Optics: measuring and testing – Position or displacement – Focus
Reexamination Certificate
1999-12-13
2001-11-27
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Position or displacement
Focus
C250S559360
Reexamination Certificate
active
06323954
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is in the field of sensor technology and concerns a process and a device for the detection or determination of the position of edges or of edge-like, narrow boundary surfaces of objects, particularly edges of very thin objects, such as paper or transparent foils.
It is known how to detect objects and edges of objects with light barriers (e.g., edge moves relative to the light barrier). Detection of the position of an edge or an object is also known (e.g., light barrier moves relative to the edge). For this, a light-emitting light source and a light-sensitive sensor device, which is positioned in the beam path of the emitted light, are utilized. The sensor device provides a sensor signal, which corresponds to the light intensity impinging on the sensor device. If an object is moved through the light beam between the light source and the sensor device, the intensity measured by the sensor is reduced as soon as a leading boundary surface or edge reaches the light beam. The measured intensity remains at the reduced value until a trailing boundary surface or edge of the object passes the light beam, at which moment the measured light intensity returns to its original value. The two steps in the measured intensity of the received light, for example, are interpreted as the leading and the trailing boundary surface or edge of the object moving through the light beam and are utilized for the measuring or positioning of the object. Reduced and not reduced intensity value can also be interpreted as the presence or absence, respectively, of an object in the field of the light barrier and can be correspondingly utilized.
The process of the known light barrier briefly described above is obviously only applicable for objects that are not transparent to the light beam used as the light barrier. This is, of course, valid not only for visible light, but also for other electromagnetic radiations with a wavelength suitable for a certain application.
SUMMARY OF THE INVENTION
The present invention is directed toward a process for detection or determination of the position of edges, and is based on the light barrier principle. The present invention increases accuracy and reduces the susceptibility for errors and is suitable for transparent objects.
The process according to the present invention represents a further development of the light barrier principle. The edges to be detected and the light are moved relative to one another such that every edge to be detected moves through the light in an object plane and intersects a direction of propagation of the light at an angle. At least during the passage of the edge through the light, as a minimum one intensity of the light is measured in a receiving zone. The light is focused on the object plane in at least one direction. In the object plane and/or in the receiving zone, optical local redundancy is generated.
As used herein, the term “optical local redundancy” is the presence of relevant optical signals in several places. The edge in the object plane, e.g., can be illuminated at several points. As a result of this, the process becomes more precise and less susceptible to individual local interferences on the object, such as dirt, scratches, etc. Furthermore, there can be several light sensors in the receiving zone. It is advantageous to subject the signals of the sensors to a common analysis, which leads to enhanced accuracy and reliability.
In a preferred embodiment of the invention, a light source and a sensor device are arranged such that light emitted from a light source impinges of the middle of the sensor. Between the light source/sensor device arrangement and an edge to be detected, a relative movement can be generated such that the edge can be moved through the light between light source and sensor device at a detection position and intersects the propagation axis of the light at an angle. The light is focused on the detection position into a light line that is as sharp as possible and as narrow as possible light line. The light line is aligned parallel to an edge to be detected, which passes the detection position.
Focusing devices are placed ahead of the sensor devices for the purpose of increasing the measured intensities. The focusing devices collect light diverging to a limited extent in the sensor devices and thereby increase the measured intensities.
For the detection of edges, an edge is now moved through the light at the detection position, to be precise such that, at least in the detection position, the edge is aligned parallel to the generated light line. While passing through the detection position of an edge to be detected, the intensity of a portion of the light not deflected by the edge is measured and/or the intensity of light, which is disturbed by the edge. The light disturbed by the edge is light that is deflected from the light beam by diffraction or refraction at the edge. For measurement of the undisturbed portion of light, a sensor is aligned along the main propagation direction or beam axis of the light. For measurement of the deflected portion of light, at least one sensor at a distance from the beam axis is foreseen.
The light intensities and/or combinations of intensities determined by different sensors are recorded and analyzed as a function of time or location. For example, the intensity may be compared to threshold values, whereby the time and/or the location, at which a threshold value is exceeded (or falls below), is interpreted as an edge passage or edge position. The threshold values are predetermined and correspond to the type of edge to be detected and/or to the optical characteristics of the object, which is delimited by the edge to be detected.
The intensity functions determined by the sensor devices can, on the other hand, also be exploited for the characterization of the optical characteristics of an edge or an object and for the determination of the threshold values mentioned above. If so required, the threshold values can be, simultaneously with the edge detection, adjusted for varying, external circumstances.
The device for the implementation of the process in accordance with the invention has, in the sense of a light barrier, a light source for the generation of light, sensor means in a receiving zone for measuring light intensities and means for creating relative movement between the light and the edges of objects to be detected in an object plane. The device also has means for focusing the light in at least one direction in the object plane and means for creating an optical local redundancy in the object plane and/or in the receiving zone.
A laser is advantageously foreseen as the light source while photodiodes may be used for the sensor devices. The light emitted by the light source is advantageously aimed directly at the sensor means. However, the light may be reflected and/or refracted between the light source and the sensor means. The light source also has focusing means for focusing the light in the object plane. The sensor means have a sensor aligned to the main direction of propagation or beam axis of the light and/or at least one sensor located at a distance from the beam axis. The device furthermore has means for creating relative movement between the light source/sensor means arrangement and an object with an edge to be detected such that the edge is moved through the detection position.
In further accordance with the present invention, the device preferably has means for evaluating (e.g., evaluation electronics), for recording and analyzing (e.g., comparison with threshold values) sensor signals, and for generating and transmitting signals corresponding to the results of the analysis, which, for example, can be further utilized for control purposes. The evaluating means preferably includes a microprocessor.
The process in accordance with the invention and means for implementing the process are in particular utilizable for detecting leading and/or trailing edges of transparent or non-transparent flat objects such as transparent foils and paper sh
Hera Rotterdam B.V.
Pham Hoa Q.
Rankin, Hill Porter & Clark LLP
LandOfFree
Process and device for the detection or determination of the... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process and device for the detection or determination of the..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process and device for the detection or determination of the... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2599241