DE102011089039A1 - Method for operating coordinate measuring machine for measuring workpiece, involves measuring movement of sensor or workpiece support by flowing electrical drive current through electric motor to effect movement of electric motor - Google Patents

Abstract

The operating method involves measuring the movement of a sensor or a workpiece support by flowing the electrical drive current (I-ist) through an electric motor to effect the movement of the electric motor. An actual-speed or an actual-acceleration of the sensor or the workpiece support are measured in a direction driven by the electric motor. A current limit value (I-max,I-min) or current limit band is determined for the electric drive current depending on the measured actual-speed or the measured actual-acceleration. An independent claim is included for a coordinate measuring machine for use with a mechanism for moving a sensor relative to a workpiece support in one direction.

Description

The invention relates to a coordinate measuring machine and a method for operating a coordinate measuring machine. The coordinate measuring machine has a mechanism (see purely exemplary the mechanics 3 of the portal type in 1 ) for adjusting a sensor relative to a workpiece holder in at least one direction, wherein the mechanism has at least one electric motor, via which the adjustment of the sensor or the workpiece holder is driven in this direction. In this case, an electrical drive current is measured, which flows through the electric motor, in order to effect a movement of the electric motor and in this way a movement of the sensor or the workpiece holder. In this case, the measured drive current is compared with a current limit value or a current limit band, and when the electric drive current reaches and / or exceeds the current limit value or when the current limit band is left, the movement of the mechanism is stopped, at least in the direction driven by the electric motor.

Such a coordinate measuring machine is known from the US patent US Pat. No. 7,627,957 B2 known. Herein is shown a coordinate measuring machine of the type mentioned above and a corresponding method for operating such a coordinate measuring machine. The said current limit value or the said current limit band is determined here as a function of a desired speed and / or as a function of a desired acceleration with which the movement of the electric motor and thus the movement of the sensor or of the workpiece holder in the relevant direction is to take place. For this purpose, a functional relationship between the desired speed and / or the target acceleration on the one hand and the current limit of the drive current or the current limit of the drive current wall on the other hand fixed.

This effectively creates a coordinate measuring machine which, in the event of a collision of moving components of said mechanism, such as a measuring carriage movable in a coordinate direction, or said sensor or said workpiece holder with persons or objects, prevents the electric motor from continuing to operate, although one Collision took place. Due to the dynamic adaptation of the current limit value or the current limit band as a function of the desired speed and / or the desired acceleration, it is also possible to ensure that collisions are detected at different speeds and accelerations.

Coordinate measuring machines with such functionality function reliably. However, the commissioning of the method is partly relatively complex, because the relationship between the desired speed and / or the target acceleration on the one hand and the current flowing through the electric motor on the other hand must be determined by sometimes consuming series of measurements. The controller namely reacts to a predetermined desired speed and / or a desired acceleration with a certain temporal behavior, which must be taken into account in the determination of the current limit or the current limit band. During acceleration processes, for example, the only limited stiffness of the mechanism tends to oscillate, which accordingly leads to a variation of the drive current. Another example is the time offset between the time of a new target speed and / or a new target acceleration on the one hand and the time of the associated actual change in the drive current on the other hand.

Another coordinate measuring machine, which uses almost exactly the same method as in the document US Pat. No. 7,627,957 B2 is shown in the publication US 2011/0192044 A1 shown.

In addition, from the document DE 100 24 976 A1 In general, a torque control device is known which compares an actual drive current of an electric motor with a desired drive current of the electric motor and generates an actuating variable signal as a function of the comparison result. It is ensured that the drive current is due to the comparison with a maximum allowable drive current below the maximum allowed value, so as to avoid a hard abutment of a test element on a body.

A disadvantage of such a procedure, however, is that the drive current is limited even by the maximum value when the test element is not in the vicinity of the workpiece to be measured. The speed at which the test element can be moved and the acceleration are therefore limited.

It is the object of the present invention to provide a coordinate measuring machine and a method for operating a coordinate measuring machine of the type specified above with an adapting to the respective acceleration and / or speed current limit or current limit band for the drive current, with the current limit or the Stromgrenzwertband easier and in particular more precisely adapted to the drive current.

The object is solved by the subject matters of the attached independent claims 1 and 17.

According to an essential idea of the present invention, an actual speed and / or an actual acceleration of the sensor or the measuring pad is measured in the direction driven by the electric motor and the current limit value or the current limiting current band for the electric drive current is measured from the measured actual speed and / or the measured actual acceleration determined.

This is surprising for the following reasons. When considering the method known from the prior art, the person skilled in the art had the expectation that only the desired speed and / or the desired acceleration would allow reliable determination of the current limit value for detecting a collision. The reason for this is that the speed and the acceleration of the sensor or the workpiece support in the direction driven by the electric motor are predetermined by the target speed and the target acceleration because these quantities are derived from the driving commands of the measurement procedure. The actually measured actual speed and the actually measured actual acceleration, however, is determined by the controller of the coordinate measuring machine and is therefore not clearly predetermined by the measurement process. In the case of a collision, therefore, there were reservations as to whether the evaluation of the actual speed and / or the actual acceleration leads to early collision detection. Surprising here is now the realization that to determine the current limit or the current limit band just not the functional relationship between the target acceleration and / or the target speed is considered, but the actual actual speed and / or the actual acceleration to Determining the current limit value or the current limit band is used.

In contrast to the determination of the current limit value or of the current limit band from the setpoint acceleration and / or the setpoint speed, in the present case, when the current limit value or the current limit band is determined from the actual speed and / or the actual acceleration, a review is carried out. The determination of the actual speed and / or the actual acceleration as well as the expected drive current and the current limit value or the current limit band requires a certain amount of computing time. Thus, the determined expected current and thus the current limit or the upper and lower current limit of the current limit band applies for a time which is a few milliseconds in the past. Therefore, the current current limit or current limit and current limit band lower current limit must always be compared to a measured drive current that is several clock cycles in the past. There is therefore a certain phase difference between the currently determined current limit value or the currently determined current limit value band on the one hand and the measured drive current, on the other hand.

The determination of the actual speed or the actual acceleration can take place here in different ways. For example, the actual speed and / or the actual acceleration can be determined from the scale values of a measuring slide of the mechanism driven by the electric motor. These scale values indicate the current position of the respective measuring carriage in the relevant direction of movement of the respective measuring carriage. To determine the actual speed, the scale values are derived according to the time. To determine the actual acceleration, the scale values are derived twice over time. Alternatively, for determining the actual speed and / or the actual acceleration, it would also be possible, for example, to use an acceleration sensor which is fastened, for example, to the relevant measuring carriage or to the sensor. The relevant acceleration sensor provides the actual acceleration directly. The actual speed can be obtained from the signal of the acceleration sensor by temporal integration.

In principle, the tachogenerator connected to the electric motor for detecting the current actual rotational speed can also be used to measure the actual speed and / or the actual acceleration. Since the actual speed is proportional to the current speed of the driven measuring carriage and thus to the speed of the sensor in the relevant direction, the signal supplied by the tachogenerator itself can already be used as the actual speed. By temporal derivative of the signal of the tachogenerator, the actual acceleration can be determined additionally or alternatively, since the derivative of the measured by the tachogenerator actual speed after the time for the acceleration of the driven measuring slide and thus to accelerate the sensor in the relevant direction proportional Signal supplies. The determination of the actual speed and / or the actual acceleration from the signal of the tachogenerator, however, is suboptimal, since the vibrations that occur during acceleration processes of the mechanics, can not be determined by this. In addition, there is often between the measured by the tachometer generator actual speed and the actual movement of the driven by the respective electric motor measuring slide a deviation due to the limited rigidity of the coupling between the measuring slide and the electric motor.

In order to determine the current limit value or the current limit value band, an expected drive current which corresponds to an expected value for the actual electrical drive current can be determined from the actual speed and / or the actual acceleration. The determination of the expected drive current can generally take place in different ways. For example, a table can be specified in which, in each case, values for the expected drive current are stored for a large number of different actual speeds and / or actual accelerations. If necessary, intermediate values can be determined via interpolation.

The determination of the values for such a table can take place in different ways.

For example, a table that only considers the actual speed can be recorded as follows. The sensor or the workpiece support is moved in the relevant direction driven by the electric motor with different constant actual speeds and the drive current occurring is measured. Actual speeds and the associated drive currents are then stored in a table. From the table thus generated, an expected drive current can be read out by determining the actual speed and reading out the associated drive current from the table.

A table that only considers the actual acceleration can be recorded as follows. The sensor or the workpiece support is accelerated in the relevant direction driven by the electric motor with different constant accelerations. During acceleration, the drive current is measured and the maximum of the drive current associated with the relevant actual acceleration is stored in a table. From the table thus generated, an expected drive current can then be read out by determining the actual acceleration and reading out the associated drive current from the table.

A table in which both the actual speed and the actual acceleration is taken into account can be recorded as follows. The sensor or the workpiece support is moved in the relevant direction driven by the electric motor with a constant actual acceleration. During the acceleration process, the actual speed increases continuously. During the acceleration process, the associated drive current is then measured for specific values of the actual speed. This process is repeated for a variety of different actual accelerations. The measured drive currents as a function of the respective actual acceleration and the respective actual speed are then stored in the table. From the table thus generated, an expected drive current can then be read in which the actual speed and the actual acceleration are determined and the associated drive current is read from the table.

