DE102015224441A1 - Method for relative positioning of a workpiece and a tool in a machine - Google Patents

Abstract

The invention relates to a method for automatic relative position determination of a first object (1) arranged on a first assembly (5) of a machine (2) and a second object (3) arranged on a second assembly (4) of the machine (2) first and the second assembly (4, 5) are moved relative to each other. This comprises a coarse measurement (S1), in which a position of the first object (1) relative to the second object (3) is detected with a first measurement accuracy, a fine measurement (S2), which is carried out after the coarse measurement (S1), in FIG a precise position of the first object (1) relative to the second object (3) is detected contactlessly with a second measuring accuracy which is higher than the first measuring accuracy, wherein between the first object (1) and the second object (3) an electric Voltage is applied, the first object (1) and the second object (3) by a relative movement of the assemblies (4, 5) are moved against each other, the more precise position of the first object (1) relative to the second object (3) is detected when a voltage breakdown occurs between the second object (3) and the first object (1), and the relative movement of the assemblies (4, 5) is stopped in response to the voltage breakdown. Furthermore, an evaluation takes place in which the precise position is stored in a computer program of the machine (2) for the control of the processing or the measurement of the first object (1) and / or the second object (3) by means of the machine (2) becomes.

Description

The invention relates to a method for determining the position of a workpiece and a tool in a machine.

The requirements for the accuracy of machine tools with rotating tools, such. B. milling machines, continue to rise. In addition to the accuracy of the actual machining, which is determined by the accuracy of the machine, the machining tool, the tool holder, etc., the accuracy + in the setting of the workpiece, or the setting of the zero point for machining increasingly a limiting factor for the achievable precision.

After a workpiece has been introduced into the machine and clamped for machining, be it on pallets or by conventional means, such as a vise, usually the clamping position of the workpiece is determined with suitable tools and fixed due to the detected clamping position of the zero point for machining.

Known from the prior art is the probing of the zero point with an automatic mechanical button. This has a stylus tip with a probe ball for probing the workpiece at one end. At the other end it is attached to a tool holder and can be exchanged for it in the machining spindle. For probing a workpiece, the machine moves the automatic probe held on the spindle via the tool holder to the workpiece until the stylus located on the automatic probe touches the workpiece and deflects far enough for the probe to switch. Modern automatic buttons are designed so that the path for the deflection of the stylus is always exactly the same and can be calibrated. When the automatic button switches, the automatic button sends a signal to the controller, which detects the actual position of the machine for that position. So any edges, holes, etc., touched and their relative position in the machine can be determined relatively accurately. Modern buttons are highly accurate. Therefore, the position of the switch for the switching point can be determined very accurately.

Nevertheless, the accuracy of this method is limited by the given process itself. After the predefined geometric elements have been touched with an automatic probe in a machine, the tool holder to which the automatic probe is attached must again be replaced from the spindle and the machining tool desired for the machining must be loaded into the spindle. In this change process, there are deviations, since the clamping position of the tool holders is never exactly identical. In addition, in most cases, the length of the automatic probe from the contact surface of the tool holder to the tip of the stylus does not match the length of the machining tool from the contact surface of the tool holder to the tool tip. If the spindle is not exactly parallel to the traversing direction of the axis, which moves the spindle in the direction of the spindle axis, additional deviations occur. The smallest tilting of the spindle leads to an offset between probing and machining. The greater the difference in length between the machining tool and the automatic probe, the more serious are these tiltings for the probing accuracy.

The invention has for its object to provide a method for determining a position of a workpiece and a tool in a machine, which avoids the disadvantages of the prior art with a simple structure and simple, cost-effective manufacturability and an exact assignment between the geometry of the workpiece allows the tool.

According to the invention the object is achieved by the combination of features of claim 1, the dependent claims show further advantageous embodiments of the invention.

It is therefore desirable in the context of the task that the positions of the zero-determining geometric elements, for. B. holes or edges, directly before processing, based on the tool to be used, are determined.

The invention thus provides a method for the automatic relative position determination of a first object arranged on a first assembly of a machine and a second object arranged on a second assembly of the machine, wherein the first and the second assembly are moved relative to one another. This includes a coarse measurement, in which a position of the first object relative to the second object is detected with a first measurement accuracy, a fine measurement, which is carried out after the coarse measurement, in which a precise position of the first object relative to the second object without contact with a second measurement accuracy is detected, which is higher than the first measurement accuracy, wherein between the first object and the second object, an electrical voltage is applied, the first object and the second object are moved by a relative movement of the assemblies against each other, the more precise position of the first object is detected against the second object when a voltage breakdown between the second object and the first object, and the relative movement of the assemblies is stopped in response to the voltage breakdown. There is also an evaluation in which the precise position in a computer program of the machine for controlling / regulating the processing or the measurement of the first object and / or the second object is deposited by means of the machine.

In the coarse measurement and the fine measurement, either the same or a different second object can be arranged on the second assembly of the machine, for example clamped in this. In this case, the second object may be, for example, a tool or a probe. In the case of fine measurement, in the case of the relative movement of the first object and the second object relative to one another, an initial distance is preferably selected based on the position detected during the coarse measurement. It is thus created a two-stage process. The second object clamped in the machine during the fine measurement is preferably in a rotation during the relative movement of the first object and / or of the second object. However, the method according to the invention is not limited to rotating objects. It can also be done with standing objects. If the first object and the second object are moved against each other, this can be done by a movement of the first object, the second object or both objects. The movement of the objects takes place in particular by moving the respectively associated assembly. Preferably, the first object is clamped in a preparatory step on the first module.

The first object is an example of a workpiece which has been clamped in the preparatory step on the first module and the second object is an example of a tool. In order to avoid an undesired removal of material during the fine measurement, a starting speed, ie a speed with which the workpiece and / or the tool is moved, must be very small. Since the position of the workpiece in the machine at the beginning of the process is not known exactly, the start-up processes had to start so far with a relatively large distance to the workpiece in order to avoid premature collision between the tool and the workpiece. Very small starting speeds lead to long-lasting starting operations. In particular, when the workpiece is to be electrically contacted at several positions, the process takes undesirably long. The method according to the invention makes possible a considerable shortening of the startup times or the position determination of the workpiece and / or tool as a whole. As a result, even with workpieces whose position in the machine is only very roughly known, in which to avoid collisions, the process for electrical contact must therefore begin with a relatively large distance between the workpiece and tool, nevertheless a relatively short time for electrical contact can be achieved ,

To explain the invention, the physical background is considered first. In an alternative method, a capacitive electrical contact is used as a variant of the electrical contacting by a voltage breakdown, which is possible in front of a mechanical contact between a tool and a workpiece at very small distances. Prerequisite for the capacitive contacting is the use of an AC voltage source. In practice, a capacitive contact, which takes place before the mechanical contact, but very difficult to achieve. For a capacitive contacting two charge carriers, in this case the workpiece and the machining tool with the largest possible surface area must be spaced as small a distance as possible. Since the tools are provided with sharp edges, the surface of the tool, which is located at a small distance from the workpiece, will always be very small in each rotational position of the rotating machining tool. As a result, even with very small distances between the workpiece and the tool, no significant capacities are created between the workpiece and the machining tool. Even when using very high frequencies for the AC voltage source, it is therefore hardly possible to detect a capacitive contacting before the mechanical contact between the workpiece and the tool. In addition, due to different cutting edge geometries of different machining tools, the electrical capacitances created when approaching between the machining tool and the workpiece would be very different. Therefore, the use of electrical capacitive contacting in practice is not readily possible.

Since a use of an electrical capacitive contacting between a workpiece and a tool in practice is not readily possible, another physical effect is used according to the invention to allow electrical contact before mechanical contact between the first object and the second object. This is a voltage breakdown. A voltage breakdown is a phenomenon known from physics, in which a sufficiently high electrical voltage is applied between two poles and the distance of the poles is reduced or the electrical voltage is increased until the voltage breakdown occurs. At the moment of voltage breakdown, an electrical current is flowing between the two poles. Here, a distinction must be made between two types of voltage breakdown, gas breakdown and vacuum breakdown. The electrical voltage required for a voltage drift generally decreases with decreasing distance between the two poles, between which a voltage breakdown is to be generated. However, according to the Paschen law, the physical behavior in gas breakdown is not linear. There is a voltage minimum under which a voltage gas breakdown is no longer possible, regardless of how much the distance between the two poles is reduced. At normal air pressure this is about 330 V in air.

If smaller electrical voltages than the minimum voltage required by the Paschen curve are applied to two poles for a voltage breakdown and the pitch of the poles is reduced further and further, mechanical contact of the poles will result in vacuum breakdown, even if the poles approach each other Air is carried out at normal air pressure. For a vacuum breakdown very high field strengths are required, d. H. very small distances and / or very high electrical voltages. A vacuum breakdown takes place at about 1000 kV / mm of electric field strength. Since the vacuum breakdown depends on the field strength, the roughness of the surface of the two poles has a very strong effect. At very small roughness peaks, there are strong field peaks, which can lead to premature voltage breakdown. In practice, even at theoretical field strengths that do not take into account the surface roughness of the poles, a vacuum breakdown of 10 kV / mm or less occurs. At very small distances between the two poles is a vacuum breakdown even at very low voltages of a few volts, z. B. 10 V, already possible.

These physical relationships are used for the position determination according to the invention of a first object and / or a second object in a machine. According to the invention, therefore, a two-stage method is proposed, which is divided into a coarse and a fine measurement, wherein the coarse measurement in a first stage and the fine measurement in a second stage. According to the invention, at least during the fine measurement, an electrical voltage is applied between the second object, in particular a rotating tool, and the first object and monitored with a suitable circuit. The second object and the first object are closed by means of axes of the machine on each other until it comes to electrical contact. At the moment of electrical contact, the positions of the axes are detected, the axes of the machine are stopped as quickly as possible and the second object is removed again from the first object. An electrical contact is contactless and takes place only via a voltage breakdown.

According to the invention, both the first object and the second object can each be an arbitrary object as long as it is electrically conductive. Preferably, the first object is a workpiece or a reference element, for. B. a measuring ball. If the first object is a workpiece, this can be processed immediately after the fine measurement with high precision. If the first object is a reference element, variable proportions of the second object can be detected, if necessary, and thus the following work steps can be adapted to the changed dimensions. Thus, the second object is preferably a tool. The dimensions of a tool may change due to wear of the tool or an imbalance and resulting at high speeds resulting larger effective diameter of the cutting and these changes can be detected immediately before use of the tool and thus can subsequent machining of a workpiece by means of the tool on the Wear or the actual effective diameter of the cutting to be adjusted. More preferably, the second object is a probing element. This makes it possible to detect a dimension of the first object, wherein in particular difficult to reach points of the first object can be approached.

In the method according to the invention, it is advantageous if the first object and / or the second object are stored electrically isolated. According to the invention, an electrical voltage is applied and monitored between the first object and the second object. This is easily possible, especially in modern machines with high-speed spindles, since the spindle shafts of such spindles are usually mounted with ceramic balls. The spindle shaft is thereby electrically isolated from the machine. A known from the prior art electrical contact, for example via brushes, an electrical voltage can be applied to the spindle shaft. About the tool holder, this is passed to the second object. The second pole of the electrical voltage can be connected to the first object or the first module, for example a machine table located below the first object.

