Abstract:
A cutting liquid supply device in a machine tool is configured to remove gas mixed in a cutting liquid supply line to improve the response of discharging a mist of cutting liquid. Cutting liquid is supplied from a pump ( 42 ) through a rotary joint ( 28 ) to a mist generation device ( 24 ) within a rotating spindle ( 29 ). The pressure of the cutting liquid is measured by a pressure sensor ( 47 ). An air vent device ( 30 ) for opening and closing, with respect to atmospheric pressure, piping ( 3 ) that supplies the cutting liquid is provided above the rotary joint ( 28 ). A detection signal is inputted in the control board ( 70 ) from the pressure sensor ( 47 ), and when the control board ( 70 ) detects, after the pump ( 42 ) stops the supply of the cutting liquid to the piping ( 3 ), that the pressure of the cutting liquid does not decrease to a level lower than a predetermined threshold value, the control board ( 70 ) instructs the air vent device ( 30 ) to open the piping ( 4 ) to the atmosphere.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a cutting liquid supply device for a machine tool. 
       BACKGROUND ART 
       [0002]    A machine tool discharging cutting liquid as a mist from a tip of a spindle is known as a machine tool reducing usage of cutting liquid to protect the environment. This machine tool discharges the cutting liquid from a tip of a tool as a mist while cutting work. However, when the spouting of the cutting liquid is late, bum-in or damage is caused. Therefore, a response to a mist spouting has been studied. 
         [0003]    For example, a machine tool disclosed in Japanese Patent No. 3087119 prevents leaking by sucking a fixed amount of cutting liquid in a cutting liquid supply line when a pump is stopped from supplying the cutting liquid. In this machine tool, late response is prevented by returning the cutting liquid sucked at the start of supply to the cutting liquid supply line again. 
         [0004]    Japanese Unexamined Patent Application Publication No. 6-201094 discloses a machine tool not discharging a mist but detecting with a monitoring device the pressure provided to piping in which lubricant is fed from a pump. In this machine tool, a bearing is prevented from burning by displaying a piping leak when the pressure is lower than a minimum alarm pressure. 
       SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
       [0005]    A pump supplies a minute quantity of cutting liquid of 10 μl/s (micro liters/second). On the other hand, the quantity of cutting liquid in the path length of the supply line increases in proportion to the path length. Gas mixed in the cutting liquid takes up a micro supply capacity of the pump, thereby reducing the response of discharging a mist of the cutting liquid after starting the pump. The pump uptime corresponds to the spindle machining time, and therefore the pump often repeats a stop and start every 5 to 10 seconds. Accordingly, the late supplying of the mist influences the quality of a product comprising the machined object. 
         [0006]    When there is a leak in the cutting liquid supply line, pressure increase is delayed. The inventors have studied and checked that the response until discharging the mist might become bad. 
         [0007]    In a machine tool in which the mist spouts from the tip of the spindle, the cutting liquid is introduced into the spindle from a rotary joint behind the spindle. In case the spindle is arranged in a horizontal direction, the rotary joint is roughly at the same horizontal level as the cutting liquid supply pump. On the other hand, in case the spindle is arranged in a vertical direction, the rotary joint is located at a higher position behind the spindle, so that a high place is formed in the cutting liquid supply line. 
         [0008]    In a process studying a cause to the bad response, it has been recognized that the gas mixed in the cutting liquid supply line gathers in the high place in the cutting liquid supply line, if there is a high place in the course of the cutting liquid supply line. 
         [0009]    An object of the present invention is to remove the gas mixed in the cutting liquid supply line and to improve the response for discharging the mist. 
