Printer

Tilt angle and tilt direction of lenticular lenses are detected precisely to correct attitude of a transported lenticular sheet with high accuracy. At least first to third lens sensors are disposed in a transport track of the lenticular sheet, aligned in a main scan direction and spaced at uneven intervals. Each lens sensor has a light-emitting element and a light-receiving element arranged to sandwich the lenticular sheet and output a detection signal corresponding to concavities and convexities of the lenticular lenses. During the transport of the lenticular sheet, the detection signals output from the first to third lens sensors are analyzed to detect the tilt direction and the tilt angle of the lenticular lenses accurately. Based on the tilt direction and the tilt angle, the attitude of the lenticular sheet is corrected in advance, preventing the lenticular sheet from skewing while stripe images are being recorded thereon.

FIELD OF THE INVENTION

The present invention relates to a printer for providing a print that looks three-dimensional to the naked eyes, and more particularly to a printer that can correct the attitude of a lenticular sheet so as to prevent it from skewing.

BACKGROUND OF THE INVENTION

A technique for creating a stereoscopically viewed image using a lenticular sheet, which has a large number of lenticular lenses arrayed in parallel to each other, has been known. This is done for example by subdividing R and L viewpoint images, which have been taken from right and left points of view, into lines, and arranging the subdivided lines (stripe images) of the R viewpoint image alternately with the stripe images of the L viewpoint image on the back of the lenticular sheet such that adjoining two stripe images are positioned underneath one lenticular lens. The R and L viewpoint images having a parallax to each other are seen as a stereoscopic image when they are observed through the lenticular lenses by the left and right eyes respectively. It is also known capturing N viewpoint images (N=3 or more), subdividing these images into stripe images, and disposing N lines of these stripe images behind one lenticular lens in order to enhance the stereoscopic effect.

Such stripe images may be printed by a printer on the reverse surface of the lenticular sheet while transporting the lenticular sheet intermittently in a sub scan direction. Immediately after each intermittent transport, a recording head is driven to record the stripe image extending in a main scan direction sequentially onto the lenticular sheet. Thus, at least two kinds of viewpoint images with a parallax to each other are recorded on the reverse surface of the lenticular sheet (see JPA 2000-292871 and JPA 2007-144974).

It sometimes happens that a lenticular sheet is conveyed aslant while multiple viewpoint images are being recorded on the reverse surface of the lenticular sheet. This is referred to as “skew”. In that case, since the longitudinal direction of the lenticular lenses is misaligned with the main scan direction during the image recording, the recording quality will be remarkably degraded. A variety of solutions for preventing the recording quality from being degraded by the skewed lenticular sheet have conventionally been developed.

JPA 2007-076084 discloses a printer that has a photo sensor nearby its recording head so as to detect the position of the lenticular lenses through the photo sensor and adjust the image recording position on the lenticular sheet based on the result of the detected position. Thus, even while the lenticular sheet is on the skew, the image recording position may be adjusted in accordance with this skew.

JPA 1996-137034 discloses a printer that corrects the attitude of the lenticular sheet in advance so as to avoid the skew during the recording. This printer detects a tilt angle of the lenticular lenses relative to the main scan direction and turns the lenticular sheet about an axis perpendicular to a transport plane according to the detection result. For the sake of detecting the tilt angle, a couple of photo sensors aligned in the scanning direction are disposed on a sheet transport track. Each photo sensor outputs a detection signal corresponding to concavities and convexities of the lenticular lenses. The tilt angle of the lenticular lenses may be detected from these detection signals.

However, in a case where the recording position of the viewpoint images is adjusted on the side of the recording head, like in JPA 2007-076084, if the lenticular sheet skews to a large extent, the viewpoint images recorded on the lenticular sheet will be so distorted that the recording quality will be degraded.

On the other hand, where the lenticular sheet is turned to correct its attitude, like in the printer of JPA 1996-137034, the viewpoint images will not have such a distortion. However, it is difficult to determine which one of detection signals output from the two photo sensors (see for exampleFIGS. 8 to 11) is ahead of or behind the other in phase. Therefore, the printer of JPA 1996-137034 cannot always detect the tilt angle or tilt direction of the lenticular lenses precisely enough to perform the attitude correction with accuracy.

Where a couple of photo sensors are aligned with each other in the main scan direction, like in the printer of JPA 1996-137034, it may be possible to calculate the tilt direction and tilt angle of the lenticular lenses from a time lag between respective times of detection of a leading end of the lenticular sheet by the two photo sensors. However, if the leading end of the lenticular sheet is not parallel to the longitudinal direction of the lenticular lenses, because of manufacture errors or other various factors, it is impossible to detect the exact tilt angle of the lenticular lenses. As a result, it becomes impossible to align the longitudinal direction of the lenticular lenses with the main scan direction.

The present invention has an object to provide a printer that can detect the tilt angle and tilt direction of the lenticular lenses with precision and correct the attitude of the lenticular sheet with high accuracy.

SUMMARY OF THE INVENTION

To achieve the above object, a printer of the present invention comprises a transport section, a recording section, at least first to third detecting sensor, an attitude adjusting section, and a control section, and records multiple viewpoint images on a lenticular sheet after correcting the attitude of the lenticular sheet for preventing the skew thereof. The lenticular sheet has a plurality of lenticular lenses formed on an obverse surface, the lenses extending in a main scan direction. The transport section transports the lenticular sheet along a transport track extending in a sub scan direction perpendicular to the main scan direction. The recording section subdivides the multiple viewpoint images into stripe images in parallel to the main scan direction, and records them on a reverse surface of the lenticular sheet. The first to third detecting sensors are disposed in the transport track and aligned in the main scan direction, to output detection signals corresponding to concavities and convexities of the lenticular lenses. These first to third detecting sensors are so arranged that at least one of three distances existing between them is different from other two distances. The attitude adjusting section adjusts the attitude of the lenticular sheet on the transport track. The control section determines, prior to the recording by the recording section, the tilt direction and angle of the longitudinal direction of the lenticular lenses relative to the main scan direction on the basis of the detection signals of the respective detecting sensors. Next, the control section controls the attitude adjusting section on the basis of the determined tilt direction and angle, so as to align the longitudinal direction of the lenticular lenses to be substantially parallel to the main scan direction.

The tilt direction is preferably determined from the detection signals of the first to third detecting sensors, whereas the tilt angle is preferably determined from the detection signals of two of the detecting sensors.

The attitude adjusting section preferably carries out attitude correction of the lenticular sheet (tilt correction of the lenticular lenses) in two steps including rough adjustment and fine adjustment. The attitude of the lenticular sheet is roughly adjusted form a first tilt direction and a first tilt angle, which are determined first. After this rough adjustment, the control section determines a second tilt direction and a second tilt angle. On the basis of these second tilt direction and second tilt angle, the attitude of the lenticular sheet is finely adjusted. In that case, the first tilt angle is determined from the detection signals of those two of the detecting sensors which are spaced at a narrower distance, and the second tilt angle is determined from the detection signals of those two of the detecting sensors which are spaced at a wider distance.

It is preferable to provide a regulation guide for regulating the attitude of the lenticular sheet on the transport track. A transport length of the lenticular sheet is measured in a period from when either one of the two detecting sensors used for the rough adjustment detects any of the lenticular lenses till when the other detects this lenticular lens. The regulation guide regulates the attitude of the lenticular sheet on the transport track so as to make this transport length smaller than a lens pitch of the lenticular lenses.

The distance between the two detecting sensors used for the rough adjustment is so determined that a transport length of the lenticular sheet in a period from when either one of these two detecting sensors detects any of the lenticular lenses till when the other detects this lenticular lens may be smaller than a lens pitch of the lenticular lenses.

Preferably, the distance between the first detecting sensor and the second detecting sensor and the distance between the second detecting sensor and the third detecting sensor are in the relation of prime numbers that they have no common divisor except “1”.

