Abstract:
A spindle device for driving a production machine includes a first sensor for detecting a first physical variable of the spindle device, and at least a second sensor for detecting a second physical variable of the spindle device. In this way, it becomes possible to determine the oscillation amplitude of the rotor of a spindle and a temperature profile of a rolling bearing. Monitoring maximum values allows identification of a crash event, whereas the temperature profile allows conclusions as to a need for maintenance. Signal evaluation can take place centrally at the spindle manufacturer&#39;s end, thereby allowing needed maintenance works to be planned long term and effectively.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application claims the priority of German Patent Application, Serial No. 103 48 608.9, filed Oct. 20, 2003, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a spindle device for operating a production machine. The present invention further relates to a monitoring system for monitoring at least one such spindle device, as well as to a method of operating a spindle device.  
         [0003]     Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.  
         [0004]     Increase in productivity is a primary goal for the manufacturing industry and the stimulus for optimization and development in the field of production planning and process technique. It is therefore of great importance to operate a primary spindle as effective as possible for a production machine, e.g. a milling machine or a lathe. To enhance and ensure a high effectiveness, the need for an automated supervision of the primary spindle is desired.  
         [0005]     For monitoring spindles effectively, existing systems provide a classification of various conditions of the spindle, i.e. establishment of limit values for measured, processed and recorded signals or information. Currently available diagnosis systems are based on the evaluation of a single vibration signal which is ascertained by a vibration sensor mounted externally to the spindle. The spindle diagnosis takes place almost in real time during periodic sensor measurement. Generated information remains hereby with the owner of the spindle. Machine manufacturers or spindle manufacturers normally do not have access to the recorded data.  
         [0006]     State evaluation is typically realized by means of a trend analysis of parameters obtained from a measuring signal, such as for example the effective value of the acceleration or the vibration speed across certain frequency ranges or amplitude spectrums. The principle of trend analysis during a periodic data acquisition is illustrated in  FIG. 1  which is a graphical illustration of the vibration amplitude of a bearing of a primary spindle as a function of the date or time. So long as the vibration amplitude in the present example of  FIG. 1  is smaller than 50 amplitude units, the vibration amplitude is in a non-critical range 1 which represents a state in which the spindle and thus the machine operates properly. In range 2 above the range 1, the vibration amplitude of the spindle bearing is between 50 and 80 amplitude units, and the spindle and thus the machine are in a state in which maintenance works needs to be scheduled and a breakdown can be expected. When the vibrations are even higher and reach the range 3 above 80 amplitude units, the spindle and thus the machine are in a state that requires immediate actions as a breakdown is imminent.  
         [0007]     The graph  4  shown in  FIG. 1  represents a typical profile of the vibration amplitude of the bearing of a primary spindle as a function of the time (date). Starting from an actual time instance  5 , a time instance  7  can be predicted through extrapolation  6  when the machine breaks down or actions are absolutely required. The time period up to the time instance  7  may thus be exploited to undertake the needed maintenance works. The limit values required for delineating the various states are ascertained through statistically obtained data. This learning process is time-consuming and produces a limit value for only a single spindle type in a particular machine and possibly for only a single particular manufacturing operation. This type of limit value determination is thus unsuitable for operation of primary spindles and other production machines.  
         [0008]     It would therefore be desirable and advantageous to provide an improved diagnosis system for spindle devices, which obviates prior art shortcomings and which is simple in structure and yet reliable in operation.  
       SUMMARY OF THE INVENTION  
       [0009]     According to one aspect of the present invention, a spindle device for driving a production machine includes a first sensor for detecting a first physical variable of the spindle device, and at least a second sensor for detecting a second physical variable of the spindle device.  
         [0010]     According to another feature of the present invention, the first physical variable and/or the second physical variable may each represent a distance traveled, speed, acceleration, or a particular direction component. This makes it possible to detect vibrations of the spindle which are generated by eccentricity or spindle components. The determination of directional components of the vibrations is especially advantageous to allow targeted maintenance works.  
         [0011]     The first physical variable or second physical variable may also represent a spindle temperature or a rotation speed of the spindle. In this way, the condition of a spindle can be determined in response to temperature limits that have been established by the spindle bearing manufacturer, and suitable actions can be triggered. The analysis in response to the temperature value can be enhanced by recording also the rotation speed of the machine. Thus, an increase in temperature may be ascribed, for example, to a momentary increase in the rotation speed of the machine, indicating that no maintenance works need yet to be scheduled.  
