Electrical discharge apparatus

Separately from an electrode jumping operation (an amount of rise of a first electrode jump (22)) aimed at discharging machining debris produced during electrical discharge machining, an electrode jumping operation (an amount of rise of a second electrode jump (23)) is inserted for which is set an amount of rise of jump with which balls or rollers used on a sliding portion of a mechanically driving part undergo one revolution or more. Further, in a case where an abnormality of a lubricant supplying unit (101) is detected, as for a program being continued, machining is stopped after the termination of the program, or machining is stopped after continuing the program within a fixed time duration, or a program other than for machining operation is made executable.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to improvements in an electrical discharge
 apparatus, and more particularly to improvements in an electrical
 discharge apparatus capable of maintaining for long periods of time the
 effect of lubricating balls or rollers used in sliding portions of
 mechanically driven parts, and improvements in an electrical discharge
 apparatus capable of preventing a decline in the operating efficiency due
 to a condition such as a machining stop during an abnormality of a
 lubricant supplying unit for supplying a lubricant to the mechanically
 driven parts.
 2. Description of the Related Art
 In an electrical discharge apparatus for machining a workpiece by supplying
 working electric power to a gap between the workpiece and an electrode
 provided in a working fluid, it is well-known that unless machining debris
 produced in the machining gap is eliminated by some method, the insulation
 between the electrode and workpiece and the repetition of electric
 discharge cannot be maintained in proper states, and that a state of arc
 discharge occurs, producing adverse effects such as a decline in the
 machining efficiency and the deterioration of characteristics of the
 machined surface.
 As a technique used in conjunction with the injection, ejection, and
 suction of a working fluid to discharge the machining debris from the
 machining gap, the so-called electrode jumping operation is known in which
 the electrode is intermittently made to undergo reciprocating motion at a
 high speed. In the case of a machining configuration for which fluid
 processing, such as the injection, ejection, and suction of the working
 fluid to discharge the machining debris, cannot be physically used, the
 electrode jumping operation is the only method of discharging the
 machining debris and is generally regarded as one of the machining
 conditions.
 An example of this electrode jumping operation is shown in FIG. 12, in
 which the ordinate shows the position of the electrode, while the abscissa
 shows the time. Parameters of the electrode jumping operation include an
 amount of rise of jump, 201, jump time 202, machining time 203, and a jump
 speed. For example, in a case where the machining depth is large, by
 securing a sufficiently large amount of rise of the jump, the discharge of
 the machining debris from the deep machined hole is made possible.
 Further, the jump speed affects the jump time (wasteful time) which does
 not contribute to machining as well as the machining-debris discharging
 efficiency. Thus, the setting of the parameters of the electrode jumping
 operation is very important to improve the machining rate by discharging
 the machining debris with high efficiency.
 In addition, to improve the machining efficiency, it is the general
 practice to repeat the electrode jumping operation at a high speed and a
 high acceleration. For example, the conditions of the electrode jumping
 operation in which the amount of rise of the jump is 0.2 mm and the
 maximum rate of arrival reaches 1,000 to 5,000 mm/min are set values which
 are commonly used frequently, and the speed and the acceleration are very
 large. Under such conditions of the electrode jumping operation, the load
 applied to mechanically driving parts, such as a ball screw and guides,
 which are generally used in the electrical discharge apparatus is very
 large, and it is difficult to form and maintain oil films of a lubricant
 on their sliding surfaces.
 Further, in the electrical discharge apparatus in which positional changes
 during machining are very small and machining is carried out for long
 periods of time as compared with general machine tools, the wear of
 sliding surfaces of the mechanically driving parts is sometimes
 accelerated locally. If the wear of the sliding surfaces continues to be
 accelerated locally, a decline in the machining accuracy, in particular,
 constitutes a problem in the electrical discharge apparatus for which
 working accuracy on the order of microns is required. Therefore, to avoid
 the occurrence of such wear, it is extremely important to supply the
 lubricant constantly or intermittently to the mechanically driving parts
 such as the ball screw and the guides.
 If the lubricant fails to be supplied to the mechanically driven parts due
 to the shortage of the lubricant or a failure of a lubricator, an advance
 in the wear of the mechanically driven parts is acceleratedly promoted,
 and the dust of wear produced continues to bite into the sliding surfaces,
 with the result being that the mechanically driven parts are subjected to
 further damage.
