Abstract:
The invention relates to a device for marking and/or scanning an object comprising a head, in particular a marking head or a scanning head, having a plurality of regular operating elements for marking and/or scanning the object, and comprising a driving mechanism for providing a relative movement of the object relative to the head in an advance direction during a working operation, at least a part of the regular operating elements being arranged in a rectangular pattern of rows and columns. The inventive device is characterized in that at least one spare operating element is provided, which is idle in case that all regular operating elements are functioning, the at least one spare operating element is movable relative to the regular operating elements, in case that one of the regular operating elements is defective, the at least one spare operating element is movable into a position in which the defective operating element is replaced by the spare operating element and the at least one spare operating element is settable to an active state. The invention further relates to a method for marking and/or scanning an object.

Description:
FIELD OF THE INVENTION 
     The present invention relates in a first aspect to a device for marking and/or scanning an object. 
     In a second aspect, the invention relates to a method for marking and/or scanning an object. 
     RELATED ART 
     A generic device for marking and/or scanning an object comprises a head, in particular a marking head or a scanning head, having a plurality of regular operating elements for marking and/or scanning the object, and a driving mechanism for providing a relative movement of the object relative to the head in an advance direction during a working operation, at least a part of the regular operating elements being arranged in a rectangular pattern of rows and columns. 
     In a conventional method for marking and/or scanning an object, the object is moved relative to the head in an advance direction during a working operation, and a marking or scanning of the object is carried out by a plurality of regular operating elements. 
     It is a general object to keep idle times or times of maintenance as short as possible. In the case that a regular operating element fails, a proper function of the device is no longer possible. Objects being not correctly marked or scanned have to be removed. This is sumptuous and interrupts the operation of the overall machine. Hence, the head has to be replaced or repaired to continue proper working operation. 
     Rising demands for high resolution applications have led to an ever-increasing amount of regular operating elements. However, as more regular operating elements are used, downtimes appear more frequently. There is thus a need for devices that allow for a good reliability and short downtimes. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to specify a device and a method for marking and/or scanning that allows for a particularly good reliability while providing an extraordinary high precision and resolution. 
     This objective is solved with a device having the features and a method as described herein. 
     Embodiments are given in the dependent claims as well as in the following description, in particular in connection with the attached figures. 
     According to the invention, the device of the above mentioned kind is characterized in that at least one spare operating element is provided, which is idle in case that all regular operating elements are functioning, the at least one spare operating element is movable relative to the regular operating elements, and in case that one of the regular operating elements is defective, the at least one spare operating element is movable into a position in which the defective operating element is replaced by the spare operating element and the at least one spare operating element is settable to an active state. 
     The method of the above mentioned kind is, according to the invention, characterized in that at least a part of the regular operating elements are arranged in a rectangular pattern of rows and columns, at least one spare operating element is provided and kept in an inactive state as long as all regular operating elements are functioning, in case that one of the regular operating elements is defective, the at least one spare operating element is moved into a position in which it replaces the defective operating element and the at least one spare operating element is activated. 
     It can be regarded as an idea of the invention to provide an additional operating element which is able to replace a regular operating element. To this end, the additional operating element can be similar or identical to the regular operating elements. Under normal conditions, i.e., if all regular operating elements work properly, the additional operating element is inactive. Thus, the additional operating element may be called a spare operating element or auxiliary operating element. As long as no regular operating element fails, the spare operating element is idle, or, in other words, deactivated or set to an inactive state. 
     An idea of the invention resides in the fact that the spare operating element is completely connected and only activated if one of the regular operating elements works incorrectly. It is advantageous that one spare operating element is able to replace an arbitrary regular operating element. This means, for a plurality of regular operating elements, only one spare operating element is required to replace any one of the regular operating elements. 
     However, it is preferred to provide several spare operating elements. It is thus possible to replace several failed regular operating elements. 
     It can be seen as another idea of the invention to provide for the spare operating elements to be movable relative to the regular operating elements in order to replace a failed regular operating element. Hence, a spare operating element is movable into a position in which it interacts with the same area of the object, with which area the regular operating element to be replaced would interact. 