If a spindle is used in the machine whose shaft is not electrically isolated from the spindle housing, then the electrical insulation can be provided at another suitable location, for. B. between spindle housing and machine, but also workpiece side, z. B. between the workpiece and machine table. With many known Methods can easily create the conditions to attach an electrical voltage between the spindle shaft and the workpiece.

It is advantageous to use a time-saving and robust method in the coarse measurement, since the position detected during the coarse measurement is further specified in the fine measurement anyway. Therefore, it is advantageous if, during the coarse measurement, the position of the first object relative to the second object is detected by a mutual mechanical probing. The mechanical probing is a process in which there is an actual mechanical contact between the first object and the second object. For example, there is a mechanical contact between a previously described automatic stylus with stylus tip or a tool and a workpiece in the machine. In the latter case, an acoustic detection can be used. Alternatively, also known from the prior art optical methods with z. B. strip projection with light and / or camera or multiple cameras or measuring laser can be used.

It is advantageous if, during the coarse measurement, the position of the first object relative to the second object is detected by a mechanical probing of the first object by a third object arranged on the second module. Thus, the third object may be an automatic probe arranged on the second assembly, which is clamped in a tool holder, and after the coarse measurement is replaced by the second object, for example a tool, which is then clamped with the aid of a tool holder. If, during the coarse measurement, the first object is scanned by means of the second object, then the method can be carried out particularly quickly, since both the coarse measurement and the fine measurement can be carried out by means of the same objects.

As an alternative to the method for coarse measurement known from the prior art, it is advantageous if, during the coarse measurement, an electrical voltage is applied between the first object and the second object, the electrical voltage being higher than the electrical voltage applied during the fine measurement , the first object and the second object are moved against each other by a movement of the assemblies, and the position of the first object relative to the second object is detected when a voltage breakdown occurs between the first object and the second object. The method according to the invention is thus considerably accelerated. The higher the respectively applied electrical voltage, the lower the associated measurement accuracy, since the voltage breakdown occurs with increasing voltage already at a greater distance between the first object and the second object. In particular, the first electrical voltage for the coarse measurement can be selected such that a gas voltage breakdown can also take place in the present medium. For example, the electrical voltage is much greater than 330 volts to choose, for. B. 1000 V or more.

According to the invention, a coarse measurement is first performed in the first stage. In particular, a relatively high electrical voltage is applied between the first object and the second object for this purpose. It comes even at a relatively large distance between the first object and the second object to a voltage breakdown (vacuum breakdown or even gas breakdown), which can be detected by a circuit. Since the voltage breakdown in the coarse measurement already takes place with a larger distance between the first object and the second object, the relative approach speed between the first object and the second object can be chosen to be relatively high. At the moment of voltage breakdown, there remains enough space between the first object and the second object to stop the axes of the machine before there is an undesirable mechanical contact between the first object and the second object. At the moment of voltage breakdown, the position of the axes and thus the relative position between the first object and the second object is detected.

Since the local roughness of the two poles, in this case of the first object and the second object, has a strong effect on the field strength required for the voltage breakdown and thus on the distance between the first object and the second object, the relative position detection between the first object and the second object with high electrical voltage between the first object and the second object are subject to greater inaccuracies. Therefore, the electrical contact with high electrical voltage is initially only a coarse measurement to determine the approximate relative position between the first object and the second object.

It is decisive for the precision measurement that the renewed approach to the electrical contact between the first object and the second object is started from a position at which no voltage breakdown still occurs at the lower electrical voltage selected for the precision measurement. For the approach movement of the fine measurement, a considerably smaller relative speed is selected between the first object and the second object. That's important because the distance at which it is comes to be detected voltage breakdown between the first object and the second object is considerably smaller due to the lower electrical voltage. The remaining distance between the first object and the second object at the moment of voltage breakdown is very small and therefore the relative speed between the first object and the second object must be chosen small so that the machine can still stop the axes before it becomes mechanical Contact between the first object and the second object comes.

Despite the small relative speed between the first object and the second object, the time required for the fine measurement is short because it can start on the basis of the previous results of the coarse measurement with a relatively small distance between the first object and the second object. The travel of the axes to be traversed until the voltage breakdown occurs can be chosen to be very short, since the approximate relative position between the first object and the second object for this position is already known from the coarse measurement.

Due to the low electrical voltage during the fine measurement, in any case only a vacuum breakdown and not a gas breakdown occurs during the fine measurement. The variations in the distance between the first object and the second object, due to the local roughness of the surfaces of the first object and the second object, in which the voltage breakdown to be detected occurs during the fine measurement, do not prove to be serious inaccuracies when the electrical Voltage is chosen so small that the distance for the voltage breakdown is very small overall. The results of the fine measurement for the position determination are very accurate due to the low electrical voltage. In practice, measurement uncertainties of less than 1 μm can be achieved.

According to the invention, a coarse measurement is first performed in the first stage. If, during the coarse measurement, the second object is approached with high applied electrical voltage to the first object, an approach is therefore already recognized at a relatively large distance. There is thus a sufficient distance even at a high speed of this movement, which allows a deceleration of the relative movement between the first object and the second object without causing a collision. In the fine measurement, the measurement accuracy is greater, and an approximation between the first object and the second object is detected only shortly before a collision. There is thus less time and distance available for braking the assemblies and thus the relative movement between the first object and the second object. It is therefore advantageous if the first object and / or the second object are moved at a higher speed during the coarse measurement than during the fine measurement.

Since a voltage breakdown material of both poles, between which the voltage breakdown occurs, is evaporated, it comes through the material evaporation to a very low material removal. This can be further minimized by limiting the energy of the voltage breakdown. This is achieved in that the current that can flow in the voltage breakdown is circuit technology limited, z. B. by limiting a maximum possible current. The current intensities to be detected for the voltage breakdown should preferably be below 1 mA in order to limit the material removal by evaporation, more preferably at a few μA or even less. As a result, the removal of material by evaporation is extremely low, so that this even at multiple electrical contact at the same position, for. B. is not relevant to reference surfaces. By limiting the maximum possible amperages at the same time a personal protection is guaranteed. It is therefore advantageous if a maximum current which flows through the second object in the event of voltage breakdown is limited.

In a second stage, that is to say in the case of fine measurement, it is provided according to the invention to carry out a fine measurement with a markedly smaller electrical voltage at the same position. Depending on the design, it may be that the fine measurement can be started directly from the stopping position of the axes of the machine after the coarse measurement, because the distance between the first object and the second object is still so large that it in this position (this distance ) at the much smaller electrical voltage for the fine measurement does not yet come to a voltage breakdown. However, it may also make sense for the machine to slightly increase the distance between the first and the second object after the coarse measurement has been started, and to remove them slightly from each other. It is therefore advantageous if between the coarse measurement and the fine measurement, a distance between the first object and the second object is increased by a relative movement of the modules, in particular so far increased that at the beginning of the fine measurement no direct voltage breakdown between the first object and the second object takes place.

It is also advantageous if the fine measurement is carried out repeatedly. In this way, an accuracy of the specified position further increases because chips, which are possibly located in a gap between the first object and the second object, for example between a rotating tool and a workpiece, are either dissipated, or at least recognized by a change in the precise position. In particular, it is advantageous if the fine measurement is repeated until the precise positions detected in two successive repetitions of the fine measurement deviate less from one another than predetermined by a tolerance range. In this way, a measuring error caused by chips can be excluded.

Furthermore, it is advantageous if during the coarse measurement the movement of the first object and / or of the second object is stopped in response to the detection of the position of the first object relative to the second object or a detection of the voltage breakdown. Thus, a collision between the first and the second object is avoided.

It is also advantageous if a multi-stage method is provided by reducing the relative velocity in the method of the first object and the second object to each other at each step, and also decreasing the voltage applied between the first object and the second object stepwise.

In addition, it is advantageous if in the coarse measurement and / or the fine measurement, the first object is a reference element, in particular a measuring ball, which is arranged in a fixed position relative to the machine. Thus, a known position is approached, which provides a reliable basis as the output value for determining a relative position according to the invention.

A machine adapted to carry out the method according to the invention has all the advantages of the method.

According to the invention, it is advantageous if the electrical voltage for the coarse measurement is higher by a factor of 5 to 10 than the electrical voltage for the fine measurement. In certain applications, however, the factor can be even higher.

The method according to the invention is particularly advantageous when the second object is a rotating machining tool, but the method is not limited to rotating machining tools. It can also be done with standing tools. Instead of machining tools, it is also possible for any other geometries to be mounted as "probing elements" on the second assembly, for example a spindle. If these "probing elements" are not rotationally symmetrical, different information about the position and geometry of a first object to be scanned, z. B. a workpiece in the machine can be determined. It is thus possible, in addition to the editing tools, to mount special probing elements with the aid of tool receptacles on the spindle, with the aid of which the measuring possibilities in a machine are considerably expanded. The probing elements can be prepared in almost any geometry. Such a probing element is thus a special kind of tool, which is intended only for a measuring process and not for processing. Another advantage of the method is that the electrical contact runs without probing force, in contrast to mechanical buttons, in which the deflection of the stylus always a probing force and a probing path are required. As a result, it is also conceivable to manufacture very filigree probing elements and to use them in the machine for electrical contacting. A disturbing deflection with a required force or a disturbing Antastweg as a mechanical button is not required.

Measuring with electrical contacting by a voltage breakdown can therefore not only on machine tools, but also on measuring machines, eg. B. coordinate measuring machines are used.

The maximum possible relative speed between the first object and the second object is determined by the distance at which voltage breakdown occurs and the reaction time required by the machine to stop the movements of the axes. In order to minimize possible dead times, it is therefore advisable to direct the signal of the detection circuit, which detects the voltage breakdown, directly to the individual inverters (drive controllers) for the axis motors of the machine and not only to the control of the machine. If the signal for the detection of a voltage breakdown is only sent to the control system of the machine, it must be recorded in the control and then forwarded from there to the individual inverters for the axis motors, usually via a bus system. It can take several milliseconds. This loss of time can be saved if, during the electrical contacting process, an input is continuously monitored on each axis motor inverter to which the voltage breakdown signal is passed directly from the detection circuit. As soon as the signal arrives, the inverters for the axis motors can react and the motors stop quickly. It is not necessary to wait for the signal from the controller via the bus system. As a result, the dead time and thus the Stopping distance shortened. Even greater relative speeds between the first object and the second object are possible without there being any contact between the first object and the second object.

If the first or second module comprises a spindle for rotatably supporting the first or second object, electrical contacting of the spindle shaft, the tool holder or the first or the second object, which functions without malfunction, is important for reliable use of the described method. The first object or the second object is an example of a tool below.

The electrical contact is realized for example via so-called contact brushes or slip rings. The permanent reliability of these electrical contact means is limited. Over time, they wear out due to the relative movement between the element to be electrically contacted (spindle shaft, tool holder or tool) and electrical contact means (eg contact brush or slip ring). The element to be contacted is an element via which an electrically conductive connection is made to the first or the second object in order to apply the electrical voltage thereto. It comes to abrasion. During rotation of the spindle shaft, tool holder or tool, the electrical contact means, i. H. the contact brushes or slip rings on the surface of the electrically contacted elements, so the rotating spindle shaft, tool holder or the tool. In addition to wear-related electrical contact interruption, it can also lead to short electrical contact interruptions due to the relative movement between electrical contact means and spindle shaft, tool holder or tool. These electrical contact interruptions can z. B. come through small bumps or impurities on the surface of the electrically contacted element. The electrical contact interruptions can be very short, d. H. in the microsecond range. Such short-term electrical contact interruptions can be easily measured with an oscilloscope.

