Method for the offline and/or online identification of a state of a machine tool, at least one of its tools or at least one workpiece machined therein

Abstract

A machine tool includes a tool and a workpiece machined by the tool, and sensors configured to detect a position of the tool and/or the tool holder holding the tool in a spatially and time resolved manner A method for offline and/or online identification of a state of the machine tool includes: a) detecting or providing positions p.sub.i of the tool and/or of the tool holder at a series of points in time i, i=1 . . . n; b) determining for the series of points in time i a series of position changes ?m.sub.i according to the formula ?m.sub.i=p.sub.i/p.sub.i-1 and a series of speed changes ?v.sub.i according to the formula ?v.sub.i=v.sub.i/v.sub.i-1 with $v_i=\frac{P_i-P_{i-1}}{t_i-t_{i-1}}$
and formula $v_{i-1}=\frac{P_{i-1}-P_{i-2}}{t_{i-1}-t_{i-2}};$
c) identifying the state of the tool, the tool holder, the machine tool and/or the workpiece machined in the machine tool based on the position changes ?m.sub.i and the speed changes ?v.sub.i.

Claims

1. A method for operating a machine tool and processing a workpiece in the machine tool, the method comprising: processing the workpiece with the machine tool, and identifying an operating state of the machine tool, either offline or online, with a control system of the machine tool by: a) for a series of time points t.sub.i, detecting positions p.sub.i of a tool of the machine tool or of a tool holder of the machine tool configured to hold the tool, with the positions being expressed as coordinates of a Cartesian coordinate system, wherein at least a position of the tool or of the tool holder is detectable by a sensor as a function of time, b) for the series of time points t.sub.i, establishing b1) a series of position changes ?m.sub.i of the tool, of the tool holder or of a preferably rotatable clamping apparatus of the machine tool configured to clamp the workpiece to be processed, in accordance with $?m_i=\frac{P_i}{P_{i-1}},$ and b2) a series of speed changes ?v.sub.i the tool, of the tool holder or of the clamping apparatus in accordance with $?v_i=\frac{v_i}{v_{i-1}},\mathrm{wherein}$ $v_i=\frac{P_i-P_{i-1}}{t_i-t_{i-1}}\mathrm{and}{v}_{i-1}=\frac{P_{i-1}-P_{i-2}}{t_{i-1}-t_{i-2}},$ determining for the position changes ?m.sub.i the respective components ?m.sub.xi, ?m.sub.yi, ?m.sub.zi and for the speed changes ?v.sub.i the respective components ?v.sub.xi, ?v.sub.yi, ?v.sub.zi in the Cartesian coordinate system, and c) identifying the operating state of the machine tool based on the position changes ?m.sub.i and the speed changes ?v.sub.i, wherein the operating state of the machine tool represents at least one of a movement of the tool or of the tool holder, a rest phase of the tool or of the tool holder, and a deviation from a predetermined movement speed of the clamping apparatus, and controlling the machine tool by the control system based on the identified operating state of the machine tool to optimize the processing of the workpiece.

2. The method of claim 1, wherein the operating state represents d) the movement of the tool and/or the tool holder d1) for processing the workpiece, in particular for carrying out cutting sequences, d2) for repositioning the tool, in particular for carrying out return movements, and d3) for changing the tool, e) a standstill time or an idle time, or f) a deviation from override commands.

3. The method of claim 1, further comprising detecting electrical parameters of drive motors of the machine tool using additional sensors.

4. The method of claim 1, further comprising determining the operating state based on further data, in particular correction factors or tool parameters, provided or established in advance; and identifying the operating state utilizing the further data.

5. The method of claim 1, further comprising analyzing the series of the position changes ?m.sub.i or of the speed changes ?v.sub.i based on a limit value consideration.

6. The method of claim 1, further comprising identifying the operating state based on case distinctions, wherein it is tested whether a value for the position change ?m.sub.i or for the speed change ?v.sub.i, or of values of respective components ?m.sub.xi, ?m.sub.yi, ?m.sub.zi for the position changes ?m.sub.i or of respective components ?v.sub.xi, ?v.sub.yi, ?v.sub.zi for the speed changes ?v.sub.i in the Cartesian coordinate system are less than 1, equal to 1, greater than 1, or 0.

