DE202008001018U1 - Sensor for the detection of objects by light diffraction - Google Patents

Abstract

Sensor for detecting objects, in particular threads or wires, by light diffraction,
with a light source (20) for illuminating the object (10),
with a detector unit (30) having at least one detector (40) for detecting at least light diffracted at the object (10),
with a control and evaluation unit (60) for evaluating measuring signals of the detector unit (30) and for outputting at least one switching signal (62, 64),
characterized,
that there is exactly one detector (40) for detecting light from at least one higher diffraction order, and
in that a means (42) for masking at least light of the zeroth diffraction order (27) and / or of non-diffracted light (28) is present or
in that a single detector (54) for detecting light of the zeroth diffraction order (27) and / or of non-diffracted light (28) and at least one further individual detector (52, 56) for detecting light of at least one higher diffraction order is present.

Description

The The present invention relates to a sensor for detection of objects, in particular of threads or wires, by diffraction of light according to the preamble of claim 1.

Such sensors are for example off JP 07 167 627 A are known and have a light source for illuminating the object, a detector unit with at least one detector for detecting at least diffracted at the object light and a control and evaluation unit for evaluating measurement signals of the detector unit and for outputting at least one switching signal.

Such devices are used, for example, to continuously check the thickness of a wire. In order to obtain information about the thickness of the wire, a spatial displacement of the first diffraction maximum is evaluated. For this purpose, the in JP 07 167 627 A described device on at least four individual detectors, which are arranged substantially in a row symmetrical to a center. The four individual detectors are spaced so that, for a typical measurement situation, the first order diffraction spots fall between the inside and outside detectors and are detected in part by both the inside and outside detectors. As the thickness of the diffractive object, such as the wire, changes, the maximum of the first diffraction order shifts. This causes a large change in a difference of the signals measured with the inside and outside detectors, which can be well detected.

For many problems, it is only important to determine whether, for example, a wire or a thread is actually present or not. For this is the in JP 07 167 627 A Although described construction is basically suitable. The solution according to this document is complex and associated with corresponding costs.

One Typical application, for example, relates to the contact of a chip used bond wires. These wires are generally made of aluminum, copper or gold and have a diameter of about 50 microns or smaller. Everyone this bond wires must be connected to the top of a small, typically rectangular pad be connected in the area of the chip. At the other end, the Bond wires with a similarly shaped larger Housing interface connected. In most Bonding machines is the appropriate tool designed so so that positioning the bond wire over one Connection point before performing the bonding process easier becomes. Such a bonding tool, for example, an angled above Underside behind the work surface and have a generally vertically arranged back. An angled Bore or a wire guide bracket with an inlet opening in the back and an exit opening in the Angled bottom of the tool allows for dispensing of the bond wire through an exit opening in the angled Bottom of the tool. Typically, an over Remote controllable terminal, which is behind the entrance of the wire guide is arranged and is movable relative to the tool, used the bond wire through the guide hole introduce. A problem with automatic bonding can occur in a random break or Tearing off a piece of bond wire on the Back of the bonding tool. Such a break can be caused are caused by errors in the wire feed of one Coil, which weakens the wire. For example if too high tension on the wire through the supply spool exercised or for similar reasons, the wire is weakened. Such a random one Breakage of the wire is undesirable and problematic.

Methods for detecting broken or otherwise missing wires, for example, in US 6,179,197 . US 6,278,409 . JP 05 162 666 and JP 02 008 152 proposed.

A The object of the invention can be seen to provide a sensor, with which reliable on the basis of the principle of light diffraction Objects, such as wires or threads detected can be and which also easy to set up is.

These The object is achieved by the sensor having the features of claim 1 solved.

preferred Embodiments of the sensor according to the invention are Subject of the dependent claims and also in the following description, in particular in conjunction with the accompanying figures.