Therefore, it is desirable to monitor the electrical contact between the spindle shaft, tool holder or tool and voltage source. According to the invention, at least one second electrical contact means, for. B. a second contact brush or a second slip ring used, which also electrically contacts the spindle shaft, the tool holder or the tool. With the aid of this second electrical contact means is monitored whether the first electrical contact means has a continuous electrical contact with the spindle shaft, the tool holder or the tool. Short-term due to the choice of the electrical contact means interruptions of the electrical contact can be made by selecting a suitable dead time, eg. B. in the microsecond range, hidden, d. H. be ignored.

Further details, advantages and features of the present invention will become apparent from the following description of exemplary embodiments with reference to the drawing. It shows:

1 a simplified representation of a machine with automatic mechanical button according to the prior art,

2 1 a representation of a first exemplary machine with a detection unit for detecting a voltage breakdown between a tool and a workpiece,

3 Representations of angular errors of a milling spindle and resulting errors,

4 a flowchart of a method according to the invention in a first exemplary embodiment,

5 an exemplary detection unit for detecting a voltage breakdown between the tool and the workpiece,

6 an electrical contacting of a spindle shaft,

7 a representation of remaining material left on machining a concave surface with a large tool,

8th a representation of an undesired paragraph in the workpiece surface after Restmaterialbearbeitung with a small tool,

9 a representation for electrical contact via a voltage breakdown with the rotating tool before performing a Restmaterialbearbeitung,

10 a tool of a machine shortly before mechanical contact of the workpiece,

11 a flowchart of a method according to the invention in a second exemplary embodiment,

12 - 14 a schematic representation of an exemplary workpiece with the tool in the presence of chips,

15 a spindle shaft with tool holder and in this tensioned non-rotationally symmetrical "probing element" for special measuring tasks,

16 1 is a representation of a second exemplary machine having a detection unit for detecting a voltage breakdown between a tool and a workpiece;

17 a schematic representation of the machining of a workpiece by means of a tool,

18 a representation of another embodiment of the machine with a capacitive coupling according to the invention,

19 a representation of the electrical contact between a tool and a reference element installed in the machine, in this case a measuring ball,

20 a representation of the electrical contact between a tool and a reference element installed in the machine, in this case a measuring ball, with different traversing directions for support point-wise detection of the geometry of the tool,

21 a representation of the erroneous detection of the length of a toric tool by electrical contact with a measuring ball, and

22 a representation of the correct detection of the length of a toric tool by electrical contacting to a measuring cylinder.

In 1 is a simplified side view of a machine designed as a milling machine according to the prior art 2 shown. On the machine table 5 , which can be moved in the direction of the arrow in an X-axis, there is a workpiece 1 , A milling spindle 4 is mounted in a Z-axis, which can be moved in two axes (Y and Z). At the milling spindle 4 is using a tool holder 10 a known from the prior art automatic mechanical probe 7 held. At the bottom of the button 7 there is a stylus, at the end of a ball is attached. When the machine 2 the machine table 5 moves in the direction of arrow X, it comes first to touch the ball of the stylus with the workpiece 1 and subsequently to the deflection of the stylus. When a defined deflection distance is reached, the automatic button switches 7 and sends a signal to the controller. At this moment, the position of the axes in the controller is detected and in this way the position of the workpiece 1 on the machine table 5 or relative to the button 7 determined.

2 is a simplified side view of a machine 2 , which is adapted to carry out the method according to the invention. The machine 2 is for example a milling machine. A first assembly of the milling machine is for example a machine table 5 , A second assembly of the milling machine is for example a milling spindle 4 , On a machine table 5 , which can be moved in the direction of the arrow in an X-axis, there is a first object, which is a workpiece 1 is. The milling spindle 4 is mounted in a Z-axis, which can be moved in two axes (Y and Z). At the milling spindle 4 is using a tool holder 10 a second object, here a tool 3 , held. The milling spindle 4 and the machine table 5 can thus be moved relative to each other. Because the tool 3 over the tool holder 10 on the milling spindle 4 is clamped, this is with the milling spindle 4 emotional. Because the workpiece 1 at the machine table 5 is curious, the workpiece becomes 1 with the machine table 5 emotional. A relative movement between tools 3 and workpiece 1 is therefore hereinafter by a movement of the respective associated assembly, so milling spindle 4 or machine table 5 reached. The machine 2 includes a controller 20 connected via a bus with the converters X, Y, Z for the motors of the axes of the machine 2 are connected. The cables to the motors are also indicated. From a detection unit 6 , which is adapted to a voltage breakdown between the tool 3 and the workpiece 1 to recognize, goes a signal cable 22 directly to the controller 20 to send a signal to the controller at the instant of voltage breakdown 20 to send. The detection unit 6 includes a detection circuit.

It is understood that the machine 2 is shown only as an example. Likewise, the tool can 3 also directly in the spindle shaft of the milling spindle 4 be tense. Also, the method is not limited to 3-axis machines. It can also be used on modern 5-axis machines where, for example, except 3 linear axes 2 further rotatable axes for pivoting and turning the workpiece 1 and / or the tool 3 are provided.

In 3 is shown how a misalignment of the milling spindle 4 and in particular the spindle shaft 25 to the direction of the vertical axis Z affects. The presentation is greatly inflated to illustrate the effect.

In the left view of the 3 you can see the spindle shaft 25 the milling spindle 4 with a tool holder 10 and a relatively short tool 3 according to the method of the invention. Relative to the lower edge of the spindle shaft 25 results in the tool tip a deviation due to the misalignment.

In the right view of the milling spindle 4 with the spindle shaft 25 is at the same misalignment of the spindle shaft 25 , ie the same angular error of the spindle shaft 25 to the direction of movement of the Z-axis, shown how the misalignment at one with the help of a tool holder 10 at the spindle shaft 25 stored automatic button 7 according to the prior art.

One recognizes from the comparison of the two representations of the 3 in that due to the considerably larger distance of the probe ball from the lower edge of the spindle shaft 25 in the right view compared to the distance of the tool tip of the tool 3 to the lower edge of the spindle shaft 25 in the left view results in a much larger deviation. If now with an automatic button 7 in such a misalignment of the spindle shaft 25 a workpiece 1 in the way in 1 is touched and then with a shorter tool 3 as in the left view of the 3 is processed, resulting in an offset, which results from the difference of the two entered Maßpfeile. This leads to undesirable machining inaccuracies. If, on the other hand, the workpiece 1 according to the invention directly with the tool 3 is touched, this offset can be avoided.

The method according to the invention can be carried out fully automatically, with the method according to the invention being able to be carried out at the beginning of the processing or else cyclically and automatically during the processing. In each case, the data of the underlying machining program is supplemented or calibrated.

4 shows a flowchart of a method according to the invention in a first exemplary embodiment. The method according to the invention is a two-stage probing method by means of electrical contacting. In one embodiment of the method, first a coarse measurement S1 and then a fine measurement S2 are carried out. The coarse measurement and the fine measurement S1, S2 each form one stage of the two-stage probing process. In this case, in a first stage, a coarse measurement and in a second stage, a fine measurement of a position of a workpiece 1 and a tool 3 in the machine 2 ,

In this first embodiment, when performing the coarse measurement and the fine measurement S1, S2 is the same tool 3 into the machine 2 clamped. The tool 3 is a machining tool, which also for later processing of the workpiece 1 through the machine 2 is being used. The tool 3 is both in the coarse measurement S1 and in the fine measurement S2 in a rotary motion.

In a preparatory step S0, the workpiece becomes 1 at the machine 2 curious; excited. Then a pre-positioning of the tool takes place 3 near the workpiece 1 in a starting position. After the pre-positioning is completed, the coarse measurement S1 is executed.

Coarse measurement S1 becomes a position of the milling spindle 4 in the machine 2 and a position of the machine table 5 in the machine 2 detected with a first measurement accuracy. Because the tool 3 over the tool holder 10 on the milling spindle 4 is clamped and the workpiece 1 at the machine table 5 is curious, thus at the same time a relative position between tool 3 and workpiece 1 certainly.

This is done by means of a voltage source 8th between the workpiece 1 and the tool 3 a first electrical voltage, for example 500 V applied. The first electrical voltage is chosen sufficiently high that there is a voltage breakdown between the tool 3 and the workpiece 1 comes as soon as between these a maximum of a predefined by the applied first electrical voltage.

As soon as the first electrical voltage is applied, the tool becomes 3 and the workpiece 1 proceed against each other. For this purpose, depending on the selected movement axis X, Y, Z or a combination of these, the tool 3 and / or the workpiece 1 emotional. Thereby a distance d between the tool becomes 3 and the workpiece 1 steadily decreasing from the starting position. At the same time a current flow through the workpiece 1 or the tool 3 supervised. This current flow is initially 0 amps, as there is a sufficient distance d between the tool 3 and the workpiece 1 exists, through which the flow of current between these elements is interrupted, at the same time a voltage breakdown is not possible.

At an approach of the tool 3 to the workpiece 1 There is a voltage breakdown as soon as a certain distance d is reached at which a voltage breakdown for the first electrical voltage is possible. This is recognized by the fact that a current flow through the workpiece 1 and the tool 3 he follows. The position in which the tool 3 and the workpiece 1 at the time of this voltage breakdown defines an initial position of the workpiece 1 opposite the tool 3 , Once the voltage breakdown is detected, coordinate information is read out which is a position of the workpiece 1 and the tool 3 describe. Because the tool 3 in the tool holder 10 is clamped and the workpiece 1 on the machine table 5 is fixed, this is done by axis positions of the machine 2 with respect to the axes X, Y and Z of the control unit 20 get saved. Thus, the position of the workpiece 1 opposite the tool 3 Detected when a voltage breakdown between the tool 3 and the workpiece 1 he follows. In addition, with a detected voltage breakdown all motors, which are the tool 3 and / or the workpiece 1 move, stopped, to make a collision between tool 3 and workpiece 1 to avoid.

The larger the between the workpiece 1 and tool 3 applied voltage is the lower the first measurement accuracy, which is based on the detection of the starting position. Since the electrical voltage applied during the coarse measurement is relatively high, the first measurement accuracy is relatively low.

After the coarse measurement S1, the fine measurement S2 is executed. The fine measurement S2 is a more precise position of the workpiece 1 opposite the tool 3 in the machine 2 detected with a second measurement accuracy, which is higher than the first measurement accuracy. Because the measurement accuracy of the between the workpiece 1 and tool 3 applied electrical voltage is dependent on that of the voltage source 8th provided voltage is reduced. For example, a second electrical voltage of 20 volts will be applied between the workpiece 1 and the tool 3 created. The second electrical voltage is chosen so high that there is a voltage breakdown between the tool 3 and the workpiece 1 comes when between these a predefined by the applied second electrical voltage d, which is less than the predefined by the applied first electrical voltage distance.

As soon as the second electric voltage is applied, the tool becomes 3 and the workpiece 1 again against each other moves. In this case, either the movement performed at the coarse measurement S1 is continued at reduced speed, or it is between the coarse measurement S1 and the fine measurement S2, the distance d between the tool 3 and the workpiece 1 increased. It is advantageous if the distance d is increased so far that at the beginning of the fine measurement S2 no direct voltage breakdown between the workpiece 1 and the tool 3 he follows.

