Thermal Transfer Recording Method and Apparatus With Control Recording Medium Before, During, and Following Recording

1. Field of the Invention

The present invention relates to a thermal transfer recording method for transferring the ink contained on an ink sheet onto a recording medium thereby recording an image thereon, and an apparatus adapted for effecting said method.

The above-mentioned thermal transfer recording apparatus includes a facsimile apparatus, an electronic typewriter, a copying machine, a printer or like.

2. Related Background Art

In general, the image recording in a thermal transfer printer is achieved by utilizing an ink sheet formed by coating a base film with a heat-fusible (or heat-sublimable) ink, selectively heating said ink sheet corresponding to image signal with a thermal head and transferring thus fused (or sublimed) ink onto a recording sheet. Said ink sheet is usually a so-called one-time ink sheet which completely loses the ink after an image recording, so that it is necessary, after the recording of a character or a line, to advance the ink sheet by amount corresponding to said recording, in order to securely bring the unused portion of the ink sheet to the next recording position. This fact increases the amount of use of the ink sheet, so that the running cost of a thermal transfer printer tends to be higher than that of the ordinary thermal printer in which the recording is made on thermal recording paper.

In order to solve such drawbacks a thermal transfer printer in which the recording sheet and the ink sheet are advanced with different speeds is proposed for example in the U.S. Pat. No. 4,456,392, the Japanese Laid-open Patent Sho 58-201686 and the Japanese Patent Publication Sho 62-58917. Also as described in said patent references, there is already known so-called multi print sheet, which is an ink sheet capable of plural image recordings, and, in continuous recording of a length L, such a multi print sheet allows users to reduce the amount of advancement of the ink sheet, during or after the image recording, to less than said length L (L/n: n>1). Such method improves the efficiency of use of the ink sheet to n times, so that a reduction in the running cost of the thermal transfer printer can be expected. This method is hereinafter called the multi-printing method.

In a thermal transfer printer for such multi-printing method, the ink sheet may generate creases or slack due to the friction between the ink sheet and the recording sheet, since the moving speed of the ink sheet is smaller than that of the recording sheet. Also in such printer, there is usually provided a cutter for cutting the recorded sheet into respective pages, and the presence of such cutter is preferable in a facsimile apparatus. However, the creases or slack in the ink sheet tends to appear more strongly in the presence of said cutter, because it is necessary to feed the recording sheet toward the cutter (so-called front feeding) after the recording of a page, and to reverse the recording sheet after the cutting operation of the cutter, until the leading end of the sheet comes close to the recording position with the thermal head (so-called back feeding).

An object of the present invention is to provide a thermal transfer recording method capable of improving the image quality, and a recording apparatus employing said method.

Another object of the present invention is to provide a thermal transfer recording method capable of reducing the consumption of the ink sheet and a recording apparatus employing said method.

Still another object of the present invention is to provide a thermal transfer recording method capable of reducing the running cost and a recording apparatus employing said method.

Still another object of the present invention is to provide a thermal transfer recording method capable of preventing the formation of creases or slack in the ink sheet and the surface smudge on the recording medium, by transporting the ink sheet by a predetermined amount in response to the transportation of the recording medium, and a recording apparatus employing said method.

Still another object of the present invention is to provide a facsimile apparatus employing a thermal transfer recording method capable of improving the image quality.

FIG. 1 is a view showing electrical connections between a control unit and a recording unit in a facsimile apparatus embodying the present invention;

FIG. 2 is a block diagram of a facsimile apparatus embodying the present invention;

FIG. 3A is a lateral cross-sectional view of said facsimile apparatus;

FIG. 3B is an external perspective view of said facsimile apparatus;

FIGS. 4A and 4B are views showing a transport system for an ink sheet and a recording sheet;

FIGS. 5 to 9 are views showing movement of the recording sheet and the ink sheet in said facsimile apparatus;

FIG. 10 is a view showing contact area of the thermal head and the platen roller;

FIG. 11 is a flow chart showing a recording sequence in said facsimile apparatus;

FIG. 12 is a flow chart showing another sequence of a step S10 in FIG. 11; and

FIG. 13 is a cross-sectional view of an ink sheet employed in said embodiment.