Much simpler, however, is when the expected drive current can be calculated from a function. In a very simple form of such determination of the expected drive current, a variable speed component proportional to the measured actual speed can easily be taken into account. The required proportionality factor can be easily determined by the sensor or the workpiece support in the relevant, driven by the electric motor direction with a high, constant actual speed v _{is moved} and the associated drive current I _is measured. The proportionality factor K _v for the variable speed component can then be determined as follows: K _v = I _is / v _is (Equation 1)

An expected drive current I _erw can then be determined as follows, following determination of the proportionality factor K _v in the regular measuring operation of the coordinate measuring machine as a function of the measured actual speed v _ist : I _erw (v _is ) = v _is · K _v (Equation 2)

In another very simple form of such calculation of the expected driving current, a variable acceleration component can be easily taken into account, which _is proportional to the measured actual acceleration a. The required proportionality factor K _a can be easily determined by the sensor or the workpiece support in the relevant, driven by the electric motor direction with a high, constant actual acceleration a _{is moved} and the associated drive current I _is measured. The proportionality factor K _a for the variable acceleration component can then be determined as follows: K _a = _I / a _is (Equation 3)

An expected drive current I _erw can then be determined as follows after the determination of the proportionality factor K _a in the regular measuring operation of the coordinate measuring machine as a function of the measured actual acceleration a _ist : I _erw (a _is ) = a _is · K _a (Equation 4)

Once the actual driving current in the electric motor, both of the actual velocity _v, as well as by the actual acceleration a _is dependent upon the accuracy with which allows a determination of the expected value of the drive current I _erw be significantly improved when both of the above Procedures to be combined: I _erw (v _is , a _is ) = v _is K _v + a _is K _a (Equation 5)

It is important in determining the proportionality factors here that first the proportionality factor K _v for the velocity component is determined. The determination can be made in the same way as was done above in connection with Equation 1 and Equation 2. Namely, after the actual acceleration a _is constant actual speed _v is equal to zero, the acceleration component a fall _{is a} .K away then. As soon as the proportionality factor K _v for the speed component is determined, the proportionality factor K _a for the acceleration component can be determined. For this purpose, the sensor or the workpiece support _is accelerated in the relevant direction driven by the electric motor with a high constant acceleration a _ist . For a predefined actual speed v _, the drive current I _ist is then measured during the acceleration process. _Is from the actual acceleration a v _is the actual speed and the measured driving current _I can then the proportionality factor K _a are determined as follows: K _a = (I _is - _v · K _v) / _A (Equation 6)

An expected drive current I can _erw then after determination of the proportionality factors K _v and K _a, in a regular measurement operation of the coordinate measuring device depending on the measured actual speed _is v and the measured actual acceleration a _is to be determined using equation. 5

It has also been shown that, besides the actual speed A _and the actual acceleration a _is a third major determinant of the proportion of the drive current is, which is still needed, the sensor or the workpiece support at all in the relevant, by the electric motor to move driven direction. There may be different reasons for this. For example, counter to the direction of travel, in which a measuring carriage is driven by the electric motor, frictional forces act. There may also be forces, because a wire harness, which contains the power supply lines and / or the signal lines for the mechanics, is deformed by the movement and thereby forces occur. Another reason may be with a vertically movable measuring carriage, that the weight forces of the measuring carriage are received by the electric motor and thereby counteracts the weight of the measuring carriage movement or when a downward movement in the direction of movement during an upward movement of the measuring carriage.

Therefore, it is particularly advantageous if, in determining the expected drive current, a basic component R corresponding to a drive current corresponding to a movement of the sensor or the workpiece support in the direction driven by the electric motor at a low constant speed is taken into account. The basic component can be a constant fundamental component R * independent of the velocity direction of the actual velocity. However, since this basic component may depend on the velocity direction of the actual velocity _{, a} basic component R ^± dependent on the velocity direction of the actual velocity v _ist can be used particularly advantageously as a basic component, this direction-dependent fundamental component R ^± assuming a first constant value R ⁺ when the measured actual speed v _{ist is} positive and assumes a second constant value R ^- when the measured actual speed v _{ist is} negative.

This basic component R can be used both in conjunction with the table described above, as well as in connection with the function just described.

Insofar as a constant basic component R * is used, the relevant measuring slide is moved in the direction driven by the electric motor at a very low speed and the drive current measured here is used as a constant basic component. Insofar as a direction-dependent basic component R ^± is to be used, the relevant measuring slide is first moved by the electric motor in a positive speed direction at a very low speed and the measured drive current is taken over as the first constant value R ⁺ and then traversed in the negative speed direction with very low speed and the In this case measured drive current as the second constant value R ^- accepted.

Essential in the use of a basic portion R is that this is determined at the very beginning, ie before the table described above is created or before the proportionality factors K _v and / or K _{a are determined} in the function. Then, the basic component in the determination of the entries of the table or in the case of the function, in the determination of the proportionality factor K _v for the speed component and / or the proportionality factor K _a for the acceleration component always is taken into account by the respective measured drive current I _is reduced by the basic component R.

A function I _erw (v _is , a _is ), with which particularly precise results for the expected drive current I _erw can be determined, looks as follows: I _erw (v _is , a _is ) = R + v _is · K _v + a _is · K _a (Equation 7)

R

= der besagte Grundanteil, also entweder der konstante Grundanteil R* oder der richtungsabhängige Grundanteil R^±

K_v

= Proportionalitätsfaktor für den variablen Geschwindigkeitsanteil

v_ist

= gemessene Ist-Geschwindigkeit

K_a

= Proportionalitätsfaktor für den variablen Beschleunigungsanteil

a_ist

= gemessene Ist-Beschleunigung

Herein mean:

R

= the said basic part, ie either the constant basic part R * or the directional basic part R ^±

K _v

= Proportionality factor for the variable speed component

v _is

= measured actual speed

K _a

= Proportionality factor for the variable acceleration component

a _is

= measured actual acceleration

By determining the actual speed v _ist and the actual acceleration _{is a} and use in Equation 7 can then be determined in a particularly simple manner, the expected drive current.

In the case of a directionally dependent fundamental component R ^± , the values R ^± , K _v and K _a can be determined as follows. First, the direction-dependent basic component R ^± is determined by the measuring slide concerned first moved by the electric motor in a positive velocity direction with very low velocity and this measured drive current _I is taken as a first constant value ⁺ R. Thereafter, the measuring slide is moved by the electric motor in the negative speed direction at a very low speed and the measured here drive current I _{is taken} as the second constant value R ^- . Thereafter, the proportional velocity factor K _v for the variable velocity component is determined by traversing the high constant velocity measuring slide v _ist and measuring the actual drive current I _ist . Since the actual acceleration a _is at a constant actual speed v _is approximately zero, then the proportional velocity factor K _v for the variable speed component can then be determined as follows: K _v = (I _is - R) / _V (equation 8)

As already described above, the basic component R is taken into account in the determination of the proportionality factor K _v for the variable speed component, in that the respective measured drive current I _{ist is} reduced by the fundamental component R, ie I _is -R of course R * should be used and in the case of a directionally dependent fundamental component R ^± instead of R depending on the direction of the actual velocity v _, either R ⁺ or R ^{- should be used} . Finally, the proportionality factor K _a is determined for the variable acceleration component by _the measuring carriage with high constant actual acceleration a is moved and the actual speed _v at a time when the actual acceleration a _and the actual driving current I _is measured , The proportionality factor K _a for the variable acceleration component can then be determined as follows: K _a = (I _is - R - _v · K _v) / _A (Equation 9)

, As already described above, the basic component R taken into account in the determination of the proportionality factor K _a for the variable acceleration component by correlating the measured drive current I _is reduced by the basic component R, so I _is also in Equation 9 - R. In the case of of course R * should be used in place of R and, in the case of a velocity-direction-dependent fundamental R ^± , instead of R depending on the direction of the actual velocity v _, either R ⁺ or R ^{- should be used} .

From the expected drive current I _erw can then be determined very easily a current limit by the expected drive current I _erw is increased by a first current value d. Please note the following. Depending on the direction of the actual speed v _ist is the drive current I _is usually positive or negative. (Note: For vertically movable measuring carriages whose weight is not compensated, for example, by a counterweight or a spring, the drive current I _can also have the same sign for both directions of the actual speed). The increase by a first current value d in the case of a positive expected drive current means that the first current value d is added, while in the case of a negative expected drive current the first current value d has to be subtracted. But you can also just use the amount of the expected drive current, so that an increase is then generally by adding the first constant current value d.

Instead of a current limit value, however, as already explained above, a current limit value wall can be used by adding to the expected drive current a first current value d to obtain an upper current limit value and subtracting a second current value e from the expected drive current to obtain a lower current limit value , As far as the first current value and second current value d e are the same in magnitude, makes the direction of the velocity, v, the _control resulting from the control value, not matter, since the upper current threshold and the lower current threshold then regardless of the speed direction are always the same distance from the expected drive current I _erw away.

As far as the first current value d and the second current value e are different, then it must, of course, in reverse direction, the speed V _control resulting from the control value, the first current value d is subtracted (thus the lower current limit of the current limit value band is obtained) and the second current value e are added (thereby the upper current limit of the current limit band is obtained).

Thus, in determining the current limit or a first current limit (upper current limit for one direction of velocity, lower current limit for the other direction of velocity) of the current limit band, the expected drive current is increased by a first current value d such that the magnitude of the current limit or the first Current limit of the current limit band is higher than the amount of the expected drive current.

In order to determine the second current limit value (lower current limit for one direction of the velocity, upper current limit for the other direction of the velocity) of the current limit band, the expected drive current is additionally reduced by a second current value e such that the magnitude of the second current limit value of the current limit band is lower than is the amount of the expected drive current.

The first current value d and / or the second current value e are constant in the simplest case. Instead of a constant first current value d and optionally a constant second current value e as well as current values may be used that vary in function of parameters such as the actual speed _v and / or the actual acceleration _a. For example, the amount of the first current value d and, if appropriate, of the second current value e for low speeds can be greater than for high speeds, because, in particular for low speeds I higher deviations of the measured drive current from the expected driving current I, _is devoted to _person, as at higher speeds ,

With regard to the mechanism for adjusting a sensor relative to a workpiece holder, the following should be noted. At the present time, there is a wealth of different mechanisms with which a sensor can be adjusted relative to a workpiece holder.