The distance d between the tool 3 and the workpiece 1 is continuously reduced in the fine measurement S2, starting from the last position, or starting from the last position plus the increased distance. At the same time, the flow of current through the workpiece continues 1 or the tool 3 supervised. This current flow is also at the fine measurement S2 initially 0 amps, as a sufficient distance d between the tool 3 and the workpiece 1 exists, through which the current flow is interrupted and a voltage breakdown is prevented. At an approach of the tool 3 to the workpiece 1 , it comes once again to a voltage breakdown as soon as a certain distance d is reached at which a voltage breakdown for the second electrical voltage is possible. This is recognized by the fact that a current flow through the workpiece 1 and the tool 3 he follows. The distance d is very small. It can thus be assumed that the tool 3 in the precise position on the workpiece 1 almost rests, but still has a defined by the second electrical voltage distance d to this. For a subsequent machining of the workpiece 1 through the tool 3 this information is used.

It is understood that, as shown in the figures, that about the axis of rotation 9 rotating tool 3 is provided with several cutting edges. The rounded cylindrical representation thus shows that during the rotation of the tool 3 resulting envelope. It is understood that in a three-dimensional representation, an enveloping body would result. This is formed by the radially outermost points of the tool, in particular the tool cutting.

Once the voltage breakdown in the fine measurement S2 is detected, the coordinate information of the axes X, Y, Z from the controller 20 read. Thus, the more precise position of the workpiece 1 opposite the tool 3 detected without contact, if in the fine measurement S2, a voltage breakdown between the tool 3 and the workpiece 1 he follows. In addition, also in the fine measurement S2 at a detected voltage breakdown all motors, which are the tool 3 or the workpiece 1 move, stopped, to make a collision between tool 3 and workpiece 1 to avoid. The movement of the tool 3 and / or the workpiece 1 is thus stopped in response to the voltage breakdown.

In the fine measurement S2, the tool becomes 3 thus initially relative to the workpiece 1 pre-positioned and then in the direction of the workpiece 1 in a direction of travel 27 procedure, with a small defined feed. The applied voltage is monitored. When a voltage breakdown takes place an immediate action, namely a detection of the axis positions of all axes of the machine 2 in the controller 20 as well as a halt of all axes and a subsequent reversal of the traversing 27 of the tool 3 relative to the workpiece 1 in the axes. The tool 3 can be relative to the workpiece 1 However, it is also possible to move the tool in only one axis, for example the vertical Z-axis 3 in all three axes of the machine 2 relative to the workpiece 1 , so also in the horizontal x-axis and y-axis, to proceed. When the tool 3 relative to the workpiece 1 has reached its original starting position again, the electrical contact measurement is complete. It can be determined in this way in the control where tool 3 and workpiece 1 located relative to each other in the work space, whether the tool 3 and / or the workpiece 1 in the correct position or whether the tool 3 has correct dimensions or is worn out by previous operations, etc. This allows correction or calibration of the machining program.

Both in the coarse measurement S1, as well as the fine measurement S2 is a maximum current, which at a voltage breakdown by the tool 3 flows limited. This is achieved in that the current that can flow in the voltage breakdown is circuit technology limited, z. B. by a sufficiently high electrical resistance with the voltage source 8th is connected in series, which limits the maximum possible current.

The following is from the controller 20 based on the specified position of the workpiece 1 opposite the tool 3 determines if the tool 3 and / or the workpiece 1 in the correct position or whether the tool 3 has correct dimensions or is worn. As a result, a correction or calibration of the machining program is possible.

In an alternative embodiment of the invention, which substantially corresponds to the first embodiment, in the coarse measurement S1, the position of the workpiece 1 opposite the tool 3 by a mechanical probing of the workpiece 1 detected. In the case of coarse measurement, S1 is instead of the tool 3 a known from the prior art automatic mechanical probe 7 as a third object in the machine 2 clamped. At the button 7 there is a stylus, at the end of a ball is attached. The machine 2 moves the button 7 with the stylus in the direction of the workpiece 1 , As a result, there is a touch of the ball of the stylus with the workpiece 1 and subsequently to the deflection of the stylus. When a defined deflection distance is reached, the automatic button switches 7 and sends a signal to the controller 20 , At this moment, the position of the axes in the controller 20 recorded and determined in this way the starting position. Instead of an automatic mechanical button 7 For example, for a coarse measurement S 1, other means for position detection, for example optical systems with fringe projection and / or cameras, can also be used. A relative inaccuracy of these systems does not bother, since the subsequent fine measurement S2, the relative position between the tool 3 and workpiece 1 clarified. After the coarse measurement, the mechanical button becomes 7 through the tool 3 replaced. Thus, in the coarse measurement S1, a mechanical probing of the workpiece takes place 1 through one on the milling spindle 4 arranged mechanical buttons 7 , where the mechanical button 7 after the coarse measurement S1 by the tool 3 is replaced.

In an alternative embodiment of the invention, the method is applied to machines 2 used, which have more than just 3 linear axes X, Y and Z, z. B. 5-axis machines, in which an additional rotary pivot unit with two rotary axes A and B is integrated. The axes of rotation A and B can during the approach between tool 3 and workpiece 1 also be moved, depending on the task of the position detection. Basically, the method can be used on machines with any axis combinations.

5 shows an exemplary detection unit 6 for detecting a voltage breakdown between the tool 3 and the workpiece 1 , This includes a circuit for monitoring the electrical contacting of the tool 3 , The spindle shaft 25 the milling spindle 4 in machine 2 is by means of two ceramic bearings 23 . 24 rotatably mounted. At one end of the spindle shaft 25 is the tool holder 10 arranged in which the tool 3 is clamped. According to the invention, it is necessary to provide an electrical voltage which is available from the voltage source 8th is provided between the tool 3 and the workpiece 1 to apply. Because the ceramic bearings 23 . 24 are not conductive, the spindle shaft 25 contacted via a first electrical contact means K1, which is for example a sliding contact, in particular a contact brush or a slip ring. A first pole of the voltage source 8th is connected via a first resistor W1 to the first electrical contact means K1. A second pole of the voltage source 8th is with the workpiece 1 connected. A voltage drop across the first resistor W1 is detected. If there is a voltage breakdown between the tool 3 and the workpiece 1 Thus, a current flowing through the first resistor W1 and thus the voltage dropping across the resistor W1 changes. In this way, the voltage breakdown by means of a voltage detector 18 detected, which measures a voltage drop across the first resistor W1.

For a reliable use of the method described is an electrical contacting of the spindle shaft 25 , the tool holder 10 or the tool 3 important, which works trouble-free. To enable monitoring, therefore, the second pole of the voltage source 8th further connected via a second resistor W2 with a second electrical contact means K2. The second electrical contact means K2 also provides an electrical connection to the spindle shaft 25 and is, for example, another sliding contact, in particular a contact brush or a slip ring. A voltage drop across the second resistor W2 is detected. There is no electrical contact between the tool 3 and the workpiece 1 , the entire current flowing through the first resistor W1 also flows through the second resistor W2. From a comparison of the currents flowing across the two resistors W1 and W2 or the voltages dropping across these resistors, it is determined whether the electrical contact means K1 and K2 operate without errors. If one of the electrical contact means K1 and K2 does not function correctly, then no or only a small current flows via the second resistor W2.

The electrical contact means K1 and K2 between the spindle shaft 25 , Tool holder 10 or tool 3 and the voltage source 8th are thus monitored. For this purpose, the second electrical contact means K2 is used, which is the spindle shaft 25 , the tool holder 10 or the tool 3 also contacted electrically. With the aid of this second electrical contact means K2 is monitored that the first electrical contact means K1 has a continuous electrical contact with the spindle shaft 25 , the tool holder 10 or the tool 3 Has.

Like in the 5 shown as an example, the monitoring is thus realized via a simple circuit. The contact brush K1 electrically conducts the positive pole of the voltage source 8th on the schematically illustrated spindle shaft 25 , The voltage source 8th is a DC voltage source. Alternatively, the voltage source 8th an AC power source. With the help of the contact brush K2 and a simple circuit becomes the spindle shaft 25 also electrically contacted and thus closed a circuit to the negative pole of the DC voltage source. The current flows from the positive pole of the voltage source 8th via the resistor W1 and contact brush K1 into the spindle shaft 25 , from there via contact brush K2 and resistor W2 to the negative pole of the voltage source 8th , If the circuit is interrupted, this is detected immediately by a change in the electrical voltage across the resistor W2 with a suitable circuit as shown. The electrical voltage drops. The electrical contacting of the spindle shaft 25 , the tool holder 10 or the tool 3 can be continuously monitored in this way. In case of an interruption of the circuit an error message can be generated.

In addition, via the resistor W1, which is in series with the voltage source 8th is switched, the maximum current flowing be limited even at high voltages to very low currents.

In some embodiments of the invention, very short breaks in electrical contact (in the microsecond range) do not interfere. Therefore, it is useful in a further embodiment of the invention to provide a dead time for a maximum allowable duration of the electrical contact interruption. Only when this dead time is exceeded, an error or a fault is reported. Electrical contact interruptions below the dead time are ignored because they are not critical to the application.

Optionally, the dead time to which an electrical contact break is ignored is kept adjustable. Depending on the application, different idle times can still be accepted. The dead time is adjusted accordingly. Next optional, it is possible the voltage of the voltage source 8th variable and z. B. to the contamination state or state of wear of the electrical contact means K1, K2 adapt. If dirty or worn, the resistance of the electrical contact means K1, K2 increases. Accordingly, the voltage differences at the resistors W1 and W2 and at the electrical contact means K1 and K2 change. Through a variable voltage source 8th can be responded to such changes.

If the voltage at the resistors W1 and W2 is evaluated simultaneously, at known voltage level of the voltage source 8th be closed, which voltage in total drops at the two electrical contact means K1 and K2. According to the voltage drop across the electrical contact means K1 and K2, the voltage of the voltage source 8th be increased or decreased to set a suitable voltage for the desired process. If the voltage drop at the electrical contact means K1 and K2 is too high, an error message can be generated.

Below is another way of electrical contacting of the spindle shaft 25 , alternatively to the above-described solutions with the contact brush or the capacitor principle shown. There will be another auxiliary ball bearing 13 on the spindle shaft 25 mounted, which is performed instead of electrically insulating ceramic balls with steel balls and thus electrically conductive is. Due to the steel balls, the auxiliary ball bearing only reaches the same speeds as the main bearings 13 the spindle shaft 25 if the diameter of the steel ball bearing is significantly smaller. It must therefore be in a slim position, z. B. at the end of the spindle shaft 25 to be assembled. It only has the function of making electrical contact with the spindle shaft 25 manufacture and must the spindle shaft 25 not additionally supported mechanically. It can therefore z. B. be a simple executed deep groove ball bearings. The outer ring of the bearing is in an electrically insulating material, for. As plastic, added and so against the spindle housing of the milling spindle 4 electrically isolated. At the same time a cable with the outer ring of the auxiliary ball bearing 13 electrically connected and from the milling spindle 4 led out. This cable can be connected to one pole of the voltage source 8th be connected. In this way, the spindle shaft 25 as required for the method according to the invention, with one pole of the voltage source 8th with the help of the electrically conductive auxiliary ball bearing 13 connected. The advantage of this electrical contacting is that it can continue to work with the electrically simpler DC voltage and that the auxiliary ball bearing has a longer life than the contact brushes, which are subject to wear due to the constant friction.

