Abstract:
In order to obtain a configuration allowing an operator to promptly identify whether a physical amount is within the normal range, this machine tool is configured so as to be provided with: sensors for sensing a physical amount showing the state of the machine tool, the normal range of the physical amount changing in correspondence with the machining condition; a setting unit for setting the normal range of the physical amount corresponding to the machining condition; and a display for displaying the normal range set by the setting unit alongside the sensing value sensed by the sensors.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Phase patent application of PCT/JP2012/060262, filed on Apr. 16, 2012, which is hereby incorporated by reference in the present disclosure in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a machine tool which has a display function of displaying a working state. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the past, there has been known a system which detects physical quantities which represent a working state of an electro-discharge machine, stores the detected values, and, when a display command is input, displays the stored detected values at a display part (for example, see Patent Literature 1). The system which is described in Patent Literature 1 displays an average working current, working speed, working fluid temperature, wire tension, etc. at the display part. The average working current, average working voltage, and wire tension are also displayed as ratios with their maximum values by bar graphs. 
         [0004]    In this regard, in an electro-discharge machine or other machine tool, if the machine is normal in state, the physical quantities which represent the state of the machine (for example, the working speed) fall in predetermined normal ranges. As opposed to this, when the physical quantities exceed the normal ranges, if continuing to operate the machine as it is, a drop in working efficiency of a workpiece, damage to the machine, or some other sort of issue is liable to arise. For this reason, the system is preferably configured so that an operator can quickly recognize if the physical quantities are in the normal ranges. 
         [0005]    However, the system which is described in Patent Literature  1  only displays the detected physical quantities. An operator cannot just look at the display and easily judge if the machine is normal in state. In particular, in an electro-discharge machine, the normal ranges of physical quantities change in accordance with the rough working or finish working or other working conditions, so judging if a machine is normal in state becomes much more difficult. 
       PATENT LITERATURE 
       [0006]    Patent Literature 1: Japanese Patent Publication No. 6-8054A 
       SUMMARY OF THE INVENTION 
       [0007]    The machine tool according to the present invention includes: a detecting part detecting a physical quantity representing a state of a machine tool, a normal range of the physical quantity changing in accordance with working conditions; a setting part setting a normal range or an abnormal range of the physical quantity in accordance with the working conditions; and a display part displaying a detected value detected by the detecting part and the normal range or the abnormal range set by the setting part. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a front view which shows a schematic configuration of a wire electro-discharge machine to which the present invention is applied. 
           [0009]      FIG. 2  is a circuit diagram which shows feed lines of working fluid in the wire electro-discharge machine of  FIG. 1 . 
           [0010]      FIG. 3  is a block diagram which shows a schematic configuration of a display device of a machine tool according to an embodiment of the present invention. 
           [0011]      FIG. 4  is a view which shows one example of normal ranges, warning ranges, and abnormal ranges which are set by a setting part of  FIG. 3 . 
           [0012]      FIG. 5  is a view which shows one example of a workpiece working screen which is displayed at a display part of  FIG. 3 . 
           [0013]      FIG. 6A  is a view which shows one example of an image which displays a working speed at the time of rough working. 
           [0014]      FIG. 6B  is a view which shows one example of an image which displays a working speed at the time of finish working. 
           [0015]      FIG. 7A  is a view which shows one example of an image which displays a working fluid pressure at the time of rough working. 
           [0016]      FIG. 7B  is a view which shows one example of an image which displays a working fluid pressure at the time of finish working. 
           [0017]      FIG. 8A  is a view which shows one example of an image which displays a water quality at the time of rough working. 
           [0018]      FIG. 8B  is a view which shows one example of an image which displays a water quality at the time of finish working. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Below, referring to  FIG. 1  to  FIG. 8B , an embodiment of a machine tool according to the present invention will be explained. Below, the case of use of a machine tool constituted by a wire electro-discharge machine will be explained, but another machine tool may also be used. 
         [0020]      FIG. 1  is a front view which shows the general configuration of a wire electro-discharge machine  100  to which the present invention is applied. As shown in  FIG. 1 , at the top of a bed  1 , a workpiece table  2  is placed. On the workpiece table  2 , a workpiece  3  is supported. Above and below the workpiece  3 , an upper head  4  and a lower head  5  are arranged coaxially with each other while straddling the workpiece  3 . Between the upper head  4  and lower head  5 , a wire electrode  6  is supported along a vertical direction. The wire electrode  6  is wound around a reel, etc., and at the time of working a workpiece, is fed between the heads  4  and  5  by a not shown feeding means. 
