JPH0426976B2 - - Google Patents

Description

[Detailed description of the invention] [Field of application of the invention]

The present invention relates to a detection device for detecting damage to a tool of a machine tool from changes in machining traces of a workpiece.

[Background of the invention]

As a conventional device for detecting tool breakage, for example, as shown in Utility Model Application Publication No. 56-33151, it is possible to optically detect the amount of chips and detect tool breakage when the amount of chips decreases. However, this device can detect tool breakage only while chips are being discharged, and does not consider detecting tool breakage when the amount of chips being discharged is small or when there are no chips being discharged. Not yet. Further, US Pat. No. 3,912,925 describes that a tool is illuminated with light and a breakage of the tool is detected by the transmitted light. This device is a good method if the change in light intensity can be clearly determined depending on the presence or absence of a tool, but it is necessary to determine the shape of the tool at a predetermined timing when the tool moves with the vertical movement of the spindle. In processing machines, where the projection size of the tool from the spindle tip is limited, the equipment becomes larger because the projector and receiver are installed in a narrow space, so it is easy to monitor the machined area during actual processing work. It's not a thing. In particular, when machining a small shape, that is, drilling a hole with a small diameter, the tool and spindle are both small, so there is little change in the amount of light on the receiving side due to blocking the transmitted light, so detection of tool breakage is not stable. Something happened.

[Object of the present invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a tool breakage detection device that eliminates the drawbacks of the prior art and can accurately and stably detect tool breakage of any size.

[Summary of the invention]

In order to achieve the above object, the present invention monitors machining traces (ie, holes) remaining after machining a workpiece, and detects changes in the surface area of the machining traces formed on the surface of the workpiece. If the tool is in a normal state, the machining trace will have a predetermined surface area, but if the tool is in a broken state, that is, if it is partially broken or broken, the machining trace will have a smaller surface area than in the normal state. Furthermore, when using an optical sensor as a monitoring means, it is normal for chips to be scattered around machining traces, but by detecting chips as being in the same or similar category as machining traces, it is possible to prevent tool breakage. Identification can be ensured. This is because the amount (number) of chips increases if the tool is normal and decreases if the tool is broken, so the tendency is the same as the increase or decrease in machining traces. This is more advantageous as the tool becomes smaller.

