Image position detector and image forming device

An image position detector includes a light emitting element to emit light to an image on an image carrier, a first light receiving element to receive a specular reflection of light from a surface of the image carrier and output a first light receiving signal, and a second light receiving element to receive a diffuse reflection of light from a surface of the image and output a second light receiving signal. The image position detector is configured to find the end position of the image according to a multiplied value obtained by multiplying values of the first and second light receiving signals by a constant coefficient.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on and claims priority from Japanese Patent Application No. 2011-114711, filed on May 23, 2011 and No. 2012-58082, filed on Mar. 15, 2012, the disclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image position detector to detect the end position of an image on an image carrier and an image forming device incorporating such an image position detector.

2. Description of the Prior Art

Japanese Patent Application Publication No. 2010-217325 discloses an image forming device to form a position correcting pattern on a paper transfer belt and read this pattern with a sensor to correct an image write timing.

Specifically, such an image forming device forms position correcting patterns for a reference color and for a primary color on the transfer belt and irradiates the patterns with infrared rays with a wavelength having a peak of spectral sensitivity characteristic relative to the primary color pattern, to detect intensity of reflection from the patterns. Then, it sets a threshold for the reflection intensity to find the center of each pattern, calculate a positional shift amount from the centers between the two colors and correct a positional shift on the basis of the calculated shift amount. Further, this device is configured not to generate diffuse rays which would otherwise affect the position detection.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an image position detector configured to detect the end position of an image, free from an influence of diffuse rays as well as an image forming device incorporating such an image position detector.

According to one aspect of the present invention, an image position detector to detect an end position of an image on an image carrier, comprising a light emitting element to emit light to the image on the image carrier, a first light receiving element to receive a specular reflection of light from a surface of the image carrier and output a first light receiving signal, and a second light receiving element to receive a diffuse reflection of light from a surface of the image and output a second light receiving signal, wherein the image position detector is configured to find the end position of the image according to a multiplied value obtained by multiplying values of the first and second light receiving signals by a constant coefficient.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

First Embodiment

FIG. 1shows a tandem-tram, indirect transfer type image forming device100which includes a paper feed tray1, an exposing unit11, an imaging unit6(6Y,6C,6M,6BK), an intermediate transfer belt5aas an image carrier, a transfer unit15(15Y,15C,15M,15BK), a fusing unit16, and a toner mark sensor17.

The image forming device100creates full color images on a paper by primarily transferring an image onto the intermediate transfer belt5aand secondarily transferring a four-color superimposed image onto the paper collectively.

The imaging unit6includes four-color electrophotographic processing units6BK (black),6M (magenta),6C (cyan),6Y (yellow) arranged in order in the rotation direction of the intermediate transfer belt5a, to form black, magenta, cyan, yellow toner images, respectively. The four processing units are configured same except for the color of images formed. In the following these units are collectively described irrespective of the colors without the added codes, Bk, M, C, Y.

The intermediate transfer belt5ais extended between a drive roller7and a driven roller8. The drive roller7is driven by a not-shown motor to move counterclockwise as indicated by an arrow inFIG. 1.

A not-shown secondary transfer roller is disposed near the driven roller8around which the intermediate transfer belt5ais wrapped for secondary transfer. A paper from the paper feed tray1is delivered by a feed roller2and a separation roller3to a secondary transfer position21. A cleaning unit20is also provided at downstream of the secondary transfer position21.

The imaging unit6includes photoreceptors9, charging units10disposed on the outer circumferences of the photoreceptors9, develop units12, transfer units15, photoreceptor cleaners13, and not-shown neutralizers. It also includes exposure portions14wbetween the charging units10and the develop units12irradiated with laser beams14from the exposing unit11.

The exposing unit11emits the laser beams14for the image colors to the exposing units14wof the photoreceptors9of the imaging unit6. The transfer units15are disposed to face the photoreceptors9via the intermediate transfer belt5a.

The exposing unit11inFIG. 2Aincludes laser diodes (LD)23Bk,23M,23C,23Y to emit laser beams14Bk,14M,14C,14Y, a polygon mirror22, and optical systems24Bk,24M,24C,24Y. The laser beams from the laser diodes23Bk,23M,23C,23Y are reflected by the polygon mirror22to the optical systems24Bk,24M,24C,24Y to adjust their optical paths and scan the surfaces of the photoreceptors9Bk,9M,9C,9Y.