The sensor of the above type is inventively further developed in that there is exactly one detector for detecting light from at least one higher diffraction order and that means for hiding at least light of zeroth diffraction order and / or non-diffracted light is present or that a single detector for detecting light of the zeroth diffraction order and / or of non-diffracted light and at least one further individual detector for detection of light from at least one higher diffraction order is present.

To the Detection of thin wires uses the present Invention, the diffraction of light, in particular laser light. This Principle is based on having a wire or similar shaped Objects, such as a thread, when illuminated with a light beam, in particular a laser beam, a diffraction pattern on a suitable positioned photosensitive element generated.

When a core idea of the invention can be considered that already with exactly one detector can be checked, if such Diffraction pattern is present or not. This refers to the first claim alternative of claim 1. This is then light the zeroth diffraction order or undiffracted light faded or hidden. For example, an effective sensor for detecting thin Wires are provided, which in a bonding machine monitors a thin wire supplied there. A suitable cover is used to prevent undiffracted light or light of the first diffraction order from the photosensitive one Element, so keep away from the detector. So if a thin wire or a similar object is present in the laser beam and the laser beam thereby at least partially interrupted will be, diffraction spots on the free surface of the detector displayed. An amplified signal can then help the control and evaluation unit analyzes and can From this corresponding switching signals are generated, which external Switch components, such as actuators, suitable.

According to one Another basic idea of the present invention, on which the second alternative of claim 1, the information, which diffracted in the undiffracted light or the zeroth order Light lies, used for the evaluation. This can be done with simple Means by a centrally positioned with respect to the diffraction pattern Single detector can be achieved. Compared to the state of the art can in the invention, a proof, for example, a bonding wire, be achieved with significantly simpler means.

The However, the invention is not based on the detection of thin wires or threads restricted. Also edges, for example of transparent objects, generate diffraction patterns, which in principle to Detection of such edges can be used. Especially for transparent objects is proof of edge with Help of a conventional transmission method difficult because the relative intensity change of the light after whose passage through the transparent body is only small. At the edge, however, the light is diffracted in a known manner and Here, the signal changes are significantly larger, so that proof in this way is greatly simplified. Furthermore, impurities in transparent Materials are detected. For example, also takes place small bubbles or other manufacturing defects Diffraction of light of the type described above, which in turn results in a corresponding easily evaluable signal change results.

When Light source come basically known light sources into consideration. Particularly preferred as a light source or used several laser diodes. At the detector or single detectors It may be useful to photodiodes or other Semiconductor photodetectors, such as CCD arrays act.

The Control and evaluation unit can be formed by a microcontroller or part of a microcontroller. Complementary or alternative can also be programmable logic components, for example FPGAs, CPLDs, GALs.

at a particularly preferred variant are exactly three optical single detectors available. In this case, a proof of a wire by evaluation a difference signal. Here, the middle of the individual detectors used to diffract the un-diffracted light or zero-order light and the outside single detectors light of the first diffraction order is detected. Accordingly the control and evaluation unit preferably for forming a difference between a zeroth order of diffraction and / or unbent Light belonging measurement signal and one to higher Diffraction orders belonging to the measurement signal set up. in principle the control and evaluation unit can also be used to form a quotient between a zeroth order of diffraction and / or unbent Light belonging measurement signal and one to higher Be arranged diffraction orders belonging to the measurement signal.

With The differential method described here may also be, for example the thickness of a wire is controlled and monitored. A certain wire thickness generates a certain difference signal, which can be taught. When the thickness of the wire changes, for example, during a manufacturing process increases or decreases, will also be the difference signal or possibly the signal quotient will change and such a change can be easily detected.