       MEANS OF SOLVING THE PROBLEMS 
       [0010]    A cutting liquid supply device of the present invention, in a machine tool including a supply line to supply cutting liquid from a pump to a mist generation device in a rotating spindle through a rotary joint, includes a pressure sensor to measure a pressure of the cutting liquid supplied from the pump, an air vent device to open and close the supply line to atmospheric pressure, and a control board. The air vent device is provided at a position above the rotary joint in the supply line. After a detection signal is inputted to the control board from the pressure sensor, and the pump is stopped from supplying the cutting liquid to the cutting liquid supply line, the control board instructs the air vent device to open the cutting liquid supply line to the atmospheric pressure when it is detected that the pressure of the cutting liquid does not decrease to a level lower than a predetermined threshold value. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  illustrates a machine tool  1  according to an embodiment of the present invention; 
           [0012]      FIG. 2  illustrates pipe lines of the machine tool  1 ; 
           [0013]      FIG. 3  illustrates pressure in a cutting liquid supply line; and 
           [0014]      FIG. 4  illustrates the flow of a monitor program  70   d.    
       
    
    
     DESCRIPTION OF THE REFERENCE NUMERAL 
       [0015]      1  machine tool 
         [0016]      2  spindle unit 
         [0017]      24  mist generation device 
         [0018]      26  compressed air supply passage 
         [0019]      27  cutting liquid supply passage 
         [0020]      28  rotary joint 
         [0021]      30  air vent device 
         [0022]      40  supply control device 
         [0023]      42  pump 
         [0024]      50  gas supply device 
         [0025]      60  tank 
         [0026]      70  control board 
         [0027]      90  operation panel 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0028]      FIG. 1  illustrates a machine tool  1  according to an embodiment of the present invention. In the following descriptions, a three-dimensional coordinate system of XYZ assumes that an X direction, a Y direction and a Z direction are respectively a lateral direction, a longitudinal direction and a vertical direction. As shown in  FIG. 1 , the machine tool  1  of the present invention includes a base  200 , a Y slide  300  that slides in the Y direction on the base  200 , an X slide  400  that slides in the X direction on the Y slide  300 , a Z slide  500  that slides in the Z direction on the X slide  400 , and a spindle unit  2  that is loaded on the Z slide  500 . This machine tool  1  is known as a vertical machine tool. The stacking of the Y slide  300 , the X slide  400  and the Z slide  500  on the base  200  may be in any order. The spindle unit  2  includes a spindle motor  20 , a spindle  21  having a mist generation device  24 , and a holder  22  to hold a tool  23 . A rotating spindle  29  from the spindle motor  20  to the spindle  21  and the bottom holder  22  extends in the vertical direction and includes a cutting liquid supply passage  27  and a compressed air supply passage  26  in the spindle. 
         [0029]    The machine tool  1  further includes a gas supply device  50  to receive compressed air from a compressed air source  80 , a cutting liquid tank  60 , a supply control device  40  provided on the Z slide, a control board  70  and an operation panel  90 . A rotary joint  28  to communicate the cutting liquid supply passage  27  to the compressed air supply passage  26  in the rotating spindle  29  is provided on the spindle motor  20 . A cutting liquid supply line includes piping  3  from the tank  60  to the supply control device  40 , piping  4  from the supply control device  40  to the rotary joint  28 , and the cutting liquid supply passage  27  in the rotating spindle. 
         [0030]    The machine tool  1  is called a vertical machine tool because the rotating spindle  29  of the spindle unit  2  extends in the downward Z direction. The rotary joint  28  is located on the top of the spindle unit  2 , the highest part of the machine tool  1 . An air vent device  30  is provided above the rotary joint  28 , which is the highest point of the cutting liquid supply line. 
         [0031]    The control board  70  controls the gas supply device  50  and the supply control device  40  according to detection signals from a level gauge  61  and a pressure sensor  47  that are mentioned later in  FIG. 2 . In addition, the control board  70  displays detections on the operation panel  90  and receives instructions from the operator. These controls are operated by running a program  70   c , which is stored in a memory unit  70   a  in the control board  70 , with a processing unit  70   b.    
         [0032]      FIG. 2  illustrates a piping system of the machine tool  1 . The mist generation device  24  to make the cutting liquid into a mist through the use of compressed air is placed in the spindle  21 . The mist generation device  24  includes a nozzle  24   a , a ball  24   b  and a compressed spring  24   c.    