 Furthermore, with the electrical discharge apparatus, since the time of
 performing unmanned operation is long, and high-accuracy machining is
 required, it is necessary to provide some protective function or other in
 preparation for such a situation in which the supply of the lubricant is
 stopped. Accordingly, a protective function is provided for forcibly
 terminating a machining program in progress in the event that the supply
 of the lubricant is stopped during the operation of the electrical
 discharge apparatus. However, if such a protective function is operated,
 since the time of performing unmanned operation is long in the electrical
 discharge apparatus as described above, the decline in the operating
 efficiency due to the stoppage of the scheduled machining in its course
 has presented a large problem.
 SUMMARY OF THE INVENTION
 The present invention has been devised to overcome the above-described
 problems, and its primary object is to obtain an electrical discharge
 apparatus capable of maintaining for long periods of time the effect of
 lubricating balls or rollers used in sliding portions of mechanically
 driving parts during the electrode jumping operation.
 In addition, a secondary object is to obtain an electrical discharge
 apparatus which has the function of monitoring the state of operation of a
 lubricant supplying unit for supplying a lubricant to the mechanically
 driving parts, and which is capable of preventing a decline in the
 operating efficiency due to the stoppage of scheduled machining in its
 course upon detection of an abnormality in the remaining amount of the
 lubricant in the lubricant supplying unit or an abnormality of the
 lubricant supplying unit.
 To attain these objects, the electrical discharge apparatus in accordance
 with the invention comprises: first electrode jumping means whereby the
 electrode is caused to jump with respect to the workpiece and in which an
 amount of rise of jump (an amount of rise of a first electrode jump) is
 set as one machining condition aimed at discharging machining debris
 produced during electric discharge; second electrode jumping means whereby
 the electrode is caused to jump with respect to the workpiece and in which
 is set an amount of rise of jump (an amount of rise of a second electrode
 jump) with which balls or rollers used on a sliding portion of a
 mechanically driving part of the electrical discharge apparatus undergo
 one revolution or more; and a unit for determining the jumping operation
 for making a comparison between the amount of rise of the first electrode
 jump and the amount of rise of the second electrode jump, wherein in a
 case where the amount of rise of the first electrode jump is smaller than
 the amount of rise of the second electrode jump, the second electrode
 jumping operation is effected in addition to the first electrode jumping
 operation.
 In addition, the electrical discharge apparatus comprises: a lubricant
 supplying unit for supplying a lubricant to a mechanically driving part; a
 lubricant-remaining-amount monitoring unit having a function of detecting
 an abnormality in a remaining amount of the lubricant supplying unit or a
 remaining amount therein and outputting the same to a controller; and a
 lubricant-supplying-unit operation monitoring unit having a function of
 detecting an abnormality of the lubricant supplying unit and outputting
 the same to the controller, wherein machining is stopped after a program
 being executed is terminated in at least any one of a first case in which
 the abnormality has been detected by the lubricant-remaining-amount
 monitoring unit, a second case in which the remaining amount of the
 lubricant detected by the lubricant-remaining-amount monitoring unit is at
 a prescribed value or below, and a third case in which the abnormality has
 been detected by the lubricant-supplying-unit operation monitoring unit.
 Further, the electrical discharge apparatus comprises: the lubricant
 supplying unit; the lubricant-remaining-amount monitoring unit; and the
 lubricant-supplying-unit operation monitoring unit, wherein machining is
 stopped after a program being executed is continued within a fixed time
 duration in at least any one of the first case in which the abnormality
 has been detected by the lubricant-remaining-amount monitoring unit, the
 second case in which the remaining amount of the lubricant detected by the
 lubricant-remaining-amount monitoring unit is at the prescribed value or
 below, and the third case in which the abnormality has been detected by
 the lubricant-supplying-unit operation monitoring unit.
 Furthermore, the electrical discharge apparatus comprises: the lubricant
 supplying unit; the lubricant-remaining-amount monitoring unit; and the
 lubricant supplying-unit operation monitoring unit, wherein a program
 other than for machining operation is made executable in at least any one
 of the first case in which the abnormality has been detected by the
 lubricant-remaining-amount monitoring unit, the second case in which the
 remaining amount of the lubricant detected by the
 lubricant-remaining-amount monitoring unit is at the prescribed value or
 below, and the third case in which the abnormality has been detected by
 the lubricant-supplying-unit operation monitoring unit.