In a further preferred simple variant, a mechanical diaphragm is present as means for fading out the zeroth diffraction order and / or unbent light. Beispielswei a photodetector can be passivated in the corresponding area by a lacquer layer.

at Another simple example is the optical detector or one or more of the optical detectors of interconnected Constructed detector parts. The means to hide the zeroth Diffraction order or unbieugtem light is hereby insofar realized than at the corresponding location no active detector surface is available. The evaluation can in these embodiments be simplified because fewer measurement signals evaluated and processed Need to become. For example, in the variant with three single detectors, the two outer detectors interconnected and thus be considered as detector parts of a single detector. For this variant, then only two signals, namely the measurement signal of the internal single detector and the cumulative Measurement signal of the external single detectors to evaluate.

The Diffraction pattern extends, for example, with a wire in a direction substantially perpendicular to the direction of the wire. So that a wire or a thread is still reliably detected can be when the wire or thread is facing its position slightly changes the sensor according to the invention, in particular tilted, it is appropriate if the detector has a detector surface whose width in the region of the means for hiding zero-order diffraction light is smallest and higher in the direction of impinges of light Diffraction orders become increasingly larger. For example the detector surface may have a waisted shape, with the waist in the area of the aperture or other Ausblendmittels located. For the claim alternative with several single detectors is preferred in view of the above aspect, if the single detectors to detect light from higher Diffraction orders each having the form of circular ring segments.

A Positioning of the sensor according to the invention a wire to be detected or monitored or Threading is particularly easy when the sensor is in housed a forked or U-shaped housing is. At the ends of the legs are then the light source or housed the detector unit.

at Another particularly preferred embodiment is the light source and the detector unit mechanically decoupled. For example, you can these components in mechanically decoupled or separate housing parts be housed. Disturbances caused by mechanical coupling transmit with the receiver unit can be reduced in this way. Such Housings are also referred to as satellite housing.

The Functionality of the sensor according to the invention is further increased when a visual display, in particular a plurality of differently colored LEDs, for signaling of operating and / or switching states available to a user is. For example, three light emitting diodes may be present be a green LED the proper Presence of a power supply and a red LED indicates a fault and where a yellow LED lights when an object, such as a wire, in the detection area was detected.

additional or alternatively, a device for acoustic Signaling of operating and / or switching states a user exist.

Further Advantages and features of the present invention will be described below explained with reference to the accompanying schematic figures.

Here in shows:

1 : In a schematic view of a first embodiment of the sensor according to the invention;

2 : The embodiment of 1 with no object in the detection area;

3 and 4 : Details of the embodiment of 1 ;

5 : Schematic view of another embodiment of the sensor according to the invention;

6 : The sensor off 5 with no object in the detection area;

7 and 8th : Details of the sensor off 4 ;

9 to 11 : Schematic views explaining the diffraction of light on small objects

A first embodiment of a sensor according to the invention 100 will be related to the 1 to 4 described. The sensor 100 has as essential components a light source 20 , a detector unit 30 and a control and evaluation unit 60 on. The light source 20 is a laser diode 20 by a laser electronics 22 is controlled. The detector unit 30 includes a detector 40 which forms the shape of an oblong rectangle points and in a central region of a mechanical aperture 42 is covered, as well as an amplifier 32 for amplifying an output signal of the detector 40 , The amplified signal 38 becomes a control unit 68 , which are part of the control and evaluation unit 60 is fed. The control and evaluation unit 60 gives a control signal 66 to the laser electronics 22 and also switching signals 62 . 64 to an external device to be controlled 70 from.

In the example shown, the sensor according to the invention 100 used to feed a wire 10 from a coil 12 to an automaton 14 to be monitored, with the semiconductor chips in housings to be contacted. For the external device to be controlled 70 For example, it may be an actor 70 act at the machine 14 and / or the means, not shown here, for feeding the wire 10 appropriate action is taken when the wire 10 for whatever reason breaks off.

Before the operation of the sensor 100 will be explained in detail in connection with the 9 to 11 described some basic principles of diffraction.