         [0033]    The nozzle  24   a  is provided at the tip of the cutting liquid supply passage  27  that passes from the rotary joint  28  and through the rotating spindle  29  to introduce the compressed air in the compressed air supply passage  26  from the side face. In addition, the ball  24   b  is located at the center and urged by the compressed spring  24   c  toward the cutting liquid supply passage  27  to close the cutting liquid supply passage  27 . When the cutting liquid in the cutting liquid supply passage  27  becomes equal to or greater than a predetermined pressure, the ball  24   b  is displaced downwardly against the elasticity of the compressed spring  24   c  to open the cutting liquid supply passage  27 . Conversely, when the cutting liquid in the cutting liquid supply passage  27  becomes equal to or less than a predetermined pressure, the ball  24   b  is displaced upwardly by the elasticity of the compressed spring  24   c  to close the cutting liquid supply passage  27 . The compressed air is supplied to the tip of the nozzle  24   a  by the compressed air supply passage  26 , and the cutting liquid, which is strongly stirred by the compressed air, is discharged as a mist from the tip of the tool  23  via center holes of the holder  22  and the tool  23 . 
         [0034]    The air vent device  30  includes a piston  30   b  in a cylinder chamber  30   a  and blocks the piping  4  for the cutting liquid with the compressed spring  30   d  through the ball  30   c . When the compressed air flows into the cylinder chamber  30   a , the piston  30   b  is displaced upwardly against the compressed spring  30   d  to place the piping  4  at atmospheric pressure. 
         [0035]    The supply control device  40  includes a pump  42 , a suction discharge device  41  and a pressure sensor  47 . The pressure sensor  47  measures the pressure of the piping  4  between the supply control device  40  and the rotary joint  28  and sends it to the control board  70  shown in  FIG. 1 . 
         [0036]    The pump  42  includes a cylinder chamber  42   a  for cutting liquid and a cylinder chamber  42   b  for compressed air in an opposed state. Connected pistons  42   c  and  42   d  are respectively provided in the cylinder chambers  42   a  and  42   b . The pistons  42   c  and  42   d  are always urged in one direction by the compressed spring  42   e . The pump  42  has check valves  45  and  46  provided at the inflow side and the discharge side, respectively. A directional valve  43  intermittently feeds the compressed air to the pump  42  to drive the pump  42 . When the compressed air is provided to the cylinder chamber  42   b  of the pump  42 , the cutting liquid is transferred by the piston  42   c  and, when the compressed air is stopped, the piston  42   d  is returned by the compressed spring  42   e  in the pump to remove the gas in the piston chamber  42   b . The removed gas is discharged to the atmosphere through the directional valve  43  and a silencer  43   a.    
         [0037]    The suction discharge device  41  includes a cylinder chamber  41   a  for cutting liquid and a cylinder chamber  41   b  for compressed air in an opposed state. Connected pistons  41   c  and  41   d  are respectively provided in the cylinder chambers  41   a  and  41   b . The pistons  41   c  and  41   d  are always urged in one direction by a compressed spring  41   e.    
         [0038]    The directional valve  44 , which feeds the compressed air to the air vent device  30 , discharges the gas in the piston chamber  30   a  of the air vent device  30  to the atmosphere through a silencer  44   a  when the compressed air is stopped. 
         [0039]    The gas supply device  50  includes a pressure regulating valve  51  to control the supply pressure of the compressed air, a directional valve  52 , and a check valve  53  to permit the compressed air in the compressed air supply line to flow through the directional valve side. The directional valve  52  includes a silencer  52   a  to receive the compressed air from compressed air supply piping  5  and to discharge the compressed air in the piping  5  to the atmosphere. The pipings  9  and  8  directly convey the compressed air from the compressed air supply  80  to the directional valves  44  and  43 , respectively. 
         [0040]    The above-mentioned directional valves  44 ,  52  and  43 , which receive the compressed air from the same compressed air source  80 , are controlled with the control board  70  shown in  FIG. 1 . Though the control board  70  is transferred to the state of “pump-ON” during cutting with the tool  23 , the directional valve  43  is controlled so as to intermittently provide the compressed air to the pump in the state of “pump-ON”. In the state of “pump-OFF”, movements to intermittently provide the compressed air to the pump are stopped. 
