Sensor apparatus

The invention relates to a sensor apparatus for detecting an object comprising a sensor head having a plurality of receiving spaces for individual sensor devices and a driving mechanism for providing a relative movement of the object relative to the sensor head in an advance direction during a detecting operation. The receiving spaces are arranged in a plurality of rows and columns, such that an array of receiving spaces with a rectangular pattern of the receiving spaces is formed, and the array of receiving spaces is tilted with regard to the advance direction such that the rows extend in a transverse direction relative to the advance direction and the receiving spaces of a successive row of the rectangular pattern are offset with regard to the receiving spaces of a preceding row of the rectangular pattern in a direction perpendicular to the advance direction.

FIELD OF THE INVENTION

The present invention relates to a sensor apparatus for detecting an object.

Such a sensor apparatus comprises a sensor head having a plurality of receiving spaces for individual sensor devices and a driving mechanism for providing a relative movement of the object relative to the sensor head in an advance direction during a detecting operation.

The invention also relates to a method for detecting an object.

In this method the object is detected by a plurality of individual sensor devices and the object is moved relative to the sensor devices in an advance direction during a detecting operation.

RELATED ART

In a known sensor apparatus the sensor devices are arranged in a linear array or row, which extends transversely to the advance direction of the product. As the sensor devices, for example photodiodes, have certain dimensions, the resolution that can be achieved with such a sensor apparatus is limited.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a sensor apparatus and a method for detecting an object having a good resolution.

The object is solved according to the invention with a sensor apparatus and a method as described herein.

The sensor apparatus is characterized in that the receiving spaces are arranged in a plurality of rows and columns, such that an array of receiving spaces with a rectangular pattern of the receiving spaces is formed, and the array of receiving spaces is tilted with regard to the advance direction such that the rows extend in a transverse direction relative to the advance direction and the receiving spaces of a successive row of the rectangular pattern are offset with regard to the receiving spaces of a preceding row of the rectangular pattern in a direction perpendicular to the advance direction.

One basic idea of the invention is to provide a sensor head with a plurality of rows of receiving spaces for individual sensor devices in order to enhance the speed of a detecting operation as compared to a sensing head having only a single row of sensor devices. The rows, in which the receiving spaces are arranged, extend in a transverse direction, that is, they extend transversely to the advance direction.

A further basic idea of the invention is to operate all sensor devices simultaneously, while the object is moved relative to the sensor head. In case that an image is detected or scanned, the original image is produced successively with an ongoing product movement.

According to the invention, at least a part of the receiving spaces of the sensor head is arranged in a regular pattern of rows and columns, wherein the columns are perpendicular to the rows. Such a pattern is referred to as a rectangular pattern of receiving spaces. In the rectangular pattern, the receiving spaces are arranged in a manner, that in each case four receiving spaces are arranged in the edges of a rectangle. The rectangular pattern may also be referred to as an orthogonal arrangement of receiving spaces. The receiving spaces are in particular arranged in a two-dimensional array or in a matrix.

It is preferred that the receiving spaces are arranged in a regular pattern, in which the pitch of the receiving spaces, that is the distance between two central points of neighbouring receiving spaces in one row or column, is constant. More particularly, it is preferred that a row pitch and column pitch are equal. The pitch of receiving spaces of the sensor head is also called the device pitch.

A basic aspect of the invention is to arrange the rows of receiving spaces for the sensor devices such that they extend transversely, but not perpendicularly, to the advance direction. Consequently, the columns of receiving spaces also extend transversely to the advance direction. The array of receiving spaces is thus rotated or tilted from a position, in which the columns are aligned with the advance direction, to a position, in which to columns are inclined or slanted with regard to the advance direction. As the receiving spaces are arranged in a rectangular array, the rows are also inclined or slanted with regard to a direction perpendicular to the advance direction.

It is preferred that the sensor head is a page-wide sensor head, that is, the sensor head has a width corresponding to the width of an object or image to be detected or scanned. The width of the object or image is defined as the dimension of the object or image of the transverse direction, in particular the direction perpendicular to the advance direction. The object or image may therefore be detected by moving the sensor head in the advance direction without overlaying a further movement of the sensor head in the transverse direction. The advance direction, which may also be called the product movement direction, is in particular a linear direction.