If in a beam path with which a screen is illuminated, a opaque object is introduced appear on the screen bright and dark areas. The intensity the lighting is at any bright or dark point of the screen proportional to the amplitude square of the incident light wave this point. The mentioned light and dark areas are created by Diffraction, whose fundamental phenomena on interference and based on the superposition principle.

Diffraction always occurs when a wavefront passes an edge area of an obstacle in the beam path. This can be made clear as follows. As the wavefront passes the edge area, secondary spherical waves emerge from a small neighborhood near the edge area. In 9 plane waves fall on a single edge area of an obstacle 10 , which may be, for example, a wire with a diameter d. The parallel lines indicate wave peaks of the wavefront, each of which is rejected by a wavelength λ. The diameter d of the object 10 is of the order of magnitude few wavelengths λ. 10 shows the incidence of a front plane wave on a small obstacle 10 whose width is in turn of the order of the wavelength of the incident wavefront. It should be noted that the wave crests and the troughs are those of the surroundings of the edge areas of the object 10 outgoing spherical waves at every point in front of a screen 18 overlap. The amplitudes of the two secondary spherical waves add up algebraically at each point, creating a new amplitude for each point. It should also be noted that the amplitudes of the two waves add, but not their intensities. This is called a superposition principle. The light intensity at each point is proportional to the amplitude square at that point. It is also said that the two spherical waves interfere with each other because the intensity depends on how the amplitudes add up at that point.

For this Two extreme examples are considered. Added at certain points a wave mountain on another wave mountain or a wave valley adds up to another wave trough, from which a total greater amplitude, which can be positive or negative can, results. The light intensity is at these points high, since the light intensity is due to the amplitude square given is. This case is called constructive interference. At certain other points, a wave crest adds up to one Wellental, from which a smaller amplitude arises, which basically can also be close to or equal to zero. The light intensity at this point is therefore almost zero. This Case is called destructive interference. All other interference effects move between these two extremes. A direct consequence of the superposition or overlay principle is that the observed intensity of the diffracted light, which on a screen falls, bright areas that by constructive Interference is caused, as well as dark, through destructive interference has affected areas or bands.

In a real diffraction experiment, the angular positions of the light and dark stripes are somewhat different from the simple expectation. The real interference pattern is due to a superposition of spherical waves from all points outside the obstacle and not just from a small peripheral area. The relative position and distribution of these bright and dark areas can be calculated and depend on the wavelength λ of the light used, the dimension of the obstacle and the distance L of the screen from the diffractive obstacle. This is in 11 indicated schematically. On the screen 18 One first observes at a position P0 a central bright area, since there the one from the edges of the object 10 Outgoing spherical waves always constructively interfere. Then arise at points P1 more maxima at which the path difference between the light paths of the edge regions of the object 10 is just a wavelength λ. The corresponding beams are in this case inclined by an angle θ against each other.

It will now be the operation of in 1 shown sensor 100 with reference to the others 2 to 4 explained. The photosensitive detector 40 is used to create a diffraction pattern 26 evidence, whereas a central pattern 27 and / or undiffracted light 28 is suppressed. When the thin wire 10 , as in 1 shown in the beam 24 is created on the detector 40 the schematically indicated diffraction pattern 26 , The longer the detector 40 is, the more diffraction orders can be detected.

If the wire 10 is removed or tears off, for example, the diffraction pattern disappears 26 and only unfrozen light falls 28 on the detector unit 30 and is there but by the aperture 42 from the detector 40 shielded. This situation is in 2 shown. The measuring signal of the detector 40 Accordingly, a transition of the situation fails 1 to the situation in 2 strong and this waste can easily be detected. For example, then the switching signals 62 . 64 the control unit 68 from HIGH to LOW or from LOW to HIGH to the actuator 70 to produce the desired reaction.