Now the present invention will be clarified in detail by an embodiment thereof shown in the attached drawings.

FIGS. 1 to 4 illustrate the thermal transfer printer of the present invention applied in a facsimile apparatus, wherein FIG. 1 is a view showing electrical connection between a control unit and a recording unit; FIG. 2 is a schematic block diagram of said facsimile apparatus; FIG. 3A is a lateral cross-sectional view thereof; and FIG. 3B is an external perspective view thereof.

At first the structure will be briefly explained with reference to FIG. 2.

In FIG. 2, a reading unit 100 for photoelectrically reading an original image and supplying a control unit 101 with digital image signals is provided with an original conveying motor and a CCD image sensor. A control unit 101 has the following structure. A line memory 110, for storing image data of each line serves to store the image data of a line from the reading unit 100 in case of the transmission or the copying, or the decoded image data of a line in case of the image data reception. Image formation is conducted by the supply of the stored data to a recording unit 102. An encoding/decoding unit 111 serves to encode the image information to be transmitted, for example by MH encoding, and to decode the received encoded data into image data. A buffer memory 112 stores the encoded image data to be transmitted or the received encoded data. The various units of the control unit 101 and the entire apparatus are controlled by a CPU 113 such as a microprocessor. The control unit 101 is further provided, in addition to the CPU 113, with a ROM 114 storing the control program of the CPU 113 and other data, and a RAM 115 for temporarily storing various data, as a work area of the CPU 113.

The recording unit 102 is provided with a thermal line head for image recording on the recording sheet by means of the thermal transfer recording method, of which structure will be explained in detail later with reference to FIG. 1. An operation unit 103 is provided with function keys operations such as starting the transmission, and input keys for entering a telephone number. A switch 103a to be operated by the operator indicates the kind of the ink sheet to be employed; a multi-printing ink sheet when it is on, or an ordinary ink sheet when it is off. There are further provided an indicating unit 104, provided in the operation unit 103 for indicating the status of the apparatus and various functions; a power supply unit 105 for supplying the electric power to the entire apparatus; a modem (modulation/demodulation unit) 106; a network control unit (NCU) 107; and a telephone unit 108.

Now reference is made to a lateral cross-sectional view in FIG. 3A and an external perspective view in FIG. 3B for explaining the structure of the recording unit 102, wherein the same components as those in FIG. 2 are represented by the same numbers.

Referring to these drawings, plain paper or the recording sheet 11 is stored as a roll 10 wound around a core 10a. Said rolled paper 10 is rotatably housed in the apparatus, so as to feed the recording sheet 11 to a thermal head 13 by the rotation, in a direction indicated by an arrow, of the platen roller 12 driven by a recording sheet conveying motor 24. A rolled sheet loading unit 10b detachably contains the rolled sheet 10. The platen roller 12 serves to transport the recording sheet 11 in a direction b, and to press an ink sheet 14 and the recording sheet 11 against a heat-generating member 132 of the thermal head 13. After the image recording with the thermal head 13, the recording sheet 11 is conveyed toward discharge rollers 16a, 16b by further rotation of the platen roller 12, then is cut into a page by the engagement of cutter blades 15a, 15b after the image recording of a page, and finally is discharged.

There are provided an ink sheet feed roller 17 on which the ink sheet 14 is wound, and an ink sheet takeup roller 18 driven by an ink sheet conveying motor to be explained later, for taking up the ink sheet 14 in a direction a. Said feed roller 17 and takeup roller 18 are detachably loaded in an ink sheet loading portion 70 of the apparatus. There are further provided a sensor 19 for detecting the remaining amount and the speed of the ink sheet 14; an ink sheet sensor 20 for detecting the presence of the ink sheet 14; a spring 21 for pressing said thermal head 13 against the platen roller 12 across the recording sheet 11 and the ink sheet 14; a sensor 22 for detecting the presence of the recording sheet; and a roller 72 for guiding the ink sheet 14.

Next there will be explained the structure of the reading unit 100.