         [0041]    The cutting liquid tank  60  has a level gauge  61  to measure the liquid level of the stored cutting liquid. The detected liquid level is transmitted to the control board  70  of  FIG. 1 . 
         [0042]    The machine tool  1  is operated as follows. When the directional valve  52  is switched to the compressed air supply side, the compressed air is provided to the mist generation device  24  through the rotary joint  28  and the compressed air supply passage  26  of the rotating spindle  29 . The compressed air flows into the cylinder chamber  41   b  of the suction discharge device  41 , pressing and displacing the piston  41   d  toward the side of the other piston  41   c  against the elasticity of the compressed spring  41   e . Accordingly, the capacity of the cylinder chamber  41   a  of the cutting liquid side is minimized. 
         [0043]    The directional valve  43  is repeatedly reciprocated and displaced between the compressed air supply side and the compressed air outflow side. When the directional valve  43  is located at the compressed air supply side, the piston  42   d  is pressed toward the side of the other piston  42   c  against the elasticity of the compressed spring  42   e , because the compressed air is supplied into the cylinder chamber  42   b . On the other hand, when the directional valve  43  is located at the compressed air outflow side, the piston  42   b  is displaced by the elasticity of the compressed spring  42   e , because the compressed air in the cylinder chamber  42   b  flows out of the directional valve  43 . The piston  42   c  of the cylinder chamber  42   a  is displaced whenever the above-mentioned operations are repeated, and therefore, the cylinder chamber  42   a  repeatedly sucks the cutting liquid in the cutting liquid tank  60  and discharges it. This is the state of “pump-ON”. 
         [0044]    The cutting liquid discharged in this way reaches the mist generation device  24  through the rotary joint  28  and the cutting liquid supply passage  27 . The ball  24   b  is pushed downwardly by the pressure of the cutting liquid against the urging of the compressed spring  24   c , and the cutting liquid supply passage  27  is open. Accordingly, the cutting liquid is made into a mist by mixing and stirring with the compressed air to flow out from the tip opening of the tool  22  to the outside through the center hole. 
         [0045]    When the supply of compressed air is stopped by displacing the directional valve  52  to the compressed air outflow side, the supply of the compressed air to the mist generation device  24  is stopped, the operation of the pump  42  is also stopped, and the supply of the cutting liquid into the cutting liquid supply line is stopped. 
         [0046]    In the suction discharge device  41 , the cutting liquid in the piping  4  is sucked by displacing the piston  41   c  by the elasticity of the compressed spring  41   e , because the compressed air in the cylinder chamber  41   b  flows out of the directional valve  52 . This operation prevents leaking of the cutting liquid in the cutting liquid supply passage  27  from the tool  23 . 
         [0047]    When the directional valve  52  is again displaced to the side for supplying the compressed air under the condition where the supply of the compressed air is stopped, the compressed air is supplied to the mist generation device  24  through the piping  5  like the above. The supplied compressed air is supplied into the cylinder chamber  41   b  of the suction discharge device  41 , where it displaces the piston  41   d  with a pressing force to the side of the other piston  41   c  against the elasticity of the compressed spring  41   e . The pressing displacement forces out the cutting liquid remaining in the cylinder chamber  41   a , and the forced cutting liquid is supplied into the cutting liquid supply line. 
         [0048]    Abnormal functioning in the cutting liquid supply line of the machine tool  1  will be explained with reference to  FIG. 3 . In addition,  FIG. 3A  illustrates a normal waveform detected by the pressure sensor  47 . This indicates the state in which the pressure which, at the time when the pump  42  is turned OFF, is within the normal pressure from P 1  to P 2 , sharply increases when the pump is turned ON, reaches the normal pressure from P 3  to P 4  when the pump  42  is turned ON, forms a pulsating current shaped pressure waveform when the pump  42  is intermittently driven, and sharply decreases to the normal pressure when the pump  42  is turned OFF. 
         [0049]    The abnormal functioning to be detected by the pressure sensor  47  can be classified roughly into the following four types. 
         [0050]      1 . The state in which the pressure is too high after the pump is turned ON ( FIG. 3B ). 