For example, mechanisms in which the workpiece holder is designed as a fixed workpiece table are customary, wherein the sensor can usually be moved via the mechanism in three coordinate directions which are perpendicular to one another. For this purpose, such a mechanism for each of the coordinate directions on a measuring carriage, which is guided along a linear guide, wherein the respective measuring carriage is driven via the said electric motor in the relevant direction and a scale is provided with an associated reading head, on the respective direction the current position of the measuring carriage can be determined. An exemplary structure of such a coordinate measuring machine is a coordinate measuring machine of the so-called portal type as described below in connection with 1 is explained in detail.

Also known coordinate measuring machines, in which the relative movement between the sensor and the workpiece support is not or not exclusively by an adjustment of the sensor, but by an adjustment of the workpiece support in one or more coordinate directions is generated. For this purpose, the mechanism in question then, as described above in connection with the adjustment of the sensor, for each of the respective coordinate directions on a measuring carriage, which is guided along a linear guide, wherein the respective measuring carriage is driven via said electric motor in the relevant direction and a scale is provided with an associated reading head over which the current position of the measuring carriage can be determined in the relevant direction.

Coordinate measuring devices are also known, in which the relative movement between the workpiece support and the sensor is generated by rotary joints. Examples of this are turntables that support the workpiece rotatably about a vertical axis of rotation, rotary swivel joints with which the sensor is rotatably and pivotally mounted at the end of the movable in three coordinate directions measuring arm or robot arms that have only swivel joints. Again, an electric motor is provided for generating the rotational movement in the rotary joints and a rotary encoder, via which the respective angle of rotation of the rotary joint can be measured.

Coordinate measuring devices are also known in which the relative movement between the sensor and the workpiece support is limited to only two coordinate directions. The third coordinate direction is determined, for example, optically via an optical distance sensor. In principle, even a mechanism is conceivable in which the relative movement between the sensor and the Workpiece support takes place in only one coordinate direction. For example, the sensor could be a digital camera which detects the entire width of the workpiece and measures the distance to the workpiece, for example, by the focus position.

Tactile sensors can be used, such as a measuring probe, in which the deflection of a touching the workpiece workpiece element can be measured in three coordinate directions or a switching probe, the touch of the workpiece with its probe element a signal emits. But it can just as optical sensors, such as a digital camera or a laser triangulation probe or other suitable sensors are used as well.

The invention makes it possible to provide reliable collision monitoring for any course of the speed and therefore also any courses of acceleration. In order to achieve a high acceleration of the sensor or the workpiece support, a correspondingly high current limit value is required. If only a slow speed is specified and only low acceleration values are permitted, the current limit can be set low.

• (a) ein elektrischer Antriebstrom, der durch den Elektromotor fließt, um eine Bewegung des Elektromotors und auf diese Weise eine Bewegung des Sensors oder der Werkstückauflage zu bewirken, wird gemessen,
• (b) eine Ist-Geschwindigkeit und/oder eine Ist-Beschleunigung des Sensors oder der Werkstückauflage in der durch den Elektromotor angetriebenen Richtung wird gemessen
• (c) abhängig von einer gemessenen Ist-Geschwindigkeit und/oder abhängig von einer gemessenen Ist-Beschleunigung, wird ein Stromgrenzwert oder ein Stromgrenzwertband (d. h. ein Bereich von Werten für den Antriebstrom, der durch einen unteren Stromgrenzwert und einen oberen Stromgrenzwert definiert ist) für den elektrischen Antriebstrom ermittelt, und
• (d) wenn der elektrische Antriebstrom den ermittelten Stromgrenzwert erreicht und/oder wenn der elektrische Antriebstrom den ermittelten Stromgrenzwert überschreitet, oder wenn das Stromgrenzwertband verlassen wird, wird die Bewegung der Mechanik zumindest in der durch den Elektromotor angetriebenen Richtung angehalten.

In particular, a method for operating a coordinate measuring machine is proposed, wherein a mechanism for adjusting a sensor is provided relative to a workpiece support in at least one direction and this mechanism has at least one electric motor, via which the adjustment of the sensor or the workpiece support is driven in this direction and the method comprising the steps of:

• (a) an electric drive current flowing through the electric motor to cause movement of the electric motor and thus movement of the sensor or workpiece support is measured;
• (b) an actual speed and / or an actual acceleration of the sensor or the workpiece support in the direction driven by the electric motor is measured
• (c) is dependent on a measured actual speed and / or dependent on a measured actual acceleration, a current limit or current limit band (ie a range of values for the drive current defined by a lower current limit and an upper current limit) for determines the electric drive current, and
• (d) when the drive electric current reaches the detected current limit and / or when the drive electric current exceeds the detected current limit, or when the current limit band is left, movement of the mechanism is stopped at least in the direction driven by the motor.

"Exceeding" the current limit value includes that the drive current in a case z. B. is greater than the current limit and in another case z. B. is smaller than the current limit. "Exceeding" is thus to be understood in the sense of "crossing over". The determination of a current limit and the monitoring of whether the current limit is reached and / or exceeded also include the possibility of a current limit band, i. H. a range of values for the drive current defined by a lower current limit and an upper current limit. It is then monitored whether the drive current is the current limit band, i. H. the region leaves, in which case the movement of the mechanism is stopped, at least in the direction driven by the electric motor. Leaving the current limit band is understood to mean that the drive current reaches and / or exceeds the upper current limit of the current limit band or reaches and / or exceeds the lower current limit of the current limit band. The verification of whether the current limit band is leaving is thus in fact the same as monitoring whether a current limit is reached and / or exceeded, except that this monitoring is done for an upper current limit and a lower current limit. This feature has been incorporated into the independent claims for the sake of clarity.

The determination of coordinates in a coordinate system is not limited to that the coordinates are Cartesian coordinates. Rather, coordinates of any kind can be determined, for example, polar coordinates, cylindrical coordinates, etc. A significant advantage of the power monitoring according to the invention is that the monitoring can remain active during an accelerated movement of the sensor or workpiece support in the relevant, driven by the electric motor direction. In principle, any desired high acceleration values can be permitted without the current monitoring having to be switched off.

As detailed above, an expected drive current is determined from the actual speed and / or the actual acceleration and from this the current limit value or the current limit band is determined. During the determination, further parameters can be used to further increase the precision, such as the ambient temperature, the temperature of parts of the coordinate measuring machine, the position of the sensor and / or the Workpiece support in a fixed coordinate system, the relative position of the sensor or the workpiece support with respect to the workpiece to be measured or with respect to other parts of the measurement setup and / or by operating conditions (such as a currently selected gear stage of a multi-stage transmission, which at the force transmission of the electric motor is used on the sensor or on the workpiece support in the relevant, driven by the electric motor direction), be determined. The consideration of such parameters further increases safety. In this way, the current limit may be closer to the current value actually required for operation. If the current limit is exceeded or the current limit is reached or exceeded or the current limit band is left, the mechanism is stopped, at least in the direction driven by the electric motor. As far as the mechanism allows an adjustment of the sensor relative to the workpiece support in several directions, the mechanism is preferably stopped in all directions,

The stopping of the mechanism in the direction driven by the electric motor can be done in different ways. In the simplest case, the electric drive current of the electric motor provided for driving in the relevant direction is switched off. In order to increase the braking effect also the electric motor can be briefly controlled so that the drive direction is reversed. In addition, the electric motor can also be short-circuited. Also, a brake may be provided, which is then triggered. Furthermore, a coupling can be provided, via which the measuring slide, which is provided for adjusting the sensor or the workpiece support in the relevant direction, is decoupled from the electric motor, so that no more forces are transmitted from the electric motor to the measuring slide. It can also be the limitation of the force and / or the torque of the electric motor to a predetermined value. This value may be fixed or depend on the operating state, the position of the coordinate measuring device and / or on other factors.

The stopping of the mechanism in the direction driven by the electric motor can additionally be made dependent on the electric drive current continuously reaching and / or exceeding the determined current limit value over a time interval of predetermined length or the electric drive current continuously determining the determined current limit band over a time interval Leaving the length of time. Alternatively or additionally, the measured electric drive current may be subjected to a smoothing of temporal fluctuations by a filter. In both cases, this can ensure that a very short-term (especially caused by a measurement error) excess or the very short-term achievement of the current limit still have no effect on the operation of the CMM.

Preferably, a plurality of electric motors of the coordinate measuring machine are provided, which together cause the movement of the sensor and / or the workpiece support. The movements of the electric motors are clearly associated with movement components of the movement of the sensor or the workpiece support. For example, in each case at least one electric motor is provided for a linear movement of the sensor or the workpiece support in the relevant direction of the linear movement, wherein each of the linear movements can take place exclusively in one of three mutually perpendicular directions. As a result, within a reachable range of motion, any desired point can thus be approached directly. In general, in the case of the plurality of electric motors, which together cause the movement of the sensor and / or the workpiece support, preferably for each of the plurality of electric motors, a current limit of the electric drive current is determined, this current limit depending on the measured actual speed and / or dependent is one of the measured actual acceleration of the movement component, which is effected by the respective electric motor.

In the case of a coordinate measuring machine with in each case at least one electric motor for the x-axis, the y-axis and the z-axis in a Cartesian coordinate system, therefore, current limit values or current limit bands for the motor currents depend on the measured actual speed values and / or dependent on the measured actual acceleration values in x-direction, in y-direction and in z-direction.