     For example, if the regular operating elements are regular marking elements, each regular marking element is positioned such that is can apply a marking to a defined area of the object. According to the invention, the spare operating element which, in this example, may be a spare marking element is positioned such that it can apply a marking to any one of these defined areas. 
     Such areas to be marked and/or scanned may also be referred to as pixels, lines or dots. 
     An idea of the invention resides in the provision that the spare operating elements are completely ready for use in the idle or deactivated state. This means, the spare operating elements may already be connected to a control and evaluation unit that drives, i.e. activates and deactivates, the spare operating elements without any further steps being necessary. 
     If the spare operating element comprises a conductor, e.g. an optical waveguide, for connecting with a marking source or scanning unit, e.g. a light emitting element and/or a light sensing element, this connection has thus been previously established. Therefore, the idle state of a spare operating element is to be understood as a state in which the spare operating element only has to be moved to a certain position for replacing a defective operating element but no further steps being necessary. 
     The rectangular pattern of regular operating elements may also be called an array, particularly a two-dimensional array. The regular operating elements and the spare operating elements, which may be built identically to the regular operating elements, may also be referred to as pixels. 
     The rectangular pattern of rows and columns consisting of regular operating elements may be tilted about an axis perpendicular to the advance direction of the object. In particular, the head may be rotatable about an axis being perpendicular to an object&#39;s surface to be marked and/or scanned. 
     In this case, a column of the rectangular pattern is not parallel to the advance direction but slightly inclined. In other words, the regular operating elements of different rows are staggered or displaced to one another in the advance direction. As a consequence, the resolution for marking and/or scanning an object does not solely depend on the distance between two neighbouring regular operating elements of one row. The resolution is rather given by the distance between a regular operating element of one row to another regular operating element of another row in a direction perpendicular to the advance direction. 
     According to a preferred embodiment of the invention, for replacing the defective operating element, the spare operating element is movable into a position in which it is aligned with the defective operating element in the advance direction. Thus, after a time offset that depends on the speed of movement in the advance direction, the position between the defective operating element and the object corresponds to the position between the spare operating element and the object. 
     Generally, it may be provided that the spare operating element is movable exactly to the location of a defective regular operating element. This means, the defective regular operating element is removed and physically replaced be the spare operating element. However, it is preferred that the spare operating element replaces a defective regular operating element in the sense that the function of the defective regular operating element is replaced. In this case, the spare operating element is not moved to the location of the defective regular operating element but rather to a position that is offset to the location of the defective regular operating element. This offset lies in the advance direction. Advantageously, no changes at the regular operating elements are thus carried out in replacing a failed or defective regular operating element. 
     To this end, according to a preferred embodiment of the invention, the head further comprises movement means, the movement means being connected to the at least one spare operating element, and the movement means are movable in order to position the at least one spare operating element relative to the regular operating elements. Advantageously, the time need for moving the spare operating element is thus reduced compared to the case that the spare operating element is moved to the location of a defective regular operating element. 
     The movement means can be of any kind suited to move the spare operating element or elements. According to an embodiment of the invention, the movement means comprise at least one spare operating element ring, and the spare operating element ring is rotatable in order to position the at least one spare operating element relative to the regular operating elements. 
     Alternatively, the movement means may comprise at least one slider or carriage onto which the at least one spare operating element is mounted, and the slider or carriage is movable in order to position the at least one spare operating element relative to the regular operating elements. 
     In case several spare operating elements are provided, each spare operating element is mounted on a respective slider or spare operating element ring. The spare operating elements are thus movable independently from each other. 
     According to still another preferred embodiment of the invention, the regular operating elements are regular marking elements for applying markings on the object, and the spare operating element is a spare marking element. Alternatively, the regular operating elements are regular scanning elements for scanning the object, and the spare operating element is a spare scanning element. 
     However, it is also possible that a number of regular operating elements are regular marking elements and another number of regular operating elements are regular scanning elements. Advantageously, markings applied to the object by the regular operating elements can instantly be checked by the regular scanning elements. In this embodiment, at least one spare marking element and/or at least one spare scanning element is provided as a spare operating element. 
     The regular operating elements may also be receiving spaces equipped with at least one, in particular exactly one, marking element, particularly a printing element. 