         [0021]    The upper head  4  is attached to a lower end of a quill  7 . The quill  7  is provided slidably in an X-direction, Y-direction, and Z-direction by a respective not shown X-axis slide mechanism, Y-axis slide mechanism, and Z-axis slide mechanism, i.e., in three perpendicular axial directions. The slide mechanisms are, for example, comprised of ball screws and servo motors, etc., for driving to rotate the ball screws. The lower head  5  is integrally connected with the upper head  4  via a not shown support arm. 
         [0022]    Due to this, the upper head  4  and the lower head  5  can move integrally in the X-axial direction and the Y-axial direction. The wire electrode  6  is maintained in a vertical posture while being made to move relative to the workpiece  3  in the X-axial direction and the Y-axial direction. While not illustrated, the wire electro-discharge machine  100  according to the present embodiment also has a U-axis slide mechanism and V-axis slide mechanism which make the upper head  4  move relative to the lower head  5  in a U-axial direction which is parallel to the X-axis and in a V-axial direction which is parallel to the Y-axis. Due to this, the wire electrode  6  can be made to incline from the vertical by a desired angle. The U-axis slide mechanism and the V-axis slide mechanism are also, for example, comprised of ball screws and servo motors which drive to rotate the ball screws, etc. 
         [0023]    At the time of working by the wire electro-discharge machine  100 , the working region of a workpiece  3  is supplied with a working fluid (for example, water). As the working fluid, instead of water, oil can also be used. Around the workpiece  3 , a not shown working tank is arranged. In the working tank, a working fluid is stored. The workpiece  3  is worked in a state immersed in the working fluid. 
         [0024]      FIG. 2  is a circuit diagram which shows feed lines of the working fluid in the wire electro-discharge machine  100 . The working fluid is stored in a working fluid tank  10 . The working fluid tank  10  has a dirty fluid tank  11  in which pre-cleaned working fluid is stored and a clean fluid tank  12  in which cleaned working fluid is stored. 
         [0025]    The working fluid inside the clean fluid tank  12  is pumped up by pumps  13  and  14  and injected from a jet nozzle  4   a  which is provided at the upper head  4  and a jet nozzle  5  which is provided at the lower head  5  to the inside of a working tank  17 . Further, the working fluid in the clean fluid tank  12  is pumped up by a pump  15 , is cooled by passing it through a cooling device  16 , then is returned to the clean fluid tank  12 . The working fluid which is ejected from the jet nozzles  4   a  and  5   a  is used for working, and then is returned from the working tank  17  to the dirty fluid tank  11 . The working fluid inside of the dirty fluid tank  11  is pumped up by a pump  18  and passes through a filter  19  to remove impurities in the working fluid. The working fluid cleaned by passing through the filter  19  is sent to the clean fluid tank  12 . 
         [0026]    A pressure of the working fluid between the pump  18  and the filter  19  (filter pressure Pa) is detected by a pressure detector  21 . A pressure of the working fluid between the pump  13  and the jet nozzle  4   a  (working fluid pressure Pb) is detected by a pressure detector  22 . A pressure of the working fluid between the pump  14  and the jet nozzle  5   a  (working fluid pressure Pc) is detected by a pressure detector  23 . A temperature T of the working fluid which passes through the cooling apparatus  16  is detected by a temperature detector  28 . A property or characteristic of the working fluid inside the clean fluid tank  12  (water quality a) is detected by a water quality detector  24 . The water quality detector  24  is a known sensor which measures an electro-conductivity of the working fluid (for example, a resistivity meter). 
         [0027]    The thus detected filter pressure Pa, working fluid pressures Pb and Pc, working fluid temperature T, water quality a, and other physical quantities represent the state of the machine. These physical quantities can be used as the basis to judge if the machine is normal in state. That is, these physical quantities have normal ranges set for them in advance. If the detected physical quantities are inside the normal ranges, it is judged that the machine is normal in state. For example, if the filter pressure Pa is a predetermined pressure or less, it is judged that the filter  19  is in a normal state where it is free of clogging. On the other hand, if the detected physical quantities are outside the normal ranges, it is judged that the machine is not normal in state. In this case, some sort of issue is liable to arise in the working operation, so it is preferable to configure the system so that the operator can determine at all times if the detected physical quantities are in the normal ranges. Therefore, in the present embodiment, the display device is configured in the following way. 