In particular, a plurality of electric motors can be provided for at least one of the movement components in order to bring about the movement of the sensor relative to the workpiece support, as is the case, for example, in gantry-type coordinate measuring machines. In this case, the current limit or current limit band is preferably determined for each of the electric motors of the same component of motion (in the case of identical electric motors, the same current limit or band may be used) and is separately monitored, whether the current limit or one of the two current limit band current limits achieved and / or exceeded for the considered electric motor. In a preferred embodiment, at least one measured value of the electric drive current is compared with an expected value during operation of the coordinate measuring machine, in particular during movement of the sensor or the workpiece support in the direction driven by the electric motor, in order to check the measurement of the electric drive current for measurement errors. The expected value can be z. B. be determined using the measured actual speed and the measured actual acceleration. Provided that the sensor or the workpiece support moves freely in the relevant direction driven by the electric motor, in this way the measurement of the electric drive current can be checked for correct functioning. For devices with more than one motor for one direction of movement (eg double drive on a gantry device in gantry or bridge design), it is advantageous not to limit the individual motor currents but the sum of the motor currents of the two motors of the dual drive.

The determination of the current limit value (or of the current limit value band), which depends on the measured actual speed and / or on the measured actual acceleration of the sensor or the workpiece support in the relevant direction driven by the electric motor, is preferably carried out by at least one computing device. Alternatively or additionally, the computing device can also initiate and / or control the measures required to stop the mechanism in the direction driven by the electric motor when the current limit is reached and / or exceeded or the current limit band is left. This functionality of the computing device can be realized by hardware and / or software.

• (a) eine Strom-Messeinrichtung, die ausgestaltet ist, einen elektrischen Antriebstrom, der durch den Elektromotor fließt, um eine Bewegung des Elektromotors zu erzeugen und auf diese Weise eine Bewegung des Sensors oder der Werkstückauflage in der betreffenden durch den Elektromotor angetriebenen Richtung zu bewirken, zu messen,
• (b) eine Ist-Geschwindigkeitsmesseinrichtung, die dazu ausgestaltet ist, die Ist-Geschwindigkeit des Sensors oder der Messauflage in der durch den Elektromotor angetriebenen Richtung zu messen und/oder eine Ist-Beschleunigungsmesseinrichtung, die dazu ausgestaltet ist, die Ist-Beschleunigung des Sensors oder der Messauflage in der durch den Elektromotor angetriebenen Richtung zu messen
• (c) eine Stromgrenzwert-Ermittlungseinrichtung, die ausgestaltet ist, abhängig von einer gemessenen Ist-Geschwindigkeit und/oder abhängig von einer gemessenen Ist-Beschleunigung, einen Stromgrenzwert oder ein Stromgrenzwertband (d. h. ein Bereich von Werten für den Antriebstrom, der durch einen unteren Stromgrenzwert und einen oberen Stromgrenzwert definiert ist) für den elektrischen Antriebstrom zu ermitteln, und
• (c) eine Betätigungseinrichtung, die mit der Strom-Messeinrichtung und mit der Stromgrenzwert-Ermittlungseinrichtung verbunden ist und die ausgestaltet ist, die Bewegung der Mechanik zumindest in der durch den Elektromotor angetriebenen Richtung anzuhalten, wenn der elektrische Antriebstrom den ermittelten Stromgrenzwert erreicht und/oder wenn der elektrische Antriebstrom den ermittelten Stromgrenzwert überschreitet oder wenn der Antriebstrom das Stromgrenzwertband verlässt

To the scope of the present invention also includes a coordinate measuring machine with a mechanism, a workpiece support for receiving a workpiece to be measured and a sensor, wherein the sensor and the workpiece holder of the mechanism in at least one direction is adjustable relative to each other, wherein the mechanism has at least one electric motor , via which the adjustment of the sensor or the workpiece support is driven in this direction. The coordinate measuring machine has the following:

• (A) a current measuring device which is configured, an electric drive current flowing through the electric motor to generate a movement of the electric motor and in this way to cause movement of the sensor or the workpiece support in the respective direction driven by the electric motor , to eat,
• (b) an actual speed measuring device configured to measure the actual speed of the sensor or the measuring pad in the direction driven by the electric motor, and / or an actual acceleration measuring device configured to perform the actual acceleration of the sensor or the measuring pad in the direction driven by the electric motor
• (c) a current limit detection means configured according to a measured actual velocity and / or a measured actual acceleration, a current limit or a current limit band (ie a range of values for the drive current determined by a lower current limit and an upper current limit is defined) for the electric drive current, and
• (C) an actuator, which is connected to the current-measuring device and with the Stromgrenzwert-detecting means and which is configured to stop the movement of the mechanism at least in the direction driven by the electric motor when the electric drive current reaches the determined current limit and / or when the drive electric current exceeds the detected current limit or when the drive current leaves the current limit band

For example, the actuating device has a switch-off device, which is connected to the current-measuring device and to the current limit value determining device and which is designed to switch off the electrical drive current when the electric drive current reaches the determined current limit value and / or if the electric drive current determined Current limit exceeds or when the electrical drive current leaves the limit band.

The coordinate measuring machine is of course set up to carry out the method according to one of claims 2 to 15. In particular for carrying out a method according to at least one of claims 2 to 11, the current limit value determination device is then set up accordingly, so that the method can be carried out.

With regard to the control-related components, such as the current-measuring device, the actual speed measuring device, actual acceleration measuring device, the current limit detection device, the actuator or the shutdown of the coordinate measuring machine is expressly emphasized that they can of course vary widely.

For example, for reasons of efficiency, multiple components may be implemented as a common program code on a microcontroller. As related for example below 2 and 3 is still shown is the actual speed and the actual acceleration required to determine the current limit or current limit band of the embodiment shown herein are determined by a time derivative of the actual position provided by the read head of the scale. These time derivatives of the actual position find as two process steps 30 and 31 in the current limit detecting means 15 instead of. Besides, the current limit detecting means calculates 15 also the current limit value or the current limit values of the current limit band. Thus, the current limit detecting means includes 15 additionally also components of the actual speed measuring device and the actual acceleration measuring device. For the actual speed measuring device and for the actual acceleration measuring device, in addition to the read head of the linear scale, the parts of the current limit value determination device that carry out the time derivatives would thus also be attributable in particular to the given exemplary embodiment.

Alternatively, individual components can also be executed as separate programs on a common multitasking microcontroller or executed on separate microcontrollers. The derivation of the measured actual position for determining the actual speed and / or the actual acceleration could thus be realized separately, so that then next to the in 2 shown current limit detection device 15 In addition, a function block for determining the actual speed and a function block for determining the actual acceleration in the controller would be provided.

Furthermore, individual or all components can also be designed analogously. In addition, analog and digital components can be accommodated on a common component.

In particular, the coordinate measuring machine can have a computer or a microcontroller which contains the current limit value determination device.

Furthermore, the scope of the invention includes a computer program which, when running on a computer or a microcontroller, determines at least the current limit value or the current limit band and optionally also initiates the measures to be taken when the current limit value is reached and / or exceeded or when the current limit band is exceeded. or controls. In particular, the computer program has program code means which can be stored on a computer-readable medium.

In addition, the scope of the invention includes a data carrier on which a data structure is stored, which determines after loading into a working and / or main memory of a computer or a microcontroller at least the current limit and optionally also when reaching and / or exceeding the current limit or when leaving the Stromgrenzwertbandes initiates and / or controls each action to be taken.

Embodiments of the invention will now be described with reference to the accompanying drawings. The individual figures show:

1 a gantry coordinate measuring machine,

2 purely schematic representation of the drive of the movable cross slide in the x direction 7 out 1 with a collision monitoring according to the invention

3 Flowchart for determining the upper current limit I _max and the lower current limit I _{min of} a Stromgrenzwertbandes in the current limit detection device 15 out 2

4 _Is representation of the actual current flowing the drive current I and the expected driving current I _erw and determined therefrom, the upper current limit value I _max and the lower current limit value I _min of a current limit value band for an exemplary profile of the target velocity _to v out for the drive 2

5 Representation of the actual flowing drive current I _is and the expected drive current I _erw and the upper current limit I _max determined therefrom and the lower current limit I _{min of} a current limit band for an exemplary course of the target speed v _soll in a collision of in 2 shown cross slide 7 with an object.

6 Representation as in 5 , wherein additionally the upper current limit I _{max-prior-art} is located, which would be determined by a conventional collision monitoring due to the target speed and / or the target acceleration and the corresponding course of the measured drive current I _{is prior art}

7 a measuring chain in the processing of a measured value of the drive current I _is

8th a purely schematic representation of the drive of the movable cross slide in the x direction 7 with one opposite 2 changed arrangement

nine Representation of the actual flowing drive current I _is and the expected drive current I _erw for an exemplary course of the desired speed v _soll of in 2 shown cross slide 7 ,

10 Description of the expected driving current I _{ext-prior-art} for the same course of the target velocity v _soll according nine , wherein the expected drive current I _{erw-prior art} with a conventional method of the target speed and the target acceleration has been determined.

11 Representation as in 10 , wherein additionally the actually measured drive current I _{ist is} shown

This in 1 shown coordinate measuring machine 11 in gantry design has a workpiece support in the form of a measuring table 1 on. The coordinate measuring machine 11 this includes a mechanism 3 over which a sensor nine relative to the workpiece support (measuring table 1 ) can be moved in all three coordinate directions x, y and z. In the case of mechanics 3 it is a so-called portal mechanism, in which only the sensor nine is moved in all three coordinate directions x, y and z, while the workpiece support (measuring table 1 ) stays calm. The mechanic 3 in this case comprises a first measuring carriage, namely a measuring table 1 spanning portal 4 , in the coordinate direction on the workpiece support indicated by the arrow y (measuring table 1 ) is movably guided. An unspecified electric motor of mechanics 3 causes the linear movement of this first measuring slide (Portal 4 ) of mechanics 3 in the y direction. In addition, a linear scale 12 the mechanics 3 provided by a likewise not shown in detail reading head of the mechanics 3 is read and thereby the current position of this first measuring slide (Portal 4 ) of mechanics 3 supplies.