         [0012]     According to another feature of the present invention, the first sensor and the at least one second sensor may be arranged in a spindle housing. This means that the diagnosis sensor technology is firmly integrated in the spindle and no external sensors are required to be attached later on.  
         [0013]     According to another feature of the present invention, the spindle device may include a memory for temporarily storing data of the first sensor and the at least one second sensor, and a controller for processing the data. Suitably, the first sensor and the at least one second sensor as well as the memory and the controller are integrated in a measuring ring which is disposed in proximity of one spindle bearing. In this way, the diagnosis assembly can easily be integrated in the spindle while the spindle in turn can be individually configured for providing the diagnosis data.  
         [0014]     According to another feature of the present invention, the spindle device may include a classification unit for rating the condition of the spindle device in response to data from the first sensor and the at least one second sensor. In this way, classification may be carried out not only externally in a central diagnosis station but directly in the spindle so that data transfer rates can be reduced. The classification may, however, also be carried out internally or externally in dependence on the respective system load.  
         [0015]     According to another aspect of the present invention, a monitoring system for monitoring at least a spindle device includes an evaluation unit for determining or predicting a maintenance need of the at least one spindle device. As a result, a manufacturer, for example, is in a position to precisely monitor the availability of a plurality of spindles. Suitably, the spindles are linked by a data network, such as the Internet.  
         [0016]     A monitoring system or diagnosis system according to the present invention affords the manufacturer of spindles or machine tools information about the life cycle or load cycle. Moreover, data stored in a ring memory may be used to analyze damages in order to assess possible warranty claims. In addition, the need for a limit value determination, as required in conventional monitoring systems, is omitted and replaced by a so-called Teach-In-Process as the required limit values, e.g. temperature limit value, are preset by the manufacturer.  
         [0017]     According to another feature of the present invention, the spindle device may include a temperature sensor for providing data for the evaluation unit which generates a temperature signal in response to the data from the temperature sensor and compares the temperature signal with a limit value for determining the maintenance need.  
         [0018]     According to another aspect of the present invention, a method of operating a spindle includes the steps of determining a first set of data in response to a first physical variable of the spindle, determining a second set of data in response to at least one second physical variable of the spindle, and operating the spindle and/or controlling an accompanying process in response to the first and second sets of data. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0019]     Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:  
         [0020]      FIG. 1  is a graphical illustration of a trend analysis during a periodic data acquisition, depicting the vibration amplitude as a function of date (time);  
         [0021]      FIG. 2  is a longitudinal section of a motor spindle according to the present invention;  
         [0022]      FIGS. 3A-3H  are graphical illustrations of measurements of different physical variables as a result of crash events;  
         [0023]      FIGS. 4A-4E  are graphical illustrations of measurements of physical variables of a spindle with typical wear;  
         [0024]      FIG. 5  is a block diagram of a variation of a spindle device according to the present invention; and  
         [0025]      FIG. 6  is a block diagram of a monitoring system for monitoring a spindle assembly. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0026]     Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.  
         [0027]     Turning now to the drawing, and in particular to  FIG. 2 , there is shown a longitudinal section of a motor spindle according to the present invention, generally designated by reference numeral  11 . The motor spindle includes a rotor  12  which is supported by bearings  13  in a spindle housing  15 . Disposed immediately adjacent to one of the bearings  13  (here, by way of example, the leftmost bearing) is a measuring ring  14  which is constructed to include several sensors, a memory element and a microcontroller. Currently preferred is the use of the following sensors for incorporation in the measuring ring  14 : three acceleration sensors for the three directions in space, two inductive distance sensors in axial direction as well as two radial inductive distance sensors, a speed sensor, and a temperature sensor. The sensors may be arranged in the measuring ring  14  in any suitable manner. Of course, it is also conceivable to integrate the sensors individually or in groups in the spindle  11 , instead of combining the sensors in a common measuring ring.  
         [0028]     The measuring ring  14  further includes a running time meter for ascertaining the running time of the spindle, whereby the ascertained running times are stored in a memory.  