         [0028]      FIG. 3  is a block diagram which shows the general configuration of a machine tool according to an embodiment of the present invention. To the control device  20 , a speed detector  25  which detects a speed of movement of the wire electrode  6  with respect to the workpiece  3  (working speed V), the pressure detectors  21  to  23 , the water quality detector  24 , the input part  26 , and the display part  30  are connected. 
         [0029]    The speed detector  25  is, for example, comprised of a rotation detector (encoder) which detects an amount of rotation of a servo motor for driving a quill (for example, X-axis servo motor or Y-axis servo motor). That is, there is a correlation between the amount of rotation of the servo motor and the position of the wire electrode  6 , so the working speed V can be determined by determining the amount of change per unit time of the position of the wire electrode  6  obtained by the rotation detector. The working speed V, for example, falls when abnormal electro-discharge occurs due to degradation of the working fluid, etc. Therefore, the working speed V is also, like the filter pressure Pa or the working fluid pressures Pb and Pc, a physical quantity which represents the state of the machine. The input part  26  can be comprised of a keyboard or touch panel, etc. The display part  30  is comprised of a liquid crystal display, CRT display, etc. 
         [0030]    The control device  20  is comprised of a processing system which includes a CPU, ROM, RAM, and other peripheral circuits, etc. The control device  20  has, as functional components, a reading part  20   a,  setting part  20   b,  and display control part  20   c.    
         [0031]    The reading part  20   a  reads signal from the detectors  21  to  25 , various setting values input by the input part  26 , the working program stored in advance in the memory, and other data. The working program may also be made to be read from outside of the control device  20 , for example, from a numerical control unit which controls the wire electro-discharge machine  100 . 
         [0032]    The setting part  20   b  sets the normal range, warning range, and abnormal range of a physical quantity in accordance with the working conditions. An abnormal range is a range which represents an abnormal state of the machine, and is set outside of the normal range. A warning range is a range which represents a warning state before the machine becomes abnormal, and is set between the normal range and the abnormal range. That is, the warning range is set contiguous with the normal range, while the abnormal range is set contiguous with the warning range. 
         [0033]    The working conditions are the amount of feed of the working fluid to the working region, the magnitude of a working voltage which is applied between the wire electrode  6  and the workpiece  3 , and other conditions which are necessary for electro-discharge machining. The working conditions differ in accordance with the rough working, finish working, and other working content. That is, the rough working condition at the time of rough working and the finish working condition at the time of finish working differ. If the working conditions differ, the normal ranges, warning ranges, and abnormal ranges of the physical quantities differ. Therefore, these ranges are set for the individual working conditions. The finish working is sometimes divided into several states with changed working conditions. The working conditions which are used are set in the working program. 
         [0034]      FIG. 4  is a view which shows one example of the normal ranges, warning ranges, and abnormal ranges which are set at the setting part  20   b.  As shown in  FIG. 4 , the normal range of the working speed V in the rough working condition is a predetermined value V1 or more (V1≦V), the warning range is a predetermined value V2 or more and less than the predetermined value V1 (V2≦V&lt;V1), and the abnormal range is less than the predetermined value V2 (V&lt;V2). On the other hand, the normal range of the working speed V in the finish working condition is a predetermined value V3 or more (V3≦V), the warning range is a predetermined value V4 or more and less than a predetermined value V3 (V4≦V&lt;V3), and the abnormal range is less than the predetermined value V (V&lt;V4). At the time of finish working, the working speed V is faster than the time of rough working, so the predetermined value V3 is larger than the predetermined value V1, and the predetermined value V4 is larger than the predetermined value V2. 