The mechanic 3 also includes a second measuring carriage (cross slide 7 ), which runs along the measuring table 1 spanning crossbeam of the portal 4 is movably guided in the direction indicated by the arrow x. The current position of this second measuring slide (cross slide 7 ) relative to the cross member of the portal 3 can be based on a second linear scale 6 the mechanics 3 also be detected by a reading head 20 the mechanics 3 (only in 2 and 8th to see) is read. The movement of the second measuring slide (cross slide 7 ) in the x-direction is by another electric motor M of the mechanics 3 (only in 2 and 8th to see).

It also includes the mechanics 3 a third, in the vertical direction movable measuring slide, namely the quill 8th , on the second measuring carriage (cross slide 7 ) is movably mounted in a vertical direction, indicated by the arrow z. At the bottom of the quill 8th is a sensor nine attached, which is designed in the present case as a tactile measuring probe. The third measuring slide (quill 8th ) with the attached thereto sensor nine can, driven by another, not closer to seeing electric motor of the mechanics 3 , relative to the second measuring carriage (cross slide 7 ) in the z direction of the Cartesian coordinate system. About a third linear scale 10 the mechanics 3 , that of another, not closer to the reading head of the mechanics 3 is read, the position of the third measuring slide (quill 8th ) are read out in the direction indicated by the arrow z. By the total of three electric motors of mechanics 3 can the sensor nine Therefore, in all three coordinate directions x, y and z are moved and thereby moves in all three coordinate directions x, y and z relative to the workpiece support (measuring table 1 ) and thus also relative to a workpiece to be measured 5 resting on the workpiece support (measuring table 1 ) is stored. As stated above, the mechanics could 3 but also be designed so that the workpiece support is movably guided in one or more directions. For example, the portal might 4 be immovable in the y-direction and for the measuring table 1 be arranged on a movable in the y-direction measuring slide, which is driven by a corresponding electric motor and whose position is determined in the y-direction over a corresponding scale and an associated read-out.

The coordinate measuring machine also includes a controller 2 , and a measuring computer 13 that in conjunction with the controller 2 stands. The measuring computer 13 passes on to the controller 2 among other things, the predefined measuring sequences, for example in the form of points to be measured on the workpiece 5 , where the controller 2 then processed on the basis of the passed measurement process this. This is the control 2 in connection with the drives of the mechanics 3 in which also the said electric motors of mechanics 3 are included. In addition, the controller is 2 also in connection with the sensor nine and the read heads of the linear scales 6 . 10 and 12 the mechanics 3 , The control 2 then moves the sensor with the drives nine according to the measuring procedure and thereby scans the workpiece 5 with the sensor nine from. It takes the control 2 from the sensor nine and from the reading heads of the standards 6 . 10 and 12 the measured values and thereby determines the measured values of the touched points on the surface of the workpiece 5 , The measured values obtained on the basis of the measuring sequence are then sent to the controller for further evaluation 2 to the measuring computer 13 returned. To be able to perform the said tasks, the controller includes 2 one or more Real-time capable microprocessors that do the job.

2 shows an abstracted representation of the drive for the movable in the x-direction second measuring carriage (cross slide 7 ) of mechanics 3 out 1 plus control 2 and measuring computer 13 , The drive in this case comprises in particular an electric motor M, which is a circulating belt 21 drives, in turn, the cross slide 7 is fixed and thereby moved in the x direction. Same components as in 1 are denoted by the same reference numerals. It is expressly pointed out that this is a highly simplified representation in which only very schematically some components of the otherwise very complex system are shown.

The control of the electric motor M takes place here as follows. From the measuring computer 13 is among other things to the controller 2 the concrete to be traversed measuring procedure passed, this measurement process includes, among other driving commands P (x, y, z), for the three coordinate directions x, y and z by the three measuring carriages (Portal 4 , Cross slide 7 and quill 8th ) to define the position to be approached. Such travel commands P (x, y, z) are sent to a so-called spline interpolator 25 the controller 2 to hand over. This spline interpolator 25 calculates, starting from the current position, a plurality of positions to be approached one after the other for the x-direction, the y-direction and the z-direction. In addition, the spline interpolator determines 25 by simple temporal derivation of these successively approached positions for the x-direction, the y-direction and the z-direction, the target speeds for the x-direction, the y-direction and the z-direction, as well as by two-fold time derivative of the target Accelerations for the x-direction, the y-direction and the z-direction. In the example illustrated here only in an abstract manner, only the target positions for the x-direction x _soll , the target velocities for the x-direction v _soll and the target accelerations for the x-direction a _{soll are} to be seen. The spline interpolator 25 indicates the x positions x _soll to be approached successively from the travel commands P (x, y, z) to a position controller 14 further. This position controller 14 is also with the cross slide 7 attached reading head 20 connected, and receives from that of the linear scale 6 read actual position x _is the cross slide 7 in X direction. By subtracting the from the reading head 20 Previous reported actual actual position x _is x _to the to moving target position is calculated, the position controller 14 the control deviation, and calculates therefrom then an algorithm, for example via a PID controller or a state regulator, a manipulated variable V _control. This manipulated variable is v _tax then the position controller 14 the controller 2 to a speed controller 18 passed in a digital power level PS. The speed controller 18 in turn is also connected to the tachometer generator TG and receives a signal _TG v, so the actual speed of the electric motor M which is proportional to the actual velocity v _is substantially the cross slide 7 in the x direction. The tachogenerator TG is, for example, a rotary transformer which generates a voltage corresponding to the rotational speed of the electric motor M.

A control error is generated by subtracting the V _control is also returned by the tachometer generator TG _TG signal v of the manipulated variable. The speed controller 18 then calculates from this control deviation via an algorithm that simulates a PID controller, a manipulated variable I _a , which corresponds to a drive current to be set. This second manipulated variable I _a is passed on to an actuator SR in the digital power stage PS. Due to the drive current I _{a to be set} , the actuator SR then adjusts the drive current which flows through the electric motor M via the electrical connections C1 and C2. The lines C1 and C2, which connect the electric motor M with the actuator SR, via a two-pole relay R2 (or two field effect transistors) out, this bipolar relay R2 is connected during normal operation so that along the line C1 and along the line C2 can flow current. In addition, a single-pole relay R3 (or a field-effect transistor) is provided between the lines C1 and C2, which is open during normal operation. This relay R3 can be turned on in the event of a collision, so that then the lines C1 and C2 are short-circuited. On the input side, the actuator SR is connected in the power stage PS via lines C3 and C4 via a two-pole relay R1 (or two field effect transistors) to a power supply unit EV. This power supply unit EV may, for example, comprise a transformer and a rectifier. The energy supply unit EV is in this case fed via a mains connection PN, which can be connected to an electrical AC power supply network.

The digital power stage PS also has a current measuring device IM or is combined with such a current measuring device with which the drive current I _ist flowing through the electrical connections C1, C2 and through the electric motor M can be measured.

During operation of the coordinate measuring machine, the digital power level PS thus corresponds to that of the position controller 14 predetermined control variable v _controlled or more accurately corresponding to the speed control by the 18 From this determined manipulated variable I _a the drive current in the electrical connections C1, C2 and controls it, wherein the digital power stage PS continuously or quasi continuously evaluates the tacho signal v _TG generated by the tachogenerator TG. The electric motor M used here in the exemplary embodiment is a DC motor. Of course, other electric motors can be used, such as three-phase motors.

In addition, a collision monitoring circuit is realized according to the invention, which in case of a collision of the second measuring carriage (ie the cross slide 7 ) or the third measuring slide (Quill 8th ) or attached to the sensor nine with a person or an object automates the complete mechanics 3 brings to a halt. This is in the controller 2 a current limit detection means 15 also provided by the reading head 20 determined scale positions x _is the linear scale 6 in the coordinate direction x reads. The current limit detection means 15 determined from the measured actual position x _is then via an algorithm that is detailed below in detail 3 will be explained, an upper current limit I _max and a lower current limit I _{min of} a threshold band. The thus calculated upper current limit value I _max and the calculated lower current limit value I _min are now determined by the current limit value determination device 15 to a comparator 16 transmitted. In addition, the electric drive current I _{ist of} the electric motor M actually measured in the digital power stage PS _{is applied} to the comparator 16 transmitted. The comparator 16 , In turn, a microcontroller, checks now whether the actual measured drive current I _is the upper current limit I _max of the current limit band exceeds or lower current limit I "exceeds" _min of the current limit band.

As already explained in detail in the introduction to the description, this comparison takes place in the sense of a review. The determination of the upper current limit value I _max and the lower current limit value I _{min of} the current limit value band in the current limit value determination device 15 (See the explanations to 3 ) require a certain amount of computing time. Thus, the determined expected current I _erw applies and thus the upper current limit I _max and the lower current limit I _{min of} the current limit band for a time which is a few milliseconds in the past. Therefore, the upper current limit I _max and the lower current limit I _{max of} the current limit band should always be compared with a measured drive current I _ist , which is several clock cycles in the past. This can simply be realized by successively measured values of the drive current I _is at regular intervals in the comparator 16 are stored and the respective current values of the upper current limit value I _max and the lower current limit value I _min lying with a few clock cycles in the past stored value of the measured drive current I _is compared.

Unless the comparator 16 determines that the actually measured driving current _I exceeds the upper current limit value I _max of the current limit band or the lower current limit value "exceeds" I _min of the current limit value band, transmitted to the comparator 16 to the relay R1, to the relay R2 and to the relay R3 a signal OFF. As a result, open both the relay R1, as well as the relay R2, the conductive connections, so that in this way both the power of the power stage PS and in particular the power supply of the electric motor M is interrupted. In addition, the relay R3 is closed, so that thereby the motor M is short-circuited. This is the second measuring carriage (cross slide 7 ) and the third measuring slide carried by it (quill 8th ) with the attached thereto sensor nine very quickly to a standstill. As a result, this is the movement of the mechanics 3 stopped in the driven by the electric motor M x-direction.