Details of the detector 40 are in the 3 and 4 shown. Out 3 is the diffraction pattern 26 with the central bright area 27 visible, whereas in 4 the situation 2 is shown where only undiffracted light 28 on the centrally arranged aperture 42 falls. The by a double arrow 43 indicated width of the aperture 42 is suitably chosen so that the central bright area 27 as completely as possible from the aperture 42 is obscured, the diffraction pattern 26 but at the same time as fully as possible can be detected.

The advantage of this method is that even a wire with a very small diameter can be detected. The sensor 100 however, may be insensitive to larger diameter wires because for such wires the diffraction pattern is less broad on the free area of the detector 40 is distributed.

A second embodiment of a sensor according to the invention will be described with reference to FIGS 5 to 8th explained.

equivalent Components are provided with the same reference numerals in all figures.

The in the 5 and 6 illustrated sensor 100 is different from the one related to the 1 and 2 described sensor 100 in that, instead of just one detector with a diaphragm in the central region, three individual detectors 52 . 54 . 56 available. The middle single detector 54 serves to light the central bright diffraction area 27 or undiffracted light 28 demonstrated. The light in the central bright area 27 is also called zero-order diffraction light. With the external detectors 52 . 56 light can be detected from higher diffraction orders. The outputs of the individual detectors 52 . 56 are interconnected. The measuring signal of the central single detector 54 is powered by an adjustable amplifier 84 amplified, whose output signal 94 a differential level 90 , which are part of the control and evaluation unit 60 is, is supplied. Another input of the differential stage 90 becomes an output signal 96 an amplifier 86 fed to the measuring signal of the interconnected external individual detectors 52 . 56 strengthened. An output signal 98 the differential stage 90 becomes the control unit 68 fed. The remaining components correspond to those with the same reference numerals in FIG 1 ,

In the example shown, the individual detectors 52 . 54 . 56 with the amplifiers 84 . 86 and the difference level 90 in a module 34 integrated.

The functioning of the in 5 shown sensor 100 will be with reference to the others 6 to 8th explained.

If, as in 5 , a wire 10 in the beam of light 24 is located, as described above, on the detectors a diffraction pattern 26 ie the external single detectors 52 . 56 deliver a measurement signal. Unlike the in 1 shown sensor 100 , in the light of the zeroth order of diffraction 27 straight from the aperture 42 is hidden, here is this light from the central single detector 54 demonstrated. The adjustable amplifier 84 can then be adjusted so that the difference signal 98 , ie the difference of the measuring signals of the central detector 54 and the two external detectors 52 . 56 takes a certain value. If the wire is now taken out, for example, tears off, as in 6 is shown, the difference signal falls 98 after the differential step 90 significantly due to the disappearance of the diffraction pattern on the outside single detectors 52 . 56 , Again, therefore, the control unit 68 suitable switching signals 62 . 64 to generate.

Again, this method works well for thin wires. However, it can also be used to detect thicker wires. In this case, the diffraction pattern is relatively weaker due to the presence of the wire in the beam path. However, the undiffracted light is partially blocked by the wire itself. Depending on the specific position of the wire then the sig nal of the central detector 54 vary, whereas the measuring signals of the external detectors 54 . 56 remained unchanged. Accordingly, there is again a significant change in the difference signal 98 which is accordingly also sensitive to thicker wires.

With the present invention provides a novel sensor, with which in particular thin wires detected can be. For example, the inventive Sensors used to prevent accidental tearing or an error when feeding the wire to a production machine to monitor. In particular, the invention relates on bonding machines which are used to miniaturized electronic Elements, such as integrated circuits or magnetic read / write heads, as they are used in hard drives to contact.

Instead of The radiation properties of light here become the diffraction of the light exploited on the object, such as the thin wire, the always occurs when a wavefront is a wall area of a Obstacle in the beam path happens. The hereby stated Signal changes are excellent for detecting smaller Suitable objects.

above Accordingly, in particular a sensor for thin wires based on the principle of light diffraction discloses that provides a switching or alarm signal when a Wire or other object to be detected no longer exists whether through demolition or misdirection. The sensor consists in one embodiment of a Laser head, an electronic detection module and a control unit. The laser head driven by the control unit generates one Laser beam whose focus is on an opaque aperture or cover or a central single detector falls.