In a preferred embodiment of the sensor head, the receiving spaces are arranged in a regular field having a fundamentally rectangular shape. By tilting the rectangular field of receiving spaces relative to the advance direction, the detecting or scanning resolution may be enhanced, while at the same time an easy manufacturing of the sensor head is maintained. Each of the receiving spaces may be equipped with at least one, in particular exactly one, sensor device for detecting an object or an image on the object. The sensor devices may in particular be optical sensor devices such as for example a photodiode. Each of the sensor devices may detect or scan a single pixel or a line of pixels arranged in the product movement direction, when the object is moved relative to the sensor head.

In a preferred embodiment of the sensor apparatus a tilting angle, which is defined as the angle between the columns and the advance direction, is smaller than 45 degrees. It is preferred, that a tilting angle is in the range of 1 to 10 degrees, more preferably 2 to 8 degrees, even more preferably 2 to 5 degrees. In conjunction with an array of 32 times 32 receiving spaces the tilting angle is preferably about 2.7 degrees. The tilting of the array of receiving spaces may be achieved by tilting the sensor head relative to the advance direction and/or by tilting the array relative to the sensor head.

In a preferred embodiment of the invention, the receiving spaces are arranged in a regular rectangular pattern and the amount of offset of the receiving spaces of a successive row with regard to the receiving spaces of a preceding row is smaller than a pitch of receiving spaces of one row. The amount of offset is in particular the distance in a direction perpendicular to the advance direction between two corresponding receiving spaces of neighbouring or adjoining rows. The amount of offset corresponds to a scan line pitch.

In other words, a scan line pitch, that is a pitch of the scan lines or pixels in a direction perpendicular to the advance direction, is preferably smaller than the device pitch of one row, that is the pitch of the receiving spaces/sensor devices of one row. The columns of the array of receiving spaces are inclined such that the successive sensor device of one column scans a pixel that is offset with regard to the advance direction compared to a pixel scanned by a preceding sensor device of the same column.

In the regular rectangular pattern the pitch of receiving spaces of one row is preferably constant. In a preferred embodiment, which results in the maximum possible resolution, the amount of offset is defined as the reciprocal value of the number of rows.

In another preferred embodiment the rectangular pattern of rows and columns is tilted to a degree, in which at least a part of the receiving spaces of at least one row of the rectangular pattern is aligned with at least apart of the receiving spaces of at least one preceding row in the advance direction.

With this embodiment, a multiple scan of one the same pixel to be scanned is possible. That is, one and the same pixel may be scanned or detected by multiple sensor devices. The receiving spaces aligned in the advance direction preferably constitute receiving spaces of directly adjacent columns.

With the possibility of reading the same pixel with multiple sensors, it is for example possible to read different colours. For instance, three sensor devices for three different colours may be arranged in the array of receiving spaces such that they are aligned in the product movement direction.

The scanning resolution may be adjusted in that the sensor head is rotatable about an axis perpendicular to the advance direction such that the amount of offset of the receiving spaces is adjustable. In particular, the sensor head is rotatable about an axis being perpendicular to a surface of the object to be scanned. Alternatively or additionally, it is also possible to rotate the array of receiving spaces/sensor devices within the sensor head.

For a movement of the sensor head it is preferred that a motor, in particular a stepper motor, is provided for rotating the sensor head, in particular at defined small angle steps in the range of 0 to 90 degrees. The motor may in particular be an electrical motor.

Generally, receiving spaces of the sensor head may be equipped with individual sensor devices. For a flexible adjustment of the sensor head to a specific scanning or a detecting operation, it may be preferable that—besides the possibility of entirely filling the receiving spaces with sensor devices—the receiving spaces are configured to be partially equipped with sensor devices. In this regard, the sensor head is operable with an only partially filled array of receiving spaces.

In a preferred embodiment at least a part of the receiving spaces is equipped with sensor devices, wherein the sensor devices comprise at least an optical sensor element, a capacity sensor element, an inductive sensor element and/or a chemical sensor element. The sensor devices may for example be optical sensors, temperature sensors or infrared sensors. With a temperature or infrared sensor, a surface temperature profile of the object to be scanned can be detected. The sensor devices may be configured to detect a colour profile or a coating thickness profile of the object.

The sensor devices may for example comprise a PIN diode, a photodiode or a phototransistor. It is also possible to use pyroelectric sensor devices or micro antennae as sensor devices.

In another preferred embodiment of the invention at least a part of the receiving spaces is equipped with optical sensor devices, wherein the optical sensor devices comprise a fibre, which is arranged in a ferrule.