The OFF signal is also sent to the drive of the first measuring carriage (Portal 4 ) for the y-direction and to the drive of the third measuring slide (quill 8th ) for the z-direction. These drives are quite analogous to those in 2 shown drive for the moving in the x-direction second measuring slide (cross slide 7 ), so that here too the corresponding relays are actuated accordingly via the signal OFF. As a result, the drive current for the electric motors of the drive in the y-direction and the drive in the z-direction is switched off and thus the movement of the mechanism 3 also stopped in the driven by the corresponding electric motor y-direction and driven by the corresponding electric motor z-direction.

The concrete function of the current limit detection device 15 out 2 is, as already stated above, now with reference to 3 explained in more detail. 3 shows the individual steps in detail. The current limit detection means 15 calculated according to step 30 From the measured actual positions x _, the actual velocity v _is by differentiation of these actual positions according to time: v _is = Δx _is / Δt

In step 31 determines the current limit detection means 15 by differentiation of the actual Velocity v _is after time the actual acceleration a _is in x-direction: a _is = Δv _is / Δt

In one step 32 is then determined from the thus actual speed _v and the detected actual acceleration a _(v, a _is) through a function I _ext, of the actual velocity v _is in the shown embodiment and the determined actual acceleration a _is dependent, an expected drive current I _erw determined. The function used here by way of example is as follows: I _erw (v _is , a _is ) = R ^± + v _is · K _v + a _is · K _a (Equation 10)

R^±

= ein von der Geschwindigkeitsrichtung der Ist-Geschwindigkeit (v_ist) abhängiger Grundanteil (R^±), wobei dieser richtungsabhängige Grundanteil (R^±) einen ersten konstanten Wert (R⁺) annimmt, wenn die gemessene Ist-Geschwindigkeit (v_ist) positiv ist und einen zweiten konstanten Wert (R^–) annimmt, wenn die gemessene Ist-Geschwindigkeit (v_ist) negativ ist.

v_ist

= gemessene Ist-Geschwindigkeit

K_v

= Proportionalitätsfaktor für den variablen Geschwindigkeitsanteil, wobei dieser den Anstieg des Antriebsstroms in Abhängigkeit von der Ist-Geschwindigkeit beschreibt

a_ist

= gemessene Ist-Beschleunigung

K_a

= Proportionalitätsfaktor für den variablen Beschleunigungsanteil, wobei dieser den Anstieg des Antriebsstroms in Abhängigkeit von der Ist-Beschleunigung beschreibt

Hereby means:

R ^±

= a fundamental component (R ^± ) dependent on the velocity direction of the actual velocity (v _ist ), this directionally dependent fundamental component (R ^± ) assuming a first constant value (R ⁺ ) when the measured actual velocity (v _ist ) is positive and assumes a second constant value (R ^- ) when the measured actual speed (v _is ) is negative.

v _is

= measured actual speed

K _v

= Proportionality factor for the variable speed component, which describes the increase of the drive current as a function of the actual speed

a _is

= measured actual acceleration

K _a

= Proportionality factor for the variable acceleration component, which describes the increase of the drive current as a function of the actual acceleration

The constants R ⁺ , R ^- , K _v and K _a can be determined relatively easily here. The constant R ⁺ is determined by the cross slide 7 is moved at a very low speed in the positive x-direction and via the drive current sensor IM in this case the driving current I _is measured. The case measured drive current I _is equal to the constant R ^+. The constant R ^- is analogously determined by the cross slide 7 is moved at very low speed in the opposite direction, ie in the negative x-direction and the driving current I flowing through the drive current sensor IM _is measured. The measured drive current corresponds to the constant R ^- .

The proportional velocity factor K _v for the variable velocity component is determined after R ⁺ and R ^{- are} determined. This is the cross slide 7 At approximately constant speed v _is traversed either in the positive x-direction or in the negative x-direction and meanwhile via the drive current sensor IM of the here running drive current I _is measured. Since the velocity is constant, the acceleration a _is then zero. When moving in the positive x-direction, the following relationship must arise from the above-mentioned function: I _erw (v _is , a _is ) = R ⁺ + v _is · K _v

By changing the equation, the result is: K _v = (I _ext - R ⁺⁾ / v _is

Since the proportionality factor K _v for the variable speed component is determined here, of course, the measured drive current I _ist must be used instead of the expected drive current in this equation, ie K _v = (I _is - R ⁺⁾ / v _is

The proportionality factor K _a for the variable acceleration component is then determined after R ⁺ and R ^- and K _{v have been} determined. This is the cross slide 7 with approximately constant actual acceleration a _is either in the positive x direction or the negative x direction process, during which at a time the actual speed _is v, the actual acceleration _is a and the driving current sensor in the case flowing driving current I _is measured. When moving in the positive x direction, the following relationship must result from the above-mentioned function I _erw (v _ist , a _ist ): I _erw (v _is , a _is ) = R ⁺ + v _is · K _v + a _is · K _a

By changing the equation, the result is: K _a = (I _ext - R ⁺ - _v · K _v) / a _is

Since the proportionality factor K _a for the variable acceleration component is determined here, of course, the measured drive current I _ist must be used instead of the expected drive current I _erw in this equation, ie K _a = (I _is - R ⁺ - _v · K _v) / a

Now that the factors R ⁺ , R ^- , K _v and K _{a have been} determined, an expected value for the drive current I _erw can now be calculated by measuring the respective actual speed v _ist and the respective actual acceleration a _is from equation 10 , On the basis of the thus calculated expected drive current I _erw, in turn, in step 33 an upper current limit I _max and a lower current limit I _min determined. To determine the upper current limit I _max is the expected Drive current I _erw in the simplest case, a constant current value d added: I _max = I _erw + d

In order to determine the lower current limit value I _min , a constant current value e is subtracted from the nominal drive current I _erw in the simplest case: I _min = I _exp - e

The current values d and e are constant in the present embodiment and equal in magnitude.

4 shows, purely by way of example a representation of the actual current flowing the drive current I _and the expected driving current I _erw and determined therefrom, the upper current limit value I _max and the lower current limit value I _{min to} v for an arbitrary example of a curve of target velocity for in connection with 2 and 3 explained circuit. Same names as in the 2 and 3 were here provided with the same reference numerals. In the exemplary embodiment described here, the setpoint speed v _is , as described above in connection with FIG 2 described the component of the velocity vector in the x direction, that of the spline interpolator 25 the controller 2 _is predetermined by the successive to be approached nominal positions x.

At time t _0, ie at the left edge of the diagram, the target speed values begin _to v (see dash-dot line) to increase linearly from a first speed value. The linear increase continues until the time t _{1 is} reached. In accordance with the linear increase of the setpoint speed v _soll , the setpoint acceleration a _soll in the x direction is therefore constant. In order to actually achieve this target acceleration, the associated electric motor M must be supplied with a slightly higher current. Accordingly, the actual driving current in the motor M runs (this corresponds to the measured current _I, see the dashed line with the reference numeral I _ist), at a higher level. By the reference I _erw (see solid line with the reference I _erw ), however, the expected drive current is referred to by the current limit detection device 15 v _is from the real actual speed and the actual acceleration a _is determined was (see step 32 in 3 ). Based on this expected drive current I _erw was from the current limit detection device 15 In addition, the upper current limit I _max and the lower current limit I _{min of} the current limit band determined.

The upper current limit I _max in the time interval [t ₀ ; t ₁ ] is reasonably constant at a slightly higher value. By contrast, the lower current limit I _min is even in the negative range. If this upper current limit I _{max of} the current limit band _is exceeded by the actually measured drive current I ist or if this current limit value I _{max is} reached, appropriate measures are taken. These measures are also initiated if the lower current limit I _{min of} the current limit band of the actual current I _{ist is} exceeded or if this current limit I _{min is} reached.

At the end of the first acceleration phase, at time t ₁ , the actual speed v has reached a value which corresponds approximately to the setpoint speed v _soll . In the further course of the movement (or motion component in the x-direction) of the target velocity v remains _to be constant until the end of the diagram. Accordingly, the driving current I _is then drops to a slightly lower value and then remains approximately constant. Although acceleration no longer takes place from time t ₁ , a relatively high drive current is still required. This must essentially be applied because the movement of the electric motor M and the moving parts driven by the motor, ie in particular the second measuring slide (cross slide 7 ), does not run smoothly. The upper current limit I _max hereby drops to a lower level than during the acceleration phase in the time interval [t ₀ ; t ₁ ].

At this point, it should be expressly mentioned again that the described procedure is purely an exemplary embodiment, which can vary widely, as was explained in detail in the introduction to the description. For example, instead of the in 2 and 3 Current limit band used with an upper current limit I _max and a lower current limit I _min only a current limit can be used.

The following will be related to 5 explains what happens in the event of a collision. 5 shows here in much the same way as 4 by the dotted line with the reference numeral v _is to be traveled speed profile according to the target speed of the movable in the x-direction second measuring carriage (cross slide 7 ), please refer 1 and 2 , It is also in 5 the actual flowing current I _is indicated by the electric motor M as a dashed line. Also plotted is that of the current limit detection device 15 determined expected drive current I _erw , and the upper current limit I _max and the lower current limit I _{min of} the current limit band, the upper current limit I _max and the lower current limit I _{min of} the current limit band from the current limit detection means 15 to the comparator 16 is delivered.

• a) Zum einen wird die Ist-Geschwindigkeit des zweiten Messschlittens (Querschlitten 7) stark verringert. Die Stromgrenzwert-Ermittlungseinrichtung 15 ermittelt deshalb aus den Positionsmesswerten x_ist eine negative Ist-Beschleunigung a_ist (also eine Bremsbeschleunigung) und eine verringerte Ist-Geschwindigkeit v_ist. Hierdurch wird folglich ein verringerter Wert für den erwarteten Antriebsstrom I_erw ermittelt, was gleichzeitig zu einer Absenkung des oberen Stromgrenzwertes I_max und des unteren Stromgrenzwertes I_min des Stromgrenzwertbandes führt.
• b) Zum Anderen versucht der Geschwindigkeitsregler 18 der digitalen Leistungsstufe PS der vom Lageregler 14 übermittelten Stellgröße v_steuer zu folgen und erhöht zusätzlich die Stellgröße I_a für den Antriebstrom im Elektromotor M, so dass der gemessene Antriebstrom I_ist zusätzlich noch ansteigt.

