JP4474074B2 - Workpiece machining method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a workpiece machining method for machining a workpiece by holding a tool on a rotatable rotor shaft having high ground resistance.
[0002]
[Prior art]
FIG. 4 is a front view of a processing portion in a conventional printed circuit board drilling machine. The cross slide 1 is supported by a moving means (not shown) so as to be movable in the left and right (Y) directions. A pair of linear guide devices 2 are fixed to the cross slide 1. The saddle 3 is supported by the linear guide device 2 and is movable in the vertical (Z) direction in the figure by a moving means (not shown). A holder 4 is fixed to the center of the saddle 3, and a spindle 5 is fixed to the holder 4.
[0003]
The rotor shaft 6 is rotatably supported on the spindle 5 by air radial bearings 7 a to 7 c and is positioned and supported in the axial direction by an air thrust bearing 8. The rotor shaft 6 is provided with a rotor (rotor) 9 in which a copper material is annularly formed. A coil (stator) 10 is arranged at a position facing the rotor 9 of the spindle 5. The coil 10 is connected to an inverter power supply 11. The inverter power supply 11 converts the commercial AC voltage input from the three-phase power supply 12 into an AC voltage having a high frequency. A drill 14 is held at the tip of the rotor shaft 6.
[0004]
A pressure foot 20 is fitted to the tip of the spindle 5. The pressure foot 20 is supported by a pair of air cylinders 21. The air cylinder 21 is supported by the holder 4. One end of the measurement terminal 22a of the digital scale 22 supported by the saddle 3 is fixed to the pressure foot 20, and the relative position between the pressure foot 20 and the holder 4 is measured. The digital scale 22 is connected to the NC device 23. A bush 24 is fixed to the tip of the pressure foot 20.
[0005]
A printed circuit board 31 is fixed to the table 30. The table 30 is movable in a direction perpendicular to the paper surface (X direction).
[0006]
Then, a blind hole having a depth H from the surface of the printed circuit board 31 (hereinafter referred to as “blind hole”) is processed in the following procedure. That is, prior to machining, the air cylinder 21 is operated, and the distance A from the lower end of the bush 24 to the tip of the drill 14 is obtained in a state where the piston rod 21a is most protruded. When the inverter power supply 11 is operated and a current is passed through the coil 10, rotational torque is generated in the rotor 9 by the magnetic field generated in the coil 10, and the rotor shaft 6 rotates.
[0007]
When the saddle 3, that is, the holder 4 is lowered in this state, first, the lower end of the bush 24 comes into contact with the printed board 31 and presses the printed board 31 against the table 30. The pressure foot 20 stops descending with the printed circuit board 31 pressed, and thereafter rises relative to the holder 4 against air pressure. The NC device 23 reads the Z-axis coordinate Z0 when the measurement terminal 22a starts to move, and lowers the holder 4 from the coordinate Z0 by A + H. As a result, it was possible to perform processing with excellent accuracy.
[0008]
[Problems to be solved by the invention]
In addition to blind holes, through holes are processed on one printed circuit board. In the case of the above-described prior art, the scale terminal is worn by sliding because the measurement terminal moves up and down even when a through-hole that does not require precise management of the depth of the hole is processed. Therefore, it was necessary to frequently check the accuracy of the digital scale and regularly replace parts to prevent a decrease in measurement accuracy.
[0009]
In addition, since the height of the drill tip is measured through the pressure foot, there is a limit to the depth accuracy of the hole.
[0010]
The applicant of the present application disclosed in Japanese Patent Application No. 2000-163681 in a workpiece machining method in which a workpiece is machined by holding a tool on a rotatable rotor shaft having high resistance to ground, and the workpiece is insulated from the ground. A workpiece machining method was proposed in which the tip position of a tool is detected by measuring the axial voltage generated on the shaft through the workpiece. According to this processing method, maintenance and inspection were easy, and the depth of the hole could be processed with high accuracy. However, if a small conductive piece (hereinafter referred to as “chip”) is attached near the tip of the tool, the end of the chip will be mistaken as the tip of the tool, resulting in a shallow hole depth. was there.
[0011]
The object of the present invention is to solve the above-mentioned problems in the prior art, to facilitate maintenance inspection, and to process a workpiece with excellent hole depth accuracy even when conductive chips adhere to the vicinity of the tip of the tool. Is in providing a way.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a rotor constituting a motor on a rotor shaft, supports the rotor shaft with an air bearing, and supplies an alternating current to the stator constituting the motor. In the workpiece processing method of rotating the rotor shaft and processing the workpiece with a tool held on the rotor shaft, the workpiece is insulated from the ground, and a non-conductive member is provided on the side of the workpiece facing the tool. When the voltage induced in the rotor shaft by the alternating current supplied to the stator is applied to the conductive member of the workpiece, the tip of the tool comes into contact with the conductive member of the workpiece It is characterized by determining .
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on the illustrated embodiments.
[0014]
FIG. 1 is a front view of a processing portion in a printed circuit board drilling machine according to the present invention, and those having the same or the same functions as those in FIG.
