JPH0619265B2 - Apparatus and method for detecting the presence or absence of a drill bit in a waveguide - Google Patents

Description

The present invention relates to a microwave detection device, and more particularly to a microwave detection device that detects the presence or absence of a drill bit in a near range.

Many detection devices used in the industry for automatically detecting the presence or absence of a tool are not sensitive enough to accurately and repeatedly detect the presence or absence of a tool when the tool is relatively small.
For example, the diameter of the holes drilled in the printed circuit board is less than 0.33 mm, and the printed circuit on a highly automated machine that makes many holes at once using a fine drill bit to drill such small holes. The board is made. Workers must load and unload stacks of printed circuit boards on multiple machines. As a result, the operator cannot continue to visually monitor the drill bit with considerable accuracy. As a result, overlooking a broken drill bit will result in a large number of defective items that must either be discarded or costly to become a product.

The present invention provides an apparatus and method for detecting the presence or absence of a drill bit at close range. In particular, the device for detecting the presence or absence of a drill bit according to the invention is suitable for detecting breakage of the drill bit during automatic operation.

The device of the present invention is easy to manufacture and can be installed on existing or new machines.

The device of the present invention surpasses conventional devices in both sensitivity and range of application.

The device of the present invention is particularly useful in such a field because it is relatively insensitive to external noise, dust and oil, which are often problems in conventional detection devices.

The microwave detection device of the present invention is a waveguide having a hole for inserting a drill bit, which is located at one end of the waveguide, sends a microwave signal into the waveguide toward the drill bit, and is reflected. A transmitting and receiving device for receiving a returning microwave signal, a transmitting microwave signal and a receiving microwave signal for generating an output signal having a component indicating whether or not a drill bit is present in the hole of the waveguide. A heterodyne mixer circuit, and a detector connected to the output of the mixer circuit for comparing the component of the output signal with a predetermined level to determine the presence or absence of the drill bit, The position of the hole in the wave tube is selected to optimize the signal strength from the mixer circuit. The transceiver device may be a transceiver. The transceiver then comprises a Gunn diode and a Schottky diode. An amplifier for amplifying the output signal may be connected between the mixer circuit and the detection device.

A hole may be drilled in the center of the waveguide and a shorting stub may be placed behind the drill bit. In that case, the short-circuit stub is arranged so as to optimize the signal strength from the mixer circuit.

Nλ / 4 or Nλ / 8 (where N is an integer,
λ is the wavelength of the transmitted signal) and a shorting stub may be placed,
Also, the hole of the waveguide is Nλ / 4 or Nλ from the transmitter / receiver.
It may be placed at / 8.

The waveguide hole may be 12.7 mm or less.

In addition, the method of the present invention includes inserting a drill bit into a hole of a waveguide, sending a microwave signal into the waveguide toward the drill bit, receiving a microwave signal reflected back from the drill bit, and transmitting the microwave signal. Heterodyning the microwave signal and the received microwave signal to produce an output signal having a component indicating the presence or absence of a drill bit in the waveguide bore, and a DC component of the output signal. Is compared with a predetermined level to determine the presence or absence of a drill bit, and the position of the waveguide hole relative to the transceiver is selected to optimize the signal strength from the mixer circuit.

A shorting stub may be placed behind the drill bit in the waveguide. In this case, drill bit to Nλ / 4 or N
A short-circuit stub is arranged at λ / 8 (N is an integer, λ is a wavelength of a transmission signal). Adjacent the drill bit to the end of the waveguide and from the microwave source to Nλ / 4 or Nλ / 8
You may arrange in the distance of.

Embodiments will be described below with reference to the accompanying drawings. The automatic punching machine 9 is used to punch very small holes in a stack of printed circuit boards 10. The machine 9 includes at least one pressure foot assembly 11 that houses a retractable drill or drill bit 12 at each drilling station. The present invention is particularly useful for drilling targets having a diameter of 0.33 mm (0.013 ") or less, but also for large size targets.