It is preferable to provide the transport track with a regulation guide for regulating skew angle of the lenticular sheet to be within a predetermined angle. It is provided that “n” represents a maximum number of those lenticular lenses which a straight line connecting the detecting sensors may concurrently cut across over the lenticular sheet when the lenticular sheet skews maximally, and S1represents a magnitude of the distance between the first detecting sensor and the second detecting sensor. It is also provided that S2represents a magnitude of the distance between the second detecting sensor and the third detecting sensor, and “M” represents any natural number from “2” to “n”. Then the S1and S2satisfy the following formulas:
S1≠{(S1+S2)/M}
S2≠{(S1+S2)/M}

The above printer comprises a recording controller that drives the recording section to record a test image elongated in the main scan direction on the lenticular sheet, a transport controller that controls the transport section such that the lenticular sheet after having the test image recorded thereon will pass through the first to third detecting sensors, and a shift amount detector that detects shift amounts of relative positions of the detecting sensors in the sub scan direction by comparing the detection signals of the detecting sensors after the test image is recorded till the test image moves past the detecting sensors. On the basis of a result of detection by the shift amount detector, the control section determines the tilt angle and the tilt direction from the detection signals of the detecting sensors, assuming that the relative positions of the detecting sensors are in alignment with each other.

The control section decides the lens pitch of the lenticular lenses on the basis of a transport length of the lenticular sheet in a cycle of the detection signals and the previously determined tilt angle. The attitude adjusting section comprises a clamper for clamping a leading end of the lenticular sheet and a turning mechanism for turning the clamper above a transport surface of the transport track.

The first to third detecting sensors consist of light-emitting elements for projecting light toward the lenticular sheet and light-receiving elements for receiving light projected from the light-emitting element.

In the printer of the present invention, three or more detecting sensors are aligned in the main scan direction such that at least a distance differs from any other distances among the distances between the sensors, whereby the tilt direction and the tilt angle of the lenticular lenses can be determined with accuracy on the basis of the detection signals from the respective detecting sensors. Thus the attitude of the lenticular sheet can be corrected to align the longitudinal direction of the lenticular lenses to be parallel to the main scan direction.

Since the tilt correction is executed in two steps: the rough adjustment being carried out on the basis of a tilt angle determined by the detection signals of two adjacent detecting sensors, and the fine adjustment being carried out on the basis of a tilt angle determined by the detection signals of two detecting sensors which are spaced at a greater distance than a distance between the two detecting sensors used for the rough adjustment, the tilt angles can be easy to calculate. As a result, the attitude correction may be accomplished in a short time.

In the case where the shift amounts of the relative positions of the detecting sensors in the sub scan direction are detected to determine the tilt angle and the tilt direction based on this detection result on the assumption that the relative positions of the detecting sensors are in alignment with each other, the accuracy in positioning the detecting sensors can be rough. As a result, the cost of manufacturing the printer may be reduced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown inFIG. 1, a printer2records parallax images (multiple viewpoint images) in a sublimation method onto the reverse surface of a lenticular sheet3, hereinafter referred to simply as the sheet3, to make a stereoscopic image visible. The printer2converts two viewpoint images to six viewpoint images and records these six viewpoint images on the lenticular sheet3.

As shown inFIG. 2, the lenticular sheet3has an array of large numbers of semi-cylindrical lenticular lenses4(hereinafter referred to simply as the lenses4) in a well-known manner on the obverse side, the reverse surface being flat. The lenses4extend in the main scan direction. The reverse surface of the lenticular sheet3is virtually divided into image segments5corresponding to the individual lenses4, one segment5being allocated to one lens4. Each image segment5is subdivided in the arrayed direction of the lenses4into a number of micro segments corresponding to the number of viewpoint images; first to sixth micro segments5ato5fin this embodiment. Stripe images provided by subdividing the six viewpoint images into lines are respectively recorded on the six micro segments5ato5f, which are allocated to the first to sixth viewpoint images in one to one relationship.

In the present embodiment, the micro segments5ato5fare each 42 μm in width (length in the sub scan direction), each stripe image having a width of 20 μm. For instance, two adjacent lines (two stripe images) of the first viewpoint image are recoded in parallel on the first micro segment5a.

Referring back toFIG. 1, the printer2is provided with a transport track12for transporting the lenticular sheet3as it is fed in through a feed-in slot11. In the transport track12, the lenticular sheet3is set with the lenses4downward and transported in the arrayed direction of the lenses4(the sub scan direction). The lenticular sheet3may be fed automatically from a cassette containing a pile of these lenticular sheets3by means of a feeding mechanism, or may be manually inserted into the feed-in slot11. It is to be noted that the lenses4are over-scaled as compared to their actual size inFIG. 1.

On a downstream side of the feed-in slot11in the sheet transport direction, a pair of feed rollers15, a set of a thermal head16and a platen roller17, an azimuth angle detector18, and a clamp unit (corresponding to a transport section and an attitude adjusting section)19are sequentially disposed. The feed roller pair15consists of a capstan roller15adriven to rotate by a motor21and a pinch roller15bto be pressed against the capstan roller15ato nip the lenticular sheet3, and feeds the lenticular sheet3toward the clamp unit19. The pinch roller15bis movable between a nipping position to nip the lenticular sheet3between the rollers15aand15b, and a release position off the lenticular sheet3.

The clamp unit19consists of a clamper23, a clamper open-close mechanism24, and a clamper drive mechanism25. The clamper open-close mechanism24switches the clamper23between a closed state for clamping a leading end of the lenticular sheet3and an open state for unclamping.

The clamper drive mechanism25drives the clamper23to move back and forth horizontally along the transport track12. Thus the lenticular sheet3, clamped by the clamper23, moves in the sub scan direction perpendicular to the main scan direction. The clamper23is moved between a clamp position for clamping or unclamping the lenticular sheet3and a terminal position downstream of the clamp position. The clamper drive mechanism25may drive the clamper23to turn about an axis that is vertical to the transport surface of the transport track12. Thus, the lenticular sheet3may turn by an appropriate angle to adjust its attitude.

The transport track12is provided with a backward transport track12aon an upstream side of the platen roller17, the backward transport track descending toward the upstream side. The backward transport track12ahas a distal end provided with a feed-out slot (not shown) for feeding out the lenticular sheet3after the recording. The backward transport track12aaccepts the lenticular sheet3as it is conveyed back to the upstream side. The backward transport track12aalso guides the lenticular sheet3to the feed-out slot.

The thermal head16and the platen roller17are opposed to each other across the transport track12. The thermal head16has two rows of heating element array16aon its lower portion, the array having a large number of heating elements aligned in the main scan direction. Arranging the heating element array16ain two adjoining rows permits recording at once two adjacent stripe images (two lines) of an identical viewpoint image. The lenticular sheet3is advanced in the sub scan direction by the width (42 μm) of the micro segment each after two lines are recorded thereon, thereby to record two stripe images adjoining in the sub scan direction on the reverse surface of the lenticular sheet3. Each heating element array16ahas a length in the main scan direction, which is slightly greater than a width (or length in the main scan direction) of a recording area on the lenticular sheet3.

The thermal head16is also movable from a pressing position for pressing recording film onto the reverse surface of the lenticular sheet3while the lenticular sheet3is on the platen roller17and the recording film is put on the reverse surface of the lenticular sheet3, to an upper retracted position away from the pressing position. The recording film includes image reception layer film27, ink film28, and backing layer film29. Each film27to29has a width that is substantially equal to the length of the heating element array16ain the main scan direction, and has such a length that permits recording on a plurality of sheets.

These films27to29are mounted to a film changing mechanism30that is installed in a way to surround the thermal head16. The film changing mechanism30has a shape of a substantially round barrel, and a pair of spools having each film27to29wound thereon are mounted on the circumferential area of the film changing mechanism30. The film changing mechanism30may rotate to bring either one of the films27to29into underneath the thermal head16while the thermal head16is in the retracted position. During the recording, the film set on the thermal head16is fed from one spool to the other spool and wound up onto the other spool in synchronism with the transport of the lenticular sheet3.

The image reception layer film27is for forming an image reception layer (base layer) on the reverse surface of the lenticular sheet3, so that color inks from the ink film28may be attached to the image reception layer. When the image reception layer film27is heated by the thermal head16while the image reception layer film27is put on the reverse surface of the lenticular sheet3, the image reception layer film27transfers the transparent image reception layer to the reverse surface of the lenticular sheet3, forming the image reception layer on the reverse surface.