         [0035]    The normal range of the filter pressure Pa of one type of filter which is used, i.e., the filter A, is a predetermined value Pa1 or less (Pa≦Pa1), the warning range is larger than the predetermined value Pa1 and less than a predetermined value Pa2 (Pa1&lt;Pa&lt;Pa2), and the abnormal range is the predetermined value Pa2 or more (Pa2≦Pa). On the other hand, the normal range of the filter pressure Pa of another type of filter which is used, i.e., the filter B, is a predetermined value Pa3 or less (Pa≦Pa3), the warning range is larger than the predetermined value Pa3 and less than a predetermined value Pa4 (Pa3&lt;Pa&lt;Pa4), and the abnormal range is the predetermined value Pa4 or more (Pa4≦Pa). Suitable normal ranges, warning ranges, and abnormal ranges are set for even the case of changing the filter which is used depending on the type of the working. 
         [0036]    The normal range of the working fluid pressure Pb in the rough working condition is a predetermined value Pb1 or more (Pb1≦Pb), the warning range is a predetermined value Pb2 or more and less than the predetermined value Pb1 (Pb2≦Pb&lt;Pb1), and the abnormal range is less than the predetermined value Pb2 (Pb&lt;Pb2). On the other hand, the normal range of the working fluid pressure Pb in the finish working condition is a predetermined value Pb3 or more (Pb3≦Pb), the warning range is a predetermined value Pb4 or more and less than the predetermined value Pb3 (Pb4≦Pb&lt;Pb3), and the abnormal range is less than the predetermined value Pb4 (Pb&lt;Pb4). At the time of rough working, the amount of feed of the working fluid is greater than at the time of finish working, so the predetermined value Pb1 is larger than the predetermined value Pb3 and the predetermined value Pb2 is larger than the predetermined value Pb4. The normal range, warning range, and abnormal range of the working fluid pressure Pc are set equal to the working fluid pressure Pb. 
         [0037]    The normal range of the water quality α in the rough working condition is a predetermined value α1 or more and less than a predetermined value α2 (α1≦α&lt;α2), the warning ranges are a predetermined value α3 or more and less than the predetermined value α1 (α3≦α&lt;α1) and the predetermined value α2 or more and less than the predetermined value α4 (α2≦α&lt;α4), and the abnormal ranges are less than the predetermined value α3 (α&lt;α3) and the predetermined value α4 or more (α4≦α). On the other hand, the normal range of the water quality α in the finish working condition is a predetermined value α5 or more and less than a predetermined value α6 (α5≦α&lt;α6), the warning ranges are a predetermined value α7 or more and less than the predetermined value α5 (α7≦α&lt;α5) and the predetermined value α6 or more and less than the predetermined value α8 (α6≦α&lt;α8), and the abnormal ranges are less than the predetermined value α7 (α&lt;α7) and the predetermined value α8 or more (α8≦cc). The predetermined values α1, α2, α3 and α4 at the time of rough working are larger than the predetermined values α5, α6, α7 and α8 at the time of finish working. 
         [0038]    The above ranges can be set by multiplying reference values of the physical quantities with predetermined coefficients. For example, the values obtained by multiplying the reference value Vo of the working speed V input in advance with the predetermined coefficients a1, a2, a3 and a4 are set as the predetermined values V1, V2, V3 and V4. It is also possible for the operator to directly input predetermined values through the input part  26  so as to set the ranges. The ranges of physical quantities which are set at the setting part  20   b  (normal ranges, warning ranges, and abnormal ranges) are stored in the memory. 
         [0039]    The display control part  20   c  uses the various data which reads through the reading part  20   a  and the ranges of physical quantities which are set at the setting part  20   b  as the basis to control the display part  30  and make predetermined images display on the display part  30 .  FIG. 5  is a view which shows one example of an image displayed on the display part  30  at the time of working the workpiece (workpiece working screen  31 ). As shown in  FIG. 5 , the workpiece working screen  31  has a plurality of display regions  32  to  38 . 
         [0040]    At the display region  32 , a path of movement of the center of the upper head  4  (wire electrode  6 ) is displayed based on the signals from the rotation detectors of the X-axis use, Y-axis use, U-axis use, V-axis use, and Z-axis use servo motors. At the display region  33 , the current X-coordinate, Y-coordinate, U-coordinate, V-coordinate, and Z-coordinate of the upper head  4  are displayed by numerical values based on the signals from the same rotation detectors of the servo motors. At the display region  34 , the working program which is currently being run among the working programs stored in advance in the memory is displayed. 