The polygon mirror22is hexahedral and each face thereof scans with each of the laser beams by one line in main scan direction.

The laser beams14BK,14M and the laser beams14C,14Y are reflected by the opposite faces of the polygon mirror22, respectively to be able to expose the four photoreceptors9concurrently. The laser diodes23are each comprised of an fθ lens to align the reflected beams at the same interval and a deflection mirror.

A toner mark (TM) sensor17inFIG. 2Bis a reflective type optical sensor and includes a light emitting element17D as an infrared light-emitting diode to emit infrared light to the intermediate transfer belt5a, a first light receiving element17Hs as a phototransistor to receive specular reflection of light from the intermediate transfer belt5a, and a second light receiving element17Hr as a phototransistor to receive diffuse reflection of light from a color pattern image on the intermediate transfer belt5a.

The light emitting element17D and the first and second light receiving elements17Hs and17Hr are supported by a case30in the main scan direction (horizontally inFIG. 2B) orthogonal to a paper delivery direction. The light emitting element17D and the first light receiving element17Hs are inclined in opposite directions at the same angle relative to a vertical line Lh of the intermediate transfer belt5a. The second light receiving element17Hr is disposed on the right side of the light emitting element17D and inclined at a larger angle than the light emitting element17D.

A shown inFIG. 3, in order to calculate necessary position shift amount data, a correction pattern for position shift29or color pattern images are generated on the intermediate transfer belt5aand read by the TM sensor17to detect position shift amounts among the four colors. After the detection, the correction patterns29are removed from the intermediate transfer belt5aby the cleaning unit20.

The correction pattern29inFIG. 3includes cyan, black, yellow, magenta pattern images29a,29b,29c,29din rectangular form extending in the main scan direction and pattern images29a′,29b′,29c′,29d′ inclined relative to the main scan direction.

The correction pattern29is moved leftward with the intermediate transfer belt5afrom the left side.

FIG. 4shows the control system of the image forming device100. It includes a controller (calculator)101to perform various controls or calculations for image generation according to a manipulation of a not-shown operation unit, and a memory102in which a later-described constant coefficient of 0.3 is stored. The controller101is configured to find the end positions and shift amounts of the pattern images29ato29dand29a′ to29d′ according to the light receiving signals of the first and second light receiving elements17Hs,17Hr, and control the exposing unit11in accordance with the shift amounts to correct image write timing.

An image position detector200is comprised of the light emitting element17D, first and second light receiving elements17Hs,17Hr, controller101, and memory102.

FIG. 5shows the waveform of the output of the toner mark sensor17when the first light receiving element17Hs inFIG. 2Breceives light from the correction pattern29inFIG. 3.

The surface of the intermediate transfer belt5ais glossy and has a several % reflection rate. The light emitting element17D and first light receiving element17Hs are placed to receive mirror reflection by the belt surface. Presence of toner on the optical path reduces the output of the first light receiving element17Hs since toner particles tend to diffuse light, decreasing an amount of light incident on the first light receiving element17Hs.

Further, a black toner does not cause diffuse reflection of light due to a low reflection rate even when the wavelength of light from the light emitting element17D is in an infrared range. However, a color toner causes diffuse reflection of light due to a high reflection rate in the infrared range, and a low amount thereof reaches the light receiving element17Hs.

Generally, the intermediate transfer belt5ais set in a high gross level so that the output of the first light receiving element17Hs when receiving light from the belt surface becomes higher than when receiving that from the color toner surface. Thereby, the toner position or image position can be detected from a decrease in the output of the first light receiving element17Hs having received light from the color toner surface.

InFIG. 5the second and sixth bottom peaks of the waveform with a greatly smaller value than the other portions correspond to the black toner portions. The light from the color toner contains diffuse reflection of light so that the output of the receiving element17Hs increases.

The bottom peaks of the waveform inFIG. 5indicate the output values of the first light receiving element17Hs having detected cyan, black, yellow, magenta toner images in order.

FIG. 6shows the waveforms G1, G2of the outputs or first and second light receiving signals of the first and second light receiving elements17Hs,17Hr when detecting a toner image or the correction pattern29, respectively.