The ink film28may be a well-known sublimate-type ink film, which has yellow ink areas, magenta ink areas and cyan ink areas formed sequentially in the longitudinal direction of the film. Each ink area has approximately the same size as the reverse surface of the lenticular sheet3. When the thermal head16heats the ink film28on the image reception layer that has been formed on the reverse surface of the lenticular sheet3, the yellow ink, magenta ink or cyan ink is sublimated to transfer to the image reception layer. Because the amount of attached ink varies depending on the amount of heat generated from the thermal head16, half-tone gradations may be reproduced.

When the backing layer film29is heated by the thermal head16while the backing layer film29is overlaid on an image that has been recorded on the lenticular sheet3, the backing layer film29transfers a white backing layer to form the backing layer on the image. The backing layer reflects light to visualize a bright and clear color stereoscopic image.

The head driver32drives the individual heating elements of the thermal head16. The head driver32drives the thermal head16such that every heating element generates the same amount of heat energy for recording the image reception layer or the backing layer. The amount of heat energy is set to be a value necessary for transferring the image reception layer or the backing layer. On the other hand, when recording an image using the ink film28, the head driver32records a full-color image in the three-color frame sequential method, wherein the heating elements are heated on the basis of respective image data of the six viewpoint images so as to change the ink densities according to the image data.

The azimuth angle detector18optically detects the tilt direction of the lenses formed on the lenticular sheet3(the direction of azimuth) and the azimuth angle θ of the lenses4, hereinafter referred to simply as the azimuth angle θ. The tilt direction indicates the direction in which the longitudinal direction of the lenses4inclines relative to the main scan direction. The azimuth angle θ indicates the magnitude of the tilt angle of the longitudinal direction of the lenses4relative to the main scan direction (seeFIGS. 8 and 9).

As shown inFIG. 3, the azimuth angle detector18has first to third lens sensors34,35and36which are aligned in the main scan direction. The first lens sensor34is positioned to face one side edge of the lenticular sheet3. The third lens sensor36is positioned to face the other side edge of the lenticular sheet3.

The second lens sensor35is positioned between the first and third lens sensors34and36but on the side closer to the first lens sensor34. Accordingly, the distance S2between the second lens sensor35and the third lens sensor36is greater than the distance S1between the first lens sensor34and the second lens sensor35. Reference numeral S3designates the distance between the first lens sensor34and the third lens sensor36.

As shown inFIG. 4A, the lens sensors34to36each consists of a light-emitting diode (LED)38located below the lenticular sheet3, and a photo sensor39located vertically above this LED38and the lenticular sheet3. The light-emitting diode38emits detection light toward the lenticular sheet3. The photo sensor39receives the detection light as transmitting through the lenticular sheet3, and outputs a detection signal according to the intensity of the detection light.

In addition, a slit board40is disposed between the photo sensor39and the lenticular sheet3. The slit board40is formed with a slit40athat limits the field of the detection light from the light-emitting diode38. The slit board40ais designed to have such a width that a light beam corresponding substantially to an individual lens4can pass through it. This will make the change in light amount steeper when the individual lens4passes through the lens sensors34to36. Besides that, it will make sure of projecting a sufficient amount of detection light onto the photo sensor39.

As shown inFIG. 4B, the intensity of the detection light received on the photo sensor39varies depending upon the positional relationship between the lens sensors34to36and the lenses4. So varies the detection signal accordingly. For example, the detection signals gradually go up after the lens sensors34to36face a border4abetween the lenses4until the lens sensors34to36face a peak4bof the lens4. The detection signals get to a peak value when the respective lens sensors34to36face the peak4b, and thereafter go down gradually until the lens sensors34to36face another border4a, and then the detection signals begin to go up gradually again.

As shown inFIG. 5, the clamper23is provided with a fixed plate42and a movable plate43. The fixed plate42is a flat plate having a length that is about twice the width of the lenticular sheet3in the main scan direction, and is positioned parallel to the transport surface. The movable plate43can swing between a clamping position for clamping the lenticular sheet3between the fixed plate42and the movable plate43, and an unclamping position for unclamping the lenticular sheet3. A spring (not shown) is disposed between the fixed plate42and the movable plate43to urge the movable plate43toward the clamping position.

The clamper open-close mechanism24consists of a camshaft45for swinging the movable plate43, an unclamping motor46for rotating the cam shaft45. The cam shaft45is disposed near the clamper23in the clamping position. The cam shaft45can rotate between a position where cams45apush up the movable plate43against the urging force of the spring to set the movable plate43to the unclamping position, and a position for releasing the push-up of the movable plate43to let the movable plate43move back to the clamping position according to the urging force of the spring. Thus the cam shaft45is driven by the unclamping motor46to rotate to move the movable plate43between the unclamping position and the clamping position, switching the clamper23to the open state or the closed state.

The clamper drive mechanism25includes a left motor49, a right motor50, a left pulley51, and a right pulley52. The pulleys51and52are attached to a rotary shaft that is mounted rotatable. A left belt53is suspended between the left motor49and the left pulley51, whereas a right belt54is suspended between the right motor50and the right pulley52.

To the left and right belts53and54are attached opposite ends of the clamper23so as to be freely rotatable about respective axes that are vertical to the transport surface. Thus, as the left motor49and the right motor50run in the same rotational direction, the clamper23is moved in the sub scan direction by means of the left and right belts53and54. On the other hand, when the left motor49and the right motor50run in the opposite directions, or when only one of them runs, the clamper23will turn above the transport surface.

The clamper drive mechanism25also includes a left guide rail55and a right guide rail56for guiding the clamper23in the sub scan direction. Inward of the guide rails55and56are disposed a left skew regulation guide57and a right skew regulation guide58. The left and right skew regulation guides57and58restrict the skew angle of the lenticular sheet3within a predetermined angle while the lenticular sheet3is being transported from the feed roller pair15to the clamp unit19.

As shown inFIG. 6, a CPU60controls overall components of the printer2. Beside the above clamper open-close mechanism24, the clamper drive mechanism25, the head driver32and the lens sensors34to36, a memory61, a motor driver62, a roller retracting mechanism63, a head retracting mechanism64, and a leading end detecting sensor65are also connected to the CPU60.

The memory61stores various programs and data for controlling the printer2. The CPU60reads out these programs and data from the memory61and processes them to control the printer2. The memory61has a RAM area that functions as a work memory served for the CPU60to execute processing as well as a temporary storage for various data.

The motor driver62drives or stops the motor21according to control signals from the CPU60, to rotate or stop the capstan roller15a. The roller retracting mechanism63is for moving the pinch roller15bto the nip position or the release position according to control signals from the CPU60. The head retracting mechanism64is for moving the thermal head16to the pressing position or the retracted position according to control signals from the CPU60.

The leading end detecting sensor65(seeFIG. 5) is located near the above-mentioned clamp position on the upstream side thereof. The leading end detecting sensor65is an optical sensor like the lens sensors34to36, and outputs a detection signal to the CPU60, indicating that the leading end of the lenticular sheet3has passed by the leading end detecting sensor65.

Sequentially executing the programs readout from the memory61, the CPU60functions as a data converter67, a head drive controller68, a clamper drive controller69, a tilt direction judging section70, an azimuth angle calculator71, or a tilt correction controller (attitude correction controller)72. The clamper drive controller69, the tilt direction judging section70, the azimuth angle calculator71and the tilt correction controller72correspond to the control section of the present invention.

The data converter67reads out the image data of the two viewpoint images from the memory61, processes these viewpoint images to convert into image data of six viewpoints. The head drive controller68controls driving the thermal head16through the head driver32.

The clamper drive controller69controls the clamper open-close mechanism24to switch the clamper23between the closed state and the open state. The clamper drive controller69controls the clamper drive mechanism25to move the clamper23in the sub scan direction or turn the clamper23.

The tilt direction judging section70analyzes the detection signals output from the first to third lens sensors34to36to determine the tilt direction when the longitudinal direction of the lenses4tilts relative to the main scan direction. The azimuth angle calculator71calculates an azimuth angle from the detection signals from the first to third lens sensors34to36and the known distances S1and S3between the lens sensors34to36.

The tilt correction controller72controls the clamper drive controller69to execute the tilt correction (attitude correction) on the basis of the judgment by the tilt direction judging section70and the calculation result of the azimuth angle calculator71, so as to turn the clamper23to make the longitudinal direction of the lenses4parallel to the main scan direction. The tilt correction is executed in two steps: rough adjustment and fine adjustment.