     The regular marking elements may be any elements suited to apply visual marks on the object, in particular laser printing elements, laser engraving elements, inkjet printing elements, needle printing elements, micro pad printing elements, water jet elements and/or electrical discharge machining elements. In order to apply different types of markings to one object, the regular marking elements may cover different types of regular marking elements. 
     A regular scanning element may be any element that is sensitive to some kind of radiation, such as electromagnetic radiation, visible or nonvisible light, sound waves, or particle waves such as electron beams. In particular, the scanning elements may be light sensitive CCD or CMOS elements. 
     However, it is preferred that at least one regular operating element comprises an optical fibre which can be coupled to a light emitting element or a light detecting element. If the fibre ends are mounted to receiving spaces that are preferably arranged in a rectangular pattern, ferrules may be used for mounting. The ferrules can be made of e.g. ceramic, plastic or glass. Preferably, a ceramic material, particularly zirconia, is used. 
     Alternatively or additionally, a number of regular operating elements may comprise mirror elements and particularly form a digital micromirror device, DMD. 
     The head can also be constructed as a monolithic device in which the regular operating elements form an integral part of the head. 
     In a preferred embodiment, at least one lens, preferably one lens per regular operating element, is provided in front of the rectangular pattern in order to direct light or other radiation from the regular operation elements to the object and/or vice versa. 
     Another preferred embodiment of the invention is characterized in that detecting means for detecting a defective operating element is provided. This is useful for replacing the defective operating element and not a working regular operating element. 
     The detecting means can be, for instance, a control circuit that detects whether an electronic unit connected with the regular operating elements works properly. If the regular operating elements are regular marking elements for laser printing or laser engraving, each regular marking element may comprise a light emitting element, e.g. one laser or LED. In this case, the control circuit is adapted to determine whether a light emitting element is defective. 
     In a second step, the row and column of the defective operating element within the rectangular pattern is determined. This may be of particular importance if the rectangular pattern is not formed by the light emitting elements themselves but by light guiding elements connected thereto, e.g. optical waveguides. Here, it has to be known to which positions within the rectangular pattern the light guiding elements respectively lead. 
     To this end, a mapping table containing information which light emitting element is connected with which position within the rectangular pattern may previously be created. This may be done by using a camera that records pictures of the rectangular pattern. The regular marking elements of the rectangular pattern are simultaneously or one after another activated. From the pictures taken by the camera it can subsequently be determined at which position within the rectangular pattern each regular marking element is located. 
     Alternatively or additionally, the camera can be used for both detecting whether a regular marking element is defective as well as the position of this defective marking element within the rectangular pattern, i.e. a row information and a column information of the defective marking element. 
     A preferable embodiment of the inventive device is characterized in that a control and evaluation unit is provided which is adapted to determine the position of the defective operating element in the advance direction and in a direction perpendicular to the advance direction. This determination of the position may be achieved by firstly identifying the defective operating element. Secondly, a tilt angle of the head about an axis perpendicular to the advance direction is determined. The position in which a spare operating element replaces a defective operating element can be calculated from the tilt angle and the column information of the failed operating element. 
     According to another embodiment of the invention, a monitoring element is provided as means for detecting a defective operating element. The monitoring element is adapted to measure markings applied on the object by the regular marking elements. Furthermore, a control and evaluation unit is provided which is adapted to determine whether a regular marking element is defective on the basis of the measured markings on the object. 
     As each regular marking element applies a marking to a specific area of the object, the regular marking elements can be distinguished by the specific areas on the object. The monitoring element may be for example a light sensing element. If it senses that a marking is not correct, i.e. a specific area is marked improperly, the position to this incorrect marking is allocated to a regular operating element. Thus, the defective operating element can be identified. 
     Furthermore, it is possible to use the monitoring element for determining a tilt angle of the head. To this end, a single regular marking element may be activated to apply a reference marking on the object. Thereupon, the monitoring element, which may be movable in a direction transverse to the advance direction, is moved until is measures the reference marking. By fundamental geometric equations, the tilt angle can be calculated using the position of the monitoring element. Alternatively or additionally, a plurality of monitoring elements may be provided for determining the position of the reference marking. 