A light source 30 illuminates an original 32, and the reflected light is guided, through an optical system (composed of mirrors 50, 51 and a lens 52), to a CCD sensor 31 for conversion into electrical signals. The original 32 is conveyed with a speed corresponding to the reading speed, by means of rollers 53, 54, 55, 56 driven by an unrepresented original conveying motor. Plural originals 32 stacked on an original stacker 57 are guided by a slider 57a, separated one by one by the cooperation of a transport roller 54 and a separating piece 58, then advanced to the reading unit 100, and discharged onto a tray 77 after image reading.

A control board 41, constituting the principal part of the control unit 101, sends various control signals to the various units of the apparatus. There are further provided a modem board 106 and an NCU board 107.

FIGS. 4A and 4B show the details of the transporting mechanism for the ink sheet 14 and the recording sheet 11, wherein the same components as those in the foregoing drawings are represented by the same numbers and will not be explained further.

Referring to FIG. 4A, an ink sheet conveying motor 25 transports the ink sheet 14 in a direction a, and a recording sheet conveying motor 24 rotates the platen roller 12, thereby advancing the recording sheet in a direction b opposite to the direction a. There are further provided gears 26, 27 for transmitting the rotation of the motor 24 to the platen roller 12; and gears 28, 29 for transmitting the rotation of the ink sheet motor 25 to the takeup roller 18. An ink sheet feed motor 85 rotates an ink sheet feed roller 7 through gears 86, 87, said roller 17 being rotated in a direction C when the ink sheet 14 is fed.

As the conveying directions of the recording sheet 11 and the ink sheet 14 ar mutually opposite as explained above, the advancing direction of the ink sheet 14 coincides with the direction of image recording in the longitudinal direction of the recording sheet 11 (direction a, which is opposite to the conveying direction of the recording sheet 11). By assuming that the conveying sheet V.sub.P of the recording sheet 11 as V.sub.P =-n.multidot.V.sub.1 wherein V.sub.1 is the conveying speed of the ink sheet 14 and the negative sign indicates that the conveying direction of the recording sheet 11 is opposite to that of the ink sheet 14, the relative speed of the recording sheet 11 and the ink sheet 4 with respect to the thermal head 13 is represented by:

which is equal to or larger than V.sub.P, and is larger than the relative speed V.sub.PI '(=V.sub.P (1-1/n)) when the recording sheet 1 and the ink sheet 14 are conveyed in the same direction in the conventional manner.

There is also known a method, in recording n lines with the thermal head 13, of conveying the ink sheet 14 in a direction a by a distance (l/m) for every (n/m) lines (wherein m is an integer satisfying a condition n>m, and l is the length of a line in sub scanning direction), and a method of recording a length L, by conveying the ink sheet 14 with a speed same as that of the recording sheet 11 but in the opposite direction, and rewinding the ink sheet 14 by L.multidot.(n-1)/n (n>1) prior to the next recording of a predetermined amount. In either case, the relative speed is V.sub.P if the recording is made while the ink sheet 14 is stopped, or 2V.sub.P if the recording is made while the ink sheet 14 is moving.

FIG. 4B shows an apparatus in which the cutter 15 is replaced by a manual cutter 15C provided at the downstream side of the discharge rollers 16. Even in such apparatus, similar effects can be obtained by a transport control excluding the backfeed process to be explained later. The following description will be made on the apparatus shown in FIG. 4A.

FIG. 1 shows the electrical connection between the control unit 101 and the recording unit 102 in the facsimile apparatus of the present embodiment wherein the same components as those in the foregoing drawings are represented by the same numbers.

A thermal head 13, which is a line head, is provided with a shift register 130 for receiving serial recording data 43 of a line from the control unit 101, a latch circuit 131 for latching the data of the shift register 130 in response to a latch signal 44, and heat-generating elements 132 consisting of heat-generating resistors of a line. The heat-generating resistors 132 are driven in m blocks, indicated by 132-1 to 132-m. A temperature sensor 133 is mounted on the thermal head 13 for detecting the temperature thereof, and releases an output signal 42, which is A/D converted in the control unit 101 and is supplied to the CPU 113. Thus the CPU 113 detects the temperature of the thermal head 13 and correspondingly regulates the pulse duration of a strobe signal 47 or the driving voltage of the thermal head 13, thereby varying the energy applied thereto according to the characteristics of the ink sheet 14.