DETAILED DESCRIPTION OF THE PRESENT INVENTION
 (First Embodiment)
 FIG. 1 illustrates an electrical discharge apparatus in accordance with a
 first embodiment of the invention. Although, in practice, machining is
 possible in the respective directions of X, Y, and Z axes, a description
 will be given by citing as an example processing in the direction of the Z
 axis. In the drawing, a head 2 is supported by a guide 3 for effecting
 linear motion, a motor shaft 6 of a servo motor 5 is coupled to a ball
 screw 4 through a coupling 7, and a ball screw nut 16 is fixed to the head
 2 side. Accordingly, the ball screw 4 is rotated by an output of the servo
 motor 5 driven by a control unit 1, and the head 2 together with the ball
 screw nut 16 moves in a vertical direction (in the Z-axis direction). A
 movement commanding signal 12 for machining is outputted from an NC
 controller 9, is amplified by a servo amplifier 10, and is sent to the
 servo motor 5 to perform predetermined movement. Further, an encoder 8
 detects a present position, and feeds back its position detection signal
 11 to the servo amplifier 10.
 In addition, working electric power is supplied to a gap between a
 workpiece and an electrode, which is fixed to the head 2 disposed in a
 working fluid, by means of an unillustrated machining power supply, and
 the machining of the workpiece progresses as the electric discharge
 occurs.
 FIG. 2 is a partial cross-sectional view illustrating the details of a
 sliding portion of the ball screw nut 16. Numeral 17 denotes balls inside
 the ball screw nut, and 20 denotes a lubricant. When the balls 17 inside
 the ball screw nut rotate by one revolution or more, the lubricant 20 is
 applied to the entire peripheries of the balls 17.
 FIG. 3 shows a determination procedure for determining the execution of a
 large electrode jumping operation (a second electrode jumping operation)
 in accordance with the first embodiment. After a set value 22 of an amount
 of rise of the electrode jump (an amount of rise of a first electrode
 jump) which is set for machining is inputted, if a unit 21 for determining
 the jumping operation determines that it is impossible to rotate the balls
 17 inside the ball screw nut by one revolution or more, a command is sent
 to the NC controller 9 to insert during machining a set value 23 of an
 amount of rise of the electrode jumping operation (an amount of rise of
 thee second electrode jump) which is large in a fixed period. If it is
 assumed that the trough diameter of the ball screw 4 is D1, the diameter
 of the ball 17 is d1, and the lead of the ball screw 4 is L, then an
 amount of rise of jump, J1, with which the balls 17 undergo one revolution
 can be imparted by J1@L.sub..Yen. d1/D1. Accordingly, to determine whether
 or not the balls can be rotated by one revolution or more, it suffices if
 a comparison is made between the amount of rise of jump, J1, and the
 amount of rise of the first electrode jump, 22. In addition, as for the
 aforementioned amount of rise of the second electrode jump, it suffices if
 the amount of rise is of such a measure that the balls 17 inside the ball
 screw nut are rotated by, for example, two revolutions (e.g., J1.sub..Yen.
 2).
 In FIG. 1, a second movement commanding signal 13 for the electrode jump is
 outputted from the NC controller 9 to the servo motor 5 through the servo
 amplifier 10 by using a separate system from that of the movement
 commanding signal 12 for machining.
 When this signal is inputted thereto, the servo motor 5 drives the head 2
 so as to perform the second electrode jumping operation for each period by
 means of the ball screw 4 and the ball screw nut 16. The encoder 8 detects
 the present position, and the position detection signal 11 is fed back to
 the NC controller through the servo amplifier 10, so that it is possible
 to consecutively check the state of the second electrode jump.
 FIG. 4 shows the locus of operation of the Z axis in a case where the
 second electrode jump command has been inputted, and the ordinate
 indicates the position of the Z axis and the abscissa indicates the time.