FIG. 7shows the same corrected by a calculation of (output signal of first light receiving element17Hs)−(output signal of second light receiving element17Hr)*coefficient of 0.3. As seen inFIG. 7, the values of the output signals by the detection of the cyan, black, yellow, magenta toner images can be made coincident.

The position shift in an image is detected by obtaining the position of each color toner image on the basis of the position of a black toner image as a reference.

By the correction inFIG. 7, diffuse reflection of light components can be removed from the output of the first light receiving element17Hs having received the light reflected by the color toner, thereby resulting in reducing a detection error.

The diffuse reflection of light by the color toner is thus scattered isotropically as shown inFIG. 8and the intensity of received diffuse reflection of light is almost constant.

Therefore, the diffuse reflection of light at the same intensity travels to the first and second light receiving elements17Hs,17Hr. However, the amounts of light received by them are different depending on the diameters of not-shown apertures provided in front of the light receiving elements17Hs,17Hr, and the constants of amplifier circuits after the receipt of light are also different. Because of this, the output signal value of the first light receiving element17Hs having received only the diffuse reflection of light is different from that of the second light receiving element17Hr having received the diffuse reflection of light, and the former is a constant multiple α of the latter.

The constant multiple α can be found by measuring the output of an optical sensor on a diffuse paper or attaching a sufficient amount of toner onto the transfer belt of a real machine not to be affected by the belt. Herein, the following equations are satisfied.
VS=VSS+VSD
VD=VDD
where VS is an output signal or light receiving signal of the first light receiving element17Hs, VD is an output signal of the second light receiving element17Hr, VSS is an output signal of a specular reflection of light component among the output signal of the first light receiving element17Hs, VSD is an output signal of a diffuse reflection of light component among the output signal of the first light receiving element17Hs, and VDD is an output signal of a diffuse reflection of light component among the output signal of the second light receiving element17Hr.

In the present embodiment the output signal VSS can be obtained by concurrently measuring the output signals VS and VD or calculating the constant multiple α. The end positions of correction pattern images are found according to the VSS to calculate a distance between the pattern images. Thus, it is made possible to reduce a detection error due to the diffuse reflection of light.

The equation for correcting the output signal or light receiving signal of the first light receiving element17Hs is as follows:
VSS=VS−α*VD

The constant multiple (α) is obtained by the following:
α=VSD/VDD

On a diffuse paper is VSS zero so that the constant multiple will be:
α=VS/VD.

FIG. 9shows a line G3indicating a distance between the correction pattern images read with the TM sensor17while changing a set angle (direction) of the first light receiving element17Hs, a line G4indicating the same when the output signal of the first light receiving element17Hs is corrected by the above equation. In comparison with the line G3, the line G4does not change along with a change in the set angle. At ±3 degree angle, the distance changes by 1.7% before the correction while it changes by 0.2% after the correction.

Note that the set angle is an angle of the first light receiving element17Hs inclined rightward (−) or leftward (+) relative to the TM sensor17disposed vertically to the intermediate transfer belt5a, as shown inFIG. 26.

Next, the reason why the diffuse reflection of light components of the output signal of the first light receiving element17Hs causes a detection error in reading the correction pattern29is described with reference toFIGS. 10-18.FIG. 10shows the orientation characteristic of an infrared light-emitting diode, andFIG. 11shows the orientation characteristic of a general infrared phototransistor.FIG. 12shows the ideal positions of the irradiation area of the light emitting element17D as LED and the detection area of the first light receiving element17Hs as phototransistor PTR with their centers coincident with each other. FIG.13shows the specular reflection of light components by the surface of the intermediate transfer belt5aand the diffuse reflection of light components by the color toner among the output signal of the first light receiving element Hs when the pattern29is ideally irradiated as shown inFIG. 12.

In the ideal positional relation inFIG. 12the position at which the diffuse reflection of light from the color toner is maximal coincides with the center of a decrease in the specular reflection of light from the belt surface (around X=1.5 inFIG. 13). A black toner does not cause diffuse reflection of light.

InFIG. 14the center of the irradiation area of the light emitting element and that of the detection area of the first light receiving element are shifted from each other.FIG. 15shows the specular reflection of light components from the belt surface and the diffuse reflection of light components from the color toner when the centers of the irradiation area and the detection area are different as inFIG. 14.