As can be seen from the diagram _, the second measuring carriage (cross slide 7 ) in the x-direction from a first speed value to a maximum speed value, and then remain constant. In the diagram shown here, however, collides the second measuring slide (cross slide 7 ) at time t _k with an object. This has the following result:

• a) First, the actual speed of the second measuring slide (cross slide 7 ) greatly reduced. The current limit detection means 15 therefore determined from the measured position values x _is a negative actual acceleration _a (that is, a deceleration) and a reduced actual speed _v. As a result, a reduced value for the expected drive current I _erw is consequently determined, which simultaneously leads to a lowering of the upper current limit value I _max and the lower current limit value I _{min of} the current limit value band.
• b) On the other hand, the speed controller tries 18 the digital power level PS of the position controller 14 V _control to follow control value transmitted and additionally increases the manipulated variable I _a for the driving current in the electric motor M, so that the measured driving current I _is additionally increased.

Thus, the actual flowing current I _is at time t _s1 exceeds the upper current limit I _max . From this time t _s1 the comparator goes 16 (see also 2 ) assumes that there is a collision and sends a signal OFF to the relay R1, the relay R2 and the relay R3 (see also 2 ), whereby, as already described above, the power supply to the power stage PS and in particular to the electric motor M is turned off and whereby the electric motor is short-circuited. As a result, the drive current I _is from the time t _{s1 from} strong and the motor M comes to a standstill.

In connection with 6 will now detail one of the particular advantages of the method according to the invention over that of the document US Pat. No. 7,627,957 B2 shown known methods. The representation after 6 is almost identical to the content 5 so that the explanations to 5 analogous to 6 be valid. about 5 going out is in 6 additionally a dotted curve with the reference I _{max-prior-art} drawn. This curve shows, by way of example, an upper current limit, which is based on the desired speed v _soll and the desired acceleration a _soll according to the method according to the document US Pat. No. 7,627,957 B2 could be determined. In addition, for the measured drive current I _{-prior art,} the curve is drawn, which would result from the upper current limit value of the drive current I _{max-prior-art} . As can be seen from this graph, the upper current limit value I _{max-prior-art} remains even after the time of the collision t _k unchanged because the upper current limit value precisely not based on the detected actual acceleration _a, and the measured actual velocity v _is determined, but based on the immutable, from the spline interpolator 25 determined target speed v _soll and the target acceleration a _soll . Thus, the measured drive current I _{ist-prior art} according to the conventional solution would have exceeded the upper current limit I _{max-prior-art} only at time t _s2 . As this example shows very impressively, by determining the current limit value or the current limit band from the actually measured actual velocity v _ist and / or the actually measured actual acceleration a _, therefore, a collision can be detected earlier, namely at time t _s1 ,

The drive current sensor IM in the digital power stage PS is constructed, for example, as related to 7 shown. An ammeter MA supplies an analog measurement signal, which is optionally supplied to an analog / digital converter AD via an analog filter AF for temporal smoothing of the measurement signal. In the converter AD, the analog signal is converted into a digital signal and time-smoothed via another optional digital filter DF. This smoothed, digital measurement signal is, as in connection with 2 to see the comparator 16 as measured drive current I _is supplied.

As mentioned above, the embodiment is in the context of a DC motor M (see 2 ). Instead of course, however, other electric motors can be used, such as three-phase motors or linear motors. In such three-phase motors and also in linear motors all three phases of the alternating voltage network are used. The current proportional to the generated torque of the electric motor can be easily determined in such electric motors, since the provided by the suppliers of such three-phase motors or linear motors available digital power levels to calculate the actually generated torque of the electric motor drive current and provide as a digital value. This provided by the digital power level value of the drive current can be further processed as well as the value measured by sensor drive current IM drive current I _is.

8th shows a purely schematic representation of the drive of the movable in the x-direction cross slide 7 with one opposite 2 together with the measuring computer 13 and the controller 2 with a changed structure. This is very similar to the presentation 2 , wherein the same components have been given the same reference numerals. A significant difference 2 This can be seen in the fact that the position controller 14 the controller 2 has now been completely shifted to the digital power level PS. The background to this is that increasingly providers offer digital power levels PS, which not only integrate the speed control of the controlled electric motor, but also take over the speed control loop upstream position control. The regulator 23 therefore assumes the function of the position controller 14 according to 2 and the downstream function of the speed controller 18 out 2 , Accordingly, now that of the read head 15 Delivered position x _is the second measuring slide (cross slide 7 ) to the controller 23 delivered. Instead of the position controller 14 out 2 now provides the spline interpolator 25 The setpoint positions x _to be approached in the x direction _{should be sent} directly to the controller 23 the digital power stage PS. Although virtually the entire attitude control and the speed control in the controller 23 the digital power stage PS has been shifted, the collision protection circuit operates completely unchanged, as described above in connection with 2 to 6 was explained. It is therefore still based on the measured actual position x _is by the current limit detection device 15 an expected drive current I _erw and therefrom an upper current limit I _max and a lower current limit I _min determined and the upper current limit I _max and the lower current limit I _min then to the comparator 16 delivered. The comparator 16 then again compares the upper current limit I _max and the lower current limit I _{min of} this current limit band with the measured drive current I _ist and sends a signal OFF when the measured drive current I _{ist of} the upper current limit I _max or the lower current limit I _{min is} exceeded. The signal OFF is from the comparator 16 transmitted to the relays R1, R2 and R3, whereby the drive current of the motor M is turned off, as described in detail above. This will cause the movement of the mechanics 3 stopped in the driven by the electric motor x-direction.

In addition, the signal OFF also, as above for 2 described to the drives for the first measuring carriage (Portal 4 ) in the y direction and for the third measuring slide (quill 8th ) in z-direction, whereby also here the drive current of the corresponding motors is switched off. This will cause the movement of the mechanics 3 also stopped in the driven by the corresponding electric motor y-direction and driven by the corresponding electric motor z-direction.

in the nine is now still a representation of the actual flowing drive current I _is and the expected drive current I _erw for an exemplary course of the desired speed v _soll of in 2 or 8th shown second measuring slide (cross slide 7 ). As can be seen from the dot-dash line with the reference v _soll , the cross slide 7 in the time interval [t _e0 ; t _e1 ] is constantly accelerated from a standstill in the positive x-direction, then in the time interval [t _e1 ; t _e2 ] is moved at a constant speed, in the time interval [t _e2 ; t _e3 ] with a constant negative acceleration braked to a standstill. In the time interval [t _e3 ; t _e4 ] is the cross slide 7 then quiet. In the time interval [t _e4 ; t _e5 ] becomes the cross slide 7 then from standstill in the opposite direction, ie in the negative x-direction constant accelerated, then in the time interval [t _e5 ; t _e6 ] moves at a constant speed, and in the time interval [t _e6 ; t _e7 ] with a constant deceleration braked again to a standstill. The current limit detection device 15 (please refer 2 or 8th ) determined expected drive current I _erw (see step 32 in 3 ) is shown here as a solid line with the reference I _erw . Also shown is the actual measured drive current I _is as a dotted line. The determination of the expected drive current I _erw by the current limit detection device 15 is so good that the deviations in one and the same diagram are very difficult to see. Therefore, in nine only those points of the actually measured driving current I _is shown as a dotted line, in which significant deviations of the measured drive current I _is to give _erw from the expected driving current I. These three deviations (two of them in the time interval [t _e3 ; t _e4 ] and one after the time t _e7 were explicitly designated by the reference symbol I _ist .) The wavy course of the expected drive current I _erw and the measured drive current I _is due to result that, in particular during acceleration oscillations. as the expected driving current I _ext from the measured actual speed _is v and the measured actual acceleration a _is derived, this vibration to flow into the calculation of the expected driving current I _erw with one, so that the expected Drive current I _erw mostly very well with the actually measured drive current I _is consistent.

In contrast, in 10 for exactly the same course of the target speed v _soll according to nine by way of example an expected drive current I _{erw-prior art shown} as a solid line, which according to the method of the publication US Pat. No. 7,627,957 B2 would be determined from the desired speed and the target acceleration. As can be seen directly from the course of the expected drive current I _prior-art , in this way in particular the oscillations which the actually measured drive current I _ist has not been detected. The reason is that this drive is current I _{ext-prior-art} from the target speed v _will and the target acceleration a _will have been determined so that actual vibrations thus will not be considered.

11 corresponds to the presentation 10 , wherein additionally the actually measured drive current I _{ist is} shown. As can be seen from this, the actually measured drive current I _ist deviates relatively strongly from the expected drive current I _{erw-prior-art} due to the oscillations. Although this is unproblematic insofar as the upper and lower current limit can simply be spaced far enough from the expected drive current I _{erw-prior art} . By the inventive determination of the expected drive current I _erw based on the actual measured actual speed and / or the actual acceleration of the expected drive current I _erw much more accurate with the actual measured motor current I _is equal, so that the upper current limit and the lower current limit closer to the expected drive current I _erw can be brought closer and a collision can be detected earlier.