It is therefore a preferred embodiment of the invention that the sensor head comprises a plurality of ferrules arranged in a two-dimensional array. The fibres arranged in the ferrules may be coupled to a sensor element for detecting a light signal received from the object.

A reliable light signal may be achieved in that a lighting element, in particular a light emitting diode (LED), is arranged within the ferrule. The lighting element may be used for illuminating the object. The light of the lighting element is reflected or scattered by the object and is detectable by a sensor element arranged at an end of the fibre.

In another preferred embodiment a sensor element, in particular a sensor diode such as a photodiode, is arranged within the ferrule. In this case, the fibre of the ferrule may be coupled to a lighting element, for example a light emitting diode, for illuminating the object. The light is reflected or scattered by the object and detected by the sensor element arranged in the ferrule.

In particular in the case that the ferrule comprises a sensor element and/or a lighting element, it is preferred that the ferrule is at least partly transparent.

In a preferred embodiment of the sensor head, the sensor head comprises a receiving plate with a plurality of receiving holes as receiving spaces. The sensor devices, for example individual ferrules with fibre ends or individual photodiodes, may be placed and fixed in the receiving spaces. It is particularly preferred that the receiving holes are through-holes, into which the sensor devices may be inserted.

In a preferred embodiment, at least a part of the receiving holes has a circular cross-section. The circular cross-section allows for a good and tight connection of individual fibre ferrules. In this regard, it is preferred that the ferrules have a circular outer shape corresponding to the circular cross-section of the receiving holes.

The ferrules may fit into the holes in medium or transition fit, such that it is possible that the ferrules may be placed in the receiving holes and removed thereof by using a simple hand tool. It is particularly preferred that no additional fixtures are needed to bond the ferrules into the holes.

For holding the ferrules tight and removable in the receiving holes, it is preferred that a capture pad is arranged at at least one surface of the receiving plate. It is preferred that the capture pad includes an elastic polymer, in particular a rubber and/or an elastomer. The capture pad is preferably made of Viton® (a trademark belonging to E.I. Dupont de Nemours & Co. of Delaware) or includes the material Viton®. The ferrules may be pushed through the capture pad and are then held in place by the capture pad as it closes the ferrule after insertion. The ferrules can be removed by pushing back through from one side of the receiving plate.

In a further preferred embodiment a lens array comprising a plurality of lenses is provided, wherein the lenses are arranged in a rectangular pattern of rows and columns corresponding to the rectangular pattern of rows and columns of the receiving spaces. The lens array may be formed as a single unit or as individual lens inserts to be coupled to the receiving spaces of the sensor head.

It is also possible to arrange a single lens instead or in addition to the lens array. In another preferred embodiment, individual lenses may be inserted into the receiving holes of the receiving plate.

An inventive method is characterized in that the sensor devices are arranged in a plurality of rows and columns, such that an array of sensor devices with a rectangular pattern of the sensor devices is formed, and the object is detected or scanned while the array of sensor devices is tilted with regard to the advance direction such that the rows extend in a transverse direction relative to the advance direction and the sensor devices of a successive row of the rectangular pattern are offset with regard to the sensor devices of a preceding row of the rectangular pattern in a direction perpendicular to the advance direction.

With an inventive method, the advantages discussed in connection with the sensor apparatus may be achieved. In particular, it is possible to achieve a high resolution in a detecting or scanning operation.

DETAILED DESCRIPTION OF THE INVENTION

The principle structure of an inventive sensor apparatus10is shown inFIG. 1. The sensor apparatus10comprises a sensor device control and driving unit12and a sensor head20that is connected to the sensor device control and driving unit12through an umbilical14. The sensor apparatus10may in particular be a pixel or matrix sensor apparatus.

FIG. 2shows a general structure of a sensor head20. The sensor head20comprises a housing21, which in the shown embodiment has a cylindrical outer shape. At a first front face of the cylindrical sensor head20a plurality of receiving spaces24is arranged in a regular rectangular pattern. The receiving spaces24are populated with individual sensor devices50, which may in particular be photodiodes or fibre ends coupled to photodiodes.

The rectangular pattern of receiving spaces24and sensor devices50, respectively, forms a two-dimensional array22, in particular with a rectangular outer shape. In the two-dimensional array22the receiving spaces24and sensor devices50, respectively, are arranged in rows30and columns32extending perpendicularly to each other.