The 6 shows this further possibility for electrical contacting of the spindle shaft 25 , At an area of the spindle shaft 25 , preferably at the upper end of the spindle shaft 25 is the auxiliary ball bearing 13 mounted, which electrically conductive steel balls 17 includes, which between an inner ring 14 and an outer ring 15 are arranged. The outer ring 15 is by means of a preferably also annular electrical insulating element 16 on the outer sleeve of the milling spindle 4 stored in the machine 2 located. As shown, the outer ring 15 with the voltage source 8th electrically connected, analogous to the structure of 2 and or 5 , The negative pole of the voltage source 8th leads to the workpiece not shown 1 , The voltage source 8th is designed as a DC voltage source.

For workpieces 1 With complex surfaces, machining often has to work with different sized tools 3 be performed. For time reasons as many areas of the workpiece surface with large tools 3 processed. In concave areas of the workpiece 1 With small inner radii, machining can be done with the big tools 3 not finished. Remaining material remains. Therefore, a Restmaterialbearbeitung with a much smaller tool 3 carried out. If the positioning of the rest material processing with the small tool 3 does not fit exactly, arise between the area, with a larger tool 3 was edited, and the area responsible for rest machining with a smaller tool 3 is processed, unwanted paragraphs in the manufactured workpiece surface. According to the invention, it is possible to start with the small tool before starting the rest material processing 3 already with a great tool 3 finished workpiece surface of the workpiece 1 in the immediate vicinity of the rest material processing to be carried out with the rotating small tool 3 to contact electrically and the rest material processing with the small tool 3 at the with a great tool 3 manufactured workpiece surface with the help of the measurement results of the electrical contacts in the immediate vicinity of the Restmaterialbearbeitung align exactly. It is usually only necessary to perform the fine measurement S2, as a coarse position of the workpiece 1 opposite the tool 3 at this time already known from a previously performed coarse measurement S1, as well as the small tool 3 from a tool measurement, z. B. in a measuring laser, or a previous processing. The alignment is not only possible by translational displacement, but optionally, in addition, a rotation in the room can be made so that the Restmaterialbearbeitung fits as perfectly as possible to the already produced surface. Such alignment processes are known from the prior art as so-called "best-fit processes".

The 7 Represents the remaining material 12 when machining a concave workpiece surface, when the tool radius of the tool 3 significantly larger than the inner radius of the workpiece to be produced 1 is.

The 8th shows the resulting paragraph on the workpiece surface of Wersktückes 1 if a residual material processing with a small tool 3 in a partial area of the workpiece 1 something was done too deeply. The result is an undesirable paragraph "A" on the surface.

The 9 shows the already by a not shown larger tool 3 produced workpiece surface of the workpiece 1 in which a residual material 12 analogous to 7 has remained in a partial area, because the inner radius of the produced, partially concave workpiece surface is smaller than the radius of the hitherto used, not shown larger tool. Therefore, in the concave area of the workpiece 1 with the relatively small inner radius, the residual material 12 with the illustrated smaller tool 3 be removed. For this rest material processing with the smaller tool 3 to fit precisely into the already produced workpiece surface, is in the vicinity of the required processing of residual material 12 the relative position of the workpiece surface of the workpiece 1 to the at the milling spindle 4 stored smaller tool 3 exactly determined by the method according to the invention. This relative position detection with the method according to the invention can take place at several positions of the workpiece surface between the smaller tool 3 and workpiece 1 be performed. It can also different starting directions between smaller tool 3 and workpiece 1 be used for the relative position detection, depending on whether this in a steeper area as in 9 represented or takes place in a rather flat area of the workpiece surface, z. B. left of the residual material 12 in 9 , With the help of the data thus obtained, the position of the rest material processing can be optimally fitted in different ways in the already existing workpiece surface, by a translational displacement of the zero point and / or by a slight rotation about one or more axes. If a sufficient number of relative position detections between smaller tool 3 and workpiece 1 was carried out at different positions, well-known from the measurement technique "best-fit" can be used to the processing of the residual material 12 with the smaller tool 3 optimally fit into the already produced workpiece surface. Here, the rest material processing for the smaller tool 3 as in the determined in their relative position with the inventive method, already existing workpiece surface fitted, ie positioned in position and rotation in space, that the remaining deviations for all performed for the fitting relative position detection between tool 3 and workpiece 1 is minimized.

It is generally after an exchange of the tool holder 10 arranged tool 3 it is not absolutely necessary to re-execute the coarse measurement S1, if this is already done prior to the replacement using a previous tool 3 or other means such as an automatic mechanical button. The tool 3 is in this case based on the earlier coarse measurement S1 to the workpiece 1 approximated. The rough length of the tool 3 can be determined beforehand in a measuring laser or similar. Nevertheless, it is advantageous to perform the fine measurement S1 again after a tool change or a processing break. Thus, inaccuracies can be compensated, for example, arise when the workpiece 1 or the machine 2 cools and thereby slightly changes its or their shape. This can be done, for example, in a period during which the workpiece 1 is pivoted for a tool change. Also inaccuracies can be compensated in this way, resulting from the fact that tools 3 when replacing, not always exactly in the same position in the tool holder 10 or on the spindle shaft 25 be positioned. 10 shows the tool 3 the machine 2 just before a mechanical touch of the workpiece 1 , The distance d is the shortest distance between tools 3 and workpiece 1 , The tool 3 is close to mechanical contact of the workpiece 1 at a distance "d" at which there is a voltage breakdown. It is in the contact position at which an electrical contact is detected for the first time. This is probably to be distinguished from a mechanical contact, which does not yet take place due to the distance "d".

Above, the method according to the invention was first described with regard to the fact that by the probing an assignment of the relative position between the tool 3 and the workpiece 1 takes place and the exact location of this assignment by electrical contacting in the machining program for further processing of the workpiece 1 stored and taken into account.

During the machining z. B. removed by milling or grinding chips 19 Distributed by the process in the work space. Part of the chips 19 also stays on the workpiece 1 be liable. In some applications, attempts are made by flushing with a lubricant or cooling lubricant, for. As emulsion or oil, the chips from the workpiece 1 keep away or remove. However, this never succeeds completely. Depending on the geometry of the workpieces 1 , the processing and the resulting direction of flight of the chips 19 it comes again and again to chip accumulation on the workpiece 1 , When working with a lubricant or cooling lubricant, the chips become stuck 19 on the workpiece 1 still favored. The chips 19 stick to the workpiece 1 , Also, the adhesion of chips 19 on the workpiece 1 favors when the workpiece 1 consists of a ferrous material and is tensioned with a magnetic disk. The field lines of the magnetic disk penetrate into the workpiece 1 and lead to a magnetic adhesion of the removed chips 19 ,

The on the workpiece 1 adhering chips 19 can in the inventive method of electrical contacting of the workpiece 1 with a rotating tool 3 interfere with an electrical current contact to be detected. Already before it is between rotating tool 3 and actual workpiece 1 comes to the voltage breakdown and so an electrical current contact is formed, by the workpiece 1 adhering chips it prematurely to a voltage breakdown between the workpiece 1 and tool 3 come. The adhesive chips 19 then become one the workpiece 1 and the tool 3 electrically connecting conductor.

The consequence is a false measurement, since the actual position for the electrical contact by voltage breakdown directly between the workpiece 1 and tool 3 not yet reached. It may be determined according to the procedure described above, a wrong position with the electrical contact and follow the subsequent processing steps with incorrectly determined data, resulting in significant damage to the destruction of the workpiece 1 can lead.

Unfortunately, the adhesion of chips can be 19 on workpieces 1 in practice, as described above, never completely avoid it. To perform a reliable electrical contact, the workpiece would have to 1 cleaned by hand before each measurement and checked for cleanliness. This is an unwanted manual intervention, especially for automated machining processes.

According to the invention is therefore advantageous for a contact position to be scanned between the workpiece 1 and tool 3 a multiple measurement, at least a two-time measurement, in particular a multiple fine measurement S2, perform. When, as described above, in the electrical contacting chips as conductive elements between the tool 3 and workpiece 1 located, then obtained at the moment of electrical contact, ie at the very small distance between the workpiece 1 adhering chips and tools 3 resulting voltage breakdown, the chips by the rotation of the tool 3 a pulse that changes their position significantly and these usually from the workpiece 1 wegschleudert.

According to the invention, it is provided that the travel direction 27 of the tool 3 relative to the workpiece 1 with which these are moved towards each other, at the moment of electrical contact (voltage breakdown) is immediately reversed to damage the workpiece 1 to avoid. The tool 3 gets back from the workpiece 1 away. The track on which the tool 3 from the workpiece 1 is removed in this way, in a safe distance position, can be arbitrarily specified.

From the safe distance position out according to the invention, a further (second) electrical contacting can be performed immediately by the tool 3 exactly on the same track on which it was previously from the workpiece 1 was removed, back to the workpiece 1 is moved until there is a voltage breakdown again. Should the tool 3 have already performed a correct measurement at the first electrical contact, so in the second electrical contact with the accuracy of the measurement tolerance of the measuring method, the same contact position for the tool 3 relative to the workpiece 1 be determined.

On the other hand, should shavings occur during the first electrical contact 19 as an electrical conductor between tools 3 and workpiece 1 have found so in the second electrical contact another contact position for the tool 3 relative to the workpiece 1 yield, as the chips 19 through the rotating tool 3 were changed in their position at the first electrical contact. As a result, a larger difference between the contact positions of the first electrical contact and the second electrical contact will result. From this larger difference can the processing of the results of the electrical contacts control 20 recognize that the first measurement must have been an incorrect measurement.

Thus, if the difference of the two electrical contacts exceeds a predetermined (fixed by the operator or in the controller firmly) tolerance value, there is the possibility of only the second electrical contact in the controller 20 to judge as correct and to discard the first, as this was faulty due to the adhering chips.

In order to further increase the reliability of the electrical contacting, it is also possible to carry out a further (third) electrical contacting in the manner described above when the predetermined tolerance value is exceeded. Again, the difference between the second and the third electrical contact can now be compared with a predetermined tolerance value and it can be concluded from this whether both of these measurements are both due to the desired direct electrical contact between the workpiece 1 and tool 3 have come about or whether again adhering chips have disturbed the measurement. In the latter case, further electrical contacts can be carried out until two successive electrical contacts lie within the predetermined tolerance.

In this way, it is possible according to the invention, even with larger chip accumulations a reliable measurement of the relative position between the workpiece 1 and tool 3 with the help of the voltage breakdown.

For very small chips, it may be advantageous to increase the predetermined number of successive electrical contacts at one location, which must be within a predetermined tolerance, to more than two electrical contacts. That gives the procedure an even higher reliability, but at the expense of the measuring time.

It is understood that this inventive approach works for any Antastrichtungen for electrical contacting. shavings 19 can be on flat, inclined or even vertical areas of the workpiece 1 adhere.

In addition, it may be useful to advance larger chips accumulation with the help of in the machine 2 eliminate existing media, eg. B. powerful air nozzles, but also lubricants or coolants. This reduces the number of electrical contacts required until two consecutive measurements are within the specified tolerance. It does not take that long for all the chips to be removed. The cleaning with the media can be made specifically at the intended locations for electrical contacting.

For operations with very low speeds, it may be advantageous to increase the speed for the electrical contact something, so in the case of electrical contact via a chip 19 (Missing measurement) is ensured that this gets a sufficiently high impulse to be thrown off.