The orientation characteristic of the LED is that it emits light at a largest intensity from the center of the irradiation area as inFIG. 10. The position at which the diffuse reflection of light from the color toner is maximal in amount does not coincide with the center of a decrease in the specular reflection of light from the belt surface (around X=1.5 inFIG. 15).

FIG. 16shows how to detect a position shift. A threshold (for example, 2V inFIG. 16) is decided from the output signal of the first light receiving element17Hs (sensor output) to find two points at which the output signal takes the threshold as the end points F1, F2of the pattern image29ainFIG. 3. The midpoints of the two end points F1, F2are determined to be the detected positions X of the pattern image29a.

Referring toFIG. 17, a broken line A indicates the sensor output inFIG. 15while a solid line B indicates the same inFIG. 13. Two points S1, S2of the solid line B and two points E1, E2of the broken line A at which the outputs take the threshold are different from each other so that detected positions will be changed accordingly.

FIG. 18show the outputs of the TM sensor having detected light from the color and black toners and corresponding detected end positions when the centers of the detection area and irradiation area are shifted from each other inFIG. 14.

The detected end positions based on the light reflected from the color toner may differ. Shift amounts by the four colors are almost the same.

Meanwhile, the black toner does not cause diffuse reflection of light and a shift in detected positions. Therefore, two points S3, S4at the threshold of 2V inFIG. 18can accurately coincide with the actual end positions F3, F4of the pattern image29b. The position of the pattern image29bcan be accurately found. Similarly, the end positions and the position of the pattern image29b′ can be accurately found.

To the contrary, the color toner causes diffuse reflection of light and a shift in detected positions. Regarding the pattern images29a,29c,29d,29a′,29c′,29d′, two points E3, E4at the threshold of 2V inFIG. 18do not coincide with the above two points S3, S4. That is, the points E3, E4are shifted from the actual end positions so that the positions of the pattern images29a,29c,29dand29a′,29c,29d′ cannot be accurately found.

Next, a description is made on the operation of the image forming device100which can accurately acquire the end positions of the pattern images with no influence of the diffuse reflection of light and the shifted centers of the irradiation area and the detection area.

The controller101inFIG. 4controls the exposing unit11and else in accordance with a manipulation of the operation unit to generate the correction pattern29on the intermediate transfer belt5a. Then, the TM sensor17reads the correction pattern29to detect the shift amounts in the four color images referring to the positions of the pattern images29b,29b′.

First, the intermediate transfer belt5ais irradiated with infrared beams from the light emitting element17D. When the correction pattern29reaches the irradiation position of the light emitting element17D along with the moving intermediate transfer belt5aas shown inFIG. 2B, the first light receiving element17Hs outputs the first light receiving signal G1and the second light receiving element17Hr outputs the second light receiving signal G2inFIG. 6.

InFIG. 19the controller101corrects the first and second light receiving signals G1, G2to the first light receiving signal G1′ (color shift detection signal) having the diffuse reflection of light components removed inFIG. 7by multiplying the value of the signal G2by the coefficient of 0.3 and subtracting the multiplied value from the value of the first light receiving signal G1.

The controller101finds the two points at the threshold inFIG. 16on the basis of the corrected first light receiving signal G1′ to find the two end positions of each of the four color pattern images29ato29dand29a′ to29d′.

Using the first light receiving signal G1′ having the diffuse reflection of light components removed, the end positions of each pattern image can be accurately obtained. Accordingly, using the black toner images or pattern images29b,29b′ as a reference, the positions of the color pattern images29a,29c,29d,29a′,29c′,29d′ can be accurately found as well as a shift amount in each color patter image from a predetermined position. The controller101controls the exposing unit11to correct the image write timing and superimpose the four color images on one another without a color shift.

With the center of the detection area shifted from that of the irradiation area inFIG. 14, the first light receiving signal G1of the first light receiving element17Hs varies as inFIG. 16while the second light receiving signal G2of the second light receiving element17Hr varies in proportion to the light components reflected by the toner inFIG. 15. Therefore, by correcting the first light receiving signal G1by G1−G2*0.3, it is possible to obtain the graph of the light components reflected by the belt surface inFIG. 15.