The microwave detection system of the present invention is shown in the figure as being retrofitted to a pressure foot assembly of a machine.
The system need not be in physical contact and may be mounted at any convenient location to detect target continuity or discontinuity. The detection system includes a waveguide 15 and a transceiver module 17. Waveguide 1
5 passes through the working zone of the drilling station and is terminated by an adjustable shorting stub 18 of the type known and widely used in the art. The illustrated waveguide has a rectangular cross section, and has an upper wide wall 20 and a lower wide wall 21.
Two small coherent holes in the center of the
9 and 19 are included. Normally, the elongated shank of the cut 12 is housed in a hole, sufficient between the cuts to allow the cut to move vertically towards and away from the work piece. There are various gaps. Although the cut is shown in a broken state in FIG. 1,
In operation, the perimeter is in the waveguide for detection.

The transceiver module 17 shown in FIG. 2 includes a local oscillator 23. The oscillator 23, which may be a Gunn diode, is positioned at one end of the waveguide for propagating the microwave signal toward the target, which is shown in the figure. Adjustable shorting stub 18 is positioned in the waveguide behind the target and is adapted to reflect a well defined return signal back toward the module. The receiver section of the module includes a detector circuit such as a Schottky diode 25 and a mixer circuit 26. The return wave signal is picked up by diode 25 and applied to the mixer along with a sample of the transmitted signal.
These two input signals are heterodyne in the mixer so that they are pulled down to baseband to produce a readily detectable DC output signal that is representative of the swing rather than the frequency of the return signal. Since the output of the mixer is directly connected to the comparator 31 through the line 29 and the amplifier 31, only the DC component of the output signal is applied to the comparator 31.

This microwave system is said to cause a change in the standing wave ratio (SWR) of a transmitted signal when a continuous target such as a thin slit is present at a predetermined position at or near the end of the waveguide. It works based on the principle. This change in SWR can be received by the receiver and generate a signal representative of the target condition. The comparator threshold can be set to detect either the presence or the absence of the target. The system is similar to a Doppler radar, but it will be clear that it does not operate on the basis of the Doppler effect, since it does not use the frequency components of the output signal in the comparator circuit. As will be described in more detail below, the system produces a clear indication of the variation in the amplitude of the DC output signal component, and the presence or presence of a particular target in or out of the transceiver, rather than its presence or presence. It is adjusted to determine the omissions.

The dimensions of the waveguide are adjusted for the particular system application to provide maximum detection sensitivity as long as the width of the waveguide allows transmission. Changes in the height of the waveguide affect the power level of the transmission and thus the overall sensitivity of the system. The location of the shorting stub is also important. Preferably, the stubs are located at a distance of Nλ / 4 or Nλ / 8 from the centerline of the target, where λ is the wavelength of the signal transmitted and N is a positive integer. This positioning of the shorting stub allows the waveguide to perform detection on the linear portion of the return signal in tune with the transmitted signal.

As mentioned above, the local oscillator propagates electromagnetic waves into the hollow rectangular waveguide terminated at the shorting stub. Tool holes 19 in the wide wall of the waveguide are minimized while providing sufficient clearance to allow the tool to move axially without contacting the waveguide. When the tool is inserted into the waveguide, the amplitude and phase of the reflected wave incident on the transceiver 17 is changed. Since the transceiver heterodyne pulls this signal down to baseband, the DC component of the signal is transferred to an easily detectable offset change. The cross-sectional dimensions of the waveguide and the operating frequency of the local oscillator are scaled to any value compatible with wave propagation of dominant modes only. Although the system is tolerant of correct tool hole 19 positioning and stub positioning, these positions are preferably optimized for the particular application.

The electric field strength of dominant mode propagation in the waveguide is shown in FIGS. FIG. 3 shows a normal electric field profile across the waveguide cross section, where the maximum electric field strength occurs at the central axis 22 of the waveguide and falls symmetrically on either side of the axis 22. Go. When the tool 12 is positioned in the waveguide, the electric field is short-circuited at the axis, causing a distinct change in the electric field profile, as shown schematically by the arrows in FIG.
By choosing the operating frequency and waveguide dimensions to be dominant mode operation only, the tool behaves like a shorting stub with respect to the incident wave, resulting in discernible changes in the phase and amplitude of the return wave. .