It does not necessarily have to be a mechanical contact between chips 19 and tool 3 come to remove them. In most cases, it is sufficient if a Span 19 from one of the tool 3 caused air movement is detected. This effect can be achieved by introducing a liquid between the workpiece 1 and tool 3 be further strengthened.

11 shows a flowchart of the method according to the invention in a second embodiment. It shows 11 a flow chart for a two-stage scanning method according to the invention, which checks by multi-fine measurement (multiple fine detection by electrical contacting), whether chips 19 have affected the electrical contact or voltage breakdown.

The second embodiment corresponds to the embodiments described above, but the fine measurement S2 is repeatedly executed as required. This is particularly advantageous when a material is processed, which when processed into electrically conductive chips on the tool 3 or the workpiece 1 can lead and this on the workpiece 1 or the tool 3 adhere.

In this second embodiment of the invention, the fine measurement S2 is first executed twice in succession. After each of the two passes, the specified position is stored as coordinate information. After the second pass, this coordinate information is compared. If these do not agree with one another, taking into account a tolerance, then it is concluded that a measurement error occurred during the fine measurement S2. If a measurement error has occurred, the fine measurement S2 is repeated again and the coordinate information of the last two repetitions are compared. This loop is repeated until the coordinate information, taking into account the tolerance, or until a maximum number of times has been reached. If the coordinate information matches, the procedure is completed and the specified position is assumed to be correct.

Thus, only the fine measurements S2 are carried out until it is ensured that no chips have a disruptive effect on the voltage breakdown. If, as provided, two or more fine measurements S2 are within a predetermined tolerance, in the previous fine measurements S2 were taken by the rotating tool 3 All chips are thrown away and the electrical contact only between tools 3 and workpiece 1 carried out. Thus, the fine measurement S2 is repeated until the precise positions detected in two successive repetitions of the fine measurement S2 deviate less from one another than predetermined by a tolerance range.

It is therefore sufficient first to carry out a rough measurement (1st stage) and then to carry out only fine measurements S2, until it is ensured that no chips are present 19 interfere with the electrical contact. If, as intended, two or more fine measurements are within a given tolerance, the previous fine measurements were taken by the rotating tool 3 All chips are thrown away and the electrical contact only between tools 3 and workpiece 1 carried out.

Again, the tool becomes 3 during fine measurement relative to the workpiece 1 pre-positioned in a starting position. Then the tool becomes 3 in the direction of the workpiece 1 proceed with a small defined feed. The voltage is monitored. When a current contact or a voltage drop takes place an immediate action, namely the detection of all axis positions by means of the controller 20 , stopping all axes of the machine 2 and a subsequent reversal of the travel direction 27 of the tool 3 relative to workpiece 1 in the respective axes to the workpiece 1 from the tool 3 to space. When the home position or starting position of the tool is reached 3 relative to the workpiece 1 for the fine measurement S2, the electrical contact measurement is completed. Up to this process step corresponds to the in 11 described fine measurement of in 4 described fine measurement S2. Subsequently, according to 11 the tool 3 again with a small defined feed in the direction of the workpiece 1 method. When there is a current contact, an immediate action takes place again, namely the detection of the axle positions and the reversal of the travel direction 27 of the tool 3 relative to the workpiece 1 as described above. The tool 3 becomes relative to the workpiece 1 in turn moved to its starting position for the fine measurement S2. Then the results of the two measurements, namely the axis positions of the axes of the machine detected during the electrical contacting, then become 2 compared. It is determined whether there are differences and whether they are smaller than a predetermined tolerance. If they are smaller than a predetermined tolerance, the fine measurement S2 has been successfully completed, wherein z. B. an average of the detected in the two fine measurements S2 two axis positions of each axis can be considered as the final measurement. If the differences of the axis positions of the axes from the two fine measurements S2 are greater than the predetermined tolerance, then it is checked whether the number of fine measurements S2, which were previously carried out, is greater than a maximum number admitted. If it is larger, the fine measurement S2 is aborted with an error message. If it is smaller, the program returns to a second second fine measurement S2. The fine measurement S2 according to the invention is thus carried out twice from the outset and at the end of the second fine measurement S2 it is decided whether the results of the two fine measurements S2 are within a predetermined tolerance. If this is the case, the measurement is complete and OK (Yes). If this is not the case (No), then it is checked how many fine measurements S2 have already been carried out at the location. If the number is smaller than or equal to the predetermined maximum permitted number, a new fine measurement S2 is performed at the location. If the number of fine measurements S2 already carried out at the location is already greater than the predetermined maximum permitted number, the fine measurement S2 is aborted at the location with an error. This prevents an infinite series of measurements from being taken in one place, perhaps because there is some other error. The 12 to 14 show the procedure according to the inventive method, in which between the workpiece 1 and around a rotation axis 9 rotating tool 3 shavings 19 are present, which on the workpiece 1 adhere. The 12 to 14 In doing so, they represent the time at which voltage breakdown occurs. The tool 3 was previously in the travel direction 27 on the workpiece 1 too moved. The 12 and 13 explain that a voltage breakdown between the tool 3 and the workpiece 1 over the chips 19 can be done. This electrical contact is faulty because the voltage breakdown in reality is not between the workpiece 1 and the tool 3 but there is an additional distance between them, the thickness of the chips 19 equivalent. The control 20 thus receives a wrong signal. This leads to a wrong measurement. To avoid such incorrect measurements and errors, as described above, the invention provides that the workpiece 1 by means of the tool 3 contacted at least twice electrically. Such a second electrical contact is in 14 shown. In contrast to the electrical contact according to 13 stick in 14 no disturbing chips 19 more on the workpiece 1 because, in the electrical contacting according to 13 through the rotation of the tool 3 were thrown off. In this second electrical contact according to 14 the voltage breakdown occurs correctly between the tool 3 and the workpiece 1 , whereby an electric current can flow or a voltage drop occurs, as has been explained above. This effect as in 14 is registered by the controller as well as the erroneous electrical contacting by means of the chips 19 in 12 or 13 , As described, the controller takes into account 20 extending in the distance between the tool 3 and the workpiece 1 resulting difference from the two fine measurements according to 13 and 14 and subsequently performs another electrical contacting measurement (fine measurement). If these have the same results as in the 14 shown, these values are based and the values from the measurement situations of 13 discarded.

The repeated execution of the fine measurement is in any case advantageous because the results of a plurality of fine measurements S2 can be used to further increase the measurement accuracy with which the precise position is detected. Thus, for example, an average value can be formed over the more precisely determined positions determined in a plurality of fine measurements S2 in order to determine a final, more precisely specified position. Alternatively or additionally, a weighting of individual fine measurements S2 can take place.

For determining several finalized positions from several fine measurements at different points of the workpiece 1 All known from the measurement technique evaluation can be used, for example, a so-called equalization calculation (best-fit) with the help smallest error squares for the individual measuring points. In this case, different degrees of freedom for the compensation process can be provided, only translational displacements and / or rotations about one or more axes. This process results in the precise position of the workpiece 1 overall relative to the tool 3 in the machine 2 based on all positions specified with fine measurements S2.

In the 13 and 14 is also the X-axis of the machine 2 symbolically represented. As described above, the specified position is detected as coordinate information, wherein at the given direction of travel 27 , which is directed along the X-axis here, a coordinate position of the X-axis is detected. So will in the 13 in a fine measurement S2 detects a first precise position P1, but due to a chip 19 is not correct. In 14 a second specified position P2 is detected, and in a subsequent fine measurement, a third precise position P3 is detected. It can be seen that the second and third specified positions P2 and P3 are close to each other. Thus, it can be concluded that no more chip between the tool 3 and the workpiece 1 located. Further, an average value which is located at the center between the second and third specified positions P2 and P3 may be determined as the final specified position.

The inventive method is not limited to rotating tools. It can also be done with standing tools. Instead of machining tools, it is also possible to use any other geometries than "probing elements" on the spindle shaft 25 be stored. An exemplary probe 26 is in to 15 shown. 15 shows the milling spindle 4 with tool holder 10 and in this tensioned non-rotationally symmetrical probing element 26 for special measuring tasks. The touch element 26 can be very filigree. It is a special case for the tool 3 because there is no machining on the workpiece 1 can perform, but only a tool 3 for pure measuring tasks. Such probes 26 are particularly well suited for the use of the method in coordinate measuring machines, which serve only the pure measurement of workpieces.

16 shows a representation of a second exemplary machine 2 with a detection unit 6 for detecting a voltage breakdown between a tool 3 and a workpiece 1 , At the in 2 shown machine 2 must the controller 20 one from the detection unit 6 First process the detected signal and then, via the bus system with which the inverters are connected to the motors, the shortest possible stopping of the individual axes of the machine 2 implement. Through this signal chain unnecessary dead time is lost. Dead time is the time between the voltage breakdown and the beginning of stopping the movement of the workpiece 1 and / or the tool 3 passes. At the in 16 shown embodiment of the machine 2 gives the detection unit 6 therefore directly a signal via an additional line to the individual converters of the axes X, Y, Z at the moment of electrical contact, ie at the moment of voltage breakdown. It is obvious that the time for stopping the movement of the axles can thereby be considerably shortened. Of course, it is also possible according to the invention, the signal of the detection unit 6 only to the inverters of the axes X, Y and Z to give and the connection to the controller 20 omit. In this case, the inverters themselves have to control the signal that they have come into electrical contact via the bus 20 pass, but this is not relevant for a quick stopping of the movement of the axes, as this is done by the inverter itself.

The 17 shows how the tool 3 along the lines 21 relative to the surface of the workpiece 1 is moved to a machining of the workpiece 1 perform.

It is particularly advantageous if the electrical voltage is an AC voltage and the AC voltage by means of a capacitive coupling of the voltage source 8th to the tool 3 is transmitted. In this case, a first pole of the voltage source 8th with the workpiece 1 coupled and a second pole of the voltage source 8th about the capacitive coupling with the tool 3 coupled. In this way, a mechanical contact, for example by sliding contacts, between the elements rotated in rotation and the voltage source 8th avoided. Thus, the known for such a mechanical contacting disadvantages such. B. wear, prevented. Instead of the mechanical contacting takes place a capacitive coupling, wherein at least one of the rotated elements, spindle shaft 25 , Tool holder 10 or tool 3 , as a side of a capacitor and a coupling element on the side of the voltage source 8th For example, a metal plate, which is arranged close to one of the rotating elements with a defined gap, acts as a second side of this capacitor. The higher the frequency of the applied AC voltage, the lower the resistance of the thus realized capacitor. In addition, by appropriate arrangement, for. B. Choice of a sufficiently large metal plate and a small distance to the spindle shaft 25 Care must be taken to ensure that the capacity is correspondingly large and that the electrical resistance for the selected AC voltage is correspondingly low.

In 18 is an embodiment of a capacitive coupling between the voltage source 8th and the tool 3 illustrated according to another embodiment. This is the voltage source 8th as an AC voltage source. The tool 3 is about the tool holder 10 electrically conductive with the spindle shaft 25 connected. Along a surface of the spindle shaft 25 is a metallic plate 11 arranged, the surface thereof along the surface of the spindle shaft 25 is arranged that is between the spindle shaft 25 and the metallic plate 11 gives a gap of small width. This creates an electrical capacitive coupling between the spindle shaft 25 and metallic plate 11 , The metallic plate 11 is with a first pole of the voltage source 8th connected electrically conductive. A second pole of the voltage source 8th is, as previously described, with the workpiece 1 connected electrically conductive.