7. The method of claim 1, further comprising: representing the series of position changes ?m.sub.i or of the speed change ?v.sub.i in a diagram as characteristic lines or in a data array; and analyzing of the operating state of the machine tool based on the representation.

8. The method of claim 1, further comprising recognizing with the method g) overloading of one of the drives of the machine tool, h) wear on the machine tool or on the tool, i) a production or workpiece fault or j) process instabilities, in particular rattling (regenerative effect).

9. The method of claim 1, wherein the method is computer-implemented.

10. A machine tool comprising: a control system configured to carry out a method as set forth in claim 1.

11. A computer-readable non-transitory medium comprising commands which, when executed by a computer, cause the computer to carry out a method as set forth in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The above-described properties, features and advantages of the invention and the manner in which these are achieved will now be described more clearly and explicitly in relation to the following description of the exemplary embodiments of the invention, which are described in greater detail by reference to the drawings. The exemplary embodiments serve to explain the invention and do not limit the invention to the combinations of features given therein, also not in relation to functional features. In addition, features of each exemplary embodiment which are suitable therefor can also be considered explicitly in isolation, removed from an exemplary embodiment, introduced into another exemplary embodiment for its enhancement and combined with any of the claims.

(2) It is shown in:

(3) FIG. 1 a schematic representation of a machine tool,

(4) FIG. 2 the working space of the machine tool shown in FIG. 1,

(5) FIG. 3 a flow diagram for the method for identifying states of a machine tool,

(6) FIG. 4 the graphical representation of a machining process,

(7) FIG. 5 a matrix U with a series of position changes,

(8) FIG. 6 a characteristic line of the torque-creating current of the z-axis for the entire processing procedure of a workpiece, and

(9) FIG. 7 a characteristic line for the drive torque of the main spindle during a single processing operation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(10) In all the drawings, identical features are provided with the same reference characters.

(11) FIG. 1 shows, by way of example as a machine tool WM, a turning and milling CNC machine CM. The machine tool WM comprises a working space AR, which can be closed off by a sliding door TR, in which two spindles SP arranged opposite one another, a main spindle SP.sub.1 and a subsidiary spindle SP.sub.2 as clamping apparatuses AV, AV are provided for clamping a workpiece WS that is to be processed (FIG. 2). Also provided in the working space AR are two movable tool holders WH.sub.1, WH.sub.2, each of which can receive a plurality of tools (not shown here). The machine tool WM further comprises a control system BE for programming, controlling and monitoring its elements.

(12) FIG. 2 shows the working space AR and the elements arranged therein in detail. The two spindles SP.sub.1 and SP.sub.2 are arranged concentrically to one another and are arranged to be rotatable about their common longitudinal axis. They also each comprise a clamping apparatus AV with which a workpiece WS to be processed can be rotated. The machine tool WM further possesses two tool holders WH.sub.1 and WH.sub.2 which are spatially displaceable in all three spatial directions. The upper tool holder WH.sub.1 comprises, as a motorized milling spindle, just three stations whereas the tool holder WH.sub.2 arranged below, as a tool revolver, is equipped with a plurality of stations.

(13) In order to detect the positions, the control system BE of the machine tool WM uses a virtual Cartesian coordinate system KS with the three machine axes x, y and z arranged orthogonally to one another. The two spindles SP.sub.1 and SP.sub.2 and the clamping apparatuses AV arranged thereon are both rotatable about the z-axis and are also displaceable along the z-axis so that workpieces can be handed over, without support by a user, from the subsidiary spindle to the main spindle or vice versa.

(14) A magazine space MG which, in the representation shown is closed by a magazine door borders on the working space AR. A larger number of tools WZ, i.e. drills, mills and suchlike is arranged in the magazine space MG which, with the magazine door open can be grasped by the upper tool holder WH.sub.1 and replaced therein or can be returned.

(15) During its operation, the machine tool WM can be in different states, that is, operating states. A distinction should herein be made between, firstly, faulty operating states and, secondly, intended operating states, so-called normal operating states. An example of a faulty operating state is the state tool break. Other operating states indicating a fault are conceivable. Intended operating states, by contrast, for example machining process, idling, override command or tool change can be represented. An override command is understood to be a manual intervention by a user of the machine tool WM which accelerates or slows down the programmed sequence of a workpiece processing. Further intended operating states can also be sequences of the aforementioned operating states if, effectively, subsections thereof are (to be) recognized. By means of the operating states recognized by the method, subsequently an analysis and, where relevant, an optimization of the processing of the workpiece WS is possible.