         [0041]    At the display region  35 , the current working speed detected by the speed detector  25  is displayed. At the display region  36 , the working fluid pressure Pb of the upper head side detected by the pressure detector  22  is displayed. At the display region  37 , the working fluid pressure Pc of the lower head side detected by the pressure detector  23  is displayed. At the display region  38 , the filter pressure Pa detected by the pressure detector  21  is displayed. At the display region  39 , the water quality a detected by the water quality detector  24  is displayed. 
         [0042]    In the present embodiment, the display regions  35  to  39  display together meter images which represent the normal ranges, the warning ranges, and the abnormal ranges of the detected values. That is, the display control part  20   c  judges the current working conditions based on the working program, reads the ranges of the physical quantities V, Pb, Pc, Pa and α ( FIG. 4 ) corresponding to the working conditions from the reading part  20   b,  and displays the meter images at the display regions  35  to  39 . 
         [0043]      FIG. 6A  and  FIG. 6B  are views which show images of the display region  35  at the time of rough working and at the time of finish working. As shown in  FIG. 6A , at the time of rough working, the numerical value display part  35   a  displays the current working speed V by a numerical value, while the meter display part  35   b  displays a bar shaped meter image  350  which has scales  350   a.  The meter image  350  displays a needle image  351  having the shape of an indicator needle over this. The needle image  351  shows the detected value of the working speed V and moves in display position along the meter image  350  in the arrow A1 or A2 direction along with a change of the working speed V. 
         [0044]    The meter image  350  is divided into three regions bordered at the predetermined values V1 and V2. The regions respectively form a normal range image  352  which corresponds to the normal range, a warning range image  353  which corresponds to the warning range, and an abnormal range image  354  which corresponds to the abnormal range. The modes of display of these images  352  to  354  differ from each other. For example, the normal range image  352  is the green color, the warning range image  353  is the yellow color, and the abnormal range image  354  is the red color. Due to this, the operator can check the position of the needle image  351  on the meter image  350  to thereby easily determine if the current working speed V is normal and how much of a margin there is until the abnormal range. 
         [0045]    As shown in  FIG. 6B , at the time of finish working as well, the numerical value display part  35   a  displays the current working speed V by a numerical value, and the meter display part  35   b  displays a meter image  350  and needle image  351 . The meter image  350  is divided into the normal range image  352 , the warning range image  353 , and the abnormal range image  354  bordered at the predetermined values V3 and V4. The display colors of these image  352  to  354  are the same as in  FIG. 6A . 
         [0046]    The meter image  350  need to set the sizes of the normal range image  352 , the warning range image  353 , and the abnormal range image  354  for the scales  350   a.  The sizes of the normal range image  352 , the warning range image  353 , and the abnormal range image  354  (for example, the length L of the normal range image  352  on the screen) may also be made equal to each other between  FIG. 6A  and  FIG. 6B . That is, the display control part  20   c  changes the display values of the scales  350   a  of the meter image  350  in accordance with the predetermined values V1 to V4 so that images  352  to  354  of constant shapes and sizes are displayed regardless of the working conditions. By configuring the system so as to display constant images  352  to  354  regardless of the working conditions in this way, the operator can easily judge the normal and abnormal state of the current working speed V. In  FIG. 6A  and  FIG. 6B , display of the scales  350   a  of the meter image  350  may also be omitted. The setting of the size of the range display can also be applied to the display of other detected values. 
         [0047]      FIG. 7A  and  FIG. 7B  are views which show images of the display region  36  at the time of rough working and finish working. As shown in  FIG. 7A , at the time of rough working, the numerical value display part  36   a  displays the current upper head side working fluid pressure Pb by a numerical value, and the meter display part  36   b  displays a semicircular meter image  360  which has scales  360   a.  On the meter image  360 , a needle image  361  which extends from the center part  360   b  of the semicircle in the radial direction and which is formed in the shape of the indicator needle is displayed to overlay. The needle image  361  displays the detected value of the working fluid pressure Pb, and pivots about the center part  360   b  in the arrow A1 or A2 direction along with a change of the working fluid pressure Pb. 
         [0048]    The meter image  360  is divided into three regions bordered at the predetermined values Pb1 and Pb2. The regions form a normal range image  362  which corresponds to the normal range, a warning range image  363  which corresponds to the warning range, and an abnormal range image  364  which corresponds to the abnormal range. The modes of display of the images  362  to  364 , like in  FIG. 6A , differ from each other. That is, the normal range image  362  is the green color, the warning range image  363  is the yellow color, and the abnormal range image  364  is the red color. Due to this, the operator can easily determine if the current working fluid pressure Pb is normal. 