In the rough adjustment, an azimuth angle is determined based on the detection signals from the first and second lens sensors34and35and the distance S1(hereinafter referred to as the azimuth angle for rough adjustment), and on the basis of this azimuth angle for rough adjustment, the lenticular sheet3is turned to correct the tilt of the lenses4. The fine adjustment consists of determining an azimuth angle based on the detection signals from the first and third lens sensors34and36and the distance S3(hereinafter referred to as the azimuth angle for fine adjustment), and correcting the tilt of the lenses4on the basis of this azimuth angle for fine adjustment.

The CPU60has other functions than the functions of the above-described components, such as a detector for detecting positional relationship between the lenticular sheet3and the clamper23, and positional relationship between the lenticular sheet3and the heating element array16a.

Positional relationship between the lenticular sheet3and the clamper23is determined based on the transport amount of the lenticular sheet3from a reference position that is where the lenticular sheet3exists at the moment when the detection signal from the leading end detecting sensor65is entered. Positional relationship between the lenticular sheet3and the heating element array16ais determined based on the transport amount of the lenticular sheet3from a peak point of the detection signal, positional relationship in the sub scan direction between the lens sensors and the lenses4at the peak point of the detection signal, distance between the azimuth angle detector18and the heating element array16a, lens pitch between the lenses4, and other factors.

The tilt correction of the lenses4(correction of the attitude of the lenticular sheet3), carried out in two steps including the rough adjustment and the fine adjustment, will now be described specifically. In the tilt correction, even while the lenses4are tilting relative to the main scan direction, if corresponding points (e.g. the peaks4b) of three different lenses4move past the lens sensors34to36respectively at the same time, the detection signals from the lens sensors34to36will reach the peak coincidentally with each other (seeFIG. 13B). In that case, it is impossible to correct the tilt of the lenses4. For this reason, the attitude of the lenticular sheet3during the transport is controlled more accurately for example using the left and right skew regulation guides57and58, thereby to restrict the tilt of the lenses4to some extent at the moment when the lenticular sheet3is clamped by the clamper23.

Specifically, the tilt of the lenses4will be controlled in a manner as set forth below. As shown inFIG. 7, a transport length of the lenticular sheet3in a period from when one lens4is detected by either one of the first and second lens sensors34and35till when the same lens4is detected by the other sensor (a difference between the distances in the sub scan direction from the first lens sensor34to the one lens4and from the second lens sensor35to the same lens4) will be depicted as a shift amount Δd1. Providing that P0represents a lens pitch of the lenses4, the attitude of the lenticular sheet3is controlled to satisfy a condition Δd1<P0during the transport.

For example, where the lens pitch P0is 0.254 mm, the distance S1is 30 mm, and Δd1is 0.254 mm, the azimuth angle θ will be θ=tan−1(0.254/30)=0.485°. Providing that the distance S3between the first lens sensor34and the second lens sensor36is 130 mm, a shift amount Δd2indicating a difference between the distances in the sub scan direction from the first lens sensor34to one lens4and from the third lens sensor36to the same lens4will be (0.254×130/30)=1.1 mm. This is 4.33 (=1.1/0.254) times as long as the lens pitch P0. Accordingly, by regulating the attitude of the lenticular sheet3during the transport so as to restrict the shift amount Δd2within 1.00 mm, the condition Δd1<P0will be satisfied without fail.

The magnitude of the shift amount Δd1varies with a change in distance S1between the first and second lens sensors34and35. Therefore, instead of regulating the attitude of the lenticular sheet3during the transport, the distance S1may be adjusted so as to satisfy the condition Δd1<P0.

At the start of the tilt correction, the clamper drive controller69controls the clamper drive mechanism25such that the clamper23conveys the lenticular sheet3in the sub scan direction so that the lenticular sheet3passes through the respective lens sensors34to36. At that time, the detection signals output from the lens sensors34to36are fed to the CPU60. Then, the tilt correction controller72actuates the tilt direction judging section70.

As shown inFIGS. 8(A) and (B), the tilt direction judging section70analyzes binary signals from the first to third lens sensors34to36to determine the tilt direction of the lenses4. InFIG. 8(as well as inFIG. 9), the detection signals are depicted to have their peaks at the borders between the lenses4, in order to avoid complicating the drawings and clarify the relationship between the lens sensors34to36and the lenses4to be detected. In practice, however, the detection signals reach the peak at the peak4bof each lens4, as shown inFIG. 4B.

The tilt direction judging section70determines a transport length LA of the lenticular sheet3in a period from when the detection signal of the first lens sensor34reaches the peak till when the detection signal of the second lens sensor35thereafter reaches the peak. The transport length LA is determined based on the number of drive pulses applied to the left and right motors (pulse motors)49and50, which are drive sources for the clamper drive mechanism25.

The shift amount Δd1as illustrated inFIG. 7is less than the lens pitch P0at that time. Therefore, if the lenses4tilt clockwise, the first to third lens sensors34to36will sequentially detect the same border4ain this order, and the transport length LA will represent a transport length in a period from when the first lens sensor34detects a border4abetween the lenses4till when this border4ais detected by the second lens sensor35.

Then the tilt direction judging section70calculates the azimuth angle θ on the basis of the determined transport length LA and the known distance S1between the first and second lens sensors34and35, using the following formula (1). Thereafter, on the basis of the calculated azimuth angle θ and the known distance S3between the first and third lens sensors34and36, the tilt direction judging section70calculates an estimated value of a transport length LB until the border4apreviously detected by the first lens sensor34is detected by the third lens sensor36.
θ=tan−1(LA/S1)  (1)
LB=S3×tan θ  (2)

The tilt direction judging section70checks whether the detection signal of the third lens sensor36reaches the peak at a position corresponding to the transport length LB with reference to the time when the first lens sensor34previously detected the border4a. If the lenses4tilt clockwise, the detection signal of the third lens sensor36will reach the peak in a position around the corresponding position to the transport length LB. Accordingly, in this case, the tilt direction judging section70judges that the lenses4tilt clockwise.

On the other hand, as shown inFIG. 9, if the lenses4tilt counterclockwise and the same lens border4ais sequentially detected by the third to first lens sensors36to34in this order, the transport length LA represents a transport length in a period from when the first lens sensor34detects the border4atill when the second lens sensor35detects the next border4a. Therefore, if the azimuth angle θ is calculated on the basis of the transport length LA in the same way as above, the calculated value will differ from the actual azimuth angle θ of the lenses4. Accordingly, if the estimated value of the transport length LB is calculated on the basis of this calculation result, the detection signal of the third lens sensor36will not have the peak value at a position corresponding to this transport length LB. In that case, the tilt direction judging section70judges that the lenses4tilt counterclockwise.

Conversely, where the lens sensors34to36are spaced equally from each other, as shown inFIG. 10, the detection signal of the third lens sensor36will also reach the peak at the position corresponding to the estimated transport length LB even while the lenses4tilt counterclockwise for example in the same way as shown inFIG. 9(A). In that case the tilt direction of the lenses4cannot be determined. This is because a transport length LB1in a period till the border4apreviously detected by the third lens sensor36is detected by the first lens sensor34, and the transport length LB sums up to be twice a wave pitch “p” of the detection signal, as determined by the following formulas (a) to (d). Note that LA1in the following formula represents a transport length in a period till the border previously detected by the third lens sensor36is detected by the second lens sensor35. Consequently, arranging the lens sensors34to36at unequal intervals like in the present invention will achieve precise judgment on the tilt direction.
S3=2×S1  (a)
LB1=LA1×(S3/S1)=2(LA1)  (b)
LB=LA×(S3/S1)=(p−LA1)×2=2(p−LA1)  (c)
LB1+LB=2(LA1)+2(p−LA1)=2p(d)

The result of judgment by the tilt direction judging section70is input to the tilt correction controller72. In the following description, a case where the lenses4tilt counterclockwise will be discussed. After the tilt direction is judged, the tilt correction controller72actuates the azimuth angle calculator71to start calculating the azimuth angle for rough judgment.