[0015]
The printed circuit board 31 is fixed to the table 30 such that the copper foil 31c faces the drill 14, and is insulated from the table 30 by the insulating layer 31i. An insulating plate 50 is placed on the upper surface of the copper foil 31c. The copper foil 31 c is connected to an input terminal 43 a of a filter (here, a band pass filter) 43 through a cable 42. The output terminal 43b of the filter 43 is connected to the input terminal 44a of the comparator 44, and the ground terminal 43e is connected to the ground. An output terminal 44 b of the comparator 44 is connected to the NC device 23. The holder 4, the pressure foot 20, and the table 30 are grounded.
[0016]
Next, the shaft voltage will be described.
[0017]
The rotor shaft 6 is supported by the air radial bearings 7 a to 7 d and the air thrust bearing 8, and does not contact the spindle 5. That is, the rotor shaft 6 and the spindle 5 are substantially electrically insulated. When a switch (not shown) of the three-phase power supply 12 or the inverter power supply 11 is turned on, a shaft voltage V0 is generated on the rotor shaft 6 via the coil 10.
[0018]
FIG. 2 is an explanatory diagram of the shaft voltage.
[0019]
When the frequency of the three-phase power source 12 is 50 Hz, the shaft voltage V0 generated in the rotor shaft 6 has the waveform shown in FIG. This waveform is shown in FIG. 3B, the frequency Vis of the three-phase power source 12 shown in FIG. 5B, that is, the voltage Vs of 50 Hz, the control frequency of the inverter power source 11 and the voltage Vi1 of 1 kHz not shown. It is substantially equal to a waveform in which a waveform of a voltage Vi2 of 3 kHz, which is three times the control frequency of the inverter power supply 11, is superimposed.
[0020]
Next, a procedure for processing a blind hole having a depth H from the surface of the printed circuit board 31 will be described.
[0021]
Prior to processing, the air cylinder 21 is operated so that the piston rod 21a protrudes most. Then, the inverter power supply 11 is operated, a current is passed through the coil 10, and the holder 4 (that is, the drill 14) is lowered while the rotor shaft 6 is rotated.
[0022]
Then, first, the lower end of the bush 24 comes into contact with the insulating plate 50, the printed circuit board 31 is pressed against the table 30 through the insulating plate 50, and the descending is stopped in this state. When the holder 4 is further lowered and the tip of the drill 14 passes through the insulating plate 50 and comes into contact with the copper foil 31c, the shaft voltage V0 generated in the rotor shaft 6 is input to the filter 43. The filter 43 outputs the voltage Vi1 (or Vi2) of the shaft voltage V0 to the comparator 44. The comparator 44 outputs a detection signal to the NC device 23 when the sine wave voltage Vi1 (or Vi2) exceeds a predetermined voltage. When receiving the detection signal from the comparator 44, the NC device 23 reads the Z-axis coordinate Z1 at that time, lowers the holder 4 from the coordinate Z1 by H, and then raises the holder 4 (that is, the drill 14). Then, it moves to the next processing position and repeats the above procedure.
[0023]
By the way, when a drilling process is performed on the printed circuit board, there is a case in which the chips 60 of the copper foil 31c cut off along with the process adhere to the tip of the drill 14 that has come out of the insulating plate 50.
[0024]
FIG. 3 shows a processing state when chips adhere to the tip of the drill.
[0025]
As shown in FIG. 6A, when the chip 60 is attached near the tip of the drill 14, the lower end of the chip 60 first comes into contact with the insulating plate 50 as shown in FIG. Since the drill 14 rotates at a high speed, most of the chips 60 are detached from the lower end of the drill 14 at the moment when the lower end contacts the insulating plate 50. Further, the chips 60 that have not detached from the lower end of the drill 14 move to the rear of the drill 14 (upward in the figure) when the drill 14 cuts the insulating plate 50. As a result, as shown in FIG. 3C, the tip of the drill 14 directly contacts the copper foil 31c.
[0026]
Thus, even when the chip 60 is attached near the tip of the drill 14, the chip 60 does not intervene between the tip of the drill 14 and the copper foil 31 c, so the position of the tip of the drill 14 Can be reliably measured.
[0027]
【The invention's effect】
As described above, according to the present invention, the chips adhering to the drill tip can be reliably removed, so that processing with excellent depth accuracy can be performed.
[0028]
Moreover, since a special process for removing chips is not required, the processing efficiency is not reduced.
[Brief description of the drawings]
FIG. 1 is a front view of a processing section in a printed circuit board drilling machine according to the present invention.
FIG. 2 is an explanatory diagram of shaft voltage.
FIG. 3 shows a processing state when chips are attached.
FIG. 4 is an explanatory diagram of the prior art.
[Explanation of symbols]
14 Drill 30 Table 31 Printed Circuit Board 31c Copper Foil 31i Insulating Layer 50 Insulating Plate 60 Chip

Claims (1)

A rotor constituting the motor is disposed on the rotor shaft, and the rotor shaft is supported by an air bearing, and the rotor shaft is rotated by supplying an alternating current to the stator constituting the motor, and held on the rotor shaft. In a workpiece machining method for machining a workpiece with a tool
The work is insulated from the ground, and a non-conductive member is disposed on the side of the work facing the tool. A voltage induced in the rotor shaft by an alternating current supplied to the stator is A method of processing a workpiece, characterized in that, when applied to a conductive member, it is determined that the tip of the tool is in contact with the conductive member of the workpiece.

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