         [0029]     As the sensors generate information, the condition of the spindle  11  can be classified not only on the basis of a single signal but on the basis of several signals. In other words, the spindle condition can be rated in response to multiple signals. This multidimensional data acquisition enables an analysis of the signal patterns of the sensors to rate the spindle condition, without requiring complicated processes to determine limit values.  
         [0030]     The state of a spindle or the condition of its bearing may change, for example through so-called crash events or also through normal wear. A crash event may, for example, be a situation in which the tool or chuck of a machine tool collides with a workpiece. Such an event impairs the entire spindle or at least parts thereof so that premature maintenance works become necessary.  
         [0031]     By combining different signal types, a crash of the spindle can be recognized through characteristic signal patterns. In the event of a crash, the direction of the force introduction determines in which of the sensors, due to its installation direction, a signal with characteristic profile can be recognized. A crash, for example, can be unambiguously determined by a combination of distance signal and acceleration signal. Even the type of crash, whether “fast” crash with dynamically imposed overload, or “slow” crash with statically imposed overload, can be identified.  
         [0032]     A fast crash normally causes per time unit ΔT a significant increase of the maximum value of a vibration signal. In other words, the maximum values measured in the event of a crash in a time period ΔT are significantly greater than the values encountered during normal operation. This is shown in  FIGS. 3A and 3B , depicting a graphical illustration of a vibration signal as a function of the time t. A general variable, e.g. the amplitude, the speed or the acceleration of a vibration signal, reaches maximum values (1), (2) and (3) during normal operation on average in the time period ΔT. In the event of a crash, the maximum value (n) is obtained which significantly exceeds the values (1), (2) and (3).  
         [0033]     For values, measured after the crash event (t&gt;t n ), two patterns are basically conceivable in dependence on the intensity of the crash. On one hand, the signal (n+1) may proceed at a same level after the crash as before the crash. In this case, the signal continues to remain in a desired range S, as shown in  FIG. 3A , so that the crash event may be identified only by the elevated value (n). On the other hand, the signal (n+1), (n+2), (n+3) may continue to remain at the level of value (n) of the crash event, or exceed the value (n), as shown in  FIG. 3B . If the maximum value of the vibration signal does not stray from the value range T even after the crash event, the crash may be qualified differently than in the graphical illustration of  FIG. 3B  in which the values continue to ascend. In both cases, the crash can be identified as a result of the excessive signals (n), (n+1), (n+2), . . . after the time instance t n .  
         [0034]      FIG. 3C  shows a diagram which depicts concretely the maximum magnitude of the vibration or distance signal for discrete time values during a fast crash, i.e. during a dynamically imposed overload. The graphical illustration corresponds to the illustration of  FIG. 3A .  FIG. 3D , on the other hand, depicts the maximum distance amplitude during a slow crash, i.e. during a statically imposed overload. In this case, the magnitude of the amplitude ascends continuously. This value change after the crash event would not be identifiable, using acceleration or speed sensors only. Thus, a distance sensor can be used to identify a slow crash and can be employed for providing a forecast.  
         [0035]     Following a crash event that has been ascertained in response to maximum values of the oscillation or distance signal at the time instance t n , two different temperature profiles can be expected depending on the degree of damage as a consequence of the crash. These temperature profiles are shown in  FIGS. 3E and 3F .  FIG. 3E  shows a steady linear, exponential or similar rise of the maximum temperature, whereas  FIG. 3F  shows the temperature to suddenly rise in the time period t&gt;t n . A limit temperature θ grenz , as given by the bearing manufacturer, should not, or only briefly, exceeded so that lubricant is not overstrained.  
         [0036]     The rotation speed range should be monitored simultaneously with the temperature profile, as shown in  FIGS. 3G and 3H  depicting graphical illustrations of discrete maximum values of the rotation speed as a function of the time T. Hereby, it is to be examined that no significant differences in rotation speed are encountered before and after a crash at time instance t=t n . As the rotation speed is elevated, the temperature signal would increase as well in dependence on the rotation speed so that an increase in temperature, even when exceeding the limit temperature θ grenz , cannot necessarily be interpreted as crash indicator. The same applies also for the interpretation of the graphs of  FIGS. 3A  to  3 D.  