The general principle of a detecting or scanning operation is shown inFIG. 3. The sensor head20is arranged in a tilted or inclined position with regard to an advance direction16of an object8to be scanned. In particular, in the tilted or inclined position of the sensor head20the receiving spaces24of different rows30are offset with regard to the advance direction16. The receiving spaces24are equipped with individual sensor devices50.

The sensor devices50of a first row30aare arranged to scan the object8along first individual lines6aparallel to the advance direction16when the object is moved in the advance direction16. The first lines6aare spaced from one another in a direction perpendicular to the advance direction16. A second row30bis offset with regard to the first row30asuch that the sensor devices50of the second row30bare arranged to scan the object8along second individual lines6bspaced from one another and spaced from the first individual lines6ain a direction perpendicular to the advance direction16. The sensor devices50of a last row30care arranged to scan the object8along individual lines6cspaced from one another and spaced from all preceding lines6a,6bin a direction perpendicular to the advance direction16.

An array22of receiving spaces24of a sensor head20is shown inFIG. 4. The receiving spaces24are formed in a receiving plate28, which may be a metal plate, for example a steel plate, for example with a thickness of approximately 5 mm. The receiving spaces24are formed as circular receiving holes26in the receiving plate28, in particular through-holes with a circular cross-section.

In a preferred embodiment the array22of receiving spaces24has a device pitch34in the row direction and in the column direction of about 1 to 4 mm, the device pitch34being defined as the distance between the central points of two adjacent receiving spaces24in one row30or column32, respectively. It is preferred that each of the receiving holes26has a diameter27of 1 to 3 mm.

In the shown embodiment, the receiving plate28comprises an array22of receiving spaces24arranged in a regular square pattern. The shown array22comprises 32 times 32 receiving spaces24with a device pitch34of 3.2 mm and a diameter27of the receiving spaces24of 2.0 mm, resulting in a width29of the array22in the row and column direction of 102.4 mm.

In addition to the array22of receiving spaces24, a plurality of spare receiving spaces25is provided for accommodating spare sensor devices51. The spare receiving spaces25are also formed as receiving holes in the receiving plate28.

InFIG. 5a fully populated receiving plate28is shown in a tilted position. The tilted position is defined in particular in that the rectangular pattern of rows30and columns32is tilted from a position in which the columns32are aligned with the advance direction16to a position in which the columns32are slanted or inclined with regard to the advance direction16.

The tilted or inclined position of the array22enhances the maximum possible resolution of the scanning. A first row30aof sensor devices50may scan the object with a resolution in the transverse direction according to the number of sensor devices50in the first row30a. That is, if the first row30acomprises 32 sensor devices50, the maximum resolution in the transverse direction is 32 lines or pixels. Due to the tilted position of the array, a second row30bis staggered with regard to the first row30ain the transverse direction, so that the sensor devices50of the second row30bmay scan lines, which are offset with regard to the lines of the first row30a. Thus, the resolution of the scanning is doubled, if the first and second rows have the same number of sensor devices50.

A third row and successive rows30are also staggered with regard to any of the preceding rows30, so that the resolution is further enhanced. The maximum possible resolution is defined by the product of the number of sensor devices50per row and the number of sensor devices50per column. For example, if the sensor head20has 32 times 32 sensor devices50arranged in a slanted or inclined array22, the maximum resolution is 1024 pixels in the transverse direction, in particular a direction perpendicular to the advance direction16.

With the tilted array22of sensor devices50a scanning line pitch35being a distance between two adjacent scanning lines is smaller than the device pitch34.

FIG. 6schematically shows different tilting angles38(cf.FIG. 5) of a sensor device array22. In the left representation ofFIG. 6the array22is tilted to a degree such that each of the sensor devices50of one column32is arranged to scan the object8along line6that is offset with regard to any of the lines being scanned by any of the other sensor devices50of the same column32when the object8is moved along the advance direction16. That is, the sensor devices50of one column32are offset with regard to any other sensor devices50of the same column32. With this configuration the maximum resolution of a given sensor head20may be achieved.

In the middle representation the array22is tilted to a degree in which a double scan of any pixel is possible. That is, the sensor devices50of one column32correspond to the sensor devices50of another column32such that one and the same pixel may be scanned by two different sensor devices50arranged in different columns32.

In the right representation the array22is tilted to a degree in which a triple scan of any pixel is possible. That is, the sensor devices50of one column32correspond to the sensor devices50of two other columns32such that one and the same pixel may be scanned by three different sensor devices50arranged in different columns32.