The characteristic or species of said ink sheet 14 is designated by the aforementioned switch 103a. It may also be identified by a mark printed on the ink sheet 14, or by a mark or a notch provided on a cartridge of the ink sheet 14.

A drive circuit 46 receives the drive signal for the thermal head 13 from the control unit 101, and generates a strobe signal 47 for driving each block of the thermal head 13. Said drive circuit 46 is capable, by the instruction of the control unit 101, of varying the voltage to a power supply line 45 for current supply to the heat-generating resistors 132 of the thermal head 13, thereby varying the energy supplied thereto. Motor drive circuits 48, 49, 88 serve to respectively drive a recording sheet motor 24, an ink sheet motor 25 and an ink sheet feed motor 85. Said motors 24, 25, 85 are composed of stepping motors in the present embodiment, but they may also be composed for example of DC motors.

FIG. 5 shows the state of the recording sheet 11 and the ink sheet 14 in a stand-by state prior to the start of recording. In this state the leading end portion of the recording sheet 11 is in the recording position by the thermal head 13. When the image recording is started from this state, the recording sheet 11 is transported in a direction b with a speed V.sub.P, while the ink sheet 14 is transported in a direction a with a speed V.sub.I, wherein said speeds are correlated by V.sub.I =V.sub.P /n.

FIG. 6 shows a state after image recording of a page, wherein the trailing end of the recorded page is in contact with the thermal head 13. Therefore, for cutting the page with the cutter 15, the recording sheet 11 has to be transported in the forward direction (b) over a distance l between the recording position of the thermal head 13 and the cutter 15. In this transportation, the recording sheet 11 has a speed V.sub.PF while the ink sheet 14 has a speed V.sub.IF, and said speeds are mutually correlated by V.sub.IF =-V.sub.PF /n. The ink sheet 14 and the recording sheet 11 are transported in mutually opposite directions, as shown in FIG. 7.

When the recorded sheet 11 is advanced until the rear end portion of the recording reaches the cutting position of the cutter 15, a motor (not shown) for driving the cutter 15 is activated by the control unit 101, whereby the cutter members 15a, 15b mutually engage to cut the recording sheet 11 into a sheet, as shown in FIG. 8. There are shown the recording sheet 11a of a recorded page; a rear end portion 11b thereof; and a leading end portion 11c thereof.

FIG. 9 shows an operation, after the cutting of the recording sheet 11, of reversing the recording sheet 11 in a direction opposite to b, until the leading end of said sheet 11 becomes positioned slightly beyond the recording position of the thermal head 13 toward the discharge rollers 16, thereby preparing for the recording the next page. For the reversing speed V.sub.PB of the recording sheet 11, the ink sheet 14 is moved in the direction a with a speed V.sub.IB =V.sub.PB /n. At the same time, the recording sheet 11a after recording and cutting is discharged by the rotation of the discharge rollers 16.

As explained above, in the transportation for the cutting of the recording sheet 11, the ink sheet 14 is moved with a speed equal to 1/n of that of the recording sheet 11, so that the moving distance of the ink sheet 14 becomes shorter (2l/n) in comparison with that of the recording sheet 11, and the waste of the ink sheet 14 is therefore reduced. In the present embodiment it is assumed that the recording sheet 11 and the ink sheet 14 are moved in mutually opposite directions, but the same effect can be obtained also when they are moved in a same direction.

If the ink sheet 14 contains a slack in the stand-by state shown in FIG. 5, the takeup roller 18 driven by the ink sheet motor 25 at the start of recording operation only serves to absorb said slack and becomes unable to advance the ink sheet 14 with the speed V.sub.I. Also in such case, the ink sheet 14 may be moved in the direction b, being dragged by the recording sheet 11 moving with the speed V.sub.P.