Thus, according to the first embodiment it is possible to accurately acquire the positions of the pattern images29a,29c,29d,29a′,29c′,29d′ from the reference pattern images29b,29b′ as well as the shift amount thereof from a predetermined position with no influence of the diffuse reflection of light and the shifted centers of the irradiation area and the detection area. In addition, the coefficient (0.3) is stored in the memory so that it can be varied and set for the TM sensor17.

Second Embodiment

The second embodiment is different from the first embodiment in that the coefficient α is determined and stored in the memory102instead of pre-stored.

First, the light emitting element17D of the TM sensor17emits infrared beams to a diffuse paper40such as a Mansell chart adhered on the intermediate transfer belt5aas shown inFIG. 20, for example. Since the VSS is zero on the diffuse paper40, the coefficient α is found by the following equation:
α=VS/VD

That is, the controller101finds the coefficient α from the light receiving signals of the first and second light receiving elements17Hs,17Hr by the above equation and stores it in the memory102.

Then, the diffuse paper40is removed from the intermediate transfer belt5a, and the correction pattern29is generated and read with the TM sensor17.

The controller101corrects the first light receiving signal G1of the first light receiving element17Hs inFIG. 19to find the end positions and positions of the pattern images29ato29dand29a′ to29d′ as in the first embodiment. Thereby, it is possible to superimpose the four color images without a color shift.

The second embodiment can attain the same effects as those of the first embodiment. The coefficient α is found using the diffuse paper40so that it can be accurately set irrespective of an individual difference of the TM sensor17.

Third Embodiment

Another example of how to determine the coefficient α is described referring toFIG. 21. In the present embodiment, first, a sufficient amount of toner is attached onto the intermediate transfer belt5aof the image forming device100as shown inFIG. 21. The light emitting element17D emits infrared light beams to the toner. The amount of toner needs to be sufficient to prevent the light from transmitting between the toner particles, reflected by the belt surface, and reaching the first light receiving element17Hs. Also, the area of the toner attachment has to be wider than the irradiation area of the light emitting element17D.

The controller101then finds the coefficient α from the light receiving signals of the first and second light receiving elements17Hs,17Hr by the above equation, α=VS/VD and stores it in the memory102.

Thereafter, it allows the cleaning unit20to remove the toner from the intermediate transfer belt5aand operates as in the first embodiment.

The third embodiment can attain the same effects as those of the second embodiment. Besides, since the coefficient α is determined by using the toner, the steps of measuring the coefficient α in advance using the diffuse paper40and inputting the measured value to the image forming device100are omissible.

Fourth Embodiment

In the fourth embodiment the constant coefficient α is found from the light receiving signal of the first light receiving element17Hs and stored in the memory102.

The correction pattern29is read with the TM sensor17. As shown inFIG. 22, the output of the first light receiving element17Hs exhibits different minimal values when receiving the light reflected from the black toner images or pattern images29b,29b′ and from the color toner images or pattern images29a,29c,29d,29a′,29c′,29d′. The coefficient α is determined to make the minimal values coincide with each other as shown inFIG. 23.

Referring toFIG. 24, the coefficient α is found by:
α=(VSclmin−VSbkmin)/VDclmax
where VSbkmin is the minimal value of the output signal of the first light receiving element17Hs having detected a black color toner image, VSclmin is the minimal value of the output signal of the first light receiving element17Hs having detected a cyan color toner image or pattern images29a,29a′, and VDclmax is the output signal of the second light receiving element17Hr when that of the first light receiving element17Hs exhibits VSclmin.

The controller101finds the coefficient α by the above equation according to the light receiving signals of the first and second light receiving elements17Hs,17Hr and stores it in the memory102. Then, it operates as in the first embodiment.

According to the fourth embodiment the coefficient α can be obtained using the correction pattern29without measuring the reflection of light in advance or using specific patterns. This can reduce the manufacturing cost of the position detector and image forming device and provide them with a lower price.

Fifth Embodiment

FIG. 25shows the toner mark sensor17according to a fifth embodiment. In the present embodiment the diffuse paper40is disposed in the body of the image forming device100and the TM sensor17is configured to be movable to a read position P1and an escape position P2.