As shown inFIG. 11(A), the azimuth angle calculator71determines the magnitude of a transport length L1from a reference point, at which the detection signal of the first lens sensor34reaches the peak, to the nearest peak of the detection signal of the second lens sensor35to the reference point. The magnitude of this transport length L1may be determined from the number of pulses applied to the left and right motors49and50. Then the azimuth angle calculator71substitutes the obtained transport length L1for the transport length LA in the above formula (1) to calculate the azimuth angle for rough adjustment.

If the nearest peak of the detection signal of the second lens sensor35is behind the peak of the detection signal of the first lens sensor34, this peak corresponds to an identical border4athat the first lens sensor34has previously detected. Therefore, the azimuth angle for rough adjustment will be approximately equal to the actual azimuth angle θ of the lenses4between the first and second lens sensors34and35.

Conversely, if the nearest peak of the detection signal of the second lens sensor35is ahead of the peak of the detection signal of the first lens sensor34, this peak corresponds to the preceding border4ato the border4athat the first lens sensor34has previously detected. Therefore, the azimuth angle for rough adjustment as calculated in this case will differ from the actual azimuth angle θ of the lenses4between the first and second lens sensors34and35. However, this is no problem because it is unnecessary to align the longitudinal direction of the lenses4to be precisely parallel to the main scan direction in the rough adjustment.

The azimuth angle for rough adjustment determined by the azimuth angle calculator71is input to the tilt correction controller72. The tilt correction controller72generates a tilt correction command to the clamper drive controller69to correct the tilt of the lenses4on the basis of the tilt direction and the azimuth angle for rough adjustment. In response to this tilt correction command, the clamper drive controller69controls the clamper drive mechanism25to interrupt transport of the clamper23in the sub scan direction and then turn the clamper23so as to set the azimuth angle for rough adjustment to zero. Thus, the tilt of the longitudinal direction of the lenses4relative to the main scan direction is roughly adjusted.

After the completion of the above rough adjustment, the clamper drive controller69controls the clamper drive mechanism25to transport the lenticular sheet3again in the sub scan direction. Then the tilt correction controller72actuates the azimuth angle calculator71to start calculating an azimuth angle for fine adjustment.

As shown inFIG. 11(B), the azimuth angle calculator71calculates the magnitude of a transport length L2from a reference point corresponding to a peak of the detection signal of the first lens sensor34to the nearest peak of the detection signal of the third lens sensor36to the reference point in the basically same way as in the calculation for the azimuth angle for rough adjustment. Then the azimuth angle calculator71substitutes the obtained transport length L2for the transport length LA in the above formula (1) to calculate the azimuth angle for fine adjustment.

The azimuth angle for fine adjustment will be approximately equal to the actual azimuth angle θ of the lenses4. Since the azimuth angle for fine adjustment is calculated after the rough adjustment, the azimuth angle θ of the lenses4has been sufficiently reduced. Therefore, if the lenses4still tilt counterclockwise in this stage, the peak of the detection signal of the third lens sensor36will come behind the peak of the detection signal of the first lens sensor34. On the other hand, when the lenses4tilt clockwise, the peak of the detection signal of the third lens sensor36will come ahead of the peak of the detection signal of the first lens sensor34.

The azimuth angle for fine adjustment determined by the azimuth angle calculator71is input to the tilt correction controller72. The tilt correction controller72generates a tilt correction command to the clamper drive controller69on the basis of the tilt direction and the azimuth angle for fine adjustment. In response to this tilt correction command, the transport of the clamper23in the sub scan direction is interrupted and, thereafter, the clamper23is turned to set the azimuth angle for fine adjustment to zero in the same way as in the rough adjustment. Thus, the tilt of the longitudinal direction of the lenses4relative to the main scan direction is finely adjusted.

After the end of the fine adjustment, the clamper drive controller69controls the clamper drive mechanism25to transport the lenticular sheet3in the sub scan direction. The tilt correction controller72compares the detection signals from the first to third lens sensors34to36, and finishes the tilt correction if the shift amounts between the respective peaks are not more than a predetermined amount. If any of the shift amounts is more than the predetermined amount, the rough and fine adjustments are carried out again. Thus the tilt correction of the lenses4is entirely completed.

Next, printing on the lenticular sheet will be described with reference to the flowchart shown inFIG. 12. First, image data of two viewpoint images of the same scene, which are viewed from different viewpoints, is fed to an input I/F (not shown) of the printer2. These two viewpoint images are temporarily stored as parallax images in the memory61. The data converter67of the CPU60reads out the image data of the two viewpoint images from the memory61to convert it to image data of six viewpoint images, and stores the image data again in the memory61.

Upon a command to start printing, the CPU60confirms that the thermal head16is in the retracted position. The clamper drive controller69of the CPU60controls the clamper drive mechanism25on the basis of detection results from a not-shown detecting sensor for the rotational position of the clamper23, e.g. a rotary encoder or the like, so as to set the clamper23substantially parallel to the main scan direction. Thereafter the clamper drive controller69moves the clamper23to the clamp position and then drives the clamper open-close mechanism24to switch the clamper23to the open state.

After the clamper23is switched to the open state, a sheet3is fed into the transport track12through the feed-in slot11. When a feed detecting sensor (not shown) detects this feeding, the CPU60controls the motor driver62to run the motor21. Thereby the lenticular sheet3is nipped between the rotating feed roller pair15and thus transported to the downstream side of the transport track12. The lenticular sheet3passes through a gap between the retracted thermal head16and the platen roller17, and moves past the azimuth angle detector18, so that the leading end of the lenticular sheet3comes in the vicinity of the clamper23and is detected by the leading end detecting sensor65.

When the leading end of the lenticular sheet3is detected by the leading end detecting sensor65, the CPU60controls the feed roller pair15to transport the lenticular sheet3farther by a constant length so as to set the leading end of the lenticular sheet3in a position where the clamper23can clamp it. Then the CPU60stops the motor21to stop transporting the lenticular sheet3.

After the transport of the lenticular sheet3stops, the clamper drive controller69controls the clamper open-close mechanism24to switch the clamper23to the closed state. Thus the leading end of the lenticular sheet3is clamped by the clamper23. After this clamping, the CPU60controls the roller retracting mechanism63to release the nip of the feed roller pair15on the lenticular sheet3.

Then the CPU60actuates the film changing mechanism30to set the image reception layer film27underneath the thermal head16and thereafter drives the head retracting mechanism64to move the thermal head16to the pressing position. Thus the thermal head16is set to press the image reception layer film27onto the reverse surface of the lenticular sheet3.

After the thermal head16is brought to the pressing position, the clamper drive controller69drives the clamper drive mechanism25to move the clamper23to the downstream side. Thus the lenticular sheet3starts being conveyed in the sub scan direction. Synchronously with this, the image reception layer film27is also advanced.

After starting transporting the lenticular sheet3, the CPU60monitors the transport length of the lenticular sheet3on the basis of the number of drive pulses applied to the left and right motors49and50of the clamper drive mechanism25. The head drive controller68of the CPU60instructs the head driver32to form the image reception layer when it is determined that the recording area of the lenticular sheet3comes close to the thermal head16.

Upon the instruction from the head drive controller68, the head driver32supplies electric power of a uniform amount to the two rows of heating element array16ato generate heat energy for heating the image reception layer film27. Thus the image reception layer film27is uniformly heated to transfer the transparent image reception layer of two lines which are elongated in the main scan direction, into the micro segment5afor instance.

After the two lines of image reception layer are formed within the micro segment5a, the clamper drive controller69controls the clamper drive mechanism25to transport the lenticular sheet3toward the downstream by a transport length corresponding to ⅙ of the previously determined lens pitch P0. This intermittent transport amount corresponds to a width of recorded two stripe images (two lines), and is equal to the width (42 μm) of each micro segment. Concurrently with this, the image reception layer film27is moved by two lines (P0/6). After this movement, the thermal head16is driven again to heat the image reception layer film27. As a result, two lines of image reception layer are newly formed in the micro segment5badjacently to the previously formed two lines of image reception layer.

In the same way, while the lenticular sheet3and the image reception layer film27are being transported, the image reception layer is formed seriatim in two lines at a time to form the transparent image reception layer finally in the whole recording area. Since the tilt correction of the lenses4has not been done in this image reception layer forming process, the range in which an image is recorded afterward can deviate from the recording area of the image reception layer. For this reason, the image reception layer should be formed in a wider range than the image recording range in order to prevent the deviation of the image from the image reception layer.