In the present second embodiment, in order to prevent such phenomenon, the ink sheet 14 is taken up at the backfeeding shown in FIG. 9 with a speed V.sub.IB satisfying a condition V.sub.IB .gtoreq.V.sub.PB wherein V.sub.PB is the reversing speed of the recording sheet. This operation avoid formation of slack in the ink sheet 14. It is therefore possible to dispense with the ink sheet feed motor 85 for driving the ink sheet feed roller 17 thereby regulating the amount of feeding of the ink sheet 14 and eliminating the slack therein. In the present embodiment it is assumed that the recording sheet 11 and the ink sheet are moved in mutually opposite directions, but it is likewise exercisable also when said sheets are moved in a same direction.

In the third embodiment, when the recording sheet 1 is transported in the direction b with a speed V.sub.PF, the ink sheet is transported with a speed V.sub.IF =V.sub.PF /n. In the backfeeding (opposite to b) of the recording sheet 11, the ink sheet 14 is stopped, and is advanced by k times (k being a natural number) in the same direction as the recording sheet 11 during said backfeeding.

When the ink sheet 14 is stopped it is in sliding contact with the recording sheet 11, as shown in FIG. 10, at the nip .DELTA.l of the platen roller 12, thus eventually resulting in so-called background smudge caused by the ink transfer from the ink sheet 11 to the recording sheet 11. In the present embodiment, therefore, there is employed an ink sheet 14 provided with a top coating, and said ink sheet 14 is stopped while said top coating is still present, namely while the background smudge is not generated. Then the ink sheet is advanced, prior to the formation of background smudge, by an amount, for example said nip amount .DELTA.l, sufficient for avoiding the formation of background smudge and is stopped again. In this manner the amount of ink sheet 14 wasted in the backfeeding operation can be limited to k.times.l. In the present embodiment it is assumed that the recording sheet 11 and the ink sheet 14 are moved in mutually opposite directions, but the same effect can be obtained even when they are moved in a same direction.

In the fourth embodiment, when the recording sheet 1 is moved toward the discharge rollers 16 with a speed V.sub.PF. the ink sheet 14 is moved with a speed V.sub.IF =V.sub.PF /n. Also in the backfeeding of the recording sheet 1 with a speed V.sub.PB, the ink sheet 14 is moved with a speed V.sub.IB =V.sub.PB /n.sub.IB, wherein n.sub.IB >n. By increasing n.sub.IB to an extent not causing the background smudge, it is possible to reduce the waste of the ink sheet 14 resulting from the transportation of the recording sheet 1 at the page cutting thereof. In the present embodiment it is assumed that the recording sheet 11 and the ink sheet 14 are moved in mutually opposite directions, but the same effect can naturally be obtained even if both sheets are moved in a same direction.

The foregoing four embodiments can be summarized as follows:

(1) When the recording sheet is moved in the forward direction with a speed V.sub.PF, the ink sheet is moved with a speed V.sub.IF =V.sub.PF /n.sub.IF (n.sub.IB being equal to n during recording). The recording sheet 11 and the ink sheet 14 may be moved in mutually opposite directions or in the same direction.

(A) First embodiment

In the backfeeding of the recording sheet 11, there is maintained a condition V.sub.IB =V.sub.PB /n, wherein V.sub.IB is the speed of recording sheet 11 at the backfeeding, and n.sub.IB is equal to n during recording.

(B) Second embodiment

In the backfeeding of the recording sheet 11, there is maintained a condition V.sub.IB .gtoreq.V.sub.PB.

(C) Third embodiment

In the backfeeding of the recording sheet 11, the ink sheet 14 is advanced k times, each by a distance .DELTA.l corresponding to the nip amount of the platen roller 12, and is otherwise stopped. "k" indicates a natural number, and .DELTA.l is assumed to be sufficiently shorter than the length of the recording sheet.

(D) Fourth embodiment

In the backfeeding of the recording sheet 11, there is maintained a condition V.sub.IB =V.sub.PB /n.sub.IB, wherein n.sub.IB is larger than n during recording.