         [0049]    As shown in  FIG. 7B , at the time of finish working as well, the numerical value display part  36   a  displays the current working fluid pressure Pb by a numerical value and the meter display part  36   b  displays a meter image  360  and needle image  361 . The meter image  360  is divided into a normal range image  362 , a warning range image  363 , and an abnormal range image  364  bordered at the predetermined values Pb3 and Pb4. The display colors of these images are the same as in  FIG. 7A . 
         [0050]      FIG. 8A  and  FIG. 8B  are views which show images of the display region  39  at the time of rough working and finish working. As shown in  FIG. 8A , at the time of rough working, the numerical value display part  39   a  displays the current water quality α by a numerical value and the meter display part  39   b  displays a bar shaped meter image  390  which has scales  390   a.  The meter image  390  is displayed with a needle image  391  of the shape of an indicator needle overlaid on it. The needle image  391  shows the detected value of the water quality α. The display position moves along the meter image  390  along with a change of the water quality α. 
         [0051]    In the water quality α, unlike in the working speed V, etc., abnormal ranges and warning ranges are set at the two sides of a normal range. Corresponding to this, the meter image  390  is divided into five regions bordered at the predetermined values α1 to α4. At the two sides of the normal range image  392 , warning range images  393  are displayed, while at the two sides of the warning range images  393 , abnormal range images  394  are displayed. The modes of display of the images  392  to  394  differ from each other. For example, the normal range image  392  is the green color, the warning range images  393  are the yellow color, and the abnormal range images  394  are the red color. Due to this, the operator can easily determine if the current water quality α is normal. 
         [0052]    As shown in  FIG. 8B , even at the time of the finish working, the numerical value display part  39   a  displays the current water quality α by a numerical value and the meter display part  39   b  displays a meter image  390  and needle image  391 . The meter image  390  is divided into a normal range image  362 , warning range images  363 , and abnormal range images  364  bordered at predetermined values α5 to α8. The display colors of these images are the same as in  FIG. 8A . 
         [0053]    According to the present embodiment, the following actions and effects can be exhibited. 
         [0000]    (1) As the physical quantities showing the state of the wire electro-discharge machine, the working speed V is detected by the speed detector  25 , the filter pressure Pa is detected by the pressure detector  21 , the working fluid pressures Pb and Pc are detected by the pressure detectors  22  and  23   c,  and the water quality α is detected by the water quality detector  24 . Further, the normal ranges of the working speed V, the filter pressure Pa, the working fluid pressures Pb and Pc, and the water quality cc in accordance with the working conditions are set in advance by the processing at the setting part  20   b,  while the detected values of these physical quantities together with their normal ranges are displayed on the display part  30  by the processing at the display control part  20   c.  Due to this, the operator can view the display of the display part  30  and easily judge if the wire electro-discharge machine is normal in state.
 
(2) By the processing at the display control part  20   c , the normal range images  352 ,  362  and  392  which define the normal ranges set by the setting part  20   b  are displayed and the images of the detected values (needle images) corresponding to the normal range images  352 ,  362  and  392  are displayed. That is, the needle images  351 ,  361  and  391  are displayed on the meter images  350 ,  360  and  390  which include the normal range images  352 ,  362  and  392 . Due to this, the operator can easily determine if the physical quantities which represent the state of the wire electro-discharge machine are in the normal ranges or not, without referring to the numerical values displayed at the numerical value display parts  35   a,    36   a  and  39   a.  
 
(3) By the processing at the display control part  20   c,  the values of the scales of the meter images  350 ,  360  and  390  are changed in accordance with the rough working, finish working, and other working conditions, and the normal range images  352 ,  362  and  392  are displayed at the display part  30  by the same shapes and sizes regardless of the working conditions. Due to this, needle image  351 ,  361  and  391  are displayed on the same meter images  350 ,  360  and  390  regardless of the working conditions, so even if the working conditions change, the operator can easily determine whether the machine is normal in state.