Total electric field in transceiver (incident wave + reflected wave)
Let V _E be V _E = V _o [expσx) + (Γexp-σx)] (1). Where V _o is the incident wave at the load, σ is the complex propagation constant of the waveguide, Γ is the complex reflection coefficient of the load, and x is the distance from V _E to the load.

A short section of waveguide can be considered lossless if the tool hole is small enough. Therefore σ is Becomes Where ω is the operating frequency (rad / sec), c is the speed of light in free space, and a is the width of the wide wall of the waveguide.

If the transceiver unit is a simple sine wave signal Aexpjω
If t is generated on the central axis, then V _E = A (expjωt) (exp-jβx) [(exp jβx) + (Γexp-jβx)] (3) is obtained from Eqs. (1) and (2). To be Since either the shorting stub or the tool presents a short circuit to the incident electric field, the load reflection coefficient is-
Is equal to 1. Therefore, Eq. (3) becomes V _E = 2A (sinβx) [exp j (ωt-βx + π / 2)] (4). Since the transceiver is directly connected to the comparator, it detects only the DC-related component of equation (4). It takes the following form.

V _Emax = ∂cos (ωt + φ) (5) where ∂ = 2A sinx and φ = π / 2−βx. When the tool is removed from the waveguide, x = lt + ls (6), and when the tool is inside the waveguide, x = lt (7). Therefore, equations (5) to (7) limit the amplitude and phase in the transceiver when the tool is present.

The invention will be described as a simple homodyne transceiver with reference to FIG. The baseband mixer DC component output of the homodyne transceiver is Where θ is an optional phase constant and k is the conversion constant of the mixer.

By using the equations (5) to (8), the following relation can be obtained for the state where the tool is removed from the waveguide.

SO _DC = KAsin [β (lt + ls)] cos [π / 2−β (lt + ls) −θ] (9) When a tool is present, SO _DC = KAsin (βlt) [cos (π / 2− βlt-θ)] (10) As can be seen from the above, by using either equation (9) or (10), the physical parameters of the target detection system can be easily optimized for a given application. Therefore, the output of the comparator can be used to trigger an automatic shutdown of the machine and / or the generation of an alarm indicating the discontinuity of the target.

It may be impossible to pass the target into the waveguide due to some dimensional constraints. In this case, the shorting stub is removed from the waveguide and the end of the waveguide is open to the atmosphere. As shown in FIG. 5, the target, which in this case is a thin wire 50, is positioned very close to the end face opening of the waveguide. Target is a positive integer (N) of λ / 4 or λ / 8 from the transceiver output
Position at double the distance. As mentioned above, the system parameters can easily be optimized for the x = lt mode of operation. In this application, the signal transmitted from the transceiver 52 along the waveguide 51 is slightly attenuated due to the lack of the shorting stub, but it can be detected so that the target state can be accurately detected.

One of ordinary skill in the art will readily devise other and alternative uses and variations of the microwave detection system of the present invention.

[Brief description of drawings]

FIG. 1 is a partial side view of a machine tool incorporating the present invention, FIG. 2 is a schematic view showing an embodiment of the present invention for detecting a target having a cut shape, and FIG. FIG. 4 is a cross-sectional view of the waveguide of the broken tool detection system shown in FIG. 2, showing the electric field strength inside the waveguide when the target is removed from the waveguide. FIG. 5 shows the electric field strength in the waveguide in the presence of a target, and FIG. 5 shows another embodiment of the invention in which the target is positioned at the end of the waveguide. It is a thing. 9 ... Automatic punching machine, 10 ... Printed circuit board (stack of), 11 ... Pressure foot assembly, 12 ... Cut, 1
5, 51 ... Waveguide, 17, 52 ... Transceiver module, 18 ... Short-circuit stub, 19 ... Hole, 20 ...
Wide upper wall, 21 ...... Lower wide wall, 23 ...... Local oscillator, 25 ...... Schottky diode, 26 ...... Mixer circuit, 29 ...... Mixer output line, 30 ...... Comparator, 31 ...... Amplifier , 50 …… Wire (target).