There can be considered further variations which are listed in the following:

(2) When the recording sheet 11 is moved in the forward direction with a speed V.sub.PF, the ink sheet 14 is moved with a speed V.sub.IF =V.sub.PF /n.sub.IF (n.sub.IF being larger than n during recording, and the ink sheet 14 being moved in a direction opposite to that of the recording sheet).

(A) Fifth embodiment

In the backfeeding of the recording sheet 11, there is maintained a condition V.sub.IB =V.sub.PB /n, wherein V.sub.IB is the speed of ink sheet 14 at the backfeeding, V.sub.PB is the speed of recording sheet 11 at the backfeeding, and n.sub.IB is equal to n during recording.

(B) Sixth embodiment

In the backfeeding of the recording sheet 11, there is maintained a condition V.sub.IB .gtoreq.V.sub.PB.

(C) Seventh embodiment

In the backfeeding of the recording sheet 11, the ink sheet 14 is advanced k times, each by a distance .DELTA.l corresponding to the nip amount of the platen roller 12, and is otherwise stopped. "k" indicates a natural number, and .DELTA.l is assumed to be sufficiently shorter than the length of the recording sheet.

(D) Eighth embodiment

In the backfeeding of the recording sheet 11, there is maintained a condition V.sub.IB =V.sub.PB /n.sub.IB, wherein n.sub.IB is larger than n during recording.

(3) During the sheet feeding, after recording, so as to bring the rear end of a page of the recording sheet 11 to the position of the cutter 15, the ink sheet 14 is advanced k times in the direction a (opposite to the direction of movement of the recording sheet 11), each time by a distance .DELTA.l corresponding to the nip amount of the platen roller 12, and is other wise stopped.

(A) Ninth embodiment

In the backfeeding of the recording sheet 11, there is maintained a condition V.sub.IB =V.sub.PB /n.sub.IB, wherein n.sub.IB is equal to n during recording.

(B) Tenth embodiment

In the backfeeding of the recording sheet 11, there is maintained a condition V.sub.IB >=V.sub.PB.

(C) Eleventh embodiment

In the backfeeding of the recording sheet 11, the ink sheet 14 is advanced k times, each by a distance .DELTA.l corresponding to the nip amount of the platen roller 12, and is otherwise stopped. "k" indicates a natural number and .DELTA.l is assumed to be sufficiently shorter than the length of the recording sheet.

(D) Twelfth embodiment

In the backfeeding of the recording sheet 11, there is maintained a condition V.sub.IB =V.sub.PB /n.sub.IB, wherein n.sub.IB is larger than n during recording.

(4) When the recording sheet 11 is fed toward the cutter, the ink sheet 14 is fed by a length in the same direction as the recording sheet 11, with a speed V.sub.IF which is equal to V.sub.PF. After the cutting of the recording sheet 14 with the cutter 15, at the backfeeding of the recording sheet 14, is reversed with a speed V.sub.IB .gtoreq.V.sub.PB (=V.sub.IF)

Thirteenth embodiment

(5) When the recording sheet 11 is moved in the forward direction with a speed V.sub.PF, the ink sheet 14 is moved with a speed V.sub.IF =V.sub.PF /n.sub.IF (n.sub.IF being larger than n during recording, and the ink sheet 14 being moved in the same direction as that of the recording sheet).

(A) Fourteenth embodiment

In the backfeeding of the recording sheet 11, there is maintained a condition V.sub.IB =V.sub.PB /n, wherein V.sub.IB is the speed of ink sheet 14 at the backfeeding, V.sub.PB is the speed of recording sheet 11 at the backfeeding, and n.sub.IB is equal to n during recording.

(B) Fifteenth embodiment

In the backfeedhng of the recording sheet 11, there is maintained a condition V.sub.IB .gtoreq.V.sub.PB.

(6) During the sheet feeding, after recording, so as to bring the rear end of a page of the recording sheet 11 to the position of the cutter 15, the ink sheet 14 is advanced k times in the direction b (same as the direction of movement of the recording sheet each time by a distance .DELTA.l corresponding to the nip amount of the platen roller 12, and is otherwise stopped.

