motor 4 and the current I drawn by the tool motor 4, the torque M (P ═ UI ═ M ω) can be determined if the angular velocity ω is known.

The spindle motor 9 is connected in a corresponding manner to the control computer 10 via a control line 14 and a sensor line 15. The spindle motor 9 may be supplied with a drive current via a control line 14. The instantaneous power of spindle motor 9 drawn by spindle motor 9 may be determined based on the current drawn by spindle motor 9 and the voltage applied to spindle motor 9, as the instantaneous torque of spindle motor 9 may be determined with a known rotational speed.

The measured value of the revolution counter 16 can be transmitted to the control computer 10 via a sensor line 15. With such a revolution counter 16, both the speed and the position of the spindle block 5 can be determined by counting the number of revolutions from the start position.

The control computer 10 may be connected to a display unit 18 via one or more data lines 17. Via the data line 17, data can be exchanged using a data exchange protocol, for example one of the general protocols for ethernet, field bus (Profibus) or so-called multi-drop interface (MPI) bus.

The monitoring computer 19 can also be connected to the control computer 10 via a data line 17, which, like the control computer 10, generally also comprises at least one processor, various memory units and output and input units. A program for monitoring the machine tool 1 is executed on the monitoring computer 19. This program can in principle also be executed by the control computer 10. In this respect, the monitoring computer 19 is not absolutely necessary.

According to a machining method known from DE 102016114631 a1, the machine tool 1 can be used to form a thread in the core hole 20 by means of the tool 3. The effective force 21 acting on the tool 3 is used here to monitor the function of the tool 3. This effective force 21 acts along the longitudinal axis of the tool 3, that is to say along the z-axis shown in figure 1. The monitoring method executed by the monitoring computer 19 to monitor the effective force 21 is described in detail below.

However, in order to better understand the monitoring method, the difficulties encountered when monitoring the machine tool 1 shall first be explained in more detail with reference to fig. 2. Fig. 2 shows a diagram in which a machining target value curve 22 for the position of the tool 3 is plotted over time. The position of the tool 3 will be understood here as the position of the tool 3 along the spindle 7. The position of the tool 3 may also be represented by the number of revolutions that the spindle motor 9 has to perform in order to move the spindle block 5 and thus the tool 3 from the zero position to a specific position. Of course, the position may also be expressed as a linear length distance between the zero position and the specific position. For the sake of simplicity, only the z position is mentioned below.

The target value of the z position is specified by the control computer 10 and is executed by means of a control device implemented in the control computer 10. This is typically a cascade controller known per se to the person skilled in the art, wherein the position deviation is controlled by an outer control loop, the speed of the spindle motor 4 is controlled by an intermediate control loop, and the torque of the spindle motor 4 is controlled by an inner control loop.

A series of times t is also marked with a dashed line in fig. 2₁To t₉. At time t₁To t₃By means of which the tool 3 is inserted into the core hole 20, an insertion movement 23 is performed. Time t₁Is a start time, and time t₃Is the time at which the tool reaches the maximum depth. During the insertion movement 23, the tool 3 is at time t₂Striking the workpiece 2. Thus, the insertion movement 23 can be subdivided into times t₁And time t₂With a closing movement 24 in between and at a time t₂And time t₃With a groove cutting motion 25 in between. During the groove-cutting movement 25, at least one helical groove is formed in the wall of the core hole 20 by means of the groove-generating region of the tool 3.

The groove cutting movement 25 is followed by a retracting movement 26 in which the tool is moved slightly backwards. At time t₃And t₄In between, the retracting movement 26 is followed by a thread cutting movement 27 in which the thread generating area of the tool 3 leaves the corresponding recess and cuts a thread in the wall of the core hole 20. For this purpose, the tool is rotated in the opposite direction to the groove cutting movement 25 and is slightly withdrawn depending on the pitch of the thread to be formed. The thread cutting movement 27 is ended as soon as the thread generating area reaches one groove or the next. This is the time t₅As in the case of (c).