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a layout diagram showing an embodiment of the present invention. In the figure, 1 is a spindle, 2 is a table disposed opposite to the spindle 1, and both are relatively moved or positioned by X, Y, and Z axis motors 3, 4, and 5, respectively. 6
is rotatably attached to the lower end of the spindle 1 with a tool, and is rotated by a spindle motor (not shown). The workpiece 7 is placed on the upper surface of the table 2, and is a thin plate. 8 is the workpiece 7
This is a through hole formed by the tool 6. A beam of light 9 is projected into the through hole 8 from the left, reflected by the workpiece 7, and then introduced into an image pickup tube, ie, a television camera 11, via an objective lens 10. The television camera 11 is an assembly of a plurality of photodetecting elements (for example, photoelectric conversion elements), and converts the image of the through hole 8 into an electrical signal. The light beam 9 projected onto the workpiece 7 is reflected by the surface of the workpiece 7, but as shown in FIG. 2, it is diffusely reflected at the processed part, that is, the through hole 8, and is therefore introduced into the TV camera 11 on the light receiving side. The intensity of the received light decreases, and the output signal a of the television camera 11 decreases in accordance with the intensity of the received light. 12 is a light source, which consists of a power source 13, a light emitting unit 14, and a condensing lens 15;
The light emitting unit 14 is controlled by the power source 13 so that it emits light of a constant intensity. 16 is a reflecting mirror provided on the path of the light beam. If optical path materials such as glass fibers are used for the path of the light beam on both the projection side and the opposite side, the path can be easily selected, which is effective for making the detection device smaller.
17 is a detection device that detects the image of the through hole 8 from the output of the television camera 11, one of the detection signals is output to the television 18, and the other is a buzzer, a colored lamp,
It is output to a display device 19 such as a light emitting element. 20 is
The NC device moves or positions the workpiece 7 within the XY coordinates by driving the X-axis motor 4 and Y-axis motor 5, and lowers or raises the tool 6 in the Z-axis direction by driving the Z-axis motor. let Furthermore,
From the NC device 20 to the detection device 17, the Z axis, that is, the tool 6
A signal is applied to rotate the . FIG. 3 is a block diagram showing a specific embodiment of the detection device 17, and the same parts as in FIG. 1 are given the same reference numerals. 21 is a camera control circuit that scans an image of the machining trace of the workpiece 7 and outputs a video signal. 2
Reference numeral 2 denotes a conversion circuit that discriminates a video signal at a predetermined signal level and converts it into a binary signal SI, and has a configuration as shown in FIG. In FIG. 4, 23 is a variable resistor for setting a predetermined signal level, 24 is a comparator, and 25 is an input terminal from the camera control circuit 21. R ₁ and R ₂ are resistors, and C ₁ and C ₂ are capacitors. 26 is an output terminal of the comparator 24 and is connected to an AND gate 27. 28 is an OR gate, which receives the synchronization signal of the TV 18 from the input terminal 29 and outputs it from the output terminal 30.
is connected to the television 18. 31 is a first gate circuit that determines the vertical synchronization sampling period of the video signal, and 32 is a second gate circuit that determines the horizontal synchronization sampling period of the video signal, detailed block diagrams of which are shown in FIGS. 5 and 6, respectively. show. FIG. 5 shows the first gate circuit that determines the vertical synchronization sampling period of the video signal SI mentioned above, and the seventh gate circuit.
The interval is determined by the number of horizontal synchronizing pulses SH that define the timing of the scanning lines _l1 to _l7 of the video signal shown in the figure.
Set AB. That is, the interval at which the vertical synchronization signal SV is output is such that the scanning line is
This corresponds to the time it takes to move from the top edge 18u to the bottom edge 18d of the screen of No. 8. And flipflop FF ₁
is connected to the set terminal S of the counter 34 and the load terminal L of the counter 34. Reference numeral 35 denotes a digital switch, through which an operator manually sets the number of scans from scanning line _l1 on the screen to position A. Since the output of the digital switch 35 is connected in parallel to the counter 34, the numerical data of the digital switch 35 is initially set in the counter by the scan start signal outputted from the AND gate 36. This determines the distance from the top edge 18u of the screen to A. The output of the flip-flop FF ₁ is input to an AND gate 36 , the other input terminal of the AND gate 36 is input with a horizontal synchronizing signal SH, and its output is connected to the subtraction input terminal of the counter 34 . Therefore, when the number of scans reaches the number set in the digital switch 35, the value of the counter 35 becomes 0 and a signal is output from the terminal _B0 , and this signal is sent to the flip-flop.
Resetting FF ₁ and flip-flop at the same time
Set FF ₂ and counter 37. Since the output of the flip-flop _FF2 becomes high level and the gate of the AND gate 38 is opened, the signal SH is applied to the subtraction input terminal of the counter 37. 39 is a digital switch connected in parallel to the counter 37, and the value of this digital switch 39 is
Corresponding to AB, when this value matches the number of scans, flip-flop _FF2 is reset. At this time, the output signal GV of flip-flop FF ₂ is in the interval AB
corresponds to FIG. 6 shows the second gate circuit that determines the horizontal synchronization sampling period of the video signal SI mentioned above;
The configuration is almost the same as that of the gate circuit. A horizontal synchronizing signal SH is connected to the set terminal S of the flip-flop FF ₃ and the load terminal L of the counter 40. 41
is a digital switch, and the operator manually switches the A from the left edge 18l of the screen of the television 18 shown in FIG.
Determine the distance to. 42 is an AND gate.
One input terminal of the AND gate 42 is connected to the output of the flip-flop _FF3 , and the other input terminal receives a clock pulse. That is, scan line l ₁
The section from the left end of ~l ₇ to A is determined. Also, in the same manner as in the case of vertical synchronization described above, flip-flop FF ₄ , AND gate 43, and counter 4
4. The section AD is defined by the digital switch 45. A signal GH which becomes high level during the scanning period AD can be obtained from the output terminal of the flip-flop _FF4 . The drive signal SF for the Z-axis motor 3 is input from the NC device 20 to the input terminal of the AND gate 27, and the clock oscillator 46
The output signal CK is input, and the video signal SI is input. The operation of the AND gate 27 will be explained using the waveform diagram shown in FIG. SV is a vertical synchronization signal, and SH is a horizontal scanning signal (H ₁ to _{H 7} ). The video signal SI is a scanning line l ₃ corresponding to the video 47 of the through hole 8 in FIG.
Only portions E, F, and G of l ₄ and l ₅ are input from the conversion circuit 22 to the AND gate 27 as high voltage levels. Signal GH has a high voltage level corresponding to section AD, and signal GV has a high voltage level corresponding to section AB. Since the signal SF is at a high voltage level while the tool 6 is lowering, the output of the AND gate 27 is obtained as the number of clock pulses corresponding to the E, F, and G portions of the signal SI, as shown in the signal SA. be able to. Signal SA is counter 4
8 and is counted and converted into an area signal. The other counter 49 is set with a value sufficient for the operator to determine the presence or absence of the through hole 8 or whether the tool 6 is damaged. That is, in the normal case,
We confirmed through preliminary experiments that the image of the large through hole 8, many chips, and the tool 6 look like shadows, and further confirmed that when the tool 6 breaks, there are small scratch marks, few chips, and no tool 6. The numerical value for determining that the image is a small shadow is also checked to determine the discriminant value for tool breakage. A comparator 50 compares the contents of the two counters 48 and 49, and outputs a signal when the count value N of the counter 48 exceeds the set value M of the counter 49. Since the output of comparator 50 is input to the set terminal S of flip-flop 51, the output of flip-flop 51 is at a high voltage level. 52 is a sequence circuit which stops the drive motors 3, 4, and 5 for the X, Y, and Z axes in response to a signal from the flip-flop 51, and displays on the display circuit 19 that the tool is broken. As described above, in the present invention, the area ABCD around the machining trace is limited, the image is captured,
The size of the shadow is monitored, and if the size of the shadow exceeds a predetermined size, the machining tool is determined to be normal.
Since tool breakage is detected when the size of the shadow does not exceed a predetermined size, broken processing tool detection is accurate and stable. Next, according to FIG.
A case will be described in which the present invention is applied to a printed circuit board drilling machine that uses 4 in combination. Pressure shaft 54
is Utility Model Publication No. 56-33151 listed in the Background of the Invention column.
As described in U.S. Pat. Compressed air from 62 is supplied to a cylinder 55 consisting of a housing 53, the outer periphery of the spindle 1, and a press shaft 54, and the lower end surface of the press shaft 54, which slides inside the cylinder 55, is pressed against the printed circuit board, which is the workpiece 7, and fixed. It is something to do. A passage hole 5 through which the light beam 9 passes is provided in the side wall of the pressure shaft 54.
6 is formed. The passage hole 56 is a long hole (approximately oval or rectangular shape, etc.) having long axes at the top and bottom. A suction port 58 for a dust removing device 57 is formed on the other side of the press shaft 54, particularly on the side away from the elongated hole 56, to constantly suck up chips and keep the inside of the press shaft 54 clean during machining operations. I try to keep it. By forming the suction port 58 and the elongated hole 56 on the side wall of the press shaft 54, and arranging the reflecting mirror 16 and the objective lens 10 outside the elongated hole 56, all chips are discharged without leaving any chips. In the case of a printed circuit board, it is effective in preventing chips from getting entangled in the printed circuit board (which is often used with a drill) and causing the board to break, and chips from adhering to the reflecting mirror 16 and the objective lens 10 to block the light beam. Especially long hole 5
As a result of experiments, it was clear that the above-mentioned effect is greater when the lens 6 is larger than the reflecting mirror 16 or the objective lens 10, or has a protruding portion. In the description of the embodiment of the present invention, the television 18 is used, but the image displayed on the television 18 can be recorded on a video tape and the processing state can be analyzed to make more effective use of the image. Also,
If the image on the television 18 is used for general purposes without being binarized, it can be used as a monitor for workers to visually check the state of processing. Furthermore, in this case, parallel lines are drawn on the vertical or horizontal axis on the screen of the television 18, or a cross-shaped cross line is drawn in the center of the screen to make it easier to see information such as the size and position of the machining trace. By including a scale for accurate sensing, the monitor becomes easier to use. Further, other photodetecting elements may be used instead of the television camera 11. Furthermore, if the light source is an intermittent light source (rectangular wave or pulsed light source) synchronized with the machining work of the tool 6 and the machining traces are monitored after machining, the temperature rise of printed circuit boards, etc. that are easily deformed by heat can be avoided. can be restricted.