         [0037]     A condition-based maintenance requires an action when the temperature, measured per time period, significantly exceeds the temperature measured on average previously and is above the admissible operating temperatures of rolling bearings or lubricant, as set by the bearing manufacturer, or exceeds the admissible limit temperature, as set by the spindle manufacturer. The temperature profile, calibrated with the rotation speed signal, provides thus a sufficient criterion for triggering a maintenance alert on the basis of previously set limit values.  
         [0038]     The trend analysis is based on a linear or exponentially ascending course of vibration signal and amount of the maximum distance amplitude, in the event of a change in the spindle condition or bearing condition.  FIG. 4A  is a diagram, depicting discrete maximum values (1), . . . (n), (n+1), . . . (n+m) as a function of time t, whereby the time instance t n  indicates a crash event. Depending on the type of crash, the maximum amount of the distance amplitude may be changed by the crash, as shown in  FIG. 4B , or may remain unaffected by the crash, as shown in  FIG. 4C , and thus continue to steadily rise. A condition-based maintenance is again triggered by the temperature profile, with a minimum temperature θ grenz min , a normal temperature θ grenz•nl , and an absolute maximum θ grenz max , may be used for interpretation and triggering the maintenance alert. For example, a service call is set off above the maximum θ grenz max , whereby again the discrete maximum speed, as shown in  FIG. 4E , should be taken into account.  
         [0039]     The operating spindle conditions may be classified with consideration of absolutely valid limit values of the bearing kinematics. The measured distance signals may hereby be used for checking the bearing kinematics. Using algorithms for computing the bearing kinematics according to Brändlein, J; Klühspiess, N.: “Die Lagerverteilung in schnell laufenden Kugellagern, Werkstatt and Betrieb ( The Bearing Distribution in Rapidly Running Ball Bearings, Workshop and Operation ), 105 th  year, 1972, No. 9, or to Harris, T., “Rolling Bearing Analysis”, John Wiley Sons, 1991, allows suppositions about parameters which characterize the bearing kinematics or stress. Taking into account geometric data of the bearing, spindle (bearing distance, shaft geometry), tool (tool diameter and tool length), and consideration of shaft flexibility as well as speed and temperature determined by the temperature sensor, the following parameter can be calculated through adaptation of the algorithm: 
        (1) maximum Hertzian area stress in the rolling contacts encountered in the bearing (p 0 ),     (2) ratio between drilling speed and roll angle speed of the rolling bodies (BRV), and     (3) leading and trailing runs of rolling body (WVN).        
 
         [0043]     A decrease in the useful life with respect to the rotation speed can be expected, if 
        (1) p 0 &gt;(2.000 . . . 2.500) MPa, depending on material of the rolling partners, here 100Cr6 and Cronidur®30 rolling bearing steels,     (2) BRV&gt;0.5     (3) WVN&gt;0.5 times the cage pocket play.        
 
         [0047]     The model formation thus allows an absolute determination of the limit value a priori, without Teach-in. When these limit values are exceeded, the useful life of the spindle is reduced. By storing the signals, optionally pre-processed signals according to above scheme, in a ring memory, in which the first stored information is also read first, the signals are made accessible to the machine manufacturer or spindle manufacturer and analyzed in a post-processing system. In this way, conclusions about warranty claims are made possible.  
         [0048]     Turning now to  FIG. 5 , there is shown that the spindle  11  may include a memory  16  for temporarily storing data of the sensors, and a controller  17  for processing the data. Suitably, the sensors as well as the memory  16  and the controller  17  are integrated in the measuring ring  14 . In this way, the diagnosis assembly can easily be integrated in the spindle  11  while the spindle  11  in turn can be individually configured for providing the diagnosis data.  
         [0049]     Referring now to  FIG. 6 , there is shown a monitoring system  18  for may be carried out not only externally in a central diagnosis station but directly in the spindle so that data transfer rates can be reduced. The classification may, however, also be carried out internally or externally in dependence on the respective system load.  
         [0050]     Referring now to  FIG. 6 , there is shown a monitoring system  19  for monitoring at least one spindle  11 , or as shown here for monitoring two spindles  11 . Of course, the monitoring system  18  may be applicable also for monitoring more than two spindles  11 . The monitoring system  18  includes an evaluation unit  20  for determining or predicting a maintenance need of the spindles  11 . As a result, a manufacturer, for example, is in a position to precisely monitor the availability of a plurality of spindles. Suitably, the spindles  11  are linked by a data network  21 , such as the Internet.  
         [0051]     While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.