     Generally, it is possible that the movement means, particularly the at least one spare operating element ring or the at least one slider, is manually movable, in particular manually rotatable. In this embodiment, an indication system may be provided for indicating an operation position of the movement means in which the at least one spare operating element is aligned with the defective operating element in the advance direction. A control and evaluation unit may be provided which is adapted to calculate the operation position from a tilt angle of the head and a column information of the defective operating element. As an indication system, the movement means may have a scale or an angle scale. Furthermore, a display may be provided, e.g., a computer display, for indicating a setting for the scale, e.g. an angle to be set at the angle scale. A user may thus easily move the movement means to the operation position. 
     However, it is preferred that the head further comprises a motor for positioning the at least one spare operating element. Here, a control and evaluation unit is provided for driving the motor to position the spare operating element into the position in which it is aligned with the defective operating element in the advance direction. In particular, the motor may move the spare operating element via the movement means, e.g. via a slider or a spare operating element ring. Advantageously, by using a motor, the spare operating element can be positioned automatically. 
     A further embodiment of the invention is characterized in that a spare operating element comprises a mirror which is movable and can be mounted on the movement means, e.g. the slider. In this case, the spare operating element further comprises a spare light emitting and/or receiving element, e.g. an optical waveguide, which is preferably located at a fixed position and directed at the mirror. Advantageously, only the mirror or the mirrors have to be moved for replacing a failed operating element while the spare light emitting and/or receiving elements remain at a fixed position. 
     According to still another preferred embodiment of the invention, a control and evaluation unit is provided that is adapted to drive the regular operating elements and the at least one spare operating element, i.e. to active and deactivate the elements, in particularly changing a power supply of the elements time-controlled. The control and evaluation unit is further adapted to drive the defective operating element time delayed in case the spare operating element is in an active state, wherein the time delay corresponds to the distance between the spare operating element and the defective operating element in the advance direction divided by the speed of the object relative to the head caused by the driving mechanism. 
     If, for instance, a marking is to be applied to the object by the defective operating element, the time delay is such that the object has been moved just an amount equal to the distance between the defective operating element and the spare operating element in the advance direction. This distance can be determined from the tilt angle of the head and the row information of the defective operating element. 
     In the following, the design and arrangement of the rectangular pattern of preferred embodiments will be described in detail. 
     The rectangular pattern of regular operating elements consists of columns and rows perpendicular thereto. In the rectangular pattern, the regular operating elements are disposed in a manner that in each case four regular operating elements are arranged in the edges of a rectangle. The rectangular pattern may also be referred to as an orthogonal arrangement of regular operating elements. 
     The distance between regular operating elements is called a pitch. It is preferred that a pitch is common between all neighbouring regular operating elements for the rectangular pattern. 
     In a preferred variant of the inventive device, the rectangular pattern of regular operating elements is tilted with regard to the advance direction such that the rows extend in a transverse direction relative to the advance direction and the regular operating elements of a successive row of the rectangular pattern are offset with regard to the regular operating elements of a preceding row of the rectangular pattern in a direction perpendicular to the advance direction. 
     According to another preferred embodiment of the invention, the amount of offset of the regular operating elements of a successive row with regard to the regular operating elements of a preceding row is smaller than a pitch of the regular operating elements of one row. 
     It is preferred that the rows extend transversely, but not perpendicularly, to the advance direction in order to enhance the resolution. Consequently, the columns also extend transversely to the advance direction. 
     The advance direction may also be called a product movement direction and is in particular a linear direction. 
     With the head tilted, the width for marking and/or scanning is defined by a distance in a direction perpendicular to the advance direction between a first regular operating element of a first row and a last regular operating element of a last row, wherein the regular operating elements of the first row and the last row are numbered in the same direction. In other words, the width for marking and/or scanning is defined by the distance in a direction perpendicular to the advance direction of two regular operating elements located diagonally opposite one another. 
     In a preferred variant of the inventive method, the head is tilted such that the width for marking and/or scanning corresponds to the width of an object to be marked or scanned. 
     The angle of rotation or tilting angle of the head is defined as the angle between the columns and the advance direction. It is preferably chosen such that a predetermined resolution is achieved, the predetermined resolution being higher than the resolution of a single row of the head. 