With regard to the course of the measured drive current I _is in nine and 11 the following comments have to be made. In the time interval [t _e0 ; t _e1 ] increases the drive current I _is initially jumped to a relatively high level and then increases with a lower slope until the end of this time interval. The reason for this is that to generate the constant acceleration in this interval due to the increasing speed and thereby increasing friction forces of the effort increases. In the time interval [t _e1 ; t _e2 ] the measured drive current I _{ist is} lowered to a lower level, which drive current is required to overcome the frictional forces occurring at the respective constant speed. In the time interval [t _e2 ; t _e3 ], the measured drive current I _is then even negative in order to achieve the necessary constant, negative deceleration. The amount of drive current I _is increasing in the time interval [t _e2 ; t _e3 ] because the friction forces in the cross slide are slowing down at a slowing speed 7 decrease and therefore the braking acceleration increasingly by the electric motor 7 must be generated. In the time interval [t _e3 ; t _e4 ] is then the cross slide 7 out 2 quiet again. The particular from nine good visible relatively high drive current shortly after reaching standstill stems, therefore, because of the cross slide 7 is already at a standstill and between the spline interpolator 25 predetermined target position x _soll and the actually measured actual position x _is a control deviation is present, the position controller 14 out 2 in the form of a manipulated variable v control to the speed _controller 18 passes. This then causes a manipulated variable I _a for the drive current, which is relatively high, because to move the cross slide 7 the friction must be overcome. The remarks made then apply analogously to the following time intervals, which show practically the same velocity profile only in the opposite direction of travel (ie in the negative x-direction).

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

• US 7627957 B2 [0002, 0005, 0118, 0118, 0124]
• US 2011/0192044 A1 [0005]
• DE 10024976 A1 [0006]

Claims (19)

Method for operating a coordinate measuring machine ( 11 ), whereby a mechanism ( 3 ) for adjusting a sensor ( nine ) relative to a workpiece support ( 1 ) is provided in at least one direction (x) and this mechanism ( 3 ) has at least one electric motor (M) via which the adjustment of the sensor ( nine ) or the workpiece support ( 1 ) is driven in this direction and wherein the method comprises the following steps: a) an electrical drive current (I _is ) flowing through the electric motor (M) to a movement of the electric motor (M) and in this way a movement of the sensor ( nine ) or the workpiece support ( 1 ) is measured, b) an actual speed (v _ist ) and / or an actual acceleration (a _ist ) of the sensor ( nine ) or the workpiece support ( 1 ) in the direction (x) driven by the electric motor (M) is measured c) depending on the measured actual speed (v _ist ) and / or depending on the measured actual acceleration (a _is ) is a current limit (I _max ) or a current limit band (ie, a range of values for the drive current defined by a lower current limit I _min and an upper current limit I _max ) for the drive electric current, and d) if the drive electric current is the current limit determined in step (c) (I _max ) reached and / or if the electric drive current exceeds the determined current limit (I _max ) or if the current limit band (I _min , I _max ) is left, the movement of the mechanism ( 3 ) stopped at least in the direction driven by the electric motor. A method according to claim 1, wherein an expected drive current (I _erw ) is determined for determining the current limit value or the current limit band from the actual speed (v _ist ) and / or from the actual acceleration (a _ist ), which corresponds to an expected value for the Actual electric drive current that _is expected for the current actual speed (v _is ) and / or the current actual acceleration (a _is ). The method of claim 2, wherein in determining the expected drive current (I _erw ) a variable speed component (K _v · v _is ) is taken into account, which is proportional to the measured actual speed (v _is ). Method according to one of claims 2 or 3, wherein in determining the expected drive current (I _erw ) a variable acceleration component (K _a · a _is ) is taken into account, which is proportional to the measured actual acceleration (a _is ). Method according to one of claims 2 to 4, wherein in the determination of the expected drive current (I _erw ) additionally a basic component (R) is taken into account, which corresponds to a drive current, which upon movement of the sensor ( nine ) or the workpiece support ( 1 ) in the direction driven by the electric motor at a low constant speed. Method according to Claim 5, in which the basic component is either a constant fundamental component (R *) independent of the direction of velocity of the actual velocity, or a fundamental component (R ^± ) dependent on the velocity direction of the actual velocity (v _ist ), and this direction-dependent background component (R ^±) takes a first constant value (R ⁺⁾ if the measured actual speed (v _ist) is positive and a second constant value (R ^-) assumes when the measured actual speed (v _ist) is negative. The method of claim 3, 4 and 6, wherein the expected drive current (I _erw ) is determined with the following function I _erw (v _is , a _is ): I _erw (v _is , a _is ) = R + v _is · K _v + a _is · K _a where: R = the constant basic component (R *) or the directional basic component (R ^± ) K _v = proportionality factor for the variable speed component v _ist = measured actual velocity K _a = proportionality factor for the variable acceleration component a _ist = measured actual acceleration Method according to one of claims 2 to 7, wherein in the determination of the current limit value (I _max ) or a first current limit value of the current limit band (I _max , I _min ), the expected drive current (I _erw ) is increased by a first current value (d), the amount of the current limit value (I _max ) or the magnitude of the first current limit value of the current limit band (I _max , I _min ) is higher than the amount of the expected drive current (I _erw ). Method according to Claim 8, in which, in order to determine the second current limit value of the current limit band (I _max , I _min ), the expected drive current (I _erw ) is additionally reduced by a second current value (e) such that the magnitude of the second current limit value of the current limit band ( I _max , I _min ) is less than the amount of the expected drive current (I _erw ). Method according to claim 8 or 9, wherein the first current value (d) and / or the second current value (e) are constant. Method according to one of the preceding claims, wherein the measured actual speed (v _ist ) is determined from the time derivative of a measured actual position (x _ist ) and / or the measured actual acceleration (a _is ) from twice the time derivative of a measured actual position (x _is ) is determined. Method according to the preceding claim, wherein the electric drive current is switched off when the electric drive current continuously reaches and / or exceeds the determined current limit value (I _max ) over a time interval of predetermined length or the determined current limit band (I _max , I _min ) continuously via Time interval of predetermined length leaves. Method according to one of the preceding claims, wherein in step (d) according to claim 1, a value is used as the electric drive current which has been obtained after smoothing of temporal fluctuations of the measured value determined in step (a). Method according to one of the preceding claims, wherein a functional relationship between the actual speed (v _ist ) and / or the actual acceleration (a _is ) on the one hand and the current limit value (I _max ) on the other hand additionally determined by one or more parameters, the are uniquely determined by one or more of the factors listed below: an ambient temperature, a temperature of parts of the coordinate measuring machine ( 11 ), a position of the sensor ( nine ) and / or the workpiece support ( 1 ) in a fixed coordinate system, a relative position of the sensor ( nine ) or the workpiece support ( 1 ) with respect to the workpiece ( 5 ) or in relation to other parts of a measurement setup and / or an operating state of the coordinate measuring machine ( 11 ). Method according to one of the preceding claims, wherein, before the electric drive current is turned off, a current direction of the electric drive current is first reversed. Method according to one of the preceding claims, wherein a plurality of electric motors (M) is provided to control the movement of the sensor ( nine ) relative to the workpiece support ( 1 ), wherein the movements of the electric motors (M) clearly movement components (x, y, z) of the movement of the sensor ( nine ) and / or the workpiece support ( 1 ) Can be assigned, wherein the steps (be carried out separately to (d) of claim 1 for each of the plurality (of electric motors M) a), wherein the actual speed (v _ist) and / or actual acceleration (a _ist) in steps (b and c) in each case for the movement components (x, y, z) are measured and depending on which the current limit (I _max ) or the current limit band (I _max , I _min ) is determined. Coordinate measuring machine ( 11 ), with a mechanism ( 3 ), a workpiece support ( 1 ) for receiving a workpiece to be measured ( 5 ) and a sensor ( nine ), whereby the sensor ( nine ) and the workpiece holder ( 1 ) of mechanics ( 3 ) relative to each other in at least one direction (x) is adjustable, wherein the mechanics ( 3 ) has at least one electric motor (M) via which the adjustment of the sensor ( nine ) or the workpiece support ( 1 ) is driven in this direction (x), and wherein the coordinate measuring machine ( 11 Comprising): (a) a current measuring device (IM), which is designed to provide an electrical drive current (I _ist) flowing through the electric motor (M) to a movement of the electric motor (M) and in this way a movement of the sensor ( nine ) or the workpiece support ( 1 ), (b) an actual speed measuring device ( 20 . 15 , Step 30 ), which is designed to be the actual speed (v _ist ) of the sensor ( nine ) or the measuring support in the direction driven by the electric motor and / or an actual acceleration measuring device ( 20 . 15 , Steps 30 . 31 ), which is designed to be the actual acceleration (a _ist ) of the sensor ( nine ) or the measuring pad ( 1 ) in the direction driven by the electric motor (M), (c) a current limit detecting means (Fig. 15 , Steps 32 . 33 ) configured depending on a measured actual speed (v _ist ) and / or dependent on a measured actual acceleration (a _is ), a current limit (I _max ) or a current limit band (ie a range of values for the drive current , which is defined by a lower current limit I _min and an upper current limit I _max ) for the electric drive current, and (d) an actuator ( 16 , R1, R2, R3), which are connected to the current measuring device (IM) and to the current limit value determination device (FIG. 15 ) connected and which is designed, the movement of mechanics ( 3 ) stop, at least in the direction driven by the electric motor, when the electric drive current (I _is ) exceeds that of the current limit detection device ( 15 ) Determined current threshold (I _max) and / or if the electrical drive current to (from the current limit determination means 15 ) Determined current threshold (I _max), or if the drive current, the current limit value band (I _min, I _max) leaves. Coordinate measuring machine according to the preceding claim, wherein the actuating device comprises a switch-off device ( 16 , R1, R2, R3) connected to the current measuring device (IM) and to the current limit value determination device ( 15 ) and which is configured to switch off the electrical drive current when the electric drive current reaches the determined current limit value (I _max ) and / or when the electric drive current exceeds the determined current limit value (I _max ) or if the drive current exceeds the current limit band (I _max , I _min ) leaves. Coordinate measuring machine according to claim 13 or 14, wherein the current limit value determining device ( 15 ) is configured to carry out the method according to one of claims 2 to 11.

Images