 Reference numeral 30 denotes the locus of the second electrode jumping
 operation, and numeral 31 denotes the locus of the first electrode jumping
 operation. Further, numeral 32 denotes the period of the second electrode
 jumping operation, while 33 denotes the period of the first electrode
 jumping operation. These two jumping operations can be respectively
 effected In separate periods irrespective of the synchronization or
 asynchronization of the timing generated. As the second electrode jumping
 operation is inserted, even in a high-speed, small-rise-amount jumping
 region where the lubricating performance of mechanically driving portions
 is particularly liable to deteriorate, their lubricating capability can be
 sufficiently maintained.
 Furthermore, if the second electrode jumping operation is executed at a
 faster speed and with a greater amount of rise, it is possible to further
 enhance the effect of thoroughly spreading over the sliding surfaces the
 lubricant applied to the outer peripheral surfaces of the balls inside the
 ball screw nut which is a component part of the ball screw. This is due to
 the phenomenon in which the faster the movement between sliding surfaces,
 the greater the thickness of the oil film. The lubricating performance of
 the mechanical driving parts can be further improved by this effect.
 Although in the foregoing example a case has been shown in which the second
 electrode jumping operation is inserted periodically, a similar advantage
 can be obtained if the second electrode jumping operation is inserted non
 periodically, as shown in FIG. 5.
 (Second Embodiment)
 FIG. 1 also shows an electrical discharge apparatus in accordance with a
 second embodiment of the invention, in the drawing, the guide 3 is fixed
 to a column (not shown), and supports guide blocks 15 fixed to the head 2
 in such a manner as to be movable only in a vertical direction (in the
 Z-axis direction).
 FIG. 6 is a partially sectional view illustrating the details of sliding
 portions of the guide 3 and the guide block 15, and reference numeral 18
 denotes balls inside the guide block, while numeral 20 denotes the
 lubricant. If the balls 18 inside the guide block undergo one revolution
 or more, the lubricant 20 is applied to the entire peripheries of the
 balls.
 FIG. 3 also shows a determination procedure for determining the execution
 of the second electrode jumping operation in accordance with the second
 embodiment. After the amount of rise of the first electrode jump, 22, is
 inputted, if the unit 21 for determining the jumping operation determines
 that this amount of rise of the jump cannot cause the balls 18 inside the
 guide block to undergo one revolution or more, the determining unit 21
 instructs the NC controller to insert the second electrode jumping
 operation during the machining. If it is assumed that the diameter of the
 ball 18 inside the guide block is d2, then an amount of rise of jump, J2,
 with which the balls 18 undergo one revolution in this case can be
 imparted by J2=.pi..times.d2 (.pi. is the ratio of the circumference to
 its diameter). Accordingly, to determine whether or not the balls can be
 rotated by one revolution or more, it suffices if a comparison is made
 between the amount of rise of jump, J2, and the amount of rise of the
 first electrode jump, 22. In addition, as for the other operation, the
 description is the same as that for the first embodiment.
 In this case as well, it is possible to obtain an advantage similar to that
 of the first embodiment in the lubrication of the balls 18 inside the
 guide blocks used as mechanically driving portions. In addition, a similar
 advantage can be obtained in a case where rollers are used instead of the
 balls inside the guide blocks.
 (Third Embodiment)
 FIG. 1 also shows an electrical discharge apparatus in accordance with a
 third embodiment of the invention. The ball screw 4 is supported on the
 column (not shown) by means of a bearing 14.
 Each of FIGS. 7A and 7B is a cross-sectional view of that portion of the
 ball screw 4 which is supported on the column by means of the bearing 14.
 Reference numeral 19 denotes a ball inside the bearing, and numeral 20
 denotes the lubricant. In the same way as in the first and second
 embodiments, if the balls 19 inside the bearing undergo one revolution or
 more, the lubricant 20 is applied to the entire peripheries of the balls.
 FIG. 3 also shows a determination procedure for determining the execution
 of the second electrode jumping operation in accordance with the third
 embodiment. After the amount of rise of the first electrode jump, 22, is
 inputted, if the unit 21 for determining the jumping operation determines
 that this amount of rise of the jump cannot cause the balls 19 inside the
 bearing 14 supporting the ball screw 4 to undergo one revolution or more,
 the determining unit 21 instructs the NC controller to insert the second
 electrode jumping operation during the machining. If it is assumed that
 the inner ring diameter of the bearing 14 is D3, the diameter of the ball
 19 inside the bearing is d3, and the lead of the ball screw 4 is L, then
 an amount of rise of jump, J3, with which the balls 19 undergo one
 revolution in this case can be imparted by J3.congruent.L.times.d3/D3.