         [0000]    It is the state in which the pressure increases beyond the limits of the normal pressure from P 3  to P 4  after driving the pump  42  in the state of the pump-ON. 
         [0051]      2 . A delay in the pressure increasing at the time the pump is turned ON ( FIG. 3C ). 
         [0000]    It takes more time than normal until the pressure reaches the normal pressure from P 3  to P 4  after the pump  42  is driven in the state of the pump-ON. 
         [0052]      3 . A delay in the pressure decreasing at the time the pump is turned OFF ( FIG. 3D ). 
         [0000]    It takes more time than normal until the pressure reaches the normal pressure from P 1  to P 2  after the pump  42  is turned off. 
         [0053]      4 . The state in which the pressure is too low after the pump is turned OFF ( FIG. 3E ). 
         [0000]    It is the state in which the pressure decreases beyond the limits of the normal pressure from P 1  to P 2  after the pump  42  is turned off. 
         [0054]    Though these abnormal states are not preceded by specific distinct causes, respectively, the causes can be expected. 
         [0055]    In the above-mentioned abnormal functioning type  1 , a case in which the pump  42  discharges a great deal of cutting fluid because of the compressed air pressure too high and a case in which the cutting liquid supply line is clogged are assumed. 
         [0056]    In the above-mentioned abnormal functioning type  2 , a case in which air enters the cutting liquid supply line, a case in which a leak occurs in the cutting liquid supply line, a case in which the cutting liquid supply passage  27  is out of order, and a case in which a leak occurs in the rotary joint  28  are assumed. 
         [0057]    In the above-mentioned abnormal functioning type  3 , a case in which air enters the cutting liquid supply line is assumed. 
         [0058]    In the above-mentioned abnormal functioning type  4 , a case in which a leak occurs in the cutting liquid supply line and a case in which poor discharge occurs in the pump  42  are assumed. 
         [0059]    The memory unit  70   a  of the control board  70  has a monitoring program  70   d  that notifies the operator by displaying warnings on the operation panel  90  and monitors and deals with the abnormal states. 
         [0060]    Hereinafter, the monitoring program  70   d  will be explained with reference to  FIG. 4 . The monitoring program  70   d  is started when the control board  70  is in the state of pump-ON (S 100 ). 
         [0061]    In a step S 101 , the pressure of the cutting liquid before the pump  42  discharges is measured by the pressure sensor  47 , and whether or not the pressure exceeds an upper threshold value P 2  is monitored. If the pressure exceeds the upper threshold value P 2 , a flag NG 1  is displayed to indicate abnormal functioning. If the pressure does not exceed it, the cutting liquid is discharged from the pump  42  by providing the compressed air to the pump  42  in a step S 105 . In a step S 106 , whether or not the pressure exceeds an upper threshold value P 4  a predetermined time after the pressure sensor  47  is turned ON, is monitored. If the pressure exceeds the upper threshold value P 4 , the flag NG 2  is displayed to indicate abnormal functioning. If the pressure does not exceed the upper threshold pressure P 4 , in a next step S 108 , whether or not the pressure is below a lower threshold value P 3  when the pressure sensor  47  is turned ON is monitored. If the pressure is below the lower threshold value P 3 , the flag NG 3  is displayed. If the pressure is not below the lower threshold pressure P 3 , in a next step S 110 , whether or not the control board  70  transits to the state of “pump-OFF” is monitored, and the operation returns to the step S 108  unless the control board  70  is in the state of “pump-OFF”. 
         [0062]    When transiting to the state of “pump-OFF”, whether or not the step S 108  has ever passed through the state of OK in a step S 111 . If even once passed, the pump  42  is stopped in a step S 114 . 
         [0063]    In a step S 115 , the pressure after the predetermined time progress after the pump-OFF is measured by the pressure sensor  47 , and whether or not the pressure exceeds the upper threshold value P 2  is monitored. If the pressure exceeds the upper threshold value P 2 , the flag NG 4  is displayed to indicate abnormal functioning. If the pressure does not exceed the upper threshold pressure P 2 , whether or not the pressure is below the lower threshold value P 1  is monitored in a step S 119 . If the pressure is below the lower threshold value P 1 , the flag NG 5  is displayed to indicate abnormal functioning If the pressure is not below the lower threshold value P 1 , the step S 119  is repeated until transiting to the “pump-ON” again in a step S 123 . 