The metallic plate 11 forms with the spindle shaft 25 a capacitor and thus allows a current flow when an AC voltage through the voltage source 8th is provided and an electrical contact (voltage breakdown) between the workpiece 1 and the tool 3 occurs. This current flow in turn leads to a voltage drop across the first resistor W1, which in turn can be detected with a circuit known from the prior art at the moment of voltage breakdown.

In all embodiments of the invention, a detection of a voltage breakdown leads to an immediate action, namely a detection of the axis positions of all axes of the machine 2 in the controller 20 , stopping all axes of the machine 2 and then a reversal of the travel direction 27 of the tool 3 and / or the workpiece 1 in the axes. The tool 3 can be moved in only one axis, for example, the vertical Z-axis, but it is also possible, the tool 3 in all three axes or more axes of the machine 2 , So also in the horizontal x-axis and y-axis and / or the axes of rotation, to proceed. When the tool 3 has reached its original starting position again, the electrical contact measurement is complete.

In the described embodiments, the tool is 3 over the metallic tool holder 10 , in which this is held, directly with the spindle shaft 25 electrically connected. If it is now due to a voltage breakdown to an electrical contact between the tool 3 and the workpiece 1 a current flows and it can easily be detected by means of a simple circuit due to the changing electrical voltage. Even with extremely short electrical contact between the workpiece 1 and the tool 3 is such a change in tension already detectable. If at the moment of the electrical contact between the tool 3 and the workpiece 1 Voltage change caused a signal is sent to the controller to the machine 2 Immediately stop or retract can be a significant intervention, ie damage to the workpiece 1 , sure to be avoided. Thus, the described method is suitable for a damage-free electrical contacting of workpieces 1 directly with the tool 3 to be used for editing. Possible inaccuracies caused by the use of an auxiliary device such as an automatic mechanical button 7 arise are avoided.

The method can be used both for processing tools with geometrically defined cutting edge, z. As milling tools, as well as geometrically indefinite cutting edge, z. As grinding tools used. The only requirement for the procedure is that even the tool 3 is electrically conductive.

Another great advantage of the invention electrical contacting directly with the tool 3 is that this can be done at any time during processing. In practice, machines are 2 especially for longer processing often not zero point stable, ie the position of the zero point changes slightly. Usually the change of the zero point is caused by thermal effects, either in the machine 2 , z. B. by heating certain components, or by the environment, eg. B. with temperature fluctuations of the machine 2 surrounding air. The change of the zero point during machining leads to undesirable deviations and inaccuracies.

In order to minimize this, it is possible with the method according to the invention to repeat the probing process with the aid of the electrical contacting at predetermined geometric elements at any time during the processing. In this case, either the coarse measurement S1 and the fine measurement S2 are executed, or only the fine measurement S2 is executed again. These predetermined geometry elements can be fixed reference elements in the machine 2 be, z. B. one or more dimensionally known balls that are installed in the workspace and are touched. But it can also parts of the workpiece 1 be yourself, z. As center holes or a parting surface that are already completed. It is of great advantage that the tool 3 does not need to be replaced, but the electrical contact can be carried out directly with this. As a result, the electrical contact compared to automatic mechanical button very time-effective. It is understood that it is advantageous to clean the geometrical elements to be touched before the electrical contact, for. B. in the machine 2 existing coolant to avoid incorrect measurements by adhering to the geometric elements chips. Alternatively, the fine measurement can be performed several times to avoid false measurements, as in 11 described. This zero point corrective probing operation by electrical contacting may be performed at arbitrary time intervals, depending on how zero point stable the machine is 2 is and what accuracies are required.

It is understood that the invention is suitable both for grinding and for milling tools, ie tools with specific and undetermined cutting edge.

According to the invention it is also possible to provide a redundancy of the electrical contacts by the workpiece 1 at several different points once or as described to avoid incorrect measurements several times with the tool 3 is electrically contacted and the results of these measurements are compared with each other. Should the measurement results of the electrical contact at one point of the workpiece 1 do not match the other measurements, for example exceeding a predetermined tolerance / deviation, the results of the electrical contacting (s) at that one location may be rejected as invalid and excluded from consideration for further processing.

This procedure can also be used if initially several electrical contacts at different points of the workpiece 1 are required, as described above, to perform a measurement at all, z. B. the position and orientation of the workpiece 1 relative to the tool 3 in the machine 2 to determine. By a correspondingly increased number of electrical contacts, it is always possible to provide a redundancy over the z. B. spanbedingte incorrect measurements are detected and excluded from the consideration.

In the case of a span-related measurement error electrical contact (voltage breakdown) is generally too early, so before reaching the desired contact position between the workpiece 1 and tool 3 , determined. The adhering chips already make the electrical contact before. This circumstance can be used to detect span-related incorrect measurements. The rotating tool 3 in such cases always has an additional distance to the actual workpiece 1 ,

The electrical contact with the rotating tool 3 on the workpiece 1 can also be used for indirect geometry measurement of the tool 3 be used by electrically contacting already finished, dimensionally known geometry elements on the workpiece 1 , z. B. the high-precision workpiece surface or a high-precision guide hole previously on z. B. a measuring machine were measured. If a pilot hole with a similar procedure as when measuring the hole with an automatic mechanical button 7 with the tool 3 repeatedly, for example, lying in the hole, opposite measuring points, is electrically contacted, with known bore diameter using the determined contact positions on the effective diameter of the tool 3 be recalculated. By electrical contacting of the known workpiece surface, the tool length can be determined.

In addition, by the inventive method of electrical contact between tool 3 and workpiece 1 on a tool measurement, as otherwise performed before processing using a measuring laser or other aids are completely dispensed with. It is enough if as in 19 represented, instead of a measuring laser, a measuring ball 28 , as it is known for calibrating automatic mechanical buttons, in the travel range of the machine 2 will be installed. Similar to a calibration ball for an automatic mechanical probe, the position of the measuring ball 28 in the machine 2 and the diameter of the measuring ball 28 known and in control 20 be deposited. If now an unknown tool 3 at the spindle shaft 25 , possibly with the help of the tool holder 10 , is stored, after switching on the milling spindle 4 on speed first a coarse measurement S1 between the rotating tool 3 and the measuring ball 28 performed to the approximate dimensions of the tool 3 to determine. After the coarse measurement S1, the exact dimensions of the tool 3 with a fine measurement S2 between the measuring sphere 28 and the tool 3 clarified. It can be done on the measuring ball 28 both the length of the tool 3 if the measuring ball 28 for electrical contact with the tool 3 is approached from above, as well as the diameter of the tool 3 be determined when the measuring ball 28 with the tool 3 approached from one side. Will the measuring ball 28 approached from several sides, the measured results can be conveyed. It is possible, as known from metrology, the exact relative position of the measuring ball 28 to tool 3 in machine 2 and the diameter of the tool 3 from the measurements of several pages. In 19 is shown as the on the machine table 5 fortified measuring ball 28 from the side with travel direction 27 from the tool 3 is approached for electrical contact. Of course it is also possible with any other traversing directions 27 , z. B. below 45 °, the measuring ball 28 with the tool 3 to contact electrically. Thus, if necessary, the entire geometry of the tool 3 be determined point by point, for example, in a spherical tool 3 the course of the tool radius R. In 20 is the electrical contact with an oblique direction of travel 27 shown. Furthermore, as an example, some traversing directions 27 indicated by dashed arrows. By repeated approach with the same travel direction 27 at the same measuring point on the measuring ball 28 can be analogous to the 12 . 13 and 14 be avoided that possibly on the measuring ball 28 adhesive chips 19 or dirt distort the measurement results.

Of course it is also possible on the measuring ball 28 only a coarse measurement S1 with the tool 3 Perform a subsequent fine measurement S2 instead of the measuring ball 28 directly between the workpiece 1 and tool 3 on on the workpiece 1 geometrically known geometric elements such as a guide bore or the workpiece surface or outer edge perform. In this way, the relative position determination between workpiece takes place directly 1 and tool 3 in high precision, whatever the machining of the workpiece 1 most important is. Alternatively, it is also possible for the coarse measurement S1 of the tool 3 instead of the measuring ball 28 technically very simple measuring equipment in the machine 2 to provide, for. As a simple photocell, which is considerably cheaper than a well-known from the art high-precision measuring laser. Since only an approximate measurement is required for coarse measurement S1, a relatively simple measuring device is sufficient.

In practice, there are also tools 3 , which stand in the center, z. B. toric tools with inserts 30 are equipped as in a cut in 21 shown. If with such a tool 3 the measuring ball 28 from above with travel direction 27 is approached for electrical contact, then is not the lowest point of cutting the inserts 30 but a wrong position in the center of the tool 3 , The tool 3 appears shorter than it actually is. Therefore it is for such tools 3 According to the invention advantageous if instead of a measuring ball 28 a measuring cylinder 29 is approached for electrical contact. Here is the measuring cylinder 29 so in the machine 2 arranged that the axis 31 of the measuring cylinder 29 at a 90 ° angle to a rotation axis 9 of the tool 3 stands. In 22 become a measuring cylinder 29 and a tool 3 with rotary axis 9 and axis 31 of the measuring cylinder 29 shown accordingly. A measuring cylinder 29 has a flat surface, which is basically for a measurement of the relative length of the tool 3 sufficient would be the advantage that even with a graduated cylinder 29 a support point by point measurement of the geometry of the tool 3 , z. B. the corner radius of a toric tool 3 , by approaching with different traversing directions 27 basically from two sides of the measuring cylinder 29 is possible, quite analogous to the representation in 20 for the measuring ball 28 ,

According to the invention, a measurement of the tool 3 according to the 19 to 22 Also used to reduce the wear of the tool 3 during, even at intervals, or after processing to capture. This may be the measured geometry of the tool 3 from the measurements taken at different times compared with each other or with the original desired geometry of the tool 3 be compared.

The electrical contact is made with the for subsequent machining with tools 3 intended processing speed. Before electrically contacting the workpiece 1 A warm-up phase can be awaited until the machine 2 is in a thermally stable state for the selected machining speed. Thermal inaccuracies caused by probing with a standing automatic mechanical button 7 according to the prior art and subsequent machining with a rotating tool 3 are avoided.

During machining, control measurements are possible at any time by renewed electrical contacting in order to change the ambient temperature of the machine 2 or other influences caused displacements between the workpiece 1 and tool 3 to capture and compensate with the help of the results of the renewed electrical contacts. There is no replacement of an automatic mechanical button 7 required. The tool 3 remains under speed at the milling spindle 4 , The machine 2 remains thermally stable.

By repeated electrical contacting of the rotating tool 3 on the workpiece 1 At defined dimensionally known geometric elements can during machining of the wear of the tool 3 be determined. If, for example, in a guide bore repeatedly opposing measuring points with tools 3 electrically contacted, the determined contact positions are due to reduced by wear diameter of the tool 1 depending on the wear always further apart. When the thus determined contact positions are compared with the values of the determined contact positions of the first electrical contacts with new tool in the guide bore, can the wear of the tool 3 getting closed. The same applies to the length of the tool 3 or the radius.