At time t₅And t₆In the subsequent shearing movement 28 in between, the tool 3 again passes through the recess into the core hole 20 in order to shear off any chips that may have occurred when cutting the thread and extending into the recess. Then at time t₆And t₇In between the reset movements 29, the tool 3 is moved back again and at time t₇And t₈In a subsequent re-cutting movement 30 to re-cut the generated thread. The re-cutting movement 30 is performed in the opposite direction to the thread-cutting movement 27. The re-cutting movement 30 therefore takes place in the opposite rotational direction with respect to the thread-cutting movement 27, while moving slightly forward. When the thread-cutting area of the tool 3 reaches a groove or said groove again, it is possible at time t₈The re-cutting movement 30 is ended and the tool 3 can be withdrawn from the core hole 20 by a retracting movement 31. In the process, the groove cutting zone and the thread cutting zone of the tool 3 are guided to the outside through the grooves.

The diagram shown in fig. 2 also shows a machining torque curve 32 recorded by the control computer 10 and read out by the monitoring computer 19 when the machining method controlled by the target value curve 22 is executed.

The negative values of the machining torque curve 32 show the acceleration of the tool 3 in the z direction toward the workpiece 2 or the deceleration of the backward movement against the z direction. A positive value of the machining torque curve 32 means that the movement in the z direction is decelerated or accelerated against the z direction. During the insertion movement 23, the tool 3 is, for example, driven from time t₁A strong acceleration in the z direction is started. At time t at the tool 3₂Shortly after the workpiece 2 is touched, the minimum value of the machining torque curve 32, i.e. the maximum value of the torque, is reached. During the groove cutting movement 25, the machining torque curve 32 rises sharply towards positive values. Once the sign of the machining torque curve 32 changes at the zero crossing, the movement of the tool 3 in the z direction is decelerated and from time t₃Acceleration is started against the z direction in order to perform the retracting movement 26.

It has been found that monitoring the machining torque profile 32 is not sufficient in practice. Therefore, as shown in fig. 3, it is conceivable to define a lower limit curve 33 and an upper limit curve 34 between which the machining torque curve 32 must lie after the recording of the machining torque curve 32. However, in a steep gradient region of the machining torque curve 32, if the lower limit curve 33 and the upper limit curve 34 are placed such that the lower limit curve 33 and the upper limit curve 34 form a band of a constant thickness around the machining torque curve 32, the distance between the lower limit curve 33 and the upper limit curve 34 may be too large. In this case, the deviation in the steep gradient region cannot be reliably detected. Alternatively, the distance to the machining torque curve 32 is selected to be constant along the ordinate. In the region of large gradients of the machining torque curve 32 incorrect error information often occurs, because small shifts in the machining torque curve 32 result in the lower limit curve 33 and the upper limit curve 34 being exceeded.

The use of the assigned lower and upper limit values 35, 36 for monitoring the extreme values of the machining torque curve 32 has also proved to be less reliable for monitoring the quality of the tool 3. This is because many variables affect the machining torque curve 32: in addition to the friction forces in the gears and bearings, the inertial forces play an important role, since in the machine tool 1, objects of large mass can move. The changes in these variables are superimposed with the changes in the forces acting on the tool 3 and on this basis the function of the tool 3 can be substantially monitored. This is because when the tool 3 is worn, the force acting on the tool 3 changes because the machine tool 1 moves the tool 3 according to the machining target value curve 22. Therefore, when the tool 3 is worn, a larger force is required than when a new tool 3 is used. However, the forces acting on the tool 3 are significantly smaller than the inertial and frictional forces and therefore cannot be easily determined based on the machining torque curve 32 recorded on the spindle motor 9.

Fig. 4 now shows a further diagram, in which, in addition to the machining torque curve 32 already shown in fig. 2 and 3, a reference torque curve 38 recorded on the basis of a reference target value curve 37 is also shown. This reference torque curve 38 is preferably recorded by the control computer 10 as an air torque curve without machining the workpiece 2 and is read by the monitoring computer 19. For example, the tool 3 can be moved to a sufficiently large distance from the workpiece 2 and there perform a reference movement in the air corresponding to the reference target value curve 37. The reference target value curve 37 corresponds to the machining target value curve 22, possibly with deviations as explained in more detail below in practice. The recording of the reference torque profile 38 may be repeated at periodic intervals.