         [0064]    The flags NG 1  to NG 5  are memorized in the memory unit  70   a  of the control board  70 . In the steps of the monitoring program  70   d , the correspondences and the warnings in cases in which the flags NG 1  to NG 5  are displayed is explained hereinafter. 
         [0065]    If the flag NG 1  is displayed in the step S 101 , the air vent device  30  works for a predetermined time in the step S 102 , and the pressure in the cutting liquid supply line is detected again in the step S 101 . A step S 103  shifts to a step S 104  when the step S 101  and the step S 102  are repeated five times, and the machine tool  1  is stopped with the warning “Air removal alarm” on the operation panel  90 . 
         [0066]    When the flag NG 2  is displayed in the step S 106 , the machine tool  1  is stopped with a warning “On-high alarm” on the operation panel  90 . On the basis of the warning, the operator checks whether the cutting liquid supply line is clogged, and restarts the machine tool under the condition that the pressure of the compressed air is reduced. 
         [0067]    When the flag NG 3  is displayed in the step S 108 , the pump  42  has its drive cycle advanced and its discharge quantity increased in the step S 109 . According to this action, the pressure of the cutting liquid is restored. However, when the flag NG 3  is repeatedly encountered many times in the step S 112 , the machine tool  1  is stopped with the warning “On-low alarm” on the operation panel  90  in the step S 113 . The operator manually operates the air vent device  30  on the basis of the warning or checks the discharge quantity of the pump  42 . 
         [0068]    When the flag NG 4  is displayed in the step S 115 , the air vent device  30  performs air venting in a step S 116 . In a step S 117 , it is repeatedly checked whether or not air venting is carried out a predetermined number of times, and if the air venting is carried out the predetermined number of times, the machine tool is stopped with warning “OFF-high alarm” on the operation panel  90  in a step S 118 . The operator manually operates the air vent device  30  based on the warning. 
         [0069]    When the flag NG 5  is displayed in a step S 119 , the pump  42  is operated until the pressure reaches the lower threshold value P 1  in a step S 120 . If it is judged that the pressure reaches the lower threshold value P 1  more than T 1  seconds after the start of operation of the pump  42  in the step S 121 , the machine tool  1  is stopped with the warning “OFF-low alarm” on the operation panel  90  in a step S 122 . The operator checks the discharge quantity of the pump or leakage from the cutting liquid supply line. 
         [0070]    As mentioned above, the monitoring program  70   d  stops the machine tool  1  when several iterations of restoring operation are automatically detected as shown in the steps S 103 , S 112  and S 117 , or when the predetermined time passes after automatically detecting a restoration, as shown in the step S 121 . 
         [0071]    In this example, in case the pressure is below the lower threshold value P 3  at the time of “pump-ON”, and abnormal functioning is detected in the response at the beginning of mist spouting (“ON-low alarm”), the discharge quantity of the pump  42  is increased, because it is not assumed only that air is in the cutting liquid supply line (the step S 109 ). On the other hand, in case the abnormal functioning is that the pressure does not decrease to the level lower than the lower threshold value P 2  at the time “pump-OFF” is detected (“OFF-high alarm”), the air vent device  30  is driven because the abnormal functioning itself does not cause poor cutting (the step S 116 ). In the case of “OFF-high alarm”, air is almost certainly in the cutting liquid supply line. Therefore, in most cases, according to this operation, the response of the mist spouting at the next occurrence of “pump-ON” can be restored. 
         [0072]    In the above-mentioned example, the number (N) of alarm judgments and the time (T) can be determined from ranges of possible values. A valve pump, a gear pump, a piston pump, a screw pump, or the like may be used as the pump  42 . Though the air vent device  30  is placed at the high point in the cutting liquid supply line, it is effective if it is placed at the high point between the pump  42  and the rotary joint  28  and higher than the rotary joint  28 .