 Accordingly, to determine whether or not the balls can be rotated by one
 revolution or more, it suffices if a comparison is made between the amount
 of rise of jump, J3, and the amount of rise of the first electrode jump,
 22. In addition, as for the other operation, the description is the same
 as that for the first embodiment.
 In this case as well, it is possible to obtain an advantage similar to that
 of the first embodiment in the lubrication of the balls 19 inside the
 bearing 14 supporting the ball screw and used as mechanically driving
 portions. In addition, a similar advantage can be obtained in a case where
 rollers are used instead of the balls inside the bearing.
 (Fourth Embodiment)
 FIG. 8 shows an electrical discharge apparatus in accordance with a fourth
 embodiment of the invention. In the drawing, an arrangement provided is
 such that a lubricant supplying unit 101 supplies the lubricant to
 mechanically driving parts 102, and a lubricant-remaining-amount
 monitoring unit 103 for monitoring the remaining amount of the lubricant
 in the lubricant supplying unit 101 and a lubricant-supplying-unit
 operation monitoring unit 104 for monitoring the state of operation of the
 lubricant supplying unit 101 transmit signals to the controller 1 while
 constantly monitoring the lubricant supplying unit 101. The
 lubricant-remaining-amount monitoring unit 103 transmits an abnormality
 signal to the controller 1 in a case where the remaining amount of the
 lubricant in the lubricant supplying unit 101 is at a prescribed value or
 below. Further, the lubricant-supplying-unit operation monitoring unit 104
 transmits an abnormality signal to the controller 1 in a case where an
 abnormality such as the operation stop has occurred.
 In a case where an abnormality has been detected by the
 lubricant-remaining-amount monitoring unit 103 or the
 lubricant-supplying-unit operation monitoring unit 104, the controller 1
 immediately outputs an instruction for an alarm display to a monitoring
 unit 107. In the controller 1, the contents of machining command signals
 that are sent from a machining command unit 105 are computed, and a
 command signal concerning the subsequent continuation of the program is
 outputted to a machining unit section 106 which actually performs
 machining.
 FIG. 9 shows the procedure of determination by the controller 1 in a case
 where an abnormality has been detected by the lubricant-remaining-amount
 monitoring unit 103 or the lubricant-supplying-unit operation monitoring
 unit 104 in the fourth embodiment of the invention. The program being
 executed is continued as it is until its end, but the starting of a new
 program is inhibited after the end.
 (Fifth Embodiment)
 FIG. 8 also shows a basic configuration of an electrical discharge
 apparatus in accordance with a fifth embodiment of the invention. FIG. 10
 shows the procedure of determination by the controller 1 in a case where
 an abnormality has been detected by the lubricant-remaining-amount
 monitoring unit 103 or the lubricant-supplying-unit operation monitoring
 unit 104 in the fifth embodiment of the invention. The program being
 executed is continued for a certain time duration t1 upon detection of the
 abnormality, by if the program does not end within this time duration, the
 program is forcibly terminated, and the starting of a new program is
 subsequently inhibited.
 (Sixth Embodiment)
 FIG. 8 also shows a basic configuration of an electrical discharge
 apparatus in accordance with a sixth embodiment of the invention. FIG. 11
 shows the procedure of determination by the controller 1 in a case where
 an abnormality has been detected by the lubricant-remaining-amount
 monitoring unit 103 or the lubricant-supplying-unit operation monitoring
 unit 104 in the sixth embodiment of the invention. If a command for
 starting the machining program is inputted from the machining command
 unit, an alarm is issued to inhibit the execution, but in the case of a
 program which does not involve machining, such as setup program, the
 starting of the program is selectively possible.
 It should be noted that although, in the fourth to sixth embodiments, a
 case has been shown in which the lubricant remaining amount monitoring
 unit 103 monitors whether or not the remaining amount of the lubricant in
 the lubricant supplying unit 101 is at a prescribed value or below, and
 transmits an abnormality signal to the controller I if the remaining
 amount is at the prescribed value or below, the signal representing the
 remaining amount in the lubricant supplying unit 101 may be transmitted
 directly to the controller 1, and the determination may be made by the
 controller 1 as to whether or not the remaining amount of the lubricant is
 at the prescribed value or below.