The reference torque curve 38 and the machining torque curve 32 are subtracted from one another using the method described in more detail below, and in this way a difference curve 39 is calculated.

Since the machining torque curve 32 is recorded during the machining of the workpiece 2 and the reference torque curve 38 is recorded without the workpiece 2, the difference curve 39 depends only on the forces acting on the tool 3 and inhibiting the movement of the tool 3 in the workpiece 2. Correspondingly, only at the time t of the tool 3₂The difference curve 39 deviates from zero only after entering the workpiece 2. Since the machining torque curve 32 and the reference torque curve 38 each indicate the torque of the spindle motor 9, and the rotation of the spindle 7 is converted into translational motion by the recirculating ball bearing 6, the restraining force that restrains the tool 3 from moving in the material is the effective force 21. The effective force 21 can be calculated from the torque M applied by the spindle motor 9 according to the formula F-2 pi M/s, where s is the path covered by the spindle block 5 along the spindle 7 during one rotation of the spindle motor 9.

In fig. 5, the difference curve 39 is shown enlarged again. As can be seen from fig. 5, the reference torque curve 38 has distinct local extrema, the magnitude of which can be monitored by setting a lower limit value 40 and an upper limit value 41. If the difference curve 39 falls below one of the lower limit values 40 or exceeds one of the upper limit values 41, the monitoring computer 19 identifies an error and writes it at least into an error log. If necessary, the monitoring computer 19 causes an error display on the display unit 18 or influences the movement of the tool 3 by sending corresponding control commands from the monitoring computer 19 to the control computer 10. These control commands may correspond to control commands generated by means of the display unit 18 and transmitted to the control computer 10, for example control commands for stopping the machine tool 1.

The limit values 40 and 41 can be distributed along the difference curve 39 such that different functional sections of the difference curve 39 are covered. During the groove cutting movement 25, the decisive factor is the function of the groove cutting region of the tool 3. The thread cutting area of the tool 3 is also important for the thread cutting movement 27. In this way, different functional areas of the tool 3 can be monitored.

The monitoring of the limit values 40 and 41 presupposes that the machining torque curve 32 and the reference torque curve 38 are not shifted in time relative to one another, since otherwise the difference curve 39 is incorrect. Therefore, it is necessary to make the start time t₁And (5) the consistency is achieved.

In order to correlate the machining torque curve 32 and the reference torque curve 38 with each other in time, the machining target value curve 22 and the reference target value curve 37 may be used. In particular, the machining target value curve 22 and the reference target value curve 37 can be superimposed by the monitoring computer 19 using the method of least square deviation. This required time shift Δ T is a measure of the relative time interval between the machining target value curve 22 and the reference target value curve 37. The monitoring computer 19 can thus also determine the relative time interval between the associated machining torque curve 32 and the reference torque curve 38. Fig. 6 shows a corresponding method.

The machining target value curve 22 and the reference target value curve 37 are particularly suitable because their routes are almost the same. The control computer 10 is typically a computer which is able to control the movement process of the machine tool 1 in real time. The movements to be performed are specified by a list of movement commands to be processed by the control computer 10, which commands are processed in turn by the control computer 10. For example, a first movement commandThe execution of the insertion movement 23 can be initiated. A subsequent second movement command may initiate the retraction movement 26. The motion commands are always executed in the same way: the partial sections of the target value curve generated on the basis of the individual movement commands are therefore always identical. The subsections of the target value curves of the insertion movement 23, the retraction movement 26, the thread cutting movement 27, the shearing movement 28, the reset movement 29, the re-cutting movement 30 and the retraction movement 31 are always the same for the various target value curves. However, the control computer 10 may have to perform other tasks between executing the motion commands, and a delay Δ t of different length occurs between executing the motion commands_n。

In order to improve the determination of the time interval between the machining target value curve 22 and the reference target value curve 37, the delay Δ t in the machining target value curve 22 and the reference target value curve 37 can be set before the adjustment process shown in fig. 6_nRemoved from the machining target value curve 22 and the reference target value curve 37 as shown in fig. 7. This can be achieved by: a transition zone 42 is designated between the zones of the target value curve and is removed in the target value curve and the associated torque curve. The transition segment 42 is specified by determining the segment of the respective target value curve corresponding to the movement command. The transition segment 42 is then generated as the target value curve segment in between.