Claims (14)

[Claims] 1. A waveguide 15 having a hole 19 into which a drill bit 12 is inserted, located at one end of this waveguide for transmitting a microwave signal into the waveguide towards the drill bit 12 and being reflected. A transmitter / receiver device 17 for receiving a returning microwave signal, a transmitting microwave signal and a receiving microwave signal for generating an output signal having a component indicating whether or not a drill bit exists in the hole 19 of the waveguide. A mixer circuit 26 for heterodyning the signal, and a detector 30 connected to the output of the mixer circuit 26 for comparing the component of the output signal with a predetermined level to determine the presence or absence of a drill bit, In the waveguide, the position of said waveguide hole 19 with respect to the device 17 is selected to optimize the signal strength from said mixer circuit 26. Microwave detection device that detects the presence or absence of a drill bit. 2. The microwave detecting device for detecting the presence / absence of a drill bit in a waveguide according to claim 1, wherein the transmitting / receiving device is a transceiver 17. 3. A microwave detecting apparatus for detecting the presence or absence of a drill bit in a waveguide according to claim 2, wherein the transceiver comprises a Gunn diode 23 and a Schottky diode 25. 4. A micro-detector for detecting the presence or absence of a drill bit in a waveguide according to claim 1, 2 or 3, wherein an amplifier 31 for amplifying an output signal is connected between the mixer circuit 26 and the detecting device 30. Wave detector. 5. A drill bit in a waveguide according to claim 1, 2, 3 or 4, wherein a hole 19 is drilled in the center of the waveguide and a shorting stub 18 is arranged behind the drill bit. A microwave detection device that detects the presence or absence. 6. The microwave detecting apparatus for detecting the presence or absence of a drill bit in a waveguide according to claim 5, wherein the short-circuit stub 18 is arranged so as to optimize the signal strength from the mixer circuit 26. 7. A waveguide hole 19 through Nλ / 4 or Nλ.
Shorted stub 1 to / 8 (N is an integer, λ is the wavelength of the transmitted signal)
The microwave detection device for detecting the presence or absence of a drill bit in the waveguide according to claim 6, wherein 8 is arranged. 8. A waveguide hole 19 is provided from the transceiver 17 to Nλ.
The microwave detection device for detecting the presence / absence of a drill bit in the waveguide according to claim 1, wherein the microwave detection device is arranged at / 4 or Nλ / 8 (N is an integer, λ is a wavelength of a transmission signal). 9. A microwave detecting apparatus for detecting the presence or absence of a drill bit in a waveguide according to claim 1, wherein the hole 19 of the waveguide is 12.7 mm or less. 10. A microwave signal transmitted by transmitting a microwave signal into the waveguide by inserting a drill bit into the hole of the waveguide and receiving a microwave signal reflected and returned from the drill bit. And a received microwave signal is heterodyned to generate an output signal having a component indicating whether or not a drill bit exists in the hole of the waveguide, and a direct current component of the output signal is set to a predetermined value. A waveguide characterized in that it comprises steps for determining the presence or absence of a drill bit in comparison with the level, and that the position of the hole in the waveguide with respect to the transceiver is selected to optimize the signal strength from the mixer circuit. A method to detect the presence or absence of a drill bit in a pipe. 11. The method of detecting the presence or absence of a drill bit in a waveguide as set forth in claim 10, wherein a shorting stub is positioned behind the drill bit in the waveguide. 12. A drill bit to Nλ / 4 or Nλ
The microwave detection device for detecting the presence or absence of a drill bit in a waveguide according to claim 11, wherein a short-circuit stub is arranged at / 8 (N is an integer, λ is a wavelength of a transmission signal). 13. A drill bit adjacent to the end of the waveguide,
From the microwave transmission point, Nλ / 4 or Nλ /
The microwave detection device for detecting the presence or absence of a drill bit in the waveguide according to claim 10, wherein the microwave detection device is arranged at a distance of 8 (N is an integer, λ is a wavelength of a transmission signal). 14. A method for amplifying a heterodyne signal.
14. A microwave detection device for detecting the presence or absence of a drill bit in a waveguide according to any one of 1 to 13.