(16) The workpiece can also be present in different states. With regard to the workpiece WS, by means of the method, a spatially-resolved identification of possible production errors is, for example, possible to reduce the effort for quality assurance.

(17) In order to establish the states, the machine tool WM is equipped with a plurality of sensors (not shown). With some of these sensors, the positions of the tool and/or the tool holder or even the clamping apparatuses can be established in a spatially and time-resolved manner. Typically, the detection of the position, i.e. the spatial coordinates P(x, y, z) of the clamping apparatuses AV and/or of the workpiece WS clamped therein, of the tool WZ and/or of the tool holders WH.sub.1, WH.sub.2 takes place for each machine axis separately by way of correspondingly suitable sensors.

(18) The position of the cutting edges of the tools WZ can, for example, also be established via the position of the tool holder in that the tool holder position is enhanced with previously provided data regarding the size of the tool in question. Similarly it is possible, for determining correction data, to measure the position of the cutting edges of the tool in the machine tool WM automatically. Further sensors are able to detect continuously the electric currents and supply voltages of the drive motors (not shown) of the machine tool by which the respective rotatable and/or displaceable elements can be driven, i.e. rotated and/or repositioned.

(19) Thus, the signals from these sensors contain data which can be captured during machine stoppages, tool changes, idling times, rapid transits, acceleration effects, the start of cut sequence and the actual machining process. The recorded data signals thus represent, inter alia, position data, drive parameters and drive power levels, correction factors or tool parameters.

(20) The method proposed for identifying states is shown schematically in FIG. 3, wherein further concepts necessary for characterization are defined in the following:

(21) The feed rate of an element can be calculated from the product of the existing feed (f) along the machine axis under observation and the associated rotary speed n, hereinafter represented, merely by way of example, for the x-axis:
v.sub.f,x=f.sub.x*n(1)

(22) For the position change of the element being observed that is necessary for state identification, the vector ?m is introduced, defined as the ratio, i.e. quotient, of its position at an arbitrary time point i to its previous position, therefore at the time point i?1. By way of example, this is set out in Equation 2 for the x-coordinate of the relevant element.

(23) $\begin{array}{cc}?m_x=\frac{x\left(i\right)}{x\left(i-1\right)}& \left(2\right)\end{array}$

(24) The method offers the possibility of being able to use the method offline and online.

(25) Furthermore, for the feed rate change in, for example, the x-direction, the relation shown in Equation 3 applies:

(26) $\begin{array}{cc}?v_{f,x}=\frac{v_{f,x}\left(i\right)}{v_{f,x}\left(i-1\right)}& \left(3\right)\end{array}$
wherein the speeds are established in accordance with

(27) $\begin{array}{cc}{v}_i=\frac{P_i-P_{i-1}}{t_i-t_{i-1}}\mathrm{and}{v}_{i-1}=\frac{P_{i-1}-P_{i-2}}{t_{i-1}-t_{i-2}}.& \left(4\right),\left(5\right)\end{array}$

(28) In a first method step 102 of the method 100 according to the invention, at a series of time points, the respective current position of the tool WZ and/or of the tool holder WH.sub.1, WH.sub.2 are captured and/or provided as data. The processing of this data which takes place in a second method step 104 according to the above Equations (1) to (5) can take place immediately as it arises, which enables an online identification of the state. Where a calculation and state identification for capture of the data take place temporally offset, this is regarded as an offline identification of the state. In a last method step 110, the identification of the state of the tool, the tool holder, the machine tool and/or the workpiece processed in the machine tool takes place on the basis of the previously established and/or provided position changes and speed changes.

(29) In principle, a distinction can be made between different cases, per machine axis and per element, for the position changes and the speed changes. Therein, it should firstly only be established in which directions the element moves. This can be established with the aid of Table 1 below. Otherwise, the position changes and the speed changes represent nothing other than the quotients of the raw data.