It should be noted that the random control deviations from the target value curves 22 and 37 should not produce a difference curve 39 value that is greater than the allowable deviation from the difference curve 39. In this respect, the lower limit value 40 and the upper limit value 41 will be set in dependence on the maximum control deviation such that incorrect error information is not randomly generated, if at all possible. However, no significant random control deviations will occur under normal conditions. If a control deviation from the target value curves 22 and 37 does occur, this is due to the occurrence of an additional force reflected in the difference curve 39, which is a desired effect.

Here, a monitoring method has been described in which the reference torque curve 38 is an air torque curve. In addition, an alternative reference torque curve may also be recorded, for example using a new copy of the tool 3. In this case, however, monitoring is made more difficult because the forces acting on the tool 3 are also included in the reference torque curve. The difference curve between the machining torque curve 32 and the alternative reference torque curve also shows a change in the effective force 21, not the effective force 21, as in the case of the curve 39. It should be noted, however, that alternative reference torque curves may be used not only in place of reference torque curve 38, but may also be used in addition. In this case, not only the effective force 21 but also the change in the effective force with time is recorded and monitored.

The monitoring method is also described herein in connection with a machining method with which a thread can be formed in the core hole 20 of the workpiece 3. However, the monitoring method described here can in principle also be applied to other machining methods in which the tool is moved in a translatory and/or rotary manner. For example, the monitoring method may also be used for monitoring drilling, turning or milling processes. By these methods, the effective force along the translation axis and/or the effective torque about the axis of rotation of the respective machine tool and a combination of the effective force or the effective torque can be determined and, if necessary, monitored.

In the case of a drilling method, for example, the effective force acting along the longitudinal axis of the drilling tool and/or the effective torque acting on the drilling tool can be determined and monitored.

During the milling process, not only the effective force acting in the z direction along the longitudinal axis of the milling head can be determined, but also the effective force acting transversely in the x or y direction on the milling head of the milling machine. Depending on the direction of movement, the forces acting transversely on the milling head can act on the milling head from different, constantly changing directions. It may therefore be advantageous if this amount of force is calculated from force components acting along the x-and y-axes of the force acting transversely on the milling head, and if it is monitored whether the amount of transversely acting force exceeds or does not reach certain limit values. In some cases, for example milling in only one direction, it may also be useful to monitor only one force component.

During turning, in which a workpiece held by a clamping tool is set into rotation about the z-axis and turned by means of the turning tool, the effective force on the turning tool in the feed direction (i.e. in the z-direction) and/or the effective forces in the x-and y-directions or the total force consisting of these force components can be determined and monitored.

The monitoring methods described herein may also be used in grinding processes.

Fig. 8 shows the arrangement of the workpiece 2 and the tool 3 during the roll grinding process. In fig. 8, the workpiece 2 is a helical-toothed gear 43 fastened to a gear shaft 44 of the machine tool 1. The gear shaft 44 is rotatable about an axis of rotation 45, sometimes referred to as the B-axis.

The tool 3 is formed by a profiled grinding wheel 46 rotating about an axis of rotation 47, sometimes also referred to as the C-axis. During the grinding process, the grinding wheel performs a linear motion 48 along the z-axis. As in the case of the machine tool shown in fig. 1, the linear movement 48 can be carried out by means of a spindle drive. The tooth surface of the gear 43 is cut by the grinding process.

Fig. 9 shows a diagram in which the machining target value curve 22, the reference target value curve 37, the machining torque curve 32, the reference torque curve 38, and the difference curve 39 are plotted. For the machining target value curve 22 and the reference target value curve 37, the position of the grinding wheel 46, in particular the position of the axis of rotation 47 (C-axis) along the z-axis, can be selected during the grinding process. For the machining torque curve 32 and the reference torque curve 38, either a torque that causes the grinding wheel 46 to rotate about the rotation axis 47 (C-axis) or a torque that acts on a main shaft (not shown in fig. 8) for linearly moving the rotation axis 47 (C-axis) of the grinding wheel 46 along the z-axis may be used.