     In another preferred embodiment of the invention, the tilting angle is smaller than 45 degrees, particularly in the range of 1 to 10 degrees, more preferably 2 to 8 degrees, even more preferably 2 to 5 degrees. 
     In still another preferred embodiment the rectangular pattern of rows and columns is tilted to a degree in which at least a part of the regular operating elements of one row is aligned with at least a part of the regular operating elements of another row in the advance direction. This embodiment provides the option of a multiple mark and/or scan of one and the same pixel. 
     For a precise movement of the head it is preferred that an electrical device, particularly a motor or a stepper motor, is provided for rotating the head in the range of 0 to 90 degrees, particularly at defined angle steps. The angle steps are in particular steps of less than 1 degree, preferably less than 0.1 degrees. 
     Concerning the enhancement of resolution by tilting the rectangular pattern, the invention is also based on the following aspect. 
     Depending on the tilting angle, on the diameter of a regular operating element, and on the pitch between regular operating elements, it might occur that marked and/or scanned areas of the object do overlap. However, the tilting angle is chosen such that at least a number of regular operating elements of one row, i.e. a preceding row, is displaced to a number of regular operating elements of another row, i.e. a succeeding row. As a consequence, the overlap between the marked and/or scanned areas of these regular operating elements is smaller than 100%. i.e. the marked and/or scanned areas are displaced to one another wherein the amount of displacement is smaller than the displacement between marked and/or scanned areas of regular operating elements of one and the same row. Thus, the tilting angle provides for an enhanced resolution. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be further described hereinafter with reference to preferred embodiments shown in the enclosed drawings, wherein show: 
         FIG. 1  a perspective view of a first embodiment of an inventive device; 
         FIG. 2  a schematic diagram of a rectangular pattern of regular operating elements and an object to be marked and/or scanned; 
         FIG. 3  a schematic diagram of a head of the first embodiment of the device according to the invention; 
         FIG. 4  a schematic diagram of a head of a second embodiment of a device according to the invention; 
         FIG. 5  a cross-sectional partial view of the head of the second embodiment of the device according to the invention; and 
         FIG. 6  a schematic diagram of a third embodiment of a device according to the invention. 
     
    
    
     Equivalent components are respectively referred to in all figures with the same reference signs. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a perspective view of a first embodiment of an inventive device  100  for marking and/or scanning an object. The device  100  comprises a head  10  and connection means  80  for connecting the head  10  to other components, e.g. a control and evaluation unit (not depicted). 
     The head  10  has a plurality of regular operating elements  30  which are adapted to mark and/or scan an object. The regular operating elements  30  are arranged in a rectangular pattern  20  consisting of rows  21  and columns  22 . The rows  21  and columns  22  are disposed perpendicularly to each other. 
     With respect to  FIG. 2 , a particularly preferred embodiment of a device for marking and/or scanning an object according to the invention will be described. In  FIG. 2 , a schematic diagram of a rectangular pattern  20  of regular operating elements  30  and an object  1  to be marked and/or scanned is depicted. 
     The object  1  is moved in an advanced direction  50  by a driving mechanism (not shown) during a working operation. In a working operation, the object  1  is marked and/or scanned with the regular operating elements  30 . 
     Here, the rectangular pattern  20  consists of nine regular operating elements  30  arranged in three rows  21  and three columns  22 . The columns  22  are tilted with regard to the advanced direction  50  about a tilting angle  41 . The columns  22  are thus not parallel to the advanced direction  50 . 
     As the object  1  is moved, each of the regular operating elements  30  is able to mark and/or scan a specific area of the object  1 , i.e. a line  2 . 
     The marking and/or scanning resolution in a direction  51  perpendicular to the advanced direction  50  is given by the distance  25  between two neighbouring regular operating elements  30  of different rows  21 , i.e. the distance in the direction  51  perpendicular to the advanced direction  50 . The distance  25  may be described by the pitch  26 , that is the distance between two neighbouring regular operating elements  30 , multiplied with the cosine of the tilting angle  41 . 
     Advantageously, by this tilted arrangement an enhanced resolution is achieved. 
     The use of a spare operating element will be described in the following with reference to  FIG. 3  which shows a schematic diagram of the head  10  of the first embodiment of the device  100  according to the invention. 