(30) TABLE-US-00001 TABLE 1 Meanings based upon the quotients Case Meaning ?m.sub.x < 1 Element travels in the negative x-direction ?m.sub.x = 1 Element travels at a constant x-level ?m.sub.x > 1 Element travels in the positive x-direction . . . . . . ?m.sub.z < 1 Element travels in the negative z-direction ?m.sub.z = 1 Element travels at a constant z-level ?m.sub.z > 1 Element travels in the positive z-direction ?v.sub.f, x < 1 Feed rate in x-direction decreasing ?v.sub.f, x = 1 Feed rate in x-direction constant ?v.sub.f, x > 1 Feed rate in x-direction increasing . . . . . . ?v.sub.f, z < 1 Feed rate in z-direction decreasing ?v.sub.f, z = 1 Feed rate in z-direction constant ?v.sub.f, z > 1 Feed rate in z-direction increasing

(31) Subsequently, on the basis of a combined consideration of two or more cases of the state, in particular the operating state of the machine tool at the observed time point of the series of time points can be established.

(32) Below, by way of example, some conditions are listed schematically on the basis of which the method can identify different operating states. a) Identification of return movements: If more than one machining process is carried out on a workpiece, then the tool must be returned to the starting point. In order to identify this state, one of the three conditions shown below must be met:
?m.sub.z>1& ?m.sub.x>1
?m.sub.z=1 & ?m.sub.x>1
?m.sub.z>1 & ?m.sub.x=1 b) Identification of standstills and idling times: In the event that, during the course of the processing, the machine tool is placed manually into an idling state, for example by a user, so that despite the rotating main spindle, no processing takes place, the condition below applies. This also applies for standstill times with a static main spindle
?v.sub.f,x=?v.sub.f,z=?v.sub.f,y=0 c) Identification of idling and/or standstill: A distinction between idling and standstill can be undertaken via the spindle rotary speed which is additionally read out from the control system BE. If the rotary speed of the clamping apparatus AV holding the workpiece WS is not equal to 0, idling is taking place. d) Identification of override commands: The control system BE of the machine tool returns manually executed override commands. These can be read out and subsequently processed. If the conditions of FIG. 4 are met, they are assigned to the machining process. Override commands do not change the conditions of FIG. 4. It is important to note that, depending upon the command, the conditions for identification of standstill times and idling times can also apply. e) Identification of the actual machining process and establishment of the individual cutting sequences: For the identification of the individual cutting sequences during continuous processing, in the first step, the signal of the feed rates of the axes is to be taken into account. In order to ensure that even low feed rates are identified as such during the mechanical processing, the possibility exists of squaring the results and then rounding them to the nearest natural number, including 0.

(33) In the next step, the position change and the change in the feed rate of the respective axes are determined with a high level of accuracy. This has the effect that small deviations can be identified.

(34) Subsequently, a further case distinction has to be carried out so that the cutting sequence currently being performed can be identified. The possible cases and the respective conditions are represented in FIG. 4. The conditions set out apply also for grooving and internal machining of the workpiece.

(35) In the exemplary embodiment shown in FIG. 4, for example, the first tool holder WH.sub.1 travels out of its rest position in the negative z-direction. The method is able to recognize this state with the aid of the quotients given. For this purpose, all the conditions cited in B1 must be met:
?v.sub.f,x=1
?v.sub.f,x=1
?m.sub.x=1
?m.sub.z<1

(36) With advancing time, the tool holder WH.sub.1 is additionally moved in the positive x-direction so that all the conditions B2 are met. On first occurrence of sensor data which meet the conditions B4, the method recognizes the start of a machining process: the start of cut sequence. The end of the machining process, the finish cut sequence, is recognized if the conditions B4 are no longer met, but rather the conditions B5 are.

(37) For the realization of the method according to the invention, the data points of the raw signal for each element relating to the respective cases for each machine axis are each stored in a matrix U as shown by way of example in FIG. 5 for an element for an axis. In the exemplary embodiment shown, for seventeen time points from a series of time points, the associated seventeen quotients are shown. Preferably, the quotients are the feed rate in the negative z-direction.

(38) If, following a selection of operating states, exclusively machining processes are to be further analyzed, then on a tool change this is to be identified and eliminated since, for the tool change, some of these conditions could also apply.