(A) Sixteenth embodiment

In the backfeeding of the recording sheet 11, there is maintained a condition V.sub.IB .ltoreq.V.sub.PB /n.sub.IB, wherein n.sub.IB is equal to n during recording.

(B) Seventeenth embodiment

In the backfeeding of the recording sheet 11, there is maintained a condition V.sub.IB .gtoreq.V.sub.PB.

(C) Eighteenth embodiment

In the backfeeding of the recording sheet 11, the ink sheet 14 is advanced k times, each by a distance A corresponding to the nip amount of the platen roller 12, and is otherwise stopped. "k" indicates a natural number, and .DELTA. is assumed to be sufficiently shorter than the length of the recording sheet.

In the backfeeding of the recording sheet 11, there is maintained a condition V.sub.IB =V.sub.PB /n.sub.IB, wherein n.sub.IB is larger than n during recording.

FIG. 11 is a flow chart for the recording sequence of a page in the facsimile apparatus of the first embodiment, and a corresponding program is stored in the ROM 114 of the control unit 101.

This sequence is started when the image data of a line to be recorded are stored in the line memory 110 and are ready for recording. At first a step S1 sends the recording data of a line serially to the shift register 130. After the transfer of said data, a step S2 releases the latch signal 44 to store the data of a line in the latch circuit 131. Then a step S3 activates the ink sheet motor 25, thereby advancing the ink sheet 14 by a distance of l/n lines in the direction a shown in FIG. 3. Then a step S4 activates the recording sheet motor 24, thereby advancing the recording sheet 11 by a distance of a line in the direction b. A line corresponds t the length of a dot recorded by the thermal head 13.

A next step S5 energizes the blocks of the heat-generating elements of the thermal head 13 in succession. When the recording of a line is completed by energizations of all m blocks, a step S6 discriminates whether the image recording of a page has been completed. If not completed, a step S7 transfers the recording data of a next line to the shift register 130 of the thermal head 13, and the sequence returns to the step S2 for effecting the recording operation as explained above.

On the other hand, if the step S6 identifies the completion of recording of a page, a step S8 feeds the recording sheet 11 toward the discharge rollers 16a, 16b approximately by the distance between the recording position of the thermal head 3 and the cutter 15. At the same time the ink sheet motor 25 and the ink sheet feed motor 85 are activated to feed the ink sheet in the direction a with a speed equal to 1/n of that of the recording sheet 11. Then a step S9 activates the cutter members 15a, 15b to into a page. Then a step S10 feeds the recording sheet 11 backwards to the next recording position. At the same time the ink sheet is fed with a speed equal to 1/n of the backfeeding speed of the recording sheet 11. Then a step S11 discharges the recorded sheet 11a from the apparatus by means of the discharge rollers 16.

The second embodiment can be achieved by executing the step S8 in the same manner as explained above, 20 and maintaining, in the step S10, the feed speed V.sub.IB of the ink sheet 14 equal to or larger than the backfeed speed V.sub.PB of the recording sheet 11 (V.sub.IB .gtoreq.V.sub.PB).

FIG. 12 is a flow chart for the feeding of the recording sheet 11 and the ink sheet 14 at the backfeeding in the 3rd embodiment, corresponding to the step S10 in FIG. 11.

A step S21 sets the value k, and a step S22 stops the feeding of the ink sheet 14. Then a step S23 feeds the recording sheet 11 with a speed V.sub.PB. Then a step S24 awaits the lapse of a predetermined time, corresponding to the time required for the abrasion of the top coating of the ink sheet 14 and the formation of smudge on the recording sheet 11 resulting from the friction between the recording sheet 11 and the ink sheet 14. After the lapse of said time, a step S25 discriminates whether "k" is "0", and, if not, a step S26 feed by the ink sheet 14 by the nip amount .DELTA.l shown in FIG. 10. Then a step S27 decreases the value of k by "1", and a step S28 terminates the feeding of the recording sheet 11.