     The head  10  may comprise a receiving plate  15  with a plurality of receiving portions  16  arranged in a rectangular pattern. The receiving portions  16  may be holes for receiving a marking and/or a scanning element, e.g. optical wave guides connected to a light emitting element or a light sensor. 
     In the embodiment shown, only a number of the receiving portions  16  is equipped with regular operating elements  30  forming a rectangular pattern  20 . The columns of the rectangular pattern  20  are again tilted with respect to the advanced direction  50  about the tilting angle  41 . 
     The regular operating elements  30  are, in this example, regular marking elements and apply markings  2  onto the object  1 . 
     As the total number of regular operating elements  30  is very large, the risk for failure of one of the regular operating elements is quite high. A failed regular operating element, i.e. a defective operating element  35 , cannot mark or scan the object  1  properly. The defective operating element  35  has thus to be replaced. 
     To this end, the head  10  further comprises a plurality of spare operating elements  31 . The spare operating elements  31  are stored in a position  48  outside of the rectangular pattern  20 . In this position  48 , the spare operating elements  31  do not replace a defective operating element  35  and are kept in an idle state, i.e. they are not used for marking and/or scanning. 
     However, the spare operating elements  31  are movable into a position  49  in which they replace the defective operating element  35 . 
     In the embodiment shown, the defective operating element  35  is firstly disconnected from its receiving portion  16 . Subsequently, a spare operating element  31  is disconnected from its receiving portion and connected to the receiving portion  16  of the defective operating element  35 . This connecting/disconnecting can be carried out manually by a user. The total time requirement for this procedure lies in the order of minutes. 
     A control and evaluation unit (not depicted) may be provided for determining the row  23  and the column  24  of the defective operating element  35 . Furthermore, a display (not depicted) may be provided for indicating to a user the row  23  and column  24  of the defective operating element  35  to be replaced. 
       FIG. 4  shows a schematic diagram of a head  10  of a second embodiment of a device according to the invention. Here, the head  10  comprises again a plurality of regular operating elements  30  disposed in a rectangular pattern of rows  21  and columns  22 . Additionally, at least one spare operating element  31  is provided in a position  48  in which it does not replace a defective operating element  35 . 
     The head  10  is further provided with movement means  60  for moving at least one of the spare operating elements  31  relatively to the regular operating elements  30 . 
     In the embodiment shown, the movement means  60  comprises at least one spare operating element ring  61  which is connected to a spare operating element  31 . Movement of the spare operating element ring  61  causes the spare operating elements  31  to move relatively to the regular operating elements  30  in a circular fashion. 
     For each spare operating element  31  one spare operating element ring  61  may be provided in order to move the spare operating elements  31  independently from each other. 
     Generally, it is possible to manually rotate the spare operating element ring  61 . However, in the depicted embodiment, the spare operating element ring  61  is driven automatically by a motor (not shown). 
     The head  10  of this embodiment of the device according to the invention is shown in  FIG. 5  in a cross-sectional partial view. As can be readily seen, the spare operating element ring  61  is accessible from an environment of the head  10  and can thus be rotated by a user. The head  10  further comprises a base body  11  which cannot be moved by rotating the spare operating element ring  61 . 
     The base body  11  is provided with at least one shielding ring  64 ,  65  for preventing light or other radiation from passing from an area between the object and the regular operating elements to the environment of the head  10  and vice versa. In the example shown, two shielding rings are provided. An inner shielding ring  64  may be a glass fiber brush ring that breaks, spreads or deludes light, particularly laser light used for marking or scanning the object. An outer shielding ring  65  may be formed from black fibers that absorb light that might have passed the inner shielding ring  64 . 
     Connected to the base body there is a receiving plate  15  which comprises several receiving portions  16  for housing the regular operating elements  30 . 
     In the embodiment shown, each of the regular operating elements  30  and the spare operating element  31  comprises a ferrule  17  and an optical waveguide  18  coupled thereto. The optical waveguides  18  can be connected to a light source for marking, particularly printing onto, an object, and/or to a sensing element, e.g. a CMOS- or a CCD-light sensing element, for scanning the object. 
     Another particularly preferred embodiment of a device  100  for marking and/or scanning according to the invention is depicted in  FIG. 6 . 