While the image reception layer is being formed, data for the tilt correction of the lenses4is collected on the basis of the detection signals from the lens sensors34to36. First is started judgment on the tilt direction of the lenses4. In the present invention, three lens sensors are arranged in the main scan direction at uneven intervals, whereby the tilt direction judging section70can judge the tilt direction of the lenses4on the basis of the detection signals from the lens sensors34to36, as illustrated inFIGS. 8 and 9. After the judgment on the tilt direction, the azimuth angle calculator71calculates the azimuth angle for rough adjustment on the basis of the detection signals from the first and second lens sensors34and35, as illustrated inFIG. 11(A).

The tilt direction of the lenses4and the azimuth angle for rough adjustment are input to the tilt correction controller72. The tilt correction controller72starts executing the correction based on the tilt direction and the azimuth angle for rough adjustment when the image reception layer is fully formed. First, the CPU60controls the head retracting mechanism64to move the thermal head16to the retracted position. At the same time, the clamper drive controller69controls the clamper drive mechanism25to interrupt the transport of the lenticular sheet3and the image reception layer film27. Next, the tilt correction controller72gives a tilt correction command to the clamper drive controller69. As a result, the clamper23turns to set the azimuth angle for rough adjustment to zero. Thus the lenticular sheet3changes its attitude to make the rough adjustment of the tilt in the longitudinal direction of the lenses4relative to the main scan direction.

After the rough adjustment is accomplished, the clamper drive controller69drives the clamper drive mechanism25to transport the lenticular sheet3to the downstream side. During this transport of the lenticular sheet3, the azimuth angle calculator71calculates the azimuth angle for fine adjustment on the basis of the detection signals from the first and third lens sensors34and36, as illustrated inFIG. 11(B). After this calculation, the transport of the lenticular sheet3is stopped, and then the clamper23is turned to set the azimuth angle for fine adjustment to zero on the basis of the result of judgment on the tilt direction and the calculation result of the azimuth angle for fine adjustment, to make the fine adjustment of the tilt in the longitudinal direction of the lenses4relative to the main scan direction.

As described so far, the tilt correction of the lenses4is executed in two steps: the rough adjustment that is executed based on the detection signals from the first and second lens sensors34and35spaced at a smaller distance, and the fine adjustment that is executed based on the detection signals from the first and third lens sensors34and36spaced at a greater distance. Thus the longitudinal direction of the lenses4can be adjusted to be parallel to the main scan direction. Particularly because the error between the calculated azimuth angle and the actual azimuth angle θ decreases as the spacing between the lens sensors increases, the fine adjustment will enhance the accuracy of the tilt correction of the lenses4. Moreover, since the azimuth angles for rough adjustment and fine adjustment can be easy to calculate, the tilt correction can be accomplished in a short time.

After the completion of the fine adjustment, the shift amounts between the peaks of the detection signals of the lens sensors34to36are measured while the lenticular sheet3is being transported to the downstream side (or to the upstream side). If the shift amounts are not more than the predetermined amount, the tilt correction is judged to be accomplished. If any shift amount is above the predetermined amount, the tilt correction is judged to be unaccomplished, and the rough and fine adjustments are executed again in the above described procedures.

When the tilt correction is judged to be accomplished, the transport of the lenticular sheet3to the downstream side is interrupted, and the lenticular sheet3is returned to the upstream side through the clamper drive mechanism25. The lenticular sheet3may also be transported to the downstream side till its trailing end moves past the azimuth angle detector18and, thereafter, transported to the upstream side. During this returning movement, the lenticular sheet3is introduced into the backward transport track12a.

While the lenticular sheet3is being returned, the CPU60determines a point when the detection signal of any one of the lens sensors34to36reaches the peak. On the basis of the transport amount of the lenticular sheet3from this peak point, the positional relationship between the lens sensor and the lenses4in the sub scan direction at the peak point, the distance between the azimuth angle detector18and the heating element array16a, the lens pitch P0and other factors, the positional relationship between the lenticular sheet3and the heating element array16ais detected.

It is to be noted that when the tilt correction is complete the lens pitch P0will coincide with the transport length of the lenticular sheet3in a cycle of the detection signal of any one of the lens sensors34to36, e.g. from one peak to the next peak of the detection signal. Therefore the lens pitch P0may be determined by the detection signal of any one of the lens sensors34to36.

When a leading edge of the recording area on the lenticular sheet3moves past the position at the thermal head16, the clamper drive controller69controls the clamper drive mechanism25to stop transporting the lenticular sheet3. Next, the CPU60actuates the film changing mechanism30to set the ink film28underneath the thermal head16and thereafter controls the head retracting mechanism64to move the thermal head16to the pressing position. This time the yellow ink area of the ink film28is laid on the reverse surface of the lenticular sheet3.

After the thermal head16is pressed on, the clamper drive controller69controls the clamper drive mechanism25to restart transporting the lenticular sheet3to the downstream side. Also in this stage, the CPU60continues monitoring the positional relationship between the lenticular sheet3and the heating element array16a. Thereafter when the heating element array16ais located in the first micro segment5aof the recording area, the head drive controller68reads out two adjacent lines of yellow image from the memory61, for example, from the first viewpoint image among the six viewpoint images, and sends them to the head driver32.

The head driver32drives the thermal head16on the basis of the two lines of yellow image data, to cause the two rows of heating element array16ato generate heat energy to heat the ink film28from the back. Thereby the yellow ink sublimated from the ink film28is put on the image reception layer in the micro segment5a. As a result, two lines of stripe images in the yellow image are recorded in parallel within the micro segment5a.

After the recording in the micro segment5a, the clamper drive controller69controls the clamper drive mechanism25to transport the lenticular sheet3to the downstream by a transport length corresponding to ⅙ of the lens pitch P0. Along with the lenticular sheet3, the ink film28is wound up to oppose an unused portion of the yellow ink area to the thermal head16in place of the used portion. After this transport, the head drive controller68reads out yellow image data of two adjacent lines of the second viewpoint image from the memory61, and sends it to the head driver32. Then the head driver32drives the two rows of heating element array16ato generate heat energy to record two lines of stripe images of the yellow image in the micro segment5b.

In the same way as above, each after the lenticular sheet3and the ink film28are transported by the length corresponding to ⅙ of the lens pitch P0, the two rows of heating element array16aare sequentially driven on the basis of two lines of yellow image data to generate heat energy to record the stripe images of the first to sixth viewpoint images respectively in the micro segments5ato5f, two lines in each segment.

When the recording of the respective yellow images of the first to sixth viewpoint images is finished, the clamper driver controller69controls the clamper drive mechanism25to stop the clamper23from transporting the lenticular sheet3. Then the CPU60controls the head retracting mechanism64to move the thermal head16to the retracted position. Thereafter the clamper drive controller69controls the clamper drive mechanism25to return the lenticular sheet3to the upstream and, when the leading end of the recording area goes by the position of the thermal head16during this returning movement, stop the transport.

Next, the CPU60actuates the film changing mechanism30to feed the ink film28so as to set the magenta ink area underneath the thermal head16. Then the CPU60controls the head retracting mechanism64to move the thermal head16to the pressing position. In the same way as for the above yellow image, while the lenticular sheet3and the ink film28are being intermittently transported to the downstream side, respective magenta images of the first to sixth viewpoint images are subdivided into the stripe images and recorded on the reverse surface of the lenticular sheet3, atop the stripe images of the yellow images. After the recording of the magenta images is complete, cyan images are recorded on the lenticular sheet3in the same procedures.

After the three color images are recorded in the recording area, the lenticular sheet3is temporarily returned to the upstream. At the same time, the film changing mechanism30is driven to move the backing layer film29to a work position, and then the thermal head16is moved to the pressing position. Then the lenticular sheet3is again transported intermittently to the downstream, while the thermal head16is driven to form the backing layer on top of the recording area having the three color images recorded thereon. The backing layer protects the three color images and also raises the reflection factor to brighten the colors.

After forming the backing layer, the CPU60controls the head retracting mechanism64to move the thermal head16to the retracted position. Then the clamper drive controller69controls the clamper drive mechanism25to move the clamper23to the clamp position and feed the lenticular sheet3into the backward transport track12a. After this movement, the clamper drive controller69controls the clamper open-close mechanism24to switch the clamper23to the open state. Thus the clamp on the leading end of the lenticular sheet3is released, and the lenticular sheet3is ejected through the feed-out slot. The above processes are repeatedly executed to print other sheets3.