 
(4) By the processing at the setting part  20   b,  the warning ranges are set contiguous to the normal ranges of the physical quantities and the abnormal ranges are set contiguous to the warning ranges. Further, by the processing at the display control part  20   c,  along with the normal range images  352 ,  362  and  392 , warning range images  353 ,  363  and  393  which define warning ranges and abnormal range images  354 ,  364  and  394  which define abnormal ranges are displayed. By displaying the warning range images  353 ,  363  and  393  in this way, it is possible to issue a warning to the operator before the wire electro-discharge machine reaches an abnormal state and prevent abnormalities in the machine in advance.
 
(5) The normal range images  352 ,  362  and  392 , the warning range images  353 ,  363  and  393 , and the abnormal range image  354 ,  364  and  394  are displayed by display colors different from each other. Due to this, the operator can clearly distinguish between the normal ranges, the warning ranges, and the abnormal ranges and can easily recognize the current state of the wire electro-discharge machine.
 
         [0054]    In the above embodiment, by the processing at the display control part  20   c,  meter images  350 ,  360  and  390  and needle images  351 ,  361  and  391  are displayed at the display part  30 . However, so long as controlling the display part  30  so as to display detected values of physical quantities which represent the state of the machine tool and normal ranges of the physical quantities set by the setting part  20   b,  the display control part  20   c  may be configured in any way. For example, the meter images  350 ,  360  and  390  may also display only the normal ranges of the physical quantities or may display only the normal ranges and the abnormal ranges. In this case, it is also possible to use the setting part  20   b  to set only the normal ranges and to deem the ranges other than the normal ranges the abnormal ranges. Alternatively, it is also possible to use the setting part  20   b  to set only the abnormal ranges and to deem the ranges other than the abnormal ranges the normal ranges. 
         [0055]    The displays of the numerical value display parts  35   a,    36   a  and  39   a  ( FIG. 6A ,  FIG. 6B ,  FIG. 7A ,  FIG. 7B ,  FIG. 8A  and  FIG. 8B ) may also be omitted. In the above embodiment, the meter images  350 ,  360  and  390  are made bar shaped or semicircular shaped, but the meter images are not limited to these shapes. So long as being displayed corresponding to the normal range images  352 ,  362  and  392 , the images of the detected values (needle images  351 ,  361  and  391 ) are also not limited to the above-mentioned shapes. The normal range images  352 ,  362  and  392 , the warning range images  353 ,  363  and  393 , and the abnormal range images  354 ,  363  and  394  are changed in display color from each other. However, so long as changing the modes of display from each other, the display colors may also be made the same. 
         [0056]    The values of the scales  350   a,    360   a  and  390   a  of the meter images  350 ,  360  and  390  are made constant, and the normal range images  352 ,  362  and  392  are displayed by different sizes when the working conditions is changed. However, it is also possible to display the normal range images  352 ,  362  and  392  by the same sizes regardless of the working conditions at the display regions  35 ,  36  and  39 . The meter images  350 ,  360  and  390  are displayed at the display part  30 . However, instead of displaying the meter images  350 ,  360  and  390 , it is also possible, for example, to attach mechanical type meters to the display part  30 . Therefore, the display part  30  may also display something other than images. 
         [0057]    In the above embodiment, as the physical quantities which represent the state of the machine tool, the working speed V, working fluid pressures Pb and Pc, filter pressure Pa, and water quality a are displayed, but the detected value T of the temperature detector  25  may also be displayed. Other physical quantities whose normal ranges change in accordance with the working conditions may also be detected. The configuration of the detecting part is not limited to the one described above. 
         [0058]    Above, a machine tool constituted by a wire electro-discharge machine is used, but the present invention can be similarly applied even to another machine tool where normal ranges of the physical quantities which represent the state of the machine tool change in accordance with the working conditions. 
         [0059]    According to the present invention, the detected values of physical quantities which change in normal ranges in accordance with the working conditions and the normal ranges of the physical quantities are displayed at the display part, so the operator can easily judge if the machine is normal in state. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           20  control device 
           20   b  setting part 
           20   c  display control part 
           21  to  24  pressure detector 
           25  speed detector 
           30  display part 
           100  wire electro-discharge machine 
           350 ,  360 ,  390  meter image 
           351 ,  361 ,  391  needle image 
           352 ,  362 ,  392  normal range image 
           353 ,  363 ,  393  warning range image 
           354 ,  364 ,  394  abnormal range image