     Once again, the device  100  comprises a head  10 , and a driving mechanism  52  for moving an object  1  in an advance direction  50 . 
     The head  10  comprises a rectangular pattern  20  consisting of rows  21  and columns  22  of a plurality of regular operating elements  30 . 
     The rectangular pattern  20  is rotated such that it forms an angle  41  between the advance direction  50  and a direction of the columns  22 . 
     Furthermore, spare operating elements  31  are provided at a position  48  outside an area used for marking and/or scanning. 
     In this preferred embodiment, a slider  62  is provided as movement means  60 . Connected to the slider  62  is one of the spare operating elements  31  such that the spare operating element  31  can be moved relatively to the regular operating elements  30  by moving the slider  62 . 
     The slider or carriage  62  is moved on a threaded rod  66  by a motor  63 , in particular a stepper engine. If the head  10  comprises a receiving plate, the threaded rod  66  may be arranged at least partially in an opening or a cut-out of the receiving plate. 
     The motor  63  can be controlled by a control and evaluation unit  70  which may be connected to the head  10  or may form a part of the head  10 . The control and evaluation unit  70  can also be connected to the driving mechanism  52  in order to control the movement of the object  1  or to determine the speed of movement. 
     The slider  62  further carries detecting means  36  for detecting markings applied on the object  1  by the regular operating elements  30 . To this end, the detecting means  36  may be a monitoring element  37  such as a light sensing element. 
     The monitoring element  37  may be used for determining the tilting angle  41 . Alternatively or additionally, the monitoring element  37  may used for determining whether a regular marking element  30  is defective as well as the position of this defective marking element  35  in the advance direction  50 . 
     For determining the tilting angle  41 , a regular marking element  30  is activated for applying a reference marking onto the object  1 . Subsequently, the slider  62  is moved until the monitoring element  37  measures the reference marking. In this position, the monitoring element  37  is aligned with the activated regular marking element  30  in the advance direction  50 . However, regarding the direction of the column  22  of the activated regular marking element  30 , the slider  62  is offset by what will be called a slider offset. 
     As the row  21  and the column  22  of the activated regular marking element  30  are known, e.g. previously determined with a camera that takes pictures of the whole rectangular pattern  20 , this slider offset can be readily determined. From the row information of the regular marking element  30 , the distance between the slider and the activated regular marking element  30  in a direction of the columns  22  is known. 
     The tilting angle  41  or α can then be calculated based on the formula:
 
tan(α)=slider offset/distance in direction of the columns.
 
     However, the monitoring element  37  can be used as well for detecting a defective marking element  35 . To this end, the monitoring element  37  is moved and monitors at the same time markings applied onto the object. The monitored markings are evaluated by the control and evaluation unit  70  to determine whether a regular operating element is defective. This may be carried out during regular operation. However, in order to facilitate this evaluation and to speed up the monitoring process, it may be provided that a reference pattern is applied to the object wherein the control and evaluation unit  70  activates the regular operating elements  30  in a predetermined order, particularly one after another. Preferably, the predetermined order is such that the slider  62  has to be moved only once across the width of the rows  21  for monitoring a marking of each regular operating element  30 . The time need of this process is thus advantageously reduced. 
     As soon as the spare operating element  31  is aligned with the defective operating element  35  in the advance direction  50 , it can be driven to replace the defective operating element  35 . As the spare operating element  31  and the defective operating element  35  are displaced to another in the advance direction  50  by an advance displacement  43 , there is a time delay between the moment when the object  1  reaches the defective operating element  35  and the moment when the object reaches the spare operating element  31 . This time delay may be calculated by dividing the advance displacement  43  by the object&#39;s speed in the advance direction. 
     In this way, a defective operating element can be replaced within seconds. It is even possible to detect whether a regular operating element is defective and subsequently replace it within a few seconds. 
     With the device according to the invention, by tilting the marking and/or scanning head it is possible to achieve a particularly good resolution. Additionally, though tilted, a defective operating element can be easily replaced, particularly in a fully automatic way. Downtimes for replacement are advantageously minimized in that additional operating elements, i.e. spare operating elements, are provided in the vicinity of the regular operating elements.