Possible Applications of this sensor include edge detection of transparent ones Objects, the detection of impurities in transparent materials and a thickness control of materials with the above Difference module.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - JP 07167627 A [0002, 0003, 0004]
• US 6179197 [0006]
• US 6278409 [0006]
• - JP 05162666 [0006]
• - JP 02008152 [0006]

Claims (16)

Sensor for detecting objects, in particular threads or wires, by light diffraction, with a light source ( 20 ) for illuminating the object ( 10 ), with a detector unit ( 30 ) with at least one detector ( 40 ) for detecting at least on the object ( 10 ) diffracted light, with a control and evaluation unit ( 60 ) for evaluating measuring signals of the detector unit ( 30 ) and for outputting at least one switching signal ( 62 . 64 ), characterized in that exactly one detector ( 40 ) is present for the detection of light of at least one higher diffraction order and that a means ( 42 ) for masking at least light of the zeroth diffraction order ( 27 ) and / or unbent light ( 28 ) or that a single detector ( 54 ) for detecting light of the zeroth diffraction order ( 27 ) and / or unbent light ( 28 ) and at least one further single detector ( 52 . 56 ) is present for the detection of light from at least one higher diffraction order. Sensor according to claim 1, characterized in that exactly three individual optical detectors ( 52 . 54 . 56 ) available. Sensor according to claim 1 or 2, characterized in that as means ( 42 ) for hiding light of the zeroth diffraction order ( 27 ) and / or unbent light ( 28 ) a mechanical diaphragm ( 42 ) is available. Sensor according to one of claims 1 to 3, characterized in that the detector ( 40 ) or one or more individual detectors ( 52 . 54 . 56 ) is constructed of interconnected detector parts. Sensor according to one of claims 1 to 4, characterized in that all individual detectors ( 52 . 56 ) are interconnected to detect light from higher diffraction orders. Sensor according to one of claims 1 to 5, characterized in that the detector ( 40 ) has a detector surface whose width in the region of the means ( 42 ) is the smallest for hiding zeroth diffraction order light and becoming progressively larger in the direction of impingement of higher diffraction light light. Sensor according to one of claims 1 to 6, characterized in that the individual detectors ( 52 . 54 . 56 ) in each case in the form of circular ring segments for the detection of light from higher orders of diffraction. Sensor according to one of claims 1 to 7, characterized in that the control and evaluation unit ( 60 ) is arranged to form a difference between a measurement signal belonging to the zeroth diffraction order and a measurement signal belonging to higher diffraction orders. Sensor according to one of claims 1 to 8, characterized in that the control and evaluation unit ( 60 ) is arranged to form a quotient between a measurement signal belonging to the zeroth diffraction order and a measurement signal belonging to higher diffraction orders. Sensor according to one of claims 1 to 9, which housed in a fork-shaped housing. Sensor according to one of claims 1 to 10, characterized in that an optical display, in particular a plurality of different colored light emitting diodes, to signal operating and / or Switching states to a user is present. Sensor according to one of claims 1 to 11, characterized in that a device for acoustic signaling from operating and / or switching states to a user is available. Sensor according to one of claims 1 to 12, characterized in that the light source is a laser diode ( 20 ). Sensor according to one of claims 1 to 13, characterized in that the detector ( 40 ) or one or more of the individual detectors ( 52 . 54 . 56 ) is a photodiode or photodiodes. Sensor according to one of claims 1 to 14, characterized in that the evaluation unit ( 60 ) is formed by a microcontroller or a programmable logic device. Sensor according to one of claims 1 to 15, characterized in that the light source ( 20 ) and the detector unit ( 30 ) are mechanically decoupled, are housed in particular mechanically decoupled housing parts.