Next the second embodiment of the present invention will be described. In the second embodiment, the distances between first to third lens sensors34to36are so adjusted as to prevent the detection signals of the lens sensors34to36from reaching the peaks coincidentally although the longitudinal direction of the lenses4tilts relative to the main scan direction. Note that the second embodiment has the same features as the above first embodiment except that the distances between the lens sensors34to36differ from each other. So those having the same function or structure as the above first embodiment will be designated by the same reference numerals and the description thereof will be omitted (the same applies to the third embodiment).

As shown inFIG. 13A, in the second embodiment, the distance S1between the first and second lens sensors34and35and the distance S2between the second and third lens sensors35and36are adjusted to be in the relation of prime numbers that they have no common divisor except “1”.

In contrast, where the distances S1and S2are in such a relation that they have a common divisor or common divisors other than “1”, as shown inFIG. 13B, the peaks of the detection signals from the lens sensors34to36will definitely coincide with each other in certain rotational positions of the lenticular sheet3where the longitudinal direction of the lenses4is not parallel to the main scan direction. In view of this, it will be understood that, where the distance S1and the distance S2satisfy the relation of prime numbers, the peaks of the detection signals from the lens sensors34to36will not coincide with each other unless the longitudinal direction of the lenses4is parallel to the main scan direction.

In this way, the second embodiment adjusts the distance S1and the distance S2appropriately, thereby to prevent the detection signals of the lens sensors34to36from having peaks coincidentally despite the tilt of the longitudinal direction of the lenses4relative to the main scan direction. Moreover, flexibility in arranging the lens sensors34to36may be improved in comparison with the first embodiment.

It is to be note that the tilt correction of the lenses4may be carried out in two steps in the second embodiment like in the first embodiment. It is also possible to turn the lenticular sheet3while monitoring the detection signals from the lens sensors34to36until the peaks of the respective detection signals coincide with each other. In this case, the calculation process as executed in the first embodiment would be unnecessary, and the possibility of false detection is eliminated because those conditions where the peaks of the detection signals from the lens sensors34to36will coincide with each other may be determined.

Next the third embodiment of the present invention will be described. Like the second embodiment, the third embodiment is configured to prevent detection signals of lens sensors34to36from having peaks coincidentally despite the tilt of the longitudinal direction of the lenses4relative to the main scan direction.

As shown inFIG. 14, the third embodiment is equivalent to the second embodiment in one aspect that respective distances S1and S2between the first to third lens sensors34to36are adjusted. However, unlike the second embodiment, the third embodiment makes use of left and right skew regulation guides57and58which are disposed on the downstream side of a thermal head16.

The lenticular sheet3is regulated in its skew angle by the left and right skew regulation guides57and58so that the lenticular sheet3will not skew beyond a predetermined angle. Accordingly, in the third embodiment, the distances S1and S2are adjusted to satisfy the following formulas (3) and (4) respectively when the lenticular sheet3skewing at the above-mentioned predetermined maximum angle moves past the lens sensors34to36. In these formulas, “M” is any natural number from “2” to “n”, wherein “n” is the maximum number of lenses4that a straight line Ls extending between the respective lens sensors34to36may concurrently cut across. In the drawing, the lenses4being concurrently cut across by the straight line Ls are indicated by bold lines, and n=5.
S1≠(S1+S2)/M(3)
S2≠(S1+S2)/M(4)

In contrast, where the distances S1and S2are each set to be equal to {(S1+S2)/M}, as shown inFIG. 5, the peaks of the detection signals from the lens sensors34to36will definitely coincide with each other in certain rotational positions of the lenticular sheet3where the longitudinal direction of the lenses4is not parallel to the main scan direction though. In view of this, it will be understood that, if the distances S1and S2satisfy the formulas (3) and (4), the peaks of the detection signals from the lens sensors34to36will not coincide with each other unless the longitudinal direction of the lenses4is parallel to the main scan direction. Thus the third embodiment will achieve the same effect as the second embodiment. Note that the tilt correction in the third embodiment may be carried out in the same way as in the second embodiment.

Next a printer80in the fourth embodiment of the present invention will be described with reference toFIG. 16. When the printer80is shipped from the factory or checked for maintenance, relative positions of respective lens sensors34to36to a thermal head16in the sub scan direction, hereinafter referred to simply as the relative positions, are detected to correct the tilt while taking account of misalignments between the detected relative positions.

The printer80may have the same configuration as the printer2of the above first embodiment, so that those being equivalent in function or structure to the components of the printer2are designated by the same reference numerals and the description thereof will be omitted. The printer80, however, has a misalignment detection mode for detecting misalignments between the relative positions of the lens sensors34to36to the thermal head16in addition to a recording mode for recording an image on the sheet3. Switching between these operational modes may be done by an operating section (not shown).

Moreover a CPU81of the printer80functions as a head drive controller82, a clamper drive controller83, a correction amount decider84, a tilt direction judging section85, and an azimuth angle calculator86besides a data converter67and a tilt correction controller72as described in the first embodiment.

The head drive controller82and the clamper drive controller83are equivalent to the head drive controller68and the clamper drive controller69of the first embodiment. The head drive controller82and the clamper drive controller83respectively control a head driver32and a clamper drive mechanism25in the misalignment detection mode, to record a test image88(seeFIG. 18) elongated in the main scan direction on a test sheet and, thereafter, transport the test sheet toward the lens sensors34to36. Note that the same sheet3as shown inFIG. 1is served as the test sheet.

The correction amount decider84is actuated while the test sheet is being transported toward the lens sensors34to36after having the test image88recorded thereon. The correction amount decider84detects misalignments between the relative positions of the lens sensors34to36to the thermal head16. Based on this detection result, the correction amount decider84decides correction amounts for correcting transport lengths LA, LB, L1and L2, which are determined from the detection signals of the lens sensors34to36, during the above described tilt correction.

The correction amounts determined by the correction amount decider84consists for example of a correction amount H1and a correction amount H2, which respectively represent amounts of displacement of the second lens sensor35and the third lens sensor36relative to the first lens sensor34. These correction amounts H1and H2are stored in a memory61or the like.

The tilt direction judging section85and the azimuth angle calculator86are equivalent to the tilt direction judging section70and the azimuth angle calculator71in the first embodiment. But the tilt direction judging section85and the azimuth angle calculator86correct the transport lengths LA, LB, L1and L2in the recording mode, which are determined from the detection signal of the lens sensors34to36, on the basis of the correction amounts H1and H2. This correction of LA and L1is done for instance by adding the correction amount H1to each of the transport lengths LA and L1if the second lens sensor35shifts to the upstream side (the side closer to the thermal head16) relative to the first lens sensor34. On the other hand, on correcting LB and L2, if for instance the third lens sensor36shifts to the downstream side (the side away from the thermal head16) relative to the first lens sensor34, the correction amount H2is subtracted from each of the transport lengths LB and L2. Based on these corrected transport lengths, the tilt direction of the lenses4and the azimuth angles for rough and fine adjustment are determined.

Now a process of deciding the correction amounts H1and H2in the misalignment detection mode will be described with reference to the flowchart ofFIG. 17. When the printer80is inspected for shipment from the marker or undergone the maintenance for replacing some parts such as the thermal head16or the lens sensors34to36, the operational mode of the printer80is switched to the misalignment detection mode.

After the switching to the misalignment detection mode, the test sheet is fed from a feed-in slot11into a transport track12and is clamped by the clamper23to be transported toward the downstream while an image reception layer is formed on the reverse surface of the test sheet, just as described in the above first embodiment. After the image reception layer is formed, the test sheet is transported toward the upstream till a leading end of the recording area goes past the thermal head16.

Next a CPU60actuates a film changing mechanism30to set an ink film28underneath the thermal head16and thereafter controls the head retracting mechanism64to move the thermal head16to the pressing position. In this stage, any color of ink area may be put on the reverse surface of the test sheet.

After the thermal head16is pressed on, the clamper drive controller69controls the clamper drive mechanism25to transport the test sheet to the downstream side. After the test sheet starts being transported, the head driver controller68controls the head driver32at appropriate timings to cause two rows of heating element array16aof the thermal head16to generate heat energy for heating the ink film28. Thereby two lines of stripe images elongated in the main scan direction are recorded on the image reception layer.