The machining target value curve 22 and the reference target value curve 37 are divided into three sections. At time t₁And t₂During the start-up phase 49 in between, the grinding wheel 46 moves a greater feed distance along the z-axis at a high feed rate. During the start-up phase 49, at time t₁A first contact between the grinding wheel 46 and the gear wheel 43 occurs. The material removal is initially low and increases as the grinding wheel 46 approaches the gear 43. The torque necessary to drive the grinding wheel 46 or the torque causing the linear motion of the rotation axis 47 (C-axis) also increases accordingly. At time t₂And t₃In between, the feed rate of the linear movement along the z-axis is reduced in the through-phase 50. During the pass-through phase 50, the axis of rotation 47 (C-axis) is substantially centered over the gear 43. During the pass-through phase 50, the contact area between the grinding wheel 46 and the gear 43 is maximized. Accordingly, the machining torque curve 32 and the reference torque curve 38 each pass through a maximum value, which is also reflected in the maximum value of the difference curve 39 in a quantitative manner. This means that the grinding power performed on the gear wheel 43 during the through phase 50 also assumes a maximum value. The exit phase 51 follows at time t₃And t₄In the meantime. During the exit phase 51, the feed rate is again increased as less and less material is removed by the grinding wheel 46. At time t₄After that, there is no longer any contact between the grinding wheel 46 and the gear wheel 43.

Figure 10 shows a process using external cylindrical grinding. In this case, the workpiece 2 is, for example, a round shaft 52 clamped in a holder that allows the round shaft 52 to rotate about an axis 53 (B-axis). To grind a circular shaft 52, the circular shaft 52 rotates about an axis 53 and moves in a linear motion 54 along the z-axis toward the grinding wheel 46 rotating about the axis of rotation 47 (the C-axis).

Fig. 11 is a diagram showing the machining target value curve 22, the reference target value curve 37, the machining torque curve 32, the reference torque curve 38, and the difference curve 39. For the machining target value curve 22 and the reference target value curve 37, the relative distance along the z-axis between the rotation axis 47 (C-axis) of the grinding wheel 46 and the axis 53 (B-axis) of the circular shaft 52 may be used. For the machining torque curve 32 and the reference torque curve 38, a torque that causes the grinding wheel 46 to rotate about the rotation axis 47 (C-axis) may be used, or a torque that causes the circular shaft 52 to rotate about the axis 53, or a torque of a main shaft (not shown in fig. 10) for performing the linear motion 54 may be used.

The process is now divided into different stages. At time t₁And t₂In the approach phase therebetween, the circular shaft 52 is moved toward the grinding wheel 46. At time t₂There is contact between the grinding wheel 46 and the circular shaft 52. At time t₂And t₃The subsequent stages in between relate toRoughing 56, in which the circular shaft 52 is moved over a relatively large distance and at a relatively high speed towards the grinding wheel 46. The roughening 56 removes a lot of material from the circular shaft 52.

At time t₃And t₄With a short feed distance and a low feed speed in the direction of the grinding wheel 46. During finishing 47, only a small amount of material is removed from the round shaft 52.

Fig. 12 shows a surface grinding process in which a grinding wheel 46 is used to grind flat the workpiece 2. The workpiece 2 performs a linear movement 58 relative to the grinding wheel 46.

Fig. 13 shows a correlation diagram with a machining target value curve 22, a reference target value curve 37, a machining torque curve 32, a reference torque curve 38 and a difference curve 39. The torque acting on the grinding wheel 46 or on a spindle (not shown) for displacing the workpiece 2 in a linear movement 58 can be used to record the machining torque curve 32 and the reference torque curve 38.