FIG. 7shows an array22of sensor devices50, wherein the sensor devices50are formed in a CCD device or CMOS device. The sides of the array22are cut such that a tilted array22is achieved, as shown inFIG. 7.

The array22of receiving spaces24and sensor devices50, respectively, does not necessarily have to be a two-dimensional array22. The receiving spaces24and sensor devices50, respectively, can also be arranged in a curved surface. Such three-dimensional structures may for example be used for scanning bottles or similar objects. A closed three-dimensional structure may for example be used for scanning a cylindrical product.

FIG. 8shows a cross-sectional view of a receiving plate28with receiving spaces24, in which sensor devices50are arranged. The receiving spaces24are formed as receiving holes26, in particular through-holes. The sensor devices50each comprise a fibre-ferrule42, in which a fibre end of a fibre56is arranged. The ferrules42are mounted into the receiving holes26.

FIGS. 8 and 9also show a capture pad70arranged at at least one surface of the receiving plate28, for holding the ferrules42tight and removable in the receiving holes24.

FIG. 9shows a sensor head20with a lens array60. The lens array60has the same pitch as the array22of receiving spaces24.

A sensor head20with individual lenses or lens inserts62inserted into receiving holes26of a receiving plate28is shown inFIG. 10. With the individual lenses62, different focal distances for non-planar objects to be scanned are possible. It is also possible to use mixed scanning technologies.

FIG. 11shows a cross-sectional view of a receiving plate28having a plurality of receiving holes26, which are arranged in a two-dimensional matrix. The receiving holes26are equipped with individual sensor devices50, the sensor devices50including a ferrule42with a channel formed therein. A fibre56is coupled to the ferrule42such that a fibre end is fixed in the channel of the ferrule42.

The fibre56is connectable to a sensor element for detecting a light signal. The sensor element may for example be a photodiode.

The ferrule42includes a lighting element52for emitting a light signal onto the object8. The lighting element52is imbedded in a housing of the ferrule42. The lighting element52may have a ring-shape such that the fibre56may pass through the lighting element52and the lighting element52is arranged around the fibre56. For illuminating the object8the ferrule42is at least partly transparent.

FIG. 12shows a cross-sectional view of a receiving plate28with receiving holes26, wherein the ferrules42arranged therein comprise a sensor element54such as a photodiode for detecting a light signal of the object8. The sensor element54is imbedded in a housing of the ferrule42. The sensor element54may have a circular shape such that the fibre56of the ferrule42may pass through the sensor element54. The object8may be illuminate through the fibres56.

In the cases that a lighting element52or a sensor element54is arranged in the ferrules42it is preferable that a lens62is arranged between the ferrule42and the object8. A plurality of lenses62may form a lens array60, as shown inFIGS. 11 and 12.

A rotatable sensor head20is shown inFIG. 13. The sensor head20comprises a receiving plate28with receiving spaces24formed therein. A motor64, in particular a stepper motor, is arranged for rotating the sensor head20and/or the receiving plate28. A transmission66, which in the shown embodiment is a belt, is arranged between an output shaft of the motor64and the sensor head20. The sensor head20may in particular have a cylindrical outer shape.

A perspective view of a fibre-ferrule42is shown inFIG. 14. The fibre-ferrule42includes a substantially cylindrical body or insert made of metal—preferably steal—, ceramic, plastic or glass. It is preferred that the ferrule42includes zirconia. The cylindrical body includes a collar46with an abutment surface44for contacting a planar surface of the receiving plate28.

The ferrule42may have one or more fibres56arranged therein.FIG. 14shows an embodiment with two fibres56,57. One of the fibres56,57may be used for illumination, that is, illuminating the object8to be detected, and the other fibre may be coupled to a sensor element. The multiple fibre-ferrules42can also be used as online pixel monitor. Failed pixels can be recognized during run time. If the fibres56,57of the ferrule42are each monitored individually, that is, each fibre is connected to a sensor element, a reliable sensor device50can be provided. This sensor device50includes a fibre break monitor. There may be no need for a ferrule42with a mirror in front.

A ferrule42with three fibres56,57,58is shown inFIG. 15. Such a ferrule42may for example be used for colour imaging. The three fibres56,57,58can form an RGB-grouping. Connecting the fibres56,57,58to sensor elements would allow for colour imaging where the RGB-configuration is used. The sensor elements can be filtered for the appropriate colour.

Generally, the fibre diameters could be increased in size to fill a major portion of the ferrule cross-section to increase signal sensitivity.