Thereafter, the transport of the test sheet toward the downstream by a distance corresponding to two line (P/6) and the recording of two lines of stripe images are alternately repeated a predetermined number of times, recording a test image88in an appropriate area on the reverse surface of the test sheet, as shown inFIG. 18. The test image88has an edge that is elongated in the main scan direction and parallel to the main scan direction regardless of the skew or tilt of the test sheet or lenses4. Therefore, the main scan direction can be determined with reference to the edge of the test image88.

After the recording of the test image88, the clamper drive controller69controls the clamper drive mechanism25to carry the clamper23to the downstream. Thereby the test sheet is transported to the lens sensors34to36.

On the other hand, as shown inFIG. 19, as the recording of the test image88starts, the correction amount decider84starts monitoring the detection signals from the lens sensors34to36. Until the lenses4on the test sheet reach the position at the lens sensors34to36, the detection signals output from the lens sensors34to36are at the maximum level. Thereafter when the lenses4move past the location of the lens sensors34to36, the detection signals of the lens sensors34to36vary according to concavities and convexities of the lenses4. When the test image88on the test sheet reaches the location of the lens sensors34to36, the detection signals output from the lens sensors34to36get to the minimum.

On the basis of the respective detection signals of the lens sensors34to36, the correction amount decider84determines transport lengths Lα, Lβ and Lγ of the test sheet in a period from the start of recording the test image88to the detection of this test image88by the individual lens sensors34to36. Since the edge of the test image88is parallel to the main scan direction, the transport lengths Lα, Lβ and Lγ will be equal to each other if the relative positions of the lens sensors34to36to the thermal head16are in alignment with each other. On the contrary, if the relative positions of the lens sensors34to36shift from each other, the transport lengths Lα, Lβ and Lγ will differ from each other in magnitude.

Thus the correction amount decider84can detect the misalignment between the relative positions of the lens sensors34to36by comparing the magnitudes of the transport lengths Lα, Lβ, and Lγ with each other. Then the correction amount decider84calculates a difference between the transport lengths Lα and Lβ, and a difference between the transport lengths Lα and Lγ, to decide the correction amounts H1and H2respectively. The correction amounts H1and H2are memorized in a memory61for use in real printing.

In a case where lens sensors34to36are disposed for example on the upstream side of the thermal head16, the test sheet is transported once to the upstream side and thereafter to the downstream side. In that case, the transport lengths Lα, Lβ and Lγ are those from the restart of transporting the test sheet to the downstream side till the test image88is respectively detected by the lens sensors34to36.

After the correction amounts H1and H2are memorized, the test sheet is ejected from the feed-out slot in the same way as in the first embodiment. Thus the process of detecting the correction amounts H1and H2is finished.

Next a tilt correction using the correction amounts H1and H2will be described with reference toFIG. 20. At the start of the tilt correction in the actual printing, the sheet3is transported toward the downstream and the tilt direction judging section85is actuated concurrently.

The tilt direction judging section85determines, as shown inFIG. 8, a transport length LA from a peak of the detection signal corresponding to the first lens sensor34to a following peak of the detection signal corresponding to the second lens sensor35. Then the tilt direction judging section85correct the transport length LA on the basis of the correction amount H1in the memory61.

After correcting the transport length LA, the tilt direction judging section85determines an estimated value of a transport length LB until the third lens sensor36detects a border4athat has previously been detected by the first lens sensor36, on the basis of the corrected transport length LA and a distance S1between the first and second lens sensors34and35, using the above formulas (1) and (2). Then the tilt direction judging section85corrects the transport length LB on the basis of the correction amount H2in the memory61.

Thereafter the judgment on the tilt direction of the lenses4is done in the same way as in the first embodiment, and the result of judgment is input to the tilt correction controller72. With the corrected transport lengths LA and LB, the tilt direction may be determined on the assumption that the relative positions of the lens sensors34to36are in alignment with each other.

After the judgment on the tilt direction, the azimuth angle calculator86is actuated to start calculating an azimuth angle for rough adjustment. As shown inFIG. 11(A), the azimuth angle calculator86determines the magnitude of a transport length L1from a reference point corresponding to a peak of the detection signal of the first lens sensor34to the nearest peak of the detection signal of the second lens sensor35to the reference point. Then the transport length L1is corrected on the basis of the correction amount H1in the memory61. Then the azimuth angle calculator86calculates the azimuth angle for rough adjustment on the basis of the corrected transport length L1in the same way as in the above first embodiment.

Thereafter, in the same way as in the above first embodiment, the tilt of the longitudinal direction of the lenses4relative to the main scan direction is roughly adjusted by turning the clamper23so as to reduce the azimuth angle for rough adjustment to zero. After the completion of this rough adjustment, the sheet3is transported toward the downstream. Then the azimuth angle calculator86starts calculating an azimuth angle for fine adjustment.

As shown inFIG. 11(B), the azimuth angle calculator86calculates the magnitude of a transport length L2from a reference point corresponding to a peak of the detection signal to the first lens sensor34to the nearest peak of the detection signal of the third lens sensor36to the reference point. Next this transport length L2is corrected on the basis of the correction amount H2in the memory61. Then the azimuth angle calculator86calculates the azimuth angle for fine adjustment on the basis of the corrected transport length L2in the same way as in the above first embodiment.

Like in the above first embodiment, the tilt of the longitudinal direction of the lenses4relative to the main scan direction is finely adjusted by turning the clamper23so as to reduce the azimuth angle for fine adjustment to zero. After this fine adjustment, stripe images are recorded on the reverse surface of the sheet3on the basis of a plurality of viewpoint images in the manner as set forth above.

Correcting the transport lengths L1and L2on the basis of the respective correction amounts H1and H2makes it possible to determine the azimuth angles for rough and fine adjustments on the assumption that the relative positions of the lens sensors34to36are in alignment with each other. Thus the accuracy in positioning the lens sensors34to36can be comparatively rough. As a result, the cost of manufacture for the printer80may be reduced. Since the relationship in relative position between the lens sensors34to36and the heating element array16ais recognizable, the stripe images can be recorded in designated positions.

Next the fifth embodiment of the present invention will be described. In the above first embodiment, the lens pitch P0is determined after the tilt correction of the lenses4. However, the lens pitch P0may for example be calculated at the same time when the azimuth angle for rough adjustment or the azimuth angle for fine adjustment is determined.

For example, providing that θ1represents an azimuth angle for rough adjustment or the azimuth angle for fine adjustment, and P1represents a transport length from an arbitrary peak of any one of the lens sensors34to36to the next peak, the lens pitch P0can be calculated using the formula (5). Thus the lens pitch P0may be determined before executing the tilt correction:
P0=P1×COS θ  (5)

In the above embodiments, the azimuth angle detector18consists of the first to third lens sensors34to36which are aligned in the main scan direction, but the number of lens sensors may be more than three. Also in this case, the spacing between the lens sensors should be adjusted so as not to space every lens sensor at a constant interval.

Although the above embodiments carryout the tilt correction of the lenses4after forming the image reception layer, the timing of carrying out the tilt correction (attitude correction) is not particularly limited, but it is possible to carry out the tilt correction before forming the image reception layer. Although the above embodiments execute the tilt correction of the lenses4by turning the clamper23with the clamper drive mechanism25as shown inFIG. 5, other attitude adjusting mechanisms may be used instead.

Although two lines of heating element array are disposed adjacent to each other in the above embodiment, it is possible to provide an appropriate gap between the two lines of the heating element array for the purpose of eliminating thermal influence between the heating element array lines. Moreover, it is possible to form an image reception layer, multiple kinds of ink layers and a backing layer sequentially on a single film.

The configurations, procedures and other features as described in the above embodiments may be combined appropriately insofar as it is consistent. Although the description of the above embodiments relates to line printers, the present invention is applicable to serial printers. Moreover the application field is not limited to the recording of viewpoint images for recording a stereoscopic image, but the present invention is usable for recording a so-called changing image in which visible images will change with a shift in the view position. Furthermore, the present invention is applicable not only to sublimate-type thermal printers but also to heat transfer type thermal printers, inkjet printers and others.