After completion of a work cycle, the currently machined geometry on the workpiece 1 directly with the tool 3 being checked. This can be done before the tool 3 again dimensionally known geometry elements on the workpiece 1 , which were not processed in the operation, be referenced, so the wear of the tool 3 be determined. With the help of the following electrical contacts between tools 3 and the workpiece 1 For example, it can be recognized at measuring points in the area which is being processed whether the geometry produced on the workpiece 1 within the desired tolerances. In this case, the previously determined wear on the tool 3 be considered mathematically. So it is also festgesellt whether the tool 3 , especially at longer tool lengths, during machining has pushed away due to Zerspankräften or due to unfavorable cutting geometry in the workpiece 1 has drawn in and thus it has come to unwanted deviations in the processing.

It is also possible to make an electrical contact firmly on the machine table 5 Install installed extra reference elements, such as DE 10 2009 037 593 A1 known. Instead of these with an automatic mechanical button 7 can contact, electrical contacts to the in DE 10 2009 037 593 A1 described reference elements according to the invention with the rotating tool 3 be performed. Such dimensional, especially in their position, known reference elements in the machine 2 You can also use the geometry of the rotating tool 3 to be measured by electrical contact. If the electrical contact according to the invention can not be completely wear-free, for example, because the machine 2 does not react fast enough and yet it leads to a mechanical contact between tools 3 and reference element comes, the fixed reference elements can also be provided interchangeable.

For calibrating an automatic mechanical button 7 For example, according to the prior art, a high-precision, dimensionally known measuring ball 28 used. This will be done with the button 7 repeatedly touched and so the switching characteristics of the button 7 certainly. Such known measuring balls 28 can also be used as fixed reference elements for the inventive method of electrical contacting by voltage breakdown with tools 3 in the machine 2 be used. Any adhering chips are caused by the rotation of the tool 3 with multiple electrical contacting at the same point of the measuring ball 28 thrown away, as previously described. So measurement errors can be avoided. This is the electrical contact of the measuring ball 28 with the tool 3 even insensitive to dirt as opposed to touching with the automatic mechanical button 7 ,

The first object became exemplary as a workpiece 1 selected. The second object was exemplified as a tool 3 selected. It should be noted that the first object, the second object and the third object may in particular be selected from any combination of tools, workpieces, reference elements and probing elements. All of these elements can be rotating or standing elements. In this case, two objects may be similar to these elements.

It follows that it is advantageous both in the coarse measurement S1 and in the fine measurement S2, a method for determining the position of a workpiece 1 and / or a tool 3 in a machine 2 execute, in which a workpiece 1 at the machine 2 is tense, in which subsequently the tool 3 with the help of the tool holder 10 or directly into the rotatable spindle shaft 25 used and the spindle shaft 25 is set in rotation, wherein between the workpiece 1 and the tool 3 an electrical voltage is applied at which the tool 3 and the workpiece 1 be moved against each other, and in which at an electrical contact between the tool 3 and the workpiece 1 a change in the applied voltage or the resulting current flow determines and the respective position of the workpiece 1 and / or the tool 3 determined and in a computer program for controlling the processing of the workpiece 1 is deposited. The electrical contact is produced by a voltage breakdown.

It is advantageous if the spindle shaft 25 and / or the workpiece 1 be stored electrically insulated. It is also advantageous if the relative movement between the workpiece 1 and the tool 3 upon reaching an electrical contact between the workpiece 1 and the tool 3 is stopped. In addition, it is advantageous if upon reaching an electrical contact between the workpiece 1 and the tool 3 and after determining the position of the workpiece 1 and / or the tool 3 the workpiece 1 from the tool 3 is moved away. Further, it is advantageous if the method at the beginning of a machining of a workpiece 1 is carried out. It is also advantageous if the method at time intervals during machining of a workpiece 1 or after machining the workpiece 1 is carried out.

It is advantageous if the workpiece 1 damage-free in electrical contact with the tool 3 is brought. In addition, it is advantageous when using the tool 3 electrically contacted area of the workpiece 1 is cleaned before electrical contact. It is also advantageous if the method is carried out automatically. Further, it is advantageous if the electrical voltage is an AC voltage and the AC voltage by means of a capacitive coupling of a voltage source 8th to the tool 3 is transmitted. It is equally advantageous if with the rotating tool 3 dimensionally known geometric elements of the workpiece 1 or in the machine 2 installed reference elements are electrically contacted to the geometry and / or wear of the tool 3 to investigate.

It is advantageous if, prior to the electrical contacting of the workpiece 1 with the rotating tool 3 a warm-up phase is awaited until the machine 2 is thermally stable. In addition, it is advantageous if the electrical contacting of the workpiece 1 with tools 3 after processing with the tool 3 made surfaces to a dimensional control of the tool 3 produced surfaces on workpiece 1 perform. Further, it is advantageous if a Restmaterialbearbeitung with a tool 3 exactly in the on the workpiece 1 already produced surfaces is fitted by already finished surfaces of the workpiece in the environment of the rest material processing to be performed 1 with the tool 3 be contacted electrically before performing the Restmaterialbearbeitung.

In the context of the invention, it is also advantageous if the workpiece 1 by means of the tool 3 is electrically contacted at least twice, wherein the detected position values of the determined contact positions are compared and in the presence of a difference of the position values, a repeated electrical contacting is performed. It is also advantageous if the difference is compared with a predetermined tolerance value and the electrical contact is repeated when the tolerance value is exceeded. Furthermore, it is advantageous if the total number of electrical contacts is determined and an error message is output when a maximum number is exceeded.

In addition, it is advantageous if during ongoing machining of the workpiece 1 through the tool 3 a running sequence of electrical contacts is checked and monitored, wherein the number of electrical contacts exactly with the number of cutting operations of the tool 3 , per revolution of the tool 3 due to the number of cutting edges of the tool 3 must match, and it is concluded with a smaller number of electrical contacts that individual cutting the tool 3 are not engaged, so z. B. broken or worn. It is also advantageous if the electrical contact between the workpiece 1 and the tool 3 via an electrically conductive bearing 13 or over a metallic plate 11 leading to the spindle shaft 25 has a gap of small width or via a sliding contact.

In addition to the above written description of the invention is to the additional disclosure hereby explicitly to the drawings of the invention in the 1 to 22 Referenced.

LIST OF REFERENCE NUMBERS

1

workpiece

2

machine

3

Tool

4

milling spindle

5

machine table

6

detection unit

7

button

8th

voltage source

9

axis of rotation

10

tool holder

11

metallic plate

12

residual material

13

Auxiliary bearings

14

inner ring

15

outer ring

16

insulating

17

steel ball

18

voltage detector

19

chip

20

control

21

row

22

signal cable

23

ceramic bearing

24

ceramic bearing

25

spindle shaft

26

probe contact

27

traversing

28

measuring ball

29

measuring cylinders

30

insert

31

Axis of the measuring cylinder

K1

first electrical contact means

K2

second electrical contact means

W1

first resistance

W2

second resistance

P1

first precise position

P2

second precise position

P3

third precise position

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009037593 A1 [0154, 0154]

Claims (17)

Method for automatic relative position determination of a first assembly ( 5 ) of a machine ( 2 ) arranged first object ( 1 ) and one at a second assembly ( 4 ) the machine ( 2 ) arranged second object ( 3 ), the first and second assemblies ( 4 . 5 ) are moved relative to each other, comprising: a coarse measurement (S1) in which a position of the first object ( 1 ) opposite the second object ( 3 ) is detected with a first measurement accuracy, a fine measurement (S2), which is carried out after the coarse measurement (S1), in which a precise position of the first object ( 1 ) opposite the second object ( 3 ) is detected without contact with a second measurement accuracy, which is higher than the first measurement accuracy, wherein: between the first object ( 1 ) and the second object ( 3 ) an electrical voltage is applied, • the first object ( 1 ) and the second object ( 3 ) by a relative movement of the assemblies ( 4 . 5 ) are moved against each other, • the precise position of the first object ( 1 ) opposite the second object ( 3 ) is detected when a voltage breakdown between the second object ( 3 ) and the first object ( 1 ), and • the relative movement of the assemblies ( 4 . 5 ) is stopped in response to the voltage breakdown, and an evaluation in which the precise position in a computer program of the machine ( 2 ) for controlling the processing or the measurement of the first object ( 1 ) and / or the second object ( 3 ) by means of the machine ( 2 ) is deposited. Method according to claim 1, characterized in that the first object ( 1 ) is a workpiece or a reference element. Method according to one of the preceding claims, characterized in that the second object ( 3 ) is a tool or a probing element. Method according to one of the preceding claims, characterized in that the first object ( 1 ) and / or the second object ( 3 ) are stored electrically insulated. Method according to one of the preceding claims, characterized in that during the coarse measurement (S1) the position of the first object (S1) 1 ) opposite the second object ( 3 ) is detected by a mutual mechanical probing. Method according to one of the preceding claims, characterized in that during the coarse measurement (S1) the position of the first object (S1) 1 ) relative to the second object by a mechanical probing of the first object ( 1 ) by a on the second module ( 4 ) arranged third object is detected. Method according to one of claims 1 to 4, characterized in that in the coarse measurement (S1): - between the first object ( 1 ) and the second object ( 3 ) an electrical voltage is applied, the electrical voltage being higher than the voltage applied during the fine measurement (S2), the first object ( 1 ) and the second object ( 3 ) by a relative movement of the assemblies ( 4 . 5 ) are moved against each other, and - the position of the first object ( 1 ) opposite the second object ( 3 ) is detected when a voltage breakdown between the first object ( 1 ) and the second object ( 3 ) he follows. Method according to one of the preceding claims, characterized in that the first object ( 1 ) and / or the second object ( 3 ) are moved at a higher speed with the coarse measurement (S1) than with the fine measurement (S2). Method according to one of the preceding claims, characterized in that a maximum current, which at a voltage breakdown by the second object ( 3 ) flows, is limited. Method according to one of the preceding claims, characterized in that between the coarse measurement (S1) and the fine measurement (S2) a distance between the second object (S1) 3 ) and the first object ( 1 ) by a relative movement of the assemblies ( 4 . 5 ) is increased, in particular so far increased that at the beginning of the fine measurement (S2) no direct voltage breakdown between the first object ( 1 ) and the second object ( 3 ) he follows. Method according to one of the preceding claims, characterized in that the fine measurement (S2) is carried out repeatedly. A method according to claim 11, characterized in that the fine measurement (S2) is repeated until the precise positions detected in two successive repetitions of the fine measurement (S2) deviate less from one another than predetermined by a tolerance range. Method according to one of the preceding claims, characterized in that during the coarse measurement (S1) a movement of the second object (S1) 3 ) and / or the first object ( 1 ) in Reaction to the detection of the position of the first object ( 1 ) opposite the second object ( 3 ) or a detection of the voltage breakdown is stopped. Method according to one of the preceding claims, characterized in that in the coarse measurement (S1) and / or the fine measurement (S2) the first object ( 1 ) a reference element, in particular a measuring ball ( 28 ) or a measuring cylinder ( 29 ), which is in a fixed position opposite the machine ( 2 ) is arranged. Method according to one of the preceding claims, characterized in that the accuracy and / or the dimensions achieved in the machine ( 2 ) performed by a coarse measurement (S1) and / or a fine measurement (S2) is checked. Method according to one of the preceding claims, in which the results of one or more coarse measurements (S1) and / or fine measurements (S2) are used to determine a result with a subsequent tool (S1). 3 ) to be performed on a with a previous tool ( 3 ) produced surface of the first object ( 1 ). Machine adapted to carry out the method according to one of claims 1 to 17.

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