【Effect of the invention】

According to the present invention, machining traces are monitored without directly monitoring the constantly moving tool shape, so tool breakage can be reliably detected. , since the machining process (from one descent to the ascent of the Z axis) is monitored,
This has the advantage that tool breakage detection is accurate and stable.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figure is an explanatory diagram showing the relationship between machining traces and output waveforms,
3 is a block diagram showing a part of FIG. 1, FIG. 4 is a detailed circuit diagram of a part of FIG. 3, FIGS. 5 and 6 are block diagrams showing a part of FIG. 3, and FIG. The figure is the first
8 is a waveform diagram explaining the operation of FIG. 3, FIG. 9 is a sectional view showing another embodiment of the present invention, and FIG. 10 is a diagram showing FIG. It is an L sectional view. 6...Tool, 7...Workpiece, 8...Through hole,
9... Luminous flux, 11... Optical sensor, 14... Light emitting section, 17... Detection device, 18... Television, 19...
... Display device, 20 ... NC device, 21 ... Camera control circuit, 22 ... Conversion circuit, 31 ... First gate, 32 ... Second gate.

Claims (1)

[Claims] 1. A table on which a workpiece is placed, a spindle that holds a processing tool, an X-axis motor and a Y-axis motor that perform two-dimensional positioning control by relative movement between the table and the spindle, and A tool breakage detection device for a machine tool is equipped with a Z-axis motor that drives and controls the Z-axis motor to move the workpiece toward or away from the workpiece in a vertical direction. A photoelectric conversion means that converts it into a signal, a control means that scans the video signal with the tool rising signal and outputs a signal corresponding to the area of the machining trace, and compares the signal corresponding to this area with a value input in advance. A tool breakage detection device for a machine tool, comprising a comparison means, and outputs a breakage signal when a signal corresponding to the area becomes larger than a pre-input value.