(39) The recognizing of a tool change can take place in the method according to the invention by way of a limit value consideration. The limit value is defined as the sum of the empirical mean value of the feed rates (U.sub.v,f(i)) stored in U and a standard deviation of 50%:

(40) $\begin{array}{cc}{\mathrm{Lim}}_{v_f}=\frac{{.Math.}_{i=1}^n{U}_{v,f}\left(i\right)}{n}?\frac{\sqrt{\frac{{.Math.}_{i=1}^n{\left(U_{v,f}\left(i\right)-\stackrel{\_}{U_{v,f}\left(i\right)}\right)}^2}{n-1}}}{2}& \left(5\right)\end{array}$

(41) As soon as a data point of the feed rate present in the matrix U exceeds this limit value, it is identified as belonging to the tool change and is set to zero in the matrix U. The indices of the values of the matrix U that are not recognized as a tool change and thus are recognized as belonging to the machining processes, are written in a vector t for the selection of the machining processes in the next step. Thus, the vector t contains only those time points in which the feed rate in the negative z-direction is not equal to 0. By way of the carry-over into the vector t, the spacings (d) of the individual measuring points from one another can be determined:
d(i)=t(i+1)?t(i){i?N|1?i?n?1}(6)

(42) This determines the values stored in d. For a coherent measuring signal, d=1. Therefore, by way of the condition b=e+1, the start value (b) of the follow-on machining process and the end value (e) of the current machining process of each individual machining process, which are not immediately identifiable as such in the matrix U shown can be established.

(43) In addition, the possibility exists of also evaluating the temporal sequences of the position change and the speed change quantitatively and therefrom of drawing conclusions regarding the operating state for freely selectable or predetermined time regions. Thus, for example, pulsing variations of the rate changes can indicate a regenerative effect within a time region under observation. With the aid of the method, it is also possible to recognize differences in the rate changes that occur during the same processing step of two identical workpieces, although produced one after the other. From this, indications of the wear of the tool used during this time can result.

(44) Furthermore, the possibility exists in a further method step 106 (FIG. 3) of capturing further internal machine signals, in particular electric current and voltage signals for the drive motors of the machine tool. For this purpose, FIG. 6 shows the torque-creating current for the drive motor responsible for a displacement along the z-axis for the whole procedure of processing of the workpiece. These comprise the individual processing times BZ and the non-productive times NZ that arise.

(45) FIG. 7 shows the extract DL from the diagram according to FIG. 6 in a higher temporal resolution. The current variation for driving the main spindle is shown over time and can be subdivided chronologically into a plurality of time portions. During a first time portion K1 between the time point to and the time point t.sub.1, the drive is in standstill. Subsequently, a needle-shaped current pulse occurs at the time point t.sub.1 as a time portion K2 which is adjoined by a time portion K3 for the drive regulation of the motor, during which the main spindle is moved to the programmed position. At the time point t.sub.2 which then arrives, the time portion K4 begins in which the tool WZ reaches the workpiece WS and makes contact. This is the start of cut sequence. The time portion K4 is also relatively short and ends at the time point t.sub.3 at which the time portion K5 for the main processing of the workpiece, i.e. the cutting process, follows. It ends at the time point t.sub.4. Then a second drive regulation K3 follows between the time points t.sub.4 and t.sub.5 and a second acceleration effect K2 between t.sub.5 and t.sub.6.

(46) Thus, in a further method step 106 (FIG. 3) such machine signals can be captured and/or provided and are taken into account in method step 110 for Identification of the state in the method step 110. This opens up the possibility of identifying unprofitable process states such as, for example, standstill times, idling times, tool changes, rapid transverses or the aforementioned override commands. In particular, taking into account the further machine signals enables faulty states to be recognized if, for example, an unexpected change in the current flow occurs (FIG. 7, arrow PF). By this means, the production process can be adapted according to need.

(47) Overall, from the continuing production process, the individual processing procedures can be recognized and established. In addition, the method represents a simple and inexpensive method for online/offline process monitoring during the entire production process.

(48) Although the invention has been illustrated and described in detail by way of the preferred exemplary embodiments, the invention is not restricted by the examples given and other variations can be derived therefrom without departing from the protective scope of the invention.