According to the fifth embodiment it is made possible to prevent the TM sensor17from be soiled with toner and else by moving the TM sensor17to the escape position P2during non-use. In addition the coefficient α can be found from the equation, α=VS/VD by moving the TM sensor17to the escape position P2.

Moreover, a not-shown shutter can be provided between the TM sensor17and the intermediate transfer belt5ainstead of moving the TM sensor17to the escape position P2, to be closed during non-use of the TM sensor17and opened during use thereof. The coefficient α can be obtained by using the diffuse paper40adhered on a shutter surface.

In the present embodiment since the diffuse paper40is provided in the device body, it is unnecessary to input the coefficient α to the image forming device100.

Sixth Embodiment

FIG. 27shows another image position detector210according to a sixth embodiment. The image position detector210includes a TM sensor17′ and the controller101.

The TM sensor17′ includes the light emitting element17D, first and second light receiving elements17Hs,17Hr, and a calculator circuit103as calculator. The calculator circuit103is incorporated in the case30inFIG. 2Band integrated with the light emitting element17D and first and second light receiving elements17Hs, Hr.

InFIG. 28the calculator circuit103is configured to multiply the value of the second light receiving signal G2of the second light receiving element17Hr by the constant coefficient of 0.3 and subtract the multiplied value from the value of the first light receiving element17Hs to acquire a corrected first light receiving signal G1′ (color shift detection signal) having diffuse reflection of light components removed as shown inFIG. 7. The constant coefficient of 0.3 is determined by a variable resistance or the like.

An example of the calculator circuit103is shown inFIG. 32. It is comprised of an operation amplifier104and resistances R1to R3, Rf. According to the calculator circuit103, the corrected first light receiving signal G1′ is obtained by:
G1′=G1(R1+Rf)/[R1(R2/R3+1)]−G2Rf/R1

The Rf/R1is the coefficient and set to 0.3. (R1+Rf)/[R1(R2/R3+1)] is set to 1.

The coefficient can be changed arbitrarily by replacing the resistance Rf with a variable resistance.

As in the first embodiment, the controller101finds the two points at the threshold of 2V on the basis of the corrected first light receiving signal G1′ to find the end positions of the four color pattern images29ato29d,29a′ to29d′ of the correction pattern29.

The graph inFIG. 29shows a detection error in color shift with the influence of the diffuse reflection of light removed while that inFIG. 30shows the same with the influence the diffuse reflection of light not removed. The vertical axis indicates detection error in color shift and the abscissa axis indicates set angle or tilt angle of the TM sensor17.

As seen fromFIGS. 29,30, with the constant coefficient at 0.3, it is possible to decrease a detection error in color shift from 30 μm to 10 μm at ±1.5 degrees of the set angle of the TM sensor17.

According to the sixth embodiment, incorporating the calculator circuit103in the TM sensor17′ and setting the resistance Rf inFIG. 32to a variable resistance can facilitate the adjustment or optimization of the coefficient at the time when the TM sensor17′ is manufactured.

Seventh Embodiment

FIG. 31shows another image position detector220according to a seventh embodiment. It includes the TM sensor17and the controller110.

The controller includes the calculator circuit103and a position detecting unit111to find the two end positions of the pattern images29ato29d,29a′ to29d′ on the basis of the first light receiving signal G1′ corrected by the calculator circuit103.

According to the seventh embodiment, incorporating the calculator circuit103in the controller110allows the use of an operation amplifier IC in which two or four operation amplifiers are integrated in a single package, resulting in downsizing the size of the device and reducing the manufacturing cost thereof.

As described above, the image position detector can accurately find the end positions of an image on the basis of a multiplied value obtained from multiplying the values of the first and second light receiving signals of the first and second light receiving elements by the constant coefficient, free from the influence of diffuse rays.

The above embodiments have described an example where the image position detector finds the two end positions of each of the pattern images29ato29d,29a′ to29d′ of the correction pattern29. The present invention should not be limited to such an example. It can be applied to an image position detector to find the end positions of different color images.

It can be applied to measurement of the color aligning accuracy of color images in layers formed by attaching a powder or liquid in layers onto the surface of an object such as an image carrier which reflects light.

Although the present invention has been described in terms of exemplary embodiments, it is not limited thereto. It should be appreciated that variations or modifications may be made in the embodiments described by persons skilled in the art without departing from the scope of the present invention as defined by the following claims.