Again, the process is divided into different stages. At time t₁And t₂In between the start-up phase 59, the grinding wheel 46 comes into contact with the workpiece 2 and gradually removes material from the workpiece 2. During the through phase 60, the workpiece 2 is passed through until the grinding wheel 46 at time t₃Starting to leave the workpiece 2. During the exit phase 61, the grinding wheel 46 still removes residual material from the workpiece 2 until at time t₄There is no longer any contact between the grinding wheel 46 and the workpiece 2. In the start-up phase 59 and the exit phase 61, the feed rate is higher than during the through-phase 60. It should be noted that the distance covered during the pass-through phase 60 is significantly greater than the distance covered during the start-up phase 59 and the exit phase 61.

In the case of the grinding process shown in fig. 8 to 13, there is a special feature that the grinding wheel 46 is cooled, usually using oil, which is injected into the bore of the grinding wheel 46. This oil is removed from the workpiece 2 during the grinding process. This creates an effective friction force. This effective friction force can be eliminated by recording the corresponding reference torque curve 38 on the workpiece 2, but without removing material. Then, the effective friction force occurs both when the machining torque curve 32 is recorded and when the reference torque curve 38 is recorded, and therefore the effective friction force is not included in the difference curve 39.

The determination of the difference curve 39 is advantageous to this extent, since the difference curve 39 is a measure of the energy input caused by the friction of the grinding wheel 46 on the workpiece. If M is the corresponding torque and ω is the associated angular velocity, the energy input per unit length becomes Δ E/Δ z-M · ω/v_zWherein v is_zIs the feed rate along the z-axis. In order to determine the locally transmitted energy, it may also be necessary to take into account the size of the contact area between the grinding wheel 46 and the workpiece 2.

In this way, it seems possible to prevent grinding burn on the workpiece 2. The workpiece is thermally damaged by so-called grinding burns. Grinding burns can lead to re-hardening or softening of certain areas in the workpiece 2 or to changes in the microstructure. In all cases, the grinding burns cannot be seen with the naked eye and can greatly reduce the service life of the finished workpiece 2 in its respective function.

The machining process can be stopped if the value of the difference curve 39 exceeds certain limit values during grinding. In principle, it is also conceivable to slow down the movement in the z-direction and/or to reduce the rotational speed of the hub 46 when certain limit values are exceeded or approached, in order to reduce the energy input and prevent grinding burns. It is advantageous to switch to an operating mode in which the reference target value curve and the reference torque curve are also available.

It should be noted that in a modified embodiment, several machining torque curves 32 and reference torque curves 38 for different drives may be recorded and monitored in parallel; for example, during the grinding process shown in fig. 8 to 13, the torque for the respective spindle drive for the movement along the z-axis and the torque for driving the grinding wheel 46 are recorded in parallel and monitored for exceeding a predetermined limit value.

It should also be noted that, in general, the drive is usually always a motorized drive with torque. In the case of linear drive, linearly acting forces will have to be taken into account instead of torques.

In the exemplary embodiment described herein, the control computer 10 and the monitoring computer 19 are separate physical units. This provides the advantage that existing machine tools 1 can be retrofitted with the monitoring computer 19. However, it is also possible to combine the control computer 10 and the monitoring computer 19 in a single physical computing unit, for example in a display unit designed as a computer.

For example, the methods described herein may also be embodied in a computer program product that is installed on and executed by the control computer 10. The monitoring methods described herein are performed when the processor subsequently processes the code of the computer program product. In an exemplary embodiment, the code may be stored on a data medium readable by a computer, such as a floppy disk, a Compact Disc (CD), or a Digital Versatile Disc (DVD). In other exemplary embodiments, the computer program product may additionally comprise code stored on a data store of a server or a group of servers. In a further exemplary embodiment, the medium may also be an electrical carrier signal for transmitting the code from the server by downloading the code to the computer.

Finally, it should be noted that features and characteristics which have been described in connection with a particular exemplary embodiment may also be combined with another exemplary embodiment, unless excluded for compatibility reasons.

Finally, it is noted that in the claims and the specification, the singular encompasses the plural unless the context indicates otherwise. In particular, when the indefinite article is used, it is intended to refer to both the singular and the plural.