The fourth embodiment can be achieved, in the step S10 shown in FIG. 11, by feeding the ink sheet, at the backfeeding of the recording sheet 11, with a speed equal to 1/n.sub.IB of the speed V.sub.PB of the recording sheet 11, wherein n.sub.IB >n.

The feeding of the recording sheet 11 and the ink sheet 14 in other embodiments can be realized in a similar manner.

If the ink sheet motor 25 is a stepping motor, the aforementioned value n can be controlled by varying the number of steps of the ink sheet 14 during the feeding of a line of the recording sheet 11, or by varying the minimum stepping angle of said motor.

FIG. 13 is a cross-sectional view of the ink sheet 14 to be employed in the multi-printing of the present invention, for example having a four-layered structure.

A second layer is composed of a base film, serving as the substrate for the ink sheet 14. Since thermal energy is repeatedly applied to a same position in case of multi-printing, it is preferably composed of an aromatic polyamide film or condenser paper which ester film can also be used for this purpose. Its thickness should be as small as possible for improving the print quality, but is preferably in a range of 3-8 .mu.m in consideration of the mechanical strength.

A third layer is composed of an ink layer capable of transfers of n times to the recording sheet. It is principally composed of an adhesive

A fourth layer is a top coating layer for preventing the pressure transfer of the ink to the recording sheet, and is composed for example of transparent wax. Thus the pressure transfer takes place only in said 4th layer, and the background smear on the recording sheet can be prevented. A first layer is a heat-resistant coating for protecting the base film of the second layer from the heat of the thermal head. Said heat-resistant layer is preferable for multi-printing in which heat energy of plural lines may be applied to a same position (if black dots occur repeatedly), but it may be dispensed with if desirable. It is particularly effective for a base film of relatively low heat resistance, such as polyester film.

The ink sheet is not limited to the above-explained example, and there may be employed an ink sheet composed of a base layer and a porous ink support layer provided on one side of the base layer and impregnated with ink, or an ink sheet composed of a base film and a heat-resistant ink layer having porous network structure and impregnated with ink therein.

Also the base film can be composed, for example, of polyimide, polypropylene, polyvinyl chloride, triacetyl cellulose, nylon or paper. The heat-resistant coating, which is no indispensable, can be composed, for example, of silicone resin, epoxy resin or melamine resin.

Furthermore, the ink coated on the ink sheet can be thermo-sublimable, instead of thermo fusible. Such thermo-sublimable ink sheet can be composed, for example, of a substrate consisting of polyethylene terephthalate, polyethylene naphthalate or aromate polyamide, and a layer of coloring material, containing spacer particles, composed of guanamine resin and fluorinated resin, and a dye.

Also the method of heating is not limited to the heating with thermal head explained above, but can involve transfer by current application or the transfer with laser beam irradiation.

In the foregoing embodiments it is assumed that the recording sheet 11 and the ink sheet 14 are moved in mutually opposite directions, but they may be moved in the same direction.

Also the recording medium is not limited to paper but can be any material accepting the ink transfer, such as cloth or plastic sheet. Also the loading of the ink sheet is not limited to the structures shown in the foregoing embodiments, but can be achieved by so-called ink sheet cassette which contains ink sheets in a casing.

As explained in the foregoing, the embodiments prevent the formation of creases or slack in the ink sheet or smudges on the surface of the recording sheet, by advancing the ink sheet in the forward direction by a predetermined amount, in the forward feeding of the recording sheet toward the discharge slot and back feeding thereof into the apparatus after the recording of a page.

Also there is obtained an effect of reducing the consumption of the ink sheet, by reducing the amount of feeding thereof in comparison with that of the recording sheet.

Furthermore, the operator can select the amount of feeding of the ink sheet for a line of the recording sheet, in consideration of the length of the information to be recorded and the remaining amount of the ink sheet.

Though the foregoing embodiments have been explained by a recording unit in a facsimile apparatus, they are not limited to such case and are likewise applicable to ordinary thermal transfer printers.

As explained in the foregoing, the present invention prevents the formation of creases or slack in the ink sheet or the formation of creases on the surface of recording medium, by feeding the ink sheet in predetermined amounts in response to the feeding of the recording medium.