 Since the invention is configured as described above, the invention offers
 the following advantages.
 As described above, the electrical discharge apparatus comprises: first
 electrode jumping means whereby the electrode is caused to jump with
 respect to the workpiece and in which an amount of rise of jump (an amount
 of rise of a first electrode jump) is set as one machining condition aimed
 at discharging machining debris produced during electric discharge; second
 electrode jumping means whereby the electrode is caused to jump with
 respect to the workpiece and in which is set an amount of rise of jump (an
 amount of rise of a second electrode jump) with which balls or rollers
 used on a sliding portion of a mechanically driving part of the electrical
 discharge apparatus undergo one revolution or more; and a unit for
 determining the jumping operation for making a comparison between the
 amount of rise of the first electrode jump and the amount of rise of the
 second electrode jump, wherein in a case where the amount of rise of the
 first electrode jump is smaller than the amount of rise of the second
 electrode jump, the second electrode jumping operation is effected in
 addition to the first electrode jumping operation. Accordingly, it is
 possible to obtain an electrical discharge apparatus capable of
 maintaining the effect of lubricating the aforementioned balls or rollers
 for long periods of time.
 In addition, the electrical discharge apparatus comprises: a lubricant
 supplying unit for supplying a lubricant to a mechanically driving part; a
 lubricant-remaining-amount monitoring unit having a function of detecting
 an abnormality in a remaining amount of the lubricant supplying unit or a
 remaining amount therein and outputting the same to a controller; and a
 lubricant-supplying-unit operation monitoring unit having a function of
 detecting an abnormality of the lubricant supplying unit and outputting
 the same to the controller, wherein machining is stopped after a program
 being executed is terminated in at least any one of a first case in which
 the abnormality has been detected by the lubricant-remaining-amount
 monitoring unit, a second case in which the remaining amount of the
 lubricant detected by the lubricant-remaining-amount monitoring unit is at
 a prescribed value or below, and a third case in which the abnormality has
 been detected by the lubricant-supplying-unit operation monitoring unit.
 Accordingly, it is possible to obtain an electrical discharge apparatus
 capable of preventing a decline in the operating efficiency since
 scheduled machining can be continued for a fixed time duration.
 Further, the electrical discharge apparatus comprises: the lubricant
 supplying unit; the lubricant-remaining-amount monitoring unit; and the
 lubricant-supplying-unit operation monitoring unit, wherein machining is
 stopped after a program being executed is continued within a fixed time
 duration in at least any one of the first case in which the abnormality
 has been detected by the lubricant-remaining-amount monitoring unit, the
 second case in which the remaining amount of the lubricant detected by the
 lubricant-remaining-amount monitoring unit is at the prescribed value or
 below, and the third case in which the abnormality has been detected by
 the lubricant-supplying-unit operation monitoring unit. Accordingly, it is
 possible to obtain an electrical discharge apparatus capable of preventing
 a decline in the operating efficiency since scheduled machining can be
 continued for a fixed time duration.
 Furthermore, the electrical discharge apparatus comprises: the lubricant
 supplying unit; the lubricant-remaining-amount monitoring unit; and the
 lubricant-supplying-unit operation monitoring unit, wherein a program
 other than for machining operation is made executable in at least any one
 of the first case in which the abnormality has been detected by the
 lubricant-remaining-amount monitoring unit, the second case in which the
 remaining amount of the lubricant detected by the
 lubricant-remaining-amount monitoring unit is at the prescribed value or
 below, and the third case in which the abnormality has been detected by
 the lubricant-supplying-unit operation monitoring unit. Accordingly, it is
 possible to obtain an electrical discharge apparatus capable of preventing
 a decline in the operating efficiency.
 As described above, the electrical discharge apparatus in accordance with
 the invention is capable of maintaining for long periods of time the
 effect of lubricating balls or rollers used in sliding portions of
 mechanically driving parts, and of preventing a decline in the operating
 efficiency due to such as a machining stop during an abnormality of the
 lubricant supplying unit for supplying the lubricant to the mechanically
 driving parts.
 Therefore, the electrical discharge apparatus in accordance with the
 invention is suitable for use in electrical discharge machining
 operations.